Foundrybench D19 Good Practice Guide

Foundrybench D19: Good practice guide on energy saving potentials and opportunities for foundries

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Grant agreement no. IEE/07/585/SI2.500402

Foundrybench

Foundry Energy Efficiency Benchmarking

Intelligent Energy – Europe (IEE)

SAVE – Industrial Excellence in Energy

D19 Good practice guide on energy saving potentials and opportunities for foundries

Document ID: Foundrybench_D19_12122011

Revision [1.0]

Authors: Joachim Helber & Mirko Steinhäuser, IfG – Institut für Gießereitechnik gGmbH, Germany

Distribution: Public (PU)

Due date of deliverable: 30.9.2011 Actual submission date: 20.12.2011

Start date of project: 1.1.2009 Duration: 36 months

Project coordinator:

Sini Eronen

Hermia Ltd.

E-mail: [email protected]

Tel: +358 40 820 4602

Project website: www.foundrybench.fi

The sole responsibility for the content of this deliverable lies with the authors. It does not necessarily reflect the

opinion of the European Communities. The European Commission is not responsible for any use that may be

made of the information contained therein

mailto:[email protected]


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1. Energy efficiency in foundries - Introduction and definitions

1.1 Energy efficiency – general introduction 6

1.2 Efficient and inefficient use of energy – sustainability 7

1.2.1 Efficient use of energy 8

1.2.2 Energy saving 8

1.2.3 Inefficient use of energy 9

1.3 Energy consumers (sinks) in foundries 10

1.4 Energy efficiency indicators in foundry industry 10

1.5 Energy sources in foundries – secondary usage 11

1.5.1 Induction furnaces as a source of heat 11

1.5.2 Hot-blast cupolas as a source of heat 11

1.5.3 Flue gas heat from a cold-blast cupola 12

1.5.4 Flue gas heat from a compressor 13

1.6 Cross boundary heat exchange – regional factors 14

1.7 Heating and cooling of premises 14

1.8 Energy costs and efficient buying 14

1.9 Political influences on energy market 18

1.9.1 Law of renewable energy (EEG) 19

1.9.2 Power-heat cogeneration law 20

2. Techniques to consider to achieve energy efficiency

2.1 Energy efficiency management systems 21

2.2 Planning targets and objectives 23

2.2.1 Continuing environmental improvement and cross-media issues 23

2.2.2 A systems approach to energy management 24

2.3 Increased process integration 25

2.4 Effective control processes 26

2.4.1 Process control systems 26

2.4.2 Quality management systems 27

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=power-heat&trestr=0x801

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=cogeneration&trestr=0x801


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2.5 Maintenance 29

2.6 Monitoring and measurement 30

2.6.1 Indirect measurement techniques 32

2.6.2 Estimates and calculation 32

2.6.3 Metering systems 33

2.7 Energy audits and energy diagnosis 34

2.8 Energy models, databases and balances 37

2.8.1 Optimization and management of utilities using models 39

2.8.2 Benchmarking 41

3. Horizontal techniques

3.1 Heat exchangers 43

3.1.1 Water-to-water heat exchangers 44

3.1.2 Air-to-air and coil heat changers 45

3.2 Heat pumps 50

3.2.1 Introduction 50

3.2.2 Air-to-air heat pumps 51

3.2.3 Ground source heat pumps 52

3.2.4 Free cooling 52

3.2.5 Rising the temperature of process cooling water 53

3.2.6 Exhaust air heat pumps 53

3.2.7 Other heat sources 54

3.2.8 Life time and maintenance of heat pumps 54

3.3 Solar heat 55

3.3.1 Solar water heating system 55

3.3.2 Costs, savings and earnings 56

3.3.3 Conditions for solar water heating systems 56

3.4 Geothermal heat 59

3.5 Chillers and cooling systems 60

3.5.1 Furnace and sand coolers 60

3.5.2 Water storage tanks 61

3.5.3 Improving chiller efficiency 61

3.6 ORC systems 62

3.6.1 System introduction 62


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3.6.2 System performance and cost 63

3.7 CHP plants 64

3.7.1 Power plants with steam boiler 64

3.7.2 Gas turbine plants 64

3.7.3 Diesel engine and generator 65

3.7.4 Microturbines 65

3.7.5 Fuel cells 66

3.7.6 Stirling engine 66

3.7.7 Economy of CHP 67

3.8 Compressed air systems 68

3.8.1 System types 68

3.8.2 Compressed Air System Controls 69

3.8.3 Compressed Air System Components 74

3.8.4 Performance and energy use 77

3.9 Heating, ventilation and air conditioning 85

3.9.1 Space heating and cooling 85

3.9.2 Ventilation 90

3.10 Lighting 100

4. Good practice examples for foundries

4.1 Coke fired furnaces – cupolas 104

4.1.1 Energetic balance 106

4.1.2 Dry inputs 108

4.1.3 Warm up of feedstock 109

4.1.4 Furnace insulation and wall cooling 109

4.1.5 Heat recovery from slag 109

4.1.6 Secondary row of tyères 110

4.1.7 Oxygen enrichment 110

4.1.8 Alternative fuels 111

4.1.9 Heat recovery from off-gas and secondary use 114

4.1.10 Runner covers 121

4.2 Electric furnaces for melting and holding (arc and induction) 122


4.2.2 (Optimal) operation cycles and handling 127

4.2.3 Electrical losses 131


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4.2.4 Sizing and warm-up of feedstock 131

4.2.5 Insulation and its twofold effect 135

4.2.6 Power factor correction 136

4.3 Gas and oil fired furnaces (crucibles, tunnel, rotating, etc.) 136


4.3.2 (Optimal) operation cycles and handling 138

4.3.3 Thermal losses 145

4.3.4 Sizing and warm-up of feedstock 148

4.3.5 Insulation 148

4.3.6 Heat recovery from off-gas 149

4.4 Thermal fate of the liquefied metal 154

4.4.1 Ladle preheating and insulation 154

4.4.2 Thermal losses on transfer 159

4.4.3 Exothermal chemical reactions 160

4.5 Pressure die casting 161

4.6 Heat treatment of the castings 163

4.7 Computer aided optimization of pouring system, feeders and castings 165

5. Emerging techniques for efficient energy use in foundries

5.1 Latent-heat storage 169

5.2 Electricity generation 171

5.2.1 Operating method of ORC-Turbines 171

5.2.2 Operating method of ORC- Gas-Piston-Machine 173

5.3 Cooling 175

5.3.1 Absorption-Cooling-Machines 175

5.3.2 Adsorption-Cooling-Machines 176

5.4 Heat transfer to the mould and heat recovery from the molding sand 177

5.4.1 Heat recovery from the molding sand 177

5.4.2 Heat recovery from the dismantled castings 178

6. Sources of Information 179


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1. Energy efficiency in foundries - Introduction and definitions

Energy efficiency (ENE) - Introduction1

It is important to keep the importance of energy efficiency in mind. However, even the single

objective of ensuring a high level of protection for the environment as a whole will often

involve making trade-off judgements between different types of environmental impact, and

these judgements will often be influenced by local considerations'. As a consequence:

it may not be possible to maximise the energy efficiencies of all activities and/or

systems in the installation at the same time

it may not be possible to both maximise the total energy efficiency and minimise other

consumptions and emissions (e.g. it may not be possible to reduce emissions such

as those to air without using energy)

the energy efficiency of one or more systems may be de-optimised to achieve the

overall maximum efficiency for an installation

it is necessary to keep the balance between maximising energy efficiency and other

factors, such as product quality, the stability of the process, etc.

the use of sustainable energy sources and/or 'wasted' or surplus heat may be more

sustainable than using primary fuels, even if the energy efficiency in use is lower.

Energy efficiency techniques are therefore proposed as 'optimising energy efficiency'

The horizontal approach to energy efficiency in all IPPC sectors is based on the premise that

energy is used in all installations, and that common systems and equipment occur in many

IPPC sectors. Generic options for energy efficiency can therefore be identified independently

of a specific activity. On this basis, BAT can be derived that embrace the most effective

measures to achieve a high level of energy efficiency as a whole. Because this is a

horizontal BREF (Best Available Technique Reference Document), BAT (Best Available

Technique) need to be determined more broadly than for a vertical BREF, such as

considering the interaction of processes, units and systems within a site. In this guideline

many described horizontal techniques have been cited to a high extend from the BREF-note.

1 European Commission, Reference Document on Best Available Techniques for Energy Efficiency, page 1


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The vertical, this foundry specific approaches are added as a self-produced result written in

the FOUNDRYBENCH-project.

1.1 Energy efficiency

According to numerous studies in 2000, the EU could save at least 20 % of its present

energy consumption in a cost-effective manner, equivalent to EUR 60 000 million per year, or

the combined energy consumption of Germany and Finland in 2000.

Contribution of energy

Accordingly, the EU has announced an Energy Efficiency Action Plan to save up to 20 % of

energy throughout the Union (about 39 Mtoe), and 27 % of energy in manufacturing

industries by 2020. This would reduce direct costs in the EU by EUR 100 000 million

annually by 2020 and save around 780 million tonnes of CO2 per year2.

Pollution prevention and control

Energy efficiency techniques are available from a wide variety of sources, and in many

languages. The information exchange showed that while individual techniques can be

applied and may save energy, it is by considering the whole site and its component systems

strategically that major energy efficiency improvements can be made. For example, changing

the electric motors in a compressed air system may save about 2 % of the energy input,

whereas a complete review of the whole system could save up to 37 %.3

Economic and cross-media issues

Energy is the same as other valuable raw material resources required to run a business –

and is not merely an overhead and part of business maintenance. Energy has costs and

environmental impacts and needs to be managed well in order to increase the business‟

profitability and competitiveness, as well as to mitigate the seriousness of these impacts.

Energy efficiency has the advantage that measures to reduce the environmental impact

usually have a financial payback. The issue often arises of cost-benefit, and the economic

efficiency of any technique can provide information for assessing the cost-benefits. In the




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case of existing installations, the economic and technical viability of upgrading them needs to

be taken into account.4

Efficiency in production units

Complex production sites operate more than one production process/units. To define the

energy efficiency of a whole site it has to be divided into smaller units, which contain process

units and utility units.5

1.2 Efficient and inefficient use of energy - sustainability

1.2.1 Efficient use of energy

Reducing energy use reduces energy costs and may result in a financial cost saving to

consumers. Energy efficiency increases as energy losses in the production, conversion,

distribution and use of energy sources decrease.

In the field of energy generation, energy efficiency can, for example, be boosted by power

plants with higher efficiency ratings or through combined generation of electricity and heat

(cogeneration).

In this way, a higher volume of energy is generated from the same volume of input fuel in the

form of coal, gas or oil. The way in which the generated energy is used can also increase

efficiency. One of the simplest ways of achieving this is to use energy-efficient appliances.

In the cases of foundries, it would be possible to increase energy efficiency by ensuring that

components like heat treatment furnaces or pipelines are well insulated, thereby keeping

heat losses to a minimum.

The use of waste heat also comes under the "increased energy efficiency" heading. The

waste heat from foundry processes can be used to generate electricity, for example. Waste

heat can also be used in drying processes, to heat service and process water or to generate

cooling energy.

1.2.2 Energy saving




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The careful use of energy is the optimum way to save energy. This means, that energy has

been used only when it is necessary. For private houses means that e.g.: Shutdown or

reduce heating if nobody is at home.

With focus on the foundry industry this means e.g. that: Elimination of energy intensive

processes if possible. A good example is to reduce ladle preheating. In foundries ladles are

often permanently under fire, even though it is known, that the ladles will not be used.

1.2.3 Inefficient use of energy

Special care is required when defining the system boundaries for energy efficiency for

complex sites. It is emphasised that in the specific examination of individual production

processes, certain energy uses might seem inefficient even though they constitute a highly

efficient approach within the integrated system of the site. Individual unit, process or system

operators not able to operate at the best efficiency may be commercially compensated in

order to achieve the most competitive environment for the integrated site as a whole.

Some examples are:

the use of steam in a drying process appears to be less energy efficient than the

direct use of natural gas. However, the low pressure steam comes from a CHP

process combined with highly efficient electricity generation

cogeneration plants located at the production site are not always owned by the

production site, but may be a joint venture with the local electricity generation

company. The steam is owned by the site operator and the electricity is owned by the

electricity company. Care should therefore be taken as to how these facilities are

accounted for

electricity is generated and consumed at the same site; however, fewer transmission

losses are achieved

within a highly integrated system, residues containing energy from production

processes are returned into the energy cycle. Examples are the return of waste heat

steam into the steam network and the use of hydrogen from the electrolysis process

as a fuel substitute gas in the heat and/or electricity generation process or as a

chemical (e.g. raw material in hydrogen peroxide production). Other examples are the

incineration of production residues in plant boilers, and waste gases burnt as fuels,


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which have a lower efficiency than using e.g. natural gas (in hydrocarbon gases in a

refinery or CO in non-ferrous metals processing)

Although not within the scope of this document (see Scope), renewable/sustainable energy

sources and/or fuels can reduce the overall carbon dioxide emissions to the atmosphere.6

1.3 Heat sinks in foundries

Heat sinks can be located either inside or outside the foundry. The first task is to pinpoint the

heat sinks. Once this has been achieved, the next step is to include the corresponding heat

sinks in the energy infrastructure. The following are the key steps for the localisation and

integration of heat sinks:7

Performance of a process and energy analysis. A Pinch analysis is a suitable

instrument for this purpose. This analysis provides precise information on the best

way to ensure intelligent interconnection and combination of energy flows in the

company. The process flows are depicted in a temperature-energy flow diagram.

Energy flows can also be portrayed with the help of a Sankey diagram. The energy

flows are normally shown as arrows, and the width of the arrow is proportional to the

magnitude of the flow it represents. A Sankey diagram provides a better overview of

energy flows than, for example, descriptive methods using figures. In addition to

showing the aforementioned energy flows, a Sankey diagram can also be used to

portray waste heat flows and possible heat sinks

Before concepts for lucrative heat transports are implemented, it is advisable to

simulate these transports on the computer

Performance of a risk analysis for the identified options (failure mode and effect

analysis - FMEA)

Performance of a profitability analysis (static and dynamic amortisation period,

internal interest rate, present value method)


7 Krenn, Ch., Fresner, J., Meixner, E.,: Energieeffizienzsteigerung in Unternehmen der stahlverarbeitenden Industrie durch

Abwärmenutzung im Niedertemperaturbereich, page 4


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If no more heat sinks can be localised in-plant (e.g. melting scrap drying, drying of coatings,

hall heating), the possibility of using energy beyond the confines of the foundry site should be

considered.

It is conceivable that energy could be put to good use by supplying district heat to other

companies. Perhaps it is also possible to use latent heat storage (phase change) materials.

1.4 Energy efficiency indicators for the foundry industry

To localize energy-saving potentials, it is important to know the energy consumption. If no

data is available, the energy consumption has to be measured. To evaluate energy efficiency

it is recommended to use defined indicators for each production process or for parts of the

focused production processes. Successive some defined indicators will be closer described.

The exactness of the result depends on the exactness of the used data. All kinds of energy

sources can be considered, e.g. natural gas, electricity, coke.

The defined indicators may be important in two different ways. On the one hand site it is

possible to capture and document the energy reduction of the own foundry or company,

within a determined period. On the other side it is possible to compare one foundry with

another foundry (benchmark).

1.5 Energy sources in foundries – secondary usage

1.5.1 Induction furnaces as a source of heat

A large part of the electrical energy fed into an induction melting furnace is converted into

waste heat. Around 20 to 30% of the total energy required by an induction melting furnace is

destroyed during the cooling process.

Utilisation of the heat contained in the cooling system is the state of the art. The temperature

of the cooling water circuit is normally between 40°C and 60°C.

In foundries, the process heat from the induction melting furnace is used for a wide range of

operations, such as:

Drying input materials for the induction melting furnace

Drying cores following smoothing


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Heating of service and process water

Heating foundry halls

1.5.2 Hot-blast cupolas as a source of heat

In hot-blast cupolas, the furnace gas containing CO is post-combusted, with temperatures

climbing up to around 900°C. The need to cool the flue gases from a cupola before

forwarding these gases to the flue gas cleaning stage creates an opportunity to utilise the

waste heat of the gases. This waste heat can be used for a wide range of applications, such

as:

Preheating of the blast required for the cupola (hot blast generation)

Supply of the heat needed for service and process water

Heating the hall air

Preheating or drying of melting scraps

Driving turbines to generate electricity

Figure 1: Schematic diagram of waste heat utilisation

The Maggi plant uses the thermal oil provided by Georg Fischer with a temperature of

around 280 degrees Celsius to generate food-grade steam with the help of a heat

exchanger. This steam is used to sterilise wet ambient ready meals.


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1.5.3 Flue gas heat from a cold-blast cupola

Flue gas losses are the volume of heat contained in the flue gas flow.

Figure 2: Flow diagram of a cold-blast cupola with heat recovery system, cooling device and fabric

filter

The necessity to cool the untreated gas before it is, for example, routed through a fabric filter

can result in the use of heat exchangers; see Figure 2.

With the help of heat exchangers, the heat from the untreated gas can be used for various

purposes, such as to provide heat for drying processes (scrap drying, drying of coatings).

1.5.4 Flue gas heat from a compressor

A further way to save energy is waste heat recovery.

In the case of so-called "box compressors" it is particularly easy to reutilise the hot cooling

air, as the cooling air flow heated to 50 to 70°C only exits the compressor at one point. By

way of example, Figure 3 shows a flow diagram for utilisation of the waste heat from a

compressor.


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Figure 3: Principle of a heat recovery system, designed for an air-cooled compact compressor with

direct utilisation of the heated cooling or ventilation air.

The heated cooling air flow can be used for a wide range of applications in the foundry:

Hot water production

Heat for drying units and room heating

1.6 Cross boundary heat exchange - regional factors

Heating and cooling are regional factors, generally with heating requirements being greater

in northern Europe, and cooling greater in southern Europe. This can affect the production

processes, e.g. the need to keep waste at a treatable temperature in waste treatment

installations in Finland in winter, and the need to keep food products fresh will require more

cooling in southern Europe, etc. Regional and local climatic variations also have other

restrictions on energy efficiency: the efficiency of coal boilers in northern Europe is generally

about 38 % but in southern Europe 35 %, the efficiency of wet cooling systems is affected by

the ambient temperature and dew point, etc.8



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1.7 Heating of premises

The heating and cooling of premises depends in a high volume on the outdoor temperature

as shown in figure 4.

Figure 4: Energy consumption depending on the outdoor temperature

For further information check chapter 3.11.

1.8 Energy costs and efficient buying

Average energy prices for the industry in the European Union (27 member states) increased

from 6.72 €-ct in 2005 to 9.36 €-ct per kilowatt hour in 2011.9 It can be observed that higher

quantities lead to lower prices as shown in figure 5 and 6 (figures are related to German

foundries only). In figure 5 you can see a relationship between purchase quantity in kWh

and price per kWh. That leads to the conclusion that the higher the electricity consumption is,

the better price you can negotiate with your electricity supplier.

9 All data on energy prices in Europe are based on current data from Eurostat.


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Figure 5: The relationship between costs and purchase quantity; based on internal data gathered in

Germany by IfG

In figure 6 you can see the relationship between the average annual outputs of liquid iron by

a hot blast furnace to the price per 100kg liquid iron. Coke has the largest share of the costs

for liquid iron, for instance, 34 percent for 6,000 tons and 40 percent for 50,000 tons.

However, the bigger the output of liquid metal, the lesser price you have to pay for energy.

For 6,000 tons you have to pay around 23 €-ct per 100kg liquid iron, but for 50,000 tons only

about 14€-ct per 100kg liquid iron.


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Figure 6: Average costs for a hot blast cupola; based on internal data gathered in Germany by IfG

As you can see in Figure 7, high voltage current causes the highest costs in a medium

frequency induction furnace. There are high voltage current costs of 8.42 €-ct for one ton

liquid iron and only 6.80 €-ct for 8 tons. In addition to that, it is possible to draw the same

conclusion for medium frequency induction furnaces as for a hot blast cupola: The bigger the

furnace size in tons, the lesser price you have to pay for energy.

Figure 7: Average costs for medium frequency induction electric furnaces; based on internal data

gathered in Germany by IfG

Though, there are also significant differences between the countries in European Union

shown in figure 8. On the one hand, companies have to pay high energy prices, for instance,

16 and 18 €-ct per kilowatt hour in island countries like Cyprus and Malta. On the other hand,

companies in Bulgaria, Estonia and Finland need to pay only about 6 cents. In the three

countries with the highest gross domestic product within the European Union, Germany,

France and United Kingdom, only France with 7.22 €-ct differs from the average of the EU-27

countries.


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Figure 8: Electricity prices in European Union, based on data of EuroStat10

The supply of electricity and heat causes variable costs, for example, for natural gas in a

combined cycle gas turbine plant, and fixed costs for the maintenance of the supply lines.

Both the variable and fixed costs will be included in the individual pricing for the industry.

Therefore, you can find a demand charge and a working charge in industry contracts. As a

result ammeters are needed which completely meter the overall energy requirements and the

maximum electricity requirement in 15 minutes intervals.

If a foundry needs, for instance, a maximum electricity requirement of 6,500 MW per year,

the demand charge would be 260,000€ by a fictitious price of 40€ per MW. Besides, there

are additional costs for the electricity requirement of 8,500 MWh per year and a fictitious

price of 40€ per MWh. All in all, total costs are 600,000€ in this example. As described

previously, the average prices for electricity in the European Union especially the working

charge increased. Therefore, it is important to implement energy efficiency measures to

reduce annual energy requirements. As the result of these measures, electricity requirement

might decrease to 7,000 MWh in the following year. Alternatively, the low gear of the

furnaces can be homogenized to avoid power peaks which increase the demand charge.

Thus, demand charge can be cut to 6,000 MW in the next contract negotiations. Ceteris

paribus, the total costs of electricity decline to 520,000€.

10 http://epp.eurostat.ec.europa.eu/tgm/table.do?tab=table&init=1&language=de&pcode=ten00114&plugin=1


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1.9. Political influences on energy market

The development of the energy market is shaped by European decisions on climate policy.

The parties to the Kyoto Protocol decided to cut anthropogenic emissions on international

level, prompting the Commission of the European Union (EU) to set out a target of an 80 to

90% reduction in CO2 by the year 2050. Increasing the share of renewables and improving

energy efficiency are two key elements in this strategy.11The introduction of emission credit

trading creates additional costs for the operators of fossil fuel power plants, and these costs

are in turn passed on to customers, including foundries. Electricity and gas prices in

Germany are among the highest in the EU,12 and this is a direct consequence of the

country's high taxes and related charges. Political decisions - the introduction of new taxes,

for example - have a major impact on these charges and levies. The so-called "energy mix"

reflects country-specific circumstances and preferences for certain sources of energy. The

energy supply system in the Federal Republic of Germany is dependent on imported input

materials, particularly with regard to the fossil fuels oil, natural gas, coal and uranium.13 As a

result, the overall German energy mix caused emissions of 508g CO2/kWh in 2009 compared

to the European average of around 420g CO2/kWh.

In early 2009, Russia interrupted its gas deliveries to the Ukraine because of a conflict

between the two countries. As Russia is also the largest supplier of natural gas to the

European Union, this soon also resulted in bottlenecks in some Eastern European countries.

This example shows that a high dependence on imports also leads to dependence in political

terms. This means that not only can the producing countries influence prices by

systematically reducing production volumes but also that conflicts in these countries can lead

to unexpected price increases.

One of the key challenges is the cross-border integration of internal national markets. Due to

the lack of alignment of national energy policies, there is still no functioning internal energy

market in the European Union overall.14 In the wake of the 1973 oil crisis, for example,

France decided to focus on nuclear energy, with the result that atomic power today accounts

for nearly 80% of supplied electricity and 40% of supplied energy.15

In contrast, nuclear

power is highly controversial in Germany, leading to decisions to exit atomic energy

11 Rat der Europäischen Union (Cf. Council of the European Union) 2007, p. 20-21.

12 Eurostat, Half-yearly electricity and gas prices, first half of year, 2009-2011 (EUR per kWh

13 Babies, H. G. et al.: Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) (Hrsg.): Reserven,

Ressourcen und Verfügbarkeit von Energierohstoffen, p. 5 14

Geden, O.: Der Energiebinnenmarkt der EU - Ein fairer Wettbewerb findet bislang nicht statt 15

Own calculations based on EuroStat


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generation by the year 2022, initially as part of the 2000 "atomic power consensus" and most

recently in legislation adopted in 2011.16

Austria, on the other hand, is reducing its dependence on imports by ensuring a high share

of hydropower in the national energy mix.17

In contrast, the installed capacity in Germany

increased from 4,403 to 4,780 MWel in the period from 1990 to 2010, with hydropower

accounting for 3.3% of gross electricity consumption at the last count. As the potential for the

construction of hydropower plants in Germany is already more or less exhausted, however,

the country is looking above all to repowering to drive the further expansion of installed

capacity. In the main, therefore, future potential is seen in the expansion of other renewable

forms of energy.

1.9.1 German Renewable Energy Sources Act (EEG)

The German Renewable Energy Sources Act (EEG) came into force in Germany in 2000

with the aim of increasing the share of renewables in overall electricity generation and

thereby ensuring the sustainable development of energy supplies,18. Similar legislation to

promote renewable forms of energy has been enacted not just in the European Union (e.g. in

Spain, France and Greece) but also worldwide.19 By paying a guaranteed remuneration for

electricity fed into the grid, the German legislation drove a steady increase in the share of

renewables in overall electricity generation in Germany from 6.4% in 2000 to 17% in the year

2010. in 2003, wind power overtook hydropower as the biggest source of renewable energy,

and in 2008 biomass climbed into second place ahead of hydropower. From 2002 onwards,

there was also noticeable growth in the area of photovoltaics, with installed capacity almost

doubling every year.20 The customers (and therefore also the majority of foundries) are the

ones who fund the promotion of electricity generation from renewables in the form of the so-

called "EEG surcharge". Parallel to the expansion of renewables, this surcharge tripled from

1.13 cents in 2009 to 3.53 cents in 2011. Following the aforementioned decision to exit

16 Federal Ministry for the Environment ; Eight power plants were shut down when the amended German Atomic

Power Act came into effect in 2011, cf. Article 1 Thirteenth Act on the Amendment of the German Atomic

Power Act 17

Österreichs E-Wirtschaft, Energie & Preise; (Energy prices in Austria) 18

Federal Ministry for the Environment ; Cf. Section 1 German Renewable Energy Sources (EEG) 19

Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Das Erneuerbare-Energien-

Gesetz – eine Erfolgsgeschichte 20

Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Das Erneuerbare Energien in

Zahlen - Nationale und internationale Entwicklung, page. 16


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nuclear power generation and the closure of several atomic power plants in Germany, the

share of renewables rose to 20% in 2011, while the EEG surcharge will remain more or less

unchanged in 2012 at 3.59 cents.21

1.9.2 German Cogeneration Act

Alongside the construction of new power plants using renewable forms of energy, there are

currently several ways of reducing emissions from existing power plants. As industrial

locations need both electricity and heating, one option is separate power generation in power

plants and heat supplies from heating plants. In Germany, the Act for Conservation,

Modernization and Expansion of Cogeneration (in short, the Cogeneration Act) promotes the

simultaneous generation of electricity and heating energy in large heat-and-power plants and

smaller unit-type heat-and-power plants, as this combined generating concept reduces the

volume of required primary energy by up to one third compared to separate generation.22

Alongside cogeneration, switching fossil energy sources can also help to cut emissions. If

used to obtain the same amount of energy, the emission ratios for lignite, coal, heating oil

and natural gas are 1 : 0.83 : 0.73 : 0.48.23 This is one of the reasons why substituting

natural gas for heating oil can reduce emissions, for example.

21 Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, EEG-Umlage bleibt bei

kräftigem Ausbau stabil 22

Schaumann, G; Schmitz, K. W.: Kraft-Wärme-Kopplung, p. 5-6. 23

Riesner, W.: Betriebliches Energiemanagement, p. 140-141.


22

2. Techniques to consider to achieve energy efficiency

2.1 Energy efficiency management systems

Management systems and system boundaries

It is important to consider an installation in terms of its component units/systems. The

maximum return on investment may be gained from considering a whole site and its

interconnected units/systems. Otherwise, changing individual components may lead to

investment in incorrectly sized equipment and missing the most effective efficiency savings.

The best energy efficiency for a site is not always equal to the sum of the optimum energy

efficiency of the component parts, where they are all optimised separately. Indeed, if every

process would be optimised independent of the other processes on the site, there is a risk

that e.g. excess steam will be produced on the site, which will have to be vented. By looking

at the integration of units, steam can be balanced and opportunities for using heat sources

from one process for heating in another process can result in lower overall site energy

consumptions.

Synergies can therefore be gained from considering (in the following order)24:

The whole site, and how the various units and/or systems interrelate (e.g.

compressors and heating). This may include considering de-optimising the energy

efficiency of one or more production processes/units to achieve the optimum energy

efficiency of the whole site. The efficient use of processes, units, utilities or

associated activities, or even if they are appropriate in their current forms needs to be

assessed.

Subsequently, optimising the various units and/or systems (e.g. CAS, cooling system,

steam system).

Finally, optimising the remaining constituent parts (e.g. electric motors, pumps,

valves).



23

To understand the importance of considering the role of systems in energy efficiency, it is

crucial to understand how the definition of a system and its boundary will influence the

achievement of energy efficiency. Furthermore, by extending boundaries outside a

company‟s activities and by integrating industrial energy production and consumption with

the needs of the community outside the site, the total energy efficiency could be increased

further, e.g. by providing low value energy for heating purposes in the neighbourhood, e.g. in

cogeneration.

Energy efficiency systems – short introduction

Management to achieve energy efficiency similarly requires structured attention to energy

with the objective of continuously reducing energy consumption and improving efficiency in

production and utilities, and sustaining the achieved improvements at both company and site

level. It provides a structure and a basis for the determination of the current energy

efficiency, defining possibilities for improvement and ensuring continuous improvement. All

effective energy efficiency (and environmental) management standards, programmes and

guides contain the notion of continuous improvement meaning that energy management is a

process, not a project which eventually comes to an end.

The best performance has been associated with energy management systems that show the

following:

• energy policy – energy policy, action plans and regular reviews have the

commitments of top management as part of an environmental strategy

• organising – energy management fully integrated into management structure. Clear

delegation of responsibility for energy consumption

• motivation – formal and informal channels of communication regularly used by

energy managers and energy staff at all levels

• information systems – a comprehensive system sets targets, monitors

consumptions, identifies faults, quantifies savings and provides budget tracking

• marketing – marketing the value of energy efficiency and the performance of energy

management both within and outside the organisation

• investment – positive discrimination in favour of 'green' schemes with detailed

investment appraisal of all new-build and refurbishment opportunities.


24

The best environmental performance is usually achieved by the installation of the best

technology and its operation in the most effective and efficient manner.


25

2.2 Planning targets and objectives

2.2.1 Continuing environmental improvement and cross-media issues

An important element of an environmental management system (EMS, which is BAT in all

IPPC sectors) is maintaining overall environmental improvement. It is essential that the

operator understands what happens to the inputs including energy (understanding the

process), and how their consumption leads to emissions. It is equally important, when

controlling significant inputs and outputs, to maintain the correct balance between emissions

reduction and cross-media effects, such as energy, water and raw materials consumption.

This reduces the overall environmental impact of the installation.

The environmental benefits may not be linear, e.g. it may not be possible to achieve 2 %

energy savings every year for 10 years. Benefits are likely to be irregular and stepwise,

reflecting investment in ENE projects, etc. Equally, there may be cross-media effects from

other environmental improvements: for example it may be necessary to increase energy

consumption to abate an air pollutant. Energy use may:

• decrease following a first energy audit and subsequent actions

• rise when additional emissions abatement equipment is installed

• decrease again following further actions and investment

• the overall trend for energy use is downwards over time, as the result of longer term

planning and investments.

Achieved environmental benefits

Long term reduction in consumptions of energy, water and raw materials, and emissions can

be achieved. Environmental impacts can never be reduced to zero, and there will be points in

time where there is little or no cost-benefit to further actions. However, over a longer period,

with changing technology and costs (e.g. energy prices), the viability may also change.

Cross-media effects

A part of the operation‟s consumptions or emissions may be higher proportionately for a

certain period of time until longer term investment is realised.

Operational data


26

Energy intensive companies often make a clears distinction between „core‟ and „non-core‟

business with little management effort devoted to the latter, unless opportunities survived

very high hurdles, such as payback periods of 18 – 24 months. For businesses which are not

energy intensive, energy costs not rarely are regarded as „fixed overheads‟ or ignored as

falling below a „threshold‟ share of costs.

Many examples collected within the FOUNDYBENCH project show longer payback periods,

especially when investments are big. But it is also clearly indicated that those investments

can be very important for a sustainable development, i. e. by generating ones own electric

power from waste heat.

Applicability

Applicable to all IPPC installations. The extent of this exercise will depend on the installation

size, and the number of the variables (also, see Achieved environmental benefits, above). A

full cross-media study is carried out rarely.

Economics

Enabling capital investment to be made in an informed manner for the reduction of the

overall environmental benefit and the best value for money25.

2.2.2 A systems approach to energy management

Work in the SAVE programme (SAVE is an EC energy efficiency programme) has shown

that, while there are savings to be gained by optimising individual components (such as

motors, pumps or heat exchangers, etc.), the biggest energy efficiency gains are to be made

by taking a systems approach, starting with the installation, considering the component units

and systems and optimising (a) how these interact, and (b) optimising the system. Only then

should any remaining devices be optimised.

This is important for utility systems. Historically, operators have tended to focus on

improvements in energy-using processes and other equipment: demand side energy

management. However, the amount of energy used on a site can also be reduced by the way

25 European Commission, Reference Document on Best Available Techniques for Energy Efficiency, page 56 f.


27

the energy is sourced and supplied: supply side energy management (this could be

considered as a top-down approach)26.


Higher energy savings are achieved at a component level (bottom-up approach). See

Examples, below. A systems approach may also reduce waste and waste waters, other

emissions, process losses, etc.

Operational data

Some details are given in the relevant sections, such as:

• Model-based utilities optimisation and management

• Chapter 3 deals predominantly with individual systems

Chapter 4 deals exclusively with foundry process efficiency improvements..

Driving force for implementation

• costs

• increased efficiency

• reduced capital investment.

2.3 Increased process integration

Intensifying the use of energy and raw materials by optimising their use between more than

one process or system27. This is site- and process-specific.


These are one or more of the following:

• improved energy efficiency

• improved material efficiency including raw materials, water (such as cooling water

and demineralised water) and other utilities




28

• reduced emissions to air, soil (e.g. landfill) and water. Other benefits are site-

dependent.

Applicability

Generally applicable, especially applicable where processes are already interdependent.

However, the options for improvement will depend on the particular case. On an integrated

site, it has to be considered that changes in one plant might affect the operating parameters

of other plants. This applies also to changes with environmental driving forces.


• cost benefits

• other benefits are site-dependent.

Economics

Cost benefits from savings in energy and other raw materials will be case dependent.

2.4 Effective control processes

At installation level, one practice (or set of conventions) for reporting should be adopted and

maintained. The boundaries for energy efficiency calculations and any changes in

boundaries and operational practices should be identified in the internal and external

historical database. This will help maintain the interpretation and comparability between

different years.

2.4.1 Process control systems

For good energy management, a proper process control and utility control system is

essential. A control system is part of the overall monitoring. Automation of a manufacturing

facility involves the design and construction of a control system, requiring sensors,

instruments, computers and the application of data processing. It is widely recognised that

automation of manufacturing processes is important not only to improve product quality and

workplace safety, but also to increase the efficiency of the process itself and contribute to

energy efficiency.


29

Efficient process control includes:

• adequate control of processes under all modes of operation, i.e. preparation, start-up,

routine operation, shutdown and abnormal conditions

• identifying the key performance indicators and methods for measuring and controlling

these parameters (e.g. flow, pressure, temperature, composition and quantity)

• documenting and analysing abnormal operating conditions to identify the root causes

and then addressing these to ensure that events do not recur (this can be facilitated

by a „no blame‟ culture where the identification of causes is more important than

apportioning blame to individuals).

Planning

There are several factors that are considered in the design of a control system. An initial

analysis of the particular process system may reveal existing restrictions to the effectiveness

of the process, as well as alternative approaches that may achieve similar or better results.

Data management and data processing are also factors that must be considered in the

design of the control system. The control system should balance the need for accuracy,

consistency and flexibility required to increase the overall efficiency of the manufacturing

process against the need to control the costs of production.

If the control system is specified sensibly, the production line will run smoothly. Under

specification or over-specification will inevitably lead to higher operating costs and/or delays

in production.

Data treatment

The operational data are collected and treated by an infrastructure which usually integrates

the sensors and instrumentation on the plant, as well as final control elements such as

valves and also includes programmable logic controllers, SCADA and distributed control

systems. All together these systems can provide timely and usable data to other computing

systems as well as to operators / engineers.

2.4.2 Quality management systems

When a product is scrapped or reworked, the energy used in the original production process

is wasted (as well as raw materials, labour and production capacity and other resources).


30

Reworking may use disproportionately more energy (and other resources) than the original

production process. Effective process control increases the amount of product(s) meeting

production/customers' specifications and reduces the amount of energy wasted.

The following arguments have been made for and against management systems:

• the parameters measured have to be relevant to achieving the required process or

product quality, rather than just parameters that can easily be measured

• statistical methods such as six sigma are effective in what it is intended for, but are

narrowly designed to fix an existing process and do not help in developing new

products or disruptive technologies. The six sigma definition is also based on arbitrary

standards, which might work well for certain products/processes, but it might not be

suitable for others

• the application of these approaches gain popularity in management circles, then lose

it, with a life cycle in the form of a Gaussian distribution

• the term ´total quality management´ (TQM) created a positive utility, regardless of

what managers meant by it. However, it lost this positive aspect and sometimes

gained negative associations. Despite this, management concepts such as TQM and

reengineering leave their traces, without explicit use of their names, as the core ideas

can be valuable

• the loss of interest/perceived failure of such systems could be because systems such

as ISO 9000 promote specification, control, and procedures rather than

understanding and improvement, and can mislead companies into thinking

certification means better quality. This may undermine the need for an organisation to

set its own quality standards. Total, blind reliance on the specifications of ISO 9000

does not guarantee a successful quality system. The standard may be more prone to

failure when a company is interested in certification before quality. This creates the

risk of creating a paper system that does not influence the organisation for the better

• certification by an independent auditor is often seen as a problem area and has been

criticised as a vehicle to increase consulting services. ISO itself advises that ISO

9000 can be implemented without certification, simply for the quality benefits that can

be achieved.


31

A common criticism of formal systems such as ISO 9000 is the amount of money, time and

paperwork required for registration. Opponents claim that it is only for documentation.

Proponents believe that if a company has already documented its quality systems, then most

of the paperwork has already been completed.

Proper quality management has been widely acknowledged to improve business, often

having a positive effect on investment, market share, sales growth, sales margins,

competitive advantage, and avoidance of litigation28.

2.5 Maintenance

Maintenance of all plants and equipment is essential and forms part of an ENEMS (Energy

efficiency management systems). It is important to keep a maintenance schedule and record

of all inspections and maintenance activities. Maintenance activities are given in the

individual sections.

Modern preventative maintenance aims to keep the production and related processes usable

during their whole operating life. The preventative maintenance programmes were

traditionally kept on a card or planning boards, but are now readily managed using computer

software. By flagging-up planned maintenance on a daily basis until it is completed,

preventative maintenance software can help to ensure that no maintenance jobs are

forgotten.

It is important that the software database and equipment file cards with technical data can be

easily interfaced with other maintenance (and control) programmes. Such indicators as

'Maintenance in Process Industry' standards are often used for classifying and reporting work

and producing supporting reports. The requirements of the ISO 9000 standards for

maintenance can assist in specifying software. Using software facilitates recording problems

and producing statistical failure data, and their frequency of occurrence. Simulation tools can

help with failure prediction and design of equipment. Process operators should carry out local

good housekeeping measures and help to focus unscheduled maintenance, such as29:

• cleaning fouled surfaces and pipes

• ensuring that adjustable equipment is optimised (e. g. in cooling and ventilation)




32

• switching off equipment when not in use or not needed

• identifying and reporting leaks (e. g compressed air, steam), broken equipment,

fractured pipes, etc, i. e. in recuperator ductings.

• requesting timely replacement of worn bearings.


Energy savings, reduction in noise (e.g. from worn bearings, escaping pressurized air).

Operational data

Preventative maintenance programmes are installation dependent. Leaks, broken

equipment, worn bearings, etc. that affect or control energy usage, should be identified and

rectified at the earliest opportunity.

Economics

Installation dependent; good housekeeping measures are low cost activities typically paid for

from yearly revenue budgets of managers and do not require capital investments.

Driving forces for implementation

Generally accepted to increase plant reliability, reduce breakdown time, increase throughput,

assists with higher quality.

2.6 Monitoring and measurement

Monitoring and measurement are an essential part of checking in an ENEMS (Energy

efficiency management systems) as they are in every „plan-do-check-act‟ management

system. This section discusses some possible techniques to measure, calculate and monitor

key characteristics of operation and activities that can have a significant impact on energy

efficiency.

Measurement and monitoring are likely to form part of process control as well as auditing.

Measurement is important to be able to acquire reliable and traceable information on the

issues which influence energy efficiency, both in terms of the amounts (MWh, kg steam, etc.)

but also the qualities (temperature, pressure, etc.), according to the vector (steam, hot water,

cooling, etc.). For some vectors, it may be equally important to know the parameters of the


33

energy vector in the return circuits or waste discharges (e.g. waste gases, cooling water

discharges) to enable energy analyses and balances to be made.30

A key aspect of monitoring and measurement is to enable cost accounting to be based on

real energy consumptions, and not on arbitrary or estimated values (which may be out of

date). This provides the impetus to change for the improvement of energy efficiency.

However, in existing plants it can be difficult to implement new monitoring devices e.g. it may

be difficult to find the required long pipe runs to provide low non-turbulence areas for flow

measurement. In such cases, or where the energy consumptions of the equipment or activity

are proportionately small (relative to the larger system or installation they are contained

within), estimations or calculations may still be used. In addition, material flows are often

measured for process control, and these data can be used to establish e.g. energy efficiency

indicators.

In case of liquid flows, for their measurement non-permanent and non-destructive equipment

may be employed. To avoid high investment costs it should be considered to engage suitable

consultants or specified measuring bureaus to carry out those types of analyses31.

Good practice example - Energy monitoring system – Peak load limitation

The foundry Van Voorden from Zaltbommel in the Netherlands designs and produces marine

propellers, jets, and yacht propellers. Castings with a weight up to 30,000 kg can be

manufactured here. The melting shop is equipped with six induction furnaces. In the past, the

foundry was worried about the overrun of the power peaks (limit value). An excess of the

agreed maximum power consumption costs the company about 85 000 € per year.

The energy control system Padicon® could optimize the production processes in the foundry.

The six induction furnaces do not operate independently as before. They now operate co-

ordinated. This programme equalizes power peaks and sinks and initializes process control.

Fluctuations in energy requirements are reduced. The result: Before using the parallel-

differential current-regulation, the foundry was driven with a peak load of 5.773 kW, the

system now regulates the peak load by 3.500 kW.

Environmental benefits:




34

the permanent reduction can be seen as a good argument for the negotiation of

electricity supply contracts.

In addition, the delivering power supply companies can plan the demand for electricity

in safer way

The process allows for any desired period a transparent overview of the electricity

consumption for each attached furnace

The installation of the energy control system in the foundry Van Voorden took place in 2009.

The investment costs amounted to about 85.000 €.

The peak load was reduced by 39 percent. With the energy control system which is keeping

the lowered and monitored power maximum, the company saves every year about 100.000

€. The return on investment is given by the foundry with the value of 1 year.

Reference

Supplier: http://www.tanneberger.de

User: Foundry Van Voorden, 5301 LZ Zaltbommel, Netherlands

2.6.1 Indirect measurement techniques

Infrared scanning of heavy machinery provides photographic proof of hot spots that cause

energy drains and unnecessary stress on moving parts. This may be used as part of an

audit. Critical equipment affecting energy usage, e.g. bearings, capacitors and other

equipment may have the operating temperature monitored continuously or at regular

intervals; when the bearing or capacitance starts to breakdown, the temperature of the

casing rises. Other measurements can be made of other changes in energy losses, such as

an increase in noise, etc32.


As part of preventative maintenance:

• avoids unexpected plant shutdown


http://www.tanneberger.de/


35

• enables planned replacement

• extends life of equipment, etc.

2.6.2 Estimates and calculation

Estimations and calculations of energy consumption can be made for equipment and

systems, usually based on manufacturers' or designers' specifications. Often, calculations

are based on an easily measured parameter, such as hours-run meters on motors and

pumps. However, in such cases, other parameters, such as the load or head and rpm will

need to be known (or calculated), as this has a direct effect on the energy consumption. The

equipment manufacturer will usually supply this information.

A wide variety of calculators are available on the internet. These are usually aimed at

assessing energy savings for various equipment.

The application of calculators should be considered against the possible cost savings of

more accurate measuring or metering, even on a temporary basis.

Care should be taken with online calculators:

• their function may be to compare the cost of utilities from different suppliers

• this advice is important: the whole system the equipment is used in must be

considered first, rather than an individual piece of equipment

• the online calculators may be too simplistic, and not take account of loading, head,

etc. A problem with estimates and calculations is that they may be used repeatedly,

year-on-year, and the original basis may become lost, void or unknown. This may

lead to expensive errors. The basis of calculations should be reviewed regularly.

Estimates and calculation require no investment in equipment; however, staff time in

performing accurate calculations should be considered, as should the cost-risk from errors33.

2.6.3 Metering systems



36

Traditional utility meters simply measure the amount of an energy vector used in an

installation, activity, or system. They are used to generate energy bills for industrial

installations, and generally are read manually. However, modern technological advances

result in cheaper meters, which can be installed without interrupting the energy supply (when

installed with split-core current sensors) and require far less space than older meters.

Advanced metering infrastructure (AMI) or advanced metering management (AMM) refers to

systems that measure, collect and analyse energy usage, from advanced devices such as

electricity meters, gas meters, and/or water meters, through to various communication media

on request or on a pre-defined schedule. This infrastructure includes hardware and software,

for communications, customer associated systems and meter data management. Energy

account centres are the units at the site where energy usage can be related to a production

variable such as throughput34.

Operational data

Enables accurate measurement energy usage to energy account centres, within an

installation, with specific units and systems.

Applicability

Where there are more than one unit system using energy. Several studies show a major

reason for energy efficiency techniques not being implemented is that individual unit

managers are not able to identify and control their own energy costs. They therefore do not

benefit from any actions they implement.

2.7 Energy audits and energy diagnosis

In general, an audit is an evaluation of a person, organisation, system, process, project or

product. Audits are performed to ascertain the validity and reliability of information, and also

to provide an assessment of a system‟s internal control. Traditionally, audits were mainly

concerned with assessing financial systems and records. However, auditing is now used to

gain other information about the system, including environmental audits. An audit is based on

sampling, and is not an assurance that audit statements are free from error. However, the



37

goal is to minimise any error, hence making information valid and reliable. The term 'energy

audit' is commonly used, and is taken to mean a systematic inspection, survey and analysis

of energy flows in a building, process or system with the objective of understanding the

energy dynamics of the system under study. Typically, an energy audit is conducted to seek

opportunities to reduce the amount of energy input into the system without negatively

impacting the output(s).

An energy diagnosis may be a thorough initial audit, or may go wider, and agree a reference

frame for the audit: a set methodology, independence and transparency of the audit, the

quality and professionalism of the audit, etc.

The different energy audit models can be divided into two main types according to their

scope35:

1. The scanning audit models.

2. The analytical models.

Within these two types, there are different models which may be specified according to their

scope and thoroughness. In reality, the audit can be specified to meet the needs of the

situation.

Some standards exist, usually within auditing companies or energy saving schemes. The first

national standard for energy audits have been created. This standard is an energy diagnosis

reference frame which:

• proposes a method to realise an energy diagnosis

• sets out the general principles and objectives of such a mission as objectivity,

independence, transparency

• expresses recommendations that are essential to reach a first class service.

For the operator, the advantages of the reference frame are the description of a consensual

method, a base faciliting dialogue, a time saving tool, examples of outputs (lists of

equipment, balances, unfolding of a monitoring campaign, etc).

The scanning models



38

The main aim of scanning energy audit models is to point out areas where energy saving

possibilities exist (or may exist) and also to point out the most obvious saving measures.

Scanning audits do not go deeply into the profitability of the areas pointed out or into the

details of the suggested measures. Before any action can be taken, the areas pointed out

need to be analysed further.

A scanning audit model is a good choice if large audit volumes need to be achieved in a

short time. These types of audits are usually cheap and quick to carry out. A scanning audit

may not bring the expected results for an operator, because it does not necessarily bring

actual saving measures ready for implementation but usually suggests further analysis of key

areas. There are two main examples of scanning model, described below36:

• walk-through energy audits

• preliminary energy audits

Walk-through energy audit

A walk-through energy audit is suitable for small and medium sized industrial sites if the

production processes are not very complicated in the sense of primary and secondary

energy flows, interconnected processes, opportunities for re-using lower levels of heat, etc.

Preliminary energy audit

The scanning energy audit model for large sites is often called the preliminary energy audit.

Audits of this type are typically used in the process industry. Although the main aim of the

preliminary energy audit is in line with the walk-through energy audit, the size and type of the

site requires a different approach. Both types have been applied within this FOUNDYBENCH

project.

The analytical models

The analytical energy audit models produce detailed specifications for energy saving

measures, providing the audited client with enough information for decision-making. Audits of

this type are more expensive, require more work and a longer time schedule but bring

concrete suggestions on how to save energy. The operator can see the savings potential and



39

no additional surveys are needed. The analytical models can be divided into two main

types37:

• selective energy audits, where the auditor is allowed to choose the main areas of

interest

• targeted energy audits, where the operator defines the main areas of interest.

These are usually:

system-specific energy audits

comprehensive energy audits.

Selective energy audit

The selective energy audit looks mainly for major savings and does not pay attention to

minor saving measures. This audit model is very cost effective when used by experienced

auditors but may, in the worst case, be „cream skimming‟. There is always the risk that when

a few significant saving measures are found, the rest will be ignored.

This method has also been used in the FOUNDRYBENCH project, especially in very big

foundries. To identify savings in the „rest‟ a repetition of the analysis after three or four years

is a valuable strategy to improve the completeness step by step.

Targeted energy audit

The content of work in the targeted energy audit is specified by detailed guidelines from the

operator and this means that most of the systems to be covered by the targeted energy audit

are known in advance. The guidelines, set by the operator, may deliberately exclude some

areas. The reason for excluding certain areas may be that they are known to be normally

non-cost relevant (or more easily dealt with)38.

2.9 Energy models, databases and balances

Energy models, databases and balances, are useful tools to carry out a complete and in-

depth energy analysis and are likely to be part of an analytical or comprehensive energy




40

audit. A model is a plan or description designed to show where and how energy is used in an

installation, unit or system (e.g. a database). The model therefore seeks to record the

technical information about an installation, unit or system. It will record the type of equipment,

energy consumption and operating data such as running time. It should be complete enough

for the task (but not excessively so), easily accessible to various users in departments such

as operations, energy management, maintenance, purchasing, accounts, etc. It may usefully

be part of, or linked to a maintenance system, to facilitate record updating, such as motor

rewinding, calibration dates, etc.

Where an energy model, database or balance is used, it may be built up based on system

boundaries, e.g.39:

• units (department, production line, etc.)

System

Individual equipment (pumps, motors, etc.)

• utility systems (e.g. compressed air, pumping, vacuum, external lighting, etc.)

Individual equipment (pumps, motors, etc.).

The auditor (or data gatherer) must take care to ensure the efficiency recorded is the real

system efficiency.

As an energy model or database is a strategic tool to carry out an energy audit, it is good

practice to validate it before use by performing a balance. The first step is to compare the

total amount of energy consumed, as derived from calculations, with the amount consumed

as shown by the metered energy supplies. Where the installation is complex, this can be

carried out at a unit or system level. If the balance between the calculated and the metered

consumptions is not achieved, then the data in the model should be rechecked, in particular

any estimations, such as load factors and working hours. Where necessary, these should be

established with greater accuracy. Another cause of errors is not identifying all the equipment

using energy.

Electrical energy

For an electric model, database or balance, the following data can be gathered for each

electrically powered device, such as motors and drives, pumps, compressors, electric

furnaces, etc.



41

• rated power

• rated efficiency

• load factor

• working hours per year.

Whereas power and efficiency are easy to detect as they are normally labelled on the device

itself, the load factor and the hours per year are estimated.

Thermal energy

The drawing up of a thermal energy model, database or balance is more complex than an

electric model. To have a complete picture of the thermal consumption, two kinds of models

(or databases or balances) are compiled: first level and second level. To compile the first

level energy model, it is necessary to take a census of all users of any kind of fuel. For any

consumer of fuel (e.g. boilers, furnaces), the following data should be recorded:

• type of fuel supplied in a specific time period, usually in a year

• kind of thermal carrier entering the boiler (e.g. pressurised water): flow rate,

temperature, pressure

• condensate: percentage of recovery, temperature, pressure

• boiler body: manufacturer, model, installation year, thermal power, rated efficiency,

exchange surface area, number of working hours in a year, body temperature,

average load factor

• burner: manufacturer, model, installation year, thermal power

• exhaust: flow rate, temperature, average carbon dioxide content

• kind of thermal carrier leaving the boiler (e.g. steam): temperature, pressure.

Though all such data should be collected, in the first level thermal model („generators‟ side‟)

only the major users of energy need to be taken into account. It is generally helpful to convert

all energies into primary energy or specific energy types used in the industry.

Applicability

The type of model and the detail of information gathered depend on the installation. An

analysis of every piece of energy-consuming equipment is often not feasible or necessary.

Electrical energy models are suitable for smaller installations. Process analysis including


42

detailed electrical and thermal power consumption is more appropriate in larger installations.

Priorities can be set to maximise the cost-benefit of the data-gathering, e.g. data on

equipment exceeding certain power consumption, or guidelines such as initially collecting

data on the 20 % of equipment that uses 80 % of the power (e.g. steam, electricity), etc. It

should be noted that as the model is used, and as ENE is gained, then the remaining

equipment can be added, again in a planned manner.40

On a foundry scale only limited simulation models are available by now reflecting the

complexity of production processes. The most advanced are designed to support factory

planning. An overview is given in [Solding; 2008]. The there as well described Discrete Event

Simulation is regarded to be the most advanced foundry approach in energy consumption

simulation on an sub-process level.

2.9.1 Optimization and management of utilities using models

Optimization and management of utilities using models brings together techniques such as

metering-, measurement systems and adds software modelling and/or control systems. For

simple installations, the availability of cheaper and easier monitoring, electronic data capture

and control, make it easier for operators to gather data, assess process energy needs, and

to control processes. This can start with simple timing, on-off switching, temperature and

pressure controls, data loggers, etc. and is facilitated by using software models for more

sophisticated control.

At the more complex levels, a large installation will have an information management system

(manufacturing and execution systems), logging and controlling all the process conditions. A

specific application is in managing the way energy is sourced and supplied (supply side

energy management, distribution management or utilities management). This uses a

software model linked to control systems to optimise and manage the energy utilities

(electricity, steam, cooling, etc.).41

Cross-media effects




43

Usually efficiencies are additive, but in some cases, if the supply/utility distribution side is not

considered, then the benefits in reducing demand are not realised, e.g. when steam savings

in one process unit simply lead to venting elsewhere if the steam system is not rebalanced.

Operational data

With increasing complexity, optimum and energy efficient operation can be achieved by

using the right tools, ranging from simple spreadsheet based simulation tools, or distributed

control systems (DCS) programming to more powerful model-based utilities management

and optimisation systems (a utilities optimiser) which might be integrated with other

manufacturing and execution systems on site.

A utilities optimisation system will be accessed by staff with a variety of backgrounds and

objectives (e.g. engineers, operators, plant managers, buyers, accounts staff). The following

are important general requirements:

• ease of use: the different users need to access the system and the system needs to

have different user interfaces as data integration with other information systems to

avoid re-entering data, e.g. such as enterprise resource planning (ERP), production

planning, data history

• robust: needs to show consistent and reliable advice to be accepted by users

• close to reality: needs to represent plant reality (costs, equipment, start-up times)

without introducing an unmanageable level of detail

• flexible: needs to be flexible so that adjustments in the changing plant environment

(e.g. temporary restraints, updating costs) can be done with little effort.

The key requirements for a model-based utilities optimiser are:

a model of the fuel, steam and electricity generation processes and distribution

system. At a minimum, the model must accurately represent:

the properties of all fuels, including the lower heating value and

composition

the thermodynamic properties of all water and steam streams on the

facility

the performance of all utility equipment over their normal range of

operation

• a model of all buy-and-sell contracts that apply to the utilities system


44

• mixed integer optimisation capability, which enables utility equipment on/off decisions

as well as discontinuities in the contract model and/or utilities process model

• online data validation and gross error detection

• open loop

• online optimisation

• the possibility to carry out 'what-if' studies for off-line studies (study impact of projects,

study impact of different types of contracts for, e.g. electricity and fuel).

Applicability

Simple control systems are applicable even in small installations. The complexity of the

system will increase in proportion to the complexity of the process and the site. Utilities

optimisation and management is applicable on sites where there are multiple types of energy

usage (steam, cooling, etc.), and various options for sourcing energy, between these energy

carriers and/or including in-house generation (including cogeneration and trigeneration. The

key requirements for a model-based utilities optimiser are a model of the fuel, steam and

power generation processes and distribution system. As a minimum, the model must

accurately represent the properties of all fuels, including the lower heating value and

composition. This may be difficult with varied and complex fuels such as municipal waste,

which reduces the possibilities of optimising the energy export.

2.9.2 Benchmarking

At its simplest, a benchmark is a reference point. In business, benchmarking is the process

used by an organisation to evaluate various aspects of their processes in relation to best

practice, usually within their own sector. The process has been described as:42

• „benchmarking is about making comparisons with other companies and then learning

the lessons which those companies each show up‟ (The European Benchmarking

Code of Conduct)

• „benchmarking is the practice of being humble enough to admit that someone else is

better at something, and being wise enough to learn how to be as good as them and

even better‟ (American Productivity and Quality Center).



45

Benchmarking is a powerful tool to help overcome 'paradigm blindness' (which can be

expressed as: 'the way we do it is best, because we've always done it this way'). It can

therefore be used to assist continuous improvement and maintaining impetus. Energy

benchmarking takes data that have been collected and analysed (see measurement and

monitoring and energy audit sections). Energy efficiency indicators are then established that

enable the operator to assess the performance of the installation over time, or with others in

the same sector.

It is important to note that the criteria used in the data collection are traceable, and kept up to

date.

Benchmarking may also apply to processes and working methods.

Energy data gathering should be undertaken carefully. Data should be comparable. In some

cases, the data may need correction factors (normalisation). For instance, to take account of

feedstock, age of equipment, etc., and these should be agreed at the appropriate level (e.g.

nationally, internationally). Key examples are to ensure that energy is compared on a

suitable basis, such as prime energy, on lower calorific values, etc.

Applicability

Benchmarking can be readily used by any installation, group of companies, installations or

trade association. It may also be useful or necessary to benchmark individual units,

processes or utilities. Validated data includes those in vertical sector BREFs, or those

verified by a third party. The period between bench markings is sector-specific and usually

long (i.e. years), as benchmark data rarely change rapidly or significantly in a short time

period. There are competitiveness issues to be addressed, so confidentiality of the data may

need to be addressed. For instance, the results of benchmarking may remain confidential, or

it may not be possible to benchmark, e.g. where only one or a small number of plants in the

EU or in the world make the same product.

With the FOUNDRYBENCH project benchmarking was important an aspect. A benchmark

system has been developed and tested with quite a number of foundries.

The mean outcome of these activities was that – because of the wide variety of foundry

processes – a very narrow discrimination of benchmark boundaries or classes of processes

rsp. sub-processes has to be carried out. The currently available data turned out to be often


46

not detailed enough to support this benchmark-approach, although in principle it would be a

useful tool.


47

3. Horizontal techniques

3.1 Heat exchangers

Heat exchangers are often applied in foundries as energy saving systems. Common

installations are heat recovery of exhaust air, cooling water of furnaces and cooling of air

compressors. There are many methods to optimise heat recovery efficiency of heat

exchanger. Some of the methods are very sophisticated and may be relevant when larger

heat recovery plants for process industry are under consideration. In foundries more interest

should be paid to finding reliable basic parameters for calculations. Most important of the

facts are:

real operation time of waste heat source

real temperature level of waste heat

real flow of waste heat

real operational of reclaimed energy = how many hours and by which effect the

reclaimed energy can be used

technical restrictions of use of waste heat

need of cleaning and maintenance of heat exchangers and system

material demand for heat exchangers due to corrosion, max temperature or

mechanical strain e.g. in cleaning

possibilities to locate heat pump and need and cost of space

need of piping, ducting, control and electricity supply

need of additional effect or flexibility due to possible changes in processes in future

savings in heating system by using heat recovery

price of electricity and saved heat in future

interest of loan in future

Quite often the finding of reliable technical parameters requires measurements and data

collection of a loner period. An occasional monitoring of a process doesn‟t usually give

sufficient information how the process works during a whole shift or a week.A practical way

to optimise an efficiency of a heat exchanger is to enquire exchangers with different

parameters and efficiencies. Sometimes it is reasonable to proceed in step by step. First to

make a low invest for a moderate system and to reserve a possibility for fulfilling the


48

efficiency or effect in future by installation of an additional heat exchanger in series with the

first one.

Instead of simple pay-off-time calculations interest calculation should be done (ROI or the

return of the investment or the internal rate of interest). With PC it is handy to study e.g. the

influence of different basic parameters on profitability on higher heat recovery effect.

3.1.1. Water-to-water heat exchangers

There are three main types of heat exchangers: counter-flow, cross-flow and parallel-flow.

Nowadays most water-to-water heat exchangers are plate heat exchangers. They work a

little as cross-flow type but mostly as counter-flow type. With formulas taken from general

hand books it is difficult or even impossible to guess exactly proper parameters of grade of

recuperation. Fortunately the manufactures have programs for dimensioning and they make

optimising and calculations free of change. In those calculations customer should consider

foiling factors to be used in programs if waste water contains impurities.

Most manufacturers have typical plate types of their own. These may have a great influence

on heat transfer and plate area and price of the unit. Enquiries from several producers are

usually worthwhile.

With plate heat exchangers it is sometimes important to choice proper type of plate joints. In

the case of dirty unit the heat exchanger may need heavy washing. Sometimes even any

kind of chemical treatment and flushing will not help the unit must be opened for cleaning.

Therefore the models that are able to be opened are available (units with gaskets). However,

normally solder joints or brazed models are good enough. In heavy use - high pressure or

temperature - welded plate joints are needed.

The hot water tanks are often used as a heat exchangers. Hot water is stored in the tank with

volume of 1 - 10 m3. The warm water is used for tap water or in some applications for heating

of premises. When heating tap water the hot water tank will be equipped with spiral tube heat

exchanger to keep tube water hygienic. The water flow in the tank has to design carefully to

have full capacity from the reservoir. The top of the tank will be filled with hot water and cold

water will be returned to the bottom of the tank. The middle level of the tank will be equipped

with a perforated plate that preserves the vertical temperature stratification in the water.

In water-to-water heat exchangers typical material is stainless 316 which is sustainable even

against low chlorine content in water. Titanium is suitable for sea water. A reliable way to


49

choose the proper material is to change experience with same type of processes and

conditions.

3.1.2. Air-to-air and coil heat changers

Air-to-air heat exchangers - recuperative and regenerative ones - have been commonly used

in ventilation and air conditioning over 40 years at least in northern countries. Some models

have been used in process industry like in paper machines or power plants even over 70

years. So there is lots of experience of them. To choose suitable model and optimal

efficiency, experience of specialised consults and manufactures should be used.

Manufacturers have programs to optimize constructional and economical characters.

If it seems that no experience can be found of some special heat recovery application it can

be reasonable to use a pilot plant trial. With a very small experiment it is possible to find and

ensure working both for main solutions and detailed design.

Foundry processes, like melting and heat treatment, are very energy intensive. Most of the

surplus energy is transferred by radiation or convection into indoor air. Air flows of foundry

ventilation and processes are reasonably high. This makes heat recovery to play important

role as energy saving options. The most common way is to recover heat from exhaust air to

a recovery liquid or directly to supply air. Heat recovery (HR) systems applied in foundries

are as follows, see figure:

-run-around cycle coils (liquid coils system)

-plate heat exchangers

-heat pipe coil

-rotary coil regenerator

stationary coil regenerator

Comprehensive measurements have to be carried out in energy analysis in foundries. The

field studies include the measurements of energy efficiency of heat recovery units (HRU) as

well. The designed and real/measured efficiency are essential data for the existing HRU.

There are number of inaccuracies dealing with the measurement. The efficiency

measurement should be measured during as cold climate as possible. If you have to low

temperature differences the inaccuracy rises rapidly. The result should be in the range of


50

less than ±10 %-units. In cold temperature (below -15 °C) you however have to realise that

the defrosting automation in the exhaust air duct can restrict instantaneous efficiency.

Supply and exhaust air flow and temperatures are to be measured before and after the HRU.

The thermal efficiency is the proportional temperature drop of temperature in relation to air

flows. In case of unequal air flows of exhaust and supply air the temperatures have to be

weighted with air flows:

2 – T1)/(T3 – T1) * 100, where (%)

T1 is outdoor temperature, (°C)

T2 is supply air temperature after HRU, (°C)

T3 is exhaust air temperature before HRU, (°C)

Extra inaccuracy occurs in the case of condensation. This slightly changes the air flow and

remarkably the temperature because of the latent heat.

The air temperatures of the regenerative rotary HRU (Heat Wheels) and plate HRU are

highly stratified. The vertical and horizontal air temperatures differs strongly, even more than

ten centigrades. This is the case especially just next to HRU. You can never trust on the

existing temperature indicators in the ventilation units. The correct temperature has to be

measured in the point of unstratified air. Usually correct point lays after the fan taking again

into account that fan rises the temperature with 0,5 - 1 °C. More exact temperature rise can

be calculated from motor and shaft power and air flow rate depending on the location of

motor either in the air steam or out of it.

Characteristic efficiency rates for supply air heating values are as follows in the case of equal

supply and exhaust air flows.

Table 1: Characteristic efficiency rates for supply air heating values

System type of HRU Heat efficiency, %

Runaround cycle coils 40 … 60

Plate heat exchanger 45 … 55


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Heat pipe coil 45 … 60

Rotary coil regenerator 65 … 80

Stationary coil regenerator 75 … 85

The simplified selection guide for heat recovery systems follows in the next table.

Table 2: General guidelines for HR-system applications

Need/condition Proper application

lack of space coils

exhaust and supply not adjacent coils

low price material need aluminium plate heat exchanger

high efficiency need (exp. energy, long lifetime) regenerator

unit must be moved for cleaning heat pipe, cleaning sector regenerator

dry dust in exhaust air only regenerator

sticky contaminant in exhaust air heat wheel or plate heat exchanger with

automatic cleaning system

recovery of humidity or drying needed regenerator

exhaust air mixing to supply air must be avoided runaround cycle coils


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Rotary coil regenerator

Exhaust air

Supply air

Counter flow plate heat

exchanger

Exhaust air

Preheated

supply air

Outdoor air

Cooled down

exhaust air Plate heat exchanger


53

Figure 9: Heat recovery systems for ventilation systems

Heat exchangers - good practice example - waste heat to dry varnish

The downstream water-paint lacquering/primering of castings (behind the casting process)

requires an energy source for the drying of the dye. Here, the most common drying furnaces

use natural gas.

The installed heat capacity of the plant is 2,250 kW based on 5 burners.

To supply this demand of energy from alternative energy sources, heat recovery from the

cupola off-gas was suitable. The exhaust gas of the hot blast cupola behind the recuperator

has a temperature well above 600 ° C. The thermal oil heat exchanger system for the

utilisation of waste heat from the cupola furnace was designed in a way that a thermal oil

flow temperature can be reached within the range of 220 to 240 °C.

In the thermal-oil-air heat exchangers (air pre heater), the temperature of the circulating air

for the lacquer drying must to be heated up at 200 °C. The available heat in the circuit here in


54

total is far higher than needed for the drying operation. Therefore, there is a potential for

more export such as the core drying to be coupled to the heat system.


Reduction of gas consumption in the colouring of up to about 70%

Improving energy efficiency

The corresponding reduction in emissions of CO2

The corresponding reduction in operating costs

Investment costs for the integration of waste heat utilisation (thermal oil recovery system) for

lacquer drying amounted to approximately EUR 1.4 million. Through the use of waste heat

for lacquer drying production costs can be reduced by about 25%.

The continuous required maintenance and repair costs of thermal oil recovery system are in

the range of about 20 000 € /y.

Due to the heat recovery system, the gas consumption for water-based lacquer drying can

be reduced to approximately 246 400 m³ /y or 2.7453 million KWh reduce /y.

This is associated with a reduction in CO2 emissions by about 490 t /y (derived from 246 400

m³ of natural gas for the gas burner).

on the assumption of a reference price for natural gas in the amount of 39.30 ct /m³,

(average costs in terms of the German foundry industry in the reference year 2010) one can

theoretically realize a saving of 96,835 € /y.

Reference

User: www.heunisch-guss.com

Short example – heat exchangers – waste heat from a thermal afterburner

A system has been developed that enables the heat generated to be recycled in an energy-

efficient manner. Waste heat from a thermal afterburner is used for preheating the

combustion air in the furnace, which is then fed to the boiler house. A temperature of 860°C

develops during the afterburning of the exhaust heat from the furnace. Heat exchangers

have been installed for efficient use, raising the temperature of the combustion air required

by the furnace from about 20°C to 350°C, thereby significantly reducing the energy

requirements of the furnace and vice versa, the waste heat escaping from the furnace

supports the combustion process in the plant. At a temperature of 160°C, it is first fed

www.heunisch-guss.com


55

through the hot flue gas stream of the afterburner, thereby heated to 520°C. The warmer the

flue gases, the more efficient the combustion process. Finally, another part of the existing

residual heat is used for heating drinking water and for providing steam in the neighboring

boiler-house. The flue gas leaves the afterburning plant at a temperature of only about

150°C, and is finally cleaned by state-of-the-art systems engineering and filters.

The entire amount of energy required for the operation of thermal afterburners is recycled

thanks to this sophisticated energy concept, being fed both to the production process and the

central heat supply. Factory and administration buildings, process baths and the water of

sanitary facilities are heated.43

3.2 Heat pumps

3.2.1 Introduction

Heat pumps are based on the same process as refrigerators: compressor sucks refrigerant

gas from evaporator. When the compressor compresses the refrigerant gas its pressure

increases and the temperature rises typically over 100°C. From the compressor the gas is

led to a condenser where the refrigerant is chilled to condensation temperature which

typically is 40...55 °C. In that phase the refrigerant is liquefied = condensed. The condense

flows to the evaporator through an expansion valve where the pressure decreases

dramatically and the liquid forms fine mist. The mist evaporates and this needs heat. The

heat comes to the mist from heat transfer coil of the evaporator. The evaporated refrigerant

gas becomes superheated gas and flows back to the compressor. This is called the Carnot-

process.

During recent years heat pumps have become more economical due to the risen oil price.

Also some technical development has been achieved. A profitability of a heat pump is based

on the ratio between the value of saved heat energy and the price of running electricity. This

ratio shall be essentially bigger than the COP of a heat pump. Coefficient of Performance

(COP) illustrates the ratio of the heat energy released by the heat pump compared to the

electricity for the compressor drive. Typical COP values vary from 2 to 6 where the value of 3

is quite normal.

COP can be estimated roughly by the formula below:

43 Best-Practice-Examples of the Non-Ferrous Metals Industry; page 11


56

COP = ηe x ηc x Thot/(Thot - Tcold), where

ηe = efficiency of electricity motor

ηc = efficiency of compressor

Thot = temperature of condensation, (K, Kelvin degree)

Tcold = temperature of evaporation, (K)

ηe x ηc = ηt = could be called total equipment efficiency and Thot/(Thot - Tcold) Carnot-efficiency, which is

the theoretical max efficiency of any heat pump.

In small - electricity motor approx. 1 - 2 kW - heat pumps equipment the efficiency is near 40

% and in big 300 kW heat pumps 70 %.

Example of a room heat pump: Heat is taken into evaporator from 0 °C outdoor air (= 273 K)

and indoor air is recycled from condenser in the temperature of 35°C (308 K) back indoors.

Temperature difference in evaporator and condenser heat exchangers is supposed to be 2°C

which corresponds with the temperatures of 271 K in the cold and 310 K in the hot side. The

coefficients of efficiency are 0,6 and 0,7. COP = 0,6 x0,7 x 310/(310 - 271) = 3,3.

3.2.2 Air-to-air heat pumps

There are many types of heat pumps. Air source heat pumps (ASHP) are variations of

coolers. Typical and well known are small units which heat premises in winter and cool them

in summer. Big air handling units or so called roof top packages, which can take care of

heating and cooling of e.g. factory halls, have been on the market more than 40 years. These

units are normally ready-to-use factory made installations with the air flows from 1 to 20 m3/s.

Outdoor temperature has a high influence on COP in ASHP. At the temperatures - 20°C

COP can be only slightly over 1, or even under 1. Some models even don't run in low

temperatures under -15°C. In cold winter conditions the evaporators get often frost that must

be melted away every now and then. The melting takes place typically with electricity that

lowers the energy efficiency of the heat pump too. However the frost melting system is

essential operation in northern areas.

3.2.3 Ground source heat pumps


57

Ground source heat pumps (GSHP) are widely used in north Europe where outdoor

temperature is low in long periods. The use of GSHP started at seventies and has grown

under last ten years. The heat to GSHP comes from wells or soil ditches where closed brine

(ethyl alcohol) pipelines are placed. Heat transfer takes place in the piping area which is

under water in the wells.

Nowadays GSHP-units are available for bigger buildings like shopping centers or factories. A

GSHP gives a COP of 2,5 - 5 regardless of outdoor temperature. However temperature of

heating water is important. GSHP usually can't generate temperature over 60°C without

additional electrical heating. The ideal heated water temperature is 30 - 40 °C which is

typical in floor or air heating. The temperature of 30 °C gives COP around 5 and 50 °C COP

3 when the brine temperature is approx. 0 °C at well outlet.

Normally the heat is transferred from the soil surface of the globe where the heat origins from

the sun radiation. From the ground surface the heat flows through the soil to the rock and

from the rock to water in the wells. The heat well has always water present and the water

heats the running brine inside the plastic pipes. The brine transfers heat to the heat pump

unit. This all means that the heat transfers through many material and surfaces. If the loose

soil layer above the solid rock is thick the heat transfer has a high resistance and the flow is

weak compared with a case where the solid rock and ground water are near the soil surface.

In the case where high heating power is needed the local thermal situation shall be

investigated carefully. Ground heat can also be used in the way of ground water pumping to

the GSHP. Normally the regulations require the water to be recycled back to the soil/rock.

3.2.4 Free cooling

If a GSHP is used it is also possible to use a free cooling system in summer without using of

compressor energy. This means that the brine or water is pumped to a free cooling heat

exchanger where cooling water can be pumped into cooler units in spaces or cooling coils in

air handling units. Temperature of cooling water depends on local conditions and varies from

12 - 18°C. This kind of dual acting use of a GSHP may improve COP both in heating and

cooling. Inside the solid rock the water flows have conclusive significance on the heat

capacity of rock/soil.

Free cooling system may be equipped with the coils of heat recovery systems or run-around

loop type. These coils consist typically of 6 to 12 rows and give effect even when there is low

temperature difference between brine and air. In summertime the free cooling system can be


58

used and in the same system the heat recovery during winter time. To control the system

only a change-over valve is needed in the piping system.

3.2.5 Rising the temperature of process cooling water

In many cases temperature of outgoing cooler waters from processes are so low that with

conventional heating water design it is not possible to use the low temperature water energy

without special arrangements. There are two possibilities to improve the situation. With larger

heat transfer surfaces of heating coils in air handling units that requires more rows in the

coils - lower temperature may be sufficient for heating supply air. Another option is to rise

temperature with a heat pump. In the case where temperature difference between heating

water and cooling water is only some tens of degrees the COP can rise reasonably high.

If heat is used to domestic water an accumulator is usually needed. The use of washing

water is at the highest after working shift and lasts a short period of 15 - 20 minutes. A

relatively small heat pump can load the accumulator during the day. Typical cooling water

source in the foundries are the furnace cooling system. The cooling effect depends on the

process phase. Outlet water temperature varies between 30 - 40 °C which must be

hightened to 55 °C to avoid the growth of Legionella bacteria in the accumulator. Also heat

from annealing or tempering or water cooled air compressors have been used to heat central

heating water or supply air.

3.2.6 Exhaust air heat pumps

Exhaust air is a conventional source of heat for heat pumps. In the system a evaporate coil is

installed in exhaust air. The factory built system applies the exhaust air as heat source and

heats up the supply air flow of the ventilation unit. Benefit of exhaust air heat pumps

compared to other heat recovery systems is that it can cool exhaust air to nearly 0 °C even

when outdoor temperature is not low. This performs a lot more heat energy. Heat can also

been used for washing water.

Typical COP is 3 meaning that the price of saved heat energy is 1/3 of the price of electricity.

Running costs of other heat recoveries are low. On the other hand the saved heating energy

with an exhaust air heat pump may be double compared with other systems. Annual energy

saving can be calculated with special programs. Roughly it can be calculated using a


59

diagram of local ambient temperature stability or degree-day number of heating. With a

graphical method regained energy is quite easily solved. One shall understand that

exploitable energy consists of energy from exhaust air and energy from the compressor.

Difficulties with using the heat of exhaust air are same as with heat recovery. Sticky

impurities in air may be a problem needing filtering or regular washing/purging of evaporator

coil.

3.2.7 Other heat sources

Heat pumps can also use energy from waters in nearby lakes, rivers or sea. Even community

or industrial waste water after cleaning treatment has been used. The rise of het source

temperature with multi stage compressors can be used. Normally the cases are very

individual and can't be described more in the text.

If there would be free waste energy at the temperature of 95 °C or more, an absorption water

chiller or heat pump could be used too. However in ordinary foundries such energy sources

are not widely available.

3.2.8 Life time and maintenance of heat pumps

As an invention the heat pump is over 150 years old. During years they have been

developed especially in compressors and control systems. Nowadays small compressors are

scroll-type and bigger ones screw-type. No pistons, sealing rings or valves are available.

Speed control is commonly used. The development has increased the life time of small

compressors that is estimated to be over 10 years. In the case of bigger compressors with

the electricity power of tens of kilowatts the lifetime is 20 to 30 years. Instead of one or two

big compressors a quite economical solution has been the use of many compressors. This

type of multi-compressor systems offers flexibility to control and reliability to running.

The need of maintenance is at the same time diminished. Small units need no maintenance

except cleaning of filter in indoor unit. Big units need normal annual checking of oil and

refrigerant level and sometimes changing of refrigerant dryer and/or filter. Service costs are

low - only 1 - 2 % of the initial investment. An investment cost of a heat pump plant depends

on the case, size, engineering and design. A rough estimation is 400 - 600 €/kW according to

the installed heat effect.


60

In economical calculations a technical lifetime of a heat pump can be estimated to be quite

long. Normally more consideration has to be paid to the real operational period of the foundry

process.

3.3 Solar heat

Solar energy offers a vast potential of energy saving options. In Europe the direct sun

radiation reach a power of 1 – 1.5 kW/m2. While the sun is not shining all the time the

average value of radiation states the potential in a better way. In Europe mean annual

energy have been reported from Tampere 1.1 MWh/m2 to Lissbon 2.1 MWh/m2. This chapter

describes in general level the hot water production system that can be applied in foundries

for supply water production or heating of premises.

3.3.1 Solar water heating system

The main components of solar water heating systems are solar panels that are called as heat

collectors. They collect heat from sun radiation and heats up running water in collectors. The

heated water will be stored in a hot water tank. A boiler or immersion heater can be used as

a back up to heat the water further to reach the needed temperature. Solar water heating

system with big tank can be applied to tap water heating system that preserves energy for

washing after each work shift.

The collectors are covered with adsorptive colour, like black and they are two types of solar

water heating panels:

- evacuated tubes

- flat plate collectors

Larger solar panels can also be arranged to provide some contribution to heating. However,

the amount of heat provided is generally small and it is not normally considered worth while.

3.3.2 Costs, savings and earnings


61

The cost range of installing a typical solar water heating system is around 1000 € per

collector m2. Savings are moderate - the system could provide most of your hot water in the

summer, but much less during colder weather. The system needs a backup heater for the

total effect of all hot water demand. It has been calculated with Middle European data that a

system dimensioned for household use cost some 4,000 € and payback time would be in the

range of 6 - 8 years. In the active use of a South European foundry the payback time would

lay in level of 5 years.

Maintenance costs are very low. Most solar water heating systems come with a five-year or

ten-year warranty and require little maintenance. You should take a look at your panels every

year and have them checked more thoroughly by an accredited installer every 3 - 5 years, or

as specified by your installer.

Solar water heating systems can achieve savings on your energy bills. Savings from a well-

installed and properly used system replacing gas heating or electric immersion heating ca be

achieved; however, savings will vary from user to user.

Depending on country it may be possible to receive payments for a solar water heating

system through government‟s Renewable Heat Incentive.

3.3.3 Conditions for solar water heating systems

The solar hot water panels will need roof space which faces east to west through south and

receives direct sunlight for the main part of the day. The panels don't have to be mounted on

a roof: they can be fixed to a frame on a flat roof or hanging from a wall. If a dedicated solar

cylinder is not already installed then the existing cylinder need to replaced or a dedicated

cylinder with a solar heating coil have to be added. Most conventional boiler and hot water

cylinder systems are compatible with solar water heating. But if the boiler is a combination

boiler and there currently is no hot water tank, a solar hot water system may not be

compatible.

In a nutshell:

Solar thermal panels commonly known as solar heating panels, provide an additional heating

source for hot water tank, see Figure 10.

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Financial-incentives/Renewable-Heat-Incentive-RHI


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Figure 10: Illustration of a typical solar heat panel system for hot water production

Short Example – solar heat – coated thin copper sheet absorbers

A German company has been using the special conductivity of the material copper for years

in order to successfully produce high-tech semi-finished copper products for use in the

renewable energies sector. These include high-tech copper sheets for industrial solar

solutions. As much solar energy as possible can excellently be converted into heat by means

of solar thermal energy if the sunlight transmits its energy onto a specially coated thin copper

sheet. These absorbers are connected to copper tubes on the back of these sheets. The

excellent conductivity of the metal transmits the heat to the heat transfer liquid running

through the tubes. For a 2.5 m2 collector, about 20 meters of copper tubes are required;

these are attached in tight loops under the absorber band. Copper tubes and sheets with

high purity surfaces Connecting the complete system to the drinking water heating or heating

water circuit ensures that, in an optimal environment, up to 60% of a building‟s hot water

requirements and up to 20% of a building‟s heating requirements can be covered by means

of a solar thermal energy system.


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Figure 11: Copper Sheet with tubes inside a Solar Cell; Copper tubes with High Purity Surface

One decisive fact for high-energy yield is that the absorber bands must have a special

surface quality: very exact and completely flat. Together with the special coating, which

ensures that about 95% of the solar radiation is converted into heat, the copper sheets are a

real high-tech product. Copper is versatile; it acts long-term and reliably in building shells and

technology. The use of copper in solar thermal energy does not only guarantee high energy

yield. The consistent application of the raw material from solar thermal energy collectors to

tube systems to building installations in the entire water and heating section also guarantees

longevity and reliability.44

Short example – solar heat - Zinc roofing with integrated hot water collectors

A water carrier consisting of heat-conducting and heat-insulated capillary pipes is mounted

underneath a protective zinc tile and connected to a collecting duct. Thanks to zinc‟s

excellent conductivity, these unglazed solar collectors also act as environment absorbers: by

means of continual low temperature heat they generate high energy production in domestic

technological systems.45 (Figure 12)

44 Best-Practice-Examples of the Non-Ferrous Metals Industry, page 36f

45 Best-Practice-Examples of the Non-Ferrous Metals Industry; page 43


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Figure 12: Heat pump system: GeoSolar System

3.4 Geothermal heat

Geothermal heat - good practice example – Borehole Thermal Energy Storage (BTES)

ITT Water and Wastewater in Emmaboda experienced the same challenge as all foundries in

northern Europe, the surplus of heat at some times of the year or the day and deficit at other

times. Excess heat from furnaces was only recovered partly at summer season, waste heat

that was not needed for hot water and therefore was cooled in a cooling tower.

In order to have a possibility to store the energy between seasons a Borehole Thermal

Energy Storage (BTES) was constructed. The BETS consists of 140 vertical boreholes, 150

metres deep with an internal space of four metres. The storage allows for an energy saving

of about 2,500 MWh per year (the total calculated amount of energy storage is 3,800 MWh,

1,300 MWh losses). The maximal effect is estimated to 2.2 MW.

Waste heat generated from the two furnaces in the melt shop (and other processes) is

pumped down into the BTES during summer season and is stored in the ground water. When

there is a need for heating at the cold season of the year, heat from the BTES can be

pumped into the internal heating circuit.


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The BTES can also be used for cooling in case the cooling tower of the foundry would break

down, i.e. the BTES gives increased process stability.

Economic benefits:

Invest: ~1.000.000€

Operational costs: 16949€/y

Return on invest: 60 months

Reference

User: Leif Rydell, ITT Water and Wastewater, Sweden

3.5 Chillers and cooling systems

3.5.1 Furnace and sand coolers

About 20 - 25 % of electrical power supplied to induction furnaces converts to heat in cooling

coil. The rate is usually bit lower in arc furnaces. The coil is cooled with water cycling in

tubes. The cooling water transfers the heat to heat exchanger. This exchanger can be

cooled by river, lake or ground water. Also cooling towers or even water chillers have been

used depending on local conditions.

Outlet temperature of cooling water is quite often 40 - 50°C. Some furnace manufacturers

allow even higher temperature. Changing the converter to be cooled first and leading water

from it to cool the coil it is possible to raise exit temperature some degrees. The difference of

temperatures between theoretical and practical operation temperatures may be due to safety

marginal needed especially with an old control system. Anyway with temperature of 35°C it is

possible to preheat domestic water but to get temperature of 55°C (needed to avoid bacteria

growing in a storage tank) a heat pump or after-heater is needed.

Sand cooling systems are usually based on pipe heat exchangers where pipe water cools

down the shake out sand. The sand temperature is often high above 150 °C and this heats

water temperature often above 70 °C. This energy offers fluctuating source for heating

energy to be recovered and stored.

Low temperature like 35°C is however quite suitable to heat supply air in air handling units. If

heat transfer surfaces of old heating coils are not large enough additional coils can be

installed. Warm water can also be used both to heat supply air and domestic water. A heat

exchanger for summer cooling is needed.


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3.5.2 Water storage tanks

If somehow the exit water temperature can be raised to 45 - 55°C it can be used to heat

domestic water. A storage tank for this is needed because normally main consumption of

water occurs after working shift when workers use showers. With this tank it is practical and

economical to design the system so that the tank efficiency would be as high as possible. A

good efficiency means that the temperature stratification of water is high: warm and chill

water are mixed in the tank as little as possible and warm water can be received almost as

much as the volume of the tank is.

There are different methods to reach the high accumulation efficiency of the storage tanks.

High and narrow tanks are good for this. Sometimes smaller tanks have been piped in series

forming a counter-flow system. It is important to make inner pipe constructions in tanks so

that incoming water spreads evenly without forming circulating flows inside the tank. Cone

structures in the heads of inlet pipes have been used to lower running speed. It is also

effective to use a perforated baffle plate in the tank to improve the stratification.

In foundries storage tanks or heat accumulators are installed in the heating network where

the primer heating source is electricity and when the price of electricity varies during time of

day (low night tariff). There are also combinations of fuel and electricity heating. Domestic

water can be heated in summer with electricity and in other times using boiler water. To

diminish electricity peak power the pressurized water tanks are widely used.

3.5.3 Improving chiller efficiency

If compressor water chillers have been used there may be possibilities to improve energy

economy even from 20 to 60 %.

Control of chiller

Normally a chilled water accumulator is used. The chiller has connected to the accumulator

with a separate piping and pump. Typically the chiller keeps coming water temperature

constant and circulation pump is running all the time. The result is poor temperature


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stratification in the accumulator and lot of starts and stops in chiller. Result is additional use

of electricity.

Improvements for traditional system are:

1. the chiller should be controlled according the temperature in the accumulator

the circulation pump should be running only when needed it is possible too

piping installations in the accumulator should be taking care of high temperature

stratification, chilled water should be supplied to the tank with a wide cone or diffuser

and return water through a cone to the upper part of the tank

coolers in the net should be controlled by 2-way valves and the circulation pump

should be speed controlled keeping pressure difference constant in the net. As a

result pumping energy is saved and better stratification in the tank is reached

With these actions it is possible to improve energy economy 10…15 %.

Free cooling

Even a better possibility to diminish energy consumption is by using a free cooling system.

Savings depend on local weather conditions. A free cooling means that with a separate free

cooling heat exchanger, brine circulation and fluid cooler the return water is chilled always

when outdoor air temperature is 1…2 degrees chiller than the return water. If the free cooling

has not enough effect the chiller can be started by a low stage. By using a water spray

system on the fluid cooler it would be possible to use free cooling partially even when

outdoor air is somewhat warmer than the return water.

The free cooling system should be designed and dimensioned taking care of cooling loads at

cold season time. These loads can come from processes and electricity room coolers etc.

Design of water temperature of cooling coils in air conditioning units

Traditional temperatures for cooling coils in air conditioning have been supply to coils 7°C

and exit 12°C. In most cases it would be possible to use 10/15°C or even higher

temperatures. If supply air from outdoors shall be dried e.g. to a dew point of 12°C, it can be

done with a separate chiller. Most room coolers normally are working with circulating air.

Savings with higher water temperature may be from 20 to 40%.

3.6 ORC systems


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3.6.1 System introduction

Organic Rankin Cycle (ORC) power plant has been developed into more practical use. ORC

power plants can effectively convert waste energy into electricity. The appropriate organic

fluid is recycling in the Rankine thermodynamic circuit network. The latest systems have

been developed from tens of kWe to MWe class plants per a single unit. Multiple systems

can be installed in parallel to achieve up to multi megawatt power station.

The process scheme is simple, see Figure 13. The Rankine cycle is a thermodynamic cycle

practically approaching to the ideal Carnot cycle. Organic media can be used as cycle gas

e.g. toluene, isopentane, ammonia, silicon oil or refrigerants like CFCs, freons etc. The

bigger the molecule mass offers higher turbine efficiency, up to 80 %.

The advantage of ORC is the benefit to apply relatively low and moderate temperatures of

waste heat sources. Typically the temperature rage varies from 100 – 300oC, but the

temperatures as low as to 73oC have been applied. This means that many industrial waste

energy sources, like cupola flue gases and cooling energy, cooling water of compressors and

furnaces can be applied. The market is growing with the technology. Many hundred of units

have been installed and still operating for many years all over the world.

Figure 13: Principle of Organic Rankine Cycle power plant

3.6.2 System performance and cost

There are several applications installed in energy sources of geothermal wells, solar energy,

industrial waste energy and engine flue gas flows. In practical installations a net electrical

efficiency of 10 – 20 % has been achieved. In general, specific investment costs for ORC


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units vary between 1,000 € and 3,000 € per fully installed kWe in the size class of 1 MWe

have been reported. For free available energy the specific operation cost range in order of

0.005 – 0.01 €/kWe have been stated. Figure 6 illustrates a commercial installation of ORC

system.

Figure 14: Illustration of a ORC power plant of size class 1 MWe (PureCycle)

3.7 CHP plants

3.7.1 Power plants with steam boiler

Combined Heat and Power plant (CHP) is a name for many type of energy generation

systems. The old CHP type is a power plant that contains a steam boiler with a steam turbine

and generator. After generator steam is condensed by using the return water of the district

heating network. A part of the steam can be used in nearby factory which typically is a paper

mill. Total efficiency of this type plant is 80 % and electrical efficiency approx. 30 %. These

power plants can use almost any fuel from domestic waste to oil and coal depending on the

boiler type. Electricity effect can vary from 1 MW to hundreds of MW.

3.7.2 Gas turbine plants

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A bit more modern type of CHP has a gas turbine plant. The turbine rotates a generator. Hot

gases from the turbine are led to a steam boiler with steam turbine and generator. After the

turbine the steam is condensed with district heating water. Total efficiency can be above

90%. Smallest conventional gas turbines have been types which are used in aeroplanes.

Turbine effect starts from 300 kW to tens of MW. In foundries more interesting CHP plants

are relatively small options.

3.7.3 Diesel engine and generator

A quite old small CHP system is a reciprocating engine - in practice diesel engine - which

rotate the generator. This type of construction is familiar of reserve power plants. Flue gas

heat can be led to a boiler. The heat from the engine block and cooler can be used for

heating premises. Electrical power varies from some tens kW to some megawatts. Oil and

gas can be used as energy source. Gas can be natural gas, gas from a gas generator using

solid bio fuel, or gas from waste. A problem especially with small engines is quite short

maintenance periods. Valves, piston rings, bearings, sealing and filters may need

maintenance after ten thousand of running hours. Big diesel engines – size of megawatts -

can run without remarkable maintenance work hundreds of thousands hours.

Diesel engines have been used directly to rotate compressors too. In the system no

generator and electricity system with losses are needed.

3.7.4 Micro turbines

A relatively new invention used in CHP is so called micro turbine plant where gas is used to

rotate turbine and generator. Rotation speed in micro turbines is high - 60,000 rpm. The

turbine can apply gas bearings which need no maintenance and friction is negligible. These

turbines were originally developed for cars. This type of CHP plant may generate electricity

from 30 kW to 400 kW. Usually several units are running in parallel.

The basic components of a micro turbine are the compressor, turbine generator, and

recuperator. The heart of the micro turbine is the compressor-turbine package, which is

commonly mounted on a single shaft along with the electric generator. Two bearings support

a single shaft. The single moving part of the one-shaft design has the potential for reducing


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maintenance needs and enhancing overall feasibility. There are also two-shaft versions, in

which the turbine on the first shaft directly drives the compressor while a power turbine on

the second shaft drives a gearbox and conventional electrical generator producing 50 Hz

power. The two-shaft design has more moving parts but does not require complicated power

electronics to convert high frequency AC power output to 50 Hz.

Figure 15: Micro turbine power system

3.7.5 Fuel cells

Under development and research work are fuel cells which can use natural gas or waste gas.

Electricity effects are from some kilowatts and higher power can be generated by using

several units. Electrical efficiency is low from 25 to 35%.

3.7.6 Stirling engine

Also an old invention Stirling engine - hot air engine - is under new research work. A Stirling

engine is a heat engine operating by the cycle of compression and expansion of air or other

gas, at different temperature levels where is a net conversion of heat energy to mechanical

work.

Invented by Robert Stirling in 1816, the Stirling engine has the potential to be much more

efficient than a gasoline or diesel engine. But today, Stirling engines are used only in some

very specialized applications, like in submarines or auxiliary power generators for yachts,

http://www.poweronsite.org/AppGuide/Chapters/Chap4/Images/Figure_4-4_Microturbine_Flow.jpg

http://en.wikipedia.org/wiki/Heat_engine

http://en.wikipedia.org/wiki/Heat

http://en.wikipedia.org/wiki/Work_%28physics%29

http://auto.howstuffworks.com/diesel.htm

http://www.howstuffworks.com/submarine.htm


72

where quiet operation is important. Although there hasn't been a successful mass-market

application for the Stirling engine, some very high-power inventors are working on it.

A Stirling engine uses the stirling cycle, which is unlike the cycles used in internal-

combustion engines.

The gasses used inside a Stirling engine never leave the engine. There are no

exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and

there are no explosions taking place. Because of this, Stirling engines are very quiet.

The Stirling cycle uses an external heat source, which could be anything from

gasoline to solar energy to the heat produced by decaying plants. No combustion

takes place inside the cylinders of the engine.

There are hundreds of ways to put together a Stirling engine. Like the steam engine, the

Stirling engine is traditionally classified as an external combustion engine, as all heat

transfers to and from the working fluid take place through the engine wall. This contrasts with

an internal combustion engine where heat input is by combustion of a fuel within the body of

the working fluid. Unlike a steam engine's (or more generally the Rankine cycle engine's)

usage of a working fluid in both its liquid and gaseous phases, the Stirling engine encloses a

fixed quantity of permanently gaseous fluid such as air.

Main benefit of the Stirling engine is can apply almost any fuel, like waste heat. Electrical

efficiency may be in the range of 10 to 25%.

Figure 16: Stirling engine and process cycle in pV-diagram

3.7.7 Economy of CHP

http://home.howstuffworks.com/composting.htm

http://en.wikipedia.org/wiki/External_combustion_engine

http://en.wikipedia.org/wiki/Internal_combustion_engine

http://en.wikipedia.org/wiki/Fuel

http://en.wikipedia.org/wiki/Rankine_cycle

http://en.wikipedia.org/wiki/File:Stirling_Cycle_color.png


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A crucial question of an economy of CHP plant is how much of the heat energy can be used

continuously year around. In the case of foundry they usually use equally heat and electricity

which make the balance a bit uneconomical. Another possibility is that the fuel is

exceptionally cheap. Also economical support from government may be vitally important.

Investment cost in small micro-CHP plants is typically 3 - 4 €/Wel. In bigger - size 1 MW -

plants costs are 0.4 – 1.5 €/Wel depending on the ratio between heat and electricity effect.

Operation and maintenance costs may be 2 - 4 cents/kWhel.

3.8 Compressed air systems

3.8.1 System types

The air compressors consume some 5 - 15 % of electricity energy of foundries but they

represent some 20 % saving potential of that. Usually savings arise from avoiding

unnecessary use and leakage, improvement of control system or applying heat recovery.

There are various compressor types the can be used, depending system size, pressure air

demand and required pressure range. In the following presentation the main emphasis is on

commonly used compressors in industry in the pressure range of 7 bar (0.7 MPa). These

compressor types are screw, scroll and piston compressors. The main components in a

compressed air system are shown in Figure 17.


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Figure 17. Compressed air system with typically audited components

1. Compressed air system leaks

2. Shut-off of unused pressure air lines

3. Bottle-necks in pressure air networks

4. Compressed air control and storage

5. Pressure drop in filters and positions of valves

6. Condensate trap function

7. Type of drier, control and operation

8. Operation of heat recovery

9. Room temperature, compressor room ventilation and intake air system

10. Oil separator operation

For systems in the 7 bar range roughly 0.1 kWh of energy will be used to produce one cubic

meter of compressed air. With electricity prices in the range of 10 cent/kWh the price of

compressed air is 1 cent/m3. Leaks and poor control of the system pushes up costs 20-

100%. Maintenance costs will increase operating costs further 10-30%. As a rule of thumb

one can estimate that the overall cost of compressed raises up to 1.5 cent/m3.


75

3.8.2 Compressed Air System Controls

Over the years, compressor manufacturers have developed a number of different types of

control strategies. Controls, such as start/stop and load/unload, respond to reductions in air

demand, increasing compressor discharge pressure by turning the compressor off or

unloading it so that it does not deliver air for periods of time. Modulating inlet and multi-step

controls allow the compressor to operate at part-load and deliver a reduced amount of air

during periods of reduced demand.

Systems with multiple compressors use more sophisticated controls to orchestrate

compressor operation and air delivery to the system. Network controls use the on-board

compressor controls‟ microprocessors linked together to form a chain of communication that

makes decisions to stop/start, load/unload, modulate, vary displacement, and vary speed.

Usually, one compressor assumes the lead with the others being subordinate to the

commands from this compressor. System master controls coordinate all of the functions

necessary to optimize compressed air as a utility. System master controls have many

functional capabilities, including the ability to monitor and control all components in the

system, as well as trending data to enhance maintenance functions and minimize costs of

operation. Other system controllers, such as pressure/flow controllers, can also substantially

improve the performance of some systems. The objective of an effective automatic system

control strategy is to match system demand with compressors operated at or near their

maximum efficiency levels. This can be accomplished in a number of ways, depending on

fluctuations in demand, available storage, and the characteristics of the equipment supplying

and treating the compressed air.

A properly configured system master control can determine the best and most energy-

efficient response to events that occur in a system. The number of things a system master

control can interface with is governed by practicality and cost limitations. System master

control layout has the capability to perform these functions:

Adjust pressure/flow controller set points

Monitor dryer dew point(s)

Monitor filter differential pressure

Monitor condensate trap function

Start/stop and load/unload compressors


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Change base/trim duties

Select appropriate mix of compressors to optimize efficiency

Select which compressor should be started/stopped relative to change in system

demand.

For example, adjustment of pressure controller set points is usually carried out to minimize

power demand and to reduce pressure air leaks during periods of low demand. Potential

saving can be 5-40 % of the systems overall consumption.

Start/stop is the simplest control available and can be applied to either reciprocating or rotary

screw compressors. The motor driving the compressor is turned on or off in response to the

discharge pressure of the machine. Typically, a simple pressure switch provides the motor

start/stop signal. This type of control should not be used in an application that has frequent

cycling, because repeated starts will cause the motor to overheat and other compressor

components to require more frequent maintenance. This control scheme is typically only

used for applications with very low-duty cycles for compressors in the 20 kW and under

range. Its advantage is that power is used only while the compressor is running, but this is

offset by having to compress to a higher receiver pressure to allow air to be drawn from the

receiver while the compressor is stopped.

Start/stop control requires usually a large volume distributions system and pressure receiver.

A required difference of 1.5 bar between start and stop pressure set points leads usually to

higher pressure levels than normally required and therefore increase in power demand.

Load/unload control, also known as constant-speed control, allows the motor to run

continuously, but unloads the compressor when the discharge pressure is adequate.

Compressor manufacturers use different strategies for unloading a compressor, but in most

cases, an unloaded rotary screw compressor will consume 15 to 35 percent of full-load

horsepower while delivering no useful work. As a result, some load/unload control schemes

can be inefficient. The compressor will work within the limits of the set values (usually 0.5-1

bar) for minimum and maximum pressure.

Some compressors are designed to operate in two or more partially loaded conditions. With

such a control scheme, output pressure can be closely controlled without requiring the

compressor to start/stop or load/unload. Piston compressors are designed as two-step


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(start/stop or load/unload), three-step (0, 50, 100 percent) or five-step (0, 25, 50, 75, 100

percent) control. These control schemes generally exhibit an almost direct relationship

between motor power consumption and loaded capacity.

Variable speed is accepted as an efficient means of rotary compressor capacity control,

using integrated variable frequency drives. Compressor discharge pressure can be held to

within +/- 0.1 bar over a wide range of capacity, allowing additional system energy savings.

In a positive-displacement rotary compressor, the displacement is directly proportional to the

rotational speed of the input shaft of the air end. However, it is important to note that with

constant discharge pressure, the actual efficiency also may fall at lower speeds, requiring an

increase in torque. Electric motors and controllers are currently available to satisfy these

needs, but their efficiency and power factor at reduced speeds must be taken into

consideration. Compressors with variable speed control should not be used if compressed air

demand is less than 20 % of the compressors maximum output.

A compressed air system analysis can highlight the true costs of compressed air and identify

opportunities to improve efficiency and productivity. Compressed air system users should

consider using an auditor to analyze their compressed air system. The cost of such analysis

is ca. 3,000 to 6,000 €. The cost of a complete system control that reads and coordinates the

functions of individual compressors is typically 4,000-10,000 €.

Many plant air compressors operate with a full-load discharge pressure of 7 bar and an

unload discharge pressure of 7.5 bar or higher. Many types of machinery and tools can

operate efficiently with an air supply at the point-of-use of 6.5 bar or lower. If the air

compressor discharge pressure can be reduced, significant savings can be achieved. A rule

of thumb for systems in the 7 bar range is: for every 0.1 bar increase in discharge pressure,

energy consumption will increase by approximately 1 percent at full output flow

Although the decrease of the discharge pressure lowers the power demand of the

compressor, it must be remembered that if the pressure falls too much, the air consumption

can rise dramatically due to longer operating times. For example, if the air pressure at the

connected equipment falls 0.7 bars below the recommended pressure level, consumption will

increase 14 %.

Compressed air systems – good practice example - intelligent compressor control


78

Hundreds of plants have updated the control system of their compressors. In old systems

every compressor has a control system of its own. In old systems start and stop limits for

pressure switches have been set in steps sequentially. This causes that the last compressor

in series has to run in relatively high pressure. Result is unnecessary power consumption, air

leakages, unstable pressure in piping network and all kind of wear in system and air

consumption devices.

An updated control system measures pressures in piping network and compressor central

and controls intelligently running of each compressor. By analyzing measuring results it is

possible to see if it is profitable to enlarge some pipelines, decentralize or centralize

compressor locations and how to select running order and set points optimally. Sometimes

even a replacement of some compressor is reasonable. A foundry had mean value 14.9

m3/min of compressed air, range 2.1...35.8 m3/min. Mean pressure in the piping was 7.88

bar(g) ja variation 4.91...8.61 bar(g).. Mean compressor power was 179 kW and the range of

variation 115...300 kW. The number of the compressors was 6 and the rated power of the

compressors motors was 295 kW. The specific power consumption was 179 kW/14.9 m3/min

= 12 kW/(m3/min). The system was measured, analyzed and updated with Sarlin-Balance-

System. Nowadays the piping pressure is 6.6 bar(g), mean power 163 kW, air consumption

21.6 m3/min and specific power 7.54 kW/(m3/min).

A foundry had mean value 14.9 m3/min of compressed air, range 2.1...35.8 m3/min. Mean

pressure in the piping was 7.88 bar(g) a variation 4.91...8.61 bar(g). Mean compressor power

was 179 kW and the range of variation 115...300 kW. The number of the compressors was 6

and the rated power of the compressors motors was 295 kW. The specific power

consumption was 179 kW/14.9 m3/min = 12 kW/(m3/min). The system was measured,

analyzed and updated with Sarlin-Balance-System. Nowadays the piping pressure is 6.6

bar(g), mean power 163 kW, air consumption 21.6 m3/min and specific power 7.54

kW/(m3/min).

With the annual running hours of 6000 h and an energy price 60 €/MWh the energy cost

savings have been: (12 - 7.75)kW/(m3/min) x 21.6 m3/min x 6,000 h/a x 0.06 €/kWh = 34,680

€/a.

Reference

Investigation: AX Consulting, Tampere Finland

Compressed air systems – good practice example – optimized compressor drives


79

Air pressure is used in foundries for a variety of applications, for example:

Powering of tools in the manufacturing sector " fettling shop”

Fill core boxes on core machines

Transport of sand by lines

Blowing of mold and core boxes by means of compressed air blow guns

Cleaning of filter units (baghouse filter ) at cyclic intervals

Compressed air is, however, the most expensive form of energy. It should be considered that

the efficiency of the compressors (compression efficiency) is low: Only 5% of the energy

used is conserved in compressed air, 95% are converted into heat.

By using variable-speed VSD compressors (VSD = Variable Speed Drive) one can

significantly reduce the energy demand. The reason for the energy saving is the optimal

operating point of the used electric motors.

The control of these compressors continuously measures the system pressure and

compares it with the desired value. In accordance with the requirements of the connected

equipment, systems, and buffer memory, the speed is increased or decreased.

Regulation of the operating pressure by the actual inspections. The oversupply of, for

example, 1 bar generates an increase of energy by about 6-7%

Reference

http://www.industrie.de/industrie/live/index2.php?menu=1&submenu=3&object_id=31356062

Compressed air systems – good practice example - the control systems of multi

compressors run

Traditional compressor running controls are based on pressure switches: starting and

stopping set point of every compressor are cascaded so that at a low air consumption the

piping pressure is high and at a top consumption low. This method brings a disadvantage

that the average piping pressure is unnecessary high causing both more leakage and more

consumption e.g. in tools and pulse cleaning systems. In old plants a system analyze shall

be done first. In such a control system deliverer monitors pressure in the piping network and

control room and electricity consumption of compressors.

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Nowadays intelligent control systems are used. The pressure of the system is measured in

piping network - not in the compressor room. The pressure set values of compressors are

floating and the compressor starting sequence is based on air output of each compressor.

As side effect of the more steady and lower pressure the life time of the compressors

increases, maintenance management improves and the process conditions in the piping

network brings better quality.

Savings by this system are from 10 % to even 40 %. Preliminary estimation of savings could

be 10 %. If the annual mean consumption is 100 kW x 4,000 h/a = 400,000 kWh, this means

savings potential of 40,000 kWh/a or 4,000 €/a by price of 100 €/MWh. Typical system cost is

20,000 €.

Reference

User: N.N

3.8.3 Compressed Air System Components

Compressors

Single- and Double-Acting Reciprocating Compressors were the most widely used in

industrial plant air systems. Piston compressors have high maintenance cost and the

compressed air contain oil mist meaning poor air quality due to high running temperature this

is why they have been widely replaced with other model in industry. They also tend to be

noisy and shaky.

Single-acting (air-cooled) operating efficiency: 7.8 to 8.5 kW/(m3/min)

Double-acting (water-cooled) operating efficiency: 5.3 to 5.7 kW/(m3/min)

Today, lubricant-injected rotary screw compressors are used in most industrial plant air

applications and for large applications in the service industries. Rotary screw compressors

provide continuous flow and do not have the type of pressure pulsations typically associated

with reciprocating compressors. Two-stage rotary screw compressors are generally more

efficient than single-stage units. Lubricant-injected rotary screw compressors are typically

less efficient than two-stage, double-acting reciprocating compressors or three-stage

centrifugal compressors. In general, rotary screw compressors are also less efficient at part-

load than reciprocating compressors.


81

Two stage (air-cooled) operating efficiency: 5.7 to 6.0 kW/(m3/min)

Lubricant-free Compressors of reciprocating and rotary air compressors are available.

Centrifugal air compressors are inherently lubricant-free. Lubricant-free compressors may be

appropriate for specific applications or to meet specific environmental regulations. Lubricant-

free rotary screw and reciprocating compressors are generally less efficient than lubricant-

injected machines.

Lubricant-free compressor do not need oil filters at all, which accordingly can be used to

lower discharge pressure. If an absorption-wheel dryer is used the loss of compressed air

as dryer purge air is completely avoided and the electrical power required to drive the drum

rotation motor is minimal (0.12 kW). No extra energy is needed to dry the compressed air

as the heat generated in the compression process is used for this purpose.

Operating efficiency: 6.4 to 7.8 kW/(m3/min)

Air Receivers

Air receivers are designed to provide a supply buffer to meet short-term demand spikes that

exceed the compressor capacity. They also serve to dampen reciprocating compressor

pulsations, separate out particles and liquids, and make the compressed air system easier to

control. In some cases, installing a larger receiver tank to meet occasional peak demands

can even allow for the use of a smaller compressor. In most systems, the receiver will be

located just after the dryer. In some cases, it makes sense to use multiple receivers, one

prior to the dryer and one closer to points of intermittent use.

There are several methods to calculate the required size of an air receiver (Var):

Var = 0.1 – 0.14 dm3 * Qcompr, where

Qcompr = air delivery of the compressor, (dm3/min)

Var = Qcompr/(8*p), where

Qcompr = air delivery of the largest compressor, (dm3/min)

p = difference between allowed maximum and minimum pressure levels, (Pa)


82

Air receivers are never too large but they can be too small. Sometimes periodically operating

large consumers of compressed air should be equipped with air receivers of their own.

Hence the whole distribution system does not need to be sized because of one consumer

and pressure fluctuations in the distribution system are minimized. A local air receiver

volume is calculated as follows:

Var = Q * t / p, where

Q = air demand of the individual consumer, (m3/min)

t = time of air consumption, (minute)

p = allowed pressure drop, (bar).

Compressed air systems – good practice example – low pressure air filter

The cleaning of the filter system in the area of the sand treatment was performed in the past

by using compressed air. With this type of cleaning was also associated a high noise level,

caused by pulses of compressed air to clean the filter (baghouse filter).

The foundry Jürgens has in the renewal of the filter in the sand conditioning a new system

selected, which is a nearly new technology in this industrial sector ( the low-pressure air

filter).This technique is already used in the woodworking industry. Background for the

implementation of the filter system was the necessary renewal of existing old filter system.

The cost reduction by improving energy efficiency is a positive side effect and results from

the reduction in air pressure demand (The purge air fan has a lower - or even no - demand of

pressurized air).

This filter technology is suitable in the area of sand conditioning, because the dusts in this

area are not difficult to handle. They are not adhesive or hot. The dust can be cleaned off

very easily as a consequence of the filter medium (filter medium). The sample filter system

has a cleaning capacity of 150,000 m³ /h.


Reduction of noise. The foundry is located in a mixed area. The permissible limits

have been complied in the past, but now they are clearly below. As reasons can be

called: The missing air pressure surges and the noise protection enclosure of noise

causing parts of the plant.


83

Increase energy efficiency by reducing the air pressure needs. Buying the new filter

system could also reduce the energy costs.

The compressed air costs were before the new filter was implemented to 2,958 €/y. The

operation of the compressed air blast cleaning was carried out in two-shift operation with

13,300 cycles per year. The compressed air costs amount to 0.22248 €/cycle.

The cost of low-pressure air filter are about 731 €/y. The operation of the low-pressure air

filter takes in two-shift operation with 13,300 cycles per year. The current cost is 0.055

€/cycle.

Reference

User: Gießerei Jürgens GmbH & Co. KG; http://www.juergens.net/

3.8.4 Performance and energy use

Compressed Air System Leaks

All compressed air systems have leaks. Leaks can be a significant source of wasted energy

in any industrial compressed air system, sometimes wasting 20 to 30 percent of a

compressor‟s output. A typical plant that has not been well maintained is likely to have a leak

rate equal to 20 percent of total compressed air production capacity. On the other hand,

proactive leak detection and repair can reduce leaks to less than 10 percent of compressor

output.

There is usually very little leakage in pressure air distribution pipes. Leaks occur most often

at joints and connections. In many cases, leaks are caused by failing to clean the threads or

by improperly applied thread sealant. Non-operating equipment can be an additional source

of leaks. Equipment no longer in use should be isolated with a valve in the distribution

system.

Leakage measurement is usually done with clamp meters and data-loggers (power use is

measured and produced air flow is defined from performance curve), which measure the

compressors electrical power during the work shift and when there is no demand on the

compressed air system (all end-use equipment is turned off). If possible, flow meters with

data-loggers can also be used.

For compressors that use start/stop controls, there is an easy way to estimate the amount of

leakage in the system. This method involves starting the compressor when there is no

http://www.juergens.net/


84

demand on the system (when all the air-operated, end-use equipment is turned off). A

number of measurements are performed to determine the average time to load and unload

the compressor. The compressor will load and unload because the air leaks cause the

compressor to cycle on and off as the pressure drops from air escaping through the leaks.

Total leakage (percentage) can be calculated as follows:

Leakage = [(t * 100)/(t+toff)] (%), where

t = on-load time (minute)

toff = off-load time (minute)

Leakage is expressed in terms of the percentage of compressor capacity lost. The

percentage lost to leakage should be less than 10 percent in a well maintained system.

Poorly maintained systems can have losses as high as 20 to 30 percent of air capacity and

power.

Leakage can also be estimated if there is a pressure gauge downstream of the receiver. This

method requires an estimate of the total system volume, including any downstream

secondary air receivers, air mains, and piping (V, in m3). The system is then started and

brought to the normal operating pressure (P1). Measurements should then be taken of the

time (T) it takes for the system to drop to a lower pressure (P2). Usually P1-P2 is between 1-

2 bar.

Leakage can be calculated as follows:

Qleak = (V * (p1-p2)/t ) * 1,25 (m3/min), where

V = volume, (m3)

p1 , p2 = pressure (bar)

t = time (minute)

The 1.25 multiplier corrects leakage to normal system pressure, allowing for reduced leakage

with falling system pressure. Again, leakage of greater than 10 percent indicates that the

system can likely be improved. These tests should be carried out quarterly as part of a

regular leak detection and repair program.

Compressed air systems – good practice example – leakage control of compressed air


85

The fittings - like hoses, quick shut-off valves, condensate traps - of a compressed air system

in foundries work in mechanically very demanding conditions. Therefore leakages are

common. Controlling leakages is a most economical way to avoid rising of running costs. A

regular auditing system is needed. At least two annual inspection tours are recommended. In

spite of that the personnel shall be educated to announce of leakages. The best way to

notice leakage is to use own ears when the foundry is quiet. The notices are then written

down and slips leaved by the leakage points. By the regular inspections leakage can be

diminished from original 20 % to 10 %, which could be acceptable - though even leakage of 4

% have been reached and recommended as a goal.

A rate of leakage can be measured in most cases by measuring the compressor power after

working shift. Usually only one compressor is needed to keep pressure in the system.

Graphical monitoring of the compressor power tells when the compressor is supplying air

and when it is resting. If all the compressors are equipped with a proportional control - speed

control or modulating - figures of the power consumption measuring may be too unclear for

estimate leakage. Then one possibility is first to calculate or at least roughly estimate the

system volume. Then after stopping a compressor the pressure in the piping is monitored. By

means of the speed of pressure dropping the leakage can be determined. If there are two or

more foundry halls and warehouses working in different shifts - the piping should be

furnished with shut-off valves with remote controlled actuators. Thus the piping net work not

needed for production can't cause leakage. Also an intelligent control system of the

compressor pressure diminish leakages keeping mean pressure lower than in simple

pressure switch systems.

As a side-effect the running hours of the compressors will diminish and life time respectively

increase in years. Lower running hours bring also some savings in maintenance costs of the

compressor centre.

Savings: the mean power consumption of the compressors is 150 kW. Annual working hours

are 4,000 h. The annual electricity energy use of the system is 600,000 kWh. A 10 % drop of

the consumption due to a better leakage control saves 60,000 kWh. With the electricity price

of 100 €/kWh this makes annually 6,000 €. Additionally the need of maintenance drop for

running hours are lower. Return: 6,000€-1,000€-500€ = 4,500€

Reference

User: N.N


86

Distribution System

The optimal pressure drop in a properly dimensioned networks is ca. 0.1 bar, which consists

of the following example parts:

Distribution pipe 0.03 bar

Connection pipe 0.005 bar

Service pipe 0.02 bar

The overall pressure drop of the whole distribution system should not exceed 0.3 bar.

Compressed air distribution system is usually never oversized, since it also acts as a peak

consumption balancing vessel, helping the compressor‟s automation. The old rule of thumb

is that a designer should first calculate the required pipe size, and then choose a pipe size

one dimension larger.

The filter is an issue of pressure drop especially when being contaminated. In filter, the

pressure drop must not be more than 0.3 – 0.5 bar, in spite of manufacturers guide (even 0.7

bar). The choice of filter should be based on air quality requirements of the compressed air.

End-use equipment

Compressed air is expensive to produce and the efficiency of many pneumatic tools is only

10…20 %. With electric tools the efficiency is significantly better but their main disadvantage

is poor ergonomics (weight). Because compressed air is also clean, readily available, and

simple to use, it is often chosen for applications in which other methods or sources of air are

more economical. To reduce compressed air energy costs, alternative methods of supplying

low-pressure end-uses should be considered before using compressed air in such

applications.

Heat Recovery

As much as 80 to 93 percent of the electrical energy used by an industrial air compressor is

converted into heat. In many cases, a properly designed heat recovery unit can recover

anywhere from 50 to 90 percent of this available thermal energy and put it to useful work heating

air or water. Typical uses for recovered heat include supplemental space heating, industrial

process heating, water heating, makeup air heating, and boiler makeup water preheating. Heat

recovery systems are available for both air and water-cooled compressors.


87

Figure 18: Principle scheme of heat recovery of a compressor

Compressed air systems – good practice example - heat recovery of compressor oil

cooling

Nowadays most compressors in foundries are screw-compressors which use oil to seal

screw contact and for lubrication. Most part of the motor power releases as heat to oil

circulation. Rest of the motor energy is taken out in the after cooler. Only some percents of

the energy go in air to piping networks. Oil coolers and the after coolers are usually

constructed of finned coils which are located in series in a cooling air flow. The air

temperature after cooler is usually 10...15°C higher than temperature in a compressor room.

By a straight ducting joint to compressors the compressor room temperature can be kept

lower compared with a heat recovery using compressor room air. Lower temperature means

little better water and oil condensation in after coolers and oil filters giving better compressed

air quality. Also compressor air mass production increases proportionally to suction air

temperature in Kelvin degrees. However, energy saving in compressor power is not achieved

by this means for thicker or heavier suction air needs equally more compression power.

A method to benefit oil cooler heat resembles a system using heat from a compressor room.

The difference is that exhaust air ducting will be connected to the oil coolers. Thus a higher

exhaust temperature can be reached. This means smaller ducting and equipment compared

with a compressor room air recovery. The system consists of shut-off damper for each

compressor and one damper for return air to the compressor room to keep it warm during


88

winter time. Additionally a damper for exhaust air to outdoors and a damper for transfer air to

heated premises are needed. Also a booster fan is usually needed especially, if transfer

ducting is long or high air velocities are needed to save space and room. By using a booster

fan a small gap in joints to compressors may be used and compressor cooling can operate

regardless of the heat recovery system. Transfer air flow as well as return air flow and

outdoor air flow to the compressor room are controlled by the compressor room temperature.

The air flow to other premises is controlled by room temperature of heated rooms: if heating

is not needed, air is blown to outdoors.

Compressor room temperature is kept in 15°C and air temperature from compressors is

30°C. Heat is used when temperature in outdoors is lower than 10°C. Motor power of the

compressors is 200 kW. Thus the transfer air volume is 200 kW/1 kWs/kg°C/(30-

10)°C/1,2kg/m3 = 5,6 m3/s. Mean effect 100kW. Heating seasons 1,200h (by max effect).

Savings: 100 kW x 1,200 h = 120 MWh, a' 50 € brings 6,000 €; Invest: ducting 20 m á 400 --

> 8,000 €; air distributions: 6 m³/s x Z x 200 x 1200 €; dampers: 6 x á 1,000 € = 6,000 €; fan:

4,000 €; controls: 4,000 €; other: 2,000 €. Invest total: 25,200 €.

Reference

User: N.N

Compressed air systems – good practice example - heat recovery of cooling air of

compressor rooms

In practice all the electric power used in compressors comes to the compressor room when

air cooled compressors are used. The room needs cooling by ventilation. Typically in

summer conditions the temperature difference between supply and exhaust air is 5...10°C.

Thus a compressor power of 100 kW needs ventilation air 8...17m3/s or 29,000...61,000m3/h.

In a heating season the temperature difference is greater and air flow smaller. In this case

the ventilation air flow is ca 2...4m3/s. This can be used to heat production premises or

warehouse. A necessity for air transfer to working area is that compressors, condensate

traps, oil separators and such are maintained so that there is no compressors room air

quality spoiling oil leakage on floor or equipment surfaces.

The heat recovery system is simple: in a heating season warm air from a compressor room is

blown to a foundry hall. In extreme cold conditions a part of the air may be blown to the

compressor room to maintain a certain minimum temperature. In summer the exhaust is

blown to outdoors. Supply air system to the compressor room is usually in every case


89

equipped with indoor-outdoor air mixing dampers or fan speed control. Equally shall the

exhaust side be equipped. In practice the investment consists of a fan with sufficient

pressure, air transfer ducting, automatically controlled in and out dampers, air distribution

devices like manually adjustable dampers and grilles and an electricity and control system.

In some cases by using transfer air some savings can be achieved in a foundry hall supply

air system, if additional air would be needed e.g. to decrease negative pressure in the hall.

In a foundry mean power of the compressors is 200 kW. To exploit the heat a ducting of 15

m is needed. The transfer air flow is 8m3/s and ducting size D 1000 mm.

Investments are:

ducting 6000 €

dampers 2000 €

transfer fan 3000 €

control and electricity 3000 €

building construction works 1000 €;

miscellaneous 2000 €

Savings: two shifts use, mean compressor effect 100 kW, heating season 1500 h means

1500 h x 200/2 kW = 150,000 kWh. If the price of the heat energy is 50 €/MWh the savings

are 7,500 €/a. Return: 14/7,5x12= 22 months.

Reference

Investigation: N.N

Compressor Energy Use Measurement and Calculation

The following data is needed for a quick calculation of electricity consumption and costs for a

compressor operating at load/unload cycles:

Load-stage power demand (kW, given by supplier)

Un-load-stage power demand (kW, given by supplier)

Load-stage annual hours of operation (h/a, from compressor monitor panel)

Un-load-stage annual hours of operation (h/a, from compressor monitor panel)

Cost of electricity (€/kWh)


90

A more accurate way to determine electricity consumption and costs involve taking electrical

measurements at the compressor. Load/unload control: Compressor performance and

system airflow requirements are determined from on-site electric power or ampere

measurements. Data logger results are used to determine short time electric loads for any

number of "day types". Generally, it is recommended that data loggers track system power

use over at least one to three days. One hour of high-resolution data is also recommended,

with readings taken at each compressor on 2 to 10-second intervals.

Airflow performance can be directly measured with appropriate meters. In most energy audits

this involves timely and costly installations and is therefore not required. Alternatively, system

air requirements can be calculated with data provided by the compressor manufacturer. The

calculated airflows are based upon e.g. 1 minute average volt and amperage readings.

Variable speed drives: Compressors with variable speed drives are more complex to

measure. If no on-site airflow data is available, the auditor must ask the compressor

manufacturer for more detailed information related to the specific compressors‟ performance.

Power or ampere measurements are performed as mentioned above. One method to

determine the air delivery at any given power or ampere reading is to monitor the rotational

speed of the compressor motor from the compressors monitor panels. For example, a

measured ampere reading of 50 A corresponds to a rotational speed of 1500 rpm. This way

the measured ampere readings on e.g. 10-second intervals can be converted to rotational

speed readings.

The following graph can then be used to calculate corresponding kW and dm3/s readings.

Note that the performance data is specific to one compressor type, model and pressure

range.

The conversion from rpm-readings to kW and ampere readings is usually done using e.g. a

linear or exponential regression-model (e.g. in Excel). An example of is given in Figure 19. In

the speed range of 3,000…4,800 rpm a conversion formula is given to covert the rpm-

readings to kW-readings. The conversion from rpm to air delivery is divided into two parts

(900…2,000 rpm and 2,000…4,800 rpm) in order to fit the given performance curve.


91

0

20

40

60

80

100

120

140

160

180

900 1100 1500 2000 3000 3615 4000 4260 4500 4800rpm

l/s

kW

P = 0,0147 x n - 6,8533Q = 0,0144 x n1,1001

Q = 124,24 x Ln(n) - 902,3

Figure 19: Compressor performance data and conversion formulas; P = power (kW), Q = air delivery

(l/s) and n = rotation speed (rpm).


92

3.9 Heating, ventilation and air conditioning

3.9.1 Space heating and cooling

Heating of premises

Infrared heating systems do emit radiant heat, e.g. to heat up rooms. The infrared radiation

permeates the air without losses, similar to sunlight, and gives their energy to surfaces when

they strive them.

Figure 20: Bright radiation infrared heating system in a foundry (Bosch Rexroth AG)46

Infrared-heating systems are divided in two parts, on the one hand bright radiation systems,

on the other hand dark radiation systems. Gas driven bright radiation systems are emitting

their infrared radiation predominantly by the heated and bright gleaming ceramic burner

plates. Gas and air is flowing through a nozzle into the bright radiation system. Inside the

bright radiation system a homogeneous compound of gas is created, which ignites. By this

combustion working temperatures of about 950°C are realized.

Dark radiation systems also produce heat by combustion of oxygen-gas-mixture, but in

closed burners with steel tubes. The combustion is not visible (dark radiation). By creating

46 Schwank GmbH - Hallenheizung - Infrarotstrahler für Hallen, http://www.schwank.de/de/referenzen/referenz-industriehallen/referenz-

giesserei.html; Infrared heating systems for factory buildings

http://www.schwank.de/de/referenzen/referenz-industriehallen/referenz-giesserei.html



93

such hot-gases the surface of the steel tubes are heated up, and so they emit their heat to

the surrounding. For these two systems natural gas and liquefied gas are used as fuel.

Heating, ventilation and air conditioning – good practice example - construction

tightness

Air leakage or air infiltration through building envelope causes significant heat loss. Draft and

even freezing problems are common as well. If the walls and roof of a building are heat

insulated the leakage through these can be estimated as follows: in a building made of

concrete the leakage equals ventilation rate 0.2 air changes per hour and in a building made

of steel plates 0.3...0.4. Any ambiguous figures may not be given because variations in

building technique and the site - open to winds - and temperature difference between indoor

and outdoor air have influence. Sometimes can be thought that the leakage is part of

necessary ventilation. This is a fact only in minor part because air leakage depends on the

wind direction and temperature. Therefore one can't count indoor air quality on this kind of

random phenomenon. One should also notice that air leakage causes heat losses 24 h/d, 7

d/week. In many cases major part of the leakage comes from clear openings and chinks

doorways, conveyors and pipelines. Also damaged seals between walls and roof made of

corrugated steel are common.

To improve building tightness is relatively easy: all the doors and other openings shall be

checked. If illumination in a foundry is turned off in a sunny day air leakage points can be

seen even in open eyes. In winter time a heat camera is an excellent means to locate and

record weak points. Worn out seals shall be replaced, cracks and chinks shall be restrained.

Polyurethane foam, profile seals, plates can be used. The conveyor openings can be

equipped with plastics strips - even double strip curtain has been used.

A foundry hall of 50,000 m3 was sealed with causing the air leakage drop from rate 0.4 to 0.2

which equals with ventilation flow 10,000 m3/h or 2.8 m3/s. Degree day number was 2,500.

Savings in heat energy were 2.8 m3/s x 1.2 kg/m3 x 1 kWs/kg°C x 2500 °C d/a x 24 h/d =

200,000 kWh which equals with 10,000 €/y with heating energy price of 50 €/MWh. Savings

in heat losses: 2.8 x 1 x 1.2 x /(12--20)=107 kW. Investments: seals and work 7,000 €.

Reference

User: N.N


94

Heating, ventilation and air conditioning – good practice example - air leakage and

draft in doorways

A door opening of e.g. 3m x 3m can cause a heat loss of 0.4...0.8 MW in winter design

conditions of -20 °C. A heat loss of this rate cools quickly any hall, causing draft and hazard

of local freezing. To minimize this following steps should be considered:

is it possible to decrease the opening time of the in case door by an automatic

opening - closing system. Many methods are available.

if workers use the door, could a separate small door been installed for this kind of

transport.

could the doorway been equipped with an air box or wind chamber.

could the doorway been furnished with a so called quick roll door that operates in

seconds.

is it possible to furnish the doorway with plastic strips - the opening totally or at least

the upper part and the sides.

is there space to use tunnel port type air curtain - a tunnel with length of opening wide

furnished inside with two side air curtains.

an air curtain.

To avoid draft an air curtain blowing from a floor grille is a most effective. Other possibilities

are to use a curtain blowing from one side or from the both sides, or a curtain blowing from

above. The last one is not effective to avoid draft on the floor level though it reduces

significantly heat losses. An air curtain blowing from a floor grille spreads dust and therefore

is often problematic. Commonly a curtain blowing from the both sides of the opening is a

realistic one. With an experienced design heat losses can be cut down to 10%.

As side-effect the production conditions improve for more even indoor temperature and

working conditions.

Savings: a door opening 3 m x 4 m = 12 m2 is furnished with an air curtain. The door is open

1,5 h/d, 5 d/week. The air balance in the foundry hall is negative = exhaust air flows are

bigger than mechanical supply air flows. The mean temperature of the ambient air in heating

season is -3 °C and the indoor temperature in calculation +12°C. In those conditions the door

opening causes a heat loss of 30 kW/m2 or 360 kW. The length of the heating season is 120

d. If the design temperature of the site is -15°C the heat loss in extreme winter conditions is


95

ca. 60kW/m² or 720 kW. Savings in mean temperature conditions with air curtain efficiency of

90 % are: 360 kW x 0.9 x 120 d x 1,5 h/d = 58,000 kWh. Because the heat loss increases

relatively significantly in colder ambient temperature and also wind increase the loss a

multiplier of 1.5 could be realistic on the mean value. Thus the annual energy savings are ca

90,000 kWh. With the heat energy price of 50 €/MWh this equals with a savings of 4,500 €/y.

The invest cost is ca 12,000...15,000 €. Maintenance and fan power costs are under 300 €/y.

Net savings are ca 4,000 €/y and pay-off time 3...4 years.

References

Investigation: AX Consulting, Tampere Finland

Heating, ventilation and air conditioning – good practice example - heating premises

In general, heaters for production halls are designed for the lowest average annual

temperature. The performance adjustment to the remaining days with warmer temperatures

was / is often realized by switching on and off the heating system.

This is not useful and not up-to-date, as starts and stops trigger higher energy consumptions,

higher losses and excessive wear. Modern lightning and heating systems are adapted to the

actual needs, taking into account the changing temperatures outside.

Infrared radiators are more efficient, because they do not need to heat up the air. They warm

up absorbing surfaces in their radiation sector. During this heating principle no carrier

medium is required to transport the heat energy. The principle of heat transfer from bright

spots and dark spots are based on heat (infrared) radiation.

The heat rays reach or machinery and equipment within few losses dependent on their

distance and absorbing surface. The ambient air temperature can be regulated by about 2 to

3°C lower than the currently available temperature for the same comfort, so energy costs can

be reduced. The manufacturer indicates for each degree drop in temperature an energy

saving of 7% on average, but this is dependent on the application and the present building.

Compared to conventional heating systems, heat lamps save up to 50% energy.


Continuously modulating burner adjust the desired room temperature, thus can

achieve a uniform temperature profile


96

The ambient air is not warmed up. With the use of light and dark spots, only the body

is heated, for example persons (thermal radiation).

The following sample calculation for radiant heaters, also known as fungus heaters, takes

into account a performance of 14 kW. These fungus heaters should be replaced by heat

lamps. On the assumption of 4,000 hours of operation per year and a price of 5.8 ct /kWh for

NPG*, the cost is shown in the amount of 324,800 ct /y.

Taking into account the statement made by manufacturers that the heat lamps can save up

to 50% less energy than conventional heating systems, this results in a cost saving of

approximately 1,624 € /y.

* The gas price includes taxes.

Reference

Supplier: Schwank GmbH; Germany

User: Bosch Rexroth AG; Germany

Heating, ventilation and air conditioning – good practice example – foundry connected

to district heating network

Before the installation, most of the cooling water from the furnaces and compressors was

cooled in a cooling tower. However, some waste heat was used for internal heating of the

building at winter time (September until April). Waste heat from one of the compressors was

used for domestic hot water.

The out-going temperature of the cooling water from the furnaces was increased to 75°C. By

doing so the water could be transferred to the district heating network of Arvika town. The

cooling water from three compressors in the production unit is also recovered in this way.

About 12 GWh can be delivered to the district heating system annually

30 % of the energy (electricity) used in the furnaces is recovered as district heating

(average over the year)

Waste heat that does not reach 75 °C is used for heating of the premises


97

The out-going temperature of the cooling water of the furnaces is set to 75°C. Since the out-

going temperature is always the same (it is controlled by the flow of cooling water), the

temperature of the furnace itself is also more uniform than before. This means that the

variations in temperature of the furnace and the equipment around it are less than before,

leading to decreased thermal wear.

Reference

User: Hans Finsberg, Arvika Gjuteri

Short example – heating - replacing the central heating system

The central heating system of the foundry got replaced by a new gas condensing boiler and

buffer tanks. This lowers the heating losses of the previous gas boiler plants. The core shop

got connected to the central heating system. An old boiler for the core shop as well as a gas

ejector for core drying could be put out of operation. For the production of fittings the cores

are inserted in the sand casting moulds to form hollows in the castings. The cores are

pressed from core sand and are to be dried before using them in the moulds.

The waste heat of the foundry‟s cooling water circuits provides basic heating for the training

and office building via floor heating. The process heat of 40 – 50°C generated in the foundry

is used in an environment friendly and resource saving way via pipelines as thermal heat

with a capacity of up to 100 kW. In addition, the waste heat of the annealing furnaces is

used. These furnaces serve the further processing of the rolled strips. Added fresh air gets

heated by the waste heat of the annealing furnaces. Up to 300 kW can be used here.

Annually, ca. 2 million kWh less gas is consumed by these energy saving measures. This

equals a reduction of CO2 emissions of 400 tonnes per year.47

3.9.2 Ventilation

General Ventilation

The purpose of general ventilation in foundry premises is to control indoor air quality and

temperature conditions. The quality of indoor air depends on the amount of impurity

emissions in relation to the ventilation rate. The temperature conditions are mainly affected

47Best-Practice-Examples of the Non-Ferrous Metals Industry; Energy Efficient Use of Heat; page 13


98

by the internal and external heat loads and the heating and cooling systems, but ventilation

has its role also.

Ventilation affects the temperature conditions in many ways. Depending on the type of the

building and the ventilation system, the heating of ventilation air takes 20-80 % of the total

energy consumption of the building.

The satisfactory indoor air quality can be achieved at the lowest energy consumption if

ventilation is dimensioned according to the impurity emission. In practise, ventilation is

usually dimensioned according to regulations, empirically or to control the temperature

conditions.

The dimensioning of general ventilation is based on control of contaminants in work place air

and/or cooling of premises. In the first case the ventilation supply air flow is defined by the

formula:

q = k1 * k2 * k3 * m / Ctv , (m3/s)

where:

q is supply air flow, m3/s

k1 is emission source effect on exposure i.e. emission spreading from the source to occupation zone

compared to background air

k2 is the mixing factor of indoor air; with dilution ventilation 1 – 1,2 and displacing ventilation 1/3 – 1

k3 is trend of future progress in indoor air target value (threshold limit value, TLV)

m is emission flow of impurities into indoor air, mg/s

is capture efficiency of local ventilation; 0 – 1

Ctv is target value of indoor air quality; usually 1/10 – 1/3 of TLV, mg/ m3

In the second case the ventilation supply air flow is based on cooling effect according the

formula:

Q = q * 1,2 * T , (m3/s)

where

Q is cooling power, kW

q is supply air flow, m3/s

is temperature difference of supply and exhaust air, K

T is capture efficiency of surplus heat; 0 – 1


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Table 3 gives the magnitude of general ventilation efficiency factor that has essential effect

on the air flow rate. The supply air distribution systems, illustrated in Figure 13, differ from

each other a lot having also high effect on annual energy use in foundries. As a general rule

it can be estimated that air exchange rate of foundry premises is 10 times per hour on an

average.


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Table 3: Ventilation efficiency i.e. mixing factor of different supply air distribution systems.

Supply air distribution system Ventilation efficiency of system

a) anemostates on ceiling level 1,0 - 1,2

b) supply air from ceiling with vertical jets 1,0 - 1,1

c) high impulse jet anemostates 1,2 - 1,5

d) anemostates above occupation level 0,6 – 0,8

e) thermal displacement ventilation 0,4 – 0,6

f) nozzle ducts above occupation zone 0,5 - 0,7

g) floor jets 0,3 - 0,6

h) cold air jets on ceiling level 1 - 2

When considering the performance of general ventilation you have to know the tightness of

the building as well. The tightness of building envelope means that the air tightness of the

structures through which the ventilation air is not supposed to flow is good. The tightness of

building envelope is one of the most important factors affecting the co-operation of structures

and HVAC engineering. It is also one of the most difficult factors to be controlled. The

influence of uncontrolled air leakages has grown as one of the most usual facts behind

draught complaints and poor energy economy as the insulation level of structures and heat

recovery efficiency has improved.

The tightness of the building is important in considering good implementation of heat

recovery, air purification and humidification. The air entering through leakages can not be

filtered or utilized in heat recovery.

When defining the general ventilation efficiency you have to be aware of air leakages in air

balance level weather you have exfiltration air or infiltration in question. Usually while you

have zero pressure difference level in the room both filtration types exist at the same time.

The exfiltration air flows out through the building envelope above the zero level and the

infiltration air flows in below the zero level. The exfiltration air transports contaminant out

from the hall thus improving the general ventilation efficiency.


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Figure 21: Choosing air distribution method for different conditions

Stratification Zone

a) Air Distribution by Ductwork

from Above

- a little excess heat

- a little impurities

- a little heat losses

c) Centralized Air Distribution from

Above



e) Thermal Displacement

- a lot of excess heat

- a lot of impurities

g) Blowing from Floor Level

- large hall, distribution of air

- otherwise difficult, a lot of impurities

b) Air Transfer and Distribution by

Jets from Above



d) Air Distribution by Ductwork

from Below

- fairly little impurities

- some excess heat

f) Air Distribution by Nozzle Ducts


- medium amount of impurities

h) Cold Air Blowing

(only during heating season)


- no impurities


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Local Ventilation

The purpose of local ventilation in foundry premises is to minimize impurity emissions and

heat load from contaminant source into indoor air by capturing contaminants as effectively as

possible. In this way local ventilation reduces the load of general ventilation, m, to control

quality and temperature conditions of indoor air. The efficiency of local ventilation is defined

as capture efficiency:

= m / M ,

where

is capture efficiency of local ventilation; 0 – 1

m is emission flow of contaminants into indoor air, mg/s

M is total emission flow of contaminants from the source, mg/s

Figure 22: Local ventilation efficiency is the capture efficiency of contaminants from the emission

source.


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Dedusting and filtration

In foundries, the ventilation exhaust air usually contains various amounts of dust. This must

be taken into account if exhaust air circulation or heat recovery is considered. In both cases,

the exhaust air must be filtered first (see Figure 14) in order to prevent problems in

occupational hygiene and to ensure that the heat recovery surfaces stay clean.

Energy cost of ventilation

Ventilation uses heating energy in the heating of supply air and electricity in operation of

fans. As an example in two shift production the supply air heating of 10 m3/s ventilation unit

uses annually heating energy asome 670 MWh/a in Finnish climate and in South Germany

some 480 MWh/a this corresponds. This corresponds to the cost of 34,000 €/a and 24.000

€/a with the energy price of 50 €/MWh. By chosing the most efficient ventilation (supply air

distribution system) the saving may rise up to 50 % when comparing displacement system to

complete mixing ventilation system, see table 3 still both systems perform equal air quality in

occupation zone and other occupational hygiene conditions. This shows 17,000 €/a saving in

Finland and 12,000 €/a saving in Germany.

By applying efficient local ventilation system one may save even more remarkably. For

example a poor local exhaust system of a induction furnace may capture only 90 % of

furnace fumes. This means 10 % of the fume mass is emitted into indoor air. This means

hourly the extra load of some 0.1 kg fume mass from 3 ton furnace to be diluted into indoor

air and exhausted out via general ventilation exhaust air flow of 33,000 m3/h in normal

foundry indoor concentration of 3 mg/m3. This means almost equal extra use of general

ventilation and the same energy cost annually as we had in the chapter above i.e. 34,000

€/a.

Reasonable energy use

The movements of air and cold surfaces induce local feeling of draught for example in neck

or ankles. The moving air transports heat from bare parts of the body efficiently. The air

temperature as well as fluctuation of air movement and temperature has major effect on the

feeling of draught.


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Development of draught feel is individual and the improvement actions must be considered

case-specifically. The first action is to measure the room temperatures. If the temperature is

at normal level (17-20°C), other reasons must be looked for.

Having draught on occupation area that causes compensation by indoor air temperature. In

foundries, where medium heavy work activity is normal, air movement above 0.25 m/s is

considered as draught in thermal conditions of below 20oC. Always when having 0.1 m/s

higher air velocity corresponds to 1oC higher indoor temperature and this means 5 % higher

annual energy cost in heating and ventilation.

Too high room temperature during heating season will waste energy and cause more indoor

air quality problems. Raising the temperature by one degree Celsius will increase the energy

consumption of the heating system by 4-5 %.

Too high temperature in spring or summer results usually from sun radiation or heavy

internal heat loads. Excessive temperatures decrease working efficiency and comfort.

In all systems, indoor air temperature must be adjustable hall-wise in winter conditions. This

is usually accomplished by thermostatic supply air control. In systems of high standard, also

adjusting of room-wise cooling is possible in warm periods. This is necessary especially

when halls next to each others have different heat loads. Ventilation can be designed so that

ventilation rate in every room can be adjusted independently according to the wishes of the

room occupants. Room-wise adjustment of air flows is relevant in premises, where the

amount of contaminant emissions vary considerably. Elimination of excessive temperatures

should be started already in the designing stage of the building and process devices.

In order to achieve good indoor climate with as low as possible energy consumption, it is

essential to control the ventilation air flow through the building as well as possible. Excessive

ventilation consumes energy and causes comfort problems. On the other hand, ventilation

may not be lower than a level dictated by health, comfort and demands of the structures. The

best energy economy can be reached as ventilation is controlled based on the actual

demand and as the ventilation rate is equal to the target value.

In service sector buildings, some 50 % of the annual heating energy of the ventilation air can

be saved by heat recovery. In industrial premises, even higher annual recovery efficiencies

are possible because of higher temperature levels. Implemented in the building stage, heat

recovery is a profitable investment especially when air flows and operation times are

considerable. Nowadays, the heating consumption can be controlled successfully by the heat

recovery technology.


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In addition to the heating energy consumption, ventilation consumes also electricity. The

electric energy consumption of fans depends on pressure level of the system, dimensioning

of ductwork and fans, operating point of fan, control strategy, dirtiness etc. The specific

electricity power (kW/m3/s) is higher in small plants than in big ones. For example the general

ventilation unit of 10m3/s uses in two shifts some 8,000 €/a with electricity price of 10 ct/kWh.

The operating times of ventilation must be selected so that unnecessary ventilation is

avoided when the premises are not in use. Demand based control can also be implemented

hall-wise.

Ventilation systems are divided according to control strategies as follows:

constant air flow systems,

multi air flow systems, where the air flow is changed in two or more steps,

variable air flow systems.

Nowadays, in addition to simple timer and thermostat controls, the following systems are in

use:

variable air flow system based on measurement of carbon dioxide (CO2 sensors

and frequency converters on fans) or carbon monoxide for example in foundries

demand control is often used in painting shops whenever paint spray is active the

ventilation is working in full power with a delay and in during drying period the

cabinet is hold in under pressure with minimal safety VOC-concentration by using

hydrocarbon sensor.

Usually, VAV means adjusting of the air flow according to temperature. In this case, varying

air flow is only used to control the cooling effect the system. During the highest cooling

demand, the supply air temperature is about 10 °C lower than room air temperature.

Heating, ventilation and air conditioning – good practice example - heat recovery with

rotary wheel in general ventilation

Rotary wheels or rotary regenerative HR-devices have big heat recovery efficiency, typically

75...80%. Wheels have no freezing problems and wheels can easily be equipped with

cleaning system like compressed air blast or pressure water washing. A heat wheel returns a


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minor part of the exhaust air or impurities to supply side. To avoid leakage of this short circuit

the pressure on the exhaust side should be kept negative by proper fan location. Also a

special purge section is commonly used to blow impurities from wheel surfaces to exhaust

side. By this means impurity circulation can be kept negligible. One should also notice that

always when air is distributed to a room a great air circulation takes place - even by using

low velocity air distribution devices.

Investments in this kind of heat recovery depends mostly on how much additional ducting

shall be used to get exhaust air and supply air to a same air handling unit room. A heat

wheel option is nowadays a standard of major air handling unit producers. In a heat recovery

economy a very important part is possible savings in the heating system investments. To

some extent savings can always be reached in a heating piping - if not in a heating center. In

some cases by using a heat recovery in a foundry extension project or in an indoor air quality

improvement project no additional heating capacity is needed in the heating center and

piping manifolds. This has saves in some projects investment as much as the heat recovery

has cost.

A foundry hall ventilation air flow is 10m3/s, running hours 12 h/d, 5d/week, design outdoor

temperature -25°C, design supply air temperature +12°C, degree day number 3,500 °Cd/a

and heat recovery efficiency 80%. Saved heating effect is 10 m3/s x 1.2 kg/m3 x 1 kWs/kg°C

x (12-25) °C x 0.8 = 355 kW. Saved heating capacity investment 355 x 80 €/kW = 28,000 €.

Saved energy: 10 x 1.2 x 3,500 x 12 x 5/7 x 0.8/1,000 = 288 MWh, or 15,000 € by energy

price 50 €/MWh. Investment: ducting, additional price in air handling unit 40,000 €. Running

costs (fan power, maintenance) 2,500 €. Netto savings 12,500. Pay-off time 40/12,5x12= 38

months.

Reference

User: N.N.


plate heat exchanger of ventilation air

With a plate heat exchanger impurities in exhaust air are kept away from supply air.

However, it is important to notice that all standard type plate heat exchangers have air

leakage between exhaust and supply air. This leakage depends on manufacturer and can be

some or some hundreds per mil. Most important is proper pressure conditions: the exhaust


107

side shall be in lower pressure than the supply side. Standard plate exchangers are

constructed of corrugated plates to improve heat transfer and to fasten the construction. This

kind of heat exchanger will clog almost as soon as a finned coil-HR. Therefore filtering of

exhaust air may compensate a great deal of energy savings. Usually a special type plate

heat exchanger with smooth plates and cleaning system is needed. HR-efficiencies of plate

heat exchanger are typically 50...60% and are just about the same as with HR-coils.

A plate heat exchanger needs more room than other HR-solutions. The effect control and

prevention of freezing need by-pass dampers. Higher efficiency may be achieved using two

exchangers in series or with a special type counterflow construction. A use of a plate heat

exchanger requires that supply and exhaust ducting comes to the same air handling unit.

Because of all arrangements needed with plate heat exchangers in an existing foundry they

are normally not able to compete economically with coil-HR. In a new plant they may be used

especially if there are no sticky impurities in exhaust air and general impurity level is

relatively low. Even in those cases one should make preparations for easy cleaning.

Typically plate heat exchangers are used in ventilation of offices, locker rooms and such.

Exhaust air flow 10m3/s, degree day number 3,000 (outdoor design -20°C), working hours

10/d, 5 d/week. HRX: 40,000 €; ducting: 20,000 €; control: 4,000 €; other: 5.000 €; Savings:

Q = 10 x 1.2 x 1 x 3,000 x 10 x 5/7 = 257 MWh, 12,900; heating capacity 10 x 1 x 1.2 x (12-

20) = 380 kW

Reference

User: N.N


coil heat exchanger of ventilation air

In existing buildings a supply- and exhaust air ducting to same air handling unit is often

expensive or there is lack of room and space. Using coils with a brine circulation loop there is

no distance limitations. The piping is easy to install either inside a building or on a roof. Also

heat recovery from harmful exhaust is possible because no short circuit from exhausts to

supply can occur.

A challenge with heat recovery (=abbreviation HR) coils is to keep them clean. An old

solution is to use exhaust air filters but they may cause a lot of running costs in foundries for

impurity content in exhaust is typically high - especially in cases of local exhaust air from


108

smelting furnaces, casting, core making, shake discharge table, sand handling. Filters may

clog in days or in a week. In those cases an automatic cleaning system and special coil

construction are needed. If impurities in an exhaust air are simple dry particles like sand dust

an air-blasting with compressed air will do. The cleaning device has a moving trail on which

the blasting nozzle moves in intervals typically once or twice a day. The coil should be

constructed of straight pipes. In some cases even a coil constructed of so called needle

pipes may be used.

Sticky impurities typically from casting need harder handling. A steam cleaner may be used.

The cleaner can be operated manually or automatically. The heat recovery coil should be

divided to suitable sections with service space between to make cleaning easy. A drain with

a dust separator is needed. A pre-heating coil in the supply air side may be of standard Cu/Al

type. On the other hand there are successful experiences of HR general ventilation air from a

cleaning department.

Effect savings in design cond.: 15 m3/s x 1.2 x 0.55 x(12-25) = 370 kW; Energy: 15 m3/s x 1.2

kg/m3 x 1 kWs/kg°C x 4,600 °Cd/a x 10 h/d x 5/7 x 0.5 = 300 MWh, 15,000 €/a (50 €/MWh).

Annual running costs are fan power 15 m3/s x 400 Pa/0.6 x 4,000 h = 14.4 MWh = 40,000 €

= 4,000 € + 1,000 € (work). Netto saving: 15,000 € - 5,000 € = 10,000 €.

Plane pipe coils: Local exhausts from casting stations have exhaust of 10m3/s.

Daily running hours are 10 and working days 5 per week. Degree day number is 4,600, for

the mean temperature of the exhaust 40 °C. Heat recovery efficiency is 50 %. Savings: Q =

10 m3/s x 1.2 kg/m3 x 1 kWs/kg°C x 4,600 °Cd/a x 10 h/d x 5/7 x 0.5 = 200 MWh, 10,000 €/a

(50 €/MWh). Annual running costs are 1,000 €. Investments: HR-coil and special ducting

joints 40,000 €; piping 20,000 €; automation 4,000 €; cleaning devices 3,000 €.

In total: 67,000 €.

Reference

User: N.N

3.10 Lighting

Lighting uses electricity energy some 10 - 30 W/m2. Although this is not much but the

potential of electricity savings is high due to the latest development of illumination

technology. In office buildings, the consumption rate is high usually of 20 - 50 % of energy

use, but in foundries this corresponds to 2 - 6 % of all energy consumption.


109

Energy consumption of lighting is to be calculated individually or by the amount of luminaires,

or based on power per unit and operational time. The definition of premises-specific lighting

energy can be based on an estimated or a certain specific power (W/m2) and surface area, or

calculated amount of the luminaires and their power unit (lamp power + power of ballasts).

Operating times will be estimated individually, using personal interviews, view of the auditor,

observations and measurements of the current lighting, but also the need of lighting and the

extent of unnecessary use.

The safety regulations give recommendations of illumination for lighting levels. Table 4

outlines the demand of illumination on work places according to the Finnish

recommendations applied to work tasks in foundries.


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Table 4: Finnish recommendations of illumination on work places, Hki 1986.

Area

Illumination, lux

Remarks lower normal higher

Core making,

machining

200 300 500 work object

Moulding 150 200 300 work surface

Pouring 150 200 300 work surface

Fettling 150 200 300 work surface

Inspection 400 500 700 add. local lightning, object

Lighting level needed increases substantially with worker´s age. In the table above three

illumination categories can be a recommendation to different age groups and the categories

may be applied to workers of below 40, 40 - 55 and over 55 years. Light efficiency of lamps

lm / W (luminous flux (lm) produced by a lamp divided by power (W) of a lamp and ballast

and the suitability of the lamps (colour, rendering colour reproducing, etc.) will be reviewed in

the audit. The light capacity and lifetime of compact fluorescent lamps is five times more

compared to original bulbs and halogen lamps, hence the energy use is efficient.

The efficiency of a thin (16 mm) T5 fluorescent lamp is good, about 100 lm/W. Different type

of luminaires have been developed in different premises, in which electronic ballasts are

used. The lamp saves its efficiency and energy due to the small size, raw materials, storage

and handling costs and the luminaire manufacturers believe in the generalization of the small

fluorescent lamp. The amount of mercury is small and the luminous flux remains stable, after

16,000 operating hours the luminous flux is 95% of the original.

Bulb fits usually only to premises where the annual use is very short. Halogen lamp suits

best for target lighting and should be used only when other efficient lighting is not available.

Bulb and halogen lamps are energy economically poor and modest in lifetime. The long

maintenance interval of lamps has a great economical impact.

Figure 23 below presents the light-efficiency of different types of lamps and also the

variation range due to lamp characteristic of some lamp types (light colour, colour

rendering/R-index, etc.). While assessing the improvement possibilities of energy efficiency

of current lamps the usability of new and more efficient lamps should also be remembered

when comparing with the mercury lamps. The light efficiency of new lamps should be audited

always individually under different operating conditions to take into account the overall

efficiency and energy loss of ballasts. The latest development of LED-lamps has increased


111

this technology in industry as well but they usually are far too expensive still compared to

metal halide lamps with high R-index. Sodium lamps offer high light efficiency but they have

a weak character of narrow spectrum. This diminishes their applications in work places of

accurate tasks and leaves them more for traffic illumination purposes. It can be stated

according to big difference between lamp types that remarkable electricity savings on the

level of 20 - 30 % may be achieved with concentration on illumination technology in

foundries. This corresponds to 1 - 3 % saving of total energy costs in foundries.

Light efficiency in lm/W

0 20 40 60 80 100 120 140 160 180

LED

Sodium Oxide

High Pressure Sodium

Metal Halide

Mercury Vapour

Blended Light

Fluorecent

Compact Fluorecent

Halogen

Glow Bulb

Figure 23: The grade levels of light efficiency of the most typical lamp types.

Good quality lighting offers several advantages that should not be ignored in energy saving

campaigns. It gives positive company image and appreciation of personnel, reduces

absence, delays retirement, has positive influence on quality, reduces defects and reject and

effects positively on housekeeping and cleaning. So, there are many reasons not to reduce

lighting intensity. Instead of that one should pay attention to select right lighting fixture and

avoid unnecessary use of lighting. Lamps should regularly be cleaned, especially fluorescent

lamps lose easily intensity. Some light fittings may be equipped with cover or clean air

purging to keep them clean for longer periods. Lamps should be changed at the same time

not one by one. Motion detectors or photocells save easily electricity e.g. meeting rooms,

dressing rooms, storerooms, parking lots.


112

4. Good practice examples for foundries

Energy efficiency in foundries – general introduction

The choice of melting assembly depends on the material to be melted, the required quality,

the required melting capacity and the mode of production. In this case, the mode of

production is taken to mean the interconnection of the iron requirements of the mould-making

unit with the provision of iron by the melting unit.

The need for liquid iron is continuous in (large-scale) series production on automatic

moulding machines. In this mode of operation, no large number of moulds is available for

casting so that melting operations have to be adapted to the iron requirements of the mould-

making unit.

There is only a low level of interconnection in the case of hand mould casting and single-

product and small-series production: a sufficient number of moulds is available, which means

that the melting unit can supply iron relatively independently of the iron requirements of the

mould-making unit. With extremely heavy castings, however, it is sometimes necessary to

keep the liquid iron hot until a sufficient quantity has been melted for the cast.

In summary, therefore, it can be said that a cupola meets the requirements of series

production while a batch furnace is more suited to single-product casting. In both cases,

however, it may be necessary to install holding options.

If the requirement for liquid iron is low, rotary drum furnaces or induction crucible furnaces

are often installed. Where requirements are high, on the other hand, the liquid iron is

generally melted in a hot-blast cupola. The economies of scale resulting solely from the

melted quantity of liquid iron are huge. Depending on the molten metal quantity, a cold-blast

cupola or an induction crucible furnace is used between these two extremes. Steel foundries

are a special case. Cupolas cannot be used here due to the wide range of different steels

and the carbon absorption during the melting process. Melting assemblies in steel foundries

therefore normally take the form of arc furnaces and induction crucible furnaces.

Melting assemblies in nonferrous metal foundries

The thought process for nonferrous metal foundries is of a similar nature. For series casting,

high melting output and a non-excessive variety of products, a shaft furnace or hearth and

tank furnace are suitable choices for an aluminium foundry as they are characterised by

extremely low melting costs. If metal requirements are low to medium and/or if there is a


113

wide variety of products, crucible furnaces (heated by gas or electricity) are used in

nonferrous metal foundries, as they are extremely flexible and only require low-level

investment. Induction crucible furnaces can be seen as an alternative to crucible furnaces if

the metal requirements for a product are in the medium range48. Due to the higher melting

temperature, these furnaces are used more frequently for copper casting - primarily brass

and bronze casting. Channel furnaces are not normally used for melting purposes in

nonferrous metal foundries but are indeed used in re-melting plants. Rotary drum furnaces

are only used in nonferrous metal foundries in special cases - for the melting of melting

scraps, for example.

4.1 Coke fired furnaces – cupolas

Figure 24 shows the design of a cupola. The favourable energy-related feature of this

melting system is the fact that the input material is melted in counterflow direction by the hot

gases; the unfavourable characteristic is that the coke in the feed column leads to reduction

of part of the CO2 to CO (Boudouard reaction).

Even when you shut down the furnace, the lining and the charge will cool down. This loss of

energy has to be put in the system again when heating the furnace up. As a consequence of

turning the furnace off, the calculated analyse or the temperature of the molten iron is not in

the optimum range. These are a few reasons where you can see that a cupola must operate

in an optimum process area to get a good efficiency.

48 Brunhuber, Ernst.: Praxis der Druckgussfertigung, Publisher ´Schiele und Schön´ 1991


114

Figure 24: Cold blast cupola

Coke fired furnaces – good practice example - melting temperature and overheating

for cupola coupled with holding electrical furnace

First of all, rational energy consumption for a hot blast or cold blast cupola is according to the

following rules:

do not oversize the cupola in comparison with the effective production (t/h)

use an additional device (oxygen, overheating) to provide for the occasional high

demands

It is known that a cupola has a correct efficiency for the metal melting and a poor one for the

liquid metal overheating, this remark is for all cupolas using coke and particular for the cold

blast cupola49. In practise the major objective for foundrymen is to provide the production at

the right time and in the right condition (high temperature for castability or intermediate

pouring) and this is the reason why it is not unusual to see a set melting temperature with an

overheating higher than required. In foundries, excess of overheating is generally not too

much important according to the operated metallurgy (inversion temperature); but it is always

good to keep in mind and ask oneself, if the melting temperature is appropriate.

49 F. Neumann, Giesserei 77, 05th March 1990


115

In fact, for example, a foundry may face the following situation with a cold blast cupola:

production 10 t /h of grey cast iron, 26 000 t liquid metal a year, average melting temperature

1504 °C, holding electrical furnace with an average pouring temperature in mould 1400 °C.

The reduction of 20 °C of the melting temperature (1484 °C) can generate a reduction of

coke consumption of about 41 t /y (~1.2E+12 J /y), and can generate an increase of

electricity consumption of about 170 MWh (~6,2E+11 J /y). According to each price of

energy, it is possible to evaluate if the saving is enough worth or not, because a new melting

temperature can change very much the habit and the way of production.

Positive point of this best practice is that each equipment (cupola and holding furnace) work

in accordance with their best efficiency. Negative point is that primary energy consumption

can not be taken for granted. Energy saving depends highly on the efficiency of the cupola

and the holding furnace present in the site, and this efficiency depends of the raw material

charged in the cupola. Every case has to be studied carefully.

4.1.1 Energetic balance

In cupolas with furnace lining, the furnace has to be heated up after each repair to the lining.

These results in energy losses due to the energy needed to achieve the heat storage volume

of lining and batch. Each furnace campaign should therefore be as long as possible.

It is also necessary to use chunky coke and to avoid abrasion during the trans shipment of

the coke wherever possible, as reduction from CO2 to CO depends on the surface of the

coke.

Increasing the height of the furnace shaft above the nozzles ensures better use of the heat

contained in the furnace gases. The rule of thumb is that the shaft height should be 5 times

the furnace diameter at the level of the tuyeres 50

Coke fired furnaces – good practice example - highest efficiency during cupola

operation (optimum operating point)

50 Merkblatt über besten verfügbare Techniken in der Giessereiindustrie (BAT in foundry industry);

Umweltbundesamt (Federal Environment Agency), July 2004

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=Federal&trestr=0x401

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=Environment&trestr=0x401

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=Agency&trestr=0x401


116

In foundries energy represents a high factor of costs. Normally in foundries with high iron

demand a cupola compared with electric units has cost advantages. But how is the energy

consumption composed? How much coke will be used and what happens when coke rate will

be changed? Which influence do alternative combustibles have? How behaves silicon loss

by oxidation and what happens with the combust proportions? There are a lot of questions

with difficult answers. With an energy and mass balance and on a basis of real examples

done with hot blast cupola with an annual capacity of 500,000 t a investigation should be

done. This will show saving potentials and their results.

On the one hand energy can be saved through the use of the heat released in the melting

process. The shell and tuyere cooling, as well as the use of the heat in the cupola gas flow,

offers possibilities here. A significant more interesting area is the effective influence of the

melting process. Additional effects in efficiency are caused by a simultaneous a change of

the general conditions such as temperature and carburization (reduction of the CO content)

of the melting process. A reduction of the coke rate is absolutely feasible here, subject to

pre-determined prerequisites. The described processes were realized in operational practise.

It is important to stress that melting plants are never identical and thus the application of the

individual measures must be tested exactly. This contribution should serve in particular for

scrutinizing your own melting process critically and providing new stimuli for optimization.

Let´s assume now that we can dispense with 20 degrees C liquid iron temperature, and also

reduce the C-content of the liquid iron by 0.1%.If these two points are now taken as a basis,

a theoretical coke rate reduction of approx 0.3% results. However, a further point comes into

consideration. If the coke rate in a cupola is reduced, the Boudouard reaction is then also

simultaneously decreased, since there is less coke in the shaft and thus also less reaction

surface is provided. The latent heat (CO content) of the hot-blast furnace gas represents the

second largest heat discharge. A reduction of CO content, and further opportunity to reduce

coke rate, are automatically the result. With the new operating figures the Si burn-off must be

considered as well.

Economic benefits: Low invest, expert optimization

Reference

Literature: 3rd International Conference on Cupolas, Reims, FR, Mar 6- 7, 2008, p. 113-122

Coke fired furnaces – good practice example - automatic pouring units for High Power

Thermal Plasma (HPTP)


117

Tecnalia has developed and patented equipment for High Power Thermal Plasma (HPTP) for

automatic pouring units its acronym is PLASMAPOUR™. Plasmapour on pouring vessels:

on a pressurized pouring furnace, adjust precisely and quickly the temperature of iron

or steel just before pouring the metal to the mould.

on an unheated bottom pour ladle, brings heat and solve the issue of temperature

drop. PLASMAPOUR™ includes a plasma torch that is combined with a metal

temperature sensor.

Applicability:

Main advantage of plasma heater:

Rapid adjustment to set point the pouring temperature

increase of electrical yield of 30%

reduction of maintenance

no more thermal losses of the pouring channel.

Drawbacks:

Difficulties to hold the temperature set point because of the high inertia

metallurgical degradation because of inductor

poor and inconstancy energetic yield

high maintenance and operative costs.

Energy saving when holding metal: a) Energy efficiency is 75% - permanent plasma

efficiency is 75-80% - with plasma compare; with inductor 40-60%; b) can be switched off

when production is off. Only terms of saving energy consumption using PLASMAPOUR™ is

the 50% less than inductor. If we take into account the electrical energy consume, raw

material for adjustment composition, temperature setting, lining and maintenance cost,

saving is 3 €/°C*ton.

References

Investigation: Technalia


118

4.1.2 Dry inputs

The input material and the coke must be stored in a dry, clean place. Any moisture has to be

removed in the furnace and this uses up heat. Sand residues on scrap or any soil that enters

the furnace has to be heated up and is slagged. In addition, these substances might react

with the furnace lining. In both cases, the result is an increased volume of slag, and this leads

to heat losses. If the furnace lining is affected and the lining becomes thinner, this increases

heat losses via the furnace wall.

Coke fired furnaces – good practice example - shelter against weathering of coke

In some foundries, coke is not sheltered from weather (rain, snow, ice) and water is

absorbed inside. Coke humidity (% mass) varies usually between 0 and 15% according to

weather and storage conditions. This quantity of water will be evaporated inside the column

of the cupola, will partly react with coke, and will be blown out to the exhaust. These

undesirable side processes are useless and require remarkable amounts of energy. If coke is

stored in a dry place, this extra energy consumption will be avoided.

According to our experience in foundries, an average value of reduction of coke consumption

could be 0.5% from the total charge. It depends greatly from weather conditions and the

charging technique of the furnace. With assumed savings of 65 MWh/y one will save roughly

2300 € per year (based on 1 kWh = 0.0355 €).

Roofed storage area or at least consequent use of soft covers rspt. tents; closed road or rail

transport. Fugitive emissions are widely reduced. Closed storage is state of the art in fugitive

emission control.

References

Investigation: CTIF Audit Energy in foundry

4.1.3 Warm up of feedstock

A good gas flow through the input material ensures effective heat transfer. In order to

achieve this, it is important that the feedstock is compact and not too bulky; otherwise, there

is the risk of hollow spaces or gas channels during the feed process, both of which negatively


119

impact heat transfer. In extreme cases, this can also lead to furnace interruptions. It is also

important that the size of input materials is suited to the furnace in order to avoid the

aforementioned problems. The rule of thumb is that the size of individual feedstock pieces

should be no bigger than one third of the diameter of the furnace.

4.1.4 Furnace insulation and wall cooling

In cupolas without lining, the furnace shell is cooled by trickling water. Water-cooled nozzles

are generally also used in these furnace types. The heat discharged in the water accounts

for around 10–15% of the energy input51 52. If this heat is to be used, the first thing that needs

to be done is to convert the open shell cooling system to a closed system. The heat can then

be used via a heat exchanger. As the temperature level is relatively low, the heat can only be

used for drying and heating or hot water production.

4.1.5 Heat recovery from slag

Around 3 percent53 54 of the fed-in heat is discharged in the slag. If the slag is extracted in dry

form, it would be possible to utilise the radiant heat. If the slag is in granulate form, it would

be possible to use the heat content of the heated water. In both cases, however, the useful

heat volume is low, which is why this heat is generally not used at all.

4.1.6 Secondary row of tyères

In the secondary wind process in a second row of nozzles, the carbon monoxide is partly

combusted in which a significant amount of heat is released55 56 57.This is also fulfilled when

51 Kraus, U.: Giesserei 67 (1980), No.3, p.55/61

52 Höhle, L.: Giesserei 66 (1979) No. 1, p. 7/11

53 Kraus, U.: Giesserei 67 (1980), No.3, p.55/61


55Dahlmann, A.; Husmann, G.: Giess.-Forsch. 28 (1976) No.2, p.81/88 u. No.3 , p. 89/101

56 Dahlmann, A.: Giesserei 66 (1979), No.1, p.2/6

57 Leyshon, H. J.: Conference on cupola operation Proceedings of AFS-CMJ-Conference, Rosmont/ILL 1980,

No.17


120

one considers that above the secondary blast level comes further to a reduction of carbon

monoxide. Other advantages of the method are:

the dependence of the temperature of the iron melting capacity is less than normal

cupolas and

at constant coke rate, a portion of foundry coke can be replaced by small-sized coke

(e.g. crushed coke).

4.1.7 Oxygen enrichment

Also, by enriching the wind with oxygen you can reduce the coke charge or increase the

tapping temperature. Because of the high cost of oxygen, it is generally not recommended, to

add continuously oxygen to the blast. Favourable is the addition of oxygen only when it is

added in the short term, e.g. in the starting period. Then you must ensures that the amount of

starting iron that may be cast into ingots must be kept low. Even after the furnace shutdowns

desired tapping temperature is reached quickly. Another advantage is that in short term

increases of the melting rate and an increased iron requirement can be satisfied. The method

which is chosen to introduce the oxygen in the furnace has an influence on the tapping

temperature. Depending on the type of entry, the iron temperature compared to normal

operation can be increased by 15 to 85 ° C58. In table 5 is given the injection of oxygen

through the wall below the nozzle level which has not been.

By slag or iron, there was damage to the water-cooled lances and strengthened local erosion

of refractory material. It was also found that carbon and silicon content were lower than by a

given tapping temperature without extra oxygen.

Table 5: Injection of oxygen through the wall below the nozzle

Type of Oxygen transfer Temperature change

- Enrichment in the blower blast + 15 K

- Feed-in to the nozzles + 40 K

- Feed-in to the hearth of the furnace via injection

58 Selby, H. J.: 45. Int.-Foundry.-Congress, Budapest 1978, lecture No. 9


121

230 mm below the nozzles + 50 K



This means carbon and silicon were burned off. The oxygen injection into the nozzle can be

viewed as a compromise between the most effective method (injection of oxygen through the

wall) and the less effective enrichment of the blast with oxygen.

It is even better if the oxygen is blown in under high pressure in discontinuous mode. The

greater penetration depth into the furnace shaft allows a higher tapping temperature59.

4.1.8 Alternative fuels

To replace the coke in the cupola by other fuels such as coal dust, oil or gas, has been trying

for decades and has also recently been supported. It is hoped that the following advantages

occur:

to replace the coke with cheaper fuels

to increase efficiency

to reduce the sulfur content

The findings are contradictory. Whereas an American study60 determined that the injection of

one part of coke dust can replace 1.3 parts of coke, studies by the Institut für Gießereitechnik

found that the injection of oil or gas does not lead to any improvement in the efficiency

rating61 62.

59 Hamberger, R.: Portal AL 1/2007; Neue Regelung für mehr Wirtschaftlichkeit gleichdruck geregelter ALJET

CSI-Verfahren; p.4-7 60

Peck,W. J.: Conference on cupola operation Proceedings of AFS-CMJ-Conference, Rosmont/ILL 1980, No.10 61

Dahlmann, A; Schock, D.; Orths, K.: Giesserei 57 (1970), No.6, p. 125/32 62

Dahlmann, A; Schock, D.; Orths, K.: Giess.-Forsch. 22 (1970), No. 1, p. 1/14 u. No. 3, p.99/105


122

Similar results were also found in experiments with a gas-oxygen burner on a hot air furnace

from Fritz Winter63. In these experiments, a portion of the coke (12.5%) was replaced by

natural gas. As natural gas was burned with pure oxygen, the amount of wind decreased by

6%. In Figure 25, the changes, based on the produced mass of iron base, are shown. As

can be seen there, the energy input by coke and silicon carbide (SiC-burning) is reduced by

6% or 9%. The energy savings is opposited by increased use of natural energy, so that a

total of 2.5% more energy to smelt the base iron in the furnace must be added. This

additional energy input is extracted as latent heat of the furnace gas. The thermally sensible

heat of the furnace gas decreases due to the reduced amount of exhaust gas and the

sensible heat of the slag due to a lower slag mass. Not considered in the calculations, the

energy needed to produce the additional oxygen that is needed for combustion of natural

gas. This increases the efficiency of the furnace would decrease even further. This example

shows also that the relative price of coke fuel additive is crucial, whether the use of additional

fuels economically worthwhile.

Figure 25: Changes in energy balance by using natural gas burner with pure oxygen

Other furnaces fired by combustible material

63 Ökologische und ökonomische Optimierung des Kupolofenschmelzprozesses durch den Einsatz von Erdgas-

Sauerstoffbrennern bei gleichzeitig möglicher Feststoffinjektion; BMBF-Förderprogramm; Integrierter

Umweltschutz in der Giessereiindustrie, 2003

http://80.149.127.212/owa/redir.aspx?C=f0c96ea8493f42d3b25505059a85b789&URL=http%3a%2f%2fdict.leo.org%2fende%3flp%3dende%26p%3dziiQA%26search%3dcombustible%26trestr%3d0x801

http://80.149.127.212/owa/redir.aspx?C=f0c96ea8493f42d3b25505059a85b789&URL=http%3a%2f%2fdict.leo.org%2fende%3flp%3dende%26p%3dziiQA%26search%3dmaterial%26trestr%3d0x801


123

Rotary drum furnaces with oxygen burner are sometimes used in smaller foundries with low

daily iron requirements. As batch furnaces, they are more flexible than cupolas and can

therefore be seen as an alternative to induction crucible furnaces, compared to which they

have the following advantages and disadvantages:

Advantages

Low procurement costs

No high connected electrical load necessary

Disadvantages:

Lower efficiency

Longer melting times

Unfavourable loading characteristics

Higher burn-off of C, Si, Mn; low and scattered yield on addition of carburising

compounds

Greater scatter of target analysis

Lower stirring effect via the longitudinal axis of the drum

At this point you can call the following method:

gas-fired cupola and the cupola from Düker64 65

Flaven oven66

The plants described have the following commons: The fuel is not charged together with the

feedstock, but is fed directly to the combustion zone. This avoids the reduction of CO2 to CO

and thus the high losses of the exhaust of normal cupola. The advantages of the shaft

furnace principle like the counter-flow heat exchange and the high specific melting capacity

(per m3 furnace room) are preserved. With the use of natural gas is achieved in addition, that

an iron is melted with a low sulfur content.

Disadvantages are:

64 Taft, R. T.: The British Foundryman Sept. 1972, p. 321/28

65 Graf, R.: Lecture on the Foundry Congress 1982 at Koblenz

66 Pacyna, H.: Giesserei 49 (1962), No. 15, p. 417/21


124

Oil and natural gas have fluctuated in recent years in Germany in the price relatively

high

The use of pulverized coal is more expensive trough the measures against the risk of

explosion

The coke in the cupola furnace delivers not only the required fuel but also forms a stable

overheating bed. In the special designs must be either coke added (Henza oven) or an

artificial overheating bed of ceramic masses must be formed (Coke less cupola).

Oil and natural gas have fluctuated in recent years in Germany in the price relatively

high.

The use of pulverized coal is more expensive trough the measures against the risk of

explosion

The coke in the cupola furnace delivers not only the required fuel but also forms a stable

overheating bed. In the special designs must be an artificial overheating bed of ceramic

masses must be formed (Coke less cupola). As a result, these furnaces have not been able

to establish themselves in Western Europe.

4.1.9 Heat recovery from off-gas and secondary use

Another way to save energy is to use the waste heat of the cupola. Since waste heat

recovery facilities require a high investment costs and only after a fairly lengthy period they

have a reasonable efficiency, the waste heat has been used especially in large furnaces with

high weekly hours of operation. Most widespread is the use of waste heat to heat the

combustion air. An example is shown in Figure 26. In this furnace is needed approximately

40% of waste heat for the blast preheating. Another 40% are under consideration of the

recuperator losses available for other purposes. In this furnace this hot water was produced

for other plants. This measure increased the overall efficiency of the furnace by 34% to about

45%67.



125

Figure 26: Hot blast cupola with gas cleaning process and recuperator for wind pre heating

In another foundry waste heat is utilized a 45-ton cupola furnace to produce steam for

heating and process purposes68. The largest part of the steam is delivered to a neighbouring

business. The steam output varies between 6 t / h and the maximum capacity of the

evaporator of 16 t / h, corresponding to a heat output of 10500 kWh / h. For fuel costs by

about 50 € / 1000 kWh, the cost savings are approximately 525 € / h. The cost for the

construction of waste heat utilization systems were estimated at about € 3.5 million. By a

decrease in the hourly steam demand and / or annual operating hours, the point is very

quickly reached, on that you can not get a cost recovery. In another foundry, the exhaust

heat of a 40-tonne cupola is used to generate electricity for their own use. The power at the

generator is 760 kW. The main reason for the poor performance of the turbine efficiency is

the single-stage Curtis turbine of only 12%. The use of multistage turbines would not be

expected due to the high investment costs. For the possible use of condensation heat for

heating purposes there is also no sufficient acceptance69. The waste heat from the cupola at

GF Mettman is for the hot blast, compressed air or electricity production which is used almost

completely. In Figure 27, the process is outlined70.

68 VDG Seminar 1985. Energieeinsparung in Giessereien (Energy savings in foundries)

69 Gallo, S.; Goria, C. A.; Mischiatti, M.; Antonini, C.: 47. Int.-Foundry Convention, Jerusalem 1980, lecture

No.14 70

Freunscht, E.; Rudolph, A.: Giesserei 76 (1989); No. 10/11, p.328/335


126

Figure 27: Concept of heat recovery plant with:

1 steam boiler 6 cooling tower 11 pump 16 turbine extraction

2 steam turbine 7 desalting plant 12 steam drum 17 condensate pump

3 generator 8 degaser 13 drum pre-heater 18 pressure reduction

4 air compressor 9 condensate lead 14 evaporative cooler

5 turbine condenser 10 feed water reservoir 15 start-up piping

That the use of internally heated recuperators in the operation of large cupola furnaces with

high annual operating hours worth, has been demonstrated by the German Foundry

Association. The comparison with a cold blast furnace is difficult, because in hot blast

furnaces normally use on the proportion of pig iron and steel scrap low percentage is higher.

Looking to complicate the comparison not only the self-heated by the recuperator comes to

the following result:

Self-heated hot-air furnace Operating costs for the recuperator operation:

gas costs: 0,09 €/100 kg liquid iron

other cots: 0,11 €/100 kg liquid iron

total costs: 0,20 €/100 kg liquid iron.

Cold blast furnace

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=evaporative&trestr=0x801

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=cooler&trestr=0x801


127

Increased consumption of coke: 1.5 kg/100 kg liquid iron

costs of cokes: 400 €/t coke

Additional costs for coke

1.5 kg coke * 0.40 €/kg coke = 0,60 €/100 kg liquid iron.

Figure 28: Cold wind cupola - Interdependence between tapping temperature and coke demand

The comparison shows that under these assumptions by the self-heated recuperator cost

savings of 0.40 € / 100 kg of liquid iron are achieved.

In the considered example, the cupola produced about 90000 tons of liquid iron in the year.

Thus, the remaining costs for self-heated hot-blast furnace are relatively low. A smaller

amount of annually produced iron, based on 100 kg of liquid iron, increase the other costs,

since they are almost fixed. At the considered example of the hot blast furnace, at an annual

quantity of 33000 tons produced it will be cheaper.

Heat recovery from off-gas and secondary use - good practice example - heat recovery

after recuperator

The need to cool the exhaust gases of a cupola before the exhaust gases are fed to an

emission control systems, opens the possibility to use the waste heat. In the past a

recuperator withdrew a portion of the raw gas and used it to heat the fresh air, which then

was blown into the cupola furnace (hot blast cupola). Furthermore, the waste heat was used

to heat the foundry hall and to generate hot service water.

The heat energy of the raw gas from the cupola could not be fully utilized. After cleaning the

air, the rest heat in the raw gas was exhaust into the environment.


128

In 2008, the Automobilguss GmbH in Singing renewed the recuperator. The efficient

operation of the recuperator allows in comparison with its predecessor a payback of 20 MW

from the raw gas of the hot blast cupola.

With the realization of the recuperator to the above mentioned fields of application for

residual heat utilization comes another buyer, the nearby factory of Nestlé Maggi GmbH,

Germany

Georg Fischer sells to the nearby Maggi factory up to 50,000 MWh of process heat per year.

The Maggi factory can replace with the related residual heat about two-thirds of the required

Benefits for the food neighbour:

Saving of natural gas. Maggi requires about 60 % less of natural gas

No additional consumption of raw materials e.g. gas

Particularly independence from increasing energy costs

Benefits for the foundry:

Calculated profitability of the investment

Leader in utilization of best practice technologies

Savings in CO2 emissions of 11 000 tons per year can be realized. About two thirds of its

required amount of natural gas can replace the Maggi factory with the residual heat.

Reference

Study: IfG gGmbH – Energy efficient foundry industry

User: Georg Fischer GmbH & Co. KG, Singen (Germany)

Heat recovery from off-gas and secondary use - good practice example - storage of

heat

Foundries produce large amounts of residual heat, which the financial point of utilisation

does not appear feasible. Too large is the time (or space) gap between generated heat (heat

source) and heat demand (heat sink).

Moreover, the use of the most medium temperature heat sources must be limited to technical

systems, which work there with good efficiency.


129

Latent heat storage allows the storage of residual heat and its structured and systematic

extraction at a later date (rspt. another place).

The use of a storage medium other than water, sodium acetate is usually used, allows the

storage of large amounts of heat in the phase transition between solid and liquid.

Through the storage of residual heat and its use later, you can save primary energy. The

heat storage capacity of a latent heat storage is currently at about 2.5 MWh.

A latent heat storage is typically positioned to complement an existing heat supply and

concentrates on the cover of the base load.

For example, the application may be made to support the existing heat system. The heat of

heat storage is fed into the return flow of the existing heating system. This causes a delayed

start of the heating system raised by the return temperature. The storage of heat and its use

at a later point in time causes the saving of primary energy.

The latent heat storage should to cover costs, to be discharged at least 100 times/y. This

means that heat transport of 250 MWh /y must be assured.

This amount of heat, for example, used to support the existing heating system in a house,

saves primary energy of the same amount. Economically better is a customer, who

consumes the heat continuously. Unloading and loading the heat storage can operate

parallel then. Consumers are for example, drying processes, pools, etc.

1 liter of light petrol fuel produces about 10 kWh of heat. The provision of an amount of 250

MWh of heat from waste heat can replace a fuel amount (primary energy) of about 25,000

liters.

This implies a reduction of CO2 emissions at a level of 7,800 kg /y (under the assumption that

during the combustion of one liter of fuel CO2 emissions of 0.312 kg /kWh are emitted).

Under the assumption of 0.78 € per liter of petrol fuel, a cost saving of approximately 19,500

€ /y is arised.

In contrast, the costs for the detection of residual heat: To be mentioned for example are the

cost for the heat exchanger and the costs for renting or buying of the latent heat storage

tank.

Reference

Supplier: http://www.latherm.de

Other furnaces fired by combustible material

http://www.latherm.de/

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=combustible&trestr=0x801

http://dict.leo.org/ende?lp=ende&p=ziiQA&search=material&trestr=0x801


130

Rotary drum furnaces with oxygen burner are sometimes used in smaller foundries with low

daily iron requirements. As batch furnaces, they are more flexible than cupolas and can

therefore be seen as an alternative to induction crucible furnaces, compared to which they

have the following advantages and disadvantages:

Advantages:

Low procurement costs

No high connected electrical load necessary

Disadvantages:

Lower efficiency

Longer melting times

Unfavourable loading characteristics

Higher burn-off of C, Si, Mn; low and scattered yield on addition

of carburising compounds

Greater scatter of target analysis

Other melting assembles that should be mentioned at this point are:

Gas-heated cupolas as well as the optimised furnace from the Düker company

Flaven furnaces

The plants described above have the following in common: the fuel is not fed in together with

the feedstock but directly into the combustion zone. This avoids the reduction of CO2 to CO

and thus the high flue gas losses of normal cupolas. The advantages of the shaft furnace

principle like counter-flow heat exchange and the high specific melting capacity (per m3 of

furnace space) are retained. The use of natural gas additionally ensures that iron with a low

sulphur content is melted.

The disadvantages are that:

There has been relatively high fluctuation in the price of natural gas and oil in

recent years

The use of pulverised coal is made more expensive by the need to take measures

to prevent explosion risks


131

The coke in the cupola not only supplies the required fuel but also creates a

stable overheating bed; in the special designs, it is therefore necessary to create

an artificial overheating bed made up of ceramic compounds

As a result, these furnaces have not been able to establish themselves in Western Europe.

4.1.10 Runner covers

In open cupola channels, the losses are mainly due to radiation. At the transition from a wide

open channel to a high channel with lid, the heat loss falls to one tenth. With a 3 m long

channel, the temperature drop is around only 1°C instead of 14°C.

Runner cover – good practice example - cupola runner cover trough fitted with lining

cover on the channel

Cupola runner troughs (spout launders) are not always fitted with a cover on the channel.

Flowing molten metal between cupola and ladle is in open air and it radiates to the workshop.

Heat loses are great (radiation, convection and conduction) and a drop of molten iron

temperature occurs significantly. If there is no cover on the channel, this drop of temperature

has to be offset for example with an overheating of the molten metal inside the cupola or with

an extra electrical consumption for the holding furnace. According to our experience an usual

average drop of temperature is 6 °C per each meter of open air spout launder. This value

can be higher if a simple launder without basement is used (for example in some

counterweight making foundries), in this case the temperature drop gets up to 11 °C/m.

Coverage of the inclined channel with blocks of concrete lining (or refractory cement) can

reduce heat losses. Temperature drop can be pressed down to 3°C/m. Example: Cold blast

cupola, production 37 000 tonnes of molten iron a year, length of channel in open air is one

meter, coke reduction obtained: 0.25% of coke split. This value can appear weak, but the

best practice is easy to install and it costs almost nothing. It is up to the foundrymen to make

the economical choice by either to reduce the overheating in the cupola or to avoid the extra

electrical consumption in the induction holding furnace.


132

As side-effect the fugitive emissions of the open runners are diminished, predominantly fine

dust and fugitive metal fumes.

In case overheating in cupola has been done, it is good to check the minimal temperature of

molten iron according to silicon and carbon rates. In extreme case, coke reduction could

reach 0.5% of coke split. With assumed savings of 82 MWh/y one will get a payback of

roughly 4700 € per year (based on 1 kWh = 0.0567 € - average in 2008-2009)

Reference

Investigation: CTIF Energy audit in foundries; France

4.2 Electric furnaces for melting and holding ( arc and induction)

Iron and tempering foundries mainly use induction crucible furnaces for melting operations.

Steel foundries additionally use arc furnaces. The advantage of arc furnaces is that they can

also perform metallurgical operations. Arc furnaces with acidic linings can only be used for

decarburisation. If an arc furnace is operated with an MgO lining, it can also remove

unwanted by-elements from the melt together with an alkaline slag.

The drawback with arc furnaces is the strong smoke formation during melting due to the high

temperature between the electrodes (> 3,000 °C) and during decarburisation due to the

injection of oxygen. Increased dust formation also occurs during slag operations. This means

arc furnaces need high-powered extraction systems for smoke and dust along with the high

energy consumption this entails.

Channel furnaces are only used for holding purposes in iron, steel and tempering furnaces,

and the connected electrical load is therefore only low. As they need to be kept hot and are

generally sump-powered, they can only be used with a high level of energy efficiency if

annual operating rates are high.

Electric furnaces for melting and holding - good practice example - ventilation –

Intelligent fan control

The process steps in a foundry, because of the high temperature level of the used materials,

are associated with significant proportions of waste heat. Here one not only has the need of

cooling systems to protect aggregates such as furnaces. For example, molding material has


133

to be cooled to a suitable temperature, too, before the next use. For the objects described

above a combination of water/air heat exchangers and fans are commonly in use. To adjust

the cooling capacity to the requirements, they can be cascaded to form groups. Thereby the

electrical supply for the electric motors is often summarized to one controller. More rarely

there are uncontrolled cooling groups running in 24-hour operation.

The simplest type of fan control is quite present, for which the corresponding fan is turned on

with the process unit of the plant which is to be cooled. This mode of operation is

independent of the actual heat load.

An improved mode of control for cooling systems is to make on-off condition for a group of

fans dependent from the actual temperature of the cooling water. An on-and off-hysteresis

must be implemented to avoid duty cycles of the electric motors. The next stage of the

controller takes into account the temperature gradient in the heat exchanger. This means

that the required cooling capacity and the cooling capacity of the fan-heat exchanger

combination has to be measured. The latter is similar to the external sensor of a heating

system. The control has to be physically related o the temperature difference between inlet

water temperature and ambient temperature. If there is no temperature difference between

inlet water and air temperature at maximum flow rate of the cold air, one can not reach

significant cooling effect. An intelligent control, in these cases, can partially shut down or turn

on the optimal number of required cooling units, thus saving electrical energy and

mechanical wear.


Saving electrical energy by situational and partial shutdown of cooling capacity

Reduce maintenance costs by reducing the effective hours of operation of the fan

motors

In principle it certainly makes sense to avoid power consumption every unnecessary minute.

But it is always necessary to have a balance between investment and benefit of the savings.

Under the assumption that breaks, planned shutdowns, and malfunctions with an abundance

ratio of about 10% of the operating hours of a 3-shift operation are characterised by low

temperatures in the cooling circuits, the result below is invoiced.

Cooler fan group of ten fans each with 0.5 kW, two groups per plant part

3-shift operation with 275 working days

10% of the hours of operation of a plant at a low temperature level


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Power consumption in "continuous operation": 2 * 275 * 24 * 0.5 kW = 6,600 kWh;

power savings with "controlled operation": 6,600 kWh * 0.1 * 11.1 cents / kWh = about 75 €

per year and fan group.

The present calculation of the amortization period of 13 years falls from relatively high if it is

calculated only on break times of plant operation.

A similar saving is given by shutdown of the fans (groups) due to non-existing Δ T for

cooling. This state is dependent on the regional climatic conditions and usually occurs in the

summer months. This is problem is mostly triggered by the fact that coolers are mounted on

black roofs with direct sun radiation exposure. Ambient temperature can exceed 35 °C

frequently there.

Reference

User: www.boschrexroth.com


The energy balance of a furnace even depends on the material you charge, as you can see

in Figure 29. Here you can see dependence on the charged material in question of specific

enthalpy. Conclusion here: The higher the specific enthalpy the more energy you have to

bring up to melt the material.

Figure 29: Specific enthalpy of different metals

www.boschrexroth.com


135

Arc furnaces

Based on electrical capacity, arc furnaces have efficiency ratings of up to 80%.71. These

efficiency levels can be achieved with large-scale furnaces if they are only used to melt scrap

metal. Ancillary times needed for decarburisation, slagging and deslagging can have a

significant negative impact on the efficiency level. It is also not possible to achieve 80%

efficiency with smaller furnaces of the kind primarily used in foundries.

Induction furnaces

The following discussion about the medium-frequency induction furnace is from an article by

D. Trauzeddel72. As shown in Figure 30, a modern medium frequency induction furnace is

more efficient than a power-frequency induction furnace, although the former losses occur for

the inverter. For this reason, they have prevailed for the smelting of cast iron in new plants,

the medium frequency induction furnaces.

Figure 30: Sankey-Diagramm of an medium frequency induction furnace

This has several causes:

71 Merkblatt über beste verfügbare Techniken in der Giessereiindustrie (BAT in foundry industry);

Umweltbundesamt (Federal Environment Agency), July 2004 72

Trauzeddel, D.: Giesserei 93 (2004), No. 4, p. 64/70





136

According to theoretical considerations, the furnace operation with a maximum

available electrical power and thus high power density at the energetically, is most

favorable. Therefore, the power consumption decreases with increasing nominal

power at the same furnace size, since with increasing power density, the proportion

of energy for the thermal losses decreases. Because of the 3-times as high power

density per ton crucible contents, for this reason medium frequency systems are

lower in energy than power frequency systems.

The MF furnace can be started with cold feedstock. Because of better

electromagnetic coupling of the solid feedstock (applies only for cast iron materials)

pure batch mode 8% less energy is needed. This is because under the Curie point

(about 900 ° C), a much higher coil efficiency can be reached. In the intersection with

90% of the installed Power the furnace can be driven. Due to the resulting lower

melting time, the heat losses are lower.

The higher efficiency is also due to the fact that in the last decade foundries worked

hard to reduce the thermal and electrical losses by optimizing the coil and the furnace

design and improvement of the converter.

Here it becomes clear that the replacement of a power-frequency induction furnace with a

modern medium frequency system, the energy efficiency of the liquid metal supply increases.

Of course, such reasoning is not the sole reason for such a major investment decision, they

can accelerate such a decision, however, and support. A less expensive and still promising

action may already be a modernization of the furnace control. The evolving experience and

knowledge on energy-efficient furnace operation can be implemented in modern computer-

based control systems. These offer the advantage that an update of the software at any time.

If you are talking about energy balances the interdependence between energy consumption

and effective output is significant. As a general rule you can say that large plants have higher

effective outputs, so here you have less specific losses and the specific energy consumption

is also lower. Conclusion here: To get the best energy efficiency use a plant with the

optimum capacity (Figure 31).


137

Figure 31: Correlation between energy consumption and effective power

The use of induction furnaces for melting metals is connected with thermal and electric

losses. On the one hand these losses are depending on the charged metal and on the other

hand they are depending on thy type of furnace you use. In the case of melting e.g. copper

or aluminium (low specific resistance) there are more thermal and electrical losses than you

would have if you melt iron based materials. The over all effectiveness of induction furnaces

depends on the electric effectiveness (connection between charged material and electric

field) and the thermal effectiveness (losses by radiation or walls; see Figure 32).

Figure 32: Thermal and electric losses by melting different metals


138

4.2.2 (Optimal) operation cycles and handling

With an overall efficiency of the furnace by 75% of energy, the consumption for the melting

cast iron up to a temperature of 1500 ° C is only 520 kWh / t with an enthalpy value of 390

kWh / t. There are also the energy consumption for dry dedusting system, water-cooling

system, hydraulic system and pump and charging equipment. The sum of these aggregates

is associated with an investment of over 15 t / h at 10 kWh / t. Studies in English and French

foundries indicate that the actual energy consumption for melting (but including warmers

measures) is much higher. There was an average of 718 kWh / t in English and of 855 kWh /

t from French foundries determined. Here is a large savings potential opened by the use of

modern medium frequency systems but also by improving the handling and operation. Up to

20% energy can be saved thus existing furnaces.

The special charm of a purely organizational measures to improve the driving and operation

is that in this is no or negligible capital expenditure is required. The goal that is pursued here,

is the optimal timing of liquid metal delivery and in casting the mould. Through the

optimization of the processes in many cases, significant energy savings are reached:

Reduction of holding periods

Reducing of the necessary overheating of the metal to compensate of delays in

casting

Reducing unnecessary startup and shutdown.

Even the way to add the carburizing affect the energy consumption, as reported. In the result

is a significant increase in the consumption when the carburizing appliance is not used at the

beginning of melting together with the metallic materials, but is introduced only after melting

into the liquid bath. A practical experience of the author assumes that in the latter case,

approximately 1 to 2 kWh / kg carburizers are also required. For a realistic value of 2%

carburizer are so max. 40 kWh / t of iron to increase in consumption can be expected. Also

note that it is better to add silicon carriers after carburizing, because with increasing silicon

content in iron decreases the carbon solubility and a higher burn-up of silicon occur.


139

Figure 33: Comparison of heat losses of induction furnaces with opened and closed lids

Energy is wasted if the heater is operated with a open lid longer than necessary (Figure 33).

As mentioned above, the radiation loss is proportional to the fourth power of temperature

difference between radiant and the illuminated surface.

Energy is "sucked" out of the oven unnecessarily when the extraction system always

operates at full power, even if no fumes are to be discharged or occurred only in a small

amount. The excess consumption can be in unfavourable cases in the order of 3%. This

corresponds to 15 kWh / t of iron.

The next point concerns the overheating of the iron. At least about 20 kWh / ton are

necessary for an increase in temperature of 50 K. When using a melting processor, the final

temperature can be observed of up to a few degrees, and hence an unnecessary

overheating is avoided.

Electric furnaces for melting and holding – good practice example - procedural control

for induction furnaces for melting and temperature holding

Electrical energy consumption is different according to the effect of lining erosion. The less

thick the lining is, the greater the heat losses are and at the opposite, the higher electrical

coupling is between induction coil and metallic charge. It is better holding molten iron with a


140

new lining induction furnace and to limit as much as possible the holding time with the

eroded induction furnace. When a foundry operates with many furnaces, it is good to have in

mind that another furnace of the same type will not have the same performance and

electrical consumption share according to its lining condition. For example: a 9 tonnes main

frequency furnace can require a surplus of 50 kWh/t according to its lining condition. For

sure, this value can not be multiplied by the annual charged metal, because the above

mentioned condition occurs not all the time. Furthermore, foundrymen have to operate with

respect to the safety rules.

Reference

Investigation: CTIF Energy audit in foundry

Electric furnaces for melting and holding – good practice example - pump cooling

system control

Cooling system for the coil of an induction furnace operates mostly with a mixture of and

glycol. Pumps drive the water through the coil and then trough a closed circuit with an

intermediate heat exchanger with the purpose of evacuating the heat. Some foundries work

in one or two shifts, and out of this time the melting platform doesn't work, too. However, it is

not rare to seen that pumps are still active (even if the induction furnace are not in an

overnight holding position with a gas burner support. In certain foundries a burner is placed

into the crucible for safety reasons in order to avoid moisture in lining during stop periods.)

Idle periods can be of many hours or days, but pumps may be still running for nothing. A

previous check must be done with respect to the winter conditions to avoid water freezing. A

stop and go system coupled in accordance with the inlet and outlet coil temperature and the

start of the melting platform can limitate the driving time of the pumps and reduce electricity

consumption. Difference temperature determines if the furnace needs still to be cooled down.

A variable speed drive is not required, but a check of this option can be done. For example:

foundry (GS iron), 2 induction furnaces 2.4 t, medium frequency (350 Hz), 2 shifts, 5 days a

week, pump puissance 40kW. Electricity consumption is reduced by 100 MWh/y. This value

is not well proven, it's less than 1% of the global electricity consumption of the foundry, but it

can help to perform an energy efficiency management. With this example, we are aware that

it is important to check at the end of each task, if the equipments are correctly switched off,

and if not, if it this necessary to let them run. A check list is undoubltly a good way to avoid


141

missing a good practice. In the present case, exhaust ventilation of the furnaces was switch

off during long stop periods, but not the pumps.

In this example the economic savings would be round about 7000 € per year if one reduces

the consumption by 100MWh/y (current costs 1 kWh = 0,0687 €; source: Eurostat 2010).

In this example the economic savings would be round about 7000 € per year if one reduces

the consumption by 100MWh/y (current costs 1 kWh = 0,0687 €; source: Eurostat 2010).

Reference

Investigation: CTIF energy audit in foundry

Electric furnaces for melting and holding – good practice example - influence of the

addition of Carburizing on electricity consumption

The way of adding carburizing additives has influence on energy demand. According to

studies carried out, a significant increase in energy consumption is realised, when the

carburizing agent is not charged at the beginning of the melting cycle together with the

metallic load. It is generally introduced after melting into the liquid bath.

Experiences from tests which were carried out in the enterprise of Otto Junker GmbH,

assume that in the latter case approximately 1 to 2 kWh /kg carburizers are required in

addition. With an addition of 2% carburizer one triggers a surplus energy consumption of

about 40 kWh /t of iron.

Care should be taken that the carbon content of the melt does increase unnecessarily.

Otherwise, this may lead to unnecessary erosion of the melting crucible. It is recommended

that the dosage of the carburizing agent is adjusted together with the charge.

Assuming a 2% addition of carburizer, the following sample calculation can be established:

Around 40 kWh /t must be applied to more energy, if the addition of the carburizer occurs

only after melting into the liquid metal bath. If the addition at the beginning of the melting

process is realised together with the metallic charge materials, the following savings can be

realized. Taking into account a current price of 13.1 ct /kWh, one gets a cost increase of

about 5.2 € /t. The scheduled 13.1 ct /kWh (one shift) reflect the average of the price span

the industry had to pay for electricity supply in the reference year 2010. The increased

burning of carbon should be included in a calculation.

References


142

Otto Junker, Simmerath, Germany

4.2.3 Electrical losses

Development activities have succeeded in significantly reducing the electrical losses73.

Losses due to the transformer, capacitors and supply lines have fallen from 5% to 4%. The

decisive improvement, however, is in the converter technology for medium-frequency

furnaces. Whereas the losses with the use of rotary converters were in the order of 16% and

even static converters had losses of 5%, the losses with today's thyristor-based converters

are down to 3%. The author believes that even further improvement is possible through the

use of IGBT converters and sees additional optimisation potential in the coil design.

Otto Junker GmbH has determined the distribution and scatter of the electromagnetic field in

the design of high-performance inductors for induction channel furnaces with the help of

numerical simulation models for this field. The conclusions derived from the findings have led

to a change in furnace design - e.g. with regard to the size of the yoke window, the size of

the channel cross-section and the type and design of the cooling bowl. As a result, the power

loss in the inductor has been reduced by 40%.

4.2.4 Sizing and warm-up of feedstock

The exact calculation of the required batch composition on the basis of the analytical values

of the feedstock and the accurate weighing and metering in the use of materials and alloy

surcharges, including corrections between set point and actual value, are basic requirements

for the avoidance of additional expense in time and energy in the melting operation.

The charging of clean and dry feedstock is paying off, as for example for the slagging of sand

that sticks to non-blasted recycled material, as much specific energy is needed as for the

smelting of iron, about 500 kWh / t. In a realistic amount of 25 kg of sand per ton of iron are

at least 12.5 kWh / t. Secondly, of course, the amount of slag is increased. Even more

serious is the impact of rusted feedstock, because the very poor coupling leads to a low

power consumption and extends the time for melting significantly.

73 Dötsch, E.: Giesserei 98 (2011), No. 6, p. 158/70


143

The adverse influence of rusted feedstock is considerably. In extreme cases, the melting of

rusted steel scrap the 2 - to 3-times as long to melt and have a 40 to 60% higher energy

expenditure. Additional factors are the higher burn up and the larger amount of slag, so that

the use of rusted material should be avoided whenever possible.

The packing density of the charging material is determined in no small magnitude of the

electromagnetic coupling and the electrical power consumption of the feed. From this result,

the power consumption, different batch times and consequently different energy consumption

levels is given. On the basis of batches with different packing density was investigated this

relationship in a very powerful medium frequency melting system under production

conditions. The tests were conducted on a smelter with a capacity of 10 tons and a rated

power of 8000 kW at 250 Hz. The empty furnace was filled once with the specified batch

composition of pig iron, cast iron scrap, return scrap, steel scrap and aggregates. Then it

was melted without recharging up to 1380°C and it was calculated the energy consumption.

The various measurements of returns and steel scrap are packing densities were in the

range 2 to 2.7 t / m³. The results show that with a decrease in the packing density of 2.5 t /

m³ to 2.0 t / m³ the energy consumption increases by about 25 kWh / t. For this reason it is

advisable to despite the additional costs in individual cases, to crush bulky recycled material

to achieve a higher packing density. At the same time, the charging is easier and reduces the

risk of bridge formation in the furnace.

At the same time in the sense of time and energy savings to emphasize a rapid and

continuous charging of the feed. Constantly high filling degree is desirable. Through the use

of movable vibrating chute, with the entire batch receiving bunker, the conditions are created.

The use of a close to the chute docks exhaust hood, reduces the radiation losses at the

same time, good coverage of the furnace gases.

The swarf have, due to its small contact area and the surface oxidation, despite of the good

packing density, only a poor electrical contact. Therefore, the melting of swarf is always

working with a sump (greater than 40%). In the case of driving without a sump with an

additional energy demand of 50 kWh / t for the melting of the swarf to count against lumpy

material, while increasing the melting time.

Figure 34 shows the influence between the packing density of the charged material and the

energy consumption by using a medium frequency induction furnace with a capacity of

10tons and a frequency of 250Hz and a nominal power of 8MW.


144

Figure 34: Interdependence between packing density and energy consumption

Electric furnaces for melting and holding – good practice example - influence of

packing density on the power consumption

The packing density of the materials for melting in an electrically operated melting furnace

has a significant influence on the energy requirement of these feed stocks.

This is because the packing density of the charging material has an influence on the

electromagnetic inductive coupling and thus on the electric power consumption of the feed.

This results in dependence on the power consumption of different charging times and

subsequently different energy requirements.

Tests were conducted on a smelter with a capacity of 10 tonnes and a nominal power of

8,000 kW at 250 Hz. The empty furnace was filled with a fixed batch of pig iron, cast iron

scrap and recycled material once. Then it was melted without recharging up to a temperature

of 1380°C, and the energy consumption was measured. By selected sizing of the cast iron

scraps and the steel scraps variations in the bulk densities between 2.0 t/m³ to 2.7 t/m³ could

be obtained. The influence of packing density is noted in the graph below. The results of the

studies show that a decrease in the packing density of 2.5 t / m³ to 2.0 t / m³ increases the

energy demand by about 25 kWh.


Through the crushing of the feed material, the charging is also easier rspt. faster


145

The crushing of the feed material in addition, the risk of bridge formation is reduced in

the furnace

Under the assumption of increasing the packing density of 2.0 t / m³ to 2.5 t /m³, the following

sample calculation can be established:

About 25 kWh /t less energy should be applied. Taking into account a current price of 13.1 ct

/kWh, the decrease in cost will be 3.3 € /t. The scheduled 13.1 ct /kWh (one shift) reflect the

average value for industrial electricity supply in the reference year 2010.

Under the assumption that the generation of 1 MWh causes approximately 0.465 tonnes of

CO2, through the use of bulky scrap a saving in CO2 emissions of 11.6 kg /t can be

ascertained.

References

Investigation: Technical Report of the IfG gGmbH "Energy Efficient foundry"

Electric furnaces for melting and holding – good practice example - influence of the

quality of scrap on the power consumption

The knowledge of the exact batch composition on the basis of the analytical values of the

starting materials, the knowledge of the exact dosage of the feedstock and the corresponding

alloy surcharges, including the corrections between the desired and actual weight are

essential for the avoidance of time and energy in the melting operation. Included in the

analysis must be the quality of the feedstock.

The batching of dry and clean feedstock makes itself felt in the energy demand. For the

slagging of sand that sticks to non-blasted recycled material, a specific energy of about 500

kWh / tonne is consumed. This corresponds roughly to the energy needed to melt iron.

Application of rusty materials should be avoided, because the use of rusty feedstock

increases the energy requirements, see table below. The use of rusted scrap requires two to

three times as long to melt and 40 - 60% higher energy consumption. Feed materials should

be stored dry at all times.


Increase of oxidation losses by the use of rusted scrap

Increase of the amount of slag


146

The unfavourable condition in with scrap with sand adhesions is used, can result in the

following example calculation:

It must be applied an extra amount of about 500 kWh /t. Taking into account a current price

of 13.1 ct /kWh, a cost increase of 65.5 € /t takes place. The scheduled 13.1 ct /kWh (one

shift) reflect the average price for the for industrial electricity supply in the reference year

2010. Under the assumption that 1 MWh generates about 0.465 tonnes of CO2, one can

save 232.5 kg CO2/ t.

References

Investigation: Report of the IfG gGmbH "Energy Efficient foundry"

4.2.5 Insulation and its twofold effect

With decreasing delivery thick, a improved efficiency of the coils is reached, the power

consumption increases, but at the same time increase the heat losses from the thinner wall

of the crucible. However, the coil losses are almost a power of then higher than the thermal

losses of the crucible wall, so that the influence of the coil losses dominate here. Also this

saves energy. I believe that this is not recommended because it increases the risk of wall

penetrations.

Abwärmenutzung bei Induktionsöfen

Only in induction crucible furnaces currently exits waste heat recovery. One uses the waste

heat that is dissipated by the cooling water. This waste heat, about 20 to 22% of input

energy, can be used in various ways. It exits reports over the use of heat pumps. Most

economic is undoubtedly the direct use of waste heat. This advantage was, for example,

used by the foundry Hundhausen74. This required the increasing of the cooling water

temperature. This was only possible for the water circuit of the induction coil, since the

cooling water outlet temperature higher than 38°C in the capacitors was not allowed. The

induction coils allow an increase to 70°C. The water cycle has been disconnected and

therefore raised the cooling water outlet temperature of the furnace coils at 65°C on average.

The hot water was delivered over a piping system to the individual delivery points, like

heating for workshop and management. The water is returned to the furnaces with a

74 Krabiell, H.; Opitz, R.: Giesserei 68 (1981), No. 19, p.561/68


147

temperature of 50°C. Is the return temperature higher than 50°C, the water is cooled by air-

cooled heat exchanger to 50°C. An oil heating system is switched on if the return

temperature falls below 50°C. The cost for this system were 2.7 million DM, the level of costs

was partially caused by the high personnel costs for engineering services, which were

necessary for the construction of the pilot plant. Saves about 70 to 80% so far for heat

generation per 1000 tons of fuel oil used in a year can be made. At a price of 0.50 DM / l of

heating oil, the capital recovery period is nearly 6 years. This value could be improved if it

were possible, especially in the summer to find additional customers.

4.2.6 Power factor correction

The furnace coil causes a phase shift of voltage and current to the effect that the voltage is

90° ahead of the current. This phase shift is offset by the capacitors, as in a capacitor the

current is 90° ahead of the voltage. The phase shift results in a reactive power that shuttles

between consumer and power plant, causing losses in the power lines due to ohmic

resistance. The aim therefore is always to keep the phase shift and therefore the reactive

power to a minimum. In induction furnaces, the phase shift is minimised by an automatic

controller that measures the phase shift.

4.3 Gas and oil fired furnaces (crucibles, tunnel, rotating, etc.)


The energy balance - also called heat balance - expresses the energy efficiency of a furnace.

It shows which parameters can be influenced to increase energy efficiency.

The energy balance of a furnace is determined by the following variables:

Qinput : Feed energy (e.g. via combusted gas)

Qobject : Energy taken on by the object or medium

Qlosses:Losses

Qreku :Feed energy or heat through the use of a recuperator

Qinput is determined by the type and amount of fuel. In addition, the chemical composition or

chemically bound energy and physically bound energy play a key role. Accordingly, Qinput is


148

made up of the chemically bound energy (solid, liquid and/or gaseous) and the physically

bound energy (solid, liquid and/or gaseous) as well as the fed-in volume per unit of time.

Chemically bound energy

The following molecules are among the most important combustible elements in fuels:

H2 Hydrogen with a calorific value of 141,197 kJ/kg

CO Carbon dioxide with a calorific value of 10,132 kJ/kg

CH4 Methane with a calorific value of 55,601 kJ/kg

C3H8 Propane with a calorific value of 50,409 kJ7kg

C4H10 Butane with a calorific value of 49,488 kJ/kg

H2S Hydrogen sulphide with a calorific value of 16,705 kJ/kg

The composition of the fuel in question therefore plays a central role in determining the

respective calorific value. This becomes clear when comparing smelting gases and natural

gas. Smelting gases have an H2 concentration of 4% and a CO concentration of 21%. The

remainder is made up of CO2 and N2, the ballast gases. By comparison, natural gas has a

CH4 concentration of between 82 and 93%. The methane concentration is quality-dependent.

The remainder is made up of ballast gases. Due to the high methane content, natural gas

has a higher overall calorific value than other gases like smelting gases. The chemical make-

up also determines the calorific value in solid fuels.

This means that the type of fuel has a major influence on the energy balance. In addition, the

share of ballast gases also determines energy efficiency and affects the energy balance.

High ballast gas concentrations absorb energy and heat during combustion via radiation and

convection. Ballast gases are therefore a hindrance to the heating of objects and of media to

be melted. In cases like these, the absorbed energy of the ballast gases can be discharged

via recuperators and therefore forwarded to the process in the form of combustion air

preheating. This has a positive effect on the efficiency level. Ballast gases reduce the

calorific value of the fuel. The physically bound energy is made up of heated ballast gases

and steam.

A further important parameter in the thermal balance is the energy absorbed by the object

and/or the feedstock, Qobjekt. Qobjekt can be increased by improving the efficiency of heat

transfer. Options include preventing contaminants and oxides, which reduce the heat transfer

ability or the heat absorption of the feedstock.

Heat losses play a key role in the combustion process. These losses are divided up as

follows:


149

Qwall,etc.: Furnace losses: the wall losses can be minimised by improved insulation

or replacement and sealing of furnace ports.

Qoff-gas: The flue gas losses can be minimised by routing the heat back into the

process using a recuperator. The discharged flue gas energy is defined as Qreku.

The losses are made up as follows: Qlosses = Qwall,etc.+ Qoff-gass + Qreku

The heat balance is defined as follows: Qinput +Qreku = Qobjekt + Qlosses

The total energy input Qinput + Qreku is defined as Qmax input.

The efficiency of the furnace is a further key element in determining energy efficiency. The

furnace efficiency is the ratio of the energy fed in to the feedstock to the energy content of

the furnace. The energy content of the furnace is made up of the absorbed energy of the

feedstock Qinput and the furnace losses Qwall,etc. The furnace efficiency represents the

implementation of the process in the furnace chamber and can be increased by increasing

convection and reducing furnace losses.

The efficiency of the furnace is defined as follows: η= Qobjekt / (Qobjekt + Qwall,etc.)

A further parameter for energy efficiency is the thermal efficiency - the ratio of the energy

supplied to the feedstock Qobjekt and the losses from the furnace Qwall,etc. to the total energy

input Qinput+Qreku.

This means the thermal efficiency is defined as follows: ηth.= (Qobjekt + Qwall,etc.) / Qmax input

Both variables - furnace efficiency and thermal efficiency - indicate the energy efficiency of

the combustion process.

4.3.2 (Optimal) operation cycles and handling

The optimum method of operating a furnace can vary quite widely. This is particularly clear if

we consider the start-up mode of the furnace. Based on their different designs, furnaces are

used for different purposes. A further aspect is the arrangement and alignment of the

burners. The start-up mode, arrangement and location of the burners has a major impact on

the efficiency of the furnace. Efficiency is also influenced by the choice of burner and fuel.

The burners of the crucible furnace are generally outside the furnace, and this renders

cooling unnecessary. Tangential arrangement of the burners increases the efficiency of heat


150

transfer to the crucible and ensures effective gas distribution around the crucible and hence

evenly balanced heating.

Figure 34: Principle draft of gas fired furnace

The furnace chamber is lined with refractory material to minimise heat loss. Heat losses can

be additionally minimised during operation by using a swivel-type lid. Crucible furnaces with

off-gas hood are seldom used nowadays. as off-gas is extracted via the melt, thereby

negatively impacting melt quality. Adaptation of the crucible to the furnace chamber makes a

key contribution to boosting efficiency. Moreover, the aging of a crucible should be monitored

over time, as replacing a crucible can also enhance energy efficiency. New crucibles have

superior heat transfer properties. A further energy efficiency measure is the avoidance of

overheating due, for example, to faulty or absent temperature controllers. In addition, the

crucible should not be fully emptied after pouring to allow improved utilisation of the melting

power.

The burners of the rotary drum furnace often point towards the arch. The refractory lining of

the rotary drum furnace is exposed to high mechanical strain during operation. For this

reason, the refractory lining is preheated via the burner to prolong the life of the lining. The

furnace is first rotated to ensure an efficient start to the melting phase that spares the lining.

During the overheating phase, the furnace rotates continuously. Efficiency is considerably

increased by replacing the cold-air burners with oxygen burners; this measure also boosts

efficiency in hearth and tank furnaces and can increase the efficiency level by between 40

and as much as 80%.


151

Efficient operation of a tunnel furnace depends to a large extent on the combustion curve. It

should be possible to control the curve with precision and in a reproducible way to suit the

casting in question. As tunnel furnaces consume a lot of energy, precise and reliable burner

control is indispensable. An intelligent combination of flat-flame burners and impulse burners

can stabilise the temperature curve to approx. 2-3°C and therefore increase efficiency.

The choice of burner also plays a key role in increasing the efficiency of the combustion

process. Various burners and selection criteria are outlined below:

Table 6: Different types of burners with several selection criteria75

Selection

criterion

Cold-air

burner

1-stage

Cold-air

burner

2-stage,

modulating

Oxygen

burner

Hot-air

burner

Recuperator

Hot-air

burner

Jacket pipe/

Recuperator

Hot-air burner

Regenerator

Application Melting Holding Melting Melting Holding Melting

Furnace type Crucible,

tank and

shaft

melting

furnace

Crucible,

tank and

shaft

melting

furnace

Tank and

rotary drum

furnace

Crucible,

tank and

shaft

melting

furnace

Crucible Crucible, tank and

shaft melting

furnace

Costs Low Low High Average Average High

Technical

firing

efficiency

50-60 % 50-65 % 85-90 % 70-80 % 70-80 % 80-90 %

Temperatures-

combustion

1200 °C 1200 °C 2000 °C 1300 °C 1300 °C 1300 °C

Temperatures

- off-gas

600-

1000 °C

600-

1000 °C

600-

1000 °C

400-

600 °C

400-

600 °C

150-

300 °C

Burner regulation and control takes a main part in (optimal) operation cycles and handling of

furnaces, too. Efficient combustion depends on the regulation and control.

Combustion or burning is a complex sequence of exothermic chemical reactions between a

fuel and an oxidant accompanied by the production of heat or both heat and light in the form

of either a glow or flames. In a complete combustion reaction, a compound reacts with an

oxidizing element, and the products are compounds of each element in the fuel with the

oxidizing element. In reality, combustion processes are never perfect or complete. In flue-

75 IFG, bdguss, Investigation: Energieeffizienter Gießereibetrieb (Energy efficient Foundry)


152

gases from the combustion of carbon (coal combustion) or carbon compounds

(hydrocarbons, wood, etc.), both unburned carbon (as soot) and carbon compounds (CO and

others) will be present. Also, when air is the oxidant, some nitrogen will be oxidized to

various nitrogen oxides (NOx) with impacts on the environment.

The combustion installations discussed in this section are heating devices or installations

using the combustion of a fuel (including wastes) to generate and transfer heat to a given

process. This includes the following applications:

boilers to produce steam or hot water

process heaters, for example to heat up crude oil in distillation units, to achieve steam

cracking in petrochemical plants, or steam reforming for the production of hydrogen

furnaces or units where materials are heated at elevated temperatures to induce a

chemical transformation, for example, cement kilns and furnaces for producing

metals.

In all of these applications, energy can be managed by control of the process parameters

and control on the combustion side. Energy management strategies relative to the process

depend on the process itself.

The heat energy resulting from the combustion of fuels is transferred to the working medium.

The heat losses can be categorized as:76

losses via the off-gas. These depend on the flue-gas temperature

losses through unburned fuel, the chemical energy of that which is not converted.

Incomplete combustion causes CO and hydrocarbons to occur in the flue-gas

Burner regulation and control helps to avoid incomplete burned fuel in the off-gas. Automatic

burner regulation and control can be used to control combustion by monitoring and

controlling fuel flow, air flow, oxygen levels in the flue-gas and heat demand. This technique

warranted an optimal oxygen-fuel relation. The optimal oxygen-fuel relation depends on:

reducing excess air flow

76 European Commission, Integrated Pollution Prevention and Control, Reference Document on Best Available

Techniques in the Smitheries and Foundries Industry, May 2005, p. 116-121


153

optimizing of fuel usage to optimize burnout and to supply only the heat required for a

process

Excess air can be minimized by adjusting the air flow rate in proportion to the fuel flow rate.

This is greatly assisted by the automated measurement of oxygen content in the flue-gases.

Depending on how fast the heat demand of the process fluctuates, excess air can be

manually set or automatically controlled. Too low an air level causes extinction of the flame,

then re-ignition and backfire causing damage to the installation. For safety reasons, there

should therefore always be some excess air present (typically 1 – 2 % for gas and 10 % for

liquid fuels).

Important for the efficiency factor is the proportion of flue gas to air. As you can see in Figure

35; the efficiency factor gets lower with increased Lambda factor (increasing dues of air).

This is a result of a higher Nitrogen due in the gas mixture. In all cases of combustion with

air, Nitrogen is a passive attendant which is only heated up – without being a reactant in the

chemical reaction.

Figure 35: Efficiency of natural gas combustion in dependence of the Lambda-Factor

As excess air is reduced, unburned components like carbonaceous particulates, carbon

monoxide and hydrocarbons are formed and may exceed emission limit values. This limits

the possibility of energy efficiency gain by reducing excess air. In practice, excess air is

adjusted to values where emissions are below the limit value.


154

Reduction of excess air is limited due to the related increase of raw gas temperature;

extremely high temperatures can damage the whole system.

The minimum excess air that is reachable to maintain emissions within the limit depends on

the burner and the process. Note that the excess air will increase when burning solid wastes.

However, waste incinerators are constructed to provide the service of waste combustion, and

are optimized to waste as fuel77.

Oxygen-firing is a other option to optimize or to reduce the content of unburned fuel and to

optimize the efficiency of the combustion process. Its use has various benefits:

an increased oxygen content results in a rise in combustion temperature, increasing

energy transfer to the process, which helps to reduce the amount of unburned fuel,

thereby increasing energy efficiency while reducing NOx emissions

as air is about 80 % nitrogen, the mass flow of gases is reduced accordingly, and

hence a reduction in the flue-gas mass flow

this also results in reduced NOx emissions, as nitrogen levels at the burners are

considerably reduced

the reduction in flue gas mass flows may also result in smaller waste gas treatment

systems and consequent energy demands, e.g. for NOx where still required,

particulates, etc.

where oxygen is produced on site, the nitrogen separated may be used, e.g. in

stirring and/or providing an inert atmosphere in furnaces where reactions can occur in

oxidizing conditions (such as pyrophoric reactions in non-ferrous metals industries)

a future benefit may be the reduced quantity of gases (and high concentration of CO2)

which would make the capture and sequestration of CO2 easier, and possibly less

energy-demanding.

The energy requirement to concentrate oxygen from the air is considerable, and this should

be included in any energy calculations. Within the glass industry, there is a large diversity in

glass melt production capacities, glass types and applied glass furnace types. For several

cases, a conversion to oxygen firing (e.g. compared to recuperative furnaces, for relatively

small furnaces and for special glass) very often improves the overall energy efficiency (taking


Techniques in the Smitheries and Foundries Industry, May 2005, p. 128, 129


155

into account the primary energy equivalent required to produce the oxygen). However, for

other cases the energy consumption for oxygen generation is as high or even higher than the

saved energy. This is especially the case when comparing overall energy efficiency of

oxygen-fired glass furnaces with end-port fired regenerative glass furnaces for large scale

container glass production. However, it is expected that further developments in oxygen-fired

glass furnaces will improve their energy efficiency in the near future. Energy savings do not

always offset the costs of the oxygen to be purchased.

Special safety requirements have to be taken into account for handling oxygen due to the

higher risk of explosion with pure oxygen streams than with air streams. Extra safety

precautions may be needed when handling oxygen, as the oxygen pipelines may operate at

very low temperatures.

Not widely used in all sectors. In the glass sector, producers try to control temperatures in

the glass furnace combustion space to levels acceptable for the applied refractory materials

and necessary to melt glass of the required quality. A conversion to oxygen firing generally

does not mean increased furnace temperatures (refractory or glass temperatures), but may

improve heat transfer. In the case of oxygen firing, furnace temperatures need to be more

tightly controlled, but are not higher than those in air-fired furnaces (only temperatures of the

cores of the flames may be higher).

The price for bought-in oxygen is high or if self-produced has a high demand on electrical

power. The investment in an air separation unit is substantial and will strongly determine the

cost effectiveness of firing with oxygen.

Reduced waste gas flows will result in the requirement for smaller waste gas treatment

systems, e.g. de NOx. However, this only applies in new builds, or to places where waste

treatment plants are to be installed or replaced78.

Another option to improve the efficiency of the combustion process, is the choice of fuel. The

type of fuel chosen for the combustion process affects the amount of heat energy supplied

per unit of fuel used. The required excess air ratio is dependent on the fuel used, and this

dependence increases for solids. The choice of fuel is therefore an option for reducing

excess air and increasing energy efficiency in the combustion process. Generally, the higher

the heat value of the fuel, the more efficient the combustion process.

This achieves energy savings by reducing excess air flow and optimizing fuel usage. Some

fuels produce less pollutants during combustion, depending on source (e.g. natural gas




156

contains very little sulphur to oxidize to SOx, no metals). There is information on these

emissions and benefits in various vertical sector BREFs where fuel choice is known to have

a significant effect on emissions. The choice of using a fuel with a lower heat value may be

influenced by other environmental factors, such as:

fuel from a sustainable source

recovery of thermal energy from waste gases, waste liquids or solids used as fuels

minimization of other environmental impacts, e.g. transport.

Various emissions are associated with certain fuels, e.g. particulates, SOx, and metals are

associated with coals. There is information on these effects in various vertical sector BREFs

where fuel choice is known to have a significant effect on emissions.

Widely applied during the selection of a design for a new or upgraded plant. For existing

plants, the choice of fuels will be limited by the combustion plant design (i.e. a coal fire plant

may not be readily converted to burn natural gas). It may also be restricted by the core

business of the installation, e.g. for a waste incinerator.

The fuel choice may also be influenced by legislation and regulations, including local and

trans boundary environmental requirements79.

Driving force for implementation:

combustion process efficiency

reduction of other pollutants emitted

Examples:

wastes burnt as a service in waste-to-energy plants (waste incinerators with heat

recovery)

wastes burnt in cement kilns

waste gases burnt, e.g. hydrocarbon gases in a refinery or CO in non-ferrous metals

processing

4.3.3 Thermal losses




157

One option to reduce possible heat losses in a combustion process consists of reducing

temperature of the flue-gases leaving the stack. This can be achieved by:

dimensioning for the maximum performance plus a calculated safety factor for

surcharges

increasing heat transfer to the process by increasing either the heat transfer rate,

(installing turbulators or some other devices which promote the turbulence of fluids

exchanging heat), or increasing or improving the heat transfer surfaces

heat recovery by combining an additional process (for example, steam generation by

using economizers) to recover the waste heat in the flue-gases

installing an air (or water) pre heater or preheating the fuel by exchanging heat with

flue gases. Note that the manufacturing process can require air preheating when a

high flame temperature is needed (glass, cement, etc.). Preheated water can be used

as boiler feed or in hot water systems (such as district schemes)

cleaning of heat transfer surfaces that are progressively covered by ashes or

carbonaceous particulates, in order to maintain high heat transfer efficiency. Soot

blowers operating periodically may keep the convection zones clean. Cleaning of the

heat transfer surfaces in the combustion zone is generally made during inspection

and maintenance shutdown, but online cleaning can be applied in some cases (e.g.

refinery heaters)

ensuring combustion output matches (and does not exceed) the heat requirements.

This can be controlled by lowering the thermal power of the burner by decreasing the

flow rate of fuel, e.g. by installing a less powerful nozzle for liquid fuels, or reducing

the feed pressure for gaseous fuels.

Reducing flue-gas temperatures may be in conflict with air quality in some cases, e.g.:

pre heating combustion air leads to a higher flame temperature, with a consequence

of an increase of NOx formation that may lead to levels that are higher than the

emissions limit value. Retrofitting an existing combustion installation to preheat the air

may be difficult to justify due to space requirements, the installation of extra fans, and

the addition of a NOx removal process if NOx emissions exceed emission limit values.

It should be noted that a NOx removal process based on ammonia or urea injection

induces a potential of ammonia slippage in the flue-gases, which can only be

controlled by a costly ammonia sensor and a control loop, and, in case of large load


158

variations, adding a complicated injection system (for example, with two injection

ramps at different levels) to inject the NOx reducing agent in the right temperature

zone

gas cleaning systems, like NOx or SOx removal systems, only work in a given

temperature range. When they have to be installed to meet the emission limit values,

the arrangement of gas cleaning and heat recovery systems becomes more

complicated and can be difficult to justify from an economic point of view

in some cases, the local authorities require a minimum temperature at the stack to

ensure proper dispersion of the flue-gases and to prevent plume formation. This

practice is often carried out to maintain a good public image. A plume from a plant's

stack may suggest to the general public that the plant is causing pollution. The

absence of a plume suggests clean operation and under certain weather conditions

some plants (e.g. in the case of waste incinerators) reheat the flue-gases with natural

gas before they are released from the stack. This is a waste of energy.

The lower the flue-gas temperature, the better the energy efficiency. Nevertheless, certain

drawbacks can emerge when the flue-gas temperatures are lowered below certain levels. In

particular, when running below the acid dew point (a temperature below which the

condensation of water and sulphuric acid occurs, typically from 110 to 170 ºC, depending

essentially on the fuel‟s sulphur content), damage of metallic surfaces may be induced.

Materials which are resistant to corrosion can be used and are available for oil, waste and

gas fired units although the acid condensate may require collection and treatment.

The strategies above _ apart the periodic cleaning _ require additional investment and are

best applied at the design and construction of the installation. However, retrofitting an

existing installation is possible (if space is available). Some applications may be limited by

the difference between the process inlet temperature and the flue-gas exhaust temperature.

The quantitative value of the difference is the result of a compromise between the energy

recovery and cost of equipment. Recovery of heat is always dependent on there being a

suitable use. See the potential for pollutant formation, in Cross-media effects, above.

Payback time can be from under five years to as long as to fifty years depending on many

parameters, such as the size of the installation, and the temperatures of the flue gases80.




159

Another possibility to reduce the thermal loses is to close the furnace openings. Heat losses

by radiation can occur via furnace openings for loading/unloading. This is especially

significant in furnaces operating above 500°C. Openings include furnace flues and stacks,

peepholes used to visually check the process, doors left partially open to accommodate

oversized work, loading and unloading materials and/or fuels, etc.

Losses are very apparent when making scans with infrared cameras. By improving design,

losses via doors and peepholes can be minimized81.

Examples:

Heat losses from a crucible furnace can be minimised by a swivel-type lid, good

insulation and a recuperator.

Irrespective of the type of furnace, the option of waste heat utilisation and the closing

of furnace ports using covers should be considered wherever possible.

Short example – thermal losses of gas fired furnaces - rotary drum furnace for aluminum

The melting process in the tilt able rotary drum furnaces with special furnace technology

requires significantly less salt input and therefore generates less waste (salt slag) compared

to conventional rotary drum furnaces. In addition, the metal recovery is up to 2 percent higher

in these furnaces.

Tilt able rotary drum furnaces were equipped with a new burner system and further modified

by installing a door system at the furnace openings to reduce heat loss and fugitive

emissions. The downstream systems, such as the filtration plants, require less capacity due

to the reduced process gas stream which has a positive effect on the lifetime of individual

equipment parts as well as on the reliable compliance with the stipulated threshold values.

From 2005 to 2008 the amounts of the recycled material could be increased while the gas

consumption and therefore the energy consumption could be reduced by an overall 39

percent per tonne during this period.

This success realized a reduction overall CO2 emissions of ca. 84 tonnes a year by

technically modifying the furnaces.82


Techniques in the Smitheries and Foundries Industry, May 2005, p. 133 82

Best-Practice-Examples of the Non-Ferrous Metals Industry; Innovative Recycling Technologies Reduce

Consumption of Resources; p.10


160

4.3.4 Sizing and warm-up of feedstock

In general, it can be said that the following factors are of relevance for boosting energy

efficiency when feeding furnaces:

No soiling or oxidation of the feedstock

Avoidance of bulky block material

Furnace should not be fully emptied

Use of the full furnace volume wherever possible when inserting feedstock

4.3.5 Insulation

The heat losses through the walls of the combustion system are determined by the diameter

and height of the furnace and the thickness of the insulation. An optimum insulation

thickness which relates energy consumption with economics should be found in every

particular case. Efficient thermal insulation to keep heat losses through the walls at a

minimum is normally achieved at the commissioning stage of the installation. However,

insulating material may progressively deteriorate, and must be replaced after inspection

following maintenance programs. Some techniques using infrared imaging are convenient to

identify the zones of damaged insulation from outside while the combustion installation is in

operation in order to plan repairs during shutdown.

Low cost, especially if carried out at shutdown times. Insulation repair can be carried out

during campaigns. Insulation repair is carried out during campaigns in steel and glass

industries83.

4.3.6 Heat recovery from off-gas

Due to the high exhaust gas losses of the melting and annealing furnaces, the largest energy

savings are achieved by the waste heat recovery. It should however only be sought if it is

technically not longer possible to arrive directly a higher use of energy. With an oil or gas


Techniques in the Smitheries and Foundries Industry, May 2005, p. 164


161

burner you should try at first to reduce the fuel consumption by minimizing the excess air,

through optimal design of the burner block or better turbulence of the air-fuel mixture.

Recovery systems typically require high capital expenditures. The waste heat recovery is

associated with inevitable losses. In addition, waste heat and energy consumption usually

are in every time not the same. It is therefore advisable to carry out in each case a thorough

feasibility study.

The availability of waste heat depends on the following points:

Heat flow per unit time, and annual hours of operation of the facility

Temperature level and in-bound latent heat energy content per m3 of gas. At low

temperature level, the use of options is limited and the heat exchange surfaces would

be greatly enlarged

For exhaust, the cleanliness is considered. For contaminated exhaust gases must be

cleaned; the heat transfer is reduced through layers of dirt on the exchange surface

Distance between collection points and consumers

Since energy storage is very expensive, should the waste heat and consumption

coincide in time

Because of the points 4 and 5, it is particularly advantageous to reduce the waste heat in the

generating unit again examples are the hot blast cupola or combustion air preheating at

burners.

Recuperative heat exchangers

This refers to heat exchangers, which are traversed by at least two media flowing

continuously in the same direction. Thereby the flowing media are separated of each other

by a closed wall. The media can be gas or water. The media guide is the direct, cross, or

counter-current. In the gas medium you can make a distinction between radiation and

convection recuperators. In radiation recuperators the radiation from the hot exhaust gas is

used for heat transfer on the wall surface. It depends to a much greater extent on the

temperature than the heat transfer by convection. The radiation recuperator is therefore only

used at high temperatures (up to 1500°C). One can expect that the heat output drops a hot,

glowing gas from 1200°C to 900°C for more than a third. With a temperature decrease from

900°C to 600°C, the heat output falls further, by a third. The operating characteristics of

convection recuperators are much cheaper. For them, the heat dissipation is much less


162

temperature dependent. Furthermore, it can be accommodated in a small space with a very

large heating surface.

Figure 36: Different operating methods of recuperators

These advantages are compared to the following disadvantages: When convection

recuperators are installed behind stoves with high exhaust temperatures, the walls of the

preceding exhaust duct take at nearly the temperature of the exhaust. Thereby may occur

overheating of the material at the front sides of the tubes and substantial temperature

differences in the material between the front and back of the pipes. This gives rise to

mechanical stresses that shows by experience that transverse cracks in the front wall pipe

occur. Convection recuperators are easily contaminated. The more compact they are built,

the specific power is higher, but the closer are the gangway that represents the available flow

of medium. When the exhaust gases are dust-containing, the convection recuperators tend

to gradual or rapid clogging, whereby the heat transfer is greatly reduced. Some relief can be

achieved if one goes from ribbed tubes to smooth tubes. However, after certain periods of

time cleaning of the plain tubes is necessary. To facilitate this, so-called register recuperators

are offered which can be pulled out for cleaning. The heavy pollution of the convection


163

recuperators leads to corrosive elements in which dusts lead to premature failure of the

recuperator. For this reason, in corrosive conditions radiation recuperators is preferred,

which are less smooth and his large surface leads to a lesser degree of pollution and

threatened corrosion. Another use for exhaust recuperators is warm or hot water production.

For the heat exchangers are used normally ribbed tubes. For dirty exhaust are also smooth

tubes offered. Through the bypass line it is possible to regulate the charging of the

exchanger. This avoids overloading of the heat exchanger or to avoid passing below the dew

point in the exhaust. The here described construction, when used as a material of high

temperature resistant steel, exhaust temperatures to 900°C can be tolerated. In recent years

the so-called recuperator burners have increasingly widespread. In this burner, the

recuperator is integrated into the burner. In another embodiment, a beamline still attached

prior to the burner. Thus, the gas is closed out and is similar in function and control accuracy

to an electric heating element.

Figure 37: Comparison of different combustion processes, with and without a recuperator

Connected circuit heat exchanger

In this type of heat exchangers, a third medium serves as a heat transfer between the heat

dissipating and heat-absorbing medium. Their system-related advantage is the relatively

large degree of independence in the sizing of flow-through paths. At the one piece

recuperative heat exchanger is a direct relationship between the heat dissipating and heat-

absorbing surface. In the arrangement of two circuit connected heat exchangers, these

surfaces are largely independent of each other. Another embodiment of the circuit connected


164

heat exchanger is developed by KGT. The heat transfer medium in this case consists of

ceramic balls.

Regenerative heat exchanger

The best known embodiments are the cowper in the blast furnaces and the heat exchanger

at SM furnaces. They are characterized by very high levels of waste heat utilization. More

recently, several companies built burner systems with regenerative combustion air

preheating. The burner system is relatively expensive and therefore only suitable for large

plants with high annual operating hours (e.g. furnaces for aluminium smelting and refining).

Another type of regenerative heat exchanger consists of a capillary formed thermal mass

fitted to a rotor. The rotor is housed in a steel housing with a connection part for the exhaust

and supply air. The rotor turns slowly and comes with each revolution with its mass-memory

sequentially with the heat-emitting exhaust and the heat-absorbing supply air in contact and

transfers the heat from the outgoing to the incoming air. An airlock zone prevents the transfer

of dust from the incoming air to the outgoing air. Regenerative heat exchangers are used to

detract the heat of the indoor air and preheat the incoming air. The energy required for

heating can be reduced by up to 70%. Partial regenerative heat exchangers are used behind

core dryers or compressor units. Their use is possible up to temperatures of 200°C.

Consumers of the generated heat

If the waste heat not lead back again to the heat generating unit (e.g. blast preheating), the

possibility to use waste heat for heating purposes and hot water (showers), is the most

frequently cited measure in the literature. The use of waste heat for heating purposes is

unfortunate because the heating demand varies greatly over the years. Therefore, it is more

economical if the waste heat is used for drying or preheating. Other possibilities are the

internal air pressure and electricity generation. Because of the high investment costs, high

annual operating hours is necessary. In examining the possibilities of using waste heat must

be considered that the energy can be sold eventual to external customers. There are several

possible applications:

Process heat or process steam for

o Drying facilities

o Refrigeration systems

o Vacuum systems

Heat for heating purposes.


165

District heating networks usually have water temperatures of at least 130°C. Normal is 150 to

180°C. Therefore, it must be waste heat, which has an appropriate temperature level.

Short example – heat recovery – regenerative combustion system for aluminum alloys

High temperatures are required for smelting aluminum alloys and aluminum recycling

material. Temperatures of up to 1,300°C are the standard. To counteract the high demand in

thermal power and the costs and emissions resulting from it, the smelting furnaces in

consideration of economic and technically most advanced aspects – converted from cold air

combustion systems to regenerative combustion systems.

Regenerative combustion system – how it works

A regenerative combustion system consists of at least one burner pair. Burner 1 heats the air

in furnace chamber to ca. 1,200 – 1,300°C. A large part of the heated air is passed on to the

material to be melted, the fumes are sucked by burner 2 and directed through a heat storage

tank – the regenerator. The exhaust fumes heat the contents of the regenerator to about

1,050 - 1,150°C. At this moment the system switches and burner 2 heats. The air for burner

2 is sucked in from the regenerator heated by the exhaust fumes of burner 1. Since this

regenerator has a temperature of 1,050 – 1,150°C at switching time, the system requires

much less energy to achieve the furnace chamber temperature of 1,300°C. Regenerative

burners use their own exhaust fumes to save power. With regenerative combustion systems

at least 85 % of the thermal power input can be re-used, thereby saving significant amounts

of power. At the same time, the installation of new combustion systems results in an increase

of the smelting performance of up to 200 %. Another positive factor is the further

considerable reduction of noise and dust emissions. The CO2 emissions reduce to 8,821

tonnes per year due to higher efficiency and the low consumption of gas.84

4.4 Thermal fate of the liquefied metal

The energy consumption for storage and transportation of liquid metals in foundries can

make up a large share of total energy. It should be hold in mind that in most time the total

84 Best-Practice-Examples of the Non-Ferrous Metals Industry; Energy Efficient Use of Heat; page 13


166

energy in this area only to be used to compensate for energy losses. Often appreciable

savings can be achieved with relatively little effort. The direction in the development of cost-

cutting is always the same, namely the reduction of heat losses, caused for example by

radiation, conduction and heat storage of the ff-linings.

If the melting assembly is a cupola, the losses begin in the cupola channel. In open chutes,

the losses are mainly caused by radiation. During the transition from a broad, open chute to a

chute with high cover the heat loss is reduced to one tenth. In a 3 m long chute, the

temperature drop instead of 14°C, only about 1°C85.

The next step is the transport of the liquid metal to the mould-making unit. Ladles are

normally used for this purpose. Treatment in the ladle is often an additional intermediate

step. Heat is lost during both steps.

In the mould-making unit, the metal is either poured directly from the ladle, poured into a

pouring device (heated or unheated) or placed in a holder furnace ready for pouring. The

heat losses occurring in these assemblies depend on the size of the assemblies and the

amount of time the metal is stored there.

Either the heat losses need to be offset by a higher tapping temperature or, in the case of

heated assemblies, holding energy needs to be provided. In the case of ladles, a

considerable amount of energy is used for preheating.

4.4.1 Ladle preheating and insulation

During the drying and preheating of ladles and furnaces energy is consumed, which should

be minimized as much as possible. In a study by Davies and the Magny86 ladle preheating

has been studied systematically. First, the temperature-time profile of a vertical cylinder pan

with a capacity of about 450 kg was investigated. The gas burner was located centrally and

the burner head was in the same level with the edge of the socket. By attaching a cover to

the ladles.

It is apparent that after 60 min preheating the temperature is by about 200°C higher or that

the temperature of 1000°C is reached in 25 to 30 minutes instead of 60 minutes. That would

mean an energy savings of 50%. After turn off the burner, the ladle cools down quickly. On

the surface of the heated inner wall, the temperature drops in the first 10 minutes of almost

300°C. In experiments with covered ladles, which remained even after the burner shut the lid

on the pan, were measured at about 30% lower thermal losses. In order to avoid

85 Landefeld, C. F.: Trans. Amer. Foundrym. Soc. (6 (1978), p. 187/92

86 Davis, K. G.; Magny, I. G.: Giessereipraxis 1983, No. 9, p. 129/38


167

unnecessary heat losses of the ladles, it is responsible for ensuring that the ladles are not

unnecessarily long heated and that they can be used immediately after preheating.

Furthermore, liner materials are known which cure without energy supply, have a very low

thermal conductivity and low heat capacity, so preheating is not necessary.

The flameless gas porous burner is an alternative to conventional ladle heaters87 88. In

porous burners, the combustion process no longer takes place in an open flame but in

porous high-temperature ceramic material. The result is flameless combustion in the form of

glowing ceramic foam. In this process, the heat is mainly transferred through radiation. The

burner has an extremely high power density (3,000kW/m²) and is very compact. In one

foundry, ladle preheating has been converted to this type of burner (Figure 38). Compared to

the previous burner, the porous burner uses around only half as much gas.

Figure 38: Pre heating station with installed porous burners

This burner is also used in the annealing furnaces in this foundry. The hot off-gases from the

ladle heater and the annealing furnaces are collected and used for water heating.

Ladle preheating and insulation - good practice example - flameless porous burner

In the present, you still can find the heating or preheating of ladles by the combustion of

charcoal. In foundries also still many conventional ladle preheating flares, based on natural

87 Giesserei 98 (2011), No. 9, p. 8

88 Keim, F.; Encinas, C.: Giesserei 98 (2011), No. 6, p. 182/86


168

gas-air burners, are found. Both methods of preheating and heating are among the aspects

of energy efficiency and environmental protection not recommended.

These kinds of preheating procedures are, generally speaking, connected to the following

disadvantages:

they may cause hot spots during preheating the ladles

cause high volume flow rates (the natural gas / air ratio is about 1/10), compared e.g.

to oxy-fuel-burner

requires a long warm-up time.

The Promeos company offers a new product to the market. Promeos develops and produces

special burners which function without open fire.

The following aspects can be combined with the Promeos technology:

Potential energy savings in the process of up to 50 per cent due to lower heating up

time

Lower emissions compared to natural gas burner with open flame

No hot spots during preheating

The flameless burner technology is individually adaptable to any geometry of ladles


Optimized heat transfer to the ladles

Reduction of carbon dioxide emissions

Reduced levels of pollution e.g. CO, NOx and CxHy

More than 200,000 € have been invested by the steel foundry Schmees into the new system

to preheat the burner ladles. This redesign of the ladles preheating station was promoted by

an environmental innovation program of the Ministry for the Environment, Nature

Conservation and Nuclear Safety in the amount of € 54,273.

According to the steel foundry Schmees the projected natural gas savings are amounted to

about 45,000 cubic meters per year. The cost saving of € 17,685 taking into account the

average procurement costs for natural gas in the amount of 39.3 cents / m³. The reference

year is 2010. This is associated with a reduction in carbon dioxide emissions of about 86 t / a

Singe station systems are available where the investment costs are between 40,000 and

50,000 €.


169

Reference

User: http://www.edelstahlwerke-schmees.de/content/index.php

Ladle preheating and insulation - good practice example - OxyFuelBurner

Still occasionally found on such is the preheating and the heating of ladles by the combustion

of charcoal. Also occasionally still be found today is the preheating and heating of ladles

using liquid melt. Both methods of heating and the preheating are among the aspects of

energy efficiency and environmental protection not recommended.

Natural gas-air burners are one way to improve the energy efficiency compared to the

aforementioned casting processes. It should be noted that restrained inert nitrogen, which is

present in the air to about 78% and requires high flow rates at the preheating and the heating

of ladles, must also be heated.

The combustion formula is given by: CH4 + 2 O2 + (8 N2) ---> CO2 + 2 H2O + (8 N2). The

natural gas-air ratio, using natural gas-air burners is about 1:10.

From energetic, environmental and metallurgical aspects, a look at O2 gas burner (oxy-fuel

burner) seems interesting:

ladle temperatures between 1,200 ° and 1,500 °C are, depending on the firing design

and ladle size are reached in 50-60 minutes

Due to high temperatures small temperature differences between of heated ladle and

melt can be realized

Gas-oxygen burners are also suitable for holding of liquid iron in furnaces and ladles


The metallurgical advantage may result from higher temperatures around 1,500 °C.

Natural gas-air burners reach temperatures of 900 -1,000 °C.

Lower heating times compared to natural gas-air burners.

huge reduction of off-gas volume (Oxy-Fuel burner: NPG / oxygen 1 / 2 versus

normal burner: natural gas / air 1 / 10). This is associated with a reduction of

emission

Budget for the use of natural gas-air burners:

http://www.edelstahlwerke-schmees.de/content/index.php


170

Per day (single layer), the heating takes place from 3 ladles with 8 tonnes. Three natural gas-

air burners are used, which also run constantly to keep the ladle warm.

After about 2.5 hours a ladle temperature of about 800°C to 900°C reached.

Demand for natural gas about 45 m³ /h per plant + air consumption (fan) about 450 m³ /h per

plant

Costs for heating a ladle: Natural gas demand is about 45 m³ /h x 2.5 h approximately 112

m³ + air consumption (fan) is approximately 1.120 m3

Scheduled costs for the provision of natural gas: 0.35 € / m³

Scheduled costs for the provision of air: 0.04 € / m³

Total direct costs for natural gas: 0.35 € / m³ x 112 m³ = € 39.20

Total direct costs for air (fan) 0.04 € /m³ x 1120 m3 = 4.48 €

Total cost: 43,68 €.

To this the cost of continuous operation for the preheating of ladles is added. An example

with 125 € is set. After all, in many foundries the ladles are kept under continuous heating.

The ladles can - in case of need -immediately be used.

€ 43.68 € x 3 cups / d = 131 € /d + 125 € /d = 256 /d: Total cost per day

Cost per year: 256 € /d x 22 d /mo = € 5,632 /mo x 12 mo/y = 67,584 €/y

Budget for the use of natural gas-oxygen burners:

Per day, the heating takes place from 3 ladles with 8 tonnes. Used for a gas-oxygen burner.

After about 1.0 hour, a ladle temperature reaches about 1200 °C.

Demand for natural gas about 30 m³ /h per plant + oxygen demand about 60 m³ /h per plant

Costs for heating a ladle: Natural gas demand for about 30 m³ /h x 1.0 h is about 30 m³ +

oxygen yields about 60 m³

Scheduled costs for the provision of natural gas: 0.35 € /m³

Scheduled costs for the provision of oxygen: 0.20 € /m³

Total direct costs for natural gas: 0.35 € /m³ x 30 m³ = 10.50 €

Total direct costs for oxygen: 0.20 € /m³ x 60 m³ = 12.00 €

Total cost: 22.50 €

Total cost per day: 22.50 € = 67.50 € x 3 pans

Cost per year: 67.50 € /d x 22 d /mo = 1.485,00 €/mo x 12 m /y = 17,820 €/a

Reference

User: Mecklenburger Metallguss GmbH, Waren

Supplier: www.ingenieurbuero-weschenbach.de

www.ingenieurbuero-weschenbach.de


171

Ladle preheating and insulation - good practice example - ladle pre heating

Conventional lining of casting or transport ladles are not only to protect the ladle itself. They

are also for insulation against heat loss during filling and transport. The switch to the

KALTEK™ board system was the result by considerations on the lookout for ways to reduce

energy costs in the melting operation.

The lining of ladles are effected by conventional bricks or cement with a thickness of about

100 mm or above. The KALTEK-board system is a cold-start system. This is the reason, why

drying and ladle preheating are omitted. Furthermore, the temperature loss is halved when

loading the pan with a KALTEK board. It can be tapped much less overheated.

Lower tapping temperatures in the furnace operation compared to conventional preheated

ladles, thus saving melting energy. No more need of drying or ladle-heating, therefore,

saving of natural gas.

From the present material change, the actual energy savings result to approximately 168,000

€/y. The KALTEK board system operates only about six to seven times with the same ladle

liner. Therefore, this technical solution is primarily for non-continuous processes. Such single

taps at a high temperature level can be found for example in steel foundries.

Case study: 5 t ladle, 5 tons furnace, 1,500°C tapping temperature If a loss of temperature

reduction by 30°C in a 5 t pan 60 kWh of energy can be saved in the overheating process,

this will corresponds to about 6 € /melt.

The energy cost savings alone do not justify the investment. They are to be measured in

combination with other criteria such as quality advantages.

Reference

Supplier: http://www.foseco.de

4.4.2 Thermal losses on transfer

Next, the heat losses are to be observed in the fore hearth. For reducing the radiation loss is

the most important requirement is that the fore hearth is fore-most closed and the beaming

faces of the liquid metal must be kept small. For the amount of heat losses, the size of the

http://www.foseco.de/


172

fore hearth is decisive. The larger the fore hearth, the larger the radiating masses, and the

greater the heat losses, the greater the required amounts of energy to hold it in balance.

The heat losses from ladles are determined by:

the lining: Depending on the type of refractory material and the thickness of the lining,

the heat transfer and heat storage is different

the type of ladle (ladle drum or cylinder frying ladle, slim or compact form): In drum

ladles is generally the bright iron surface smaller. They have a more favourable

surface / volume ratio, thus the heat losses are lower

the number and size of ladles: By optimizing the iron transport (number of decanting,

waiting times of the ladles), the casting line, the arrangement of fusion and casting

line to another and the daily operating time of the ladles, the number and / or size of

the ladles can be reduced. This reduces heat loss and energy consumption to

preheat the ladles

the temperature of the ladle: convection and radiation losses of the ladle are

dependent on the surface temperature of the ladle

from the cover of the ladle: The use of a lid will only bring success if he is not red hot,

and radiates this heat. The same applies to bath surfaces covered with slag. Because

of the rising of warm air should ladles can be parked down with the opening during

long breaks.

The temperature losses during storage and transportation of liquid iron must firstly be

compensated by preheating of ladles and offset of the tapping temperature. Especially in the

cupola, with its poor efficiency of overheating, the temperature loss should therefore be kept

as low as possible. For more drastic temperature losses, energy losses occur when the

temperature of liquid metal drops below the required casting temperature. In this case, it may

happen that iron must be poured into ingots, or committee created by cold run and the cycle

portion is increased.

4.4.3 Exothermal chemical reactions

The use of exothermal feeders can increase the yield, as the exothermal reaction allows the

metal to be kept warm for longer in the feeder, and this in turn permits smaller modules. The

solidification time can be extended to two to three times the normal time.


173

Even greater metal savings can be achieved using the so-called mini-feeder developed in

1977 by the Rexroth foundry in Lohr/Main together with the former Lüngen company. The

efficiency of the various feeder types is shown in Figure 3989.

Figure 39: Comparison of feeding efficiency of different feeder types

4.5 Pressure die casting

This section addresses factors that are of specific relevance for high-pressure casting, as

these factors also apply to low-pressure casting. The following pages will look at general

energy economy options in areas such as compressed air generation, ventilation systems,

lighting and similar.

The process is similar in both pressure casting methods and consists of:

Melting

Where necessary, finishing, refining and ladle transport to the individual machines

89 Ergül, H.; Fischer, S.; Skerdi, U.: Giessereipraxis 2008, No.3, p. 80


174

Holding in heated furnaces

Pouring and solidification of the metal in the die, involving die heating/cooling

Removal of the casting from the mould, spraying of the mould

Closing of the die

The die has to be preheated before it is inserted in the machine, and this uses up a

considerable amount of energy. The use of porous burners can reduce energy consumption

by around 50%90.

According to studies by Ueli Jordi91 the energy used in pressure casting foundries is divided

more or less equally between gas and electricity. The biggest energy consumer in pressure

casting foundries is melting, and the overall energy breakdown in a foundry of this kind is as

follows:

Gas: around 60–85% is used by the melting and holding processes

Gas: around 15–40% is used by the infrastructure and ancillary processes, such

as the preheating of the die before and during use as well as heating energy

Electricity: 30–50% is used by the primary process chain - the energy needed for

melting and operation of the pressure casting machines complete with ancillary

devices

Electricity: 50-70% is used by the infrastructure and ancillary processes for

lighting, compressed air generation, ventilation systems etc.

In the operation of a pressure casting cell, the machine itself is the biggest consumer of

energy, followed by the heating and cooling devices (approx. 27 %). At KSM Castings92

controllers for phase angle control ensure that the pumps are switched from partial load to

full load extremely rapidly, thereby reducing the volume of electricity needed for pump

operation.

With highly intricate castings, the energy needed to heat the die is reduced by shortening the

cycle time. This is possible due to the use of water-free release agents of the type described

in a report93. As the release agent contains only very little water, the mould no longer needs

to dried with compressed air following spraying - a time-consuming task. Moreover, spraying

does not overly cool the die, which then requires less heating-up.

90 Keim, F.; Encinas, C.: Giesserei 98 (2011), No. 6, p. 182/86

91 Ueli Jordi: Lecture at the symposium „Energy efficiency in foundries“, 11./12. March 2010 in Frankfurt

92 Geisler, S.: Giesserei-Erfahrungsaustausch 2008, No. 7+8, p. 28/31

93 Togawa, K. u. a.: Giesserei 98 (2011), No. 11, p. 26/29


175

The use of heat insulation plates to insulate the pressure casting mould can also save

heating energy94. Less time is needed to heat the pressure casting mould to operating

temperature, and the mould gives off less heat during the operating process - which means

there is less need for heating energy.

In the case of thick-walled castings, it is important to ensure that the casting temperature is

kept as low as possible. This saves energy at the pouring furnace and means that the die

does not need to be cooled to the same extent as would otherwise be necessary. Use of the

aforementioned release agent also has advantages with these castings. The die is hardly

cooled at all by the evaporating water but almost exclusively via the cooling channels in the

die - and this creates the option of using the waste heat through recooling of the coolant.

The number of temperature control devices can also be reduced. At KSM Castings95, it was

established that there are temperature control circuits for pressure casting moulds with

similar temperatures. The circuits were not operated separately but connected in series in a

ring arrangement. Every temperature control device that was not needed generated energy

savings of around 60 MWh a year.

The volume of energy consumption in the various operating statuses also provides some

interesting insights.

Aus den angegebenen Werten sieht man deutlich, dass durch eine verbesserte

Fertigungssteuerung und weniger Unterbrüchen erhebliche Mengen an Energie eingespart

werden kann.

The listed figures clearly show that improved production control and fewer interruptions can

save significant volumes of energy.

At KSM Castings, weekend shutdowns of compressors, cooling towers, extraction systems,

heating devices, cooling systems and lights reduced energy consumption by around 40%

over the two weekend days.

Finally, improved yields resulting from redesign of the gating systems, more precise cooling

of the die and a reduction in the number of defective castings also help to considerably

reduce energy consumption, as between 600 and 1,000 kWh of energy is needed for the

melting and overheating of one tonne of aluminium returns96 97.

94 Malphohl, K.; Hillen, R.: Giesserei 97 (2010), No. 5, p. 74/82

95 Geisler, S.: Giesserei-Erfahrungsaustausch 2008, No. 7+8, p. 28/31

96 Malphohl, K.; Hillen, R.: Giesserei 97 (2010), No. 5, p. 74/82

97 Energy costs in UK non ferrous foundries; Foundry Trade Journal 1994, No. 14, p. 23/25


176

4.6 Heat treatment of the castings

Heat treatment of the castings – good practice example - top hat heat treatment

furnace / seal hearth insulation

Concerning heat treatment furnaces, an important point is to keep the heat inside the

chamber. The less heat transfer through walls and fumes is, the better the energy efficiency

will be. In most of the installations, there is heat loss at the joint (seal) of the openings. Heat

loss for a top hat furnace is often remarked by foundrymen in the area between the

stationary hearth and the movable bell-shaped cover. Wall temperature is higher there than

at the rest of the surface. This joint requires attention and maintenance. Low maintenance

costs are achieved by creating a joint of sand many millimetres high at the junction between

cover and hearth. An alternative is a depth of lining sheets used for the walls.

For example: 1 top hat heat treatment furnace with a consumption of 1800 kW natural gas,

capacity 30 t, new design (2006), two-speeds-burners, and modulating flap on fumes duct for

inlet chamber pressure control, inside temperature 1000°C, increase of walls temperature

near the seal 180-200°C. With an enhanced seal, energy (natural gas) consumption can be

reduced by about 0.3 -0.8%. This value is not well proven but this good house keeping

practice costs nothing and is simple to do. Within the given example invest would be 1200 €

and the possible energetic savings will be round about 13.25 MWh/y, if the furnace produces

10 000 t/y by 333 cycles and consumes 7.5 MWh per cycle. In numbers this will cause a

decrease in energy costs by about 440-640 € per year (based on 1 kWh = 0.0322 € –

Source: Eurostat 2010). The economy of the example is strongly determined by the lifetime

of the seal

Reference

Investigation: CTIF Energy survey on site

Good practice example

Heat treatment of the castings – good practice example - etection of the waste heat

from castings and heat treatment furnaces


177

The detection accruing residual heat is often made to be difficult. The time gap between heat

accumulation (heat source) and heat demand (heat sink) is too large. Moreover, the use of

the most medium temperature heat sources must be limited to technical systems. The

difficulty of using waste heat also refers to the detection of waste heat from castings, which

are positioned to cool off in the hall or on the outside grounds.

For example, a foundry has used the waste heat released by the cooling of heat-treated

castings into the air. The waste heat created by the wall heat losses of the heat treatment

furnace were also employed. This technique can be applied to hot raw castings after shake

out, too. The rising warm air is trapped in a lower open, isolated elevated tank. From there

the air is ducted by a pipe network, from which it is delivered by diffusers for space heating in

the fettling shop.

The heat capacity of this plant is in the range of 4200 MJ/h and allows an annual saving of

about 200 tonnes of fuel oil.

It requires a kind of collecting bell with great volume and air channels with large cross

sections. The heat collecting hood should be pretty close to the heat source. Good insulation

of the system is required.

Assuming that 200 tonnes of fuel oil can be saved, the following sample calculation can be

established:

If the combustion of one litre of fuel oil produces 2.6 kg of CO2 emissions, a CO2-saving

potential of about 520 tonnes of CO2 can be realized.

Assumptions:

Density of fuel oil: 0.85 kg /l

1 kg fuel oil results in 2.6 kg CO2

If one takes into account an oil price of 54.85 € /100 l in the reference year 2010 (sector

average), one can realize in the ideal case a cost saving of 93,000 € by the use of waste

heat.

Reference

Investigation: Technical Report of the IfG gGmbH "Energy Efficient foundry"

4.7 Computer aided optimization of pouring system, feeders and castings


178

Computer aided optimization of pouring system, feeders and castings – good practice

example– energy requirements of different types of feeding systems

Avoiding reject caused by shrinkage the casting process is using insulating feeder for feeding

the castings. The feeder acts here in the simplest case, called natural feeder, as an

additional liquid iron-storage during the solidification of the component.

The feeder is made respectively shaped from the same moulding materials as the whole

mould using insulating or exothermic feeder sleeves.

A central point in the feeder interpretation - in addition to the saturation length - are the

solidification times within the feeder and within the mould. So to ensure a long-lasting supply

the feeder module has to be bigger than the casting module. That means its time of

solidification has to be longer than that of the casting.

An improved variation of the feeder technology compared to the natural feeders are

insulating feeders respectively the next level are exothermic feeders, which are characterized

by their reduced size at the same values for the module. Compared to traditional natural

feeders the spreading is improved by savings on volume of liquid iron.

The saved amount of liquid iron per component respectively mould is directly correlated with

the reduction of used energy in the preparation of the required amount of melt.


Increase spreading due to lower demand for liquid iron, this means lowering the

melting energy costs.

Reduction of energy use in cleaning and transport of casted feeders

Calculation for example:

A natural feeder with a geometric module of 2.00 has in considered construction a volume of

1.35 dm³ = 1,350 cm³. An insulating and exothermic feeder with appropriate module of the

natural feeder on the other hand has a volume of only 300 cm³. The lower volume of 1,050

cm³ corresponds to a volume of ca. 6.5 kg saving of liquid iron. Per feeder one can save

following calculated electricity costs:

6.5 kg * 620 kW/1000kg* 11.1 ct / kW = 44.8 ct. From an economic point of view the savings

in energy have to be compared with the increased costs of exothermal feeders.

Reference

User: www.foseco.de

www.foseco.de


179


example - increase of energy efficiency by increasing the cut out

Energy cost savings can be achieved by an increased cut off. The cut off is the generated

net weight, based on the gross weight in a manufacturing process. The increase of the cut off

may be directly resulting in a reduction of the melting and material costs.

The cut off can be increased, for example, by several measures:

Proper design of the cut out and feeding system

Reducing the variations in the chemical composition

Reduction of metal loss (spray losses)

Constant pouring temperature

The increase of the cut off leads - in addition - to a reduction in metal consumption and for

example to a reduction of additives per tonne of good castings.

If the cut off for example increased from 60% to 70%, the savings in energy costs are (10/70)

* 100 = 14.3%.

To produce one tonne of cast iron (net rough cast) about 600 - 700 kWh (statistical average)

of electricity for electrically operated furnaces are necessary. Alternatively about 100 kg of

coke for the cupola is necessary. For example the demand for electrical energy to produce

one tonne of good castings is reduced from 700 kWh to about 600 kWh. If the energy carrier

coke is used as the provision of electric energy then this is equivalent to a reduction in CO2

emissions by about 100 kg /t. A production of 10.000 tonnes good cast iron per year results

in a reduction in CO2 emissions by about 1,000 t *).

*) EU standard factor for the electric induction melting: 466 t CO2/y

Reference

Supplier: http://www.magmasoft.de/ms/home_en/index.php


example - bionic - learning from nature

http://www.magmasoft.de/ms/home_en/index.php


180

Cast components are partially exposed to high mechanical loads. Therefore, mechanical

requirements and minimal use of materials must be well coordinated in the construction.

Oversized components require without apparent purpose higher energy input in the casting

and subsequent processing.

The structure bionic allows it to determine component-oriented power flow geometry

proposals in the design and construction phase. The aim is to avoid failure critical stress

peaks with the minimum use of materials at the same time, which are based on strategies

such as those found in the tree or bone growth. The subsequent technical implementation of

the design process takes into account, that further impulses are coming from the simulation

and ensuring a practical topology optimization. This approach is used by default in this

foundry in development projects. This allows a high degree of material and energy efficiency.

Weight reduction in the long version of 13.5 tonnes to 9.0 tonnes (weight reduction of 33%)

Under an assumption of a 13.5 ton component, one can perform the following sample

calculation:

Assuming an energy consumption of 600 kWh per tonne of liquid iron in the ideal case, this

will correspond to a required power of 8,100 kW. Under the assumption of 33% weight,

reduction by bionic aspects results in an improvement of power supply costs, CO2 emissions,

as well as production costs. Reducing of the required power to 2,673 kWh per component

Reduction in CO2 emissions by 1,243 kg per component under the assumption that one kWh

causes 0.466 kilogram of CO2 .

Reduction of manufacturing costs by about 350 € per component, in the assumption of power

purchase costs height of 13.1 ct/kWh (pure melting current) without taxes.

The electricity costs are in the 2-shift operation, on average, at 12.4 ct/kWh and a 3-shift

operation at 11.1 cents/kWh. Reference year 2010.

Reference

User: www.huhag.de

www.huhag.de


181

5. Emerging techniques for efficient energy use in foundries

5.1 Latent-heat storage

A heat storage tank is a energy storage. The latent heat storage system gives us the

opportunity to save residual heat and transfer the heat back to any kind of energy later. The

storage of heat is strongly influenced by the so-called latent heat. Latent heat is known as

the heat absorbed or released during the phase transition. Figure 40 shows the principles of

latent heat storage in relation to water as storage medium.

* PCM = Phase Change Material (see table7).

Figure 40: Latent and sensible heat

The difficulty of finding an ideal storage medium, is to find a material which is able to do

phase transition frequently and invertible, and that over a long period (e.g. 15 years). Table 7

shows materials which have an interesting temperature range for foundries and do fulfil the

given criteria.


182

Table 7: Heat storage material and their melting temperatrures

Element group Material Melting temperature [°C]

Paraffine Paraffin sludge 34

Paraffin-mixtures 50 - 90

Salt hydrate and there mixtures Sodiumacetat-Trihydrate 58

Glauber salt 32

Bariumhydroxide 78

Magnesium hexahydrate 117

Sugaralcohols In development 90 - 180

By using salts and there eutectic mixtures it is theoretically possible to realise storage

temperatures of round about 200°C

Figure 41: Summary of different materials and there potential for latent heat storage

Advantages of latent heat storage to conventional heat storage systems:

Higher storage density with less temperature difference

Less volume for the same heat capacity

Heat transfer on a relative constant temperature level

minor heat losses (~1% per day)


183

Possible applications for the future is to work as a cache between times where heat is

produced and times where heat is needed.

5.2 Electricity generation

Usually the waste heat of the discharged air is not used to produce electricity, except in the

cupola process. The reason for this is that conservative water steam turbines do not work

economically at temperatures under 500°C. It would be nice to use this heat to produce

electricity. To realise this the ORC-Technology works at temperatures from 240-500°C with

an organic medium. Organic mediums could be used useful on turbines or on steam-cock-

machines.

In addition to the ORC-process , another process called Kalina-process is known to store

energy. The main difference is that in the Kalina-process the used medium is used water-

ammonia-mixture. This variant of the ORC-process covers temperatures of about 130°C.

5.2.1 Operating method of ORC-Turbines

With ORC-plants it is possible to produce electricity at lower temperatures and lower

pressures as known in common power plants. The main reason for this is the used mediums,

as like ammonia, butane and pentane instead of steam. Common power plants do not work

effective in an operation area of 1MW, and for such a plant the invest is very high.

In ORC-plants a thermo-oil is heated up first, which transfers the energy in the recuperator to

an organic medium which has an apparent lower boiling point than water.

After that the energy is transferred by the secondary circle and so the ORC-turbine can

produce electricity.


184

Figure 42: Schema of an ORC-Steam-Turbine-Process


Electricity generation II – Waste heat ORC – steam turbine

Foundries produce large amounts of heat their utilisation is often not possible. The reason for

this is often the lack of agreement between heat gains (heat source) and heat demand (heat

sink).

To increase energy efficiency, there is the possibility of using the waste heat to generate

electricity. For power generation from waste heat, the Organic Rankine Cycle technology can

be used. The Organic Rankine Cycle technology uses an organic working medium. Electricity

generation can thus be done with lower temperatures than is possible through the use of

water as a medium.


Reduction of CO2 emissions

Self-sufficient with electricity from waste heat or feeding electricity into the public

electricity grid


185

As part of a performance audit in a foundry, the possibility of using an ORC system has been

studied. The investment costs for the ORC system amounted to approximately 1 Million €.

Apart from the actual ORC module costs, cost for the replacement and the cost of connecting

to the plant as well as their commissioning are usually added.

From the aforementioned feasibility study, however, the following information can be

recorded for orientation, referring to an ORC system, which has been optimized

economically. The amortization period was calculated at about 7 - 8 years

Pre-requisites:

Temperatures in the thermal oil system above 250 °C.

Greater than 6,000 operating hours/y, 3-shift operation

Based on the following engine performance as part of the feasibility study: 2,730

MW

Reference

Supplier: Maxxtec AG - Germany

5.2.2 Operating method of ORC- Gas-Piston-Machine

Even today industry can make use of ORC-steam expansion motors, which work on coke

basis. These plants can be operated economically in regions of 100-200kW.

The ORC-steam expansion motor is based upon circle process. Within this process it is

possible to use heat sources with a temperature of 200-500°C for electric generation. Figure

43 shows the mentioned circle process.


186

Figure 43: Cycle process of the ORC-Technology98


Electricity generation I - Electricity generation from waste heat - ORC steam engine

Large amounts of free waste heat arising process related in foundries. As a result of

temporal or spatial separation of supply and demand, respectively heat source and heat sink,

the technical use is often difficult. In addition, the use of the most in the medium temperature

range lying heat sources are limited to technical systems, which operate in this area with

reasonable good efficiency.

For the utilization of waste heat to generate electricity at moderate temperatures, there is the

Organic Rankine Cycle (ORC) technology as a method. This technique generates electricity

with lower input temperatures than it is required using water as the working medium. In the

present application, a foundry ORC system with a gas piston engine is used. The required

temperatures (around 240 °C) are provided by the hot blast cupola furnace. Planned in a

second phase of energy recovery is the connection of the aluminium melting furnaces as an

additional heat source to the ORC process.

98 DeVeTec GmbH, http://www.devetec.de/index.php/energiegewinnung-abwaerme/orc-technologie


187


Saving of natural gas to generate heat energy

Reduction of CO2 emissions by 8,280 tonnes annually

References:

User: http://www.frankenguss.de/

5.3 Cooling

Cold produced can be used for example for purposes of building cooling. It may be that the

cold can also be used for cooling of the castings. To provide cooling can now be used on two

technologies. It is the absorption chillers and adsorption chillers.

5.3.1 Absorption-Cooling-Machines

Absorption chillers are thermally driven chillers. The heat can by a district heating network, a

cogeneration plant or be provided by a waste heat source. As an example, waste heat

source hot air from the melting process can be used. The temperatures should be between

about 85 and 95°C. The cold produced can be used for example for purposes of the sand

cooling. The cooling capacity of absorption chillers of suppliers in Germany and Austria is

between 15 kW and 2,300 kW. The COP (Coefficient of performance = the ratio of recovered

refrigerant supplied heat for this) is about 0.7 for single-stage systems99.

99 E-Bridge Consuting GmbH, Studie über KWK-Potentiale in Österreich (Endbericht), November 2005, p. 26

http://www.frankenguss.de/


188

Figure 44: Schema of an absorption cooling machine

5.3.2 Adsorption-Cooling-Machines

An adsorption chiller is a thermally driven chiller. The adsorption chiller consists of two

working chambers filled with sorbent and a condenser and an evaporator. Silica gel is usually

used as a sorbent and water as a refrigerant.


189

Figure 45: Schema of an adsorption cooling machine

There are running simultaneously from two processes. First, the evaporation of the

refrigerant and the resulting refrigerant vapor adsorption by the adsorbent. On the other, the

desorption of the adsorbent and subsequently bound refrigerant condensing the resulting

steam.

As can be switched cyclically between two adsorbent beds may be, with only a quasi-

continuous adsorption refrigeration process can be realized. Water-silica gel adsorbent can

use driving temperatures of 60°C.

The COP (Coefficient of performance = the ratio of recovered refrigerant supplied to this

heat) is about 0.4. The maximum cooling of the hot water is 13 K, at low temperatures,

however, only 5 – 6°K100.The cooling capacity of adsorption is approximately between 50 kW

and 500 kW101.

5.4. Heat transfer to the mould and heat recovery from the molding sand

5.4.1 Heat recovery from moulding sand

In the literature on this point is very shallow. Therefore, some theoretical considerations for

the casting of cast iron foundry in a series of enclosed and aspirated pouring, cooling section,

100 BHKW-Infozentrum GbR, http://www.kwkk.de/kwkk-technologien/adso.html 101 E-Bridge Consuting GmbH, Studie über KWK-Potentiale in Österreich (Endbericht), November 2005, p. 27, http://www.code-

project.eu/wp-content/uploads/2009/05/AT-Report-Art-6-Potential-German-English-Summary.pdf

http://www.kwkk.de/kwkk-technologien/adso.html

http://www.code-project.eu/wp-content/uploads/2009/05/AT-Report-Art-6-Potential-German-English-Summary.pdf



190

and foundry sand preparation. After casting the iron gives up its heat to the surroundings.

Sand in foundries primarily on the shape and sand in small part to the ambient air.

Of course there also from the sand mold during the cooling part of the heat to the ambient air.

Assuming that the castings are poured with approximately 1,400°C and evacuated at about

400°C, then give the castings about 280 kWh / t to the environment and the sand.

Can we use this heat content of 50% (= 140 kWh / t), then in the winter months, when

available, for example, 5,000 t casted iron, 700,000 kWh. For the appropriate amount of heat

required to approximately 71,000 l of fuel. This corresponds to about 60,000, - €.

Comparing the amount of 700,000 kWh of heat with the amount of heat produced during the

smelting of iron in the cold blast cupola, one comes to the following result. Cold blast

furnace: coke rate: 12.2%; waste heat (latent and sensible): 495 kWh / t, approximately 80%

of usable heat.

Result: usable heat: 5,000t x 495 kWh / x 0.8 ≈ 2,000,000 kWh.

Unfortunate is that the exhaust from pouring and cooling line, and the sand plant is highly

polluted and the sand is cooled by evaporation of water very often. Also, the temperature

level in both areas is not very high so that a direct use of waste heat difficult to achieve.

Therefore appears as the best way to heat after the filters through the regenerators factory

building fresh air transfer.

5.4.2 Heat recovery from dismantled casting

Cast and sand are separated in a shakeout tube, cools the water-wetted sand from the

casting on. This heat is then found in the sand. The residual heat in the castings may be

small and unprofitable for heat utilization.

However, be separated in a sand-cast and shakeout, where part of the heat is released. An

advantage is that the heat is concentrated at this point is generated and can therefore be

used with heat exchangers. The disadvantage is that the air is dusty and the strong heat is

relatively low.

The same applies to the further cooling of the casting out of the box. Except that here the

heat is not concentrated incurred. Example calculation (assumptions as above): Dismantle

temperature: 400°C, the temperature behind shakeout: 300°C. Incidental heat in the winter

months: 5,000 t x 500 kJ / (TXK) x 100 ° K: 3,600 kWh / kJ ≈ 70,000 kWh.

With a recovery of 50% is the 35,000 kWh or about 3,500 liters of heating oil. The unpacked

cast iron shall be cooled in a cooling tunnel or cast cool conveyor of 300 ° C to 50 ° C


191

(assumptions as above): Incidental heat in the winter months: 5,000t x 500kJ / (TXK) x

250°K: 3,600 kWh / kJ ≈ 170,000 kWh. With a recovery of 50% is the 85,000 kWh, or about

8,500 liters of heating oil. Due to the relatively low temperature level heat to the hall can only

be used for heating or water heating.


192

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