EPSRC thermal management of industrial processes · exhaust gas temperature of reheat furnaces can...

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Newcastle University

EPSRC: Thermal Management of Industrial Processes

National sources of low grade heat available from the process industry

Progress Report

(Feb. 2011)

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List of Abbreviations

AEA: Energy and Environment

BERR: Department for Business Enterprise and Regulatory Reform (previously Department

for Trade and Industry)

BF: Blast Furnace

BFG: Blast Furnace Gas

BOF: Basic Oxygen Furnace

EA PAS: Environment Agencies Public registers

EAF: Electric Arc Furnace

NAP: National Allocation Plan

NEPIC: North East of England Process Industry Cluster

UNEP: United Nations Environment Programme

Unit

PJ: Peta Joule (=1015

J)

TWh: Tera Watt-hour (=1012

Wh)

Mt/yr: Million tons per year

List of figures

Figure 1: Schematic of a heat exchanger................................................................................ 7

Figure 2: Heat Transfer Efficiency versus Source Temperature .............................................. 8

Figure 3: Map of industrial heat [3] ....................................................................................... 9

Figure 4: Industrial heat load by industrial sector [3] ........................................................... 10

Figure 5: Schematic representation of a steel production plant ............................................. 14

List of tables

Table 1: Waste heat sources in major industrial processes (cf. Table 11.7 of [7]) .................... 6

Table 2: Steel capacity ......................................................................................................... 14 Table 3: Specific energy consumption and energy consumption splits within Steel industry

processes ............................................................................................................................. 14 Table 4: gas composition in Steel processes ......................................................................... 15

Table 5: Characterization and classification of potentially recoverable low grade heat gas

streams in the steel industry................................................................................................. 25

Table 6: Characterization and classification of potentially recoverable low grade heat cooling

water streams in the steel industry ....................................................................................... 25

Table 7: Gas waste heat sources and potential for recovery .................................................. 26 Table 8: Cooling water waste heat sources and potential for recovery .................................. 27

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Contents Research context ................................................................................................................... 4

Introduction .......................................................................................................................... 5

1. Developing an Industrial heat load map .......................................................................... 8

2. Potential test case studies ............................................................................................. 10

3. Waste heat survey guidelines ........................................................................................ 11

4. Case Study: Steel production process ........................................................................... 12

4.1. Coke production process ........................................................................................... 16

4.2. Sinter process ........................................................................................................... 17

4.3. Blast Furnace (BF) process ....................................................................................... 18

4.4. Basic Oxygen Steelmaking (BOS) process................................................................ 19

4.5. Continuous casting process ....................................................................................... 20

4.6. Hot mill process ....................................................................................................... 21

4.7. Cold mill process ...................................................................................................... 22

4.8. Annealing process .................................................................................................... 23

4.9. Power plant .............................................................................................................. 24

4.10. Low grade heat classification-Summary for Steel production process case study ... 26

4.10.1. Gas .................................................................................................................... 26

4.10.2. Cooling water .................................................................................................... 26

4.11. Potential uses ........................................................................................................ 26

4.11.1. Gas ....................................................................................................................... 26

4.11.2. Cooling water ....................................................................................................... 27

4.12. Concluding remarks .............................................................................................. 27

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Research context

This report presents the progress achieved in the first six months of work of the EPSRC:

Thermal Management of Industrial Processes project.

The first stage of Newcastle University’s part of this project is to identify the sources of low

grade heat available from the process industry across the UK. Once identified, as many of

these sources as possible will be quantified and characterized.

The objectives of this report are to:

- Identify and characterize opportunities for low grade heat recovery in the UK process

industry.

- Present the first test case study which is that of a steelworks

- Classify waste heat sources in the Steel Industry

The main available sources of information which have been used so far are:

1. UNEP

2. AEA

3. EA PAS database (http://www2.environment-agency.gov.uk/epr/)

4. NAP allocation database

5. NEPIC

6. Trade organisations

7. Steel Industry partner

https://owa.ncl.ac.uk/OWA/redir.aspx?C=9aa965a6fc93488e93a62fe354cc3cbd&URL=http%3a%2f%2fwww2.environment-agency.gov.uk%2fepr%2f

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Introduction

Waste heat refers to the heat absorbed by the environment. According to the Energy

Management Handbook [1],“Waste heat is that energy which is rejected from a process at a

temperature high enough above the ambient temperature to permit the economic recovery of

some fraction of that energy for useful purposes”. Heat recovery is a generic term used for a

large range of procedures involved with reusing heat otherwise wasted in the environment.

The importance of low-grade heat recovery projects has inevitably increased over the last

couple of years with the current concern for environmental issues and the associated political

policy requiring carbon dioxide emission reduction, as well as general concerns about fuel

security. The Climate Change Act 2008 [2] sets reduction targets, based on 1990 levels, of a

reduction of 80% by 2050 and an interim target of at least 34% by 2020. Given that the

industrial sector represents 40% of the overall CO2 emissions in the UK [3], pressure has

been put on it. For instance, the Climate Change Levy (CCL) [4], a levy on energy use was

applied to industry with a dispensation of 80% available to certain energy-intensive industries

in the form of Climate Change Agreements (CCAs) in return for undertaking energy saving

measures towards predefined goals. The Government have announced that this will be

reduced to 65% by April 2011 [5] thus raising energy costs further. Therefore, the new

priorities in industry’s agenda have become to invest more and more in sustainable

technology.

Although a lot has already been done in the past to use energy more efficiently, the industrial

potential for waste heat recovery still represents a thermal energy market potential of some

144 PJ currently lost from industrial processes [6].

This project is particularly interested in low grade heat. The widely accepted definition of this

is, typically, ~250°C or less [7].

However, as shown in Table 1, this can vary over the process industries. For example the

exhaust gas temperature of reheat furnaces can reach up to 600°C in the Steel industry, and in

the Chemical and Oil industries processes can reject warm gas into the environment with

temperatures up to 340°C.

Therefore, the temperature range to consider for the identification of low grade heat sources

will depend on the process industry considered for the analysis.

The main problem in most potential heat recovery applications is how to make effective use

of any recovered heat. There are usually technical solutions to the actual process and the

decision is not normally “can it be done?” but “is it worth it?” A key factor in this decision is

the quality of the available heat. The temperature of the heat source is the overriding limiting

factor since, clearly, it must be higher than the required sink temperature. However, the

concept of exergy, which is more normally concerned with the efficiency of heat engines, is

also useful in the comparison of different heat sources. Exergy is the maximum quantity of

technical work one can get from a given low grade heat source.

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Table 1: Waste heat sources in major industrial processes (cf. Table 11.7 of [7])

Industry

Plant source

Heat content

(GJ/annum)

Temperature

(°C)

Nature

Steel Coke oven stack gas 3.88E+06 190 Gas

Steel Sinter from sinter plant 5.52E+06 250 Radiant heat

Steel Blast furnace stoves 5.50E+06 250 Pressure Energy Gas

Steel Blast furnace stoves 3.75E+06 300 Pressure Energy Gas

Steel

Finishing soaking pit

reheat furnaces 1.49E+07 200-600/300-400 gas

Steel

Cooling water from

reheating furnaces 1.72E+07 20-40 Water

Glass Container glass melting 2.02E+06 160-200 Gas

Glass Container glass melting 2.02E+06 140-160 Gas

Glass Flat glass melting 1.27E+06 160-200 Gas

Glass Fibre glass melting 140-160 Gas

Glass Domestic glass melting 1.80E+06 Gas

Glass Other glass melting Gas

Oil Processing furnaces exhaust 6.56E+07 340 Gas

Oil Boiler exhaust 1.94E+07 230 Gas

Oil Condensate 4.80E+06 82 Water

Oil Process water 2.92E+07 50 Water

Oil Condenser cooling water 7.30E+06 45 Water

Chemical Processing furnace exhaust 2.10E+07 340 Gas

Chemical Boiler exhaust 2.30E+07 230 Gas

Chemical Condensate 4.00E+06 82 Water

Chemical Process water 1.00E+07 50 Water

Chemical Condenser cooling water 2.10E+07 45 Water

Electricity Flue gases 1.80E+08 130 Gas

Electricity Cooling water 1.00E+09 25 Water

For any given state defined by the temperature T and the entropy S, with respect to the

ambient standard state , , the specific exergy is defined as, for a continuous flow [8]:

[1],

where h is the enthalpy.

For a fluid stream, the exergy may be written as [8]:

[2],

where is the fluid specific heat capacity in J/(kg.K) and is the fluid stream mass flow

rate in kg/s.

The efficiency of a system producing work from a supply of heat is normally considered in

terms of the first law of thermodynamics which considers that the energy within a process is

conserved. The efficiency is often defined according to the first law in terms of the net

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work output and the energy input. However, this analysis provides no indication of how the

efficiency compares to the maximum efficiency possible, which is not 100%. This is due to

the second law of thermodynamics (which, as was stated by Lord Kelvin, says that it is

impossible to convert heat completely into work). This current study takes this into account

by using the concept of exergy. More precisely, according to Equation (1), exergy accounts

for the irreversibility of the process due to the increase in entropy. Consequences of the

second law of thermodynamics create therefore fundamental constraints on the efficiency of a

heat engine related to the operating temperatures.

In the context of low grade heat recovery, exergy refers to the maximum amount of work

which can be delivered from a system operating between “high” source temperature and

ambient temperature. It is clearly a measure of the quality of the heat source and, hence, its

usefulness in the consideration of heat recovery applications. Heat recovery necessarily

involves heat transfer and this results in a loss of exergy, i.e. the exergy of the recovered

stream is less than that of the source stream. In other words, the efficiency of the transfer is

temperature dependent and according to Equation (2), exergy is always destroyed when the

process involves a temperature gradient. The exergy efficiency needs to be considered instead

of the energy efficiency. The importance of the exergy efficiency was clearly underlined by

Winter [9] for the design of future industrial processes constrained by energy savings and

CO2 footprint reductions.

In order to define the exergy efficiency of the heat transfer between the source and the

environment, the heat transfer is approximated as a counter flow heat exchanger (cf. Figure

1).

From this approximation, the exergy efficiency, η between the heat source and the

environment can be defined as follows:

η = ΔExc / ΔExh [3],

In effect, the efficiency given by Equation (3) is the actual increase in the exergy of the cold

stream ΔExc compared to the maximum possible exergy available for transfer given by the

difference ΔExh.

Figure 1: Schematic of a heat exchanger

As an example of the effect of temperature on the exergy efficiency, consider a counter-flow

heat exchanger with a 10°C approach temperature, the approach temperature being the

minimum temperature difference between the hot fluid and the cold fluid. Th represents the

temperature of the source stream with

while Tc represents the temperature of the

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environment sink with

.

Hot and cold streams are supposed to have same heat capacity. Here, T0 = 5°C and = 20°C.

Figure 2: Heat Transfer Efficiency versus Source Temperature

Figure 2 shows the efficiency variation with the hot fluid source temperature, . The heat

transfer efficiency from heat to power decreases as the temperature goes down.

Thus, a high source temperature provides greater choice of applications but also a more

efficient transfer process.

The temperature of the source is of primary importance but the actual energy conversion

depends on many other factors. In fact, the usefulness of the source will also depend on the

quantity, the reliability of supply, the form (gas or liquid, corrosive/non-corrosive) and the

ease of access. Ultimately, a source is not useful unless potential users are found. Users must

be located within a certain distance of the plant, this distance depends on the distance the heat

can be economically transported.

Heat is usually transported via water or steam. According to the report by Terra Infirma [10] ,

steam with temperature in the range of 120-250°C can be transported over ~3 to 5 km while

water with temperature in the range of 90-175°C can be transported over 30 km. Other

sources cited in that same report mentioned that 9 miles (~15km) is the economic limit for

low-grade heat.

In fact, how far heat can be transported depends on several factors. If heat is assumed to be

transported via a pipe, the heat loss factor which is the ratio between heat loss and the

quantity of heat supplied by the source, depends on the efficiency of pipe insulation but also

on the average size of the pipe and the temperature of the fluid circulating in the pipe relative

to the annual average of the outdoor temperature. The profitability of the heat recovery

project also depends on the cost invested in heat transportation, the total cost being the sum

of the cost for pipeline installation, for heat losses and for pumping power [11].

Hence, heat transport is case specific and further research will include the definition of a

methodology for determining the distance threshold above which no potential users can be

found for economic heat recovery solution.

1. Developing an Industrial heat load map

In July 2006, the market potential for surplus heat from industrial processes in the UK was

6065707580859095

100

35 50 70 90 110 130 150 170 190

Exe

rgy

Effi

cie

ncy

(%

)

Hot Fluid source temperature (°C)

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estimated at 144PJ (40TWh) by the Carbon Trust [6] and more recently at, 65 PJ (18 TWh)

by the Government’s Office of Climate Change [12] and 36-71 PJ (10-20 TWh) in a report by

McKenna [3].

These figures reflect a great potential which remains unexploited until now.

It should be noted that obtaining exact national data on waste heat is difficult, so most of

those investigations extrapolated from industrial CO2 emissions, probably due to the relative

ease of obtaining emissions data. This goes some way towards explaining the large variations

between the figures given above.

Figure 3: Map of industrial heat [3]

McKenna [3] developed a procedure to determine the quantity of thermal energy released into

the environment, based on CO2 emission and energy consumed by industries. Emission

factors which give the average emission rate of Carbon released per unit of energy produced

were taken from [13]and energy consumption split by industrial sector was taken from [14].

The emission factors and energy consumption split by industrial sector were then used to

calculate the fuel consumption from combustion. The latter was then used to determine the

heat load for this fuel consumption and the conversion efficiency from fuel to heat estimated

from Carnot cycle efficiency. The actual heat load was weighed against heat recovery factor

for each sector. The recoverable part of the heat load was assumed to be half of the heat

exhaust fraction. In this analysis, temporal variation in heat load was neglected. The head

loads were assumed to be constant over the year.

The results of this investigation are presented in Figure 3. The distribution of industrial heat

loads is represented by the empty circles while the potential for heat recovery is represented

by the solid circles. It is clear from this map that the high temperature recovery potential

concentrates into 3 main centres corresponding to iron and steel plants. This map [3] has

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already been overtaken by an economic downturn in the industry, resulting in the mothballing

of part of one of the sites. As part of this project, information presentation will be

investigated so large singular sites do not obscure smaller more diffuse, although still

valuable, recovery opportunities.

The energy use for heat is plotted for different types of industry in Figure 4. Low recovery

represents the heat recovery potential of source temperature in the range 100-500°C and high

recovery the heat recovery potential of source temperature higher than 500°C. This

investigation does not include the potential for temperature lower than 100°C. While the heat

recovery potential was underestimated, Figure 4 can be used to determine the sectors with

highest heat loads.

Figure 4: Industrial heat load by industrial sector [3]

The largest heat user is the Iron and Steel sector with a heat load around 213 PJ followed by

the chemical sector with 167 PJ. The Food and Drink, Pulp and Paper, Cement, Glass,

Aluminium and Ceramics sectors are also significant heat users.

With regards to Figure 4, test case studies will consider most of these industrial sectors. Other

important key sectors in the UK process industry are Pharmaceutical and Biotechnology and

Oil/Biofuel as illustrated by the large number of companies in this sector which are members

of the North East of England Process Industry Cluster (NEPIC, website:

http://www.nepic.co.uk/).

2. Potential test case studies

Following the identification of the sectors with the largest heat demand, companies who are

influential in these sectors will be approached to provide case study material. These are the

sectors being considered:

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- Iron and Steel

- Chemical/ Petrochemical

- Food and Drink

- Pulp and Paper

- Cement

- Pharmaceutical and Biotechnology

- Oil and Biofuel

Given the importance of Small and Medium-sized Enterprise (SME) in the UK economy and

given the large number of SME working in different industrial sectors, one of the test case

studies can be based on the selection of a cluster of companies in the Northeast ( in

collaboration with NEPIC) within which both heat sources and potential users would be

identified. This case study would demonstrate industrial ecology for heat transfer, allowing

the investigation of the potential for synergistic relationships across sectors.

3. Waste heat survey guidelines

It is important to define a methodology while processing industrial partner data for

identifying waste heat.

First, all the thermal energy streams containing sensible and/ or latent heat that flow from the

plant into the environment are identified.

For each thermal energy stream, the following information is given:

Waste heat source composition

Gas moisture content

Flow rate

Temperature

Ease of access for utilisation

Heat content or specific enthalpy

Reliability of supply

Secondly, the accuracy of the collected data will be established by determining the total heat

balance of the system under investigation. This will be verified by double checking with the

industrial partner.

There are a large number of types of plant and equipment from which waste heat is available.

The following three basic heat sources can be identified:

- Gases and vapour

- Liquids

- Solids (the least common category)

Potential for waste heat recovery exists in items common to many sites in the process

industries such as [1]:

- Air compressors

- Boilers

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- Prime movers

- Refrigeration plants

- Distillation plants

- Dryers

- Dyeing and finishing plants

- Evaporators

- Furnaces

- Gas turbines

- Kilns

- Ovens

- Pasteurisers

- Process coolers

- Process heaters

- Spinning and weaving equipment

- Sterilisation equipment

- Ventilation equipment

- Washers

The standard gas volume reference conditions used in this study will be those of ISO 13443

which defines a temperature of 15ºC and a pressure of 101325 kPa.

4. Case Study: Steel production process

The steel production consists of 3 main steps:

- Iron making

- Steel making

- Steel casting and rolling

Figure 5 shows a schematic diagram of the steel production process.

Steel production in the UK is concentrated in the Blast Furnace (BF) / Basic Oxygen Furnace

(BOF) route (for primary steel) and the Electric Arc Furnace route (for secondary steel).

4.1. Primary steel production process

Data from a thermal energy audit in a steelworks has been provided by Corus. Data is

averaged over the year. The steelworks produces nearly 5 million tons of steel slabs per

annum. The steel capacity of the plant is given in Table 2 at different stages of the production

process.

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Coal

Coke oven

Blast furnace

Molten Iron

Coke

CO gas

Basic oxygen furnace

Iron Ore

Sinter

Powder

BF gas

Power plant

Low carbon steel

Continuous casting (Concast)

Slab

Coil

Hot mill

Cold mill

Annealing processing line

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Figure 5: Schematic representation of a steel production plant

Table 2: Steel capacity

Total BF

capacity

(Mt/yr)

Total sinter

capacity

(Mt/yr)

Total coke

capacity

(Mt/yr)

Total liquid

steel capacity

(Mt/yr)

Capacity

as cast

(Mt/yr)

4.3 4.7 0.9 4.9 4.7

Table 3: Specific energy consumption and energy consumption splits within Steel industry processes

Operation SEC

(GJ/t)

COG/BFG/

natural gas Solid fuel Electricity Steam Other

Coke ovens 2.95 0.93 0.02 0.05

Sinter strands 1.64 0.08 0.85 0.07

Blast furnace 14.7 0.75 0.01 0.24

Basic oxygen

furnace 1.44 0.19 0.39 0.42

Continuous

casting 0.31 1.00

Slab mill 2.87 0.36

0.64

Hot rolling 2.43 0.35 0.65

Cold rolling 1.69 0.56 0.44

Pickling 1.27 0.67 0.33

Electric Arc

furnace 2.50 0.75 0.25

McKenna [3] produced an approximation of the Specific Energy Consumption (SEC) and

energy consumption splits by process for a steelworks (cf. Table 3). The information

contained in Table 3 can be used in order to determine the total heat balance for each process

of the steelworks under investigation once waste heat sources are identified.

The Steel production plant is composed of the following individual processes:

- Coke oven

- Sinter

- Blast Furnace (BF)

- Basic Oxygen Furnace (BOF)

- Continuous casting

- Hot mill

- Cold mill

- Annealing processing line

- Power plant

Steel production is a continuous process and therefore the waste heat sources are highly

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consistent over time.

Table 4: gas composition in Steel processes

GAS BLEND H2 O2 N2 CO2 NO2 CO SO2 CH4 H2O

Coke Oven Gas 0.61 0.002 0.03 0.017 0 0.07 0 0.245 0

Blast Furnace Gas 0.035 0 0.465 0.25 0 0.25 0 0 0

BOS gas 0.02 0 0.13 0.15 0 0.7 0 0 0

Sinter Gas 0 0.1667 0.7562 0.0415 0 0 0 0 0.0345

Fume 0 0.21 0.79 0 0 0 0 0 0

Coke oven flue gas 1 0 0.068 0.725 0.052 0 0 0 0 0.0156

Blast Furnace flue gas 1 0 0.079 0.705 0.202 0 0 0 0 0.014

Ammonia incinerator gas 2 0 0.18 0.68 0.01 0.0049 0.00589 0.0665 0 0.0526

Underfiring gas

at the coke oven 3 0 0.0735 0.715 0.127 0 0 0 0 0.085

Data provided by Corus for this study has been drawn together from various sources.

Information on gases came from the environmental department of the participating site.

Information on cooling water was obtained from cooling tower manufacturers.

Various types of information were collated from the plant’s control rooms and from contacts

on site.

Data error margin is reported to be ±10%. Data are averaged over approximately a year.

Steam waste heat has not been quantified by the thermal energy audit used for this study but

according to Corus, the steam energy waste from the 11 bar system is estimated at 0.83 PJ/yr,

which is equivalent to ~ £5millions of natural gas utilisation. Cardiff University is in the

process of assessing the steam thermal energy losses and redesigning the steam distribution

system.

A description of each process is given in the following sections. For each process, the

low-grade heat sources are identified in orange. Intermediate heat streams are given in red

while incoming gas streams are given in blue and incoming products are given in green.

Each stream is characterised by the temperature, the mass flow rate and the specific enthalpy

calculated at a temperature of 15ºC and a pressure of 101325 kPa.

For gas heat source analysis, composition is also necessary. Gas molar fractions and molar

masses are given in Table 4.

The same properties are unknown for the input streams but would be necessary for a full

energy balance check as recommended in Section 3.

1 The composition was determined for 8% oxygen combustion 2 The ammonia stream is combusted at ~1000°C. It was assumed that at such high temperature only NO2 was

formed. The waste gas was then diluted with air to reach 210°C temperature. 3 The composition of underfiring coke oven is derived from the mixture of 50% coke oven flue gas and 50%

blast furnace flue gas.

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4.1.1. Coke production process

Coke ovens produce coke from coal for use in the Blast Furnace as a reducing agent and fuel.

Within the oven coal is heated for several hours or days to produce coke through pyrolysis.

The main sources available for thermal energy recovery (cf. orange stream) are gas

underfiring at maximum temperature of 220°C and cooling water at 40°C. Most of the gas

from the coke oven is reused in the plant and therefore is not available for recovery.

Gas underfiring

Heat not quantified

(No data available)

Heat available: 46 MW

Air

Coal

Coke oven

Cooling + Chemical recovery


Heat available: 0.9 MW

Cooling water

Raw gas

Lean gas

NH3

combustion

gas



NH3 gas prior

to dilution


External Quench of hot coke

Coke for quenching

Steam

Quenched coke

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4.1.2. Sinter process

Sinter plants produce the fine powder of iron ore for injection into the BF.

Sinter gas at a maximum temperature of 180°C and cooling water at 50°C are the main

streams available for recovery.

Air

Iron ore

Mixing

Furnace

Breaker bar + Cooler Sinter bed

Fan

Powder to BF

; ;






Cooling water

End of sinter gas

De-dust gas

Combustion gas

EPS

Stack 1

Stack 2

End of sinter

strand

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4.1.3. Blast Furnace (BF) process

The blast furnace is the vessel within which iron ore is reduced by coke at high temperatures

to yield pig iron. The main sources available for recovery are cooling water at maximum

temperature of 40°C, fume (air) at 50°C and BF flare gas at 200°C. Combustion gas is reused

in the power plant.

; ; Heat available: 2.7 MW

BF b BF a


Tuyere



Convector hood

Air Hot stoves

Cooling water

Copperwork

Powder

Blast Furnace vessel (BF a/BF b)

Coke Limestone

Dust catcher

; ;


Cooling water

Venturi scrubber Cooler

Gas

Cast house Fume (Air)

Combustion gas (CO, BF)



Skimmer

Slag

Liquid iron

; ; Heat available: 14 MW

Flare BF gas

Gas

Stack


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4.1.4. Basic Oxygen Steelmaking (BOS) process

The BOF converts pig iron into steel by adding oxygen to remove the carbon, as well as

amounts of silicon, manganese and phosphorous.

The waste heat sources are from the fume (air) at a maximum temperature of 50°C, BOS gas

at a maximum temperature of 150°C and cooling water at 35°C.



Molten iron

Ladle





Desulphurization

Oxygen

Extraction

Fume

Cooling water

BOS gas

Fume

Steel

Primary BOS

Extraction A10A

Fume

Secondary BOS

Fluxes Secondary cooler

Slag

BOS gas

Slag

Burnt lime


Laddle preheaters 1 to 4

NG Combustion gas

; ; ; Heat available: 2.5 MW

Steel for concast

20

4.1.5. Continuous casting process

The continuous casting process is a batch wise process in moulds before reheating for rolling.

Water is the only waste heat source available in continuous casting with a maximum

temperature of 42°C.

Water spray

Caster 1 Caster 2


Low carbon steel + Alloy

Caster 3

Water

Water





Steam

Steam

Steam

Slab

Slab

Slab


Water


Water spray



Water spray

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4.1.6. Hot mill process

The steel still needs to be reheated in order to be malleable enough to roll.

In this process the waste sources are available as water at a maximum temperature of 38°C.


Water return

Cooling water




; ; ; Heat available: 74 MW

Slab yard

Re-heat furnace a

Coiler

Roughing mills

Run-out table

Coils

Re-heat furnace b

Cooling water

Slab for rolling Gas

Cooler

Air

Cooling water


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4.1.7. Cold mill process

The metal passes through rollers at a temperature below its recrystallization temperature in

order to increase metal yield strength and hardness.

Note that the fume at 30°C and extraction gas (air) at 40°C provide less than 1 megawatt of

energy. No data is currently available for the cooling water from this process.

Cooling water

Not quantified (No data available)

Coil from hot mill

Quenching tank

Stretch leveler

Pickling line



Fume (air)

Coils

Extraction gas

Cold rolling


http://en.wikipedia.org/wiki/Recrystallization_(metallurgy)

23

4.1.8. Annealing process

This process induces metal ductility in steel from the cold mill.

Waste heat source which has been identified and available for recovery is in the exhaust gas

stream from heat treatment process at 600°C.

Coil from cold mill

Heat treatment

High cooling rate Gas Jet

Cooler (HGJC)


Temper mill

Coils

Accumulator

Electrostatic oiler

Exhaust gas


Quench tank 1

Quench tank 2


Cooling water


Cooling water


Cooling water from entry

Cooling water from exhaust

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4.1.9. Power plant

The power plant recovers (Blast Furnace and Coke Oven) combustion gas heat in order to

convert it into electricity. It corresponds to a Rankine cycle for steam. The excess of steam or

steam bleed-off is drawn from the boiler through the continuous blow down system, the latter

being the only low grade heat source available in the power plant unit.

Steam represents a potential source for recovery. No information is available for steam

bleed-off in the power plant but the total steam loss within the site is estimated to be ~26

MW.

Continuous blow

down system

Steam (Bleed off)

Water to condense steam

(Dock supply)

Turbine

Boilers


CO and BF combustion gas

Boiler A


Pump



Boiler D


Steam



Boiler B

tion gas (Margam B, Mitchell 6&7)

Cooling water to

Condenser



Boiler C

25

Table 5: Characterization and classification of potentially recoverable low grade heat gas streams in the steel industry

Location Type Composition Tout

(°C)

Quantity

(kg/s)

Exergy

(MW) H2 O2 N2 CO2 CO CH4 NO2 H2O

Cold mill stretch

leveller

Stretch leveller

extraction fume 0 0.21 0.79 0 0 0 0 0 30 12 0.002

Cold mill Pickle line extraction gas 0 0.21 0.79 0 0 0 0 0 40 22 0.014

BOS Primary Hot metal pouring fume 0 0.21 0.79 0 0 0 0 0 50 60 0.088

BOS Secondary Fume 0 0.21 0.79 0 0 0 0 0 50 86 0.125

BOS Primary BOS gas 0.02 0 0.13 0.15 0.7 0 0 0 70 32 0.125

BOS primary Hot metal pouring fume 0 0.21 0.79 0 0 0 0 0 40 191 0.126

BF a flare BF gas 0.03 0 0.585 0.128 0.257 0 0 0 200 3 0.148

BOS primary Dephulsurisation gas 0.02 0 0.13 0.15 0.7 0 0 0 150 10 0.229

Casthouse (north) Fume 0 0.21 0.79 0 0 0 0 0 50 185 0.27

Casthouse (south) Fume 0 0.21 0.79 0 0 0 0 0 50 185 0.27

Sinter Dedust Sinter gas 0 0.21 0.79 0 0 0 0 0 50 245 0.36

BF b Flare BF gas 0.03 0 0.585 0.128 0.257 0 0 0 200 10 0.443

End of sinter Strand Sinter gas 0 0.21 0.79 0 0 0 0 0 180 36 0.734

Ammonia

incinerator NH3 combustion gas 0 0.18 0.68 0.01

0.005

89 0 0.0049 0.0526 210 10.75 0.827

Coke oven gas

underfiring

mixture of FB and Coke

Oven gas 0.3 0.001 0.3 0.075 0.2 0.13 0 0 220 100 5.128

Main stack Sinter gas 0 0.1669 0.7562 0.0415 0 0 0 0.0345 130 388 6.666

Power plant bleed

off Water vapour 0 0 0 0 0 0 0 1 N/A N/A N/A

Table 6: Characterization and classification of potentially recoverable low grade heat cooling water streams in the

steel industry

Type Location Tout(°C) Quantity(kg/s) Exergy (MW)

Cooling water Breaker bar cooler (sinter) 50 9 0.016

Cooling water Gas wash (BF b) 41 257 0.311

Cooling water Hot mill re-heat furnace B 38 233 0.337

Cooling water Hot mill re-heat furnace A 38 218 0.353

Cooling water Gas wash (BF a) 35 307 0.466

Cooling spray Caster 3 40 200 0.535

cooling / quench water Hot mill run out table 35 444 0.599

Cooling water Caster 3 33 542 0.62

Cooling water Open cooling (BF a) 35 665 0.651

Cooling water Copperwork (BF b) 40 1405 0.701

Cooling water Tuyere (BF b) 37 417 0.81

Cooling water BOS primary (North & South) 35 565 0.824

Cooling water Open cooling (BF b) 36 511 0.882





Main recirculating cooling

water Coke oven 40 556 1.518

dirty water return hot mill 35 1827 2.457

26

4.1.10. Low grade heat classification-Summary for

Primary steel production process case study

As identified in previous sections, the sources of low grade heat come mainly from stacks and

cooling towers. In this section, gas and cooling water streams identified in previous sections

are classified in terms of their exergy (values provided by the steelworks) and characterised

with the properties defined in Section 4.

4.1)10.1. Gas Table 5 gives the main properties of gas low grade heat streams classified as a function of

their exergy values. For gas, exergy is given by Equation (2). It depends on temperature, mass

flow rate and calorific capacity of the streams. The most exergetic stream has a temperature

of 130ºC but is available in higher quantity (388 kg/s).

4.1)10.2. Cooling water

Cooling water low grade heat streams are characterised in Table 6.

The exergy of the water streams depends on the temperature difference in the cooling towers.

Streams with highest mass flow rate present the highest exergy.

4.1.11. Potential uses

Some initial recommendations for waste heat source utilisation are specified in this section.

4.1)11.1. Gas

Table 7 lists the main gas sources identified in the processes as a function of their temperature

range and gives an indication for potential recovery technology.

Table 7: Gas waste heat sources and potential for recovery

Source Temperature Potential uses

Extraction systems Typically 30-80 oC

Heat pipes, ORC, Kalina, Biomass

drying, coal drying

Combustion stacks 150-250 oC Heat pipes, ORC, Kalina, Biomass

drying, coal drying

BF stoves 200 oC Heat pipes, ORC, Kalina, Biomass

drying, coal drying

CO underfiring gases 220 oC Heat pipes, ORC, Kalina, Biomass

drying, coal drying

Steam from casters and continuous

blow-down system Not quantified Steam boiler

27

4.1)11.2. Cooling water

If the temperature is high enough (typically > 80°C), the Kalina cycle can be used for

recovery of cooling water stream heat (cf. Table 8).

Table 8: Cooling water waste heat sources and potential for recovery

Source Potential uses

Cooling water

systems with

ΔT<25 °C and

high flows

Heat pumps,

space/office/buildings heating

Cooling water

systems with

ΔT>40 °C and

high flows

Heat pumps and Kalina,

space/office/buildings heating

4.1)11.3. Concluding remarks

Streams have been characterised by their temperature, mass flow rate, composition (for gas

streams), specific enthalpy and they have been classified in terms of their exergy which

represents the maximum technical work one can get from the stream heat.

Low grade heat sources identified as potentially recoverable mainly come from cooling

towers and stacks throughout the plant and are available either as gas or cooling water. The

specific heat consumed by each Steel making process unit can be approximated as the sum of

the specific steam and natural gas consumptions given in Table 3. For a capacity of 4.9.106

tons of steel produced per annum and based on exergy values of the waste streams given in

Table 6 and Table 7, the percentage of low grade heat can be determined for each process unit

as shown in Table 9. This report shows that the recoverable potential for low grade heat

represents approximately 1.1% of the heat consumption. This is nevertheless equivalent to

approximately to 60 MW. Table 9: Percentage of low grade heat in each unit of the primary steel making process

Operation

Heat consumption

(MW) Flue gas stream

(%) Cooling water stream

(%)

Steam stream (%) Low grade heat

(%)

Coke ovens 449.1977423 1.33 0.34 1.66

Sinter strands 236.9824962 3.27 0.01 3.28

Blast furnace 4522.431507 0.03 0.08 0.11 Basic oxygen

furnace 136.4840183 0.51 0.60

1.11

Continuous casting 30.82699137 0.00 19.82 19.82

Hot rolling 245.4195205 0.00 1.53 1.53

Cold rolling 115.5390665 0.00 0.01 0.01

Total 6193.366 0.25 0.5 0.42 1.1%

28

It is worth mentioning that low temperature gas with recovery potential does not exceed

250ºC in the steel industry although gas streams with higher temperature are available within

the plant but either recovered internally or inaccessible for over-the-fence activities. Gas

streams with the highest exergy are not those with the highest temperature (130ºC) but those

available in higher quantity.

Potential for cooling water heat recovery is available throughout the steelworks in large

quantities with a maximum temperature of 50ºC. Despite low temperature range, cooling

water represents a recoverable potential of approximately 30 MW.

The next section attempts to extrapolate this finding to the steel sector.

4.2. Secondary steel production process

Secondary Steel is produced in an Electric Arc Furnace (EAF) in which the scrap is

electrically heated (cf. Figure 6). Figure 7 gives the overview of the mass streams in an EAF.

An estimate of the energy consumed is given in Table 10. The total specific energy

consumption is in the range 2.3-2.7 GJ/t with 1.25-1.8 GJ/t for the electricity use. In the UK

and according to [3], the EAF specific consumption is 2.5 GJ/t and 0.75% of the energy

consumed is electricity which corresponds to about 1.8 GJ/t. As a first approximation, the

heat consumption can be considered as equivalent to the electricity consumption given that

the EAF is perfectly insulated. EAF emission mass streams are given in Figure 7. They

represent the main source of waste energy since the cooling water is not available for

recovery as it circulates in a closed cycle. The European Commission reported in [15] that

85-90% of the emissions from EAF are recoverable and that the primary off gas represents

95% of the emissions. It is therefore conservative to assume that the heat recovery fraction is

15% of the heat consumption (~1.8 GJ/t). According to [16], after cooling at about 200-300

°C, the primary gas is mixed with the secondary gas at 50-70 °C coming from the canopy

hood situated over the EAF in order to reach the filtering at a temperature typically below

130°C. The temperature of the flue gas from the EAF is approximated to 140 °C before the

filtering (typically between 130 and 200°C). The potential for low grade heat in the

Secondary steel production process sector can be estimated from the calculation of the exergy

of the flue gas stream. Table 11 gives the list of the EAF in the UK with the heat consumption

and potential for low grade heat.

Figure 6: Schematic presentation of a Electric Arc Furnace (EAF) [17]

Filtering

Flue gas for

recovery

29

Figure 7: EAF mass stream overview [18]

30

Table 10: Input and output mass stream from a EAF [18]

Table 11: EAF low grade heat potential in the UK

Location Capacity

(105 tons/annum) Heat consumption

(MW) Waste heat recovery potential

(MW)

Celsa UK (Cardiff) 1.2 71 1.92

Thamesteel (Sheerness) 0.72 43 1.15

Outokumpu (Sheffield) 0.54 32 0.86

Corus UK Ltd (Rotherham) 1.25 74 2

Forgemasters (Sheffield) 1.30 7.8 0.2

4.3. Overview of the steel sector

The European Union Emissions Trading Scheme (EU ETS) [19] was launched in 2005 to

meet its GHG emissions reduction target under the Kyoto Protocol. The EU has to make an

eight per cent reduction on 1990 levels by 2012.

Under the EU ETS, energy intensive industries must monitor and annually report their GHG

emissions. The list of the energy intensive industries published by the European Commission

in 2007 [20] was used in order to identify the main heat emitters in the sector steel. It is worth

mentioning that some of the large heat emitters recently have or are in the process of closing

down which reduces significantly the potential compared with previous market potential

estimates such as in [21]. The potential for low grade heat as steam, water and flue gas was

estimated for each industry whose emissions were listed in [20] and whose heat consumption

and percentage for low grade heat were estimated, based on the results presented in the

previous sections. The results are summarized in Table 12. The total potential for low grade

31

heat recovery in the Steel sector is estimated to be approximately 137 MW, i.e. approximately

1.2 TWh. This represents less than 10% of the potential estimated in 1994 and reviewed in

[22]. Apart from the fact that some of the large heat emitters have closed down, another

reason for such a difference is that the potential estimated in this study considers the exergy

instead of the energy content which only represents the useful part of the heat sources

identified. This represents nevertheless a significant amount of energy with regards to the

potential uses as discussed in the next section. The low grade heat sources were located on a

map as shown in Figure 8 with the associated potential for low grade heat recovery for both

primary and secondary steel making processes.

Table 12: Low grade heat recoverable potential in the Steel sector in the UK

Type of products Capacity

(105tn/an)

Gas (MW) Water (MW) Steam (MW)

Total low grade heat

recoverable potential (MW)

EAF steel 6.21 8.03 0 0 8.03

Primary steel 9.6 31 35 59 125

Hot and cold rolling for

automotive steel making

2 3.76 0 0 3.76

NA NA 43 35 59 137

Figure 8: mapping of low grade heat potential in the Steel sector

4.4. Uses for low grade heat

In order to harness the potential of the low grade heat identified in the Steel sector, there is a

32

need for matching the sources with potential end-users in the surrounding of the plant. The

review by Ammar et al. [22] have identified how low grade heat could be used in the future to

reply to the societal needs. The most attractive application is to produce electricity. The

feasibility of such application is however limited to temperature higher than typically

approximately 70°C for the most advanced Rankine cycle derivatives. This is the case for

more than 50% of the flue gas streams identified. One of the most important challenges is to

harness the potential of the waste water streams abundantly available at lower temperatures

(between 35 and 55°C). As underlined in Section 4.11, space heating/cooling can be an

interesting alternative for low temperature. Typical heat and cooling loads are provided in

Table 13 . Table 13: Typical heat and cooling loads

Heat load Maximum thermal

energy consumption (kW)

Minimum thermal energy

consumption (kW) Sources

Office (per m2) 0.1 0.001

energy audit data

Middlebrough

School (per pupil) 0.15 1.15 Energy audit data

County Durham

Greenhouse (per m2) 55 0.1 Bremer Energie Institut

Data centre (per rack) with COP ~ 2 60 30 [23]

Supermarket (per m2) with COP~4 0.16 0.04 [24]

The viability of a low grade heat recovery projectdepends on whether the heat available can

economically be transferred from the source to an identified sink. So far, however, there has

been little discussion about the economic distance from the source to the sink. Industrial heat

is usually transported via water or steam. According to the report by Terra Infirma [25], steam

with a temperature of 120-250°C can be transported over approximately 3 to 5 km while

water with a temperature of 90-175°C can be transported over 30 km. Other sources cited in

that same report mentioned that 9 miles (around 15km) is the economic limit for low-grade

heat. In fact, how far heat can be transported depends on several factors. If heat is assumed to

be transported via a pipe, the heat loss factor, which is defined as the ratio between heat loss

and the quantity of heat supplied by the source, depends on the pipe material and the

efficiency of its insulation, pipe diameter and the temperature of the fluid circulating in the

pipe. The profitability of any heat recovery project will also depend upon the cost invested in

heat transportation, the total cost being the sum of the pipeline installation, heat losses and

pumping cost [11]. For long distances (typically over 10 km), sorption processes are efficient

heat transportation systems [26] [27] Recently, Lin et al. [28] investigated the performance

and the economics of a 500 MW transportation system over 50 km, with the heat coming

from a nuclear plant. They showed a payback period of 3 years and 8 months for the whole

system. Less waste heat is available for free from the process industry and therefore the

economics of the low grade heat recovery project need to be revised accordingly. However

this is nevertheless evidence of a potentially economic method to transport low grade heat.

The economic distance can be defined as the limit for economically transferring low grade

heat from the source to the sink. The value of the economic distance is likely to increase over

time as the price of the fuel equivalent to the low grade heat recovery savings is likely to keep

33

increasing. Within the scope of this study, the feasibility of using low grade heat to provide

heating is examined for 3 characteristic transportation radii from the heat source; 1 kilometer,

9 kilometers and 25 kilometers. Port Talbot is chosen as a case study. The heat map produced

by the Department of Environment, Food and Rural Affairs (DEFRA) is used in order to

determine the heat potential from the demand side. The results are summarized in Table 12

for the different characteristic distances from Port Talbot steelworks. Table 14: Heat consumers at different radii from Port Talbot Steelworks

Heat consumers 25 km 9 km 1 km

Public Buildings (MW) 2.141 0 0

Commercial Offices (MW) 0.757 2 0

Hotel and Catering (MW) 2.642 0 0

Other Services (MW) 1.025 8 0

Retail (MW) 2.518 5 0

Sport and Leisure (MW) 0.613 0 0

Small Scale Industrial (MW) 41.991 0 0

Domestic (MW) 100.72 3 0.2

Schools (MW) 0.866 0 0

Hospitals (MW) 0.675 0 0

Warehouses (MW) 1.775 0 0

Total (MW) 155.7 18 0.2

Most of the heat demand is located more than 9 km away from the heat sources identified in

the steelworks. Within a radius of 25 km, the potential for heat demand overcome the heat

supply with approximately 155 MW. Most of the heat demand comes from households.

Industrial low grade heat could therefore be integrated in a new district heating scheme to

retrofit community heating.

34

References:

1. Turner C. W. and S. Doty, Waste-heat recovery, in Energy management handbook.

2006, Fairmont Press: Lilburn.

2. HM Government, Climate Change Act 2008: Chapter 27. 11/26/2008.

3. Mc Kenna, R.C., Industrial energy efficiency Interdisciplinary perspectives on the

thermodynamic, technical and economic constraints, in Department of Mechanical

Engineering. 2009, University of Bath.

4. HM Treasury The climate change levy package. 2006: London.

5. HM Treasury, Budget 2010: London.

6. The Carbon Trust. About the Carbon Trust. [cited 2010; Available from:

http://www.carbontrust.co.uk/about.

7. Profiting from low-grade heat, The watt committee on Energy report No. 26. 1994,

London: The institution of Electrical Engineers.

8. Perrot, P., A to Z of Thermodynamics. 1998: Oxford University Press.

9. Winter, C.-J., Energy efficiency, no: It's exergy efficiency! International Journal of

Hydrogen Energy, 2007. 32(17): p. 4109-4111.

10. Potential uses of waste heat from a proposed new power station at Blyth. Report by

Terra Infirma for the National Industrial Symbiosis Project (NISP). 2008.

11. Hlebnikov, A. and A. Siirde, The major characteristic parameters of the Estonian

district heating networks and their efficiency increasing potential. Energetika, 2008.

54(4): p. 67-74.

12. BERR, Heat Call for Evidence. 2008, Department for Business Enterprise &

Regulatory Reform: London.

13. Choudrie, S.L., et al., UK Greenhouse Gas Inventory, 1990 to 2006. 2008, DEFRA:

London.

14. BERR, ECUK Table 1.14: Overall energy consumption for heat and other end uses by

fuel 2006. 2008: London, [spreadsheet].

15. Technical Note on the Best Available Technologies to Reduce Emissions of Pollutants

into the Air from Electric Arc Steel Production Plants. 1994, European Commission.

16. Griffini, G.P.a.N., De-dusting plants for electric arc furnaces, in Millinium Steel. 2005,

VAI Pomini SrI: Millan, Italy.

17. Kirschen, M., L. Voj, and H. Pfeifer, NO2 emission from electric arc furnace in steel

industry: contribution from electric arc and co-combustion reactions. Clean

Technologies and Environmental Policy, 2005. 7(4): p. 236-244.

18. Best Available Techniques Reference Document on the Production of Iron and Steel.

2001, European Commission.

19. Ellerman, A.D. and B.K. Buchner, The European Union Emissions Trading Scheme:

Origins, Allocation, and Early Results. Review of Environmental Economics and

Policy 2007. 1(1): p. 66-87.

20. EU ETS Phase II National Allocation Plan (2008-2012). Appendix E: NAP data. 2007,

European Commission.

21. Boddy, J.H., Sources of heat, in Profiting from low-grade heat, Thermodynamic cycles

for low-temperature heat sources, The Watt Committee on Energy Report No. 26, A.W.

Crook, Editor. 1994, The institution of Electrical Engineers: London.

22. Ammar, Y., et al., Review of low grade thermal energy sources and uses from the

process industry in the UK. Special issue, Applied Energy Journal, In press.

23. Almoli, A., et al., Computational Fluid Dynamic Investigation of Liquid Rack Cooling

in data centres. Special issue. Applied Energy Journal, In press.

24. Lazzarin, R.M. and F. Castellotti, A new heat pump desiccant dehumidifier for

supermarket application. Energy and Buildings, 2007. 39(1): p. 59-65.

http://www.carbontrust.co.uk/about

35

25. Bujak, J., Energy savings and heat efficiency in the paper industry: A case study of a

corrugated board machine. Energy, 2008. 33(11): p. 1597-1608.

26. Mazet, N., et al., Feasibility of long-distance transport of thermal energy using solid

sorption processes. International Journal of Energy Research, 2010. 34(8): p.

673-687.

27. Kang, Y.T., et al., Absorption heat pump systems for solution transportation at

ambient temperature -- STA cycle. Energy, 2000. 25(4): p. 355-370.

28. Lin, P., R.Z. Wang, and Z.Z. Xia, Ammonia-water absorption cycle - a prospective

way to transport low grade heat energy over long distance, in SET2010 -9th

International Conference on Sustainable Energy Technologies. 2010: Shanghai,

China.

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