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Co-funded by the Intelligent Energy EuropeProgramme of the European Union

Introduction - Theory - Exercises - Business Case - Summary

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Overview

Introduction Theory

Approach (some remarks) Main components Compressed air flow rate Inappropriate air users Leakage Parameters that influence

consumption

Exercises Business Case Summary

Introduction - Theory - Exercises - Business Case - Summary

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AIR IS FREE….BUT COMPRESSED AIR ISN’T FREE

ENERGY EFFICIENCY OF MOST

OF COMPRESSED AIR PLANTS IS

QUITE LOW

COMPRESSED AIR CAUSES A COST THAT ISN’T

ALWAYS TAKEN IN ACCOUNT

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Electric energy costs

Leakage costs

Maintenance cost

Plant modification cost

The costs of electric energy reach the 73% of total cost

during the life of air compressed system.

REASONS FOR EXCESS

COST

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Reasons for exces consumption

Introduction - Theory - Exercises - Business Case - Summary

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Optimizzation of air compressed system will deliver savings of up to 35 %.

Introduction - Theory - Exercises - Business Case - Summary

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Approach (some remarks)

1. Identify how much air flow and pressure each user machine needs

2. Find the right place for each user machine

3. Identify the right place for compressed air machines

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MAIN COMPONENTS

1. Air inlet filter

2. Air compressor, electric motor and panel

control

3. Air treatment (oil separator, dryer, filtration)

4. Storage tank

5. Distribution Network

Fonte: Improving air system performance DoE - Energy Efficiency and Renewable Energy

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Compressed air flow rate

- inappropriate air users

- leakage

The flow rate produced a direct bearing on consumption.

The compressed air flow rate depended on requirements.

Therefore must be avoided:

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Inappropriate air users

Transport of powders at low pressure

Ventilation

Agitation liquids

Cleaning in general

Removal of defective products from a line

Blowers

Mechanical arm

Electrobrushes

Mechanical agitators

Fans; Blowers

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LEAKAGE

• Accurate assessment with specific equipment

• Rough estimate

If more than 5% requires action!!

How to assess the losses?

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Parameters that influence consumption

• L is the work

• M is the mass flow rate of air

• R is the universal gas constant,

• T1 is the inlet air temperature (°K),

• β is the ratio between the compression end pressure and beginning of compression,

• m is the exponent of the transformation,

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Choose an appropriate level

The increase of a bar of produced air pressure causes an

increase of about 7% of the energy consumption

The increase of a bar of produced air pressure causes an

increase of about 7% of the energy consumption

If the process requires two pressure levels is good to evaluate the installation

of two compressors instead of one (with the need to achieve the lowest

pressure by reducing valves).

Parameters that influence consumptionMaximum pressureMaximum pressure

The operating pressure of a compressor directly affects the power consumption and

energy consumption.

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• Increase in operating costs

• Small diameters, lower installation costs, more losses and hence higher

operating costs

The pressure drop of the network (pipes) should never result in a pressure

drop greater than 0.1 bar

• The level of surface finish of the tubes affects the load losses

Parameters that influence consumptionPressure dropPressure drop

The pressure drop of the network (pipes) should never result in

a pressure drop greater than 0.1 bar

The pressure drop of the network (pipes) should never result in

a pressure drop greater than 0.1 bar

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• The minor work is assured in the case of an isothermal transformation m = 1

• The work is greater in the case of an adiabatic m = 1.4

Parameters that influence consumptionType of transformationType of transformation

To get closer to an isotherm must carry away heat during

compression

To get closer to an isotherm must carry away heat during

compression

The removed heat can be used

• Only 10% of the electricity consumed by a compressor is converted into

useful energy to compress the air

• 90% of the electrical energy is converted into heat to be eliminated, but that

can be recovered (heating environment, pre-heat combustion air, heating hot

water, pre-heat process water)

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The work made by the compressor for compressing the air increases with

increasing temperature of the inlet

• The temperature of the input should be as short as possible, consistent with

current environmental conditions

• Do not take air from the compressor room or another, it is always best to take

air from the outside

• The starting point must be taken possibly in the north and in the shaded area

Parameters that influence consumptionInlet air temperatureInlet air temperature

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The air quality depends on its content:

• Particulate.

• Water (expressed in temperature of the dew point of the air pressure)

• Oil (measure)

• Material of the network and its state

Parameters that influence consumptionAir qualityAir quality

Air quality must be adapted to the needs of the process

Air quality has a greater cost.

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WaterThe water comes from atmospheric moisture in the airRemoving water from the air can be done:

- At central Referigeration- At the local level Steam Traps

The refrigeration is more efficient, but more expensive from the point of view of plant and exercise.The steam traps have a lower cost of installation, but require higher maintenance costs and leads to losses of air.

Parameters that influence consumptionAir qualityAir quality

Particulate matter can be removed by input filters

The oil can be removed by filters or at the source, using oil-free compressors.The two solutions should be evaluated as a function of the different costs.

The oil-free compressors increase the cost of installationThe filters increase the costs of operation and maintenance

The filters should be checked regularly

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1. Start - stop (power 5-10 kW)

2. Running load - idling - stop (power> 10 kW)

3. Speed control of Compressors

Regulation system are influenced by:

• Oversized Compressor

• Control of the compressor speed

• The presence of a storage tank

Parameters that influence consumptionRegulation systemRegulation system

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•Meets sudden demands for air

•Allows for greater stability in the level of pressure on the network

•Reduces Stop & Go of the compressor

•Provides sizing the compressor below the maximum values pressure

• The option of installing secondary tanks near the isolated users and / or highly

intermittent can be consider

Sizing of the storage tank

•The size of the tank depends on the extent of changes in the demand for air.

The size should be at least 10 times the volume of air produced by the

compressor (l/s)

•The size of the tank affects the sizing of the compressor

Parameters that influence consumptionSTORAGE TANKSTORAGE TANK

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• Do not oversize the compressor

• Storage Tank

• Control of the compressor speed

• Type of compressor

• High efficiency engine

Parameters that influence consumptionCompressor & controlCompressor & control

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Acquisition of data on consumption of electricity

• Can I make special measures? (High cost, more accurate)

• Can I use the data available? (low-cost, lower precision)

Parameters that influence consumptionHow to handle the compressed air systemHow to handle the compressed air system

Evaluate the cost of compressed air

Introduction - Theory - Exercises - Business Case - Summary

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LEAKAGE REDUCTION

What is the effect of a hole of 10 mm in a compressed air network (@ 7 bar pressure)

Introduction - Theory - Exercises - Business Case - Summary

a.Up to 10 kW loose

b.Up to 40 kW loose

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HOLE (mm)

Flow rate @ 7bar (l/s)

Power loss (kW)

1 1,2 0,4

3 11,1 4

5 31 10,8

10 124 43

Introduction - Theory - Exercises - Business Case - Summary

LEAKAGE REDUCTION

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HIGH EFFICIENCY ENGINES

How much to save by replacing a standard engine with a high efficiency engine?

a. Up to 1%

b. Up to 5%

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Power [kW]

HIGH EFFICIENCY MOTOR

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REDUCTION OF AIR SUCTION TEMPERATURE

How much energy savings can be obtained with the cooling air inlet 5°C?

a. Up to 2%

b. Up to 10%

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Technical literature reports that a

reduction of 5 °C of compressor input

air temperature (with respect to usual

temperature) would allow saving of 2%

of yearly consumed kWh.

REDUCTION OF AIR SUCTION TEMPERATURE

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Practical examplePorsche industry

Introduction - Theory - Exercises - Business Case - Summary

Description:

In 1997, the system of compressed air production of "plant2 " of the German

automobile factory Dr. Ing hc F. Porsche AG near Stuttgart was constituted by a

screw compressor - cooled water (22,2 m3/min, FAD) plus four reciprocating

compressors water cooled from 15 m3/min each.

The maximum operating pressure was 8.7 bar.

An analysis on the compressed air system, carried out by specialists of a factory

compressors, noted compressed air demand varies between 15 and 65 m3/min.

By processing all relevant data has been defined a new compressed air system

with optimized use of energy.

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Action taken:

The new system was divided into two stages comprising only air-cooled screw

compressors.

Load peaks were satisfied with the use of three machines with a 5.62 m3/min

FAD each, while the base load was covered with four compressors with a FAD of

16.4 m3/min each.

All seven compressors are managed by a centralized control system.

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Results:

The optimization of the compressed air system allowed us to calculate the cost

of energy and make energy savings.

the operating pressure was lowered from 8.5 to 7.5 bar and the specific power

of the overall compression station has been reduced from 8.19 to 6.19 kW /

(m3/min).

The total savings amounted to 483000 kWh of electricity per year.

Furthermore have been spared approximately € 55,000 in savings for non-

consumption of cooling water.

The optimization of the compressed air system has been realized with a

reasonable payback time

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Excess energy consumption through compressed air is

caused by technichal as well as behavioural issues.

Through the optimization of the compressed air plant

savings of up to 35 % are possible.

The leakage reduction can effect up to 20 % energy

saving.

Adoption of high efficiency engines can effect up to 5 %

energy saving.

A reduction of 5 °C of compressor input air temperature

would allow saving of 2% of yearly consumed kWh.

Repetition

Introduction - Theory - Exercises - Business Case - Summary