CAS EEMaking

Enhancement Happen

Part 3: Potential

of compressed

air energy

e!ciency

CAS EE – Making Enhancement Happen

Part 3

Potential of compressed air energy efficiency

Enersize Ltd

Pasi PeltomaaJanuary 2011

ENERSIZE LTD Friitalantie 13, FI-28400 Ulvila T +358 207 980 310 info@enersize.com www.enersize.com

Contents

Purpose of this document! 1

Introduction! 2

1 Compressed air is expensive utility! 3

2 Surveys of CAS energy efficiency potential! 5

3 Global compressed air systems electricity consumption! 7

3.1 European Union CAS electricity consumption! 8

3.2 United States and China CAS electricity consumption! 10

3.3 Australia, Malaysia and South Africa CAS electricity consumption! 10

3.4 Estimations for Brazil, Russia, India and Japan CAS electricity consumption! 11

4 Global saving potential of industrial compressed air systems! 13

4.1 Saving potential versus compressor electricity consumption! 14

4.2 Saving potential versus electricity production of wind turbines ! 15

4.3 Saving potential versus coal based electricity production ! 16

Conclusions! 17

References! 18

Copyright © 2010 Enersize Ltd! i

Purpose of this document

This document is the third part of Enersize Ltd’s “CAS EE - Making Enhancement Happen”

document. The purpose of this third part is to introduce the reader to the potential of compressed

air energy efficiency. In the second part — “CAS EE – MEH” — the reader was introduced to some

basic information concerning industrial compressed air systems. The conclusion stated that one

should always look at the basics of industrial compressed air systems from an energy efficiency

point of view. With this document we look more deeply into the potential of compressed air energy

efficiency. This document gives a clearer understanding of why compressed air is an expensive

utility.

With this document we also collect information on earlier surveys on compressed air systems,

which have all found significant potential for improving energy efficiency. It seems that compressed

air systems consumed 4.2% of all electricity in the world, and there is also an existing significant

amount of long-term savings potential in industrial CAS.

Part three of CAS EE - MEH pointed out very clearly the significant amount of savings potential in industrial compressed air systems.

Copyright © 2011 Enersize Ltd! 1

Introduction

The energy efficient point of view for compressed air systems is important - there is no doubt

about it. With this document we collect together more facts to better understand the importance of

energy efficiency in compressed air systems. The statement that compressed air is an expensive

utility has reliable arguments. So, when questioning the use of compressed air, the core question is

the need for compressed air.

There has been a lot of research into identifying the potential of compressed air systems’ energy

efficiency. We take a look at some literary reviews to identify those earlier studies which have been

concerned with compressed air systems’ energy efficiency potential.

Today it is a fact that compressed air systems typically consume 10% of industrial electricity on the

global level. This estimate has been verified in the United States and Australia, and this was also

identified formerly in the EU-15. Recent research for the EU-27 has not yet taken place, but this

document will try to give some estimates concerning EU-27 compressed air systems’ electricity

consumption.

Today, China is a major player in compressed air systems’ electricity consumption, due to the rapid

growth of its GDP. Actually, it has grown steadily by about 10% per year since 2003. New industrial

plants have been built and the production processes of existing plants are expanding and

changing, so compressed air usage in China has been growing rapidly.

Recent estimates state that compressed air systems consumed 4.2% of all electricity in the world.

So it seems that we can easily save 16.75 TWh annually in world compressed air systems. This

16.75 TWh of annual electricity consumption means 10,469 200 kW compressors or 20,938 100

kW compressors, and the compressors are running 8,000 hours annually.

Copyright © 2011 Enersize Ltd! 2

1 Compressed air is expensive utility

It is no secret that industrial compressed air systems are an expensive utility. This sentence is still

so important a statement that we should take a closer look at it to better understand compressed

air systems, and also the importance of the energy efficient use of compressed air.

Firstly, we need to know some basic principles of compressed air behaviour. Two important factors

in compressed air are heat and pressure. Air consists of molecules which are held together by

molecular forces. When air is in a receiver, molecules bounce on the receiver wall and generate

pressure. When the temperature gets higher, the movement of air molecules increases and higher

pressure is generated. There is an inverse relationship between pressure and volume: if the air is

compressed to a smaller volume, the pressure increases inversely [BOGE 2004, Elliot 2006].

We have to take a look at thermodynamics to better understand how air compresses. First we

need to know that when compressed air is in a steady state, it consists of only internal energy,

which does not depend on pressure. Internal energy depends on gas temperature, so the same

mass of air consist of the same energy, thus it is at 8 bar or atmospheric pressure. So,

compressed air actually does not consist of almost none of energy. The following explanation gives

an example of this. We have a compressor with a 30 kW electrical engine. After compressing, the

compressed air is cooled down to same temperature as the intake air. According to the first law of

thermodynamics, we must remove the same amount of heat flow from the compressor station so

that the temperature keeps a steady state. When compressed air is at the intake air temperature, it

does not transfer any of the energy that was used to produce the compressed air [Airila et al.

1983; Ellman et al 2002].

At this stage one might ask why we need to remove heat from the compressed air. The answer is

this: we do not live in an ideal world, i.e. the real world affects the compressing process. Actually,

all parts which are in contact with the compression process extract heat. Also, some parts, such

as the electrical motor, convert electrical energy into heat due to inefficiencies in electrical motor,

and thus are not a part which compresses air. So air gets hot when it is compressed with

compressors. We can ask further if it is wrong if compressed air is hot. Yes, it is. If we think about

the efficiency of the compression process, we can see that the more heat is removed from the

compressed air, the more efficient the compression process will be. This is because the air density

decreases when the air gets hotter. A receiver which has an air temperature is 80 ℃ and air

pressure of 12 bar has the same amount of air as a receiver which has an air temperature of 38 ℃

and air pressure of 7 bar [Elliot 2006].

It seems that temperature is the troublemaker in compressed air systems. Temperature acts like

pressure, increasing inversely with the volume change [Elliot 2006]. Heat must be rejected from

compressed air and by this we almost lose all electrical energy which the compressor has taken in

(if compressed air is cooled down to the intake air temperature, it is not transferring any of the

energy which was used to produce the compressed air). The following picture (Picture 1) shows

how electrical energy is distributed in a screw compressor with oil injection cooling.

Copyright © 2011 Enersize Ltd! 3

Picture 1. Electrical energy distribution in a screw compressor with oil injected cooling [BOGE

2004].

At this stage one might ask is there any sense in using a compressed air system. One remarkable

character of compressed air justifies its use: compressed air has the capability to do work and this

capability is possible to use in numerous actions (take a look to CAS EE - MEH Part 2 to see the

different kinds of applications where compressed air can be used). This compressed air character

is so outstanding everywhere in the world that it leads to a situation where compressed air systems

are very popular despite the total inefficiency of compressed air production. At this stage we

should remember the CAS EE - MEH Part 2 documentation. Because atmospheric air is still free

and compression of it is very expensive, the need for compressed air is a core question.

If we take a look at the life cycle costs of a compressed air system, we can see that the energy

cost is a major component of CAS. If we split the energy cost and take a look at how the energy is

divided, we can see that only a small fraction of consumed energy gets a point of use, and with

this chapter, there should be no doubt about it.

Energy is the biggest cost in the life cycle costs of a compressed air system, and the fact is that

typically a compressed air system uses a lot more energy than is needed to meet demand.

Researchers have argued that there is a 5–50% potential to increase energy efficiency, depending

on the site [Qin & McKane 2008; Radgen & Blaustein 2001; U.S. DoE 2001]. Compressing

atmospheric air is expensive and the way of using this expensive compressed air in industry is very

inefficient. It is not very wrong to say that compressed air is an expensive utility.

Copyright © 2011 Enersize Ltd! 4

2 Surveys of CAS energy efficiency potential

As was previously thought, an industrial compressed air system is an expensive utility and it is not

a secret. So there have been a lot efforts to find the potential to improve the energy efficiency of

compressed air systems. There have been several surveys on compressed air systems which have

all found significant potential for improving energy efficiency. Here some of those surveys are

discussed.

The U.S. Department of Energy with technical support from Compressed Air Challenge® (CAC)

commissioned the following survey at 2001: The Assessment of the Market for Compressed Air

Efficiency Services. The report is based on assessment of 91 CA equipment distributors, the

assessment of 222 industrial CAS end users, interviews with some veteran CA efficiency

consultants and reanalysis of some collected data from the Motor Market Assessments in 1997.

The survey found that if recommended improvement measures whose payback time was under

three year were implemented, energy savings would total 15,670 GWh per year or $747 million at

current industrial electricity rates. The survey realized that the implementation of CA efficiency

measures are very low [U.S. DoE 2001].

The European Commission, under the SAVE Programme with support by the French Environment

and Energy Management Agency (ADEME), the Fraunhofer Institute for Systems and Innovation

Research (ISI), the Department of Energetics – University of L`Aquila (DoE) and the Education

Consulting Engineering (ECE), launched the Compressed Air Systems in the European Union

survey in 2001: Energy, Emissions, Savings Potential and Policy Actions. The survey found that the

energy efficiency of many CASs is low. Case studies show that savings from 5–50% are possible.

They found that possible economical and technical energy savings amount to 32.9 % and are

achievable over a 15-year period [Radgen & Blaustein 2001].

Fraunhofer ISI together with the German Energy Agency launched the Druckluft effizienct

campaign in Germany based of the results of the Compressed Air Systems in the European Union

survey. The electricity consumption of CA applications in Germany is approximately 14 TWh per

year. A 30% savings potential in Germany means savings of 5 TWh or the output of two coal-fired

power stations. The Druckluft effizienct campaign tries to activate that savings potential. The

survey found that if savings potential identified (20% of 14 TWh) in the audit campaign are

projected to 50,000 German companies, the annual economic savings in Germany are 2.8 TWh.

To achieve these savings requires an investment of EUR 126 million. With an average electricity

price of 4 ct/kWh the annual cost savings from these measures would be around EUR 110 million,

which means a payback time of just over a year [Radgen 2002].

Pacific Energy Associates, Inc. and Research Into Actions, Inc. were contracted by the Northwest

Energy Efficiency Alliance and conducted the following survey: Market research report:

Compressed Air Efficiency. The key findings of the survey were that there are significant

opportunities to save energy in the compressed air market place, and also that most customers

and contractors are not currently acting to optimize the efficiency of CAS. The survey found that

savings in the surveyed plants can constitute 30–50% of the CA load, and for some industries 10–

20% of the plant electric load [PEA Inc. & RIA Inc. 2000].

Copyright © 2011 Enersize Ltd! 5

Aspen Systems Inc., contracted by the Public Service Electric and Gas Company and Pacific

Energy Associates, conducted the Compressed Air Systems Market Assessment survey in the

Public Service Electric and Gas Service Territory. The survey found that PSE&G industrial

customers spend about $35 million a year on CA. They estimate that 30% of those costs might be

saved, which is over $11 million [Aspen Systems Inc 2003].

Motiva Oy, a Finnish expert company promoting efficient and sustainable energy use, launched the

PATE project in Finland in 2003, and in 2008 there were 25 analyses according to the PATE

compressed air energy audit model. In the first stage of PATE project in 2003–2005 it was found

that Finnish industrial compressed air systems use 1.4 TWh electricity annually. A 20% savings

potential in compressed air systems was also recognized, meaning an annual savings potential of

280 GWh [Hietaniemi & Lappalainen 2005].

Saidur, R., Rahim, M. and Hasanuzzaman, M. from the University of Malaya in Kuala Lumpur in

Malaysia have conducted a very wide literary review concerning compressed air energy use,

savings and the payback period of energy efficient strategies. They have looked at compressed air

systems energy audits and the energy use of compressed air systems. They present broad

estimates for energy savings, payback periods and emission reductions of several energy efficient

actions. They also take a look at computer tools for compressed air analysis [Saidur et al. 2010].

Copyright © 2011 Enersize Ltd! 6

3 Global compressed air systems electricity consumption

Finpro conducted a global market insight into compressed air energy efficiency services survey for

Enersize Oy. The conclusion of the survey for estimating the size of global energy efficiency

markets for compressed air systems was EUR 1.3 billion [Mizera 2010]. We need some calculation

to open this EUR 1.3 billion potential and also to get a clearer view of the size of global CAS

electricity.

First, the total world electricity consumption was 18,187 TWh in 2007 [Mizera 2010]. Global

industrial electricity consumption is 42% [IEA 2009]. Typically, compressed air systems use

approximately 10% of industrial electricity consumption, for example, in the European Union (this

estimate is from the former EU-15, which is now the EU-27), the United States, and also Australia

[AMEI of Australia; Radgen & Blaustein 2001; U.S. DoE 2001]. Also, for example, in China

compressed air systems use 9.4% of all electricity [CMP 2001] and in South Africa compressed air

systems use 9% of industrial electricity consumption [Marais et. al 2009], and in Malaysia

compressed air systems consume 9% of the total industrial energy use [Saidur et al. 2009]. To

arrive at an estimate for the global average CAS electricity consumption, we can do the following

calculation:

! ! !

With the above calculation we arrive at the size of global compressed air systems electricity

consumption, i.e. 764 TWh. Here are some factors to understand the size of the estimated global

CAS electricity consumption. When we are comparing global electricity consumption and global

CAS electricity consumption, we can see that global CAS electricity consumption is 4.2% of global

electricity consumption:

! ! !

Total electricity consumption in the EU is 3,168 TWh, with industry consuming 40% of the EU’s

total [Mizera 2010]. So industry in the EU consumes the following amount of electricity:

! ! !

If we are comparing global CAS electricity consumption and EU industry electricity consumption,

we can see that global CAS electricity is 60.2% of the EU’s industrial electricity consumption:

Copyright © 2011 Enersize Ltd! 7

! ! !

From the global point of view, industrial compressed air systems are a very relevant part of

electricity consumption. Industrial compressed air systems represent 10% of industrial electricity

consumption and 4.2% of all global electricity consumption.

3.1 European Union CAS electricity consumption

Is it possible that the estimates in the previous section are too optimistic for compressed air

electrical consumption? Radgen & Blaustein have argued that compressed air systems consumed

80 TWh electricity in the EU-15 [Radgen & Blaustein 2001], and Peter Radgen has argued that

compressed air systems global electricity consumption is about 400 TWh [Radgen 2005; Radgen

2006]. Radgen & Blaustein estimated in 2001 that future electricity consumption (2005–2015) of

compressed air systems in the EU-15 would be approximately 79–80 TWh if business continued

as usual [Radgen & Blaustein 2001].

Let’s take a closer look at the electricity consumption of compressed air systems in the European

Union. Radgen & Blaustein’s study looks most closely at compressed air systems in France,

Germany, Italy and the United Kingdom. Greece, Portugal and Spain are handled together. They

gave the following estimates for the electricity consumption of compressed air systems in the

countries surveyed in the following table (Table 1).

CAS % of industrial electricity consumptionCAS % of industrial electricity consumptionCAS % of industrial electricity consumption

France (11 %) Germany (7 %) Italy (11 %) United Kingdom (10 %)

Table 1. CAS % of industrial electricity consumption [Radgen & Blaustein 2001]

If we look at industrial electricity consumption in 2007 in the above countries and by using the

above estimates for CAS electricity consumption, we get the following table (Table 2):

Copyright © 2011 Enersize Ltd! 8

Tot. el. consumption

(TWh)

El. consumption in

industry (%)

CAS electricity

consumption (TWh)

France 481.41 31 16.4

Germany 591.03 46 19.0

Italy 339.20 47 17.5

United Kingdom 373.36 34 12.7

Table 2. CAS electricity consumption in France, Germany, Italy and the United Kingdom. Produced

from Mizera 2010.

Together the above CAS electricity consumption is:

! !

This is quite an enormous amount of electricity, and we haven’t yet taken account of the other 23

EU countries. If we estimate that in all the other countries compressed air systems account for

10% of industrial electricity consumption, we get the following amount of electricity for the other 23

EU countries (Austria, Belgium, Cyprus, Denmark, Finland, Greece, Ireland, Luxembourg, Malta,

the Netherlands, Portugal, Spain, Sweden, Estonia, Latvia, Lithuania, Bulgaria, the Czech

Republic, Hungary, Poland, Romania, Slovakia, Slovenia), which is the basis of Mizera’s

calculations [Mizera 2010]:

! ! ! ! !

Together we get the following amount of electricity:

! ! !

Compressed air systems in the European Union’s 27 countries consume 122.8 TWh of electricity.

This amount is arrived at by estimating that compressed air systems in all countries in the EU, with

including France (11%), Germany (7%) and Italy (11%), account for 10% of all industrial electricity

consumption.

Copyright © 2011 Enersize Ltd! 9

3.2 United States and China CAS electricity consumption

Industrial electricity consumption in the United States in 2001 was 964 TWh [Senniappan 2004],

and in Mizera’s calculations it is 987 TWh (2007 value) [Mizera 2010]. We can use Mizera’s data

and also informations of the U.S. DoE and Senniappan’s [U.S. DoE 2001; Senniappan 2004] to

calculate the electricity consumption of compressed air systems in U.S. industry, which gives us

the following amount:

! ! !

Let’s take a look at China. It seems that compressed air systems account for an outstanding

amount of electricity consumption in China. They consume over 9% [Li et. al 2008] or 9.4% [CMP

2001] of all electricity. China is growing rapidly, its GDP has grown steadily by about 10% per year

since 2003 [Abdelaziz et. al 2011]. New industrial plants have been built and the production

processes of existing plants has expanded and changed, so compressed air usage in China has

also been growing rapidly [Qin & McKane 2008]. China’s electricity consumption was 3,483 TWh in

2008 [CIA - The World Factbook, China]. From the above information we see that the electricity

consumption of compressed air systems in China is the following amount:

! ! ! !

If we assume that compressed air systems account for 10% of industrial electricity consumption in

China, we get the following amount (industry consumes 70% of China´s electricity [Abdelaziz et. al

2011]):

! ! !

3.3 Australia, Malaysia and South Africa CAS electricity consumption

Compressed air systems in Australia account for 10% of industrial electricity consumption [AMEI of

Australia]. Australia’s electricity consumption was 222 TWh in 2007 [CIA - The World Factbook,

Australia] and industry consumes 50% of electricity in Australia [Hickling 2006]. So the size of

Australia’s industrial compressed air systems electricity consumption is the following:

Copyright © 2011 Enersize Ltd! 10

! ! !

South Africa’s compressed air systems account for 9% of industrial electricity consumption [Marais

et. al 2009]. South Africa's electricity consumption in 2007 was 215.1 TWh [CIA - The World

Factbook, South Africa], the industrial sector consumes 37.7% and mining consumes 15% of

electricity [Staatskoerant 2008]. Mining is one of the main industries in South Africa [Wikipedia -

Economy of South Africa 2010], so in the following calculation industrial and mining electricity

consumption are combined:

! !

Malaysia’s compressed air systems account for 9% of the total industrial energy use [Saidur et al.

2009]. Malaysian industry used 38.6% of all energy in 2005, which was 175.2 TWh [Ninth Malaysia

Plan]. By this estimate, Malaysian compressed air systems consume the following amount of

electricity:

! ! ! !

3.4 Estimations for Brazil, Russia, India and Japan CAS electricity consumption

We should take a look at electricity consumption in 2007 in three of the four BRIC countries and

also Japan. The BRIC countries are Brazil, Russia, India and China. China was already discussed

in an earlier section. BRIC is a term which Jim O`Neill, chief economist at Goldman Sachs, coined

in 2001 in the paper “Building Better Global Economics BRICs” [Kowitt 2009]. If we look at

electricity consumptions in 2007 in the above four countries and their industries and use estimates,

CAS electricity consumption is 10% of industrial electrical consumption and we get the following

table (Table 3):

Copyright © 2011 Enersize Ltd! 11

Tot. el. consumption

(TWh)

El. consumption in

industry (%)

CAS electricity

consumption (TWh)

Brazil 412.69 49 20.2

Russia 897.68 50 44.9

India 609.74 45 27.4

Japan 1082.72 33 35.7

Table 3. Estimates for CAS electricity consumption in Brazil, Russia, India and Japan. Produced

from Mizera 2010.

Earlier sections have estimated electricity consumption of compressed air systems for the following

areas: China 323.2 TWh or 240.7 TWh, the European Union 122.8 TWh, the United States 98.7

TWh, Russia 44.9 TWh, Japan 35.7 TWh, India 27.4 TWh, Brazil 20.2 TWh, Malaysia 15.8 TWh,

Australia 11.1 TWh, South Africa 10.2 TWh. Together with China’s 323.2 TWh, this amounts to 710

TWh. If China’s portion is 240.7 TWh, then 710 TWh decreases to 627.4 TWh.

With a rough calculation that the global electricity consumption of compressed air systems is 10%

of industrial electricity consumption, we arrived at the previously mentioned 764 TWh. It seems that

764 TWh might not be too high an estimate for the global electricity consumption of compressed

air systems because a lot of countries are missing from the above calculations.

Copyright © 2011 Enersize Ltd! 12

4 Global saving potential of industrial compressed air systems

The previous section discussed annual electricity consumption of industrial compressed air

systems. A very common estimate for long-term savings potential of industrial compressed air is

found in Radgen & Blaustein’s research. They found that the typical savings potential in

compressed air systems is 32.9%. This savings potential can be achieved over a 15-year period,

because they assumed that the large majority of system components are replaced within this time

frame [Radgen & Blaustein 2001]. We use 764 TWh of electricity consumption to arrive at the

estimate for the total savings potential::

! ! !

and in a 15-year period this is annually:

! ! !

By assuming an electricity price of 0.08 "/kWh, we arrive at an annual savings potential in terms of

euro:

! !

And with an electricity price of 0.05 "/kWh the savings potential is:

! !

Because the average cost of industrial electricity consumption is 0.09–0.12 "/kWh [#e$lija et. al

2009], we should also calculate the savings potential with 0.10 "/kWh as the electricity price:

! !

Regardless of the electricity price, the annual savings potential is significant.

Copyright © 2011 Enersize Ltd! 13

4.1 Saving potential versus compressor electricity consumption

The annual savings potential is huge in electricity consumption. By calculating how many

compressors we need to consume 16.75 TWh of electricity annually, we get a realistic comparison

to understand the size of the annual savings potential. Let’s take a look at the electricity

consumption of one 100 kW compressor and one 200 kW compressor, which are both running

approximately 8,000 hours:

! !

! !

With 10,469 200 kW compressors, we get 16.75 TWh annual electricity consumption:

! ! ! !

If we use only 100 kW compressors, we need to double the number of compressors for 16.75

TWh annual electricity consumption:

! ! ! !

The conclusion is that we need 10,469 200 kW compressors or 20,938 100 kW compressors, and

the compressors are running for 8,000 hours annually to get 16.75 TWh of electricity consumption.

From this we can think that if we could improve the energy efficiency of compressed air systems

annually to 16.75 TWh, we would make huge savings on the electricity consumption of a huge

number of compressors. In the future, if we could have energy efficient industrial compressed air

systems according to, for example, the BAT level (a situation where global CAS energy efficiency

improvements would lead to 251.3 TWh of electricity energy savings) (see more information on

BAT in CAS EE - MEH Part 2) we would save an enormous amount of electricity. Of course, this

means that we need to change our views of compressed air systems towards more energy

efficient thinking. We would have to start to systematically improve energy efficiency and, as

Radgen & Blaustein have said, we could achieve this savings potential in a 15-year period,

because with this time frame the large majority of system components will be replaced.

Copyright © 2011 Enersize Ltd! 14

4.2 Saving potential versus electricity production of wind turbines

We can compare the annual savings potential of compressed air systems, for example, to

renewable energy sources. In this section we are looking at wind turbines. If 16.75 TWh must be

produced annually with 2 MW or 3 MW wind turbines, the needs for the number of wind turbines is

remarkable. Typically, wind turbine power capacity factors are 20–40% [RERL].

One 2 MW wind turbine produces the following amount of electricity annually with a capacity factor

of 30%:

! ! !

One 3 MW wind turbine produces the following amount of electricity annually with a capacity factor

of 30%:

! ! !

The number of wind turbines needed for creating 16.75 TWh of electricity with 2 MW wind turbines

is:

! ! ! ! !

And for creating 16.75 TWh of electricity with 3 MW wind turbines the number is:

! ! ! ! !

If we increase the energy efficiency of industrial CAS for 16.75 TWh annually, we would not need

the electricity production of 3,187 2 MW wind turbines or 2,124 3 MW wind turbines.

Copyright © 2011 Enersize Ltd! 15

4.3 Saving potential versus coal based electricity production

Comparing the 16.75 TWh annual savings potential to the amount of coal that is needed to

generate this annual electricity in a coal-fired power station, reveals the huge amount of coal

needed. We need to know what the coal energy density is and what the efficiency of coal power

plants is and how much direct CO2 emissions are created by burning coal to produce 1 kWh of

electricity. The approximate coal energy density is 24MJ/kg [Fisher 2003] and in kWh/kg the

density is:

! ! ! !

Coal’s useful energy output is typically 30% of the energy density 6.67 kWh/kg [Wikipedia – Coal

2010]:

! ! ! ! !

Burning of 1 kg of coal produces 2 kWh of electricity. With the following calculations it is possible

to see how many kilograms of coal we need to produce 16.75 TWh of electricity:

! !

Because 1 kg of coal releases 2.93 kg of CO2 emissions, and burning of 1 kg of coal produces 2

kWh electricity, the direct CO2 emissions for 1 kWh are [Wikipedia - Coal 2010]:

! ! ! ! !

16.75 TWh of electricity generated in coal-fired power plants creates the following amount of CO2

emissions:

! !

Copyright © 2011 Enersize Ltd! 16

ConclusionsCompressing atmospheric air into compressed air is expensive because of thermodynamics, and

the way of using this expensive compressed air in industry is very inefficient. However, compressed

air has the capability to do the work and this characteristic is so outstanding and vital everywhere

in industry around the world that we have a situation where compressed air systems are very

popular despite the total inefficiency of compressed air production. If somebody would have

invented a compressed air system for the first time in the 21st century, it would probably not have

been so commonly used as it is now.

There has been a lot of research into realizing the energy efficiency potential of compressed air

systems. The most extensive research has been done in the European Union and the United

States. The most recent wide ranging research is that of Saidur et al. Their literary survey contains

very good research into compressed air energy efficiency. According to all the research, there

should be an awareness concerning the energy efficiency of compressed air systems. How well is

this awareness implemented in daily actions in industry on the shop floor level? Not so well.

With calculations for the electricity consumption of global compressed air systems, we improved

our understanding of the potential energy efficiency of compressed air systems. It seems that

today China is a major player in industrial compressed air systems. China’s compressed air

systems consume over 9% of its electricity. This is lot of more than the European Union and the

United States together.

With a very well known long term energy efficiency potential of 32.9%, there is over 250 TWh of

savings potential in global compressed air systems. This savings potential is possible to achieve

within a 15-year period, because within this time frame the large majority of system components

will be replaced. The annual compressed air systems savings potential of 16.75 TWh is

comparable to the annual electricity production of 3,187 2 MW wind turbines or 2,124 3 MW wind

turbines.

It is a fact that the energy cost is a major component of a compressed air system. In this

document we have seen that only a small fraction of consumed energy gets a point of use. It is

also a fact that a compressed air system typically uses a lot more energy than is needed to meet

the demand. Researchers have argued that there is 5–50% potential to increase energy efficiency,

depending on the site. The method of using expensive compressed air in industry is very inefficient.

Calculations of the electricity consumption of compressed air systems and savings potential back

up the argument for accepting and understanding the fact that compressed air is an expensive

utility which is used very inefficiently in industry.

Copyright © 2011 Enersize Ltd! 17

ReferencesAbdelaziz, E., Saidur, R., Mekhilef, S., 2011. A review on energy saving strategies in industrial

sector. Renewable and Sustainable Energy Reviews 15 (2011) 150-168.

Air and Mine Equipment Institute of Australia. Efficient compressed air systems. Referred

22.12.2010 http://www.energyrating.gov.au/library/pubs/aircomp-brochure.pdf

Airila, M., Hallikainen, K., Kääpä, J., Laurila, T., 1983. Hydor: Kompressorikirja. Korpivaara Oy

Hydor Ab. ISBN 951-99433-8-2. Helsinki 1983, KK laakapaino.

Aspen Systems Inc. 2003. Final Report, Compressed Air Systems Market Assessment in the

Public Service Electric and Gas Service Territory; Aspen Systems Corporation. July 7, 2003.

CIA - The World Factbook. Australia. Referred 28.12.2010. https://www.cia.gov/library/

publications/the-world-factbook/geos/as.html

CIA - The World Factbook. China. Referred 28.12.2010. https://www.cia.gov/library/publications/

the-world-factbook/geos/ch.html

CIA - The World Factbook. South Africa. Referred 29.12.2010. https://www.cia.gov/library/

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