EXERGY ANALYSIS OF CEMENT PLANT : A REVIEW

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Oct 27, 2013 (3 years and 10 months ago)

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VSRD International Journal of Mechanical, Civil, Automobile and Production Engineering, Vol. 3 No.

7

July
2013

/
271

e
-
ISSN :
2249
-
8303, p
-
ISSN : 2319
-
2208
©
VSRD

International Journals

:
www.vsrdjournals.com

REVIEW
ARTICLE

EXERGY

ANALYSIS OF CEMENT
PLANT

:

A
REVIEW

1
Shrikant Kol
*

and
2
Alok Chaube

1
Research Scholar
,
2
Professor,
1,2
D
epartment of
Mechanical
Engineering
,

Jabalpur Engineering
College
,
Jabalpur, Madhya Pradesh
,
INDIA.

*
Corresponding
Author:

kolshrikant@gmail.com

ABSTRACT

The cement production has one
of the

most intensive industry in the world .In order to produce raw materials preparation, clinker, preheater
and rotary kiln are

widely used in cement plant. Therefore, many studies on the efficient use of energy were carried out in the past.
Moreover these study
, w
hich are based on exergy analysis, focus on cement plant application only. This paper review exergy analysis,
exergy b
alance, and exergy efficiency for cement plant. In this review paper energy uses at different section of cement plant, specif
ic
energy consumption, cement plant production process. Coal contribute major share of fuel used in cement plant. However, along

wi
th
conventional fuels, industries are moving towards the use of alternative fuels to reduce

environmental pollution. It is

reported that cement
industries are moving from wet process to dry process as it consume less energy compared to wet process. The kil
n has capacity 600 ton
-
clinker per day this plant use in dry type rotary kiln system. It was found that about 40% of the total input energy was bein
g lost through
hot fuel gas, cooler stack and kiln shell. Some possible way t
o recover the heat losses by us
ing
waste recovery heat generation system, that

recovers approximately 15% of the total input energ
y.

Keywords

:

Cement Plant, Exergy Analysis, Waste Heat Recovery, Rotary Kiln.


1.

INTRODUCTION

Extensive application of exergy analysis can lead to reduce
the natural resources use
and thus to decrease the
environmental pollution. T
he
main purpose of exergy
analysis is detected and asses quantitatively the
thermodynamic analysis imperfections causes of thermal
chemical processes. The exergy method of thermodynamic
analysis is based u
pon both the first and the second laws of
thermodynamic together, while the energy analysis is based
upon the first law only .It is a feature of the exergy concept
to allow quantitative assessment of energy degradation.

The
energy consumption is ranged fro
m 4 to 5 GJ/ton of cement
was indicated by studies. A share of energy consumption of
cement industry in
the industrial field is
12% to 15%. And
it represents 2% to 6% of total energy co
nsumption in terms
of
countries

[
1]
.

The process of manufacture of ceme
nt can be divided into
three basic steps, preparation of raw

materials,
pyr
oprocessing to produce clinker
and grinding and
blending clinker with other products

to make cement. The
raw materials obtained from the quarry are crushed, ground
and mixed

as slur
ry in the wet process and a powder in the
dry process. This mixture is then fed into a

calciner and
preheater

before being fed into the kiln

for pyroprocessing
(clinker formation). The

kiln reaches

temperatures greater
than 1400ºc
. The clinker nodules prod
uced and any
additives

are then ground to the desired fineness in the
cement grinder. Pyroprocessing consumes

99% of the fuel
energy while electricity is mainly used to operate both raw
materials (33%) and

clinker (38%) crushing and grinding
equipment. Pyr
oprocessing requires another 22% of the

electricity hence it is the most energy intensive step of the
production process
.

2.

EXERGY SYSTEM

The
total exergy of a system can be divided into four
components, namely; physical exergy, Ex
ph
, kinetic exergy,
potent
ial exergy and chemical exergy .

In a cement
production process, however, the kinetic exergy and
potential exergy are n
egligible compared to other
two

[
9]
.

The specific physical exergy can be expressed as:

Ex
ph

= (h


h
o
)



T
o

(S


S
o
)



… (1)

Assuming ideal gas flow with constant specific heat, we
have;

Ex
ph

= C
p

(T


T
o
)


T
o

(C
p

ln T/T
o
-
R ln P/P
o
)

… (
2)

F
or the solid and liquid streams :

Ex
ph
= (C
p

(T
-
T
o
)


T
o

ln T/T
o
)

v (P
-
P
o
)


… (3)

Assuming constant specific volume, v, at T
o

with neg
lect of
change in pressure, the last items in equations (2) and (3)
can be neglected. Chemical exergy is the maximum
possible work that can be acquired during a process that
brings the system from environmental condition (T
o

, P
o
) to
the dead state (T
o
, P
o
,
μ
oi
) . The chemical exergy of the
ideal gas and liquid mixtures is computed from:

ex
ch

= sum of xi (ex
choi

+ RT
o

ln(x
i
))

Where xi is the molar ratio of the species i, and ex
choi

is the
standard chemical exergy.

Shrikant Kol and Alok Chaube


VSRDIJMCAPE, Vol. III (
V
I
I
),
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2013 /
272






Fig. 1 :
Schematic of the Maihar Cement Plant


Three exergy efficiencies of a cement kiln plant are defined
as
follows:

Exergy efficiency,



= clinker formation exergy


exergy
input.

It corresponds to the net thermal efficiency,



,
defin
ed as
the fraction of fuel heat that is consumed as

l
atent heats of
various clinker forming reactions
.


Anergy,

,

defined as the ratio of the exergy loss to the
exergy input. It is expressed as follows:



=


/



The exergy
destroyed or the irreversibility of a system, I
sys
,
is given as:

I
sys

= ex
input




ex
output

= To S
gen

Where
S
gen

is the entropy generated

3.

LITERATURE REVIEW

Shaleen Khurana, Rangan Banerjee and Uda Gaitonde
studied (2002)


The cement industry is an intensive
industry consuming about 4GJ per to
n of cement produced.
A t
hermodynami
c analysis for cogeneration

plant

using the
waste h
eat

st
ea
m

is not easily available
.
Data from a
working 1 Mt per annum plant in India was used to

arriv
e at
an energy balance for the
pyroprocessing unit. A steam
cycle is selected to recover the heat from the streams using
a waste heat recovery steam generator and it is estimated
that about 4.4 MW of electricity can be generated. This
represented an

improvement of about 10% in terms of
primary energy efficiency of the plant. Around 30% of the

energy requirement of the plant can thus be met from the
cogeneration system. Extrapolating to

the cement
production in India this offers a potential of about 45
0 MW
and is an economically

viable option for cement
plants

[
2]
.

Unal Camdali and Ali Erisen studied (2004)

-

Cement
production facilities are often located in ru
ral areas and
close to quarries

where the raw

materials required for
cement production are
present, i.e. limestone and shale.

Although energy analysis, based on the first law of
thermodynamics, is used to reduce heat losses or

enhance
heat recovery, it does not give any information on the
degradation of energy that occurs in the

process. Exergy
analysis, based on the first and second laws of
thermodynamics, facilitates improvement of

the operation
or technology by clearly indicating the locations of energy
degradation in the process. In this study, the applications of
energy and exergy analyses a
re examined for a dry system
rotary burner

(RB) with pre
-
calcinations in a cement plant
Shrikant Kol and Alok Chaube


VSRDIJMCAPE, Vol. III (
V
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),
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273



of an important cement producer in Turkey. The RB
includes

thermal and chemical
processes

[
3]
.



Heat losses by conduction, convection and radiation
from the RB are about

3% of the heat

coming into the
system. Although this ratio is seen to be low, the total
amount is very considerable

from the viewpoint of
process duration. So, it is significant to reduce heat
losses by using

insulation materials for the RB.



Waste air als
o transfers a very important amount of
energy from the RB. Accordingly, the

amount of air
coming into the RB should be controlled.



The percent of lost exergy is 35.6% of the total
exergies. This is the highest ratio after the exergy

percent of stack gases.

The exergy losses in the RB are
caused by chemical reactions, forming of

clinker, heat
transfer and other reasons.



Stack gases and the waste air in them have a
considerable amount of exergy. It is possible to use

the
unused portion of this energy in other

applications.



Although the energy efficiency is about 97%, the
exergy efficiency is 64.4%. So, it is seen that

exergy
analysis accounts for the operation, indicating the
locations of energy degradation in

the process.



The exergy efficiency at another plan
t in Tur
key was
obtained to be 64.5%
. This value is

close to the value
obtained in this study

Tahsin Engin and Vedat Ari studied (2004)

-

A

detailed
energy audit analysis

which can be directly

applied to any
dry kiln system
has been

made for a specific ke
y cement
plant. The distribution of the input heat energy to the
system

components showed good agreement between the
total input and output energy and gave significant

insights
about the reasons for the low overall system efficiency.
According to the resul
ts

obtained, the system efficiency is
48.7%. The major heat loss sources have been determined
as kiln

exhaust (19.15% of total input), cooler exhaust
(5.61% of tota
l input) and combined radiative
and

convective heat transfer from kiln surfaces (15.11% of t
otal
input). For the first two losses, a

conventional WHRSG
system is proposed. Calculations showed that 1 MW of
energy could be

recovered. For the kiln surface, a
secondary shell system has been proposed and designed. It
is

believed that the use of this s
ystem would lead to 3 MW
of energy saving from the kiln surface.

Hence, the total
saving for the whole system has b
een estimated to be nearly
4 MW

which

indicates an energy recovery of 15.6% of
the
total input energy. The pay
back period for the two

systems

is expected to be less than 1.5 yr
[3]
.

Jiangfeng Wang and Yiping Dai studied (2008)
-

The
cement production is an energy intensive industry with
energy typically accounting for 50

60% of

the production
costs. In order to recover waste heat from the preheat
er
exhaust and clinker cooler

exhaust gases in cement plant,
single flash steam cycle, dual
-
pressure steam cycle, organic
Rankine cycle

(ORC) and the Kalina cycle are used for
cogeneration in cement plant. The exergy analysis for each
cogeneration

system i
s examined

and a parameter
optimization for each cogeneration system is achieved by

means

of genetic algorithm (GA) to reach the maximum
exergy efficiency. The optimum performances for

different
cogeneration systems are compared under the same
condition. T
he results show that the exergy

losses in
turbine, condenser, and heat recovery vapor

generator are
relatively large

and reducing the

exergy losses of these
components could improve the performance of the
cogeneration system. Compared

with other systems

th
e
Kalina cycle could achieve the best performance in cement
plant

[
4]
.

M.B. Ali ,R saidur and M.S. Hossain studied (2010)
-

It
has been found that cement manufacturing is an energy
intensive

industry consuming about 12

5% of total
industrial energy

use. Th
erefore, sizeable amounts of
emissions are released to the

atmosphere as a result of
burning fossil fuels to supply energy

requirements of these
industries. Emissions are produced from

the calcinations
process as well. For these reasons, special attention

is
needed on the
clinker production to reduce CO
2

emissions.

It was identified that there are several effective measures
those

can be applied in cement industries to achieve
emissions reductions

target. One of the most cost
effective
ways is to capture CO
2

from the flue gases and store it away
into the soil or ocean. This

can reduce carbon emissions by
as much as 65

70%. By reducing

clinker/cement ratio with
the ad
dition of various additives, CO
2

emissions can be
reduced substantially. However, it was found

that

the
substituting fossil fuels with alternative fuels may play a
major

role in the reduction of carbon dioxide emissions.
These measures

will reduce environmental impacts along
with the overall of quality

cement production
[5]
.

N.A. Madlool and R. Said
ur studied (2011)

-

The exergy
analysis, exergy balance, and exergetic efficiency in the

cement industry.

It is found that the implementation of exergy analysis on the
production line is a very efficient way for improving the
performance of the system and
reduction of energy costs.



In spite of the highest energy efficiency for raw mill
and farina mill, the exergy efficiency remains lower
than 26%. On the other hand, the trass mill has the
lowest exergy efficiency within the cement plant.



The exergy efficien
cies and irreversibility vary from 18
to 49% and 136.22 to 607.89 respectively and the
efficiency’s values of exergy at varying dead
-
state
temperatures in cement industry are proportional
inversely with dead
-
state temperatures.



The main irreversibility sou
rce in the cement industry
is the
rotary kiln

whereas the raw feed pre
-
heating
causes the lowest irreversibility within the cement
plant.



In the cogeneration systems, the biggest exergy loss
occurs in the turbin
e expansion process

and the
condensation proc
ess represents the second process of
Shrikant Kol and Alok Chaube


VSRDIJMCAPE, Vol. III (
V
I
I
),
July
2013 /
274



largest exergy loss in the single fly ash and dual
-
pressure cycles. On the other hand, the condensation
process and represents the largest exergy loss and the
heat addition process in SP boiler is the second process
of
the largest
exergy loss in the ORC

while the
absorption process considers the largest exergy loss
and the heat addition process in the kalian
cycle

[
6]
.

N.A. Madlool and R.
saidur studied

(2011)

-

The cement
sub
-
sector consumes approximately 12

15% of tota
l
industrial energy use. It has been observed that there are
many economically viable

technologies available to reduce
energy use and emissions

associated with the burning fuel
to produce electrical energy.

However, international,
regional and local
experiences indicate

that due to lack of
technical knowledge of the staff about the

energy
-
efficiency
measure, lack of government policies, plant

specific

operational conditions, investors’ preferences, and high

initial capital costs despite the fact that
the payback period
of

the technology is short, these available technologies are
not

fully utilized. Therefore, awareness campaign through
mass

media, information dissemination through different
innovative

approach should be devised for effective energy
eff
iciency

practices for an industrial
facility

[
7]
.

Wendell
de Queiroz Lamas, Jose Carlos Fortes Palau
(2012
)

Cement is the main component of concrete which
is in turn ,the second most consumed material on earth in
addition the cement industry is one of th
e most intensive
energy consumptions. The modern plants often have
nominal production capacity exceeding one million tons per
year. To produce one ton of cement, you need the
equivalent of 60
-
130kg of fuel and 110kwh of electricity.
Due to the large consum
ption of energy which represents
over 30


of the total production cost for the cement
industry, the reduction in spending on energy inputs is a
major motivation for technology advances in the production
process of cement. To reduce the costs of fossil fuel

consumption (non renewable source), the technique of co
-
processing has been employed for introducing alternative
fuel as part of the manufacturing process. This technique
provides a lower cost of production, introducing fuel waste
from different industria
l activities, besides contributing to
the reduction of environmental liabilities; they generate
waste when discarded in appropriate places.

It

is

evident

that
the

cement

industry

sector

highly intensive

in

energy

consumption

and

should

be

consider
ed
in

studies

on

energy
planning, especially

with

the

change
s in
its

energy

matrix

,which

has

occurred

continuously

since

the

oil

crisis

in 70
year
s
still

that

this

change

is

very

heterogeneous

when

one

considers

each

manufactures

cement. The ecological

analysis

is

done

through

comparison

between

ecological

efficiency,

pollution

indicator and values

for

CO
2

equivalent

from

cement

industry

rate
before

and

after

adoption

of

waste

reuse
s

[
1]
.

4.

CONCLUSION

Following conclusions can be drawn from this
study:



The data
collected from a1Mt per annum working
cement plant was used to arrive at an energy balance
for the pyroprocessing unit. The waste heat was
estimated at 35


of the energy input. A retrofit steam
cycle was selected and for the considered plant about
4.4 MW o
f power can be generated from waste heat
streams. This represents an improvement of about 10


in terms of primary

energy efficiency of the
plant

[
1]
.



Exergy analysis based on the first law and second law
of thermodynamic, facilities improvement of the
oper
ation or technology by clearly indicating the
location of energy degradation in the process. In this
study, the applications of energy and exergy analysis
are examined for dry system rotary burner with pre
-
calcinations in cement plant of an impo
rtant cemen
t
producer in
Turkey

[
2]
.



The exergy analysis for each co
-
generation system is
examined and a parameter optimization for each
cogeneration system is achieved by means of genetic
algorithm to reach the maximum exergy efficiency
.The optimum performances for

different cogeneration
systems are compared under same condition.



Ecological efficiency

methodology

provides

a

way

to

show

that waste material
s

are

a

viable

source

of

alternative

fuel

to

kilns. Despite tires

incineration,

this

policy

maintains

the

same

efficiency

because

it

policy

associated

to

technologies

of

gases purification and

reuse

of

these

gases

in

cogeneration. i.e.
CH
4

as
combustion fuel

in

engines

or

reuse
s
of

gases

heat

into

heat recovery steam

generator

(HRSG)

systems

[
3]
.

5.

REFERENCES

[1]

Wendell de Queiroz Lamas, Jose Carlos Fortes Palau, Jose
Rubens de Camargo. Waste materials co
-
processing in
cement industry: Ecological efficiency of waste reuse.
Renewable and Sustainable Energy Reviews19 (2013) 200
-
20
7

[2]

Shaleen Khurana, Rangan Banerjee.
Energy balance and
cogeneration for a cement plant. Applied Thermal
Engineering 22 (2002) 485

494

[3]

Unal Camdali Ali Erisen. Energy and exergy analyses in a
rotary burner with pre
-
calcinations in cement production.
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3017

3031

[4]

Zafer Utlu, Ziya Sogut, Arif Hepbasli, Zuhal Oktay. Energy
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2489

[5]

G. Kabir, A.I. Abubakar, U.A. El
-
Nafaty.

Energy audit and
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unit

of a
typical dry process cement plant. Energy 35 (2010) 1237

1243

[6]

Tahsin Engin,Vedat Ari. Energy auditing and recovery for
dry type cement

rotary kiln systems
––
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Conversion and Management 46 (2005) 551

562

[7]

M.G
. Rasul,

W.
Widianto, B. Mohanty. Assessment of the
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2965

Shrikant Kol and Alok Chaube


VSRDIJMCAPE, Vol. III (
V
I
I
),
July
2013 /
275



[8]

Rachel Woodward, Noel Duffy. Cement and concrete flow
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-
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[9]

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Applied Energy 86 (2009) 941

948

[10]

N. Hamidi, M. Omidvari, M. Meftahi.
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[13]

Hrvoje Mikulcic
,

Milan Vujanovic
,

Neven Duic.
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the CO2 emissions in Croatian cement industry,

Applied
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[14]

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Energy Procedia 4 (2011) 2716

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[15]

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Wolfgang Krumm.


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International
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-
1689





Shrikant Kol and Alok Chaube


VSRDIJMCAPE, Vol. III (
V
I
I
),
July
2013 /
276