a research on exergy consumption and potential of total co2 emission in the turkish cement sector

9
A research on exergy consumption and potential of total CO 2 emission in the Turkish cement sector M. Ziya SÖG ˘ ÜT Technical Sciences and Computer Applications Center, Military Academy, Ankara, Turkey article info Article history: Received 20 August 2010 Received in revised form 4 November 2011 Accepted 4 November 2011 Available online 14 December 2011 Keywords: Cement Clinker Exergy analysis Efficiency Carbon dioxide emissions abstract In this study, exergetic efficiency of Turkish cement production and CO 2 emissions caused by the sector due to exergetic losses and environmental effects are examined, considering the clinker production between 1999 and 2007. As a first step, exergy analyses based on dead state temperature and production data of clinker are carried out according to the second law of thermodynamics. Consequently, CO 2 emis- sions of the clinker production according to exergy losses, improvement and anergy potentials are deter- mined. Exergy efficiency of the kiln and exergetic improvement potential are found as 43.04% and 123.29 10 6 GJ/h respectively on average. In this system, CO 2 emissions caused by exergetic losses are calculated as 75.18 10 6 kg/h, 25.06 10 6 kg/h and 81.45 10 6 kg/h respectively on average for the coal mixture, natural gas and fuel-oil. At the end of the study, the present technique is suggested as a useful tool to improve energy policies and provide energy conservation measures, especially in this type of industrial processes. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Cement is an important construction ingredient. As in other energy-intensive industries, issues of productivity, growth and model formation in the cement sector are issues discussed around the world, including Turkey, from various perspectives. The ce- ment sector is one of the most energy-intensive production sec- tors. Recently, in this sector, there has been an increasing interest about using energy and exergy modeling for energy-utili- zation assessments in order to achieve energy savings, and hence, financial and most importantly environmental benefits. Exergy analyses are vitally important to improve the effectiveness of the production process and to evaluate the energy-saving technologies in the cement sector [1]. In Turkey, energy consumption of the industrial sector is expected to be 56% of the total consumption by 2010 [2]. As the energy consumption and its costs keep increasing, energy saving studies are becoming more and more important. The ratio of energy costs, an important parameter in the total production cost, has reached 50%. Energy cost of cement sector has the highest pro- portion with 55%, compared with other industrial sectors [3]. The energy consumption costs of industrial sectors in Turkey have been given in Fig. 1. Cement producing sector has been growing steadily since 2000, peaking in 2007 with an approximate average 8%. Production rose to 2.77 billion tons, following the 12% increase of 2006 [4]. Annual growth in this sector between the years 2000 and 2007 is shown in Fig. 2. Turkish cement sector has an important potential with its production capacity among the world and Europe countries. In the production cement, Turkey has the tenth place in the world and fourth in Europe after Italy, Germany and Spain [5]. According to several research results energy consumption per ton of cement is between 4 and 5 GJ/ton. Energy consumption share of the cement sector in industry is between 12% and 15%. In terms of total energy consumption, this share changes between 2% and 6% [6]. Electric and heat energy based on fossil fuel such as coal and natural gas are energy resources used commonly in cement production. Electric energy is used for the product flow and rotating the ball mill as well as obtaining cement from grind- ing raw material process. Dispersion of energy consumption in this industrial field is given in Fig. 3. The consumption rate of fossil fuel as a source of heat energy is 92% in cement production. Electric energy forms the remaining rate of consumption [7]. In clinker production, alternative fuels such as coal, lignite, import coal, fuel-oil, or natural gas are sources of heat energy in rotary kiln processes. In other processes except rotary kiln, waste gas and dust mixture coming from rotary kiln are used as the sources of heat energy. 60% of the electricity used in production is consumed by raw material and cement grinding sections [6]. Cement production plants use dry or wet systems in their pro- duction methods. In Turkey, production is made using dry system 0196-8904/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2011.11.004 Address: Technical and Computer Applications Center, Army Academy, Ankara, Turkey. Tel.: +90 542 553 99 81. E-mail address: [email protected] Energy Conversion and Management 56 (2012) 37–45 Contents lists available at SciVerse ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman

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Energy Conversion and Management 56 (2012) 37–45

Contents lists available at SciVerse ScienceDirect

Energy Conversion and Management

journal homepage: www.elsevier .com/ locate /enconman

A research on exergy consumption and potential of total CO2 emission in theTurkish cement sector

M. Ziya SÖGÜT ⇑Technical Sciences and Computer Applications Center, Military Academy, Ankara, Turkey

a r t i c l e i n f o

Article history:Received 20 August 2010Received in revised form 4 November 2011Accepted 4 November 2011Available online 14 December 2011

Keywords:CementClinkerExergy analysisEfficiencyCarbon dioxide emissions

0196-8904/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.enconman.2011.11.004

⇑ Address: Technical and Computer Applications CeTurkey. Tel.: +90 542 553 99 81.

E-mail address: [email protected]

a b s t r a c t

In this study, exergetic efficiency of Turkish cement production and CO2 emissions caused by the sectordue to exergetic losses and environmental effects are examined, considering the clinker productionbetween 1999 and 2007. As a first step, exergy analyses based on dead state temperature and productiondata of clinker are carried out according to the second law of thermodynamics. Consequently, CO2 emis-sions of the clinker production according to exergy losses, improvement and anergy potentials are deter-mined. Exergy efficiency of the kiln and exergetic improvement potential are found as 43.04% and123.29 � 106 GJ/h respectively on average. In this system, CO2 emissions caused by exergetic losses arecalculated as 75.18 � 106 kg/h, 25.06 � 106 kg/h and 81.45 � 106 kg/h respectively on average for the coalmixture, natural gas and fuel-oil. At the end of the study, the present technique is suggested as a usefultool to improve energy policies and provide energy conservation measures, especially in this type ofindustrial processes.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Cement is an important construction ingredient. As in otherenergy-intensive industries, issues of productivity, growth andmodel formation in the cement sector are issues discussed aroundthe world, including Turkey, from various perspectives. The ce-ment sector is one of the most energy-intensive production sec-tors. Recently, in this sector, there has been an increasinginterest about using energy and exergy modeling for energy-utili-zation assessments in order to achieve energy savings, and hence,financial and most importantly environmental benefits. Exergyanalyses are vitally important to improve the effectiveness of theproduction process and to evaluate the energy-saving technologiesin the cement sector [1].

In Turkey, energy consumption of the industrial sector isexpected to be 56% of the total consumption by 2010 [2]. As theenergy consumption and its costs keep increasing, energy savingstudies are becoming more and more important. The ratio ofenergy costs, an important parameter in the total production cost,has reached 50%. Energy cost of cement sector has the highest pro-portion with 55%, compared with other industrial sectors [3]. Theenergy consumption costs of industrial sectors in Turkey have beengiven in Fig. 1.

ll rights reserved.

nter, Army Academy, Ankara,

Cement producing sector has been growing steadily since 2000,peaking in 2007 with an approximate average 8%. Production roseto 2.77 billion tons, following the 12% increase of 2006 [4]. Annualgrowth in this sector between the years 2000 and 2007 is shown inFig. 2. Turkish cement sector has an important potential with itsproduction capacity among the world and Europe countries. Inthe production cement, Turkey has the tenth place in the worldand fourth in Europe after Italy, Germany and Spain [5].

According to several research results energy consumption perton of cement is between 4 and 5 GJ/ton. Energy consumptionshare of the cement sector in industry is between 12% and 15%.In terms of total energy consumption, this share changes between2% and 6% [6]. Electric and heat energy based on fossil fuel such ascoal and natural gas are energy resources used commonly incement production. Electric energy is used for the product flowand rotating the ball mill as well as obtaining cement from grind-ing raw material process. Dispersion of energy consumption in thisindustrial field is given in Fig. 3. The consumption rate of fossil fuelas a source of heat energy is 92% in cement production. Electricenergy forms the remaining rate of consumption [7].

In clinker production, alternative fuels such as coal, lignite,import coal, fuel-oil, or natural gas are sources of heat energy inrotary kiln processes. In other processes except rotary kiln, wastegas and dust mixture coming from rotary kiln are used as thesources of heat energy. 60% of the electricity used in productionis consumed by raw material and cement grinding sections [6].

Cement production plants use dry or wet systems in their pro-duction methods. In Turkey, production is made using dry system

Nomenclature

Cp specific heat capacity (kJ/kg K)ex specific exergy (kJ/kg)_E energy rate (kJ/h)_Ex exergy rate (kJ/h)_I irreversibility rate, exergy consumption rate (kJ/h)h specific enthalpy (kJ/kg)m mass (kg)_m mass flow rate (kg/h)

P pressure (kPa)R gas constant (kJ/kgK)s specific entropy (kJ/kgK)T temperature (�C or K)CO2 carbon dioxide emission (kg CO2/h)_W work rate or power (kJ/h)

IP improvement potential (kJ/h)

Greek lettersgI energy (first law) efficiency (%)gII exergy (second law) efficiency (%)

Indicesph physicalch chemicaldest destroyedgen generationin inputout output0 dead-state or reference environment

38 M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45

with pre-calcinations. In such production systems, energy con-sumption is very high for each process of the production line.When structural features of the parts are investigated, it is ob-served that important amount of energy is lost from surfaces,although proper insulation has been achieved. One of the maingoals of such industry foundations, whose energy inputs are high,is to ensure continuity, quality and low cost for their energy inputs.Studies that aim to make use of the waste energy and increase en-ergy efficiency are being carried out intensively in these processes.

A significant number of studies have been reported in the en-ergy saving field. Among them, there are very important anddeductive papers, indicating both energy efficiency and energysaving potential in the cement industry. Sheinbaum and Ozawa(1998) stated that a decrease at the rate of 28% in energy densityand 17% in carbon dioxide emission which produced by sector isobserved; and all of these decrease results from the use of thewaste heat and conducted process improvement studies [8]. Inthe study conducted by Khuara et al. (2001), in which energy uselevels of Mexican cement industry and carbon dioxide emissionsare examined, some inductions were made pertaining to foundinga cogeneration system, in the light of the findings obtained bymaking energy balance in a cement foundation [9]. In their studies,Worreli and Galitsky (2004) examined the efforts for improvingenergy efficiency in cement production in the USA, and proposedsome energy saving technologies that may play vital role in theclinker process [10]. Camdali et al. (2004) carried out energy andexergy analyses for a dry system rotary burner with pre-calcina-tions in a cement plant of an important cement producer in Turkey.The percent of lost exergy was found as 35.6% of the total exergiesusing the actual values, and the values of the first and second law

5550

303030

2525,1

2015

12,510

7,5

0 10 20 30 40 50 60Ratio of energy cost

CementAmonia

AluminiumSteelGlass

ManurePaper

CeramicsMetallurgy

Textilefood

Refinery

Indu

stri

al S

ecto

r

Fig. 1. Energy cost distribution [2].

efficiencies were compared. As a result of this comparison, energyand exergy efficiencies were 97% and 64.4%, respectively [11].

It is a well known fact that in every part of the production linesin a cement plants, there are high waste energy potentials. In thisstudy, efficiency of cement production taken by reference clinkerproduction between the years 1997 and 2007 and environmentaleffects caused by exergetic losses have been investigated. Firstly,based on the operational data of the Clinker production and annualdead state temperature, exergy analyses have been implementedaccording to the second law of thermodynamics; and the exergeticimprovement and anergy potentials have been calculated. Then,according to average exergy losses, the exergetic improvementand anergy potentials consumed and CO2 emissions of the rotarykiln processes taken exemplary have been fixed for fossil fuel suchas coal, natural gas and fuel-oil. Finally, resulting CO2 emission,fossil fuels like coal, natural gas and fuel-oil are used, has been cal-culated taking exergy losses, improvement and anergy potentialsinto consideration.

2. Cement sector

Turkey is a cement exporting country. In this section of thestudy, present status and future production and consumptiontrends of cement sector is examined. In Turkish cement sector,cement production has an upward trend as of 2001 in parallel withdevelopments of civil sector and the production capacity reached50.7 Mton in 2007. The production capacity is close to 2010 projec-tion of State Planning Agency (DPT). Capacity of clinker productionin 2009 is expected to be 63 Mton with an increase rate of 40%. InTurkey, usage rates of clinker capacity and cement grinding capac-ity reached 89.8% and 67.09% respectively [7,12]. Distribution ofcement and clinker production between 1999 and 2007 years isgiven in Fig. 4. Data concerning the years from 1994 to 2004 areactual production values [13]. For evaluation of projection, the dataconcerning 2004–2013 period are production projections culledfrom ninth development plan of DPT. As for the data about 2013–2020 period are production projections calculated based on rate4.11% annual average envisaged in ninth development plan.According to this approach, capacity of cement production can meetthe demand, provided that grinding capacity 10.03 Mton/yearadded for 2020. According to this data, distribution of Turkeycement projection is given in Fig. 5. In parallel with this, it isobserved that an increase in demand in clinker production will beafter 2015. This demand is estimated to be 9.67 Mton/year at2020. Clinker production projection of Turkey is given in Fig. 6.

CIS: Commonwealth of Independent States

Fig. 2. Cement production of the world between the years 2000 and 2007 [3].

Import coal42%

Petrococ32%

Domestic coal25%

Other fuel1%

1.5 Mton 1.9 Mton

2.5 Mton

0.1 Mton

Fig. 3. Distribution of energy consumption in cement production [6].

05

10152025303540455055

1999 2000 2001 2002 2003 2004 2005 2006 2007Years

Pro

duct

ion

(Mto

n)

Cement

Clinker

Fig. 4. Distribution of cement and clinker production in Turkey between the years1990 and 2007 [12].

0

10

20

30

40

50

60

70

80

Years

Para

met

ers

(Mto

n/ye

ar)

Production 24.42 38.8 53 62.15 76.02

Current plant capacity(Mton/year)

24.42 38.8 53 62.15 65.98

Demand capacity (Mton/yeat) 0 0 0 0 10.04

1990 2004 2010 2015 2020

Fig. 5. Projection of Turkey cement production.

0

10

20

30

40

50

60

70

Years

Clin

ker

prod

uctio

n

(M

ton/

year

)

Production (Mton/year)

Current plant capacity(Mton/year)

Demand capacity(Mton/year)

20.25 32.78 44.17 49.72 58.47

20.25 32.78 44.17 48.8 48.8

0 0 0 0.92 9.67

1990 2004 2010 2015 2020

Fig. 6. Clinker production and projection in Turkey between the years 1990 and2020 [12,13].

M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45 39

2.1. Description of the dry system with pre-calcine cement productionline

Cement production is highly energy intensive and involvesheating, calcining and sintering of blended and ground chemicalcombinations of calcium carbonates (limestone), silica, alumina,iron ore, and small amounts of other materials, which are chemi-cally altered through intense heat to form a compound with bind-ing properties [15].

There is a range of different kiln designs, but all rely on thesame basic processes. Raw feed passing through the kiln is heatedto very high temperatures by burning fuel and is transformed

chemically and physically into a gray pebble-like material calledclinker. Consequently, clinker is ground to produce cement. Themain steps in the cement production studied are illustrated inFig. 7. These steps include mainly raw materials preparation, clin-ker production and the eventual grinding. Raw materials, including

Raw materials preparation

Limestone cyclone Pirite cyclone

Raw mill

Leaking air Gas

farine + humidity + steam + gas + air

Separator Return

Farine cyclones

Pre-heater

Rotary Kiln

Coal cyclones

Primer air

Cooling

Clinker cyclone

Adding

material

cyclones

Cement mill

Cement Cement Cement

Clay cyclone

Trass cyclone

Trass and limestone

Gas

Cyclone Cyclone Cyclone

Fig. 7. Flow diagram of a cement plant process operation line [14].

40 M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45

limestone, chalk, and clay, are mined or quarried, usually at a siteclose to the cement mill. These materials are then ground to finepowder in the proper proportions needed for the cement. Prepara-tion of raw materials involves primary and secondary crushing ofthe quarried material, drying the material, undertaking importantstep in the raw mill to ensure an even distribution of the properlyproportioned components of the raw mix, so that the clinker willbe of uniform quality [16].

The energy consumption in raw materials preparation accountsfor a small fraction of the overall primary energy consumption(less than 5%), although it represents a large part of the electricityconsumption [15]. Clinker is produced by burning a mixture ofmaterials, mainly limestone (CaCO3), silicon oxides (SiO2), alumi-num, and iron oxides. There are four stages in this production:evaporation and pre-heating, calcining, clinkering, and cooling. Inmodern kilns, the raw material is preheated in four to five stagesusing the waste heat of the kiln, or it is pre-calcined.

Evaporation and pre-heating remove moisture and raise thetemperature of the raw mix preparatory to calcining. Calciningtakes place at 800–900 �C and breaks the calcium carbonate downinto calcium oxide and carbon dioxide, which is evolved in the pro-cess. Clinkering completes the calcinations stage and fuses the cal-cined raw mix into hard nodules resembling small gray pebbles.Kiln temperatures in the burning zone range from 1350 �C to1450 �C, and retention times in this zone are 4–6 s. The outputfrom this process, called clinker, must be cooled rapidly to preventfurther chemical changes.

Clinker production is the most energy-intensive step, account-ing for about 80% of the energy used in cement production. Clin-kering is critical to the quality of cement and requires accuratecontrol of the energy input. Insufficient heat will cause the clinkerto be under burnt, containing unconverted lime, and reducing thehydration (setting and hardening) properties of the resulting ce-ment. Excess heat will shorten the life of the refractory bricks lin-ing the kiln, may damage the kiln shell and diminish productreactivity.

The high temperatures required for burning of the raw mix im-ply that the process is energy intensive and electrical energy is re-quired for mixing. The largest energy demand for fuel is forburning of the raw mix [17]. Flow diagram of the rotary kiln pro-cess is illustrated in Fig. 8.

During the final stage of cement production, known as finishmilling, the clinker is ground with other materials (which impartspecial characteristics to the finished product) into a fine powder.Up to 5% gypsum and/or natural anhydrite are added to regulatethe setting time of the cement. Other chemicals which regulateflow ability or air entrainment may also be added. Many plantsuse a roll crusher to achieve a preliminary size reduction of theclinker and gypsum. These materials are then sent through ballor tube mills (rotating, horizontal steel cylinders containing steelalloy balls), which perform the remaining grinding. The grindingprocess occurs in a closed system with an air separator that dividesthe cement particles according to size. Material that has not beencompletely ground is sent through the system again. Once the pro-

C2

C3

C4

C1A-C1B

Farine

Gas to Farine mill

Leaking air

Leaking air

Leaking air

Leaking air

Leaking air Leaking air

Coal mix

Carrier air

Primer air Secondary air

Clinker

F1 F2 F3 F4 Trass mill

Cooling chimney

Leaking air

Rotary burner

Cooling

Preh

eate

r cy

clon

es

Fans

Clinker

Fig. 8. Flow diagram of the rotary kiln process.

M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45 41

duction of cement is complete, the final product is transferred viabucket elevators and conveyors to large storage silos in the ship-ping department. Most of the cement is transported by railway,truck, or barge in bulk or 43 kg (94 pound) multi-layered paperbags. Bags are used primarily to package masonry cement. Oncethe cement leaves the plant, distribution terminals are sometimesused as an intermediary storage prior to distribution. The sametypes of conveyor systems used at the plant, are used for loadingcement at the distribution terminals [18].

3. Theoretical analyses

For a general steady state (and) steady-flow process; the follow-ing balance equations are applied to find the work and heat inter-actions, the rate of exergy decrease, the rate of irreversibility andthe energy–exergy efficiencies [19]. The mass balance equationcan be expressed in the rate form as,

X_min ¼

X_mout ð1Þ

where _m is the mass flow rate, and the subscript in stands for inletand out for outlet. For a general steady state and steady-flow pro-cess, assuming no changes in kinetic and potential exergies, thegeneral exergy balance can be expressed in the rate form as:X

_Exin �X

_Exout ¼X

_Exdest ð2Þ

whereP _Exin is the total input exergy,

P _Exout is the total outputexergy,

P _Exdest is the total exergy destruction in through theboundary of the system. If the Eq. (2) is writed more detail;

X1� T0

Tk

� �_Q k � _W

� �þX

_minðexph;in þ exch;inÞ

�X

_moutðexph;out þ exch;outÞ

¼X

_Exdest ð3Þ

where _Qk is the heat transfer rate through the boundary at temper-ature Tk at location k, _W is the work rate, exph is the physical exergy,exch is the chemical exergy. For a general steady state (and) steady-flow process, exph becomes;

exph ¼ ðh� h0Þ � T0ðs� s0Þ ð4Þwhere s is the specific entropy and the subscript zero indicatesproperties at the dead state of P0 and T0 [20]. The exergy destroyedor the irreversibility may be expressed as follows:

_I ¼ _Exdest ¼ T0S0 ð5Þ

where Sgen is the rate of entropy generation, while the subscript ‘0’denotes conditions of the reference environment [21]. The standardstate of the gas denotes a hypothetical state at P0, T0 when the gasunder consideration has the properties of an ideal gas. The Standardchemical exergy of gaseous reference species can be, therefore, ex-pressed as [22];

_Ech ¼ _mRT0 lnP0

Pkð6Þ

Different ways of formulating exergetic efficiency proposed inthe literature have been given in detail elsewhere [23]. The exer-getic efficiency expresses all exergy input as used exergy, and allexergy output as utilized exergy. Therefore, the exergetic efficiencygII becomes;

42 M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45

gII ¼_Exout

_Exin

ð7Þ

CO2 emission in thermal systems, caused by energy losses, isdependent on the type of fuel used and the waste energy potential.It can be expressed as;

CO2 ¼xCO2

P _Q W

gIð8Þ

where xCO2 is the unit energy CO2 emission coefficient,P _QW is the

amount of total waste energy. In the works where such waste en-ergy is exploited, depending on the recycled energy potential, totalCO2 should be calculated taking CO2 emissions caused by heat boil-ers used in buildings into consideration. Hence, Total CO2 emission(P

CO2) may be expressed as follows;XCO2 ¼ CO2iþ DCO2j

¼ xCO2 iP _Q Wi

gIi

xCO2 jP _Q BWj

gIj

!ð1� wRiÞ ð9Þ

whereP _QBW is total energy of boilers, w is rational exergy effi-

ciency. w is the function among environment temperature, wasteheat and the temperature of water going out from boiler [24].Rational exergy efficiency (w) can be written as;

wRi ¼1� T0

Ta

� �1� T0

Tf

� � ð10Þ

where T0 is the environment temperature, Ta is the temperature ofwaste heat, and Tf is the water temperature of boiler. Van Gool(1997) has also noted that maximum improvement in the exergyefficiency for a process or system is obviously achieved when theexergy loss or irreversibility ð _Exin � _ExoutÞ is minimized [25]. Conse-quently, he suggested that it is useful to employ the concept of anexergetic ‘‘improvement potential’’ when analyzing different pro-cesses or sectors of the economy. Hammond and Stapleton (2001)give this improvement potential in a rate form, denoted IP [26].

IP ¼ ð1� gIIÞX

_Exin � _Exout

� �ð11Þ

where gII is the exergy efficiency, ðP _Exin � _ExoutÞ is the total

exergy difference of the system. According to second law of thethermodynamic, IP describes recovery potential in exergy lossesor irreversibility’s of the system.

4. Results and discussion

Electricity, local lignite and petro-coke are used in the factory asthe basic energy sources of cement production. The distributionrate, according to the used energy types in the cement productionof total energy consumption, has been materialized at an averageof 19% for the electricity, 54% for the local lignite and 27% for thepetro-coke. The average specific energy consumption value hasbeen found 8.50 MJ/h per ton of cement.

Waste energy points which emerge in the heat processes on thecement production lines, have been determined. These are outputof the front cyclone, rotary kiln, trace and multi cyclone output ofthe cooler unit, trace mill, farine mill, coal mill and electro-filterinputs.

In Turkey, having clinker is the same for all plant except, the dif-ferences of mixture ratio at raw material in process of dry cement.This study takes mass ratios of clinker for exergy analyses andgives the mass flow rate of production in years.

In all of the production lines, fluid funnel gases serve as heatcarriers. In determining the yearly gas amount, clinker average

has been used. According to this, clinker average between the years2002 and 2006 is found as 32.72 Mton/h. Besides, temperaturesranges of gas flows, averages of mass flow rates and reference tem-peratures of gasses are determined separately and the tempera-tures and mass flows are given in Table 1.

The clinker production processes have been evaluated as opensystems, having continuous flows, and the approval below hasbeen granted for exergy analyses according to the second law ofthermodynamics:

� The systems have been assumed as a steady state in a steadyflow processes.� Kinetic and potential energy changes of input and output mate-

rials have been ignored in all of the processes.� No heat is transferred to the raw mills, trass mills and coal mills

from outside.� Electrical energy produces shaft work in all processes.� The change in the ambient temperature has been neglected.� Exergy losses happening in the connection of the pipelines

among units and processes have been ignored.� The reference (dead state) temperature is taken ambient tem-

perature and the reference (dead state) pressure is taken as101.325 kPa.� The mass balances of the raw, trass and coal mills contain the

non-chemical reaction in the exergy analyses of the processes;they have a covered atomic balance. In the exergy analyses ofprocesses, the approval below has been taken into consider-ation. The only chemical reaction occurs as a result of burningin the rotary kilns. Consequently, the chemical exergy of thisunit has also been calculated in the processes.

Exergy analyses are arranged for all processes on the productionlines of the cement. According to these analyses, the flow diagramof the cement production line, which demonstrates the exergy flowof whole processes on the cement production line, has been shownin Fig. 9. According to the results of the exergy analysis based onthe data and with the Eqs. (1)–(7), it has been identified that thehighest thermal mass transfer, the highest energy flow and exergyloss on the production lines occurs in the rotary kiln processes.This study has focused on especially rotary kiln processes whichhave high exergy losses.

In exergy analyses made for this study, to evaluate the environ-mental factors caused by this loss in processes; at first changes inthe external environment temperature have been investigated andit has been found to be between �18 �C and 41 �C.

According to these values which are accepted as dead state tem-perature, exergy analyses of the rotary kiln processes have beenmade by using Eqs. (1)–(7) between the years 1999 and 2007. Inthis study, exergy efficiencies, exergy losses, improvement and an-ergy potential of the processes have been also calculated and theresults are given in Table 2. Exergy efficiencies of the processeshave been calculated by using Eq. (7) and the changes in efficiencyvalues are given in Fig. 10.

Exergy efficiency of the rotary kiln processes are found between39.54% and 50.01% and average are calculated as 43.41%. Exergyloss of the rotary kiln processes based on the exergy analyses isfound as average of 217.73 � 106 GJ/h. Energy recovery potentialto be obtained from exergy loss according to dead state tempera-tures has been calculated by using Eq. (2) and distribution of thetemperature values found are given in Fig. 10. In the process,energy recovery potential are found 106.68 � 106 GJ/h for the low-est temperature, 133.01 � 106 GJ/h for the highest temperatureand 123.29 � 106 GJ/h for the average. These values show thatapproximately 56.62% of the waste energy may be recovered.

An inverse dispersion has been observed between average exer-gy efficiencies and improvement potentials in each year. While an

Limestone Clay+ Ferrite

-0.19 %

Gas + dust + ash

97.92 %

100%

Far

ine

mill

Return from separator

1.89%

Leaking air 0 %

Exergy losses

74.36 %

Air + gas + steam + humidity43.98 %

25.34 %

Farine cyclones56.02 % 10

0%

Exergy losses79.88 %

20.12%

58.22%

FARINE MILL PROCESS

79.88%

8.23

%

58.36%0.57%

Fuel

Carrier air

23.89 %

19.94 %

9.09%

Primer and leaking air50.97%

Exergy losses

Pre

heat

er

Rotary Kiln

Cooling

7.75%

Clinker

39.67%

63.5

7%

ROTARY KILN PROCESS

COAL MILL PROCESS

TRASS MILL PROCESS

The coal mix. Return from separator

0.53 %

99.47 %Gas + dust + ash

Leaking air0 %

4.31%

The coal mix.3.71 %

57.37 %

Gas + dust + ash to electro-filiter

10.79%

LimestoneTrass0 %

Leaking air

Gas + dust98.12 %

Tras mix.Return from separator

Gas + dustto electro-filiter

The trass mix.

1.88 %

8.46%

4.27%

Exergy losses

87.27%

Exergylosses

81.19 %

Gas + dustto electro-filiter

Coal Mill

Trass Mill

36.43%

Exergy losses from cyclones

21.84 %

Leaking air 0 %

41.28%

9.69%

76.11%

23.75%

45.60%

Lignite + petro cok0 %

Fig. 9. Average exergy flow of the cement production in Turkey.

Table 2Exergy analyses of the clinker production based on the dead state temperature.

Dead statetemp. (�C) (min.,max. average)

Clinker(kg/h � 106)

Exin

(GJ � 106)Exout

(GJ � 106)gII (%) I

(GJ � 106)Exdest

(GJ � 106)Anergy(GJ � 106)

Clinker (kg/h � 106)

Exin

(GJ � 106)Exout

(GJ � 106)gII (%) I

(GJ � 106)Exdest

(GJ � 106)Anergy(GJ � 106)

1999 2000�18 27.97 351.62 136.36 38.78 132 215.26 83.48 28.95 355.76 141.13 0.3967 129.49 214.63 85.14

41 377.89 152.68 40.40 134.22 225.21 90.99 382.95 158.03 0.4127 132.10 224.92 92.82Average 363.99 143.97 39.54 133.01 220.03 87.02 368.56 149.01 0.4042 130.80 219.55 88.76

2001 2002�18 28.75 354.91 140.16 0.3949 129.94 214.75 84.81 29.50 358.08 143.82 0.402 128.20 214.26 86.06

41 381.91 156.94 0.4109 132.52 224.97 92.45 385.78 161.03 0.417 130.94 224.75 93.81Average 367.63 147.98 0.4024 131.25 219.65 88.40 371.13 151.84 0.4090 129.58 219.28 89.71

2003 2004�18 30.42 361.96 148.30 0.41 126.12 213.66 87.54 32.80 372.00 159.90 0.430 120.92 212.09 91.17

41 390.53 166.06 0.425 129.02 224.47 95.45 402.80 179.05 0.445 124.29 223.75 99.46Average 375.41 156.57 0.4170 127.58 218.84 91.26 386.66 168.83 0.4365 122.73 217.83 95.10

2005 2006�18 36.40 387.18 177.45 0.458 113.60 209.73 96.12 38.20 394.77 186.23 0.472 110.16 208.54 98.38

41 421.36 198.70 0.472 117.66 222.66 105.00 430.65 208.53 0.484 114.57 222.12 107.55Average 403.28 187.36 0.4645 115.62 215.92 100.31 411.67 196.62 0.4775 112.34 215.05 102.70

2007�18 41.50 408.69 202.32 0.495 104.21 206.37 102.16

41 447.66 226.54 0.506 109.22 221.12 111.90Average 427.04 213.61 0.5001 106.68 213.44 106.76

Table 1Gas flow and temperature value of the gas.

Unit Range of the gas temperature (K) Reference temperature of the gas (K) Reference mass flow of the gas (kg/h � 106)

Multi-cyclone chimney 420–485 453 63555.77To trass mill from cooling 850–890 874 26158.99Pre-heater cyclones 590–670 633 101498.03Exiting of the farine mill 330–410 377 40973.72Exiting of the coal mill 330–400 374 31625.65Exiting of the trass mill 310–390 354 26158.99

Mass flow of the clinker: 32.72 Mton/h.

M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45 43

0

20

40

60

80

100

120

140

1999 2000 2001 2002 2003 2004 2005 2006 2007Data

Para

met

ers

Exergetic efficiency (%)Improvement potential (GJ)

Fig. 10. Exergy efficiencies and improvement potential of the rotary kiln processes.

1999 2000 2001 2002 2003 2004 2005 2006 2007

Anergy

Improvement Potential

Exergy Losses

0

5

10

15

20

25

30

Eff

ects

of

CO

2 em

issi

on

Data

Fig. 12. Changes of CO2 emissions for the natural gas consumption.

1999 2000 2001 2002 2003 2004 2005 2006 2007

Anergy

Improvement Potential

Exergy Losses

0

10

20

30

40

50

60

70

80

Eff

ects

of

CO

2 em

issi

on

Data

Fig. 13. Changes of CO2 emissions for the coal consumption.

44 M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45

increase in production capacity of clinker exergy efficiency is pos-itively observed, it causes a decrease in improvement potential.

Global warming and its causes have led to an environmentalawareness in cement sector as well as in many other sectors. In re-cent years related to this effect, the studies to decrease CO2 emis-sion and environmental pollution caused by cement productionhas become widespread.

Although improvements can be made to the existing processes,these would not bring about significant reductions in carbon diox-ide. The cement industry represents a small yet significant propor-tion of total global carbon dioxide emissions (7% globalanthropogenic pollution). 4.8% of these emissions produced bythe cement industry, 50% result from the chemical processing,40% from the burning of fuel, 5% from transportation, and theremaining 5% from electricity used in three manufacturing opera-tions (see Fig. 11) [27].

In the study, CO2 emissions causing exergy losses in clinker pro-duction have been examined with respect to natural gas, coal andfuel-oil. In Turkey, coal and petro-coc are generally used as fuel, inrotary kiln processes. However, a particular evaluation has beenmade for fuel-oil in the study.

Major parts of waste energy produced in the processes havebeen thrown away from the kiln surfaces and chimney to externalenvironment. Amounts of CO2 emission based on the energy recov-ery potential of the waste energy and anergy have been calculatedby using Eqs. (8)–(11) for the natural gas, fuel-oil and coal whichhave been selected as alternative fuel.

In the study, also reduction of CO2 emissions based on exergylosses and improvement potentials have been investigated andaccording to results of the analyses, average improvement poten-tial has been found as 56.64%. Average unstoppable the entropycontribution of exergy losses in rotary kiln processes has been cal-culated as 43.36%.

The study, has examined CO2 emissions in rotary kiln processcaused by exergetic losses in case natural gas from fuel types is

Fig. 11. Portion of CO2 produced by the cement

used for cement production. Changes of CO2 emissions are also ex-plored considering the improvement potential of processes, andthe results are given in Fig. 12. In case of used natural gas abso-lutely in rotary kiln processes, potential of CO2 emissions havenenvironmental effect was found as 25.06 � 106 kg/h. It will materi-alize to decrease 56.64% average for CO2 emissions in case meetingprescribed improvements in improvement potential. Neverthelesspotential of CO2 emissions not preventing was determined to affectenvironment as 10.87 � 106 kg/h.

In Turkey as primarily fuel is generally used coal. In the study, itseems that CO2 emission dependent on coal is there times averagebigger than natural gas. According to 9 years examined in thestudy, Changes of CO2 emissions caused coal consumption is givenin Fig. 13. Even if necessary improvements in rotary kilns are pro-vided, it is calculated that will be an effect in coal consumption by32.60 � 106 kg/h average. Emission effect of this value has beendetermined 1.3 times average as regards total emission effectcaused exergetic losses in natural gas consumption.

industry and breakdown those sources [24].

1999 2000 2001 2002 2003 2004 2005 2006 2007

Anergy

Improvement Potential

Exerg losses

0

1020

30

4050

6070

80

90

Data

Eff

ects

of

CO

2 em

issi

on

Fig. 14. Changes of CO2 emissions for the fuel-oil consumption.

M. Ziya SÖGÜT / Energy Conversion and Management 56 (2012) 37–45 45

In cement sector, fuel-oil generally is not preferred as a fuel.Owing to evaluation of fossil fuel effects, in the study has beenexamined also CO2 emissions caused fuel-oil consumption. CO2

emissions caused fuel-oil depend on clinker production has beencalculated between the years 1999 and 2007 and results are givenin Fig. 14. In the case of consumption of fuel-oil in rotary kiln pro-cesses, it has been calculated that an average amount of81.45 � 106 kg/h CO2 emission will occur. Even though all the tech-nical improvements have been done, it has been seen that an aver-age of 35.31 � 106 kg/h emission oscillation will affect theenvironment. It has been confirmed that the fossil fuels are themost problematic fuels in terms of environmental side-effects inthe case of consumption of fuel-oil in rotary kiln processes.

5. Conclusion

In the study, exergetic efficiency of cement production inTurkey between the years 1997 and 2007 was examined consider-ing clinker production as reference. Consequently, CO2 emissionscaused by the sector due to exergetic losses based on fuel typeswere investigated. According to exergy analyses, annual exergeticefficiency of clinker production was found 43.41% on average.Exergetic improvement potential of processes was calculated as123.29 � 106 GJ/h. This value corresponds to 56.62% of exergeticlosses. Potential of CO2 emissions caused by exergetic losses basedon available fuel types was calculated and for the coal mixture,natural gas and fuel-oil were found 75.18 � 106 kg/h, 25.06 �106 kg/h and 81.45 � 106 kg/h on average respectively.

Some suggestions on how to improve the processes in cementsector are given below. Active energy managements must beformed, firstly, to constitute a sustainable energy system whichcan lead to positive social and environmental effects in the cementsector, which has intense energy consumption. Energy manage-ments should approach primarily the subjects, such as improve-ment of isolation in production processes, using alternative fuelin rotary kilns, constituting of politics between efficiency with pro-duction and stock controls.

The results of analyses show that the rise in production capacitycauses a proportional increase of efficiency in these processes.Therefore; cement plants which aim to increase energy efficiencyhave to arrange their production strategy according to maximumcapacity by taking their production potentials into consideration.

Improvement of processes in cement sector must be resumed asregard to decrease exergetic losses, which affect negative environ-mental parameters. Furthermore, in such thermal processes, prior-ity should be given to converting high waste energy potentials touseful energy by the energy recovery systems. This useful energymay be recycled conveniently with the recycling models to heatingand cooling energy for residential areas around such plants.

To sum up, it is obligatory to make policies that ensure a perma-nent and sustainable energy approach in the cement sector, whichrequires a great deal of energy consumption. Thus, only in this way,supply of the energy can be met with the least financial, environ-mental and social cost.

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