Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013, Article ID 197913, 9 pageshttp://dx.doi.org/10.1155/2013/197913
Research ArticleThe Evaluation of Solar Contribution in Solar Aided Coal-FiredPower Plant
Rongrong Zhai, Yongping Yang, Yong Zhu, and Denggao Chen
School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China
Correspondence should be addressed to Rongrong Zhai; [email protected]
Received 17 October 2012; Revised 11 January 2013; Accepted 29 January 2013
Academic Editor: Kalvala Srinivas Reddy
Copyright ยฉ 2013 Rongrong Zhai et al.This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Solar aided coal-fired power plants utilize various types of solar thermal energy for coupling coal-fired power plants by using thecharacteristics of various thermal needs of the plants. In this way, the costly thermal storage system andpower generating systemwillbe unnecessary while the intermittent and unsteady way of power generation will be avoided. Moreover, the large-scale utilizationof solar thermal power and the energy-saving aim of power plants will be realized. The contribution evaluating system of solarthermal power needs to be explored. This paper deals with the evaluation method of solar contribution based on the second law ofthermodynamics and the principle of thermoeconomics with a case of 600MW solar aided coal-fired power plant. In this study,the feasibility of the method has been carried out. The contribution of this paper is not only to determine the proportion of solarenergy in overall electric power, but also to assign the individual cost components involving solar energy. Therefore, this study willsupply the theoretical reference for the future research of evaluation methods and new energy resource subsidy.
1. Introduction
Since the energy crisis in the 1970s, the major developedcountries of the world started a series of projects involvingsolar thermal power generation for energy substitution.Among the developments in this field, the research ofAmerica, Israel, Spain, Germany, and Italy began first andare consequently the most mature [1]. Solar energy as a formof clean energy has broad application prospects. Moreover,coupling with coal-fired power plants as a type of solar powerutilization has been presented and investigated by manyresearchers.
Pai proposed the integration of a solar concentratorfield to a 210MWe coal-fired power plant [2]. Gupta andKaushik found that using solar energy as a substitute forfeed water heaters is more advantageous than using solarenergy alone for power generation [3]. From a theoreticalperspective, the solar aided coal-fired power generation sys-temhasmany advantageswhen comparedwith a photovoltaicpower generation system. However, the popular utilization
of this technology has been relatively slow. The reasons forthis apathetic uptake have been concluded as follows: (a)variations of solar radiation can cause operation difficultiesand (b) no reasonable evaluating systems have been built forthe contribution of solar energy in the integrated system.Thestudy about solar aided coal-fired power generation systemmostly concentrates on performance analyses, integrationmodes, operations optimization, and so on. Since Gaggioliand El-Sayed comprehensively concluded the history ofsecond law costing method, thermoeconomic analysis hasbecome a powerful scheme applied extensively in design,operation, and reform of energy systems [4, 5]. Thoughthermoeconomic methods are multitudinous, the objectivesof most existing analysis techniques still can be includedin the determination of (a) the appropriate allocation ofeconomic resources to optimize the design and operation ofa system and (b) the economic feasibility and profitabilityof a system [6]. The methods can be roughly divided intotwo classes: algebraic methods and calculus methods [4, 5].The thermoeconomic analysis of solar aided coal-fired power
2 International Journal of Photoenergy
generation system has already begun. Suresh and Reddydealt with the 4-E (namely, energy, exergy, environment, andeconomic) analysis of solar aided coal-fired power plants witha subcritical and a supercritical power plant as references [7];Baghernejad andYaghoubi presented a new thermoeconomicmethod applying a genetic algorithm for optimization of anintegrated solar combined cycle system [8].
The previous research as mentioned above has investi-gated the integration of a solar concentrator fieldwith a powerplant. However the integrated system introduces solar energyinto the individual components in the traditional powerplants, the researches about how to evaluate the contributionof solar energy in the system are hardly found.
A thermoeconomic method of evaluating solar contribu-tion in the integrated system is firstly proposed in this paper.A new built 600MW solar aided coal-fired power generationunit is considered as a reference power plant. According tothe design parameters, the contribution proportion has beenachieved, and the generation cost has also been explored byusing sensitivity analysis method.
2. System Descriptions andthe Proposed Problem
Figure 1 shows the diagramof the solar aided coal-fired powerplant. In the solar field, several parabolic trough collectorsare connected and the heating material is heat transferoil. The oil-heat exchanger is a tube-shell heat exchanger.The parabolic trough collectors and the oil-heat exchangertogether are called solar driven oil-water heat exchanger inthis paper.
In a typical reheated steam coal-fired power plant, thecombustion of coal takes place in the boiler. The unsaturatedboiler feedwater from the condenser enters the boiler aftergoing through four low-pressure reheaters (HTR1, HTR2,HTR3, and HTR4), three high-pressure reheaters (HTR5,HTR6, and HTR7), and a deaerator (Deaerator). The outletsuperheated steam from the boiler is transported to thehigh-pressure cylinder to produce power, then, after beingreheated in the boiler, drives the intermediate and lowerpressure cylinders. Finally, the exhaust is condensed in thecondenser. It can be seen from Figure 1 that the extractionsfrom different positions of the cylinders ((1)โ(8)) are used toheat the feedwater via feedwater reheaters.The 600MWsolaraided coal-fired power plant is similar to the reheated steamcycle system.The difference lies in that a solar aided oil-waterheat exchanger has been added. When the solar radiation isstrong (e.g., in the day), the steam extraction (1) is cut offand HTR7 will not be in operation; the feedwater will beheated in the oil-heat exchanger. Conversely, when the solarradiation is week (e.g., in the night), the oil-heat exchangerwill not be in operation and the plant will operate in thesame manner as the base plant. In the solar field (as shownin the dash block in Figure 1), several parabolic collectors areconnected using heat transfer oil as the heating medium ina tube-shell heat exchanger. The parabolic collectors and theoil-heat exchanger together are called solar driven oil-waterheat exchanger (SDOHE) in this paper.
It can be seen from Figure 1 that the solar contributionconcentrates on providing heat to the feedwater. After heat-ing, the feedwater flows into the boiler, then, after a seriesof processes, the thermal energy is finally translated intoelectrical power.
The principle behind the solar aided coal-fired powergeneration system is to supply thermal energy by substitutinghigh pressure feedwater heaters with oil-water heat exchang-ers. During a series of circulation, the energy contributes tothe system power output indirectly. Therefore, it is meaning-ful to discuss how to evaluate the solar energy contributionin the solar aided coal-fired power plant.
3. Evaluation Model of SolarEnergy Contribution
According to the first and second laws of thermodynamics,evaluation models based on energy balance and exergybalance are the possible methods for evaluating energycontribution such as solar energy and fuel.Themethod basedon energy balance just considers the magnitude of energywithout taking energy grade into account. The evaluationbased on exergy balance has added energy grade to thesystem, while the nonequivalence of the same value of exergyat different points in the system has never been considered.Therefore, the evaluation based on the index of technicaleconomics and energy equivalence has been explored in thisstudy. The approach proposed in this paper is called thethermoeconomic cost method, considering both the energygrade and the nonequivalence.
The thermoeconomic cost method includes three stepsas shown in Figure 2. Firstly, the contribution proportionsof solar energy and coal in every exergy flow needs tobe confirmed. Secondly, according to the thermoeconomicconcept, the values of each cost flow can be achieved.Thirdly,the contribution of solar economic cost will be calculatedwith the above data.
3.1. Confirming the Ratio of Solar Energy against Coalaccording to Each Exergy Flow. This part is shown in Figure 2,Box 1. For the convenience of the analysis, Figure 1 hasbeen simplified as shown in Figure 3. The system includessix subsystems: (1) oil-water heat exchanging driven bysolar energy; (2) boiler preheating, steam generating, andsuperheating; (3) high-pressure cylinder of turbine; (4) boilerreheating; (5) intermediate- and low-pressure cylinder ofturbine; and (6) heat exchanging.Themain parameters of thesystem such as the temperature, enthalpy, and flow rate arelisted in Figure 3.
The exergy balance equation of each subsystem is asfollows.
(1) The exergy loss of oil-water heat exchanging is givenby ๐ธ9+ ๐ธ6โ ๐ธ1.
The proportion of solar exergy loss assumed to be ๐ฟ1.
Then the loss will be, ๐ฟ1(๐ธ9+ ๐ธ6โ ๐ธ1), and the exergy loss
of feedwater will be, (1 โ ๐ฟ1)(๐ธ9+ ๐ธ6โ ๐ธ1).
The exergy achieved by water will be written as follows:๐ธ1โ ๐ธ6+ (1 โ ๐ฟ
1)(๐ธ9+ ๐ธ6โ ๐ธ1).
International Journal of Photoenergy 3
000
Solar driven oil water heatexchanger
30 ro
ws
16 collectors
Oil
WPUMP
WPUMPSDOWHE
SDFW
P
......
...
ยท ยท ยท
ยท ยท ยท
ยท ยท ยท
ยท ยท ยท
566
281.651237.93 32.54
136.3
170.4719.56
Boile
r
HP IP IP LP LP
5663600.54 3.58 MP 1420.6 t/h
3398.78 24.2 MP 1563.975 t/h
Generator600 MW
๐
๐
๐
๐
Condenser
(1) (4) (6)(2) (5) (8)
(9)
(7)(3)HTR7 HTR6 HTR5 HTR4 HTR3 HTR2 HTR1
Dea
erat
or
H-kJ/kg
H-kJ/kg
301.582967.13143375
456.63374.7959844
365.243191.9277739
253.932973.0681237
127.722730.2340622
84.872620.3960449
54.782446.1533821
365.243191.9284148
(1) (2) (3) (4) (5) (6) (7) (8) (9)
๐-โC
๐-โC
๐-kg/h
Figure 1: Layout of the solar aided coal-fired power plant.
๐ธ
๐ธ
๐ธ
๐ถ
๐ถ
๐
๐ถ๐
๐ผ
๐ฝ
๐ฟ(1)
(2)
(3)
Figure 2: Schematic representation of the calculating process of the thermoeconomic cost evaluation.
It equals the exergy released by solar energy, which maybe written as follows: ๐ธ
9โ ๐ฟ1(๐ธ9+ ๐ธ6โ ๐ธ1).
The proportion of solar energy at point 1 may become asfollows:๐ผ1= (๐ผ6[โ (1 โ ๐ฟ
1) ๐ธ9+ ๐ฟ1๐ธ6+ (1 โ ๐ฟ
1) ๐ธ1]
+ (1 โ ๐ฟ1) ๐ธ9โ ๐ฟ1๐ธ6+ ๐ฟ1๐ธ1) (๐ธ1)โ1.
(1)
(2)The total exergy loss of preheater, steam generator andsuperheater is given by ๐ธ
10+ ๐ธ1โ ๐ธ2.
The proportion of coal exergy loss assumed to be ๐ฟ2.
Then the exergy loss of waterwill be, (1โ๐ฟ2)(๐ธ10+๐ธ1โ๐ธ2),
and the exergy achieved by water will be written as follows:๐ธ2โ ๐ธ1+ (1 โ ๐ฟ
2)(๐ธ10+ ๐ธ1โ ๐ธ2).
It equals the exergy released by coal, whichmay bewrittenas follows: ๐ธ
10โ ๐ฟ2(๐ธ10+ ๐ธ1โ ๐ธ2).
The proportion of solar energy at point 2 may become asfollows:
๐ผ2=๐ผ1[โ (1 โ ๐ฟ
2) ๐ธ10+ ๐ฟ2๐ธ1+ (1 โ ๐ฟ
2) ๐ธ2]
๐ธ2
. (2)
(3) The proportions of solar energy at the import andexport of turbine are equal.
For the third subsystem, the equation will be given by
๐ผ3= ๐ผ2= ๐ผ7. (3)
For the fifth subsystem, the equation will be given by
๐ผ5= ๐ผ4= ๐ผ8. (4)
(4)The total exergy loss of reheater is given by ๐ธ11+ ๐ธ3โ
๐ธ4.The proportion of coal exergy loss assumd to be ๐ฟ
3.
Then the exergy loss of coal will be ๐ฟ3(๐ธ11+๐ธ3โ๐ธ4), and
the exergy loss of water will be (1 โ ๐ฟ3)(๐ธ11+ ๐ธ3โ ๐ธ4).
The exergy achieved by water will be written as follows:๐ธ4โ ๐ธ8+ (1 โ ๐ฟ
3)(๐ธ11+ ๐ธ3โ ๐ธ4).
It equals the exergy released by coal, whichmay bewrittenas follows: ๐ธ
11โ ๐ฟ3(๐ธ11+ ๐ธ3โ ๐ธ4).
The proportion of solar energy may become as follows:
๐ผ4=๐ผ3[โ (1 โ ๐ฟ
3) ๐ธ11+ ๐ฟ3๐ธ3+ (1 โ ๐ฟ
3) ๐ธ4]
๐ธ4
. (5)
(5) The total exergy loss is given by ๐ธ5+ ๐ธ7+ ๐ธ8โ ๐ธ6.
The proportions of exergy loss at point 7 and 8 areassumed to be ๐ฟ
4and ๐ฟ5.
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1
3
4
56
7 8
9
๐ถ๐2 ๐ถ๐3 ๐ถ๐4 ๐ถ๐5
๐ถ๐6๐ถ๐1
(1)
(4)
(6)
(2) (5)(3) 12 11 1310
1 ๐ธ1๐ผ1๐ถ1๐1๐ฝ1
2 ๐ธ2๐ผ2๐ถ2๐2๐ฝ2
3 ๐ธ3๐ผ3๐ถ3๐3๐ฝ3
4 ๐ธ4๐ผ4๐ถ4๐4๐ฝ4
5 ๐ธ5๐ผ5๐ถ5๐5๐ฝ56 ๐ธ6๐ผ6๐ถ6๐6๐ฝ6
7 ๐ธ7๐ผ7๐ถ7๐7๐ฝ7
8 ๐ธ8๐ผ8๐ถ8๐8๐ฝ8
9 ๐ธ9๐ผ9๐ถ9๐9๐ฝ9
10 ๐ธ10๐ผ10๐ถ10๐10๐ฝ1011 ๐ธ11๐ผ11๐ถ11๐11๐ฝ1112 ๐ธ12๐ผ12๐ถ12๐12๐ฝ1213 ๐ธ13๐ผ13๐ถ10๐13๐ฝ13
Sub system (1) ๐ถ๐1๐ฝ๐1Sub system (2)๐ถ๐2๐ฝ๐2Sub system (3)๐ถ๐3๐ฝ๐3Sub system (4) ๐ถ๐4๐ฝ๐4Sub system (5)๐ถ๐5๐ฝ๐5Sub system (6) ๐ถ๐6๐ฝ๐6
281.71237.9
1563975Enthalpy-kJ/kgFlow rate-kg/h
5663398.8
1563975
301.62967.1
1420600
5663600.5
1420600
32.42324.3982740
240.81048.9
1563975
301.62967.1143375
272.42324.3437860
(1) (2) (3) (4) (5) (6) (7) (8)Temperature -โC
Figure 3: Schematic representation of solar aided coal-fired power generation system.
Then, the exergy loss at point 7 will be ๐ฟ4(๐ธ5+ ๐ธ7+ ๐ธ8โ
๐ธ6).The exergy loss at point 8 will be ๐ฟ
5(๐ธ5+๐ธ7+๐ธ8โ๐ธ6), and
the exergy loss at point 5 will be (1โ๐ฟ4โ๐ฟ5)(๐ธ5+๐ธ7+๐ธ8โ๐ธ6).
The equation will be written as follows:
๐ผ6= (๐ผ7[๐ธ7โ ๐ฟ4(๐ธ5+ ๐ธ7+ ๐ธ8โ ๐ธ6)]
+ ๐ผ8[๐ธ8โ ๐ฟ5(๐ธ5+ ๐ธ7+ ๐ธ8โ ๐ธ6)]
+ ๐ผ5[๐ธ5โ (1 โ ๐ฟ
4โ ๐ฟ5)
ร (๐ธ5+ ๐ธ7+ ๐ธ8โ ๐ธ6)]) (๐ธ
6)โ1.
(6)
The proportion of solar energy will be ensured by using (1)โ(6).
3.2. The Exergy Follow Cost C Will Be Ensured by Thermoe-conomic Analysis. This part is shown in Figure 2, Box 2.According to Figure 3, the system includes 6 subsystems and13 exergy flows. The equation satisfied by each subsystem isgiven by:
๐ถin + ๐ถ๐ = ๐ถout, (7)
where ๐ถin and ๐ถ๐ are, respectively, the energy cost of importand the cost of others, and ๐ถout is the energy cost of export.
Then, for the first subsystem, the equation is given by thefollowing:
๐ถ6+ ๐ถ9+ ๐ถ๐1= ๐ถ1. (8)
For the second subsystem, the equation is given by thefollowing:
๐ถ1+ ๐ถ10+ ๐ถ๐2= ๐ถ2. (9)
For the third subsystem, the equation is given by thefollowing:
๐ถ2+ ๐ถ๐3= ๐ถ3+ ๐ถ7+ ๐ถ12. (10)
For the fourth subsystem, the equation is given by thefollowing:
๐ถ3+ ๐ถ11+ ๐ถ๐4= ๐ถ4. (11)
For the fifth subsystem, the equation is given by thefollowing:
๐ถ4+ ๐ถ๐5= ๐ถ5+ ๐ถ8+ ๐ถ13. (12)
For the fifth subsystem, the equation is given by thefollowing:
๐ถ5+ ๐ถ7+ ๐ถ8+ ๐ถ๐6= ๐ถ6. (13)
The cost of solar exergy flow ๐ธ9is given data, and then we
will get the equation as follows:
๐ถ9
๐ธ9
= ๐9. (14)
International Journal of Photoenergy 5
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1
3
4
56(1)
(4)
(6)
(2) (5)(3)
7 8
9๐ถ6๐ฝ6
๐ถ2๐ฝ2
๐ถ9๐ฝ9
๐ถ1๐ฝ1
๐ถ7๐ฝ7 ๐ถ8๐ฝ8
๐ถ5๐ฝ5
๐ถ3๐ฝ3
๐ถ4๐ฝ4
๐ถ๐6๐ฝ๐6
๐ถ๐5๐ฝ๐5๐ถ๐3๐ฝ๐3 ๐ถ๐4๐ฝ๐4
๐ถ๐1๐ฝ๐1
๐ถ๐2๐ฝ๐2
๐ถ13๐ฝ13
๐ถ11๐ฝ11
๐ถ10๐ฝ10
๐ถ12๐ฝ12
1213
1110
Figure 4: The schematic of cost flows.
The costs of coal exergy flows ๐ธ10and ๐ธ
11are given data,
and then the equation will be as follows:
๐ถ10
๐ธ10
=๐ถ11
๐ธ11
= ๐10= ๐11. (15)
The costs of ๐ธ2, ๐ธ3, and ๐ธ
7have been given, and then the
equation may be as follows:
๐ถ2
๐ธ2
=๐ถ3
๐ธ3
=๐ถ7
๐ธ7
. (16)
The costs of ๐ธ4, ๐ธ5, and ๐ธ
8have been given, and then the
equation will be as follows:
๐ถ4
๐ธ4
=๐ถ5
๐ธ5
=๐ถ8
๐ธ8
. (17)
According to (8)โ(17), the cost of each exergy flow will beensured.
3.3. According to the Thermoeconomic Analysis of the SolarPart, the Cost Proportions of Solar Energy in Each Exergy FlowWill Be Ensured. This part is shown in Figure 2, Box 3. Forthe convenience of analysis, Figure 3 has been simplified asshown in Figure 4. The system still includes six subsystems.
According to the data above, the solar energy parts ineach exergy flowhave just been considered alone, and the costproportions of solar energy will be explored.
Equations of each subsystem have been given as follows.(1)The cost equation of oil-water heat exchanging is given
by the following:
๐ถ6๐ฝ6+ ๐ถ9๐ฝ9+ ๐ถ๐1๐ฝ๐1= ๐ถ1๐ฝ1. (18)
(2) The cost equation of preheating, steam generating,and superheating is given by the following:
๐ถ1๐ฝ1+ ๐ถ10๐ฝ10+ ๐ถ๐2๐ฝ๐2= ๐ถ2๐ฝ2. (19)
(3)The cost equation of turbine is given by the following:
๐ถ2๐ฝ2+ ๐ถ๐3๐ฝ๐3= ๐ถ3๐ฝ3+ ๐ถ7๐ฝ7+ ๐ถ12๐ฝ12. (20)
Table 1: Main designed parameters of coal-fired power plant.
Parameters Values UnitsCapacity 600 MWParameters of main steam 24.2/566/566 MPa/โC/โCFeedwater mass flow rate 1645.15 t/hCondenser pressure 4.9 kPaFeedwater temperature 272.3 โCCoal consumption rate 257.4 g/kWh
(4) The cost equation of reheating is given by the follow-ing:
๐ถ3๐ฝ3+ ๐ถ11๐ฝ11+ ๐ถ๐4๐ฝ๐4= ๐ถ4๐ฝ4. (21)
(5)The cost equation of turbine is given by the following:
๐ถ4๐ฝ4+ ๐ถ๐5๐ฝ๐5= ๐ถ5๐ฝ5+ ๐ถ8๐ฝ8+ ๐ถ13๐ฝ13. (22)
(6) The cost equation of heat exchanging is given by thefollowing:
๐ถ5๐ฝ5+ ๐ถ7๐ฝ7+ ๐ถ8๐ฝ8+ ๐ถ๐6๐ฝ๐6= ๐ถ6๐ฝ6. (23)
Since the cost of solar energy achieving is free, we assume๐ถ9= 0 and ๐ฝ
9= 0.
For the second and third subsystems, the import exergyflows of 10 and 11 will be 0, which means the solar parts in 10and 11 will be 0:
๐ฝ10= ๐ฝ11= 0. (24)
Since the costs of ๐ธ2, ๐ธ3, and ๐ธ
7are equal, (25) can be
obtained as follows:
๐ฝ2= ๐ฝ3= ๐ฝ7. (25)
Since the flow rates of ๐ธ4, ๐ธ5, and ๐ธ
8are equal, (26) can
be obtained as follows:
๐ฝ4= ๐ฝ5= ๐ฝ8. (26)
The cost proportions of solar energy ๐ฝ will be ensured byusing (18)โ(26).
4. Case Study
4.1. Main Parameters. A coal-fired power plant of 600MWin China has been chosen as the base plant, with the maindesigned parameters shown in Table 1. Coal is the supply fuelof the power plant, with the following components: moisture= 9.9%, ash = 23.7%, hydrogen = 3.11%, nitrogen = 1.01%,sulphur = 2%, oxygen = 2.78%, carbon = 57.5%, and LHV =21981 kJ/kg.
The solar aided coal-fired power plant is using the samecoal as the base case, except for the solar driven oil-water heatexchanger and the steamcut-off, other structures are the sameas the base case. The data of solar field is based on real datafrom theGEGS-VI station inUSA [9โ11]. Somemodificationshave been made to make it suitable for the case in this
6 International Journal of Photoenergy
Table 2: Main parameters of the collector field.
Parameters Values UnitsSolar irradiation 925 W/m2
Area of per collector 235 m2
Number of collector in each row 16Rows of collectors 30 RowsInlet temperature of heat transfer oil 250 โCOutlet temperature of heat transfer oil 328 โC
Table 3: Main designed parameters of solar aided power plant.
Parameters Values UnitsCapacity 600 MWFeedwater temperature 281.65 โCCoal consumption rate 243.7 g/kWhThermal efficiency 50.41 %Exergy efficiency 48.07 %Area of all collectors 112800 m2
paper. The collects are LS-2 parabolic trough collects fromLUZ Company [9], and the diagram and main parametersof the collectors are shown in Table 2. The collector field iscomposed of 30 rows of 16 solar collectors which are parallellyinstalled. The heated heat transfer oil flows into the oil-water heat exchanger and the cooled heat transfer oil will bepumped back into the oil cycle.
Themain designed parameters of solar aided power plantare shown in Table 3.
For the solar aided coal-fired power plant, the energyefficiency and exergy efficiency can be defined as follows:
๐energy =๐คoutput
๐coal + ๐solar, (27)
where ๐energy is the energy efficiency, ๐คoutput is work output,๐coal is the energy of coal, and ๐solar is the energy of solar.
๐exergy =๐คoutput
๐ธcoal + ๐ธsolar, (28)
where ๐exergy is the exergy efficiency, ๐ธcoal is the exergy ofcoal, and ๐ธsolar is the solar exergy.
It can be seen from Tables 1 and 3 that the coal consump-tion rate of solar aided coal-fired power plant is less than thatof the coal-fired power plant.
The capital cost of the plant is shown in Table 4 [12โ18]. The investment includes the cost of facilities and themaintaining cost. The cost of coal is 140 dollars/ton [19].
4.2. Results and Sensitivity Analysis. Based on the methodol-ogy proposed in Section 3, the solar contributions in 600MWsolar aided coal-fired power plant have been evaluated. Theresults of solar exergy proportion and solar cost proportionhave been shown in Tables 5 and 6, respectively.
The overall exergy proportion of solar power in the plantcan be calculated using ๐ผ = (๐ผ
12ร๐ธ12+๐ผ13ร๐ธ13)/(๐ธ12+๐ธ13)
and the result is 4.84%.
Table 4: The investment of the plant.
Items Cost (dollars)Solar concentration field 37528560.00Oil-water heat exchangers 4192170.00Super heaters of the boiler 168235561.38Reheaters of the boiler 22941212.92High-pressure turbine 24723323.22Intermediate-pressure turbine 26877786.50Low-pressure turbine 42734428.98Condenser 14550480.00Other heat exchangers 21149680.00Deaerator 3156810.00Pumps 673317.35
Table 5: Exergy value of each flow and the proportion of solarpower.
Exergy flows Exergy value (MJ/h) Exergy Proportion ofsolar ๐ผ Percent
๐ธ1 555712.8 ๐ผ1 48.39๐ธ2 2447325 ๐ผ2 6.55๐ธ3 1563747 ๐ผ3 6.55๐ธ4 2065157 ๐ผ4 4.09๐ธ5 89036.6 ๐ผ5 4.09๐ธ6 422330.4 ๐ผ6 4.72๐ธ7 157822.2 ๐ผ7 6.55๐ธ8 362203.9 ๐ผ8 4.09๐ธ9 357271.6 ๐ผ9 100๐ธ10 3551430 ๐ผ10 0๐ธ11 941377.7 ๐ผ11 0๐ธ12 664758.2 ๐ผ12 6.55๐ธ13 1495293 ๐ผ13 4.09
Table 6: Exergy cost of each flow and the proportion of solar power.
Cost flow values Cost proportion ofsolar ๐ฝ Percent
๐ถ1 5903 ๐ฝ1 1.98๐ถ2 22724 ๐ฝ2 0.70๐ถ3 14520 ๐ฝ3 0.70๐ถ4 18896 ๐ฝ4 0.56๐ถ5 815 ๐ฝ5 0.56๐ถ6 5745 ๐ฝ6 0.70๐ถ7 1465 ๐ฝ7 0.70๐ถ8 3314 ๐ฝ8 0.56๐ถ9 0 ๐ฝ9 100๐ถ10 16181 ๐ฝ10 0๐ถ11 4289 ๐ฝ11 0๐ถ12 6833 ๐ฝ12 0.78๐ถ13 15032 ๐ฝ13 0.62
International Journal of Photoenergy 7
It can be seen from Table 5 that the proportion of solarexergy is 100 percent in the ninth exergy flow. This isdue to the solar energy from the solar exergy flow sharinga contribution ratio of 100 percent. As exergy flows, theproportion of solar exergy shows a decreasing trend. Thetwelfth and the thirteenth exergy flows shown in Table 5represent the exergy in system work (i.e., electric power).The proportions of solar power are 6.55% and 4.09%. Theoverall exergy proportion of solar power is 4.84%byweighingthe proportions in the twelfth and thirteenth exergy flows.In the system, considering the proportion of exergy flows,the contribution of solar power can be measured by itsproportion of 4.84% in the overall electric power. For thesystem with a rated capacity of 600MW, in this case, about29.04MWof electric power is contributed to solar power andthe rest 570.96MW is contributed to coal-fired.
The overall cost proportion of solar power in the plant canbe calculated using ๐ฝ = (๐ฝ
12ร ๐ถ12+ ๐ฝ13ร ๐ถ13)/(๐ถ12+ ๐ถ13)
and the result is 0.67%.It can be seen from Table 6 that the cost of solar exergy
flow is zero in the exergy cost of the ninth flow. This isbecause the solar energy has been considered to be free inthe analysis. The exergy cost of the twelfth and thirteenthflows in Table 6 shows the exergy costs of electricity, and theproportions of solar power are 0.78% and 0.62% in them. Byweighing the proportions of solar power in the twelfth andthirteenth flows, we can obtain that the proportion of solarpower in the electric exergy cost is 0.67%. In this system,considering the exergy cost of flows, the proportion of thecost of solar power and solar equipments is 0.67%. For thesystem, a rated capacity of 600MW, in this case, the cost ofsolar energy, and solar equipment share a proportion of 0.67%in the cost of electric power, and the rest (99.33%) comes fromcoal and other equipment. Comparing the calculated solarpower exergy generated with the proportion of cost of solarpower exergy generated, the proportion of 4.48% of solarpower exergy generated is much larger than the proportionof 0.67% of cost of solar power exergy generated.
(1) Sensitivity Analysis of Coal Cost. When the coal costchanges from 100 to 180 dollars/ton, the trend of cost ofelectricity is shown in Figure 5 and the trend of the overallcost proportion of solar is shown in Figure 6.
The power generation cost is calculated as follows:
๐electricity =๐ถelectricity
๐ธelectricity, (29)
where ๐electricity is the cost of power generation, ๐ถelectricity isthe exergy cost of electricity, and ๐ธelectricity is the generatingcapacity.
The exergy cost of electricity includes two aspects,namely, fixed costs and variable costs. The fixed costs includeequipment costs, material costs, depreciation costs, opera-tion, andmaintenance fees, and the variable costs include fuelcosts, environmental costs, water charges. In order to takeadvantage of the calculation method proposed in this paper,all of the costs (except the fuel costs) have been converted to
100 120 140 160 1802.5
3
3.5
4
4.5
5
Coal prices ($/๐ก)
The c
ost o
f pow
er g
ener
atio
n (1
0โ2$/
kWh)
The solar aided coal-fired power plantThe coal-fired power plant
Figure 5: The change of cost of electricity with coal cost.
the equipment costs.Therefore, in this case, the cost of powergeneration is calculated as follows:
๐electricity =๐ถ12+ ๐ถ13
๐ธ12+ ๐ธ13
. (30)
It can be seen from Figure 5 that the cost of electricityincreases from 2.67 cents/kWh to 4.62 cents/kWh in the solaraided coal-fired power plant with the coal prices increasefrom 100$/t to 180$/t. The power generation cost of 600MWpower plant is 3.81 cents/kWh, and that of the coupled powerplant power is 3.64 cents/kWh when the coal price is 140$/t.In the terms of coal price, the COE of a solar aided powerplant is less than the one of coal-fired power plant. Assolar energy is added to the solar aided system, in thecondition of saving coal (with lower coal consumption rate),considering the solar energy is free, the COE of a coupledpower plant will be lower than the original thermal powerplant. However, compared to the pure solar power generationsystem, the coupled system uses the turbines, generators andother key equipment of the original thermal power system,and the work efficiency of the replaced high-temperaturehigh-pressure high-grade steam ismuch higher than the puresolar thermal power generation. Therefore, the COE of thecoupled power generation system is less than the pure solarpower generation system.
It can be seen from Figure 6 that with the coal priceincreasing from 100$/t to 180$/t, the ๐ฝ is reduced from 0.92%to 0.51%, about 0.41 points. The reduction trend tends to beslower with the increase of the coal price.
(2) Sensitivity Analysis of Solar Facilitiesโ Investment. Whenthe investment of solar facilities changes from 60% to 140%,the trend of the cost of electricity is shown in Figure 7 andthe trend of the overall cost proportion of solar is shown inFigure 8.
Figure 7 shows that, with the solar equipment priceincrease, the proportion of solar equipment increases in the
8 International Journal of Photoenergy
100 120 140 160 180
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
๐ฝ(%
)
Coal prices ($/๐ก)
Figure 6: The change of the overall cost proportion of solar withcoal cost.
60 80 100 120 1403.6
3.623.643.663.68
3.73.723.74
3.763.78
3.83.82
The c
ost o
f pow
er g
ener
atio
n (1
0โ2$/
kWh)
The cost of solar equipment (%)
The solar aided coal-fired power plantThe coal-fired power plant
Figure 7:The change of the cost of electricity with the solar facilitiesโinvestment.
equipment costs, so the COE of solar aided power plantincreases. Therefore, the production of cheap solar collectordevices is good for power plant in low-cost operation.
It can be seen from Figures 7 and 8, with the changeof the cost of solar equipment from 60% of the calculationcost to 140% of the calculation cost, that the cost of powergeneration increases from 3.63 cents/kWh to 3.65 cents/kWh;the ๐ฝ increases from 0.53% to 0.79%, which is about 0.26points.
5. Conclusions
This paper proposed thermoeconomic cost method for solarcontribution study in solar aided coal-fired power plantand analyzed the plant based on the newly constructed andreconstructed 600MW power plant.
60 80 100 120 140The cost of solar equipment (%)
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
๐(%
)
Figure 8:The change of the overall cost proportion of solar with thesolar facilitiesโ investment.
Based on the second law of thermodynamics and theprinciple of thermoeconomics, this paper proposed theevaluation of solar contribution in the solar aided coal-firedpower plant, which can be used to assign the individual costcomponents involving solar energy. Its feasibility has beenproven by analyzing a newly constructed power plant. Theresult shows: that when operating at the rated capacity, theproportion of solar power in overall electric power is 4.84%,which is about 29.04MW.
Nomenclature
๐ธ๐: The exergy value of the ๐th exergy flow๐ฟ๐: The ratio of solar exergy loss in the total exergy
loss when running the ๐th equipment๐ผ๐: The ratio of solar exergy flow in the ๐th exergy
flow๐๐: The unit cost of the ๐th exergy flow๐ถ๐: ๐ถ๐= ๐๐โ ๐ธ๐. The cost of the ๐th exergy flow, as
the energy cost๐ถ๐พ๐: The nonenergy cost of the ๐th subsystem๐ฝ๐: The exergy cost ratio of the solar contribution
in the ๐th exergy flow๐ฝ๐พ๐: The ratio of the solar side of the nonenergycosts of the ๐th subsystem.
Acknowledgments
The research work is supported by China National Nat-ural Science Foundation (no. 51106048), the FundamentalResearch Funds for the Central Universities and the Programfor 863 Project (2012AA050604). The authors have no otherrelevant affiliations or financial involvement with any organi-zation or entity with a financial interest in or financial conflictwith the subject matter or materials discussed in the paperapart from the one disclosed.
International Journal of Photoenergy 9
References
[1] D. Mills, โAdvances in solar thermal electricity technology,โSolar Energy, vol. 76, no. 1โ3, pp. 19โ31, 2004.
[2] B. R. Pai, โAugmentation of thermal power stations with solarenergy,โ Sadhana, vol. 16, no. 1, pp. 59โ74, 1991.
[3] M. K. Gupta and S. C. Kaushik, โExergetic utilization of solarenergy for feed water preheating in a conventional thermalpower plant,โ International Journal of Energy Research, vol. 33,no. 6, pp. 593โ604, 2009.
[4] Y. M. El-Sayed and R. A. Gaggioli, โCritical review of secondlaw costingmethodsโI: background and algebraic procedures,โJournal of Energy Resources Technology, vol. 111, no. 1, pp. 1โ7,1989.
[5] R. A.Gaggioli andY.M. El-Sayed, โCritical review of second lawcosting methodsโII: calculus procedures,โ Journal of EnergyResources Technology, vol. 111, no. 1, pp. 8โ15, 1989.
[6] M. A. Rosen and I. Dincer, โThermoeconomic analysis ofpower plants: an application to a coal fired electrical generatingstation,โ Energy Conversion andManagement, vol. 44, no. 17, pp.2743โ2761, 2003.
[7] M. V. J. J. Suresh, K. S. Reddy, and A. K. Kolar, โ4-E (energy,exergy, environment, and economic) analysis ofsolar thermalaided coal-fired power plants,โ Energy for Sustainable Develop-ment, vol. 14, no. 4, pp. 267โ279, 2010.
[8] A. Baghernejad and M. Yaghoubi, โExergoeconomic analysisand optimization of an Integrated Solar Combined CycleSystem (ISCCS) using genetic algorithm,โ Energy Conversionand Management, vol. 52, no. 5, pp. 2193โ2203, 2011.
[9] A. M. Patnode, Simulation and performance evaluation ofparabolic trough solar power plants [Ph.D. thesis], University ofWisconsin, Madison, Wis, USA, 2006.
[10] T. Stuetzle, Automatic control of the 30MWe SEGS VI parabolictrough plant [M.S. thesis], University of Wisconsin, Madison,Wis, USA, 2002.
[11] T. Stuetzle, N. Blair, J. W. Mitchell, and W. A. Beckman,โAutomatic control of a 30 MWe SEGS VI parabolic troughplant,โ Solar Energy, vol. 76, no. 1โ3, pp. 187โ193, 2004.
[12] M. A. Lozano, A. Valero, and L. Serra, โTheory of the exergeticcost and thermoeconomics optimization,โ in Proceedings of theInternational Symposium on International Conference on EnergySystems and Ecology (ENSEC โ93), Cracow, Polland, 1993.
[13] C. Frangopoulos,Thermoeconomic functional analysis: amethodfor optimal design or improvement of complex thermal systems[Ph.D. thesis], Georgia Institute of Technology, 1983.
[14] M. R. von Spakovsky, A practical generalized analysis approachto the optimal thermoeconomic design and improvement ofreal-world thermal systems [Ph.D. thesis], Georgia Institute ofTechnology, 1986.
[15] J. Uche,Thermoeconomic analysis and simulation of a combinedpower and desalination plant [Ph.D. thesis], Department ofMechanical Engineering, University of Zaragoza, 2000.
[16] J.Uche, L. Serra, andA.Valero, โThermoeconomic optimizationof a dual-purpose power and desalination plant,โ Desalination,vol. 136, no. 1โ3, pp. 147โ158, 2001.
[17] J. L. Silveira andC. E. Tuna, โThermoeconomic analysismethodfor optimization of combined heat and power systems. Part I,โProgress in Energy and Combustion Science, vol. 29, no. 6, pp.479โ485, 2003.
[18] Y. Yang, Y. Cui, H. Hou, X. Guo, Z. Yang, and N. Wang,โResearch on solar aided coal-fired power generation system
and performance analysis,โ Science in China, Series E, vol. 51,no. 8, pp. 1211โ1221, 2008.
[19] B. Zhang and J. Ma, โCoal price index forecast by a newpartial least-squares regression,โ Procedia Engineering, vol. 15,pp. 5025โ5029, 2011.
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