Exergetic analysis and performance evaluation of parabolic trough concentrating solar thermal power plant (PTCSTPP)

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<ul><li><p>lu</p><p>110oad,</p><p>alyughiesci</p><p>f electon. A monven</p><p>PTCSTPP are available in literature. Few of them are discussed here.Wittmann et al. [2] proposed a methodology to set up aneconomically optimized bidding strategy at the energy exchange.Quaschning et al. [3] proposed a new method for estimating theoptimized solar eld size as a function of the solar irradiance.</p><p>in the collector-receiver assembly.Gupta and Kaushik [9] carried out the energy and exergy anal-</p><p>ysis for the different components of a proposed conceptual directsteam generation solar trough power plant. It was found that themaximum energy loss takes place in the condenser followed by thesolar collector eld (including the trough concentrators andabsorbers), while the maximum exergy loss occurs in the solarcollector eld. Palenzuela et al. [10] presented a thermodynamicevaluation of different congurations for coupling parabolic-trough</p><p>* Corresponding author. Tel.: 91 9891742963.</p><p>Contents lists available at</p><p>Ener</p><p>els</p><p>Energy 39 (2012) 258e273E-mail address: vundelaap@gmail.com (V.S. Reddy).would lead to greenhouse gas emissions. Development of solarenergy power generation technologies on a large scale is requiredfor controlling environmental problems. Then coal can also playa comparablymajor and long-term role for future. So far, 921MWofconcentrated Solar Power (CSP) plants has been installed world-wide and Parabolic Trough Concentrators contributing 93% of totalinstalled capacity. It required direct normal solar radiation and it isthe major drawback of it. A heat storage reservoir must be inte-grated into the oil circuit as suggested by Vogel and Henry [1] toaccess its power around the clock.</p><p>Numbers of design and performance evaluation methods of</p><p>The exergetic performance analysis not only determines themagnitudes, location and causes of irreversibilities in the plants,but also provides more signicant assessment of the individualcomponents efciency of plant [6]. Siva Reddy et al. [7] presentedcomponent wise energy and exergy analysis review of differentthermal power plants. Kaushik et al. [8] has presented second lawanalysis based on the exergy concept for a solar thermal powersystem. Relevant energy ow and exergy ow diagrams are drawnto show the various thermodynamic and thermal losses. It wasreported that the main energy loss takes place at the condenser ofthe heat engine part whereas the maximum exergy loss takes placeParabolic troughThermal powerExegetic analysisEnergetic analysisPTCSTPPSTPP</p><p>1. Introduction</p><p>India is the major consumers oeconomic growth and large populatiload electric power generation by c0360-5442/$ e see front matter 2012 Elsevier Ltd.doi:10.1016/j.energy.2012.01.023average energetic efciency can be increased from 22.01% to 22.62% for the location of Jodhpur, and incase of Delhi, it can be increased from 20.98% to 21.50%. Year round average exergetic efciency can beincreased, from 23.66% to 24.32% for the location of Jodhpur and in case of Delhi, it can be increased from22.56% to 23.11%. Land areas required for the 50 MWe thermal power plants are 79.2 ha and 118.8 harespectively for the locations of Jodhpur and Delhi.</p><p> 2012 Elsevier Ltd. All rights reserved.</p><p>ricity due to the rapidassive increase in basetional coal red plants</p><p>Birnbaum et al. [4] suggested an additional thermal inertia tostabilize the steam temperature for a safe turbine operation. Gauland Rabl [5] investigated the incidence-angle modier for parabolictroughs to clarify the connection between collector tests andprediction of long-term energy delivery by a collector array.Keywords:and exergetic efciencies of PTCSTPP increased by 1.49% and 1.51% with increasing pressure from 90 to105 bar respectively. Progression of the STPP from the variable load to full load conditions, the year roundAvailable online 17 February 2012 a Rankine heat engine have been optimized for maximum efciency. It has been found that, the energeticExergetic analysis and performance evasolar thermal power plant (PTCSTPP)</p><p>V. Siva Reddy a,*, S.C. Kaushik a, S.K. Tyagi b</p><p>aCentre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhib Sardar Swaran Singh National Institute of Renewable Energy, Jalandhar-Kapurthala R</p><p>a r t i c l e i n f o</p><p>Article history:Received 9 July 2011Received in revised form16 December 2011Accepted 14 January 2012</p><p>a b s t r a c t</p><p>Energetic and exergetic anplant system (parabolic trolosses as well as efcienc(PTCSTPP) under the spe</p><p>journal homepage: www.All rights reserved.ation of parabolic trough concentrating</p><p>016, IndiaWadala Kalan, Kapurthala 144601 (Punjab), India</p><p>sis has been carried out for the components of the solar thermal powercollector/receiver and Rankine heat engine). The energetic and exergeticfor typical parabolic trough concentrating solar thermal power plant</p><p>c operating conditions have been evaluated. Operating pressures for</p><p>SciVerse ScienceDirect</p><p>gy</p><p>evier .com/locate/energy</p></li><li><p>Fig. 3. Direct normal irradiation (DNI). Variation for length of day throughout the year</p><p>V.S. Reddy et al. / Energy 39 (2012) 258e273 259solar power plants and desalination facilities in a dry location.Blanco-Marigorta [11] performed exergetic analysis and evaluationof two different cooling technologies for the power cycle ofa 50 MWe solar thermal power plant. Kopac and Hilalci [12] studiedthe effect of ambient temperature on the exergy efciency of Cat-alagzi power plant in Turkey. The highest exergy losses were re-ported in the boiler, whereas highest energy losses take place in thecondenser. It was also found that an increase in ambient temper-ature decrease the exergy efciency of all the components ofa power plant except the condenser. In this analysis, they assumeda constant condenser pressure at different ambient temperatureswhich are not consistent with the actual situation. Aljundi [13]studied energy and exergy analysis of Al-Hossien power plant inJordan and showed that maximum exergy destruction occurs in theboiler (77%) followed by the turbine (13%). He also discussed theeffect of varying the reference environment state on the exergyanalysis and found that for moderate change in the reference state,no signicant changes in the performance of themajor componentsare realized.</p><p>In the present analysis, the tropical locations of Jodhpur and</p><p>Fig. 1. Direct normal irradiation (DNI). Variation for length of day throughout the yearfor the location Jodhpur.Delhi are selected. The DNI, ambient temperature and windvelocities are collected from EERE website [14]. Direct NormalIrradiation (DNI) variation for length of the day throughout the year</p><p>Fig. 2. Dry bulb temperature. Variation for length of day throughout the year for thelocation Jodhpur.for the location of Jodhpur is illustrated in Fig.1. The DNI of the solarradiation for the location Jodhpur is highest in the month ofFebruary and lowest in August. Highest DNI length of the day is 11 hin June and lowest is 8 h for December. Dry bulb temperaturevariation for length of the day throughout the year for the locationof Jodhpur has been shown in Fig. 2. The DNI variations for thelocation of Delhi have been shown in Fig. 3. The DNI of the solarradiation for the locations Delhi is highest in November and lowestin August. Highest DNI length of the day is 11 h in June and lowest is6 h for December. Dry bulb temperature variation for length of theday throughout the year for the location Delhi has been shown inFig. 4. Monthly average wind speed (m/s) variation for length of theday throughout the year for the locations of Jodhpur and Delhi areshown in Fig. 5. In Jodhpur, wind velocity is high therefore theconvective heat loss of the receiver is higher in Jodhpur comparedto Delhi. The designed DNI for the location of Jodhpur and Delhi aretaken as 870W/m2 and 620W/m2 respectively for parabolic troughthermal power plant model analysis. (This is considered based onthe available average peak solar irradiation throughout the year).</p><p>An attempt has been made to develop a model for solar eld</p><p>for the location Delhi.using the Matlab simulation program for present study. TheRankine power cycle is separately modeled with an engineering</p><p>Fig. 4. Dry bulb temperature. Variation for length of day throughout the year for thelocation Delhi.</p></li><li><p>equation solver [15]. Detailed exergetic analysis procedure forparabolic trough thermal power plant has been explained. Most ofthe researchers [12,13] assumed a constant pressure in the</p><p>tion in the last stage of the low pressure turbine outlet by consid-</p><p>consists of parabolic - trough mirror. The solar radiations areconcentrated on the focal line and impinge on an absorber tube.Heat is transferred by heat transfer uid Therminol VP-1 oil asshown in Fig. 7. Parabolic Trough Collector Array consists of 80loops; each loop contains 4 collectors for Jodhpur and 6 collectorsfor Delhi location on the basis of the DNI availability to obtaindesign operating temperature of Therminol VP-1. Each collector ismade up of twelve modules of 12.27 m long. Parabolic trough hasbeen placed NeS collector axis orientation, because the total annualenergy is greater than the one collected for E-W orientation.Therminol VP-1 oil at 566 K is pumped from a cold storage tankthrough the receiver where it is heated to 643 K and then on toa hot tank for storage. When power is needed from the plant, hotTherminol VP-1 oil is pumped to a boiler that produces super-heated steam for a conventional Rankine cycle system. From theboiler, Therminol VP-1 oil returned to the cold tank where it isstored and eventually reheated in the receiver. In over analysis thepower plant working in the daytime (6e10 h based on theavailability of solar radiation) only. In a direct two-tank thermalenergy storage system with 3 h of full-load storage capacity can beuse to produce constant power output. In the analysis, PTCSTPP iscompared here for two cases (variation of load of STPP and full loadoperation of STPP).</p><p>Fig. 5. Monthly average wind speed (m/s). Variation for length of day throughout theyear for the locations Jodhpur and Delhi.</p><p>V.S. Reddy et al. / Energy 39 (2012) 258e273260ering a variation of condenser pressure with respect to ambienttemperature. Exergetic and energetic performance analysis of thePTCSTPP are compared here for two different cases (variation ofload of STPP and full load operation of STPP).</p><p>2. System description of 50 MWe PTCSTPP</p><p>The solar thermal power system consisting of two subsystems,the collector - receiver subsystem and Rankine heat enginesubsystem is shown in Fig. 6. The collector receiver subsystem</p><p>aA Acondenser even though the ambient temperature varied consider-ably, which is not consistent with the actual situation. The noveltyof present study is that, the exergetic and energetic optimization ofthe operating pressures of the Rankine cycle for the maximumpossible efciency has been done with an allowable dryness frac-HPH1</p><p>20</p><p>17</p><p>Boiler </p><p>EXP1</p><p>HPH2</p><p>H</p><p>Parabolic Trough Collector Array</p><p>CP</p><p>CP</p><p>ColdTank</p><p>b</p><p>21</p><p>HotTank</p><p>A</p><p>A Collector</p><p>Module12</p><p>Module1</p><p>Fig. 6. Simplied schematic view of the 50 MThe Rankine heat engine subsystem consists of high and lowpressure turbine (HPT and LPT), Boiler (B), condensate extractpump (CEP), boiler feed water pumps (BFP), a dearetor, a generator(G), a condenser, three low pressure feed water heaters (LPH), twohigh pressure feed water heaters (HPH) and circulating pumps (CP).The feed water is preheated in three low pressure closed feedwaterheaters, a deaerator, and two high pressure closed feedwaterheaters. It enters the boiler at the maximum steam temperature ofthe power cycle at nearly 643 K. In order to avoid a large humidityfraction in steam at the turbine exhaust, steam reheating is alsoconsidered for modeling. T-S cycle diagram is presented in Fig. 8.</p><p>3. Thermodynamic analysis for 50 MWe PTCSTPP</p><p>The analysis of the individual components of PTCSTPP (Fig. 6)has been carried out by ignoring the kinetic and potential energychanges and assuming steady state operation.</p><p>Deaerator</p><p>7</p><p> C</p><p>LPH1LPH2LPH3</p><p>1213</p><p>16</p><p>18</p><p>8</p><p>5</p><p>2</p><p>11</p><p>1</p><p>4</p><p>19 3</p><p>22</p><p>6</p><p>15</p><p>BFP</p><p>G</p><p>109</p><p>LPT</p><p>14</p><p>EXP2CEP</p><p>P-Drum</p><p>1</p><p>HPT</p><p>23</p><p>25 2924 26 2827</p><p>EXP3 EXP4 EXP5We parabolic trough solar power plant.</p></li><li><p>3.1. Thermal power plant (TPP) subsystem</p><p>Fig. 7. Parabolic trough collector.</p><p>V.S. Reddy et al. / EnergyIn an open ow system there are three types of energy transferacross the control surface namely working transfer, heat transfer,and energy associated with mass transfer and/or ow. The rst lawof thermodynamics or energy balance for the steady ow process ofan open system is given by:</p><p>X_Qk _m</p><p>hi </p><p>C2i2</p><p> gZi</p><p> _mho C</p><p>2o2</p><p> gZo _W (1)</p><p>Where Qk heat transfer to system from source at temperature Tk,and W is the net work developed by the system. The other nota-tions C is the bulk velocity of the working uid, Z, is the altitude ofthe stream above the sea level, g is the specic gravitational force.</p><p>The energetic or rst law efciency hI of a system and/or systemcomponent is dened as the ratio of energy output to the energyinput to system/component i.e.</p><p>hI Desired output PowerInput Power supplied</p><p>(2)</p><p>Second law analysis is a method that uses the conservation ofmass and degradation of the quality of energy along with theentropy generation in the thermodynamic point of view andimprovement of energy systems. Exergetic analysis is a usefulmethod; to complement but not to replace energy analysis.Fig. 8. T-S diagram of 50 MWe parabolic trough solar power plant.The exergy ow for steady ow process of an open system isgiven by</p><p>X1 Ta</p><p>Tk</p><p>_Qk </p><p>Xin</p><p>_mJi JW Xout</p><p>_mJo _Idestroyed (3)</p><p>J _mhh0 h0o</p><p> Tas s0</p><p>i(4)</p><p>h0 h C2</p><p>2 gZ (5)</p><p>_Idestroyed Ta _Sgen (6)</p><p>where Ji and Jo are exergy associated with mass inow andoutows are respectively, JW is useful work done on/by system,_Idestroyed is irreversibility of process and h</p><p>0 is the methalpy assummation of enthalpy(h). The irreversibility may be due to heattransfer through nite temperature difference, mixing of uids atdifferent temperature and mechanical friction. Exergetic analysis isan effective means, to pinpoint losses due to irreversibility in a realsituation.</p><p>The exergetic or second law efciency is dened as</p><p>hII Actual thermal efficiency</p><p>maximum possible reversible thermal efficiency Exergy output</p><p>Exergy input(7)</p><p>To analyze the possible realistic performance, a detailed exergyanalysis of the Rankine heat engine has been carried out byignoring the kinetic and potential energy change. For steady stateow the exergy balance for a thermal system is given as below:</p><p>JW Xnk1</p><p>1 Ta</p><p>Tk</p><p>_Qk </p><p>Xrk1</p><p>_mJ</p><p>i </p><p>_mJ</p><p>o</p><p>k Ta _Sgen</p><p>(8)</p><p>The key component of exergetic analysis of thermal power planthas been explained in Appendix A.</p><p>Owing to uctuation in availability of solar radiation, solarthermal power plant to be performs at part load conditions. Themain equations characterizing part-load model for components inthe power cycle based on the mass ow rate of steam are givenbelow.</p><p>According to Bartlett [16], the percent reduction in turbine (HPTand LPT) efciency, as a function of the ow ratio:</p><p>% Reducti...</p></li></ul>