Design Optimization of a Hybrid Solar-Geothermal Power Plant

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1 Design Optimization of a Hybrid Solar- Power Plant Hybrid Solar Power plant Rafika Maali 1 *,Taar Kir 2, Ammar Ben Braim 1 1 Researc Unit Applied Termodynamic UR11ES8, Cemical Engeerg Processes /National Scool of Engeers, University of Gabes, Gabes, Tunisia 2 Researc Unit Applied Termodynamic UR11ES8, Mecanical Engeerg/ National Scool of Engeers, University of Gabes, Gabes, Tunisia 1 rafikamaali@gmail.com*, 2 taerkir@yaoo.fr, 1 ammar.benbraim@enig.rnu.tn (*: Correspondg Autor) Abstract: In recent years, te researc is focused on te electric energy product witout generation environmental pollution. As result new energy conversion Tecnologies are developed usg green energy. Te Organic Ranke Cycle (ORC) is a one of te vestigated Tecnologies due to its advantageous impact on te environment and te possibility to run under small generation temperature. In te present work an optimization design is conducted on a ybrid power plant (Solar ) workg accordg to Organic Ranke Cycle. Te power plant is maly constituted by an evaporator, a preeater, an air condenser, a steam turbe and a pump.mass and energy balances are establised troug te different components. Model is performed usg Equation Engeerg Solver (EES) software. Several plant design configurations are considered. Te optimum values of operatg parameters leadg to te best performance are determed. Keywords: Organic Ranke Cycle; evaporatg; energy balance; solar energy; geotermal energy; ybrid power plant. I. INTRODUCTION Te generation of electricity from eat is based on te steam turbe cycle. However, tis type of termodynamic cycle becomes less profitable at low temperature (below 34 C). Te Organic Ranke Cycle ORC is used for te production of electricity from a eat source at low temperature. Organic fluid is used te ORC cycle under specific operatg conditions. Several previous works are conducted on te organic fluid selection and te analyze of te ORC cycle performances among tem we present te followg vestigations. Delta et al. [1] studied an ORC cycle usg several workg fluids suc as: pentane, R245fa, R134a, R123ze, R123yf, R123, DR-2, C6FK, Toluene, D4 and D5. Takg to consideration te system efficiency and te turbe size, autors recommended n-pentane fluid for low temperature applications sce its flammability cannot be expected. He et al. [2] ave selected n-pentane among twenty workg fluids used subcritical ORC considerg operatg pressure, eat excange capacity and turbe size. Also Lakew et al. [3] recommended n-pentane among six candidates dependg on te energy production capacity and component size. Te objective of tis work is to study an ORC te sub-critical cycle for wic te sligtly supereated refrigerant steam is expanded troug te turbe. Four configurations of te ORC cycle will be studied were te ma difference is te type of te generation ot source (Solar energy, geotermal energy). II. CHOICE OF WORKING FLUID A. Te criteria for te workg fluid selection Te coice of workg fluid is based on certa properties. Moreover, tis fluid sould be termally and cemically stable, non-toxic, non-flammable, and expensive. Also tis fluid sould ave good eat transfer properties and suitable ODP (global warmg potential) [4]. Several autors ave suggested tat an ideal workg fluid for te Ranke cycle must satisfy te followg termodynamic and pysical criteria [5]: Te critical temperature of te workg fluid must be muc iger tan te igest temperature of te cycle (subcritical case). Te saturation pressure at te maximum cycle temperature must not be exceeded. Te saturation pressure at te mimum temperature of te cycle 1

2 must not be too low to avoid te problems of sealg and penetration of te ambient air te system. Te Triple pot must be muc lower tan te mimum ambient temperature tat is desired. A low specific eat value of te liquid is required. Also low viscosity, ig latent eat of vaporization, ig termal conductivity and wettg capacity of te workg fluid are preferred. B. Selection and verification Takg to consideration te results of te previous works and te expected values of te generation temperature for considered power plants ( 1 C), te selected workg fluid is n-pentane C 5 H 12. Te caracteristics of n pentane are grouped table I. TABLE I. Caracteristics of n pentane Caracteristics value Molecular formula C 5 H 12 Toxicity Low Flammability Very ig ODP GWP 3 Molar mass (Kg/mol) 72,15 Critical Temperature ( C) 196 Critical Pressure (bar) 33,7 Turbe discarge dry III. ORGANIC RANKINE CYCLE Te Organic Ranke Cycle, ORC, operates similarly to te normal Ranke cycle. Te ma difference between tem is te workg fluid type. In fact te Ranke Cycle usually runs usg wereas te ORC uses an organic fluid. Benefits and application fields of te Organic Ranke Cycle are as follows: A. Advantage of te Organic Ranke Cycle Te ORC tecnology attracts a lot of attention for generatg electricity from low temperature termal sources its advantages are dicated te followg [6]: - Simple Startg Metod. - Automatic and contuous operation. - Simple Matenance Procedure. - Witout operator request. - Long plant life (> 2 years). - No need to demeralize. - No need for degassg. B. Applications of te Organic Ranke Cycle ORC tecnology focuses on four ma major applications: geotermal, eat recovery, biomass, and solar energy [7]: energy sources are different. Dependg on its temperatures tey can be classified as Low, Medium and Hig. Te correspondg tresolds are below 1 C, between 1 C and 15 C, and up to 15 C, respectively [8]. Organic Ranke (ORC) cycle can be used to recover waste eat by vaporizg te boilg organic fluid te evaporator. Te advantage of tis tecnology is te reduction of environmental impacts caused by fossil fuels [9]. Tere are studies concerned wit te conversion to electrical energy of various eat sources at low or medium temperature. Tese sources used biomass combustion for cogenerations [1-13]. Conversion of solar energy to electricity or eat is possible, tey are four tecnology for power generation: eliostats, parabolic trougs, lear Fresnel reflectors and parabolic reflectors operatg above 3 C [14]. Te configuration cosen durg tis work is parabolic trougs solar generator. IV. THE ORC SYSTEM DESCRIPTION In tis part we will study different ORC cycle configurations. Tey are depleted by te used ot source type as follows: - ORC, - Solar ORC, - Hybrid ORC cycle were geotermal energy is used for preeatg and solar energy is used to eat and evaporate te workg fluid of te solar termal power plant. - Hybrid ORC cycle were geotermal energy is used for preeatg and evaporation wile te solar energy is used for supereatg. A calculation model is establised to determe te cycle efficiency, net power and workg fluid flow rate. A. Turbe model Te entalpy of te workg fluid at te outlet of te turbe is calculated usg te followg equation ( ) (1) t, out t, t, is t, t, out, is Were, denote entalpy and energy efficiency respectively. Moreover,te subscripts t, out and represent respectively te turbe, outlet and let Power output of te turbe is given by w m ( ) (2) t wf t, t, out Were m denote mass flow rate, Moreover,te subscripts wf represent te workg fluid, 2

3 B. Condenser model Te air ambient is used as cold source of te ORC system. Te global balance can be represented by tis equation Q m ( ) (3) out wf cd, cd, out. Were Q is te amount of eat transfer, Moreover,te subscripts cd represent te condenser C. mp model: Te entalpy of te workg fluid at te outlet of te pump is calculated usg te followg equation p, out, is p, p, out p, (4) p, is Power output of te pump is given by W m ( ) (5) p wf p, out p, te subscripts p and is pump and isentropic represent respectively te D. Preeater and evaporator models: Te amount of eat transferred troug te evaporator is given by Q m ( ) (6) wf ev, out ev, Te eat rate transferred to te preeater can be written as follows: Q mwf ( ) (7) pr pr, out pr, Te workg fluid te supereater receives a eat flux calculated by: Q m ( ) (8) sp wf sp, out sp, E. Net power and termal efficiency: Te power generated by te system is given by : Wnet mwf t, out t, t p, out p, p (9) Te energetic effeciency can be determed as follows : W net t (1) Q V. RESULTS AND DISCUSSION A. ORC configuration: A scematic process sceme is sown Fig. 1, Evaporator Fig. 1. ORC configuration. Te cycle is illustrated on te diagrams T-s as sown Fig. 2. Tis diagramm also sows also te pc pots between n-pentane and te transfer fluids durg te cycle ,6 bar 1,163 bar,2,4,6,8 Fig. 2. Temperature Entropy diagram of n-pentane geotermal ORC. Accordg to te pc values, it is noted tat te evaporation temperature is limited by te temperature of te ot source. Tis will affect te cycle performance. Te obtaed net power is about kw and te energy efficiency is around 2.41%. B. Solar ORC configuration: A scematic process sceme is sown Fig. 3, Evaporator Fig.3. Solar ORC configuration. m Te diagram T-s related to tis configuration is presented Fig. 4, Valve,27 bar,76 bar,2,4,6,8 Termal storage 3 3 Turbe Fields Turbe 3

4 Fig. 4. Temperature Entropy diagram of n-pentane solar ORC For tis configuration, te obtaed net power is equal to kw and te energy efficiency is equal to 1.75%. It is noted tat te evaporation temperature order of 1 C. Tis may crease te cost of te solar cycle. C. Solar supereatg te geotermal ORC configuration: Te power plant is represented by Fig. 5, supereater Fig. 7. preeatg te solar ORC configuration Fig. 8, sows te n-pentane T-s diagram obtaed for te last configuration ,76 bar 3-5,27 bar,2,4,6,8 Valve Preeater and evaporato Fields mp Termal storage condenser Fig.5. Solar ORC configuration. Turbe Fig. 8. Temperature Entropy diagram of n-pentane solar ORC wit geotermal preeatg. For tis cycle it as been observed tat te results are close to tat of only solar ORC cycle. But te advantage is to decrease te cost of solar cycle. VI. CONCLUSION For tis configuration te obtaed result is presented fig. 6: ,27 bar,76 bar,2,4,6,8 Fig. 6. Temperature Entropy diagram of n-pentane geotermal ORC wit solar supereatg. In tis case, a net power of 12 kw is obtaed wit an energy efficiency equal to 2.194%. D. preeatg te solar ORC configuration: A scematic process sceme is sown Fig. 7 Valv Pre Field supereater m Termal storage condenser 3 Turb In tis study analysis is conducted on te performances of four configuration of ORC cycle usg n-pentane as workg fluid. Accordg to te obtaed results, te suitable configuration is te ybrid cycle for wic te geotermal energy is used for organic fluid preeatg. REFERENCES [1] B. Datla and J. Brasz, "Organic Ranke Cycle System Analysis for Low G WP Workg Fluids,"International Refrigeration and Air Conditiong Conference,212/1/1/ 212. [2] C. He, C. Liu, H. Gao, H. Xie, Y. Li, S. Wu, et al., "Te optimal evaporation temperature and workg fluids for subcritical organic Ranke cycle,"energy,vol.38, pp , 212. [3] A. A. Lakew and O. Bolland, "Workg fluids for lowtemperature eat source,"applied Termal Engeerg, vol. 3, pp , 21. [4] R. Beit, Small and Micro Combed Heat and Power (CHP) Systems Advanced Design, Performance, Materials And Applications: Elsevier, 211. [5] O. Badr, S. D. Probert, and P. W. O'Callagan, "Selectg a workg fluid for a Ranke-cycle enge," Applied Energy, vol. 21, pp. 1-42, [6] S. Quoil, M. Van Den Broek,S. Declaye, P. Dewallef, V. Lemort, Tecno-economic survey of Organic Ranke Cycle (ORC) systems RENEWABLE AND SUSTAINABLE ENERGY REVIEWS,VOL. 22,PP , 213. [7] BF. Tcance, G. Lambros,A. Frangoudakis, G. Papadakis, "Low-gradeeatconversion to power usg Organic Ranke Cycles are view of various applications",renew Susta Energy Rev;vol.15: , 211. [8] S. Quoil, M. Van Den Broek,S. Declaye, P. Dewallef, V. Lemort, Tecno-economic survey of Organic Ranke Cycle 4

5 (ORC) systems RENEWABLE AND SUSTAINABLE ENERGY REVIEWS,VOL. 22,PP , 213. [9] Bundela PS, Cawla V. Sustaable development troug waste eat recovery. American Journal of Environmental Sciences;6(1):83 9,21. [1] I. Muammad, P.Byung Sik,K.Hyouck Ju,L.Dong Hyun and U.Muammad Termo-economic optimization of Regenerative Organic Ranke Cyclefor waste eat recovery applications Energy conversion and managemant , 214. [11] I.Obernberger, A.Hammerscmid Biomass fired CHP plant based on an ORC cycle Project ORC-STIA-Admont, Fal Report, Bios-energy system, 21. [12] I.Obernberger, P.Tonofer, E.Reisenofer Description and evaluationoftenew 1 kwel organic ranke cycle process tegrated te biomass CHP plant Lienz Austria. Euroeat and Power, 22. [13] G.Qiu, Y.Sao, J.Li, H.Liu, SB Riffat Experimental vestigation of a biomassfired ORC-based micro-chp for domestic application s. Fuel. 96: , 212. [14] C.Zou Hybridizationof Solar and Energy Bot Subcritical and Supercritical Organic Ranke cycles Energy Conversion & Management, 81, 72 82,

Optimized geothermal binary power cycles

Optimized geothermal binary power cycles Optimized geotermal binary power cycles Kontoleontos E., Mendrinos D., Karytsas C. Centre for Renewable Energy Sources, 9t km Maratonos ave., 9009 Pikermi Attikis, Greece ABSTRACT Tis study as been carried