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Performance analysis of Germencik Geothermal Power Plant
Energy 52 (2013) 192e200
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Energy journal homepage: www.elsevier.com/locate/energy
Performance analysis of Germencik Geothermal Power Plant Murat Unverdi a, *, Yunus Cerci b a b
Department of Mechanical Engineering, Sakarya University, Sakarya, Turkey Department of Mechanical Engineering, Adnan Menderes University, Aydın, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 July 2012 Received in revised form 2 November 2012 Accepted 30 December 2012 Available online 16 March 2013
The objective of this study is to calculate the efficiency of exergy in Germencik Geothermal Power Plant, which has a power output of 47.4 MWe. As being the largest one in Turkey, this plant is operated by double-flash system which is based on the method of analysis of energy and exergy to evaluate its performance. The exergy analysis has been applied to the whole plant considering the first and the second laws of thermodynamics for each equipment. In this study, by using the actual data values the losses of exergy have been determined and the flow diagram of exergy has been illustrated. When making calculations, we have accepted dead state temperature as 15 C, and dead state pressure as 101.325 kPa s. The plant has 7 production and 6 reinjection wells. From these production wells, geothermal fluid reaches the plant at an average temperature ranging from 194 C to 214 C, pressure of 23 barse30 bars and a total flow rate of 688.87 kg/s. An exergy input of 134,124 kW is obtained from these wells. The largest exergy input of 36,395 kW is obtained from OB-14 and this accounts for 27.1% of total exergy input. Moreover, major exergy losses and their exergy input account for 3.34% (4478 kW) for valves, 22.72% (30,477 kW) for high and low-pressure separation process during the decomposition of geothermal fluid, 5.1% (6837 kW) for turbine-generator during the conversion of steam into mechanic work, 9.41% (12,622 kW) for cooling tower, 5.53% (7414 kW) for internal use, and finally 22.68% (30,415 kW) for reinjection wells. Additionally, the second law efficiency of turbine-generator has been found to be 87.4% and the second law efficiency of overall plant has been found to be 35.34%. The obtained results have been given in tables and the largest loss of exergy has been determined to occur in separators. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Geothermal energy Exergy analysis Germencik Geothermal Power Plant
1. Introduction The energy sources can be split into three categories: fossil fuels, renewable sources, and nuclear sources. The availability of abundant quantities of energy is an essential condition for the wellbeing and development of our modern industrial societies. As the population and economic activity increase, the global consumption of energy rises continuously. The principal primary energy sources which are used to satisfy this ever-increasing demand in all the economic sectors are fossil fuels. Although available in large quantities, they are neither infinite nor renewable [1,2]. The majority of energy produced in the world today is obtained from fossil fuels, i.e. coal, petroleum, natural gas and nuclear energy. In addition, sustainable and environmentally friendly resources, such as hydroelectric and geothermal, solar, wind, biogas, and wood, are
* Corresponding author. Tel.: þ90 505 530 85 99; fax: þ90 264 295 56 01. E-mail addresses: [email protected], [email protected] (M. Unverdi). 0360-5442/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2012.12.052
also utilized. Geothermal energy, a relatively benign energy source when compared with other energy sources due to reduction in greenhouse gas emissions, is used for electricity generation and direct utilization. Turkey is one of the countries with significant potential in geothermal energy. It is estimated that if Turkey utilizes all of its geothermal potential, the country can meet 14% of its total energy consumption (heat and electricity) from geothermal sources. Therefore, today geothermal energy is an attractive option in Turkey to replace fossil fuels [3,4]. Fundamental use of geothermal source at higher temperatures is power production. There are many geothermal-based power production systems available in practice. Three major types of power plants are operating today: dry-steam plants, flash-steam plants and binary-cycle plants where binary and combined flash/ binary plants are more recent designs. For high-temperature geothermal source (above 150 C) the suitable technologies are single and double-flash power plants. These plants may use geothermal water directly to produce power. For geothermal source having medium temperature (between 90 and 150 C), it is better to use binary power plants which run indirectly on geothermal. They
M. Unverdi, Y. Cerci / Energy 52 (2013) 192e200
Nomenclature E_ X_ h _ m s _ W Q_ T P
energy rate (kW) exergy rate (kW) specific enthalpy (kJ/kg) mass flow rate (kg/s) specific entropy (kJ/kg K) work (kW) heat (kW) temperature ( C) pressure (bar)
Greek letters J specific exergy (kJ/kg) h efficiency (%) Subscripts i inlet o outlet tr irreversible 0 reference state
utilized an organic fluid instead of geothermal water as the working fluid. For example, it can be ethanol, benzene, toluene, n-pentane and iso-pentane. Lower-temperature (below 90 C) geothermal resources are best suited for direct uses [3,5e9]. Lee suggested that geothermal resources be classified to reflect their ability to do thermodynamic work and then classified geothermal as low, medium and high-quality resources rather than low, medium-, and high-temperature resources. These resources with reference to SExI (specific exergy indices), SExI < 0.05, 0.05 SExI < 0.5 and SExI 0.5, respectively [10]. Performance analysis of a hypothetical double-flash geothermal power plant is performed and variations of fundamental characteristics of the plant are examined by Dagdas. The selected values for the power plant and the geothermal field are those of conditions in western Turkey. Reservoir temperature and geofluid mass flow rate are selected to be 210 C and 200 kg/s, respectively. From the same geothermal fluid flow rate, the double-flash power cycle can generate 20e25% more power than the single-flash cycle. However, double-flash technology is more expensive because of the extra equipment [11,12]. Bodvardson and Eggers compared single- and double-flash power plants using their exergy tables. It was shown that the exergetic efficiencies of a single-flash and double-flash cycle are 38.7% and 49% respectively [13]. Cerci evaluated performance of an 11.4 MW single-flash geothermal power plant in Denizli Turkey, along with major plant components. Major exergy destructions occurred due to the separation of steam from the geofluid, the discharge of the brine from the separator, turbine, generator and compressor inefficiencies, and the discharge of steam to the environment. The largest exergy destruction occurred during the discharge of the brine into the Menderes River. The second law efficiency of the plant was calculated to be 20.8% [14]. DiPippo, examined the second law assessment of binary plants generating power from lowtemperature geothermal fluids. The results show that binary plants can operate with very high second law or exergetic efficiencies even when the motive fluids are low-temperature and low-exergy. Exergetic efficiencies of 40% or greater have been achieved in certain plants with geofluids having specific exergies of 200 kJ/kg or lower. The main design feature leading to a high second law efficiency lies in the design of the heat exchangers to minimize the loss of exergy during heat transfer processes. Another important feature is that low-temperature cooling water that
193
allows a once-through system for waste heat rejection is available for higher second law efficiencies [15]. Kanoglu performed exergy analysis of an existing 12.4 MW existing binary geothermal power plant using actual data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy flow diagram and compared to the energy flow diagram. The causes of exergy destruction in the plant include the exergy of the working fluid lost in the condenser, the exergy of the brine that is reinjected, the turbineepump losses, and the preheaterevaporizer losses. The exergy destruction at these sites accounts for 22.6, 14.8, 13.9 and13.0% of total exergy input to the plant, respectively. The exergetic efficiency of the plant is determined to be 29.1% based on the exergy of geothermal fluid at the vaporizer inlet, and 34.2% based on the exergy drop of the brine across the vaporizerepreheater system [16]. Ganjehsarabi et al. analyzed Dora II geothermal power plant with 9.5 MW net power output is carried out by using actual plant data to evaluate plant performance and pinpoint the locations of exergy losses. The exergy losses take place through losses in the vaporizer, preheater, turbines, pumps and cooling tower, and the reinjection of the geothermal fluid. The exergy destruction ratios for these units and processes accounts for 7.97%, 1.25%, 11.93%, 1.3%, 14.92% and 32.18% of the total exergy input to the plant, respectively [17]. Chen et al. analyzed and proposed a supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle can achieve thermal efficiencies of 10.8e13.4% with the cycle high temperature of 393 Ke473 K as compared to 9.7e10.1% for the organic Rankine cycle, which is an improvement of 10e30% over the organic Rankine cycle [18]. Desai and Bandyopadhyay analyzed 16 different organic fluids as a working medium for the basic ORC (Organic Rankine Cycle) and modified Organic Rankine Cycles. Their obtained based on the 16 dry fluids, on an average, 16.5% improvement in thermal efficiency. The maximum improvement of 34.3% has been observed for n-perfluro pentane [19]. Hettiarachchi et al. the optimum cycle performance is evaluated and compared for working fluids that include ammonia, HCFC123, n-Pentane and PF5050. An exergy analysis reveals that the ammonia cycle efficiency has been largely compromised for the minimum plant cost. Ammonia is the preferred selection followed by HCFC123, nPentane and PF5050, respectively, although the latter has the most preferable physical and chemical characteristics [20]. Shengjun et al. presented an investigation on the parameter optimization and performance comparison of the fluids in subcritical ORC and transcritical power cycle in low-temperature (80e100 C) binary geothermal power system. Their results indicate that the choice of working fluid varies the objective function and the value of the optimized operation parameters are not all the same for different indicators. R123 in subcritical ORC system yields the highest thermal efficiency and exergy efficiency of 11.1% and 54.1%, respectively. Although the thermal efficiency and exergy efficiency of R125 in transcritical cycle is 46.4% and 20% lower than that of R123 in subcritical ORC, it provides 20.7% larger recovery efficiency [21]. Franco analyzed and discussed the exploitation of low temperature, water-dominated geothermal fields with a specific attention to regenerative Organic Rankine Cycles. The geothermal fluid inlet temperatures considered are in the 100e130 C range, while the return temperature of the brine is assumed to be between 70 and 100 C. The performances of different configurations, two basic cycle configurations and two recuperated cycles are analyzed and compared using dry organic fluids as the working fluids. The dry organic fluids for his study are R134a, isobutane, n-pentane and R245fa. Effects of the operating parameters such as turbine inlet
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temperature and pressure on the thermal efficiency, exergy destruction rate and Second Law efficiency are evaluated. The possible advantages of recuperated configurations in comparison with basic configurations are analyzed, showing that in a lot of cases the advantage in terms of performance increase is minimal but significant reductions in cooling systems surface area can be obtained (up to 20%) [22]. Franco and Villani analyzed exploitation of lower temperature, water-dominated geothermal fields and a methodology for optimizing geothermal binary plants is discussed. The geothermal fluid inlet temperatures considered are in the 110e 160 C range, while the return temperature of the brine is assumed to be between 70 and 100 C. The analysis shows that the brine specific consumption, ranging from 20 to 120 kg/s for each net MW produced, and the efficiency of the plants, ranging from 20% to 45% in terms of Second Law efficiency, are dictated mainly by the combination of the brine inlet temperature, the brine rejection temperature and the energy conversion cycle being used [23]. Ozgener et al. investigated energy and exergy analysis of SGDHS (Salihli geothermal district heating system) in Manisa, Turkey. As a result, the total exergy losses account for 2.22, 17.88 and 20.44%, respectively, of the total exergy input to the entire SGDHS. The overall energy and exergy efficiencies of the SGDHS components are also studied to evaluate their individual performances and determined to be 55.5 and 59.4%, respectively [24]. Kecebas et al. studied AFJET (Afyon geothermal district heating system) in Afyon, Turkey is considered and actual thermal data are collected and employed for analysis. Using actual system data, an evaluation of the district heating system performance, energy and exergy efficiencies, and exergy destructions in the system is conducted in this regard. The energy and exergy efficiencies of the entire AFJET are found to be 37.59% and 47.54%, respectively [25]. 2. Germencik geothermal field Aydin Germencik is a high-temperature geothermal field located west of the Menderes Graben within the boundaries of Alangullu-Omerbeyli. Between 1982 and 1988 nine exploration and production wells were first opened by the Mineral Research and Exploration (MRE). As a result of geological, geophysical, geochemical tests and studies and drilling works, well temperatures were determined to be over 200 and 215 C, and the highest temperature reservoir was found to be 232 C. Properties of the wells are listed in Table 1. The project application of the Guris Holding Co. GEGCO (Gurmat Electricity Generation Co. Inc.) was established in 1999 with the purpose of building and operating the Aydin Germencik geothermal electricity power plant. According to the results of the geophysical evaluation report made by the MRE after 2002, the field was extended to over an area of 50 km2. Between 2007 and 2008 nine wells were drilled by the Gurmat Electricity Generation Co. Inc. using new drilling techniques. The wells called OB-5, 6, 10,
Table 1 The depth and the temperature of the wells in the field. Well no
Depth (m)
Temperature ( C)
Well no
Depth (m)
Temperature ( C)
OB-1 OB-2 OB-3 OB-4 OB-5 OB-6 OB-7 OB-8 OB-9
1001 975 1195 285 1302 1100 2398 2000 1466
203 232 232 217 219 221 227 221 213
OB-10 OB-11 OB-14 OB-17 OB-19 AG-22 AG-24 AG-25 AG-26
1524 965 1205 1706 1651 2260 1252 1838 2432
224 210 228 228 227 205 199 191 195
11, 14, 17 are used for production, the wells called OB-8, 9, AG-22, 24, 25 and 26 are used for the reinjection of the geothermal water and the well called OB-3 is used for the reinjection of the condensed water. 3. Germencik Geothermal Power Plant The first test runs were initiated by the Gurmat Electricity Generation Co. Inc. in March 2009 in the first stage of the project, a 47.4 MWe power plant was constructed. In the second stage, the plan is to increase the capacity of the plant to approximately 100 MWe. Electricity generation from about 694.44 kg/s of geothermal fluid is projected in the eight production wells in the field. Approximately 20.8 million cubic meters of geothermal fluid will be produced per year in the geothermal reservoirs and approximately 16.4 million cubic meters (79%) of this amount will be pumped into the reinjection wells located in the west of the field. In addition, about 100 tons/hour of condensed water in the condenser will be pumped back into the reservoir. According to the current projection, five wells in the west of the field (below 150 C) are suitable for a binary cycle. The fact that the reservoir temperature in the field is above 220 C enables the plant to be safe and low-cost, and makes a twostage steam separation system (Double Flash) necessary. Thus, besides separating the same amount of steam as the single-stage steam separation system (Single Flash) does, Double flash separation provides 10e15% more power generation. The plant employs 50e60 members of staff. 3.1. Working principle of the power plant Currently, there are seven production wells and six injection wells at the plant. The reservoir, from the production wells, reaches the earth at temperatures between 197 and 215 C, at pressures between 22 and 29 bars and several kinds of inhibitors are injected at wells head. By providing the means for mixing of the reservoir fluid obtained from the production wells, the reservoir enters HPS (high-pressure separators). High-pressure steam is first obtained here. The reservoir which leaves the HPS is sent to the reinjection wells after the steam is removed for the second time in the LPS (low-pressure separators). In the dehumidification process, the vapors obtained from the HPS and LPS are for the last time exposed to a high pressure and low pressure demister respectively and are then sent into the turbine. The turbine inlet temperature for the high pressure line is 156.5 C, 5.972 bars, and for the low pressure 106.1 C, 2.132 bars pressure. Approximately 7.4 MWe of 47.4 MWe power obtained from the turbine is used for equipments at the plant. The remaining portion is sent to the Germencik shunt field from where it is distributed all over Turkey. The turbine outlet pressure is about 0.86 bar. The exit pressure is in the form of vacuum and varies depending on whether the collector, centrifugal vacuum pumps and ejectors are activated or not. The geothermal fluid is sent to the condenser units after finishing the expansion process in the turbine. Figs. 2 and 3 shows T-s diagram of the plant. The main objective in the condenser unit is to re-inject the environmentally harmful gases underground instead of releasing them into the atmosphere by condensing all the incondensable gases. The geothermal fluid leaving the turbine and reaching the main collector is subjected to a water spray process with the help of cooling-water. The geothermal fluid condensed in the main condenser is sent to the water-cooling tower to be cooled. Meanwhile, the condensed fluids are reinjected back into the ground at an approximate temperature of 40 C, at 12 bar pressure and with a flow rate of 38.89 kg/s by means of the OB-3 well which is operated about 10 h a day. The cooling tower inlet temperature is 40 C, the
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195
Fig. 1. Flow diagram for Germencik Geothermal Power Plant.
flow rate is 3683.23 kg/s and the outlet temperature is 20 C. Cooling water is sent into the main condenser with a flow rate of about 3333.23 kg/s and to the intermediate collectors (intercondenser A, B and after condenser) with a flow rate of 0.69 kg/s. During the cooling about 334.86 kg/s steam is released into the
atmosphere. In addition, the incondensable gases are liquefied in the main collector in 3 stages. With the aid of the ejectors in the power plant (1, 2, 3, 4), they are sent to the inter-condenser A, B and then to the after condenser by applying a vacuuming process in order to liquefy the gases in the main collector. First of all, in the
Fig. 2. T-s diagram for Germencik Geothermal Power Plant.
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Fig. 3. Germencik Geothermal Power Plant.
inter-condenser A and B, the cooling-water coming from the cooling tower is sprayed into the gases drawn from the main condenser through the ejectors (1, 2, 3) with the vacuuming process in order to liquefy them. Then, the liquefied gases are sent to the main condenser, the unliquidated gases are sent to the ejector (4) and the incondensable gases are sent to the centrifugal vacuum pumps. By applying a vacuuming process with the aid of ejector (4), the cooling-water coming from the cooling tower is sprayed into the incondensable gases drawn from the inter-condenser A and B in the after condenser, just like the process applied in the intercondenser A and B. The gases liquefied in the after condenser are sent to the main condenser. The gases which remain uncondensed in the inter-condenser A and B are liquefied for the last time with the aid of centrifugal vacuum pumps and the after condenser. Centrifugal vacuum pumps (A, B, C, D) work with the same principle as the ones in the heat exchangers; uncondensed gases flow from within and the coolingwater flows from without. In this way, after the liquefaction of the gases, the remaining incondensable gases are released into the atmosphere with a flow rate of 14.58 kg/s. Some components for the turbine are listed in Table 2.
Table 2 A list of some components for the turbine.
Rated output (at generator terminal) Rated speed at turbine Turbine design pressure for construction at HP main stop valve Turbine design temperature for construction at HP main stop valve Turbine design pressure for construction at LP main stop valve Turbine design temperature for construction at LP main stop valve Number of stage Quantity of cooling water Property of cooling water Temperature of cooling water (at design) Quantity of cooling oil (at design) Oil temperature at cooler outlet and inlet
4. Methods 4.1. Exergy analysis of the plant Exergy analysis of the plant was calculated for steady-flow conditions systems by using mass, energy and exergy equations to calculate the energy and exergy values of each point for the numbers in the flow diagram given in Fig. 1 and the results are tabulated in Table 3. In these calculations, steady-state pressure was taken as 101.325 kPa and temperature as 15 C [26]. EES (Engineering Equation Solver) software has been used for analysis [27]. The selected fluid property for the analysis is Steam_NBS. The mass balance for the steady-flow conditions systems is calculated from equations (1)e(3)
X
_i m
X
_ system _ o ¼ Dm m
_ system ¼ 0 Dm
Turbine and accessories Type of turbine
The geothermal fluid separated from the separators is reinjected back into the ground at a temperature of 110.3 C, 35 bar pressure and with a flow rate of 541.65 kg/s by means of the brine injection pump. Its flow diagram is shown in Fig. 1.
Mitsubishi single cylinder, double flow, top exhaust, dual pressure 47.400 kW 3000 rpm 14 bar g
200 C 3.5 bar g 150 C Double flow of 6 stage 90 m3/h Recirculation water 19.1 C 48 m3/h 45 C and 60 C
X
_i ¼ m
X
(1)
(2)
_o m
(3)
and the energy balance from equation (4)
X
E_ i
X
E_ o ¼
X
DE_ system
(4)
If the kinetic energy and potential energy change are neglected in equation (5),
_ ¼ Q_ W
X
X _ i hi þ Vi2 =2 þ gzi _ o ho þ Vo2 =2 þ gzo m m (5)
_ ¼ Q_ W
X
_ i hi _ o ho m m
(6)
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197
Table 3 Values measured and calculated in the plant for each point in the flow diagram. State no
Substance
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O CO2 H2O H2O H2O H2O H2O H2O H2O H2O H2O
Phase Liquid Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Liquid Liquid Liquid Sup. vapor Sup. vapor Liquid Liquid Sup. vapor Sup. vapor Sup. vapor Liquid Sup. vapor Sat. liquidevapor Liquid Liquid Gas Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid
mix. mix. Mix. mix. mix. mix. mix.
mix.
Temp. T ( C)
Pressure P (bar)
Enthalpy h (kJ/kg)
Entropy s (kJ/kg K)
Mass flow _ (kg/s) rate, m
15 205.3 e 206.6 e 212 e 197.2 e 214.6 e 213.3 e 214.6 e 160 166.1 164.9 164.9 157.8 107 110.5 110.5 157.4 106.1 159 20 156.5 56 47.4 40 e 20 20 40 110.3 110.3 110.3 110.3 110.3 110.3
1.01325 23.012 8.732 21.012 7.012 25.512 6.962 21.812 6.862 28.012 7.962 27.012 8.752 30.012 8.762 6.512 7.862 7.762 13.612 5.360 1.512 1.622 36.012 5.630 1.120 5.920 1.462 4.960 0.140 2.252 2.902 2.042 2.312 4.012 13.012 35.212 35.512 35.612 35.862 35.112 35.472
63 876.5 876.5 882.3 882.3 907.0 907.0 840.1 840.1 918.9 918.9 912.9 912.9 919.0 919.0 675.7 702.3 697.0 697.4 2759.4 448.7 463.5 466.0 2756.3 2686.9 2757.7 84.0 2759.6 2602.3 198.6 167.8 e 84.1 84.2 168.6 465.1 465.1 465.1 465.1 465.1 465.1
0.224 2.380 2.394 2.392 2.415 2.442 2.471 2.303 2.319 2.466 2.492 2.454 2.475 2.466 2.488 1.943 2.004 1.992 1.991 6.816 1.385 1.424 1.421 6.787 7.339 6.768 0.296 6.851 8.051 0.670 0.572 e 0.296 0.296 0.572 1.419 1.419 1.419 1.419 1.419 1.419
e
equation (6) is obtained andexergy equations
X_ i X_ o X_ dest ¼ DX_ system
(7)
DX_ system ¼ 0
(8)
X_ i X_ o ¼ X_ dest
(9)
where
_j X_ ¼ m
(10)
j ¼ ðh h0 Þ T0 ðs s0 Þ
(11)
equation (11) is obtained.
4.2. Exergy losses in the plant The exergy input from the seven production wells at the plant is a total of 134,124 kW the largest of which is from the OB-14 well, the input of which is 36,395 kW and corresponds to 27.1% of the total exergy input. A total of 4478 kW total exergy loss occurs in the valves and it corresponds to 3.34% of the total exergy input. During
81.94 81.94 95.83 95.83 90.28 90.28 73.61 73.61 179.16 179.16 88.89 88.89 79.16 79.16 341.66 347.21 312.49 312.49 103.38 60.59 541.65 541.65 87.57 56.94 13.33 3333.24 74.24 131.18 3722.12 3683.23 14.58 0.69 0.69 38.89 76.94 94.72 78.61 118.89 137.50 54.44
j (kJ/kg)
Energy rate, E_ (kW)
Exergy rate, X_ (kW)
e 186.0 182.0 188.1 181.6 198.2 189.8 171.9 167.3 203.2 195.6 200.7 194.7 203.4 196.8 112.3 121.3 119.5 120.1 777.3 47.7 51.2 54.5 782.6 552.6 789.4 0.1 767.4 260.7 5.9 3.5 e 0.2 0.3 4.5 54.2 54.3 54.3 54.3 54.2 54.3
e 66,661 66,661 78,515 78,515 76,188 76,188 57,200 57,200 153,342 153,342 75,547 75,547 67,761 67,761 209,319 221,957 198,126 198,230 278,755 23,366 216,907 218,262 235,845 149,411 35,928 69,860 200,183 333,100 504,821 385,787 e 15 15 4108 30,935 38,084 31,607 47,804 55,280 21,890
e 15,237 14,904 18,024 17,399 17,890 17,129 12,646 12,307 36,395 35,033 17,837 17,299 16,095 15,575 38,357 42,086 37,325 37,495 80,348 2883 27,689 29,501 68,522 31,462 10,525 28 56,961 34,186 21,879 12,650 e 0 0 173 4169 5135 4262 6449 7449 2951
Specific exergy,
the separation process of the Lp-Hp separators, 30,477 kW exergy losses occur and it corresponds to 22.72% of the total exergy input. After the separation process 30,415 kW exergy losses occur in the reinjection wells and it corresponds to 22.68% of the total exergy input. During the conversion of steam to mechanical work 6837 kW exergy losses occur in the turbine-generator pair and it corresponds to 5.1% of the total exergy input. In the cooling tower 12,622 kW exergy losses occur and it corresponds to 9.41% of the total exergy input. 7414 kW exergy losses occur in the internal usage in the plant and it corresponds to 5.53% of the total exergy input. 1495 kW exergy losses occur in the pumps, collectors, centrifugal vacuum pumps and OB-3 well and it corresponds to 1% of the total exergy input. In addition, 131 kW exergy losses occur in the OB-14 transfer pump and 556 kW exergy losses occur in the brine injection pump. The remaining 39,700 kW is net electrical power. Its exergy flow chart is shown in Fig. 4. The second law efficiency for the turbinegenerator pair and the whole plant is found from equations (12) and (13).
_ out;net =W _ tr hturbine ¼ W hturbine ¼ 47; 400=54; 237 ¼ 87:4% X
X_ in ¼ 134; 124 kW
(12)
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Fig. 4. Exergy flow chart for the geothermal power plant.
X
_ out;net ¼ 47; 400kW X_ out ¼ W
_ out;net =X_ hII ¼ W in hII ¼ 35:34%
(13)
5. Discussion and result Changing the environment is sometimes thought to be one way to increase plant efficiency, but it is not possible to do so. Due to the fact that during reinjection the temperature of the fluid is high (110 C), it can be used in fields where the temperature values are suitable. We can examine these areas as follows. U In addition to five wells (below 150 C) located in the west of the field together with the fluid reinjected, a pre-heated binary or an ORC (Organic Rankine Cycle) can be established, as an alternative design, which can increase the efficiency of the plant. For these cycles, fluids such as R134a, R152, R245fa, iso-pentane, npentane, isobutane can be used. In addition, according to the
analysis reports, it was determined that, depending on MW per unit power generation in the ORC (Organic Rankine Cycle), a 100 kg/h flow rate is required for 110 C geothermal fluid (reinjected in this power plant) and when it comes to 150e 160 C geothermal fluid, geothermal fluid ranging from 25 to 40 kg/h flow rate per MW is required. The amounts of geothermal fluid consumption of some temperature-dependent gases required for power generation in ORC are given in Fig. 5. Since the fluid reinjected in the Germencik Geothermal Power Plant is about five times greater than the flow rate necessary to generate power from the Organic Rankine Cycle, the amount of power generation as shown in Table 4, can be achieved from the fluid reinjected in this power plant. For example, if iso-pentane is selected as the working fluid to generate power from the fluid reinjected, the thermal efficiency of the current power plant can increase by about 16%, if isobutane is used, the thermal efficiency increases by about 12% with the alternative design established in the plant. This way,
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Fig. 5. The amount of geothermal fluid consumption of some temperature-dependent gases for every MW [22,33]. Table 4 Binary cycles and power production quantity which can be established in accordance with the existing power plant.[22,28] Plant and location
Geothermal temperature ( C)
Cycle
Working fluid
Gross capacity (kWe)
Kutahya-Simav, Turkey
145
R124
2900
42
37.39
Nigorikawa, Japan Otake, Japan Husavik, Iceland Wineagle, USA Nagqu, China Altheim, Austria Wabuska, CA, USA Neustadt-Glewe, GER Birdsville, Australia Chena Hot Spring, AK, USA
140 130 124 110 110 106 104 98e100 98e99 74
Rankine with superheat Rankine Rankine Kalina Rankine Rankine Rankine Rankine Rankine Rankine Rankine
R114 Isobutane NH3eH2O Isobutane Iso-pentane C5F12 Iso-pentane C5F12 R114 R134a
1000 1000 1700 700 1000 1000 1750 230 150 400
50 14.7 53 63 69 86 34.3 120.8 200 57.9
10.83 36.85 17.37 6 7.85 6.23 27.64 1.03 0.41 3.74
electricity can be produced. The overall efficiency of the power plant can increase by 25e45% with such fluids and designs. U Since there are residential areas and agricultural activities are undertaken around the plant, together with greenhouse heating, this fluid can be utilized for district heating. For example, for district heating; the exergy efficiency of the power plant can increase by 60% according to a design aimed at heating a 3.600 housing unit area with a 70 C reservoir temperature on average, the exergy efficiency of the power plant can increase by 40% Table 5 Comparison of Kızıldere and Germencik Geothermal Power Plants. Values
Kızıldere Geothermal Power Plant [14]
Germencik Geothermal Power Plant
Total mass flow rate input in the plant (kg/s) High-temperature reservoir ( C) Steady-state temperature ( C) Steady-state pressure (kPa) Total exergy input in the plant (kW) Second law efficiency (%) Steam separation Reinjection Power output (kWe)
282.84
688.87
239.9
214.6
15
15
101.325
101.325
54,649
134,124
20.8
35.34
Single flash e 11,400
Double flash Ok 39,700
Specific brine consumption (kg/s)/MW
Compatible with Germencik Geothermal Power Plant (MWe)
according to a design aimed at heating a 10.000 housing unit area with a 40 C reservoir temperature on average, the exergy efficiency of the power plant can increase by 45% according to a design aimed at heating a 7.500 housing unit area with a 110 C reservoir temperature on average. For greenhouse heating; 100 MWt district heating can be achieved for an approximately 450.000 m2 area and 95 C [25,30e32]. Additionally, instead of releasing gases into the atmosphere at 14.58 kg/s, dry ice production can be achieved by placing a compressor and intercooler on the current system in the plant. Although the initial investment costs of the addition of the compressor and intercooler to the plant are high, it is thought that gas sales revenue will meet the initial investment costs in the long run. However, the addition of the compressor and intercooler to the plant will lead to a 5% loss of plant efficiency [14e16,28,29]. In this study, it was determined in which parts of the plant exergy losses occur by applying exergy analysis in general as well as to the equipments separately. According to the calculations, maximum exergy losses occur in the separators and these losses correspond to 22.72% of the total losses. In addition, exergy losses occur during the whole cycle. Exergy losses that occur in the cooling tower, in the reinjection wells, in internal usage and in the turbine-generator pair correspond to 9.41%, 22.68%, 5.53% and 5.1% respectively. The second law efficiency of the plant was found to be 35.34%. In Table 5, the values of the Germencik Geothermal Power Plant were compared to those of the Kızıldere Geothermal Power Plant the performance analysis of which was made before.
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As shown in Table 5, the increase in the efficiency of the equipments used in the power plant in parallel with developing technology increased the efficiency of the Germencik power plant. In addition, the operation of the Germencik Geothermal Power Plant according to the two-stage steam separation system was observed to have increased the efficiency. Although the chosen steady-state temperature and pressure may influence the efficiency of plants, it was concluded that the Germencik power plant runs more efficiently. 6. Conclusions In this study, energy and exergy analysis were carried out in Germencik Geothermal Power Plant. When evaluating the performance analysis, exergy efficiency for each piece of equipment and for the plant as a whole was calculated by using the pressure and temperature values measured in the plant. The exergy flow diagram was plotted for the exergy losses. This study reached the following conclusions: Compared to other geothermal fields and power plants (Kizildere, Salavatli), Germencik geothermal field and power plant is a field of high temperature and high qualifications. The exergy efficiency and the efficiency of the turbinegenerator pair of the plant were found to be 35.34% and 87.4% respectively. The operation of the Germencik Geothermal Power Plant according to the two-stage steam separation system (double flash) significantly increased the efficiency. Geothermal fluid reinjection ensures the continuity of the field and prevents environmental pollution, but 7.4 MWe used by the pumps during the reinjection of the fluid causes a decrease in the efficiency of the power plant. It was determined that the greatest exergy loss in the plant occurs in the separators (30,477 kW). Dry ice production can be achieved by placing a compressor and an intercooler in the current system and by using the gas released into the atmosphere at 14.58 kg/s. Due to the high temperature values of the fluid reinjected, it can be utilized in the areas of greenhouse heating, domestic heating, heat pumps, thermal spring path and aquaculture with suitable temperatures or power plant efficiency can be increased by 25e45% establishing a binary cycle together with the production wells located in the west of the field. An integrated geothermal plant should be established in order to improve the efficiency of the field and in order to benefit fully from the current reservoir. Acknowledgments We would like to thank Ergun Isler, operations manager of the Gurmat Electricity Generation Co. Inc. and the staff for their contribution to make this study possible. Special thanks for their contribution to the Adnan Menderes University. References [1] Galanis N, Cayer E, Roy P, Denis ES, Désilets M. Electricity generation from low temperature sources. Journal of Applied Fluid Mechanics 2009;2(2):55e67.
[2] Erdogdu E. A snapshot of geothermal energy potential and utilization in Turkey. Renewable and Sustainable Energy Reviews 2009;13:2535e43. [3] Ratlamwala TAH, Dincer I, Gadalla MA. Performance analysis of a novel integrated geothermal-based system for multi-generation applications. Applied Thermal Engineering 2012;40:71e9. [4] Celik MY, Sabah E. The geological and technical characterization of ÖmerGecek geothermal area and the environmental impact assessment of geothermal heating system. Environmental Geology 2002;41:942e53. [5] Yari M. Exergetic analysis of various types of geothermal power plants. Renewable Energy 2010;35:112e21. [6] Kuo C, Hsu S, Chang K, Wang C. Analysis of a 50 kW organic Rankine cycle system. Energy 2011;36:5877e85. [7] Siddiqi M, Atakan B. Alkanes as fluids in Rankine cycles in comparison to water, benzene and toluene. Energy 2012;45:256e63. [8] Saleh B, Koglbauer G, Wendland M, Fischer J. Working fluids for lowtemperature organic Rankine cycles. Energy 2007;32:1210e21. [9] Coskun C, Oktay Z, Dincer I. Performance evaluations of a geothermal power plant. Applied Thermal Engineering 2011;31:4074e82. [10] Lee KC. Classification of geothermal resources by exergy. Geothermics 2001; 30:431e42. [11] Dagdas A. Performance analysis and optimization of double-flash geothermal power plants. Journal of Energy Resources Technology 2007;129:125e33. [12] DiPippo R. Small geothermal power plants-design, performance and economics. GHC Bulletin 1999;20(2):1e8. [13] Bodvardson G, Eggers DE. The exergy of thermal water. Geothermics 1972; 1(3):93e5. [14] Cerci Y. Performance evaluation of a single flash geothermal power plant in Denizli Turkey. Energy 2003;28:27e35. [15] DiPippo R. Second law assessment of binary plants generating power from low-temperature geothermal fluids. Geothermics 2004;33:565e86. [16] Kanoglu M, Bolatturk A. Performance and parametric investigation of a binary geothermal power plant by exergy. Renewable Energy 2008;33:2366e74. [17] Ganjehsarabi H, Gungor A, Dincer I. Exergetic performance analysis of Dora II geothermal power plant in Turkey. Energy 2012:1e8. [18] Chen H, Goswami DY, Rahman MM, Stefanakos EK. A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power. Energy 2011;36:549e55. [19] Desai NB, Bandyopadhyay S. Process integration of organic Rankine cycle. Energy 2009;34:1674e86. [20] Hettiarachchi HDM, Golubovic M, Worek WM, Ikegami Y. Optimum design criteria for an organic Rankine cycle using low-temperature geothermal heat sources. Energy 2007;32:1698e706. [21] Shengjun Z, Huaixin W, Tao G. Performance comparison and parametric optimization of subcritical organic Rankine cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation. Applied Energy 2011;88:2740e54. [22] Franco A. Power production from a moderate temperature geothermal resource with regenerative organic Rankine cycles. Energy for Sustainable Development 2011;15:411e9. [23] Franco A, Villani M. Optimal design of binary cycle power plants for waterdominated, medium-temperature geothermal fields. Geothermics 2009;38: 379e91. [24] Ozgener L, Hepbasli A, Dincer I. Energy and exergy analysis of Salihli geothermal district heating system in Manisa, Turkey. International Journal of Energy Research;29:393e408. [25] Kecebas A, Kayfeci M, Gedik E. Performance investigation of the Afyon geothermal district heating system for building applications: exergy analysis. Applied Thermal Engineering 2011;31:1229e37. [26] Cengel YA, Boles MA. Thermodynamics: an engineering approach. 5th ed. New York: McGraw-Hill; 1998. [27] Alvarado FL, Klein SA. Engineering equation solver, F-chart software; 2012. [28] Tchanche BF, Lambrinos Gr, Frangoudakis A, Papadakis G. Low-grade heat conversion into power using organic Rankine cycles a review of various applications. Renewable and Sustainable Energy Reviews 2011; 15:3963e79. [29] Heberle F, Brüggemann D. Exergy based fluid selection for a geothermal organic Rankine cycle for combined heat and power generation. Applied Thermal Engineering 2010:1326e32. [30] Ozgener L, Hepbasli A, Dincer I. Energy and exergy analysis of the Gonen geothermal district heating system, Turkey. Geothermics 2005;34:632e45. [31] Hepbasli A, Canakci C. Geothermal district heating applications in Turkey: a case study of IzmireBalcova. Energy Conversion and Management 2003;44: 1285e301. [32] Bakos GC, Fidanidis D, Tsagas NF. Greenhouse heating using geothermal energy. Geothermics 1999;28:759e65. [33] Franco A, Vaccaro M. An integrated “Reservoir-Plant” strategy for a sustainable and efficient use of geothermal resources. Energy 2012;37:299e310.
Contents lists available at SciVerse ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Performance analysis of Germencik Geothermal Power Plant Murat Unverdi a, *, Yunus Cerci b a b
Department of Mechanical Engineering, Sakarya University, Sakarya, Turkey Department of Mechanical Engineering, Adnan Menderes University, Aydın, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 July 2012 Received in revised form 2 November 2012 Accepted 30 December 2012 Available online 16 March 2013
The objective of this study is to calculate the efficiency of exergy in Germencik Geothermal Power Plant, which has a power output of 47.4 MWe. As being the largest one in Turkey, this plant is operated by double-flash system which is based on the method of analysis of energy and exergy to evaluate its performance. The exergy analysis has been applied to the whole plant considering the first and the second laws of thermodynamics for each equipment. In this study, by using the actual data values the losses of exergy have been determined and the flow diagram of exergy has been illustrated. When making calculations, we have accepted dead state temperature as 15 C, and dead state pressure as 101.325 kPa s. The plant has 7 production and 6 reinjection wells. From these production wells, geothermal fluid reaches the plant at an average temperature ranging from 194 C to 214 C, pressure of 23 barse30 bars and a total flow rate of 688.87 kg/s. An exergy input of 134,124 kW is obtained from these wells. The largest exergy input of 36,395 kW is obtained from OB-14 and this accounts for 27.1% of total exergy input. Moreover, major exergy losses and their exergy input account for 3.34% (4478 kW) for valves, 22.72% (30,477 kW) for high and low-pressure separation process during the decomposition of geothermal fluid, 5.1% (6837 kW) for turbine-generator during the conversion of steam into mechanic work, 9.41% (12,622 kW) for cooling tower, 5.53% (7414 kW) for internal use, and finally 22.68% (30,415 kW) for reinjection wells. Additionally, the second law efficiency of turbine-generator has been found to be 87.4% and the second law efficiency of overall plant has been found to be 35.34%. The obtained results have been given in tables and the largest loss of exergy has been determined to occur in separators. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Geothermal energy Exergy analysis Germencik Geothermal Power Plant
1. Introduction The energy sources can be split into three categories: fossil fuels, renewable sources, and nuclear sources. The availability of abundant quantities of energy is an essential condition for the wellbeing and development of our modern industrial societies. As the population and economic activity increase, the global consumption of energy rises continuously. The principal primary energy sources which are used to satisfy this ever-increasing demand in all the economic sectors are fossil fuels. Although available in large quantities, they are neither infinite nor renewable [1,2]. The majority of energy produced in the world today is obtained from fossil fuels, i.e. coal, petroleum, natural gas and nuclear energy. In addition, sustainable and environmentally friendly resources, such as hydroelectric and geothermal, solar, wind, biogas, and wood, are
* Corresponding author. Tel.: þ90 505 530 85 99; fax: þ90 264 295 56 01. E-mail addresses: [email protected], [email protected] (M. Unverdi). 0360-5442/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2012.12.052
also utilized. Geothermal energy, a relatively benign energy source when compared with other energy sources due to reduction in greenhouse gas emissions, is used for electricity generation and direct utilization. Turkey is one of the countries with significant potential in geothermal energy. It is estimated that if Turkey utilizes all of its geothermal potential, the country can meet 14% of its total energy consumption (heat and electricity) from geothermal sources. Therefore, today geothermal energy is an attractive option in Turkey to replace fossil fuels [3,4]. Fundamental use of geothermal source at higher temperatures is power production. There are many geothermal-based power production systems available in practice. Three major types of power plants are operating today: dry-steam plants, flash-steam plants and binary-cycle plants where binary and combined flash/ binary plants are more recent designs. For high-temperature geothermal source (above 150 C) the suitable technologies are single and double-flash power plants. These plants may use geothermal water directly to produce power. For geothermal source having medium temperature (between 90 and 150 C), it is better to use binary power plants which run indirectly on geothermal. They
M. Unverdi, Y. Cerci / Energy 52 (2013) 192e200
Nomenclature E_ X_ h _ m s _ W Q_ T P
energy rate (kW) exergy rate (kW) specific enthalpy (kJ/kg) mass flow rate (kg/s) specific entropy (kJ/kg K) work (kW) heat (kW) temperature ( C) pressure (bar)
Greek letters J specific exergy (kJ/kg) h efficiency (%) Subscripts i inlet o outlet tr irreversible 0 reference state
utilized an organic fluid instead of geothermal water as the working fluid. For example, it can be ethanol, benzene, toluene, n-pentane and iso-pentane. Lower-temperature (below 90 C) geothermal resources are best suited for direct uses [3,5e9]. Lee suggested that geothermal resources be classified to reflect their ability to do thermodynamic work and then classified geothermal as low, medium and high-quality resources rather than low, medium-, and high-temperature resources. These resources with reference to SExI (specific exergy indices), SExI < 0.05, 0.05 SExI < 0.5 and SExI 0.5, respectively [10]. Performance analysis of a hypothetical double-flash geothermal power plant is performed and variations of fundamental characteristics of the plant are examined by Dagdas. The selected values for the power plant and the geothermal field are those of conditions in western Turkey. Reservoir temperature and geofluid mass flow rate are selected to be 210 C and 200 kg/s, respectively. From the same geothermal fluid flow rate, the double-flash power cycle can generate 20e25% more power than the single-flash cycle. However, double-flash technology is more expensive because of the extra equipment [11,12]. Bodvardson and Eggers compared single- and double-flash power plants using their exergy tables. It was shown that the exergetic efficiencies of a single-flash and double-flash cycle are 38.7% and 49% respectively [13]. Cerci evaluated performance of an 11.4 MW single-flash geothermal power plant in Denizli Turkey, along with major plant components. Major exergy destructions occurred due to the separation of steam from the geofluid, the discharge of the brine from the separator, turbine, generator and compressor inefficiencies, and the discharge of steam to the environment. The largest exergy destruction occurred during the discharge of the brine into the Menderes River. The second law efficiency of the plant was calculated to be 20.8% [14]. DiPippo, examined the second law assessment of binary plants generating power from lowtemperature geothermal fluids. The results show that binary plants can operate with very high second law or exergetic efficiencies even when the motive fluids are low-temperature and low-exergy. Exergetic efficiencies of 40% or greater have been achieved in certain plants with geofluids having specific exergies of 200 kJ/kg or lower. The main design feature leading to a high second law efficiency lies in the design of the heat exchangers to minimize the loss of exergy during heat transfer processes. Another important feature is that low-temperature cooling water that
193
allows a once-through system for waste heat rejection is available for higher second law efficiencies [15]. Kanoglu performed exergy analysis of an existing 12.4 MW existing binary geothermal power plant using actual data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy flow diagram and compared to the energy flow diagram. The causes of exergy destruction in the plant include the exergy of the working fluid lost in the condenser, the exergy of the brine that is reinjected, the turbineepump losses, and the preheaterevaporizer losses. The exergy destruction at these sites accounts for 22.6, 14.8, 13.9 and13.0% of total exergy input to the plant, respectively. The exergetic efficiency of the plant is determined to be 29.1% based on the exergy of geothermal fluid at the vaporizer inlet, and 34.2% based on the exergy drop of the brine across the vaporizerepreheater system [16]. Ganjehsarabi et al. analyzed Dora II geothermal power plant with 9.5 MW net power output is carried out by using actual plant data to evaluate plant performance and pinpoint the locations of exergy losses. The exergy losses take place through losses in the vaporizer, preheater, turbines, pumps and cooling tower, and the reinjection of the geothermal fluid. The exergy destruction ratios for these units and processes accounts for 7.97%, 1.25%, 11.93%, 1.3%, 14.92% and 32.18% of the total exergy input to the plant, respectively [17]. Chen et al. analyzed and proposed a supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle can achieve thermal efficiencies of 10.8e13.4% with the cycle high temperature of 393 Ke473 K as compared to 9.7e10.1% for the organic Rankine cycle, which is an improvement of 10e30% over the organic Rankine cycle [18]. Desai and Bandyopadhyay analyzed 16 different organic fluids as a working medium for the basic ORC (Organic Rankine Cycle) and modified Organic Rankine Cycles. Their obtained based on the 16 dry fluids, on an average, 16.5% improvement in thermal efficiency. The maximum improvement of 34.3% has been observed for n-perfluro pentane [19]. Hettiarachchi et al. the optimum cycle performance is evaluated and compared for working fluids that include ammonia, HCFC123, n-Pentane and PF5050. An exergy analysis reveals that the ammonia cycle efficiency has been largely compromised for the minimum plant cost. Ammonia is the preferred selection followed by HCFC123, nPentane and PF5050, respectively, although the latter has the most preferable physical and chemical characteristics [20]. Shengjun et al. presented an investigation on the parameter optimization and performance comparison of the fluids in subcritical ORC and transcritical power cycle in low-temperature (80e100 C) binary geothermal power system. Their results indicate that the choice of working fluid varies the objective function and the value of the optimized operation parameters are not all the same for different indicators. R123 in subcritical ORC system yields the highest thermal efficiency and exergy efficiency of 11.1% and 54.1%, respectively. Although the thermal efficiency and exergy efficiency of R125 in transcritical cycle is 46.4% and 20% lower than that of R123 in subcritical ORC, it provides 20.7% larger recovery efficiency [21]. Franco analyzed and discussed the exploitation of low temperature, water-dominated geothermal fields with a specific attention to regenerative Organic Rankine Cycles. The geothermal fluid inlet temperatures considered are in the 100e130 C range, while the return temperature of the brine is assumed to be between 70 and 100 C. The performances of different configurations, two basic cycle configurations and two recuperated cycles are analyzed and compared using dry organic fluids as the working fluids. The dry organic fluids for his study are R134a, isobutane, n-pentane and R245fa. Effects of the operating parameters such as turbine inlet
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temperature and pressure on the thermal efficiency, exergy destruction rate and Second Law efficiency are evaluated. The possible advantages of recuperated configurations in comparison with basic configurations are analyzed, showing that in a lot of cases the advantage in terms of performance increase is minimal but significant reductions in cooling systems surface area can be obtained (up to 20%) [22]. Franco and Villani analyzed exploitation of lower temperature, water-dominated geothermal fields and a methodology for optimizing geothermal binary plants is discussed. The geothermal fluid inlet temperatures considered are in the 110e 160 C range, while the return temperature of the brine is assumed to be between 70 and 100 C. The analysis shows that the brine specific consumption, ranging from 20 to 120 kg/s for each net MW produced, and the efficiency of the plants, ranging from 20% to 45% in terms of Second Law efficiency, are dictated mainly by the combination of the brine inlet temperature, the brine rejection temperature and the energy conversion cycle being used [23]. Ozgener et al. investigated energy and exergy analysis of SGDHS (Salihli geothermal district heating system) in Manisa, Turkey. As a result, the total exergy losses account for 2.22, 17.88 and 20.44%, respectively, of the total exergy input to the entire SGDHS. The overall energy and exergy efficiencies of the SGDHS components are also studied to evaluate their individual performances and determined to be 55.5 and 59.4%, respectively [24]. Kecebas et al. studied AFJET (Afyon geothermal district heating system) in Afyon, Turkey is considered and actual thermal data are collected and employed for analysis. Using actual system data, an evaluation of the district heating system performance, energy and exergy efficiencies, and exergy destructions in the system is conducted in this regard. The energy and exergy efficiencies of the entire AFJET are found to be 37.59% and 47.54%, respectively [25]. 2. Germencik geothermal field Aydin Germencik is a high-temperature geothermal field located west of the Menderes Graben within the boundaries of Alangullu-Omerbeyli. Between 1982 and 1988 nine exploration and production wells were first opened by the Mineral Research and Exploration (MRE). As a result of geological, geophysical, geochemical tests and studies and drilling works, well temperatures were determined to be over 200 and 215 C, and the highest temperature reservoir was found to be 232 C. Properties of the wells are listed in Table 1. The project application of the Guris Holding Co. GEGCO (Gurmat Electricity Generation Co. Inc.) was established in 1999 with the purpose of building and operating the Aydin Germencik geothermal electricity power plant. According to the results of the geophysical evaluation report made by the MRE after 2002, the field was extended to over an area of 50 km2. Between 2007 and 2008 nine wells were drilled by the Gurmat Electricity Generation Co. Inc. using new drilling techniques. The wells called OB-5, 6, 10,
Table 1 The depth and the temperature of the wells in the field. Well no
Depth (m)
Temperature ( C)
Well no
Depth (m)
Temperature ( C)
OB-1 OB-2 OB-3 OB-4 OB-5 OB-6 OB-7 OB-8 OB-9
1001 975 1195 285 1302 1100 2398 2000 1466
203 232 232 217 219 221 227 221 213
OB-10 OB-11 OB-14 OB-17 OB-19 AG-22 AG-24 AG-25 AG-26
1524 965 1205 1706 1651 2260 1252 1838 2432
224 210 228 228 227 205 199 191 195
11, 14, 17 are used for production, the wells called OB-8, 9, AG-22, 24, 25 and 26 are used for the reinjection of the geothermal water and the well called OB-3 is used for the reinjection of the condensed water. 3. Germencik Geothermal Power Plant The first test runs were initiated by the Gurmat Electricity Generation Co. Inc. in March 2009 in the first stage of the project, a 47.4 MWe power plant was constructed. In the second stage, the plan is to increase the capacity of the plant to approximately 100 MWe. Electricity generation from about 694.44 kg/s of geothermal fluid is projected in the eight production wells in the field. Approximately 20.8 million cubic meters of geothermal fluid will be produced per year in the geothermal reservoirs and approximately 16.4 million cubic meters (79%) of this amount will be pumped into the reinjection wells located in the west of the field. In addition, about 100 tons/hour of condensed water in the condenser will be pumped back into the reservoir. According to the current projection, five wells in the west of the field (below 150 C) are suitable for a binary cycle. The fact that the reservoir temperature in the field is above 220 C enables the plant to be safe and low-cost, and makes a twostage steam separation system (Double Flash) necessary. Thus, besides separating the same amount of steam as the single-stage steam separation system (Single Flash) does, Double flash separation provides 10e15% more power generation. The plant employs 50e60 members of staff. 3.1. Working principle of the power plant Currently, there are seven production wells and six injection wells at the plant. The reservoir, from the production wells, reaches the earth at temperatures between 197 and 215 C, at pressures between 22 and 29 bars and several kinds of inhibitors are injected at wells head. By providing the means for mixing of the reservoir fluid obtained from the production wells, the reservoir enters HPS (high-pressure separators). High-pressure steam is first obtained here. The reservoir which leaves the HPS is sent to the reinjection wells after the steam is removed for the second time in the LPS (low-pressure separators). In the dehumidification process, the vapors obtained from the HPS and LPS are for the last time exposed to a high pressure and low pressure demister respectively and are then sent into the turbine. The turbine inlet temperature for the high pressure line is 156.5 C, 5.972 bars, and for the low pressure 106.1 C, 2.132 bars pressure. Approximately 7.4 MWe of 47.4 MWe power obtained from the turbine is used for equipments at the plant. The remaining portion is sent to the Germencik shunt field from where it is distributed all over Turkey. The turbine outlet pressure is about 0.86 bar. The exit pressure is in the form of vacuum and varies depending on whether the collector, centrifugal vacuum pumps and ejectors are activated or not. The geothermal fluid is sent to the condenser units after finishing the expansion process in the turbine. Figs. 2 and 3 shows T-s diagram of the plant. The main objective in the condenser unit is to re-inject the environmentally harmful gases underground instead of releasing them into the atmosphere by condensing all the incondensable gases. The geothermal fluid leaving the turbine and reaching the main collector is subjected to a water spray process with the help of cooling-water. The geothermal fluid condensed in the main condenser is sent to the water-cooling tower to be cooled. Meanwhile, the condensed fluids are reinjected back into the ground at an approximate temperature of 40 C, at 12 bar pressure and with a flow rate of 38.89 kg/s by means of the OB-3 well which is operated about 10 h a day. The cooling tower inlet temperature is 40 C, the
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195
Fig. 1. Flow diagram for Germencik Geothermal Power Plant.
flow rate is 3683.23 kg/s and the outlet temperature is 20 C. Cooling water is sent into the main condenser with a flow rate of about 3333.23 kg/s and to the intermediate collectors (intercondenser A, B and after condenser) with a flow rate of 0.69 kg/s. During the cooling about 334.86 kg/s steam is released into the
atmosphere. In addition, the incondensable gases are liquefied in the main collector in 3 stages. With the aid of the ejectors in the power plant (1, 2, 3, 4), they are sent to the inter-condenser A, B and then to the after condenser by applying a vacuuming process in order to liquefy the gases in the main collector. First of all, in the
Fig. 2. T-s diagram for Germencik Geothermal Power Plant.
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Fig. 3. Germencik Geothermal Power Plant.
inter-condenser A and B, the cooling-water coming from the cooling tower is sprayed into the gases drawn from the main condenser through the ejectors (1, 2, 3) with the vacuuming process in order to liquefy them. Then, the liquefied gases are sent to the main condenser, the unliquidated gases are sent to the ejector (4) and the incondensable gases are sent to the centrifugal vacuum pumps. By applying a vacuuming process with the aid of ejector (4), the cooling-water coming from the cooling tower is sprayed into the incondensable gases drawn from the inter-condenser A and B in the after condenser, just like the process applied in the intercondenser A and B. The gases liquefied in the after condenser are sent to the main condenser. The gases which remain uncondensed in the inter-condenser A and B are liquefied for the last time with the aid of centrifugal vacuum pumps and the after condenser. Centrifugal vacuum pumps (A, B, C, D) work with the same principle as the ones in the heat exchangers; uncondensed gases flow from within and the coolingwater flows from without. In this way, after the liquefaction of the gases, the remaining incondensable gases are released into the atmosphere with a flow rate of 14.58 kg/s. Some components for the turbine are listed in Table 2.
Table 2 A list of some components for the turbine.
Rated output (at generator terminal) Rated speed at turbine Turbine design pressure for construction at HP main stop valve Turbine design temperature for construction at HP main stop valve Turbine design pressure for construction at LP main stop valve Turbine design temperature for construction at LP main stop valve Number of stage Quantity of cooling water Property of cooling water Temperature of cooling water (at design) Quantity of cooling oil (at design) Oil temperature at cooler outlet and inlet
4. Methods 4.1. Exergy analysis of the plant Exergy analysis of the plant was calculated for steady-flow conditions systems by using mass, energy and exergy equations to calculate the energy and exergy values of each point for the numbers in the flow diagram given in Fig. 1 and the results are tabulated in Table 3. In these calculations, steady-state pressure was taken as 101.325 kPa and temperature as 15 C [26]. EES (Engineering Equation Solver) software has been used for analysis [27]. The selected fluid property for the analysis is Steam_NBS. The mass balance for the steady-flow conditions systems is calculated from equations (1)e(3)
X
_i m
X
_ system _ o ¼ Dm m
_ system ¼ 0 Dm
Turbine and accessories Type of turbine
The geothermal fluid separated from the separators is reinjected back into the ground at a temperature of 110.3 C, 35 bar pressure and with a flow rate of 541.65 kg/s by means of the brine injection pump. Its flow diagram is shown in Fig. 1.
Mitsubishi single cylinder, double flow, top exhaust, dual pressure 47.400 kW 3000 rpm 14 bar g
200 C 3.5 bar g 150 C Double flow of 6 stage 90 m3/h Recirculation water 19.1 C 48 m3/h 45 C and 60 C
X
_i ¼ m
X
(1)
(2)
_o m
(3)
and the energy balance from equation (4)
X
E_ i
X
E_ o ¼
X
DE_ system
(4)
If the kinetic energy and potential energy change are neglected in equation (5),
_ ¼ Q_ W
X
X _ i hi þ Vi2 =2 þ gzi _ o ho þ Vo2 =2 þ gzo m m (5)
_ ¼ Q_ W
X
_ i hi _ o ho m m
(6)
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197
Table 3 Values measured and calculated in the plant for each point in the flow diagram. State no
Substance
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O CO2 H2O H2O H2O H2O H2O H2O H2O H2O H2O
Phase Liquid Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Sat. liquidevapor Liquid Liquid Liquid Liquid Sup. vapor Sup. vapor Liquid Liquid Sup. vapor Sup. vapor Sup. vapor Liquid Sup. vapor Sat. liquidevapor Liquid Liquid Gas Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid
mix. mix. Mix. mix. mix. mix. mix.
mix.
Temp. T ( C)
Pressure P (bar)
Enthalpy h (kJ/kg)
Entropy s (kJ/kg K)
Mass flow _ (kg/s) rate, m
15 205.3 e 206.6 e 212 e 197.2 e 214.6 e 213.3 e 214.6 e 160 166.1 164.9 164.9 157.8 107 110.5 110.5 157.4 106.1 159 20 156.5 56 47.4 40 e 20 20 40 110.3 110.3 110.3 110.3 110.3 110.3
1.01325 23.012 8.732 21.012 7.012 25.512 6.962 21.812 6.862 28.012 7.962 27.012 8.752 30.012 8.762 6.512 7.862 7.762 13.612 5.360 1.512 1.622 36.012 5.630 1.120 5.920 1.462 4.960 0.140 2.252 2.902 2.042 2.312 4.012 13.012 35.212 35.512 35.612 35.862 35.112 35.472
63 876.5 876.5 882.3 882.3 907.0 907.0 840.1 840.1 918.9 918.9 912.9 912.9 919.0 919.0 675.7 702.3 697.0 697.4 2759.4 448.7 463.5 466.0 2756.3 2686.9 2757.7 84.0 2759.6 2602.3 198.6 167.8 e 84.1 84.2 168.6 465.1 465.1 465.1 465.1 465.1 465.1
0.224 2.380 2.394 2.392 2.415 2.442 2.471 2.303 2.319 2.466 2.492 2.454 2.475 2.466 2.488 1.943 2.004 1.992 1.991 6.816 1.385 1.424 1.421 6.787 7.339 6.768 0.296 6.851 8.051 0.670 0.572 e 0.296 0.296 0.572 1.419 1.419 1.419 1.419 1.419 1.419
e
equation (6) is obtained andexergy equations
X_ i X_ o X_ dest ¼ DX_ system
(7)
DX_ system ¼ 0
(8)
X_ i X_ o ¼ X_ dest
(9)
where
_j X_ ¼ m
(10)
j ¼ ðh h0 Þ T0 ðs s0 Þ
(11)
equation (11) is obtained.
4.2. Exergy losses in the plant The exergy input from the seven production wells at the plant is a total of 134,124 kW the largest of which is from the OB-14 well, the input of which is 36,395 kW and corresponds to 27.1% of the total exergy input. A total of 4478 kW total exergy loss occurs in the valves and it corresponds to 3.34% of the total exergy input. During
81.94 81.94 95.83 95.83 90.28 90.28 73.61 73.61 179.16 179.16 88.89 88.89 79.16 79.16 341.66 347.21 312.49 312.49 103.38 60.59 541.65 541.65 87.57 56.94 13.33 3333.24 74.24 131.18 3722.12 3683.23 14.58 0.69 0.69 38.89 76.94 94.72 78.61 118.89 137.50 54.44
j (kJ/kg)
Energy rate, E_ (kW)
Exergy rate, X_ (kW)
e 186.0 182.0 188.1 181.6 198.2 189.8 171.9 167.3 203.2 195.6 200.7 194.7 203.4 196.8 112.3 121.3 119.5 120.1 777.3 47.7 51.2 54.5 782.6 552.6 789.4 0.1 767.4 260.7 5.9 3.5 e 0.2 0.3 4.5 54.2 54.3 54.3 54.3 54.2 54.3
e 66,661 66,661 78,515 78,515 76,188 76,188 57,200 57,200 153,342 153,342 75,547 75,547 67,761 67,761 209,319 221,957 198,126 198,230 278,755 23,366 216,907 218,262 235,845 149,411 35,928 69,860 200,183 333,100 504,821 385,787 e 15 15 4108 30,935 38,084 31,607 47,804 55,280 21,890
e 15,237 14,904 18,024 17,399 17,890 17,129 12,646 12,307 36,395 35,033 17,837 17,299 16,095 15,575 38,357 42,086 37,325 37,495 80,348 2883 27,689 29,501 68,522 31,462 10,525 28 56,961 34,186 21,879 12,650 e 0 0 173 4169 5135 4262 6449 7449 2951
Specific exergy,
the separation process of the Lp-Hp separators, 30,477 kW exergy losses occur and it corresponds to 22.72% of the total exergy input. After the separation process 30,415 kW exergy losses occur in the reinjection wells and it corresponds to 22.68% of the total exergy input. During the conversion of steam to mechanical work 6837 kW exergy losses occur in the turbine-generator pair and it corresponds to 5.1% of the total exergy input. In the cooling tower 12,622 kW exergy losses occur and it corresponds to 9.41% of the total exergy input. 7414 kW exergy losses occur in the internal usage in the plant and it corresponds to 5.53% of the total exergy input. 1495 kW exergy losses occur in the pumps, collectors, centrifugal vacuum pumps and OB-3 well and it corresponds to 1% of the total exergy input. In addition, 131 kW exergy losses occur in the OB-14 transfer pump and 556 kW exergy losses occur in the brine injection pump. The remaining 39,700 kW is net electrical power. Its exergy flow chart is shown in Fig. 4. The second law efficiency for the turbinegenerator pair and the whole plant is found from equations (12) and (13).
_ out;net =W _ tr hturbine ¼ W hturbine ¼ 47; 400=54; 237 ¼ 87:4% X
X_ in ¼ 134; 124 kW
(12)
198
M. Unverdi, Y. Cerci / Energy 52 (2013) 192e200
Fig. 4. Exergy flow chart for the geothermal power plant.
X
_ out;net ¼ 47; 400kW X_ out ¼ W
_ out;net =X_ hII ¼ W in hII ¼ 35:34%
(13)
5. Discussion and result Changing the environment is sometimes thought to be one way to increase plant efficiency, but it is not possible to do so. Due to the fact that during reinjection the temperature of the fluid is high (110 C), it can be used in fields where the temperature values are suitable. We can examine these areas as follows. U In addition to five wells (below 150 C) located in the west of the field together with the fluid reinjected, a pre-heated binary or an ORC (Organic Rankine Cycle) can be established, as an alternative design, which can increase the efficiency of the plant. For these cycles, fluids such as R134a, R152, R245fa, iso-pentane, npentane, isobutane can be used. In addition, according to the
analysis reports, it was determined that, depending on MW per unit power generation in the ORC (Organic Rankine Cycle), a 100 kg/h flow rate is required for 110 C geothermal fluid (reinjected in this power plant) and when it comes to 150e 160 C geothermal fluid, geothermal fluid ranging from 25 to 40 kg/h flow rate per MW is required. The amounts of geothermal fluid consumption of some temperature-dependent gases required for power generation in ORC are given in Fig. 5. Since the fluid reinjected in the Germencik Geothermal Power Plant is about five times greater than the flow rate necessary to generate power from the Organic Rankine Cycle, the amount of power generation as shown in Table 4, can be achieved from the fluid reinjected in this power plant. For example, if iso-pentane is selected as the working fluid to generate power from the fluid reinjected, the thermal efficiency of the current power plant can increase by about 16%, if isobutane is used, the thermal efficiency increases by about 12% with the alternative design established in the plant. This way,
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199
Fig. 5. The amount of geothermal fluid consumption of some temperature-dependent gases for every MW [22,33]. Table 4 Binary cycles and power production quantity which can be established in accordance with the existing power plant.[22,28] Plant and location
Geothermal temperature ( C)
Cycle
Working fluid
Gross capacity (kWe)
Kutahya-Simav, Turkey
145
R124
2900
42
37.39
Nigorikawa, Japan Otake, Japan Husavik, Iceland Wineagle, USA Nagqu, China Altheim, Austria Wabuska, CA, USA Neustadt-Glewe, GER Birdsville, Australia Chena Hot Spring, AK, USA
140 130 124 110 110 106 104 98e100 98e99 74
Rankine with superheat Rankine Rankine Kalina Rankine Rankine Rankine Rankine Rankine Rankine Rankine
R114 Isobutane NH3eH2O Isobutane Iso-pentane C5F12 Iso-pentane C5F12 R114 R134a
1000 1000 1700 700 1000 1000 1750 230 150 400
50 14.7 53 63 69 86 34.3 120.8 200 57.9
10.83 36.85 17.37 6 7.85 6.23 27.64 1.03 0.41 3.74
electricity can be produced. The overall efficiency of the power plant can increase by 25e45% with such fluids and designs. U Since there are residential areas and agricultural activities are undertaken around the plant, together with greenhouse heating, this fluid can be utilized for district heating. For example, for district heating; the exergy efficiency of the power plant can increase by 60% according to a design aimed at heating a 3.600 housing unit area with a 70 C reservoir temperature on average, the exergy efficiency of the power plant can increase by 40% Table 5 Comparison of Kızıldere and Germencik Geothermal Power Plants. Values
Kızıldere Geothermal Power Plant [14]
Germencik Geothermal Power Plant
Total mass flow rate input in the plant (kg/s) High-temperature reservoir ( C) Steady-state temperature ( C) Steady-state pressure (kPa) Total exergy input in the plant (kW) Second law efficiency (%) Steam separation Reinjection Power output (kWe)
282.84
688.87
239.9
214.6
15
15
101.325
101.325
54,649
134,124
20.8
35.34
Single flash e 11,400
Double flash Ok 39,700
Specific brine consumption (kg/s)/MW
Compatible with Germencik Geothermal Power Plant (MWe)
according to a design aimed at heating a 10.000 housing unit area with a 40 C reservoir temperature on average, the exergy efficiency of the power plant can increase by 45% according to a design aimed at heating a 7.500 housing unit area with a 110 C reservoir temperature on average. For greenhouse heating; 100 MWt district heating can be achieved for an approximately 450.000 m2 area and 95 C [25,30e32]. Additionally, instead of releasing gases into the atmosphere at 14.58 kg/s, dry ice production can be achieved by placing a compressor and intercooler on the current system in the plant. Although the initial investment costs of the addition of the compressor and intercooler to the plant are high, it is thought that gas sales revenue will meet the initial investment costs in the long run. However, the addition of the compressor and intercooler to the plant will lead to a 5% loss of plant efficiency [14e16,28,29]. In this study, it was determined in which parts of the plant exergy losses occur by applying exergy analysis in general as well as to the equipments separately. According to the calculations, maximum exergy losses occur in the separators and these losses correspond to 22.72% of the total losses. In addition, exergy losses occur during the whole cycle. Exergy losses that occur in the cooling tower, in the reinjection wells, in internal usage and in the turbine-generator pair correspond to 9.41%, 22.68%, 5.53% and 5.1% respectively. The second law efficiency of the plant was found to be 35.34%. In Table 5, the values of the Germencik Geothermal Power Plant were compared to those of the Kızıldere Geothermal Power Plant the performance analysis of which was made before.
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As shown in Table 5, the increase in the efficiency of the equipments used in the power plant in parallel with developing technology increased the efficiency of the Germencik power plant. In addition, the operation of the Germencik Geothermal Power Plant according to the two-stage steam separation system was observed to have increased the efficiency. Although the chosen steady-state temperature and pressure may influence the efficiency of plants, it was concluded that the Germencik power plant runs more efficiently. 6. Conclusions In this study, energy and exergy analysis were carried out in Germencik Geothermal Power Plant. When evaluating the performance analysis, exergy efficiency for each piece of equipment and for the plant as a whole was calculated by using the pressure and temperature values measured in the plant. The exergy flow diagram was plotted for the exergy losses. This study reached the following conclusions: Compared to other geothermal fields and power plants (Kizildere, Salavatli), Germencik geothermal field and power plant is a field of high temperature and high qualifications. The exergy efficiency and the efficiency of the turbinegenerator pair of the plant were found to be 35.34% and 87.4% respectively. The operation of the Germencik Geothermal Power Plant according to the two-stage steam separation system (double flash) significantly increased the efficiency. Geothermal fluid reinjection ensures the continuity of the field and prevents environmental pollution, but 7.4 MWe used by the pumps during the reinjection of the fluid causes a decrease in the efficiency of the power plant. It was determined that the greatest exergy loss in the plant occurs in the separators (30,477 kW). Dry ice production can be achieved by placing a compressor and an intercooler in the current system and by using the gas released into the atmosphere at 14.58 kg/s. Due to the high temperature values of the fluid reinjected, it can be utilized in the areas of greenhouse heating, domestic heating, heat pumps, thermal spring path and aquaculture with suitable temperatures or power plant efficiency can be increased by 25e45% establishing a binary cycle together with the production wells located in the west of the field. An integrated geothermal plant should be established in order to improve the efficiency of the field and in order to benefit fully from the current reservoir. Acknowledgments We would like to thank Ergun Isler, operations manager of the Gurmat Electricity Generation Co. Inc. and the staff for their contribution to make this study possible. Special thanks for their contribution to the Adnan Menderes University. References [1] Galanis N, Cayer E, Roy P, Denis ES, Désilets M. Electricity generation from low temperature sources. Journal of Applied Fluid Mechanics 2009;2(2):55e67.
[2] Erdogdu E. A snapshot of geothermal energy potential and utilization in Turkey. Renewable and Sustainable Energy Reviews 2009;13:2535e43. [3] Ratlamwala TAH, Dincer I, Gadalla MA. Performance analysis of a novel integrated geothermal-based system for multi-generation applications. Applied Thermal Engineering 2012;40:71e9. [4] Celik MY, Sabah E. The geological and technical characterization of ÖmerGecek geothermal area and the environmental impact assessment of geothermal heating system. Environmental Geology 2002;41:942e53. [5] Yari M. Exergetic analysis of various types of geothermal power plants. Renewable Energy 2010;35:112e21. [6] Kuo C, Hsu S, Chang K, Wang C. Analysis of a 50 kW organic Rankine cycle system. Energy 2011;36:5877e85. [7] Siddiqi M, Atakan B. Alkanes as fluids in Rankine cycles in comparison to water, benzene and toluene. Energy 2012;45:256e63. [8] Saleh B, Koglbauer G, Wendland M, Fischer J. Working fluids for lowtemperature organic Rankine cycles. Energy 2007;32:1210e21. [9] Coskun C, Oktay Z, Dincer I. Performance evaluations of a geothermal power plant. Applied Thermal Engineering 2011;31:4074e82. [10] Lee KC. Classification of geothermal resources by exergy. Geothermics 2001; 30:431e42. [11] Dagdas A. Performance analysis and optimization of double-flash geothermal power plants. Journal of Energy Resources Technology 2007;129:125e33. [12] DiPippo R. Small geothermal power plants-design, performance and economics. GHC Bulletin 1999;20(2):1e8. [13] Bodvardson G, Eggers DE. The exergy of thermal water. Geothermics 1972; 1(3):93e5. [14] Cerci Y. Performance evaluation of a single flash geothermal power plant in Denizli Turkey. Energy 2003;28:27e35. [15] DiPippo R. Second law assessment of binary plants generating power from low-temperature geothermal fluids. Geothermics 2004;33:565e86. [16] Kanoglu M, Bolatturk A. Performance and parametric investigation of a binary geothermal power plant by exergy. Renewable Energy 2008;33:2366e74. [17] Ganjehsarabi H, Gungor A, Dincer I. Exergetic performance analysis of Dora II geothermal power plant in Turkey. Energy 2012:1e8. [18] Chen H, Goswami DY, Rahman MM, Stefanakos EK. A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power. Energy 2011;36:549e55. [19] Desai NB, Bandyopadhyay S. Process integration of organic Rankine cycle. Energy 2009;34:1674e86. [20] Hettiarachchi HDM, Golubovic M, Worek WM, Ikegami Y. Optimum design criteria for an organic Rankine cycle using low-temperature geothermal heat sources. Energy 2007;32:1698e706. [21] Shengjun Z, Huaixin W, Tao G. Performance comparison and parametric optimization of subcritical organic Rankine cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation. Applied Energy 2011;88:2740e54. [22] Franco A. Power production from a moderate temperature geothermal resource with regenerative organic Rankine cycles. Energy for Sustainable Development 2011;15:411e9. [23] Franco A, Villani M. Optimal design of binary cycle power plants for waterdominated, medium-temperature geothermal fields. Geothermics 2009;38: 379e91. [24] Ozgener L, Hepbasli A, Dincer I. Energy and exergy analysis of Salihli geothermal district heating system in Manisa, Turkey. International Journal of Energy Research;29:393e408. [25] Kecebas A, Kayfeci M, Gedik E. Performance investigation of the Afyon geothermal district heating system for building applications: exergy analysis. Applied Thermal Engineering 2011;31:1229e37. [26] Cengel YA, Boles MA. Thermodynamics: an engineering approach. 5th ed. New York: McGraw-Hill; 1998. [27] Alvarado FL, Klein SA. Engineering equation solver, F-chart software; 2012. [28] Tchanche BF, Lambrinos Gr, Frangoudakis A, Papadakis G. Low-grade heat conversion into power using organic Rankine cycles a review of various applications. Renewable and Sustainable Energy Reviews 2011; 15:3963e79. [29] Heberle F, Brüggemann D. Exergy based fluid selection for a geothermal organic Rankine cycle for combined heat and power generation. Applied Thermal Engineering 2010:1326e32. [30] Ozgener L, Hepbasli A, Dincer I. Energy and exergy analysis of the Gonen geothermal district heating system, Turkey. Geothermics 2005;34:632e45. [31] Hepbasli A, Canakci C. Geothermal district heating applications in Turkey: a case study of IzmireBalcova. Energy Conversion and Management 2003;44: 1285e301. [32] Bakos GC, Fidanidis D, Tsagas NF. Greenhouse heating using geothermal energy. Geothermics 1999;28:759e65. [33] Franco A, Vaccaro M. An integrated “Reservoir-Plant” strategy for a sustainable and efficient use of geothermal resources. Energy 2012;37:299e310.