Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 68 (2015) 12 – 21
2nd International Conference on Sustainable Energy Engineering and Application, ICSEEA 2014
The electricity power potency estimation from hot spring in Indonesia with temperature 70-80°C using organic Rankine cycle Ghalya Pikraa,*, Nur Rohmaha, Rakhmad Indra Pramanaa, Andri Joko Purwantoa a
Research Centre for Electrical Power and Mechatronics – Indonesian Institute of Sciences Komplek LIPI, Jl. Sangkuriang, Bandung 40135, Indonesia
Abstract This paper presents the electricity power potency estimation from hot spring in Indonesia with temperature 70-80°C using Organic Rankine Cycle (ORC). ORC is a system that able to generate electricity with a low heat source temperature, making it suitable to be used to generate electricity with hot spring as heat source. Organic fluid is used as working fluid in the system. Temperature and volume flow rate of the hot spring is used as the data. The regions to be analyzed are area that has hot springs temperature between 70-80°C. The cold water temperature to be used in the analysis was assumed 5°C lower than ambient temperature. R227ea was chosen as working fluid in the system. The analysis begins by calculating hot spring mass flow rate to determine heat input. Analysis was continued by calculating heat output. End of the analysis are determiningturbine power and thermal efficiency. Results of the analysis indicate that Lompio - 1 is the area that has the highest electricity potential compared to other areas with 130.13 kW turbine power and thermal efficiency of 5.71%. Areas that have the lowest electricity potential is Kambahan with 1.14 kW turbine power and 5.63% thermal efficiency. © 2015 by by Elsevier Ltd. B.V. This is an open access article under the CC BY-NC-ND license © 2015The TheAuthors. Authors.Published Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Scientific Committee of ICSEEA 2014. Peer-review under responsibility of Scientific Committee of ICSEEA 2014
Keywords: electricity generation; hot spring; organic Rankine cycle (ORC); R227ea
1. Introduction Dependence on fossil fuel and global warming impact, encourage energy system transition to energy systems based on renewable resources. In fact, the potential of renewable energy such as biomass, geothermal, solar energy,
* Corresponding author. Tel.: +62-22-2503055; fax: +62-22-2504773. E-mail address:
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1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Scientific Committee of ICSEEA 2014 doi:10.1016/j.egypro.2015.03.227
Ghalya Pikra et al. / Energy Procedia 68 (2015) 12 – 21
water energy, wind energy, and ocean energy has not been widely used in Indonesia. Indonesia is one of the richest countries that had 40% of potential geothermal reserves of the world, but its utilization for power generation until now only 4.1% of the total potential [1, 2].Geothermal system in Indonesia is generally a high-temperature hydrothermal system (> 225°C), only a few locations have temperatures between 125-225°C[2]. The presences of subsurface hydrothermal system are often indicated by the presence of geothermal surface manifestation, such as hot spring, geyser, fumarol, mud pool, steaming ground and altered rock [3]. The hot springs are part of the potential geothermal manifestation that can be used as a heat source for power generation. Hot springs in Indonesia usually have temperature below 100°C. ORC is a system that can generate electricity with a low heat source temperature. The use of ORC systems for power plants with low temperature heat sources can provide excellent performance compared with other technologies[4-7]. In addition, ORC is a system that is flexible, secure and has low maintenance costs [8-10]. Therefore, the organic Rankine cycle power plant is suitable to be used as heat source using the hot springs. ORC power plant that uses a commercial scale using the hot springs has been conducted in several countries. Holdmann was reporting ORC in Chena Hot Spring, Alaska, geothermal heat sources with temperatures 73°C, the working fluid R134a, water cooling fluid temperature 4.4°C, can produce a capacity of 210 kW and an efficiency of 8.2%[11]. Working fluid used in the analysis is R227ea. R227ea is a suitable fluid for heat source temperature below 100°C[12-14]. R227ea is not explosive, not poisonous, and enables to operate at above atmospheric pressure to prevent the leakage of the cycle to the ambient air[15]. This paper will analyze the potential power of the hot springs in Indonesia using the ORC system. The location of hot springs to be analyzed were those that have heat source temperatures between 70-80°C.Result of this paper is expected to be a reference in the development of power generation system using the hot springs as a heat source based on the organic Rankine cycle in Indonesia, so the utilization of the hot springs as renewable energy can be one solution to overcome the energy crisis problem. 2. Methodology Electricity generation using hot springs as a heat source was analyzed using the ORC system. ORC is a system that can work at low temperatures. Therefore, the system is suitable to be used for generating electricity using the hot springs at temperatures below 100°C. ORC system with a heat source hot springs is shown in Fig. 1. The ORC system operation principle as shown in Fig. 1 is the same as the conventional Rankine cycle, but in this case, the working fluid is an organic fluid of low boiling point instead of water. The working fluid is pumped into the evaporator. Working fluid is heated and vaporized by the heating fluid (hot springs) at constant temperature and pressure to the saturated vapor phase in the evaporator tube. Isentropic working fluid is expanded to low pressure in the turbine and drives the electrical generator to produce electrical energy. Output of the turbine working fluid is condensed in the condenser and then pumped back to the evaporator. Cooling fluid used is river water/ wells that are exist in the area. R227ea is a working fluid that is used in analyzing the potential power of hot springs in Indonesia. R227ea physical properties are shown in Table 1.The assumptions to analyze ORC system are steady state condition, working pressure through condenser and evaporator are constant, working fluid at inlet refrigerant pump/ outlet condenser is saturated liquid (condition at point 1) and at inlet turbine/ outlet evaporator (condition at point 3) is saturated vapor, turbine and pump work adiabatically, and kinetic and potential energy are negligible. Energy balance is used in the analysis. T-s diagram which is shown in Fig. 2 was made to simplify the analysis. Energy balance equation and thermodynamic analysis calculation of ORC refers to Moran[16].
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Ghalya Pikra et al. / Energy Procedia 68 (2015) 12 – 21
Hot Spring
output Input
Condenser DC Turbine Generator
Input
Evaporator
output
River Water / Well
Refrigerant Pump
Fig. 1. ORC electricity generation using hot spring as heat source. Table 1. Physical properties of R227ea. Data
Chemical name
1, 1, 1, 2, 3, 3, 3-Heptafluoropropane
Chemical formula
CF3CHFCF3
Molecular weight
170.03 g/mol
Boiling temperature
-15.6°C
Critical temperature; Critical pressure
102.8°C; 29.8 bar
ODP; GWP
0; 2900
Hazard Rating: Health; Flammability; Reactivity
2; 1; 0
Temperature (°C)
Properties
100 80
3
60 40
2s
20
2
4s
4
1
0 1
1.2 1.4 Entropy (kJ/kg °C)
1.6
Fig. 2. T-s diagram.
2.1. Energy balance at the evaporator Analysis was started by determining energy balance at the evaporator. Energy balance at the evaporator is use to calculate heat input/ evaporator capacity. Heat input is calculated to determine the amount of heat that can be use in
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Ghalya Pikra et al. / Energy Procedia 68 (2015) 12 – 21
the system to produce electricity. Mass flow rate of the hot spring must be calculated before calculating heat input. The calculations of hot spring mass flow rate and energy balance at the evaporator are shown in equation (1) and (2). ݉ሶ݄ ݓൌ ݓ݄ݍൈ ߩ݄ݓ
(1)
ܳ݅݊ ൌ ܳ݁ ܽݒൌ ݉ሶ݄ ݓൈ ݓ݄ܥൈ ൫݄ܶݓǡ݅݊ െ ݄ܶݓǡ ݐݑ൯ ൌ ݉ሶ ݂݁ݎൈ ሺ݄͵ െ ݄ʹ ሻ
(2)
where ݉ሶ݄ ݓis heat source (hot spring) mass flowrate (kg/s); ݓ݄ݍis heat source (hot spring) volume flowrate (m3/s); ߩ݄ ݓis density of the hot spring (kg/m3); ܳ݅݊ = ܳ݁ ܽݒis heat input/ evaporator capacity (kW); ݓ݄ܥis specific heat of heat source/ hot spring (kJ/kg°C); ݄ܶݓǡ݅݊ is heat source input temperature (°C); ݄ܶݓǡ ݐݑis heat source output temperature (°C); ݉ሶ ݂݁ݎis refrigerant mass flow rate (kg/s); ݄ʹ is refrigerant enthalpy at outlet refrigerant pump/ at inlet evaporator (kJ/kg); and ݄͵ is refrigerant enthalpy at outlet evaporator/ inlet turbine (kJ/kg). 2.2. Energy balance at the refrigerant pump Analysis continued by calculating mass and volume flow rate of the refrigerant through energy balance at the pump. Refrigerant volume flow rate was calculated to determine refrigerant pump specification that will be used in the system. Energy balance at the refrigerant pump and calculation of refrigerant mass and volume flow rate are shown in equation (3) and (4). ߟ ൌ
ܹ ǡݏ ܹ
݂݁ݎݍൌ
ൌ
݉ሶ ݂݁ݎൈሺ݄ ʹ ݏെ݄ ͳ ሻ ݉ሶ ݂݁ݎൈሺ݄ ʹ െ݄ ͳ ሻ
ൌ
݉ሶ ݂݁ݎൈ߭ ͳ ሺܲʹ െܲͳ ሻ ݉ሶ ݂݁ݎൈሺ݄ ʹ െ݄ ͳ ሻ
݉ሶ ݂݁ݎ
(3) (4)
ߩͳ
where ߟ is isentropic efficiency of the refrigerant pump; ܹǡ ݏis power of isentropic refrigerant pump (kW); ܹ is power of the refrigerant pump (kW); ݄ͳ is refrigerant enthalpy at inlet refrigerant pump/ outlet condenser (kJ/kg); ݄ʹ ݏis refrigerant isentropic enthalpy at outlet refrigerant pump/ at inlet evaporator (kJ/kg); ߭ͳ is specific volume at inlet refrigerant pump/ outlet condenser (m3/kg); ܲͳ is refrigerant pressure at inlet refrigerant pump/ outlet condenser (bar); ܲʹ is refrigerant pressure at outlet refrigerant pump/ inlet evaporator (bar); ݂݁ݎݍis refrigerant volume flow rate (m3/s); and ߩͳ is refrigerant density at inlet refrigerant pump/ outlet condenser (kg/m3). 2.3. Energy balance at the turbine Next analysis is calculating turbine power. Turbine power was calculated to estimate the electricity that can be produced at the system. Energy balance at the turbine is shown in equation (5). ܹ
݉ሶ ݂݁ݎൈሺ݄ ͵ െ݄ Ͷ ሻ
ߟ ܶ ൌ ܹ ܶ ൌ ݉ሶ ܶݏ
݂݁ݎൈሺ݄ ͵ െ݄ Ͷ ݏሻ
(5)
where ߟ ܶ is turbine isentropic efficiency; ܹܶ is turbine power (kW); ܹܶ ݏis isentropic turbine power (kW); ݄Ͷ is refrigerant enthalpy at outlet turbine/ inlet condenser (kJ/kg); and ݄Ͷ ݏis refrigerant isentropic enthalpy at outlet turbine/ inlet condenser (kJ/kg). 2.4. Energy balance at the condenser Analysis was continued with energy balance at the condenser. Energy balance at the condenser is used to calculate the heat output/ condenser capacity. Heat output is calculated to determine mass and volume flow rate of the cooling fluid. Volume flow rate need to be calculated for determining specification of the pump. Energy balance at the condenser and calculation of cooling fluid mass and volume flow rate are shown in equation (6) and (7).
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ܳ ݐݑൌ ܳܿ ݀݊ൌ ݉ሶ ݂݁ݎൈ ሺ݄Ͷ െ ݄ͳ ሻ ൌ ݉ሶܿ ݓൈ ݓܿܥൈ ൫ܶܿ ݓǡ ݐݑെ ܶܿ ݓǡ݅݊ ൯ ݓܿݍൌ
(6)
݉ሶ ܿݓ
(7)
ߩ ܿݓ
where ܳ ݐݑൌ ܳܿ ݀݊is heat output/ condenser capacity (kW); ݉ሶܿ ݓis mass flow rate of cooling fluid (kg/s); ݓܿܥis specific heat of cooling fluid (m3/s); ܶܿ ݓǡ݅݊ is input temperature of cooling fluid (°C); ܶܿ ݓǡ ݐݑis output temperature of cooling fluid (°C); ݓܿݍis volume flow rate of cooling fluid (m3/s); and ߩܿ ݓis density of cooling fluid (kg/m3). 2.5. Thermal efficiency of the system Last analysis is calculating thermal efficiency of the system (ߟ) ݄ݐ. Thermal efficiency is calculated to determine the performance of the ORC system. Calculation of thermal efficiency is shown in equation (8). ߟ ݄ݐൌ
ܹܶ െܹ
(8)
ܳ݅݊
3. Data Design primary data is hot spring source in Indonesia that has temperature between 70-80°C shown in Table 2. Analysis of the potency for electricity power using hot springs as heat source with a temperature of 70-80°C was conducted to determine the feasibility of the hot springs to be used as a heat source in power generation. Several data assumptions were made for the analysis. The assumption data is shown in Table 3. Table2. Potential area of hot spring in Indonesia with temperature 70-80°C. Province
Hot Spring Location
Thw
pH
(°C) Sumatera Utara
Roburan Dolok - 1
79 – 100.7
Roburan Dolok - 2 Sumatera Barat
acid
Tambient
qhw
(°C)
(l/min)
Reference
30
30 - 120
[17-19] [20-22]
neutral
Cubadak - 1
74.8
6.35
27.3
120
Cubadak - 3
72.7
6.47
27.3
60
S. Limau
61 – 73.5
7 – 7.3
29 – 30.6
60
Kambahan
52 – 73.4
7.5
23 – 27.4
27
Mudik
41 - 73
5.8 - 7
29
150
Pincurak – 1& 2, Sitabu – 1 & 2
23.6 – 78.6
4.35 – 6.93
22 – 23.6
120 - 180
[28]
Jawa Barat
Cimanggu
78
6.8
15*
70
[29]
Sulawesi Tengah
Lompio - 1
78
8.15
30
3,000
[30-33]
Lompio - 2
62 – 76.6
7.1 – 8.24
30
2,880
Lompio - 6
77
7.1
30
< 60
Pulu - 1
78.9
8.46
25
240
[30, 34]
Pamandian
74.4
8.5 – 8.6
25.8
240
[35, 36]
Kanan Kumbi
52.2 – 72.4
7.7 – 8.2
25
240
Sulawesi Tenggara
Kaendi - 1
73
6.35
26
30
[37, 38]
Maluku
Tehoru - 4
68 – 71.3
6.587
28.4
30
[39, 40]
Maluku Utara
Losseng - 2
77.4
6.82 – 7.32
32.7
300 – 360
[41]
Sulawesi Selatan
[23-27]
Note: * Especially for Cimanggu area, because there is no reference ambient temperature, we have made measurements directly to Cimanggu, and get the data of cooling water temperature is 15°C.
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Ghalya Pikra et al. / Energy Procedia 68 (2015) 12 – 21 Table 3.Assumptiondata for calculation. Province
Hot Spring Location
qhw
Thw,in
Thw,out
T3
Tamb
Tcw,in
Tcw,out
T1
Sumatera Utara
Roburan Dolok – 1& 2
(l/min)
(°C)
(°C)
(°C)
(°C)
(°C)
(°C)
(°C)
120
79
69
69
30
25
35
35
Sumatera Barat
Cubadak - 1
120
74.8
64.8
64.8
27.3
22.3
32.3
32.3
Cubadak - 3
60
72.7
62.7
62.7
27.3
22.3
32.3
32.3
S. Limau
60
73.5
63.5
63.5
30.6
25.6
35.6
35.6
Kambahan
27
73.4
63.4
63.4
27.4
22.4
32.4
32.4
Mudik
150
73
63
63
29
24
34
34
Pincurak – 1& 2, Sitabu – 1 & 2
180
78.6
68.6
68.6
23.6
18.6
28.6
28.6
Jawa Barat
Cimanggu
70
78
68
68
15
15
25
25
Sulawesi Tengah
Lompio - 1
3,000
78
68
68
30
25
35
35
Lompio - 2
2,880
76.6
66.6
66.6
30
25
35
35
Lompio - 6
60
77
67
67
30
25
35
35
Pulu - 1
240
78.9
68.9
68.9
25
20
30
30
Pamandian
240
74.4
64.4
64.4
25.8
20.8
30.8
30.8
Sulawesi Selatan
Kanan Kumbi
240
72.4
62.4
62.4
25
20
30
30
Sulawesi Tenggara
Kaendi - 1
30
73
63
63
26
21
31
31
Maluku
Tehoru - 4
30
71.3
61.3
61.3
28.4
23.4
33.4
33.4
Maluku Utara
Losseng - 2
360
77.4
67.4
67.4
32.7
27.7
37.7
37.7
73.2
63.2
63.2
31.7
26.7
36.7
36.7
Losseng - 3
Note: T3 is temperature at inlet turbine/ outlet evaporator (°C) and T1 is temperature at inlet refrigerant pump/ outlet condenser (°C).
Temperature difference of cooling water temperature with ambient air temperature is 5°C. Temperature difference between the temperature of the hot springs in and out, as well as the cooling fluid temperature difference in and out, each of which is 10°C. Temperature R227ea at refrigerant pump inlet/ outlet condenser is saturated liquid and assumed to be equal to the temperature of the condenser outlet cooling fluid, and temperature R227ea at turbine inlet/ outlet evaporator is saturated steam conditions assumed to be equal to the temperature of the hot springs outlet evaporator. 4. Result and discussion The analysis begins by calculating the heat input/ evaporator capacity. Heat input is calculated to determine the amount of heat that goes into the ORC system, so the amount of electricity potency can be determined. Heat input value is influenced by the volume flow rate of the heat source (hot springs). The result of the calculation is shown in Fig. 3. Fig. 3 showed that the heat input in Lompio - 1 is the largest, amounting to 2,045.68 kW. This happens because the hot springs in Lompio - 1 have a high volume flow rate, which is about 3,000 l/min. These results indicate that the higher the volume flow rate of the hot springs, the higher the heat that can be entered into the system. The next analysis is to calculate the refrigerant flow rate and heat output/condenser capacity. The heat output is calculated to obtain the volume flow rate of the cooling fluid. If the volume flow rate of the cooling fluid has been calculated, then the pump specifications can be determined. The results of the calculation of the refrigerant flow rate, heat output and cooling fluid flow rate are shown in Table 4.
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3500 3000
qhot-spring (l/minute)
2500
Qin (kW)
2000 1500 1000 500 0
Hot Spring Location Fig. 3. Graph of hot spring volume flow rate and heat input to regions. Table 4.Calculation result of refrigerant flow rate, heat output and cooling fluid flow rate. Province
Hot Spring Location
݉ሶ݂݁ݎ
qref
Qout
݉ሶܿݓ
qcw
(kg/s)
(l/min)
(kW)
(kg/s)
(m3/s)
Sumatera Utara
Roburan Dolok – 1& 2
0.66
29.39
76.92
1.84
0.0018
Sumatera Barat
Cubadak - 1
0.65
28.85
77.14
1.85
0.0019
Cubadak - 3
0.33
14.55
38.73
0.93
0.0009
S. Limau
0.34
15.15
38.90
0.93
0.0009
Kambahan
0.15
6.54
17.41
0.42
0.0004
Mudik
0.83
37.15
97.12
2.32
0.0023
Pincurak – 1& 2, Sitabu – 1 & 2
0.93
40.78
114.24
2.73
0.0027
Jawa Barat
Cimanggu
0.35
15.23
44.26
1.06
0.0011
Sulawesi Tengah
Lompio - 1
16.52
737.70
1,928.82
46.17
0.0464
Lompio - 2
15.94
711.79
1,855.10
44.40
0.0446
Lompio - 6
0.33
14.80
38.60
0.92
0.0009
Pulu - 1
1.26
55.24
152.67
3.65
0.0037
Pamandian
1.29
56.73
154.12
3.69
0.0037
Kanan Kumbi
1.29
56.60
154.21
3.69
0.0037
Sulawesi Tenggara
Kaendi - 1
0.16
7.15
19.31
0.46
0.0005
Maluku
Tehoru - 4
0.17
7.42
19.46
0.47
0.0005
Maluku Utara
Losseng - 2
2.04
91.95
232.34
5.56
0.0056
Losseng - 3
2.06
92.32
234.03
5.60
0.0056
Sulawesi Selatan
Table 4 showed that the highest heat output is hot spring at Lompio - 1. The high of heat output means the pump of cooling fluid need high specification. This means the bigger heat output, the bigger volume flow rate needed for condensation process in the system. Analysis followed by calculating the turbine power. Turbine power is calculated in order to determine the electrical power produced at the ORC system. Turbine power calculation results for each region are shown in Fig. 4.
Ghalya Pikra et al. / Energy Procedia 68 (2015) 12 – 21
2500 Qin (kW)
2000
qref (l/minute) 1500
Wt (kW)
1000 500 0
Hot Spring Location Fig. 4. Graph of heat input and turbine power to regions.
Turbine power associated with heat input and the volume flow rate of the refrigerant. The higher the heat input, the value of the volume flow rate of the refrigerant will be higher as well, so that the turbine power generated in the system will be even greater. Lompio - 1 area gains the largest turbine power as compared with other regions, namely 130.13 kW. The lowest turbine power is Kambahan area with 1.14 kW of turbine power. This happens because Lompio - 1 has the highest heat input and volume flow rate of the refrigerant compared to most other regions, and Kambahan has the smallest heat input and refrigerant volume flow rate. In addition, Lompio - 1 hot springs have the highest flow rate compared to other areas, so as to produce a high power turbine as well. Final analysis is calculating performance of the system. The result of thermal efficiency calculation is shown in Fig. 5.Thermal efficiency is influenced by temperature difference between the operating temperature and the cooling fluid temperature. The higher the temperature difference between the operating temperature and cooling fluid temperature, the thermal efficiency will be greater. Fig. 5 shows that Cimanggu has the largest value of thermal efficiency compared with other regions, which is 7.28%. This happens because Cimanggu have operating temperature 68°C and cooling fluid temperature 15°C, thus placing Cimanggu into area that has the highest temperature difference between operating temperature and cooling fluid temperature compared to other regions.
Fig. 5. Graph of temperature difference and thermal efficiency to regions.
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5. Conclusions The electricity power potency estimation from hot spring in Indonesia with temperature 70-80°C using Organic Rankine Cycle gives the conclusion that the volume flow rate of hot springs can determine the value of the electricity generated in the ORC system. Hot springs in Lompio is a region that has the largest volume flow rate, which is 3,000 l/m. The resulting heat input Lompio - 1 area is 2,045.68 kW, so the generated turbine power is 130.13 kW. The temperature difference between operating temperature and cooling fluid temperature affects the thermal efficiency of the system. The higher of the temperature difference, the thermal efficiency is greater. Cimanggu has the highest temperature difference compared to other regions, namely 53°C, resulting 7.28% thermal efficiency of the system. Acknowledgement We would like to thank all researchers in Research Centre for Electrical Power and Mechatronics –Indonesian Institute of Sciences for their supports on enormous tangible and intangible resources. A special thank is also given to program Kompetitif LIPI 2013-2014 for providing fund for this research. References [1] A. F. Fiyah and A. S. Bahri, "Pemodelan Dinamika Massa Reservoir Panas Bumi Menggunakan Metode 4D Microgravity," Jurnal Sains dan Seni Pomits, vol. 1, pp. 1-4, 2012. [2] A. Sugiyono, "Keekonomian Pengembangan PLTP Skala Kecil," in Prosiding Seminar Nasional Teknik Kimia Indonesia dan Musyawarah Nasional APTEKINDO 2012, 2012, pp. 33-39. [3] P. Utami and Soetoto, "Peran Citra Penginderaan Jauh dalam Pengembangan Sumber Daya Panas Bumi," in Prosiding Pertemuan Ilmiah Tahunan X Masyarakat Penginderaan Jauh Indonesia, Mataram, 2001, pp. [IV-18]-[IV-24]. [4] S. Quoilin, et al., "Experimental study and modeling of an Organic Rankine Cycle using scroll expander," Applied Energy, vol. 87, pp. 1260– 1268, 2010. [5] W. Li, et al., "Effects of evaporating temperature and internal heat exchanger on organic Rankine cycle," Applied Thermal Engineering, vol. 31, pp. 4014-4023, 2011. [6] Y. Dai, et al., "Parametric optimization and comparative study of organic Rankine cycle (ORC) for low grade waste heat recovery," Energy Conversion and Management, vol. 50, pp. 576–582, 2009. [7] M. Bianchi and A. D. Pascale, "Bottoming cycles for electric energy generation: Parametric investigation of available and innovative solutions for the exploitation of low and medium temperature heat sources," Applied Energy, vol. 88, pp. 1500–1509, 2011. [8] J. P. Roy, et al., "Performance analysis of an Organic Rankine Cycle with superheating under different heat source temperature conditions," Applied Energy, vol. 88, pp. 2995–3004, 2011. [9] A. I. Papadopoulos, et al., "On the systematic design and selection of optimal working fluids for Organic Rankine Cycles," Applied Thermal Engineering, vol. 30, pp. 760–769, 2010. [10] S. Quoilin and V. Lemort, "Technological and Economical Survey of Organic Rankine Cycle Systems," presented at the 5th European Conference: Economics and Management of Energy in Industry, Portugal, 2009. [11] G. Holdmann, "Final Report: 400kW Geothermal Power Plant at Chena Hot Springs, Alaska," Chena Power, LLC 2007. [12] W. Nowak, et al., "Wstêpne wyniki badañ prototypowego ukladu minisilowni z ORC zasilanej woda o temperaturze 100°C," Przeglad Geologiczny, vol. 58, pp. 622-625, 2010. [13] N. Rohmah and G. Pikra, "Pengaruh Temperatur dan Kualitas Uap R227ea terhadap Kinerja Organic Rankine Cycle pada Sumber Kalor Bertemperatur 70°C," in Prosiding Seminar Nasional Rekayasa Energi, Mekatronik, dan Teknik Kendaraan, Bandung, 2013, pp. 57-62. [14] A. Borsukiewicz-Gozdur and W. Nowak, "Comparative analysis of natural and synthetic refrigerants in application to low temperature Clausius–Rankine cycle," Energy, vol. 32, pp. 344-352, 2007. [15] A. Borsukiewicz-Gozdur, "Experimental investigation of R227ea applied as working fluid in the ORC power plant with hermetic turbogenerator," Applied Thermal Engineering, vol. 56, pp. 126-133, 2013. [16] M. J. Moran and H. N. Shapiro, Fundamentals of Engineering Thermodynamics, 6th ed. United States of America: John Wiley & Sons, Inc., 2008. [17] D. Iim, et al., "Penyelidikan Geologi dan Geokimia Terpadu Daerah Panas Bumi Sampuraga, Kabupaten Mandailing Natal, Sumatera Utara," in Proceeding Pemaparan Hasil Kegiatan Lapangan dan Non Lapangan Tahun 2007 Pusat Sumber Daya Geologi, 2007, pp. [6-1][6-11]. [18] S. Widodo, et al., "Penyelidikan Geolistrik dan Head On di Daerah Panas Bumi Sampuraga, Mandailing Natal – Sumatera Utara," in Proceeding Pemaparan Hasil Kegiatan Lapangan dan Non Lapangan Tahun 2007 Pusat Sumber Daya Geologi, 2007, pp. [16-1]-[16-9]. [19] A. Sugianto, et al., "Penyelidikan Terpadu Daerah Panas Bumi Sampuraga, Kabupaten Mandailing Natal, Sumatera Utara," in Proceeding Pemaparan Hasil Kegiatan Lapangan dan Non Lapangan Tahun 2007 Pusat Sumber Daya Geologi, 2007, pp. [20-1]-[20-11].
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