- Email: [email protected]
Adoption of Kalina cycle as a bottoming cycle in Wayang Windu geothermal power plant
Available Available online online at at www.sciencedirect.com www.sciencedirect.com
ScienceDirect
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Energy Procedia Procedia 00 00 (2017) (2017) 000–000 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 142 Energy Procedia 00(2017) (2017)1147–1152 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
Adoption of Kalina cycle as a bottoming cycle in Wayang Windu The 15th International Symposium on District Heating and Cooling geothermal power plant Assessing theaa*,feasibility of usingFauzi the Soelaiman heat demand-outdoor bb Lukman Adi Prananto Tubagus Muhammad , Muhammad Azizaa temperature function for aof long-term district heat demand forecast Institute Technology, Institute of of Innovative Innovative Research, Research, Tokyo Tokyo Institute Institute of Technology, 2-12-1 2-12-1 I6-10, I6-10, Ookayama, Ookayama, Meguro-ku, Meguro-ku, Tokyo Tokyo 152-8552, 152-8552, Japan Japan aa
bb Institut
Jl. Ganesha Ganesha No.10, No.10, Lb. Lb. Siliwangi, Siliwangi, Bandung, Bandung, Jawa Jawa Barat Barat 40132, 40132, Indonesia Indonesia Institut Teknologi Teknologi Bandung, Bandung, Jl.
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract Abstract
We We present present the the study study of of electricity electricity generation generation by by utilization utilization of of the the Kalina Kalina cycle cycle system system (KCS) (KCS) as as aa bottoming bottoming cycle cycle in in the the Wayang Wayang Windu the thermal thermal energy energy from from the the waste waste brine brine discharged discharged to to the the earth earth crust crust as as aa heat heat Windu geothermal geothermal power power plant. plant. The The KCS KCS converts converts the source. Based on the brine temperature condition, KCS 11 is the most suitable system among others owing to excellent performance source. Based on the brine temperature condition, KCS 11 is the most suitable system among others owing to excellent performance atAbstract low to to mid-regime mid-regime temperatures. temperatures. The The constraints constraints of of the the investigation investigation are are focused focused on on the the consideration consideration of of minimum minimum silica silica at low content. The The system system is optimized based based on on the the most most optimum optimum saturation index index (SSI) (SSI) standard standard of of the the brine, brine, owing owing to to high high SiO SiO22 content. saturation is optimized District heatingmass networks addressed in thecan literature as1660.30 one of the effectivefrom solutions the ammonia-water ratio of ofare thecommonly working fluid. fluid. The system system generate kW most of electricity electricity 48 kg/s kg/sfor of decreasing unused brine brine ammonia-water mass ratio the working The can generate 1660.30 kW of from 48 of unused greenhouse gas emissions fromwhile the building sector. These systems requireOwing high investments which are returned through thefrom heat with 13.20% thermal efficiency maintaining the proper SSI standard. to the nearly zero cost of heat production with 13.20% thermal efficiency while maintaining the proper SSI standard. Owing to the nearly zero cost of heat production from sales. Due the changed climate conditions and building Windu renovation policies, heatplant. demand in the future could decrease, the brine, thistosystem system can support support the electrification electrification of Wayang Wayang geothermal power the brine, this can the of Windu geothermal power plant. prolonging the investment return period. © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. ©The 2017 Thescope Authors. Published Ltd. main ofresponsibility this paper isby to Elsevier assess the feasibility of using the heat demand – outdoor temperature function for heat demand Peer-review under of the scientific committee of the 9th International on Applied Energy. Peer-review under responsibility of the scientific committee of of the the 9th 9th International International Conference Conference on on Applied Applied Energy. Energy. Peer-review under responsibility of thelocated scientific committee forecast. The district of Alvalade, in Lisbon (Portugal), was used as aConference case study. The district is consisted of 665 buildingsKalina that vary both construction periodpower and plant; typology. Three weather scenarios (low, medium, high) and three district Keywords: Kalina cycle; cycle; Wayang Windu Keywords: cycle;inbottoming bottoming cycle; geothermal geothermal power plant; Wayang Windu renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications 1. Introduction 1. Introduction (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Located in the of territory, Indonesia possess highest potential of the geothermal energy, covering Located in slope the ring ring of fire fire increased territory, on Indonesia possessthethe the highest potential covering The value of coefficient average within range of 3.8% up to of 8%the pergeothermal decade, thatenergy, corresponds to the almost 40% (29,000 MWe) of the total world’s potential, as reported in Potential of Geothermal Energy Review in almost 40% (29,000 MWe) of the total world’s potential, as reported in Potential of Geothermal Energy Review in decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and Indonesia [1]. Against this background, by far, the exploration of geothermal energy into electricity has only accounted Indonesia Against this background, far,hand, the exploration of geothermal into electricity has(depending only accounted renovation[1]. scenarios considered). On the by other function intercept increasedenergy for 7.8-12.7% per decade on the for 4.6%scenarios). from all all The geothermal energy could reserves. Various issues the with barely for 4.6% from geothermal energy reserves. Various issues including the remote remote location withconsidered, barely road road coupled values suggested be used to modify theincluding function parameters for location the scenarios and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and ** Corresponding +81-3-5734-3809 Corresponding author. author. Tel.: Tel.: +81-3-5734-3809 Cooling. E-mail address: address: [email protected] [email protected] E-mail
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 1876-6102 © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 9th 9th International International Conference Conference on on Applied Applied Energy. Energy. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 10.1016/j.egypro.2017.12.370
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
1148 2
infrastructure, or the protected forest area in the vicinity of geothermal area, resulted the slow acceleration of geothermal power plant development [2,3]. Therefore, any attempt is necessary to boost the performance of a currently operating geothermal power plant, including a method to utilize a waste fluid of geothermal power plant. Energy recovery from the waste brine can be approached by applying bottoming cycle. In this case, low-grade heat energy from brine is transferred to the low-boiling-point working fluid inside the heat exchanger. For low-grade heat source utilization, several cycles have been studied including the organic Rankine cycle (ORC) [4], Goswami cycle [5], and the Kalina cycle [6]. However, for the temperature ranges from 100 °C to 120 °C, the applicable geothermal cycles are limited to Kalina cycle and ORC, because the working fluids requires to be superheated using the low heat source. As the comparison between Kalina and ORC, Zhang et al. found that Kalina cycle obtained a better result for the utilization of heat source with low temperature [7]. Kalina cycle can generate 10–20% higher efficiency than the ORC when the temperature of heating fluid is below 537 °C. However, the optimization of the cycle was not performed in their experiment. The working fluid in the KCS is a mixture of water and ammonia (NH 3). The mixture has advantages compared to the ORC such as low freezing temperature, large variant of condensation and boiling temperature, and flexible thermodynamic properties. Moreover, Bombarda et al. reported that the KCS has less complex design that the typical ORC due to low logarithmic mean temperature differences [8]. However, most of KCS studies focused on the utility configuration or the numerical analysis without analyzing the performance based on the ammonia-water mixture variation. The present study analyzes the adoption of the KCS as a bottoming cycle that uses heat from waste brine from the separator in the Wayang Windu geothermal power plant in Indonesia. Brine is considered unfavorable for heating fluid due to some disadvantages such as corrosive and scale forming. Therefore, the consideration of minimum brine temperature based on the SSI is necessary in this system. Table 1 provides information about the brine separated from the main working fluid of the power plant. Table 1. Characteristics of brine from the Wayang Windu geothermal power plant Parameter
Value
Brine temperature
180.7 °C
Brine pressure
1.02 MPa
Discharge rate
48 kg/s
SiO2 content
853 mg/L
2. Modeling and Simulation 2.1. Calculation of silica (SiO2) sedimentation In a geothermal power plant system, working fluid is pumped from inside the Earth’s crust. Unlike other types of power plant, a geothermal power plant uses natural fluid heated by an underground heat source to obtain energy. The working fluid from the geothermal well is not always pure water, and impurities therefore limit its use. Separator utilities play a crucial role in protecting the steam turbine and other plant utilities by splitting the stream flowing from the well into a pure water steam (i.e. the working fluid) and waste brine. The brine separated from the clean water steam is reinjected into the Earth’s crust, which is a missed opportunity owing to the high energy content of brine. This study proposes a bottoming cycle to convert thermal energy from the waste brine before reinjected to the earth crust by applying the KCS. However, working fluid heated by the waste brine is limited by the lowest allowable of brine temperature before the occurrence of SiO2 sedimentation, the most abundant particulates inside the brine. To obtain the minimum reinjection temperature of the brine, the ratio of SiO2 concentration in the brine divided by the equilibrium SiO2 concentration for a certain temperature (silica saturation index (SSI)) [9], is analyzed to ensure that sedimentation does not occur inside the brine pipe. Based on Table 1, the highest SiO2 content is 853 mg/L. The density is 2200 kg/m3, and the SiO2 content is thus 387.73 ppm (S1). The Fourier and Marshall equation is used to calculate the molar solubility of amorphous SiO2 in pure water within the temperature range of 90–340 °C [10]:
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
𝐿𝐿𝐿𝐿𝐿𝐿10𝑠𝑠 = −6.116 + 0.01625𝑇𝑇 − 1.758 × 10−5 𝑇𝑇 2 + 5.257 × 10−9 𝑇𝑇 3
1149 3
(1)
where, T is the brine temperature, and S is the SiO2 content. The SSI can then be obtained using the SiO2 content number calculated as 𝑆𝑆
SSI = 𝐼𝐼 .
(2)
𝑆𝑆
The limit of allowable SSI is below 1.0. Therefore, to avoid the scaling of SiO2, and to consider 5% tolerance, the minimum temperature of brine is set at 113 °C. 2.2. KCS modeling Brine from the Wayang Windu geothermal power plant has a temperature of around 180 °C. The KCS most suitable in this case is therefore KCS 11 [11]. A typical cycle of KCS 11 is shown in Fig. 1. Besides common utilities such as a turbine generator (A) and feedwater pump (G), KCS 11 has a high temperature (HT) evaporator unit (B), low temperature (LT) evaporator unit (C), HT recuperator unit (D), LT recuperator unit (E), and condenser unit (F). Processe modeling and intensification are conducted with the principles of process integration technology to minimize the exergy lost, therefore improve the total energy efficiency [12,13].
Fig. 1. Schematic of KCS 11
The working fluid used in the KCS is a binary mixture of ammonia and water. The thermal properties of this mixture are distinct from those of ammonia or water as pure substances. The Peng–Robinson equation [14] expressed by Eq. (3) is thus used to calculate the properties of the working fluid. P= a=
𝑅𝑅𝑅𝑅
𝑉𝑉𝑚𝑚 − 𝑏𝑏
−
0,54724𝑅𝑅 2 𝑇𝑇𝑐𝑐2 𝑃𝑃𝑐𝑐
a𝛼𝛼
2 + 2𝑏𝑏𝑉𝑉 − 𝑏𝑏 2 𝑉𝑉𝑚𝑚 𝑚𝑚
,
,
(3) (4)
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
1150 4
b=
0,0778𝑅𝑅𝑇𝑇𝑐𝑐 𝑃𝑃𝑐𝑐
(5)
,
𝛼𝛼 = (1 + (0.37464 + 1.54226𝜔𝜔 − 0,26992𝜔𝜔2 ) (1 −
𝑇𝑇 0,5
𝑇𝑇𝑐𝑐 𝑟𝑟
(6)
2
)) ,
where, b is the volume correction, a is a molecular interaction parameter, and ω is an acentric factor. The next step of modeling is to make assumptions about the data. Some conditions are assumed to ensure the analysis is accurate. The following assumptions are made in establishing the model. Table 2. Assumptions for the establishing model Parameter
Assumptions
Turbine efficiency
82%
Generator efficiency
100%
Pump efficiency
75%
Pressure drop in heat exchanger
35 kPa
Pressure drop in pipeline and separator
negligible
The performance of the proposed system is evaluated by determining the thermal efficiency written as following. Here, 𝑊𝑊𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛 is the power produced by the electric generator minus the house-load power consumption and pumping operation. =
𝑊𝑊𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛
𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 +𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒
(7)
3. Result and Discussion For working fluid optimization, the ammonia mass ratio is varied between 82 and 88 wt%. The ammonia mass ratio is optimized with regard to the generated power and feedwater pump pressure. Fig. 2 shows the correlation of the feedwater pressure and generated power for different evaluated ammonia mass ratios. The power plant produces the highest power at an 86 wt% ammonia mass ratio with 3.2 MPa feedwater pressure.
Fig. 2. Generated power versus feedwater pressure for different ammonia mass ratios
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
1151 5
Following the optimization of the ammonia mass ratio, the pinch temperature is simulated in conjunction with the feedwater pump pressure and generated power. Fig. 3 shows the correlation between the feedwater pressure and generated power for each evaluated pinch temperature.
Fig. 3. Feedwater pressure versus turbine power at different pinch temperatures
The maximum feedwater pressures in this cycle is set at 3.2 MPa due to temperature cross occurrence at the higher pressure, resulting in a fault of the system. Pinch temperature is calculated within the regimes of 2.0–3.2 MPa. From the variation of pinch temperature (5,10,15, and 20 °C), the most optimal performance is achieved at 5 °C, as shown in Fig. 3. After the pinch temperature and the ammonia-water mixture ratio are determined, full plant calculation is carried out to reveal the electricity generation from the proposed KCS. From the simulation, the waste brine from the Wayang Windu plant can supply 1734 kW of electricity with 13.20% thermal efficiency. With 53.04 and 20.66 kW of house load to the feedwater pump and air condenser fan, the net energy of the system is 1660.30 kW. Considering the extremely low cost of the heat source, the utilization of waste brine in every geothermal power plant can support the electrification significantly without discharging any pollutant to the atmosphere.
Fig. 4. Detailed results for the optimized system
1152 6
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
4. Conclusion A waste brine utilization by the adoption of KCS 11 in the Wayang Windu geothermal power plant has been proposed. Despite the low-grade heat source from the brine, the optimum ammonia-water mixture in the KCS 11 can generate electricity while maintaining the safety of the brine sedimentation due to the low-temperature condition. The system can generate 1660.30 kW of electricity from 48 kg/s of waste brine with 13.20% thermal efficiency. With this investigation, the electrification of the geothermal power plant can be increased by the application of bottoming cycle to recover energy from the waste brine. Acknowledgements The authors express their great appreciation to Star Energy Geothermal Wayang Windu Ltd. for assistance in providing data required for this study. This study is supported by the Indonesia Endowment Fund for Education (LPDP). References [1] Nasruddin, Alhamid MI, Daud Y, Surachman A, Sugiyono A, Aditya HB, Mahlia TMI. Potential of geothermal energy for electricity generation in Indonesia: A review. Renew Sustain Energy Rev 2016;53:733–740. [2] Darma S, Gunawan R. Country Update: Geothermal energy use and development in Indonesia. Proc World Geothermal Congress 2015, Melbourne, Apr 19–25, pp. 25–30. [3] Mujiyanto S, Tiess G. Secure energy supply in 2025: Indonesia’s need for an energy policy strategy. Energy Policy 2013;61:31-41. [4] Aziz M, Kurniawan T, Oda T, Kashiwagi T. Advanced power generation using biomass wastes from palm oil mills. Appl Thermal Eng 2017;114:1378–1386. [5] Chen H, Goswami DY, Stefanakos EK. A review of thermodynamic cycles and working fluids for the conversion of low-grade heat. Renew Sustain Energy Rev 2010;14:3059–3067. [6] Nasruddin, Usvika R, Rifaldi M, Noor A. Energy and exergy analysis of kalina cycle system (KCS) 34 with mass fraction ammonia-water mixture variation. J Mech Sci Technol 2009;23:1871–1876. [7] Zhang X, He M, Zhang Y. A review of research on the Kalina cycle. Renew Sustain Energy Rev 2012;16:5309–5318. [8] Bombarda P, Invernizzi CM, Pietra C. Heat recovery from diesel engines: A thermodynamic comparison between Kalina and ORC cycles. Appl Therm Eng 2010;30:212–219. [9] Brown K. Thermodynamics and kinetics of silica scaling. Int Work Miner Scaling 2011. [10] Fournier RO, Marshall WL. Calculation of amorphous silica solubilities at 25 °C to 300 °C and apparent cation hydration numbers in aqueous salt solutions using the concept of effective density of water. Geochim Cosmochim Acta 1983;47:587–596. [11] He J, Liu C, Xu X, Li Y, Wu S, Xu J. Performance research on modified KCS (Kalina cycle system) 11 without throttle valve. Energy 2014;64:389–397. [12] Aziz M. Power generation from algae employing enhanced process integration technology. Chem Eng Res Des 2016;109:297–306. [13] Aziz M, Zaini IN, Oda T, Morihara A, Kashiwagi T. Energy conservative brown coal conversion to hydrogen and power based on enhanced process integration: Integrated drying, coal direct chemical looping, combined cycle and hydrogenation. Int J Hydrogen Energy 2017;42:2904– 2913. [14] Karimi MN, Ahmad M. Optimization of Kalina Cycle. Int J Sci Res 2016;5:2244–2249
ScienceDirect
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Energy Procedia Procedia 00 00 (2017) (2017) 000–000 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 142 Energy Procedia 00(2017) (2017)1147–1152 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
Adoption of Kalina cycle as a bottoming cycle in Wayang Windu The 15th International Symposium on District Heating and Cooling geothermal power plant Assessing theaa*,feasibility of usingFauzi the Soelaiman heat demand-outdoor bb Lukman Adi Prananto Tubagus Muhammad , Muhammad Azizaa temperature function for aof long-term district heat demand forecast Institute Technology, Institute of of Innovative Innovative Research, Research, Tokyo Tokyo Institute Institute of Technology, 2-12-1 2-12-1 I6-10, I6-10, Ookayama, Ookayama, Meguro-ku, Meguro-ku, Tokyo Tokyo 152-8552, 152-8552, Japan Japan aa
bb Institut
Jl. Ganesha Ganesha No.10, No.10, Lb. Lb. Siliwangi, Siliwangi, Bandung, Bandung, Jawa Jawa Barat Barat 40132, 40132, Indonesia Indonesia Institut Teknologi Teknologi Bandung, Bandung, Jl.
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract Abstract
We We present present the the study study of of electricity electricity generation generation by by utilization utilization of of the the Kalina Kalina cycle cycle system system (KCS) (KCS) as as aa bottoming bottoming cycle cycle in in the the Wayang Wayang Windu the thermal thermal energy energy from from the the waste waste brine brine discharged discharged to to the the earth earth crust crust as as aa heat heat Windu geothermal geothermal power power plant. plant. The The KCS KCS converts converts the source. Based on the brine temperature condition, KCS 11 is the most suitable system among others owing to excellent performance source. Based on the brine temperature condition, KCS 11 is the most suitable system among others owing to excellent performance atAbstract low to to mid-regime mid-regime temperatures. temperatures. The The constraints constraints of of the the investigation investigation are are focused focused on on the the consideration consideration of of minimum minimum silica silica at low content. The The system system is optimized based based on on the the most most optimum optimum saturation index index (SSI) (SSI) standard standard of of the the brine, brine, owing owing to to high high SiO SiO22 content. saturation is optimized District heatingmass networks addressed in thecan literature as1660.30 one of the effectivefrom solutions the ammonia-water ratio of ofare thecommonly working fluid. fluid. The system system generate kW most of electricity electricity 48 kg/s kg/sfor of decreasing unused brine brine ammonia-water mass ratio the working The can generate 1660.30 kW of from 48 of unused greenhouse gas emissions fromwhile the building sector. These systems requireOwing high investments which are returned through thefrom heat with 13.20% thermal efficiency maintaining the proper SSI standard. to the nearly zero cost of heat production with 13.20% thermal efficiency while maintaining the proper SSI standard. Owing to the nearly zero cost of heat production from sales. Due the changed climate conditions and building Windu renovation policies, heatplant. demand in the future could decrease, the brine, thistosystem system can support support the electrification electrification of Wayang Wayang geothermal power the brine, this can the of Windu geothermal power plant. prolonging the investment return period. © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. ©The 2017 Thescope Authors. Published Ltd. main ofresponsibility this paper isby to Elsevier assess the feasibility of using the heat demand – outdoor temperature function for heat demand Peer-review under of the scientific committee of the 9th International on Applied Energy. Peer-review under responsibility of the scientific committee of of the the 9th 9th International International Conference Conference on on Applied Applied Energy. Energy. Peer-review under responsibility of thelocated scientific committee forecast. The district of Alvalade, in Lisbon (Portugal), was used as aConference case study. The district is consisted of 665 buildingsKalina that vary both construction periodpower and plant; typology. Three weather scenarios (low, medium, high) and three district Keywords: Kalina cycle; cycle; Wayang Windu Keywords: cycle;inbottoming bottoming cycle; geothermal geothermal power plant; Wayang Windu renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications 1. Introduction 1. Introduction (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Located in the of territory, Indonesia possess highest potential of the geothermal energy, covering Located in slope the ring ring of fire fire increased territory, on Indonesia possessthethe the highest potential covering The value of coefficient average within range of 3.8% up to of 8%the pergeothermal decade, thatenergy, corresponds to the almost 40% (29,000 MWe) of the total world’s potential, as reported in Potential of Geothermal Energy Review in almost 40% (29,000 MWe) of the total world’s potential, as reported in Potential of Geothermal Energy Review in decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and Indonesia [1]. Against this background, by far, the exploration of geothermal energy into electricity has only accounted Indonesia Against this background, far,hand, the exploration of geothermal into electricity has(depending only accounted renovation[1]. scenarios considered). On the by other function intercept increasedenergy for 7.8-12.7% per decade on the for 4.6%scenarios). from all all The geothermal energy could reserves. Various issues the with barely for 4.6% from geothermal energy reserves. Various issues including the remote remote location withconsidered, barely road road coupled values suggested be used to modify theincluding function parameters for location the scenarios and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and ** Corresponding +81-3-5734-3809 Corresponding author. author. Tel.: Tel.: +81-3-5734-3809 Cooling. E-mail address: address: [email protected] [email protected] E-mail
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 1876-6102 © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 9th 9th International International Conference Conference on on Applied Applied Energy. Energy. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 10.1016/j.egypro.2017.12.370
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
1148 2
infrastructure, or the protected forest area in the vicinity of geothermal area, resulted the slow acceleration of geothermal power plant development [2,3]. Therefore, any attempt is necessary to boost the performance of a currently operating geothermal power plant, including a method to utilize a waste fluid of geothermal power plant. Energy recovery from the waste brine can be approached by applying bottoming cycle. In this case, low-grade heat energy from brine is transferred to the low-boiling-point working fluid inside the heat exchanger. For low-grade heat source utilization, several cycles have been studied including the organic Rankine cycle (ORC) [4], Goswami cycle [5], and the Kalina cycle [6]. However, for the temperature ranges from 100 °C to 120 °C, the applicable geothermal cycles are limited to Kalina cycle and ORC, because the working fluids requires to be superheated using the low heat source. As the comparison between Kalina and ORC, Zhang et al. found that Kalina cycle obtained a better result for the utilization of heat source with low temperature [7]. Kalina cycle can generate 10–20% higher efficiency than the ORC when the temperature of heating fluid is below 537 °C. However, the optimization of the cycle was not performed in their experiment. The working fluid in the KCS is a mixture of water and ammonia (NH 3). The mixture has advantages compared to the ORC such as low freezing temperature, large variant of condensation and boiling temperature, and flexible thermodynamic properties. Moreover, Bombarda et al. reported that the KCS has less complex design that the typical ORC due to low logarithmic mean temperature differences [8]. However, most of KCS studies focused on the utility configuration or the numerical analysis without analyzing the performance based on the ammonia-water mixture variation. The present study analyzes the adoption of the KCS as a bottoming cycle that uses heat from waste brine from the separator in the Wayang Windu geothermal power plant in Indonesia. Brine is considered unfavorable for heating fluid due to some disadvantages such as corrosive and scale forming. Therefore, the consideration of minimum brine temperature based on the SSI is necessary in this system. Table 1 provides information about the brine separated from the main working fluid of the power plant. Table 1. Characteristics of brine from the Wayang Windu geothermal power plant Parameter
Value
Brine temperature
180.7 °C
Brine pressure
1.02 MPa
Discharge rate
48 kg/s
SiO2 content
853 mg/L
2. Modeling and Simulation 2.1. Calculation of silica (SiO2) sedimentation In a geothermal power plant system, working fluid is pumped from inside the Earth’s crust. Unlike other types of power plant, a geothermal power plant uses natural fluid heated by an underground heat source to obtain energy. The working fluid from the geothermal well is not always pure water, and impurities therefore limit its use. Separator utilities play a crucial role in protecting the steam turbine and other plant utilities by splitting the stream flowing from the well into a pure water steam (i.e. the working fluid) and waste brine. The brine separated from the clean water steam is reinjected into the Earth’s crust, which is a missed opportunity owing to the high energy content of brine. This study proposes a bottoming cycle to convert thermal energy from the waste brine before reinjected to the earth crust by applying the KCS. However, working fluid heated by the waste brine is limited by the lowest allowable of brine temperature before the occurrence of SiO2 sedimentation, the most abundant particulates inside the brine. To obtain the minimum reinjection temperature of the brine, the ratio of SiO2 concentration in the brine divided by the equilibrium SiO2 concentration for a certain temperature (silica saturation index (SSI)) [9], is analyzed to ensure that sedimentation does not occur inside the brine pipe. Based on Table 1, the highest SiO2 content is 853 mg/L. The density is 2200 kg/m3, and the SiO2 content is thus 387.73 ppm (S1). The Fourier and Marshall equation is used to calculate the molar solubility of amorphous SiO2 in pure water within the temperature range of 90–340 °C [10]:
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
𝐿𝐿𝐿𝐿𝐿𝐿10𝑠𝑠 = −6.116 + 0.01625𝑇𝑇 − 1.758 × 10−5 𝑇𝑇 2 + 5.257 × 10−9 𝑇𝑇 3
1149 3
(1)
where, T is the brine temperature, and S is the SiO2 content. The SSI can then be obtained using the SiO2 content number calculated as 𝑆𝑆
SSI = 𝐼𝐼 .
(2)
𝑆𝑆
The limit of allowable SSI is below 1.0. Therefore, to avoid the scaling of SiO2, and to consider 5% tolerance, the minimum temperature of brine is set at 113 °C. 2.2. KCS modeling Brine from the Wayang Windu geothermal power plant has a temperature of around 180 °C. The KCS most suitable in this case is therefore KCS 11 [11]. A typical cycle of KCS 11 is shown in Fig. 1. Besides common utilities such as a turbine generator (A) and feedwater pump (G), KCS 11 has a high temperature (HT) evaporator unit (B), low temperature (LT) evaporator unit (C), HT recuperator unit (D), LT recuperator unit (E), and condenser unit (F). Processe modeling and intensification are conducted with the principles of process integration technology to minimize the exergy lost, therefore improve the total energy efficiency [12,13].
Fig. 1. Schematic of KCS 11
The working fluid used in the KCS is a binary mixture of ammonia and water. The thermal properties of this mixture are distinct from those of ammonia or water as pure substances. The Peng–Robinson equation [14] expressed by Eq. (3) is thus used to calculate the properties of the working fluid. P= a=
𝑅𝑅𝑅𝑅
𝑉𝑉𝑚𝑚 − 𝑏𝑏
−
0,54724𝑅𝑅 2 𝑇𝑇𝑐𝑐2 𝑃𝑃𝑐𝑐
a𝛼𝛼
2 + 2𝑏𝑏𝑉𝑉 − 𝑏𝑏 2 𝑉𝑉𝑚𝑚 𝑚𝑚
,
,
(3) (4)
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
1150 4
b=
0,0778𝑅𝑅𝑇𝑇𝑐𝑐 𝑃𝑃𝑐𝑐
(5)
,
𝛼𝛼 = (1 + (0.37464 + 1.54226𝜔𝜔 − 0,26992𝜔𝜔2 ) (1 −
𝑇𝑇 0,5
𝑇𝑇𝑐𝑐 𝑟𝑟
(6)
2
)) ,
where, b is the volume correction, a is a molecular interaction parameter, and ω is an acentric factor. The next step of modeling is to make assumptions about the data. Some conditions are assumed to ensure the analysis is accurate. The following assumptions are made in establishing the model. Table 2. Assumptions for the establishing model Parameter
Assumptions
Turbine efficiency
82%
Generator efficiency
100%
Pump efficiency
75%
Pressure drop in heat exchanger
35 kPa
Pressure drop in pipeline and separator
negligible
The performance of the proposed system is evaluated by determining the thermal efficiency written as following. Here, 𝑊𝑊𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛 is the power produced by the electric generator minus the house-load power consumption and pumping operation. =
𝑊𝑊𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛
𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 +𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒
(7)
3. Result and Discussion For working fluid optimization, the ammonia mass ratio is varied between 82 and 88 wt%. The ammonia mass ratio is optimized with regard to the generated power and feedwater pump pressure. Fig. 2 shows the correlation of the feedwater pressure and generated power for different evaluated ammonia mass ratios. The power plant produces the highest power at an 86 wt% ammonia mass ratio with 3.2 MPa feedwater pressure.
Fig. 2. Generated power versus feedwater pressure for different ammonia mass ratios
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
1151 5
Following the optimization of the ammonia mass ratio, the pinch temperature is simulated in conjunction with the feedwater pump pressure and generated power. Fig. 3 shows the correlation between the feedwater pressure and generated power for each evaluated pinch temperature.
Fig. 3. Feedwater pressure versus turbine power at different pinch temperatures
The maximum feedwater pressures in this cycle is set at 3.2 MPa due to temperature cross occurrence at the higher pressure, resulting in a fault of the system. Pinch temperature is calculated within the regimes of 2.0–3.2 MPa. From the variation of pinch temperature (5,10,15, and 20 °C), the most optimal performance is achieved at 5 °C, as shown in Fig. 3. After the pinch temperature and the ammonia-water mixture ratio are determined, full plant calculation is carried out to reveal the electricity generation from the proposed KCS. From the simulation, the waste brine from the Wayang Windu plant can supply 1734 kW of electricity with 13.20% thermal efficiency. With 53.04 and 20.66 kW of house load to the feedwater pump and air condenser fan, the net energy of the system is 1660.30 kW. Considering the extremely low cost of the heat source, the utilization of waste brine in every geothermal power plant can support the electrification significantly without discharging any pollutant to the atmosphere.
Fig. 4. Detailed results for the optimized system
1152 6
Lukman Adi Prananto et al. / Energy Procedia 142 (2017) 1147–1152 Prananto et al. / Energy Procedia 00 (2017) 000–000
4. Conclusion A waste brine utilization by the adoption of KCS 11 in the Wayang Windu geothermal power plant has been proposed. Despite the low-grade heat source from the brine, the optimum ammonia-water mixture in the KCS 11 can generate electricity while maintaining the safety of the brine sedimentation due to the low-temperature condition. The system can generate 1660.30 kW of electricity from 48 kg/s of waste brine with 13.20% thermal efficiency. With this investigation, the electrification of the geothermal power plant can be increased by the application of bottoming cycle to recover energy from the waste brine. Acknowledgements The authors express their great appreciation to Star Energy Geothermal Wayang Windu Ltd. for assistance in providing data required for this study. This study is supported by the Indonesia Endowment Fund for Education (LPDP). References [1] Nasruddin, Alhamid MI, Daud Y, Surachman A, Sugiyono A, Aditya HB, Mahlia TMI. Potential of geothermal energy for electricity generation in Indonesia: A review. Renew Sustain Energy Rev 2016;53:733–740. [2] Darma S, Gunawan R. Country Update: Geothermal energy use and development in Indonesia. Proc World Geothermal Congress 2015, Melbourne, Apr 19–25, pp. 25–30. [3] Mujiyanto S, Tiess G. Secure energy supply in 2025: Indonesia’s need for an energy policy strategy. Energy Policy 2013;61:31-41. [4] Aziz M, Kurniawan T, Oda T, Kashiwagi T. Advanced power generation using biomass wastes from palm oil mills. Appl Thermal Eng 2017;114:1378–1386. [5] Chen H, Goswami DY, Stefanakos EK. A review of thermodynamic cycles and working fluids for the conversion of low-grade heat. Renew Sustain Energy Rev 2010;14:3059–3067. [6] Nasruddin, Usvika R, Rifaldi M, Noor A. Energy and exergy analysis of kalina cycle system (KCS) 34 with mass fraction ammonia-water mixture variation. J Mech Sci Technol 2009;23:1871–1876. [7] Zhang X, He M, Zhang Y. A review of research on the Kalina cycle. Renew Sustain Energy Rev 2012;16:5309–5318. [8] Bombarda P, Invernizzi CM, Pietra C. Heat recovery from diesel engines: A thermodynamic comparison between Kalina and ORC cycles. Appl Therm Eng 2010;30:212–219. [9] Brown K. Thermodynamics and kinetics of silica scaling. Int Work Miner Scaling 2011. [10] Fournier RO, Marshall WL. Calculation of amorphous silica solubilities at 25 °C to 300 °C and apparent cation hydration numbers in aqueous salt solutions using the concept of effective density of water. Geochim Cosmochim Acta 1983;47:587–596. [11] He J, Liu C, Xu X, Li Y, Wu S, Xu J. Performance research on modified KCS (Kalina cycle system) 11 without throttle valve. Energy 2014;64:389–397. [12] Aziz M. Power generation from algae employing enhanced process integration technology. Chem Eng Res Des 2016;109:297–306. [13] Aziz M, Zaini IN, Oda T, Morihara A, Kashiwagi T. Energy conservative brown coal conversion to hydrogen and power based on enhanced process integration: Integrated drying, coal direct chemical looping, combined cycle and hydrogenation. Int J Hydrogen Energy 2017;42:2904– 2913. [14] Karimi MN, Ahmad M. Optimization of Kalina Cycle. Int J Sci Res 2016;5:2244–2249