- Email: [email protected]
Thermodynamics study of flash–binary cycle in geothermal power plant
Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
Contents lists available at ScienceDirect
Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser
Letter to the Editor Thermodynamics study of flash–binary cycle in geothermal power plant
a r t i c l e
i n f o
Keywords: Flash–binary cycle Optimization Heat exchanger Organic working fluid
a b s t r a c t This paper was conducted to evaluate the performance of a flash–binary cycle if applied to geothermal power plant (PLTP), where the source of heat came from the residual brine from the separator which was generally re-injected into wells. In the study of flash–binary cycle, there are four types of organic working fluids considered for the binary cycle, namely i-pentane, n-pentane, i-butane, and n-butane. Optimization process was carried out on the performance of plant systems. This paper also discussed the limitation factor to get maximum net power, like: flash pressure, evaporator pressure, pinch temperature, scaling formation, and thermal design in heat exchanger (preheater, evaporator, and air cooled condenser). Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved.
1. Introduction Nowadays the world is experiencing environmental problems, especially climate changes problems caused by global warming. One of the causes of global warming is the greenhouse effect. If it is pursued further, it will give a conclusion that it is because the emission of carbon dioxide (CO2 ) generates by the use of fossil fuels that are not controlled. The rapid industrial development that occurred today brings the impact to use greater energy [1]. Basically energy sources can be grouped into two, namely nonrenewable and renewable energy. Examples of non-renewable energy sources are: oil, natural gas, and coal, while the examples of renewable energy sources are: geothermal, wind, sea water, and sunlight. One important issue from the direction of world energy development is green energy, so the development of renewable energy sources particularly suitable to overcome these problems. Indonesia in the form of its geographical nature is potential for renewable energy sources, especially geothermal energy. Geothermal energy will be converted to electrical energy, because electricity is more easily used in daily life. In this paper will be studied the utilization of flash–binary cycle to increase the electricity production at a plant, so it will be very important to be learned.
cycle that can be used to treat it. The cycle is called flash–binary cycle [2]. Data which is used in the process simulation is the data obtained from geothermal wells in the unit geothermal power plant (PLTP) in Lahendong, North Sulawesi. The input data for brine in this study are: mass flow rate 400 t/h, temperature 170 ◦ C, and pressure 8 barg. The assumptions which are used: the air temperature which is entered condenser is determine 28 ◦ C, there are pressure drop in preheater and evaporator 50 kPa, also in condenser 34 kPa, isentropic efficiency of turbine is 85% and for pump is 75%, type of heat exchanger for evaporator is kettle and preheater is two pass shell, and pinch temperature which are analyzed in the preheater and evaporator are 5, 10, 15 and 20 ◦ C. Those assumptions are used to simplify the existing problems, so that the objectives of this study can be obtained [3]. The model and process simulation of flash–binary cycle will be done. After having obtained the optimum conditions that can produce the greatest power, the next step is thermal design for preheater and evaporator [11]. The method which is available in Gas Processors Suppliers Association (GPSA) is used to do thermal design for air cooled condenser. The results obtained from GPSA method are the main dimension of air cooled condenser, fan diameter, pressure drop, fans power. 3. Results and discussion
2. Material and methodology Geothermal power plant (PLTP) in Lahendong operates with the supply of production well which is water dominated. Vapor and liquid phase can be separated by using separator. Steam is used to drive steam turbines that can produce electricity up to 20 MW, while the liquid is injected back into the bowels of the earth. Seeing the potential energy possessed by the liquid minerals (brine) which still has a high pressure and temperature, this paper will discuss the
The state of equations which will be used is Peng–Robinson (PR). It can be seen from Fig. 1, if we use organic working fluid, it will be suggested to use Peng–Robinson (PR) or Redlich–Kwong–Soave (RKS) [4]. The other problem which must be analyzed in geothermal power plant is formation of scale. There are three methods which will be used to analyze scaling: Fournier, DiPippo, and Silica Scaling Index (SSI). The details explanation can be read on the reference.
1364-0321/$ – see front matter. Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.rser.2011.05.019
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
5219
Fig. 1. Flowchart to use state of equation. Sinnot [17].
These methods are used to know the recrystallization temperature of silica. We must prevent the brine out temperature not less than it. If the brine out temperature less than recrystallization temperature of silica, it will form scale in the tube/pipe. It will obstruct the fluid flow in the pipe/tube. The summary of recrystallization temperature from those methods can be seen in Table 1 [12].
Table 1 Comparison of recrystallization temperature with any methods.
Recrystallization temperature (◦ C)
Fig. 2. Flash–binary models from HYSYS package program.
Fournier
DiPippo
SSI
117,82
121,85
122
5220
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
Fig. 5. Net powers when evaporator pressure constant but pinch temperature and flash pressure independent.
Fig. 3. Turbine power when pinch temperature constant 5 ◦ C but evaporator and flash pressures be independent.
From Table 1 we can see that SSI method has the tightest temperature compare with others. It means that SSI method will be safest than others when it is used. Because of that, we will use SSI method in all analyzes about scale formation [5]. In Fig. 2, it will be shown the flash–binary models. The upper schematic represents flash cycle and the lower represents binary cycle. If we combine, it becomes flash–binary cycle. There are three independent parameters which will be analyzed, i.e. flash pressure (2), evaporator pressure (e), and pinch temperature (T11 –Te ) [6]. It is very difficult to analyze all the parameters independently. So, in analyze the independent parameters, it will be made one parameter be constant. In Fig. 3, it will be shown the graph where the pinch temperature constant but the flash and evaporator pressure be independent. From that figure we can see that when flash pressure be smaller, the organic turbine power becomes smaller too but the steam turbine power becomes higher. Evaporator pressure does not affect steam turbine power but effect organic turbine power where there is an optimum value. Fig. 4 will be shown the graph when flash pressure constant, but pinch temperature and evaporator pressure are independent. In that graph, it is shown that steam turbine power will be constant when evaporator pressure becomes higher. Organic turbine power will have one maximum value when evaporator pressure becomes higher. The smaller pinch temperature, the higher organic turbine power can be produced.
On the last, in Fig. 5 we will see the graph which shown the condition when evaporator pressure constant but pinch temperature and flash pressure are independent. We can see from that figure, when flash pressure becomes smaller, the net power also becomes smaller. But, there is an optimum value for flash pressure to produce maximum net powers. Now, it will be analyzed the effect of variation working fluid for the power plant performance, especially net power [13]. In Fig. 6, it will be shown the graph for i-pentane working fluid. We will see the effect of evaporator and flash pressure to the net power produced. There is also limitation in scaling. The above graph represents any parameters, i.e. brine out temperature, net power, and Silica Scaling Index (SSI). We can read the graph from the direction of arrows. For example: when evaporator pressure 2200 kPa and flash pressure 790 kPa, it can produce 1.4 MW net power, SSI factor 0.97, and brine out temperature
Fig. 6. Net power, SSI, and brine out temperature for i-pentane when evaporator and flash pressure be varied.
Table 2 Net power comparison of any working fluids. Parameters ◦
Fig. 4. Turbine power when flash pressure constant but pinch temperature and evaporator pressure be independent.
Pinch temperature ( C) Flash pressure (kPa) SSI Evaporator pressure (kPa) Net power (kW)
i-Butane
n-Butane
i-Pentane
n-Pentane
15 500 0.97 3500 2915.79
5 600 0.97 3533 3057.31
5 600 0.97 1500.60 3077.64
5 500 0.97 1187.50 2793.85
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
5221
Table 3 Input layout when design evaporator. Process conditions Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/allow dP Fouling resistance
Hot tube 0 158.9 600 0.0003
Shell geometry TEMA type Inside diameter Orientation Hot fluid
AKT 1550 Horizontal Tubeside
Tube geometry Type Length Tube OD Pitch
Plain 8.534 25.4 32
108.38 0 143.8 50
Cold shell 0
34.49 1
1530 0.0002
50
Wall thickness Layout angle Tubepasses
1.651 45 2
kg/s Weight fraction vapor ◦ C kPa/kPa m2 K/W
mm
m mm mm
150 ◦ C. If the value of SSI becomes higher than 1, it will form scale. So it must be prevented the value of SSI higher than 1 [7]. In analyze the others working fluid, i.e. n-pentane, i-butane, and n-butane, we use the same method like i-pentane. We can see the effect of variation working fluid in Table 2. From Table 2, i-pentane can produce the highest net power among all. The optimum condition which can produce maximum power will be used in thermal design process. Now we will design the heat exchanger (preheater and evaporator) thermally. First step in thermal design process, we must choose the material which will be used in shell and tube. The material for shell is carbon steel ASTM a516-60, because shell will be passed with working fluid. Tube will be used duplex stainless steel SAF 2205 (ASTM 789), because tube will be passed with brine which
mm ◦
has a high chloride and low pH (sour). Duplex stainless steel will resist on uniform corrosion and pitting (localize corrosion). In thermal design of heat exchanger, the standard which will be used is Tubular Exchanger Manufacturers Association, Inc. (TEMA) [8]. Evaporator will be used kettle type (AKT) and preheater will be used two pass shell type (AFT). We need input process and design parameters when design evaporator and preheater [9]. From Table 3, it will be shown the input needed (process and design parameters) when design evaporator. The output results from evaporator thermal design will be shown in Table 4. The same method is used to design preheater thermally. The input layout can be seen in Table 5.
Table 4 Output result from evaporator thermal design. Process conditions Fluid name Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/Avg dP/Allow. Fouling
Cold shellside i-Pentane
Hot tubeside Brine
(kg/s) (Wt. frac vap.) (◦ C) (kPa) (kPa) (m2 K/W)
0 138.8 1530.02 3.287
34.4943 1 138.9 1528.38 50 0.0002
0 158.9 600 4.01
108.376 0 143.8 598 50 0.0003
Exchanger performance Shell h Tube h Hot regime Cold regime EMTD
(W/m2 K) (W/m2 K) (–) (–) (◦ C)
2856.9 3974.37 Sens. liquid Flow 10.8
Actual U Required U Duty Area Overdesign
(W/m2 K) (W/m2 K) (MW) (m2 ) (%)
783.5 685.98 7.274 983.927 14.22
Shell geometry TEMA type Shell ID Series Parallel Orientation
(–) (mm) (–) (–) (◦ )
AKT 1550 1 1 0
Baffle geometry Baffle type Baffle cut Baffle orientation Central spacing Crosspasses
(–) (Pct Dia.) (–) (mm) (–)
Support
Tube geometry Tube type Tube OD Length Pitch ratio Layout Tubecount Tube Pass
(–) (mm) (m) (–) (◦ ) (–) (–)
Plain 25.4 8.534 1.2598 45 1474 2
Nozzles Shell inlet Shell outlet Inlet height Outlet height Tube inlet Tube outlet
(mm) (mm) (mm) (mm) (mm) (mm)
205.004 307.087 59.545 965.865 307.087 307.087
Thermal resistance, % Shell Tube Fouling Metal
27.43 22.66 41.52 8.397
Velocities, m/s Shell side Tubeside Crossflow Window
Flow fractions A B C E F
0 1 0 0 0
0.17 0.43 0.11 0
1673.07 1
5222
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
Table 5 Input layout when design preheater. Process conditions Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/allow dP Fouling resistance
Hot tube 0 143.79 600 0.0003
Shell geometry TEMA type Inside Diameter Orientation Hot fluid
AFT 1420 Horizontal Tubeside
Tube geometry Type Length Tube OD Pitch
Plain 8.534 25.4 32
108.38 0 125 50
mm
m mm mm
Cold shell 0 41.19 1574.05 0.0002
34.49 0 138.8 50
kg/s Weight fraction vapor ◦ C kPa/kPa m2 K/W
Baffle geometry Type Cut Spacing
Single segmental 25 600
Wall thickness Layout angle Tubepasses
1.651 45 2
% mm
mm ◦
Table 6 Output result from preheater thermal design. Process conditions Fluid name Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/Avg dP/Allow. Fouling
Cold shellside i-Pentane (kg/s) (Wt. frac vap.) (◦ C) (kPa) (kPa) (m2 K/W)
0 41.19 1574.07 19.469
34.4943 1 138.8 1564.34 50 0.0002
0 143.8 600 4.725
108.379 0 125 597.65 50 0.0003
Exchanger performance Shell h Tube h Hot regime Cold regime EMTD
(W/m2 K) (W/m2 K) (–) (–) (◦ C)
1306.09 4415.01 Sens. Liquid Sens. Liquid 21.7
Actual U Required U Duty Area Overdesign
(W/m2 K) (W/m2 K) (MW) (m2 ) (%)
595.48 514.19 9.155 822.183 15.81
Shell geometry TEMA type Shell ID Series Parallel Orientation
(–) (mm) (–) (–) (◦ )
AFT 1420 1 1 0
Baffle geometry Baffle type Baffle cut Baffle orientation Central spacing Crosspasses
(–) (Pct Dia.) (–) (mm) (–)
Single-Seg. 25 Parallel 600 13
Tube geometry Tube type Tube OD Length Pitch ratio Layout Tubecount Tube Pass
(–) (mm) (m) (–) (◦ ) (–) (–)
Plain 25.4 8.534 1.2598 45 1230 2
Nozzles Shell inlet Shell outlet Inlet height Outlet height Tube inlet Tube outlet
(mm) (mm) (mm) (mm) (mm) (mm)
205.004 205.004 64.135 64.135 307.087 307.087
Thermal resistance, % Shell Tube Fouling Metal
45.59 15.5 32.45 6.46
Velocities, m/s Shell side Tubeside Crossflow Window
Flow fractions A B C E F
0.092 0.639 0.124 0.144 0
We must input process and design parameters when design preheater. The result of preheater thermal design can be seen in Table 6 [10]. In design air cooled condenser, will be used the method in GPSA. The details of the method can be seen in the References [14]. The thermal design result with method in GPSA can be viewed behind, i.e.: -
Fan diameter 4.5 m Total fan power 216.96 kW Total fan 6 Tube diameter 25.4 mm Tube length 13.72 m, etc.
Hot tubeside Brine
0.43 0.5 0.49 0.68
4. Conclusion Peng–Robinson state of equation adequately good to be applied in flash–binary analyzes. There are relationships between flash pressure, evaporator pressure, and pinch temperature in produce maximum net power. If pinch temperature becomes smaller, the net power will become higher. The limitation of this case is the dimension of heat exchanger which will be used. There is an optimum value for flash and evaporator pressure to produce maximum net power. From the analyzed result, it is concluded that i-pentane can produce the biggest net power among us. The net power which is produced from simulation process must be corrected with
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
thermal design results. After the net power is corrected, it becomes 2991.98 kW. The conditions to produce maximum net power are: flash pressure 600 kPa, evaporator pressure 1500.60 kPa, pinch temperature 5 ◦ C. The thermal efficiency is 12.29% and utilization efficiency is 23.06%. The evaporator which will be used is kettle type AKT with shell diameter 1.55 m, tube length 8.53 m, tube diameter 25.4 mm, and tube thickness BWG 16. Whereas, the results of thermal design of preheater are: two pass shell type AFT, shell diameter 1.42 m, tube length 8.53 m, tube diameter 25.4 mm, and tube thickness BWG 16. Air cooled condenser which is design needs 6 fans, the total power needed is 219.96 kW. The type of air cooled condenser which will be used is forced draft type, because needs smaller power than induced draft type. The fan diameter is 4.55 m. The model of the power plant in this paper is based on limited data. The model can be improved and economical analyzes made if more data and information is obtained. Acknowledgements I would like to express my deepest gratitude for my supervisors, Dr. Ari Darmawan Pasek and Prof. T.A. Fauzi Soelaiman for their guidance and advice throughout the project. Finally, my deepest thanks go to my family and friends for their pray, moral and emotional support. References [1] DiPippo Ronald. Geothermal power plants: principles, applications, case studies, and environmental impact. Massachusetts, USA: Darmouth; 2008. [2] Edwards JE. Design and rating shell and tube heat exchangers. Teesside, UK: P&ID Design Ltd; 2008. [3] El-Wakil MM. Power plant technology. USA: McGraw Hill, Inc; 1984. [4] Engineering Data Book Gas Processor Suppliers Association (GPSA), 12th, 2004, OK, USA. [5] Founier RO. The solubility of silica in hydrothermal solutions: practical applications. California, USA: U.S. Geological Survey; 1973. [6] Fournier RO, Marshall WL. Calculation of amorphous silica solubilities at 25–300 ◦ C and apparent cation hydration numbers in aqueous salt solutions
[7] [8] [9] [10] [11]
[12] [13]
[14] [17]
5223
using the concept of effective density of water. Geochim Cosmochim Acta 1983;47:587–96. Fournier RO, Potter RW. A revised and expanded silica (Quartz) geothermometer. Geoth Res Coun Bull 1982;11(10):3–12. Hewitt GF. Process heat transfer. New York, Wallingford, USA: Begill House; 2000. Incropera Frank P. Fundamental of heat and mass transfer. USA: John Wiley and Sons; 2002. Jones JB, Dugan RE. Engineering thermodynamics. USA: Prentice Hall; 1995. Kindle CH, Mercer BW, Elmore RP, Blau SC, Myers DA. Geothermal injection treatment: process chemistry, field experiences, and design options. Richland, WA, USA: Pacific Northwest Laboratory, Battelle Mem., Inst., PNL-4767; 1984. Mukherjee Rajiv. Effectively design of heat exchangers. USA: American Institute of Chemical Engineering; 1998. Nugroho Andi. Evaluation of waste brine utilization from LHD Unit III for electricity generation in Lahendong Geothermal Field, Indonesia. Reykjavik, Iceland: United Nations University; 2007. Park Chan S. Fundamental of engineering economics. USA: Prentice Hall; 2004. Sinnott RK. Chemical engineering design. 4th ed. Oxford, UK: Elsevier; 2005.
Further reading [15] Saptadji, Nenny M dan Ali Ashat. Basic geothermal engineering. Diktat Mata Kuliah Program Studi Teknik Perminyakan, Institut Teknologi Bandung, Indonesia, 2001. [16] Seider WD, Seader JD, Lewin dan DR. Product & process design principles: synthesis, analysis and evaluation. 2nd ed. USA: Wiley; 2004.
Ari Darmawan Pasek 1 T.A. Fauzi Soelaiman 1 Christian Gunawan ∗ Thermodynamics Laboratory, Institute Technology Bandung, Bandung, Indonesia ∗ Corresponding author. E-mail address: chr15 [email protected] (C. Gunawan) 1
Mechanical Engineering, ITB, Indonesia. 17 April 2011 Available online 18 July 2011
Contents lists available at ScienceDirect
Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser
Letter to the Editor Thermodynamics study of flash–binary cycle in geothermal power plant
a r t i c l e
i n f o
Keywords: Flash–binary cycle Optimization Heat exchanger Organic working fluid
a b s t r a c t This paper was conducted to evaluate the performance of a flash–binary cycle if applied to geothermal power plant (PLTP), where the source of heat came from the residual brine from the separator which was generally re-injected into wells. In the study of flash–binary cycle, there are four types of organic working fluids considered for the binary cycle, namely i-pentane, n-pentane, i-butane, and n-butane. Optimization process was carried out on the performance of plant systems. This paper also discussed the limitation factor to get maximum net power, like: flash pressure, evaporator pressure, pinch temperature, scaling formation, and thermal design in heat exchanger (preheater, evaporator, and air cooled condenser). Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved.
1. Introduction Nowadays the world is experiencing environmental problems, especially climate changes problems caused by global warming. One of the causes of global warming is the greenhouse effect. If it is pursued further, it will give a conclusion that it is because the emission of carbon dioxide (CO2 ) generates by the use of fossil fuels that are not controlled. The rapid industrial development that occurred today brings the impact to use greater energy [1]. Basically energy sources can be grouped into two, namely nonrenewable and renewable energy. Examples of non-renewable energy sources are: oil, natural gas, and coal, while the examples of renewable energy sources are: geothermal, wind, sea water, and sunlight. One important issue from the direction of world energy development is green energy, so the development of renewable energy sources particularly suitable to overcome these problems. Indonesia in the form of its geographical nature is potential for renewable energy sources, especially geothermal energy. Geothermal energy will be converted to electrical energy, because electricity is more easily used in daily life. In this paper will be studied the utilization of flash–binary cycle to increase the electricity production at a plant, so it will be very important to be learned.
cycle that can be used to treat it. The cycle is called flash–binary cycle [2]. Data which is used in the process simulation is the data obtained from geothermal wells in the unit geothermal power plant (PLTP) in Lahendong, North Sulawesi. The input data for brine in this study are: mass flow rate 400 t/h, temperature 170 ◦ C, and pressure 8 barg. The assumptions which are used: the air temperature which is entered condenser is determine 28 ◦ C, there are pressure drop in preheater and evaporator 50 kPa, also in condenser 34 kPa, isentropic efficiency of turbine is 85% and for pump is 75%, type of heat exchanger for evaporator is kettle and preheater is two pass shell, and pinch temperature which are analyzed in the preheater and evaporator are 5, 10, 15 and 20 ◦ C. Those assumptions are used to simplify the existing problems, so that the objectives of this study can be obtained [3]. The model and process simulation of flash–binary cycle will be done. After having obtained the optimum conditions that can produce the greatest power, the next step is thermal design for preheater and evaporator [11]. The method which is available in Gas Processors Suppliers Association (GPSA) is used to do thermal design for air cooled condenser. The results obtained from GPSA method are the main dimension of air cooled condenser, fan diameter, pressure drop, fans power. 3. Results and discussion
2. Material and methodology Geothermal power plant (PLTP) in Lahendong operates with the supply of production well which is water dominated. Vapor and liquid phase can be separated by using separator. Steam is used to drive steam turbines that can produce electricity up to 20 MW, while the liquid is injected back into the bowels of the earth. Seeing the potential energy possessed by the liquid minerals (brine) which still has a high pressure and temperature, this paper will discuss the
The state of equations which will be used is Peng–Robinson (PR). It can be seen from Fig. 1, if we use organic working fluid, it will be suggested to use Peng–Robinson (PR) or Redlich–Kwong–Soave (RKS) [4]. The other problem which must be analyzed in geothermal power plant is formation of scale. There are three methods which will be used to analyze scaling: Fournier, DiPippo, and Silica Scaling Index (SSI). The details explanation can be read on the reference.
1364-0321/$ – see front matter. Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.rser.2011.05.019
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
5219
Fig. 1. Flowchart to use state of equation. Sinnot [17].
These methods are used to know the recrystallization temperature of silica. We must prevent the brine out temperature not less than it. If the brine out temperature less than recrystallization temperature of silica, it will form scale in the tube/pipe. It will obstruct the fluid flow in the pipe/tube. The summary of recrystallization temperature from those methods can be seen in Table 1 [12].
Table 1 Comparison of recrystallization temperature with any methods.
Recrystallization temperature (◦ C)
Fig. 2. Flash–binary models from HYSYS package program.
Fournier
DiPippo
SSI
117,82
121,85
122
5220
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
Fig. 5. Net powers when evaporator pressure constant but pinch temperature and flash pressure independent.
Fig. 3. Turbine power when pinch temperature constant 5 ◦ C but evaporator and flash pressures be independent.
From Table 1 we can see that SSI method has the tightest temperature compare with others. It means that SSI method will be safest than others when it is used. Because of that, we will use SSI method in all analyzes about scale formation [5]. In Fig. 2, it will be shown the flash–binary models. The upper schematic represents flash cycle and the lower represents binary cycle. If we combine, it becomes flash–binary cycle. There are three independent parameters which will be analyzed, i.e. flash pressure (2), evaporator pressure (e), and pinch temperature (T11 –Te ) [6]. It is very difficult to analyze all the parameters independently. So, in analyze the independent parameters, it will be made one parameter be constant. In Fig. 3, it will be shown the graph where the pinch temperature constant but the flash and evaporator pressure be independent. From that figure we can see that when flash pressure be smaller, the organic turbine power becomes smaller too but the steam turbine power becomes higher. Evaporator pressure does not affect steam turbine power but effect organic turbine power where there is an optimum value. Fig. 4 will be shown the graph when flash pressure constant, but pinch temperature and evaporator pressure are independent. In that graph, it is shown that steam turbine power will be constant when evaporator pressure becomes higher. Organic turbine power will have one maximum value when evaporator pressure becomes higher. The smaller pinch temperature, the higher organic turbine power can be produced.
On the last, in Fig. 5 we will see the graph which shown the condition when evaporator pressure constant but pinch temperature and flash pressure are independent. We can see from that figure, when flash pressure becomes smaller, the net power also becomes smaller. But, there is an optimum value for flash pressure to produce maximum net powers. Now, it will be analyzed the effect of variation working fluid for the power plant performance, especially net power [13]. In Fig. 6, it will be shown the graph for i-pentane working fluid. We will see the effect of evaporator and flash pressure to the net power produced. There is also limitation in scaling. The above graph represents any parameters, i.e. brine out temperature, net power, and Silica Scaling Index (SSI). We can read the graph from the direction of arrows. For example: when evaporator pressure 2200 kPa and flash pressure 790 kPa, it can produce 1.4 MW net power, SSI factor 0.97, and brine out temperature
Fig. 6. Net power, SSI, and brine out temperature for i-pentane when evaporator and flash pressure be varied.
Table 2 Net power comparison of any working fluids. Parameters ◦
Fig. 4. Turbine power when flash pressure constant but pinch temperature and evaporator pressure be independent.
Pinch temperature ( C) Flash pressure (kPa) SSI Evaporator pressure (kPa) Net power (kW)
i-Butane
n-Butane
i-Pentane
n-Pentane
15 500 0.97 3500 2915.79
5 600 0.97 3533 3057.31
5 600 0.97 1500.60 3077.64
5 500 0.97 1187.50 2793.85
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
5221
Table 3 Input layout when design evaporator. Process conditions Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/allow dP Fouling resistance
Hot tube 0 158.9 600 0.0003
Shell geometry TEMA type Inside diameter Orientation Hot fluid
AKT 1550 Horizontal Tubeside
Tube geometry Type Length Tube OD Pitch
Plain 8.534 25.4 32
108.38 0 143.8 50
Cold shell 0
34.49 1
1530 0.0002
50
Wall thickness Layout angle Tubepasses
1.651 45 2
kg/s Weight fraction vapor ◦ C kPa/kPa m2 K/W
mm
m mm mm
150 ◦ C. If the value of SSI becomes higher than 1, it will form scale. So it must be prevented the value of SSI higher than 1 [7]. In analyze the others working fluid, i.e. n-pentane, i-butane, and n-butane, we use the same method like i-pentane. We can see the effect of variation working fluid in Table 2. From Table 2, i-pentane can produce the highest net power among all. The optimum condition which can produce maximum power will be used in thermal design process. Now we will design the heat exchanger (preheater and evaporator) thermally. First step in thermal design process, we must choose the material which will be used in shell and tube. The material for shell is carbon steel ASTM a516-60, because shell will be passed with working fluid. Tube will be used duplex stainless steel SAF 2205 (ASTM 789), because tube will be passed with brine which
mm ◦
has a high chloride and low pH (sour). Duplex stainless steel will resist on uniform corrosion and pitting (localize corrosion). In thermal design of heat exchanger, the standard which will be used is Tubular Exchanger Manufacturers Association, Inc. (TEMA) [8]. Evaporator will be used kettle type (AKT) and preheater will be used two pass shell type (AFT). We need input process and design parameters when design evaporator and preheater [9]. From Table 3, it will be shown the input needed (process and design parameters) when design evaporator. The output results from evaporator thermal design will be shown in Table 4. The same method is used to design preheater thermally. The input layout can be seen in Table 5.
Table 4 Output result from evaporator thermal design. Process conditions Fluid name Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/Avg dP/Allow. Fouling
Cold shellside i-Pentane
Hot tubeside Brine
(kg/s) (Wt. frac vap.) (◦ C) (kPa) (kPa) (m2 K/W)
0 138.8 1530.02 3.287
34.4943 1 138.9 1528.38 50 0.0002
0 158.9 600 4.01
108.376 0 143.8 598 50 0.0003
Exchanger performance Shell h Tube h Hot regime Cold regime EMTD
(W/m2 K) (W/m2 K) (–) (–) (◦ C)
2856.9 3974.37 Sens. liquid Flow 10.8
Actual U Required U Duty Area Overdesign
(W/m2 K) (W/m2 K) (MW) (m2 ) (%)
783.5 685.98 7.274 983.927 14.22
Shell geometry TEMA type Shell ID Series Parallel Orientation
(–) (mm) (–) (–) (◦ )
AKT 1550 1 1 0
Baffle geometry Baffle type Baffle cut Baffle orientation Central spacing Crosspasses
(–) (Pct Dia.) (–) (mm) (–)
Support
Tube geometry Tube type Tube OD Length Pitch ratio Layout Tubecount Tube Pass
(–) (mm) (m) (–) (◦ ) (–) (–)
Plain 25.4 8.534 1.2598 45 1474 2
Nozzles Shell inlet Shell outlet Inlet height Outlet height Tube inlet Tube outlet
(mm) (mm) (mm) (mm) (mm) (mm)
205.004 307.087 59.545 965.865 307.087 307.087
Thermal resistance, % Shell Tube Fouling Metal
27.43 22.66 41.52 8.397
Velocities, m/s Shell side Tubeside Crossflow Window
Flow fractions A B C E F
0 1 0 0 0
0.17 0.43 0.11 0
1673.07 1
5222
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
Table 5 Input layout when design preheater. Process conditions Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/allow dP Fouling resistance
Hot tube 0 143.79 600 0.0003
Shell geometry TEMA type Inside Diameter Orientation Hot fluid
AFT 1420 Horizontal Tubeside
Tube geometry Type Length Tube OD Pitch
Plain 8.534 25.4 32
108.38 0 125 50
mm
m mm mm
Cold shell 0 41.19 1574.05 0.0002
34.49 0 138.8 50
kg/s Weight fraction vapor ◦ C kPa/kPa m2 K/W
Baffle geometry Type Cut Spacing
Single segmental 25 600
Wall thickness Layout angle Tubepasses
1.651 45 2
% mm
mm ◦
Table 6 Output result from preheater thermal design. Process conditions Fluid name Flow rate Inlet/outlet Y Inlet/outlet T Inlet P/Avg dP/Allow. Fouling
Cold shellside i-Pentane (kg/s) (Wt. frac vap.) (◦ C) (kPa) (kPa) (m2 K/W)
0 41.19 1574.07 19.469
34.4943 1 138.8 1564.34 50 0.0002
0 143.8 600 4.725
108.379 0 125 597.65 50 0.0003
Exchanger performance Shell h Tube h Hot regime Cold regime EMTD
(W/m2 K) (W/m2 K) (–) (–) (◦ C)
1306.09 4415.01 Sens. Liquid Sens. Liquid 21.7
Actual U Required U Duty Area Overdesign
(W/m2 K) (W/m2 K) (MW) (m2 ) (%)
595.48 514.19 9.155 822.183 15.81
Shell geometry TEMA type Shell ID Series Parallel Orientation
(–) (mm) (–) (–) (◦ )
AFT 1420 1 1 0
Baffle geometry Baffle type Baffle cut Baffle orientation Central spacing Crosspasses
(–) (Pct Dia.) (–) (mm) (–)
Single-Seg. 25 Parallel 600 13
Tube geometry Tube type Tube OD Length Pitch ratio Layout Tubecount Tube Pass
(–) (mm) (m) (–) (◦ ) (–) (–)
Plain 25.4 8.534 1.2598 45 1230 2
Nozzles Shell inlet Shell outlet Inlet height Outlet height Tube inlet Tube outlet
(mm) (mm) (mm) (mm) (mm) (mm)
205.004 205.004 64.135 64.135 307.087 307.087
Thermal resistance, % Shell Tube Fouling Metal
45.59 15.5 32.45 6.46
Velocities, m/s Shell side Tubeside Crossflow Window
Flow fractions A B C E F
0.092 0.639 0.124 0.144 0
We must input process and design parameters when design preheater. The result of preheater thermal design can be seen in Table 6 [10]. In design air cooled condenser, will be used the method in GPSA. The details of the method can be seen in the References [14]. The thermal design result with method in GPSA can be viewed behind, i.e.: -
Fan diameter 4.5 m Total fan power 216.96 kW Total fan 6 Tube diameter 25.4 mm Tube length 13.72 m, etc.
Hot tubeside Brine
0.43 0.5 0.49 0.68
4. Conclusion Peng–Robinson state of equation adequately good to be applied in flash–binary analyzes. There are relationships between flash pressure, evaporator pressure, and pinch temperature in produce maximum net power. If pinch temperature becomes smaller, the net power will become higher. The limitation of this case is the dimension of heat exchanger which will be used. There is an optimum value for flash and evaporator pressure to produce maximum net power. From the analyzed result, it is concluded that i-pentane can produce the biggest net power among us. The net power which is produced from simulation process must be corrected with
Letter to the Editor / Renewable and Sustainable Energy Reviews 15 (2011) 5218–5223
thermal design results. After the net power is corrected, it becomes 2991.98 kW. The conditions to produce maximum net power are: flash pressure 600 kPa, evaporator pressure 1500.60 kPa, pinch temperature 5 ◦ C. The thermal efficiency is 12.29% and utilization efficiency is 23.06%. The evaporator which will be used is kettle type AKT with shell diameter 1.55 m, tube length 8.53 m, tube diameter 25.4 mm, and tube thickness BWG 16. Whereas, the results of thermal design of preheater are: two pass shell type AFT, shell diameter 1.42 m, tube length 8.53 m, tube diameter 25.4 mm, and tube thickness BWG 16. Air cooled condenser which is design needs 6 fans, the total power needed is 219.96 kW. The type of air cooled condenser which will be used is forced draft type, because needs smaller power than induced draft type. The fan diameter is 4.55 m. The model of the power plant in this paper is based on limited data. The model can be improved and economical analyzes made if more data and information is obtained. Acknowledgements I would like to express my deepest gratitude for my supervisors, Dr. Ari Darmawan Pasek and Prof. T.A. Fauzi Soelaiman for their guidance and advice throughout the project. Finally, my deepest thanks go to my family and friends for their pray, moral and emotional support. References [1] DiPippo Ronald. Geothermal power plants: principles, applications, case studies, and environmental impact. Massachusetts, USA: Darmouth; 2008. [2] Edwards JE. Design and rating shell and tube heat exchangers. Teesside, UK: P&ID Design Ltd; 2008. [3] El-Wakil MM. Power plant technology. USA: McGraw Hill, Inc; 1984. [4] Engineering Data Book Gas Processor Suppliers Association (GPSA), 12th, 2004, OK, USA. [5] Founier RO. The solubility of silica in hydrothermal solutions: practical applications. California, USA: U.S. Geological Survey; 1973. [6] Fournier RO, Marshall WL. Calculation of amorphous silica solubilities at 25–300 ◦ C and apparent cation hydration numbers in aqueous salt solutions
[7] [8] [9] [10] [11]
[12] [13]
[14] [17]
5223
using the concept of effective density of water. Geochim Cosmochim Acta 1983;47:587–96. Fournier RO, Potter RW. A revised and expanded silica (Quartz) geothermometer. Geoth Res Coun Bull 1982;11(10):3–12. Hewitt GF. Process heat transfer. New York, Wallingford, USA: Begill House; 2000. Incropera Frank P. Fundamental of heat and mass transfer. USA: John Wiley and Sons; 2002. Jones JB, Dugan RE. Engineering thermodynamics. USA: Prentice Hall; 1995. Kindle CH, Mercer BW, Elmore RP, Blau SC, Myers DA. Geothermal injection treatment: process chemistry, field experiences, and design options. Richland, WA, USA: Pacific Northwest Laboratory, Battelle Mem., Inst., PNL-4767; 1984. Mukherjee Rajiv. Effectively design of heat exchangers. USA: American Institute of Chemical Engineering; 1998. Nugroho Andi. Evaluation of waste brine utilization from LHD Unit III for electricity generation in Lahendong Geothermal Field, Indonesia. Reykjavik, Iceland: United Nations University; 2007. Park Chan S. Fundamental of engineering economics. USA: Prentice Hall; 2004. Sinnott RK. Chemical engineering design. 4th ed. Oxford, UK: Elsevier; 2005.
Further reading [15] Saptadji, Nenny M dan Ali Ashat. Basic geothermal engineering. Diktat Mata Kuliah Program Studi Teknik Perminyakan, Institut Teknologi Bandung, Indonesia, 2001. [16] Seider WD, Seader JD, Lewin dan DR. Product & process design principles: synthesis, analysis and evaluation. 2nd ed. USA: Wiley; 2004.
Ari Darmawan Pasek 1 T.A. Fauzi Soelaiman 1 Christian Gunawan ∗ Thermodynamics Laboratory, Institute Technology Bandung, Bandung, Indonesia ∗ Corresponding author. E-mail address: chr15 [email protected] (C. Gunawan) 1
Mechanical Engineering, ITB, Indonesia. 17 April 2011 Available online 18 July 2011