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ISSN: 2090-4541
Journal of Fundamentals of Renewable Energy and Applications
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Geothermal Energy Potentials and Technologies in Thailand

Nattaporn Chaiyat1*, Chatchawan Chaichana2 and Fongsaward S. Singharajwarapan3

1School of Renewable Energy, Maejo University, Chiang Mai, Thailand

2Department of Mechanical Engineering, Chiang Mai University, Chiang Mai, Thailand

3Groundwater Technology Service Center, Chiang Mai University, Chiang Mai, Thailand

Corresponding Author:
Nattaporn Chaiyat
School of Renewable Energy
Maejo University, Chiang Mai
Thailand
Tel: +6653-875-461
E-mail: [email protected]

Received date: August 01, 2014; Accepted date: September 23, 2014; Published date: September 30, 2014

Citation: Chaiyat N, Chaichana C, Singharajwarapan FS (2014) Geothermal Energy Potentials and Technologies in Thailand. J Fundam Renewable Energy Appl 4:139. doi:10.4172/2090-4541.1000139

Copyright: © 2014 Chaiyat N, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

This paper presents a concept for using the geothermal energy in Thailand. The geophysical properties and the suitable technologies are considered; moreover the prototypes of the suitable technology have been constructed and tested the system performances. The potential of 97 hot springs in Thailand are classified into three groups as high, moderate and low potential. Organic rankine cycle is selected for 12 high potential hot springs to generate electricity 3,909 kWe. Absorption chiller and 8 moderate potential hot springs could be produced the total cooling capacity 304 kW and the payback period is 22 months. Central drying room and 8 moderate potential hot springs could be used in the heating process at 406 kW and the payback period is 15 months. Drying room integrated with vapor compression heat pump is represented for boosting 26 low potential hot springs. The upgrading heat around 2,002 kW could be used for drying the agricultural products 200 Ton/d which the payback period is 29 months. It could be found that the geothermal energy potential in Thailand could be developed from 46 hot springs to be used for heat and power at around 6.6 MW.

Keywords

Geothermal energy; Organic rankine cycle; Heat pump system; Drying room; Absorption chiller.

Introduction

Geothermal energy is one type of renewable energy which the Thailand government sets a geothermal policy to increase the power generation to be 1 MW in 2021. Department of Mineral Resources of Thailand [1] reports 112 hot springs in Thailand. In 2008, Chiang Mai University (CMU) [2] also reported 97 potential of hot springs in Thailand and classified them into three groups as high, moderate and low potential which is shown in Figure 1. For high potential hot spring, the surface water temperature is higher than 80°C. Moderate potential hot spring refers the surface water temperature between 60-80°C and low potential hot springs represents the surface water temperature is lower than 60°C. Thus, the aim of this research is to study the appropriate technologies for using geothermal energy in Thailand.

fundamentals-renewable-energy-hot-springs-Thailand

Figure 1: Location map of hot springs in Thailand.

For technology to generate electricity, the various literatures are presented such as Chaiyat and Chaichana [3] reported using high temperature hot spring at higher than 90°C to generate the electricity by using a binary system and a thermoelectric module. Combs et al. [4] studied the small geothermal power plant in America and Japan at capacity around 100-1,000 kW. The technologies of the slim hole and binary-cycle technology were selected to use for the off-grid area. And, the environment affect from the geothermal power plant was lower than the fossil power plant which was similarly Brophy [5], Kose [6] and Dagdas [7]. For the simulation studies, the selection of suitable working fluids for the organic rankine cycle (ORC) system was the hot issue which had many reports to study this topic such as Hettiarachchi et al. [8], Schuster et al. [9], Guo [10], Sauret et al. [11], Liu et al. [12], Edrisi et al. [13], Li et al. [14], and Rodriguez et al. [15]. It was found that the suitable working fluid of those results were different because the system conditions of each study were different. But the most suitable working fluid of those studies introduced R-134a and R-245fa. In generating electricity process, the ORC system was compared with a Kalina cycle in term of efficiency. Guzovic et al. [16] studied the geothermal energy to power plant in Croatia. The high temperature hot spring at 175°C was supplied to binary system which of organic rankine cycle and kalina cycle. The simulated results shown the ORC cycle had a higher thermal efficiency and energy efficiency compared with the kalina cycle. Moreover, a low potential geothermal at hot water temperature around 61-80°C in China had studied by Aneke [17]. R-134a ORC system was chosen to produce electricity and the system efficiency was around 8.8%.

For the cooling technology, an absorption chiller is presented by various literatures. Kanoglu and Cengel [18] reported economic evaluation of geothermal power generation, heating, and cooling. It found that geothermal heating and geothermal absorption cooling were revenue higher than geothermal power generation about 3.1 times and 2.9 times, respectively. Kececiler et al. [19] simulated the absorption refrigeration cycle by using hot spring in Sivas, Turkey as heat source. The simulation results also shown that hot spring in Sivas did not be used efficiently in electricity generation. Kairouani and Nehdi [20] presented a novel combined refrigeration system which was absorption system cascaded with conventional compression system. The modified system increased the efficiency around 37-54% which was similarly the research of Ayala et al. [21], Seara et al. [22] and Kairouani and Nehdi [23].

For technique for drying process, Chaiyat and Chaichana [24] presented 2 types of drying processes which are a central drying room and a geothermal heat pump for drying room. The central drying room used hot spring to direct supplied into the drying room. For geothermal heat pump, a R-290 vapor compression heat pump for upgrading hot spring temperature around 40-50°C to be hot water around 70°C for using in the drying room. Heat pump dryer was found to be an effective equipment with low energy consumption as reported by Singharajwarapan and Chaiyat [25] which used low potential hot spring at temperature around 50°C to generate hot water temperature around 70°C for the drying room. Pendyala et al. [26], Chou et al. [27], Clements et al. [28], Young et al. [29] and Sadchang [30] also reported using single-stage vapor compression heat pump in the drying processes. Duddumpudi [31] presented CO2 heat pump to generate hot water which reduced the severe environmental problems causing by synthetic refrigerants which corresponded with Stene [32] and Whitea [33].

From the literatures review, the various techniques are applied with hot spring. But, hot springs in Thailand are different with other geothermal resources. Thus, the main objective of this work is to study the suitable technique for using with each geothermal energy potential in Thailand. Moreover, the prototypes and case studies of each technique in Thailand are presented and tested for evaluating the system performances. And, the physical properties of hot springs in Thailand are used to analyze the appropriate technology of each geothermal energy potential.

System descriotions and equations

Figure 2 shows a cascade useful concept for geothermal energy as based on hot spring temperature. For high potential hot spring, the surface hot spring temperature at higher than 80°C is presented to generate electricity by oganic rankine cycle. For moderate potential at temperature between 60-80°C, the various technologies could be apply with the moderate hot spring temperature which are the absorption chiller for cooling process and an central drying room for drying process. For low potential hot spring, the vapor compression heat pump is combined with the drying room at surface hot spring temperature lower than 60°C. For the hot spring temperature lower than 60°C, the use in entertainment processes such as sauna and hot pool are introduced, after that, hot spring is leaved to the environment.

fundamentals-renewable-energy-cascade-useful-geothermal-energy

Figure 2: The concept of cascade useful for geothermal energy.

Organic rankine cycle

Figure 3 shows the main components of the ORC system which are boiler, turbine, generator, condenser and pump. In the conventional ORC, high temperature heat is absorbed at the boiler (QB) at temperature around 80-120°C which in this study is hot spring. After that the working fluid at the high pressure and temperature enters to the turbine (state 1) for producing the electricity at the generator (WTur). Next, the working fluid at the low pressure (state 2) is condensed at the condenser by cooling fluid at temperature around 30-40°C. The working fluid in liquid phase (state 3) is pumped to the boiler (state 4) and the new cycle is started again.

fundamentals-renewable-energy-organic-rankine-cycle

Figure 3: Schematic diagram of organic rankine cycle.

Absorption chiller

Absorption heat pump is one type of heat pump at using heat as the main energy which having 2 types are absorption chiller for cooling process and absorption heat transformer for boosting high temperature heat.

Figure 4 shows a schematic diagram of absorption chiller, at the generator, a binary liquid mixture consisting of a volatile component (absorbate) and a less volatile component (absorbent) is heated at a medium temperature around 80°C. Part of the absorbate boils at a high pressure (PC) and a generator temperature (TG) at state 1. The vapor fluid at concentration around 90% of absorbate is purified to be 100% of absorbate by analyzer and rectifier at state 2. The pure absorbate condenses in the condenser at a condenser temperature (TC) to be liquid at state 3. After that, the absorbate in liquid phase is throttled to the evaporator at state 4 of which an evaporator pressure (PE) is lower than that of the condenser. The evaporator is heated at a low temperature (TE) around 0-20°C and the absorbate in form of vapor enters the absorber which has the same pressure as the evaporator at state 5. Meanwhile, liquid mixture from the generator, at state 6 is sent through a solution heat exchanger at state 7 into the absorber to the low pressure at state 8 through expansion device. In the absorber, the strong solution absorbs the absorbate vapor and the weak solution leaves the absorber at state 9 at a medium temperature (TA) around 40-50°C which is same the condenser temperature (TC). The weak solution at state 9 from the absorber is then pumped to the high pressure through the solution heat exchanger at state 10 into the generator again at state 11 and new cycle restarts.

fundamentals-renewable-energy-absorption-chiller

Figure 4: Schematic diagram of absorption chiller.

Drying room

A schematic diagram of geothermal drying room is shown Figure 5. Hot spring flows through a piping tube at point 1 to a heat exchanger at point 2. A blower at point 3 is used to drive low temperature air through the heat exchanger to be hot air at point 4. The high temperature heat is flowed to drying area, where agricultural products are contained at point 5. After that hot air transfers heat to the products, the air temperature will decrease while the air humidity will increase. For reducing the air humidity, the fresh air from outside is conducted to reduce the air humidity in the drying room via a small window at point 6 while the high humidity air is released to the ambient via a top duct at point 7.

fundamentals-renewable-energy-central-drying-room

Figure 5: A schematic diagram of central drying room.

Vapor compression heat pump for drying room

A conventional technique to upgrade low temperature heat to a higher temperature level is heat pump system. The common method could be performed by vapor compression heat pump (VCHP) which the main components are compressor, condenser, evaporator and expansion valve as shown in Figure 6. The working fluid has a low boiling temperature. At state 1, the fluid in vapor phase is compressed in the compressor to state 2 and the vapor condenses in the condenser at a high pressure and temperature to be liquid at state 3. The liquid is then throttled to a low pressure at state 4 via the expansion device and the temperature drops down thus the fluid could absorb low temperature heat at the evaporator where the fluid boils at low temperature to be vapor again and the new cycle restarts.

fundamentals-renewable-energy-vapor-compression-heat-pump

Figure 6: Schematic diagram of vapor compression heat pump.

Materials and Methods

Organic rankine cycle

For high potential geothermal energy, hot spring temperature at more than 80ºC has been introduced to generate electricity. At the present, only one geothermal electricity is available in Thailand at Fang District, Chiang Mai Province. The technology used is organic rankine cycle with 300 kWe capacity of power plant as shown the descriptions in Table 1.

Properties Data
Operation system Organic Rankine Cycle (ORC)
Working fluid R-601a (Isopentane)
Hot spring flow rate1 (L/s) 16.5 (75% of maximum flow rate)
Slim hole deep (m) 86
Hot spring temperature entering ORC (°C) 115
Hot spring temperature leaving ORC (°C) 77
Cooling water flow rate (L/s) 72.2
Cooling water temperature entering ORC  (°C) 20
Gross electrical power (kWe) 300
Total electrical power (kWe) 200

Table 1: Descriptions of Fang geothermal power plant [34].

From Table 1, it could be found that the ORC power plant of Fang, Chiang Mai uses the reservoir heat source from 86 m of hot spring hole to generate electricity. Thus, in this study, the reservoir temperature will be evaluated by the geochemistry of surface hot spring. After that, the surface and reservoir temperature are used to find out the potential of geothermal power plant in Thailand combined with the system performance of Fang geothermal power plant.

Absorption chiller

For moderate potential geothermal energy, the hot spring temperature between 70-80ºC has been suggested to use in cooling process. The cooling unit in this study is absorption cooling system as shown a schematic diagram in Figure 4. A prototype of 10 kW ammonia-water absorption chiller is designed and constructed to freeze the agricultural products in a well- insulated room. Mae Jan hot spring, Chiang Rai, Thailand with having the hot spring temperature around 98ºC from 56 m of slim hole is used to test the cooling performance of the absorption chiller. The descriptions and photographs of the testing unit are shown in Table 2 and Figure 7, respectively. For the testing results, the geothermal energy potential will be presented with the absorption technique by the physical data of hot spring in Thailand.

Devices Type Properties
Cold room Isowall •Thickness 3 in

•Size 3.6 m × 3.6 m × 3 m

Generator Flooded shell and tube heat exchanger •Capacity 16 kW

•Shell diameter 150 mm

•Tube size 9.525 mm × 850 mm × 40 tube

•Heating area 1.016 m2

Analyzer Steel column of analyzer •Purified fluid to 99.95% of ammonia

•Size 100 mm × 1,100 mm

Rectifier Shell and tube heat exchanger •Capacity 1 kW

•Shell size 150 mm × 200 mm

•Tube size 9.525 mm × 3,000 mm

Condenser Plate heat exchanger •Capacity 11.2 kW

•Size 110 mm × 300 mm × 50 plate

•Heating area 1.25 m2

Receiver Vertical type •Volume 0.5 m3

Evaporator Fin and tube heat exchanger •Capacity 11.2 kW

•Heating area 1.25 m2

Absorber Shell and tube heat exchanger •Capacity 15.3 kW

•Shell size 150 mm × 850 mm

•Tube size 9.525 mm × 26,000 mm

•Heating area 0.98 m2

Table 2: Descriptions of the cold room and absorption chiller.

fundamentals-renewable-energy-Mae-Jun-hot-spring

Figure 7: The prototype of absorption chiller at Mae Jun hot spring, Thailand.

Drying room

For moderate potential hot spring, the surface water temperature between 60-80ºC has been also suggested to use in drying process as shown the system descriptions in Figure 5. The geothermal drying room is developed to dry the agricultural products in a well-insulated room. Mae Jan hot spring, Chiang Rai, Thailand as shown in Figure 6(b) is also used to test the heating performance of drying system. The descriptions and photographs of the testing unit are shown in Table 3 and Figure 8, respectively. Finally, the testing results of prototype will be used to predict the guidelines of the geothermal drying room in Thailand.

Devices Properties
Dryer room •Thickness 3 in

•Size 3.3 m × 4.8 m × 3.2 m

Heating coil •Fin and tube heat e×changer

•Size 2.413 m × 1.197 m

•Piping tube API 40, 1/2 in

Motor •Power 5 hp

•Speed 1,450 rpm

Blower •Diameter 1.2 m

Table 3: Descriptions of drying room and equipment.

fundamentals-renewable-energy-prototype-drying-room

Figure 8: The prototype of drying room at Mae Jun hot spring, Thailand.

Drying room by using single-stage vapor compression heat pump

For low potential hot spring, the surface water temperature lower than 60ºC has been used in drying process by using vapor compression heat pump (VCHP) to upgrade heat to be around 70°C and supply into drying room. The working steps of the drying room with heat pump system start with the hot water enters the system as shown in Figure 9. The hot water transfers heat to the working fluid, which evaporates accordingly. The resultant vapor is then pressurized by the compressor. After that, upgrading heat is extracted at the condenser and sent into heating coil in the drying room. The air inside the room is then heated by the heating coil.

fundamentals-renewable-energy-geothermal-drying-room

Figure 9: Schematic diagram of the geothermal drying room by using 2-stage VCHP.

The prototype of R-123 VCHP is set with the well-insulated testing room. Hot spring temperature around 55ºC from 85 m of slim hole, Huai Mak Liam hot spring, Chiang Rai, Thailand is used to test the integrated unit. The descriptions and prototypes of R-123 heat pump and testing room are shown in Table 4 and Figure 10, respectively.

Devices Type Properties
Drying room Isowall •Thickness 3 in

•Size 3.3 m × 4.8 m × 3.2 m

Indirect Heat E×changer Gasket plate heat e×changer (hot spring to hot water) •Capacity 15 kW

•Heating area 0.8 m2

Hot water pump1 Centrifugal pump •Capacity 0.37 kW

•Flow rate 80 L/min

Hot water receiver1 and 2 Vertical steel tank •Capacity 10 L

Compressor Open type compressor •Capacity 3 kW

•Volume flow rate 25 m3

Condenser Plate heat e×changer (R-123 to hot water) •Capacity 20 kW

•Heating area 3.65 m2

Evaporator Plate heat e×changer (R-123 to hot water) •Capacity 15 kW

•Heating area 2.88 m2

E×pansion  valve Orifice type •Capacity 15 kW

Table 4: Descriptions of geothermal drying room and 2-stage heat pump components.

fundamentals-renewable-energy-single-stage-VCHP

Figure 10: The photograph of geothermal drying room by using single-stage VCHP.

Drying room by using two-stage vapor compression heat pump

In this study, the 2-stage vapor compression heat pump is used to upgrade hot spring temperature around 40-50°C to be around 80-85°C for the drying room. R-134a and R-123 are chosen as the working fluids in the 2-stage heat pump system. Huai Mak Liam hot spring, Chiang Rai, Thailand with having the surface water temperature around 45°C from 30 m of the slim hole is used to test the heating efficiency of the prototype. A schematic diagram of geothermal drying room integrated with 2-stage VCHP is shown in Figure 11. The descriptions and photographs of testing unit are shown in Table 5 and Figure 12, respectively.

fundamentals-renewable-energy-geothermal-drying-room--2-stage-VCHP4

Figure 11: Schematic diagram of the geothermal drying room by using 2-stage VCHP.

Devices Type Properties
Drying room Isowall •Thickness 3 in

•Size 2.4 m × 4.8 m × 2.3 m

Hot water pump Centrifugal pump •Capacity 0.37 kW

•Flow rate 60 L/min

E×pansion tank Vertical steel tank •Capacity 10 L

Compressor 1 Hermetic compressor
R-134a
•Capacity 2 kW

•Volume flow rate 11.46 25 m3/h

Compressor 2 Open type compressor
R-123
•Capacity 3 kW

•Volume flow rate 25 m3/h

Condenser Plate heat e×changer
(R-123 to hot water)
•Heat capacity 20 kW

•Heating area 1.64 m2

Economizer Plate heat e×changer
(R-134a to R-123)
•Heat capacity 15 kW

•Heating area 2.39 m2

Evaporator Plate heat e×changer (hot water to R-134a) •Heat capacity 8.75 kW

•Heating area 1.64 m2

E×pansion valve 1 Orifice type thermostatic orifice 04 •Capacity 20 kW

•Pressure ratio 3.305

E×pansion valve 2 Orifice type thermostatic orifice 06 •Capacity 12 kW

•Pressure ratio 3.87

Sub cool 1 Plate heat e×changer
(hot water to R-134a)
•Heat capacity 2 kW

•Heating area 0.64 m2

Sub cool 2 Plate heat e×changer
(hot water to R-123)
•Heat capacity 8 kW

•Heating area 0.64 m2

Dying coil Plate heat e×changer
(hot water to air)
•Capacity 20 kW

•Heating area 2.88 m2

Table 5: Descriptions of geothermal drying room and 2-stage heat pump components.

fundamentals-renewable-energy-drying-room-by-using-2-stage-VCHP

Figure 12: The geothermal drying room by using 2-stage VCHP.

Results and Discussions

Generating electricity process by using ORC technology

The geothermal resources in Thailand are evaluated and compared with Fang geothermal power plant to assess the primary energy potential. The results stated that 12 geothermal resources are capable to generate the electrical power as shown in Table 6.

  Hot springs   Province Temp(°C) Quartz1 (°C) Flow (L/s) ORC2 (kWe) ORC3 (kWe)
Mae Jan1 Chiang Rai 93 163.35 1.1 18.39 137.94
Mae Jan2 Chiang Rai 93 160.75 5.56 92.89 696.67
San Kam Phaeng Chiang Mai 88.5 147.64 5.56 92.89 696.67
Doi Sa Ket Chiang Mai 96.3 144.65 0.26 4.35 32.60
Fang Chiang Mai 98.1 142.59 1.56 26.08 195.62
Pong Duead Chiang Mai 95 142.59 5.56 92.89 696.67
Thep Pha Nom Chiang Mai 98.9 141.70 1.65 27.59 206.91
Pong Pa Mae Hong Sorn 87.4 126.40 0.23 3.85 28.84
Mueang Paeng Mae Hong Sorn 96 125.42 5.56 92.89 696.67
Nong Haeng Mae Hong Sorn 81.1 122.07 3 50.16 376.20
Chae Son Lampang 83.7 120.69 1.1 18.39 137.94
Mae Jork Phare 80.7 116.35 0.05 0.84 6.27
Sum 521 3,909

Table 6: Geothermal resources with electricity generating.

From Table 6, it could be seen that 12 high potential hot springs at the surface temperature higher than 80°C could be produced the total electricity around 521 kWe. Moreover, if the reservoir energy is extracted, the higher power energy could be generated compared with the surface potential. Table 6 also shows the electricity from reservoir energy at around 3,909 kWe.

Cooling process by using absorption chiller

Absorption chiller is constructed and tested the cooling efficiency. Table 7 shows the testing data of ammonia-water single-stage absorption refrigeration. It could be seen that the absorption unit could be decreased the minimum air temperature in the cold room to be around 1°C as shown in Figure 13 which is given hot spring temperature around 98°C. The testing results is also shown the EERAB at around 0.6 which is lower than the other researches because a big size of refrigerant pump at power consumption around 1.03 kWe is taken in the absorption unit.

Tair,i,,E (°C) Tair,o,E (°C) TCW,i (°C) THW,i (°C) THW,o (°C)
9.86 6.04 24.78 97.95 85.88
TG (°C) QG (kW) QE (kW) COP1 EER2 (kWth/kWe)
91.17 15.13 9.56 0.63 0.59

Table 7: The average testing data of absorption chiller.

fundamentals-renewable-energy-evaporator-air-temperature

Figure 13: The photograph of evaporator at the air temperature in cold room around 1 °C.

For economic evaluation, the cold room at capacity 3,000 kg by using the 10 kW absorption system is also carried out with 10 sets of cooling per month, 24 hours per freezing set. At the time of assessment with the construction cost about 20,000 USD and the payback period is 22 months.

Table 8 shows 8 moderate potential hot springs at temperature between 70-80°C at the most found in the northern area of Thailand. Moreover, Table 8 also shows the total cooling capacity at around 304 kW of absorption chiller from 8 hot spring resources.

  Hot spring   Province Temp Flow Absorption1 Drying2
(°C) (L/s) (kW) (kW)
Pu Feang Chiang Rai 73.3 4.5 113 150
Sop Pong Chiang Rai 79.3 0.44 11 15
Pong Phra Bat Chiang Rai 73.1 3.8 95 127
Thung Pong Chiang Mai 75 1.19 30 40
Tha Pai Mae Hong Sorn 78.9 1.44 36 48
Mae Um Long Mae Hong Sorn 78.8 0.19 5 6
Pho Thong Tak 74.8 0.1 3 3
Klong Plag Pau Phangnga 74.8 0.48 12 16
Sum 304 406

Table 8: Geothermal resources with cooling potential.

Drying process by central drying room

The central drying room is constructed with a dimension of 3.30 m×4.80 m×3.20 m at capacity of about 3 Ton (3,000 kg) of agricultural products. It generates room temperatures to be over 80°C. The hot water transfers heat into the heating coil in the drying room. The air inside the room is heated by the 20 kW heating coil. Efficiency test of the empty drying room showed that the room temperature increases from 25°C to be over 80°C within 5 minutes. The heating efficiency of drying room is around 80% (ηDrying) with the water temperatures entering and leaving of the system as 98°C and 87°C, respectively. And, Figure 14 also shows the drying product at 12 hours of cherry.

fundamentals-renewable-energy-cherry-drying-room

Figure 14: The photograph of cherry in drying room at hot air temperature around 95 °C.

For economic results, the evaluation is also carried out with 15 sets of drying per month, 24 hours per drying set. At the assessment with the drying room and operation system cost about 11,000 USD and the payback period at around 15 months is found.

From the testing data of the central drying room, it could be seen that if moderate potential hot springs as shown Table 8 are used in the drying process, the total heating capacity at around 406 kW could be used for extracting moisture of the agricultural products.

Drying process by vapor compression heat pump

The drying room integrating with the heat pump system is constructed giving an intake capacity of about 3 Ton (3,000 kg) of agricultural products. It generates the air room temperatures between 60-75°C. From the testing results as shown in Table 9, it could be seen that efficiency test of the empty drying room showed that the room temperature increased from 25°C to be 70°C within 3 hours. The energy efficiency ratios (EERs) of the VCHP and the drying room are 3.02 kWth/kWe and 1.39 kWth/kWe, respectively, with the water temperatures entering and leaving of the VCHP system as 49.60°C and 48.61°C, respectively. Economic evaluation is also carried out with 15 sets of drying per month, 24 hours per drying set. At the time of assessment with the construction budget of about 20,000 USD, the payback period is 13 months.

Descriptions Data
Mass flow rate of hot spring (kg/s) 0.75
Hot spring temperature entering at the evaporator (°C) 49.60
Hot spring temperature leaving at the evaporator (°C) 48.61
Heat capacity of hot spring (kW) 3.10
Mass flow rate of hot water entering at the condenser (kg/s) 1.33
Hot water temperature leaving at the condenser (°C) 72.80
Hot water temperature entering at the condenser (°C) 71.40
Heat capacity of hot water (kW) 7.78
Electrical power consumption of single-stage VCHP (kWe) 2.58
Electrical power consumption of drying room (kWe) 5.60
EERVCHP (kWth/kWe) 3.02
EERDrying room (kWth/kWe) 1.39

Table 9: The average testing results of geothermal drying room and single-stage VCHP.

Table 10 shows the average testing results of the 2-stage vapor compression heat pump combining with the geothermal drying room. It could be found that hot spring temperatures entering and leaving at the evaporator are around 44.80°C and 37.60°C, respectively, and heat capacity of hot spring is around 6.52 kW. While, the heat pump system could be upgraded heat to be hot water temperature around 84.10°C at the useful heat capacity and the EERVCHP around 20.67 kW and 4.17 kWth/kWe, respectively. The drying room efficiency in term of EER is around 2.57 kWth/kWe. For economic results, the investment costs of the drying room and the 2-stage VCHP are 25,000 USD and the cost of electrical power consumption is around 1,000 USD/y with 15 sets of drying per month, 24 hours per drying set. While the revenue from the geothermal drying room is around 10,500 Baht/y, thus the payback period is around 29 months.

Descriptions Data
Mass flow rate of hot spring (kg/s) 0.22
Hot spring temperature entering at the evaporator (°C) 44.80
Hot spring temperature leaving at the evaporator (°C) 37.60
Heat capacity of hot spring (kW) 6.52
Mass flow rate of hot water entering at the condenser (kg/s) 1.03
Hot water temperature leaving at the condenser (°C) 84.10
Hot water temperature entering at the condenser (°C) 79.40
Heat capacity of hot water (kW) 20.67
Electrical power consumption of 2-state VCHP (kWe) 4.62
Electrical power consumption of drying room (kWe) 7.37
EERVCHP (kWth/kWe) 4.17
EERDrying room (kWth/kWe) 2.57

Table 10: The average testing results of geothermal drying room and 2-stage VCHP.

From the testing results of heat pump dryer, it could be found that 26 low potential hot springs as shown Table 11 could be developed for boosting heat process at the total heating capacity around 2,002 kW, and the agricultural products as around 200 Ton/d could be dried in the heat pump drying room.

Hot spring Province Temp (°C) Flow (L/s) Heat pump1 (kW)
Pong Na Kham Chiang Rai 65.9 0.52 28
Houy Mhak Leam Chiang Rai 56.6 7 376
Pha Sert Chiang Rai 66.2 2.38 128
Huay Sai Khaow Chiang Rai 56.5 1.96 105
Pong Arong Chiang Mai 52.3 0.78 42
Ban Yang Pu Toa Chiang Mai 51.7 0.2 11
Non Klang Chiang Mai 68.8 3.5 188
Pa dauk Chiang Mai 55.8 0.81 44
Mal Li Ka Chiang Mai 68.1 0.25 13
Pha Bong Mae Hong Sorn 65.5 0.67 36
Wiang Nuea Lampang 61.2 0.94 50
Ban Pong Nam Ron Lampang 56.2 1.12 60
Ban Pan Jen Phare 53.8 0.23 12
Wad Slang Phare 65.7 0.8 43
Ban Pong Lam Pang Sukhothai 55.6 0.16 9
Pa Ja Lern Tak 60 0.36 19
Boek Lueng Rachburi 57.3 5 269
Pong Long Ranong 56.2 0.26 14
Ban Khao Noi Surat Thani 52.1 1.53 82
Rat Ta No Go Sai Surat Thani 61 2.38 128

Table 11: Geothermal resources with boosting heat potential

From the above results, it could be noted that 46 hot springs in Thailand could be useful in generating electricity process, cooling process, heating process and boosting heat process. Moreover, 6.6 MW useful capacity from geothermal energy could be developed in Thailand.

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