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Performance of thermal energy transportation based on absorption heat pump cycle over 200 m distance – Solution transportation absorption chiller
Accepted Manuscript Performance of thermal energy transportation based on absorption heat pump cycle over 200m distance - Solution transportation absorption chiller Atsushi Akisawa, Fumi Watanabe, Koji Enoki, Toshitaka Takei PII: DOI: Reference:
S1359-4311(16)33667-5 http://dx.doi.org/10.1016/j.applthermaleng.2017.08.107 ATE 10990
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
27 November 2016 21 May 2017 21 August 2017
Please cite this article as: A. Akisawa, F. Watanabe, K. Enoki, T. Takei, Performance of thermal energy transportation based on absorption heat pump cycle over 200m distance - Solution transportation absorption chiller, Applied Thermal Engineering (2017), doi: http://dx.doi.org/10.1016/j.applthermaleng.2017.08.107
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Performance of Thermal Energy Transportation Based on Absorption Heat Pump Cycle over 200m Distance - Solution Transportation Absorption Chiller Atsushi Akisawa1†, Fumi Watanabe1, Koji Enoki2, Toshitaka Takei1 1 Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology,2-24-16 Nakacho, Koganei, Tokyo, 184-8588, Japan 2 The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan E-mail: [email protected]† Highlights - A solution transportation absorption chiller of 90kW was examined experimentally. - The COP in steady state was measured with the transportation distance up to 1000 m. - The COP of the absorption cycle is constant nevertheless of the distnace. - Heat transportation by the solution transportation is techonologically feasible. ABSTRACT The authors proposed “Solution Transportation Absorption Chiller” which is driven by wasted heat and transfers absorbent solution instead of chilled water. It consists of generator-condenser pair on the heat source side, absorber-evaporator pair on the demand side and pipelines between them. In this study, the authors investigated the heat transportation performance of the system experimentally with the distance of 100m, 200m and 1000m. The results suggest that the proposed system can work for transporting cooling with ammonia-water mixture as the working fluid. It was obtained that the COP of the system was the same as that of conventional absorption chiller without transportation. In other words, the performance does not suffer from the new function of long distance transportation. It can be concluded that the solution transportation is technologically feasible and also effective to replace conventional fossil fuels with remote wasted heat sources.
Keywords: Thermal energy transportation, absorption chiller, solution transportation, ammonia-water, COP 1.
INTRODUCTION It is widely understood that reducing CO2 emission is one of quite important issues to mitigate the global warming. One of the effective measures to reduce the emission is energy conservation, that is, consuming fossil fuels as small as possible. Heat cascading system [1] was proposed to rationalize thermal energy use from the viewpoint of the second Law of thermodynamics so that thermal energy should be used along the temperature declining. So called “heat cascading” suggests organizing heat use processes in order to repeat heat recovery and reuse along the temperature from combustion level of more than 1000 degree of Celsius down to the ambient. A typical example is utilizing discharged heat from one factory in the other factories. From the technological point of view, thermally driven heat pumps are regarded as key technologies to enhance heat cascading systems. Absorption chillers are broadly used in buildings and factories to produce cooling from discharged heat of co-generation systems, for instance. Because they can substitute for electrically driven chillers, it is expected to reduce electric power demand and associated fossil fuel consumption, consequently to suppress the peak load for power utility systems. Recently in district heating/cooling systems (DHC), cooling supply is growing much more than heating in Japan. It implies that reducing primary energy consumption for cooling services is predicted to become an inevitable issue in the future. Another problem to construct heat cascading systems is that there exists geographical mismatch between the location of wasted heat sources and the places of heat demand. Heat demand is distributed mainly in urban areas while heat sources such as factories or refuse incineration plants are located outside city areas. It is, therefore, required to transport thermal energy from heat sources to heat demand over long distance to utilize unexploited discharged heat. Heat transportation is considered essential to establish integrated heat cascading systems to reduce primary fuel consumption effectively. Heat transportation is a traditional issue to utilized unexploited heat from industry, for example. Chemical components such as methane or methanol are examined to transfer thermal energy over long distance [2]. Exothermic and endothermic reactions work to absorb heat from outside and discharge heat to demand side, respectively. In the case using methanol, H2 and CO decomposed from methanol at heat
1
source side with the temperature of 150-200 degC are transported to user side, where methanol synthesis reaction is operated to supply heat of 150 degC. Then methanol goes back to the heat source side. These systems incorporate pipelines to transport chemical components. In contrast, there exists batch systems to carry phase change materials by truck vehicles [3], [4], [5]. It is possible to transfer thermal energy of different temperature levels of 50 degC or 100 degC by selecting appropriate PCM materials. Heat of 100 degC can be converted into cooling at heat use side. This kind of system has been operated some places in Japan to utilize waste incineration heat [6]. Transporting chemical materials by trucks also works for heat transportation in the similar way. Ogura analyzed a system with "chemical heat pump container" which uses CaSO4 and water as the working pair [7]. A model analysis of PCM transportation to utilize industrial surplus heat for district heating system was conducted by Ciu et al. which compared the performance by transportation modes such as trucks, railways and maritime [8]. One of the authors proposed a new idea of transporting thermal energy for refrigeration based on absorption heat pump mechanism, which is called “Solution Transportation Absorption Chiller (STA in short)” [9]. STA systems transport solutions and refrigerant from heat source side to heat demand side instead of transporting secondary medium such as chilled water like in conventional DHCs. Since STA systems transfer thermal energy not in the form of sensible heat but in concentration difference of the solutions, the systems have an advantage of no insulation requirement. Akisawa et al. [10] presented experimental results of STA which working fluid was LiBr-water and discussed that COP of STA is the same as that of conventional absorption chiller without transportation. The study also shows possibility of improving the COP when the condensation heat is recovered by the working solution. Experiments of STA was examined by Lin et al. [11] with the working fluid of ammonia-water. Because LiBr can crystalize at low temperature environment, LiBr-water is not necessarily good material for STA. In contrast, ammonia-water will be a candidate fluid for STA because it never crystalizes. The experimental setup consisted of the pipes of 30m with the cooling capacity of 100W. Although the experiment was preliminary, it is considered too small to understand realistic behavior of STA systems. Akisawa et al. [12] constructed an experimental setup of STA based on a commercialized ammonia absorption chiller of 18kW. It also incorporated three pipes of 50m to transport ammonia and ammonia-water solutions. It was reported that STA was effectively working to supply refrigeration even with 50m transportation. Kang et al. [13] proposed the application of STA for type 2 heat pump (heat transformer) to utilize cold energy of LNG. Akisawa et al. [14], [15] investigated the effect of STA in terms of reducing primary energy consumption when the system utilizes discharged heat from refuse incineration power plant. It is interesting to note that ammonia-water based STA can supply not only cooling but also heating which is generated at the absorber to provide hot water. The objectives of this study are to examine actual performance of STA with the cooling capacity of 90kW, to measure the COP with/without solution transportation and to observe how the solution transportation influences the performance of the absorption refrigeration cycle. In this study, long distance transportation is emulated in such a way that pressure drop through the pipes is adjusted to the equivalent condition of given transportation distance. The study focused on the steady state behavior of the experimental machine of STA. 2.
SOLUTION TRANSPORTATION ABSORPTION CHILLER Absorption chillers are well known technology to produce cooling for air-conditioning or refrigeration for industrial processes [16]. Conventional DHCs install absorption chillers in the center plant and produce chilled water which is, then, distributed to heat demand side to supply cooling service. Generally, absorption cycle consists of four major heat exchangers named evaporator, absorber, generator and condenser (represented by the symbols of E, A, G and C in Fig. 1). Cooling is generated when ammonia evaporates in the evaporator. The refrigerant vapor is then absorbed into the weak solution at the absorber. In this process weak solution changes to strong solution. When the strong solution is heated in the generator, the refrigerant vapor goes out to the condenser where it turns into liquid by cooling. Then the liquid refrigerant returns to the evaporator and repeats the same process continuously. It should be noted that STA system locates the evaporator-absorber pair of absorption chiller at the demand side and its generator-condenser pair at the heat source side and connects these pairs with pipelines for transporting the absorption solutions and the refrigerant. Figure 1(a) and (b) show the schematic of thermal energy transportation by conventional system as well as STA system, respectively. Both systems utilize wasted heat and finally satisfy cooling load at the demand side nevertheless of different system configurations. In other words, both systems achieve the same function of cooling supply, which implies that thermal energy can be transferred by transporting the solutions and the refrigerant separately. From this point of view, it can be said that thermal energy is converted and stored
2
in the concentration difference of the working media. STA system is regarded as an application of chemical potentials to heat transportation.
Fig. 1. Principle of heat transportation by STA.
From the above mentioned unique aspect of STA systems to transfer thermal energy, the systems have the following advantages. Because thermal energy is converted into the concentration difference, no insulation is required for the pipelines. While conventional chilled water transportation requires quite large mass transportation because of small temperature difference, solution transportation suggests relatively small mass transportation. It is also expected that smaller pipes need less construction materials and cost, which will improve the economy of DHC systems. Associated with the second point above, STA systems reduce pumping power to circulate working fluids between heat source side and demand side even though STA needs an extra pipeline to send refrigerant to demand side. According to the simulation analysis, required pumping power of STA system is reduced quite significantly compared with conventional chilled water transportation when the STA system supplies the same cooling effect as the conventional one does. For a given pipe diameter, pumping power of STA is about 1/100-1/1000 as small as that of chilled water transportation (Kang et al, 2000). Concentration of the transported media is physically kept constant whatever the distance is. It means that thermal energy stored in the media is absolutely hold over any long trip. In sum, STA systems are considered suitable for thermal energy transportation over long distance, which certainly assist effective use of wasted heat in urban areas. 3. EXPERIMENTAL FACILITY 3.1. Experimental rig One of the authors already examined STA by experiments not only with the water-LiBr system (Akisawa et al, 2005) but also with ammonia-water system (Akisawa et al, 2012) in order to verify the principle. The results revealed that cooling transportation based on the solution transportation was technologically feasible. However, transportation distance was 50m in the case of ammonia-water STA and the capacity of cooling was 18 kW. A small-scale commercialized ammonia-water chiller was modified to have the solution transportation pipes to examine STA function. Because it was a product of small scale chiller, the flow diagram was different from that of large scale one. The objective of this study is to observe the behavior of STA with real scale ammonia absorption chiller. Therefore an experimental rig of 90kW cooling capacity was constructed, which is equipped with the same controlling system as general ammonia absorption chillers have. Figure 2 shows the photo of experimental rig. The rig is basically similar to single effect absorption chiller and consists of main heat exchangers, which are separated from each other, and solution heat exchanger to recover heat of the weak solution from the generator to the strong solution. In order to implement heat transportation through transferring the solutions, the rig has pipelines between generator/condenser pair and absorber/evaporator pair. Because it was difficult to install long pipelines
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due to the limited space, the following ideas to cope with the transportation distance were adopted to construct the experimental rig. The machine has solution pipelines with the diameter of 125A instead of the normal diameter of 25A. The pipeline volume is adjusted to the same volume of the 25A pipe with the length of 200m. The length of the 125A pipes was determined to be approximately 9m. Because large diameter gives small pressure drop, the pressure drop is controlled by extra valves in accordance with the given length of the 25A pipe. Long distance transportation can be emulated by controlling the pressure drop accordingly. As can be seen in the photo, the pipelines of 125A has zigzag shape to be installed in the narrow space. Also the pipelines are bare tube without thermal insulation. Figure 3 shows the flow diagram of the experimental machine of STA. The configuration of the refrigeration cycle basically reflects actual ammonia absorption chillers. The lefthand side is supposed to be located in wasted heat source side and takes wasted heat to regenerate the strong solution in the generator. Since only ammonia refrigerant should be separated and returned to the evaporator, ammoniawater absorption chillers basically have a rectification column between the generator and the condenser to eliminate water. The right hand side represents the equipments supposed to be located in heat use side. Three pipelines of ammonia refrigerant, strong solution and weak solution are connecting the both sides. The cooling produced by the machine is canceled to cool down the cooling water from the absorber. Brine is circulating as a fluid to carry the cooling effect, which inlet and outlet temperature is controlled to keep given temperature. The density and temperature of the refrigerant, strong solution and weak solution are measured by the Coriolis mass flow meters(accuracy± 1kg m-3) at the each transportation pipes inlet and Thermocouples type K (accuracy± 0.5 degC) at the each transportation pipes inlet and heat exchanger inlet. The ammonia solution concentration (error± 1.3 %) are calculated by the density and temperature. The mass flow rate of each solution is also measured by the Coriolis mass flow meters (accuracy± 0.5 %) at the transportation pipes inlet. The mass flow rate of the brine and the temperature of brine inlet and outlet are measured by the Electromagnetic flow meter (accuracy ± 2 %) and PT 100 temperature sensors(accuracy ± 0.15 degC). Cooling output (error ± 6.6 %) is calculated by the mass flow rate and temperature. The mass flow rate of the steam, pressure of the steam inlet and temperature of steam inlet and outlet are measured by the Differential pressure flow meter (accuracy ± 3 %), Bourdon tube pressure gauge (accuracy ± 4.8 kPa) and PT 100 temperature sensors(accuracy ± 0.2 degC). The enthalpy of steam inlet and outlet is calculated by the temperature and pressure. Steam input (error ± 0.3 % ) are calculated by the mass flow rate and enthalpy.
Fig. 2. Photo of the experimental rig.
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Fig. 3. Schematic flow diagram of STA system. 3.2. Controlling system The following control operations are employed to stabilize the machine. They are actually the same ones as large scale chillers have. The temperature of the generator is controlled by adjusting the steam flow rate from the boiler. The liquid level of the generator is controlled by the flow rate of the weak solution. The temperature of the condenser is controlled by the flow rate of the cooling water. The flow rate of the reflux from the condenser to the rectification column is controlled to keep the outlet temperature of refrigerant vapor from the rectifier. The liquid level of the evaporator is controlled by the flow rate of the refrigerant from the condenser. The temperature of the brine outlet is controlled by changing the circulation of the strong solution to the absorber through the bypass line (See Fig. 3). When the cooling load is reduced, the mass flow rate of the strong solution is decreased by the controller in order to reduce the mass flow of the refrigerant returning to the evaporator. 3.3. Experimental conditions The specification of the experimental machine of STA is summarized in Table 1. The capacity of 90kW is a practical size of ammonia absorption chiller. Here, the temperature of wasted heat is assumed 120-130 degC, that is, low pressure steam level. COP (Coefficient of Performance) is defined as the ratio of the cooling output to the heat input, which indicates the energy conversion efficiency of the refrigeration cycle. The objective of the experiments is to investigate the effect of solution transportation on the steady state performance of the ammonia-water absorption cycle. In this study, the settings of transportation distance are 200m, 500m and 1000m. As mentioned before, the pressure drop of the solution pipes were adjusted to the distance accordingly as shown in Table 2. Reference case is a normal absorption chiller without solution transportation, which is expressed as 0m distance. The reference case is emulated when the bypass lines beside each solution transportation pipe work (See Fig. 3). The brine temperature was set at 5 degC and 10 degC for the outlet and inlet, respectively. Though ammonia-water absorption chillers are normally used for freezing, it is assumed that STA provides chilled water for cooling purposes in this study. The pressure of the evaporator and the absorber was approximately 0.4MPa while that of the condenser and the generator was about 1.6MPa.
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Table 1 Specifications of the experimental machine. Specification Value 90 0 0.3 32 0.6 4(W) x 3(L) x 4(H) 9
Item Cooling capacity Evaporation temperature Steam pressure Cooing water temperature COP Size Weight
Unit kW degC MPa degC m tons
Table 2 Settings of pressure drop. Pipeline Refrigerant Strong solution Weak solution
Pressure drop (kPa) 500m 10 100 60
200m 0 40 20
4.
1000m 10 210 120
EXPERIMENTAL RESULTS First, the normal absorption chiller mode with 0m transportation was examined to know the flow rates of the refrigerant, the strong solution and the weak solution. The pressure drop settings were then calculated, which are summarized in Table 2. Because the mass flow rate of the strong solution is the largest among three fluids, the pressure drop is the highest as well. The pressure drop for the refrigerant is considered negligible due to small amount of the flow rate. The pressure drop is enough small compared with the pressure difference between the two sides. It indicates that no additional pump is required to transfer the refrigerant and the weak solution. The internal pressure difference can drive the transportation in the experiments. When the pressure drop through solution pipelines becomes large, it causes smaller mass flow rate. In order to keep the same mass flow rate, the flow was controlled by the solution pump. Figure 4 indicates that the mass flow rates are almost equal for any transportation distance. Figure 5 shows concentration of ammonia in the solutions and refrigerant. The concentration of the refrigerant at the outlet of the condenser holds as high as 99.4%. While the strong solution has the concentration at approximately 45%, that of the weak solution is around 30%. It was found that the concentration kept almost the same value for any transportation distance. It suggests that the cycle behavior is considered independent of the distance of the solution transportation. Similar stable behavior was observed in terms of temperature in the cycle. Figure 6 shows that the temperature of selected points in the flow diagram (numbered in Fig. 3) are common among all distance cases. As is the same as general absorption chillers, there exists a heat exchanger to recover heat from the weak solution from the generator, which temperature is high at point 10, to increase the temperature of the strong solution before going into the generator. The temperature at point 11 indicates the outlet temperature of the weak solution at the heat exchanger, which is as low as approximately 30 degC close to the ambient temperature. It suggests that heat loss during the solution transportation will be very small due to the small temperature difference between the weak solution and the environment. It, in turn, suggests that the solution heat exchanger needs to have enough capacity to keep the COP as high as possible. For the case of 500 m distance, the heat loss through the pipeline of the weak solution is 3 kW while the generator heat input is 140 kW. It should be noted that the loss is as small as 2 % of the heat input. Another viewpoint is exergy for evaluating the cycle. Exergy input to the generator is 29 kW when the steam temperature is 125 degC assuming the ambient temperature is 32 degC. On the other hand, the exergy destruction by the weak solution transportation is 0.5 kW for the case of 500 m distance. The destruction is less than 2 % in this case, which suggests that the solution transportation is not significant in terms of exergy as well. Consequently, it can be said from the experimental results that the cycle of STA holds the same behavior in steady state nevertheless of the distance between the generator/condenser side and the evaporator/absorber side.
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0m
200m
500m
1000m
Mass flow rate (kg h-1)
1400 1200 1000 800 600 400 200 0 Refrigerant
Strong solution Weak solution
Fig. 4. Effect of transportation distance on mass flow rate.
Ammonia concentration (%)
0m
200m
500m
1000m
120 100 80 60 40 20 0 Refrigerant
Strong solution Weak solution
Fig. 5. Effect of transportation distance on ammonia concentration.
0m
200m
500m
5
7
1000m
120
Temperature (degC)
100 80 60 40 20 0 1
2
3
4
6
8
9
10 11 12
-20 Fig. 6. Effect of transportation distance on temperature.
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Heating input
COP 160
0.6
120
0.4
80
0.2
40
0
Heat duty (kW)
Cooling output
COP (-)
0.8
0 0m
200m
500m
1000m
Fig. 7. Effect of transportation distance on COP. Therefore, it is expected that STA has almost the same performance with any distance cases. Figure 7 compares cooling output, heat input to the cycle and the COP of all cases. The COP indicates only thermal conversion performance of the cycle from the heat input to the refrigeration output. As shown in the graph, the COP of each case is commonly about 0.6. It should be emphasized that the result clearly indicates that the thermal performance of STA is not affected by the transportation distance even though the distance influences the power consumption of the pump to an extent. Based on the results mentioned above, it has been confirmed that STA, an ammonia absorption cycle with solution transportation, does not suffer from the transportation distance in terms of COP. It is remarkably interesting that the additional function of heat transportation gives no damage on the cycle performance as an absorption refrigeration cycle. This feature is supposed to be extended for longer distance cases more than 1000m because the cycle configuration is basically identical. When the transportation distance becomes longer, the solution pump has to have larger capacity accordingly to overcome the pressure drop. On the other hand, the pressure drop of the weak solution possibly dominates the transportation distance because it should be less than the pressure difference between the high pressure side and the low pressure side. It is approximately 1.2 MPa in this experimental setup, which is considered equivalent to 10km of the pipeline. If the distance is more than that, an additional pump is required to transfer weak solution from the generator side to the absorber side. 5.
CONCLUSION This study investigated the technological feasibility of thermal energy transportation by solution/refrigerant transportation. This technology named STA is an extended scheme of ammonia-water absorption refrigeration cycle. An experimental facility of 90kW was built to examine the real performance with solution transportation for the distance of 200m, 500m and 1000m which was emulated by adjusting the pressure drop in the solution pipes. The following was found out based on the experimental results. Although the distance of transportation changes, internal states of the cycle such as temperature and ammonia concentration remain the same. Solution transportation distance does not affect the performance of STA in terms of COP. The COP is observed to be 0.6 which is the same as that of conventional ammonia absorption chillers without transportation. It can be concluded that the function of thermal energy transportation is technologically feasible by means of solution transportation. It is interesting to note that such additional function can be attained without any functional damage to the absorption cycle performance. The behavior of STA in steady state was clarified to be insensitive to transportation distance in this study. On the other hand, dynamic response of the system is possibly different from the behavior of conventional ammonia absorption chiller without solution transportation. The experimental facility of STA developed in this study was employed to measure actual dynamic behavior of ammonia-water absorption cycle with solution transportation of 200m, which will be investigated in the next steps. It is
8
expected to provide insights to understand how STA should be designed, operated and controlled appropriately.
ACKNOWLEDGEMENT This study was financially supported by New Energy and Industrial Technology Development Organization, an agency of the Japanese government. The authors also appreciate the cooperation of JX Nippon Oil and Energy Corporation who jointly conducts the project as a partner. REFERENCES [1] T. Kashiwagi, Eco-energy system for urban area. Transaction of Japan Society of Mechanical Engineers. 98 (917) (1995) 261–265 (in Japanese) . [2] Q. Ma, L. Luo, Z. R. Wang, G. Sauce, A review on transportation of heat energy over long distance: Exploratory development, Renewable and Sustainable Energy Reviews. 13 (6–7) (2009) 1532– 1540. [3] A. Kaizawa, H. Kamano, A. Kawai, T. Jozuka, T. Senda, N. Maruka, N. Okinaka, T. Akiyama, Technical feasibility study of waste heat transportation system using phase change material from industry to city, ISIJ International. 48 (4) (2008) 540–548. [4] T. Nomura, N. Okinaka, T. Akiyama, Technology of latent heat storage for high temperature application: A review. ISIJ International. 50 (9) (2010) 1229–1239. [5] T. Nomura, N. Okinaka, T. Akiyama, Waste heat transportation system, using phase change material (PCM) from steelworks to chemical plant. Resources, Conservation and Recycling. 54 (11) (2010) 1000–1006. [6] Sanki Engineering Co. Ltd. Homepage. www.sanki.co.jp/product/thc. 2016 (accessed June 2016) (in Japanese). [7] H. Oguraa, Energy recycling system using chemical heat pump container. Energy Procedia. 14 (2012) 2048–2053. http://dx.doi.org/10.1016/j.energy.2016.05.003. [8] J. NW. Chiu, J. C. Flores, V. Martin, B. Lacarriere, Industrial surplus heat transportation for use in district heating, Energy. 110 (2016) 139-147 [9] Y. T. Kang, A. Akisawa, Y. Sambe, T. Kashiwagi, Absorption heat pump systems for solution transportation at ambient temperature STA cycle, Energy. 25 (4) (2000) 355–370. [10] A. Akisawa, K. Araki, T. Miyazaki, Y. Ueda, T. Takei, Application of ammonia-water absorption cycle to transfer cooling and heating at ambient temperature, Proc. of 5th Asian Conference on Refrigeration and Air-conditioning, Tokyo. 2010 [11] P. Lin, , R. Z. Wang, Z. Z. Xia, Q. Ma, Experimental investigation on heat transportation over long distance by ammonia-water absorption cycle, Energy Conversion and Management. 50 (2009) 2331–2339. [12] A. Akisawa, T. Tomita, Y. Ueda, T. Takei, Heat transportation experiment over 50m by Solution Transportation Absorption chiller and its dynamic simulation, Proc. of 22nd Annual meeting of Environment and Engineering in JSME. Sendai, 2012 (in Japanese). [13] Y. K. Jo, J-K. Kim, S. G. Lee, Y. T. Kang, Development or type 2 solution transportation absorption system for utilizing LNG cold energy, International Journal of Refrigeration, 30 (2007) 978–985. [14] A. Akisawa, Y. Hamamoto, T. Kashiwagi, Performance of thermal energy transportation based on absorption system -Solution transportation absorption chiller-, Proc. of International Sorption Heat Pump Conference. Denver, 2005. [15] A. Akisawa, S. Mori, Y. Ueda, K. Araki, Performance of double effect solution transportation absorption cycle to utilize condensation heat of refuse power generation, Proc. of 23rd IIR International Congress of Refrigeration. Prague, 2011. [16] K. E. Herold, R. Radermacher, S. A. Klein, Absorption chillers and heat pumps, CRC Press. 1996
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S1359-4311(16)33667-5 http://dx.doi.org/10.1016/j.applthermaleng.2017.08.107 ATE 10990
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
27 November 2016 21 May 2017 21 August 2017
Please cite this article as: A. Akisawa, F. Watanabe, K. Enoki, T. Takei, Performance of thermal energy transportation based on absorption heat pump cycle over 200m distance - Solution transportation absorption chiller, Applied Thermal Engineering (2017), doi: http://dx.doi.org/10.1016/j.applthermaleng.2017.08.107
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Performance of Thermal Energy Transportation Based on Absorption Heat Pump Cycle over 200m Distance - Solution Transportation Absorption Chiller Atsushi Akisawa1†, Fumi Watanabe1, Koji Enoki2, Toshitaka Takei1 1 Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology,2-24-16 Nakacho, Koganei, Tokyo, 184-8588, Japan 2 The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan E-mail: [email protected]† Highlights - A solution transportation absorption chiller of 90kW was examined experimentally. - The COP in steady state was measured with the transportation distance up to 1000 m. - The COP of the absorption cycle is constant nevertheless of the distnace. - Heat transportation by the solution transportation is techonologically feasible. ABSTRACT The authors proposed “Solution Transportation Absorption Chiller” which is driven by wasted heat and transfers absorbent solution instead of chilled water. It consists of generator-condenser pair on the heat source side, absorber-evaporator pair on the demand side and pipelines between them. In this study, the authors investigated the heat transportation performance of the system experimentally with the distance of 100m, 200m and 1000m. The results suggest that the proposed system can work for transporting cooling with ammonia-water mixture as the working fluid. It was obtained that the COP of the system was the same as that of conventional absorption chiller without transportation. In other words, the performance does not suffer from the new function of long distance transportation. It can be concluded that the solution transportation is technologically feasible and also effective to replace conventional fossil fuels with remote wasted heat sources.
Keywords: Thermal energy transportation, absorption chiller, solution transportation, ammonia-water, COP 1.
INTRODUCTION It is widely understood that reducing CO2 emission is one of quite important issues to mitigate the global warming. One of the effective measures to reduce the emission is energy conservation, that is, consuming fossil fuels as small as possible. Heat cascading system [1] was proposed to rationalize thermal energy use from the viewpoint of the second Law of thermodynamics so that thermal energy should be used along the temperature declining. So called “heat cascading” suggests organizing heat use processes in order to repeat heat recovery and reuse along the temperature from combustion level of more than 1000 degree of Celsius down to the ambient. A typical example is utilizing discharged heat from one factory in the other factories. From the technological point of view, thermally driven heat pumps are regarded as key technologies to enhance heat cascading systems. Absorption chillers are broadly used in buildings and factories to produce cooling from discharged heat of co-generation systems, for instance. Because they can substitute for electrically driven chillers, it is expected to reduce electric power demand and associated fossil fuel consumption, consequently to suppress the peak load for power utility systems. Recently in district heating/cooling systems (DHC), cooling supply is growing much more than heating in Japan. It implies that reducing primary energy consumption for cooling services is predicted to become an inevitable issue in the future. Another problem to construct heat cascading systems is that there exists geographical mismatch between the location of wasted heat sources and the places of heat demand. Heat demand is distributed mainly in urban areas while heat sources such as factories or refuse incineration plants are located outside city areas. It is, therefore, required to transport thermal energy from heat sources to heat demand over long distance to utilize unexploited discharged heat. Heat transportation is considered essential to establish integrated heat cascading systems to reduce primary fuel consumption effectively. Heat transportation is a traditional issue to utilized unexploited heat from industry, for example. Chemical components such as methane or methanol are examined to transfer thermal energy over long distance [2]. Exothermic and endothermic reactions work to absorb heat from outside and discharge heat to demand side, respectively. In the case using methanol, H2 and CO decomposed from methanol at heat
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source side with the temperature of 150-200 degC are transported to user side, where methanol synthesis reaction is operated to supply heat of 150 degC. Then methanol goes back to the heat source side. These systems incorporate pipelines to transport chemical components. In contrast, there exists batch systems to carry phase change materials by truck vehicles [3], [4], [5]. It is possible to transfer thermal energy of different temperature levels of 50 degC or 100 degC by selecting appropriate PCM materials. Heat of 100 degC can be converted into cooling at heat use side. This kind of system has been operated some places in Japan to utilize waste incineration heat [6]. Transporting chemical materials by trucks also works for heat transportation in the similar way. Ogura analyzed a system with "chemical heat pump container" which uses CaSO4 and water as the working pair [7]. A model analysis of PCM transportation to utilize industrial surplus heat for district heating system was conducted by Ciu et al. which compared the performance by transportation modes such as trucks, railways and maritime [8]. One of the authors proposed a new idea of transporting thermal energy for refrigeration based on absorption heat pump mechanism, which is called “Solution Transportation Absorption Chiller (STA in short)” [9]. STA systems transport solutions and refrigerant from heat source side to heat demand side instead of transporting secondary medium such as chilled water like in conventional DHCs. Since STA systems transfer thermal energy not in the form of sensible heat but in concentration difference of the solutions, the systems have an advantage of no insulation requirement. Akisawa et al. [10] presented experimental results of STA which working fluid was LiBr-water and discussed that COP of STA is the same as that of conventional absorption chiller without transportation. The study also shows possibility of improving the COP when the condensation heat is recovered by the working solution. Experiments of STA was examined by Lin et al. [11] with the working fluid of ammonia-water. Because LiBr can crystalize at low temperature environment, LiBr-water is not necessarily good material for STA. In contrast, ammonia-water will be a candidate fluid for STA because it never crystalizes. The experimental setup consisted of the pipes of 30m with the cooling capacity of 100W. Although the experiment was preliminary, it is considered too small to understand realistic behavior of STA systems. Akisawa et al. [12] constructed an experimental setup of STA based on a commercialized ammonia absorption chiller of 18kW. It also incorporated three pipes of 50m to transport ammonia and ammonia-water solutions. It was reported that STA was effectively working to supply refrigeration even with 50m transportation. Kang et al. [13] proposed the application of STA for type 2 heat pump (heat transformer) to utilize cold energy of LNG. Akisawa et al. [14], [15] investigated the effect of STA in terms of reducing primary energy consumption when the system utilizes discharged heat from refuse incineration power plant. It is interesting to note that ammonia-water based STA can supply not only cooling but also heating which is generated at the absorber to provide hot water. The objectives of this study are to examine actual performance of STA with the cooling capacity of 90kW, to measure the COP with/without solution transportation and to observe how the solution transportation influences the performance of the absorption refrigeration cycle. In this study, long distance transportation is emulated in such a way that pressure drop through the pipes is adjusted to the equivalent condition of given transportation distance. The study focused on the steady state behavior of the experimental machine of STA. 2.
SOLUTION TRANSPORTATION ABSORPTION CHILLER Absorption chillers are well known technology to produce cooling for air-conditioning or refrigeration for industrial processes [16]. Conventional DHCs install absorption chillers in the center plant and produce chilled water which is, then, distributed to heat demand side to supply cooling service. Generally, absorption cycle consists of four major heat exchangers named evaporator, absorber, generator and condenser (represented by the symbols of E, A, G and C in Fig. 1). Cooling is generated when ammonia evaporates in the evaporator. The refrigerant vapor is then absorbed into the weak solution at the absorber. In this process weak solution changes to strong solution. When the strong solution is heated in the generator, the refrigerant vapor goes out to the condenser where it turns into liquid by cooling. Then the liquid refrigerant returns to the evaporator and repeats the same process continuously. It should be noted that STA system locates the evaporator-absorber pair of absorption chiller at the demand side and its generator-condenser pair at the heat source side and connects these pairs with pipelines for transporting the absorption solutions and the refrigerant. Figure 1(a) and (b) show the schematic of thermal energy transportation by conventional system as well as STA system, respectively. Both systems utilize wasted heat and finally satisfy cooling load at the demand side nevertheless of different system configurations. In other words, both systems achieve the same function of cooling supply, which implies that thermal energy can be transferred by transporting the solutions and the refrigerant separately. From this point of view, it can be said that thermal energy is converted and stored
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in the concentration difference of the working media. STA system is regarded as an application of chemical potentials to heat transportation.
Fig. 1. Principle of heat transportation by STA.
From the above mentioned unique aspect of STA systems to transfer thermal energy, the systems have the following advantages. Because thermal energy is converted into the concentration difference, no insulation is required for the pipelines. While conventional chilled water transportation requires quite large mass transportation because of small temperature difference, solution transportation suggests relatively small mass transportation. It is also expected that smaller pipes need less construction materials and cost, which will improve the economy of DHC systems. Associated with the second point above, STA systems reduce pumping power to circulate working fluids between heat source side and demand side even though STA needs an extra pipeline to send refrigerant to demand side. According to the simulation analysis, required pumping power of STA system is reduced quite significantly compared with conventional chilled water transportation when the STA system supplies the same cooling effect as the conventional one does. For a given pipe diameter, pumping power of STA is about 1/100-1/1000 as small as that of chilled water transportation (Kang et al, 2000). Concentration of the transported media is physically kept constant whatever the distance is. It means that thermal energy stored in the media is absolutely hold over any long trip. In sum, STA systems are considered suitable for thermal energy transportation over long distance, which certainly assist effective use of wasted heat in urban areas. 3. EXPERIMENTAL FACILITY 3.1. Experimental rig One of the authors already examined STA by experiments not only with the water-LiBr system (Akisawa et al, 2005) but also with ammonia-water system (Akisawa et al, 2012) in order to verify the principle. The results revealed that cooling transportation based on the solution transportation was technologically feasible. However, transportation distance was 50m in the case of ammonia-water STA and the capacity of cooling was 18 kW. A small-scale commercialized ammonia-water chiller was modified to have the solution transportation pipes to examine STA function. Because it was a product of small scale chiller, the flow diagram was different from that of large scale one. The objective of this study is to observe the behavior of STA with real scale ammonia absorption chiller. Therefore an experimental rig of 90kW cooling capacity was constructed, which is equipped with the same controlling system as general ammonia absorption chillers have. Figure 2 shows the photo of experimental rig. The rig is basically similar to single effect absorption chiller and consists of main heat exchangers, which are separated from each other, and solution heat exchanger to recover heat of the weak solution from the generator to the strong solution. In order to implement heat transportation through transferring the solutions, the rig has pipelines between generator/condenser pair and absorber/evaporator pair. Because it was difficult to install long pipelines
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due to the limited space, the following ideas to cope with the transportation distance were adopted to construct the experimental rig. The machine has solution pipelines with the diameter of 125A instead of the normal diameter of 25A. The pipeline volume is adjusted to the same volume of the 25A pipe with the length of 200m. The length of the 125A pipes was determined to be approximately 9m. Because large diameter gives small pressure drop, the pressure drop is controlled by extra valves in accordance with the given length of the 25A pipe. Long distance transportation can be emulated by controlling the pressure drop accordingly. As can be seen in the photo, the pipelines of 125A has zigzag shape to be installed in the narrow space. Also the pipelines are bare tube without thermal insulation. Figure 3 shows the flow diagram of the experimental machine of STA. The configuration of the refrigeration cycle basically reflects actual ammonia absorption chillers. The lefthand side is supposed to be located in wasted heat source side and takes wasted heat to regenerate the strong solution in the generator. Since only ammonia refrigerant should be separated and returned to the evaporator, ammoniawater absorption chillers basically have a rectification column between the generator and the condenser to eliminate water. The right hand side represents the equipments supposed to be located in heat use side. Three pipelines of ammonia refrigerant, strong solution and weak solution are connecting the both sides. The cooling produced by the machine is canceled to cool down the cooling water from the absorber. Brine is circulating as a fluid to carry the cooling effect, which inlet and outlet temperature is controlled to keep given temperature. The density and temperature of the refrigerant, strong solution and weak solution are measured by the Coriolis mass flow meters(accuracy± 1kg m-3) at the each transportation pipes inlet and Thermocouples type K (accuracy± 0.5 degC) at the each transportation pipes inlet and heat exchanger inlet. The ammonia solution concentration (error± 1.3 %) are calculated by the density and temperature. The mass flow rate of each solution is also measured by the Coriolis mass flow meters (accuracy± 0.5 %) at the transportation pipes inlet. The mass flow rate of the brine and the temperature of brine inlet and outlet are measured by the Electromagnetic flow meter (accuracy ± 2 %) and PT 100 temperature sensors(accuracy ± 0.15 degC). Cooling output (error ± 6.6 %) is calculated by the mass flow rate and temperature. The mass flow rate of the steam, pressure of the steam inlet and temperature of steam inlet and outlet are measured by the Differential pressure flow meter (accuracy ± 3 %), Bourdon tube pressure gauge (accuracy ± 4.8 kPa) and PT 100 temperature sensors(accuracy ± 0.2 degC). The enthalpy of steam inlet and outlet is calculated by the temperature and pressure. Steam input (error ± 0.3 % ) are calculated by the mass flow rate and enthalpy.
Fig. 2. Photo of the experimental rig.
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Fig. 3. Schematic flow diagram of STA system. 3.2. Controlling system The following control operations are employed to stabilize the machine. They are actually the same ones as large scale chillers have. The temperature of the generator is controlled by adjusting the steam flow rate from the boiler. The liquid level of the generator is controlled by the flow rate of the weak solution. The temperature of the condenser is controlled by the flow rate of the cooling water. The flow rate of the reflux from the condenser to the rectification column is controlled to keep the outlet temperature of refrigerant vapor from the rectifier. The liquid level of the evaporator is controlled by the flow rate of the refrigerant from the condenser. The temperature of the brine outlet is controlled by changing the circulation of the strong solution to the absorber through the bypass line (See Fig. 3). When the cooling load is reduced, the mass flow rate of the strong solution is decreased by the controller in order to reduce the mass flow of the refrigerant returning to the evaporator. 3.3. Experimental conditions The specification of the experimental machine of STA is summarized in Table 1. The capacity of 90kW is a practical size of ammonia absorption chiller. Here, the temperature of wasted heat is assumed 120-130 degC, that is, low pressure steam level. COP (Coefficient of Performance) is defined as the ratio of the cooling output to the heat input, which indicates the energy conversion efficiency of the refrigeration cycle. The objective of the experiments is to investigate the effect of solution transportation on the steady state performance of the ammonia-water absorption cycle. In this study, the settings of transportation distance are 200m, 500m and 1000m. As mentioned before, the pressure drop of the solution pipes were adjusted to the distance accordingly as shown in Table 2. Reference case is a normal absorption chiller without solution transportation, which is expressed as 0m distance. The reference case is emulated when the bypass lines beside each solution transportation pipe work (See Fig. 3). The brine temperature was set at 5 degC and 10 degC for the outlet and inlet, respectively. Though ammonia-water absorption chillers are normally used for freezing, it is assumed that STA provides chilled water for cooling purposes in this study. The pressure of the evaporator and the absorber was approximately 0.4MPa while that of the condenser and the generator was about 1.6MPa.
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Table 1 Specifications of the experimental machine. Specification Value 90 0 0.3 32 0.6 4(W) x 3(L) x 4(H) 9
Item Cooling capacity Evaporation temperature Steam pressure Cooing water temperature COP Size Weight
Unit kW degC MPa degC m tons
Table 2 Settings of pressure drop. Pipeline Refrigerant Strong solution Weak solution
Pressure drop (kPa) 500m 10 100 60
200m 0 40 20
4.
1000m 10 210 120
EXPERIMENTAL RESULTS First, the normal absorption chiller mode with 0m transportation was examined to know the flow rates of the refrigerant, the strong solution and the weak solution. The pressure drop settings were then calculated, which are summarized in Table 2. Because the mass flow rate of the strong solution is the largest among three fluids, the pressure drop is the highest as well. The pressure drop for the refrigerant is considered negligible due to small amount of the flow rate. The pressure drop is enough small compared with the pressure difference between the two sides. It indicates that no additional pump is required to transfer the refrigerant and the weak solution. The internal pressure difference can drive the transportation in the experiments. When the pressure drop through solution pipelines becomes large, it causes smaller mass flow rate. In order to keep the same mass flow rate, the flow was controlled by the solution pump. Figure 4 indicates that the mass flow rates are almost equal for any transportation distance. Figure 5 shows concentration of ammonia in the solutions and refrigerant. The concentration of the refrigerant at the outlet of the condenser holds as high as 99.4%. While the strong solution has the concentration at approximately 45%, that of the weak solution is around 30%. It was found that the concentration kept almost the same value for any transportation distance. It suggests that the cycle behavior is considered independent of the distance of the solution transportation. Similar stable behavior was observed in terms of temperature in the cycle. Figure 6 shows that the temperature of selected points in the flow diagram (numbered in Fig. 3) are common among all distance cases. As is the same as general absorption chillers, there exists a heat exchanger to recover heat from the weak solution from the generator, which temperature is high at point 10, to increase the temperature of the strong solution before going into the generator. The temperature at point 11 indicates the outlet temperature of the weak solution at the heat exchanger, which is as low as approximately 30 degC close to the ambient temperature. It suggests that heat loss during the solution transportation will be very small due to the small temperature difference between the weak solution and the environment. It, in turn, suggests that the solution heat exchanger needs to have enough capacity to keep the COP as high as possible. For the case of 500 m distance, the heat loss through the pipeline of the weak solution is 3 kW while the generator heat input is 140 kW. It should be noted that the loss is as small as 2 % of the heat input. Another viewpoint is exergy for evaluating the cycle. Exergy input to the generator is 29 kW when the steam temperature is 125 degC assuming the ambient temperature is 32 degC. On the other hand, the exergy destruction by the weak solution transportation is 0.5 kW for the case of 500 m distance. The destruction is less than 2 % in this case, which suggests that the solution transportation is not significant in terms of exergy as well. Consequently, it can be said from the experimental results that the cycle of STA holds the same behavior in steady state nevertheless of the distance between the generator/condenser side and the evaporator/absorber side.
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0m
200m
500m
1000m
Mass flow rate (kg h-1)
1400 1200 1000 800 600 400 200 0 Refrigerant
Strong solution Weak solution
Fig. 4. Effect of transportation distance on mass flow rate.
Ammonia concentration (%)
0m
200m
500m
1000m
120 100 80 60 40 20 0 Refrigerant
Strong solution Weak solution
Fig. 5. Effect of transportation distance on ammonia concentration.
0m
200m
500m
5
7
1000m
120
Temperature (degC)
100 80 60 40 20 0 1
2
3
4
6
8
9
10 11 12
-20 Fig. 6. Effect of transportation distance on temperature.
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Heating input
COP 160
0.6
120
0.4
80
0.2
40
0
Heat duty (kW)
Cooling output
COP (-)
0.8
0 0m
200m
500m
1000m
Fig. 7. Effect of transportation distance on COP. Therefore, it is expected that STA has almost the same performance with any distance cases. Figure 7 compares cooling output, heat input to the cycle and the COP of all cases. The COP indicates only thermal conversion performance of the cycle from the heat input to the refrigeration output. As shown in the graph, the COP of each case is commonly about 0.6. It should be emphasized that the result clearly indicates that the thermal performance of STA is not affected by the transportation distance even though the distance influences the power consumption of the pump to an extent. Based on the results mentioned above, it has been confirmed that STA, an ammonia absorption cycle with solution transportation, does not suffer from the transportation distance in terms of COP. It is remarkably interesting that the additional function of heat transportation gives no damage on the cycle performance as an absorption refrigeration cycle. This feature is supposed to be extended for longer distance cases more than 1000m because the cycle configuration is basically identical. When the transportation distance becomes longer, the solution pump has to have larger capacity accordingly to overcome the pressure drop. On the other hand, the pressure drop of the weak solution possibly dominates the transportation distance because it should be less than the pressure difference between the high pressure side and the low pressure side. It is approximately 1.2 MPa in this experimental setup, which is considered equivalent to 10km of the pipeline. If the distance is more than that, an additional pump is required to transfer weak solution from the generator side to the absorber side. 5.
CONCLUSION This study investigated the technological feasibility of thermal energy transportation by solution/refrigerant transportation. This technology named STA is an extended scheme of ammonia-water absorption refrigeration cycle. An experimental facility of 90kW was built to examine the real performance with solution transportation for the distance of 200m, 500m and 1000m which was emulated by adjusting the pressure drop in the solution pipes. The following was found out based on the experimental results. Although the distance of transportation changes, internal states of the cycle such as temperature and ammonia concentration remain the same. Solution transportation distance does not affect the performance of STA in terms of COP. The COP is observed to be 0.6 which is the same as that of conventional ammonia absorption chillers without transportation. It can be concluded that the function of thermal energy transportation is technologically feasible by means of solution transportation. It is interesting to note that such additional function can be attained without any functional damage to the absorption cycle performance. The behavior of STA in steady state was clarified to be insensitive to transportation distance in this study. On the other hand, dynamic response of the system is possibly different from the behavior of conventional ammonia absorption chiller without solution transportation. The experimental facility of STA developed in this study was employed to measure actual dynamic behavior of ammonia-water absorption cycle with solution transportation of 200m, which will be investigated in the next steps. It is
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expected to provide insights to understand how STA should be designed, operated and controlled appropriately.
ACKNOWLEDGEMENT This study was financially supported by New Energy and Industrial Technology Development Organization, an agency of the Japanese government. The authors also appreciate the cooperation of JX Nippon Oil and Energy Corporation who jointly conducts the project as a partner. REFERENCES [1] T. Kashiwagi, Eco-energy system for urban area. Transaction of Japan Society of Mechanical Engineers. 98 (917) (1995) 261–265 (in Japanese) . [2] Q. Ma, L. Luo, Z. R. Wang, G. Sauce, A review on transportation of heat energy over long distance: Exploratory development, Renewable and Sustainable Energy Reviews. 13 (6–7) (2009) 1532– 1540. [3] A. Kaizawa, H. Kamano, A. Kawai, T. Jozuka, T. Senda, N. Maruka, N. Okinaka, T. Akiyama, Technical feasibility study of waste heat transportation system using phase change material from industry to city, ISIJ International. 48 (4) (2008) 540–548. [4] T. Nomura, N. Okinaka, T. Akiyama, Technology of latent heat storage for high temperature application: A review. ISIJ International. 50 (9) (2010) 1229–1239. [5] T. Nomura, N. Okinaka, T. Akiyama, Waste heat transportation system, using phase change material (PCM) from steelworks to chemical plant. Resources, Conservation and Recycling. 54 (11) (2010) 1000–1006. [6] Sanki Engineering Co. Ltd. Homepage. www.sanki.co.jp/product/thc. 2016 (accessed June 2016) (in Japanese). [7] H. Oguraa, Energy recycling system using chemical heat pump container. Energy Procedia. 14 (2012) 2048–2053. http://dx.doi.org/10.1016/j.energy.2016.05.003. [8] J. NW. Chiu, J. C. Flores, V. Martin, B. Lacarriere, Industrial surplus heat transportation for use in district heating, Energy. 110 (2016) 139-147 [9] Y. T. Kang, A. Akisawa, Y. Sambe, T. Kashiwagi, Absorption heat pump systems for solution transportation at ambient temperature STA cycle, Energy. 25 (4) (2000) 355–370. [10] A. Akisawa, K. Araki, T. Miyazaki, Y. Ueda, T. Takei, Application of ammonia-water absorption cycle to transfer cooling and heating at ambient temperature, Proc. of 5th Asian Conference on Refrigeration and Air-conditioning, Tokyo. 2010 [11] P. Lin, , R. Z. Wang, Z. Z. Xia, Q. Ma, Experimental investigation on heat transportation over long distance by ammonia-water absorption cycle, Energy Conversion and Management. 50 (2009) 2331–2339. [12] A. Akisawa, T. Tomita, Y. Ueda, T. Takei, Heat transportation experiment over 50m by Solution Transportation Absorption chiller and its dynamic simulation, Proc. of 22nd Annual meeting of Environment and Engineering in JSME. Sendai, 2012 (in Japanese). [13] Y. K. Jo, J-K. Kim, S. G. Lee, Y. T. Kang, Development or type 2 solution transportation absorption system for utilizing LNG cold energy, International Journal of Refrigeration, 30 (2007) 978–985. [14] A. Akisawa, Y. Hamamoto, T. Kashiwagi, Performance of thermal energy transportation based on absorption system -Solution transportation absorption chiller-, Proc. of International Sorption Heat Pump Conference. Denver, 2005. [15] A. Akisawa, S. Mori, Y. Ueda, K. Araki, Performance of double effect solution transportation absorption cycle to utilize condensation heat of refuse power generation, Proc. of 23rd IIR International Congress of Refrigeration. Prague, 2011. [16] K. E. Herold, R. Radermacher, S. A. Klein, Absorption chillers and heat pumps, CRC Press. 1996
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