DEVELOPMENT OF TRIPLE-EFFECT ABSORPTION CHILLER-HEATER

Transcription

1 DEVELOPMENT OF TRIPLE-EFFECT ABSORPTION CHILLER-HEATER Kiyoyuki Mori, Japan Gas Association Masahiro Oka, Japan Gas Association Toshikuni Ohhashi, Japan Gas Association 1. INTRODUCTION Working at the request of the New Energy and Industrial Technology Development Organization (NEDO), since 2001 the Japan Gas Association (JGA) has been working on the development of a new triple-effect absorption chiller-heater in conjunction with four absorption chiller-heater manufacturers. Targets for the chiller-heater under development call for a reduction of over 30 percent in energy consumption over current double-effect absorption chiller-heater. A description of the development project is given below. 2. BACKGROUND AND OBJECTIVES OF DEVELOPMENT In recent years, energy conservation has become an important issue in air conditioning systems, and improvements are constantly being made in electrically powered heat pumps, centrifugal refrigeration machines, and other types of systems, which compete with absorption chiller-heaters, and this has led to an increase in demand for improvement in the efficiency of absorption chiller-heaters as well. However, over 20 years have passed since double-effect systems first began to be widely used, and while many improvements have been made, once a cooling COP of 1.35 is reached, there will be essentially no room left for further improvements. Thus in order to achieve further increases in efficiency, research will have to be performed towards the development of multi-effect systems. 1-6 (Note that the term COP refers to the ratio of the heating/cooling performance vs. the amount of heat input from the gas fuel as measured using a higher heating value (HHV).) The objective of the current project is to develop triple-effect absorption chiller-heaters, which would make it possible to realize much higher levels of efficiency and to work towards the development of a commercially viable version of such a system. 3. PROJECT DESCRIPTION 3.1. Principles and features of triple-effect absorption chiller-heater systems The triple-effect absorption chiller-heater being developed in this project consists of an ordinary double-effect lithium bromide (LiBr) /H 2 O cycle with an added high-temperature high-pressure generator. As may be seen in the Dühring diagram in Figure 1, there are a total of three generators (a high-temperature, a middle-temperature, and a low-temperature generator). By using gas heating or

2 some other form of heat source to Gas heat the high-temperature generator and using the high-temperature heat as it cascades downward : High-Temperature through the absorption cycle, it is Generator H 2 O possible to obtain a higher cooling : Middle-Temperature Generator COP than is possible with a C : Low-Temperature Generator double-effect system. The reasons LiBr/H 2 O C: Condenser why this design has been adopted E: Evaporator E A A: Absorber may be summarized as follows. (1) A LiBr/H 2 O system provides Temperature the best possible efficiency. Figure 1: The principles of a triple-effect cycle (2) Using this system together in conjunction with a system already proven in double-effect systems makes it possible to limit the amount of technology which must be developed to that used in the part of the system added to the double-effect system, thus increasing the probability that a commercially viable system might be developed within the limited amount of time allowed for development. (3) This design makes it possible to use many parts, which are already used in double-effect systems, thus helping to reduce production costs. However as may be seen from Figure 1, in a triple-effect system, the pressure and the temperature of the high-temperature generator are higher than in a conventional system. It is for this reason that it becomes necessary to develop technologies to make it possible to meet governmental restrictions concerning the safety of the boiler and pressure vessel and to prevent corrosion from occurring as a result of increases in the temperature of the LiBr solution. Pressure 3.2. Development targets The specifications called for under the current development project are as shown in Table 1 below. Note that these specifications call for the achievement of a cooling COP of 1.60 or higher (as measured using a higher heating value) through the use of the triple-effect cycle. In addition, in order to make it possible to respond to demand for replacement systems in existing buildings, these specifications also call for the total volume of the system to be kept within 120 percent of the volume of current systems, and in order to meet these objectives work is being performed to increase the efficiency and compactness of the absorber, evaporator, solution pump, and other components. Work is also being conducted on the development of technologies to make use of waste heat of co-generation systems. By improving the gas reduction ratio during usage of the waste heat by 20 percent or more over our current Genelink, absorption chiller-heater with auxiliary waste heat recovery.

3 Description Item Target Current system Increased efficiency through use of a triple-effect system CGS waste heat reuse technology Cooling COP 1.60 or higher (based on HHV) 1.07 Volume 120% or less (when compared to 100% current double-effect systems) Gas reduction ratio 20% or higher (when using waste 15% heat of co-generation systems) Table 1: Development targets 3.3. Issues involved in development As noted above, since the high-temperature generator in a triple-effect system would reach higher levels of pressure and temperature than in a conventional system, technologies must be developed to help prevent corrosion and a new once-through boiler type high-temperature generator must be developed in order to ensure increased safety. In addition to these factors, consideration must also be given to the technological difficulties, which might be involved in cycle optimization, increasing the efficiency and compactness of components, developing technologies for the use of waste heat of co-generation, and optimizing the control system Project organization An organizational chart showing the overall project organization and the participating manufacturers is shown in Figure 2 below. Ministry of Economy, Trade and Industry (METI) Japan Gas Association Development flow New Energy and Industrial Technology Development Organization (NEDO) Hitachi Industries Co., Ltd. Yazaki Corporation Kawasaki Thermal Engineering Co., Ltd. Parallel flow Bypass flow Reverse flow Daikin Industries, Ltd. Series flow Figure 2: Organizational chart The main roles of JGA is playing in this project are to oversee and direct the conduct of the project as a whole, to perform cycle simulations, to perform evaluations of corrosiveness, to evaluate

4 the performance of prototype systems, and to develop policies regarding means of dealing with safety regulations and other types of regulations. The absorption chiller manufacturers, on the other hand, are responsible for developing component technologies and prototype systems and performing evaluations of prototypes and performance. Since each of the participating manufacturers uses its own different solution flow system in their current double-effect systems, each manufacturer will develop its own flow system for use in the triple-effect system based on the flow system used in their current systems. Views of the double-effect flow systems used in each of the current systems and views of the flow systems being developed for the triple-effect systems are shown in Table 2 below. Note that Daikin Industries is developing a new improved flow system because it has decided that it would be too difficult to reach the target performance level using a simple series flow system. Finally, note that the prototype systems being developed by each of these manufactures are expected to have cooling capacities in the range of kw. Double-effect Double-effect Double-effect Hitachi Industries Co. Ltd. (Parallel flow) Triple-effect Yazaki Corporation (Bypass flow) Triple-effect Kawasaki Thermal Engineering Co. Ltd. (Reverse flow) Triple-effect

5 Daikin Industries, Ltd. (Series flow) Double-effect Triple-effect Simple series Improved design Table 2: Existing double-effect flow systems and new triple-effect flow systems now under development 3.5. Project schedule A rough overview of the project schedule is shown in Table 3 below. Note that the term of the project extends over four years in all until FY2004, and that plans call for the development of working commercial systems in about two years from that time. Item to be evaluated Fiscal Year Optimization of absorption cycle Development of technologies to prevent corrosion Development of technologies designed to improve efficiency and compactness Development of once-through high-temperature generator Development of waste heat usage technologies Production and evaluation of 527 kw prototype system Production and evaluation of first prototype system K H, Y, D Production and evaluation of second prototype system K H, Y, D Research directed towards development of a commercially viable system K: Kawasaki Thermal Engineering Co. Ltd. H: Hitachi Industries Co. Ltd., Y: Yazaki Corporation, D: Daikin Industries, Ltd. Table 3: Project schedule

6 4. RESULTS OF DEVELOPMENT WORK PERFORMED THUS FAR 4.1. Optimization of absorption cycle To gain a better understanding of the flow systems used in the double-effect systems currently being produced by the four participating manufacturers, a simulation program has been created and used to discover what cycle conditions would be required in order to achieve development objective using each of these flow systems and to learn more about the characteristics of each of these flow systems. An example of the results obtained from these simulations is shown in Figure 3. Temperature of [] Series 230 Bypass Reverse 220 Parallel Cycle COP[-] Figure 3: Comparison among cycle COP of four flow systems 4.2. Development of anti-corrosion technologies In order to construct a database which could be used by each of the participating manufacturers in selecting the proper metallic materials and inhibitors to be used in preventing corrosion, a series of tests were performed beginning first with a basic autoclave testing and then moving on to the testing of pipes closer to those which would be found in an actual system, and then high-temperature generator model tests were performed to evaluate the effectiveness of the materials and inhibitors used, thus confirming that the inhibitors being tested remained effective even at solution temperatures of over 200 C. An example of the results obtained from the autoclave testing is shown in Figure 4. In this particular test, a Li 2 MoO 4 inhibitor was used, and the concentration of the inhibitor was varied between 0, 100, and 300ppm, and the measurements here show the results obtained under each of these sets of conditions in terms of the amount of corrosion occurring over time to the carbon steel when the temperature of the solution was kept on 220 C. Amount of carbon steel corrosion [mg/cm 2 ] ppm Li 2 MoO 4 100ppm Li 2 MoO 4 300ppm Li 2 MoO Operation Time [hours] Figure 4: Results of autoclave test

7 Condenser Separator Mixing tank Cooling water Gas storage chamber Test pipe Refrigerant tank Electric heater Refrigerant pump Figure 5: Schematic diagram of pipe test A view of the methods used in pipe testing is shown in Figure 5.In the pipe testing, an electric heater was installed around a test section of pipe to heat the solution and generate a natural convection current within the solution inside the test system. Unlike the results that would be obtained by performing static autoclave testing, this method results in heat transfer and LiBr solution flow, thus making it possible to perform an evaluation of the corrosion characteristics of a system closer to that of an actual system. An example of the results obtained from the pipe tests is shown in Figure 6. In the test shown Amount of H2 gas Nml/h H2 gas Li2MoO Li2MoO4 concentration [ ] here, Li 2 MoO 4 was added to the absorption fluid at a concentration of 500ppm and the solution was then heated to a temperature of 153 C over a period of 150 hours, to a temperature of 200 C over a period of 200 hours, and then to a temperature of 220 C over a period of 1,950 hours, and measurements were taken of the Operation time [hours] amount of hydrogen gas generated and changes in the concentration of Figure 6: Results of pipe test Li 2 MoO 4 over time under each of these three sets of conditions Production and evaluation of a 527kW prototype system In order to verify the effectiveness of the triple-effect cycle and identify any problems that might exist in terms of durability, a 527kW prototype system was developed. A view of this prototype system

8 is shown in Figure 7, and a list of the target performance specifications and actual tested performance is given in Table 3. High- In the tests performed in temperature order to initial performance of the generator prototype system, it was found that while the cooling COP fell short of the project target of 1.6, it was possible to obtain a level of 1.49, which cannot be achieved using current double-effect systems, thus providing Figure 7: Appearance of 527kW prototype system evidence of the effectiveness of the triple-effect cycle system. After subjecting the prototype system to an accelerated durability test of 2000 hours of operation, the system was dismantled and checks were performed of the high-temperature generator, the liquid/vapor separator, the high-temperature solution pump, and other components. Item Target specification Actual performance Cooling capacity 527 kw 539 kw Cooling COP 1.4 or higher 1.49 High-temperature generator pressure 0.2 MPaG or less 0.19 MPaG High-temperature generator temperature Chilled water temperature (inletoutlet) Chilled water flow rate 90.7 ton/h 91.0 ton/h Power consumption 7.6 kw External dimensions Weight of system in operation 13.4 ton Table 4: Target performance specifications and actual tested performance As a result of these inspections it was found that no damage could be seen to have occurred to the interior of the heating tubes, the liquid/vapor separator, or the high-temperature solution pump axle bracket which make up the high-temperature generator combustion chamber, i.e., that component of the system which might be considered critically important in determining the durability of a triple-effect system.

9 After the completion of the dismantling and inspection of the system, the system was reassembled and restored to its original condition, and field tests were performed at a monitoring site so that the performance of the system could be observed under actual operating conditions and so that an evaluation could be performed of the system s durability. The results of the tests performed using the 527kW prototype system were then used to design and produce a new 1054kW prototype system, and although this system does not meet design targets in that it has a volume of 150 percent of that of current systems, it did reach the design target of providing a cooling COP of CONCLUSION A 527kW prototype system was reached a cooling COP of 1.49, a level that cannot be reached using double-effect systems. If it does prove possible to develop a working commercial version of a triple-effect absorption chiller, then it would be possible to develop systems providing much higher levels of efficiency than those of electric heat-pump systems, thus providing a clear advantage over electric systems and making it possible to look forward to the increased use of gas heating and cooling systems. Furthermore, using waste heat of co-generation systems would make it possible to improve the efficiency of such system to the point where they would become comparable to high-efficiency centrifugal refrigeration systems designed for use exclusively as cooling systems, and it would also contribute significantly to increasing the efficiency and encouraging more widespread use of gas co-generation systems. REFERENCES 1. Wang Hongbin, Lu Zhen, Li S Hixiang Research on Triple Effect Absorption Chiller/Heater, 20 th International Congress of Refrigeration, IIR/IIF, Sydney, F. Ziegler, G. Alefeld: Coefficient of Performance of Multistage Absorption Cycle, Rev. Int. Froid 1987 Vol.10 September. 3. L. W. Burgett, M. D. Byards, K. Schultz: Absorption Systems: The Future, More Than a Niche? ISHPC 99, Proc. of the Int. Sorption Heat Pump Conf. (1999). 4. F. Ziegler: Recent Developments and Future Prospects of Sorption Heat Pump Systems, Int. J. Term. Sci. (1999) 5. S. Kujak, K. Schultz: Demonstration of a Direct-fired Triple-effect Absorption Chiller, Energy Engineering Vol.97 (2000) 6. R. C. Devault: Triple-effect Absorption Chiller Cycles, 1992 International Gas Research Conference