Study On Two Stage Compressor Based On Metal Hydrides

Environmental protection has become a tough issue in all over the world. As a secondary energy source, hydrogen is a promising clean fuel in the 21st century. Therefore, it is globally recognized that hydrogen is an ideal candidate to replace the limited primary fossil fuel. Supported by the National 863 Project and the National Natural Science Foundation of China, after two suitable metal hydride alloys has been chosen according to the requirements of the two stage compression system, this paper completed the CFD simulation on reactor filled with alloys and built up the two stage compression system, whose characteristics and operating conditions have been studied through experiments later. The main conclusions were as follows:According to the requirements of two stage compressor based on metal hydrides, La0.4Y0.6Ni4.8Al0.2 alloy and La0.3Y0.7Ni4.8Mn0.2 alloy have been used as the working material for the first stage compression system and the second stage compression system, respectively.The computational fluid dynamics (CFD) method was used to simulate the performance of heat and mass transfer on the reactor bed with segmental baffle plate. The simulation on the reactor bed with different numbers of baffles and research on the unsteady state of the bed under a particular baffle number were carried on.The flow performance of reactor increased and heat transfer properties of reactor changed less with the baffle number. Hence, the baffle of spiral-plate type was indicated to optimize the above reactor. Thought the simulation process, it was proved that the new type reactor showed better heat and mass transfer performances than the reactor with segmental baffles.For the first stage compression system (lower pressure), the optimal operating parameters have been purposed as hydrogen-absorbed time for 3min, absorption pressure at 2.5MPa, absorption temperature at 293K, desorption temperature at 363K, and the heating time for 30s, cooling time for 50s, hydrogen-desorbed time for 250s. Through the experiments, it was found that the pressure in buffer vase was over 8MPa after three compression cycles. And for the second stage compression system (higher pressure), alloys absorbed the hydrogen from the buffer vase in the outlet of first stage compression system. After several tests, its optimal operating parameters were set as hydrogen-absorbed time for 3min, absorption temperature at 303K and desorption temperature at 428K. As a result, the two stage compressor with optimal operating parameters could realize the continuous ab/desorption process and compress the hydrogen from 2.5MPa to 36.5MPa in a compressing ratio of 14 after ten cycles. The average hydrogen flow and hydrogen-desorbed amount was 11.75L/min and 25.7mol, respectively. The compression energy efficiency of whole system was 3.9%.