Combined screw compressor ― expander in fuel cell application

摘要

Fuel cells, currently being developed for automotive applications, require a supply of pressurized air at about 3 bars abs. This is expelled in the reaction products, mainly as water and nitrogen, at approximately 100°C. The power input required to compress the air is approximately 20% of the cell electrical output. Hence, for the cell efficiency to be acceptable and to recover water from the reaction products, power needs to be generated by expansion of the reaction products and used to reduce the electrical output from the cell that is consumed by the compressor. It is shown that a twin screw machine can perform both the compression and expansion functions using only one pair of rotors. Moreover, by proper location of the ports, mechanical friction losses within it will be less than if the two functions are performed in separate machines.