On-site demonstration of an elevated temperature hydrogen clean-up unit for fuel cell applications

Abstract

Hydrogen from coal-based syngas is usually purified by deep desulfurization and decarbonization scrubbing technologies. Such electricity consuming processes cost a large number of heat exchangers and compressors. In this study, a two-stage demonstration unit had been constructed and demonstrated to purify hydrogen (including useful nitrogen for ammonia synthesis) from on-site sideline shift gas mixture at Yangmei Fengxi ammonia plant. For the first stage, an 8-column hydrogen purification process by novel elevated temperature pressure swing adsorption (ET-PSA, operated at 180 to 220 °C) was developed and demonstrated to capture H2S and CO2 simultaneously by hydrophobic activated carbon (AC) to reduce the impurities compared to that of room temperature PSA. Working condition at elevated temperature was proved to be appropriate and stable for reversible H2S removal by AC. The second stage was a temperature swing adsorption for deep purification of CO to 0.2 ppm by commercial CuCl monolayer dispersed zeolites (PU-1 synthesized by Beijing Peking University Pioneer Technology Co., Ltd.). In order to examine the standard of trace impurities such CO and H2S in product H2, the purified H2 was offered to a 3 kW proton exchange membrane fuel cell (PEMFC) stack to prove that all carbon and sulfur impurities met the demand not only for ammonia synthesis, but for PEMFC as well. Besides, two novel PSA steps: high pressure steam rinse and low pressure nitrogen purge were adopted to improve H2 recovery to above 93%. To demonstrate its stability, over 2500 h of operation had been carried out on the small-scale demonstration rigs by far.