Optimization of steam-methane reforming process using PSA off gas

This study aims to analyze the effect of PSA off gas utilization on fuel processing system combined with PSA (Pressure Swing Adsorption) system to produce more than 99% hydrogen for LT-PEMFC (Low Temperature Proton Exchange Membrane Fuel Cell) supply. An analysis was performed to optimize the operating conditions of a fuel processing system coupled with a PSA system by utilizing PSA off-gas to supply hydrogen to a 10 kW LT-PEMFC system. The performance and efficiency of the entire system were investigated at a steam-methane reactor temperature of 600 °C–800 °C, a water gas conversion reactor temperature of 200 °C–400 °C, a PSA recovery ratio of 60%–95%, a pressure of 1 bar, and 9 bar using Aspen Plus®, Aspen adsorption®, and Aspen Energy Analyzer® simulators. The sensitivities of various parameters affecting the process were analyzed to obtain optimized conditions for the entire system. Simulation results show that the optimal reformer temperature depends on the PSA recovery. The overall maximum efficiency is 78.67% at a process pressure of 9 bar the PSA recovery ratio of 95% and a temperature of 800 °C. In contrast, the highest efficiency under the 1 bar process condition is 70.55%, with an operating temperature of 600 °C and PSA recovery of 95%, which is relatively lower than the 9 bar process. Subsequently, pinch analysis and economic analysis including exergy analysis according to PSA recovery were conducted on these processes, showing that the thermal efficiency of the 9 bar process is relatively higher. The economic analysis indicated that the optimal profit is achieved at a PSA recovery of approximately 70∼75% and more than 40.2% of energy can be saved by utilizing PSA off gas to supply reaction heat for methane-steam reforming.