Economics of hydrogen recovery processes for the purification of hydroprocessor purge and off-gases

Pressure swing adsorption, membranes and conntercurrent gas-liquid contacting were evaluated for the purification of hydrocracker and hydrotreater purge and off-gases. Industrial cases relevant to upgrading and refining were examined, and the most economic and technically suitable options were determined. For pressure swing adsorption (PSA), surprisingly, the best economics were at lower recoveries, when tail gas met fuel gas pressure requirements. This eliminated tail gas compression which is relatively expensive. Membranes were marginally better than PSA at higher feed pressures (similar to 7.0 MPa), and there was no advantage in combining these processes due to loss of economies of scale. Countercurrent gas-liquid contacting, which recovers hydrogen near feed pressure, has an advantage over both PSA and membrane when the feed pressure is high. A sensitivity analysis indicated that high feed gas capacity, high purity, and a low fuel gas price favor hydrogen recovery processes. The impact of increased recovery and purity on the economics of hydrogen recovery was negligible compared to the effect of unit sizes (economy of scale). (C) 1999 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.