Integration with Additional PSA System

An earlier proposal to partially recover H2 from these waste gases was to recompress the gas to a pressure of -7-8 atm and to employ a two-column, four-step Skarstrom PSA cycle65 consisting of adsorption, countercurrent depressurization, countercurrent purge, and pressurization with a part of the pure H2 product steps.66 About 

60%-70% of H2 from the main PSA waste gases can be recovered as pure H2 by this route, and the recovered H2 can be used to purge the main PSA adsorbers.26,66 The net result is increased overall H2 recovery by the integrated process. For example, the H2 recovery of the Gemini process described earlier can be increased from 87% to 95% by this option.26 This increase in H2 recovery becomes more important as the costs of natural gas and hydrogen continue to rise. 

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