MIXED CONDUCTING MEMBRANES FOR PRESSURE-DRIVEN HYDROGEN SEPARATION FROM SYNGAS

Introduction Integrated Gasification Combined Cycle (IGCC) systems show tremendous potential for very efficient, environmentally friendly power generation. In IGCC systems, a combined cycle is employed in which syngas (CO+H2) is used to drive a gas turbine and the exhaust gases are then used to heat water/steam to generate superheated steam that drives a steam turbine. IGCC systems typically operate at efficiencies higher than 40%, whereas coalburning plants that employ flue gas desulfurization processes reach a maximum efficiency of 34%. A number of demonstration projects, such as the Wabash River Coal Gasification Repowering Project in Indiana and the Pinon Pine IGCC Power Project in Nevada, have been carried out as part of the Department of Energy (DOE) Clean Coal Technology Program. Despite the significant potential of IGCC systems, economic considerations still limit their wide-spread commercial applicability. Fortunately, the total hydrogen in raw syngas is usually greater than 200% of the required amount. Thus, one critical advance that would significantly enhance the commercial viability of IGCC systems is the recovery of hydrogen fuel from syngas as a byproduct. There are a number of technologies and combinations of technologies being considered as alternatives for recovery of hydrogen from syngas. These technologies include membrane separation, pressure swing adsorption (PSA), methanation and nitrogen wash techniques. Each of these techniques has its strong points, and the choice of the specific technique is usually dictated by the economics of the process and the purity of hydrogen desired. Since ultra-high purity (>99 %) H2 is a high value commodity, a technique that could generate such a high purity gas stream would be most attractive from an economic standpoint.