Energy and environmental research emphasizing low-rank coal -- Task 3.10, Gas separation and hot-gas cleanup

Abstract

Catalytic gasification of coal to produce H{sub 2}-, CO-, and CH{sub 4}-rich mixtures of gases for consumption in molten carbonate fuel cells is currently under development; however, to optimize the fuel cell performance and extend its operating life, it is desired to separate as much of the inert components (i.e., CO{sub 2} and N{sub 2}) and impurities (i.e., H{sub 2}S and NH{sub 3}) as possible from the fuel gas before it enters the fuel cell. In addition, the economics of the integrated gasification combined cycle (IGCC) can be improved by separating as much of the hydrogen as possible from the fuel, since hydrogen is a high-value product. Researchers at the Energy and Environmental Research Center (EERC) and Bend Research, Inc., investigated pressure-driven membranes as a method for accomplishing this gas separation and hot-gas cleanup. These membranes are operated at temperatures as high as 800 C and at pressures up to 300 psig. They have very small pore sizes that separate the undesirable gases by operating in the Knudsen diffusion region of mass transport or in the molecular sieving region of mass transport phenomena. In addition, H{sub 2} separation through a palladium metal membrane proceeds via a solution-diffusion mechanism for atomic hydrogen. This allows the membranes to exhibit extremely high selectivity for hydrogen separation. Specific questions to be answered in this project include: what are the effects of membrane properties (i.e., surface area, pore size, and coating thickness) on permeability and selectivity of the desired gases; what are the effects of operating conditions (i.e., temperature, pressure, and flow rate) on permeability and selectivity; what are the effects of impurities (i.e., small particulate, H{sub 2}S, HCl, NH{sub 3}, etc.) on membrane performance?