Integration of Air Separation Unit With H2 Separation Membrane Reactor in Coal-Based Power Plant

Abstract

A novel process configuration consisting of integrating the air separation unit with a H2 separation membrane reactor (HSMR) in a coal gasification based coproduction facility with near zero emissions is described. The plant utilizes an air separation unit operating at elevated pressure to produce an Intermediate Pressure (IP) N2 stream in addition to the O2 required by the coal gasifier. The syngas produced by the gasifier after cleanup is supplied to the membrane reactor which produces H2 by shifting the carbon monoxide while simultaneously separating the H2. The IP N2 is used as sweep gas to assist in the separation of the H2 diffusing across the membrane walls by decreasing the partial pressure of the H2 on the permeate side. The total pressure of gases on the permeate side may thus be increased such that the H2 / N2 mixture may be fed directly to the gas turbines at the required pressure without requiring cooling and compression of the H2. An added advantage is that the total pressure differential across the membrane wall is reduced. The N2 in the fuel gas functions both as a thermal diluent for reducing the formation of nitrogen oxides and as additional motive fluid for expansion in the turbine. The carbon dioxide rich gas (non-permeate) leaving the membrane reactor after catalytic oxidation of the residual combustibles constitutes the carbon capture stream which may be further compressed and pipelined for CO2 sequestration. High purity H2 may be coproduced for export from a portion of the H2-N2 stream leaving the HSMR utilizing a Pressure Swing Adsorption (PSA) unit. The techno-economic advantages of such a coproduction facility are addressed.