CO2 sequestration from IGCC power plants by means of metallic membranes

This paper in vestigates novel IGCC plants that employ hydrogen separation membranes in order to capture carbon dioxide for long-term storage. The thermodynamic performance of these membrane-based plants are compared with similar IGCCs that capture CO2 using conventional (i.e., solvent absorption) technology The basic plant configuration employs an entrained-flow, oxygen-blown coal gasifier with quench cooling, followed by an adiabatic water gas shaft (WGS) reactor that converts most of CO contained in the syngas into CO2 and H-2. The syngas then enters a WGS membrane reactor where the syngas undergoes further shifting; simultaneously, H-2 in the syngas permeates through the hydrogen-selective, dense metal membrane into a counter-current nitrogen sweep flow. The permeated H-2, diluted by N-2, constitutes a decarbonized fuel for the combined cycle power plant whose exhaust is CO2 free. Exiting the membrane reactor is a hot, high pressure raffinate stream composed primarily of CO2 and steam, but also containing fuel species such as H2S, unconverted CO, and unpermeated H-2. Two different schemes (oxygen catalytic combustion and cryogenic separation) have been investigated to both exploit the heating value of the fuel species and produce a CO2-rich stream,for long term storage. Our calculations indicate that, when 85 vol % of the H-2+CO in the original syngas is extracted as H-2 by the membrane reactor, the menbrane-based IGCC systems ore more efficient bv similar to 1.7 percentage points than the reference IGCC with CO2 capture based oil commercially ready technology.