CO2 Sequestration From IGCC Power Plants by Means of Metallic Membranes

This paper investigates 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 shift (WGS) reactor that converts most of CO contained in the syngas into $CO2$ and $H2$⁠. The syngas then enters a WGS membrane reactor where the syngas undergoes further shifting; simultaneously, $H2$ in the syngas permeates through the hydrogen-selective, dense metal membrane into a counter-current nitrogen “sweep” flow. The permeated $H2$⁠, diluted by $N2$⁠, 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 $H2$⁠. 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 $85vol%$ of the $H2+CO$ in the original syngas is extracted as $H2$ by the membrane reactor, the membrane-based IGCC systems are more efficient by $∼1.7$ percentage points than the reference IGCC with $CO2$ capture based on commercially ready technology.