CO2 Sequestration From IGCC Power Plants by Means of Metallic Membranes

Abstract

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 85%vol 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.