Simulation of an Oxygen Membrane-Based Gas Turbine Power Plant: Dynamic Regimes with Operational and Material Constraints

Abstract

This paper investigates the transient behavior of a natural gas-fired power plant for CO2 capture that incorporates mixed-conducting membranes for integrated air separation. The membranes are part of a reactor system that replaces the combustor in a conventional gas turbine power plant. A highly concentrated CO2 stream can then be produced. The membrane modules and heat exchangers in the membrane reactor were based on spatially distributed parameter models. For the turbomachinery components, performance maps were implemented. Operational and material constraints were emphasized to avoid process conditions that could lead to instability and extensive stresses. Two load-control strategies were considered for the power plant with a gas turbine operating at constant rotational speed. In the first load-control strategy, variable guide vanes in the gas turbine compressor were used to manipulate the mass flow of air entering the gas turbine compressor. This degree of freedom was used to control the turbine exit temperature. In the second load-control strategy, variable guide vanes were not used, and the turbine exit temperature was allowed to vary. For both load-control strategies, the mean solid-wall temperature of the membrane modules was maintained close to the design value. Simulation reveals that the membrane-based gas turbine power plant exhibits rather slow dynamics; fast load following was hence difficult while maintaining stable operation. Comparing the two load-control strategies, load reduction with variable air flow rate and controlled turbine exit temperature was found to be superior because of the considerably higher and faster load reduction capability, increased stability of the catalytic combustors in the membrane reactor, and higher power plant efficiencies.