Impacts of exhaust gas recirculation (EGR) on the natural gas combined cycle integrated with chemical absorption CO2 capture technology

Abstract

AbstractIncreasing CO2 concentration in exhaust gas is a potentially effective method to reduce the high electrical efficiency penalty caused by chemical absorption. By varying the exhaust gas recirculation (EGR) ratio, the exhaust gas mass flow and CO2 concentration fed to the chemical absorption unit change. The impacts of EGR applied to a combined gas turbine cycle were investigated quantitatively on the energy demand of MEA-based chemical absorption. Simulations show that compared to a combined cycle without EGR, a recircualtion ratio of 50 could increase CO2 concentration from 3.8mol% to 7.9mol% and reduce the mass flow of the absorber feed stream by 51.0%. Correspondingly, the total thermal energy consumption of the reboiler is reduced by 8.1%. From the aspect of electrical efficiency, the optimized EGR ratio is about 50%, which can increase the overall efficiency by 0.4 percentage point of NG LHV, compared to the system without EGR. In addition, EGR reduces the O2 concentration in exhaust gas. On one hand, the low oxygen concentration may have negative effects on combustion stability and completeness, which can be offset by oxygen enrichment or novel combustor configuration; but on the other hand, it may result in positive effects on the reductions of NOx emission and amine degradation