Natural gas combined cycle with exhaust gas recirculation and CO2 capture at part-load operation

Abstract

This paper aims to evaluate part-load operation of a natural gas combined cycle (NGCC) power plant with exhaust gas recirculation (EGR) and a CO2 capture plant. Several studies have demonstrated the feasibility and the advantages of EGR at full load, but operation at part load is also important because it is a common condition when NGCC power plants are being used as backup for renewables. The results of this study show that the number of absorber trains is reduced from 4 to 3 with EGR. The efficiency of the NGCC plant with EGR was 0.5% points higher than a conventional NGCC at full load as a result of a higher CO2 concentration in the flue gas. However, this efficiency advantage decreased as the load was reduced from 100% to 50%, with both cases presenting the same efficiency at 50% load. This means that there was no benefit from the effect of EGR at lower loads. The efficiency of a NGCC plant with EGR and CO2 capture configuration decreased from 52.6% to 45.9% when the load was reduced from 100% to 50% compared with a conventional NGCC where the efficiency changed from 52.1% to 45.9%. It was concluded that a NGCC plant with EGR and CO2 capture is viable, results in lower capital costs due to the smaller number of absorber trains and yields slightly higher efficiencies, for operation at part-load down to 50%.