Gas turbines for carbon capture

The objective of this research was to investigate the influence of selective exhaust gas recirculation (S-EGR) applied to gas-fired systems and determine if energy and economic savings can be realised. The gas turbine experimental campaigns evaluated the performance of a micro gas turbine (mGT) under S-EGR conditions, simulated by injecting CO2 into the compressor inlet. The mGT performance was affected under these conditions in terms of efficiency, compressor operation and emissions, however, this was more prominent at part loads. The flue gas CO2 concentrations increased by up to 6 times (up to 10.1 vol% at 60 kWe) with respect to the reference case without S-EGR,which can be beneficial to improve the downstream amine capture plant (ACP) performance, as demonstrated by subsequent experimental campaigns. The first assessed ACP performance with flue gas CO2 concentrations of 5.2-9.0 vol%. The results showed that the specific reboiler duty reduced by 21% and the liquid-to-gas ratio increased from 2.59 to 4.22 between the lowest and highest flue gas CO2 concentrations tested. The plant performance was also analysed at varying reboiler temperatures (124-127°C), using a flue gas with 9.0 vol% CO2 concentration. The results indicated that the overall specific reboiler duty and CO2 capture efficiencies reduced at lower reboiler temperatures. Overall, the results indicate that S-EGR operation in the gas turbine could be beneficial since it can lead to reductions in overall energy costs. The economic analysis evaluated the application of two S-EGR configurations (parallel and hybrid) in combined cycle gas turbine (CCGT) power plants, with the cost of electricity ranging from $82-90 and $82-93 per MWhe, respectively. The cost of CO2 avoided for the parallel and hybrid schemes varied from $80-105 and $83- 119 per tonne of CO2 avoided. The sensitivity analysis performed also demonstrated the economic competitiveness of S-EGR against ACP and EGR.