Part load operation of natural gas fired power plant with CO₂ capture system for selective exhaust gas recirculation

This work investigates base and part load operation of natural gas combined cycle power plant integrated with post-combustion CO₂ capture plant and selective exhaust gas recirculation scheme. Decarbonizing of natural gas combined cycle power plant is complex due to the higher flue gas flow rate with the least CO₂ content ~ 3–4 vol% with residual 20% O₂ and 77% N₂ content. Therefore, the effect of series, parallel and hybrid selective exhaust gas recirculation is examined, a concept where selectively CO₂ can be recycled back and mixed into the ambient air to the inlet feed of the compressor thereby reducing the flue gas flow rate and enhancing CO₂ content at the inlet of capture plant. The study is novel in a way that part-load performance at 80, 60 and 40% for parallel and hybrid scheme of selective exhaust gas recirculation is analyzed through process simulation in Aspen Plus for 606 MW commercial-scale natural gas combined cycle power plant coupled with an amine-based CO₂ capture plant. It is found that the simulation results of power plant and CO₂ capture plant model agrees well with the experimental results. Further, the performance results show the viability of base and part load operation of natural gas combined cycle power plant integrated with CO₂ capture plant by enhancing the CO₂ concentration for hybrid configuration to approximately 19 vol%. For parallel configuration, CO₂ content increases to around 13–14 vol% at 70% recirculation ratio in comparison to 6.6 vol% for simple EGR at 35% ratio. It is found that the selective exhaust gas recirculation offers more stable combustion by maintaining O₂ content at 19 vol% at combustor inlets for parallel and hybrid cases and the flue gas flow rate reduces to 68 and 70%, respectively thus reducing the size of the capture plant. The specific reboiler duty for hybrid, parallel, and series configuration reduces to 3.19, 3.25, and 3.31 MJ/kg CO₂, respectively in comparison to 3.54 MJ/kg CO₂ for base case natural gas combined cycle power plant coupled with MEA-based CO₂ capture unit. Whereas for 80 to 40% load change, the specific reboiler duty drops from 1.78% to 1.14% for parallel and hybrid configurations, respectively. In conclusion, hybrid selective exhaust gas recirculation configuration shows less efficiency penalty from base load to 40% part load and results in a decrease in specific reboiler duty in comparison to parallel configuration. Therefore, the study is innovative in an aspect that part-load performance at 80, 60 and 40% is performed, and results show a similar pattern as of baseload operation.