Thermodynamic and exergoeconomic analysis of a dual expansion and triple recuperation supercritical CO2 power cycle driven by DME-oxygen combustor

A direct-fired supercritical CO2 power cycle with a novel layout and dimethyl ether (DME) as fuel is proposed, named the dual expansion and triple recuperation cycle (DETRC). To obtain accurate cycle simulation results, the combustion products' state parameters and species concentrations are used as the inputs of cycle simulation, which are obtained from a three-dimensional combustion simulation. The performance of DETRC is compared with those of the direct-fired Allam cycle and other published direct-fired cycles. The effects of the CO2 recycling ratio, excess oxygen coefficient, in-combustor pressure, and turbine outlet pressure on the thermodynamic and exergoeconomic performance are investigated to obtain the optimal operating variables for DETRC. The results indicate that DETRC has excellent thermodynamic and exergoeconomic performance. Compared to the Allam cycle, the exergy losses of recuperators and coolers are reduced significantly, thermal efficiency is increased by 25.45 %, and the unit product cost is reduced by 18.31 % in the DETRC. Compared to the directfired cycles in the literature, the thermal and exergy efficiencies increase, and oxygen consumption reduces. The effect of the CO2 recycling ratio or excess oxygen coefficient on DETRC is non-monotonic. As the CO2 recycling ratio or excess oxygen coefficient increases, the thermal and exergy efficiencies increase and then decrease, and the unit product cost decreases and then increases. With in-combustor pressure increasing, the thermal and exergy efficiencies increase, unit product cost decreases, and the cycle performance is improved. As turbine outlet pressure increases, the thermal efficiency increases and then decreases, exergy efficiency increases, and unit product cost decreases and then increases. The optimal operating variables are that the CO2 recycling ratio is 0.95, the excess oxygen coefficient is 1.20, the in-combustor pressure is less than 30 MPa, and the turbine outlet pressure is 5.5 MPa.