Improvement design and analysis of a supercritical CO2/transcritical CO2 combined cycle for offshore gas turbine waste heat recovery

Abstract

The supercritical CO2 (S–CO2) and transcritical CO2 (T-CO2) combined cycle is considered a promising technology for offshore gas turbine waste heat recovery. To further improve the thermodynamic and economic performances of the S–CO2/T-CO2 combined cycle for offshore gas turbine waste heat recovery, a new system layout is proposed in this paper. The net power output and net present value (NPV) are chosen as the objective functions of thermodynamic and economic performances, respectively. Compared to the basic systems presented by previous researchers, the new proposed S–CO2/T-CO2 combined cycle layout is modified in two aspects. One is that the residual heat of the topping S–CO2 cycle can be recovered by the bottoming T-CO2 cycle. The other is that a split flow branch is added in the bottoming T-CO2 cycle. The sensitivity analysis of different systems is carried out to explore the allowable ranges of independent parameters. Compared with the two basic layouts (Basic-I and Basic-II), the simulation results at the design point reveal that the proposed system has more than 10.53% increment on the net power output and 7.87% increment on the net present value (NPV). Besides, the multi-objective optimization results indicate the proposed system attains at least 8.30% increment on the optimized net power output and 3.79% increment on the optimized NPV at the same time. It is proved that the proposed system can be applied in some practical cases from the thermodynamic and economic views.