Performance Improvement of a Supercritical CO2 and Transcritical CO2 Combined Cycle for Offshore Gas Turbine Waste Heat Recovery

The supercritical CO₂ (S-CO₂) and transcritical CO₂ (T-CO₂) combined cycle is a promising technology for the waste heat recovery of the offshore gas turbine. In this paper, a new system layout is proposed to investigate the thermodynamic and economic performances improvement of the S-CO₂-T-CO₂ combined cycle. Compared to the original systems, the residual heat of the topping S-CO₂ cycle is recovered and extra recuperation is added to the bottoming T-CO₂ cycle. Sensitivity analysis of different systems is carried out based on the mathematical model and multi-objective optimization is conducted. The net power out and the net present value (NPV) are chosen as the objective functions of thermodynamic and economic aspects. The results reveal that at the design point, the improved system has more than 8.23% increment on the net power output and 3.55% increment on the NPV. Besides, the optimized net power output of the improved system attains at least 5.16% increment with 3.15% increment for the optimized NPV at the same time. The improved system can be applied in some practical cases from both the thermodynamic and economic views.