Thermoeconomic Optimization of COOLCEP-S: A Novel Zero-CO₂-Emission Power Cycle Using LNG (Liquified Natural Gas) Coldness

This paper presents a thermoeconomic optimization of a novel zero-CO₂ and other emissions and high efficiency power and refrigeration cogeneration system, COOLCEP-S† which uses the liquefied natural gas (LNG) coldness during its revaporization. It was predicted that at the turbine inlet temperature (TIT) of 900°C, the energy efficiency of the COOLCEP-S system reaches 59%. The thermoeconomic optimization determines the specific cost, the cost of electricity, and the system payback period. The optimization started by performing a thermodynamic sensitivity analysis, which has shown that for a fixed TIT and pressure ratio, the pinch point temperature difference in the recuperator, ΔT_p1, and that in the condenser, ΔT_p2, are the most significant unconstrained variables to have a significant effect on the thermal performance of this novel cycle. The thermoeconomic analysis of the cycle (with fixed net power output of 20 MW and plant life of 40 years) shows that the payback period with the revenue from electricity and CO₂ mitigation was ∼5.9 years, and would be reduced to ∼3.1 years when there is a market for the refrigeration byproduct. The capital investment cost of the economically optimized plant is estimated to be about $1,000/kWe, and the cost of electricity is estimated to be 0.34–0.37 CNY/kWh (∼0.04 $/kWh). These values are much lower than those of conventional coal power plants being installed at this time in China, which, in contrast to COOLCEP-S, do produce CO₂ emissions at that.