Multi-objective optimization of a novel supercritical CO2 cycle for waste heat recovery from a gas engine's flue gas

Abstract This paper presents a novel optimal supercritical CO2 cycle for waste heat recovery (WHR) from a 1 MW gas engine's flue gas. In the present simple cycle, heat is absorbed from the hot flue gas in two stages. Following compression, CO2 is split, allowing a portion of it to absorb heat from hot CO2 leaving the turbine. At optimal conditions, the low-temperature (LT) heater and recuperator efficiently preheat CO2, increasing heat absorption from the flue gas and reducing the heat rejection through the pre-cooler, leading to increased output power and thermal efficiency. Thermodynamic and economic models are developed, and two cases of analyses and optimization using the differential evolution (DE) algorithm are performed. Firstly, the cycle's decision variables are optimized for maximum power output, and the cycle offers 181.67 kW of net power and the levelized cost of energy (LCOE) is 0.1061 /kWh. In comparison to recent studies using complex configurations under similar conditions, it produces more net power with low LCOE. The second case involves a 3E (energy, exergy and economic) analysis and multi-objective optimization using the Pareto frontier, yielding a power output of 178.57 kW with an LCOE of 0.0922/kWh, achieving a 13.10% reduction in the LCOE with 1.71 % loss in the power output. The present optimal cycle is a simple, compact, efficient and economical WHR system for a gas engine's flue gas.