Multi-Objective Optimization of a Novel Supercritical CO2 Cycle for Waste Heat Recovery From a Gas Engine’s Flue Gas

Abstract

Abstract. This article presents a novel optimal supercritical CO2 cycle for waste heat recovery (WHR) from a 1-MW gas engine’s flue gas. In this cycle, heat is absorbed from the hot flue gas in two stages. Following compression, the working fluid is split so that a portion can absorb heat from the hot CO2 leaving the turbine. Under optimal conditions, the low-temperature (LT) heater and recuperator efficiently preheat CO2, increasing the heat absorption from the engine’s flue gas and reducing heat rejection through the precooler, leading to increased output power and thermal efficiency. Hence, thermodynamic and economic models are developed, and two analyses and optimization cases using the differential evolution (DE) algorithm are performed. First, the cycle’s decision variables are optimized for maximum power output, yielding 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. The second case involves a 3E (energy, exergy, and economic) analysis and multiobjective 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 only a 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.