Thermoeconomic analysis and multiobjective optimization of a combined gas turbine, steam, and organic Rankine cycle

Abstract

Because of the fossil fuels crisis in recent years, efficient working of power producing cycles has gained considerable importance. This study presents a detailed exergoeconomic analysis of a proposed combination of a gas turbine (GT), a steam Rankine cycle (SRC), and an organic Rankine cycle (ORC), which are coupled together to obtain the maximum heat recovery of the GT exhaust gas. The proposed cycle was analyzed from both thermodynamic and economic viewpoints. The exergy efficiency and product cost rate of the introduced cycle were optimized simultaneously using multiobjective optimization with seven decision variables, including steam turbine inlet pressure and temperature, ORC turbine inlet pressure, ORC and steam turbine back pressures, and pinch point of heat exchangers. Sensitivity analysis revealed that the steam turbine back pressure and inlet pressure had the highest impact on product cost rate and exergy efficiency, followed by ORC turbine inlet pressure and back pressure. Also, the exergoeconomic analysis showed that the combustion chamber had the highest sum of exergy destruction costs and investment costs; more attention should thus be paid to its design procedure. Under the design conditions, the exergy efficiency of 40.75% and product cost rate of 439 million $/year could be achieved.