Exergoeconomic analysis of a combined cycle system utilizing associated gases from steel production process based on structural theory of thermoeconomics

Exergoeconomic analysis plays an important role in finding ways to improve the performance of a complex thermal system. In this article, exergoeconomic analysis had been performed for a combined cycle system, which was proposed by authors, utilizing associated gases (blast-furnace gas, coke oven gas and sintering waste gas) from steel production process based on structural theory of thermoeconomics. Three exergoeconomic indexes (the cost difference, the relative cost difference and the exergoeconomic factor) were calculated to evaluate the thermoeconomic performance of each component. Moreover, the influences of the decision variables (the pressure ratios and the isentropic efficiencies of air compressor and blast-furnace-gas compressor, the temperature of combustion products entering gas turbine, and the isentropic efficiencies of gas turbine and steam turbine) and the capital costs (equipment purchase and fuel) on the unitary exergetic and monetary costs of production were also investigated. The analysis shows the deep relations of the unitary costs to the changes in these parameters and the superiorities of the proposed system emerging gradually through comparing with other systems (the combined cycle system with afterburning chamber in heat recovery steam generator, the combined cycle system without afterburning combustion, and the power generation system of steam turbine).