Exergoeconomic analysis of a novel trigeneration cycle based on steel slag heat recovery and biogas production in steelmaking plants

This study presents an analysis of a combined heating, cooling and power cycle that recovers the thermal energy of waste steel slag. The cycle utilizes the biogas produced from anaerobic digestion process of wastewater and sewage of residential areas. A thermodynamic model used for the trigeneration cycle and the performance of the cycle investigated from exergy and exergy-economic aspects. The power production capacity of the cycle, the cooling capacity and hot water production rate achieved 700 kW, 40 tons of refrigeration and 29400 kg/h, respectively. Also, the results of exergy-economic analysis indicate that the costs of power exergy, cooling and heating produced by the combined cycle are 30.14 $/h, 28.73 $/h and 29.25 $/h, respectively. Among six working fluids that examined for the organic Rankine cycle, R123 had the highest efficiencies (16% to 28%) in the turbine inlet temperature range of 200 degrees C to 420 degrees C and the highest output power was about 50 kW. Moreover, the highest growth rate of exergy efficiency and power generation in this temperature range observed when HFE7000 used as the working fluid.