Geothermal assisted Rankine cycle for performance enhancement of a biomass-driven power plant; Thermoeconomic and environmental impact assessment

In view of the environmental concerns of increasing fossil fuel consumption, the renewable energy sources are promising alternatives, among which the biomass and geothermal energies are the two most common and mature ones. In the present research, a novel Electricity Generation System (EGS) driven by hybrid biomass fuel and geothermal source is developed and its performance is compared with Typical EGS (TEGS) driven by only the biomass fuel. The TEGS consists of a gas turbine cycle and a steam Rankine cycle equipped with an open-feed water heater (OFWH). In the proposed Hybrid Electricity Generation System (HEGS), the geothermal energy is deployed to heat the feedwater before entering the OFWH, as a result the bottoming Rankine cycle yields more electricity. However, a comprehensive investigation from technical and economic standpoints is required to compare its performance with the relevant TEGS. Therefore, through the application of thermodynamic, thermoeconomic, and environmental methodologies, the considered EGSs performance are modeled and comprehensively analyzed. Based on the modeling results, the maximum exergetic efficiency for the TEGS and HEGS is achieved, respectively as 40.8% and 43.05% under the gas turbine inlet temperature of 1550 K. Final optimal operating conditions are determined through a multi-criteria optimization respect to exergetic efficiency and cost criteria. Under these working conditions, the LCOE and exergetic efficiency for the TEGS are calculated to be respectively as 71.22 $/MWh and 43.22%. At this point, net electricity, total exergy destruction rate, and CO2 emission rate are estimated to be as 7750 kW, 9446 kW, and 0.7401 kg/kWh, respectively.