Thermodynamic modelling and thermoeconomic optimization of a biogas energy plant in Afyonkarahisar

This thesis carried out thermodynamic modeling and thermoeconomic optimization of a biogas power plant in Afyonkarahisar. The power plant has four gas engines and produces 4000 kW of power with 96 tons of chicken manure daily. In the preheated gas cycle used in the power plant, the exhaust gases are used once after the turbine and released into the atmosphere. The existing power plant has been optimized thermodynamically and thermoeconomically to use the waste heat of the exhaust gases, which still have high energy and less gas emission to the environment. For this purpose, three models have been developed that can be integrated into the existing power plant to recover the waste heat of exhaust gases. Thermoeconomic analysis and optimization are performed with the data obtained by making a detailed thermodynamic analysis of the developed models. Analyzes and optimizations of the systems are performed in EES (Engineering Equation Solver) software, and the results are compared by making detailed energy and economic simulations of the systems in Aspen Plus software with the data obtained. In Model 1, it is proposed to integrate ORC (Organic Rankine Cycle) to produce additional electricity using the waste heat of exhaust gases. In Model 2, a heating unit and a cooling unit have been proposed for heating and cooling by using waste exhaust gases in addition to electricity generation In Model 3, hydrogen production is proposed to produce electricity from waste heat of the exhaust gases, together with ORC, from the by-products of biogas and preheating with exhaust gases to store excess electricity from water. According to the thermodynamic and thermoeconomic analysis results of the optimized power plant, the energy and exergy efficiencies of Model 1 are 50.74% and 44.47%. By producing 5043 kW of net power, the unit electricity cost has been calculated as 0.03778 $/kWh. The power capacity, energy and exergy efficiencies of Model 2 are 4000 kW, 74.88% and 50.62%, respectively. Unit costs of electricity produced, heating and cooling have been calculated as 0.04176 $/kWh, 0.0352 $/kWh and 0.0178 $/kWh, respectively. The net power capacity, energy and exergy efficiencies of the Model 3 are 5792 kW, 41.55% and 36.42%, respectively. The unit cost of the electricity produced has been calculated as 0.03922 $/kWh. Finally, the mass flow rate and unit cost of hydrogen produced from biogas by-products by using the electricity produced in ORC were calculated as 0.007447 kg/h and 3.191 $/kg, respectively. Keywords: Biogas, Thermodynamic analysis, Thermoeconomic analysis, Optimization