Techno-economic optimization of biogas-fueled micro gas turbine cogeneration systems in sewage treatment plant

Abstract

The aim of this paper is to investigate the feasibility of a combined cooling, heating, and power generation system with a micro turbine using biogas as the fuel to supply the heat and electricity demands in a real wastewater treatment plant. The plant is optimized using the system’s total cost rate and the amount of the produced biogas as objective functions. The anaerobic digester is modeled using the ADM1 model. The optimization variables include digester hydraulic retention time, compressor pressure ratio, isentropic compressor efficiency, recuperator pinch time temperature, turbine isentropic efficiency, turbine input temperature, and the number of micro turbines. In the first scenario (business as usual), the optimal values of the system’s total cost rate and the amount of the produced biogas are 0.02561 $/s and 12.6235*103m3/day, respectively. In the environmental scenario, the optimum values of the total cost rate and the biogas flow rate are 0.0652 $/sand 12.6901*103m3/day, respectively. Scenario 1 has lower values of total cost rate and levelized cost of electricity and higher CO2 emissions than scenario 2. The surplus of electricity from the plant may be exported to the grid in the first scenario. However, some electricity will be imported from the grid in scenario 2. Finally, the effects of some important parameters have been assessed on the total cost rate using Sobol sensitivity analysis. Hydraulic retention time, power purchase price, and discount rate have the highest impacts on the system’s total cost rate by 15% while AD temperature has the lowest effect on total cost rate by 6%. In general, the results of this paper could be employed as a decision support tool for policy makers in energy sector as well as wastewater treatment plant managers to supply the energy demand of their plant.