Energy, Exergy, Exergoeconomic and multi-objective optimization of an integrated geothermal trigeneration system

In the present paper, energy, exergy, and exergo-economic assessment and multi-objective optimization of a geothermal CCHP cycle are proposed. The original coal-fed multi-utility cycle was recently proposed: here, an updated geothermal fueled version, working with primary heat at lower temperature and with a supercritical power cycle, is investigated. In order to optimize this system, nine different design variables are considered. Two defined objective functions are exergy efficiency and cost rate (the sum of purchase costs and exergy destruction costs). Besides, a sensitivity analysis of effects of inlet pressure of turbine 1 (which works in the supercritical condition) and inlet temperature of turbine 2 changes on the cycle performance and exergy and economic parameters are investigated. Also, the effect of well depth on electricity cost and LCOE has been considered. Results show that increasing the inlet pressure of turbine 1, raises the exergy efficiency, net work, electricity and investment, and O&M costs and decreases the LCOE and heat production for heating consumption. Also, exergy analysis of the system shows that the highest exergy destruction is related to low-pressure vapor generator. According to economic analysis, results illustrate that increasing the well depth causes a rise in LCOE and electricity cost. Besides, increasing the inlet temperature of turbine 2, raises the exergy efficiency and reduces the exergy destruction of the cycle. This cycle's obtained optimization results show that the exergy efficiency at the selected optimum state is 22.4% higher, and the cost rate is 15.7% lower than the base case. Additionally, at the optimum point, the exergy destruction, total PEC, and electricity cost are 14.2%, 6%, and 9.5% lower than the base case, as well as COP is 10.7% higher than the base case.