Optimal configuration for a low-temperature geothermal CHP plant based on thermoeconomic optimization

Abstract

Abstract In this paper, we propose a thermoeconomic optimization procedure for four configurations of low-temperature geothermal combined heat-and-power (CHP) plants. The series, parallel, preheat-parallel and HB4 configurations are investigated. Electricity is produced via an organic Rankine cycle (ORC) and two types of district heating (DH) systems are considered for the heat delivery: a 90/60 and a 65/40 DH system. The objective is to maximize the net present value (NPV) of the CHP plant for given DH system requirements. We conclude that, under the assumptions considered, the NPV can be increased from\xa0−2.81MEUR (unprofitable) for a stand-alone electrical power plant to 12.5, 28 and 58MEUR (economically feasible) for the optimal CHP, and for a heat demand of 5, 10 and 20\u202fMW th, respectively. Also, the exergetic plant efficiency is higher for the CHP plants, which means that the geothermal energy source can be utilized in a better way. Furthermore, we have found that the series CHP is generally the optimal CHP configuration. Only for the 90/60 DH system and low heat demands, the HB4 is more suitable. Compared to the simple series and parallel CHPs, the HB4 configuration has a 16% and 5.5% higher NPV, for heat demands of 5 and 10\u202fMW th, respectively.