Influence of the pinch-point-temperature difference on the performance of the Preheat-parallel configuration for a low-temperature geothermally-fed CHP

In this work, we investigate the performance of the so-called Preheat-parallel CHP configuration, for the connection to a thermal network (TN). A low-temperature geothermal source (130°C), and the connection to a 75°C/50°C and a 75°C/35°C thermal network are considered. For a pure parallel CHP configuration, the brine delivers heat to the ORC and the thermal network in parallel. However, after having delivered heat to the ORC, the brine in the ORC branch still contains some energy which is not used. The Preheat-parallel configuration utilizes this heat to preheat the TN water before it enters the parallel branch, where the TN water is heated to the required supply temperature. The Preheat-parallel configuration is especially favorable when connected to a thermal network with a low return temperature, a large temperature difference between supply and return temperatures—thereby exploiting the preheating-effect—and for high heat demands.