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

In this paper, we focus on the effect of the pinch-point-temperature difference (∆Tpinch) on the plant performance. ∆Tpinch is directly related with the size and cost of the heat exchangers and strongly influences the preheating-effect, which is the most characteristic feature of the Preheat-parallel configuration. First, we present the results of a detailed sensitivity analysis of ∆Tpinch. A higher ∆Tpinch results in a lower preheating-effect, a lower net power output and, correspondingly, lower plant efficiency. Furthermore, we compare the performance of the Preheat-parallel configuration with the convenient parallel and series CHP configurations. For all three configurations, the performance decreases with an increase of ∆Tpinch. For the considered thermal network requirements, the net power generation is the highest for the Preheat-parallel configuration. With respect to the parallel configuration, the gain in net power generation stays approximately constant (75°C/35°C TN) or decreases (75°C/50°C TN) with the imposed pinch-point-temperature difference. With respect to the series configuration, the gain in net power generation increases for a higher value of ∆Tpinch. This means that the impact of ∆Tpinch is the biggest for the series configuration, followed by the Preheat-parallel configuration, and that the impact on the performance of the parallel configuration is the smallest.