Improving plant-level heat pump performance through process modifications

Abstract

Heat pumps are a promising option to decarbonize the industrial sector. However, their performance at a plant-level can be affected by other process changes. In this work, process changes that improve the heat pump's performance have been identified using Process Change Analysis (PCA), where the background pinch point is used as a reference point for appropriate placement. The effects of the process changes on the heat pump's work requirements are studies by introducing exergy to PCA to form the split exergy grand composite curve. This graph shows the work potential of the streams connected to the heat pump and therefore its work targets. The framework is demonstrated in two case studies. In a biodiesel production plant, it allowed to identify technologies that enhance heat pump performance while reducing overall heating requirements. Here, a heat pump transfers 1.9 MW with a COP of 4.2 but incurs a 40 kW penalty for transferring heat above the background process's pinch temperature. Replacing the wet water washer with a membrane separation unit avoided this penalty, while drastically reducing energy requirements from 0.9 MW to 0.3 MW. in a vinyl chloride monomer-purification process, PCA showed how the extraction of heat by the heat pump impacted the formation of the background pinch, from which an implementation strategy was derived that increased the heat pump's plant-level performance by 6.5% with respect to standard implementation.