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.

Steam generating heat pumps show great potential for reducing carbon emissions in the industrial sector. However, predicting their performance is challenging as the exergy destruction of e.g., compressors and expansion valves increases with the temperature lift and condenser temperature. With over seventy design improvements mentioned in the literature, selecting the most effective design improvements is crucial. In this study, energy and exergy-based methods were compared in their ability to identify design improvements for a single stage subcritical heat pump to produce steam from hot condensate. The energy-based method suggested the addition of a sequential compressor with an intermediate cooler; however, this design did not improve the heat pump's techno-economic performance. The suggestion of adding either an internal heat exchanger or a flash vessel by exergy-based methods did lead in both cases to improved techno-economic performance. The internal heat exchanger performed best and increased the coefficient of performance from 2.3 to 2.8 and reduced operational costs by 0.8 M€ after 5 years of operation. Additionally, the initial investment decreased by 135 k€, and the total costs of operation decreased from 10.3 M€ to 8.7 M€. These findings show that exergy-based methods are the way forward in identifying effective design improvements for steam generating heat pumps.

Heat pumps have the potential to significantly reduce CO2 emissions in the industrial sector. However, their performance is likely to be affected by other process changes that are implemented to meet the CO2 reduction goals. This article aims to show how Process Change Analysis can be used to identify process changes that not only reduce total heating requirements but also improve the performance of a heat pump. The core of this analysis is the relation between the heat transfer by the heat pump and the pinch point of the processes excluding the heat pump connections, i.e. the background process. The impact of these changes is assessed with the help of a newly introduced approach, named the split exergy grand composite curve. The method is applied to a biodiesel production plant, a representative process for low-temperature processes where heat integration is limited by a single separation unit. Here, a heat pump could transfer about 1.9 MW from the condenser to the reboiler of the distillation column with a COP of 4.2 and a penalty of 30 kW, as heat is transferred above the pinch temperature of the background process. The penalty can be avoided by a process change that consists of replacing the wet water washer with a membrane separation unit, which increases the heat pump's COP to 4.8. Process Change Analysis thus proved to be a useful approach to identifying technologies that could be placed alongside with a heat pump and improve its performance, whilst reducing overall heating requirements.