Using Process Change Analysis to assess heat pump performance in a changing biodiesel production plant

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.