Break-even of high-temperature heat pump integration for milk spray drying

Abstract

Heat pumps are a promising solution for reducing greenhouse gas emissions because they harness environmental or waste heat and can use renewable electricity. Technologically, temperatures up to 160 °C can already be achieved with market-available heat pumps while heat pumps achieving temperatures up to 200 °C are under development. This study focuses on the economic break-even points of market-available, prototypical and simulative heat pump concepts for milk spray drying using the Grand Composite Curve and the Modified Energy Transfer Diagram. Applying a regression-based targeting algorithm, the economic break-even price ratio and technical limit of the corresponding heat pump types are identified and quantified by the Heat Pumping Recovery Rate. The examined heat pump concepts show promising results for future energy price scenarios with the break-even point for full supply of milk spray drying up to 210 °C at electricity-to-reference-fuel price ratios of 1.20 for close-to-market Stirling heat pumps to 1.56 for simulated transcritical cascade cycles. Market-available heat pumps reach drying temperatures of 127.3 °C achieving coverage rates of 60.3% with price ratio requirements of 1.41. The results also emphasise the importance of adapting heat pumps to the process requirements precisely, especially for reaching high sink temperatures. Based on specific process requirements and the presented targeting methods, the selection of refrigerant and the configuration of the heat pump cycles should be done to minimise the Levelised Cost of Heating.