Analysis and design of an ultra-high temperature heat pump using CO2 providing carbon-neutral industrial heat

Ensuring a CO2-neutral supply of process heat is critical for advancing the energy transition in industrial sectors. One promising approach is the integration of high-temperature heat pumps, powered by renewable electricity, to generate process steam, which is widely used in the chemical industry at pressures up to 110 bar. An ultra-high temperature heat pump concept with supercritical CO2 as the working medium, designed for the supply of a generic chemical plant, was developed as part of the project CO2NEICHEM. This study evaluates this high-temperature heat pump using a transcritical reverse Brayton cycle with an internal heat exchanger and an expansion turbine. The process involves compressing water to operating pressure, followed by preheating, evaporation and superheating using the transcritical reverse Brayton cycle for heat supply. Various circuit designs and key sensitivities are analyzed to optimize performance. Additionally, it is explored how the efficiency of the heat pump varies with process steam pressure and superheating temperature. Furthermore, part load operation is considered by varying the heat source flow. In all configurations, the study investigates thermodynamic modeling details of the cycle and its heat exchangers and turbomachinery and the resulting performance. Moreover, first drafts of the turbomachinery design are presented for a selected application case.