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.

Carbon dioxide (CO₂) is a commercially viable working fluid for transcritical high-temperature heat pumps (HTHPs), but its low critical temperature (31°C) limits efficiency with cold sources above 40°C. Using a CO₂-based mixture with a higher critical temperature dopant can mitigate this issue by reducing temperature differences at the evaporator and enhancing heat transfer. This study focuses on fluorobenzene (C₆H₅F) as a dopant due to its high critical temperature, low cost, negligible global warming potential, and regulatory compliance in Europe.

To address the lack of vapor-liquid equilibrium (VLE) data for CO₂-fluorobenzene mixtures, an experimental campaign is conducted at the University of Brescia to measure bubble points using an isochoric apparatus. The data are used to select the most suitable equation of state for cycle calculations.

The heat pump’s analysis – both at design and off-design- is evaluated in a case study of integration with an Air Separation Unit (ASU). Waste heat from the ASU’s main air compressor is exploited through an intermediate closed-loop water cooling circuit operating at around 90°C. The heat pump upgrades this thermal energy to supply a local district heating network with a design supply temperature of 110°C. At this design point, the system achieves a coefficient of performance (COP) of 7.7, decreasing to 6.2 for higher off-design supply temperatures (e.g., 127°C).

Climate change necessitates innovative solutions for producing clean energy and decreasing atmospheric CO­₂ levels. Using CO­₂ as a working fluid in geothermal applications is a smart strategy to achieve this goal, as it has the potential to outperform conventional water-driven geothermal systems in terms of power produced, and for some cases, simultaneously increase the amount of CO­₂ that can be geologically sequestered. Power plant technology plays an important role in maximizing the value of geothermal resources. This is achieved through versatile power plant components that, barring large differences in CO­₂ purity, can operate across various geothermal systems. This research compares the use of similar power plant components and technologies across various types of CO₂-based geothermal energy systems: hydrothermal systems with CO₂ as a secondary working fluid, Advanced Geothermal Systems (AGS), Enhanced Geothermal Systems (EGS), and CO­₂-Plume Geothermal (CPG) systems. After providing ranges in possible operating conditions of these systems, the study employs TANGO (Techno-economic Analysis of Geo-energy Operations) to calculate the extracted energy and the Levelized Cost of Electricity (LCOE) for an example AGS, EGS, and CPG project, each with 10 MWe installed capacity. The findings indicate that CO­₂ is an effective geothermal working fluid and that most CO­₂ equipment can be used across the different geothermal systems. Given the extensive drilling required for AGS, LCOEs of CPG and EGS were found to be more competitive at current well construction costs.