China has commissioned its first geothermal heating plant that utilizes supercritical CO2.

The China Huaneng Group Co. has initiated operations at its first geothermal heating plant in Zhengzhou, Henan Province, which employs supercritical carbon dioxide as the working fluid.

According to the diagram released by the company, this system features a single borehole that reaches a depth of 2500 meters. Subcritical CO2 is injected into the borehole at 10 ºC, where it is heated by the surrounding formation and then released as supercritical CO2 at 80 ºC. This supercritical CO2 is directed to a heat exchanger, which heats water that is subsequently sent to a heat pump.

The company claims that using supercritical CO2 will enhance heat extraction efficiency by approximately 20% and decrease energy consumption by 10%. Designed as a closed system, it does not draw groundwater or disrupt the underlying geological environment. Once fully operational, the system will meet the winter heating needs of over 18,000 m² of residential space.

The idea of utilizing supercritical CO2 in geothermal energy extraction has been extensively studied over the years. Notable examples include the CO2 Plume Geothermal concept developed at ETH Zürich in Switzerland and the technology behind the German startup Factor2 Energy.

It is essential to highlight that previous methods involving CO2 in geothermal systems typically entailed injecting it and allowing it to circulate within the geological formation. In contrast, China Huaneng's method circulates CO2 within a closed system. Nevertheless, the benefits of using CO2 remain applicable, as its higher kinematic viscosity enables greater heat absorption, while the thermosiphon effect minimizes the power required to circulate the fluid.