New process offers promising route to decarbonising thermal energy

Around 90% of the world’s energy use is linked to the generation or manipulation of thermal energy (heat). This typically involves fossil fuels, such as coal, oil or gas, which are some of the major contributors to carbon emissions and climate change. Finding ways to decarbonise heat supplies is crucial if we want to make energy sustainable. Alongside increasing reliance on renewable energy sources, such as solar and wind, the recovery of industrial waste heat offers a promising route to reducing carbon emissions. However, a key challenge remains – neither of these options is as stable as fossil fuel. For researchers, a key focus now is to find more effective ways to store thermal energy until it is needed, and optimise its transmission, especially over long distances.

In a study, published in the KeAi journal Energy and Built Environment, researchers at China’s Shanghai Jiao Tong University outline a new process that reduces one of the greatest issues around thermal energy storage and transmission – heat loss to ambient air temperatures – by up to a third.

Corresponding author Zhenyuan Xu, an associate professor at the university’s Institute of Refrigeration and Cryogenics, explains: “Right now, the most commonly-used technology for thermal energy storage and transmission is hot water. However, as the temperature of the water must be higher than the ambient, inevitably there is heat loss. This problem grows when we need to store thermal energy for a long period, as in the case of seasonal solar energy, or transmit it over long distances; for example, to distant industrial zones.”

According to Xu, one solution developed by researchers is to use a liquid-gas absorption system to store the thermal energy in chemical potential – in other words, the energy is only released when a change in the number of particles is triggered.

But while this system has proved effective, the limited range of working fluids available to support it have become a major constraint. Along with co-author Jintong Gao, Xu tested using absorbents comprised of ionic liquid (IL) – essentially, salt in a liquid state. They were drawn to IL’s many favourable properties, including its ability to draw moisture from the air and low corrosivity.

Gao says: “We found that the energy storage density of IL-based mixtures was around 33% greater than other options commonly used today. And, importantly, as the ILs can be manually designed, there are many opportunities to further enhance the effectiveness of this process.”

The pair have also developed a method to help identify effective ILs for use in the system. Gao adds: “We believe that this research could contribute to the decarbonisation of thermal energy in the near future.”

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Contact the author: Zhenyuan Xu, xuzhy@sjtu.edu.cn