Decarbonisation Technology August 2022 issue

How moving bed heat exchange technology is driving innovation in thermal energy storage Decarbonising through advances in heat exchange technology

Gerald Marinitsch, David Moon and Lowy Gunnewiek Solex Thermal Science

F ossil fuels have been at the centre of a truly remarkable period of development and growth for the global population. In recent decades, however, the negative environmental impact and increasingly high economic cost of fossil fuel use have powered what many are dubbing the “next energy transition” – or should we say “energy evolution” – as we search for new ways to decarbonise our energy use. Today, this drive to decarbonise our energy needs can be found everywhere – from discussions about a circular economy to the environmental, social and governance (ESG) strategies of businesses around the world. Given the energy needs of today’s highly connected and mobile world, a tremendous amount of work and money is being directed toward making decarbonised and renewable energy available to us when we need and want it. This is leading to a pressing need for more readily available energy storage, from which a variety of different technologies are currently available or being developed, such as batteries, pumped hydro, and green hydrogen. One of the more notable and promising developments in this arena relates to long- duration thermal energy storage (LD-TES) systems that use solid particles. This technology is garnering significant interest and investment primarily because it is targeting a need for storage systems that can provide energy for a period of 10 hours and more. To date, this has not been realised. An example of this is taking the thermal energy that can be generated from concentrated solar power (CSP) and transferring it to solid

particles so it can be stored and used later when the sun is not shining. To enable this option for LD-TES, a new generation of moving bed heat exchangers (MBHEs) are also being developed so the thermal energy can be extracted from solid particles and subsequently converted into a useable energy form such as electricity. In this article, we will reflect on how changing energy demands have brought us here, along with the unique challenges associated with storing and recovering thermal energy. We will also explore recent developments in vertical tube and diffusion-bonded MBHEs that are being used – specifically, in CSP systems that incorporate LD-TES. Included will be a discussion around the background requirements for these types of systems, along with design considerations and challenges for MBHEs when being implemented. Lastly, we will highlight several examples taken from work currently under way that will help illustrate the potential for these particle- based LD-TES systems in helping us evolve to a more decarbonised energy system. Changing energy demand Prior to the Industrial Revolution, electricity played an insignificant role. Rather, chemical energy sources such as biomass or oil were common – and useful in that this energy was in a form that was ‘stored’ and useable whenever needed and wanted. Combustion (oxidisation reaction) of the ‘fuels’ typically liberated this energy for use. Concern about carbon dioxide emissions from combustion did not exist then as it does today.