Reaction Engines and Brunel University London engaged in ground breaking project to optimise supercritical CO2 for waste heat to power conversion
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Reaction Engines’ commercial Applied Technologies division has recently been engaged in a ground breaking project with Brunel University London to design and build a first-in-class primary heat exchanger utilising supercritical CO2 as the working fluid.

Brunel University had been reviewing current methodologies for waste heat recovery in industrial processes, specifically heat recovery opportunities for energy optimisation in the steel/iron, glass and cement industries. Industrial waste heat is energy that is generated through industrial processes which is lost and released into the environment. With Reaction Engines’ expertise in heat transfer technology, Brunel engaged the Applied Technologies team with a view to identifying and developing a more viable solution for the capture and re-use of high grade (high temperature) waste heat.

 

Supercritical CO2 
Using supercritical CO2 (sCO2) as the working fluid in power cycles instead of steam increases the efficiency and flexibility of the overall heat recovery and allows for a significantly smaller footprint. Utilising waste heat reduces the carbon intensity of processes by reducing the energy consumption and hence lowering operating costs.
In a sCO2 cycle, the working fluid remains in the same supercritical state throughout the process. The turbines for sCO2are significantly smaller than steam turbines because of the high density of the working fluid and the lower pressure ratio. This holds true for most of the components and there is no need for the massive condensers associated with steam plants. It is estimated that sCO2 turbines could be as little as 10% of the size of a steam equivalent. Furthermore, sCO2 power systems can operate over a wide range of temperatures with higher efficiencies than steam.

Space Technology
The main challenge for the university was to find a partner who could provide a compact and modular solution, which could handle the very high temperatures and high pressures required. Reaction Engines was a logical choice owing to the ground breaking thermal management technology developed under the SABRE programme. SABRE’s heat exchanger, or “precooler” as it is officially known, was validated in 2019 at temperatures representative of Mach 5 flight and has the ability to quench gas temperatures in excess of 1000 °C down to ambient near instantaneously and within a very small volume.

Reaction Engines Applied Technologies utilises the heat exchange technology developed for SABRE and adapts it for commercial industries where thermal management is a key factor for to performance. The team is currently involved in adapting this revolutionary technology in various sectors including aerospace, motorsport and energy.

The sCO2 Primary Heat Exchanger
Having identified supercritical CO2 as a working fluid to demonstrate, Brunel required a primary heat exchanger to capture the heat with a specification exceeding the state of the art. The heat exchanger required a very low shell side (flue gas) pressure drop, yet able to withstand working pressures up to 130 bar, and temperatures up to 650°C.
Using proprietary modelling software, the Applied Technologies team designed and developed a heat exchanger to deliver the required performance well within the pressure drop requirements – as well as the capability to deliver additional heat recovery for a future proofed system. The installed system captures the waste heat from within an exhaust duct. The recovered thermal energy is converted into electrical power (via a turbine) for export to the local grid. The complete primary heat exchanger was designed to ASME BPVC and was fully CE marked (Cat. IV PED).

The Future
Using sCO2 in place of steam has the potential to provide a step change in electrical power generation, whether from waste heat, primary or renewable energy sources. It is estimated that the UK industrial sector consumes as much as 17% of the UK’s overall energy consumption and also generates about 32% of its overall CO2 emissions. Industrial uptake of a thermal management system that harnesses currently wasted heat energy would be a step in the right direction for the UK’s ambitious goal of becoming net carbon neutral by 2050.

Whilst the realisation of SABRE and hypersonic flight remains a mission for Reaction Engines, adapting its technologies into the commercial sector to contribute to a more sustainable and environmentally stable world is increasingly important. Through this project with Brunel University, Reaction Engines has once again demonstrated its ability to innovate solutions for a brighter, more efficient and sustainable future.

For full technical specifications, read the case study here.