Case Study:
Primary heat exchanger for waste heat recovery system

Background

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, food and ceramic 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 exchange 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.

About Brunel University

Brunel University’s research focuses on areas in which it can integrate academic rigour with the needs of governments, industry and the not-for-profit sector, delivering creative solutions to global challenges and bringing economic, social and cultural benefit.

Brunel’s Research Institutes and Research Centres pioneer world-leading research inspired by an ambition to address society’s most pressing challenges.

The challenge

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

Supercritical CO₂

Using supercritical CO₂ as the working fluid in power cycles instead of steam increases the efficiency 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 sCO₂ are significantly smaller than steam turbines because of the high density of the working fluid, this holds true for most of the components and also there is no need for the massive condensers associated with steam plants. It was estimated that sCO₂ turbines could be as little as 10% of the size of a steam equivalent. Furthermore, sCO₂ can operate over a wide range of temperatures with higher efficiencies than steam.

Creating value

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 an exhaust duct, and converts it to useful electrical energy (via a turbine) for export to the electrical grid. The complete primary heat exchanger was designed to ASME BPVC and was fully CE marked (Cat. IV PED).

Heat Exchanger Technical Speciﬁcations:

	Tube Side	Shell Side
Design Pressure	153 bar	~0.1 bar
Temperature	500°C	600°C
Design Code	ASME BPVC Sect. VIII Div 1	CE marked under PED (Cat IV)
Duct Sizing	n/a	500 x 500 mm

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Case Study:Primary heat exchanger for waste heat recovery system