Recycled factory heat can benefit industries in sustainability movement

EU funded research is analysing recycled factory heat to create novel systems that recover waste heat and return it for reuse in industrial process lines.

Industrial processes account for more than a fourth of Europe’s primary energy consumption, producing a tremendous amount of heat. During many of these processes, heat is lost to the environment as exhaust or through discharge streams. Recovering and reusing this heat reduces energy consumption, emissions and pollutants. It also enables industries to reduce costs, meet regulations and improve their corporate images with broader impacts on competitiveness. One of the greatest challenges with recycled factory heat is dealing with the immense variety of exhaust temperatures and constituents, which makes it difficult to use off-the-shelf heat exchangers. The EU-funded ETEKINA project has established novel tailor-made heat pipe heat exchangers (HPHEs) that have been successfully piloted in the ceramics, steel and aluminium industries.

A broad design space meets the needs of complex exhaust streams

Both heat pipes are tubes sealed at each end and contain a working fluid at saturation, meaning any increase in temperature will cause it to vaporise. They are employed for heat management in applications such as computers, satellites and spacecraft. In an HPHE, the heat pipes are installed in bundles attached to a plate and placed in a casement. A heat source such as exhaust gas flows into the lower section.

The working fluid vaporises and rises within the pipes, where a heat sink such as cool air flows into the top part of the shell and absorbs the heat. The enclosed structure cleverly minimises heat loss while the plate minimises cross-contamination between the exhaust gas and the air. HPHEs also require smaller surface areas for greater heat transfer relative to conventional approaches, making them extremely efficient and mitigating fouling. The real challenge is choosing the parameters such that the greatest possible heat is recovered from complex waste streams. There are, however, multiple variables, including the number, diameter, length and material of the heat pipes; their assembled configuration; and the working fluid.

From models to factories- recycled factory heat benefits

Despite the immense parameter space, computational fluid dynamics and transient system simulation (TRNSYS) modelling were developed in order to assist scientists in designing bespoke HPHEs for three industrial applications. For instance, the crossflow, finned and fouling resistant HPHE was designed to recover waste heat from a ceramic’s roller hearth kiln. This was the first in this configuration to be applied within the ceramics industry. The heat pipe shells were created out of carbon, steel, and water was the working fluid.

“We have exceeded the project’s target of a minimum of 40% waste heat recovery from exhaust streams,” explained Hussam Jouhara of Brunel University London and technical and scientific coordinator of the ETEKINA project. “Our HPHEs are also much more compact than conventional heat exchangers, saving valuable factory space. In addition to their efficiency, which lowers costs and emission, they also have a short return on investment.”

The systems effectively recovered heat without any cross-contamination and successfully funnelled it back to the factory to be utilised in other processes. The HPHE concept developed in the context of ETEKINA is highly scalable and has the potential to be adapted to any type of industrial exhaust over a large temperature range and for a variety of heat sinks, including air, water, and oil. A novel replicability tool will help to quickly assess the waste heat recovery potential of future customers and help in the effort to accelerate recycled factory heat.

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