Best practice and heat recovery in gas fired continuous furnaces 

Companies from the UK steel and brick making industries have come together to explore ways of recovering waste heat and making their furnaces more efficient – helping to reduce energy and carbon emissions.

The steel and ceramics sectors both use gas-fired furnaces in continuous operation at temperatures in excess of 1,000°C. Although both industries currently utilise some of the waste heat – for example, to help dry out bricks – the Best Practice and Heat Recovery in Gas Fired Continuous Furnaces project explored the potential for further energy savings.

“There is currently a huge drive for greater efficiency in these industries,” says Oliver Milling, Principal Researcher at the Materials Processing Institute, which led the project. “Alongside net zero targets, there is demand from the construction industry – which forms a big market for steel and bricks – for products with a lower carbon footprint. And, of course, rising fuel costs are a big impetus to reduce the amount of gas these furnaces use.”

Part-funded by the Transforming Foundation Industries Fast Start Competition, the project brought together one of the UK’s largest steel manufacturers, British Steel, and one of its largest brick and tile makers, Wienerberger UK, with energy recovery specialists Heatcatcher Ltd and energy consultants Low Carbon Europe Ltd.

“Even modest efficiencies can result in significant fuel savings – for example, using waste heat to raise the temperature of combustion air by 40 degrees can reduce the amount of gas used by between 3-9%.”

Wienerberger operator wearing a high visibility jacket standing in front of an open brick firing furnace with stacks of bricks inside

The team compared a reheating furnace operated by British Steel with brick kilns operated by Wienerberger UK. They mapped the energy flows of both processes to give a clear understanding of where energy, particularly heat, enters and leaves, where it is recycled, and where it is used in further processes.

The analysis identified opportunities to utilise more of the waste heat, including:

  • Re-using heat from the cooling systems to pre-heat the combustion air in brick kilns
  • Generate electricity from excess heat in the furnace cooling system
  • Use heat from the steel furnace exhaust to generate electricity by installing a heat-capturing turbine called an organic rankine cycle turbine.

The project also looked at the efficiency of burners in the furnaces. “There are combustion efficiency improvements to be made by using more modern burners. These provide better control of airflow, which means the amount of gas used can be reduced but still achieve the same combustion. There is also the potential to use burners that can introduce clean-burning hydrogen into the fuel mix,” says Milling.

“The catch is that they are expensive, and installation disrupts the production process. However, as the technology improves – and the need to reduce the amount of gas used increases – the payback periods are shortening.”

Gas pressure gauges for a large industrial gas fired furnace

The project findings have been taken on board by partners, with Wienerberger UK investigating waste heat ideas and British Steel exploring future combustion efficiency options. The results have also been shared more widely across the two sectors, which includes more than 40 other brick kilns and 20 steel reheat furnaces.

Milling believes the project has value to other Foundation Industries, too. “Even modest efficiencies can result in significant fuel savings. For example, using waste heat to raise the temperature of combustion air by 40 degrees can reduce the amount of gas used by between 3-9%, which represents a saving of between 5 and 50 kilowatt-hours of energy per tonne of finished product,” he says.

“Any industry using high-temperature processes, which includes all the Foundation Industries, is facing the same challenges to its energy consumption, so could benefit from looking at heat flows in their operation and comparing with best practice across the industry.”

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