In a paper titled, “Direct Flame Impingement (DFI) – a new oxy-fuel based technology for continuous annealing of aluminum strip,” Linde senior nonferrous expert Henrik Gripenberg will discuss DFI technology, applications, and pilot test results. The presentation is part of the Aluminum Processing Symposium.

Annealing aluminum autobody sheet is our No. 1 candidate for this patented oxyfuel process.

—Henrik Gripenberg

Combustion, notes Linde, is all about fuel, oxygen and ignition. Air contains only 21% oxygen, the remaining 79% is ballast—mostly nitrogen. In combustion processes, all this ballast is negative; in other words, it does not contribute to the combustion, but has to be heated up, consuming unnecessary extra fuel.

If oxygen, not air, is used to combust a fuel, all the heat transfer mechanisms, convection, conduction and radiation, can be promoted at the same time. This results in a faster, more even heating process, which cuts the total heating time thus allowing for more production capacity and flexibility. The flue gas volumes are reduced by up to 80% with no more need for bulky flue gas systems or recuperators.

With Linde’s Direct Flame Impingement technology, oxyfuel flames directly heat the metal strip as it passes through the annealing furnace. The process can achieve heat transfer rates up to 10 times higher than those in conventional fuel-fired furnaces. The Linde DFI technology has been boosting productivity of continuous steel hot-dip galvanizing lines for nearly 10 years, with capacity increases in excess of 25%.

Firing with oxyfuel flames directly onto the material results in a highly effective heat transfer for increased furnace throughput.