The Linde Group, Murray Hill, N.J., has developed Direct Flame Impingement oxyfuel-based technology for continuous annealing of cold-rolled aluminum strip. In DFI technology, oxyfuel flames directly heat the metal strip as it passes through the annealing furnace, enabling a capacity increase of 50%, cost reduction of 50%, and reduced scaling losses and dross formation.
The DFI oxygen burners are arranged in rows, with multiple burners to cover the entire width of the strip. The rows are mounted in modules, and each module consists of two burner rows firing from above and below the strip. The material temperature rises very quickly within a compact furnace body, resulting in heat transfer rates up to ten times higher than those in conventional fuel-fired furnaces.
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. Heating and cleaning can be done in the same operation.
Details about the new technology were presented at TMS 2015, March 15-19, at Walt Disney World in Orlando, Florida. In a paper titled, “Direct Flame Impingement (DFI)” Linde senior nonferrous expert Henrik Gripenberg discussed DFI technology, applications, and pilot test results.
