SUCCESSFUL USE OF FLAMELESS OXYFUEL IN STEEL REHEATING

Using oxyfuel combustion in steel reheating provides higher throughput and substantial fuel savings. Accordingly, oxyfuel has many benefits, but also some drawbacks like hot spots in furnaces and thermal NOx generation. However, by making the combustion “Flameless” by creating a ‘volume combustion’, these issues can be overcome, and additional advantages can be achieved. This paper describes different solutions, both fully flameless and semi flameless, which have been developed and implemented in steel reheating and annealing furnaces. Over the past three decades, Linde has made more than 160 oxyfuel installations in all types of reheating furnaces, both batch and continuous, and for production of all different steel grades. Since 2003, focus has been on using Flameless Oxyfuel, hitherto resulting in 112 successful installations, 90 of these operating fully with 100 % Flameless Oxyfuel. This paper describes results from these installations, which include fuel savings of up to 60 %, increased throughput by up to 50 %, substantial reductions of CO2 and NOx emissions, much improved temperature uniformity of the heated steel, reduction of scale losses by up to 50 %. Cases with conversion from air-fuel to Flameless Oxyfuel will are described. These examples comprise installations in soaking pit furnaces, rotary hearth furnaces, roller hearth furnaces, and walking beam furnaces with up to 300 t/h nominal capacity, and for production of carbon steel, engineering steel, and stainless steel grades at companies in USA, Europe, and Asia.