Development of an Energy-Efficient Burner for Heat Treatment Furnaces with a Reducing Gas Atmosphere*

One of the main reasons for metal loss of semi-finished metal products during heating in reheating and heat treatment furnaces is scale formation. In the presented project a burner is developed which produces a low oxidizing / reducing atmosphere in the furnace. The concept is realized by a recuperative burner, which generates a reducing furnace atmosphere due to fuel rich combustion of natural gas and air. The complete combustion of the furnace atmosphere is ensured by the injection of additional air and takes places in an open radiant tube resulting in a high energy efficiency. In this paper numerical and experimental results are presented and discussed. The numerical results showed the huge impact of the secondary air swirl on the post-combustion in the annular gap which is formed between the open radiant tube and the burner. Mixing phenomena in the annular gap results in a nearly complete post-combustion at low and high swirl angles of the additional combustion air (ω = 0°, ω = 90°). Instead of that, at a swirl angle of ω = 45° the entire reaction from CO to CO2 was not ensured within the boundaries of the numerical model. The quality of the post-combustion was experimentally evaluated by measuring the CO-emissions in the off-gas channel. These were lower than 50 mg/m3 in a wide range of operation. The NOx-emissions are lower than 121 mg/m3 at all tested cases.