Experimental investigation for the development of burners for low scale reheating of semi-finished metal products

Industrial furnaces for the reheating of semi-finished metal products are often direct fired with natural gas and air. Oxidation of the metals exposed to the furnace atmosphere causes significant material losses and additional work during furnace operation and in further processing. A reheating concept for direct fired reheating furnaces, which reduces scale formation, was developed. It involves fuel rich combustion, post-combustion of the unburned off-gas and efficient preheating of the combustion air. Based on this concept a prototype-burner was developed which produces a low oxidizing atmosphere in the furnace. The concept is realized by a recuperative burner generating a reducing furnace atmosphere with 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 as part of the burner resulting in a high energy efficiency. In order to investigate the process an experimental system is set up, consisting of a model of the burner and a combustion chamber for temperature and off-gas measurements. The experimental investigations focus on the reheating of copper and steel in direct fired furnaces with recuperative burners. This paper presents the influence of furnace atmosphere, especially the air ratio of the combustion of natural gas and air in the furnace, on the metal loss of copper and steel samples due to surface oxidation. In addition, the parameters for a stable post-combustion and the efficiency of the process are investigated. The experimental results show the impact of different parameters on the temperature distribution and heat transfer in the open radiant tube and off-gas emissions.