Energetic analysis of reheating furnaces in the combustion of coke oven gas, Linz-Donawitz gas and blast furnace gas in the steel industry

•Coke oven (COG), Linz-Donawitz (LDG) and blast furnace (BFG) gases were evaluated.•Heat losses were estimated for COG/LDG and COG/BFG mixtures in a reheating furnace.•Heat of exhaust gases was recovered to preheat the load and the combustion air.•Fuel consumption was reduced by 18.9% and 21.1% for each preheating.•Furnace efficiency was increased by 23.3% and 15.2%, respectively. The reheating furnace of the steel industry was evaluated in the present study, which uses the gas mixture from coke oven (COG), steelmaking process “Linz-Donawitz” (LDG) and blast furnace (BFG); with the production of steel laminates being its main activity. Two methods were developed in this work to deal with energy consumption. The first dealt with improved estimation of heat losses in the furnace, and the second dealt with recovery of heat and its use in load preheating and combustion air preheating. These evaluations were intended to determine the best selection of material for insulation of the furnace, in order to increase heat transfer, to obtain an economy in fuel consumption, and to improve technical energy indicators of production and heat generation, as well as to improve the efficiency of the furnace and the combustion process. When developing the present study in the reheating furnace it was evidenced an economy in the fuel consumption of the COG/LDG mixture of 6606 m3/h and 4627 m3/h for the load preheating and the air preheating, respectively. In addition, efficiency of the furnace was increased by 23.3% and 15.2%, with the technical energy indicators improved by 18.9% and 13.2% in each case. For the COG/BFG mixture, the results obtained were similar.