Effect of Preheated Top Gas and Air on Blast Furnace Top Gas Combustion

Abstract

The coke consumption in blast furnaces (BF), directly related to the energy consumption and CO₂ emission from BF, is reduced with the increase of hot blast temperature. To establish the flame temperature of more than the blast furnace gas (BFG) adiabatic flame temperature of 1587 K by using only BFG without any additional high calorific value gases such as coke oven gas, the effect of preheating of BFG and/or air on the BFG combustion temperature was investigated based on thermodynamic heat balance and the computational fluid dynamic (CFD) simulations. Thermodynamic evaluation and CFD simulated results showed that air preheating was not effective to raise the BFG combustion temperature compared with BFG preheating or simultaneous preheating of air and BFG at the same preheating temperature. The less efficiency of air preheating was explained based on the small heat content of preheated air. The blast temperature of 1700 K was obtained without adding high calorific value gases by preheating only BFG to 873 K or simultaneous preheating both BFG and air to 700 K. Compared with air or simultaneous preheating of air and BFG, BFG preheating will be a suitable approach to increase BFG combustion temperature. This is not only because the supply of heat content to the combustion zone, but also the enhanced mixing introduced by the large inlet gas velocity difference between air and BFG promotes rapid CO burn-up.