Numerical Simulation of CO and NO Emissions During Converter Off-Gas Combustion in the Cooling Stack

Abstract

Oxygen converter steelmaking produces a large amount of high temperature off-gas. During pre- and postcombustion of converter off-gas in the cooling stack, CO concentration at the outlet is always over emissions standards, and NO emission is still paid little attention. In the article, CO and NO emissions are investigated during converter off-gas combustion by computational fluid dynamics (CFD). The simulation results indicate that CO emission is above 0.5%–2%, and NO emission is up to 150 ppmv at the precombustion stage of off-gas during 7–15% of blowing oxygen time. The poor mixing of both off-gas and the air that is sucked in, and too high combustion temperature (above 2000°C) result in high CO emission. In order to increase combustion efficiency of off-gas and to reduce CO concentration, the air supply mode must be improved to effectively organize the mixing of off-gas and air in the cooling stack. The high combustion temperature of off-gas and the poor mixing of both off-gas and the air that is sucked in facilitate the formation of thermal-NO during the pre- and postcombustion of off-gas. In order to reduce NO emission, both the air stoichiometry and temperature profiles in the cooling stack must be controlled.