Numerical Simulation of By-Product Fuel Combustion in a Tangential Gas-Fired Boiler: Effect of Proportion and Angle on Coke Oven Gas

Abstract

The use of low calorific value residual gas generated in the metallurgical process, including blast furnace gas (BFG), coke oven gas (COG), and Linz-Donawitz gas (LDG), to replace coal can save energy and reduce pollutant emissions. Here, a numeral model was developed to stimulate the combustion characteristics of a 75 t/h tangential combustion boiler burning a mixture of BFG and COG. The effect of COG burners downdip on temperature distribution, flow field, NOx emission, and flue gas temperature deviation was analyzed and discussed under two different COG input heat proportions (20% and 30%). The numerical simulation was performed in Fluent and validated by field experiments. The simulation result showed that, under COG input heat proportions of 20% and 30%, the flue gas temperature in the horizontal gas pass slightly decreased when the COG burners tilted down. The area with a temperature greater than 1,500°C (1,773.15 K) near the COG burners also shrank, and the NOx emission under the two fuel schemes slumped by 46.8 mg/m3 and 82.8 mg/m3, respectively. Although increasing the proportion of COG input heat aggravated the NOx pollution, tilting the COG burners down offset this negative influence. Furthermore, tilting the COG burners down slightly reduced the swirling intensity of the furnace and improved the deviation in the horizontal gas pass. Blending more COG reduced the swirling intensity in the furnace and the velocity deviation in the horizontal gas pass. In general, tilting the COG burners down reduced pollution emissions and superheater deviation problems when more COG was mixed in the boiler to improve the combustion of BFG.