Numerical study on oxy-fuel combustion characteristics of industrial furnace firing coking dry gas

Abstract

One of the most promising methods for clean utilization of hydrocarbon fuels and CO2 capture is oxy-fuel combustion. However, report on oxy-fuel burning of industrial gas is still limited. In the study, numerical simulation was conducted to explore the oxy-fuel combustion performance of a coking dry gas fired industrial furnace. A modified weighted sum gray gas (WSGG) model with a four-gray body and fourth-degree temperature polynomial was proposed for both air and oxy-fuel combustion with the introduction of the fourth graybody. The impacts of oxygen content, excess oxygen ratio, oxygen purity, and dehydration efficiency on combustion and heat transfer were mainly investigated. The maximum furnace temperature increases significantly, and the high temperature region inside the furnace shrinks and moves downward as the oxygen content rises. The H2O content increases from ∼20% to ∼37%, and the CO2 content decreases from ∼77% to ∼60%. The furnace temperature is up to 1835 K under air conditions, while the furnace temperature is reduced by 195 K under oxy-fuel condition of 21% O2 content. The composition of flue gas barely changes as the excess oxygen ratio increases from 1.02 to 1.20. Although the CO2 enrichment in flue gas and the improvement of oxy-fuel combustion performance benefit from an increase in oxygen purity, the combustion performance further advances little when it is raised to over 98%. Additionally, when dehydration efficiency grows, radiant heat transfer decreases and the flue gas temperature at the furnace outlet rises. The content of O2 and N2 has little relationship with dehydration efficiency. This study aids in understanding the actual oxy-fuel combustion process of an industrial gas-fired boiler and offers a possible theoretical basis for clean burning of petrochemical combustible gas and carbon capture.