Effect Of HCl,CO,and NO In Coal-Fired Flue Gas On SO₃ Formation

Oxy-fuel combustion is a kind of carbon dioxide capture technologies during combustion.Compared with air combustion,Oxy-fuel combustion has lower emissions but higher concentrations of gaseous pollutants in the flue gas such as SO_X,HCl,CO,and NO_X.SO₃concentration in oxy-fuel combustion can be 4-6 times higher than that in air combustion,which will raise the dew point of sulfuric acid vapor and increase the risk of low-temperature corrosion.So far,the formation characteristics of SO₃ during oxy-fuel combustion has been widely studied,but there are very few reports about the effect of polluted gases in the flue gas?such as HCl,CO,and NO?on SO₃ formation.The concentrations of these gases are all relatively higher in oxy-fuel combustion.And the gases can cause not only environmental pollution,but also corrosion on the boiler system.So it matters to study the effect of these gases on SO₃ formation,which can provide theoretical support for controlling and reducing emissions of SO₃ and other gases.In this study,homogeneous experiments and heterogenous experiments were designed and carried out separately on a horizontal tube furnace system and a drop tube furnace system to explore the effect of HCl,CO,and NO on SO₃ formation.Besides,sensitivity analyses were done using kinetic simulation software CHEMKIN-PRO to reveal the mechanisms of the interactions between SO₃ and the gases.The results showed that HCl could inhibit SO₃ formation in the heterogenous environment during oxy-fuel combustion.With the increase of HCl concentration,SO₃ concentration decreasd,but the decreasing rate became lower.HCl might inhibit SO₃ formation by generating HO₂ radical and H₂O which were negative to SO₃ formation.CO could promote SO₃ formation in dry and wet homogeneous environment and heterogenous environment during oxy-fuel combustion.With the increase of CO concentration,SO₃ concentration increased,but the increasing rate became lower.CO might promote SO₃ formation by generating O radical and OH radical which were positive to SO₃formation and consuming HO₂ radical which was negative to SO₃ formation.NO could promote SO₃ formation in dry homogeneous environment and heterogenous environment during oxy-fuel combustion.With the increase of NO concentration,SO₃concentration increased in homogenous environment,but the increasing rate became lower.However,SO₃ concentration increased first and then decreased in heterogenous environment.This might be due to the fact that the increase in NO concentration reduced the burnout of pulverized coal and led to a reduction in sulfur emissions.NO might promote SO₃ formation by generating O radical and OH radical which were positive to SO₃ formation and consuming HO₂ radical and H radical which were negative to SO₃ formation.