Emission of NO and SO₂ in a 300 kW Pilot Scale O₂/RFG Combustion

The present work was addressed toward the NO and SO₂ emission results on a 300 kW pilot scale facility, and discussed the impact of the different flue gas recycle ratios on the O₂/RFG coal combustion. In this study, a Chinese lean coal was burned with air and three kinds of O₂/RFG conditions in the pilot scale oxy-fuel coal combustion facility. The composition of the flue gas was sampled and analyzed by the FT/IR gas analyzer. The ashes were sampled in different place and analyzed to study the burnout rate and the mineral transformation. And in-furnace limestone injection under the air and oxy-fuel condition was used to study the desulfurization efficiency. The comparison was made between the air combustion and O₂/RFG combustion. It can be seen that NO_x emissions decrease significantly (296 mg/MJ for air-firing, 80–145 mg/MJ for oxy-firing), compared with the air condition and three kind of oxy-fuel condition. It can be seen that the low NO_x characteristic of the Oxy-fuel combustion causes lower emission of NO compared with the air combustion. For the emission of SO₂, Fuel-S to SO₂ conversion rate dropped from 77% in air to 50% under O₂/RFG condition. And the desulfurization efficiencies of the air combustion and O₂/RFG combustion were 28.4 and 59.1%, respectively. The contribution of SO₂ enriched in the flue gas to the desulfurization efficiency was more than the contribution of increased reactivity of the limestone. By the analyzing of the ash, it was the similar between the air combustion and O₂/RFG combustion.