Nitrogen Oxides, Sulfur Trioxide, and Mercury Emissions during Oxy-fuel Fluidized Bed Combustion of Victorian Brown Coal

摘要

This study investigates, for the first time, the NO_x, N_2O, SO_3, and Hg emissions from combustion of a Victorian brown coal in a 10 kWth fluidized bed unit under oxy-fuel combustion conditions. Compared to air combustion, lower NO_x emissions and higher N_2O formation were observed in the oxy-fuel atmosphere. These NO_x reduction and N_2O formations were further enhanced with steam in the combustion environment. The NO_x concentration level in the flue gas was within the permissible limit in coal-fired power plants in Victoria. Therefore, an additional NO_x removal system will not be required using this coal. In contrast, both SO_3 and gaseous mercury concentrations were considerably higher under oxy-fuel combustion compared to that in the air combustion. Around 83% of total gaseous mercury released was Hg~0, with the rest emitted as Hg~(2+). Therefore, to control harmful Hg~0, a mercury removal system may need to be considered to avoid corrosion in the boiler and CO_2 separation units during the oxy-fiiel fluidized-bed combustion using this coal.