Mercury Speciation in Air-Coal and Oxy-Coal Combustion

To study the effect of air-coal and oxy-coal combustion on mercury emission, Xuzhou bituminous coal was burnt in a 6 kWth fluidized bed at 800 and 850°C in four atmospheres: air, 21%O₂/79%CO₂, 30%O₂/70%CO₂, 40%O₂/60%CO₂ analysed with an online flue gas analyzer. Ontario Hydro method (OHM) was employed to measure mercury speciation in flue gas. The result indicated that more elemental mercury and oxidized mercury are released when burned in O₂/CO₂ atmosphere than in air at 800°C, while the situation is just opposite, when coal was burnt at 850°C, less Hg⁰ and Hg²⁺ in O₂/CO₂ atmosphere than in air. The concentration of Hg⁰ rises as temperature increases both in the conditions of the air combustion and oxy-coal combustion, but the concentration of Hg²⁺ increases with the increase of temperature only in the condition of air combustion and decreases in the oxy-coal combustion. With the increase of the oxygen concentration which is in the range of 21–40%, the concentrations of Hg⁰ and Hg²⁺ decrease first and then increase. When excess air coefficient increases, the oxygen content is higher and the vaporization rate of Hg⁰ and Hg²⁺ decrease.