| As one of the important atmosphere pollution source, mercury releasing from coal-fired flue gas causes mercury pollution, and directly or potentially does harm to environment. With the fact that coal combustion contamination being more serious, environmental protection being aware of, related environmental protection law and regulation working out and carrying out, especially microelements test technology developing, the problem that microelements contamination caused by coal combustion are coming to given more and more prominence. In recent years, researchers have begun to study mercury speciation and transformation during coal combustion, which is just commenced in our country. Therefore, studying on mercury speciation and transformation during coal combustion has very important significance.Experimental study was conducted on a one-dimensional coal combustor. Ontario-Hydro method recommended by EPA was applied to determine mercury speciation in flue gas during combustion of two different coals. Results show that Hg0 is the main format in vapor phase mercury. The content of Hg0 is 33%～88%, and Hg2+ is 12%～67%.The influence of different coal type, combustion temperature, reaction time, flue gas atmosphere and grain diameter of coal on mercury was studied. Results are following: Mercury may release in a shot time under the condition of high combustion temperature above 700℃. The content of vapor phase mercury in the two different coals both are below 10μg/m . Coal type also has impact on mercury speciation transformation. The content of Hg0 in the lignite flue gas is more than that in the bituminous coal flue gas, but Hg2+ reverses. Oxidizing atmosphere is beneficial to oxidize Hg0, but reducing atmosphere does not. Small grain diameter of coal helps to mercury liberation.Elementary reactions about mercury were analyzed including chemical thermodynamics and chemical kinetics. Important reaction mechanism about mercury oxidizing in coal fired flue gas is obtained. |
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