| Mercury emissions from coal-fired power plants have been identified as hazardous pollutants to human health and the environment. Since a large amount of the anthropogenic mercury emissions of the atmospheric contaminants, the speciation and control of mercury in coal-fired power plants are currently an active topic of research. Because the mercury speciation and its transformation play a significant role to control the mercury emission, researchers focuses the characteristic and mechanism of mercury transformation among its speciations in coal-fired flue gas. For the purpose of analyzing the mercury emission characteristics in coal-fired power plant, two trials are conducted in this study, one is to measure mercury speciations in-situ by sampling the feeding coal, the bottom ash, the flue gas and the fly ashes collected from each different electric field of the electrostatic precipitator (ESP) simultaneously in a 220 MW pulverized coal combustion boiler system; the other is to establish a mathematic models to predict the oxidized mercury fraction with variation of the flue gas temperatures and chlorine in coals.A new-built mercury isokinetic sampling system in accordance with the standard Ontario Hydro Method (OHM) recommended by US Environmental Protection Agency (EPA) was recently fabricated in Southeast University, which was used into the flue gas mercury sampling before and after ESP locations in a selected utility 220 MW pulverized coal boiler-system of a power plant. On the operation conditions of the boiler loads at 50%, 75%, and 100% of the boiler maximum continuous rate (MCR), the distribution of mercury speciations of Hg0, Hg2+and HgP in flue gas were detected. The mercury balance of this power plant was derived from measured data based on samples of coal, bottom ash, fly ashes and flue gases. The conclusion were obtained as follows(:1)The mercury speciation varied greatly when going through the the ESP. Of the total mercury in flue gas, the proportion of Hg2+ is about 13.3% before ESP and 9.1% after ESP, while that of the Hg0 is about 84.7% before ESP and 90.7% after ESP, as well as that of the HgP is about 2.0% before ESP and 0.2% after ESP. (2) The absorption of mercury on fly ashes was found strongly dependent on unburnt carbon content in fly ashes and slightly on the particle sizes, which implies that the physical and chemical features of some elemental substances enriched to fly ash surface also have an non-ignored affects to the mercury absorption(.3)The concentrations of chlorine, oxygen and NOx in flue gas have positive correlation with the formation of the oxidized mercury, but the existence of sulphur has positive influence on formation of the elemental mercury. (4)The mercury balance shown that the bottom ash is shared only about 0.95% of the total mercury feeding the boiler, while 70.35% was emitted into the atomasphere as a gasous phase mercury along with 27% was converted into the particle-bound merury captured by the ESP.Using the chemical thermal equilibrium analysis, the speciation of mercury in flue gas varied with temperatures and mercury and chlorine conents in coals was predicted. For a Hg-Coal-Cl system and Hg-Coal-Cl-O system, the speciation of oxidized mercury affected by chlorine was studied and discussedin oxidation atmosphere in flu gas. The results showed that: (1) In the high temperature zone of over 800K in coal combustion, elemental mercury is the most thermal stabilized form, at the temperature of below 600K in area of typical APCD's, HgCl2 is the dominant species. (2) In the oxidation atmosphere and at low temperature zone, the elemental Hg will react actively with chlorine in the flue gas to form HgCl2. The greater the chlorine concentration, the more of oxidized mercury and the wider temperature zone of forming HgCl2. (3) The amount of HgO in flue gas is much few than HgCl2 in the coal-fired flue gas. Although this chemical thermal equilibrium prediction model could not accurately predict the mercury...
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