| Mercury is one of the highly toxic trace heavy metals and non-essential for life elements in the ecosystem. It is one of the priority pollutants controlled by international organizations and governments. Research on mercury emissions from human activities showed that the emission from coal-fired flue gas was an important source of mercury in the environment. Because China is the largest producer and consumer of coal in the world, the attention on emission of mercury from coal combustion has been paid internationally. China was considered as the largest mercury emission country in the world with 42% contribution. The coal-fired power plants and heating were the largest contributors, accounting for about 47% of mercury emission in China.In order to objectively understand the status of Chinese mercury emissions and pollution, especially the emission from coal-fired flue gas, it is necessary to establish a reliable method on measurement firstly. In this dissertation, a measurement method of mercury in coal-fired flue gas was developed based on the integration of catalytic oxidation and adsorption, and then was applied in several coal-fired power plants. The amount emission of mercury from Chinese coal-fired power plants was estimated and predicted on the basis of the above field results. Meanwhile, the mercury in flue gases from waste incineration, iron-smelting, coking and mercury recovery industries was also determined by the method tentatively. The research results were as followed:1. The method developed to determine the mercury in flue gas was as followed: Sampling mercury from flue gas with the selected catalytic oxidation sorbent with the optimal temperature, flow and time 120 °C, 0.3-0.5 L/min and 2 h respectively. The higher mercury recovery could be obtained by leaching the sorbent after the adsorption with 4 mol/L HCl-saturated KCl solution. The operations were simple and easy, and the results’ stability was high. The Cu-Co-Al-based sorbents were more suitable for the adsorption of mercury in the flue gas than the Mn-Co-Al-based because of their higher stability. After regenerating, the adsorption function of the sorbents was declined. Compared with the HJ543 method in GB13223-2011, ontario hydro method and 30 B method, this method was easier to promote the application in China with advantages of security, cheap and convenience. Compared with Tekran3300 series mercury continuous emission monitoring system(Hg-CEM), the average deviation between the detected datas from the two methods was less than 20%.2. Characterization of the the sorbents structure before and after the adsorption of mercury by means of XAFS and AAS technology showed that both Co and Cu were coordinated with O on the Cu-Co-Cl-Al sorbents with 1.50-1.53 ? and 1.41 ? of the bond lengths, respectively. The crystal was between the tetrahedral and octahedral in symmetry. The crystal structure was not changed after the adsorption of Hg, which showed that the Co and Cu oxide on the sorbent could be quickly restored after the catalytic oxidation of Hg and then participated in the reaction continuously. The Mn was coordinated with O and Br on the Mn-Co-Br-Al sorbents with 1.32 ? and 2.21 ? bond lengths. A part of Mn was reacted after the adsorption of Hg, so that the sorbent’s stability was changed. This means that the Mn oxide on the sorbent couldn’t be restored after the catalytic oxidation of Hg, which is the reason that the Cu-Co-Cl-Al was more efficient than Mn-Co-Br-Al. The valence of Hg on the regenerated sorbent was lower than the original one, and the adsorption quantity of Hg was also low. Presumably, Hg might be coordinated with O, while the Hg on the original sorbent coordinated with halogen.3. Researches on mercury emissions and removals by existing pollution control devices of six coal-fired power plants in China have been carried out. The results were as followed: The relative distributions of Hg in bottom ash, in electrostatic precipitator(ESP), in flue gas desulfurization(FGD) and in stack ranged from 0-2.50%, 0-23.4%, 2.21%-87.1% and 21.8%-72.7%, respectively. Total mercury concentrations in stack gases were ranged from 1.56-5.95 μg/m3. The 44.2% of average mercury was removed by ESP+FGD devices. The mass balances of mercury in the course were ranged in 74.32%-118.68% for the six power plants, which were within the acceptable range(70%-130%). The average emission factors before ESP, after ESP and after FGD of the six power plants were 0.162 g/ton, 0.115 g/ton and 0.071 g/ton, respectively.4. The increased mercury emission by coal-fired power plants in China has been remained in recent 10 years. The emission in 2000 was 59.33 tons and was increased to 134.61 tons in 2010. Calculated based on the data of 2005, the mercury emission of coal-fired power plants in China was accounted for about 21.7% of the global mercury emissions from power plants. The dust removal and desulfurization devices in power plants have played very important role to reduce Hg emission from the flue gas. It was estimated that 518.64 tons and 230.42 tons of Hg were catched by dust removal devices and the desulfurization units in coal-fired power plants from 2000 to 2010.5. The detected method was also tried to use for the Hg determination in flue gas from multi industries. The mercury content in untreated flue gas from medical waste incineration plant was 214.92 μg/m3. After cyclone, lime powder, activated carbon injection device and a bag filter, the mercury content was reduced to 4.20 μg/m3, which was up to 96% of the mercury removal efficiency. The mercury concentration in the flue gas emissions of two incineration plants of municipal waste was 3.94 μg/m3 in average. The average mercury content in the flue gas from an industrial waste incinerator was 1.17 μg/m3. The average mercury concentration in the flue gas in the smelter of iron ore was 8.16 μg/m3. The average concentration of mercury in the flue gas from a coking plant emission was 13.90 μg/m3. The average concentration of mercury in the flue gas from a mercury recycling plant was up to 34.9 mg/m3 and 41.5 mg/kg and 1.57 g/kg in the soil and plant leaves near the chimney respectively were detected. The Hg emissions from industries above should be paid more attention to.In summary the research above provided an approach to view the Hg pollution in our country. Further research is needed because of the complexity of flue gas components and operating conditions. |
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