| Mercury and its compounds are highly bioaccumulation and toxicity, causing great harm to the humans and ecosystem. Coal-fired power plants are the largest source of anthropogenic mercury emissions. Engineered solutions, such as the injection of halogenated activated carbon into the flue gas stream have been proposed to capture Hg from the flue gas. However, Coal-fired fly ashes have also been extensive studied as mercury sorbent because of its abundance, low cost. But the types and proportions of mercury compounds on the surface of fly ash adsorbent are less involved. And the chemical reaction mechanisms of removal mercury by the coal-fired plant fly ash modified sorbent are not clear still. This paper as the main research purpose, because the thermal decomposition temperature of different mercury species was different, mercury species are can be identified by a method utilizing a temperature-programmed thermal decomposition setup. Thus the chemical reaction mechanism of oxidation and adsorption processes during the injection of modified fly ash adsorbent in coal-fired power plant would be deduced indirectly.The self-designed lab-scale unit of mercury compound thermal decomposition, in which the more common and coal-fired power plants generally may contain pure mercury compounds samples in fly ash were studied by means of temperature programming thermal decomposition. The results showed that the thermal decomposition release characteristics of several kinds of mercury compounds which were for a certain power plant fly ash after heat treatment as matrix and their essence release characteristics existed certain differences. Compared different adding ways of the same kind of mercury compounds, and understand the impact of the thermal decomposition release characteristics of the different ways of adding, thus determine the best adding way to reflect the ombination form of mercury compounds and the surface of fly ash, and provide the basis for the analysis of samples in the next chapter.A coal-fired power plant fly ash and other solids samples were analyzed, and the mercury mass balance calculation of the power station was gained, the removal effect of mercury in flue gas of the equipment parts in coal-fired power plants was understanded preferably. The mercury mass balance calculation shows:the mercury generated in coal combustion process of coal-fired power plant mainly composed of three parts:mercury in flue gas, mercury in desulfurization gypsum and mercury in the fly ash, and mercury in flue gas emptying accounted for 45% of all mercury. And samples were analysed by thermal decomposition methods, the mercury species were identified, so as to explore the whole migration transformation process of mercury in coal-fired power station. The mercury in coal-fired power plant fly ash compound may be HgCl2, HgS and HgO. Mercury compounds of desulforization gypsum in coal-fired power plant may be Hg2Cl2 HgCl2 and HgS, Hg2SO4 and HgO.The entrained-flow reactor can reflect the injection process and two-phase flow characteristics of the flue gas and the fly ash, and it was closer to the actual power plant flue gas adsorption process compared to the fixed bed. In this paper, the experimental study was carried to understand the mercury adsorption mechanism with HBr modified fly ash sorbent in a lab-scale entrained-flow reactor. The main conclusions are as follows: compared to the unmodified fly ash, the mercury adsorption efficiency improved significantly after modification with HBr; for the unmodified fly ash, the main species of mercury were HgCl2 and HgS, whereas for the HBr-modified fly ash, the main species of mercury were HgBr2, HgS and HgO; the mercury species adsorbed by HBr modified fly ash was HgBr2 and HgO; the fine ash had a better mercury adsorption performance than coarse ash, which is most likely due to the higher specific surface area. And the major mercury species present were also HgBr2 and HgO. At the same time, the influence of NO to carry mercury adsorption mechanism of HBr modified fly ash in the entrained-flow reactor. The results showed that the performance of adsorption of mercury for HBr modified fly ash has been enhanced significantly when the NO was added in flue gas. The mercury adsorption efficiency and its concentration change rate will increase with the increase of the NO concentrations. The mercury adsorbed by HBr modified fly ash, in the entrained-flow reactor, exists in two forms, HgBr2 and HgO. In the experiments of mercury adsorption with HBr modified fly on the entrained-flow reactor, the main role of NO is to promote the generation of the HgBr2, and the reaction between HBr and NO2, HBr+NO2→HONO+Bt,be the key steps. |
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