| This paper gives a systematic and comprehensive research on the mercury (Hg) emission and control of coal-fired power plant in China with the support of the National High-tech Research and Development Program (863) and the National Natural Science Foundation. It includes characteristics of mercury emission from the coal-fired boiler in Chinese power plant, stabilization of mercury on the activated carbon's surface, adsorption mechanism of gaseous mercury on the activated carbon (AC) and modification the AC surface to enhance adsorbability of mercury, etc.It firstly investigated the Hg emission characteristics of six typical large coal-fired boilers using the advanced sampling equipments and analytical instruments in China. Through a study of the distribution of mercury content in combustion products of the six boilers, it found that the ratio of Hggas is above 80% of the total Hg with the electrostatic precipitator (ESP); the ratio of Hggas is reduced below 25% with the ESP and wet flue gas desulfurization (WFGD); especially, with the ESP, WFGD and Selective Catalytic Reduction (SCR), the ratio of Hggas is lower than 5%. According to the mercury emissions estimation model, the total amount of mercury emission of every 100MW is about 40～50 Kg/year. The ratio of Hggas to Hgsolid is affected by the equipped air pollution control device in the tail flue. The total amount of mercury emission from power plant was approximately 193.644 tons, which included 147.014 tons of Hggas and 46.630 tons of Hgsolid in China in 2005.The stability of mercury on the AC's surface was studied in the different environments, such as solution environment, heated environment and natural deposition environment. According to the experiment, TCLP is a reliable laboratory accelerated assessment method, which can act as a reference method to evaluate the stability of mercury on the AC. Mercury appeared to be stable on AC in the solution environment according to leaching tests. However, the stability of mercury adsorbed on the oxidation treated AC was not better than that of untreated carbon on the whole. Mercury leaching showed strong pH dependence. Compared with the neutral pH test, lower and higher pH leaching tests for mercury were more effective for removing Hg. As was the result of mercury thermal desorption in air condition, there was much more mercury released from AC when heated either longer time or higher temperature for both kinds of mercury. In addition, it seemed that Hg°was bonded more firmly on AC than Hg2+. According to the natural deposited experiment results, the Hg was stable in both fly ash and AC, and would not significantly affect the environment.Using the experimental solution, the adsorption mechanism of Hg on AC was investigated before the research of enhancing Hg adsorption stability of AC. Thinking of adsorption mechanism experimental phenomena, it can conclude that the adsorption mechanism of Hg0 on AC is not simple physical adsorption, but complicated chemical adsorption. If there are no any chemical elements existing on the surface, AC will not adsorb the Hg°through Van der Waals force and chemical force in N2 ambience. According to the experiment, sorption of Hg2+ on AC showed the both chemical and physical characteristics. Based on the experimental results and analysis, the AC adsorption mechanism of Hg°in a simulated flue gas is that the Hg°is oxidized to Hg2+ by acidic atmosphere with the help of C catalysis on the AC's surface, and at the same time Hg2+ is adsorbed by active adsorption sites. It believes that the physical structure characteristic of AC's surface may work on adsorption capacity. Moreover, the oxidation of pre-impregnated oxidative chemical elements on the surface of AC can be instead of that of acidic atmosphere during the adsorption process. It provides direct experimental evidence for the acquisition or manufacture of adsorbent with high efficiency and high stability.Several types of S were introduced into the ACs through different modification. Compared the adsorption capacity of different modified ACs, the modified methods were arranged in order of efficacy as follows: 600℃-S-deposition > 200℃-S-deposition > (NH4)2S-dipping > free radical with SO2 source > S (CCl2)-dipping > Na2S-dipping. As the experimental results of TCLP, the Hg is quite stable on all modified ACs in general water environment. YK-AC-600℃-S-Hg and MZ-AC-600℃-S-Hg showed the enhanced trend of Hg stability on surface in the low temperature environment. (NH4)2S dipping modification enhanced the stability of Hg on the ACs. Considering adsorption capacity and stability, (NH4)2S dipping is the best way among various sulfur modification methods.Based on the result of Hg adsorption mechanism research and the tail flue structure of coal-fired power plant, the chemical adsorption model of AC injection in flue for coal-fired mercury control was established. It can simulate and study the effect of injection amount, particle diameter, flue-gas temperature, flue-gas velocity, mercury concentration, and flue length on the mercury adsorption of AC.
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