Research Of Coal-fired Power Plant Fly Ash On The Dynamic Absorption Characteristics Of Mercury

In China’s energy structure, thermal power plays an important role. Each year, the combustion of coal emissions into the environment a lot of toxic substances-mercury. According to the statistics, coal-fired power plant mercury emissions accounted for 1/3 of anthropogenic mercury emissions, and serious threat to the human survival and ecological balance of the environment, and the coal-fored power plant mercury pollution problem has been got more and more attention of people. According to the finding of the research of mercury pollution, the fly ash of coal-fired power plant has a certain adsorption characteristics of mercury in the flue gas, and is a potential mercury removal sorbent with a good market prospects. Therefore, in this paper we choose A and B two kinds of fly ash as the research objects, research the mercury adsorption characteristics of different coal-fired power plant fly ash. In order to improve their ability of fly ash to take off the mercury, we modified the fly ash by the chemical reagents, and do a series of studies of modified fly ash to explore the reaction mechanism of mercury and modified fly ash.In order to study the mercury adsorption characteristics of fly ash under the flow state, this paper developed a carrying-bed mercury removal platform, and conduct the accuracy researchs about various components of the experimental platform to ensure the obtained data real and effective. In the experimental platform, research the factor of different fly ash, different reagents modified, different concentrations of reagent modified and different temperatures, different residence times, different flue gas composition et al on the effect of fly ash adsorption of mercury.,and take fly ash mercury efficiency and adsorption rate two evaluation methods from the final results and reaction rate two aspects to make a more comprehensive evaluation of the mercury removal performance of fly ash, in order to explore a practical mercury removal technology for the coal-fired power plant.First, this paper made a industrial analysis about the pulverized of the A and B two kinds of coal-fired power plant, measuring the mercury content and unburned carbon content in fly ash. Use the HBr and NH4Br two chemical reagents to modified the A and B fly ash, and researchs the specific surface area, pore volume and pore size of the fly ash before and after modification. Study the variation of bromine content and surface structure in different concentration reagent modified fly ash, and get the important characterize information from different samples.The study found that different plant fly ash has a different mercury removal ability. Under the same circumstances, A fly ash mercury removal capability is stronger than B ash. The higher of unburnt carbon content, the greater of surface area, the smaller of aperture, the stronger of mercury capture of fly ash. Use HBr and NH4Br to modifies the fly ash, the mercury adsorption capacity of fly ash can greatly improve, and the HBr midified fly ash has a better mercury removal capability than the NH4Br modified fly ash. Increase the feeding amount of modified fly ash or the initial concentration of mercury in the flue gas can increase the chances to contact between the modified fly ash and mercury in the flue gas, thereby improving their mercury removal ability of fly ash.The adsorption of modified fly ash include physical adsorption and chemical adsorption. Improve the temperature can promote the chemical adsorption of modified fly ash, while to some extent undermined the physical adsorption of modified fly ash. The study found that the mercury removal ability of modified fly ash will improve when improve the temperature of flue gas, and the temperature has a bigger effect on the NH4Br modified fly ash than HBr modified fly ash.The impact of residence time on modified fly ash mercury adsorption base on the time and the flow field:with the increase of residence time, the reaction time between modified fly ash and mercury increased, but the amount of gas decrease in the reactor, the mixing effect of modified fly ash and flue gas becomes worse. The experiment results show that:the mercury removal efficiency of HBr modified fly ash decreases when the residence time increase, while the NH4Br modified fly ash show a downward trend after the first rise. However, with the increase of the residence time, the adsorption rate in the two modified fly ash has been increased.The flue gas composition and content will impact the adsorption of modified fly ash in the reactor. The flue gas of NO、NO2、HCl、O2 has a strong oxidation, and will make synergy with bromine of the modified fly ash, thus will promote modified fly ash adsorpte mercury. The impact of SO2 gas is more complicated, in the lower levels, SO2 gas will inhibit adsorption of mercury of the modified fly ash; in the higher levels, SO2 gas will promote the adsorption of mercury of modified fly ash. After collect and analysics the fly ash in the different position of the carrying-bed mercury removal platform found that the mercury in flue gas mainly enriched in the fine particle surface. The bigger of specific surface area, the higher the mercury content in fly ash.