Coal Adsorption Purification Process Of Mercury Emissions Of Pollutants, Migration And Numerical Simulation

Coal-fired power plants are primary sources of mercury emission into the atmosphere, which seriously harmed the ecological environment and human health. It’s important for removal and control of mercury pollutants to understand the mercury emission and transformation through combustion process. For recent years, researches on mercury transition in pulverized coal combustion process focused on simple simulation based on chemical dynamics and only few field testing measurements at power stations have been published. The studies which apply the kinetic reaction mechanism of mercury to simulate the emission and transformation in actual boilers are rarely reported. Activated coke adsorption is an advanced dry-based removal technology for pollutant purification. The activated coke desulfurization has been used in practical applications, but the systematic study on the mechanism of the heavy metal removal by activated coke is still lack.The thesis consists of the following parts:In order to understand the mercury oxidation process, a full scale pulverized coal fired boiler (410t/h) was chosen as research object, the impact of different operating parameters and complex contents of flue gas on characteristics of release, distribution and transition of mercury was investigated through the chemical thermodynamic equilibrium and chemical kinetics methods. The three dimensional distribution of elemental mercury and oxidized mercury in actual boiler furnace and downstream duct of flue gas were obtained. The simulation results show that Eddy Dissipation Conception (EDC) model is more accurate to predict the characteristics of release, distribution and transition of mercury. When temperature of flue gas is above1000K, elemental mercury is the dominant form. By contrast, the oxidized mercury is the main form and the chlorine plays an important role in the generation process of mercury chloride when temperature range is about500-900K in the downstream flue gas path. HC1and HOC1are crucial in the mercury oxidation process. The species such as Cl>Cl2anticipate in the oxidized reactions and Cl2is the key specie when producing HgCl2. The concentration of mercury chloride increases rapidly with the temperature falling. The content of mercury chloride is about92.36%and mercuric oxide is7.64%.A series of tests concerning mercury adsorption by activated coke were conducted with a bench-scale, fixed-bed reactor, the adsorptive properties and the effect of complex flue gases on the removal characteristic were obtained. The results indicate that the adsorption performance of Hg0with activated coke is influenced by SO2obviously and inhibition is observed in the removal process in the CO2/N2/O2/SO2/Hg0system. The complex impact of NO on the adsorptive capacity of Hg0also is found that NO with lower concentration promotes the adsorption of elemental mercury while inhibits at higher value in the CO2/N2/O2/NO/Hg0system. The increasing concentration of NO with the stationary concentration of SO2has a promotion to mercury adsorption while O2, NO, SO2and Hg0exist simultaneously. However, the increasing concentration of SO2could enhance the mercury adsorption at the initial stage and prevent at the latter stage.The kinetics studies on mercury adsorption by activated coke were also carried out in this paper. The results show that in the CO2/N2/O2/NO/Hg0system, removal efficiencies are similar for different initial elemental mercury concentrations and the removal efficiency increases with the increasing of the initial elemental mercury concentration. The uptake process of mercury in activated coke follows the pseudo-second order kinetics model and the chemical adsorption is dominant in the adsorption process. In the CO2/N2/O2/NO/Hg0system and the CO2/N2/O2/SO2/Hg0system, the chemical adsorption or chemical reaction occurs in the adsorption process with the increasing of temperature and the optimal temperature is observed at423K for the best mercury removal under both systems. The Bangham equation is applied to describe the adsorption behavior in the CO2/N2/O2/NO/Hg0system and the absorption rate constants are acquired at different temperature with following relationship as k423K> k463K> k403K.