Oxidation Kinetics Of Homogeneous Mercury And Chromium In Coal Combustion Process

Coal is an important energy in China, coal combustion is the primary source of pollutions which cause great destructions to the ecological environment. In addition to SOX, NOX, CO2 and particulate matters, trace element is also an important pollution, which emit from coal combustion process. Because of trace element's combined qualities of potential toxicity, environmental persistence and potential for bioaccumulation, it not only causes serious diseases of respiratory systems, but also contaminates water resource, soil and causes the destruction of the ecological environment. The release and transformation of trace element during coal combustion process contains a complex physics and chemical mechanism. The systemic research on the trace element during coal combustion can help to the precise prediction and efficient control of the trace element pollution.In this thesis, two kinds of toxic trace elements, namely mercury and chromium, were studied by the method of kinetic modeling. Firstly, the transformation regularness of the mercury and chromium species was described, and the influencing factor, the intrinsic physics and chemical properties of trace element itself, combustion conditions (include temperature and atmosphere) and the chlorine concentrations in the flue gas. Three major methods were introduced later, which are sampling and on-line analysis, chemical equilibrium analysis and chemical kinetics analysis separately.Secondly, an overall kinetics model for mercury oxidation in the flue gas is development involving the submechanisms of SOX conversion chemistry and NOX/SOX interaction. At present, the mechanism of SOX/Cl is not well known that it was considered in a rough mode. Effects of flue gas constituents of NO, NO2 and SO2 on mercury speciation were evaluated by kinetic model. When either of NO/NO2 or SO2 was added to the simulated flue gas, NO and NO2 are effective Hg oxidation inhibitors, SO2 weakly inhibit homogeneous Hg oxidation only at high concentrations. When two of NO/NO2 or SO2 was added to the simulated flue gas, synergistic effect between NO2/SO2 and NO2/HCl was observed; Oppositely, no synergistic effect was found between NO/HCl and SO2/HCl. That is to say, SO2 or HCl has potential effect on Hg oxidation through the interactions with NO2. It can be concluded that SO2 is an important matter in mercury oxidation and is indispensable in the construction of mercury kinetics model.Finally, chromium kinetic model in the relatively simple system of Cr/O2/Cl2 was developed, and then the transformation of chromium species in flue gas was studied. Because of the lack of kinetic parameters, thermodynamic analysis was only made for Cr/O2/H2 system, which established the foundation for further study of kinetic models.