Study On The Mercury Removal Performance Of Coal Fired Flue Gas Using Black Liquor Of Wheat Straw Pulping

This Paper does research on the mercury removal efficiency and related mechanisms of wheat straw pulping black liquor under the background of definite stipulation of the mercury discharge from coal fired power’s flue gas. Under the current condition of bubble column reactor, the paper studies on the effect of mercury absorption by different components of black liquor, while taking the chemical reaction characteristics into consideration. Meanwhile, this paper discusses the mechanisms of absorption process in a combination of liquid mass transfer theory, chemical kinetics, chemical thermodynamics, electrochemistry theory and surface adsorption theory. The experiment results were as follows:(1) The study shows the mercury removal efficiency is affected by chloride, bromide and sulfate in black liquor. These substances accelerate the mercury’s oxidation process. The removal efficiency and the overall macro rate of mercury rise slightly with the concentrations increasing of these substances.(2) Possible reactions of chemical equations for mercury removal using oxidant was speculated by related electrochemical theory. In addition, chemical thermodynamics standard equilibrium constant KΘ of these reactions were calculated, which verified these reaction would occur, and most of these reactions were irreversible reaction.(3) Through the mass transfer analysis of mercury adsorption process by black liquor, the physical and mass transfer parameters were calculated under the participation of oxidant. On this basis, the chemical absorption enhancement factor β and chemical reaction rate constant k2 were deduced and calculated.(4) The activation energy Ea of chemical reaction with only oxidant involved was also calculated by the Arrhenius empirical formula and parameters above all. The calculation result shows that the absorption reaction is a fast reaction with the participation of oxidant. The rate of mercury oxidation process is controlled by the chemical reaction. The reaction is occurred completely when mercury transferred into the liquid film, which does not diffuse into the liquid bulk. And the chemical reaction is enhanced by the adding of inorganic, which also accelerate the rate of absorption reaction and increase the activation energy. All of these enhanced the mercury removal efficiency by black liquor.(5) The mercury removed by DMSO is an adsorption-based process, which accompanied by certain chemical reactions, but the removal effects of mercury in chemical reactions are not obvious. As a whole, mercury removal effect of DMSO is poor, and the increasing concentration of DMSO for mercury removal efficiency is not obvious. The mercury removal by DMSO is enhanced by the physical dissolve in original solution.(6) As a kind of surfactant, sulfonate lignin has a very significant impact on mercury removal efficiency. The abundant SL in black liquor make the mercury absorption becomes a kinetically controlled process, and it reduce the impact of solution diffusion on mercury absorption process, then enhance the absorption capacity of black liquor. In addition to greater adsorption capacity, the high concentrations of SL in black liquor can also enhance the mercury removal stability of black liquor by the impact on surface molecules arrangement.