Research And Application On The Additive Enhanced Limestone-gypsum Flue Gas Desulfurization

Limestone-gypsum wet flue gas desulphurization is a technology that is widely used. To imporve the desulfurization efficiency and the utilization of limestone, additives be used to strengthen the process. The principle of wet limestone scrubbing was reviewed. One of the key problems, oxidation of sulfite, was summarized as well and the effect of additives on oxidation kinetics of sulfite was investigated. By use of self-designed bubbling reactor in laboratory scales, the enhanced process that inorganic and organic additives for the oxidation of sulfite was investigated experimentally.In presence of manganese sulfate, magnesium sulfate, the symbol of the metal additives, macroscopical oxidation kineticas of sulfite was studied. It is shown that manganese sulfate is effective. The total oxidation reaction is determined by the dissovled rate of calcium sulfite in the presence of manganese sulfate. The reaction rate is 0.75 level response for the concentration of calcium sulfite and 0 level response for manganese ions, pH. The apparent activation energy is 73.5 KJ·mol^-1. The reaction rate increased with the increasing air flow in certain extent, but excessive increase in air flow will cause slow response. Magnesium sulfate can form MgSO3 0 neutral ions which can promote the dissolution of limestone and SO₂ absorption. The reaction rate is 0.5 level response for the pressure of oxygen and 0 level response for magnesium ions, concentration of sulfite. Magnesium sulfate increases the reaction rate constant and did not affect the series of reactants.Experiments demonstrated that benzoic acid, as symbol of organic acid, can suppress the decreasing of pH value of scrubbing liquid and reduce the resistance of liquid phase and gas phase mass transfer. While the benzoic acid has surface-active effect, can increases the effective mass transfer area of desulfurization. Benzoic acid is more significant additive, which can effectively promote the oxidation process, thus improving the desulfurization effciency.The use of Limestone-gypsum wet flue gas desulphurization based on Magnesium at Zhangjiakou sub-critical Power Plant Unit 2×300MW application were studied. Results indicate that adding an effective synergist could increased the desulfurization efficiency and reduced the scale plugging problems, greatly reduced the power consumption rate, and the annual cost savings is about 1.8 million (to run for 10 months).