Research On Synergism Mechanism And Basic Application Of Desulfurization Additive For Wet Flue Gas In Large Coal-Fired Boiler

At present, the limestone-lime washing technology is one of the mostwidely used process for wet flue gases desulfurization in power plants. In ourcountry, with the introduction of increasingly stringent environmental policyand emissions standards, numerous plants were forced to expand the scale ofdesulfurization system to meet the sulfide oxide emission standards. This willbring about unprecedented economic and environmental pressures to theenterprises. More and more research has focused on the desulfurizationadditives, which can improve the desulfurization performance. In this paper,variety kinds of additives, for example, inorganic salts, organic acid, organicamine and solvents and so on., were used to investigated the strengthen effectsof the desulfurization performance by limestone slurry. The experimentalresults can be conclude as follows:In this dissertation, a bubble absorption reactor was used to assess theperformance of SO2by adding some additives in limestone slurry through pH–stat method. The results show that sodium citrate and magnesium sulfate cannotably enhance the pH buffering performance and promote the desulfurzationefficiency. Four kinds of organic acids additives (benzoic acid, adipic acid,citric acid and tartaric acid) can obviously improve the pH bufferingperformance and increase the sulfur capacity in slurry. The synergisticmechanism of organic acids added in limestone slurry was studied and theresults indicated that the larger the ionization constants, the larger thestrengthen SO2absorption performance. Compared with the limestone slurrywithout any additives，It is greatly improve the desulfurization efficiency byadded ethylidene double morpholine or MDEA in limestone slurry. The mainreason is that1-methyl-2-pyrrolidone(NMP) containing tertiary amine groupswith alkaline and dimethyl sulfoxide (DMSO) can react with SO2,and thusenhanced the pH buffering performance of limestone slurry and promoted theabsorption of SO2by limestone slurry.The oxidation kinetics of sulfite was studied under the condition ofWFGD. The results show that in the range of initial concentration of calcium sulfite from5to50mmol/L, the oxidation rate of calcium sulfite increased asthe increasing concentrations of sulfite. On the other hand, when pH value wascontrolled in the range of5~8, the oxidation rate of sulfite ions increased withthe increase of pH value.The effects of additives on catalytic oxidation of sulfite were investigatedalso in this paper. The experimental result show that the promoting effect ofmanganese sulfate for catalytic oxidation of calcium sulfite was extremelyoutstanding, while the role of magnesium sulfate is only second to manganesesulfate. This is because that the presence of metal ion catalyst can accelerate theformation rate of free radicals, and thus promote the oxidation rate of sulfiteroot. Adipic acid was also conducive to the oxidation of sulfite, since it canfacilitate the leaching of metal ions in limestone slurry.The influences of additives on the gypsum of crystallization inductiontime, crystal morphology and particle size distribution were reseached in thispaper. SEM characterization results confirmed that magnesium sulfate canpromote the process of gypsum crystallization, increase the gypsum particlesize, and prompting gypsum crystallization from needle-shaped crystal forminto columnar. It is good for gypsum modification of dehydration performanceby added magnesium sulfate. The experimental results can be also concludethat the characterization of gypsum crystallization were improved by addedcitric acid. And at the presence of citric acid the crystal morphology of gypsumwas changed from needle almost entirely into short columnar, which was infavour of gypsum dehydration.The effects of three kinds of additives on the properties of limestonedesulphurization were tested in the lab-scale spray tower. The results show thatthere is obvious promote effect for desulfuization performance by addedsodium citrate and EDTA disodium. And the pH buffering capacity wassignificantly enhanced by added benzoic acid and citric acid in limestone slurry.However, the enhanced degree of desulfurization peformance by addedcompound additives (benzoic acid-manganese sulfate) is better than a singleadditive.