Fgd Gypsum Calcining Process And Wall Materials In Applied Research

Flu gas desulfurization gypsum is a kind of byproduct produced in the process of wet desulphurization, its main component is calcium sulfate dihydrate and its color is yellowish-white. With the development of our country's desulfurization project, flu gas desulfurization gypsum is another type of solid waste in thermal power plant except the fly ash, plenty of land are used for the storage of flu gas desulfurization gypsum, polluting the environment. So studying the property of flu gas desulfurization gypsum and comprehensively making use of it are benefit for the development of our country's desulfurization project.Flu gas desulfurization gypsum was taken as the research object, its basic properties, such as the flu gas desulfurization gypsum's chemical composition, phase composition, were studied by means of chemical composition analysis, X-ray diffraction, scanning electron microscopy, grain-size analysis and thermo gravimetric analysis, and flu gas desulfurization gypsum's basic properties were also compared with nature gypsum; the calcination technology that flu gas desulfurization gypsum changed into calcined gypsum from flu gas desulfurization were also discussed. The effect of retarder, water retaining agent, water reducing agent and water repellent on calcined gypsum from flu gas desulfurization were studied, calcined gypsum from flu gas desulfurization was modified by adding additive, and the possibilities of using calcined gypsum flu gas desulfurization to product wall-building material, such as rendering material, thistle board and plaster block, were discussed. Corn straw fiber was taken as reinforcement material to enhance the strength of calcined gypsum from flu gas desulfurization, the effect of methods of fiber doping, fiber length and fiber dosage on samples properties were checked, corn straw fibers were modified by the methods of alkaline treatment, grafting treatment and coating treatment, in order to enhance the mechanical property of composites further more.The results indicate that: flu gas desulfurization gypsum's chemical composition is similar with the calcined natural gypsum, the content of calcium sulfate dehydrate is up to 95%, the content of impurity is little, grain-size is smaller than calcined natural gypsum, and Micro crystalline particles are likely to be cylindrical and slaty. The effect of the calcination technology using two step method is ;notable, first, flu gas desulfurization gypsum is dryinged at the temperature of 50℃for 2h, and then calcined at the temperature of 155℃. The initial setting time of the Calcined flu gas desulfurization gypsum using this technology is 6min, final setting time is 9min, flextural strength is 3.35 MPa, and compressive strength is 7.88MPa, all of the above properties are better than national requirements.Citric acid, bone glue and sodium metaphosphate are selected as retarder, the results imply that: with the increasing of doping dosage, retardation effect is more notable, but the strength of samples reduce obviously, Under the guarantee of owning good strength, the single type of retarder can not prolong the setting time, so the effect of compound retarder is better. With the increasing of water retaining agent, water retaining effect is better, but the addition of CMC and dextrin reduce the strength at the same time, only the MC can increase the strength of sample. With the increasing of water reducing agent, the water reduction rises, but the strength of samples go up first, then fall, the effect of calcium lignosulfonate is best. The doping dosages of each additive are: compound retarder made up of Citric acid, bone glue and sodium metaphosphate is 0.4%, MC is 0.3%, calcium lignosulfonate is 0.5%.Through the factory production testing,the products of calcined gypsum from flu gas desulfurization modified by the above additive accord with related national standards.The strength of calcined gypsum from flu gas desulfurization is enhanced by the addition of corn straw fiber; the interfacial bonding between the maize straw fibers and desulfurization gypsum is improved, due to the modification of fibers using alkaline treatment, grafting treatment and chemical coating treatment, resulting in that the mechanical properties of composite is increased further more. The results indicate that: when the length of corn straw fibers is 1.0-2.0cm, corn straw fibers are modified by the coating treatment using polyvinyl alcohol and asphaltum, and the doping dosage of corn straw fibers is 3%, the mechanical properties of samples are enhanced obviously: the flextural strength is enhanced by 200%, and the compressive strength is enhanced by 125%.