脱硫石膏煅烧工艺及在墙体材料中的应用研究

【作者】 柏玉婷；

【导师】 李国忠；

【作者基本信息】 济南大学 ， 材料加工工程， 2010， 硕士

【摘要】 脱硫石膏是火电厂湿法脱硫过程中,用石灰或石灰石浆液吸收烟气中的二氧化硫,反应生成的副产物,其主要成分为二水硫酸钙（CaSO₄·2H₂O）,颜色多为黄白色。随着我国脱硫工程的发展,脱硫石膏已成为火电厂中继粉煤灰后的又一大固体废物,占用大量土地,污染环境。因此研究掌握脱硫石膏的性质,将其变废为宝加以综合利用,对于促进我国脱硫工程的进一步发展大有裨益。本文以脱硫石膏为研究对象,利用化学成分分析、XRD分析、SEM分析、粒度分析、热分析等手段,研究了脱硫石膏化学成分、相组成、微观形貌、细度、热性能等基本性能,并与天然石膏进行了对比;探讨了脱硫石膏煅烧成为脱硫建筑石膏的煅烧工艺。研究缓凝剂、保水剂、减水剂、防水剂等对脱硫建筑石膏的影响规律,采用不同外加剂对脱硫建筑石膏改性,探讨了利用脱硫建筑石膏生产抹面材料、纸面石膏板、石膏砌块等墙体材料的可行性。以玉米秸秆纤维为增强材料,提高脱硫建筑石膏制品的强度,考查了纤维掺加方法、长度、掺量对试样性能的影响规律,采用碱处理法、接枝法、包覆法对玉米秸秆纤维进行表面改性,期望进一步提高复合材料的力学性能。研究结果表明,脱硫石膏的化学组成和矿物组成与天然石膏相似,二水硫酸钙含量可达95%以上,杂质较少,细度小于天然石膏,微观结晶颗粒多成柱状和板状。采用预烘干+煅烧的二步法工艺煅烧脱硫石膏效果最好,即先在50℃下烘干2h,进而在155℃下煅烧。此工艺条件下煅烧的脱硫石膏,初凝时间6min、终凝时间9min、抗折强度3.35MPa,抗压强度7.88MPa,均达到或超过了国家关于建筑石膏优等品的性能要求。在外加剂研究方面,主要研究了柠檬酸、骨胶、偏磷酸钠这三种缓凝剂,分析结果可知,随着缓凝剂掺量的加大,缓凝效果越来越好的同时试样的强度却明显下降,单一的缓凝剂很难达到在保证强度的前提下延长凝结时间的效果,所以采取复合缓凝剂效果较好。对于保水剂而言,随着掺量的增加保水效果越来越好,但是羧甲基纤维素及糊精的加入都造成了不同程度的强度损失,而甲基纤维素却对试样强度有增强效果。分析五种减水剂的实验结果,可以发现,随着减水剂掺量的增大,减水率上升,但试样强度先升后降,木质素磺酸钙系减水剂效果最优。各种外加剂的成分及掺量为:以柠檬酸、骨胶、偏磷酸钠为主要成分的复合缓凝剂,掺量0.4%;甲基纤维素类保水剂,掺量0.3%;木质素磺酸盐系减水剂、掺量0.5%。经工厂实验证明,以上外加剂改性后的脱硫建筑石膏制品均可符合国家相关标准要求。掺加玉米秸秆纤维后,提高了脱硫建筑石膏制品的强度,采用碱处理法、接枝法、包覆法对玉米秸秆纤维进行表面改性,有效改善了玉米秸秆纤维与石膏基体的界面结合状况,进一步提高了复合材料的力学性能。实验结果表明,取1.0-2.0cm长度的玉米秸秆纤维,经聚乙烯醇+沥青包覆法改性后,按脱硫建筑石膏重量的3%,采用秸秆纤维与脱硫建筑石膏干拌后加水的同掺法制得复合材料,较脱硫建筑石膏空白样,试块的力学性能有显著提高,抗折强度提高了200%,抗压强度提高了125%。更多还原

【Abstract】 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%.更多还原