| At the same time of the rapid development of thermal power, coal, mining and other industries, a large amount of high-temperature dusty gas was discharged into the air, causing a great harm on human health and environment. In order to achieve sustainable development of economy and society, the high-temperature dust must be removed. Currently, the mostly studied dust removal technologies included cyclone dust removal, electrostatic precipitation, wet dust extraction, medium filtering and so on. Compared to the former several dust removal technologies, medium filtering had a lot of advantages such as high dust removal efficiency(removal efficiency of 90% to 99%), no secondary pollution, full use of resources as well as good economic benefit. High temperature dust removal materials were the key technology of filtering dust removal. It is the best choice to use porous ceramic for high temperature dust removal. It had a lot of advantages such as low production cost, high filtration efficiency, uniform pore size and easy to control, long service life and so on. Andalusite had many advantages such as excellent high temperature mechanical properties, acid and alkali resistance and thermal shock resistance, and the andalusite mineral resources are fairly abundant in China. Using andalusite to prepare high-temperature dust removing porous ceramics has great development prospect. By using the method of particle accumulation and adding pore-forming agent, this paper attempts to take andalusite as main raw material to prepare andalusite porous ceramic support with high porosity, flexural strength and good thermal shock resistance, which could be used for high temperature dust-removing. In order to prepare gradient ceramic filter materials, Ceramic fiber membrane layer and filter layer were coated on the surface of the matrix. The composition, structure and properties of andalusite porous ceramics were studied by using modern testing technologies. The mechanism of pore forming and the bonding mechanism among fiber membrane, filter layer and the support were discussed.The formula of series X and Y were designed by using Xinjiang Korla andalusite, Xingzi kaoline, Guiguang talc, industrial Al2O3, PSZ, sintered tabular corundum. By the method of particle accumulation and semi-dry pressing, andalusite porous ceramic support used for high temperature dust removal was made. After firing at different temperature, the water absorption, porosity, bulk density and bending strength of samples were done and the phase composition, microstructure of samples were studied by modern testing technology such as XRD, SEM and so on. The effect of different andalusite graduation ratio on the porosity, bending strength and microstructure of samples were studied. The experimental results showed that X2 samples(when the graduation ratio was 48 mesh: 250 mesh = 60:40, wt%) fired at 1420? had the best performance. The water absorption of X2 series samples was 8.09%, porosity of 18.26%, bulk density of 2.26g/cm3 and bending strength of 39.34 MPa. The main phase were mullite and cordierite, second phase were ?-quartz; Y5 samples(when the graduation ratio was 48 mesh: 250 mesh = 35:65, wt%) fired at 1460?had the best performance. The water absorption of Y5 series samples was 14.53%, porosity of 32.05%, bulk density of 2.21g/cm3 and bending strength of 41.09 MPa. The main phase were mullite and cordierite, second phase was zirconium silicate. SEM microstructure analysis demonstrated that most of the pores in X2 samples were three-dimensional and interconnecting ones. There were some pores whose aperture were more than 100?m and the average pore size was 7.51~118.23?m. The pores size of Y5 samples distributed homogeneously. Most of the pores were narrow and connected ones and the average pore size was 6.43~44.16?m. The research on mechanism of particles packing into pores indicated that in order to obtain samples with high porosity, the ratio of different particles must be controlled reasonably. Also, high porosity could be obtained by reshaping the raw material particles by ball milling to gain particles with shape of spherical or ellipsoidal.On the basis of graduation ratio experiment, the porosity of samples was improved by adding pore-forming agent. The four factors graduation ratio, firing temperature, graphite content(plus) and 700 mesh Si C content(plus) which influenced the performance of samples were evaluated with the L9(34) orthogonal design. The optimum formula A2(48 mesh andalusite 60wt%, 250 mesh andalusite 10wt%, the Xingzi kaolin 13wt%, Guiguang talc 13wt%, industrial Al2O3 4wt%, plus graphite 30wt%, plus 700 mesh Si C0.1wt%) was ascertained by the orthogonal analysis. The water absorption of A2 series samples fired at 1360?was 22.86%, porosity of 39.16%, bulk density of 1.71g/cm3 and bending strength of 46.70 MPa. The bending strength has decreased 13.45% after 30 times thermal shocks(room temperature to 1000?, air-cooled), reaching 40.42 MPa. The main phase were mullite and cordierite.SEM analysis showed that most of the pores in A2 samples were interconnecting ones.The pores size distributed homogeneously and the average pore size was 8.33~51.67?m.The methods to improve the porosity of samples were studied by changing the firing temperature and andalusite particle graduation ratio. On the basis of the formula A2, the influence of firing temperature on the properties of samples was discussed in a temperature range of 1320~1420?. The results showed that the porosity of samples couldn't be improved significantly by changing the firing temperature, but the bending strength could be increased significantly, as the firing temperature increased from 1360? to 1380?,the bending strength increased from 46.70 MPa to 91.33 MPa. T series graduation ratio experiments were designed. Experimental results found that when andalusite particle graduation ratio was 48 mesh(300?m): 120 mesh(125?m) = 60:40(wt%), the water absorption and porosity of T2 samples fired at 1280? reached the maximum. The water absorption of T2 series samples was 23.72%, porosity of 40.28%, bulk density of 1.70g/cm3 and bending strength of 39.34 MPa. The bending strength has decreased 3.69% after 30 times thermal shocks(room temperature to 1000?, air-cooled) and the porosity increased to 40.31%. The mechanism of improving the porosity was to increase the particle size of tiny particle andalusite. When the particle size of tiny particle andalusite increased from 63?m to 125?m, the porosity of samples increased from 39.16% to 40.28% and the firing temperature decreased from 1360? to 1280?.A1 samples(firing temperature of 1360?) with the best comprehensive properties were selected as matrix material. A set of ceramic fiber membrane formulas contained aluminum silicate fiber and A1 formula powder were designed. A layer of ceramic fiber membrane was coated on the surface of the matrix as fiber transition layer. A1 formula powder(250 mesh) was used as ceramic particle filter membrane formula to prepare ceramic filter membrane layer. Finally, a kind of porous ceramic filter materials which could be used for high temperature dust removal was prepared. The influence of sintering temperature and different fiber content on the membrane material and the bonding performance between the membrane and matrix material were studied. The acid and alkali resistance of optimum samples were tested. The pore size and distribution of the matrix, fiber transition layer and filtering membrane was tested by using SEM and professional image analysis software Image-pro Plus 6.0. Experimental results show that there has excellent bonding properties among the matrix, fiber transition layer and filtering membrane. Fiber transition layer contained 80wt% fiber and fired at 1080 had the best performance. ?The pore size of andalusite porous ceramic matrix was 40~45?m, the pore size of fiber transition layer was 7~9?m, the pore size of filtering membrane was 2.5~10?m.The acid resistance of the sample was 99.35% and alkali resistance was 98.49%, meeting the application requirement of high temperature dust removal. The study on the bonding mechanism among fiber membrane, filter layer and the support showed that it was better to make the composition of fiber membrane and filter layer similar or identical with the composition of the support.The surface of samples was flat and had no cracks because the thermal expansivity of fiber membrane, filter layer and the support were similar. |
PDF Full Text Request