| High-temperature industries such as metallurgy,building materials,chemicals and electricity generate large amounts of high-temperature flue gas every year.The hot flue gas has high-grade waste heat,complex composition and properties.Dust particles tend to adhere to the surface of the heat exchanger,causing problems such as reduced heat exchange efficiency and even depositional clogging.Hot flue gas dedusting refers to the gas-solid separation of flue gas directly under high temperature conditions to achieve gas purification.The purified hot flue gas can be denitrated at high temperature and recover high-grade waste heat.Therefore,hot flue gas purification technology is an important new energy-saving and environmental protection technology.The asymmetric porous ceramic membrane filter tube is the core component of the hot flue gas dedusting system,and is composed of a support for carrying the filter membrane and a filter membrane for dust removal.The reliability,safety,filtration efficiency and filtration accuracy of ceramic membranes are inseparable from their mechanical properties and pore structure.This dissertation aims to prepare silicon carbide porous ceramic membranes with low cost,high strength,high porosity and low filtration pressure drop.The effect of different kinds of additives,their contents,sintering temperature and the proportion of aluminum and silicon in the additive on the microstructure,structural composition and thermal shock resistance of the membrane carrier was studied systematically.The permeability and filtration pressure drop of ceramic membranes were also characterized.?1?A novel process for preparing porous SiC ceramic supports was successfully developed.SiC particles were coated with mixed sol?tetraethyl orthosilicate and aluminum sol?and pore former?charcoal powder?in a two-step process.SEM image confirmed that the starting powders after coating possessed a double-layer structure.The mass transport process between the surface-coated particles was described by the double-sphere model during sintering process.Results revealed that the porous SiC ceramic supports prepared by this novel process had considerable strength?more than 21.96 MPa?and high porosity?more than 34.71%?.As well as the SEM exhibited that the supports presented a higher three-dimensional connected pore structure,which was proved by the low pressure drop?lower than 58 Pa?when the airflow linear velocity reached 1.0 m·min-1.The conclusion showed that as-prepared supports by using SiC powders coated by mixed sol and pore former have broad application prospects in the field of hot flue gas cleaning.?2?On the basis of the prepared silicon carbide supports,corundum-based membranes were prepared on the macro-porous SiC supports using silica-sol as the binder by dip coating method.The effect of the corundum particle size on the surface morphology,pore structure and size distribution of the membranes was studied,and the membrane performance was evaluated by testing the gas permeability and pressure drop.The results indicate that for the SiC supports with97?m average pore size,the surface of the as-prepared membrane has no visible pinholes or cracks when the ratio between the supports pore size and membrane particle size is smaller than5.As the particle size increases from 5 to 63?m,the average pore size of the membrane enlarges from 2.2 to 21.5?m,the gas permeability increases from 13.6 to 304.9 m3/?m2·h·kPa?,and the pressure drop decreases from 4549.4 to 197.1 Pa,respectively.The as-prepared membranes with20?m particle size are promising for hot gas filtration due to the good balance of the filtration precision and gas permeability. |
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