Industrial high-temperature flue gas often contains gases harmful to the environment such as nitrogen oxides, sulfur oxides and dioxins. These gases need to be dedusted before they can be removed by processes such as catalytic oxidation, otherwise the soot particles in the high dust content gas will adhere and the catalytic efficiency of the catalyst carrier will decrease.The traditional process is to first cool the high-temperature flue gas (water-cooling) and then remove the dust. Since the best working temperature of many excellent catalysts is above 300℃, the flue gas after dust removal needs to be heated in the later process,which consumes a lot of energy.
Ceramic membranes and supports contain a large number of fine pore structures, giving them a large specific surface area. The surface of these pores is a good carrier for the catalyst, and after the catalyst is loaded on this surface, the flue gas purification of desulfurization and denitration can be realized while removing dust. The integrated technology can not only reduce equipment volume and investment, but also reduce equipment operating costs.
At present, home and abroad dust removal technologies mainly include cyclone dust removal, bag dust removal, electric dust removal, electric bag dust removal, moving granular bed dust filter, porous inorganic membrane filtration and other dust removal methods. Cyclone dust removal has poor dust removal efficiency and cannot meet environmental protection emission requirements, which is generally only used for pre-dedusting. Bag dust removal is limited by the temperature resistance and corrosion resistance of the filter material. The use temperature cannot be too high. Generally, it is used below 250 ℃, which obviously cannot meet the needs of high temperature flue gas purification. Electric dust removal has problems such as unstable corona discharge, short electrode life, sensitivity to flue gas components, and high-temperature insulation. It is also not suitable for long-term use at high temperatures (generally below 380°C). The moving granular bed dust filter is resistant to high temperature and corrosion, but its filtration efficiency is not yet ideal, and the dust emission concentration is high. Metal membranes and filter material made of metal are expensive, and their applications are limited due to their inability to resist corrosion and wear. Among other filtration methods, the dust removal technologies that have been studied or are being studied include ceramic woven filters, ceramic fiber filters, etc. The filtration efficiency of these filters can reach more than 99%, but they all have the problems such as low strength, easy blockage.
The filter element of the ceramic membrane filter consists of multiple ceramic tubes arranged in bundles of multiple groups, or arranged in a certain arrangement, and placed on the tubesheet in the filter. The arrangement of filter elements mainly considers the distribution of airflow and other factors, and the filter elements mainly control the filtration accuracy by the membrane layer and the ash cake formed on the surface of the membrane layer. Ceramic membrane filters have been used in coal gasification, waste incineration, waste pyrolysis, regenerated ferrous metal melting, precious metal recovery, fluidized bed metal purification, boiler installations, chemical manufacturing and glass melting, and other fields, with significant dust removal effects.
2.1 Process of ceramic membrane separation technology cleaning high temperature flue gas
The asymmetric structure of the ceramic membrane element has the structural characteristics of small pore size of the membrane separation layer and large pore size of the support layer. One of the purposes of this design is to reduce the resistance during filtration, because it is the membrane that really plays the role of filtration and separation. Secondly, the pore size gradient is changed so that most of the soot particles are trapped when they pass through the membrane surface. The particles passing through the separation layer are getting larger and larger due to the size of the channel, and the adsorption force is getting smaller and smaller, so it is not easy to be blocked by adsorption in the channels of the support layer, so as to achieve the purpose of efficient separation.
2.2 Advantages of ceramic membrane separation technology in high temperature flue gas cleaning
The porous ceramic membrane filter has outstanding advantages such as high temperature resistance, corrosion resistance, high mechanical strength, stable structure and no deformation, long service life, and it can achieve functional regeneration through many times of cleaning, so it is considered as one of the best choices of dust removal in high temperature flue gas. Compared with cyclone dust collectors, wet dust collectors, bag dust collectors and high-efficiency electrostatic precipitators, the porous ceramic filter has a higher dust removal efficiency, exceeding 99.9%, and its filtration performance, especially the filtration efficiency for ultrafine dust particles below PM2.5 is unmatched by other dust collectors. In addition, the porous ceramic filter material will not cause secondary pollution, and it is one of the most suitable and promising materials for the deep purification of high-temperature dust-containing flue gas.
3. Prospect of ceramic membrane separation technology in high temperature flue gas cleaning
With the development of coal gasification technology, coal liquefaction technology, fluidization technology, clean coal technology, and powder engineering technology, ceramic membranes for purification of high-temperature dusty gas are under urgent demand. For this, the further development of new ceramic membrane filter material technology research, improvement of product quality, and reduction of production costs are of great significance to the improvement of industrialization level. The development of ceramic membrane purification technology for industrial high-temperature dust-containing flue gas can effectively reduce the emission concentration of smoke and dust, reduce PM2.5 particulate matter emissions in industrial flue gas, and recover high-grade heat energy in the flue gas. Enhancing the level of coordination between industrial development and the environment and making positive contributions to sustainable development and the construction of an environmentally friendly society are required in order to improve the quality of atmospheric environment.