Silicon carbide ceramic membrane filter tube has two important components, namely, a coated membrane carrier made of large-sized silicon carbide particles and one or more ceramic membranes made of small-sized ceramic particles. It is a porous ceramic with an asymmetric filtration structure. The advantage of this structure is that it ensures sufficient filtration efficiency and filtration accuracy, and because of the large pore size, the filtration pressure drop is low, and the energy consumption is also reduced.
During the operation of the high-temperature ceramic membrane filter, the high-temperature dusty flue gas will enter the filter from the inlet and flow from the outer wall to the inner wall of the porous ceramic membrane filter tube under external pressure. In this process, the dust particles in the flue gas are blocked on the outer wall of the ceramic tube membrane, and the clean hot gas flows out from the inner wall. With the increase in the number of filtrations and time, the thickness of the ash cake on the outer wall of the ceramic membrane will continue to increase, and the filtration pressure drop on both sides of the inner and outer walls of the filter will increase accordingly. When the set value is reached, the system will be pulsed back-blown by the back-blowing device to remove the ash cake on the outer wall by injecting high-pressure gas. During the periodic pulse backwashing process, since the injected high-pressure gas is much lower than the temperature of the dusty flue gas, the porous ceramic membrane filter tube needs to withstand periodic thermal shock, cold shock, and the filtration pressure difference between the inner and outer walls. This reflects the importance of the mechanical strength and thermal shock resistance of the ceramic membrane filter tube.
In addition, due to the complex nature of high-temperature flue gas, the solid particles may contain oxides and sulfides of various elements (such as sodium, potassium, calcium, iron, aluminum, silicon, etc.), etc., and the porous ceramic membrane filter tube needs to have good resistance to chemical erosion under high-temperature environment.
Key points for the preparation of silicon carbide porous ceramics for filtration
There are many factors that affect the strength of ceramic membranes. If the scope is limited to the microstructure of porous ceramics, “porosity” is the most important, followed by porosity, pore shape, size, distribution, etc.
A large number of studies have shown that strength and porosity are in a competitive relationship, but the speed at which the strength of porous ceramics decreases with increasing porosity is different in different porous ceramic structures. For example, the strength of porous ceramics sintered from granular ceramic powders decays exponentially with increasing porosity; while the strength of porous ceramics prepared by the bio-template method has a strong orientation along the pore direction, which is different from porous ceramics prepared by particle accumulation. How to coordinate strength and porosity is the key to the preparation process.
At present, porous SiC ceramics are mainly prepared by replication, foaming, and adding pore-forming agents. Different processing methods are developed and applied to different industrial fields and use environments to meet the requirements of porosity, pore size, and connectivity. However, since the sintering temperature of porous SiC ceramics is at least above 1600℃, the key to popularizing the use of porous SiC ceramics is how to reduce its preparation temperature and thus reduce costs.