Chemical industry, medicine, pesticide, fine chemical industry, metallurgy and other industries will encounter processes such as filtration, washing and drying of strong corrosive media such as dilute sulfuric acid, hydrochloric acid, hydrofluoric acid, aqua regia, and chloride ions. It cannot be used, and if the concentration of corrosive medium exceeds 5% to 8%, even titanium is helpless. In this case, the selection of filter material is often a thorny issue, especially when there is a strong corrosive medium and the process temperature is high, the corrosion will be more serious. Although Monel and Hastelloy can be used, the cost is too expensive and generally unaffordable.
The anti-corrosion design of the three-in-one flat filter, washing and drying has been placed in a very important position. For the selection of multifunctional crystallization filtration washing and drying equipment, various grades of stainless steel alloy materials can meet most production and use requirements. However, highly corrosive materials (high concentration of acid and alkali, high content of chloride ions, etc.) are unavoidable in some production, and the selection of materials in such cases needs to be more cautious. The improved design of corrosion-resistant structures generally starts from three aspects:
1. Corrosion-resistant design of flat three-in-one filter plate
The three-in-one shell of flat-type filtration, washing and drying can adopt the special structure of thermal rolling modified polyethylene, PTFE welding lining, and spraying PTFE (HALAR), which can meet the filtration, washing and drying of various materials. process needs.
For the automatic hydraulic filter cake discharge system, a piston-type automatic jacking structure can be used to meet the needs of various corrosion-resistant lining structures or composite plate lining structures. Especially the lower flat plate filter structure has a complex structure, and a special structure in which the filter plate and the filtrate collection system can be separated can be used, which is convenient for applying various lining structures, and the filter cloth can be tightened without fixing bolts, and can be conveniently passed through the automatic hydraulic system Detach the filter chassis from the equipment, and perform operations such as filter replacement.
2. Corrosion-resistant design of filtering, washing and drying three-in-one stirring shaft seal
For the stirring scraping and pushing system, an S-shaped stirring structure can be used, which is relatively easy to corrode the lining.
The hydraulic lifting stirring shaft seal can adopt the upper packing sealing structure with PTFE lining and spraying structure. Since the stirring shaft needs to be raised and lowered continuously, a reliable, wear-resistant and anti-corrosion sleeve with a certain strength should be considered on the stirring shaft. Hard polytetrafluoroethylene, silicon carbide, ceramics, titanium, Hastelloy, etc. Corrosive material.
3. Corrosion-resistant design of the stirring device of the chemical grade filter washing dryer
The stirring device requires certain strength and wear resistance due to its movement, and the spray coating layer is relatively thin, so the polytetrafluoroethylene plate should be used.
PTFE sheets can be made into various shapes, and the joints can be welded. The flat-plate three-in-one mixing system is not suitable for lining PTFE plates because it needs to stir and scrape dry materials such as filter cakes. Generally, it is necessary to use titanium-lined or Hastelloy-lined plates according to the corrosiveness of the materials. The method is to use pure titanium or Hastelloy to make it if necessary.
The design of the three-in-one filter washing and drying machine generally requires reasonable material selection and design according to specific conditions such as materials and temperature, such as various types of filter holes or filter surfaces. When the temperature is not high, sprayed polyethylene structures can be used. ; When the process temperature is higher than 90 ℃, or the medium is a mixture of dilute sulfuric acid, hydrochloric acid, hydrofluoric acid, aqua regia, chloride ions, etc., the structure of lining PTFE can be used.
The three-in-one corrosion-resistant structure of flat plate filter, washing and drying is often a combined structure after reasonable selection of several materials such as polyethylene, polytetrafluoroethylene, titanium or Hastelloy. The more reasonable the material selection, the more reliable the corrosion resistance. Wuxi ZhangHua has done a lot of design and development work in this area, and has developed a more reasonable corrosion-resistant structure, which not only solves the filtration and washing problems of many strong corrosive media, but also can be accepted by users in terms of price.