The process treatment of powder particles refers to many unit operations in which the process materials are powder particles and their mixtures, and are mainly physical changes, including granulation, crushing, classification, dust removal, filtration, sedimentation, centrifugal separation, drying, crystallization, mixing, conveying, feeding, packaging and other processes. The device is called process treatment device.
Powder granulation technology is the main branch of powder processing. With the improvement of environmental protection and automation of production process, granulation of powder products has become an inevitable trend of powder post-treatment technology in the world.
The research on powder technology and equipment in China began in the mid-1980s. After years of efforts, the powder granulation technology in China has reached a certain level. The equipment scale can basically meet the requirements of powder granulation. The existing powder treatment technologies can be divided into four categories.
Stirring granulation is to infiltrate a certain liquid or binder into the solid fine powder and stir it properly, so that the liquid and solid fine powder are in close contact with each other to produce cohesive force and form pellets. The most commonly used mixing method is through the turning, rolling and curtain type falling movement of the disc, cone or barrel drum during rotation. According to the forming method, it can be divided into rolling pellets, mixed pellets and powder pellets. Typical equipment include pelletizing drum, swashplate granulator, cone drum granulator, disc granulator, drum granulator, kneader, drum mixer, powder mixer (hammer type, vertical shaft type, belt type), curtain dropping granulator, etc.
The advantages of the stirring method are that the forming equipment is simple in structure, the single unit output is large, and the particles formed are easy to dissolve quickly and have strong moisture permeability. The disadvantages are that the particle uniformity is not good, and the strength of the particles formed is low. At present, the maximum processing capacity of such equipment can reach 500 tons/hour, and the maximum particle diameter can reach 600 mm. It is mostly suitable for mineral processing, chemical fertilizer, fine chemicals, food and other fields.
Pressure forming method is a dense state in which the powder material to be granulated is confined to a specific space and compacted by applying external force. According to the different physical systems of the applied external force, the pressure forming method can be divided into molding method and extrusion method.
Typical molding equipment includes heavy-duty block press, bench press, concrete block press, brick press, heavy-duty film maker, etc. Its advantage is that it can produce large lumps, and the materials made also have considerable mechanical strength. Its disadvantage is that the scope of application of the equipment is small, and it is not easy to demould some materials. This kind of equipment is mostly used in construction, pharmaceutical and other fields.
Extrusion is the main method of pressure forming granulation in powder industry in China. According to the working principle and structure, the extrusion granulation equipment can be divided into vacuum pressure bar granulator, single (double) screw extrusion granulator, model press, plunger extruder, roller extruder, roller gear granulator, etc. This kind of equipment can be widely used in petrochemical, organic chemical, fine chemical, pharmaceutical, food, feed, fertilizer and other fields. This method has the advantages of strong adaptability, large yield, uniform particle size, good particle strength and high granulation rate.
DLJ series shredding granulator developed on the basis of single screw granulator can well solve the problem of crushing colloidal materials, and can be widely applied to the shredding and granulation of high molecular weight polyacrylamide, sodium polyacrylate and other materials, expanding the application scope of extrusion granulation.
For the granulation of materials requiring special shape particles (such as annular, clover shaped, porous, etc.), the plunger extruder is generally used. At present, the research on plunger extruder in China has become more and more perfect. The plunger diameter is in the range of 50~250 mm, and the particle diameter is optional in the range of 2~20 mm. More than 20 kinds of particle shapes can be achieved.
Spray and dispersion mist method this method is to make highly dispersed liquid or semi-liquid materials directly into solid particles in specific equipment. This granulation equipment includes spray drying tower, spray dryer, granulation tower, spouted bed and fluidized bed dryer, as well as pneumatic conveying dryer, etc. The common characteristics of this spray and dispersed mist granulation method are: the liquid feed must be pumpable and dispersible; The granulation process should generally be continuous, automatic and large-scale operation; The granulation system must be designed to recover or recycle the powder to solve the wear consumption of materials and powder entrainment; The particle size of the product is generally limited to less than 5mm. The advantage of this kind of equipment is that the granulation process and drying process of materials are carried out at the same time. The equipment can be widely used in pharmaceutical, food, chemical, mining and ceramic industries. The disadvantage is that the particle strength is low and the particle size is small. At present, the particle diameter prepared by such equipment can be as small as 50~500 μ m, or even smaller, and the maximum output can exceed 30 t/h (such as urea prilling tower).
Hot melt molding hot melt molding is to use the low melting point characteristics of products (generally lower than 300 ℃) to condense and crystallize the molten materials into the required sheet, strip, block, hemispherical and other shapes through a special condensation method. According to the working principle of the forming equipment, it can be mainly divided into rotary drum flaker and rotary cold belt mold drop forming device.
Drum flake is a cooling crystallization process. The molten material in the material tray contacts with the cooled drum, forming a material film on the drum surface. Through the heat exchange between the material film and the drum wall, the material film is cooled and crystallized, and the crystalline material film is scraped off by the scraper to become a sheet product. The drum flaker has compact equipment, high drum accuracy, good cooling effect and wide application range. It has the advantages of both flake forming and drying, and can be widely used in the production of polymer products such as petroleum resin and polyethylene oligomer, as well as organic chemical products such as phthalic anhydride, maleic anhydride and higher fatty alcohol. Rotary drum flaker has been widely used in powder industry in China, and its technology is mature.
The rotary cold strip drop molding device adopts thin steel strip heat transfer and atomization spray cooling, which has good heat transfer effect, high cooling efficiency, fast material solidification and molding, and wide application range of materials, and can produce products in hemispherical, strip, block, sheet and other shapes. The double speed regulating driving device of distributor and steel belt can be adjusted according to the production capacity and physical parameters, which is easy to realize automatic control; The whole production process is pollution-free, the product purity is high, no impurities are brought in, and it is easy to realize continuous operation; Due to the reverse bending of the steel strip at the discharge end, the bonding surface between the solidified material layer and the steel strip is separated, so the powder is less, the discharge is easy, and the particle shape is easy to maintain.
More than 100 sets of this technology and equipment have been industrialized and applied in China, and a number of invention patents have been obtained. The technology has been close to the international advanced level.
