Particle size reduction equipment

The process by which a solid is reduced to particle sizes of less than about 100 pm by using any type of particle-size reduction equipment. Examples micronized talc, micronized pigment. 

This equipment includes alternatives to shredding, alonig with wire removal systems. Recently alternative shreddin particle size reduction equipment has been developed. Of particular interest is the development of the hydroblasting system where the rubber is removed from the belting and bead wire with high pressure water. The water not only separates the rubber from the beat wire and otho cwd material, but it also produces tire chips at a particle size of 13 - 25 mm (1/2 - 1 in.). 

Two classes of grinding equipment are used to prepare dispersions. The first, the coUoid mill, does not effect a particle size reduction but does break down aggregates of fine particles. CoUoid mills are used for such powders as clays, precipitated whiting, etc. Sometimes these mills are used to process zinc oxide but for dipped mbber products that is not satisfactory. 

Figure 5-5X. Type R-500. Very high shear radial flow impeller for particle size reduction and uniform dispersion in liquids. By permission, Lightnin, (Formerly Mixing Equipment Co.) a unit of General Signal.

Bond terms Ei the work index, and expresses it as the amount of energy required to reduce unit mass of material from an infinite particle size to a size L2 of 100. im, that is q = 00. The size of material is taken as the size of the square hole through which 80 per cent of the material will pass. Expressions for the work index are given in the original papers 8,9) for various types of materials and various forms of size reduction equipment. 

Mechanical methods of powder production, also known as mechanical attrition, typically require a brittle material, or at least one that becomes brittle during processing. There are various types of equipment that perform particle size reduction. 

Comminution, or particle size reduction of solids, is considerably different from that of the breakup of one liquid by dispersal as small droplets in another. Particle size reduction is generally achieved by one of four mechanisms (1) compression, (2) impact, (3) attrition and (4) cutting or shear. Equipment for particle size reduction or milling includes crushers (which operate by compression, e.g., crushing rolls), grinders (which operate principally by impact and attrition, although some compression may be involved, e.g.,... 

Particle size reduction may be achieved with different kinds of miUing equipment such as media miUs. Alternatively, flow impingement or ultrasound methods can be used for dispersion. Some of the pigments can also be dissolved in certain solvents and reprecipitated as extremely fine particles. AU of these processes generate a considerable amount of fresh surface. If unstabilized, these surfaces collapse back together and particle size reduction... 

If the particle size of the biomass fuel or feedstock is not predetermined by its history, as is the case for sawdusts, nutshells, and a few other waste biomass materials, size reduction is usually carried out with one or more units that make up the front end of the total processing system. Many different kinds of machines are employed. Generally, the size of the feed is reduced by grinding, cutting, or impact mechanisms. Not all of the designs are suitable for biomass energy applications because the equipment is customized for certain uses or the cost of size reduction is excessive. Agricultural crops and woody biomass are also usually processed by different types of machines. A brief review of the basic types of machines that are or have been used for biomass follows to illustrate the variety of size-reduction equipment and their biomass applications. 

Clement, S. Purutyan, H. Narrowing down equipment choices for particle-size reduction. Chem. Eng. Progress-June 2002, 50-54. 

Fig. 1 The four basic types of size reduction equipment used to produce fine solid particles (A) crushers and shredders (B) hammermills (C) colloid mills and (D) fluid energy mills.

The particle size reduction tests for various selected biomass types have been executed in the pilot installation of CIEMAT. A flow diagram of the installation is shown in Figure 1. Basically, the equipment consists of two hammer mills connected in series, the first one has a nominal power of 11 kW and is used for pre-grinding (emshing). The second hammer mill has a nominal power of 15 kW and is used for refining the pre-ground biomass. 

---