Pneumatic conveying equipment sizing

Suspended Particle Techniques. In these methods of size enlargement, granular soHds are produced direcdy from a Hquid or semiliquid phase by dispersion in a gas to allow solidification through heat and/or mass transfer. The feed Hquid, which may be a solution, gel, paste, emulsion, slurry, or melt, must be pumpable and dispersible. Equipment used includes spray dryers, prilling towers, spouted and fluidized beds, and pneumatic conveying dryers, all of which are amenable to continuous, automated, large-scale operation. Because attrition and fines carryover are common problems with this technique, provision must be made for recovery and recycling. 

The dryers may be of the open-center type or the center-fill type. The former are equipped with lifting vanes or flights on the inside shell to carry fuel up the sides and disperse in the hot gas stream. In the open dryers the diameter is limited to about 2.5 m, and these provide a cheap and reliable system with low horsepower requirement. In the center-fill system, an internal structure helps to pneumatically convey the particles within the dryer. The center-fill dryer processes wet fuel according to its density. Particles of a particular moisture content are automatically maintained at a fixed bed temperature within a section of multizoned rotating cylinder. As moisture is evaporated from the particle it moves further along the dryer. This means that the dryer can handle particles of different sizes that need a broad spectrum of residence times, from a few minutes up to 1 h. 

The final step in compounding involves taking the molten mixture of resin and additives, now called compound, and forming it into pellets. These pellets are typically conveyed to the converting equipment by pneumatic systems. To ensure that the material feeds into the converting equipment consistently, compounded pellets must be uniform in size, flow easily, and preferably have a smooth, slick surface. 

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