Solid pneumatic conveyors

FIG. 12-33 Cocurrent gas-solids flow in a vertical-lift dilute-phase pneumatic conveyor. 

Pneumatic-Conveyor Dryers A pneumatic-conveyor dryer consists of a long tube or duct carrying a gas at high velocity, a fan to propel the gas, a suitable feeder for addition and dispersion of particulate solids in the gas stream, and a cyclone collector or other separation equipment for final recoveiy of sohds from the gas. 

Use of enclosed belt conveyors, chutes or pneumatic conveyors for solids. 

Pneumatic conveyors are for high capacity, short distance (400 ft) transport simultaneously from several sources to several destinations. Either vacuum or low pressure (6-12 psig) is employed with a range of air velocities from 35 to 120 ft/sec depending on the material and pressure, air requirements from 1 to 7 cuft/cuft of solid transferred. 

McKee, S. L., Dyakowski, T., Williams, R. A., and Bell, A., Solids Flow Imaging and Attrition Studies in a Pneumatic Conveyor, Powder Tech., 82 105(1995)... 

Sampling from pneumatic conveyors parallels gas sampling. The exception is that solids loadings can be as high as 50 kg of solids per kg of gas. Commercially available samplers extract particles directly from a transport line. Fixed position samplers are mounted directly on the pneumatic conveyor pipe. Devices are available which extract samples from the product stream by the projection of a sample tube into the flow. Particles impact on the tube and fill the open cavity. The tube is then withdrawn, and an internal screw discharges the collected material (20). In another model, the RX Sampler (manufactured by Gustafson) (29), samples are withdrawn using compressed air. 

The performance of pneumatic conveyors is sensitive to several characteristics of the solids, of which the most pertinent ones are... 

Most powder systems are transported at some time during their manufacture as flowing streams Hoppers are emptied by screw or belt conveyors, powders are transferred to bagging operations by screw or pneumatic conveyors and many solids are transported through pipes. A general rule in all sampling is that whenever possible the sample should be taken when the powder is in motion. This is usually easy with... 

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