Grains, pneumatic transport

The pneumatic transportation of bulk solids through pipelines has been in existence for over one hundred years. Some of the earlier applications included the vacuum unloading of grain from ships and the extraction of sawdust from timber mills. 

O. Molerus, A. Burschka, Pneumatic transport of coarse-grained materials, Chem. Eng. Process. 34 (1995) 173-184. 

If one continues to increase the velocity of the fluidizing stream, eventu-ally it will exceed the settling velocity of the largest particle in the bed, and then the entire bed will be conveyed upward. This ceases to be a fluidized bed and becomes a pneumatic transport pipe, which is widely used to move granular solids such as grain, portland cement, or plastic pellets [14]. As a rule of thumb, fluidized beds operate with gas superficial velocities of 1 to 3ft/s (0.3 to 1 m/s) pneumatic transport operates with superficial velocities of 30 to 60ft/s (10 to 20 m/s). 

Pneumatic Pipelines. Pneumatic pipe systems are used to move blood samples, medicine, and suppHes between buildings in hospital complexes cash and receipts in drive-up banks parts and materials in factories refuse from apartment complexes and grain, cement, and many other materials. Most of these are small diameter and usually short however, a 17-km, 1220-mm dia pneumatic pipeline has been used to transport rock in the former Soviet Union since 1981, and a 3.2-km, 1000-mm dia line has moved limestone from the mine to a cement plant in Japan since 1983 (22). 

Another type of automatic sampler is the Woodside sampler, which consists of chains carrying small cups (Figure 13.6). The chains pass through the grain stream, the buckets fill and empty directly into a hopper, from which the sample can be transported by gravity pneumatically or manually into the test laboratory. The size of sample delivered by a Woodside sampler can be regulated by the number and size of the cups. The modern tendency is to move toward the diverter-type sampler. These are generally more flexible than the Woodside sampler. For example, peas are very hard and more or less round, and tend to bounce into and out of the small cups of a Woodside sampler. Diverter samples are not subject to this source of error. 

The composition is then washed several times with -hexane or any other non-polar solvent to extract all the acetone. The composition is obtained as grey coarse grains. The material is transferred either manually in stainless steel trays (Figure 18.2) and dried in an oven as depicted in Figure 18.3 or transported in pneumatic feeding lines under inert gas as depicted in Figure 18.4. 

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