Feeder systems, dilute-phase

Rotary, star valve feeder used especially as solids feeders for dilute-phase pneumatic conveying to provide an air lock and to feed solids. Seal/wear depends on Ap and abrasiveness of powder. For pressure systems keep Ap <80 kPa for vacuum systems Ap <40 kPa. Provide an air vent to take the air loss away from the gravity flow of the solids and to control the filling of the star. 

Feeders for dilute-phase conveying systems (a) venture feeder and (b) star feeder. 

For proper operation of a dilute-phase, pneumatic conveying system the solids fed into the pipeline must be carefully controlled. Two common types of feeders are the venturi feeder and the rotary valve or star feeder, illustrated in Figure 3.31. The venturi feeder is only suitable for low-pressure systems. The rotary valve feeder, also known as star feeder as described previously in this chapter is widely used for feeding medium-pressure conveyors. This feeder is efficient and simple in principle, but requires careful design in order to minimize air leakage. Excessive air loss from feeders, wastes power, causes dust, and leads to system instability. Rotary feeders work well on free-flowing, nonabrasive powders and special types are available for more difficult materials. 

Typical dilute phase systems are shown in Figures 8.5 and 8.6. Blowers are normally of the positive displacement type which may or may not have speed control in order to vary volume flow rate. Rotary airlocks enable solids to be fed at a controlled rate into the air stream against the air pressure. Screw feeders are frequently used to transfer solids. Cyclone separators (see Chapter 9) are used to recover the solids from the gas stream at the receiving end of the transport line. Filters of various types and with various methods of solids recovery are used to clean up the transport gas before discharge or recycle. 

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