Pneumatic conveying power requirements

Rotary valves have been specified for the receivers of the vacuum pneumatic conveying systems (RV-601 and RV-602) and for the feeders (RV-40 1) and receivers (RV-501) of the positive-pressure system transferring powder from the dryers to the extruders. Perry72 gives some recommended sizes for rotary valves. The power required by all these valves will probably not exceed 2 kw and will be ignored. 

TABLE 5.1. Flow Rates and Power Requirements of Vacuum and Low Pressure Pneumatic Conveying Systems ... 

Equipment for pneumatic conveying is described in Section 5.2 along with some rules for calculating power requirements. Here the latter topic will be supplemented from a more fundamental point of view. 

The hydrodynamics of gas-solid transfer is complex and the literature is voluminous, as indicated by the 224-page coverage by N.P. Cheremisinoff and R. Gupta, Handbook of Fluids in Motion, Butterworth, pp. 623-847, Chapters 23-31, 1883. Equipment for pneumatic conveying is described in Section 5.2 along with some rules for calculating power requirements. Here the latter topic will be supplemented from a more fundamental point of view. 

During the past five decades, gas-solids hydrodynamics studies principally have concentrated on solids phase measurements and characterization and have largely ignored the gas phase. Pneumatic conveying is an example solids are the commodity of interest the gas phase is only important in the sense that power requirements for blowers and compressors should be minimized. In studies of bubbling and turbulent fluidized beds, experimentalists study the spatial and temporal distribution of bubbles, but, typically, they employ solids measurement devices from which gas phase hydrodynamics are inferred. Circulating fluidized bed researchers also have devoted considerable attention to the solids phase, but since 1988 only 40 publications have appeared that deal with gas phase hydrodynamics. 

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. 

Calculate the power required to convey pneumatically 1500 kg/h of a flour of 1300 kg/m density, with the particle size distribution given in Table 3.11. The... 

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