Dilute-phase conveying vacuum system

Dilute Phase Conveying. Dilute conveying systems, sometimes called disperse conveying or stream conveying, operate as positive pressure systems at pressures up to 100 kPa (14.5 psig), or as negative pressure systems (vacuum conveying) at pressures up to —50 kPa (—500 mbar). 

Positive displacement blowers Positive displacement blowers are probably the most commonly used type of compressor for dilute phase conveying systems. They provide an ideal match, in terms of pressure capability, with the conventional low pressure rotary valve, and are a typical working combination on many plants. They can be used as vacuum pumps, or exhausters, as well as blowers. The principle of operation is illustrated in Figure 4.26. Twin rotors are mounted on parallel shafts within a casing, and they rotate in opposite directions. As the rotors turn, air is drawn into the spaces between the rotors and the casing wall, and is transported from the inlet to the outlet without compression. As the outlet port is reached, compression takes place when the air in the delivery pressure pipe flows back and meets the trapped air. 

A vacuum conv ing system was designed to dilute-phase convey crushed bath (median size... 

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. 

Dense-phase conveying, also termed "nonsuspension" conveying, is normally used to discharge particulate solids or to move materials over short distances. There are several types of equipment such as plug-phase conveyors, fluidized systems, blow tanks, and, more innovative, long-distance systems. Dilute-phase, or dispersed-phase conveyors, are more versatile in use and can be considered the typical pneumatic conveying systems as described in the literature. The most accepted classification of dilute-phase conveyors comprises pressure, vacuum, combined, and closed-loop systems. 

Dilute-phase pneumatic conveying systems (a) pressure system, (b) vacuum system, (c) combined system, and (d) closed-loop system. 

Vacuum (negative-pressure) dilute-phase pneumatic conveying. Fig. 1, often is selected for reasons of convenience (e.g. several feed points, any leakage inwards), but without consideration of the relatively high rates of velocity increase and high pick-up velocities (i.e. compared to positive-pressure systems. Fig. 2). The fundamental differences between these two types of transport are demonstrated by tiie following examples. 

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