Pneumatic Transport Phase
Types of pneumatic transport
Dilute Phase transport
Dense Phase transport
Airlock Rotary Valve
Product inlet / Injector
Conveying speed / velocity
Air volumetric and mass flowrate
Pipe Equivalent Length
Solids velocity in pipe
Pipe Diameter or Bore
Selecting dilute or dense phase
1. Geldart Classification
Be careful, not all the solids can be transported with any technology. Actually, the adequacy of a particular technology will depend on the fluidization properties of the solid to be transported. Before designing a system, the class of the solid must be established. Such class is determined thanks to a classification proposed by Geldart in 1973.
Class A : powders adapted to dense phase conveying, they have a very high and lasting aeration. They can be transported at high concentration but do not form naturally some plugs, an active system is therefore require to create them.
Class B : powders adapted to dense phase conveying, will naturally flow in plugs (dune)
Class C : these cohesive powders are probably not transportable in dense phase, however some exceptions exist
Class D : these powders can be transported in dense phase at concentration in between class B and class A
Figure 1 : Geldart classification
2. The different solids / air phases in a pneumatic transport line
It is important to understand how the concepts of lean phase and dense phase translate on the way the product is flowing in the pipe. Basically, depending on the velocity of the transporting gas, 5 flow regimes can be identified.
Table 1 : Conveying phases
It must be noted that the particles circulate at a lower speed than the gas. Depending on the flow regime, the particle average speed can be 0.4 to 0.8 times the gas velocity.
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