The two forms of dense phase conveying
 

There are two types of dense phase conveying:

• pulse conveying
• dune flow

With pulse conveying, a dense mass of product is alternately guided through the transport system with air. This creates a system in which plugs of powder are transported in a controlled manner. A characteristic of pulse conveying is a low flow velocity (approx. 6 m / s) at a lower pressure (approx. 3 Bar) compared to Dense Phase Transport. The reason for this is the relative mixing ratio of air to product. Plug Transport is used for the same types of powders as Dense Phase Transport is used for. However, with Plug Transport, it must be taken into account that a small part of the product mixes with the air between the plugs. That powder will damage during transportation. Plugging Transport can be realized with a vacuum or overpressure system. Experience shows that with a vacuum system the plugs maintain themselves better than with overpressure systems. A clear explanation cannot be given for this. In tests it appears that the overpressure causes too great a relative speed difference between the powder particles. This allows the top of the plug to be blown away, causing the entire plug to collapse. The Proppen Transport then changes into a Duinen Transport. Just like with air transport, there are no options for extra air injectors at Proppen Transport. These will cause the wads to fall apart, turning it into a Dunes Transport.

Another form of Dense Phase Transport is Duinen Transport, a transport type that combines the properties of the other three transport types. The mixing ratio between the air and the powder is roughly the same as that for Proppen Transport. The flow velocity is somewhat higher than with Plug Transport (approx. 10 m / s) and the pressure is slightly lower (approx. 2 Bar). A dense mass of powder will form at the bottom of the pipes as a result of precipitation of the product. In the transition area of ​​the dense mass and the flying mass, a rippling surface is created, hence the name Duin Transport. In this area, both powder particles will take off and fly away, and powder particles will precipitate, creating dunes. At the places where a dune starts to form, the dune will become larger due to the growing number of collisions. At the rear, however, the dune will also release powder due to relative underpressure. In this way the system remains somewhat in balance. There is a chance that a dune will become too large, or that a clot will form that will be transported through the system in an uncontrolled manner. This can cause congestion. Since the powder can transport itself in different phases, this must be taken into account. The chance of collisions and thus damage to a more brittle powder is high, but the speed at which this happens is lower than with Air Transport. Additional air injectors are not used with this type of transport, as they have no positive effect on the transport. Duinen Transport can be realized with both a vacuum and an overpressure system.