Yang Fluidization, Solids Handling, and Processing

686 Fluidization, Solids Handling, and Processing

Figure 3. Classification of dense phase systems by vendors.

One can construct a number of different systems that would convey material in the dense phase condition. Figures 4–16 is a compilation of these systems indicating their unique characteristics.

The Gatty system has air injected from a sub-pipe mounted inside the main conveying line. Since this system is without controls, it performs better for well-behaved plastic pellet systems. It is difficult to maintain a low velocity conveying condition with this system, Marcus et al. (1990).

The Buhler Fluidstat system was first developed by Munschelknautz using a series of bypass pipes every half meter or so. Solids having good air retention properties are handled nicely with this system. A variation of this technique is the Moller Turbuflow system. The designers of this system claim that turbulence is regenerated in the conveying line.

A trace air system uses a series of boosters employing a pressure regulator and a check valve. The Semco systems is depicted in Fig. 6. Dynamic Air incorporates a similar concept controlling the air volume rather than the pressure.

Warren Springs Laboratories has developed a pulsed conveying system consisting of a flow vessel and an air knife downstream from the discharge valve as shown in Fig. 8. The plug lengths are controlled by the air knife operation time. An intermittent solids feed system shown in Fig. 9 can also control the size of the plug from both the air injection time and the discharge valve timing.

Buhler has also developed a Takt-Schub system which incorporates a double pulse system. The blow vessel has two gas inlet valves whose timing can be controlled. The system is operated in an alternating pulsing manner.

Dense Phase Conveying 689

Figure 9. Intermittent solids feed system.

Figure 10. Takt-Schub system by Buhler.

Dense Phase Conveying 693

Figure 16. Molerus dense phase transport system.

2.0ADVANTAGES OF DENSE PHASE CONVEYING

There have been a number of advantages that have been listed for dense phase conveying by Paul (1990). These are quoted as

(i)Decreased energy usage due to significantly reduced volumes of air.

(ii)Reduced material breakage or degradation due to slower conveying velocities.

(iii)Reduced pipeline wear due to lower conveying velocities.

(iv)Smaller conveying pipeline sizes due to heavier line loading capabilities.

(v)Smaller dust collection requirements at the material destination due to lower conveying air volumes.

In addition Paul has prepared a chart listing the characteristics of the dense phase conveying in comparison to dilute and medium dense phase systems as shown in Fig. 17.

Vendors have used certain types of dense phase conveying operations. In the trade, these vendors and their unique modes of transport have been classified in Fig. 3.