Blow tank feeder

Figure 7. Conventional blow tank feeders (a) bottom-discharge arrangement (b) top-discharge arrangement.

For the general purpose of minimizing air flow, transport velocity, wear and power, the fluidized dense-phase mode of flow is preferred for long-distance applications. Efficient blow tank feeders, rotary-screw compressors, refrigerated dryers and stepped-diameter pipelines also are recommended. For products that are not suited to fluidized dense-phase, the possible modes of flow include dilute-phase (suspension flow) or bypass conveying (Wypych, 1995a). 

At the downstream end of the pipeline it is necessary to disengage the solids front the gas and this is most usually carried out in cyclone separators (See Volume 2, Chapter 8). However, there may be a carry-over of tine particles which must be eliminated before the gas is vented, and gas filters or electrostatic precipitators may be used for this purpose (See again Volume 2, Chapter 8). At the upstream end, the particles must be introduced using some form of positive feeder, such as a rotary valve or a blow tank. 

With the advent of high-pressure feeders after World War II (e.g., blow tanks, screw pumps), many designers and users began to apply pneumatic conveying to much greater distances and/or capacities (e.g.,... 

Some typical conventional blow tank designs are illustrated in Fig. 7. This type of feeder has been used successfully in industry to handle a wide range of products over relatively short distances (e.g., L = 100 to 200 m). However, the application of this type of blow tank to greater distances and/ or capacities (usually in conjunction with a second blow tank unit in series or parallel to ensure an essentially continuous mode of flow) resulted in a number of problems. 

For pressure systems one often finds lock hopper or gate lock feeders. These units operate similar to the blow tanks. 

One of the most troublesome aspects of gas-solid flow design is devising a proper feeder. Blow tanks are simple devices for penumatic conveying of solids. Basically, the tank is filled with the solid and emptied through a pipeline by the expanding compressed gas admitted to the tank. These units can operate under a wide range of... 

Fig. 2. Schematic of the new feeder unit, based upon (be original blow tank but modified to become a pressurised mass flow hopper with screw discharger.

Using the thin layer initial condition the lower layer increases in height due to mass transfer from the upper to lower layer. Thus the initial mass of solids in the upper layer must be sufficient to form the lower layer. In order to achieve this the volume fraction of the gas in the upper layer must be reduced, otherwise the model will fail when the gas volume fraction in the upper layer reaches unity. Using the thick layer option there is no need to do this since the mass transfer is in the opposite direction. As a result selecting initial conditions using the thick layer option is more straightforward. This corresponds with the almost foil-bore flow of densely packed material may be observed at the discharge from a blow tank (pressure vessel) feeder. 

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