Blow tank design

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. 

To avoid these problems, a number of significant developments have occurred in the area of blow tank design, such as  

These developments have resulted in a much more reliable and efficient blow tank feeding system, especially for long-distance applications, as shown in Fig. 8. Such systems now have been used successfully in many installations throughout Australia to meet the increasingly demanding requirements of conveying capacity and distance. 

It should be realized also that either option shown in Fig. 9 or 10 will produce a non-symmetrical flow pattern inside the blow tank (i.e., due to preferential feeding at the blow tank outlet) and hence, promote the possibility of arching, rat holing and/or formation of dead regions. For these reasons, the combined fluidizing-discharge-cone and cone-dosing valve system shown in Fig. 8 is preferred. 

Case Study. As a part of the initial design of two 350 MW units for a coal-fired power station, it was required to  

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Improved blow tank design to ensure an efficient and controlled discharge rate of material. 

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.,... 

Pneumatic conveying dense phase No jJow or flow < design plugged line/mal-function of line boosters because of stuck check valve/high humidity. Solids fed to conveying line < design ratio of air to fluidize in the blow tank relative to convey is too small/fault in control system. 

Based on these concept design parameters, the plant was designed, installed and commissioned and has been operating successfully ever since. The operators confirmed that the blow tank pressure reached approximately 200 kPa g when ms = 22.5 t/h was selected for the furthest tapping point (namely, L = 120m). 

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... 

The conveying characteristics for the polyethylene pellets are typical of those of similar pelletised materials, and of pipeline systems designed to artificially create permeability in the material being conveyed. A pressure minimum point was clearly identified, but doubts were expressed about the merging of the constant pressure lines at low air flow rates, as this clearly has important system control implications. The blow tank control characteristics were not derived, since the work undertaken for Ref [1] was primarily for the purpose of determining pipeline conveying characteristics. 

Once the filter cake on the filter leaf reaches design thickness (18-22 mm), the filter tank is emptied and the residual oU is removed by blowing with dry steam or air (or air/inert gas). Recommended conditions and expected results for cake blowdown are given in Table 14. 

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