Pneumatic conveying is used for movement of solids over relatively short distances. It is generally suitable only for free-flowing particles in the range 20 μm to 50 mm, as finer dusts tend to stick to the pipes, while larger particles are hard to entrain. In pneumatic conveying, the solids are trans-ported in suspension in a gas. The solids may be either dilute phase, with void fraction typically greater than 95%, or dense phase, with void fraction as low as 50%. The velocity of carrier fluid must be large enough to keep the particles suspended; see Coulson, Richardson, Backhurst, and Harker (1999), Chapter 5. Pneumatic conveying can be used for both horizontal and vertical trans-port of solids, including making pipe turns. Sharp turns are generally avoided, as these cause solids attrition and pipe abrasion. In a pneumatic conveying system, the solids are usually fed from a hop-per via a rotary vane feeder that prevents backflow and are entrained into the gas flow, as shown in Figure 18.17(b). Pneumatic conveying can also be used under slight vacuum, as a means of unload-ing feed tankers or lifting solids into silos. A flexible feed hose attached to the silo is used to suck up the solids, rather like a domestic vacuum cleaner. A vacuum compressor is used to pull air
Pneumatic conveying is used for movement of solids over relatively short distances. It is generally suitable only for free-flowing particles in the range 20 μm to 50 mm, as finer dusts tend to stick to the pipes, while larger particles are hard to entrain. In pneumatic conveying, the solids are trans-ported in suspension in a gas. The solids may be either dilute phase, with void fraction typically greater than 95%, or dense phase, with void fraction as low as 50%. The velocity of carrier fluid must be large enough to keep the particles suspended; see Coulson, Richardson, Backhurst, and Harker (1999), Chapter 5. Pneumatic conveying can be used for both horizontal and vertical trans-port of solids, including making pipe turns. Sharp turns are generally avoided, as these cause solids attrition and pipe abrasion. In a pneumatic conveying system, the solids are usually fed from a hop-per via a rotary vane feeder that prevents backflow and are entrained into the gas flow, as shown in Figure 18.17(b). Pneumatic conveying can also be used under slight vacuum, as a means of unload-ing feed tankers or lifting solids into silos. A flexible feed hose attached to the silo is used to suck up the solids, rather like a domestic vacuum cleaner. A vacuum compressor is used to pull air
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