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SCEO_L4 - Selected Chemical Engineering Operations Selected...

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Selected Chemical Engineering Operations Selected Chemical Engineering Operations LECTURE - 4
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Selected Chemical Engineering Operations Properties and Handling of Particulate Solids Introduction Particle shape Particle size Mixed particle size and size analysis Screen analysis Wet and dry screening – Example Properties of particulate masses Storage of solids Pressure in bins and silos Flow out of bins Conveying Mixing of solids
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Selected Chemical Engineering Operations Pressure in Bins and Silos When granular solids are placed in a bin or silo the lateral pressure exerted on the walls at any point is less than predicted from the head of material above that point There usually is friction between the walls and the solid grains because of interlocking of the particles, the effect of this friction felt throughout the mass The frictional force at the wall tends to offset the weight of the solid reduces the pressure exerted by the mass on the floor of the container The vertical pressure on the vessel floor or the packing support is much smaller than that exerted by a column of liquid of the same density and height
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Selected Chemical Engineering Operations Pressure in Bins and Silos When the height of the solids column is greater that about three times the diameter of the container additional solids have no effect on the pressure at the base the additional mass of solids is carried by the walls and foundation, not by the floor of the vessel In granular solids a high pressure does not always increase the tendency of the material to flow, as it does in a liquid Increased pressure often packs the grains more tightly together and makes flow more difficult In extreme cases the combination of gravitational and frictional forces at some point in the container causes the solids to arch or bridge
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Selected Chemical Engineering Operations Flow Out of Bins Solids tend to flow out of any opening near the bottom of a bin
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