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 – best discharged through an opening in the floor
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This note was uploaded on 02/29/2012 for the course CHEMICAL 312 taught by Professor Profsureshgupta during the Spring '12 term at Birla Institute of Technology & Science.

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SCEO_L4 - Selected Chemical Engineering Operations Selected...

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