Design Approach to Dilute Phase Pneumatic Conveying

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Design Approach to Dilute Phase Pneumatic
Conveying
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Steps in Dilute Phase Conveying Design

• Material and Gas properties (density, size shape,
  viscosity, etc.)
• Specify desired conveying rate
• Estimate pipe diameter (with a little practice
  you get a feel for what works)
• Calculate saltation velocity
• Check loading (mass solids/mass gas)
• If gt 10 to 15 then need larger diameter pipe
• If lt 1 then need smaller diameter pipe

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Steps Continued

• Calculate pressure drop
• May require iteration
• If too large, may need to gradually increase pipe
  sizes (telescoping)
• Do not let velocity drop below saltation velocity
• Size blower

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Components sum to total pressure drop
Hopper
Blower
Filter
4.
2.
3.
1.
5.

• Blower, silencer, inlet filter
• Acceleration
• Horizontal pipe section
• Pipe bends
• Vertical pipe section

Other Components Cyclone Dust collector Filter Va
lves
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Acceleration

• Gas (outside of blower) and particles must
  accelerate up to operating velocity
• Conveying gas velocity
• Gas density
• Particle velocity
• Pipe cross sectional area
• Conveying rate (mass/time)
• Solids loading

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Must relate Vp and Vg

• Vg Vp slip velocity
• Empirical relation by Hinkle (1954)
• dp particle diameter (meters)
• Particle density in kg/m3
• In English units
• dp in feet
• density in lbm/ft3

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Bends

• Major source of wear/attrition
• Pressure loss associated with re-acceleration of
  gas and solids
• Bends usually specified by a ratio of the bend
  radius to pipe diameter R/D
• Typical in conveying R/D 6 to 12

R
D
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Bends

• Chambers and Marcus (1986)
• R/D gt 6, B 0.5
• R/D 4, B 0.75
• R/D 2, B 1.5

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Horizontal Pipe

• Pressure loss associated with frictional losses
  by gas and solids
• L length of horizontal section
• solids friction factor
• Use experimental data if available

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Solids Friction Factor

• For dp gt 500 microns
• For dp lt 500 microns
• where

Terminal Velocity
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Vertical

• Pressure loss accounts for frictional losses plus
  static head (gravity)

Bulk density
Void fraction of gas phase (recall for fluidized
beds voidage is typically 0.4 to 0.7)
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Example