ENVE 4003

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ENVE 4003

• PARTICULATE MATTER Primary emission control
  devices
• Dividing collection devices

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PRIMARY PARTICULATES CONTROL DIVIDING
COLLECTION DEVICES

• Surface and depth filters
• Scrubbers
• IDEA Divide the flow into small parts and bring
  it in contact with large surface area
• Filter fibers and the cake collected on them
• Water droplets

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Filtration

• Surface velocity (face velocity, approach
  velocity, superficial velocity, air to cloth
  ratio) Vs Q/A
• Pressure drop for flow through porous media
• ?Ptotal ?Pfilter ?Pcake

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Figure 9.12 de Nevers

• Flow through a surface filter

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Cake accumulation

• Input accumulation

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Figure 2.5 Cooper and Alley

• Typical cost relationships for fabric filters

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Figure 9.13 de Nevers

• Typical industrial baghouse

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Figure 6.3 Cooper and Alley

• Cutaway view of a shaker baghouse

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Figure 6.6 Cooper and Alley

• Schematic diagram of a pulse-jet baghouse

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Particle capture mechanisms

• Hole size in filter medium typically much larger
  than particles that are efficiently collected
  (Fig6.1 Cooper and Alley)
• Mechanisms that contribute to particle capture
• Impaction
• interception
• diffusion
• At high velocities the last mechanism is
  ineffective, pinholes may form in the cake that
  correspond to the openings in the filter medium
  (Fig 9.16 de Nevers)

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Figure 6.1 Cooper and Alley

• A new, clean, woven filter cloth

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Figure 9.16 de Nevers

• Pinhole leaks in surface filters

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Figure 9.17 de Nevers

• Flow of gas and particles around a cylinder

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Target (collection) efficiency
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Target (collection) efficiency

• Impaction and interception mechanisms depend on
  air flow around a target.
• Stokes stopping distance
• Impaction parameter (separation number)
• Figure 9.18 (de Nevers) shows ?t vs Ns

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Figure 9.18 de Nevers

• Target efficiency as a function of separation
  number

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Scrubbers

• Bring the flow of gas in contact with a large
  number of liquid droplets representing a large
  surface area
• Natural occurrence rainfall
• Fig. 9.21 de Nevers

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Figure 9.21 de Nevers

• Volume of air for rainstorm mass balance

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Removal of particles from a volume of air
during a rainstorm
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Removal of particles from a volume of air
during a rainstorm

• e.g. Q/A 0.1 inches in 1 hr, Ddrop 1 mm
• dparticle 3 ?m, C0 100 ?g/m3
• ?t 0.22 (Ns 0.23) C/C0 0.43

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Removal of particles in a crossflow scrubber
(Fig. 9.22 de Nevers)

• Make Ddrop small, and/or ?z large
• Both measures would result in some liquid
  droplets being carried out of the scrubber

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Figure 9.22 de Nevers

• Crossflow scrubber

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Removal of particles in a counterflow scrubber
(Fig. 9.23 de Nevers)

• As Vt ? VG , C ? 0
• But, this means droplets are nearly stationary
  with respect to the container
• ? flooding

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Figure 9.23 de Nevers

• Conterflow scrubber

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Removal of particles in a co-flow scrubber (Fig.
9.24 de Nevers)

• We need high relative velocity between gas and
  droplets without loosing the droplets or flooding
  the equipment.
• IDEA Introduce the water droplets at right
  angles to gas but let them go out with the gas,
  then separate them in a cyclone.
• This is in effect a modification of the way a
  cross-flow scrubber is operated.

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Figure 9.24 de Nevers

• Co-flow scrubber

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Figure 9.26 de Nevers

• Venturi scrubber

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Removal of particles in a co-flow scrubber

• Integration difficult because VG, Vrel, ?t all
  change with x (Fig. 9.25 de Nevers)
• Ddrop is non-uniform, and not constant with x

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Figure 9.25 de Nevers

• Behaviour of VG, Vrel and efficiency with
  distance in co-flow scrubber

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Figure 9.27 de Nevers

• Pressure drop and aerodynamic cut diameter for a
  typical venturi scrubber

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Figure 9.28de Nevers

• Penetration and pressure drop for a collection of
  scrubbers

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