Separation Vs Filtration

1
Separation Vs Filtration

• Removal by Inertial Impaction
• Uses the energy from the fluid
• Removal of larger particle size, 10 micron and
  above
• Used for bulk removal

• Removal by Direct Impaction
• Uses Filter Media with close mesh size (and
  inertial device)
• Removal of fine particle size, typically 1 micron
  and above
• Used for both bulk aerosol removal

2
Factors Influencing Gas Filtration Selection

• Removal Efficiency, location of the filter system
• Properties of Gas, flow rate
• Type and quantity of Particle to be removed and
  its properties
• Operating pressure temperature
• Type of controls required
• Pressure drop allowed Turn-down Ratio
• Material specification

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Information Required

• Location Removal Efficiency
• Type Property of Contaminant Oil in
  particular
• Gas Property or MW or Sp. Gravity
• Flow Rate Min / Max
• Operating Pressure Min / Max
• Operating Temperature Min / Max
• Allowed pressure drop
• Liquid Holding time or capacity
• Controls required
• Configuration Horizontal, Vertical, In-line
• Special material, if any, required

4
Flow Rate

• Flow rates converted to ACFM or ACFS.
• At low pressure ACFM will be higher than at High
  Pressure.
• At high temperature ACFM is higher than at low
  temperature .
• SCFM and LB/Hr are independent of pressure and
  temperature while ACFM is sensitive to these.

5
Operating Pressure

• Low pressure increases the ACFM.
• High pressure increases cost of separator.
• High pressure increases density resulting in
  decrease in density difference between gas
  liquid and separation becomes more difficult.
• Drop in allowable shear force and therefore
  reduced velocity. (rV2)
• Mass flow rate is independent of pressure for a
  given SCFM.

6
Operating Temperature

• High Temperature increases ACFM.
• Influences filter element selection.
• Influences material selection.
• Influences control instrument selection.
• Mass flow rate is independent of temperature for
  a given SCFM.

7
Gas Property

• Composition influences MW.
• MW decides specific gravity.
• Specific gravity influences density based on
  operating pressure and temperature.
• Density influences velocity through the device
  and the size of the Separator.
• ACFM is independent of MW for a given SCFM.

8
Type of Contaminant

• Solids, solids and liquids, liquids.
• Nature of liquid and volume flow rate, Liquid/Gas
  ratio,
• Density of liquid.
• Viscosity of the liquid, if high drainage would
  be a problem, may require a mesh pad foe vane
  packs.
• Surface tension, if shear stress drops,
  re-entrainment would occur.
• Above factors dictate size, type of device and
  controls required.

9
Removal Efficiency

• Inertial Separators typically can remove only 10
  micron and above.
• Vane will not guarantee removal of solids.
• If heavy oil is present may require mesh pad
  addition.
• Re-entrainment occurs at high gas velocity,
  dictates size of filter vessel.
• Influences filter element selection .
• Influences configuration.

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Liquid Holding

• Location of the system.
• Is slug involved.
• Type of Draining Automatic or Manual.
• Volume flow rate of liquid.
• Above factors decide sump capacity type of
  control.
• Sump capacity dictates separator size.

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Compressibility Factor

• Compressibility Factor, Z, corrects the gas
  density for deviations from the ideal gas law.
• Use client specified value or use TEMA or
  Chemical Engineers Handbook.
• Use 1 if details not known.

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Design Considerations

• Inlet velocity not to exceed rV2 4500, based on
  TEMA guidelines.
• Inlet to have a baffle to break the momentum and
  to protect against slugs.
• If oil or other liquid contaminants expected,
  vane pack with/without mesh pad or multi-cyclone
  type device required.
• If vane is selected for first stage and if inlet
  is directly in front, to use agglomerator .
• Holding capacity required.
• Size of inlet/outlet to vessel size.

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