DRY GAS SEALS

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DRY GAS SEALS
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• Dry gas seals are basically mechanical face seals
• consisting of a mating (rotating) ring and a
  primary (stationary) ring
• During operation, grooves in the mating ring
  generate a fluid-dynamic force
• causing the primary ring to separate from the
  mating ring, thus, creating a "running gap"
  between the two rings.
• A sealing gas is injected into the seal,
  providing the working fluid for the running gap
  and the seal between the atmosphere or flare
  system and the compressor internal process gas.

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Dry Gas Seal Arrangement
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Typical Dry gas seal
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Seal Face of Dry gas
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Theory of Non-Contact
Demo
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Dry Gas Seal Arrangement in K-2115/K-4115
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Dry Gas Seal Arrangement in K-2115/K-4115
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F 1
FLARE
PRIMARY SEAL GAS SUPPLY
FIT
FROM COMPRESSOR DISCHARGE
PCV
START UP SUPPLY N2
FIT
F 2
SECONDARY SEPARATION GAS SUPPLY N2
PCV
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Dry Gas Seal Supply Console - PID
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Understanding Seal Gas Supplies to Dry Gas Seal
Primary Seal

• Primary Seal Gas is, typically, Filtered gas
  from the compressor discharge side, injected in
  to the Seal Chamber (the primary inboard seal
  chamber)
• A major part of the this injected gas will flow
  back to the compressor through the inner
  labyrinth at the process gas side.
• This achieves the prevention of emissions from
  the compressor to the atmosphere.
• A small quantity of gas will pass thro the
  dynamically separated gap of seal faces to the
  intermediate chamber between the inboard
  outboard seals
• Since this cavity is vented, the rate ( quantity
  per minute) of gas flowing out is measured
  downstream.
• This is the indication of the leakage rate of the
  seal.
• A minimum rate of leakage will be always
  present. Increase in the rate of leakage beyond
  design limits indicates reduced seal
  performance/ Efficiency

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Understanding Seal Gas Supplies to Dry Gas Seal
Secondary Seal ( Containment seal )

• Secondary Seal is a backup seal which seals the
  leakage
• from primary seal chamber
• Nitrogen is injected in to this secondary Seal
  Chamber
• The Secondary Seal Functions as a safety seal to
  avoid emissions to atmosphere in case of
  excessive leakage in the primary seal
• Separation seal ( Barrier seal)
• This seal also works in conjunction with a
  separation labyrinth situated between the
  bearing housings and Seal Chambers
• The separation gas is also Nitrogen, injected in
  to the separation labyrinth
• The main purpose of Separation gas supply is to
  prevent the oil in the bearing side from
  entering the seal Chamber.
• Presence oil in the seal chamber will cause
• damage to the Dry gas seal components

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Operational Guide Lines Dry Gas Seals
Seal Gas Supply Quality
The Quality of Gas fed to the seals must be clean
and Dry- Coalescing Filters to filter 2 microns
shall be used in the Dry gas Supply Console.
Pressure Drop across the Filters shall be
monitored and filters must be renewed to
achieve good seal performance
Seal Gas Supply flow
The seal gas supply flow must be sufficient
enough to ensure that the seal is Supplied with
sufficient filtered gas during operation with
excess gas going back in to the Compressor
casing. This is will provide an ideal sealing
environment to maintain the optimum seal
performance
Seal Gas Leakage Trends
Seal performance is monitored through leakage
trends. Occasional Spikes In the leakage due
process parameter variations, shaft movement,
speed changes are no cause for alarm. But
persistent trend of higher leakage may give a
forewarning of seal problems
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Operational Guide Lines Dry Gas Seals
Reverse Rotation
Reverse Rotation should be avoided as it will
damage the delicate parts of a Dry Gas Seal
Reverse Pressure
Reverse pressure under static condition will
result in an increase in static leakage. Under
Dynamic condition, reverse pressure can result
major damage to the Dry Gas Seal System
components.
Slow Roll
In Turbine Driven compressors Slow roll below
1000 rpm be avoided. The separation of seal
faces will not be achieved under such condition.
Seal faces will be running with contact which
will damage the geometry of the grooves in the
seal face
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