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DRY GAS SEALS. 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

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Presentation Transcript
slide2

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.

slide6

Lift off of stationary ring achieved by increased pressure at the taper portion.

Theory of Non-Contact

Demo

slide9

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

slide11

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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1

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

slide14

2

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