Dry gas seals are basically mechanical face 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 fluiddynamic 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.

Dry Gas Seal Arrangement

Typical Dry gas seal

Seal Face of Dry gas

Theory of Non-Contact Demo Lift off of stationary ring achieved by increased pressure at the taper portion.

Dry Gas Seal Arrangement in K-2115/K-4115

PRIMARY SEAL GAS SUPPLY F 1 FLARE FIT FROM COMPRESSOR DISCHARGE PCV START UP SUPPLY N 2 FIT F 2 SECONDARY & SEPARATION GAS SUPPLY N 2 PCV

Dry Gas Seal Supply Console - P&ID

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

Understanding Seal Gas Supplies to Dry Gas Seal Secondary Seal ( Containment seal ) ØSecondary Seal is a backup seal which seals the leakage from primary seal chamber ØNitrogen is injected in to this secondary Seal Chamber ØThe 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 ØThe separation gas is also Nitrogen, injected in to the separation labyrinth ØThe main purpose of Separation gas supply is to prevent the oil in the side from entering the seal Chamber. ØPresence oil in the seal chamber will cause damage to the Dry gas seal components bearing

Operational Guide Lines –Dry Gas Seals 1 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

Operational Guide Lines –Dry Gas Seals 2 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