GAS CONDITIONING UNIT (GCU)

Dry Gas Seals have the advantage of very long life and high reliability; however this reliability totally depends on the cleanliness, dryness and quality of gas that is delivered to the inboard cavities around the Dry Gas Seals.

The function of protection of the Dry Gas Seal by way of conditioned gas is carried out by the Gas Conditioning System which is often referred to as the Gas Conditioning Unit (GCU).

At most of Dry Gas Seal operation, the existing DGS Control Systems could not function properly due to the changes in gas composition, serious problems are emerging due to its limitations with the existing control systems, hence an upgrade to GCU capability is vital.

The greatest concern is that recent gas composition has indicated the gas is becoming wetter which may lead to liquid contamination of the Dry Gas Seal and ultimately seal failure. The changes in gas composition were not predicted or planned for in the original GCU design meaning there is no possibility that the existing system will manage these changes in gas composition.

Key Requirements of the GCU Upgrade

The absolute minimum vital requirements that the GCU upgrade most include are:

• Improved liquid removal by way of multi stage filtration
• A heater to elevate process gas temperature adequately above the process gas dew line
• A standby booster for non-dynamic running states (start-up, shutdown, slow roll)

Seal Gas Conditioning

Seal gas entering the primary seal area must be clean and dry (99.98% free of entrained liquid particles 3 microns and larger) and should be filtered to at least 10 micron solid particles. In addition, at least 36°R (20°K) dew point margin (superheat) is essential throughout the dry gas seal system. To ascertain this margin, a phase map computer simulation of the dry gas seal system from the primary seal gas supply point to the primary vent must be carried out to evaluate any potential for seal gas condensation. The temperature of the seal gas must be measured at the point of seal gas entry to the seal, not at the source of seal gas supply