DGS CONTROL SYSTEM

The Dry Gas Seal Control System is designed to provide the following features:

• Filter the process gas and supply clean gas to the primary seal
• Regulate the differential pressure of seal gas.
• Monitor seal performance and
• Provide Alarm/ shut down signals.

Gas from either compressor’s discharge or from an alternate source passes through the filters, to be regulated at pressure slightly higher than the compressor suction/ balance line pressure. This clean & dry gas is then directed to the seals.

Since the seals mating rings rotate with shaft, small amount of gas are pumped inward between the faces. A sealing dam restricts gas flow providing a pressure rise in the outer portion of the faces. This creates a small gap between the faces that keeps them separated to prevent any wear. A small amount of gas pass through the faces and is directed to the control panel where instruments monitor seal performance and provide measurements about the seals operation based on this leakage flow and pressure.

Appropriate action should be taken in regards to the control panel measurements to maintain the equipment’s safe operation.

Notes:

• Regulated Seal Barrier Gas Pressure should be maintained 0.3/0.5 bar higher than the compressor suction / balance line pressure. This can be controlled with the help of differential pressure control valve arrangement installed in the filter skid.
• Variation to this value (higher or lower) depends upon the stability of such pressure and will vary from installation to installation.
• To maintain constant barrier gas flow to the seals, one filter is operating while the other one is in standby.
• The most important component in the control panel system is the filter and Differential pressure control valve. The ability to maintain a supply of clean, dry gas will provide the best probability of long seal life.

The control panel designed to control & monitor of dry gas seals installed in both Drive end & Non drive end side of the compressor.

Seal Gas Control Methods

The flow of seal gas to a primary seal is controlled by either a flow control method or a differential pressure control method. The main objective of both types of control methods is to positively sweep the seal gas across the process gas labyrinth to prevent a reverse flow of process gas into the dry gas seal.

A flow-control system controls the supply of seal gas to the seals by regulating the seal gas flow through an orifice upstream of each seal. It includes a valve with a remote flow controller that compares the seal gas flow to each seal and adjusts the flow control valve to maintain a minimum 16 fps (4.9 m/s) flow velocity across the inner process labyrinth seal based on “high select reference pressure” for each seal, measured downstream of the flow orifices.

DRY GAS SEAL BOOSTER SYSTEM

The use of dry gas mechanical shaft seals in centrifugal compressors has increased dramatically in the past 25 years. Preventing contamination of the gas used by these seals is necessary to assure long life. Gas Compression Systems dry gas seal pressure boosters ensure that gas quality is maintained during startup, settle-out and pressurized hold conditions.

• Models conform to CE ATEX Explosion-proof requirements
• Wetted parts conform to NACE MR0175 & MR0103
• Designed in accordance with ASME Section VIII, Division and CE PED
• Distance piece design prevents mixing of the gas and drive air
• Dynamic seals are filled Teflon and require no lubrication
• 2500+ hour operating life with no maintenance required
• Suitable for continuous operation

This technology changes everything. This direct electrically driven gas conditioning booster is the only electrically powered booster designed from the ground up, inside to outside for gas conditioning to protect your valuable dry gas seals. This development offers the most efficient and cost effective dry gas seal protection solution.

• No Air Supply
  No need for a high capacity, high quality and costly air drive supply.
• Significant Wear Reduction
  No piston seals or other high wear seal items to wear out.
• No leakage Losses
  Direct magnetic coupling design means there is no seal leakage and no need for costly seal monitoring devices.
• Higher Efficiency
  Direct electric drive offers the best levels of efficiency.
• Higher Reliability
  Longer life means a huge reduction in operating expenditure.

GAS CONDITIONING SOLUTIONS FOR THE TURBO MACHINERY INDUSTRY

• System Integration
  Hugely simplified system integration requiring simplified input and output signals.
• System Intelligence
  The FSD Turbo Booster can be provided with an intelligent interface to further increase system intelligence.
• Enhanced System Intelligence
  Embedded technologies allow a booster master module to communicate

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