The seals and their protection system prevent the escape of process gas along the axis of the compressor. The seal oil system delivers the reserve oil and gas required for the operation of the oil seals of the floating compressor ring.
The seal assembly typically consists of two oil seals with carbon ring, spacer and housing. Seal oil is introduced between the two seals at a pressure slightly higher than the suction pressure of the compressor. The leakage of oil is controlled by the free space established between the inner diameter of the seal and the external diameter of the shaft
A small part of the oil drips through the internal seal towards the process gas, creating the seal. This oil is returned to the lubricating oil tank through a high-pressure trap and a degassing system upstream of the oil tank. The balance of the inlet oil flows through the outer seal and returns directly to the oil tank.
The sealing oil at a slightly higher pressure than the buffer gas is injected between the two carbon seals of liquid film to prevent the buffer gas from leaking into the lubrication system. The mixture of sealing oil and buffer gas is separated in the oil seal trap where the buffer gas returns to the suction of the compressor and the oil returns to the oil tank.
The standard seal oil system includes the following primary components:
- Turbine-driven main seal oil pump
- Auxiliary and backup seal oil pump
- Seal oil filter with differential pressure switch and gauge
- Seal oil differential pressure regulation system
- Seal oil flow control valve
- Buffer gas differential pressure regulation system
- Dual traps, one for each compressor seal
- Degassing flue
- Flame arrestor for field installation on degassing flue vent
- Sight glasses, strainers and relief valves
- Pressure and differential pressure gauges and switches
Dry gas seal system:
The dry gas seal system consists of two closely related systems: the gas seal system and the air cushion system. The seal gas system maintains a barrier between the process gas in the compressor of the compressor bearings.
The buffer air system maintains separation of the lubricating oil from the compressor bearing from the dry gas seals.