The Importance of Pressure Relief in Liquid Ring Compressor Piping

Many refineries have installed or have plans to install flare gas recovery systems.  Liquid Ring Compressors (LRC) are common on these systems because of their ability to handle two phase fluids. An LRC is a type of Positive Displacement (PD) machine, but it functions differently from conventional PD machines.

An LRC operates effectively only when the liquid ring is maintained. Unlike a reciprocating compressor, it lacks valves, and unlike a rotary PD compressor, it doesn’t continuously alter the internal volume unless the sealing water is properly regulated. If the water level is too high or too low, the compressor behaves more like a centrifugal pump, albeit an inefficient one.

If the LRC discharge is blocked while the compressor is running, it will merely stall; it will not keep building pressure indefinitely as other PD machines might. Instead, it may experience excessive vibration and heat buildup, potentially causing failure of the shaft or impeller. It could also trigger a shutdown due to high electrical current. Installing a pressure safety valve at the compressor is uncommon.

For managing risks effectively, regardless of the setup between the compressor and the separator, the following measurements are advised:

• Temperature at the compressor inlet and outlet
• Supply water temperature (both high and low extremes)
• Low supply water flow
• Suction pressure (both high and low extremes)
• High discharge pressure
• Elevated compressor vibration
• High motor amps
• Liquid level in the separator (monitoring both high and low levels)

Additionally, it’s crucial to check the water level in the compressor before starting it up, however, the level monitoring design heavily depends on the piping configuration.

If you have design questions or poor reliability with Liquid Ring Compressors or flare gas recovery systems, Becht can help.