Gas molecular weight has an impact on compressor surge as when it reduces.
What are the factors which should be considered during an on-going site operation with continuous feed?
A surge may be linked to feed changes?
Gas molecular weight & compressor surge
Re: Gas molecular weight & compressor surge
Yes, a decrease in gas molecular weight has a severe and direct impact on centrifugal compressor surge.
Feed composition changes are one of the primary triggers for unexpected surge events in continuous operations.
Here is how the physics work: A centrifugal compressor operating at a constant speed generates a specific amount of "head" (energy added to the gas). When the molecular weight of the gas drops, the gas becomes less dense. Compressing a lighter gas produces less discharge pressure for the same amount of volumetric flow.
Feed composition changes are one of the primary triggers for unexpected surge events in continuous operations.
Here is how the physics work: A centrifugal compressor operating at a constant speed generates a specific amount of "head" (energy added to the gas). When the molecular weight of the gas drops, the gas becomes less dense. Compressing a lighter gas produces less discharge pressure for the same amount of volumetric flow.
Re: Gas molecular weight & compressor surge
Older or simpler anti-surge controllers rely on a fixed surge line programmed for a specific gas MW. If the feed becomes lighter, the actual surge line shifts to the right (higher flow required to prevent surge). The ASV might not open in time because the control system thinks the compressor is still in a safe operating zone.
Re: Gas molecular weight & compressor surge
If you are dealing with a continuous feed where the composition (and thus the MW) is fluctuating, operators and control systems must closely monitor several variables:
Anti-Surge Control System Tuning: Older or simpler anti-surge controllers rely on a fixed surge line programmed for a specific gas MW. If the feed becomes lighter, the actual surge line shifts to the right (higher flow required to prevent surge). The ASV might not open in time because the control system thinks the compressor is still in a safe operating zone.
Compressor Speed (RPM): If the MW drops, the compressor must spin faster to deliver the same required discharge pressure. If the compressor is motor-driven and already operating at maximum speed, you will be unable to compensate for the lighter gas.
Suction Temperature and Pressure: Density is the underlying factor. A decrease in suction pressure or an increase in suction temperature makes the gas less dense—exactly like a drop in MW. If a drop in MW coincides with a hot day (higher suction temp), the risk of surge multiplies.
Discharge System Resistance: To keep a compressor out of surge with a lighter gas, the system backpressure must be reduced. This might mean opening downstream control valves or adjusting the process to accept a lower operating pressure.
Anti-Surge Control System Tuning: Older or simpler anti-surge controllers rely on a fixed surge line programmed for a specific gas MW. If the feed becomes lighter, the actual surge line shifts to the right (higher flow required to prevent surge). The ASV might not open in time because the control system thinks the compressor is still in a safe operating zone.
Compressor Speed (RPM): If the MW drops, the compressor must spin faster to deliver the same required discharge pressure. If the compressor is motor-driven and already operating at maximum speed, you will be unable to compensate for the lighter gas.
Suction Temperature and Pressure: Density is the underlying factor. A decrease in suction pressure or an increase in suction temperature makes the gas less dense—exactly like a drop in MW. If a drop in MW coincides with a hot day (higher suction temp), the risk of surge multiplies.
Discharge System Resistance: To keep a compressor out of surge with a lighter gas, the system backpressure must be reduced. This might mean opening downstream control valves or adjusting the process to accept a lower operating pressure.
Re: Gas molecular weight & compressor surge
Thanks, appreciate all the inputs.