As we all know, the key to any gas compression process is preventing gas escaping. At best, a leak makes the compression ineffective, at worst it can result in potentially lethal consequences.
Over the past few decades, dry gas seals have replaced floating ring wet seals as the go-to technology for centrifugal compressors. But what do they actually do? How do they work? How do they remain effective? Where can problems arise – and how do you prevent them? In our recent podcast, Ken Takon, rotating equipment consultant, breaks down the science and answers the following questions:
How does a dry gas seal work?
A dry gas seal is a non-contact seal, created by a consistently pressurized flow of gas maintaining a tiny gap between a shaft-mounted rotating seal ring and a stationary seal ring, to prevent the escape of process gases. This barrier is around four microns, which is about one-twentieth the width of a human hair.
Why is it better than a conventional liquid seal?
Because the two rings do not touch and do not require lubricating oil, dry gas seals eliminate the risk of contamination between the two rings, making them much more effective than a liquid seal.
Does this mean it’s safer?
Yes– dry gas seals are generally much safer, and especially when it comes to harmful, hazardous or explosive gases. A wet seal risks processed gas building up in the seal or reservoir, potentially building up explosive conditions in the vapor space above the oil which could be sparked by, say, an electrical fault. Not only that, but if the degassing of the sour oil drain in a wet system isn’t 100%, it risks reducing the flashpoint of the oil from 220 degrees centigrade to as low as 90 degrees. This creates an operating risk and makes disposal of the oil both difficult and dangerous.
What about the cost?
Dry seals are cheaper, too. A wet seal system needs a whole system of reservoir, degassing tank, heaters and filters, not to mention the pipes and valves – most of which you won’t need with a dry gas seal. And without all those extras, it consumes less energy – which makes it cheaper to run and is better for the planet, too.
Are there any downsides?
As its name suggests, a dry gas seal needs clean, dry gas. This is vital – just the smallest particle of matter or trace of liquid can damage the seal faces and risk a leak. You therefore need a support system that finely filters your gas to ensure it survives its numerous changes in temperature and pressure on its journey to the seals. It needs to maintain its quality in all conditions, including start-up and during a pressurized hold, so you need to be able to monitor that quality at all times.
Interested in learning more? Listen to the full podcast HERE or investigate ESD’s technical and non-technical courses at https://www.esd-simulation.com/