Non-contacting, Steam Turbine Gas Seal

[sinectica]

Has anybody experience in Steam Turbine Gas Seals? Are this sealing method reliable. How about it's cost?
I'm thinking about to change some traditional carbon ring seals of steam turbines into non-contacting seal.
What could be the benefits?

Thank you so much,

Marc

 

[JJPellin]

We have non contacting steam seals installed in one large turbine. It has been in service for 2 years. The seals that we installed are a bi-directional wavy face design. The seals cost about $6000 (US) each. We installed the seals as part of the original installation of the turbine and are very satisfied. There is no noticeable steam leakage. I was concerned about damaging the seals during unit commissioning (rolling the shaft to do the coupling alignments) or unit start-up (slow rolling the turbine). We have had repeated starts and stops on this turbine and still have no detectable leakage. I chose the bi-directional design so that our two spare seals are identical in case we would have a repeat failure on one end of the turbine. Most designs are rotationally specific (spiral groove). We are considering converting some existing turbines. However, it is difficult to justify the cost to retrofit an existing turbine unless it has had a lot of trouble with the carbon rings such as bearing failures, water in the oil, high maintenance costs, etc.