Hello to all,
ours is a once through steam generator with operating Pressure 56 Bar, for flushing the feed water lines we are using Instrument air . i would like to know upto what pressure we can pressurize our OTSG tubes with Instrument Air. Can we go upto 6 bar Air pressure? Expecting your feedback in this.
Thanks in Advance.

Hello to all,
ours is a once through steam generator with operating Pressure 56 Bar, for flushing the feed water lines we are using Instrument air . i would like to know upto what pressure we can pressurize our OTSG tubes with Instrument Air. Can we go upto 6 bar Air pressure? Expecting your feedback in this.
Thanks in Advance

Hello Guruswamy,
Can you please explain why you need to flush the tubes at all?
Depending on the tube layout, the use of air can mean that some of it can get trapped in pockets. This can create a lot of heat transfer problems, sometimes leading to tube rupture.
Is air-flushing recommended by the OTSG vendor? Instrument air can contain impurities that contaminate the water as well; at 56 barg, you really don't want that, so please think through all this carefully. I think the air pressure is the least of your problems.

Dear Mr.Narayan
Our plant is in under preservation. So we need to preserve our all equipments like Gas turbine (Doing FSNL every 15 days), Rotating a generator Rotor 180Deg like wise we are purging our OTSG tubes with Air to remove the Moisture/Water content.
Pls advise us what to do???
Regards
Gurusamy

Guruswamy,
Assuming it is possible to drain the OTSG completely. please consider using -40C dew point air or N2. You can get such a gas by boiling off liquid air or N2. Blow this gently through the OTSG after warming it to +20C. Measure the dew point at the exit with a recorder. Initially it will be high, but at some stage it will level out to -5C or thereabouts, when the OTSG is dry enough. The first time will take several hours or even days depending on how the tubes and bends are configured. keep the OTSG under dry air or N2 (-40C dewpoint) at about 50mm water pressure.
If you want to 'blow dry' the tubes, pressure does not help, but velocity does. You need high velocities to pick up liquid water particles initially. That mean high capacity oil free blowers, but you may not need more than about 200mm H2O pressure head to blow the air through. The air may have to be desiccated or heated to make it dry enough.
If you use N2, full safety precautions are required as N2 can kill people.
What is FSNL?

FSNL - Full Speed No Load