Warming up HP steam header

[coolcando]

We have a HP steam header through which 4 different plants (plus one Power plant)can either export or import HP steam.Many times when one or all plants r down, the header will be cold(Atmospheric condition).Before any plant can start using steam from power plant it has to be warmed up to a perticular temperature.Also for the purpose of venting steam(during warm up)we r designing a Steam vent Silencer.
Header warm up rate is approximately 50 C per hour.

My question is How do I calculate steam flowrate necessary to get this warm up rate? I need this flowrate also to specify my steam vent silencer.

Thanks for any help

 

[TBP]

Why are you venting any amount of steam during warm-up? What is the operating pressure? Is the steam superheated?

Properly selected & installed steam traps will discharge any air present, and will pass the higher condensate load during the start up. Even if it is necessary to manually vent air, this will normally be done at very low pressures.

 

[BigInch]

Shouldn't your priority be draining condensate?

http://virtualpipeline.spaces.msn.com

 

[sshep]

I am with BigInch on this- you should be focused on draining the condensate (and venting noncondensibles). I can't believe that a warmup scenario could be related to a steam vent sizing basis.

There should be a warm up valve around the isolation valve for any section of the steam header which will be brought down. This warmup valve is typically 2" to avoid an unreasonable condensate slug which could cause a serious hammers if it can't be drained. The steam traps are typically bypassed straight to grade via oversized start-up drains. The purpose is to insure a well drained system. The main valve is not opened until the header is blowing steam out the trap bypasses. This is done after the trap bypasses are closed (sometimes these are closed in sequence as the header warms) and the normal traps are online. The header will come up to pressure. At that point the main block valve can be opened to put the header fully and safely on line. There is no "steam venting" in a normal sense.

50C/hr warm up rate seems an ambiguous basis for design as the header does not warm up uniformly. At fast warm-up rates (ie imaging just wheeling the steam wide open into a cold header) the hammer that can occur with a slug of condensate not well drained can be frightening- I have seen the aftermath of an 8" blind flange bursting off from exactly this sort of uncontrolled warmup, but fortunately no injuries.

best wishes,
sshep

 

[BigInch]

Deadly & frightening.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

yikes, to top it off, temperature cycling is not a good thing either.

 

[BigInch]

Ya. Start up of anything is the worst of everything all at the same time. I'm always amazed at how many steady state designs you see out there where NOBODY ever thought about the start up scenario at all. They just count on having 20% more power, 50% more transient pressure allowable and a field installed vent or drain at every high and low point.

http://virtualpipeline.spaces.msn.com

 

[MJCronin]

cool,

It has been my experience that steam system components with "significant thicknesses" (such as steam drums, turbine casings etc.) or thick castings require a slow heat up time.

I have never heard of a slow heat-up time to protect relatively thin-walled steam piping (headers).

What is your header material, diameter and wall thickness ?

Are there thick steel castings ( i.e.e valve bodies) that are part of the system you are trying to protect ?

The comments and recommended actions mentioned above about valve bypasses and condensate drainage are valid and have been around for a long time, but thier purpose is to protect the system from waterhammer.

Have you seen Wayne Kirsner's superb and informative website ?

http://www.kirsner.org/pages/articlesAlt.html

More information please...

-MJC