×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Vacuum relief from steam collapsing

Vacuum relief from steam collapsing

Vacuum relief from steam collapsing

(OP)
Could you all discuss vacuum relief due to steam 'collapsing' (condensing) in a tank not protected for full vacuum, which does not have an open connection to atmosphere?

Vacuum protection from pump out, drain out, thermal vacuum, all seem to have relatively small vacuum relief flows compared to steam collapsing in the vessel.

For the steam collapsing case there is a credible scenario in which the tank could be filled with the steam.  There is also a credible scenario where cold water could flow into the vessel.

Lets assume a vessel is filled with steam at 212 deg F and there is a flow of 250 gpm of water a 60 deg F into the vessel.

The most conservative method to calculate this is 250 gpm * 8.34 lb/gal* (212 F - 60 F) = 316920 BTU removed/min.

316920 BTU/min / 970 BTU/lb = 326 lb/min of steam * 26 ft3/lb = 8500 ft3/min of air through vacuum protection.

If your tank is rated for only 4" of water column you are talking about many vacuum breakers.

The problem I see with this method is it assumes that heat is transferred instantly to the water as it flow in and the temperatures reach equilibrium.  I would think the rate of steam collapse/heat transfer is dependent on the amount of surface area that the cold water is in contact with the steam.  A fine spray of water would condense more steam than a stream of water.

The second problem is that with that air inflow rate even if your tank is 100,000 gallons the steam would totally be replaced < 2 minutes.

I know enough to diagnose my problem that I am incorrectly calculating the rate at which the steam could possibly condense, however I do not know enough to accurately calculate what the real rate would be.

RE: Vacuum relief from steam collapsing

I think that the difficulty of determining a reasonable rate is the reason that "steam out" and "rated for full vacuum" go together.   Granted that is just my experience.  Maybe some of the others have a more involved picture.

Regards
Stonecold

RE: Vacuum relief from steam collapsing

(OP)
Stonecold:  That is a definate consideration for the future.  I want full vacuum or at least more than inches of water column in the future.

25362: Thank you for the link.  Its ironic that someone asked the same exact question only like an hour after I did.  Perhaps one of the mechanical engineers I asked for help...

RE: Vacuum relief from steam collapsing

I think katmar provided an excellent response in the referenced thread as to the rate of condensation.  You can assume very effective mixing of the cold water with the steam; it's quite close to reality.

The real question is why would the tank ever be filled with steam?  It is very dangerous to allow steam to flow into an atmospheric tank.  Why would you do so?  If the tank is not well insulated, even a rainstorm could cause a rapid collapse in pressure.  If there is a real need, then I'm afraid you will not be able to use an atmospheric tank.  Switch to an ASME pressure vessel (at considerable expense) or find a way to live without the steam.  I don't think there are any other options.
Doug

RE: Vacuum relief from steam collapsing

Diborane:

Are you considering scenaros where a vessel is being steamed out to eliminate hydrocarbons before being opened for entry by workers?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources