×
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

Kettle Boiler: shellside velocity criterion

Kettle Boiler: shellside velocity criterion

Kettle Boiler: shellside velocity criterion

(OP)
Dear All,
There is a process condenser which generates steam in a kettle-type boiler.

What should the (average)vertical velocity of generated steam be so that a normally  accepted level of disentrainment is achieved? What should the velocity be for flowsheet, and what should be the maximum allowable velocity? I would assume that the criterion would be a value for the term rho.v2.

The condenser/ boiler is fitted with a demister, but I feel that the demister should not have to carry out disentrainment below a certain small droplet size.

RE: Kettle Boiler: shellside velocity criterion

Can't say I did any calculations, but we have a very similar operation, except we're just cooling, not condensing tube side. We keep the level enough to just keep the tubes submerged. So the disengagement area is just 30inx19ft at the water surface with ~7-8" from the surface to the nozzles. The take off is 3 3" nozzles, which expand to a 6" common header. We have produced upwards of 8,000 lbs/hr of 100psig steam and haven't seen excessive trapping out in the steam header (to me indicating no water carry over). I'll leave the calculations to you, how this compares with your application.  

I hope this helps.

RE: Kettle Boiler: shellside velocity criterion

Would you clarify why you mention vertical vapor velocity instead of horizontal velocity ?

In my experience, the vertical vapor velocity is used for an evaluation of the situation near CHF. The horizontal velocity is used in a seperator type equation. A good discussion of seperators can be found in the Engineering Data Book of GPSA, Vol 1, section 7.

RE: Kettle Boiler: shellside velocity criterion

(OP)
I mention vertical velocity because the reboiler has  a short, fat tube bundle, with dia about 3m and tube length 7m. The reboiler shell is about 5 m dia, thus liquid surface area is approx 5m x less than 7m: nearly square.

RE: Kettle Boiler: shellside velocity criterion

OK, I see your problem.

One suggestion is to refer to a Art Montemayor post in the Heat Transfer & Thermodynamics engineering forum of several years ago. In his post he discusses both The Souders-Brown and the gravity seperation method.

Another suggestion is to log on to: www.amisto.com/products/eliminators. They have guidance on what vapor load factor in using the Souders-Brown method.

RE: Kettle Boiler: shellside velocity criterion

Correction to my last post.
The URL should contain amistco, not amisto

RE: Kettle Boiler: shellside velocity criterion

HTRI program runs on allowable entrainment of < 2% wt Entrainment has 2 major is the adverse effects:

1.Excessive pressure drop
2.Effect on bottom tray efficiency,of the vapor is part  of a reboiler circuit in distiilation..etc

Up to 5% wt vapor is allowed as long as your DelP is <0.2 psi/100 ft

When you calculate DelP ,use 10% wt liquid as a safety margin

Regards

RE: Kettle Boiler: shellside velocity criterion


My 2 ¢ pledge. One typical problem with this type of boilers resides in the measurement of level. The s.g. of the water in the external indicator is ~1.0, while that inside the boiler may be perhaps ~0.5 due to the steam bubbles.

That is one reason for keeping the top of the kettle well above the top tube of the bundle (say, doubling the height of the top tube) which is itself covered with boiling water.
 
Sometimes domes with demisters are placed on top of the kettle to improve steam quality and to reduce entrainment of boiler feed water (BFW) in the steam.

If the steam -not generated from clean condensate and containing BFW- is to be further superheated, solid deposits due to entrainment may cause the tubes to fail. However, if the steam is used to reboil a nearby vessel, entrainment is, in general, not considered a major problem.


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