×
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

Question about finned tubes in a flue gas reheater

Question about finned tubes in a flue gas reheater

Question about finned tubes in a flue gas reheater

(OP)
L.S.,

We apply a few flue gas reheaters with finned tubes in one of our power plants. The fin density is 196 fins per meter. The flue gas in question may still contain some fly ash after passing the E-filter. The reheater is situated after the wet desulphuriser. Therefore the fluwe gas contains quite some condensate droplets or aerosols. The acidity is quite high ( pH = 0 .. 2 ). The finned tubes tend to corrodate heavily and clogg. In a german book about heat exchangers I read that the spacing between two fins in normal industrial applications should not be less then 4 mm. For dirty industrial gases they even advice to increase the spacing to about 15 mm.

I would like to hear from fellow collegues whether they have dealt with the same kind of problem, whether the fin spacing really is a determining factor and what fin and pipe should be selected to prevent extensive corrosion.

Karel Postulart, The Netherlands
Nuon Power Generation

RE: Question about finned tubes in a flue gas reheater

Yobbo,

I think this is a fairly rare application, so there may not be much response to your question.  I have worked on a few of these types of heaters, but not many.  

It appears that your heater is a direct flue gas heater from your description, and probably uses steam as a heat source.

First, I think the design you have is very likely to become fouled from carry-over from the scrubber.  It's also very likely to corrode as well.

The fin spacing you have now is very close.  Fewer fins would be better.  However, if you have the space for it, a bare tube design would be even better than that.  I am hesitant to suggest materials, but some type of stainless would probably be a good  choice for this.  

The alternate heating system that I have seen heats air, rather than flue gas.  The air is heated to a much higher temperature, then blended with the cool flue gas to get the bulk temperature well above the dew point.  This type of heater can use ordinary aluminum fins with a very close fin spacing (typically about 10 fins/inch or 394 fins/meter).

Regards,

Speco

RE: Question about finned tubes in a flue gas reheater

(OP)
Hello Ione and Speco,

Thank you for your usefull responses to my thread. As it is rather impossible to prevent any carry over from the scrubber I think I will try to size a heat exchanger with a transfer area as large as feasibly possible with straight pipes.

Karel Postulart, The Netherlands
Nuon Power Generation

RE: Question about finned tubes in a flue gas reheater

Where there is a chance of carry over from the scrubber you should run smooth tubes.
Do you have a washdown method (ala soot blowers)?
I have seen this service eat up super-austenitic and super-ferritic tubing.  The first bundles (wettest) were replaced with C276 and the super-ferritic was used on the others.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Question about finned tubes in a flue gas reheater

(OP)
Hello Edstainless,

Also thank you for your usefull comment. I will take it to heart and consult our corrosion specialist on your suggestion.

With best regards.

Karel Postulart, The Netherlands
Nuon Power Generation

RE: Question about finned tubes in a flue gas reheater

I don't know about the mass rate and temperature of the flue gases, however, may be you should consider passing the flue gases thru another boiler.

RE: Question about finned tubes in a flue gas reheater

If your heat transfer equipment was sized such that it required the extended surface (fins), then it will be woefully short on performance as a bare tube.  However, once your finned surface becomes clogged, then it is virtually useless, so bare tubes may give better performance than clogged fin tubes even though the performance is reduced.  What is inside the tubes as the heating medium?

rmw

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