9 replies to this topic

[process.eng88]

The book "Chemical Engineering Design by Towler and Sinnott" states the following under the section "Design of Forced-Circulation Reboilers":

The normal practice in the design of forced-convection reboilers is to calculate the heat transfer coefficient assuming that the heat is transferred by forced convection only. This will give conservative (safe) values, as any boiling that occurs will invariably increase the rate of heat transfer. ...............................................
...............................................


The critical flux in forced-convection boiling is difficult to predict. Kern (1950) recommends that, for commercial reboiler designs, the heat flux should not exceed 63,000W/m2 (20,000 Btu/ft2h) for organics and 95,000W/m2 (30,000 Btu/ft2h) for water and dilute aqueous solutions. These values are now generally considered to be too pessimistic.

After reading this I'm confused as to what value I should use as maximum critical flux for the design of the Forced-Circulation Reboiler for my design project.

I hope some forum member can share the maximum critical flux value for the design of Forced-Circulation Reboilers in the modern industry.

The book "Chemical Process Equipment Selection and design by Couper, et al" states that the work by Polley in following book provides the design procedure for Forced-Circulation Reboilers:

"Developments in Heat Exchanger Technology- Editor: Duncan Chisholm (1980)"

Thus, I guess its chapter "Reboilers" should contain some updated info regarding the maximum critical flux for the design of Forced-Circulation Reboiler.

I can't access this particular book by Duncan Chisholm as my university library doesn't have it.

I hope some forum member can check that book.

Edited by student88, 19 April 2012 - 08:16 AM.

[breizh]

Hi,
Consider this resource , in particular section 5 .

http://www.wlv.com/p...ok/databook.pdf.

Take a look at Coulson & Richarson's chemical engineering design volume 6 , it might support your query.

Zuber's and Mostinski's equations
Hope this helps

Breizh

Edited by breizh, 19 April 2012 - 08:38 AM.

[process.eng88]

Breizh:

Thanks.

R K SInnott, the author of Coulson & Richarson's chemical engineering design volume 6 is one of the co-authors of the book "Chemical Engineering Design by Towler and Sinnott".

I just checked it..... It states exactly what I've quoted from "Chemical Engineering Design by Towler and Sinnott".

I searched Chapter 5 of the Wolverine Tube Heat Transfer Databook II but couldn't find the requested information.

[Art Montemayor]

Student188:

Why don't you use our Forum's SEARCH engine? I've written many posts on this specific subject and the recommended maximum heat transfer flux used for heaters and reboilers. For example, I've always successfully used and recommended 15,000 to 18,000 Btu/hr-ft².

Are you seeking a formal, recognized value for heat flux or a recommendation?

[process.eng88]

Sorry I forgot about the search feature of the forums. I had just searched through books.

I guess a formal/ recognized value for heat flux would be more appropriate as I wish to provide literature references in my design calculations.

Is your recommendation of 15,000 to 18,000 Btu/hr-ft² for all types of reboilers generally or specifically for forced circulation reboilers ?

[srfish]

student88

Is the reboiler in a vertical or horizontal position? There is a difference and most of the data is for the vertical position.

[process.eng88]

srfish:

I've verified from the published flowsheets of fatty acid fractional distillation by two different companies that the orientation of the reboiler is vertical

According to the following link, the forced recirculation reboiler for the fatty acid distillation column is of the suppressed vaporization type
http://www.desmetbal....com/fat51.html

[srfish]

There is a correlation by Katto & Ohmo that is good but quite complex to use. It is located in the Int. J. Heat Mass Transfer 27(9) p. 1641-1648. HTRI has a simplier version of the equations.

Other literature sources are:
Handbook of Phase Change by Kandlikar
Boiling Heat Transfer & Two-Phase Flow by Tong & Tang

[process.eng88]

srfish:

Thanks.

Your feedback is really appreciated.

The link for Int. J. Heat Mass Transfer 27(9) p. 1641-1648 is http://www.sciencedi...01793108490276X

However, this article doesn't fall under the subscription of my university.

I hope some forum member can kindly upload the softcopy of the full text of this article.

[process.eng88]

I have read that the selection of the pump operating upstream of the forced circulation reboiler affects the performance and efficiency of the forced circulation reboiler.

According to literature, generally what is the recommended type of pump required for the operation of a forced circulation reboiler ?


Generally, in our student design project, we're using canned motor centrifugal pumps for our fatty acids plant as they are recommended for oleochemicals.

Is it fine if I select a canned motor centrifugal pumps for the operation of the forced circulation reboiler handling fatty acids as well?

Edited by student88, 22 April 2012 - 09:00 AM.