16 replies to this topic

[Abdessamed1961]

Hello everyone;

i would like to ask for your  help with kettle type reboiler design, i have an existing kettle reboiler that uses steam (hot side) to heat butane (cold side), i'm seeking to replace  steam with hot oil.

For Butane and steam i have all the properties (mass flow, temperature In and Out, density,specific heat...), and for hot oil the new heating fluide i have some properties ( density, specific heat, flash point, pour point, viscosity index, viscosity), i have the the heat duty and also the existing geometry (dimensions, number of tubes, area..).

 

My question is: how can i  find the mass flow and the temperature in and out of the hot oil rerquired to heat Butane?

 

i wish a beautiful day for everyone.

[fallah]

Hello everyone;

i would like to ask for your  help with kettle type reboiler design, i have an existing kettle reboiler that uses steam (hot side) to heat butane (cold side), i'm seeking to replace  steam with hot oil.

For Butane and steam i have all the properties (mass flow, temperature In and Out, density,specific heat...), and for hot oil the new heating fluide i have some properties ( density, specific heat, flash point, pour point, viscosity index, viscosity), i have the the heat duty and also the existing geometry (dimensions, number of tubes, area..).

 

My question is: how can i  find the mass flow and the temperature in and out of the hot oil rerquired to heat Butane?

 

i wish a beautiful day for everyone.

 

Hi,

 

As a simple and quick estimation you can use heat calculation formula Q=mc_pΔT with knowing heat duty (Q) value and supposing the outlet temperature value is the same as that of the steam to keep the same temperature approach, then calculating the hot oil mass flow rate based on the relevant velocity criteria, and finally find the inlet temperature of the hot oil...

[breizh]

Hi,

A few documents about Hot oil.

https://durathermflu...es/calculators/

May I ask why this change?

Good luck.

Breizh 

Attached Files

•  Understanding Reboiler Heat Flux Limitations_CCTI_2010.pdf   465.13KB   85 downloads
•  HTF-66.pdf   85.54KB   100 downloads
•  hot oil design guide.doc   687KB   80 downloads
•  heat transfer calculator.xls   26KB   116 downloads

[Bobby Strain]

If you don't have access to good design software you should engage the service of someone who does.

 

Bobby

[Abdessamed1961]

- Thank you Mr.fallah, i tried that but i wasn't sure if what i was doing is the right procedure.

 

- Mr.Breizh Thank you so much for the valuable documents. the steam process got old and causing problems, so for a revamping we decided to change the heating process and switch to hot oil loop system. 

 

- Mr.bobby i use Aspen EDR but i prefer to carry my calculation manuallly then use the software.

[Bobby Strain]

So, do both then come back to us.

 

Bobby

[AnbIran]

Can anyone introduce a detailed guideline for hydraulics of kettle reboilers (or excel calculation sheet)?

[latexman]

Did you use Search on the site?  Did you not find what you are looking for?  Tell us what you have done.

[breizh]

Hi,

As suggested above: Guideline For Fixing Levels For Reboiler - Industrial Professionals - Cheresources.com Community

 

Breizh

[AnbIran]

Did you use Search on the site?  Did you not find what you are looking for?  Tell us what you have done.

 

 

Yes I searched on this site but couldn't find what I was looking for, anyway I followed detailed piping section and related help in HTRI software and could balance pressures ( a little higher pressure at return compared to inlet)

 

 

Hi,

As suggested above: Guideline For Fixing Levels For Reboiler - Industrial Professionals - Cheresources.com Community

 

Breizh

like always thanks a lot for helping and sharing and addressing documents and information. 

 

--------

 

 

But currently I have some problems on my final design.

 

The most important is cross flow velocity which may cause fluid elastic and fluid induced vibration. I can decrease this velocity by increasing bundle diameter or tube pitch, but currently I have already used high tube pitch ratio (1.33) and high bundle diameter ( currently 7 % overdesign with only 0.05 bar shell side pressure drop with a short length pipe as long as 3600 mm)

 

does anyone have any other suggestion to overcome this problem? my current bundle diameter is 600 mm, even increasing diameter to 700 which results 45 % over design cant decrease cross flow velocity enough. 

Edited by AnbIran, 11 February 2024 - 02:52 AM.

[Nikolay_]

At my point, the calculated velocity is a local velocity and doesn't relate to the whole bundle where natural convection is working. I'm not sure that the kettle reboiler can have a vibration due to the shell side cross flow velocity. If it's local, I think there's a way to work around it mechanically.

[breizh]

Hi,

Additional document.

Note: take a look at Perry's chemical engineer's handbook and/or Kern Process heat transfer.

 

Breizh 

Attached Files

•  Selection_of_Reboilers_for_Distillation.pdf   831.82KB   71 downloads

[AnbIran]

At my point, the calculated velocity is a local velocity and doesn't relate to the whole bundle where natural convection is working. I'm not sure that the kettle reboiler can have a vibration due to the shell side cross flow velocity. If it's local, I think there's a way to work around it mechanically.

yes, in some specific points of bundle velocity passes maximum acceptable critical cross velocity. 

[Pilesar]

The kettle has pool boiling. You only need to support the tubes in a kettle reboiler. The shell side flow is essentially vertical and conventional baffles are in the way. If your kettle reboiler is vibrating, there may be larger problems with your exchanger. Vaporizing butane with steam can be tricky if the temperatures are far apart due to high heat flux. Have you checked whether you are close to an unstable boiling regime? You don't want to make lots of bubbles very fast unless there is a good plan for the vapor to get away from the tubes. It would be wise to have your calculations reviewed by an experienced exchanger designer before committing to purchase.

[AnbIran]

The kettle has pool boiling. You only need to support the tubes in a kettle reboiler. The shell side flow is essentially vertical and conventional baffles are in the way. If your kettle reboiler is vibrating, there may be larger problems with your exchanger. Vaporizing butane with steam can be tricky if the temperatures are far apart due to high heat flux. Have you checked whether you are close to an unstable boiling regime? You don't want to make lots of bubbles very fast unless there is a good plan for the vapor to get away from the tubes. It would be wise to have your calculations reviewed by an experienced exchanger designer before committing to purchase.

 

Thanks my friend.

 

The calculated heat flux in my reboiler is far less than critical heat flux (order of 40 compared to 200) and the temperature difference is typical and suitable (around 50 Celsius degree) for heavy naphtha .

 

finally, I could overcome this problem by these three measures:

 

1- increased tube length to divide the flow which passes through cross area of each zone of bundle to more zones across length of tube, less flow passes flow area between tubes at each zone. I didn't decrease bundle diameter in result of increasing tube length, but if it is needed it can positively affect on decreasing cross flow velocity because the length of path (vertical path through bundle) decreases.

 

 

2- I used 45-degree tube layout configuration because it provides the most flow area perpendicular direction flow of cold fluid.

 

3- I used 1.33 ratio for tube pitch instead of 1.25 which generally are used. 

Edited by AnbIran, 16 February 2024 - 02:08 AM.

[Pilesar]

If you have vibration problem in a kettle reboiler (very unusual and I really cannot visualize how) then just add more tube supports.

[breizh]

Hi,

To support your work 

Breizh

Attached Files

•  wolverine heat transfer.pdf   5.68MB   59 downloads