13 replies to this topic

[aransari85]

Hi All,

This is my first post in this forum..

I am very happy to join this great site..

Let us discuss something about Thermosyphon Reboiler, You might be aware of its benifits that it has good heat transfer efficiencies.

Its rule of thumb that 1:4 is the vapor/liquid ratio in the outlet of reboiler.

When as a vertical length of tubes, liquid starts vaporizing, and density of the mixture is reducing, which is a driving force to overcome the resistances in inlet, outlet and through reboiler..

There is need to provide sufficient head of liquid in inlet line to have desired amount of flow (Design flow) in the reboiler.

I have prepared a excel sheet for calculating some basic hydrauli parameters, which can be useful for further reboiler design.

Please find attached spreadsheet for same, your valuable inputs are welcome to make this spreadsheet more accurate and robust.

Regards,
Abdul Rashid Ansari

Attached Files

•  Thermosyphon Reboiler Hydraulics.xls   21KB   4238 downloads

[S.AHMAD]

1. Good effort
2. More useful if u can prepare some notes and instructions
3. Better if you can make the program more user fiiendly

[paulhorth]

Aransari,
Please note that there are two types of thermosyphon reboiler. You have studied a vertical thermosyphon, with boiling in the tube side. There is also the horizontal thermosyphon, with boiling in the shell side, which in my view is a much better choice than the vertical.

Advantages of the horizontal type compared with the vertical include:

• the length of the tubes is not connected with the hydraulic balance. This allows the designer more flexibility, to use a longer tube bundle and get more area within a given shell diameter.
• The length of the shell does not affect the height of the attached column or the elevation of the reboiler relative to the column
• two feed lines and vapour return lines can be used
• liquid heating medium such as hot oil is better suited to the tube side, giving a better film coefficient
• turndown is better because the height of the vapour and liquid legs are (roughly) independent of the amount of vaporisation.

I agree with you that the vapourisation ratio should be about 25% on a MASS FLOW basis. I believe that the hydraulic balance can be modelled with both HTRI and HTFS design programs.

Paul

[kkala]

For those not familiar with thermosyphon reboilers (like me), but interested in having a brief introductory picture of their hydraulic design and arrangement, the spreadsheet is useful.

[aransari85]

Hi Paul,

Thanks for your valuable inputs..

I have considered vertical thermosyphon for this case, i will also work out on horizontal one.

yes i have seen, this is also possible in HTRI.. I have prepared this to have hand calculation feel, what is happening at backend and to have better understanding.

Regards,
ARA

[Nightwish]

Guys, it is a good design to have skirt height of tower (drum) that provides a driving force equal 3 times  the calculated pressure drop in the thermosyphon circuit.

[kabtik]

Aransari has done a good job. Please  include your formulae and be more generous with words to describe what you are doing.

A reference will also be appreciated. Keep it up

[kbsrinivas]

how to set h1? is it by trail and error 

could you give some guidelines on setting the liquid level heights .

[gegio1960]

My experience, from two different points of view.

REFINERY) here ts are widely used as reboilers for distillation column: vertical, process in the tubes, vaporization at about 25%

REFRIGERATION) used for oil cooling (tube side) by evaporating refrigerant (shell side): horizontal (slightly sloped), with vaporization in the shell at about 90%

[surabhi]

on what factors does residence time depend???

[Bobby Strain]

??

Bobby

[Dipankarc84]

One minor comment,

 

The vapor fraction of 25% on Mass Fraction basis is applicable for Hydrocarbons only. In case of Water (due to higher volume of expansion on vaporization) that limit is recommended to be as low as 10%

 

Regards
Dipankar

[masino]

this will be good for preliminary step for further analysis in HTRI

 

I appreciate it

[Padmakar Katre]

One minor comment,

 

The vapor fraction of 25% on Mass Fraction basis is applicable for Hydrocarbons only. In case of Water (due to higher volume of expansion on vaporization) that limit is recommended to be as low as 10%

 

Regards
Dipankar

 

 

Good work Abdul,

Good point Dipankar, just a small addition, it's the vapor RhoV2 which decides how much minimum % vaporization we can opt before system enter into the probable zone of instability. Good to check for vapor-volume fraction in addition to weight fraction as it has much higher effect once it enters inside column. Good work and good comments.

Edited by Padmakar, 18 June 2013 - 02:39 AM.