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Vacuum Distillation Column

vacuum distillation column mechanical design wall thickness

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#1 Hucky

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Posted 13 April 2016 - 12:54 PM

Hi there,

 

I am currently designing a Vacuum distillation column operating at around 10 kPa absolute and 80 degrees C. I am at the stage where I need to decide on the wall thickness and obviously need it to be thick enough to not collapse on itself. I am planning on using carbon steel as the material of construction, grade A285.

 

Everywhere I have read says that columns with an external pressure have a very complicated way of calculating the required thickness for a particular material. I was wondering if there are any rules of thumb or previous cases etc that I can use to avoid doing the full calculations?

 

Thanks, Will 



#2 Art Montemayor

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Posted 13 April 2016 - 07:55 PM

Will:

 

The calculations for determining the wall thickness of a vessel under vacuum are not complicated.  They are iterative and detailed if you employ the ASME Code, Section VIII.  The calculations for the vessel heads - or end closures are probably more complex, but what I've done in the past is apply the same wall thickness for the heads as the correct, calculated wall thickness for the cylindrical section.  The cylindrical section yields a thicker plate thickness requirement than that for the heads, so you would be not only safe in using the same thicknesses, but you would also make it a more efficient welding job when joining both types of components.

 

The way I've set up the calculation in the past was by using a spread sheet.  Today, you have programs that make these vessel calculations.  You can forget about any "Rules of Thumb".  There are none that I've ever heard about.



#3 Hucky

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Posted 14 April 2016 - 01:34 AM

OK I will give it a go, thanks for your help!



#4 Hucky

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Posted 14 April 2016 - 02:20 AM

Hello again,

 

I'm working through it at the moment, and you were right in saying it is not complicated. 

Would you recommend any head shape to use? Hemi-spherical or ellipsoidal etc etc 



#5 Art Montemayor

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Posted 14 April 2016 - 11:52 AM

Hucky:

 

You need to have more basic data to make a decision on which type of head is appropriate, correct, or better for your application.  You have to state the design temperature and pressure as well as the material.  You also have to know certain basic and common sense criteria.  For example, a hemi head is the perfect, and most strongest of all heads.  However, it is plagued with welding problems and manual labor costs.  Hemis are almost always used only on very high pressure applications and in large sizes (above 7-10 meters) where the cost and weight of the material is important.

 

Usually, the ellipsoidal head is the type most used in process vessels.  It fills a happy medium in process vessel applications.

 

Read and study the attached information to learn more about vacuum design in pressure vessels.  You don't have to study Mechanical Engineering, but it certainly doesn't hurt and it gives you great insight and engineering abilities to know ASME code and other important pressure vessel codes and information.

Attached File  External Pressure Design for Vessels.docx   2.81MB   62 downloads

Attached File  External Vessel Pressure.docx   37KB   45 downloads

Attached File  Pressure Vessel Heads.docx   381.08KB   43 downloads

Attached File  Cylindrical Shell 1.1.xlsm   38KB   48 downloads

Attached File  Ellipsoidal Head ver 1.1.xlsm   101KB   42 downloads

Attached File  Elliptical Head ver 2.11.xlsm   35.92KB   41 downloads

Attached File  Flanged and Dished Head ver 1.1.xlsm   123.49KB   38 downloads

Attached File  Process Vessel Design - Brownell 1959.pdf   9.26MB   75 downloads



#6 Hucky

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Posted 14 April 2016 - 03:39 PM

Thank you so much! You have been a great help






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