13 replies to this topic

[trungphu]

Hello,

Could someone give me some advance in designing manways for a distillation column of 0.9 m in diameter? My column is18,4 m in height with 38 trays. How many manways should I need for the column and which location?

Regards.

Edited by trungphu, 15 November 2012 - 03:58 AM.

[fallah]

trungphu,

Manway in trayed column will normally provided at the top, below bottom tray, at the feed tray and at any other tray around which removable internals are located. Manway at intermediate points should be located such that maximum spacing of two manways doesn't exceed 15 trays.

Fallah

[Art Montemayor]

Trungphu:

There are definite and logical reasons for installing manways in distillation columns. You need to have confined vessel entry in order to inspect, clean, and make repairs inside the column from time-to-time. These needs can be important, especially if you are distilling liquids that can corrode, clog, erode, or cause damage inside the column.

Taking the above obvious and practical facts into consideration, you then have to use your common sense to resolve how you can meet those needs. Obviously you first must consider what is the quality and nature of the liquids that you are going to introduce into the column. Secondly, you should also consider what kind of internals you are proposing to install inside your column. Are the internals subject to working loose (such as bolted down trays, bubble caps, etc.? Do you have moving parts inside your columns subject to wear and erosion – such as valve trays? Do you have mist eliminator mesh pads inside the column?

With the above considerations, you then make a sketch of your column and select those critical areas and spaces where you need access and entry and place your manways appropriately so that you can easily and safely reach those spaces.

Normally you will discover:

1) Manways should be at least 24 inches diameter in size to be practical from a safety viewpoint. This has been found to be the minimum size for a man with an airpack and tools to gain safe internal access.

2) In order to have mobility and space for working inside a column once you are inside, the column should be at least 4 feet internal diameter – preferably 5 feet as a minimum. Any trays inside should be spaced at least 24” apart. Otherwise, a human will not be able to maneuver inside and be able to safely work and also quickly exit from the column should an emergency arise while inside. These are important and critical points to always bear in mind when “engineering” a column. If you are going to order a workman to enter a confined space, you have the moral obligation to ensure his safety to enter, work, and exit the confined space safely.

3) Any column less than a meter (39 inches) in diameter will normally have fixed, bolted, or welded trays (unless it is packed). That being the case, you will also find that it is impractical to expect that your 0.9 meter diameter column is going to allow a human to gain safe entry into it. You are going to have to decide on either installing a manway at each tray – including the usual one for the sump – or seal welding each tray permanently and forget about gaining access to them. You can always consider packing for a small diameter column - especially structured packing instead.

If your column is to have 38 trays, then that makes your column approximately:

Space between tray = 2 feet
Height for trays = 2 x 38 =76 feet
Top vapor space = 4 feet
Column sump height = 6 feet
Total net column height, s/s = 86 feet
Additial height for top head and skirt = 8 feet
Total, overall column height = 94 feet.

As you can see, your column has an L/D = 94/3 =31; it resembles a length of spaghetti. It isn’t practical.

[trungphu]

Mr. Fallah
Thanks for your advances.

Mr. Montemayor

Thank you so much for your clearly guidance. As you said, it is impractical to design manways in my column. So in this case, should I fabricate column with shell flanges in order to repair it if something wrong happen in the future. My vessel entry is no need to inspect, clean, and make repairs inside the column from time-to-time. My trays is sieve tray.

And, could I reduce the tray spacing to 1.35 feet in order to reduce the height of column?

Regards.

Edited by trungphu, 17 November 2012 - 08:33 AM.

[Art Montemayor]

Trungphu:

It is unfortunate that you continue to feed us basic data in bits and pieces. This makes continuing to help you a very tiresome and wearisome job. Why you don't simply supply us with ALL of the basic data upfront in your very first posting is something I fail to comprehend. That would make helping you so much easier, accurate, and simpler. Now you tell us you are using sieve trays. You still have not said anything about the quality of your liquids - as I have stated in my above posting. That would have given notice that you don't have to worry about going inside the column in the near future.

You could simply put two access manways on your column: one at the top vapor space and another at the bottom sump. This would enable you to install the segmental sieve trays by bolting them into position from the top, down to the bottom section.

No one can comment about the tray spacing without you calculating the minimum one - which should depend on how high your vapor velocity is and how high you intend to carry your tray liquid level. 1.35 feet might be OK, but it is subject to calculations and things like foaming, entrainment, etc. You haven't furnished even one calculation or a sketch in all of your queries, so I can't have an idea of what you are taking into account.

[trungphu]

Dear Mr.Motemayor

My column is a distillation column that fractionate 3000kg/h of an acetone-benzene solution containing 0.3656 mole fraction acetone at bubble point . It is desired to produce a distillate containing 0.9851 mole fraction acetone and a residue containing 0.006713 mole fraction acetone. And benzen is toxic.

Obviously, I calculated what you said above. I also calculated the pressure drop by Bennett correlation I hope you will take a look at my attach excel file here.

Attached Files

•  Trungphu column.xlsx   13.77KB   89 downloads

Edited by trungphu, 17 November 2012 - 10:15 PM.

[trungphu]

Ps:
I quite not sure the meaning of some terminologies such as '&ndash', '&rdquo','&ldquo'. I'm not a native speaker in English.^^

Thanks for your consideration.

[kkala]

Ps:I quite not sure the meaning of some terminologies such as '&ndash', '&rdquo','&ldquo'. I'm not a native speaker in English.^^ Thanks for your consideration.

Indeed there is a problem, also expressed in http://www.cheresour...e-calculations/ '> http://www.cheresour...e-calculations/ . It has to be settled.

[Art Montemayor]

Trungphu:

For some unexplained reason my ability to type in the fonts and responses to posts is not working in my editor. I will try to get this resolved with the Forum Administration. All my formatted responses are reproduced as ASCII type.

In the meantime, look at the attached work I have produced for you. This is the MINIMUM amount of engineering work I would expect from a student such as you who claims that he is seriously trying to build a distillation column for his university. I could go into more detail, but for now I want to clearly show you and all other students (as well as professional engineers) what a detailed and well organized sketch can tell you at a glance without going into verbal descriptions.

This is the type of accurate, succinct and detailed engineering explanations that are required not only when discussing the topic, but also when specifying your needs to suppliers and workmen. Therefore, if you are seriously working on fabricating a distillation column, you should have ALREADY generated such detailed sketches.

Why you have not shared them with this forum is known only to you.

Attached Files

•  Trungphu Column Rev1.xlsx   210.81KB   144 downloads

[trungphu]

Mr Montemayor

Thank you so much for your reply and comments on my attach.
I made some mistakes in my attach. I'm sorry for that. I also have a question that I wrote on my attach. Hope that you will take a look at it.

Attached Files

•  Trungphu Column Rev1.xlsx   213.29KB   28 downloads

[Art Montemayor]

Trungphu:

I have added a typical manner that can be used to install internal trays in a distillation column to the Sketch Tab in Rev2 of your workbook. I hope this shows clearly how someone would install the internals. All of this work, as I have stated, is based on using very skilled and accurate craftsmanship labor and design.

I do not agree on your method to determine the column diameter. I use the Souders-Brown method to determine the column diameter. I do not relate the flooding design to the entrainment design of the Souders-Brown method. The Souders-Brown method is well known and documented; you have not furnished any references to your calculations.

Do my sketches fully address the method and procedures you have raised regarding designing and fabricating your column?

Attached Files

•  Trungphu Column Rev2.xlsx   217.44KB   85 downloads

[trungphu]

Mr. Montemayor

Once again, thank you so much for help.

My calculations refer to Sinnott's Chemical Engineering Design. From my viewpoint, it is based on Souders - Brown equation. The vapor velocity must be below the flooding vapor velocity which can cause excessive liquid entrainment. The way the author determine the vapor velocity is the same as Sounders -Brown equation.

Your sketches are perfect and clearly. Actually, I have one more question that I stated on the attached file.

Regards

Attached Files

•  Trungphu Column Rev2.xlsx   217.58KB   34 downloads

Edited by trungphu, 19 November 2012 - 11:59 PM.

[Art Montemayor]

Trungphu:

Always keep a logical, chronological numbering control of your revised documents. This is standard, logical engineering practice around the world. Otherwise, you will wind up with a situation of not knowing what revision came first or last – or which is the present one. You failed to number your latest submittal as Rev3. That is why I am submitting Rev4 with my comments and revisions.

I don’t understand why you don’t seem to visualize or understand that the sieve trays are drilled and bolted into position. I clearly have stated so more than once and have gone to the pains of showing the bolt holes in all my sketches – albeit, not all the bolt holes. I thought that showing you some of the bolt holes would suffice to give you the clear idea of how the trays are assembled, but I guess I failed.

I have included fancier and more detailed illustrations of how the column is fabricated and assembled. I hope this puts the finishing touches on this topic.

Attached Files

•  Trungphu Column Rev4.xlsx   830.42KB   164 downloads

[trungphu]

Mr. Montemayor

I'm sorry for making mistake in numbering my revision. I'm just a student , maybe I'm lack of experiences in engineering practice, but I have a passion for it. That why I'm always curious about how something was installed.

Moreover, I'm not a English native speaker. I just learn English by myself. Therefore, it is sometimes difficult to me to totally understand an English text, especially text regarding mechanical field.

Anyway, thanks for taking time for my questions. After reading carefully your revision one more time, I can now visualize your guidances.

I apologize for any inconvenience I have caused.


Regards

Edited by trungphu, 21 November 2012 - 11:00 AM.