Talk:Continuous distillation

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[edit] New Stub article

I just added a ChE schematic of a continuous fractional distillation tower I just made and a general stub designation to this short stub of an article.

1. Does anyone know of a more specific stub designation that can be used? If so, go ahead and change it.

2. Take a look at the new pic I just added and if you can suggest any corrections, let me know; I can fix it. This pic was made in the same style as the 3 existing pics in Batch distillation, which were made by User:GM-BP, except the lossless *.png file format was used instead if the lossy *.jpg file format. Please don't make it fuzzy by turning it into a *.jpg file anywhere along the line. If you have Windows XP, you should be able to edit *.png files using Windows-Paint, if nothing else.

H Padleckas 18:34, 24 October 2006 (UTC)

Hi HP, I would like to suggest two minor alterations in your drawings.

1. I know it is pedantic, but I'd alter the product lines to enter tanks on their side. (This is customary) If refined products are sprinkled on top of the liquid, you will soon have a spark (static) and a fire.

2. Alter the reflux to a lower tray so that it can contact the hotter liquid there and allow a secondary chance of purification

3. There is one more comment, it is rather a request: could you show a bubble tray in detail please ? (unless I've missed it ?)

I can't think of anything else, except to thank you for the invitation. In turn you are invited to pass your comments on what I have done (if it is not too rude)LouisBB 01:08, 2 December 2006 (UTC)

Hi again I've just found one other little thing that needs changing, namely on the second drawing. I've just noticed that some of your bottoms are going straight in the product tank.

This is not general practice as reboilers are designed normally with a weir inside them, so that liquid that comes down from the column is heated, boiled and it is the overflow that goes out, not dirctly into the tank: it is passed to a cooler first, but even before that it passes through a heat exchanger which preheats the feed for instance, to improve thermal efficiency of the process. (These guys in the refinery think up all sorts of things)

I don't expect you to draw all that, but the reboiler could show a weir with entry on the heated side of it and takeoff on the other. I'll have a look at what you've written on reboilers, unless somebody looks at it before me. All the best, {[User:LouisBB|LouisBB]] 01:30, 2 December 2006 (UTC)

[edit] More about stub category

The best stub category I could come up with was "Chemical Reaction." There isn't one for chemical engineering/processes. NielsenGW 18:51, 24 October 2006 (UTC)

H Padleckas, I changed the stub to an "engineering stub" which is much more appropriate than the "chemical reaction" stub. I also added the word "industrial" into the lead-in sentence. I think your sketch is excellent as is!! I would only suggest that it would be improved if you added the word "reflux" to each of the lines returning to the tower from the horizontal drums beneath the condensers and the word "product" (or "distillate") to each the lines leading to a receiver from the horizontal drums. Also, I don't understand the valves in the lines leading to the receivers ... they are half blue and half black. I think it would be better to just delete the valves, they really aren't necessary. That also applies to the valve leading into the bottoms receiver. - mbeychok 20:58, 24 October 2006 (UTC)

In the aforementioned pic, I plan to make the following changes recommended by mbeychok:

1. Label the 4 return lines from the coindenser drum re-entering the tower as "reflux".

2. Label the 4 lines collecting final distillate product as "distillate product".

3. Eliminate the valves above of all 5 receivers. They were in the batch distillation diagrams, but come to think of it, they were needed there to "sequentially" direct which receiver the distillate would go to as the batch distillation progressed to heavier fractions. In a continuous steady-state operation, such directing is not needed since each fraction has its own condenser lines, but still there must be some valve or device somewhere controlling the reflux ratio. However, in view of Dirk Beetstra's request for simplicity, I will simply take out these valves.

When comparing this pic to mbeychok's industrial fractionator pic in Fractional distillation, I have left out the distillate pump below the reflux drum, the offgas line, and the label for the "Reflux drum". Again in view of Dirk Beetstra's request for simplicity, I will leave these out in my pic.

Finally for this current pic, I was thinking of putting in a "feed pre-heater" with a symbol similar to the reboiler, but I won't do it (another complication) unless someone recommends it. Any comments on that?

Practically finished but not yet uploaded this new pic version. H Padleckas 05:25, 27 October 2006 (UTC)

Finished, uploaded. H Padleckas 06:03, 28 October 2006 (UTC)

I could also make a similar introductory pic for use at the top of this article with a shorter tower and only 2 fraction outputs, 1 distillate fraction output (instead of 4) and 1 bottoms fraction. The 4-distillate pic would still be used futher down showing muliple fractionation like in oil refineries. Any comments?

Practically finished but not yet uploaded this new pic. H Padleckas 05:25, 27 October 2006 (UTC)

Finished, uploaded. H Padleckas 06:03, 28 October 2006 (UTC)

[edit] More about drawings

Finally, the lab fractional distillation pic in the Fractional distillation shows somewhat primitive lab technique. If nobody is working on a better pic, I plan to try to make a better pic (someday-LOL). However, if you're already working on a better pic, tell me so I won't bother. H Padleckas 00:23, 25 October 2006 (UTC)

I have not started on this pic. H Padleckas 05:25, 27 October 2006 (UTC)

Sounds fine to me. - mbeychok 01:12, 25 October 2006 (UTC)

H Padleckas, I really like your Tray_Distillation_Tower picture - very easy to follow. I think the shading from dark to light blue as you move up the column is very nice - I think I tried this elsewhere but with less success. It only remains to animate it!(←joke). Quantockgoblin 16:56, 7 November 2006 (UTC)

[edit] Rearrangement and expansion

Hello to all:

Dirk Beetstra believed quite strongly that this article need to be re-organzied and explained better to make it more understandable, especially by non-specialists. He contacted me and, after about 3-4 days of intense collaboration of working in his sandbox along with comments from H Padleckas, we agreed on a new version. That new version was just used to over-write the old version. It pretty much contains everything that was in the previous version in a re-arrangement of the order of sections. It also contains a new "Examples" section. - mbeychok 16:42, 1 December 2006 (UTC)

Hi, I've modified the definition removing some of the stuff that belongs elsewhere, altered the Principle but it needs LINKS. LouisBB 01:08, 2 December 2006 (UTC)

1. The last paragraph of Principles ought to be revised so that it is nor a repetition of what has been said earlier.

1. Repetition is not good, indeed.(answer moved Dirk Beetstra ^{T C} 11:28, 3 December 2006 (UTC))

I agree there is some repetition between what you added at the top part of Principles and what already existed at the bottom of that section using Image 2 as part of the explanation. I happen to think that the pre-exsisting part and using Image 2 is somewhat clearer than what you added. However, in the interest of collaboration which is the spirit of Wikipedia, perhaps it is better to leave the slight repetition. mbeychok 20:25, 2 December 2006 (UTC)

Thanks for not wiping what I said here, although, the way you written it down might read better? Perhaps the two ought to be combined and using it to replace what I said, and we should refer to a detailed picture here. LouisBB 08:52, 3 December 2006 (UTC)

2. Are we certain that the Debutaniser example, which does not really belong here, improves the article?

2. I am not sure, I am not a chemical engineer, I must confess, I used an explanation of the subject to me by MBeychok to write the examples, maybe I misinterpreted a debutaniser as another distillation. But I am sure there are other industrial distillations besides crude oil, which can serve as an example.(answer moved Dirk Beetstra ^{T C} 11:28, 3 December 2006 (UTC))

I agree that the Debutanizer example is really not needed, but it was added by Dirk Beetsra who felt it was useful. After all, a debutanizer is just as much a common continuous distillation column as is a crude oil fractionator or any other fractionator. But I would not object if it were deleted. mbeychok 20:25, 2 December 2006 (UTC)

3. The multicomponent continuous distillation drawing makes the binary mixture drawing really superfluous (as a reader you can get a bit too overwhelmed with repetitions) but a picture or a proper drawing of a single tray or an enlarged section of the column wold be really instructive.

3. No, I don't believe so, the multicomponent picture might scare people of (except when people are really talked through the picture step by step). See also my general thoughts, below. IMHO, I would keep the simple picture with the principle, and use the big one next to the improvements.(answer moved Dirk Beetstra ^{T C} 11:28, 3 December 2006 (UTC))

I believe Images 2, 3, and 4 are all needed. Image 2 desicts a simple system for the newcomer to this field. Image 3 depicts a more complex tower as they exist in the real world. Then there is a drawing of the inside of a bubble cap tower in Image 4 to explain what trays look like. If you want an enlarged section of only a few trays, there is such a drawing by Henry Padleckas in the Theoretical plate article. That is very clearly stated further down in the article in the "Plates and Trays" section and a link is provided. Please read that. mbeychok 20:25, 2 December 2006 (UTC)

For a simple picture reflux, reboiler, and tanks are unnecessary and are repeated later.

The link to trays/plates should come here, where we are mentioning it first. My contention is also, that a reflux does not belong to the basic picture, as its basic function is, perhaps, to substitute an extra plate. You could also do without a reboiler, and you often do, I think. LouisBB 08:52, 3 December 2006 (UTC)

Do you believe reflux can "perhaps substitute for an extra plate"?? That is completely erroneous! When designing a distillation tower, increasing the design amount of reflux can decrease the need for many, many trays ... and decreasing the amount of design reflux can increase the the need for many, many more trays. To say that "reflux does not belong in the basic picture" is completely, completely erroneous!! In fact, any process design engineer worth his/her salt makes a thorough study of the number of trays versus the amount of reflux so that he/she can choose the optimum balance between the cost of more trays versus the cost of providing more reflux. - mbeychok 06:15, 4 December 2006 (UTC)

As for Image 2 which is a drawing of a simple binary distillation column ... no industrial distllation column, simple or complex, gets built and operates without reflux and and without some means of adding heat to the column (most usually a reboiler). That is why Padleckas correctly included reflux and a reboiler in Image 2. - mbeychok 17:55, 4 December 2006 (UTC)

4. I propose to add sections Variations and Improving separating efficiency, but I shall see Beetstra's sandbox first.

4. I fully agree, that would be in line with my general answer, below. Don't bother to see my sandbox for that, this is now the working copy, the sandbox is empty.(answer moved Dirk Beetstra ^{T C} 11:28, 3 December 2006 (UTC))

Beetstra's sandbox is now empty and transferred to here. As for Improving separating efficiency that is also discussed further in this article as it now stands where it explaining that efficiency can be increased by increasing either or both reflux and the number of trays. As for Variations, Wikeipeidi has articles on Distillation, Fractional distillation, Batch distillation, Azeotropic distillation, Extractive distillation, Vacuum distillation and Steam distillation as well as McCabe-Thiele method, Fenske equation, Absorption and many more. This article was not intended to cover that entire spectrum. It was intended only for the large-scale, continuously operating distillation towers used in industry that operate 24 hours a day, 7 days a week for two or three years between maintenance shutdowns.

Please don't misinterpret this remark, I realize that you only became involved in this subject a few days ago, but I have always found it very useful to read and to study what is already available before starting to suggest or make changes or expansions. mbeychok 20:25, 2 December 2006 (UTC)

Thanks for your suggestion. I'll take note of it. I did not mean a complete description of all that was said before, but steam introduction was mentioned, which is a specific case, and I was thinking of another specific example, the use of a separate steam operated stripper, to add an extra product quality controle variable of a side stream, (which can be used instead of direct steam intoduction) and using a flash vaporiser before the feed enters the column to reduce column loading (eg when the column is used for a feed containing more volatiles than what it was originally designed for) LouisBB 08:52, 3 December 2006 (UTC)

5. I suggest: Category: Chemical engineering: Unit operations. See Perry (I only have a copy of the 1950 edition) Section 8. General theory of diffusional operations Introduction: "The diffusional operations - Distillation, solvent extraction, and gas absorption, have a common theoretical foundation" I don't think we should argue too much with that. LouisBB 15:33, 2 December 2006 (UTC)

5. Suitable category for these articles, indeed.

The Category:Chemical engineering and Category:Unit operations are already listed at the bottom of the article so as to direct the readers to more information. Perry's Handbook is already referenced 4 times in the article. I don't understand what else is needed. mbeychok 20:25, 2 December 2006 (UTC)

There seems to have been a question on where to categorise the article. Why was this question put if it was already answered? LouisBB 08:52, 3 December 2006 (UTC)

Where did anyone question how to categorize the article? I haven't been able to find such a question. It is now and has been assigned for quite some time to the "Distillation", "Industrial processes", "Chemical engineering" and "Unit operations" categories. They are listed quite clearly at the bottom of the article, just as they should be. - mbeychok 05:59, 4 December 2006 (UTC)

Hi, I saw your addition to the principle, though the line is clear to me, I feel that some things might have a better place in the design and theory part, whilst keeping the principle 'simple'. I know and understand that this has nothing to do with a real-life continuous distillation (and I have discussed this with MBeychok as well), but I believe that the principle does not have to be the explanation of a full-fetched system, a continuous distillation is also a continuous distillation without plates, and without reflux, though it is not industrially used as such, and the separation is very lousy, but I think we should not confuse 'principle' with 'operation'. Hence I tried to split these two paragraphs out in the sandbox version. I see that your edits give a complete picture, but I am afraid that it confuses people who are not familiar in the field (there are now a couple of run-on sentences, which require some concentration to read). I know that I am giving an outsider view, but I am only trying to give my views as such, while I am trying to understand what those big towers are now actually doing. I see forward to more improvements in the article. --Dirk Beetstra ^{T C} 19:15, 2 December 2006 (UTC)

I reinstated the copy in my sandbox. Please have a look! --Dirk Beetstra ^{T C} 17:18, 3 December 2006 (UTC)

[edit] Response to some of LouissBB's edits

LouisBB, the reason I changed your wording about pumping the feed into a distillation column and instead used the word "routed into" was to make it more general. When the bottoms of a depropanizer column which operates at a much higher pressure flows into a next column such as a debutanizer or depentanizer operating at a much lower pressure, a pump is not needed at all. There are just as many cases of that situation as there are cases of needing a pump. That's why "routing" is a better choice of wording than "pumping". After all, we are concerned in this article with distillation rather than exactly how the the feed is gotten into the column.

The feed does not necessarily begin to boil when it enters a column because it "expands". Columns feeds may be sub-cooled at the column's operating temperature and pressure, or they may be saturated (at their boiling point), or they may be partially vaporized, or they may be superheated as they enter. If they are sub-cooled, then they will be heated and vaporized by the heat input into the column's reboiler. If they are saturated, then they will be boiled and vaorized, again by the reboilers heat input. Only when a feed is at a much higher pressure than the column, will there be any flashing and vaporizing as it enters. Again, to be general rather than specific, we should avoid discussing expansion which is specific to only some cases.

Please read the McCabe-Thiele method article and read the section on q-lines that explains the different thermal conditions of a tower's feeds. Also, please read the Flash evaporation article to read about flashing of high-pressure liquids as they expand.

Before I retired after a 50-year career, I quite literally designed hundreds of continuous distillation columns and the cases discussed above (pumping not always needed and various feed thermal conditions) are quite common in any refinery or large petrochemical plants and other industrial facilities.

I am going to change those wordings back as I had edited him and ask you to please keep in mind that the article must be generalized to fit all cases. Also, the linking to other existing article is better in some cases than trying to cover in one article what is already covered in other articles. Besides this Continuous distillation article, there are articles on Distillation, Fractional distillation, Fractionating column, McCabe-Thiele method, Fenske equation, Batch distillation, and many others .... and it is well to keep that in mind. It would also be well to read them all to familiarize yourself with what they cover. This Continuous distillation article is not meant to cover the entire spectrum of distillation ... only large, industrial continuously operating columns. With best wishes to a fellow retiree, mbeychok 17:14, 2 December 2006 (UTC)

I wish to avoid any conflict by all means, but I am certain that telling the reader that the feed does not just arrive into the column is important. I would class it more important than reflux, for instance, in fact that is why I proposed to transfer Reflux to a section on Improving separation efficiency.

Forget about pump, if you think that other cases are as frequent, although, I suspect pumping is as frequent as other cases altogether. The provision of a continuous driving force is an essential part of continuous distillation. We might as well forget about heating as well, because you can introduce the feed as vapours, and cool the column. Then, of course, the entering vapours will start to rise and condense to produce the liquid downflow. Do we need to be as specific as that? However, mentioning some sort of driving force is important.

Then again: why do we hide the fact that expansion occurs as the feed enters. That is exactly what causes the partial vaporisation of a liquid feed. Surely, expansion takes place in all cases, that is what pressure drop is up the column.

I do see the point in the comment from Dirk Beetstra that talking about plates and trays is not general, it is a convenient way of conveying the principle. However, there is a way to overcome this objection: after all, we are citing all sorts of specific cases in this article. LouisBB 08:52, 3 December 2006 (UTC)

[edit] Second rewrite

After the latest addition of LouisBB, a second rewrite of the article has been performed. As MBeychok described after the previous rewrite, I believe quite strongly that it is possible to explain the majority of this article so non-specialists can understand this subject. MBeychok and I have again collaborated in the rewrite, and we have now agreed on this version, which incorporates the additions and some of the suggestions made by LouisBB.

Some short explanations of the intentions: The article now starts with an introduction which tells what this article is about, continuous distillation, which is one of the major separation techniques in the chemical industry. After that follows the principle, which explains, as the title says, the principle. The description in this section is not a description of a real, operating process, to use continuous distillation for complex mixtures several other enhancements to the process have to be made, and these are described in the following section 'design and operation'. It describes in a bit more detail how column feed works, enhancements on the separation process, and some overhead arrangements. Finally an example of an actual process (distillation of crude oil) is described, which is intended to show the true complexity of an actual distillation. For more information, the discussion and history can still be found in my sandbox. --Dirk Beetstra ^{T C} 21:32, 5 December 2006 (UTC)

I think we all owe a vote of thanks to Dirk Beetstra for developing this compromise by collaboration. - mbeychok 22:42, 5 December 2006 (UTC)

You're welcome! --Dirk Beetstra ^{T C} 22:52, 5 December 2006 (UTC)

This looks like a pretty nice article now. What do you think about making it a candidate for Good Article? Walkerma 04:26, 6 December 2006 (UTC)

If Dirk doesn't mind my talking for him, we both think it is a great idea. Please pursue it and thanks. - mbeychok 04:43, 6 December 2006 (UTC)

I indeed think that is a good plan. Thanks Martin! --Dirk Beetstra ^{T C} 07:41, 6 December 2006 (UTC)

I was going to nominate the article tonight, but I noticed a small problem. At the end of the article it says "Examples" but there is only really one example given. Do you plan to add any other examples? Or should the "Examples" heading be removed and "Continuous distillation of crude oil" become the main header for that section? Thanks again for your great work, Walkerma 06:09, 8 December 2006 (UTC)

Previously on my Talk page, I was asked to review this article, which I did; and I said I would add some explanation here and there, but that it would take me a while since I was busy. Well, I finally got a chance to add my $2 worth to that article. I wrote an introduction that explained what continuous distillation is in about as simple a way as I could write it for the "average guy," and I moved the industrial discussion to a new section called "Industrial application." I also changed the statement that said the system was kept in a constant equilibrium to the system is kept in a steady state, and then briefly explained steady state as it pertains to continuous distillation. I put in a couple other minor changes. Another thing I was thinking about was whether reflux ratio should be defined in the "Reflux" subsection.

I practically finished a modification of Quantockgoblin's "lab" diagram of "Distillation scheme with column", previously inserted as Image 2 in Dirk Beetstra's draft of "Continuous distillation" then taken out. I don't like it that much, but I think I'll upload it sometime into Wikipedia anyway, but I think I'll leave it up to somebody else to insert into an article. Other than that, I guess I'm pretty much done with this article. H Padleckas 18:32, 10 December 2006 (UTC)

Henry, there is a problem in defining reflux ratio in that there are two definitions of that term: (1) the classical definition that defines the reflux ratio as R/D where R is the molar reflux flow rate and D is the molar liquid distillate rate and (2) the definition used by many process designers and controllers that defines the reflux ratio as R/F where R is the molar reflux rate and F is the molar feed rate (as in the random example articles at [1], [2] and [3]). Thus, in the interest of simplicity, it may be better to just define the reflux as this article now does. - mbeychok 22:35, 10 December 2006 (UTC)

[edit] Renaming of "Examples" heading

Walkerma, we're getting a bit too far indented, so I started a new header about your suggested renaming. We once did have two examples, but one was deleted. How about we leave the one example as you suggested and change the heading from "Examples" to simply "Crude oil distillation" which is a bit more brief? Just a suggestion, I don't feel too strongly about it. - mbeychok 07:00, 8 December 2006 (UTC)

Done - I thought the same. I did a quick copyedit of the last paragraph too, I hope that was OK. Now nominated. Walkerma 08:13, 8 December 2006 (UTC)

Looks good, thanks Martin for the nomination! --Dirk Beetstra ^{T C} 08:51, 8 December 2006 (UTC)

[edit] GA review

A good article has the following attributes.

1. It is well written.

Yes.

2. It is factually accurate and verifiable.

Yes, although more references would be an improvement.

3. It is broad in its coverage.

Yes.

4. It follows the neutral point of view policy.

I don't think it is biased in any way.

5. It is stable, i.e. it does not change significantly from day to day and is not the subject of ongoing edit wars.

it is stable.

6. It contains images, where possible, to illustrate the topic.

Yes.

Pass. Congratulations. TimVickers 00:38, 28 December 2006 (UTC)

Thanks, TimVickers. You have made all our hard work (and it was very truly hard at times) worthwhile. Happy New Year! - mbeychok 00:56, 28 December 2006 (UTC)

Few pointers,

• don't write (see image 1) see image2 etc
• I saw a two, one sentence paragraphs
• Only the title of the article should be bolded (distiller, bottoms)
• if you want to go for FA you will need more references

I suggest you get a Peer-review M3tal H3ad 02:29, 28 December 2006 (UTC)