Images of Distillation Columns

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IMAGES OF DISTILLATION COLUMNS(GOOGLE DISTILLATION COLUMN IMAGES)

https://reader009.{domain}/reader009/html5/0505/5aed5095b7b70/5aed50972fbcb.jpg No one drew a satisfactory picture of a distillation column. I

understand to some extent why most of the pictures youhave been exposed to do not show the details that are neededfor a tray to work. You all need to go by D-107 and spendsome time looking at the tray cartridge there. Thedowncomers are pipes in the cartridge . A typical largercolumn uses the side of the tower as part of the downcomermost of the time.

Notice how the trays physically separate the column intomany different stills. The downcomers and weirs seal theseparation ( and notice how separate is spelled ) while allowing

the liquid to flow down the column. The vapor goes upthrough the holes in the trays and passes through the liquidthat is held up on the trays.

This is another sketch that has the parts wellshown. The axial flow example the flowgoes from the middle to the outside (withcircular or radial flow and not a commondesign) and then from the outside to themiddle. You can also split a large tray intotwo trays. This would be like putting two of the cross flow systems back to back.
http://www.modular-process.com/images/distillation-column-internals.jpghttp://www.modular-process.com/images/distillation-column-internals.jpghttp://www.modular-process.com/images/distillation-column-internals.jpg


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The downcomers are written in here rather than drawn

in. This is a popular drawing and is reused severaltimes in various Wikipedia topics. At the bottom of this file is an expanded view o f this same picture thatshows the downcomers.

http://upload.wikimedia.org/wikipedia/commons/e/e9/Tray_Distillation_Tower.PNG

This is a bubble cap tray. Most of the chimneys dont havethe caps on them. The vapor comes up the chimney andthen down the outside of the chimney and into contact withthe liquid on the tray. You can see the weir on the rightside of the tray that keeps the caps covered in liquid. Thisdesign has a very high turndown ratio. It cant weep liquidand will hold a level under almost all situations. There is ahole (one or more) in the tray somewhere to drain it if thecolumn is shut down. Otherwise you could not clear thetower for maintenance.www.indiamart.com
http://upload.wikimedia.org/wikipedia/commons/e/e9/Tray_Distillation_Tower.PNGhttp://upload.wikimedia.org/wikipedia/commons/e/e9/Tray_Distillation_Tower.PNGhttp://upload.wikimedia.org/wikipedia/commons/e/e9/Tray_Distillation_Tower.PNG


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This is a stylized picture of a bubble cap column.They did not draw the downcomers that areneeded to keep the vapor from bypassing the tray.This is a common short cut in drawing columnsbut there are always downcomers in the mostcommon tray designs. There are some designswhere the liquid simply falls from one tray toanother but these are very inefficient because the

liquid and vapor do not have enough contact toequilibrate.

Distillation columns use this principle effectively repeating the separation process at individual trays withina column. Such columns may have over a hundred trays on which VLE ( vapor liquid equilibrium ) isoccurring. Depicted below is a cartoon cut-away of a small section of a tray-type distillation column. Twosieve trays are shown. Hot vapor (shown in white) flows up through the holes in the sieve tray andvigorously bubbles through the liquid (shown in blue). The vapor and liquid mix on this tray and the newmixture boils. The composition of the liquid, x , leaving the will be enriched in the less volatile componentwhile the composition of the vapor, y , will be enriched in the more volatile component. The vapor rises up tothe next tray where it will contact a liquid of larger x and mixing and re-equilibration will again occur. Theliquid leaving the tray will flow over the weir and down the downcomer to the next tray where it will mix withthe vapor on that tray. In this way, x tends to become smaller at each lower tray, while y tends to increaseat each tray higher in the column. VLE refers to the relationship between the x and y values on each tray.

At equilibrium, the temperature and pressure of the liquid and vapor phases will be equal, but thecompositions will not. Why is this? There are two main factors that make the vapor and liquid compositions

different at equilibrium: the pure component vapor pressures and the nonidealities in the liquid phase.These two factors are discussed more fully in the next section on the Thermodynamics of VLE . However,to understand fully these factors, one needs to understand the molecular nature of the liquid and vaporphases and how the properties of the fluids arise from the molecular interactions. The section on MolecularInterations will help understand this relationship of molecular interactions and the resultant phasebehavior. Both of these sections should be studied before running the simulator.
http://www.et.byu.edu/~rowley/VLEfinal/background2.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background2.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background2.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background4.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background4.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background4.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background4.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background4.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background4.htmhttp://www.et.byu.edu/~rowley/VLEfinal/background2.htm


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www.et.byu.edu The picture and text above were from thissite. We have sieve trays in T- 100. If you dont have enoughvapor flow to keep the liquid from running through the holes,sieve trays dont keep much liquid on the trays. This reducestheir turndown ratio dramatically.

http://www.answers.com/topic/continuous-distillation isa web site with some very good text (and one of thepictures above) on distillation.

Distillation pressure

The pressure under which a distillation is performed is amatter of choice, although operation at pressures moreremoved from atmospheric becomes more costly.

Altering the pressure of a distillation can serve to alter the vapor-liquid equilibrium relationship, afeature that can be used to advantage.

Because of the relationship between vapor pressure and temperature, the temperatures within adistillation column are lower for lower pressures. Vacuum distillation is an effective means of maintaining lower temperatures for separations involving heat-sensitive materials.

Steam distillation is an alternative to vacuum distillation for separations of organic substances. Inthis process, steam is fed directly to the bottom of a column and passes upward, composing asubstantial fraction of the vapor phase. The combined partial pressures of the organic substancesbeing distilled are thereby lessened, giving the lower temperatures characteristic of a vacuumdistillation. http://www.answers.com/topic/distillation

Industrial distillation is typically performed in large, vertical cylindrical columns (as shown inimage 2) known as "distillation towers" or "distillation columns" with diameters ranging fromabout 65 centimeters to 6 meters and heights ranging from about 6 meters to 60 meters or more.
http://www.et.byu.edu/http://www.et.byu.edu/http://www.answers.com/topic/continuous-distillationhttp://www.answers.com/topic/continuous-distillationhttp://www.answers.com/topic/vacuum-distillationhttp://www.answers.com/topic/vacuum-distillationhttp://www.answers.com/topic/vacuum-distillationhttp://www.answers.com/topic/distillhttp://www.answers.com/topic/distillhttp://www.answers.com/topic/distillhttp://www.answers.com/topic/distillationhttp://www.answers.com/topic/distillationhttp://www.answers.com/topic/distillationhttp://www.answers.com/topic/distillhttp://www.answers.com/topic/vacuum-distillationhttp://www.answers.com/topic/continuous-distillationhttp://www.et.byu.edu/


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Image 3 (on the left): Chemical engineering schematicof a continuous fractionating column. Typical of many

drawings, it fails to show the downcomers. Pleaseremember that the downcomers are there in almost everycolumn design that involves trays. The only exception Ihave seen are some designs for handling very dirtymaterials and they will look a lot like the sketch on theleft.. Image 3 depicts an industrial fractionating columnseparating a feed stream into one distillate fraction and onebottoms fraction. However, many industrial fractionatingcolumns have outlets at intervals up the column so thatmultiple products having different boiling ranges may bewithdrawn from a column distilling a multi-component

feed stream. The "lightest" products with the lowest boilingpoints exit from the top of the columns and the "heaviest"products with the highest boiling points exit from the

bottom.

Image 4 (on the left): Chemical engineering schematic of typical bubble-cap trays in a fractionating column. Asmentioned above, the downcomers are written in hereand not drawn in. They extend below the puddle of fluidat a side of the column to seal the flow of vapor and forceit through the trays and into intimate contact with the liquidon the trays.

Industrial distillation towers are usually operated at acontinuous steady state. Unless disturbed by changes infeed, heat, ambient temperature, or condensing, the amountof feed being added normally equals the amount of productbeing removed.

It should also be noted that the amount of heat entering thecolumn from the reboiler and with the feed must equal theamount heat removed by the overhead condenser and withthe products.

http://www.answers.com/topic/fractionating-column
http://www.answers.com/topic/reboiler-1http://www.answers.com/topic/reboiler-1http://www.answers.com/topic/reboiler-1http://www.answers.com/topic/fractionating-columnhttp://www.answers.com/topic/fractionating-columnhttp://www.answers.com/topic/fractionating-columnhttp://www.answers.com/topic/reboiler-1


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Industrial fractionating columns use external reflux to achieve better separation of products .[3][5] Reflux refers to the portion of the condensed overhead liquid product that returns to the upper partof the fractionating column as shown in Image 3.

Inside the column, the down flowing reflux liquid provides cooling and condensation of upflowing vapors thereby increasing the efficacy of the distillation tower. The more reflux and/ormore trays provided, the better is the tower's separation of lower boiling materials from higherboiling materials.

The design and operation of a fractionating column depends on the composition of the feed and aswell as the composition of the desired products. Given a simple, binary component feed, analyticalmethods such as the McCabe-Thiele method [5][6][7] or the Fenske equation [5] can be used. For amulti-component feed, simulation models are used both for design, operation and construction.

Bubble-cap "trays" or "plates" are one of the types of physical devices which are used to provide

good contact between the up flowing vapor and the down flowing liquid inside an industrialfractionating column. Such trays are shown in Images 4 and 5.

The efficiency of a tray or plate is typically lower than that of a theoretical 100% efficientequilibrium stage . Hence, a fractionating column almost always needs more actual, physical platesthan the required number of theoretical vapor-liquid equilibrium stages.

This is an expanded view of image 4 (above).Here they drew the downcomers. Notice thatthe pressure drop through the tray above holdsthe liquid in the downcomer above the level of

the liquid on the tray. There is usually anoverflow weir between the downcomer andthe active part of the tray that is not shown.

lorien.ncl.ac.uk / ming /distil/distilint.htm This is avery good web site for distillation information. Theauthor of this site also wrote some of theinformation above. You will have to paste it intoyour browsers address box to access it.

Bennett Willis
http://www.answers.com/topic/fractionating-column#cite_note-Kister-2#cite_note-Kister-2http://www.answers.com/topic/fractionating-column#cite_note-Kister-2#cite_note-Kister-2http://www.answers.com/topic/fractionating-column#cite_note-Kister-2#cite_note-Kister-2http://www.answers.com/topic/mccabe-thiele-method-1http://www.answers.com/topic/mccabe-thiele-method-1http://www.answers.com/topic/mccabe-thiele-method-1http://www.answers.com/topic/fractionating-column#cite_note-Beychok-5#cite_note-Beychok-5http://www.answers.com/topic/fractionating-column#cite_note-Beychok-5#cite_note-Beychok-5http://www.answers.com/topic/fenske-equationhttp://www.answers.com/topic/fenske-equationhttp://www.answers.com/topic/fenske-equationhttp://www.answers.com/topic/fenske-equationhttp://www.answers.com/topic/simulationhttp://www.answers.com/topic/simulationhttp://www.answers.com/topic/simulationhttp://www.answers.com/topic/theoretical-plate-1http://www.answers.com/topic/theoretical-plate-1http://www.answers.com/topic/theoretical-plate-1http://www.answers.com/topic/simulationhttp://www.answers.com/topic/fenske-equationhttp://www.answers.com/topic/fenske-equationhttp://www.answers.com/topic/fractionating-column#cite_note-Beychok-5#cite_note-Beychok-5http://www.answers.com/topic/fractionating-column#cite_note-Beychok-5#cite_note-Beychok-5http://www.answers.com/topic/mccabe-thiele-method-1http://www.answers.com/topic/mccabe-thiele-method-1http://www.answers.com/topic/fractionating-column#cite_note-Kister-2#cite_note-Kister-2http://www.answers.com/topic/fractionating-column#cite_note-Kister-2#cite_note-Kister-2

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Images of Distillation Columns