US1952639A - Distillation of hydrocarbons - Google Patents

Description

March 27,1-934. E W, THIELE 1,952,639 i DISTILLATION OF HTYDROCARBONS Filed June` 30, 1952 i l z 4 s t 5 l INVEN'TOR ATTORNEY Patented Mar. 27, 1934 UNITED STATES PATENT OFFICE 1,952,639 DISTILLATION OF HYDROCARBONS Ernest W. Thiele, Chicago, Ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application June 30, 1932, Serial No. 620,101 5 Claims. (Cl. 196-94) This invention relates to the fractional disin the sidestripper. Other objects will become tillation of a composite liquid such as a mixture apparent as this description proceeds. of hydrocarbons as present in petroleum, In its broadest aspect my invention contem- In the modern practice of fractional distillaplat-eS the withdrawing rOln 2 fraetienting 5 tion it has become customary to effect the frac- Column 0f a Vapor Sideout which may be fraC- 60 tionation in a fractionating tower such as a tienilly COndenSed eS desired and Which will bulohel tower. Unless otherwise modified this have a lower end point than the out taken overtower eifects two cuts, the first, a vapor overhead head in the main tower. In one of its embodiand the second, a condensate or bottoms. one of ments my invention contemplates the withdrawal 1o the modifications employed in order to increase of a vapor side out from the tower at a point 'o5 the number of cuts is that of sidentripping. below the point of introduction of the stock which As practiced, this consists in withdrawing from iS undergoing freCtiOnatiOn inthe main tower. an intermediate point in the tower a portion of In Order t eid in en understanding of Iny inthe liquid condensate which is led into an auxilvolition l have illustrated it in the accompanying l iary unit and further fractionated by means of drawing in which the Single fleure illustrates e 70 the addition of heat or stripping Steam oppiiod side elevation, somewhat diagrammatic in charat the hase. rrhis practice is illustrated in U. s. aoter. of a form of apparatus useful in the carry- Patent 1,680,421, granted to Lewis. One of the, ing Out 0f my invention. In the aeeelnpenying advantages of this practice of. Side str1pping is drawing l is a pipe line by which the stock to be 2o that the withdrawn portion may be offootivoiy fractionated is introduced into the fractionating 75 stripped with much less steam than would be Column 2- This Column may be of aniT of the necessary' to accomplish a like result in the main types customarily employed in the fractionation bubble tower. A serious disadvantage of this 0f liquids, but I Prefer t0 employ and have illuspractice, however, lies .in the fact that in the trated the tower es the Well-known bubble type.

fractionation of hydrocarbons in a bubble tower equipped with reflux cooling ooils 3. bubble plates so there is always more or less entrainment of heavy 4 and liquid dOwnCOlnerS 5- Adieeent the tOP 0f fractions in the rising vapors within the tower. the towel iS e VeDOi Outlet pipe 6. A condensate This entrained liquid tends to contaminate the Outlet 7 iS proVlded heerthe bottom 0f the tewercondensate on the several trays. Moreover, the Directly Cenneeted t0 the Outlet pipe 7 iS a valved liquid Withdrawn will generally contain heavy llhe 8 for WlthdraWlhg bottoms and leading them 85 ends condensed from the vapors introduced into t0 any Suitable equipment fOr further reiing or the tower. The condensate withdrawn for side- .for StOrege- A Velved line 9, provided With a Suitstripping. almost invariably, therefore, contains able Pump 9'. branches frein the pipe 'l and leads portions of the bottoms or heaviest fractions into a still 10, illustrated as a pipe still but which which should otherwise be withdrawn from the may be 0f any Suitable type. fOr imparting heet 90 bottom of the moin towen SteomSido Sti-ipping into the oil introduced into said still. A return doos not remove the heavy fractions from the Sido line 11 leads from the still and re-enters the colcut. The cut Withdrawn and stripped in the side umn 2 et e peint adjacent the bottom thereof. stripper is therefore not as clean a cut as is de- The Vapor Outlet Pipe 6 may he Provided With 4o sirable. This is particularly the case where the any suitable Condenser 12 for Cooling the vapors 95 stock which is being fractionated is a dirty stock. ,Withdrawn through the Dine 6- Frein the Con- My invention has foi` one of its objoots the denser l2 the branched pipe 13 conducts the overwithdrawoi of an intermediate ont from the head either through valved branch 14 which leads bubble tower in such a fashion as to avoid the t0 any Suitable equipment fOr further refining or contamination by bottoms. A further object of for storage or through valved line 15 which may loo my invention is the provision for withdrawing an he previded fer withdrawing a predetermined intermediate cut at a .point below* the point of part of the overhead from pipe 13 and returning 'introduction of the Stool; which is undergoing some of the condensed overhead to the tower 2 for fractionation. A still further object of my inrefluX- so vention is the withdrawal of an intermediate out One or more of the trays in the tower 2. such as los and the fractionation of a cut without the necestrey 4', md-y be equipped with Sump 16' or other sity of supplying steam and additionai heat for suitable meansfor collecting condensate which fractionation and with the resulting elimination may be withdrawn from the tower through valved of expensive pumps, furnace coils and compliline 16, which leads into an 4auxiliary column 17.

cated lines required where reboiling is necessary The auxiliary column may be of any suitable type 11o for stripping the condensate introduced into it and may be provided with suitable bubble trays 18 and liquid downcomers 19. Valved line 20 is provided adjacent the bottom of the tower for introducing steam or other form of heat. Adjacent the bottom of the auxiliary tower is outlet pipe 21 for drawing 01T the stripped condensate from the tower. Adjacent the top of the auxiliary tower is an outlet pipe 23 for withdrawing the uncondensed vapors and stripping steam. The line 23 may suitably be branched to provide a valved line 22 for reintroducing vapors into the column 2 as well as a valved line 23 for withdrawing as a separate cut some of the stripped vapors. Valved line 23 leads into a condenser 24 or other suitable cooling apparatus for condensing the vapors and separating steam therefrom. The condenser 24 isprovided with suitable outlet 25 for condensed oil, suitable outlet 43 for withdrawing condensed steam and suitable outlet 44 for withdrawing uncondensed oil vapors. f

The tower 2 is provided with a valved pipe 26 which leads to an auxiliary rectifying column 27 which may be of any suitable type but which is illustrated as provided with reiiux condensing coils 28, bubble trays 29 and liquid downcomers 30. Adjacent the bottom of the auxiliary tower is a branched condensate outlet pipe 31, one branch of whichva1ved pipe 32, leads to storage or any suitable refining equipment and the other branch 33 equipped with a suitable pump 33 if desired leads to the tower 2 for reintroducing into the tower any portion of the condensed liquids desired.

Adjacent the upper end of the auxiliary tower 27 is a vapor outlet 34 which leads to a cooling coil or other condensing means 35, the outlet 36 0f which leads to a separator 37 from which is withdrawn through valved line 38 any condensed liquids and from line 39 any uncondensed vapors. Line 39 is branched, one branch of which, line 40, leads to the tower 2 and the other branch, valved line 42, leads to any suitable means for renement or to storage. Line 40 may be provided with a check valve or suitable pressure regulating Valve 41 for controlling the pressure of the vapors vented back into the tower 2. Or in place of Valve 41 I may employ a pump to force vapors into the column 2 and reduce the pressure in 37.

The operation of the equipment is as follows: The liquid oil which may have been previously heated to any desired degree and by any suitable means, such as by introduction into the reflux coil 3, is introduced through pipe 1 into tower 2 at a point intermediate the top and bottom thereof. Any vaporzed portion of the introduced oil tends to rise in the tower, and conversely, any unvaporized portion tends to seek a lower level as is well known in this art. The rising vapors are rectified by passing through the condensate on the trays with the aid of bubble caps or to any equivalent contact means, and are fractionally condensed by contact with the cooling coil 3 and any reux liquid which may be introduced through the pipe l5. The uncone densed vapors are drawn off through pipe 6 where they are cooled to any desired degree in the condenser 12 and after any suitable portion thereof has been withdrawn through pipe 15 to be returned as reflux to the tower 2, may be carried through line 14 to storage or for further refinement.

The rel'iux and unvaporized liquid portion of the feed descends through the column in counterflow to rising vapors or steam, the volatile components being substantially removed thereby. The condensed liquid adjacent the bottom of the tower is withdrawn through the outlet pipe 7. Part of this Withdrawn oil may, if necessary, be withdrawn through the valved line 9 and heated to any desired degree by means of a pipe still such as that shown as 10 in the drawing or by any suitable heating means such as a shell still or by indirect heating. This heated oil is recycled back into the tower through line 11 to furnish heat for fractionation in the column. Any Vdesired portion of the condensate in the bottom of the tower may be withdrawn through valved line 8 for storage. l

The description hereabove is of a conventional fractionating tower for effecting fractionation of oil or other mixed hydrocarbons into two major cuts, a bottoms and an overhead. It will be obvious that other forms of towers may be used such as that wherein the oil is introduced at the top of the tower as well as that in which the bubble trays are replaced with various other kinds of contact elements. If desired, an additional cut may be withdrawn at a point intermediate the top and bottom of the tower by means of withdrawing condensate from sump 16' or other suitable collecting means for the condensate and introduced by valved line 16 to auxiliary stripper 17. In the auxiliary stripper the withdrawn cut is subj ected to the stripping action of steam. The liquid oil withdrawn from tower 2 tends to seek a lower subjected to the countercurrent action of steam introduced by line 20 at the bottom of the tower 17. Obviously, other inert vapors may be used in lieu of steam, provided the desired stripping eifect is obtained. The stripped condensate is withdrawn from the bottom of the sidestripper through line 21. The stripped vapors and stripping steam are taken overhead from the tower through line 23. If desired part or all of these vapors may be reintroduced into column 2 through valved line 22. If desired, part or all of the withdrawn vapors and stripping steam may be passed through condensing means and water separator 24. From such densed gases through stripper is well known in the art and is described in U. S. Patent 1,680,421. granted to Lewis. The tower 2 may be provided with one or more steam strippers of the type just described. Invariably these steam strippers, in order to give most satisfactory results, must be placed at points above the point of introduction (pipe line l) of the oil to the column 2.

One or more additional auxiliary columns may be provided as follows: vapors may be withdrawn withdrawal pipe 31. One arm of this branched pipe, valved line 32, leads to storage or to any suitable means for effecting further refining.

The other branch, valved line 33, leads to the tower 2 for reintroducing to the tower any desired part or all of the condensate from the side column 27, Uncondensed vapors from the tower 27 are withdrawn through line 34 and after being cooled in a condenser 35 or other suitable cooling means are introduced into receiver 37, Condensate may be withdrawn from the receiver through valved line 38 and uncondensed vapors withdrawn through branched line 39. One arm of the branched line 39, namely valved line 42, leads to `storage or any suitable means for further refining this fraction. The other arm of the branched line, line 40, leads into the tower 2 for venting vapors thereunto in any desired quantity. This line 40 may suitably to provided with a check valve 4l or other suitable pressure valve, if desired, in order that'vapors from tower 27 may be vented back into tower 2 at any desired pressure.

The idea of withdrawing a vapor side cut possesses many features to commend it. Thus while the prior art liquid side cut operates effectively when the cut is taken at a point in the main tower above the point of introduction of the stock to be fractionated, it is not feasible where it is desired to take a cut at a point below the point of introduction. This is because the condensate while stripped of light ends in the sidestripper is not rectified with respect to the heavier ends. If the stock be a dirty one the condensate from the sidestripper Vis not clean and therefore contains undesirable ingredients. It is also necessary to provide heat for effecting the stripping and while the stripping steam aside from lowering vapor pressure does possess some heat, in most practice the heat sufficient for this purpose cannot be supplied from the stripping medium alone, therefore reboiling-must frequent- 1y be resorted to.

On the other hand, the vapor draw-off does not require the addition of more heat and the condensate obtained from the 'side tower is a much cleaner cut than could be obtained by a liquid draw-off. Much expensive apparatus such as reboiling coils, pumps and steam lines are dispensed with. Moreover, while the liquid drawoiT as generally practiced provides for the reintroduction of the stripping steam and stripped vapors into the main tower with the consequent dilution of the vapors therein with steam. the vapor draw-off does not possess this disadvantage.

The vapor draw-off I have found to be exceptionally well adapted to fractionation where the desired intermediate cut is one in which the stock to be treated is rich in substances boiling just below the desired initial boiling temperature of the cut. I have also found my process to be extremely useful in the treatment of dirty stocks and in the withdrawal of cutsffrom towers in which there is excessive entrainment.

It will be obvious that the quantity of side-cut withdrawn through the vapor line 26 may be regulated by any of the several means, for example, by the valve shown in the line 26 or by the pressure maintained in the receiver 37. This pressure may be further regulated, if desired, by the vent valve 4l.

As many apparently widely different embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that I do not limit myself to the foregoing example or description as indicated in the following patent claims.

I claim:

l. In the fractional distillation of hydrocarbon oils, the method of taking off a clean intermediate cut from a relatively heavy or dirty stock which comprises passing oil vapors countercurrent to liquid oil andV within a contact apparatus, withdrawing a portion of said oil vapors from said contact apparatus at a point intermediate the extremities thereof, fractionally condensing the withdrawn oil vapors and returning the uncondensed portion thereof to the contact apparatus at a point above that at which the vapors were withdrawn from the apparatus.

2. In the fractional distillation of hydrocarbon oils, the method of taking off a clean intermediate cut from a relatively heavy or dirty stock which comprises passing oil vapors countercurrent to liquid oil and within a contact apparatus, withdrawing a portion of said oil vapors from said contact apparatus at a point intermediate the extremities thereof, fractionally condensing the withdrawn oil vapors in separate Contact apparatus and returning part of the condensate from said separate contact apparatus to the main contact apparatus and returning the uncondensed vapors from said separate contact apparatus to the main contact apparatus` 3. In the fractional distillation of hydrocarbon v oils, the method of taking off a clean intermediate cut from a relatively heavy or dirty stock which comprises passing oil vapors countercurrent to liquid oil and within a contact apparatus, withdrawing a portion of said oil vapors from said contact apparatus at a point intermediate the extremities thereof, fractionally condensing the withdrawn oil vapors in separate contact apparatus,.returning the condensate from said separate contact apparatus to the main contact apparatus, cooling the vapors from the second contact apparatus and venting said vapors into the main contact apparatus.

4. In the fractional distillation of hydrocarbon oils, the method of taking off a clean intermediate out from a relatively heavy or dirty stock whichY comprises passing oil vapors countercurrent to liquid oil and within a bubble tower, introducing the stoclr. to be fractionated in the bubble tower at a point intermediate the top and bottom of the tower, withdrawing a portion of said oil vapors from said bubble tower at a point below the point of introduction of the said stock, fractionally condensing the withdrawn oil vapors in a separate bubble tower and returning the uncondensed vapors from said separate bubble tower to the main bubble tower at a point above that at which the vapors were originally withdrawn.r

5. In apparatus for the fractionation of hydrocarbon oils, a tower equipped with a plurality of elements for effecting contact between vapors and liquid therein, means for passing vapors countercurrent to the liquids therein, means for introducing material to be fractionated into said tower at a point intermediate the upper and lower extremities thereof, means for withdrawing a portion of the vapors in said tower at a point below said means for introducing the material to be fractionated, separate means for fractionally condensing the withdrawn'vapors and means for returning the uncondensed vapors to said tower at a point above that at which the vapors were originally withdrawn from said tower.

ERNEST W. THIELE.

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