US2049247A - Method for distillation of odls - Google Patents

Description

July 28, 1936. J BURKHARD 2,049,247

METHOD FOR DISTILLATION OF OILS Filed Feb. 24, 1934 z'she ets-sheet 1 ATTORNEY- July 28, 1936.

M. J. BURKHARD METHOD FOR DISTILLATION OF OILS Filed Feb. 24, 1934 2 Sheets-Sheet 2 INVENTOR v ATTORNEY Patented July 28, 1936 PATENT OFFICE METHOD FOR DISTILLATION OF OILS Myron J. Burkhard, Ridgewood, N. J., assignor to Socony-Vacuum Oil Company Incorporated, New York, N. Y., a corporation of New York Application February 24, 1934, Serial No. 712,689

1 Claim: (01. 19694) This invention has to do with the fractionation of petroleum hydrocarbons and/or similar mixtures, and is specifically directed to method and means for the stripping of light ends from the products of such operation for the improvement of the flash point.

It is customary in the operation "of fractionating oils to remove one or more products from the side of the main fractionating tower. These side cuts'-or 'side streams" are usually intended for us'eas finished product, and as such, must meet specifications governing theflash point. To meet such specifications, it is essentialthat all of the light ends be removed from the side stream.

' Present methods for the removal of these light ends make use of asecond tower, equipped with bubble capplatesoffithe usual type. The side stream'from the ,main tower'is allowed to flow down over the plates in the side tower, and steam is passed through it in countercurrent flow. The vapors and steam from the side tower are returned to the main tower. The amount of vapor to be removed is very small in proportion to the amount of oil to be treated, and the bubble tower-is essentially an instrument for the contacting of a large amount of vapor with a proportionally very muchsmaller amount of liquid. Consequently in the operation of "steam stripping, comparatively inefficient contacting of steam with oil occurs, and the result is frequently a very prodigal use of steam for the result accomplished. By the theory of partial pressures, applied to this operation,v

a small use of steam'should be expected, but inspection of quantities from actual operation indi cates an excessive steam use.

It has therefore been an object of this invention to devise a more eflicient method of contacting steam and oil for the removal of light ends from side stream fractionation products. As a part of this object, there has been the provision of proper means whereby the conceived method may be executed.

For a more perfect understanding of the method and the means whereby it is accomplished, reference is now made to the drawings attached to and made a part of this specification, wherein there are set forth a diagrammatic section of the apparatus used, and several showings of its application.

In the drawings, Fig. 1 shows a section of the apparatus, diagrammatic in form.

Fig. 2 shows how this apparatus may be applied externally to the fractionating tower.

Fig. 3 shows how the method may be applied internally to a fractionating tower.

In Fig. 1, I indicates the shell of the side stream stripping tower equipped with an oil inlet 2, an oil outlet 3, and a vapor outlet 4. The lower portion of the tower, adapted to retain a pool of the liquid under treatment to a depth indicated by the surface 5, is provided with a partition 6. This partition is perforate, the total area of such perforations being sufiicient to allow free but slow circulation between the two chambers thus formed. The particulars and arrangement of these perforations is immaterial, so long as the above function is accomplished.

In'one of these chambers, below the level 5 and adjacent the oil inlet pipe 2 is a steam jet pump I, of the usual Venturi type, fed with steam through pipe 8, controlled by valve 9. This steam jet pump is arranged to entrain oil from the pool in which it is located, and so located that a substantial portion or all of the incoming oil is so entrained. Its capacity is such that the amount of oil so pumped is greater than the amount of oil to be treated in the same length of time. The oil and steam from the jet pump'rise through the mixing tube I0, wherein an intimate and thorough mixture of the steam with the oil is accomplished. The riser preferably ends in an L II, turned to direct the flow of mixed steam and oil against the shell of the tower. Below this point of discharge there is arranged a plurality of baflles I2, designed to give a flow area whereon the oil may be spread out for the fullest liberation of steam and light end vapors. The last bafile should be so placed that the oil from it falls into the chamber adjacent the oil-outlet pipe 3. A mist separator, which may be a layer of chemical tile, a dry bubble cap plate, or a grid type of separator, is placed in the top of the tower to prevent the escape of liquid particles entrained in the vapor.

The stripping vessel is equipped with a drain valve I4, and the withdrawal of stripped product is controlled by valve I5.

In some methods of operation it is preferable to withdraw the whole of the liquid on the plate at the desired side cut point, strip it, and return the portion not desired for product to the next plate in sequence in the main tower. This may be accomplished by bringing all of the plate liquid, instead of a fraction of it, to the stripper through line 2. After stripping, the stripper outlet stream flowing through pipe 3 is properly divided by adjustments of valves I5 and I6, and the liquid flowing through valve I6 is returned to the plate in the main tower below the plate from which the liquid was withdrawn. This liquid being entirely free from light ends,

the equilibrium conditions on the plates below which it is returned are bettered, and the entire tower operation may be improved thereby. If desired, this stream may be given a controlled cooling before its return to the tower, thus enabling a closer control on the end point of the product withdrawn above its point of return.

In Fig. .2, it is shown how the methodiand apparatus may be applied to ordinary fractionating equipment. In this figure, pump |8 forces oil to be distilled through coils in heating furnace. I 9, and the heated oil is carried through transfer line 20 into fractionator 2|.. Overheadrlvaporss are taken from tower 2| through line. 22, and bottoms through line 23. Stripping steammay be introduced through line 24;l Aside. stream taken ofif through line 2, and'introduced into stripper equipped similarly'to'thatfshowneini Fig. l, and bearing like numerals on each part. In case only the portion desired for side product is' withdrawnith'roughline 2, valves. |4 and.|6 remainiclosedo and'the strippediside-product is drawn through valve-l5; Ifzitis desired-:to-strip. all of;the' plate liquid at:the point of withdrawal,- valve: I 5 will :be; adjusted to remove theamount required. for product, valve 4 will remain closed,- andrall liquid coming through line 2 and: notileaving-through valve;-|5' will pass throughvalve |6-- andcpump: |'|:to be returnecbto-the main.frac:- tionating; tower.

In .Eig. 3, I.-have.=-shown how the method may be applied on thee-interior of.a-.tower.. In-thiscase: in? the main fractionator;25, betweembubble-trays 2B:and- 21, a-.spacexis=set aside. and

equipped: with..partition-28-, through which-.va-

poazswmay-pass by means of chimney 29, equipped. with hood-.30: Liquid from plate 21 is deposited above partition -28 .by.pipe 3 I, and steam jet-pump 32, mixing tube 33, .and steamcontrolyalve. 34 exercisethe same functionsas before, .thersteamed liquid-being .dischargedonplates 35, which may. beas shown, or may be merely a spiral trough. along the-insideotthe tower wall. The steamed oil.should: be delivered to-the-side of. the. oil. pool-remote from .inlet 3|, andinthe usual.icase,. the relative-.volume of the. tower space is. sufficiently great thatthe. fiowback to the jet is slow. and.without. great. likelihood .of 'short circuiting, so the equivalent of bafile Bof Fig.1: maybe dispensed.with. Stripped oilmay. be removed through-line 36, and the. opening of valve-3'! will'control the amount withdrawn.to product, while. 38. will control the amount re-. turnedto plateZB'through lines. 39'and 40. If it'.it-:.de':sired,- ariser 4| may be attached topipe 40, so that if the opening of valve 38 is not sufficient, the collected oil may be drawn off without overflowing through the chimney. In case it is not desired to treat all of the oil normally flowing between plate 21 and plate 26, the valve 42 in line 3| may be closed partially, admitting to the stripper only so much oil as is desired, the remainder passing through valve 43 and line 44 to"the; lowerrplate.

It'is' of course realized'th'at a commercial interpretation of the apparatus pertinent to this method will not embrace all of the supplementary piping; set 'fortirim Fig. 3. This is because at the time of design, the method for use in any one case-willprobably-discard all but one alternate. F'orinstance;.ifiit'isxiecided that the particular unit wilI'operate best when stripping all of the dowrrflowi-ngzliqniil pipe 3| will be entirely without valves, and valve 38 and pipes 39 and 40 willbe installed. If it is desired to treat only a: portiom. pipe: 3| will be :supplied. with valve 42;.valves 4-3 Band pipe 44 will :be.-used, and =va-lve- 38: and 39i and 40 =n1eed: not. be installed. Where :pertinent; the control-of outflowthrough 1 line :3B.-may; be accomplishedby liquid "level control valves after the manner common. intheart;. In any case; all of the modifications which might.be=.made.in any; of the apparatus set-forth: which will still. enable itsv functioning. to .-accom.-- plish -the..method disclosed areconsideredto be.-. equivalents. and-withinthescope of.the invention except by the followingaclaimv I claim:.

The method-of. removing low boiling; constituentsfrom: a mixture of hydrocarbon oils) which consists-of the followingstepss Maintaininga pool. of. oil, introducing oil to be..stripped there-- into,- withdrawing oil from thepool adjacent-the. point: of. entry. of l the. feed, -admixingstearn with oil.- so withdrawn by introducing. steam.- to. theoil.at.the point .of withdrawal andipassing. steam. and .oil..together in .a..turbulently. flowing stream through. a passage-of substantial length, discharginggthe steam .andoilinto. avapor .space. and sep; arating steamandllight vapors. from.0il-,' flowing. the. oil in..films.to. furthenefict. vapor. separation, returning: the. oil.'to the pool, controlling. said. steam .-to admit solely thereby theentire heat requirementsofthe process,-control1ing the amount of.oilladmixed.with.steam so that it is inv excess. of the amount fed to..the process per. unit time, andwithdrawingpilfrom the .pool at a .point ad jacent thepointofi entry of oil from the vapor disengaging. step.

MYR'ON' J'. BURKHARD'.

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