US2325839A - Rectifying hydrocarbons - Google Patents

Description

ug- 3, 1943. DU Bols EAsTMAN ETAL 2,325,839

RECTIFYING HYDROCARBONS Filed Jan. 7, 1941 VDI/1.0m

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DU BOIS EASTMAN LOREN P..SCOVILLE IN VE N T ORS ff. @A

THE/R ATTRNEYS- Patented Aug. 3, 1943 v assignments, to The` Texas Company, New York, vN. Y., a corporation of Delaware' Application January 7, 1941, Serial'No. 373.396 f' f4 anims'. (C1. 19e- 7711) j,

This invention is concerned witha fractionating or rectifying process wherein hydrocarbon liquid or reflux condensate formed or collected .inY the operation is subjected to reboiling er stripping and contemplatesk certain novel improvements in which a liquid non-miscible with hydrocarbons is introduced intol the reflux condensate or unvaporized material to lower the partial pressure thereof for reboiling.

A primary object of the invention is fto mak possible the use of a heating or stripping medium available at lower pressure thanthat under. which the' vrectifying and reboiling operation is conducted. Thus, for instance, it frequently happens that in oil refining plants steam isavailable only'vat relatively Ylowpressures such aslOO- 150 lbs., while it is desired to reboil tor strip distillate stocks under pressures considerably in excessv of the steam pressure. Thus in rectifying or stabilizing gasoline or naphtha distil- -lates it is desirable to conduct the operation at pressures generally in excess of 150 lbs. and ordinarily at pressures of theorder of 20G-400 lbs.

In many'plants steam is availableonly at pressures under 150 lbs. and cannot be obtained at higherk pressures exceptv bythe installation of expensive high pressure equipment.

In accorda-nce withk our.` invention this` low pressure steam vis employed fin suchA a way that itis made available'for stripping or reboiling Fi operations conducted at pressures considerably in excess VV'of the` existing steam pressures. VIn practicing the invention'the relativelyflow pressure steam is brought into indirect heat exchange with the liquid in the reboiler and watercr other suitablenon-misoible liquid is introduced-into suchlliquid to lower the partial' pressure thereof so that the desired reboiling or stripping'may be accomplished. Y

An important object ofthe inventionfis to accomplish the stabilizing or rectification of gasoline without impairing'thel color thereof. The practice of the invention makes' possibleya reduction inrthemaximum temperature applied in the rectifying and reboiling operationl of. some 50 F.-100 F. yand this lowered temperature is of advantagein accomplishing the stabilization without impairment of color. f

In practicing-the invention the hydrocarbons to be fractionated orstabilized are Vintroduced into a rectifying zone in which reflux condensate or residual unvaporized material is Vsubjected to reboiling or stripping under superatmospheric pressure. Steam which may-.be at a pressure considerably below that obtaining in the rectifying andreboiling zones vis brought into indirect v heat exchange with the liquider reiiuxcondensateand as ay result Aof thev heath exchange the liquid isV heated and condensation of steam'oc-k curs, the resultantI condensed steamA is accumulated, preferably at a temperature not materially below the Vboiling point under the pressure employed, and the hotconden'sate is introduced into the liquid in the reboiler to lower the partial pressure thereof. Thus.-v by the simultaneous action of the indirect heat exchange with the low `pressure steamand lthe injection of the hot-,icondensate from; the steam into the liquid Yunder-V going rebo'iling .the Vdesired stripping or reboiling ofthe liquid i's-'accomplished- 1 In the following detailed description `of vthe invention it'lwill be describedjspecically aslap? plied to the stabilizing of 'gasoline distillate. Y

Figure 1 is a diagrammaticfelevationof an apparatus` adapted for the practice of the inven; Y'

tion.

Fig. 2 is `a diagrammatic elevation'rroffa modiy fied form of the invention'.l *u i 1 rReferring to Figure 1 the hydrocarbon o-il or distillate to be fractionated' orrectiiiedis introduced by ajpump IIltoia lfectifyingVv towerv II. v The tower'is equipped with bubble vtrays or other suitable lelements for'promoting vapor-,liquid contact. Theo'verhead v`Vaporsor gases pass to a condenser coil I2 whichidischarges,into ajdisf tillate receiver for'Y -gasfseparator I3; vThe tower is proyi'ded'with s'uitablegcoolingor refluxing means whichmay include meansfor returning a portion ofj the distillate from receiver I3Jto'anl upper section ofthe tower. n' l, v. A

The heating and'stripping means for the rece tifying tower II includes areboiler I4. *A steam line I5 furnishes steam'to'a'.v coil I6 disposed withf in the reboiler drum I4. 'Anfoverow baille or .Weir VIIis provided in the reboiling drumv so as to insure the maintenancel of va body of lhydro,-

carb'on liquild'incontact with thev steam heatingV `coill'wY t 'l Residuall unvaporized material fromfthebottom of tower II flowsv through a line I 8 :to a drip drum a I9 Y disposed beneath 'the 'reboiler `drum I4 andany watercont'ained inthe oil isfseparated out in the drip drum `while the separated Vvoil passes thence through a line 20 intojthereboiler I4 so`as to maintain 'a bodyrv of liquid hydrocarbon about vthesteam coil IB. Vapors' and gases evolved inthe reboiler drum I4 pass through a vapor line 2l 'te the tower I I; rThe reboiled hydrocarbon liquid flowsoverthe weir'I'I and is withdrawn through a line 22.-' l' A The heat exchange coil I6 is provided with a j discharge line 23 leading -to a steam trap 24 which permits the condensed water, condensed as a result of the heat exchange in the reboiler, to flow through a line 25 to a hot water accu*-` mulator or surge drum 2,6 wherein the water accumulates preferably at temperatures only slightly below `fthe "{condensingf point under the pressure employed in the operation. A line 21 may be provided communicating with the conmulator 25 and a draw-oil line 28.mayjbepro vided for drawing oi excess `Water from the accumulator and returning itby vway'of.-line 21 to the steam source. l Y j i Hot water from the accumulator tisiwthdrawn through a line 28 by a pump 30 and forced through a discharge line 3l toaspraypipe32 disdensed steam line 25 for by-passing the accuj drawn through a line 45while the hydrocarbon distillate flows through a line 46 into which water is injected through a line 41 for passage to a reboiler. The reboiler is in the form of a shell 48 containing a plurality of tubes 49V interconnecting a bottom header 50 and a top header 5I. The commingled hydrocarbon distillate and wa- .terelows ythrough thebottom header 50 thence through the 'tubular elements 48 tothe upper header 5I Steam is introduced into Vthe shell 48 Vthrough a steam line 52 and is discharged through a jline 53. The reboiled condensate, including volatilized Water and hydrocarbons,

. lpassesthroughalinet'nl into the lower section of :the tower Ma, Vxpreferably above the liquid level therein, wherein'the volatilized constituents separatetfrom'the liquid and the rectied distillate Y, iswithdrawn through a line 55. The water which posed within the reboiler I4. The pipe 32 may Y be formed with a plurality of perforations'and itjsjadvantageous to disposea trough toreceive .thewater from .theppe'so that the water may flowovertheedges of thetrough and .drop down nt0.--,the body .oiliquid .being reboiled. The

. tr-,oughgmay ,Well be provided with-.serratedzedges sojthat.thefwaterlwill drip-down .inaplurality of streams. The water .on coming .in .contact with thev` liquid beingheatedby -thesteam coil `l5 is .subjeotedto vaporizatiomand serves tolower the.partialpressureof the'liquid. By introducingV the .waterain .a heated condition,v not greatly below. the` condensing `pointoi steam under the pressure-.employed inthe operation, the lowering in sthe ypartial Ipressure .is accomplished without any undue cooling of .the-liquid .undergoing re 1.

boiling. .TheY volatilizved hydrocarbons and steam evolvedfin -the .reboiler fdrum Vt4 pass through the'vapor line 21| -to the .tower H.

Thesteam vapors Vwhich Venter the tower `Il from qthe. vapor lline 2 .l are condensed Vin the tower, usually in the lower trays of the tower, and the,.eondensed water Ydravvnoil with thereuX condensate ilowing -through the line-l8. .A .water separator drum 33 having .a liquid level indioator!! is disposed beneath the drip drum andreceives.liquidtherefrom throughan-inclined pipe. 'line water flows throughfthe inclined pipe'.-35.to1the separator 33 displacing the .hydrocarbon .oil which isgforced upwardly through the'inclined pipe.. and the .water collecting :in the .separator 33 is withdrawn through` a line y355. Ifdesired the watercollectingin .the drum33' may be .vthdrawn'through a line .31 communicating with{.theaccumulatin'g .drum .2Bfor .preferably with the pump intake line`29.so `that the sepay rated .water may .be pumped lback .to .therspray line .32 Q in the reboiler.

".Itisaclvantage'ous to .provide a-rlow controller .30 suitablyoonnected to-anoriice 3.9 in .thedischarge .line 3,! .of ,the pumplSGandconnected to a valve in `the steam yline A0 .for .supplying steam to the lpump .3D so asV .to provide .automatici control `for'the delivery of'aconstant amountoffwatm to the spray .pipe .32. It.. is `also advantageous to providea.temperaturecontroller 4I Vhaving Ya connection'42 .to the vapor line .21| .and a-connection Z13 to .the steam line .l5-so .as to .maintaina contioation. The .rectifying tower will ordinarily beunder .a lpressure .approxi-mating 300 lbs. .and the temperaturein .the .bottom of -the tower l.will be `about 270 F. Vto .380F. Thevoverhead1product from thetower which Acollects in the receiving drum .L3 '.will .consist .essentially -or entirely of normally gaseous hydrocarbons. Gasoline from the'. bottom .of the .tower .together .with-condensed steam .flows .to the drip drumwhereinthewater issepanated out while the gasolinepasses .to the reboiler drum J4. .Steam .available at 150 lbs.

pressureisadmitted throughiline yl 5 ytothe steam heating coil .n LS. .Hot .water-formed from the Y condensed -steam vaccumulates .in lthe `surge -drum stant .temperature .in xthe vapor Astream leaving thereboilen l Y l In. .the modification .of .the .invention illustrated infFigure Z'theoil ordistillate to .be .fractionated Y or stabilizedis introduced by Dllmpl 0a toa tower J Iorwhichis similar tothe tower I! .o i Figure l. Reflux condensate andcondensed steam accumuf late 'on a trapout tray.44. The wateris Avvith- 25 at temperaturesof about 340 .to 360 F and a constantlsupplyfof .hotwateris -directed through ,thespray l:pipe-32 into fthe .heated v gasoline.AAV .The volatilized hydrocarbons and water vapor leave the reboiler ata vtemperature .offabout 300 F. vvto .450 F.Y Whencharging'distillate to the .rectifying .tower ,at a rate of 20O barrels per. hour theratefof water injection .into the :reboiler willbe .about .1-6 `gallons per minute2v the mini.- murn .amount required varying'V-.with Y.the boiling characteristics .of the distillate being rrectied and withtheamount of refluxing in -the tower. It is convenient to provide a small -openingin-.the Weir .l1 near the bottom .thereof .sothat-in Icase theamountof water1-introduced into the `reboiler drum should tbe .mxcessyof that .which `will .be

vaporized gtherein -the -water .will now :through .thisl opening .and (the .accumulation of water will be prevented. 1

ordinarily .the .steam win beeedensed .in the' lower .trays of :the tower. -It is .-advisable,.how ever, to provide on a numberof lselectedqtrays in .the .tower :means` for `preventing the :accumu- 1rationof .waterin theuppergsections ofthe tower. An advantageous arrangement is to provide such trays with a relatively small-opening inthe weir or .condensateoveriiow baille adjacent the .bottom 1 of the trayfso as to `insure the .draining .of the'water. Y" w While we have described a particular embodiliquid product, conducting said hydrocarbon liquid product to a reboiling zone, passing steam, under a lower pressure than that at which said l hydrocarbon liquid product is maintained in the reboiling zone, in indirect heat exchange with the hydrocarbon liquid product therein to eifect heating of the hydrocarbon liquid and condensation of a portion of the steam, collecting Vre sultant water, formed in the condensation of the steam, in an accumulating zone, Withdrawing water from the accumulating zone and introducing it under increased pressure into direct contact with said liquid product to lower Vthe Y partial pressure thereof for reboiling, passing resultant volatilized hydrocarbons and vaporized Y,Water from the reboilingA Zone to the rectifying zone andsubjecting said volatilized hydrocarbons and water vapors to reflux condensation therein.

2. In the rectification of hydrocarbons wherein the hydrocarbons are subjected to rectification and a liquid product thereof Lsubjected to -reboiling under superatmospheric pressure, theYA process that comprises passing steam in indirect heat exchange with hydrocarbon liquid in the reboiling zone, under a pressure lower than that obtaining in the reboiling zone, to effect heating of the hydrocarbon liquid and condensation of at least a portion of the steam, introducing resultant water, formed in the condensation of the steam, into direct contact with :the hydrocarbon Vliquid to lower the partial pressure thereof for reboiling, passing resultant volatilized.hydrocarbons and vaporized water from the reboiling i zone to the rectifying zone, subjecting said volatilized hydrocarbons and water vapors to reflux condensation therein, collecting resultant A hydrocarbon Yliquid. and lwateiqseparating the water from the `hydrocarbon liquid, directing the separated hydrocarbonliquid to the reboiling Zone and withdrawing a nal 'hydrocarbon liquid product from the reboiling zone.v

3. In the rectiiicatiorr of hydrocarbons the process that comprises subjecting hydrocarbon A oil to rectification in a rectifying vzone under superatmospheric pressure, passing vliquid oil from the rectifying Vzone to la reboiling Zone maintained under superatmospheric pressure,

`passing steam under a pressure lower than that obtaining in the reboiling zone in indirect heat exchange with hydrocarbon oil` in said reboiling,

zone to thereby heat the hydrocarbon oil to a vaporizng temperature and condense atleast a portion of the steam, separating resultant Vhot water from uncondensed steam, directing separated-hot water into direct contact with hydrocarbon .oil in ythe reboiling zone to lower the partial pressure thereof, passing resultant hydrocarbon vapors and Vsteam from the reboiling zone to the rectifying zone and subjectingA hydrocarbon'vapors and steam therein to reflux con- Vdensationto effect condensation of vapors and 4. The method ofrectifying gasoline that corn-` prises subjecting the gasolineto rectification in a rectifying zone under superatmospheric presi' sure, passing liquid gasoline from the rectifying zone to a reboiling zone maintained under superatmospheric pressure, passing steamcunder ay pressure lower than that obtaining in the re-` boiling zone in indirect heat exchange with liquid gasoline in said reboiling zone to thereby eiTect vaporization of lighter hydrocarbons contained'in the gasoline andto condense a portion of the steam, separating resultant hot water from uncondensed steam, directing separated'- hot water into direct contact with gasoline in the reboiling zone to lower the partial pressure 'Y thereof, passing said lighter hydrocarbons and vsteamfrom the reboiling zone to the rectifying zone and subjecting hydrocarbon vapors and steam therein to reilux condensation to effect condensation of vapors and steam.

DU BOIS EASTMAN. L'OREN P. SCOVIILE.

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