Патент USA US2404677код для вставки
July 23, 1194s," w. Vc. WILSON n marrow. Dx'snpwrml# _ VFina oat, `29; 1941.1 ____ V 52 rz; c Trauer/NG „___ Town l 'c r /30 1 ` sa ,88 0, _ 2,404,611 Patented July 23, 1946 2,404,677 UNITED STATES PATENT OFFICE 2,404,677 FRACTIONAL DISTILLATION Warren C. Wilson, Rahway, N. J., assignor to Standard Oil Development Company, a corpo ration of Delaware Application October 29, 1941, Serial No; 416,980 9 Claims. (Cl. 19d-94,) 2 1. This invention relates to the fractionation of ` and in this way provides the necessary liquid re vapor mixtures >and more particularly relates `to . controlling the temperature .of the top of a frac flux for fractionating the hydrocarbon vapors. tionating tower by controlling the temperature of the reflux liquid introduced into the top of the fractionating tower. olf and run through heat exchanger equipment and the recovered. heat is transferred to the fresh In my process the liquid sidestream is drawn In the fractionation of vapors containing dif ferent constituents such as hydrocarbon vapors `it is usual practice to control the temperature at feed. In this manner the heat is recovered from the top of the tower. With my `invention itis desirable to circulate the maximum quantity of liquid from the tower in order to increase the the top of the fractionatîng tower by regulating the quantity of reflux liquid introduced into th‘e top of the fractionating tower. The reflux liquid ~ Also, it is desirable to transfer as much heat as heat transfer coeñ‘lcient of the h'eat exchangers. possible from the liquid to the fresh feed in order may be cooled in various ways but if the rate of to secure maximum efliciency. reiiuxing is held constant and the temperature is controlled by regulating the quantity of waterpassed to the coolers there is danger of vaporiza move the correct amount of heat, however, it is tion of the water and by loss of water due to vaporizatîon corrosion of the heat exchange coil In order to re . necessary to provide a cooler or coolers in addi tion to the heat exchangerl equipment so that when the amount cf h'eat transferred `from the hot liquid to thev fresh feed is not sutlicient to Water used in these cool give the required fractionation inthetower, the ers is in many cases salt water which is more cor rosive at h'igher temperatures. . 20 additional heat may be removed by the cooler. or surface will result. According to my invention, the reflux liquid is This means then that as the temperature` of the fresh feed is increased or as the heat exchanger equipment becomes fouled the load on the cooler withdrawn from the fractionating tower at a constant rate and passed in indirect heat ex change with fresh feed and another medium to 25 If all of the liquid after passing `through the heat exchangers were to be passed to the cooler, recover heat and then the partially cooled reflux it would then be necessary to regulate the quan liquid is passed to another heat exchanger where is increased. i . l i ` ` y , cooling water is‘used. When using the reflux tity of Vwater going to the coolers. This could Y recovered from the reflux and put into the fresh _cient water is always, flowing through the> cooler either be done by hand or by anautomatic con liquid as a heat exchange medium, it is desirable to obtain maximum heat recovery before 'cooling 30 trol valve in th‘e water line. However, if this were done there would be times when very little if with water. _any heat would have to be removed from the According to my invention, the danger` of va cooler and under` that condition the valve con porization of the cooling water and resultant cor trolling the water to the cooler would be closed rosion of parts of the heat exchanger is avoided and without replenishing the supply of water the by holding substantially constant the quantity of 35 temperatureof the water in the cooler would water passing to the cooler or coolers and regu gradually rise until it reached th'e vaporization 'lating the temperature of the reflux liquid by temperature of water and it wouldv then be evap lay-passing a portion of the partly cooled reflux orated. With such a condition there would be liquid around th'e heat exchangers or coolers. 40 severe corrosion of the cooler. In order to pre According to my invention maximum heat is vent this the equipment is laid out so that suñi feed without running the danger of operating the cooler at salt water temperatures considerably to take care ofthe maximum heat load. Then if less than that maximum heat load is required in excess of those required to prevent corrosion. k45 the reflux liquid is by-passed around the cooler In order to fractionate the vapors it is `necessary which means `that very little if any temperature to vaporize the feed stock in the bottom of the rise would `occur onA the water going thrcugh the tower and then remove heat somewhere up the cooler and at no time would the temperature of tower. This heat removal can be accomplished the water reach the vaporization point and there by condensing vapors and refluxing the condensed 50 by start corrosion. Y . . liquid, but according to my invention, the heat is In the drawing: ` . l . » , removed by removing a sidestream of hot liquid, Figure 1 represents one form of apparatus which cooling this liquid outside the tower, and then may be used to carry out my invention; and reinjecting it. The reinjected cooled‘liquid con Figure 2 represents one form-of control valve »denses a part of the vapors coming up the tower 55 whichmay loe-used. ~ ‘ » ~ > 2,404,677 3 4 o through line 84 is the lightest fraction separated Referring now to the drawing, the reference from the liquid feed. character ID designates a line through which the J Y Returning now to the reflux liquid withdrawn liquid to be fractionated is passed by pump I2. from top trap-out tray 5ft, the reflux liquid is Where hydrocarbon liquids are to be fractionated, the oil feed comprises light naphtha or heavy 5 passed through line 64 by pump 85 and then through valved line 86 through the -heat eX naphtha or any other desired hydrocarbon frac~ changers I6 and 24, previously described, where tion from lwhich it is desired to separate suitable vthe reñux liquid is cooled by indirect îcontact with fractions. V«Ii'iqu'id Y mixtures ‘other lthan hydro lthe liquid feed introduced through line I0. If carbon mixtures may be fractionated according to . 10 ^desired, the refiux liquid may be in part or all my invention. v`“by-passed around the heat exchangers IB and `‘1`2llîthrough Icy-pass line 88 having a valve 9B. The cooled reflux liquid is then passed through I8 and through another coil 22 in a second heat line‘g‘SZ; and! through cooler 94 for cooling the exchanger 24 for preheating the vliq'uidifeed."P Dur ing passage through the C'CîlS l4'ar`1d'~22, the liq- 15 'reflux Yliquid to the desired temperature. The cóoler'Ss is preferably a closed cooler. The tem uid feed is indirectly contacted with reflux liq The liquid feed is passed through coil Ill‘in heat exchanger I6 and then passed -throughv :line .fperature responsive device 63 in line $5, herein uid withdrawn from a fractionating tower@ .to> be hereinafter described. If desired, onlyioneheat before described, is connected by a line 95 to a control valve 95 in line S8 which communicates exchanger may be used or the feed may be passed through other heat exchangers for additional 2O with line V92. Device 6-8 may control valve 96 by Nheating. Ái’I-‘he“preheated- >liquidy *feed is 'passed `~velectrical'rnean's, by air "pressure or,` in any suit A‘able mannerfïñ‘or example, thé temperature at through ‘linetZIìl andï‘through the -heating coilv 2B “in 'aheater 32/‘to'bring`the'liquid-‘feed‘toî the de i -sired'temperatura il Geein line "56 is transmitted-‘to a temperaturecon v‘trol instrument ‘ such . as a` Leeds- and' Northrup - i ‘Inlet line "IU'is provided with a *valve-¿'¿Sârand 25 “fMicromaxjy which in turn controls'the pressure on the diaphragm valve 96. Byï~regulating the -"outlet‘linè’25 -is`provided» with a> valve .42 for by» 1 air pressure on the diaphragmfofvalve'ßß in re f passingrthe Lheat exchangers~` ‘I t `and` 24Min which v"eveht'the ~liquid'feed` is passed through k„by-pass ' sponse‘to temperature'changes,ï'the valve iseither "“jlinerëiic having a valve ‘42. ’ The ‘heated ‘liquid *raised-or lowered and this in `turn :regulates 'the "feed-fromithe"heatingcoil‘Zß'is introducedinto» 30 ' flow: through linè S3. ' Other controfm'eans‘may -`"the'ilowerfportion oi" aA fractionating “tower M be fused. VV‘These control ‘valves andL associated "*through*line'V ï'provid’ed‘with46. trap-out ""The‘ fractionating'ßtower trays'äßj'EZ ‘and"54. ‘44 The 'îvheatedivapor's‘from the liquid feed “pass” upward ' parts'are` well known equipment available on the v7market and- furtherV detailed description ofthe equipment is not believed necessary. ' ".ti'onated` ‘to‘L separate llighterA 'constituents from ""heavier"constituents, " The Vfractionatingv tower `:mayhe’ofïiany’suitable construction'such as a V '» Asshown in the drawing,"the temperature re sponsive device 63‘is a bulb or the like >containing vM13/“through” the‘fractionating‘ tower ` ‘and’ 'are Afrac~ y 35 aïliduid or liquids having desired vapor pressures ` at'~"the"cperating temperatures. `An> increase in temperature‘in line Alili _results in ari‘increase in 'j trays are-'provided 'so "that dif- 40 pressure' in‘devi’ce S8 which is transmitted through , line 95 to the pressure responsive valve-‘SBSVThe "ferent 'fractions :may be `removed‘from :the‘frac “L tionating'towerîßd The 'fraction having the’high„ f valve~ 96Y and 'associated parts- shown- irî'Figure 2 -i"nubble'tower, l"'î'lî‘he''trap-out " -estlooiling range` is“ withdrawn from "thetrap-out ï will now v'be described. The control` valve 9G comprises a valve housing Vtray 48. ..A lighter fraction is withdrawnffrom “the-next higher" trap-‘out""tray "52 and~- a lighter' 451- saiaßvaivefmc and a vaiveïseat mar- valve’ioo M"fraction is withdrawn from thetop traplo'ut‘trav ‘ thas a '-»valveïstem'iIM "passingi'through agland “T545 "The unva'porized heavier 'constituents lcoln 'packing H36. ‘f The> upper 'end of‘stem ’I F34’ :is Íse *""le‘ctthe'bottomi‘ofthe fractionating tower ¿i4 ~~ cured to a‘m-ovable f member ror'ïdiaphragm * : I B8 ""at ‘I I2. *Positioned >between'‘idiaph'ragm I-ß8`and «packing ‘I'êliik is a spring:surrounding'stem "IIL "»is‘witlîdrawn’throu'gh’line 53 and may beA further "treated to .separate desired constituents theree ."Lfrom. "Iïhe'" fraction 'withdrawn 'from trap-out tray '52 is 'passed‘through ,line'iiZ and maybe fur-_l The diaphragm housing II 5 has a fixed-»rear wall l il 81 and «sidefwall» I 22‘forrningA a cup‘shaped :cham-ber to which the-»diaphragm‘ïl‘ßß is secured. >»Housing IIS is lrigidly secured, to the Valve hous Alîth'er’treated 4Las‘ 'desired Vto separate" desired con-“ 55«ing199 bymembersv I24andY-l26. Tube -or line'Sä f .communicates withthe housing I I6. ‘ >From the above it will be seen thatias the: tem » .peratureat ßßiincreasesithe liquid intemperature "’stituent's therefrom. " The relatively lightfraetion ""cbllectingfon ïi the top trap-outßtray '54 is" with -¿drawn ‘through'liné ‘64 and is cooled as will be responsive device Will have .its temperaturefin hereinafter'moré fully' described- to provide cool I.reflux-liquid,for'the' fra'ctionating tower TM. ' @F0` creasedrandl the pressure incline 95` williincrease. "The .'uncon'dens'ed vapors ¿forming the" lightest ." The’. increaseinepressure will move§diaphragm portion' of‘théliquid feed pass overlfi'eadv through ->line 65"which.' is'lprovided with. atemp‘erature Y ‘Y or paiîtlyfclose valve |00 and this will causel'the ¿|08 down against the action ofspring IIIIA to close liquid to be passed through lineÍISU and cooling " "responsive ’deviceJEB for controlling.’A the-tempera ture 'of ‘the’ reflux -liquid introduced into’- the frac ' vtiona'tin‘g'tower'êli'as'willbe hereinafter described ‘ r'irrgreater detail. " The overhe'ad'vapors arep'assed 5 couilaz inthe cooler’ s4 .to reduœ‘tne tempera ' ture of thereñux liquid. t . ' The cooled liquid from the coil îI32`îis`- then >passed through line ’§34 where it join’s‘the'r’eflux ` v'through' heat “exchangers 'I2 vand "I4" where' Vthey 'liquid by-’passed around the'coolerf'fSlI andjpass nfares" indirectly -contacted' Awith îcooling water to condense and cool the vanors.‘1"The condensed 70"ing"through' line- 93. 'The' reñuxîi'quid‘ìs" then and cooled vapors are passedthrough‘line "I6 to ' ~ a `> gas'"separatorl "18Minu 'which ’ thefgases'jare“ sep aratedf fromf'"liuuidl~ zthe ‘gases’ passing kf'overh‘ead ‘ <^ through linel "82 - andr` the‘liduidvv being with-drawn through bottom line `IM. ” passedA through line l|36 and introduced ‘into the top \ portion "of" the fractionatingLtowe?’flllîiabove vvthe-top trapáout 'tray' `~54, ’ Preferably, thef'rela tively“ `cooled-reflux' 'liquid 'ist' introduced' ‘into’ a 2,404,677 5 ferential pressure valve |38, hereinafter described example of fractionating hydrocarbon oils will in greater detail, to insure satisfactory operation in housing ||6 on control valve 96 will decrease and spring ||4 will force the diaphragm |08 up beV given. A hydrocarbon mixture such as a heavy naphtha having an A. P. I. gravity of about 50° and having an initial boiling point of about 200° F. and a final boiling point of 435° F. is passed through the heater 28 and heated to a wardly to open valve |00. temperature of about 625° F. while maintained of the control valve 96. If the temperature at 68 decreases the pressure . f The cooling water for the cooler 94 is intro duced through line |42A and overflows through line |44. According to my invention, the amount of water passing to the cooler 94 is not regulated under pressure of about 50 lbs. per square inch gauge. The vapors are fractionated in the frac tionating tower 44. Unvaporized residual oil withdrawn from the bottom ofthe fractionating or controlled but the cooler is kept full of water tower 44 through line 56 has a boiling range of all of the time by using an excess of the maxi about 560° F. to about '100° F. and has an mum requirement. In this way corrosion of the A. P. I. gravity of about 26°. apparatus due to vaporization of the water is 15 The hydrocarbon fraction withdrawn from the eliminated. The temperature of the reflux liquid lowest trap-out tray 48 has an A. P. I. gravity is controlled by ley-passing the cooler 94. In of about 36° and an initial boiling point of about order'to obtain the desired temperature, all or 400° F. and a final boiling point of about 620° F. a portion of the reflux liquid is by-passed around This fraction is withdrawn at a temperature of the cooler 94. about 360° F. The fraction withdrawn from the The cooling >water used in the cooler 94 is pref trap-out tray 52 has an A. P. I. gravity of about erably ñrst used for cooling overhead vapors from 44.2°, an initial boiling point of about 275° F. the fractionating tower 44, The cooling water and a final boiling point of about 390° F. The may comprise any available water such as salt lighter fraction withdrawn from the trap-out water, well water, etc. The cooling water is tray 52 is at a temperature of about 310° F. The passed through line | 46 by pump |48 and through reflux liquid withdrawn from the `topitrap-out the heat exchangers 14 and 12 where the cooling ’ tray 54 has an A. P. I. gravity of about 60°, an initial boilingpoint of about 100° F. and a final boiling point of about 320° F. The reñux liquid withdrawn through line `64 is at a temperature water indirectly contacts the vapors passing through line 66. During this heat exchange, the cooling water has its temperature raised a small amount. The cooling water is then passed through line |52 and introduced into the cooler 94 through line |42 as above described. If desired, the Ifractionating tower 44 at its lower portion may be provided with a reboiler. of about 225° F. tower are at a temperature -of about 225° F. and after being condensed by passing through the coolers and'condensers 12 and 14, the distillate collected in the separator 13 forms the lightest Diiferential pressure valve |38 will now be de scribed. Two pressure conneotions |60 and |62 are taken as indicated, one on each side of cooler 94, 'I’hese pressure connections are connected by lines |64 and |66 to a differential pressure regu lator instrument, such as is manufactured by the American Meter Company or the Foxboro Meter Company, and which is shown diagrammatically as including pressure chambers |68 and |10 con nected by a line |12, Line |12 communicates with a valve memberI |14 into which air is sup» plied by line |16. The air under pressure sup plied through valve member |14 depends on the differential pressures in chambers |68 and |10 and is passed through line |18 to control valve |38. This control instrument regulates the air pressure on` diaphragm valve |38 either raising or lowering the valve in order to maintain a con stant differential pressure across the cooler 94. l The vapors leaving the top of the fractionating v fraction of the naphtha, This light distillate has an A. P. I. gravity of 62°, an initial boiling point of about 60° F. and a final boiling point of about 290° F. In order to maintain the tempera* ture of the top of the tower at about 225° F. and further to obtain the desired amount of frac tionation, the reflux liquid is returned to the top of the tower and the splash pan |31 at a tem perature of about 150° F. The ratioof the re flux to the vapors passing overhead is about 4 to l b-y weight. . l The cooling water is introduced into the cooler 64 at a substantially constant rate to maintain 50 the cooler full of cooling water. The reflux liquid lis'passed through heat ex Ichangers i6 and 24 to recover heat from the reflux liquid.V The reflux liquid has its tempera This differential pressure regulator is preferably 55 ture reduced to about 200° F. after having passed through the heat exchangers I6 and 24. In this used in order to take care of the wide range in -way the maximum amount of heat is recovered from the reflux liquid. 'I‘he temperature of the |32 when only a very small part of the total liquid -reflux liquid is controlled by the temperature being circulated is run through the cooling coil responsive device 68 in the outlet line 66 from |32 and when the major portion of the liquid is being run through the cooler. In order to operate 60 the fractionating tower 44. If the vapors passing overhead through line 66 from the fractionating valve 96 properly there must be a fairly constant tower 44 are at too low a temperature, the re differential pressure across the cooling coil. flux liquid is too cold and the temperature re When a large portion of the stock is going sponsive device 68 moves the control valve 96 through the cooling coil a pressure drop is builtl toward open position to permit by-passing of up by the resistance to the flow of this liquid. the reñux‘liquid through lines 98 and |36 around However, when only a small portion is going the cooler 94. through the cooling coil there would be practi If the vapors passing overhead through line cally no resistance and therefore no pressure 66 are at too high a temperature, the reflux drop. Valve |38 merely holds this differential pressure constant. Other means may be used to " liquid temperature is too high in which event the temperature responsive device 68 effects accomplish this result. While the apparatus may be used generally movement of the control valve 90 in line 98 to ward closed >position and more of the reflux for the fractionation of liquid mixtures, it is es pecially adapted for the separation of hydro liquid is passed through line |30 and coil |32 in carbon mixtures into desired fractions. One 75 cooler 94, pressure drop which may occur acrosscooling coil . 8 7 trolled Vbythe ,temperature in the `upper -portion ' The side streams taken through lines 58 and 52 may be passed to separate stripping towers of said fractionating Zone, to separate lighter constituents therefrom which 3. A method of fractionating liquids compris ing mixtures of different constituents which `com prises heating a liquid feed andintroducing it are .preferablyA returned to the fractionating tower 44. If desired, instead of controlling the process with a temperature responsive device at the top ofthe tower 44, a similar arrangement may be into a lfractionating zone, fractionating the va pors to separate lower boiling constituents from higher boiling constituents, passing vapors of» low er boiling constituents overhead, withdrawing a used to regulate the temperature at any place in the tower where the stock is to be circulated through a water cooler. relatively light liquid from the upper portion- of said vfractionating zone atV a constant rate, pass e ing the withdrawn relatively light liquid through Other hydrocarbon mixtures may be fraction ated as for example hydrocarbon mixtures re a cooler, supplying a cooling medium to said cool sulting from the cracking o-f hydrocarbon oils er at a substantially constant rate in excess of the maximum cooling required, by passing at least or heavier oils may be fractionated to separate a portion of the relatively light liquid around said them into desired fractions and my invention cooler, returning ‘the combined cooled relatively may be used in fractionating lthese mixtures. light liquid at a constant rate to said fractionat Or,V other mixtures may be fractionated. ing zone as reflux liquid, and controlling the rela >While one form of apparatus has been shown for carrying out my invention and one Specific 20 tive amounts of the relatively light liquid passing through and >around said cooler bythe tempera example has been disclosed, it is to be under ture in the upper portion of said fractionating stood that these are by way of illustration only and various changes and modifications may be Zone. made without departing from the spirit of the 4. A method according to‘claim 1 whereinîthe reflux liquid withdrawn from' the upper portion invention. of said fractionation zonelis passed in indirect heat exchange with fresh liquid feed of said frac I claim: 1. In the fractionation of mixed vapors in a fractionating Zone to separate desired constitu ents, the steps of removing reflux liquid from the upper portion of said fractionating zone at a con stant rate, passing the reflux liquid through a cooler, passing a cooling medium through said cooler at a substantially constant rate in excess of the maximum cooling required and regulating tionation zone, before it ispassed through said cooler. 30 ' ` 'n 5. A method according to claim 1 whereinv the differential pressure across said cooler vis kept substantially constant independent of the amount of reflux liquid passed through said cooler. 6. A method according to claim 3 wherein the the temperature of the reflux liquid to be re 35 relatively light liquid withdrawn from the upper turned at a constant rate to saidy fractionating portion of said fractionating zone is ypassed* in tower by by-passing at least a portion of the re indirect heat exchange with the liquid feedbefore flux liquid around said cooler, the relative flow itis passed through said cooler to obtain maxi of the reflux liquid through and around said cool mum heat recovery from the relatively light er being controlled by the temperature in the 40 upper portion of said fractionating zone. ’7. A method according to claim 3 wherein the 2,'In the fractionation of mixed vapors in a relatively light liquid withdrawn from the'upper fractionating zone to separate desired constitu portion of said fractionating Zone is passed in liquid. . y _ l ents, the steps of removing reflux liquid from indirect heat exchange with the liquid feed before the upper portion of said fractionating zone at a itis passed through said cooler and wherein fur ther thecooling medium is water and the'water before being passed to said cooler is passed in indirect heat exchange with the overhead vapors constant rate, passing the reflux liquid in heat exchange relation with the liquid .feed passing to said iractionating zone to obtain maximum heat recovery from the reflux liquid, then passing from said fractionating zone to cool and. con the partly cooled reflux liquid through a water 50 dense the overhead vapors. cooler, passing water through said cooler at a 8.- A method according to claim 1 wherein hy substantially constant rate in excess of the maxi drocarbon mixtures are fractionated to separate mum cooling required and regulating the temper lower »boiling hydrocarbons from condensate oil. ature of the reflux liquid to be returned at a con 9. A method according to claim 2 wherein hy stant rate to said fractionating tower by by-pass 55 drocarbon mixtures are fractionated to separate ing at least a portion of the reflux liquid around lower boiling .hydrocarbons from condensate oil. said cooler, the relative flow of the reflux liquid through and around said Water cooler being con WARREN C. wILsoN. l i l .