US2018475A - Conversion of hydrocarbon oils - Google Patents

Description

Oct. 22, 1935. R. F. TRow CONVERSION OF HYDROCARBON OILS Filed May 4, 1935 N -i ww a. v Lawn# w BYlQ f M* ATTORNEY '.HHIIIIIIIUHHHHUI @NH2 kr Wknm R kw JQ xas ...NMBS \u @l i V of relatively cool charging stock or by rei'luxing `with a suitable oil, to recover therefrom la clean Patentes Oer. 22,- 193s UNITED STATES CONVERSION oF maocimnon' oms I melma F. mw, Port Arthur, Tex., 'manor to The Texas Company, New. York, N. Y., a corporation oi.' Delaware Application 'my 4, 193s, sei-m No. ssoo s claim. (ci` lss-49) This invention relates'to the pyrolytic conversion of hydrocarbon Oils, more particularly petroleum oils,. to oils of -lower boiling points.

My invention has for an object the provision of a process for converting hydrocarbon oils which is capable of producing a high .yield of light distillate of high anti-knock value and a low yield of heavy distillate or fueloil from a dirty stock, that is to say, ,a stock which cannot be subjected to a drastic cracking operation prof ducing a high yield of gasoline per ypass without excessive coke formation. l My invention has for a further object the provision of a method ofI stripping a plurality o! tars of dierent characters drawn from pressure reaction vessels, whereby residual Afuel oils of desired characteristics may b e obtained in an adenlarged reaction vessels or stills-from which vapors and residual oils in liquid form are separately withdrawn, and more especially to opera, tions of the sO-called low-liquid-level type, in which liquid is withdrawn irom the reaction vessel or vessels at a rate sumcient to prevent aca cumulation of liquid voil Within said vessel or vessels.

My invention contemplates delivering a chars-17 ing stock, such, for example, as a dirty gas oil.` or a reduced crude resulting from a previous topping operation, preferably ai'ter heating the same to a moderate crachng temperature, into a dephlegmating and distilling zone supplied with hotl vapors produced elsewhere in the system. In the dephlegmating zone the more volatile constituents of the charging stock are vaporized and the resultant vapors, together with other vapors from the distillation zone, -are withdrawn to a vfractionating zone where they are fractionated, lfor example, by indirect contact with a stream gas Oil fraction suitable for drastic cracking, and a light distillate comprising naphtha on gasoline. lly invention further contemplates the cracking ofthe clean gas-oil fraction in the manner l indicated, that is to say at a relatively high temperature of for example from 900 to 1050 F., the cracked products being delivered to one or a. separation ofvapors and unvaporized or residual liquid occurs. the latter preferably being withdrawn at a rate sufficient to prevent accuniulation Oi liquid oil in the reaction vessels or stills. The vapors withdrawn from thel reaction 10 vessels or stills are passed to the dephlegmating zone where they are brought into contact with i'resh charging stock as aforesaid. Unvaporized oil collecting within the dephlegmation zone,- comprising residual constituents of the charging 15 stock and constituents condensed out oi' the' vapors entering from the reactin vesselsor stills, is delivered to one or more of the reaction vesselsor stills, preferably by being commingled with the stre of hot cracked products entering the 20 same from the high temperature cracking coil.

My invention further contemplates withdrawing 'residual' or unvaporized liquid from one or more of the reaction vessels or stills and subjecting it, preferably while in transit through a 25 heating coil, to a moderate cracking temperature ci',- for exple, from 820 to 880 F. for a sumcient time to brealror reduce the viscosity of the liquid without ca deposition of coke to an undesirable extent, d .discharging the viscosity- 30 broken stream into a tar stripper or autoedistillation zone. Unvaporized liquid withdrawn from one or more oi said reaction vessels at a subsequent point with respect to the dow of vapors through the same, may be introduced into the tar 35 x stripper-without being passed through a heating coil, and preferably with the La :u oi relas tively cool oil to reduce volatilization thereof and to produce a combined fuel oil residue of desired characteristics.

In the auto-distillation zone, the loil ortar is, subjected to a reduced pressure ascompared to the pressure Obtaining in the reaction. vessels and more particularly in the viscosity-breaking furnace coils, and by means vof this reduction of 45.

pressure lower-boiling constituents of the Oil or tar are liberated in vapor form, while heavy residual constituents suitable for use as fuel oil remain unvaporiaed and are withdrawn.

' rlhe liberated vapors are' preferably f ractionat- 50 ed to recover therefrom low-boiling constituents such as heavy vnaphtha or lightlgas oil, and a heavier fraction, tor example, a heavy gas oil. The light gas oil iractionmay be combined with the clean gas 'oil .from the. fractionation? zone 55 more enlarged reaction vessels or stills in which 5 about to enterv the aforesaidv high-temperature cracking coil, ormay be used as a redux in the main fractionation zone or the dephlegmation zone, or both.

The heavy gas-oil fraction, on theother hand, may be withdrawn from the system or combined with fresh charging stock for delivery to the dephlegmating zone. With regard to the conditions under which the viscosity breaking of the liquid removed from the reaction vessel or vessels is carried out, it may be said that lin general the temperature employed will be suilicient to' produce a material reduction oi.' the viscosity of the'liquid without causing the deposition of coke to al material extent and to effect a limited amount of cracking per pass, for example, from 6% to 8% of gasoline per pass, and at the most not over 12% of gasoline per pass. As has been indicated hereinabove, a suitable temperature is from 820 to 880 F. The effect of this viscosity-breaking treatment is to make it possible ultimately to obtain larger yields of valuable light cracked distillate without subjecting the liquid thus treated tovan operation which would result in excessive coke formation. v

In order 'that my invention may bel clearly set forth and understood, I now describe with reference to the drawing accompanying and forming part of this specification a preferred manner in which my inventionmaybc practiced and embodied. In this drawing,

'I'he single figure is amore or less diagrammatic elevational view of apparatus for accomplishing the conversion of hydrocarbon oil to oils of lower boiling point in accordance with my invention.

This apparatus includes a furnace I having high-temperature heating coils 2 and an econo- .mizer or relatively low-temperature heating coil 3, and also a separately nred furnace 4 having a heating or soaking coil l. v

In the present instance, there are provided three enlarged reaction vessels or stills l, I and 8 adapted to receive products from the coils 2.

but it will be readily understood by those skilled in the art that the number of such vessels or stills maybe varied in accordance with the requirements of individual instances. The dephlegmating zone referred to hereinabove is located within a suitable vessel Il which may besimilar to the reaction vessels or stills 0, 1 and 8 but is preferably provided with internally disposed baiiles Ii, and the dephlegmation and fractionation of the l vapors removed from the vessels I8 is carried out' in a f-ractionating tower I2 of suitabledeisn and preferably provided with a plurality of internal- -1y disposed plates or trays I2. -Many suitable forms of plates and trays are known in the art and no particular type need be described here in detail. v

Further dephlegmation of vapors not condensed in the fractionating tower`I2 may be acomplished in a dephlegmator I 4 provided with a heat-exchange coil Il, while vapors leaving the dephlegmator I4 may be cooled in a condenser I6, the condensed products passing to a gas separator I1.

The apparatus, as shown, additionally comprises a tar stripper or auto-distillation vessel 20 which is divided by means of a trap-out tray 2| into a flashing or evaporating section 22, preferably provided with internally-disposed bailes 23, and a dephlegmating or fractionatins. 'Section 24 which may -be provided as shown with :,oisms suitable internallyplates or trays 2l.

.Uncondensed vapors from the fractionating section 24 of the tar stripper 20 pass to a cooling coil or condenser 28, the resultant products beins passed to a gas separator 2'I.l As shown, theapii paratus additionally comprises ooolingcolls 28,

28 and 38, fuel inlets 2i and I2 in the furnace I and 4, respectively, and various conduits, pipes or transfer -lines, valves and. pumps which will be referred to more specincallyI hereinbelow. l0 In practicing my invention, a chargingv stock, for example, a dirty gas oil, a reduced crude or a mixture thereof, is withdrawn from a source (not shown) through a conduit 35 by means of a pump Il and may jinitially be passed through l5 the heat-exchange coil Ilwher'e, by indirect contact with hot vpapors passing through the dephlegmator I4, the charging stock may be heated to a temperature of, for example, from4 400 to 450 F. It will, however, be understood that if the i0 charging stock is already in a heated condition, it need not be passed through the heat-exchange coil I5, in which event, it is desirable to supply a suitable reu'x oil to the dephlegmator I4. or to the fractionation tower I2 to replace 25 reflux which would otherwise be produced by indirect contact of the vapors entering the dei phlegmator I4 with the relatively cool charging stock passing through the heat-exchange coil-II. The heated charging stock then passes under 80 a suitablelpressure through a conduit 31 to the coil 2 within the furnace I, where it is raised to a moderate cracking temperature, for example', a temperature lof from '750 to 825 F. and preferably about 780 F. 'I'he heated charging stock 35 flows from the coil 2 through a'conduit 40 having valved branch conduits 4I and 42 leading preferably to the central andlower portions, respectively, of the dephlegmator Il. By regulation of the control valves located within the conduits 4I 40 and-42 it will be apparent that the stream of oil thus delivered to the vessel III may be suitably proportioned betweenithe conduits 4I and 42, or may be entirely delivered througheither of said conduits.v

Within the dephlegmator I0 the charging stock is. subjected 'to direct contact with hot products from the still 8 entering the lower portion of the vessel I0 through aconduit 42 and a combined 'volatilizing and dephlegmating effect occurs, 4re- 50 sulting in the vaporization ofthe more volatile constituents of the heated charging stock aswell as condensation/of the heavier constituents of the vaporsfrom the still 8. This dephlegmating and fractionating effect may be promoted by means of 55 a relatively cool reflux oil introduced to theuptower I2, the vapore are fractionated to produce a clean liquid fraction suitable for high-temperature cracking, such as a gas oil or the like. This l yfraction collects in the'lower portion of the frac-- tionating tower I2 and is withdrawn through a conduit 40. The fractionation is promoted by 70 means of reux oil supplied t9 the tower I 2through a line 48, which may serve, as shown, to return to the tower I2 constituents condensed by contact of the vapors with the heat-exchange coil I! in the dephlegmator I4. Alternatively. however, the is.

. .l reflux supplied to the tower I2 may comprise suitable oil from some other source. l

The uncondensed vapors reaching the top of the fractionating tower |2 pass to the dephlegmator I4 through a vapor pipe 41 and from the dephlegmator Il through a vapor Apipe 48 to the condenser I6. The yresultant mixture of condensate and gas passes `from thecondenser I6 through a line 5| having a valve 52 to the gas separator i1, from which gas and naphtha. or

' light cracked gasoline distillate may be withdrawn through valved conduits 53 and 54, respectively.

A portion of the gas oil collecting in the bottom of the fractionating tower |2 may be withdrawn from the conduit 46 through a branch conduit 55 having a valve 56, and may be delivered by pump 51 to acooling coil 30, from which it passes by Way of the conduit into the upper4 part of the dephlegmator I0 to serve as refluxtherein.

The remaining portion or all of the gas oil collecting in the bottom cf the fractionating tower .I2 passes through a conduit 60 having a valve 6| and a pump 62 to a conduit 6 3, through which the gas oil is delivered under suitable pressure of, for

example, from 200 to 600 pounds per square inchor higher, to the high-temperature coils 2 located in the furnace l. During itsgpassage tothe coils 2, this `oil. is brought to Aa relatively high cracking temperature of, for example, from 900 to 1050 F., as aforesaid, and the cracked products then .pass through a transfer line 64, having a valve 64' for effecting reduction of 4pressure when desired, l

through a vapor line 68 to the-next reaction ves' sel- 8 v.while the separated liquid is withdrawn from-.the bottom of the reaction vessel 1 through a conduit 69- having a valve 10.

Further separation. occurs in the reaction vessel 8, theiseparatedliquidbeing withdrawn from the bottom of 'the same'through a conduit 1| having a valve 12.. .The valves61,'l10'and 12 are prefer- -ably-sofcontrolled to maintain the liquid levels within-the respective reaction -vessels 6, 1 and 8 at a point as low asl possible :while still permitting operation of the usual float mechanism device (not' shown). Thevapors then pass from the reaction vessel 8/into the `lower part of the dephlegmator I0. Liquid collecting inthe bottom of the latter, comprising residual .unvolatilized portions ofthe charging stock combined with condensedconstituents of thevapors entering from the reaction vessel 8, .as `well* asf..resldual constituents' of any reflux. introduced throughf'the conduit' I4, is withdrawn .fromithefbottonrfof the dephlegmator I8 through 'a' conduit-13having a valve 13 and may bel delivered by means of a pump 14' `and a conduit 15 'to the vtransfer line 63 where it is commingledlwith the stream of cracked prorlucts'pass .ing to the first'reaction'ye'ssel 6.

As an alternative |mode o f procedure the liquill withdrawn from the bottom ofthe'dephlegmator ||ly maybe v'delivered directly to the reaction vessel 6 but it is ordinarily. preferable to introduce it to the transfer line .64 as described.

Accordingto the preferred form of my inven-` tion, the liquid or tar withdrawn from the reaction vessel 6 through the conduit 66 is delivered under the iniluence of -the pressure obtaining in the vessel 6 to the coily 5 located within the furnace 4, Where it is subjected to a moderate cracking temperature of, for example, from 820 to 880 I F. and preferably above 860 F. It is preferred to .maintain the oil passing Athroughthe coil 5 under an elevated pressure offor example about 200 pounds per square inch; Where the pressure withshown) may be provided in the conduit 66. Y

y The viscosity-broken stream leaving the coil 5 then passes through a conduit 16 having a pressure-reducing valve 11 into the evaporating section 22 of the tar stripper 20, Where flashing or auto-distillation takes place resulting in the vaporization of the lower-boiling.constituents of the liquid thus introduced.

The relatively refractory i liquid Withdrawn from the reaction .vessel v1-through the conduit 68 may befpassed throughajconduit 18 having a valve v-19.and combined with that withdrawn from. the vessel .6., for delivery to the coil5. f Pref!`4 r erably.' however, oil or` tar withdrawn from theI lin lthe vessel 6 is insuflicient to accomplish this, a pump (not vessel 11s combined with still more refractory tar I r.from the reaction vessel 8 .by passing it through a'conduit80 having a valve 8| and communicating with the conduit 1|, through whichA the combined tar is .delivered to the tarstripper 20.'

, In order to depress volatiliz'ation of the more refractoryygas voilfconstituents from the tardei livered tofthe tar stripper 20` from the reaction vessel 8 or from the reaction vessels 1A and/8, such tar maybe cooled in any suitable manner, as for example by meansy of relatively cool fuel-oil introduced lto the conduit 1|..through a line 82 which preferably communicates with the 'conduit` 1| between a pressure-reducing valves 83 'locatedtherein and the tar stripper 2 This feature of my invention is of considerable# value and importance irrespective. of other fea-' tures of my invention, and may be applied to the stripping of tars oi varying character for the purpose of producing therefrom a fuel oil residuof desired viscosity or pour test is obtained by inclusion therein of relatively refractory oil, While permitting the volatilization andy separation of gas oil or the like which is less refractory and more suitable. for further cracking. Where desired, the tar withdrawn from the reaction vessel 6 or from the reaction vessels 6 and 1, as the casev may be, may be delivered directly, without cracking or further heating, to the tar stripper 20.

Residual fuel oil is withdrawn from the bottom of the section 22 through'la conduit 84 having ai valve 84 and leading to the cooling coll 29 from um of `desired character, in which a final product which the .cooled yfueloil may. bel deliveredto v storage. A portion of this cooled fuel oil may be through lthe conduit 82, whereinare located a pump 8.5,and a valve-82. l

The vapors pass .fromithe' evaporating section` 22-nto the fractionating section 24 througha vapor line 86. `Within thesection 24, fractionation of the vapors occurs under the influence of 'reflux oil introduced to the-.upper portion of the f returnedto vthe-.conduit 1I for .eoolirigpuposes prise a heavy gas-oil fraction', collectinf'the trapout tray 2| from which they are withdrawn `through a conduit 88 having a valvedvbranc." `on'- of section 24 ythrough a conduit 81,' and heavier' constituents of the vapors, which ordinarily com--4 duit es leading through the cooling con zato storage. By means of a branch conduit 90 having a'valve Stand a pump 92 part or. all of thisv heavy gas-oil vfraction may be delivered to-ihe conduit 31 'for delivery to the coils! and admission kto the dephlegmator I9.

Uncondensed vapors reaching the top of the fractionating section 24 pass througha vapor pipe `94 to the condenser 26 and the resultant mixture of condensate and gas passes to the separator 21 from which gas and condensate, which may comprise a light gas-oil or a heavy naphtha, are withdrawn through valved conduits 96 and 91, respectively. A portion of the condensate withdrawnthrough the conduit 91 may be diverted through a branch'conduit 98 having al valve 99 and a pump |00, by means of which it is delivered through the conduit 8l to the fractionating section 24 of the tar stripper 2li tot serve -as reflux therein. 'I'he remaining portion of the condensate, or if vother cooling means are provided for the fractionating section 2l vof the tar stripper 20. all of the condensate, may be delivered through a conduit IiiI having a valve |02 and a pump |03- and through a branch conduit IM having a valve I 05 to the conduit 63, where it is commingled with gas-oil cycle stock withdrawn from the bottom of the fractionating tower I2 for delivery to the coils 2.

Alternatively, this condensate may be dellvered as .reflux to the fractionating tower I2, through a branch conduit I 06 having a valve IIII, or to the dephlegmator I through a suitable connection (not shown).

'I'he pressures maintained throughout the system may vary considerably but in general', as has been stated hereinabove, the pressures in the coils 2, 3 and lare maintained within a suitable range of, for example, from 200 to 600 pounds per squarey inch. While similar pressures be maintained in other portions of the system, it is ordinarily preferred to maintain somewhatlower, pressures of, for example, from 150 to 350 pounds per square inch, in the reaction vessels i, I and l, the distillation vessel Il and the fractionating tower I2. The pressures within the `tar stripper 20 are preferably much lower, for example, from atmospheric pressure or below to 50 pounds per square inch. By means of a pressure-reducing valve |09 located in the line '43, pressures of 150 pounds per squarev inch, or even less, may be carried in the dephlegmator II .and fractionating tower I2, where so desired.

'It will be obvious to those skilled in the art. therefore, that my invention is' not limited to the specific details of the illustrative example or ex'` amples set forth and described hereinabove, but may variously be practiced and embodied within the scope of the claims hereinafter made.

I claim 1. The process which comprises subjecting a hydrocarbon oil to cracking in-aseries of crack'- ing stages under superatmospheric pressure, withdrawing residual liquid from an earlier stage and subjecting it to distillation inl a zone of reduced pressure, withdrawing a second residual withdrawing residual liquid from an earlier stage and subjecting it to distillation in a zone of reduced pressure,l withdrawing a second residual liquldin amore advanced state of cracking from a later stage, cooling said second liquid and introducing it into said reduced pressure distillation zone, withdrawing a final f combined 'residual liquid from said reduced pressure' distillation zone and regulating the degree ofcooling of said second residual liquid to produce a iinal combined residual liquid of a predetermined uidii. 5 The processwhichcomprise's subjecting a hydrocarbon oil to. cracking inl a series ofcracking stages under superatmospheric pressure,

vwithdrawing residual liquid from an earlier stese, l5

subjecting it to-a moderate cracking tempera- 'y ture and flashing the-resultant products in a zone of lower pressure. withdrawing a second' stream of residual liquid in a more advanced' stateof cracking from a later stage. cooling said second stream and introducing it into said lowpressure zonc,'and separately withdrawing Ypor and a final residual liquid from' said low pressure zone.

4. In aprocess of cracking hydrocarbon 011,25 wherein said oil is progressed through a series of cracking stages, the steps which comprise withdrawing residual products of cracking from an earlier stage and flashing the same in a zie of lower pressme to liberate lower-boiling constituents in vapor form. withdrawing residual products of further cracking from a' later stage, cooling the residual products withdrawn from said later stage, directing the cooled products into said zone of lowerpressure, and separately withdrawing liberated vapors and a combined nal residuum from said zone of lower pressure.

/ 5.-'Ihe/process of converting hydrocarbon oil into oils of lower boiling points, which comprises subiectingsaidoilinadistillauonstagetodirect 40 contact with hot vapors produced in the system. thereby vaporizinglighter constituents of -said oil, fractionating vapors from, said-'distillation stagetorecvertherefromalightdistillateand a heavier. recycle stock fraction. subjecting said c5 recycle stock to a relatively high cracking temperature-while in transitthroush a heating coil. discharging the cracked products into a plurality of reaction stages arranged in series, passing vapors from the-last oi' said stages in the series 50 into said distillation stage, withdrawing residual liquid from an earlier reaction stage and nashingitinazoneoflowerpressuretoliberate lower-boiling constituents in vapor form, with drawing residual liquid in a more state of cracking from a later reaction Stage. cooling it and flashing it into said 'ame of and separately withdrawing vapors residuum from said zone of lower pressure.`

6.'I he process of converting hydrocarbouoil0 into oils of lower boiling points, which comprises subjecting said oil in a distillation stage in direct contact with hot vapors produced in the system; thereby vaporizing lighter constituents of said oil, fractionating vapors from said distillation 05' stage to recover therefrom 1a light distillate and a heavier recycle stock fraction, subjecting said recycle stock to a relatively high cracking temperature while in transit through a heating coil, discharging the cracked products into a plurality of reaction 'stages arranged in series, passing vapors from the last of said stages in the series into said distillation stage, withdrawing residual liquid from an earlier reaction stage and 'ilashing it into a zone of lower pressure to liberate lower-boiling constituents in vapor form, withdrawing residual liquid in a more advanced state of cracking from a later reaction stage, cooling it and flashing it in said zone of lower pressure, separately withdrawing vapors and liquid residuum from said zone of lowerpressure, fractionating` said vapors to recover a heavy cendensate'l therefrom, directing said condensate with liquid withdrawn from said distillation zone, into con'- tact with hot cracked products passing from said high temperature heating coil to said reactionl stages.

RICHARD F. TROW.

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