US2777801A

US2777801A - Combination crude distillation and oil refining process

Info

Publication number: US2777801A
Application number: US259654A
Authority: US
Inventors: Raymond E Bittner; Channing C Nelson
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1951-12-03
Filing date: 1951-12-03
Publication date: 1957-01-15
Anticipated expiration: 1974-01-15
Also published as: ES206563A2

Description

a 1957 R. E. BITTNER ETAL 2,777,801

COMBINATION CRUDE DISTILLATION AND OIL REFINING PROCESS Filed Dec. 3, 1951 3 Sheets-Sheet 2 FQAdT ouATok E35 FILTER 57 -1A .Qa morzcl E. [bzltaev CUE gaming Ci. IZaLsoQ Bm/eabors wbggw Clbbor'rzeg United States Patent Ofi ice 2,777,801 COMBINATION CRUDE DISTILLATION ANT) OIL REFINING PROCESS Raymond E. Bittner, Westfield, and Channing C. Nelson, Cranford, N. 3., assignors to Essa Research and Engineering Company, a corporation of Delaware Application December 3, 1951, Serial No. 259,654 12 Claims. (Cl. 196-49) The present invention is concerned with the refining of mineral oils and with the conversion of petroleum into more valuable hydrocarbon oil products. More particularly, the invention is concerned with an improved process for obtaining maximum yields 'of low boiling products of the motor fuel and heating oil boiling ranges and minimum yields of heavy products, such as fuel oils and tar with a minimum of processing steps and a substantially reduced investment and operating cost. In its more specfic aspect, the invention involves a series of integrated distillation and catalytic and/ or thermal conversion stages wherein products from all stages may be conducted to a single product fractionation stage and treated therein in such a manner that atopped crude obtained as liquid residue of a crude distillation stage is stripped of relatively high boiling constituents. This application is a continuation-in-part of Serial No. 153,372, filed April 1, 1950, for Raymond E. Bittner and Channing C. Nelson entitled, Combination Crude Distillation and Oil Refining Process, now abandoned.

In its broad concept the invention relates to the efiicient removal of relatively high boiling constituents from a topped crude oil utilizing product vapors from a fluid catalytic cracking operation.

It is well known in the art to produce topped or reduced crudes by subjecting the crude to various distillation operations. This topped crude comprising gas oil constituents boiling in the range from about 650 F. to 1100 F., and higher boiling constituents is then handled in a manner to secure a maximum segregation of these gas oil constituents. Normally, this is secured by the utilization of a vacuum distillation operation. The gas oil fraction segregated in the vacuum distillation operation is passed to a catalytic cracking process.

The fluid catalytic cracking plant is composed of three sections: cracking, regeneration, and fractionation. The cracking reaction takesplace continuously in one reactor, the spent catalyst being removed continuously for regeneration in a separate vessel, from which it is returned to the cracking vessel Continuity of flow of catalyst as well as or" oil isthus accomplished, and the characteristic features offixed-hed designs involving the intermittent shifting of reactors through cracking, purging, and regeneration cycles are eliminated.

Regenerated catalyst is withdrawn from the regenerator and flows by gravity down a standpipe, wherein a willciently high pressure head is built up on the catalyst to allow its injection into the fresh liquid oil stream. The resulting mixture of oil and catalyst flows into the reaction vessel, in which gas velocity is intentionally low, so that a high concentration of 'catalystwill result. The cracking that takes'place results in carbon deposition on the catalyst, requiring regeneration of thecatalyst. The cracked product oil vapors are Withdrawn from the top of the reactor after passing through cyclone separators to free them of any entrained catalyst particles, While the spent catalyst is withdrawn from the bottom of the reactor and is injected into a stream of undiluted air which carries the catalyst into the regeneration'vessel. The products 'of combustion resulting from'the regeneration of the catalyst leave the topof this vessela-ndpass through a series of cyclones where the bulk of the entrained catadesirably high output of heavy fuel Patented Jan. 15, 1957 lyst is recovered. The regenerated catalyst is Withdrawn from the bottom of the vessel to complete its cycle.

accordance with the present invention, an improved operation is secured wherein the vacuum distillation operation is eliminated. In conventionalcrude oil distillation and conversion processes the recovery of maximum yields of motor fuel and heating oil products has been usually accomplished by subjecting light and heavy naphthe fractions from the crude still to further fractionation and, if desired, to suitable thermal or catalytic refining treatments, such as reformation, isomerization, hydro forming, alkylation, etc., thermally or catalytically cracka gas oil fraction from the crude still to recover further low boiling product by subsequent fractionation of the cracked products and subjecting the reduced crude to a further distillation at reduced pressures to produce tar and additional low boiling products, principally gas oil to be processed with the gas oil fraction from the crude still as mentioned above. These processes require a plurality of product fractionators yielding several streams of products of desirable boiling ranges. For economic heal: recovery, large numbers of heat exchange apparatus are required both within each unit and in combination between units. Vast tank facilities must be provided to permit storage of the various products prior to blending in esired proportions. The vacuum distillation equipment used for working up the reduced crude is expensive with respect to investment, operation and maintenance. As a result of these complications, conventional type combination processes must be operated on a relatively large scale to be economical. Normally, refining capacities in excess of, say, about 20,000 bbL/day of crude are required to make operations of this type pay while smaller refineries must be designed on the basis of an often unoil and other products of a relatively low commercial value.

The present invention overcomes this difficulty and afiords various additional advantages :as will be apparent from the description below wherein reference will be made to the accompanying drawing.

In accordance with the present invention, the vacuum still for reduced crude distillation is eliminated and 'substantial savings in-fractionating equipment and tankage facilities are realized by supplying substantially all the vaporous products of the'various stages of a combination process as Well as the reduced crude from the crude distillation to asingle product fractionation stage and using these vapors to strip the reduced crude in the fractionation stage ofall its distillable constituents. For thispurpose, the crude oil maybe subjected to distillation in a conventional crude distillation unit to'produce an overhead stream of light virgin naphtha, a separate heavy naphtha stream, a still heavier stream ofthe kerosene and diesel oil range and reduced crude bottoms. The reduced crude bottoms may still contain the gas oil fraction intended in .part at least for feed stock to a gas oil cracking step. The kerosene fraction may be recovered as product directly from the crude still because further conversion will not substantially enhance its value as kerosene or diesel oil. All 'other'fractions are supplied to a single product fractionator substantially as follows.

Reduced crude of the'type just mentioned may :be

passeddir'ectly to an upper portion of the lower contacta ing section of a substantially conventional fractionating column. The heavy naphtha stream may be subjected to.

high temperature thermal or catalytic reformationv or other conversion conducive to an improvement of its motor fuel qualities. The total vaporized efiluent from this conversion stage is fed to the fractionating column at a point below the feed point of reduced crude, substantially at the "temperature of the conversion stage. The light naphtha entersthe fracuct fractionation stage.

improvement processes 7 and/ or kerosene fractions are .jected to the conversions described above,

tionating column at a point below the reduced'crude feed point, and can be preheated beforehand if desired. Various final product streams may be recovered from the product fractionator which may include a fuel gas overhead, a low boiling fraction of the motor fuel boiling range, a heating oil fraction, a gas oil fraction, and a heavy bottoms fraction of the fuel oil range. in addition, there may be produced a gas oil fraction which contains the virgin gas oil fraction desired for feed to further conversion equipment together and in admixture with a recycle or converted fraction in approximate optimum ratio for ultimate conversion operation. Most of these gas oil constituents may be passed to a preferably catalytic cracking stage to be converted therein into additional amounts of motor fuel, diesel oil, gas oil range cycle stock and heavy bottoms. The total efiiuent of this cracking stage is passed without substantial heat loss to the product fractionator likewise at a point below the reduced crude feed, but preferably above the feed points of the reformate and light virgin naphtha. In this manner, the reduced crude or equivalent thereof is subjected to successive countercurrent heating, vaporization and stripping action, first with vapors from the gas oil cracking process which are heavier and may be at a lower temperature than the naphtha vapors used and thereafter with the low molecular weight and, preferably, higher temperature naphtha vapors.

When operating substantially in the manner described above, extremely large volumes of process vapors are available and utilized for reduced stripping with the effect that the volume of heavy fuel finally produced may be kept at a minimum, and lower than may be accomplished in conventional operation involving atmospheric distillation. A single heavy fuel fraction is obtained in which all heavy constituents formed in the various stages are combined and which may be subjected to a single filtering treatment to recover a final low sediment fuel oil of best quality. These advantages are in addition to the obvious savings of heat exchange equipment resulting from the elimination of various intermediate heating and cooling operations and to those of intermediate tankage requirements resulting from the use of a single prod- It will be appreciated that the invention in its broadest aspect is not limited to the type and number of intermediate conversion stages referred to above which depend entirely on the character of the crude oil to be processed and the types, quality, and relative proportions of the desired products. Other conversion stages may be added or substituted for those mentioned. Other conversion stages Which may be added into the process of the invention include hydroforming and/ or other octane for the virgin naphtha. Thermal or suspensoid visbreaking, coking, etc. may be applied to the bottoms from the tower. In accordance with the basic principle of this invention, the product vapors of all these stages will be suppliedto the single product fractionation stage substantially as described above.

In certain cases, the process of the invention may be further simplified by eliminating the crude still and feeding the whole crude oil directly into the product fractionator. This may be possible if not required. When so operating, the whole crude may be fed to an upper portion of the vlower contacting section of the product fractionator. A heavy naphtha stream and gas oil cracking stock may be withdrawn from the fractionator and subparticularly to reformation and catalytic cracking. The vaporized products of these conversions may then be returned .to the product fractionator at a point below the crude feed point. Also light naphtha and overhead gases from the frac tionator may be returned to the fractionator bottom to assist in crude stripping. In all other respects the operation of the process will be substantially analogous to that indicated above.

Having set forth its general nature and objects, the invention will be best understood from the more detailed description hereinafter which refers to the accompanying drawing wherein Figures 1 and 1A show a schematical flow plan of a preferred modification of the combination process in accordance with the invention; and

Figure 2 illustrates semi-diagrammatically and in greater detail a catalytic cracking system of particular utility for the combination process of the invention.

Referring now in detail to Figures 1 and 1A of the drawing, the system illustrated therein essentially comprises a crude still 10, a naphtha reformer schematically shown by element 30, a product fractionator 40, a cracking stage schematically illustrated by element 50, and fuel oil filtering facilities at 90. The functions and coaction of these elements with be forthwith explained using as an example the refining of a medium gravity crude of the type of Arabian Qatar crude in a refinery having a capac separate virgin naphtha V ity of about 10,000 bbl. of crude per day. it should be understood, however, that the system may be used for the refining of diflerent types of crude at a larger or smaller scale in a generally analogous manner.

In operation, the crude oil is pumped from line 1 by means of pump 3 via line 5 through heat exchangers 6 to a heating coil located in furnace 7 wherein it is heated to a temperature suitable to vaporize a substantial portion of the oil. The oil so heated is passed through line 9 to a lower portion of still 10 which it may enter at a temperature of about 750-800 F. and a pressure of about 40-70 p. s. i. g. Still 10 may be provided with a plurality of horizontal bubble cap plates 12 to improve fractionation of the feed in a conventional manner. Reflux may be accomplished with the aid of partial con densers 14 arranged in the top of still 10. For the purposes of the present example, still 10 may be so operated that three distillate streams and distillation bottoms are produced as follows.

Allcrude constituents boiling removed together as a vapor stream of light virgin naphtha overhead through line 16 at a temperature of about 300-350 F. This stream may amount to about 20 to 25% of the crude charged. A liquid stream of heavy naphtha having a 500 F. is removed through line 18 from an upper portion of still 10 at a point below condensers 14. About 20 to 25% of the crude charged is recovered through line 18. A kerosene or diesel oil out boiling within the range of about 400 to 700 F. and amounting to about 17 to 23% of the crude is drawn oif through line 20. The remainder of the charge, amounting to about 30 to 50% and consisting predominantly of constituents boiling above 700-800 F. is withdrawn as reduced crude through line 22 from the bottom of still 10. The kerosene cut removed through line 20 is normally suitable for kerosene or diesel oil purposes Without further treatment and it may be passed directly to storage. The other fractions may be treated in accordance with the present invention as will be forthwith described. 7

The light virgin naphtha vapors in line. 16 may be passed'directly to a lower portion of product fractionator 40. lf desired, this vapor stream may be preheated to about 800 to 1000 F. to conform with the heat requirements of fractionator 40. This may be done by bypassing at least a portion of the vapors in line 16 through a coil 17 located in convection section 32 of reformer furnace 30 operated as will be described hereinafter.

The heavy naphtha stream may be pumpedby pump 26 through line 28 at a pressure of about 900-1100 p. s. i. g. to a thermal reforming stage. This reforming stage may be of any conventional design well known in the art. As indicated in the drawing, it may comprise a conventional tube furnace oil residence time of about 18 to 25 liquid volumes per volume of reaction space per hour (v./v./hr.) at about 1000-1100 F. and about 1000 p. s. i. g. pressure. At

below about 250 F. are

30 designed to provide foran.

straw these conditions, the octane-rating of the naphtha may search octane number without excessive ma1lygaseous hydrocarbons:

peratureand pressure through line '34 provided with pressure release device-such as valve "or vcnturr 'lv mto-a lower portion of fractionator 40 a: a: point close to-the eed point ofline 36- Under the conditions-of the-reduced fractionator pressure of about 5-45 pas. i. g., the naphtha is substantially completely vaporized when entering the lower portion of fractionator40.--

The reduced crudein line 22 maybe passed'directly" to the lower portion of 'fractionator 40-substantially-at the temperature of its withdrawal from still"1'0.- Line 22 'feeds into fraetionator dfl at a point above'the feed points of lines 16 and 345' In this manner, the vapors supplied throughlines 16 and-34 pass upwardly through fractionator 49 against-the downwardly flowing reduced crude to' strip the latter -of-vaporizable constituents. This efiect and the operation of fractionator 40 will be described'in greater detail later on;

At this point it is noted that a side stream of gas-oil range hydrocarbons amounting toabout '45 to 60% on crude and boiling between about 600 and 1000 to 1100 P. which is suitable asa catalytic cracking stock, maybe withdrawn from an intermediate section of'frac-- tionator 46 via a gas oil refiux system comprising pump 43 and

lines

42, 44 and passed through line 46 to a catalyticcracl'ing stageSG. Any conventional cracking sys-- tern adapted to convert gas oil range'hydroearbonsintolower boiling oils, particularly of the motor fuel range; maybe used. Continuous or batch operatiou-rnay beemployed in fixed bed, moving bed, fluid or-suspensoid systems. Heat required-for crackingmay be supplied-as preheat of process materials and/eras sensible heat-of exothermically' regenerated'cata'lyst or in any other conventional manner. Modified natural or-synthetic clayor geltype catalysts such as-activated'montmorillonite clays, silica-alumina, silica-magnesia composites and other conventional cracking catalysts maybeemployed-attemperatures of about 800l000 F. and pressures of-about atmospheric to 25 p. s. i. g., all in a manner known=-per se. A cracking system ofiferingparticular advantages moon nection with the present invention willbe-describedin greater detail later on with reference to Figure 2 'ofthe drawing.

The total hydrocarbon effluent of cracking stage 50 is passed substantially at the cracking temperature-bf about 800-l000 F. throughline-52 tothe-lower portion of fractionator 4t preferably at a point intermediatebe' tween the feed points of the reduced crude-on the one side and of the reformed and virgin naphthas on the other side. if cracking stage 59 isoperated'at aruelevated pressure, the pressure may be released: by valve 52a to fractionator pressure; In most cases, the-cracked material enters fractionator 4G in the vapor state to-euhancethe stripping action of the vapors supplied through

lines

16 and 34.

As indicated in Figure 1A, fractionator 4G'comprises a lower stripping section A and an upper combined'fractionation-adsorption section B. Both sections areprovitled With suitable means forimproviug the countercurrent contact between downilowing"liquidand upwardly flowing vapors. For the purpose of stripping, adiscand-doughnut baffle arrangement has been-found to be most elicient and such is shown' schcmatically for sectionA by elements 41. Section B isillustrated to con tain a number of bubble cap plates 54' to enhance the eihciency or the fractionation-absorptionprocess. Sections A and Emery operate as follows.

Stripping section A receives, aside-fromthe vapor and liquid streams supplied through

lines

16, 34, 52 and'-22;- a liquid top feed comprisingagas oil cut rcmoved from the bottom of section. B via line- 42' and suppliedto section A via line 44. This gas oil is fed to section A to 1 providei control ov that section' i'uorderto obtain: the-desiredendpoint and cleanupon the gas oil. All the-hcat required forstripping and fractionation in-fractionator 46 is preferably supplied as sensible heat of the hydrocarbon streamsentering section A to maintaina vapors rising through section A strip the downwardly flowing gas oil out; reduced crude and cracked liquid products or" substantially all their-distillable constituents and this vapor-mixture passesonat a temperature of about 700 to 750 F. intofractionation-absorption section B--to bet-reated as will be described later on.

The reduced crude firom line 22 which may contain as much as about of gas oil suitable for feedto the catalytic unit is countercurrently stripped and heatedby the cracked vapors at, say, about 875 1 and 8 p. s. i. g. and then by the virgin naphtha vapors at,- say, about 800 F. and by the reformate at abGutlOZS -F. Thepartial pressure etfect of the other streams and the heat content thereof are sufiicient to cause the gasoil constituents of the reduced crude to vaporize. The net effect of the process in sectiouA then is-(l) a bottom stream of unfluxed-fuel oil amounting to about l520% on crude and containing about -90% of flashed reduced crude, about 2 to 4% of reformer'tar, and'about 8 to 11% of heavy oil from the catalytic operation, all blended automatically so that it may be fiuxed with about 50% oflight diesel oil blending stock for-fuel oil viscosity correction; (2) vapors containing all of the distillate productsto be obtained fromfractionator 40 and leaving section A overhead at about 800 F.

A heavy material containing; all the non-distillable constituents of the crude charged and 'of the fractions converted in stages 30 and 50 collects at about- 2G-830 F. in the bott'orn'zone-of section A fromwhichit may be withdrawn vialine 47; If desired, the temperature in the bottom of section A maybe reduced ten-say, about 700 F. by recycling heavy bottoms from line 4'7"by means-0f pump =49 via cooler 53 and line 55. The bottoms quenching may be desirable to prevent cracking and coking of the heavy liquid products. Combin'ed reduced crude amountingto about '15 to-20% on crude may be recovered through line 81" to be further treated as will appear hereinafter.

At the-conditions of the present example about 1000 to 1500 mols/hr. of hydrocarbon vapors will beavailable in section A about to-200 mols/hr. of liquid. This favorable vapor-liquidratio results iu-a substantially quantitative strippingeifect being afiorded in section A. The number of disc-and-doughnutbaflles and the dimenposcs of the present example, this section may be approximately 12 indiameter and 3G in-height andis equipped with 7 sets of disc-and-doughnut type contacting devices.

Vapors passing upwardly to sectionB of the fractionator 4G-are fractionated with gas-oil reflux through line 44 and cooler 45. Gas oil is withdrawn through line 42 at about 650 -750- F; and maybe divided into 3 streams, namel-y fl') refluxthrough line' 44 as; described; (2-) a liquidfproduct amounting to about- 2.0 to- 3.0%" on-crude for heavy diesel oil blending through line 48 and-cooler 61 totankage; 3) about 45-'60% on crude of catalytic feedstock which is fed directlyte the cracking-section by'pump' 43- through-line 46. This gas oil contains'all otthe 600 -l05 0 F. beiliugrange fraction.

Passing now to section B The gas stream .contains;appreciable quantities-"of gasoline constituents: audit is; therefore; necessary" to compress;- absorb; and; refractionate thisstream to recover its r the reflux and heatremoval -in temperature of, say, about- S20--830 F. inthe lowestportion of-section A. The

gasoline constituents. This may be avoided by combining both low pressure absorption and fractionation in the upper section A of fractionator 40. For this purpose, one of the pumparounds normally used merely for heat removal and returned to a point close to its withdrawal may be used as an absorption medium by returning it to a point substantially above that from which it is withdrawn.

The operation of the upper part of section B is disclosed and claimed specifically in the copending Rich et al. application Serial No. 153,332, filed April l, 1950, and assigned to the same interests. It will be briefly described herein insofar as its contributes to the essential advantage claimed for this invention, which resides in making small refineries fully competitive with large refineries. For specific details said copending Rich et al. application is hereby referred to.

roduct vapors leaving the gas oil fractionating section and entering the heating oil withdrawal plate contain heating oil, total naphtha and gas. diately above the heating oil withdrawal line 56, these product vapors which may be at about l0-520 F. are cooled by contact with cool heating oil at about 130 F. entering the tower through line 62. Heating oil is condensed out and falls along with the cooled part entering through line 623 and both are withdrawn from the tower through line 56. The cool heating oil in line 68 is saturated with C5, C4 and Cs constituents to form a fat oil. The light fractions are stripped out by ascending naphtha and gas product vapors, thus increasing the concentration of said fractions in the naphtha condensing zone and increasing the absorption thereof in the naphtha.

Heating oil is withdrawn at about 480500 F. through line 56, most of it being cooled in cooler 58 and returned to the top section B by pump 60 and line 62 as absorber lean oil, the remainder being stripped in stripper 57 and taken through line 78 to flux and product vapors being returned through line 59.

Product vapors above the inlet of line 68 thus consist of the naphtha fractions and gas fractions normally encountered plus an abnormal quantity of C4, C5, and Co which were absorbed as previously explained in the top of section B. Such vapors and heating oil are fractionated by reflux pumped back through line 76 and the fractionated vapors may be taken from the tower at about 5 p. s. i. g. and 215 F. through line 66 and may be compressed by a one stage blower 69. Naphtha with an excess of light fractions is condensed in condenser 72, stripped of the excess light fractions in 73 and, except for the part returned as reflux through line 76, sent to final product tankage through line 7% Gas and light fractions are led back to the absorber portion of section B through line 77 where countercurrent absorption of the desired light fraction by the lean oil as previously described takes place. The number of plates between

lines

56 and 62 is preferably increased by about 10 to over that of normal fractionator designs. By using this technique it is possible to absorb essentially all of the C5+ fractions in the gas entering the top section of fractionator 40. In addition, as much as 75% of the C4 components can be absorbed. The gas leaving the top of fractionator 40 through line 64 is thus stripped of its valuable gasoline components and can be passed directly to fuel uses. A naphtha or gasoline cut may be recovered via line 70. Such gasoline can be withdrawn at temperatures of about 120-l50 F. in spite of the low pressure employed. If the crude is such or the distribution of products so demand, it is possible to operate section A at pressures below that in the absorber portion in the top section B-say 5 to 15 p. s. i. in order to permit reduction of crude to very low bottoms, while at the same time obtaining high C4 recovcries in section B by maintaining higher pressure.

The gasoline fraction is uncontaminated with the pumparound medium as described above and is con In the section imrnedensed in an external condenser, part of the naphtha being returned to the tower for fractionation. The number of plates to be provided in section B depends on the type of crude charged and the products desired. For the purposes of the present example, 2 plates may be used between the reduced crude inlet and gas oil withdrawal, 4 between gas oil and heating oil, 5 for. stripping of gas fractions from the heating oil, 3 for naphtha-heating oil fractionations, and 10-15 plates for the absorption of light components in the top portion of section B.

As indicated in the drawing, final products may be recovered as follows. Gasoline of 400- F. end point amounting to about 50 to 60% on crude and having an octane rating of about 75 to may be passed via line 70 to tankage. About 20 to 30% of gasoline on crude may be recirculated by pump 74 via line 76 to section B to serve as reflux. Final heating or light diesel oil may, be recovered via line 78 at a rate of about 20.0 to 30.0% on crude. About 23% on crude of a heavy diesel oil stock may be obtained via line 48.

Returning now to the combined reduced crude type bottoms withdrawn through line 31, they may, if desired, be blended with gas oil or lighter fractions supplied through line 83 to adjust their viscosity to meet specifications. The bottoms maybe cooled to about 200 to 500 F. in cooler 85 and passed through line 87 to filtering facilities 90. Conventional sand filters, rotary or porous sintered ceramic filters may be used to remove from the combined residue all suspended or slurried solid particles, such as coke, catalyst carried over from cracking stage 50, etc. The solids removed in filtering facilities 90 may be discarded via line 92 or passed to catalyst recovery means (not shown). A fuel oil grade residuum is recovered via line 94. Combination filtering in this manner of thermally cracked tar, catalytic slurry and crude residuum avoids compatibility problems arising upon conventional blending of materials of this type and permits the recovery of a fuel oil relatively low in sedi ment.

The system illustrated in Figure 1 permits of various modifications. As previously pointed out, one or more reduced crude visbreaking or coking stages may be included. Certain of the effects contemplated by such coking stages maybe accomplished by, operating the bottom portion of section A of fractionator 40 at visbreaking conditions, for example at 875 to 950 F. Similarly, part or all of the bottoms in line 47 may be subjected, for example, in unit 82 to visbreaking and/or coking to produce a heavy residuum and coke to be passed on from a stripper 84 through lines 86 and 81 to separating means 90 and lighter materials which may be returned from stripper 84 through line 88 to a middle portion of section A to be subjected therein to stripping and fractionation as described above.

Catalytic, rather than thermal, reforming may be employed in reforming stage 30 using such conventional catalysts as oxides and sulfidesof groups V, VI or V111 metals, preferably supported on a suitable carrier, temperatures of about 850-1100 F. and pressures from atmospheric to about 400 p. s. i. g. in the presence or absence of extraneous hydrogen, all in a manner known per se. Other refining treatments such as bauxite treating, clay treating, etc. may follow reforming stage 30,

provided that most of the hydrocarbon effluent of such stages is supplied to fractionator 40 as described above.

While a variety of catalytic cracking systems may be used as cracking stage 50, fluid catalytic cracking involving the continuous production of cracked efiluent and continuous catalyst circulation between cracking and regeneration stages is most suitable for the purposes of the present invention. A system of this type which may be incorporated to particular advantage into the process of the present invention will be briefly described hereinafter with reference to Figure 2 of the drawing. It should be understood, however, that no claim is made herein to. the system. of Figure 2 in itself which forms a part'of the present invention only insofar asitsup plies a catalytically cracked efiluent' suitable forthepur' poses of the present invention'and as it'is particularly which the process of the advantages. A system of the type shown in Figure-2 is disclosed and claimed as such in the-copending Packie application Serial No. 159,276, filedMay l, 1950} and assigned to the same interests; This'copending 'app1ica' tionmay be referred to for'alldetailsof operation and design which are not specifically disclosed herein.

Referring now to Figure 2 of the'drawing, the system illustrated comprises a fluidtype reactor 110 and a fluid 130 arranged approximately at type catalyst regenerator level. Catalyst transfer between the vessels is elfected through U-bend connecting lines 13'4 'and 112.- Overflow line 134 "extends up into theregenerator 13010 the desired catalyst level. Catalyst overflows from-the top of the catalyst'bed intoth'e withdrawal-well of'line-134' and flows through the-U-bend intd'reactor 116. The

upper portion of line 134 acts as a conventional stand pipe aerated with steam 'through'tapst while the U-bend section functions as a seal toprevent reverse-flowof oil vapors into the regenerator 130. To initiate the catalyst flow during the starting-up period, steam maybe injected through line 135' intothe U-bend.- The gas oil feed from line 46 may 'bepassed-substantiallyat the temperature at which it is recovered it'l through lines da and 97'intoline- 134 '-closeto its point of entrance into reactor 110. If desired, the gas oil may be preheated to 600 650 F. in'exchanger 95 in heat exchange with regenerator flue-gases and passed on to line 97." Spent catalyst flows from reactor 116 through a stripper 126 and line'112-to the regenerator 130 via a dense phase riser 113 which terminates at a point closely below the dense phase 'level'in regenerator 130. Densities of the order of -25 lbs. per cu. ft. may be used in riser 113 as compared to conventional regenerator riserswhich operate at densities of about Vz-Z lbs. per cu. ft. The density in this dense phase riser is about Me of that in the standpipe'section of pipe 112. They greater catalyst density in the. reactor 110, stripper 126. and standpipe portion 112a of line 112as compared to the lesser density in the riser portion 113 of line 112-provides the driving force 'forcatalyst circulation between the vessels. For start-up purposes a steam'injector 119 located inthe U-bend maybe-used. The density-.in:the riser. 113 is maintained at a lower level than thatin standpipe'112 by the injection of 'air from booster blower 117 through line 116 into riser 113. Therate of catalyst circulation is controlled byregulzition of the injection air rate through control valve 115. Control valve 115 may be controlled as a function of the reactor temperature to maintain the latter at any desired level. The remainder of the combustion air is'introduced into the regenerator via an auxiliary-burner 121' from blower 113. Auxiliary burner I21 maybe used during the start-up to supply heat to the'systeini No combustion normally takes place therein when the system is in operation.

The efiectiveness of the U-b'end seal'legs stems'from the fact that the air injection point in line 112 and the oil injection point in line 134*are located above the U-bend seals. t

The'pressure in"reg'enerator-130' may be controlled by a throttle valve 133 arranged in stack 'lin'e'136""of' regenerator 130. In this manner, regenerator. 130 -may be maintained at all times at substantially they-same pressure as reactor 110, for which purpose a difierential pressurecontroller may be used. to operate valve 138. If the pressure dhferential between. the two. vessels is thus maintained at a suitable level; the seal legs of pipes112 and 134 will prevent. gasesfrorn passing from one vessel into the other. As afurther safety prefrom fractionator F6203, V205, M110, C1203, SaO, T1203,

caution, a valve 150. may" be. arranged in the riser portion of pipe"134"and"a similar valv e l52 in-the riser portion ofpipe 112." The valve 150"'is closed-in the event'that the catalyst fiow'through pipe 134 ceases."

Similarly, valve 152'is closed in the 'event the catalyst now through pipe 112 ceases."

Both reactor and regenerator are preferably superficial gas velocities of about 2.5-4 ft. per second.

In order to reduce catalyst losses, regenerator 130 and reactor 111? may be'provided with two stages of cyclones 1413 "and 120, respectively. carryover to fractionator 40 may thus be considerably reduced; If desired,'a slurry'of catalyst recovered from filtering means 91 via line 92 may be returned directly to reactor 110 via line 97.

Distributing grids 154 and'156 may be employed-in the bottom of

vessels

110 and 130, respectively. However, distributing cones 122 below grid 154 and above the outlet of riser 113." Stripper 126 may be provided with dis'c-and-doughnutbafiies 127.

In other respects, operation-of the system illustrated in Figure 2 may be substantiallyconventional, suitable conditions including temperatures of about 800l000- R, preferably about 800'-900 F., pressures of about atmospheric to 100 p. s. i. g., preferably about 5-15 p. s.-i. g., catalyst hold-up equivalent to 1 to 5 'weight' parts'of'oil per hour per part of catalyst, and catalyst to oil ratios of about 3-15, preferably about 5 to 7' by weight;

The catalytic'materials used in the fluidized catalyst cracking operation, in. accordance with the present in vention, are conventibnalcracking catalysts; These catalysts are oxides of metals of groups II, 111, IV and V=ofthe periodictable. A preferred catalyst comprises sili'ea-alamina whereintheweight percent of the alumina is in therange frcm about 5 to 20%. These catalysts may also-contain a third-constituent, as for example, T1102, W03, M00, BeO, Bios', CdO; U03, B203, S1102, MgO and C6203 present'in-the concentration from 0.05% to 0.5%. The size of the catalyst particles is usually below about-200 microns. Usually at least 50% of the catalyst has a micron size in the range from about 20 80. Under these conditions with the superficial velocities as given, a fluidized bed is maintained-wherein the lowersection "of the reactor, a dense catalyst phase exists while in-the upper area of the reactor a dispersed phase exists.

The advantages which render the system illustrated in Figure 2 particularly suitable for the present invention accrue chiefly-from the described combination of the overflow principle with the provision of seal legs in the catalyst circulation pipes, preventing gas hlow' back and the dense phaseriser 113 terminating closeiy below the bed-level. These advantages are numerous and im' portant. They include smaller line diameters and simpler mechanical construction'of' the solids circulation-lines; the eliminationof slide valves for controlling catalyst flow with attendant reduction in pressure drop to about A ofconventional pressure drops and in maintenance requirements; reduction in vessel elevation about-60%; reduced air pressure resulting in investment savings since at least 90% of the air passes directly to auxiliary burner 121 at a relatively low pressure; reduced size and cost of regenerator and reactor which may be shop fabricated rather than field fabricated; etc.

The systems illustrated in the drawing may be modified by various conventional features. For example, under certain circumstances it may be desirable to use a socalled double-flange heat exchanger in place of exchanger 95. Such exchangers prevent mixing of the heat ex changing fluids upon failure at the point where the tube passes through the header flanges. Forthis. purpose, these exchangers are provided with a. vented space between The amount ofcatalyst" and- 142'may be 'provided' 11 7 separate flanges supporting the tubes, one flange serving toseal the header space, the other to seal the exchanger space. Heat exchange surface requirements for product recovery or reflux cooling in the fractionating tower may be reduced in certain cases by direct water injection into the system at suitable points.

The temperature and pressure conditions specified in the above example for the operation of fractionator 40, particularly of stripping section A are those best suited for the crude here specified. They may vary to a certain extent depending chiefly on the boiling characteristics of the crude charged, as will be readily understood by those skilled in the art. For example, for a lighter crude the temperature in the bottom of section A may be somewhat lower, and vice versa. I

The present invention is broadly concerned with the effective removal of gas oil constituents from a topped or reduced'crude containing the same reduced crude containing these gas oil constituents to the stripping action of the vaporous product produced in a fluid catalytic cracking operation. In accordance with the broad concept of the present invention the topped crude is introduced into a lower section of a fractionation zone while the vaporous product frorn'the fluid catalytic cracking operation is introduced into the fractionation zone at a point below the point of introduction of the topped crude. In accordance with a more specific adaptation of the present invention, the feed comprising constituents boiling in the range from about 650 F. to ll F. is removed from the fractionation zone at a point above the point of introduction of the topped crude. By this is meant that the feed may comprise constituents boiling anywhere in the range of from about 650 to ll00 F.

By this process a desirable clean feed stock for the catalytic cracking operation is secured by actually employing catalytically cracked vapors in the fractionation zone as a stripping medium for removing relatively high boiling gas oil constituents from a topped crude containing the same. By the present operation it is possible to remove from a topped crude, by a method other than by a vacuum distillation operation, substantially all of the hydrocarbon constituents in the reduced crude boiling up to about 1100 F.

Another distinct advantage of thepresent invention is that it is known that the recycle stock to a fluid catalytic operation should preferably boil within the boiling range of the feed stock.

Example 1 The fraction of cycle gas oil from catalytic cracking which boils above the boiling point of the fresh feed stock is composed primarily of condensed ring aromatic compounds (4 and more rings per molecule). These compounds give very high coke yields on subsequent cracking, and their removal by distillation prior to recycling will permit greater conversion of cycle gas oil to useful products for a given coke production than will cracking of the raw, undistilled cycle stock. Data on cracking a raw cycle stock and an overhead fraction cut to 950 F. show a 30% reduction in coke and a small increase in the amount converted at the same cracking conditions:

Raw Cycle 86% Over- Stock head Cut to Conversion (lOO-gas oil) 29 30 Gas-wt. percent 5.7 5. 6 O1 vol. percen 5.0 5.8 Gas0line-vol. perco 13. 2 l5. 9 Cokewt. percent i 8 3 5 7 The raw cycle stock in this case was obtained from cracking a high boiling virgin gas oil. With lower boiling by subjecting the virgin gas oil, the temperature to obtain the advantage described.

Heretofore, in order to secure this it was necessary to remove the recycled stock from the catalytic cracking operation, segregate the fraction boiling in the feed stock boiling range and combine this segregated fraction with the fresh feed as recycle. In accordance with the present operation this is secured automatically inasmuch as the products from fractionator 40 are defined by boiling range and Without regard to whether the material is virgin or cracked. In other words, the gas oil stream withdrawn through line 42, which constitutes the feed to the cracking stage, consists of all virgin fractions of the desired boiling range plus all cracked fractions of that same boiling range. Lower boiling and higher boiling cracked fractions, which are both less desirable for recycling to the cracking stage, are withdrawn as heating oil product and bottoms product respectively and are excluded from the cracking stage feed. Thus, there is obtained the desired segregation without additional equipment.

The identity of the boiling ranges of the virgin and recycle feed streams imposes rather narrow limits on the amount of recycle feed relative to the amount of virgin feed distilled from the topped or reduced crude charged to the fractionator. 'Ihe'amount of recycle, and therefore the amount of total cracking feed, required to maintain the unit in balanced operation has been found to be a function of the initial boiling temperature of the topped or reduced crude charged to the fractionator and the final conversion to which the virgin feed distilled therefrom is cracked. For a practical range of operating conditions (defined below) this relationship may be expressed approximately by the following equation:

F=[(0.037) T30.l] C--3.41T+2793 where:

expressed as volume pertopped or reduced crude F=total feed to cracking stage,

cent on material distilled from in fractionator.

T=initial vapor temperature cut point, F., of topped or reduced crude charged to fractionator (true boiling point basis).

C=Conversion of material distilled from topped or reduced crude in fractionator, defined as minus final yield of cycle gas oil boiling above 430 F. true boiling point, volume percenton material distilled from topped or reduced crude in fractionator. The final yield of cycle gas oil so used in measuring conversion should include only products withdrawn from the unit and should not include such material as constitutes the recycle stream.

same.

Example 2 A fluid catalytic cracking unit was operated under the following conditions:

Catalytic cracking unit:

Fresh Feed 12,000 B./D. Total feed 15,000 B./D. Reactor product (vapor) to cornbina- 200,000 #/hr. tion fractionator. 925 F.

The combination fractionator was operated under the following conditions:

cycle stock would be redistilled at lower 13 C mbin on .frac ionator:

Atmospheric. reduced crude '1-5,00,0;B./D.

feed (650 F. vapor temperature.+.) ;(:15; API) Gas oil vaporized from ,re-;6,000 'B./D.

.duced crude (650 F. va-

por temperature 950 F. vapor temperature) (24 API).

Stripping zone conditions-" 800 F. and 8 p. s. i. g.

From the above it is to be noted that 6,000 barrels per day of gas oil constituents were recovered from the re duced crude feed to the combination fractionator. If this operation were conducted under identical operating temperatures and pressures without the utilization of the 200,000 lbs. per hour of product vapors substantially no gas oil constituents would be recovered from the reduced crude.

Example 3 A fluid catalytic cracking unit was operated under the following conditions:

Catalytic cracking unit:

Fresh feed 5,500 B./D. Total feed 9,000 B./D. Reactor product (vapor) to fraction- 125,000 #/hr.

900 F. The combination fractionator was operated under the following conditions:

Combination fractionator;

Whole crude feed (35 API) 16,000 B./D. Crude vaporized (100-950 13,000 B./D.

F. vapor temperature). Gas oil (550-950", F. vapor 5,500 B./D.

temperature) (27 API). Stripping zone conditions 825 F. and 8 p. s. i. g.

From the above it is to be noted that 5,500 barrels per day of gas oil constituents were recovered. If this operation were conducted without utilizing the product vapors from the catalytic cracking unit, substantially no recovery of gas oil constituents would be secured.

What is claimed is:

1. Improved process for the production of high quality petroleum products boiling in the motor fuel boiling range which comprises passing a reduced crude containing gas oil constituents boiling up to about 1150 F. into a fractionation zone operated at a pressure in the range of about to p. s. i. g., removing from said fractionation zone at a point above the point of introduction of said reduced crude a gas oil fraction containing hydrocarbon constit uents boiling up to about 1150 F., subjecting said gas oil fraction to a catalytic cracking operation at temperatures in the range from about 800 F. to 1000 F. and pressures in the range from atmospheric to 50 lbs. per sq. in. gauge, removing from said catalytic cracking operation cracked products and introducing the same into said fractionation zone at a point below the point of introduction of said reduced crude.

2. In a combination crude distillation and a catalytic hydrocarbon conversion process, the improvement which comprises subjecting crude oil to distillation to produce a distillate and a reduced crude fraction comprising a substantial quantity of hydrocarbon constituents boiling in the gas oil boiling range, passing said reduced crude fraction to a product fractionation zone operated at a rela tively low pressure operated at a pressure in the range of about 5 to 15 p. s. i. g., stripping said reduced crude in a manner to remove said substantial quantity of hydrocarbon constituents boiling in the gas oil boiling range with vapors of said distillate and with hydrocarbon vapors produced in a catalytic crac g operation and comprising constitutents boiling in the motor fuel boiling range, segregating said hydrocarbon constituents boiling in the 14 a Oil bo g ran n .sa dff actionatio qnen emoving d ,cracking th sam in sa d catalytic slsin 'zon operatedat a relatively low pressu i 11 ,21 manner to-produce at least a portion of said vapors used for stripping said reduced crude insaidfractionationzone.

3. In a combination crude distillation and a catalytic hydrocarbon conversion process, the improvement which comprises subjecting crude oil to distillation to produce a distillate and a reducedcrudapassing said reduced crude to a product fractionation zone operated at a relatively low pressure, subjecting a portion of said distillate to a conversion treatment, passing vapors of said converted portion and of virgin distillate to said fractionation zone operated at a pressure in the range of about 5 to 15 p. s. i. g., stripping said reduced crude with said vapors in said fractionation zone, recovering product distillate fractions and reduced crude bottoms from said zone, withdrawing a distillate fraction of intermediate boiling range from said zone, subjecting said intermediate fraction to a catalytic low pressure cracking conversion to produce an efiiuent containing lower boiling constituents, introducing said efliuent into said zone and stripping said reduced crude in said zone with vapors of said effluent.

4. The process of claim 3 in which said zone has a lower stripping section and an upper combined fractionation and absorption section, said reduced crude is supplied to the top of said stripping section, said vapors are supplied to a lower portion of said lower section, said product distillate and gas oil fractions are removed from said upper section, and said reduced crude bottoms are recovered from the bottom of said lower section.

5. The process of claim 3 in which said reduced crude is stripped by subjecting it to a two-stage heating, vaporization and stripping action, first With vapors of said effluent and secondly with said first named vapors.

6. The process of claim 5 in which at least a portion of said efiluent vapors is heavier but of a lower temperature than said first named vapors in the course of said stripping action.

7. The process of claim 3 in which a material of the fuel oil boiling range obtained from said crude oil is subjected to a high temperature thermal treatment at conditions severe enough to cause at least a reduction of viscosity.

8. The process of claizn 7 in which vapors produced in said thermal treatment are passed to a lower portion of said fractionation zone wherein said stripping takes place.

9. A simplified process for refining crude oil comprising in combination the steps of: fractionating the crude oil at a pressure which is not below atmospheric pressure segregating the naphtha fraction boiling below about 500 F, and the reduced crude fraction boiling above about 700 F, passing said reduced crude fraction to a product fractionation zone operated at a pressure of about 5 to 15 p. s. i. g., passing hot vapors of said naphtha fraction to said product fractionation zone at a point below the introduction of said reduced crude fraction, hereby upwardly flowing naphtha vapors contact downwardly flowing liquid reduced crude resulting in vaporization of the gas oil fraction of said reduced crude, segregating said gas oil fraction as a distillate product from the fractionation zone, catalytically cracking at least a portion of said segregated gas oil fraction forming cracked products, and introducing said cracked products to the said fractionation zone below the point of introduction of said reduced crude and above the point of introduction of said naphtha, whereby vapors of said cracked products contact downwardly flowing liquid reduced crude and whereby at least a portion of the cracked products is segregated as a distillate product with said gas oil fraction and is recycled to the cracking zone.

10. The process defined by claim 9 in which about 1000 to 1500 mols/hr. of hydrocarbon vapors are provided to strip about to 200 mols/hr. of liquid.

11. The process defined by claim 9 in which the said downwardly flowing heating oil acts as a reflux agent and absorption medium for vaporous constituents.

References Cited in the meet this patent UNITED STATES PATENTS Keith Oct. 3, 1939 Ocon Aug. 25, 1942 Edrnister June 19, 1945

Claims

1. IMPROVED PROCESS FOR THE PRODUCTION OF HIGH QUALITY PETROLEUM PRODUCTS BOILING IN THE MOTOR FUEL BOILING RANGE WHICH COMPRISES PASSING A REDUCED CRUDE CONTAINING GAS OIL CONSTITUENTS BOILING UP TO ABOUT 1150*F. INTO A FRACTIONATION ZONE OPERATED AT A PRESSURE IN THE RANGE OF ABOUT 5 TO 15 P.S.I.G., REMOVING FROM SAID FRACTIONATION ZONE AT A POINT ABOVE THE POINT OF INTRODUCTION OF SAID REDUCED CRUCE A GAS OIL FRACTION CONTAINING HYDROCARBON CONSTITUENTS BOILING UP TO ABOUT 1150*F., SUBJECTING SAID GAS OIL FRACTION TO A CATALYTIC CRACKING OPERATION AT TEMPERATURE IN THE RANGE FROM ABOUT 800*F. TO 1000*F. AND PRESSURES IN THE RANGE FROM ATMOSPHERIC TO 50LBS. PER SQ. IN. GAUGE, REMOVING FROM SAID CATALYTIC CRACKING OPERATION CRACKED PRODUCTS AND INTRODUCING THE SAME INTO SAID FRACTIONATION ZONE AT A POINT BELOW THE POINT OF INTRODUCTION OF SAID REDUCED CRUDE.