US2636844A - Process for the conversion of reduced crudes in the presence of an added naphtha - Google Patents

Description

Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE PROCESS FOR THE CONVERSION OF RE- DUCED CRUDES IN THE PRESENCE OF AN ADDED NAPHTHA Application August 29, 1950, Serial No. 182,036

(Cl. 19E-49) 9- Claims.

The present invention relates to a method of treating hydrocarbons. More particularly, the invention pertains to a method of producing from relatively heavy or high boiling hydrocarbon oils of the type of topped or reduced crude or similar heavy residues increased quantities of motor fuel range fractions of improved quality as Well as higher boiling distillate fractions suitable for further cracking. In its broadest aspect, the invention provides for contacting heavy residua of the type mentioned together with a naphtha fraction in a treating zone with hot subdivided fluidized solids at temperatures conducive to the A coking of the residua and the reforming of the materials including lubricating oils, waxes, resins, vfuel oils, asphalt, etc. depending on the origin :and character of the crude. More recently, however, the demand for motor fuels has increased so greatly that it has become extremely difficult to satisfy the motor fuel market by merely processing crude distillates in the manner indicated above. This situation has prompted considerable research and development Work directed toward an efhcient conversion of crude residua into additional quantities of motor fuels. The two most common methods used for this purpose in current practice are viscosity-breaking and coking of reduced crude.

Viscosity-breaking involves a treatment of reduced crude or the like at elevated temperatures for a short period of time adequate for the forlmation of an additional quantity of gas oil and about -15% of gasoline. The gas oil forms a suitable feed stock for thermal or catalytic crack- 'ing and may be converted into gasoline in this tions of gasoline of, say, about -35% in addition to gas oil and hydrocarbon gases together with solid coke. readily than vis-breaking to the purpose of producing maximum amounts of gasoline from reduced crude in the most economic manner, particularly in view of the fact that sufficient coke is produced to supply by combustion the heat requirements of the process. Therefore, the research efforts of the industry most recently have concentrated on improvements of this type of operation. Broadly the present invention is concerned with such improvements.

One of the major difficulties complicating a successful coking operation results from the heavy deposition of coke in the coking vessels and transfer lines requiring frequent and timeconsuming cleaning periods. This problem has been solved or at least greatly alleviated prior to the present invention by admixing with the residuum to be coked substantial proportions of a subdivided inert adsorbent solid such as petroleum or other coke, pumice, kieselguhr, spent clay, sand, or the like, which serves primarily as a carrier for the coke formed so as to prevent coke deposition on equipment Walls and also as a scouring agent removing coke deposits from the walls. The high surface area provided by these solids also accelerates and intensifies the cracking reaction whereby larger yields of gasoline Within shorter holding times may be obtained Without any danger of deactivation of the solids by carbon deposits or ash constituents of the feed. The coke deposited on the solids may be burnt off in cyclic or continuous two-vessel operation to generate and supply to the coking vessel the heat required for coking.

While fixed bed and suspensoid systems have been suggested for this type of operation, the s0- called iiuid solids technique offers greatest advantages With respect to temperature control, heat economy, ease and continuity of operation and equipment dimensions. This technique in its application to the coking of reduced crude involves the injection of the feed into a relatively dense highly turbulent bed of hot subdivided solids having a particle size of about 30G-400 mesh, iluidized by a gas flowing upwardly through the bed at a linear superficial velocity of about 0.3-5 ft. per second to give the bed the appearance of a boiling liquid separated by a definite interface from an upper dilute suspension of solids-ingases and gasiform products. Volatile coking products are removed overhead and further treated after the removal of entrained solids. Coke carrying solids are continuously passed to a fluid-type combustion Zone wherein they are fluidized by a combustion-supporting gas and coke is burnt olf to heat the solids to a temperature higher than coking temperature. Hot solids This process lends itself more are continuously recirculated to the coking Zone in amounts `sufficient to supply most of the heat required therein.

While this procedure affords excellent heat control and utilization as well as better yields of desirable products as compared to other systems, it does not avoid certain disadvantages inherent in reduced crude coking as such. One of these disadvantages resides in the fact that the gas oil produced by coking has a low quality as a catalytic cracking feed stock due to its high content of condensed ring aromatics which produce excessive amounts of coke on the cracking catalyst. It would be highly desirable, therefore, if the coking operation could be run to more severe conditions in such a manner as will produce very little gas 4oil and correspondingly increased amounts vof gasoline. However, when conditions are used which are adapted drastically to reduce the gas 4oil yield, most of .the additional conversion normally `goes to gas and coke, yrather than to gasoline. Another drawback not. overcome by fluid .operation as such is the low octane number of the gasoline produced by coking in the most usual .ooking temperature range of 800-1000 F., which rarely exceeds about 75 as determined by the research method so that extensive reforming is required to render the gasoline useful as a basis for a fuel for modern high compression engines. The present invention substantially alleviates these diiiiculties.

Itis, therefore, the principal object of the present invention to provide an improved fluid-type process of coking crude residuum or similar materials which affords increased yields of motor fuel range products of better quality.

`Other and more specific objects and advantages will appear from the description of the invention given below with reference to the accompany-ing drawing, th-e sin-gle figure of which is a schematical ow plan of a system adopted to carry out a preferred embodiment of the invention.

It has-'now been found that increased yields of gasoline range hydrocarbons of satisfactory oc tane rating may be obtained directly by coking residual oils such as topped or reduced crudes on iluidized catalytically inert solids such as sand, petroleum coke, pumice or the like when the coking treatment is carried out at temperatures in excess of l000 F., preferably between 1050 and 1150 F. in the presence of substantial proportions, at least 25% and preferably about 5075 vol. per cent on total hydrocarbon feed, of

4 430 F. -and serving as .a fiuidizing medium replacing or `supplementing steam or other conventional fluidizing gases. Total hydrocarbon feed rates of about 0.5-5 w./hr./w. are suitable for these operations. While appreciable improvements, particularly with respect to gasoline yields, are obtainable when using naphthas of any origin, it has been observed that excellent results are secured when highly saturated naphthas of the type of virgin naphtha are employed.

Prior to the present invention it has been suggested to add various gas oil fractions to crude residua undergoing .coking in fixed bed, fluid or suspensoid operation, chieiiy for the purpose of fluxing the residuum and aiding in its vaporization while taking advantage of the cracking conditions prevailing in .the coking zone for a .production of additional gasoline by cracking the gas oil. As far as is known, no beneficial influence vof this gas oil addition on the yield and quality of the gasoline produced ,from the residual .oils proper has been observed heretofore. The naphtha fractions added yin accordance with this invention, on the other hand, are highly refractory and not subject to much cracking at the coking conditions, such cracking products as may be formed being less desirable than the naphtha feed. Their use in place of gas oils, therefore, appeared undesirable prior to `the discovery of their beneficial synergistic effect resulting from their use in accordance with the present invention.

This synergistic effect is illustrated by the following experiments.

EXAMPLE I ln a 1.6 diameter iiuid-type laboratory unit externally heated to coking temperatures, sand having a particle size of about -180 microns was luidized with steam or naphtha vapors at a linear superficial vapor velocity of about 2.8-3 ft./sccond. Crude residuum preheated to about *IOW-800 F. was injected into a lower portion of the uidized bed separately from the Iiuidizing vapors. The naphtha used was fa heavy virgin naphtha (boiling range 250-430 F.) obtained from East T xas and Coastal crudes. The oil residuum was a 2.4% So. Louisiana vacuum residuuni inspecting as follows:

Gravity, API 11.9 Conradson carbon, wtQper `cent 12.8 Furol viscosity at 210 F., sec .396

I-/C atomic ratio 1.56

The conditions and results of these coking exnaphtha boiling within the range of about 120- 55 periments are summarized in the table below.

Table I Run No 1 1I I In 1v v Feed Mixture:

Vol. percent Residuum 50 34 34 0 Vol. percent Naphtba 0 50 66 66 100 Temperature, F 1,100 1,121 1,130 1, 100 1, 138 Feed Rate, wt. ofoil per hr. per Wt.

of solids 1.05 l. 33 2.15 2. 22 1. 37 Steam Diluent, wt. percent Feed.-. 74 35 1 0 1 0 0 Obs. Calc.3

Product Distribution:

Coke, wt. percent 10.8 7. 4 5. 8 5. 2 4. 2 0.3

Cl-a- Gas, Wt. percent,... 19.3 24.9 27. 6 22. 3 23.0 30.5

C4/430" F. Gasolinc- Vol. percent on Feed 33. 4 55. 2 59. 7 67.6 61.6 v70.5 CFR-Res., Oct No 92.2 87.5 89.5 84.5 84.5 87.8 430/700 F., V01. percent 13.0 8. 9 5. 9 2. 7 4.4 700 Fri-Buns., Vol. pcrcent. 31.6 9.6 4. 9 6. 6 10.7

See footnotes at end of table.

Table I-Continued Run No I II III IV V Yields from '.Residuuru:2

Coke, Wt. percent 10. 8 14. 5 16. 5 14. 7 Cl-Cg Gas, Wt. percent 19. 3 17. 2 14.9 12.4 C4/430 F., Vol. percent 33. 4 40. 4 45. 6 56. 2 Research Blending No. Bbls./

o Bbls.4 2,120 2, 46o 2, 82o 3, 34o 430/700" F., Vol. percent 13.0 17.8 17.4 7.9 700 F.+Btms., Vol. percent 31. 6 19. 2 14. 4 19. 4

1 Naphtha fed equivalent to about 29 Wt. percent steam diluent.

correlations to give observed octane number in run IV.

4 Research Blending Number bbls. of gasoline per 100 bbls. of residuum fed, indicates quantitatively the effectiveness of the product for blending into the gasoline pool in order to establish a standard higher octane number.

The above data demonstrate that replacement of steam by naphtha as the fluidizing agent has marked synergistic effects in the form of increased conversion of the residuum and of increased blending values for the C4/430 F. gasoline product. The data from run No. I (no added naphtha) combined with those obtained from thermal conversions of naphtha, of the type of run No. V were calculated for the octane number level obtained in run No. IV. These calculated data are listed next to the observed data in run No. IV. A comparison of the calculated data with those observed in run No. IV shows that a much higher conversion was obtained by the simultaneous use of residuum and naphtha in accordance with the invention than could be expected on the basis of the individual conversions of the residuum and naphtha. The Yields from Residuum included in Table I for runs in which residuurn and naphtha were fed further demonstrate the improved conversion and product distribution for the operation in accordance with the invention. The conversion of residuum constituents boiling above 700 F. (700 F.-|-bottoms) is extremely high for the naphtha runs as compared with run No. I. The enhanced production of C4/430u F. gasoline when using naphtha is also shown by the Research Blending Numbers which indicate that a greater gasoline Value is obtained from the residuum as such when coked in the presence of naphtha than by treating the residuum alone, in spite of the slightly lower octane number. The above data also show that this improvement is enhanced as the naphtha proportion is increased from 50 to 66 vol. per cent and as the temperature is decreased from 11301100 F. For best results, the naphtha feed should, therefore, not be less than 50% and may be as high as 75 vol. per cent while the temperature should not substantially exceed 1130 F. The lower temperature limit is drawn by the fact that the oetane values of the gasoline drops off sharply at temperatures substantially below 1100 F. and particularly below 1050 F.

A further advantage resides in the fact that coking in the presence of naphtha reduces coke formation on total feed as likewise shown in Table I which greatly facilitates a heat balanced operation because heat produced by combustion of the coke can be entirely utilized by the process without the need of resorting to steam generation or other Waste heat recovery procedures. At the same time the naphtha is thermally reformed. Furthermore, with naphtha replacing the steam as the iiuidizing agent the expense of steam production is saved and the amount of energy required to heat and vaporize the naphtha is utilized in the processing of this fraction and is not lost.

A possible explanationof the synergistic effects afforded by the process of the invention is the availability of hydrogen vin the naptha for hydrogen transfer. Any such hydrogen transfer, however, appears to be directed toward the heavier fractions as acceptors which are thereafter further cracked because no appreciable reduction in the unsaturation of the lighter fractions has been observed.

It has been indicated above that the use of gas oils in coking crude residua as suggested in the prior art affords no advantages with respect to motor fuel yields from the residuum as such. This is borne out by the experimental work reported beloW.

EXAMPLE II The laboratory unit described in Example I was operated at the fluidization conditions set forth in Example I. However, instead of naphtha a clarified catalytic cycle gas oil (boiling range '700-970 F.) was injected into the fluidized sand bed. About 75 wt. per cent of steam on total hydrocarbon feed was used for fluidization in all runs. The coking temperature was uniformly 1100 F. The residual oil was a 16% West Texas residuum of the following inspection.

Gravity, API 11.0 Conradson carbon, wt. per cent 15.0 Furol viscosity at 210 F., sec 96.6

H/C atomic ratio 1.53

The results obtained are summarized in the table below.

Table II Feed 16% W. 50/50 Mixture Tex. Ggllc' Residuum/Cycle Residuum l Oil Calc. Run No VI VII from VI Observed and VII VIII Feed Rate of Coke, Wt.

Percent 0. 8 2.9 6.4 5. 2 (lz-Gas, Wt. Percent- 24.9 20.1 22. 5 17.4 C4/430" F., V01. Percent.. 37. 2 30 3 33. 7 31. 9

l CFR-Res. Octane No. 96.5 96 8 95.3 430 F.+Bottoms, Vol.

- Percent 35. 4 49. 7 42 6 49.1 Gravity, API -1. 9 4. 8

A comparison of the observed results of run No.v

C4/430" F. gasoline for the run carried out with residuum gas oil as compared with those, to. be. expected on the basis of the sep-arate performance of these materials. On the other hand.. when operating in accordance with the invention, both conversion and gasoline yield are substantially increased as shown in Example I.

In carrying out the present invention, in practical operation greatest advantages are secured when the naphtha feed and the residuum feed are charged separately to the bottom and top, respectively, of the fluidized bed of hot carrier solids. The naphtha feed may be supplied in liquid or vapor form to the bottom of the reactor. Upon contacting the hot solids the naphtha is vaporized and partially cracked to form a limited amount of normally gaseous hydrocarbons. The combined vapors andv gases serve simultaneously as a sole or supplementary fluidizing agent and as.r a4 synergistic reactant in the coking operation. The reduced crudefis preferably sprayed in the liquid. state on top of .the dense fluidized solids bed through a, substantial portion of the disperse phaseV above the. iiuidized bed.

The, liquid residuum falling through the disperse phase is heated by the rising gaseous effluents fromI the` bed which are in turn cooled by the falling liquid feed stock. The hot liquid feed then enters the bed at the top and behaves in a conventionall manner. and vaporized in the bed, leaves the bed in a gaseous state and is Cooled by the incoming feed. Another portion of the oil is converted to coke deposited on the surface of the inert solids of the bed. The coked solids. are transferred to a combustion zone or regenerator wherein the coke is consumed and the solid is heated and returned to the reactor at a rate to maintain the desired high bed temperatures. This type of operation permits, therefore, the coexistence of a` hot bed i and a relatively cool disperse phase above the bed which provides substantial advantages over conventional operation.

The cold residuuni feed being heated by exchange with gaseousbed eiliuents will undergo Thus, in effect the individual hydrocarbons are cracked as they reach a given temperature and then are quenched immediately to lower temperatures to avoid further cracking and quality degradation. In conventional operation with the feed entering at the bottom of the bed, cracked materials must pass through the-entire bed and hot disperse phase before quenching and this long contact time at high temperatures causes fur-` ther cracking and seriously degrades the distil-v late quality With the formation of high gas yields, particularly in the case of high temperature ook--r mg.

It frequently happens: that at the optimum conditions for coking, a particular residuum, the severity of reforming of the naphtha feed, is.v sube stantially below optimum. Thus, it has been found that the optimum naphtha feed rate for best residuum processing is not necessarily-the best from the standpoint of reforming the Some of the oil is cracked naphtha. Eer example.M when the naphtha feed rate is high enough to afford efcient residuum coking, the reforming severity may be rather low. This difnculty may be overcome in accordance with a specific modification of the invention by partially reforming the naphtha portion of the feed in a coil prior to its being contacted with the resduum undergoing coking. The reforming coil may be heated by immersing the same in the nuidized bed of hot solids either in the reactor or the regenerator portion of the system or both. Since highest temperatures of about 11001300 F. prevail in the regenerator, at least a portion of the reforming coil is preferably located therein. It may be desirable to provide several reforming coils in parallel so that the residence time of the naphtha in the coils may be varied by varying the number of Coils placed in service. In this manner, the reforming severity of the naphtha portion o f the feed may be varied over a wide range and controlled within narrow limits while still maintaining the coking reactor under optimum conditions for upgrading the residuum portion of the feed. For example, at optimum residuum coking temperatures. of 1G50ll50 F. and a totalv hydrocarbon feed rate of about 0.5-5 vv./hr./W. the naphtha should be reformed at conditions including 10501200 F. coil outlet temperature, 0-1,0G0 p. s. i. g. pressure and contact times, of 5 seconds to 2 minutes. Water or steam may be mixed withk the naphtha feed to aid in adjusting the contact time and partial pressure of the oil.

A further modification of the invention which may be adopted for the same purpose involves recycling of a portion of the naphtha fractions recovered from the coking zone, with a corresponding reduction in the feed rate of fresh naphtha. The higher this recycle rate the greater the reforming severity so that by proper selection of the. recycle rate the reforming severity may be controlled at any desired value. Naphtha recycle rates of about lli-50% of fresh residuum are normally suitable for this purpose at the coking; conditions of the invention. Instead of recycling a portion of the total naphtha it may be desirable in many cases to recycle all or a part of some particular cut from the naphtha boiling range. For example, the naphtha product from the coking zone may be fractionated into a light naphtha cut and a heavy naphtha cut, and the recycle stream taken from only one of these cuts. In this way the boiling range of the naphtha produced be likewise controlled.

Having set forth its objects and general nature, the invention will be best understood from the following more detailed description of a specific example and preferred modification of the inventionk wherein reference willA be made to the accompanying drawing.

Referring now in detail t0 the drawing, a mixed SouthLouSiana crude oil of about 38 API gravity or a similar material is introduced into the systemthrough line i by means of pump 3 and discharged via line 5 into a coil 'i disposed in furnace 9;. The oil is heated in coil i to a temperature With-cin the range, offrom about 500-l0Go F. under a sauge pressure of 5-500 p. s. i. g. The heated oil isA withdrawn from coil l through line ll and discharged into crude distillation still i3 from which a normally gaseous overhead amounting to about 0.1-1.0 wt. per cent on feed is Withdrawn via line I5, a naphtha cut boiling up vto abo,uti430F. and amounting toabout 30-35 vol.y

per cent on feed is drawn off through line l1, a

gas oil fraction boiling Within the range of about 430-915 F. and amounting to about 45-60 vol. per cent on feed is recovered through line I9, and crude residuum boiling upwards of about 915 F. having a gravity of about 10-20 API and amounting to about -25 vol. per cent on feed is drawn oif the bottom via line 2|. The hydrocarbon gases recovered through. line I5 may be used as fuel or for any other` conventional purpose. A portion of the naphtha cut in line |1 may be recovered through line 23 to be further processed or utilized outside the system in any suitable manner. The remainder of the naphtha cut is passed on through line Il' to the coking portion of the system to be treated therein in accordance with the present invention as will be presently described. The gas oil cut in line I9 is preferably subiected to catalytic cracking as will appear more clearly hereinafter.

The heavy bottoms in line 2| constitute the residuum portion of the feed for the coking process of the invention. This reduced crude is passed in the liduid state and at a temperature of about 500-800 F. to a suitable spraying nozzle 21 arranged in the upper portion of coking vessel 25. The design of vessel 25 may be that of conventional iiuid solids contacting vessels suitablefor dense phase bottom drawoff operation comprising a substantially cylindrical shell with a conical bottom containing a gas-solids feeding and distributing device 29 in the form of an inverted cone having a perforated top Vessel 9.5 contains a dense turbulent mass M25 of subdivided catalytically substantially inert solids such as sand, pumice. coke, clay. etc. having a particle size of of about 30-400 mesh and fluidized by upflowing vapors entering through device 29, to form an interface L25 separating mass M55 from an upper disperse phase D25. The design of vessel 25 and the iiuidizing conditions maintained therein are preferably such as will permit a residence time of the upowing vapors in mass M25 of about 3-60 seconds and a descending time of the licuid residuum through dispersed phase D25 of about 0.5-10 se-conds, depending on the degree of dispersion of the spray and the velocity of the upflowing gases. l'n commercial operation the distance over which the liquid residuum descends through the disperse phase may be about 5-20 ft., preferably upwards of 10 ft. Dense phase linear supercial gas velocities of about 0.3-5 ft./sec. may be maintained to establish apparent densities of about -60 lbs /cu. ft. in mass M25 and about .U01-0.1 lbs/cu. ft. in phase D25, depending on the composition and particle size of the inert solidand the iiuidizing gas velocity. The liquid residuum feed rate may be about 0.15 to 3 w./hr./vv. The temperature Within mass M is preferably maintained at about 10501150 F. by circulating hot solids as will appear more clearly hereinafter.

To accomplish the synergistic effects described above and to provide vapors for the fluidization of mass M25, virgin naphtha is passed from line to vapor-solids feed line 3| of coking vessel 25. This naphtha may be fed from line Il directly into line 3|, if desired after preheating to about 400-800 F. in preheater 33 in heat exchange with nue gases from a generator or heater 35. However, preheating in this manner is not essential. Immediately upon contact with the hot solids in line 3| which are preferably at a temperature "of about ll501300 F. the naphtha is vaporized and slightly cracked to become suitable as a fluidizing medium.V Preferably, however, 'at least a portion tof .the naphtha inline is upassed by pump v35 via line 3l' to either one or more of several reformer coils imbedded in a fluidized solids mass M maintained at a temperature of about 1150 1300 F. in heater 35 as will be presently described. Water may be added from line 38 in amounts of up to about 10 wt. per cent of the naphtha. Coils 39 are so designed and operated that the naphtha is heated to a temperature of 1050"- 1200 F. during its passage through `coils 39 and is maintained therein for about 5-120 seconds, including residence time outside heater vessel 35 whereby extensive thermal reforming is accomplished. Elevated pressures of, say, about 200- 1000 p. s. i. g. may be applied in coils 39, if desired. The naphtha leaving coils 39 through line 4| may, after pressure release in valve 42, reenter line and pass to line 3| as previously described. In any case, the naphtha feed rate to line 3| may be maintained at about 0.25-4 W./hr./w. for the purposes here involved.

The amount of coke deposited on the solids is only one-third to two-thirds as much as when feeding residuum alone at the same solids to oil rate; however this does not necessarily mean that the coke make based on residuum alone has been reduced (there may actually be even a slight increase) but that there is a reduction in coke based on total oil feed. This reduction of coke on total feed aids in obtaining a heat balanced operation while still burning coke as fast as it is made. Expressed another Way, coking of the residuum alone produces an excess of coke over that required to furnish heat for the coking; in the present process this excess is utilized to supply heat for upgrading the naphtha.

The contact solids may be coke itself in which case this material will, of course, be essentially 100% coke at all times. In case a material like sand is used the coke content may be maintained at a fairly high level, say 5-20%. This has the effect of giving good burning rates and good utilization of the air in heater-vessel 35. The solids leaving the reactor may have a coke content that is 0.5% to 10% higher than that of the solids leaving the heater-vessel. This figure depends upon the amount of coke deposited by the particular feed used and the ratio of solids circulation rate of oil feed rate. Fluidized solids carrying about 5 to 100 Wt. per cent of coke may be withdrawn downwardly from vessel 25 through a conventional standpipe 43 at a rate of about 1-10 times the total oil feed rate by weight. Small amounts of an aeration and/or stripping gas such as air, flue gas, steam, etc. may be supplied to standpipe 43 through one or more taps t in a conventional manner. rThe Withdrawn solids pass from standpipe 43 to line 45 wherein they are picked up by air to form a relatively dilute suspension which is passed through a distributing device similar to device 29 into the lower portion of heater 35 to form therein dense uidized mass M35 separated by an interface L35 from a disperse phase D35 substantially as described with reference to coking vessel 25. As a result of the combustion of coke taking place in heater 35, the solids in mass M55 may be reheated to a temperature of about 1150"-1300o F. which should be at least about higher than the temperature of mass M25. About LOGO-6,000 cu. ft. of air per barrel of total feed are normally sufiicient to burn off all the coke formed in vessel 25 and to maintain the system in heat balance at the conditions specified. Flue gases containing entrained solids nes may be passed through a gas-solids separator i9l and thence via line 5| to preheater 33 or via line 53 to any desired purpose. Separated solids may be returned to mass Mss via line y55 or, if of undesirable size, discarded via line 51. Make-up solids may be supplied via line 50.

Fluidized solids at the temperature of mass M35 are withdrawn from vessel 35 through standpipe 6| aerated and/or stripped with steam or inert gas etc. via tap or taps t. The reheated solids pass from standpipe 8| into pipe 3| wherein they are picked up by the naphtha from line and returned via device 29 to vessel 25 substantially at the rate at which they were withdrawn therefrom, so as to supply heat required in vessel 25 as sensible heat of reheated solids.

Vaporous coking products containing entr-ained solids fines in a concentration as indicated above are passed upwardly through disperse phase D25 countercurrently to descending liquid residuum feed which is preheated and pretreated thereby to give off relatively low temperature coking4 constituents. Simultaneously, the coking products are quenched to a temperature approximating or somewhat above the feed temperature of the residuum feed and most of the solids entrainment is scrubbed out so that no special gassolids separation equipment is required and excessive cracking is avoided.

The vaporous products amounting to about 90/95 wt. per cent on total feed pass through line $3 at a temperature of about 700'-1000' F. into a fraction-ating column 65. About 20-30 wt. per cent of product gases based on total feed may be taken overhead from fractionator '65 through line 57| and used for any desired purpose. VFor example, this gas may contain 25-40 wt. per cent propylene which can be converted into-high quality gasoline by polymerization by well know-n means. Fractionator bottoms boiling upwards of about 9'50'o F. and amounting to about 1-1'0 vol. per cent fon total feed are withdrawn through line 68 either to be passed through line H to tankage for fuel oil use or to be recycled via lines "I3 and 2| to the ltop, of `coking vessel "25 to be retreated as described above. A gas oil cut boiling within the range of about 43m-950 F. and amounting to about -125 vol. per cent of the total naphtha plus residuum yfeed may be withdrawn via line 11 and combined with the virgin catalytic cracking feed stock flowing through line i9 to be treated therewith as will appear hereinafter. Any desired portion of this cut may be withdrawn through line 15 to be passed to tan'kage or further fractionated into narrower Ycuts for use as kerosene, heating cils, diesel fuel, and the like.

A naph'tha cut boiling up to about 430 and amounting to vabout 50-70 vol. 'per cent on total feed is recovered through line 19. It may be passed to tankage or gasoline blend-ing via line 8|. If desired, a proportion of this naphtha amounting to about lil-15% on the 'residuum 'feed may be returned v-a lines `'83 and l'f to coking vessel to be retreated and further reformed therein as `described above.

When operating in the manner described above, f

about `lO-60 vol. per cent of .gasoline range naphtha may be produced from the reduced :crude portion of the feed as compared with only about -40 vol. per cent 'when operating in the absence of naph-tha added to the coking zone. These naphtha yields do not include 'the .additional naphtha that is obtainable by polymerization of the propylene in the gas.

Returning now to the catalytic cracking feed stock in line l'9, this'may be `cai'a'lytically cracked in any conventional manner, that is in fixed bed, moving bed, fluid solids or Asuspensoid operation. By way of example, a conventional fluid catalyst dense phase type of operation has been schematically illustrated in the drawing. The operation of a system of this type is well known to those skilled in kthe art and will only be briey described for the sake of completeness.

A cracking catalyst of fluidizable size such as a synthetic rcomposite of silica gel With alumina Aand/or magnesio., or any other conventional `cracking catalyst is Iiuidized in reactor and circulated via standpipe 81, air feed line 39 and distributing device to regenerator 0| wherein coke deposits lare burned oif in the fluidized state, flue gases being withdrawn via cyclone 93 and line 95. Hot regenerated catalyst is returned at a temperature slightly above cracking temperature through standpipe 91, oil feed line 99 and distributing device |00 to reactor 85 at a rate adequate to vaporize the feed and to supply the heat required for cracking. The cracking feed stock from line |'9 is supplied to line 90 as indicated. Any desired amount of steam may be added via line 10| to assist in uidization and to control cracking conditions.

Suitable conditions for running a cracking system-of this type are well known in the art. They include cracking temperatures of Aabout 800-950 F., pressures of about 0-50 p. s. i. g., regenerator temperatures of about 10001l00 F., supercial linear fiuidizing gas velocities of about 0.3-3 ft. per second at `catalyst particle sizes of about 50- 400 mesh, vand :oil feed rates of about 0.5-10 w./hr./w.

Cracked products are withdrawn overhead from reactor 65 via cyclone |03 and may be passed through line |05 to a fractionator |01. fNormally gaseous hydrocarbons may be withdrawn from fractionator |01 through line |00. They are suitable as feed materials for alkylation cr polymerization processes. Catalytically cracked naphtha boiling within the range of up 'to about 430 F. may -be recovered through line and passed to lgasoline blending. Heating oil may be withdrawn via line I|3 and then passed to storage or recycled to reactor 85 for further cracking at vrecycle ratios of about 10-50 volumes per volume of fresh cracking feed. Catalytically cracked heavy bottoms boiling upwards Vof about 700 F. are drawn off through line H5. They may be either passed to fuel oil storage via .line |11 -or :added to the residuum feed of coking vessel 25 vialine |19 to be coked in vessel 25 vas described ."above. The ultimate residuurn lfeed to cracking vessel 25 may contain any virgin and cracked residues in any desired proportion rbut the concentration of cracked residuum will 'usually be limited to about '25-40%, because that is about the production ratio of heavy catalytica-lly cracked resi-dues to virgin residuum that will be produced in usual refinery practice.

The system illustrated in the drawing permits rvof various modifications. If desired, small amounts `of `steam or other .additional iiuidizing gns'may be added to vessel 25 through line |2I. Catalytically cracked naphtha from line may be 'added via line l1 to .the naphtha feed of vessel 25 in any desired proportion. Fractionators 8, 65 andfor |01 maybe operated .insuch a manincr as to yield two separate fractions of different boiling range within the naphtha range and `either one of the two fractions may be used Ain "poking vessel 25. Distributing grids extending 'over the entire cross-section of vessels 2,5, 35, 85

. 13 and' 9i may be used in combination with suitable solids withdrawal wells to replace distributing cones 29, lil, Si! and IDU. It desired, steam generating coils R may be inserted in heater 3b and steam recovered via a conventional recovery system i2l. In case petroleum coke is used as the inert solid, product coke may be recovered from reactor 25 via line 29.

The crude distiilation shown is an atmospheric distillation only, giving an atmospheric residuum. Where modern distillation equipment is available the bottoms from this still may go to a second still operated under 25-30 inches of vacuum where an additional amount of virgin gas oil may be removed and sent to catalytic cracking. The bottoms from this second still constitute a vacuum residuum and may serve as the feed to the coking vessel Virgin residuum may, if desired, be drawn o line 2i through line 22 for use in fuel oils, asphalts, and the like. Other modications may appear to those skilled in the art.

The above description and exemplary operations have served to illustrate specific embodiments of the invention but are not intended to be limiting in scope.

What is claimed is:

l. in a process for cracking heavy residual oils to form gasoline and lower boiling hydrocarbons the improvement which comprises introducing a stream of said residual oil into a turbulent iiuidized bed of subdivided solids in a conversion zone, maintaining said conversion zone at a temperature between about 1050" F. and ll50 F., circulating a stream of solids from said conversion zone through an extraneous heater and back. to said conversion Zone to maintain said tem-- perature, maintaining said residual oil within said conversion Zone and in contact with said hot fluidzed solids for a period sufficient to convert at least by volume of said residual oil into gasoline, and passing a stream of virgin naphtha boiling within the range of about 25o to 430 F. into the bottom p-ortion of said fluidized bed in an amount suiiicient to maintain said bed in a iiuidized state.

2. The process den-ned in claim l wherein said naphtha stream is utilized to return solids from said heating zone to said conversion zone.

3. rEhe process dened in claim l wherein said heavy oil is sprayed into the top of said conversion zone above the level of said bed.

4. A process for cracking heavy residual oils to form gasoline and low boiling hydrocarbons which comprises introducing a stream or" said oil into a turbulent iiuidized bed of finely divided solids maintained in a conversion zone, circulating said solids from said conversion zone through an extraneous heater and back to said conversion zone to keep said conversion zone at a temperature between 1050" and 1150 maintaining said residual oil within said conversion Zone for a period sunicient to convert at least 40% of said oil into gasoline, introducing a stream of virgin naphtha boiling within the range of about 250 F. to 430 F. into the bottom portion of said conversion Zone in an amount suficient to maintain said bed in said turbulent i'luidized state, removing vap-orous products from the upper end of said conversion Zone, separately fractionatm ing said products to segregate a gasoline fraction, a gas oil fraction and a residual fraction, returning said residual fraction to said conversion Zone, withdrawing said gasoline fraction as a product of the process and subjecting said gas oil fraction to further cracking 'treatment ina zone separate and independent from said conversion zone.

5. The process of producing gasoline from heavy residual hydrocarbon oils which comprises maintaining a dense turbulent mass of subdivided solids fluidized by an upfiowing gasiform medium to form an interface separating sai-d mass from an upper disperse phase of substan tial height, in a coking zone, maintaining said mass at a coking temperature of about 1050"- ll50 F., spraying said oils in the liquid state into an upper portion of said disperse phase, supplying vapors of virgin naphtha boiling within the range of about 250-430 F. to a lower' portion of said mass in amounts of about 25-75% of the to-tal hydrocarbon oil feed to said mass, said vapors forming at least a major proportion of said gasiform medium whereby vaporous coking products including gasoline are formed in said coking zone and coke is deposited on said solids, withdrawing vaporous products through said disperse phase countercurrently to said sprayed liquid oil to p-reheat and pretreat the latter and scrub entrained solids from said products, withdrawing coke-carrying solids from said mass, subjecting said withdrawn solids to combustion in the iiuidized state in a separate combustion zone at a temperature of about 11501300 F. but higher vthan said coking temperature, returning solids substantially at said combustion ternperature from said combustion zone to said coking zone to supply heat thereto.

6. The process of producing gasoline from crude petroleum which comprises subjecting crude petroleum to distillation to produce a virgin naphtha fraction, boiling within the range of about 25T-430 F.; a gas oil fraction and a heavy residue, passing at least a portion of said naphtha fraction to a lower portion of a coking zone, passing at least a portion of said heavy residue substantially in the liquid state to an upper portion of said coking zone, maintaining in said coking zone a dense turbulent mass of subdivided solids fluidized by upflowing vapors of said naphtha fraction to form an upper interface at a point intermediate the feed points or said naphtha fraction and said residue, maintaining said mass at a coking temperature of about 10501200 F. in contact with said vapors and said residue, passing gasiform coking products upwardly from said interface countercurrently to and in direct contact with downwardly flowing liquid residue in said coking zone, withdrawing gasiform products from the top portion of said coking zone, fractionating said withdrawn products to pro-duce a second naphtha fraction, a second gas oil fraction and a second heavy residue, returning a portion of said second naphtha fraction to said lower portion of said cohing zone, withdrawing coke-carrying solids downwardly from said mass, passing said withdrawn solids to a heating zone, subjecting said solids in said heating zone to a combustion reaction in the form of a second dense turbulent mass of solids iiuidized by upwardly iiowing combustion-supporting and iiue gases, maintaining said second mass at a temperature higher than said coking temperature and returning highly heated solids from said second-named mass to said rstnamed mass at a rate sufficient to maintain said first-named mass at said coking temperature.

7. The process of claim 6 in which at least a portion of the naphtha passed to said coking zone is subjected to reforming conditions of tern- 15 perature and pressure in indirect heat exchange with said second-named mass, prior to the passage of said naphtha to said coking zone.

8. The process of claim 6 in which at least a portion of said second residue is passed substantially in the liquid state to said upper portion of said coking zone.

9. The process of claim 6 in which at least a portion of said gas oil fractions is subjected to catalytic cracking, cracking products being fractionated to produce cracked naphtha, heating oil and cracked heavy residue, and in which at least a portion of said cracked heavy residue is passed in the liquid state to said upper portion of said coking zone.

CHARLES N. KIMBERLIN, JR. CLARK E. ADAMS.

ROBERT W. KREBS. ROGER W. RICHARDSON.

References Cited in the le of this patent Number UNITED STATES PATENTS

Claims (1)

1.IN A PROCESS FOR CRACKING HEAVY RESIDUAL OILS TO FORM GASOLINE AND LOWER BOILING HYDROCARBONS THE IMPROVEMENT WHICH COMPRISES INTRODUCING A STREAM OF SAID RESIDUAL OIL INTO A TURBULENT FLUIDIZED BED OF SUBDIVIDED SOLIDS IN A CONVERSION ZONE, MAINTAINING SAID CONVERSION ZONE AT A TEMPERATURE BETWEEN ABOUT 1050*F. AND 1150* F., CIRCULATING A STREAM OF SOLIDS FROM SAID CONVERSION ZONE THROUGH AN EXTRANEOUS HEATER AND BACK TO SAID CONVERSION ZONE TO MAINTAIN SAID TEMPERATURE, MAINTAINING SAID RESIDUAL OIL WITHIN SAID CONVERSION ZONE AND IN CONTACT WITH SAID HOT FLUIDIZED SOLIDS FOR A PERIOD SUFFICIENT TO CONVERT AT LEAST 40% BY VOLUME OF SAID RESIDUAL OIL INTO GASOLINE, AND PASSING A STREAM OF VIRGIN NAPHTHA BOILING WITHIN THE RANGE OF ABOUT 250 TO 430*F. INTO THE BOTTOM PORTION OF SAID FLUIDIZED BED IN AN AMOUNT SUFFICIENT TO MAINTAIN SAID BED IN A FLUIDIZED STATE.

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