US2789082A - Dual bed process for coking and catalytic cracking of hydrocarbons - Google Patents

Description

April 15,1957 F. T. BARR ETAL 2,789,082

DUAL BED PROCESS FOR COKING AND CATALYTIC CRACKING OF' HYDROCARBONS Filed Sept. 29, 1954 Jaunes: U'. Ebro-wr;

United States Patent DUAL BED PROCESS FOR COKING AND CATA- LYTIC CRACKING F HYDRGCARBONS Frank T. Barr, Summit, .lames W. Brown, Elizabeth, and Charles E. JaImig, Rumson, N. i., assignors to Esso Research and Engineering Company, a corporation of Delaware Application September 29, i954, Serial No. 459,074

14 Claims. (Cl. 19649) This invention relates to the art of converting hydrocarbons and relates especially to a process wherein relatively heavy hydrocarbons are coked in contact with dense, liuidized solids. it includes as a further feature, a coking process wherein the resulting vapors or vapor products are thereafter cracked in Contact with a dense,

Various processes have been proposed elsewhere for converting hydrocarbons by first removing catalyst-contaminating constituents in a coking step and, usually after intervening condensation and fractionation in pipe stills where the heavier or coke-forming bottoms were separated, cracking the resulting gas oil in the presence of a uidized catalyst. However, such processes were often characterized by the production of gasoline of undesirably low quality during coking; by coking problems in fractionation zones and elsewhere; by difficulties in attempting to utilize in the process the heat liberated during catalyst regeneration. In some designs, especially where no extraneous condensation and fractionation was provided for between the coking and cracking stages, excessive contamination of catalyst by coke tended to occur.

It is among the objects of the invention to improve the overall quality of gasoline produced in a dual zone process, or a coking process followed by catalytic cracking to reduce catalyst contamination by the feed thereto, to eliminate the need for intermediate condensers and fractronating towers, to avoid increased Conradson carbon characteristics of the feed to the cracking zone or sludge formation due to polymerization of coker products between the coking and cracking stages, and to improve the eat balance and coke product recovery of the process. These and other objects will appear more clearly from the following specification and claims.

lThe accompanying drawing schematically illustrates a iiow diagram and apparatus suitable for the carrying out of the present invention. The invention will be described by giving a specific example of feed stock and treatment thereof, though obviously not limited thereto.

in practicing the invention, a residual petroleum stock such as a reduced crude having a gravity of about API may be passed through line l to a suitable heat exchanger 2, which may be, for instance, a coil immersed in the hot fluidized catalyst bed in a regenerator vessel 3. On passing through heat exchanger 2, the feed gets preheated to a temperature between about 400 and l000 F., preferably between 600 and 700 F. The most desirable preheat temperature will depend upon various heat balance considerations, as will be discussed later. The

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preheated liquid feed from coil 2 and! or other feed introduced at point la is introduced through line 4 into the dense fluidized bed 5 of preheated particulate solids, e. g. finely divided coke particles, where it is vaporized and partially coked. g

The actual feed introduction to the mobile or so-called fluid bed 5 can be carried out in several ways. For instance, spray nozzles 9 may be evenly spaced across a horizontal cross-section of the coker on a series of straight or circular manifolds above the bed, either in a single horizontal plane or in a plurality of vertically spaced planes, so as to give a shower or liquid curtain extending horizontally across substantially the entire vessel. With such an arrangement, some advantage may be obtained even in the absence of illustrated trays i1 and 13 by keeping valve 6 open and valves 7 and S closed and by delivering the liquid feed from line 4 to bed 5 directly through the spray nozzles 9, provided that the nozzles are located a substantial distance, e. g. l0 to 20 feet, above the dense bed level i8 so as to cause effective scrubbing of the vapors. ln such a case, the feed vapors produced by contact of the oil with the hot solids in bed 5 pass countercurrently, i. e. upwardly, through the shower of relatively cool, descending oil feed. By this means entrained coke lines are scrubbed out and the heaviest, i. e. the highest boiling components of the rising vapors are condensed and reuxed to coking bed 5. However, such spray scrubbing of the vapors is often only incomplete, may result in entrainment of droplets of undesirably heavy components of the feed by the rising vapors into the overhead or catalytic cracking zone 20, to be described, and therefore does not represent a preferred embodiment of the invention. Also, less uniform feed distribution in the coke bed is obtained when the feed nozzles are high above the bed level.

Consequently, in the preferred embodiment of the invention, valve 6 is closed or at least partly closed and the partially preheated feed is introduced through open valve 7 and line 10 onto a transverse vapor-liquid contacting plate 11 of any suitable type and then onto a lower plate 13, so that the feed may pick up hirther preheat from the upowing vapors which must pass through the liquid layers before entering the coker. The liquid hydrocarbon pools on plates 11 and 13 may be maintained at a suitable temperature between about 600 to 1000 F., but preferably below 850 F. to avoid undue coking, and act as scrubber means for the hot vapors ascending from coking bed 5 to the overhead or cracking zone Z0. Thus the heavy, coke-forming ends contained in the coker vapors are effectively removed by partial condensation of the vapors while entrained dust, e. g. coke dust, is also removed from the rising vapor stream.

From the upper contacting plate or tray 11 the liquid mixture which contains feed, heavy condensate and slurried coker solids may be caused to overow directly into coker bed 5 maintained at about 850 to ll00 F., but preferably is first passed through downcomer 12 onto one or more lower plates 13 before being pumped through lines 14, valve 8 and distributive spray nozzles 9 into the coking zone 5. Unlike in the alternative embodiment mentioned above, here nozzles 9 need not be spaced across the entire cross-section of the vessel, since it is not among their primary functions to produce aspray for scrubbing the ascending vapors. However, even here uniform feed distribution is desirable. A portion of the effluent from lower plate 13 may be recycled through line 15 and cooler 16 onto the upper plate 11, in order to control the temperatures of the scrubbing plates. If desired, a slurry settler 21 or an equivalent separation device such as a filter may also be connected to line 14 so as to prevent build up of coke lines in the scrubbing section.

. I 3 Coking zone 5 is partially filled with nely divided inert solids, such as coke ranging in size between 40 and 150 microns, through which an aeration gas such as steam from line 17is passed in an upward direction along with oil vapors generated in the coking process to produce a totalsuperlicial vapor velocity of about 1.5 to 3 feet per second. This maintains the solids within the coker in the form of a dense uidized bed having a density of about 20 to 40 lbs./cu. ft. and having an upper level 18 above which extends a more dilute phase having a density of only about 0.01 to 1 lb./cu. ft. The uidized solids in zone 5 at any given time may amount to about 0.1 to 5 lbs.' per lb. per hour of injected hydrocarbon feed and are maintained at a temperature of about 800 to 1200 E, the temperature preferably being such that the heavy constituents of the hydrocarbon feed are converted to a solid carbonaceous residue or coke, without, however, converting any substantial fraction of the feed into naphtha orV gasoline type products. Generally the residence time of the hydrocarbon vapors in the coking bed 5 may range from about 3 to 25 seconds before passing in rapid succession through scrubber plates 13 and 11 and through perforated plate 19 into catalytic cracking bed 20. Net coke product, which forms as coke is deposited upon the original particles, may be withdrawn from the fluid bed in coker zone 5 through line 22. Also, some of the withdrawn coke may be recycled to coke bed 5 after passage through a grinder or other size reducing device, thereby maintaining the particle size distribution of the coke in the cracking zone within a range suitable for proper operation.

The-major importance of the present invention lies in the'fact that it -allows easy removal both of coke fines and of coke-forming heavy ends from the coker vapor products before the catalytic cracking step where these constituents, if not otherwise removed, would rapidly contaminate the catalyst and thus put an undue load on the regeneration system. Specifically, as the vapors Vascending from coking bed 5 pass through the liquid on the contacting plate 13, entrained dust or fine particle coke is scrubbed out and the resulting suspension or vslurry'of coke in liquid feed is returned to the coke bed 5 through line 14 and sprays 9. Moreover, it must be noted that the advantages of the present invention can also be-substantially realized in cases where it may be desirable to add part or all of the oil at a lower point in bed 5. For example, oil feed may be delivered via line 17,with or without the addition of the recycle solids from line 22. Cracking and/or vaporization Vof this oil contributes Vto aeration of the bed in zone 5, while liquid for the scrubbing plates may be obtained by an increased rate of recycling of oil through lines 14 and 15 and water cooler 16 to upper plate 11.

Where more than one scrubber plate is used as illustrated, it is preferred to maintain the temperature on the bottom plate 13 in a range between a lower limit of about 750 or 850 F. and the temperature of the coking zone, so that entrained solids are scrubbed out, but relatively little condensation of the passing vapors, and also only a minimum of further coking, occurs thereon. The vapors scrubbed on plate 13 then rise up and through an upper contact plate 11 which is maintained at a somewhat lower temperature, e. g. between about 600 and 800 F. so that the heavy ends, which would otherwise result in extremely high carbon yields on catalytic cracking, are

removed from the ascending vapors by partial condensation. In this manner, most of the scrubbing is elected on the upper plate at' a relatively'low temperature which minimizes coking,-while the gradient between the plates facilitates preheating the incoming and downflowing feed to Ythe oil flowing through the scrubber. Contact'time of the oil with the vapors can be minimized so as to avoid excessive cracking and coke deposition in the scrubbing system. The presence of soilds in the oil also helps, by its scouring action, to prevent diflculties in the outlet and scrubber equipment due to coke deposition. Operation of the scrubber at lower temperatures will give more condensation of heavy ends from the Coker overhead. -Thus operating conditions in the scrubber can be regulated to give the optimum balance between the components going to catalytic cracking and the heavy ends which are `recycled to the coking section or withdrawn from the system.

In some cases it may be preferable to use a scrubbing oil other than fresh oil feed. For example, this may be a heavy extraneous oil or, as previously mentioned, may consist simply of the heavy ends themselves which are condensed out of the Coker overhead and then recycled, preferably after clarication thereof in slurry settler 21 and cooling in exchanger 16 to give the required temperature control.

Solids loading in the slurry should be controlled within the range of about 0.1 to 1.0 lb./ gal. in order to avoid any tendency to plug the equipment. Also, it is possible to add cyclones between the coking and scrubbing sections in order to reduce solids carryover. In some cases, particularly where entrainrnent is high, as due to high velocity operation, this may be very desirable, if not essential, but usually will be unnecessary where the liquid spray is properly distributed across the entire vessel.

As indicated earlier, the scrubbing plate may serve as an inexpensive means for preheating the feed, and it will be understood, 1of course, that fresh feed may be introduced directly onto lower plate 13 rather than upper plate 11 as shown in the drawing. Also, it will be understood that a system containing a greater number of scrubbing plates can be used instead of the two plates illustrated, or, alternatively, the advantages of the invention can be achieved at least to some extent even when only a single scrubbing plate is used, serving the dual purpose of removing coke nes and partially condensing the heavy, coke-forming vapor constituents.

The considerations involved in the selection of operating temperature in the scrubber will now be discussed in greater detailf A major factor is that the scrubbing should be such as to give the Vdesired cut point on the coker overhead, so as to exclude undesirable heavy ends from'the cracking zone. This cut point should besuch as to give the best over-all process, and balance the relative conversions in the coking and cracking zones. The 'cut point given by the scrubber will depend upon ternperature, pressure, amount of gas and vapors flowing, characteristics of the scrubbing oil, number of scrubbing plates, etc. From these, the operating temperature may be calculated using the usual engineering procedures. Having determined the proper scrubbing temperature, the equipment is then designed to meet the required heat balance. The latter may preclude passing all of the feed through the scrubber if insuicient heat is available. This may alect the desired preheat which must be obtained in preheat coil 2 or equivalent preheat furnace. Similar considerations will show whether it is necessary to include a heat exchanger on a recycle oil stream.

The characteristics of the feed and other conditions may make it advantageous to use an extraneous oil for scrubbing. Oil from the scrubbing section can be withdrawn from the system and may constitute one of the product fractions.

From contacting plate 11 the uncondensed hydrocarbon vapors pass upwardly. In the arrangement shown in the drawing they pass through a perforated distributor plate 19 directly into a cracking Zone wherein iinely divided cracking catalyst such as activated clay or a silicaalumina composite is maintained as a dense iluidized bed 20 by the upward passage of thevapors therethrough. Sometimes may be desirable to make the` diameterof the cracking zone which contains catalyst bed 20 greater than the diameter of the underlying coking zone to prevent excessive vapor velocities in catalyst bed 20, which otherwise may result from the increase in total vapor volume during catalytic conversion. The cracked hydrocarbon vapors together with inert gas, e. g. steam, introduced into the lower coking bed are withdrawn from the cracking zone through a cyclone 23 and passed through a line 24 to a conventional fractionation system for recovery. The contact time of the vapors in cracking zone may range from about l0 to 30 seconds at about 800 to 12.00 F., the Vapor velocity, fluidize'd bed depth and apparent density of the dense phase being in the same general range as in the earlier described coking zone. Entrained catalyst fines are separated from the cracked vapors in cyclone 23 and returned to the cracking zone through dip leg 25 which extends below the upper level 26 of the dense iluidized catalyst bed 20.

Spent catalyst maybe withdrawn from catalyst bed 20 through standpipe 27, which may be provided with one or more taps 3i for admission of minor amounts of an aeration gas and pseudo-hydraulically lifted into regenerator vessel 3 by means of an oxygen-containing gas such as air injected into the withdrawn catalyst through line 28. Above the perforated distributor plate 29 in regenerator 3 the catalyst is again maintained as a dense iluidized bed having an upper level 30 while the carbonaceous deposit is burned olf the catalyst at a temperature of about l050 to l250 F. in a manner well known per se. Low regenerator pressures in the neighborhood of about l p. s. i. g. are preferred so as to save on air compression costs, but where desired the combustion may be carried out at other pressures which may range from l to 25 p. s. i. g. The tiue gas produced in the regenerator is removed overhead through entrainment separator 32 and line 33 while the recovered catalyst fines are preferably returned to the dense bed in the regeneration zone.

Hot regenerated catalyst is recycled from regenerator 3 to the dense catalyst bed 20 in the cracking zone, thereby keeping the activity of the catalyst at a relatively high level and also supplying the necessary sensible heat and heat of reaction to the cracking zone. Thus, regenerated catalyst may be returned to the cracking reactor through line 34. However, since the feed to the cracking zone consists of vapors at high temperature, the sensible heat requirement for cracking is usually small, making excess regeneration heat available in other parts of the process. -For instance, it may be desirable to construct line 34 in indirect heat exchange with a feed preheater or a steam generator 45 to remove some heat from the catalyst returning to the reactor. This permits operating at higher catalyst to oil ratios in the cracking step than would be possible with uncooled regenerated catalyst. Some of the hot regenerated catalyst may also be aerated and circulated from regenerator 3 through line 35 to indirect heat exchanger 36 which is submerged in the uidized bed 5, thereby supplying the required coking heat as described and claimed in copending application Serial No. 227,169 of J ames W. Brown, tiled on May 19, l951; or heat may be exchanged directly by mixing coke and catalyst of diiferent sizes, and separating the catalyst from the resulting mixture by elutriation as described and claimed in copending application Serial No. 230,746 of James W. Brown and Charles E. iahnig, filed on June 9, 1951, now Patent No. 2,655,464. Alternatively or additionally, excess heat may be used for other purposes such as product reboiling or steam generation. For example, a water coil may be immersed in hot fluidized catalyst either directly in the regenerator bed or in a separate vessel through which hot catalyst is circulated either from the reactor or the regenerator.

Of course, where none of the regeneration heat is transferred to the coking zone, other means must be used for supplying the necessary heat to the coking zone. For example, such heat may be obtained by withdrawing a portion of the coke from ui'dized bed 5 lthrough standpipe 39 and burning a portion of the withdrawn coke in transfer line 40 after mixing with air admitted through line 41a. I f desired, heat can also be supplied by contacting the vcoke with hot iiue gases, formed by combustion under Acontrolled conditions in an auxiliary burning zone. The heated coke is -then separated from the ue gases in entrainment separator 41h and returned to coke bed 5 through leg 42 provided with aeration taps 43. Where desired, va portion of the hot coke from separator 41h may also be branched Volf through standpipe 44 and mixed into the fresh yfeed from line so as to preheat the latter, and to control coke accumulation in the preheat circuit. Regardless whether all of the hot coke from separator 41b is returned ydirectly to coke bed 5 or Whether some of it is added to the feed, a substantial `advantage is obtained by this use lof the transfer line coke heater. Moreover where partial combustion of the coke in the transfer 'line is feasible, there is also the ladvantage that this increases the surface area of the circulating coke so that improved coking is obtained in the coking zone.

Having described vspecific embodiments of the invention as -well as suitable methods of operation, it will be understood that this has been done for purposes of iliustration and not of limitation. On the contrary, the described invention may be varied and modified in numerous ways which will occur to persons skilled in the art without departing from the scope and spirit of the present disclosure or of the appended claims.

For instance, -beyond the scope of the specific exampies given, the invention is broadly applicable to conversion of whole or reduced crude petroleum stocks containing heavy components as well as cycle stocks having a boiling range above about 900 to ll50 F. (atmospheric equivalent) and a gravity of 20 API or lower, and even to lighter stocks such -as gas oils. The importance of the invention lies in the -fact that it permits ready control of end boiling point of the vapor products obtained from the coking Zone. This is of special importance when the vapors are passed as such directly to the catalytic cracking zone. Even Where the vapors are condensed or partially condensed before going to catalytic cracking, the same advantages are obtained. Solid coke as well as feed fractions having strong coke forming tendencies or containing catalyst contaminants are kept out of the catalytic cracking zone by intimate scrubbing with a liquid hydrocarbon maintained at the desired temperature, the condensed heavy yfractions being returned .to the coking zone and there substantially completely converted to coke and lighter products. Accordingly, the invention is of particular value in processes wherein vapor-V ized petroleum stocks having high coke forming tendencies as indicated by Conradson carbon values between about 5 to 35, such as reduced crudes obtained by atmospheric or vacuum distillation and representing about the bottom 2 to 25 vol. percent of the virgin crude distilled, are passed to a catalytic conversion zone. However, beside crude stocks, the invention may be applied to claried cycle oil from catalytic cracking, to various pitches, tars from visbreaking operations and the like.

if desired, and especially where contact plates are used for scrubbing, the oil feed or portions thereof may be vadded at a low point in the coking bed while the rest of the feed may be added higher up. Thus, clarified oil represents a refractory stock which makes relatively high carbon in catalytic cracking, and which it is desired to destroy. This can best be accomplished by injecting it near the bottom of the coking bed. Heavy bottoms from the scrubber can be handled in a similar manner.

Prior to feeding to the coker, the heavy feed stocks may be cut back with naphtha or other light products, and preferably preheated to temperatures ranging from 200 to l000 F., or especially 600 to 800 F. Moreover, the hydrocarbon feed-may also be diluted in the various reaction zones Vwith steam, recycle gas or other inert gas in amounts up to about 500 to 5000 cubic Vfeet (at coker conditions) per barrel, since such diluent may often be necessary to raise the gas velocity to a proper level vfor liuidization. Generally it is desirable to operate at linear superficial gas velocities ranging from about 0.5 to 5 or 10 feet per second so .as to establish apparent densities in the dense uidized phase of about 10 to 50 lbs/cu. ft. and about 0.01 to 5 lbs/cu. ft. in the disperse phase thereabove, as is well known per se.

The contact solids in `the coker are preferably coke particles ranging in size from to about 500 microns, or preferably from 40 to 150 microns, through other finely divided, essentially inert solids such as sand, spent clays, pumice and the like may similarly be used where a coke product of high inorganic ash content can be tolerated.

The Contact solids used in the catalytic cracking zone may be any finely divided cracking catalyst such las activated clays, activated alumina, synthetic composites of silica with about to 50% alumina, or other conventional cracking catalysts such as those containing silica together `with magnesia and/or yboria. The solids in the cracking zone may also contain a conventional reforming catalyst such as activated carbon, clay or bauxite, whereby the octane number of the naphtha produced in the coker may be improved and higher boiling hydrocarbons are cracked. The particle size of the cracking zone catalyst, as well as the apparent densities and superficial gas velocities prevailing in the cracking and regeneration zones are substantially within the same limits as given above with reference to the eoker solids.

t Reaction conditions may include coking temperatures of about 800 to 1200 F.,preferably 850 to 1l00 F., catalytic cracking temperatures of about 800 to 12.00 F., preferably 950 to 1100 F., Iand catalyst regeneration temperatures of about 10007 to 1300 F., preferably 1100 to 1200o F. Of course, the regeneration temperature must not be chosen so high as to cause serious deterioration of the catalyst being used, it being well known that various catalysts cannot be heated above certain readily determinable temperatures without permanently reducing their catalytic activity. f

ln the coking and cracking zones the weight ratio of oil to ytotal solids in the vessel at a given moment may be from about 0.1 to 5 Ilbs./lb./l:tr., and the oil vapors rising from the scrubbing plates into the catalytic cracking zone preferably are characterized by a boiling range below about 950 F. or less, and in any case below 1200 F. The ratio of coke to oil fed to line 1 may be from 0 up to about 0.5 or 1.0 lb./lb. Pressures in the `coking and cracking zones may range between about 5 and 100 p. s. i. g., although pressures in the lower part of this range will usually be used, especially in the regeneration zone.

Furthermore, the physical arrangement of the illustrated apparatus may be modified in various ways. For instance, while feed preheater coil 2 is shown wholly submerged below the catalyst level 30 in the regenerator, it is possible to vary the catalyst level so as to expose more or less of the heat exchanger surface above the level, thereby controlling the degree -to which the `liquid feed is preheated. Also, while the heat exchanger 36 within the coker has been schematically illustrated =as a coil, a shell-and-tube type heat exchanger as illustrated in copending application Serial No. 227,169, nowrPatent No.y 2,734,850, granted Feb. 14, 1956, of lames W. Brown or any other heat exchanger of suita-ble design may be used likewise. Moreover, while the feed is shown to be first preheated in the regenerator coil 2, a'conventional preheat furnace may be used; or it is entirely feasible to introduce cold feed directly onto plate 11 where it can be preheated by the hot vapors rising through it; or

the feed,` Vcold or preheated, may be introduced directly onto lower plate 13. Y Y

vIn the present disclosure fiuidirzed coking and catalytic cracking have lbeen combined to particular `advantage in a dual zone process as regards equipment and heat economy. Important features where the dual 'zone arrangement is used are that the feed vaporized in the Vfirst zone is fed directly to the second Zone after separation of its heavy, coke-forming or catalyst contaminating constituents by partial condensation, the coke particles are kept entirely segregated from the catalyst and are not mixed or contacted therewith, as has been proposed in other processes. By keeping the two materials segregated there is no possibility of catalyst being lost due to sticking on the coke particles. Moreover, coke is excluded from the catalyst section to avoid possible contamination and increased load on the regeneration equipment. Thus, the combination gives maximum efficiency, and wide flexibility without operability problems,A and with minimum equipment required.

Having given a full description of the invention and of the manner and process of using it, the invention is particularly pointed out and distinctly claimed as follows:

What is claimed is:

1. In a process wherein a petroleum stock is cracked in a conversion zone in the presence of a dense iiuidized bed of cracking catalyst and wherein the cracking catalyst is recycled between the conversion zone and a regeneration zone where spent catalyst is regenerated in a dense fluidized bed by combustion with an oxygen-containing gas, the improvement which comprises introducing residual petroleum feed boiling predominantly above 900 F. into a coking zone wherein nely divided coke particles are maintained as a dense fiuidized bed with a more dilute phase thereabove, contacting the residual stock with the coke particles at a temperature between about'850 and 12.00 F. to form additional coke and hydrocarbon vapors, circulating a portion of said coke particles Ybetween said coking zone and a separate heating zione so as to supply heat to said coking zone, withdrawing net coke product from the coking zone, withdrawing resulting vapors upwardly from the dense fluidized coke bed and scrubbing the rising hydrocarbon vapors and entrained coke in the aforesaid dilute phase by passage through a pool of hydrocarbon liquid maintained ata temperature between about 600 and 800 F., thereby removing undesirable heavy hydrocarbon ends and the entrained coke from the Vrising hydrocarbon vapors and forming a slurry of coke in hydrocarbon liquid, removing the said slurry from said hydrocarbon pool, recycling said hydrocarbon liquid including said heavy ends to said coking zone, passing the uncondensed vapors from the pool upwardly through a superimposed cracking zone containing a dense fluidized bed of finely divided solid cracking catalyst at about 800 to 1200o F. and withdrawing cracked product vapors from the cracking zone for recovery.

2. A process according to claim 1 in which thescrubber slurry is withdrawn from the system.

3. A process according to claim 1 wherein hot regenerated catalyst is cooled by indirect heat exchange before returning to the conversion zone.

4. A process according to claim 1 wherein residual petroleum feed is mixed with finely divided coke and preheated to 600 to 700 F. by indirect heat exchange with the dense catalyst bed in the regeneration zone before the feed is introduced into the coking zone.

5. In a process wherein a petroleum stock is cracked in a conversion zone in thepresence of a dense fluid bed of cracking catalyst at about S00 to 1200 F. and wherein the cracking catalyst is recycled between the conver- Ysion zone and a regeneration zone where spent catalyst is regenerated in a dense fluidized bed by combustion with an oxygen-containing gas, the improvement which comprises introducing agas oil containing residual petroleum stock boiling partially above 900 F. into an upper pool of hydrocarbon liquid kept at a temperature between about 600 and 800 F. in a coking zone wherein finely divided coke particles are maintained as a dense iluidized bed with a more dilute phase therabove, the said upper pool being maintained in the said more dilute phase, contacting the residual stock with the coke particles at a temperature between about 800 and l200 F. to form additional coke and hydrocarbon vapors, circulatingT a portion of said coke particles between said coking zone and a separate heating zone so as to supply heat to said coking zone, withdrawing net coke product from the coking zone, withdrawing resulting vapors upwardly from the dense tluidized coke bed and scrubbing the rising hydrocarbon vapors and entrained coke in the aforesaid dilute phase by passage through a lower pool of hydrocarbon liquid maintained at a temperature between 800 to 1000 F., thereby removing the entrained coke from the raising hydrocarbon vapors and forming a slurry of coke in hydrocarbon liquid, passing the scrubbed vapors upwardly through the upper pool of hydrocarbon liquid and thereby removing heavy ends from said vapors by partial condensation, passing the hydrocarbon liquid containing the heavy ends from the upper pool to the said lower pool and with the aforesaid slurry back to the dense fluidized coke bed for further coking, passing the uncondensed vapors from the upper pool upwardly through said catalytic conversion Zone which is maintained superimposed above said upper pool, and withdrawing cracked product vapors from the conversion zone for recovery.

6. A process according to claim which comprises the specific steps of introducing the feed into an upper liquid hydrocarbon pool, overflowing the liquid hydrocarbon into a lower pool, withdrawing coke-containing liquid hydrocarbon from the lower pool, settling the coke from the withdrawn liquid, passing a portion of the withdrawn liquid to the coking zone, cooling claried withdrawn liquid and recycling the cooled liquid to the upper pool.

7. A process according to claim 5 wherein heat is supplied to the coking zone by withdrawing a portion of the coke particles from the coking zone, mixing the withdrawn coke particles with an oxygen-containing gas to form a suspension of coke in gas, thereby burning a fraction of the coke particles and raising the temperature of the unburnt portions of coke particles, separating the remaining hot coke particles from the suspension, and returning the separated coke particles to the dense fluidized coke bed in the coking zone.

8. A process for converting a coke-forming liquid hydrocarbon feed stock into lighter products which comprises contacting the feed stock in the presence of hot finely divided inert solid particles maintained in a coking zone in the form of a dense uid bed with a disperse phase thereabove at a temperature of at least 800 F., withdrawing coke-containing solid particles from the dense coking bed, passing the withdrawn coke-containing particles to a heating zone and returning the heated particles to said coking zone to supply heat thereto, withdrawing the resulting hydrocarbon vapors and entraned solids upwardly from the dense coking bed, scrubbing substantially all of the upwardly passing hydrocarbon vapors in the disperse phase of the coking zone by intimate contact with a liquid hydrocarbon maintained at a temperature below about 1000 F. and low enough to condense undesirable heavy ends from said vapors, passing said liquid hydrocarbon including the condensed heavy ends to said coking bed, passing scrubbed vapor products to a catalytic cracking zone containing uidized powdered catalyst, and circulating said powdered catalyst between said cracking zone and a separate regeneration zone to regenerate the catalyst and to supply the heat of reaction to said cracking zone.

9. In the process of converting heavy hydrocarbon oil to lighter products, including gas oil, and coke, by contacting said oil at a temperature in the range of about 850 to 1l00 F. in a coking zone with a dense turbulent, fiuidized bed of nely divided heat-carrying solid par ticles to thermally crack said heavy oil to vapors and carbonaceous residue, wherein the resulting gas oil contains undesirable heavy ends which include contaminants injurious to cracking catalysts and the like, with which said gas oil may subsequently be treated, the improvement which comprises passing the thermally cracked vapors and entrained solids directly from the coking zone upwardly through a scrubbing zone containing a pool of liquid hydrocarbon maintained at a temperature below about l000 F. and low enough to condense said undesirable heavy ends from said vapors, passing liquid hydrocarbon from the pool, including the condensed heavy ends to the coking zone as at least part of the feed thereto, and removing the scrubbed vapor products from the scrubbing zone for further treatment.

l0. Process according to claim 9 wherein the scrubbing liquid is maintained at a temperature below about 850 F.

l1. Process according to claim 9 wherein the scrubbing includes a plurality of steps of intimate contact of the vapors with liquid hydrocarbon maintained at temperatures within the range of 600 to 1000" F.

l2. Process according to claim 9 wherein the thermally cracked vapors from the coking zone are removed at suliicient velocity to entrain solid particles which tend to minimize coke deposition in the system.

13. A process for converting a heavy coke-forming liquid hydrocarbon feed into lighter products including gas oil suitable for feed to catalytic cracking which comprises contacting the heavy feed stock with hot, iinely divided and substantially catalytically inert solid particles maintained in a coking zone in the form of a dense iluid bed with a disperse phase of said particles above said bed, at a temperature in the range of about 850 to 1100 F., maintaining said contact between feed and particles for a time sucient to substantially convert the feed to vapors which contain an objectionable high boiling component including cracking catalyst contaminant material and to coke residue which is substantially deposited upon said particles, withdrawing coke carrying particles to a heating zone to heat them and returning heated particles to said coking zone to supply heat thereto, withdrawing the hydrocarbon vapors and entrained solids upwardly from the dense coking bed, scrubbing said upwardly passing hydrocarbon vapors by passing them directly to a scrubbing zone and by intimately contacting them with a liquid hydrocarbon scrubbing oil maintained as a liquid pool at a temperature below about 1000 F. and low enough to condense said objectionable high boiling component from said vapors, recycling part of the scrubbing oil of said pool, including said condensed high boiling component, to the scrubbing zone and passing the remainder thereof to the coking zone as feed thereto.

14. Process according to claim 13 wherein the scrubbing oil comprises at least a part of the original feed.

References Cited in the tile of this patent UNITED STATES PATENTS 2,340,974 Myers Feb. 8, 1944 2,420,542 Jahnig May 13, 1947 2,655,464 Brown et al Oct. 13, 1953

Claims (1)

1. IN A PROCESS WHEREIN A PETROLEUM STOCK IS CRACKED IN A CONVERSION ZONE IN THE PRESENCE OF A DENSE FLUIDIZED BED OF CRACKING CATALYST AND WHEREIN THE CRACKING CATALYST IS RECYCLED BETWEEN THE CONVERSION ZONE AND A REGENERATION ZONE WHERE SPENT CATALYST IS REGENERATED IN A DENSE FLUIDIZED BED BY COMBUSTION WITH AN OXYGEN-CONTAINING GAS, THE IMPROVEMENT WHICH COMPRISES INTRODUCING RESIDUAL PETROLEUM FEED BOILING PREDOMINANTLY ABOVE 900*F. INTO A COKING ZONE WHEREIN FINELY DIVIDED COKE PARTICLES ARE MAINTAINED AS A DENSE FLUIDIZED BED WITH A MORE DILUTE PHASE THEREABOVE, CONTACTING THE RESIDUAL STOCK WITH THE COKE PARTICLES AT A TEMPERATURE BETWEEN ABOUT 850 AND 1200*F. TO FORM ADDITIONAL COKE AND HYDROCARBON VAPORS, CIRCULATING A PORTION OF SAID COKE PARTICLES BETWEEN SAID COKING ZONE AND A SEPARATE HEATING ZONE SO AS TO SUPPLY HEAT TO SAID COKING ZONE, WITHDRAWING NET COKE PRODUCT FROM THE COKING ZONE, WITHDRAWING RESULTING VAPORS UPWARDLY FROM THE DENSE FLUIDIZED COKE BED AND SCRUBBING THE RISING HYDROCARBON VAPORS AND ENTRAINED COKE IN THE AFORESAID DILUTE PHASE BY PASSAGE THROUGH A POOL OF HYDROCARBON LIQUID MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 600 AND 800*F., THEREBY REMOVING UNDESIRABLE HEAVY HYDROCARBON ENDS AND THE ENTRAINED COKE FROM THE RISING HYDROCARBON VAPORS AND FORMING A SLURRY OF COKE

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