US2756195A - Cracking of heavy hydrocarbons with inert solids - Google Patents

Description

C. E. ADAMS July 24, 1956 CRACKING OF HEAVY HYDROCARBONS WITH INERT SOLIDS Filed April 15 1951 QEAc-HQN 'PRODUCT Aun @H UENT EAQTOL Cio/usa FLunn Somos EJED HYDlocAlboN FEED Il' il...)

FLmmzAw-lom lO Q Cola Mm/M H EAT ExcHAMGaL Qb T057 Clbborrlez United States Patent CRACKING OF HEAVY HYDROCARBONS WITH INERT SOLIDS Clark E. Adams, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Application April 13, 1951, Serial No. 220,816

2 Claims. (Cl. 196S5) This invention relates to improvements in the thermal cracking of relatively heavy hydrocarbons such as crude residua. More particularly it relates to vapor phase cracking in the presence of rather coarse particles of a dense, substantially non-porous and abrasion-resistant contact material, which particles are maintained in the conversion zone as a dense fluidized bed. As coke is formed around the fluidized Contact particles, it is continuously ground off and blown from the conversion zone to a separation zone for recovery and further use.

In the treatment of heavy petroleum materials such as reduced crude which contains large quantities of low gravity tar and the like, it is practically impossible to convert such feed stocks to valuable products in the gasoline and gas oil range without simultaneously converting substantial proportions of the charge to coke which usually interferes with the continuance of the conversion process; also coke recovery has not been heretofore feasible to any great extent, thereby further detracting from the economy of such processes. Particularly in conventional thermal units using cracking coils and drums, coke formation has greatly restricted the permissible severity of the operation and increased the frequency of shut-downs required for cleaning. Similarly, the rapid rate of coke formation resulting from the cracking of heavy hydrocarbons has precluded their treatment by iiXed-bed catalytic processes, and recovery of coke as such has been entirely impractical in the latter. Moreover, the excessive coke formation also rendered catalytic cracking of heavy hydrocarbons in fluid units impractical, inasmuch as the catalyst required regeneration at a very high rate and this in turn required the combustion of substantially all the coke, which was produced in amounts far exceeding the heat requirements of the conversionprocess. Such regeneration also required the handling of tremendous amounts of solid catalyst and coke, it being remembered that even in present commercial fluid cracking units employing gas oil as a feed, and requiring relatively moderate rates of catalyst regeneration, the catalyst alone'is being circulated at a rate of about 30 tons per minute. In view of the aforementioned diiiiculties, a practical process for converting heavy petroleum materials into valuable distillate fractions and a recoverable coke product has long been looked for in the art and is the subject of the present invention. n z

The attached drawing illustrates a preferred arrangement of operating the novel process. Referring in detail to the. drawing, 1 represents a reactor which is in the form of a cylindrical vessel. In the reactor a body of iiuidized solid particles 2 is maintained which particles are rather coarse, dense, inert, and attrition resistant. As an example, a suitable material of this sort is rounded sea sand, or one may use metal shot, ceramic beads orother particles of similar characteristics. The solid particles may range in size from 70 to 1000 microns, preferably 150 to 500 microns, and have a packed density greaterthan 1, preferably between 1.2l and 4. Fluidization of the particles is maintained by keeping the linear between the reaction Zone and the cyclone.

gas velocity in the reactor greater than 2 ft./sec., preferably between 2 and 5 ft./sec. or at as high a velocity as possible without carrying an appreciable portion of the contacting solids from the bed.

A heavy hydrocarbon feed is introduced into the lowerpart of reactor 1 through line 3 and distributor nozzle 4 at such a rate that under the reaction conditions there is sufficient time for the coking reaction to take place without a build-up of tarry residue which would cause loss of uidization by agglomeration of the particles. Depending on reaction conditions, the hydrocarbon feed rate may be between about 0.1 to 4.0 parts by weight per hour per weight of contact particles, allowing a residence time for the hydrocarbon reactant of about 0.1 to 10 seconds or more. The process may be carried out at any temperature suitable for obtaining the desired product distribution, usually between 800 and 2000 F., and preferably between 900 and l400 F. The pressure in the reactor may range between about 0 and 150 pounds, preferably between 5 and 25 pounds per square inch gage.

The hydrocarbon feed may be a reduced crude obtained by atmospheric or vacuum distillation, representing, for instance, about 2 to 25 vol. per cent of the Whole crude distilled. Typically such reduced crudes boil above 900 to 1150 F. atmospheric equivalent) and have gravities between about 0 and 20 API. However, instead of a reduced crude, other residual stocks such as clarified oil from catalytic cracking, pitch, tar from visbreaking and the like may similarly be used in the present process. Also the heavy hydrocarbon feed may be cut back with naphtha or other light products to reduce its viscosity. Alternatively, where the feed is Very viscous, it may be preheated before injection into the reactor to make it more fluid, preheat temperatures ranging from about 200 to 1000 F., or preferably from 600 to 800 F.

Furthermore the feed may be diluted with steam, recycle gas, or other inert or hydrocarbon gases in amounts of about 500 to 5000 cubic feet per barrel, the diluent gas offering a convenient means for maintaining the gas velocity in the dense uidized bed 2 at the desired level. The diluent such as steam may be introduced into reactor 1 either through line 3 as a mixture with the feed, or the diluent may be introduced separately through one or more gas lines 5, or some diluent may be introduced at either place.

Gaseous and normally liquid reaction products together with diluent leave the uidized solids reaction Zone overhead as a gas While the coke formed around the sand particles and then ground off due to the incessant impingement of the articles upon each other is suspended in the effluent gases. use of high velocity gas jets 6 in the sand bed, the jets being preferably attached to diluent lines 5. The eiuent gases are passed through a separating device such as internal cyclone 7 where the finely ground, solid coke is separated from the vaporized products and diluent. Alternatively, the cyclone may be installed outside of the reactor, butin that case it is necessary to insulate it and to provide for make up of any heat lost in transfer of the products to the cyclone. Maintenance of the cyclone temperature substantially .at the level prevailing in thev reaction zone is necessary as a portion of the vaporized product leaves the reaction zone very nearly at its dew point and would be lost in the cycle by condensation on the separated coke, if heat were lost from the products Moreover, condensation of such product tar on the coke would tend to cause agglomeration and reduce the desiredl ease .of handling the coke product. The gaseousvand vaporized product and ldiluent pass from cyclone 7 through line 8 is removed from the cyclone in a iiuidized condition Patented July 24, 1956l Coke abrasion may also be accelerated by 3 through pipe 9 into which an "inert liuidizing gas is introduced at a suitahlerate `'through 'one 'or more lines '10.' Thus the coke can be pneumatically transported in further. pipes to retinery furnaces (not shown). or to other convenient'locatons.

As a furtherl alternative, the finely ground coke suspended in the product lvapors may be carried overhead from reactor 1 with the product `stream directly "through line 8 without any `mechanical separation Vand the coke can "then be isolated in the product recovery system '(n'ot shown) as a paste with a minor amount of tarry residue. This isolation can be carried .out by means of settling and/or filtration such as in a Dorr thickener, or 'by distilling off 'the volatile components leaving the 'coke concentrated inthe residual fraction. This pasty mass of coke and tarryresidue may be molded by means of heat and pressure into briquettes for use as industrial or household fuel.

Heat of reaction lis preferably supplied to reactor 1 indirectly in anyone of numerous ways which are known per se and'which have no particular bearing von the present invention, For example, as illustrated in `the drawing, the required heat may be supplied to the uidized solids in bed 2 by means of the heat exchanger 11 from an external furnace preferably using as fuel a portion of the coke or process gas produced in the unit. Of course, if desired, other available fuels may similarly be used tosupply the heat required.

Alternatively, it ist also possible to supply the heat of reaction by direct introduction of air or other oxygencontaining gas into the bottom of reactor 1 through line `5 or through similar lines specially provided for this purpose and located below the feed inlet, whereby some of` the coke formed on the sand by conversion of the hydrocarbon feed is burned. However, in such an arrangement it is desirable that the feed inlet 4 be located at least one-tenth to one-third of the reactor height above the air inlet 6 so as to keep combustion of valuable feed components to a minimum. Still another alternative of supplying the heat of reaction involves the use of a more or less conventional two-vessel system wherein cokeeoated solids from the reactor are transferred to a regenerator vessel where the burning reaction is carried out and the hot regenerated particlescontaining a large portion of the `resulting heatare then recycled to theireactor at a rate adequate to supply the necessary heat of reaction. This last method, however, risthe least desirable one since it involves the loss-of the main advantages of the vpresent invention, which are, firstly, a one-vessel system requiring minimum .recirculation of 'contact particles, and secondly, a high degree of coke recovery for use outside of the system in uncontaminated, readily usable form.

An example further illustrating the mode of operation as well as the advantages of the present invention is given below.

Example A `reactor 1 substantially as shownin 4the drawing and having an inside diameter of 2.9 inches was charged with 3300 grams of 35-80 mesh of rounded sea sandand the sand was uidized to form a dense, fixed bedzhaving a distinct upper level by introducing steam into the-bottom of the reactor. The reactor was maintained at 12-70 F. by means of external heat and 2.4% South Louisiana vacuum residuum having a .gravity of 11.9 API `was fed through a spray nozzle 4 for a period of threeihours at a rate of 1480 grams per hour together with (550 gramsfper hour of steam. Additional steam twas fedto the bottom of the reactor through diluent lines 5, below nozzle 4, at 1450 grams per hour. Product vapors and diluent were taken overhead through a sintered metal filter, having an average porosityfof about 3'5 microns. The metal iilter was used instead offthe "cyclone-'separator shown in'thedrawing. The upward velocity of the-gas leaving'thedense, tluid'bed was Vabout 2;'6"feettper=second,

of which about l.9 feet per second was attributable to the total 'steam diluent introduced Vinto the vessel while the product gas and other reaction vapors accounted for the other 0.7 foot per second of the velocity of the gas phase leaving the reactor bed.

The withdrawn reaction products and diluent were recovered in conventional equipment for subsequent work up, and .after completion `of `the run the solids which previously constituted the fluid bed were discharged from the reactor after cooling to room temperature. The discharged solids weighed 3:55() grams and showed on analysis `l0.9 weig'ht ypercent carbon and 0.2 weightpercent hydrogen. Another solid fraction amounting to 682 grams was recoveredas a deposit from the 'overhead metal iilter and showed .an analysis of 76.1 weight percent carbon and 1.1 Aweight percent hydrogen. This lter deposit, although contaminated with some sand due to the short disengaging space between the solids bed and filter inthe'small-scale 'test unit employed, thus accounts for 4nearly '60% of the total coke made in this relatively short run and illustrates the practicability of recovering a `major lproportionof the total coke product in a'nearly pure statefrom separation means located at the top of a reactor operated in'accordance with the present invention. In lother similar runs iilter deposits of even higher coke content havebeen recovered, running `up to 89.6 weight percent carbon and 1.7 weight percent hydrogen, the remainder being ash.

Torecapitulate, this invention relates to improvements in the conversion of `relatively heavy hydrocarbons to form liquid products of lower viscosity and coke in a relatively-pure, recoverable state, and particularly includes processes wherein a heavy viscous 4hydrocarbon is heat treated atsufiiciently high temperatures -to form solid coke .instead'of tarry residues, in addition to the principally desired light distillate fractions. The treatment according to the present invention is carried out in the presence of a solid material such as seasand on vwhich f the colte-forming constituents of the feed are deposited. The contact materially characteristically has a high density and coarse particle size to permit high -gas velocity in the reactor without appreciable entrainment. Another important characteristic of the contact material used is its high `resistance to attrition, which resistance is necessary for the maintenance of rmore or less the original particle size'distribution throughout an entire run which may last for yperiods ranging from a few days to several months. Furthermore, high attrition resistance is also required to avoid contamination of the coke product with entrained iinestofabraded contactfmaterial.

In the preferred modification of Vthe invention no oxidativeregeneration' of the-contact rnaterial'is necessary, inasmuch as, -after the attainment of equilibrium conditions,the coke is abraded from the tiuidized contact material at a rate` which equals vits rate of formation on the contactl particles. 'Unlike the coarse, dense contact particleswhichcontinuously settle back into the fluidizedbed inl the conversion zone, the abraded coke particles are entrained overhead from the reactor in the vaporized conversion products and are mechanically separated from the latter at atemperature above the dew point of the overhead products. The separated coke particles `are readily fluidizable and as such are easilytransportable. A proper Tamount of the recovered coke particles maybe burned in a furnace which is arranged in indirect heat exchange relation with rthe cracking zone so as to supply theheat of` reaction to the latter.

Having described the ypresent invention, including a preferred embodiment thereof, it will be understoodthat numerous I'modifications and variations of the invention may "bemadebypersonsfskilled in theart without departingfrom `its scopefand spiritas defined Ain the appended claims.

1. A process vfor 'cracking reduced vcrude which comprises providing a permanent dense, uidized bed of -attrition resistant sand particles having a particle diameter of at least 150 microns and a packed densi-ty between 1.2 and 4 in the lower portion and a dilute phase zone in the upper portion of a reaction zone kept at a tem perature between 900 and 1400 F., injecting reduced crude into the dense bed of particles at a rate of between 0.1 to 4.0 parts 'by weight per hour per part of sand particles, also injecting a high velocity stream of a diluent gas near the bottom of the reaction Zone so as -to give a total gas Velocity in the dense bed of about 2 to 5 feet/sec. but not in excess of the entrainment velocity of the sand particles, thereby causing an abrasion of coke deposited on the sand particles substan-tially at the rate of its formation from the crude, withdrawing a stream of gaseous products containing the abraded coke suspended therein from the upper portion of the reaction zone wherein entrained san-d particles become subs-tantially disengaged from the gaseous stream, passing the gaseous stream into a separa-tion zone maintained within the upper portion of the reaction zone substantially at the same temperature as the reaction zone temperature, withdrawing a stream of gaseous products and a stream of finely powdered coke from `the separation zone, passing a portion of the recovered coke to an external combustion zone, supplying an oxygen-containing gas yto the combustion zone and supplying the resulting heat -to the reaction zone by indirect heat exchange wi-th the dense uidized bed so as to maintain the bed at the desired temperature without returning the remaining coke to the reaction zone.

2. A process for cracking a heavy hydrocarbon oil feed which comprises providing a permanent dense, fluidized bed of attrition resistant inert, solid, inorganic particles selected from the group consisting of sand, metal shot and ceramic beads having a particle diameter of at least 150 microns and a packed density between 1.2 and 4 in the lower portion and a dilute phase zone in the upper portion of a reaction zone kept at a temperature between 900 and 1400 F., injecting the heavy oil into the dense bed of particles at a rat-e of between 0.1 to 4.0 parts by weight per hour per part of inert particles, also injecting a high velocity stream of a diluent gas near the bottom of the reaction zone so as to give a total gas Velocity in the dense `bed of about 2 to 5 feet/sec. but not in excess of the entrain-ment velocity of lthe inert particles, thereby causing an abrasion of coke deposited on .the inert particles substantially at the rate of its formation from lthe feed, withdrawing a stream of gaseous produots containing the abraded coke suspended therein from the upper por-tion of the reaction Zone wherein entrained inert particles become substantially disengaged from the gaseous stream, passing the gaseous stream into a separation zone maintained within the upper portion of the reaction zone substantially at the same temperature as the reaction zone temperature, and separately withdrawing a stream of gaseous products and a stream of iinely powdered coke from the separation zone without returning the coke to the reaction zone.

References Cited in the le of this patent UNITED STATES PATENTS 2,340,974 Myers Feb. 8, 1944 2,364,145 Hup-pke et al. Dec. 5, 1944 2,388,055 Hemminger Oct. 30, 1945 2,412,152 Huit Dec. 3, 1946 2,412,879 Fischer Dec. 17, 1946 2,421,651 Reeves lune 3, 1947 2,428,715 Marisic Oot. 7, 1947 2,436,160 Blanding Feb. 17, 1948 2,459,824 Leer Ian. 25, 1949 2,464,257 Pelzer et al Mar. l5, 1949 2,471,104 Gohr May 24, 1949 2,542,887 Watson Feb. 20, 1951 2,585,984 Alexander et a'l. Feb. 19, 1952 2,606,144 Leler Aug. 5, 1952

Claims (1)

1. A PROCESS FOR CRACKING REDUCED CRUDE WHICH COMPRISES PROVIDING A PERMANENT DENSE, FLUIDIZED BED OF ATTRITION RESISTANT SAND PARTICLES HAVING A PARTICLE DIAMETER OF AT LEAST 150 MICRONS AND A PACKED DENSITY BETWEEN 1.2 AND 4 IN THE LOWER PORTION AND A DILUTE PHASE ZONE IN THE UPPER PORTION OF A REACTION ZONE KEPT AT A TEMPERATURE BETWEEN 900 AND 1400* F., INJECTING REDUCED CRUDE INTO THE DENSE BED OF PARTICLES AT A RATE OF BETWEEN 0.1 TO 4.0 PARTS BY WEIGHT PER HOUR PER PART OF SAND PARTICLES, ALSO INJECTING A HIGH VELOCITY STREAM OF A DILUENT GAS NEAR THE BOTTOM OF THE REACTION ZONE SO AS TO GIVE A TOTAL GAS VELOCITY IN THE DENSE BED OF ABOUT 2 TO 5 FEET/SEC. BUT NOT IN EXCESS OF THE ENTAINMENT VELOCITY OF THE SAND PARTICLES, THEREBY CAUSING AN ABRASION OF COKE DEPOSITED ON THE SAND PARTICLES SUBSTANTIALLY AT THE RATE OF ITS FORMATION FROM THE CRUDE, WITHDRAWING A STREAM OF GASEOUS PRODUCTS CONTAINING THE ABRADED COKE SUSPENDED THEREIN FROM THE UPPER PORTION OF THE REACTION ZONE WHEREIN ENTRAINED SAND PARTICLES BECOME SUBSTANTIALLY DISENGAGED FROM THE GASEOUS STREAM, PASSING THE GASEOUS STREAM INTO A SEPARATION ZONE MAINTAINED WITHIN THE UPPER PORTION OF THE REACTION ZONE SUBSTANTIALLY AT THE SAME TEMPERATURE AS THE REACTION ZONE TEMPERATURE, WITHDRAWING A STREAM OF GASEOUS PRODUCTS AND A STREAM OF FINELY POWDERED COKE FROM THE SEPARATION ZONE, PASSING A PORTION OF THE RECOVERED COKE TO AN EXTERNAL COMBUSTION ZONE, SUPPLYING AN OXYGEN-CONTAINING GAS TO THE COMBUSTION ZONE AND SUPPLYING THE RESULTING HEAT TO THE REACTION ZONE BY INDIRECT HEAT EXCHANGE WITH THE DENSE FLUIDIZED BED SO AS TO MAINTAIN THE BED AT THE DESIRED TEMPERATURE WITHOUT RETURNING THE REMAINING COKE TO THE REACTION ZONE.

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