US2885272A - Apparatus for fluid bed coking of heavy oils - Google Patents

Description

y 5, 1959 t c. N. KIMBERLIN, JR., E-rA 2,885,272

APPARATUS FOR FLUID BED COKING OF- HEAVY OILS Filed Oct. 7. 1953 Charles N. Kimber/in Jr Clark E. Adams .Jo/ Mose, J: Inventors L/ndsa Griff/n Jr By hWAIMrnEy Patented May 5, 1959 APPARATUS FOR FLUID BED COKING OF HEAVY OILS Charles N. Kimberlin, Jr., Clark E. Adams, John F. Moser, Jr., and Lindsay I. Griflin, Jr., Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application October 7, 1953, Serial No. 384,574

3 Claims. (Cl. 239-284) The present invention relates to the injection of heavy oils into fluid bed conversion systems such as coking apparatus and the like. The invention has particular application to a feeding system for the conversion of heavy viscous residual oils such as crude oil residua and the like to more volatile products.

In the prior art various systems have been proposed for converting heavy residual oils by coking to produce lower boiling components and coke. Thus, it has been proposed that the heavy petroleum residua may be converted to gasoline, gas oil, etc., with some degradation to coke, by heating the oil for a predetermined period of time to a temperature between about 800 and 1100 F., more or less. One of the most practical processes which has been proposed for this purpose is a fluid bed coking process, wherein the oil is introduced into a fluidized bed of preheated solid particles. The hot particles are prefera-bly catalytically inert and may consist of sand, glass beads, metal shot, and various other materials having suitable heat transferring characteristics. Finely divided particles of coke derived from the petroleum residua itself are frequently preferred because they are produced in the process and are of relatively low economic value. However, the other materials mentioned may be used quite satisfactorily when desired.

A major problem in the use of beds of fluidized solid particles as heat carrying media has been to obtain a uniform dispersion of the heavy oil feed throughout the bed. Petroleum residua are usually highly viscous. During their conversion by thermal cracking and due to the boiling off of the more volatile constitutents they become progressively more viscous and tacky. As a result, whenever relatively large droplets of such material are introduced into a mass of solid particles, considerable agglomeration takes place. Particles of the solid material, for example coke particles of the preferred size range of about 20 to 400 microns average particle diameter, become cemented or secured together by the viscous residue to form relatively large agglomerate particles. If this agglomeration continues a point is soon reached where the fluidized bed ceases to be fluid and bogs down. This may result in complete shutdown of the apparatus, requiring that is be opened up and cleaned out before operations can be resumed. Since operations of this character are usually carried out in large scale apparatus .such a shutdown is a very expensive procedure resulting in considerable economic losses.

I Agglomeration can be reduced and sometimes eliminated by adopting a very slow feed rate so that the agglomerated particles are burned and broken up at least .as fast as they are formed. With ineflicient feed systems, however, this results in low throughput and consequent .low operating efliciency. Hence an object of the present invention is to obtain better feed dispersion on or among ,the solid particles which comprise the fluid bed. When this is accomplished higher operating rates can be tolerated without undue agglomeration or bogging down of the fluid bed and the whole process is thus made considerably more eflicient.

According to the present invention it has been found that oil feed may be more efflciently supplied to a fluid bed by introducing the oil into a region wherein the solid particles are somewhat more disperse and moving more rapidly than in the average section of the fluid bed. To accomplish this a special zone of relatively rapid solids movement and relatively dispersed particles is set up within the bed. The feed is introduced into this special zone so as to be distributed more evenly upon the solid particles therein and substantially reduce the agglomeration and bogging tendencies described above. The relatively dispersed particles permit more even feed distribution. The invention will be more completely understood by reference to the attached drawings wherein two embodiments, each comprising a fluidized bed of solid particles in a suitable reactor, are shown. In both, arrangements are included for a special zone within the fluid bed designed to take care of the eflicient distribution of the viscous oil feed on the solid particles which comprise the bed. Fig. 1 shows a system wherein preheated solids are introduced from an external source and Fig. 2 shows a system wherein the solids may be heated in the same vessel, if desired.

Referring now to Fig. 1 of the drawing, there is shown diagrammatically a reactor 11 containing a mass of solid particles of fluidizable size range, for example, from 20 microns or less up to /8 inch average particle diameter or more. A bed of these solids, fluidized in a conventional manner, is indicated at 13 with an upper level at 15. Fluidizing gas is introduced at one or more inlets such as 17 at the bottom of the reactor. Depending upon the amount and velocity of the fluidizing gas, the level 15 of the top of the bed may rise or fall within certain limits as is well understood in the art. Air or oxygen may be used as the fluidizing gas Where it is desired to heat the bed in vessel 11 directly, but this is not usually preferred in this embodiment. Fluidizing gas is preferably an inert gas such as steam, carbon dioxide, nitrogen or the like. Steam is usually preferred because it is readily condensed and separated from the products formed in the coking operation. Additional aeration gas which may be steam or other inert material may be introduced through additional inlets such as 19. The solid particles of coke, sand or the like, are usually preheated in a separate zone or a separate vessel and introduced into vessel 11 in any suitable manner. They may be brought in at the top or at the bottom in ways which are well understood in the art. In some cases they may be brought in through side openings in the reactor 11. After they have performed their function, or have become cooled to such a degree as to reduce their effectiveness as heat carriers, they may be withdrawn through conduit means not shown and returned to a heater or 'burner as is well understood in the art.

It will be understood that the fluidized bed of solids 13 is normally quite dense. Its density may vary, depending upon the type of solid particles used and the degree of aeration employed. The apparent density of such a bed may vary from as little as 20 pounds per cubic foot up to as much as 50, 60 or even more. In any case, the usual fluidized bed is too dense to permit injection of a spray of liquid such as preheated residuum over any appreciable area. Thus the solid particles near the outlet of a feed nozzle or jet usually receive much more of the feed than the particles more remote from that point. This is one of the major causes of agglomeration and bogging in the average fluidized coking bed. In the present invention a zone of relatively disperse solid particles is established within a fluidized bed by setting therein a deflecting or flow directing tube which is open at both ends, indicated at 21. This tube, which may be called a draft tube, is so located as by supporting means 22 that its lower end is well above the bottom of the fluid bed which, in the present instance, is supported upon a perforate partition or grid 23. The upper end of the tube 21 likewise is usually kept below the upper level 15 of fluid bed 13. In other words, the tube 21 is preferably completely immersed within the fluid solids bed with both of its ends covered by mobile fluidized solids. This arrangement provides for a high velocity, low density zone within draft tube 21 and a low velocity, high density zone in the expanded section above draft tube 21.

In some cases, for example when coking at higher temperatures above about 1100 F. for the production of olefinic and aromatic hydrocarbons for chemical use, it may be desirable to extend the upper end of draft tube 21 to the upper level 15 of bed 13 or even slightly higher. This avoids over-cracking by long contact in a low velocity, high density zone above draft tube 21.

In order to disperse the feed and also to spread out the particles of solid material within the draft tube 21 a conduit 25 is provided with one or more openings at its upper end 27. The upper end 27 is inserted into the lower end of draft tube 21. A stream of the oil to be fed to the reactor is brought into the conduit 25, preferably preheated to a temperature below thermal cracking temperature, but high enough to permit ready atomization. A preheat temperature between about 300 and 750 F. is usually preferred, a temperature between 500 and 700 F. being especially preferred. Along With the feed there is introduced a stream of atomizing gas in this embodiment of the invention. Such a gas may be steam or other inert gas such as carbon dioxide or nitrogen although hydrocarbon gases or hydrogen may also be introduced if desired. The use of such an atomizing gas is not always absolutely necessary since the forcible spray of the feed itself through nozzle 27 tends to create a draft upwardly through the tube 21. Gas or vapor velocity should be suflicient, however, to result in a dispersion or super-fluidization of solid particles within the draft tube. Usually an auxiliary gas is required to obtain satisfactory dispersion of the solid particles within the draft tube.

It will be understood that as the jet of feed, with or without the atomizing gas, is introduced into the draft tube a circulation of the fluidized solids is promoted from the bottom of the draft tube up through the tube and over its upper end. This provides a continuous flow of oil coated particles from the draft tube into the upper area of the fluid bed.

By injecting the feed onto relatively dispersed particles in the draft tube a more uniform coating of the particles is achieved. As the coated particles emerge from the top of the draft tube they are mixed immediately with the major mass of fluidized solids in the upper portion of bed 13. The ratio of feed to solids is such that the bed as a whole remains relatively dry. Within the tube itself the velocity of the solid particles is substantially greater than outside of the tube. As a result, little or no agglomeration takes place within the draft tube. The time of coking within the vessel is adjusted depending upon the type of conversion desired, the temperature of the bed, and the nature of the feed stock. Thus, the average residence time may vary from only a second or two to as much as several minutes in various types of coking conversions. When conversion is completed the gaseous and vaporous coker products along with the fluidizing and aeration gases, etc. pass upwardly out of the bed 13 into a cyclone separator 31 having a solids return line 33 and an overhead product outlet line 35. Entrained solids are separated and returned to the fluid bed whereas the vapor and gaseous products are .4 taken into suitable condensing or fractionation means, or to other recovery equipment not shown.

As indicated above, it is preferable to add some gas to the atomizing nozzle 25,27. However, at high temperatures there is suflicient cracking of the feed taking place to supply the gas velocity needed to induce solids circulation through the draft tube. Experiments in a small scale apparatus showed that the introduction of feed in this manner could be carried out very successfully. When a draft tube was used the operating time in hours before the bed became bogged due to agglomeration was very materially extended as indicated in the following data. Sand of mesh size 35 to was used as the fluidized heat transfer solids and the bed was operated at a temperature of 1100 F. A heavy residual feed stock obtained from a large Eastern United States refinery was employed as the feed. Other data are listed in the table.

TABLE I Comparison operation with and without draft tube in identical c.f.s. unit laboratory pilot plant 1 Run voluntarily terminated.

For a large scale apparatus, particularly in an apparatus having a fluidized bed of large diameter, it is desirable to introduce the feed at several points and for this purpose a plurality of draft tubes and injection nozzles may be required. The invention contemplates the use of such a system as will provide for eificient feed distribution and minimum agglomeration and bogging of the bed. It will be understood that various modifications may be made as will be apparent to those skilled in the art.

Referring now to Fig. 2 of the drawing, there is shown a somewhat diiferent form of the invention, utilizing the principle of creating a relatively sparse solids zone within the fluid bed and feeding the residuum into this zone to obtain more uniform dispersion. A reactor vessel 51 is adapted to hold a fluidized bed 53 of preheated solid particles, such as coke introduced at any suitable point, and fluidized by an upflowing gasiform fluid at a velocity of 0.5 to 5 ft. per second. Such a fluid, e.g. air or steam, may be introduced through an inlet 55 and distributor 57. Solid particles may be brought in with this stream of fluid. Air may be introduced with or in lieu of steam to cause partial combustion of the coke, when it is desired to add heat to the reactor.

A draft tube, shown in two parts which are a lower section 59 having a flared upper end 61 and an upper section 63, is supported firmly within vessel 51 in any suitable manner so as to withstand the churning motion of the fluid bed 53. The top of the tube section 63 is preferably substantially below the normal upper surface 65 of bed 53 though it may approach this surface or extend above it under some circumstances.

Reduced crude oil to be coked is introduced through an inlet line 67 having an upturned nozzle 69 at its inner end to spray the feed upwardly inside the upper draft tube 63. The oil is preferably preheated to a temperature below coking temperature, e.g. to 300 to 800 F. It is also brought in under suflicient pressure to spray forcibly upward. The heat in the coking zone rapidly vaporizes the feed, producing a strong upwardly flowing current of gaseous hydrocarbons. This current causes an active flow of the coke particles so as to disperse them comparatively sparsely within the draft tube, causing circulation of the coke upwardly inside the tube and downwardly outside of it,. as indicated by the arrows 71, 73, 75, 77.

Part of the solids reenter the upper section by passing within the flared portion 61 of the lower tube, but part circulate down completely around and up through the latter.

By adding air at the bottom, the coke particles may be partly or fully heated in the reactor vessel to supply the heat requirements. In this case the circulation, as controlled by the draft tube, tends to establish a temperature gradient in the bed. The hot solids at the bottom mix with the solids at the top but this mixing is impeded somewhat by the counter flow of the solids through the gap between the upper and lower draft tubes. In this way, solids may be heated at the bottom and gradually fed into the upper coking level. However, as indicated above, the solids may be partially or entirely heated outside the reactor if desired.

Since coke is formed faster than it is consumed, in most cases, product coke may be withdrawn through an outlet 81 controlled by a valve 83 to keep the system in balance. Where extraneous heating is required, part of the coke from line 81 may be recycled to a heater or burner, not shown, and returned through line 55.

An auxilary fluid, such as steam, is preferably introduced through a line 85 to flow upwardly inside the draft tube system, and the velocity of this fluid will help control the dispersion and rate of circulation of the solids within the reactor. In some cases this fluid may not be required. Water may be injected, and converted to steam, instead of supplying preformed steam, where the thermal balance permits.

Stripping steam may also be introduced through a line 87 to strip coke flowing out through line 81. The usual cyclone 89 may be provided for separating solids from the efiluent vapors and gases which flow out through an outlet 91. A solids return line 93 extends into the bed 53 from cyclone 89.

It is believed that the operation of the system will be obvious from the above description. Coking takes place as a result of contact of the feed with the solid coke particles. Because the particles are relatively sparse within draft tube 63, a more uniform dispersion may be obtained than in a more dense part of the bed. Any liquid deposited on the inner walls of draft tube 63 is quickly cleaned off by the vigorously upflowing solids which pass through this tube. The interposition of steam or water through line 85 tempers the upflowing hot particles and stabilizes the temperature in the upper part of the bed where coking takes place.

Obviously, sand, spent catalyst, shot, beads, and other solid particles may be used in either of the systems illustrated in lieu of coke. The latter is usually preferred, however, because it is a product of the process and because it can be burned or partially burned, without extraneous fuel, to provide the needed heat of reaction. Alternatively, extraneous fuel such as gas or torch oil, etc., may be used with or in lieu of the coke, to supply heat requirements.

What is claimed is:

1. An apparatus including a reactor for contacting a heavy oil feed and solids, said reaction vessel being adapted to contain a relatively dense fluidized solids mass therein, solids separation means positioned in the upper portion of said vessel above said fluidized solids mass, draft tube means internally positioned within the center portion of said reaction vessel for circulating solids within said vessel, said draft tube means extending upwardly from the lower portion of said reaction vessel and terminating substantially below said solids separation means in the upper portion of said vessel, said draft tube means having unobstructed, open-ended bottom and top terminal portions of substantially equal free cross section, said draft tube means comprising two alined tubular sections with the upper section being arranged in the upper portion of said vessel and said lower section being arranged in the bottom portion of said vessel and spaced from said upper portion, the upper end of said lower section being flared outwardly and of a larger diameter than said upper section, means for introducing oil into said draft tube means at a point above the lower end of said draft tube means to contact and mix the oil with dispersed solids flowing upwardly through said draft tube means, means for introducing gasiform material into said draft tube means whereby solids are passed upwardly through said draft tube means and downwardly around said draft tube means for recirculation through said vessel and between the surrounding dense fluidized solids and the interior of said tubular sections.

2. An apparatus as defined in claim 1 wherein said means for introducing oil includes a pipe extending into the lower portion of said upper section and includes an upturned nozzle at its inner end to spray the oil feed upwardly inside said upper tubular section.

3. An apparatus as defined in claim 2 wherein said means for introducing said gasiform stream includes a pipe extending into the lower tubular section to aid in the circulation of solids through said draft tube means.

References Cited in the file of this patent UNITED STATES PATENTS 2,445,328 Keith July 20, 1948 2,597,346 Lefier May 20, 1952 2,606,144 Lefrer Aug. 5, 1952 2,687,992 Leifer Aug. 31, 1954 2,780,586 Mader Feb. 5, 1957

Claims (1)

1. AN APPARATUS INCLUDING A REACTOR FOR CONTACTING A HEAVY OIL FEED AND SOLIDS, SAID REACTION VESSEL BEING ADAPTED TO CONTAIN A RELATIVELY DENSE FLUIDIZED SOLIDS MASS THEREIN, SOLIDS SEPERATION MEANS POSITIONED IN THE UPPER PORTION OF SAID VESSEL ABOVE SAID FLUIDIZED SOLIDS MASS, DRAFT TUBE MEANS INTERNALLY POSITIONED WITHIN THE CENTER PORTION OF SAID REACTION VESSEL FOR CIRCULATING SOLIDS WITHIN SAID VESSEL, SAID DRAFT TUBE MEANS EXTENDING UPWARDLY FROM TJE LOWER PORTION OF SAID REACTION VESSEL AND TERMINATING SUBSTANTIALLY BELOW SAID SOLIDS SEPERATION MEANS IN THE UPPER PORTION OF SAID VESSEL, SAID DRAFT TUBE MEANS HAVING UNOBSTRUCTED, OPEN-ENDED BOTTOM AND TOP TERMINAL PORTIONS OF SUBSTANTIALLY EQUAL FREE CROSS SECTION, SAIDF DRAFT TUBE MEANS COMPRISING TWO ALINED TUBULAR SECTIONS WITH THE UPPER SECTION BEING ARRANGED IN THE UPPER PORTION OF SAID VESSEL AND SAID LOWER SECTION BEING ARRANGED IN THE BOTTOM PORTION OF SAID VESSEL AND SPACED FROM SAID UPPER PORTION, THE UPPER END OF SAID LOWER SECTION BEING FLARED OUTWARDLY AND OF A LARGER DIAMETER THAN SAID UPPER SECTION, MEANS FOR INTRODUCING OIL INTO SAID DRAFT TUBE MEANS AT A POINT ABOVE THE LOWER END OF SAID DRAFT TUBE MEANS TO CONTACT AND MIX THE OIL WITH DISPERSED SOLIDS FLOWING UPWARDLY THROUGH SAID DRAFT TUBE MEANS, MEANS FOR INTRODUCING GASIFORM MATERIAL INTO SAID DRAFT TUBE MEANS WHEREBY SOLIDS ARE PASSED UPWARDLY THROUGH SAID DRAFT TUBE MEANS AND DOWNWARDLY AROUND SAID DRAFT TUBE MEANS FOR RECIRCULATION THROUGH SAID VESSEL AND BETWEEN THE SURROUNDING DENSE FLUIDIZED SOLIDS AND THE INTERIOR OF SAID TUBULAR SECTIONS.

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