US2872411A - Method of mixing liquids and solids in a fluidized hydrocarbon conversion process - Google Patents

Description

1959 R. w. KREBS El AL 2,872,411

- -METHOD OF MIXING LIQUIDS AND SOLIDS IN A FLUIDIZED Feb. 3

HYDROCARBON CONVERSION PROCESS Filed June. '8. 1953 v mmZmDm ROBERT W. KREBS |NVENTORS J MES W. B ROwN 2,372,411 Patented Feb. 3, 1.959

METHOD OF MIXING LIQUIDS AND $951533 EN A FLUIDIZED 'HYDROCARBUN CQNVERSKGN PRUQIESS Robert WJKmhs, 'Baton Rouge, lba., and James W.

Brown, "Elizabeth, N. .1 assignors to Essofi leseareh and Engineering Company, a corporation of Deiaware Applicationiiune fi,1953, Serial Nb. 360,392

4*Giairns. cums-457 This invention relates to a process for treating hydrocarbons and more particularly relates to the cracking or coking of heavy residual oils to produce lower boiling hydrocarbons and coke.

The hydrocarbon residual oil which is to be cracked according to the present process'is a high boiling hydrocarbon oil which cannot be vaporized at ordinary pressures without cracking the high boiling constituents. The residual oil -may be that produced by distilling crude petroleum oil at ordinary atmospheric pressure or under Vaporous products of coking are taken overhead and further treated as. desired to recover lower boiling hydrocarbon-fractions. During coking more coke-is, formed and some coke may be withdrawn from the process as product coke. Coke particles from the coking zone or.reactor may be stripped to remove volatile hydrocarbons therefrom. -Some of the stripped coke particles maybewithdrawn as product coke and the rest of the 'cokeparticles.are-..passed.to a burner where they may be maintained in a .dense'fluidized condition and contacted with air or other oxygenrcontaining gas to burn some of the coke particles .and to supply heat :to the coke particles. Or a high velocity transfer line burner may 'be-used. The heated coke particles are then returned to the coking zone to supply heat thereto.

One of theproblems in the fluid coking of residual or other heavy oil ,feeds is the distribution of the heavy residual oil feed on the coke or other inert hot particles in the fluid bed .in the coking zone. In previous work on coking difliculty was experienced when oil was fed in atone side of the reactor. The opposite Wall of the reactor has in some instances coked up because of the impingement of oil feedagainst such opposite wall. The

presentinvention overcomes this problem.

According to the present invention better mixing of the solids and heavy feed oil is obtained and this permits operations at a higher oil feed rate than could otherwise be accomplished :without causing agglomeration of coke particles-.of'the bed or loss of fluidization of the coking bed. According to the present invention there is provided a high-velocity zone outside of or in the dense-fluidized coking zone and the feed oil is injected or introduced into .this region "at one or more places.

inert particles such as coke or thelike. .12 has a level indicated at 14 with a diluteiphase 16 thereinto theupflow leg'or riser'ZZ of U bend 24.

In the invention agglomeration of the coke particles atthe oil feed injection point is prevented by providing a high velocity line for the coke particles and injecting the residual oilfeed-into this high velocity line in which the motion of the coke or other solids isso turbulent that good distribution of the 'oil on the particles is obtained, while at the same time it is diflicult for the particles to stick together because of their momentum at the high veiocity.

In one form of the invention the aeration steam which is to fluidize the lower part of the bed ofsolids in'the coking zone is first used to'obtain high solid flow rates through an external circulating leg into which the residual oil feed is introduced at one or more points. This double use of aeration steam for the feed injection section is one-importantsaving. The circulating leg is preferably a U-bend which is used to withdraw solids from the-coking bed and return them through a dense phase riser -into which the oil feed is introduced. Other'forms of circulating legs may be'used. In addition in some caseshot solids from the burner may be introduced into the riser or upflow leg before the oil feed is introduced.

In another form of the invention, the high velocity zone is created in an internal circulating leg.

In the-drawingz Fig.1 representsdiagrammatically one form of apparatus adapted'for carrying out theprocess of the present inventionusing an external circulating leg;

Fig. 2 represents an enlarged vertical cross section of the-preferred means of introducing oil feed into the circulating leg; and

ig. 3 diagrammatically represents a modified form of apparatus in which-an internal circulating leg is used.

Referring now toFig. l or the'drawing, the'reference character 10 designates a reactor or coking zone containing a fluidized dense bed 12 of solid finely divided The dense bed above. The inert solids of the fluidized bed IZ'have a particles size between about 50 and 600 microns, preferably between about and '40G'microns and may combetween about 800 and 1606 E. or higher. When coking to produce motor fuel such as'gasoline, temperatures in the lower range of about 808 to about l200 F., preferably about 900 to 1108" F. will be used, whereas, when coking at extremely high temperatures to produce chemicais such as unsaturated hydrocarbon gases and aromatic hydrocarbons, temperatures in thc'higher range ofabout 1200 F. to about 1600" E, preferably about 1250 .to 1450'F. will be used.

The preheated oil feed isintroduced through line 18 Riser 22 empties into the bottom portion of reactor it preferably at the lower conical section 25 thereof. Solids from thedense fluidized bed T2 are withdrawn through downflow leg or standpipe 26. The U-bend 24 forrnsan externalsolids circulating means whereby a high velocity zone is provided whereinto the residual oil is fed through one or more points. More than one U-bend may be used if desired but the number is kept small to provide relatively large diameter legs of the U-bend to reduce heat losses and toprovide more mixing volume with less attendant pipe wall surface.

, Aeration steam which is usuallyintroduced into the fluid bed 12 and which is required to fluidize the lower portion of the dense bed 12 is introduced through line or lines 28 above valve or restricted orifice 30 arranged in riser 22. Orifice 30 provides suflicient pressure drop to control the solids circulation within the desired limits. Instead of using orifice 30 a slide valve (not shown) may be used in downflow leg or standpipe 26 to control the rate of flow of solids through the circulating means. The preferred means of control of flow, however, is to control the amount and point of introduction of steam or gas through line 28, line 54- and other lines (not shown) similarly located along the line 22. Valve 30 is then used only as a positive shut-off valve.

The preferred form of introducing the residual oil feed into riser 22 is shown in an enlarged detail in Fig. 2. The upflow leg of riser 22 is preferably provided intermediate to its ends with a constricted zone or Venturi section 32 at which zone the gas velocity and solids velocity are accelerated. The residual oil is introduced near the point of maximum solids and gas velocity. The point or points of oil feed introduction is preferably a short distance or slightly downstream from the first region of maximum constriction and may be slightly downstream from the venacontracta or point of maximum gas velocity at 34.

Oil feed from line 13 is passed to manifold 36 from which the oil is fed through a plurality of nozzles 38, preferably high velocity nozzles. The constricted zone 32 is shown as provided with openings 40 for nozzles 38. By introducing the oil feed at this region of high gas and solids velocity, good distribution of the oil on the solids is obtained due to the turbulent motion of the solids. At the same time the hot particles containing the distributed oil feed do not stick together because of their momentum at the high velocity. The oil feed is well mixed with the hot solids in the riser 22 and the mixture is then introduced continuously into the center of the large dense fluid highly turbulent bed 12 in the reactor 10 as an up-draft stream so that wet solids are kept away from the internal wall of reactor 10 for the maximum length of time and no coking of the oil takes place on the internal wall of the reactor.

By using a relatively long riser line, time is allowed for some cracking to take place in the riser line. This reduces solids holdup in the reactor 10 and at the same time provides more gas in the riser line 22 for aeration of the fluid bed 12 in reactor 10.

If desired, residual oil feed from line 18 may be introduced into riser 22 at more points above and below the constriction 32 as shown at 42 and 44. Injection lines may extend into the solids stream in riser 22, pointing upward so as to keep the high velocity feed jet from impinging on the walls of riser 22. An internal nozzle of this type should be insulated on the outside to keep the metal at feed temperature and thus prevent coking.

manner to a temperature between about 500 and 750 F. before being introduced into the reactor 10. The preheating of the heavy oil is done to reduce the viscosity of the oil feed and render it fluid and also to reduce the heat load in the reactor. The oil feed comprises a residual petroleum oil such as tar, pitch, crude residuum,

heavy bottoms or other similar hydrocarbon stock hav-' ing an API gravity between about -10 and 20, a Conradson carbon between about 5 and 50 wt. percent and an initial boiling point between about 850 and 1200 F. Some steam may be added with the oil feed in line 18 if desired.

The fluidized bed 12 is maintained as such by the upflowing hydrocarbon gases and vapors formed by the coking of the oil feed and by the steam added through line 28 to riser 22. The superficial velocity of the gases and vapors passing upwardly through the bed 12 is between about 0.5 and 5 feet per second when using finely divided coke of about 50 to 400 microns and at a superficial velocity of about 1 to 2 feet per second, the density of the fluidized bed will be about pounds per cu. ft., but may vary between about 30 and 60 pounds per cu. ft. depending on the gas velocity and particular particle size range selected.

Vaporous products of coking leave bed 12 and pass overhead through cyclone separator or the like 56 arranged in the top interior of the reactor 10. The vaporous products contain entrained solids and the separator 56 is used to separate or recover entrained solids and return them through dip leg 58 to dense fluidized bed 12. The separated vapors pass overhead from separator 56 through line 60 for further treatment as by fractionation, condensation etc. to recover desired products.

tandpipe 26 may be provided with one or more aerating or fluidizing lines 62. The bottom of U-bend 24 may be aerated by introducing gas through one or more lines 64.

Returning now to the reactor 10, coke or coked particles are withdrawn from the dense bedas a dense fluidized mixture through line 66 and preferably passed through stripper diagrammatically shown at 68 to remove volatile hydrocarbons therefrom. Stripping gas from the stripper is returned to the reactor.

When more coke is being produced than is necessary to supply heat to the reactor, it can be withdrawn as product coke from line 70 through line 72.

Coke particles from line 70 which are to be burned in the burner diagrammatically shown at 48 are mixed with Constrictions similar to that shown at 32 may be used in riser 22 at these other points of feed injection.

Instead of introducing residual oil feed through line 42, a more refractory oil feed such as cycle oil or condensate oil separated from the products of coking may be introduced through line 46 and line 42 to crack the more refractory oil stock at a higher temperature and also hold it at a cracking temperature for a longer period of time. The temperature of the hot solids in U-bend 24 may be increased by introducing hot solids such as coke particles from burner or combustion zone 4%, later to be described in greater detail, through line 49 and line 50 into riser 22 above valve or orifice 30. Additional hot coke from the burner 48 may be passed through line 52 into down flow leg or standpipe 26 of U-bend 24.

Steam may be introduced into riser 22 above constriction 32 and at line 54 if desired. The amount of steam introduced through line 28 controls the rate of circulation of solids through U-bend 24 as above described.

The'oil feed is preferably preheated in any suitable air or other oxygen-containing gas introduced through line 74, preferably at the inlet of burner 48 which may be a low velocity dense fluidized bed burner or a high velocity transfer line burner to burn coke and raise the temperature of the coke particles to a temperature about 50 to 600 F. higher than that of the particles in the dense bed 12 in the coking zone. The temperature in the burner may be between about 1100 F. and 1600 F. The hot coke particles from burner 48 are passed through line 49 in any suitable manner and some of the hot coke 7 particles are returned through line 73 to the bottom portion of dense bed 12 in the coking zone. The rest of the hotcoke particles from line 49 are passed through lines tributed at the bottom of the reactor 10 either by conventional perforated grid, a packed conical section or a number of open conical inlets. The distribution grid or the like may be omitted, if desired. 2

Referring now to Fig. 3 the @flme reference characters r are used forndesignatrng the parts as in- Fig. 1. Certain parts "have" been omitted from Fig. 3.but thishas been :done merely to simplify the description. In this modificartion an internal recycle means is'used which comprises --a:;=draft--tube=' 82. Drafttube 82 is an open ended 'pipe arrangedvertical with its bottom end 84-spaced above the bottom 25 of reactor and with its open upper end 86 below dense bed level 12 so that the tube 82 is submerged in the dense bed 12.

As shown in the drawing residual oil feed is passed through line 88 and introduced into an intermediate portion of draft tube 82 through one or more nozzles 90 preferably discharging upwardly into tube 82 in the direction of flow of solids through tube 82. Aerating gas such as superheated steam is introduced into tube 82 below the locus of introduction of oil feed. The steam is passed through line 92 and injected into tube 82 through one or more nozzles 94. A high rate of solids circulates from the conical bottom 25 of reactor 10 up through draft tube 82 past the steam injection point 94 and the oil feed nozzles 90.

In the preferred form of draft tube the oil feed is injected into a constricted zone such as a Venturi section as described above in connection with Fig. 1 in riser 22 at 32. As described in connection with riser 22 in Fig. 1, the residual oil may be introduced at a plurality of regions into draft tube 82 in a similar manner. Also if desired more refractory stock may be introduced into tube 82 at a region below that of the introduction of the residual oil feed. The diameter of the draft tube may be varied between about /5 to /2 the diameter of the reactor. When the draft tube is relatively narrow, more gas may be added to result in a higher velocity in the draft tube without exceeding the desired velocities of 3 to 5 ft. per second at the interface 14.

In a specific example about 100 barrels per day of residual hydrocarbon oil having an API gravity of 10, a Conradson carbon of 18 and an initial boiling point of about 1150 F. may be introduced into riser 22 through line 18. The oil is preheated to about 600 F. The temperature in riser 22 and dense bed 12 is 1000 F. and in the burner 48 is 1150 F. About 5 wt. percent of steam on the oil fed through line 18 is introduced into riser 22 through line 28 below the constriction 32. The amount of steam introduced through line 28 may be varied between about 2 and 5 wt. percent on the oil feed. The 5 wt. percent of steam is adequate to produce a solids circulation rate of about 50 solids to oil ratio in riser 22.. With different amounts of steam the solids circulation rate in riser 22 may be varied between about and 80 solids to oil ratio which is two to nine times the solids to oil ratio circulated between the burner and reactor vessels in previous coking processes.

The riser 22 may be between about 10 and 50 feet in length, the longer sizes being preferred to allow time for some cracking to occur in the riser and thus provide more gas in the riser for aeration of the fluid bed 12 and to reduce reactor solids hold up. When using one riser 22 and a circulation of 10,000 lbs. to 25,000 lbs. of coke per hour riser 22 has a diameter between about 0.3 and 0.4 foot and the constriction 32 at its vena contracta is between 0.1 and 0.2 foot. The reactor 10 is between about 1 and 2 feet in diameter and between 10 and 30 feet in height.

In the above example all the hot coke particles from burner 48 were introduced into dense bed 12 from line For a similar size design for the modification shown in Fig. 3 and the same size reactor, the draft tube will be between about 5 and 15 feet in length and between 0.3 and 1 foot in diameter and arranged between about 1 and 5 feet above the bottom 25 of vessel or reactor 10.

about 48 and-80 mesh. The superficial velocity of the gas in the reactor 10 was about 1 ft. per second at the bottom and-the density-of thefluid bed 12 was about 40 lbs. per cubic foot. .The superficialgas velocity in constriction 52 was about 5.0 feetuper second andithesolids to gas ratiorpassingv through .theaconst'riction '32 is about 10 lbs. per cubic foot.

The overhead products from line 60 were quenched to a temperature of about 800 F.

The yields obtained from the above example were as follows:

C wt. percent 6.5

C vol. percent 2.8 C 430 F., vol. percent 15.0 430-650" B, vol. percent 10.7 6501050 B, vol. percent 30.0 1050 F.+, vol. percent 30.0 Coke wt. percent -1 10.0

About lbs. of coke per hour are withdrawn as product coke through line 72.

The above example is given for purpose of illustration only and the invention is not to be restricted thereto as modifications and changes may be made by those skilled in the art without departing from the spirit of the invention.

If it is desired to raise the temperature of the solids in standpipe 26 or riser 22 or to maintain a desired temperature therein, hot particles from burner 48 may be passed through line 52 and/or 50.

This invention is capable of feeding residua or residual oils which contain large amounts of solids such as coke or sediment which would plug the conventional spray type nozzle. Larger amounts of slurry oil containing solids may be returned to the unit to compensate for loss of coke fines from the coking unit.

What is claimed is:

1. A process for thermally cracking heavy hydrocarbon oils which comprises contacting hydrocarbon oil containing extremely high boiling constituents with inert solids in a dense fluidized highly turbulent bed of finely divided solids in a cracking zone maintained at a temperature between about 800 and 1600 F. to produce lower boiling hydrocarbons While depositing coke on the solids, removing inert solids from said dense bed and passing them first downwardly and later upwardly as a high velocity solids stream through a recycle passageway extending below said dense bed, introducing heavy hydrocarbon oil into the rapidly flowing solids stream contained in the vertical upflow portion of said passageway at a point thereof which is constricted in diameter, introducing a gas into said upflow portion of said passageway below the region of introduction of oil to increase the velocity of gases and solids passing therethrough and in part thereto a high turbulence, passing the resulting mixture into the bottom portion of said fluid dense bed, removing solids from said cracking zone and passing them through another conduit to a combustion zone for contact with an oxygencontaining gas to burn coke and heat the solids particles to a temperature above that existing in the cracking zone, returning at least part of the heated solids from said combustion zone to said dense fluidized bed in said cracking zone to supply heat thereto and removing hot vaporous reaction products leaving said dense fluidized bed overhead.

2. A process as defined in claim 1 wherein at least another part of the heated solids from said combustion zone is passed to said upflow portion of said passageway.

3. A process according to claim 1 wherein said constricted region comprises a Venturi section.

4. The process of claim 1 in which the vertical upflow portion of said passageway is of sufficient length so as to permit some cracking to take place therein.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Schdnberg Nov. 10, 1931 Clarke Aug. 10, 1943 5 Munday July 10, 1945 8 Kubicek Oct. 30, 1945 Gohr Dec. 13, 1949 Odell June 19, 1951 Nicholson Nov. 8, 1955 Krebs Jan. 24, 1956 OflFut May 1, 1956

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