US2700642A

US2700642A - Coking of heavy hydrocarbonaceous residues

Info

Publication number: US2700642A
Application number: US225096A
Authority: US
Inventors: William J Mattox
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1951-05-08
Filing date: 1951-05-08
Publication date: 1955-01-25
Anticipated expiration: 1972-01-25

Description

Jan. 25, 1955 w. J. MATTox 2,700,642

COKIN@ oF HEAVY HYDRocARBoNAcEoUs REsInuEs Filed May s, 1951 a sheets-sheet 1 I o 2 g u1 u v J (D s@ G d O l D, d d Ln l -H ci T 3L; L0 f' J l 23 o f1 l :o 4 o L0 Ln l el O 3 2 K l v d l 'I5 i il l q) 4J i Q m; m L 0J lLl l @l y 0 l o f QJ@ e' COKING OF HEAVY HYDROCARBONACEOUS REASIDUES Filed May 8, 1951 2 Sheets-Sheet 2 G ILAQLED IZODLJCTS Excess @ons Am: FLUE GAS 'llasmuum 2 FEED j TIzANsi-al LNE. (ZO burma?. @Hem-EL FHL-2 Jillian? mattox {Srzvenbor had# Clbborrze .expansion coetcient.

'carriers are usually highly adsorptive.

United States Patent@ COKING F HEAVY HYDROCARBONACEOUS RESIDUES .William J. Mattox, Baton Rouge, ard Oil DevelopmentCompany, .ware

La., assignor to Standa corporation of Dela- The present :invention Irelates to a method of treating hydrocarbons. More particularly, the invention pertains to a method of upgrading heavy hydrocarbon materials, such as topped or reduced crude, asphalt, pitch or similar heavy residues to produce more valuable, lower boiling oils including gas oils suitable as feed stock for catalytic cracking, gasoline, lunsaturated and aromatic hydrocarbons suitable for use as chemicals or starting materials therefor, etc., as well as coke. Briey, the invention provides for contacting the residuum feed at coking conditions with a mass of linely divided .solids having a substantially higher thermal coeicient of expansion than the coke formed in the coking reaction and subjecting these solids carrying coke deposited thereon to temperature changes conducive to a disintegration of the coke layer Vby,a change in `size of the supporting solids particle having the higher thermal .Heretofore, heavy residues of the type specified, particularly atmospheric or ,vacuum crude distillation residues have been `subjected to coking at relatively severe conditions for the production of motor.fuels, heat ing .oil and gas oils. The coke produced in Vthis reaction is more than sufficient to supply `by combustion the heat requirements of the process. On the otherhand, complications arise from excess coke deposits on the walls of the coking zoneand in transfer linesrequ iring frequent .interruption for the purpose of `cleaning out the coke. To alleviate these diiculties subdivided, inert, adsorbent solids such as coke,.pumice, sand, or the like have been added to the residuum feed to serve as a carrier material forthe coke and asa scouring agent preventing cokedeposition on the equipment walls. The coke deposited on these solids may be burnt olf incyclic or continuous fashion to regenerate the solids and to supply-the heat required for coking.

While moving bedand-suspensoid type systems have been proposed for thistype of operation, the s/o-called iiuid solids technique offers greatest advantages ,with respect to temperature control, heateconomy, ease and continuity of operation aswell as equipment dimensions. .This technique involves the injection of the feed into a relatively `dense highly turbulent bed kof hot subdivided solids ranging in size from about 30 to about 400 mesh. Fluidization is accomplished by gases and vapors flowing kupwardly through the bedat a linear superficial velocityofabout 0.3-3 ft. per second to give the bed the appearance of a boiling liquid. Volatile coking products are removed overhead while coke-carrying solids maybe withdrawn directly, from theuidizedbed, reheated in `aseparate Cokefburningzone.Operated at a temperature above coking temperature and `returned to the coking zone for heat supply.

.While this technique atfordsconsiderable thermal and procedural advantages over othersystems, its adaptation to commercial scale operation has been impeded by various diiculties. The solids used as coke andheat The result 4is that valuable, volatile coking products are adsorbed by the solids and lost in the reheating zone by combustion. When non-adsorptive solids are used in a conventional manner the utility of the'product vcoke as 'a fuel or 'for other purposes is considerably reduced. Furthermore, since more coke is produced in the coking reaction than is required for heat generation, ,coke accumulates on the solids particles to vincrease their size, necessitating continuous or intermittent grinding of the solids to maintain their uidizable size. The present inventionovercomes these diculties and affords various other advantages as will appear hereinafter.

It is, theerfore, the principal object of the present invention to provide an improved process for coking hydrocarbonaceous residues in the presence of subdivided solids serving as cokecarriers. Other and more specific objects will appear from the following description of the invention wherein reference will be made to the accompanying drawing in which Figure l is a semi-diagrammatical illustration of a system adapted to carry out an embodiment of the invention; and

Figure 2 is a similar illustration of a system applying the process of the invention to a somewhat modified type of operation.

-In accordance with the present invention, heavy hydrocarbonaceous residues are contacted at coking conditions with a dense, turbulent uidized mass of finely divided metallic carrier solids which have a density and thermal coei'licient of expansion substantially higher than those of the coke vdeposited thereon. Coke deposited on these solids in the course of the coking operation is removed by subjecting the coked solids to a temperature change of sulicient magnitude to break up the coke layer as the result of the difference in contraction or expansion of the coke and the supporting solids. The broken coke separates from the solids particles in the form of a loose nely divided material which may be removed from the carrier solids to any desired extent by elutriation, centrifugal separation or similar means. If desired, the carrier solids of the invention may be chosen to exert a catalytic effect in the coking lreaction by promoting desulfurization or conversion into particularly desirable products, such as aromatics or other reactions, for example, iron and its alloys act as desulfurization catalysts while copper and its alloys have aromatization activity.

When operating in accordance with the invention, carry-over of volatile coking `products into the coke-burning zone by adsorption on the carrier solids is practically eliminated'because of the low surface area of the carrier solids involved. The original size of the carrier solids may be retained without a special grinding stage. Excess coke may be recovered in pure form Iand in a state of subdivision increasing its utility as lamp black. as a powdered fuel and for various other purposes. The removal of the coke from the mass of carrier solids may be readily so Yconducted as to leavevsuiicient coke admixed with, and/or adhering to, lthe carrier .solids forlthe pur.- pose of generating by coke combustion the heatrequired by the coking reaction.

The thermal coefficient of expansion ofthe `carrier solids should be at least twice, and preferably at least three times, that of the coke within the temperature range involved in the temperature change used for breaking up the coke layers. .When using suchsolids, temperature changes of about 50-300 F. are suitable for lthe purposes of the invention. Frequently'such changes occur in the normal operation of continuous coking operations involving solids circulation between coking and coke-burning'zones. In other cases, 'temperature changes of this magnitude maybe incorporated without seriously affecting 'the heat balance of` the systems.

In illustration vofv the type of carrier solids useful for the purposes of the invention, a number of metals land alloys are listed below together with their thermal expansion coeicientsat the temperatures of determination, as compared withcarbon. H owever, thelinvention is notlimited to the solids listed.

of thermalv expansion of carbon and [Increase in length/unit lengthl 0.]

The thermal expansion coeicient of metals generally increases with increasing temperatures while that of carbon is littleaiected by temperature variations. It will be seen, therefore, that all carrier solids listed above have coefiicients at least about three times that of carbon within the temperature range of, say, about 800-1300 F. normally associated with coking operations. Of these solids, copper or brass and 20% Ni steel are generally preferred, the former because of their catalytic effect favoring coke desulfurization and the formation of highly aromatic cokng products, the latter because of its combination of high density with a high expansion coeicient.

Carrier solids of the above or similar type may be used in the form of spheres, oval, rod-shaped or irregularly shaped particles having a size of about 50 microns to about 1A inch diameter, sizes of about 200-1000 microns being preferred to permit fluidization at gas velocities of about l-S ft. per second in commercially practical reactors and to facilitate separation from the broken up coke particles. In order to enhance coke disintegration in the separation phase, the latter is-preferably carried out with the solids in a highly turbulent fluidized state conducive to the rapid disintegration of the broken coke.

-Having set forth its objects and general nature, the invention will be best understood from the following more detailed description of specic embodiments read with reference to the drawing.

Referring now to Figure 1 of the drawing, the system illustrated therein essentially comprises a fluid-type coker 5, a centrifugal-type separator or cyclone 21, and solids reheater or burner 30. The functions and coaction of these elements will be forthwith described using the production of highly aromatic oils by coking reduced crude as an example. It will be understood, however, that this may be used in a generally analogous manner for coking operations of different types.

In operation, a heavy residual oil such as bottoms from van atmospheric or vacuum crude still may be supplied at still temperature to line 1 wherein the oil is mixed with hot ycarrier solids supplied from a conventional aerated standpipe 3 at a temperature of about l350l400 F. as will appear more clearly hereinafter. The carrier solids, which maybe supplied through line 3 at a rate of about 2-40 weights/wt. of residuum, are preferably spheroidal particles vof copper or brass having a particle size of about 200-1000 microns diameter. The oil feed is partially vaporized upon contact with the hot carrier solids and the mixture of vapors, liquid oil and solids is passed to a lower portion of coker 5 through a suitable distributing device such as grid 7. Additional uidizing medium such as steam, hydrocarbon gases or vapors, etc. may be added via line 9 and, if desired, together with the feed through line 1. The temperature in coker 5 is preferably maintained at about l2001250 F. suitable for coking. The solids in coker 5 are maintained in the form of a dense turbulent mass M5 uidized by the upiiowng gases and vapors to resemble a boiling liquid having a definite interface L5 and an apparent density of about 80-150 lbs. per cu. ft. Linear superficial gas velocities within mass M5 of about 2-5 ft. per second are suitable for this purpose. At' the conditions vspeciiiedthe oil feed is converted into high yields of naphthav and higher boiling range products rich in aromatic constituents while about 'on `the carrier particles.V

10-15 wt. per cent of coke based on feed is deposited Volatile coking products are withdrawn overhead from lever L5 to be passed via line 11 to conventional product recovery equipment (not shown), if desired after separation of entrained solids and/or coke in cyclone separator 13 provided with solids return pipe 15.

Carrier solids coated with coke may be withdrawn from mass M5 (substantially at the rate of solids supply through line 1) through a conventional standpipe 17 aerated and/or stripped through one or more taps t. At least a major proportion of the solids in standpipe 17 is discharged into line 19 wherein they are picked up and quenched to a temperature of about 800-850 F. by steam or any other relatively inert gas of suitably low temperature. A 'dilute suspension of solids-in-gas is formed in line 19 and passed to separation stage 21 which may have the form of a conventional cyclone separator of relatively low efficiency. As the result of the considerable temperature drop from the temperature level of coker 5 to that of quench line 19, the carrier particles undergo a contraction of greater magnitude than that of their coke layers, thereby cracking vthe latter. The cracked-up coke is further disintegrated in cyclone 21 due to frictional forces, so that most of the coke may be removed through line 23 as entrainment in quenchy gas to be recovered therefrom in any suitable manner, for instance by a filter, electrical percipitator or the like.

Carrier solids 'usually containing suicient coke to maintain the heat balance of the process are withdrawn from separator 21 via standpipe 2S or the like and passed to line 27 supplied with air. A dilute suspension of solids in air is passed through grid or similar distributing device 29 into a lower portion of burner 30 to form therein a uidized rnass Mao having an interface L30 in a manner` similar to M5. Combustion in mass M30 is'preferably so controlled that the carrier solids are heated to about l3501400 F. and substantially all the carbon is consumed. Flue gases are removed via line 32, if desired, after separation of entrained solids in cyclone 34 provided with dip-pipe 36. Reheated carrier solids substantially free of coke are returned to line 1 through standpipe 3 aerated and/ or stripped via taps t, as described above. If desired, separator 21 may be so operated that less coke than that required for heat generation is withdrawn through line 25. In this case, a suitable proportion of the cokecarrying solids in standpipe 17 may be passed directly via line 38 and air lines 40 and 27 to burner 30. The temperature differential between coker 5 and burner 30 is sucient to break up the coke layers whereby coke combustion is enhanced.

An operation in which expansion rather than contraction of the carrier solids is relied upon for coke separation is illustrated in Figure 2 of the drawing. This svstem, which comprises a fluid-type coker 205, a transfer line burner 220, and a separator 222 will be described in connection with an essentially thermal coking of a crude residuum. However, other analogous applications may occur to those skilled in this art.

Referring now in detail to Figure 2, the residual oil feed may be charged through line 201, admixed with hot carrier solids supplied from standpipe 203 and passed through grid 207 to Coker 205 wherein a uidized mass M705 having a levelLzosl isv formed with the aid of uidizing gas supplied through line 209, substantially in the manner described with reference to analogous elements of Figure l. However. in the case of the system of Figure 2 a 20% Ni steel is preferablv used as the carrier solid which mav he supplied to line 201 at a temperature of about l250l350 F. to maintain mass Mons at-a coking temperature of about 975-1025 F. Volatile coking products are recovered via line 211 after passage through cvclrme 213 provided with dio-pipe 215. similarly as described with reference to Figure l.

Coke carrying solids withdrawn through aerated standpipe 217 are suspended in air in line 218. The suspension formed may be passed upwardly throughl a transfer line burner 220 at a superficial linear gas velocity of about 5-15 ft. per second conducive to hindered settling and high turbulence of solids at an apparent density of about 20-50 lbs. per cu. ft. The temperature in burner 220 may be about l250-l350 F. providing a sufficient temperature differential kkover the coker temperature to permit rapid crack-up of the coke deposited on the steel particles.

At the conditions specitied, only about 1,40-1/3 of the coke formed in coker 205 is burned in burner 220 to supply the heat requirements of the process.

Flue gases containing entrained carrier solids and broken up excess coke discharge into cyclone separator 222 in which further coke disintegration to a line powder takes place. This line coke powder is completely entrained by the ue gas withdrawn through line 225 and may be recovered by filtering or by electrical precipitation. Carrier solids free of carbon may be returned via standpipe 203 substantially at the temperature of burner 220 as described above.

While in the foregoing description reference has been made chiefly to fluid-type coking which is the preferred embodiment of the invention, it is noted that the invention has a more general applicability. Substantial advantages may be secured by using the carrier solids of the invention in slurry type, moving bed, transfer line or suspensoid coking system, and even in ixed bed operation, as will be understood by those skilled in the art. The invention may also be applied to other processes involving the deposition of coke, particularly to other catalytic hydrocarbon conversions, in a generally analogous manner.

Other modifications within the spirit of the invention may appear to those skilled in the art.

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

What is claimed is:

1. The process of coking heavy residual oils in the presence of subdivided solids, which comprises contacting heavy residual oil at a coking temperature in a coking zone with a dense, turbulent, lluidized mass of small metallic carrier solids having a thermal coeicient of expansion at least twice that of coke, whereby said oil is cracked and a coke layer is deposited on said solids, recovering volatile cracking products from said coking zone, passing coked carrier solids to a thermal treating zone, subjecting said coked carrier solids in said treating zone to a change in temperature of sucient magnitude to cause a substantial change in the particle size of said carrier solids as the result of said high thermal expansion coeicient, whereby said coke layer is cracked to form coke fragments, separating said solids from said fragmented coke, recovering coke so separated, reheating said carrier solids by combustion of the residue of the coke formed in said process to a temperature exceeding said coking temperature and returning said reheated carrier solids to said coking zone.

2. The process of claim 1 in which said solids are selected from the group consisting of copper and brass.

3. The process of claim 1 in which said solids comprise nickel steel.

4. The process of claim l in which said temperature change is a temperature reduction of about 50-300 F.

5. The process of claim 1 in which said temperature change is a temperature increase of about 50-300 F.

6. The process of claim 1 n which said solids have a particle size of about 200-1000 microns.

The process of coking heavy residual oils in the presence of subdivided solids, which comprises contacting heavy residual oil at a coking temperature in a coking zone with a dense, turbulent, iiudized mass of small spheroidal metallic carrier solids having a thermal coeicent of expansion at least three times that of coke, whereby said oil is cracked and a coke layer is deposited on said solids, recovering volatile cracking products from said coking zone, separately withdrawing coked carrier solids from said coking zone, cooling said withdrawn carrier solids to a temperature about 50-300 F. below said coking temperature, whereby said layer is cracked to form coke fragments, subjecting said solids and coke fragments in a separation zone to a centrifugal motion to separate carrier solids from coke, recovering separated coke from said separation zone, passing separated carrier solids from said separation zone to a heating zone, burning coke produced in said process in said reheating zone in contact with said carrier solids to reheat the latter to a temperature higher than said coking temperature, and returning carrier solids so reheated to said coking zone substantially at said higher temperature.

8. The process of claim 7 in which said coking temperature is about 12001250 F. and said carrier solids are selected from the group consisting of copper and brass.

9. The process of claim 7 in which at least a portion of said carbon burned in said heating zone is supplied from said separation zone.

10. The process of coking heavy residual oils in the presence of subdivided solids, which comprises contacting heavy residual oil at a coking temperature in a coking zone with a dense, turbulent, iiuidized mass of nely divided spheroidal metallic carrier solids having a thermal coei-lcient of expansion at least three times that of coke, whereby said oil is cracked and a coke layer is deposited on said solids, recovering volatile cracking products from said coking Zone, separately withdrawing coked carrier solids from said coking zone, subjecting said withdrawn carrier solids to a limited combustion in a heating zone to raise the temperature of said solids about 50-300 F. above said coking temperature, whereby said layer is cracked to form coke fragments and part of said fragmented coke is burned, passing a mixture of carrier solids and unburned coke to a separation zone, subjecting said mixture to centrifugal motion in said separation zone to separate coke from carrier solids, recovering coke from said separation zone, and passing separated carrier solids from said separation zone to said coking zone substantially at said raised temperature.

l1. The process of claim 10 in which said carrier solids are suspended in said combustion zone in a combustionsupporting gas to form a relatively dense, turbulent, uidized mass, liue gases being withdrawn from said combustion zone together with said mixture.

The process of claim 10 in which said carrier solids have a catalytic desulfurization activity.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. THE PROCESS OF COKING HEAVY RESIDUAL OILS IN THE PRESENCE OF SUBDIVIDED SOLIDS, WHICH COMPRISES CONTACTING HEAVY RESIDUAL OIL AT A COKING TEMPERATURE IN A COKING ZONE WITH A DENSE, TURBULENT, FLUIDIZED MASS OF SMALL METALLIC CARRIER SOLIDS HAVING A THERMAL COEFFICIENT OF EXPANSION AT LEAST TWICE THAT OF COKE, WHEREBY SAID OIL IS CRACKED AND A COKE LAYER IS DEPOSITED ON SAID SOLIDS, RECOVERING VOLATILE CRACKING PRODUCTS FROM SAID COKING ZONE, PASSING COKED CARRIER SOLIDS TO A THERMAL TREATING ZONE, SUBJECTING SAID COKED CARRIER SOLIDS IN SAID TREATING ZONE TO A CHANGE IN TEMPERATURE OF SUFFICIENT MAGNITUDE TO CAUSE A SUBSTANTIAL CHANGE IN THE PARTICLE SIZE OF SAID CARRIER SOLIDS AS THE RESULT OF SAID HIGH THERMAL EXPANSION COEFFICIENT, WHEREBY SAID COKE LAYER IS CRACKED TO FORM COKE FRAGMENTS, SEPARATING SAID SOLIDS FROM SAID FRAGMENTED COKE, RECOVERING COKE SO SEPARATED, REHEATING SAID CARRIER SOLIDS BY COMBUSTION OF THE RESIDUE OF THE COKE FORMED IN SAID PROCESS TO A TEMPERATURE EXCEEDING SAID COKING TEMPERATURE AND RETURNING SAID REHEATING CARRIER SOLIDS TO SAID COKING ZONE.