US2717865A - Coking of heavy hydrocarbonaceous residues - Google Patents

Description

Sept- 13, 1955 c. N. KIMBERLIN, JR., Erm. 2,717,865

COKING OF HEAVY HYDROCARBONACEOUS RESIDUES Filed May 17, 1951 3 Sheets-Sheet 1 s r o ww b .m m Q53@ 33U Q l .M Amm m m, w .In e UCN |52 |12@ lll. .TTI m PT. n@ Erw@ .F im? me Smrmu im a rn AI .3% a 4 0 mi@ Qmmu T my @Ham O @ZMIU N955,5 huan* mw ...,dmaao NL Ib1a 2 P10] m3MV.\|

Sept. 13, 1955 c. N. KIMBELIN, JR., Erm.

COKING OF' HEAVY HYDROCARBONACEOUS REISIDUES Filedl May 17 1951 LIQLHD Laval.

55- ,Morom C F @rag 3 Sheets-Sheet 2 rzv embers Sept. 13, 1955 c. N. KIMBERLIN, JR., Erm. 2,737,865

COKING OF HEAVY HYDROCARBONACEOUS RESIDUES Filed May 17, 1951 3 Sheets-Sheet 3 United States Patent Oiice 2,717,865 Patented Sept. 13,4 1,9155

`COKING Oli-HEAVY HYDROCARBGNACEOUS RESIDUES Charles N.- Kimberiin, Jr., and C F Gray,

La., assignors to Esso Research pany, a corporation of Delaware Application May 17, 1951, Senn No. 226,893' Claims.A (Cl.-196t.55)

Baton Rouge, and Engineering Compresence'of subdivided solidswhile maintaining turbulence y in' the liquid phase undergoing coking.

I'n the past, heavy residual oils particularly the residues from atmospheric or vacuum crude' distillationhave been coked in intermittent processes wherein thel feed stock is heatedv tov coking temperatures and discharged in liquid f phase into a heat insulated soaking drum to remain therein` at coking'conditions for a suflicient length of time to effect thedesredf conversion into lower boiling products.`

In the course of this heat treatment large quantities of hard adherent coke are formed which is deposited on the walls of the heating coils and soaking drum. At frequent intervals the process must be interrupted to remove coke! deposits and thus toI prevent plugging and overheating of the equipment. Y

Various proposals have been made to cope with coke formation inL a manner permitting continuous operation of the coking process. For example, stirring and scraping means of many types have been suggested for incorporation into'thefsoaking drum tokeep the coke from adhering to thev drum walls andv to produce the coke in the form of a` loose particulate mass which may be continously removed from the bottom of the drum. Aside from` the fact that the irregular size and shape of the coke so producedV greatly complicate its smooth continuous removal, methods of this type fail to prevent coke deposition in the heating coils where the danger of overheating and hazardous pipe failure is particularly great; More successful methods are those in which a finely' divided solid such as sawdust, coke, sand, or the like is added to the `oil1 feed with the result that the coke formed is deposited on the added solids to form coked particles of relatively uniform size and shape which may be more readily removed in continuous operation and which simultaneously serve as a scouring agent to remove loosely adheringc'oke deposits from the equipment Walls. However, neither this expedient alone nor in combination with stirring means of the type previouslysuggested completely eliminates reactor fouling by coke deposition. ent invention overcomes this difficulty.

It is therefore the principal object of the present invention to provide improved means for preventing coke deposition on the reactor walls in systems for the liquid phase coking of heavy hydrocarbonaceous residues. Other and more' specific objects and advantages will appear from'the4 following description of the invention wherein reference will' be made to the accompanying drawing in which:

The presp Fig. 1 is a semi-diagrammatical illustration of a system adapted to carry out a preferred embodiment of the invention; and

Figs. 2 and 3 are similar illustrations, on a larger scale, of soaker designs suitable tov carry out preferred modifications of the invention.

It has now been found that reactor fouling by coke deposition on the reactor walls in the liquid phase coking of heavy oils of the type specifiedy may be completely avoided by diluting the feed stock withl a light distillate of 'the naphtha boiling range, carrying out the coking reaction in the presence of added subdivided seed solids and maintaining the reactants in a state of high turbulence during the coking reaction. The diluent and seed solids 'are' added to the heavy oil feed prior to the heating of the latter to coking temperatures. The added diluent decreases the viscosity of the reaction mixture and thus substantially increases the scouring effect of the solids andthe slurrying effect of turbulence. In addition when the naphtha diluent is present the coke tends to separate as a hard, non-tacky, granular precipitate which does not stick to the vessel walls; in the absence of the diluent the coke first separates as an adhering, gummy precipitate which sticks to the walls and is then finally converted to hard coke.

The process of the invention is applicable to all types of crude distillation residues as well as to whole crudes. The diluent may be virgin naphtha or a corresponding cut produced in the coking process, having a boiling range of about 100 to 650 F. but preferably about 250 to 450 F. Suitable proportions of diluent may vary froml about 20 to 120 vol. percent, preferably about 50-10'04 vol. percent of the total residual oil feed, i. e. fresh residual oil plus Vrecycle bottoms, if any. The seed solids may be those known in the art such as coke, sand, various clays, silica gel, kieselguhr, sawdust, etc. However, coke, particularly coke produced in the coking process s the preferred solid which may be employed in amounts of about l5 to 100 lbs., preferably about 30 to 60 lbs. per barrel of total fresh and recycle oil feed. The particle size of the seed solids may vary within wide ranges say from about 5-250 microns, the smaller sizes such as 5-50 microns being generally preferred. Turbulence in the reaction mixture undergoing coking may be maintained by various conventional mechanical stirring means, the injection of the feed through draft tubes arranged in the coking zone, or similar means.` It is preferred however to create turbulence by tangential injection of the feed into the wide endV of a plurality of cone type soaking drums in series and withdrawing the product from the narrow ends of the drums.

Regarding the conditions of the coking reaction, pressures sufiicient to maintain a diluent concentration of the order specified above in the liquid reaction medium and to prevent the vaporization of most of the light coking products should be used. Pressures of about 1000-3000Y p. s. i. g. preferably about 2000 p. s. i. g. are suitable at they temperatures and conversions most desirable for liquid phase coking. These temperatures may vary between about 750 and about 900 F., and preferably about 800-850 F., and should be correlated to the residence time of the feed at coking conditions. For example, at coking temperatures up to about 750 F. reaction times of say about 2-4 hours or more may be required fora conversion. to products boiling below 1050 F. whereas at temperatures as high as 950 F, or higher a reaction period of 2-10 minutes may be suiiicient for the same purpose. At a temperature of 775 F. the residence time may be l-2 hours, at 800 F. 1/2 l hour and at 850 F. 5,-20 minutes for the same conversion.

Having set forth its objects and general nature the inf vention will be best understood from the following more 3 detailed description wherein reference will be made to the drawing.

Referring now to Fig. 1 of the drawing, a crude residuum such as a 2.5 to 3.5% South Louisiana residuum having a gravity of about 12 API and a Conradson carbon of about 17% may be supplied from line 1 by pump 3 to line 5 at a pressure of about 10004000 p. s. i. g. Fresh seed coke having a particle size of about 5-100 microns may be fed to line 1 from lock hopper 7 or the like to start up the operation, and at certain intervals, as required. However, in normal operation seed coke is preferably supplied from line 9 in the form of a slurry of ground product coke in heavy recycle bottoms and heavy naphtha from the coking treatment as will appear more clearly hereinafter. line 9 the contents of line 5 may consist of a mixture of about to 75 vol. percent of fresh feed, 5 to 45 vol. percent of product bottoms and 15 to 55 vol. percent of product naphtha, this mixture containing about 15 to 100 lbs. of seed coke of 5-100 microns particle size per barrel. This slurry is passed through a fired coil 11 located in a furnace 13, wherein it is heated to'a'vtemperature of about 80G-850 F. at a pressure of about 2000 p. s. i. g., more or less. Coil 11 is preferably so designed that the feed attains a velocity of at least 4 ft. per second which may reach as much as 10 ft. per second. In this manner, the liquid flow through coil 11 is maintained highly turbulent. This turbulence in combination with the scouring action of the seed coke and the presence of the naphtha diluent prevent coke deposition on 11i the coil walls even within residence times sufficient to permit substantial coking of the feed in coil 11 itself.

The efuent of coil 11 is passed substantially at the temperature and pressure of coil 11 via line 15 to an upper portion of soaker or soaking system 17 wherein it is maintained in a highly turbulent state substantially at the temperature and pressure of coil 11 for a time sufficient to convert about 50 to 90% of the heavy oil feed into distillate products and coke. As pointed out above the time required for this purpose depends to a large extent on the prevailing temperatures. At the conditions here specified total residence times of the feed at temperatures above 800 F. in coil 11 and soaker 17 may vary between about 5 and 60 minutes. Suitable methods for creating turbulence in soaker 17 will be described herein later on with reference to Figs. 2 and 3.

The coked products contain liquid distillate oils and diluent, some vaporized light products, some gases, unconverted feed and slurried seed coke now having a slightly increased particle size due to coke deposition thereon. This product mixture is withdrawn via line 19 from the bottom of soaker 17 and passed to product fractionator 23 after pressure release to substantially atmospheric pressure in release valve 21. Fractionator 23 is preferably so operated that four distillate fractions are produced as follows. Gas and light naphtha boiling below about 200 F. and amounting to about 4-8 wt. percent dry gas and 4-9 vol. percent light naphtha based on residuum feed, are removed as overhead through line 25. Heavy naphtha having a boiling range of about 200-420 F. and amounting to about 4 to 10 vol. percent of residuum feed is removed through line 27. This naphtha is net production in addition to the naphtha diluent mixed with the feed. A heating oil fraction boiling between about 430 and 650 F. and amounting to about 14 to 2S vol. percent may be recovered via line 29 and a gas oil boiling above 650 F. and amounting to about l2 t0 27 vol. percent of residuum feed may be withdrawn through line 31. Non volatile fractions containing the seed coke and product coke in suspension collect in the bottom of fractionator 23 where they may be stripped of lighter materials by steam injected through line 33. These heavy bottoms are withdrawn through line in amounts of about 10 to 50 vol. percent of the total residuum feed. The yield figures given above apply to a feed conversion Downstream of the junction with of -90% to coke, gas and liquid boiling below 1050 F. The heavy bottoms withdrawn through line 35 are preferably further treated as follows.

About 50 to 70 vol. percent of the bottoms in line 35 are branched off into line 37 and passed to a disintegrating device 39 such as a conventional ball mill, rod mill, or the like wherein the coke particles are ground to the above specified particle size desirable for the feed coke. The slurry now containing fine seed coke is pumped by pump 41 into line 9 at the pressure of line 5 and mixed with product naphtha supplied at the same pressure from line 43 as will appear more clearly hereinafter. The total slurry in line 9 is passed to line 5 and coil 11 as described above.

Returning now to line 35, the remainder of the fractionator bottoms is passed through line 45 to any suitable, preferably continuous filtering device such as a conventional rotary filter 47 cooperating through line 49 and buffer tank 51 with a vacuum pump 53 taking suction from the interior of rotary filter 47. The bottoms slurry in line 45 is passed to the surface of filter 47. Part of the liquid constituents is sucked into the interior of filter 47 leaving a wet filter cake of coke. As the filter rotates the filter cake encounters a spray of heavy prodnct naphtha branched off line 27 through line 55 and spray nozzle 57. The naphtha feed rate through nozzle 57 may be about 0.1 to 1 volume per volume of fresh feed. The liquid bottoms adhering to the filter cake are substantially completely washed out by the naphtha spray and carried therewith into the interior of filter 47 wherefrom the liquid is removed via line 49 into tank 51. Coke free of heavy bottoms is removed from filter 47 by a scraper 59 and may be conveyed in any suitable manner through line 61 to a stripper 63 wherein adhering naphtha may be removed by stripping steam supplied through line 65. Product coke may be recovered through line 67 in amounts of about 10 to 20 wt. percent of total residuum feed.

The mixture of wash naphtha and filtrate bottoms collecting in tank 51 is withdrawn through line 69 and pumped by pump 71 into line 43 to be further treated as described above.

In view of the importance of strong turbulence in soaker 17 methods suitable for this purpose are illustrated in some detail in Figs. 2 and 3.

Referring now to Fig. 2, the method illustrated therein employs a single soaker which may take the place of soaker 17 of Fig. 1 like elements being identified by like reference characters. Soaker 17 is provided in its middle section with a concentrical draft tube 75 of smaller diameter and height. A stirring propeller 77 supported by a driving shaft 79 is arranged in the lower portion of draft tube 75. Driving shaft 79 is supported in stuffing box 81 and driven by a motor 83 in a direction which f1 causes propeller 77 to take suction from above and to exert a downward propelling action. The effluent from coil 7 enters soaker 17 through line 15 and is withdrawn through line 19 at rates conducive to maintain in soaker 17 a liquid level L in the upper portion. A compressed gas such as product gas or any other inert gas may be supplied through line 85 to protect the bearing surfaces from the abrasive action of the reaction slurry. Under the influence of the stirring and pumping action of propeller 77 which may have a speed of 10 to 100 R. P. M. the feed is circulated at a high speed downwardly through draft tube 75 and upwardly in the space between draft tube 75 and the walls of soaker 17 while at the same time assuming a rotary motion in the direction of the rotation of propeller 77, at least within draft tube 75, as indicated by the ow arrows. The turbulence so created is in most cases sufficient for the purposes of the invention. In some cases, it may even be sufficient to inject the feed from line 15 at a high velocity, in a downward or upward direction, directly into the upper or lower portion respectively, of draft tube 75, without the provision of any mechanical stirrer or propeller. the frictional forces involved make such a rather inecient.

A method for creating turbulence of considerably higher efficiency without the requirement of' mechanical stirring action or moving parts is illustrated in Fig. 3. In this case, three soaking vessels 17a, 17b and 17c take the place of soaker 17 of Fig. 1. These vessels have the form of inverted cones. The hot feed enters through line and ilows through vessels 17a, 17B `and 17C in series from top to bottom of each vessel filling the same substantially completely with liquid. 17a is connected by line 87 to the the bottom of vessel 17b to the top of vessel 17c by line 89 to permit this flow. Coked products are withdrawr through line 19.

In order to create the desired turbulence in vessels 17a, 17b, and 17c the feed is tangentially injected into the wide end of each vessel at a relatively high velocity ol However, procedure assumes a highly turbulent rotary motion a generally downward direction in all vessels. The retarding action of frictional forces is at least balanced and may by proper design and operation of the system be overcompensated by the increasing angular velocity of the liquid on its rotary downward path of steadily decreasing radius. The subdivision of soaker 17 into a plurality of vessels as shown permits higher rotation velocities at relatively low feed rates and feed injection velocities and thus more ecient turbulence. It will be understood, of course, that any one or all of the vessels 17a, 17b and/or 17e` may have the form of upright cones receiving the feed in the bottom and discharging from the top. This arrangement may even be preferable in some cases, because having the cones with the small end on top will avoid the collection of gas pockets in the soakers which would have the undesired effect of decreasing the residence time of the liquid in the soakers.

While the systems illustrated by the drawing are tube and tank type arrangements representing the preferred modication of the invention it is noted that in many cases soaker 17 may be completely eliminated, provided Example A 2.5% South Lousiana residuum having a gravity of about 12 API and a Conradsoh carbon of about 17% was diluted with an equal volume of heavy virgin naphtha (boiling range 300-400 F.). Coke having a particle slurry so obtained was treated for 1.6 hours in a stirred autoclave at a maximum pressure of 2000 p. s. i. g. and a temperature of 800 F. The results of the run were as follows:

Conversion to coke, gasand liquid boiling below l050 F., percent 88.9 Net yields:

Coke, wt. percent 18.5 Dry gas, wt. percent 7.7 Light and heavy naphtha, vol. percent 16.7 Heating oil, 430/650 F., vol. percent 25.9 Gas oil, 650/l050 F., vol. percent 25.9 Material boiling above 1050, vol. percent 11.1

served' to illustrate specific embodiments of the invention but are not intended to be limiting in scope.

F. and about l5 l00 lbs. of inely div1ded coke per barrel of residue and about 50-90.% of said residues into distillate oils andl carbonaceous residue, while maintaining in the vesselV to supply said naphtha diluent.

3. The continuous process of coking heavy hydrocarbonaceous residues, which comprises mixing said residues with substantial proportions of a napththa diluent boiling in the range of l0() to 650 of coke in liquid product from said soaking zone.

4. The process of claim 1 in which said naphtha diluent has a boiling range of 250 to 450 F.

5. The process of claim 4 in which said conditions include temperatures of about 800-850 F., pressures of about 1000-3000 p. s. i. g. and residence times of about 5-60 minutes, and said nely divided coke has a particle size of about 5-250 microns.

6. The process of claim 2 in which said naphtha diluent has a boiling range of 250 to 450 F.

7. The process of claim 6 in which said conditions include temperatures of about 800-850 F., pressures of about 1000-3000 p. s. i. g. and residence times of about 5-60 minutes, and said finely divided coke has a particle size of about 5-250 microns.

8. The process of claim 3 in which said conditions include temperatures of about 800 to 850 F. and pressures of about l000-3000 p. s. i. g., said residence time is about 5-60 minutes, said ncly divided coke has a particle size of about 5-250 microns and said naphtha diluent has a boiling range of 250 to 450 F.

9. The process of claim 3 in which the said slurry is subjected to distillation in a distillation zone to produce distillate fractions including a naphtha fraction and a gas oil fraction and heavy carbonaceous residue-containing bottoms, withdrawing said bottoms and separating at least a portion of said withdrawn bottoms into carbonaceous residue and liquid.

10. The process of claim 9 in which at least a portion of said separated carbonaceous residue is returned to said hydrocarbonaceous residues to supply at least a portion of said seed coke and at least a portion of said naphtha fraction is returned to said hydrocarbonaceous residues to supply at least a portion of said naphtha diluent.

1,592,772 Bergius July 13, 1924 8 Thomas June 16, Read Dec. 7, Davis et al. Feb. 8, Meyers Feb. 8, Tuttle May 9, Hemminger Sept. 19, Fischer Dec. 17, Reed Nov. 9,

FOREIGN PATENTS Sweden June 26, Great Britain June 8, Great Britain Aug. 4,

Claims (1)

1. THE CONTINUOUS PROCESS OF COKING HEAVY HYDROCARBONACEOUS RESIDUES, WHICH COMPRISES MIXING SAID RESIDUES WITH ABOUT-50-100 VOL. PERCENT OF NAPHTHA DILUENT BOILING IN THE RANGE OF 100* TL 650 F. AND ABOUT 15-100 LBA. OF FINELY DIVIDED COKE PER BARREL OF RESIDUE AND SUBJECTING THE MIXTURE FORMED IN A SUITABLE REACTION VESSEL TO LIQUID PHASE COKING CONDITIONS CONDUCIVE TO A CONVERSION OF ABOUT 50-90% OF SAID RESIDUES INTO DISTILLATE OILS AND CARBONACEOUS RESIDUE, WHILE MAINTAINING IN THE VESSEL SUFFICIENT TURBULENCE TO PREVENT COKE DEPOSITION ON THE WALLS OF THE VESSEL AND TO PROMOTE DEPOSITION OF THE CARBONACEOUS RESIDUE ON THE FINELY DIVIDED COKE.

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