US2699421A

US2699421A - Coking reactor

Info

Publication number: US2699421A
Application number: US186808A
Authority: US
Inventors: Benjamin T Borgerson; Kenneth A Smith
Original assignee: Sinclair Refining Co
Current assignee: Sinclair Refining Co
Priority date: 1950-09-26
Filing date: 1950-09-26
Publication date: 1955-01-11
Anticipated expiration: 1972-01-11

Description

Jan- 11, 1955 B. T. BoRGERsoN ETAI. '2,699,421

COKING REACTOR Filed Sept. 26. 1950 2 Sheets-Sheet 2 ATTORN EYS United States Patent O COKING REAcToR Benjamin T. Borgerson, Homewood, and Kenneth A. Smith, Park Forest, Ill., assignors to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application September 26, 1950, Serial No. 186,808

5 Claims. (Cl. 2oz-6) Our invention relates to improved means for effecting the coking of hydrocarbon oils in the presence of a body of coke particles maintained in circulation within a reaction vessel at a coking temperature. A basic difliculty in treating the residual oils for maximum recovery of distillate oil by coking is in the handling of the coke product. Conventionally, coking processes usually operate on a semi-continuous basis by charging oil to a coking chamber until the chamber is lled with coke and then switching to another coking chamber while discharging the coke from the rst chamber. Because of the cost and difficulty involved in cooling and discharging the coke agglomerate from the usual coking chamber, coking processes have had limited commercial acceptance for preparation of cracking charge stocks from residual oils and for the reduction of residual oils to a minimum quantity of non-distillable product. In application Serial No. 121,575 led October l5, 1949, Kenneth M. Watson has described a continuous coking system wherein the residual oil is introduced to a body of coke particles which is maintained in a fluidized condition in a reaction Vessel from which large particles are continuously and selectively withdrawn as formed to maintain the reaction system in equilibrium. In this way, the coke is selectively deposited on the adsorbent surfaces of the coke particles without troublesome deposit on the metal surfaces of the equipment and gradual build-up as an agglomerate filling the reaction vessel.

Successful operation of the Watson process requires that the coke particles be maintained in agitation or `circulatory motion to prevent solidication of the bed halting the process, to ellect uniform distribution of the loil charge within the reaction zone in order to promote the coking reaction to the optimum extent and to permit withdrawal of the coke product in the form of large coke particles by elutriation. Because of the diculty in vaporizing the charge oil and because of the mass of coke particles required in the reaction vessel to provide the substantial time factor needed for the coking reaction, large quantities of steam or other vaporous media are required to maintain the body of coke particles in circulatory motion in reasonably uniform contact with the oil charge. Although steam requirements are reduced for the same volume of coke particles by increasing the ratio of bed height or length to diameter (L/D), increase in the ratio of the height to the diameter is limited by the occurrence of slugging or bumping resulting in loss of contact between coke particles and vapors, excessive coke carry-over with the reactor vapor efuent and possible damage to the equipment. We have now devised, however, a system for effecting circulation of coke particles within the reaction vessel which improves contact of the adsorbent coke particles with the oil charge, permits the use of high L/D beds and appreciably reduces the requirements for steam or other vaporous media. Our invention also is particularly adapted to economically developing and maintaining very high coking temperatures within the reaction zone.

According to our invention, a body of coke particles is maintained in a vertically enlarged reaction vessel into a lower portion of which the hydrocarbon oil charging stock is continuously introduced. A stream of coke particles is circulated upwardly in the body of coke particles through an internal passageway of restricted crosssectional area, or chimney. Circulation is maintained by injection of high velocity steam or other vapor at a ICC low point in the body of coke particles and continues from above the internal passageway downward through the annulus around the passageway. The downwardly circulating particles are deected inwardly toward the internal passageway and through a restricted annular outlet section to the region of the body of coke particles below the internal passageway. The preheated hydrocarbon charge oil is injected into the body of coke particles below the internal passageway, large coke particles are selectively withdrawn from a lower portion of the reaction vessel by elutriation, and vapors are withdrawn overhead from an upper portion of the reaction vessel.

Two coking reactors of our invention are illustrated diagrammatically and in section in the accompanying drawings. From a consideration of the drawings, it will be apparent that the coking reactors of our invention are characterized structurally by a tapered or funnel-like shape to the lower section of the reaction vessel in cooperating relation with a cylindrical open-ended reactor internal or chimney vertically disposed within the reaction vessel.

In the attached drawings Figure I is a diagrammatic view of one form of the invention showing the reactor vessel including the internal passageway having a funnelshaped section below the internal passageway; Figure II is a diagrammatic view of a second form of the invention showing the enlarged annular section surrounding the lower portion of the chimney and means for introducing combustion air to this enlarged section.

In the coking reactor of Figure I, preheated black oil charge is introduced into reaction vessel 10 through line 11 and dispersion nozzle 12. Dispersion steam may be provided through connection 13 if desired. A body of coke particles with the approximate bed level indicated at 14 is maintained within the reaction vessel 10. Disposed within the reaction vessel 10 is an open-ended internal cylinder or chimney 17 providing an internal passageway upwards through the body of coke particles within reaction vessel 10. The lower portion of the reaction vessel 10 is a tapered or funnel-shaped section 15 which opens into elutriator pipe 16. The point of oil introduction is into the body of coke particles below the lower open end of internal passageway 17 in such a manner as to obtain good dispersion and contribute to the circulation of the coke particles upward through the internal passagewav. Circulation is effected bv iniection of steam or other vapor through connection 30. The point of vapor iniection is at the low point in the bed in order to avoid stagnant areas below the point of inlet. Elutriating steam is iniected at a lower portion of elutriator 16 bv means of connection 18, and the larger coke particles built up in the process settle from the svstem through the annular section surrounding the circulation vapor inlet against the rising elutriation vapors. Under the iniluence of the circulation steam. the elutriator steam and the dispersed charge oil, circulation of coke particles and adsorbed oil is effected upward through the internal chimney 17 and downward through the surrounding annulus 17A. The inward deflection of the descending particles accelerated bv passage through the relatively restricted annular outlet section 17B appears to have a surprising influence on maintenance of the desired circulation. Large coke particles formed bv build-up of coke from the charge oil are selectively withdrawn through elutriator pipe 16, at a rate controlled bv steam iniection through connection 18. Lock hopper 19 is provided to control flow of coke product from elutriator 16 and to maintain or remove the bodv of coke particles from the reaction vessel 10. Oil and steam vapors are removed overhead from the reaction vessel 10 through line 20 to a distillate oil recovery system.

ln the coking reactor illustrated in Figure II, preheated oil charge is introduced to the reaction vessel 50 by line 51 and dispersion nozzle 52. Dispersion steam may be introduced if desired through connection 53. A body of coke particles having an approximate bedl level at 54 is maintained within the reaction vessel 50. Opening into the tapered bottom of the reaction vessel 5t) is elutriator 56 into which elutriation steam is admitted through connection 57 and in which lock hopper 58 is provided to control ow of coke product from elutriator 56 and to 'reaction vessel- 50.-

maintain or remove the body of coke particles from the through line 71 to maintain circulation while coke particles descending down the walls of the tapered section ofthe reaction vessel 50 contactv the elutriationvapors in the annular section surrounding line 71. Disposed -within the reaction vessel 50; is` an' open-ended cylinder 'tion is to provide. controlled burning. of` a portion ofthe coke made in the reaction inorder to obtain a particularly highcoking temperature for'the reaction. Preferably, the enlarged, annular sectiorr 60 is equipped ror gas Afiring to insure proper ignitionr as by injection of fuel gasthrough line 72, bustle pipe 73' and'jets 74. With continuous gas tiring, excess air is supplied so that some vcoke is burned. Flue gas is removed from the upperportion ofthe enlarged annular section 60 through. hoodedr disengaging pipes 66, collector section pipe-66A and line 67. Sealing steam is introduced through connection 68 and bustle pipe 69 aboveV the pointv ofue gas exit in order to avoid combustion of oil vapors or oil adsorbed on thesurfaces of thecoke particles in the upper portion of the coke'bed which is not yet reduced tocoke, and to prevent the ilue gas from contaminating thev oil-vapors and loading gas plant. Oil and' steam vapors are removed overhead from reaction vessel 50 through line 70 and the distillate oil productv is separated in the usual product recovery system.

In operation according to our invention, a circulating rnotion within thev body of'l coke particles is maintained and supplemented by injection of steam to the lower portion of the,` body of cokel particles by action of the steam injected through the elutriator and to some extent by action of the vaporized and dispersed charge? oil'. The stream of# coke particlesy moves upwardly through the internal passageway disposed? Within ther'reactiorr vessel t'o the upper level ot`= the bed as a dilute phase; i. e. as, low as 2-3 pounds per cubicffootin-y density. Coke, particles descend from the upper portion of the bed downward through the'v annular passageway by gravity but are aided to an important-extent bymeans of'the'accelerating effect of the deflection of the descending stream offparticles through the relatively restricted lowerl annular-outletscc tion or' orilce inwardly to; jointhe ascending stream of cokev particles. Thus, the bedappearsy to descend at a uniform velocity through the annulusuntil it reaches the tapered section where the vdescendingy body of particles .is tur-ned iny and tends. tobev swept 11p-by the steam injected at the foot of the bed. A levell'of coke abovey the top of the Vchimney isV advantageous in: that it tendsfto bathe-:the flow from the top of the chimney. The-bed level should not be so: high as to: forml a Zone of 'unstable circulation and advantageouslythe height ofthebody of coke particles above thef chimney should not exceed the diameter ofl the; reactiony vessel.

Wehave found that'circulation is maintained within the system without sluggingl or other interference with uniformity of particleow and'particle-uid contact at surprisingly low ratesl of vapor injection for the high L/Dl ratios involved. We have found'that required vapor injectionl rates are reduced and the-circulation is v.increased by locating the lower endof the internal passageway at` the maximum height above the vapor injection point which ispossiblewithout` causing slugging at aparticular vapor injection rate. Thus as the height of the chimney above the point of vapor entry is increased, the rate of cokecirculation per given vapor rate increasest up tozthe point of instability.

The principles of operation are illustrated intherfollowing design tests, on` reactor forms. embodying our invention.

f I'n a. model ofv a il'uidized coker of 3% I. D., anL internal cylindrical chimney of 1%6 I. D. was employed. Thev coker had a tapered section extending over 4 of height above the vapor injection point., At the vapor injection p,oint,.tl'1el coker was tapered to 1%" I. D. The circulation was tested by filling the coker with. lill-3.0 mesh coke particles at an ai'r rate of' 17 S. C'. F. M. i11- Circulation steam isV introduced troduced through the bottom of the reactor. The maximum` height forthel chimney above the vapor injection point without slugging was 5" as shown below:

Coke Cirin Annulus, )FL/min.

Height 22.2 (Verge of slugging) 17. 2.

3.1, 24.0 (Slugging).

Circulation Air Rate, S. C. F. M. Rate, FL/mm 22.2 (Verge of slugging).

A plot of data obtained in terms of height in inches against velocity of circulation for different air rates showed that increasing height above the grid increased circulationfor a given air rate.

The following. data were obtained using a coker having a tapered section extending over 3 of height above. the vapor injection point. At the vapor injection point the cokerwas tapered to 15/32-" I. D. Slugging. first occurred at. a chimney heightv of 13. but recovery to stable operatlon wasV effected by reducmgthe helght to4 11". The amount of coke 1n. the bedremained constant. The arr rate. was marntalned at 17 S. C. Coke cir- Coke ve- Distance ofchimney above.` vaporinjection culationlocity in point, .111. rate, lbs./ Vannulus,.

min. Ft./min.

0 0 10. 9' 4.0 1.4.9 5:5 19.9 7.3 23.4 8.6 27.1 10.0 32.6 12.0 `40.7 15.0 46.4 17.1 50.7 1&7 50.7 18.7 54.3v 20.0 1 Slugglng l Recovered stable operation after slugging when lowered back to 1l in.

Using a larger chimney, 21 O. D. and 25/16" I. D., 1.7.5. SL C. P. M. was establishedas the minimumv air rate. Withthe chimney height at 7", the circulation rate in the; annuluswas 11.5 ft./rnin; Aty 9V", slugging occurrcdirr they annulus, but at 8" slugging stopped and circulationl wasrreestablished atl a rate of l5 ft./min. with onlyoccasional minor slugging in the chimney.

rPheV coking reaction is: conducted' according to our invention .by use of 'a sufficient' volume of coke particles oflsa-y about 10E to 'S10-mesh size range to adsorbY the net coke make from thel oil charged. and ina reaction vessel ofy sufficient volume to, accommodatethe vapor volumes involved... A. highy coking temperature. is advantageously employed to obtain high capacity in any given sized equipment 'but a low pressure; e; g. atmospheric orsubatmospheric `toabout-5.0? p. s. i.; g. isv employed. YCoking ternperaturesr'ranget from about 850 to 1200? F. Ordinarily, the coking temperature within the. reaction zone is limited l.by thejheater:L outlet temperaturein preheating the oil charge, usually about 925 to 975 F. for a black oil charge, depending upon the particular heater. design. Additional heattherefore is usually supplied bysuperhcating theV clutri'atingv and'circul'ating vapors injected into the reaction vessel. However, as described above, operating according to the coke circulating system of our invention readily permits in situ combustion of a portion of the coke make to supply heat within the reaction zone. Additional heat may be supplied using gas burners. The directed circulation path of the coke particles within the body of coke particles in the reaction vessel according to our invention results in progressive ow through oil injection, adsorption, distillation and solid coke formation stages of the reaction without excessive heterogeneous mixing. As a consequence, direct air or oxygen injection to the reaction vessel may be employed in the later stages of coke particle circulation to burn a portion of the coke make without consequent destruction of valuable portions of the oil charge and product. Also ue gases can be separately withdrawn without overloading the product recovery and vapor handling system.

We claim:

1. In the coking of hydrocarbon oils in the presence of a body of coke particles at a coking temperature, the method of maintaining a body of coke particles in a vertically enlarged reaction vessel, circulating coke particles upward through an internal passageway of restricted cross-section within the body of coke particles to an upper level of the body of coke particles by vapor injection below the passageway and downward through an annular zone surrounding the internal passageway, deflecting the downwardly circulating particles through a restricted annular outlet section and inwardly toward the upwardly circulating stream of particles below the internal passageway, passing a preheated chargeV oil into the body of coke particles belowl the internal passageway and upwardly through said passageway, selectively withdrawing large coke particles by elutriation with a vaporous elutriation medium from the lower portion of the reaction vessel and withdrawing vapors from the upper portion of the reaction vessel.

2. The method of claim 1 in which the vapor injected for circulation is steam.

3. The method of claim 1 in which a portion of the coke in the downwardly circulating coke particles is burned by air injection at a low point in the annular zone surrounding the internal passageway and in which flue gas is separately removed from the reaction vessel.

In apparatus for coking hydrocarbon oils, a vertically enlarged reaction vessel having an inwardly tapered lower section, an elutriator pipe opening into the bottom of the reaction vessel, an open-ended cylindrical chimney disposed within the reaction vessel with its lower portion cooperating with the tapered section of the reaction vessel to provide an annular outlet section opening into the lower portion of the reaction vessel above the elutriator, means for injecting a circulation vapor at a low point of the tapered section, means for injecting an oil charge stock into the circulation vapor at a point in the lower portion of the reaction Vessel below the chimney which then passes upwardly through said chimney, means for injecting a vaporous elutriating medium into the elutriator pipe and means for removing vapors from the upper portion of the reaction vessel.

5. In apparatus for coking hydrocarbon oils, a vertically enlarged reaction vessel having an inwardly tapered lower section, an elutriator pipe opening into the bottom of the reaction Vessel, an open-ended cylindrical chimney disposed within the reaction vessel with its lower portion cooperating with the tapered section of the reaction vessel to provide an annular outlet section opening into the lower portion of the reaction vessel above the elutriator, an enlarged annular section in the reaction vessel surrounding the lower portion of the chimney, means for injecting combustion air into the enlarged. annular section, means for removing iiue gas from the reaction vessel, means for injecting a circulation vapor at a low point of the tapered section, means for injecting an oil charge stock into the circulation vapor at a point in the lower portion of the reaction vessel below' the chimney which then passes upwardly through said chimney, means for injecting a vaporous elutriating medium into the elutriator pipe and means for removing vapors from the upper portion of the reaction Vessel.

References Cited in the tile of this patent UNITED STATES PATENTS 2,339,932 Kuhl Jan. 25, 1944 2,378,342 Voorhees et al. June l2, 1945 2,418,003 Angell Mar. 25, 1947 2,445,328 Keith lluly 20, 1948 2,456,796 Schutte Dec. 2l, 1948 2,459,824 Leffer Jan. 25, 1949 2,582,710 Martin lian. 15, 1952 2,582,711 Nelson lian. 15, 1952 2,606,144 Leder Aug. 5, 1952 FOREIGN PATENTS 600,326 Great Britain Apr. 6, 1948

Claims

1. IN THE COKING OF HYDROCARBON OILS IN THE PRESENCE OF A BODY OF COKE PARTICLES AT A COKING TEMPERATURE, THE METHOD OF MAINTAINING A BODY OF COKE PARTICLES IN A VERTICALLY ENLARGED REACTION VESSEL, CIRCULATING COKE PARTICLES UPWARD THROUGH AN INTERNAL PASSAGEWAY OF RESTRICTED CROSS-SECTION WITHIN THE BODY OF COKE PARTICLES TO AN UPPER LEVEL OF THE BODY OF COKE PARTICLES BY VAPOR INJECTION BELOW THE PASSAGEWAY AND DOWNWARD THROUGH AN ANNULAR ZONE SURROUNDING THE INTERNAL PASSAGEWAY, DEFLECTING THE DOWNWARDLY CIRCULATING PARTICLES THROUGH A RESTRICTED ANNULAR OUTLET SECTION AND INWARDLY TOWARD THE UPWARDLY CIRCULATING STREAM OF PARTICLES BELOW THE INTERNAL PASSAGEWAY, PASSING A PREHEATED CHARGE OIL INTO THE BODY OF COKE PARTICLES BELOW THE INTERNAL PASSAGEWAY AND UPWARDLY THROUGH SAID PASSAGEWAY, SELECTIVELY WITHDRAWING LARGE COKE PARTICLES BY ELUTRIATION WITH A VAPOROUS ELUTRIATION MEDIUM FROM THE LOWER PORTION OF THE REACTION VESSEL AND WITHDRAWING VAPORS FROM THE UPPER PORTION OF THE REACTION VESSEL.