US3162593A

US3162593A - Fluid coking with cracking of more refractory oil in the transfer line

Info

Publication number: US3162593A
Application number: US181406A
Authority: US
Inventors: Charles L Persyn
Original assignee: Tidewater Oil Co
Current assignee: Tidewater Oil Co
Priority date: 1962-03-21
Filing date: 1962-03-21
Publication date: 1964-12-22
Anticipated expiration: 1981-12-22

Description

Dec. 22, 1964 C, L, PERSYN 3,162,593

FLUID COKING WITH CRACKING OF MORE REFRACTORY OIL IN THE TRANSFER LINE I Filed March 2l, 1962 A TTORNEV United States Patent O 3,l62,53 FLUED Cml WH'H CRASEQNG Gli MORE REFRAQTSRY GEL EN @H- ERANSFER LNE Charles L. Persyn, Concord, Calif., aasignor to Tidewater @il Company, Los Angeles, Calif., a corporation of Delaware Filed Mar. 21, 1962, Ser. No. lSlAil 4 Claims. (Cl. L20S- 53) This invention relates to an improved petroleum relining process involving improvements in iiuid coking for upgrading of heavy oils. More specific aspects of the invention relate to novel relationships between catalytic cracking and iluid coking.

As is well known in the art, the duid coking process uses a fluid colting vessel or reactor and an external heating vessel, eg., a uid bed burner. A fluid hed of solids, preferably coke particles produced by the process having a size in the range of about 40 to 1000 microns, is maintained in the Cokin(T zone by the upward passage of a iiuidizing gas, usualiy steam. The temperature of the bed is maintained at about 950 F. by circula.'ng solids (coke) to the heating vessel (coke burner) and back. The heavy mineral oil to be converted is injected into the iluid bed and upon Contact with the hot solids undergoes pyrolysis evolving lighter hydrocarbon vapors and depositing coke on the solids. The turbulence of the iiuid bed normally results in substantially isothermal conditions and in thorough and rapid distribution of the heavy injected oil. `Product vapors, alter heavy entrained solids are removed, are withdrawn overhead from the coking vessel and sent to a scrubber and fractionator for cooling and separation. Generally, a stream of the coke particles is continuously withdrawn from the coking vessel or reactor and passed to the burner, where some of its is burned to heat the remainder, and heated coke is continuously recirculated to the reactor.

ln the scrubber the heavier constituents of the effluent product vapor are condensed, usually with the aid of a quench oil, which may be at least a portion of the heavy oil fed to the coking reactor, in order to remove any coke particles and other undesirable heavy elements inthe form or a slurry, this slurry being then fed to the coiring reactor for further treatment. From the top of the scrubber, the cracked vapors pass to the ractionator, where they are separated into gas, gasoline, and a light gas oil. The Light gas oil is normally used as charge stock for catalytic cracking o any of several types, including the more recent hydrocracking.

From a point near the top of the scrubber there is also Withdrawn a stream of heavy gas oil, which, by reason of its nitrogen content, ash content, or aromaticit is decidedly unsuitable as a catalytic cracking feed stock because it fouls the catalyst. Heretoiore, this heavy gas oil has been used principal-ly as an element of fuel oil. However, fueloil is not nearly such a profitable product as gasoline; so attempts have been made to'recycle this l it could be reduced completely tolighter distillates. As conversion of this material must ta1 e place in thefvapor phase because its boiling range islovver than that of the heavy feedstock, such recycle operation is not attractive. Because vthe Coking temperature in the coking reactor is relatively low, high conversion of the refractory heavy gas oil is dilicult to obtain and apparently less than 5% heavy gas oil through the coking reactor in the hope that ih/ii Patented Dec. 22, 3.9%@

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of it is converted by such recycle. This results, then, in excessive recycle rates. This diiiiculty cannot economically be circumvented by increasing the coking temperature in the coking reactor, because such an increase would resuit in excessive thermal degradation and loss of the light distillate products.

it has also been suggested that this heavy gas oil be cracked at very high temperatures (e.g., 12G0 F. to 1600" F.) to produce gases, but this requires separate reactors and results in products that generally are less valuable than gasoline and catalytic cracking charge stock.

have found, however, that by introducing the heavyV gas oil into the transfer stream of coke coming from the coke burner to the coking reactor, in which stream the temperature is higher than in the reactor bed, being in the neighborhood of ll0O to l150 F., a considerable amount of the heavy gas oil can be converted to gasoline, light gas oil suitable for catalytic cracking, and etiluent gases, while certain other portions take on characteristics like that of the oill in the recycle slurry, so that further recycle, possibly until extinction, becomes feasible.

Another petroleum process which has achieved great importance is that of catalytic cracking, including the more recently developed hydrocracking. Catalytic cracking units require a charge stock muchhigher in grade than that of iiuid coking units. In fact, iiuid coking units are customarily addedl to reiineries for the purpose of handling residuum which would be certain toy foul catalytic cracking units and which would give very poor results in other types of cracking units. As already mentioned, the light gas oil produced by a uid coking unit is good charge stock for the catalytic cracking unit, and it is produced in even greater quantity by the use of-the present invention. Other suitable charge stocks come from other portions of the refinery.

In the catalytic cracking unit most of the charge stock is upgraded to gasoline and other high grade products. The remainder, a heavy fraction containing (in a duidized catalytic cracking process) entrained catalyst, is settled out and a clarified portion is decanted oli. This portion, known as decanted oil, is fairly low-grade stock, which heretofore has been used mainly as fuel oil. It has many of the characteristics of coker heavy gas oil and the effects of adding it to a fluid coker are similar to those obtained from adding heavy Coker gas oil.

I have found that decanted oil from a iiuid catalytic cracking unit can also he upgraded by charging it to the hot coke line.

Thus, the invention links iiuid coking and iiuid catalytic cracking in a new wayand accomplishes a novel type of recycle and cracking for both the decanted oil from the catalytic cracking unit andy the heavy gas Oil obtained from the Coker unit.

Other objects and' advantages of therinvention will appear from the following description of a preferred ernbodiment thereof.

The drawing is a diagrammatic representation of processing steps incorporating the principlesof the present invention, and illustrates diagrammatically yboth a fluid catalytic oracle-lng unit and auidcoking unit operating in conjunction with eachother. For purposes of sirnplicity, most of the steam inlets, pumps, blowers, coolers, and similar details well known to the art have been omitted.

The drawing illustrates a lluid coking reactor 1 and aisaeas a coke burner 2. In the coke burner 2 coke is burned to provide heat for the cokingreactor 1 and hot coke is returned to the coking reactor 1 `through a hot line 3,

preferably and normally entering the upper part of reactor 1 as indicated in the drawing. To the colting reactor 1, which is at a temperature of between 925 and 1000 F., a charge stock of Vresiduum and recycled slurry enters below the hot coke (see the drawing) from lines 4 and 5 via a suitable manifold system. The injected oil contacts a bed 6 of iluidized cokel and undergoes pyrolysis, evolving lighter hydrocarbon vapors and depositing additional coke on the coke particles.

Fluidization gas, eg., steam, is injected at numerous points, indicated in the drawing by lines 7 and 8, to maintain uidization of the coke particles and to eect transfer of coke from the burner Z to the reactor 1. Coke particles, after having been stripped of entrained hydrocarbons and after having oversize particles screened out and removed through a line' 9, are withdrawn from the base ofthe vessel 1 and sent to the coke burner 2 through line 10, to which steam or air is supplied as by a line 11.

Coke in excess of Vthat neededrfor burning andrecirculation to the reactor 1, where it supplies heat for the exothermic coking reaction, is withdrawn from the burner 2 y through a line 12. v

From the reactor 1, the vaporous conversion products are withdrawn overhead through cyclone separators 13 which remove fine particles of entrained coke and return the fresh feed may be fed as quenchoil through a line 15 and from which a slurry is withdrawnthrough aline y 16 for recycle either to the Vquench line 15 (after settling in a settler 17 and cooling in a heat exchanger19) or to the recycle line 5 or both. From the scrubber 14, the uncondensed eiiluent passes overhead through a line 18 to a fractionator unit 20 where various fractions are taken off, such as gases and gasoline vapor'in line 21, a light gas oil (boiling below 630 F.) in line 22, land a heavy portion that is recycled as reux byline 2.3. Near thetop of the scrubber 14, heavy gas oil (mostly boiling in the 600-900 F. range) is withdrawn by a line 24.

Heretofore, the heavy gas oil withdrawn through the line 24 has been passed to storage (represented by a tank 25') for disposal as fuel oil. in the

present invention valves

26 and 27 `may be linstalled in the line 24 and part or `all of the heavy gas oil may be ysent through the valve 27 and a line 28 into the hot coke riser line 3 at a point 30 where the coke is about ll00 'tol l150 F. The oil entering theV line 3 at the point 30 vaporizes almost instantly and acts as a fluidizing vaporso that much less, if any, steam need be added-through the line 8 orY Y elsewherefin the liney 3 in order to impart proper movement to the coke fluidized in the line 3. 'While passing with this very hot coke through the'line 3 into the reactor 1, this heavy gas oil-Which cannot `be cracked bycontact with the coke in the reactor 1iscracked to yield additional light gas oil, gasoline, gases, and a residue lof Y heavier gas oil, much of -Which becomes part of the re-V I cycle slurryV and may be-capaole of cracking when recycled with it. Po,ssibly,'the very volatility of the heavyV gas oilcombines with itsrefractoriness to prevent'crack- Y ing when it isfed to the coking reactor bed by lessening kthe dwell timeitherei surely there is Vno such effecten dwell j Y time when itis fed to the line 3, since it has to; pass -j` through that Vline.A` At any-rate, the desired cracking of,Y

a substantial partis attained by thisinvention. Another part Vgoes into the; heavy gasoil lineZ- again'for Va re- Y cycle to thelirieifror to theffuel oilstorage unit 25. f 'Y As illustratedin lthe drawing, the; lightVV gas oil V,withdrawn through the line 22 isV charged via lines 3,1 andv 32 to a` fluidized catalyticy crackn'gfreactor 33 along with ,other catalytic cracker charge stock. Catalyst fromV a regenerator 34 is fed inV a fluidi'zed conditionthrough the line'v32'gto thereactor, and isfreturned through line' Y35 from the reactor 33 to the regenerator 34. The eiluent fromrthe reactor 33 passes through a line 36 to a fractionator 37, whence gas and gasoline are taken oif through a line 33light gas oil through line 39, and heavy cat- 5 alytic gas oil through line 40 (having quite different properties from the heavy coker gas oil in line 24). A bottoms fraction'containing catalyst fines which were entrained in the vapors in the line 36 is passed by a line 41 to a Dorr Yclarifier 42;,whence a decanted oil is withdrawn through a line 43. This decanted'oil (having a boiling range substantially; between 600 and 900 F.) Y has heretofore been sent to fuel oil such as to the storage tank 2'5 through line 45. According to a specific embodiment of this invention, ka portion at least of this decanted oil is diverted by yvalves 46 and 47 into the line 28 andl is` charged into the hot coke line 3, where it is cracked in a reaction similar to that of the heavy gas oil which it resembles in manyways.V If desired, the two may be charged as a mixture.

v Turning now vto a specific example, a residuum feed stock coming into the coking'unit 1 through the charge line 4 may be as follows:

Y TABLE I 20 Properties of Feed Stock Residuum Charged to the l Coking Reactor API gravity 8.0 30 Conradson carbon, wt. percent 14.3 Surfur, wt. percent 2.7 A.S.T.M. distillation (i3-1160), F.: TBP 614 Y 10% 891 33% 1000 The conditions in thercoking reactor 1 are shown in Table yII.y Y Y TABLE II Operating ConditionsV in Cokz'ng Reactor Pressure, p,.s.i.g Feed inlet temperature, F. 620 Reactor temperatures, F.: 5 Dense phase 970 `Dilutephase 1015 lBurner temperature, F. 1150 Vapor holding time, total seconds 18 VCokein reactor, tons 800 5a'Coke circulation, tons/minute 45 to 55 The heavy gas oil eiuent (line 24) has the following properties: f

Y TABLE III as f Properties o'f the Heavy Gas Oil Eiuenl Gravity, API, 10.7 Y Conradson carbon, wt.vpercent' 0.83 50 Pourpoint, 'F.1 Y 70 Sulfur, percent 1.77 'Nitrogen wt. percent 0.97

Viscosity: 1 f 5 I s v, sSFatizzfrF. f 3s` Y @5 SSUar210?F.i Y Y 55.6y

` YMetals,p'.p.m.:fY 1- Y' v Vanadium 0.014V

` Nickel-f Distillation, F., (distilled at For the purpose of comparison in this example, this heavy gas oil is divided into three samples, and, at separate times, each sample is separately charged to the coking system. Sample 1 is processed in the reactor 1, and Samples 2 and 3 are processed in the line 3, all under the conditions given in Table IV, where the Samples 1, 2, and 3 are compared with a Sample 0 representing the conventional processing in which the heavy gas oil is not recycled at all.

TABLE IV Fluid Coking of Heavy Gas Oil of Table III, Operating Data Sample No 0 1 2 3 Fresh Feed Rate, b./d 42, 000 42, 000 42, 000 42, 000 Recycle Rate, Vol. Percent of Fresh Feed 40. 0 40. 0 40. 0 40, 0 Heavy Coker Gas Oil:

To Hot Coke Riser Line, b.ld 0 0 5,000 5, 000 To Coker Reactor, bJd 0 5, 000 0 0 Recycle Rate, Considering Heavy Coker Gas Gil as Recycle, Vol. Porcent of Fresh Feed 40.0 51. 9 51.9 51.9 Reactor Holdup, Tons of Coke.. 800 S00 800 800 Reactor Temperature, Bed, o F 070 970 970 970 Reactor Temperature, Vapor Phase,

F 1, 015 1,015 1,015 1,015 Reactor' Pressure, p.s. 1 12 12 12 Burner Temperature, 1, 150 1, 160 1, 130 Temperature at Hot Coke Riser Line l 1,150 1,150 1,150 1, 100 Coke Burned, Tons/Day 520 520 520 520 Steam to Hot Coke Transfer Line,

lhs/hr 49,000 50,000 32, 000 30,000

The coke circulation rate is in all four cases between 45 and 55 tons per minute, the addition of up to 5000 b./d. of heavy gas oil apparently not requiring a material increase in burner temperature or circulation rate of coke.

The yields of these three samples are as follows:

TABLE V Samples Normal Operttion 1 2 3 Dry gas (C: Minus) M i 3.0.1.!(1 27, 090 i 2T, 790 34, 390 3l, 02o Total Propanes, b /d 2, 814 2, 854 3, 824 3, 354 Total Butanes. b./d l, 974 1, 999 2, 444 2, 269 Gasoline (390 F. ot 90% Dist.) b./d l2, 222 12, 372 l2, 892 13, 002 Light Gas Oil (600 F. at l 90% Dist), b./d 4,578 l 4,738 4,703 4,983 Heavy Gas Oil (030 F.

plus), b./d 13, 692 1 13, 282 l 10, 420 1 1l, 207 Coke, gross, M ibs/d a, e46 3, @so 3, ses 3, cs2

1 Net after deducting the 5,000 b./d. heavy gas oil recharged.

From Table V it will be seen that straight recycling of heavy gas oil to the coking reactor (Sample 1) accomplishes little, while the introduction of the heavy gas oil into the hot coke riser in accordance with the invention (Samples 2 and 3) produces good yields of desirable products.

It will be noted especially that gasoline and light gas oil, suitable for catalytic cracking charge, are increased a substantial amount by the invention and that the heavy gas oil has been substantially reduced.

it is also to be noted that a transfer line temperature of 1100 F. affords substantially better yields of gasoline and light gas oil than a temperature of 1150 F., indicating that further increases would be even less desirable.

As a further example, consider a decanted oil from catalytic cracking, having the following properties:

The decanted oil of Table V is divided into three samples, Sample 4 being fed at one time to the coking reactor, Sample 5 at another time to the line 3 at 1150 F. and Sample 6 at still another time to the same line 3 at l100 F., the temperature being controlled by small changes in the burning and recycle rates of the coke. Yields from the three samples are shown in Table VII, together with the yields from normal operation, Sample 0, in which there is no addition of any decanted oil.

TABLE VII Fluid Cokz'ng Yields of Samples 4, 5, and 6 Samples Normal Opera- 4 5 6 tion Dry Gas (C2 minus) M s.c.f./d. 27, 000 27,665 33, 600 30, 450 Total Propanes, b./d 2,81 ,84 3, 73S 3, 276 Total Butanes, b./d 1,974 1,994 2,436 2, 226 Gasoline (39 Rate Di ,d 12,222 12, 317 12, 516 12, 558 Light Gas Oil (600 F. at 90% Dist.), b./d 4, 578 4, 723 4, 703 4, G20

Heavy Gos Oil (630 F. Plus), b./d 13, B02 18, 297 15, 442 16, 192 Coke, Gross, M lbs/d 3, 046 3, 690 3, 844 753 a carbons by contact with a dense uidized bed of heated coke particles in a coking zone and the bed is maintained at coking temperature by circulation of coke particles from said bed to a burning zone wherein a portion thereof is burned to heat the remainder substantially above the temperature of said bed and thus heated colse particles art returned to said bed through an elongated transfer zone,

the method of simultaneously cracking a heavy oil more refractory and more volatile than said charge oil which comprises introducing only said more refractory oil into said transfer zone to travel therethrough in contact with heated coke particles therein, for a distance suflicient that said more refractory oil is cracked therein at a temperature substantially above that to which said charge oil is subjected. 2. A process as in claim 1 wherein the more refractory oil is a heavy gas oil. i

3. A process as in claim 1 wherein the more refractory oil is a decant oil.

4. A process as in claim l wherein the more refractory oil is a mixture of a heavy gas oil and a decant oil.

References Cited in the le of this patent UNITED STATES PATENTS 2,777,802 Peet lan. 15, 1957 2,868,715 Jahnig et al Jan. 13, 1959 2,894,897 Post July 14, 1959 2,920,032 Vander Ploeg et al Ian. 5, 1960

Claims

1. IN A FLUID COKING PROCESS WHEREIN A HEAVY HYDROCARBON CHARGE OIL IS CRACKED TO LOWER BOILING HYDROCARBONS BY CONTACT WITH A DENSE FLUIDIZED BED OF HEATED COKE PARTICLES IN A COKING ZONE AND THE BED IS MAINTAINED AT COKING TEMPERATURE BY CIRCULATION OF COKE PARTICLES FROM SAID BED TO A BURNING ZONE WHEREIN A PORTION THEREOF IS BURNED TO HEAT THE REMAINDER SUBSTANTIALLY ABOVE THE TEMPERATURE OF SAID BED AND THUS HEATED COKE PARTICLES ART RETURNED TO SAID BED THROUGH AN ELONGATED TRANSFER ZONE, THE METHOD OF SIMULTANEOUSLY CRACKING A HEAVY OIL MORE REFRACTORY AND MORE VOLATILE THAN SAID CHARGE OIL WHICH COMPRISES INTRODUCING ONLY SAID MORE REFRACTORY OIL INTO SAID TRANSFER ZONE TO TRAVEL THERETHROUGH IN CONTACT WITH HEATED COKE PARTICLES THEREIN, FOR A DISTANCE SUFFICIENT THAT SAID MORE REFRACTORY OIL IS CRACKED THEREIN AT A TEMPERATURE SUBSTANTIALLY ABOVE THAT TO WHICH SAID CHARGE OIL IS SUBJECTED.