US2655464A - Residuum coking and cracking - Google Patents

Description

Oct. 13, i953 J. w. BROWN ETAL RESIDUUM COKING AND CRACKING 5 Shets-Sheet l Filed June 9. 1951 FLUE GAS To FQACUQNATQL #IGM-i Of- 13, 1953 J. w. BROWN ETAL RESIDUUM COKING AND CRACKING l 2,655,464 Filed June 9. 1951 3 Sheets-Sheet 2 FLue @A5 E To Drzonucr 22 g 12mm/:lv 121 u4- 112:

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f iOiGL f STnAM T-T I G 2 es E. Ua agg gn-venborfs Oct. 13, 1953 J. w. BROWN ETAL RESIDUUM COKING AND CRACKING 2,655,464 Filed June 9. 1951 3 Sheets-Sheet 3 CATALYST QE GE M E QATOQ 181 [2E AcToQ E Patented oci. 13, p 1953 2 655 464 RESIDUUM CGKING AND CRACKING James W. Brown, Elizabeth, and Charles E. Jahnig, Red Bank, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application June 9, 1951, Serial No. 230,746 5 Claims. Cl. 196`49) is primarily accomplished thereafter in a catalo tamination, and a maximum yield of high quallytic manner. Specifically, the vapors resulting ity motor fuel fractions. Other objects will be from the coking zone are passed to a cracking apparent from the subsequent description of the carbonaceous deposit. A characteristic feature a heavy hydrocarbon feed is contacted with hot the coking zone as well as the catalytic cracking bed, followed by a cracking step wherein the zone are supplied by direct mixing of hot reresulting hydrocarbon vapors are contacted with generated catalyst with the inert solids 1n a mixa dense fluid bed of a cracking catalyst having ing zone, whereupon catalyst and reheatedinerts a particle size distribution substantially differ- However, such processes have not been `cornmeroff while in a dense iluid phase, a heat exchange cially attractive in view of the great heat restep wherein the hot regenerated catalyst is quirements involved, especially since it has been mixed with coke particles withdrawn from the a feed cut which had to be revaporlzed in the ation or the like into its two principal compofeeding of a'heat carrying medium such as coke 35 ing of the seed coke withdrawn from the coking similarly Valuable extraneous fuels such as fuel 40 illustrated by severalspeciiic examples wherein gas. In still other known fluid coking processes. reference is made` to the accompanying drawing. coke and a cracking catalyst or inert inorganic Fig. 1 is a semi-diagrammatic illustration of to mixing with hot regenerated catalyst in a separate mixing and elutriation zone whence reheated coke particles are returned to the cokng Zones and regenerated catalyst is returned to the catalytic cracking zone;

Fig. 2 illustrates an alternative modification of the invention, according to which the catalytic cracking zone is superimposed on the coking zone in the same vessel which also contains the mixing-and-elutriation Zone in direct communication with the coking zone; and finally Fig. 3 illustrates a third alternative according to which low temperature coking oi the hydrocarbon feed is essentially completed in a transfer line wherein the feed is mixed with hot coke particles prior to admission to the catalytic cracking acne wherefrom relatively fine catalyst is entrai ed overhead with the product vapors eventual recycling to the cracking zone whereas the relatively coarse coke is withdrawn at the bottom and mixed with further amounts of hydrocarbon feed.

Referring now in detail to Fig. l of the drawing, reduced crude such as an 8% bottoms fraction of about lil-30 Conradson carbon, oi about 5 AP gravity and obtained from the vacuum distillation of a West Texas crude 'or a similar heavy residue is sup-plied to coking Zone 2 through line i as a liquid at a temperature of about 300 to 800 F., or preferably at about 700 lneit solids, preferably petroleum coke particles having a particle size in the range between about 100 and 500 microns are maintained in the cokf 35 coking zone, e. g. at 1000 F., but a substantial ing Zone at a temperature of about 850 F. to 950 F. as a dense, turbulent, uidized bed 3 having an upper level d and an apparent density of about l to 50 lbs/cu ft. with densities of about 0.01 to lbs/cu. ft. above level 4, whileAV an inert gas such as steam introduced through lines 30, 3| and 32 as later described is being passed upwardly through the coke particles at a linear superficial velocity of about 0.5 to 5 feet per second.

The vapors produced in the hot coking Zone 5 2. are passed therefrom through perforated plate 5 into the superimposed catalytic cracking Zone 5 maintained at about 900 F. to 1000D F. and containing a dense, turbulent, fluidized bed 1 of a cracking catalyst such as one of the known synthetic silica-alumina composites. The physical characteristics of catalyst bed 1 are essentially similar to those of the coke bed 3 described above, except that the catalyst particle size is within the range of about 50 to 150 microns and is preferably at least to 50 microns smaller than the smallest particles constituting a substantial portion of the coke in bed 3, so as to assure an efficient separation of the two solids in the subsequent elutriation. Thus, for instance, when coke ranging in size down to about 100 microns is used in the coker, the catalyst particles are preferably in the range between 20 and 50 or 80 microns, but when the coke particles of the process range in size between about 365 200 and 300 microns, catalyst particles in the range up to about 150 microns may be used. The cracked. hydrocarbon vapors are withdrawn from cracking zone Ei through cyclone 8 or other gas- I solid separator means and passed through line 0 to a conventional finishing system for recovery of naphtha, gas oil and other desired hydrocarbon fractions.

Spent catalyst is withdrawn from bed 1 through standpipe l0, which may have taps ll 7 for admitting a small amount ci an aeration gas, and the withdrawn catalyst is finally mixed with air admitted through line l2 and passed to regenerator I3 where carbonaceous deposits are 5 burned off the catalyst in fluid phase at a temperature of about 1100* F. to l250 F. in a manner well known per se. Excess heat may be removed from the system by means of heat exchanger l4 and hot regenerated catalyst is use l0 to supply the heat requirements of the coking zones as well as the catalytic cracking zones in the manner described later herein. Moreover, especially where exchanger Hi is intended for preheating feed and thus supplying a portion l5 of the regeneration heat directly to the coker, it

may be necessary to locate the exchanger in a separate vessel through which hot catalyst is circulated. This allows greater flexibility and control over regeneration temperature without 20 causing undue coking of feed within the heat exchanger, as might otherwise be the case if regenerator temperature permitted only a low feed circulation rate through the exchanger when immersed directly in the regenerator bed as shown in Fig. l.

Coke from bed 3 of the coking zone is withdrawn through downcomer l5 to another stage It where the coke is again maintained as a dense, turbulent, fluidized bed ll and where any unconverted, oily residuum which may be adhering to some of the coke particles is cracked and converted into vapors and dry coke. The second and any further consecutive stages are preierably at a higher temperature than the main advantage is obtained even when all stages are at the same temperature 'as the main coking Zone 2, since the main purpose of such staging is the prevention of oil soaked, incompletely 40 coked particles leaving the coker bed in the coke portion withdrawn to the mixer as later described, which portion is a fairly representative sample of the particle mixture present in the particular bed.

For example, where only a one-stage coker is used, 22% of the coke withdrawn therefrom will have a residence time equal to less vthan 25% of the average or nominal holdup time, and such particles usually exhibit a considerable degree of stickiness. But, by using a 2-stage or even a 3-stage coker, the percentage of particles being withdrawn from the last stage having a residence time equal to less than 25% of the average total holdup Vis reduced drastically to l0 and 4%, respectively, and consequently the stickiness of the resulting coke product is materially decreased.

Net coke product may be withdrawn from the last bed l1 through pipe I8, it being particularly desirable to remove those coke particles which have grown too large for good iiuidiaation in the system. Control of the coke particle size in the system can be achieved by screening out the largest coke particles while recycling the smaller ones, or the withdrawn particles may even be ground before being returned to the system. However, where grinding is employed, it is desirable to remove also the fines from the coke to be returned, as otherwise such coke fines would eventually become mixed with the catalyst and undesirably increase the necessary amount of carbon burning capacity.

A side stream of the coke from the dry coke bed l1 is withdrawn through line I8 to mixer- '5 elutriator 20 where the coke particles are mixed rwith hot catalyst particles withdrawn from remildest cracking conditions. After passage generator I3V through line 2| while an inert gas through coke bed |01 the hydrocarbon vapors such as steam is introduced into the bottom of liberated in the coking steps pass overhead from they exhange heat so that the catalyst is cooled below the cracking section |09 and next to coking and the coke heated to about 1100 F'. and more- 10 section |05.

over, due to the previously described difference in In the cracking section the hydrocarbon vapors particle size, the relatively fine catalyst is stripped flow up through the dense, turbulent. iuidized bed from the Iiuidized mixture in vessel 20 and enof cracking catalyst |2 at about 900 F.1000 F'.

lytic conversion step. Spent catalyst is stripped with steam in zone |28 Coarse coke particles, essentially free of catalyst in the usual manner and goes through line I to and reheated by contact with the regenerated e regenerator ||6 where the carbonaceous dethrough standpipe 23 and after admixing with 20 combustion. Air is bloivn into the regenerator of the hot mixing vessel V and standpipe 24 30 opening |24 to the segregated mixingsectionlHin her bed |1 and pipe I8 described earlier herein S eam Withdrawn from the coker bed |01 through Referring to Fig 2 the modification illustrated .Wall Opening |25 Which is located at a level intel ereln accomphshes the purposes 0f the lnvenmediate between the Catalyst 111181; |24 and the zone is directly in the main reactor and conseinjected thTOllgh line |29 at the bottom of the quently requires a, high pressure-drop grid bemixing Section at a rate to giVe an upward gas tween the coking zone and the superimposed cat- Velocity in the mixing section between about o 1 in the Conversion Z0netrained upward from the catalyst-coke mixture In Operating this system, the heavy hydrowhile the coke particles are uidized but are not carbon feed preheated to about 700 F. is intro- Substamlally entraned overhead.

duced through line |0| and heated to about 800 The regenerated Catalyst is thus carried into to 1100 11". by mixing With colse particles Withthe Cracking SCOD |09 Where it again becomes line |0|a is then passed upwardly through transthe Ffgellelatr- This facilitates Operating the fer line |04 at a rate of about 15 to 50 feet per 55 Crackbmg react@ at H1 temperature IOWeI than second, equivalent to a transfer line residence that 1I1 the C0k1ng Zone. The relatively coarse with only a minimum formation of thermally System can be Obtained by elutration, Screening, cracked naphtha. After this first-stage coking iii vSelective CyGlOne action 0r the like. For instance, the transfer line, colii'ng of the feed is completed `this can be done by locating a cyclone |26 in soine in the Coker bed |01 Where any eolie particles 0r even in all Openings of the reactor grid |10 containing a surface Iilm of incoinpletely coked and by withdrawing the separated coke nes from from the system at least periodically, or with the product coke.

Likewise, where catalyst particles tend to stick to the coke in the heat transfer mixer so that they would be eventually rejected from the system along with the product coke, further modification of the system may be desirable. For example, the cufculty can be overcome by mixing the coke as it leaves the coking bed. with hot recycle coke and then providing sufficient holding time to dry the coke in an intermediate zone before it contacts the hot catalyst in the heat transfer zone and stripping steam can be added to assist the operation.

Referring back to grid which supports the catalyst bed in the cracking section |09 above the dilute phase of the coking section |05, it is important that the pressure drop across the grid be such as to cause the desired upward flow of catalyst from the mixer-elutriator iii to the catalyst bed ||2 while preventing fiow of catalyst to the coker bed |01 throughwall opening |25. The required pressure drop will usually range between about 1 and 5 or 10 pounds per square inch and must be at least enough to offset the differential between the hydrostatic pressure exerted by the relatively dense upward stream of catalyst fines suspended in steam in the upper portion of the mixer-elutriator section of the reactor vessel the apparent density of this phase being between about 10 and i0 lbs. per cu. ft., and, on the other hand, the adjacent dilute phase existing above level |08 of the fluid coker bed |101. In general, the velocity through the openings in grid l l0 should be maintained in the proper range to give the required pressure drop so as to coinpensate for the lower density in the dilute phase above level |08 compared to that in the upper part of zone In the operation of this system, the temperature at the coke-catalyst mix point is regulated to give the desired heat balance. The coke circulation rate is controlled by the valve in line |02 to supply the desired heat to coking zone |05, and the catalyst rate will be fixed by the heat released in the regenerator and the difference between the temperatures in lines H5 and |23, although auxiliary cooling (or heating) means may be provided. Also, additional flexibility is possible by iowing part of the catalyst through bypass line |30. These controls allow operation over a wide range of coker, cracking, and regeneration temperatures, and provide flexibility in catalyst/ oil ratio.

Fig. 3 illustrates still another embodiment of the invention. In operating this system a liquid residuum of the type previously described, preheated to about 300 to 800 F. may be supplied through line |42. Hot inert solids, specifically coke having a particle size of about 100 to 500 microns may be added from standpipe his at a temperature of about 900 to 1100 F. in an amount of about 700 to '7,000 lbs/barrel. By this addition of hot coke the temperature of the feed may be raised to about 800 to 1000 F. whereby the more volatile components of the feed are more or less completely vaporlzed without, however, being converted to naphtha and lighter products in any substantial degree. The less volatile components of the feed are deposited on the coke particles during their travel through line |43 and before they enter the reactor |40. In particular it is desirable to make line |43 sufciently long to allow for a residence time therein of about 0.5 to 5 seconds so that substantially all inorganic salts'and other contaminants as Well as a large proportion of carbon from the asphaltenes `and other carbon forming constituents of the feed are deposited on the coke particles and the resulting carbonaceous deposit is sufficiently dried to avoid undue stickiness of the coke particles after they enter reactor |46.

The resulting dispersion of coke in hydrocarbons may enter reactor |46 through distributing grid |68 to form above the grid a dense turbulent fluidized bed or mass M146 of the type specified earlier with reference to the reactors of Figures 1 and 2. About r100 to 5,000 lbs. of hot regenerated catalyst per barrel of feed may be supplied f from standpipe |50 as will appear hereafter. As

in the previously described examples, this catalyst has a particle distribution range below the range of the above-described coke particles, for instance, the catalyst may have a particle size up to about microns and must be readily entrainable at the fluidization conditions of reactor |46. Mass M146 is maintained at a temperature of about 900 to 1l00 F. conducive to the desired catalytic cracking operation and may be composed of a highly active silica-alumina composite or other known cracking catalyst.

Reactor |46 may be provided with an elutriation well |52 into the bottom of which an elutriation gas such as steam or a light hydrocarbon gas is admitted via line |54. Preferably the elutriation well is a small-diameter vertical section which extends downwardly from a point just below dense bed level Lus so as to be in open communication with dense, fluidized bed M146 and is preferably lled with a packing of bodies of non-fluidizable size, such as Raschig rings or the like, having interstices which permit percolation of the fluidized solids within the packing. The elutriation gas may be supplied via line |54 at a rate sufficient to elutriate from packed section |52 substantially all the catalyst so that coke particles practically free of catalyst may be withdrawn via standpipe |-4i and supplied to line |43 in the manner and for the purpose described above. Any desired portion of the withdrawn coke may be drawn off standpipe ldd via line |50 for the removal of net product coke, together with the contaminants deposited thereon. Purified or make-up solids may be supplied to the system via line |50, as for example seed coke, or make-up catalyst.

The catalyst which may contain up to about 3 wt. per cent of coke is readily entrained by the product vapors and elutriation gas and carried in the form of a dilute suspension overhead from mass Mms through line |00 into separator |62 from which product vapors may be passed to recovery via line |04. Separated catalyst, preferably stripped of hydrocarbons by injection of an inert gas such as steam through one or more taps t to a stripping zone may be supplied via line |56 to a lower portion of catalyst bed M168 in regenerator |65. Simultaneously, air is blown into regenerator |08 through line |'0 and grid |12 at conditions suitable to maintain the catalyst mass Misa in a dense, turbulent condition at a temperature of about 1000 to 1280o F. by combustion of coke deposits in a manner well known per se and heretofore outlined in connection with the catalyst regenerators of Figs. 1 and 2. Flue gases and entrained catalyst may pass into cyclone |14 from which separated catalyst fines may be returned via dip leg |153 or discarded via line |18, flue gases being withdrawn via line |80. Make-up catalyst may be added aanmet- Q Having described specific embodiments of the ble to the treatment of heavy residual crude reactor temperatures, as otherwise the Wet coke be reduced -crudesobtamed hy atmospheric or andai-'1ct coke `particles are mixed therein in a.

to tar from visbreaki'ng operations and to other 20 by mixing with about 0.2 to 2 parts of hot regencles in Vapor, as lle 3| 0f Fg- 15 1m@ |04 40 ereneto cokerxsoldsthugh-it wiilbe underperse phases above the dense beds'. In elutriation zones such as zone of` Fig. '1, zone `H I `o1' 50 sql'dsas'hretofo described; va

on the particle size and density, @as -well as lsize 105s fbrtlyt' 'ugto size from aboutrlOO to i300 or -500 microns,

Moreover ,partculaylm startmlgup the open ,eneration in a manner obvious to those smiled as hereafter `described at somewhat greater lThe inert sonas are heldlup mule primary 75 `catalyst regenerator such. as Vessel i168 and inally 11 returned therefrom Vthrough standpipe 150 t0 the reactor.

Reaction conditions may include coking ternabout 800 to 1200 F., catalytic cracking temperatures of about 800 to 1000 F. and catalyst regeneration temperatures of about 1000 to 1200 or 1300 F., depending on the nature of the catalyst used. Oi course, the regenerator temperature and the rate of circulation of catalyst and coke to the inert solids are reheated to the temperature by direct heat exchange lyst before separation and recyclingI version zones, are so adjusted as to tended temperature conditions both in the zones and the catalytic cracking zones.

Having given a full description of the invention and of the manner of using it, the invention is particularly pointed out and distinctly claimed in the appended claims.

We claim:

1. A process for convertng a residual petroleum feed stock boiling predominantly above 900 F. into ts and coke which lighter produc comprises introducing the residual stock into a primary coking zone to the congive the incoking wherein coke particles of a size between 100 and 500 microns are maintained at a temperature between about 800 and 1100 F. as a dense fluidized bed with a less dense phase thereabove, and wherein the petroleum stock is vaporized and partially coked substantial conversion to naphtha and lighter products, passing the resulting petroleum vapors upwardly through a cracking zone maintained at about 900 to 1100 F. and containing a dense luidized bed of cracking catalyst ranging in particle size up 100 microns with a less dense phase above said bed, recovering cracked vapor products from the cracking zone, passing spent catalyst from the cracking zone to a regeneration zone maintained at a temperature between about 1000 and 1300 F. through which an oxygen-containing gas is passed in an upward direction at a rate sufficient to maintain the catalyst particles as a dense uidized mass while burning ofi deposited carbon, overflowing the coke particles containinga wet coat of partially coked feed from the aforesaid primary coking zone to at least one secondary coking zone wherein the cokeparticles are maintained at a tem- `perature above 800 F. as a dense luidized mass by upward passage of a dry inert gas therethrough, recovering dry net coke product from the secondary coking zone, passing a portion of the dried coke from the secondary coking zone to a mixing zone, also passing a portion of catalyst at a temperature above 1100 F. from the regeneration zone to the mixing zone and there intimately mixing it with the dried coke, passing an inert gas upwardly through the resulting particle mixture in at the minimum fluidization rate of the coke and tively returning the entrained catalyst particles from the mixing zone to the conversion process, withdrawing catalyst-iree, reheated coke particles from the bottom of the mixing zone and returning the reheated coke to the primary coking zone. 2. A process according to claim 1 wherein the secondary coking zone, the primary coking zone and the catalytic cracking rone are superimposed above each other in the sequence recited.

3. A process according to claim 1 wherein some coke withdrawn from the 'mixing zone is returned to each of the coking zones and wherein the secondary coking zone is maintained at a temperature' between 1000 and 1200 F. and substantially higher than the temperature oi the primary coking zone.

4. A process for converting a residual hydrocarbon feed characterized by a Conradson carbon value in excess of 5 which comprises preheating the feed to a temperature between 600 and 800 F., mixing the feed with coke particles ranging in size between about and 300 microns and heated to a temperature between about 800 and 1200 F. to form a dilute suspension of coke in hydrocarbon vapors, passing the resulting suspension at a temperature oi about 800 to 1100 F. through an elongated and constricted primary coking zone at a superficial gas velocity of about 5 to 50 feet per second to a secondary coking zone of wider diameter wherein the upward gas velocity is within the range between 0.5 and 4 feet per second and wherein the suspended coke particles are accordingly maintained as a dense, turbulent, uidized mass, withdrawing the resulting hydrocarbon vapors from the secondary coking zone into and upwardly through a catalytic cracking zone superimposed thereabove, interposing a pressure drop of about to 5 lbs/sq. in. in the path of the hydrocarbon vapors between the secondary coking zone and the cracking zone, contacting the hydrocarbon vapors with catalyst particles ranging in about 0 and 80 microns and a dense turbulent fluidized mass in the lower portion of the cracking zone at a temperature of about 900 to 1100 F., withdrawing cracked hydrocarbon vapors overhead from the cracking zone, withdrawing spent catalyst from the dense turbulent mass of the cracking zone and passing it to a regeneration zone where it is maintained as a dense, turbulent, fluidized mass and regenerated by upward passage of an oxygen-containing gas therethrough at a temperature between 1000 and 1200 F., withdrawing hot catalyst from the regeneration zone and passing it to a lower portion of a mixing zone located adjacent to the secondary coking zone and below the cracking zone, overowing coke particles from the dense turbulent mass oi the secondary coking zone into an upper portion oi the mixing zone where the coke becomes reheated by countercurrent contact with the regenerated catalyst, introducing an inert gas near the bottom of the mixing zone at a rate sufficient to entrain the catalyst particles from the catalyst-coke mixture into the superimposed cracking zone, withdrawing reheated coke particles from the bottom portion of the mixing zone, and mixing the withdrawn coke with incoming iced.

5. A process for converting heavy hydrocarbons which comprises mixing a heavy hydrocarbon feed with coke particles ranging in size between about 100 and 300 microns and heated to about 900 to 1200 F. to form a dilute suspension of oilcoated coke particles in hydrocarbon vapors, passing the resulting suspension through a constricted elongated coking zone at a temperature between 800 and 1100 F. at a rate of 5 to 50 feet per second for a time of about 0.5 to 5 seconds and thereby coking the oily coat deposited on the coke particles, thereafter introducing the suspension into a cracking zone oi relatively large cross-section wherein the upward velocity of the hydrocarbon vapors is reduced to about 0.5 to 5 feet per second and wherein the introduced suspension becomes `mixed with cracking catalyst oi the reheated n vapors overhead from the cracking zone. 15

JAMES W. BROWN. CHARLES E. JAHINIG.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR CONVERTING A RESIDUAL PETROLEUM FEED STOCK BOILING PREDOMINANTLY ABOVE 900* F. INTO LIGHTER PRODUCTS AND COKE WHICH COMPRISES INTRODUCING THE RESIDUAL STOCK INTO A PRIMARY COKING ZONE WHEREIN COKE PARTICLES OF A SIZE BETWEEN 100 AND 500 MICRONS ARE MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 800 AND 1100* F. AS A DENSE FLUIDIZED BED WITH A LESS DENSE PHASE THEREABOVE, AND WHEREIN THE PETROLEUM STOCK IS VAPORIZED AND PARTIALLY COKED WITHOUT SUBSTANTIAL CONVERSION TO NAPHTHA AND LIGHTER PRODUCTS, PASSING THE RESULTING PETROLEUM VAPORS UPWARDLY THROUGH A CRACKING ZONE MAINTAINED AT ABOUT 900 TO 1100* F. AND CONTAINING A DENSE FLUIDIZED BED OF CRACKING CATALYST RANGING IN PARTICLE SIZE UP TO ABOUT 100 MICRONS WITH A LESS DENSE PHASE ABOVE SAID BED, RECOVERING CRACKED VAPOR PRODUCTS FROM THE CRACKING ZONE, PASSING SPENT CATALYST FROM THE CRACKING ZONE TO A REGENERATION ZONE MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 1000 AND 1300* F. THROUGH WHICH AN OXYGEN-CONTAINING GAS IS PASSED IN AN UPWARD DIRECTION AT A RATE SUFFICIENT TO MAINTAIN THE CATALYST PARTICLES AS A DENSE FLUIDIZED MASS WHILE BURNING OFF DEPOSITED CARBON, OVERFLOWING THE COKE PARTICLES CONTAINING A WET COAT OF PARTIALLY COKED FEED FROM THE AFORESAID PRIMARY COKING ZONE TO AT LEAST ONE SECONDARY COKING ZONE WHERE-

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