US2920032A - Fluid contact coking of hydrocarbon oils - Google Patents

Description

Jan. 5, 1960 A. R. VANDER PLox-:G EVAL 2,920,032

FLUID CONTACT coKING oF HYDRocARBoN oms Filed Dec. 1, 1954 'inoperable Zones of the initial contacting and'at remote points thcre- UnitedA States Patent* FLUID CONTACT coKING' oF y HYDRocARBoN oILs Application December 1, 1954, serial No. 472,281

4 claims. (cl. 20s-127) This invention relates to the cracking and coking of hydrocarbon oils in contact with highly heated'powdered or pulverulent coke under fluidized conditions and pertains to a process in which the coke particles are withdrawn from the cracking and coking reactor and subjected to combustion to burn a portion of the coke and hot coke returned to the reactor.

An essential object of the invention is to providewa process capable of continuous operation for extended periods of time. Diiculty has hitherto been experlenced in maintaining ilnidization during a run. Efforts to operate this type of process have encountered loss in uidization due to the agglomeration of coke particles with heavy residual hydrocarbon material with resultant plugging of the system and stoppage of the operation. lt has now been discovered that a highly critical factor in establishing and maintaining proper fluidization resides in the particular manner of rst contacting the oil with the coke particles. The invention provides a method Vfor this' contacting and for maintaining eflicient fluidized conditions. In'accordauce with the invention the oil and coke particlesv are maintained under uidized conditions in a reaction zone with the formation of a dense phase and a superposed dilute phase, the oil is introduced into the reaction zone at an intermediate point in the dense phase therein, iluidization is established and maintained by admitting a uidizing medium, such as steam or light hydrocarbons, into the lower portion of the reaction zone, coke is Withdrawn from the dense phase, dispersed with air or oxygen-containing gas and directed through a transfer line to a super-posed coke burning zone wherein burning of a portion of the coke is eected under iluidized conditions, highly heated coke is withdrawn from the dense phase of the coke burning zone and is passed by gravity ow downwardly into the dense phase of the reaction zone. This method of procedure enables the proper initial contacting of the coke particles with the oil so as to avoid serious agglomeration and to maintain uidization in the reaction zone. The oil `is preferably introduced into the dense phase of the reaction zone by being discharged therein in a downward direction against the rising vapors and gases which it has been found facilitates the proper dispersion of the oil on the coke particles.

We find that the temperature in the immediate vicinity of the charge nozzle or nozzles, that is, where the oil is irst brought into contact with the coke particles is exceedingly critical in maintaining proper fluidization in the reaction zone. In this zone of initial contacting the maximum heat load for heating the charge oil to reactor Aconditions and for providing at least a portion of the heat of cracking is located. lf the heat load becomes excessive coke agglomeration with unvaporized charge will occur as a result of the low temperatures involved and if the condition continues the system will become Thermocouples are provided at the zone or I'ifatented Jan. 5, 1960 from by means of which the processy may be accurately controlled. Thus, for instance, if agglomeration occurs at any point the fact is quickly reflected in a drop in temperature (a temperature dilerential between the point and the mass of the fluidized bed) and the matter can be remedied before serious agglomeration occurs.

During -a run there isa general tendency for the average particle size of the coke to continually increase with a concurrent disappearance of the finer mesh coke. In practicing the invention the coarser coke particles are selectively withdrawn from the reactor-burner cycle so as to thus maintain in the system coke of proper sizes for uidization. Preferably, this separation is applied to the coke flowing from the coke burner to the reactor and thev coarser coke together with agglomerates that may have been formed is withdrawn from the system while the liner coke continues the cycle to the reactor.

The process is adapted particularly for cracking and coking of residual stocks, such as reduced crude petroleum, cracked residues, heavy residues from shale oil, tars from the carbonization of coal and other heavy residues, to produce gasoline as well as gas oil such as is adapted for subsequent catalytic cracking.

For the purpose of more `fully disclosing the invention reference is had to the accompanying drawing which is a diagrammatic elevational view of an apparatus constructed in accordance with the invention and constituting an embodiment thereof.

The apparatus includes a reactor or coking drum 10 and a coke burner or separator 11 which is positioned above the reactor or coking chamber. Oil to be subjected to cracking and coking in contact with pulverulent or nely divided coke in the reactor 10 is introduced through a line 12 provided with a plurality of branch lines such as 12a, 12b, and 12C, each having one or more nozzles 13 for distributing the oil into contact with the coke particles in the reactor. Steam or other gas is introduced through a ring distributor 14 at the bottom of the reactor and serves to maintain a iiuidized condition of the oil and coke in the reactor.

Coke from the dense phase is withdrawn from the b ottom of the reactor 10 and is picked up by means of air or oxygen-containing gas and delivered through line 15 and distributor 15a to the coke burner and separator 11. The line 15 constitutes both a transfer line and a burner. Fluidized conditions are maintained in the chamber 11 and highly heated coke is withdrawn from the lower portion of the chamber and delivered by gravity ow through a standpipe 16 at an intermediate point in the reactor 10 within the dense phase therein. The lines 15 and 16 are of ample diameter, such as for example 24 in a large unit, and are constructed with gentle angles so as to avoid the liability of having either of the lines obstructed by any coke deposits. Flue gas leaves the coke burner 11 through a cyclone or separator 17 having a dip leg 18 for returning coke particles to the dense phase therein.

Instead of introducing the charge oil into the reactor at a plurality of different levels therein the oil may be introduced at one level which should be immediately adjacent the outlet of the coke return line 16. But coke is dilicult to maintain in a properly fiuidized condition. The uidization characteristics may be improved by increasing the vapor velocity from the reactor but coke carryover from the reactor imposes a limit to this method of improving fluidization. Furthermore, there is always the possibility of depositing too much oil on the coke about the charge entry point with the danger of agglomeration. The method of distributing the charge oil by introducing it at different levels in the iluidized bed is generally a better method of distributing the charge oil and at the same time avoiding coke carryover from the reactor.

The vapors and gases evolved in the reactor 1t) are removed through a cyclone or separator 19 positioned in the dilute phase therein and provided with a dip leg 20 extending into the dense phase to return the separated coke particles. The vapors and gases pass out through vapor line 21;

Air or oxygen-containing gas is introduced by a blower 22 and line 23, thence through line 24 into the tubular burner and transfer line 15. An air preheater 25 is provided for starting up but after operating conditions have been established the air preheater is cut out since the ternperature of the coke being removed from the reactor is adequate to initiate burning in the transfer line i5.

In the fluid contact coking process there is a tendency as the run proceeds for the build-up in the system of coke particles of increased size. vThe enlarged particles interfere with proper uidization and may cause agglomeration and plugging of the system. Accordingly, a portion of the coke is regularly withdrawn from the cycle, preferably at a point downstream from the colte burner, and this coke is subjected to classication to segregate the larger sized coke particles from the liner colte and the larger sized colte is removed from the system. rlhis separation may be accomplished in various ways such as by screening, centrifugalclassifying and gaseous elutriation. A shown in the drawing a portion of the colte ilowing in line 16, only a minor portion required, is withdrawn and conducted by a line 26 to an elutriator 27. Steam er other gaseous medium admitted through a distributor 2S fluidizes the colte particles in the chamber 27 with the resultyant formation of a dense phase and a dilute phase therein. The coarser particles are concentrated in the dense phase and are removed by a line 29 from the system to constiute the product coke of the process. The finer coke particles are removed in the steam or other gases and are conducted by a line 30 to the reactor 10 preferably entering the reactor through the conduit 16. Thus the larger sized colle which might interfere with proper iluidization is selectively withdrawn from the system.

By initially contacting the oil with the coke particles in the reactor at an intermediate point in the dense phase of the uidized mass so as to avoid agglomeration and provide good fluidizing conditions and then by selectively removing during the run any coke particles of too large a size for good fluidization fa condition of effectual lluidization is continuously maintained in the reactor.

A coke hopper 31 is provided for storing coke between runs and for furnishing make-up coke when required. At the end of a run the coke in the system is removed to the hoper through unloading lines (not shown) and at the beginning of the run coke from the hopper is blown to the coke burning chamber through a loading line (not shown). Normally, there is suicient fine coke in the system for the desired contacting and iluidizing in the reactor but at times the amount of coarser colte removed from the system may increase so as to require the addition of malte-up coke. This may be accomplished by withdrawing coite from the hopper 31 and slurrying it with a liquid, preferably oil. Thus oil is introduced by a pump 32 through a line 33 picking up cokeV from the hopper and directing it to the reactor preferably at a lower point therein. It sometimes happens that when the makeup coke is admitted to the system as a dry powder there is a considerable tendency for this coke to be carried out of the system; by introducing the coke wetted with the oil this loss in coke is avoided;

The vapor line 21 from the reactor 10 extends to a fractionating tower 34 for fractionating the reaction products delivered from the reactor. The overhead vapors from the tower 34 pass through a' vapor line 3S to a condenser and distillate receiver (not shown). The charging stoel: or a portion thereof is introduced through a line 36 into the vapor line 21 to provide cooling and to prevent cokihg in vthe vapor line.v The mixture of charging stock and effluent vapors and gases from the reactor ow into the `4 lower portion of the fractionator 34. Unvaporized charge stock together with heavy reflux condensate is withdrawn from the bottom of tower 34 and is directed by a pump 37 through the line 12 to the reactor. In some cases a portion of the charging stock may be directed to the lower portion of the fractionator 34 although generally it is found that all of the charging stock may well be introduced through the vapor line.

Steam is a good fluidizing medium for the process. Light hydrocarbons including normally gaseous hydrocarbons as well as the lighter liquid hydrocarbons are also satisfactory and at times may be more economical than steam. Thus selected portions of the lighter hydrocarbons produced in the process, such as propane and butane fractions and naphtha, may be recycled for promoting fluidization in the reactor. In one method of operation efuent from the reactor 10 is recycled to the reactor. In such operation the vaporous stream is preferably subjected to partial cooling to separate the higher boilingcomponents and the vaporous constituents are recycled by a compressor or blower. These various methods of recycling fractions of the reactor efliuent are used to supplant, or preferably merely to reduce, steam requirements.

When good fiuidizing conditions are being maintained in the reactor the temperature is fairly uniform throughout the fluidized mass. Thus, for example, when operating within a range of 975-l000 F. as indicated by a thermocouple located near the outlet of the charge nozzle the temperature shown by a thermocouple positioned at a more remote point in the uidized mass will normally be within about 5 F. of the temperature of the first thermocouple. A spread of about 10-15" F. between these two temperatures indicates that agglomeration about the charge nozzle is beginning to occur. By observing the temperatures between points adjacent the charge nozzles and at remote points in the uidized mass it is possible to quickly observe any tendency toward agglomeration so that the condition may be remedied before it gets serious. The condition may be corrected by various means; the temperature may be raised by increasing the temperature in the coke burner, the steam partial pressure in the reactor may be increased, steam may be introduced into the oil charge line or injected about the charge nozzle. Thus by getting a timely warning by means of the temperature differential any tendency toward agglomeration may be checked and conditions of good fluidization maintained.

The temperature in the reactor will generally be of the order of 900 F. and 1000 F. Velocities and rates of flow and other conditions will vary considerably with the size of the equipment and with other factors. In a typical operation the temperature in the reactor is 975 F. under l0 p.s.i.g. pressure with a coke to oil ratio of about 10:1. Reduced crude of 16 API gravity is charged to the vapor line 21 at a rate of 125 bbls./hr. reducing the temperature therein to 825 F. With a pressure of 7 p.s.i.g. in the fractionator 34 and a temperature of 800 F. at the bottom thevoil is delivered by pump 37 to the reactor at a temperature of 780 F. Steam is admitted to the reactor at a rate of 6,300 lbs./ hr. With a hold-up in the system of 58.9 tons of coke, coarse coke is removed from the system through line 29 at a rate of 1.47 tons/hr. The temperature in the coke burner is 1075 P. under a pressure of 7 p.s.i.g.

In a modification of the process different types of charging stock may be admitted into different points in the reactor and the lighter or more refractory stocks admitted into the lower portion of the dense phase and the heavier stocks admitted at a higher point. Thus, for example heavy virgin stocks such as reduced crude may be admitted into an upper portion of the dense phase bed and recycle gas oil admitted into a lower portion.

Obviously, many modications and variations of the invention, as hereinbefore set forth, may be made without vdeparting from the spirit and scope thereof, and

1. A continuous process for the cracking and coking of a heavy hydrocarbon oil that comprises subjecting said oil to contact with coke particles in a dense phase fluidized bed reaction zone maintained at a temperature within the range of about 900 to 1000* F., introducing said oil at an intermediate level in said reaction zone whereby said oil is distributed over the coke particles therein, introducing a fluidizing medium comprising steam into said reaction zone, withdrawing coke from said reaction zone and subjecting said withdrawn coke to combustion, recycling resultant highly heated coke to said reaction zone, determining the temperature at a rst point adjacent to the point at which said oil is introduced into said reaction zone, determining the temperature at a second point within said reaction zone at.

a point remote from said rst point whereby conditions preventing agglomeration prevail so long as the temperature of said first and second points are substantially the same, and increasing the temperature of said reaction n 2. The process of claim 1 wherein said reaction zone temperature and the ratio of steam to oil in said reaction zone are increased responsive to a temperature differential between said rst and said second points in excess of 10 F.

3. The process of claim l wherein said reaction zone temperature is increased and steam is introduced with said oil responsive to a temperature dierential between said irst and said second points in excess of 10 F.

4. The process of claim 1 wherein said reaction zone temperature is increased and steam is injected about thev oil inlet point responsive to a temperature dierential between said rst and said second points in excess of.

References Cited in the file of this patent UNITED STATES PATENTS 2,707,702 Watson May 3, 1955 2,717,867 Jewell et al Sept. 13, 1955 2,719,114 Leffer Sept. 27, 1955 y2,731,400 Jahnig et al. Jan. 1, 1956 2,788,312 Moser Apr. 9, 1957 OTHER REFERENCES Petroleum Processing, September 1953, pages 1316-

Claims (1)

1. A CONTINUOUS PROCESS FOR THE CRACKING AND COKING OF A HEAVY HYDROCARBON OIL THAT COMPRISES SUBJECTING SAID OIL TO CONTACT WITH COKE PARTICLES IN A DENSE PHASE FLUIDZIED BED REACTION ZONE MAINTAINED AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 900 TO 1000*F., INTRODUCING SAID OIL AT AN INTERMEDIATE LEVEL IN SAID REACTION ZONE WHEREBY SAID OIL IS DISTRIBUTED OVER THE COKE PARTICLES THEREIN INTRODUCING A FLUIDIZING MEDIUM COMPRISING STEAM INTO SAID REACTION ZONE, WITHDRAWING COKE FROM SAID REACTION ZONE AND SUBJECTING SAID WITHDRAWN COKE TO COMBUSTION, RECYCLING RESULTANT HIGHLY HEATED COKE TO SAID REACTION ZONE, DETERMING THE TEMPERATURE AT A FIRST POINT ADJACENT TO THE POINT AT WHICH SAID OIL IS INTRODUCED INTO SAID REACTION ZONE, DETERMING THE TEMPERATURE AT A SECOND POINT WITHIN SAID REACTION ZONE AT A POINT REMOTE FROM SAID FIRST POINT WHEREBY CONDITIONS PREVENTING AGGLOMERATION PREVAIL SO LONG AS THE TEMPERATURE OF SAID FIRST AND SECOND POINTS ARE SUBSTANTIALLY THE SAME, AND INCREASING THE TEMPERATURE OF SAID REACTION ZONE WITHIN SAID RANGE OF ABOUT 900 TO 1000*F. RESPONSIVE TO A TEMPERATURE DIFFERENTIAL BETWEEN SAID FIRST AND SAID SECOND POINTS IN EXCESS OF 10*F. THEREBY MAINTAINING CONDITIONS PREVENTING AGGLOMERATION.

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