US2923678A - Continuous contact coking of two feeds with the second feed entering upstream of the first feed - Google Patents

Description

Feb. 2, 1960 A. H. SCHUTTE CONTINUOUS CONT CT COKING OF TWO FEEDS WITH THE SECOND FEED ENTERING UPSTREAM OF THE FIRST FEED Filed June 12, 1958 2 Sheets-Sheet 1 28 1 .1. Q 1 w 52 l i 30 Ezac/a fiactor J0 Z9 fiactionafork M ycle iock I I 19 Pmdzwt w W, MENTOR .vizggzasjfikizry'ckuite United States Patent O CONTINUOUS CONTACT COKING OF TWO FEEDS WITH THE SECOND FEED ENTERING UP- STREAM OF THE FIRST FEED Au'gust H. Schutte, Hastings on Hudson, N.Y., assignor to The Lummus Company, New York, N.Y., a corporation of Delaware Application June 12, 1958, Serial No. 741,986

3 Claims. (Cl. 208-55) This invention relates to a continuous contact cracking or coking of liquid hydrocarbons such as reduced crude and a cycle stock to provide selective cracking.

This application is a continuation-in-part of my copending application Serial No. 374,561, filed August 17, 1953,

now abandoned, and is a modification of the' invention disclosed in my copending application, Serial No. 581,246,

treating and the residue liquid on the particles moves downward with the column and ultimately forms a dry integrated part of the particles so that only vapors and dry solids are removed from the reaction system. The dry particles may then be reheated andreturned to the reaction By control of the contact particle temperature, system pressure and oil to solids ratio, I have effectively processed heavy stocks to produce coke and substantial yields of gas.

My present invention is based on a modification of the foregoing method by which I obtain an unusually high conversion per pass to produce maximum yields of gasoline from stocks that under normal circumstances are entirely unsuited either for catalytic conversion because of the high yield of carbon or are unsuited for thermal cracking due to premature coking or very low conversion per' pass.

My present invention is more specifically drawn to the utilization of a continuous contact system as hereinbefore described wherein different types of oil are applied to the continuously moving bed.

As an example of such an operation, I may charge to the unit, a reduced crude at a temperature of from about 650 to 850 F. and a cycle stock at a temperature of from about 600800 F. The cycle stock may come from a catalytic cracking operation on virgin gas oil or on a mixture of virgin and coker gas oils. The cycle stock, particularly if it comes from catalytic cracking, will normallly have a lower' carbon residue than the reduced crude charge and will also be of a more refractory character, i.e., more difficult to convert into gasoline. By introducing the cycle stock into the circulating coke stream, which is at a temperature of from about 1 850 to 1100 F., at a point upstream of the reduced crude inlet, the cycle stock Will be subjected to short time cracking at the maximum temperature. Since there is a relatively small amount of carbon residue and extremeknown.

2,923,678 i atented Feb. 2, 1960 1y high boiling hydrocarbons in the cycle stock, there will be a very small amount of heavy material deposited on the coke particles and the circulating coke, will, therefore, be essentially dry when it enters the reduced crude mixing zone. The vapors from the cycle stock cracking zone will pass through the reduced crude mixing zone and through the wetted bed in the reactor, which is preferably at a pressure of from 15 to p;s.i.g., as described in my patent application Serial No. 581,246. The purpose of the double injection is essentially one of selective cracking, subjecting the more refractory charge material to maximum severity conditions and the less refractory high carbon residue material to milder conditions followed by suflicient coke residence time to produce a dry coke.

Further objects and advantages of my invention will appear from the following description of a preferred form of embodiment thereof, taken in connection with the attached drawing in which:

Fig. 1 is a schematic elevation with parts in section of the major elements of my continuous coking or cracking system.

Fig. 2 is also a schematic drawing showing in outline a combination of contact and catalytic cracking.

A continuous coking cycle utilizing a gravity flowing mass of granular particles as disclosed in the above identified application includes a heating of the granular petroleum coke particles which are ultimately made in the system and the passage of such particles through a closed path to a reactor through which the particles pass downwardly by gravity. The liquid hydrocarbon charge which is uniformly distributed over the particles is converted by the heat of the particles to produce lowerboiling vapors and a dry coke coating on the particles. At least five minutes, and in some cases as much. as 40 minutes coke travel time, 'is required to convert the heavy ends 'to a completely free flowing dry bed of coke, part of which is removed as product with the balance recycled back through another closed path to the heater for reuse.

More specifically, in accordance with my present invention, the reactor is indicated at 10 and is normally a tall cylindrical vessel to: which the coke particles and liquid charge are continuously fed at the top and through which the particles travel downward solely by gravity while the liquid is converted by the dry coating on the coke particles. The vapors'may be removed from under a suitable disengager 12 and thence out through the outlet 14 to which quench liquid may be introduced at 16.. The relatively light end products in gaseous form are then removed at 18 and passed to a fractionator 19 as is well Suitable pressure controls, not shown, will be provided tomain'tain a pressure in the reactor of about several atmospheres and generally from 15 to 100 p.s.i.g. Higher pressures may be employed than are usual in solely residuum operations so as to increase the cracking per pass on the lower boiling positions present in the cycle stock.

Thedry solids pass through a bottom drawoif device generally indicated at 20,,more specifically described in my.U.S. Patent No. 2,658,031, such drawolf preferably including a series of vertical splitter plates so that there is a'uniform flow of the particles throughout the reactor coking in the vapor outlet14.

The dry coke particles discharge through the line 26 which extends to the elevated disengager 28. A relatively low pressure is maintained on this hopper by the control valve 30 so that the transfer of particles may be mechanically accomplished by the superior pressure in the re actor 10. The line 26 is preferably tapered and by throttling the discharge of particles from the open end of line 26 by limiting the rate of drawoff from disengager 28 by the setting of valve 32, the particles move in the line 26 in mass flow condition as more particularly described in my copending application Serial No. 412,803, filed February 26, 1954, and as described hereinafter.

The flow of particles from the disengager 28 is preferably through the classifier 34 which may be provided with an internal screen 36 to separate out the largest particles which are removed through the outlet valve 38. The-smaller sized particles are discharged into the reheater 40 through the line 42.

The reheater 40 which is operated at approximately atmospheric pressure, is supplied with air and a fuel gas through the lines 44 and 46 respectively, which discharge to burners 48 mounted in the upper wall, such burners being disposed to heat the particles by radiation and convection. Flue gases are removed through collector 49 and line 50 to the stack 52. The hot coke particles discharge in a substantially uniform manner through the outlet 54.

To obtain a suitable mass flow transfer of the particles from the outlet 54 of the reheater 44) at nearly atmospheric pressure to the higher pressure reactor 10, it is convenient to use tandem vessels 56 and 58 which are provided with valves 56a and 58a, such valves in turn being cyclically controlled by controller 60. The controller 60 also controls a pressure steam line 62 and a vent valve 78 to alternately pressure and depressure chamber 56. With the lift chamber 58 at 100 p.s.i.g. and

the coke reheater at 2 p.s.i.g., the coke flow in the lift lines 64 feeding the reactor is continuous. The lock chamber 56 serves to deliver the solids from the low pressure reheater 40 to the high pressure lift chamber 58 without causing pressure fluctuations in the rest of the system. The coke level in the reheater 40 and in the lift chamber 58 fluctuates slightly with the intermittent delivery of solids to and from the lock chamber 56.

The lift lines operate at all times in a fully dense, packed manner due to the fact that the reactor 10 always contains the maximum amount of solids. As a result the mass flow materially differs from prior types of fluid flow. If for example, in a fluid type flow system, the gas rate is increased with a constant solids rate, the flow line density decreases and the pressure drop decreases. In

the mass flow operation as heretofore described, there is I no change in flow line density because of the packed nature of the particles and with the increase in gas rate there is an increase in pressure drop.

' The complete control of flow is accomplished by the valve 32 which can be set at any desired rate within the limits of flow of the apparatus. This establishes a cone or pile of repose of particles surrounding the upper end of the lift line 26 which will completely throttle flow when the particles engage the top of the disengager 28. The flow from the disengager 28 then controls the movement of the particles from the bottom of lift chamber 58 which is at the same rate as the rate of withdrawal from the bottom of the reactor 10 into line 26 and into the top disengager 28. Preferably the steam line 62 may be fed from a refinery steam line of from 120 to 150 p.s.i.g. This is normally enough for the continuous elevation of the particles to the required height. A sixty foot sealing and lifting line 26 requires a minimum pressure of about 30 p.s.i.g. to operate and it will effectively resist high differential pressures even up to 300 p.s.i.g., without excessive gas flows.

With proper structural arrangement, the pressure in reactor 10 is more than sufiicient to overcome the pressure drop required for operation of the reactor outlet lift line 26. Since the oil vapors are withdrawn at an intermediate level and there is an upward flow of stripping steam from steam inlet 22, oil vapors are prevented from leaving the reactor through line 26 with the solids. Part of the total steam introduced into the reactor bottom will therefore flow with the solids through line 26 and will provide the lifting medium requirements of this line. Since the reactor 10 is at elevated pressure, maintained by controlling the pressure in the oil vapor drawoff line 14, and since the reactor always contains the maximum inventory of solids, it is not necessary to provide displacement steam equivalent to the volume of the flowing solids particles. Also, the steam requirement for displacing the void volume between the solids particles has been provided in order to do the stripping in the lower section of the reactor, below the vapor drawotf 14. The net steam required for operating the lift line 26 is therefore very small, amounting to only the steam required to produce the required pressure drop in the line.

The use of the dense packed or mass flow line 26 for a combination of solids transport and high differential pressure makes it possible to operate the reactor at elevated optimum pressures while maintaining the reheater at essentially atmospheric pressure, thus minimizing its cost and the work required for supplying combustion air. Differential pressure controllers are eliminated and the long sealing legs common in catalytic cracking processes are unnecessary. A practical, safe and easily operated design is obtained which reduces the overall height of the equipment to less than one half that required for conventional systems. These economies and advantages can be obtained at pressure differentials that are impossible with the usual methods of solids circulation such as dilute phase lift lines or fluidized transport. The relative pressures given as an example above are in no way limiting as far higher differentials may be obtained at moderate increase in power requirement for lift lines.

Provision is made at to draw off the larger particles separated by the secondary screen 36a, and if desired, such materials may be passed in part through the crusher 76 and thence returned to the reheater 40.v The net amount of coke product made may be drawn off through line 79 which is in communication with the drawoif line 75.

The liquid charge is applied to the moving particles as more particularly described in my copending application Serial No. 581,246 in which a cycle stock in line may be introduced to the moving particles passing through line 64 as by a series of inlets indicated at 86. This cycle stock may be coker recycle or outside recycle from line 85. Simultaneously a reduced crude may be applied to the contact material at 87.

Since the cycle stock is charged to the mixing zone at a temperature of from about 600 to 800 F. and the reduced crude is usually charged to the mixing zone at a temperature of from about 650 to 850 F., wherein the circulating coke is reheated preferably to a temperature of from about 850 to 1100 F., upon initial contact, vaporization and rapid cracking occurs. It has been found that if the resulting foam of unvaporized oil and vapor is forced to take apressure drop of at least 20 of water in passing through the restricted colurnn of coke below the feed points, uniform contact and wetting of the coke particles are assured since the vapor liquid mixture is forced to travel through all the Summary of operating data Temperature, Pressure, Time,

F. p.s.i.g. Minutes Oil Charge-Reduced Crude 650-850 011 ChargeGyc]e Stock.. 600-800 Coke Entering Reactor 850-1, 100 Reactor 15 Coke Through Reactor -40 Reheater t Atmospheric crude oils, particularly those containingrelatively large .20

amounts of sulfur and metal compounds.

The crude topping facilities at 95 are entirely conventional in nature and; are usually operated at a temperature 'of from about 500 to 700. F. and at a pressure of from atmospheric to p.s.i.g. Sucha unit will produce 'a'light virgin gasoline overhead at 96, straight run distillate fuels 97 (if required by-.the market), a light virgin gasoil 98 and a reduced crude 99. There duced crude is charged through line 101 into the lower section of a contact fractionator 19 which is usually operated at atemperature of from about 700 to 800 F. and at a pressure of from to 50.p.s.i.g. and to which the excess heat in the coker vaporshere inafter described are conducted by line 14 to flash off a portion of' the reduced crude as heavy virgin gas oil. The rereduced crude and coker recycle 104 is Withdrawn from the bottom of the contact fractionator 19 and charged through line 106'directly to the particle inlet line 64 and the contact coker 10. A heater 105 may be used if necessary to maintain the desired oil inlet temperature of from 650 to 850 F.

A portion of the light virgin gas oil 98 is introduced through line 110 into the top of the contact fractionator 19 to condense the virgin gas oil and coker oil plus a portion of the coker gasoline. The net overhead 112 is condensed at 114, water is decanted in the coker distillate drum at 116 which is preferably operated at a temperature of from about 100 to 120 F. and at a pressure of from 30 to p.s.i.g. The unstable coker gasoline from coker distillate drum 116 is introduced through the line 118 into the regenerated catalyst riser 120 as charge to a conventional fluid catalyst reactor 122 which is usually operated at a temperature of from about 850 to 1100 F. and at a pressure of from-atmospheric to 18 p.s.i.g. The wet gas in line 124from the coker distillate drum 116 may be sent to a gas plant (not shown).

The sidestream gas oil product 126 from the contact fractionator 19-and the balance of the virgin light gas oil 98 constitutes the remainder of the fresh feed charge to the fluid unit 122 through line 127.

The reactor vapors '130 from the fluid catalytic reactor 122 are sent to a conventional bubble tower 132. The overhead 134 from this tower at a temperature of from about 250 to 290 F. is condensed at 136 to produce wet gas and unstabilized gasoline in drum 137 operated at a temperature of from about 80 to 120 F. and at atmospheric pressure. The unstabilized gasoline may be drawn off in part at 138 and used in part as reflux at 140. The sidestream 142 of light catalytic gas oil at a temperature of from about 480 to 500 F. is split between reactor recycle 143 and distillate fuel oil 144, depending on market requirements and overall 6 132 is introduced into the particle lift line 64 for-com tact in coker 10 as a separate oil charge through line 148. Since this material is of relatively low carbon residue and is more refractory than the virgin reduced crude, it will be introduced preferably into the coke circulating stream at a point upstream of the reduced crude contacting zone.

Summary of operating data A preferred example of the operation of my process in accordance with my invention is as follows:

Charge-Reduced crude Gravity 12.5 API.

I.B.P. 741 F. Flash point 605 F. Ramsbottom carbon 13.8 Catalytic recycle oil Gravity 8.8 API.

I.B.P. 424 F. Flash point 345 F. Ramsbottom carbon 7.3 Y Particle materialpetroleum coke:

Size, average in 0.l570.25 Bulk density lbS./cu. ft 65 Interparticlevoids percent 31 Intraparticle voids do 4 Procedure.-Catalytic recycle oil is charged at 655 F. to coke particles, reheated to a temperature of 1048 F., moving upwardly in the lift line at a circulation rate of 9 tons/hr. The reduced crude, is charged at 779 F. to the coke particles (1033 F.) moving upwardly in the lift line, down stream of the point of catalytic recycle oil charge. The temperature of the coke entering the reactor, with the hydrocarbon charges, is 890 F. The temperature of dry coke particles leaving the bottom of the reactor is 961 F. with the reactor operating under a pressure of 40 p.s.i.g. The average residence time of the coke particles in the reaction zone is 19 minutes.

This combination contact-catalytic cracking scheme will produce a maximum amount of catalytic cracking conversion required. The heavy catalytic gas oil or charge stock with a minimum amount of thermal cracking. It utilizes the fluid reactor for retreating the high sulfur unstable coker gasoline. It also affords a method of converting the heavy catalytic cycle stock into further yields of gasoline, coke and gas. In conventional refinery operation, this heavy catalytic cycle gas oil is usually blended into Bunker C fuel oil because no satisfactory cracking method exists Which will give high gasoline yield on this stock without rapid coking of the equipment.

The steps of preparing a catalytic charge stock from reduced crude by contact coking, utilizing the excess heat in the coker efliuent vapors for distilling the lower boiling portions of the reduced crude charge and for preheating a light virgin gas oil, catalytically cracking the virgin and coker gas oils and retreating the coker gasoline in the same catalytic reactor and thermally cracking the heavy catalytic gas oil in a contact cracking operation under short-time high temperature conditions followed by the passage of the resultant vapors through a wetted bed as described in copending patent application, Serial No. 262,719, now U.S. Patent No. 2,846,373, is not only unique but of major economic value.

The above scheme is a method of carrying out these steps with a maximum heat economy and a minimum of installed equipment. It is particularly attractive to the refiner faced with the problem of producing high quality gasolines and minimum fuel oil from low grade crude oil such as, Santa Maria,'Mississippi, heavy Mexican and crudes from Near Eastern sources.

While I have shown and described a preferred form of embodiment of my invention, 1 am aware that modifications may be made that are within scope and spirit of the disclosure herein and of the claims appended hereinafter.

I claim:

1. In the method of continuously converting a heavy residual hydrocarbon liquid charge into lower boiling hydrocarbon vapors and a solid residue by contacting the liquid in a heated condition at a temperature below incipient coking with a continuously moving body of heated particulate coke solids at a temperature of from about 850 to 1100 F. while passing through a sealed reaction space, wherein said solid residue becomes a part of said coke solids and said lower boiling hydrocarbon vapors are passed to a fractionation Zone in which excess heat provided by said lower boiling hydrocarbon vapors aids in flashing off a portion of introduced fresh hydrocarbon feed to produce therefrom a catalytic cracking charging stock and reduced crude recycle oil, the improvement which comprises applying said reduced crude recycle oil to said coke solids prior to principal coke formation, and applying a more refractory cycle oil derived from the catalytic charging stock to the coke particles at a predetermined position upstream from said first application.

2. The method for producing high qualitymotor fuel from liquid hydrocarbonswhich comprises; applying a cycle oil to a continuously upwardly moving body of heated particulate coke solids at a temperature of from said liquid hydrocarbons to form said heavy residual? oil and a catalytic charging stock, introducing said catalytic charging stock to a catalytic reactor to effect at least partial conversion of said charging stock to catalytic vapors and introducing said catalytic vapors, and unconverted portionof said catalytic charging stock to a second fractionation zone to form said cycle stock and said high quality motor fuels.

3, The method for producing high quality motor fuels from liquid hydrocarbons as claimed in claim 2 wherein said particulate coke solids are withdrawn from said disengaging zone and circulated through a closed heating zone wherein said solids are reheated and returned to said continuously upwardly moving body thereof.

References Cited in the file of this patent UNITED STATES PATENTS,

2,340,974 Myers Feb. 8, 1944 2,416,608 Backenbury Feb. 25, 1947 2,419,519 Evans Apr. 22, 1947 2,598,058 Hunter May 27, 1952 2,719,114 Leifer Sept. 27, 1955 2,731,396 Harding etal; Ian. 17, 1956 2,835,629 Berg May 20, 1958

Claims (1)

1. 2. THE METHOD FOR PRODUCING HIGH QUALITY MOTOR FUEL FROM LIQUID HYDROCARBONS WHICH COMPRISES, APPLYING A CYCLE OIL TO A CONTINUOUSLY UPWARDLY MOVING BODY OF HEATED PARTICULATE COKE SOLIDS AT A TEMPERATURE OF FROM ABOUT 850 TO 1100*F. TO VAPORIZE AND CRACK SAID CYCLE OIL, APPLYING A LESS REFRACTORY HEAVY RESIDUAL OIL TO SAID CONTINUOUSLY UPWARDLY MOVING BODY OF HEATED PARTICULATE COKE SOLIDS AT A POSITION DOWNSTREAM FROM SAID FIRST APPLICATION TO EFFECT PARTIAL VAPORIZATION THEREOF, DISCHARGING SAID COKE SOLIDS AND HYDROCARBON VAPORS INTO AN EXPANDED DISENGAGING ZONE TO EFFECT AT LEAST PARTIAL CONVERSION OF SAID VAPORS TO LOWER BOILING HYDROCARBONS, CONTACTING SAID THUS FORMED HYDROCARBON VAPORS AND LOWER BOILING HYDROCARBONS IN A FRACTIONATION ZONE WITH SAID LIQUID HYDROCARBONS TO FORM SAID HEAVY RESIDUAL OIL AND A CATALYTIC CHARGING STOCK, INTRODUCING SAID CATALYTIC CHARGING STOCK TO A CATALYTIC REACTOR TO EFFECT AT LEAST PARTIAL CONVERSION OF SAID CHARGING STOCK TO CATALYTIC VAPORS AND INTRODUCING SAID CATALYTIC VAPORS, AND UNCONVERTED PORTION OF SAID CATALYTIC CHARGING STOCK TO A SECOND FRACTIONATION ZONE TO FORM SAID CYCLE STOCK AND SAID HIGH QUALITY MOTOR FUELS.

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