US2868719A - Fluid coking process using transfer-line burner - Google Patents

Description

Jan. 13, 1,959

H. Z. MARTIN ETAL FLUID GOKING PROCESS USING TRANSFER-LINE BURNER 2 Sheds-Sheet 2 *FLUE GAS Filed Jan. 6, 1954 FROM COKER V AERATING GAS GAS

INVENTORS JOHN W-HERRMANN HOMER Z. MARTIN CHARLES E. JAHNIG BY an; um

+ COKER ATTORNEY FLUID COKING PROCESS USING TRANSFER-LINE BURNER Homer Z. Martin, Cranford, and Charles E. Jahnig, Red Bank, N. J., and John W. Hermann, Woodside, N. Y., assignors to Esso Research and Engineering Company, a corporation of Delaware Application January 6, 1954, Serial No. 402,474

4 Claims. (Cl. 208157) This invention relates generally to a method for supplying heat to endothermic processes utilizing heat contained in high temperature particulate solids. It more particularly pertains to a process for upgrading petroleum oils by contacting the oils With hot fluidized solids. Specifically, it pertains to a process for heating a fluidized solids bed in a'residuum coking vessel and to an'apparatus par ticularly adapted for such heating.

' United States Patent- Endothermic processes utilizing a fluidized solids bed to supply heat for the reaction have previously been suggested. Typical processes are ones for the coking of heavy petroleum oils water gas manufacture, and catalytic cracking of petroleum oils. In these processes, a portion of the fluidized bed is generally continuously withdrawn, circulated to an external burner and recycled back to the reaction bed to supply the necessary heat. This external burner is either a burner that has a fluidized solids bed, a fixed bed, a gravitating bed of the Thermofor type or a dispersed phaseburner wherein the carbon particles are carried along by the combustion air. This invention pertains to the last type of burner mentioned, the dispersed phase burner, or transfer-line type burner. In this type of heating arrangement, the withdrawn solids are mixed with the combustion air and transferred through a pipe or conduit while the burning occurs. The gaseous products of combustion and the heated solids are then separated, the solids being recycled to the reactor vessel. It is possible by the transfer line burner to secure a limited controlled combustion at high throughputs. This 3 invention proposes an improvement on the transfer line burner whereby the length of the burner can'be greatly decreasesd or conversely the throughput and fuel efliciency of the burner greatly increased for a given burner length.

,In the conventional method of operating the burner, the solids Withdrawn from the fluidized bed are mixed with the combustion air atthe inlet of the burner. Consequently, the low temperature at which the solids are available from the reactor, about 950 F., inhibits or deters the combustion reaction, i. e., the initial combustion proceeds slowly. According to the present invention, this difliculty is overcome by mixing the stream of solids from the reactor with the products of combustion at or near the outlet of the transfer line burner.

It is known that the burning rate of coke increases as the coke temperature increases and, therefore, any increase of the operating temperature of the burner will reduce the required length of the burner. However, merely working with higher temperatures will also require more air for combustion because of the greater heat loss in the flue gases and because higher temperatures favor the generation of carbon monoxide instead of carbon dioxide. In this invention, a major portion of the coke circulated from the reactor to the transfer line burner is injected into the upper portion or the top or outlet of the transfer line, while high temperature coke is recycled to the inlet of the burner. In this way, the working temperature of the burner is increased. Combustion initiates and procecds rapidly because the inlet temperature of the, solids is raised by the recycle. At the same time, there is no additional heat loss to the flue gas because the outlet stream from the transfer line is cooled by the incoming coke from the reactor. After this cooling, the solids are separated from the gases and a portion of the solids, now heated, is transferred to the reactor and the remaining portion is recycled to the transfer'line burner. Alternately, the hot combusted solids are removed before the flue gas is quenched with the cooler solids from the reactor. All of the hot solids separated are then recycled to the burner or a portion thereof is sent to the reactor. It will be seen that this scheme allows operating the combustion zone at a much higher temperature than would otherwise be possible, whereby rapid and complete combustion is insured. High fuel efficiency is obtained by using a cooler circulating solids stream to quench the flue gas.

An object of this invention is to provide an improved method for maintaining the temperature of the fluidized solids reactor bed at a reaction temperature. Another object is to operate a transfer line burner, used for supplying high temperature particulate solids to an endothermic process, more efliciently and economically than has heretofore been possible. Furthermore, a specific object is to provide a method for heating a bed of fluidized coke particles in a petroleum residuum coking vessel. Other objects and advantages will appear more clearly as the attached drawings, which form part of the specification, are discussed in detail.

In the drawings, Figure 1 shows a process adapted to carry out the proposals of this invention using a transfer line burner. Figure 2 shows a second modification of the transfer line burner adapted to achieve the objects of this invention. Figure 3 shows the apparatus of Figure 2 in a horizontal position. Figure 4 shows a fourth modification of the burner.

Although the invention will be described in conjunction with the fluid coking vessel using carbon particles, it is to be understood that the invention is capable of broader application. Rather than having a fluid bed as is described, a transfer line reactor or coker can :be used to accomplish the pyrolsis. Also, it is not necessary that the solid particles be pure carbon or coke. It has previously been suggested that inert fluidized solids, e. g., sand be used in the coking vessel. During the course of the reaction, the inert solids have carbon deposited-on them. These solids are then transferred to a burner vessel where this carbon coating is removed by combustion. The catalytic cracking process also operates in the same manner, i. e., the catalyst receives a carbon deposit in the reactor vessel which is consumed in a regeneration zone. The transfer line burner is the catalyst regeneration zone. Also, by quenching the combustion products with contaminated catalyst, the catalyst is stripped of hydrocarbons before regeneration. Further, various proposals have been made wherein fluidized carbon particles are used in a water gas generator. The transfer line burner of this invention is capable of being used to heat the fluidized solids bed in such a water gas generator. Although it is contemplated that the reactor for the endothermic process for which this burner is designed, will operate on the fluidized solids technique, it is possible by this invention to supply high temperature particulate solids to reactors havinggravitating beds.

Table I compares the conventional type of transfer line burner to the one proposed in this invention. In this comparison, the outlet temperature and the coke circulation rate through the burning zone are the same in both bases. In order to maintain the same coke throughput, the recycle ratio in the modified burner must be one unit greater than in the conventional burner. quantity of recycle makes up for they reactor coke which Patented Jan. 13, 1959 The additional.

is not fed to the burning zone in the burner of this invention. It can be seen that by using the modified method of coke feed, the length of the burner can be reduced to less than half of its original value.

Referring now to the drawings, in Figure 1, the main items of equipment as shown are a coking vessel 3, a transfer line burner 20, and a solids-gas separator or cyclone 24. The feed to the process, which is generally 2 composed of fresh vacuum residuum and a recycle bottoms fraction from the coker effluent fractionator (not shown), enters the process through line 1 and is injected into the fluidized bed by nozzle 5. The coking arrangement, per se, does not form a part of this invention and its manner of operation will not be elaborately presented. The oil feed is coked in the fluid bed evolving hydrocarbon vapors and depositing coke on the fluidized particles. The vapors pass upwardly through an adsorptive bed 30, more fully described hereinafter, to cyclone 6 wherein the entrained solids are separated and returned to the bed by dipleg 7. The vapors then pass overhead by line 8 to a product fractionator. The fluid bed has a temperature of about 900 to 1000 F. To maintain this temperature, a portion of the fluidized solid bed is continuously withdrawn by line 11 and transferred to the burner. Heated particles from the burner at a temperature of about 1300 F. are returned to the fluidized bed by line 12.

There will usually be an excess of coke produced in this process. For this reason, provision is made by line 9 to remove this excess coke as product.

Fluidizing steam is admitted to the bottom of the coker by line 16. This steam serves not only to fluidize the carbon particles, but also to strip them of hydrocarbon vapors in the lower portion of the coker vessel.

Referring now to the transfer line burner 20, a recycle fraction of carbon particles enters the bottom of the burner by line 15 and is mixed with combustion air, supplied by line 21. The burning mixture is transferred upwardly through the burner at a velocity above about 10 ft./sec., e. g., 60 ft./s. After the combustion has proceeded to the desired extent, the mixture is quenched near the top of the burner by the cooler solids withdrawn from the coking vessel by line 11. After this quenching, the material is transferred to separator 24- where the 60 combustion gases or flue gases are removed by line 25' and transferred to other processes, such as a waste heat boiler to recover the specific heat of the gases. The separated solids are divided and a portion returned to the coker vessel by line 12 and the remaining portion recycled to the transfer line burner by line 15.

In order to effect circulation of the quench solids to the burner, it is necessary in the uprising conduits to admit aerating gas, e. g., steam, to the conduit, at one or more o points. For this reason, steam lines 18, 18 and 18 are shown as admitting steam to line 11.

Table II presents a Specific example of an operation of the apparatus as is shown in Figure 1. The letters A, B, C, etc. 'of the'drawing refer to this table.

4 Table II Feed:

12.9% West Texas vacuum reslduum (75 A P. I. gravity, 21.4% Conradson carbon B./S.D. 23,000 1000-l F. recycle from fractionator B,/S.D. 4,600 Products:

Coke (wt. percent) 23.0 C (wt. percent 11.0 C 1,000 F. (vol. percent) 79.0 Operating Conditions for Coker:

Coker hold-up tons 100 Coker temperature F 1000 Solids Circulation:

Location Rate, Temperatnre, F.

1,300 1.000 1,000 1, 330 (avg) 1, 30 1,330

In Figure 2, the same type of coking vessel is shown with a modified version of the transfer line burner. The burner itself has an upflowing stream of solids in zone D and a downwardly moving recycle stream of solids in zone E, the two zones being separated by bafile 69.

The feed enters the coking vessel 53 through line 51. Excess product coke formed in the process is withdrawn by line 55 through valve 56. Product gases are removed overhead by line 54. A portion of the fluidized solids bed is continuously withdrawn by line 57 and transferred to the overhead line 68 of the burner vessel where it quenches the hot gaseous products of combustion. After the quenching, the flue gas is separated from the solids in a cyclone 73 and removed from the process by line 74. Separated solids flow downwardly, regulated by valve 76, through pipe 75 to the modified transfer line burner. There this solid stream is mixed with a descending stream 7 0- of internally recycled hot coke particles in the burner. At the base of the burner, this mixture is met with combustion air admitted to the vessel by line 66. The burning mixture 71 then moves upwardly. As an alternate, this recycle stream canbe admitted to the combustion zone 65 near the inlet or at one or more intermediate points along the combustion zone for the purpose of controlling the temperatures in the combustion zone.

The top portion of the vessel is enlarged to promote rough separation of the solids-gas mixture. This separating zone need not be an integral part of the burner but could be a separate cyclone. The rough separation could be effected by other means such as by baffles or vanes. The gaseous products continue upward with accompanying entrainment of solids. At the base of the enlarged section, a withdrawal is made by line 72 of the heated coke particles and the particles are transferred to the reactor. The remaining portion of solids in the enlarged section is recycled to the burner inlet. This recycle flow is regulated by valve 67 to control the loading of solids in burning zone 71. This loading normally will be in the a range of 0.5 to 5 pounds per cubic foot and the gas velocity 20 to feet per second.

As before, steam is admitted to the process by line 58. A portion passes through line 59 to the reactor to fluidize the coke bed. Further amounts of steam are used to aerate the fluidized circulating solids in lines 57 and 72. Steam is admitted to line 57 by lines 61 and to line 72 by lines 63 at aplurality of points.

Table III presents the solid circulation rate for the apparatusof Figure 2. The other conditions, .such as the type of feed, are essentially the same as in Figure 1.

Table III Location Rate, Tempera- T./M. ture, F.

9. 25 1, 500 9. 25 1,000 0. 64 1, 000 33. 45 1, 385 (avg) 24. 2 1, 500 9. 25 1, 072 G. 33. 45 1,340

In Figure 3, the apparatus of Figure 2 is shown as being in, a horizontal position. All like parts have the same number, difierentiated only by the subscript a. In the drawing, 65:: is the burner vessel. A bafl'le 69a separates the combustion zone 7111 from the recycled solids zone 70a. The combustion gas is admitted to the combustion zone by line 66a. The preliminary solids gas separation is made in a vertical vessel 78. Hot solids are withdrawn through line 72 to be circulated to the coker vessel. A recycle stream is withdrawn from the separator and transferred through passageway 70a to the inlet of the combustion zone. Aerating gas is admitted to the recycle passageway at one or more points by line 80. This gas aids in circulating the solids and can be used to regulate the amount of solids internally recycled. The hot combusa tion gases pass overhead by line 68a and are met by the cool solids from the coker in line 57a. The quench mixture is then separated in cyclone 73a, the flue gas passing overhead by line 74. The heated solids then pass downwardly through line 75a to the transfer line burner.

The process and apparatus of Figures 2 and 3 are flexible in that both high and low temperature coke from the burner can be returned to the reactor. Thus, part of the recycle stream at about 1500 F. can be returned to the reactor, as well as the lower temperature coke from the final cyclone separator.

If desired, the flue gases can be used for stripping heavy ends, contaminants, etc., from a circulating coke stream. To do this, the coke to be stripped is mixed with thehot flue gas and then passed through a final cyclone where it is recovered. It can then be returned to the adsorption zone 30 (see Figure l) which consists of a layer of coke located in the top of the coking reactor. Coke overhead vapors are contacted in this bed to remove contaminants and heavy ends. A separate coke stream is preferably used in this circuit, and it is activated or treated by this method to increase the surface area and adsorptive capacity. Also, the coke can be activated by burning or heating it in the presence of steam, carbon dioxide or other inert gases.

The adsorption bed 30 is maintained at a temperature lower than that of the fluid bed so that heavy ends are removed from the coke product vapors by controlled partial condensation. This removes metal contaminates and high boiling material from the products, thereby improving their quality, especially when gas oils for catalytic cracking are the desired product. The absorptive bed is maintained at the lower temperature by means of heat exchangers on the feed coke stream to the bed or by cooling coils in the bed. Also it is possible to directly inject a coolant, such as water, into the bed to cool it.

Of course, material from the adsorptive bed can'be transferred to the combustion zone 20 to remove the heavy ends and fresh coke from separator 24 can be added to the bed.

Figure 4 depicts another modification of the combustion vessel. This vessel differs from the other forms of the burner previously described in that deflecting vanes or helical baffles are used to achieve solids gases separation.

Briefly, the carbon containing solids from the reactor are transmitted to the burner 80 by line 81. Aerating gas is admitted by line 82 at the bottom of a riser 83, to convey the solids upward. Line 83 injects the solids into the 6 vessel wherein the contact hot flue gases, at a temperature of about 1500 F., cooling the gases to about 1050 F.

The quenched mixture then flows past a curved vane '84 which imparts a rotary motion to the suspension. A major portion of the solids are thereby forced outwardly through the inner wall 85 of the vessel, which has suitable openings or slots to permit passage of the solids, into a annulus. The solids then fall through conduit 86 to a concentric solids reservoir 89. A portion of these solids before entering the reservoir may be withdrawn and recycled to the reactor via lines 87 and 88.

Solids from the reservoir gravitate to the base of the burner through conduit 90. Solids flow is controlled by damper valve 101 or other similar control device. If the solids in the system are coke formed in the process, then it may be desired to remove a portion of the coke as prod uct through lines 91 and 92. Conveying steam isadmitted to the product coke line by line 93.

Combustion air is admitted to the base of the burner by line 94 and conveys the solids upward at a velocity of about 60 feet per second. A major portion of the solids, heated to a temperature of about 1500 F. by the combustion, is separated from the flue gases by helical baflle 95 and enters reservoir 89. High temperature solids are then withdrawn from the reservoir by line 88 and transferred to the reactor.

After this separation, the flue gases are quenched, as before described, and then, after passing through bame 85, have substantially all entrained solids removed by baffles 96 before being removed from the burner by line 97. The solids removed from the flue gas by bafiies 96 are returned to the reservoir by conduit 98.

As an aid to temperature control in the combustion zone, lines 99and 100 admit cool solids from the reactor near the base and at intermediate points along the combustion path. Normally, only a small proportion, if any, of solids from the reactor will be so introduced into the combustion chamber.

Many modifications of the invention will be apparent to those skilled in the art. Accordingly, it is to'be understood that this invention is not to be limited by the foregoing examples but only by the following claims.

What is claimed is:

l. A method of coking hydrocarbon oils which comprises the steps of contacting hydrocarbon oils with fluidized particulate solids at coking conditions in a coking zone to produce vaporous reaction products and carbonaceous residue which is deposited on said solids, separating and recovering said vaporous reaction products from said coking zone, removing relatively cool solids from said coking zone, admixing said relatively cool solids with substantially vaporous combustion products in the terminal portion of a transfer line heating zone thereby heating the solids, recovering heated solids in a final separation zone from the effluent from said transfer line heating zone circulating at least a portion of said recovered heated solids to the inlet portion of said transfer line heating zone, roughly separating in an initial separation zone in an intermediate portion of said transfer line heating zone further amounts of heated solids from combustion products prior to admixing said relatively cool solids with combustion products, transferring a portion of said heated solids to said coking zone to supply heat therto, circulating heated solids from said initial separation zone to the inlet of said transfer line heating zone, admixing therewith a free oxygencontaining gas in combustion supporting amounts and passing the resulting mixture through said transfer line heating zone.

2. A method of coking hydrocarbon oils which comprises the steps of contacting hydrocarbon oils with fluidized particulate solids at coking conditions in a coking zone to produce vaporous reaction products and carbonaceous residue which is deposited on said solids, separating and recovering said vaporous reaction products from said .coking .zone, removing relatively cool solids from said coking zone, admixing said relatively cool solids with predominantly vaporous combustion products in the terminal portion of a transfer line heating zone thereby heating the solids, recovering heated solids in a final separation zone from the efiluent from said transfer line heating zone, roughly separating in an initial separation zone in an intermediate portion of said transfer line heating zone further amounts of heated solids from combustion products, transferring a portion of said heated solids to said coking zone to supply heat thereto, internally recycling heated solids from said initial separation zone to the inlet of said transfer line heating zone, admixing with the recycled heated solids a free oxygen-containing gas in combustion supporting amounts and passing the resulting mixture through said transfer line heating zone.

3. A method of coking hydrocarbon oils which comprises the steps of contacting hydrocarbon oils with fluidized particulate solids at coking conditions in a coking zone to produce vaporous reaction products and carbonaceous residue which is deposited on said solids, separating and recovering said vaporous reaction proclucts from said coking zone, removing relatively cool solids from said coking zone, admixing said relatively cool solids with predominantly vaporous combustion products in the terminal portion of a vertical disposed transfer line heating zone thereby heating the solids, recovering heated solids in a final separation zone from the efiiuent from said transfer line heating zone, roughly separating solids from combustion products by settling in an initial separation zone in an intermediate portion of enlarged cross-sectional area of said transfer line heating zone, transferring heated solids from said final separation zone to said coking zone' to supply heat thereto, circulating heated solids from said initial separation zone to the inlet of said transfer line heating zone, admixing therewith a free oxygen-containing gas in combustion supporting amounts and passing the resulting mixture through said transfer line heating zone.

4. A method of coking hydrocarbon oils which comprises the steps of contacting hydrocarbon oils With fluidized particulate solids at coking conditions in a coking zone to produce vaporous reaction products and carbonaceous residue which is deposited on said solids, separating and recovering said vaporous reaction products from said coking zone, removing relatively c001 solids from said coking zone, admixing said relatively cool solids with predominantly vaporous combustion products in the terminal portion of a vertically disposed transfer line heating zone thereby heating the solids, recovering heated solids in a final separation zone from the efiluent from said transfer line heating zone, the recovery being effected by imparting a rotary motion to the suspension about the axis of flow whereby solids are ejected outwardly through suitable openings in the confines of said transfer line heating into a collection zone, roughly separating further amounts of heated solids from combustion products in an-initial separation zone in an intermediate portion of said transfer line heating zone by imparting the above described rotary motion, transferring a portion of said heated solids to said coking zone to supply heat thereto, circulating another portion of said heated solids to the inlet of said transfer line heating zone, admixing therewith a free oxygen-containing gas in combustion supporting amounts and passing the resulting mixture through said transfer line heating.

zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,700,017 Brown Jan. 18, 1955 2,734,021 Martin et al. Feb. 7, 1956 2,736,687 Burnside et al. Feb. 28, 1956 FOREIGN PATENTS 620,708 France Ian. 24, 1927 649,196 Germany Aug. 18, 1937 1,056,346 France Oct. 21, 1953

Claims (1)

1. A METHOD OF COKING HYDROCARBON OILS WHICH COMPRISES THE STEPS OF CONTACTING HYDROCARBON OILS WITH FLUIDIZED PARTICULATE SOLIDS AT COKING CONDITIONS IN A COKING ZONE TO PRODUCE VAPOROUS REACTION PRODUCTS AND CARBONACEOUS RESIDUE WHICH IS DEPOSITED ON SAID SOLIDS. SEPARATING AND RECOVERING SAID VAPOROUS REACTION PRODUCTS FROM SAID COKING ZONE, REMOVING RELATIVELY COOL SOLIDS FROM SAID COKING ZONE, ADMIXING SAID RELATIVELY COOL SOLIDS WITH SUBSTANTIALLY VAPOROUS COMBUSTION PRODUCTS IN THE TERMINAL PORTION OF A TRANSFER LINE HEATING ZONE THEREBY HEATING THE SOLIDS, RECOVERING HEATED SOLIDS IN A FINAL SEPARATION ZONE FROM THE EFFLUENT FROM SAID TRANSFER LINE HEATING ZONE CIRCULATING AT LEAST A PORTION OF SAID RECOVERED HEATED SOLIDS TO THE INLET PORTION OF SAID TRANSFER LINE HEATING ZONE, ROUGHLY SEPARATING IN AN INITIAL SEPARATION ZONE IN AN INTERMEDIATE PORTION OF SAID TRANSFER LINE HEATING ZONE FURTHER AMOUNTS OF HEATED SOLIDS FROM COMBUSTION PRODUCTS PRIOR TO ADMIXING SAID RELATIVELY COOL SOLIDS WITH COMBUSTION PRODUCTS, TRANSFERRING A PORTION OF SAID HEATED SOLIDS TO SAID COKING ZONE TO SUPPLY HEAT THERTO, CIRCULATING HEATED SOLIDS FROM SAID INITIAL SEPARATION ZONE TO THE INLET OF SAID TRANSFER LINE HEATING ZONE, ADMIXING THEREWITH A FREE OXYGENCONTAINING GAS IN COMBUSTION SUPPORTING AMOUNTS AND PASSING THE RESULTING MIXTURE THROUGH SAID TRANSFER LINE HEATING ZONE.

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