BE529069A - - Google Patents

Description

       

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   The present invention relates to the conversion of hyi @@ - carbon oils, such as coal tars, shale oils, pitches, asphalts, total petroleum crude materials, a distillate and residual fractions thereof. here, or mixtures of these materials.



   The invention relates more especially to a process for coking heavy petroleum residues in contact with hot fluidized solids, and to an apparatus specially intended for such coking.



   The ever increasing demand for high quality motor fuels increasingly imposes the need to improve heavy petroleum residues to obtain distillates, and especially gas oil suitable for catalytic cracking into high quality motor fuel. One method of producing gasoline from a heavy residue, commonly in use for many years, is to pass the oil through a heating coil where it is heated to an incipient cracking temperature. and transferring it to a coking drum where it is held until it is converted to vapors and coke. The operation is continued until the drum is nearly filled with coke.

   After that, the circulation of hot oil in the drum is interrupted and, after sufficient cooling, the coke is broken up into large pieces and removed. To make the operation continuous through a coil, a series of coking drums can be provided for each coil, so that oil can be transferred from one drum to another, as needed. This process is commonly referred to as delayed coking. Cooling the coking drums and removing coke is laborious and time-consuming work.



   More recently, it has been proposed to coke heavy waste oils by injecting them into a coking vessel containing a fluidized bed of hot finely subdivided solids. The heavy oil adheres to the solid particles and undergoes pyrolysis, developing lighter hydrocarbon vapors and depositing a carbonaceous residue on the solids. In this process, the necessary heat is provided by circulating a stream of this solid through an external heating zone, usually a combustion zone, and then returning this solid to the coking vessel.



  This offers a great advantage over the delayed coking process, in that the operation is continuous. However, so far no such industrial installation has been installed.



   Contact solids, or heat carriers, used in this fluidized solids coking process usually consist of coke produced in the process. Other particulate solids can, however, be used, such as refractory particles, sand, spent catalyst, pumice, and the like. References made herein to particulate coke as a heat carrier solid will be understood as being illustrative and not limiting.



   The development of this type of process has revealed a cer. a number of problems. A particular serious problem is the tendency of the bed to lose fluidity due to the agglomeration of particles caused by the clumping constituents of heavy oil. If this happens, the entire bed may solidify. It is then necessary to stop the operation, to cool the coking vessel, to break the coke into large pieces, and to remove it from the vessel, as in the delayed coking process.



   Another serious problem is the formation of coke deposits in the vapor space above the bed and in the pipe carrying the effluent vapor, due to condensation and / or polymerization of the vapors from the apparatus. of coking. Another problem is that it is necessary to use relatively large amounts of external fluidizing gas to maintain the fluidity of the bed. This has the effect of diluting the vapors leaving the vessel and increasing the size and complexity of the subsequent fractionation and separation plant.

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   Another problem is to produce a gas oil suitable for catalytic cracking which is free of carbon and ash-forming constituents, and metallic impurities, such as dU! nickel and vanadium, which deactivate the cracking catalyst.



   Another difficulty is the proper adjustment of the dimensions and the size distribution of the heat-carrying particles.



  As coke is formed on the particles, they continue to grow, so that, unless some means are provided to provide fine particles, the particles grow to a point where they cannot be. suitably fluidized or circulated through the burner.



   The object of the present invention is to provide an improved process and apparatus for fluid coking, which successfully overcome the above and other drawbacks. Other objects, as well as the nature and the advantages of the invention, will emerge clearly from the following description, in which reference is made to the accompanying drawings.



   Figure 1 is a schematic view of the apparatus forming part of the present invention, and in which the method may be carried out.



   Figure 2 is an enlarged view of the upper separating and fractionating section of the coking vessel of Figure 1, some parts shown in section.



   FIG. 3 is, on a larger scale, a detailed view of the injection nozzle.



   Figure 4 illustrates a variation of the invention, specially designed to store and provide coke in grains - or primary for the coking system.



   Referring to Figure 1, the liquid feed enters the coking system through line 1. Feeds especially suitable for the present invention are heavy or reduced raw materials, or vacuum generated deposits. , or other heavy petroleum hydrocarbons, containing a significant amount of constituents which cannot be vaporized without decomposition. Such feeds may have, for example, an API gravity of about 0 to 20, for example, 1.9, and a Conradson carbon content of about 5 to 40% by weight, for example 30%.

   This feed is preferably preheated by customary means including heat exchange with product streams, up to about 400-300 F, e.g. 700 F, so as to keep its viscosity reasonably low and reduce the viscosity. heat load on the coking unit. From the feed line 1, the liquid feed is introduced into the bed 2 of fluidized, turbulent, dense coke arranged in the lower part of the coking vessel 3. To avoid the possibility that the bed loses its fluidity, and does not get thick, it is important that the feed is quickly and evenly distributed over the individual particles in the bed.

   Although the highly turbulent fluidized nature of the bed causes the feed to disperse rapidly throughout the bed, it is best not to rely solely on bed turbulence to effect feed dispersion. In order to prevent wetting of the coke particles at the point of injection of the feed and thereby incur the risk of the bed becoming slaked, the feed is preferably injected into the bed in a series. of points, at the. times along the circumference and vertically. As shown, the feed passes through a multiple conduit 4 having branches 5 communicating with nozzles at (see Figure 3). Any type of nozzle can be used which will provide a fine dispersion of the feed without requiring large amounts of dispersion gas.

   A nozzle especially good for this purpose is the type with
 EMI2.1
 If ¯ nozzle, to which the feed is fed in the nozzle, in mixture .., .......... - '1 ............, .. ...!.:.-..........., - I .'- ra "" .. t: ....- -t

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 with dispersion vapor through a central duct having an orifice
2. The duct is surrounded by an annular passage 3 through which steam or purge passes to keep this zone free of coke and allow removal of the nozzle. The spray rate of the oil-vapor mixture is preferably between 50 and 200 feet per second. The mixture in question, at the end of the nozzle, can comprise 25 to 30% by volume of steam.



   It is generally possible to supply between J50 and 450 barrels of oil per nozzle per day. These nozzles are preferably retractable, allowing removal of the core and its cleaning, if it is clogged or loaded with coke.



   The bottom of the container, below the injection point of the feed, is preferably of a smaller diameter. This section serves as a separation or cleaning section (stripping zone) as will be described below. The middle section, where the feed is injected, preferably flares outwards. from bottom to top, and the top of the container is narrowed to a smaller diameter for reasons given below.



   The coke particles in the bed are maintained in a turbulent fluidized state by the ascending gases and vapors. These gases and vapors will include fluidizing and separating gas, and vapors and gases formed by the coking of the feed. The gases rising in the lower part of the bed meet additional gases formed in the upper part, so that the volume of gas increases continuously as the gas rises through the bed. The speed of the gas, in the lower part of the bed, must be appropriate to maintain fluidization and to achieve the desired separation or cleaning.

   By flaring the walls outward in the feed injection zone, the increase in gas volume, resulting from vaporization, is more or less compensated by the increase in the diameter of the container, so that the gas velocity is maintained more or less uniform throughout the depth of the bed, although there may be some increase in velocity on the top side of this bed.



   The average surface velocity of the ascending gases is preferably maintained between 0.1 and 5 feet per second, preferably between 1 and 3 feet, depending on the size of the particles making up the bed. Higher speeds will increase turbulence but reduce the density of the bed.



   As mentioned above, the individual particles comprising the bed tend to grow as the operation proceeds, and it is necessary to maintain control of the particle size. It is preferable to use solids having an average particle size of between 0 and 1000 microns in diameter, preferably between 150 and 300 microns. In some cases, the range of particle sizes may vary outside of these limits without causing difficulty. Preferably no more than 5% of the particles are greater than 500 microns in size, while particles smaller than 40 microns tend to clump or are entrained out of the system with the gases.

   It is usually desirable to have from 5 to 20% of 40 to 125 micron particles to improve fluidization and to clean the middle part of the plant, as will be described below. Although smaller particles provide a larger surface area, very fine particles are subject to agglomeration and other difficulties.



   The coking temperature can be between 350 and 1200 F, preferably between 900 and 1100 F. Higher temperatures allow higher rates of feed and increase in capacity msis can tend to cause overcracking of the vapors with a resulting lowering. yield of the desired distillation products.



   The coking operation is usually carried out at a pres-

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 relatively low pressure, such as 0 to 50 pounds per square inch of effective pressure. Although the process can be carried out at a pressure below atmospheric pressure or at higher pressures, it is generally preferred to operate at a steam outlet pressure sufficient to force the vapors to and through a subsequent plant. of fractionation and separation. For this purpose, the effective outlet pressure can be between: and 25 pounds per square inch, usually between 5 and 15 pounds. The pressure in the lower part of the container will be a little higher, due to the hydrostatic pressure developed by the fluidized bed.



   As noted above, the lower portion of the coking bed, below the feed injection point, serves as a separation or cleaning zone. Steam or other separation or cleaning gas, such as light hydrocarbon gases, is injected into this zone through a pipe 11 to separate hydrocarbons from coke before removal of the latter from the coking zone. By locating the separation zone at the bottom of the reaction apparatus, the excess separation vapor displaces the rising hydrocarbons through the coking zone and helps maintain the desired turbulence and fluidity therein. section.



  The speed in the separation apparatus can be between 0.1 and 5 feet per second. The separation or cleaning vapor can be injected into the vessel through nozzles at high speed to cause friction wear or grinding of the larger particles to maintain the desired particle sizes. For this purpose, the gas can be injected at jet speeds of about 200 to 3000 feet per second. The total amount of steam injected into the coking and separation zones can be about 5 to 30% of the liquid hydrocarbon feed, with 6 to 15% being the preferred range. If desired, disc and slanted wall baffles can be provided in the separation zone to improve contact between steam and solids.



   As mentioned above, the liquid hydrocarbon feed is injected into the reaction apparatus through nozzles 6 at different levels and is uniformly deposited on the coke particles constituting the dense turbulent fluidized bed.



  The rate of the hydrocarbon feed can be about 0.1 to 3 weight per hour per weight of solids present in the following fluidized bed, the composition of the feed, the coking temperature, the residence time of the solids in the bed, and other factors. The limiting factor is the ability to maintain the bed in a highly turbulent fluidized state. If the feed rate is too high, the solid particles tend to stick together, forming larger agglomerates and, unless precautions are taken, the entire bed may solidify and lose its fluid characteristics. This should be avoided, or the process becomes impossible to carry out, and the plant must be closed and the solidified bed removed from the coking vessel.

   Various methods can be used to indicate potential bed impasto conditions. For example, a reduction in turbulence or a viscosity of the bed indicates impasto conditions of the bed. During normal operations, there is significant bed turbulence. A reduction in the amplitude or frequency of these turbulence bursts indicates a power impasto of the bed, and that corrective steps should be taken, such as reducing the rate of the feed to an increase in power. temperature.



   In the fluidized bed, the feed is converted to solid coke and hot hydrocarbon vapor. The vapors leaving the bed carry entrained solids. To allow some of these solids to separate from the vapors, the best solution is usually to maintain the level of bed 12 a substantial distance below the top of the vessel. It is advantageous to have a certain minimum quantity = of solids entrained in the clearance space 13 greater than the level of the

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 bed.

   The heat contained in the entrained solids will help to maintain the temperature in this zone at a higher level and will provide adsorbent surfaces, thus preventing condensation and coking of the higher boiling vaporous products. In addition, the entrained solids will serve to clean the walls of the vessel of any coke which tends to settle there.



   It is also desirable to minimize the residence time of vapors in this zone to prevent further thermal cracking. To this end, the cross section of the vessel 10, above the level 12 of the fluidized bed, is reduced, so as to increase the speed of the upward vapors in the release zone 13. This increased speed results in a higher speed. large quantity of coke, shortens the residence time of the vapor, and keeps the walls of the reaction apparatus warmer, and thus minimizes condensation and coking, as well as thermal vapor cracking . The speed of the gases in the zone of release can be between 2 and 5 feet per second, depending on particle sizes and other factors.

   If desired, additional coke, preferably at a higher temperature, can be introduced into the clearance space to increase the cleaning or purging action of entrained solids and to raise the temperature of the vapors below. above their dew point. The vapors pass from the top of the venting zone into dust separators, such as cyclones 14, which serve to separate entrained coke particles from the vapors. The separated fines are returned to the bed through immersion pipes 15.



   Aeration gas can be injected into the submerged pipes 15 through a pipe 16 '. The amount of aeration gas thus introduced can be controlled to control the amount of solids separated by the cyclones. For example, in some cases it may be desirable to maintain a certain minimum of solids in the cyclone outlet line to remove any coke that may form there. By increasing the amount of gas added to the dip pipes, the amount of solids separated by cyclones can be reduced. The cyclones themselves are preferably arranged in a solid transverse wall 16 which prevents vapors from reaching the stable area above the cyclones, and thus prevents coke from forming in this area. .

   Cyclones 14, the vapors pass through chimneys 17 to go into a fractionation and washing or purification tower 18, mounted directly above the coking vessel.



   The chimneys 17 preferably discharge the hot hydrocarbon vapors against heated baffles 19. These are arranged at a suitable distance above the bottom of the tower 18, and the space below these baffles forms a zone. receiver for the heavy condensate formed in the washing apparatus. This prevents heavy condensate from falling back into the chimneys and forming coke deposits there.



   The chimneys 17, baffles 18 and all other walls separating the coking vessel 3 from the washing tower 18 are preferably strongly insulated to minimize condensation and coking of the hydrocarbon vapors in the air. the chimneys and in the lower section of the washing tower. Heating elements may be provided around the walls of the chimneys 17 and the outlet pipes of the cyclones to keep the walls warmer than the vapors as a further aid in preventing undesirable condensation and coking. The heating elements shown are in the form of superheated steam coils, enveloping the walls.

   This heating vapor can be preheated by indirect heat exchange with hot solids in a coke burner described later, and can be released to the atmosphere, so as not to further dilute the vapors passing to an installation. subsequent fractionation and condensation. Or, hot flue gas from the burner

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 Coke can be used instead of steam, in heating coils.

   Superheated steam can be injected directly into the hot vapors to minimize coking, diluting the vapors and lowering their condensing temperature. -
The temperature in the bottom of tower 18 is regulated to condense the heavier portions of the vapors, which contain metallic impurities, such as compounds of iron, nickel and vanadium, originally present in the vapor. the feed and carried to the top with the vapors.



  They will contain the solids carried away through the cyclones.



   The temperature at the bottom of tower 18 is controlled by introducing a stream of quenching oil through line 21. This stream also serves to immediately cool the vapors from the coker, thereby stopping polymerization and drying. 'other degradation reactions. As shown, the condensate collected at the bottom of the tower is removed through line 24, some of this condensate being sent to a refrigerator 26 (Figure 1) and returned to the tower above a series of pipes. disc baffles and inclined plates 27. A portion of this recycle stream may be sent to the bottom of the tower through line 28 to further cool the products removed therein.

   The maximum temperature at the base of the tower should not exceed approximately 750 F in order to prevent coking in this section of the installation.



   The temperature required to condense metal impurities will depend on the nature and amount of these impurities present in the feed. It is preferable to operate at the maximum temperature which will achieve impurity removal. For most feeds the final boiling point of the products leaving the lower section will be between 950 and 1050 F, although for some feeds it can drop to 700 F. As the products leaving the washing tower are Composed of a large mixture of vapors and gases, the end point of uncondensed vapors will be much higher than the temperature maintained in the tower.



   Instead of cooling and recycling the heavy condensate to the lower section of the tower, other means of cooling can be used. For example, fresh food can be provided in this section. In this case, the waste feed will be preheated by contact with hot vapors. The preheated feed can then be sent through lines 24 and 34 into the coking vessel.



   The vapors remaining uncondensed in the bottom of the washing section of the tower pass from the bottom to the top through a series of bubbling bell trays, arranged in the top of the tower, where they are subjected to fractionation to condense. an additional fraction of the gas oil boiling range. The condensate formed in the upper section collects in a collection plate 29 and is removed in the form of secondary flow through line 31.

   Part of this stream is pumped to be returned to the lower section of the tower, below the collector tray, through line 32, as additional washing and cooling means, and another part of this stream. Current can be pumped through a refrigerator 33 and introduced into the top of the tower to act as reflux.



   The temperature at the top of tower 23 is preferably above the dew point of the vapor, that is, at a temperature of at least 200 to 225 F. This prevents condensation of the vapor. vapor which, if allowed to occur, could cause emulsion and corrosion problems in the top of the tower. The temperature of the vapors leaving the top of the tower can be around 300 F for the above tower temperatures.



   The heavy condensate fraction, removed from the bottom of the tower

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 stage 18, through line 24, and not recycled for quenching and washing, as described above, is pumped through line 34 back to coking vessel 3. This heavy condensate can be mixed with the feed either fresh, before injection, or alternatively, may be injected through separate nozzles, preferably in the lower part of the coking vessel. Alternatively, this heavy feed can be introduced into the vacuum tower for further fractionation to remove the light, easily vaporizable hydrocarbons. This practice significantly reduces the recycling rate. The deposits from the vacuum tower can then be sent to the coking vessel.

   The vacuum tower may be the same tower in which the raw material from the coking feed is distilled.



   The gas oil removed as a side stream through line 31 constitutes one of the end products of the process. This oil, being a condensate relatively free from carbon components and waste ash, and metallic impurities, can be subjected to catalytic cracking to form high quality gasoline.



   Uncondensed vapors and gases are removed from the top of tower 18 through line 36, and sent to a water-cooled condenser 37 (Figure 2) and then to a separator drum 38, where the liquid distillate collects. separates from uncondensed gas. The liquid will include the naphtha fraction along with water. The naphtha is removed from the separator through line 39 and can be subjected to further processing, such as hydroforming, desulfurization, stabilization, etc., to obtain products of the desired quality. Condensed water is removed from drum 40 through line 41. Wet gas is removed through line 42 and can be discharged or further processed to recover desired products.

   Instead of further fractionating the vapors coming from the washing section to separate the diesel, naphtha and gases, as just described, all the vapors coming from the washing zone can be sent directly, without further fractionation, to a catalytic cracking zone.



   Returning now to the coking vessel, a stream of solids is continuously removed from this vessel through a vertical line 43 which connects to the vessel at a point spaced some distance above the bottom. The space of the coking vessel, below this connection of the line 43, serves as a well or capture means to collect any large pieces or agglomerates which could serve to plug the transfer lines. These agglomerates can be periodically removed through line 50. This line 43 has a mesh cage or basket 44 around its inlet end to prevent large pieces or agglomerates from getting lodged in the line and in the connecting lines. , and stop traffic.



   Line 43 connects at its lower end to a vertically inclined conduit 45 which in turn reaches a vertical riser 46, a section 47 of which projects upwardly into the lower part of the container. heater 48, below the level of a fluidized solids bed maintained therein. To ensure proper circulation of the solids from the coking vessel 3 to the burner vessel 48, care must be taken to keep the solids aerated during their journey through these conduits. The coke particles tend to deaerate very quickly, and it is necessary to add a fluidizing gas at points 49 along the lorg of the inclined duct 45 to prevent this duct from becoming blocked.



   An additional carrier gas is injected into the lower end of the riser pipe 46 through a pipe 51 to regulate the density in this section of the installation. If desired, part of the air required for combustion can be injected into the riser.

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   The main stream of air required for combustion is introduced through line 52 into an auxiliary burner 5.;. Fuel for combustion can be supplied to the auxiliary burner through line 54. The auxiliary burner is normally used to heat the unit at the start of operation. After the unit is heated to a suitable temperature, the fuel supply is stopped, and the heat necessary for the operation is obtained by burning heat formed in the process. In some cases, however, it may be more economical to burn liquids or foreign gases, rather than coke.

   In some cases, the coke in the burner vessel 43 can be heated by combustion gases from the auxiliary burner Gases, either air or hot combustion gases, as appropriate, pass from the burner auxiliary 5 @, in the bottom of the main burner container 43. The outlet of the burner 53 is provided with a cap 55 intended to prevent the solids from passing from the main burner into the combustion zone of the auxiliary burner.



   Gases entering the bottom of the burner pass from bottom to top through the vessel body at a rate controlled to maintain a dense turbulent bed of solids 56 in the bottom of the burner vessel.



   The coke particles are heated in the burner vessel 43 to a temperature substantially higher than that maintained in the coking vessel. For example, the temperature of the burner vessel can be 1000 to 1500 F, usually about 200 to 300 F above the coking temperature.



   Hot solids overflow from the burner vessel in a vertical return line 57 and are returned to the coking vessel, as will be described below. Spent combustion gases leaving bed 56 to pass through cyclone separators 53 and 59 for removal of entrained solids are then discharged to the stack through line 60. The solids separated in the cyclones are returned to the stack. reads through dip pipes b1 and 62. If desired, these can discharge into or near the vertical pipe 57, so as to transport, preferably, the fines from the burner to the vessel. of coking.



   The pipe 57 is connected at its base to a pipe 63 1 =; clin; relative to the vertical and which, in turn, is connected to a vertical riser 64. A carrier gas is introduced into the riser 64 by a valve line 64 'to adjust the density in said riser. 64. This is connected to the upper part of the coking vessel 3 below the level of the bed. A portion of these hot solids may pass through line 66 into clearance space 13 and into the cyclone inlet 14, to supply heat to the vapors of the coking apparatus, to clean the walls and to provide heat. adsorbent surfaces.

   In the case where the vapor fractionation device of the coker is not superimposed thereon, it is sometimes advantageous to introduce additional quantities of hot solids into the pipes leaving the cyclones. This coke, used to prevent plant fouling, can conveniently be steam activated to increase its surface area.



   The circulation of the coke between the containers is achieved by keeping the density in the risers 47 and 64, lower than the de + sity in the pipes 43 and 57 and the fluidized beds, so that the pressure generated at the base of these pipelines before the valves serve as a driving force to circulate solids. The valves 67 and 65 respectively provided in the pipes 43 and 57 serve to create a pressure drop sufficient to prevent reverse circulation of the solids caused by pressure surges in the coking system.



  The speed of circulation to the burner, for example, can be regulated by valve 67 of line 43 and by adjusting the quantity of incoming gas.

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 in riser 46. The installation can be designed to take a maximum pressure drop of about 4 pounds per square inch, through spool 67. Downpipe 57 is designed to normally maintain a solids level of 10. 15 feet below the solids level in the burner, so changes in the level in the downline can compensate for pressure surges in the system.



   The rate of circulation of solids between the coking vessel and the burner is controlled to provide the heat required for the process, and will depend on the temperature difference between the vessels. For a temperature difference of 200 F, the weight of the hot solids introduced into the coking vessel can be between about 8 to 10 times the weight of the oil charged per unit time.



   The dimensions of the coking vessel should be such as to give the oil distributed over the coke sufficient time to be converted into vapors and coke, so that the solids entering the burner are practically free of. unvaporized oil. The residence time of the solids in the reaction apparatus can be 3 to 10 minutes or more.



   The amount of coke formed in the process will be greater than that required to provide heat to the process. In the simplest form of the invention, this excess coke is removed from the bottom of the risers 43 or 57. For this purpose, removal lines 68 and 69 are connected to a line 70 in which the coke. is unloaded. A stream of carrier gas, such as steam, carries the coke through line 70 to storage. Prior to this, the coke can be suitably quenched, for example with water, to prevent ignition of the coke on contact with the atmosphere.



     As mentioned above, during the operation, the particles? Individual components of the fluidized bed in the coking vessel increased in size due to the deposition of coke. To maintain the desired amount of solids in the system within the desired particle size range, it is necessary to replace larger particles with finer particles. This can be accomplished by breaking up some of the larger frictional wear particles, as previously described. Preferably, a portion of the removed coke is crushed or reduced, in another manner, to smaller dimensions, and returned to the system.

   To reduce the importance of this grinding, the solids removed from the coker, before being discharged from the unit or sent to the burner, are preferably graded to selectively retain the finest particles. in the system, so that only a selected fraction of larger particles pass to the burner or are removed from the process as product and to be reduced to smaller dimensions.



   This is illustrated in Figure 4 of the drawings. To avoid repeating certain parts already shown, only the lower part of the coking vessel 3 and of the burner 48 is shown. The top half of the installation is the same as in Figures 1 and 2.



   Referring to the drawing, some or all of the solids removed from the coking vessel through vertical line 4 @ pass through line 72 to the mid section of an enlarged vessel for separation by settling or settling or elutriation, 73, where they are contacted with an ascending stream of separation or elutriation gas, introduced through line 74, below the solids entry point. The velocity of the rising gas passing through vessel 73 is adjusted to carry up a selected finer fraction of the solids, while allowing a larger fraction to be collected at the bottom of the vessel.



   The elutriation apparatus preferably contains several chi-

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 Perforated transverse rods which serve to break localized currents and thus increase the efficiency of the separation. When gas passes from the bottom up through such an elutriation apparatus at a suitable rate, and a mixture of solid particles of different sizes is sprayed or uniformly introduced, in another way, through from an intermediate part of the apparatus, the relatively large particles fall to the bottom, while the fine particles are entrained upwards and escape with the elutriation gas through a line 75 to return to the zone of. reaction.).

   In this way, fine particles capable of serving as grain or primary coke are retained in or continuously recycled to the coking zone.



   The two main variables affecting such separation of coarse and fine solids are the speed of the elutriation gas and the rate of feed of the particle mixture to the column. In order to remove a large portion of fine particles, coarse particles, the speed of the elutriation gas should be at least 1.5 to 3 times, for example about twice, the free fall speed of the larger particles. to be removed from the top. As the gas velocity is increased, less fine particles fall to the bottom with the coarse material. At the same time, however, when the gas velocity exceeds the free fall velocity of the particles of the coarse fraction, some of these coarse particles will be carried off the top and contaminate the fines.

   For practical purposes, the elutriation gas velocity can range from about 3 feet / second, if it is desired to recover fine particles of about 150 microns in diameter and finer, and about 30 feet / second if Top carry solids should include particles approximately 1000 microns in diameter. Obviously, the optimum velocity of the elutriation gas will vary somewhat, depending on the case, depending on the size of the particles that one may wish to separate, the. desired fine particle recovery efficiency, permissible contamination of fine particles by coarser material, and solids feed rate.

   Likewise, with relatively small apparatus, relatively higher speeds may be preferred so as to prevent an excessive amount of fine particles from descending with the larger material.



   The rate of solids feed to the elutriator also has a pronounced effect on the degree of separation. For a given gas velocity, as the feed rate increases, the amount of descending fine particles increases. If there is any amount of coarse material going out the top, because the gas velocity exceeds the free fall rate of the desired fine particles, an increase in the solids feed rate will decrease the rate. quantity of coarse matter going out from the top. At the same time, the total amount of material going from the top will decrease in proportion to the amount falling to the bottom.



  Accordingly, there is an optimum ratio of solids feed rate to gas rate for each gas velocity, which ratio will give only a small amount of coarse material in the top product, and only a small amount of coarse material in the top product. small amount of fine particles in deposits at the bottom.



   For example, to separate coke particles of about 250 microns and smaller (free fall rate of about 4 feet / second), from larger coke particles, Table I shows the best range of the rate. solids feed versus gas rate for each given gas velocity.

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  TABLE I.
 EMI11.1
 
<tb> Speed <SEP> of <SEP> gas <SEP> Feed rate <SEP> <SEP> + <SEP> rate <SEP> of <SEP> gas
<tb>
<tb> 4 <SEP> feet / sec. <SEP> 0.05 <SEP> - <SEP> 0.075 <SEP> lb / foot <SEP> cubic
<tb>
<tb> 5 <SEP> 0.075 <SEP> - <SEP> 0.125
<tb>
<tb> 6 <SEP> 0.0125- <SEP> 0.20
<tb>
<tb> 3 <SEP> 0.15 <SEP> - <SEP> 0.25 <SEP>
<tb>
<tb> 10 <SEP> 0.25- <SEP> 0.35
<tb>
 
If the ratio of the feed rate to the gas rate is less than given above, more coarse material is removed from the top, and the capacity of the column is decreased. Conversely, when ratios higher than those given above are used, the amount of fine particles lost to the bottom becomes high. This is illustrated in Table II.



   TABLE II.
 EMI11.2
 
<tb>



  Speed <SEP> of <SEP> free fall <SEP> <SEP> of <SEP> fine <SEP> particles,
<tb>
<tb> feet / second <SEP> 4 <SEP> 4 <SEP> 4 <SEP>
<tb>
<tb> Speed <SEP> of gas <SEP>, <SEP> feet / second <SEP> 6 <SEP> 6 <SEP> 6
<tb>
<tb>
<tb> Feed <SEP> rate <SEP> + <SEP> gas <SEP> rate <SEP>, <SEP> pounds /
<tb>
<tb> foot <SEP> cube <SEP> 0.076 <SEP> 0.20 <SEP> 0.267
<tb>
<tb>
<tb>% <SEP> of <SEP> particles <SEP> fine <SEP> in <SEP> the <SEP> products
<tb>
<tb> of <SEP> vertex <SEP> 30 <SEP> 32.8 <SEP> 73.7
<tb>
<tb>
<tb>% <SEP> of <SEP> particles <SEP> fine <SEP> in <SEP> the <SEP> deposits <SEP> 15 <SEP> 5.7 <SEP> 17.1
<tb>
<tb>
<tb>% <SEP> of <SEP> particles <SEP> fine <SEP> total <SEP> outgoing <SEP> in <SEP> the
<tb>
<tb>
<tb> repositories <SEP> 15.7 <SEP> 17.5 <SEP> 40,

  0
<tb>
<tb>% <SEP> of <SEP> particles <SEP> coarse <SEP> total <SEP> outgoing
<tb>
<tb>
<tb> in <SEP> the <SEP> repositories <SEP> 81.0 <SEP> 94.5 <SEP> 89.7
<tb>
 
Instead of using a dilute phase elutriator of the type described, the elutriator may contain very large stuffing, such as Raschig rings or other material. In addition, to remove particles much larger than the average circulating coke, eg aggregates 0.5 inch in diameter or larger, dense phase separation can be used.



   The large solids which concentrate in the bottom of the separator 73 are removed through line 77. The large solids removed, most of which have dimensions in the range of about 200 to 800 microns, with some agglomerates or larger particles and some smaller or fine particles, can be separated into three portions. A portion constituting the net coke produced in the process can be removed through line 78 and, after suitable cooling with a spray of water or the like, sent to storage. This produced coke can amount to about 10 to 35% by weight, for example 25%, based on the residual hydrocarbon feed to the reaction apparatus, and can be used as a fuel, as a metallurgical coke. , etc.



   Another portion of the coarse coke, which may be about 5 to 15 times, for example about 10 times, the weight of the waste hydrocarbon feed, is recirculated through a heating zone to provide heat. to reaction apparatus 3. Hence, coke from line 77 passes through lines 79, 45 and 46 to burner vessel 48. Or, the coke can be heated in a transfer line burner at. high speed of another usual type.



   The third portion of coarse coke, removed from the elutda-

 <Desc / Clms Page number 12>

 tion, passes through line 32 to a mill 33. This latter portion is a relatively small portion, normally only about 10 to 15% by weight of the waste feed, or only about 1% of the coke leaving the apparatus. reaction, but nevertheless it constitutes one of the critical characteristics of the invention. Preferably, although not necessarily, the coke stream is cooled to a moderate temperature, i.e., about 100 to 250 F, before it is actually introduced into the mill.

   This cooling can be carried out in any convenient way, for example, by passing the coke in the aerated state through a heat exchanger containing a water cooled coil. The crusher 83 can be of the ball or roller mill type, or other types of mills suitable for the treatment of coke can also be used, such as hammer mills, horizontal grinders. , or a current grinding with a gas jet. In mill 33, the coarse coke is ground to produce a large fraction of particles smaller than about 200 microns. The grinding should be sufficient to provide the primary coke grains needed to control the particle sizes in the coker.

   This required quantity of grains can be equal to about 5 to 10% by weight based on the waste hydrocarbon fed to the process. Generally, a sufficient number of primary particles should be supplied to the system to equal the number removed or lost. The number of coke particles in the system will be reduced by product coke removed, fines carried off the top, particle agglomeration, etc.



   As a typical example, the coke fed to the mill, which may be of dimensions primarily between about 200 and 500 microns, can be ground until about 30 to 50% by weight of the ground coke mixture is less than 100 microns. , to provide the desired fine particles as a grain or primer coke for return to the coking reaction apparatus.



   However, as such a primary coke is preferably a narrow fraction of approximately 50 to 150 microns in size, this required, in the coking processes previously referred to, sieving of the ground material to give the fraction of desired dimensions. . According to the present invention, this screening phase is removed by returning coke from the mill 83 to the elutriation apparatus 73, as shown, through line 34.



   As a further procedure of the present invention, the elutriation zone is placed in the lower part of the reaction apparatus 3 below the separation or cleaning zone. In this arrangement, the same gas stream can be used for the elutriation of the coke produced, in the classification of the crushed coke, for the separation or cleaning of the spent heat-carrying coke, and for the aeration of the coker. . This reduces the consumption of steam or other fluidizing gas, and decreases the load in the reaction apparatus and the product processing plant.



   The advantages, given by the present invention, of elutriation in connection with the grinding of the primary coke, in fluid coking processes, are further illustrated by the following cases where a fluidized coking plant having a fluidized coking rate is used. 23,000 barrels per day of oil pitch feed and total coke manufacture of 10% feed price, or 400 tonnes per day, operating according to a scheme as shown in Figure 4. The results are summarized in Table III.

 <Desc / Clms Page number 13>

 
TABLE III.



  Coke brewing requirements.
 EMI13.1
 
<tb>



  Case <SEP> no. <SEP> 1 <SEP> 2 <SEP> 3 <SEP> 4
<tb>
<tb> <SEP> dimensions of the primary <SEP> coke <SEP>,
<tb>
<tb> microns <SEP> 110 <SEP> 110 <SEP> 55 <SEP> 55
<tb>
<tb> Dimensions <SEP> of the <SEP> coke <SEP> average <SEP> in
<tb>
<tb> circulation, <SEP> microns, <SEP> 195 <SEP> 195 <SEP> 195 <SEP> 195
<tb>
<tb> Elutriation <SEP> Perfect <SEP> None <SEP> Perfect <SEP> None
<tb>
<tb> Coke <SEP> removed
<tb>
<tb> (to <SEP> the <SEP> crusher <SEP> and <SEP> as
<tb>
<tb> product)
<tb>
<tb> Tons / day <SEP> 434 <SEP> 490 <SEP> 403 <SEP> 409
<tb>
<tb> Average <SEP> dimensions, <SEP> microns <SEP> 258 <SEP> 195 <SEP> 234 <SEP> 195
<tb>
<tb> Primary <SEP> Coke <SEP> required, <SEP> tonnes /
<tb>
<tb> day <SEP> 34 <SEP> 90 <SEP> 3 <SEP> 9
<tb>
<tb> <SEP> power of <SEP> grinding,

   <SEP> HP <SEP> 22 <SEP> 45 <SEP> 6 <SEP> 15
<tb>
<tb> Distribution <SEP> of <SEP> dimensions
<tb>
<tb> of <SEP> coke <SEP> in <SEP> circulation
<tb>
<tb>% <SEP> on <SEP> 20 <SEP> meshes <SEP> (833 <SEP> microns) <SEP> 0 <SEP> 1
<tb>
<tb> 35 <SEP> "<SEP> (417 <SEP>" <SEP>) <SEP> 10 <SEP> 30
<tb>
<tb> 48 <SEP> "<SEP> (295 <SEP>" <SEP> 0 <SEP> 32 <SEP> 0 <SEP> 58
<tb>
<tb> 60 <SEP> "<SEP> (246 <SEP>" <SEP> 18 <SEP> 46 <SEP> 44 <SEP> 70
<tb>
<tb> 80 <SEP> "<SEP> (175 <SEP>" <SEP> 32 <SEP> 77 <SEP> 86 <SEP> 87
<tb>
<tb> 100 <SEP> "<SEP> (147 <SEP>" <SEP> 92 <SEP> 86 <SEP> 93 <SEP> 92
<tb>
<tb> 150 <SEP> "<SEP> (104 <SEP>" <SEP> 100 <SEP> 100 <SEP> 98 <SEP> 97
<tb>
<tb> 200 <SEP> "<SEP> (<SEP> 74 <SEP>" <SEP>) <SEP> 100 <SEP> 99
<tb>
<tb> 325 <SEP> "<SEP> (43 <SEP>" <SEP>) <SEP> 100
<tb>
 
In cases 1 and 3 of perfect elutriation,

   all particles larger than specified fall and are removed from the bottom, while particles of specified size and finer are removed from the top. A practical, industrial scale installation can easily be made to operate almost like a perfect elutriation apparatus, losing relatively little fine material from the bottom or coarse material from the top. The grain or primer coke requirements with such an industrial elutriator may be only about 20-30% higher than with a perfect elutriator.



   Referring to Table III, it will be appreciated that Case 1 operates with near perfect elutriation so that substantially all particles 110 microns in diameter or smaller are entrained through the top into the elutriator and returned. to the reaction apparatus as a bean or primary coke, and only the larger particles are sent to the mill or removed as product. On the other hand, in case 2, the elutriation apparatus is completely bypassed so that coke from the reaction apparatus passes directly to the mill, and the ground coke mixture is returned from the mill directly to the mill. reaction apparatus.

   Accordingly, in case 1, the relatively large particles are selectively crushed, while in case 2 a considerable amount of coarse material circulates in the system. As a result of this preferential grinding of coarse particles, and the preferential return of fine particles to the reaction apparatus, the weight of grain or primary coke required, as well as the corresponding grinding power, is. much smaller in case 1 than in case 2.



   Similar conclusions can also be drawn from a comparison of cases 3 and 4, where the coke is ground to a much finer size. In addition, a comparison of cases 1 and 3, or 2 and 4, shows that when the size of the primary coke is reduced by about half, the required amount of primary coke is very much reduced (about 10 times less). This is because the amount of primary coke required is

 <Desc / Clms Page number 14>

 roughly proportional to the cube of the average particle diameter.

   In other words, since the main purpose of the primary coke is to keep the average particle sizes constant, by providing a number of relatively small particles, it will be evident that this number of particles in a given total weight. increases rapidly as the average particle size decreases. However, excessively small primary coke is impractical due to the consequent difficulty in preserving such fine particles from being blown out of the system. For example, while 110 micron particles can be recovered very efficiently in a single separator cyclone, 55 micron particles will normally require a two-stage cyclone, and even smaller particles. will be more difficult to recover.



   It can be noted from the foregoing description of Fig. 4 that the present invention allows for an unusual efficient use of coke, since fines suitable as grain or primer coke are selectively retained in the reaction apparatus or immediately returned to the reaction apparatus. this, but are not allowed to pass to the burner, or to be removed with the coke produced, In addition, the selective combustion of coarse particles in the burner reduces the amount of grinding which is otherwise required to maintain the suitable distribution of particle sizes.



   The following example shown in Table IV relates to a coker unit capable of processing approximately 3800 barrels of Elk Basin petroleum residue, obtained from vacuum distillation, and having a specific weight of 0.83 and a carbon number. Conradson by 30%; this example will help. to better understand the invention.



     TABLE IV.



    Coking vessel.



  Dimensions Upper right side (clearance area) 9 feet in diameter by 20 feet Wide diameter (below dense bed) 11 feet in diameter by 16 feet
6 inches Middle conical section 4 feet in diameter by 11 feet in diameter over
34 feet Section of the separation system (stripper) 4 feet x 10 feet Bed depth 60 feet (including separation system) Operator conditions Temperature 950 F Effective outlet pressure 11 pounds per square inch Weight of solids in fluidized bed 70 tonnes Speed of bottom gas: 1ft / sec .; summit: 3.5 ft / sec.



  Weight of oil feed to the coking apparatus per hour per weight of solids in said apparatus 0.5 Amount of separation vapor and friction wear to the bottom of the bed 3265 pounds per hour Vapor effective pressure to nozzle inlet 425 pounds per square inch Amount of separating and thinning vapor added at a higher point 4940 pounds per hour Effective pressure of vapor entering fluidizing nozzles at low pressure 90 pounds per square inch Pressure relief device washing and fractionation tower Dimensions 7 feet 6 inches x 40 feet Operating conditions Bottom temperature 700 F

 <Desc / Clms Page number 15>

 Capture plate for diesel - temperature 500 F Top temperature 275 F Effective pressure at the bottom 10 pounds per square inch

  Effective pressure at the top 95 pounds per square inch Oil temperature extinguishing heavy condensate at the bottom of the tower 500 F quantity 2910 barrels per day treatment Quantity heavy condensate recycled to coker unit 1290 barrels per day treatment Gasoil reflux temperature to the top washing area 500 F quantity 1270 barrels per day treatment Diesel reflux temperature towards tower top 235 F quantity 9740 barrels per day treatment
 EMI15.1
 Burner R6cipielt Dimensions 11 feet 9 inches x 32 feet Operating conditions
Temperature 1125 F Top effective pressure 12 pounds per square inch Solids supply to burner 22 tons Air flow 8830 standard cubic feet per minute Air blower discharge effective pressure 32.6 pounds per inch Circulation rate between vessel 4,

  3 tons per minute / square coker and burner vessel Under the above set of conditions, the process is expected to produce approximately 226 barrels, per processing day, of naphtha having an API gravity of 48.7, approximately 2320 Barrels, per processing day. treatment, of purified gas oil having an API gravity of 17.3, about 2.51 million standard cubic feet of wet gas having an average molecular weight of 26.3, and about 152 tons of excess coke per day of processing.



   -Although the coking unit forming the object of the present invention has been described and illustrated in simplified form, it will be understood that a complete industrial unit will include a large number of additional devices, such as pumps, valves, temperature, pressure and level indicators, recorders and regulators, storage tanks, aeration and pressure valves, emergency flow lines, storage tanks, etc.



   CLAIMS.



   A method of converting hydrocarbon oils, which comprises injecting a series of streams of an oil into an enlarged coking vessel containing a mass of finely divided solid material, circulating said solids through a external heating zone and their return to said coking vessel to maintain said vessel at a coking temperature between 900 and 1200 F, the passage of the gaseous material from the bottom up through said coking vessel at a speed adjusted to maintain said mass of solids in a dense turbulent fluidized state, maintaining said oil in said coking vessel for a period of time sufficient to convert this oil into vapors and coke,

   removing the vapors thus formed from the top of said container by an outlet means, separating high boiling end products. from said vapors, returning at least a portion of said high-boiling end products to the coking vessel for subsequent cracking, and separating the excess coke formed in the process.


    

Claims (1)

2. The method of claim 1, wherein the currents <Desc / Clms Page number 16> of oil are injected into the coking vessel in a series of different vertical planes. 3. The method of claim 2, wherein the oil streams are injected rapidly into said coking vessel at a series of points arranged peripherically around said vessel in each of said planes. 4. A process according to claims 1 to 3, wherein additional high temperature solids are introduced into said vapor removed from the coking vessel. 5. A process according to claims 1 to 4, wherein the vapors exiting from said outlet means are immediately cooled to a temperature of the order of 700 to 850 F. 6. The method of claims 1 to 5, wherein a portion of the solids flowing through said coking vessel and said heating zone are removed and sent to a grading apparatus where the finer particles are separated and. returned to said coking vessel, the larger particles are removed, and some or all of said large particles are made to reduced dimensions, and the divided particles are returned to said process. 7. The method of claim 6, wherein the solids are classified in an elutriation apparatus or deposition or decantation separation by a gas passing from the bottom up through the solids in said elutriation apparatus at a rate sufficient to entrain the finest particles. 8. The method of claims 6 and 7, wherein said solids in this method have a size of substantially on the order of 50 to 500 microns, and wherein said fine particles are less than about 175 microns. 9. A method according to claims 6 to 8, wherein said divided particles are returned to the classification area. 10. A process according to claims 6 to 9, wherein a part of the larger particles are removed from said process as a product. The method of claims 6 to 10, wherein a major portion of said larger particles is transferred to said external heating zone in which they are heated, and the heated particles are returned to said coking vessel to provide it with heat. the heat. 12. The method of claim 1, wherein said heating zone comprises a fluidized solids burner, in which heat is generated by partial combustion of the solids with an oxidizing gas. 13. The method of claims 1 to 12, wherein said vapors are removed from said mass of finely divided solid matter at a rate which will entrain and maintain a substantial amount of solids in the region above that mass. 14. A method according to claims 1 to 1, wherein a washing zone is superimposed on the. said coking vessel, in which the vapors are cooled and the higher boiling end products of said vapors are condensed to be recycled to the coking vessel. 15. A method according to claims 1 to 14, in which part of the solids entrained in said vapors is removed at or near the outlet means. <Desc / Clms Page number 17> 16. The method of claims 1 to 15, wherein the solids removed from said coking vessel are separated from the adhering hydrocarbons in a separation or cleaning zone located in the lower part of this coking vessel, the gas used in this separation zone thus also serving to fluidify said mass of solids. 17. The process of claim 1, wherein the coke removed from the process is subjected to classification whereby only relatively coarse coke is removed as a product, and finer coke is selectively retained in the process. . 18. A process according to claims 1 to 17, wherein said hydrocarbon oils are waste petroleum oils containing metallic impurities which deactivate the cracking catalyst and which contain constituents which cannot be vaporized without cracking. 19. The process of claims 1 to 18, wherein said finely divided solid material is coke produced by said process, and which has a feed of substantially on the order of 50 to 500 microns. 20. Apparatus for the conversion of heavy waste oils, which comprises an enlarged coking vessel, a series of nozzles extending through the walls of said vessel, means for introducing said oil through said nozzles, means for introducing said oil through said nozzles. maintaining a dense turbulent fluid mass of solids in said vessel, means for circulating a stream of solids from said coking vessel to an external heating zone with return to said vessel to maintain the latter at a temperature sufficient to convert said oil in vapors and in coke, an outlet duct for the vapors at the top of the receptacle, a washing tower superimposed on said outlet, means for cooling said vapors in the washing tower in view of to partially condense these vapors, and means for returning the partially condensed vapors to the coking vessel. 21. The apparatus of claim 20, and further comprising cyclone separators in the top of the vessel, means for returning solids separated in said cyclone, to the coking vessel, below the level of the vessel. mass of solids, which is there. 22. Apparatus according to claims 20 and 21, which further comprises means for injecting solids from said heating zone into the inlet of these cyclones. 23. The apparatus of claims 20 to 22, wherein said enlarged coking vessel has a lower downwardly tapered portion whereby the velocity of the rising gases in said vessel is maintained substantially constant. 24. Process for the conversion of hydrocarbon oils, as described above. 25. Apparatus for the conversion of hydrocarbon oils, as described above with reference to the accompanying drawings.