US2732330A

US2732330A - Extcaneoos

Info

Publication number: US2732330A
Authority: US
Publication date: 1956-01-24
Anticipated expiration: 1973-01-24

Description

Jan. 24, 1956 R. w. KREBS ETAL CONVERSION OF HYDROCARBON OILS WITH THE USE OF FLUIDIZED SOLID PARTICLES Filed on. 31, 1950 QEGENE QATOQ,

ExTQAN 5005 I GASES Qobemt (D .Krebs QFICLPLQS L'l. IQLmbev-Iindrr Cltborneg United StatesPatentO CONVERSION OF HYDROCARBON OILS WITH THE USE OF FLUIDIZED SOLID PARTICLES Robert W. Krebs and Charles N. Kimberlin, 31"., Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application October 31, 1950, Serial No. 193,062 6 Claims. (Cl. 196-52) The present invention relates to amethod and apparatus for treating hydrocarbon oils. More particularly, the invention pertains to the production of gasoline as well as higher boiling distillate fractions from heavy hydrocarbon oils of the type of topped or reduced crude or similar heavy residues. In its broadest aspect the invention provides for contacting heavy residues of the type mentioned with hot subdivided fluidized solids at temperatures conducive to the coking and cracking of the residues and producing the vapors and gases required for fluidization by pre-cracking a portion of the residue feed. I

In refining crude oil it is standard practice first to subject the crude to simple distillation or topping to produce various distillate fractions, such as naphtha, heating oil and gas oil cuts boiling up to about 800950 F. Most of these distillate fractions are normally converted into high quality gasoline range motor fuels by such conventional treatments as thermal and/ or catalytic reforming and cracking, or similar operations.

The residue from the crude distillation may be processed to yield valuable high molecular weight materials including lubricating oils, waxes, resins, fuel oils, asphalt, etc. depending on the origin and character of the crude. More recently, however, the demand for motor fuels has increased so greatly that it has become extremely difficult to satisfy the motor fuel market by merely processing crude distillates in the manner indicated above. This situation has prompted considerable research and development work directed toward an efficient conversion of crude residua into additional quantities of motor fuels. The two most common methods used for this purpose in current practice are viscositybreaking and coking of reduced crude.

Viscosity-breaking involves a treatment-of reduced crude or the like at elevated temperatures for ashort period of time adequate forthe'formation of an addi- Broadly, the present invention is concerned with such improvements.

One of the major difliculties complicating a successful coking operation results f1 om the heavy deposition of coke in the coking vessels and transfer lines requiring frequent and time-consuming cleaning periods. This problem has been solved or at least greatly alleviated, prior to the present invention, by admixing with the residuum to be coked substantial proportions of a subdivided inert adsorbent solid, such as petroleum or other coke, pumice, kieselguhr, spent clay, sand, or the like, which serves primarily as a carrier for the coke formed so as to prevent coke deposition on equipment walls and also as a scouring agent removing coke deposits from the walls. The high surface area provided by these solids in some cases as, for example, with spent clay, also accelerates'and intensifies the cracking reaction whereby larger yields of'gasoline within short holding times may be obtained without any danger of deactivation of the solids by'carbon deposits or ash constituents of the feed. The coke deposited on the solids may be burnt off in cyclic or continuous two-vessel operation to gen tional quantity of gas oil .and about 5..15% of gasoline'.

The gas oil forms a suitable feed stock for-thermal. or catalytic cracking and may be converted into gasoline in this manner. However, extensive cracking facilities in addition to the crude still and vis-breaking units are indispensable for the production of satisfactory quantities of gasoline by vis-breaking of reduc ed crude.

The other method, i. e., coking of reduced cr u de is a much more drastic heat treatment usually carried out at higher temperatures, ofsay, about 800 1000 F. and for longer times. It results in direct production of increased proportions of gasolineof, say, about l535% in addition to gas oil and hydrocarbon gases together with solid coke. This process lends itself more readily than vis-breaking to the purpose of producing-'maximurn' amounts of gasoline from reduced-crude-in' the most' economical manner, particularly in'vie'w' of the fact that sufficient coke is produced to supply by combustion the heat requirements of the process. Therefore, the re search eiiorts ofthe industry mostrecently.'have con-l1 erate and supply to the coking vessel'the heat required for coking.

While fixed bed and suspensoid systems have been suggested for this type of operation, the so-called fluid solids technique offers greatest advantages with respect to temperature control, heat economy, ease and continuity of operation and equipment dimensions. This technique in its application to the coking of reduced crude involves the injection of the feed into a relatively dense highly turbulent bed of hot subdivided solids having a particle size of about 30-400 mesh, fluidized by a gas flowing upwardly through the bed at a linear superficial velocity of about 0.23 ft. per second to give the bed the appearance of a boiling liquid separated by a definite interface fro-m an upper dilute suspension of solids in gases and gasiform products. Volatile coking products are'removed overhead and further treated after the removal of entrained solids. In some of the adaptations of the process, .coke carrying solids are continuously passed to a fluid type combustion zone wherein they are fluidized by a combustion-supporting gas and coke is burnt oil to heat the solids to a temperature higher than coking temperature. Hot solids are continuously r'ecirculated to the coking zone in amounts suflicient to supplymost of the heat required therein.

While this procedure affords excellent heat control and utilization as well as better yields of desirable products as compared to other systems, certain difliculties arise in connection with the fluidization of the heat carrying solids. It is necessary to fiuidize these solids before the heavy residue feed is introduced into the reactor. For. this purpose, steam or inert gas, such as fluegas or recirculated process gas have been proposed in the past. Substantial amounts of these extraneous fluidizing gases are required, particularly when operating at relatively lowtemperatures of, say, less than ll00 P. which have been found'to be highly beneficial for establishing a de-. s'irable product distribution in the eflluent ofthe coking" zone. For'example, expedimental data indicate that in cracking vacuum residua over inert solids at temperatures below 1000 F., more than 35 wt. per cent of steam based on residue charged is required to prevent excessive coke deposition and loss of fluidization. Even at temperatures as high as 1'l00 F.'the' minimun'rfluidizing j steam requirement is about-"10 20 wt. percent; The

provision of llu'idizing g ases' 'in these proportions adds considerably to the costof the cracking process. The present-invention substantally alleviates thisdifficulty'. It is, therefore, the principal'object of the'present' invention to provide an improved fluid-type process and apparatus for coking and cracking crude residua or similar materials wherein the amount of extraneous fluidizing gas required may be substantially reduced. Other and more specific objects and advantages will appear from the description below wherein reference will be made to the accompanying drawing, the single figure of which is a semi-diagrammatic illustration of a system adapted to carry out a preferred embodiment of the invention.

In accordance with the present invention, at least a substantial proportion and preferably at least a major proportion of the fiuidizing gas required for the fluidization of hot solids contacted with the heavy residue to be coked is produced by gasifying a minor proportion of the residue feed. For this purpose, a minor proportion of the residue feed is contacted with a narrowly confined, i. e., small diameter, dense, fluidized bed of hot solids at conditions conducive to substantially complete gasification by vaporization and cracking, of all gasifiable constituents of said minor feed proportion. The vapors and gases so produced are passed upwardly through an expanded, i. e. large diameter, dense fluidized bed of hot solids superimposed on, and in direct contact with, said confined bed in such a manner that the gases leaving the confiincd bed properly fluidize the expanded bed. The remainder of the residue feed is fed directly to the upper expanded bcd. Proper fluidization of the lower confined bed, particularly in its lower portions may be accomplished by supplying a relatively small amount of an extraneous fiuidizing gas, such as steam or recycle gas to the bottom portion of the confined bed. Because of the small diameter of this confined bed the total amount or extraneous fluidizing gas required for proper fiuidization of this bed is substantially smaller than that which would be required to fluidize a solids bed of uniform diameter but sufiicient hold-up to coke and crack the entire teed supplied thereto in a single stream. When operating in this manner, proper fluidization may be accomplished without the requirement of excessive amounts of extraneous fiuidizing gas, such as steam, even when operating at relatively low temperatures of, say, about 850-l050 F. The invention, therefore, has particular utility in connection with this type of low temperature operation.

In accordance with the preferred embodiment of the present invention, solids heated in a fluid-type combustion zone to a temperature above the desired coking and cracking temperature, say to a temperature of about 900- 120G F., are first contacted with about 5-30% of the heavy residue feed stock in a lower constricted portion of a fluidized solids bed so as to accomplish substantially complete gasification and coking of the feed therein. A small amount of steam or other fluidizing gas may be fed to this portion of the fluid bed to establish a proper fluidizing gas velocity of about 1-l0 ft. per second. The temperature in the constricted portion should be relatively high, say about l000l150 F. and the feed residence time about t to 5 seconds when calculated as a vapor. The upper expanded portion of the fluidized bed may be maintained at the desired relatively low coking and cracking temperature of about 8501050 F., the gaseous efliuent of the lower zone serving to fluidize the upper portion of the bed so that the remainder of the residue feed may be supplied thereto without the danger of fluidization troubles. Substantially larger vapor residence times of, say, about 5-60 seconds are provided in the upper portion of the fluidized bed. The treating temperatures mentioned may be readily maintained by continuously passing highly heated solids from the combustion zone to a lower portion of the constricted bed and from there into the expanded portion of the bed. However, a substantial, and in many cases even a major portion, of the total hot solids required for this purpose may be directly supplied from the combustion zone to a lower portion of the upper expanded portion of the fluidized bed. The

relative dimensions of the two beds of different diameter should be such that the amount of extraneous gas added to the constricted zone plus the gas produced therein by cracking and vaporization are sufficient to establish a proper fiuidization velocity of about 0.2-3 ft. per second in the upper expanded bed. The solids used for the purposes of the invention may be either inert, such as petroleum coke, sand, pumice, etc., or catalytic, such as activated clays, synthetic silica-alumina or silica magnesia composites. and the like.

The advantage secured by this type of operation is highly significant. For example, a process may normally require 10 wt. percent of steam for proper fluidization in a reaction vessel of uniform diameter. The average molecular weight of the products of complete gasification of the feed may be of the order of 15 to 45. A typical figure often used in calculations is 28. The total fluidizing gas requirement may, therefore, be supplied by subjecting merely 16% of the residuum feed to complete gasification in accordance with the invention. This percentage may be calculated 'by applying the ratio of molecular weights to the percentage of steam which would otherwise be used, e. g.

Having described its objects and general nature, the invention will be best understood from the more detailed description hereinafter in which reference will be made to the accompanying drawing.

Referring now to the drawing, the system illustrated therein essentially comprises a reactor 5 and a heater 30,

, the functions and coaction of which will be presently described using the coking and cracking of a 2.4% South Louisiana residuum as an example. It should be understood, however, that the system may be employed to a similar treatment of other feed stocks in a generally analogous manner. While heater 30 is of conventional cylindrical design suitable for fluid-type dense phase drawoif operation, reactor 5 consists of a small-diameter lower cylindrical section A and a cylindrical large-diameter upper section B. The ratio of the diameters of sections A and B may be about 0.1 to 0.4 and the ratio of the heights of sections A and B about 0.3 to 1.

In operation, the reduced crude is supplied to the system from line 1 essentially in the liquid state at a temperature of about 500-800 F. The feed is divided into two portions. A major proportion of, say, about 80 to is supplied directly to a lower portion of section B of reactor 5, preferably by means of suitable spraying devices, via manifold lines 7. The remainder of the feed .is supplied via line 9 in a similar manner to a lower portion of section A of reactor .5 at a point above distributing means such as perforated plate or grid 11 arranged in the bottom of section A. Simultaneously, highly heated solids such as coke, sand or a contact clay, having a fluidizable particle size of about 30400 mesh, suspended in a fluidizing gas such as steam are supplied from line 13 through grid 11 at a temperature of about ll00-1500 F., preferably about l2001300 F., as will appear more clearly hereinafter. About 0.1 to 0.3 parts of steam and about 5 to 20 parts of solids supplied through line 13 per part of the total reduced crude feed supplied to section A are normally adequate for the purposes of the invention.

The hot solids entering section A through grid 11 are first contacted in section A with the minor feed portion supplied through line 9. As a result of the relatively high temperature of the solids and the relatively high solids: feed ratio in secion A, the liquid feed is immediately vaporized and extensively cracked in section A so that a highly turbulent fluidized solids mass MA is formed therein having an apparent density of about 10 to 30 lbs. per cu. ft. and providing for a vapor residence time of about 1 to S'seconds. For the typeand particle size of the solids here involved, the dimension of section A may be chosen to establish linear superficial vapor velocities in mass MA of about 1 to 10 ft. per second. Heat is absorbed in section A by the vaporization and cracking reaction with the efiect that the temperature of mass MA is fairly uniform at about l050-1150 F.

Under the influence of the continuous feed of hot solids to the bottomof section A, fluidized solids flow upwardly into section B. Immediately upon entering section B, substantially at the temperature of mass MA the solids are contacted with the major portion of the reduced crude feed supplied through manifold 7. Thereupon vaporization, coking and cracking takes place. Additional vapors and gases are formed and coke is de posited on the solids. However, inspite of the increased amounts of gases and vapors present in zone B, their.

linear superficial velocityis maintained within a range of about 0.3 to 2ft. per second, suitable for fluidization so that a dense turbulent mass MB having an apparent density of about 20 to 60 lbs. :per cu. ft. and a' definite upper interface L5 is formed within section B above mass MA. As a result of the endothermic reactions taking place in massMB, the temperature of the latter may be readilymaintained at the desirable lower level .of about 850 1000 F. "The hold-up of mass Mn may be such as will provide for a vapor residence time of about 5 to 60 sec. therein. In this manner, proper fluidization is assured even at the relatively low temperatures of mass MB while using only about of the amount of steam which would be required for'proper fluidization of mass MB in the absence of the'small diameter lower section A. A'mixture of gasiform reaction products and'steam containing about 0.001 to 0.02 lbs. per cu. ft. of suspended solids fines flows overhead'from interface L5 and may be subjected to gas-solids separation in any suitable equipment, such as a cyclone separator 15. Separated solids fines may be returned to mass MB via dip-pipe 17. Product vapors and gases now substantially free of entrained solids may be passed via line 19 to conventional product recovery equipment (not shown).

Fluidized solids carrying coke deposited at a rate of about 5 to 25 lbs. per 100 lbs. of residium fed may be withdrawn from well 21 through standpipe 23, stripped and aerated with small amounts of a suitable gas, such as air, flue gas, steam, etc., supplied through taps t in a manner known per se. The withdrawn solids may be passed from standpipe 23 into line 25 at a rate similar to that of the solids supply via line 13. Line 25 receives a combustion-supporting gas, such as air and/ or oxygen, from line 27 in amounts adequate to permit the removal of about 0.5 to 3.0% of coke from the solids by combustion. About 140 to 200 standard cu. ft. of air per pound of carbon are normally suitable for this purpose. The relatively dilute suspension of solids-in-air or the like may be passed from line 25 through a distributing device 29 similar to grid 11 into the lower portion of heater 30 to form therein a dense fluidized mass M30 similar in appearance and behavior to mass MB. Combustion of coke taking place in heater 30 is so controlled that the solids in mass Mac are reheated to a temperature of about 11001500 P. which should be at least 50 F. higher than the temperature of mass MA. Flue gases containing entrained solids fines and flowing overhead from level L30 may be passed through gas-solids separator 32 and thence via line 34 to any desired purpose. Separated solids may be returned to mass M30 via dip-pipe 36 or discarded via line 38. The fluidized solid which is preferably used in the process is coke. Under the usual conditions, more coke is produced in the reaction vessel than is needed to supply the heat for the process through combustion in heater 30. The excess coke is withdrawn through line 38 and may then be used for any desired purpose. In the event that an extraneous solid, such as a clay or sand, is used, it is often advantageous "via taps t.

6 to withdraw a stream of that material bearing an appreciable amount of carbon so that it may be regenerated or burned .in outside equipment both for recovery of the solid and the potential heat in the carbon. Make-up sol.- ids may be added via line 40.

Fluidized solids may be withdrawn from heater 30 at the temperature of mass Mzothrough well 42 and stand: pipe 44 aerated and/or stripped with steam or inert gas The reheated solids pass from standpipe 44 into line 13 wherein they are picked up by fluidizing gas, particularly steam supplied through line 46, to be fed to section A of reactor 5 as described above.

When catalysts, such as activated clay or a synthetic silica-alumina, are used in place of, or in addition to, the inert solids'referred to above, care should betaken to avoid catalyst deactivation by overheating the same in the carbon-burning state. This may be accomplished by maintaining the heater temperature at a level not substantially exceeding 1200 F. or at an even lower temperature. The reduction in temperature may be com: pensated for .by increasing the catalyst circulation rate, thus keeping the quantity of heat transferred substantially constant. When it is desiredto supply a portion, for example, say, 50-90% of the solids reheated in heater 30 directly to the upper expanded section B of reactor 5 this may be accomplished by means of line 50 leading into the bottom of section B. Other modifications within the spirit of the invention may appear to those skilled in the art.

- The invention willbe further illustratedby the following specific example.

Example Section A Section B Pitch Rate, B/D Reactor Vessel Diameter, Ft- 4. 5 -15 Bed Height, Ft

Pressure, Lb./Sq. In. Ga-. 30 25 Fluid Bed Density, Lb./Cu 20 50 Pitch Weight Space Velocity 3. 6 0. 7 Fluid Coke Feed Rate, LbJMi 2,310 11, 550 Avg. Temperature of Coke entering Bed, F 1,150 1, 140 Temperature of Bed, F. 1, l, 040 Coke/Oil Feed Ratio 10 5. 6 Wt. Percent Steam on Feed 5 0. 5 Superficial Velocity of total gases at inlet, Ft./Sec. 5. 9 0. 5

At the above conditions good fluidization is obtained in the main reaction zone B with the use of only 0.5% steam on feed, fiuidization being accomplished mainly by the action of the cracked products from the lower reaction zone A.

The above description and exemplary operations have served to illustrate specific embodiments of the invention but are not intended to be limiting in scope.

What is claimed is:

1. In the process of producing distillate fractions from heavy residual hydrocarbon oils by contacting heavy residual hydrocarbon oil at coking conditions with a dense turbulent mass of subdivided hot solids fluidized by an upwardly flowing gasiform medium, the improvement which comprises introducing an original gasiform medium, which is only a minor part of the total fluidizing medium required, into the bottom of the dense turbulent mass, supplementing said medium by producing a major proportion of said gasiform medium requirements by contacting a minor proportion of liquid heavy residual hydrocarbon oil for a relatively short time with a narrowly confined fluidized mass of said hot solids maintained at 7 a relatively high coking temperature and fluidized at a relatively high linear gas "velocity, said minor proportion of liquid being introduced above the bottom of said mass and separately from the original gasiform medium so as to coke and gasify said minor proportion substantially completely within said short time, passing gases so produced into a laterally expanded second mass of hot solids superimposed on and in direct contact with said first named mass, the two masses constituting a single uninterrupted fluidized bed, so as to fiuidize said second mass at a relatively low linear gas velocity, supplying a major proportion of the heavy residual hydrocarbon oil directly to said second mass, contacting said major oil proportion with said second mass for a relatively long time sufficient for converting said major oil proportion into distillate oils and coke, recovering distillate oils overhead from the fluidized bed, passing coke-carrying solids from said bed to a combustion zone, burning coke off said coke-carrying solids in said combustion zone to reheat said solids to a temperature substantially higher than said relatively high coking temperature and returning at least a portion of the solids so reheated to said first named mass to supply said hot solids thereto.

2. The process of claim 1 in which a portion of 'said reheated solids is passed directly to said second mass.

3. The process of claim 1 in which the feed ratio of solids to oil in said first named mass is substantially greater than the feed ratio of solids to oil in said second mass.

4. In the process of producing distillate hydrocarbon fractions and coke from heavy hydrocarbon oil by contacting said oil at a coking temperature range of about 350 to 1050 F, with a mobile mass of non-catalytic preheated solids of fluidizable particle sizes, the improve ment which comprises very substantially reducing inert fluidizing gas requirements by establishing a fluidized bed of said solids of narrow cross-section in its lower portion and broader cross-section in its upper portion, introducing at the bottom of said bed a relatively small stream of extraneous inert gasiform fluidizing medium which is suflicient to start fiuidizing the bed at its narrow bottom part but inadequate to fluidize it at a broader higher level, introducing in liquid state part of the heavy oil to be coked into the narrow lower portion above the bottom and separately from the inert gasiform medium, continuously supplying hot solids to the lower portion to vaporize and crack the oil so fed and to provide vapors for substantially supplementing the bed-fluidizing action of the inert gasiform medium, and introducing a further part of the heavy oil as a liquid spray directly to the broader upper portion of the bed for conversion to distillate and coke.

5. Process according to claim 4 wherein the solid particles are predominantly coke particles produced in the process.

6. Process according to claim 4 wherein part of the coke produced is withdrawn from the system as product and part is reheated and returned to the fluidized bed for continuing the process.

References Cited in the file of this patent UNITED STATES PATENTS 2,360,622 Roetheli Oct. 17, 1944 2,379,711 Hemminger July 3, 1945 2,382,755 Tyson Aug. 14, 1945 2,402,875 Cornell June 25, 1946 2,436,486 Scheineman Feb. 24, 1948 2,446,678 Voorhies Aug. 10, 1948 2,460,404 Ward Feb. 1, 1949 2,461,958 Bonnell Feb. 15, 1949 2,707,702 Watson May 3, 1955 FOREIGN PATENTS 577,831 Great Britain June 3, 1946

Claims

1. IN THE PROCESS OF PRODUCING DISTILLATE FRACTIONS FROM HEAVY RESIDUAL HYDROCARBON OILS BY CONTACTING HEAVY RESIDUAL HYDROCARBON OIL AT COKING CONDITIONS WITH A DENSE TURBULENT MASS OF SUBDIVIDED HOT SOLIDS FLUIDIZED BY AN UPWARDLY FLOWING GASIFORM MEDIUM, THE IMPROVEMENT WHICH COMPRISES INTRODUCING AN ORIGINAL GASIFORM MEDIUM, WHICH IS ONLY A MINOR PART OF THE TOTAL FLUIDIZING MEDIUM REQUIRED, INTO THE BOTTOM OF THE DENSE TURBULENT MASS, SUPPLEMENTING SAID MEDIUM BY PRODUCING A MAJOR PROPORTION OF SAID GASIFORM MEDIUM REQUIREMENTS BY CONTACTING A MINOR PROPORTION OF LIQUID HEAVY RESIDUAL HYDROCARBON OIL FOR A RELATIVELY SHORT TIME WITH A NARROWLY CONFINED FLUIDIZED MASS OF SAID HOT SOLIDS MAINTAINED AT A RELATIVELY HIGH COKING TEMPERATURE AND FLUIDIZED AT A RELATIVELY HIGH LINEAR GAS VELOCITY, SAID MINOR PROPORTION OF LIQUID BEING INTRODUCED ABOVE THE BOTTOM OF SAID MASS AND SEPARATELY FROM THE ORIGINAL GASIFORM MEDIUM SO AS TO COKE AND GASIFY SAID MINOR PROPORTION SUBSTANTIALLY COMPLETELY WITHIN SAID SHORT TIME, PASSING GASES SO PRODUCED INTO A LATERALLY EXPANDED SECOND MASS OF HOT SOLIDS SUPERIMPOSED ON AND IN DIRECT CONTACT WITH SAID FIRST NAMED MASS, THE TWO MASSES CONSTITUTING A SINGLE UNINTERRUPTED FLUIDIZED BED, SO AS TO FLUIDIZE SAID SECOND MASS AT A RELATIVELY LOW LINEAR GAS VELOCITY, SUPPLYING A MAJOR PROPORTION OF THE HEAVY RESIDUAL HYDROCARBON OIL