US2736690A - Integrated process for coking, agglomerating and calcining hydrocarbon oil - Google Patents

Description

Feb. 28, 1956 W, J. MATTOX ET AL INTEGRATED PROCESS FOR COKING, AGGLOMERATING AND CALCINING HYDROCARBON OIL.

Filed May 13, 1954 I (I 1\ 5 I w 95 L\..--- l A. 77 {HEATER 75 1 73 I7 35 f I] T n 2, HM

9 3. 3 f f IMIXER OR K 37 33 I IPELLETIZER I I I34 I33 I35 I I 39 FlG.-I I3! on. FEED 57 5;; H5 93 f k-d us 63 I \57 64 04 II 49 5s 56 COAL 65 P6! 1/ H3 COKER 9 66 K $62 59 MIXER/ I CALCINER I49 60 97 A l I47 99 '3 -14! I03 i F IG.'2

William J. Maflox Roger W. Richardson Inventors Robert W Krebs By fl Aflorney United States Patent INTEGRATED PROCESS FOR COKING, AG- GLOMERATING AND CALCINING HYDRO- CARBON OIL William J. Mattox, Roger W. Richardson, and Robert W. Krebs, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application May 13, 1954, Serial No. 429,664 6 Claims. (Cl. 202-26) The present invention relates to an improved petroleum coke product and process of preparing it. More particularly, the invention relates to the preparation of stable, attrition resistant pellets of coke from petroleum coke particles of a size and type fluidizable in a gas stream, such as are derived from the coking of heavy oils, e. g. residua, in a fluidized solids coking process.

As pointed out in greater detail in a copending application, Serial No. 224,801, filed by Krebs on May 5, 1951, the conventional practice for coking heavy oils has been the coil and soaking tank method, the so-called delayed coking process. This process, although producing a grade of coke that is very satisfactory for some purposes, has certain disadvantages such as the filling of the soaking drum with coke which has to be removed manually or mechanically, with consequent interruption of the process.

More recently, the so-called fluid-solids technique has been successfully applied to the coking of heavy petroleum residua and the like. In this process, finely divided solid particles of suitable heat-carrying properties, such as clay,

carborundum, ceramic beads, metallic particles, and especially coke particles formed in the process, are utilized to supply thermal requirements. These solids also form nuclei upon which new layers or deposits of coke are formed as the oil is converted to more volatile products plus the coke.

The process just described is now well known. It may be carried out in a fluidized bed of the particulate solids, as described for example in an application of Pfeilfer et al., Serial No. 375,088, filed August 19, 1953. It may be carried out also by contacting a moving stream or suspension of the particles with the oil, as is also known.

The processes just described result in production of coke particles, or coke-laden particles, which grow by accretion of coke deposits. The particles must remain fluidizable until removed from the bed or other coking zone and consequently they are usually not larger than about 400 or 590 microns average diameter. These particles, though fluidizable, are usually too large for direct use in power plants using powdered coal, for example, but they are too fine for many other uses.

' Hence an important object of the present invention is to form relatively large pellets of the coke product from coke particles of much smaller, i. e. fluidizable size. In general, the product pellets may be from 10 to 1000 or more times the size of the original coke particles, a desirable size being from about A to /2 inch or more in pellet average diameter. The product pellets are preferably hard, dense and compact, have good electrical conductivity, and are preferably rather low in content of sulfur, ash, and volatilizable matter.

Another object of the invention is to utilize the tacky or adherent, properties of green fluidizable coke, while still hot and fresh from a fluid solids coking zone, to form agglomerates or pellets thereof. A further object is to use a bed or mass of the green fluidizable coke as a quenching medium for the vaporized coker products 2,736,690 Patented Feb. 28, 1956 and/or to remove or condense heavy ends and entrained solids from the vapor products. By means of such quenching medium, the use of water or steam as a quenching medium for the vapors, which frequently gives emulsion difficulties when the vapors are condensed, may be reduced or eliminated.

A still further object is to make use of the heavy ends, etc., so removed, to enhance agglomeration, i. e. to serve as agglutinant material. I

Still another object is to use, in a preferred modification, an extraneous agglutinant which is relatively lower in volatilizable matter than petroleum pitch or residuum such as has previously been proposed. For this purpose a more specific object is to use bituminous coal, subdivided preferably to a fluidizable particle size, in admixture with the fluidizable coke, as a pelletizing or agglutinant or cementing agent. The combination, broadly, of. bituminous coal with coke is known, but the present invention mixes coal with a specific type of coke under critical conditions with a new and useful result. An ancillary object is to recover volatilized coal products along with the volatilized coker vapors from the oil.

An additional object is to produce a pelletized cokeof higher quality than the normal product from a fluid bed coking process. The product of this invention is suitable for use in manufacture of electrodes such as are used in reduction of aluminum ores and related industrial processes. A similar and related object is to produce pelletized coke of optimum unit size and mechanical strength and stability for handling in conventional transporting and feeding equipment, e. g., for use as solid combustible fuel in conventional heating and power generating equipment. In appropriate cases, combustion accelerators, such as oxidation promoters, or anti-corrosion agents, such as lime, anti-boiler-fouling agents, etc., may be added to the coke.

A further object is to form and/or compact the product by pressing, e. g. by extrusion into pellets while the coke is green or fresh and in optimum pelletizing condition, to improve its density, electrical conductivity, mechanical stability, resistance to attrition, and/or other needed properties.

The invention and its objects will be more fully understood by reference to a detailed description of preferred embodiments thereof. For this purpose, reference will next be made to the accompanying drawings.

Fig. 1 shows more or less diagrammatically a coking the coke heater or burner and certain other conventional elements omitted.

Referring now to Fig. 1, there is shown a coking system of the general type disclosed in the aforesaid Pfeifier et al. application. The system comprises a fluidized solids bed type coking vessel 11 and a fluid bed burner or heater 13. The general manner of operation of these vessels is now well known in the art.

Oil, for example a reduced crude, usually a heavy residuum, is fed onto or preferably into a fluidized bed 15 of preheated particles of coke, e. g. through nozzles or feed lines 17. The heat carried into the reactor by the solid particles of coke causes vaporization ofvolatile portions of the feed and thermally cracks or cokes the the remainder, forming new deposits or layers of coke on the original coke particles introduced into the bed. These particles, now enlarged by coke deposition and cooled by the vaporization and cracking, are witht; drawn from the coker. A sufficient portion of the coke is taken through lines 19 and 21 to a burner or heater 13. Here they are burned or partially burned by contacting with an oxidizing gas, usually air. The particles thus heated are returned through lines 23, 25 and 27 to the coker to repeat the process. The process and apparatus so far described are known in the art.

The heat requirements for the coking operation do not require that all of the product coke be burned. Usually only a small part, in some cases 20% or less, of the total product coke is required to supply the thermal energy required for coking. Hence, product coke is withdrawn, either periodically or continuously as desired, e. g. through a line 31 at the bottom of the coker vessel. A feed control or metering device 33, such as a star feeder or the like may be used. In some cases, the coke'may flow simply by gravity. and the feed control device 33 may be merely a valve of suitable type. Alternatively, instead of taking the relatively cool and green coke from thereactor, a drier and hotter coke, lower in volatile matter may be withdrawn from the burner 13, e. g. through line 35, and utilized as hereinafter described.

The proper operation of a fluid solids coking bed requires that the solids to oil ratio be high enough at all times to keep the bed fairly dry and avoid agglomeration. In other words, the oil should be rapidly vaporized and coked so that most of the coke particles in the coking bed are too dry to adhere to each other in the bed which would form agglomerates. On the other hand, the product coke withdrawn from the system can be handled more easily if it is agglomerated into larger particles. The final coke product, moreover, should preferably be of high density and it should have a low content of volatile matter, for most commercial applications. The green coke, as it normally comes from the coker, must be calcined to reduce its volatile content considerably when it is to be used for making carbon electrodes of the type used in the aluminum industry, for example. The green coke has a typical volatiles content of 3 to 7% by weight when measured by heating to 1742 F. Usually this should be reduced to less than 1%.

Hence, according to the present invention, the product coke, from the coker 11, or from burner 13, if preferred, is taken from the coker-burner system into a pelletizer or mixer 39. Here it is mixed with a suitable agglutinant, preferably a finely divided bituminous coal or a heavy pitch. Coal, when used, should have a sufficient content of bituminous or plastic material, at the temperature where the coal softens or begins to melt, to supply bonding material for cementing the coke particles together. The amount of coal or pitch required depends upon the dryness of the coke, its particle size, its temperature, etc., as well as upon the characteristics of the agglutinant. In general, the proportions of coke to agglutinant will be between 1 to l and 30 to l by weight, preferably between to 1 and 20 to l. The green coke from the coker requires very little agglutinant. If taken from the burner, it requires somewhat more.

Bituminous coal normally begins to soften at a temperature around 750 F. and its plasticity usually disappears at around 950 F. The coke from a fluid bed coker is usually within or slightly above this general temperature range. By bringing part or all of the coke from theburner or heater 13, e. g. by connecting line 35 on the burner coke outlet to the connection 37 on line 31, hotter coke may be brought into the pelletizing or mixing vessel 39. The connecting line is omitted for clarity of other parts.

The agglutinant, e. g. finely divided bituminous coal, is fed from a hopper 41 by means of a suitable feeder or flow control unit 43 in conduit 45. This unit may be a star feeder or screw conveyor, etc., or it may be simply a valve when the coal is of free flowing type. Lime, anticorrosion, or anti-boiler-fouling agents may be added with the coal if needed. Alternatively a viscous oil, pitch or the like may be supplied as a fine spray from a feed line 46 to the bed to supplement the coal or to take its place.

The vessel 39 is shown to be of generally tapered or conical shape, roughly, with its wider end upward, somewhat similar to the apparatus described in the Krebs et al. application mentioned above. A grid 47 across the narrow lower part of the vessel provides a support for solids contained therein. A compartment 49 at the bottom below the grid receives a fluidizing gas such as steam or hydrocarbon gas at elevated temperature from a suitable source, e. g. line 51. This gas passes up through grid 47 to keep the bed of solids, coal and coke, fluidized and in motion. The gas velocity is such as to keep non-agglomerated particles actively in motion but low enough to allow large agglomerates, of the desired product size, to settle to the bottom of the vessel 39 where they can be withdrawn through a line 53. A control valve or a feeding device, such as a star feeder where gravity flow is not obtainable, may be provided to move the pelletized product coke out of the mixer or pelletizer vessel 39.

The pelletized coke, still relatively green and at an elevated temperature, leaves the mixer or pelletizer 39 through line 53 to a compactor or extruder 55. The latter may be of any suitable type. As shown, it comprises a compacting screw 56 driven through a gear 57 by any suitable source of power. The screw, preferably but not necessarily of the diminishing pitch type, forces the coke downwardly into a narrowed outlet from which the compacted coke passes into a calciner 59. A burning or elutriating gas at very high temperature, e. g. 1800 to 2800" F., is fed through line 60 to fluidize or at least agitate the pellets and elutriate fine particles from them. The resulting product becomes very dry and hard and is free or substantially free of volatilizable matter. The addition of steam through line 60 will in some cases be advantageous for improving the quality of the coke pellets. The gas passes overhead, elutriating fine particles which are separated in a cyclone 61, the fine particles being taken off through a solids outlet 62. The hot gases pass overhead through line 63, under control of a valve 64 to heat recovery means, not shown. The separated solids are propelled through line 65 by a suitable gas such as steam or hydrocarbon to join the solids inlet line 27 to the coker.

. The fluidizing gas in the pelletizer or mixing vessel 39 passes overhead through a cyclone 67 with a gas or vapor outlet line 69 and a solids return line 71. In some cases it is desirable to return some of the very fine coke dust to the coker and a line 73 is provided for this purpose, connected to return line 71 and controlled by a valve 75. Suitable lifting gas'may be provided to propel the solids through line '73 by any conventional means, e. g., a line connected at'74. This finely divided coke may be taken from the cyclone dip leg and mixed into the oil feed, as by a mixer 77 of any suitable type so as to increase the allowable feed rate, as described in an application of Griffin et al., Serial No. 421,416, filed April 6, 1954. Products from line 69 are taken to a suitable recovery apparatus, not shown. Ordinarily they are combined with vapor products from the coker unless all the latter are passed through the vessel 39.

In many cases it may be desirable to pass part or all ofthe coker vapors through the pelletizer or mixer 39 to condense heavy ends or separate finely divided solid particles therein into the coke product. Because of its admixture with coal, and/or other cooling effects, etc., the temperature in vessel 39 is definitely lower, e. g. 50 to 200 F. or more below that in the coker when coke is supplied from coker outlet 31. As noted above, the temperature in vessel 39 may be controlled by bringing hotter coke from the burner outlet 35. Hence, heavy ends of the coker vapors may be condensed if desired and remain in the bed to assist in cementing the coke into large agglomerate particles. Volatile matter is driven out of the large particles later'in unit 59. The calcined coke may be taken out of the calciner 59, by the outlet 97, controlled by valve or feeder 99.

To convey the coker product vapors to vessel 39, a line 85 from coker cyclone 87. receives the coker product vapors. Entrained solids are separated, or at least partially separated, in this cyclone and returned to the coker bed through line 89. A valve 91 is provided to permit, if desired, the flow of the vapor products directly to recovery apparatus not shown. A branch line 93, under control of valve 95, is provided to lead part or preferably all of the coker vapors into the mixer or pelletizer 39.

It will be understood that the pelletized coker product need not always be calcined immediately and in some cases not be calcined at all, e. g. if it is to be used as fuel. In such situations the calciner 59 may be disconnected or bypassed. Also, it may not be necessary to use coal to cause agglomeration especially when heavy ends of the coker vapors are condensed in the product coke. Cooling means, such as a coil, may be inserted in mixer vessel 39 to control condensation, if desired and feeder 43 may be shut down.

Referring now to Fig. 2, there is shown the coker part of a system, similar to that of Fig. l, with the coke heater or burner omitted. The coker vessel 101 has a coke outlet line 103 and a return line 104 connecting to the burner, not shown. A product coke outlet line 105 has a flow control valve, meter, or feeder 106, by means of which product coke is passed to a riser 107. Here the product coke is impelled by a gas stream, e. g. a stream of superheated steam, hydrocarbon gas, flue gas, or hydrogen or hydrocarbon supplied through line 109.

The impelling gas conveys the solids into a mixer or calciner vessel 111 where they are fluidized and mixed with finely divided coal supplied from a hopper 113 by a valve or star feeder 114. The gases from this vessel pass overhead through a line 115 controlled by a valve 116 or they may be passed back into coker 101 via line 117 under control of valve 119.

Coker vapors may be brought from the coker outlet line 131 through line 133 under control of valves 134 and 135 to the bottom of the mixer vessel 111. In this case, the gas from line 109 of course must not be of combustion supporting character and it may be kept to a minimum in quantity. In some cases it may be shut off entirely. The product vapors then pass through line 115 to recovery apparatus of conventional type, not shown, or they may be combined with products from line 131 if valve 135 is open.

The coke, suitably mixed with coal in vessel 111, is withdrawn to an extrusion device which may be the same general type as that of Fig. 1, i. e. a screw-type extruder 141, mounted in a casing 143 having a bottom outlet 145 of reduced diameter through which the solids are compacted and extruded. This screw is driven through its shaft 147 by a gear or equivalent driving element 149 by any power means, not shown, as will be obvious.

The green coke from the coker frequently has sufficient content of viscous oil to form a solid block, lump, or briquette when pressed while still hot. In some cases, as noted above, the coal can be omitted. In some cases the heavy ends of the coker vapors, condensed onto the coke just before pressing, afford sufiicient agglutinant. Other materials, such as lime, etc., may be added as needed.

It will be understood that an important feature of the invention is the pelletizing of product coke while still hot, to secure maximum agglutination or cementing with a minimum of volatile matter being included. At the same time, the feature of utilizing the bed of coke, fresh from the coker (or heater) and only moderately cooled to quench and/or strip undesirable materials from the coker vapor products is an important feature. The latter makes it possible to improve very considerably the quality of a coker gas oil, removing therefrom undesirable materials such as heavy ends which contain objectionable proportions of catalyst contaminants. Otherwise these contaminants may cause considerable difiiculty in subsequent catalytic cracking of the products.

It will be understood also that in some cases the fluid bed pelletizing unit 39 of Fig. 1 is essential while in other cases, as shown in Fig. 2, it may be omitted, particularly where the coke product will agglomerate readily at higher temperature.

A specific example of a desirable operation is as follows:

A heavy 1 2% West Texas residuum may be coked at a coking temperature of about 950 F., using fluidizable coke preheated to a temperature of about 1100 F. About of'the net coke product iscontinuously removed through line 31, Fig. 1, by the star feeder 33 to vessel 39. The remaining 20% is burned in heater 13 to provide the heat requirements of the entire system.

The coke entering vessel 39 is mixed with about 10% of its weight of finely ground bituminous coal having a particle size generally below 400 microns. The resulting temperature in vessel 39 is preferably somewhere near 800 F. Temperature may be controlled where necessary by inserting heating or cooling coils in the vessel where needed as noted above.

After mixing long enough to accumulate a small mass of pellets or agglomerate particles in the bottom of vessel 39, the agglomerates are withdrawn through line 53 to the compactor or extruder 55. The upward gas velocity in the bottom of vessel 39 is sufliciently high to prevent substantial quantities of fine coke from flowing out through line 53. The compactor extrudes the coke into calciner vessel 59.

Hot flue gas, superheated by adding air and combustible gas thereto, is fed into calciner 59 through line 60 at a temperature of 2400 to 2800 F. Alternatively, preheated air, at a temperature of at least 1000 F., is fed into the calciner to heat the coke to the same general temperature range by partial combustion. The separated fines pass through line 65 to the coker where they mix with the reheated coke. The volume of these coke fines is small, compared with the main stream of the coke from line 25, so that they do not greatly affect the coker temperature.

The calcined coke is removed at a temperature above 2000 F. It may be cooled in any suitable manner, as by heat exchange, for efiicient use of its heat. The same is true of the gases passing overhead through line 63.

What is claimed is:

1. An integrated process for preparing relatively large, dense, coke compactions which comprises the steps of coking a heavy hydrocarbon oil by contacting the oil coking charge stock at a coking temperature with a body of coke particles maintained in the form of a dense, turbulent, fluidized bed in a reaction zone wherein the oil is converted to product vapors and carbonaceous solids are continuously deposited on the coke particles; removing product vapors from the reaction zone; circulating the coke particles through an extraneous heating zone wherein a portion of them are heated and back to the reaction zone to supply heat thereto; withdrawing coke particles from the reaction zone to a mixing zone wherein they are admixed with an agglutinant at a lower temperature than the coking temperature and one in the range of about 750 to 950 F., the resulting system being maintained in the form of a dense, turbulent, fluidized bed; withdrawing resultant coke agglomerates which settle through the dense, turbulent, fluidized bed from the lower portion of the mixing zone and promptly compacting the agglomerates in a compacting zone.

2. The process of claim 1 in which the proportion of coke to agglutinant utilized in the mixing zone is in the range of about 1-30z1.

3. The process of claim 2 in which the agglutinant is a heavy petroleum pitch.

4. The process of claim 2 in which the agglutinant is a finely divided bituminous coal.

5. The process of claim 1 including the additional step 7 of calcining the compactions at a temperature in the range of 1800 to 2800 F.

6. The process of claim 1 in which the coking temperature is about 950 F. and the agglutinant is obtained by passing coker product vapors into the fluidized bed in the mixing zone whereby heavy condensible ends agglutinant are deposited thereon.

References Cited in the file of this patent UNITED STATES PATENTS 2,177,226 Rice et a1. Oct.24, 1939 8 Whaley June 13, 1950 Schutte et a1 June 10, 1952 Schutte Jan. 6, 1953 Martin May 26, 1953 Brown Oct. 20, 1953 Lefier Dec. 1, 1953 Alexander et a1. July 20, 1954

Claims (1)

1. AN INTEGRATED PROCESS FOR PREPARING RELATIVELY LARGE, DENSE, COKE COMPACTIONS WHICH COMPRISES THE STEPS OF COKING A HEAVY HYDROCARBON OIL BY CONTACTING THE OIL COKING CHARGE STOCK AT A COKING TEMPERATURE WITH A BODY OF COKE PARTICLES MAINTAINED IN THE FORM OF A DENSE, TURBULENT, FLUIDIZED BED IN A REACTION ZONE WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS SOLIDS ARE CONTINUOUSLY DEPOSITED ON THE COKE PARTICLES; REMOVING PRODUCT VAPORS FROM THE REACTION ZONE; CIRCULATING THE COKE PARTICLES THROUGH AN EXTRANEOUS HEATING ZONE WHEREIN A PORTION OF THEM ARE HEATED AND BACK TO THE REACTION ZONE TO SUPPLY HEAT THERETO; WITHDRAWING COKE PARTICLES FROM THE REACTION ZONE TO A MIXING ZONE WHEREIN THEY ARE ADMIXED WITH AN AGGLUTINANT AT A LOWER TEMPERATURE THAN THE COKING TEMPERATURE AND ONE IN THE RANGE OF ABOUT 750* TO 950* F., THE RESULTING SYSTEM BEING MAINTAINED IN THE FORM OF A DENSE, TURBULENT, FLUDIZIED BED; WITHDRAWING RESULTANT COKE AGGLOMERATES WHICH SETTLE THROUGH THE DENSE, TURBULENT, FLUIDIZED BED FROM THE LOWER PORTION OF THE MIXING ZONE AND PROMPTLY COMPACTING THE AGGLOMERATES IN A COMPACTING ZONES.

Images