US2899376A

US2899376A - Liquid phase - boo

Info

Publication number: US2899376A
Authority: US
Publication date: 1959-08-11
Anticipated expiration: 1976-08-11

Description

Aug. 11, 1'959 R. W. KREBS ET AL COKING HEAVY OILS WITH INERT SOLIDS `IN TWO STAGES Filed Oct. 30, 1953 ALTE R NAT IVE PRODUCT COKE LIFT GAS

4- SHOT SLURRY Ji N STRIP GAS INVENTORS ROBERT W. KREBS CHRLES N.KIMBERLIN,JR

ATTORNEY United States Patent O COKING HEAVY OILS WITH INERT SOLIDS IN TWO STAGES Robert W. Krebs and Charles N. Kimherlin, Jr., Baton Rouge, La., assignors to Esso Research and Engineering Company, a `corporation of Delaware Application October '30, 1953, Serial No. 389,360 6 Claims. (Cl. 208-53) The present invention relates to improvements in coking heavy oils. The invention relates more specifically to a process and an apparatus for'converting petroleum residua and other heavy hydrocarbon oils by treating them rst in liquid phase and under mild conditions and subsequently treating the unconverted oil more drastically in vapor phase by contacting with mobile, hot solid particles of catalytically inert material. Preferably, in the first coking stage relatively `coarse particulate heatecarrying solids are passed downwardly by gravity through the oil primarily in liquid'phase, to cause partial conversion to vapor products, and the feed is then contacted at higher temperatures and primarily in vapor phase With other and more finely divided heatcarrying solid particles. In the preferred embodiment of the invention, the latter particles are in the form of a uid bed. In some cases and for some purposes, however, they may be contacted in a transfer line or even in a non-fluid but moving bed.

In the conversion of heavy hydrocarbon oils by coking, it has been known for some time that product distribution is more satisfactory if the coking is carried out` at fairly low temperature. Higher temperatures result in increasing proportions of gaseous and coke products with corresponding reduction in proportions of products which boil within the motor fuel and gas oil ranges. In coking to produce motor fuels, it is particularly desirable to produce a large proportion of good quality gas oil which can be converted in turn, by a conventional catalytic cracking operation, into a high grade motor fuel.

Despite the advantages of iluid bed coking, this type of conversion process has centain definite limitations at lower temperature ranges. Feed rates must be lowered considerably at temperatures below about l000'F. to avoid bogging the fluid bed. For this reason there are certain advantages in the older and more conventional delayed coking operation when it is desired tov operate at relatively low temperatures. However, the conventional delayed coking process, which uses a soaking drum that must be cleaned out periodically, is quite objectionable in other respects. In the prior art, delayed coking operations commonly are at about 900 F.

Hence, an object of the present invention is to obtain asvfar as practicable the advantages of both systems in a single system, without some of their disadvantages.

According to the present invention, the objectionable deposition of -coke in a delayed coking drum is largely and in many cases completely avoided by passing heatcarrying solids of coarse particle side, for example shot or shot-like particles, through the drum to serve as bases for the deposition of coke and to keep the drum walls relatively clean. In this way the coke formed during mild conversion of the feed is carried out of the drum so that it can remain in service continuously. This removes a major limitation on this type of operation.

'Conversion at mild conditions gives good product disicc drastic enough to obtain high conversion levels. To

raise the conversion levels, according to the present invention, the unconverted feed in the rst stage is used to slurry the coarse heat-carrying particles or vshot and the slurry of oil and solid particles is then taken to a second and more drastic conversion stage. In this stage other heat-carrying particles, preferably more finely divided on the average than the first, carry on the conversion. Preferably the latter solids are in the form of a turbulent, uidized bed and in such quantity and` at such a temperature level that this conversion stage is largely -in vapor phase. Upon contacting the hot particles in the second stage, the unconverted feed from the first stage is rapidy vaporized and cracked thermally. The coarse solids or shot-like particles which were carried into lthe second stage in a slurry are rapidly dried, the oil deposited thereon being vaporized and coked. The proportions of hot solids to liquid feed in this second stage are such that the uid bed at all times is substantially dry and free from agglomeration and bogging. While operating conditions may vary for different feed stocks and for different types and proportions of hot particulate solids, it is preferred to operate the first stage at a temperature range between about 800 and 900 F. and for a time sufficient to accomplish substantial but not complete conversion of the feed. Residence or coking time in this first or liquid stage may vary from about l0 minutes to 4 hours or more. The second stage coking in the fluid bed is carried out at a substantially higher temperature, preferably appreciably above 900 F., a desirable range being between about 950 and 1050 F. This raises the over-all conversion to a high level without excessive conversion to coke and/or gas and the combined product is satisfactory in quantity and quality. Y

After the coarse solids have passed into the fluid bed, carrying coke deposited thereon in the first or liquid conversion phase, they are rapidly dried. Along withj the solids which comprise the fluid bed proper, they growl in particle size by accretion of coke layers deposited thereon. The temperature of the bed must be maintained in the face of the endothermic reaction and the feed vapozation heat requirements. Hence, the solids, both coarse and fine, are circulated to a heater or burner where they are reheated and then recycled. Reheating Yis preferably accomplished by burning part of the prod-I finely divided solids which comprise the fluid bed or the bulk thereof also are preferably coke particles of particle size between about 20 and 400 microns in average diameter. Some of the latter may overlap in size n. rangel the larger or shot-like particles. If materials other: p

tribution in some respects, as noted above, butit is not 'than coke are used for the coarse particles, excessive coke burning may be required in the heatento decoke them. Y y,

The system preferably is so operated that about 70 to.V

%, preferably about 85%, of the total conversion takes".

yplace in the soaking zone (liquid phase at low'tempeaf-l' ture). Formation of coke precursors, soft spongy solids, in this zone may amount to 10-l5% or more, based on Weight ofthe feed. Hence, most of the liquid products are producedin the mild rst stage, but most of tlfecok'e' production (which may total 10 to 25% of the totalfed or more -with some feed stocks) is produced in the second or iluid bed zone where the operating temperature is considerably higher. In conventional delayed coking, and in the first phase of the present process, as much as l to 20% or more of soft solid coke may be produced. In -the present case, however, this soft coke-like material is substantially converted in the second phase lso that rthe over-all production of coke of low volatile content may be less than the apparent coke formed in the first stage. Over-all conversion to liquid products is higher and quality better than in single phase uid coking at the same temperature and feed rate.

The invention will be more fully understood with reference to the detailed description of a presently preferred embodiment thereof which is illustrated diagrammatically in the accompanying drawing.

Referring to the drawing, a colting drum or vessel 11 is adapted to receive a liquid residuum or other heavy oil feed stock through a feed line 13. The feed may be preheated in a coil or heater, not shown, to a temperature up to 800 F. or so. The preheat temperature should not be sufficiently high to cause coke deposition in the coil or other preheater but is preferably about as high as can be tolerated without such deposition. The feed is converted primarily in liquid phase in the vessel 11 which is somewhat analogous to the conventional delayed coking drum.

In the conventional coking drum, however, although the oil is usually agitated, coke is formed in substantial quantities on the walls of the drum which finally becomes so completely lled that it must be taken out of service and the coke removed. In the present invention, the drum remains in service continuously, at least for a long period of time. A stream of coarse solids or shot, that is, solid heat-carrying particles of somewhat larger size than conventional fluidized solids, is supplied through a line 15 having a manifold outlet 17 in the top of the drum 11. The shot, preferably particles of coke of 100 to about 500 microns average diameter, ows out of the manifold outlet nozzle 17 and drops by gravity through the liquid oil in the vessel 11. These particles are preheated to such a temperature as to maintain within the drum a coking temperature between 800 and 900 F. The feed rates of the oil and the shot or other coarse particles are adjusted so as to keep the oil in the vessel for a sufficient time to convert a major portion thereof by mild cracking into vapor or vaporizable products such as gasoline and gas oil. These products pass overhead through a line 19. At a coking temperature in the liquid phase, for example, of 900 F., some constituents boiling at more than 900 F. may be carried over with the vapors overhead and at the same time some components boiling below 900 F. may remain in @the liquid. In other words, this system does not and need not give clean cut separation at a sharply defined cut point. In an average case, perhaps 40 to 50% of the feed will go overhead in the rst stage, the remainder passing in the slurry to the second stage.

Some coke is deposited on the particles falling through the oil in vessel 11 but coke which tends to deposit on the walls of the vessel is consistently scrubbed olf by the falling particles. Thus coke accumulates on the coarse particles and is flushed with the particles from the bottom of vessel 11 through an outlet 21. This product, consisting of an oil slurry carrying the shot and the coke deposited thereon, is conveyed by a pump 23 through a line 25 to a fluid solids bed in a vessel 27.

T he shot and coke slurry taken from the primary coke drum 11 is distributed through a plurality of nozzles 29 into a uid bed of preheated solid particles operating at a temperature preferably between 950 and 1050 F.

This fluid bed preferably comprises a high proportion of coke particles of substantially smaller size than the shot which are rained through the liquid phase in drum 11. A desirable particle size for the fluid bed coke is between 20 and 200 microns although some particles may be as large as 400 microns average diameter. Upon contact with the hot solids in the bed of the second stage, the more volatile constituents of the slurry are quickly vaporized, whereas the less volatile begin to crack.

As indicated, the above operation of a uid bed at a temperature above 950 F. is more satisfactory and efcient from the standpoint of capacity than operation at a lower temperature. Data have been obtained in laboratory tests indicating that for each 30 to 50 F. below 950 F. the feed rate to a fluid bed must be cut in half. Conversely for each 30-50" F. above 950 F. the feed rate may be doubled. Hence, the capacity of a uid bed coking unit is extremely dependent upon the operating temperature. For this reason a substantial part of the coldng is carried out, where the character of the feed stock permits, in the coking drum preferably leaving Y mainly a very heavy residuum for conversion in the fluid bed. As indicated above, however, some lower boiling constituents are carried over since a sharp cut is not obtained in the liquid stage operation. The fluid solids bed is operated at a higher temperature than would be desirable for good product distribution if the whole feed were cracked in the fluid bed. This results in good product distribution from the rst stage plus a high conversion level in the second ait higher feed rates than otherwise would be possible.

In order to carry out the uid bed coking operation, a stream of hot coke, of particle size smaller, on the average, than the coarse particles in the first stage, is supplied to an upper portion of a bed through a line 31 leading from a burner or heating vessel 33. Vaporization and cracking are rapid and the coker products, in vapor or gaseous form, pass overhead through a solids separator such as a cyclone 35. The separated solids are returned to a fluid bed through a solid line 37. The vapor products from the second stage, now free from solids, pass overhead through a line 39 to join the products from the pri mary coking phase in line 19. Both products are taken to a suitable fractionation and recovery system of a conventional type, not shown. If desired, the products may be recovered separately to avoid mixing the products from line 39 with those from line 19. The latter tend to become more unsaturated with increased coking temperatures.

The slurry feed rate through line 25 to the fluid bed should be adjusted so that the uid bed remains substantially dry, in order that no substantial agglomeration and bogging of the bed can take place. The spent solids, both tine and coarse, are withdrawn from the bottom of the coker vessely 27 through a stripping section 41, a steam line 43 being provided for stripping the occluded conversion products from the coke. The coke is then returned through a return bend 45 and line 47 to the burner or heater 33. Product coke may be withdrawn from the system through line 49 or from the burner side if desired. It will be understood that both the large particles or shot, which were passed through the first or liquid stage, and the -fluidizable coke, which forms the bulk of the fluid bed in vessel 27 and which did not go through .the first stage, pass through line 45, 47 to the burner or heater.

The burning vessel or heater 33 is adapted to contain a fluidized bed of coke, all the heat carrying solids, e.g. coke, including the nely divided solids which supply the heat to iluid bed 27 and the coarse solids which supply the heat to the liquid phase coker. These solids are all reheated by burning part of .the coke therefrom in the preferred arrangement. However, where product coke is of sufficient value, extraneous fuel such as gas, torch oil, or the like may be introduced with the air or oxygen which supports combustion within the burner.

The burner vessel contains a baille 51 which connects with a standpipe for reheated solids to be returned to the fluid coking bed. It is connected to line 53 and return bend S which in turn is connected to the ud bed feedline 31 previously described.l Appropriate valves may be provided in both of the lines 31 and 47, etc., to control' Part of the solids in burner vessel 33 flow downwardly? from the bottom of the vessel through a line 61 into an elutriator 63. The latter may be of any suitable type such as a packed or partially packed column within which an upow stream of air or oxygen, introduced through line 65, is flowing.

The arrangement is such that the relatively ne vsolids are carried upwardly by elutriation through a line 67 and returned to the burner, whereas the coarse solids ow downwardly by gravity through line 69 and are returned through line 1-5 to the liquid phase coking drum 11. A lifting gas, such as steam or hydrocarbon gas, is introduced at 71 to propel the coarse solids or sho back to the coking drum.

Instead of withdrawing product coke through line 49, it may be withdrawn through a branch line 73 from line 67 as indicated in the drawing. This arrangement ayoids the withdrawal of the coarse coke particles which may be needed inthe liquid phase coker.

It will be observed that suitable aeration gases may be introduced into the various lines as required and that the apparatus may be modified in various ways as will be apparent to those skilled in the art. The flue gases from the burner pass upwardly through a separator 75 and an outlet 77, entrained solids being returned to the burner bed through line 79 in conventional fashion.

In general, operation in the first stage at a temperature as low as 800 F. will require a residence time of up to 4 hours or so. At 900 F. a residence time in the neighborhood of 30 minutes in the liquid phase may be found ample. It will be understood that the passage of the hot coarse particles or shot through this stage accomplishes several results not found in conventional delayed coking operations. These include (l) the supply of most of the heat by the hot solids, eliminating drastic preheating and resultant coke deposition in heating coils, etc., (2) the coarse particles provide a very large total surface for coke deposition, the wall surface of the drum being comparatively very minor, (3) the falling shot tend to abrade off the walls any incipient coke formations tending to deposit thereon. All three of these effects help to keep the apparatus clean. `It is not necessary to dangle chains and other apparatus down into ythe coking drums, to be pulled out by a heavy tractor or locomotive when the drum cokes full, as has frequently been done in the prior art. Another advantage is that the fluid bed of Ithe second phase is not only a coking zone but also a vaporization zone for a part of the feed. As noted above, a sharp cut point is not obtained in the first stage, moreover the downflowing coarse hot particles continue to visbreak the feed in the drum as it flows down and out through the slurry line. Appreciable proportions of relatively lowboiling fractions are promptly ashed olf upon entry into the hot iluid solids bed of the second stage.

The present application is a continuation in part of application Serial No. 232,523, allowed U,S. 2,775,546, of the present inventors, filed June 20, 1951. In the parent application a solids bed is used to flash low boiling conversion products and some solids are recirculated to a liquid phase coking stage.

While the above description has referred to the use of coke as the heat-carrying solid material, sand ceramic beads, mullite shot, metal lings, shot, and other materials may be substituted. Coke is preferred in most cases because of its ready availability as a product of the process. By using coke it is not necessary to continue burning in the heater vessel 33 until all of the coke deposited is removed from the coarse particles to be returned verted to coke and vapors; the improvement whichcomtothe liquid phase coker. This frequently is of consider-` able advantage.

K What is claimed is:

l. In a combination hydrocarbon oil fluid coking process wherein an oil is initially subjected to relatively mild long time conversion conditions at a temperature in the range of 800 to 900 F. in a liquid phase delayed coking zone to cause substantial conversion to vapors and c vaporizable liquid, and then the unconverted liquid resi- 1'0 due of said oil and said vaporizable liquid are passed to the fluid coking zone of a two-vessel hydrocarbon oil fluidized solids coking system comprising a fluid coking zone and a heating zone to be further completely conprises'passing preheated shot of relatively large particle size downwardly through said liquid phase delayed coking zone to supply a major lportion of the necessary heatv thereto and to remove coke precursors therefrom, passing said shot along with the vaporizable liquid and unconverted liquid residue to said fluid coking zone whereby said shot is dried, then owing said shot to said heating zone along with the portion of the fluidized solids transferred from said iluid coking zone to said heating zone to be reheated therein, and separating and returning said shot so reheated to said delayed coking zone.

2. The process of converting heavy oil to more volatile products which comprises contacting oil feed in liquid phase with a mass of preheated particles of solid heat transferring material of suicient particle size to fall freely by gravity through said oil and in suicient mass to maintain a liquid phase coking temperature between about 800 and 900 F. for a sufficient contact time to accomplish substantial conversion to vapors and vaporizable liquid products, removing vapor products therefrom, flowing a stream of said particles in a slurry of the liquid products and unconverted oil to a fluid bed coking zone containing a mass of finer particles, contacting said liquid products and unconverted oil in said zone with a sufficient mass of preheated iluidized solid heat carrying particles to vaporize and crack the liquid products and unconverted oil under substantially dry fluid bed conditions, withdrawing vaporous products, withdrawing solids from said fluid bed zone to a heating zone, separating finer particles from the coarse particles, and passing heated coarse particles to the top of the liquid phase, said coarse particles passing downwardly therethrough by gravity.

3. The process of claim 2 wherein the coarse particles are coke particles of at least 100v microns average diameter.

4. The process of converting heavy oil feed to more vvolatile products which comprises maintaining said oil in a liquid mass in a delayed coking zone at a temperature of G-900 F., downwardly passing by gravity heated, relatively coarse solids having an average diameter of at least microns through said liquid mass to supply at least a major part of the heat necessary to preserve said temperature thus causing substantial conversion of said oil in the liquid phase to vapors and coke, said coke depositing on said coarse particles, passing a slurry of unvaporized oil and said coarse particles to a fluid bed coking zone, said iluid bed coking zone containing a mass of relatively iiner particles at a temperature above 900 F., contacting said slurry with said bed of finer particles to vaporize and crack said unvaporized oil, withdrawing vaporous products from said fluid bed coking zone, and removing solids from said coking zone for heating and passage to said delayed coking zone and said fluid bed zone.

5. The process of claim 4 wherein about 70 to 90% of the total conversion of said oil feed takes place in said delayed coking zone, and wherein said fluid bed zone operates at a temperature of about 950 to 1050 F.

6. In a combination hydrocarbon oil lluid coking process wherein an oil is initially subjected to relatively 7 mild long time conversionzconditions at a temperature in the range of 800 to 900 F. in a liquid ,phase delayed coking zone to produce vaporous euent, unvaporized oil and carbon deposits, and wherein the unconverted liquid residue of said delayed coking zone is passed to the uid coking zone of a two-vessel uid bed coking system comprising Va fluid coking zone `and a heating zone for conversion therein; the improvement which comprises passing heated, relatively coarse solids averaging at least 100 microns in diameter downwardly through said delayed coking zone to supply a major portion of the requisite heat thereto along with serving as a site for deposition of carbon, maintaining said oil in said delayed coking zone for a time suicient to obtain therein 70 to 90% of the total ultimate .conversion of said oil, passing said coarse solids along with unvaporized oil residue as a slurry from said delayed coking zone to said fluid bed coking zone, contacting said slurry'with a fluid bed of References Cited in the file of this patent UNITED STATES PATENTS 2,388,055 Hemminger Oct. 30, -1945 2,446,247 Scheineman Aug. 3, 1948 2,543,884 Weikart Mar. 6, 1951 2,605,214 Galstaun July 29, 1952 2,690,990 Adams et al. Oct. 5, 1954 2,719,114 Leffer Sept. 27, 1955

Claims

1. IN A COMBINATION HYDROCARBON OIL FLUID COKING PROCESS WHEREIN AN OIL IS INITIALLY SUBJECTED TO RELATIVELY MILD LONG TIME CONVERSION CONDITIONS AT A TEMPERATURE IN THE RANGE OF 800* TO 900*F. IN A LIQUID PHASE DELAYED COKING ZONE TO CAUSE SUBSTANTIAL CONVERSION TO VAPORS AND VAPORIZABLE LIQUID, AND THEN THE UNCONVERTED LIQUID RESIDUE OF SAID OIL AND SAID VAPORIZABLE LIQUID ARE PASSED TO THE FLUID COKING ZONE OF A TWO-VESSEL HYDROCARBON OIL FLUIDIZED SOLIDS COKING SYSTEM COMPRISING A FLUID COKING ZONE AND A HEATING ZONE TO BE FURTHER COMPLETELY CONVERTED TO COKE AND VAPORS; THE IMPROVEMENT WHICH COMPRISES PASSING PREHEATED SHOT OF RELATIVELY LARGE PARTICLE SIZE DOWNWARDLY THROUGH SAID LIQUID PHASE DELAYED COKING ZONE TO SUPPLY A MAJOR PORTION OF THE NECESSARY HEAT THERETO AND TO REMOVE COKE PRECURSORS THEREFROM, PASSING SAID SHOT ALONG WITH THE VAPORIZABLE LIQUID AND UNCONVERTED LIQUID RESIDUE TO SAID FLUID COKING ZONE WHEREBY SAID SHOT IS DRIED, THEN FLOWING SAID SHOT TO SAID HEATING ZONE ALONG WITH THE PORTION OF THE FLUIDIZED SOLIDS TRANSFERRED FROM SAID FLUID COKING ZONE TO SAID HEATING ZONE TO BE REHEATED THEREIN, AND SEPARATING AND RETURNING SAID SHOT SO REHEATED TO SAID DELAYED COKING ZONE.