US2871183A - Conversion of hydrocarbons - Google Patents

Description

Jan- 27, 195 B. l. SMITH ET AL 2,871Ql83 CONVERSION OF HYDROCARBONS Filed Sept. 21. 1954 1 PRODUCTS FLUE GASES LOW TEMPERATURE BURNER M U U D S E R 22 FLUIDIZATION TRANSFER LINE REACTOR HIGH TEMPERATURE BURNER LIGHT GASES Brook Smith Inventors: Edward ion XC John W. Herrmonn Attorney United States Pa e '0" CONVERSION OF HYDROCARBONS Brook I. Smith, Elizabeth, and Edward D. Boston, Westfield, N. J., and John W. Herrmann, Woodside, N. Y., assignors to Esso Research and Engineering Company, a corporation of Delaware Application September 21, 1954, Serial No. 457,382

6 Claims. (Cl. 208-54) atoms, and preferably having 2 or 3 carbon atoms, and' for converting normally liquid hydrocarbons such as coal tars, asphalts, cycle stocks, petroleum tars, whole petroleum crudes, distillates and residual fractions therefrom, or mixtures thereof. A paramount feature of the present invention is the convertingof petroleum oils and light gases therfrom in a system utilizing a single inventory of heat transferring particulate contact solids such as spent catalyst, sand, refractory beads, etc. Preferably, coke produced by the process is the contact solid used. References herein to the use of coke as heat carrying particles will be understood, however, to be exemplary and not limiting.

In the conversion of petroleum hydrocarbons by contact with heat-carrying substantially catalytically in-ert solids, two distinct processes are envisioned; namely, coking mainly for production of liquid fuel products or intermediates (fuels coking) and, secondly, conducting the cracking operation at a higher temperature for the production of chemical raw materials or intermediates such as ethylene, butadiene, aromatics, etc. These two types of conversion processes are generally carried out under considerably dilferent conditions.v The charging stock to a fuels coking operation usually is a heavy, high boiling, low value petroleum residuum containing ashforming constituents, high Conradson carbon, and catalyst contaminants that render other methods of upgrading unattractive. temperatures in the range of 850 to 1200" F. As a relatively long time must be allowed for the cracking reaction, the fuels coking operation requires a fairly large hold-up of coke in proportion to the oil feed rate in order to avoid bed bogging and agglomeration of the solid particles. Because of the long reaction time required, a fluidized solids bed coking system is preferred.

In contrast, thermal cracking to produce unsaturates of low molecular Weight is generally carried out in a higher temperature range upwards of from 1200 F. in order to obtain high yields of the desired products. It is custom- The operation is generally conducted at 2,871,183 Patented Jan. 27, 1959 a fuels coking process wherein oils are pyrolytically converted to yield naphthas and higher boiling distillates suitable for motor fuels, furnace fuels or for further treatment such as catalytic cracking, into a combination with a thermal cracking process wherein light hydrocarbon gases are converted to materials such as diolefins and olefins useful as chemicals or chemical intermediates. Preferably, the light gases are obtained from the fuels coking products. By means of this integration, this invention succeeds in obtaining from a petroleum oil, in economically balanced proportions, high yields of desira-' ble chemical compounds and of light and middle distillates while producing as an ultimate degradation product a petroleum coke of superior quality.

Although the process of this invention may be most advantageously carried out in a three-vessel system, i. e.,

a fuels coking zone, a high temperature thermal cracking zone and a contact solids heating zone, other variations or combinations in the number of reaction vessels used will be readily apparent to those skilled in the art. Thus a reduction in the number of vessels can be made by conducting two of the operations in separate zones within one vessel. Further, in certain applications, the present process may be suitably combined with other refining processes such as catalytic cracking to augment its ad vantages.

Another object of this invention is to devise an integrated process utilizing the fluidized solids technique wherein selected fractions of petroleum derivatives are converted at high temperatures by contact with a continuously circulating stream of contact solids maintained at different optimum reaction temperatures in successive reaction zones, whereby optimum product yields and distributions are secured. It is a further object to provide for in the integrated process, specific processing sequences whereby unnecessary and undesirable secondary thermaltached drawing, forming a part of the specification, is

discussed in detail.

The drawingdiagrammatically depicts one preferred embodiment of'the present invention. This embodiment is designed to process in a three-vessel system two different feed stocks, e. g., a heavy petroleum oil such as a vacuum residuum and light hydrocarbon gases such as propane and/or ethane. A'salient feature of the process illustrated is that the effluent from the high temperature transfer line thermal cracking zone is introduced into the base of a somewhat lower temperature fluid bed fuels coking zone. Here it is quenched and is used to supply heat and most or all of the fluidization gas to the fuels coking zone. zone can, however, be separately quenched and separated,

' if desired. Prompt quenching of the cracked gases from The effluent from the high temperature following manner.

degradation and can be accomplished by other means, such as by the injection of water, steam, cool solids, etc. into the cracked gases.

Briefly the objects of this invention are attained in the A single inventory of heat-carrying particulate petroleum coke is circulated through the combination process supplying heat to a plurality of thermal cracking reactors. The coke removes from the reaction zones the carbonaceous residues produced. The heatcarrying coke is first heated in a heating zone, preferably a. combustion zone wherein either a portion of the cokeor extraneous fuel such asnatural gas or fuel oil is burned, heating the coke to a temperature in the range of 900 to 2000 F. At least a portion of the coke is heated to a temperature above the highest reaction zone temperature. This high temperature coke is circulated to a thermal cracking zone, preferably a transfer line reactor. Here it contacts and converts light, hydrocarbon gases. The hot solids maintain the zone at a temperature in the range of 1200 to 1800 F. whereby chemical products such as diolefins and olefins are produced. Diluents, such as steam, may be used, if desired. This coke, along with another portion of coke from the heating zone, if desired, is then circulated from the high temperature zone to a fuels coking zone. The latter is, preferably, a fluidized solids coking zone, although it may also be a transfer line zone. An oil, for example, a heavy petroleum residual oil, is injected into the fuels coking zone and undergoes pyrolysis in contact with the hot fluidized coke particles at a temperature in the range of 850 to 1200 F. This thermal cracking produces relatively lighter butnormally liquid hydrocarbons such as naphthas and gas oils and a small amount of gas. Some coke is produced and is deposited on the coke particles of the fluid bed. The coke or part thereof is then returned to the heating zone to be reheated therein. A portion of the net coke produced is removed from the process.

With particular reference to the attached drawing, a preferred process will be described for the conversion of a heavy, low value residual oil such as a petroleum vacuum residuum. The major items of equipment shown in the drawing are a combustion vessel or burner 1, a transfer line, high temperature thermal cracker 10, and a.

lower temperature fluid bed coking vessel 20 designed to produce light and middle distillates. Light hydrocarbon gases are used as the feed stock to the high temperature zone. These may be obtained from any convenient source within the refinery. Preferably, however, these gases, e. g., predominantly ethane and/or propane, are obtained from the efiluent of the low temperature coker 20. While a fuels coker may produce substantial amounts of ethylene and propylene, there ordinarily is not a sufficient amount produced to warrant recovery of the gases.

By integration of the high temperature cracking step with the fuels coking process, the amount of ethylene, for example, may be substantially increased by cracking the ethane content of the low temperature or fuels coker light gaseous product at a high temperature, e. g., 14-00 to 1600 F. and at relatively short vapor residence times, e. g., 0.01 to 10 seconds.

Referring to the drawing, it can be seen that the system has but a single inventory of circulating heat transferring contact solids, e. g., coke'particles of about -1000 microns in diameter produced by the process. As some of the vessels operate with a fluidized bed of the coke, it is preferred to maintain coke in the process having a size range of about 40 to 1000 microns, although this size rangemay go beyond these limits in some cases.

Heat, for the process is generated by burning a portion of the coke produced by the cracking reactions. In cases where the value of the coke is greater than liquid or gaseous fuels, the latter may be burnt to impart. part or all of the required heat to the solid particles. A. fluid bed of burning coke is maintained in a low temperature burner vessel 1 by air supplied by line 3. This burher operates at a temperature in the range of 950 to 1300 F. Flue gas generated by the combustion passes overhead after having entrained solids removed by a cyclone system and is removed from the vessels by line 5. Heat exchange means can be used to extract the specific heat content ofthe flue gas before venting it. As is later described, this heat exchange can be made by direct contact with a portion of the circulating coke in the system.

in order to supply the necessary high temperature solids to the high temperature cracking zone, an auxiliary or high temperature burner 2 is used. Solids are transferred from the low temperature burner El to the high temperature burner 2 by means of standpipe 6. Air supplied to the high temperature burner by line 4 serves to fluidize and partially burn the solids in the burner. The temperature of solids is raised therein to about 1300 to 2000 F. The flue gases resulting from the high temperature combustion pass upwardly through line 9 to the low temperature burner. Here they are cooled by heat exchange with the fluid bed of solids contained therein.

Other less preferred means of supplying heated solid particles to the process can, of course, be used. Thus in place of fluid beds, gravitating or moving beds may be used within the. vessels 1 and 2. Alternatively, a transfer line burner may also be used. Instead of operating two combustion zones at two different temperatures, one combustion zone operating at a high temperature may be used and the coke circulation rate to the low temperature fuels coker may be correspondingly decreased.

The high temperature cracking zone in this example is :1V transfer line reactor 10 operated at a temperature in the range of l200 to 1800 F., preferably 1400" to 1700 F., and a hydrocarbon partial pressure in the range of 5 to 40 p. s. i. The solids, along with the vaporous conversion products, are transferred through the reactor 10 at velocities above about 10 ft./sec., e. g., 60 ft./sec. High temperature coke is supplied to reactor 10 by line 8 and line 11 introduces the light gases to be converted. The time-temperature conditions during the gas (i. e., ethane, propane) cracking are preferably chosen to limit ethane conversion per pass to about 50 to 65% in order to obtain high (70 to wt. percent) ethylene yield on ethane cracked and to minimize the formation of methane. The ratio of light feed gases to high temperature solids may vary from 0.1 to 5 standard cu. ft./ lb.

It is preferred to conduct the effluent including entrained solids from the transfer line reactor directly to the fuels coker. The cracked light gases will then be quenched by the cooler solids in the fuels coker to a temperature substantially below their cracking temperature and the eflluent from the chemical reactor will serve to supply heat and fluidization gas to the fuels coker, thereby decreasing heat requirements and fluidization steam requirements. However, to avoid commingling of the products from the two reactors, gases issuing from the transfer line reactor may be conveyed through a separate cyclone system to remove entrained solids and thence to a conventional separating and final processing system. It will be appreciated, however, that by conveying the overhead from the transfer line reactor to the fuels coker, the need for, a solid separation system, e. g., a cyclone is eliminated.

The fuels fluid bed coking reactor 20 has maintained in it a fluid bed of particulate coke in a manner well known by the art. The coking temperature in this fuels reactor may vary from about 850 to 1200 F. Lower temperatures in the, range of 850 to 1000 F. are used when. heavier distillates suitable as feed to a catalytic cracking process are desired, andv somewhat higher temperatures in the. range of 1000 to 1200 F. are used when lighter distillates, e. g., naphthas, are desired as the primary product. An inert gas, preferably steam, may besupplicd by line. 16v to the base of the fuels coker to supply fluidization gas thereto or to augment the fluidizetion gas supplied by the chemicals coker. Gas rates are adjusted to maintain fluidization velocities in the range of 0.2 to 5 ft./sec.

The petroleum oil to be upgraded, which may be suitably preheated to reduce the heat load on the system, is injected into the vessel by line 17. Any source of oil may be used as feed to the coker including whole crudes, but, preferably, low value oils such as vacuum residua or cycle stocks are used. Preferably, the oil is injected into the vessel through suitable dispersion nozzles at a plurality of horizontal and vertical points so as to obtain uniform dispersion of the oil on the contact solids. The oil injection rate may vary from 0.1 to 2.0 lbs. of oil/hr./lb. of solids contained in the vessel. Conditions are adjusted so as to obtain from 5 to 25 wt. percent C conversion on a coke-freebasis. C conversion on a cokefree basis is defined as: 100 times wt. percent of product having 3 or less carbon atoms divided by the wt. percent of fresh feed less the wt. percent of coke formed. The cracked vapors, upon emerging from the fluid bed, pass through a cyclone system 19 whereby entrained solids are removed and returned to the bed, and then are taken overhead by line 18. This coker product may be further processed in a conventional manner, e. g., by fractionation, hydrocracking, reforming, desulfurization, etc. to obtain the light gases and heavier liquid products of desired quality. 1

The heavy liquid bottoms from the fuels coker can be recycled to the coker for further treatmentor may be recycled to an auxiliary coking zone where it may be subjected to somewhat more severe conditions of temperature and pressure because of its refractory nature. If a secondary fuels coking zone is used,.the vapors from this zone can be reintroduced into the primary fuels coking zone.

In a preferred embodiment of the invention there is separated from the dry gases from the fuels coker ethane and other light paraffinic hydrocarbons and these are transferred to the high temperature cracking zone to be cracked to unsaturated chemical compounds. Paraflinic gases from catalytic cracking, field ethane and propane, or other light hydrocarbon gases may also be fed to the high temperature cracking zone.

In order to supply heat to the fuels coker, coke is circulated from the low temperature burner via line 7 in the amounts of 2 to 20 lbs./lb. of oil injected into the coker. Coke is removed from the base of the fuels coking reactor by standpipe 22 and circulated to the low temperatureburner to be reheated;- Toremove liquid hydrocarbons that may adhere to this coke removed by the standpipe, the coke. can be stripped with steam or other gases.

There normally will be an excess of coke produced by the cracking reaction and this excess is removed by line 12. This coke will be of superior quality as compared to the coke produced in the conventional fluid coking process. Normally, fluid coke has a relatively high sulfur content, particularly, when a sulfurous oil is charged. In the present invention as the coke is repeatedly contacted with light gases at a high temperature in the transfer line reactor, the coke will be substantially desulfurized and this desulfurization enhances the value of the coke removed as product.

The following Table I presents a specific example of the pertinent operating conditions applicable to this process and presents a specific example of the products obtainable, from the feed stock indicated, when the process is operated in accordance with the conditions presented in the table. The effluent from the chemicals reactor is discharged into the fuels coker. The ethylene and propylene products and the gases introduced into the chemicals reactor are obtained by the separation of the fuels coker efiluent by well known processes such as distillatron, low temperature absorption, sulfuric acid absorption of olefins, etc. i

6 TABLE I Operating conditions:

Contact solid Petroleum coke.

Particle size 40 to 1000 microns. Median particle size 250 microns.

Total coke inventory.. 400 tons.

Low temperature burner Pressure at top of bed Temperature Coke hold-up (45 lbs./

c. f. bed density) tons. Air injection rate 45,000 s. c. fJmin.

High temperature burner Pressure at top of bed 15 p. s. i. g.

1 0 p. s. i. g. 1125 F.

Temperature 1675" F. Coke hold-up (45 lbs./

0. f. bed density).. 20 tons. Air injection rate 10,000 s. c. f./min.

Fuels, fluid bed, coker Pressure at top of bed 7 p. s. i. g. Temperature 950 F.

0;, conversion per pass Coke hold-up (45 lbs./

0. f. bed density)- 200 tons. Oil injection rate 5,000 lbs/min. Volume of gases supplied from chemicals reactor 7,400 s. c. f./ min.

Chemical, transfer line, reactor 7 wt. percent.

Pressure, outlet 21 p. s. i. g. Temperature, outlet 1500 F. Density of coke-gas suspension 1 lb./c. f. Hydrocarbon gas injec:

tion rate 4,200 s. c. f./min. Average vapor residence time 0.4 second.

Coke circulation rates From high temperature burner to transfer line reactor From low temperature burner to high temperature burner From low temperature burner to fuels coker 27.5 tons/min. From fuels coker to low temperature burner 30.6 tons/min.

Feed stockEast Texas vacuum residuum 4.0 API gravity 24 wt. percent Conradson carbon 850 F.+ boiling point 0.1 wt. percent ash 1.51 H/C atomic ratio The light hydrocarbon gases introduced into the transfer line reactor comprise:

2.0 vol. percent CH 56.5 vol. percent C H 7.5 vol. percent C H 30.1 vol. percent C H 3.9 vol. percent C H Products, percent based on feed 2.5 tons/min.

2.5 tons/min.

games All 1015' F.+ material from fuels coker products is recycled to coker to extinction.

The present invention is susceptible to variations, particularly in the manner of circulating the heat-carrying solids, to effect certain heat economies.- Thus, the eifluent from the high temperature chemicals cracking operation, with or without entrained solids, can be separately quenched by solidswithdrawn from the relatively cooler fuels coker. Or solids withdrawn from the lower temperature fuels coker can be used, in addition to the abovedescribed quenching or separately therefrom, to quench and abstract heat from the burner flue gases. This latter variation is most advantageously used when a high temperature transfer line burner is used to supply heat to the process; Reference to co-pending application, Conversion of Heavy Petroleum Hydrocarbons, Serial No. 457,383 by Martin and Herrmann filed contemporaneously herewith, will make these and other variations readily apparent.

Having described the invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

1. A process wherein hydrocarbons are converted which comprises injecting a normally liquid, heavy petroleum oil into a fuels coking zone containing particulate coke maintained as a relatively dense fluidized bed at a temperature below 1200 F., whereby said heavy petroleum oil undergoes pyrolysis upon contact with said particulate coke evolving substantial quantities of relatively light hydrocarbon vapors having less than 6 carbon atoms and including ethane, distillate vapors and heavy ends, separating thus formed light hydrocarbon vapors having less than 6 carbon atoms and contacting said vapors with another portion of particulate coke maintained at a temperature above 1200" F. in a transfer line reactor zone to obtain ethane conversions in the range of 50-60% per pass, separating as product the efliuent of said transfer line reactor zone from said portions of particulate coke, circulating particulate coke so separated to a combustion zone to be partially combusted and heated therein to a temperature in the range of 900 to 2000 F., at least a portion of the coke being heated to a temperature above the temperature in said transfer line reactor zone, and passing heated coke to said fuels coking zone and to said transfer line reactor zone.

2. The process of claim 1 wherein said hydrocarbon light gas comprises hydrocarbons having up to 4 carbon atoms, when said other portion of particulate coke is maintained at a temperature in the range of 1400' to 1600 F. in said transfer line reactor at a hydrocarbon partial pressure of 5 to 40 p. s. i., and wherein the efiluent including entrained solids from said transfer line reactor is injected into the relatively dense fluidized bed of said fuels coking zone.

3. The process of claim 2 wherein said combustion zone comprises a relatively large holdup fluidized solids combustion zone operating at a temperature in the range of 950 to 1300 F. and a smaller holdup fluidized solids combustion zone operating at a temperature in the range of l300 to 2000 F. wherein particulate coke is circulated from said relatively large holdup combustion zone through said smaller holdup combustion zone and then circulated through said transfer line reactor to said fuels coking zone, wherein particulate coke is circulated from said relatively large holdup combustion zone to said fuels coking zone, and wherein particulate coke is circulated from the relatively dense fluidized bed of said fuels coking zone to said relatively large holdup combustion zone.

4. A combined process for converting heavy, high boiling petroleum oils containing catalyst contaminants which comprises thermally cracking said oil at relatively low temperatures in a coking zone by contacting it in liquid phase with heat-carrying particulate solids maintained as a relatively dense fluidized bed at a temperature in the range of 850 to 1200 F. to form light gases, distillate vapors, heavy ends and coke, separating said light gases and contacting them in a high temperature, transfer line thermal cracking zone with highly heated particulate solids at a temperature in the range of l400 to 1700" F. to produce unsaturated hydrocarbons, and promptly quenching said unsaturated hydrocarbons to prevent their degradation.

5. The process of claim 4 wherein said unsaturated hydrocarbons are quenched by injection into the lower portion of said fuels coking zone.

6. The process of claim 4 wherein solids are withdrawn from said coking zone and injected into the efliuent from said high temperature thermal cracking zone to quench said efliuent and arrest further hydrocarbon conversion thereof.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS WHEREIN DYDROCARBONS ARE CONVERTED WHICH COMPRISES INJECTING A NORMALLY LIQUID, HEAVY PETROLEUM OIL INTO A FUELS COKING ZONE CONTAINING PARTICULATE COKE MAINTAINED AS A RELATIVELY DENSE FLUIDIZED BED AT A TEMPERATURE BELOW 1200''F. WHEREBY SAID HEAVY PETEOLEUM OIL UNDERGOES PYROLYSIS UPON CONTACT WITH SAID PARTICULATE COKE EVOLVING SUBSTANTIAL QUANTITIES OF RELATIVELY LIGHT HYDROCARBON VAPORS HAVING LESS THAN 6 CARBON ATOMS AND INCLUDING ETHANE, DISTILLATE VAPORS AND HEAVY ENDS, SEPARATING THUS FORMED LIGHT HYDROCARBON VAPORS HAVING LESS THAN 6 CARBON ATOMS AND CONTACTING SAID VAPORS WITH ANOTHER PORTION OF PARTICULATE COKE MAINTAINED AT A TEMPERATURE ABOVE 1200''F. IN A TRANSFER INE REACTOR ZONE TO OBTAIN ETHANE CONVERSIONS IN THE RANGE OF 50-60% PER PASS, SEPARATING AS PRODUCT THE EFFLUENT OF SAID TRANSFER LINE REACTOR ZONE FROM SAID PORTIONS OF PARTICULATE COKE, CIRCULATING PARTICULATE COKE SO SEPARATED TO A COMBUSTION ZONE TO BE PARTIALLY COMBUSTED AND HEATED THEREIN TO A TEMPERATURE IN THE RANGE OF900'' TO 2000'' F., AT LEAST A PORTION OF THE COKE BEING HEATED TO A TEMPERATURE ABOVE THE TEMPERATURE IN SAID TRANSFER LINE REACTOR ZONE, AND PASSING HEATED COKE TO SAID FUELS COKING ZONE AND TO SAID TRANSFER LINE REACTOR ZONE.

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