US 3909392 A
An improved fluid catalytic cracking process providing improved product yield and selectivity employs a regenerated hydrocarbon conversion catalyst having improved activity and a low level of residual coke, desirably less than 0.05 wt. % on catalyst, obtained by burning coke from spent catalyst under balanced conditions supporting substantially complete combustion of carbon monoxide with provision for recovery of evolved heat by transfer directly to the catalyst particles particularly within a dilute-phase zone in the regenerator vessel. Effluent gas from the regenerator may be discharged directly to the atmosphere with no discernible effect upon ambient air quality.
Claims available in
Description (OCR text may contain errors)
United States Patent Horecky, Jr. et al.
[ 51 Sept. 30, 1975 FLUID CATALYTIC CRACKING PROCESS WITH SUBSTANTIALLY COMPLETE COMBUSTION OF CARBON MONOXIDE DURING REGENERATION OF CATALYST Assignee: Standard Oil Company, Chicago, 111.
Filed: May 22, 1974 Appl. No; 472,111
Related U.S. Application Data Continuation of Ser. No. 262,049, June 12, 1972, abandoned, which is a continuation-in-part of Serl No, 203,396, Nov. 30, 1971, abandoned.
2,884,303 4/1959 Metl'ailer 252/417 2,981,676 4/1961 Adams et al... 208/120 2,985,584 5/1961 Rabo et a1. 208/120 3,004,926 10/1961 Goering 1. 252/417 3,039,953 6/1962 Eng 08/1 0 3,351,548 ll/l967 Payne et a1. 08/120 3,513,087 5/1970 Smith 208/159 3,563,911 2/1971 Pfeiffer (it all 252/417 3,661,800 5/1972 Pfeiffer et a1. 252/417 3.838,036 9/1974 Stine et a1 208/164 3,844,973 10/1974 Stine et a1 208/164 Primary Examiner-Delbert E. Gantz Assistant E.\aminer.lames W. Hellwege Attorney, Agent, or FirmMorton, Bernard, Brown, Roberts and Sutherland  ABSTRACT An improved fluid catalytic cracking process providing improved product yield and selectivity employs a regenerated hydrocarbon conversion catalyst having  U.S. Cl. 208/120; 252/417; 208/164 improved activity and a low level of residual coke, de-  Int. Cl. C10G 11/18, B01] 29/38 bl 1 mi 005 t 7 c til t ht" d b  Field of Search 252/417, 419; 208/120, 655 a 3 208/164 burning coke from spent catalyst under balanced con ditions supporting substantially complete combustion of carbon monoxide with provision for recovery of  References Cited evolved heat by transfer directly to the catalyst parti- UNITED STATES PATENTS cles particularly within a dilute-phase zone in the re- 2,382,382 8/1945 Carlsmith et a1. 252/417 generator vessel, Effluent gas from the rcgcncrator 2398739 4/1946 Greensfclder--- 252/417 may be discharged directly to the atmosphere with no 2,398,759 Al'lgfill discernible effect p ambient air 2,414,002 1/1947 Thomas et a1. 252/4l7 2,425,849 8/1947 Voorhees 252/242 29 Claims, 3 Drawing Figures Upper Sac/Ion 23 37 Laws! 1 Section l3 12 a i 4i 5 I ,l/ a
.L/ T l US. Patent Sept. 30,1975 Sheet 1 of 3 3,909,392
US. Patent Sept. 30,1975 Sheet 2 of 3 3,909,392
Upper Section IL;
CARBON ON REGENERATED CATALYST FLUID CATALYTIC CRACKING PROCESS WITH SUBSTANTIALLY COMPLETE COMBUSTION OF CARBON MONOXIDE DURING REGENERATION OF CATALYST This application is a continuation of application Ser. No. 262,049, filed June 12, 1972, now abandoned which in turn is a continuation-in-part of application Ser. No. 203,396, filed Nov. 30, 1971, now abandoned.
BACKGROUND OF THE INVENTION Catalytic cracking of heavy petroleum fractions is one of the major refining operations employed in the conversion of crude petroleum oils to desirable fuel products such as high-octane gasoline fuels used in spark-ignited internal combustion engines. Illustrative of fluid catalytic conversion processes is the fluid catalytic cracking process wherein suitably preheated high molecular weight hydrocarbon liquids and vapors are contacted with hot, finely-divided, solid catalyst particles, either in a fluidized bed reactor or in an elongated riser reactor, and maintained at an elevated temperature in a fluidized or dispersed state for a period of time sufficient to effect the desired degree of cracking to lower molecular weight hydrocarbons typically present in motor gasolines and distillate fuels. Suitable hydrocarbon feeds boil generally within the range from about 400 to about 1200F. and are usually cracked at temperatures ranging from 850 to 1050F.
In a catalytic process some non-volatile carbonaceous material, or coke, is deposited on the catalyst particles. Coke comprises highly condensed aromatic hydrocarbons which generally contain 4-10 wt. hydrogen. As coke builds up on the catalyst, the activity of the catalyst for cracking and the selectivity of the catalyst for producing gasoline blending stock diminish. The catalyst particles may recover a major proportion of their original capabilities by removal of most of the coke therefrom by a suitable regeneration process.
Catalyst regeneration is accomplished by burning the coke deposits from the catalyst surface with an oxygencontaining gas, such as air. Many regeneration tech niques are practiced commercially whereby a significant restoration of catalyst activity is achieved in response to the degree of coke removal. As cokeis progressively removed from the catalyst, removal of the remaining coke becomes most difficult and, in practice, an intermediate level of restored catalyst activity is accepted as an economic compromise.
The burning of coke deposits from the catalyst requires a large volume of oxygen or air. Oxidation of coke may be characterized in a simplified manner as the oxidation of carbon and represented by the following chemical equations:
C. O26 Reactions (a) and (b) both occur typical catalyst regeneration conditions wherein the catalyst temperature may range from about 1050 to about 1300F. and are exemplary of gas-solid chemical interactions when regenerating catalyst at temperatures within this range. The effect of any increase in temperature is reflected in an increased rate of combustion of carbon and a more complete removal of carbon, or coke, from the catalyst particles. As the increased rate of combustion is accompanied by an increased evolution of heat, whenever sufficient oxygen is present, the gas-phase reaction (c) may occur. This latter reaction is initiated and propagated by free radicals.
A major problem often encountered and sought to be avoided in the practice particularly of fluid catalyst regeneration is the phenomenon known as afterburning, described, for example, in Hengstebeck, Petroleum Processing, McGraw-Hill Book Co., 1959, at pages and and discussed in Oil and Gas Journal, volume 53 (no. 3), 1955, at pages 93-94. This term is descriptive of the further combustion of CO to CO as represented by reaction (0) above, which is highly exothermic. After burning has been vigorously avoided in catalyst regeneration processes because it could lead to very high temperatures both damaging to equipment and believed to cause permanent deactivation of catalyst particles. All fluid catalyst regenerator operators have experienced afterburning and, with their ingenuity, a very substantial body of art has developed around numerous means for controlling regeneration techniques so as to avoid afterburning. More recently, as operators have sought to raise regenerator temperatures for various reasons, elaborate arrangements have also been developed for control of regenerator temperatures at the point of incipient afterburnin g by suitable means for control of the oxygen supply to the regenerator vessel as set forth, for example, in U.S. Pat. Nos. 3,161,583 and 3,206,393 as well as in U.S. Pat. No. 3,513,087. In typical contemporary practice, accordingly, with avoidance of afterburning, the flue gas from catalyst regenerators usually contains very little oxygen and a substantial quantity of CO and CO2 in nearly equimolar amounts.
Further combustion of CO to CO is an attractive source of heat energy because reaction (c) is highly exothermic. Afterburning can proceed at temperatures above about 1 100F. and liberates approximately 4350 BTU/ lb. CO oxidized. This typically represents about one-fourth of the total heat evolution realizable by complete combustion of coke. The combustion of CO can be performed controllably in a separate zone, or CO boiler, after separation of effluent gas from catalyst, as described in, for example, U.S. Pat. No. 2,753,925, with the released heat energy being employed in various refinery operations such as the generation of high pressure steam. Other uses of such heat energy have been described in U.S. Pat. Nos. 3,012,962 and 3,137,133 (turbine drive) and U.S. Pat. No. 3,363,993 (preheating of petroleum feedstock). Such heat recovery processes require separate and elaborate equipment but do serve to minimize the discharge of CO into the atmosphere as a component of effluent gases. This serves to avoid a potentially serious pollution hazard.
Silica-alumina catalysts, employed conventionally for many years in various processes for the cracking of petroleum hydrocarbons, are not particularly sensitive to the level of residual coke on catalyst provided that the coke level be no greater than about 0.5 wt. However, silica-alumina catalysts have largely been supplanted by catalysts additionally incorporating a crystalline aluminosilicate component and known as zeclites or molecular sieves. The molecular sievecontaining catalysts are much more sensitive to the residual coke level, being greatly affected both with regard to catalyst activity and to catalyst selectivity for conversion of feed to the desired product or products. Due to the difficulties encountered in conventional catalyst regeneration techniques as set forth above for removal of the last increments of residual carbon, the practical coke level usually corresponds to a residual coke content on regenerated catalyst within the range from about 0.2 to about 0.3 wt.
Enhanced activity and selectivity are achievable with sieve-type cracking catalysts at low coke levels, providing an attractive incentive for discovering a means for reducing residual coke levels still further. Coke levels below 0.05 wt. are greatly to be desired but usually cannot be achieved by commercially practicable means. The need for such things as larger regeneration vessels and greater catalyst -inventory together with greater heat losses and the like all serve to discourage attainment of ideal equilibrium catalyst activity levels.
SUMMARY OF THE INVENTION This invention relates to an improved fluid catalytic cracking process, including an improved process for the regeneration of catalysts employed in fluid catalytic conversion of petroleum feedstocks wherein the catalyst is deactivated by the deposition of coke on the catalytic surfaces. A practical method for the regeneration of conversion catalysts, particularly fluid cracking catalysts, has now been discovered and is sustainable over a long period of operation, enabling the coke level on regenerated catalyst to be maintained at an extremely low level while simultaneously maintaining a favorable heat balance in the conversion unit and providing a flue gas stream having an extremely low carbon monoxide content.
In a preferred embodiment of the invention, the combustion of carbon monoxide to carbon dioxide is carried substantially to completion within the regeneration vessel in a subsequent and usually relatively dilute secondary catalyst regeneration zone advantageously at a temperature between about 1200 and l500F., desirably between about I250 and I450F. Partially regenerated catalyst from a relatively dense primary catalyst regeneration zone can be controllably flowed through the secondary zone in an amount and at a rate sufficient to absorb substantially all of the heat released by the combustion occurring in the secondary zone. Although most of the coke is burned from the catalyst in the primary zone, additional coke is burned from the partially regenerated catalyst while present in the secondary zone and catalyst substantially free of coke may be recovered for recycle to the hydrocarbon conversion zone. Heat from the combustion of carbon monoxide absorbed by the regenerated catalyst provides part of the process heat required in the conversion zone. Additionally, the flue-gas stream released from the secondary regeneration zone is substantially free of carbon monoxide.
In another embodiment of the invention substantially all of the combustion, including both the oxidation of coke or carbon and the oxidation of carbon monoxide, occurs within a single relatively densephase regeneration zone in response to the proper control of principally the regeneration temperature and gas velocity.
An outstanding advantage of this invention lies in providing a regenerated catalyst generally possessing enhanced activity and selectivity characteristics more closely approaching those of fresh conversion catalyst particularly for use in conversions effected at very short contact times in riser reactors. Accordingly, higher conversions of feedstock and higher yields of desirable conversion products may be achieved. The controllably balanced conservation of heat additionally provides an effective heat reservoir without requiring a large proportion of catalyst relative to oil in the fluidized conversion zone or the retention of a large quantity of catalyst in the regeneration vessel.
The carbon monoxide content of the flud gas from this novel regeneration process can be maintained at less than about 0.2 vol. for example, about 500l000 ppm. Advantageously, the content is even lower, for example, wihthin the range from 0 to 500 ppm. This low concentration of carbon monoxide in the flue-gas stream permits the direct release of effluent gases to the atmosphere while meeting ambient air quality standards. This advantage of the invention additionally permits the elimination of capital expenditures otherwise required for installation ofCO boilers and associated turbine-type devices or other means for partial recovery of energy.
The novel regeneration process of this invention is advantageous practiced as a key step in the fluid catalytic cracking process where at least a substantial portion of the conversion is effected in a dilute-phase transfer line or riser reactor system requiring very active catalysts employed at relatively high space velocities. Catalyst regenerated by the process of this invention desirably contains less than 0.5 wt. coke and advantageously no more than about 0.01 wt. coke. This extremely low coke level is especially preferred when employing fluid cracking catalysts containing crystalline aluminosilicates, otherwise known as zeolites or molecular sieves. The cracking activity of sievecontaining catalysts and their selectivity for converting feed to desired products are both dramatically affected in a favorable direction by the increased elimination of residual carbon or coke during regeneration.
DESCRIPTION OF THE DRAWINGS The attached drawings,
FIGS. 1 and 2, provide elevational views, partly in section, of embodiments of apparatus suitable for catalyst regeneration according to the process of this invention.
The chart presented in FIG. 3 illustrates the beneficial effects relative to conversion and yield achieved by diminishing the carbon, or coke, content of regener ated fluid cracking catalyst to the unusually low levels mentioned previously.
DETAILED DESCRIPTION OF THE INVENTION The process of this invention provides a regenerated conversion catalyst having a very low coke content, desirably less than 0.05 wt. and preferably within the range from 0.01 to 0.03 wt. by control of the substantially complete combustion of coke therefrom, together with substantially complete combustion of carbon monoxide gas in the presence of catalyst particles, with enhanced recovery of the evolved heat of combustion by heating catalyst particles and mass transfer of the heated catalyst particles to the conversion process. The process employs an unusually high and sustained regeneration temperature which requires carefully balanced controls to maintain the temperature sufficiently high to afford substantially complete combustion of carbon monoxide while not permitting the temperature to range so high that catalyst particles become thermally deactivated or that the regeneration vessel and internals become unsafe or inoperative. The temperature may advantageously range from about l200 to about 1500F., desirably from about l250 to about 1450F., although in some instances temperatures as low as about 1 l50F. within lower regions of the regeneration vessel have been satisfactory.
This invention is particularly useful in the fluid catalytic conversion of petroleum feedstocks and is advantageously employed where at least a substantial portion of the conversion is effected in a dilute-phase transfer line or riser reactor system. This invention makes possible an enhanced degree of energy conservation within a cyclic process for the catalytic conversion of petroleum feedstocks which includes provision for separation of catalyst from conversion products, regeneration of the separated catalyst and recycle of the regenerated catalyst to the reactor for the conversion of additional feedstock, wherein an increased proportion of heat energy is utilized within the cyclic system by improved continuous transfer from the exothermic to the endothermic processing zones. A particularly suitable petroleum conversion process for the practice of this invention comprises the fluid catalytic cracking process for the conversion of petroleum gas oils and heavier petroleum stocks to hydrocarbon components suitable for blending into fuels for automotive engines, jet power plants, domestic and industrial furnaces, and the like.
The process of this invention contemplates the contacting of a stripped, deactivated petroleum conversion catalyst, such as a fluidizable hydrocarbon-cracking catalyst deactivated by the deposition thereon of carbonaceous deposits or coke and stripped with steam, with an oxygen-containing regeneration gas in a regeneration vessel which may suitably be adapted to the countercurrent flow of catalyst and regeneration gas. Substantially complete regeneration of catalyst particles, accomplished by the combination of carbonaceous deposits or coke, may occur in one relatively dense catalyst bed together with combustion of substantially all carbon monoxide present to carbon dioxide. More frequently, substantial regeneration of catalyst particles occurs in one or more relatively dense fluidized catalyst zones contained within a first or primary regeneration zone situated in the bottom section of the regeneration vessel. Combustion is effected by providing to the dense zone or zones at combustion temperature a quantity of regeneration gas, passing upwardly, sufficient to afford at least an amount of oxygen equal to that required stoichiometrically for the complete oxidation of carbon monoxide formed in the course of oxidation of the coke. Partially spent regeneration gas leaving the lower section, comprising carbon monoxide, carbon dioxide and oxygen, contained suspended or entrained particles of at least partially regenerated catalyst. The partially spent regeneration gas passes from the dense-bed zone to a relatively dilute-phase, fluidized and dispersed second regeneration zone, wherein the combustion of carbon monoxide is substantially completed at a temperature suitably maintained above about 1250F., and desirably above about 1300F., by suitably controlling means so that the temperature within the second regeneration zone does not exceed about 1500F. and advantageously does not greatly exceed about 1450F. The regeneration temperature within the dense bed is maintained at a temperature within the range from 1 150 to l400F., desirably about 1250F., to initiate and sustain the further oxidation of carbon monoxide to carbon dioxide.
Somewhat lower temperatures may be employed where an added CO combustion catalyst is present.
Catalyst particles from the dilute phase, now essentially completely freed of coke deposits, are largely separated from the hot regeneration gas stream by passage into a series of cyclones with the catalyst particles being returned to the dense-phase zone by means of cyclone dip-legs. Alternatively, the regenerated catalyst particles from the dilute phase may pass directly from the cyclone dip-legs to a suitable standpipe or hopper means for return directly to the conversison reactor. The flue gas stream, usually containing some oxygen but substantially free of carbon monoxide, is discharged to the atmosphere or passed through suitable heat-exchange means for recovery of the sensible heat of the gases.
Although temperature control within the secondary dilute-phase regeneration zone may be effected in part by addition of steam or by a water spray, directed preferably into the region of the cyclones and other internal portions of the regeneration vessel structure, the dilute catalyst phase is desirably loaded with as much catalyst as required for the heat of combustion of CO to be absorbed by the catalyst particles prior to their entry into the cyclones and return to the dense-bed catalyst phase.
Suitably controlled and balanced loading of the dilute phase may, for example, be effected by employing a suitable gas velocity through the dense-bed zone or catalyst advantageously may be circulated by a suitable cycling means from the dense phase into the dilute phase zone. The cycling of catalyst may, for example, suitably be effected by means of an independently controlled eductor or catalyst-lift system to achieve an enhanced transfer of heat to the catalyst particles.
Regenerated catalyst particles, having an unusually low residual coke content, are finally recovered from the dense-phase zone and passed at substantially densebed temperature through a standpipe to the conversion reactor for contacting with fresh hydrocarbon feed or a mixture thereof with recycled hydrocarbonfractions. When this novel technique is incorporated in the fluid catalyst cracking process, regenerated catalyst can be returned to the cracking reactor at-a much higher temperature as well as higher activity than in heretofore conventional operations.
Many fluid catalytic cracking units are operated on the heat balance principle, depending upon combustion of coke for the evolution of heat required in the process. Such units have not been able to fully utilize the potential benefits of the highly active zeolite or molecular sieve catalysts which can especially be achieved in riser reactors where contact times between catalyst and oil vapors may be extremely short. The type of op eration which affords high conversion coupled with high selectivity favors a low ratio of catalyst to oil in the riser which leads to less coke being available for generation of combustion heat in the regenerator. Accordingly an external heat soruce such as a feed pre-heat furnace, must be added or, alternatively, the unit must be operated at a lower throughput of fresh feed. Such undesirable features are avoided by the process of this invention which permits efficient recovery of additional heat for transfer by regenerated catalyst particles to the riser reactor. The heat of combustion of coke in conventional operations is about 12,000 BTU/lb. The process of this invention increases the available heat to about 17,000 BTU/lb. This higher heat of combustion raises the regenerator temperature, lowers the level of coke on regenerated catalyst and lowers the catalyst circulation rate while providing improved yields at a given conversion level.
The attached drawings, FIGS. 1 and 2, are illustrative, without limitation, of embodiments of this invention. Regeneration of spent catalyst from any suitable petroleum conversion process can be effected in an improved manner by the novel process of this invention. Indeed, this improved process may be employed benefially in many existing petroleum conversion process units, particularly fluid catalytic cracking units without limitation as to the spatial arrangement of cracking, stripping end regeneration sections thereof.
FIG. 1 is illustrative of one embodiment of this invention employing bottom entry of stripped, spent catalyst to the regenerator. Spent catalyst particles from a stripping zone enter from the bottom of regeneration vessel 1, flowing upwardly through inlet lines 2 and 3 and discharging into the dense catalyst bed through discharge heads 4 and 5. The dense-phase catalyst bed is maintained within the bottom section 6 of the regenerator vessel and extends upwardly to the catalyst phase interface 7. Catalyst within the dense-phase bed is fluidized by the flow of combustion air through line 8, valve 9 and line 10 to air ring 11. Substantially balanced air flow patterns through the regeneration zones may be achieved by the use of additional air rings, not shown, as required. Combustion of coke contained on the spent catalyst with air is initiated within the densephase bed. Higher temperatures may be achieved by temporarily burning a stream of torch oil, for example a decanted oil, witin the bed. Torch oil may be added by passage through line 12, valve 13 and 14 which terminates in a nozzle located above the air ring 11. Fluidizing air velocities continuously carry some of the catalyst particles upwardly into the dilute-phase zone which occupies the upper section 15 of the regenerator vessel; i.e., the section above the catalyst phase interface 7. Combustion of coke continues in the dilute-phase zone and the largely spent combustion gas together with entrained catalyst finally is withdrawn into cyclone separators and 21. Most of the catalyst particles are separated in the first-stage cyclones and discharged downwardly through dip-legs 22 and 23 into the dense-phase zone. Gases and remaining catalyst particles are passed through interstage cyclone lines 24 and 25 to secondstage cyclone separators 26 and 27 where substantially all of the remaining catalyst is separated and passed downwardly through dip-legs 28 and 29 into the densephase bed. Substantially spent combustion gas then passes through lines 30 and 31 into plenum 32 and finally is discharged from the regenerator vessel through line 33. This may be followed by suitable heat exchange, not shown, with refinery stream or for production of process steam. Regenerated catalyst from the dense bed is withdrawn through stand pipes 34 and 35, fitted with collector heads 36 and 37, for return to the catalytic conversion process.
Although the supply of combustion air normally provides an excess of oxygen over the amount required to effect complete combustion of the coke on the catalyst particles to steam and carbon dioxide, combustion of coke is not completed in the dense-bed phase. Additionally, the combustion gases rising from the densebed zone contain a substantial quantity of carbon monoxide as well as carbon dioxide and oxygen. The remaining coke on catalyst and carbon monoxide are substantially completely burned in the dilute-phase zone with evolution of much heat. When carbon monoxide burns in the dilute phase a high temperature zone will usually be present throughout much of the dilutephase zone and particularly at approximately the location indicated by X and can readily be viewed through a window, not shown, at that horizontal plane. Control of regeneration temperature within the dilute-phase zone is effected in part through absorption of heat by the mass of cataylst particles either carried upwardly by the rising combustion gas stream or educted upwardly from the dense bed through educator tube 40 and cataylst distributor head 41 where a rain, or fountain, of catalyst particles disperses into the dilute-phase zone. Catalyst is educated by means of air, steam or other inert gas entering through line 42, valve 43 and jet tube 44 which extends a short distance into the lower end of eductor tube 40. Excessive temperature levels in the top section of the regenerator may be further controlled by distrubution of steam, for example through lines 45 and 46, valve 47 and line 48 to steam pod 49. Temperatures in the vicinity of the plenum may also be controlled with steam fed through line 50, valve 51 and line 52 to steam ring 53 which surrounds plenum 32. Additional cooling if desired may be provided by use of a water spray, not shown, which may advantageously be directed within the region of interstage cyclene lines 24 and 25.
FIG. 2 is illustrative of an embodiment of this invention employing side entry of stripped, spent catalyst to the regenerator and providing a net countercurrent flow of catalyst and regeneration gas. Spent catalyst enters regeneration vessel 101 flowing downwardly through inlet line 102 located on the side of the regeneration vessel to provide entry into the dense-phase catalyst bed maintained within bottom section 106 a short distance below catalyst phase interface 107. Fluidization of catalyst particles within the dense-phase bed is effected by the flow of combustion air through line 108, valve 109 and line 110 to air ring 111. Additional air rings, not shown, may be employed as desired for further balancing of air flow patterns through regeneration zones. As described in FIG. 1, combustion of coke of the spent catalyst particles is initiated within the dense-phase zone where higher temperatures as desired may be achieved by temporary burning of a torch oil stream within the zone. Such torch oil may be added through line 112, valve 113 and line 114 terminating in a nozzle. Fluidizing air velocity may be controlled to continuously carry catalystparticles upwardly for purposes of heat absorption into the dilute-phase zone which occupies the upper section 115 of the regenerator vessel; i.e., the section above the catalyst phase interface 107. Combustion of coke as well as of carbon monoxide continues in the dilute-phase zone and the largely spent combustion gas together with the en trained portion of catalyst particles finally is withdrawn into cyclone separators and 121. Most of these catalyst particles are separated in the first-stage cyclones and discharged downwardly through dip-legs 122 and 123 into the dense-phase zone. Genes and remaining catalyst subsequently pass through interstage cyclone lines 124 and 125 to second-stage cyclone separators 126 and 127 where substantially all of the remaining catalyst is separated and passed downwardly through dip-legs 128 and 129 into the dense-phase bed. Substantially spent combustion g as then passes through lines 130 and 131 into plenum 132 and finally is discharged from the regenerator vessel through line 133. Regenerated catalyst from the dense bed is withdrawn through standpipes 134 and 135, fitted with collector heads 136 and 137, for return to the catalytic conversion process. I
As described for FIG. 1, carbon monoxide burns in the dilute phase providing a high temperature zone throughout much of the dilutephase zone and particularly at approximetely the location indicated. by X. Control of regeneration temperature within the dilutephase zone is effected largely through absorption of heat by the mass of catalyst particles carried upwardly by the rising combustion gas stream. Temperatures in the vicinity of the plenum, cyclone and connecting lines may, as required, be reduced with steam fed through line 150, valve 151 and line 152 to steam ring 153 which surrounds plenum 132. Water spray means, not shown, may similarly be employed.
Suitable petroleum fractions include light gas oils, heavy gas oils, wide-cut gas oils, vacuum gas oils, kerosenes, decanted oils, residual fractions, reduced crude oils and cycle oils derived from any of these, as well as suitable fractions derived from shale oil, tar sands processing, synthetic oils, coal hydrogenation and the like. Such fractions may be employed singly or in any desired combination.
Suitable catalysts include those containing silica and- /or alumina. Other refractory metal oxides such as magnesia or zirconia may be employed limited only by their ability to be effectively regenerated under the selected conditions. With particular regard to catalytic cracking, preferred catalysts include combinations of silica and alumina, containing 10-50 wt. alumina and particularly their admixtures with molecular sieves or crystalline aluminosilicates. Admixtures of clayextended aluminas may also be employed. Such catalysts may be prepared by any suitable method such as impregnation, milling, cogelling, and the like, subject only to provision of the finished catalyst in a physical form capable of fluidization.
Suitable molecular sieves include both naturallyoccurring and synthetic aluminosilicate materials, such as faujasite, chabazite, X-type and Y-type aluminosilicate materials, and ultrastable, large-pore crystalline aluminosilicate materials. The metal ions contained therein are exchanged in large part for ammonium or hydrogen ions by known techniques. When admixed with, for examble, silica-alumina to provide a petroleum crackling catalyst, the molecular sieve content of the fresh finished catalyst particles is suitably within the range from 5 to wt. desirably 8-10 wt. An equilibrium molecular-sieve cracking catalyst may contain as little as about 1 wt. crystalline material.
The stripping vessel is suitable maintained essentially at conversion reactor temperature in the range from 850 to 1050F. and desirably will be maintained at about 950F. Preferred stripping gas is steam although nitrogen, other inert gas or flue gas may be employed, introduced at a pressure, usually in the range from 10 to 35 p.s.i.g., suitable to effect substantially complete removal of volatile components from the spent conversion catalyst. Stripped spent catalyst particles enter the dense-bed section of the regenerator'vessel through suitable lines and valving fromthe stripping vessel.
Entry may be from the bottom or from the side, desirably near the top of the dense-bed fluidized zone. The dense-phase fluid-bed regeneration stage (or stages) is usually maintained at a pressure in the range from 5 to 50 p.s.i.g. and a temperature in the range from 1150 to 1400F., desirably about l250F. The regeneration gas may be air, oxygen, oxygen-enriched air or other oxygen-containing gas mixture suitable for combustion of coke deposited on silica, alumina and/or aluminosilicate surfaces. The regeneration gas enters the bottom dense-bed stage from a blower or compressor. A fluidizing velocity suitably in the range from 0.2 to 4 feet/- second, desirably about 0.5 to about 3 feet/second, is maintained in the dense-bed regeneration stage (or stages).
The regeneration gas fluidizing the dense-bed is suitably charged to the regenerator in an amount somewhat in excess of that required for complete combustion of coke (carbon and hydrogen) to carbon dioxide and steam. The excess of oxygen may vary from about 0.1 to about 25% of the theoretical oxygen requirement but advantageously need not be greater than about 10%. For example, when air is employed as the regeneration gas in a 10% excess of air provides only about 2 vol. oxygen in the effluent spent gas stream.
Even though a substantial excess of oxygen be present in the dense-phase bed, combustion of both coke and carbon monoxide is conventionally incomplete with the oxidized carbon being converted usually to a nearly equimolar mixture of carbon monoxide and carbon dioxide. The material rising from the dense-phase fluid bed should be hot enough to initiate the complete combustion of carbon monoxide. Usually this requires a temperature level of at least about 1200F., desirably about 1275F. This temperature level may be initially attained by the burning of torch oil within the dense bed, with appropriate increase in the amount of oxygen introduced into the regenerator, and thereafter carbon monoxide combustion can be sustained with torch oil burning. Flame or spark ignition provides another suitable means for initiating the combustion. Although the regeneration gas rising into the dilute-phase zone usually contains from 2 to 10 vol. oxygen when employing air, sustained CO combustion may be aided by the injection of additional air or oxygen at a point just above the interface of the dense and dilute catalyst zones. The requisite temperature may be lowered by inclusion of a combustion catalyst or promoter within the regeneration zone. For example, a suitable metallic bar or mesh network or screen may be inserted in the combustion zone. Alternatively, fluidizable metal compounds, particularly powdered oxides of transition group metals, e.g., ferric oxide (Fe O manganese dioxide (MnO rare earth oxides and the like may be added to the catalyst charge or confined on catalyst trays situated in the regenerator vessel. For example, iron oxide powder fluidizable with the conversion catalyst may be added to the catalyst in an amountup to at least about 0.5 wt. desirably about 0.2 wt. %,'with no observable harmful effects on the catalyst or the conversion process. Use of such reagents may lower the temperature required to initiate and sustain combustion by as much as about F.
Although further combustion of carbon monoxide occurs quite rapidly at the maintained dense-bed temperature, much of this combustion actually occurs in the upper dilute-phase zone as the gas stream rapidly sweeps upwardly. Less catalyst is present in the dilute phase and with less heat-absorbing medium the temperature rises rapidly. Combustion of carbon monoxide in the dilute-phase zone can be observed visually through an observation port and appears as an intensely orange flame or fireball. The temperature within this zone is maintained higher than in the dense-bed zone and advantageously maintained within the range from about l200 to about 1500F., desirably from about l250 to about 1450F., and preferably from about 1300 to about 1400F. Such combustion temperatures have historically been avoided in the petroleum conversion art because of concern for mechanical efficiency and stability and catalyst quality. Effective temperature control in the dilute-phase zone may be achieved by maximizing the heat transfer to catalyst particles within the dilute-phase section of the regenerator. This requires significantly increasing the incidence of catalyst particles in the dilute phase. This may be accomplished by any suitable means including, for example, increasing the gas velocity so that more catalyst is swept into the dilute phase or by otherwise loading the dilute phase with hot catalyst from the dense-phase zone. Such loading may advantageously be accomplished by external circulation of catalyst from the dense bed to the dilutephase zone or by eduction within the regenerator vessel through a catalyst fountain to increase the catalyst density appropriately. Such eduction may be effected with a controlled jet of steam, air, inert gas or a suitable combination thereof. This catalyst heat sink so provided surprisingly absorbs in excess of 80% of the heat of CO combustion in the dilute-phase zone so that most of the heat energy is conserved within the cyclic system for efficient use in the endothermic hydrocarbon conversion, or cracking, zone. Accordingly external cooling, as by water or steam, need only be applied in un' usual instances to critical equipment at a few points within the top section of the regenerator vessel. For example, steam cooling may be applied to the plenum area and a water or steam spray system is made available for application to the cyclones, interstage lines and cyclone hangers.
Catalyst within the dilute phase is partly carried into a separation zone, usually comprising cyclone separators arranged in a plurality of stages, from which catalyst is returned directly through dip-legs to the densebed zone and spent regeneration and combustion gases are collected in a plenum and finally discharged for suitable recovery of the heat energy contained therein. Recovery processes for heat from flue gas include steam generation, spent catalyst stripping, indirect heat exchange with various refinery streams and particularly with feed to the particular conversion process, and employment in various drying or evaporation arrangements.
Recovery of heat by absorption in catalyst particles and return of the catalyst to the dense phase serves also to assure maintenance of a suitably high temperature within the dense-phase zone. The dense-phase temperature under relatively typical equilibrium conditions may closely approach about 1300F. so that combustion of the final increments of difficulty removable coke becomes substantially complete. Accordingly, regenerated catalyst from the dense-phase zone, suitably containing from about 0.1 to about 010 wt. desirably 0.01 to 0.05 wt. and preferably about 0.01 to about 0.03 wt. carbon, or coke, can be withdrawn from the regenerator at a temperature within the range from about l200 to about 1450F., desirably from about 1250 to about 1300F., and returned to the conversion reactor for mixing therein with fresh petroleum feedstock, optionally together with recycle or other hydrocarbon stock, thereby eliminating the need for additional preheating of the feedstock.
The improved performance of the regenerated catalyst of this invention is dramatically illustrated by the charts presented in FIG. 3. Laboratory studies on a gas oil fraction were conducted with a typical silicaalumina cracking catalyst, containing about 25 wt. alumina, designated as catalyst B, and with a molecular sieve catalyst, containing both silica-alumina and crystalline aluminosilicate components, designated as catalyst A. Catalyst response to the carbon level on the catalyst after regeneration was measured in terms of degree of conversion of feed and effect on gasoline yield (C -430F.) at constant conversion. Over the broad range of residual carbon contents studied, the silicaalumina catalyst (catalyst B) was quite insensitive while the sieve-containing catalyst (catalyst A) was consis tently more sensitive to these parameters and extremely sensitive thereto at low carbon levels on catalyst. The incentive for removing coke from catalyst as completely as possible, and certainly to a level below about 0.05 wt. is clearly apparent.
A further benefit from this novel regeneration pro' cess relates to the unusually low carbon monoxide content in the effluent gas stream from the regenerator. Whereas, flue gas from conventional regeneration of cracking catalysts usually contain about 6 to 10% carbon monoxide, a similar amount of carbon dioxide and very little oxygen, the flue gas from regeneration in accordance with this invention generally contains less than 0.2% and often no more than about 5500 ppm. carbon monoxide. The oxygen content of the flue gas is not critical and may vary from about 0.1 to about 10%, advantageously being within the range from 1 to 3%. From an ecological point of view the extremely low level of carbon monoxide in the flue gas stream is highly desirable and meets existing standards for ambient air quality. Indeed, whenever required the remaining carbon monoxide may suitably be burned in the exhaust from the regenerator flue gas stack. From a process point of view, heat recovery by downstream combustion of carbon monoxide in a CO boiler or after burner arrangement is avoided, with consequent substantial savings in process equipment and operational costs.
Optimum use of this invention is an integral part of a fluid cracking unit employing a fluidizable cracking catalyst, such as a silicaalumina catalyst having a crystalline aluminosilicate or molecular sieve component, in a transport, or riser reactor with attendant provision for stripping of spent, coked catalyst followed by regeneration of the spent catalyst according to the process of this invention. Preferably, cracking occurs exclusively in the riser reactor and a following dance catalyst bed in not employed. In the typical case where riser cracking is employed for conversion of a gas oil, the throughput ratio (TPR), or volume ratio of total feed to fresh feed, may vary from 1.0 to 2.0. The conversion level may vary from 40 to 100% and advantageously is maintained above about 60%, for example, between about 60% and about By conversion is meant the percentage reduction of hydrocarbons boiling above 430F. at atmospheric by formation of lighter materials or coke. The weight ratio of catalyst to oil in the riser reactor may vary within the range from 2 to 10 so that the fluidized dispersion will have a density within the range from 1 to 5 pounds/cubic foot. Desirably the catalyst-oil ratio is maintained at no greater than about 5 and preferably within the range from about 3 to about 5. The fluidizing velocity may range from about 20 to about 60 feet/second. The riser reactor should preferably be substantially vertical, having a ratio of length to average diameter at least about 25. For production of a typical naphtha product the bottom section mixing temperature within the riser reactor is advantageously maintained at about 1000F. for substantially complete vaporization of the oil feed so that the top section exit temperature will be about 950F. Under these conditions, including provision for a rapid separation of spent catalyst from effluent oil vapor, a very short period of contact between catalyst and oil will be established. Contact time within the riser reactor will generally be within the range from about 3 to about seconds and preferably within the range from about 3 to about 7 seconds. Shorter contact times are preferred because most of the hydrocarbon cracking occurs during the initial increment of contact time and undesirable secondary reaction are avoided. This is especially important if higher product yield and selectivity, including lesser coke production, is to be realized.
Short contact time between catalyst particles and oil vapors may be achieved by various means. For example, catalyst may be injected at one or more points along the length of a lower, or bottom, section of the riser. Similarly, oil feed may be injected at multiple points along the length of the lower section of the riser reactor and different injection points may be employed for fresh and recycle feed streams. The lower section of the riser reactor may, for this purpose, include up to about 80% of the total riser length in order to provide extremely short effective contact times conducive to optimum conversion of petroleum feeds. Where a following dense catalyst bed is employed, provision may also be made for injection of catalyst particles and/or oil feed directly into the dense bed zone.
Although the conversion conditions set forth above are directed to the production of gasoline as fuel for spark-ignition internal combustion engines, the processing scheme may be suitably varied to permit maximum production of heavier hydrocarbon products such as jet fuel, Diesel fuel and heating oils.
EXAMPLES The following examples are illustrative of the process of this invention without limitation on the scope thereof.
EXAMPLE I Mid-continent gas oil (234 API) having a boiling range from 650 to 1050F. was cracked in a fluidized transport-type reactor at an average cracking temperature of 960F. The throughput ratio (weight total feed/- weight fresh feed) was 1.34 and the total feed rate was 36,000 bbl/day. The catalyst particles comprised silicaalumina together with 10 wt. crystalline aluminosilicate or molecular sieve material and circulated at a rate of 19.6 tons/minute. The weight ratio of catalyst to oil in the cracking zone was 3.7.
Effluent from the riser reactor was passed to a separation zone and fed into a cyclone separator. Hydrocarbon products were removed and spent catalyst was passed downwardly through the cyclone dip-leg into a stripping zone maintained at 950F. The settled catalsyt was stripped with steam to remove remaining volatile material prior to regeneration.
Stripped spent catalyst, containing 0.9 wt. coke on catalyst, was fed into the bottom section of a regenerator vessel where it was fluidized with air in a densephase catalyst bed maintained at l250l275F. (aver age temperature was 1260F.) by combustion of coke and occasional combustion of torch oil as required. The air rate was set to provide approximately 14.0 lbs. air per lb. coke on spent catalyst. Some catalyst was entrained in the rising air stream and carried into the dilute-phase catalyst zone in the upper portion of the regenerator vessel about the interface with the dense bed. Additional catalyst was swept upward through three eductor tubes, each fitted with a dispensing head, with a jet stream of steam and dispersed to provide a descending fountain of catalyst. Combustion of carbon monoxide within the dilute-phase zone produced a fireball visible through a viewing port in the side wall of the regenerator. The temperature in the area near the fireball was about l450F. Gases and entrained catalsyt were passed from the dilute-phase zone into a series of cyclone separators with catalyst being returned directly to the dense-phase zone. The temperature at the cyclone inlet was held at approximately 1400F. with catalyst and water spray as required, the water spray being directed below the inlet of the cyclone system. The gas stream leaving the cyclone system was passed first to a plenum area located at the top of the top of the regenerator vessel and then was discharged at 1250F. Catalyst was withdrawn from the dense-phase bed as required through a standpipe at 1250F. for return to the transport reactor.
Analysis of the regenerated catalyst indicated the residual coke content to be only 0.03 wt. The catalyst particles were white to light gray in color. Analysis of the effluent gas indicated the carbon monoxide content to be 0.0 vol. and the oxygen content to be 1.9 vol. The cracking conversion was 67.7 vol. on feed. From heat balance calculations coke was burned at the rate of 20,700 lbs./hr., liberating 17,800 BTU/lb. coke. Of the total heat evolved, over was absorbed in the regenerated catalyst and thus kept within the cyclic fluid cracking system.
EXAMPLE II Three test periods on a commercial fluid catalytic cracking petroleum conversion unit are compared with prior operations on the same unit at similar conversion levels and feed rates in Table I. The catalyst employed was of the molecular sieve type and the hydrocarbon feed was a typical Mid-continent type gas oil. The comparisons clearly show an improvement in gasoline naptha (C -430F.) yield. With the lower coke level on both spent and regenerated catalyst and corresponding higher activity, the catalyst circulation rate (which controls the catalyst-oil ratio) is lowered to hold a selected conversion level. The carbon monoxide content of the effluent gas is significantly diminished and indeed can be reduced to nearly 0.0 vol.
EXAMPLE 111 Two test periods on the same commercial unit are compared in Table II with calculated data based on computer-programmed simulation (i.e., conventional) runs at identical feed rate, conversion level and cracking reactor average temperature. The weight ratio of catalyst to oil is greatly reduced, reflecting the lower circulation rate adequate to achieve the desired con- 2 version, when catalyst is regenerated according to the process of this invention. The yield of C;,-430F. naphtha is significantly increased with little change apparent in lighter products. There is a significant decrease in the coke yield with this increment being converted to valuable cracked products. The gasoline yield is not only increased but the octane number is also higher,
thus providing more barrel-octanes for blending pur poses from a given amount of feed.
EXAMPLE IV Test conditions similar to those of Example I (but without the eductor tube in use) were employed to determine the minimum level of carbon monoxide content reasonably to be achieved in the regenerator stack. The amount of excess air was varied while maintaining the dense fluidized bed temperature within the regenerator at about 12901300F. and sampling effluent gases from the stack. Results set forth in Table 111 clearly show that carbon monoxide levels as low as 8 ppm. can readily be achieved by the process of this invention. Modest extrapolation of these data suggests that it is not unreasonable to anticipate operation with no detectable amount of carbon monoxide in the stack gas.
TABLE 1 COMPARATIVE CA'I ALYST REGENERATION TESTS Test Period 1 2 3 A B A 15 A B Feed. MB/D 29.9 29.4 41.0 40.6 39.7 38.0 Conversion, vol. '7: 68.0 71.5 61.4 59.4 66.3 67.4 Reactor Av. Temperature, I-'. 942 960 946 940 960 900 Pressure, p.s.i.g. 17.1 20.0 19.2 21.3 18.6 20.5 Catalyst circulation, tons/min. 20.6 28.1 21.7 34.5 21.9 29.4 Catalyst-oil wt. ratio 5.2 6.0 4.1 6.5 4.2 5.4 Regcnerator Dense Bed Temperature, F. 1218 1204 1236 1 173 1255 1204 Cvclone Inlet Temperature, F. 1380 1210 1376 1140 1388 1185 C6ke burn. M 1b./hr. 18.3 25.5 20.5 28.7 21.3 28.1 Carbon on spent cat. wt. "/1 0.85 1.18 0.77 1.00 0.80 0 97 Carbon on rcgen. cat, wt. 7( 0.05 0.37 0.04 0.35 0.03 0.22 Wt. ratio. air/coke 14.7 11.2 14.0 11.2 14.6 11.4 Effluent gas, vol. "/1
CO 16.0 10.6 16.4 10.0 16.0 10.6 Co 0.0 9.4 0.5 9.6 0. 9.0 O" 1.7 0.4 1.0 0.4 2.1 0.7 Products Dry gas 1- C;,, Wt. Z 7.8 9.7 6.7 6.9 8.6 8.2 Iso-butane, vol. '7! 4.6 6.2 4.0 4.5 4.0 5.1 N-hutane vol. k 1.4 1.6 1.3 2.2 1.3 1.3 Butenes vol. "/1 7.0 7.4 6.6 5.8 7.2 8.0 C-,430F. vol. '/I 56.8 52.2 51.1 47.0 54.3 51.9 Cbkc, wt. /1 4.7 6.6 3.9 4.9 4.1 5.7
A Test Period B Prior Operation TABLE I1 COMPARISON OF ACTUAL AND SIMULATION DATA Test Period 1 2 Simulated Actual Simulated Actual Feed, B/D 41.378 41,378 35,904 35.904 Conversion. vol. 61.8 61.8 67.7 67 7 Reactor Av. Temperature, F. 944 944 960 960 Catalyst Circulation, tons/min. 5,9 19}; 37 5 l9; Cata1ystoi1 ratio 5.3 3.5 6.1 3.7 Regenerator Dense Bed Temperature F. 1143 1245 1 43 25 Cyclone Inlet Temperature, "F. 1383 1371 Coke burn, M 1b./hr. 30.03 20.02 29.03 20.72 Carbon on spent cat. wt. "/1 1.06 0.86 0.96 0.91 Carbon on g nat. t. 0.34 0.03 0.34 0.03 Products C and lighter. vol. 71 11.84 11.87 14.67 15.99 Iso-butane 5.24 3.43 5.85 4.20 N-hutane 1.49 0.98 1.74 0.94 Butenes 6.33 5.98 7.57 7.13 Pentanes 4.19 3.27 4.83 3.14 Pentenes 3.65 3.48 4.00 4.16 46.96 51.05 49.88 52.70 Coke, Wt. '71 5.54 3.70 6.15 4.39 Gasoline Octane 89.75 90.4 89.7 90.3 No.
Table III Effect of Excess Oxygen on Carbon Monoxide Content of Stack Gas Regencrator Stack Gas Analysis "Oxygen analyses obtained with Hays. Acratmn. Serial M2990. -57: scale.
"Carbon monoxide analyses obtained with Union Carbide. Modcl 3020. Carbon Monoxide Analyser.
"Carbon dioxide analyses obtained by Orsat method.
It is claimed:
1. In a process for catalytically cracking petroleum feedstock wherein fluidizable cracking catalyst which has been deactivated with coke deposits is withdrawn from the cracking reaction zone, stripped of volatile material, passed to a regeneration zone, and recycled after regeneration to the reaction zone, the method comprising:
a. contacting deactivated, coked catalyst particles with oxygen-containing regeneration gas to provide an excess of oxygen in a regeneration zone and burning substantially all of the coke from the cata lyst particles at regeneration temperatures;
b. initiating and sustaining combustion of carbon monoxide produced by said burning through contact with oxygen-containing gas in the regeneration zone at a temperature sufficient to combust substantially all of the carbon monoxide in the regeneration zone but not so high that said cracking catalyst is thermally deactivated;
. providing a sufficient amount of catalyst in the regeneration zone to absorb a major portion of the heat of combustion liberated by said combustion of carbon monoxide and to maintain said carbon monoxide combustion temperature; d. conducting said substantially complete combustion of carbon monoxide in the regeneration gases undergoing combustion, with the velocity of gases in the regeneration zone being such to provide contact of said regeneration gases with fluidized cracking catalyst particles in an amount sufficient to absorb a major portion of the heat of combustion liberated by said combustion of carbon monoxide and to maintain said carbon monoxide combustion temperature; absorbing said major portion of the heat of combustion of carbon monoxide in said fluidized cracking catalyst particles in direct heat-exchange contact with regeneration gases undergoing combustion in said regeneration zone and thereby maintaining said temperature for combusting substantially all of the carbon monoxide in the regeneration zone; f. withdrawing from the regeneration zone effluent gas having a low content of carbon monoxide; and
g. withdrawing from the regeneration zone regenerated catalyst particles having a low content of residual coke for passage to said reaction zone.
2. The process of claim 1 wherein said cracking catalyst comprises silica, alumina and crystalline aluminosilicate.
3. The process of claim 1 wherein said combustion of carbon monoxide is at a temperature of about 1250F. to about 1450F.
4. The process of claim 3 wherein said withdrawn regeneration zone effluent gas contains no more than about 0.2 volume carbon monoxide and said withdrawn regenerated catalyst particles contain no more than about 0.05 weight coke.
5. The process of claim 4 wherein regeneration gases undergoing combustion are in contact with an amount of fluidized cracking catalyst particles sufflcient to absorb greater than about of the heat of combustion liberated by said combustion of carbon monoxide.
6. The process of claim 5 wherein said cracking catalyst comprises silica, alumina and crystalline aluminosilicate.
7. The process of claim 6 wherein the cracking reaction zone is in a cracking reaction vessel of the transport type.
8. In a process for catalytically cracking petroleum feedstock wherein fluidizable cracking catalyst which has been deactivated with coke deposits is withdrawn from the cracking reaction zone, stripped of volatile material, passed to a regeneration zone, and recycled after regeneration to the reaction zone, the method comprising:
a. contacting deactivated, coked catalyst particles with oxygen-containing regeneration gas to provide an excess of oxygen in a lower dense-phase catalyst section of the regeneration zone and burning therein substantially all of the coke from the catalyst particles at regeneration temperatures;
b. initiating and sustaining combustion of carbon monoxide produced by said burning through contact with oxygen-containing gas in an upper dilute-phase section of the regeneration zone to combust substantially all of the carbon monoxide in the regeneration zone;
c. circulating fluidized regenerated cracking catalyst particles upwardly from said lower dense-phase section into said upper dilute-phase section in an amount sufficient to absorb a major portion of the heat of combustion liberated by said combustion of carbon monoxide;
d. absorbing said major portion of the heat of conr bustion of carbon monoxide in said circulated fluidized regenerated cracking catalyst particles in direct heat-exchange contact in said upper dilutephase section with said regeneration gas;
e. withdrawing from the regeneration zone effluent gas having a low content of carbon monoxide; and
. withdrawing from the regeneration zone regenerated catalyst particles having a low content of residual coke for passage to said reaction zone.
9. A cyclic, continuous process for fluid catalytic cracking of petroleum hydrocarbons and catalyst regeneration, wherein active, fluidizable cracking conversion catalyst particles become spent while cracking a petroleum hydrocarbon feedstock within a cracking reaction zone, spent catalyst particles containing coke are continuously withdrawn from the reaction zone and stripped in an inert gas stream, stripped spent catalyst particles are thereafter reactivated by burning coke therefrom in a fluidized regeneration zone having a lower dense-phase section and an upper dilute-phase section, maintained at a regeneration temperature sufficiently high to effect substantially complete burning of coke, and hot regenerated cracking catalyst particles are recycled to said cracking reaction zone for use in said fluid catalytic cracking, comprising the steps of:
a. introducing spent cracking catalyst particles, after stripping of residual volatile petroleum material, into a lower dense-phase section of a fluidized regeneration zone contained within a regeneration vessel and maintained at regeneration temperature;
b. introducing into the lower section of said regeneration zone an oxygen-containing regeneration gas stream in an amount in excess of that required for complete combustion of the coke contained in the spent catalyst particles and at an upward velocity sufficiently high to effect fluidization of said cracking catalyst particles;
c. burning coke from the spent cracking catalyst particles in contact with said oxygen-containing regeneration gas stream in said lower section of said regeneration zone at said regeneration temperature while maintaining said catalyst particles in a densephase fluidized state by the upward flow of said oxygen-containing gas stream, to provide a mixture comprising fluidized regenerated cracking catalyst particles, together with oxygen, carbon monoxide and carbon dioxide;
(1. substantially completing the combustion of carbon monoxide in said regeneration gas stream to carbon dioxide in an upper dilute-phase section of said regeneration zone at a temperature sufficiently high to support combustion of carbon monoxide;
e. circulating fluidized regenerated cracking catalyst particles upwardly from said lower section into said upper section in an amount sufficient to absorb a major portion of the heat of combustion liberated by said combustion of carbon monoxide;
f. absorbing said major portion of the heat of combustion of carbon monoxide in said circulated fluidized regenerated cracking catalyst particles in direct heat-exchange contact in said upper section with said regeneration gas stream;
g. separating a spent regeneration gas stream, containing carbon dioxide, excess oxygen and any unconverted carbon monoxide, from entrained catalyst particles and discharging the spent regeneration gas stream from the regeneration vessel;
h. withdrawing regenerated cracking catalyst particles, substantially free of coke and conserving the absorbed heat of combustion of said carbon monoxide, from said regeneration zone and introducing said withdrawn regenerated cracking catalyst particles into the cracking reaction zone; and
i. cracking a petroleum hydrocarbon feedstock with said regenerated cracking catalyst particles in said cracking reaction zone under fluidizing conditions.
10. The process of claim 9 wherein the combustion of carbon monoxide is substantially completed by controlling the temperature in the upper section of the regeneration zone at a level higher than that maintained in the lower section of the regeneration zone, while sustaining the combustion of carbon monoxide with oxygen, at least in part by adjusting the rate of curculation of regenerated cracking catalyst particles from the lower section of the regeneration zone.
11. The process of claim 9 wherein the oxygencontaining regeneration gas stream comprises air or oxygen-enriched air, flowing upwardly to provide fluidization of the lower dense-phase section of the regeneration zone, the regeneration temperature within the lower section of the regeneration zone is maintained within the range from about ll50 to about l400F., and the temperature within the upper section of the regeneration zone is maintained within the range from about l2()0 to about l500F.
12. The process of claim 9 wherein the cracking catalyst particles comprise silica and alumina together with crystalline aluminosilicate.
13. The process of claim 9 wherein the cracking reaction zone is a fluidized catalytic cracking reaction zone, supplied with petroleum cracking catalyst consisting essentially of 35-89 wt. silica, 10-50 wt. alumina and l-l5 wt. crystalline aluminosilicate.
14. The process of claim 9 wherein the regenerated cracking catalyst particles contain no more than about 0.05 wt. coke and the spent regeneration gas stream contains no more than about 0.2 vol. carbon monoxide.
15. The process of claim 9 wherein additional regenerated cracking catalyst particles are circulated upwardly from the lower dense-phase section of the regeneration zone into the upper section of the regeneration zone and dispersed within said upper section, in an amount sufficient to absorb substantially all of the evolved heat of combustion and in response to the temperature of the dilute-phase zone.
16. The process of claim 9 wherein at least about of the evolved heat of combustion of carbon monoxide is absorbed in the regenerated cracking catalyst particles and transferred therein to the cracking reaction zone.
17. The process of claim 9 wherein the burning of carbon monoxide within the upper section of the regeneration zone initiated by burning sufficient torch oil within the dense-phase zone, while additionally introducing to said zone sufficient oxygen-containing gas to afford complete combustion of the torch oil, to provide a partially spent regeneration gas passing upwardly into said upper section at a temperature sufficiently high to sustain combustion of carbon monoxide, and thereafter ceasing the combustion of torch oil.
18. The process of claim 9 wherein the burning of carbon monoxide within the upper section of the regeneration zone is initiated by momentary actuation of a spark-ignition means situated within and near the bottom of said upper section, and thereafter ceasing the spark ignition.
19. The process of claim 9 wherein the withdrawn regenerated cracking catalyst particles are introduced into the cracking reaction zone at a temperature of at least about l,200F.
20. The process of claim 9 wherein the regenerated cracking catalyst particles are returned to the cracking reaction zone at substantially the temperature maintained in the lower dense-phase section of the regeneration zone.
21. The process of claim 9 wherein the cracking reac tion zone is contained within a cracking reaction vessel of the transport type.
22. The process of claim 9 wherein the cracking of petroleum hydrocarbon feedstock with regenerated cracking catalyst particles is effected in said cracking reaction zone under fluidizing conditions providing a cracking reaction time within the range from about 3 to about 10 seconds.
23. A cyclic, continuous process for fluid catalytic cracking of petroleum hydrocarbons and catalyst regeneration, wherein coke is burned from spent cracking catalyst particles in contact with an excess of an oxygencontaining regeneration gas stream in a fluidized dense-phase lower section of a regeneration zone and carbon monoxide from said burning of coke is further burned to carbon dioxide in a dilute-phase upper section of said regeneration zone in contact with sufficient catalyst particles to absorb most of the heat of combustion of said carbon monoxide, comprising the step of circulating additional catalyst particles into the upper section of the regeneration zone through an eductor tube situated within the regenerator vessel, said eductor tube extending substantially vertically from near the bottom of the dense-phase lower section to near the top of the dilute-phase upper section of the regeneration zone and terminating in a distributing head, the eduction of catalyst being effected with ajet stream of a gas directed upwardly into a bottom section of the eductor tube, whereby the additional catalyst particles are lifted and dispersed substantially uniformly into a top portion of the upper section of the regeneration zone.
24. The process of claim 9 wherein spent catalyst particles and the oxygen-containing gas are introduced separately into a bottom section of the lower densephase section of the regeneration zone and regenerated catalyst particles are withdrawn from a top section of the lower dense-phase section of the regeneration zone.
25. The process of claim 9 wherein spent catalyst particles are first contacted with an excess of an oxygen-containing regeneration gas in the lower densephase section of the regeneration zone maintained at a temperature within the range from about l,l50 to about 1,400F., and carbon monoxide is thereafter substantially completely burned to carbon dioxide within the upper dilute-phase section of the regeneration zone, at a temperature maintained within the range from about l,200 to about l,450F.
26. The process of claim 25 wherein regenerated catalyst particles are withdrawn from the regeneration zone at a point near the top of the lower dense-phase section of the regeneration zone and at a temperature of about 1,250F.
27. A cyclic, continuous process for fluid catalytic cracking of petroleum feedstock and catalyst regeneration, comprising the steps of:
a. continuously feeding petroleum feedstock and regenerated fluidizable cracking catalyst particles, said catalyst particles being at a temperature of at least about 1,200F., to a bottom section of a fluid catalytic cracking reaction vessel in weight proportions selected to provide a catalyst-oil ration within the range from about 2 to about 10;
b. mixing the fluidizable cracking catalyst particles with the petroleum feedstock in said bottom section of the cracking reaction vessel, whereby the petroleum feedstock is substantially completely vaporized at a mixing temperature of about 1000F. to provide a fluidized mixture of catalyst particles and petroleum vapors;
c. passing the fluidized mixture of catalyst particles and petroleum vapors upwardly through the cracking reaction vessel at a fluidizing velocity within the range from about 20 to about 60 feet per second, whereby the cracking reaction is effected and the cracking reaction time is controlled within the range from about 3 to about 10 seconds;
d. continuously withdrawing a fluidized mixture of spent catalyst particles having carbonaceous material deposited thereon and petroleum vapors, including cracked petroleum vapor products, from a top section of the cracking reaction vessel at a temperature of about 950F., rapidly separating said spent cracking catalyst particles from said petroleum vapors, including cracked petroleum vapor products, and stripping said separated spent catalyst particles in an inert gas atmosphere at a stripping temperature of about 950F.;
e. continuously feeding stripped spent cracking catalyst particles into a lower section of a fluidized catalyst regeneration zone, contained within a catalyst regeneration vessel, together with an oxygencontaining regeneration gas in excess over the amount required for the complete combustion of the carbonaceous material deposited upon the spent cracking catalyst particles, said gas flowing at a fluidizing velocity upwardly through the regeneration zone, said fluidizing velocity being within the range from about 0.5 to about 3 feet/second; burning a major portion of the carbonaceous material from the spent cracking catalyst particles within the lower section of the fluidized catalyst regeneration zone at a temperature maintained within the range from about 1 to about l400F., to provide a partially spent regeneration gas containing carbon monoxide;
g. burning substantially all of the remaining carbonaceous material from the catalyst particles in the presence of the partially spent regeneration gas within an upper section of the fluidized catalyst regeneration zone at a temperature maintained within the range from about l,200 to about h. simultaneously burning substantially all of the carbon monoxide contained in the partially spent regeneration gas within the upper section ofthe fluidized catalyst regeneration zone at a temperature within the range from about l,200 to about l,450F.;
. circulating fluidized regenerated cracking catalyst particles upwardly from said lower section into said upper section in an amount sufficient to absorb at least about 80% of the heat of combustion liberated by said burning of carbon monoxide;
j. absorbing said major portion of the heat of combustion of carbon monoxide in said circulated fluidized regenerated cracking catalyst particles in direct heat-exchange contact in said upper section with said regeneration gas stream;
k. discharging substantially spent regeneration gas, containing no more than about 2000 ppm carbon monoxide together with from about 1.0 to about lytic cracking reaction vessel is of the transport type.
29. The process of claim 27 wherein the cracking reaction time is controlled within the range from about 3 to about 7 seconds.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa e 1 Of PATENT'NO. 3,909,392 g 5 DATED September 30, 1975 Carl J Horecky Jr. Robert J. Fahrig; Robert J. Shields Jr. INVENTOMS) and Claude O. MdKinney It IS certrtred that error appears rn the above-rdentified patent and that sard Letters Patent are hereby corrected as Shown below Column Line 1 57 "occur typical" should be occur under typical 2 12 "After burning" should be Afterburning 2 60-61 "zeclites" should be zeolites 3 57 "densephase" should be dense-phase 4 6 "flud" should be flue 4 l0 "wihthin" should be within 4 2O "advantageous" should be advantageously 4 26 "0.5" should be 0.05
5 31 The word "coke" should appear within quotation marks; 5 36 "combination" should be combustion 5 6O "suitably" should be suitable 6 ll "conversison" should be conversion 6 51-52 The words 'molecular sieve" should appear within quotation marks 6 59 "soruce" should be source 7 l2 "benefially" should be beneficially 7 15 "end" should be and 7 34 "witin" should be within 7 35 "and 14" should be and line 14 8 l2 "cataylst" should be catalyst 8 14-15 "cataylst" should be catalyst 8 l4 "educator should be eductor 8 l7 "educated" should be educted 8 22 "distrubution" should be distribution 8 29 "cyclene" should be cyclone 8 44-45 "through regeneration zones" should be through the regeneration zones Continued.
owner) sures PATENT OFFICE @ETEFEQATE 0F CORRECTION G PATENT NO- 3,909,392
ATED September 30, 1975 C l J. H reck Jr. Robert J. Fahrig; Robert J. Shields Jr. mvENToms) aid Claud O. IcKinney t! rs certrtred that error appears In the ab0ve|denti tred patent and that said Letters Patent are hereby corrected as shown below Page 2 Qf 5 Column Line 8 46 "of the spent catalyst" should be on the spent catalyst 8 51 "Fluidizing" should begin a new paragraph; 8 63 "Genes" should be Gases 8 64 After "catalyst" add particles 9 ll "dilutephase" should be dilute-phase Q 9 l2 "approximetely" should be approximately 9 36 "alumina and" should 'be alumina, and 9 37 The words "molecular sieves" should appear Within quotation marks; 9 44 The words "molecular sieves" should appear within quotation marks; 9 51 "examble" should be example 9 52 The words "molecular sieve" should appear within quotation marks; 9 55 The words "molecular sieve" should appear within quotation marks; 9 57 "suitable" should be suitably 1O 24 The word "in" should be deleted; Q 10 39 "with" should be without 10 59 Insert after "0.5 wt.%".
11 62 "difficulty" should be difficultly ll 65 "001" should be 0.01
. 12 13-14 The words "molecular sieve" should appear within quotation marks;
12 40 After "3%" add and desirably no more than about 2%.
12 54 The Words "molecular sieve" should appear within quotation marks; 12 59 "dance" should be dense 12 6O in not" should be is not Q Continued.
INl'ifil) STATES PATENT OFFICE 1 r w 1 fi (1BR FIFHJATE ()l CORRELTION PATENT NO. 3,909,392
DATED September 30, 1975 INVENTOWS, Carl J. Horecky, Jr.; Robert J. Fahrig; Robert J. Shields. Jr.;
and Claude O. McKinney it Is cemfaed thal error appears 1n the above-ldentlfied patent and that said Letters Patent are hereby corrected as she-m beiow Page 3 of 5 Column Line 13 1 After "atmospheric" add pressure 13 26 "reaction" should be reactions 13 65 The words "molecular sieve" should appear within quotation marks e 14 27 "caxalsyt" should be catalyst l5 9 Before "circulation" add catalyst 20 23 "curculation" should be circulation 2O 64 After "zone" add is 22 16 "ration" should be ratio 24 7 Before l,2OOF." add "about".
lgncd and Scaled this thirtieth a 0 March 1976 [SEAL] D y f Arrest.
RUTHV C. MAnsoN C. MARSHALL DANN Q "nesmlg 011m (ummissimu'r uj'PaIenIs and Trademarks