CA1152052A - Flue gas pollutants control in particulate catalyst regeneration - Google Patents
Flue gas pollutants control in particulate catalyst regenerationInfo
- Publication number
- CA1152052A CA1152052A CA000379192A CA379192A CA1152052A CA 1152052 A CA1152052 A CA 1152052A CA 000379192 A CA000379192 A CA 000379192A CA 379192 A CA379192 A CA 379192A CA 1152052 A CA1152052 A CA 1152052A
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- CA
- Canada
- Prior art keywords
- catalyst
- regeneration
- bed
- coke
- sulfur
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G11/00—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
- C10G11/14—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils with preheated moving solid catalysts
- C10G11/18—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils with preheated moving solid catalysts according to the "fluidised-bed" technique
- C10G11/182—Regeneration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J29/00—Catalysts comprising molecular sieves
- B01J29/90—Regeneration or reactivation
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Organic Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Catalysts (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Treating Waste Gases (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Flue gas pollutants are removed from catalyst regeneration flue gas by burning coke off coke-containing catalyst particles and burning carbon monoxide in a regen-eration zone, reacting sulfur trioxide with alumina in the regeneration zone to form a solid, and heating the flue gas after removing the flue gas from the regeneration zone.
Flue gas pollutants are removed from catalyst regeneration flue gas by burning coke off coke-containing catalyst particles and burning carbon monoxide in a regen-eration zone, reacting sulfur trioxide with alumina in the regeneration zone to form a solid, and heating the flue gas after removing the flue gas from the regeneration zone.
Description
01 L~LUE GAS POLLUTANTS CONTROL IN
PARTICULATE CATALYST REGENERATION
BACKGROUND OF THE INVENTION
This invention concerns the art of catalyst 05 regeneration. More specifically, the present invention concerns a method for burning sulfur-contaminated and nitrogen-contaminated coke off particulate catalyst, while decreasing gaseous pollutants contamination of flue gas formed in the coke burning.
Cata:Lytic cracking is a well-known commercial process using particulate catalyst in a moving bed or a fluidized bed. Cracking conditions include the absence of externally supplied molecular hydrogen, whereas hydro-cracking is carried out in the presence of molecular hydrogen. In catalytic cracking, an inventory of particulate cal:alyst is continuously cycled between a cracking reactor and a catalyst regenerator. In a fluidized cata:Lytic cracking (FCC) system, hydrocarbon feed is contacl:ed with catalyst particles in a hydrocarbon cracking zone, or reactor, at a temperature of about 425C-600C, u~;ually 460C-560C. The reactions of hydrocarbons at the elevated operating temperature result in deposition of carbonaceous coke on the catalyst parti-cles. The resulting fluid products are separated from the coke-deactivated, spent catalyst and are withdrawn from the reactor. ~oke-containing catalyst particles are stripped of voLatiles, usually by means of steam, and passed to the catalyst regeneration zone. In the catalyst regenerator, the spent catalyst is contacted with a prede-termined amount of molecular oxygen. A desired portion ofthe coke is bu]ned off the catalyst. The coke burning step restores ,-atalyst activity and simultaneously heats the catalyst to, e.g., 540C-815C, usually 590C-730C.
Flue gas formed by combustion of coke in the conventional 01 catalyst regenerator may be treated for removal of partic-ulates and conversion of carbon monoxide, after which the flue gas is normally discharged into the atmosphere.
Most fluidized catalytic cracking systems now 05 use zeolite-containing catalyst having high cracking ac-tivity and selectivity. Zeolite-type catalysts have a particularly hiigh cracking activity when the concentration of carbon on the catalyst after regeneration is relatively low. It is therefore generally desirable to burn as much coke off zeolit:e-containing catalysts as is possible, so as to obtain a relatively high activity and selectivity in carrying out h~drocarbon cracking. It is also often desirable to burn carbon monoxide as completely as possi-ble during catalyst regeneration to retain as much heat energy as possible in the cracking system. Retention of heat energy is especially important when high catalyst cracking select:ivity leads to low concentration of coke on the spent cata]yst. Among the ways suggested to enhance coke burning tc~ increase catalyst cracking selectivity and to burn more carbon monoxide to provide process heat, is enhanced carbon monoxide combustion in a dense-phase fluidized cata]yst bed in the catalyst regenerator.
Carbon monoxide burning may, for example, be promoted by use of an active, combustion promoting metal. Metals have been used commercially for this purpose, either as an integral component of the cracking catalyst particles or as a component of a discrete particulate additive, in which the active metal is associated with a support other than the catal~rst particles. Additive particles are mixed with catalyst particles in the circulating particulate solids inventory. Various ways of employing carbon mon-oxide combustion promoting metals in cracking systems have been suggested in the patent art. In U.S. Patent No.
PARTICULATE CATALYST REGENERATION
BACKGROUND OF THE INVENTION
This invention concerns the art of catalyst 05 regeneration. More specifically, the present invention concerns a method for burning sulfur-contaminated and nitrogen-contaminated coke off particulate catalyst, while decreasing gaseous pollutants contamination of flue gas formed in the coke burning.
Cata:Lytic cracking is a well-known commercial process using particulate catalyst in a moving bed or a fluidized bed. Cracking conditions include the absence of externally supplied molecular hydrogen, whereas hydro-cracking is carried out in the presence of molecular hydrogen. In catalytic cracking, an inventory of particulate cal:alyst is continuously cycled between a cracking reactor and a catalyst regenerator. In a fluidized cata:Lytic cracking (FCC) system, hydrocarbon feed is contacl:ed with catalyst particles in a hydrocarbon cracking zone, or reactor, at a temperature of about 425C-600C, u~;ually 460C-560C. The reactions of hydrocarbons at the elevated operating temperature result in deposition of carbonaceous coke on the catalyst parti-cles. The resulting fluid products are separated from the coke-deactivated, spent catalyst and are withdrawn from the reactor. ~oke-containing catalyst particles are stripped of voLatiles, usually by means of steam, and passed to the catalyst regeneration zone. In the catalyst regenerator, the spent catalyst is contacted with a prede-termined amount of molecular oxygen. A desired portion ofthe coke is bu]ned off the catalyst. The coke burning step restores ,-atalyst activity and simultaneously heats the catalyst to, e.g., 540C-815C, usually 590C-730C.
Flue gas formed by combustion of coke in the conventional 01 catalyst regenerator may be treated for removal of partic-ulates and conversion of carbon monoxide, after which the flue gas is normally discharged into the atmosphere.
Most fluidized catalytic cracking systems now 05 use zeolite-containing catalyst having high cracking ac-tivity and selectivity. Zeolite-type catalysts have a particularly hiigh cracking activity when the concentration of carbon on the catalyst after regeneration is relatively low. It is therefore generally desirable to burn as much coke off zeolit:e-containing catalysts as is possible, so as to obtain a relatively high activity and selectivity in carrying out h~drocarbon cracking. It is also often desirable to burn carbon monoxide as completely as possi-ble during catalyst regeneration to retain as much heat energy as possible in the cracking system. Retention of heat energy is especially important when high catalyst cracking select:ivity leads to low concentration of coke on the spent cata]yst. Among the ways suggested to enhance coke burning tc~ increase catalyst cracking selectivity and to burn more carbon monoxide to provide process heat, is enhanced carbon monoxide combustion in a dense-phase fluidized cata]yst bed in the catalyst regenerator.
Carbon monoxide burning may, for example, be promoted by use of an active, combustion promoting metal. Metals have been used commercially for this purpose, either as an integral component of the cracking catalyst particles or as a component of a discrete particulate additive, in which the active metal is associated with a support other than the catal~rst particles. Additive particles are mixed with catalyst particles in the circulating particulate solids inventory. Various ways of employing carbon mon-oxide combustion promoting metals in cracking systems have been suggested in the patent art. In U.S. Patent No.
2,647,860, it is proposed to add 0.1 l weight percent chromic oxide t:o a crac~ing catalyst used in a moving bed 01 system to promote combustion of carbon monoxide to carbon dioxide and to prevent afterburning. In U.S. Patent No.
3,808,121, it is proposed to introduce relatively large sized particles containing a carbon monoxide combustion 05 promoting metal into a cracking catalyst regenerator. The circulating particulate solids inventory, comprised of relatively smaLl-sized catalyst particles, is cycled between the cracking reactor and the catalyst regenerator, while the comblJstion promoting particles remain in the regenerator because of their size. Oxidation promoting metals such as cobalt, copper, nickel, manganese, copper-chromite, etc., impregnated on an inorganic oxide such as alumina, are disclosed.
Belgian Patent Publication No. 820,181 discloses the use of cracking catalyst particles containing a Group VIII noble metal or rhenium to provide CO combustion dur-ing regeneration o~- the catalyst. The combustion promoter is used in an amount of a trace to 100 ppm. No. 820,181 teaches that including such combustion promoting metals in the catalyst results in an increase in formation of coke and hydrogen when the catalyst is employed for hydrocarbon cracking.
U.S. Patents No. 4,072,600 and No. 4,093,535 disclose the addition of trace amounts of Group VIII noble metals or rhenium to a cracking catalyst inventory in order to enhance combustion of CO in a catalyst regenera-tor. These patents teach that it is well known that the presence of a hydrogenation/dehydrogenation component in a cracking catalyst is detrimental to the cracking process because of the resulting undesirable increase in coke and hydrogen formation in cracking. The patents teach that detrimental results are caused by the reaction conditions employed in a cracking reactor, which favor undesirable reactions. According to these patents, ideally, the least ~2Q52 01 possible amount of the carbon monoxide combustion promo-ting metal necessary to convert the desired amount of CO
to CO2 should be used, since this ideal least possible amount would have the least adverse effect on the hydro-OS carbon cracking step. According to these patents, mini-mization of the concentration of the carbon monoxide combustion promoter in a catalytic cracking system can be accomplished by monitoring the flue gas leaving the cata-lyst regenerator and adjusting the rate of addition of combustion promoter such that the least amount of promoter necessary to completely burn carbon monoxide is added.
U.S. Patent No. 4,153,535 discloses a cyclic fluidized cracking process using a zeolite-type cracking catalyst, a metallic reactant (which reacts with sulfur oxides) selected from sodium, magnesium, calcium, stron-tium, barium, scandium, titanium, chromium, molybdenum, manganese, cobalt, nickel, antimony, copper, zinc, cad-mium, lead, the rare earth metals (more than 20 elements), their compounds and mixtures thereof, and a metallic oxi-dation promoter selected from ruthenium, rhodium, palla-dium, osmium, iridium, platinum, vanadium, tungsten, ura-nium, zirconium and silver. A similar system is disclosed in U.S. Patent No. 4,240,899.
Representative catalyst regeneration patent literature is shown in the following patents: U.S. Patent No. 3,909,392 describes a scheme for enhancing carbon monoxide combustion by thermal means. Catalyst is used to provide a heat sink in the dilute phase above a fluidized bed for the increased heat production. British Patent Publication 2,001,545 describes a two-stage system for a regenerating catalyst, with partial catalyst regeneration being carried out in the first stage and secondary, more complete regeneration carried out in the second stage ~ith a separate regeneration gas. U.S. Patent ~o. 3,767,566 describes a two-stage regeneration scheme in which partial sz 01 regeneration takes place in an entrained catalyst bed, and secondary, more complete regeneration takes place in a dense fluidized catalyst bed. A somewhat similar regener-ation operation is described in U.S. Patent No. 3,902,990, 05 which discusse.s the use of several stages of regeneration, with dilute and dense-phase beds of catalysts being employed, and with the use of plural streams of regenera-tion gas. U.S. Patent No. 3,926,843 describes a plural-stage regeneration scheme in which dilute phase and dense-phase coke burning are performed. British PatentPublication No. 1,499,682 discloses use of a combustion-promoting metal for enhancing carbon monoxide combustion.
It has been suggested, e.g., in U.S. Patent No.
3,699,037, to reduce the amount of sulfur oxides in FCC
regenerator flue gas by adding particles of Group IIA
metal oxides and/or carbonates, such as dolomite, MgO or CaCO3, to the circulating catalyst in an FCC unit. The Group IIA metals react with sulfur oxides in the flue gas to form solid sulfur-containing compounds. The Group IIA
metal oxides lack physical strength. Regardless of the size of the particles introduced, they are rapidly reduced to fines by attrition and rapidly pass out of the FCC unit with the catalyst fines. Thus, addition of dolomite and the like Group IIA materials is essentially a once-through process, and relatively large amounts of material must be continuously added in order to reduce the level of flue gas sulfur oxides.
It has also been suggested, e.g., in the U.S.
Patent 3,835,031, to reduce the amount of sulfur oxides in an FCC regenerator flue gas by impregnating a Group IIA
metal oxide onto a conventional silica-alumina cracking catalyst. The attrition problem encountered when using unsupported Group IIA metals is thereby reduced. However, it has been found that Group IIA metal oxides, such as magnesia, when used as a component of cracking catalyst, 01 have a rather pronounced undesirable effect on the activ-ity and selectivity of the cracking catalysts. Such unde-sirable effects are particularly apparent when the magne-sium compound is used in an amount sufficient to appre-05 ciably diminish the amount of sulfur oxides in the fluegas. The addition of a Group IIA metal to a cracking catalyst results in two particularly noticeable adverse consequences relative to the results obtained in cracking without the presence of the Group IIA metals: (1) the yield of the liquid hydrocarbon fraction is substantially reduced, typically by greater than 1 volume percent of the feed volume; and (2) the octane rating of the gasoline or naphtha fraction (75-430F boiling range) is substan-tially reduced. Both of the above-noted adverse conse-quences are seriously detrimental to the economic viabil-ity of an FCC cracking operation, so that even complete removal of sulfur oxides from regenerator flue gas would not normally compensate for the simultaneous losses in yield and octane which result from adding Group IIA metals to an FCC catalyst. The same can generally be said for the numerous reactant metals disclosed as sulfur oxides reactants in U.S. Patent No. 4,153,535, discussed above.
Alumina has been a component of many FCC and moving-bed cracking catalysts, but normally in intimate chemical combination with silica. Alumina itself has low acidity and is generally considered to be undesirable for use as a cracking catalyst. The art has taught that alu-mina is not selective, i.e., the cracked hydrocarbon prod-ucts recovered from an FCC or other cracking unit using an alumina catalyst would not be desired valuable products, but would include, for example, relatively large amounts of C2 and lighter hydrocarbon gases.
U.S. Patent No. 4,071,436 discloses the use of alumina for reducing the amount of sulfur oxides in the flue gas formed during cracking catalyst re~eneration.
s~s~
01 The alumina can be used in the form of a particulate solid mixed with cracking catalyst particles. In some cases, alumina contained in the cracking catalyst particles is also suitable, however, alumina contained in conventional 05 cracking catalyst is usually not very active, since it is intimately mixed with a large fraction of silica.
U.S. Patents No. 4,115,250 and No. 4,115,251 disclose the synergistic use of oxidation-promoting metals for carbon monoxide burning in combination with the use of alumina for re<3ucing the amount of sulfur oxides in crack-ing catalyst regenerator flue gas. When alumina and highly active oxidation-promoting metals are both included in the same particle, alumina in the particle is rela-tively ineffecl:ive for removing sulfur oxides from the regenerator flue gas, especially in the presence of even a small amount of carbon monoxide. On the other hand, when the alumina and combustion-promoting metal are used on separate particles circulated together in a cracking system in physical admixture, the ability of the alumina to reduce the level of sulfur oxides in the flue gas can be considerably enhanced.
One problem encountered in some cracking opera-tions using met:al-promoted complete carbon monoxide com-bustion-type regeneration has been the generation of unde-sirable nitrogen oxides (NOX) in the flue gas formed byburning coke. For example, U.S. Patent Wo. 4,235,704 discloses a mel:hod for controlling nitrogen oxides by adjusting the concentration of carbon monoxide combustion promoter in re]Lation to the level of nitrogen oxides in flue gas exiting a catalyst regenerator. In many cases, however, it is desired to have a larger amount of comhus-tion promoter present, than could be feasible in the '704 patent method. The present invention is directed, in part, toward providing a catalyst regeneration system which accomplishes a high degree of coke removal and )5Z
01 complete carbon monoxide combustion within a catalyst regeneration system, while substantially decreasing the concentration of nitrogen oxide present in flue gas formed by burning the coke, without recourse to overly restric-05 tive limitations on the use of combustion promoters.
SUMMARY OF ~HE INVENTION
I have found that a particulate catalyst whichhas been contaminated by sulfur-containing and nitrogen-containing coke deposition can be regenerated by burning off sufficient coke to provide an essentially carbon-free, regenerated catalyst, and a flue gas free from carbon monoxide, nitrogen oxides and sulfur oxides can be formed in carrying out the regeneration by (a) passing a regener-ation gas including free oxygen upwardly through a dense-phase fluidized bed of particulate solids comprising sub-stantially coke-free particles of the catalyst in a regen-eration zone, and removing the regeneration gas from the regeneration zone; (b) introducing the coke-containin~
catalyst particles into the bed and generating carbon oxides, nitrogen oxides and sulfur oxides in the bed by burning the coke; (c) burning sufficient carbon monoxide within the bed to maintain regeneration gas above the bed at a temperature below 735C and not higher than 27C
above the maximum temperature of regeneration gas within the bed and to provide a carbon monoxide concentration of less than 0.5 volume percent in regeneration gas removed from the regeneration zone, and introducing sufficient free oxygen in~o the bed to provide at least 1 volume percent free oxygen in regeneration gas removed from the regeneration zone; (d) including in the particulate solids an amount of a sulfur dioxide combustion promoter suffi-cient to provide substantial incremental conversion of sulfur dioxide to sulfur trioxide within the bed; (e) including reaclive alumina in the particulate solids, and decreasing the amount of sulfur oxides in regeneration gas _9_ 0l removed from the regeneration zone by forming a sulfur-containing and aluminum-containing solid from the sulfur trioxide and the reactive alumina; and (f) removing regen-eration gas from the regeneration zone and decreasing the 05 amount of nitrogen oxides in the regeneration gas by main-taining the regeneration gas at a temperature above 760Cfor at least l second.
In another embodiment of the invention, I have found that a particulate catalyst which has been contam-inated with su]fur-containing and nitrogen-containing coke can be regenerated, and a flue gas with decreased levels of carbon monoxide, nitrogen oxides and sulfur oxides can be formed in carrying out the regeneration by (a) forming carbon monoxide, gaseous sulfur oxides and gaseous nitrogen oxides by reacting free oxygen with the coke in a regeneration zone; (b) decreasing the amount of the carbon monoxide by reactïng the carbon monoxide with free ox~gen in the regeneration zone in the presence of a carbon monoxide combustion promoter; (c) decreasing the amount of the gaseous su].fur oxides and forming a sulfur-containing solid in the regeneration zone by reacting the sulfur oxides with reactive alumina contained in a substantially silica-free particulate solid other than the catalyst present in the regeneration zone in physical admixture with the catalyst; and (d) withdrawing gas including the nitrogen oxides from the regeneration zone at a temperature be]ow 735C and decreasing the amount of the nitrogen oxidec; by maintaining the gas at a temperature above 760C for at least one second outside the regeneration zone.
DESCRIPTION OF THE DRAWING
The attached drawing is a schematic representa-tion of one preferred embodiment of the present invention.
Referring to the drawing, there is shown a regeneration vessel 1. Coke-containing catalyst is introduced into the vessel 1 through a conduit 3, and substantially coke-free catalyst is removed by way of a conduit 5. A dense-phase fluid-ized bed 7 of substantially coke-free catalyst is maintained in the vessel 1. Regeneration gas is introduced into the lower end of the vessel through a conduit 9 and discharged into the re-generation zone through a distributor 11. The regeneration gas passes upwardly through a distribution grid 13, through the fluidized bed 7, and out of the upper end of the dense-phase bed, indicated by a line at 15 in the drawing. Substantially all the coke in the spent and partially regenerated catalyst present in the fluidized bed is ~preferably burned with free oxygen intro-duced in the regeneration gas. Regeneration gas (flue gas) leaving the top 15 of the bed 7 passes into a cyclone separator 17. Entrained solids are s~perated from the flue gas in the cyclone and returned to the dense-phase catalyst bed through a dipleg 19. The flue gas is then withdrawn from the vessel 1 at a temperature below 735C thro~gh a conduit 21 and passed into a furnace (not shown) to decrease its nitrogen oxides con-centration. Fuel gas and oxygen are introduced into the furnace and burned in admixture with the flue gas to heat the flue gas to a temperature above 760C. After an appropriate residence time at a temperature above 760C in the furnace flue gas with a reduced nitrogen oxides content is removed. Conventional elements of the embod:Lment depicted, such as controlling means, pumping and valve means, and the li]ce, are not shown in the drawing and are not described in order to simplify the explan-ation. The use and disposition of such elements will be clear to those skilled in the art.
~ - 10 -ClS2 As used herein, the term "substantially coke-free catalyst" refers to catalyst which contains less than 0.2 weight percent carbon.
05 As used herein, the term "dense-phase fluidized bed" means a f:Luidized bed of particulate solids having a density of at :Least 12 pounds per cubic foot.
As used herein, the term "regeneration gas"
includes the gas mixtures (e.g., air) introduced to the catalyst regenerator, the gas mixtures present in the regenerator, and the gas mixtures removed from the regenerator (i.e., flue gases).
Cata:Lysts that are best adapted for regeneration according to this invention are those in the form of par-ticulate solids. Preferably, catalyst to be regenerated is sized appropriately for catalytic use in an entrainedbed or flui~ized bed catalytic conversion system. With reference to the types of catalytic hydrocarbon conversion operations pre~3ently practiced commercially, this inven-tion is especially advantageous for regeneration of FCC
catalysts; however, use of the invention is not limited to FCC catalyst regeneration operations, and can be used for treating any coke-contaminated particulate catalyst which can be wholly or partially reactivated by coke burnoff.
A regeneration zone employed in carrying out the invention may be supplied by a suitable vessel or chamber, capable of conlain~ng regeneration gas and catalyst particles at the desired temperature and pressure. Suit-able vessels and chambers will be readily apparent to those skilled :in the art from the description herein.
Co~ventional F(~C cracking catalyst regeneration vessels and chambers, i-or example, can suitably be employed.
The regeneration gas or gas mixture introduced into the catalyst regenerator must provide an appropriate free oxygen (molecular oxygen) supply to the regenerator.
~Z~52 01 Normally, air is quite suitable for use in supplying free oxygen, but use of air is not essential. For example, pure oxygen or oxygen-enriched air can also be used, if desired. Conventional gases present in commercial FCC
OS operations, suc:h as free nitrogen (molecular nitrogen), carbon dioxide, steam, and the like, may suitably be present in fluidizing and entrainment gases.
In general, regeneration conditions maintained in the regenerator include a combination of temperature and pressure sufficient to permit the specified or desired degree of coke combustion, carbon monoxide combustion and sulfur dioxide combustion to take place, in the manner discussed herein. The temperature of the regeneration gas is maintained below 735C. Temperatures of 540C-735C
are normally quite suitable. Temperatures of 590C-730C
are preferred. Preferably, the rates of flow of regen-eration gases, entrainment gases and particulate solids such as catalyst particles through the regeneration system are maintained at levels which provide a dense-phase fluidized bed of particulate catalyst in the regeneration zone. Fluid bed operation can be accomplished in a conventional manner by maintaining upward superficial gas velocities appropriate to the size and density of catalyst particles undergoing regeneration and by maintaining catalyst introduction and withdrawal rates at proper levels. The operating pressure in the regenerator is usually not particularly critical. Absolute pressures of 1-2n atmospheres are generally quite suitable. Pressures of 1.5-5 atmospheres are preferred.
It will be apparent to those skilled in the art that the amount: of coke contained in spent, deactivated catalyst, as well as the concentrations of sulfur and nitrogen in the coke, will vary widely depending on such factors as the composition and boiling range of the hydro-carbon feed with which the catalyst has previously been ~Z~5;2 01 contacted, the composition of the catalyst, the type of hydrocarbon conversion or treatment system in which the catalyst is used (e.~., moving bed, fluid bed, entrained bed), etc. The benefits of regeneration according to the 05 invention can be obtained with coke-containiny catalysts which have a coke concentration varying over a broad range and for catalysts contaminated with coke having sulfur and nitrogen contents which can vary over a broad range.
In one embodiment of the invention, a dense-phase fluidized bed of substantially coke-free particulate catalyst is preferably maintained in a regeneration zone, such as an app!ropriate vessel, chamber, or the like. The average carbon content of the catalyst particles in a dense-phase bed as a whole, when a dense-bed regeneration is employed, is preferably less than 0.2 weight percent.
Particularly preferably, the average concentration of coke carbon present in the catalyst particles in a dense-phase bed as a whole is less than 0.1 weight percent. In carrying out regeneration in a dense-phase bed system, coke-containing, deactivated catalyst is preferably introduced into the dense-phase fluidized bed at a con-trolled rate, and substantially coke-free catalyst is removed from the fluidized bed at a rate appropriate to maintain the bed at the desired size, density, and average particle coke content. Preferably, coke-containing, spent catalyst parti~les are introduced into a relatively lower level of the dense-phase fluidized bed, and the substan-tially coke-free catalyst particles are removed from a relatively higher level of the bed. Because of the high turbulence and good overall mixing inherent in the fluid-ized bed system, however, catalyst present in any portion of the fluidized bed includes a minor proportion of partially regenerated catalyst particles mixed with a major proportion of substantially completely coke-free particles. Co]ce-containing catalyst is preferably ~ z~z 01 introduced into the regeneration zone at a rate low enough so that the average coke content of catalyst particles in the bed as a whole is not raised above 0.2 weight percent, and preferably not above 0.1 weight percent. That is, 05 catalyst withdrawn from any part of the bed is, as a whole, substantially coke-free.
In the embodiment using a dense-phase fluidized bed, a regeneration and fluidizing gas including free oxygen is preferably introduced into the lower end of the dense-phase fluidized bed. Regeneration gas is passed upwardly through the bed, removed from the upper end of the bed and withdrawn from the regeneration zone. Enough free oxygen is preferably introduced into the bed to provide an oxidizing atmosphere containing at least one volume percent free oxygen in all parts of the dense-phase fluidized bed, as well as in the flue gas removed from the regeneration zone. Of course, the lowest average free oxygen concentration will normally be found in the flue gas portion of the regeneration gas, since it is furthest downstream in the regeneration gas pathway. Likewise, the maximum temperature is usually found in the regeneration gas downstream from the dense-phase bed. Preferably, the regeneration gas introduced to the regenerator contains enough free ox~ygen to provide at least 2 volume percent free oxygen in the regeneration gas in all parts of the dense-phase bed and in the regeneration gas downstream of the dense-phase bed (flue gas).
A carbon monoxide combustion promoter is pref-erably included in admixture with the catalyst particles, e.g., in the dense-phase fluidized bed in preferably an amount necessary to provide combustion, preferably within a dense-phase bed, of su]bstantially all carbon monoxide generated by coke burning. Sufficient carbon monoxide is preferably burned within the regeneration zone so that regeneration gas removed from the regeneration zone (i.e., 5;2 01 flue gas) contains less than 0.5 volume percent carbon monoxide. Preferably, sufficient carbon monoxide is burned within the dense-phase bed in the regenerator to provide less than 0.05 volume percent carbon monoxide in 05 the flue gas.
Conventional carbon monoxide combustion promo-ters can be usled, if necessary, to provide adequate com-bustion of carbon monoxide. Most transitional metals and their oxides are to some extent active for promoting carbon monoxidle combustion. Preferred carbon monoxide combustion promoters are metals or compounds of metals selected from ruthenium, rhodium, palladium, iridium, platinum, copp~er, chromium and manganese. Platinum is a particularly preferred carbon monoxide combustion promoter.
When a carbon monoxide combustion promoter is used in the embodiment carried out with a dense-phase fluidized bed, the amount of promoter employed is pref-erably an amount sufficient to provide complete carbon monoxide combustion within the dense-phase bed. Complete carbon monoxide conversion within a dense-phase fluidized bed is indicated, for example, by (1) the substantial absence of carbon monoxide in flue gas withdrawn from the regeneration zone, and (2) a maximum temperature in regeneration gas above (downstream from) the dense-phase catalyst bed which is not more than 27C above the maximum temperature of the regeneration gas in the dense-phase bed. Preferably, the maximum temperature of the regen-eration gas downstream from the dense-phase bed does not exceed 15C above the maximum temperature of regeneration gas in the dense-phase catalyst bed. Of course, the maximum temperature of the regeneration gas above the dense-phase bed may suitably be lower than the maximum dense-phase gas temperature, althouqh this is not a typical mode of operation unless extraneous cooling is c~
01 employed. Since these concurrent conditions, i.eO, (l) low flue gas C() concentration and (2) relatively low maximum downstream regeneration gas temperature, indicate essentially connplete carbon monoxide burning in a dense-05 phase bed, the prior art teachings as to the use of carbonmonoxide combustion promoter provide no incentive to use any combustion promoter if use of a promoter is not neces-sary to obtain complete combustion. Likewise, the prior art provides no incentive to employ a greater concentra-tion of combusl:ion promoter than necessary to obtaincomplete, dense-phase bed combustion when a combustion promoter is us~d, and, in fact, the art teaches that use of more than the necessary amount of promoter is detrimen-tal because of the adverse effect on the hydrocarbon conversion SteE)-According to another aspect of the invention,sulfur oxides iormed by co~e burning are removed from the regeneration gas within the regeneration zone by reacting at least the sulfur trioxide with reactive alumina. The alumina useful for the reaction may be included in all or a portion of the catalyst present in the regeneration zone or may be inclllded in essentially catalytically inert particles present in the regeneration zone in physical mixture with the catalyst. Suitable alumina is not in intimate combination with more than 40 weight percent silica and is preferably substantially free from silica in intimate combination. Suitable alumina has an average ~surface area oi- at least 50 square meters per gram, preferably at ]east lO0 square meters per gram. Alurnina is suitable for use in carrying out the invention if it contains an average of more than about 50 parts per million (weighl:) of "reactive alumina", as determined by treating particles containing the alumina by the following steps:
Z~5;2 01 tl) passing a stream of a gas mixture containing, by volume, 10~ wat:er, 1% hydrogen sulfide, 10~ hydrogen and 79% nitrogen over the alumina-containing particle continu-ously at a temperature of 1200F and atmospheric pressure 05 until the weight of the particle is substantially con-stant;
(2) passing a stream of a gas mixture containing, by volume, 10% wat:er, 15% carbon dioxide, 2% oxygen and 73%
nitrogen over t:he particle resulting from step (1) at a temperature of 1200F and atmospheric pressure until the weight of the particle is substantially constant, the weight of the particle at this time heing designated "Wa";
and (3) passing a stream of a gas mixture containing, by volume, 0.05% sulfur dioxide, and, in addition, the same gases in the same proportions as used in step (2), over the particle resulting from step (2) at a temperature of 1200F and atmospheric pressure until the weight of the particle is substantially constant, the weight of the particle at this time being designated "Ws".
The ~eight fraction of reactive alumina in the solid particle" designated "Xa", is determined by the formula Xa = Ws-Wa x Molecular Wt. Alumina Wa 3 x Molecular Wt. Sulfur Trioxide Various known and commercially available crack-ing catalysts include a sufficient concentration of reac-tive alumina to be at least somewhat useful in carrying out some embodiments of the invention, particularly those catalysts which include a preponderance of alumina in their overall composition. On the other hand, many conventional-a:Lumina-containing catalysts contain substantially no reactive alumina. Most, if not all, conventional catalysts include both silica and alumina.
It is felt thal~ the substantial absence of reactive 01 alumina in man~r alumina-containing catalysts is the result of intimate connbination of silica and alumina in the cata-lysts, especia]ly cracking catalysts containing 50 weight percent or more silica, which tends to combine intimately OS with alumina in a manner that renders the alumina rela-tively inactive for reaction with sulfur oxides.
Cata]ysts containing a relatively large amount of alumina present as a discrete phase (free alumina) can be prepared by employing starting materials containing 5n~-60% or more of alumina or an alumina precursor, as well as by forming catalyst from materials such as clays known to contain at least some discrete, free alumina.
See for example, U.S. Patent No. 4,166,787. A discrete alumina phase, including reactive alumina, can be added to a previously mcide catalyst by impregnation as described in U.S. Patent No 4,115,249.
When discrete, alumina-containing particles are mixed with the catalyst particles in order to supply reac-tive alumina, l:he alumina-containing particles are prefer-ably substantially free from silica. Discrete alumina-containing parl:icles may contain more than 50 ppm (weight)of reactive alumina. The alumina content of the particles is generally alc least 60 weight percent and preferably at least 90 weighl: percent. A preferred form of alumina is gamma alumina. Alpha alumina is unsuitable, because of its low surface area and lack of reactivity.
According to one preferred embodiment of the invention, a sulfur dioxide combustion promoter is included in a dense-phase fluidized bed of the catalyst in an amount sufficient to provide substantial incremental conversion of sulfur dioxide to sulfur trioxide within the dense-phase fluidized bed. The prior art provides no incentive to include a combustion promo~er of any kind in a regenerator in which substantially all carbon monoxide is already being burned in a dense-phase fluidized bed.
~2~5'~
01 For example, when a carbon monoxide combustion promoter, such as platinum, is employed, the art teaches the desirability oi adding as small an amount of promoter as necessary to obtain complete carbon monoxide conversion.
05 From the standpoint of the prior art, use of as little promoter as necessary is justified on both technical and economic grounds. Technically, addition of more hydro-genation/dehydrogenation activity to a catalyst is widely taught to be undesirable because of the expected increase in coke and hydrogen formation in the cracking step.
Economically, l:he art provides no justification for using more combustion promoter than necessary to accomplish the goal recognized by the art, i.e., complete burning of carbon monoxide, so that use of additional combustion promoter would be merely an unjustified expense to the refiner.
Regenerator conditions sufficient to provide complete combu!~tion of carbon monoxide in a cracking catalyst reyenerator, whether or not burning is aided by a carbon monoxide combustion promoter, will normally result in some degree of combustion of sulfur dioxide to form sulfur trioxide. Since the total amount of sulfur dioxide formed in the regeneration zone is extremely small rela-tive to the amount of carbon monoxide formed, it is reasonable to expect that regeneration conditions suffi-cient to cause burning of substantially all carbon mon-oxide in a regenerator would be inherently sufficient to burn most of the sulfur dioxide to form sulfur trioxide.
Contrary to the teachings of the art as to the effect of carbon monoxide combustion promoters, and con-trary to expectations regarding the degree of sulfur di-oxide combustion in a complete CO-combustion system, I
have found that inclusion of a sulfur dioxide combustion promoter in a regenerator, in conjunction with, and in addition to, regeneration conditions (with or without ~ ~52~52 01 carbon monoxide combustion promoters) sufficient to achieve substantially complete combustion of carbon monoxide within the dense-phase bed, results in a striking enhancement of sulfur dioxide combustion. Moreover, when 05 free alumina is included in the particulate solids in the regenerator, inclusion of the sulfur dioxide combustion promoter also results in a striking and unexpected decrease in the sulfur oxides content of flue gas removed from the catalyst regenerator, as compared to the same regeneration system without the sulfur dioxide combustion promoter.
A su:Lfur dioxide combustion promoter may be included in the particulate solids in the regenerator in an amount sufficient to provide a substantially increased conversion of ~3ulfur dioxide to sulfur trioxide and a substantial decrease in the amount of sulfur oxides in flue gas leaving the regenerator, relative to the sulfur dioxide combusltion flue gas and sulfur oxides concentra-tion achieved ~ith regeneration conditions tWith or without use of a carbon monoxide combustion promoter) sufficient to provide complete carbon monoxide combustion in the dense-phase bed. A sufficient amount of the sulfur dioxide combustion promoter is preferably included in the regenerator to incrementally decrease the sulfur oxides concentration in the flue gas leaving the regeneration zone by at lea~st 10 percent (calculated as SO2), relative to SOx removal in a conventional complete CO combustion mode of operation. Particularly preferably, a sufficient amount of the <;ulfur dioxide combustion promoter is included with the solids in the re~enerator to decrease the sulfur oxides content of the flue gas leaving the regenerator by at least 50 percent.
Conventional sulfur dioxide oxidation promoters can be used. Most transition metals and metal compounds such as the ox:ides are to some extent active for promoting ~f~G52 01 combustion (or oxidation) of sulfur dioxide to sulfur tri-oxide. Preferred sulfur dioxide combustion promoters are metals or compounds of metals selected from ruthenium, rhodium, palla<3ium, iridium, platinum, copper, chromium, 05 manganese and ~anadium. Platinum is a particularly preferred sulfur dioxide combustion promoter.
The sulfur dioxide oxidation promoter may be present in a portion of the catalyst particles. It may also be present in essentially cataiytically inert parti-cles physically mixed with the catalyst particles. TheS2 combustion promoter may also be present in the bed in fixed or combined form such that it remains within the regeneration zone, rather than being introduced and withdrawn along with the catalyst particles and alumina particles.
Further according to the present invention, the amount of nitrogen oxides present in regeneration (flue) 7as removed from the catalyst regeneration zone is decreased by maintaining the re~eneration gas at a tem-perature above 760C for at least l second. Preferably, the flue gas, after removal from the re~enerator, is heated to a temperature of ~00C to 1050C. Preferably, flue gas resid~ence time in the heat treatment is main-tained between 2 and lO seconds.
The heating step may be performed by direct or indirect heat introduction. Preferably, heating is carried out by direct heat introduction, as by mixing a fuel (and free oxygen, if necessary) with the flue gas and combusting the fuel to increase the temperature of the flue ~as to the desired level. Combustion may, for example, be carried out in a boiler of conventional design, by mixing the flue gas with fuel and air or by combusting fuel gas and air in a conventional burner and mixing the resulting hot mixture of combusted fuel and air with the flue 7as.
01 PREFERRED EMBODIME~T
The invention can best be further explained by reference to the preferred embodiment shown in the attached drawing.
05 The invention is preferably employed in a system for burning co]ce off spent FCC catalyst. The catalyst is preferably one containing 0.1 to 60 weight percent of a zeolite component and a matrix or binder containing silica and alumina, particularly preferably a matrix with more than 50 weight percent alumina, and having a substantial concentration of reactive alumina. A dense-phase fluidized bed of substantially coke-free (averaging less than 0.1 weight percent coke) FCC catalyst particles is maintained in the regeneration vessel 1. The particles in the fluidized bed have an average carbon concentration of less than 0.1 ~weight percent, so that the concentration of carbon on regenerated catalyst removed through the conduit 5 is less than 0.1 weight percent. Spent catalyst containing about 0.5 weight percent coke is introduced into the bed through the conduit 3 and regenerated catalyst is withdrawn through the conduit 5 at essentially the same rate. Coke in the spent catalyst has a sulfur concentration of about 1.0 weight percent and a nitrogen concentration of about 1.0 weight percent. Regeneration conditions are first adjusted to provide essentially complete combustion of coke in the dense-phase fluidized bed and carbon monoxrde in the regeneration gas, with flue gas leaving the regenerator at a temperature substantially below 735C. Sufficient free oxygen is introduced into the bed through the distributor 11 to burn essentially all the coke off the spent catalyst and to maintain the average carbon content of catalyst in the bed at less than 0.1 weight percent, i.e., substantially coke-free cata-lyst. Essentially all the carbon monoxide generated in the bed 7 is burned within the dense-phase bed, so that ~2~52 01 the temperature difference hetween the gas in the bed 7 and the flue gas entering the cyclone 17 is less than 10C
and the flue gas removed from the regenerator through the conduit 21 contains less than 0.05 volume percent carbon 05 monoxide. Sufficient excess free oxygen is introduced into the bed 7 so that the flue gas in the conduit 21 contains at least 2 volume percent free oxygen. A carbon monoxide combu,stion-promoting additive comprising 0.1 weight percent platinum on alumina particles is mixed with the catalyst particles in the bed 7 in an amount suffi-cient to provide substantially complete combustion of carbon monoxide within the dense-phase bed 7 and to main-tain the maximum temperature of the regeneration gas in the dilute-phase region of the regenerator at below 27C
above the temperature of the regeneration gas in the bed 7. Preferably, the maximum temperature in the dilute-phase region iS maintained within 10C above or below the maximum temperature in the dense-phase bed 7. Preferably, the temperature in the bed 7 is maintained at about 677C. Preferably, the temperature of the regeneration gas (flue gas) above the bed 7 is maintained below 704C, especially preferably below 687C. Typically, the above conditions are maintained by a nominal catalytically active platinum concentration, based on total circulating solids inventory, of about 0.1-1 ppm (weight). Under these regenera~ion conditions, the concentration of sulfur oxides in the regeneration gas in the conduit 21 is found to be about 300 ppm (volume). The rate of flow of nitro-gen oxides in the conduit 21 is found to be about 160 pounds per hour, calculated as ~2~ equivalent to about 400 ppm (vol.) concçntration. A sulfur dioxide combustion - promoter is next added to the catalyst particles in the bed 7 in an amount sufficient to cause substantial conver-sion of sulfur dioxide to sulfur trioxide and to decrease substantially ~he concentration of sulfur oxides ~ ~Z052 in the regeneration gas. A su~fic1ent amount of a sulfur dioxide combustion promoter comprising 0.1 weight percent platinum on alumina i.s added to the catalyst ln the bed 7 to maintain a nominal platinum concentration of 10 ppm (weight) in the solids in the becl 7. ~pray-dried particles of alumina are also added to the fluidi2ed bed in an amount sufficient to main-tain 10 weight percent alumina in the bed. After addition of the sulfur dioxide combustion promoter and alumina particles, the sulfur oxides concentration in the flue gas in the conduit 21 is found to be only about 65 ppm (volume).
The rate oi flow oE nitrogen oxides in the flue gas in the conduit 21 is again measured and found to be about 200 pounds per hour calculated as ~2 (equivalent to about 500 ppm (vol.) concentration). The flue gas is then ~assed into a boiler and heated to a temperature of about 870C by firing fuel gas. The flue gas is held at the elevated temperature in the boiler for about 5 seconds and then released. The rate of flow of nitrogen oxides in the gas in the conduit 21 is measured and found to be about 50 pounds per hour above that for the boiler operating without flue gas addition (equivalent to only about 125 ppm (vol.) concentration with respect to the flue gas with-drawn from the regenerator through the conduit 21).
A preferrecl embodiment of the invention having been described, a number of equivalents and modifications of the illustrated embodiment will be apparent to those skilled in the art. These alternatives are intended to be within the scope of the invention, as defined in the appended claims.
~' ~,...
Belgian Patent Publication No. 820,181 discloses the use of cracking catalyst particles containing a Group VIII noble metal or rhenium to provide CO combustion dur-ing regeneration o~- the catalyst. The combustion promoter is used in an amount of a trace to 100 ppm. No. 820,181 teaches that including such combustion promoting metals in the catalyst results in an increase in formation of coke and hydrogen when the catalyst is employed for hydrocarbon cracking.
U.S. Patents No. 4,072,600 and No. 4,093,535 disclose the addition of trace amounts of Group VIII noble metals or rhenium to a cracking catalyst inventory in order to enhance combustion of CO in a catalyst regenera-tor. These patents teach that it is well known that the presence of a hydrogenation/dehydrogenation component in a cracking catalyst is detrimental to the cracking process because of the resulting undesirable increase in coke and hydrogen formation in cracking. The patents teach that detrimental results are caused by the reaction conditions employed in a cracking reactor, which favor undesirable reactions. According to these patents, ideally, the least ~2Q52 01 possible amount of the carbon monoxide combustion promo-ting metal necessary to convert the desired amount of CO
to CO2 should be used, since this ideal least possible amount would have the least adverse effect on the hydro-OS carbon cracking step. According to these patents, mini-mization of the concentration of the carbon monoxide combustion promoter in a catalytic cracking system can be accomplished by monitoring the flue gas leaving the cata-lyst regenerator and adjusting the rate of addition of combustion promoter such that the least amount of promoter necessary to completely burn carbon monoxide is added.
U.S. Patent No. 4,153,535 discloses a cyclic fluidized cracking process using a zeolite-type cracking catalyst, a metallic reactant (which reacts with sulfur oxides) selected from sodium, magnesium, calcium, stron-tium, barium, scandium, titanium, chromium, molybdenum, manganese, cobalt, nickel, antimony, copper, zinc, cad-mium, lead, the rare earth metals (more than 20 elements), their compounds and mixtures thereof, and a metallic oxi-dation promoter selected from ruthenium, rhodium, palla-dium, osmium, iridium, platinum, vanadium, tungsten, ura-nium, zirconium and silver. A similar system is disclosed in U.S. Patent No. 4,240,899.
Representative catalyst regeneration patent literature is shown in the following patents: U.S. Patent No. 3,909,392 describes a scheme for enhancing carbon monoxide combustion by thermal means. Catalyst is used to provide a heat sink in the dilute phase above a fluidized bed for the increased heat production. British Patent Publication 2,001,545 describes a two-stage system for a regenerating catalyst, with partial catalyst regeneration being carried out in the first stage and secondary, more complete regeneration carried out in the second stage ~ith a separate regeneration gas. U.S. Patent ~o. 3,767,566 describes a two-stage regeneration scheme in which partial sz 01 regeneration takes place in an entrained catalyst bed, and secondary, more complete regeneration takes place in a dense fluidized catalyst bed. A somewhat similar regener-ation operation is described in U.S. Patent No. 3,902,990, 05 which discusse.s the use of several stages of regeneration, with dilute and dense-phase beds of catalysts being employed, and with the use of plural streams of regenera-tion gas. U.S. Patent No. 3,926,843 describes a plural-stage regeneration scheme in which dilute phase and dense-phase coke burning are performed. British PatentPublication No. 1,499,682 discloses use of a combustion-promoting metal for enhancing carbon monoxide combustion.
It has been suggested, e.g., in U.S. Patent No.
3,699,037, to reduce the amount of sulfur oxides in FCC
regenerator flue gas by adding particles of Group IIA
metal oxides and/or carbonates, such as dolomite, MgO or CaCO3, to the circulating catalyst in an FCC unit. The Group IIA metals react with sulfur oxides in the flue gas to form solid sulfur-containing compounds. The Group IIA
metal oxides lack physical strength. Regardless of the size of the particles introduced, they are rapidly reduced to fines by attrition and rapidly pass out of the FCC unit with the catalyst fines. Thus, addition of dolomite and the like Group IIA materials is essentially a once-through process, and relatively large amounts of material must be continuously added in order to reduce the level of flue gas sulfur oxides.
It has also been suggested, e.g., in the U.S.
Patent 3,835,031, to reduce the amount of sulfur oxides in an FCC regenerator flue gas by impregnating a Group IIA
metal oxide onto a conventional silica-alumina cracking catalyst. The attrition problem encountered when using unsupported Group IIA metals is thereby reduced. However, it has been found that Group IIA metal oxides, such as magnesia, when used as a component of cracking catalyst, 01 have a rather pronounced undesirable effect on the activ-ity and selectivity of the cracking catalysts. Such unde-sirable effects are particularly apparent when the magne-sium compound is used in an amount sufficient to appre-05 ciably diminish the amount of sulfur oxides in the fluegas. The addition of a Group IIA metal to a cracking catalyst results in two particularly noticeable adverse consequences relative to the results obtained in cracking without the presence of the Group IIA metals: (1) the yield of the liquid hydrocarbon fraction is substantially reduced, typically by greater than 1 volume percent of the feed volume; and (2) the octane rating of the gasoline or naphtha fraction (75-430F boiling range) is substan-tially reduced. Both of the above-noted adverse conse-quences are seriously detrimental to the economic viabil-ity of an FCC cracking operation, so that even complete removal of sulfur oxides from regenerator flue gas would not normally compensate for the simultaneous losses in yield and octane which result from adding Group IIA metals to an FCC catalyst. The same can generally be said for the numerous reactant metals disclosed as sulfur oxides reactants in U.S. Patent No. 4,153,535, discussed above.
Alumina has been a component of many FCC and moving-bed cracking catalysts, but normally in intimate chemical combination with silica. Alumina itself has low acidity and is generally considered to be undesirable for use as a cracking catalyst. The art has taught that alu-mina is not selective, i.e., the cracked hydrocarbon prod-ucts recovered from an FCC or other cracking unit using an alumina catalyst would not be desired valuable products, but would include, for example, relatively large amounts of C2 and lighter hydrocarbon gases.
U.S. Patent No. 4,071,436 discloses the use of alumina for reducing the amount of sulfur oxides in the flue gas formed during cracking catalyst re~eneration.
s~s~
01 The alumina can be used in the form of a particulate solid mixed with cracking catalyst particles. In some cases, alumina contained in the cracking catalyst particles is also suitable, however, alumina contained in conventional 05 cracking catalyst is usually not very active, since it is intimately mixed with a large fraction of silica.
U.S. Patents No. 4,115,250 and No. 4,115,251 disclose the synergistic use of oxidation-promoting metals for carbon monoxide burning in combination with the use of alumina for re<3ucing the amount of sulfur oxides in crack-ing catalyst regenerator flue gas. When alumina and highly active oxidation-promoting metals are both included in the same particle, alumina in the particle is rela-tively ineffecl:ive for removing sulfur oxides from the regenerator flue gas, especially in the presence of even a small amount of carbon monoxide. On the other hand, when the alumina and combustion-promoting metal are used on separate particles circulated together in a cracking system in physical admixture, the ability of the alumina to reduce the level of sulfur oxides in the flue gas can be considerably enhanced.
One problem encountered in some cracking opera-tions using met:al-promoted complete carbon monoxide com-bustion-type regeneration has been the generation of unde-sirable nitrogen oxides (NOX) in the flue gas formed byburning coke. For example, U.S. Patent Wo. 4,235,704 discloses a mel:hod for controlling nitrogen oxides by adjusting the concentration of carbon monoxide combustion promoter in re]Lation to the level of nitrogen oxides in flue gas exiting a catalyst regenerator. In many cases, however, it is desired to have a larger amount of comhus-tion promoter present, than could be feasible in the '704 patent method. The present invention is directed, in part, toward providing a catalyst regeneration system which accomplishes a high degree of coke removal and )5Z
01 complete carbon monoxide combustion within a catalyst regeneration system, while substantially decreasing the concentration of nitrogen oxide present in flue gas formed by burning the coke, without recourse to overly restric-05 tive limitations on the use of combustion promoters.
SUMMARY OF ~HE INVENTION
I have found that a particulate catalyst whichhas been contaminated by sulfur-containing and nitrogen-containing coke deposition can be regenerated by burning off sufficient coke to provide an essentially carbon-free, regenerated catalyst, and a flue gas free from carbon monoxide, nitrogen oxides and sulfur oxides can be formed in carrying out the regeneration by (a) passing a regener-ation gas including free oxygen upwardly through a dense-phase fluidized bed of particulate solids comprising sub-stantially coke-free particles of the catalyst in a regen-eration zone, and removing the regeneration gas from the regeneration zone; (b) introducing the coke-containin~
catalyst particles into the bed and generating carbon oxides, nitrogen oxides and sulfur oxides in the bed by burning the coke; (c) burning sufficient carbon monoxide within the bed to maintain regeneration gas above the bed at a temperature below 735C and not higher than 27C
above the maximum temperature of regeneration gas within the bed and to provide a carbon monoxide concentration of less than 0.5 volume percent in regeneration gas removed from the regeneration zone, and introducing sufficient free oxygen in~o the bed to provide at least 1 volume percent free oxygen in regeneration gas removed from the regeneration zone; (d) including in the particulate solids an amount of a sulfur dioxide combustion promoter suffi-cient to provide substantial incremental conversion of sulfur dioxide to sulfur trioxide within the bed; (e) including reaclive alumina in the particulate solids, and decreasing the amount of sulfur oxides in regeneration gas _9_ 0l removed from the regeneration zone by forming a sulfur-containing and aluminum-containing solid from the sulfur trioxide and the reactive alumina; and (f) removing regen-eration gas from the regeneration zone and decreasing the 05 amount of nitrogen oxides in the regeneration gas by main-taining the regeneration gas at a temperature above 760Cfor at least l second.
In another embodiment of the invention, I have found that a particulate catalyst which has been contam-inated with su]fur-containing and nitrogen-containing coke can be regenerated, and a flue gas with decreased levels of carbon monoxide, nitrogen oxides and sulfur oxides can be formed in carrying out the regeneration by (a) forming carbon monoxide, gaseous sulfur oxides and gaseous nitrogen oxides by reacting free oxygen with the coke in a regeneration zone; (b) decreasing the amount of the carbon monoxide by reactïng the carbon monoxide with free ox~gen in the regeneration zone in the presence of a carbon monoxide combustion promoter; (c) decreasing the amount of the gaseous su].fur oxides and forming a sulfur-containing solid in the regeneration zone by reacting the sulfur oxides with reactive alumina contained in a substantially silica-free particulate solid other than the catalyst present in the regeneration zone in physical admixture with the catalyst; and (d) withdrawing gas including the nitrogen oxides from the regeneration zone at a temperature be]ow 735C and decreasing the amount of the nitrogen oxidec; by maintaining the gas at a temperature above 760C for at least one second outside the regeneration zone.
DESCRIPTION OF THE DRAWING
The attached drawing is a schematic representa-tion of one preferred embodiment of the present invention.
Referring to the drawing, there is shown a regeneration vessel 1. Coke-containing catalyst is introduced into the vessel 1 through a conduit 3, and substantially coke-free catalyst is removed by way of a conduit 5. A dense-phase fluid-ized bed 7 of substantially coke-free catalyst is maintained in the vessel 1. Regeneration gas is introduced into the lower end of the vessel through a conduit 9 and discharged into the re-generation zone through a distributor 11. The regeneration gas passes upwardly through a distribution grid 13, through the fluidized bed 7, and out of the upper end of the dense-phase bed, indicated by a line at 15 in the drawing. Substantially all the coke in the spent and partially regenerated catalyst present in the fluidized bed is ~preferably burned with free oxygen intro-duced in the regeneration gas. Regeneration gas (flue gas) leaving the top 15 of the bed 7 passes into a cyclone separator 17. Entrained solids are s~perated from the flue gas in the cyclone and returned to the dense-phase catalyst bed through a dipleg 19. The flue gas is then withdrawn from the vessel 1 at a temperature below 735C thro~gh a conduit 21 and passed into a furnace (not shown) to decrease its nitrogen oxides con-centration. Fuel gas and oxygen are introduced into the furnace and burned in admixture with the flue gas to heat the flue gas to a temperature above 760C. After an appropriate residence time at a temperature above 760C in the furnace flue gas with a reduced nitrogen oxides content is removed. Conventional elements of the embod:Lment depicted, such as controlling means, pumping and valve means, and the li]ce, are not shown in the drawing and are not described in order to simplify the explan-ation. The use and disposition of such elements will be clear to those skilled in the art.
~ - 10 -ClS2 As used herein, the term "substantially coke-free catalyst" refers to catalyst which contains less than 0.2 weight percent carbon.
05 As used herein, the term "dense-phase fluidized bed" means a f:Luidized bed of particulate solids having a density of at :Least 12 pounds per cubic foot.
As used herein, the term "regeneration gas"
includes the gas mixtures (e.g., air) introduced to the catalyst regenerator, the gas mixtures present in the regenerator, and the gas mixtures removed from the regenerator (i.e., flue gases).
Cata:Lysts that are best adapted for regeneration according to this invention are those in the form of par-ticulate solids. Preferably, catalyst to be regenerated is sized appropriately for catalytic use in an entrainedbed or flui~ized bed catalytic conversion system. With reference to the types of catalytic hydrocarbon conversion operations pre~3ently practiced commercially, this inven-tion is especially advantageous for regeneration of FCC
catalysts; however, use of the invention is not limited to FCC catalyst regeneration operations, and can be used for treating any coke-contaminated particulate catalyst which can be wholly or partially reactivated by coke burnoff.
A regeneration zone employed in carrying out the invention may be supplied by a suitable vessel or chamber, capable of conlain~ng regeneration gas and catalyst particles at the desired temperature and pressure. Suit-able vessels and chambers will be readily apparent to those skilled :in the art from the description herein.
Co~ventional F(~C cracking catalyst regeneration vessels and chambers, i-or example, can suitably be employed.
The regeneration gas or gas mixture introduced into the catalyst regenerator must provide an appropriate free oxygen (molecular oxygen) supply to the regenerator.
~Z~52 01 Normally, air is quite suitable for use in supplying free oxygen, but use of air is not essential. For example, pure oxygen or oxygen-enriched air can also be used, if desired. Conventional gases present in commercial FCC
OS operations, suc:h as free nitrogen (molecular nitrogen), carbon dioxide, steam, and the like, may suitably be present in fluidizing and entrainment gases.
In general, regeneration conditions maintained in the regenerator include a combination of temperature and pressure sufficient to permit the specified or desired degree of coke combustion, carbon monoxide combustion and sulfur dioxide combustion to take place, in the manner discussed herein. The temperature of the regeneration gas is maintained below 735C. Temperatures of 540C-735C
are normally quite suitable. Temperatures of 590C-730C
are preferred. Preferably, the rates of flow of regen-eration gases, entrainment gases and particulate solids such as catalyst particles through the regeneration system are maintained at levels which provide a dense-phase fluidized bed of particulate catalyst in the regeneration zone. Fluid bed operation can be accomplished in a conventional manner by maintaining upward superficial gas velocities appropriate to the size and density of catalyst particles undergoing regeneration and by maintaining catalyst introduction and withdrawal rates at proper levels. The operating pressure in the regenerator is usually not particularly critical. Absolute pressures of 1-2n atmospheres are generally quite suitable. Pressures of 1.5-5 atmospheres are preferred.
It will be apparent to those skilled in the art that the amount: of coke contained in spent, deactivated catalyst, as well as the concentrations of sulfur and nitrogen in the coke, will vary widely depending on such factors as the composition and boiling range of the hydro-carbon feed with which the catalyst has previously been ~Z~5;2 01 contacted, the composition of the catalyst, the type of hydrocarbon conversion or treatment system in which the catalyst is used (e.~., moving bed, fluid bed, entrained bed), etc. The benefits of regeneration according to the 05 invention can be obtained with coke-containiny catalysts which have a coke concentration varying over a broad range and for catalysts contaminated with coke having sulfur and nitrogen contents which can vary over a broad range.
In one embodiment of the invention, a dense-phase fluidized bed of substantially coke-free particulate catalyst is preferably maintained in a regeneration zone, such as an app!ropriate vessel, chamber, or the like. The average carbon content of the catalyst particles in a dense-phase bed as a whole, when a dense-bed regeneration is employed, is preferably less than 0.2 weight percent.
Particularly preferably, the average concentration of coke carbon present in the catalyst particles in a dense-phase bed as a whole is less than 0.1 weight percent. In carrying out regeneration in a dense-phase bed system, coke-containing, deactivated catalyst is preferably introduced into the dense-phase fluidized bed at a con-trolled rate, and substantially coke-free catalyst is removed from the fluidized bed at a rate appropriate to maintain the bed at the desired size, density, and average particle coke content. Preferably, coke-containing, spent catalyst parti~les are introduced into a relatively lower level of the dense-phase fluidized bed, and the substan-tially coke-free catalyst particles are removed from a relatively higher level of the bed. Because of the high turbulence and good overall mixing inherent in the fluid-ized bed system, however, catalyst present in any portion of the fluidized bed includes a minor proportion of partially regenerated catalyst particles mixed with a major proportion of substantially completely coke-free particles. Co]ce-containing catalyst is preferably ~ z~z 01 introduced into the regeneration zone at a rate low enough so that the average coke content of catalyst particles in the bed as a whole is not raised above 0.2 weight percent, and preferably not above 0.1 weight percent. That is, 05 catalyst withdrawn from any part of the bed is, as a whole, substantially coke-free.
In the embodiment using a dense-phase fluidized bed, a regeneration and fluidizing gas including free oxygen is preferably introduced into the lower end of the dense-phase fluidized bed. Regeneration gas is passed upwardly through the bed, removed from the upper end of the bed and withdrawn from the regeneration zone. Enough free oxygen is preferably introduced into the bed to provide an oxidizing atmosphere containing at least one volume percent free oxygen in all parts of the dense-phase fluidized bed, as well as in the flue gas removed from the regeneration zone. Of course, the lowest average free oxygen concentration will normally be found in the flue gas portion of the regeneration gas, since it is furthest downstream in the regeneration gas pathway. Likewise, the maximum temperature is usually found in the regeneration gas downstream from the dense-phase bed. Preferably, the regeneration gas introduced to the regenerator contains enough free ox~ygen to provide at least 2 volume percent free oxygen in the regeneration gas in all parts of the dense-phase bed and in the regeneration gas downstream of the dense-phase bed (flue gas).
A carbon monoxide combustion promoter is pref-erably included in admixture with the catalyst particles, e.g., in the dense-phase fluidized bed in preferably an amount necessary to provide combustion, preferably within a dense-phase bed, of su]bstantially all carbon monoxide generated by coke burning. Sufficient carbon monoxide is preferably burned within the regeneration zone so that regeneration gas removed from the regeneration zone (i.e., 5;2 01 flue gas) contains less than 0.5 volume percent carbon monoxide. Preferably, sufficient carbon monoxide is burned within the dense-phase bed in the regenerator to provide less than 0.05 volume percent carbon monoxide in 05 the flue gas.
Conventional carbon monoxide combustion promo-ters can be usled, if necessary, to provide adequate com-bustion of carbon monoxide. Most transitional metals and their oxides are to some extent active for promoting carbon monoxidle combustion. Preferred carbon monoxide combustion promoters are metals or compounds of metals selected from ruthenium, rhodium, palladium, iridium, platinum, copp~er, chromium and manganese. Platinum is a particularly preferred carbon monoxide combustion promoter.
When a carbon monoxide combustion promoter is used in the embodiment carried out with a dense-phase fluidized bed, the amount of promoter employed is pref-erably an amount sufficient to provide complete carbon monoxide combustion within the dense-phase bed. Complete carbon monoxide conversion within a dense-phase fluidized bed is indicated, for example, by (1) the substantial absence of carbon monoxide in flue gas withdrawn from the regeneration zone, and (2) a maximum temperature in regeneration gas above (downstream from) the dense-phase catalyst bed which is not more than 27C above the maximum temperature of the regeneration gas in the dense-phase bed. Preferably, the maximum temperature of the regen-eration gas downstream from the dense-phase bed does not exceed 15C above the maximum temperature of regeneration gas in the dense-phase catalyst bed. Of course, the maximum temperature of the regeneration gas above the dense-phase bed may suitably be lower than the maximum dense-phase gas temperature, althouqh this is not a typical mode of operation unless extraneous cooling is c~
01 employed. Since these concurrent conditions, i.eO, (l) low flue gas C() concentration and (2) relatively low maximum downstream regeneration gas temperature, indicate essentially connplete carbon monoxide burning in a dense-05 phase bed, the prior art teachings as to the use of carbonmonoxide combustion promoter provide no incentive to use any combustion promoter if use of a promoter is not neces-sary to obtain complete combustion. Likewise, the prior art provides no incentive to employ a greater concentra-tion of combusl:ion promoter than necessary to obtaincomplete, dense-phase bed combustion when a combustion promoter is us~d, and, in fact, the art teaches that use of more than the necessary amount of promoter is detrimen-tal because of the adverse effect on the hydrocarbon conversion SteE)-According to another aspect of the invention,sulfur oxides iormed by co~e burning are removed from the regeneration gas within the regeneration zone by reacting at least the sulfur trioxide with reactive alumina. The alumina useful for the reaction may be included in all or a portion of the catalyst present in the regeneration zone or may be inclllded in essentially catalytically inert particles present in the regeneration zone in physical mixture with the catalyst. Suitable alumina is not in intimate combination with more than 40 weight percent silica and is preferably substantially free from silica in intimate combination. Suitable alumina has an average ~surface area oi- at least 50 square meters per gram, preferably at ]east lO0 square meters per gram. Alurnina is suitable for use in carrying out the invention if it contains an average of more than about 50 parts per million (weighl:) of "reactive alumina", as determined by treating particles containing the alumina by the following steps:
Z~5;2 01 tl) passing a stream of a gas mixture containing, by volume, 10~ wat:er, 1% hydrogen sulfide, 10~ hydrogen and 79% nitrogen over the alumina-containing particle continu-ously at a temperature of 1200F and atmospheric pressure 05 until the weight of the particle is substantially con-stant;
(2) passing a stream of a gas mixture containing, by volume, 10% wat:er, 15% carbon dioxide, 2% oxygen and 73%
nitrogen over t:he particle resulting from step (1) at a temperature of 1200F and atmospheric pressure until the weight of the particle is substantially constant, the weight of the particle at this time heing designated "Wa";
and (3) passing a stream of a gas mixture containing, by volume, 0.05% sulfur dioxide, and, in addition, the same gases in the same proportions as used in step (2), over the particle resulting from step (2) at a temperature of 1200F and atmospheric pressure until the weight of the particle is substantially constant, the weight of the particle at this time being designated "Ws".
The ~eight fraction of reactive alumina in the solid particle" designated "Xa", is determined by the formula Xa = Ws-Wa x Molecular Wt. Alumina Wa 3 x Molecular Wt. Sulfur Trioxide Various known and commercially available crack-ing catalysts include a sufficient concentration of reac-tive alumina to be at least somewhat useful in carrying out some embodiments of the invention, particularly those catalysts which include a preponderance of alumina in their overall composition. On the other hand, many conventional-a:Lumina-containing catalysts contain substantially no reactive alumina. Most, if not all, conventional catalysts include both silica and alumina.
It is felt thal~ the substantial absence of reactive 01 alumina in man~r alumina-containing catalysts is the result of intimate connbination of silica and alumina in the cata-lysts, especia]ly cracking catalysts containing 50 weight percent or more silica, which tends to combine intimately OS with alumina in a manner that renders the alumina rela-tively inactive for reaction with sulfur oxides.
Cata]ysts containing a relatively large amount of alumina present as a discrete phase (free alumina) can be prepared by employing starting materials containing 5n~-60% or more of alumina or an alumina precursor, as well as by forming catalyst from materials such as clays known to contain at least some discrete, free alumina.
See for example, U.S. Patent No. 4,166,787. A discrete alumina phase, including reactive alumina, can be added to a previously mcide catalyst by impregnation as described in U.S. Patent No 4,115,249.
When discrete, alumina-containing particles are mixed with the catalyst particles in order to supply reac-tive alumina, l:he alumina-containing particles are prefer-ably substantially free from silica. Discrete alumina-containing parl:icles may contain more than 50 ppm (weight)of reactive alumina. The alumina content of the particles is generally alc least 60 weight percent and preferably at least 90 weighl: percent. A preferred form of alumina is gamma alumina. Alpha alumina is unsuitable, because of its low surface area and lack of reactivity.
According to one preferred embodiment of the invention, a sulfur dioxide combustion promoter is included in a dense-phase fluidized bed of the catalyst in an amount sufficient to provide substantial incremental conversion of sulfur dioxide to sulfur trioxide within the dense-phase fluidized bed. The prior art provides no incentive to include a combustion promo~er of any kind in a regenerator in which substantially all carbon monoxide is already being burned in a dense-phase fluidized bed.
~2~5'~
01 For example, when a carbon monoxide combustion promoter, such as platinum, is employed, the art teaches the desirability oi adding as small an amount of promoter as necessary to obtain complete carbon monoxide conversion.
05 From the standpoint of the prior art, use of as little promoter as necessary is justified on both technical and economic grounds. Technically, addition of more hydro-genation/dehydrogenation activity to a catalyst is widely taught to be undesirable because of the expected increase in coke and hydrogen formation in the cracking step.
Economically, l:he art provides no justification for using more combustion promoter than necessary to accomplish the goal recognized by the art, i.e., complete burning of carbon monoxide, so that use of additional combustion promoter would be merely an unjustified expense to the refiner.
Regenerator conditions sufficient to provide complete combu!~tion of carbon monoxide in a cracking catalyst reyenerator, whether or not burning is aided by a carbon monoxide combustion promoter, will normally result in some degree of combustion of sulfur dioxide to form sulfur trioxide. Since the total amount of sulfur dioxide formed in the regeneration zone is extremely small rela-tive to the amount of carbon monoxide formed, it is reasonable to expect that regeneration conditions suffi-cient to cause burning of substantially all carbon mon-oxide in a regenerator would be inherently sufficient to burn most of the sulfur dioxide to form sulfur trioxide.
Contrary to the teachings of the art as to the effect of carbon monoxide combustion promoters, and con-trary to expectations regarding the degree of sulfur di-oxide combustion in a complete CO-combustion system, I
have found that inclusion of a sulfur dioxide combustion promoter in a regenerator, in conjunction with, and in addition to, regeneration conditions (with or without ~ ~52~52 01 carbon monoxide combustion promoters) sufficient to achieve substantially complete combustion of carbon monoxide within the dense-phase bed, results in a striking enhancement of sulfur dioxide combustion. Moreover, when 05 free alumina is included in the particulate solids in the regenerator, inclusion of the sulfur dioxide combustion promoter also results in a striking and unexpected decrease in the sulfur oxides content of flue gas removed from the catalyst regenerator, as compared to the same regeneration system without the sulfur dioxide combustion promoter.
A su:Lfur dioxide combustion promoter may be included in the particulate solids in the regenerator in an amount sufficient to provide a substantially increased conversion of ~3ulfur dioxide to sulfur trioxide and a substantial decrease in the amount of sulfur oxides in flue gas leaving the regenerator, relative to the sulfur dioxide combusltion flue gas and sulfur oxides concentra-tion achieved ~ith regeneration conditions tWith or without use of a carbon monoxide combustion promoter) sufficient to provide complete carbon monoxide combustion in the dense-phase bed. A sufficient amount of the sulfur dioxide combustion promoter is preferably included in the regenerator to incrementally decrease the sulfur oxides concentration in the flue gas leaving the regeneration zone by at lea~st 10 percent (calculated as SO2), relative to SOx removal in a conventional complete CO combustion mode of operation. Particularly preferably, a sufficient amount of the <;ulfur dioxide combustion promoter is included with the solids in the re~enerator to decrease the sulfur oxides content of the flue gas leaving the regenerator by at least 50 percent.
Conventional sulfur dioxide oxidation promoters can be used. Most transition metals and metal compounds such as the ox:ides are to some extent active for promoting ~f~G52 01 combustion (or oxidation) of sulfur dioxide to sulfur tri-oxide. Preferred sulfur dioxide combustion promoters are metals or compounds of metals selected from ruthenium, rhodium, palla<3ium, iridium, platinum, copper, chromium, 05 manganese and ~anadium. Platinum is a particularly preferred sulfur dioxide combustion promoter.
The sulfur dioxide oxidation promoter may be present in a portion of the catalyst particles. It may also be present in essentially cataiytically inert parti-cles physically mixed with the catalyst particles. TheS2 combustion promoter may also be present in the bed in fixed or combined form such that it remains within the regeneration zone, rather than being introduced and withdrawn along with the catalyst particles and alumina particles.
Further according to the present invention, the amount of nitrogen oxides present in regeneration (flue) 7as removed from the catalyst regeneration zone is decreased by maintaining the re~eneration gas at a tem-perature above 760C for at least l second. Preferably, the flue gas, after removal from the re~enerator, is heated to a temperature of ~00C to 1050C. Preferably, flue gas resid~ence time in the heat treatment is main-tained between 2 and lO seconds.
The heating step may be performed by direct or indirect heat introduction. Preferably, heating is carried out by direct heat introduction, as by mixing a fuel (and free oxygen, if necessary) with the flue gas and combusting the fuel to increase the temperature of the flue ~as to the desired level. Combustion may, for example, be carried out in a boiler of conventional design, by mixing the flue gas with fuel and air or by combusting fuel gas and air in a conventional burner and mixing the resulting hot mixture of combusted fuel and air with the flue 7as.
01 PREFERRED EMBODIME~T
The invention can best be further explained by reference to the preferred embodiment shown in the attached drawing.
05 The invention is preferably employed in a system for burning co]ce off spent FCC catalyst. The catalyst is preferably one containing 0.1 to 60 weight percent of a zeolite component and a matrix or binder containing silica and alumina, particularly preferably a matrix with more than 50 weight percent alumina, and having a substantial concentration of reactive alumina. A dense-phase fluidized bed of substantially coke-free (averaging less than 0.1 weight percent coke) FCC catalyst particles is maintained in the regeneration vessel 1. The particles in the fluidized bed have an average carbon concentration of less than 0.1 ~weight percent, so that the concentration of carbon on regenerated catalyst removed through the conduit 5 is less than 0.1 weight percent. Spent catalyst containing about 0.5 weight percent coke is introduced into the bed through the conduit 3 and regenerated catalyst is withdrawn through the conduit 5 at essentially the same rate. Coke in the spent catalyst has a sulfur concentration of about 1.0 weight percent and a nitrogen concentration of about 1.0 weight percent. Regeneration conditions are first adjusted to provide essentially complete combustion of coke in the dense-phase fluidized bed and carbon monoxrde in the regeneration gas, with flue gas leaving the regenerator at a temperature substantially below 735C. Sufficient free oxygen is introduced into the bed through the distributor 11 to burn essentially all the coke off the spent catalyst and to maintain the average carbon content of catalyst in the bed at less than 0.1 weight percent, i.e., substantially coke-free cata-lyst. Essentially all the carbon monoxide generated in the bed 7 is burned within the dense-phase bed, so that ~2~52 01 the temperature difference hetween the gas in the bed 7 and the flue gas entering the cyclone 17 is less than 10C
and the flue gas removed from the regenerator through the conduit 21 contains less than 0.05 volume percent carbon 05 monoxide. Sufficient excess free oxygen is introduced into the bed 7 so that the flue gas in the conduit 21 contains at least 2 volume percent free oxygen. A carbon monoxide combu,stion-promoting additive comprising 0.1 weight percent platinum on alumina particles is mixed with the catalyst particles in the bed 7 in an amount suffi-cient to provide substantially complete combustion of carbon monoxide within the dense-phase bed 7 and to main-tain the maximum temperature of the regeneration gas in the dilute-phase region of the regenerator at below 27C
above the temperature of the regeneration gas in the bed 7. Preferably, the maximum temperature in the dilute-phase region iS maintained within 10C above or below the maximum temperature in the dense-phase bed 7. Preferably, the temperature in the bed 7 is maintained at about 677C. Preferably, the temperature of the regeneration gas (flue gas) above the bed 7 is maintained below 704C, especially preferably below 687C. Typically, the above conditions are maintained by a nominal catalytically active platinum concentration, based on total circulating solids inventory, of about 0.1-1 ppm (weight). Under these regenera~ion conditions, the concentration of sulfur oxides in the regeneration gas in the conduit 21 is found to be about 300 ppm (volume). The rate of flow of nitro-gen oxides in the conduit 21 is found to be about 160 pounds per hour, calculated as ~2~ equivalent to about 400 ppm (vol.) concçntration. A sulfur dioxide combustion - promoter is next added to the catalyst particles in the bed 7 in an amount sufficient to cause substantial conver-sion of sulfur dioxide to sulfur trioxide and to decrease substantially ~he concentration of sulfur oxides ~ ~Z052 in the regeneration gas. A su~fic1ent amount of a sulfur dioxide combustion promoter comprising 0.1 weight percent platinum on alumina i.s added to the catalyst ln the bed 7 to maintain a nominal platinum concentration of 10 ppm (weight) in the solids in the becl 7. ~pray-dried particles of alumina are also added to the fluidi2ed bed in an amount sufficient to main-tain 10 weight percent alumina in the bed. After addition of the sulfur dioxide combustion promoter and alumina particles, the sulfur oxides concentration in the flue gas in the conduit 21 is found to be only about 65 ppm (volume).
The rate oi flow oE nitrogen oxides in the flue gas in the conduit 21 is again measured and found to be about 200 pounds per hour calculated as ~2 (equivalent to about 500 ppm (vol.) concentration). The flue gas is then ~assed into a boiler and heated to a temperature of about 870C by firing fuel gas. The flue gas is held at the elevated temperature in the boiler for about 5 seconds and then released. The rate of flow of nitrogen oxides in the gas in the conduit 21 is measured and found to be about 50 pounds per hour above that for the boiler operating without flue gas addition (equivalent to only about 125 ppm (vol.) concentration with respect to the flue gas with-drawn from the regenerator through the conduit 21).
A preferrecl embodiment of the invention having been described, a number of equivalents and modifications of the illustrated embodiment will be apparent to those skilled in the art. These alternatives are intended to be within the scope of the invention, as defined in the appended claims.
~' ~,...
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for burning sulfur-containing and nitrogen-containing coke off coke-containing particles of a catalyst, which comprises:
(a) passing a regeneration gas including free oxygen upwardly through a dense-phase fluidized bed of partic-ulate solids comprising substantially coke-free particles of said catalyst in a regeneration zone, and removing said regeneration gas from said regeneration zone;
(b) introducing said coke-containing catalyst parti-cles into said bed and generating carbon oxides, nitrogen oxide and sulfur oxides in said bed by burning said coke;
(c) burning sufficient carbon monoxide within said bed to maintain regeneration gas above said bed at a maxi-mum temperature below 735°C and not higher than 27°C above the maximum temperature of regeneration gas within said bed and to provide a carbon monoxide concentration of less than 0.5 volume percent in regeneration gas removed from said regeneration zone, and introducing sufficient free oxygen into said bed to provide at least 1 volume percent free oxygen in regeneration gas removed from said regener-ation zone;
(d) including in said particulate solids an amount of a sulfur dioxide combustion promoter sufficient to provide substantial incremental conversion of sulfur di-oxide to sulfur trioxide within said bed;
(e) including reactive alumina in said particulate solids, and decreasing the amount of sulfur oxides in regeneration gas removed from said regeneration zone by forming a sulfur-containing and aluminum-containing solid from said sulfur trioxide and said reactive alumina; and (f) removing regeneration gas from said regeneration zone and decreasing the amount of nitrogen oxides in said regeneration gas by maintaining regeneration gas outside said regeneration zone at a temperature above 760°C for at least 1 second.
(a) passing a regeneration gas including free oxygen upwardly through a dense-phase fluidized bed of partic-ulate solids comprising substantially coke-free particles of said catalyst in a regeneration zone, and removing said regeneration gas from said regeneration zone;
(b) introducing said coke-containing catalyst parti-cles into said bed and generating carbon oxides, nitrogen oxide and sulfur oxides in said bed by burning said coke;
(c) burning sufficient carbon monoxide within said bed to maintain regeneration gas above said bed at a maxi-mum temperature below 735°C and not higher than 27°C above the maximum temperature of regeneration gas within said bed and to provide a carbon monoxide concentration of less than 0.5 volume percent in regeneration gas removed from said regeneration zone, and introducing sufficient free oxygen into said bed to provide at least 1 volume percent free oxygen in regeneration gas removed from said regener-ation zone;
(d) including in said particulate solids an amount of a sulfur dioxide combustion promoter sufficient to provide substantial incremental conversion of sulfur di-oxide to sulfur trioxide within said bed;
(e) including reactive alumina in said particulate solids, and decreasing the amount of sulfur oxides in regeneration gas removed from said regeneration zone by forming a sulfur-containing and aluminum-containing solid from said sulfur trioxide and said reactive alumina; and (f) removing regeneration gas from said regeneration zone and decreasing the amount of nitrogen oxides in said regeneration gas by maintaining regeneration gas outside said regeneration zone at a temperature above 760°C for at least 1 second.
2. A method according to Claim 1 wherein parti-culate solids in said bed contain an average carbon con-centration of less than 0.1 weight percent.
3. A method according to Claim 1 wherein regenera-tion gas removed from said regeneration zone includes less than 0.05 volume percent carbon monoxide.
4. A method according to Claim 1 wherein sufficient free oxygen is introduced into said bed to provide at least 2 volume percent free oxygen in regeneration gas removed from said regeneration zone.
5. A method according to Claim 1 wherein a carbon monoxide combustion promoter comprising at least one metal or compound of a metal selected from ruthenium, rhodium, palladium, iridium, platinum, copper, chromium and manga-nese is included in said particulate solids in an amount sufficient to provide said temperature differential.
6. A method according to Claim 1 wherein said sul-fur dioxide combustion promoter comprises at least one metal or compound of a metal selected from ruthenium, rhodium, palladium, iridium, platinum, copper, chromium, manganese and vanadium.
7. A method according to Claim 1 wherein said sul-fur-containing and nitrogen-containing coke is deposited on said coke-containing catalyst particles by cracking hydrocarbons with said catalyst particles in the absence of added hydrogen.
8. A method according to Claim 7 wherein said cata-lyst particles include a zeolitic crystalline alumino-silicate component.
9. A method according to Claim 1 wherein not more than 5 weight percent of particles in said fluidized bed include a substantial concentration of said sulfur dioxide combustion promoter.
10. A method according to Claim 1 wherein said cata-lyst particles contain less than 50 weight percent silica, excluding silica included in a zeolitic crystalline alumi-nosilicate.
11. A method for burning sulfur-containing and nitrogen-containing coke off coke-containing particles of a catalyst, comprising:
(a) forming carbon monoxide, gaseous sulfur oxides and gaseous nitrogen oxides by reacting free oxygen with said coke in a regeneration zone;
(b) decreasing the amount of said carbon monoxide by reacting said carbon monoxide with free oxygen in said regeneration zone in the presence of a carbon monoxide combustion promoter;
(c) decreasing the amount of said gaseous sulfur oxides and forming a sulfur-containing solid in said regeneration zone by reacting said sulfur oxides with reactive alumina contained in a substantially silica-free particulate solid other than said catalyst present in said regeneration zone in physical admixture with said catalyst; and (d) withdrawing gas including said nitrogen oxides from said regeneration zone at a temperature below 735°C
and decreasing the amount of said nitrogen oxides by maintaining said gas at a temperature above 760°C for at least one second outside said regeneration zone.
(a) forming carbon monoxide, gaseous sulfur oxides and gaseous nitrogen oxides by reacting free oxygen with said coke in a regeneration zone;
(b) decreasing the amount of said carbon monoxide by reacting said carbon monoxide with free oxygen in said regeneration zone in the presence of a carbon monoxide combustion promoter;
(c) decreasing the amount of said gaseous sulfur oxides and forming a sulfur-containing solid in said regeneration zone by reacting said sulfur oxides with reactive alumina contained in a substantially silica-free particulate solid other than said catalyst present in said regeneration zone in physical admixture with said catalyst; and (d) withdrawing gas including said nitrogen oxides from said regeneration zone at a temperature below 735°C
and decreasing the amount of said nitrogen oxides by maintaining said gas at a temperature above 760°C for at least one second outside said regeneration zone.
12. A method in accordance with Claim 11 wherein said carbon monoxide combustion promoter is platinum.
13. A method in accordance with Claim 11 wherein said catalyst particles include a zeolitic crystalline aluminosilicate component.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16353580A | 1980-06-27 | 1980-06-27 | |
| US163,535 | 1980-06-27 | ||
| US23538781A | 1981-02-17 | 1981-02-17 | |
| US235,387 | 1981-05-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1152052A true CA1152052A (en) | 1983-08-16 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000379192A Expired CA1152052A (en) | 1980-06-27 | 1981-06-09 | Flue gas pollutants control in particulate catalyst regeneration |
Country Status (9)
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| AU (1) | AU543055B2 (en) |
| BR (1) | BR8104064A (en) |
| CA (1) | CA1152052A (en) |
| DE (1) | DE3124647A1 (en) |
| FR (1) | FR2485394A1 (en) |
| GB (1) | GB2081597B (en) |
| IT (1) | IT1211071B (en) |
| NL (1) | NL8103103A (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ZA814005B (en) * | 1980-06-27 | 1982-08-25 | Chevron Res | Flue gas pollutants control in particulate catalyst regeneration |
| EP0100531A3 (en) * | 1982-08-03 | 1984-07-04 | Air Products And Chemicals, Inc. | A process for the regeneration of particulate matter with oxygen and carbon dioxide |
| US4507397A (en) * | 1983-07-28 | 1985-03-26 | Chevron Research Company | Semi-continuous regeneration of sulfur-contaminated catalytic conversion systems |
| GB8921190D0 (en) * | 1989-09-19 | 1989-11-08 | Shell Int Research | Apparatus for gas distribution |
| CA2156464C (en) * | 1994-09-30 | 1999-07-20 | Raghu K. Menon | Reduction of emissions from fcc regenerators |
| US7470412B2 (en) * | 2005-12-21 | 2008-12-30 | Praxair Technology, Inc. | Reduction of CO and NOx in regenerator flue gas |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4206039A (en) * | 1975-12-19 | 1980-06-03 | Standard Oil Company (Indiana) | Catalytic cracking with reduced emission of noxious gases |
| CA1093050A (en) * | 1975-12-19 | 1981-01-06 | Iacovos A. Vasalos | Catalytic cracking with reduced emission of noxious gases |
| US4204945A (en) * | 1976-03-11 | 1980-05-27 | Chevron Research Company | Removing pollutants from flue gas in nonzeolitic catalytic cracking |
| US4071436A (en) * | 1976-03-11 | 1978-01-31 | Chevron Research Company | Process for removing sulphur from a gas |
| CA1154735A (en) * | 1978-09-11 | 1983-10-04 | Stanley M. Brown | Catalytic cracking with reduced emissions of sulfur oxides |
| US4235704A (en) * | 1979-08-20 | 1980-11-25 | Exxon Research & Engineering Co. | Method of reducing oxides of nitrogen concentration in regeneration zone flue gas |
-
1981
- 1981-06-09 CA CA000379192A patent/CA1152052A/en not_active Expired
- 1981-06-22 AU AU72022/81A patent/AU543055B2/en not_active Ceased
- 1981-06-23 FR FR8112294A patent/FR2485394A1/en active Granted
- 1981-06-23 DE DE19813124647 patent/DE3124647A1/en not_active Withdrawn
- 1981-06-26 GB GB8119825A patent/GB2081597B/en not_active Expired
- 1981-06-26 BR BR8104064A patent/BR8104064A/en unknown
- 1981-06-26 JP JP56099562A patent/JPS5756042A/en active Granted
- 1981-06-26 NL NL8103103A patent/NL8103103A/en not_active Application Discontinuation
- 1981-06-26 IT IT8122602A patent/IT1211071B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| GB2081597B (en) | 1983-10-26 |
| NL8103103A (en) | 1982-01-18 |
| FR2485394B1 (en) | 1985-04-19 |
| JPS5756042A (en) | 1982-04-03 |
| FR2485394A1 (en) | 1981-12-31 |
| DE3124647A1 (en) | 1982-06-16 |
| JPS6323831B2 (en) | 1988-05-18 |
| AU543055B2 (en) | 1985-03-28 |
| IT1211071B (en) | 1989-09-29 |
| IT8122602A0 (en) | 1981-06-26 |
| AU7202281A (en) | 1982-01-07 |
| BR8104064A (en) | 1982-03-16 |
| GB2081597A (en) | 1982-02-24 |
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