CA1072527A - Process for initiating and controlling dense-bed oxidation of coke and catalyzed oxidation of co to co2 in an fcc regeneration zone - Google Patents
Process for initiating and controlling dense-bed oxidation of coke and catalyzed oxidation of co to co2 in an fcc regeneration zoneInfo
- Publication number
- CA1072527A CA1072527A CA258,417A CA258417A CA1072527A CA 1072527 A CA1072527 A CA 1072527A CA 258417 A CA258417 A CA 258417A CA 1072527 A CA1072527 A CA 1072527A
- Authority
- CA
- Canada
- Prior art keywords
- regeneration gas
- catalyst
- conversion
- regeneration
- spent
- 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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- 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
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
- B01J8/1809—Controlling processes
-
- 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
-
- 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
- C10G11/187—Controlling or regulating
-
- 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
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/00017—Controlling the temperature
- B01J2208/00026—Controlling or regulating the heat exchange system
- B01J2208/00035—Controlling or regulating the heat exchange system involving measured parameters
- B01J2208/0007—Pressure measurement
-
- 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
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/00017—Controlling the temperature
- B01J2208/00106—Controlling the temperature by indirect heat exchange
- B01J2208/00265—Part of all of the reactants being heated or cooled outside the reactor while recycling
-
- 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
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/00539—Pressure
-
- 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
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/00548—Flow
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P30/00—Technologies relating to oil refining and petrochemical industry
- Y02P30/40—Ethylene production
Abstract
ABSTRACT OF THE DISCLOSURE
A process for initiating and controlling the regeneration of spent fluid catalytic cracking catalyst containing catalytically effective amounts of a C0 conversion promotor and for the essentially complete catalytic conversion of C0 to C02 both in a dense bed of catalyst maintained in an FCC regeneration zone.
The process comprises (a) passing to a dense-phase catalyst bed in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate sufficient to oxidize coke to produce partially spent regeneration gas, (b) oxidizing coke at first oxidizing conditions including a catalyst bed first temperature of from 399°C to 677°C to produce regenerated catalyst and partially spent regeneration gas containing C0, (c) increasing the catalyst bed temperature from said first temperature to a second temperature of from 677°C to 760°C, (d) passing to the catalyst bed fresh regeneration gas at a second flow rate stoichiometrically sufficient to essentially completely oxidize C0 to C02, (e) oxidizing in said catalyst bed, maintained at second oxidizing conditions including the presence of said C0 conversion promotor, C0 to produce spent regeneration gas, (f) analyzing spent regeneration gas to obtain a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a pre-determined free-oxygen concentration, and (g) thereafter regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially complete conversion of C0 to C02. The process is generally distinguishable from the prior art in terms of the C0 conversion temperature employed.
A process for initiating and controlling the regeneration of spent fluid catalytic cracking catalyst containing catalytically effective amounts of a C0 conversion promotor and for the essentially complete catalytic conversion of C0 to C02 both in a dense bed of catalyst maintained in an FCC regeneration zone.
The process comprises (a) passing to a dense-phase catalyst bed in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate sufficient to oxidize coke to produce partially spent regeneration gas, (b) oxidizing coke at first oxidizing conditions including a catalyst bed first temperature of from 399°C to 677°C to produce regenerated catalyst and partially spent regeneration gas containing C0, (c) increasing the catalyst bed temperature from said first temperature to a second temperature of from 677°C to 760°C, (d) passing to the catalyst bed fresh regeneration gas at a second flow rate stoichiometrically sufficient to essentially completely oxidize C0 to C02, (e) oxidizing in said catalyst bed, maintained at second oxidizing conditions including the presence of said C0 conversion promotor, C0 to produce spent regeneration gas, (f) analyzing spent regeneration gas to obtain a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a pre-determined free-oxygen concentration, and (g) thereafter regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially complete conversion of C0 to C02. The process is generally distinguishable from the prior art in terms of the C0 conversion temperature employed.
Description
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~ . * * ~ACKGROUND OF THE INVENTION * *
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:. Field of the Invention The field of art to which this invention pertains is hydrocarbon ~: . processing. More particularly~ the invention relates to a regeneration prosess for the oxidative removal of coke from a spent FCC catalyst and . for the catalytic conversion of CO to CO2.
Description of the Prior Art :~ :- Regeneration techniques in which a fluidizable spent catalyst is regenerated in a regenerat;on zone occupy a large segment of the chemical ~' :
arts. The patents which have attempted to solve problems associated with .:::.
.:.................................... regeneration of spent fluidizable catalyst have generally dealt with maxi-mum removal of coke on catalyst while at the same time attempting to prevent :~ or minimize the conversion of carbon monoxide to carbon dioxide within any .:: portlon of the regeneration zone. .
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~ Specifically, it has been present refinery practice to operate , conventional regeneration zones to preclude essentially complete conver-sion of C0 to C02 anywhere within the regeneration zone and especially in the dilute-phase catalyst region where there is little catalyst present to absorb the heat of reaction and where heat damage to cyclones or other separation equipment can therefore result. Essentially complete C0 conver-sion in conventional regeneration zones was prevented quite simply by lim-iting the amount of fresh regeneration gas passing into the regeneration zone. Without sufficient oxygen present to support the reaction of C0 to :::.
C02, afterburning simply cannot occur no matter what the temperatures in the regeneration zone. As well, temperatures in the regeneration zone were ; - generally limited to less than about 677C- by the proper selection of ;1~; hydrocarbon reaction zone operating conditions or fresh feed streams or re-,.' cycle streams. At these temperatures the rate of reaction of C0 oxidation was considerably reduced so that should upsets occur more of an excess of , fresh regeneration gas would be required for C0 conversion than would be needed at temperatures higher than about 677C. The flue gas produced, '~ containing several volume percent C0, was either vented directly to the - ~ atmospheré or used as fuel in a C0 boiler located downstream of the reyen-eration zone.
,. . .Usual practice, familiar to those skilled in the art of FCC pro-cesses, has been to initially manually regulate the flow of fresh regenera-tion gas to the regeneration zone in an amount sufficient to produce par--~ tially spent regeneration gas but insufficient to sustain essentially complete C0 conversion while at the same time limiting regeneration zone temperatures to about 677C. This flow rate required was usually equlvalent to about 8 to 12 pounds of air per pound of coke. When reasonable steady state control was achieved the flow rate of fresh regeneration gas was then typically reg-ulated directly responsive to a small temperature differential between the .~. ,; . .
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~: flue gas outlet temperature (or the dilute phase disengaging space temper-ature) and the dense bed temperature to maintain automatically this proper `-. flow rate of fresh regeneration gas to preclude essentially complete con-. .
- version of C0 to C02 anywhere within the regeneration zone. As the tem-perature difference increased beyond some predetermined temperature differ-ence, indicating that more conversion of C0 was taking place in the dilute , phase, the amount of fresh regeneration gas was decreased to preclude essen-tially complete conversion of C0 to C02. This method of control is exempli-fled by Pohlenz U.S. Patents 3,161,5~3 and 3,206,393. While such method produces a small amount Of 2 in the flue gas, generally in the range of : . ~
0.1 to 1 vol. % 2~ it precludes essentially complete conversion of C0 to , : C2 wit~in the regeneration zone.
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: Until the advent of zeolite-containing catalysts, there was little economic incentive for essentially complete conversion of C0 to C02 within ~: ~ 15 the regenerat.on zone. The heat of combustion that might have been removed was simply not needed by the process; there was generally no feed preheat ; for the hydrocarbon reaction zone and the larger coke yield obtained with the amorphous catalysts in the hydrocarbon conversion ione was usually suf-ficient when burned in the regeneration zone to provide the heat required for the overall process heat balance at the lower hydrocarbon conversion zone ; temperatures then employed without requiring such additional heat inputs as - feèd preheat. The use of the zeolite-containing FCC catalysts with their lower coke-producing tendencies and the use of higher hydrocarbon conver-sion zone temperature, however, often made additional heat input into the ; 25 FCC process necessary. Typically additional heat was provided by burning ex-ternal fuel such as torch oil in the regeneration zone or by preheating the - ~ FCC hydrocarbon feed in external preheaters. Thus heat was typically being - added to and then later removed from the FCC process by two external instal-~: lations, a feed preheater and a C0 boiler, each representing a substantial : :,:
capital lnvestment.
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By the process of our invention coke from a spent fluidizable cracking catalyst containing catalytically effective amounts of a C0 conver-;, sion promotor is oxidized and essentially complete catalyzed conversion , of C0 to C02 is initiated and controlled within a dense-phase bed of cata-lyst in a regeneration zone. The recovery in the dense-phase catalyst bed . . of at least a portion of the heat of reaction of C0 combustion permits either reduced feed preheat requirements or higher hydrocarbon reaction zone tem-; peratures without additional feed preheat while at the same time eliminating :. an air pollution problem without the need for an external C0 boiler. More specifically, the use in our process of a fluid catalytic cracking catalyst j , containing catalytically effective amounts of a C0 conversion promotor permits .. either the same rate of C0 conversion to occur at a temperature as much as C- or more lower than that required with no C0 conversion promotor or : ; a faster rate of C0 conversion to occur at a particular temperature than t~at - 15 which would occur at the same temperature without the use of a C0 conversion promotor. It is this latter advantage which is of particular commercial im-portance. Without a C0 conversion promotor, uneven dispersion of fresh regen-eration gas within the dense-phase catalyst bed often requires higher reyen--; eration zone temperatures or higher fresh regeneration gas rates than desired ` Z0 to maintain a sufficiently fast rate of C0 conversion so that essentially complete conversion of C0 takes place within the regeneration zone. To - increase the regeneration zone temperature torch oil was burned in the re-; generation zone or increased amounts of slurry oil were recycled back to the : hydrocarbon reaction zone so that the spent catalyst would contain !nore coke ; 25 which could be burned in the regeneration zone to increase the temperature.
- Increased fr~sh regeneration gas rates, besides using blower capacity, often ..~. overloaded cyclone separation devices and produced higher amounts of flue gas particulate emmisions (catalyst) than allowed by air pollution regulations.
.~ The use of the C0 conversion promotor permits the elimination of torch oil . .
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or increased slurry oil recycled rates and a reduction in the amount of ex-.;. cess fresh regeneration gas and thus gives back to the refiner more FCC
- ~ process flexibility.
~, While the prior art broadly teaches -the use of temperatures greater than about 677C. in regeneration zones ~see for example Bunn U.S. Patent 3,751,359i Iscol et al U.S Patent 3,261,777i Pfeiffer et al U.S. Patent 3,563,911, and Lee et al U.S. Patent 3,769,203) and also broadly discloses control of air flow rates responsive to oxygen in the flue gas D (see for example Thomas et al U.S. Patent 2,414,002 and Gerhold et al U.S.
Patent 2,466,041), the process of our invention is distinguishable since it requires rather than avoids essentially complete conversion of C0 to C02 within the regeneration zone. Our process furthermore recognizes that oxi-: ~ dizing C0 is not effected by the single factor of high temperature, that is, temperatures above about 677C.; indeed, the process of our invention requires as a distinct step the passlng of sufficient fresh regeneration gas to the dense bed to make possible the essentially complete conversion of - C0 to C02. Without sufficient 2 present, temperatures higher than about 677c. will neither initiate nor sustain afterburning. A temperature of about 677C. is initially required to provide ~ sufficiently fast rate o-f reaction, once C0 conversion is initiated, to ensure that it will be essen-tially completed within the dense bed of the regeneration zone.
P~lor art related to the use of C0 conversion promotors i!l regen-eration zones is U.S. Patent 3,808,121. In the process of that invelltion, ~; coke and C0 oxidation are accomplished by employing two separate catalysts of different particle size ~nd composition: a hydrocarbon conversion cat-'~ alyst and a C0 oxidation catalyst. Moreover, the C0 oxidation catalyst is maintained within a conventional-type regeneration zone and does not pass out of that zone to the hydrocarbon reaction zone as does the catalyst employed : ~ in the process of our invention.
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S~M~RY QF I~E INVENIION
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. . It is, accordingly, a broad objective of the pro oe ss of this inven-tion to provide a regeneration process for the oxidation of coke from a spent ::- fluidizable catalyst o~ntaining catalytically effective amDunts of a ao oon-: version promDtor and for the essentially oonplete catalyzed conversion of CO to produ oe regenerated catalyst and spent regeneratio~ gas in a nEnner such-that at least a portion of the heat of CO ccnversion is recovered within the regeneration zone. It is additionally an objective of our invention.to provide for a re-duction in t~e mini~um temperature required for essentially complete CO conver-sion and to provide for an increase in the rate o~ CO conversion throuah the use : of a CO conversion promDtor rater than thr~ugh the use of high regeneration zone .
. bemperatures or fresh regeneration gas rates. It is a further objective of our process to provide that sufficient fresh regeneration gas be available to ensure essentially corgplete oombustion of 0 to CO2 in spite of variations that may ;: occur in the amDunt of coke on spent catalyst entering the-regeneration zone.
: : In brief summary, our invention is, in one e~bodiment, a pro oe ss for the regeneration of co~e-contaninated fluid catalytic eracking catalyst com-: .
., prising catalytically effective amnunts of a C~ conve~sion prom~tor and for the ::-;. . essentiaLly oo~plete catalytic conversion of carbon ~onoxide to carbcn dioxide .
which process comprises the steps of: (a) passing to a dense-phase catalyst bed.:in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate sufficient to oxidize coke to produot partially spent regeneration gas;
(b) oxidizing coke at first oxidizing conditions including a catalyst bed first ter~erature of from about 399C. to about 677C. to produce regenerat~d catalyst and partially spent regeneration gas containing OO; (c) increasing the catalyst bed ter~eratuLre from said first te~perature to a seoond b~erature of~frcm a~out 677C. to about 760C.; (d) passing to the catalyst bed fresh regeneration gas . ................................... .
i at a second flow rate stoichiometrically sufficient to essential.ly co~,pletely -. oxidize :',., ' '`'' ' .. }~ 6-~ ~ ., ~.;- bm/~
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` CO to C02i (e) oxidizing in said catalyst bed, maintained at second oxidizing . .,. ~
- cDnditions including the presenCe of said CO conversion promotor, CO to pro-duce spent regeneration gas; (f) analyzing spent regeneration gas to obtain k a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a predetermined free-oxygen concentrationi and, (9) there-after regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen con-centration thereby ensuring essentially complete conversion of CO to C02.
Other objects and embodimentsof ~he present invention encompass details about catalysts, operating features, and operating conditions; all : of which are hereinafter disclosed in the following dis~ussion of each of these facets of our invention.
; BRIEF DESCRIPTION OF THE DRAWING
; Having thus described the invention in brief general terms, ref-erence is now made to the drawing in order to provide a better understanding of the present invention. It is to be understood that the drawing is pre-sented only in such detail as is necessary for an understanding of the invention and that minor items have been omitted therefrom for the sake of simplicity and that the scope and spirit of our invention is not to be ., limited thereby.
The attached drawing depicts schematically the side View of a re-generation zone suitable for carrying out the process of our invention. Spent catalyst containing typically from about 0.5 to 1.5 wt. ~ coke passes from a hydrocarbon reactlon zone (not shown) into regeneration zone 1 via llne ~ 25 9. Catalyst is maintained within regeneration zone 1 in dense bed 3. Freshly ; regenerated catalyst is removed from dense bed 3 and regeneration zone 1 : ;.. .
'` via line 4 and returned back to the hydrocarbon reaction zone. Control ~ valve 5, typically a slide valve, in line 4 is utillzed to control the .. . ,. ~
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quantity of regenerated catalyst leaving regeneration zone 1 and passing into the hydrocarhon reaction zone.
Line 14 may enter line 9 for the purpose of admitting one of several particular fluids. The fluid may ke a strippin~ medium such as steam to cause .
the remDval of adsorbed and interstitial hydrocarhons from the spent catalyst kefore the catalyst is passed into regeneration zone 1. The fluid may be an aeration medium such as air or steam for the p~urpose of keeping the spent catalyst in line 9 in a ~luidized state thereby ensuring an even flow of catalyst into the regeneration zone. The fluid may also be a hydroci~rbon liquid or gas added to the regeneration zone as an additional exte m al fuel for the pu4pose of increasing the temperature within the regeneration zone.
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;~ Fresh regeneration sas is intr~du oe d via line 6 into dense bed 3. The fresh regeneration gas passes through distributing device 8 which allows the gas to he more readily dispersed within den æ hed 3. T~pically, the distributing ; devi oe can be a metal plabe containing holes or slots therein or a pipe grid arrangement hoth of ~hich are familiar to tho æ skilled in the art~ In the ,~. , pre æn oe of sufficient fnesh regeneration gi~s and at a den æ bed tem~erature of ~`; at least about 677C. oxIdation of coke and essentially co~plete afterburning of CO to CO2 takes plaoe in the dense bed to produo~ regenerated catalyst and spent regeneration gas.
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Spent regeneration gas, along with entrained regenera-ted catalyst passes out of den æ bed 3 and into dilute phase region 2 which i~ positioned , . .
above and in oo~munication with dense ked 3. Separation ~eans 12, typically a -` cyclone separating devi oe , is located in dilute phase region 2 and is used to - achieve a substan-tial æparation of spent regeneration gas and entrained catalyst.
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Although the drawing sh~ws only one such cyclone, it is anticipated that mNltiple :, ~ cyclone arranged for parallel or æ ries flG~
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.~' of the gas and catalyst could be so positioned in dilute phase 2. As shown - in this drawing the spent regeneration gas passes out of zone 1 via line 10 while substantially all the catalyst passing into the cyclone is recovered through dipleg 13 which passes the catalyst downward toward or into dense : ~ 5 bed 3. Spent regeneration gas passes out of regeneration zone 1 via line 10 at a rate controlled by valve 11. Valve 11 in line 10 can be operated to main'tain a given pressure within the reyeneration zone or more preferably ' may be operated to maintain a given pressure differential between the regen-eration zone and the hydrocarbon reaction zone.
'~ 10 Line 15 which is connected to line 10 passes a sample of the spent , regeneration gas to analyzing means 16. Analyzing means 16 is any instru-ment known in the art by which the concentration of free-oxygen present in ' the spent regeneration gas can be measured.
,, Regulating means 7 is connected to fresh regeneration gas inlet ' 15 line 6 and regulates the rate of regeneration gas passed into regeneratioll ~'' zone 1 based on the,measub~ed free oxygen concentration determined by analy-zing means 16. Specifically, in the particular apparatus shown in the `~ ,, drawing, analyzing means 16 is connected to the regulating means 7 via con-: trol means 19 which is connected to the regulating means 7 via means 18.
; ,' 20 Control means 19 has a setpoint input signal corresponding to a predeter-mlned free-oxygen concentration represented by line 20 and can receive an ,, output signal from the analyzing means which is responsive to the quantity of free-oxygen passing through line 10. The control means can colnpare thjs :,' free-oxygen quantity with a setpoint or desired free-oxygen concentration and via means 18 can pass a control means output signa'l to the regulating , ~, means 7 to alter the flow of regeneration gas into the regeneration zone de-pending upon the deviation of the measured free-oxygen concentra-tion from the desired predetermined free-oxygen concentration in the spent regeneration gas.
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Regulating means 7 can be any apparatus which can control the quantity of a gas stream passing through a line. Specifically, the regu~-. ating means can include a compressor which passes fresh regeneration gas through line 6 at a desired rate. The compressor can be altered in its operation to change the rate of flow of fresh regeneration gas passing through line 6 depending upon the free-oxygen content in the spent regen-eration gas passing through line 10. Other regulating means include valves to regulate the flow of regeneration gas through the line or combinations of flow control loops including an orifice connected to pressure control-i 10 lers and control valves in a manner which enables the regulation of a re-: . .
.. ~ generation gas passing through line 6 into the regeneration zone 1.
~ Control means 19 ~s any apparatus which can generate an output ; signal which responds to a deviation of an input signal fed to it from a desired set point value which the control means at~empts to maintain: In ` 15 normal operations an input signal fed to the control means v~a line 17 is ; read by the control means. The deviation, if any, of this signal from the setpojnt input signal represented by line 20 which is programmed lnto con-: ~ trol means 19 is determined. An output signal passes via means 18 to the regulating means in accordance with the deviation of the input value to the control means.
The materials of construction of the regeneration zone can be ,` metal or other refractory materials which can withstand relatively the ,;.
high temperatures and the attrition conditions present in fluldized regen-;. eration processes.
* * DESCRIPTION OF THE INVENTION * *
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:., At the outset, the definition of various terms used herein will .~ be helpful to an understanding of the process of our invention.
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The term "afterburning" as generally understood by those skilled in the art means the incomplete oxidation of C0 to C02 within the regenera-tion zone or the flue gas line. Generally afterburning is characterized by a rapid temperature increase and occurs during periods of unsteady state operations or process "upset". It is, therefore, usually of short duration until steady state operations are resumed.
In contrast to afterburning, the term "essentially complete con-version of Cû" shall refer to the intentional, sustained, controlled, and essentlally complete combustion of C0 to C02 within the regeneration zone and more specifically within a dense-phase bed of catalyst maintained in the :~.'' regeneration zone. "Essentially complete" shall mean that the C0 concentra~
tion is the spent regeneration gas (hereinafter defined) has been reduced ~ to less than about 1000 ppm and more preferably less than 500 ppm.
: The term "spent catalyst'as used in this specification means catalyst withdrawn from a hydrocarbon conversion zo~e because of reduced ~; activity caused by coke deposits. Spent catalyst passing into the dense-. . .
: phase catalyst bed can contain anywhere from a few tenths up to about 5 ,.:
;~ wt. 0 of coke, but typically in FCC operations spent catalyst will contain ~- from about 0.5 to about 1.5 wt. 'b coke.
The term "regenerated catalyst" as used in this speci;icati~n shall mean catalyst from which at least a portion of coke has been removed.
Regenerated catalyst produced by our process will generally contain less than about 0.5 wt. ~ coke and more typically will contain from about 0.01 ~- to about 0.15 wt. b coke.
- ~ 25 The term "regeneration gas" as used in this specification shall mean, in a generic sense, any gas which is to contact catalyst or which - has contacted catalyst within the regeneration zone. Specifically, the ;i term "fresh regeneration gas" shall include Free-oxygen-containing gases ... .
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- ~07;~527 such as air or oxygen enriched or deficient air which pass into the den æ -phasebed of the regeneration zone to allow oxidation of coke from the spent catalyst and essentially camplete oonversion of CO. Usually the fresh regeneration gas will be air. Free-oxygen shall refer to unoombined oxygen present in a regene-ration gas.
m e term "partially spent regeneration gas" shall refer to regeneration gas which has contacted catalyst within the dense-phase bed and which oontains areduoed quantity of free-oxygen as oo~pared to fresh regeneration gas. Partiallyspent regeneration gas will generally contain several v~lume per oe nt each of nitrogen, free-oxygen, OE bon monoxide, carbon dioxide, and water. More specifically, the partially spent regeneration gas will senerally contain f w m about 7 to about 14 vol. ~ each of carbon monoxide and carbon dioxide.
The term "spent regeneration gas" shall mean regeneration gas which contains a redu oe d concentration of CO as ccmpared to partially sFent regeneration gas. Preferably the spent regeneration gas will contain less than about 1000 ppmof CO and more typically and preferably less than about 500 ppm. CO. FYee oxygen, carbon dioxide, nitrogen, and water will also be present in the spent regeneration gas. The free-oxygen ooncentration of the spent reseneration gas will generally be greater than 0.1 vol. ~ of the spent regeneration gas~
The ter~s "dense-phase" and "~dilute-phase" are ccmmcnly used terms in the art of ~CC to generally characterize catalyst densities in various parts of .,. ~j ~ the regeneration zone. ~hile the demarkation density is somewhat ill-defined, . ., `~` as the term "dense-phase" is used herein it shall refer to regions within t~e ~?:~ 3 ' regeneration zone where the catalyst density is greater than about 240 kg/m :. .
and as "dilute-phase" is used herein it refers to regions where the catalvst density is less than abou-t 240kg/m3. Usually the dense-phase density will be in the range of from about 320 to 640 kg/m3 or ~,.
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- more and the dilute-phase density will b m.uch less than 240 kg/m and in the ; : range o~ from about.l.6 to akout 80 kg/m . Catalyst densities within FCC vessels - are oommonly measured by measuring pressure or head differen oe s across pressu~e -; taps installed in the vessels and spa oe d at known distances apart.
. Our pro oe ss basically centers around a pnocess for oxidizing coke . .
from a spent catalytic cracking catalyst containing catalytically effective amounts of a CO oonversion promotor and for initiating and o~ntrolling essentially oomplete : ' conversion of CO, in tho presen oe of the promotor, to CO2 within a dense-phase bed.
o~ catalyst maintained in a regeneration zone.
In the process of our invention coke oxidation and essentially complete . catalyæed conversion of CO to CO2 are initiated and take pla oe within a dense ;~ catalyst bed in the regeneration zone and at least a portion of the heat of oombustion of CO is recovered by the regenerated catalyst for use within the FCC
prccess. Regenerated catalyst which passes to the hydrocarbon reaction zone is therefore at a higher te~perature than regenerated catalyst produced by a non~
CC-burning regeneration zone thereby permitting a reduction or elimunation of external feed preheat. P~dditionally, the CO conversion is oontrolled to ensure essentially oomplete elimination of atmospheric CO pollution without the require-ment of an external CO boiler. r~oreover the process of our invention is applicable :: 20 to present day regeneration units without extensive modifications or revamp.
i ~ Additionally it is a feature of our process tha-t the essentially . o~nplete conversion of CO to C02 is cat~lyzed by catalytically effective amou~ts . of a CO conversion promotor which passes as part of the ~luid cracking catalyst throughout the FCC pro oe ss. I'he rate of coke oxidation is not affected by employing a fluid catalytic cracking catal~st containing a CO oonversion promotor nor is the conversion of hydrocarbons within the hydrocarbon oonversion zone but the rate of CO oonversion is increased~
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With a C0 conversion promotor the kinetic rate constant for the reaction C0 + ~2 ~~ C2 may be increased typically from Z to 5 times or more. Thus ;. a faster rate of C0 conversion can be obtained in the presence of a C0 con-version promotor at a given regeneration zone temperature and oxygen con-centration than can be obtained without the promotor. Since perfect disper-; ; sion and ideal mixing of the fresh regeneration gas within the catalyst in ; the dense-phase bed are never achieved, it has often happened that the rate . of reaction of C0 oxidation must be increased to ensure that essentially '' D complete conversion of C0 occurs within the dense bed. The rate of reaction has been increased by increasing the regeneration zone temperature or by -:.` increasing the fresh regeneration gas (oxygen concentration). Regeneration ;. zone temperatures were increased by such methods as burning torch oil in .. . .
; the regeneration zone increasing the amount of slurry oil recycle to the ,. .. .
~: hydrocarbon conversion zone thereby producing more coke to be burned, pre-, 15 heating the fresh regeneration gas to the regeneration zone, preheating the ` :~ feed to the hydrocarbon conversion zone ar by a combinatjon of such methods.
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. Such methods generally increase the ope~ating cost of the FCC process and . .
.. . take away some of the flexibility of the FCC process. Employing an FCC
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~ catalyst containing catalytically effective amounts of a C0 conversion pro-;~.
:~ 20 motor permits a reduct;on or elimination of torch oil burning and slurry .. oil recYcle. a reduction or elimination of fresh regeneration gas and feed ...,~, . . .
~' preheat, and a reduction in the amount of excess fresh regeneration gas required for essentially complete conversion of C0 within the regeneration , : zone.
Suitable catalysts for use in the process of our inVention can comprise any of the catalyst known to the art of fluid catalytic cracking : and contalning catalytically effective amounts of a C0 conversion promotor.
~` The term "catalytically effective amounts" shall generally mean such amounts ; -14-.'~. `, '- . , .
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of a promotor as will increase the kinetic rate constant of C0 conversion :. .
; to C02. Such amounts can be from a few weight parts per million up to about 20 wt. ~ or more of the FCC catalyst. More preferably such amounts will range from about 100 wt. ppm. to about 10 wt. % of the FCC catalyst.
Suitable C0 conversion promotors shall broadly comprise one or more oxides selected from the transition metals and the rare earth metals. Par--. ticularly suitable C0 conversion promotors will comprise one or more oxides selected from the group consisting of vanadium oxide, chromium oxide, man-ganese oxide, iron oxide, cobait oxide, nickel oxide, copper oxide, palladium oxide, platinum oxide, and rare earth metal oxides. The C0 conversion Pro-motors can be incorporated into amorphous FCC catalysts comprising silica and/or alumina or into any of the zeolite-containing FCC catalysts by any suitable metho~ known to the catalyst manufacturing art such as copre-cipitation or cogelling or impregnation. Suitable zeolites include both naturally occuring and synthetic crystalline aluminosilicate materials known to the art such as faujasite, mordenite, chabazite, type X and type Y zeo-: lites, the the so-called "ultrastable" crystalline aluminosilicate materials.
i, In order to initiate and sustain essentially complete combustion -~ of C0 to C02 within the dense bed of a regeneration zone t~o requirements .~ 20 must be met: the dense bed temperature must be high enough to produce a ; sufficient fast rate of reaction of C0 oxidation and the quantity of fresn regeneration gas must be at least sufficient stoichiometrically for essen-~ tially complete C0 oxidation.
`~ The ratP of reaction of C0 oxidation must be sufficiently fast to permit essentially complete combustion of C0 within a reasonable gas resi-dense time in the dense bed of the regeneration zone. If the rate of reac-tion is too slow, it is possible that all of the C0 combustion wili not be completed ln the time interual that partially spent regeneration gas is in . '~ .
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the dense bed where there is sufficient catalyst density to absorb the heat . of reaction. In this situation, C0 conversion can then take place in the - dilute phase region of the regeneration zone or in the flue gas line out-side of the regeneration zone where it is not desirable. Temperature above some minimum with or without the presence of a C0 conversion promotor is therefore important to insure the proper rate or reaction.
The proper quantity of fresh regeneration gas is important because .~ without sufficient oxygen present to support the reaction of C0 oxidation - to C02, the reaction will not occur no matter what the temperature is in the ,, 10 regeneration zone. Furthermore, it is important that some excess of fresh ...
, ~ regeneration be present beyond that stoichiometrically requ;red to ensure ``; the essentially complete conversion of the C0.
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. ~ It is generally recognlzed that FCC regeneration zone operation - is essentially adiabatic. While it is true that some heat is lost to the ~ ~ 15 surroundings that amount of heat is a small fraction of the total heat -` ~ released. Since regeneration zone operation is essentially adiabatic, the i. 2 regeneration zone temperature is a direct function of the amount of fuel ., ~, .
' burned in the regeneration zone. As the total amount of fue~ increases the regeneration zone temperature increases. Until intentional conversion of cn to C02 is initiated in the regeneration zone, the fuel is primarily coke ; ~ on spent catalyst but will also include any adsorbed or interstitial hYdro-carbons passing into the regeneration zone with the spent catalyst or any "torch oil" burned in the regeneration zone. Indeed, during initial FCC
process startup the fuel is primarily torch oil until sufficient coke has ` 2S been built up on the catalyst. When intentional conversion of C0 to C02 is initiated then C0 con-tributes significantly to the total fuel burned in the - regeneration zone.
: Thus b~ controlling either the amount of fuel passed into the .
regeneration zone or the fresh regeneration gas which would allow the fuel .
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to be burned, the regeneration zone temperature can be controlled at any `~. temperature from about 399C. up to about 760C. The amount of coke ; can typically be controlled by varying the hydrocarbon reaction zone op-- erating conditions such as temperature or by vary;ng the composition of the feedstock to that reaction zone. Specifically, more coke is produced as the hydrocarbon reaction zone conditions become more severe or as the feedstock becomes heavier, that is, as the Conradson carbon content in-creases.
; It has been common practice to limit the operating temperatures of conventional (non-CO-burning~ regeneration zones to about 677 C. On FCC processes employing amorphous catalysts this was generally done by limiting the hydrocarbon reaction zone temperature to some maximum or by limiting the amount of coke-producing slurry oil recycled to the hydro-. i,. . - .
~. carbon reaction zone to some maximum. These maximums are determined, for ~, any particular feedstock, primarily by operating experience on the FCC
process. On FCC process employing zeolite-containing catalysts where less ~ coke was produced it often became necessary to burn torch oil to maintain -~ a regeneration zone temperature of about 677 C. A temperature near around ; 677C. was desired to produce the hottest possible regenerated catalyst .~ ~ 20 yet ~he temperature was limited to a maximum of about 677C. both for possible metallurgy limitations and because the rate of reaction of after-burning,should it occur during process upsets, was relatively slow.
In the process of our invention spent catalyst containing cata- -~
lytically effective amounts of a CO conversion promotor and fresh regen-.
eration gas are first passed to a dense bed in the regeneration zone. More specifically, fresh regeneration gas is lnitially passed into the dense bed at a first flow rate sufficient to oxidize coke to produce partially spen-t ~ regeneration gas. Even more specifically, this first flow rate will prefer-., . , , ' .
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ably ke in the range equivalent to about 8 b~ about 12 grams of air per gram of ; coke entering the regeneration zone. Coke is then oxidized at first oxidizing aonditions to produoe regenerated catalyst and partially spent regeneration gas.
First oxidizing conditions will include a dense bed temperature of ; ;
;~; from about 399C to about 677C. not because of any metallurgical limitation . ., but because the rate of reaction of afterkurning, should it occur during unsteady startup conditions, is relatively slcw. During startup, torch oil will be burned in the reqeneration zone until sufficient coke is deposited on the catal~st in the hydr~carkon reaction zone~ Thereafter torch oil will gradually be reduoe d or eliminated as the amount of coke on spent catalyst increases and the dense bed ,~ temperature will be limited to about 677C. by the methods described above.
~ Other first oxidizing conditions will include an aperating pressure of from about -- atmospheric pressure to about 4.4 atm. with the pre~erred range being from about ~ 2 to about 3.7 atm. A~ditionally, superficial fresh regeneration gas velocities -~, will ke limited to the transport velocity, that is, the velocity past which the catalyst w~uld be carried out of the dense bed upward into the dilute phase region.
Superficial gas velocities will therefore preferably be less than about 1 metre ,~ per second with 0.5 to 0.8 metre per seoond being the usual range.
~ After coke is being oxidized to produce regenerated catalyst and ~ 20 partially spent regeneration gas the dense bed temperature is then increased to a second tem~erature of from akout 677C. to about 760C. so that the rate of CO
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- oxidation when it is allowed to occur will be sufficiently fast to ensure essentially complete conversion of CO to C~2 within the dense bed. m e temperature can be increased by any of several ~ethods or ca~bination of methods.
The severity of operating conditions in the ~' ~
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; hydrocarbon reaction zone can be increased thereby producing more coke on . spent catalyst; the amount of slurry oil recycle to the hydrocarbon reac-tion zone can be increased to produce more coke on spent catalysti torch oil can again be added or increased to the regeneration zone; stripping of spent catalyst can be reduced thereby allowing more combustible material to pass with the spent catalyst into the regeneration zone; or, a heavier `~ feedstock can be employed.
The fresh regeneration gas is next increased from the first flow . . .
, rate to a second flow rate stoichiometrically sufficient to permit essentially completely oxidation of CO to C02 thereby producing spent regeneration gas.
"~r,,, This second flow rate will more preferably be in the range equivalent to a-bout 12 to about 16 grams of air per gram of coke entering the regeneration ,~ zonP. Carbon monoxide is then oxidized in the dense bed at second oxidiz-,r,g , ; conditions to produce spent regeneration gas. ~ith ~he dense bed temperature ~ 15 at the second temperature of from about 677C- to about 760C., essen-. . .
.~ tially complete conversion of CO to C02 within the dense bed will occur - essentially spontaneously as soon as the fresh regeneration gas rate is increased to the second flow rate. Since the oxidation of CO is exothermic it will not be necessary, once CO oxidation has been initiated, to continue 20 the measures that were employed to increase the dense bed temperature to .` the second temperature.
Second oxidizing conditions will include a temperature from about 677C. to about 760C. and a superficial fresh rege~eration gas velocity limited as described above to the transport velocity. Operating pressure - 25 will be from about atmospheric pressure to about 4.A atm. with the preferred range being from about 2 to about 3.7 atm.
~ At this state of regeneration zone operation, it 1s possible that ; normal ~ariations which occur in feedstock flow rate and particularly com-. ~ .
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, this state of operation is just sufficient ~or essentially complete oxida-"'.... tion of C0 to C02 with no provision for an excess. The C0 concentration ,.~ . :, ; 5 of the spent regeneration gas may increase during these intervals from a ',., preferred concentration of less than about 500 ppm. to se~eral thausand : .~
,s ~ ppm. C0. The proces$ of our invention includes steps to prevent this and ~, to ensure the essentially complete combustion of CO to C02 in sp;te of such variations.
Specifically in our process the spent regeneration gas is analyzed , ~ by analyzing means to obtain a measured free-oxygen concentration and that ,', measured concentration is then compared with a predetermined free-oxygen .
concentration. The predet,ermined free-oxygen concent,ation of the spent -. regeneration gas will represent an amount of free oxygen in excess of that ` 15 stoichiometrically required for C0 oxidation. Thereafter, the fresh regen-~' eration gas rate is regulated at a third flow rate to maintain a measured :.~
t- free-oxygen concentration equal to the predetermined -free-oxygen concentra-: .
tion thereby ensuring essentially complete conversion of C0 to C02. The ~'. third flow rat2 will therefore be higher than the second flow rate. Typi-,,;~, 20 cally the third flow rate will be equlvalent to about 13 to about 17 grams of air per gram of coke.
The free-oxygen concentration of the spent regeneration gas Will ~ generally be greater than about 0.1 volume percent of the spent regeneration -~` gas stream and more specifically can be from about 0., vol. ~ free oxygen ' 25 to about 10 vol. ~ or more free oxygen. Preferably, the Free-oxygen con-; ' centration will be from about 0.2 vol. ~ to about 5 vol. % of the spent regeneration gas and more preferably will be from about 1 vol. % to about , , 3 vol. %.
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:, I . i 7;~S~7 The analyzing means used in the process of this invention to : measure the free oxygen concentration in the spent regeneration gas can include any apparatus capable of measuring the concentration f 2 in a gas mixture comprising 2. CO, C02, N2, H2, and light hydrocarbons in con-r 5 centrations ranging from volume parts per million to many volume percent~
Specifically included are Orsat, gas chromatographic, and mass spectro-graphic apparatus. Samples of flue gas may be periodically wlthdrawn ` manually from the process and manually analyzed or may be automatically . .
withdrawn and analyzed continuously or at programmed time intervals by sampling and analyzing means.
After the measured free-oxygen concentration has been determined and compared with the predetermined free oxygen concentration a regulating - means will be adjusted manually or automatically if necessary to pass more or less fresh regeneration gas into the regeneration zone. Typically, the regulating means wili comprise a valve for controlling flow or a con-trol device which can control speed or discharge pressure of a fresh re-- generatjon gas compressor to change the flo~ rate of fresh regeneration gas into the regeneration zone. In an automatic system, the analyzing means may generate and send to a control means an output signal representing the measured free-oxygen concentration The control means may typically con-nect the analyzing means to the regulating means or may be incorporated within the design of either and have a variable setpoint representing the predetermined free oxygen concentration. The control means recei~es the analyzing means output signal, compares it to the setpoint value and if a differential exists, passes a signal to the regulating means to change the - fresh regeneration gas rate into the regeneration zone so that the measured free-oxygen concentration in the spent regeneration gas will equal the pre-~ determined free-oxygen concentration. The analyzing means, control means, ::
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~ The following examples are presented to illustrate some of the - features and advantages of the process of our invention and are not in-tended to unduly restrict the limits of the claims appended hereto.
EXAM LE I
In this example coke and C0 were oxidi~ed in a regenerator oper-ating at a dense bed temperature of about 732 C. and a pressure of about ~ 3.7 atm. Approximately 945.000 kg/hr of spent catalyst containing about '1,. D 10 0.8 wt. ~ coke was passed into the regenerator while the input of air to ;~ ~ the regenerator was rnaintained at a ratio of about 14.60 grams of air per gram of coke.
The air input rate to the regenerator was controlled to maintain a predetermined free-oxygen concentration in the spent regeneration gas to about 1-2 vol. ~. The conversion of C0 to C02 was substantially complete and was maintained steadily and continuous1y within the dense bed of cata-lyst in the regenerator. The superficial gas velocity was about 0.85 metre/
second.
By being able to control the conversion of C0 in the dense bed of the regenerator the reactor temperature was able to be raised to about 538C. with no additjon of feed preheat which increased conversion and the quantity of gasoline and lighter compounds produced.
`. EXAMPLE Il : In this example, a comparison is made between the operations of .. ZS a commercial FCC unit before and after essentially complete C0 conversion : was initiated and controlled.
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Commercial FCC Operation Before and After CO Convers~on ~ ~lithoutCO Conversion ; CO ConversionTaking Place_ : 5 Reactor Temperature, C. O 530 530 Regenerator Dense Phase Temp., OC.677 732 Regenerator Dilute Phase Temp., C.699 734 Feed Preheat Temp., 363 260 ; Conversion, L.V.~ 79.4 79.1 Coke Yield, wt.~ 5.4 4.6 Gasoline Yield, L.V.~ 63.2 65.6 CO in Flue Gas, Vol.'l,10.1 0.0*
C02 in Flue Gas, Vol. ',u 9.7 16.7
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~ . * * ~ACKGROUND OF THE INVENTION * *
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:. Field of the Invention The field of art to which this invention pertains is hydrocarbon ~: . processing. More particularly~ the invention relates to a regeneration prosess for the oxidative removal of coke from a spent FCC catalyst and . for the catalytic conversion of CO to CO2.
Description of the Prior Art :~ :- Regeneration techniques in which a fluidizable spent catalyst is regenerated in a regenerat;on zone occupy a large segment of the chemical ~' :
arts. The patents which have attempted to solve problems associated with .:::.
.:.................................... regeneration of spent fluidizable catalyst have generally dealt with maxi-mum removal of coke on catalyst while at the same time attempting to prevent :~ or minimize the conversion of carbon monoxide to carbon dioxide within any .:: portlon of the regeneration zone. .
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~ Specifically, it has been present refinery practice to operate , conventional regeneration zones to preclude essentially complete conver-sion of C0 to C02 anywhere within the regeneration zone and especially in the dilute-phase catalyst region where there is little catalyst present to absorb the heat of reaction and where heat damage to cyclones or other separation equipment can therefore result. Essentially complete C0 conver-sion in conventional regeneration zones was prevented quite simply by lim-iting the amount of fresh regeneration gas passing into the regeneration zone. Without sufficient oxygen present to support the reaction of C0 to :::.
C02, afterburning simply cannot occur no matter what the temperatures in the regeneration zone. As well, temperatures in the regeneration zone were ; - generally limited to less than about 677C- by the proper selection of ;1~; hydrocarbon reaction zone operating conditions or fresh feed streams or re-,.' cycle streams. At these temperatures the rate of reaction of C0 oxidation was considerably reduced so that should upsets occur more of an excess of , fresh regeneration gas would be required for C0 conversion than would be needed at temperatures higher than about 677C. The flue gas produced, '~ containing several volume percent C0, was either vented directly to the - ~ atmospheré or used as fuel in a C0 boiler located downstream of the reyen-eration zone.
,. . .Usual practice, familiar to those skilled in the art of FCC pro-cesses, has been to initially manually regulate the flow of fresh regenera-tion gas to the regeneration zone in an amount sufficient to produce par--~ tially spent regeneration gas but insufficient to sustain essentially complete C0 conversion while at the same time limiting regeneration zone temperatures to about 677C. This flow rate required was usually equlvalent to about 8 to 12 pounds of air per pound of coke. When reasonable steady state control was achieved the flow rate of fresh regeneration gas was then typically reg-ulated directly responsive to a small temperature differential between the .~. ,; . .
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~: flue gas outlet temperature (or the dilute phase disengaging space temper-ature) and the dense bed temperature to maintain automatically this proper `-. flow rate of fresh regeneration gas to preclude essentially complete con-. .
- version of C0 to C02 anywhere within the regeneration zone. As the tem-perature difference increased beyond some predetermined temperature differ-ence, indicating that more conversion of C0 was taking place in the dilute , phase, the amount of fresh regeneration gas was decreased to preclude essen-tially complete conversion of C0 to C02. This method of control is exempli-fled by Pohlenz U.S. Patents 3,161,5~3 and 3,206,393. While such method produces a small amount Of 2 in the flue gas, generally in the range of : . ~
0.1 to 1 vol. % 2~ it precludes essentially complete conversion of C0 to , : C2 wit~in the regeneration zone.
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: Until the advent of zeolite-containing catalysts, there was little economic incentive for essentially complete conversion of C0 to C02 within ~: ~ 15 the regenerat.on zone. The heat of combustion that might have been removed was simply not needed by the process; there was generally no feed preheat ; for the hydrocarbon reaction zone and the larger coke yield obtained with the amorphous catalysts in the hydrocarbon conversion ione was usually suf-ficient when burned in the regeneration zone to provide the heat required for the overall process heat balance at the lower hydrocarbon conversion zone ; temperatures then employed without requiring such additional heat inputs as - feèd preheat. The use of the zeolite-containing FCC catalysts with their lower coke-producing tendencies and the use of higher hydrocarbon conver-sion zone temperature, however, often made additional heat input into the ; 25 FCC process necessary. Typically additional heat was provided by burning ex-ternal fuel such as torch oil in the regeneration zone or by preheating the - ~ FCC hydrocarbon feed in external preheaters. Thus heat was typically being - added to and then later removed from the FCC process by two external instal-~: lations, a feed preheater and a C0 boiler, each representing a substantial : :,:
capital lnvestment.
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By the process of our invention coke from a spent fluidizable cracking catalyst containing catalytically effective amounts of a C0 conver-;, sion promotor is oxidized and essentially complete catalyzed conversion , of C0 to C02 is initiated and controlled within a dense-phase bed of cata-lyst in a regeneration zone. The recovery in the dense-phase catalyst bed . . of at least a portion of the heat of reaction of C0 combustion permits either reduced feed preheat requirements or higher hydrocarbon reaction zone tem-; peratures without additional feed preheat while at the same time eliminating :. an air pollution problem without the need for an external C0 boiler. More specifically, the use in our process of a fluid catalytic cracking catalyst j , containing catalytically effective amounts of a C0 conversion promotor permits .. either the same rate of C0 conversion to occur at a temperature as much as C- or more lower than that required with no C0 conversion promotor or : ; a faster rate of C0 conversion to occur at a particular temperature than t~at - 15 which would occur at the same temperature without the use of a C0 conversion promotor. It is this latter advantage which is of particular commercial im-portance. Without a C0 conversion promotor, uneven dispersion of fresh regen-eration gas within the dense-phase catalyst bed often requires higher reyen--; eration zone temperatures or higher fresh regeneration gas rates than desired ` Z0 to maintain a sufficiently fast rate of C0 conversion so that essentially complete conversion of C0 takes place within the regeneration zone. To - increase the regeneration zone temperature torch oil was burned in the re-; generation zone or increased amounts of slurry oil were recycled back to the : hydrocarbon reaction zone so that the spent catalyst would contain !nore coke ; 25 which could be burned in the regeneration zone to increase the temperature.
- Increased fr~sh regeneration gas rates, besides using blower capacity, often ..~. overloaded cyclone separation devices and produced higher amounts of flue gas particulate emmisions (catalyst) than allowed by air pollution regulations.
.~ The use of the C0 conversion promotor permits the elimination of torch oil . .
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or increased slurry oil recycled rates and a reduction in the amount of ex-.;. cess fresh regeneration gas and thus gives back to the refiner more FCC
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~, While the prior art broadly teaches -the use of temperatures greater than about 677C. in regeneration zones ~see for example Bunn U.S. Patent 3,751,359i Iscol et al U.S Patent 3,261,777i Pfeiffer et al U.S. Patent 3,563,911, and Lee et al U.S. Patent 3,769,203) and also broadly discloses control of air flow rates responsive to oxygen in the flue gas D (see for example Thomas et al U.S. Patent 2,414,002 and Gerhold et al U.S.
Patent 2,466,041), the process of our invention is distinguishable since it requires rather than avoids essentially complete conversion of C0 to C02 within the regeneration zone. Our process furthermore recognizes that oxi-: ~ dizing C0 is not effected by the single factor of high temperature, that is, temperatures above about 677C.; indeed, the process of our invention requires as a distinct step the passlng of sufficient fresh regeneration gas to the dense bed to make possible the essentially complete conversion of - C0 to C02. Without sufficient 2 present, temperatures higher than about 677c. will neither initiate nor sustain afterburning. A temperature of about 677C. is initially required to provide ~ sufficiently fast rate o-f reaction, once C0 conversion is initiated, to ensure that it will be essen-tially completed within the dense bed of the regeneration zone.
P~lor art related to the use of C0 conversion promotors i!l regen-eration zones is U.S. Patent 3,808,121. In the process of that invelltion, ~; coke and C0 oxidation are accomplished by employing two separate catalysts of different particle size ~nd composition: a hydrocarbon conversion cat-'~ alyst and a C0 oxidation catalyst. Moreover, the C0 oxidation catalyst is maintained within a conventional-type regeneration zone and does not pass out of that zone to the hydrocarbon reaction zone as does the catalyst employed : ~ in the process of our invention.
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. . It is, accordingly, a broad objective of the pro oe ss of this inven-tion to provide a regeneration process for the oxidation of coke from a spent ::- fluidizable catalyst o~ntaining catalytically effective amDunts of a ao oon-: version promDtor and for the essentially oonplete catalyzed conversion of CO to produ oe regenerated catalyst and spent regeneratio~ gas in a nEnner such-that at least a portion of the heat of CO ccnversion is recovered within the regeneration zone. It is additionally an objective of our invention.to provide for a re-duction in t~e mini~um temperature required for essentially complete CO conver-sion and to provide for an increase in the rate o~ CO conversion throuah the use : of a CO conversion promDtor rater than thr~ugh the use of high regeneration zone .
. bemperatures or fresh regeneration gas rates. It is a further objective of our process to provide that sufficient fresh regeneration gas be available to ensure essentially corgplete oombustion of 0 to CO2 in spite of variations that may ;: occur in the amDunt of coke on spent catalyst entering the-regeneration zone.
: : In brief summary, our invention is, in one e~bodiment, a pro oe ss for the regeneration of co~e-contaninated fluid catalytic eracking catalyst com-: .
., prising catalytically effective amnunts of a C~ conve~sion prom~tor and for the ::-;. . essentiaLly oo~plete catalytic conversion of carbon ~onoxide to carbcn dioxide .
which process comprises the steps of: (a) passing to a dense-phase catalyst bed.:in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate sufficient to oxidize coke to produot partially spent regeneration gas;
(b) oxidizing coke at first oxidizing conditions including a catalyst bed first ter~erature of from about 399C. to about 677C. to produce regenerat~d catalyst and partially spent regeneration gas containing OO; (c) increasing the catalyst bed ter~eratuLre from said first te~perature to a seoond b~erature of~frcm a~out 677C. to about 760C.; (d) passing to the catalyst bed fresh regeneration gas . ................................... .
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- cDnditions including the presenCe of said CO conversion promotor, CO to pro-duce spent regeneration gas; (f) analyzing spent regeneration gas to obtain k a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a predetermined free-oxygen concentrationi and, (9) there-after regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen con-centration thereby ensuring essentially complete conversion of CO to C02.
Other objects and embodimentsof ~he present invention encompass details about catalysts, operating features, and operating conditions; all : of which are hereinafter disclosed in the following dis~ussion of each of these facets of our invention.
; BRIEF DESCRIPTION OF THE DRAWING
; Having thus described the invention in brief general terms, ref-erence is now made to the drawing in order to provide a better understanding of the present invention. It is to be understood that the drawing is pre-sented only in such detail as is necessary for an understanding of the invention and that minor items have been omitted therefrom for the sake of simplicity and that the scope and spirit of our invention is not to be ., limited thereby.
The attached drawing depicts schematically the side View of a re-generation zone suitable for carrying out the process of our invention. Spent catalyst containing typically from about 0.5 to 1.5 wt. ~ coke passes from a hydrocarbon reactlon zone (not shown) into regeneration zone 1 via llne ~ 25 9. Catalyst is maintained within regeneration zone 1 in dense bed 3. Freshly ; regenerated catalyst is removed from dense bed 3 and regeneration zone 1 : ;.. .
'` via line 4 and returned back to the hydrocarbon reaction zone. Control ~ valve 5, typically a slide valve, in line 4 is utillzed to control the .. . ,. ~
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quantity of regenerated catalyst leaving regeneration zone 1 and passing into the hydrocarhon reaction zone.
Line 14 may enter line 9 for the purpose of admitting one of several particular fluids. The fluid may ke a strippin~ medium such as steam to cause .
the remDval of adsorbed and interstitial hydrocarhons from the spent catalyst kefore the catalyst is passed into regeneration zone 1. The fluid may be an aeration medium such as air or steam for the p~urpose of keeping the spent catalyst in line 9 in a ~luidized state thereby ensuring an even flow of catalyst into the regeneration zone. The fluid may also be a hydroci~rbon liquid or gas added to the regeneration zone as an additional exte m al fuel for the pu4pose of increasing the temperature within the regeneration zone.
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;~ Fresh regeneration sas is intr~du oe d via line 6 into dense bed 3. The fresh regeneration gas passes through distributing device 8 which allows the gas to he more readily dispersed within den æ hed 3. T~pically, the distributing ; devi oe can be a metal plabe containing holes or slots therein or a pipe grid arrangement hoth of ~hich are familiar to tho æ skilled in the art~ In the ,~. , pre æn oe of sufficient fnesh regeneration gi~s and at a den æ bed tem~erature of ~`; at least about 677C. oxIdation of coke and essentially co~plete afterburning of CO to CO2 takes plaoe in the dense bed to produo~ regenerated catalyst and spent regeneration gas.
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Spent regeneration gas, along with entrained regenera-ted catalyst passes out of den æ bed 3 and into dilute phase region 2 which i~ positioned , . .
above and in oo~munication with dense ked 3. Separation ~eans 12, typically a -` cyclone separating devi oe , is located in dilute phase region 2 and is used to - achieve a substan-tial æparation of spent regeneration gas and entrained catalyst.
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Although the drawing sh~ws only one such cyclone, it is anticipated that mNltiple :, ~ cyclone arranged for parallel or æ ries flG~
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.~' of the gas and catalyst could be so positioned in dilute phase 2. As shown - in this drawing the spent regeneration gas passes out of zone 1 via line 10 while substantially all the catalyst passing into the cyclone is recovered through dipleg 13 which passes the catalyst downward toward or into dense : ~ 5 bed 3. Spent regeneration gas passes out of regeneration zone 1 via line 10 at a rate controlled by valve 11. Valve 11 in line 10 can be operated to main'tain a given pressure within the reyeneration zone or more preferably ' may be operated to maintain a given pressure differential between the regen-eration zone and the hydrocarbon reaction zone.
'~ 10 Line 15 which is connected to line 10 passes a sample of the spent , regeneration gas to analyzing means 16. Analyzing means 16 is any instru-ment known in the art by which the concentration of free-oxygen present in ' the spent regeneration gas can be measured.
,, Regulating means 7 is connected to fresh regeneration gas inlet ' 15 line 6 and regulates the rate of regeneration gas passed into regeneratioll ~'' zone 1 based on the,measub~ed free oxygen concentration determined by analy-zing means 16. Specifically, in the particular apparatus shown in the `~ ,, drawing, analyzing means 16 is connected to the regulating means 7 via con-: trol means 19 which is connected to the regulating means 7 via means 18.
; ,' 20 Control means 19 has a setpoint input signal corresponding to a predeter-mlned free-oxygen concentration represented by line 20 and can receive an ,, output signal from the analyzing means which is responsive to the quantity of free-oxygen passing through line 10. The control means can colnpare thjs :,' free-oxygen quantity with a setpoint or desired free-oxygen concentration and via means 18 can pass a control means output signa'l to the regulating , ~, means 7 to alter the flow of regeneration gas into the regeneration zone de-pending upon the deviation of the measured free-oxygen concentra-tion from the desired predetermined free-oxygen concentration in the spent regeneration gas.
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Regulating means 7 can be any apparatus which can control the quantity of a gas stream passing through a line. Specifically, the regu~-. ating means can include a compressor which passes fresh regeneration gas through line 6 at a desired rate. The compressor can be altered in its operation to change the rate of flow of fresh regeneration gas passing through line 6 depending upon the free-oxygen content in the spent regen-eration gas passing through line 10. Other regulating means include valves to regulate the flow of regeneration gas through the line or combinations of flow control loops including an orifice connected to pressure control-i 10 lers and control valves in a manner which enables the regulation of a re-: . .
.. ~ generation gas passing through line 6 into the regeneration zone 1.
~ Control means 19 ~s any apparatus which can generate an output ; signal which responds to a deviation of an input signal fed to it from a desired set point value which the control means at~empts to maintain: In ` 15 normal operations an input signal fed to the control means v~a line 17 is ; read by the control means. The deviation, if any, of this signal from the setpojnt input signal represented by line 20 which is programmed lnto con-: ~ trol means 19 is determined. An output signal passes via means 18 to the regulating means in accordance with the deviation of the input value to the control means.
The materials of construction of the regeneration zone can be ,` metal or other refractory materials which can withstand relatively the ,;.
high temperatures and the attrition conditions present in fluldized regen-;. eration processes.
* * DESCRIPTION OF THE INVENTION * *
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:., At the outset, the definition of various terms used herein will .~ be helpful to an understanding of the process of our invention.
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The term "afterburning" as generally understood by those skilled in the art means the incomplete oxidation of C0 to C02 within the regenera-tion zone or the flue gas line. Generally afterburning is characterized by a rapid temperature increase and occurs during periods of unsteady state operations or process "upset". It is, therefore, usually of short duration until steady state operations are resumed.
In contrast to afterburning, the term "essentially complete con-version of Cû" shall refer to the intentional, sustained, controlled, and essentlally complete combustion of C0 to C02 within the regeneration zone and more specifically within a dense-phase bed of catalyst maintained in the :~.'' regeneration zone. "Essentially complete" shall mean that the C0 concentra~
tion is the spent regeneration gas (hereinafter defined) has been reduced ~ to less than about 1000 ppm and more preferably less than 500 ppm.
: The term "spent catalyst'as used in this specification means catalyst withdrawn from a hydrocarbon conversion zo~e because of reduced ~; activity caused by coke deposits. Spent catalyst passing into the dense-. . .
: phase catalyst bed can contain anywhere from a few tenths up to about 5 ,.:
;~ wt. 0 of coke, but typically in FCC operations spent catalyst will contain ~- from about 0.5 to about 1.5 wt. 'b coke.
The term "regenerated catalyst" as used in this speci;icati~n shall mean catalyst from which at least a portion of coke has been removed.
Regenerated catalyst produced by our process will generally contain less than about 0.5 wt. ~ coke and more typically will contain from about 0.01 ~- to about 0.15 wt. b coke.
- ~ 25 The term "regeneration gas" as used in this specification shall mean, in a generic sense, any gas which is to contact catalyst or which - has contacted catalyst within the regeneration zone. Specifically, the ;i term "fresh regeneration gas" shall include Free-oxygen-containing gases ... .
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- ~07;~527 such as air or oxygen enriched or deficient air which pass into the den æ -phasebed of the regeneration zone to allow oxidation of coke from the spent catalyst and essentially camplete oonversion of CO. Usually the fresh regeneration gas will be air. Free-oxygen shall refer to unoombined oxygen present in a regene-ration gas.
m e term "partially spent regeneration gas" shall refer to regeneration gas which has contacted catalyst within the dense-phase bed and which oontains areduoed quantity of free-oxygen as oo~pared to fresh regeneration gas. Partiallyspent regeneration gas will generally contain several v~lume per oe nt each of nitrogen, free-oxygen, OE bon monoxide, carbon dioxide, and water. More specifically, the partially spent regeneration gas will senerally contain f w m about 7 to about 14 vol. ~ each of carbon monoxide and carbon dioxide.
The term "spent regeneration gas" shall mean regeneration gas which contains a redu oe d concentration of CO as ccmpared to partially sFent regeneration gas. Preferably the spent regeneration gas will contain less than about 1000 ppmof CO and more typically and preferably less than about 500 ppm. CO. FYee oxygen, carbon dioxide, nitrogen, and water will also be present in the spent regeneration gas. The free-oxygen ooncentration of the spent reseneration gas will generally be greater than 0.1 vol. ~ of the spent regeneration gas~
The ter~s "dense-phase" and "~dilute-phase" are ccmmcnly used terms in the art of ~CC to generally characterize catalyst densities in various parts of .,. ~j ~ the regeneration zone. ~hile the demarkation density is somewhat ill-defined, . ., `~` as the term "dense-phase" is used herein it shall refer to regions within t~e ~?:~ 3 ' regeneration zone where the catalyst density is greater than about 240 kg/m :. .
and as "dilute-phase" is used herein it refers to regions where the catalvst density is less than abou-t 240kg/m3. Usually the dense-phase density will be in the range of from about 320 to 640 kg/m3 or ~,.
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- more and the dilute-phase density will b m.uch less than 240 kg/m and in the ; : range o~ from about.l.6 to akout 80 kg/m . Catalyst densities within FCC vessels - are oommonly measured by measuring pressure or head differen oe s across pressu~e -; taps installed in the vessels and spa oe d at known distances apart.
. Our pro oe ss basically centers around a pnocess for oxidizing coke . .
from a spent catalytic cracking catalyst containing catalytically effective amounts of a CO oonversion promotor and for initiating and o~ntrolling essentially oomplete : ' conversion of CO, in tho presen oe of the promotor, to CO2 within a dense-phase bed.
o~ catalyst maintained in a regeneration zone.
In the process of our invention coke oxidation and essentially complete . catalyæed conversion of CO to CO2 are initiated and take pla oe within a dense ;~ catalyst bed in the regeneration zone and at least a portion of the heat of oombustion of CO is recovered by the regenerated catalyst for use within the FCC
prccess. Regenerated catalyst which passes to the hydrocarbon reaction zone is therefore at a higher te~perature than regenerated catalyst produced by a non~
CC-burning regeneration zone thereby permitting a reduction or elimunation of external feed preheat. P~dditionally, the CO conversion is oontrolled to ensure essentially oomplete elimination of atmospheric CO pollution without the require-ment of an external CO boiler. r~oreover the process of our invention is applicable :: 20 to present day regeneration units without extensive modifications or revamp.
i ~ Additionally it is a feature of our process tha-t the essentially . o~nplete conversion of CO to C02 is cat~lyzed by catalytically effective amou~ts . of a CO conversion promotor which passes as part of the ~luid cracking catalyst throughout the FCC pro oe ss. I'he rate of coke oxidation is not affected by employing a fluid catalytic cracking catal~st containing a CO oonversion promotor nor is the conversion of hydrocarbons within the hydrocarbon oonversion zone but the rate of CO oonversion is increased~
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With a C0 conversion promotor the kinetic rate constant for the reaction C0 + ~2 ~~ C2 may be increased typically from Z to 5 times or more. Thus ;. a faster rate of C0 conversion can be obtained in the presence of a C0 con-version promotor at a given regeneration zone temperature and oxygen con-centration than can be obtained without the promotor. Since perfect disper-; ; sion and ideal mixing of the fresh regeneration gas within the catalyst in ; the dense-phase bed are never achieved, it has often happened that the rate . of reaction of C0 oxidation must be increased to ensure that essentially '' D complete conversion of C0 occurs within the dense bed. The rate of reaction has been increased by increasing the regeneration zone temperature or by -:.` increasing the fresh regeneration gas (oxygen concentration). Regeneration ;. zone temperatures were increased by such methods as burning torch oil in .. . .
; the regeneration zone increasing the amount of slurry oil recycle to the ,. .. .
~: hydrocarbon conversion zone thereby producing more coke to be burned, pre-, 15 heating the fresh regeneration gas to the regeneration zone, preheating the ` :~ feed to the hydrocarbon conversion zone ar by a combinatjon of such methods.
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. Such methods generally increase the ope~ating cost of the FCC process and . .
.. . take away some of the flexibility of the FCC process. Employing an FCC
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:~ 20 motor permits a reduct;on or elimination of torch oil burning and slurry .. oil recYcle. a reduction or elimination of fresh regeneration gas and feed ...,~, . . .
~' preheat, and a reduction in the amount of excess fresh regeneration gas required for essentially complete conversion of C0 within the regeneration , : zone.
Suitable catalysts for use in the process of our inVention can comprise any of the catalyst known to the art of fluid catalytic cracking : and contalning catalytically effective amounts of a C0 conversion promotor.
~` The term "catalytically effective amounts" shall generally mean such amounts ; -14-.'~. `, '- . , .
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of a promotor as will increase the kinetic rate constant of C0 conversion :. .
; to C02. Such amounts can be from a few weight parts per million up to about 20 wt. ~ or more of the FCC catalyst. More preferably such amounts will range from about 100 wt. ppm. to about 10 wt. % of the FCC catalyst.
Suitable C0 conversion promotors shall broadly comprise one or more oxides selected from the transition metals and the rare earth metals. Par--. ticularly suitable C0 conversion promotors will comprise one or more oxides selected from the group consisting of vanadium oxide, chromium oxide, man-ganese oxide, iron oxide, cobait oxide, nickel oxide, copper oxide, palladium oxide, platinum oxide, and rare earth metal oxides. The C0 conversion Pro-motors can be incorporated into amorphous FCC catalysts comprising silica and/or alumina or into any of the zeolite-containing FCC catalysts by any suitable metho~ known to the catalyst manufacturing art such as copre-cipitation or cogelling or impregnation. Suitable zeolites include both naturally occuring and synthetic crystalline aluminosilicate materials known to the art such as faujasite, mordenite, chabazite, type X and type Y zeo-: lites, the the so-called "ultrastable" crystalline aluminosilicate materials.
i, In order to initiate and sustain essentially complete combustion -~ of C0 to C02 within the dense bed of a regeneration zone t~o requirements .~ 20 must be met: the dense bed temperature must be high enough to produce a ; sufficient fast rate of reaction of C0 oxidation and the quantity of fresn regeneration gas must be at least sufficient stoichiometrically for essen-~ tially complete C0 oxidation.
`~ The ratP of reaction of C0 oxidation must be sufficiently fast to permit essentially complete combustion of C0 within a reasonable gas resi-dense time in the dense bed of the regeneration zone. If the rate of reac-tion is too slow, it is possible that all of the C0 combustion wili not be completed ln the time interual that partially spent regeneration gas is in . '~ .
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the dense bed where there is sufficient catalyst density to absorb the heat . of reaction. In this situation, C0 conversion can then take place in the - dilute phase region of the regeneration zone or in the flue gas line out-side of the regeneration zone where it is not desirable. Temperature above some minimum with or without the presence of a C0 conversion promotor is therefore important to insure the proper rate or reaction.
The proper quantity of fresh regeneration gas is important because .~ without sufficient oxygen present to support the reaction of C0 oxidation - to C02, the reaction will not occur no matter what the temperature is in the ,, 10 regeneration zone. Furthermore, it is important that some excess of fresh ...
, ~ regeneration be present beyond that stoichiometrically requ;red to ensure ``; the essentially complete conversion of the C0.
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. ~ It is generally recognlzed that FCC regeneration zone operation - is essentially adiabatic. While it is true that some heat is lost to the ~ ~ 15 surroundings that amount of heat is a small fraction of the total heat -` ~ released. Since regeneration zone operation is essentially adiabatic, the i. 2 regeneration zone temperature is a direct function of the amount of fuel ., ~, .
' burned in the regeneration zone. As the total amount of fue~ increases the regeneration zone temperature increases. Until intentional conversion of cn to C02 is initiated in the regeneration zone, the fuel is primarily coke ; ~ on spent catalyst but will also include any adsorbed or interstitial hYdro-carbons passing into the regeneration zone with the spent catalyst or any "torch oil" burned in the regeneration zone. Indeed, during initial FCC
process startup the fuel is primarily torch oil until sufficient coke has ` 2S been built up on the catalyst. When intentional conversion of C0 to C02 is initiated then C0 con-tributes significantly to the total fuel burned in the - regeneration zone.
: Thus b~ controlling either the amount of fuel passed into the .
regeneration zone or the fresh regeneration gas which would allow the fuel .
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to be burned, the regeneration zone temperature can be controlled at any `~. temperature from about 399C. up to about 760C. The amount of coke ; can typically be controlled by varying the hydrocarbon reaction zone op-- erating conditions such as temperature or by vary;ng the composition of the feedstock to that reaction zone. Specifically, more coke is produced as the hydrocarbon reaction zone conditions become more severe or as the feedstock becomes heavier, that is, as the Conradson carbon content in-creases.
; It has been common practice to limit the operating temperatures of conventional (non-CO-burning~ regeneration zones to about 677 C. On FCC processes employing amorphous catalysts this was generally done by limiting the hydrocarbon reaction zone temperature to some maximum or by limiting the amount of coke-producing slurry oil recycled to the hydro-. i,. . - .
~. carbon reaction zone to some maximum. These maximums are determined, for ~, any particular feedstock, primarily by operating experience on the FCC
process. On FCC process employing zeolite-containing catalysts where less ~ coke was produced it often became necessary to burn torch oil to maintain -~ a regeneration zone temperature of about 677 C. A temperature near around ; 677C. was desired to produce the hottest possible regenerated catalyst .~ ~ 20 yet ~he temperature was limited to a maximum of about 677C. both for possible metallurgy limitations and because the rate of reaction of after-burning,should it occur during process upsets, was relatively slow.
In the process of our invention spent catalyst containing cata- -~
lytically effective amounts of a CO conversion promotor and fresh regen-.
eration gas are first passed to a dense bed in the regeneration zone. More specifically, fresh regeneration gas is lnitially passed into the dense bed at a first flow rate sufficient to oxidize coke to produce partially spen-t ~ regeneration gas. Even more specifically, this first flow rate will prefer-., . , , ' .
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ably ke in the range equivalent to about 8 b~ about 12 grams of air per gram of ; coke entering the regeneration zone. Coke is then oxidized at first oxidizing aonditions to produoe regenerated catalyst and partially spent regeneration gas.
First oxidizing conditions will include a dense bed temperature of ; ;
;~; from about 399C to about 677C. not because of any metallurgical limitation . ., but because the rate of reaction of afterkurning, should it occur during unsteady startup conditions, is relatively slcw. During startup, torch oil will be burned in the reqeneration zone until sufficient coke is deposited on the catal~st in the hydr~carkon reaction zone~ Thereafter torch oil will gradually be reduoe d or eliminated as the amount of coke on spent catalyst increases and the dense bed ,~ temperature will be limited to about 677C. by the methods described above.
~ Other first oxidizing conditions will include an aperating pressure of from about -- atmospheric pressure to about 4.4 atm. with the pre~erred range being from about ~ 2 to about 3.7 atm. A~ditionally, superficial fresh regeneration gas velocities -~, will ke limited to the transport velocity, that is, the velocity past which the catalyst w~uld be carried out of the dense bed upward into the dilute phase region.
Superficial gas velocities will therefore preferably be less than about 1 metre ,~ per second with 0.5 to 0.8 metre per seoond being the usual range.
~ After coke is being oxidized to produce regenerated catalyst and ~ 20 partially spent regeneration gas the dense bed temperature is then increased to a second tem~erature of from akout 677C. to about 760C. so that the rate of CO
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- oxidation when it is allowed to occur will be sufficiently fast to ensure essentially complete conversion of CO to C~2 within the dense bed. m e temperature can be increased by any of several ~ethods or ca~bination of methods.
The severity of operating conditions in the ~' ~
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; hydrocarbon reaction zone can be increased thereby producing more coke on . spent catalyst; the amount of slurry oil recycle to the hydrocarbon reac-tion zone can be increased to produce more coke on spent catalysti torch oil can again be added or increased to the regeneration zone; stripping of spent catalyst can be reduced thereby allowing more combustible material to pass with the spent catalyst into the regeneration zone; or, a heavier `~ feedstock can be employed.
The fresh regeneration gas is next increased from the first flow . . .
, rate to a second flow rate stoichiometrically sufficient to permit essentially completely oxidation of CO to C02 thereby producing spent regeneration gas.
"~r,,, This second flow rate will more preferably be in the range equivalent to a-bout 12 to about 16 grams of air per gram of coke entering the regeneration ,~ zonP. Carbon monoxide is then oxidized in the dense bed at second oxidiz-,r,g , ; conditions to produce spent regeneration gas. ~ith ~he dense bed temperature ~ 15 at the second temperature of from about 677C- to about 760C., essen-. . .
.~ tially complete conversion of CO to C02 within the dense bed will occur - essentially spontaneously as soon as the fresh regeneration gas rate is increased to the second flow rate. Since the oxidation of CO is exothermic it will not be necessary, once CO oxidation has been initiated, to continue 20 the measures that were employed to increase the dense bed temperature to .` the second temperature.
Second oxidizing conditions will include a temperature from about 677C. to about 760C. and a superficial fresh rege~eration gas velocity limited as described above to the transport velocity. Operating pressure - 25 will be from about atmospheric pressure to about 4.A atm. with the preferred range being from about 2 to about 3.7 atm.
~ At this state of regeneration zone operation, it 1s possible that ; normal ~ariations which occur in feedstock flow rate and particularly com-. ~ .
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~" position will result in intervals in which all of-the C0 is not essentially ,'. completely converted to C02. The flow rate of fresh regeneration gas at ..:
, this state of operation is just sufficient ~or essentially complete oxida-"'.... tion of C0 to C02 with no provision for an excess. The C0 concentration ,.~ . :, ; 5 of the spent regeneration gas may increase during these intervals from a ',., preferred concentration of less than about 500 ppm. to se~eral thausand : .~
,s ~ ppm. C0. The proces$ of our invention includes steps to prevent this and ~, to ensure the essentially complete combustion of CO to C02 in sp;te of such variations.
Specifically in our process the spent regeneration gas is analyzed , ~ by analyzing means to obtain a measured free-oxygen concentration and that ,', measured concentration is then compared with a predetermined free-oxygen .
concentration. The predet,ermined free-oxygen concent,ation of the spent -. regeneration gas will represent an amount of free oxygen in excess of that ` 15 stoichiometrically required for C0 oxidation. Thereafter, the fresh regen-~' eration gas rate is regulated at a third flow rate to maintain a measured :.~
t- free-oxygen concentration equal to the predetermined -free-oxygen concentra-: .
tion thereby ensuring essentially complete conversion of C0 to C02. The ~'. third flow rat2 will therefore be higher than the second flow rate. Typi-,,;~, 20 cally the third flow rate will be equlvalent to about 13 to about 17 grams of air per gram of coke.
The free-oxygen concentration of the spent regeneration gas Will ~ generally be greater than about 0.1 volume percent of the spent regeneration -~` gas stream and more specifically can be from about 0., vol. ~ free oxygen ' 25 to about 10 vol. ~ or more free oxygen. Preferably, the Free-oxygen con-; ' centration will be from about 0.2 vol. ~ to about 5 vol. % of the spent regeneration gas and more preferably will be from about 1 vol. % to about , , 3 vol. %.
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:, I . i 7;~S~7 The analyzing means used in the process of this invention to : measure the free oxygen concentration in the spent regeneration gas can include any apparatus capable of measuring the concentration f 2 in a gas mixture comprising 2. CO, C02, N2, H2, and light hydrocarbons in con-r 5 centrations ranging from volume parts per million to many volume percent~
Specifically included are Orsat, gas chromatographic, and mass spectro-graphic apparatus. Samples of flue gas may be periodically wlthdrawn ` manually from the process and manually analyzed or may be automatically . .
withdrawn and analyzed continuously or at programmed time intervals by sampling and analyzing means.
After the measured free-oxygen concentration has been determined and compared with the predetermined free oxygen concentration a regulating - means will be adjusted manually or automatically if necessary to pass more or less fresh regeneration gas into the regeneration zone. Typically, the regulating means wili comprise a valve for controlling flow or a con-trol device which can control speed or discharge pressure of a fresh re-- generatjon gas compressor to change the flo~ rate of fresh regeneration gas into the regeneration zone. In an automatic system, the analyzing means may generate and send to a control means an output signal representing the measured free-oxygen concentration The control means may typically con-nect the analyzing means to the regulating means or may be incorporated within the design of either and have a variable setpoint representing the predetermined free oxygen concentration. The control means recei~es the analyzing means output signal, compares it to the setpoint value and if a differential exists, passes a signal to the regulating means to change the - fresh regeneration gas rate into the regeneration zone so that the measured free-oxygen concentration in the spent regeneration gas will equal the pre-~ determined free-oxygen concentration. The analyzing means, control means, ::
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;~ and regulating means may all be connected by methods known in the art and `~ can be incorporated iuto a single control unit.
~ The following examples are presented to illustrate some of the - features and advantages of the process of our invention and are not in-tended to unduly restrict the limits of the claims appended hereto.
EXAM LE I
In this example coke and C0 were oxidi~ed in a regenerator oper-ating at a dense bed temperature of about 732 C. and a pressure of about ~ 3.7 atm. Approximately 945.000 kg/hr of spent catalyst containing about '1,. D 10 0.8 wt. ~ coke was passed into the regenerator while the input of air to ;~ ~ the regenerator was rnaintained at a ratio of about 14.60 grams of air per gram of coke.
The air input rate to the regenerator was controlled to maintain a predetermined free-oxygen concentration in the spent regeneration gas to about 1-2 vol. ~. The conversion of C0 to C02 was substantially complete and was maintained steadily and continuous1y within the dense bed of cata-lyst in the regenerator. The superficial gas velocity was about 0.85 metre/
second.
By being able to control the conversion of C0 in the dense bed of the regenerator the reactor temperature was able to be raised to about 538C. with no additjon of feed preheat which increased conversion and the quantity of gasoline and lighter compounds produced.
`. EXAMPLE Il : In this example, a comparison is made between the operations of .. ZS a commercial FCC unit before and after essentially complete C0 conversion : was initiated and controlled.
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Commercial FCC Operation Before and After CO Convers~on ~ ~lithoutCO Conversion ; CO ConversionTaking Place_ : 5 Reactor Temperature, C. O 530 530 Regenerator Dense Phase Temp., OC.677 732 Regenerator Dilute Phase Temp., C.699 734 Feed Preheat Temp., 363 260 ; Conversion, L.V.~ 79.4 79.1 Coke Yield, wt.~ 5.4 4.6 Gasoline Yield, L.V.~ 63.2 65.6 CO in Flue Gas, Vol.'l,10.1 0.0*
C02 in Flue Gas, Vol. ',u 9.7 16.7
2 in Flue Gas, Vol. % 0.2 2.1 ` ~Actual determination was 350 ppm.
. The above data demonstrates-the advantages of reduced ieed pre-heat, higher conversion, and higher gasoline yield made possible by the process of our invention. As well, CO pollution has essentially been elim-inated without tne requirement of an external CO boiler.
EXAMPLE III
This example shows a comparison of operations from a commercial FCC process before and after an FCC catalyst containing a CO conversion promotor was used in the regeneration zone where1 for both operations, es-` ~ sentially complete conversion of CO to C02 was taking place. Data are shown in Table 2.
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BeforeAfter S Reactor Temperature, C. 535 533 ~: Feed Rate, m3/hr 185 178 '~ S Slurry Oil Recycle, 3/hr7.8 5.7 Feed Preheat, C. - -Regenerator Temperatures, C. 169 185 Cyclones 780 738 Dilute Phase 717 703 Dense Phase 715 703 : Air lleat3er 169 185 Air Rate, m /min 2,040 1,810 Superficial Velocity, m/sec 1.1 0.9 :,. .
Spent Regen. Gas Analysis C2~ vol. % 12.5 16.5 0,, vol. ' 4.4 1.2 ;; C'O , vol . ppm. < 500 ~ ~
: . .
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The comparison shows a significant reduction in air rate of from 2,040 m3~min to 1,810 m3/min made possible by employing an FCC catalyst con-~ taining a CO conversion promotor. This reduction in air rate reduced the `~ superficial velocity of the air in the regeneration zone from 1.1 m/sec to .~ 0.9 m/sec and resulted in lower catalyst loss from the regeneration zone.
~; 20 Lower regeneration zone temperatures, a reduced slurry oil recycle, and a ~ ::
:` smaller excess of 2 in the spent regeneration gas are also shown for . . the operation which employed catalyst containing a CO conversion promotor.
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. The above data demonstrates-the advantages of reduced ieed pre-heat, higher conversion, and higher gasoline yield made possible by the process of our invention. As well, CO pollution has essentially been elim-inated without tne requirement of an external CO boiler.
EXAMPLE III
This example shows a comparison of operations from a commercial FCC process before and after an FCC catalyst containing a CO conversion promotor was used in the regeneration zone where1 for both operations, es-` ~ sentially complete conversion of CO to C02 was taking place. Data are shown in Table 2.
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BeforeAfter S Reactor Temperature, C. 535 533 ~: Feed Rate, m3/hr 185 178 '~ S Slurry Oil Recycle, 3/hr7.8 5.7 Feed Preheat, C. - -Regenerator Temperatures, C. 169 185 Cyclones 780 738 Dilute Phase 717 703 Dense Phase 715 703 : Air lleat3er 169 185 Air Rate, m /min 2,040 1,810 Superficial Velocity, m/sec 1.1 0.9 :,. .
Spent Regen. Gas Analysis C2~ vol. % 12.5 16.5 0,, vol. ' 4.4 1.2 ;; C'O , vol . ppm. < 500 ~ ~
: . .
:
The comparison shows a significant reduction in air rate of from 2,040 m3~min to 1,810 m3/min made possible by employing an FCC catalyst con-~ taining a CO conversion promotor. This reduction in air rate reduced the `~ superficial velocity of the air in the regeneration zone from 1.1 m/sec to .~ 0.9 m/sec and resulted in lower catalyst loss from the regeneration zone.
~; 20 Lower regeneration zone temperatures, a reduced slurry oil recycle, and a ~ ::
:` smaller excess of 2 in the spent regeneration gas are also shown for . . the operation which employed catalyst containing a CO conversion promotor.
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Claims (12)
1. A process for the regeneration of coke-contaminated fluid catalytic cracking catalyst containing catalytically effective amounts of a C0 conversion promotor and for the essentially complete catalytic con-version of carbon monoxide to carbon dioxide which process comprises the steps of:
a. passing to a dense-phase catalyst bed in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate suffi-cient to oxidize coke to produce partially spent regeneration gas;
b. oxidizing coke at first oxidizing conditions including a catalyst bed first temperature of from 399 °C. to 677° C. to produce regen-erated catalyst and partially spent regeneration gas containing C0;
c. increasing the catalyst bed temperature from said first temperature to a second temperature of from 677° C. to 760 °C.;
d. passing to the catalyst bed fresh regeneration gas at a sec-ond flow rate stoichiometrically sufficient to essentially completely oxidize C0 to C02;
e. oxidizing in said catalyst bed, maintained at second oxi-dizing conditions including the presence of said C0 conversion promotor, C0 to produce spent regeneration gas;
f. analyzing spent regeneration gas to obtain a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a predetermined free-oxygen concentration; and, g. thereafter regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially com-plete conversion of C0 to C02.
a. passing to a dense-phase catalyst bed in a regeneration zone said catalyst and fresh regeneration gas at a first flow rate suffi-cient to oxidize coke to produce partially spent regeneration gas;
b. oxidizing coke at first oxidizing conditions including a catalyst bed first temperature of from 399 °C. to 677° C. to produce regen-erated catalyst and partially spent regeneration gas containing C0;
c. increasing the catalyst bed temperature from said first temperature to a second temperature of from 677° C. to 760 °C.;
d. passing to the catalyst bed fresh regeneration gas at a sec-ond flow rate stoichiometrically sufficient to essentially completely oxidize C0 to C02;
e. oxidizing in said catalyst bed, maintained at second oxi-dizing conditions including the presence of said C0 conversion promotor, C0 to produce spent regeneration gas;
f. analyzing spent regeneration gas to obtain a measured free-oxygen concentration and comparing the measured free-oxygen concentration to a predetermined free-oxygen concentration; and, g. thereafter regulating fresh regeneration gas at a third flow rate to maintain the measured free-oxygen concentration equal to the predetermined free-oxygen concentration thereby ensuring essentially com-plete conversion of C0 to C02.
2. The process of Claim 1 wherein said C0 conversion promotor com-prises one or more oxides selected from vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, palladium oxide, platinum oxide, and rare earth metal oxides.
3. The process of Claim 1 or 2 wherein said regeneration zone comprises a dense-phase catalyst bed and a dilute-phase catalyst region super-imposed over said bed.
4. The process of Claim 1 wherein said first flow rate of fresh regeneration gas is equivalent to 8 to 12 grams of air per gram of coke.
5. The process of Claim 1 wherein said second flow rate of fresh regeneration gas is equivalent to 12 to 16 grams of air per gram of coke.
6. The process of Claim 1 wherein said second oxidizing conditions include a temperature within the range of from 677°C to 760°C.
7. The process of Claim 1 wherein said partially spent regeneration gas contains from 7 to 14 vol. % each of C0 and C02.
8. The process of Claim 1 wherein said predetermined free-oxygen concentration is within the range of from 0.1 to 10 vol. % of the spent regeneration gas.
9. The process of Claim 8 wherein said predetermined free-oxygen concentration is within the range of from 0.2 to 5 vol. % of the spent regeneration gas.
10. The process of Claim 1 wherein said spent regeneration gas contains less than 1000 ppm. C0.
11. The process of Claim 10 wherein said spent regeneration gas contains less than 500 ppm C0.
12. The process of Claim 1 being operated within a pressure range of from 1 to 4.4 atmospheres.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60185175A | 1975-08-04 | 1975-08-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072527A true CA1072527A (en) | 1980-02-26 |
Family
ID=24409020
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA258,417A Expired CA1072527A (en) | 1975-08-04 | 1976-08-04 | Process for initiating and controlling dense-bed oxidation of coke and catalyzed oxidation of co to co2 in an fcc regeneration zone |
Country Status (29)
| Country | Link |
|---|---|
| JP (1) | JPS5242492A (en) |
| AT (1) | AT353753B (en) |
| AU (1) | AU501360B2 (en) |
| BE (1) | BE844870A (en) |
| BR (1) | BR7605098A (en) |
| CA (1) | CA1072527A (en) |
| CS (1) | CS226165B2 (en) |
| DD (1) | DD126209A5 (en) |
| DE (1) | DE2633995C3 (en) |
| DK (1) | DK350076A (en) |
| EG (1) | EG12448A (en) |
| ES (1) | ES450414A1 (en) |
| FI (1) | FI61513C (en) |
| FR (1) | FR2320137A2 (en) |
| GB (1) | GB1551925A (en) |
| GR (1) | GR61129B (en) |
| IE (1) | IE43837B1 (en) |
| IL (1) | IL50141A (en) |
| IN (1) | IN155728B (en) |
| IT (1) | IT1066750B (en) |
| MX (1) | MX143792A (en) |
| NL (1) | NL7608620A (en) |
| PH (1) | PH13774A (en) |
| PL (1) | PL107089B3 (en) |
| PT (1) | PT65408B (en) |
| SE (1) | SE427427B (en) |
| TR (1) | TR18951A (en) |
| YU (1) | YU39970B (en) |
| ZA (1) | ZA764638B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61127613A (en) * | 1984-11-22 | 1986-06-14 | Mitsui Toatsu Chem Inc | Purifying method of carbon dioxide |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE792165A (en) * | 1971-11-30 | 1973-05-30 | Standard Oil Co | PERFECTED PROCESS OF CATALYTIC CRACKING WITH SENSITIVELY COMPLETE COMBUSTION OF CARBON MONOXIDE DURING CATALYST REGENERATION |
| JPS4951195A (en) * | 1973-05-30 | 1974-05-17 | ||
| BE832738A (en) * | 1975-08-26 | 1975-12-16 | PROCESS FOR INITIATING SUBSTANTIALLY COMPLETE OXIDATION OF CO TO CO 2 IN A DEPLETED CATALYST REGENERATION ZONE |
-
1976
- 1976-07-26 PT PT65408A patent/PT65408B/en unknown
- 1976-07-27 IL IL50141A patent/IL50141A/en unknown
- 1976-07-29 DE DE2633995A patent/DE2633995C3/en not_active Expired
- 1976-07-30 FI FI762190A patent/FI61513C/en not_active IP Right Cessation
- 1976-07-30 IN IN1360/CAL/76A patent/IN155728B/en unknown
- 1976-08-02 YU YU1901/76A patent/YU39970B/en unknown
- 1976-08-02 FR FR7623569A patent/FR2320137A2/en active Granted
- 1976-08-02 ZA ZA764638A patent/ZA764638B/en unknown
- 1976-08-03 IE IE1711/76A patent/IE43837B1/en unknown
- 1976-08-03 GB GB32257/76A patent/GB1551925A/en not_active Expired
- 1976-08-03 ES ES450414A patent/ES450414A1/en not_active Expired
- 1976-08-03 DK DK350076A patent/DK350076A/en not_active Application Discontinuation
- 1976-08-03 NL NL7608620A patent/NL7608620A/en not_active Application Discontinuation
- 1976-08-03 AU AU16528/76A patent/AU501360B2/en not_active Expired
- 1976-08-03 CS CS765077A patent/CS226165B2/en unknown
- 1976-08-03 DD DD194198A patent/DD126209A5/xx unknown
- 1976-08-03 SE SE7608715A patent/SE427427B/en not_active IP Right Cessation
- 1976-08-04 PL PL1976191617A patent/PL107089B3/en unknown
- 1976-08-04 MX MX165772A patent/MX143792A/en unknown
- 1976-08-04 JP JP51093094A patent/JPS5242492A/en active Pending
- 1976-08-04 IT IT50765/76A patent/IT1066750B/en active
- 1976-08-04 CA CA258,417A patent/CA1072527A/en not_active Expired
- 1976-08-04 GR GR51408A patent/GR61129B/en unknown
- 1976-08-04 EG EG477/76A patent/EG12448A/en active
- 1976-08-04 BE BE169547A patent/BE844870A/en not_active IP Right Cessation
- 1976-08-04 AT AT577876A patent/AT353753B/en not_active IP Right Cessation
- 1976-08-04 TR TR18951A patent/TR18951A/en unknown
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- 1976-08-04 BR BR7605098A patent/BR7605098A/en unknown
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