Note: Descriptions are shown in the official language in which they were submitted.
104z;~77
¦ This invention relates to an improved fluid catalytic cracking
¦ process, and is more specifically directed to the completion of the combustion
¦ of CO in fluidized cracking unit catalyst regenerator flue gas, without the
¦ use of a conventional CO boiler. The CO combustion is completed in a
¦ flue gas combustor, wherein the heat of combustion is recovered by heat
-I exchange with cracking catalyst particles and advantageously utilized
¦ within the system. The improved fluid cracking process of this invention
includes essentially complete combustion of CO remaining in catalyst
regenerator flue gas in a manner which substantially reduces auxiliary
10 1 heating equipment and expense in the overall fluid cracking unit operation.
¦ Advantageously, the process of this invention is adaptable to conventional
hydrocarbon catalytic cracking units to reduce operating 0sts and to
¦ replace or assist preheat operations.
¦ This invention is psrticularly useful in the fluid catalytic cracking
15 of mineral oil feedstocks and iB advantageously employed where at least a
substantial portion of the cracking is effected in a dilute-phase transfer
line or riser reactor system and products having a lower boiling range
than the feed are obtained. This invention makes possible an enhanced
extent of energy production and conservation within a cyclic process for
I
:~ 20 1 the catalytic cracking of hydrocarbon feedstocks boiling above the gasoline
¦ range, which includes provision for separation of catalyst from conversion
products, regeneration of the separated catalyst and recycle of the regenerated
catalyst to the reactor for the cracking of additional feedstock, wherein an
;increased proportion of heat energy is utilized within the cyclic system by
25 improved continuous transfer from the exothermic to the endothermic
~. . ,1, ~
104Z377
or in an elongated riser reactor, and the mixture is maintained at an elevated
temperature in a fluidized or dispersed stflte for a period of time ~umcient
to effect the desired degree of cracking to lower molecular weigm hydro-
carbons typically present in motor gasolines and distillate fuels. Suitable
5 hydrocarbon feeds boil generally above the gasoline boiling range, e.g.,
; within the range from about 400 to about 1200F., and are usually cracked
at temperatures ranging from about 850 to 1050F.
In the catalytic process, some non-volatile carbonaceous material,
or coke, i8 deposited on the catalyst particles. Coke compriseæ highly
l0 condensed aromatic hydrocarbons which generally contain a minor amount
of hydrogen, say about 4-10 wt. %. As coke builds up on the catalyst, the
activity of the catalyst for cracking and the selectivity of the catalyst for
producing gasoline blending stocks diminish. The catalyst particles may
recover a major proportion of their original capabilities by removal of
lS most of the coke therefrom in a suitable regeneration process.
Catalyst regeneration is accomplished by burning the coke deposits
from the catalyst surface with molecular oxygen-containing gas, such as
air. Many regeneration techniques are practiced commercially, whereby
signiffcant restoration of catalyst activity is achieved in response to the
20 degree of coke removal. As coke is progressively removed from the catalyst,
removal of the remaining coke becomes most difficult, and, in practice, an
intermediate level of restored catalyst activity is accepted as an economic
, compromise .
The burning of coke deposits from the catalyst requires a large
25 volume of oxygen or air. Oxidation of coke may be character~ed in a
simplified manner as the oxidation of carbon and represented by t}le following
chemical equationæ:
:'
-2-
1 1~42377
¦ (a) C + 2 ~ CO2
¦ (b) 2C + 2 ~ 2CO
~, I (c) 2CO + 2-- ~2CO2.
¦ Reaceions (a) and (b) both occur under typical catalyst regeneration con-
5 1 ditions, wherein the catalyst temperature may range from about 1050 toabout 1300F., and are exemplary of gas-solid chemical interactions when
¦ regenerating catalyst at temperatures within this range. The effect of any
increase in temperature is reflected in an increased rate of combustion of
carbon and a more complete removal of carbon or coke from the catalyst
particles. As the increased rate of combustion is accompanied by an
increased evolution of heat, whenever sufficient oxygen is present, the
gas-phase reaction (c) may occur. This latter reaction is initiated and
propagated by free radicals.
; ~ ~ A major problem often encountered and sought to be avoided in
lS~ the practice, particularly of fluid catalyst regeneration, is the phenomenon
known as "afterburning", described, for example, in Hengstebeck,
Petroleum Processing, McGraw-Hill Book Co., 1959, at pages 160 and 175,
and discussed in Oil and Gas Journal, Volume 53 (No. 3), 1955, at pages
93-94. This term is descriptive of the further combustion of CO to CO2,
. 20 as represeMed by reaction (c) above, which i8 highly exothermic. After-
~ .
;; burning has been vigorously avoided in catalyst regeneration processesbecause it could lead to very high temperatures which may damage equip-
ment and cause permanent deactivation of the catalyst particles. Many fluid
catalyst regenerator operations have experienced afterburning, and a very
25 substantial body of art has developed around numerous means for controllinF
'~
-3-
104Z;~77
regeneration techniques so as to avoid afterburning. More recently, aR
¦ operators have soughe to raise regenerator temperatures for various reasons,
elaborate arrangements have also been developed for control of regenerator
temperatures at the point of incipient afterburning by suitable means for
5 ¦ control of the oxygen supply to the regenerator vessel as set forth, for
¦ example, in U.S. Patents Nos. 3,161,583 and 3,206,393, as well as in U.S.
Patent No. 3,513,087. In typical contemporary practice, accordingly, with
avoidance of afterburning, the flue gas from catalyst regenerators usually
contains very littIe oxygen and a substantial quantity of CO and Ca in
10 nearb equimolar amounts.
I
Further combustion of CO to Ca is an attractive source of hea.
energy because reaction (c) i~ highly exothermic. Afterburning can proceed
at temperatures above about 1100P., and liberates approximatel~r 4350 BTU/lb .
o CO oxidized. This typically represents about one-fourth of the total
15 ~ heat evolution realizable by complete combustion of coke. The combustion
~ of CO~ has been performed controllably in a separate CO boiler, after separa-
; tion of ~efnuent gas from catalyst, as described in, for example, U.S. Patent
~f ~ No. 2,753,925, with the released heat energy being employed in the genera-
tion of high pressure steam. Other uses of such heat energy have been
de~cribed in U.S. Pàtent~ Nos. 3,01a,96a and 3,137,133 (turbine drive)
and U.S. Patent No. 3,363,993 (preheating of petrolèum feedstock). Such
heat recovery processes serve to minimize the discharge of CO into the
tmosphere as a component of efnuent gases and to avoid a potentially
~5~ serious pollution hazard.
25 1
I -4-
~ `'' I
4Z377
;~ This inventioA relates to an improved fluid catalytic
cracking process, and is more specifically directed to the
completion of the combustion of CO in fluidized crac~ing unit
catalyst regenerator flue gas, without the use of a conventional
CO boiler. The CO combustion i$ completed in a flue gas combus-
tor, wherein the heat~of combustion is recovered by heat exchange
with cracking catalyst particles and advantageously utilized
within the system. The improved fluid cracking process of this
invention includes essentially complete combustion of CO remain-
10 - ing in catalyst regenerator flue gas in a manner which substan-
tially reduces auxiliary heating equipment and expense in the
overall fluid cracking unit operation. Advantageously, the
process of this invention is adaptable to conventional hydro-
carbon catalytic cracking units to reduce operating costs and
to replace or assist preheat operations.
Thus the present invention provides a hydrocarbon
catalytic cracking process, including hydrocarbon cracking and
catalyst regeneration, comprising regenerating fluidized hydro-
carbon cracking catalyst particles, which have been deactivated
~ 20 with coke deposits while employed in said hydrocarbon cracking,
- in a catalyst regenerator at regeneration temperature by contact
~- with an oxygen-containing gas stream to combust coke on the
.-
catalyst and produce a carbon monoxide-containing flue gas,
passing said carbon monoxide-containing flue gas from the
catalyst regenerator, oxidizing said carbon monoxide-containing
flue gas from the catalyst regenerator to substantially com-
pletely combust carbon monoxide contained therein to form a
- combusted effluent of reduced carbon monoxide content, with-
drawing catalyst from the catalyst regenerator, passing said
withdrawn catalyst, which is relatively free of carbonaceous
material, in heat exchange relation with said comhusted effluent
to transfer beat generated from the carbon monoxide combustion
B~ ~ _5_
`\ 104~377
to said cracking catalyst particles, and conveying the resulting
heated catalyst particles to said catalytic cracking process.
In another aspect, the present invention provides a
hydrocarbon catalytic cracking process, including the completion
of catalyst regeneration carbon monoxide-containing flue gas
combustion, comprising regenerating fluidized hydrocarbon
cracking catalyst particles which have been deactivated with
coke deposits while employed in the hydrocarbon cracking process,
in a catalyst regenerator at regeneration temperature by contact
With an oxygen-containing gas stream to combust coke on the
catalyst to produce a carbon monoxide-containing flue gas,
passing said carbon monoxide-containing flue gas from the
catalyst regenerator, combining said flue gas with an oxygen-
containing gas to form a combustible gaseous mixture, igniting
said combustible gaseous mixture to substantially complete the
combustion of the carbon monoxide contained therein, transfer-
ring heat generated from said carbon monoxide combustion at a
plurality of heat transfer areas to a plurality of hydrocarbon
cracking catalyst particle streams containing particles with-
drawn from said catalyst regenerator, said particles being
relatively free of carbonaceous material, and conveying resulting
hot hydrocarbon catalyst particle streams to the hydrocarbon
cracking process for heat exchange.
In a further aspect, the present invention provides
a hydrocarbon catalytic cracking process, including hydrocarbon
:;;
cracking and catalyst regeneration, comprising regenerating
fluidized hydrocarbon cracking catalyst particles, which have
been deactivated with coke deposits while employed in said
:: hydrocarbon cracking, in a catalyst regenerator at regeneration
.. 30 temperature by contact with an oxygen-containing gas stream to
combust coke on the catalyst and produce a carbon monoxide-
- containing flue gas, passing said carbon monoxi`de-containing
~ r -5a-
16~4Z377
flue gas from the catalyst regenerator, oxidizing said carbon
monoxide-containing flue gas from the catalyst regenerator to
combust carbon monoxide contained therein to form a combusted
effluent of reduced carbon monoxide content, withdrawing
~ catalyst from the catalyst regenerator, passing said withdrawn
catalyst, which is rèlatively free of car~onaceous material,
in heat exchange relation with said combusted eff.luent to
transfer heat generated from the carbon monoxide combustion
. to said cracking catalyst particles, and conveying the resulting
heated catalyst particles to said catalytic cracking process.
.~ This invention is particularly useful in the fluid
catalytic cracking of mineral oil feedstocks and is advanta-
~- geously employed where at least a substantial portion of the
~ cracking is effected in a dilute-phase transfer line-or riser
; reactor system and products having a lower boiling range than
the feed are obtained. This invention makes possible an
enhanced extent of energy production and conservation within
.~
~ a cyclic process for the catalytic cracking of hydrocarbon
. ~
feedstocks boiling above the gasoline range, which includes
20- provision for separation of catalyst from conversion products,
regeneration of the separated catalyst and recycle of the
regenerated catalyst to the reactor for the cracking of addi-
:tional feedstock, wherein an increased proportion of heat energy
is utilized within the cyclic system by improved continuous
transfer from the exothermic to the endothermic
~"
-,
~ -Sb-
104Z3'~7
¦ processing zones. A particularly suitable process for the practice of this
¦ invention comprises the fluid catalytic cracking process for the conversion
¦ of petroleum gas oils and heavier petroleum stocks to hydrocarbon com-
I ponents suitable for blending into fuels for automotive engines, jet power
¦ plants, domestic and industrial furnaces, and the like.
¦ The process of this invention contemplates passing flue gas
¦ containing CO and C02 from a fluid cracking unit catalyst regenerator, at
¦ normal regenerator exit temperature and composition, to a combustor in
¦ which the CO is ignited in the presence of air or other oxygen-containing
10 ¦ gas, and in which the heat of combustion is transferred, either by direct
contact or indirect heat exchange to cracking catalyst particles, which are
¦ cycled through the fluidized cracking unit. The term "combustor" is used
herein to designate the general area of the flue gas flow path outside of the
regenerator vessel at which CO combustion occurs, and is not restricted to
15 ¦ a particular structure.
The completion of CO combu~tion in this invention is accomplished
without the necessity for a CO boiler type design, as conventionally
~''`.f~ employed in the prior art, although the combustor area may be adapted to
include combustion initiators and promoters, and includes adaptation for
catalyst particle transport and heat transfer, as more fully set forth below .
~'~f~ ¦ The combustor, which may be in the flue gas or transfer line, may include
linings and/or may be constructed of high temperature-resistant ceramics,
,metals, and the like, in the combustion and heat transfer areas. Such
materials, which are generally used in the construction of high-temperature
-25 1 equipment, are well known in the art, and may be chosen according to the
specific operating conditions employed.
I
I
-6-
,, 11
11~4Z377
¦ The regenerator flue gas carbon monoxide combustion of thi~
¦ invention is conducted in the flue gas combustor in the presence of oxygen
¦ which is introduced as air or other oxygen-containing source. The oxygen
¦ source may be supplied to the transfer line at or just ahead of the point of
5 ¦ ignition, or it may be supplied in addition to, or, as the normal oxygen
¦ source to the catalyst regeneration vessel. When oxygen is supplied to the
¦ combustor via the regeneration vessel, it enters the transfer line with the
¦ flue gases, and the necessity for additional oxygen injection equipment
¦ may be avoided or reduced. However, when the oxygen source is fed to the
10 ¦ combustor, as, for example, by injection from a source other than the
regenerator flue gas, close control of combustion rate and, therefore, heat
¦ transfer rate, can be attained. This advantage may become particularly
¦ important when combustion is desired at two or more locations, as more
¦ fully discussed below.
15 ¦ CO combustion completion may be facilitated by various methods.
¦ For example, torches may be employed ae the point of ignition to achieve
¦ ignition temperatures. Such torches include torch oil injection devices,
which feed highly flammable, hot burning oil or other fuel, to the desired
¦ locations within the flue line. A single torch or a plurality may be employed
20 ¦ and arranged at different points within the combustion area. Other methods
¦ may be used in addition to, or in place of, torches, and include oxidants,
catalyzers, promoters and promotion systems. Among these promoters or
¦ catalysts are oxidation-promoting metals and/or their oxides and salts,
¦ and include such metals as iron, nickel, vanadium, copper, the rare earths
25 ¦ and their oxides and salts, and the like. Such promoters may be in the
I
301 -7-
11 l
~ 104Z377
¦ form of annealed particles, linings, honeycombs, screens, grids, and the
¦ like, and may be situated in the transfer line combustor in any known
¦ manner, such as, for example, by mechanical support. When such promoters
¦ are in a form which could impede catalyst particle flow, e.g. a honeycomb
5 ¦ structure, the openings may be large enough to permit catalyst particle
¦ flow, or catalyst particles may be fed to the hot flue gas down-stream from
the promoters, or the catalyst may recover the heat of combustion by other
methods which permit continuous particle flow, e .g. by indirect contact and
in such case catalyst-promoter contact can be avoided.
Suitable catalysts employed in this invention include those con-
. taining silica and/or alumina. Other refractory metal oxides such as
magnesia or zirconia may be employed limited only by their ability to be
. effectively regenerated under the selected conditions. With particular
regard to catalytic cracking, preferred catalysts include combinations of
15 silica and alumina, containing 10-50 wt. % alumina, and particularly their
admixtures with "molecular sieves" or crystalline aluminosilicates. Admix-
tures of clay-extended aluminas may also be employed. Such catalysts may
be prepared by any suitable method such as impregnation, milling, cogelling,
and the like, sub~ect only to provisions of the finished catalyst in a physical
20 form capable of fluidization.
Suitable "molecular sieves" include both naturally-occurring and
; synthetic crystalline aluminosilicate materials, such as faujasite, X-type
and Y-type aluminosilicate materials, and ultrastable, large-pore crystal-
line aluminosilicate materials. The alkali metal ions contained therein are
25 exchanged in large part by hydrogen ions and polyvalent metal ions,
,,
I -8-
lU4Z377
e.g. rare earths, by known techniques. When admixed with, for example,
silica-alumina to provide a petroleum cracking catalyst, the "molecular
sieve" content of the catalyst particles is suitably within the range from
about 5 to 15 wt. %, desirably 8-10 wt. %. An equilibrium "molecular sieve"
cracking catalyst may contain as little as about 1 wt. 96 cryetalline material.
The transfer of heat evolved from the CO combustion to the
catalyst particles is an important aspect of this invention. The heat may
be transferred to the cstalyst particles, either directly or indirectly,
although direct transfer may maintain heat losses at a minimum. The
catalyst particles are transferred to the CO combustor at a point before,
~; at, or downstream from where essentially complete combustion occurs.
The catalyst particles which are to be fed to the combustor may normally
be taken from the cracking catalyst regenerator or from the outlet of a
regenerated catalyst slip~stream cooler. They may come from the catalyst
stripper, which is normally employed between the regeneration vessel and
the cracking reactor, especially at the catalyst exit of the latter from the
reactor, from a source of fresh catalyst feed, or from a combination of any
or all of these sources The catalyst particles can be fed to the flue gas
line or directly to the combustor by conventional methods used to convey
; I particles, such as pumping or by a conventional standpipe, using flue gas,
air, steam, or the like, and the particles may be fed directly into the flue
; ~ gas transfer line before, at, or just downstream from the CO combustion
area . The catalyst particles may be withdrawn from the regenerator with
cyclones via a dip-leg by lift gases, or the particles may be allowed to flow
through the regeneration bed and be withdrawn directly from the bed with
'' '
:,
_9_
~ '' 11 ~
104Z377
the flue gas. Withdrawal may be accomplished by employing specially
equipped by-passes around the regenerator cyclones with automatic
temperature control. The catalyst particles may be combined with the flue
gas and the mixture may flow at a controlled temperature through a chimney
5 in the regenerator vessel plenum floor having control valves. The control
valves could be responsive to the automatic temperature control of the
by-passes and deliver temperature-controlled catalyst particles to the
combustor via the flue gas line to recover heat generated from CO combustion
from either the CO contained in the catalyst particle-flue gas mixture, or
lO from a separate flow of flue gas, or both.
Combustion of CO-containing catalyst regenerator flue gas exiting
from the regenerator at temperatures of, for example about 1050 to 1300F.,
will generate about 4,300 BTUtlb. of CO oxidized, which heat may be sub-
stantially recovered by heat exchange with the cracking unit catalyst particles
15 Typically flue gas from a catalyst regenerator contains, for example, from
about 3 to about 10 or more percent carbon monoxide and amounts of carbon
dioxide in this range. A mixture of one-to-one CO2/CO flue gas, for
example, may result in a gas temperature increase of 600F. or more in the
substantial absence of catalyst, e.g., an increase of about 1000F. The
20 actual temperature increase in the presence of the catalyst is dependent
~- upon the mass flow rate of the catalyst particle "heat sink". The catalyst flow
rate is dependent upon the desired heat exchange and catalyst temperature
increase. Flue gas flow rates to the special heat recovery facilities may, for
example, be as low as about 10 and as high as about 15 pounds per pound
25 ~ or coke on the o slyst pessed to the re~onerstor from the crsckirF reector,
-10-
. 11
104Z~77
but preferably the flue gas flow rates are in the range of about 11 to 13
pounds per pound. Catalyst particle flow rates may be, for example, from
about 1 to about 10, preferably from about 1 to about 6, e.g., about 4,
pounds per pound of flue gas which passes in heat exchange relation~hip
with the catalyst .
The essentially completely combusted flue gas from the combustion
processes of this invention has an unusually low carbon monoxide content.
Whereas flue gas from conventional regeneration of cracking catalyst usually
contains from about 6 to 10 percent carbon monoxide, a similar amount of
10 carbon dioxide and very little oxygen, the nue gas from regeneration and
subsequent carbon monoxide combustion in accordance with this invention
generally contains less than about 0 . 2 percent C0, for example, no more
: ~ than about 500 to 1000 parts per million carbon monoxide. Advantageously,
the flue gas carbon monoxide content is even lower, for example, within
; ~ the range from about 0 to about 500 ppmv . The oxygen content of the flue
gas is, of course, not of primary importance from an ecological point of
view and may often vary from about 0.1 to about 10 percent, advantageously
¦ being within the range from about 1 to about 3 percent and preferably no
more than about 2 percent in order to restrict the amount of flue gas and
conserve heat within the regeneration reactor and combustor sy~tem. From
a process point of view, heat recovery by down~tream combustion of carbon
~; monoxide in the carbon monoxide combustor process of this invention,
-~- results in consequent substantial savings in process equipment and opera-
tional costs while still meeting the existing standards for ambient air
25 ! quaIity for c~ monoxidc emiYsions. In one embodiment, C0-containing
::
' -11-
11~)42377
flue gas may be mixed with catalyst and ignited in the line and combustion
completed, e.g., by passing the mixture through combustion promoters,
and may be passed through a heat recoverv zone in the line through which
added catalyst particles are fed. The hot, completely combusted flue gas
continues to pass through the flue gas line to another heat recovery zone
through which other catalyst particles pass at a rate sufficient to recover
remaining recoverable heat. The catalyst streams may emanate from a
single source or from separate sources, and may be combined after heat
transfer for a single purpose or may be continued as separate streams for
different purposes. Many other variations may be made, depending upon
the particular requirements of a given system. For example, two or more
combustion areas may be employed wheréin partial combustion is achieved
by close oxygen control, and each is followed by a contiguous heat exchange
~ zone. In this or the above embodimentæ many variations may be made.
; lS For example, two or more particle streams may receive any predetermined
proportion of the recoverable heat, rather than equal amounts. Likewise,
similar linear flow rates may be employed with varying volumetric flow
rates. The choice of setting dependent and independent variables is one
of design, and, ideally, the system may advantageously be designed so as
; ~ 20 to permit variation of any one or more of the conditions involved.
Other embodiments of this invention may employ indirect heat
transfer between the combusted flue gas and the catalyst particles. Heat
transfer media, such as high heat capacity fluids, may convey the heat
from the gases to the particles or the particles may be fed through a heat
, ~ 25 exchsnge system for indirect heat exchange with the flue gas. For example,
"
'''~
-12-
1~4Z3~7
¦ the flue gas may pass through one side of a tubular heat exchanger and the
¦ particles may pass through the other side to receive substantially all the
¦ heat of combustion. The indirect heat exchange system may alternatively
¦ be an annular space heat exchanger, whereby combusted gases surround
5 ¦ an inner tube or pipe containing the particles. This may be accomplished
¦ by forming an annular space within the transfer line by arranging a pipe
¦ or tube coaxially and concentrically within the line and passing the
¦ catalyst particles through it.
¦ As stated either direct or indirect heat exchange methods may be
¦ utilized in this invention, and such methods may include one or more heat
¦ recovery or heat exchange zones. Where a plurality of zones are used, a
¦ single combustion area or a plurality of such areas are advantageously
¦ included with a plurality of any direct or indirect heat exchange system,
¦ or with any combination of such systems, depending upon the ultimate
15 ¦ operations in which the heated particles will be employed.
¦ In thcse embodiments in which direct heat exchange occurs, the
¦ catalyst particles may be recovered by conventional cyclones or other gas-
¦ particle separating devices. After the catalyst particles leave the combus-
tion-heat exchange area, whether the heat exchange is direct or indirect,
ao they may be returned to the cracking system by known particle conveying
means. In one embodiment, the transfer line combustor or combustors are
placed in a position of greater elevation than the component in the cracking
system to which the heated particles are returned, and the return is con-
- veniently accomplished by gravitation. Alternatively, the particles may be
25 ¦ conveyed to the mbustors by grsvitstionsl mesns snd, ~itsr hsst recovery,
-13-
11
1~4Z377
may be lifted, as, for example, by standpipe or high-level hoppers, to a
height where distribution or return may be conducted, selectively or
otherwise, by gravitation, or they may be returned directly by ~uch
lifting methods. In yet another embodiment, the heated cataly~t particles
` S are pumped directly to any desired component in the fluidized cracking
system .
As mentioned, the heated catalyst particles may be returned to any
; ~ one or a number of locations within the cracking system. Preferably, the
~; particles, receiving heat from the exothermic combustion of the CO, are
fed to a component in which an endothermic reaction occur~ i e .g ., the
cracking zone. However, the catalyst particles may be returned to either
endothermic or exothermic reaction sites and such sites may use additional
heat, and the sites are generally at a temperature lower than that of the
heated catalyst particles. Thus the catalyst particles may be returned or
sent to any area which may use heat which may be transferred from the
particles.
Among the components or areas in the fluidized cracking unit to
which the heated catalyst particles may supply heat are the catalyst
rege~neration vessel, the reactor, and various preheat furnaces and
recycle lines, as well as product hydrocarbon lines leading to the frac-
eionating column and the like. When heated catalyst particles are recycled
or sent to the catalyst regenerator, they may be introduced into any one
or a combination of locations which will usefully accept the additional heat.
They may be introduced directly into the regenerator dense fluidized
- catalyst bed to assist in the initiation or sustaining ot burning, which
''''
~,.......
~ 30 -14-
104Z377
I removes the residual coke from the particles pa8~ed to the ve~el from the
¦ reactor, snd thereby substantiAlly reduce or even obviate auxiliary heQtln~
¦ needs, e.g., oil preheater9 or fuel burner9 in the dense bed . In addltion.
I the heated particles may be combined with coked catalyst feed jU9t before
S ¦ or at the point of entry to the regenerator. Other points of introduction
: ¦ peculiar to particular regeneration systems may likewise be used.
¦ When the particles are introduced to the reactor, they may be
¦ combined with regenerated particles being returned to the reactor, or they
may be separately injected into the reactor. Additionally, the heat in the
catalyst particles due to heat exchange in the CO combu8tor, may be trans-
ferred to hydrocarbons within the process. This may be accomplished by
~: known heat exchange methods, as for example, discussed above, and the
¦ heat may be transferred to fresh, uncracked hydrocarbon feed to bring it
up to reactor temperature and to thereby a9sist the conventional fre8h feed
reactor preheater . The heat of the catalyst particles may also be transferred
to cracked hydrocarbon product by conventional mean8 as the cracked
hydrocarbons exit the reactor and enter the fractionator, or to water to make
,, l
steam. -
By the process of this invention, flue gas entering the CO combustion
area relea8e 9ufficient heat upon completion of combustion to be equivalent
to a 600F. or much higher temperature rise in the catalyst. This can be don
without at any time heating the catalyst above about 1500F. In one embodi-
ment, cooled catalyst is used as the cool~t to reduce the flow rates, e.g.,
cataly8t particles may be quickly added to the combusted hot flue gas so that
2S ¦ the temper~tur the reauUing mixture may immediately drop below abou~
-15-
104Z377
1500F. For example, when the catalyst pQrticles are removed from the
regenerator at typical regeneration temperatures of about 1050 to 1300F.,
the particles may be cooled in a conventional catalyst cooler by about 150
to about 700F. before heat is transferred to them from the completely
combusted hot flue gases. Typically, where the catalyst regeneration
temperature is about 1175F., the catalyst particles may be cooled down
to a temperature between about 475 and a~out 1025F.
The catalyst temperature is preferably kept below about 1500F.
because catalyst particles are somewhat temperature-sensitive in that high
temperatures, e.g., above about 1450 to 1500F. for cracking catalysts,
may have detrimental effects on them and impair their catalytic abilities
as wèll as their structural characterisl;lcs. It is, therefore, desirable in
practicing the process of the present invention to conduct staying of heat
release and heat recovery. Alternatively, the exceedingly hot gas may be
~ ~ 15 suddenly contracted with the quantity of catalyst particles needed to cool
: J ~ ~ the mixture to below 1500F . without allowing the particles at any time to
exceed 1500F. The safe maximum temperature for each system depends
upon the particular catalyst employed, and such temperatures are well
known in the art. The temperature of the catalyst particles which recover
. ~ 20 the CO heat of combustion is generally raised up to about 300 to 1000F.
. ,:
~ ~ and is preferably not raised above about 1500F. final particle temperature.
~ This invention is more fully described by the following example
and drawing which is set forth for illustrative purposes.
Mid-continent gas oil (23.4API), having a boiling range from 650
25 to 1050F., is cracked in a fluidized transport-type reactor at an average
'`
-16-
11
ll 104Z377
cracking temperature of 960F. The throughput ratio (weight total
feed/weight fresh feed) is 1. 34 and the total feed rate i9 36 ,000 bbl/day .
The catalyst particles comprise silica-alumina together with 10 wt. %
''t crystalline aluminosilicate or molecular sieve material (Y-type ion exchanged
5 with hydrogen and rate earth metals) and are circulated between the
reactor and regenerator at a rate of 19.6 tons/minute. The weigm ratio
of catalyst to oil in the cracking zone is 3 . 7 .
Efnuent from the riser reactor is passed to a separation zone and
fed into a cyclone separator. Hydrocarbon products are removed from the
10 cyclone separator and spent catalyst is passed downwardly through a
cyclone dip-leg into a stripping zone maintained at 950F. The settled
catalyst is ~tripped with steam to remove the remaining volatile material
prior to regeneration.
Stripped, spent catalyst, containing 0 . 9 wt . % coke thereon, is
15 fed to the fluidized cracking unit catalyst regenerator vessel, shown sche-
matically in the Figure, generally as 1. The spent catalyst is fed to the
vessel via inlet line 3 and is fluidized by rising gases fed to the vessel
through air line 5 and/or through additional lines at the bottom of the
vessel (not shown). The fluidized particles are maintained in a dense bed
20 at about 1175F. by combustion of the coke and combustion of torch oil,
as injected through line 7 in the Figure as needed. The air rate is set at
approximately 11 lbs. air per lb. coke on the spent catalyst and closely
controlled to prevent undesired or excessive "afterburning" within the
regeneration vessel. Cyclones and other conventional equipment (not
25 shown) are contained within the reaction vessel and effectively separate
3~ -17-
1~4Z;~7
the flue gas from the fluidized particles. Auxiliary temperature lowering
means are maintained in the upper portion of the vessel, such as ~team
injector 9 in the Figure to avoid "afterburning" in the vessel.
Regenerated catalyst particles are removed from the regenerator
via line 11 where they are separated into two streams and are, in part, sent
to the flue gas combustor heat exchange area via line 13 and, in part,
returned to the cracking reactor via line 15. In this example, about half
of the particles is fed to the flue gas transfer line as compared to the flow
back to the reactor, although less or more of the catalyst particles may be
fed to the transfer line.
Flue gas exits the regenerator via flue gas line 17 and passes to the
combustor, shown generally as 1g. Air is introduced at line 21 to the flue
; gas which arrives at the combustion area at about 1200F., and the gas is
ignited as by an oil torch (not shown), and the combustion is sustained by
lS iron oxide grid promoters at 23. The combusted flue gas continues down thetransfer line and, just downstream from combustion area 19, regenerated
catalyd particles from line 13 are combined in high turbulence with the
gaseous mass. The catalyst particle-combusted Fas mixture passes down
the transfer line as very rapid direct heat transfer occurs in a short zone
- ~ 20 in the area 27. The catalyst particles and flue gas temperatures reach an
equilibrium and heat transfer is essentially complete before the mixture
arrives at cyclone as where it separates at 31. The heated catalyst particles
exit cycle 29 at 33 for passage back to the cracking system, and the flue gas
. .~
exits at 35.
-18-
1!)4;~377
In this example, hot catalyst particles enter the transfer line at
about 1175F. and exit the line at about 1425F. These c~talyst particles
are then conveyed to the catalyst regenerator where heat is transferred
from the hot catalyst to the cooler entering catalyst. Individual particles
5 have not exceeded about 1500F. at any point. The flue gas entering the
flue gas line contained about 5 . 0% carbon monoxide and after combustion
completion the exiting flue gas contained less than 0 . 2% carbon monoxide .
~::
.,
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