Note: Descriptions are shown in the official language in which they were submitted.
8~3'7~
FIELD O~ T~ INVENTIOli
The present invention relates to the field of
flui~ized catalytic cracking of hydrocarbon feedstocks. In
particular, this invention relates to an improved process and
apparatus for ca~alytically cracking hydrocarbon feedstocks
at elevated temperatures wherein catalys't regeneration is
conducted in two steps comprising separate relatively low and
high temperature regeneration stages and where feedstocks to
said method are controlled to obtain a desired product
distribution and improved yields of high octane blending
stock, C3-C4 olefins and light cycle oil/distillate. In
another aspect, this invention relates to an improved process
and apparatus of catalytically cracking hydrocarbon
feedstocks which relates catalyst activity and selectivity to
processing parameters to improve the conversion of available
refinery materials.
BACKGROUND OF T~E IMVENTION
Combination fluidized catalytic cracking (FCC)-
regenerdtion processes wherein hydrocarbon feedstocks are
contacted with a continuously regenerated freely moving
finely divided yarticulate catalyst material under conditions
permitting conversion into such useful products as olefins,
fuel oils, gasoline ana gasoline blending stocks are well
known. Such FCC processes for the conversion of high boiling
portions of crude oils comprising vacuum gas oils and heavier
components customarily re~erred to as residual oils, reduced
crude oils, vacuum resids, atmospheric tower bottoms, topped
crudes or simply heavy hydrocarbons and the like have been of
much interest in recent years especially as demand has exceeded
the availability of more easily cracked light hydroc~'rbon
feedstocks. 'I'he cracking of such heavy hydrocarbon
feedstocks which comprise very refractory components, e.g.
. ' :
2~ 97~3
-- 2
polycyclic aromatics and asphaltenes and the like, capable of
depositing relatively large amounts of coke on the catalyst
during cracking, and which typically requires severe
operating conditions including very high temperatures has
presented problems associated ~ith plant construction
materials and catalyst impairment.
At present, there are several processes available
for fluidized catalytic cracking of such heavy hydrocarbon
feedstocks. A particularly successful and much preferred
0 approach which avoids such problems as mentioned above is
described, for example, in U.S. Patent Nos. ~,664,77a;
4,601,814; 4,336,160; 4,332,674; and 4,331,533.
In such processes, a combination fluidized
catalytic cracking-regeneration operation is provided wherein
catalyst regeneration is successively carried out in separate
relatively lower and higher temperature regeneration zones
each independently operating under selected conditions to
provide hot, fully regenerated catalyst with very limited
catalyst impairment per catalyst regeneeation cycle. Such
~0 hot regenerated catalyst is then employed in the high
temperature, highly selective catalytic cracking and
simultaneous conversion of both high and low boiling
components contained in heavy hydrocarbon feeds.
Due to the nature of heavy hydrocarbon feeds,
crackin~ in such FCC processes as described above
increases selectivity tending toward light cycle gas-oil
and higher boiling materials production. These products are
often employed as a component of diesel fuels and furnace
oils preferably after hydrotreating or caustic treating.
Catalytic cracking of such feeds, however, tends to oppose
selectivity to lower boiling components for use as gasoline
blending stocks, or as precursors for synthesizing gasoline
blending stocks, especlally those of higher octane values.
It is believed that such competing effects arise in part due
to carbon laydown on the catalyst as the catalyst travels
97~3
_ 3
o
through zones in the reactor. As the amount of carbon on the
catalyst increases along the reaction path, the gasoline
and light olefin selectivity from the heavy feed decreases.
The higher the molecular weight of the feed hydrocarbon, the
greater the carbon on catalyst competing ef~ect because
higher molecular weight components tend to contain more
polynuclear aromatic compounds and asphaltenes which yield
more coke upon initial cracking and vaporization than other
compounds. Of the aromatic compounds, the polynuclear
compounds not only crack at a slower rate, but will also have
a much higher selectivity to C2 and lighter gases and coke
production, while the mono- and di-aromatics and the alkyl
side chains of naphthene components tend not only to crack at
a faster rate, but also tend to exhibit a higher selec~vity to
gasoline and desired light olefins such as propylene,
butenes, pentenes and hexenes. Therefore, as such heavier
hydrocarbon feed undergoes cracking the heavier hydrocarbon
feed components should be subjected to a reduced residence
time at extremely hign temperatures in order to limit the
cracking thereof as much as possible to paraffinic side
chains and mono- and di-aromatics in general to reduce
excessive coke production. Alternatively, gasoline
selectivity is optimized by more severe catalytic cracking
operations oE light hydrocarbon feeds, e.g. higher catalyst-
to-oil ratios, longer residence times and relatively higher
temperatures, than are desirable in the cracking of heavier
feeds.
It often is desirable to operate FCC processes in a
manner which maximizes the production of a given product or
products, especially in the absence of competing effects such
as mentioned above. For example, either one or both of the
gasoline/light olefins and light cycle oil products may be
desired in order to produce large quantities of high octane
gasoline and gasoline precursors while simultaneously
producing increased quantities of fuel oil distillates and
2~ 7~
_ 4
diesel fuel. This i5 especially so in light of current
environmental concerns which have necessitated a reduction in
pollution by-products o~ combustion from autamobiles ~rom the
use of leaded gasoline products. Therefore, unleaded
gasoline blend stocks having a hiyh octane number are much in
demand~ It would, therefore, be desirable to expand the
operating envelope of such useful process as described above
to increased selectivity to high octane material and light
olefins while simultaneously selectively catalytically
cracking economical heavy hydrocarbon feeds to heavy naphtha,
and distillates or light and heavy cycle oils and higher
boiling materials.
Tnere are a number of ways of accomplishing
these goals. The method described in U.S. Patent No.
lS 3,617,497 discloses segregating hydrocarbon ~eed and
charging the relatively lower molecular weight feed
fraction or fractions near the bottom of an elongated
riser reaction zone and the relatively higher molecular
weight feed fraction or fractions progressively further
up the riser. Cracking of the lighter hydrocarbon feed
in the absence of heavy hydrocarbon feed is thus
accomplished on a low carbon content catalyst to
maximize gasoline selectivity. Although feed residence
times can be established in such a process by controlling
the total charge rate of hydrocarbon to the riser,
catalyst-to-oil ratios and reaction temperatures are
diEficult to optimize for maximum gasoline and light
cycle oil selectivity, respectively.
A more versatile method Eor optimizing
cracking selectivity from relatively lower and higher
boiling feeds is described by U.S. Patent No. 3,617,496.
In such a process, cracking selectivity to gasoline
production is improved by fractionating the Eeed hydrocarbon
into relatively lower and higher molecular weight fractions
capable o~ being cracked to gasoline and charging said
26)(~97B
-- 5 --
fractions to separate riser reactors. In this manner, the
relatively light and heavy hydrocarbon feed fractions are
cracked in separate risers in the absence o~ each other,
permitting the operation of the lighter hydrocarbon riser
under conditions favoring gasoline selectivity, e.g.
eliminating heavy carbon laydown, convenient control of
hydrocarbon feed residence times, and convenient control of
the weight ratio o~ catalyst to hydrocarbon feed therein
thereby affecting variations in individual reactor
10 temperatures.
Other processes which si,nilarly employ the use of
two or more separate riser reactors to crack disimilar
hydrocarbon feeds are described, for example, in U.S. Patent
No. 3,993,556 (cracking heavy and light gas oils in separate
15 risers to obtain improved yields of naphtha at higher octane
ratings); U.S. Patent No. 3,928,172 (cracking a gas oil
boiling range feed and heavy naphtha and/or virgin naphtha
fraction in separate cracking zones to recover high
volatility gasoline, high octane l~lending stock, light
20 olefins ~or alkylation reactions and the like); U.S. Patent
No. 3,~94,935 (cata~lytic cracking of heavy hydrocarbons, e.g.
gas oil, residual material and the like, and a C3-C4 rich
fraction in separate conversion zones); U.S. Patent No.
3,801,493 (cracking virgin gas oil, topped crude and the
25 like, and slack wax in separate risers to recover, i~er
alia, a light cycle gas oil fraction for use in Eurnace oil
and a high octane naphtha fraction suitabIe for use in motor
fuel, respectively); U.S. Patent No. 3,751,359 (cracking
virgin gas oil and intermediate cycle gas oil recycle in
30 separate respective feed and recycle risers); U.S. Patent No.
3,448,037 (wherein a virgin yas oil and a cracked cycle gas
oil, e.g. intermediate cycle gas oil, are individually
cracked through separate elongated reaction zones to recover
higher gasoline products); U.S. Patent No. 3,~24,672
X~ 713
(cracking topped crude and low octane light reformed gasoline
in separate risers to increase gasoline boiling range
product) and U.S~ Patent No. 2,900,325 (cracking a heavy gas
oil, e.g. gas oils, residual oils and the lik~, in a first
reaction zone, and cracking the same feed or a dif~erent feed,
e.g. a cycle oil, in a second reaction zone operated under
different conditions to produce high octane gasoline).
SUMMARY OF THE INVENTION
It is therefore an object of the presenk invention to
provide an improved process and apparatus for catalytically
cracking hydrocarbon feedstocks at elevated temperatures
wherein catalyst regeneration is conducted in two or more
steps comprising separate relatively higher and low~r
temperature regeneration stages.
It is a further object of this invention to provide such
a process wherein feedstocks thereto are contr~lled to obtain
a desired product distribution and improved yields of high
octane gasoline blending stock and light olefins.
It is still another object of this invention to provide
an improved process and apparatus of catalytically cracking
hydrocarbon feedstocks at elevated temperatures which relates
catalyst activity and selectivity to processing parameters of
individual heavy hydrocarbon and naphtha boiling range
material to improve the selective conversion thereof to light
cycle gas oils and said gasoline blending stocks and light
olefins, respectively.
Additional objects of the pxesent invention will become
apparent from the following description.
In a broad aspect, the present invention provides, in a
fluidi~ed catalytic cracking-regeneration process for cracking
hydrocarbon feedstocks or the vapour thereof with a cracking
catalyst consisting of separate first and second catalyst
regeneration zones wherein said catalyst is regenerated in
said first and second regeneration zones, successively, by
combusting hydrocarbonaceous deposits on the catalyst in the
presence of an oxygen-containing gas under conditions
,
:. . . , . :
- 7- 2~0~7~3
effective to produce a first regeneration zone flue gas rich
in carbon monoxide and a second reyeneration zone flue gas
rich in carbon dioxide, wherein temperatures in the first
regeneration zone range frGm about 1100F to about 1300F, and
temperatures in the second regeneration zone range from about
1300F to about 1800F, a method for improving the process
which comprises the steps: (a) cracking a first hydrocarbon
feed comprising gas oil, residual oil boiling range material
or mixtures thereof in a first elongated riser reactor in the
presence of regenerated cracking catalyst supplied from the
second catalyst regeneration zone at a temperature of at least
1300F, a catalyst-to-oil ratio of from 5 to 10, and residence
time of from 1 to ~ seconds and where coke is deposited on
said catalyst in an amount less than 1.2 weight percent
thereof, to obtain vaporous conversion products of the first
hydrocarbon feed comprising a heavy naphtha fraction and
materials lower ~oiling than said heavy naphtha fraction, a
light cycle oilO a heavy cycle oil, and materials higher
boiling than said heavy cycle oil, while simultaneously (b)
cracking a second hydrocarbon feed comprising virgin naphtha,
intermediate and heavy cracked naphtha boiling range material
or mixtures thereof in a second elongated riser reactor in the
presence of regenerated cracking catalyst supplied from the
second catalyst regeneration zone at a temperature of at least
1300F, a catalyst-to-oil ratio of from 3 to 12, and residence
time of from 1 to 5 seconds, and where coke is deposited on
said catalyst in an amount less than 0.5 weight percent
thereof, to obtain vaporous conversion products of the second
hydrocarbon feed comprising gasoline boiling range material
having a high aromatic content and octane number and light
hydrocarbon material from a light cycle oil material and (c)
passing and combining the vaporous conversion products from
the first and second elongated riser reactors in a common
disengaging zone therein separating entrained catalyst
particles from vaporous product material and passing the
combined conversion products to a fractional distillation zone
to recover at least a gasoline boiling range material fraction
- 8 ~ 97~
and lighter gaseous hydrocarbon material fraction, a heavy
naphtha boiling range material fraction, a light cycle oil
boiling range material fraction and a heavy cycle boiling
range material fraction including slurry oil and higher
boiling material fractions.
In another broad aspect, the present invention provides,
in a fluidized catalytic cracking-regeneration process -Eor
cracking hydrocarbon ~eedstocks or the vapour thereof with
finely-divided cracking catalyst in a fluidized state to
produce cracked products and spent catalyst particles having
hydrocarbonaceous deposits thereon, stripping vaporous
hydrocarbon products from the catalyst particles, transferring
the fouled catalyst to a first regeneration zone wherein the
catalyst is partly regenerated by combusting substantially all
the hydrocarbon associated with the hydrocarbonaceous deposits
on the catalyst at temperatures of less than about 1300F in
the presence of oxygen-containing gas at pressures ranging
from about 15 to about 40 psig and in amounts effective to
produce a first regeneration zone flue yas having a carbon
monoxide content from about 2 to about 80 volume percent, then
transferring the partly regenerated catalyst to a second
regeneration zone wherein the catalyst is fully regenerated by
combusting substantially all the hydro-carbonaceous deposits
remaining on the catalyst surface at temperatures ranging from
about 1300F to about 1800F in the presence of oxygen-
containing gas in amounts effective to produce a second
regeneration zone flue gas having a carbon monoxide content of
less than about 1200 parts per million by volume, a method for
improving the process which comprises the steps: (a) cracking
a first hydrocarbon feed comprising gas oil, residual oil
boiling range material or a mixture thereof in a first
elongated riser reactor in the presence of regenerated
cracking catalyst supplied from the second catalyst re-
generation zone at a temperature of at least 1300F, a
catalyst-to-oil ratio of from 5 to 10, and res.idence time of
from 1 to 4 seconds and where coke is deposited on said
catalyst in an amount less than 1.2 weight percent thereof, to
- 8a - ~ B
obtain vaporous conversion products of the first hydrocarbon
feed comprising a heavy naphtha fraction and materials lower
boiling than said heavy naphtha fraction, a light cycle oil, a
heavy cycle oil, and materials higher boiling than said heavy
cycle oil, while simultaneously (b) cracking a second
hydrocarbon feed comprising virgin naphtha, intermediate
cracked naphtha or heavy cracked naphtha, or a mixture
thereof, boiling range material in a second elongated riser
reactor in the presence of regenerated cracking catalyst
supplied from the second catalyst regeneration zone at a
temperature of at least 1300F, catalyst-to-oil ratio of from
3 to 12, and a residence time of from 1 to 5 seconds and where
coke is deposited on said catalyst in an amount less than 0.4
weight percent thereof, to obtain vaporous conversion products
of the second hydrocarbon feed comprising gasoline boiling
range material having a high aromatic content and octane
number and lighter hydrocarbon material from a light cycle oil
material, and (c) passing and combining the vaporous
conversion products from the first and second elongated riser
reactors in a common disengaging zone therein separating
entrained catalyst particles from vaporous product material
and passing the combined conversion products to a fractional
distillation zone to recover at least a gasoline boiling range
material fraction and lighter gaseous hydrocarbon material
fraction, a heavy naphtha boiling range material fraction, a
light cycle oil boiling range material fraction, and a heavy
cycle boiling range material including slurry oil and higher
boiling material fractions.
In a further broad aspect, khe present invention
provides, an apparatus for use in a fluidized catalytic
cracking-regeneration process for cracking hydrocarbon
feedstocks with a cracking catalyst comprising: (a) a first
riser reactor containing a fluidized bed of finely divided
regenerated catalyst particles for contacting gas oil and/or
residual oil boiling range material therewith to produce an
effluent comprising cracked products and spent catalyst
particles having hydrocarbonaceous deposits thereon: (b) a
- 8b -
-ZB~
second riser reactor con~aining a fluidized bed of finely-
divided regenerated catalyst particles for contacting virgin
naphtha, intermediake cracked naphtha or heavy cracked naphtha
boiling range material or a mixture thereof therewith the
catalyst particles to produce an effluent comprising cracked
products and spent catalyst particles having hydrocarbonaceous
deposits thereon; ~c) a separating zone for receiving the
effluent from the first and second riser reactors and
separating cracked products from spent catalyst particles; (d)
a stripping zone for receiving spent catalyst particles from
the separating zone and separating vaporous hydrocarbon
material from the spent catalyst in the presence of a
stripping gas: (e) a first fluidized catalyst regeneration
zone for receiving the spent catalyst particles from the
stripping zone and combusting substantially all the hydrogen
associated with the hydrocarbonaceous deposits on the catalyst
particles at temperatures of from about 1100F to about 1300F
in the presence of an effective amount of oxygen-containing
gas at pressures ranging from 15 to 40 psig, and producing a
first catalyst regeneration zone flue gas having a carbon
monoxide content of from about 2 to about 8 volume percent,
and partially regenerated catalyst, said first regeneration
zone also having an inlet for receiving the oxygen-containing
gas required therein for fluidizing and combustion; (f) a
second fluidized catalyst regeneration zone for receiving the
partially regenerated catalyst from the first catalyst
regeneration zone and combusting substantially all the
hydrocarbonaceous deposits on the catalyst at temperatures
ranging from 1300F to 1800F and at pressures from 10 to 40
psig, in the presence of an effective amount of oxygen-
containing gas and producing a second catalyst regeneration
zone effluent gas having a carbon monoxide less than 1200
parts per million and fully regenerated catalyst having a
carbon content of less than about 0.03 weight percent said
second regeneration zone also having an outlet for passing the
fully regenerated catalyst to the first and second riser
reactors, (a) and (b), respectively, for further contacting of
.
- 8c -
the hydrocarbon feedstocks and an inlet for receiving o~ygen-
containing gas required therein for fluidizing and combustion;
and (g) a fractional distillation zone for receiving the
cracked products from the separating zone (c) and vaporous
hydrocarbon material from step (d) to recover product
fractions therefrom.
As will be appreciated by those skilled in the art, a
major advantage provided by the present invention is the
flexibility to simultaneously select operating conditions
specifically sui~ed to achieve the optimum desired conversion
of available refinery materials and selected hydrocarbon
feedstocks to desired products. In particular, the novel
arrangement of apparatus and processing concepts of this
invention, as more fully discussed below, substantially
obviates problems related to high regenerator and catalyst
temperatures encountered in catalytic cracking of high boiling
hydrocarbon feedstocks, generally referred to as heavy
hydrocarbons herein and boiling initially at least 400F or
higher, to produce gasoline and lower and higher boiling
hydrocarbon components. Thus conditions favourable for
cracking such feedstocks can be encouraged in a respective
riser reactor. Moreover, severe conditions needed for
selectively causing the desired cracking reactions of naphtha
boiling range feedstocks in a respective riser reactor to high
octane gasolines in addition to light olefins, useful as
gasoline precursors via, for example, alkylation can be
encouraged. Advantage can be taken of increased reaction
temperatures, increased catalyst-to-oil ratios and extended
hydrocarbon vapour residence time in contact with the catalyst
and unit operating pressure.
The process and apparatus of the present invention will
be better understood by reference to the following detailed
discussion of specific embodiments and the attached
:
97~3
g
FIGURE which illustrates and exemplifies such embodiments.
It is to be understood, however, that such illustrated
embodiments are not intended to restrict the present
invention, since many more modifications may be made within
the scope of the claims without departing from the spirit
thereo f .
DESC~IPTIO~ OF T~E D~ G
. . ~
The FIG~RE is an elevational schematic o~ the
process and apparatus of the present invention shown in a
combination fluidized catalytic cracking-regeneration
operation wherein two respective riser reactors are provided
for independently catalytically cracking heavy hydrocarhon
feeds and lighter naphtha feeds, wherein catalyst regeneration
is successively conducted in two separate relatively lower
and higher temperature zones.
DETAILED DISCUSSION OF SP~CIFIC
EMBODIME~TS OF T~e INVENTION
The catalytic cracking process of this invention
relates to the cracking of economically obtained heavy
hydrocarbon Eeedstocks generally referred to as gas oils,
residual oils, gas oils comprising residual components,
reduced crude, topped crude, and high boilin~ residual
hydrocarbons comprising metallo-organic compounds and the
like. These are among several terms used in the art to
describe portions of crude oil such as a gas oil with or
without a higher boiling hydrocarbon feed portion which may
comprise metallo-organic compounds, and essentially all other
heavy hydrocarbon feedstocks having a Conradson carbon of at
least 2 weight percent and boiling initially at least 400F,
with approximately 20 weight percent or more of the
components therein boiling at about lU00F or above.
_ 10 _
Products obtained from cracking such feedstocks
include but are not limited to yasoline and gasoline boiling
range products boiling from C5 to 425F, light cycle oil
boiling in the range from 425F ~o oOO/670F, a heavy cycle
oil product inclusive of product higher boiling than light
cycle oil and boiliny up to ~00F and above, and a slurry oil
boiling from about 670F up to 970F. Additionally, a heavy
cracked naphtha is produced and drawn down as the front end
of the light cycle oil distillate or produced separately, and
10 which boils in the range from 330F to 425F.
The process of this invention also relates to
the cracking of light, heavy and intermediate virgin
naphthas boiling in the range from 10F to 450F and heavy
FCC naphthas boiling in the range ~rom 150~ to 425F, to
produce, among other things, high octane gasoline, light
olefins for alkylation or other reactions to produce high
octane blending stoc~ or for petrochemical manufacture, and a
common light cycle oil stream.
The heavy hydrocarbon feedstock typically
comprising a mixture of vacuum gas oils and residual oils is
introduced into a first elongated riser reactor and mixed
therein with a highly active freshly regenerated cracking
catalyst at a temperature at least above about 1300F. The
hydrocarbon ~eed is preferably first mixed with steam or
other gas at such temperature and conditions as to Eorm a
highly atomized feedstream, which is then mixed with the hot
regenerated catalyst to form a generally vaporous hydrocarbon-
catalyst suspension. After catalytic conversion of hydro-
carbon feed material~ a suspension separation device or
disengaging vessel arrangement containing, for exarnple,
separator cyclones employed at the riser discharge separates
entrained catalyst ~rom vaporous hydrocarbon feed material
including ceacked products of conversion.
Simultaneously or separately with that operation
above, a naphtha feed is introduced into a second elongated
1 1 2~9~7~
riser reactor under conditions to obtain mixing therein with
hot freshly regenerated cracking catalyst at a temperature at
least above 1300F and under conditions so as to form a
vaporous hydrocarbon-catalyst suspension which after
catalytic conversion of naphtha feed material flows from the
riser discharge into the disengagement device to separate
entrained catalyst from vaporous material and additional
cracked products of conversion.
The combined vaporous hydrocarbon products leaving
the separator cyclones are then separated in a downstream
fractionation column to products more fully discussed
hereinbelow. The spent catalyst particles recovered from
each respective riser reactor in the cracking operation are
thereafter stripped of entrained hydrocarbon material via
treatment with steam or some other suitable stripping gas at
an elevated temperature in the range of about 880F to about
1050F, and then successively passed to first and second
(relatively lower and higher temperature) catalyst regeneration
zones, such as fully described, for example, in U~S. Patent
Nos. 4,664,778, 4,601,814; 4,336,160; 4,332t674; and
4,331,533.
Generally, in such processes, the stripped spent
catalyst is passed to a dense fluid bed of catalyst in a
first catalyst reyeneration zone maintained under oxygen and
temperature restricted conditions below about 1300F, and
preferably not above about 126~F. Combustion of hydro-
carbonaceous material or coke deposited on the spent catalyst
in the first regeneration zone is conducted at relatively
mild temperatures and conditions sufficient to burn
substantially all the hydrogen present in the coke deposits
and a portion of the carbon. The regenerator temperature is
thus preferably restricted to a temperature and conditions
which do not accelerate catalyst deactivation by exceeding
the hydrothermal stability of the catalyst or the metallurgical
limits of a conventional low temperature regenerator
2~89~1~
-12 -
operation. Flue gases relatively rich in carbon monoxide are
recovered from the first regenerator zone and can be
directed, for example, to a carbon monoxide boiler or
incinerator and flue gas cooler to generate steam by
promoting a more complete colnbustion of available carbon
monoxide therein, prior to combination with other process
flue gas streams. Such combined streams can then be passed
through a power recovery prime mover section to gene,r,~e
process compressed aic in the manner set forth in copen~ing
Canadian Patent Application No. 614,765 dated September
~9, 1989 o~ned by the Applicant.
A partially regenerated catalyst of limited '
temperature and comprising carbon residue is recovered
rrom the first regenerator zone substantially free of
hydrogen in the coke, and is passed to a second separate
unrestraineo higher temperature catalyst regeneration zone
wherein the remaining relatively carbon-rich coke deposits
are substantially completely burned to carbon dioxide at an
elevated catalyst temperature preferably within the range of
130~~ to to 16~0F, and possibly up to 1800F, in an
environment with minimal steam from combustion of water or
other sources.
The second regeneration zone is designed to
limit catalyst residence time therein at the high temperature
while attaining a carbon burning rate required to achieve a
residual carbon on recycled hot catalyst particles less than
about 0.05 weight percent and more preferably less than about
0.0~ weight percent.
Hot flue gases obtained from the second regeneration
zone can be fed to external cyclones for recovery of
entrained catalyst fines before further utilization, for
example, in combining with the prior combusted first
regeneration zone flue gas in the manner set forth above.
The hot fully regenerated catalyst particles are
then passed through respective catalyst collecting zones and
- .
-13 _ Z~ 7~
conduits to the first and second riser reactors for further
cracking operation in th~ manner described hereinabove.
The subject apparatus to carry out the process of
this invention is thus a combination catalyst-regeneration
operation comprising separate first and second, relatively
lower and higher temperature, ca~alyst regeneration zones
operat2d unde~ conditions such as described above, thereby
supplying hot regenerated catalyst to first and second
elongated riser reactors for independently catalytically
cracking respective hydrocarbon feeds under operating
parameters permitting selective conversion to desi~ed
products. A fractional distillation zone is also provided
~or receiving the cracked product mixture from said first and
second riser reactors to separate products therein.
Referring now to ~he FIGURE, there is shown an
apparatus adapted for performing a pre~erred embodiment of
the process of the present invention. Accordingly, first and
second elongated hydrocarbon riser reactors 8 and 108,
respectively, are provided wherein a fresh high boiling heavy
hydrocarbon feed to be catalytically cracked, typically
comprising a gas oil or residual oil or a mixture thereof, is
introduced into a lower portion of first riser reactor ~ by
conduit means 4 through a multiplicity of streams in the
riser cross section charged through a plurality of horizontally
spaced apart feed injection nozzles indicated by injection
nozzle 6. Such nozzles are preferably atomizing feed
injection nozzles of the type described, for example, in U.S.
Patent No. 4,434,049, or some other suitably high energy
injection source. Steam, fuel gas, carbon dioxide or som~ other
suitable gas can be introduced into the feed injection nozzles
through conduit means 2 as an aerating, fluidizing or diluent
medium to facilitate atomization or vaporization of the
hydrocarbon feed.
~897~3
Hot regenerated catalyst is introduced into the
riser reactor ~ lower portion by conduit means 10 and caused
to flow upwardly and become commingled with the multiplicity
o hydrocarbon feed streams in the riser reactor 8 cross
section, and in an amount sufficient to form a high
temperature vaporized mixture or suspension with the
hydrocarbon feed. The high temperature suspension thus
formed and comprising hydrocarbons, diluent, Eluidizing gas
and the like and suspended (fluidized) catalyst thereafter
passes through riser ~ which is operated in a manner known to
those skilled in the art.
Cracking conditions in riser 8 to produce cracked
products comprising light olefins, cracked gasoline and
heavier cracked oils from the high boiling component heavy
feed are well known. The heavy feed comprising high
molecular weight components tends to contain an appreciable
amount of polynuclear aromatic compounds which yield more
coke on cracking than other compounds, and which crack with
lower selectivity to desired products but greater selectively
to C2 and lighter gases and coke. Thus the heavier
hydrocarbon feed components are preferably subjected to
relatively reduced residence times at higher temperatures
in order to obtain high octane gasoline and light cycle oil
yields, and the operation terminated before appreciable
cracking or condensation of polyaromatics occur therein
producing excessive coke formation, and extra C2 and lighter
gases. Cracking conditions preferably include nominal
residence times of from 1 to 4 seconds, with a riser
temperature profile of regenerated catalyst temperatures
from 1300F to 1600F, feed preheat temperatures from
250F to 750F, mix-zone outlet temperatures ~rom 1000F to
1100F, catalytic zone inlet temperatures from 900F to
11~0F, and riser reactor outlet temperatures from 870F to
1030F, and riser pressures ranging from 15 to 40 psig.
Catalyst-to-oil ratios based on total feed can range from 5
39~F~
-15
to 10, with coke on regenerated catalyst ranging from 0.3 to
1.2 weight percent. The amount of diluent added through
conduit means 2 can vary depending upon the ratio of
hydrocarbon to diluent desired for control purposes. If, for
example, stea'n is ~mployed as a diluent, it can be present in
an amount of from about 2 to 8 percent by weight based on the
hydrocarbon charge.
First riser reactor 8 effluent comprising a
mixture of vaporized hydrocarbon and suspended catalyst
particles including cracked products of catalytic
conversion passes from the upper end of riser 8 through
discharge through an initial separation in a suspension
separator means indicated by 26 such as an inertial separator
and/or passed to one or more cyclone sepaeators ~8 located in
the upper portion of vessel 20 for additional separation of
volatile hydrocarbons from catalyst particles. ~eparated
vaporous hydrocarbons, diluent, stripping gasiform material
and the like is withdrawn by conduit 90 for passage to
product recovery equipment more fully discussed hereinbelow.
Spent catalyst from the cracking process separated
by means 26 and cyclones 28 and having a hydrocarbonaceous
product or coke Erom heavy hydrocarbon cracking and metal
contaminants deposited thereon is collected as a bed of
catalyst 30 in a lower portion of vessel 20. Stripping gas
such as steam is inteoduced to the lower bottom portion of
the bed by conduit means 32. Stripped catalyst is passed
from vessel 20 into catalyst holidng vessel 34, through flow
control valve V34 and conduit means 36 to a bed of catalyst
38 being regenerated in vessel 40, the first catalyst
regeneration ~one. Oxygen-containing regeneration gas such
as air is introduced to a bottom portion of bed 38 by conduit
means 42 communicating with air distributor ring 44.
Regeneration zone 40 as operated in accordance with
procedures known in the art is maintained under conditions as
a relatively low temperature regeneration operation generally
-16 ~ 9 ~8
o
below 1300F and preferably below 1260F and under conditions
selected to achieve at least a partial combustion and removal
of carbon deposits and substantially all of the hydrogen
associated with the deposited hydrocarbons material from
catalytic cracking. The combustion accomplished in the first
regeneration zone 40 is thus accon~plished under such
conditions to form a carbon monoxide rich first regeneration
zone flue gas stream. Said flue gas stream is separated from
entrained catalyst fines by one or more cyclone separating
means, such as indicated by 46. Catalyst thus separated from
the carbon monoxide rich flue gases by the cyclones is
retu~ned to the catalyst bed 38 by appropriate diplegs.
Carbon monoxide rich flue gases recovered from the cyclone
separating means 46 in the first regeneration zone by conduit
means 50 can be directed, for example, to a carbon monoxide
boiler or incinerator and/or a flue gas cooler (both not
shown) to generate steam by a more complete combustion of
available carbon monoxide therein, prior to com~ination with
other process flue gas streams and passage thereof through a
power recovery prime mover section, in the manner discussed
hereinabove. In the first regeneration zone it is therefore
intended that the regeneration conditions are selected such
that the catalyst is only partly regenerated in the removal
of hydrocarbonaceous deposits therefrom such that sufficient
~5 residual carbon remains on the catalyst to achieve higher
catalyst particle temperatures above 1400F, preferably up to
about 160~F, and up to 1800F as required upon more complete
removal of the carbon from catalyst particles by combustion
thereof with excess oxygen-containing regeneration gas in a
second cataly.st regeneration zone discussed hereinbelow.
Partially regenerated catalyst now substantially
free of hydrogen in residual carbon deposits on the catalyst,
is withdrawn fro.~ a lower portion of bed 38 for transf~r
upwardly through riser 52 to discharge into the lower portion
of a dense rluid bed of catalyst 54 in an upper separate
Z~97~
- 17-
second catalyst regeneration zone 58. Lift gas such as
compressed air is charged to the bottom inlet of riser 52 by
a hollow stemplug valve 60 comprising flow control means (not
shown).
Conditions in the second catalyst reyeneration zone
are operated in a manner known in the art to accomplish
substantially complete carbon burning removal from the
catalyst not removed in the first regeneration zone.
Accordingly, regeneration gas such as air or oxygen enriched
0 gas is charged to bed 54 by conduit means 62 communicating
with an air distributor ring 64. As shown in the FIGURE,
vessel 58 in the second regeneration zone is substantially
free of exposed metal internals and separating cyclones such
that the high temperature regeneration desired may be
effected without posing temperature problems associated with
materials of construction. The second catalyst regeneration
zone is usually a refractory lined vessel or manufactured
from some other suitable thermally stabl,e material known in
the art wherein high temperature regeneration of catalyst is
accomplished in the absence of hydrogen or formed steam, and
in the presence of sufficient oxygen to effect substantially
complete combustion of carbon monoxide in the dense catalyst
bed S~ to focm a carbon dioxide rich flue gas. ~hus,
temperature conditions and oxygen concentration may be
unrestrained and allowed to exceed 1600DF and possibly reach
as high as 1800F oc as required to substantially complete
carbon combustion. However, temperatures are typically
maintained between 13009F and 1600F.
In this catalyst regeneration environment residual
carbon deposits remaining on the catalyst following the first
temperature restrained regeneration zone are substantially
completely removed in the second unrestrained temperature
regeneration zone. The temperature in vessel 58 in the
second regeneration zone is thus not particularly restricted
to an upper level except as possibly limited by the amount of
-18 -
carbon to be removed therewithin and heat balance restrictions
of the catalytic cracking-regeneration operation. If
desired, the second regeneration zone 58 can be provided with
a means (not shown) for removing heat ~rom the regenerator
therein enabling a lower regenerator temperature as desired
to control such heat balance restrictions. Examples of heat
removal means which are preferred include controllable
catalyst coolers such as described in U.S. Patent Nos.
2,970,117 and ~,064,039. In such preferred means, a po-rtion
of the catalyst in the regenerator is withdrawn from a lower
port theroef, passed downwardly out of the regenerator, then
lifted, for example, with air as a fluidized bed through an
indirect water cooler steam generator, then lifted into an
upper port of the regenerator. If desired, the cooled
catalyst can alternatively be reintroduced into a lower port
of the regenerator. Depending upon the coke forming
tendencies of the heavy hydrocarbon feeds to be processed,
e.g. the Conradson carbon residue values o~ the feedstocks,
the cooler can be sized accordingly.
As described above, sufficient oxygen is charged to
vessel 58 in amounts supporting combustion of the residual
carbon on catalyst and to produce a relatively carbon
dioxide-rich Elue gas with traces of carbon monoxide present.
The CO2-rich flue gas thus generated passes with some
entrained catalyst particles from the dense fluid catalyst
bed 54 into a more dispersed catalyst phase thereabove from
which the flue gas is withdrawn by one or more conduits
represented by 70 and 72 co~municating with one or more
cyclone separators indicated by 74. Catalyst particles thus
separated from the hot flue gases in the cyclones are passed
by dipleg means 76 to the bed of catalyst 54 in ~he second
regeneration zone 58. CO2-rich flue gases absent catalyst
fines and combustion supporting amounts of CO are recovered
by one or more conduits represented by 78 from cyclones 74
2C3~ 37~
19 -
for use, for example, as described hereinabove in combination
with the first regeneration zone flue gases.
Catalyst particles regenerated in zone 5~ at a high
temperature are withdrawn by refractory lined conduits 80 and
81 for passaye to collection vessels 82 and 83, respectively,
and thence by conduits 84 and 85 through flow control valves
V84 and V~5 to conduits lu and 12 communicating with
respective riser reactor ~ as above discussed, and with a
second riser reactor 108 more fully discussed hereinbelow.
Aerating gas can be introduced into a lower portion of
vessels 82 and 83 by conduit ~eans 86 communicating with a
distributor ring within said vessels. Gaseous material
withdrawn from the top portion of vessels 82 and 83 by
conduit means d~ passes into the upper dispersed catalyst
phase of vessel 58.
Simultaneously with the heavy hydrocarbon feed
cracking operation described hereinabove, a naphtha feed
stream to be catalytically cracked, e.g., light, intermediate
or heavy virgin naphtha along with selected cracked naphthas
if desired, is introduced into a lower portion of the second
elongated riser reactor ln8 by conduit means 14 through a
multiplicity oE streams in the riser cross section charged
through a plurality of horizontally spaced apart feed
injection nozzles indicated by 16. Such nozzles aee
preferably atomizing feed injection nozzles or similar high
energy injection nozzles of the type described hereinabove.
As in Eirst riser reactor 8, hot freshly regenerated
catalyst is introduced into the riser reactor 108 lower
portion by conduit means 12 and caused to flow upwardly and
become commingled with the multiplicity of hydrocarbon feed
streams in the riser reactor 108 cross section, and in an
amount sufficient to form a high temperature vaporized
mixture or suspension with the hydrocarbon feed. Also as in
first riser reactor 8, steam, fuel gas or some other suitable
gas can be introduced into the feed injection nozzles through
.
-20 - 2 ~ 7 8
conduit means 2 to facilitate atomization and/or vaporization
of the hydrocarbon feed, or as an aerating, fluidizing or
diluent medium. The high temperature suspension thus formed
and comprising hydrocarbons, diluent, fluidizing gas and the
like, and suspended (fluidized) catalyst thereafter passes
through riser 10~ which is preferably operated independently
from the first riser reactor 8 in a manner to selectively
catalytically crack relatively low boiling naphthas to
desired products, including high octane gasoline and 3asoline
precursors, and light olefins.
Such cracking conditions in second riser reactor
108 to selectively produce desired cracked products from the
naphtha feeds are well known. For example, it is known that
heavy carbon laydown on the catalyst, e.g. hydrocarbonaceous
material or coke build up (which can be liberally contributed
by heavy feed residual oils and the like) is a greater
detriment to gasoline selectivity when cracking a relatively
low boiling feed, such as virgin naphthas or heavy cracked
naphthas, than with cracking a relatively high boiling feed,
e.g. residual oil and the like, although it can be a
detriment to both. Therefore, a net advantage in terms of
gasoline selectivity is achieved by permitting the low
molecular weight feed to undergo cracking in the second riser
reactor 108 independent of first riser reactor 8 and in the
absence of the heavy feed and substantiai coke laydown. It
is also known that heavy feed undergoes cracking at lower
selectivity to ~asoline and gasoline precursors than lighter
hydrocarbon Eeeds. Thus, as mentioned hereinabove, it is
advantageous to first subject heavier hydrocarbon feed
components to reduced residence times and very high
temperatures to limit the cracking as much as possible to
paraffinic side chains and mono- and di-aromatics in general
in the first riser reactor 8 to control excessive coke build
up, while simultaneously and independently increasing the
severity of cracking naphtha feeds in the operation of second
-
8978
21
riser reactor 108 under the combined influence of such
variables as longer residence times, and higher catalyst-to-
oil ratios thereby increasing mix zone outlet and catalytic
zone inlet temperatures in the presence of low carbon on
catalyst ef~ects mentioned hereinabove. Moreover, by
employing separate riser reactors 8 and 108 to optimize feed
conversion as desired. It will be therefore appreciated that
such carbon on catalyst effects and diluent effects described
hereinabove are independent and can be manipulated in an
advantageous manner in the process of the present invention
to cooperate and enhance gasoline selectivity in the overall
system.
Thus, in accordance with the process and novel
arrangement of apparatus of this invention as shown above, it
is possible to select optimal operating conditions in the
second riser reactor 108 substantially independent of first
riser reactor 8 which conditions are specifically suited to
catalytically crack naphtha feed therein providing increased
recovery of desired high octane gasoline products, and light
olefins while simultaneously operating the first riser
reactor under the aforementioned conditions favorable for
optimal conversion of heavy high boiling feeds to gasoline
and light cycle oil boiling range material.
It is also known that increased catalytic
conversion of virgin and cracked naphthas provides products
with increased octane numbers plus large yields of light
oLefins such as butenes and propylene, which are valuable
petrochemical dimerization and alkylation charge stocks, and
that high temperature recracking of cracking FCC gasoline
components also improves octane numbers. Such conversion to
the desired products increases with increasing conversion
temperatures. Thus, it will be appreciated by those skilled
in the art that the process and novel arrangement of
apparatus in the present invention in addition to providing
~5 selective control of optimal cracking conditions of specific
- 22 ~ ~ 78
feeds, also provides extremely hi~h cracking temperature
capability made possible ~y the use of first and second
catalyst regeneration zones favorable for high temperature
cracking and increased conversion of naphtha feeds to such
desired products as mentioned above.
In accordance with that above, naphtha is
preferably catalytically cracked in second riser 108 under
conditions involving nominal residence times oE from l to 10
seconds, with feed preheat temperatures from 220~F to
700F, riser reactor mix zone outlet temperatures from 102F
to 1200F, eiser reactor catalytic zone inlet temperatures
frQm 980F to 1200F and riser reactor outlet temperatures
from 950F to 1050F, with riser pressures ranging from 15
to 35 psig. Catalyst-to-oil ratios in the second riser
reactor based on total feed can range ~rom 3 to 12 with coke
make on regenerated catalyst ranging from 0.1 to 0.5 weight
percent.
Effluent from the second riser reactor 108
therein comprising a vaporized hydrocarbon-catalyst
suspension including catalytically cracked products of
naphtha conversion passes from the upper end of riser
108 through dicharye through an initial separation in a
suspension separator means indicated by 26 such as described
hereinabove and/or passed to one or more cyclone separators
~5 28 located in the upper portion of vessel 20 for additional
separation of volatile hydrocarbons from catalyst particles,
also as described above. Separated vaporous hydrocarbons,
diluent, stripping gasiform material and the like can ~e
withdrawn by conduit 90 for combination with such material
from the cracking operation in riser reactor 8, and for
passage to product recovery equipment.
Spent catalyst from the cracking process in riser
reactor lOa and separated by means 26 and cyclones 28 is
collected in catalyst bed ~0 and thence regenerated in the
- 23-
manner described hereinabove in the first and second
regeneration zones.
The mixture comprising separated vaporous
hydrocarbons and materials from hydrocarbon cracking rom the
cracking operations in riser reactors 8 and 108 is withdrawn
by conduit means 90 and transfer conduit means 94 to the
lower portion of a main fractional distillation column 98
wherein product vapor can be fractionated into a plurality of
desired component fractions. From the top portion of column
98, a gas fraction can be withdrawn via conduit means 100 ~or
passage to a "wet gas" compressor 102 and subsequently
throuyh conduit 104 to a gas separation plant 106. A light
liquid fraction comprising FCC naphtha and lighter C3-C6
olefinic material is also withdrawn from a top portion of
column 98 via conduit means 107 for passage to gas separation
plant 106. Liquid condensate boiling in the range of
C5-430F can be withdran from gas separation plant 106 by
conduit means 110 for passage of a portion thereof back to
the main fractional distillation column 98 as reflux to
maintain a desired end boiling point of the naphtha product
fraction in the range of about 400F-430F.
Products produced in the gas separation plant 106
comprise a C3/C~ light olefin LPG fraction which can be
passed via conduit means 111 for further processing into
ethylene and propylene in processing means not shown,
including an off gas comprising lighter boiling material
withdrawn in conduit means 112; a light FCC gasoline product
boiling up to about 180F; an intermediate FCC gasoline
product boiling in the range from 100F to about 310F; and a
3~ heavy FCC gasoline boiling in the range ~rom 310F to about
430F, which can be withdrawn, generally, in conduit means
113.
A pump around conduit means 114 in communication
with the upper portion of column 98 is provided for supplying
at least a portion of a heavy FCC naphtha stream via conduit
~)89~
_ 24-
means 4, 116 and 14 to the feed injection nozzles 16 of the
second riser reactor 108 where it is combined with the hot
regenerated catalyst introduced by conduit 12 to form a
suspension in the manner set forth hereinabove. Heavy FCC
naphtha can thus be recycled and recracked in such manner in
the presence of the virgin naphtha feed introduced by conduit
means 14 to simultaneously catalytically crack both virgin
and heavy FCC naphthas under optimum conditions selective for
producing high octane gasoline and gasoline feedstocks. In
such an arrangement, it is also contemplated cracking heavy
FCC naph~ha recycle in riser 108 as described above alone or
in combination with virgin naphtha.
rhe heavy FCC naphtha may also be passed all or in
part via conduit means 114 and 4 to feed injection nozzle 6
of the first riser reactor 8 where it is combined with the
hot regenerated catalyst introduced by conduit means 10 to
form a suspension in the presence of the heavy hydrocarbon
feed for catalytic recracking in combination with cracking
said heavy hydrocarbon feed and to optimize a desired product
distribution.
Further, in such an arrangement of the present
invention it is contemplated passing virgin naphtha feed
through ~eed conduits 14 to conduit 4 and thence to feed
injection nozzle 6 of the first riser reactor ~ and
catalytically cracking virgin naphtha in combination with
cracking heavy hydrocarbon fèed introduced by conduit 4.
The process and apparatus of the peesent invention
also contemplates providing materials lighter and lower
boiling than heavy FCC naptha to be catalytically recracked
alone or in combination with recycled heavy FCC naphtha,
virgin naphtha and/or heavy gas oil/residual hydrocarbon
feeds. Such material includes selected FCC gasoline cuts
which can be withdrawn from the gas plant 106 via conduit
means 10~ and 114, and thereafter supplied to conduit means 4
35 and/or 14 for introduction into feed nozzles 6 and 16 of the
~ 7
-25 -
first and second riser reac~ors, respectively, for such
catalytic recracking.
A portion of the heavy FCC naphtha stream can also
be passed through conduit means 114 to conduit means 160 as a
lean oil material for gas generation plant 106.
A light cycle gas oil (LCO)/distillate fraction
containing naphtha boiling range hydrocarbons is withdrawn
from column 98 throuyh conduit means 124, said LCO/distillate
fraction having an initial boiling point in the range of
10 about 300F to about 430F, and an end point of about 600F
to 670F. The LCO/distillate fraction can be further
processed in a stripper vessel (not shown) within which said
LCO/distillate fraction is contacted with stripping vapors
thereby stripping the lighter naphtha components from said
fraction, and producing a stripped LCO/distillate stream
which can thereafter be passed to a hydrotreater or other
appropriate processing means for conversion into diesel
blending stock. Stripped vapors therefrom comprising naphtha
boiling range material can be passed by means (not shown)
from said stripper vessel back to the main product
fractionator.
It is also contemplated in the process and
apparatus of the present invention of passing a portion of
the thus produced LCO/distillate via conduit means 124 to
conduit 14 to be used in conjunction with othec naphtha and
heavy hydrocarbon feed streams described hereinabove to
optimize a desired product distribution.
A non-distillate heavy c~cle gas oil (HCO) fraction
having an initial boiling range of about 600F to about 670F
is withdrawn from column 98 at an intermediate pOillt thereof,
lower than said LCO/distillate fraction draw point, via
conduit .neans 126. Although not indicated in the FIGURE, at
least a portion of the HCO stream can be passed to conduit 4
for recracking in riser reactor 8 in the manner herein
provided.
. .
8~78
From the bottom portion of column 98, a slurry oil
containing non-distillate HCO boiling material is withdrwan
via conduit means 132 at a temperature of about 600F to
700F. ~ portion of said slurry oil can be passed from
conduit 132 through a waste heat steam generator 134 wherein
said portion of slurry oil is cooled to a temperature of
abou~ 450F. From the waste heat steam generator 134, the
cooled slurry oil flows as an additional reflux to the lower
portion of column ~8. A second portion of the thus produced
slurry oil withdrawn via conduit 136 flows as product slurry
oil.
It will be apparent to those persons skilled in the
art that the apparatus and process of the present invention
is applicable in any conformation of combination fluidized
catalytic cracking-regeneration processes employing first and
second (respectively lower and higher temperature) catalyst
regeneration zones. For example, in addition to the
"stacked" regeneration zones described in the embodiment of
FIGURE 1, a "side-by-side" catalyst regeneration zone
configuration which is described, or example, in U.S. Patent
Nos. 4,601,814; 4,336,160 and 4,332,672 may be employed
herein.
