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Патент USA US2405922

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Aug. 13, ‘1946.
Filed June 1, 1945
Patented Aug. 13, A1946
Joseph B. Wyman, Roxana, Ill., and Henry I).
Loeb, San Francisco, Calif., assignors to Shell
Development Company, San Francisco, Calif.,
a corporation of Delaware
Application .lune 1, 1945, Serial No. 597,000
2 Claims.
(ol. 19e-52) `
This invention relates to catalytic cracking
and related conversions of hydrocarbon oils in
fluid catalyst systems.
More particularly, the
invention relates to a method for initiating cata
lytic cracking in fluid catalyst catalytic crack
ing systems which aiford certain advantages and
tinuously withdrawn via standpipe it. Before en
tering the standpipe the catalyst is partially
stripped or iiushed of hydrocarbons by contact
with stripping steam introduced at the bottom
of the reactor via line 5. The partially spent cat
alyst withdrawn via, standpipe 4 is picked up by
eliminates certain dangers that are inherent in
a stream of regeneration gas (air) and carried
the present methods.
via line 6 to the regenerator D-2. In order to
Fluid catalyst catalytic cracking, as the name
maintain a positive control of temperature and
implies, denotes a catalytic cracking process in 10 prevent overheating of the catalyst in the regen
which the cracking catalyst in the form of a fine
erator, al portion of the fluidized catalyst is con
powder is utilized while in a ñuidized or so-called
tinuously withdrawn via standpipe 'l and circu
pseudo-liquid state, as distinguished from pellets
lated back to the regenerator through a recycle
or a freely suspended powder. A characteristic
catalyst cooler C-l by means of air introduced
of ñuid catalyst catalytic cracking is that' the 15 via line 8. The regenerator is provided with in
ñnely divided cracking catalyst is continuously
lets such as 9a and 9b provided with nozzles for
circulated through a cracking zone and through
the injection of torch oil to supply additional .
a separate regeneration zone. There are two
heat when it is necessary. The regeneration .
main systems of fluid catalyst catalytic cracking
gases after passing through the ñuidized bed of
and several modiñcations of each.
2O catalyst undergoing regeneration are passed
In one of the systems the catalytic cracking is
through internal cyclone separators (not shown)
eifected in a so-called up-flow or top-draw-olf re
to separate and recover the major part of sus
actor. In this system the vaporous hydrocarbon
pended catalyst particles and then leave the re
product leaves the reactor at the top carrying
generator via lines l Ga and IUb. These gases are
in suspension an amount of catalyst substantially 25 cooled and passed through a Cottrell precipita
equivalent to the amount continuously supplied
tor or other means of recovery to remove addi
t0 the reactor at the bottom with the feed. The
4bulk of the suspended catalyst is separated in
a separate chamber or apparatus and returned
to the reactor or regenerator, and the vaporous
product passes to a fractionating system. In the
other main system the catalytic cracking is ef
fected in a so-called down-flow or bottom-draw
oiï reactor. Since this latter system is the most
widely used of the two, a, typical modification of
Returning to the reactor, the hydrocarbon va
pors after passing through the bed of fluidized
catalyst are passed through internal cyclones
(not shown) to separate and recover the bulk of
the suspended catalyst. The vapors then pass
overhead via line l! to fractionating column
such a system will be used in explaining and
tional amounts of suspended catalyst, but since
this has no bearing on the invention it has not
been included in the diagram. `
Reactor D-I in one instance is about 2l
illustrating the process of the invention. How
feet in diameter and about 47 feet in height. ever, the process of the invention is applicable
Line ll is 36 inches inside diameter by about 820 ~
to both systems. To assist in this description,
feet long. Fractionator E--I is 16 feet in diame
reference is had to the attached drawing form 40 ter and 76 feet in height, In fractionator E-l
ing a part of this speciñcation wherein there is
the product is separated into four fractions: (l)
shown by means of diagrammatic figures not
A light fraction including gasoline and product
drawn to scale a simplified iiow of the more perti
gases which is withdrawn overhead via line l2;
nent portions of what is known in the art as a
standard fluid catalyst catalytic cracking plant.
(2) a light gas oil which is withdrawn via line
45 I3 to a side strippel` E-Z; (3) a heavy gas oil
In operation the oil to be cracked, after suitable
which is withdrawn via line M to a side stripper
preheating, enters via line I. This oil picks up
E-3; and (4) a slurry which is withdrawn from
a quantity of the freshly regenerated catalyst
the bottom via line l5. This slurry consists of
from standpipe 2 of regenerator D-2 and the
finely divided catalyst which escaped separation
mixture passes via line 3 to the reactor'D-l. 50 in the internal cyclones of D-l (for example, 50
Line 3, in one actual case, is two lines, each 25
tons per day) suspended in a portion ofthe un
inches inside diameter. In reactor D-l there
converted oil, This slurry is frequently passed
is maintained a more or less constant level of
through a thickener and the concentrated slurry
iiuidized catalyst. In order to maintain this level,
returned to the reactor. Since, however, this has
a, portion of the partially spent catalyst is con 55 no bearing on the invention, the thickening step
has not been indicated in the diagram. The va
porous overhead product withdrawn via line I2
is passed through a cooler (condenser C-1) by
which the temperature is reduced to such an
extent that the main portion of the normally
liquid products is condensed.
The product is
then passedl to a fractionator reflux drum F-~l2.
Condensed water may be withdrawn via line 18a.
A portion of the hydrocarbon condensate is usu
ally recycled to the fractionating column to serve>
as reflux. The uncondensed gases are withdrawn
such time as oil is cut in. If this is not carefully
looked after, the lines will become plugged. Also,
even small amounts of finely divided catalyst can
do great damage if allowed to pass over into the
compressor J-Zâ. These elements of danger can
be minimized by exceptionally carefully managed
cooperation of the several chosen and trained
operators. They are nevertheless there and real,
and become of increasing importance as the
valves, instruments, etc., become less dependable
due to the erosion and corrosion of previous pe
riods of use.
from the top via line I6 and compressed by com
The start-up procedure of the present inven
pressor J-28. The remainder of the liquidV hy
tion, which has been. tested and adopted in com»
drocarbon product from F-'l24 is then` addedvia
mercial plants, differs materially from the con
line I1 and pump J-Zti and the mixture further
ventional procedure. Its main advantage over
cooled in cooler C-i3. The product passes to’
the conventional procedure is in the substantial
an intermediate gas separator F-HL Further
elimination of the more important oi these haz
amounts of condensed water may be withdrawn
ards; The start-up of a fluid catalyst catalytic
via line I8b. Hydrocarbon gas is withdrawn via
line I9. The liquid condensate is withdrawn via 20 cracking plant, according to the process of the
invention, may be described»- in connection with
line 20. In practice a second stage ofï compres
the attachedr diagram as follows:
sion and cooling is usually employed and- the
After checking the equipment. compressor J--l
products are then subjected to rectified absorp
is started and air is blown via lines 2l, 22, 23, 2G
tionV to recover a dry gas and a stabilized distil
late. However, these operations have no bearingl 25 and 61 tothe regenerator D-2. Some air is also
passed via lines 23, 2t and l?V through recycle
on the present invention and have not been indi
cooler C-l. Air may also be introduced into the
catedV in the diagram.
regenerator and/or reactor system at other points,
While the operation of the system as above
as'considered desirable or convenient».
described is basically quite simple, it is by no
means simple to start up such a plant. The oper 30 Air heater B`----l, using gas introduced under
pressure via» lines 21 and 28, is started. Part of
ation ordinarily supplies its own heat, steam, etc.,
the'air' is passed via lines 2| and 29 to the com
from the regeneration of the spent catalyst. Con
bustion Zone and the remainder is passed via
sequently, none of the apparatus is iired- There
lines- 2l and 22 to the heater. The hot air con
is, however, an enormous amount of metal and
catalyst which has to be brought up to a rela 35 taining some ñue gas (for example, 15% oxygen)
is passed to the regenerator and reactor systems
tively high temperature before any oil can be
as described. Part of the hot air is removed from
introduced into the unit. Furthermore, it is es
the regenerator, for instance, via lines I 0a and
sential that .the catalyst be kept continuously mov
|525, and part is removed from the top of the re
ing in order to> avoid serious plugging of valves,
actor, for instance, from vent 30 at the top of
lines, etc. Furthermore, the equipment repre
line H.
sents a very large investment and is easily dam
Likewise, air and gas are introduced via lines
aged by allowingl any one ‘of a- number of'varîables
2e' and 20 to 9, flue gas generator B-Z to pro
such as weight of catalyst, pressure, tempera
duce a' hot relatively inert gas which is passed
ture, and velocity of catalyst to exceed certain
rather restricted limits. Even if the equipment 45 via lines 3l, 32", 33 and 3d .to various partsV of the
fractionating section. The hot flue gases are like
is not damaged the plugging of a line or some
Wise withdrawn via vent 30 at the top of line Il.
other upset causing loss of circulation may re
A portion may also be withdrawn via line 35 to
quire shutting the plant down, cleaning and start
flush out line l2, cooler C-l, sepa 'ator F--i2
ing all over again.
In the method in common use the regenerator 50 and line I6. Vent 30 and line 35 are preferably
throttled to maintain a. positive pressure of, for
is brought up to temperature by the burning of
instance, 5 p. s. i. in fractionator E-l .
torch oil; the reactor is brought up to tempera
Cooling water may be circulated through con
ture first by steaming and then by recirculation
densers C-‘I and C-IB.
of hot catalyst; and the fractionating equipment
The various aeration bleeds may be cut in to
is brought up to temperature bythe use of super 55
various parts of the reactor and regenerator sys
heated steam. When everything is at a suitable
' temperature and otherwise ready, oil is cut in and
then the conditions of' flow are gradually ad
tems, as desired. In those cases where steam is
used as an aeration medium, superheated steam
is preferably cut in as the temperature reaches
justed to'give‘ the desired operation. This method
of starting up’,_although in general use, has several 60 about 500° F. Thus, for example, superheated
steamY is cut in to reactor D-l via lines 5 and 5a
elements _of danger, both with respect to the equip
ment and to the operating personnel. The great
est danger lies in> the fractionating section. It is
extremely difficult and time-consuming to bring
when the reactor temperature is above 300° F.
and preferably 500° F. Care is taken that the
flow in line l l between the fractionator and vent
every inch of the large apparatus' and numerous 65 30 is towards vent 35i.V
When thev temperature in regenerator D-Z is
lines to a temperature above about 250° F. to in
above about 500° F., catalyst is slowly introduced
sure thev absence of liquid Water remaining from
via line 36, the rate of addition being such that
the previous processing er condensed from the
the temperaturel does not fall below about 450°
steam used for heating. If even small plugs of
water are present in the system there is great 70 F. Valve 3'1 is closed so that only superheated
steam is introduced into the reactor. When sui'îtl-`
danger of damaging the fractionatinfg column.
cient catalyst has been introduced (for example,
There is danger of collapsing the fractionating
150 tons or more), catalyst is transferredv to the
columndue'to a temporary steam failure, plugged
reactor via; lineV 3v and circulation of catalyst be
valves, or carelessness. Finely divided catalyst
must be kept out of the fractionating system until 75 tween the reactor and regenerator is started.
Steam introduced via lines 5a and l may be used
for this purpose.
When the temperature in the regenerator is
about 600° F. the combustion of torch oil intro
duced via lines 9a and 9b is started. The catalyst
inventory is gradually increased and the tem
perature of the hot air introduced into the regen
erator is gradually reduced by cutting back in the
is introduced into the system initially. Also, dur
ing the initial stages of the use of steam, the
steam is used in conjunction with the hot air or
hot ñue gas. This system avoids the condensa
tion of appreciable amounts of water and avoids
the danger of blowing out the plates of the frac
tionation column when feed is cut in due to
slugs of water. Aside from avoiding the several
fuel supplied to air heater B-l. In the mean
dangers, the process of the invention is advan
time the fractionator is being heated by the hot 10 tageous in that the amount of superheated steam
inert flue gas.
The lower section of the frac
tionating tower E-I is also preferably flushed
required is much less than in the conventional »
practice. This is, of course, of considerable eco
with a hot heavy oi1 such as gas oil introduced,
nomic importance not only because of the cost
for example, via line 38.
of superheated steam, but also in View of the
When the temperature of the catalyst is about 15 smaller boiler capacity required to supply the
750° F. and the temperature in fractionator E-I
plant. By using the described start-up procedure
is at least 230° F., outlet 30 is closed and line 35
is opened suiiiciently to avoid excessive pressure
in the fractionator E-i. The gas in fractionator
» the plant may be brought on stream in at least
as short a time as that required using the con
ventional start-up procedure; in many instances
E-I is now a mixture of hot inert iiue gas from 20 considerable operating time may be gained by
flue gas generator B-Z and superheated steam
from the reactor,-with the direction of flow re
versed. Circulation of catalyst is continued until
the smoothness of coming “on-stream.”
the temperature of the catalyst is in the neigh
ing plant comprising a reactor system compris
We claim as our invention:
1. In bringing on stream a fluid catalyst crack
borhood of 775° F.-800° F., and the oxygen con 25 ing a fluid catalyst reactor and a fractionation
tent of gases withdrawn via line 35 is below a
system comprising a fractionating column, Said
safe limit, (for instance, 0.2%), at which time
the flow of ñue gas to the reactor is displaced
by a ñow of fuel gas (such as reiinery or natural
gas) introduced Via lines 39 and i, This gas
passes through the reactor and the iractionator
and the gas compression system, line 35 being
closed. This gas may advantageously be recycled
through the conventional gas absorption plant
fractionation column communicating directly
with said reactor, the combination of steps com
prising heating the reactor by passing hot air
therethrough and simultaneously heating the
fractionating column by passing hot flue gas sub
stantially free of oxygen therethrough, withdraw
ing said gases as a common stream from a point
between said reactor and said fractionating co1
(not shown) , the rate being gradually increased. 35 umn, thereby confining said gases to the respec
During this period of catalyst recycle a small
amount of the catalyst is carried over into the
lower section of the fractionator E-L When
the concentration of the catalyst in the oil in the
bottom of the fractionator becomes sufficient to
produce a suitable slurry (for example, 4% cat
alyst), circulation of the slurry to the reactor
via lines l5 and 4G may be started. At this time
the reactor temperature should be above '700° F.
Feed oil is then gradually cut into the reactor
via line I, the recirculation of gas via line 39
being discontinued, and the conditions of tem
perature, flow rates, etc., adjusted.
It will be noticed that in the described example
tive systems, and continuing the passage of said
gases until the temperatures in the systems are
sufficiently high to allow the introduction of
superheated steam without substantial condensa
tion to water.
2. In bringing on stream a fluid catalyst crack
ing plant comprising a reaction system compris
ing a fluid catalyst reactor and a fractionation
system comprising a fractionating column, said
fractionating column communicating directly
with said reactor, the combination of steps com
prising heating the reactor by passing hot air
therethrough, simultaneously heating said frac
tionation column by passing hot flue gas sub
of start-up procedure, the reactor-regenerator 50 stantially free of oxygen therethrough, with
system and the fractionation system are heated
drawing said gases as a common stream from a
and flushed with two separate gas streams flow
point between said reactor and said fractiona
ing in opposite directions and issuing at a com
tion column, continuing the passage of said hot
mon point between the two systems.- The gas
air until the temperature in the reaction system
circulated through the reaction system is hot air, 55 is above the condensation temperature of super
then hot air plus steam, then steam alone, and
heated steam and then substituting superheated
iinally steam alone plus hydrocarbon gas, while
steam for the hot air, continuing the passage of
the gas circulated through the fractionation sys
said hot flue gas through the fractionation col
tem is hot flue gas substantially free of oxygen,
umn until the temperature is above the condensa
later flue gas plus steam, and iinally steam plus 60 tion temperature of superheated steam, then dis
hydrocarbon gas. The direction of now of the hot
continuing the withdrawal of gases from said
inert flue gas in the fractionation system and the
point between said reactor and said fractionation
slight positive pressure prevents the introduction
column and withdrawing the superheated steam
of any air or steam from the reactor entering
from the reactor through the fractionating sys
the fractionation system and avoids al1 danger 65 tem with said hot ñue gas, and ñnally discontinu
of collapse of the fractionating column due to a
ing the use of said hot flue gas and purging the
partial vacuum. This system allows cooling wa
reactor and fractionation system by cycling hy
ter to be circulated in the condenser C--l and
drocarbon gas with said steam seriatim there
C-l3 during start-up and avoids the danger of
damaging these pieces of equipment. It will also 70
be noted that in the described procedure no steam
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