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2,410,284
Patented Oct. 29, 1946
V
>2,410,284
CATALYTIC CRACKING >'SYSTEM
Robert C. Gunness, Chicago, Ill., :and Joseph W.
Jewell, Summit, N. J., assignorsof one-.half 'to
Standard ’Oil Company, a corporation of lIn
ldiana, and one-half >to The M. W. -Kellogg vCom
pany, a corporation of Delaware
>App'lieationmpril 24, 1941, .serial »16.390304
-6'Claîms.
(c1. 1196-52)
.
2
l
upon to handle the Acatalyst powder. An 'object
Thisv invention relates Lto .a .catalytic cracking
system and it~ pertains more particularly to a
large scale 'commercial .method >and lmeans for
of our invention is ’toprov'ide a commercial sys
eñecting catalytic cracking .in _a powdered or
from 'low levels to.high‘levelsand’wherein it’flows
by gravity'from 'high Vlevels ~to low .levels through
tem'w'here'in catalyst vis„pneumatically transferred
fluid-type catalyst system.
_ In 'the .powdered orv fluid-type catalyst system a
out the entiresystem.
_
_
_
A 'further 'object-is to ,prevent the loss croat@
lyst vnot only from _reactor -_and regenerator'gas'es
but ‘from Vaeration 'gases V,and,pneumatic conveyor
gases .throughout 'all partsof thejsystem‘and _to
remove leven. finely .divided dust 'from all gases
powdered catalysteiîects the conversion .of gas
oil or ~heavier "hydrocarbons intogasoline while
the _.catalystis suspended 'in yhydrocarlzlon vapors.
Spent catalyst is separated `from reaction >gases
^ and vapors and 'is then .suspended 1in a regenera
tion vgas whereby carbonaceous deposits `are -«re
moved from vthe catalyst’by controlled oxidation.
Regenerated catalyst Ais -then separated fromre
generation Agases Vand .returned l.to the cracking
Step.
vented from 'the system. A_furth'er object isto
Various proposals have been made-forthede
sign of commercial crackingxsystems >along the
hoppers, cyclone separators. etc. with ‘an‘_e_‘_ectro-
provide improved methods and means forhan
dling and utilizing the "dust which _is separated
from vented gases. .A v’further object'isto provide
an improved .system of 'upper and lower catalyst
static _precipitator so that, the entire system will
functionr _smoothlyand îeiîiciently Without over
above lines but -.the actual `use of 'theprocess has
heretofore been limited to 'experimental or labo ZO loading at any _point and `»Without undesirable
surges 'in xpressure _or losses in jheat. çA further
ratory rsystems. _An .object of ourinvention'is to
provide a v'fluid-type catalytic cracking `system
Objectis to‘provide improved ‘methods andjmeans
for large commercial units, e..g., .a unit which
for obtaining a substantially _uniform ymixture of
will convert about 10,000 -barrels .per Vday of
_charging stock into .large ,yields of .high .quality
naphthaswhich .may be 'marketed Aas .premium
motor fuels .or which V.may Íform base stocks for
catalyst entering :the 'reactor is always substan
.regenerated catalyst__frorn various separation sys
tems sothatthfe distribution ,of particle sizesof
tially the same.
_
_
_ _
_
A `further ob'jec't’is to provide van improvedgen
eral layout for a 'fluid-type catalytic cracking
One probleminthe .design of .commercial .-ñuid
type catalytic cracking .systemsis .thatoff utilizing 30 system whereby the reaction, 'regeneration and
the heat developedlin '.there'generation step. An
fractionation .parts vof the system .are all ¿inte
grated to formY a un’it of _maximum eñiciency, _A
object _of ourinvention >is .to ,provide an improved
further 'object is to insure the V_operation of this
method ,and meansfíorsolving thisproblem. Our
unitary system and all ’parts thereof under vopti
object 4is Ato kprovide a .unitary-system wherein a
mum conditions o‘f 'temperature'pressure cata
minimum amount »of .extraneous heat .or energy
lyst densitygetc.. in order that maximumjga s_o‘ine
will .have to be supplied. wherein vthe .excess .heat
aviation gasoline.
_
yields may be obtained, a minimum amount of
carbon maybe deposited on the catalyst, valu
in reaction ,.produóts, .regeneration gases and re
cycled regenerated catalyst ismostefîectively‘uti
able kgas oil fractions maybe obtained from the
lized for supplying lhefat `to vthe .fractionation sys
tem, for preheating .chargin'gstock .for generat 40 heavier-than-gasoline products, and gas '_produc
tion (particularly "the 'production fof methane,
ing-steam. etc. _A ‘further .object >is ,to „provide .a
ethane'and ethylene) maybe reduced to a mini
method and means -for Èobtainingaccurate .tem
mum. Other objectsof .the invention will be ap
perature control inall ,partsof the system and/.or
parent as the detailed description 'thereof pro
minimizing .the .expense of heat >en_clfiangers .and
heatingand Vcooling equipment.
- ,A very serious >problem iin »the operation of >a
ñuid 4catalyst cracking system is thatof storing
and handling .the powdered catalyst, maintaining
thecatalyst fluent rinall .parts o'f ,thesystem, pre
45
ceeds.
_
_
__
_
_
_
.
.In 'broad outline our inventionfcontemplates
a vertical up-ïfiow reactor vchamber ‘which dis
charges .into _an enlarged settling 'zone at _the
base Aof which is an “upper hopper’f~ for spent
venting .undue catalyst attrition,.minimizing cat 50 catalyst .and .in the top of which arefcentrifuges
for removing practically all of >the >catalyst ‘from
aly'st losses and transferring catalysts from ,low
gases and vapors before they leavethe vsettling
zone. Catalyst «is suspended .in vincoming hydro
carbon vapors, `-carriedloy .said vapors Iinto >the
acterized by -low eüciency and which .become
rapidly worn by erosion or abrasion when called 55 base of the reactor, and maintained at a density
pressure zones lto .hi-gh ,pressure Zones without
the .use of .mechanical ,impellers Which are _,char
2,410,284
4
3
about 10 to 25, preferably 15 to 18 pounds per
cubic foot within the reactor at a temperature
of about 800 to 1000° F., preferably 900 to 950° F.
drum and another part may supply heat in the
fractionation and steam generation system. We
may, however, eliminate the surge drum and gen
and a pressure of about atmospheric to 50 pounds,
preferably 8 to 15 pounds per square inch. The
erate steam directly in regeneration gas or re
cycle catalyst exchangers.
'Ifhe product fractionation system _may thus
catalyst-to-oil ratio .in the incoming stream may
receive heat from the regeneration system and
range from about 1:1 to about 8:1 but is prefer
ably about 4:1. The average vapor contact time
in the reactor may be about 4 to 40 seconds, pref
erably about 10 to 20 seconds. The average vapor 10
it may likewise recover traces of catalyst from
product gases so that such catalyst may be re
turned to the reactor. Reaction products are
velocity through the reactor may be about 0.4 to
preferably introduced at the base of a combina
4, preferably about 1.5 to Zfeet per second.
The regenerator is a much larger up-flow
chamber which is likewise superimposed by an
tion fractionating tower and scrubber which may
upper hopper for regenerated catalyst and in the
slurry of recovered catalyst in heavy oil as a
bottom fraction. We may utilize the heat from
be operated at a pressure of about 5 pounds gauge.
We may separately remove one or more gas oil
enlarged settling zone at the base of which is an 15 fractions as side streams from this tower and a
top of which are centrifugal separators for re
the bottom fraction for preheating charging stock
moving unsettled catalyst frcm reaction gases
and then for the preheating of water from which
before they leave the top of the settling zone.
Spent catalyst is introduced to the lower part 20 steam is to be generated. Also, we may utilize
the heat from this bottom fraction or from a
of the regenerator by means of air and the
clean heavy gas oil withdrawn from a point ad
average vertical velocity of air and combustion
jacent the tower for reboiling or stripping one
gases in the regenerator is about 0.4 to 4.0, prefer
or more of the gas oil side streams.
ably about,1.5 or 2 feet per second so that the
The cooled
catalyst density in the regenerator is about 10 to 25 bottoms or heavy gas oil fractions may then be
returned to the top of the scrubbing section of
25. preferably 18 to 20 pounds per cubic foot. A
the tower for maintaining the desired tempera
large amount of regenerated catalyst from the
ture at this point in the fractionation system.
upper hopper is recycled through a catalyst
‘The gasoline and gases which are taken over
cooler to the regenerator and is reintroduced
thereto at a temperature >of about '750 to 900, 30 head from the combination fractionating tower
and scrubber may be cooled and compressed to
preferably about 840° F. Spent catalyst may
a pressure of about 135 to 150 pounds per square
enter at about 850 to 950° F., preferably about
inch. After the removal of water the compressed
900° F. The average temperature of catalyst
gases and liquids may be charged to a fractiona
entering the regenerator may be about 850° F.
The regeneration may be effected at a tempera 35 tion system forming a part of the unit or may
be charged to other fractionation systems which
ture of about 950 to 1050“ F., preferably about
may form a part of the reñnery in which'the
1000“ F. and under a pressure of atmospheric to
unit is located.
50 pounds. preferably about 8 to 16 pounds per
The invention will be more clearly understood
square inch. The amount of air required for re
turning recycled catalyst to the regenerator, in 40 from the following detailed description read in
troducing spent catalyst into the regenerator and '
conjunction with the accompanying drawing
supporting combustion in the regenerator may be
about 13 to .15% by weight of the spent catalyst
which is charged to the regenerator but will de
which forms a part of the specification and which
constitutes a schematic ñow diagram of our im->
proved system.
pend of course on the amount of carbonaceous 45
The invention will be most clearly understood
from the detailed description of a preferred em
material that must be burned from the catalyst.
bodiment but it should be understood that the
Catalyst is maintained in fluent form in all
invention is not limited to the 'specific charging
hoppers, standpipes, etc., by means of an inert
stocks. operating conditions, and features herein
aeration gas which is usually steam. Aeration
gas from all parts of the fresh and regenerated 50 described. The charging stock may be any gas
oil or heavier hydrocarbon distillate which is ob
catalyst system is passed through a Cottrell pre
tained from natural crude petroleum or from
cipitator for the removal of catalyst dust so that
hydrocarbon synthesis or from hydrocarbon con
catalyst losses are reduced to a minimum. Fresh
catalyst may be transferred to an upper hopper
version processes. The operating conditions will
and mixed with Cottrell fines before being ad
necessarily depend upon the activity and physical
mixed with regenerated catalyst and charged to
the system.
The finer catalyst particles separated by the
Cottrell precipitator and by cyclone separators
properties of the specific catalyst and the extent
of conversion which is desired. Many modifica
tions and alternatives of the details herein set
forth will be apparent from this detailed descrip
is either agglomerated. reconditioned, or thor GO tion to those skilled in the art.
The catalyst is preferably of the silica-alumina
oughly mixed with coarser catalyst particles so
or silica-magnesia type and may be prepared by
that ra uniform catalyst mixture is introduced
intothe reactor.
The last traces of catalyst may be separated
from reaction products in a combination frac
tionatine.r and scrubbing tower and returned with
a small amount of the heavy oil fraction to the
reaction zone.
^
the acid treating of natural clay such as ben
tonite. exempliñed by the commercial ‘V‘activated”
65 clay “Super-Filtrol,” or by synthetlcally prepar
i ing a powdered silica-alumina or silica-magnesia
mixture. An excellent catalyst may be prepared
byball-milling silica hydrogel with alumina or
.
The gas oil feed passes through various heat
exchangers to a surge drum or furnace charge 70
drum. If the surge drum is employed gas oil "
may be cycled therefrom through heat ex
magnesia using about 2 to 30%, for example about
15% of alumina or magnesia. The ball-milled
dough may be dried at a temperature of aboutV
240° F. and then activated by heating toV a tem
changers for absorbing heat from hot regenera
perature of about 900 to 1000o F.
tion gases and regenerated catalyst. A part of
this heatedl gas oil maygo to the furnace charge
l
Another method Vof preparing a highly active
y cracking catalyst is toformf a gel from dilute
:antan
..5
‘6
sodium isilicate in the presen‘ce‘o'f an ‘aluminum
salt ïby fthe'additi‘on of excess >'dilute sulfuric acid.
The resulting Ágel is preierablyîbo'iled for -fan hour
ployed. A`i'l.1so,`-it »should -¿be 'understood that the
temperatures of the gas ‘oil at various points fin
¿the system ¿may vvary and may be different than
thosestated in ï'th-is rspeciñc example.
or two with an excess-of dilute ammonium hy
Charging stock »from ¿drum 26 viis introduced »by
droxide solution l'before washing, 'after which Vitis
‘pump 132 and »line '?3‘3 »into -coils 34a of lpipe still
dried and heated as .inthe previous example.
'35. This »pipe‘s't‘ill may lbe designed with three
The silica alumina catalyst may be :rendered
downwardly fired radiant sections
lva ’lower
more -stable at high temperatures bythe Aaddition
confvectionisection. The charging stock r`from lline
thereto »of zirconia l’in either smaller or :larger
10 33" may »be iirst passed -'through ‘tubes ¿34a in »the
amounts than alumina.
lconvection section and then ythrough ‘tubes 53412
The lball-‘milled silica »m'agnesi'a catalyst vmay
»in the kfirst downwardly ‘ïñred ¿radiant section.
I‘be 'improved -by 1pretreating the magnesia with 'a
'Steam »from generator 29 is passed by line í3lì`~to
thorium nitrate solution'sotha't the iinished cata
coils «in »this radiant section l'and We Amay ¿intro
lyst may, 'for instance, have fthe >following com
-position:
15 duce an -amoun't of steamequívalent to about ’5%
by weight ~o"f the >stock charged. The oil may
Per cent
‘Silica
_______________________ _-_ _________ __
`Magnesia
.'I‘h'ori'a
--.___
~
v
-
c-.
66
'enter ycoils y’3419 at about '775° F. and about 75
27
pounds per'squa‘reiné-h and ma'yïleave -thes‘ecoils
_______________ __- ________________ __
at aftemperature of 1z'ftb'ou't 840° Ffan'd a pressure
7
20 of faboutSO pounds per'square Linch.
In'coils -*31H7
-No invention is claimed in the composition of
‘the :charging ‘stock is completely vaporized, 'the
yCata'lys't'per lse and -no further description of the
introduced Vs'te'aïr’r'i assuring ycomplete vaporiza'tion.
catalyst is therefore necessary.
»After complete vaporization in series íiow
The `catalyst in this speci'ñc example is in pow,
through vcoiïlsïß'éb the charge is superheated while
deredformwith a 'particle size of about 10 to 100 25 passing lin parallel rfiowî'through coils y34o inthe
microns, i. e., -with about 50% of the vcatalyst
second downwardly heated radiant sectionof the
`»passing about >a 400 meshscreen. The invention
furnace. The pressure drop through coils 33117115
is applicable, however, to other'catalyst sizes pro
relatively Ílow and superheated vapors may leave
vided only that the catalyst be’of vsuch sizes and
these coils at atemperature of‘about'9001'to 1000°
»density >»that it ‘may Aëbe aerat'ed and handled as a 30 F., 'Tio-r `example yabout ^91ï5° F., at a pressure of
ñuid in 'the manner îherein‘described.
about 1-8 to -2'0 pounds Aper square inch gage.
The îfeed vstock from Àsource -ID may 'be a Mid
"-I'h'e third downwardly 'heated ‘radiant section
Continent gas oil-or van'iixture‘of such'gas oil with
oi ¿the furnace is employed ¿for ‘superheating
»the gasoil >seperated 'from catalytic vor thermal
steam toa temperature of about 900° îF. lor more.
conversion products and in the example Íherein 35 The Vsteam -may Vbe introduced ‘into the super
described the charge may >consist Yof 7500 >barrels
heating vcoils `through lline 36a, passed through
periday of `virgin ygas oi-l and >2500 barrels per day
superheating fcoils 3l 'and then distributed to
-‘of -gas oil ’from refinery ‘conversion -systems. This
various Lparts of the systemfthrough the'line des
charging stock 'may Yhave -a gravity Y“o‘f 'about >30
ignated “process steam.” To avoid unduly com
to 35, Vfor example, 31.1° A. -P. I. so that the'charg 40 plicatin'glthe drawing these process steam distrib
ing rate may 'be Vabout 126.800 pounds per hour.
The stock ‘m‘ayenter heat >exchanger II -a-t about
>room >temperature and >leaves this Aexcl'lalflger »at
about 200° F.
It may be 1further heated in -eX
changer! 2 »to about »290° Rand thenf'by exchanger
t3 ‘to about »450° F. -at which temperature 'it may
«be introduced through line «I4 -to gas roil surge
drum yI5 which `may -be at -a pressure of 'about >25
pounds per square inch. This drum rr-nayvbefabout
8 to >l0 `feet in diameter by v20 feet long.
50
A part `of the gas oil ~which is pumped `from
drum i5 by pump I6 through line I'I may be
passed vby line I8 around the tubes »of catalyst
cooler l 9 and returned by line 20 to line -2‘I . An
other ypart of the gas oil pumped by pump I6 l
through line 'I ‘I «may pass -through Iline 22. `through
>iiue gas cooler 23 and thence by pipe -24 -to line
2l. IThe »stream from line `ZI is split, a part of it
passing by line 25 to »furnace charge drum -26 and
apart passing through line 21 to various heaters 60
in the fractionation system. After it has Asup
plied .heat in the .fractionation system this gas
ïuting lines will be omitted and we will merely in
dicate ther-points >throughout thesystem at which
'process steam is introduced. A part of this ’su
'per 'he'ate‘d‘steam may be passed‘through line 37a
for supplying ~loieat or energy in the system or
elsewhere and 4another part may be passed
through line -S‘lb'for ad-mixture with steam from
generator 29 'and line ï36h. A part of the vsteam
from l'generator i219 may thus be superhe'ated to
various levels 'for any desired use and another
part-Cof vthis steam may >be passed by line 36e for
supplying heat or generatin'gpower in this or any
other system.
y
.It "should be stated ‘that the charging stock to
coils '35a »may ¿include about 500 :barrels per day
of about ‘20° LA. P. I. yproduct bottoms containing
about ‘1100 fto 1200 or more pounds per hour of
powdered catalyst, this >slurry being introduced
through 'lin'e ’ 38.
-In addition “to v»the 4steam introduced through
line 136, steam maybe introduced into the trans
fer «line >39 through line 40 in amount-s of about
oilis returned :through line >28 to steam generator
41or€5% y:by weighto'ffcharging stock. The trans
29 and thence back through line 30 to storage
fer Pliïne vapors then pass through line l4I wherein
drum I_5. The temperature >of the gas-oil leaving 65 they pick up `powdered catalyst Vfrom -standpipe
heat exchangers I9 vand v23 is vabout l‘600°
the
4-2. This standpipe may be about 25 or 26 inches
temperature of the Vgas .oil returning from the
inside dia-meter byla'bout '66 'or 67 ffeet high. The
Afraction-ation system through »line 28 >is about
pressure above »slide valve or star `’feeder :43 'mal7
528°
and it is admixed with suñioient amount
be_:'ab‘out V19 jor 20 pounds per square inch and
of-hotgas oil vfrom line 25 and line v3l so that the
the pressure in linen~4l Iat -ïthis point y'maybe'about
gas loil entering the steam generator iis "about
' 141/2 or y‘lâïpounds per square rinch. The amount
550° F. A‘The gas yoil leaving the :steam generator
oi »catalyst fso introduced `fi`nto 'the hydrocarbon
is about '450° F. While a single steam generator
vapors 'is preferably such as t'o ygive a catalyst
is shown in the drawing it should be' understood
to-’oil Weight ratio yof about 4:1 ‘to y5:1 for exam
that a ’plurality of such generato-rs maybe em
ple about 630,000 to 635,000 pounds per hour olf
„25410,284
7
catalyst may be picked up by the vapor stream at
this point. The temperature of this catalyst may
be about 950 to 1050° F. and the oil temperature
be controlled so that the suspended catalyst-oil
mixture may have a temperature of about 950
to 1000° F. This mixture may be introduced into
the reactor at a pressure of about 13 pounds per
square inch.
The `products are introduced at the base of a
combination fractionating tower and scrubber 54
which is preferably operated at about ñve pounds
gauge pressure with a bottom temperature of
about 590° F. and a top temperature of about
240° F. A line 55 may be provided for by-passing
the charge around the reactor if for any reason
the reactor is shut down. The vertical velocities
in the reactor may be controlled to a certain
The density of the catalyst in entering vapor
stream may only be about 1 pound per cubic foot 10 extent by varying the amount of steam which is
introduced into the charging stock vapors or by
but the catalyst tends to settle into a dense turbu
by-passing sonne of the charging stock vapors
lent suspended catalyst phase in the reactor the
directly to the fractionating tower or by varying
density of which phase may be about 15 to 18
the quantity of charge. If the pressure at the
pounds per cubic foot. Due to the turbulence,
base of standpipe 42 falls below safe limits the
i. e., the “internal recycling” occurring in this
charging stock is automatically diverted through
dense catalyst phase a substantially uniform
temperature prevails throughout the reactor
line 55 bymeans of a pressure controlled valve
so that there canV be no possibility of charging
which temperature may be about 900 to 950° F.
stock vapors flowing upwardly in the standpipe
The reactor may be a cylindrical vessel about 12
or 13 feet inside diameter and about 25 feet high zo and entering the space above the regenerator.
In the base of tower 54 residual catalyst parti
with cone tops and bottoms as illustrated in the
drawing. The average vertical vapor velocity in
cles are scrubbed out of the reaction products so
the reactor may be about 1 to 3 feet per second,
that they may be returned by line 38 to pipe still
preferably about 11/2 to 2 feet and the average
coils as hereinabove described. For each volume
vapor contact time may range from about 5 to 25 of bottoms which are so withdrawn we prefer to
40 seconds or more, usually about 10 to 16 sec
recycle about 25 or 30 volumes through heat ex
changer I3 and one or more coolers 56 back to
onds.
the scrubbing section of the tower in order to
maintain a tower temperature at the top of the
15 or 16 feet inside diameter by about 35 to 50 30 scrubbing section of about 580° F. One of the
feet high. The settling chamber is provided with
coolers 56 or other heat exchangers in the frac
a cone-shaped bottom which co-acts with the top
tionation system may be employed for preheating
sides and discharge pipe 46 of the reactor to form
the water which is charged to steam generator 29.
an upper hopper for settled and separated cata
An emergency draw-off line 51 is provided but is
` superimposed above the reactor we provide an
enlarged settling chamber 45 which may be about
lyst. Pipe 46 may be about 5 or 6 feet in diam
eter and above this pipe we may provide a baffle
41 for distributing reaction gases and vapors to
generally not used.
A heavy gas oil fraction may be withdrawn
from the tower through line 53 and passed
through heat exchanger I2 and cooler 59. Aboutl
gether with suspended catalyst throughout the
cross-sectional area of the catalyst separator,
2,400 to 2,500 barrels per day of this 25.6° A. P. I.
thus preventing any chimneying eiïect. The 40 gas oil may be withdrawn from the system
density of catalyst in pipe 46 may be only about
through line 60 and another part reintroduced
.6 pound per cubic foot. The vertical upward ve
locity of gases and vapors in separator 45 may
be about ll/z to 2 feet per second. About 1000 to
2000 pounds per hour of process steam is intro
duced through line 48 and distributor 49 for
to the tower through line 6I for maintaining the
desired temperature gradient. This stream pro
vides the gland oil for various pumps in the sys
tem, such oil being introduced to pump glands
through line Gla and returned through line ßlb.
maintaining settled catalyst in aerated condition
Line G2 is provided for venting any excess gas
and for stripping products therefrom. The low
from surge drum I5 or furnace charge drum 26
velocity of these aeration or stripping gases, how
to an intermediate point in the fractionating
ever, permits the catalyst to settle in the upper
tower. Line 62 is connected by line 62a to surge
hopper space and to assume a density of about
drum I5 and by line B2b to furnace charge drum
25 pounds per cubic foot.
26.
In order to remove as much catalyst as pos
Light gas oil is removed from tower 54 through
sible from reaction gases before they leave this
draw-offs 63 and stripped in side stream stripper
separation zone we prefer to employ a series of 55 64, the overhead being returned through line 65
cyclone separators 50, 5I and 52 in chamber 45
to tower 54. The heat for effecting this side
each of the separators being provided with dip
stream stripping may be obtained from hot gas
legs 50d, 5Ia, and 52a extending well below the
oil which is introduced from line 2'1 through line
level of the settled catalyst in the upper hopper.
55 to heat exchanger 5'! and is returned through
With a pressure in the upper hopper of about 9 60 line 68 to line 28. Indirect stripping is desired
pounds per square inch we may have a pressure
in View of the large amount of steam already
in primary cyclone 50 of about 81/2 pounds, in
present in tower 54. About 2,400 to 2,500 barrels
secondary cyclone 5| of about 8 pounds, and in
per day of 35° A. P. I. gravity light gas oil may
tertiary cyclone 52 of about 'l1/2 pounds. The dif
be withdrawn through line 69.
ference between the pressure in chamber 45 and 65
About 45,000 barrels per day of liquid may be
in these cyclones is balanced by the head of set
withdrawn through line 10, passed through heat
tled catalyst in the respective dip legs.
exchanger I I and cooler 'II and returned through
By employing four cyclones in each stage we
line 'I2 at a temperature of about 150° F. for
may remove about 45,000 pounds per hour of cat
refluxing the top of the tower so that the over
alyst from the iirst stage, about 4,000 pounds per
head from this tower is at a temperature of about
hour from the second and about 1,000 pounds per '
240° F. Due to the large amount of steam present
hour from the third so that the ñnal gases leav
at this point, substantially all of the 400° F. end
ing the separation zone through line 53 will con
point naphtha will thus be taken overhead.
tain only about 800 to 1,200 pounds of unrecov
The overhead from tower 54 is passed by line
ered catalvst per hour.
'I3 through cooler 'I4 to. primary low-pressure
2.4103284.
separator 15 which operates at about 100° F. and .
about .atmospheric` orY lpound gauge pressure.
Condensed water is removed from this separator
throughline '16. The gases from this separator
are» compressed by compressor 'i1 and the liquids
10
C3v or a mixture of C3 and C4 hydrocarbons, is
Withdrawn through line |05 to a polymerization
plant or other system in order that it may be con
verted into high quality motor' fuel or otherwise
e utilized.- The bottoms from tower 90 is With
drawn» through heat exchanger |06v and cooler
pressurev separator 80. The high-pressure sepa
rator is at a temperature.l of about 100° F. but-at
a pressure of about l35vto 150 pounds per square
inch. Condensed water may -be removed from
this stage through line'liôa. It should be under
stood that while We. have only illustrated two
stages of separation we may use three or more
stages, i. e., we may employ an intermediate stage
|01. This fraction may amount to about 1600 to
1700 barrels per day of 98.5° A. P. I. absorption
naphtha.
Gases from the high pressure separator may
be withdrawn through line 8|a to a separate ab
sorber system or introduced through line 8| into 20
the base of absorber 82. Liquids from the high
,
y
‘
,
'
'
Barrels per day
Heavy-gas oil
2,445 _
Light gas oil
2,445
with thev separator at about 25v pounds pressure 15 Heavy naphtba
and wevmay withdraw additional water from this
Light naphtba
intermediate separator.
`
To recapitulate; .the following products may be
produced from the 10,000 barrels per- dayl charge:
3,340
„
C3 andiCii hydrocarbons _______________ __
1,650
570
Total yield by volumev (i. e..
104.5% on stool; charged)_ ____ __ 10,450
The gases separated from receivers. 95.- and |03
may be returned by 1ines95aand1|03a to thefbase
83av to' a separate fractionation system or maybe
of absorber tower 82. In addition» tot-he large
pumped through line 33` and heat exchangers 84
and' 84a to an intermediate point in still 85. rl‘he 25 volumetricvyield of liquidv and liqueñed products
pressure separator may be pumped through line
heat for this still may be supplied by gas oil from
line 2'! and line 85, which leads to heaters 84a and
We obtain about 1,400 to 11,500 pounds per hour
of dry gas from fuel gas line 92 and we obtain a
considerable» amount of heat fromy the carbon
81, the cooled gas oil being returned through line'
which is depositedv on the catalyst. This` heat
88 to line 25. The_bottoms from the still pass
through exchanger 84 andI coolerv 39. A part of` 30 recovery from carbonaceous deposits on catalysts
will noW be described in further detail.
this stream amounting to about 3,300 to 3,400
Spent catalyst is. discharged from the upper
barrels per day may be withdrawn through line
hopper in chamber 45 to one‘or more standpipes
Sil-as a 50.3° A. P. I.. heayy >naphtha. Another
|08 of a suitable height tomaintain the desired
part of this stream is returned byline 9| through
cooler 9|@ to the top of tower S2 for absorbing 35 pressure which in this case may be about 75 to 80
feet.> The pressure above the slide valve at the
light hydrocarbons from gases which are with
bottom ofV this standpipe may be about 22 to 23
drawn from the system through line 92 for use
pounds per square inch and the temperature of
as fuel or for any other purpose. Rich oilfrorn
the catalyst may be about> 900° F. Compressed air
the base of the absorber is pumped` through line
93 to the still along with liquid from the. high 40 from line |09 is introduced under` pressure of
about 17 or 18 pounds per square inch .and in
pressure separator 00.
. >
amounts of about 16,000 to 18,000 pounds. per
The top of the absorber 32jis connected by
hour for picking upl catalyst fromÍthe base of
lines 92a and 92h to the top of surge drum I5
the standpipe- and carrying it through line | l0v to
` and by lines 92a and 92e to the top of charge
drum 2E. A substantially'constant pressurev is 45 the base of regenerator chamber |||. This re
generator is. preferably about 1_8 feet inside dia-m
maintained in these drumsgi. e., a pressure of
eter by about 50 feetvhigh.
„
about 25 pounds per square inch in drum |.5 and
As inthe caseV of reactorY 44 there isl an en
about 75 pounds per square inch in drum 26 by
larged settling chamber ||2 above the regener
gases from absorber 82, valve 92dbeing controlled
in accordance Withthe desired maximum pressure 50 ator, thisv settling chambery or separator- being
about 22 feet inside diameter and about 25~to 40
in drum |5»and valve- 92e being controlled in ac
feet high. The»> inclined upper Wallsof the re
cordance with the desired maximum pressure in
generator terminate in pipev |~| 3 and the spacefbe
drum 25. Valves |520v and 62dy are set to relieve
tween pipe ||3 and the walls ofV chamber |r|2
at'slightly higher pressures than that’maintained
by-92c and 92h, and since absorber` 82 normally 55 form an- upper hopper. for regenerated catalyst.
The catalyst Which «settles in this 11101161' hOPDeI‘
operates under a pressure ol’r about 135 pounds per
isv aerated by steam introduced through «lineI | I4
square inch we may maintain any ldesired lower
into distributor ||5.
pressure in the gas oil drums bythe use of thesev
It is essential that the temperature in the re
gas lines and Vpressure controlled valves.
The overhead from still 35 is passed through 60 generator be maintained within safe> limits (from
the standpoint of catalyst activity), for example
condenser 94 to .receiver 95.A A part` ofthe con
950 to 1050° F. or about 1000° F. AV considerable
densate is recycled through line 96 for useas re_-~
amount of the-heat generated by thevcombustion»
flux in the top of still 851 and another partis
of carbonaceous deposits must be absorbed in
passed by'line'91f through exchanger |06.; to an
intermediate point of` rectifier or stabilizer 98. 65 and removed fromthe regenerator if »the tem'-`
perature is tobe» held within desired limits. In
The heat for the base of thisv stabilizer may be
order to control'wthe »temperature in' thev regen>-v
obtained by passing gas oil from line 21 andline
eator we recycle about-three> times ¿as much cata->
99 through heat exchanger |00`and returning the
lyst as is introduced through ‘line‘ llß‘vand; wev
cooled gas oil through line` |0| back .to line> 28.
Overhead'from tower' 98 is lcooled in coolerl |02 70 cool this recycled~ catalyst before itis returned
to the regenerator. ' More speciñcally we w-ith-v
and introduced into receiver |03. A part ofv this
draw catalyst'from the upper hopper. inl chamber
condensate from‘thisv receiverzis recycled through
| I2 to one or more standpipes |"||ì‘, which may beA
line |041fo`r refluxvin tower 98.1 Thebalance of
about 95 feet >in height andßabout'Zï‘ or` 3 feet'inv
thisy condensate; lwhich mayJ amountl to about :577V
barrels per day, and which consists> essentially- of 75 diameter. The pressure> of the catalyst above
2,410,284
11
12
' tive cyclone separators. The pressure in cham
ber |I2 may be about 8 pounds per square inch,
the lower valve may be about 24 or 25 pounds per
square inch. The catalyst in this standpipe as
well as in standpipes 42 and |08 are provided
there may be a half pound pressure drop through
each cyclone separator and about 5 or 6 pounds
with means for introducing aeration steam so
that the catalyst is »maintained in fluent con CII pressure drop between the top of the separator
zone and the discharge end of heat exchanger
dition throughout the entire length of the stand
23 so that the gases leave this heat exchanger
pipe.
through line |28 at a pressure of about 1 or 2
Compressed air from line II'I is introduced at
pounds per square inch gauge.
a pressure of about 19 or 20 pounds per square
Instead of single heat exchanger or flue gas
cooler 23 we may employ a plurality of such heat
exchangers in parallel or in series. The gases
inch and in amounts of about 71,000 pounds per
hour. The compressed air picks up the catalyst
from the base of standpipe I|6 and conveys it
via line II8, through heat exchanger I9 wherein
may pass downwardly through the exchanger in
a considerable amount of the heat contained in
stead of upwardly, as shown. The ilue gases are
this recycled catalyst is picked up by gas oil in
cooled from about 1000° F. to about 675° F. in
these exchangers and the gas oil is heated from
about 450 to about 600° F. as hereinabove de
scribed. Other heat exchange ñuid than gas oil
may, of course, be used and the cooling may be
troduced through line I8 and withdrawn through
line 20. Heat may be absorbed from the recycled
catalyst, by other fluids than gas oil, and if de
sired steam may be generated‘directly >in this
exchanger. The temperature of the suspended
recycled catalyst at the base of exchanger I3
may be about 950 to 960°? F. and the temperature
of the suspended catalyst at the top ofl this heat
to different temperatures than those given in this
example.
The gases from line |23 are introduced at the
base of Cottrell precipitator |29 at a pressure of
about 1/2 pound per square inch gauge. They are
withdrawn therefrom through line |2911 to a suit
able stack at about atmospheric pressure.
The upper hopper in chamber II2 only holds
enough catalyst for about a 5 to 20 minute oper
ation of the reactor and in order to insure a sub
exchanger may be about 940° F. or lower.
When this recycled catalyst is admixed with
spent catalyst in the base of regenerator III
the average inlet temperature to the regenerator
may be about 850° F. but throughout the body
of the regenerator a substantially constant tem
perature of about 1000C F. will prevail. With the 30 stantially constant catalyst level in this upper
hopper we provide a large used catalyst hopper
amounts of air, regenerator size, and tempera
|30 which may be about 20 feet in diameter and
tures as above set forth, the vertical velocity of
about 45 or 50 feet high. If the level in the up
up-ilowing gases in the regenerator should' be
per hopper rises above desired limits regenerated
about l to 3, or more precisely, about 1% to 2
catalyst is Withdrawn through standpipe H6 and
feet per second. The pressure at the base of the
line |3| to the used catalyst hopper |30. If the
regenerator may be about 16 pounds per square
catalyst level in the upper hopper gets too low,
inch and the gases may enter the base of the re
used catalyst from this hopper is introduced into
generator at the rate of about/£00 cubic feet per
the upper hopper through line |32 by means of
second. The pressure at the top of the regen
erator maybe about 9 pounds per square inch and 40 process steam introduced through line I 33. Thus
a substantially constant level of catalyst in the
the gases may leave the top of the regenerator at
upper hopper is always maintained.
the rate of about 650 cubic feet per second. The
Fresh catalyst is introduced into the system
average density of the catalyst in the regenera
from hopper |34. Instead of introducing this
tor maybe about 18 to 20 pounds per cubic foot.
Baille» II-9y distributes the regeneration gases i fresh catalyst directly with regenerated catalyst
and suspended catalyst uniformly throughout the
we prefer to first admix it With catalyst fines dis
charged from the Cottrell precipitator. Fresh ~
enlarged separating zone in chamber | I2 and the
catalyst is picked up by air from line |35 and in
bulk of the catalyst settles out of the gases in this
troduced by line I 36 to an upper hopper |31 the
To obtain more complete catalyst removal we 50 air being separated from the catalyst in this up
per hopper and introduced through lines |38 and
prefer to mount a plurality of cyclone separators
|39 into the base of the Cottrell precipitator.
in the upper part of the separator. Primary cy
The fines from the base of the Cottrell precipi
clones- |20 may pick up gases through inlet pipe
tator are discharged into hopper |40 (which may
|2I in which gases the catalyst content may be
about 375 to 400 grains per cubic foot. The gases f be in the lower part of theprecipitator itself)
and are there admixed with fresh catalyst in
discharged from these primary cyclones to sec
troduced from hopper |31 through line I4'I. The
ondary cyclones |22 through line |23 may con
fresh catalyst thus introduced is to replace cat
tain only about 75 grains of catalyst per cubic
alyst losses from the system and it may amount
foot. The gases which leave the secondary cy
to only about 160 to 170 p'ounds per hour. This
clones through line |24 and enter tertiary cy
amount of catalyst does not supply the desired
clones |25 may have a catalyst content of only
amount of coarse material for the fines and we,
about 36 grains per cubic foot. The gas dis
therefore, introduce about ñfty times as much
charged from the tertiary cyclones through lines
regenerated catalyst from line |42 as-is ,intro
|26 and. |21 may have only about 20 grains of cat
duced through line IlII, This mixture of fresh
alyst per cubic foot or less. It should be under
and regenerated catalyst with the Cottrell fines
stood that any-number of cyclones may be em
zone.
v
Y
ployed` in the primary, secondary and tertiary
not only serves to add sufficient coarse material
stages and that any number of stages may be used
to obtain a desired catalyst consistency but it
likewise raises the temperature of the fresh cat
alyst and Cottrell fines so that the resulting mix
without departing from the invention.
.
Each cyclone has its dip leg |20a, |22a and
|25a which extends lwell below the level ofthe
ture will be about 820° F.'
'
'
settled catalyst in the upper hopper and the dif
If the Cottrell precipitator were mounted at
ferent heads of catalyst in these dip legs com
a sufficiently high elevation the pressure at the
pensate for the Vdifference between the pressure
base of standpipe |43 might be sufficiently great
in chamber ||2 and the pressures in the respec 75 to permit direct introduction of the catalyst'fmes
1.4
dium inexchangers» |49` andf23 „the gas oil charge
mixture back to' upper hopper in chamber H2.
With the lower mounting the pressure at the
baseïiQff standpipe M3- may be only about 6 or ’7
pounds per` square inch; We, therefore,> pick
up: this catalyst mixture at the base of stand
pipe> |;4;3 with process steam introduced through
line- I'Mfand--convey it through line |45 to any up
per hoppen |46, the separated steam being dis
charged through line |41 into line |28Í and Cot
trellprecipitator |29.,` Standpipe |48» depending
from-hopper |46 may beV of suiiicient length, i. e.,
about 50 to 60 feet, to give a pressure at itsbase
may beintroduceddirectly` from line I4 through
line |4a to line 25 and thence. to thel furnace
charge drum.
5
»
Also we have already indicated that' a down
war‘dregeneration gas flow may beemployed in
exchanger 23-,and that hopper lßllimay be elimi
nated. vThus they regeneration gases from line
may Lbe introduced thro-ugh line |21a into
10 thetopvof exchanger 2'3r and the cooled- gases
from this exchanger may be conductedY directly
by line |28a to the base of Cottrell precipitator
of about 12er 13,pounds_ per square inch. Cata
lystjy may be pickedà upy from the basel of this
|29. By employing a sufñciently tall standpipe
s_tandpipe byrstearnl introduced through line |49
15 pump> for forcing powdered solids into a zone of
I431or by using a Fuller-Kenyon pump (a screw
higherî pressure) at the base of this standpipe,
we may return the Cottrell lignes mixture through
line |45a and` |50- back to chamber H2 Without
vvInstead of admixing- the Cottrell fines with
the necessity of employing hopper |46. Other
coarser catalyst andrreturning it to the system
we may withdraw the catalyst rines and rework 20 modiñcations and alternative procedures. will be
apparent from the above description to those
them into additional catalyst material?of larger
andconveyed thereby through line |50 into sep
aration chamber H2.
y
particle size.l The‘catalystíines may be incor
porated into additional silica gel or mixed gels
orQ` it 'may be pelleted or> agglomerated in any
skilledin the art.
may vary through a considerable range andwhile
inIthi's'eXample weA employ catalyst of aboutì 300
of the >system for obtaining product separation, it
is utilized for supplying heat to the charging
~
From the above description it will be seen that
wehave accomplished the objects of. our inven
known manner and thereafter crushed, if neces 25 tion andl have provided a unique and remark
ably effective commercial system. The heat of
sary, to obtain the desired particle size. The
regeneration is utilized in the fractionation part
particle size of catalyst charged»y to the system
to> 400 imesh, or finer, it should be understood 30 stock, and it is utilized for the generation of
processïsteam which is employed throughout> the
tha-t, we may. entirely remove the finest catalyst
system as a> catalyst conveying andaerating me
powder and'operate with aÀ particle size of 'about
dium. The catalyst storage andhandlingrmeans
100 todo() mesh or> even of about 50 to 200 mesh.
provides a remarkably effective fiexibility of> con.
Thevapor. velocities in the reactor willyof course,
be higher when coarser catalyst` is employed but 35 trol. Catalyst losses are reduced to a minimum.
shouldl in. al1 cases be adjusted to give the de
siredde'nse phase conditions.
ì
The catalyst inthe used catalyst hopper and
the’fresh catalyst hopper must be maintained in
aerated condition.y Process steam from. line |5|
is employed for.` the aeration gas inthe used cat
alyst hopper. but> air from line |52 may be used
foraerating the> fresh catalyst hopper. Aera
tionfg'ases from the top of these hoppers may be
withdrawn through lines |53, |54, |55 and |39
tothe baseof Cottrell precipitator |29. The cat
alyst. in all ofthe standpipesis preferably vaerated
>with._processvsteam and as hereinabove described
all, of this. raerating "gas on the fresh and regen
erated -catalyst eventually passes through Cot
trellprecipitator. |29 before it is discharged from
the system.v
s
-
Again it should be pointed out that our inven
tionisnot limited to the» operating detailshere
inabove,4 described. It has already been sug
We claim:
1~. in. apparatus. of the class described, a gas
oilsurge drum, a steam generator, a pipestill, a
catalyst regeneration system including a heat ex
40 changer, a catalyst conversion system, a product
fractionation system including a heat exchanger,
meansfor-passing gas oil from said surge drum
throughthe heat exchanger included in said re
generation >system whereby the gas oílisheated
r by the heat produced in the regeneration system,
means for passing a part of saidheated gas oil
through saidy pipe still, thence through said con
Vversionsystem- and thence to said fractionation
system, means for passing parts of said heated
gas. oilïthrough the heat exchanger inv said frac
tionation system and through said steam gener
ator and thence back to said gas oil surge drum,
means for introducing spent catalyst from the
conversion'system to the regeneration system and
55 means for introducing regenerated catalyst from
gested that instead of using gas oil for absorbing
,heat` in exchangers»v I9 and 23 we may utilize
theregeneration system to the conversion sys
other heat exchange duid. Infact, the surge
2, The. apparatus .-deñned by claim 1 which in
cludesvmeans for superheating the steam gener
drum l5V and the recycle‘lines associated there
with-.f may be entirely eliminated and We may
simply close> the valve in line | 'I and introduce
water through line Ila, preferably water which
has been previously treated or preheated. This
Water may be converted into steam at a pressure
tem.
-
,
60 ated in said steam generator and means for in
troducing said superheated steam to both spent
and regenerated catalyst for effecting aeration
thereof.
3. A duid-type catalytic cracking system which
of about 135 to 150 pounds per square inch in 65 comprises a gas oil surge drum, a regeneration
exchangers I9 and 23 and the steam so generated
system containing a heat exchanger, a fractiona
may be introduced through line 2|a to line 36
tion system containing a heat exchanger, a steam
(the subsequent Valve in line 2| being closed).
generation system~ means for passing gas oil from
A part of this steam may be introduced in coils
said surge drum to the heat exchanger in the
34h to facilitate vaporization of charging stock. 70 regeneration System, means for passing hot gas
Another part may be introduced through line 35a
oil from the regeneration system heat exchanger
to steam superheating coils 31. Other parts may
to the fractionation system heat exchanger,
be withdrawn from the system through lines 36h
means for passing gas oil from said regeneration
and 36e as hereinabove described. When Water
system heat exchanger to said steam generator,
is used instead of gas oil as a heat exchange me- 7 5 and means for passing gas oil from said fraction- '
2,410,284
15
16A
ation system heat exchanger and steam generator
40 seconds, settling catalyst solids from upñowhv
respectively back to said gas oil surge drum.
ing vapors in a settling space above said dense
4. A catalytic cracking system which _comprises
catalyst phase, centrifugally separating residual
a gas oil furnace charge drum, a pipe still furnace
containing gas oil heater coils and steam super
heater coils, a reactor, a spent catalyst separator
above the reactor, a regenerator, a regenerated
catalyst separator above the regenerator, a re
discharged from the conversion Zone, passing va
pors from which catalyst has been centrifugally
separated into a scrubbing zone, recycling liquid
generated catalyst cooler below'the regenerator,
a regeneration gas heat exchanger, a product
fractionation system including a plurality of heat
exchangers, means for ` introducing a gas oil
charging stock through some of said lasty named
heat exchangers to said gas oil furnace charge
drum and thence through said oil heater coils to
said reactor, means for passing catalyst from the
regenerated catalyst separator to said reactor
along with the heated gas oil vapors from the
pipe still coils, means for separating catalyst from
reaction vapors in said spent catalyst separator,
:means for passing reaction products from said
,spent catalyst separator to said fractionation
system, means for passing spent catalyst from
:said spent catalyst separator to said regenerator,
means for recycling catalyst from said regenera
tor separator through said catalyst cooler and
back to said regenerator, means for utilizing the
heat abstracted from the catalyst in the catalyst
cooler and from the gasesin the regeneration gas
exchanger for the generation of steam, means for
passing a part of the generated steam through
:said steam superheating coils and means for in
troducing said superheated steam at a plurality
«of points in the system for maintaining catalyst
in aerated form.
.
5. rI'he method of effecting catalytic cracking
which comprises maintaining a column of silica
:alumina cracking catalyst in aerated condition at
fa" temperature of about 1G00Q F., said catalyst
having a partielle size below about 100 microns,
suspending catalyst from the base of said column
in a stream of hydrocarbon charging stock which
is higher boiling than gasoline, employing a cata
lyst-to-oil weight ratio in the general vicinity of
5:1, introducing the catalyst suspended in the
catalyst material from vapors before they are
from the base of said scrubbing zone through a
cooling zone and back to the scrubbing Zone at
a point above the point at which vapors are in
troduced thereto whereby residual catalyst mate
rial is scrubbed out of vapors in said scrubbing
zone, returning catalyst scrubbed from said va
pors to said conversion zone with charging -stock
introduced thereto, condensing and removing
heavier-than-gasoline components in an initial
fractionation Zone immediately above and com
municating with said scrubbing zone, removing
substantially all gasoline boiling range hydrocar
bons overhead from said fractionation zone
through a cooling zone to a separating zone prior
to subsequent fractionation whereby the scrub
bing and initial fractionation are effected at a
pressure below conversion pressure and said pres
sure is supplied by the pressure on stock charged
to the conversion zone.
6. A catalytic cracking system which com
prises a pipe still furnace containing gas oil heat
er coils and steam superheater coils, a reactor,
spent catalyst separation means, a spent catalyst
standpipe, a regenerator, a regenerated catalyst
separation means, a'regenerated catalyst stand
pipe, a regenerated catalyst cooler below the re
generator, a regeneration gas heat exchanger, a
product fractionation system including a plural
ity of heat exchangers, means for introducing a
gas oil charging stock through at least some of
said last-named heat exchangers and thence
through said voil heater coils to said reactor,
means for passing separated regenerated catalyst
from the regenerated catalyst standpipe to said
reactor along with the heated gas oil vapors from
the pipe still coils, means for passing separated
spent catalyst from the spent catalyst standpipe
along with air to said regenerator, means for
passing reaction products from the spent catalyst
charging stock stream at a low point in a con
separation means to said fractionation system,
version Zone, maintaining a pressure in the con
means for recycling separated regenerated cata
version zone within the approximate range of at
lyst through said catalyst cooler and back to said
mospheric to 50 pounds per square inch, main
taining a temperature in said conversion Zone in 50 regenerator, means for utilizing the heat ab
stracted from the catalyst in the catalyst cooler
the general vicinity of 800° to l000° F., passing
and from the gases in the regeneration gas ex
hydrocarbon vapors upwardly throughA said con
changer for the generation of steam, means for
version zone at a velocity in the general vicinity
passing a part of the generated steam through
of 1 to 3 feet per second whereby a dense turbu
said steam superheating coils and means for in
lent suspended catalyst phase is maintained the
troducing said superheated steam into at least
density of which is within the approximate range
one of said standpipes for maintaining the cata
of about 10 to 25 pounds per cubic foot, maintain
lyst in aerated form therein
'
ing a sufficient amount of said dense phase cata
ROBERT C. GUNNESS.
lyst material in said zone to obtain a vapor con
JOSEPH W. JEWELL.
tact time'within the approximate range of 5 to 60
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