Method and means for separating suspensions of gasiform material and fluidizable solid particle material

In a reactant-fluid catalyst suspension system, an arrangement of apparatus is provided contiguous with a riser discharge which centrifugally initially separates the suspension into a solids phase and a gasiform material phase prior to discharge from the riser. The catalyst may be further stripped if desired in equipment above and about the riser discharge. The arrangement contributes substantially to the efficiency and economics of the separation of catalyst from gasiform products including products of hydrocarbon conversion and combustion products of catalyst regeneration.

BACKGROUND OF THE INVENTION 
This invention is concerned with a special method and means for separating 
solids-gasiform material suspensions formed in fluidized solids contact 
systems. It is particularly concerned with an arrangement of apparatus and 
the method of using for effecting an efficient separation of fluid 
catalyst from hydrocarbon vapors or combustion product gases immediately 
adjacent to the discharge of a riser contact zone. 
In cyclone separators normally employed, a suspension comprising a gasiform 
material with entrained finely divided solid particle material is 
introduced horizontally into the separator in a tangential manner so as to 
impart a spiral or centrifugal and swirling moment to the suspension. This 
centrifugal moment causes the solids to be thrown to the outer wall of the 
cyclone separator for movement downward to a collecting zone or hopper 
therebelow. The gasiform material centrifugally separated from solids is 
removed by a central zone ended passageway extending from a plane beneath 
the suspension tangential inlet upwardly through the top of the cyclone 
separator. A reduced pressure exists on this gasiform material withdrawal 
passageway. A particularly useful application of the centrifugal separator 
is in connection with reactions employing fluidizable catalyst particles 
such as the catalytic treatment of petroleum fractions by cracking, the 
regeneration of catalyst in upflowing riser type systems, the synthesis of 
hydrocarbons from CO and H.sub.2, the conversion of methanol and related 
low boiling alcohols to liquid hydrocarbons and other well-known prior art 
fluid catalyst operations. 
In modern-day refinery operations employing fluid catalyst cracking 
operations, enormous amounts of catalyst suspended in a reactant material 
are handled in a riser conversion zone and an upflowing catalyst 
regeneration zone. It is necessary to rapidly separate the suspensions 
into a catalyst phase and a gasiform product phase following a desired 
contact time within the riser contact zone to obtain desired gasiform 
product material. The present invention is concerned with an arrangement 
of apparatus particularly suitable for effecting this separation of the 
suspension in an efficient manner but also in an arrangement of equipment 
of smaller dimensions contributing significantly to the economics of the 
system. 
SUMMARY OF THE INVENTION 
The present invention is concerned with an arrangement of apparatus and 
method of operation for separating a suspension of gasiform material and 
finely divided solid particle material. More particularly, the present 
invention is concerned with the method and means for separating a 
suspension of regenerated catalyst from combustion product gases or a 
hydrocarbon conversion product of catalytic cracking from catalyst 
particles very rapidly after a selected hydrocarbon residence time in a 
riser reaction zone so that over-cracking of the reaction product can be 
minimized and the catalyst exposure to deactivating product material 
substantially reduced. 
The present invention is concerned with reducing the equipment inventory 
and size thereof for effecting the separation of a suspension of finely 
divided solid fluidizable particle material from gasiform material. In yet 
another aspect, the present invention is concerned with minimizing 
catalyst particle hold-up in an arrangement of reaction apparatus so that 
the overall catalyst inventory of the system may be kept at a desired low 
level. 
The present invention is particularly concerned with obtaining a rapid 
separation of a suspension comprising fluidized catalyst particles and 
reaction product material following traverse of a riser reaction zone 
permitting relatively short contact time hydrocarbon conversion for a time 
period less than about 10 seconds and more usually less than about 5 
seconds. The present invention is particularly useful for separating 
reaction suspensions completed in a time span of about 2-3 seconds or 
less. It has been found that present day cyclonic separating equipment 
arrangements are less adequate than desired since they have been found to 
contribute to overcracking due to catalyst hydrocarbon residence time 
therein and a loss in desired product amounting up to about 3 percent. 
Thus, a gasoline loss due to over-cracking in cyclone separators can be up 
to about 1.5 volume percent based on fresh feed. 
The method and means of this invention are particularly suitable for use 
with high activity crystalline zeolite conversion catalyst wherein it is 
desired to particularly restrict the catalyst-hydrocarbon contact time, 
the catalyst inventory, minimize the formation of coke and maximize the 
yield of desired product. Thus, it is contemplated effecting the 
conversion of gas oil to gasoline boiling product with a highly active 
crystalline zeolite conversion catalyst employing a reaction temperature 
within the range of about 950.degree. F. to about 1050.degree. F. and a 
hydrocarbon residence time in contact with suspended catalyst particles 
restricted to within the range of 0.5 to about 3 seconds. In such an 
operation, it is preferred that the catalyst hydrocarbon suspension pass 
through the riser essentially in plug flow arrangement so that the 
catalyst residence time in the riser reaction is not substantially longer 
than the hydrocarbon residence time. However, it is contemplated operating 
with a catalyst slip factor as high as about 0.5, where slip factor is 
defined as the ratio of hydrocarbon residence time to catalyst residence 
time. 
In the arrangement of apparatus of this invention, stator means comprising 
fixedly positioned curved blades positioned below the riser discharge 
induce a centrifugal motion to the rising suspension sufficient to cast 
solid particles to the riser wall before discharge therefrom. The solids 
thus rejected from reactant product gasiform material are substantially 
immediately subjected to centrifugal co-current contact with stripping 
steam in a chamber of restricted dimensions about the riser discharge 
which collects the stripped catalyst at its walls for flow downwardly to 
withdrawal means in a manner similar to that of the normal cyclone 
separator. Separated reactant product and steam pass through an open 
passageway of smaller diameter than said riser diameter and coaxially 
aligned therewith, extending through the upper surface of the chamber of 
restricted dimensions. The apparatus above briefly described is housed 
within a second vessel of restricted diameter and comprising cyclone 
separators in an upper portion thereof with means for stripping catalyst 
therebelow.

Referring now to FIG. I by way of example, the upper discharge end of a 
riser reactor 2 is shown. The open discharge end of the riser is housed 
coaxially within a larger diameter vessel 4 and provides an annular space 
"A" between the cylindrical wall of vessel 4 and the wall of riser conduit 
2. Vessel 4 is provided with a sloping bottom 6 to which a catalyst 
withdrawal conduit 8 is provided adjacent thereto. The top of vessel 4 is 
closed by member 10 and provided with a gasiform material withdrawal 
conduit 12 coaxially positioned within vessel 4 and with riser 2. Conduit 
12 of diameter "C" is smaller in diameter than riser 2 of diameter "B" by 
an annular distance H. In addition, the top open end of riser 2 is spaced 
apart from the bottom open end of conduit 12 by distance "D". A stripping 
gas is introduced tangentially into vessel 4 adjacent the top surface 10 
thereof by conduit 14 of diameter "G". The bottom open end of conduit 12 
is spaced from the top surface 10 of vessel 4 by a distance "F". 
Positioned within an upper portion of riser conduit 2 and below the open 
upper end thereof by a distance E is positioned an arrangement of fixed 
curved stator blades 16 about a closed conduit 18 comprising a conical top 
portion with hemispherical shaped bottom 20. In the arrangement of the 
figure, there are two or more, such as four, curved stator blades 16 in a 
specific arrangement which are fixedly positioned between conduit 18 and 
the wall of riser 2 and function in the manner herein discussed. The 
number employed will be a function of the suspension throughput and 
diameter of the riser. 
The design relationship of the separator means above briefly described 
contemplates in a specific embodiment of using an annular cross-section of 
dimension A which is twice that of the cross-section area of the riser 
conduit and comprising dimension B. Diameter B is larger than diameter C 
of the gas outlet conduit 12 by a factor of 1.5 and it may be within the 
range of (1.2 to 1.7). Diameter B is preferably 1.8 times the height D but 
it may be within the range of about (1.5 to 2.0). Height E is preferably 
1.4 times the diameter B but it may be within the range of about (1 to 2). 
Height F is preferably 4 times the diameter "G" of pipe 14. In operation, 
it is preferred to employ a stripping steam flow rate equivalent to 2 
pounds of steam per thousand pounds of catalyst to achieve rapid 
separation of hydrocarbon product from physically separated catalyst 
particles. However, the steam flow rate may vary within the range of 1 to 
3 pounds of steam per thousand pounds of catalyst. 
In operation, a suspension of hydrocarbon vapors and catalyst particles 
passed upwardly through riser conduit 2 is caused to rotate by fixed 
curved stator blades 16, thereby throwing the catalyst by centrifugal 
action to the wall of the riser above the blades so that the catalyst will 
pass into vessel 4 through annular space "H". Stripping steam introduced 
co-currently by conduit 14 further promotes the centrifugal separation of 
hydrocarbon vapors from catalyst particles by displacement and the 
stripping action of the tangentially introduced steam. The stripped and 
separated hydrocarbon vapors with stripping steam (S.S.) enter the bottom 
of open ended withdrawal conduit 12 for passage through additional 
centrifugal separators before passage to fractionation equipment not 
shown. The catalyst thus separated flows down the walls of vessel 4 for 
withdrawal therefrom by conduit 8 and passage to a second stripping 
operation as particularly discussed with respect to FIG. II. 
Referring now to FIG. II, there is shown a riser reactor with the separator 
arrangement of FIG. I comprising a catalyst collecting vessel in open 
communication with a stripping vessel, and conduit means to complete the 
catalyst circulation between a catalyst regenerator not shown and the 
riser hydrocarbon conversion means. 
The riser reactor 2 with separator arrangement attached as shown and 
discussed with respect to FIG. I is housed in a larger vessel 22 of 
restricted diameter and provided with cyclone separator means 24 in the 
upper portion of the vessel and above chamber means 4. It is contemplated 
employing a plurality of cyclone separator 24 in the upper portion of 
vessel 22 and comprising a plurality of pairs of at least 2 in sequential 
arrangement. Hydrocarbon conversion products and stripping gas are 
recovered from cyclones 24 by conduit 26 communicating with a common 
header pipe not shown and in open communication with a downstream 
fractionation zone not shown. Conduit means 28 are provided in the bottom 
portion of vessel 22 for introducing fluidizing or stripping gas to the 
bottom portion of collected catalyst particles discharged from conduit 8 
and from cyclone diplegs 30. The bottom portion of vessel 22 may be 
arranged as a restricted annular catalyst stripping zone with a downwardly 
sloping bottom communicating with a catalyst withdrawal standpipe, thus 
excluding stripping zone 32 shown in the drawing. A separate zone or 
chamber 32 may be provided, however, as shown in the figure. On the other 
hand, vessel 22 comprising a sloping bottom may pass catalyst directly to 
external stripper 32. Stripping chamber 32 is provided with a plurality of 
downwardly sloping baffles 34 which may be disc and donut arranged baffles 
over which the catalyst passes counter-current to upflowing stripping gas 
introduced by conduit 36 to a lower portion of the stripping chamber. 
Stripped catalyst is withdrawn by conduit 38 for passage to catalyst 
regeneration. 
The hydrocarbon conversion system comprising riser 2 and related downstream 
equipment is arranged to effect the catalytic upgrading of hydrocarbons 
charged thereto. For example, low quality naphthas may be catalytically 
improved in quality and octane rating by a selective conversion thereof in 
the presence of a suitable crystalline zeolite hydrocarbon conversion 
catalyst. In addition, high boiling hydrocarbons comprising atmospheric 
and vacuum gas oils, residual oils and cycle oil products of cracking may 
also be converted to desired product under particularly selected operating 
severity conditions. Thus, it is contemplated maximizing the conversion of 
gas oils to gasoline by employing selected high temperature cracking 
conditions restricting the hydrocarbon contact time with the catalyst 
within the range of 0.5 to 4 seconds and more usually not more than about 
2 or 3 seconds. The hydrocarbon reactant may be charged to the bottom of 
the riser reaction zone by conduit 40 communicating with a multiple feed 
nozzle inlet means 42 for admixture with hot regenerated catalyst at a 
temperature of at least 1300.degree. F. and more usually at least about 
1350.degree. F. in conduit 39. A high temperature catalyst oil suspension 
thus formed is caused to flow substantially in plug flow arrangement 
through the riser under sufficiently high velocity conditions contributing 
particularly to the yield of desired gasoline or light fuel oil product. 
The high temperature conversion of the gas oil feed may be substantially, 
if not completely, reduced by the addition of a different boiling range 
hydrocarbon of reduced temperature to the suspension in one or more 
downstream portions of the riser as by conduits 44 and 46. On the other 
hand, a suspension forming vaporous material lighter than gas oil, such as 
low quality naphtha and/or lighter hydrocarbon material comprising C.sub.5 
and lighter hydrocarbons may initially contact the freshly regenerated 
catalyst before contacting a gas oil feed charged to a downstream portion 
of the riser by conduits 44 or 46 for conversion to gasoline or a light 
fuel oil product. In any of the hydrocarbon conversion operations above 
discussed, it is contemplated employing a riser reactor 2 of the same 
diameter throughout its vertical height or the riser may be of restricted 
diameter in a lower portion to particularly promote a plug flow high 
velocity hydrocarbon conversion operation of selected duration followed by 
conversion of a higher boiling feed, a cycle oil product of cracking, a 
residual oil or additional gas oil feed may be charged in an expanded 
larger diameter downstream portion of the riser reactor conduit. 
During conversion of hydrocarbons, the catalyst employed accumulates 
products of conversion including hydrocarbonaceous material and coke. 
Catalysts used to convert hydrocarbons and known in the prior art include 
amorphous and crystalline silica-alumina catalyst and mixtures thereof. 
For example, the catalyst may be a mixture of small and large pore 
crystalline zeolite. Generally, such crystalline zeolite catalysts are 
lower coke producers than the amorphous cracking catalysts and may be more 
effectively used at high temperature under very short catalyst/hydrocarbon 
contact times of less than about 8 seconds. The crystalline silica-alumina 
catalyst may be a faujasite crystalline zeolite such as "Y" faujasite, a 
mordenite type of zeolite or mixtures of the same. In addition, it is 
contemplated employing with either of these zeolites, a special class of 
crystalline zeolites represented by ZSM-5 crystalline zeolites and 
characterized by a pore opening of at least 5 Angstroms, a silica-alumina 
ratio of at least 12 and a constraint index within the range of 1 to 12. 
In modern refinery operations whether one uses a single or dual component 
cracking catalyst such as a mixture of faujasite with either amorphous 
silica/alumina, mordenite or ZSM-5 crystalline zeolite, it is desirable to 
include a CO oxidation promoter. Crystalline zeolite cracking catalysts 
are generally known as low coke producers and the presence of the CO 
oxidation promoter helps to increase the recovery of heat by the catalyst 
during combustion of coke and CO in a catalyst regeneration zone not 
shown. 
Some metal components suitable for promoting the combustion of carbon 
monoxide disclosed in the prior art include copper, nickel, chromium, 
manganese oxide or copper chromite. Some recently issued applications to 
this subject of CO combustion include Ser. No. 649,261, filed Jan. 15, 
1976 now U.S. Pat. No. 4,072,600, and 703,862, filed July 4, 1976 now U.S. 
Pat. No. 4,064,037. The subject matter of these applications is 
incorporated herein by reference thereto. U.S. patents of interest to the 
concepts of this invention and having a bearing on techniques for 
regenerating cracking catalysts are U.S. Pat. Nos. 4,035,284, issued July 
12, 1977; 3,893,812, issued July 8, 1977; and 3,926,778, issued Dec. 16, 
1975. 
The riser reactor, suspension separator and stripping arrangement of FIG. 
II may be used with substantially any catalyst regenerator arrangement 
known in the prior art. For example, the regenerator may comprise a dense 
fluid bed of catalyst superimposed by a more dispersed catalyst phase in 
which arrangement the burning of carbonaceous material is promoted in at 
least the dense fluid bed of catalyst and the burning of carbon monoxide 
is promoted in either one or both of the dense and dispersed catalyst 
phases. In such an arrangement, it is desirable to maximize the recovery 
of heat generated particularly when using low coke producing crystalline 
zeolites as the catalyst. Thus, the recovery of heat from the dispersed 
phase of catalyst may be promoted by introducing at least partially 
regenerated catalyst into the dispersed phase as a separate stream of 
catalyst and/or by increasing the flow rate of regeneration gas to the 
fluid bed so as to expand it, carry more catalyst into the dispersed 
catalyst phase, and remove a distinct demarkation between the dense 
catalyst phase and the dispersed catalyst phase. The bed of catalyst in 
such an arrangement may be caused to circulate by introducing spent 
catalyst tangentially to the dense fluid catalyst bed adjacent its upper 
interface or to a lower portion of the bed. It is contemplated effecting 
regeneration of the catalyst in a regenerator configurations, as 
represented by U.S. Pat. No. 4,035,284, which permit the recovery of 
regenerated catalyst from the dispersed catalyst phase, from upper and 
lower portions of the more dense phase of catalyst and for mixing 
regenerated catalyst particles with spent catalyst particles to form a 
mixture thereof at an elevated temperature of at least 1100.degree. F. and 
preferably at least 1175.degree. F. so that upon contact with oxygen 
containing regeneration gas, rapid ignition and burning of carbonaceous 
material will be accomplished. This mixing of spent and regenerated 
catalyst particles may be accomplished within the dense fluid bed of 
catalyst, in a riser mixing zone discharging into the dense fluid bed of 
catalyst or into the more dispersed catalyst phase above a dense fluid bed 
of catalyst being regenerated. 
When adapting the suspension separation arrangement of FIG. I to the upper 
end of a riser catalyst regeneration zone such as shown in the patents 
above-identified and particularly about the upper end of riser 8 of U.S. 
Pat. No. 3,926,778, it is contemplated providing cylindrical vessel 4 with 
a bottom open end to provide an annular catalyst discharge zone about the 
riser. In addition, vessel 4 may be extended downwardly about the riser 8 
portion of the regenerator so that the collected bed of regenerated 
catalyst will be relatively shallow above the catalyst withdrawal 
standpipes of the regeneration zone. Thus, it is clear that the suspension 
separation method and means herein discussed is applicable for separating 
a suspension of regenerated catalyst from combustion product gases as well 
as for separating a suspension of hydrocarbon conversion particularly 
discussed above. 
In yet another embodiment, it is contemplated using flue gas rather than 
steam introduced by conduit 14 to facilitate the separation of regenerated 
catalyst from combustion product gases. On the other hand, it has been 
found that no additional gaseous material need be added as by conduit 14 
in order to obtain a satisfactory separation of the suspension. This is 
particularly true when using the arrangement for separating a suspension 
of hot regenerated catalyst from combustion product gases. Stripping of 
the regenerated catalyst may be accomplished before withdrawal by 
standpipes or a special section of the withdrawal standpipe. 
Having thus generally described the means and method of using in accordance 
with this invention and described specific embodiments thereof, it is to 
be understood that no undue restrictions are to be imposed by reason 
thereof except as defined by the following claims.