Process and arrangement for separating particulate solids

In this invention a cyclonic separation method and apparatus discharges particulate solids and gaseous fluids into a separation vessel from a discharge opening of a central conduit and withdraws separated gaseous fluids from the separation vessel with a recovery conduit having an inlet located below the discharge opening. Recovery of separated gases using cyclonic separation is improved by the specific location of the recovery piping inlet which reduces the entrainment of fine particles with the gases.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to processes for the separation of 
particulate solids from gases. More specifically, this invention relates 
to the separation of catalyst and gaseous materials from a mixture thereof 
in a cyclonic disengaging vessel. 
1. Description of the Prior Art 
Cyclonic methods for the separation of solids from gases are well known and 
commonly used. A particularly well known application of such methods is in 
the hydrocarbon processing industry were particulate catalysts contact 
gaseous reactants to effect chemical conversion of the gas stream 
components or physical changes in the particles undergoing contact with 
the gas stream. 
The FCC process presents a familiar example of a process that uses gas 
stream to contact a finally divided stream of catalyst particles and 
effects contact between the gas and the particles. The FCC processes, as 
well as separation devices used therein are fully described in U.S. Pat. 
Nos. 4,701,307 and 4,792,437, the contents of which are hereby 
incorporated by reference. 
The most common method of separating particulate solids from a gas stream 
uses a cyclonic separation. Cyclonic separators are well known and operate 
by imparting a tangential velocity to a gases containing entrained solid 
particles that forces the heavier solids particles outwardly away from the 
lighter gases for upward withdrawal of gases and downward collection of 
solids. Cyclonic separators usually comprise relatively small diameter 
cyclones having a tangential inlet on the outside of a cylindrical vessel 
that forms the outer housing of the cyclone. 
Cyclones for separating particulate material from gaseous materials are 
well known to those skilled in the art of FCC processing. In the operation 
of an FCC cyclone tangential entry of the gaseous materials and catalyst 
creates a spiral flow path that establishes a vortex configuration in the 
cyclone so that the centripetal acceleration associated with an outer 
vortex causes catalyst particles to migrate towards the outside of the 
barrel while the gaseous materials enter an inner vortex for eventual 
discharge through an upper outlet. The heavier catalyst particles 
accumulate on the side wall of the cyclone barrel and eventually drop to 
the bottom of the cyclone and out via an outlet and a dip leg conduit for 
recycle through the FCC arrangement. Cyclone arrangements and 
modifications thereto are generally disclosed in U.S. Pat. Nos. 4,670,410 
and 2,535,140. 
The FCC process is representative of many processes for which methods are 
sought to quickly separate gaseous fluids and solids as they are 
discharged from a conduit. In the FCC process one method of obtaining this 
initial quick discharge is to directly connect a conduit containing a 
reactant fluid and catalyst directly to a traditional cyclone separators. 
While improving separation, there are drawbacks to directly connecting a 
conduit discharging a mixture of solids and gaseous fluids into cyclone 
separators. Where the mixture discharged into the cyclones contains a high 
loading of solids, direct discharge requires large cyclones. In addition, 
instability in the delivery of the mixture may also cause the cyclones to 
function poorly and to disrupt the process where pressure pulses cause an 
unacceptable carryover of solids with the vapor separated by the cyclones. 
Such problems are frequently encountered in processes such as fluidized 
catalytic cracking. Accordingly, less confined systems are often sought to 
effect an initial separation between a mixture of solid particles and 
gaseous fluids. 
U.S. Pat. Nos. 4,397,738 and 4,482,451, the contents of which are hereby 
incorporated by reference, disclose an alternate arrangement for cyclonic 
separation that tangentially discharges a mixture of gases and solid 
particles from a central conduit into a containment vessel. The 
containment vessel has a relatively large diameter and generally provides 
a first separation of solids from gases. This type of arrangement differs 
from ordinary cyclone arrangements by the discharge of solids from the 
central conduit and the use of a relatively large diameter vessel as the 
containment vessel. In these arrangements the initial stage of separation 
is typically followed by a second more complete separation of solids from 
gases in a traditional cyclone vessel. 
BRIEF SUMMARY OF THE INVENTION 
It has now been discovered that the efficiency of a cyclonic separation 
that centrally discharges particles into a separation chamber may be 
surprisingly improved by changing the point from which the gaseous stream 
is collected. In accordance with this discovery collecting the gaseous 
fluids recovered by separation of the fluid and solids from an outlet 
located below the inlet of a central conduit that discharges the gaseous 
fluids and solids will increase the efficiency of separating the gaseous 
fluids from the solids. This improvement in the separation is particularly 
helpful in processes where a quick separation between the gaseous fluids 
and the solid particles are desired. The improvement in the separation is 
achieved with only minimal addition to the structure of the separation 
system. Through the addition of a small amount of conduit the separation 
efficiency achieved by an open disengaging vessel will provide very low 
catalyst loadings and in some cases will approach catalyst loadings 
obtained by traditional cyclone designs. 
Accordingly, in one embodiment this invention is an apparatus for 
separating solids from a stream comprising a mixture of gaseous fluids and 
solid particles. The apparatus includes a separation vessel and a mixture 
conduit that extends into the separation vessel and defines a discharge 
opening located within the vessel. The discharge opening discharges the 
stream of gaseous fluids and solid particles into the vessel and imparts a 
tangential velocity to the stream. The separation vessel defines an outlet 
for discharging particles from a lower portion of the vessel. In 
accordance with this invention a gas recovery conduit defines an inlet for 
withdrawing gaseous fluids from separation vessel at a location below the 
discharge opening. 
In another embodiment this invention is an apparatus for separating solid 
particles from a stream comprising a mixture of gaseous fluids and solid 
particles. The apparatus includes a containment vessel, a separation 
vessel located within the containment vessel that has an open bottom and a 
central conduit extending vertically into the separation vessel. The 
separation vessel houses at least two curved conduits that communicate 
with and extend radially from the central conduit. Each arm defines a 
discharge opening for the tangential discharge of the stream into the 
separation vessel. A gas recovery conduit defines an inlet below and 
radially inward from the discharge conduit for collecting gaseous fluids 
from the separation vessel. 
In another embodiment this invention is a method for separating solid 
particles from a stream comprising a mixture of solid particles and 
gaseous fluids. The method passes the mixture of solid particles and 
gaseous fluids into a separation vessel through a central conduit and 
tangentially discharges the mixture from a discharge opening into the 
separation vessel. The method collects gaseous fluids from the separation 
vessel at a location below a discharge opening and withdraws gaseous 
fluids from the separation vessel. Solid particles pass out of the 
separation vessel at a location below the discharge opening and the inlet. 
Additional details and embodiments of the invention will become apparent 
from the following detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
The apparatus of this invention comprises a separation vessel into which a 
mixture conduit that contains the mixture of solid particles transported 
by a gaseous fluid discharges the particles and gaseous fluid mixture. The 
separation vessel is preferably a cylindrical vessel. The cylindrical 
vessel promotes the swirling action of the gaseous fluids and solids as 
they are discharged tangentially from a discharge opening of the mixture 
conduit into the separation vessel. The separation vessel will preferably 
have an open interior below the discharge opening that will still provide 
satisfactory operation in the presence of some obstructions such as 
conduits or other equipment which may pass through the separation vessel. 
The discharge opening and the conduit portion upstream of the discharge 
opening are constructed to provide a tangential velocity to the exiting 
mixture of gaseous fluids and solids. The discharge opening may be defined 
using vanes or baffles that will impart the necessary tangential velocity 
to the exiting gaseous fluids and solids. Preferably the discharge outlet 
is constructed with conduits or arms that extend outwardly from a central 
mixture conduit. Providing a section of curved arm upstream of the 
discharge conduit will provide the necessary momentum to the gaseous 
fluids and solids as they exit the discharge opening to continue in a 
tangential direction through the separation vessel. The separation vessel 
has an arrangement that withdraws catalyst particles from the bottom of 
the vessel so that the heavier solid particles disengage downwardly from 
the lighter gaseous fluids. The bottom of the separator vessel may be 
completely open to permit solid particles to fall freely from the 
separation vessel or a bed of solid particles may be maintained at the 
bottom of the separation vessel. 
An essential feature of this invention is the location of the outlet from 
the separation vessel for withdrawing the gaseous fluids from the 
separation vessel. The outlet of the separation vessel for the gaseous 
fluid is provided the inlet of a withdrawal conduit that extends into the 
separation vessel. The inlet to the withdrawal conduit is located below 
the discharge openings of the central conduit. The withdrawal conduit can 
have any configuration provided it defines the inlet at the required 
location below the discharge openings. The discharge opening is preferably 
spaced outwardly with respect to the inlet to the gas recovery conduit. 
Arrangements that use curved conduits to impart the tangential velocity 
are particularly preferred again since the discharge openings are readily 
located in an outer portion of the separation vessel relative to the inlet 
for the gas recovery conduit. 
The apparatus and method of separating solid particles from a mixture of 
gaseous and solid particles as disclosed by this invention is useful in 
any process that seeks a good initial separation of solid particles from 
gaseous fluids in a separation system that is more open than traditional 
cyclones. Those skilled in the art are aware of a variety of processes 
that utilize fluidized particles and require the separation of particulate 
material from the gaseous fluids used for transport of the particles. The 
remainder of this invention is described in the context of a specific 
application of this invention to an FCC reactor arrangement. Those skilled 
in the art of particle separation and transport will readily appreciate 
the application of this invention to other processes where separation of 
particles from gaseous fluids is desired. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Looking then at FIG. 1, the schematic illustration depicts a separation 
arrangement in a reactor vessel 10. A central conduit in the form of a 
reactor riser 12 extends upwardly from a lower portion of the vessel 10 in 
a typical FCC arrangement. The central conduit or riser preferably has a 
vertical orientation within the separation vessel and may extend upwardly 
from the bottom of the separation vessel or downwardly from the top of the 
separation vessel. Riser 12 terminates in an upper portion of reactor 
vessel 10 with an curved conduit in the form of an arm 14. Arm 14 
discharges a mixture of gases fluids and solid particles comprising 
catalyst. In a reactor arrangement as depicted by FIG. 1 the gaseous fluid 
comprises product vapors. 
Tangential discharge of gases and catalyst from a discharge opening 16 
produces a swirling helical pattern about the interior of reactor vessel 
10 below the discharge opening 16. Centripetal acceleration associated 
with the helical motion forces the heavier catalyst particles to the outer 
portions of reactor vessel 10. The gases, having a lower density than the 
solids, more easily change direction and begin an upward spiral with the 
gases ultimately traveling into a gas recovery conduit 18 having an inlet 
20. Inlet 20 is located below the discharge opening 16. The gases that 
enter gas recovery conduit 18 through inlet 20 will usually contain a 
light loading of catalyst particles. Inlet 20 recovers gases from the 
discharge conduit as well as stripping vapors which are hereinafter 
described. The loading of catalyst particles in the gases entering conduit 
18 are usually less than 1 lb/ft..sup.3 and typically less than .1 
lb/ft.sup.3. 
Gas recovery conduit 18 passes the separated gases into a cyclone 22 that 
effects a further removal of particulate material from the gases in the 
gas recovery conduit. Cyclone 22 operates as a conventional cyclone in a 
conventional manner with the tangential entry of the gases creating a 
swirling action inside the cyclones to establish the well known inner and 
outer vortexes that separate catalyst from gases. A gaseous stream 
relatively free of catalyst particles exits the reactor vessel 10 through 
an outlet 24. 
Catalyst recovered by cyclone 22 exits the bottom of the cyclone through a 
dip-leg conduit 23 and passes through a lower portion of the reactor 
vessel 10 where it collects with catalyst from the discharge opening 16 in 
a catalyst bed 28. Catalyst from catalyst bed 28 passes downwardly through 
a stripping vessel 30 where countercurrent contact with a stripping fluid 
through a series of stripping baffles 32 displaces product gases from the 
catalyst as it continues downwardly through the stripping vessel. 
Stripped catalyst from stripping vessel 30 passes through a conduit 31 to a 
catalyst regenerator 34 that rejuvenates the catalyst by contact with an 
oxygen-containing gas. High temperature contact of the oxygen-containing 
gas with the catalyst oxidizes coke deposits from the surface of the 
catalyst. Following regeneration catalyst particles enter the bottom of 
reactor riser 12 through a conduit 33 where a fluidizing gas from a 
conduit 35 pneumatically conveys the catalyst particles upwardly through 
the riser. As the mixture of catalyst and conveying gas continues up the 
riser, nozzles 36 inject feed into the catalyst, the contact of which 
vaporizes the feed to provide additional gases that exit through discharge 
opening 16 in the manner previously described. 
In the arrangement depicted in FIG. 1, reactor vessel 10 serves as both a 
separation vessel and a containment vessel for the process overall. FIG. 2 
depicts a modified arrangement wherein a separate containment vessel and 
separation vessel are provided. Looking then at FIG. 2 a central conduit 
in the form of a reactor riser 38 delivers a mixture of catalyst particles 
and gases to a pair of arms 40 that tangentially discharge the mixture of 
catalyst particles and gases into a separation vessel 42 through discharge 
openings 44. The tangential delivery of the mixture of catalyst particles 
and gases effects separation in the manner previously described with the 
catalyst particles passing downwardly through the separation vessel 42 and 
out of a lower portion of the separation vessel, through an outlet 46. 
Prior to passing through outlet 46, catalyst collects in a bed 48 
contained within the separation vessel 42. An initial displacement of 
gases comprising product hydrocarbons may be effected in bed 48 by contact 
with a stripping fluid. In the arrangement of FIG. 2, stripping fluid is 
delivered to the underside of a baffle 50 and passes through a series of 
holes in baffle 50 (not shown). 
Gas recovery conduit 52 withdraws gases comprising product hydrocarbons and 
stripping medium from the separation vessel at a location below discharge 
opening 44 through an annular inlet 54 defined by an enlarged conduit 56 
that shrouds the end portion of riser 38 to a location below discharge 
openings 44. Holes provided in the sides of shroud 56 provide slots 
through which arms 40 pass. The structure of shroud 56 and arms 40 again 
provide the preferred structure wherein the gases and catalyst are 
discharged at a radial distance from the center of riser 38 that is 
greater than the distance from inlet opening 54 such that the gases 
containing a lower concentration of catalyst are removed closer to the 
center of the separation vessel 42 and riser 38. Additional stripping 
takes place below separation vessel 42 and stripping fluid passes upwardly 
across a bed surface 58. 
A reactor vessel 60 serves as a containment vessel that houses the 
separation vessel 42 and also confines gases passing across bed surface 
:58. Gases in the upper volume of reactor vessel 60 enter the gas recovery 
conduit 52 through a series of ports 62. The combined stream of separated 
gases from inlet 54 and additional stripping fluid and gases from port 62 
pass upwardly through recovery conduit 52 and into a traditional cyclone 
separator 64 that again effects a further separation of the remaining 
catalyst that is still entrained with the gases. Gases exit the top of 
cyclone 64 through an outlet 66 while recovered catalyst particles pass 
downwardly through a dip-leg conduit 68 at a rate regulated by a flapper 
valve 70. Catalyst from dip-leg conduit 68 as well as bed 48 pass out of 
the reactor vessel for stripping in the manner previously described. 
The separation vessel and recovery conduit arrangement of FIG. 2 uses 
shroud 56 to provide an annular opening 54 that is more fully depicted in 
FIG. 3. As shown in FIG. 3 shroud 56 surrounds riser 38 to provide the 
annular opening 54. FIG. 3 shows the previously described slots at 
reference number 57 through which arms 40 extend out through the sides of 
shroud 56. The slotted arrangement allows for differential expansion of 
riser 38 relative to the shroud and separation vessel. A slotted 
arrangement is preferred so that shroud 56 and the associated recovery 
piping may be supported from cyclones 64. In addition, separator vessel 42 
may also be supported from recovery piping 52. FIG. 3 also shows the 
location of multiple dip pipes and flapper valves that correspond to the 
usual practice of providing two or more cyclones in a symmetrical 
relationship and communication with the gas recovery conduit. 
The use of an annular opening for the recovery of gaseous fluids from below 
the discharge openings is susceptible to other arrangements. One such 
arrangement is depicted in FIG. 4 which illustrates a modification to the 
arrangement of FIGS. 2 and 3. FIG. 4 shows the upper end of separation 
vessel 42 from FIG. 2 and a lower portion 52' of the gas recovery conduit. 
Riser 38 is essentially the same as that disclosed in FIGS. 2 and 3 and 
extends upwardly to near the top of the separation vessel 42. The inlet to 
the recovery conduit 52' shows a modified shroud 56' that defines partial 
annular conduits 70. Conduits 70 extend downwardly past the arm 40 to 
define inlets 72 that are located below the arm 40 to withdraw gases from 
below the discharge opening. 
The geometry of conduits 70 are shown more clearly in the cross-section 
provided by FIG. 5. The conduits 70 have inner walls 74 and outer walls 76 
that are closed at the vertical ends to define partial annular openings 
72. This arrangement has the advantage of eliminating the slots that were 
needed in the sides of shroud 56 as depicted in FIGS. 2 and 3 to 
accommodate arms 40. The conduits 70 provided by this arrangement are 
completely closed to prevent the small bypassing of fluids that can occur 
through the slot 57 in shroud 56. In this arrangement the shroud 56 is 
completely closed to prevent any ingress of fluids into the recovery 
conduit above the discharge opening.