Multi-stage regeneration of catalyst in a bubbling bed catalyst regenerator

A process and apparatus for regeneration of spent FCC catalyst in a bubbling bed regenerator having a stripper mounted over the regenerator. Spent catalyst is regenerated in a fast fluidized bed coke combustor heated by direct contact heat exchange with catalyst recycled to the coke combustor via an internal "trough" trap. Catalyst recycle flow to the combustor is controlled by varying gas flow in the trough trap.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a process and apparatus for stripping and 
regenerating fluidized catalytic cracking catalyst. 
2. Description of Related Art 
In the fluidized catalytic cracking (FCC) process, catalyst, having a 
particle size and color resembling table salt and pepper, circulates 
between a cracking reactor and a catalyst regenerator. In the reactor, 
hydrocarbon feed contacts a source of hot, regenerated catalyst. The hot 
catalyst vaporizes and cracks the feed at 425.degree.-600.degree. C., 
usually 460.degree.-560.degree. C. The cracking reaction deposits 
carbonaceous hydrocarbons or coke on the catalyst, thereby deactivating 
the catalyst. The cracked products are separated from the coked catalyst. 
The coked catalyst is stripped of volatiles, usually with steam, in a 
catalyst stripper and the stripped catalyst is then regenerated. The 
catalyst regenerator burns coke from the catalyst with oxygen containing 
gas, usually air. Decoking restores catalyst activity and simultaneously 
heats the catalyst to, e.g., 500.degree.-900.degree. C., usually 
600.degree.-750.degree. C. This heated catalyst is recycled to the 
cracking reactor to crack more fresh feed. Flue gas formed by burning coke 
in the regenerator may be treated for removal of particulates and for 
conversion of carbon monoxide, after which the flue gas is normally 
discharged into the atmosphere. 
Catalytic cracking has undergone progressive development since the 40s. The 
trend of development of the fluid catalytic cracking (FCC) process has 
been to all riser cracking and use of zeolite catalysts. A good overview 
of the importance of the FCC process, and its continuous advancement, is 
reported in Fluid Catalytic Cracking Report, Amos A. Avidan, Michael 
Edwards and Hartley Owen, as reported in the Jan. 8, 1990 edition of the 
Oil & Gas Journal. 
Modern catalytic cracking units use active zeolite catalyst to crack the 
heavy hydrocarbon feed to lighter, more valuable products. Instead of 
dense bed cracking, with a hydrocarbon residence time of 20-60 seconds, 
less contact time is needed. The desired conversion of feed can now be 
achieved in much less time, and more selectively, in a dilute phase, riser 
reactor. 
Although reactor residence time has continued to decrease, the height of 
the reactors has not. Although the overall size and height of much of the 
hardware associated with the FCC unit has decreased, the use of all riser 
reactors has resulted in catalyst and cracked product being discharged 
from the riser reactor at a fairly high elevation. This elevation makes it 
easy for a designer to transport spent catalyst from the riser outlet, to 
a catalyst stripper at a lower elevation, to a regenerator at a still 
lower elevation. 
The need for a somewhat vertical design, to accommodate the great height of 
the riser reactor, and the need to have a unit which is compact, 
efficient, and has a small "footprint" has caused considerable evolution 
in the design of FCC units, which evolution is reported to a limited 
extent in the Jan. 8, 1990 Oil & Gas Journal article. One modern, compact 
FCC design is the Kellogg Ultra Orthoflow converter, Model F, which is 
shown in FIG. 1 of this patent application, and also shown as FIG. 17 of 
the Jan. 8, 1990 Oil & Gas Journal article discussed above. The compact 
nature of the design, and the use of a catalyst stripper which is 
contiguous with and supported by the catalyst regenerator, makes it 
difficult to expand or modify such units. The catalyst stripper design is 
basically a good one, which achieves some efficiencies because of its 
location directly over the bubbling bed regenerator. The stripper can be 
generously sized, does not have to fit around the riser reactor as in many 
other units, and the stripper is warmed some by proximity to the 
regenerator, which improves stripper efficiency slightly. 
Although such a unit works well in practice, the regenerator operates with 
a relatively large catalyst inventory, a much larger catalyst inventory 
than would be required in a high efficiency regenerator. The long 
residence time, and relatively high steam partial pressure associated with 
single stage bubbling bed catalyst regeneration causes an undesirable 
amount of catalyst deactivation. We realized that it would be beneficial 
if the regenerator environment could be made drier, and/or if catalyst 
regeneration in such a regenerator could be conducted in stages, rather 
than in a single dense bed. 
Some or our recent work has been directed to achieving multi-stage 
regeneration in such bubbling dense bed regenerators, such as our U.S. 
Pat. Nos. 5,032,251, 5,034,115 and 5,047,140 which are incorporated by 
reference. 
Although all of the improvements listed above were in the right direction, 
they were not the complete solution. The approaches discussed above 
generally led to higher particulate loading than was desired in the dilute 
phase region above the bubbling dense bed. The approaches did not permit 
as much control as was desired in regard to the amount of catalyst 
recirculation to the coke combustor. Finally, we wanted to be able to 
achieve true multi-stage regeneration of catalyst, with complete CO 
combustion in the first stage, but only partial coke combustion. We had 
three goals: 
1. Provide a simple and reliable way to control regenerated catalyst 
recycle to a fast fluidized bed coke combustor in an Orthoflow 
regenerator. 
2. Have the benefits of high superficial vapor velocity first stage 
regeneration in a coke combustor immersed in a bubbling dense bed, without 
undue increase in dust loading in vapor space above the dense bed. 
3. Incorporate a relatively fail safe method for achieving complete CO 
combustion, but only partial coke combustion, in such a regenerator, 
without adding large amounts of Pt to the FCC catalyst inventory. 
We developed several designs or modifications which reached the above 
goals. 
BRIEF SUMMARY OF THE INVENTION 
Accordingly, the present invention provides a fluidized catalytic cracking 
process wherein a heavy hydrocarbon feed comprising hydrocarbons having a 
boiling point above about 650.degree. F. is catalytically cracked to 
lighter products comprising the steps of: catalytically cracking said feed 
in a catalytic cracking zone operating at catalytic cracking conditions 
including a riser top temperature of about 950.degree. to 1075.degree. F. 
by mixing, in the base of a riser reactor, a heavy crackable feed with a 
source of hot regenerated catalytic cracking catalyst withdrawn from a 
catalyst regenerator, and cracking said feed in said riser reactor to 
produce catalytically cracked products and spent catalyst which are 
discharged from the top of the riser into a catalyst disengaging zone; 
separating cracked products from spent catalyst in said catalyst 
disengaging zone to produce a cracked product vapor phase which is 
recovered as a product and a spent catalyst phase at a temperature of 
about 950.degree. to 1075.degree. F. which is discharged from said 
disengaging zone into a catalyst stripper contiguous with and beneath said 
disengaging zone; steam stripping said spent catalyst with stripping steam 
in said stripping zone to produce a stripper vapor comprising cracked 
products and stripping steam which is removed from said stripping zone as 
a product and a stripped catalyst phase which is discharged into a 
vertical standpipe beneath said stripping zone; discharging stripped 
catalyst from said standpipe into a coke combustor catalyst regeneration 
zone contiguous with and beneath said stripping zone; heating said 
stripped catalyst in said coke combustor to at least 1100.degree. F. by 
adding a controlled amount of hot regenerated catalyst having a 
temperature from 1200.degree. to 1500.degree. F. from a fluidized bed of 
regenerated catalyst at least partially covering said coke combustor; 
regenerating said stripped and heated catalyst in said coke combustor at 
catalyst regeneration conditions including a temperature above 
1100.degree. F., contact with an oxygen containing gas at a superficial 
vapor velocity above 3 feet per second and sufficient to maintain at least 
turbulent or fast fluidized bed conditions to produce at least partially 
regenerated catalyst and flue gas; discharging upwardly from said coke 
combustor a dilute phase mixture of flue gas and at least partially 
regenerated FCC catalyst into a superimposed dilute phase transport riser 
mounted above said coke combustor; discharging from said dilute phase 
transport riser at least partially regenerated FCC catalyst and flue gas; 
separating said discharged FCC catalyst from flue gas and collecting said 
discharged FCC catalyst in a second fluidized bed having a depth of at 
least 2 feet and encompassing at least a portion of said coke combustor; 
recycling regenerated catalyst from said second fluidized bed into said 
coke combustor by removing regenerated catalyst via a vertical trough 
recycle means having a top and a bottom with: a height of at least 2 feet; 
an inlet in said top portion thereof for regenerated catalyst immersed in 
said second fluidized bed; an outlet in said bottom portion in said coke 
combustor; at least one fluidizing gas inlet at an elevation intermediate 
said top and said bottom for fluidizing gas; controlling, at least 
periodically, the flow of recycled catalyst from said second fluidized bed 
to said coke combustor by changing the amount of fluidizing gas added to 
said vertical trough; and withdrawing regenerated catalyst from said 
fluidized bed and charging same to said base of said riser reactor. 
In an apparatus embodiment, the present invention provides an apparatus for 
the fluidized catalytic cracking of a heavy feed to lighter more valuable 
products comprising: a riser reactor cracking means having a base portion 
connective with a source of heavy feed and connective with a regenerator 
vessel; a riser outlet at the top of the riser reactor connective with a 
catalyst disengaging means adapted to separate a cracked product vapor 
stream from a spent catalyst stream, and discharge said spent catalyst 
into a catalyst stripper means; a primary catalyst stripping means, 
located above and supported by said regenerator vessel, said stripping 
means adapted to receive spent catalyst from said disengaging means and 
contact said spent catalyst with a stripping gas to produce a stripper 
effluent vapor stream and a stripped catalyst stream which is discharged 
down into a primary stripper catalyst standpipe; and a coke combustor 
catalyst regeneration means at least partially within said regenerator 
vessel having: an inlet for stripped catalyst, an inlet for regeneration 
gas, an inlet for recycled regenerated catalyst, and an outlet in an upper 
portion thereof for flue gas and catalyst; a dilute phase transport riser 
mounted above said coke combustor having: an inlet in a base portion 
thereof for flue gas and catalyst discharged from said coke combustor 
outlet, and an outlet in an upper portion thereof discharging catalyst and 
flue gas within said regenerator vessel; a vertical trough recycle means 
having a top and a bottom and: a height of at least 2 feet; an inlet in 
said top for regenerated catalyst in said second regenerator vessel; an 
outlet in said bottom in said coke combustor; at least one fluidizing gas 
inlet at an elevation intermediate said top and said bottom; a regenerated 
catalyst recycle means having an inlet in regenerator vessel and an outlet 
in said base of said riser reactor.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 is a simplified schematic view of an FCC unit of the prior art, 
similar to the Kellogg Ultra Orthoflow converter Model F shown as FIG. 17 
of Fluid Catalytic Cracking Report, in the Jan. 8, 1990 edition of Oil & 
Gas Journal. 
A heavy feed such as a gas oil, vacuum gas oil is added to riser reactor 6 
via feed injection nozzles 2. The cracking reaction is completed in the 
riser reactor, which takes a 90.degree. turn at the top of the reactor at 
elbow 10. Spent catalyst and cracked products discharged from the riser 
reactor pass through riser cyclones 12 which efficiently separate most of 
the spent catalyst from cracked product. Cracked product is discharged 
into disengager 14, and eventually is removed via upper cyclones 16 and 
conduit 18 to the fractionator. 
Spent catalyst is discharged down from a dipleg of riser cyclones 12 into 
catalyst stripper 8, where one, or preferably 2 or more, stages of steam 
stripping occur, with stripping steam admitted by means not shown in the 
figure. The stripped hydrocarbons, and stripping steam, pass into 
disengager 14 and are removed with cracked products after passage through 
upper cyclones 16. 
Stripped catalyst is discharged down via spent catalyst standpipe 26 into 
catalyst regenerator 24. The flow of catalyst is controlled with spent 
catalyst plug valve 36. 
Catalyst is regenerated in regenerator 24 by contact with air, added via 
air lines and an air grid distributor not shown. A catalyst cooler 28 is 
provided so that heat may be removed from the regenerator, if desired. 
Regenerated catalyst is withdrawn from the regenerator via regenerated 
catalyst plug valve assembly 30 and discharged via lateral 32 into the 
base of the riser reactor 6 to contact and crack fresh feed injected via 
injectors 2, as previously discussed. Flue gas, and some entrained 
catalyst, are discharged into a dilute phase region in the upper portion 
of regenerator 24. Entrained catalyst is separated from flue gas in 
multiple stages of cyclones 4, and discharged via outlets 8 into plenum 20 
for discharge to the flare via line 22. 
In FIG. 2 (invention) the changes made to the old unit are shown, and many 
essential and/or conventional details, such as the catalyst cooler have 
been omitted. 
FIG. 2 shows three inventions, which work very well together to achieve 
true multi-stage regeneration in an Orthoflow regenerator. 
A heavy feed such as a gas oil, vacuum gas oil is added to riser reactor 
210 via feed injection nozzles not shown. Hot regenerated catalyst flow 
into the base of the riser is controlled by ceramic plug valve assembly 
209. The cracking reaction is completed in the riser reactor, which 
discharges spent catalyst and cracked products discharged from the riser 
reactor pass through riser cyclones which separate most of the spent 
catalyst from cracked product. Cracked product is removed via upper 
cyclones and a conduit to the fractionator. 
Spent catalyst is discharged down from a dipleg of riser cyclones 212 into 
catalyst stripper 208, where one, or preferably 2 or more, stages of steam 
stripping occur, with stripping steam admitted by means not shown in the 
figure. The stripped hydrocarbons, and stripping steam, pass into 
disengager 214 and are removed with cracked products after passage through 
upper cyclones 216. 
Catalyst is regenerated in one or more stages in the regenerator by contact 
with air in various parts of the vessel. 
The first stage of regeneration occurs in a fast fluidized bed coke 
combustor 238. Spent catalyst discharged from the stripper standpipe 
contacts primary regeneration air added via air line 280 and air 
distributor 285. 
The spent catalyst is usually at the riser top temperature, or 2.degree. to 
5.degree. F. below this because a small amount of cooling usually occurs 
during stripping. This catalyst can be at 950.degree.-1075.degree. F., but 
in most units is around 975.degree.-1025.degree. F. Although quite hot, it 
is not hot enough to achieve rapid coke combustion, a temperature of at 
least about 1100.degree. F., and preferably 1200.degree. F. or higher, is 
needed for this. Such temperatures were easily achieved in the prior art 
by adding the stripped catalyst to the bubbling dense bed of catalyst at 
1300.degree. F. or so, and the large inventory of hot regenerated catalyst 
would heat the spent to a high enough temperature to burn coke within the 
residence time allowed within the regenerator. 
The process of the present invention uses a coke combustor, operating at 
fast fluidized bed conditions, and with a short catalyst residence time in 
the coke combustor. It is essential to recycle some hot regenerated 
catalyst into the coke combustor via trough recycle means 232. This has an 
inlet connective with the second fluidized bed, region 265, at the bottom 
thereof. Hot regenerated catalyst passes down through the passageway 
defined by the walls of trough recycle means 232 and a sidewall 286 of the 
coke combustor, with recycled catalyst passing via opening 234 into the 
fast fluidized bed region 230. Preferably the recycled catalyst is added 
near the base of the coke combustor, but this is not essential, 
fluidization is so vigorous in the coke combustor that it could be added 
to a side or even an upper portion thereof. 
The flow of regenerated catalyst is controlled by varying the amount of 
fluidizing gas added to the trough via upper and lower gas inlets 390 and 
380, respectively. 
Partially, or totally, regenerated catalyst is discharged up from the coke 
combustor into transition region 235, where a gradual reduction in cross 
sectional area of the coke combustor, as shown by inverted funnel 242, 
forces an increase in superficial vapor velocity and dilute phase flow of 
catalyst and flue gas into dilute phase transport riser, region 240. 
Catalyst and flue gas are discharged from the transport riser via a 
plurality of symmetrical scoop disengagers 250. Flue gas passes via 
arcuate or semi-circular openings 255 into a dilute phase region 260. A 
majority of the spent catalyst, and usually well in excess of 90% passes 
down sidearms 257 into a second fluidized bed, region 265. 
Additional regeneration of catalyst preferably occurs in this second 
fluidized bed, which will usually be a bubbling dense bed region. 
Additional, or secondary air, will be added via air line 290 and 
distributor means 295 to this bed. Even if no additional catalyst 
regeneration is needed it will be necessary to add fluffing air to 
maintain fluidization in this region. 
Flue gas, and/or fluffing air, and entrained catalyst associated therewith 
pass from dense bed region 265 into dilute phase region 260 above the 
dense bed. In this dilute phase region the two flue gas streams combine, 
flue gas from the coke combustor and flue gas (or fluffing air) from the 
second bed and enter the inlet horn of a plurality of primary cyclones 
300. Recovered catalyst is discharged via diplegs 305 into the bubbling 
dense bed region. Vapor discharged from the primary cyclones then enters a 
plurality of secondary cyclones 310, which removes remaining entrained 
catalyst and fines and discharges a regenerator flue gas stream via vapor 
outlet 320 into external plenum 325. 
Preferably the regenerator operates with a CO combustion additive on 
relatively large size particles, such as TCC beads. Such fast settling CO 
combustion promoter will remain a long time in the fast fluid bed region 
230, because its slip rate is similar to that of the superficial vapor 
velocity in the FFB region. Even when the bead slip rate substantially 
exceeds the superficial vapor velocity in the FFB region there will be 
considerable traffic of beads into the transition region 235 because of 
the way fluidized beds operate, and once in the transition region, and 
certainly in the dilute phase region 240 the vapor velocity will be 
sufficient to sweep the beads along with the flow of gas in the dilute 
phase region. Beads will be almost completely recovered by the scoop 
disengagers, and will rapidly settle or pass through the dense bed region 
265 and flow around to catalyst recycle means 232. 
Regenerated catalyst is withdrawn from the regenerator dense bed region 265 
by plug valve assembly 209 and discharged into the base of the riser 
reactor 210 to contact and crack fresh feed. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
FCC FEED 
Any conventional FCC feed can be used. The process of the present invention 
is especially useful for processing difficult charge stocks, those with 
high levels of CCR material, exceeding 2, 3, 5 and even 10 wt % CCR. 
The feeds may range from the typical, such as petroleum distillates or 
residual stocks, either virgin or partially refined, to the atypical, such 
as coal oils and shale oils. The feed frequently will contain recycled 
hydrocarbons, such as light and heavy cycle oils which have already been 
subjected to cracking. 
Preferred feeds are gas oils, vacuum gas oils, atmospheric resids, and 
vacuum resids, and mixtures thereof. The present invention is very useful 
with heavy feeds having, and with those having a metals contamination 
problem. With these feeds, the possibility of reduced burning load in the 
regenerator, and even more importantly, the possibility of a dryer 
regenerator, because of reduced hydrogen content of coke, will be a 
significant benefit. 
FCC CATALYST 
Any commercially available FCC catalyst may be used. The catalyst can be 
100% amorphous, but preferably includes some zeolite in a porous 
refractory matrix such as silica-alumina, clay, or the like. The zeolite 
is usually 5-40 wt.% of the catalyst, with the rest being matrix. 
Conventional zeolites include X and Y zeolites, with ultra stable, or 
relatively high silica Y zeolites being preferred. Dealuminized Y (DEAL Y) 
and ultrahydrophobic Y (UHP Y) zeolites may be used. The zeolites may be 
stabilized with Rare Earths, e.g., 0.1 to 10 Wt % RE. 
Relatively high silica zeolite containing catalysts are preferred for use 
in the present invention. They withstand the high temperatures usually 
associated with complete combustion of CO to CO.sub.2 within the FCC 
regenerator. 
The catalyst inventory may also contain one or more additives, either 
present as separate additive particles, or mixed in with each particle of 
the cracking catalyst. Additives can be added to enhance octane (shape 
selective zeolites, i.e., those having a Constraint Index of 1-12, and 
typified by ZSM-5, and other materials having a similar crystal 
structure), adsorb SOX (alumina), remove Ni and V (Mg and Ca oxides). 
Additives for removal of SOx are available from several catalyst suppliers. 
CO combustion additives, or FCC catalyst with CO combustion promoter built 
into the catalyst, are available from most FCC catalyst vendors. Such 
additives have fluidization properties similar to conventional FCC 
catalyst, and circulate with the catalyst. 
The preferred non-circulating, large particle additives may be purchased 
from vendors such as Intercat. The large balls of CO combustion promoter 
taught by Wilson Jr. et al in U.S. Pat. No. 3,808,121 may be used, or even 
fresh or spent reforming catalyst. These noncirculating promoters may be 
used as a supplement for, or preferably a complete or partial replacement 
of conventional circulating CO combustion promoters. 
The FCC catalyst composition, per se, forms no part of the present 
invention. 
CRACKING REACTOR/REGENERATOR 
The FCC reactor and regenerator shell 24, per se, are conventional, and are 
available from the M.W. Kellogg Company. 
The modifications needed to implement the claimed invention are well within 
the skill of the art, when supplemented with the teachings herein. Some 
general and specific guidelines follow, directed both to the FCC process 
in general, and the claimed invention. 
FCC REACTOR CONDITIONS 
Conventional riser cracking conditions may be used. Typical riser cracking 
reaction conditions include catalyst/oil ratios of 0.5:1 to 15:1 and 
preferably 3:1 to 8:1, and a catalyst contact time of 0.1 to 50 seconds, 
and preferably 0.5 to 5 seconds, and most preferably about 0.75 to 2 
seconds, and riser top temperatures of 900.degree. to about 1050.degree. 
F. 
STRIPPING CONDITIONS 
Conventional stripping operating conditions may be used. Preferably hot 
stripping, as taught in our earlier patents, is practiced. Typical hot 
stripper operating conditions include temperatures which are at least 
20.degree. F. above the temperature in the conventional stripping zone, 
preferably at least 50.degree. F. above the temperature in the 
conventional stripper, and most preferably temperatures in the hot 
stripper are at least 100.degree. F. or more hotter. 
A stripping gas or medium, preferably steam, is used in all strippers. 
Preferably from 0.5 to 5.0 wt % steam, based on the weight of spent 
catalyst, is added to the stripping zone, in addition to the amount of 
stripping steam used in the conventional stripper. 
COKE COMBUSTOR/CATALYST RECIRCULATION 
The process of the present invention calls for a coke combustor immersed 
within the fluidized bed of regenerated catalyst maintained in an 
Orthoflow type regenerator, such as that shown in the figures. 
The design of a coke combustor is not, per se, the present invention, such 
devices are used in refineries throughout the world. The invention 
involves a new process and apparatus for controlling the amount of hot 
regenerated catalyst which is recycled into the coke combustor from the 
bubbling dense bed. This catalyst recycle is essential to heat the coke 
combustor enough to "light" it. For this reason, all commercial high 
efficiency regenerators are believed to operate with catalyst recycle, 
using an external catalyst recycle line, with catalyst flow controlled by 
one or more hydraulic slide valves. These valve, usually cost over 
$1,000,000, and usually are used in pairs to permit maintenance work 
during operation. They are believed essential by most refiners for 
positive control over catalyst recirculation to the coke combustor. 
An alternative was proposed for use in an Orthoflow type regenerator which 
involved used of a suspended bell coke combustor. U.S. Pat. No. 5,032,251, 
incorporated by reference, disclosed such a design which will work but 
requires relatively large open areas, in part because the delta P, or 
head, available to control flow is much less--on the order of 1 to 5 
feet--than the head available in a conventional high efficiency 
regenerator design (non-Orthoflow). The '251 design could permit large 
swings in catalyst flow if the second dense bed catalyst level changes, 
and may not lend itself to operation with a special (large bead) CO 
combustion promoter we would like to be able to use. Many refiners want a 
more positive means of controlling catalyst recirculation to the coke 
combustor, preferring one that is not so sensitive to slight changes in 
dense bed level. 
We discovered a way to reliably control the flow of recycled regenerated 
catalyst to the coke combustor, without using slide valves. Our device is 
unusual. It bears some resemblance to 1/2 of a U trap valve but our 
fluidizing gas inlet is on the wrong side of the U trap, besides only 
having 1/2 of the U trap. A preferred design is shown in FIG. II. 
The preferred, FIG. II design, has a sealed coke combustor. A U trap or 
preferably a trough conduit as shown in FIG. II transfers hot regenerated 
catalyst from the second fluidized bed to the coke combustor provides. 
This design also provides an ideal way to reliably move both the 
conventional FCC catalyst and bead type CO combustion promoter from the 
dense bed region to the coke combustor. 
By control of the amount of fluidizing gas used at one or more places 
within the device, flow can be essentially turned off or flow unimpeded. 
Unlike most valveless catalyst flow control means, this trough flow 
controller reduces catalyst circulation as air flow is increased. This 
effect will be discussed at greater length in the discussion of trough 
design. 
While use of, e.g. a fluidized U trap to move fluidized catalyst from one 
fluidized bed to another is not new, it has never been done in a coke 
combustor immersed in an Orthoflow regenerator, and never been done in 
such a way that increasing air flow decreased catalyst flow. The trap 
concept of FIG. II, which is only 1/2 of a classical U trap, and with 
fluidization gas on the wrong side of the U, works especially well when 
transporting a mix of bead CO combustion promoter and FCC catalyst, in 
that the beads can help seal the base of the trap or trough, or limit 
catalyst flow therethrough, if desired. 
Most of the implementation of the design of the trough is conventional and 
routine. Those skilled in the design of cracking units can calculate the 
relative sizes of the bubbling dense bed, the fast fluid bed region, the 
relative head available to drive fluid flow from the dense bed region to 
the FFB region, and size the unit from there in accordance with the 
following guidelines. 
We prefer to operate with a bubbling dense bed having a depth of at least 2 
and less than 20 feet, preferably with 4 to 15' and most preferably with 5 
to 10' of depth. We prefer to minimize the size of the bubbling bed. There 
should be enough bed depth to seal the return line to the reactor and to 
seal trough recycle line and to provide the residence time desired for 
additional catalyst regeneration, if any, in the bubbling bed. We refer to 
a bubbling dense bed, because in practice most of these units will 
continue to operate this portion of the units as a bubbling dense bed (to 
meet other unit constraints such as catalyst entrainment in the dilute 
phase region), but more vigorously fluidized regimes may be used, such as 
turbulent fluidized beds. 
When operated as a conventional bubbling dense bed, with a superficial 
vapor velocity of around 2 to 21/2 fps, the bubbling dense bed density 
will typically range from around 29 to 30 #/cubic foot to 30 to 35 #/cubic 
foot. There are different places to measure such densities, and different 
ways of interpreting results, but these numbers are typical. 
The coke combustor, of or fast fluid bed region should have a depth at 
least equal to that of the bubbling bed, and may be much deeper, or 
taller, than the bubbling bed. FFB regions having a depth 20% or 50% or 
even 100% greater than the bubbling bed are contemplated. In many 
installations the FFB region will share a common floor with the bubbling 
bed (the floor being the shell of the previous regenerator vessel), and 
the FFB height will be from 10' to 20-25'. Superficial vapor velocity in 
the FFB region is the primary factor in creating a fast fluidized bed 
region. The superficial vapor velocity may range from a low of around 3 up 
to about 10 fps. For most FCC units, these are the upper and lower limits 
on fast fluidization, with velocities lower than this giving bubbling 
fluidized bed conditions, and velocities higher than this leading to 
dilute phase flow. Preferably the FFB region operates at about 4 to 8 feet 
per second, and most preferably at about 4.5 to 6 fps of superficial 
vapor velocity. 
When operating as a conventional FFB, the superficial vapor velocity will 
be around 5 fps, and the dense phase density may range from a value of 
around 5 #/ft.sup.3 up to 10 to 15 #/ft.sup.3, while the upper regions of 
the FFB region will be in dilute phase, with a much lower density, perhaps 
ranging from as low as around 1-11/2 #/ft.sup.3 up to 2-5 #/ft.sup.3. 
Again there are different ways and places to measure these densities, but 
those skilled in the cracking arts would recognize these vapor velocities 
and catalyst densities as typical of fast fluid bed conditions. 
The trough or valveless catalyst transfer means permitting catalyst to flow 
from the bubbling dense bed region to the coke combustor preferably has a 
cross sectional sufficient to permit the desired amount of catalyst to 
flow from one region to the other. In many units, from 0.3 to 3, and 
preferably from 1 to 2, weights of hot regenerated catalyst will flow into 
the coke combustor per weight of stripped catalyst entering the coke 
combustor. It is important to have at least about 1100.degree. F. in the 
coke combustor to "light" the coke combustor, and most refiners recycle 
much more than this minimum amount. 
Because the material in the trough will usually be in the dense phase, a 
small trough, with only 3 to 25% of the surface area of the FFB region 
will usually surface. 
The trough or transfer means should have a height equal to at least 50% of 
the dense bed depth, and preferably has a height equal to the dense bed 
depth, or more. If the dense bed is 6' deep, a trough should be at least 
3' deep. 
The trough should include one or more air or other fluidizing gas inlet 
means, preferably at a plurality of elevations in the trough. If both FFB 
and bubbling bed region share a common floor, and the bubbling bed region 
is 6' deep, and the trough comprises a scallop or cut length of pipe 4' 
long, fluidization air inlets may be provided at 1' and 3' above grade. 
The fluidization air should not be added at the base of the trough, or at 
a 0' elevation as that would cause most of the air to short circuit 
directly into the FFB region. 
Addition of fluidizing air at such intermediate trough elevations, 1' and 
3' will reduce the density of material in the trough, and reduce the head 
or driving force used to move catalyst from the bubbling bed to the FFB 
region. If large amounts of fluidizing air or other gas are added, this 
trough region can be forced into the fast fluidized bed flow regime so 
that there will be very little driving force (only 2' in this scenario) 
and the material flowing will have a low density, so that not much 
catalyst will be transferred from the bubbling bed region to the FFB. 
Reducing the amount of fluidizing air added to the trough will increase the 
density of material in the trough, and increase catalyst flow from the 
second bed to the FFB region. The density in the trough can be increased 
to 15-40 #/ft.sup.3 depending of superficial vapor velocity in the 
fluidized bed in the trough. 
This sort of arrangement, a common floor for FFB, trough base, and bubbling 
bed, will complicate circulation of bead or other large particulate 
catalyst, and is included to show the relative elevations of dense bed, 
trough depth, and trough air inlets. It would be necessary to provide some 
means for transferring bead CO combustion promoter from the dense bed 
region to the FFB region independent of the trough, if the trough inlet 
were 4' up in the dense bed. Thus a small notch could be cut in the base 
of the FFB region, or in the trough, to allow a limited amount of catalyst 
traffic, and for return of entrained large particles or bead CO combustion 
promoter to the FFB region. 
Preferably the trough inlet is near the base or floor of the bubbling bed 
region, as shown in FIG. II. This makes the trough an almost automatic 
method of recycling entrained large bead CO combustion promoter to the FFB 
region. 
CIRCULATING CO COMBUSTION PROMOTER 
Use of a circulating CO combustion promoter in the regenerator or 
combustion zone is not essential for the practice of the present 
invention, however, it is preferred. These materials are well-known. 
U.S. Pat. Nos. 4,072,600 and 4,235,754, which are incorporated by 
reference, disclose operation of an FCC regenerator with from 0.01 to 100 
ppm Pt metal or enough other metal to give the same CO oxidation, may be 
used with good results. Very good results are obtained with as little as 
0.1 to 10 wt. ppm platinum present on the catalyst in the unit. 
NON-CIRCULATING CO COMBUSTION PROMOTER 
The trapped, or non-circulating CO combustion promoters, are a preferred 
but not essential part of the present invention. They provide a way to 
achieve complete CO combustion in the coke combustor, but only partial 
coke combustion. 
By the term non-circulating, we mean that the CO combustion promoter does 
not have fluidization characteristics like the conventional FCC catalyst. 
Preferably the FCC regenerator is designed so that the large particle CO 
combustion promoter will have at least an order of magnitude longer 
residence time in the FFB region of the regenerator than the conventional 
FCC catalyst, and preferably 2 or 3 orders of magnitude more residence 
time in the regenerator considered as a whole than the FCC catalyst. 
The "non-circulating" promoters preferably circulate a lot within the 
regenerator, i.e., they preferably will have considerably up and down 
mobility within the coke combustor, and also may circulate freely from the 
second dense bed back to the coke combustor. 
We believe this free circulation of catalyst, and of a fast settling larger 
particle coke combustor which does not circulate, is the key to a robust 
design. Our approach, when coupled with appropriate regenerator design, 
lends itself to operating with unusual amounts of Pt combustion promoter 
in the catalyst, but without sending this Pt to the cracking reactor. 
The non-circulating promoter is preferably a relatively high surface area, 
alumina rich material, which is highly attrition resistant. Moving bed 
cracking catalyst support, with or without any zeolite present, provides 
an excellent support for our preferred CO combustion promoter. Such 
supports are about 1/8" in diameter and are readily fluidized. Moving bed 
cracking units used an "air lift" to move such particles around moving bed 
cracking units, provided sufficiently high vapor velocities are present. 
Such materials are also amazingly strong, even though they have an 
apparent bulk density similar to that of conventional FCC catalyst. 
These support materials, which may be termed for purposes of convenience, 
"bead CO combustion promoter" will have usually have particle sizes above 
200 microns, and preferably of 250 to 25,000 microns, more preferably 500 
to 12,500 microns. The TCC bead catalyst discussed above, having a roughly 
1/8" diameter (roughly 3000 microns) has almost ideal fluidization 
properties, as it has a settling velocity at FCC conditions of around 6-8 
fps, and will stay a long time within the FFB region, and yet be able to 
move freely within the region. This permits the benefits of high Pt 
loading to be seen or felt throughout the FFB region, rather than in just 
a thin layer where larger particles would accumulate. 
Less preferred are conventional moving bed reforming catalysts, or even 
conventional sized particles of fixed bed reforming catalyst, typically 
spheres or extrudates having an average particle size of about 1/16th 
inch. The extrudates do not have the favorable flow characteristics of 
spheres, and are not preferred, but they should work. Spent reforming 
catalyst may be better used in many refineries as a non-circulating CO 
combustion promoter than as Pt source. 
The optimum size and physical properties of the non-circulating support 
correlates to a great extent with the unit design. If a refiner wishes to 
operate with a CO combustion promoter, and coke combustor design, so that 
the promoter is essentially trapped within the CO combustion promoter, 
then a relatively dense, fast settling promoter, with relatively large 
amounts of Pt present is preferred. Large, dense extrudates will work well 
in such service, but much of the coke combustor will operate without the 
apparent presence of Pt because of the rapid settling characteristics of 
such materials. 
When a refiner wishes to promote extensive circulation of non-circulating 
promoter from the coke combustor through the dilute phase transport riser 
to the second dense bed, a bead type promoter is preferred along with 
superficial vapor velocities sufficiently high to ensure transport of 
beads throughout, and out of, the FFB region. To maximize use of promoter 
to transfer heat, and to also promote CO combustion, it will be best to 
adjust the settling characteristics in the coke combustor and transport 
riser to that of the bead, so that circulation rates of beads approach, or 
even exceed, the circulation, by weight, of conventional cracking 
catalyst, and also to operate so that 30 wt % to 50 wt % or even more of 
the particulate matter in the coke combustor is recycled beads rather than 
FCC catalyst. 
This approach has many advantages. The residence time of the FCC catalyst 
in the high steam environment of the coke combustor is reduced. Heat 
transfer from the second bed (of hot regenerated catalyst) is accomplished 
to a great extent by transferring heat from catalyst in the second dense 
bed to the beads sinking through the second bed and returning to the coke 
combustor. Reducing the residence time of spent catalyst in the coke 
combustor, and presence of large amounts of Pt in the coke combustor, 
provides a broad operating window in which partial coke combustion, but 
complete CO combustion, may be achieved. Conditions can be set so that the 
coke combustor can reliably burn from, e.g., 10 to 90% of the total coke 
on catalyst while achieving complete CO combustion at all times. 
By complete CO combustion we do not necessarily mean that the flue gas 
discharged from the dilute phase transport riser will contain 100 ppm or 
less CO, but we do mean that the flue gas will contain so little CO that 
the amount of afterburning can be readily tolerated when this stream 
combines with an oxygen rich flue gas from the second fluidized bed. 
SCOOP DISENGAGER 
The coke combustor and dilute phase transport riser discharge a mixture of 
catalyst and flue gas into the dilute phase region above the second 
fluidized bed, or second dense bed, in the Orthoflow regenerator, 
preferably via a scoop disengager. 
In conventional high efficiency regenerators the mixture is simply 
discharged, usually sideways or down, into a large diameter region above a 
bubbling dense bed. This would cause disastrous particulate loading in a 
conventional regenerator, but can be tolerated in single stage high 
efficiency regenerators because of the way catalyst and flue gas are 
discharged and because of the low superficial vapor velocities in the 
second dense bed and dilute phase region above it. 
Unrestrained discharge of catalyst into a dilute phase region in an 
Orthoflow regenerator would cause excessive catalyst traffic in the dilute 
phase. While a cyclone separator could be added to the dilute phase riser 
discharge, this also adds a lot of weight, cost, and pressure drop to the 
unit. 
The design of the present invention uses a scoop disengager to effect a 
90+% separation of FCC catalyst from flue gas exiting the transport riser. 
Of course such a design will recover well over 99% of bead type promoter, 
if bead type CO combustion promoter is used. It achieves enough separation 
of FCC catalyst to permit much higher superficial vapor velocities to be 
used in the second fluidized bed.