Heat exchanger with backmix and flow through particle cooling

A method and apparatus for cooling hot particulate material uses a heat exchanger zone having an upper portion that operates in a flow through mode and a lower part that operates in a back mix mode. Particulate material descends from a collection zone into an upper inlet of a heater exchanger. The exchanger contains a series of tubes for indirect heat exchange of the particulate material with a cooling fluid. Particulate material leaves the exchanger through an outlet located at a mid portion of the exchanger. The section of the exchanger between the inlet and outlet comprises the flow-through portion. Particulate material undergoes further heat exchange below the outlet of the exchanger in the backmix portion. Fluidizing gas that enters at the bottom of the exchanger provides the necessary turbulence for particle interchange on the backmix portion of the cooler as well as transport of the particulate material through the flow through portion of the exchanger. The method and exchanger design facilitates the addition of surface area to the exchanger and increases the heat removal duty in the backmix portion of the exchanger.

FIELD OF THE INVENTION 
This invention relates to methods and heat exchangers for heating or 
cooling particulate material. More particularly, this invention relates to 
methods for heating or cooling hot particles by indirect heat exchange and 
heat exchangers for use therein. 
BACKGROUND OF THE INVENTION 
Heat exchangers for heating or cooling particulate comminuted or fine grade 
material by indirect contact with a heating or cooling fluid are well 
known. Heat exchangers of this type maintain the particulate material in a 
fluidized state with fluidizing medium that passes upwardly through a bed 
of the material. A series of conduits comprising tubes, channels or coils 
are positioned within the fluidized bed. A fluid passes through the 
conduits to add or remove heat from the fluidized solids by indirect heat 
exchange. Fluidized solids are continuously supplied to the fluidized bed 
and fluidized solids are continuously withdrawn from the bed. Methods of 
supplying or withdrawing solids from the bed through exchanger include 
flow through and backmix type exchangers. There are two basic versions of 
flow through coolers; one uses gravity feed wherein particulates enter an 
upper inlet and exit a lower outlet, and the other employs fluidized 
transport that moves particles from a lower inlet past the cooling 
conduits and out an upper outlet. In a backmix operation particles are 
circulated through a common inlet and outlet that exchanges particles with 
the rest of the process. 
Heat exchangers for the indirect heating or cooling of particulate material 
have found widespread application in a number of industrial processes. 
These processes include treatment of mineral matter, the handling of 
metallurgical ores, the manufacture of petrochemicals and the conversion 
of hydrocarbons. A number of exchanger configurations have evolved to suit 
the needs of these different processes. 
Indirect heat exchangers of the above-described type have been finding 
increasing use as particle coolers on the regenerators of processes for 
the fluidized catalytic conversion of hydrocarbons. The fluidized 
catalytic cracking process (hereinafter FCC) has been extensively relied 
upon for the conversion of hydrocarbon streams such as vacuum gas oils and 
other relatively heavy oils into lighter and more valuable products. In 
the FCC process, starting hydrocarbon material contacts a finely divided 
particulate catalyst which is fluidized by a gas or vapor. As the 
particulate material catalyzes the cracking reaction, a by-product of the 
cracking reaction referred to as coke is surface-deposited thereon. A 
regenerator, which is an integral part of the FCC process, continuously 
removes coke from the catalyst surface by oxidation. Oxidation of the coke 
releases a large amount of heat which in part supplies the heat input 
needed for the cracking reaction. As FCC units have been called upon to 
process heavier feeds, greater amounts of coke must be removed in the 
regeneration zone with a corresponding increase in the amount of heat 
generated therein. This additional heat poses a number of problems for the 
FCC process. The excess heat can upset the thermal balance of the process 
thereby requiring a lowering of the circulation of hot catalyst from the 
regenerator to the reactor which in turn can lower the yield of valuable 
products. In addition, the excess heat may raise temperatures to the point 
of damaging the equipment or catalyst particles. Therefore, it is 
advantageous to have a means of lowering the regenerator temperature. For 
reasons of temperature control and process flexibility, heat exchangers 
having cooling tubes located outside the regenerator vessel have become 
the method of choice. 
An important consideration in the FCC process as well as other processes 
that involve the handling of particulate material is the transport of the 
particulate material. It is often difficult to incorporate a heat 
exchanger having the necessary dimensions to provide the desired degree of 
particulate heat transfer into the constraints of the process arrangement. 
In the main, these constraints involve obtaining sufficient exchanger 
length to accommodate the required surface area of the exchanger conduits 
and providing inlets and outlets for the movement of the particles between 
the exchanger and the rest of the process unit. In the case of an FCC 
process unit, addition of a particle heat exchanger may necessitate 
raising the entire structure, or the incorporation of extra conduits and 
fluidization devices in order to meet the exchanger design requirements. 
When the particle heat exchanger is added to a newly designed FCC unit, 
the increased elevation and/or added conduits and fluidization devices 
raise costs and complicate construction of the unit. It is also popular to 
retrofit particulate heat exchangers into existing FCC process units. In 
these cases, the structural constraints may not only add to the cost of 
the unit, but may not permit the incorporation of a particulate exchanger 
having the desired heat removal capacity. 
The use of a backmix type exchanger, as previously mentioned, will simplify 
the incorporation of the particle heat exchanger into any process since it 
only requires the use of a single inlet/outlet conduit. However, the 
overall heat exchange capacity of this type of device is limited by the 
amount of catalyst circulation that can be obtained over its vertical 
length. Moreover, the overall heat transfer per length of cooling conduit 
available in the backmix cooler is lower than in the flow through type 
exchanger where catalyst flows from an inlet in one end of the heat 
exchanger to an outlet at the opposite end. Finally, an additional layout 
constraint of the backmix type cooler is its need for a very large 
inlet/outlet conduit in order to obtain adequate particle circulation 
between a retention, the heat exchanger and the region where the particles 
are withdrawn and retrieved. Therefore, a backmix type exchanger cannot 
overcome many of the layout problems associated with the incorporation of 
a remote particle heat exchanger into a process that requires heating or 
cooling of particulate material. 
INFORMATION DISCLOSURE 
U.S. Pat. No. 2,377,657 issued to G. W. Watts shows a process involving the 
transport of particulate material, comprising a catalyst for use in a 
fluidized catalytic cracking process, by gravity flow into an inlet 
located at one end of an elongated heat exchanger that cools the particles 
by indirect contact with water. The water passes through a series of 
conduits for the generation of steam. Cooled particles leave through an 
outlet located at an opposite end of the exchanger and are upwardly 
transported away from the outlet by a fluidizing medium. This reference is 
cited for its general showing of a particle heat exchanger having a 
gravity feed of particulate material. 
U.S. Pat. No. 2,862,798 issued to McKinney teaches a process for cooling 
FCC catalyst particles wherein the particles are withdrawn from a 
regenerator by gravity flow and transported by a fluidizing medium 
upwardly through a particulate heat exchanger for indirect cooling with a 
cooling fluid. The fluidizing medium transports the catalyst upwardly to a 
cooler outlet and back to the regenerator. This reference shows the use of 
a fluidizing medium to transport particulate material through a heat 
exchanger. 
U.S. Pat. No. 2,970,117 issued to Harper shows a particle heat exchanger 
that receives hot catalyst particles from an FCC regenerator through an 
upper inlet and empties the particles from a lower outlet into a riser 
conduit that uses a fluidizing gas to transport the cooled catalyst 
particles back to the regenerator. This reference shows the use of a 
fluidizing medium to transport cooled particulate material back to the 
vessel from which it was withdrawn. 
U.S Pat. No. 3,672,069 issued to Reh et al. shows a backmix type fluidized 
bed heat exchanger where catalyst is mixed by a fluidizing gas in a series 
of compartments and transported across the top of the compartments. Each 
succeeding compartment has a lower elevation so that the particles 
gravitate to a final compartment from which the particulate material is 
withdrawn. Conduits within the compartments receive a heat exchange fluid 
for cooling or heating of the particulate material. This reference shows 
the generalized use of backmix type particle heat exchangers. 
In U.S. Pat. No. 2,492,948 a heat exchanger for cooling particulate 
material receives FCC catalyst particles at its upper end through an outer 
annular area which carries the catalyst to the bottom of the heat 
exchanger where a fluidizing medium transports the catalyst upwardly 
through a series of conduits containing cooling fluid and ejects the 
catalyst back into the regenerator at a higher elevation than that from 
which it was withdrawn. This reference shows a particle heat exchanger 
having internal means for receiving and transporting catalyst through the 
device. 
U.S. Pat. No. 4,439,533 issued to Lomas et al. depicts a particle heat 
exchanger of the backmix type that exchanges FCC catalysts between the 
heat exchanger and a catalyst particle retention zone in the regenerator. 
This reference shows the use of a backmix catalyst cooler in an FCC 
process. 
U.S. Pat. No. 4,434,245 issued to Lomas et al. is directed to the use of a 
particle heat exchanger in an FCC process having a catalyst disengaging 
zone and a separate combustion zone. Hot catalyst particles are taken from 
the disengaging zone, transported downwardly through the cooler in 
indirect heat exchange with a cooling fluid and taken from the bottom of 
the heat exchanger to a lift riser for transport of the catalyst into the 
combustion zone. This reference shows the use of a particle heat exchanger 
in an FCC process having a lower combustion zone and an upper catalyst 
retention zone. 
In U.S. Pat. No. 4,396,531, hot catalyst from the retention zone of an FCC 
regenerator supplies particulate catalyst to a heat exchanger for cooling 
the particulate catalyst by indirect contact with water and transfers the 
cooled catalyst to an FCC reactor. This reference shows the removal of 
cooled particulate material from the FCC regeneration zone. 
U.S. Pat. No. 4,238,631 issued to Daviduk et al. shows a heat exchanger for 
cooling particulate catalyst from an FCC regenerator having a hot catalyst 
inlet in the middle of the heat exchanger vessel, a catalyst outlet at the 
bottom of the heat exchanger vessel for returning catalyst to the 
regenerator, and a conduit at the top of the exchanger for venting gas 
from the heat exchanger back to the regenerator. Cooling fluid conduits 
located below the catalyst inlet remove heat from the catalyst by indirect 
heat exchange therewith. This reference shows a particle inlet in a mid 
portion of a particle heat exchanger. 
U.S. Pat. No. 2,735,802 issued to Jahnig depicts a particulate heat 
exchanger that receives particulate catalyst from an FCC regenerator 
through an inlet located at a mid portion of the heat exchanger. Catalyst 
is returned to the regenerator through an outlet located at the bottom of 
the heat exchanger and a conduit located at the top of the heat exchanger 
vents gases back to the regenerator. The exchanger has conduits above and 
below the catalyst inlet for circulating coolant. The inventory of 
catalyst particles in the heat exchanger is adjusted to vary the level of 
catalyst in the heat exchanger and in contact with the cooling conduits in 
order to vary the amount of heat removal. This reference shows a heat 
exchanger with heating and cooling conduits above and below a particle 
inlet. 
SUMMARY OF THE INVENTION 
This invention is a method of heating or cooling particulate material by 
indirect heat exchange of the particles with a heat exchange fluid in a 
heat exchanger having an upper flow through portion and a lower backmix 
portion. Using a backmix exchanger zone below a flow through exchanger 
zone provides additional surface for the cooling conduits and increases 
the total heat removal capacity of the exchanger. Operation of the 
exchanger is also simplified by this design since the heat removal 
capacity of the exchanger can be varied by regulating the amount of 
fluidizing gas or vapor that enters the backmix portion of the exchanger. 
The percentage of heat removal from the backmix portion can be increased 
to its maximum or reduced to zero by using fluidizing gas varying in 
amount from a maximum to none at all. 
It is an object of this invention to increase the heat transfer capacity of 
particle heat exchangers. 
It is a further object of this invention to provide a method of cooling 
particles and a particle heat exchanger having improved heat transfer 
capacity. 
Another object of this invention is to provide a particle heat exchanger 
that is easily adapted to the configuration of the equipment supplying the 
particles. 
A yet further object of this invention is to improve the method of 
regulating heat transfer in the indirect heat exchange of particles with a 
heat exchange fluid. 
Accordingly, in one embodiment, this invention is a method for indirect 
heat exchange between fluidized particles and a heat exchange fluid. The 
method comprises collecting hot particles in a particle collection zone, 
at a first elevation, and transferring the particles by gravity flow 
through a particle inlet to the top of heat removal zone located at a 
second elevation below the first elevation. The particles are fluidized in 
a heat removal zone, at least in part, by introducing a fluidizing gas 
into the heat removal zone. Heat is removed from the particles in the heat 
removal zone by indirect heat exchange with the heat transfer fluid in a 
first section where the particles flow from the inlet to an outlet in a 
central portion of the heat removal zone and in a second section below the 
inlet and outlet wherein there is no net particle flow. Relatively cool 
particles are recovered from the heat removal zone through the particle 
outlet and pneumatically transported from the outlet to the first 
elevation. 
In a further embodiment, this invention is a process for cooling hot 
fluidized catalyst. The method includes passing catalyst particles having 
coke deposited thereon to a combustion zone, passing an oxygen-containing 
gas into contact with the catalyst to oxidize the coke contained thereon, 
withdrawing hot catalyst from the regeneration zone, and passing the hot 
catalyst to a remote heat removal zone through a catalyst inlet. 
Relatively cool catalyst particles are recovered from the heat removal 
zone through a catalyst outlet. Heat is removed from the catalyst by 
indirect heat exchange with a cooling fluid in an upper section of the 
heat removal zone and a lower section of said heat removal zone. The upper 
section of the heat removal zone has a net flow of catalyst particles 
therethrough while the lower section of the heat removal zone has no net 
catalyst particle flow. The catalyst in the heat removal zone is fluidized 
by passage of a fluidizing gas therethrough. 
In a yet further embodiment, this invention is directed to an apparatus for 
heating or cooling fluidized particles. In combination, the apparatus 
contains a vertically oriented elongated heat exchanger for indirectly 
contacting the particles with a heat transfer fluid, with the exchanger 
having upper and lower heat removal sections, a plurality of heat exchange 
tubes, each tube having a substantial surface area in each of said 
sections, and a particle inlet and particle outlet located at opposite 
ends of the upper heat removal section for admitting particles and 
withdrawing particles from said exchanger. 
Other embodiments, details and arrangements of the present invention are 
described in the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention, in its process aspects, consists of steps for the 
heating or cooling of a fluidized particulate solid. The method and 
apparatus of this invention can be used for either the heating or cooling 
particles, however, for the sake of simplicity, the description will only 
make reference to particle cooling. An important application of the 
invention will be in a process for the combustion of a combustible 
material from fluidized solid particles containing the combustible 
material, including the step of introducing oxygen containing combustion 
gas and the fluidized solid particles into a combustion zone maintained at 
a temperature sufficient for oxidation of the combustible material. The 
combustible material will be oxidized therein to produce a dense phase 
fluidized bed of hot fluidized solid particles cooled by the process of 
this invention. 
The above combustion zone may be in dilute phase with the hot particles 
transported to a disengaging zone wherein the hot particles are collected 
and maintained as the first mentioned bed, or the combustion zone may be 
in dense phase and in itself comprise the first bed. 
In a particularly important embodiment of the invention, there will be 
included steps for the regenerative combustion within a regeneration zone 
of a coke containing FCC catalyst from a reaction zone to form hot flue 
gas and hot regenerated catalyst, disengagement and collection of the hot 
regenerated catalyst, cooling of the hot regenerated catalyst in a heat 
removal or, as more often referred to, cooling zone comprising the heat 
exchanger of this invention and the return of the cooled regenerated 
catalyst to the regeneration or reaction zone for control of the 
temperatures of the catalyst in the regeneration zone. For the purposes of 
an FCC process, the term "hot regenerated catalyst" means regenerated 
catalyst at the temperature leaving the combustion zone, from about 
1300.degree. to about 1400.degree. F., while the term "cool regenerated 
catalyst" means regenerated catalyst at the temperature leaving the 
cooling zone, the latter of which is up to 200.degree. F. less than the 
temperature of the hot regenerated catalyst. 
Reference will now be made to FIG. 1 for a discussion of the particle heat 
exchanger and the method of invention. In FIG. 1, regeneration gas, which 
may be air or another oxygen-containing gas, enters a combustion zone 10 
through a line 11, and is distributed by a dome style distribution grid 
12. Air leaving the grid mixes with coke contaminated catalyst particles 
entering the combustion zone through a conduit 13. These streams are shown 
as flowing separately into the combustor zone 10, however, each stream 
could flow together into a mixing conduit before entering combustion zone 
10. Coke contaminated catalyst commonly contains from about 0.1 to about 5 
wt. % carbon, as coke. Coke is predominantly comprised of carbon, however, 
it can contain from about 5 to about 15 wt. % hydrogen, as well as sulfur 
and other materials. The regeneration gas and entrained catalyst flows 
upward from the lower part of combustion zone 10 to the upper part thereof 
in dilute phase. The term "dilute phase", as used herein, shall mean a 
mixture of catalyst particles and gas having a density of less than 30 
lbs/ft.sup.3, and "dense phase" shall mean such mixture equal to or more 
than 30 lbs/ft.sup.3. Dilute phase conditions, that is, a catalyst/gas 
mixture of less than 30 lbs/ft.sup.3, and typically 2-10 lbs/ft.sup.3, are 
the most efficient for coke oxidation. As the catalyst/gas mixture ascends 
within combustion zone 10, the heat of combustion of coke is liberated and 
absorbed by the now relatively carbon-free catalyst, in other words by the 
regenerated catalyst. 
The rising catalyst/gas stream flows through a riser conduit 14 and 
impinges upon the top of a lateral conduit 15, which impingement changes 
the direction of flow of the stream and directs the catalyst and gas 
mixture through outlets 16. The impingement of the catalyst/gas stream 
upon surface 15 and the change of direction through outlets 16 causes most 
of the hot regenerated catalyst flowing from the combustion zone to 
disengage from the flue gas and fall to the bottom portion of 
disengagement zone 20 which comprises a hot particle collection chamber or 
fluid particle collection section. Although zone 20 is referred to as a 
disengaging zone, this term also embraces the possibility that additional 
regeneration or combustion may be carried out in this zone. The catalyst 
collection area of the disengagement zone may be an annular receptacle, as 
shown, or any other shape appropriate for collecting catalyst particles. 
Catalyst in the bottom of the collection zone is maintained as a dense bed 
26 having an upper level 27. The gaseous products of coke oxidation and 
excess regeneration gas, or flue gas, and the uncollected portion of hot 
regenerated catalyst particles flow up through disengagement zone 20 and 
enter catalyst/gas separators such as cyclones 21 through an inlet 22. 
Catalyst particles separated from the flue gas falls from the cyclones to 
the bottom of disengagement zone 20 through dip legs 23 and 24. The flue 
gas exits disengagement zone 20 via conduit 25, through which it may 
proceed to associated energy recovery systems. 
Hot catalyst particles are removed from the disengaging zone and 
transferred to an FCC reactor via a conduit 44 or returned to the 
combustion zone via conduit 46. A valve 48 regulates catalyst flow through 
conduit 46. Catalyst particles are also returned to the combustion zone 
following prior passage through a cooling zone. 
With further reference to FIG. 1, the cooling zone is comprised of a heat 
exchanger 30 having a vertical orientation with the catalyst in the shell 
side and the heat exchange medium, supplied and recovered by lines 32 and 
33, passing through a tube bundle 31. The preferred heat exchange medium 
would be water, which, in further preference, would change only partially 
from liquid to gas phase (steam) when passing through the tubes. It is 
also preferable to operate the heat exchanger so that the exchange medium 
is circulated through the tubes at a constant rate. The tube bundle in the 
heat exchanger will preferably be of the "bayonet" type wherein one end of 
the bundle is unattached, thereby minimizing problems due to the expansion 
and contraction of the tubes when exposed to and removed from the high 
regenerated catalyst temperatures. The heat transfer that occurs is, from 
the catalyst, through the tube walls, and into the heat transfer medium. 
The upper portion of heat exchanger 30 is in sealed communication with the 
bottom portion of the disengagement zone through a conduit portion 34 and 
an inlet 35 which serves as a withdrawal point for removing catalyst from 
dense bed 26. Cool catalyst is withdrawn from a mid-portion of exchanger 
30 and returned to the combustion zone 10. Catalyst is withdrawn from the 
mid-portion through an outlet 37 and delivered to a conduit 38 having a 
flow control valve 39. Valve 39 regulates catalyst particle flow out of 
conduit 38. That portion of the heat exchanger bounded by inlet 35 and 
outlet 37 is referred to as the flow through portion and operates with a 
net flow of catalyst through this portion. The portion of the heat 
exchanger below outlet 37 is termed the backmix portion. The lower or 
backmix portion of the exchanger will have at least 10% of the heat 
removal capacity of the exchanger and preferably will have a heat removal 
equal to at least 25% of the total heat removal capacity of the exchanger. 
Fluidizing gas, preferably air, is passed into a lower portion of the shell 
side of heat exchanger 30 via lines 36 and 40, thereby maintaining a dense 
phase fluidized particle bed in the shell side. Lines 36 and 40 have 
valves 36' and 40' respectively positioned thereacross to regulate the 
flow of fluidizing gas. The fluidizing gas effects turbulent backmixing in 
the backmix portion of the heat exchanger and allows catalyst particle 
transport through the flow through portion of the exchanger. It is only 
necessary to add fluidizing gas to the exchanger through lower fluidizing 
gas line 36. As fluidizing gas flows upward, it effects the necessary 
backmixing for heat transfer in the backmix portion of the heat exchanger 
and as it passes into the flow through portion of the heat exchanger, 
provides fluidization for catalyst particle transport. Heat removal, or in 
other words heat exchanger duty, can also be controlled by adjusting the 
flow rate of gas addition through line 36. A higher flow rate will 
increase heat transfer and raise the exchanger duty. Although it is only 
necessary to add the fluidizing gas to the bottom of the heat exchanger, 
fluidizing gas may be added at any number of locations. Adding fluidizing 
gas at the locations as shown in FIG. 1, allows independent control of 
exchanger duty in the backmix portion. A minimum amount of fluidizing gas 
is always needed to maintain good catalyst transport through the flow 
through portion of the cooler. Line 40 can be used to supply all or a 
portion of this minimum fluidizing gas when heat removal demands require 
little or no duty from the backmix portion of the exchanger. This permits 
the flow of fluidizing gas through line 36 to be regulated to zero, if 
necessary, however, a minimal amount of fluidizing equal to less than 5% 
of the total will be added through the bottom nozzle whenever the 
exchanger is in operation. 
The tube bundle shown in the exchanger is of the aforementioned bayonet 
type in which all of the tubes are attached to a single tube sheet located 
at the bottom of the heat exchanger. A typical configuration of tubes in 
the bayonet-type bundle would be one inch tubes each ascending from an 
inlet manifold 42 in the head of the exchanger up into the shell through a 
three inch tube sealed at its top. Each one inch tube empties into the 
three inch tube in which it is contained just below the sealed end of the 
three inch tube. A liquid, such as water, would be passed up into the one 
inch tubes, would empty into the three inch tubes, would absorb heat from 
the hot catalyst through the wall of the three inch tubes as it passed 
downward through the annular space of the three inch tubes and would exit 
the heat exchanger, at least partially vaporized, from outlet manifold 43. 
It is important in the FCC process that the quantity of hot particles 
which enter heat exchanger 30 be sufficient to maintain a depth of dense 
phase fluid catalyst bed which substantially submerges the tubes in the 
dense phase bed. Submersion of tubes prevents overheating of tubes when 
circulation o cooling fluid is temporarily interrupted. Overheating poses 
problems when the tubes are made of carbon steel or other low metallurgy. 
The flow through portion of the exchanger is used to transfer cooled 
catalyst particles from the exchanger to the combustion zone. Cooled 
catalyst entering the combustion zone effects an overall temperature 
reduction throughout the combustion and disengagement zone. The flow 
through type of operation is characterized by large heat transfer rates 
that achieve a high degree of catalyst cooling. 
The backmix portion of the exchanger further reduces the temperature of the 
catalyst once it has passed through the flow through portion. It is known 
that backmixing can be obtained within the heat exchanger at reasonable 
superficial gas velocities that will circulate catalyst down the length of 
the backmix portion. The fluidizing gas addition affects the heat transfer 
coefficient directly by affecting the superficial velocity over the heat 
exchanger tubes and indirectly by influencing the extent of mass flow of 
catalyst through the backmix portion of the heat exchanger. The higher 
mass flow will also result in a higher heat exchanger duty because the 
average catalyst temperature in the backmix portion will be higher thereby 
providing a higher temperature difference to which the amount of heat 
transfer is directly proportional. Additional details on the operation of 
a backmix cooling zone can be found in U.S. Pat. No. 4,439,533. 
The use of a lower backmix and an upper flow through portion allow the heat 
exchanger to retain a simple design and have a longer length than could 
not have been obtained with either type of heat exchanger alone. If a flow 
through type heat exchanger having gravity feed of particles were used, 
the length of the exchanger would be limited by the height between the 
catalyst withdrawal point 35 and the outlet 37. Although there is enough 
overall height to use a backmix type cooler having the length shown in 
FIG. 1, the backmix circulation of catalyst over such a long length would 
require excessive amounts of fluidization gas and, in addition, would have 
low overall heat transfer performance. 
FIG. 2 shows the particle heat exchanger of this invention in combination 
with a different type of FCC regenerator. The regenerator has a single 
chamber in a vessel 50. Spent catalyst containing coke in an amount of 
from 0.1 to 5 wt. % enters the regenerator through a conduit 52. A lower 
conduit 54 delivers air to the regenerator which is distributed across the 
transverse cross-section of the vessel 50 by a distributor 56. Passage of 
the air through the catalyst oxidizes coke from the surface of the 
catalyst and maintains the catalyst as a dense fluidized bed 57 having a 
level 58. Regeneration gas and any catalyst entrained therein is carried 
upward and enters the cyclones through inlet 62. Cyclone dip legs 64 
return catalyst particles to bed 57. A nozzle 66 carries the regeneration 
gas from cyclones 60 and out vessel 50. Regenerated catalyst having a 
reduced coke concentration exits a lower portion of vessel 50 through a 
conduit 68 and reenters a reaction zone (not shown). 
A heat exchanger 70 communicates with catalyst bed 57 through a conduit 72. 
Heat exchanger 70 operates in substantially the same manner as exchanger 
30 shown in FIG. 1 and differs mainly in the orientation of the bayonet 
tubes and the means and method of returning catalyst to the regenerator. 
Exchanger 70 has a plurality of bayonet tubes 73 consisting of an inner 
tube that receives a heat exchange medium from an inlet manifold 74 and an 
outer closed end tube that returns the heat exchange medium to an outlet 
manifold 76. Lines 78 and 78' supply and remove the heat exchange medium 
from the cooler 70. An outlet 80, located in a mid-portion of the 
exchanger carries cool catalyst particles out of the exchanger and divides 
the exchanger into an upper portion that operates in a flow through mode 
and a lower portion that operates in a backmix mode. Fluidization gas can 
enter the exchanger through either or both of two fluidizing gas inlets 82 
and 84 located respectively just below outlet 70 and at the bottom of the 
exchanger. A conduit 86 takes cool catalyst from the outlet 80 at a rate 
regulated by a control valve 88. Cool catalyst flows out of conduit 86 in 
an external riser 90. A line 92 admits fluidization gas into riser 90 
which contacts the relatively cool catalyst and transports it back into 
the dense bed 57. 
The heat exchanger of this invention is especially useful in FCC 
arrangements of the type shown in FIG. 2. In these arrangements, the 
horizontal portion of line 92 lies very close to the ground elevation. 
Therefore, the length of the flow through type cooler cannot be increased 
without raising the entire regeneration vessel 50. This invention 
increases the length and corresponding heat transfer area of the cooler 
without raising the elevation of the entire vessel by utilizing space 
below the exchanger outlet and ground that would otherwise be unused. 
Locating the inlet and outlet manifolds at the top of the cooler 
facilities removal of the tube bundle by permitting it to be lifted from 
the top of the exchanger 
The following example demonstrates the advantages of using the exchanger of 
this invention to reduce the temperature of catalyst entering the reaction 
zone when processing a moderately heavy FCC feed. These examples are 
based, in part, on engineering calculations and commercial experience with 
similar operating units. The feed in this example is a blend of vacuum gas 
oil and residual oil having the properties set forth in Table 1. 
TABLE 1 
______________________________________ 
GRAVITY, .degree.API 26.2 
SULFUR, WT. % 1.2 
CONRADSON CARBON, WT. % 
1.74 
NICKEL WT. - PPM 1 
VANADIUM WT. - PPM 2 
VOL % AT 1050.degree. F. 
10 
______________________________________ 
EXAMPLE 
In this example the FCC feed was processed in an FCC reactorregenerator 
having an FCC riser reaction zone at process conditions summarized in 
Table 2. This example used a particle heat exchanger designed in 
accordance with this invention in an FCC unit of the configuration of FIG. 
1. The exchanger had a surface area of 975 square feet in the backmix 
portion and 975 square feet in the flow through portion. Fluidization gas 
was added only at the bottom of the exchanger at a rate of 166,000 
standard cubic feet per hour. Yield results for the feed conversion and 
conditions at selected locations of the process unit are given in Table 2. 
TABLE 2 
______________________________________ 
PROCESS CONDITIONS 
______________________________________ 
SPENT CATALYST 1000 
TO COMBUSTOR TEMP., .degree.F. 
REGENERATED CATALYST 1332 
TO REACTOR TEMP., .degree.F. 
CATALYST TEMP. 1332 
AT COOLER INLET, .degree.F. 
CATALYST TEMP. 1132 
AT COOLER OUTLET, .degree.F. 
COOLER DUTY IN BACK MIX 17 
PORTION COOLER 10.sup.6 BTU/HR. 
DUTY IN FLOW THROUGH 33 
PORTION, 10.sup.6 BTU/HR. 
CATALYST ADDITION, #/BBL 0.27 
YIELDS 
C.sub.2 -WT. % 4.24 
C.sub.3 LV. % 11.83 
C.sub.4 LV. % 15.35 
C.sub.5 -GASOLINE LV. % 59.51 
LCO LV. % 13.69 
CO LV. % 7.78 
COKE WT. % 5.82 
TOTAL LV. % 108.15 
______________________________________ 
The FCC embodiments illustrated by the Figures and the Example is only one 
possible application of the present invention which in its broadcast sense 
is a process for heating or cooling fluidized particles for any purpose. 
The apparatus aspect of the present invention in its broadest sense, as 
summarized above, may also be identified in the Figures.