Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Th~ present invention relates to an apparatus for
and a method of separating particles from a gas stream,
and is particularly useful in the field o~ recovering
energy from the discharge gas flow from a fluid catalytic
cracking unit regenerator vessel.
In the past it has been known to recover energy
from the discharge flow from a catalytic cracking unit
regeneratorvessel by passing the discharge gases through
a waste heat boiler using the recovered heat to boil water
to generate a steam flow which can then pass through a
power recovery turbine. However, the efficiencies of the
waste heat boiler and of the turbine used in the ste~m
system leads to a very poor recovery rate of th~ total
available energy in the outlet stream from the catalytic
cracking unit regenerator.
In accordance with one aspect of the present
invention we provide apparatus for separating solid particles
from a gas stream comprising a plurality of cyclone separator
ve~sels connected in parallel to be fed from a common gas
source and to discharge to a common gas outlet, each of the
cyclone separator vessels having a cylindrical separator
chamber of substantially uniform internal diameter along its
length of from 20 inches to 40 inches~ and being provided with
means for discharging the separated solid particles from the
bottom of the said cylindrical separator chamber. Such a
sepaxating apparatu~ i~ capable of a very high separation
efficiency coupled with a low rate of erosion by the solid
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particles which enter the separator vessel by way of the
inlet stream, and hence can be used to separate all or
substantially all erosive solid particles from the discharge
stream of a catalytic cra~king unit regenerator thereby
allowing the discharge flow to enter directly into a power
recovery turbine. Thu~s the recovery of energy from the
fluid catalytic cracking unit regenerator discharge flow
can be carried out more efficiently than hitherto by
separating ou~ the solid particles from the discharge flow
from the regenerator vessel, using the separating apparatus
of the present invention and then passing the separated
gases directly into a power recovery turbine.
The ~hoice of the particular diameter range in
accordance with the present invention enables an extremely
efficient separating action to be achieved with nevertheless
a very low degree of erosion of the separator vessel walls
so that the customary refractory or ceramic lining in the
separator chamber can be avoided. For optimum results the
inlet velocity to the individual separator vessels will be
carefully related to the vessel diameter to give best
separating efficiency with minimum erosion of the walls of
the separating vessels. Although the range of diameters
available in the cylindrical cyclone separator chambers
of the present invention extends from 20" to 40",
preferably 24" to 36", we find that a diameter of 30" gives
optimum results.
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Where the assembly of cylindrical cyclone
separators is to supply the power recovery turbine in a
fluid catalytic cracking unit~ the avoidance of refractories
or ceramics in the separator vessels is particularly
advantageous since this eliminates the possibility of parts
of the separator lining breaking away and constituting a
safety hazard to the blades of the power recovery turbine.
In a preferred form of the present invention, therefore,
each of the cylindrical cyclone separator chambers is formed
of austenitic steel ~ithout any inner anti-erosion lining.
The low erosion rate in the separatin~ apparatus of the
present invention results both from the fact that the
separator vessels are cylindrical, rather than conical or
part-conical, and from the fact that the diameter of the
separator vessel proper is in the range of from 24 inches
to 30 inches. ~f course a conical or part-conical solids
^ collecting hopper may be provided at one end of the
cylindrical separator vessel but there will be no appreciable
vortical gas flow at that part of the device so no erosion
w~ll be expected.
Advantageously all of the cyclone separator vessels
are fed from a common inlet manifold and they discharge to
a common outlet duct by means of one or more discharge
manifolds.
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More advantayeously, each cyclone separator
vessel has a respective solids-collecting hopper which
discharges to a solids collector vessel for centralised
removal of the recovered solidsO
Desirably the individual cyclone separator
chambers are each pressurised to the same pressure as the
exhaust duct from a catalytic cracking unit regenerator,
and the system pressure is maintained along the solids
discharge pipe from each cyclone separator vessel~
Alternatively, if desired, the various cyclone
separator vessels can be incorporated in a main pressure
vessel~ This has the advantage of simplified pressuri-
sation of the separating apparatus but can often provide
difficulties of maintenance or replacement of individual
cyclone separators, when necessaryO
Conveniently each cylindrical cyclone separator
has its respective solids-collecting hopper attached at
its lower end and the main cyclone separator vessel
opens into the solids-collecting hopper at a location
~0 spaced bel.ow the top of the solids hopper so as to a:Llow
the swirling solid particles to be flung radially
outwardly from the gas vortex in the separator, thereby to
separate from the gas stream which can then escape
vertica.lly upwardly along the core of the vortex towards
the gas discharge duct at the top of the cylindrical cyclone
separator vesselO
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According to the present invention we also
propose a method of ope.rating a fluid catalytic
cracke~ unit comprising: discharging the product gas
and entrained particulate solids from secondary cyclone
separators within the regenerator chamber and conveying
the stream to a gas/particle sepa:rating assembly
comprising a plurality of individual cylindrical cyclone
: separator vessels in parallel, each cyclone separator
vessel having an internal diameter in the range from 20
inches to 40 inches, and the number of separators being
chosen to suit the exhaust gas flow rate from the
catalyst regenerator; recovering the particles of
catalyst from the solid discharge section of each of the
individual cylindrical cyclone separating vessels;
collecting the cleaned gas discharge flow from each
separator of the assembly in a common discharge flow, .
passing this co~non discharge flow to an energy recovery
turbine; and using the energy recovery turbine to drive .
an air compressor for supplying the inlet air to the
regenerator chamber.
In order that the present invention may more
readily be understood the following description is given
by way of example, with reference to the accompanying
drawings in which:-
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- Figure 1 is a side elevational view showing a
cyclone separator cluster in accordance with the present
nventlon;
Figure 2 is a top plan view of the cluster of
S Figure 1,
Figure 3A is a schematic view showing a prior
art energy recovery system for a fluid catalytic cracking
unit, and Figure 3B shows a possible more efficient
arrangement using separating apparatus in accordance ~-
with the present invention.
In Figures 1 and 2, there can be seen a cluster
of individual cylindrical cyclone separator vessels 1
around a partially refractory-lined inlet manifold 2 in
the form of the exhaust line ~rom a high pressure catalytic
cracking unit regenerator. The individual cyclone separator
vessels 1 have feed ducts 3 which introduce the particle-
laden gas tangentially into the top of each separator
to generate a vortex coaxially within the vessel 1.
From the top of each of the cylindrical separator
vessels 1, the particles swirl round the axis of the
chamber while descending towards a solids~collector hopper
4 at the foot of each cylindrical vessel 1, while the gases
from the core of the vortex, now cleaned of substantially
all the solids content, are discharged upwardly through
exhaust duct 5 into the respectlve one of two exhaust
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manifolds 6a and 6_o
sy the time the solids content has dropped into
the solids-collecting hopper 4, separation will have been
complete and the particles then build up in a pile in the
bottom of the conical hopper section 7 before descending
along the inclined dust-discharge pipe ~ into a central
dust-collector vessel 9.
In accordance with the present invention, each
of the cylindrical cyclone separator vessels has an
inner diameter of from 20 inches to 40 inches and can
consequently be matched to the desired gas throughput
rate, so as to be subject to a sufficiently reduced
degree of erosion (as compared with the erosion experienced
in a conventional conical cyclone separator) that the walls
of the cylindrical separator chamber of the vessel 1 and
those of the solids-collecting hopper 4 at the foot of each
vessel 1 can be formed of austenitic .cteel without the
need for any refractory lining to improve the erosion-
resistance properties of the chamberO The length o the
cylindrical separator chamber will be designed appropriate
to the degree of separation ef~iciency re~uiredO In the
preferred embodiment of the apparatus the internal diameter
of the cyclone separator vessels 1 is 30 inches~
Each of the separator chambers has an optimum
throuyhput rate of solids-laden gas for separation, so as
th~ total throughput of ~he separa~r unlt i9 required to
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be increased, for example in order to incorporate the
separator assembly into a larger catalytic cracking plant,
so the number of individual cylindrical separators of the
form shown at 1 in Figure 1 has to be increased, if
possible without departing from the preferred cyclone
separator vessel diameter of 30 inches but definitely
remainin~ within the range of values ~ from 20 inches to
40 inches.
A further feature of the present invention lies
in the fact that each separator vessel together with its
inlet ducting 3, its gas outlet ducting 5 and its dust
outlet pipe 8 forms part of the pressurised system in the
exhaust from the catalytic cracking unit regeneratorO
Thus rather than being encased within a pressure vessel,
each of the separators together with its feed and
discharge ducting constitutes a separate pressure vessel
to which access can readily be obtained for maintenance and/
or removal when required. Equally, it is possible to
incorporate adjustment means in the system connected to
each individual cyclone separator vessel so that the
system can be tuned for optimum separation efficiency
of each individual cyclone separator vessel in the assembly.
Not only does the design of cyclone separator
apparatus according to the present invention allow the use
of austenitic steel without introduciny any erosion hazard,
but also the austenitic material is sufficiently heat-
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resistant to accommodate a steady running temperature of1,450F in the inlet stream, with occasional transients
up to 1800F. By choosing a cyclone separator vessel
diameter in the range of 20 inches to Llo inches, it is
possible to ensure that the individual cyclone separators
will be free from blockage or build up of solidsO The
feed rate of s`olids-laden gas through each inlet pipe 3 w.ill
be carefully calculated to permit optimum separation levels
to be achieved within the separator without overloading
the separator to the extent that dust and other solid -
particles build up in the disentrainment hopper 4 at a
rate which is higher than can be accommodated by the
solids discharge pipe 8.
With the austenitic steel walled cylindrical
cyclone separator chambers 1 proposed in Figures 1 and 2,
it is possible to maintain the internal pressure of
approximately ~.0 atmospheres absolute, while nevertheless
operating at the extremely high temperatures without any
need for a refractory or other ceramic lining within the
cylindrical cyclone separator chamber 1.
Another advantage of providing a cluster of
individual cylindrical cyclone separator vessels forming
separate pressure vessels of an .integrate~ assembly, lies
ln the fact that a continuous pressurised feed of the
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separated solids component from the conical section 7 of
the solids collecting hopper, along the solids discharge
pipe and into the central solids collector vessel 9, can
be established without the need for additional conveying
means to transfer the collected solids to the central
collector~ Furthermore, the discharge from the collector
vessel 9 can be by way of pneumatic conveying using
the gas pressure prevailing in the cyclone separator
ehamber 1 as the conveying gas (in this case approximately
1% of the discharge gas flow entering the cyclone separator
assembly will be used for conveying away the solids in the
form of a pneumatically eonveyed stream).
Alternatively, a valve may be provided at the
bottom of the solids collector vessel 9 and equipped with
some form of air lock to preserve gas pressure within the
colleetor vessel g while allowing intermittent discharge of
the collected solids onto a mechanical conveyor for disposal.
For example the eollector vessel 9 may discharge through
a first shut-off valve, into a disentrainment hopper whose
outlet ineludes a second shut-off valve.
Figures 3A and 3B exempli.fy the advantages which
can be derived using the cyclone separator assembly shown
in Figures 1 and 2.
Figure 3A illustrates a conventional energy
recovery system in a fluid catalytic cracker unit and shows
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that the regenerator vessel 10 includes both primary and
secondary separators 11 and 12, respectively, of
conventional form feeding a discharge pipe 13 leading to a
waste heat boiler 14. The spent flue gas from the boiler
14 i~ discharged through flue 15 while water heated in the
boiler is converted to steam in the line 16 to be fed
to the inlet of a steam turbine 17. The shaft of the
steam turbine 17 is linked to an air compressor 18 to
supply air to the înlet feed to the regenerator vessel 10.
In the e~ample of Figure 3A, if the efficiency
of the waste heat boiler is assumed to be 30%, and the
efficiency of the combination of steam turbine 17 and
compressor 18 (14%), then for every one hundred units of
heat energy in the stream passing along pipe 13 from the
regenerator chamber 10, thirty of these units are present
in the steam line 16 and only four of these units of energy
will be evident in the line from the air compressor 18.
Since the feed to the catalytic cracking regenerator chamber
10 requires twelve units o heat in the air supply~ eight of
the units, i.e. 8% of the energy requirement, must be
supplied from outside the system by external topping up.
A much more efficient way of recovering the
energy in the line 13 can be appreciated from the
alternative system illustrated in Figure 3 B where again
the regenerator chamber 10 has primary and secondary
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cyclone separators 11 and 1~ of conical design, with the
secondary conical cyclone separators 12 feeding a discharge
line 13. This discharye line feeds a separating system 19
which is in fact the assembly or cluster of individual
cyclone separating vessels 1 illustrated in Figures 1 and
2 and runs with a very high separating efficiency. The
solids content is removed from the discharge flow and
then the flow passes on from the separating cluster 19
into a discharge line ~ towards the gas turbine 17aO
~ow that there has been no pressure loss due to
the escape of flue gases ~as through flue 15 in Figure
3A) the pressure in the feed to the gas turbine 17a is
much higher and so also will be the pressure in the
discharge line 21 from the turbine 17a. This discharge
gas stream from the turbine 17a can therefore enter the
waste heat boiler 14a where again the heat energy is used
to generate a flow of steam in line 16a while the waste
gas is e~hausted through the flue 15a. The gas turbine
17a is linked directly by its output shaft to the input
shaft of a primary air compressor 18a which supplies the
total air feed requirements for the cracking regenerator
chamber 10. Alternatively the turbine 17a may dri~e an
electric generator for supplying electrical power for
use on plant or for other purposes.
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The steam from the waste heat boiler feeds a
steam turbine 17b from which part of the inlet air
supply is generated by means of the directly coupled
secondary air compressor 18bo
The degree of efficiency of the revised system
shown in Figure 3B is such that of every one hundred
units of energy leavi.ng the regenarator chamber 10,
twelve units will appear in the flow of air from the
primary air compressor 18a into the regenerator chamber
10, while a further three units of energy will appear
in the air flow from the secondary air compressor 18b.
A simple comparison of the result of the two
systems shown in Figures 3A and 3B indicates that
whereas in Figure 3A the energy recovery system was
capable of meeting only 1/3 of the energy input
requirements for the chamber 10, the system in Figure
3B enabled the primary compressdr 18a alone to meet the
full energy requirements, and the secondary compressor
18b offered a surplus energy availability corresponding
to 1/4 of the total energy requirements for the reactor
10 (i~e~ three units as compared with the energy require-
ment of twelve units for the regenerator 103O
The system of Figure 3B is an idealised
situation which has been unattainable in practice due to
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the difficulty of combatting erosion in the primary
exhaust gas turblne 17a. It has been known in the past
for turbines protected by a prior art cyclone separator
system, to become useless after a runnlrlg time of a mere
eight hours due to erosion occurring within the conical
cyclone separators~
In a practical example using the cyclone
separator assembly in accordance with the present
invention, a fluid catalyticcracking unit regenerator
discharging solids-laden gas at a pressure of 2.5
atmospheres absolute was arranged to feed a cluster of
16 cylindrical cyclone separator vessels 1 arranged to
be fed from the common exhaust line 13 (Figure 3B)~ The
cluster of vessels 1 (equivalent to the schematically
~: 15 illustrated cyclone separator 19 in Figure 3B) then had
its gas discharge passed through conduit 6a to a common
feed line into the gas turbine 17a. Because of the
much higher efficiency of separation afforded by the
cyclone separator assembly in accordance with the present
invention, the turbine life has been extended to a
considerable extentO For example, there was no measurable
loss of turbine efficiency after 27,000 hours running time.
With the cyclone separator assembly in accordance
with the present invention it is generally true that the
solids carryover in the air exik l.ine from the separators
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has only 5% in the form of particles la:rger than 10
microns in diameter.
In one particular example, the analysis of the
particles dischargedfrom the cyclone separator assembly
in accordance with the invention was such that 95% of
the carryover was less than 10 microns:~ 94% of the
carryover was known to have been less than 5 microns,
and 92.5% was less than 2.5 micronsO Since particles of
two microns or less i.n diameter pass through a power
recovery turbine without even impacting the blades, it
is clear that the efficiency of separation made possible
by the cyclone separator assembly of the present invention
is adequate for providing a satisfactory life to the
turbine. Equally, it is known that particles of 10 : -
microns or more are certain to contact a blade at some
stage during a pass through a power recovery turbine and
the fact that a mere 5% of the carryover is likely to be
greater than 10 microns provides evidence of the fact that
there is a very low likelihood of blade damage by particle
impact~
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