Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR THE CLEAN-UP OF PARTICULATE-CONTAINING GASES
The need for clean-up of particulate containing
gases for environmental purposes as well as for purposes
05 of system economics and efficiency is well known.
Although electrostatic precipitlators have been used by
many industri~s their history of poor performance and
large down times leave them undesirable for many uses.
Conventional cyclone separation means are widely used in
a variety of situations including many where the capacity
of multiple cyclones are required. Cyclone ~fficiency is
greatest with heavier loaded gas streams, i.e. gases
- containing larger amounts of particulate. Exiting gas
streams from initial or primary clean-up syste~s, i.e.
the overflow gases, in many instances contain environ-
mentally unacceptable levels of particulates and must
thus undergo further clean-up before exhaust to the
atmosphere is permitted. Moreover, where the particulate
entrained in the flue gas is of value, i.e. comprises
catalyst or other costly procPss reagents, secondary and
tertiary clean-up of the exiting flue gases is econom-
ically, as well as environmentally, dictated. In some i-
instances, such as flue gases from the second stage of a
two-stage catalyst regeneration system, the temperatur~
of the flue gases is hi~h and the relative amount of par-
- ticulates to the volume of gas is very low so that the
effectiveness of cyclone separation has been questionable.
Generally, there are a number of problems associated
in situations where such additional flue gas clean-up is
required, especially in process plants with capacities
which require more than one cyclone in parallel. When- i!
ever cyclones are used, the pressure differential
through the separator means must be watched in order to
avoid an imbalance whereby particles exiting as underflow
are sucked back in~o the separator. Typically, exit
diplegs are used with the dipleg ends beneath a fluidized
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bed of the separated particles. When multiple cyclones
are utilized, it is important that the essential charac-
teristics of the flue gases, and in particular the
pressure, antering each of the different cyclone units be
05 kept uniform. Small pressure changes in the fluidized
bed can detrimentally effect cyclone operation by cre-
ating pressure imbalances. A common plenum or chamber
configuration for the cyclones has been used in order tD
aid maintenance of egual inlet pressures for multiple
cyclones as disclosed in U.S. Patent No. 4,257,788.
Nevertheless, control of the pressure differential
between cyclone inlets and outlets, particularly, the
underflow outlet continues to be a problem.
Combined processes for catalytic cracking of hydro- F
carbons and catalyst regeneration are known in the art
and are typical of processing where secondary flue gas
clean up is mandated both environmentally and economic-
ally because of the catalyst value~ One such combined
system is that described in U.S. Patent Nos. 4,331,533;
4,332,674 and 4,336,160, for converting residual oils by
high temperature catalytic cracking and the associated
high temperature catalyst regeneration. The CO2 rich
flue gases exiting from the second stage regeneration are
at high temperatures, such as about 1300F to 1800F, and
have entrained catalyst fines and sulfur oxides.
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Brief Description of the Invention
This invention relates to a process for cleaning
particulate containing gases by inputting the particulate
containing gases at a first pressure into cyclone sepa-
rators to separate the particula~e containing gases into
a substantially particulate free gas overflow and a gas
containing particulate underflow, exiting the underflow
at a second pressure and controlling the amount of gas in
the underflow by controlling the difference between the
first pressure and second pressure.
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In the preferred embodiment of the invention, a
housing is separated into an upper or first zone and a
lower or second zone with the cyclone separators located
in the first zone. The particulate-containing gases are
05 passed into the first zone and portions of these gases
~nter each cyclone separator at uniform conditions of
pressure. In each cyclone these gases are separated into
a substantially particulate free gaseous overflow and a
gas containing particulate underflow which underflow
exits through diplegs or other means into the second
7one. ~he amount of gas in the underflow is controlled
by controlling the difference between the pressure in the
first zone and the pressure in the second zone. This is
preferably accomplished by controlling the pressure in
the second zone such as by controlling the amount of gas
exiting the second zone~ The amount of gas in the
underflow is preferably in the range of about 0.5 to 5.0
volume percent of the particulate containing gases passed
into the first zone.
The method for this invention is particularly useful
in utilizing flue ~ases from a second stage catalyst
regeneration from fluid catalyst cracking processes, such
as that described in U.S. Patent Nos. 4t331,533; 4,332,674
and 4,336,160. High temperature flue gases containing catalyst
particles as described therein are cooled according to the
present invention by being first passed through suitable means to
produce steam and reduce the temperature of the flue gases The
cooling of the flue gases reduces the viscosity of the flue gases
and lowers the volume of the gases so that increased dust loaaing
is obtained, all of which result in higher efficiency in the
operation of the cyclone separators. The cooled flue gases at the
reduces temperature are then fed into the first zone to be
processed as described above the invention also pro-
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vides means for removing sulfur oxides from the overflowgases.
It is an object of this invention to separate
particulate containing gases into a gaseous overf'ow and
05 a gas containing particulate unclerflow while controlling
- the amount of gas in the particulatè underflow.
It is another object of this invention to process
particulate containing gases by passing the particulate
containing gases at a first pressure into separating
means to separate the particulate-containing gases into a
gaseous overflow and a gas-containing particulate under-
flow at a second pressure and controlling the amount of
gas in the underflow by controlling the differT ce
between the first pressure and the second pressure.
It is a further object of this invention to provide
a system for processing high temperature flue gases from
a combined hydrocarbon catalytic conversion and two-stage
catalyst regeneration process to generate steam, to
separa~e catalyst fines therefrom and to remove sulfur
oxides therefrom.
Other features and advantages of the invention will
be apparent from the ~ollowing more particular descrip-
tion of preferred embodiments as illustrated in the
accompanying drawing. The drawing is not necessarily to
2~ scale, emphasis instead being placed upon illustrating
the principles of the invention.
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Brief Description of the Drawing --
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The drawing is a schematic illustration of the
various components used in one embodiment of this inven-
tion wherein the particulate-containing gases are flue
gases from a catalyst regeneration process.
Detailed Description of the Draw ng
-35 A system for processing particulate containing gases
is disclosed in the drawing. A closed housing 2 is '~;
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divided into an upper zone 4 and a lower zone 6 by a
baffle 8. A plurality of cyclone separators 10 arxanged
in parallel are mounted in the upper zone 4. An exit
passage, e.g. a dipleg 12, extends from each of the
05 cyclone separators 10 and passes through the baffle 8
into the lower zone 6 using the bellows 14. An en-
trance 16 is provided in the wall of the upper zone 4 so
that particulate containing yases may be passed through
the entrance 16 into the upper zone 4. A conduit lB is
10 connected at one end 20 for fluicl communication with the
lower zone 6 and at the other encl 22 is connected for
fluid communication with a stripper cyclone 24. Sepa-
rated catalyst fines move from the stripper cyclone 24 to
the lower zone 6 through conduit ~6. Substantially
15 particulate ~ree gas moves from the stripper cyclone 24 Lr
through conduit 28. ~eans 30 are provided in the con- ,~
duit 28 so that an orifice through which the particulate
free gas moves may be varied for a purpose to be de-
scribed below.
Particulate containing gases are charged through
entrance 16 into the upper zone 4 in which a plurality of
parallel arranged cyclone separators 10 are provided with ~-
separate flue gas inlet openings thereto. The individual
cyclone diplegs 12 pass downwardly through a solid baffle -
member 8 separating upper zone 4 from a lower catalyst
collecting zone 6 therebel~w. The diplegs 12 used in
this invention are much shorter than conventional diplegs --
and are provided only t~ assure a passageway through the O-
baffle 8. In the preferred embodiment, the length of the r~
30 dipleg 12 from the top 12a, at the junction of the `~
dipleg 12 with the lower conical portion of the cyclone --
separator, to the end 12b of the dipleg is at least three -
times the diameter of the dipleg. The diplegs 12 are '
sealed with respect to baffle 8 by the expandable bel- t~-
35 lows 14 permitt:ing maintaining a lower pressure in lower t
zone 6 than in upper zone 4. In this arrangement of
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apparatus the particulate-containing gases to be treated,
e.g. flue gases, with entrained particulates, are charged
into zone 4 for evenly distributed flow at uniform, i.e.
substantially equal, conditions of velocity, pressure,
05 etc. into each of the plurality of cyclone separators 10.
Preferably the velocity of the particulate containing
gases charged to the inlets of the cyclone separators 10
iq within the range of about 75 to about 110 feet per
second. Since the cyclone separators 10 are located
within the upper zone 4, portions of the particulate
containing gases enter each of the cyclone separators 10
under essentially the same, i.e. uniform, conditions.
Cyclone separated particulates pass downwardly,through
the cyclone separator to the cyclone dipleg 12 and then :~
to lower zone 6 maintained at a pressure lower than that
in upper zone 4. Since the upper zone 4 is at a slightly ,-
different pressure than the lower zone 6, the diplegs can
be relatively short and are used only to provide a ,~
passageway from the upper zone 4 to the lower zone 6.
Some of the original gas moves as underflow gas with the
particulates into the lower zone 6. The presence of some
quantity of underflow gas in the particulate underflow is
a necessity to avoid intermittent back flow in diplegs
between the cyclone separators with subsequent loss of
efficiency resulting from slight pressure pulsations
during operation. The underflow gas may be removed from
the lower zsne 6 and passed through a suitable conduit to
a water wash zone as explained below or to the atmosphereO ~
If exhausted directly to the atmosphere, suitable scrubber ~~
30 means can be located in the upper zone 4. The pressure ~f.
in the lower zone 6 is controlled by varying a restrict-
ing orifice so that the flow of the underflow gas into
the lower zone 6 is in the range of 0.5 to 5.0 percen~ by
volume of the ~otal flue gas entering into the upper
35 zone 4. Collected catalyst fines may be withdrawn from l~-
the bottom of zone 6 through a lock hopper system 32 and
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then conveyed by conduit 34 to the regeneration zone or
to another part of a fluid catalytic cracking process by
conduits as desired. Other means such as pressurized gas
and/or a catalyst classifier may be used instead of the
05 lock hopper system.
In the preferred embodiment, the gases of the
gas-containing particulate underflow are recovered from
the lower zone 6 and passed by conduit 18 to a smaller
stripper cyclone ~4 outside the lower zone 6 from which
they are vented to the a~mosphere or recovered and
processed as discussed below. The flow of the underflow
gas through the diplegs 12 with the separated particu-
lates is controlled so as not to exceed more than about
0.5 to 5.0 percent by volume of the total flue gas
lS entering the upper zone 4 by varying a restricting
orifice in the means 30 in the conduit 28 connected ~o -
stripper cyclone 24. Varying the restricting orifice
controls the pressure in the lower zone 6. Since the
amount of gas in the underflow depend~ on the difference
~20 in pressure in the upper zone 4 relative to the lower
zone 6, controlling *he pressure in the lower zone 6 will ~-
control the difference in pressure and therefore, the
amount of gas in the underflow.
The above de~cribed method for the processing of
particulate containing gases is particularly useful in
the reco~ering of catalyst fines from the hot flue gases
discharged from the second stage of a two stage catalyst s
regeneration system. These hot flue gases contain both '-
catalyst fines and sulfur oxides.
Referring now to the drawing, there is provided an
- arrangement of apparatus for recovering catalyst fines
entrained with hot regeneration flue gas without encoun-
tering many of the prior art problems associated with
separating hot sour flue gases and pressure balance c
dipleg requirements for recovery of cyclone separated
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catalyst fines, particularly with multiple cyclones. In
a particular arrangement of catalyst regeneration in
stages, the highest temperature flue gases which are CO2
rich and recovered from the uppermost catalyst regenera-
05 tion zone ~re at an elevated temperature above about1300F up to about 1800F. On the other hand, the flue
gases recovered from the first stage of catalyst regenera-
tion rich in CO combustion product gases comprising
sulfur oxides r steam and some hydrogen sulfide are
recovered at a temperature within the range of about
1100F up to about 1500F. In the regeneration sequence
used in this invention, it is intended that the uppermost ~-
second stage of catalyst regeneration be at a higher
temperature than the first stage by a considerable amount
to achieve desired catalyst temperatures as discussed in
Patent Nos. 4,331,533; 4,332,674 and 4,336,160.
The second stage of catalyst regeneration is normal-
ly effected at a pressure lower than the pressure in the
first stage by about 5 to 10 psig. Typical pressure in
the second stage is in the range of 10 to 25 psig,
preferably about 15 psig. Thi~ lower pressure decreases
the water partial pressure and thus, increases the -
catalyst stability. The pressure utilized depends upon -
the pressure balance of the system to achieve desired
catalyst flow therethrough. It will be recognized by
those skilled in the art, however, that the flue gas ~
processing system hereafter described may be employed ^
with a process comprising a single stage of catalyst
regeneration permitting lower temperature catalyst
regeneration or with each stage of a two-stage catalyst
regeneration operation herein described either alone or
combined. Combusting CO rich regeneration flue gases in - !
a zone external to the regeneration zone is further !-.
contemplated. High temperature product gases recovered ,t~,:
from such combustion may be used in generating process
steam either separately or in combination with hot CO2
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rich regeneration flue gases recovered from the second
stage of catalyst regeneration before processing to
remove entrained catalyst fines and sulfur oxides as
discussed below.
0~ In the arrangement illustrated in the drawing, a
second stage catalyst regeneration zone 36 i5 disclosed.
Regeneration zone 36 is provided with radiating conduit
means 38 in open communication with external cyclone
separators 40. Diplegs 42 return separated catalyst
lO particles from the cyclone separator to a mass of cata- -
lyst being regenerated in zone 44. ~igh temperature flue
gases rich in CO2 and comprising entrained particles of
catalyst are recovered from the cyclone separation zones
as a combined flue gas stream-46. The flue gases with
15 entrained catalyst fines may enter the cyclone separators
40 at a veloci~y within the range of about 70 to 150
ft./second but preferably not above about 110 ft.~second
when employing catalyst particles of an average particles
size selected from within the range of about 60 microns
20 up to about 100 microns. ;
High temperature combustion flue gases in excess of T',
about 1300F with entrained catalyst fines in conduit 46
are passed to a steam generator 48 wherein the flue gas
is typically passed downwardly through steam generator 48
25 in indirect heat exchange with boiler feed water passed
upwardly through a plurality of finned heat exchange
tubes. The fins preferably extend in a longitudinal
direction so as to lessen the tendency to exode and
provide for a self cleaning effect. The steam generator
30 or indirect heat exchanger may be housed in a larger ;~
diameter weather shield permitting upflow of cooling air
to cool the shell t-emperature of the heat exchanger
sufficient to permit the use of carbon steel or low
chrome steel. It is preferred that the velocity of the
35 flue gases entering the heat exchanger be adjusted to L
provide a velocity thereof not substantially above about
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75 feet per second for flow therethrough and recovery
therefrom at substantially the same velocity~ The flow
of flue gases into and downwardly through the heat
exchanger is substantially a sel:E cleaning operation~
05 which keeps the tubes with heat collecting fins clean for
maximum heat exchange with boilex feed water. In one
specific operating environment the flue gas with entrained
fines is recovered from the heat exchanger at a pressure
sufficiently elevated for cascade through the system
discussed below. Thus the pressure of the flue gas may
be in the range of about 10 to 25 psig when passed
- through a conduit of a size restriction which increases
the heat exchanger discharge velocity of about!75 feet
per second to a higher velocity up to about 100 or 150
feet per second and at a lower temperature not substan
tially exceeding and preferably below about 1000F.
Significant advantages are attributable to processing
cooler flue gas with entrained catalyst particles. That
is, downstream cyclone separating means are much more
efficient since the flue gas viscosity is lower and the
volume of ~he gas becomes lower permitting the use of 'r
smaller and more efficient cyclones. Also the entrained
catalyst fines or dust loading of the cooled flue gas ~-
necessarily increases which contributes to improving
cyclone separation efficiency. A further significant
advantage resides in minimizing the need for hot vapor
expansion joints and for permitting the use of less
expensive carbon steel for downstream cooled flue gas
cyclones and for vessels housing a plurality of such
cyclones. ~he cooled gases move through conduit 50 and
- then through entrance 16 into the upper zone 4 to be
processed as described above.
Flue gases separated from entrained catalyst fines
~y the plurality of parallel arranged cyclones 10 are
35 collected in means 52 and pass as a common flue gas `-~
stream in conduit 54 for discharge to the atmosphere
where permitted or processed as hereinafter discussed.
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The flue gases recovered from a catalyst regeneration
zone will comprise sulfur oxides in a concentration
dictated in substantial measure by the heavy oil feed
subjected to the catalytic cracking process in which the
05 catalyst is initially employed and the extent of sulfur
removed with cracked reaction products. Thus flue gases
separated from one or more catalyst regeneration zones
and separated from entrained catalyst fines as above
discussed may require further treatment to recover sulfur
10 oxides particularly therefrom before venting to the -
atmosphere. Therefore, in accordance with the flue gas
treatment process of this invention, cooled flue gases
comprising sulfur oxides and relatively free of catalyst
fines, i.e. in which the entrained particles or fines
15 have been minimi7-ed according to the process of this
invention, are passed in contact with a water wash and a
compound of ammonia in 20ne 56 to react with sulfur
oxides to form sulfates thereof recoverable from the flue
gases before venting thereof to the atmosphere by means 5g.
20 Chemicals other than ammonia compounds can be used to
absorb or complex the sulfur oxides. Flue gases recovered
from stripper cyclone 24 may also be passed to said water
wash step as required to remove sulfur oxides. In some
instances, conduit 60 is provided to add gas to assist in
25 moving catalyst particles through and out of the lower -
zone 6 through the lock hopper system.
In yet another aspect, it is not unusual to add up
to about 10% of fresh catalyst for a daily replacement ~
rate. ~owever, depending upon the the place of addition ~--30 in the circulating catalyst system, it is observed that - ~;
some of the fresh catalyst will be rapidly lost before -
use as equilibrium catalyst in the circulating cat`alyst
system. To obviate this condition, it is proposed to add
the makeup catalyst under appropriate conditions to the
3~ circulating catalyst in the combination operation up~
stream of the riser hydrocarbon feed inlet but downstream É
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of the ultimate catalyst regeneration zone in one or more
catalyst regeneration zone arrangements. On the other
hand CO rich flue gas combustion products may be added by
conduit 62 to conduit 46 for charge to heat exchanger 48.
05 It is also contemplated employing more than one indirect
heat exchanger in parallel flow arrangement for recover-
- ing heat from high temperature flue gases derived from
either one or both of the two-stage regeneration zones
discussed above. In any of these arrangements it is
preferred that combustion flue gas products be cooled to
a level consistent with maintaining an economic opera
tion.
Having thus generally discussed the metho~ and
process of this invention and particularly described and
discussed operating embodiments ~hereof, it is to be
understood that no undue restrictions are to be imposed
by reasons thereof except as defined by the following
claims.
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