Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR SEPARATING SOLID MATERIAL
IN A CIRCULATING Fl.UIDIZED BED REACTOR
The present invention relates to an apparatus for separating solid
particles from the flue gases of a reactor and for recycling the
separated solids to the reactor.
Circulating fluidized bea technique has long been used in various
reactors such as calcinators and recently to a larger extent in
combustion furnaces and gasifiers. In the known applications, the
separation of solid6 is carried out in a conventional cyclone
separator having a vertical axis and a hopper-shaped bottom. The
cylindrical vortex chamher of the cyclone is provided with a gas
discharge pipe which guides the gases upwards and the solids are
recycled to the reactor through a stand pipe via a gas trap. The
gas trap is employed to prevent reactor gase6 from flowing into
the cyclone through the stand pipe. A mechanical trap is most
commonly used as a gas trap. In more advanced applications a
fluidized bed of sand in a U-pipe is known to have been applied
for the purpose. The solids recycling system becomes complex and
expensive especially in high temperature reactors. Part of the air
required for fluidizing the gas trap flows upwards in the stand
pipe which has a detrimental effect on the separation of solids,
in particular on the 6eparation of light and fine particles.
Furthermore, the rising gas flow decreases the transport capacity
of the stand pipe.
As is known, a substantial vacuum and a high axial flow velocity
are created in the centre of a conventional cyclone due to which
the cyclone tends to draw the particles from the stand pipe. The
suction flow generated in this way has usually no tangential
velocity. Thus, almost all the solid material the flow carries
with it is transported out through the centre pipe of the cyclone.
A recycling system provided with a conventional cyclone is
therefore very sensitive to the suction flow from the stand pipe
and requires a reliable gas trap.
In steam boiler applications the use of a conventional
cyclone results in disadvantageous constructions a~ a conventional
cyclone divides the boiler into a separate combustion chamber and
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~ convection part downstream of the cyclone between which the
equipment for recycling the solids must be installed.
Mechanical gas traps are rapidly worn particularly in hot
condition and breakdowns in their operation are frequent.
5 Also, applications having a conventional cyclone in~talled inside
the reactor are known in which the whole solids recycling system
is built inside the reactor. This application has, however, severe
disadvantages such as cor~osion and erosion of the cyclone, as
cooling of the supporting structure cannot be arranged in a simple
way. Furthermore, as is the case in conventional cyclonss, the
arrangment inside the reactor is subject to sensitivity to the
suction flow from the stand pipe.
It is an object of the invention to provide an apparatus by whiQh
solid particles can be efficiently separated from flue gases
discharged from a circulating fluidized bed reactor, and recycled
to a desired point in the reactor.
In general terms, the present invention provides apparatus for use
with a circulating fluidized bed reactor, for separating solid
particles from the flue gases of the reactor and for recycling the
solid particles to the reactor, the apparatus comprising: a flue
duct for guiding the flue gases of the reactor obliquely
downwardly and away from the reactor; a vortex separator chamber
having a generally horizontal axis; deflecting means for changiny
the direction of the flow of a ma~or portion of the gases exiting
from said flue duct to direct the ga~es into said vortex separator
chamber; a return duat communicating with said flue duct and with
one end of said vortex separator chamber; and a ga~ discharge
concentric with ~aid generally horizontal axis and disposed in an
end wall of the vortex separator chamber.
The invention will now be described by way of exemplary
embodiments with reference to the accompanying diagrammatic,
simplifi ed dra~i ~gs, wherein:
Fig. 1 illustrates an embodiment of the invention in a vertical
sectional view taken along line A-A of Fig. 2;
Fig. 2 is a top view of the apparatus of Fig. l;
Fig. 3 is a view of a part of Fig. 1 in the direction of the
arrow B;
Fig. 4 is another embodiment of the invention in a vertical
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sec-tion taken along line C~C of Fig. 5;
Fig. 5 is a top view of the apparatu~ of ~ig. 4;
Fig. 6 is an alternative embodiment of the construction
illustrated in Fig. 3;
Fig. 7 is yet another embodiment of the construction
illustrated in Fig. 3; and
Fig. 8 is a sectional view taken along line D-D of Fig. 2.
In Figs. 1, 2 and 3, reference numeral 1 refers to a vertical
fluidized bed reactor from the upper part of which the flue gases
flow obliquely downwardly and away from the reactor 1, through a
flue duct 2. A separator 3 is disposed beside the reactor 1 such
that the inlet section of its horizontal vortex chamber 4 and the
discharge end of the flue duct 2 are di posed in a downwardly
tapering transition chamber 5 which is formed between a lower wall
6 of the flue duct 2 and an intarmediata wall 7 connected
tangentially to the cylindrical jacket of ~he vortex chamber 4.
The transition chamber 5 constitutes the inlet of a return duct
for solid material. The return duct 8 has a diameter which is
~maller than the diamater of the vortex chamber 4.
A gas discharge outlet 10, which is concentric with the horizontal
axis of the vortex chamber 4, i8 arranged in that end wall 9 of
the vortex chamber which i6 opposite to the end at which the
vortex chamber 4 communicates with the flue duct 2. The discharge
outlet 10 is connectsd through a pipe 11 to a convection part 1~
of the reactor. There is no axial pa6sage in the end wall of the
separator opposite to the end wall 9. The width b of the gas
channel 2 is ~maller than the axial length B of the vortex chamber
4. The flue duct 2 is offset relative to the axial length of the
vortex chamber 4.
The flue duct 2 guides the flue gases of the reactor ohliquely
downwards to the tran~ition chamber 5 acting as a pre-separator,
wherein the main portion of the flue gases i~ deflected upwards
(counter-clock-wise in FIG. 1) to the vortex chamber 4,
tang~ntially thereto. Due to the change of direction a major part
of the flue gases, the solid material contained in the gases is
separated and recirculated to the reactor. A part of the remaining
601ias is separated to the cylindric wall of the vortex chamber
and is projected against the intermediate wall 7 between the
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vortex chamber 4 and the return duct 8 from which it ~alls down to
the return duct 8. As ment.i.~ned above, the purified gases are
discharged through the axial outlet 10 to the convection part 13.
In the embodiment illustrated in FIGURES 4 and 5, the reactor 21
communicates through a pair of flue ducts 22~, 22b, with coaxial
separators 23a, 23b. The gases leaving the upper part of the
reactor 21 are at first directed, by the flue ducts 23a, 23b,
obliquely downwardly and away from the reactor 21. Each flue duct
22a, 22b is associated with one of the separators 23a, 23b. As in
the first embodiment described, the main portion of the gases
coming through each duct 22a, 22b changes its direction and flows
obliquely upwards to an associated vortex chamber 24a, 24b of the
respective separator 23a, 23b. In the embodiment shown, the vortex
chambers 24a, 24b are co-axial with each other. The upper part of
a return duct 28 and a respective lower wall 26a 26b connecting
the respective flue ducts 22a, 22b with the return duct 28, are
arranged to be ~ubstantially parallel with the direction of flow
in flue ducts ~2a, 22b. Thus, they guide the solid particles
æeparated by the change of the direction of flow of the gases,
directly to the return duct 28, much in thes fashion of the first
embodiment described.
The wallæ 27a 21b (only 27b being visible in FIGURE 4) between
the vortex chambers 24a, 24b and the return duct 2a form with the
wall of the return duct 28 a slope terminatlng at a respective
edge 31a. 31b. As in the first example of FIGURES 1 3, the sloping
wall 27a, 27b of each vortex chamber guides the separated solid
material slantin~ly downwards to the return duct 28 which is
common to both vortex chambers 24a, 24b. ~he respective end walls
~ 2~b of the vortex chambers 24a, 24b are each provided with a
gas outlet passage 30a. 30b. The gas outlet passages 30a, 30b are
concentric with the vortex chambers 24a, 24b and with each other.
~hey connect their associated vortex chambers 24a, 24b with a
discharge channel 25 common to both separators and leading to a
common convection part ~3.
The separator illu~trated in Fig. 6 is imilar to the separators
illustrated in Figs. 1, 2 and 3 except that in FIGURE 6 there are
two adjacent return ducts 18 and 38 for the separated ~olids are
connected to the associated vortex chamber 4. The diameter b of
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..he return duct 18 is equal to the width of the flue duct 2 of the
reactor. The inlet of the seasnd return duct 38 i~ located at the
same end of the vortex chamber 34 as the gas outlet 20.
The vortex chamber 34 i6 provided with a partition wall 36
S disposed between the port of the flue duct 2. The partition wall
has an orifice, 80 as to form, in eff~ct, two adjacent vortex
chamber sections 3S. 37.
The return duct 18 receives both the solids separated by the
change of the directi~n of flow and the solids ~eparated on the
walls of the vortex chamber 34. On the other hand, the return duct
38 receives only the solids separated on the wall of the vortex
chamber section 37. Thus, the solid material returned by duct 38
is finer than the material returned by duct 18.
The separat~r i~lustrated by Figs. 7 and 8 is provided with two
adjacent vortex chambers ~4 and ~4 having different diameters. The
vortex chamber 44, having a larger diameter, i8 ~imilar to that
illustrated in Figs. 1, 2 and 3 e~cept that the outlet 40 in its
end i~ connected to the concentric vortex chamber 54 having a
smaller diameter. The gas outlet ~0 in the end wall ~1 of the
smaller vortex cham~er 54 i6 connected through a pipe 52 to a
convection part 53. The solid material return duct 48 connected to
the larger vortex chamber section 44 is similar to the duct 8 in
Figs. 1, 2 and 3. The solid material return duct 58 is connected
tagentially t~ ~he smaller vortex chamber section 54.
The separatox is two-staged. In the first stage aoarse material is
separated at 810w peripheral speeds and in the second stage finer
particles at hiyh peripheral speeds.
As to its flow technology, the sy6tem of the present invention
differs from the conventional system, in that the solid material
is recirculated to the reactor carried by the gas flow (1 - 10 %
of the gases). As the flue duct 2, 22 i8 directed towards the
inlet of the solid matsrial return duct, the dynamic pressure of
the gas and the solid material facilitates circulation of the
solid material whereby the separation rate is incrsased.
Furthermore, the apparatus according to the invention provides the
following advantages compared to a conventional cyclone separator:
- as the flue duct is directed obliquely downwards, no solid
material is accumulated at its bottom; in conventional
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separators the accumulationa reduca markedly the separation
capacity;
- since a major portion of the dust flowing in is separated in
the transition chambsr 5, tha dust does not overload the
vortex chamber 4;
- as a major portion of the dust i6 removed before the flue
enters the vortex chamber, the separator can be dimensioned
for separation of greater amount of dust;
- for the same reason, a vortex chamber can be run at higher
speeds as the erosion ~& not as severe as in chambers
operating with more heavlly particle laden flues;
- a vortex motion occurs only in the vortex chamber, not in the
solid material discharge channel.
Also, structural advantages are achieved with the system of the
present invention, in particular:
- compact construction;
- e~pansion joints can be avoidedi
- the connection to the convection part and the reactor is
simple;
- connection of the gas discharge is simple, it can be arranged
at either or both ends of the vortex chamber.
The invention is not limited to the embodtments presented herein
as examples only. It can be modified to a greater or lesser degree
wihtout departing from the scope of the present invention.
~5 Accordingly, we wish to protect by Letters Patent which may is~ua
on this application all such embodiments as properly ~all within
the scope o~ our contr~bution to the art.
