Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A COAL FEED SYSTEM FOR
A FLUIDIZED BED REACTOR
BACKGROUND OF THE INVENTION
The present invention relates to fluidized beds and,
more particularly, to a coal feed system for a fluidized bed
reactor.
Fluidized bed reactors, in the form of combustors,
boilers, steam generators, and the like have long been
recognized as an attractive and effective means of
generating heat. In these arrangements, air is passed
through a bed of particulate material which normally con-
sists of a mixture of iner~ material and a particulate
fossil fuel such as coal, to fluidize the bed and to promote
the combustion of the fuel. When the heat produced by the
lS fluidized bed is utilized to convert water to steam, thefluidized bed 5ystem offers an attractive combination of
high heat release, improved heat transfer to surfaces within
the bed and compact boiler size.
In these type arrangements, the particulate fuel
material must be continuously, or at least periodically,
distributed into the bed to replenish the spent material
expended in the combustion process. Many of these arrange-
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ments utilize in-bed feeding systems in which the par-
ticulate ~uel material is introduced directly into the bed
from a point below the upper surface of the bed. However,
these in-bed systems present problems since the lateral
transfer or distribution of the materials through the bed is
relati-~ely poor requiring a multiplicity of feed points to
prevent hot spots or cool spots which increases the cost of
the installation.
Other systems utilize a feeder for distributing the
particulate fuel material from a position above the upper
surface of the bed where it falls by gravity onto the latter
surface. ~owcver, since a great majority of the commercial
coal that is available is of a relatively large particle
size range, which may extend from very small particles to and
including particles that will pass through a two-inch screen,
this ejection of the particulate fuel material onto the
upper surface of the bed presents problems. For example the
combination of the upwardly rising combustion gases and air
passing through the bed will blow relatively small material
0 out the top of the combustor before it is burned.
SUMMARY OF THE INVENTION
Accordingly the present invention seeks to
provide a coal feed system for a fluidized bed reactor in
which an optimum distribution of a particulate fuel
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material of a relatively large particle size range is achieved.
Further the present invention seeks to provide a system of
the above type in which the particulate fuel material is
separated into a relatively coarse material which is distributed
to the upper surface of the bed and a relatively fine material
which is distributed into the bed at a point below the upper
surface to the bed, the relatively fine material being entrained
by water in the separation process to form a slurry which is
injected into the bed.
~he invention in one aspect pertains to a fluidized bed
reactor comprising a housing with grate means supported in the
housing and adapted to receive a bed of par-ticulate material a-t
least a portion of which is combustible. Means are provided for
passing air through the grate means and the particulate material
to fluidize the particulate material and separator means
including a screen receiving particulate fuel material and
separating same into relatively coarse particulate fuel material
and relatively fine particulate fuel material. Means discharge
water onto the screen to promote the separation of the coarse
material from the fine rnaterial and form a slurry containing the
fine material. Means connected to the separating means receives
the relatively coarse material and distributes the relatively
coarse material to the upper surface of the bed. Means connected
to the separating means receives the slurry containing the
relatively fine material and means is connected to the slurry
receiving means for distributing the slurry into the bed below
the upper surface of the bed.
Another aspect of the invention pertains to a method of
operating a fluidized bed reactor comprising the steps of
supporting a bed of particulate material at least a portion of
which is combustible, passing air through the particulate
material to fluidize the particulate material, separating a
particulate fuel material into relatively coarse material and
relatlvely fine material whereby the relatively fine particles
pass through a screen, discharging water onto the screen to
promote the separation of the coarse material from the fine
material and for forming a slurry containing the fine material,
distributing the relatively coarse material to the upper surface
of the bed and distributing th~ slurry .into the bed below the
upper surface of the bed.
DESCRIPTION OF THE DRAWING
The above brief description, as well as further objects,
features, and advantages, of the present invention will be more
fully appreciated by reference to the following detailed
description of a presently preferred but nonetheless illustrative
embodiment in accordance with the present invention, when taken
in connection with the accompanying drawing which is a partial
sectional partial schematic view of the reactor of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawing, the reference numeral 10 refers in
general to the fluidized bed reactor of the present invention in
the form of a boiler consisting of a front wall 12,
a rear wall 14, and two sidewalls, one of which is
shown by the reference numeral 16. The upper portion of the
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boiler is not shown for the convenience of presentation, it
being understood that it consists of a convection section, a
roof and an outlet for allowing the combustion gases to
discharge from the boiler, in a conventional manner.
A bed of particulate material, shown in general by the
reference numeral 18, is disposed within the boiler 10 and
rests on a perforated grate 20 extending horizontally in the
lower portion of the boiler. The bed 18 can consist of a
mixture of discrete particles of inert material and fuel
10 material such as bituminous coal.
An air plenum chamber 22 is provided immediately below
the grate 20 and an air inlet 24 is provided through the
rear wall 14 in communication with the chamber 22 for
distributing air from an external source (not shown) to the
15 chamber. A pair of air dampers 26 are provided in the inlet
24 for controlling the flow of air into the chamber 22. The
dampers 26 are suitably mounted in the inlet 24 for pivotal
movement about their centers in a response to actuation of
external controls (not shown) to vary the effective openings
20 in the inlet and thus Gontrol the flow of air through the
inlet and into the chamber 22. Since the dampers 26 are of
a conventional design they will not be de~cribed in any
further detail. Although not shown in the drawing, it is
understood that a bed light-off burner is mounted through
the front wall 12 immediately above the grate 20 for ini-
tially lighting.off the bed 18 during startup.
A screen separator, shown in general by the reference
numeral 30 is located externally of the boiler 10 and i.s
adapted to receive particulate fuel material, such as coal,
of a relative large particle size range from an external
source (not shown) via a duct 32. The separator 30 includes
a screen 34 which is sized so as to permit the relatively
fine particles to pass through while preventing passage of
the relatively coarse particles. As an example, the screen
; can be adapted to separate particles greater that 1/16 oE an
inch in dlameter from those less that 1/16 o~ an inch. The
particle~ on the screen 34 are washed by water Erom three
spray bars 36 disposed adjacent the separator 30. The water
aids in the separation proces~ and entrains the relatively
fine particles as they pass through the screen 34 into the
lower portion of the separator 30.
A distributor 40 is mounted on the wall 12 of the boiler
10 and includes a hop~er 42 for receiving the coarse coal
particles ~rom a duct 44 extending from the upper portion
of the separator 30 above the screen 34. The distributor 40
operates to feed .the coarse coal particles 34 by gravity,
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onto a rotating blade assembly 46 which opera~es to propel
the coarse particles through an opening in the wall 12 into
the interior of the boiler 10 and onto the upper surface of
the bed 18.
A storage tank 50 is located externally of the boiler
10 and receives the slurry contain:ing the fine particles
from the separator 30, via a duct 52. A pump 54 extends
between an inlet duct 56 connected to the tank 50 and an
outlet duct 58, extending through the wall 12 to pump the
slurry containing the fine particles from the tank 50 into
the bed lS.
To start up the bed 18, the dampers 2~ a~sociated with
the air inlet 24 are opened, and air i~ thus distributed
upwardly through the chamber 22, through the perforations in
the grate 20 and into the bed 18. This loosens the par-
ticulate material in the bed 18 and reduces material packing
and bridging.
A light-off burner is fired to heat the material in the
: bed 18 until the temperature of the material reaches a pre-
determined level, at which time the separator 30 and the
spray bars 36 are activated to separate the fine particles
from the coarse materials. The distributor 40 and the pump
54 are activated to introduce the coarse materials to the
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upper surface of the bed 18 and the slurry containing the
fine materials into the bed.
After the bed 18 has been fluidized and has reached a
predetermined elevated temperature, the light-off burner
is turned off while the distributor 40 and the pump 54 con-
tinue to distribute the particulate fuel to the bed 18 in
accordance with predetermined feed rates.
It is thus seen that the present invention provides an
effective yet simple method of insuring optimum distribution
of particle fuel material of a relatively large particle
5 ize range.
. It is a still urther object of the present invention
to provide a system o~ the above type which minimize9 e~cape
of the relatively fine materials from the bed.
It is a still further object of the present invention
to provide a system of the above type in which the com-
bustion and sulfur capture efficiency of the fluidized bed
are increased.
It is understood that if the reactor of the present
invention is used for steam generation, a plurality of
heat exchange tubes carrying water may be routed through the
interior of the boiler 10 in a conventional manner with these
tube3 being omitted in the drawing for the convenience of
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presentation.
A latitude of modification, change and substitution is
intended in the foregoing disclosure and in some instances
some features of the invention will be employed without a
corresponding use of other features. Accordingly, it is
appropriate that the appended claims be construed broadly
and in a manner consistent with the spirit and scope of the
invention herein.
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