Note: Descriptions are shown in the official language in which they were submitted.
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FLUIDIZED BED FUEL FEEDER
TECHNICAL FIFTn
This invention relates to boiler fuel feed hg in general
and more specifically to an underfeed fluidized bed boiler fuel
feeder.
BACKGRCUND ART
In recognition of their inherently cleaner and potentially
more efficient fuel buTning properties, fluidized bed boilers are
now seriously being considered as viable suppler.ents to the
traditional pulverized coal and stoker fiTed vapor generating UlLitS
of today.
Briefly, a fluidized bed boiler burns granulated coal Ln
a floating fluid-like suspension called a fluidized bed. In
~M;tion to the coal, a sorbe~t ~usually limestone) is i~troduced
into the bed to absorb a portion of the noxious gases generated as a
result OI the burning process. 3y introducing fluidi~ mg air 'ro~
beneath the burning zone through an air distribution plate or ~rough
the fu~nace floor, the buTm ng coal actu~lly floats above the rlate
or the flooT on a cushion of air as it is consumed. As a result of the
enhanced c~mbus ion process, greater quantities of heat may be
generated.
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And, as a consequence of the introduction of the sorbent,
undesirable pollution levels are substantially reduced.
As a result of the fluidized bed design, it is
necessary to distribute the coal-limestone mixture in a
uniform manner over the entire cross-sectional area of the
bed. Present technology requires that there be one fuel
distribution point for each nine square feet of bed area.
This means that a boiler rated at a modest 80,000 pounds-
steam per hour would require approximately twenty such points.
As the rated capacity of the boiler increases, the number of
necessary feed points will correspondingly increase.
Some of the present day fluidized bed designs
utilize peripheral wall mounted feed nozzles to distribute
the fuel and/or sorbent mixture into the bed. As the size of
the boiler increases, it may become very difficult to intro-
duce an even fuel distribution over the entire bed surface
from wall mounted nozzles.
Other concepts include positioning the feedpipes
and/or the fuel nozzles within the bed above the plate or
above the furnace floor. Unfortunatelyt these designs may
lead to feeder component erosion, overheating and plugging.
Furthermore, the replacement of such units may prove to be
difficult as well.
Clearly, an improved fuel feeder design is
desirable.
SUMMAR~ OF THE I_NVENTION
In contradistinction to the above mentioned feeder
designs, the disclosed fuel feeder introduces the granular
material upwardly from beneath the air distribution plate or
the furnace floor directly into the base of the fluidized bed
at a controlled velocity.
Thus, according to the present invention there
is provided in combination with a vapor generator having a
furnace fired by a fluidized bed of granular material,
perforated plate means for introducing fluidizing air into
the furnace, underfeed means for supplying the material
through the plate means comprising at least one discharge
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conduit, at least one material supply conduit, the discharge
conduit having one end communicating with the supply conduit
and at least one end communicating with the bed, the discharge
conduit having a total cross-sectional flow area substantially
greater than the cross-sect.ional flow area of the supply
conduit to substantially reduce the velocity of the granular
material entering the furnace.
In one embodiment, material is introduced into
the bed through a perforated bowl-shaped feed nozzle disposed
beneath the air distribution plate. A perforated, horizontal
feed member connects
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S the nozzle to a feedpipe via a blanked distributor tee. This blanked
design reduces the possibility of solids induced erosion from occurring
within the YariOus componen~s. In addition, undesirable backflow
which may occur during low or zero power generation periods will be
reduced by virtue of the incorporation of the horizontal feed member
within the nozzle. Furthermore, the perforations in the nozzle and
in the member aid in the fluidization of the bed. By incorporating
the nozzle flush with the plate, rather than inserting it within the
bed itself, coking and the potential of overheating the port are reduced.
A second embodiment introduces the fuel-sorbent mixture
through a blanked T-shaped feed nozzle disposed above the air distri
bution plate. Enveloping the nozzle, there is disposed a perforated
protective housing detachably affixed to the nozzle by a slidable
collar. The perforations aid in the fluidization of the bed above the
housing while they simLltaneously prevent the nozzle from overheating.
A third embodiment is a modification of the second embodi^
ment discussed above. However, the nozzle has been adapted foT use in
fluidized bed boilers e~loying water-cooled furnace floors.
BRIEF DESCFIPTION OF THE DRAWINGS
Figure 1 is a sectional side view of a fuel feeder taken
along line 1-1 of Figure 2.
Figure 2 is a plan view of Figure 1 partially broken away.
Figure 3 is an alternate embodiment of the invention.
Figure 4 is an alternate embodiment of the invention taken
along line 4-4 of Figure 5.
Figure 5 is a plan view of FiguTe 4 parti lly broken away.
Figure 6 is a side view viewed along line 6-6 of Figure 4
partially broken away.
Figure 7 is an alternate embodiment of the invention taken
along line 7-7 of Figure 8.
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Figure 8 is a plan view of Figure 7 partially bro~en away.
Figure 9 is a sectional side view of Figure 8 taken along
line 9-9.
Figure 10 is an alternate embodiment of the invention.
S BEST MDDES FOR CARRYING OUT THE INVENTION
FiguTesl and 2 disclose an embodiment ~Embodiment 1) of an
underfeed granular fuel feeder 10 employing a bowl-shaped discharge
conduit or nozzle 12. Other cavity-shaped nozzles, such as teardrops,
ovals and rectangles may be employed as well. The no zle 12 sealably
engages air distribution plate 14 through aperture 16 disposed within
the plate 14. Although one aperture 16 is depicted, it should be under-
stood that a fluidized bed boiler will contain a mLltiplicity of such
apertures. The plate 14 contains a plurality of similarly sized ver-
tically oriented first perforations 26. As can be seen from the figures,
the apertures 16 are larger than the perforations 26. The nozzle 12
is sealably affixed to the lower portion of the plate 14 by flange 18.
The path of the fluidizing air, supplied by a windbox (not
shown) is represented in all the figures by directional aTTcw 100.
Horizont~lly disposed feed member 20 projects into the
lower portion of nozzle 12. The member 20 is connected tO blanked T-
shaped distributor 22 via horizontal extension 23, which, in turn, is
connected to supply conduit or feedpipe 24. It has been detenmined that,
by employing a shielding pla~e or blank 30 in the distributor 22,
erosion to the tee due to the flowing granulated materials entrained
therein may be greatly reduced.
Although the distributoT 22 shown is T-shaped, other distri-
butor configuTations may be utilized as well. For example, if two
nozzles are to be fed from a single feedpipe, the distributor may be
in the shape of a blanked cross.
The nozzle 12 and the membeT 20 contain a pluTality of second
perforations 28. The necessity of first perforations 26 and second
perforations 28 will becone evident from the ensuing discussion.
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Figure 3 (Alternate Embodiment lA) depicts the fuel feeder
10 equipped with a detachable wear-block 32 fastened to the por~ 12
by fasteners 34~ In the event that the gTanLlar material stream
substantially erodes the block 32, it may be easily replaced frcm
below the distribution plate 14.
Figures 4, 5 and 6 disclose an,alternate embodiment (Embodi-
ment 2) of the fuel feeder 10. Again, air distribution plate 14 con-
tains first perforations 26 and an aperture 16. However, the grar.ular
s terial is introduced into the base of the fluidized bed by discharge
conduit or blanked T-shaped nozzle 36 having legs 38 and 40. Leg 38
further includes reduction 3&~The nozzle 36 is capped by shielding
plate or blank 42 and is attached to the supply conduit or fe æpipe
24. Leg extensions 48 and 50 may be employed if a longer flow channel
is desired. Their use will be explained moTe fully in the subsequent
discussion. Note that the extension 50 includes first offse~ 52.
Protective housing 54, positioned directly on the plate 14,
encloses the nozzle 36. Note that the housing includes two openings
64 and 66 and-the upper sectio~ 60 contains a plurality of perforations
62
The no-zle 36 is designed to be replaceable by employing
sliding collar 68. Note that the collaI includes second offset 70.
By breaking tack weld 7Z, the collar 68 may be slid over the
extension 48 andthe n~hct~n38Atoward the body of the nozzle 36. This
step frees the second offset 70 from the constraining influence of the
ZS opening 64. By cutt mg the feedpipe 24 with a torch, the noz~le m2y r
be easily removed by drcpping it through the aperture 16. Thus, there
is no need to physi~ally enter onto the dis~ributor plate 14 to remo~e
the nozzle 36.
To install a new nozzle, the above recited steps are followea
in re~erse order. That is, first a suitable collar 68 is slidably
fitted aboutthe reduction 38Aandthe extension 48. The noz71e is then
placed within the housing (from beneath the plate 14) so that the first
offset 52 is properly positioned within the opening 66~ The collar 6&
is then slid away from the body of the nozzle 36 so that the second
offset 70 is properly positioned within the opening 64. A tack weld 72
is then applied to ~oin the collar 63 to the reduction 38A.
Referring specifically to Figure 6, note how the housing 5~
permits the fluidizing air to pass upwardly through it via perforations
62.
Figures 7, 8, 9 and 10 ~Alternate Embodiment 3) depict the
nozzle 36 mounted above a water-cooled furnace floor 74. Larger si_ed
fluidized bed boilers may require such floors to reduce heat induced
furnace expansion and contraction differentials.
The floor 74 consists of a plurality of spaced parallel tubes
76 connec~ed to one another by a series of tube plates or ligaments 78
disposed therebetween. CThe designations 76A and 78A shown in the
various figures are employed merely to differentiate adjacent tubes
and ligaments.) Note that the ligaments 78 and 78A do not fully extend
throughout the floor. Rather, they are purposely gaFped to form a
plurality of apertures 16 ~only one of which is shown) between the
tubes. As in E~bodiment 2, the nozzle 36 is situated directly over
the aperture 16.
The ligaments 78 and 78A include a plurality of perforations
90 to allow the fluidizing aiT to enter into the bed area above the
floor 74. Known means, such as bubble caps (not shown), may be
employed to expedite the introduction of ~he air into the bed.
Although Embodiments 2 and 3 share the same basic design,
they, obviously, are mounted differently within the furnaces. Whereas7
the housing 54 (as shown in Embodiment 2~ is positioned directly upon
the distTibution plate 14, the housing 54 (as shown in Embodiment 3)
is oriented above the floor 74. Compare FiguTes 4 and 7.
FilleT bars 80 and 80A disposed be~ween tubes 76 and 76A and
attached to ligaments 78 and 78A act as supporting surfaces for support
frame 82. The frame 82 is composed of side walls 82A, 82B, 82C and 8ZD.
The housing 54 is, in turn, attached to the frame 82.
In view of the fact that the furnace floor 74 is composed of
a plurality of fluid carrying ~ubes 76, it is undesiTable to CUt the
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tubes to remove the housing 54 in the event that the port 36 needs to
be replaced. Instead, by mounting the filler bars and support brac~ets
upon the tubes dlring initial shop fabrication, there will be no need
to cut the tubes at a later date to effec~l~te the removal of a nozzle.
S As a further attestation to the versatility of the protective
housing-nozzle combination, the nozzle may be rotated and fixed
through angle 84 within the housing. See figure 10. Although the
angylar deployment of the nozzle will utlimately depend on the physical
layout of the bed, it is contemplated that the angle 84 fall within a
range from 0 degrees to about 12 degrees.
This angular nozzle deployment was prompted by the fact that
; closely spaced co-linear nozzles may interfere with each other's fuel
distribution pattern. By employing angled nozzles, the feeders m~y be
placed relatively close to each other without the need foT staggering
them across the bed.
The invention and the manner of applying it may, perhaps,
be better understood by a brief discussion of the principles under-
lying the various embodiments.
As was stated previcusly, fluidized bed boilers rely on a
floating cushion effect that permits more efficient burning of the fuel
in suspension. Fluidizing air, usually vertically introduced mto the
bottom of the furnace through a perforated distribution plate or
through the furnace floor, maintains the fluid bed in suspension. A
problem, however, develops in the manner of introducing fuel and
sorbent to the bed. Wall mNunted fe~ders may not introduce the ma-
terial erenly into the central portions of the bed. Furthe~more, it
may be undesirable to place a feedpipe and/or a distribution assembly
within the bed itself, since debilitating overheating, c~ing and
plugging may result.
The present invention eliminates these problems while sim-
ultaneously introducing a ~uel-sorbent mixture directly into the base
of the bed from beneath the air distribution plate or the fin~ce Il ~ .
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As was discussed at the outset, large boilers will require
a large number of fuel-sorbent entrance points. One contemplated
method of feeding this large nunber of points is to pneumatically
transport the material from a remote storage site to the boiler by
~ multiplicity of flow paths using (non-fluidizing) air as a transport
medium. It is contemplated that the granLlar material flow rate
will be approximately 40-50 feet per second. ContTast this with the
contemplated bed superficial velocity of about 4-7 feet per second.
If the material is permitted to enter the bed at high velocities,
so,me of the particles may be blcwn out of the bed proper before being
afforded the opportunity to mix and react within the bed. Naturally,
each individual fluidized bed boiler design will be confronted by its
own set of design parameters; however, it should be understood that
large material-bed velocity ratios are clearly undesirable. The dis-
closed embodiments permit the material stream to be decelerated beforeintroduction into the bed.
Embodiments 1 and lA employ a nozzle 12 having a substantially
greater cross sectional flow area than the cross sectional flow area
of the feedpipe 24. It is preferred that the nozzle flow area be
about sixteen times greater than that of the feedpipe. This orientation
will, in turn, s~bstantially reduce the veloci~y of the ~aterial flow-
`; ing into the bed area. Material flow rates would be reduced from
about 50 feet per second to a more desirable 3.1 feet per second.
However, this ratio need not be fixed. Obviously, different bed
designs will re~uire different sized nozzles and different velocities.It should be understood that high flow rates are necessary to supply
a fluidized bed boiler with sufficient fuel. However, when the fuel
is actually introduced into the furnace, relatively low velocities are
desirable to permit sufficient mixing time and to prevent excessive
erosion to the various fuel feeder components resulting fr~m rapid
granular material flcw rates.
Mention was briefly made regarding the second perforations
28 disposed wnthin the feeder 10. They serve in several capacities.
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First of all, they aid in the fluidization of the bed by supplying
fluidizing air fro~ a windbox (not shown) located below the air dis-
tributor plate. Secondly, the perforations allow the fluidizing air to
diffuse the granulated material entrained within the nozzle and
assist in its introduction into the bed. Thirdly, the fluidizing air
will help cool the nozzle during furnace operation. In addition, the
perforations will ~ d in cooling the nozzle after the furnace is shut
dcwn since the bed materials will still contain large amounts of
residual heat for an appreciable length of ~ime. As a consequence,
the life expectancies of the valious feeder components will be greatly
increased.
Embodiments 2 and 3 encourage an even horizontal scattering
of gTanLlated material above the plate or furnace floor transve~sely
to the direction of the fluidizing air stream. This orientation will --
induce a thorough mixing of the material within the bed while simLl-
taneously reducing debilitating backflow and plugging. Indeed, leg
extensions 48 an~ 50 may be utilized to vary the ultimate flow pattern
into the bed. -
As in embodiments 1 and lA, the diameter of the total dis-
charge flow area of the nDzzle 36 is a function of the desired finalmaterial flow velocity. T~sts have indicated that the total nozzle
discharge flow area should be about two times greater than that of the
feedpipe cross sectional area. This substantially greater total c~oss
secti~nal flow area will result in substantially reduced material fl~w
~elocities.
For example, if the initial ~low velocity is 50 feet per
second, the final velocity of the material, after passage through the
two legged feeder as shown in the figures would be 25 feet per second.
However, in contrast to embodiments 1 and LA, final velocities may be
somewhat higher since there is no vertical velocity component to
contend with. Again, each set of circumstances will dictate the
necessary design parameters.
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The protective housing 54 serves a dual function. One, it
will maintain the nozzle at a temperature substantially equal to that
of the fluidizing air. Otherwise, the temperature of the nozzle
would rise to tha~ of the much hotter bed. This undesirable situation
would shorten the life of all the fuel feeder components and greatly
in rease the possibility of coking within the otherwise hotter fuel
feeder. Two, the housing allows fluidizing air to coveT the area
where the feeder is located. This will prevent a hot, dead ~unflui-
dized) area fT~m forming above the feeder.
Although Embodiments 2 and 3 depict two legs 38 and 40, it
may be advantageous to employ a single leg. In such a case, in order
to reduce the velocity of the granulaT material, the diameter of the
single leg must be larger than the diame~er of the feedpipe. Con~ersely,
it may be desirable to increase the number of legs. A greater numbeT of
legs would reduce the number of feedpipes. However, the underlying
!` 15 principles previously discussed would apply to these orientations as
well.
It should be mentioned that all of the embodiments utilize a
blanked constructio~. Although conventional elbows and tee may be
used, it is preferable to employ shielding plates or blanks. Distli-
butor 22 ~&mbodiments 1 and lA) includes blank 30 whereas the noz~le 36
~Embvdiments 2 and 3) includes blank 42. It has been long Xnown that
~`~ any flowm g granLlated stream will eventually erode the piping that
contains it. This debilitating process is exacerbated when the stream
is forced to change direction as in the case of an elbow OT a tee.
However, by employing a blanked construction, as is depicted
m the various embodiments, erosion is greatly reduced. It has been
dete~Lned that the granulated material tends to form a cushioning
pocket within the recess adjacent to the blank. This stationary pocket
~- pTotects the underlying vulnerable pipe sulfaces from the eroding
action of the flowing stream. As the pocket itself is gradually eroded,
new material replaces the worn material. This continuing exhaustion-
replenish~ent cycle ex~ends the life of the various CQmpOnentS involved.
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Although the above discussion concerns itself with a coal-
limestone m~xture, it should be understood that the invention is not
limited to this particular combination of materials. The discharge
connection may be utilized for both single material or mLlti-~aterial
granLlar s~reams.
While in accordance with the provisions of the statutes
there is illustrated and tescribed herein specific embodiments of the
invention, those skilled in the art will understand that changes may
be made in the form of the invention covered by the claims, and that
certain features of the invention may sometimes be used to advantage --
without a corresponding use of the other features.
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