Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ le invention rela~es -to fluidised bed furnaces where com-
bustion promoting gas, normally air, is forced through and "fluidises",
that is maintains in motion~ a bed of particulate material including or
~o l~hich is added combustible fuel, normally solid such as coal, or even
liquid fuel su~h as oil.
Prior to introduction of fuel, beds of such furnaces require
their incombustible particulate material to be fluidised and heated a~
least to the combustion temperature of the fuel to be added. From the
point of viel~ of simplici*y of furnace construction, this preheating is
probably most conveniently done by burners, say oil burners, in the
combustion chamber above the bed. However, from the point of view of
efficiency, the preheating is best done from below or within the bed
material, but this does lead to more complex structures that are less
easy to repair and main-tain.
According to the presen-t invention there is provided a fluid-
bed furnace having in a combustion chamber a fluidised bed of imcombust-
ible particulate material within which fuel is to be burnt and a remov-
able elongate chamber having a single extension surrounded by and
extending through the bed material from one end of the bed, said single
extension housing a bed preheating burner extending from said one end of
the chamber and said chamber being connected to spaced upstanding dis-
charge pipes or ducts extending from upper parts of the chamber extension
into the bed material to supply ~luidising combustion promoting gas into
the bed mater;al substantially over the whole bed.
Preferably, the ch~nber is bodily removable from the f.urnace
from said one end of the bed.
Preferably also, the discharge pipes or ducts are spaced along
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a plurality of feed pipes or ducts e.~tending -transversely of a said
chamber and in communication therewith.
It is also proposed herein that two or more combustion chambers
eacil equipped with their own preheating and combustion gas discharge
systems be provided in generally side-by-side relation. Then, within an
overall enclosure of refractory material, preferably externally insulated,
one or more vertical partitions may conveniently define the combustion
chambers to either side thereof. In a preferred embodiment, a dual-
chamber furnace has a single central partitlon wall between the two
chambers with access thereto for repair or maintenance purposes from side
walls of the overall enclosure.
Another proposal of this invention is to provide a pre-heating
burner housing and combustion promoting gas distribution plenum chamber
in a do~nwardly V- or U-shaped section trough below the bed proper. Such
a trough of that section may be provided, at its lowest part and chamber,
; with an e~traction arrangement, such as a worm screw, for the bed material
and particularly for removal of ash, heavy incidental incombustibles of
the fuel, and agglomorated material that sinks through the bed material.
Clearly, a
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wor~ scre~-type extraction element ~ay convenientl~ extend
p~rallel with the pre-combustion burner housing of gas
pl~num chamber ~nd extend at least betweeD ends of the
furnace b~d.
~he or each combustion cha~ber conveniently has its
bed extend beyond an internal baffle or wall~ usually
vertical, forcing exhaust gases to rise over its top,
preferabl~ with a subsequent forced do~.nturn thereof towards
a furnace exhaust, so that at least some entrained solid
material from the bed will drop out on the rise or fall of
the exhaust gas and back onto the bed ~naterial itself~ ~or
a plural, preferably dual, chamber furnace as mentioned
above~ a single furnace exhaust may be provided in an end
chamber common to the fur~ace cha~bers~
Another proposal hereof concerns material extractio~
; includi~g coarse or agglomerated combustion residues from
a low part o~ the bed preferably with return of fine
material to the combustio~ chamber.
O~e embodi~ent o~ the invent-ion will now be described,
1 20 b~ way ~f example, with reference to the accompany1ng
I drawings, in which:-
F:igure 1 is a section through a furnace chamber;
~igure 2 is a section taken at ri.ght angles to that Or
Figure 1 through a dual-chamber furnace;
Figure 3~is an incomplete par-t sectional plan view of
the furnace of Figure 2 showing one furnace bed.
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In Fi6ure ~, a ~ed of fluidisable incombustible
p~rticulate ma~erial, normall~ sand, shown at 10 extends
from a refractory end wall 11 of the f~rn3ce that has a
downwardly inclined solid fuel leed 12 to the upper surface
of the bed from a hopper 13 via a sealed rot~r~ feed 14.
At its other end the bed is bounded by a riser 15 from
the furnace b~se t~ a step 16 of refractor~ material. Figure
2 shows two such ~urnace chambers within an overall
furnace enclosure having bed bounding side walls 205 21
and central partition 22, and a top plate or wall 23, all
o~ refractory material.
This top wall is shown with rei~forcementsana support
girders~ Desirably it may be o~ any convenient prefabricated
form to allow its ready removal and repl~cement both to
facilitate repair and maintenance and allow shipping with
parts tempaIarily stowed within the furnace chamber.
l At a position closer to the step 16 than the end wall
`; 11, but spaced therefrom, each combustion chamber ha~ a
transverse vertical wall 241 slid in ~etwêen side wall
protrusions 25, and extending from immediately above the
bed material to a position short of the cha~ber top 23 which,
at a position above the riser 15 to step 16 has a transverse
short depending wall 26. ~hus exhaust gases will be forced
upwardly and then downwardly over the top of wall 25 and
towards a furnace exhaust 28 substantially centrally of
furnace end wall 29 spaced from and extending from below
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the step 15 -to form an exhaust chamber 30, usually and
preferably commo~ to both combustion chailibers.
The bottom of each furnace chamber has a V-shaped
trough 32 within and to a total depth above which the
nco~bustible bed material is disposed. At its base 3~,
each such trough has a material extxaction worm screw
34 e~tending the full length of the trough below the bed.
Above this worm screw 34 is a combined pre-heater burner
housing and combustion promoting gas plenum chamber 35 of
elGngate c~lindrical form ~1BO extending the fuIl length
of the bed. hn oil or gas burner 36 is housed at o~e end
37 of th~chamber and communication is provided at least
at spaced positions along the length of the chamber with
T-shaped gas distribution ducts or pipes 38 of which
the cross pipes have a ~uralit: of spaced gas release he~ads
39 extending upwardly therefrorl,.
It mag be found convenierit ill building the fl~nace to
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provide a 1edge at each side o~ ~ch combustion ch~nber to
upport and~or locate ends of t.~ T-shaped distribution
members thereb~ allowing them to be simpl~ lifted out for
maintenance or repair purposes. ~he downwardly directed
inlets of these T-pipes 38 may rit i.nto re-entrantly edged
holes 40 in the c~lindrical chani~)er or, and perhaps
preferabl.y, are located in a channel thereof that may be
closed except where it is to register with such a T-pipe,
but will still allow ready removal of the cha7nber whenever
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r~quired.
The entire furnace structure is shown supp~rted on
girder 42 located l~der side and partition walls there~f
w-th the troughs disposed between them. Access doors 44
to the furnace chamber proper and 45 to the exhaust chamber
are shown in the side walls.
In ~peration, eombustio~ pro~oting gas, usually air,
will be pressurised by a fan 46, a~d supplied to the bl~ner
mounting end of the chamber 35 for discharge into the bed
13 of incombustible materi~l. 0~ start up, the burner 36
will be lit to heat the fluidising gas. When the bed
material reaches the desired ignition temperature for fuel
supplied via feed 12 that fuel will start to feed in and
the burner 76 may be extinguished as normal furnace
operation ta~es place.
It will be noted from ~igure 3 that the ends of
partition wall 22 have transversely extending parts 50
to each side and side walls 20, 21 have extensions 52
at the positio~ o~ riser 15 to ~rther c~nstra~n the
exhaust gas ~low path and facilitate drop out of entrained
particles. If desired collectio~s of such particles on
the shelf 16 may be returned to the bed by an inclined
at least intermi-ttently vibratable plate on the shelf 16.
It will be appreciated that -the worm screw 34 could
be replaced by other suitable feeding means1 such as a
pneumatic feed. It is also a valuable aspect o~ this
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invention to provide a return of fine extracte~ material to the combustion
chamber. To that end, we show a screening system 60, upon whic~ lumps of
agglomerate material ~ill collec-t and from which they may be removed, and a
transfer conveyor 62 of any suitable type, e~g. pneumatic, scraper, bucket or
the like, to take the fine material bac~ to the combustion chamber at 64, which
may be a sealed feed from a conveyor reception hopper. This is usually
preferable to the conveyor 62 feeding directly into the solid fuel hopper 13,
but that could be done if desired and any problems concerning wear and possibly
erratic fuel dilution are within tolerable limits.
We also envisage that the chamber 30 could have gas delivery tubes
taken directly from upper parts thereof instead of the gas discharge piping 38.
Such tubes could be radial oE a chamber 30 of generally circular cross-section
as shown or could be medially bent, but should result in substantially even gas
delivery across the width of the bed in the plane of Figure 2.
Another possibly advantageous modification of the chamber 30 is to
line it with refractory, typically a castable material, to limit expansion
thereof, which could be significant given that the chamber itself will usually
be of stainless steel. Then~ short tubes welded to the upper part and ending
in flanges can be coupled by bolting to flanges terminating the inlet tubes of
the gas discharge
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piping sets 38. The flan~es are readily made tolera~t of
di~ferential eXpansion by slottins fro~ edges between ~olt
holes.
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