Note: Descriptions are shown in the official language in which they were submitted.
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CO~L-W~'rF'~ ~UI~ER ASSEM~LY AND METHOD
B~C~ O~ND OF` THE T~VEN'rrON
Thi~ invention rPlates to a burner assembly and method for
burning a mixture of coal and water and mor~ particularly, to such
an assembly and method in which both high velocity air and low
velocity air are introduced to support the coal-water mixture in
the combustion process.
Coal-water mixtures, i.e., pulverized coal mixed with up to 30
water, provide an attractive al~ernative to natural qas or oil for
use in bDrners in boilers, vapor generators, or the like, since a
coal-water mixture can be pumped, stored and atomi~ed like a liquid
fuel, yet is not as expensive.
However, to burn such a fuel requires a design approa~h dif-
ferent from that used isl conventional liquid fuel burners since the
latter have comparatively high flame propagation rates in the pri-
mary combustion zone providing the capability of easy ignition and
flame stabilization. High flame propagation rates allow for the
use of high velocity combustion air, and traditionally this type of
burner use~ a single fitr~am o~ high velocity combustion air.
However, this design approach has proved unsuitable in burning
coal/wat~r mixtures resultin~ in the inability to stabilize the
flame without the use of high capacity oil or ga~fired ignitors
and in heavy fall-out of unburned coal particles from the flame
envelope.
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5U~M_~lY OF rrtlE INVENTION
It is therefore an object of the present invention to provide a
burner assemb1y and metllod for a coal-water mixture burner in which
a~ceptable ignition ~n~ fL.~ s~abili~y are achieved.
It is another object of the present invention.to provide an
a~semb1y and ~ethod of the above type in which fall-out of unburned
coal particles from the f~ame enve1Ope is minimized.
It is a further object of the present invention to provide an
assembly and method of the above type which eliminates any adverse
effect on the injection nozzle.
It is a still further object of the present invention to pro-
vide an a~sembly and method of the above type in which adequate
residence time of the mixture in the combustion area is insured.
It is a still further object of the present invention to pro-
vide an assemb1y and method of the above type in which a compact,
low velocity, high telnp~rature "drying zone~ is provided wherein
the coal partio1es can be sufficient1y dried before re1ease to the
main flame envelope.
Toward the fu1fillment o~ these and other objects, the burner '.
20 assemb1y and method of the present invention features the introduc- !
tion of a "dua1 ve1Ocity" combustion air system. The first zone
provide~ a "pri~ary combustion and drying zone" and has extremaly
low (less than 15 ft./sec.) velocity swirlin~ air applied around
the injected coal/water mixture. This zone is a substantial part
of the total burner throat area and is lined with refractory
mater~al. The secondary zone provides the main mass of combustion
air which is introduced at relatively high rotating velocity lup to
150 ft./sec.) around the periphery of the first zone~
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s~IEF D_ c-l-p-~rlo-N OF THE DRAWINGS
The above brief description as well as further objects,
features and advantages of the present inuention will be more fully
a~preci~ted by r~ r.~nc~ to the followinq detailed description o~
presently preferred but nonetheless illustrative embodiment~ in
accordance with the present invention when taken in conjunction
wi th the accompanying drawings which is a partial schematic, par-
tial cross-sectional view depicting the burner assembly of the pre-
sent invention.
DE~CRIPTION OF TRE PREFERRED ~MBODIMENT
The assembly and method of the present invention wlll be
described in connection with a vapor generator for the purposes of
example, with the reference numeral 1~ in FIG. 1 of the drawings
referring,to a wall which forms a portion o the furnace ~ection of
the ~enerator.
A casinq wall 12 extend~ in a spaced, parallel relation with
the wall 10 to define an interior portion 14, it being understood
that the latter is bounded by upper and lower walls, as viewed in
FIG. 1, to define an enclosure, or windbox, which receives air from
a source, such as a fan, with the direction of the a.ir flow being
shown in general by the flow arrows in FIG. 1.
An annular refractory collar 16 extends adjacent and within an
opening formed in the wall 10 with its inner surface being shaped
to define a throat portion 18 surroundins a combustion zone 20.
A tubular refractory throat 22 is provided adjacent the com-
bustion zone 20 and together with the refractory throat 18 de-fine3
an annular passage 24. A tubular extension 26 is provided on the
throat 22 and has an outwardly flared annular end portion 28 which
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suppor~s a circular ~ d~lnper 30. A pair of rollers ~2 are
mo~lnted on th~ s.licit' damper 30 and are in a rollin~ engagement with
a track 34 for p~rmit~in~ .s1id;lble mo~emcnt o~ the damper 30 rela-
tive to the casirlq w~lll l~ to define and selectiv~ly vary the size
of an inlet 3u ~Lin~ b~tw~en the flared end ~ortion 28 of the
extension 26 and the casing wall 1~. As a result,.some of the air
from the windbox 14 will pasY through the inlet 36, and into and
through the extension 26 and the throat 22.
A burner asse~nbly, shown in general by the reference numeral
40, extends through the casin~ wall 12 with its discharge end bein~
located a slight distance inwardly fro~ the correspondinq end por-
tion of the throat 22. The burner assembly 40 includes a fuel ~un
42 having a barrel 44 extending wi~hin a tubular casing 46 in a
slightly spaced relationship, and an air inlet 48 adapted to intro-
duce cooliu~ air between the barrel 44 and the casing 46. The
discharge end 44a of the barrel extends sliqhtly outwardly from the
casin~ 46 and is adapted to inject a mixture of coal and water in a
s~bstantially conical pattern into the combustion zone 20 and the
interior of the furnace. It is understood that an ato~izer ~not
shown) is provided on the discharge end 44a to atomize the fuel
froln the gun 42. The ca~ing 46 is supported by a support structure
50 disposed on the exterior surEac~ of the casing wall 12, and a
stationary swirler stabilixer, shown in general by the reference
numeral 52, is disposed on the leading end portion of the casing
46. The function of the swirler stabilizer 52 will be described in
detail later.
A ~lurality of register vanes 54 are journaled between a first
annular plate 56 disposed adjacent the refractory collar 16, and a
second annular plate 58 extending outwardly from, and supported by,
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the refractory throdt 22. ~lthough only two vanes 54, are shown in
the drawiny, several addi~ion~l vane~ are disposed in ~ circular
relationship arouncl th~ latt~r throat. The plates 56 and 58 thus
define a passage for s~ndar~ air from the winclbox 14 that passes
thronyh the re-3ist~r v~rlis 5~, t-~lr~ gh ttle ann~l~r passa~e 2~, and
into the combustion ~one 20. ,
A slide da~per 60 is provi~ed which defines, and varies the
size of, an inl~t 62 for the air passing throuqh the register vanes
54. The slide damper 60 is supported by the annular plate 58 an~ ¦
has two wheels 66 that ride on a track 68 for selectively varying
the size of the inlet 62 and therefore the amount of secondary air
passing through the register vanes 54, the path 24 and to the com-
bustion zone 20.
As ~hown in the drawings, the slide damper 30 is in a relati-
vely closed position, thus defining a relatively small inlet
opening 36 so that the velocity o the primary air passing into the ~,
annular passage between the burner assembly 40 and the refractory
throat ~2 and its casing 26 is relatively low, such as 1~ feet per
second. The slide damper 60 is maintained in a relatively open
2~ po5ition permitting a hiqher velocity, such as 15a feet per second,
of air flow through the reqister vane 54, the annular passage 24,
and to the combustion zone 20.
In operation, the burner assembly 40 discharges the coal-water
mixture in a substantially conical pattern into the combustion zone
20 and the mixture is ignited by any conventional ignitor (not
shown). The primary air from the windbox 14 passes tbrough the
inlet ~6 at a relatively low velocity and through the annular
chamber between the burner assembly 40 and the throat 22 and its
extension 26 as shown by the flow arrowsO The air then pa~ses
3791
through the swirler ~tc~ .er 52 where relatively low velocity
vortex and stron~ recircu1~ion ~ones are created around the
discharge end 44a of the barr~l 44.
S~condary air frofll t~,~ windbox 14 passes through the inlet 62
at a relatively high velocity and continues throuyh the register
vanes 54 where a swirlîn~ effect i~ imparted to the air as it
passes thro~gh the annular passage 24 into the co~bustion zone 20
as also -Qhown by the flow arrows. This high velocity ~ir envelop~
the substantially conical discharge pattern of the coal-water mix-
1~ ture discharging from the burner assembly 40 and create~ an optimum
rotational vortex which shapes the flame and causes flow reversals
of the particulate fuel back toward3 the di~charge end 44a of the
burner a~qembly 40. This results in superior ignition and flame
st~bility and an adequate residence time of the fuel particles in
the combustion zQne. Pn~bient t~mperature cooling air is introduced
throuqh inlet 48 and passes through the annular space between the
barrel 44 and the casing 46. The presence of the inner reEractory
throat 22 enables a high temperature zone to be maintained to
insure that the water content of the fuel mixture is flashed.
It is thus seen that as a result of the foregoing, alI of the
advantages of the use of the mixture of coal and water can be
achieved yet assuring satisfactory ignition, flame ~tability, ade-
quate re~idence time of the coal particles, and insulation of the
burner discharge nozzle.
A latitude of modification, change, and substitution is
intended in the foregoing disclosure and in some instances some
featu~es of the invention will be employed without ~ 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 s~ope of the invention therein.
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