U.S. patent application number 14/893883 was filed with the patent office on 2016-05-05 for gas premix burner.
This patent application is currently assigned to BEKAERT COMBUSTION TECHNOLOGY B.V.. The applicant listed for this patent is BEKAERT COMBUSTION TECHNOLOGY B.V.. Invention is credited to Geert FOLKERS, Eric HEUVELING, Wilhelm Salvatore VAN DEN BERG.
Application Number | 20160123580 14/893883 |
Document ID | / |
Family ID | 48740923 |
Filed Date | 2016-05-05 |
United States Patent
Application |
20160123580 |
Kind Code |
A1 |
VAN DEN BERG; Wilhelm Salvatore ;
et al. |
May 5, 2016 |
GAS PREMIX BURNER
Abstract
A gas premix burner including a perforated plate, a woven wire
mesh or an expanded metal sheet; and a woven, knitted or braided
burner deck having metal fibers supported by the perforated plate,
woven wire mesh or expanded metal sheet. The woven, knitted or
braided burner deck has at least a zone with a high density of at
least 1250 g/dm.sup.3. The zone with a high density includes at
least 25% of the surface of the burner deck
Inventors: |
VAN DEN BERG; Wilhelm
Salvatore; (Zuidlaarderveen, NL) ; HEUVELING;
Eric; (Valthermond, NL) ; FOLKERS; Geert;
(Bruchterveld, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BEKAERT COMBUSTION TECHNOLOGY B.V. |
Assen |
|
NL |
|
|
Assignee: |
BEKAERT COMBUSTION TECHNOLOGY
B.V.
Assen
NL
|
Family ID: |
48740923 |
Appl. No.: |
14/893883 |
Filed: |
July 1, 2014 |
PCT Filed: |
July 1, 2014 |
PCT NO: |
PCT/EP2014/063902 |
371 Date: |
November 24, 2015 |
Current U.S.
Class: |
122/17.1 ;
431/329 |
Current CPC
Class: |
F23D 14/02 20130101;
F23D 14/145 20130101; D03D 15/12 20130101; F23D 2203/102 20130101;
F23D 2203/1017 20130101; F23D 2900/00019 20130101; F24H 1/186
20130101; F23D 2212/201 20130101 |
International
Class: |
F23D 14/14 20060101
F23D014/14; F24H 1/18 20060101 F24H001/18; F23D 14/02 20060101
F23D014/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 2013 |
EP |
13174661.2 |
Claims
1-13. (canceled)
14. A gas premix burner comprising: a perforated plate, a woven
wire mesh or an expanded metal sheet; and a woven, knitted or
braided burner deck comprising metal fibers, supported by said
perforated plate, woven wire mesh or expanded metal sheet; wherein
said woven, knitted or braided burner deck comprises at least a
zone with a high density of at least 1250 g/dm3; wherein the zone
with a high density includes at least 25% of the surface of the
burner deck.
15. The gas premix burner as in claim 14, wherein said woven,
knitted or braided burner deck comprises a zone or zones with a
density less than the density of said zone with high density.
16. The gas premix burner as in claim 15, wherein one or more
sections of the burner deck of said burner are double curved; and
wherein said zone or zones of the burner deck with density less
than the density of said zone with high density, comprise at least
part of said one or more sections of the burner deck that are
double curved.
17. The gas premix burner as in claim 15, wherein said zone or
zones of the burner deck with density less than the density of said
zone with high density comprise the circumference of the burner
deck.
18. The gas premix burner as in claim 14, wherein said zone with a
high density does not cover points of the burner deck that have a
smallest radius of curvature less than 5 mm.
19. The gas premix burner as in claim 14, wherein said burner deck
comprises a zone or zones with a density lower than 900 g/dm3; and
wherein said burner comprises an ionization electrode, and wherein
a zone with a density lower than 900 g/dm3 is provided at the
location of said ionization electrode.
20. The gas premix burner as in claim 14, wherein said burner deck
comprises a zone or zones with a density lower than 900 g/dm3; and
wherein said burner comprises an ignition electrode, and wherein a
zone with a density lower than 900 g/dm3 is provided at the
location of said ignition electrode.
21. The gas premix burner as in claim 14, wherein said burner deck
has over its full surface a constant density.
22. The gas premix burner as in claim 14, wherein said burner deck
has over its full surface a constant mass per unit of area.
23. The gas premix burner as in claim 14, wherein said burner deck
is not over its full surface bonded to said perforated plate, woven
wire mesh or expanded metal sheet.
24. The gas premix burner as in claim 14, wherein said burner deck
is bonded locally to said perforated plate, woven wire mesh or
expanded metal sheet.
25. The gas premix burner as in claim 14, wherein said burner deck
is bonded to said perforated plate, woven wire mesh or expanded
metal sheet at edge zones of said burner deck.
26. The gas premix burner as in claim 14, wherein said burner deck
is soft welded over at least part of its surface to said perforated
plate, woven wire mesh or expanded metal sheet.
27. A boiler or water heater comprising a gas premix burner as in
claim 14.
Description
TECHNICAL FIELD
[0001] The invention relates to gas premix burners that have a
woven, knitted or braided burner deck comprising metal fibers. Such
gas premix burner can e.g. be used in boilers or in instantaneous
water heaters.
BACKGROUND ART
[0002] Gas premix burners with a knitted or woven fabric comprising
metal fibers as burner deck positioned on a perforated plate or
woven screen (a woven wire mesh) which is acting as gas
distribution plate are known. It is a benefit of such burners that
the burner deck (e.g. a knitted or woven fabric) can freely expand
when hot, while the perforated plate or the woven wire mesh is
remaining sufficiently cool. Such burners are e.g. known from U.S.
Pat. No. 4,657,506 and WO2004/092647.
DISCLOSURE OF INVENTION
[0003] The primary object of the invention is to provide an
improved gas premix burner.
[0004] A first aspect of the invention is a gas premix burner
comprising: [0005] a perforated plate, a woven wire mesh or an
expanded metal sheet; [0006] a woven, knitted or braided burner
deck comprising metal fibers, supported by the perforated plate,
woven wire mesh or expanded metal sheet. The burner deck is the
surface on which the combustion of the premix gas occurs after the
premix gas has flown through it.
[0007] The woven, knitted or braided burner deck comprises at least
a zone with a high density of at least 1250 g/dm.sup.3.
[0008] The zone with a high density includes preferably at least
25%, more preferably at least 30%, more preferably at least 40%,
even more preferably at least 70%, of the surface of the burner
deck.
[0009] In a preferred embodiment; the zone of a high density covers
the complete burner deck.
[0010] Preferably, the zone with a high density has a density of at
least 1350 g/dm.sup.3, more preferably of at least 1400 g/dm.sup.3,
more preferably of at least 1450 g/dm.sup.3, more preferably of at
least 1500 g/dm.sup.3, more preferably of at least 1750 g/dm.sup.3,
even more preferably of at least 2000 g/dm.sup.3. And preferably
below 3500 g/dm.sup.3, more preferably below 2500 g/dm.sup.3.
[0011] The value of the density for a burner deck can be set by
compressing a fabric to a specific thickness for use as burner
deck.
[0012] Preferably, the zone with a high density is not connected
via metal bonds to the perforated plate, woven wire mesh or
expanded metal sheet supporting the woven, knitted or braided
burner deck.
[0013] It is known that boilers in which heat is generated by a
burner can show thermo acoustical instabilities. The result is
noise that can be very irritating. In gas premix burners, air is
fed by a fan and mixed with combustible gas, e.g. by means of a
venturi, and introduced in a premixing chamber after which the
premix of gas and air is combusted after flowing through a porous
burner deck. The hot flue gas transfers its thermal energy to a
fluid in a heat exchanger after which the flue gas is evacuated
through a chimney. The combination of parts of the boiler results
in it that noise is generated, e.g. by the gas flow through the
fan. The presence of the flame can amplify any noise that is
present, from a level that the noise is not audible up to levels
that are very annoying. Noise is a standing wave. The flame is not
constant over time. The short term fluctuations in the flame can
coincide with the frequency of the noise resulting in amplification
of the standing waves (and consequently of the noise). This process
is called thermo-acoustic instability. The burner needs to be
operated over a certain load range and also in a range of the air
to gas ratio. This creates a large range of possible conditions of
operation of the boiler, that each need to be sufficiently silent
in operation, meaning that acoustic instabilities should be
sufficiently low over the full range of modulation of the burner.
The interactions between the different parameters are believed to
be extremely complex and not understood. A known solution in the
use of mufflers in the boilers, however this is an expensive
solution.
[0014] Surprisingly, the gas premix burners of the invention have
shown to have substantially less thermo acoustic instabilities than
prior art gas premix burners.
[0015] The use of knitted burner decks is preferred, because it
allows manufacturing of burners with a more complex double-curved
burner deck shape. The knitted burner deck can be using spun yarns
comprising metal fibers of discrete length, using metal
multifilament yarns, or using metal monofilaments.
[0016] In a preferred embodiment, the woven, knitted or braided
burner deck comprises a zone or zones with a density less than the
density of the zone with high density.
[0017] Preferably the zone or zones with density less than the
density of the zone with high density has a density lower than 1100
g/dm.sup.3, preferably lower than 1000 g/dm.sup.3, but preferably
higher than 800 g/dm.sup.3, more preferably higher than 900
g/dm.sup.3.
[0018] Preferably the zone or zones with density less than the
density of the zone with high density cover at least 20%, more
preferably at least 30%, even more preferably at least 40% of the
surface of the burner deck.
[0019] A burner deck with zones of different densities can be
obtained by different levels of compression of different zones of
the fabric that is used for the burner deck.
[0020] Embodiments with zones with different densities have shown
to provide synergistic benefits, in that the presence of such zones
of the burner deck with lower density than the density of the zone
with high density further reduces acoustic instabilities.
[0021] In a preferred embodiment, one or more sections of the
burner deck of the gas premix burner are double curved; and the
zone or zones of the burner deck with density less than the density
of the zone with high density, comprise at least part of, and
preferably in full, the one or more sections of the burner deck
that are double curved.
[0022] Where a surface is at a point on it double curved, there is
at that point no direction in which the radius of curvature at that
point is infinite. As an example, a cylindrical burner is a burner
that has a single curved surface. A sphere is an object that is
double curved over its full surface.
[0023] This preferred embodiment allows easy production of double
curved burners according to the invention. In zones in which the
fabric that will form the burner deck is less compressed, it can
more easily be deformed, allowing draping and mounting the fabric
on the supporting perforated plate, woven wire mesh or expanded
metal sheet, while obtaining synergistic benefits of less
thermo-acoustic instabilities and the benefits of using a fabric as
burner deck.
[0024] The use of knitted burner decks is preferred as knitted
fabrics allow more easily setting different levels of density by
different levels of compression of the knitted fabric that will be
used as burner deck.
[0025] In a preferred embodiment of the invention, the zone with a
high density does not cover points of the burner deck that have a
smallest radius of curvature of less than 5 mm, preferably of less
than 8 mm.
[0026] Geometrically, at each point of the burner deck, many radii
of curvature can be defined; each of them is associated with a
particular cut according to a plane containing the normal line to
the burner deck at the point under consideration. The intersection
of this plane with the burner deck results in a trajectory. The
radius of curvature is the radius of the circle in the intersecting
plane, which osculates to second order the trajectory at the point
under consideration. Out of all these possible planes, containing
the normal line through the point under consideration, with
associated trajectories and radii of curvature, the smallest radius
can be determined for each position of the burner deck.
[0027] In a preferred embodiment of the invention, the zone or
zones of the burner deck with density less than the density of the
zone with high density comprise the circumference of the burner
deck. Such burners have shown better results.
[0028] In a preferred embodiment of the invention, the burner deck
comprises a zone with a density lower than 900 g/dm.sup.3,
preferably lower than 750 g/dm.sup.3. Preferably the burner
comprises an ionization electrode and/or an ignition electrode, and
a zone with a density lower than 900 g/dm.sup.3 (and preferably
lower than 750 g/dm.sup.3) is provided at the location of the
ionization electrode and/or at the location of the ignition
electrode.
[0029] Preferably, the zone with a density lower than 900
g/dm.sup.3 (and preferably lower than 750 g/dm.sup.3) covers less
than 20%, more preferably less than 10%, of the surface of the
burner deck.
[0030] Such embodiments have specific synergistic benefits: [0031]
When an ignition pen is installed at such a zone, ignition of the
burner is reliably facilitated, eliminating problems of bad, late
or noisy ignition. [0032] When an ionization pen is installed at
such a zone, ionization current measurement by means of the
ionization pen can be used in a broad load range of the burner as a
reliable indication of the air to gas ratio of the gas premix
burner and hence as input for the modulation of the air to gas
ratio supplied to the gas premix burner. Improved modulation
contributes to the avoidance of acoustical instabilities, as the
burner can be better controlled to avoid falling into a range of
operation in which acoustical instabilities could occur.
[0033] In a preferred embodiment of the invention, the burner deck
has over its full surface a constant density.
[0034] Preferably, the burner deck has a mass per unit of area
larger than 1000 g/m.sup.2, preferably larger than 2000 g/m.sup.2
and preferably smaller than 2750 g/m.sup.2. Examples of fabrics
that can be used for the burner deck are knitted fabrics with a
specific weight of 1250 g/m.sup.2 or 1400 g/m.sup.2 or 2400
g/m.sup.2.
[0035] In a preferred embodiment, the burner deck has over its full
surface a constant mass per unit of area
[0036] In preferred embodiments, the burner deck is not over its
full surface bonded to the perforated plate, woven wire mesh or
expanded metal sheet supporting the burner deck.
[0037] In preferred embodiments of the invention, the burner deck
is bonded locally, e.g. via spot or line welding, to the perforated
plate, woven wire mesh or expanded metal sheet supporting the
burner deck.
[0038] In preferred embodiments of the invention, the burner deck
is bonded to the perforated plate, woven wire mesh or expanded
metal sheet at edge zones of the burner deck, and preferably only
bonded at the edge zones of the burner deck.
[0039] In a preferred embodiment, the burner deck is soft welded
over at least part of its surface to the perforated plate, woven
wire mesh or expanded metal sheet. Preferably the soft welding is
performed over at least 50% of surface of the burner deck, more
preferably over at least 75% of its surface, and even more
preferably substantially over its full surface or over its full
surface. Preferably the soft welding is performed (e.g. by means of
capacitor discharge welding) such that when pulling the woven,
knitted or braided burner deck from the perforated plate, woven
wire mesh or expanded metal sheet, the soft welded bonds between
the woven, knitted or braided burner deck and the perforated plate,
woven wire mesh or expanded metal sheet are broken rather than that
breakage in the woven, knitted or braided burner deck occurs. The
test method to determine that the burner deck is soft welded, is
pulling in peel-off mode: an edge portion of the burder deck is
removed from the perforated plate, woven wire mesh or expanded
metal sheet, and folded over 180.degree.. Pulling the burner deck
is then done by hand or using pliers, wherein the pulling force is
exerted parallel with the perforated plate, woven wire mesh or
expanded metal sheet, in a direction of 180.degree. to the burner
deck. In pulling, the force builds up until the burner deck is
progressively peeled off from the supporting perforated plate,
woven wire mesh or expanded metal sheet leaving no metal fibers of
the burner deck on the supporting perforated plate, woven wire mesh
or expanded metal sheet (indicating that soft welding occurred); or
until progressively destroying the burner deck at least partly
wherein metal fibers of the burner deck remain attached to the
supporting perforated plate, woven wire mesh or expanded metal
sheet (indicating that no soft welding occurred). Within the limits
of the described "pulling in peel-off mode" the conclusion whether
or not the burner deck is soft-welded to the supporting perforated
plate, woven wire mesh or expanded metal sheet is independent of
further parameters.
[0040] Such embodiments have shown further improvement in the
reduction of thermo-acoustical instabilities.
[0041] In embodiments in which the burner deck is over part of its
surface or over its complete surface bonded via soft welding to the
perforated plate, woven wire mesh or expanded metal sheet, the
benefits of using a woven, knitted or braided burner deck
comprising metal fibers are maintained. The benefits are that when
the burner is in use the woven, knitted or braided burner deck can
freely expand; and the perforated plate, the woven wire mesh or the
expanded metal sheet remains sufficiently cool.
[0042] Preferably the woven, knitted or braided burner deck
comprises or consists out of spun yarns, which comprise metal
fibers of discrete length.
[0043] In a preferred embodiment, the woven, knitted or braided
burner deck comprises yarns comprising or consisting out of metal
filaments. With filament is meant a fiber of virtually infinite
length. The yarns comprising metal filaments can be metal
multifilament yarns or can be metal monofilament yarns.
[0044] In a preferred embodiment, the burner deck is one layer of a
woven, knitted or braided fabric, placed on the perforated plate,
woven wire mesh or expanded metal sheet.
[0045] In a preferred embodiment, the burner deck is knitted, woven
or braided using yarns comprising or consisting out of a plurality
of metal filaments or metal staple fibers in the cross section, or
using yarns consisting out of metal monofilaments.
[0046] In a preferred embodiment, the surface of the woven, knitted
or braided burner deck at the other side than the side of the
perforated plate, woven wire mesh or expanded metal sheet is not
covered by another metallic object, such that the surface of the
woven, knitted or braided burner deck is, when the burner is in
use, the surface on which combustion takes place.
[0047] Examples of preferred metal fibers are stainless steel
fibers. A specifically preferred range of stainless steel fibers
are chromium and aluminium comprising stainless steel fibers as in
DIN 1.4767, e.g. as are known under the trademark FeCrAlloy.
[0048] Preferred are metal fibers with equivalent diameter of less
than 50 .mu.m, more preferably of less than 40 .mu.m. With
equivalent diameter of a fiber is meant the diameter of a circle
with the same surface area as the cross sectional area of that
fiber.
[0049] Preferred metal fibers for use in the invention, e.g.
stainless steel fibers, with an equivalent diameter less than 50
micrometer or less than 40 micrometer, e.g. less than 25
micrometer, can be obtained by a bundle drawing technique. This
technique is disclosed e.g. in U.S. Pat. No. 2,050,298,
US-A-3277564 and in U.S. Pat. No. 3,394,213. Metal wires are
forming the starting material and are covered with a coating such
as iron or copper. A bundle of the covered wires is subsequently
enveloped in a metal pipe. Thereafter the thus enveloped pipe is
reduced in diameter via subsequent wire drawing steps to come to a
composite bundle with a smaller diameter. The subsequent wire
drawing steps may or may not be alternated with an appropriate heat
treatment to allow further drawing. Inside the composite bundle the
initial wires have been transformed into thin fibers which are
embedded separately in the matrix of the covering material. Such a
bundle preferably comprises not more than 2000 fibers, e.g. between
500 and 1500 fibers. Once the desired final diameter has been
obtained the covering material can be removed e.g. by solution in
an adequate leaching agent or solvent. The result is a bundle of
metal fibers.
[0050] Alternatively metal fibers for use in the invention, such as
stainless steel fibers, can be manufactured in a cost effective way
by machining a thin plate material. Such a process is disclosed
e.g. in U.S. Pat. No. 4,930,199. A strip of a thin metal plate is
the starting material. This strip is wound a number of times around
a rotatably supported main shaft and is fixed thereto. The main
shaft is rotated at constant speed in a direction opposite to that
in which the plate material is wound. A cutter having an edge line
extending perpendicularly to the axis of the main shaft is fed at
constant speed. The cutter has a specific face angle parallel to
the axis of the main shaft. The end surface of the plate material
is cut by means of the cutter.
[0051] Yet an alternative way of producing metal fibers for use in
the invention is via extraction or extrusion from a melt of a metal
or metal alloy.
[0052] Another alternative way of producing metal fibers for use in
the invention is machining fibers from a solid block of metal.
[0053] Yarns, comprising or consisting out of metal fibers, for the
production of the knitted fabric, the braided fabric or the woven
fabric for use in the invention can e.g. be spun from stretch
broken fibers (such as bundle drawn stretch broken fibers) and/or
can e.g. be yarns made from shaved or machined fibers. The yarns
can be plied yarns, e.g. two ply, three ply . . . . Preferred
fabrics made from metal fibers have a mass per unit of area of
between 0.6 and 3 kg/m.sup.2; preferably between 0.7 and 3
kg/m.sup.2, even more preferred between 1.2 and 2.5 kg/m.sup.2.
[0054] The knitted fabric, the braided fabric or the woven fabric
can also comprise metal monofilaments. The knitted fabric, the
braided fabric or the woven fabric can e.g. be produced out of
metal monofilaments.
[0055] In a preferred embodiment, the knitted fabric, the braided
fabric or the woven fabric has a mass per unit of area between 0.6
and 1.3 kg/m.sup.2, more preferably between 0.6 and 0.9
kg/m.sup.2.
[0056] Preferably, the gas premix burner of the invention is suited
for use in a boiler or water heater.
[0057] The second aspect of the invention is a boiler or water
heater comprising a gas burner as in the first aspect of the
invention.
[0058] Features of different embodiments and of different examples
of the invention may be combined while staying within the scope of
the invention.
BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS
[0059] FIG. 1 shows an example of a gas premix burner of the
invention.
[0060] FIG. 2 shows an example of an inventive burner with a
double-curved burner deck.
[0061] FIGS. 3 and 4 show cross sections of the burner of FIG.
2.
[0062] FIG. 5 shows the knitted fabric used for the burner deck of
the burner of FIG. 2.
[0063] FIG. 6 shows another example of an inventive burner with a
double-curved burner deck.
[0064] FIGS. 7 and 8 show cross sections of the burner of FIG.
6.
MODE(S) FOR CARRYING OUT THE INVENTION
[0065] FIG. 1 shows an example of a gas premix burner 100 of the
invention. The gas premix burner 100 has a single-curved knitted
burner deck. The knitted fabric consists out of spun stainless
steel fiber yarns knitted into a fabric. The knitted burner deck
110 is supported by a perforated metal plate 130. The knitted
burner deck 110 has two zones with different densities. A zone 140
with a high density and a zone with a lower density 160, at which
an ignition pen 170 is mounted. In the same way a zone with a lower
density can be foreseen at an ionization electrode. It is also
possible to provide the burner with a burner deck of uniform
density equal to the density of the zone 140 of high density of the
burner 100 of FIG. 1.
[0066] Table I summarizes the results of trials with the burner of
FIG. 1. All trials have been performed with the same burner
geometries (except for modifying the knitted burner deck as
indicated in table I) and with a uniform density of the knitted
burner deck.
TABLE-US-00001 TABLE I Results for burner decks with a constant
density A B C 1400 1000 Thermo-acoustic instabilities present
during normal operation 2400 1200 Thermo-acoustic instabilities
present during normal operation 1400 1273 Thermo-acoustic
instabilities only present during start-up sequence. 2400 1500
Thermo-acoustic instabilities only present during start-up sequence
1400 1750 Burner operates well (no thermo-acoustic instabilities
under all possible circumstances) 2400 2000 Burner operates well
(no thermo-acoustic instabilities under all possible circumstances)
A: Mass per unit of area of the knitted burner deck (g/m.sup.2); B:
Density (g/dm.sup.3) of knitted burner deck; C: Observation of
thermo-acoustic (TA) instabilities
[0067] FIG. 2 shows an example of a gas premix burner 200 according
to the invention with a burner deck comprising double curved
sections. The burner 200 comprises a knitted metal fiber yarn
burner deck 210 supported by a woven metal wire mesh (not shown on
FIG. 2) and a metal plate 235. FIGS. 3 and 4 show the cross
sections of the burner 200 along lines III-III and IV-IV
respectively. FIGS. 3 and 4 show the woven metal wire mesh 330, 430
supporting the knitted metal fiber yarn burner deck 310, 410 and
the plate 335, 435 welded along the edges of the knitted metal
fiber yarn burner deck 310, 410 to the knitted metal fiber yarn
burner deck 310, 410. This welding operation creates a weld between
the metal plate 335, 435 and the knitted metal fiber yarn burner
deck 310, 410 and through the applied heat at the same locations
also between the knitted metal fiber yarn burner deck 310, 410 and
its supporting woven metal wire mesh 330, 430.
[0068] FIG. 5 shows the knitted metal fiber yarn fabric 510 that is
used for the burner deck of the burner shown in FIG. 2. The fabric
510 shows sections with different density. A first section consists
out of zones 541 of high density. A second section consists out of
zones 551 with density less than the density of the zones 541 with
high density. An optional zone 560 can be present with density
lower than 900 g/dm.sup.3 (e.g. a density of 875 g/dm.sup.3), zone
at which an ionization electrode and/or an ignition pen can be
advantageously be installed.
[0069] Table II summarizes the results of trials performed on the
burner shown in FIGS. 2-5, compared to the same burner geometry and
a prior art knitted burned deck.
TABLE-US-00002 TABLE II Results for burner deck with different
density levels A B C D 1400 1400 950 Much less TA instabilities
present; less risk of TA instabilities when disturbing factors
occur 2400 1714 950 Much less TA instabilities present; less risk
of TA instabilities when disturbing factors occur 1400 2333 950 No
TA instabilities, minimized risk of occurrence of TA instabilities
when disturbing factors occur 2400 3000 950 No TA instabilities,
minimized risk of occurrence of TA instabilities when disturbing
factors occur A: Mass per unit of surface area of knitted burner
deck (g/m.sup.2); B: Density (g/dm.sup.3) of the zone with high
density; C: Density (g/dm.sup.3) of the zone with density less than
the zone with high density; D: Observation of thermo-acoustic (TA)
instabilities.
[0070] FIG. 6 shows another example of a gas premix burner
according to the invention with double-curved sections. The burner
600 comprises a knitted metal fiber yarn burner deck 610 supported
by a woven metal wire mesh 630 and a metal plate 635. FIGS. 7 and 8
show the cross sections of the burner 600 along lines VII-VII and
IV-IV respectively. FIGS. 7 and 8 show the woven metal wire mesh
730, 830 supporting the knitted metal fiber yarn burner deck 710,
810 and the plate 735, 835 welded along the edges of the knitted
metal fiber yarn burner deck 710, 810 to the knitted metal fiber
yarn burner deck 710, 810. This welding operation creates a weld
between the metal plate 735, 835 and the knitted metal fiber yarn
burner deck 310, 410 and through the applied heat at the same
locations also between the knitted metal fiber yarn burner deck
310, 410 and its supporting woven metal wire mesh 730, 830.
[0071] The burner deck 610 has a central zone 642 where it is
single curved and two end sections 652 where it is double curved. A
knitted metal fiber fabric of 1400 g/m.sup.2 is used as burner
deck.
[0072] In a first example of this burner, the density of the burner
deck was constant over its complete surface, 1500 g/dm.sup.3.
[0073] In a second example of this burner, the density of the
burner deck at the two double curved end sections 652 and at the
transition into the single curved central zone 642 is 950
g/dm.sup.3. The density of the burner deck in the central zone is
1700 g/dm.sup.3.
[0074] In both examples of this burner, the selection of the burner
deck resulted in improved thermo-acoustic behaviour of the burner
compared to prior art burners of the same burner deck geometry.
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