Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title: M~-~O~ OF FORMING RADIANT FIBER BURNER
FIELD OF THE lNv~NlION
The present invention relates to a radiant
burner for the combustion of gaseous fuel/oxidant mixtures,
and more particularly to a method for production of such a
burner.
BACKGROUND
The combustion of gaseous fuels requires mixing
of the fuel gas with a source of oxidant. This source of
oxidant is most commonly normal ambient air. "Oxygen-
enriched" air is also obtainable by a variety of methods inknown manner. Each gaseous fuel has lower and upper
flammability limits which define the minimum and maximum
fuel content of the fuel/oxidant mixture in order for
combustion to occur. Depending on the gaseous fuel and the
fuel concentration of the fuel/oxidant mixture, the
resulting flame will possess a characteristic flame speed.
The flame speed is the velocity at which the flame will
propagate towards the source of the fuel/oxidant mixture
supply. A stable flame front (i.e., leading edge of the
flame) is established, when the velocity of the fuel/oxidant
supply equals the flame speed.
The propagation of a flame front depends on the
leading edge of the flame being able to raise the
temperature of the fuel/oxidant mixture through which it is
propagating to a minimum temperature (ignition temperature)
in order for the chemical reaction of combustion to occur.
If unable to continually raise the fuel/oxidant mixture to
the ignition temperature, the flame front will establish
itself at a point where it was last able to achieve the
required temperature rise of the fuel/oxidant mixture.
The purpose of a "premix" burner is to provide
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a controlled flow of fuel/oxidant mixture to the area
intended for the combustion process (flame zone). When
the flow rate of the fuel/oxidant mixture through a burner
reduces, the port velocity reduces. This typically causes
the flame front to establish itself closer to the actual
burner port(s). As the flame front anchors closer to the
burner port(s), thermal energy from the base of the flame
will heat up the material forming the burner port(s). The
temperature resistance of the burner port material
therefore is one limiting design feature for establishing
a minimum allowable port velocity. When flame speed
exceeds port velocity, the flame front will attempt to
propagate through the burner port(s). Energy absorbed by
the burner port material tends to ~'quench~ the flame
front. If the flame front can raise the fuel/oxidant
mixture to ignition temperature despite the quenching
effect of the port material, the flame might propagate
through the port(s) and ignite the fuel/oxidant mixture
upstream of the burner port(s). This undesirable
condition is called flashback or pre-ignition. This
condition can also occur if the burner port material
itself gets hot enough to ignite the fuel/oxidant mixture
upstream of the burner port(s). These design limitations
restrict the ability of burners to accommodate a large
turndown ratio (i.e., fuel input range), and hence,
operating range for the burner.
Many conventional burners are not intended to
operate as radiant bodies. Such burners are often formed
from steel either with slot-shaped or circular ports. As
such, they produce hot combustion gases, with
insignificant radiant heat.
Radiant burners are preferred for a number of
applications. They have the advantage of maintaining a
lower flame temperature and hence, reducing the production
of nitrous oxides.
Burners intended to be capable of operation as
radiant bodies exist in a variety of forms, for example:
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solid clay ported ceramics manufactured by Hamilton
Procelains and Schwank; fibrous permeable matrices
manufactured by Alzeta Pyrocore and A.O. Smith.
The solid clay ported types are restricted to
low levels of energy per unit surface area, are not
capable of wide input rate turndown and possess relatively
high thermal conductivity conducive to pre-ignition if
overheated. They are therefore typically used for fixed
input burners for use in open atmosphere.
The fibrous permeable matrix types allow the
fuelloxidant mixture to permeate only through the matrix
of fibers. Therefore these types operate in a
predominantly subcutaneous combustion mode. They possess
only modest turndown capability because of the
predominance of subcutaneous combustion operation and the
inherent flame quenching that occurs especially at low
fuel input rates. They can also suffer from extraordinary
fuel and/or oxidant filtration requirements to prevent
clogging.
U.S. Patent 4,673,349 (Abe et al.) discloses a
high temperature surface combustion burner plate made from
a ceramic porous body with a plurality of throughholes.
However, little teaching is given on the formation of the
throughholes, and it simply refers to forming these either
by pins during the molding, or subsequently by drilling.
Neither technique provides a satisfactory method
for the quick, economic production of burners. Pins can
become stuck in the burner or rupture it during removal,
while drilling is very time-consuming. What is therefore
desired is a method of manufacturing a burner capable of
withst~n~ing elevated temperatures so as to act as a
radiant body which method is simple and reliable. The
burner should possess a low thermal conductivity yet have
sufficient flame thermal quenching characteristics to
minimize or eliminate flashback/pre-ignition. The method
should provide passageways which are not prone to clogging
so as to only require reasonable filtration. The method
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should enable burners of a variety of shapes or dimensions
to be produced to accommodate scaling of energy input range
or adaptation to various combustion chamber orientations.
The burner should be economical to produce.
SU~RY OF THE PRESENT lNVI!iNllON
In accordance with the present invention, there
is provided a method of forming a burner for a gaseous
mixture of a fuel and an oxidant, the method comprising:
(a) forming a random mix of refractory fibers,
which preferably comprise pre~o~;n~ntly alumina and silica;
(b) forming a burner body of a predetermined
shape including an inlet for a fuel and oxidant mixture;
(c) treating the burner blank with colloidal
silica and subsequently baking the burner blank to bond and
preshrink the fibers; and
(d) forming passageways in the burner blank by
perforating the burner body with pin means solely by
punching.
The body of the burner can be initially
fabricated by a known method, preferably slurry vacuum
forming. The fibers can comprise any suitable ceramic or
refractory fibers, capable of bonding to form a rigid body
capable of withstanding temperatures encountered in use.
Further, the fibers should be capable of forming a body that
permits permeation of gas through interstices of the fibers.
The body should be sufficiently rigid and strong that ports
or passageways can be formed by perforation with no
significant damage to the body; this encompasses fiber
compositions that may require subsequent treatment, e.g.
with colloidal silica, before forming the ports. A chemical
analysis of the initial fabricated body is typically
represented by a percentage by weight analysis as follows:
Ferric Oxide FeO3 0.53 - 0.97
Titanium Oxide TiO2 0.70 - 1.27
Magnesium Oxide MgO Trace
Calcium Oxide CaO 0.04 - 0.07
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Alkalies as Na20 0.08 - 0.15
Boron Oxide B203 0.03 - 0.06
Organics 1.36 - 2.47
Alumina and Silica Balance
The organic catalyst outgasses at temperatures
about 300~F (149~C) while complete elimination of organic
material is realized by baking at 1,000~F (538~C) or more.
These fibers are capable of continuous use at temperatures
up to 2,250~F (1232~C) and exhibit excellent thermal shock
characteristics up to 3,100~F (1,704~C) which is the
nominal melting point. The fibers appear white to cream
in color. Thermal conductivity (BTU/Hr/FT2/degreeF/inch
of thickness) nominally ranges from 0.49 at 600~F to 1.23
at l,800~F (10.9 at 316~C to 27.5 at 982C kW/cm2/C/cm of
thickness).
Treatment with a solution of up to 20~ colloidal
silica for rigidizing, and baking at a nominal 2,000~F
(1,093~C) temperature or higher for fiber bonding and
preshrinking, is included in the fabricating process for
this composition. Linear shrinkage ranges from 1.0 to 2.6
percent depending on initial fiber density and baking
temperature. At this stage the fiber matrix embodiment is
described as a "burner blank .
The burner blank is subjected to a subsequent
fabrication method to form ports for passage of the
fuel/oxidant mixture through the fiber matrix of the
material. These ports are the primary passages with some
permeation of the fuel/oxidant mixture occurring within
the matrix. Sizing and spacing of these ports can vary to
suit the application.
While individual steps of the method may be
known, the combination of these steps produces a burner
blank possessing the physical and mechanical properties
necessary for compatibility with the port forming method.
The combination of specifications also produces a fiber
matrix of suitable flame quenching characteristics so as
to provide a burner which is flashback/pre-ignition
2~3~5a
resistant when proper port sizings are incorporated. If
the fibers are not properly treated during the primary
fabrication of the burner blank, the desired process of
port formation will not be achievable, and various failure
modes would occur during port formation.
The physical size of the burner will be
determined by the combustion chamber into which it is to
be used, the fuel input, and the port loading capabilities
of the burner. The port loading is dependent on the
fuel/oxidant mixture being used.
Inadvertent damage to the fiber matrix after
final fabrication of the burner head can be repaired
provided the damage is limited and localized. A method of
repair, which forms part of the present invention,
comprises applying a localized wetting of colloidal silica
or the mixing of preshrunk fibers with a solution of
colloidal silica and applying the mixture as a filler
depending on the degree and depth of damage to the fiber
matrix. Air drying of the colloidal silica solution is
adequate. Silica crystals will bond the fibers as the
aqueous solution evaporates. These silica crystals tend
to increase local density and reduce inter-fiber spaces
thereby reducing localized permeation of the fuel/oxidant
mixture with a characteristic reduction in localized
subcutaneous combustion and radiative emission.
Preferably, the burner body or blank is
perforated by means of a comb assemblies, each of which
comprises a plurality of parallel pins. For a cylindrical
burner body, the comb assemblies would be aligned parallel
to the axis of the cylinder and pressed into the cylinder,
from generally diametrically opposite positions. The comb
assemblies can then be withdrawn, and the cylinder indexed
through a predetermined angle, to enable the operation to
be repeated. By repeating the steps, the entire
cylindrical surface of the burner body or blank can be
perforated. Further, one set of pins can be axially and
circumferentially offset or staggered relative to the
s o
other, to give a staggered array of ports, where desired.
Advantages of the present invention are:
(a) a high degree of resistance to
flashback/pre-ignition is obtained even in modulated
operation over a wide range of fuel/oxidant proportions
and volumetric flow rates;
(b) the formation of relatively large ports
(compared to inter-fiber spaces) through the fibrous
matrix minimizes susceptibility to clogging thereby
minimizing filtration requirements;
(c) the material of the present invention, when
prepared to the specifications cited, enables the
machining of ports or the forming of ports by a
perforating process which results in a low cost burner;
(d) the material of the present invention is
capable of withstanding elevated temperatures enabling it
to act as a radiant body which when created behind the
flame envelope produces a more luminous flame which
enhances radiative energy transfer from the flame;
(e) the porous inter-fiber space permits
permeation of the fuel/oxidant mixture thereby obtaining
partial subcutaneous combustion to create a radiant
surface and an ionized ground plane for the adaptation of
electronic flame rectification safety control systems;
(f) the thermal insulating characteristic of
the fiber matrix maintains low interior burner head
surface temperatures enabling simple and low cost means of
attachment of the burner to the fuel/oxidant supply
system;
(g) the fabricating methodology results in a
cost-effective burner providing unique characteristics
compared to other radiant burners currently available; and
(h) the fibrous matrix can be field-repaired if
limited localized damage to the fiber-to-fiber bonds
occurs.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
For a better understanding of the present
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invention and to show more clearly how it may be carried
into effect, reference will now be made, by way of
example, to the accompanying drawings in which:
Figure 1 is an isometric view showing one
embodiment of the fiber burner;
Figure 2a - c shows various port arrays;
Figure 3 shows an internal support baffle for
mounting longer burners in a horizontal position; and
Figures 4 shows a front view of an apparatus for
forming passageways in the burner; and
Figure 5 is an electrical schematic of a control
circuit of the apparatus of Figure 4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The burner 2 is in the form of a cylinder with
one closed end 4 and another open end 6, forming an inlet
for a gas/air mixture. The cylinder has an internal
cylindrical wall 8, and an external cylindrical wall 10.
The closed end wall has a similar thickness to the
cylindrical sidewall. At either end, there are an inlet
end portion 12 and an outlet end portion 14, which are
left unperforated. A main, central portion 16 of the
cylinder is perforated to incorporate ports through the
cylinder wall, as shown. The inlet end portion 12
facilitates mounting to a fuel/oxidant supply system by
suitable means and provides for offsetting the flame zone
from the mounting arrangement by a desired amount.
The burner body is formed from bonded refractory
fibers, predominantly alumina and silica, although Kaolin
fibers may alternatively be used. The body of the fiber
matrix is initially fabricated by a common method known as
a slurry vacuum forming, into the desired burner shape. A
chemical analysis of the initial fabricated body is
typically represented by a percentage by weight analysis
and is as follows:
Ferric Oxide FeO3 0.53 - 0.g7
Titanium Oxide TiO2 0.70 - 1.27
Magnesium Oxide MgO Trace
2 12~
'.,~
Calcium Oxide CaO 0.04 - 0.07
Alkalies as Na20 0.08 - 0.15
Boron Oxide B203 0.03 - 0.06
Organics 1.36 - 2.47
Alumina and Silica Balance
The organic catalyst outgasses at temperatures
about 300~F (149~C). Here, the organic material is
completely eliminated by baking at l,000~F (538~C) or more.
These fibers are capable of continuous use at temperatures
up to 2,250~F (1232~C) and exhibit excellent thermal shock
characteristics up to 3,100~F (1,704~C) which is the
nominal melting point. The fibers appear white to cream
in color. Thermal conductivity (BTU/Hr/FT2/degreeF/inch
of thickness) nominally ranges from 0.49 at 600~F to 1.23
at 1,800~F (10.9 at 316C to 27.5 at 982C kW/cm2/C/cm of
thickness).
The fibers are treated with a solution of up to
20% colloidal silica for rigidizing, and are then baked at
a nominal 2,000~F (1,093~C) temperature or higher for fiber
bonding and preshrinking. This treatment has been found
essential for fibers of the above composition, as
otherwise the fibers are too soft for the ports or
passageways to be formed reliably. These steps are
included in the primary fabricating process. Linear
shrinkage ranges from 1.0 to 2.6 percent depending on
initial fiber density and baking temperature. At this
stage the fiber matrix is described as a "burner blank".
The burner blank is then subjected to a
subsequent fabrication method to form ports for passage of
the fuel/oxidant mixture through the fiber matrix of
material.
The ports are formed by a punching operation, as
detailed below. Where a punching operation is used, a
sharp or needle-shape punch is used, which effectively
displaces the fibers of the burner body to the side,
rather than punching out a cylindrical plug of material.
The ports are the primary passages with some
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permeation of the fuel/oxidant mixture occurring within or
through the matrix. Sizing and spacing of these ports can
vary to suit the application. Embodiments to date have
incorporated round ports with diameters ranged from 0.055
to 0.099 inch (1.4 to 2.5mm) and a version with linear
slot port widths of 0.125 inch (3.2mm).
The spacing of ports is typically on a staggered
array when utilizing round ports.
Figure 2 shows a variety of different port
arrays with the ports denoted 18. In Figure 2a, the ports
have, as shown, a horizontal spacing of .19 inches in each
row, and a vertical spacing, between alternate rows of .32
inches. In Figure 2b, the spacing in each row is reduced
to .12 inches, and alternate rows are now spaced by .29
inches. Finally, the version as shown in Figure 2c has a
port spacing in each row of .29 inches, and the spacing
between alternate rows of .16 inches. The spacing should
be chosen to give the desired gas flow characteristics.
Further the ports should be sufficiently far apart that
the burner blank does not suffer significant damage during
the port forming operation.
In an alternative arrangement, each port has a
size of nominally 1/16 inch (1.6 mm) diameter. Spacing
between ports in the same lateral or axial row is
nominally 9/32 inch (7.1 mm) with staggered lateral rows
of ports offset axially by nominally 9/64 inch (3.6 mm).
Radial spacing between staggered rows is nominally 1.5
degrees to form a uniform staggered pattern, with the
radius such that the circumferentially spacing is
comparable to the axial spacing. The pattern and size of
ports is adaptable to variation to suit the applications.
Following the formation of the ports, the burner is
cleaned as far as possible of any residual dust, debris
and small particles caused by the port-forming process;
this is achieved by using compressed air.
Following this, there is an optional further
step of treating the burner with colloidal silica, which
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again can comprise up to 20% colloidal silica. After
soaking in the colloidal silica, the burner is then
treated to a low temperature bake at 200~F (95~C) simply to
dry the silica. The purpose of this step is to repair any
minor fractures or damage caused by the port-forming
process. It is also recognised that the port-forming
process, despite any cleaning, may leave small particles
of debris within the ports and elsewhere, which could
subsequently become dislodged and block one or more ports.
This treatment step is intended to secure any such debris
in place, so that it cannot clog or block any ports.
In use, the burner will be subjected to
temperatures well above 200~F, but still below the earlier
baking temperature of 2,000~F. Such temperatures will
further assist in bonding the silica to the fibers of the
body.
The burner blank fabricating process thus
includes a number of steps, namely:
(a) forming the basic body shape from a
particular fiber density and composition;
(b) subsequent soaking treatment with a
specified concentration of colloidal silica; and
(c) baking at a specified minimum temperature.
The combination of these steps produces a burner
blank possessing the physical and mechanical properties
necessary for compatibility with the port forming method.
Further, it produces a fiber matrix of suitable flame
quenching characteristics so as to provide a burner which
is flashback/pre-ignition resistant when proper port
sizings are incorporated. If the fibers are not properly
treated during the primary fabrication of the burner
blank, the desired process of port formation will not be
achievable. In other words, the present invention
includes a certain combination of primary steps to produce
burner blanks with appropriate physical and mechanical
properties. Without them, the fiber-to-fiber bonds in the
matrix will not have the correct properties, which will in
2123.St~
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turn lead to various failure modes during the port forming
process.
As shown, the preferred embodiments of the
burner are cylindrical with one closed end. Dimensions
and shape are generally unrestricted subject to the
application of the finished product. Embodiments to date
have incorporated primary burner blank cylinder shapes
with length/diameter ratios ranging from 1.5 to 2.7.
Fiber wall thicknesses of 1/2 to 1 inch (1.27 to 2.54cm)
1~ and fiber densities of nominally 14 to 28 LB/FT3 have been
used.
The physical size of the burner will be
determined by the combustion chamber into which it is to
be used, the fuel input, and the port loading capabilities
of the burner. The port loading is dependent on the
fuel/oxidant mixture being used. Typical port loading
parameters of the invented burner in practical use, when
using Natural Gas with air as oxidant, range from 4130 to
61900 BTU/Hr/Sq.Inch (1,875 to 28,100 kW/m2) of port area.
The fuel/air mixture may vary over a practical
range of 6% to 9~ CH4 without flashback/pre-ignition
occurring.
Inadvertent damage to the fiber matrix after
final fabrication of the burner head can be repaired
provided the damage is limited and localized. A method of
repair, which forms part of the invention, comprises
applying a localized wetting of colloidal sil-ica-or- the
mixing of preshrunk fibers with a solution of colloidal
silica and applying the mixture as a filler depending on
the degree and depth of damage to the fiber matrix. Air
drying of the colloidal silica solution is adequate.
Silica crystals will bond the fibers as the aqueous
solution evaporates. These silica crystals tend to
increase local density and reduce inter-fiber spaces
thereby reducing localized permeation of the fuel/oxidant
mixture with a characteristic reduction in localized
subcutaneous combustion and radiative emission.
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Figure 3 shows an inner support 20 used when
mounting the burner in a horizontal orientation. This
support 20 is cross-shaped in section. It prevents a
bending moment from imposing a tensile stress on the upper
cross-section of the cylinder wall.
Figure 4 shows plan views of an apparatus or
perforator machine for forming the ports. In Figure 4,
the framework comprises an inverted U-section channel base
21 with two upright channel-section supports 22. Upper
cross members 23 and lower cross members 24 are secured
between the upright supports 22 on both the front and rear
facing surfaces. Mounting brackets 25, 26, 27 are
provided for attachment of other components in desired
positions. An upper collar 28 is centrally mounted
between the upper cross members 23. A concentrically
mating weighted cap 29 is provided which fits into the
upper collar 28. In Figure 4, upper cross members 23,
lower cross members 24, upper collar 28 and cap 29 are
omitted for clarity.
A compressed air filter/regulator/lubricator
assembly 30 is mounted on the bracket 25. An automatic
air valve 31 with bleed valves 57 on each of two exhaust
ports is mounted to the base 21 below and behind the
assembly 30. An air cylinder 32 is mounted on each of the
uprights 22. A rotary indexer table 33 with a spacer 34
is centrally mounted between the uprights 22. A hollow
steel inner tube 35 is fixed in coaxial alignment with the
rotary table 33. A platform 36 is mounted on the rotary
table 33 and incorporates vertical pins 37. A vacuum pipe
38 is attached to the underside of the channel base 21,
and is in communication with the inside of the inner
support 35 via a central passage through the rotary
indexer table 33, table spacer 34 and platform 36. A comb
holder 39 is attached to the shaft of each air cylinder 32
with a reinforcing bracket 40. Two adjustable stops 41 are
attached to each comb holder 19, and arranged to abut the
upright supports 22. A pin guide 42 with upper and lower
~1~35~0
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spacers 43, 44 is provided on each side of the inner
support 35. Additional pin guide spacers can be mounted
through the upper and lower cross members 23, 24. A
"comb" assembly 45 is clamped in each comb holder 39.
Each comb assembly 45 has multiple solid pins spaced as
required. Linear slides 46 are mounted on brackets 26 and
secured to the ends of the comb holders 39, to maintain
the combs 45 vertically aligned. Electrical ~end"
switches 55, 56 are mounted on brackets 27. A switch
"trip" bar 47 is mounted on each linear slide 46 for
actuating the switches. Tubing connects the
filter/regulator/lubricator assembly 30 in series with the
automatic valve 11 which is turn is connected to the air
cylinders 32 in a parallel arrangement for control of a
compressed air supply separately provided to the
filter/regulator/lubricator assembly 30. A control box 48
with a power supply cord 49 houses a momentary
start/resume switch 50, a momentary abort switch 51, an
alarm buzzer 52 and an electrical power rectifier and
transformer assembly 53. A commercially available indexer
module 54 is electrically connected with the control box
components 49, 50, 51, 52, 53, the end switches 55, 56 and
the automatic air valve 31 per the wiring arrangement of
Figure 5.
Orientation and geometric inter-relation of
components is further described as follows. The central
vertical axis of the rotary-indexer table 33, table spacer
34, inner support 35 and upper collar 28 is the focal axis
to which all components reference. The uprights 22 are
equidistant from the focal axis with inner facing surfaces
tangentially oriented, and diametrically opposed except
for a circumferential offset equal to the circumferential
spacing of adjacent lateral rows of burner ports. The
pins of the two comb assemblies 45 are axially offset by
half the spacing of the pins, to give a staggered port
array. The air cylinders 32, comb holders 39, comb
assemblies 45, linear slides 46 and pin guides 42 are all
~2~
in radial alignment with their respective uprights 42.
The air cylinders 32 move the comb holders 39 and comb
assemblies 45 back and forth along their respective radial
axis. The linear slides 46 maintain the vertical
S alignment of the comb assemblies 45 and comb holders 39.
The comb holder stops 41 limit the travel of the air
cylinder 32 shafts. The pin guides 42 have a vertical
column of holes through which the pins of the comb
assemblies 45 reciprocate with the shaft motion of the air
cylinders 32. The inner support 35 has a vertical column
of holes, indicated schematically at 60, on each side in
radial alignment with the air cylinders 32 at vertical
spacings equal to the pin spacing of the comb assemblies
45. The pins of the comb assemblies 45 mate with the
lS holes in the inner support 35 when shaft motion of the air
cylinders 32 advances the comb holders 39 and the comb
assemblies 45 toward the focal axis. The top edge of the
inner support is serrated, as shown as 62. the upper
cross members 23 minimize cantilever flexing of the
uprights 22 and provide mounting for the front and rear
upper pin guide spacers 44.
Referring to Figure 5, this shows an electrical
schematic of the connections to the indexer controller 54.
A parallel inputtoutput connection to the indexer 54 is
shown at 70, and in known manner, comprises 25 pins of a
D~ type male plug. An input for 120 volt AC supply is
shown at 72, with a branch connection at 74 for the
indexer 54. The transformer 53 provides a 24 volt DC
power supply. The air control valve 31 is connected
between the supply lines.
As shown, the DC output of the transformer 76 is
connected to the connector 70, for supplying power to the
indexer controller 54. The end or limit switches 55, 56
are connected as shown, and are shown in the open
positions indicating no limit position reached. The cycle
abort switch S1 and the cycle momentary start/resume
switch S0 are connected as shown. The alarm buzzer 52
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provides at least a 600 ohm resistance is connected to the
connector 70 as shown. A relay 78, also providing at
least a 600 ohm resistance is connected to the connector
70 for actuating contacts to supply power to the air
control valve 51.
The operation of this preferred embodiment of
the perforator apparatus will now be described. With the
air cylinders 32 in a retracted position, an operator
manually removes the weighted cap 29 and lowers a burner
blank, indicated at 64 (and shown in section) down through
the upper collar 28. The burner blank 64 is slid down
around the inner support 35 with a reciprocating rotatory
action if necessary so that the serrated upper edge of the
inner support 35 removes any excess material on the inside
diameter of the burner blank 64. This ensures as tight a
fit between the inner support 35 and the burner blank as
possible. The burner blank 64 is pressed vertically
downward onto the indexer table platform 36 so that the
vertical pins 37 fully penetrate the burner blank 64.
These pins 37 maintain angular alignment of the burner
blank 64 with the rotary indexer table 33. The weighted
cap 29 is replaced and ideally fits snugly over the closed
end of the burner blank, removing excess material on the
outer diameter if necessary, to maintain vertical
alignment of the burner blank and prevent the burner blank
rising up off of the rotary table platform 36. In known
manner, external connections of electrical power,
compressed air and optional vacuum (now shown) are made.
The compressed air supply is connected to the
filter/regulator/lubricator assembly 30 and through
control of the automatic valve 31 provides the motive
force to push the pins of the comb assemblies through the
walls of the burner blank 64 and subsequently retract
them. Upon connection, the compressed air immediately
passes through the automatic valve 31 to the shaft end of
the air cylinders 32 to position the comb assemblies 45 in
their retracted position. The momentary start/resume
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switch 50 initiates sequential control of all automated
functions which is performed by the commercially available
indexer module 54. A variety of functions can be
programmed.
The primary functions begin with checking of the
retracted position end switches 55 (Figure 5). If the comb
holders 39, hence the comb assemblies 45, are in their
fully retracted positions, the trip bars 47 on the lower
linear slides 46 will cause the retracted position end
switches 55 to electrically signal the indexer module 54.
If full retraction of both comb assemblies 45 is
confirmed, the automatic air valve 31 is activated which
switches the compressed air to the non-shaft end of the
air cylinders 32. This causes the shaft of the air
cylinders 32 to advance and push the pins of the comb
assemblies 45 through the walls of the burner blank 64.
If the pins of the comb assemblies 45 fully penetrate the
walls of the burner blank and properly mate with the
mating holes in the inner support 35, then the trip bars
47 on the lower linear slides 46 cause the forward
position end switches 56 to electrically signal the
indexer module 54. If full advance of both comb
assemblies 45 is confirmed by closure of both switches 56,
the automatic valve 31 is switched back so that compressed
air is passed to the shaft end of the air cylinders 32
which causes the comb assemblies 45 to return to the
retracted position. The retracted position and switches
55 are again checked to confirm full retraction of both
comb assemblies 45. If confirmed, the rotary indexer
table 33 is activated to rotate the burner blank through
the desired number of degrees. The sequence described
continues until a full rotation and hence complete
perforation of the burner blank has been obtained. Should
the full retracted or advanced positions fail to be
signalled to the indexer module 54 by the end switches 55,
56, the indexer module 54 is programmed to halt sequencing
and activate the alarm buzzer 52. The momentary
2~23~
'""~
- 18 -
start/resume switch 50 enables the operator to resume the
perforation process after correction of the malfunction.
The momentary abort switch 51 enables the operator to
irretrievably halt the sequencing at any time.
S The total angle through which the indexing table
36 needs to turn will depend upon the alignment of the two
comb assemblies 45. Where staggered ports 18 are
required, for example as shown in Figure 2, then two
different comb assemblies 45 are used, with their
individual pins axially offset by an amount equal to half
the pin spacing, as noted above. Then, the indexer table
33 is rotated through a full 360~. Additionally, an
angular offset is provided for one of the combs 45, so
that the holes punched by it are both axially and
circumferentially spaced from the holes punched by the
other comb assembly 45.
Where it is not required to provide a staggered
perforated holes, the comb assemblies 45 can be configured
to provide sets of holes in essentially the same location,
along the axial length of a burner, and be exactly
diametrically opposed. Then, each assembly 45 will
perforate the holes for half of the burner blank 64, and
it is only necessary for it to rotate through 180~.
It is preferred for the spacing of the ports or
passageways 18 to be at least four times the port
diameter, to ensure adequate supporting material around
each port, during the punching operation.
Three separate embodiments of the invented fiber
burner have been made and tested in controlled laboratory
conditions since April 1984. All three embodiments
utilize cylindrical geometry with one closed end as shown
in Figure 1, but are of different dimensions and utilize
two different fiber densities.
The smallest embodiment measured nominally 3
inch (7.6cm) outside diameter by 2 inch (5.lcm) inside
diameter by 6 1/2 inch (16.5cm) outside length. Samples
of this embodiment were operated to determine long term
~1~3~
-- 19 --
durability. One sample was cycled through more than 7,600
cycles and amassed over 1,800 operating hours. Another
sample was operated on a primarily continuous basis for
over 2,200 hours. Neither sample showed any major
deterioration.
The largest embodiment measured nominally 6 inch
(15.2cm) outside diameter by 4 inch (10.2cm) inside
diameter by 16 inch (40.6cm) outside length. A sample of
this embodiment has been tested in a boiler during the
heating seasons of 1986-87 and 1987-88 amassing over 6,300
operating hours. This embodiment has shown the capability
of being operable over a range of energy input from
100,000 to 1,500,000 BTU/Hr ~29.3 to 439.3 kW).
