Note: Descriptions are shown in the official language in which they were submitted.
~31~
FLAME DETECTOR
BACKGROUND OF THE INVENTION
The present invention relates generally to flame de-
tectors and specifically to an apparatus for conducting radia-
tion from the combustion zone of a burner to a detector device.
An essential element in the sa~ety and control of
boilers used in power generating equipment, and the Like, is
the ability to reliably detect the existence of flame at the
burner. A detector of this sort, which has proved remarkably
effective, is dislosed in a co-pending application o Horn,
Canadian Serial No. 21Q,218, filed September 27, 1974. This
detector is, as well as others may be, utilized in conjunction
with the present invention in those applications where a
- straight line of sight may not be available to view a selected
burner combustion zone.
In the above noted application, the combustion zone
was ~elected for its useful concentration of infrared radiation.
While it is not intended to limit the present invention to that
portion of the spectrum, it is a useful area to discuss for
purposes of explanation.
In certain boilers, burners are construct~d so as
to be movable during firing and it has been found that a
useful area of the combustion zone may not be within the line
of sight of the detector at all times. The invention dis-
closed herein therefore is especially useful for these applica-
tions.
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93~
The choice of a fiber optic system seems a reasonable
beginning for such a system. However, various diffficulties
revealed themselves in the course of development. One especially
troublesome problem was the transmission characteristics of
the energy transmitted. For e~ample, energy outside the
visible spectrum is required for an accurate determination of
the existence of a main burner flame in many applications, how
ever, many fiber optic materials were found to attenuate the
enexgy so drastically as to render the signals obtained essen-
tially useless. Conventional fiber optics materials provedunsatisfactory. Other materials exhibiting proper transmission
characteristics were not suited for adaptation to a fib~r
optics application.
Another major difficulty encountered was the high
temperature environment within the boiler which would fuse
the bundle and render it ineffective.
In addition to the foregoing difficulties, there
are limits to which different bundles of optics may be flexed
and for a particular size of the individual fibers, these
~0 considerations added to the constraints in the development
of the subject of the present invention.
The present invention was developed so as to be
adaptable with the highly effective detector described above
in the Horn application. However, other detectors responsive
to radiant energy may be used. For example, in the present
invention, since the attenuation of the energy transmittal
is extremely low from one end o the fiber optics bundle to
the other, it can be said that any detector system which can
directly view the flame or burner combustion zone can also
be utilized with the present invention in the event that it
1~ -2-
93~8~L
is necessary to place the detector remotely from the combus-
tion zone of the burner.
In addition to the foregoing, it has been found
that fiber optics have a tendency to exhibit substantial opti-
cal losses unless each of the fibers in the optics bundle is
clad with a material which reduces interference between adja-
cent fibers in the bundle. ~he cladding, however, has a ten-
dency to deteriorate in the hostile environment of a furnace
burner area. With certain fiber optics materials, therefore,
it has been found that unsatisfactory optical communication
is exhibited, thus rendering some systems ineffective to
transmit a sufficient quantity of radiation from the combustion
zone to a remote receiving de~ice.
It is therefore an object of the present in~ention
to provide a flame detection system for use with burners of a
movable type.
It is another object of the present invention to
provide a flame detection system wherein the detector may be
remotely located from the burner combustion zone.
It is another object of the present invention to
provide a flame detector apparatus wherein energy from a
selected area of the combustion zone is communicated to the
detector for reliable indication of the existence of a flame.
It is yet another object of the present invention
to provide a flame detector apparatus utilizing an improved
optical system capable of transmitting sufficient quantities
o radiation for detection of a flame.
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3~
.
SUMMARY OF THE INVENTION
There has been provided a flame de-tection device
or boiler systems wherein a radiation sensitive means is
responsive when energized by incident radiation of a selected
bandwidth to produce a signal indicative of the existence of
flame. ~ light pipe means including a lens system collects
incident radiation in a selected area of the combustion zone
of a burner and a flexible tube couples the radiation sensitive
means and the lens system. A fiber optics bundle conveys the
collected incident radiation from the lens system to the
detector, said fiber optics bundle of an extruded l~igll puri~y
unclad quartz material capable of conveying the radiation with-
out significant attenuation thereof.
Thus broadly, the invention contemplates a flame
detector device for a boiler furnace which comprises a
movable mounted burner, a radiation sensitive means outside
of the furnace and responsive when energized by incident
radiation of a selected energy band width to produce a signal
indicative of the existence of a flame, a lens of quartz
~0 material, and a lens housing supporting the lens with the
lens housing being connected with the burner so that the
lens is focused on the combustion zone of the burner.
flexible tube is connected at one end to the housing and at
the other end to the radiation sensitive means, and a fiber
optics bundle extending through the flexible tube conveys
the collected radiation from the lens to the radiation
sensitive means, with the fiber optics bundle comprising
fibers of extruded unclad quartz material capable of conveying
radiation without significant loss thereof.
~a~9;~8::~
For a better understanding of the present invention
together with other and further objects thereof, reference is
directed to the following description taken in connection with
the accompanyin~ drawin~s, while its scope wil]. be pointcd o~t
in the appended claims.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of the lower furnace
section of a boiler partly in section to show the detectors
of the present invention;
` FIG. 2 is a more detailed illustration of the detec-
tor system shown in FIG. l;
FIG. 3 is an exploded view of the detector system
and more specifically the light pipe construction of the detec-
tor of FIG. 2; and
FIG. 4 is a detail of the fle~ible tu~e.
.
1~3~
DESCRIPTION OF THE PREFERRED EMBODIMENT
The boiler configuration illustrated in elevational
view, FIG. 1, is one of a number of different types in which the
apparatus of the present invention may be adapted to operate.
The boiler 10 includes boiler walls 11 and at least one burner.
While a number of burners 15a, 15b are shown, the apparatus of
the present invention is equally adaptable to single and
multiple bank burners. The burners 15a, 15b inject an appro-
priate fuel shown by the arrows 17 into respective combustion
zones 12a and 12b. The detector system shown generally at 16
view their respective combustion zones 12a or 12b for certain
selective frequencies of radiant energy which have been found
useful in reliable detection of the flame. For example, the
infrared band exists in useful ~requencies in the area as 12a or
12b and for this reason, those areas are discussed in further
detail.
The burners shown in FIG. 1 may be adapted to be
movable so that the combustion zones 12a and 12b move as the
respective burners 15a and 15b are moved through an exemplary
~0 arc 13 shown in FIG. 1. For example, if it is desired to
change the temperature of a certain portion of a boiler, the
burners 15a and 15b may be moved downwardly or upwardly so
as to regulate the overall temperature of the boiler as is
well known in the art. The system of the present invention
is adapted so as to move the detector system 16 with th~
associated burner structure 15 so that the detector system 16
is always viewing the same selected combustion zone 12a or 12b
as its associated burner 15a and/or 15b. Thus, the detector 16
is connected with its associated burner structure 15 for move-
ment therewith.
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The manner in which the detector system 16 i9 movedand secured relative to the burners 15a and/or 15b may be changed
in accordance with the type of boiler.
In FIG. 2, the detector system 16 associated with
burner 15a includes an end piece 20 which is aligned with the
combustion zone 12a through a window 18 in the boiler wall 11.
The end piece 20 is coupled to a housing 21 which includes a
lens system shown in detail in FIG. 3, discussed below. Coupled
to the housing 21 is flexible tube structure 22 which flexes
as the position o~ the end piece and housing 21 are moved
relative to the combustion zone 12a. The left end of flexible
tube 22 is connected by coupling means 23a to an end of the
detector housing ~4 which includes the detector responsive to
incident radiation, which is generally shown at 25. Similarly,
coupler means 23b couples the right end of the flexible tube
22 to housing 21.
As previously mentioned, there are a number of
kinds o~ quartz material which are capable of transmitting the
preerred range of radiation and in the present invention,
materials sold under the trademarks INFRASI~L and SUPERSILL
manufactured by Amersil, Inc., Hillside~ New Jersey, are those
~hich are preferred in the present invention. For reasons dis
cussed further in the specification, these two materials exhibit
optical characteristics which have permitted their use in a
hostile environment without significant loss of the radiation
transmitted by the fiber optics bundle.
As the burner of FIG. 1 is moved for changing the
direction of the burner flame, the combustion zone 12a is
also affected thereby, such that as the combustion zone changes
the end piece 20 and associated housing 21 follow the combustion
3~
zone and obtain a uniform line of sight on the combustion
zone and therefore provide an accurate detection of the existence
of the flame.
In FIG. 3 there is shown an exploded view of the
light pipe structure wherein end piece 20 is provided with a
tapered sleeve member 20a. The sleeved portion 20a engages
with an appropriately sleeved portion 21a of the housing 21.
The end piece 20, also includes openings 27 which provide for
the passage of currents of gas and air so that the end piece
20 does not become clogged with particulate material while
vie~Ying the combustion zone of the flame.
The housing 21 has a generally cylindrical opening
lg of varying diameter passing entirely therethrough along
a central axis thereof. An annular detent at 29 is adapted
to receive a lens 26. The lens is held in place by the end
piece 22 being sleeved at 21a, 22a when the apparatus is
assembled.
The lens 26 focuses the incident radiation which
passes through the end piece 20. This radiation is focused
~0 upon one end 27A of a bundle of fiber optics 28. This bundle
carries the incident radiation down its entire length to the
remote end o~ the bundle 28 for communication with the detector
25. The fiber optics bundle 28 includes coupling members 30
which are disposed at opposite ends of the fiber optics bundle
for securing them in a package and also for coupling the ends
thereof with the housing 21 and of detector 25 respectively.
One coupling member 30 engages with the housing mem~
ber 31 in opening 31a. Coupling means 23a and 23b engage with
respective threaded openings 33 and 21b in the housing members
31 and 21 respectively. These couplings secure the light
pipe structure as illustrated in FIG. 3.
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The fiber optics bundle 28 is specially manufactured
by an extrusion process such that the diameter of each of the
fibers of the bundle is about 0.019 inches in diameter and the
bundle consists of about 30 to 40 fibers. These dimensions
and specifications have been found to be useful and effective
to transmit sufficieni amount of the incident radiation for
the purposes of the present invention. However, other dimen-
sions may be utilized if another application were required.
The fiber optics bundle 28 may be manufactured from
one of a number of kinds of high purity quartz material
possessing in varying degrees the characteristic of being able
to transmit ultraviolet and infrared radiation without signi-
ficant attenuation. There is at least one other material of
the high purity quartz type available for transmitting only
infrared radiation, which may be used in application when other
special energies are not required. The lens 26 is also manu-
factured from the same materials as the fiber optics bundle.
However, the lens might be of one type of material in order
to filter out all radiation except, for example, in~rared and
therefore simplify the manufacturing process. In such a case,
if an IR detector were required, the fiber optics bundle might
be manufactured from the high purity quartz material capable
of transmitting any of the desired frequencies required. The
lens, on the other hand, might be manufactured of the high
purity quartz material which would filter out all but the IR
range. These are examples of the flexibility which might be
built into the system for the various applications and modi-
fications to which the system is adaptable.
3~8:~L
The flexible tu~e 22 is specially manufactured
in the present invention so as to limit the flex of the over-
all light pipe to the radius o~ curvature of about ~our feet
when fully flexed. This i5 necessitated by the characteristics
of the fiber optic bundle 28 which, when extruded to the dia-
meters noted above, may exceed their flexibility limits if
bent in a tighter radius than four feet as indicated above.
In order to insure that the tubing 22 of the light pipe struc-
ture conforms to the required radius of curvature and con-
straint, a specially formed flexible tubing 22 structure hasbeen developed. In FIG. 4, a portion of the cross-section
of the light pipe is illustrated wherein two adjacent sections
22a and 2~b are shown. The flexible tubing 2~ basically
consists of a helically wrapped metal, preferably stainless
steel, with adjacent engaging ends 32a and 32b having the
opposite curved arcuate sections 33a and 33b. These sections
engage as indicated while a stopping member 34 is ~itted
between the arcuate sections 33a and 33b as the fle~ible
tube 22 is wrapped. The tube, when bent, will be limited in
~0 its flexibility by the inclusion of the stopping member 34
because the ends 32a and 32b will be prevented from approaching
each other by the width of the stopping member 34. The width
of the stopping member 34 may be varied to give greater or
less flexibility to the pipe. However, the particular con-
figuration is provided such that the tube has a radius and
curvature limit of four feet.
In the present invention, the length of the light
pipe structure shown in FIG. 3 may vary from about four to
about eight feet. However, it has been found that a greater
length may be utilized if the detector housing 24 must be
-10
placed at a great distance from the combustion zones 12a and
12b. This increased length capability may be attributed to
the superior radiation transmittal qualities of the fiber
optics bundle which, as previously noted, does not signifi-
cantly reduce the energy transmitted from the zone 12a or 12b
to the detector 25.
As previously noted in the Background, it has been
found that in general, it is necessary to clad individual
ibers in a fiber optics bundle in order to reduce interference
and optical losses of the fiber optics bundle. This cladding
effects the index of refraction of the fiber optics material
at the boundary of each of the filaments such that the radia-
tion transmitted is refracted within the bundle.
Since the burner area in a furnace is a severely
hostile environment, cladding of fiber optics materials is
ineffective since the cladding has a tendency to peel and
deteriorate, thus reducin~ the efficiency of the energy trans-
mission. The fiber optics bundle of the present invention
utilizes an unclad material which while exhibiting some losses
of the radiation, transmits sufficient amount of the energy
so as to provide a reliable indication of a flame at the
receiving end of the bundle which is coupled to the flame
detector 25.
It has been found that the materials chosen for
fabricating the fiber optics bundle, namely INFRASILL and
SUPERSILL carry sufficient energy for transmission to the
flame detector 25 when extruded to a diameter of about 0.019
inches as previously mentioned. This preferred sizing of
the fibers as well as the quality of the material itself render
the cladding of the fiber optics filaments unnecessary thereby
a8~
limiting the problems associated with deterioration of the
claddin~ in the hostile environment of a burner area. The
present system therefore reduces the cost of manufacture as
well as reducing the possibility of failure of the flame detec-
tor system due to a breakdown in the communications link
between the end piece 20 and the flame detector 25.
There has thus been shown a system for transmitting
information as to the combustion characteristics of a burner
utilizing a flame detection apparatus which is capable of
following the combustion zone of such a burner and effectively
transmitting the information over a light pipe structure capable
of superior transmittal qualities.
While there has been shown what at present is con-
sidered to be the preferred embodiment of the present invention,
it should be obvious to those skilled in the art that various
changes and modifications may be made therein without departing
from the invention. It is therefore aimed in the appended
claims to cover all such changes and modifications as fall
within the true spirit and scope of the invention.
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