U.S. patent number 3,831,561 [Application Number 05/397,355] was granted by the patent office on 1974-08-27 for device for early detection of rupture of the pressure part of a boiler.
This patent grant is currently assigned to Mitsubishi Jukogyo Kabushiki Kaisha. Invention is credited to Ryuichi Sato, Takashi Yamamoto, Kenichi Yasukouchi.
United States Patent |
3,831,561 |
Yamamoto , et al. |
August 27, 1974 |
DEVICE FOR EARLY DETECTION OF RUPTURE OF THE PRESSURE PART OF A
BOILER
Abstract
A device for early detecting any abnormal conditions of a boiler
from the sound wave which is generated when water or steam spouts
from the pressure part of the boiler. The device is adapted for use
in an atmosphere, such as a recovery boiler, which is liable to
contamination, and comprises a gate circuit for shutting a sound
wave transmission tube and shutting an output of a microphone upon
actuation of soot blowers of the boiler so as to protect the device
against detrimental effects imposed thereon by the operation of the
soot blowers, means for cleaning the transmission tube by passing
pressurized air therein while the output of the microphone is being
shut down, means for cooling the sound wave transmission tube,
means for detecting an abnormal condition of the microphone by
passing pressurized air in the vicinity of said microphone and
means for detecting clogging of the sound wave transmission tube by
pressure.
Inventors: |
Yamamoto; Takashi
(Togitsu-machi, JA), Yasukouchi; Kenichi (Nagasaki,
JA), Sato; Ryuichi (Nagasaki, JA) |
Assignee: |
Mitsubishi Jukogyo Kabushiki
Kaisha (Tokyo, JA)
|
Family
ID: |
14150349 |
Appl.
No.: |
05/397,355 |
Filed: |
September 14, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Sep 25, 1972 [JA] |
|
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47-95907 |
|
Current U.S.
Class: |
122/379; 122/504;
122/392; 340/605 |
Current CPC
Class: |
F22B
37/42 (20130101) |
Current International
Class: |
F22B
37/42 (20060101); F22B 37/00 (20060101); F22b
037/48 () |
Field of
Search: |
;122/379,392,504
;340/242,421 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sprague; Kenneth W.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. A device for early detecting a rupture of the pressure part of a
recovery boiler having soot blowers, comprising:
a. a sound wave transmission tube open at its forward end in the
furnace of the recovery boiler and connected at its rear end
through a three-way valve to a conduit having a microphone disposed
therein,
b. means for applying the output of said microphone to a band-pass
filter and the output of said filter to a gate circuit which
produces an output signal indicating rupture,
c. means for injecting pressurized air into the rear end of said
sound wave transmission tube through a further valve and said
three-way valve,
d. means for injecting pressurized air into the open end portion of
said sound wave transmission tube adjacent the wall of said furnace
of the recovery boiler through said further valve, and
e. control means for closing said gate circuit, opening said
further valve and operating said three-way valve to communicate
said sound wave transmission tube with said further valve before
the start of soot-blow of said recovery boiler, and for opening
said gate circuit, closing said further valve and operating said
three-way valve to communicate said sound wave transmission tube
with said conduit after the termination of soot-blow.
2. A device according to claim 1, in which means is additionally
provided for injecting pressurized air into said conduit from a
nozzle through another valve.
3. A device according to claim 1, in which means is provided for
detecting a pressure difference between the pressure in the rear
end portion of said sound wave transmission tube and the pressure
in the other end portion of said sound wave transmission tube open
in said furnace.
4. A device according to claim 1, in which means is provided for
cooling said sound wave transmission tube.
5. Apparatus for providing an early indication of rupture of the
pressure part of a recovery boiler having a plurality of
soot-blowers;
a sound tube transmission tube open at its forward end in the
boiler,
microphone means for detecting an acoustical wave in said tube and
producing an electrical signal,
a band-pass filter connected to said microphone means and receiving
said electrical signal,
means for indicating an alarm,
electrical gate means connected between said alarm indicating means
and said band-pass filter for passing the filtered signal in a
closed condition and blocking the filtered signal in an open
condition and
control means connected to said soot-blowers for causing said gate
means to be in said closed condition only while said soot-blowers
are not operating.
6. Apparatus as in claim 5 including means for detecting a pressure
differential between the pressure in the rear portion of said tube
and the portion of said tube open in said boiler.
7. Apparatus as in claim 5 further including means for supplying a
stream of air into said open end of said tube when said soot
blowers are operating to prevent clogging.
8. Apparatus as in claim 5 further including means for providing a
flow of air into said tube adjacent said microphone means to
simulate rupture and check said microphone means.
Description
BACKGROUND OF THE INVENTION
In a soda recovery boiler in which a pulp digester liquid is burned
to recover chemicals and heat, the pulp digester liquid is
discharged into the boiler furnace from a black liquid discharge
nozzle of the soda recovery boiler in the form of fine particles.
The water and volatile components contained in the pulp digester
liquid evaporate and the liquid is decomposed, while the fine
particles of the liquid fall to the boiler furnace bottom, forming
a char bed at the furnace bottom which consists essentially of
carbon and inorganic chemicals. The inorganic chemicals in the char
bed melt and form a so-called smelt pool beneath the char bed.
In the event that water intrudes into the soda recovery boiler
furnace for any reason, the water evaporates explosively, and
further, a water gas reaction occurs in the char bed and the
following reaction between the smelt and water occurs in the smelt
pool:
Na.sub.2 S + 4H.sub.2 O > Na.sub.2 SO.sub.4 + 4H.sub.2
This reaction is usually accompanied by an explosion more intense
than the rapid explosive evaporation of water. Therefore, if a
rupture of the boiler pressure part is the cause of penetration of
water, even in a slight amount, into the boiler furnace, the
opening of the rupture will be enlarged by the pressurized water or
steam gushing therethrough and the amount of water or steam
intruding into the boiler furnace gradually increases, inducting
further small explosions and making the rupture opening larger and
larger, with the consequence that a serious explosion is induced
which not only causes heavy damage to the soda recovery boiler
itself but also endangers the operators of the boiler. Thus, it
becomes necessary to stop the operation of the soda recovery boiler
immediately upon intrusion of water into the boiler furnace. For
preventing the explosion of the soda recovery boiler caused by the
intrusion of water into the boiler furnace, it is most important to
make a careful inspection and necessary repair of the boiler prior
to the operation and also to train the operators to operate the
boiler in a way which precludes accidents.
However, if water unfortunately has intruded into the boiler
furnace, the intrusion of water should be detected as early as
possible and the operation of the boiler should be stopped at once
to minimize the chance of accident. Nevertheless, no attempt has
been made in the past to provide a method by which the intrusion of
water or steam into the soda recovery boiler can be positively
detected and, although a considerable number of these types of
accidents have been experienced in the United States and Canada,
the abnormal condition of the boiler has always been detected first
by the operator by inspection of the boiler furnace interior upon
sensing an abnormal sound in various noises occurring during the
operation of the soda recovery boiler, e.g., the sound of
continuous small explosions in a smelt dissolving tank, the
combustion noise in the boiler furnace and the operating noises of
induced and forced draft funs.
Abnormal conditions of the boiler caused by water or steam
intruding into the boiler furnace from the pressure part of the
boiler, include abnormal sound waves and vibrations occurring
incident to the intrusion of the water or steam, and, when the
boiler is a soda recovery boiler, an increase of the steam partial
pressure in the furnace gases and the generation of hydrogen due to
the reaction between the smelt deposited on the furnace wall and
the spouting water or steam.
It is practically impossible to utilize the steam partial pressure
increase and the generation of hydrogen gas, of the abnormal
conditions mentioned above, for the early detection of the water or
steam spouting from the pressure part of the recovery boiler. This
is because the increase ratio of the steam partial pressure or
hydrogen partial pressure is very small since the amount of the
furnace gases is extremely large, and because the steam partial
pressure in the furnace is originally high and a fluctuation of the
steam occurring incident to the fluctuations of the concentration
and amount of the black liquid is large since the black liquid
injected into the soda recovery boiler furnace from the black
liquid discharge nozzle is undried and contains a large amount of
water.
It is considered that a rupture of the boiler pressure part can be
detected early by sensing the abnormal vibrations occurring
incident to the spouting of water or steam from the boiler pressure
part. Namely, when a rupture has occurred at the pressure part of
the boiler for any reason and the water or steam spouts from the
opening of said rupture at sonic or supersonic speed, abnormal
sound waves and vibrations are generated at or in the vicinity of
the rupture opening. The frequencies of the abnormal sound waves
and vibrations are as high as 20 KH.sub.Z and the vibrations in
such a high frequency range are propagated in steel member
connected to the pressure part of the boiler and reach a detection
end provided at a suitable position of the boiler structure. The
detection end detects the abnormal vibrations transmitted directly
in the steel member.
In a boiler, an operation called soot-blow, i.e., blowing the
boiler with pressurized steam, is periodically performed to remove
soot and other substances deposited on the wall of water tubes. The
amount of pressurized steam used for soot-blow is so large as
compared with the mount of steam to be detected spouting from the
rupture at the pressure part that the detection of the abnormal
vibrations is extremely difficult while being interfered by
soot-blow. One boiler is usually provided with 10 to 20 soot
blowers which are operated sequentially (the operating time of each
soot blower being 2 to 10 minutes) to complete one cycle of
soot-blow in a period of 1 to 2 hours. In an ordinary utility
boiler, two to three cyclic operations of the soot blowers once
every day are sufficient for soot-blow and a detecting device for
detecting the vibrations or sound wave generating incident to the
spouting of water or steam can operate normally during the rest of
the time. However, in case of boilers, such as a soda recovery
boiler, in which the amount of depositing soot is large, soot-blow
must be carried out continuously almost all day long, and in case
of the soda recovery boiler in particular, the correct detection of
water or steam leakage is quite difficult, despite the fact that
water or steam leakage will possibly result in a serious
accident.
In view of the foregoing, there can be considered the use of such a
detecting device which is provided with a gate circuit which will
open to transmit an output of the detecting device only when the
soot blowers are not in operation, and which therefore, can even be
used with such a boiler which calls for continuous soot-blow almost
throughout the period of operation, for detecting periodically a
leakage of water or steam due to a rupture of the pressure part to
preclude detrimental effects otherwise induced by the leakage.
However, as a result of the experiment conducted by the present,
inventor using a soda recovery boiler of the type shown in FIG. 1,
in which a pressure pipe 01 having an 0.5 mm diameter opening
intentionally formed therein is connected to an inlet of an
economizer and a detection head of a vibration detecting device of
the type described is attached to a position 02 less than 5 m
distant from a discharge opening of a member connected to said
pressure pipe, and by causing water and steam to spout from said
opening during the operation of the boiler, it was found that the
frequency spectrum of the vibration is substantially the same as
the frequency spectrum of the normal vibration as shown in FIG. 2,
and the abnormal vibration caused by the spouting water and steam
cannot be detected. This means that the normal vibration of the
boiler during operation is considerably large over the range from
low frequency to a high frequency of 20 KH.sub.Z, as compared with
the abnormal vibration caused by the spouting of water or steam,
depending upon the position of the detection head, and the abnormal
vibration cannot be detected by filtering the normal vibration of
the boiler, so that the positive detection of the spouting of water
or steam from the vibration transmitting in the boiler structure is
difficult.
Nevertheless, it is essential in case of a failure of the boiler
pressure part, to detect a leakage of the degree mentioned above as
early as possible and to take the necessary measure for preventing
explosion.
On the other hand, the sound wave which is generated incident to
the spouting of pressurized water or steam through a rupture
opening formed in the pressure part of the boiler, for any reason,
at the sonic velocity or supersonic velocity, expands within the
boiler furnace and fills the interior of said furnace while
reflecting on a water-cooled pipe surrounding the furnace. Part of
the sound wave is absorbed by the water-cooled pipe and other
members connected to the furnace, but the other part propagates in
air and reaches a sound wave detector or the like provided at a
suitable location of the furnace wall. This sound wave is at a
level equal to or several times that of the dark ground noise of
the boiler in the frequency range from a low frequency of about 3
KH.sub.Z to a supersonic frequency of 20 KH.sub.Z. Therefore, the
spouting sound can be detected relatively simply from the dark
ground noise of the boiler by detecting the sound wave and passing
it through a sound filter of a suitable frequency range. In this
way, it becomes possible to detect a slight water or steam leakage
which cannot be detected from the vibration transmitted in the
boiler structure. To prove this, the present inventor conducted an
experiment in which a pressure pipe (indicated at numeral 01 in
FIG. 1) having an 0.5 mm diameter opening intentionally formed
therein was connected to an inlet of an economizer, in exactly the
same manner as in the experiment for detecting vibrations described
above, and a detection head of a sound wave detecting device was
attached to a manhole 03 of the economizer, and then water and
steam were caused to spout from said opening during the operation
of the boiler, with the result shown in FIG. 3. It will be seen
that the frequency spectrum of the sound generated by the spouting
water or steam reaches a level several times higher than that of
the boiler dark noise in the frequency range from 30 to 20
KH.sub.Z. This shows that the spouting sound of water or steam can
be sufficiently detected by passing the sound through a filter of
the frequency range of 3 to 20 KH.sub.Z.
In the preclusion of explosion in a soda recovery boiler, there is
more necessity for detecting a water and steam leakage at the
furnace part of overheater part than for detecting the leakage at
the economizer part, as stated previously and thus it becomes
necessary to provide further that the leakage at the furnace part
and the superheater part can be detected. However, it is
impracticable to cause water or steam to spout at the furnace part
of the actual boiler because such practice involves the danger of
explosion. Therefore, the present inventor at first made an attempt
to confirm through experiment that air can be used in lieu of water
and steam, and found that the frequency spectrum of the sound wave
generated by pressurized air of 5 kg/cm.sup.2 spouting from a 5 mm
diameter opening is very close to the frequency spectra of the
sound waves generated by saturated water and saturated steam of a
pressure of 90 kg/cm.sup.2 spouting from an 0.5 mm diameter
opening, and that air is well usable as a substitute for water and
steam. Based on such knowledge, the present inventor conducted an
experiment using air over the entire region of the boiler, and
confirmed that air can be sufficiently usable even in the actual
boiler. Namely, compressed air of a pressure of 5 kg/cm.sup.2 was
discharged from a 5 mm diameter opening at the position of each of
a starting burner nozzle (indicated by numeral 04 in FIG. 1) and a
black liquid spray nozzle (indicated by numeral 05 in FIG. 1) and
the pressure levels of the generated sounds in the frequency range
from 3 to 20 KH.sub.Z were sensed by a sound detection end 07
provided at the outlet of the furnace and recorded on linear
coordinates, with the result shown in FIG. 5. The sounds had
sufficient sound pressure levels as indicated at a and b in FIG. 5.
This also means that spouting of water or steam from an 0.5 mm
diameter opening can be well detected.
SUMMARY OF THE INVENTION
The present invention has for its object the provision of a device
adapted for use with a general boiler for detecting promptly a
spouting of water into the boiler furnace due to rupture of the
pressure part of the boiler and thereby for minimizing the chance
of accident, the device when used with a soda recovery boiler
enabling the operator to detect the intrusion of water or steam
into the boiler furnace early and positively, to stop the boiler
upon occurrence of such condition and thereby to preclude a
dangerous accident of the boiler.
Another object of the invention is to provide a device of the
character described above, which is provided with means for
enabling the device to maintain its normal detecting function
without being affected by the operation of soot blowers.
Still another object of the invention is to provide a device of the
character described above, which is provided with means for
cleaning the device with pressurized air so as to enable the device
to maintain its normal detecting function even when used in an
atmosphere liable to contamination, such as a soda recovery
boiler.
Still another object of the invention is to provide a device of the
character described above, which is provided with means for
determining whether a microphone to detect a sound wave generating
as a result of rupture of the pressure part is in the normal
operative state or not.
A further object of the invention is to provide a device of the
character described above, which is provided with means for
detecting a clogging of the device due to contamination soda to
ensure the satisfactory function of the device even when the device
is used in an atmosphere liable to contamination.
An additional object of the invention is to provide a device of the
character described above, which is thermally protected and has a
high detection sensitivity.
Other objects and advantages of the invention will become apparent
from the following description of an embodiment of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 - 5 are diagrams for explaining the background of the
present invention, of which:
FIG. 1 is a diagram for explaining a setup which was used for
examining the boiler pressure part rupture detecting effect of the
subject device in a conventional soda recovery boiler;
FIG. 2 is a diagram exemplifying a comparison between the frequency
spectra of the normal vibration of the boiler and an abnormal
vibration of the same due to rupture;
FIG. 3 is a diagram exemplifying a comparison between the frequency
spectra of the dark ground noise of the boiler and an abnormal
noise of the same due to rupture;
FIG. 4 is a diagram exemplifying a comparison between the frequency
spectra of the water, steam and air gushing sounds;
FIG. 5 is a diagram exemplifying a recorded air gushing sound at
the boiler furnace part;
FIG. 6 is a view exemplifying the position of the device according
to the present invention as applied to a soda recovery boiler;
FIG. 7 is a block diagram illustrating briefly the construction of
the device according to the invention;
FIGS. 8 and 9 are views exemplifying a preferred embodiment of the
device of the invention; and
FIG. 10 is a flow sheet for explaining the operation of the device
of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The device according to the present invention will be described
herein as applied to a soda recovery boiler, with reference to the
drawings. FIG. 6 shows a portion of the soda recovery boiler, in
which reference numeral 1 designates a boiler furnace tube, 2 a
superheater, 3 a boiler tube, 4 an economizer, 5 manholes, 6 a peep
hole and 7 the location of a sound wave detection head.
FIG. 7 shows in block diagram the construction of the device
according to the invention. As shown, the device of the invention
comprises a microphone 8 for converting sound waves into electric
signals, a band-pass filter 9 for setting the spouting sounds of
water or steam at a frequency optimum for detection, and monitor
means 10 including a spouting sound level indicator and an
alarm.
FIGS. 8 and 9 exemplify the practical construction of a fixed type
sound wave detection head which is to be disposed, for example, at
the position 7 in FIG. 6.
The detection head generally indicated by numeral 11 comprises an
air-cooled sound wave transmission tube 12, an electric three-way
valve 13, a sound wave transmission tube 14 and a microphone 15.
Since this detection head 11 is left mounted on the furnace wall,
particular consideration is given thereto to render it resistive to
heat and dust proof.
A cooling chamber 16 is provided around the sound wave transmission
tube 12 for cooling tube 12 with air. The provision of the cooling
chamber 16 is advantageous in reducing the length of the
transmission tube 12 and achieving detection with high sensitivity,
without attenuating a high frequency sound wave to be detected.
Reference numeral 17 designates a cooling air inlet tube; 18 a
pressure regulator for the flow rate of the cooling air so as to
eliminate detrimental effect on the detecting device of the noise
which would be generated by the flow of cooling air when the flow
rate of cooling air is excessively high; 19 a reference leakage
sound generating hole for generating a reference leakage sound
which is used for checking a performance degradation of the
microphone or an abnormal operation of the detecting device; 20 an
inlet tube for leakage sound generating air; 21 an electric air
valve for opening and closing the leakage sound generating air
passage; and 22 a branch tube diverging from the cooling air inlet
tube 17.
In order to prevent the inlet opening of the sound wave
transmission tube 12 from being clogged with soot attaching to the
inner wall of the furnace at the portion where the detection head
is mounted, a flashing air inlet chamber 23 is provided for
injecting flashing air into the sound wave transmission tube 12 in
four directions. Reference numerals 24 and 25 designate a flashing
air inlet tubes. The electric three-way valve 13 is provided
between the sound wave transmission tubes 12 and 14, which severs
communication between the sound wave transmission tubes 12 and 14
to shut down the transmission of sound wave to the microphone 15
and establishes communication between said sound wave transmission
tube 12 and the flashing air inlet tube 25, at the time of soot
blow, providing for passage of flashing air in said flashing air
inlet tube 25 and sound wave transmission tube 12 through an
electric air valve 26 which is then open.
A pressure sensor 28 is provided for issuing an alarm in the event
when the sound wave transmission passage has clogged with soot
attaching to the inlet portion of the sound wave transmission tube
12. This pressure sensor 28 is designed such that it will issue an
alarm when the pressure difference between the internal pressures
of the sound wave transmission tubes 12 and the furnace, or the
internal pressure of the sound wave transmission tube 12 reaches a
certain level. Reference numerals 27 and 29 designate tubes for
supplying the internal pressures of the furnace and sound wave
transmission tube to pressure sensor 28.
Reference numeral 30 designates a bracket for mounting the
microphone on the sound wave transmission tube 14, which is made of
a heat insulating material; 31 an O-ring; 32 a cooling air outlet
tube; 1 a furnace cooling water tube; 34 a heat insulating material
and 35 a housing.
The forward end of the sound wave transmission tube 12 has the
shape of an exponential horn for damping waves of low frequencies
below about 3 KH.sub.Z.
FIG. 10 shows a block diagram of an example of the detecting device
of the invention for explaining the operation principle of the
device. The detecting device shown comprises a band-pass filter 36,
a gate 37 opened and closed in response to signals from control
means 38, a monitor and a soot blower controller which generates
signals for actuating and stopping soot blowers.
As stated previously, the operation of the soda recovery boiler is
accompanied by heavy attachment of soot and calls for repetitive
soot-blow operations. Therefore, the detection of the leakage sound
has to be made in the interval between the soot-blow operations.
When a certain soot blower is set in operation for a period of 2 to
10 minutes, the electric three-way valve 13 is actuated by the
signal from the controller 38 and the sound wave transmission
passage leading to the microphone 15 is shut down by said valve, to
prevent overloading of the microphone. Then, the electric valve 26
is opened to flash the sound wave transmission passage. In this
case, the gate 37 is held closed to shut down the transmission of a
signal from the band-pass filter 36 to the monitor 39 and thereby
to prevent erroneous operation of the detecting device otherwise
caused by the noises from the soot blower and flashing air
flow.
The electric valve 26 is closed concurrently with the termination
of the operation of the first soot blower and, therefore, flashing
of the sound wave transmission passage ends. Then, the electric
three-way valve 13 is actuated to open the sound wave transmission
passage leading to the microphone 15 and the gate 37 is also
opened. If water or steam is spouting through a rupture formed in
the boiler pressure tube in this case, such condition is detected
by the sound wave detection head 11 and transmitted to the monitor
39 through the band-pass filter 36 in the form of a high frequency
signal.
Then, the second soot blower is set in operation, whereupon the
electric three-way valve 13 is actuated to shut down the sound wave
transmission passage leading to the microphone and concurrently the
gate 37 is closed and the electric valve 26 is opened, so that the
sound wave transmission passage is flashed again. The interval
between the termination of operation of the first soot blower and
the start of the second soot blower is only about 30 to 100
seconds. With the detecting device of the invention, however, it is
possible to monitor the boiler periodically all day long by making
use of such a short period of time.
The detecting device of the invention, as stated above, is provided
with pressure sensor 28 for detecting clogging of the inlet portion
of the sound wave transmission passage 12 by soot. This pressure
sensor 28 transmits a signal to the controller informing it of
heavy deposition of soot, when the internal pressure of the sound
wave transmission tube 12 or the pressure difference between the
internal pressures of said sound ave transmission tube and the
furnace, at the time of soot-blow, has reached a preset value.
When it is desired to check the performance of the microphone or
the operation of the detecting device, the electric three-way valve
13 is actuated to close the sound wave transmission passage leading
to the microphone and the electric valve 21 is opened, either
automatically from the controller 38 or manually, at a suitable
time when the soot blowers are not in operation, and thereby air is
caused to discharge from the reference leakage sound generating
hole shown in FIG. 8 to generate the reference leakage sound, and
concurrently the gate 37 is opened. An alarm is issued indicating
the performance of the microphone being degraded or the operation
of the detecting device being abnormal, when the leakage sound is
below a preset level.
In the event when water or steam has intruded into the furnace, the
overheater or the economizer of the soda recovery boiler upon
occurrence of a rupture in the pressure tube and an abnormal sound
wave has been generated, the abnormal sound wave spreading in air,
upon reaching the microphone 15, is immediately converted into an
electric signal which is discriminated from the electric signal,
created from the dark noise of the boiler, by the band-pass filter
36 and transmitted to the monitor 39 through the gate 37 which is
then open.
The monitor 39, upon receiving such electric signal, transmits a
signal to alarm means, such as a buzzer or a lamp, to actuate the
same, to means for automatically stopping the boiler, or to the
soot blower controller 40 for stopping the soot blowers only.
Alternatively, an arrangement may be made such that the monitor,
upon receiving the electric signal, will continue its monitoring
operation for a while and transmit the alarm actuating signal or
boiler stopping signal after confirming that the boiler is in a
dangerous condition.
It is also possible to preset in the monitor 39 the frequency, the
amplitude or the duration of an abnormal sound wave which will be
received by the monitor and which indicates that the boiler is in
the dangerous condition.
The detecting device of the invention, as has been described in
detail by way of example herein, monitors constantly an abnormal
condition of the boiler by detecting the sound wave, generating
from water or steam leaking from the boiler pressure tube and
spreading in air or trapped in the furnace, by the detection head
attached to the furnace wall, converting the sound wave into
electric signals and discriminating the electric signal from the
signals originating from the dark ground noises of the boiler by
the band-pass filter. With the device of the invention, it is
possible to detect the occurrence of a rupture of the pressure
part, such as the water tube, of the boiler early and positively,
and upon detecting the abnormal sound wave, the device converts it
into an electric signal, or pneumatic or hydraulic signal which is
transmitted to the alarm means or explosion preventing means to
actuate the same automatically, whereby the occurrence of explosion
in the boiler furnace can be avoided and thereby heavy damages to
the facility as well as persons can be avoided which would
otherwise be caused by the explosion.
Many changes and modifications in the above-described embodiment of
the invention can, of course, be carried out without departing from
the scope thereof. Accordingly, that scope is intended to be
limited only by the scope of the appended claims.
* * * * *