Field Of Invention
The present invention generally relates to fossil fuel fired boilers. More
particularly, the present invention relates to a sound sensing apparatus to detect
sound waves emanating from various locations inside the fossil fuel fired boilers.
Background of the Invention
The superheated high-pressure steam is produced in a boiler and channeled to
turbine-generators to produce electricity. However, the steam generation process
from the fossil fuel fired boiler is largely dependent on a stale combustion
process. Abnormalities in combustion process such as excess air, or partial
combustion of fuel may lead to instabilities and impede the smooth steam
generation process. Further, the fossil-fuel fired boilers emanates audible noise
during the operation.
The noises can be from combustion process, abnormalities in air flow and from
tube leakages. Generation of such noises is more pronounced in pulverized coal
fired boilers due to combustion being vigorous and leakage of steam at high
pressure.
In order to avoid such unpredictable disturbances, it becomes necessary to
monitor the boiler operation continuously so that any abnormalities can be
detected in the nascent stage itself and corrective actions can be taken to avoid
costly/ secondary damages. One of the known methods of monitoring boiler
operations, is monitoring the sound from the boiler at various zones in order to
instantly identify the abnormalities such as combustion instabilities and tube
failures.
One of the conventional methods to detect sound is implemented through
manual intervention wherein the operator may take a walk around the different
elevations of the boiler and listening to the sounds through openings provided in
the boiler outer surfaces and identifies any abnormalities in sound including the
source-location. Such methods are highly operator dependent and unreliable
involving tedious trials. This method results in intermittent monitoring only and
does not take care of a continuous monitoring of the sound.
Therefore there is a need for an automated detection of audible sounds at a
nascent stage emanating from combustion and leakage abnormalities.
Objects of the Invention
It is therefore, an object of the invention to propose an apparatus for detecting
sound waves emanating inside Fossil fuel fired boilers, propose a method to
which eliminates the disadvantages of prior art.
Another object of the invention is to process the sound signal emanating
detecting abnormalities.
Summary of the Invention
Accordingly, there is provided an apparatus for detecting sound emanating
from inside the fossil-fuel fired boilers, comprising a sound sensing device
constituting a tube angularly mounted to the water wall of the boiler; an
electronic sensor of a sensor assembly mounted at a spaced-apart position in
respect of the side of the boiler; a ball valve provided as a part of a tube
assembly for isolation purpose and having a bend; a Teflon coupling provided to
protect the sensor from high temperature environment; and an air purging tube
enabled to evacuate the residues in the form of fly ash/dust particles inside a
stub pipe.
The sound sensing apparatus described herein works on the principle of directing
the sound waves emanating from the boiler by employing sound wave guide
tubes such that the electronic sensing circuitry is isolated from the harsh
environment of the boiler. In addition the apparatus is provided with parts for
isolating the sensor electronics from heat and parts for purging the wave guides
for periodic cleaning. The sound sensing apparatus consists of sound directing
tubes, components required for air purging arrangement, isolation valve, heat
insulated spacer and heat insulated coupling and a flange matching with the
flange mounting to a stub installed in the location where the sounds are to be
monitored. An electronic circuitry is also incorporated to amplify the signal
detected by a microphone and facility for checking the functioning of sound
signal amplifier by an integrated sound source in the same enclosure.
Brief Description of the Accompanying Drawings
Figurel- depicts a general arrangement of sound wave guiding tubes of the
apparatus of the invention.
Figure 2 shows a sound sensing apparatus according to the invention.
Figure 3 shows an electronic circuitry incorporated in the electronic sensor
assembly (105) of the sound sensing apparatus of the invention.
Figure 4- shows a mounting method of the sound sensing apparatus on boiler
wall.
Detailed Description of a Preferred Embodiment of the Invention
A boiler is divided into a number of critical zones for identifying the areas in
which the tube leakage or combustion abnormalities are more likely to occur. In
each zone, at least one sound sensing apparatus is installed. As shown in Fig.-l,
the inventive sound sensing apparatus consists of a sonic tube (110) which is
used for transmitting the sound waves to the electronic sensor assembly (105)
mounted at a proximal end of the sonic tube (110) for conversion of the
acquastic signals in to electrical signal. A stub adapted for mounting of the sonic
tube (110) comprises a SS flange (103) on to which a matching Teflon flange
(109) is fitted using bolts, nuts and washers (106). The stub is attached to the
base of the sonic tube (110). The sonic tube (110) consists of a ball valve (101)
provided with a handle. Means for manual purging (107) is also provided . The
distal end of the sonic tube (110) is provided with a bent tube (102) on to
which an electronic sensor assembly (105) is mounted on a SS sleeve. Teflon
couplings are provided to avoid heat conduction from the combustion zone of the
boiler to the sensor electronics (120) assembly (105).
The detailed description of the associated electronic sensor assembly is shown in
figure 2. The sensor assembly (105) is located at one end of a sound sensing
tube (104). Associated sensor electronics (120) consisting of sonic transducer
capsule and a sound source (120) connected to a pre-amplifier circuit (127) are
molded into a single component to prevent the dust and heat to ingress inside
the sensor assembly (115). The molded electronics (120) is placed inside a
sensor casing having an outer thread (110) that enables it to be screwed into the
sound sensing tube (114).
The electronics is held in position using at least two SS bushing (119, 113) and
covered by a Teflon bush (112) using SS fixing screws (114). The molded
electronics (120) is covered on the top by a Teflon disc (115) and a neoprene
bushing (116). A thin polyester film (117) is used in between the bushings
(119,113). The entire arrangement is covered by a SS wire mesh (118) to
protect the sensing electronics (120) from heat and dust. The sound sensed is
converted to its electrical equivalent and the corresponding analog output is
taken through a 6-pin connector assembly (lll).The Sensor assembly (105) is
provided with a piezoelectric buzzer (130) integrated in to the same enclosure.
The buzzer (130) can be activated by closing the switch externally during the
diagnostic testing of the electronics assembly (105).
In order to install the sound sensing apparatus in the boiler water walls, the
usually straight water wall tubes are bent to create a plurality of openings in the
identified
zones within the boiler structure for sensing the sound signals. As shown in
figure -4, the bent tubes create an opening at the location of welded joints. As
shown in figure -5, the opening is covered with a seal box filled with a refractory
and provided with the stub with flanges, for mounting the sound sensing
apparatus.
The sonic tube (110) is mounted to the water wall at an angle of 45 degrees
upwards. The associated electronic sensor (105) is mounted at least 1.5 meters
away from the side of the boiler. For isolation purpose, a ball valve (101) is
provided as a part of the tube assembly (110) that has a 45 deg. bend, such that
during maintenance, the associated electronic sensor assembly (105) can be
taken out.
Teflon coupling is provided to protect the sensor (104) from the high
temperature environment. Manual purging means (107) is provided in order to
evacuate the residues like fly ash/ dust particles available inside the stub pipe.
The requirement for purging air provision is shown in figure 1. The stub (107)
connecting to the air header is fitted with a check valve (108). Provision is made
available in the sound sensing device for manually purging the assembly
periodically once in a week or as and when required based on experience. It is
done by opening the check valve in the pneumatic purge line for 5 to 10 seconds
or as required after getting experience. The isolating valve (101) is to be kept
closed during purging operation in order to protect the sensor and should be
kept opened, after completion of purging while the purging check valve (108)
should be kept closed.
A seal box (refer fig. 5) is used for mounting the base of the sound sensing
device to the surface of the boiler. Seal box arrangement (131) is provided with
the opening for guiding the sound waves from the zone into the sound sensing
apparatus and finally to the electronic sensor assembly (105) mounted at the
end of tube (110).
The sound sensing apparatus is mounted on the stub flange (107) using a
matching Teflon flange (109). The sound sensing apparatus is mounted at an
angle of around 45 degrees to the vertical.
It is to be understood that the description of the preferred embodiment (s)
herein is (are) to be considered only illustrative, rather than exhaustive, of the
present invention. Those of ordinary skill will be able to make certain additions,
deletions, and or modifications to the embodiment (s) of the disclosed subject
matter without departing from the spirit of the invention or its scope, as defined
by the appended claims and those modifications are not eligible to be depicted
as new ideas/ invention described herein.
WE CLAIM:
1. An apparatus for detecting sound emanating from inside the fossil-fuel
fired boilers, comprising:
a sound sensing device constituting a tube angularly mounted to the water
wall of the boiler;
an electronic sensor of a sensor assembly mounted at a spaced-apart
position in respect of the side of the boiler;
a ball valve (101) provided as a part of a tube assembly for isolation
purpose and having a bend;
a Teflon coupling provided to protect the sensor from high temperature
environment; and
an air purging tube (107) enabled to evacuate the residues in the form of
fly ash/dust particles inside a stub pipe.
2. The apparatus as claimed in claim 1, comprising an air purging means
having one each check valve (108) and an isolation valve (101) for
effectively isolating the sensor assembly during purging.
3. The apparatus as claimed in claim 1, wherein the sensor assembly
comprises a sonic transducer, a sound source connected to a pre-amplifier
circuit, and a piezoelectric buzzer.
4. The apparatus as claimed in claim 1, comprising a seal box device for
mounting the sound sensing device, the seal box device disposed with an
opening on the surface of the boiler to allow egress of sound signal.
5. An apparatus for detecting sound emanating from inside the fossil-fuel
fired boilers, as substantially described and illustrated herein with
reference to the accompanying drawings.

The invention relates to an apparatus for detecting sound emanating from inside
the fossil-fuel fired boilers, comprising a sound sensing device constituting a tube
angularly mounted to the water wall of the boiler; an electronic sensor of a
sensor assembly mounted at a spaced-apart position in respect of the side of the
boiler; a ball valve (101) provided as a part of a tube assembly for isolation
purpose and having a bend; a Teflon coupling provided to protect the sensor
from high temperature environment; and an air purging tube (107) enabled to
evacuate the residues in the form of fly ash/dust particles inside a stub pipe.