Image analysis – Histogram processing – For setting a threshold
Patent
1988-06-14
1990-03-06
Boudreau, Leo H.
Image analysis
Histogram processing
For setting a threshold
382 22, 340577, 250554, G06K 900
Patent
active
049072811
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an image analysis method for flame monitoring for controlling the combustion of pulverized fuel.
BACKGROUND OF THE INVENTION
Pulverized fuel combustion implies a method in which the fuel, i.e., coal in conventional combustion but also peat to an increasing extent, is milled into a very fine-grained dust, which is then blown to the boiler via a nozzle using stack flue gas or air as the carrier. In coal- and peat-fired power plants, pulverized fuel combustion is a common method of combustion which inherently merits an extremely high value to improvements in the ignition and combustion of pulverized fuel.
Monitoring of the combustion process is availed to reduce the proportion of expensive auxiliary fuels. The monitoring operation is implemented in several ways, of which optical flame detectors are gaining ground thanks to the large information available from them.
A conventional method of monitoring combustion in a burner is to use a video camera, often called a fire-box camera. The video camera that produces a black-and-white or color video signal is located in a heat-resistant and cooled protective tube. In addition to air cooling, some cameras are provided with water cooling. The camera installations are generally provided with an automatic protection that ejects the camera out from the fire-box when a system malfunction is encountered.
Furthermore, flame monitoring is implemented with pyrometers sensitive to radiation intensity as well as with other types of detectors tuned to a narrow band of wavelengths. The quality of the combustion process is evaluated on the basis of flame instability (from the "DC" and "AC" components of flame intensity). A more advanced version of the aforementioned method is the cross-correlation method, also called the incremental volume method.
Use of a camera in the conventional methods is restricted to the monitoring of the averaged combustion process. The operation of a single burner can be monitored only at the ignition of the first flames and the extinction of the last flames. Detectors of the pyrometer category are hampered by such factors as placement and alignment of the detector, low temperature of the flame, etc. Some types of detectors are prone to erroneous response to nearby flames and background radiation from the walls of the fire-box. A disadvantage of the cross-correlation method is, for instance, its high sensitivity to changes in burning rate.
SUMMARY OF THE INVENTION
The aim of the present invention is to overcome the disadvantages of the prior art technology and to provide a totally new kind of monitoring system for the ignition and combustion of pulverized fuel including a flame monitoring system which is integral with the boiler's protective system and conforms to regulations issued by authorities. The invention is based on monitoring the ignition and combustion process over a large area by means of a video camera and on the localization of the ignition area by the identification of the average intensity level corresponding to the maximum intensity changes on selected lines of the video signal, after which the space coordinates corresponding to this intensity level in the complete video frame signal are determined.
More specifically, the method in accordance with the invention is characterized by aligning each fire-box camera to see the flame essentially from the side, repetitively processing the video signal to average intensity levels and determining the spatial or temporal coordinates of the continuous video signal.
The invention provides outstanding benefits.
The method in accordance with the invention provides high reliability because the combustion process is analyzed over a large area. Furthermore, the method can be adapted to accept a predefined permissible ignition area. Moreover, the method is compliant with different ignition and combustion conditions. Thanks to the compliancy of the method, the number of false alarms can be appreciably reduced. In accordance with the invention, a common analyzing apparatu
REFERENCES:
patent: 4396903 (1983-08-01), Habicht et al.
patent: 4555800 (1985-11-01), Nishikawa et al.
patent: 4561104 (1985-12-01), Martin
Apajalahti Marja
Hanioja Timo
Hirvonen Juhani
Hoynanmaa Mikko
Kohola Pekka
Boudreau Leo H.
Imatran Voima Oy
Santos Daniel
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