Research On Flame Safety Monitoring And Combustion Diagnosis Methods For Coal Fired Utility Boiler

The combustion stability of utility boilers is directly relative to that a power plant runs safely and economically. Therefore a furnace safeguard supervisory system (FSSS) with complete function, credible performance must be equipped with utility boilers.Nowadays the equipments for detecting flame in utility boilers are mainly using infrared, ultraviolet or visible light probes which judge the flame "YES" or "NO" according to the detected flame radiative intensity and flame frequency. Because of the complexity of coal combustion dynamic characteristic, the variation of coal properties and swing of the burners, such probes are all difficult to calibrate, so they often misdiagnosed while running which affects the normal running of boilers.The image flame detector has the advantages of visibility, more information, up to human vision, so that it can avoid the above accidents availably.In this thesis, advanced computer image processing technology was adopted, based on flame image luminosity information, chroma information and radiative transfer equation, to reconstruct the temperature distribution field in a utility boiler, to research for a quantitative method for judging the combustion stability of flame, to look for the NOx, SO2 formation mechanisms and the emission disciplines, to seek for the effects of oxygen pressure, pulverized coal particle diameter heating velocity and atmosphere on pulverized coal combustion velocity, and to summarize various factors that affects the content of combustible in fly-ash. Finally, the above researched results, combining the utility boiler operation parameters and coal property data were used to diagnose the pollutants emission and the content of combustible in fly-ash.First, researches were carried at a lab and at a utility boiler respectively, the flame images of stable combustion, deflagration, flameout were acquired. By the comprehension and analysis to flame statement, the seven characteristic values of flame luminance, high temperature flame luminance,flame area, high temperature flame area, high temperature ratio, centroid offset distance and circularity are picked up. These seven characteristic values construct a characteristic matrix. And then based on principal component analysis (PCA), a method that can monitor and diagnose the stability of flame was put forward, which is based on the two statistic of Hotelling T2 and SPE to monitor the every-moment image data vectors to check them whether they exceed their own controllable limit. As long as one of them exceeds the limit, abnormity combustion can be concluded. The experimental research shows that the method can recognise and judge the combustion state of burning flame real-time and availably, and visually shows the result with SPE fig, Hotelling T2 fig and PCA fig, at one time, by the method of supporting vector machine(SVM) to identify and sort characteristic vetors and original image data, the results between basing on PCA and supporting vector machine show that they are accordant.Second, the coal combustion experiment was carried at a heat-balance and at the pulverized coal lab, and the results of experiments on NOx, SO2 formation mechanism shows that: With the decrease of coal particle diameter, the improvement of oxygen pressure, the increase of heating rate, the pulverized coal burns more quickly. The combustion rate of pulverized coal in a mixture gas of oxygen, carbon dioxide and nitrogen is slower with the less oxygen pressure, but its absolute value is far less than that it in atmosphere or in pure oxygen. Within the normal operation range, the more furnace temperature, exceed air coefficient, ratio of first to second wind, the more NOx and SO2 in a certain extent. Within the normal operation range, the content of combustible in fly-ash is inverse proportion to exceed air coefficient, proportion to ratio of burned wind ratio of recycled gas, ratio of fuel, pulverized coal diameter(invarible exceed air coefficient), and it has an optimum value with the capability heat load changing.Besides, many experiment...