Dissertation > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Fuel and combustion

Study on Combustion Characteristics of Coal Jet Flame in High Temperature Air and Low NO_x Combustion Optimization of Coal-fired Boiler

Author ZhengLiGang
Tutor ZuoKeFa;ZhouZuo
School Zhejiang University
Course Engineering Thermophysics
Keywords Nitrogen oxides Pulverized coal jet High temperature air combustion O2/CO2 Co-flow burner Porous media Combustion Optimization Optimization algorithm Support Vector Machine Neural Network
Type PhD thesis
Year 2009
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With the increase in energy consumption and environmental protection needs to improve control of pollutant emissions become an important issue in the field of environment and energy field. Nitrogen oxides (NOx) is one of the major pollutants emitted by the power station coal-fired boiler, in order to meet increasingly stringent emissions standards of the country, to seek means of control on all levels to become the focus of today's research to control NOx emissions. In this context, this paper carried out both studies, high temperature air combustion characteristics of pulverized coal jet, the second is based on artificial intelligence Low NOx emissions of coal-fired boiler combustion optimization. High temperature air combustion technology has been proven in the gas-fired industrial furnaces can achieve energy saving, reduce the effect of pollutant emissions, but relative lack of coal-fueled high temperature air combustion research. Coal-fired boiler low NOx combustion optimization based on artificial intelligence can effectively reduce NOx emissions, the need for further research on the modeling and optimization algorithms. The main content of this paper consists of two parts, the first part of high temperature air combustion characteristics of pulverized coal jet, the second part is based on artificial intelligence 300 MW twin furnace coal-fired boiler low NOx combustion optimization studies. The research topics include: (1) the occurrence of high temperature air. In this thesis, the products of combustion of propane gas in the fuel lean combustion conditions as high temperature air required for the combustion of pulverized coal jet. To this end, the design of a porous material flame stabilization co-flow burners, the central jet pulverized coal jet. The minimum co-flow average temperature of 850 K, the maximum co-flow average temperature to 1138 K. In the test under the experimental conditions, the high-temperature air temperature Tcoflow uniform area of ??approximately 40 mm × 100 mm (axial) (radial), influenced by propane flow temperature level of approximately 1000-1100 K. The co-flow burner oxygen concentration of about 7-9%, the 1000-1100 K about high-temperature air temperature Tcoflow high temperature air. (2) Based on the flame oscillation frequency of the image processing with the flame height measurements jet flame oscillation frequency measured using high-speed photography. The conclusion of the study show that the oscillation frequency of the oscillation frequency of the upper part of the flame the lt; flame Central lt; oscillation frequency of the root of the flame. Flame oscillation frequency with a wind speed, the speed for the powder, coal particle size, with increasing rank coal increases, and the root region of increase is greater than the change in the region of the middle and upper amplitude; first increase with the stoichiometric ratio ? and then lower; flame oscillation frequency does not substantially change with 02/CO2 ratio. (3) coal jet in high temperature air combustion carbon burnout characteristics, the nitrogen emission characteristics. Water-cooled probe the coal jet sampling, elemental analysis and ash content determination of the ash sample. The experimental results show that, as the high-temperature air temperature decreases, the oxygen concentration is increased, the rate of carbon remaining lower, i.e. the higher the rate of burnout. When the primary air is 02/CO2, as the oxygen concentration increases, bituminous coal and anthracite carbon residual rates are reduced. Under the same conditions, 02/CO2 combustion environment anthracite greater than bituminous coal, bituminous coal containing a high ash hinder the gasification reaction of CO2 with C. Meanwhile, with the high-temperature air temperature decreases, the increase in oxygen concentration, the residual rate of anthracite elemental nitrogen is lower than the residual rate of the elemental carbon, but the difference is not large. (4) high temperature air combustion of pulverized coal jet the initial NOx emissions research when the primary air to air in the four groups of high-temperature air parameters studied in this paper, bituminous coal and lignite NOx variation similar to that, with the high temperature air temperature decreases oxygen concentration decreases NOx emission values. Bituminous coal combustion initial NOx 389-299 mg/m3, the lignite combustion initial NOx for 1313 to 1080mg/m3.; Initial stage of combustion NOx Emissions of SH anthracite and bituminous coal and lignite, with the reduction of the high-temperature air temperature, oxygen concentration rose high NOx emission values ??increased to 513-767 mg/m3. When the primary air to CO2, the nozzle exit position at a distance of 300 mm position to the downstream of the jet, the initial NOx emission characteristics of lignite burning bituminous coal, lignite combustion initial NOx advance restore. When the primary air is 02/C02, with the increase in the oxygen concentration in the primary air, bituminous coal combustion initial NOx emissions increase, anthracite initial stage of combustion NOx emissions decreased first and then increase may be due to the ignition delay caused Fire elongated reduce the peak flame temperature. Oxyfuel can effectively reduce NOx emissions from the early stages of burning, according to the type of coal, the reduction of 38.78% -59.87% when the primary air to air, anthracite coal finer the lower the concentration of the initial NOx emissions, the conventional pulverized coal The air combustion showing similar rules. (5) coal-fired boiler NOx emissions prediction model. Twin furnace for a 300 MW coal-fired boiler, by cross-correlation analysis of the dependencies between the boiler operating parameters and NOx emissions. In order to eliminate the linear correlation may exist between the boiler parameters, the boiler parameters on principal component analysis. The results showed that just 18 principal component accounted for 99.999% of the 21 parameters of the final final prediction of NOx emission model input is reduced to 19 boiler operating parameters. SVR model to predict the highest accuracy, validation data on the average relative error of 1.59%, the execution time of 164sec, GRNN model is followed, BP neural network in the model again, the worst linear model. The SVR model the execution time GRNN only 16.7%, the BPNN 3.9%. (6) Low NOx emission combustion optimization. NOx emission model based on coal-fired boilers, the use of genetic algorithm GA, ant colony algorithm ACO Estimation of Distribution Algorithms EDA and particle swarm optimization PSO find the input parameters of the model (that is, the boiler operating parameters, wind speed and the second speed) excellent. The four algorithms of computing time: 120.18sec 120.14 sec, 84.68 sec, 29.17 sec.

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