| Energy and environment are two important problems in modern society. China is a country rich in coals, and power generation in China mainly relies on coal-fired thermal power generation. Coal smoke pollution caused by coal combustion is the main source of air pollution in China, so strictly controlling pollutant emission during coal combustion and simultaneously realizing high-efficiency, low-pollution combustion of coal are of great benefits in society, economy and environment. In this dissertation, coals used in power plant in Shandong province were selected as studied objects, by means of experimental investigation, theoretical analysis and calculating simulation, together with measuring data from large-scale coal-fired boiler in operation in power plant, characteristics of sulfur and nitrogen pollutants coordinated emission during coals combustion were specially studied to direct engineering practice.Because combustion characteristics of coals have direct effect on characteristics of various pollutants emission during coals combustion, combustion characteristics of coals used in power plant were studies with thermo-gravimetric analyzer in the beginning of the dissertation. Regularity of effect of coal property on ignition characteristics, combustion stability, burn-off characteristics were discussed, and combustion characteristics of blended coals were emphasized to study. The results showed that for single component coal, coal activity decreased with coal rank increasing , and initial temperature corresponding to volatile emission increased, ignition temperature increased, temperature corresponding to maximum weight loss rate of combustion increased, fixed carbon burn-off rate declined, combustion stability index decreased, so ignition and burn-off characteristics would become bad. For blended coals with approximately identical component coal rank in combustion characteristics, characteristic parameters of combustion were between that of component coals, and with the blended proportion of the component coal in the blended coal increasing, combustion characteristics of blended coals would be more near to that of the component coal, but extent of this effect would vary with different component coal rank. For blended coals with distinctly different component coal rank in combustion characteristics, the combustion characteristics would be strongly different from that of component coals. Combustion stability index of single component coal were larger than that of blended coals, so ignition and combustion characteristics of blended coals would become bad in general. Combustion characteristics of blended coals could not be simply figured out by the linear correlation with that of component coal ranks.Characteristics of sulfur and nitrogen pollutants emission during coal combustion in power plant were systematically studied by means of experimental system for pulverized coal combustion, thermo-gravimetric analyzer and high temperature reactor. Formation mechanism and emission characteristics of sulfur pollutants (SO2, H2S) and nitrogen pollutants (NO, NO2) were particularly studied during pulverized coal combustion for different coal rank. And regularities of effects of coal property and operating conditions on characteristics of sulfur and nitrogen pollutants emission were further investigated. It is found that concentration curve of SO2 emission was of obvious two peaks in shape, and it was due to emission of sulfur in coal at different stages. For different coal rank, emission rate of sulfur in coal was different. Also concentration curve of H2S emission was of two peaks in shape, but time corresponding peak value in concentration curve of H2S was earlier than that of SO2. Generally, the more sulfur content in coal was, the higher concentration of SO2 emission was, but emission time of sulfur in coal of higher volatile content was earlier than that of lower volatile content. When particle size of pulverized coal increased, the concentration of H2S in the center of flame increased, emission amount of SO2 decreased, and emission time of sulfur would prolonged. As excess air coefficient increased, emission of sulfur in coal would quicken, and concentration of SO2 increased, concentration of H2S decreased substantially. With oxygen concentration increasing, the whole emission time of sulfur shorten. Increasing ratio of primary air to secondary air, concentration of H2S decreased, and concentration of SO2 increased. Adding near-wall air could clear reducing atmosphere in local area, and make concentration of SO2 deeply decrease. At atmosphere contain CO, emission rate and emission amount of SO2 decreased obviously, but that of H2S increased, total conversion rate of sulfur was less than that at air atmosphere. With temperature increasing, emission time of sulfur shorten, and ultimate emission amount of sulfur increasedDuring pulverized coal combustion, emission process of nitrogen pollutants could be divided into two stage: early-stage prompt formation and later-stage gradual release, and characteristic curve of nitrogen pollutants emission was of two peaks in shape. Formation of NOx was mainly at the stage of pulverized coal ignition, and with nitrogen content in coal increasing, concentration of NO emission increased while the conversion rate of nitrogen in coal to NO decreased. In the case of the same nitrogen content in coal, the more volatile content was, the more concentration of NO emission would be. When coalification increased, concentration NO emission would decreased. With ratio of oxygen to nitrogen in coal increasing, emission rate of nitrogen increased, and emission amount of nitrogen increased. Conversion rate of nitrogen in coal to NO decreased with smaller pulverized coal fineness, so lower concentration of NO emission could be realized by smaller pulverized coal fineness. When humidity in coal increasing, emission amount of NO would decrease in general. The amount of NO formation increased with excess air coefficient increasing during coal combustion. Concentration of NO emission varied obviously with different ratio of primary air to secondary air, and adding near-wall air could reduce concentration of NO emission. Because of reducing action of CO to NO, concentration of NO emission decreased. Fuel-NOx emission was of characteristics of formation in middle temperature, and amount of NO emission was maximal in temperature ranges from 700℃to 800℃. Amount of NO2 formation were found to be strongly dependent on combustion temperature and precursor NO concentration. Large quantities of NO2 decomposed when temperature increased. Formation concentration of NO2 increased accordingly with concentration of NO increasing.Overall considering interaction of sulfur and nitrogen in combustion, regularity of coordinated action of sulfur and nitrogen pollutants during pulverized coals combustion were studied with exploring. Regularity of effect of different form of sulfur in coal on characteristics of nitrogen pollutants emission and regularity of effect of SO2 concentration on NO formation at different atmosphere were emphasized to study, and regularity of effect of nitrogen on emission of sulfur in coal during pulverized coals combustion were investigated in the mean time. The results showed that there was great effect of different form of sulfur in coal on characteristics of nitrogen pollutants emission. Sulfur in the form of simple substance chiefly affected peak value and peak width of concentration curve of nitrogen pollutants emission, and it is relevant to coal rank. There was outstanding effect of sulfur in the form of pyrite on characteristics of nitrogen pollutants emission, pyrite in coal would restrain reaction reducing NO with semi-coke in the lean oxygen condition, and it is advantageous to NO formation. There was distinctively different effect of SO2 concentration on NO formation at different atmosphere, when SO2 concentration increased, amount of NO formation obviously decreased at oxidizing atmosphere, while it was just opposite at reducing atmosphere. NO also affected emission characteristics of sulfur in coal, and brought emission of sulfur in coal forward, initial concentration of SO2 formation increased. Characteristics of SO2 emission were of different regularity with different volatile content in coal. It was also found that there was effect of combustion temperature on coordinated action in emission of sulfur and nitrogen pollutantsCharacteristics of sulfur and nitrogen pollutants coordinated emission during blended coals combustion were experimental studied. Coordinated actions of component coal ranks in blended coals during sulfur and nitrogen pollutants emission were emphasized to investigate along with regularity of effect of blended coals with different coal ranks on sulfur and nitrogen pollutants emission. It was found that blended coal combustion can promote release of sulfur at first stage, and final emission amount of SO2 may be reduced by means of blending high-sulfur coals with low-sulfur coals. On the whole, concentration and final emission amount of SO2 during blended coals combustion accorded with calculating value based on the weighted means of the component coals, and with the blended proportion of the component coal in the blended coal increasing, characteristics of SO2 emission would be more near to that of component coal. But concentration of H2S emission was different from calculating value based on the weighted means of the component coals, and it would be larger or less than calculating value. For blended coals combustion, there was a linear correlation between formation amount of NOx and nitrogen contents in blended coals. Concentration curve of NO emission during blended coals combustion is generally of the two peaks in shape, and the region on the peak value of concentration of NO emission is wider. Concentration and time of NO emission is generally between that of component coals, but they were different from the calculating value based on the weighted means of the component coals to a certain extent. There was great effect of temperature on nitrogen pollutants coordinated emission during blended coals combustion, concentration curve of NO emission only showed one peak in shape at lower temperature, but two peaks appeared at higher temperature, and the higher temperature, the more prominent two peaks in shape, the more amount of nitrogen emission.Characteristics of pollutants emission during pulverized coal combustion in large-scale coal-fired boiler in power plant were simulated and forecasted by means of mathematical model. According to pulverized coals combustion features and pollutant formation characteristics, relevant theory and mathematical model such as multiphase flow, heat transfer, mass transfer, turbulent combustion and pollutant formation and so on, and corresponding numerical calculating method are used to numerically simulate combustion process in furnace and the regularity of pollutants formation in different operating conditions for different coal ranks, and regularity of velocity field distribution, temperature field distribution, gas-phase concentration field distribution in furnace and so on were obtained. Calculated results showed that in simulated combustion conditions, turbulent intensity in the whole furnace was very high, and mixture of pulverized coal and gas flow were quite uniform, flame permeating degree in furnace were high, so it is advantageous to ignition, combustion and burn-off of pulverized coal. Flame formed high temperature area adjacent to burner at the center of furnace, and formation concentration of both fuel-NOx and thermal-NOx in that area were highest. With decreasing secondary air flow rate and increasing burn-off air flow rate, highest temperature in the area adjacent to burner in furnace decreased, and high temperature area would move towards upside of furnace, formation concentration of NOx decreased. According to simulated calculation results, and using the measuring data from coal-fired boiler in operation, technical measures were put forward to optimize combustion and control pollutants emission.The soft measuring model was established to achieve precise prediction and on-line measurement of concentration of sulfur and nitrogen pollutants release from coals combusting in large-scale coal-fired boiler in the power plant. By means of soft measurement technology based on hyper CMAC neural network, soft measuring model for concentration of pollutants release from coals combusting in large-scale coal-fired boiler in the power plant were raised on the basis of an in-depth study on principle, structure and algorithm of hyper CMAC neural network. In this model, coal property is described by a general ignition characteristic index—Fz number, sulfur content Sar and nitrogen content Nar in coal, to reflect the effect of coal property on characteristics of sulfur and nitrogen pollutant emission; Furnace temperature T and oxygen concentration CO2 or excess air coefficientαl at furnace outletare used to reflect the effect of combustion condition on characteristics of sulfur and nitrogen pollutant emission. The soft measuring model for concentration of sulfur and nitrogen pollutants emission during coals combustion would be obtained through training and learning for sample data. For blended coal, blended proportion of the component coal in the blended coal needed to be included in the model besides parameters concerned with property of component coal and combustion condition in furnace. Coordinated action of sulfur and nitrogen pollutants during pulverized coals combustion was also taken into account in the model. Calculating and emulating results indicate that the soft measuring model based on CMAC neural network technology could implement accurate forecast and on-line measurement to concentration of sulfur and nitrogen pollutant emission during coals combustion in large-scale coal-fired boiler in the power plant. It would be effective to guide operator in the power plant to optimize combustion and control pollutants emission.To sum up the above, starting with studies on combustion characteristics of coals, characteristics of sulfur and nitrogen pollutants emission during coal combustion were systematically studied in the dissertation, along with regularity of coordinated action of sulfur and nitrogen pollutants were further investigated, and coordinated actions of component coal ranks in blended coals during sulfur and nitrogen pollutants emission were particularly studied. In the meantime, by means of mathematical model, combustion process in furnace and the regularity of pollutants formation were numerically simulated. Based on CMAC neural network technology, soft measuring model was established to achieve accurate forecast and on-line measurement of concentration of sulfur and nitrogen pollutants release from coals combusting in large-scale coal-fired boiler in the power plant, and further guide operator in the power plant to control combustion process. The theoretical foundation was supplied to utilize diverse coal rank and blended coal in the power plant, optimize combustion and control pollutants emission.
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