【作者】 陆智；

【导师】 周志军； 刘建忠；

【作者基本信息】 浙江大学 ， 工程热物理， 2008， 硕士

【摘要】 随着我国工业化进程的推进,电力工业的发展,作为我国主要能源的煤炭的消费量将逐年扩大,NO_x作为燃煤电站锅炉的排放烟气的主要污染物之一,对环境造成严重的污染。控制好电站锅炉的燃烧与污染物排放对我国的可持续发展有着重要的意义。本论文以萧山电厂420t/h四角切圆燃煤锅炉为研究对象,通过实验室研究、现场热态试验和数值模拟,制定了锅炉的SOFA低NOx燃烧技术改造。利用热天平试验台,研究了电厂燃煤的着火、燃烧特性,分析了煤种、升温速率等因素对煤的燃烧特性的影响,结果显示,电厂燃用的煤种的着火点温度、稳燃指数、燃尽指数有较大的差别。大混35002的着火温度最低,只有363℃,着火温度最高的大混35007达到424℃,二者相差60℃;着火稳燃特性指数与着火温度呈现出相同的规律,大混35002最大,达到3.21,大混35007最小,为2.84。燃尽性能方面,大混35007的燃尽性能最好,燃尽特性指数高达145.31,准混和大混106的燃尽性能相近,燃尽指数分别为120.31和124.40,大混35002的燃尽性能最差,燃尽指数只有71.03。在沉降炉试验台上,对各煤种在不同的过量空气系数下NO_x排放特性和不同温度下NO_x排放特性进行了系统的试验研究,并对其产生的原因进行分析,对于这4种煤种,综合考虑NOx的排放和焦炭的燃尽,一次燃烧区的过量空气系数应控制在0.85左右。无论是在氧化性气氛还是在还原性气氛下,当炉温超过1300℃,NO_x生成量将大幅度的增加,因此主燃区温度最好控制在1300℃以下。对锅炉的NO_x排放特性进行了热态试验研究。锅炉低负荷运行时,锅炉运行氧量过高,造成NO_x排放浓度过高。双磨投运方式下,三次风量较大,起到部分再燃作用,NO_x排放量相对其它磨煤机投运方式最小。运行氧量小于3%时,过量空气系数增加,NO_x生成量迅速增加;运行氧量大于3%时,过量空气系数增加,NO_x的增加趋缓。对于现有的燃烧器布置,给粉方式的变化对NO_x排放浓度影响不大。在保证一次风刚性,不出现煤粉沉积的前提下,低一次风速下NO_x的排放较低。对于现有的燃烧器,锅炉配风方式对NO_x排放的影响有限。根据试验结果,结合锅炉实际制定了两套低NO_x改造方案,并通过数值模拟对改造方案的燃烧和NO_x排放进行了预测。数值模拟结果显示,改造后锅炉燃烧状况较好,炉膛温度场连续均匀,锅炉燃烧完全,NO_x排放量大大降低,并且方案一的效果优于方案二。更多还原

【Abstract】 With the acceleration of industrialization process and the development of the power industry, the consumption of coal was increasing year by year. The combustion of fuels generate more and more NO_X emission, which can lead to serious atmosphere pollution. Control of the combustion and pollution of power plant were important for the sustainable development of our country.A Corner-tangential-boiler of 420t/h in Xiaoshan thermal power plant was studied in the thesis by means of experiments and field tests and numerical simulation, then the low NO_X Combustion Technology reform sheme by SOFA method was designed.Through the method of the thermo gravimetric analysis, studied the factor that influencing the coal combustion characteristic, including the ignition and combustion characteristic, analyzed the coal kind and elevation of temperature speed. The results revealed that the ignition temperature、steady combustion numeric and burnout index of different coal types had obvious difference.The ignition-temperature of dahun35002 was 363°C ,which was the lowest one of the coal samples, The ignition-temperature of dahun35007 was 424℃,which was the highest one of the coal samples,the discrepancy between them was greater than 60℃;The law of steady combustion numeric was the same as The law of ignition-temperature. The burnout index of dahun35007 was 145.31, which was the highest one of the coal samples,the burnout index of dahun106 and zhunhun was 120.31 and 124.40 respectively,The Combustion Efficiency of dahun35002 was the poorest, The burnout index of it was only 71.03.The Experimental Investigation on the influence of different excess air factor and temperature on the NO_x emission characteristics of different coal types was carried out on subsiding furnace, and their causes analyzed. By comprehensive consideration of NO_x emission and the coke burnout,the excess air factor in the main combustion zone was controlled at 0.85.When the furnace temperature was over 1300℃,the NO_x emission was greatly increased either in the oxidizing atmosphere or in the reducing atmosphere,so the temperature of main combustion zone had best controlled below 1300℃.Hot state tests on the NO_X emission of the boiler was carried out. When the boiler operated at low load,the oxygen concentration was over high,then causing NO_X emission too highly.When two coal mills operated, Tertiary-Air Coal Rebuming reduced NO_X Release.When the oxygen concentration was below 3%,NO_X emission increased greatly as the oxygen concentration rised. When the oxygen concentration was above 3%,the increasing rate was easting up.For the existing burner, pulverized coal distribution had little influence on NO_X emission. Ensuring primary air Stable,on this premise,low primary air velocity can lower the NO_X emission. For the existing burner, optimizing air distribution only had limited influence on NO_X emission.Based on the test result,two low NO_X and combined with practical boiler operation,two low NO_X reform schemes was desighed,then a predicton of reform scheme combustion and NO_X emission was made by numerical simulation.The simulation results showed that the boiler operated stably; the temperature field was uniformity; complete combustion was reached, NO_x emission reduced greatly,and the scheme one had better reconstruction effect than the scheme two.更多还原