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。
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.
引文
[1]谌天兵,武建军,韩甲业,燃煤污染现状及其治理技术综述[J].煤,2006(2)
[2]黄诗坚,NOx的危害及其排放控制[J].电力环境保护,2004(1)
[3]国家环保总局,2007年全国大气环境状况,2008
[4]张莉,浅析光化学烟雾的污染问题[J],四川环境,2005
[5]肖晓存,王雪纳,大气中氮化物的污染与防治[J].煤炭技术,2005(8)
[6]李玉江,吴涛,德国燃煤电厂氮氧化物的控制技术[J].环境科学研究,200(4)
[7]火电厂大气污染物排放标准GB13223-1996
[8]火电厂大气污染物排放标准GB13223-2003
[9]池作和等,可调浓度煤粉浓淡分流器在萧山电厂的应用,锅炉技术,1996.2
[10]刘汉涛,李慧,李英杰.煤粉燃烧燃料氮析出研究进展[J].山东建筑工程学院学报,2004,Vol.19(4):69-72,80.
[11]岑可发,姚强.高等燃烧学[M]:浙江大学出版社.2002.
[12]Lans RPvd,Glarborg P,Dam-Johansen K.Influence of Process Parameters on Nitrogen Oxide Formation in Pulverized Coal Burners[J].Prog Energy Combust Sci,1997,Vol.23):349-377.
[13]Wójtowicz MA,R.Pels J,A.Moulijn J.The fate of nitrogen functionalities in coal during pyrolysis and combustion[J].Fuel,1995,Vol.74(4):507-516.
[14]Glarborg P,A.D.Jensen,J.E.Johnsson.Fuel nitrogen conversion in solid fuel fired systems[J].Progress in Energy and Combustion Science,2003,Vol.29:89-113.
[15]刘银河,刘艳华,车得福.煤中灰分和钠添加剂对煤燃烧中氮释放的影响[J].中国电机工程学报,2005,Vol.25(4):136-141.
[16]Wargadalam V J.Homogeneous formation of NO and N2O from the oxidation of HCN and NH3 at 600-1000℃[J].Combustion and Flame 2000,Vol.120(4):465-478.
[17]孙林兵,倪中海,张丽芳,宗志敏,魏贤勇.煤热解过程中氮、硫析出形态的研究进展[J].洁净煤技术,2002,Vol.3(8):47-49.
[18]Spinti JP,Pershing DW.The fate of char-N at pulverized coal conditions[J].Combustion and Flame,2003,Vol.135(299-313).
[19]L.D.Smoot,D.T.Pratt.煤粉燃烧与气化[M]:清华大学出版社,1983.6.
[20]Lorenz H,E.Carrea,M.Tamurac.The role of char surface structure development in pulverized fuel combustion[J].Fuel,2000,Vol.79):1161-1172.
[21]吴碧君,刘晓勤燃煤锅炉低NOx燃烧器的类型及其发展[J]电力环境保护,2004,20(3):24-27
[22]肖理生,曾汉才,金锋,韩军分级燃烧最佳一次风空气系数的实验研究[J]动力工程,2001,21(1):1042-1045.
[23]曾汉才大型锅炉高效低NOx燃烧技术的研究[J]锅炉制造,2001,1:1-11.
[24]张建文低NOx直流煤粉燃烧器设计简介[J]锅炉技术,2000,31(6):23-28.
[25]王春昌燃煤锅炉新三区低NOx燃烧技术的研究探讨[J]热力发电,2005,4:1-7.
[26]邱广明煤粉炉的分级燃烧技术研究[J]热能动力工程,2000,15(89):556-559.
[27]BENESCHA WA,FARWICK H.Modern Concepts in STEAG'power Plant[J].International Journal for Power Plant Technology,1998,(12):44.
[28]Sisto Bertacchi,Franco Donatini and Sauro Pasini.The Control of Nitrogen Oxides(NOx) Emission in Enel's Oil and Coal Fired Units[A].In:The forum for the changing Power Generating Industry in Europe[C].Milan,Italy.Fiera Milano,1998.
[29]HUIJBREGTS WMM,JANSSENJ B,RENS O CJ.Corrosion in low NOx firing condition[A].In:The forumfor the changing Power Generating Industry in Europe[C].Milan,Italy:Fiera Milano,1998.
[30]MAX F J,KOCH G,SCHMIDT W.Low NOx bituminious coal tangential firing system of the 750 MWpower station unit bexbach I[R].EVT-BERICHT,1998,12.
[31]沈伯雄,孙幸福,王成东,秦磊,王瑞再燃法烟气脱硝技术[J]化工环保,2005,25(4):114-116.
[32]曾庆广,王阳,董建勋,伊磊,朱天旭,陈坚,阮国荣,徐剑风,冯余龙,丁杰康常规煤粉作为再燃燃料的燃料分级燃烧试验研究[J]中国电力,2005,38(4):5-7.
[33]钟北京,傅维标再燃过程中HCN对NOx还原的重要性[J]燃烧科学与技术,2000,6(1):77-83.
[34]梁秀俊 高正阳 阎维平 煤粉再燃过程中HCN与NH3的反应机理分析[J]华北电力技术,2004,4:19-21.
[35]钟秦选择性非催化还原法脱除NOx的实验研究[J]南京理工大学学报,2000,24(1):68-71.
[36]路涛,贾双燕,李晓芸关于烟气脱硝的SNCR工艺及其经济分析[J]现代电力,2004,21(1):17-21.
[37]孙德荣,吴星五我国氮氧化物烟气治理技术现状及发展趋势[J]云南环境科学,2003,22(3):47-49.
[38]王智化,周昊,周俊虎,樊建人,岑可法不同温度下炉内喷射氨水脱除NOx的模拟与试验研究[J]燃料化学学报,2004,32(1):48-52.
[39]顾恒祥,燃料和燃烧,西北工业大学出版社,1993
[40]孙学信,燃煤锅炉燃烧试验技术与方法,中国电力出版社,2002
[41]朱益群,屠建君.煤燃烧特征点变化规律的研究[J].热能动力工程,1997,12(5):332-334
[42]张保生 新型干法水泥回转窑中低品位燃料燃烧特性和窑内燃烧过程研究浙江大学博士学位论文2007
[43]蔡正千热分析高等教育出版社,1993年8月第一版
[44]高正阳,方立军,周健,等.混煤燃烧特性的热重试验研究[J].动力工程,2002,22(3)1764-1767,1749
[45]孙学信 煤粉热解及燃烧煤燃烧国家重点实验室论文集,1993
[46]傅维镳 煤燃烧理论及其宏观通用规律[M].1版.北京:清华大学出版社,2003.
[47]韶关发电厂经济配煤项目实验室研究报告.2007.7.
[48]宋国良 高浓度煤粉着火低NOx排放特性的机理及试验研究,浙江大学博士学位论文,杭州:2006
[49]吴双应,李友荣,卢啸风,等.再燃烧技术原理及其影响因素分析[J]冶金能源,2002,21(2):26.
[50]周昊 大型电站锅炉氮氧化物控制和燃烧优化中若干关键性问题的研究浙江大学博士学位论文
[51]方磊 三次风再燃降低NOx排放的研究浙江大学硕士论文
[52]曹红加,唐必光,许洪波煤粉浓淡燃烧方式对电站锅炉NOx排放影响的试验研究[J]中国电机工程学报,2004,24(8):230-232
[53]秦裕琨,李争起,孙锐,孙绍增,吴少华风包粉煤粉燃烧原理及实验研究[J]中国电机工程学报,2000,20(5)
[54]王恩禄,罗永浩,彭玲,陆方,章明川分级燃烧降低四角切向燃用低挥发份煤电站锅炉NOx的排放水平[J]热力发电,2004(03)
[55]周力行湍流两相流动与燃烧的数值模拟[M]北京:清华大学出版社,1991
[56]韩占忠,王敬,兰小平FLUENT-流体工程仿真计算实例与应用[M]北京:北京理工大学出版社,2004.6
[57]刘霞,葛新锋Fluent软件及其在我国的应用[J]能源研究与利用,2003(2)
[58]王瑞金,张凯,王刚Fluent技术基础与应用实例[M]北京:清华大学出版社,2007(2)
[59]刘向军,徐旭常采用不同哦网格比较伪扩散对四角切圆型炉膛流场计算的影响[J]燃烧科学与技术,1997(2)
[60]潘维,池作和,斯东波,阮涛,岑可法四角切圆燃烧锅炉炉膛网格生成方法的研究[J]动力工程,2005,25(3)
[61]潘维,池作和,斯东波,阮涛,岑可法200MW四角切圆燃烧锅炉改造工况数值模拟[J]中国电机工程学报,2005,25(8)
[62]朱彤,马喜辰,董鹏,秦裕琨切向燃烧炉膛中网格划分方法对数值模拟的影响[J]哈尔滨工业大学学报,1997,29(5)
[63]Blacker T.The Cooper Tool[A].Proceedings of the 5~(th) International Meshing Roundtable,Pittsburgh,1996:13-29