330 MW机组超低排放改造后锅炉爆管原因分析及对策
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摘要
随着国家对环保要求的日益提高,氮氧化物(NO_x)成为火电厂继除尘、脱硫后气态污染物排放控制的重点。现役机组进行超低排放改造工作时,相应的锅炉燃烧系统也需改动。燃烧系统的改动对炉内温度场的变化有直接影响,炉管氧化皮生成及脱落问题一直是超(超超)临界机组主要治理问题,而亚临界机组氧化皮问题未得到有效关注。锅炉低氮燃烧器改造主要沿用四区理论即热解区、主燃烧区、还原区、燃尽区,以初期降低过量空气系数的方式延迟燃烧,这对炉内温度场产生一定影响,而此时燃烧器的改动将加剧炉内温度场变化,刺激炉内抗氧化裕度较低管材的敏感性。针对某电厂330 MW亚临界机组超低排放改造后连续发生多次爆管事件,通过对爆管原因、管材老化情况及炉内温度场前后变化等进行对比,确认炉内温度场变化引起的末级过热器T23管材氧化皮生成剥落引发爆管的主要原因为抗氧化裕度较低。针对亚临界锅炉在燃烧器改造后可能引发的次生问题进行研究,提出要加强超低排放改造期间对燃烧器改动后炉内温度场发生变化的重视;亚临界机组中SA213-T23材质在炉内温度场升高20℃左右后,易发生氧化皮生产加速、金属组织老化加速等问题。亚临界机组应加强对氧化皮的检测,掌握管材老化程度,选材方面应适当扩宽管材抗氧化裕度。
With the increasing requirements of environmental protection,nitrogen oxides( NO_x) have become the focus of gas pollutant emission control after dust removal and desulfurization in thermal power plants.The corresponding boiler combustion system should also be changed when the existing units are reformed for ultra-low emission.The change of combustion system has a direct impact on the temperature field in the furnace.The formation and shedding of oxide scales in furnace tubes has been the main treatment problem of ultra-supercritical units,while the oxide scales of sub-critical units have not been effectively concerned.The reformation of low nitrogen burner of boiler mainly uses four-zone theory,namely pyrolysis zone,main combustion zone,reduction zone and burnout zone,to delay combustion by reducing excess air coefficient in the initial stage,which has a certain impact on the temperature field in the furnace.At this time,the change of burner will aggravate the change of temperature field in the furnace and stimulate the sensitivity of tubes with lower oxidation margin in the furnace.In this paper,several tube bursts occurred continuously after the retrofit of 330 MW subcritical unit with ultra-low emission in a power plant.By comparing the causes of tube bursts,the aging of tubes and the changes of temperature field in the furnace before and after the retrofitting,it is confirmed that the main cause of tube burst caused by the change of temperature field in the furnace is the low oxidation margin.In view of the secondary problems that may arise from the retrofitting of subcritical boilers,it is proposed that attention should be paid to the change of temperature field in the furnace after the retrofitting of the burner during the retrofitting of ultra-low emission boilers.When the temperature field of SA213-T23 in the subcritical unit rises by about 20 ℃,the acceleration of oxide scale production and the acceleration of aging of metal structure are prone to occur.The subcritical unit should strengthen the detection of oxide scale,grasp the aging degree of pipes,and expand the antioxidant margin of pipes appropriately in material selection.
With the increasing requirements of environmental protection,nitrogen oxides( NO_x) have become the focus of gas pollutant emission control after dust removal and desulfurization in thermal power plants.The corresponding boiler combustion system should also be changed when the existing units are reformed for ultra-low emission.The change of combustion system has a direct impact on the temperature field in the furnace.The formation and shedding of oxide scales in furnace tubes has been the main treatment problem of ultra-supercritical units,while the oxide scales of sub-critical units have not been effectively concerned.The reformation of low nitrogen burner of boiler mainly uses four-zone theory,namely pyrolysis zone,main combustion zone,reduction zone and burnout zone,to delay combustion by reducing excess air coefficient in the initial stage,which has a certain impact on the temperature field in the furnace.At this time,the change of burner will aggravate the change of temperature field in the furnace and stimulate the sensitivity of tubes with lower oxidation margin in the furnace.In this paper,several tube bursts occurred continuously after the retrofit of 330 MW subcritical unit with ultra-low emission in a power plant.By comparing the causes of tube bursts,the aging of tubes and the changes of temperature field in the furnace before and after the retrofitting,it is confirmed that the main cause of tube burst caused by the change of temperature field in the furnace is the low oxidation margin.In view of the secondary problems that may arise from the retrofitting of subcritical boilers,it is proposed that attention should be paid to the change of temperature field in the furnace after the retrofitting of the burner during the retrofitting of ultra-low emission boilers.When the temperature field of SA213-T23 in the subcritical unit rises by about 20 ℃,the acceleration of oxide scale production and the acceleration of aging of metal structure are prone to occur.The subcritical unit should strengthen the detection of oxide scale,grasp the aging degree of pipes,and expand the antioxidant margin of pipes appropriately in material selection.
引文
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[13]李英,高增,侯君明.超临界锅炉过热器氧化皮形成和剥落机理分析及预防措施[J].热力发电,2007,37(11):77-80.LI Ying,GAO Zeng,HOU Junming,et al.Analysisi of mechnisms for oxide skin foramtion and exfoliation in superheater of supercritical boilers as well as preventive measures thereof[J].Thermal Power Generation,2007,37(11):77-80.
[14]LIU Hu,LIU Yinhe,YI Guangzhou,et al.Effects of air staging conditions on the combustion and NOxemission characteristics in a 600 MW wall fired utility boiler using lean coal[J].Energy&Fuels,2013,27(10):5831-5840.
[15]RIBEIRETE A,COSTA M.Impact of the air staging on the performance of a pulverized coal fired furnace[J].Proceedings of the Combustion Institute,2009,32(2):2667-2673.
[16]杨富,章应霖,任永宁,等.新型耐热钢焊接[M].北京:中国电力出版社,2006:72-86.
[2]ZHU Lihui,MA Xueming.Microstructural evolut ion of 2.25C r-16W-V-Nb heat resis tant steel during creep[J].Material Science and Technology,2002,19(2):126-128.
[3]邓永清,朱丽慧,王起江,等.国产T23钢高温组织演变及其对性能的影响[J].钢铁研究学报,2007,19(8):46-50.DENG Yongqing,ZHU Lihui,WANG Qijiang,et al.Effect of microstructure evolution during creep on properties of domestic-made T23 steel[J].Journal of Iron and Steel Research,2007,19(8):46-50.
[4]周振丰,张文钺.焊接冶金与金属材料焊接性[M].北京:机械工业出版社,1988.
[5]赵慧传,贾建民,陈吉刚,等.超临界锅炉末级过热器爆管原因分析[C]//超(超)临界锅炉用钢及焊接技术协作网第三次论坛大会论文集.天津:电力行业电力锅炉压力容器安全监督管理委员会,2009:571-577.
[6]成鹏,赵建仓,梁振新,等.超超临界锅炉T23钢水冷壁裂纹原因分析[C]//超(超)临界锅炉用钢及焊接技术协作网第三次论坛大会论文集.天津:电力行业电力锅炉压力容器安全监督管理委员会,2009:551-555.
[7]伍宇鹏,王伟,钟万里,等,火电厂锅炉受热面管氧化皮脱落事故原因分析[J].广东电力,2013,26(3):91-94.WU Yupeng,WANG Wei,ZHONG Wanli,et al.Analysisi on accident reason for fall-off of oxide skin of heating surface tnbe of thermal power plant boiler[J].Guangdong Electric Power,2013,26(3):91-94.
[8]宝钢T23高压锅炉管评定试验阶段小结[R].上海:宝山钢铁股份有限公司钢管分厂,2004.
[9]张鄂婴,王向斌,陶生智,等.T23钢在大型常规电站锅炉上的应用[J].热力发电,2005,35(3):68-72.
[10]耿波,刘江南,赵颜芬,等.T91钢高温水蒸气氧化层形成机理研究[J].铸造技术,2004,25(12):914-918.GENG Bo,LIU Jiangnan,ZHAO Yanfei,et al.Mechanism of the formation of the oxidation layers of T91 steel tube under the high temperature water vapor[J].Foundry Technology,2004,25(12):914-918.
[11]李耀君.氧化皮脱落导致的过热器管爆管分析[J].热力发电,2005,35(6):56-59.
[12]曾令大,张开利,陈启卷,等.超临界锅炉蒸汽侧氧化皮生成原因与对策[J].中国电力,2010,43(12):46-50.ZENG Lingda,ZHANG Kaili,CHEN QIjuan,et al.Formation mechanism and preventive measure for steam side oxide scale in superheater of supercritical boilers[J].Electric Power,2010,43(12):46-50.
[13]李英,高增,侯君明.超临界锅炉过热器氧化皮形成和剥落机理分析及预防措施[J].热力发电,2007,37(11):77-80.LI Ying,GAO Zeng,HOU Junming,et al.Analysisi of mechnisms for oxide skin foramtion and exfoliation in superheater of supercritical boilers as well as preventive measures thereof[J].Thermal Power Generation,2007,37(11):77-80.
[14]LIU Hu,LIU Yinhe,YI Guangzhou,et al.Effects of air staging conditions on the combustion and NOxemission characteristics in a 600 MW wall fired utility boiler using lean coal[J].Energy&Fuels,2013,27(10):5831-5840.
[15]RIBEIRETE A,COSTA M.Impact of the air staging on the performance of a pulverized coal fired furnace[J].Proceedings of the Combustion Institute,2009,32(2):2667-2673.
[16]杨富,章应霖,任永宁,等.新型耐热钢焊接[M].北京:中国电力出版社,2006:72-86.