机组超低排放改造后锅炉爆管原因分析及对策

随着国家对环保要求的日益提高,氮氧化物(NOx)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 (NOx) 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