Abstract: Taking a coal-fired power plant as an example, after low-NOx combustion retrofit in Boilers 1 and 2, the problem of burner burnout in the two boilers arises and the NOx emissions from Boiler 1 are about 100 mg/Nm3 more than those from Boiler 2, which endangers the secure operation of the boilers and the normal commissioning of the denitration equipments. Therefore, the cause analysis on these problems is made from the aspects of retrofit design, equipment manufacturing and operation modes. The analysis figures out that: (1) in the low-NOx combustion retrofit design for Boiler 2, coal type changes are not taken into account, only the routine measures for combustion stabilization are taken and the surrounding air damper opening degree is small, which leads to local high temperatures in the burner zone and coal powder accumulation and combustion in the primary air pipes caused by burner anti-wear ceramic shedding. (2) during the burner manufacturing of Boiler 1, the sealing plates between the burner nozzles are not welded following the design requirements. The coal powder is brought back to the burner separators by negative pressure reflux and burned on the separators, which results in burner burnout. Meanwhile, the gaps between the burner nozzles are not sealed, causing serious auxiliary air leakage and reducing the effects of air staged combustion, which leads to high NOx emissions. Based on the above analysis, the improvement is carried out, thus the problems existing in Boilers 1 and 2 are solved effectively. The improvement can provide guidance on solving similar problems for other power plants.

Key words: low-NOx combustion retrofit, retrofit scheme, equipment manufacturing, operation mode, burner burnout, NOx emission