| At present, in order to meet the requirements of increasingly stringent emissions requirements, some of the new opposed firing boilers have been implemented with low nitrogen technology transformation. Staged air distribution, as an important measure, forces furnace to divide into the oxygen enriched zone and fuel enriched zone, resulting in the purpose of reducing the generation of NOx. But the practice shows that low nitrogen transformation can increase the possibility of the high temperature sulfur corrosion of water wall. It becomes a key problem to be solved urgently for the safe operation of units. In this thesis, for a 600 MW opposed firing boiler, a numerical simulation method is used to investigate the flow dynamics and optimization of a single closing-to-wall air device and to examine the combustion characteristics of the furnace after installing closing-to-wall air devices.First, this thesis introduces the high temperature corrosion problems in a 600 MW opposed firing boilers and experimentally determine the type of corrosion and flue gas atmosphere near the water wall. Secondly, according to the characteristics of the regional distribution of corrosion, the closing-to-wall air device is arranged in the middle of the side wall. By numerical simulation, the air flow rate is determined, and the device is optimal designed. The results show that the aim of the closing-to-wall air device can be achieved and the device will not cause erosion of the water cold wall. Finally, the combustion in furnace with the closing-to-wall air device is conducted; the reason of high temperature corrosion and the effect of the devices are analyzed; the effects of the device on the combustion and pollutant emissions are compared under different loads. The results indicate that the closing-to-wall air device can wreck the reducing atmosphere near the water wall, whereas it has little influence on the combustion of the furnace and pollutant emissions. |
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