Research On The Technology Of Low-NOx Combustion System Of The Power Plant Boiler

Separated overfire air combustion technology is one of the primary means of power enterprises to reduce NOx emissions; however, the low-NOx combustion technology may also cause the high temperature corrosion of boiler water wall, so it is necessary to study the low NOx combustion system and the factors affecting high-temperature corrosion.The paper adopts a420t/h tangential firing combustion pulverized coal boiler as a research object. The combustion process of the boiler is simulated by Fluent software. The height of SOFA, the SOFA air ratio, SOFA layout and the SOFA air angle which effect on the flue gas temperature distribution, residual rotation and the situation NOx generated are analyzed. The calculation of kinetic reaction mechanism integrated with the flue gas composition analysis is used to study the factors, which include the temperature and oxygen, affected on the transformation mechanism of H2S beside the water wall under reducing condition.The simulated results show that:With the increase of the height of SOFA, NOx emissions gradually reduce and then increased at last, boiler efficiency also reduce. The best height of the SOFA is near4m; with the increase the ratio of separated overfire air, the NOx emissions gradually decrease, however, the combustion efficiency and boiler efficiency is growing lower. The optimal ratio of the separated overfire air is about22%. The arrangement of separated overfire air nozzle affect the combustion process of pulverized coal, compared with scattered arrangement, centralized arrangement has a greater influence of the furnace airflow structure, its penetrating ability is reinforced, velocity attenuation is lower, however, the temperature of the flue gas is long and narrow distributed. Scattered arrangement has a better effect on the eliminating residual rotation than centralized arrangements. With the diameter of deflecting circle of a single pair SOFA increases, the high temperature region of the SOFA level inwardly shrink, whereas in the region of the former back wall, the high-temperature region slightly closer. As can be seen from the furnace exit gas flow vector, when the angle of a single pair SOFA deflecting within5°, the eliminating result aren’t obvious.The main productions of H2S vary with the reaction conditions, COS is mainly produced in highly reducing conditions and SO2is dominant production under oxidizing atmosphere. Peak concentration of S2only can be obtained at mildly reducing conditions and moderate temperature; meanwhile, most of H2S is oxidized to SO2when the temperature is above1300K. A turning point is found when the concentration of O2is about2%, and simulation results comply with experimental measurements.