| Air staging is one of the most common technologies in low-Nitrogen combustion to reduce the NOx emission used in power plants. The topic in this paper includes two different units of tangential firing boiler, which were retrofitted by air staging. The retrofits were based on numerical simulation and experimental study. The explorations of low-NOx factors were followed closely by changing the oxygen content, pulverized coal recirculation and tertiary air. The baffle’s opening size, swing angle and layer number of SOFA also were taken into account.To make clear of the current circumstances, Fluent program was used to simulate the velocity, temperature, components and pollutant. The results were similar to the data achieved from the field tests, which proved the rationality that the model selected. The optimal scheme also could be predicted by further simulations through air staging as follows:the installation elevation of SOFA for 420 t/h was 21.25 m and maked the SOFA rate of 24%; simulations on air staging for 100 t/h presented the maximum temperature was lower than 1500℃ and the scheme could reach the denitration efficiency of 30.5%.Retrofits were conducted on these two boilers referenced to the numerical simulation. Both of them were added the SOFA, but there were different in retrofitting on tertiary air:the boiler of 100t/h used the dense thin separation technology on it, while the other was not.Finally, the low-NOx factors were explored after the retrofit conducted on these two boilers. The explored drew the conclusions that the emission of NOx would decrease while the unburned carbon would increase when decreasing the oxygen content. It was recommended that kept the oxygen content no less than 3%; similarly, the NOx would also decrease when keeping SOFA nose angle up. Otherwise, the operation mode of pulverized coal system could have efforts on the emission of NOx. At last, results of performance examination indicated that NOx emission could be controlled below 300 mg/Nm3 on these two boilers and retrofits on low-nitrogen combustion met the demand. |
