不同燃尽风率下炉内NO_x生成特性空间分布研究

Study of Low NO_x Transformation for Variable Overfire Air Rate in Spatial Distribution

运用CFD软件模拟不同燃尽风率下炉内NOx生成特性,根据相应的煤质选择了合适的NOx模型,模拟的结果能够较好地与改造前后的实测数据吻合,验证了模型的准确性。在该数值模型的基础上,针对不同燃尽风率的模拟结果进行分析,阐述NOx的生成特性在不同燃尽风率下的变化。结果表明,空间分布法能够详细地描述炉内燃烧状况及NOx生成。燃尽风率的变化对挥发分的析出影响较小。高燃尽风率使得主燃区缺氧程度加深,焦炭的燃尽会被推迟,主燃区还原性气氛得到增强,主燃区燃料型和热力型NOx的生成速率均有所下降,NOx浓度得以降低。但主燃区剩余未完全燃烧物质及焦炭推迟燃尽使得在燃尽区有更多HCN被氧化产生燃料型NOx,使得最高燃尽风率下炉膛出口的NOx浓度不一定达到最低。控制出口NOx的浓度主要是根据煤质合理选择燃尽风率,控制主燃区燃料型NOx的生成和燃尽区燃料型NOx的反弹。

Using CFD software to simulate different rates of overfire air NOx formation characteristics in furnance.According to the characteristics of the coal,select the appropriate NOx model.The simulation shows that the date can be consistent with the measured before and after transformation.It verifies the accuracy of the model.Base on this numerical model,a method called spatial distribution is used to analyze the results of different rates of overfire air by simulating.Describes the characteristics of NOxformation at different rate of overfire air.The results show that the spatial distribution method can describe the combustion conditions in the furnance and NOx formation in detail.Changing overfire air rate have a less affected on volatile release.In a high overfire air rate,the coke burn out will be postponed and the reducing atmosphere will be enhanced.In the primary combustion zone,the fuel and thermal NOx rates has declined.NOx concentration is reduced.But the unburned substances and the coke delays burn out makes more HCN to be oxidized to produce fuel NOx.This makes under the highest rate overfire air the furnace exit NOx concentration does not reach the minimum.The main idea to control export concentration of NOx is to choose a overfire air rate based on the characteristics of the coal so that can control the formation of fuel NOx in the main combustion zone and rebound in the burnout zone.