600MW墙式对冲锅炉低氮燃烧技术改造的数值模拟

Numerical Simulation on Low NO_x Combustion Technological Transformation of a 600MW Boiler With Opposed Wall Swirling Burners

采用三维全尺寸稳态数值模拟方法对某电厂600MW超临界墙式对冲锅炉低氮燃烧技术改造进行了分析研究。为了使全炉模拟中入口边界设定更接近于实际的运行工况,先进行单只燃烧器的数值计算,并通过用户自定义函数程序实现燃烧器出口真实的风粉空间分布形态边界条件与炉膛入口边界条件的无差对接,以提高炉内数值计算的精准度。与以往的模型相比,将计算控制区域扩展到包括水平烟道和尾部竖井在内的整个流动传热区域。结果表明:基准工况下,氧浓度在每层主燃烧器的中心横截面达到峰值,炉内烟气流经每层主燃烧器后NO浓度均急剧增加;改造工况下,由于环形回流区与中心回流区的共同作用,每层主燃烧器中心横截面的氧浓度处于一个波动周期内的较低水平,而还原性的CO恰位于峰值附近,因此流经每级主燃烧器区域的烟气NO浓度呈现逐渐降低趋势。此外,研究表明合理的低氮燃烧技术改造方案不会对炉内各受热面的换热产生不良影响。

3-D full-scale steady numerical simulation technique was employed to study on low NOx combustion technological transformation of a 600 MW supercritical boiler with opposed wall swirling burners. Single burner was numerically calculation in advance for the sake of obtaining more realistic inlet boundary setting in the furnace simulation.In order to improve the calculation accuracy by means of undifferentiated connection of boundary condition between burner outlet and furnace inlet with actual spatial distribution of air and pulverized coal, user-defined functions （UDF） was compiled. Compared with past models, computing control domain was extended to whole flow and heat transfer region including boiler level gas flue and tail shaft flue. The results show that O2 concentration reaches wave crest at each centre cross-section of pulverized coal burner layers under baseline condition. Hence, NO concentration increases sharply when flue gas flows through each layer of pulverized coal burners.While the centre cross-sections of pulverized coal burner layers are at lower level in an O2 concentration cycle of fluctuation and adjacent CO concentration peaks with the combination of both annular reverse flow zone and center reflux zone under reconstructive condition, so NO concentration of flue gas in those regions decreases dramatically. Furthermore, this study shows that reasonable low NOx combustion technological transformation scheme exerts no adverse influence on surfaces heat transfer.