School of Energy Science and Engineering, Harbin Institute of Technology, 92, West Dazhi Street, Harbin, 150001, People's Republic of China.
Environ Sci Pollut Res Int. 2020 May;27(14):16900-16915. doi: 10.1007/s11356-020-08275-5. Epub 2020 Mar 6.
Numerical simulations were conducted to study the effects of the pulverized-coal bias distribution in the primary air on the coal combustion and NO generation characteristics of a 600-MW down-fired boiler with multiple-injection and multiple-staging combustion technology. The total pulverized-coal in the primary air was kept constant, and the ratio of the pulverized-coal mass flux in the fuel-rich coal/air flow to the total pulverized-coal mass flux (RPR) was set as 60%, 70%, 80%, and 90%. By changing the RPR, the excess air coefficient of the fuel-rich flow was adjusted from 0.700 to 0.467. It was found that numerical simulation results were almost in agreement with cold modeling and in situ experimental results respectively, including the flow fields in the lower furnace at the RPR of 80% and the heating processes for the fuel-rich coal/air flow at the RPR of 90%, which verified the rationality of the numerical model and the grid. The simulation results indicated that the change of RPR has little effect on the symmetry of the flow field in the furnace. With the increase of the RPR from 60 to 90%: (1) the maximum airflow declination angle near the tertiary air slot decreased from 71 to 66°, which indicates that the downward airflow penetration depth gradually decreased; (2) the ignition distance of the fuel-rich coal/air flow decreased from 1.2 to 0.9 m, and the high-temperature area in the furnace hopper decreased and the position gradually moved away from the hopper water walls; (3) the oxygen consumption rate at the initial combustion stage constantly accelerated, and the fuel NO generation rate under the fuel-rich flow nozzle increased first and then decreased; (4) the NO emissions at the furnace exit dropped from 778 to 662 mg/m at 6% O, and the carbon in the fly ash decreased from 5.87 to 5.52%. Increasing the RPR reasonably controlled the excess air coefficient of the fuel-rich flow, and realized the high-efficiency combustion in the furnace and the reduction of NO emissions simultaneously.
采用数值模拟的方法，研究了一次风煤粉偏置对采用分级燃烧技术的 600MW 四角切圆锅炉煤粉燃烧和 NO 生成特性的影响。一次风中的总煤粉量保持不变，富燃料煤粉/空气流量中的煤粉质量通量与总煤粉质量通量的比值（RPR）设定为 60%、70%、80%和 90%。通过改变 RPR，调整富燃料流的过量空气系数从 0.700 到 0.467。结果表明，数值模拟结果与冷态模化和原位实验结果基本吻合，包括 80%RPR 时下部炉膛流场和 90%RPR 时富燃料煤粉/空气流的加热过程，验证了数值模型和网格的合理性。模拟结果表明，RPR 的变化对炉膛流场的对称性影响较小。随着 RPR 从 60%增加到 90%：（1） tertiary 风箱附近的最大气流偏转角从 71 减小到 66°，这表明向下气流的穿透深度逐渐减小；（2）富燃料煤粉/空气流的点火距离从 1.2 减小到 0.9 m，炉膛料斗中的高温区减小，位置逐渐远离料斗水壁；（3）初始燃烧阶段的耗氧率不断加快，富燃料流喷嘴下的燃料 NO 生成率先增加后减少；（4）炉膛出口处的 NO 排放量从 778 减少到 662 mg/m 在 6%O 下，飞灰中的碳从 5.87 减少到 5.52%。合理增加 RPR 控制了富燃料流的过量空气系数，实现了炉膛内的高效燃烧和 NO 排放的降低。
