基于CFD-DPM模拟的中速磨煤机风粉分配特性

Investigation on air-coal distribution characteristics of medium-speed coal mill based on CFD-DPM simulation

中速磨煤机是燃煤电厂制粉系统的重要部件,承担原煤的研磨、干燥、运输等,磨煤机出粉管的风粉分配性能直接关系燃煤电厂的安全稳定高效运行。基于CFD-DPM方法,在全结构、足尺度、考虑实际运行中转动部件条件下,开展磨煤机内部气固两相流动研究。在网格无关性验证和模型验证的基础上,研究中速磨煤机粉管出口风粉分配特性,揭示煤粉分配不均匀的成因,进而提出在分离器折向门处于同一高度的筒壁上布置导流块体结构,改善粉管中粉量分配均匀性。结果表明,风环区域对磨煤机阻力贡献最大,分离器区域和粉管区域阻力较为接近,模拟条件下二者之和占磨煤机阻力的份额为28.3%~29.4%;各粉管之间风速差异很小,但粉量差异显著,其原因是风粉混合物受到磨辊的阻碍作用,被分为3股,从而进入分离器内锥体的风粉混合物呈现不均匀状态;在分离器折向门处于同一高度的筒壁上布置导流块体结构,可使各粉管风粉分配均匀性得到显著改善。

The medium-speed coal mill,which undertakes the task of grinding,drying and transportation of raw coal,etc.,is an important part of the coal pulverizing system in coal-fired power plants.The performance of air-coal distribution in the outlet pipes of the coal mill is directly related to the safe,stable and high-efficiency operation of the coal-fired power plants.Based on the CFD-DPM method,the gassolid two-phase flow inside the coal mill was investigated under the conditions of full structure,full scale with the consideration of the rotational parts in actual operation.On the basis of grid-independent verification and model validation,the air-coal distribution characteristics in the medium-speed coal mill outlet pipes were investigated to reveal the causes of the uneven distribution of pulverized coal.Furthermore,the flow-guide block structure was proposed to set on the cylindrical wall of the coal mill at the height same as that of the separator inlet,in order to improve the uniformity of the air-coal distribution in the outlet pipes.The results show that the air ring region contributes the most to the mill resistance,while the resistances of the separator and the outlet pipe regions are close to each other,and the sum of the two accounts for 28.3%~29.4%of the mill resistance under the simulation conditions.The difference in the air velocity of the outlet pipes is very small,whereas the mass of pulverized coal differs greatly.The latter is due to the fact that the air-coal mixture is divided into three streams resulting from the hindering effect of the grinding rollers,so that the distribution of the air-coal mixture entering the separator cone is uneven.By setting the flow-guide block structure on the cylindrical wall of the coal mill,a significant improvement on the uniformity of the pulverized coal in the outlet pipes can be achieved.