中速球式磨机流场分析及结构优化

发布时间：2019-05-30 00:22

【摘要】：中速球式磨机利用碾磨件相互挤压作用来磨制煤粉,集研磨、烘干、传输、分选等工序于一体,其流程简单、粉磨效率高。现已经广泛用于钢铁、火电、水泥以及其它工业领域。但在实际生产中出现了许多问题,如压损很大、产量不稳定、煤粉粒度变粗、过粉现象严重等。掌握磨腔内流场分布规律和粉磨机理,为腔内结构优化提供理论指导,并对提高粉磨效率和降低能耗具有重要的意义。本文以江苏大\丶派杓蒲蟹⒌腅M型磨机为研究对象,依据CFD技术和工程流体动力学理论,采用离散相模型(DPM),湍流模型Realizable k-ε及SIMPLE算法对磨腔湍流运动进行数值模拟。分析研究磨腔速度场、压力场、温度场、颗粒轨迹和流线等特性。先对气相流场进行数值模拟,待其收敛后,再加入离散颗粒相,颗粒运动采用随机轨道模型,对气固两相流采用单向耦合的方法,最后根据模拟结果对风环、风室及灰斗进行结构优化。综合分析结果表明:中速球式磨机腔内流场具有明显的三维旋转流动特性,运动主要由突扩运动、射流、回流、和绕流运动耦合而成。当气体经过风环时速度很大,形成射流,在灰斗与磨盘间形成涡流区。在风环处高温热风与煤粉颗粒开始耦合,并伴随着大量的能量交换,上升的气流夹带煤粉颗粒向上运动,较大颗粒落回磨盘,较小的颗粒随气流进入分离器中再次分离,不合格的煤粉通过灰斗落回磨盘。受磨盘和磨球旋转的影响,气流沿着磨球做绕流运动,磨球周围形成许多小涡流。磨机在运行过程中能耗大,压降很大。通过增加入磨风量来研究气流的变化规律,结果表明随着气流增加,风环处风速增加明显,但磨腔内压损也明显增大。根据磨腔流场仿真结果并结合工程中出现的问题,本文对中速磨机的结构优化主要侧重于风环、风室以及灰斗的改进,并对改进模型进行流场分析。通过封堵部分风环后,风环出口处的流量增加,但压损也明显增加。针对风室结构,在风室底部入口安装导流板。分析表明,各风环处的流通量分布趋于均匀化,有利于气粉耦合和传递。对灰斗的锥体进行延长,数值模拟结果表明流场湍流脉动现象较弱,纵向涡流明显减小。通过分析可以看出,结构优化后的中速磨机湍动现象、粉体输运效率均有所改善,磨机内压力损失有不同程度的下降。
[Abstract]:The medium speed ball mill uses the mutual extrusion of grinding parts to grind pulverized coal, which integrates grinding, drying, transmission, separation and other working procedures. The process is simple and the grinding efficiency is high. It has been widely used in iron and steel, thermal power, cement and other industrial fields. However, there are many problems in practical production, such as large pressure loss, unstable output, thicker particle size of pulverized coal, serious overpowder and so on. Mastering the distribution law and grinding mechanism of flow field in grinding cavity provides theoretical guidance for the optimization of intracavity structure, and is of great significance to improve grinding efficiency and reduce energy consumption. This paper is based on Jiangsu University. According to CFD technique and engineering fluid dynamics theory, the discrete phase model (DPM), turbulence model Realizable k-蔚 and SIMPLE algorithm are used to simulate the turbulent motion of the grinding cavity. The velocity field, pressure field, temperature field, particle trajectory and streamline of the grinding cavity are analyzed and studied. The numerical simulation of the gas phase flow field is carried out, and then the discrete particle phase is added after it converges. The stochastic orbit model is used for the particle motion, and the unidirectional coupling method is used for the gas-solid two-phase flow. Finally, according to the simulation results, the wind ring is used. The structure of air chamber and ash hopper is optimized. The comprehensive analysis results show that the flow field in the cavity of the medium speed ball mill has obvious three-dimensional rotating flow characteristics, and the motion is mainly composed of sudden expansion motion, jet, reflux, and flow around the motion. When the gas passes through the wind ring, the velocity is very large, forming a jet and forming a vortex zone between the ash bucket and the grinding disk. At the air ring, the high temperature hot air and pulverized coal particles begin to be coupled, and with a large amount of energy exchange, the rising air flow carries the pulverized coal particles upward, the larger particles fall back to the grinding disk, and the smaller particles enter the separator again with the air flow. The unqualified pulverized coal falls back into the grinding disk through the ash bucket. Under the influence of the rotation of the grinding disk and the grinding ball, the air flow moves around the grinding ball, and many small swirls are formed around the grinding ball. In the operation process of the mill, the energy consumption is large and the pressure drop is very large. The variation of air flow is studied by increasing the air volume. The results show that with the increase of air flow, the wind speed at the wind ring increases obviously, but the pressure loss in the grinding cavity also increases obviously. According to the simulation results of grinding cavity flow field and combined with the problems in engineering, the structure optimization of medium speed mill mainly focuses on the improvement of air ring, air chamber and ash bucket, and the flow field analysis of the improved model is carried out. After blocking part of the wind ring, the flow rate at the outlet of the wind ring increases, but the pressure loss also increases obviously. According to the structure of the air chamber, the guide plate is installed at the bottom entrance of the air chamber. The analysis shows that the flux distribution at each wind ring tends to be uniform, which is beneficial to the coupling and transmission of gas and powder. The cone of the ash bucket is prolonged. The numerical simulation results show that the turbulent pulsation of the flow field is weak and the longitudinal vortex is obviously reduced. Through the analysis, it can be seen that the turbulent phenomenon of medium speed mill after structure optimization, the powder transport efficiency has been improved, and the pressure loss in the mill has decreased to varying degrees.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TH69

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