立式同轴离心磨机磨矿理论与试验研究

【作者】 胡天喜；

【导师】 文书明；

【作者基本信息】 昆明理工大学 ， 矿物加工工程， 2008， 博士

【摘要】 磨矿是选矿、冶金、化工及建材等行业的重要作业,其设备磨机也是生产中的主要设备。磨矿作业对整个国民经济影响很大,目前我国每年有100亿吨以上矿料需要粉碎,全国每年的发电量有5%以上消耗于磨矿,全国每年有100万吨以上钢材消耗于磨矿,因此,磨矿作业的增效降耗具有十分重要的意义。基于这个目的,昆明理工大学开发研制了一种新型的粉磨设备—立式同轴离心磨机。立式同轴离心磨机是一种离心式磨机,主要由筒体、机架、传动机构、给料机构、导向机构和排料机构组成,其工作原理可以简单描述为：物料在高速旋转的筒体带动下作离心运动,并在筒体内导向板的作用下改变运动轨迹,发生冲击、挤压和磨剥作用而被磨碎。本论文以新型的立式同轴离心磨机为研究对象,采用理论分析、数值模拟和试验相结合的方法对立式同轴离心磨机的磨矿理论进行了一些基础性的研究。研究内容主要涉及以下六个方面：本文对立式同轴离心磨机的结构特征和工作原理进行了详细分析,研究认为,立式同轴离心磨机具有以下几个方面的主要优点：磨机单位容积生产能力高,磨机不需要使用衬板,磨机可用于介质磨和自磨,磨机可用于粗磨和超细磨以及产品粒度均匀。磨机内物料主要受来自研磨介质和自身的冲击力、挤压力和剪切力的联合作用而粉碎。筒体内物料所受的离心力的计算式为：C=(?),通过计算发现,在设计的转速范围内,磨机旋转产生的离心加速度为重力加速度的15-45倍。筒体内的两相流的速度和压力分布基本符合强制涡的速度和压力分布规律,即在磨机筒体的同一横截面上,离中心越远的地方速度和压力越大,离中心越近的地方速度和压力则越小。立式同轴离心磨机内流场的受力和运动状态非常复杂。对磨机内介质的受力状况和运动状态进行了分析,推导出了钢球冲击运动过程的轨迹方程为：y-y0=(?)(χ0-χ)。从运动轨迹方程可以看出,冲击运动轨迹仅与导向板在磨机筒体内的位置有关,而与其它因素无关。推导出了钢球冲击到筒壁瞬间的合速度v求解公式为：v=(?),磨机中钢球冲击到筒体上的冲击速度v与磨机转速n及筒体半径R成正比例关系。通过调节磨机筒体内导向板的角度α就可以调节法向分速度vn和切向分速度v,的大小,从而调节冲击力和剪切力的大小推导出了钢球对物料的冲击力F求解公式为：F=(?),磨机钢球介质对物料所产生的冲击力F与钢球质量m、磨机转速n和筒体半径R都呈线性增加的关系,与导向板角度α的余弦值成正比例关系。推导出了钢球在单位时间内的冲击频率K求解公式为：钢球在单位时间内的冲击频率K与磨机转速n及导向板的位置参数α、β有关,而与筒体半径R无关,提高磨机转速能增加钢球在单位时间内对物料的冲击频率,从而提高粉磨效率。利用CFD软件对立式同轴离心磨机流场进行数值模拟,可以看出流场的速度梯度变化,即离筒体中心越远的流体速度越大,离筒体中心越近的流体速度则越小。压强变化较大的区域位于导向板附近的区域,在导向板的前后两端压强较大,是主要的研磨区域；在导向板与筒体之间的夹层压强较小,研磨效果较差。进一步研究发现,磨机粉磨的主要区域是远离筒体中心靠近筒壁的环形带,其中导向板前后两端附近区域为冲击粉碎的主要区域,其它区域为压力与磨剥粉碎的主要区域。磨机的转速、给矿量和浓度是磨矿过程的主要操作参数,对磨矿结果有直接影响。用硫铁矿作原料进行立式同轴离心磨机自磨参数试验研究,结果表明：磨机转速和给矿量对磨矿效果有很大的影响。在相同的磨机转速下,产品的平均粒度随着给矿量的减少而减小,但随着给矿量逐步减少,平均粒度的减小幅度有所变缓。随着磨机转速的提高,磨机的处理能力迅速提高,同时产品平均粒度迅速减小,证实了提高磨机转速能大大促进磨矿效率的提高。磨矿浓度对磨矿效果有一定的影响。当磨矿浓度为55%时,产品粒度较大,磨矿效果相对较差,而磨矿浓度在60%-70%之间的产品粒度则比较接近,当磨矿浓度为70%时,矿浆的粘度较大,会造成排料不畅。因此,将磨矿浓度选择为60%-65%是比较合适的。在进行与普通球磨机磨矿对比试验后发现,立式同轴离心磨机每吨矿耗电与球磨机基本相当,但立式同轴离心磨机的单位容积生产率为球磨机的4.57倍,说明这种新型磨机在增加磨矿效率方面具有较大的优势。用钒钛磁铁矿尾矿作原料进行介质磨矿的参数试验研究,结果表明：当给矿量不变时,磨矿产品的细度随着转速的提高而减小,转速越高,越有利于细磨。当磨机转速一定时,磨矿产品的细度随着给矿量的增加而增大,且变化梯度逐步增大。磨矿动力学反映了磨矿的快慢程度。本文通过在不同的磨机转速下对立式同轴离心磨机的磨矿动力学进行试验研究,研究发现：通过推导可以得到磨矿产品粒度分布的磨矿动力学方程通式：Ri(t)=Ri(0)exp[-k(d)tn(d)],由该磨矿动力学方程通式,通过曲线拟合求参数的方法,可以得出不同磨机转速时的立式同轴离心磨机的磨矿动力学方程,从而可以求出任意时刻、任一粒级的磨矿产品分布率。当磨机转速相同时,磨矿速率随磨矿时间的增加而减小,并且磨矿速率的减小在较短的时间内更加明显,时间越长,减小的趋势越缓慢,尤其是当转速较高的时候,物料将在很短的时间内被磨得很细。当磨矿时间相同时,磨矿速率随磨机转速的提高而迅速增大,转速越高,这种趋势越明显。更多还原

【Abstract】 Grinding is an important operation in the industries of mineral processing, metallurgy, chemical engineering and building materials and so on, which greatly affects the entire national economy, because over 10 billion tons of ores need to be comminuted annually in China, over 5 percent of eletricity power of the whole country and 1 million tons of steel are consumed in the grinding stage annually. Therefore, improving efficiency and reducing consumption in the grinding operation is of great significance. For this purpose, Kunming University of Science and Technology developed a new type of grinding equipment-Vertical Coaxial Centrifugal Mill (VCCM). VCCM is a kind of centrifugal mill, and is mainly made up of drum, frame, driving device, feed device, oriented device and discharge device. The operating principle of VCCM can describe as:the materiel makes the centrifugal movement drived by the high speed rotation drum, then its movement track is changed by the oriented plate in the drum, thus the materiel is ground by the combined action of impact, extrusion and shear.Some basic researches on the grinding theory of the VCCM are made in this Ph.D dissertation by the methods such as theoretical analysis, numerical simulation and laboratory experiment. The main contents are as follows:Detailed analysis of structural characteristics and operating principle of VCCM shows that VCCM has several main advantages:high production capacity of unit volume, almost no liner consumption, extensive using in either conventional grinding or autogenous grinding, either for coarse grinding or ultrafine grinding and uniform size of product, etc.. In VCCM, Material is comminuted by the joint role of impact force, extrusion force and shear stress from the grinding media and other materials. The calculation formula of centrifugal force of the materiel in the drum is C(?). The centrifugal acceleration made by drum rotation are 15-45 times than the gravity acceleration when the mill speed is inside the pale of design. The speed and pressure distributions of two-phase flow in the drum almost accord with the distribution law of speed and pressure of forced eddy, namely, in the same cross section of the drum, the farther away from the center, the larger the speed and pressure are, vice versa.The state of the force and movement of the flowfield in VCCM is very complex. After analyzing the state of the force and movement of the medium in VCCM, the trajectory equation of the impact movement of the steel ball is concluded:y-y0=(?)(x0-x). From the above equation, it can be founded that the impact trajectory is.only related to the position of the oriented plate in the mill drum. The formula used to calculate the whole speed of impact movement is obtained as:v=(?) The speed v, which is the steel ball impacting to the drum wall, is in a direct ratio with the rotating speed n and the drum radius R. The normal speed vn and the tangential speed v, can be regulated by regulating the angle a of the oriented plate in the mill, consequently, the impact stress and shear stress can be regulated. The formula used to calculate the impact stress F of the steel ball to the materials is concluded: F=(?). The impact stress F of the steel ball to the materials has the linear increasing relationship with the mass of steel ball m, the drum speed n and its radius R, and the cosine value of angle a of the oriented plate. The formula used to calculate the impact frequency K of steel ball in unit time is also concluded K is associated with the speed n and the position parameters a andβof the oriented plate, and is in no relationship with radius R. As a result, increasing the drum speed can increase of the impact frequency of steel ball to the materials in unit time, thereby the grinding efficiency is improved.The numerical simulation of the flowfield in VCCM by the software CFD shows that the changing principle of velocity gradient of the flowfield, namely, the farther the fluid is from the the center of the drum, the higher speed it has. The region where the pressure changes largely locates in the vicinity of the oriented plate, especially in the two ends of the oriented plate, which is the main grinding region. The pressure, however, is small in the region between the plate and drum, thus the grinding efficiency is low. Further study shows that the main grinding region is closed, to the liner of drum, in which the vicinity region at both ends of the oriented plate is the main region of impact comminution and other region is the main region of abrasion comminution.Mill speed, throughput and grinding concentration are the main operating parameters of grinding process, which have a direct effect on the results. Autogenous grinding parameter tests of VCCM with pyrite ore show that mill speed and throughput have great influence on the grinding performance. When the mill speed is constant, the average size of the production is reduced with the decreasing of throughput, but with gradual reducing of the throughput, the decreasing degree of the average size becomes gentle. With increasing of the mill speed, the capacity rises rapidly, while the average size of products quickly decreases, which confirms that increasing of the mill speed can greatly improve the grinding efficiency. Grinding concentration has a certain impact on the grinding performance. The grinding performance is relatively poor due to the coarse products when the grinding concentration is 55%. However, it changes gently when the grinding concentration is improved between 60% and 70%. When the grinding concentration is 70%, the pulp viscosity is too larger to discharge smoothly. Therefore, the appropriate grinding concentration is from 60% to 65%. The results of comparative tests show that the eletricity power consumptions per ton ore of the VCCM and the conventional ball mill (CBM) are almost same, but the production capacities of unit cubage of VCCM are 4.57 times than CBM, hence the VCCM will play an important role in increasing the grinding efficiency.The conventional grinding parameter tests are conducted using Vanadium-titanium magnetite tailings, and the results obtained show that the fineness of product decreases with the increaing of mill speed when the throughput is invariable, and the higher the speed, the higher efficiency of fine grinding obtain. When the mill speed is constant, the fineness of product increases with the increasing of throughput, and the changing gradient gradually increases.Grinding kinetics can reflect the grinding velocity. Experimental investigations on grinding kinetics of VCCM under the different mill speed reveal that the general grinding kinetics equation of product size distribution can be demonstrated as:Ri(t)= Ri(0)exp[-k(d)tn(d)]. The grinding kinetics equation of VCCM under different mill speed can also be demonstrated from the general equation through the curve fit method, thus the distribution rate of grinding products in any time and any size can be calculated. When the mill speed is constant, the grinding velocity decreases with the increasing of grinding time, and the decreasing trend is obvious in a short period of time. The longer the time, the gentler the decreasing trend, especially under a high mill speed, the materials will be ground to very fine in a very short period of time. When the grinding time is constant, the grinding velocity increases rapidly with increasing of the mill speed, and the higher the mill speed, the more obvious the trend is.更多还原