湿煤颗粒聚团碰撞解聚的离散元模拟研究

采用离散元法中的粘结模型模拟湿颗粒聚团中液桥的粘结行为,基于离散元软件EDEM及其二次开发构建了等径小颗粒粘结而成的湿煤聚团模型,对于聚团与柔性筛板的碰撞行为进行模拟,研究了碰撞物理过程中聚团内部各部分粘结破碎的规律,分析了碰撞速度,筛板倾斜角度和聚团的旋转速度对于聚团解聚程度的影响,结果表明粘结的破碎区域首先发生在聚团与筛面的接触区,随后由下而上,由中心向四周扩散。碰撞后聚团的解聚程度随着碰撞速度的增大而增大,随着筛板倾斜角度的增大而减小,增大颗粒的旋转速度,有利于聚团的解聚。     

硬脂酸钠改性碳酸钙在水中聚团及机理研究

为了解有机改性对碳酸钙颗粒在水介质中聚团的影响及其机理,进而为调控其聚团行为创造前提,以硬脂酸钠改性碳酸钙为对象,从改性影响碳酸钙表面自由能、影响颗粒聚团的热力学趋势和影响颗粒间相互作用能方面对改性碳酸钙颗粒在水介质中的聚团机理进行了研究。结果表明,碳酸钙经硬脂酸钠改性,导致碳酸钙颗粒聚团前后的能量变化由5.62 m J/m2增大至71.98 m J/m2,说明改性使碳酸钙颗粒在水介质中聚团趋势增大;另外,水介质中,改性碳酸钙作用能在颗粒间距大于6 nm范围为排斥性质,在约8 nm处出现能垒,在颗粒间距小于5 nm范围因疏水作用能为主导而呈强烈吸引性质。推断改性碳酸钙颗粒在外部能量作用下越过能垒,再通过疏水相互作用聚集是聚团的内在机制。     

油酸钠作用下磁铁矿与硫化矿物间异相聚团研究

为了采用聚团-磁选的方式回收微细粒级硫化矿物, 研究了油酸钠作用下, 微细粒硫化矿物与磁铁矿之间的异相聚团机理。结果表明, 静电力和疏水力是硫化矿物与磁铁矿颗粒间形成聚团的主要作用力。pH=4.0时, 2种矿物动电位均小于20 mV, 且油酸钠在两种矿物颗粒表面吸附量最大, 矿物颗粒间易发生异相聚团, 人工混合矿聚团-磁选回收率达到最大, 为87%; pH>7.0时, 2种矿物动电位均大于60 mV, 由于磁铁矿表面油酸钠吸附量大幅降低, 疏水力减小, 导致聚团效果变差, 硫化矿回收率显著降低。     

微细粒弱磁性矿物极弱磁场复合高分子聚团研究

高分子絮凝一直被认为是微细粒溺磁性矿物选择性聚团的有效方法之一。本研究在高分子絮凝过程中引入有少量磁种参与的极弱磁场磁（种）聚团机制,即极弱磁场复合高分子聚团,明显强化了高分子絮凝作用,在保持良好选择性的同时增强了聚团能力。通过较为深入的显微照相与表面物理化学研究,本文还将介绍这种复合聚团的粒间作用方式模型和能量模型,并揭示复合聚团机理。     

细粒白云石疏水聚团的原位研究

采用聚焦光束反射测量仪和颗粒录影显微镜原位观测了-30 μm细粒白云石在脂肪酸类药剂GJBW以及煤油诱导下的疏水聚团尺寸和形貌,考察了GJBW浓度、煤油用量、油滴粒度、pH值和搅拌速度的影响。结果表明,GJBW诱导形成了疏松的支链结构聚团,微米级油滴能显著增大聚团尺寸和强度,形成较紧密的球形结构聚团。搅拌速度较高时聚团有所破坏,但当搅拌速度降低时,聚团可以重构。原位表征能更准确地揭示细颗粒的疏水聚团过程。     

微细粒辉钼矿疏水聚团及聚团浮选研究

为了解决微细粒辉钼矿难以通过传统浮选回收的难题,以煤油为添加剂,以聚团粒度与规则度为表征手段,探讨微细粒辉钼矿疏水聚团过程中聚团的形成、破坏和重组形为,并在此基础上研究了聚团对微细粒辉钼矿浮选效果的影响。结果表明：聚团的形成与搅拌速度和煤油用量密切相关;搅拌速度越高,聚团形成越快;煤油用量可以显着提高聚团强度,以承受高应力剪切,煤油用量越高,使得聚团破碎和重组所需要的搅拌速度越大,时间越长;聚团规则度受搅拌速度和煤油用量影响非常明显,搅拌速度越大,煤油用量越大,聚团变得越规则。与常规浮选相比,聚团浮选使得微细粒辉钼矿的上浮率显著提高,聚团浮选效果与疏水聚团过程中搅拌强度紧密相关,搅拌速度越高,达到最大上浮率所需时间越短,添加煤油能够显著提高辉钼矿上浮率。     

微细粒黑钨矿复合聚团理论研究

对黑钨矿与磁铁矿的复合聚团进行了扫描电镜研究,建立了复合聚团模型,推导了黑钨矿与磁铁矿粒间的磁作用能计算公式．计算结果表明,在颗粒间距为２５～１００ｎｍ以至更远的距离内,黑钨矿与磁铁矿颗粒之间存在着吸引势能,可相互吸引形成复合聚团;并从理论上较好地解释了黑钨矿与磁铁矿形成复合聚团的内在依据及复合聚团具有较大致密度和较高稳定性的原因．     

动能输入对高泥化煤泥水疏水聚团的影响

通过对高泥化煤泥水中微细粒进行表面接触角测定、Zeta电位测试、聚团形态观测及疏水聚团沉降试验,考察了动能输入对十八烷基三甲基氯化铵(1831)作用下微细煤泥颗粒疏水聚团的影响规律,并通过扩展的DLVO理论对1831作用前后煤泥水中微细粒间作用势能进行了计算,分析了动能输入条件下高泥化煤泥水疏水聚团的作用机理。结果表明:动能输入有利于促进1831改善煤泥颗粒表面疏水性,增强1831降低颗粒表面电负性的效果;合理的动能输入能够促进煤泥颗粒形成结构紧密的疏水聚团,提高煤泥水疏水聚团沉降效率。势能计算结果进一步证实合理的动能输入是1831作用下煤泥颗粒疏水聚团的必要条件;同时还表明煤泥颗粒在1831作用下形成疏水聚团的主要原因是"吸附电中和"和疏水作用,其中以疏水作用为主导。     

浮选系统中颗粒与气泡的碰撞行为研究

浮选设备中气泡与颗粒的碰撞是一个复杂的力学过程,本文设计了一套电磁弹射装置,将颗粒以可控的速度和角度射向水中的静止气泡,用以简化模拟真实的浮选现象。高速相机被用来监测这一碰撞过程,通过对图像进行分析,提取了颗粒的运动参数以及气泡的变形信息,研究了颗粒与气泡的作用时间与液膜排液规律,并推导了一个数学模型来预测碰撞现象的时间尺度并提出了黏附判据。     

浮选系统中粗颗粒与气泡的碰撞行为研究

浮选设备中气泡与颗粒的碰撞是一个复杂的力学过程,本文设计了一套电磁发射装置,将颗粒以可控的速度和角度射向水中的静止气泡,用以简化模拟真实的浮选现象。高速相机被用来监测这一碰撞过程,然后对图像进行分析,提取了颗粒的运动参数以及气泡的变形信息,研究了颗粒与气泡的作用时间与液膜排液规律,并推导了一个数学模型来预测碰撞现象的时间尺度并提出了黏附判据。     

基于PFC 2D高梯度磁场下煤粉干式磁选行为模拟

为了清晰认识煤粉磁选行为的特性,选取矩形磁钢-锥形聚磁介质闭合磁系提供高梯度磁场环境,建立了煤粉干式磁选过程磁性颗粒动力学模型。基于二维离散元软件PFC 2D,研究了干式磁分离过程磁性颗粒运动行为,考察了磁场强度、极距、比磁化率、锥角对颗粒运动轨迹中位移、速度、平均不平衡力的影响。结果表明：磁场强度、比磁化率越大,颗粒在磁场中受力越大,位移、速度变化越明显,有益于颗粒的磁力捕集;保持颗粒距锥尖相对距离l/2,极距越小,位移、速度变化趋势越大,越有利于磁性颗粒的吸附、系统的稳定;锥角为π3时,颗粒所受磁场力最大,系统易达到平衡状态;锥角对系统影响最弱,比磁化率较极距、磁场强度对系统影响大。     

A preliminary numerical investigation of agglomeration in a rotary drum

In this paper, the discrete element method (DEM) is employed to analyse the wet granulation process. It is essentially a computer simulation of various types of interactions of particles in a rotating drum that eventually results in tracking of trajectories of each particle and particle agglomerates. Non-linear spring-dashpot type contact models are used to monitor particle–particle and particle–wall interactions. The contact between the particles in the presence of a binder is modelled by the well-known JKR theory. To establish the potential of this numerical approach, a 10-cm rotating drum is simulated with a polydispersed system of particles of top size 1 mm. A scraper is suitably located within the drum to restrict the motion of the adhered particles along the mill shell. A spray zone is located within the drum such that the particles receive the binder dosage only within this spray zone. A drying time is also specified beyond which the particles no longer adhere together. Implementation of these ideas within the computer program makes the simulation more realistic, which in turn allows prediction of the steady-state size distribution of the agglomerates.     

铅锌尾矿在旋流器超重力环境内分离特性研究

通过对颗粒分离理论、铅锌尾矿分选处理工艺等进行分析,提出适用于铅锌尾矿分选的反向流化结构旋流器,利用锥面反向流化作用,快速分离具有密度差异的铅锌尾矿。结果表明,轴向压力值在不同径向截面处对应的值不同,整体上随轴向距离的增大而降低,且在圆锥段获得最大压力值;轴向速度分布呈对称分布,不同轴向截面处的轴向速度增减趋势有区别,颗粒分布主要集中在锥段;随着反向流化速度的增加,PbO矿粒从主要集中分布于旋流器器壁逐渐扩散至整个旋流器流场范围内,大密度PbO颗粒在器壁富集量先增加后降低;当反向流化速度为0.01m/s、进料速度为4m/s时,PbO颗粒达到最大回收率86.7%和富集比22.5,铅锌尾矿颗粒间的分离性能最佳。该研究成果为国内外铅锌尾矿的回收利用提供依据与借鉴。     

A preliminary investigation into magnetic separation process using CFD

The performance of magnetic separation units relies on the interaction between magnetic, hydrodynamic, gravitational, and inter particle forces. These forces are controlled by process as well as design parameters. In order to get a better understanding of the separation process we have developed a mathematical model using a computational fluid dynamics framework to follow the separation behavior of particles as in a wet high intensity magnetic separator. A three-dimensional, Eulerian-Eulerian model has been developed to predict the flow profile, as well as the concentration profile of solid particles between two parallel plates. The Navier-Stokes equations are used to predict the flow profile for the liquid phase. The model equations have been solved using the finite volume solver available in the commercial computational fluid dynamics (CFD) software, Fluent, to estimate the volume fraction of magnetic particles captured by the plates. Simulation results show that most of the magnetic particles are trapped on the magnetic plate which has also been observed experimentally.     

Applying discrete element modelling to vertical and horizontal shaft impact crushers

The PFC3D (particle flow code) that models the movement and interaction of particles by the DEM techniques was employed to simulate the particle movement and to calculate the velocity and energy distribution of collision in two types of impact crusher: the Canica vertical shaft crusher and the BJD horizontal shaft swing hammer mill. The distribution of collision energies was then converted into a product size distribution for a particular ore type using JKMRC impact breakage test data. Experimental data of the Canica VSI crusher treating quarry and the BJD hammer mill treating coal were used to verify the DEM simulation results.Upon the DEM procedures being validated, a detailed simulation study was conducted to investigate the effects of the machine design and operational conditions on velocity and energy distributions of collision inside the milling chamber and on the particle breakage behaviour.     

Capture of impacting particles on a confined gas–liquid interface

Film flotation is highly dependent upon how well wanted and unwanted particles are separated at the gas–liquid free surface. Single particle experiments and modelling analysis can be undertaken to determine a critical impact velocity at which the optimum separation is likely to occur. However, in commercial film flotation systems the higher loading density of the free surface can result in interactions that change the critical impact velocity. To investigate this influence, film flotation experiments have been undertaken with 4, 5 and 6 mm diameter spherical polypropylene particles with water, sucrose and surfactant (CTAB) solutions contained within vessels of varying dimensions and wettability (static contact angle). Experimentally it was observed that for a given particle diameter the critical impact velocity was found to decrease with decreasing vessel diameter, especially when the particle-to-vessel diameter ratio increased beyond about 0.2. Conversely, the critical impact velocity was found to be relatively independent of the liquid depth; but did decrease with decreasing static contact angle in the region where the vessel wall had an influence. The experimental system was also modelled using the Young–Laplace equation using both static and advancing contact angle measurements for both the particle and vessel surfaces. The model predictions were generally in good agreement with the experimental observations, including showing an increase in particle penetration depth with increasing vessel diameter and meniscus profiles, both at the particle impact point and the wall of the vessel. The predictions were improved when the advancing contact angle was used, especially for the smaller diameter vessels where there was more liquid motion. Finally, a model to determine the critical (minimum) diameter of vessel required so that the cavity profile generated by the impacting particle is unlikely to be influenced by the vessel walls is presented.     

粒度对方解石冲击粉碎影响研究

JK标准落重试验的样品粒度范围为-63.0+13.2mm。为了研究粒度尺寸对颗粒抗冲击粉碎能力的影响,以天然方解石为研究对象,将矿石粒度范围拓展到-13.2+4.75mm。通过JK落重试验方法分别测定-63.0+13.2mm和-13.2+4.75mm两个粒级范围内矿石抗冲击粉碎特性参数,以此来分析研究不同试验条件下颗粒抗冲击粉碎能力的变化。试验结果表明,方解石物料的冲击粉碎存在较明显的粒度效应,且随着粒度的减小,颗粒抵抗冲击粉碎的能力增大。这为运用JKSimMet软件中的变速率模型进行模拟时,粒度效应对模拟结果的影响提供了理论支持。     

The effect of microhydrodynamics on bubble-particle collision interaction

Interactions between particles and bubbles are influenced by hydrodynamic forces of the aqueous medium in which the flotation process takes place. This paper investigates the effect of liquid hydrodynamic forces working at short inter-surface separation distance, referred to as microhydrodynamic forces, on the bubble-particle collision (encounter) interaction. The full equation of particle motion around an air bubble with either a mobile surface (e.g., the potential flow) or an immobile surface (e.g., the Stokes flow) has been solved and analyzed numerically. The effect of particle density, size and film thickness (i.e., inter-surface separation distance) on the bubble-particle collision angle and efficiency has been examined. The new results were compared against the results obtained under the condition that microhydrodynamic effect has been ignored (the conventional theory). The effect of microhydrodynamics on the collision angle and efficiency has been found significant. Generally, the microhydrodynamic effect decreases the collision efficiency due to retarding the particle approach to the rising bubble surface. There also exists a critical set of particle size and density, where the collision angle is minimal, for both the mobile and immobile bubble surfaces. Away from the critical particle size and density the collision angle increases to 90°.     

流化床选择性排渣的实验研究

根据流态化分选和终端速度差异分选原理,提出了一种采用不均等配风的选择性排渣的方法,搭建了流化床选择性排渣的可视化冷态实验台,研究了压力分布、流化风速、床料粒径分布对排渣分选效果影响。结果表明:不均等配风时,由床内压力分布特点可知床内颗粒存在循环流动特点;当高风速与低风速的比值越大,其对颗粒度分选效果越好;在相同的高风速与低风速比之下,随床内细颗粒比例的增加,由于粗细颗粒的混合程度增加,分选效果会变差;不均等配风的排渣方式能够实现对细颗粒的分选。