Energy efficient slurry holding and transport

Slurry suspension in holding tanks and transport through pipelines are essential elements in the modern mining and mineral processing industry. This paper presents methods to improve the energy efficiency of solids suspension in tanks and slurry transport through pipelines for low viscosity Newtonian slurries. Research has been conducted using laboratory experiments and analysis using established equations. It is shown that there are many similarities between these two traditionally separated research areas. It is concluded that energy per unit solids mass generally varies with solids concentration for both systems. The specific energy can be minimised by operating at a suitable solids concentration, for example in the range of 20–30% (v/v) for the slurry properties considered in this paper. It is also concluded that the specific energy generally decreases with the size of equipment, i.e. tank diameter or pipe diameter, although this effect tends to plateau at large sizes. It was found that when a slurry pipeline is used as a reactor, it generally requires more power to suspend solids per unit solids mass than a mixing tank. Great energy saving can be achieved by operating a slurry tank with baffles removed, if off-bottom solids suspension is the limiting factor. Basic equations for specific energy consumption (SEC) are included.     

A comparison of the critical impeller speed for solids suspension in a bench-scale and a pilot-scale mechanical flotation cell

This paper compares the critical impeller speed results for 6 L Denver and Wemco bench-scale flotation cells with findings from a study by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2007. Evaluation of solids suspension in a pilot-scale mechanical flotation cell: the critical impeller speed. Minerals Engineering 20, 233–240; Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621–629] conducted in a 125 L Batequip flotation cell. Understanding solids suspension has become increasingly important due to dramatic increases in flotation cell sizes. The critical impeller speed is commonly used to indicate the effectiveness of solids suspension. The minerals used in this study were apatite, quartz and hematite. The critical impeller speed was found to be strongly dependent on particle size, solids density and air flow rate, with solids concentration having a lesser influence. Liquid viscosity was found to have a negligible effect. The general Zwietering-type critical impeller speed correlation developed by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621–629] was found to be applicable to all three flotation machines. The exponents for particle size, solids concentration and liquid viscosity were equivalent for all three cells. The exponent for solids density was found to be less significant than that obtained by the previous authors, and to be consistent with values reported in the general literature for stirred tanks. Finally, a new dimensionless critical impeller speed correlation is proposed where the particle size is divided by the impeller diameter. This modified equation generally predicts the experimental measurements well, with most predictions within 10% of the experimental.     

重介质浅槽分选机流场及临界分选粒度研究

重介质浅槽分选机广泛应用于动力煤的分选,为了研究浅槽内部流场对分选效果的影响,采用FLUENT软件模拟了W26F54浅槽分选机的内部流场,计算了浅槽不同位置的临界分选粒度。研究结果表明:浅槽内部悬浮液存在涡流和折回流;水平流和上升流的流量比显著影响浅槽内部的速度场、密度场,流量比过大或过小都不利于物料分离或输送,流量比为8∶2时浅槽内速度场和密度场分布较为理想,有利于物料分选和悬浮产物的输运;浅槽不同区域的临界分选粒度不同,随浅槽高度的增加呈先减小后增大的趋势。     

前混合水射流超细粉碎煤粒的试验研究

以山西西山煤样为原料,开发了一种适合于煤炭物性的前混合水射流超细煤粉试验装置,研究了加载压力、循环碰撞次数和浓度对超细煤粉大小及分布的影响,并利用激光粒度仪对所得超细煤粉进行了粒度分析,用ξ电位实验研究了超细煤粉颗粒悬浮体系的分散性.试验表明,采用角形喷嘴淹没水射流技术,可以在循环碰撞为3~4次、加载压力为43~50 MPa的工艺条件下将料浆比为25%~35%的煤粒粉碎至d 50<22.6 μm,为采用前混合水射流方法粉碎煤炭制备高性能水煤浆燃料提供了理论基础和关键技术.     

基于粉煤覆盖技术对预防煤堆自燃的数值模拟

通过对煤碳储存环境特点的分析,利用FLUENT软件,选择太阳辐射加载模型、化学反应模型和P-1辐射3个基本模型对70 mm厚度粉煤覆盖下煤堆内的温度分布、氧气体积分数分布变化规律进行数值模拟。模拟结果表明:该模型可以有效预测煤堆自燃的倾向性,对覆盖70 cm厚度粉煤煤堆的温度分布和氧气体积分数分布模拟结果分析可以看出,粉煤覆盖可以一定程度上抑制煤堆内的低温氧化反应,防止煤堆自燃,因此粉煤覆盖是一种新型的防治煤堆自燃的方法。     

The utilization of forward osmosis for coal tailings dewatering

The feasibility of dewatering coal tailings slurry by forward osmosis (FO) membrane process was investigated in this research. A prototype cell was designed and used for the dewatering tests. A cellulosic FO membrane (Hydration Technology Innovations, LLC, Albany, OR) was used for the dewatering studies due to its high fouling resistance. Representative samples of coal tailings slurry were collected from the thickener outflow at American Coal Company (Galatia, Illinois). Characterization studies were conducted to obtain particle size distribution (PSD), total dissolved solids (TDS) and the solids content of the slurry. The impact of the slurry properties such as solids weight percent, osmotic pressure, and particle size on the dewatering rates was determined. Furthermore, the impact of slurry conditioning by the addition of flocculant and gypsum on the rate and extent of dewatering was also investigated. Dewatering to a total solids content of more than seventy weight percent from an initial solids content of approximately thirty percent was achieved in all cases. The dewatering rate and extent were found to be a function of particle size, particle shape, TDS content, and mixing. The membrane material was shown to withstand repeated use over a period of thirty trials without deterioration of performance. The results obtained from this research suggest that osmotic dewatering of coal refuse slurry is feasible.     

High concentration suspension pumping

Environmental and economic considerations require that tailings disposal systems are performed using much higher solids content than was previously deemed acceptable. These new high concentration systems have many benefits, particularly lower water consumption, smaller impoundment areas and reduced solids’ mobility. These systems require that the solids are pumped out to the deposition sites as non-Newtonian suspensions which are generically, although nearly always erroneously, called pastes. This paper will present results gathered in recent years which demonstrate that such suspensions are almost invariably stratified, especially if the suspension’s size distribution is wide, a prerequisite for co-disposal systems. It will also show that the transport pressure gradients are substantially different from those predicted from simplistic paste theory for full size plant. These findings will be supported by experimental observations using both visual, MRI and ERT tomography data and from mathematical modelling results.     

Evaluation of solids suspension in a pilot-scale mechanical flotation cell: The critical impeller speed

This paper investigates solids suspension in a pilot-scale mechanical flotation cell in terms of the critical impeller speed, N_js. Understanding solids suspension has become increasingly important in recent years due to dramatic increases in flotation cell sizes but appears to be relatively poorly researched. The critical impeller speed is commonly used to indicate the effectiveness of solids suspension in stirred tanks, but has seldom been investigated in flotation cells. In this study, critical impeller speeds were visually determined and concentration profiles were measured through sample withdrawal in a 125 l Batequip (Bateman) pilot flotation cell. Two solids size fractions (75–106 and 150–250 μm) were tested, in ungassed and gassed conditions (J_G = 0, 1 cm/s) and at various impeller speeds (300–900 rpm). The effectiveness of solids suspension was quantified in three ways; (i) the extent of off-bottom solids suspension, (ii) the extent of axial solids distribution (suspension height) and, (iii) the variability of axial solids distribution. Consistent trends were found when these effectiveness criteria were considered against relative impeller speed, in terms of percentage of critical impeller speed, N/N_js. As per definition, off-bottom solids suspension was found to be complete at or above 100% of N_js, with significant sedimentation occurring as the impeller speed dropped below 60% of N_js. Suspension heights consistently reached a level equivalent to 90% of the tank diameter at the critical impeller speed, and dropped off significantly as N/N_js dropped below 60%. The relative standard deviation of the vertical solids distribution consistently reached a value of around 30% at N_js. The paper concludes that the critical impeller speed, as per stirred tanks, is an appropriate measure for describing and benchmarking the effectiveness of solids suspension in a mechanical flotation cell. The authors speculate that, when solids suspension is considered as a precondition to flotation, flotation cells should not be operated at specific ‘impeller speeds’ but rather at specific ‘percentages of critical impeller speed’ analogous to the ‘critical speed’ used in the operation of grinding mills.     

A technique for measuring flotation bubble shell thickness and concentration

Froth structure is known to significantly affect flotation performance. However, little information is generally available on the loading of solids on bubbles in the froth. It has been noted in foam studies that the bubble shell is very viscous and distinctly separate from the inter-bubble lamellae. In froth flotation, these bubble shells contain hydrophobic solids selectively attached, while the inter-bubble lamellae contain both hydrophobic and hydrophilic solids, which are non-selectively entrained. In this technical note we introduce a measurement technique to measure directly the bubble shell thickness and solids concentration. This measurement allows the collection of particles due to attachment to bubbles and from transport in the inter-bubble lamellae to be estimated. It is found that an increase in the surfactant concentration decreases the solids concentration in the bubble shell. The average bubble shell thickness closely corresponds to the particle size, which is in agreement with previous studies.     

深海采矿中继站底部Y形管流动状态研究

针对深海采矿泵管输送试验系统中Y形管内流场复杂和矿石泄露风险等问题,采用CFD-DEM方法,对不同速度、不同体积浓度和不同粒径的矿石颗粒进行数值模拟计算,分析了Y形管内颗粒群的运动特性和流场分布规律。结果表明,Y形管内流场分布受弯管曲率和Y形管入口流量分配影响;颗粒群在弯管内贴壁流动,受到上升流作用后颗粒向上偏移;当上升流流速不足、颗粒体积浓度高及颗粒粒径较大时,会造成颗粒沿着底部管道流失,随着上升流速减小、颗粒体积浓度增大及颗粒粒径增大,颗粒通过底部管道流失不断增大;颗粒流的存在导致Y形管内低压漩涡区强度和尺度均减弱。     

煤颗粒分布对油煤浆流变特性的影响

采用神华煤和煤直接液化循环油配制成油煤浆，考察了煤的颗粒大小、颗粒分布以及浓度对煤浆流变特性的影响.试验结果表明：当浓度较低时，煤浆在比较宽的浓度范围内表现为牛顿流体；浓度较高时，表现为具有剪切稀化行为的假塑性流体.利用双峰级配理论，将粗颗粒煤粉加入细颗粒中可降低煤浆体系的黏度.但继续增大粗颗粒在煤粉中的比例，体系的黏度又会增大，而且煤浆的流变性能也发生改变.在试验条件下，粗细颗粒质量百分比为40∶60时体系具有最低的黏度，煤浆性质由同浓度的细颗粒体系的非牛顿流体转变为牛顿流体.因此，改变煤浆体系中煤的颗粒分布可在保持较高浓度时制备出具有较低黏度的油煤浆.     

水沙混合物裂隙渗流特性分析

水沙在裂隙或破碎岩石中的渗透特性具有复杂性,研究水沙裂隙渗流特性对于揭示突水溃沙机理具有重要意义。利用自制的水沙裂隙渗流试验仪器,通过改变沙粒径、浓度等因素进行水沙渗透试验,获得水沙在裂隙中流动的滞后性特征。通过水沙裂隙渗流试验,得到了岩石裂隙中水沙渗流速度-压力梯度滞环曲线,分析了滞环曲线的特征,简单解释了滞后现象的原因。得到其渗透压力梯度与渗流速度在一个循环周期内形成了一条封闭滞后曲线,根据曲线的是否有交叉和往返曲线的距离分为4种变化类型;随沙粒径和沙浓度增大,曲线由Ⅰ型向Ⅳ型转化。滞后性指标用最大滞后量G_p和滞环面积S描述,随沙粒径和浓度增大,这两者均呈增大趋势,但增幅并不同步。进一步,利用ANSYS Fluent软件进行水沙裂隙渗流场的数值模拟,获得了在不同因素影响下渗流场的变化规律。数值模拟结果表明,粗糙裂隙流场物理量随时间波动;粗糙裂隙中水沙流动受壁面约束作用,表现出流场物理量空间分布的随机性。模拟结果显示裂隙中水沙渗流场不稳定,渗流场的压力损失与沙粒径呈反向变化。裂隙横截面上水沙流体时均速度和湍动能分布受沙粒径和沙体积浓度影响很大,表现为极值点的位置偏移。此研究可以为进一步研究浅埋煤层突水提供参考。     

搅拌桨叶距槽底距离对导流筒稀土搅拌槽搅拌特性的影响分析

搅拌桨叶距槽底距离对导流筒稀土搅拌槽的搅拌特性有着至关重要的影响。为了获取桨叶底距对导流筒稀土搅拌槽搅拌特性影响的规律,以江西赣南某稀土企业容积为10m3导流筒搅拌槽数据为模型,利用Solidworks软件建立了导流筒搅拌槽及搅拌桨三维模型,运用Fluent流体仿真软件对其进行了数据处理,并选取了四组桨叶距槽底距离(450、500、550、600mm)试验数据,以甘油水溶液为载体对导流筒稀土搅拌槽料液混合过程进行了仿真模拟,然后以时均速度分布、速度、力矩和搅拌功率数值等参数作为评价依据,对导流筒搅拌槽该参数下的搅拌特性进行了分析评价,仿真试验结果表明:当搅拌桨叶距槽底距离为550mm时,该导流筒搅拌槽内料液轴向循环能力最强,搅拌槽整体流场分布也最好。随后又在现场进行了不同搅拌桨叶距槽底距离下的搅拌特性试验,将模拟结果与现场试验结果进行了对比验证,验证了现场实验结果与模拟分析结论的高度一致性。现场测定了搅拌桨叶距槽底距离为550mm时搅拌力矩为6.56N·m,搅拌功率为8 239W。研究结果将为导流筒搅拌槽的内部结构设计、安装提供理论和实践参考。     

颗粒粒径对浮选机固—液两相流场分布特征影响研究

针对充气机械搅拌式浮选机,运用CFD流体模拟软件进行了颗粒粒径对浮选机固—液两相流场分布特征的影响研究。通过模拟分析可知:离散相矿物颗粒与连续液相两相之间相互作用较小,流场分布特征基本保持一致,微细粒矿物颗粒粒径对浮选机内部固—液两相流场特性影响较小。转子及定子表面压力分布值与颗粒粒径有较大的关系,且在此处区域附近湍流动能较大,保证了矿物颗粒在该区域的较好分散性。     

搅拌调浆机制的固-液悬浮特性

通过固-液两相试验来模拟实际调浆过程,根据不同搅拌机制下物料在槽内的分布规律,总结累积浓度方差、区间浓度方差、离底悬浮能力以及有效作用范围等参数及概念来表征物料的悬浮特性,并以此对典型轴流式流场与径流式流场作用于两相介质的功效进行系统的分析,对常用附件（导流筒、挡板）的添加对悬浮效果的影响进行了总结。指出物料悬浮过程是由离底悬浮能力与有效作用范围共同决定的过程。同样操作条件下,物料悬浮水平较低时,搅拌体系的悬浮能力主要由离底悬浮能力决定;在实现较好离底悬浮时,有效作用范围的影响逐渐占据主导地位。     

Influence of particle size on wear rate in compressive crushing

The influence of particle size on wear rate in compressive crushing of rock was investigated experimentally. A test apparatus was developed to replicate the squeezing wear that is present in many rock crushers. Silica sand of different size classes between 0.725 and 2.03 mm was used. The crushing load was varied. The results show a strong relationship between particle size and wear rate. The wear rate increases as particle size increases. Not only mean particle size, but also size distribution width also has an influence on wear rate. From some theoretical considerations, an alternative wear model was derived, that matches experimental data well. In the new model, the wear is proportional to particle size and to the square root of the pressure.     

砂矿颗粒沉降运动规律试验研究

在滨海砂矿开采中, 为给管道输送工业设计提供必要的试验数据和优化输送参数, 从沉降机理出发对不同颗粒级配的砂矿进行了单颗粒及群体颗粒沉降试验研究, 分析了粒径及浓度对颗粒沉降规律的影响, 得出了沉降速度计算公式。结果表明, 浓度和颗粒直径是影响群体沉降速度的主要因素; 所得沉降速度计算公式的计算值与实测值误差较小, 可为砂矿管道输送参数计算提供参考。     

电选摩擦器气体流动及单颗粒运动特性研究

为研究电选摩擦器内气固运动特性,建立了三种摩擦棒不同分布特征的摩擦器数学模型,运用标准k-ε湍流模型及颗粒轨道模型,对摩擦器内气固两相流流场进行了数值模拟,主要研究了气体相对压力场、相对速度场分布情况;并以粒径为10、40、74μm的球形颗粒为研究对象,分析了编号43的单个颗粒运动情况。研究结果表明,摩擦棒对气体流动过程的干扰作用明显,摩擦棒间距对气相流场分布影响很大;摩擦棒背部的负压区和回流区面积沿气体运动方向逐渐增大;摩擦棒分布特征和粒径对摩擦器内颗粒速度变化趋势影响大,颗粒粒径与运动轨迹长度成正比,与速度成反比。     

Optimal particle acceleration in a jet mill nozzle

The optimal profile of the accelerating nozzle of a jet mill is computed to provide a maximum particle velocity at the nozzle outlet. To describe one-dimensional monodispersed flow in the nozzle, the well-known set of differential equations is employed. The influence of both particle size and solids/gas mass flow rate on the optimal nozzle profile is studied. Computations show that an employment of optimized nozzles is beneficial for relatively low solids loading. An increase in particle velocities at the optimized nozzle outlet reaches 25% compared to those in a conical nozzle if the solids/gas mass flow ratio equals unity.