一种新型浮选柱的数值模拟及性能研究

自主研制了一种新型多级规整填料浮选柱,应用计算流体力学软件FLUENT6.3.26进行数值模拟计算,对其内部的气液两相流动进行了考察,采用了欧拉-欧拉多相流模型,对气相的模拟采用单一气泡尺寸,液相湍流采用了标准k-ε模型,两相之间的动量传输仅考虑曳力作用。通过模拟,获得了不同实验条件下浮选柱内部的气液速度场分布、气含率分布等,对部分模拟结果进行了定量比较。结果表明随着气相流量的增大,浮选柱内部气含率增大,液体循环速度增大,从而气液之间混合更加充分,这对于提高浮选柱的分选效率和设备的放大有重要意义。在唐山钱家营开滦煤矿选煤厂进行了以其煤浆为原料的浮选性能的测试,在气体1.25 m³/h,进料0.05 L/h条件下20 min停留时间获得了精煤灰分10.28%,尾煤灰分43.39%,精煤产率52.53%的指标,与该厂浮选精煤灰分10.58%相接近。     

毛细管内气液两相流动的CFD模拟

毛细管精馏是一种分离共沸物系的新型分离技术,它利用毛细管的固-液相互作用来改变液体混合物的汽液平衡。毛细管通道内的气液两相流型在低气速时以泰勒流为主,今使用计算流体力学方法,对毛细管内泰勒流的多种影响因素,如:壁面作用、气液速率以及流体物性等进行了研究。首先考察壁面作用的影响,发现壁面粗糙度能改变气液柱形状和流场,粗糙度增大使通道内气液两相流型由泰勒流向泡状流转变,流动状态由层流向涡流转变。模拟不同接触角下的气液流动,发现壁面吸附作用在一定程度上影响气液柱长度和气液界面间的形状。通过模拟不同气液速率下的气液流动,观察气液柱长度与气液速率之间的关系。对模拟气液柱长度进行量纲分析,得到了泰勒流的气液柱长度的关联式,将该式与文献测定值进行比较,发现在一定范围内吻合较好。     

气含率与浮选动力学常数的研究

气含率大小是决定浮选柱回收能力和分选效果的重要参数之一,浮选柱内气含率直接决定了气泡荷载上浮矿物的数量与质量,从而决定了浮选过程中精矿的产率和回收率。本文考察了磷矿在充填浮选柱的浮选过程中,表观气体流速和矿浆质量分数对充填浮选柱捕集区气含率的影响。将浮选过程中的气含率与浮选动力学常数相联系,并结合充填浮选柱的工艺特征,推导出了具体的关联式。     

充填式浮选柱中径向返混及流速分布对浮选效果影响的研究

建立了充填式浮选柱的二维混合模型,并对该模型进行了数值法求解,探讨了径向返混系数和轴向气、液流速沿径向的分布对充填式浮选柱捕集区的回收率的影响.结果表明,增大径向返混系数有助于提高回收率;轴向气、液流速沿径向的分布越均匀越好;气速的不均匀分布将对回收率造成较大影响.分析结果对提高充填式浮选柱的浮选效果具有一定的理论指导意义.     

浮选柱内流体流动CFD模拟

建立了考虑气相分布的浮选柱流体流动模型,并在此基础上计算了不同气速分布条件下,浮选柱内流体流动的状况.     

充填浮选柱分选胶磷矿的工艺研究

充填浮选柱是一个复杂的气液固三相体系。本文考查了用充填浮选柱分选胶磷矿的主要操作参数的影响，讨论了Ｐ２Ｏ５的品位的沿柱高的分布，证实了充填浮选柱具有优良的分选性能，并为寻求缩短胶磷矿浮选工艺流程的途径提供了依据。     

浮选设备流体力学特征参数研究现状

浮选设备是矿物加工工程领域一种重要的气液反应装置，主要包括浮选机和浮选柱。浮选设备应用已有百年历史，随着选矿技术水平的提高，浮选设备逐渐向自动化、大型化的方向发展。近年来对浮选设备内流体力学特征参数的研究解析越来越多，进一步促进了设备的合理放大和优化。本工作在简要介绍目前浮选设备的发展和应用现状后，总结了国内外学者对浮选设备内气泡尺寸、气含率和气泡速度3个重要流体力学特征参数的检测方法和研究现状，提出了在今后研究中，开发以机器视觉为核心的检测技术和强化侵入式检测装置的适用性是流体力学特征参数检测手段的发展方向之一。     

充填浮选柱中停留时间分布的微机在线测试

1 前言 充填式浮选柱是一种新型的浮选装置,尤适用于细粒浮选。使用中,常可将浮选柱划分为上下两个区域。上部为泡沫区,下部为捕集区。在柱内,物料和气体呈逆向流动。 为解决浮选柱的设计、优化、放大等实际问题,需要建立数学模型来模拟浮选柱的混合特性。因此,有必要对浮选柱的传递特性进行研究。     

开孔金属泡沫内气液两相流动的可视化

开孔金属泡沫内流动特性的研究多局限于局部流动特性的分析,大尺寸（100cm²以上）金属泡沫内气液两相宏观流动特性的研究目前较为缺乏。为了深入认识金属泡沫内气液两相流动特性,本文通过光学可视化手段,对金属泡沫多孔介质薄层内的气/液驱替、液/气驱替两相流动过程进行研究,分析了入侵流体的流速及金属泡沫的孔径对泡沫薄层内两相流动的影响。结果表明：在气/液驱替流动方面,随着空气流速的增大,气液两相的界面形态由毛细指状结构过渡到黏性指状结构,随着泡沫孔径的减小,部分排水现象愈加显著;在液/气驱替流动方面,气液界面较为规则,近似呈锥形,且流速越大,界面锥角越大、长度越小,试验中仅在最小孔径的金属泡沫中捕捉到明显的部分驱替现象,并且随着水流速的减小愈加显著。     

液柱脱硫塔流动特性的实验研究

通过实验研究了液柱塔的流动特性 ,回归出了液柱喷射高度及液柱塔的阻力损失公式 ,回归计算值和实验测量数据吻合很好 .同时还测定了液柱塔的轴向压力分布和压力梯度分布 ,发现液柱塔中存在压力和压力梯度急剧变化的区段 ,该区段正是气液传质吸收的关键部分 .研究结果可为液柱塔的设计和操作提供参考 .     

Gas‐Liquid Mass Transfer Approach applied to the Modeling of Flotation in a Bubble Column

A kinetic model developed to describe flotation in a bubble column is presented. This model, developed on the basis of the theory of mass transfer in gas‐liquid flows, makes explicit in its formulation the effect of the superficial saturation of bubbles on the kinetics of flotation. The model is applied to the simulation of flotation column experiments for which the classical first‐order models, commonly used in flotation modeling, are insufficient to represent the flotation kinetics. The results of the simulations obtained under different hypotheses of simplification and compared to experimental data show that the model succeeds in representing the flotation kinetics in these cases.     

PROFILE OF LIQUID FLOW IN BUBBLE COLUMNS

Equations for the liquid velocity profile and the average gas hold-up in bubble columns including cocurrent flow are proposed. It is shown that the inversion point of liquid flow can be used as the characteristic parameter for calculating the liquid flow profiles and gas hold-up. A tracer method was developed to measure the inversion point of liquid flow in bubble column reactors. For water as the liquid phase this inversion point was found at a distance from the column axis of 0·70 0·73 times the column radius. Besides, bubble velocities and bubble diameters in water and methanol-water solutions were determined, using a 5-point conductivity microprobe. It was found that in dilute solutions of methanol the bubble velocity is lower than in pure water. With increasing superficial gas velocity, the bubble velocity steadily increases in pure water, whereas in methanol-water solution it first decreases and, after reaching a minimum, increases too.     

ON OPTIMUM TEMPERATURE OPERATIONS IN DEACTIVATING FIXED-BED REACTORS

Equations for the liquid velocity profile and the average gas hold-up in bubble columns including cocurrent flow are proposed. It is shown that the inversion point of liquid flow can be used as the characteristic parameter for calculating the liquid flow profiles and gas hold-up. A tracer method was developed to measure the inversion point of liquid flow in bubble column reactors. For water as the liquid phase this inversion point was found at a distance from the column axis of 0·70 0·73 times the column radius. Besides, bubble velocities and bubble diameters in water and methanol-water solutions were determined, using a 5-point conductivity microprobe. It was found that in dilute solutions of methanol the bubble velocity is lower than in pure water. With increasing superficial gas velocity, the bubble velocity steadily increases in pure water, whereas in methanol-water solution it first decreases and, after reaching a minimum, increases too.     

Local hydrodynamics of gas–liquid-nanoparticles three-phase fluidization

The laser Doppler anemometer (LDA) and conductivity probes were used for measuring the local hydrodynamic performances such as gas holdup and liquid velocity in a lab-scale gas–liquid–TiO₂ nanoparticles three-phase bubble column. Effects of operating parameters on the local gas holdup and liquid velocity were investigated systematically. Experimental results showed that local averaged axial liquid velocity and local averaged gas holdup increased with increasing superficial gas velocity but decreased with increasing TiO₂ nanoparticles loading and the axial distance from the bottom of the bubble column. A three-dimensional computational fluid dynamic (CFD) model was developed in this paper to simulate the structure of gas–liquid–TiO₂ nanoparticles three-phase flow in the bubble column. The time-averaged and time-dependent predictions were compared with experimental data for model validation. A successful prediction of instantaneous local gas holdup, gas velocity, and liquid velocity were also presented.     

Operating Characteristics and Performance of a Monolithic Downflow Bubble Column Reactor in Selective Hydrogenation of Butyne‐1,4‐diol

The effects of flow condition, bubble dispersion level, and liquid flow rate on the behavior of a novel monolithic downflow bubble column (M‐DBC) were investigated using a reaction model, the palladium‐catalyzed hydrogenation of butyne‐1,4‐diol. The stable and closely packed homogeneous bubble dispersion present in the bulk region of the M‐DBC allowed effective introduction of the gas‐liquid phase for formation of Taylor flow inside the monolith channels. The condition defined as the minimum level dispersion was required in order to obtain high selectivity towards the intermediate product, cis‐2‐butene‐1,4‐diol. Enhanced reaction rates were obtained at increasing the dispersion level and lowering the liquid flow rate. Comparison with the DBC employing 5 % Pd/C powder catalyst and 1 % Pd‐on‐Raschig‐ring revealed a better performance of the M‐DBC (1 % Pd loading) with the advantage of smaller reaction volume and intensified reaction rate. As an alternative to conventional three‐phase reactors, the M‐DBC was so simple due to its inherent characteristic operation and no specially designed device is required.     

环流浮选塔用于含油污水处理的实验研究

以空气/含柴油污水为模拟介质体系,在环流浮选塔(外筒体内径100 mm,高932 mm;导流筒内径59 mm,高780 mm)上考察了操作气速、液相流量及浮选塔上部空间填料设置对油-水分离效率的影响. 结果表明,分离效率随操作气速增大先增后降,随液体流量增大而降低;与传统空筒式浮选塔相比,环流浮选塔的分离效率比常规空筒式浮选塔有显著提高. 实验确定的最佳操作气速为0.015~0.02 m/s,最佳液相流量为20 L/h,在环流浮选塔上部设置填料的情况下,油-水分离效率最高可达57.3%. 基于实验数据建立了涉及气泡特性、液相物性、气液相流量及油滴返混影响因素在内的分离效率的经验模型,与实验值吻合较好.     

LIQUID PHASE BACKMIXING IN BUBBLE COLUMN REACTORS—A NEW CORRELATION

Bubble column reactors are widely used in many industrial applications due to their simplicity of operation. Although simple to operate, bubble columns are difficult to scale-up due to the uncertainties in the estimation of some non-adjustable design parameters. One of these design parameters is the liquid phase backmixing.

The present work proposes a new correlation to estimate the liquid phase backmixing in bubble column reactors. The correlation is based on principles originally developed for flow through porous media and uses experimental data obtained over a wide range of operating conditions. This correlation is simple to use and requires parameters which are easily available or can be measured on a small scale apparatus. The proposed correlation shows a significant improvement over available literature correlations and is applicable to three phase systems as well.     

An experimental study of copper sulfide flotation in a packed cyclonic–static microbubble flotation column

A method using a cyclonic–static microbubble flotation column packed with fluid guiding media was proposed for improving flotation efficiency of copper sulfide. The installation of packed fluid guiding media in a cyclonic–static microbubble flotation column was for changing flow pattern in 10 the column by avoiding strong cyclonic flow in the upper region of the column, which can cause bubble-particle detachment. Therefore, the attached particles can be more likely to enter the froth zone instead of swirling in the column. The flow rectification contributed to a smaller bubble size in the column and significantly reduced the number of big bubbles with diameter above 1 mm. This scenario was caused by the damping of swirling liquid motion where bubbles tended to 15 concentrate and coalescence in the center of an eddy. The packed fluid guiding media changed the hydrodynamics in the upper column from a cyclonic flow to a gentle flow and as a result improve the column separation. The application of packed fluid guiding media can decrease the bubble-particle detachment and the flotation recovery of copper sulfide could constantly improve with the installation of packed fluid guiding media in the FCSMC column.     

Comparison of Hydrodynamics and Mass Transfer in Airlift and Bubble Column Reactors Using CFD

Computational Fluid Dynamics (CFD) is used to compare the hydrodynamics and mass transfer of an internal airlift reactor with that of a bubble column reactor, operating with an air/water system in the homogeneous bubble flow regime. The liquid circulation velocities are significantly higher in the airlift configuration than in bubble columns, leading to significantly lower gas holdups. Within the riser of the airlift, the gas and liquid phases are virtually in plug flow, whereas in bubble columns the gas and liquid phases follow parabolic velocity distributions. When compared at the same superficial gas velocity, the volumetric mass transfer coefficient, k_La, for an airlift is significantly lower than that for a bubble column. However, when the results are compared at the same values of gas holdup, the values of k_La are practically identical.