取消药剂消耗的电脱盐污水物理法预处理

炼油废水中油分与悬浮物的高效、低耗分离关乎石化行业的绿色发展和减污降碳目标。针对电脱盐污水中油分与悬浮物复合以及水质波动问题，本文通过组合亲水性和亲油性颗粒介质构建组合颗粒微通道分离床层，并耦合旋流再生开发沸腾床分离技术，相继通过小试和中试试验验证组合颗粒微通道分离对电脱盐污水的脱固除油预处理效果，并针对中国石化某炼油厂的电脱盐污水提出物理法预处理工程方案，对比分析物理法预处理工艺相较传统“老三套”的经济性差别。沸腾床分离器中高速摄像可视化测试表明，组合颗粒能够实现油滴有效捕集，且亲水颗粒的引入对分离效果未产生负面影响；针对油分和悬浮物浓度剧烈波动的实际电脱盐污水，现场1m³/h沸腾床分离器出水含油率和固含量可稳定控制在20mg/L和50mg/L以内，而10m³/h沸腾床分离中试试验证实物理法预处理工艺可长周期持续实现出水维持稳定。相较于“均质+隔油+气浮”传统预处理工艺，物理法预处理工艺取消了聚合氯化铝（PAC）和聚丙烯酰胺（PAM）等药剂消耗，并同时避免了气浮浮渣等危险废物的产生，同时体现了经济和环保优势。     

Effect of electric field on the hydrodynamics of fluidized nanoparticles

The effect of electric field on the hydrodynamics of nanoparticles was studied in a fluidized rectangular bed, with electrodes attached to two parallel walls. It was shown that the electric field of the order of 3 times the gravity markedly decreased the bed expansion and increased the solids volume fraction of nanoparticles fluidized by air. In these experiments, a light diode assembly was utilized to infer the local solids volume fractions within a rectangular bed of 10 nm silica particles. These experimental measurements yielded a two dimensional solids volume fraction distribution within the rectangular bed. The experimental results provided some new insights into the distribution of solids within the bed. The agglomerate diameters were computed using a momentum balance with the drag given by the Ergun equation and the empirical Richardson-Zaki method. Both methods yielded agglomerate diameters of the order of 100 μm and showed dependence on the strength of the electric field. The electric field decreased the granular temperature of the nanoparticles.     

气体干法净化旋流吸附耦合设备压降特性

气体干法净化旋流吸附耦合设备将旋流分离和移动床吸附/过滤分离有机结合,可适应较宽的温度范围,为高温气体净化提供了一种新思路。在不加尘及不同的移动床循环速率和旋风入口气速下对该设备进出口静压差进行了测量和分析。实验结果表明,设备静压差在整个运行过程中较为稳定,有较强的可预测性,无量纲标准偏差维持在0.4%以内;实验范围内,移动床循环量的大小对设备静压差没有影响;设备压降与旋风入口气速呈现出良好的二次方程（抛物线）关系;将设备实际压降划分为进口管路沿程摩擦损失、入口天圆地方摩擦损失、旋流体摩擦损失、内置移动床摩擦损失和出口管路沿程摩擦损失五个部分;获得了旋流体摩擦损失及设备实际压降与入口速度头的关联方程;该设备的阻力系数与普通旋风分离器相比,没有明显增大;初步加尘实验确认了旋风壳体与移动床之间旋流作用的存在,为进一步结构优化提供了参考。     

A Granular Bed for Use in a Nanoparticle Respiratory Deposition Sampler

A granular bed was designed to collect nanoparticles as an alternative to nylon mesh screens for use in a nanoparticle respiratory deposition (NRD) sampler. The granular bed consisted of five layers in series: a coarse mesh, a large-bead layer, a small-bead layer, a second large-bead layer, and a second coarse mesh. The bed was designed to primarily collect particles in the small-bead layer, with the coarse mesh and large-bead layers designed to hold the collection layer in position. The collection efficiency of the granular bed was measured for varying depths of the small-bead layer and for test particles with different shape (cuboid, salt particles; and fractal, and stainless steel and welding particles). Experimental measurements of collection efficiency were compared to estimates of efficiency from theory and to the nanoparticulate matter (NPM) criterion, which was established to reflect the total deposition in the human respiratory system for particles smaller than 300 nm. The shape of the collection efficiency curve for the granular bed was similar to the NPM criterion in these experiments. The collection efficiency increased with increasing depth of the small-bead layer: the particle size associated with 50% collection efficiency, d₅₀, for salt particles was 25 nm for a depth of 2.2 mm, 35 nm for 3.2 mm, and 45 nm for 4.3 mm. The best-fit to the NPM criterion was found for the bed with a small-bead layer of 3.2 mm. Compared to cubic salt particles, the collection efficiency was higher for fractal-shaped particles larger than 50 nm, presumably due to increased interception.

Copyright 2015 American Association for Aerosol Research     

Modified tribo-charging device for the electrostatic separation of plastics from granular industrial wastes

Tribo-electrostatic separation is the solution of choice for the selective sorting of various plastics contained in a granular mixture. This work is aimed at validating the efficiency of a modified compressed-air-operated tribo-charging device for the electrostatic separation of mixed granular plastics originating from industrial waste. The experiments are carried out with a mixture of mm-size orange and beige PVC granules, using a free-fall electrostatic separator. At optimum operating conditions, 93% of the orange PVC and 96% of the beige PVC were recovered at purities higher than, respectively, 99% and 95%. The numerical simulation of charged particles trajectories facilitates the interpretation of the experimental results and the analysis of the factors that affect the efficiency of the separation process: high-voltage level, configuration of the electrodes system, and position of the feeding unit.     

Continuous particle separation with localized AC-dielectrophoresis using embedded electrodes and an insulating hurdle

This paper reports a microfluidics-based lab-on-a-chip device combining the alternating current (AC) dielectrophoresis (DEP) and pressure-driven flow for separation of particle/cell mixtures. The dielectrophoretic separation is achieved by a hybrid design using a PDMS (poly-dimethylsiloxane) hurdle and a pair of embedded metal electrodes to generate localized non-uniform AC electric field. Since the particles and the cells are transported through the small DEP separation region, the negative effects associated with the Joule heating and exposure to the electric field have been significantly reduced. Mixtures of polystyrene particles of different sizes and yeast cells with polystyrene particles were successfully separated at AC electric field of 200 kHz.     

多孔板干扰床中细粒煤分离特性研究

为提高干扰床对细粒煤的分选效果,将一种多孔板应用于干扰床,采用实验与数值模拟相结合的方法,研究了多孔板对细粒煤分选密度、颗粒分布的影响及多孔板干扰床的流化特性。结果表明:多孔板使各粒级分选密度更加均匀,粒度-分选密度曲线斜率由-0.518增至-0.448,强化了颗粒的密度分离,提高了分选效果。高密度颗粒(1.70、1.90 g/cm3)主要集中在床层底部,低密度颗粒(1.40、1.50 g/cm3)主要集中在床层上部,其体积分数分别为29.79%、32.86%、48.90%、20.81%,错配颗粒比较少,实现了煤粒的有效分选。干扰床床层悬浮区密度不是煤粒分选密度,其平均值为1.23 g/cm3,且在高度方向上并不均匀。多孔板干扰床中形成了多孔板分级—板间流化区—多孔板与边壁间流化区的多级分选模式,能在一定程度上抑制高低密度颗粒错配,实现细粒煤的高效分选。     

Application of inductive heating to granular media: Modelling of electrical phenomena

A model is examined in order to predict the behaviour of a granular bed made with conductive particles subjected to an inductive electromagnetic field. The model shows how heat generated in the bed can be described by its electric impedance for the high-frequency generator required for inductive heating. Once the relationship between electrical characteristics and power dissipation has been established, comparisons between experimental and theoretical results are presented and the validity of the model is discussed.     

BUBBLE COMPUTATION, GRANULAR TEMPERATURES, AND REYNOLDS STRESSES

Bubbles were simulated in a two-dimensional fluidized bed with a constant inlet velocity using two computer codes, the IIT code and the MFIX code. The computational results were compared to the Jung et al. (2005) experiments in a thin bubbling bed of 530 μm glass beads. The use of higher order numerics produces better bubble resolution due to smaller numerical diffusion. The computed bubble sizes and their distributions agreed with the experiments. The simulations show that there is no bubble formation for sufficiently elastic particles.

CFD computations and previous experiments show that in the bubbling fluidized beds there exist two random oscillations. The first kind is due to random oscillations of particles and is measured by the conventional granular temperature. The second one is due to motion of bubbles and gives rise to Reynolds type stresses. It is shown that the particle granular temperature is much smaller than the bubble-like granular temperature computed from the average of the normal Reynolds stresses, measured by Cody using a shot noise technique.     

喷动床内气固二相流动行为的计算模拟

采用双流体模型结合颗粒动理学理论对喷动床内气固二相流体流动行为进行了计算模拟研究。模型中运用颗粒动理学理论描述颗粒相应力封闭流体控制方程,使用Gidaspow曳力模型描述气固相间作用。喷动床内颗粒在浓相区的体积分数很大,采用Schaeffer′s模型描述颗粒间的摩擦应力。模拟计算结果表明,喷动床内分喷射区、喷泉区、环隙区3个区域,在射流入口处形成一个瓶颈。模拟计算得到的颗粒速度和空隙度分布与实验数据进行比较,计算结果与实验结果吻合较好。     

颗粒床-旋流耦合分离器不同操作模式下的性能分析

通过实验分别考察了满床/空床操作模式对内置颗粒床-旋流耦合分离器分离性能的影响,获得了两种操作模式下的设备压降和捕集效率。通过改变入口粉尘浓度、入口气速和粉尘颗粒种类,发现满床操作条件下的分离效率比空床操作条件下的分离效率高,且前者压降较低。通过对出口粉尘粒径的分析,含有捕集颗粒的内置颗粒床可有效提高5 μm以下的粉尘颗粒的捕集效率,弥补了离心分离的短板。引入性能指数对不同操作模式进行定量分析,验证了满床操作条件下的耦合分离设备具有更好的综合分离性能。     

Size separation of particulates in a trommel screen system

This paper describes the design and testing of a trommel screen system for the separation of undersized particulates. The trommel screen system consisted of a cylindrical separation device that rotated to perform size separation. A series of experiments were carried out at room temperature to demonstrate the screening efficiency of this method under different operating conditions. The dynamic model and velocity analysis of undersized particulates in the trommel body are also discussed. The experimental results show that the screening efficiency could be enhanced by using a mass flow rate of 360 cm/s, a dust concentration of 10,000 ppmw, an inclination angle of the trommel body of 5° and a rotational speed of the trommel body of 43 rpm. Moreover, the results also indicate that this type of method could be useful for dust particulate separation in a moving granular bed filter system. The main focus of the current study is the development of a trommel screen system for a moving granular bed filter that could be applied in a high-temperature environment.     

A hybrid approach to computing electrostatic forces in fluidized beds of charged particles

In particulate flow devices particles acquire electric charge through triboelectric charging, and resulting electrostatic forces can alter hydrodynamics. To capture this effect, the electrostatic force acting on individual particles in the device should be computed accurately. Electrostatic force is calculated using a hybrid approach consisting of: (1) long‐range contributions from an Eulerian electric field solved using the Poisson equation (2) short‐range contributions calculated using a truncated pairwise sum and (3) a correction to avoid double counting. Euler‐Lagrange simulation of flows incorporating this hybrid approach reveals that bed height oscillations in small fluidized beds of particles with monopolar charge decreases with increasing charge level, which is related to lateral segregation of particles. A ring‐like layer of particles, reported in experimental studies, forms at modestly high charge levels. Beds with equal amounts of positively and negatively charged particles are fluidized in a manner similar to uncharged particles. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2282–2295, 2016     

Removal of Submicron Silica Particles from tert-Amyl Alcohol by Dielectric/Electric Packed Bed Filtration

Abstract

A packed bed with an applied electric field is used to remove submicron and nanometer particles from a nonconducting or slightly conducting solution. Several studies have shown that the application of an electric field to a packed bed significantly increases the performance of the filtration. To enhance the electric-field filtration efficiency, it is desired that the packing materials have a higher dielectric constant than the solution so that the electric-field lines will be diverted into the packing materials.

In the present studies, a dc voltage of 0 to 8 kV/cm is applied to a packed bed (2.5-cm diameter and 3.0-cm length) filled with 1-mm-diameter glass beads. The filtration medium contains submicrometer or nanometer SiO₂ particles dispersed in tert-amyl alcohol. Two particle sizes are investigated: the average particle sizes are about 300 nm and 50 nm, respectively.

Visible light spectrophotometry is used to estimate the amount of SiO₂ particles in the effluent. The experimental results are presented as a series of breakthrough curves. The effect of the applied electric field on the breakthrough curve on two different particle sizes is presented. Depending on the applied electric field and the conductivity of the system, heating of the packed bed may occur. The operating current and temperature of the packed bed are also presented.     

颗粒移动床内不稳定运动的计算颗粒动力学模拟

采用考虑滚动摩擦的三方程离散单元法（DEM）模型对侧开孔的移动床中的颗粒流动进行了数值研究。结果表明，计算颗粒动力学(CGD)方法可对复杂颗粒系统内颗粒的运动行为进行准确的预测，包括时均速度场和脉动速度场。讨论了模型中颗粒摩擦参数的重要影响，并对颗粒流动表现出的间歇现象进行了分析。颗粒流动与流体流动有相似之处，都存在随机的脉动，但颗粒流的随机脉动机理与流体中的湍流机理有很大不同，颗粒流动会表现出很强的不连续性。     

Segregation in a stirred fluidized bed

A bed of particulate solids supported by an upward current of gas can be stirred at moderate power input per unit volume using thin horizontal rods mounted on a vertical shaft. The bed is fluidized, but bubbles are suppressed below a critical value of the fluidizing velocity. Stirring increases bed bulk density and reduces the minimum fluidizing velocity. Segregation in a stirred fluidized bed is enhanced with both flotsam and jetsam tracer particles, but the rate of segregation is reduced with flotsam tracers. The stirred fluidized bed may be useful as a device for dry separation of solids.     

Prediction of particle motion in a two-dimensional bubbling fluidized bed using discrete hard-sphere model

The solids motion in a gas-solid fluidized bed was investigated using a discrete hard-sphere model. Detailed collision between particles and a nearest list method are presented. The turbulent viscosity of gas phase was predicted by subgrid scale (SGS) model. The interaction between gas and particles phases was governed by Newton's third law. The distributions of concentration, velocity and granular temperature of particles are obtained. The radial distribution function is calculated from the simulated spatio-temporal particle distribution. The normal and shear stresses of particles are predicted from the simulated instantaneous particle velocity. The pressure and viscosity of particles are obtained from both the kinetic theory of granular flow and the calculated stresses of particles. For elastic particles the individual lateral and vertical particle velocity distribution functions are isotropic and Maxwellian. The observed anisotropy becomes more pronounced with increasing degree of inelasticity of the particles.     

粗糙颗粒动理学及流化床内气固流动的数值模拟

基于气体分子动理学和颗粒动理学理论,考虑颗粒旋转流动对颗粒碰撞能量交换和耗散的影响,建立粗糙颗粒动理学。采用Chapman-Enskog颗粒速度分布函数,提出了颗粒相应力、热通量和颗粒碰撞能量耗散计算模型。采用欧拉-欧拉气固双相流模型,数值模拟鼓泡流化床内气体-颗粒两相流动特性。模拟结果得到了床内颗粒相速度和脉动速度分布,与Yuu等实验结果相吻合。分析不同的切向弹性恢复系数对颗粒相拟总温的变化规律,结果表明在低颗粒浓度时颗粒拟总温随切向弹性恢复系数而增加。