Blend uniformity and powder phenomena inside the continuous tumble mixer using DEM simulations

Powder mixing is an essential operation in pharmaceutical, food, and petrochemical industries. Pharmaceutical companies have been working in the implementation of continuous processes as an alternative to the batch process using the food and drug administration process analytical technology initiative. The main goal was to understand the mixing phenomena inside the continuous tumble mixer and monitor blend uniformity using discrete element method. Results demonstrated that the main mixing mechanism is convection similar to the common tumbling mixers. This mechanism is driven by the bulk flow of the particles, due to the mixer rotation. The simulations' results, demonstrated that the cohesion reduces the concentration variability due to the higher holdup, particle interactions, and mean residence time. The blend uniformity at the exit of the system was measured and a relationship between relative standard distribution, cohesion, and the collision frequency was found. © 2014 American Institute of Chemical Engineers AIChE J, 61: 792–801, 2015     

DEM‐simulation of the magnetic field enhanced cake filtration

Using the discrete element method, we simulate numerically the cake formation and growth in magnetic field enhanced cake filtration to give further insight on the mechanisms of the structuring of the filter cake due to the interaction of magnetic, hydrodynamic, and mass forces. The motion of the discrete particles is obtained by applying the three‐dimensional Newton's equations to individual particles, allowing for both external forces (gravity, applied magnetic field) and particle–particle interactions calculated using the modified DLVO‐theory. Continuous liquid phase flow is assumed as one‐dimensional. The simulation results compare favorably with reported experimental data, 1 and can be used to delineate the regimes associated with different liquid flow and magnetic field effects that are observed experimentally. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

A segment probability method for calculating the molecular weight distributions of linear polycondensates in a continuous reactor

The molecular weight distribution (MWD) of polymers is a target of the optimization and control of industrial polymerization processes, as it dictates the processability and properties of polymers. A method, named as segment probability method, is developed to calculate the MWD of polycondensates produced by monomers of types A₂ and B₂ in a continuous reactor. It considers a growing chain as being composed of A and B segments in the middle of the chain and two terminal segments at the chain ends. It calculates the propagation probabilities of these different types of segments upon taking into account both the polycondensation and side reaction kinetics as well as the residence time distribution of the continuous reactor. The method is validated by poly(butylene terephthalate) (PBT) obtained from an industrial polymerization process composed of a continuous esterification reactor. The MWDs of the PBT calculated by this method are in agreement with those measured by size exclusion chromatography with mean square errors less than 10%.     

Particle‐scale investigation of the solid dispersion and residence properties in a 3‐D spout‐fluid bed

Three‐dimensional modeling of the gas–solid flow in a spout‐fluid bed is conducted at the particle‐scale level. Both the local and systematic dispersion behaviors of solid phase are initially investigated. Then, the solid circulating and resident behaviors are discussed. The results demonstrate that vigorously lateral solid dispersion appears in the spout region and the periphery of the fountain, whereas intensely vertical dispersion exists in the central region of the bed. Moreover, the inlet configuration of bed strongly affects the distribution of lateral dispersion, while its influence on the vertical one disappears in the fountain. Strong anisotropy of solid dispersion along the three directions is obtained. Systematic dispersion intensity along the vertical direction is an order of magnitude larger than the lateral one. In addition, two circulating patterns of solid phase can be identified. Solid residence time is the smallest in the spout region and the largest in the bottom corner. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2788–2804, 2014     

DEM study of granular flow characteristics in the active and passive regions of a three‐dimensional rotating drum

Three‐dimensional modeling of the solid motion in a lab‐scale rotating drum has been conducted via the discrete element method. After validating the simulated results with available experimental data, the active‐passive interface was identified, following which particle‐scale information in these two regions, in particular the influences of fill level and rotating velocity, were obtained. The results demonstrate that: (1) the total number of particles in the passive region is three times that in the active, (2) the transverse and axial velocities span a wider range in the active region, with the transverse values being greater, (3) the collision force is much higher in the active region, with the greatest magnitudes in the y direction relative to that in the x and z directions, (4) particle displacements are generally lower and have a narrower distribution in the active region, (5) the local solid residence time (SRT) distribution profiles are similar axially in that the highest SRT magnitudes are at the center region of the bed, while the other parts of the bed have uniform SRT magnitudes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3874–3888, 2016     

Residence time distribution analysis from a continuous couette flow device around critical taylor number

This paper presents an experimental study of residence time distribution (RTD) analysis by pulse response technique in a continuous Couette flow device with rotating inner cylinder and stationary outer cylinder. Two kinds of experimental tests using pulses of tracer dye solution and particles resulting from a fast precipitation were performed in the region near the critical Taylor number characterizing boundary between laminar and laminar vortex flow. For most experiments performed in laminar and laminar vortex flow regime around the critical Taylor number over the ranges 0 < T_a < 120 and 0 < R_e < 5.5 the normalized response can be described by a dispersion model. The results of the critical Taylor number as characterized by the minimum dispersion number appear consistent with both theoretical predictions and other empirical observations.     

DEM‐CFD modeling of particle systems with long‐range electrostatic interactions

To investigate dynamic behaviors of monocharged particle systems, a direct truncation (DT) method and a hybrid particle‐cell (HPC) method are implemented into the discrete element method coupled with computational fluid dynamics (DEM‐CFD) with defined cutoff distances. The DT method only considers electrostatic interactions between particles within the cutoff distance while the HPC method computes electrostatic interactions in the entire computational domain. The deposition process of monocharged particles in a container in air was simulated using the developed DEM‐CFD. It was found that using the DT method, the macrostructure, evolution of granular temperature, and radial distribution function of the particle system were sensitive to the specified cutoff distance. In contrast, using the HPC method, these results were independent of the specified cutoff distance, as expected. This implies that, although electrostatic interactions between particles with large separation distances are weak, they should be considered in DEM‐CFD for accurate modeling of charged particle systems. © 2015 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 61: 1792–1803, 2015     

Mixing performance comparison of milliscale continuous high‐shear mixers

Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.

     

Embedding a Gaussian discrete‐time autoregressive moving average process in a Gaussian continuous‐time autoregressive moving average process

Abstract. Embedding a discrete‐time autoregressive moving average (DARMA) process in a continuous‐time ARMA (CARMA) process has been discussed by many authors. These authors have considered the relationship between the autocovariance structures of continuous‐time and related discrete‐time processes. In this article, we treat the problem from a slightly different point of view. We define embedding in a more rigid way by taking account of the probability structure. We consider Gaussian processes. First we summarize the necessary and sufficient condition for a DARMA process to be able to be embedded in a CARMA process. Secondly, we show a concrete condition such that a DARMA process can be embeddable in a CARMA process. This condition is new and general. Thirdly, we show some special cases including new examples. We show how we can examine embeddability for these special cases.     

Modeling gas‐particle two‐phase flows with complex and moving boundaries using DEM‐CFD with an immersed boundary method

An immersed boundary method (IBM) has been developed and incorporated into the coupled discrete element method and computational fluid dynamics (DEM‐CFD) approach to model particulate systems consisting of a compressible gas and solid particles with complex and/or moving boundaries. The IBM is used to deal with the interaction between gas and complex and moving boundaries by using simple rectangular grids to discretize the fluid field. The developed method has been applied to simulate some typical powder handling processes (e.g., gas fluidization with an immersed tube, segregation in a vertically vibrated bed, and pneumatic conveying). Good agreement is achieved between the present simulation results and the experimental ones reported in the literature. It has been demonstrated that the capacity of DEM‐CFD is enhanced with the incorporation of IBM, which can be used to simulate a wide range of problems that could not be handled with the conventional DEM‐CFD method. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1075–1087, 2013     

白钨矿连续酸浸槽内固体颗粒的流动特性实验及模型研究

以停留时间分布（RTD）为评价指标,对硫磷混酸浸出白钨矿的连续浸出槽内固相颗粒流动行为进行实验研究。同时探究了进料流量、搅拌转速、连续浸出槽中物料进出口位置组合对固相颗粒流动行为的影响。实验结果表明：随着进口流量的增大,一开始槽内的返混程度得到了增强,量纲为1化方差变大,但是继续增大进口流量,进口处物料的横向迁移速度加强,使槽内流体流动趋向平推流,导致量纲为1化方差减小;量纲为1化方差随着搅拌转速的增大而增大,但是此时在槽下部区域会逐渐形成循环死区,槽内死区体积分数随之增大;平均停留时间随着物料进出口位置的变化而发生变化,下进下出的进出料位置组合其平均停留时间最大,且最接近理论平均停留时间。最后利用非理想流动模型来表征实验过程中的停留时间分布,模型拟合的停留时间曲线与实验测量的曲线吻合程度良好。     

Flow behavior in a corotating twin‐screw extruder of pure polymers and blends: Characterization by fluorescence monitoring technique

The objective of this work was to investigate the flow behavior of pure polymers and blends, especially miscible polymer/polymer systems, in a corotating twin‐screw extruder (TSE) using an online fluorescence monitoring device. An immiscible blend was also studied for the sake of comparison. The fluorescence signal was obtained by using synthesized fluorescence tracers added to the melt at very low concentrations. These tracers consisted of two styrene‐maleic anhydride copolymers (SMA) labeled with anthracene. The investigated blends were SMA8 (8 wt % of MA in SMA)/polystyrene (PS), SMA14 (14 wt % of MA in SMA)/styrene acrylonitrile copolymer (SAN), and poly(methyl methacrylate) (PMMA)/ethyl acrylate‐methyl methacrylate copolymer (PMMAEA). The residence time distribution (RTD), the mean residence time (t ), the dimensionless variance (σ_θ²), the Peclet number (Pe) and the fluorescence peak intensity distribution of pure polymers and binary polymer systems were investigated and interpreted in terms of polymers rheological properties. It was observed that polymers presenting higher viscosity or higher pressure showed longer residence time. A difference in behavior was also observed for the RTD of miscible and immiscible blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The influence of influent distribution and blood content of slaughterhouse wastewater on the performance of an anaerobic fixed‐film reactor

This paper evaluates the performance of a laboratory‐scale anaerobic fixed‐film reactor (AFFR) with arranged media treating slaughterhouse wastewater. The reactor was operated at 20 °C, its organic loading rate was increased from 1.8 to 9.2 kg COD m^?3 d^?1, and it had a short hydraulic residence time (5–9 h). The influence of wastewater concentrations on its performance was studied by artificially increasing the blood content of the wastewater. The efficiency of the removal of organic matter decreased from 70% to 54% as the superficial velocity increased from 0.12 to 0.97 m h^?1, due mainly to distribution defects, as had been confirmed experimentally by tracer tests. The kinetics of the anaerobic processes was limited by substrate availability, even at high COD concentrations (between 700 and 1100 mg dm^?3) due to a high content of slowly biodegradable and inert compounds present in the wastewater from the slaughterhouse. It was observed that a large amount of the organic matter had accumulated inside the reactor instead of being removed by methanogenic digestion. Furthermore, the fraction of organic matter held inside the reactor varied significantly in relation to the blood content of the wastewater. Copyright © 2005 Society of Chemical Industry     

基于催化剂颗粒停留时间分布的双峰聚乙烯牌号切换优化

针对环管-流化床串联的Borstar双峰聚乙烯工艺,建立了包括催化剂切换在内的双反应器串联牌号切换模型,使产品牌号的切换时间最短、过渡料数量最少。同时,推导了双反应器串联工艺中,存在催化剂切换时各反应器内聚合物的瞬时与累积性能指标（熔融指数与密度）的模型。研究表明,对于涉及催化剂切换的牌号切换,最优策略是采用催化剂分步进料方式,综合考虑新旧催化剂对操作参数的不同要求及各反应器内残留原催化剂比重对最终产品性能的影响,从而达到明显缩短切换时间、有效抑制操作变量急剧变化、平缓产品性质变化轨迹的优化目的。     

High‐throughput packed‐bed microreactors with in‐line analytics for the discovery of asphaltene deposition mechanisms

Understanding asphaltene nanoaggregation kinetics is a key to predicting the deposition in pure quartz‐grain porous media. High‐throughput quartz packed‐bed microreactors (μPBRs) were, therefore, designed to provide mechanistic insights by merging oilfield chemistry and microchemical systems. In‐line UV‐Vis spectroscopy and pressure transducer were used to characterize the stable packing of quartz particles with porosity of ～40% and permeability of ～5.5 × 10^?13 m². Temperature (25.0–90.0°C), n‐heptane composition (50.0–80.0 vol %), and n‐alkane (n‐C₅ to n‐C₉) were all observed to influence asphaltenes deposition in the porous media, and reduced dispersion was obtained in the damaged packed‐bed by estimating dispersion coefficients and the Bodenstein number. Deposition by mechanical entrapment dominated the mechanism in all scenarios, as discovered by the simplified Kozeny–Carman and Civan's permeability‐porosity relationships. The results could aid in the design of remediations that minimize production losses of considerable economic magnitude. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3534–3546, 2014     

水合肼连续蒸发技术总结

介绍了一种尿素法生产水合肼的新工艺－连续蒸发技术,对利用该工艺的5kt/a水合肼生产装置进行了总结,指出该技术的主要优点是：蒸发过程连续、稳定,洗罐周期较长,解决了连续蒸发系统堵塞问题,盐、碱分别回收利用,实现氯碱生产中盐资源闭路大循环。另外,指出该工艺中需完善的主要问题在于氧化反应问题和多效蒸发问题。     

Discrete element reduced‐order modeling of dynamic particulate systems

One of the key technical challenges associated with modeling particulate processes is the ongoing need to develop efficient and accurate predictive models. Often the models that best represent solids handling processes, like discrete element method (DEM) models, are computationally expensive to evaluate. In this work, a reduced‐order modeling (ROM) methodology is proposed that can represent distributed parameter information, like particle velocity profiles, obtained from high‐fidelity (DEM) simulations in a more computationally efficient fashion. The proposed methodology uses principal component analysis (PCA) to reduce the dimensionality of the distributed parameter information, and response surface modeling to map the distributed parameter data to process operating parameters. This PCA‐based ROM approach has been used to model velocity trajectories in a continuous convective mixer, to demonstrate its applicability for pharmaceutical process modeling. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3184–3194, 2014     

动态膜分离式酶反应器连续操作运行方式评价与研究

应用动态膜分离技术开发研制的新型多功能酶反应器,实现了在进行酶解反应过程中同时分离产物的耦联操作。在该反应器上完成了使用菊粉酶、糖化酶等单基质酶不同操作形式的水解实验,考察了不同操作方式下反应器内流体流动的特性,并分别导出了停留时间分布函数式,从而对连续酶解过程的不同运行方式进行了对比性评价研究。     

Modeling granular material blending in a rotating drum using a finite element method and advection‐diffusion equation multiscale model

A multiscale model is presented for predicting the magnitude and rate of powder blending in a rotating drum blender. The model combines particle diffusion coefficient correlations from the literature with advective flow field information from blender finite element method simulations. The multiscale model predictions for overall mixing and local concentration variance closely match results from discrete element method (DEM) simulations for a rotating drum, but take only hours to compute as opposed to taking days of computation time for the DEM simulations. Parametric studies were performed using the multiscale model to investigate the influence of various parameters on mixing behavior. The multiscale model is expected to be more amenable to predicting mixing in complex geometries and scale more efficiently to industrial‐scale blenders than DEM simulations or analytical solutions. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3277–3292, 2018