Determination of coalescence kernels for high-shear granulation using DEM simulations

Discrete element method (DEM) modeling is used in parallel with a model for coalescence of deformable surface wet granules. This produces a method capable of predicting both collision rates and coalescence efficiencies for use in derivation of an overall coalescence kernel. These coalescence kernels can then be used in computationally efficient meso-scale models such as population balance equation (PBE) models. A soft-sphere DEM model using periodic boundary conditions and a unique boxing scheme was utilized to simulate particle flow inside a high-shear mixer. Analysis of the simulation results provided collision frequency, aggregation frequency, kinetic energy, coalescence efficiency and compaction rates for the granulation process. This information can be used to bridge the gap in multi-scale modeling of granulation processes between the micro-scale DEM/coalescence modeling approach and a meso-scale PBE modeling approach.     

Numerical simulation of the gas–liquid flow in a laboratory scale bubble column: Influence of bubble size distribution and non-drag forces

In the present work, a computational model based on an Eulerian–Eulerian approach was used for the simulation of the transient two-phase flow in a rectangular partially aerated bubble column. Superficial gas velocities (U_G) ranging from 0.24 to 2.30 cm/s were used throughout both the experiments and the simulations. The calculated results were verified by comparing them with experimental data including measurements of gas hold-up, plume oscillation period (POP) and Sauter mean bubble diameter. The study shows the effect of mesh refinement, time-step and physical model selection, the latter regarding the role of bubble size distribution and non-drag forces, on the computational results. According to the results presented here, the representation of bubble populations using multiple size groups (MUSIG model) instead of a single group improves the prediction of the experimental parameters under study. Additionally, the results obtained after including the virtual mass force term do not differ considerably from those obtained including only the drag force. On the contrary, as a consequence of introducing the lift force term into the model, the gas hold-up is overestimated and a non-symmetric bubble plume oscillation appears, a fact that is not experimentally observed.     

CFD simulation of bubble columns incorporating population balance modeling

A computational fluid dynamics (CFD)-code has been developed using finite volume method in Eulerian framework for the simulation of axisymmetric steady state flows in bubble columns. The population balance equation for bubble number density has been included in the CFD code. The fixed pivot method of Kumar and Ramkrishna [1996. On the solution of population balance equations by discretization—I. A fixed pivot technique. Chemical Engineering Science 51, 1311-1332] has been used to discretize the population balance equation. The turbulence in the liquid phase has been modeled by a k-ε model. The novel feature of the framework is that it includes the size-specific bubble velocities obtained by assuming mechanical equilibrium for each bubble and hence it is a generalized multi-fluid model. With appropriate closures for the drag and lift forces, it allows for different velocities for bubbles of different sizes and hence the proper spatial distributions of bubbles are predicted. Accordingly the proper distributions of gas hold-up, liquid circulation velocities and turbulence intensities in the column are predicted. A survey of the literature shows that the algebraic manipulations of either bubble coalescence or break-up rate were mainly guided by the need to obtain the equilibrium bubble size distributions in the column. The model of Prince and Blanch [1990. Bubble coalescence and break-up in air-sparged bubble columns. A.I.Ch.E. Journal 36, 1485-1499] is known to overpredict the bubble collision frequencies in bubble columns. It has been modified to incorporate the effect of gas phase dispersion number. The predictions of the model are in good agreement with the experimental data of Bhole et al. [2006. Laser Doppler anemometer measurements in bubble column: effect of sparger. Industrial & Engineering Chemistry Research 45, 9201-9207] obtained using Laser Doppler anemometry. Comparison of simulation results with the experimental measurements of Sanyal et al. [1999. Numerical simulation of gas-liquid dynamics in cylindrical bubble column reactors. Chemical Engineering Science 54, 5071-5083] and Olmos et al. [2001. Numerical simulation of multiphase flow in bubble column reactors: influence of bubble coalescence and breakup. Chemical Engineering Science 56, 6359-6365] also show a good agreement for liquid velocity and gas hold-up profiles.     

辛醇废碱液除油工艺研究

简要介绍了聚结除油工艺机理及研究进展,通过酸化破乳试验及聚结填料的优选试验,确定了聚结除油的最佳pH值、最佳填料及工艺条件。在此基础上进行了辛醇废碱液的聚结除油试验,结果表明,辛醇废碱液中C8以上有机相去除率高达80%以上,COD去除率可达50%左右,说明该工艺适合用于辛醇废碱液中C8以上有机相的去除。     

Electrostatic Attraction of Particles: The Implications of Field Theory on Coalescer Design

Abstract

A body of literature exists describing macro scale investigations with electrostatic coalescers based on DC, pulsed DC, and AC fields when applied to crude de-watering, de-salting, etc. Unfortunately, the push to very compact coalescers raises a requirement for detailed understanding of the fundamental physics of micro scale particle-particle attractions. Experience with frequency-controlled coalescer systems indicates a frequency dependency in the coalescence behaviour. (In-house data indicates a potential for increasing droplet growths by factors as high as four when comparing line frequency experiments to optimal frequency experiments.) The literature indicates that this variability may in-turn be related to particle (and coating) transport behaviour as well as electrophoretic separation of film macromolecules. The purpose of this work is to present the results of work aimed at reviewing and interpreting locally acquired data with respect to coalescence behaviour of real and model crude oils acquired using laboratory coalescer models.     

Investigations on the role of surfactants in mechanical emulsification using a high-pressure homogenizer with an orifice valve

The objective of the research work presented in this paper is to elucidate the role of surfactants during mechanical emulsification. To find out whether droplet disruption or stabilization, or both, are influenced by emulsifiers, the time for disruption and stabilization were calculated approximately. Recent developments in the institute have shown that elongational flow is the most efficient flow regime to produce emulsions with submicron droplets. Experiments, therefore, were carried out using a high-pressure homogenizer with an orifice valve. To illustrate the emulsification process the process was videotaped using a high-speed camera. Calculations for the experimental conditions investigated show that a large number of subsequent disruption steps can take place in the elongational flow. The surfactant is capable of adsorbing at newly formed droplets between subsequent disruption steps. Thus, the total disruption process can be facilitated by surfactants. Further, comparing adsorption time and residence time in the elongational flow shows that stabilization of newly formed droplets in the elongational flow is possible. The emulsification experiments show that between subsequent disruption steps the surface load is not balanced over the droplet’s surface. The results indicate that the adsorption process is governed by adsorption from the subsurface to the surface. The pictures obtained by videotaping support the results of calculations and emulsification experiments: droplet deformation with and without surfactant is not significantly different. If stabilization is poor, droplets recoalesce and the disruption result is reversed.     

Behaviour of an oil-in-water emulsion stabilized by β-lactoglobulin in an in vitro gastric model

The behaviour of β-lactoglobulin (β-lg)-stabilized emulsions (1.0 wt% protein and 20.0 wt% soy oil) using pepsin digestion under simulated gastric conditions (37 °C, pH 1.2 and 34 mM NaCl ionic strength, with continuous shaking at approximately 95 rev/min for 2 h) was investigated. Changes in particle size, ζ-potential and microstructure were monitored as a function of incubation time in the gastric fluid. Initially, β-lg formed a stable anionic emulsion at pH 7, but the emulsion underwent extensive droplet flocculation, with some coalescence, on mixing with the simulated gastric fluid. The ζ-potential values gradually changed from −57.1 ± 0.5 mV to +17.6 ± 1.2 mV because of pH change and peptic hydrolysis of the interfacial layer. Native β-lg was largely resistant to pepsin attack but, when β-lg was present at the interfacial layer of the oil-in-water emulsion, it was rapidly hydrolysed by pepsin, as shown by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The droplet flocculation and the coalescence observed during hydrolysis were markedly dependent on the digestion time.     

Bubble coalescence efficiency near multi-orifice plate

Bubble coalescence reduces specific area and weakens the work performance of bubble column. The bubble coalescence near gas sparger which is caused mainly by bubble growing is different from the ones occurring in major liquid. Bubble coalescence efficiency near gas sparger is influenced by many factors including sparger configuration, gas flow rate, bubble deformation, solution composition, etc. This work has conducted a set of visual experiments to study the coalescence characteristics near multi-orifice plate. The experiment parameters cover a wide range of conditions including large scope of gas flow rate,different kinds of solution and orifice configurations. The experimental results suggest that coalescence time is applicable to reflect the influence of the pitch of orifices and gas flow rate on bubble coalescence efficiency. As the number of orifices increases, bubble coalescence efficiency is reduced by the disturbance from the bubbles at adjacent orifices. A hindering coefficient is used to consider the hindering effect of additives on bubble coalescence efficiency. Finally a new calculation expression is established to predict bubble coalescence efficiency near multi-orifice plate whose fundamental form is based on the logistic curve of binary response. The calculated values that refer to this calculation expression are well consistent with the experimental results.     

Coalescence Deformation of Bubble Pairs Generated from Twin Nozzles in CMC Solutions

A coupled level‐set/volume‐of‐fluid method, under the consideration of the rheological characteristics of a fluid, is employed to investigate numerical coalescence deformation of bubble pairs generated at two adjacent nozzles in carboxymethyl cellulose aqueous solutions. The satisfactory agreement between numerical results and experimental measurements proves the validity of this approach in predicting the surface evolution of bubbles. Simulated results show that the bubble coalescence process involves four stages of independent growth, rapid mergence, radial expansion, and vertical stretching. The various effects of surfactant concentration, gas flow rate, nozzle spacing, and nozzle diameter on the aspect ratio depend greatly on each coalescence period.     

Drying behavior of acrylic latexes

The drying behavior of a series of monodisperse acrylate-based emulsion polymers was studied with respect to two existing drying models. The latexes were all film forming poly(methyl methacrylate-co-butyl acrylate)-based materials, having different polymer morphologies. Crosslinks were introduced via the addition of ethylene glycol dimethacrylate comonomer to the emulsion synthesis, while the molecular weight was reduced by addition of CBr₄ chain transfer agent. Weight loss experiments showed no discernible differences in the drying behavior of the various latexes, but environmental scanning electron microscopy (ESEM) indicated marked differences. It was found that a percolation model developed by Croll describes the drying process well. However, certain experimental observations were not consistent with theory. ESEM revealed that the most ‘fusible’ of the latexes formed a skin during drying, prior to the complete evaporation of the water. It was postulated that the skin remained sufficiently porous to allow unhindered water flux.