CFD validation for flyash particle classification in hydrocyclones (original) (raw)

Hydrocyclones are getting more and more interest from various industries. They are widely used to separate particulates from liquid at high throughput because of their advantages like simple structure, low cost, large capacity and small volume, require little way of maintenance and support structure. Modeling of complex and multiphase flow behavior inside the hydrocyclone is done usually with the help of computational fluid dynamic study. Current study involves experimental investigation of separation performance characteristics of the hydrocyclone using new design parameters. For experimental purpose, a new hydrocyclone was designed with insertion of solid rod, at central portion of conical section of hydrocyclone, inside the hydrocyclone . By which air core could be eliminated effectively and hydrocyclone performance is improved. This effect may be observed due to reduction of radial and axial components of velocity and turbulence in the area near the entrance of the vortex finder. Therefore, the flow field characteristics inside the hydrocyclone with no air core become more suitable for separation. Also the effect of flow rate, vortex finder depths, air core and particle interaction were studied experimentally. A new arrangement was suggested to eliminate the air core formed inside the hydrocyclone. In this case, effect of diameter and height of solid rod inserted inside the hydrocyclone with changing total inlet flow rate was studied experimentally. Three-dimensional geometry and meshing of hydrocyclone is created in Gambit, preprocessor of commercial software—Fluent, for hydrodynamic study.

Effectiveness and efficiency of hydro-cyclone separators are highly dependent on their geometrical parameters and flow characteristics. Performance of the hydro-cyclone can, therefore, be improved by modifying the geometrical parameters or flow characteristics. The mining and chemical industries are faced with problems of separating ore-rich stones from the nonore-rich stones. Due to this problem a certain amount of precious metals is lost to the dumping sites. Plant managers try to solve these problems by stockpiling what could be useless stones, so that they can be reprocessed in the future. Reprocessing is not a sustainable approach, because the reprocessed material would give lower yield as compared to the production costs. Particulate separation in a hydro-cyclone has been investigated in this paper, by using computational fluid dynamics. The paper investigated the influence of various flow and geometric parameters on particulate separation. Optimal parameters for efficient sep...

Common applications of hydrocyclone include classification, thickening, de-sliming and de-gritting. In all the operations cyclone separators usually operate under high solid loading conditions. Computational Fluid Dynamic (CFD) models developed so far are unable to predict the behaviour at high percentage of solids. Therefore, present paper aimed to develop CFD model corrected with suitable rheological model, particle drag and lift forces to account particle fluid interactions at high volume fractions. Turbulence is resolved using large eddy simulation. Drag is corrected with solids loading; rheology is modelled using Newtonian model corrected with fines. CFD predicted two-phase water split and air-core data is validated against Electrical Resistance Tomography (ERT) and High Speed Video camera (HSV) measured data. The influence of feed solids on the air core size also investigated. Multiphase simulations ran with 0-50% feed solid loadings are analyzed and validated in terms of cut size and efficiency. Modified CFD model is able to predict the data with reasonable accuracy. Turbulent dispersion index is also calculated to quantify the dispersion effect on the particles. Additional validation in terms of cut size in 250 mm Krebs cyclone (Devullapalli, 1997) is also provided in comparison with discrete phase model and pure mixture model.

"A critical assessment is presented for the existing numerical models used for the performance prediction of hydrocyclones. As the present discussion indicates, the flow inside a hydrocyclone is quite complex and there have been numerous numerical studies on the flows and the particle motions in hydrocyclone, with a wide range of turbulence and multiphase models tested. Two-equation k-epsilon and RNG k-epsilon models flow velocities with empirical modifications were led to poor results, especially the tangential components in comparison with experimental measurements. Most of the recent studies have utilized the Reynolds stress models (RSM) with different degrees of complexity in the pressure-strain correlation. These RSM studies showed good agreements with velocity measurements. Unfortunately, the velocity profiles were not validated in most of the RSM cases where multiphase particle tracking were applied. Finally, large eddy simulation (LES) is the most advanced turbulence model applied in recent hydrocyclone numeric studies. Besides the additional information on precising the air core correctly, LES provides an additional accuracy in predicting the velocity profiles or the grade efficiency in comparison to the RSM. The multiphase models have been successfully applied in a hydrocyclone to model the Lagranizian motions of spherical particles. Eulerian-Eulerian model have been used to account for the particles effect on the fluid viscosity. Simplified Eulerian model (mixture) model predictions for solid transportation in cyclone were well predicted. Further, the inclusion of modified slip velocity calculation in the Mixture model improves the efficiency predictions close to the experimental data at low feed solid loadings. In future studies, the focus should be to model the three-dimensional flow in a hydrocyclone using at least the Reynolds stress model/LES. The particle tracking should at least include the effects of the turbulence on the particles. All these developed models will only applicable to low feed solid concentration levels. Since most of these models neglect the particle-particle interactions, a more comprehensive numerical method of modified Mixture model is applied for simulating solids flow in hydrocyclones for high feed solids concentration. Explicit models for accounting hindered settling and turbulent diffusion investigated for high feed solid concentrations in industrial cyclones are encouraging." Keywords: hydrocyclone; multi-phase modelling; computational fluid dynamics; classification; turbulence; viscosity

Cyclone separators have exist since the 1800's and are still widely used in many industries. Although hydrocyclone are geometrically simple, the physics describing the flow and separation processes which occur in them is complex. Over the decades many researchers have studied these devises and have developed a number of theories and empirical models for design purposes. In practice, most cyclones are design using some type of empirical information. Physical prototypes are then built, tested and tuned until an acceptable level of performance is obtained. Recent advancement in numerical methods and in the performance capabilities of moderately priced computers have opened the possibility of developing computer-based methods, which can be effectively used for hydrocyclone design study. This is where this project play part, a study of multiphase flow in hydrocyclone with different configuration of parameters are manipulate using computer model will be proposed. In this model, the mi...