Sharpness Of Separation Research Articles

Linking separation sharpness with the characteristics of axial velocity wave zone in a hydrocyclone

Maximizing separation sharpness is critical for the design and operation of hydrocyclones but remains difficult to achieve. This work presents a numerical study on the relationship between separation performance and the characteristics of axial velocity wave zone to understand the reasons for the limited separation sharpness. The results showed that this zone is featured as an inherent transition region, with extensive secondary vortices formed between inner and outer spiral flows. The presence of this zone adversely affects the fluid-solid momentum transfer, causing prolonged residence time and accumulation of intermediate-sized particles. The separation sharpness shows a strong dependence on the characteristics of axial velocity wave zone, which are further controlled by geometric parameters. Increasing the symmetry of flow field and optimizing the spatial distribution of this zone can help increase the separation sharpness while its size shows little effect.

Experimental investigation of the grade efficiency of a zigzag separator

An experimental study is conducted on a pilot-scale zigzag air separator (ZZS) to study the effects of varying the solid feed mass stream, the mean channel air velocity, and the number of channel segments onto the grade efficiency. Spherical glass beads are classified. A straight pipe separator model (PSM) is modified for the ZZS and fitted to the experimental data to estimate the relative cut-point settling velocity, the separation sharpness, the relative rise velocity, the diffusion coefficient, and the particle loading. The proposed model is thoroughly investigated with regard to all important parameters, e.g. the estimated particle loading is shown to be more precise than the ratio of the solid and air mass stream, used in many publications. Finally, the relative rise velocity is shown to be only a function of the particle loading, making the experimental results within the model collapse.

Study on interaction effects between the hydrocyclone feed flow rate and the feed size distribution

Interactive effects between feed flow rate and feed size distribution (FSD) are numerically investigated. The results show that, for too large or too small feed flow rate, when the FSD increases, the content of solid particles misplaced to the overflow or underflow increases, leading to a decrease in separation sharpness. These results can be explained by the multiphase flow pattern and solid particle spatial distribution. What's more, when the feed flow rate too small, the differences between the equilibrium radiuses of different sized particles are small, resulting in low separation sharpness. When the feed flow rate is too large, the regular distribution of different sized particles in the radial direction is severely destroyed. Based on the results from this study, in order to achieve the desired separation performance and the precise particle separation, it is recommended to adapt to changes in the FSD by appropriately increasing the feed flow rate.

Development of separation sharpness model for hydrocyclone

Abstract Hydrocyclones are mechanical devices used in classifying and separating many different types of materials. A classification function of the hydrocyclone has been continually developed for solid–liquid separation. In the classification process of solids from liquids, it is desirable to reduce the amount of misplaced material; therefore, the separation sharpness, α (alpha), is a parameter that helps in evaluating misplaced material and has been developed as a model to help the designer predict the performance of the classification. However, the problem with the separation sharpness model is that it cannot be used outside the range of conditions under which it was developed. Therefore, this research aimed to develop the separation sharpness model to predict more accurately and cover a wide range of conditions using the multiple linear regression method. The new regression model of separation sharpness was based on a wide range of both experimental and industrial data-sets of 431 tests collaborating with the additional experiments of 117 tests that were obtained from a total of 548 tests. The new model of separation sharpness can be used in the range of 30–762 mm hydrocyclone body diameters and feed solid concentrations in the range of 0.5wt%–80 wt%. When compared with the experimental separation sharpness, the accuracy of the separation sharpness model prediction has an error of 4.53% and R2 of 0.973.

Size fractionation of magnetic nanoparticles by magnetic chromatography

Magnetic chromatography is a promising method for fractionation of magnetic nanoparticles with respect to their size and/or magnetic properties. In this study, we investigate the effect of different magnetic field sources and operation modes on the retention of magnetic nanoparticles which pass through a chromatographic column filled with a fine magnetizable matrix. For nanoparticles in the size range between 50 and 400 nm, both constant magnetic fields and square wave AC fields with amplitudes of around 2 mT, result in retention factors of up to 2, while still showing good particle recoveries of more than 95%. In contrast, when using the ‘on-off’ magnetic field operation reported previously, retention factors of only 1.4 could be achieved. We also demonstrate that single domain magnetic nanoparticles show retention factors of 1.2–1.4 even without the application of an external magnetic field, due to their spontaneous magnetization. By using a combination of online UV-measurement and sample collection followed by the determination of the particle size distribution (PSD) by dynamic light scattering, a quantification of the fractionation efficiency could be achieved. Despite the short column of only 12 cm and the high specific throughput of more than 30 column volumes per hour a separation sharpness of 0.62 could be attained, demonstrating the high potential of the method for scalable nanoparticle fractionation.

A Detailed study of Applying Gravity Separation to Lead and Zinc Carbonate Ore for Smithsonite Concentration Using DMC

ABSTRACT Gravity separation of a low-grade lead and zinc carbonate ore (case study: Angouran mine, Zanjan, Iran) was investigated based on detailed laboratory and modeling studies. The authors used two types of laboratory sink-float evaluations with single density and multiple densities to demonstrate the effectiveness of Dense Medium Cyclone (DMC) as a new application to separate lead and zinc minerals, in particular, zinc carbonate (Smithsonite) from silica and limestone gangue. The laboratory tests included determining floats from five to six density intervals that descended between the densities of the light and heavy minerals. In addition, the authors used MODSIMTM process simulation software to determine the optimum separating density, zinc grade of concentrate and tailings products, yield and metal recovery. The results showed the possibility of successful gravity separation of the ore. To optimize DMC gravity separation operation in the plant, the circuit was sampled and the effect of important parameters influencing separation performance was studied. The separation efficiency (sharpness) and plant performance to separate valuable minerals were determined by estimating the partition curve for the particle size distribution limited to 0.5–5.6 mm range. The performance indicating parameters including the short circuit fractions to sinks and floats, the separation sharpness and the separating density were estimated to be equal to 0.0116, 1.5885, 20.4 and 3.18, respectively, using the non-linear optimization tool of Excel (Solver) based on least squares method.

Numerical analysis of flow field and separation characteristics in hydrocyclones with adjustable apex

In the present study, we proposed an adjustable apex structure to achieve the goal of online adjustment of the apex diameter of a hydrocyclone. And a computational fluid dynamics (CFD)-based numerical simulation was conducted to study the internal flow field and the separation characteristics of an adjustable apex hydrocyclone. The results show that for the hydrocyclone with the conventional apex, the total pressure drop gradually increases as the diameter of the apex decreases, but it exhibits a general downward tendency after the insertion of the adjustable cone. In addition, the tangential velocity of the adjustable apex hydrocyclone is greater than that of the conventional hydrocyclone in the forced vortex region and smaller in the free vortex region. Moreover, the insertion of the adjustable cone to the conventional apex can increase the total separation efficiency of the hydrocyclone by up to 15.81% without a significant change in the separation sharpness.

Classification performance of semi-inverted hydrocyclones

Researchers have reported in the past that inclined hydrocyclone operation can provide a lower water split to underflow and much coarser cut sizes. However, semi-inverted hydrocyclones (inclined higher than the horizontal position) have not been investigated in detail. This paper presents the results of a comprehensive study that was carried out at the Julius Kruttschnitt Mineral Research Centre (JKMRC) using a semi-inverted (SIV) hydrocyclone. A 250 mm hydrocyclone was tested with a modified cone. The modified cone extended the operational range of the hydrocyclone. The SIV hydrocyclone was tested at different inclinations and operating feed pressure using three different slurry feeds. A significant reduction in the water split (WS) to coarse was achieved at semi-inverted positions. WS values of 3–5% at 135° inclination were achieved. The change in WS did not influence the sharpness of separation (α). Stable operation and sharpness of separation were achieved, despite the appearance of roping-like underflow discharge in semi-inverted operation.

Effects of underflow orifice diameter on the hydrocyclone separation performance with different feed size distributions

The interaction effect between feed size distribution (FSD) and underflow orifice diameter (Du) is crucial for the adjustment of the hydrocyclone in plant but not clearly understood. This paper presents a numerical study on effects of FSD on separation performances of hydrocyclones at a wide range of Du. The numerical results show that both small or large Du will cause numerous particles being misplaced to the overflow or underflow products, resulting in poor separation performance. These results can be well explained using the predicted water flow pattern and particle distribution. Moreover, there are intense interaction effects between the Du and the FSD. It is pointed out that for an extremely small Du, the cut size explodes, and the separation efficiency and separation sharpness deteriorate rapidly with the increase of feed median size (d0.5). These behaviors are mainly due to the increase in the coarse particle content as d0.5 increases, resulting in an increase in the extent of particle accumulation near the spigot. Such accumulation causes a decrease in the tangential velocity and a break in the air core, which in turn leads to a decrease in the flow field stability. Thereby, regular distribution of the particle equilibrium radius along the radial direction is destroyed. As Du increases, the separation performance of the hydrocyclone is no longer affected by fluctuations in the FSD. Based on results from this study, it is recommended a moderate increase in Du is competent to mitigate the adverse effects caused by fluctuations in the FSD, to achieve the expected cut size, and relatively high separation precise for particles.

Study of Underflow Diameter, Vortex Finder, Cylindrical and Conical Lengths of a Hydrocyclone to Achieve High Separation Sharpness

In the past, the main function of a hydrocyclone was to separate solids from a liquid. At a later time, it has been continually developed for classification functions in addition to separation. Therefore, this research aimed to study experimentally the effects of underflow diameter, vortex finder, cylindrical and conical lengths of a hydrocyclone on separation sharpness. The separation sharpness was studied using a 40-mm hydrocyclone body diameter. The tested suspension was a mixture of silica and water. The silica particles have a mean diameter of 8.097 µm at a feed-flow rate of 1 m3/h. The experimental result revealed that an increase in the separation sharpness resulted from either increasing vortex finder or conical length of the hydrocyclone, either decreasing underflow diameter or cylindrical length. To increase the separation sharpness of the 40-mm hydrocyclone, the designer should consider the hydrocyclone dimensions by choosing an underflow diameter of 2.4 mm, vortex finder length of 40 mm, cylindrical length of 60 mm and conical length of 280 mm.

Design boundary layer structure for improving the particle separation performance of a hydrocyclone

This study aims to address the problem of fine particle entrainment in the underflow of a hydrocyclone. To improve the separation performance of hydrocyclones, we investigated the effect of the boundary layer structure. Several completely cylindrical structures were developed based on the conventional cylindrical-conical structure. By modifying the bottom structure of the completely cylindrical hydrocyclones, the entrainment of fine particles can be reduced, and the separation sharpness can be improved. Ultimately, a W-shaped apex was proposed. A computational fluid dynamics (CFD)-based numerical simulation was conducted to compare the performance of different hydrocyclone structures. The variations of the pressure field, velocity field, air-core shape, density field, and separation performance were investigated, and the results were compared with classical experimental data to verify the accuracy of the numerical simulations. The results show that the total pressure drops and the radial pressure gradients in type B (with a cylindrical section), type C (with a 3° gradient cylindrical section), and type E (with a W-shaped apex) hydrocyclones are lower than those in the type A (a conventional cylindrical-conical-shaped hydrocyclone), which is beneficial for reducing the energy loss and increasing the throughput. In the completely cylindrical hydrocyclones, the axial velocity is reduced, and the residence time of the particles is prolonged, which facilitates the sufficient separation of the particles. In addition, a high-density suspension layer forms near the apex in the completely cylindrical hydrocyclones. This suspension layer causes elutriation and hence reduces the entrainment of fine particles in the underflow. In the completely cylindrical hydrocyclones, the recovery rate and entrainment of fine particles in the underflow are reduced, and the separation sharpness is improved. The type E hydrocyclone has the least entrainment of fine particles and has a separation sharpness that is between those of type A and types B, C, and D (with a 3° gradient cylindrical section and a 150° sloping bottom).

Ultrafine desliming using a REFLUX™ classifier subjected to centrifugal G forces

Ultrafine desliming of a silica feed, covering the particle size range of 0–100 µm, was investigated using a pair of 171 mm × 178 mm cross-section REFLUXTM Classifier modules subjected to 55 G force in a spinning centrifuge. The modules consisted of a system of inclined channels, with perpendicular spacing of 1 mm, formed through 3D printing, attached to a fluidized bed housing. This centrifugal system is termed the REFLUXTM Graviton. The feed was varied from 36 to 115 L/min with concentrations from 2 to 30 wt% solids. Continuous steady state separations at cut sizes from 20 μm down to 5 μm and Ep values of 3–6 μm were routinely achieved. The hydrodynamic benefits of the so-called inclined settling effect multiplied with the hydrodynamic benefits of centrifugal forces, resulting in better than 1000-fold throughput advantage over conventional settling. The partition curves exhibited a strong “fish-hook” effect influenced by both the fluidisation velocity and the underflow-exit tube diameter. The diameter of the tube also had a significant effect on the sharpness of the separation. When the tube was undersized, the excess solids partitioned into the overflow resulting in poorer sharpness of separation. Conversely, when the tube was oversized, some material that should have exited in the overflow instead bypassed to the underflow. Experiments also found an optimum fluidisation velocity, below which inadequate fluidisation resulted in excessive fine particles exiting in the underflow and above which the sharpness of separation deteriorated due to excessive mixing.

Numerical analysis of the flow field and separation performance in hydrocyclones with different vortex finder wall thickness

High separation sharpness of hydrocyclones is an ultimate goal for the classification process and has attracted considerable attention. The existence of some special flow patterns, such as short-circuit flow and circulation flow, play an important role in the separation process and have not been clearly understood. This paper presents a numerical study of the effects of vortex finder wall thickness on the flow field and separation performance. More importantly, the formations and effects of short-circuit flow, circulation flow, and axial velocity wave zone (AVWZ) were investigated and understood. The simulation results were analyzed in terms of pressure drop, water velocity, separation efficiency, and particle distribution. The results indicate that a thicker vortex finder wall could reduce pressure drop, tangential velocity magnitudes, and the flow rates of both short-circuit flow and circulation flow but increase the fluctuations of axial and radial velocities especially beneath the vortex finder where the AVWZ is formed. The leakage effect of short-circuit flow on sub-coarse particles is less significant than the fluctuation effect of AVWZ. The circulation flow in pre-separation space is beneficial to re-separate the sub-fine and sub-coarse particles to improve the separation sharpness. Consequently, the hydrocyclone with a thin-walled vortex finder is more beneficial for efficient classification.

Prediction of separation performance of hydrocyclones by a PC-based model

The separation performance of hydrocyclone is affected by many variables, the values of which have to be selected carefully for achieving the optimal design and operation of such a separator. This selection can be done by either empirical or numerical model. The empirical model provides convenience for industrial use by simply correlating cyclone performance indicators with variables under specific conditions. The numerical approach is more general and often performs well in explaining the underlying fundamentals of hydrocyclone operations, though it can also predict the unit performance at the cost of much longer computation time. In this work, an empirical prediction model is developed based on the extensive numerical results acquired by Computational Fluid Dynamics (CFD). This model covers a broad range of conditions. In particular, for the first time, it systematically considers the effects of material density and feed solid concentration at different hydrocyclone geometries. The validity of the model is confirmed by the reasonable agreement between the predicted and measured results in terms of cut size, separation sharpness, pressure drop, and water split. The comparison of the model with others in predicting performance indicators and partition numbers against the measurements shows that the new model is more accurate over the ranges of the variables considered.

INCREASING THE EFFECTIVENESS OF STABILIZATION COLUMNS IN THE OIL AND GAS INDUSTRY

According to the results of the study, we found that increasing the pressure in a stabilization column improves the sharpness of separation of butanes from pentanes. As a result, the product quality is getting better. The pilot-industrial runs confirm the possibility of improving the effectiveness of the stabilization columns in various processes by increasing the pressure within the permissible limits.

An overview of operating parameters and conditions in hydrocyclones for enhanced separations

Abstract Hydrocyclones are widely employed in both heavy and light industries. However, exact mechanisms underlying enhanced-separation technologies developed by optimizing operating parameters and conditions in hydrocyclones remain unclear. Accordingly, many research groups have conducted numerous investigations to expand the application range of hydrocyclones by optimizing operating parameters and conditions. This paper presents a comprehensive state-of-the-art review of the aforementioned hydrocyclone enhanced-separation technologies, which are classified into two groups: (i) operating parameters, including feed flow rate, feed pressure, feed density difference, feed particle parameters (concentration, size, shape, and arrangement), and feed fluid parameters (viscosity and rheology); and (ii) operating conditions, including electrical hydrocyclones, magnetic hydrocyclones (electromagnetic field and permanent magnetic field), magnetic fluids hydrocyclones, electrochemical hydrocyclones, flocculant-assisted hydrocyclones, hydrocyclones enhanced by flotation, hydrocyclones enhanced by control particles; hydrocyclones enhanced by adjusting back pressure, and hydrocyclones enhanced by monitoring and automatic control. These enhanced-separation technologies were analyzed and summarized based on the critical separation-performance parameters, such as separation efficiency, cut size, split ratio, energy consumption, capacity, and separation sharpness. It is hoped that both reviewed contents and proposed challenges may be helpful to the researchers and eventually yield some perspective knowledge, which results in the improvement of economic feasibility of separation by hydrocyclones.

Effects of feed size distribution on separation performance of hydrocyclones with different vortex finder diameters

Interactions between feed size distribution and separation performance for hydrocyclones with different vortex finder diameters (Do) are crucial for hydrocyclone designs but not clearly understood. In this work, the optimum range of Do is numerically confirmed for a 50mm diameter hydrocyclone using computational fluid dynamics. Furthermore, effects of feed size distribution (FSD) on separation performance for hydrocyclones with different Do are discussed. For a given FSD, the lower limit of Do can be determined from the flow stability characterized by lower turbulence intensity and larger tangential velocity. Below the lower limit, a large proportion of fine particles report to the underflow. The upper limit can be determined from separation performance. Above the upper limit recovery to the underflow for coarse particles decreases drastically, which is caused by an outward shift of the locus of zero vertical velocity (LZVV) and an inward shift of particles equilibrium radius. For a given Do, FSD has no significant effects on partition curves when Do is in the optimum range. When Do is above the optimum range, both recovery to underflow for coarse particles and separation sharpness are decreased as the feed median size increases. In summary, when Do is in the optimum range, the hydrocyclone can adapt to different FSD to obtain the expected cut size by self-adjusting the LZVV and particles equilibrium radius. This method for determining the optimum range of Do is based on flow pattern characteristics and can be used as a universal tool for hydrocyclone design.

Model-based experimental data evaluation of separation efficiency of multistage coarse particle classification in a zigzag apparatus

In most industrial processes dealing with particles, separation of fine (or light) and coarse (or heavy) particles in a fluid flow is an essential part to obtain the required product quality. These separation processes are typically designed based on the particles' terminal settling velocity as the dominant property. In this work, sand and gravel have been selected as suitable model grains representing mineral and agricultural raw materials and products. The terminal settling velocity depends on stochastically distributed physical and granulometric particle properties like size, density, and shape. Separation experiments in a pilot-scale zigzag separator have been performed using different channel velocities and solid mass loadings in order to improve the understanding of the separation process in this complex turbulent flow. Then, classification has been modeled as a multistage cross-flow separation process in a turbulent air flow. Performance has been analyzed and discussed with respect to separation functions and characteristic parameters like cut size, separation sharpness, separation stage utilization, and product quality, quantified by cumulative product purities of over- and underflow as well as specific energy consumption. Finally, a SMART analysis has been used to identify optimal process parameters. The obtained cut sizes differ significantly from those found in literature. Thus, a more detailed analysis accounting for aerodynamics and turbulence is developed to show the significant influence of channel geometry on separation efficiency.

Design of a new double layer spreading plate for a turbo air classifier

In order to improve the material dispersion and reduce the probability of collision and aggregation of particles in a turbo air classifier, compared to a single layer spreading plate, a new double layer spreading plate based on theoretical analysis on the material dispersion is presented in this paper. Discrete phase simulations between the single and double layer spreading plates are implemented using Fluent 6.3.26. The different travelling time of particles via the upper and lower plates indicates the double layer spreading plate can improve the material dispersion and the simulated Tromp curves of the single and double spreading plates also show the cut size and the imperfection are decreased while the sharpness of separation is increased for the turbo air classifier with the double layer spreading plate. Calcium carbonate classification experimental results are in agreement with the simulated results. Compared to single layer spreading plate, the cut size can be decreased up to 25.24% and the sharpness of separation can be increased up to 52.47% for double layer spreading plate, and the imperfection of Tromp curve for double layer spreading plate is smaller that means it closer to the ideal classification curve. It shows the double layer spreading plate put forward in this paper can effectively improve the material dispersion in the classifiers.

Numerical simulation of industrial hydrocyclones performance: Role of turbulence modelling

Abstract Flow in industrial hydrocyclones is always turbulent, selection of suitable turbulence model is key for accurate predictions. This paper aims to find the appropriate turbulence model for the hydrodynamic predictions in industrial hydrocyclones. Two-phase and multiphase simulations are conducted in various size industrial hydrocyclones using volume of fluid and modified mixture models coupled with Reynolds Stress Model (RSM), Detached Eddy Simulation and Large Eddy Simulation (LES) turbulence models. Assessment of turbulence model effect on two phase flow field is made with respect to air-core, flow split, mean and turbulent velocities. The simulated flow field in 75 and 250 mm hydrocyclones is validated against literature based Laser Doppler Velocimetry, in-house high speed video and Electrical Resistance Tomography measurements. Mean density segregation contours and radial density profiles variation at different axial positions in a 350 mm dense medium cyclone is compared against Gamma Ray Tomography data. Turbulent intensity profiles are compared to display the turbulence levels. Further turbulence effect on the particles in various size hydrocyclones is analyzed by dispersion index formulation. Multiphase flow predictions in 75 and 250 mm hydrocyclones with RSM and LES models are compared against classical experimental classification performance in terms of cut size and sharpness of separation.