Entrainment Of Fine Particles Research Articles

Facet-Dependent Charge Density of Serpentine: Nanoscopic Implications for Aggregation and Entrainment of Fine Particles.

Deciphering the facet-dependent surface properties of clay minerals holds vital significance in both fundamental research and practical engineering applications. To date, the anisotropic local charge density of serpentine surfaces still remains elusive, and thus, the interaction energies and associated aggregate structures between different crystal planes of serpentine cannot be quantitatively determined. In this work, different crystal planes of serpentine (i.e., SiO basal, MgOH basal, and edge) were selectively exposed, and their surface potentials and charge densities were determined using atomic force microscopy (AFM) force measurements coupled with Derjaguin-Landau-Verwey-Overbeek (DLVO) theory fitting. The SiO and edge planes consistently exhibited a permanently negative surface charge, whereas the point of zero charge (PZC) on the MgOH plane was estimated to be pH 9.0-11.0. Based on the interaction energy calculation between different serpentine planes, the aggregation structures of serpentine were predicted. Combined with scanning electron microscopy observation of freeze-dried samples, SiO-MgOH and MgOH-edge associations were found to dominate the aggregate structures at pH ≤ 9.0, thereby resulting in a stacking or "card-houses" structures. In contrast, all of the plane associations exhibited the repulsive interaction energy at pH 11.0, which led to a completely dispersed system, ultimately causing the most severe fine particle entrainment during froth flotation. Our work provides quantitative clarification of facet-dependent surface properties and aggregate structures of serpentine under different pH conditions, which will help improve the fundamental understanding of colloidal behaviors of clay minerals.

Clogging and permeability reduction dynamics in porous media: A numerical simulation study

The dynamics of fine particle entrainment, transport, and deposition within pore systems, and in particular, the capacity for mobile fines to impair permeability within porous media is critical in many industrial applications. Considerable effort has been expended over the past several decades to identify and parametrize the governing factors that control permeability reduction, with studies employing a combination of physical experimentation and numerical simulation toward this aim. The objective of this work was to numerically investigate the impact of pore space geometry and fine sizes on the clogging dynamics of porous media. The clogging dynamics were characterized by the length of clogging zone (LCZ), the critical throat size of clogging (CTZC), the clogged fraction of throats (CFT), and the permeability reduction (PR). We implemented a computational fluid dynamics-discrete element method (CFD-DEM) numerical framework with a four-way coupling scheme to obtain insights into throat clogging and permeability reduction within heterogeneous porous media utilizing four different monodisperse suspensions. Geometries of porous media were extracted from 3D images of sand packs obtained using micro-computed tomography. The geometries had porosity values ranging from 0.35 to 0.57 and initial permeabilities between 1.35 and 26.32 μm2. CFD-DEM simulations were performed on each geometry four times, varying the injected fine particle size from 5 to 15 μm diameters. Findings indicate that pore systems with tortuosity <1.28 and angles of solid grains orientation larger than 46o tend to have shorter length clogging zones and greater permeability reduction. Furthermore, although systems with porosities higher than 0.48 tend to have a relatively high clogged fraction of throats, they undergo lower permeability reduction. It was also observed that within the studied pore systems, injection of fine particles larger than 7 μm into systems with aspect ratios higher than 2.5, results in a lower fraction of clogged throats. Additionally, for the studied pore networks,< 7 μm fine particles injected into porous media with a large pore body (> 66 μm) and throat (> 22 μm) radii tended to result in larger clogging zones and a greater critical throat size of clogging.

Effects of bottom profile on the circulation and classification of particles in cylindrical hydrocyclones

The cylindrical hydrocyclone has been increasingly used in coarse classification due to its reduced fine particle entrainment, but the loss of coarse particles to overflow remains an intractable problem. Based on the notion that the strong circulation flow caused by the flat bottom structure bears primary responsibility for the problem, this study designs eight unique bottom profiles to regulate the particle circulating flow and attempts to correlate particle circulation flow with classification performance. The effects of the bottom profile on flow field characteristics, particle spatial distribution, circulation flow rates, and grade efficiency are explored in detail using validated models in a Φ200 mm cylindrical hydrocyclone. The findings suggest that bottom profiles have the greatest effect on the axial velocity near the bottom and the grade efficiency of intermediate and coarse particles, while all unique designs have the potential to lower turbulence intensity. An ascending segment near the wall or a descending segment near the axis can help to mitigate the misplacement of coarse particles by reducing particle circulation flow without affecting the entrainment of fines appreciably. Additionally, two circles are found on each side of the cut plane, which is conducive to releasing coarse particles from the circulation flow. Regulation of particle circulation flow by adjusting bottom profile parameters can improve separation performance.

Study on the Application of a Reflux Classifier in the Classification of Ultrafine Ilmenite

Mineral classification is an important preparation operation in the process of beneficiation. The classification effect directly affects the production capacity of grinding machines, product quality, subsequent separation of the concentrate grade, and recovery. To improve mineral classification accuracy and provide technical ideas for enriching the separation of fine materials, this paper proposes the use of a trapezoidal inclined channel agitated reflux classifier (TARC) to classify ultra-fine ilmenite. The principle of this separating system is based on a hindered settling effect and fluidization theory. This study focuses on the factors influencing the particle separation through the optimization of different experimental conditions. A satisfactory 10 µm classification efficiency of 67.89% could be obtained when the ore pulp concentration was 15%, the agitation speed was 350 r/min, and the underflow flux was 16 cm3/min. The TARC realized a continuous feeding classification of fine particles within a narrow particle size range, with 10 µm as the limit size, and an effective reduction in the entrainment of fine particles in the underflow and coarse particles in the overflow phenomena, thus achieving improved classification efficiency.

Experimental study of the separation performance of a hydrocyclone with a compound curve cone

The entrainment of fine particles in the underflow and coarse particles in the overflow is a well-known problem in separation using a conventional cylindrical–conical hydrocyclone that reduces the separation accuracy and efficiency. To address this problem, this paper presents a hydrocyclone equipped with a compound curved cone (the CCC hydrocyclone). The CCC hydrocyclone was experimentally compared with a hydrocyclone with a conventional straight cone (the CSC hydrocyclone) in terms of five separation performance metrics, namely, the split ratio, total separation efficiency, concentration and particle size of the products, and grade efficiency. To provide further guidance on the application of the CCC hydrocyclone in real-world production, the effects of three process parameters—the underflow apex diameter and the particle mass concentration and pressure of the feed—on the separation performance of the CCC hydrocyclone were investigated in depth. Moreover, the CCC hydrocyclone was successfully used in a real-world industrial application.

A numerical CFD investigation of sand screen erosion in gas wells: Effect of fine content and particle size distribution

Sand screen is frequently used as a sand control device in oil and gas wells to prevent or minimize sand production. However, the sand screen may undergo mechanical erosion due to continuous impingement and passage of sand particles through its apertures. In addition, the design of most sand screens’ spacing allows fine particles <44 μm to pass through. According to previous studies, the existence of fines can also lead to erosion failures. In this study, the Eulerian-Lagrangian approach of dense discrete phase model (DDPM) has been used and evaluated for computational fluid dynamics (CFD) based erosion modelling of sand screen erosion because of the entrainment of fine particles in gas flow. Two sand types having different particle size distributions (PSD) and fine concentrations were studied. For the CFD erosion simulation, four erosion models were used, and then the effect of PSD of fines-inclusive sand particles on erosion magnitude has been investigated. The CFD simulation results were validated against the output of a reliable experimental-based correlation. Erosion results using McLaury model showed the least error and good agreement compared to the other models. For the two investigated sand types, using PSD for erosion prediction using CFD resulted in a higher value of maximum erosion when compared with the constant size simulation results. The value of the maximum erosion has increased 105.9% from the constant size results for sand type-I and 82.5% for sand type-II. The paper presents the first-ever comprehensive analysis study of its kind about the effect of fines-inclusive sand on the erosion of sand screen, considering the particle size distribution (PSD). The results of this study revealed the importance of considering erosion caused by fines, especially at high flow velocities.

Parameter optimization of an industrial water injection hydrocyclone in the Taixi coal preparation plant

ABSTRACT An industrial water injection hydrocyclone was adopted in the Taixi coal preparation plant to overcome the shortcoming of fine particle entrainment in the underflow and improve the grading efficiency. Parameter optimization of the hydrocyclone was critical prior to putting it into production. A particle swarm optimization optimized support vector machine (PSO-SVM) model based on uniformly designed experiments was built. It was satisfactory in accuracy as the average of the absolute of relative error was 1.73% for the training dataset, and the relative error of the test dataset was 8.43%. The trends of grading efficiency versus underflow port diameter, inlet pressure and water injection pressure were analyzed, respectively. It was found that the maximum efficiency was obtained when underflow port diameter was 50 mm, inlet pressure was 0.25MPa and water injection pressure was 0.04 MPa.

Semi-Continuous Froth Discharge to Reduce Entrainment of Fine Particles in Flotation Cells Subject to Low-Mineralized Froths

An operational strategy is proposed to improve the metallurgical performance of flotation cells subject to low-mineralized froths. This strategy consists of using a semi-continuous discharge into the concentrate, in which the froth is operated under loading and unloading periods. A transient model is developed to evaluate the proposed approach. The model is calibrated using experimental data from two industrial flotation banks. The metallurgical performances of the last cells of these banks are then simulated, considering the semi-continuous froth discharge. The results show that the semi-continuous mode significantly reduces gangue entrainment, improving the concentrate grade while maintaining approximately the same recovery. The semi-continuous strategy demonstrates good potential to enhance the metallurgical indexes under low-mineralized froths, as those in the last cells of rougher flotation banks.

Experimental research on the separation performance of W-shaped hydrocyclone

The entrainment of fine particles in underflow of a grinding-classification hydrocyclone can cause ore over-grinding, reducing both the metal recovery and the ball mill throughput. This problem is addressed in this study by proposing a W-shaped hydrocyclone that effectively reduces the fine particle in the underflow. The separation performance of the W-shaped hydrocyclone was investigated in depth by experimentally studying the influences of a structural parameter, a physical property parameter, and an operating parameter on the split ratio, the yield, the product concentration, the product particle size, and the classification efficiency of the W-shaped hydrocyclone. And then the W-shaped hydrocyclone was scaled-up and successfully used in an industrial site. The results show that replacing a conventional hydrocyclone with the W-shaped one can reduce the −75 μm particle content in the underflow by 1.46 percentage points, increased the classification efficiency by 8.32 percentage points, and reduced the circulating load by 33.38%.

Effect of Overflow Pipe on the Internal Flow Fields and Separation Performance of W-Shaped Hydrocyclones

The entrainment of fine particles in underflow of a grinding-classification hydrocyclone can cause ore overgrinding, which will lead to reductions in both metal recovery and ball mill throughput. To address this problem, this paper proposed a W-shaped hydrocyclone that can effectively reduce underflow fine particle entrainment. Experimental tests and numerical simulations were employed to deeply investigate overflow pipe diameter influence on the separation performance and internal flow field of W-shaped hydrocyclones. The effects of overflow pipe diameter on air core shape, velocity field, pressure field, and separation performance were studied. The results revealed that as the diameter of the overflow pipe increased, air core gradually stabilized, and air core diameter gradually increased. The diameter of stabilized air core was approximately 45% to 55% of overflow pipe diameter. As overflow pipe diameter increased, hydrocyclone pressure drop decreased, energy consumption was reduced, the tangential velocity decreased, outer vortex axial velocity did not change significantly, and inner vortex axial velocity gradually increased. At the same time, zero-velocity points gradually moved outward, and the inner vortex region expanded. By the increase of overflow pipe diameter, both the underflow yield and split ratio gradually decreased, the coarse particle content in the overflow product increased, and the fine particle content in the underflow product gradually decreased.

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).

Fine particle entrainment in fountain confined conical spouted beds

Many applications of the conical spouted beds involve operations using coarse and fine particle mixtures, which require high gas velocities due to the coarse particles, thereby leading to fine particle entrainment. In order to avoid entrainment, a new device has been proposed to confine the fountain. Thus, a study has been conducted on the influence the geometry and configuration of both confiner and draft tube have on particle entrainment, operating pressure drop, operating air flow rate and maximum cycle time. The results show that the fountain confiner greatly stabilises the operation and significantly reduces (above 50%) particle entrainment, but its influence on the other parameters is of rather low significance. Furthermore, the distance between the lower end of the device and the bed surface has a great impact on the performance of the spouted bed regime. Entrainment monitoring throughout time showed that its rate depends on the configuration, but remains constant with time.

Effect of Oleic Acid on Froth Properties and Reverse Flotation Performance of Thermal Coal

Reverse flotation was proposed as a potential method for the upgradation of low rank thermal coal. Higher combustible matter recovery in the float could be obtained using reverse flotation method compared to conventional flotation method. In order to reduce the entrainment of fine particles, oleic acid (OA) was used as froth regulator in coal reverse flotation process. Experimental data showed that the total volume of froth product in the absence of OA was almost 3 times more than that in the presence of 0.45 kg/Mg OA dosage. Reverse flotation results showed that the ash content of froth product increased with the increase of OA dosage which indicated that the entrained coal particles could be decreased by the addition of froth regulator OA.

Analysis of key mixing parameters in industrial Wemco mechanical flotation cells

Flotation performance in mechanical cells is strongly influenced by hydrodynamics. Hydrodynamics is driven by the action of the impeller which is responsible for mixing in the cell. This paper evaluates key mixing parameters in three industrial Wemco mechanical flotation cells (#144, #164, #190; 14.2, 28.3, 42.5 m3). Residence time distributions, circulation times, impeller pumping capacities, impeller Flow numbers and power intensities are presented. RTD studies are based on LiCl tracer measurements. RTD studies showed that the #190, #164 & #144 behave as 2.1–2.4, 1.2 and 1.0 tanks in series respectively. Circulation times for the #164 and #144 were much shorter than the #190. The #190 and #164 had the highest pumping capacities. Dimensionless Flow numbers varied from 0.12 to 0.22. Iron losses by entrainment of fine particles (<45 µm) were higher in the #164, due to the higher intensity of mixing.

Fountain confined conical spouted beds

Particle entrainment is a serious problem in spouted bed contactors when operation is carried out using beds made up of ultrafine particles, irregular ones and fine and coarse particle mixtures. Accordingly, the conventional conical spouted bed has been modified by inserting a fountain confiner in the contactor, and a study has been carried out on the efficiency of the confinement device to avoid fine particle entrainment. Furthermore, the influence of the geometry of the device on the hydrodynamics of conical spouted beds has been studied. The results show that the fountain confiner largely avoids fine particle entrainment, i.e., 60–70% reduction depending on the type of draft tube used. Furthermore, the fountain confiner reduces the operating bed pressure drop and the maximum cycle time of the particles in the contactor, but has no effect on the minimum spouting velocity. Nevertheless, the greatest advantage of the fountain confiner lies in the stabilization of the fountain and the homogenisation of the solid circulation in the bed, which leads to a significant increase in the gas-solid contact in the fountain.

Combined effect of acoustic agglomeration and vapor condensation on fine particles removal

A novel preconditioning process using the combined effect of acoustic agglomeration and vapor condensation for fine particles removal with high efficiency was presented. The effect of operation parameters on the enlargement and removal of fine particles were investigated experimentally. Particle size distribution and number concentration with and without external fields were measured by Electrical Low Pressure Impactor (ELPI). The results showed that the stage removal efficiency of fine particles was about 10–23% by acoustic agglomeration only with sound pressure level (SPL) of 150dB. However, it was significantly improved by the combined effect of acoustic agglomeration and vapor condensation, reaching up to 53–80% with a SPL of 150dB and supersaturation degree (S) of 1.2. Fine particle entrainment factor in acoustic field increased with the supersaturation degree, as well as the removal efficiency. While the supersaturation degree was lower than 1.0, the removal efficiency was extremely low, and increased slightly with the supersaturation degree. However, removal efficiency increased with the supersaturation degree rapidly when the supersaturation degree was higher than 1, which was improved by about 50% as the supersaturation degree increased from 1.0 to 1.4. The coupling external fields cannot be formed when the supersaturation degree was lower than the critical one, resulting in low removal efficiency. Removal efficiency was increased substantially to 63% in the supersaturation degree of 1.2, even in a low SPL of 130dB. It indicates that high removal efficiency can be obtained in the combined effect of acoustic agglomeration and vapor condensational growth even in low intensity acoustic field.

Effect of entrainment in bubble load measurement on froth recovery estimation at industrial scale

Froth recovery was calculated in a 130m3 mechanical cell of a rougher flotation circuit. This was done by bubble load determinations along with mass balance surveys. Valuable grade in the bubble load decreased in the −38μm due to fine particles entrained to the chamber of the device. The effect of fine particle entrainment on froth recovery was evaluated. A comparison between results from the raw bubble load data (assuming all particles were transported by true flotation) with those from corrected bubble load information (subtracting fine particle entrainment) was carried out. Entrainment occurred due to hydraulic transport in the bubble rear, which corresponds to the worst case scenario for froth recovery estimation. Results showed that the relative error was less than 0.3%, which allowed validation of the bubble load measurement as an effective methodology for froth recovery estimation at industrial scale.

The theoretical partition curve of the hydrocyclone

In many cases, the hydrocyclone partition curve exhibits a non-monotonic course in the fine particle range. The so-called fish-hook effect indicates an increased separation of the fine fraction, which is of practical interest and has a positive effect on solid/liquid separation. However, for classification purposes, the separation is less distinct. In this contribution an equation of a partition curve containing a fish-hook is derived considering the laws of disturbed settling in dense, polydisperse suspensions. The following effects are considered: the entrainment of fine particles in the boundary layer of the coarse settling particles, the hindered settling due to the increased effective density and viscosity of the fluid, and the counter flow of the displaced fluid caused by the settling particles. The calculations indicate that the fish-hook effect is primarily caused by fine particle entrainment, which is influenced by the feed solid content and the feed particle size distribution. An approximated analytical solution for the partition curve is presented for aRosin–Rammler–Sperling–Bennet (RRSB)-distributed feed. Experiments using 25-mm hydrocyclone confirm the calculations.

Acoustic streaming in gas-fluidized beds of small particles

An increasing number of applications rely on the use of gas-fluidized beds of small particles to enhance processes based on the mass/heat transfer between a gas and a solid. On the other hand, experimental studies have shown that application of high-intensity acoustic fields serves to further intensify fluidized bed processes. It is well known that the fluid streaming developed around the surface of a solid body subjected to a sound wave leads to a notable increase of the mass/heat transfer. However, several additional phenomena are observed in sonoprocessed fluidized beds requiring a close examination. In a sonoprocessed fluidized bed, acoustic streaming is superposed on the fluidizing gas flow, which exhibits large fluctuations within the bed at a local level due to long-range hydrodynamical interactions. Attenuation due to viscous friction and thermal conduction on the surface of the small particles is expected to play a relevant role. Fine particles may be entrained by the acoustic flow field whereas acoustic streaming on the surface of not entrained particles gives rise to an increased drag. Entrainment of fine particles in the sound wave may serve to improve fluidization uniformity in dense beds or to induce particle agglomeration in diluted beds. Acoustic streaming leads also to a large-scale fluid recirculation characterized by velocities sufficiently high as to affect the fluidized bed dynamics. A substantial modification of the dynamics of fluidized beds may thus occur depending on intervening physical parameters such as particle size and density, sound wave intensity and frequency, fluid properties, fluidization regime and system size. In this manuscript, the main features of acoustic streaming and the associated phenomena due to the application of high-intensity acoustic fields on fluidized beds are analyzed from a review on the fundamentals of acoustic streaming and observations on sonoprocessed fluidized beds. Results inferred from this analysis are expected to help assess the optimum conditions under which sound assisted process intensification would be maximized in each particular application.

Combined column and cell flotation process for the treatment of PAH contaminated hazardous wastes produced by an aluminium production plant

The aluminium electrolytic plants generate PAH and fluoride contaminated wastes which are usually classified as hazardous material. These residues are generally disposed in secure landfill sites. A flotation cell process was previously developed to remove PAH from these aluminium industry wastes. The tests were done on composite samples made of particle size fractions under 50 mm. The efficiency of the flotation cell process was demonstrated but the high quantity of concentrate produced (14.0%) during the air injection period, because of the solid entrainment, raised the treatment cost. The aim of this study was to reduce the entrainment of fine particles in order to obtain an efficient and economic technology. The process initially developed was modified: the smallest particle size fraction (<0.5 mm) of the composite sample was treated in a flotation column, whereas the other particle size fractions (0.5–50 mm) were treated in a flotation cell. The separated treatment allowed to reduce the entrainment during the air injection period of the flotation cell step from 14.0% to 10.1%. The optimum total solids of the pulp and cocamidopropylhydroxysultaine (CAS) concentration were 3.33% and 0.50% (w w −1) for the flotation column, and 15% and 0.25% (w w −1) for the flotation cell. This combined flotation process minimized the total entrainment which allowed a 23.6% abatement of the concentrate quantity initially produced, and reduced the PAH concentrations of the wastes under the authorized limit of 1000 mg kg −1.