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The heterogeneous structures of the gas-solid flow in riser and downer reactors determine reactor performance but are not fully understood. This paper presents a numerical study of the hydrodynamic characteristics of cohesive particles in a riser and a downer. This is done by the combined approach of discrete element method (DEM) for particles and computational fluid dynamics (CFD) for the gas phase. The numerical results show that this CFD-DEM model can reproduce different annular dense distributions of particles in the fully developed sections of the riser and downer. This realization requires suitable periodic boundary conditions applied to both the gas and solid phases in the flow direction as well as adequately fine meshes. The flow behaviors are analyzed in detail in terms of particle flow pattern, cluster behaviors, gas and solid velocities and forces acting on particles. Also, the dependence of the dense solid ring in the downer on some pertinent variables related to pipe geometries, material properties, and operational conditions is examined. Unlabelled Image • Heterogenous gas-solid flows in both riser and downer reactors are simulated. • This is done using the CFD-DEM model via consistent model setups. • The model can realistically capture complex annular flow structures in both reactors. • Flow structures are analyzed in detail in terms of micro-scale information. • Dependence of the dense solid ring in the downer on a few variables is examined. [ABSTRACT FROM AUTHOR]

This paper comprehensively analyzes the transportation of iron-bearing solid materials in industrial-scale transfer chute stations by a GPU-DEM model. It considers five chute head designs, including the traditional rock box, impact plate, and hood, as well as the modified micro-boxed alternatives to the impact plate and hood. Particle flow and energy dissipation are analyzed to understand the energy consumption, wall wear, and particle degradation and segregation. The numerical results show that the localizations of different energy dissipation mechanisms significantly differ, resulting in differences in particle degradation and segregation across the chutes considered. The rock box chute is susceptible to the largest degradation and segregation. The micro-box impact plate leads to the least degradation, and the traditional hood causes the best mixing performance. It also shows that segregation becomes more severe as the particle flow stream loses greater energy at the earlier stage of the particle dropping. [Display omitted] • Industrial-scale chute transfer of iron ore is analyzed by a GPU-DEM model. • Both conventional and modified head chute designs are evaluated comprehensively. • The location and mechanisms of energy dissipation affect transfer performance. • A micro-boxed design helps reduce material degradation and wall damage. • Particle segregation is correlated with local energy dissipation. [ABSTRACT FROM AUTHOR]

The control of burden distribution at blast furnace (BF) top is of paramount importance and mostly practiced in daily operations. However, to date, an effective method for optimizing top burden distribution under different conditions is yet unavailable. This paper presents a numerical method to achieve this goal using a well-developed and validated multi-fluid BF process model. The model simulates the BF region between burden surface and slag surface. First, a study of top burden distributions confirms that a uniform ore-to-coke distribution presents the highest process efficiency but a sharp pressure drop across the cohesive zone (CZ), which can lead to unstable production. Then, a top burden optimization method is proposed and tested. This is done by loading more coke to the central area while keeping uniformity in other areas. This burden control method decreases the in-furnace pressure drop significantly. When the coke charged into the central area is controlled properly, the gas flow there can be reasonably developed, and the process efficiency shows comparable to that of uniform burden distribution. These results are analyzed in terms of in-furnace flow, heat and mass transfer. Finally, as an example, a method to achieve the simulated optimum burden is proposed for use in a BF operation. This is done by use of DEM model simulating the flow of particle from the rotating chute into the throat in a BF top. This optimization methodology is considered applicable to other BFs. Unlabelled Image • Top burden distribution is studied by a CFD based blast furnace process model. • An optimum strategy is proposed to achieve high process efficiency and stability. • It loads more coke to the central area while keeps uniformity in other areas. • A method for obtaining the optimum distribution for BF operation is proposed. • This is based on a DEM based burden charging model. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the tribocharging process during pneumatic conveying using computational fluid dynamics (CFD) and the discrete element method (DEM). It simulates tribocharging by the condenser model, considering the frictional charge important to pneumatic conveying. The model is validated by comparing the simulation results with the specific charge measurements in the hopper and chute. Via the model, the cumulative charge and its effect on the performance of horizontal pneumatic conveying are quantified. A phase diagram is established to predict particle charging modes with respect to solid concentration and gas velocity. The flow characteristics are analyzed to understand charging phenomena. It shows that particle charge accumulation is critical for developing distinct particle patterns, such as particle ring, cluster, and plug. The plug flow causes rapid charge accumulation and significant fluctuations in particle flow rate and gas pressure, which can be mitigated under properly controlled operating conditions. [Display omitted] • Tribocharging in horizontal pneumatic conveying is studied by a CFD-DEM model. • The frictional charge is incorporated into the condenser model in the modeling. • The charging behavior and conveying performance are studied. • A phase diagram is provided to predict charging modes under the present conditions. • The charging process is analyzed using particle-wall contact number and force. [ABSTRACT FROM AUTHOR]

The interaction force between fluid and particles in particulate flows is highly dependent on the rheology of fluid. In some engineering applications, like mineral processing, the rheological behaviour of the carrier fluid is characterized by a yield-pseudoplastic non-Newtonian model. The immersed boundary method (IBM) is a numerical strategy to simulate the interaction between phases in the particulate systems using a Cartesian fixed grid. It imposes the solid boundary condition in the computational domain through a modification (e.g. a forcing term) in the governing equations. However, there is still little study in the literature discussing the applicability of different IBMs to yield-pseudoplastic flows. In this paper, the numerical methodology in several versions of immersed boundary methods, including the Volume Penalization IBM (VP-IBM), Indirect Imposition of Discrete Forcing IBM (ID-IBM), and Direct Imposition of Discrete Forcing (DD-IBM), is described. The numerical implementation of the methods is first validated using Newtonian benchmark cases. Then the solvers are utilized for the simulation of yield-pseudoplastic cases with stationary or moving particles. The investigation shows that in the explicit forcing methods, like VP-IBM and ID-IBM, the forcing procedure is conducted using an intermediate solution over the entire computational domain. The dependence of viscosity to strain rate in non-Newtonian cases leads to an inevitable sharp change in viscosity near the solid surface, giving rise to stiffness of the intermediate solution in the interface region. This makes the explicit forcing approaches based on intermediate solution incompatible with the flows with non-Newtonian yield-pseudoplastic rheology. On the other hand, the implicit forcing used in DD-IBM directly implements the boundary conditions on the boundary cells, making this method free from the perturbations related to the highly viscous solid region. In this regard, the simulation with the Direct Imposition IBMs like ghost-cell shows a good agreement between the predicted results and the experimental measurements for the stationary/moving cases. Therefore, it is shown that the DD-IBM is a reliable approach to modelling non-Newtonian flows. • Investigation on the applicability of different immersed boundary methods to a yield-pseudoplastic flow. • Developing numerical solvers based on the most common immersed boundary methods such as VP-IBM, ID-IBM, and DD-IBM. • Fundamental accuracy issues in VP-IBM and ID-IBM for non-Newtonian flows due to their dependence on an intermediate solution. • Superior performance by the implicit forcing approach implemented in the DD-IBM solver. [ABSTRACT FROM AUTHOR]

The inlet and sideline configuration modifications are widely investigated to alter regional particle fluid flow conditions, considering pressure, turbulence and erosion, therefore to improve energy saving and compartment longevity of centrifugal slurry pump. This paper aims to analyse pump hydraulic and erosion characteristics with proposed pump sideline and inlet configuration retrofit by the DDPM method. Specifically, the inlet guide vane number () and angle (), and sidelining vane (SDV) curvature are investigated in quantitative manner. Accordingly, by adjusting inlet vane configuration and placement, a trade-off between wall erosion and hydraulic performance is observed. The sidelining vane (SDV) design is suggested to avoid resultant counter-current flow formulation, therefore, to mitigate turbulence induced erosion in impeller and volute. However, the SDV modification effect on pump hydraulic head and efficiency is found marginal. In general, this study offers realistic guideline for performance improvement and device upgrading of centrifugal slurry pumps. [Display omitted] • Designated pump configuration effectiveness is justified with particle fluid flow dynamic and erosion condition. • The inlet guide vane number (N v) and angle (β) are analysed in quantitative manner. • The sidelining vane (SDV) modification presents trade-off on performance improvement and erosion mitigation. • The proposed inlet and sideline flow condition impacts volute erosion characteristics greatly. [ABSTRACT FROM AUTHOR]

Liquid bridges between wet particles affect pneumatic elbow erosion, but the associated mechanism remains unclear. This paper presents a numerical study of elbow erosion using a combined approach of computational fluid dynamics and discrete element method facilitated with erosion and capillary force models. Particle dynamics and the elbow erosion location, depth and ratio are analysed in detail. The results show that wet particles tend to adhere to the inner wall of the elbow during transport under the effect of liquid bridges. This phenomenon forms a particle layer that covers the impact area, thereby substantially decreasing both the erosion depth and ratio of the elbow. A U-shaped erosion scar is observed in the extrados of the elbow when conveying wet particles. Additionally, the effects of gas velocity and moisture content on particle flow and elbow erosion are revealed to clarify the differences between dry and wet particles. [Display omitted] • Flow behavior and elbow erosion of wet particles are studied by a CFD-DEM model. • Wet particles tend to adhere to the inner wall of the elbow reducing its erosion. • A U-shaped erosion scar is observed in the extrados of the elbow for wet particles. • Effects of gas velocity and moisture content on particle flow and erosion are revealed. • The result elucidates differences between dry and wet particles. [ABSTRACT FROM AUTHOR]

Shear is a common phenomenon in practical mineral processes, particularly in pipeline transportation. When applied to realistic polydisperse systems consisting of particles of different sizes, shear can lead to distinct interactions of each size component with the carrier fluid, resulting in segregation between sizes. This paper focuses on the effect of size segregation induced by shear on the settling process of suspension flows containing different-sized spherical particles. In this regard, the bidisperse system is considered as the simplest example of polydisperse flows, ensuring the investigation retains the essential features of the system of interest without added complexity. The Volume Penalization Immersed Boundary Method, as a resolved Eulerian–Lagrangian CFD-DEM approach, is employed to gain detailed information on individual particles. A simple cross shear is generated by the moving side walls, and its effect is initially evaluated on two simulation cases containing single spherical particles of different sizes. The results from the single particle simulation cases reveal a higher acceleration of the larger particle towards the centreline due to the higher lateral force proportional to its size. The resolved approach is then used for the bidisperse multiparticle systems with diameter ratios of l = 2 and l = 5 , both subjected to a similar sheared field. In the suspension with l = 2 , the scalar dispersion function, which measures the degree of migration of each size component between the side walls, indicates segregation by size as the shear rate increases. This is evident in the motion of large particles towards the centre and the accumulation of smaller particles near the walls, which arises from higher proportional force on the larger particles observed in the single particle simulation cases. Although the increase in the diameter ratio to l = 5 does not significantly change the migration behaviour of large particles, it provides a more uniform distribution of smaller ones. In this case, the small particles find it more easily to fit into the gaps between the large particles for l = 5. Overall, this accumulation of each size component at specific regions in the sheared domain affects the local interaction of settling particles with the fluid flow, resulting in an increase in the settling rate of large particles up to 40% in the considered bidisperse cases. This highlights the impact of shear on the interaction of spherical particles in a multiple sized system, specifically in the practical sheared applications including mineral slurries transportation. [Display omitted] • An investigation was conducted on the sedimentation of sheared bidisperse flows using an IBM-DEM approach. • In a sheared field, larger particles accumulate more in the central regions, while smaller ones locate closer to the walls. • Segregation of particles by their size affects their interaction with the fluid during sedimentation. • An increase of up to 40% is observed in the settling rate of larger particles under the considered shear rates. [ABSTRACT FROM AUTHOR]

Sedimentation of multi-sized particles is a common phenomenon in mineral applications like tailings management. The mutual interplay of particles in bidisperse flows creates a complex interaction between different-sized particles and fluid in comparison to a mono-sized system. This paper focuses on investigating particle settling in a bidisperse system. To this end, the Volume Penalization Immersed Boundary Method (VP-IBM), as an Eulerian–Lagrangian solver, is employed to provide detailed information about individual particles in a multiparticle system. The solver is first tested for settling cases in an unbounded domain with single and multiple mono-sized particles, and the predictions show a reasonable agreement with existing correlations for their average settling velocity. The validated IB solver is then used to describe the settling behaviour of bidisperse systems with different concentration and diameter ratios. Change in the concentration ratio is provided by replacing some of the faster large particles with the slower small ones, which reduces the hindrance caused by the opposing upward flow and leads to an increase in the settling velocity of both components. The variation in diameter ratio, on the other hand, is made by keeping the large particle diameter constant and reducing the size (and increasing the number) of small particles but maintaining a fixed total concentration. The effect of this change depends on the particle settling Reynolds number. It is found that for a low particle Reynolds number with dominant viscous forces, when the diameter ratio increases, the settling velocity of large particles decreases, while this trend is opposite for a higher Reynolds number flow. Because inertia forces are dominant at higher Reynolds numbers, the influence of the smaller component on the settling velocity of the larger component can be approximated by considering two factors: first, combining fluid and smaller particles to give a pseudo-fluid with a mean density of this mixture, and second, taking into account the role of small particles settling in inducing upward opposing flow. These findings allow a correlation to be derived for the settling velocity of bidisperse systems at high settling Reynolds numbers. The equation relates each size component in bidisperse flow to a counterpart monodisperse suspension for which reliable settling correlations are available. [Display omitted] • A detailed study was conducted on bidisperse flow sedimentation using the IBM-DEM approach. • Increase in concentration ratio of suspension enhances the settling rate of both size components. • The effect of diameter ratio is dependent on the settling Reynolds number of suspension. • The settling velocity of each size component can be characterized using a pseudo-fluid model. • A correlation for bidisperse flows was proposed based on an equivalent monodisperse suspension. [ABSTRACT FROM AUTHOR]

• The work concerns coarse particle conveying in the small absorber sphere system. • Present an overview of recent experiments and discrete element simulation at INET. • We present some CFD-DEM results of coarse particle conveying obtained so far. Pneumatic conveying of absorber spheres in the pebble-bed high-temperature gas-cooled reactor is a special application of pneumatic conveying technique in the nuclear engineering. It may be regarded as an intermittent circulation of absorber spheres between the side reflector boring and the storage bin in the reactor. The whole process consists of several sub-processes, e.g., the granular discharge from the sphere storage bin into the boring, granular discharge from the side reflector boring into the feeder, particle entrainment in the feeder, sphere conveying in the transport pipe, and gas-solid separation in the storage bin. We give a brief summary of the experimental and discrete element simulation work done recently at the Institute of Nuclear and New Energy Technology of Tsinghua University, mainly from the viewpoint of gas-solid flow and granular flow. CFD-DEM coupling simulation is recently conducted to investigate the coarse particle conveying in the small absorber sphere system. We present some CFD-DEM simulation results of coarse particle conveying in ambient air and high-pressure helium gas. Based on the needs of engineering practice and scientific research, some research requirements are suggested. Further work is still needed, to make a comprehensive understanding of the conveying process, and to optimize the design and operation of the conveying system. [ABSTRACT FROM AUTHOR]

Vortex elbows are generally used to mitigate erosive wear while conveying fine particles. This paper presents a modified vortex elbow designed to handle coarse particles. Gas–solid flows and wall erosion of the modified vortex elbow are studied by the combined approach of discrete element model for particles and computational fluid dynamics for the gas phase. The validity of the model is first examined by comparing the predicted pressure drop and wall erosion with experimental measurements for a standard elbow. Then, via the model, the effects of particle size on the flow characteristics and elbow erosion of the modified vortex elbow are quantified and compared with those of the standard elbow. The results show that the vortex elbow decreases the maximum penetration ratio and total penetration depth for all the particle sizes considered. These effects become more significant for larger particles. The wall erosion is also elucidated using flow characteristics. [Display omitted] • A modified vortex elbow featuring an elliptical chamber is proposed. • The gas-solid flow and wall erosion of the elbow is studied by a CFD-DEM model. • Effects of particle size on flow characteristics and elbow erosion are quantified. • The erosion of the vortex reduces by up to 58% than that of the standard elbow. • The anti-erosion mechanism is elucidated using flow characteristics. [ABSTRACT FROM AUTHOR]