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The chemical looping hydrogen production (CLHP) process is a new approach for hydrogen ( H 2 ) fuel production. The proposed process consists of three reactors which are air reactor (AR), fuel reactor (FR) and steam reactor (SR). In this study, the gas solid flow behaviour in a cold model of the proposed CLHP process was simulated using computational fluid dynamics (CFD) with kinetic theory of granular flow. The effect of drag coefficient models on the pressure profile of each reactor was investigated and the results from the modified Syamlal–O’Brien drag model agreed well with the experimental data. The model was further used to investigate effects of the operating parameters on the hydrodynamics profiles of each reactor. The solid flux increased with the increasing of inlet velocity of AR and FR but decreased with the increasing of the inlet velocity of SR. At the same time, the solid flux increased with the increasing of the solid inventory.

A TFM–DEM hybrid model is introduced for modeling of the complex gas–solid flows in a pilot scale Coal Beneficiation Fluidized Bed (CBFB). The gas and the dense solid phases are modeled using an Eulerian-Eulerian or two fluid model (TFM), while the beneficiated coal particles are modeled as a dilute phase by the discrete element method (DEM). In this work, the influence of some key operation parameters on particle segregation behavior is studied, including fluidized air velocity, bed depth, and coal feed ratio and bed medium properties. Their effects are evaluated using a single coal sample of diameter 4.3 mm. Particles are divided into five different density fractions to represent the wide density range of raw coal samples. The simulation results demonstrate that by increasing the fluidizing air velocity from 1.2 u mf to 1.8 u mf of the dense medium solids, the segregation degree of beneficiated coal particles is significantly reduced, but the segregation time is only slightly decreased. Increasing the particle feed mass or decreasing the bed depth has a similar influence on CBFB operation. Both help to improve particle segregation, but a shallower bed is demonstrated to be more effective for coal beneficiation. A decrease in the medium density can reduce the bed cut density as well as the beneficiation limit for lighter samples, while a decrease in the medium size will increase the back-mixing effects, resulting in reduced beneficiation quality. Hydrodynamic forces acting on the beneficiated particles are also quantified from the simulation results. By analyzing the magnitude and direction of each force acting on discrete particles, the mechanisms influencing particle segregation under different operation conditions are explained at the particle scale.

Particle segregation behavior in a coal beneficiation fluidized bed (CBFB) is numerically studied using a TFM–DEM hybrid model, in which the gas and the dense solid phases are modeled using a Eulerian–Eulerian or two fluid model (TFM), while the beneficiated coal particles are modeled as a dilute phase by the discrete element method (DEM). For validation purpose, the numerical model was setup using geometric and operating conditions similar to a laboratory experimental model with the bed thickness set to one particle diameter to save computational cost. For a fixed gas injection velocity, the influence of particle size and density of the beneficiated samples was studied. It was found that the particles would segregate along the bed height due to the density differences with the degree of segregation being strongly influenced by particle size. Obvious segregation occurs for the coarse samples (6.7 mm and 4.3 mm) and little segregation occurs for the particles smaller than 3 mm. The flow patterns and segregation kinetics were qualitatively comparable with those observed in physical experiments conducted under similar conditions. On this basis, the underlying mechanisms governing particle segregation have been explained in terms of the hydrodynamic forces acting on individual particles. It was demonstrated that the segregation of coarse particles was mainly controlled by the balance between gravity and the local pressure force, while fine particles were more strongly affected by the direct drag forces from the gas phase and the continuum solid phase, thus making them difficult to separate.

This paper reports on an assessment of the bubble-induced electrical resistance in the Hall-Heroult process for primary aluminium production through a combined use of physical and numerical modelling. Using a physical air–water model, the transient bubble dynamics beneath the bottom surface of an anode was captured using a digital camera. Bubble morphology information obtained from the experiment was used to set up a numerical model. Computational fluid dynamics (CFD) modelling was applied to predict the current flow and the corresponding voltage drop across the electrolytic cell with and without the presence of bubbles. The predicted bubble-induced voltage drop for a current density of 0.7 A cm−2 is about 0.11 V for a bubble coverage of 37 % and 0.29 V for a bubble coverage of 50 %. These values are within the range of experimental measurements reported for commercial cells. The predictions show that the presence of bubbles does not greatly affect global current distribution within the whole cell, but it does significantly affect the local current flow at the anode-bath interface. Locally high current flow occurs at the contact point of the anode bottom surface, bubble and liquid. In addition to the effect of bubble coverage, the bubble size and bubble thickness affect the voltage drop significantly.

A novel dry slag granulation process based on a spinning disc is being developed by CSIRO. This process utilises centrifugal force to break up molten slag into droplets, which are then quenched into solidified granules by a flow of cold air. In this process the sensible heat of slag is recovered as hot air. In the present work, a previously developed steady-state, two-dimensional and multiphase CFD model was applied to perform parametric numerical experiments to investigate the effects of a number of parameters on the liquid film thickness at the disc edge, which included liquid mass feeding (pouring) rate, disc spinning speed, disc radius, liquid viscosity, density and surface tension. The modelling results were compared with experimental data and were found to be in good agreement. To reduce the number of simulations needed, Box and Behnken's fractional factorial design of numerical experiment was adopted. Furthermore, in order for the modelling results to be applicable to atomisation of different liquids using spinning discs of different sizes, a dimensionless correlation was developed based on dimensional analysis of the numerical simulation data. The modelling results indicate that the liquid film thickness can be significantly influenced by the disc radius and spinning speed, the liquid mass feeding rate, viscosity and density, whereas the liquid surface tension has a negligible effect.

The supersonic separator is a novel compact tubular device for natural gas dehydration. The separation mechanism is not well understood for the complicated fluids with a delta wing located in the supersonic flows. We investigated the gas swirling separation characteristics in supersonic velocities using the Reynolds stress turbulence model. The results showed that the Laval nozzle designed with the cubic polynomial and Foelsch's analytical methods formed an extremely stable and uniform supersonic flow. The delta wing generated a strong swirling flow with the centrifugal acceleration of around 107 m s−2 to remove the condensed liquids from the mixture. However, the supersonic flow was quite sensitive to the delta wing, which led to the disturbance and non-uniformity of the gas dynamic parameters. This violent variation in the supersonic flow had a secondary action on the condensation, even resulting in the re-evaporation of the condensed liquids.

Aluminium metal production through electrolytic reduction of alumina in a cryolite bath is a complex, multi-physics, multi-scale process, including magneto-hydrodynamics (MHD), bubble flow, thermal convection, melting and solidification phenomena based on a set of chemical reactions. Through interactions of the different forces applied to the liquid bath combined with the different time and length scales, self-organised fluctuations occur. Moreover, the MHD behaviour causes a complex metal pad profile and a series of surface waves due to the meta-stable condition of the metal/cryolite interface. The large aspect ratio of an industrial cell, with a footprint of 20 by 4 m and at the same time having dimensions approaching just 30 mm of height for the reaction zone, prevents an integrated approach where all relevant physics are included in a single mathematical model of this large degree of freedom system. In order to overcome these challenges, different modelling approaches have been established in ANSYS® FLUENT®; Three models are used to predict details of specific physics: one to predict the electro-magnetic forces and hence the metal pad profile, a second that resolves details of the local bubble dynamics around a single anode and a third for the full cell bath flow. Results from these models are coupled to allow integration of the different phenomena into a full cell alumina distribution model. The current paper outlines each of the approaches and presents how the coupling between them can be realized in a complete framework, aiming to provide new insight into the process. This is a submitted manuscript of an article published by Elsevier Ltd in Applied Mathematical Modelling, 2 December 2016.

Supersonic quenching of magnesium vapour plays a pivotal role in the carbothermal reduction process for magnesium and the production of fine magnesium powders. Modelling of this process has previously been based on Classical Nucleation Theory in a one-dimensional flow expansion without considerations of background gas turbulence and the associated heat and mass transfers. This paper presents a single-velocity field, multi-component fluid model that overcomes the above shortcomings. The model has been validated using steam condensation data and applied to study supersonic quenching of magnesium vapour in a laboratory-scale Laval nozzle. Modelling results indicate a strong dependence of the vapour condensation characteristics on parameters such as vapour concentration and choice of carrier gas. The model is potentially a useful tool for designing and up-scaling processes that utilise supersonic quenching of metallic vapours.

This paper presents a numerical study of a gas-particle flow in three inclined rectangular jets in crossflow. The predicted gas phase velocities and particle phase velocities are validated against previously reported experimental data. Two turbulence models, the standard k–ɛ model and Shear Stress Transfer (SST) model, are used to model the gas phase turbulence. This work shows that both models provide acceptable predictions of the gas flow and mixing generated by the three jets. Neither model could accurately reproduce the jet core and the flow near bottom wall. The particle phase in this flow comprises a large number of small particles. Thus particles follow the gas phase flow closely and any errors in the turbulence model and gas flow predictions are passed on to the particle phase simulation. This paper also includes a literature review on rectangular jets in crossflow and gas-particle laden jets in crossflow.

Gas vortices generated in the freeboard of a bubbling fluidised bed have become the centre of increasingly more research due to the advances in experimental technology. The behaviour of gas flow in the freeboard of a bubbling fluidised bed is of interest for applications such as the gasification of coal where reactions of gas mixtures, as well as gas–particle heat and mass transfer take place. Knowledge of the hydrodynamics of the gas within the freeboard can be hard to characterise, especially the detailed behaviour of gases escaping from bubbles that erupt at the bed surface. In the present study, experiments were conducted on a rectangular three-dimensional gas–solid fluidised bed. The experiments used a particle imaging velocimetry (PIV) measurement technique to visualise and measure the gas flow within the freeboard after a single bubble eruption. A computational study was carried out using Eulerian–Eulerian, kinetic theory of granular flow approach with a quasi-static flow model and with LES used to account for gas turbulence. Results from a three dimensional simulation of the experimental fluidised bed were compared with experimental velocity profiles of gas flow in the freeboard of the gas–solid fluidised bed after a bubble eruption. The CFD simulations showed a qualitative agreement with the formation of the gas vortices as the bubble erupted. Consistent with experimental findings the CFD simulations showed the generation of a pair of vortices. However, the simulations were unable to demonstrate downward flow at the centre of the freeboard due to particles in free fall after a bubble eruption event was observed in the experiments. Velocity profiles from the CFD data are in reasonably good agreement with the characteristic trends observed in the experiments, whereas the CFD model was able to predict the gas vortices phenomena and the velocity magnitudes were over-predicted.

This paper describes the mathematical formulation and modelling issues of a computational fluid dynamics (CFD) model of a 375 MW utility furnace. This tangentially-fired furnace is fuelled by high moisture content brown coal from coal mines at Latrobe Valley in Victoria, Australia. The influences of different turbulence models, particle dispersion, and radiation models on the CFD prediction are investigated. Two turbulence models, standard k-e model and Shear-Stress Transport (SST) model, provide similar predictions that are in good agreement with the plant data. The effect of particle dispersion on the prediction is found to be insignificant for this high-volatile brown coal. The predicted wall incident radiation flux based on two radiation models, namely, discrete transfer (DT) model and P-1 model are compared against power plant measurements. The comparison reveals that the DT model provides good prediction of the radiation profiles, while the P-1 model considerably under-predicts the wall incident radiation flux.

The aerodynamic development of fully turbulent isothermal jets issuing from rectangular slot-burners was modelled by obtaining a solution to the Reynolds averaged Navier–Stokes equations. A finite-volume method was used with the standard k–e , RNG k–e and Reynolds stress turbulence models. The slot-burners were based on physical models, which were designed to be representative of typical burner geometries found in tangentially-fired coal boilers. Two cases were investigated, in which jets from three vertically stacked rectangular nozzles discharged at 90° and then 60° to the wall containing the burner. The nozzle angle had little effect on jet centreline velocity decay, with the 60° nozzle showing a marginally higher rate of decay. The jets from the 60° nozzles were found to deviate slightly from their geometric axis slightly due to internal pressure redistribution in the flow at the nozzles. The simulations were validated against the physical models and were found to reproduce the flow field of the jets accurately with the Reynolds stress model producing the best results.

To help improve hygiene in a copper smelter building, a correlation-based computer model of the gas extraction system was developed and used in conjunction with experimental observations to investigate the effects of process parameters on extraction performance. The model predicted that 28% of the total flow originated from in-leakage, and reduction of the in-leakage would cause a nearly equivalent amount of infiltration through the converter hoods, thus reducing fugitive emissions. It was also found that improved operational practices (closing and maintaining hood gages, isolating converters on standby) could double the draft within the converter hoods while decreasing the total flow rate by nearly 10%.

The carbothermic reduction of magnesia to produce magnesium offers the potential of a lower energy and higher productivity route for metal production compared to existing industrial routes. The reaction of magnesia and carbon produces a magnesium and carbon monoxide vapor. Slow cooling of that vapor will allow the reaction to quickly revert and the prevention of this reversion reaction is a major technical challenge. Two main approaches can be taken to prevent reversion and allow recovery of the metal product: rapid quenching of the vapor and dissolving the magnesium directly in a suitable metal solvent before reversion can occur. The commercial viability of either carbothermic route to magnesium is closely connected to the physical chemistry of each system.

The paper presents the results of a computational model of erosion in a fluidised bed and a corresponding erosion experiment. The experiment has been simulated using the CFX [CFX-F3D, Version 4.1, Flow Solver User Manual, Computational Fluid Dynamics Services, AEA Industrial Technology, Harwell Laboratory, Oxfordshire, UK, 1995] code with computational models of hydrodynamics (hydrodynamic model A and kinetic theory model) and erosion (Finnie and kinetic theory). The experiment has been conducted at room temperature using a horizontal acrylic tube immersed in a rectangular fluidised bed for a total of 126 h of run. Erosion measurements were made every 14 h at eight equally spaced positions around the tube. The results show an induction period of 42 h. Most of the wear occurred around the bottom of the tube with the maximum at an angle of about 45° from the tube bottom. The kinetic theory model predictions are in good agreement with the experimental results.

Dust lift-off from conveyors forms a significant environmental and operational problem for operators in the mining, power generation and process industries. One means of reducing dust lift-off is to provide airflow deflectors or other aerodynamic modifications to the conveyor. A computational fluid dynamics (CFD) model has been developed to take into account the effect of wind direction, velocity and conveyor guarding on the dust loss from conveyors. The model is developed in the framework of CFX4. Experimental measurements of dust lift-off from the surface of a bed of ore in a wind tunnel at different wind velocities are used to characterise the dust. Based on the experimental data a model for predicting the mass and particle size distribution lifted from the bed surface at different air velocities is developed. The dust loss model is coupled to a Lagrangian particle-tracking model to predict particle trajectories. Validation of the model is undertaken by comparing CFD predictions against wind tunnel test work and shows good agreement. Results are presented for a typical conveyor design. The combination of experimental and CFD modelling is found to be a powerful tool for analysing dust loss from conveyors and can be extended to stockpiles and other situations where dust loss is a problem. The model can readily be extended to account for heat and moisture transfer in beds of porous materials.

Fluidized bed systems have the potential to be widely used in the power generation, mineral processing and chemical industries. One factor limiting their increased use is the lack of adequate design techniques for scaling such systems. A model has been developed for simulating gas–solid fluidized bed plant. The model uses a multiphase Eulerian–Eulerian technique to predict the transient behaviour of fluidized bed systems. The commercial CFD code CFX is used as the computational framework for solving the discretized equations. To overcome the problem of accurate geometrical representation experienced in previous models a body fitted grid system is employed. The model is used to predict isothermal flow in a three-dimensional bubbling fluidized bed. Predictions of the three-dimensional model show bubble formation with gas bubbles or voids preferentially moving along the centre of the bed. Predicted behaviour is qualitatively consistent with experimental observations.

Fluidized beds are widely used in many process industries including the food and pharmaceutical sectors. Despite being an intensive research area, there are no design rules or correlations that can be used to quantitatively predict the solid mixing in a specific system for a given set of operating conditions. This paper presents a numerical study of the gas and solid dynamics in a laboratory scale fluidized bed coating process used for food and pharmaceutical industries. An Eulerian–Eulerian model (EEM) with kinetic theory of granular flow is selected as the modeling technique, with the commercial computational fluid dynamics (CFD) software package ANSYS/Fluent being the numerical platform. The flow structure is investigated in terms of the spatial distribution of gas and solid flow. The solid mixing has been evaluated under different operating conditions. It was found that the solid mixing rate in the horizontal direction is similar to that in the vertical direction under the current design and operating conditions. It takes about 5 s to achieve good mixing.

The aerodynamics of fully turbulent jets supplied from rectangular slot-burners was modelled using the Reynolds Averaged Navier–Stokes (RANS) model. Three different turbulent models were considered, such as standard k-ε, RNG k-ε and Reynolds stress turbulence models. The recessed-type nozzle geometry was investigated to determine the effect of burner geometry on jet development. The slot-burner was based on physical models, which were designed to be representative of typical burner geometries found in tangentially-fired coal boilers. The study was validated against the physical models. The detailed flow field obtained from the simulations was used to explain the aerodynamic development of jets in such burners. It was found that the addition of a recess section to the nozzle geometry introduced significant changes to the flow due to complex pressure and mixing fields being set up inside the recess, which altered the jets once they exited into the open atmosphere.

Fume and hygiene hoods are widely used to prevent fugitive emissions from charge ports, tap holes and many other openings in mineral processing and smelting vessels. The highly buoyant nature of the fume combined with often complex geometries make the design of these hoods difficult with traditional engineering tools. However, by combining the traditional engineering approach with computational fluid dynamics (CFD) techniques, a clear understanding of the shortfalls of an existing system can be obtained, and an optimised hood design can be achieved. This paper reports on a combined engineering and CFD analysis of a fume extraction system for a zinc slag fumer charge port. The engineering model revealed that the existing plant components (bag house and fan) were not capable of capturing the required amount of fume, and that the original hood design was flawed. The CFD model was then used to predict the fume capture and emission from the existing hood. CFD model predictions showed that increasing the draft flow rate by an order of magnitude would only give a marginal improvement in fume capture. Using findings of both the models enabled a new fume capture hood to be designed. CFD analysis of the new hood revealed that a significant improvement in fume capture is possible. Construction and installation of the hood has been performed and a 65% reduction in fume emission was achieved, thus significantly mitigating a long-standing emission problem.

Vortex shedding in a bank of three rectangular burner-jets was investigated using a CFD model. The jets were angled to the wall and the whole burner was recessed into a cavity in the wall; the ratio of velocities between the jets varied from 1 to 3. The model was validated against experimentally measured velocity profiles and wall pressure tapings from a physical model of the same burner geometry, and was generally found to reproduce the mean flow field faithfully. The CFD model showed that vortex shedding was induced by a combination of an adverse pressure gradient, resulting from the diffuser-like geometry of the recess, and the entrainment of fluid into the spaces separating the jets. The asymmetry of the burner, a consequence of being angled to the wall, introduced a cross-stream component into the adverse pressure gradient that forced the jets to bend away from their geometric axes, the extent of which depended upon the jet velocity. The vortex shedding was also found to occur in different jets depending on the jet velocity ratio.