Paul Zulli

An experimental and numerical study of the angle of repose of coarse spheres

This paper presents a numerical and experimental study of the angle of repose of mono-sized coarse spheres, a most important macroscopic parameter in characterising granular materials. Numerical experiments are conducted by means of a modified discrete element method. Emphasis is given to the effects of variables related to factors such as particle characteristics, material properties and geometrical constraints. The results show that under the present simulation conditions, the angle of repose is significantly affected by the sliding and rolling frictions, particle size and container thickness, and is not sensitive to density, Poissons ratio, damping coefficient and Youngs modulus. Increasing rolling or sliding friction coefficient increases the angle of repose, while increasing particle size or container thickness decreases the angle of repose. Based on the numerical results, empirical equations are formulated for engineering application. The proposed simulation technique and equations are validated by comparing the physical and numerical experiments, where focus is given to the effects of particle size and container thickness.

Numerical simulation of the gas-solid flow in a bed with lateral gas blasting

Abstract This paper presents a numerical study of the gas–solid flow in a bed by a Combined Continuum and Discrete Model (CCDM). Numerical experiments are carried out to simulate the motion of 10,000 spherical particles of 4 mm diameter caused by lateral gas blasting into a bed with its thickness equal to the diameter of particles. It is shown that, depending on the gas velocity, the bed can transform from a fixed bed to a fluidised bed or vice versa. Two zones can be identified in such a bed: a stagnant zone in which particles remain in their initial positions, and a mobile zone in which particles can move in various flow patterns. If the gas velocity is in a certain range, the mobile zone is confined in front of the gas inlet, forming the so-called raceway in which particles can circulate. If the gas velocity is higher than a critical value, fluidisation results, with the mobile zone growing by the combined effect of bubble penetration and shearing between moving and static particles until a stable state where the boundary separating the mobile and stagnant zones is unchanged. The dependence of raceway and fluidisation phenomena on gas velocity has been examined in terms of the size and shape of the mobile zone, gas-solid flow patterns and forces acting on individual particles. It is found that large interparticle forces occur along the boundary between the mobile and stagnant zones, whereas large fluid drag forces occur at the roof of a raceway or bubble. The predictions of transition between the static and dynamic states, and the complicated hysteretic behaviour in terms of either bed pressure drop or raceway size are in good agreement with the experimental observations.

Evaluation of effective thermal conductivity from the structure of a packed bed

Abstract This paper presents a method to evaluate the effective thermal conductivity from the packing structure of a packed bed of mono-sized spheres in the presence of a stagnant fluid. The evaluation is based on two aspects: (i) the heat transfer between particles, which is obtained under some simplified conditions; and (ii) the connectivity of particles in a packing, which is determined from the packing structure measured by Finney. Three heat transfer mechanisms or paths are considered in the present modelling, including the conduction through the solid particles and stagnant fluid between non-contacted particles, the conduction through the solid particles and stagnant fluid and the conduction through the contact area between contacted particles. The validity of this approach is verified by the good agreement between measured and calculated results for a packed bed over a wide range of solid-to-fluid thermal conductivity ratio and for packed beds with particles of different thermal conductivities.

Stress distribution in a sandpile formed on a deflected base

This paper presents a study of the pressure distribution beneath a sandpile by means of discrete element method. Simulations were performed with spheres of different properties for wedge-shaped sandpiles formed on bases of different degrees of deflection. The results are analyzed in terms of the stress distribution, and normal and shear pressure distributions beneath a sandpile. It is shown that the interparticle forces in a sandpile are highly disordered and mainly propagate with large force chains. Base deflection has a significant effect on the normal pressure distribution when a sandpile is formed with multisized particles and small sliding friction coefficients. However, it is not the sole factor leading to a normal pressure distribution with a dip, particularly when a sandpile is formed with monosized particles.

Gas-liquid-powder flow in moving particles : Operational and non-operational regimes

Abstract An experimental study has been carried out for gas–liquid–powder–solid four-fluid flow in a packed bed. This system simulates the complex flow conditions in an ironmaking blast furnace which involves the upward flow of gas and unburnt coal/char and the downward flow of coke and molten iron and slag. It is shown that depending on the flow conditions, both steady and unsteady state flows can be observed, giving the so-called operational and non-operational regimes. The effects of solid, liquid, powder and gas flow conditions on the two regimes have been quantified. The non-operational regime stems from the flooding caused by high superficial gas and liquid velocities, and powder mass flux and/or hanging caused by high powder mass flux and low gas velocity. The operational regime expands with an increase in solid velocity, and contracts with an increase in gas and liquid velocities and/or powder mass flux.

Experimental and numerical simulation of discrete liquid flow in a packed bed

This paper presents a combined experimental and numerical method to simulate the liquid flow in a packed bed. Two types of the experiments, i.e. liquid percolation without gas flow and liquid flow with gas cross flow, were conducted using a three- or two-dimensional cold model, respectively. A mathematical model has been proposed for the numerical simulation of the liquid flow. This model was developed using a force balance approach combined with stochastic considerations, in which the liquid flow was treated as a discrete phase with stochastic dispersion based on the experimental observations. Accordingly, the interactions between liquid and the packed bed, and liquid and gas have been experimentally investigated and then were used to determine the model parameters involved in the model. The behavior of the liquid flow in packed beds can numerically be simulated using the proposed model. A reasonable agreement has been achieved between the model predictions and the experimental measurements.

A simplified mathematical model for gas–solid flow in a blast furnace

This paper presents a numerical study of the behaviour of solid flow in a two-dimensional blast furnace with or without gas flow. The mathematical model, as a simplified version of the more detailed model developed earlier, is similar to the so-called viscous flow model but the method to determine the stagnant zone profile is similar to that used in the kinematic model. The study shows that the simplified model is able to capture the key flow characteristics of solid flow in a blast furnace and describe reasonably the effects of gas and solid flowrates, and particle properties, although the predicted quasi-stagnant zone may be smaller. The advantage of the present approach is that it can be readily implemented in a full process model that needs to have a quick response to change for the purpose of control and optimisation.

An Integrated Model of Coal/Coke Combustion in a Blast Furnace

A three‐dimensional integrated mathematical model of the combustion of pulverized coal and coke is developed. The model is applied to the region of lance‐blowpipe‐tuyere‐raceway‐coke bed to simulate the operation of pulverized coal injection in an ironmaking blast furnace. The model integrates two parts: pulverized coal combustion model in the blowpipe‐tuyere‐raceway‐coke bed and the coke combustion model in the coke bed. The model is validated against the measurements in terms of coal burnout and gas composition, respectively. The comprehensive in‐furnace phenomena are simulated in the raceway and coke bed, in terms of flow, temperature, gas composition, and coal burning characteristics. In addition, underlying mechanisms for the in‐furnace phenomena are analyzed. The model provides a cost‐effective tool for understanding and optimizing the in‐furnace flow‐thermo‐chemical characteristics of the PCI process in full‐scale blast furnaces.

Current Status and Future Direction of Low-Emission Integrated Steelmaking Process

In 2006 the Australian steel industry and CSIRO initiated an R&D program to reduce the industry’s net greenhouse emission by at least 50%. Given that most of the CO2 emissions in steel production occur during the reduction of iron ore to hot metal through use of coal and coke, a key focus of this program has been to substitute these with renewable carbon (charcoal) sourced from sustainable sources such as plantations of biomass species. Another key component of the program has been to recover the waste heat from molten slags and produce a by-product that could be substituted for Portland cement.

Modelling the gas-liquid flow in an ironmaking blast furnace

A mathematical model is presented to describe the discrete flow of liquid within and below the blast furnace cohesive zone. The model is developed based on a force balance approach to describe the liquid flow and a stochastic treatment to take into account the complex packing structure. The interaction between gas and liquid flows has been included in the governing equations, so that the localised liquid flow in a packed bed can be modelled with or without gas flow. The validity is demonstrated by comparing model predictions and measurements obtained under different gas and/or liquid flow conditions. Application of the model to blast furnace is discussed with reference to the interaction between gas and liquid phases and the effect of cohesive zone shape.