Granular Motion in a Rotary Kiln: the Transition from Avalanching to                    Rolling

Davidson, John; Scott, D. M.; Bird, Paul; Oliver, Herbert; Powell, Andrew; Ramsay, H. T.

doi:10.14356/kona.2000021

Cited by 27 publications

(11 citation statements)

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“…Metcalfe et al 1995, Shinbrot et al 1999, Hill et al 1999, Gray 2001 are often used in the pharmaceutical and food industry, while rotary kilns and inclined rotating cylinders (e.g. Davidson et al 2000, Spurling et al 2001) are favoured by chemical engineers for sintering, calcination, humidification, oxidation, drying, mixing, induration, reducing, gas-solid reaction, incineration, heating, cooling and cement production, because they allow continuous feed. These fields represent a substantial worldwide financial turnover.…”

Section: Introductionmentioning

confidence: 99%

A three-phase mixture theory for particle size segregation in shallow granular free-surface flows

2006

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Particle-size segregation within granular materials is of great technological significance yet it is still very poorly understood. There are several causes for segregation, but this paper focuses on kinetic sieving which is the dominant mechanism in dense gravity-driven shallow free-surface flows, or, granular avalanches. The segregation model is derived from a three-phase mixture theory composed of large particles, small particles and a passive interstitial fluid. Steady-state solutions are constructed for a normally graded inflow in a steady uniform flow field. This problem is of fundamental interest, because it shows how an unstably stratified layer readjusts into a stable configuration. Expansion fans and concentration shocks are generated and sufficiently far downstream inversely-graded segregated layers form, with the larger particles overlying the finer ones. The distance for complete segregation to occur is shown to increase with rising fluid density and tends to infinity as its density approaches that of the grains. If the particles are buoyant then the initial configuration is stable. An exact time-dependent two-dimensional solution is constructed for plug-flow, which exploits the uncoupling of material columns of grains in the absence of shear. This yields insight into the nature of more complex numerical solutions for strong shear, which are computed with a high resolution, shock-capturing numerical scheme.

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Section: Introductionmentioning

confidence: 99%

A three-phase mixture theory for particle size segregation in shallow granular free-surface flows

2006

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“…The scale of granular materials processing is vast, with applications in the bulk chemical, pharmaceutical, mining, food and agricultural industries. In many of these processes, such as in rotational mixers (Shinbrot & Muzzio 1999) and huge continuous feed rotational kilns (Davidson et al 2000), segregation occurs in shallow granular avalanches that develop in the free-surface layer of the flow. A knowledge of the segregation within these avalanches is therefore vital to understanding the segregation and mixing in more complex granular flows with solid-liquid phase transitions (Williams 1968, Gray & Hutter 1997.…”

Section: Introductionmentioning

confidence: 99%

Time-dependent solutions for particle-size segregation in shallow granular avalanches

2006

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Rapid shallow granular free-surface flows develop in a wide range of industrial and geophysical flows, ranging from rotating kilns and blenders to rock-falls, snow slab-avalanches and debris-flows. Within these flows, grains of different sizes often separate out into inversely graded layers, with the large particles on top of the fines, by a process called kinetic sieving. In this paper, a recent theory is used to construct exact time-dependent two-dimensional solutions for the development of the particle-size distribution in inclined chute flows. The first problem assumes the flow is initially homogeneously mixed and is fed at the inflow with homogeneous material of the same concentration. Concentration shocks develop during the flow and the particles eventually separate out into inversely-graded layers sufficiently far downstream. Sections with a monotonically decreasing shock height, between these layers, steepen and break in finite time. The second problem assumes that the material is normally graded, with the small particles on top of the coarse ones. In this case, shock waves, concentration expansions, non-centred expanding shock regions and breaking shocks develop. As the parameters are varied, non-linearity leads to fundamental topological changes in the solution, and, in simple-shear, a logarithmic singularity prevents a steady-state solution from being attained.

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“…An alternative was given by Davidson et al [10] based on microscope analysis in which a single particle sliding down a slope with surface friction is considered. In the analysis of force balance, it was assumed that (i) the inclination of the slope is tan h c and (ii) the friction coefficient between the particle and the slope is tan h r .…”

Section: Model Studiesmentioning

confidence: 99%

“…Moreover, the parameters needed for the model calculation (e.g., thickness of the avalanching particle layer) are difficult or even impossible to measure on a real rotary kiln. Relatively simple models were provided by Mellmann [2], Henein et al [9], and Davidson et al [10] to calculate the avalanche time. The input parameters for calculation are known as operating parameters or as online measurable.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, theoretical models from Mellmann [2], Henein et al [9], and Davidson et al [10] for the calculation of avalanche time are briefly described and compared. The avalanching flow of irregularly shaped rice particles is then experimentally investigated on a 165 mm ID rotating cylinder with filling degrees varying from 10 % to 35 %.…”

Section: Introductionmentioning

confidence: 99%

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Avalanche Time of Granular Flows in Rotary Kilns

2010

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Discrete avalanching is the dominant motion of granular beds in industrial rotary kilns. The avalanche time is an important parameter influencing the heat-and material transfer inside the kiln. Experiments are conducted on a rotating cylinder to measure the time evolution of avalanches. Nonspherical particles (rice) and low filling degrees are used in order to simulate the operating conditions in industrial kilns. The difference between the average critical angle and stop angle of the avalanche is found to be in the range of 7°-9°, i.e., much higher values than ever reported in literature. As the filling degree is three times increased, the average critical angle is found to be approximately constant, whereas the average stop angle is slightly increased and the avalanche time is increased by 20 %. For all experimental configurations, the average avalanche time occupies about 35 %-38 % of the total circle time (elevation time plus avalanche time). Experimental data are used to test theoretical models from different authors. Comparison demonstrates that the models proposed by Mellmann and Davidson et al. can predict well the increasing tendency of average avalanche time with filling degrees. The former has higher accuracy with errors less than 5 % for all experiments. Results of this work are useful for kiln design and further theoretical studies on dynamics of granular avalanches.

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Granular Motion in a Rotary Kiln: the Transition from Avalanching to Rolling

Cited by 27 publications

References 0 publications

A three-phase mixture theory for particle size segregation in shallow granular free-surface flows

A three-phase mixture theory for particle size segregation in shallow granular free-surface flows

Time-dependent solutions for particle-size segregation in shallow granular avalanches

Avalanche Time of Granular Flows in Rotary Kilns

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