Laws of motion of particles in a jigging process

The laws of motion of particle groups in a jigging process are studied. These describe the macroscopic phenomena that occur during jigging. During jigging the heavier and bigger particles concentrate at the bed bottom while lighter and smaller particles move to the upper part of the bed. Particles with equivalent properties tend to concentrate at a certain position centered around the inherent height of their distribution. The particle distribution variance gradually diminishes to some asymptotic value. The state equation group of the jigging bed is deduced and a calculation method, called the λ value judgment method, is proposed. The method is used to calculate the layer number and the inherent height of each particle group. A mathematical expression for the particle distribution variance is also given.

The Ejffect of Vertical Internal Baffles on Fluidization Hydrodynamics and Grain Drying Characteristics

The effect of vertical internal baffles on the particle mixing and graindrying characteristics in a batch fluidized bed column is investigated. Experimental work wascarried out in a 3m high rectangular fluidized bed dryer of cross sectional area of 0.15 m x 0.61 mat different operating conditions using paddy, a group D particle, as the fluidizing material. Theresults of the study showed that the fluidized bed dryer system with vertical internal baffles gavebetter particle mixing effect in the bed of particles than that without vertical internal baffles.This is due to the fact that the vertical internal baffle act as gas bubble breakers by breaking upthe large gas bubbles into smaller ones. The smaller bubbles cause a more vigorous mixing in the bedof particles before finally erupting at the bed surface. This improves the contacting efficiencyand enhanced the heat and mass transfer of the fluidized bed system. Thus a higher drying rate wasobtained in the falling rate period because the higher contacting efficiency increases theevaporation rate at the particle surface. However, the drying rate in the diffusion region showslittle improvement because the moisture diffusivity does not depend on the contacting efficiency.The fluidized bed dryer with vertical internal baffles could therefore be used in the initial rapiddrying stage in a two stage drying strategy for paddy. The insertion of vertical internal bafflesinto a fluidized bed system improves the processing of Group D particles in a fluidized bed systemespecially if the system is large in scale.

A state-of-the-art review on transition between the fast fluidization and pneumatic transport of Geldart group B particles

The fluidization state in the circulating fluidized bed(CFB)boiler is crucial to its stable and safe operation.However,up to now,the research field has not reached unanimity on whether the fluidization regime that the upper furnace of the boiler operates in is the fast fluidization or pneumatic transport.To this end,this paper reviewed relevant research on the transition between the fast fluidization and pneumatic transport of Geldart group B particles,including the flow characteristics of the fast fluidization,the transition condition between the fast fluidization and pneumatic transport,the determination methods of the transport velocity utr and saturation carrying capacity G_(s)* and the influencing factors on these two parameters.Previous research findings can provide certain guidelines for the design and optimization of the CFB boiler,and result in plenty of prediction correlations for utr and G_(s)*.Nonetheless,owing to insufficient data available on Geldart group B particles,especially the ones obtained under high temperature or pressure conditions and in large-scale CFB apparatuses,the existing correlations are not well suited for the prediction of u_(tr) and G_(s)* of Geldart group B particles.Thus,further efforts are urgently demanded on the fast fluidization transition of Geldart group B particles.

Gas-solid flow in a high-density circulating fluidized bed riser with Geldart group B particles

We carried out experiments to explore and characterize the gas-solid flow dynamics of Geldart group B particles in a dense circulating fluidized bed riser. By reducing the pressure drop across the solid control valve and increasing the solid inventory in the storage tank, a high solid circulation rate and a solid holdup above 0.075 throughout the riser were simultaneously achieved. At a solid-to-gas mass flux ratio of approximately 105, flow transitioned from fast fluidization to a dense suspension upflow. In the axial direction of the riser, solid holdup had an exponential profile, increasing with increasing solid circulation rate and Jot decreasing superficial gas velocity. From the riser＇s center to its wall, the solid holdup increased markedly, exhibiting a steep parabolic profile. Increasing the solid circulation rate increased the radial non-uniformity of the solid concentration, while increasing the superficial gas velocity had the opposite effect, In our dense circulating fluidized bed riser, Geldart group B particles had similar slip characteristics to Geldart group A particles,

Reaction performance of fluidized bed catalytic reactor of Group C^(+)particles

Group C particles are often regarded as non-fluidizable but have proven to effectively fluidize with nanoparticle addition,which results in small bubbles and a high gas holdup in the dense phase during the experiments.Group C^(+)particles provide an increased surface area for gas-solid contact and improve the reaction performance,especially for gas-phase catalytic reactions.On the basis of a previous study of the ozone decomposition reaction using Group C^(+)particles,a two-phase model was used to evaluate the reactor contact efficiency,and was used to compare the partial oxidation performance of the n-butane to maleic anhydride reaction in fluidized-bed catalytic reactors of Group C^(+)and Group A particles.The reactor with Group C^(+)particles achieved a higher n-butane conversion and MAN yield compared with that using Group A particles,based on the identical catalyst quantity or on the same gas residence time.Therefore,the reactor with Group C^(+)particles can achieve the same reaction conversion and yield with fewer catalysts or a smaller reactor size,or both.Therefore,the fluidized bed catalytic reactor of Group C^(+)particles is expected to be of major significance in industrial processes,especially for gas-phase catalytic reactions.