Effects Of Static Bed Height Research Articles

Bed Fluctuation Ratio for Regular and Irregular Particles in Gas-Solid Tapered Fluidised Beds

The fluctuation ratios for regular and irregular particles have been investigated in gas-solid tapered fluidised beds. Based on dimensional analysis, models have been developed with the system parameters viz. geometry of tapered bed, particle diameter, static bed height, density of solid and gas, and superficial velocity of the fluidising medium. Effects of static bed height, particle diameter and tapered angle on fluctuation ratio have been investigated. A comparison has been made between the estimated values of bed fluctuation ratios using the proposed models, experimental values and the model available in literature for conical beds. It has been found that the average absolute errors between the experimental measured values and the predicted values from the proposed models are within ±15%.

Effect of static bed height in the upper fluidized bed on flow behavior in the lower riser section of a coupled reactor

To study olefin reduction by using an auxiliary reactor for FCC naphtha upgrading, a large-scale cold model of a riser-bed coupled to an upper fluidized bed was established. The effect of static bed height in the upper fluidized bed on particle flow behavior in the lower riser was investigated experimentally. A restriction index of solids holdup was used to evaluate quantitatively the restrictive effect of the upper fluidized bed. Experimental results show that, under the restrictive effect of the upper fluidized bed, the riser could be divided into three regions in the longitudinal direction: accelerating, fully developed and restriction. The axial distribution of solids holdup in the riser is characterized by large solids holdup in the top and bottom sections and small solids holdup in the middle section. Overall solids holdup increased with increasing static bed height in the upper fluidized bed, while particle velocity decreased. Such restrictive effect of the upper fluidized bed could extend from the middle and top sections to the whole riser volume when riser outlet resistance is increased, which increases with increasing static bed height in the upper fluidized bed. The upper bed exerts the strongest restriction on the area close to the riser outlet.

Detailed measurements of flow structure inside a dense gas–solids fluidized bed

Detailed local flow structures are investigated in bubbling and turbulent fluidized bed with FCC particles. The operating conditions ranges from 0.06 to 1.4 m/s. Extensive experiments are carried out using a newly developed optical fiber probe system, which can measure the solids concentration and velocity at multi-points. The results reveal that with increasing U g, local solids concentrations go through three evolution stages, reflecting a gradual regime transition process. Under all operating conditions, upflowing and descending particles co-exist at all measuring locations. The upflowing particle velocity is strong function of both superficial gas velocity and spatial position. However, the descending particle velocity mainly depends on superficial gas velocity. The bed radial symmetry and the effects of static bed height on the local flow structures are also investigated.

Hydrodynamic characteristics of spout-fluid bed: Pressure drop and minimum spouting/spout-fluidizing velocity

Experimental investigations on the hydrodynamic characteristics were carried out in a two-dimensional spout-fluid bed with cross section of 300 mm × 30 mm and height of 2000 mm. Six kinds of Geldart group D particles were used as bed materials. The effects of static bed height, particle property, spout nozzle width and fluidizing gas velocity on the pressure drop, maximum spouting pressure drop, minimum spouting velocity and minimum spout-fluidizing velocity were systematically studied. The results show that the total bed pressure drop appears a spouted bed characteristic when increasing the spouting gas velocity and keeping the fluidizing gas velocity constant, while it appears a fluidized bed characteristic when increasing the fluidizing gas velocity and keeping the spouting gas velocity constant. The maximum spouting pressure drop required to initiate spouting increases with static bed height and particle density, but decreases with particle diameter, spout nozzle width and fluidizing gas velocity. The minimum spouting and spout-fluidizing velocities both increase with static bed height, particle diameter, spout nozzle width. The minimum spout-fluidizing velocity increases while the minimum spouting velocity decreases with fluidizing gas velocity. Additional, correlations considered all of the above effects were developed to predict the minimum spout-fluidizing and spouting velocities of the spout-fluid bed, which were in satisfied agreement with the present experiments and some published experimental results.

Contribution of Local Reactions in the Grid Zone to the Performance of a Jetting Fluidized Bed Gasifier of Coal Char

The effects of gasification conditions, namely bed temperature, static bed height, and nozzle diameter, on the concentrations of H 2 , CO, and CO 2 were investigated using a batchwise fluidized bed gasifier of coal char. Gas concentration profiles in the bed could be explained by the production of gases chiefly via combustion, steam gasification, CO 2 gasification, and the diffusion of produced gases. The temperature dependence of gas concentrations indicates that steam gasification occurred in the lower part of the grid zone at a higher bed temperature and the selectivity of CO production via combustion in the boundary region of the jet and annulus also increased. The results of the effect of static bed height suggest that CO 2 gasification mainly proceeded in the bubbling zone and the local reactions in the grid zone were hardly influenced by gas and solid behavior or reactions in the upper part of the bed. Though the diameter and height of the jet would be dependent on nozzle diameter, the effect of nozzle diameter on the local progress of gasification in the grid zone was hardly observed. It can be concluded that gasification proceeded in both the bubbling zone and annulus region, especially near the distributor, while combustion mainly occurred in the jet and boundary of the jet and annulus.

Continuous Drying of Slurry in a Jet Spouted Bed

ABSTRACT he performance of a laboratory scale jet spouted bed (JSB) for drying rice flour slurry was studied. The bed consisted of ceramic balls (5028 mm diameter) and the rice flour slurry was sprayed onto the moving particle surface near the inlet part. All the experiments were carried out at the jet spouting regime. This regime has high bed void fraction and violent movement and collision of bed particles. As a result, the dried product layer is attrited from particle surface as a fine powder and entrained from the bed by the spouting air. The experimental result were presented to show the effects of static bed height, inlet air flow rate and temperature, and feed concentration and flow rate on the outlet air temperature, thernal efficiency, and mean particle size and moisture content of the product. Asimple mathematical model, which is based on the conservation of mass and energy equations, was developed. Predicted results agreed well with those obtained from the experiment.