Bed In Static Geometry Research Articles

Granular material drying and energy analysis of a scaled-up rotating fluidized bed dryer of fixed geometry

The present investigation is focused on the grain drying in a scaled-up rotating fluidized bed in static geometry (RFB-SG) dryer, and then gradual cooling of the dried hot grains in the temperature stabilization unit (TSU). A freshly harvested crop in abundance seeks massive energy consumption in the drying process. Hence, to minimize these losses, energy-exergy analysis of grain-drying, for the inventory of 500 to 3000 g paddy, at temperature of 328–338 K and AFR 400–600 m3/h. It is observed that with the increase of drying air velocity and drying temperature positively affect both the production rate and production cost. Due reduction in drying time, cost, and energy requirement, the drying efficiency is improved. The energy utilization is found to be maximum of 3.52 kJ/s, at the AFR of 600 m3/h and the temperature of 338 K. Furthermore, the time of temperature stabilization of dried grains is observed 38 s with no effect on the nutritional value of the grains.

Experimental investigation of paddy drying characteristics in a slitless rotary fluidized-bed dryer

This research manifests the performance analysis of a novel slit-less rotating fluidized bed in static geometry (SL-RFBSG) using a local food grain paddy. From the economic point of view of the drying process, system economy, and system complexity, this dryer is developed without slit and rectangular air inlets. The performance of the developed dryer is evaluated, considering the effect of various operating parameters, namely loading capacity of grain, operating temperature, air flow rate, drying time and grain quality. The SL-RFBSG dryer's energy utilization, product quality, and overall drying performance are affected by increasing drying air temperature, air flow rate, and inventory. Hence, the drying efficiency of the developed dryer is increased by 20.5%, while 78% of milling rice is recovered.

Numerical study of the hydrodynamics and heat transfer characteristics of gas–solid in a slit-less rotating fluidized bed in static geometry

A rotating fluidized bed in static geometry (RFB-SG) without slits is presented in this paper as a research objective. The concept of RFB-SG is highly beneficial in numerous industrial operations such as granular drying, particle coating, mixing, agglomeration, and combustion. In this study, a three-dimensional CFD model is developed using the commercial software ANSYS FLUENT 14.5, to investigate hydrodynamics and heat transfer characteristics of gas–solid in the vortex chamber. The analysis of the flow pattern of gas–solid and the prediction of fluidization capacity have been made, using appropriate parameters. The findings showed that the significant factors, such as inlet air velocity, solid-bed thickness, the volume fraction of solids, solids pressure, and heat transfer coefficient, influenced the reactor capacity. It is observed that the solid inventories of 300 and 500 g have been fluidized perfectly at inlet air velocities of 30 m s−1 and 44 m s−1, respectively. The overall operating and drying costs are found to be decreased due to the reduction in fluidization air requirements.

Design considerations for small scale rotating fluidized beds in static geometry with screens for fine particles

Design of a small scale rotating fluidized bed (RFB) with diameter of 4–6cm to fluidize 40–80μm diameter particles was investigated using computational fluid dynamics (CFD). Simulations explored the impact of the following components on pressure drop and fluidized behavior of the device: particle size, particle density, outer diameter, solids loading, height, number of inlet slots, inlet slot width, angle of inlet slots, chimney diameter, chimney number of slots, chimney slot width, chimney slot angle, and position of the chimney relative to the inlets. Fluidized behavior was evaluated based on a “fluidization quality” metric yielding information about the distribution of particles in the device. Although additional work is required to elucidate design guidelines for small scale RFBs for fine particles, the initial designs evaluated in this work indicate potential for developing a fluidized bed of relatively small diameter, presenting opportunities for process intensification for numerous potential applications.

Solids velocity fields in a cold-flow Gas–Solid Vortex Reactor

In a Gas–Solid Vortex Reactor (GSVR), also referred to as a Rotating Fluidized Bed in Static Geometry, a fluidized bed is generated in a centrifugal field by introducing the gas via tangential inlet slots to the reactor chamber. Better heat and mass transfer are observed, making this a promising reactor type for Process Intensification. Developing GSVRs on industrial scale requires, amongst other, a good insight and understanding of the hydrodynamics of the granular flow. In the present work experiments are performed over a wide range of operating conditions in a cold flow pilot-scale set-up. The set-up has a diameter of 0.54m, a length of 0.1m and 36 tangential inlet slots of 2mm. Different materials with solids density between 950–1800kg/m3 and particle diameters of 1–2mm, at varying gas injection velocities from 55 to 110m/s are tested between minimum and maximum solids capacities. All these operating conditions are used to follow the change of granular flow by performing PIV. The rotating fluidized bed can change from a smoothly rotating, densely fluidized bed to a highly bubbling rotating fluidized bed depending on the operating conditions. Bubbling diminishes with increasing solids density and particle diameter. Experimental measurements of azimuthal particle velocity fields in a GSVR are for the first time reported. Azimuthal solids velocity is found to decrease with higher solids density and larger particle diameter. The critical minimum fluidization velocity, that is the minimum velocity at which the complete bed is fluidized, is calculated and the centrifugal bed behavior is mapped in terms of a dimensionless radial gas velocity and a dimensionless particle diameter, as conventionally done for gravitational beds.

Bed stability and maximum solids capacity in a Gas–Solid Vortex Reactor: Experimental study

A Gas–Solid Vortex Reactor (GSVR), in literature also referred to as Rotating Fluidized Bed in Static Geometry (RFB-SG), is a promising reactor type for Process Intensification (PI) with respect to reactor volume reduction. Although replacing gravitational by centrifugal force has been considered since the seventies, the hydrodynamics of the reactor flow and the bed behavior remain largely unknown. In the present work experiments have been carried out in a cold flow GSVR with diameter of 0.54m, length of 0.1m and 36 inlet slots of 2mm. Gas injection velocities of 55–111m/s and particles with densities of 950–1800kg/m3 and diameters of 1–2mm have been applied. Depending on solids density, particle diameter and gas injection velocity the bed behavior can be considered as stable, semi-stable or unstable. For semi-stable and stable flow regimes the effect of the above process conditions on the maximum solids capacity was investigated. With increasing solids density, the bed stability considerably decreases, while the maximum solids capacity increases. By increasing the gas injection velocity, both the bed stability and the maximum solids capacity increase. Once bed stability is accomplished, a further increase of the gas injection velocity does not affect the maximum solids capacity. With increasing particle diameter, the bed stability decreases while the maximum solids capacity increases.

Rotating fluidized bed with a static geometry: Guidelines for design and operating conditions

Abstract Computational fluid dynamics (CFD) simulations of the hydrodynamic behavior of rotating fluidized beds in static geometry (RFB-SG) are carried out for gas–solid flows. The rotating motion of the reactor bed is induced by the tangential injection of the gas along the circumference of the fluidization chamber. Steep gradients in the gas velocity fields both in radial and tangential direction generate turbulence. The radial and tangential drag forces fluidize the particle bed in both radial and tangential direction. An Eulerian two-fluid model is used. Gas phase turbulence is accounted for by a k–e model adapted for rotational flows. The RFB-SG simulations provide guidelines for a design and operation with a high efficiency in gas–solid momentum transfer, excellent gas–solid separation and limited solids losses. Hydrodynamic variables like the centrifugal force, the injection pressure, the radial and tangential slip velocities, solids hold-up are calculated for both polymer particles (300 μm, 950 kg/m3, Geldart Group B) and glass beads (70 μm, 2500 kg/m3, Geldart Group A) to allow for a comparison among different fluidization chamber designs. Unstable bed behavior, like slugging and channeling, is also numerically predicted.