Comparison of fibre optical measurements and discrete element simulations for the study of granulation in a spout fluidized bed

Abstract

Spout fluidized beds are frequently used for the production of granules or particles through granulation. The products find application in a large variety of applications, for example detergents, fertilizers, pharmaceuticals and food. Spout fluidized beds have a number of advantageous properties, such as a high mobility of the particles, which prevents undesired agglomeration and yields excellent heat transfer properties. The particle growth mechanism in a spout fluidized bed as function of particle-droplet interaction has a profound influence on the particle morphology and thus on the product quality. Nevertheless, little is known about the details of the granulation process. This is mainly due to the fact that the granulation process is not visually accessible. In this work we use fundamental, deterministic models to enable the detailed investigation of granulation behaviour in a spout fluidized bed. A discrete element model is used describing the dynamics of the continuous gas-phase and the discrete droplets and particles. For each element momentum balances are solved. The momentum transfer among each of the three phases is described in detail at the level of individual elements. The results from the discrete element model simulations are compared with local measurements of particle volume fractions as well as particle velocities by using a novel fibre optical probe in a fluidized bed of 400 mm I.D. Simulations and experiments were carried out for two different cases using Geldart B type aluminium oxide particles: a freely bubbling fluidized bed and a spout fluidized bed with the presence of droplets. It is demonstrated how the discrete element model can be used to obtain information about the interaction of the discrete phases, i.e. the growth zone in a spout fluidized bed. Eventually this kind of information can be used to obtain closure information required in more coarse grained models.

Modelling of Spouted and Spout-Fluid Beds: Key for Their Successful Scale Up

“…Four different scaling approaches and a full scale approach were tested in the simulation of a spout-fluid bed by Banerjee and Agarwal [114]: one based on parcels, one proposed by Glicksman et al [170], one proposed by Link et al [171], and one based on the terminal particle velocity, proposed by the authors. Banerjee and Agarwal [114] found that their method was both the most reliable in reproducing the behaviour of particles and the most efficient in reducing the number of simulated particles, thus optimising the computational time.…”

Investigation on Dynamic Calibration for an Optical-Fiber Solids Concentration Probe in Gas-Solid Two-Phase Flows

“…Calibration of a probe is finding a calibration curve with experiments and computations to convert the voltage time series into solids concentration time series [24]. The appropriate calibration method must be suitable for a wide range of solids concentrations from very low concentrations up to the solids concentrations of a packed bed [14]. However, it is difficult to generate a reference suspension of particles with a given concentration, and it is nearly impossible to produce a homogeneous gas-solid flow.…”

Modeling of Gas‐Particle Turbulent Flow in Spout‐Fluid Bed by Computational Fluid Dynamics with Discrete Element Method

“…It has been successfully applied in industrial processes including, among others, combustion [2,3], gasification [4][5][6], drying [7] and granulation [8,9]. However, the hydrodynamics of the spout-fluid bed are much more complex than those of the conventional spouted bed, flow characteristics and scale-up cannot be predicted with confidence at this stage of development [10].…”

“…In previous work, Link et al [8,9,13,14] studied particle fluxes, flow regimes and granulation process in a rectangular spout-fluid bed, based on a hard-sphere model developed by Hoomans et al [15]. Zhong et al [16] reported a 3D CFD-DEM simulation of gas and solid turbulent flow in a rectangular spout-fluid bed with V-shape base by incorporating a k-e turbulent model and a DEM model (i.e.…”