Experimental and numerical investigations of a pseudo-2D spout fluidized bed with draft plates

Spout fluidized beds are often utilized for gas-solid contacting operations involving physical and/or chemical transformations with simultaneous heat and mass transfer such as drying, coating, granulation, combustion, gasification etc. This is because these beds combine advantages of both spouted and fluidized beds. Since the development of the spout fluidized bed, several geometrical modifications have been proposed to optimize the bed performance. One of these modifications often applied in granulation and coating industries includes a draft tube insertion inside the bed, which results in improved performance by providing a restriction on lateral particle flow providing clear distinction for wet spout and dry annulus zones. Moreover, the insertion of the draft tube leads to a stable spouting at lower flow rates, due to the reduced bypassing of the inlet gas (from spout to annulus). In this work, the hydrodynamic characteristics of a spout fluidized bed with draft plates was studied to identify the flow characteristics by constructing a flow regime map by image analysis and a fast Fourier transform of the measured pressure signal. In addition, the captured images were used to determine the particle velocity via particle image velocimetry (PIV). Furthermore, simulations were carried using a discrete particle model with a sub grid scale turbulence model for two regimes, namely the spouting-with-aeration and fluidized bed-spouting-with-aeration (dispersed spout), which are of most interest from an industrial view point. The obtained results were compared with previously obtained experimental data i.e. PIV. This study highlights various flow pattern observed during operation of spout fluidized bed with a draft plate over a wider operating conditions, which is useful to select proper operating conditions; whereas the experimental data can be used for computational fluid dynamic (CFD) model validation, which serve as a building block for design and scale-up at higher operational scales. Besides this, the quantitative information such as particle velocity, residence time distribution, solid mixing and circulation can be obtained after suitable post processing hence useful in optimizing the bed performance. (C) 2013 Elsevier B.V. All rights reserved.