Optimization of prismatic spouted bed apparatuses using novel experimental setup and discrete particle modelling

No abstract

Investigations on the spouting stability in a prismatic spouted bed and apparatus optimization

This paper deals especially with spouting stability in a slot-rectangular (prismatic) spouted bed. The flow stability was characterized by the pressure drop evaluation (the uniformity and amplitude of the fluctuations) and visual observations (the flow symmetry). The effect of several geometrical conditions, such as the inlet design, prismatic angle and draft plates on the bed behaviour was investigated for different particles and bed inventories exposed to different air flow rates. The prismatic angle was found to have a strong impact on the spouting characteristics. A method to improve significantly the spouting quality and to make the spouting stability independent on the gas inflow velocity is presented. Compared to the reference geometry the prismatic angle was changed to a higher value and the apparatus was equipped with draft plates. Whereas, to achieve a stable spouting in a wide range of the air flow rates the design of draft plates should be customized to the bed inventory. Dependent on the static bed height full or open-sided draft plates should be used. In the proposed apparatus implementation, the maximum spouting velocity was almost eliminated for large particles (Geldart D), i.e. a highly coherent dense spouting can pass continuously into the dilute-like stable regime, without stability loss at intermediate gas velocities. The spouting of Geldart B particles is also improved

Characterization and CFD-DEM modelling of a prismatic spouted bed

In this study a prismatic spouted bed was characterized experimentally and modelled by means of 3D CFD-DEM simulations. The main focus was on the investigation of the influence of the gas flow rate on the bed dynamics and spouting stability. Pressure drop time series obtained at different gas velocities were used for the identification of flow regimes by means of the frequency domain and of chaotic properties such as the correlation dimension and Kolmogorov entropy. The gas and particle dynamics were investigated through simulations of different operational regimes: the spouting onset, as well as stable and instable regimes. A 3-D bed behaviour, typical for slot-rectangular beds, was found. A good agreement between simulations and experiments in the particle flow patterns, bed expansion and dynamics of characteristic gas pressure fluctuations was achieved. The particle dynamics as a function of the gas velocity was investigated for the entire bed. For one of the stable regimes, the bed regions showing different particle dynamics (spout, fountain and annulus) were characterized in detail. A regime map showing the stable operational window in dependence on an inlet-to-bed size ratio and gas velocity is also provided

CFD-DEM simulations of the gas and particle dynamics in a novel prismatic spouted bed

In this investigation a prismatic spouted bed apparatus with two horizontal gas inlets was modeled by using a Discrete Element Model (DEM) coupled with Computational Fluid Dynamics (CFD), also called Discrete Particle Model (DPM). The bed hydrodynamics were characterized experimentally by means of high speed video recordings and Fast Fourier Transformation (FFT) of the measured pressure drop signal. Different operational regimes could be identified by the FFT. The simulations were performed at the gas flow rates corresponding to the minimum spouting velocity ums, to the upper end of the dense spouting domain and to the instable region at high gas velocities. The simulations predict well the expansion of the particle bed, the particle flow patterns, and characteristic pressure drop fluctuations for all studied regimes. Single peaks in the FFT power plots, characteristic to the stable dense spouting, were obtained and are in good agreement with experiments regarding the frequency of the pressure fluctuations. The irregular pressure behaviour resulting in additional peaks in the FFT spectra was predicted accurately by the DPM model. The spouted bed was characterized regarding the particle micromechanics in the apparatus regions with different particle dynamics, such as the annulus, fountain and spout

Characterization and CFD-DEM modelling of a prismatic spouted bed

In this study a prismatic spouted bed was characterized experimentally and modelled by means of 3D CFD-DEM simulations. The main focus was on the investigation of the influence of the gas flow rate on the bed dynamics and spouting stability. Pressure drop time series obtained at different gas velocities were used for the identification of flow regimes by means of the frequency domain and of chaotic properties such as the correlation dimension and Kolmogorov entropy. The gas and particle dynamics were investigated through simulations of different operational regimes: the spouting onset, as well as stable and instable regimes. A 3-D bed behaviour, typical for slot-rectangular beds, was found. A good agreement between simulations and experiments in the particle flow patterns, bed expansion and dynamics of characteristic gas pressure fluctuations was achieved. The particle dynamics as a function of the gas velocity was investigated for the entire bed. For one of the stable regimes, the bed regions showing different particle dynamics (spout, fountain and annulus) were characterized in detail. A regime map showing the stable operational window in dependence on an inlet-to-bed size ratio and gas velocity is also provided