Characterization of the fluid dynamics and discrete element modelling of a novel spouted bed apparatus
Dipl.-Ing. Vitalij Salikov
Spouted beds are well known for their good mixing properties and also for their intensive heat and mass transfer between the fluid and the solid phases. The main difference of spouted beds in comparison with conventional fluidized beds is the variable apparatus cross-section as function of the apparatus height. Furthermore, the fluidization gas is not supplied into the apparatus equally distributed over a gas distributor plate, but enters the process chamber as a gas jet with high gas velocities.
This technology is often applicable for “problematic” solids:
- Small and light or very big particles,
- Non-spherical particles (aspect ratio >> 1),
- Broad particle size distributions causing segregation.
Objectives of the project
- Characterization of a novel type of spouted bed with adjustable gas inlets in form of two symmetrical slits,
- Development of an operation regime map, which take into account the stable and unstable spouting ranges,
- Investigation of the influence of apparatus geometry, process and material parameters and apparatus optimization regarding the flow stability,
- Liquid injection into the apparatus to poof the apparatus concept for future coating and granulation studies. Investigation of the heat and mass transfer under wet conditions.
- A transparent experimental setup with adjustable geometry (Fig. left)
- High-speed pressure measurements
- High-speed video camera
(ii) Modelling and simulation
- DPM (Coupling of Computational Fluid Dynamics and Discrete Element Method, Fig. right)
The bed behaviour was characterized experimentally by means of high speed recordings and the Fast-Fourier-Transformation of the measured pressure drop time series. A regime map was constructed, where the location of the domain of the dense spouting and the transition lines between other regimes can be obtained. Investigations on the effect of the shape of the central profile, the angle of the prismatic apparatus region and draft plates on the flow stability were performed.
DPM-simulations were performed at the gas flow rate corresponding to the spouting initiation, to the upper end of the spouting domain and to the instable region. The simulations predict well the expansion of the particle bed, the particle flow patterns and characteristic pressure drop fluctuations of all studied regimes. Single sharp peaks in the FFT power plots, characteristic to the stable dense spouting, were obtained, with a good agreement in the frequency of the pressure fluctuations. The irregular pressure behavior resulting in many additional peaks in FFT plots were also predicted accurately by the DPM model. The comparison of chaotic properties obtained with Deterministic Chaos Theory showed also a good agreement with experiments. The identified flow mechanisms governing the spouting termination are the growing spout instability by alternating spout deflections and incoherence.
The obtained results were condensed in an optimized geometry design, providing the significant improved spouting stability.
Salikov V., Antonyuk S., Heinrich S. (2012), Using DPM on the way to tailored prismatic spouted beds, CIT.
Salikov V., Antonyuk S., Heinrich S., Sutkar V.S., Deen N.G., Kuipers J.A.M. (2015), Characterization and CFD-DEM modelling of a prismatic spouted bed, Powder Techn.
Salikov V., Heinrich S., Antonyuk S., Sutkar V.S., Deen N.G., Kuipers J.A.M. (2015), Investigations on the spouting stability in a prismatic spouted bed and apparatus optimization, Advanced Powder Techn.
German Research Foundation (DFG) and Technology Foundation STW, HE 4526/5