Effect of particle shape on bubble dynamics in bubbling fluidized bed

Particle shape can significantly affect the bubble dynamics of bubbling fluidized beds (BFB). In this paper, findings obtained from simulations using CFD-DEM are summarized to discuss the effect of particle shape on bubble dynamics and bubble properties such as bubble size, shape and velocity at a single orifice and uniform fluidized bed. Particles with aspect ratios at 0.5 (oblate), 1 (spherical) and 2 (prolate) are employed to represent disc-like, spherical and rod-like particles, respectively. Both single jet and uniform fluidized bed simulations demonstrate that the bubble forming/rising regions, bubble coalescence locations, and bubble splitting phenomena are significantly influenced by particle shape. The CFD-DEM results for bubble size and bubble velocity show good agreement with literature correlations.

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Improved models for predicting bubble velocity, bubble frequency and bed expansion in a bubbling fluidized bed

Chemical Engineering Research and Design ◽

10.1016/j.cherd.2018.11.002 ◽

2019 ◽

Vol 141 ◽

pp. 361-371 ◽

Cited By ~ 12

Author(s):

Cornelius Emeka Agu ◽

Lars-Andre Tokheim ◽

Marianne Eikeland ◽

Britt M.E. Moldestad

Keyword(s):

Fluidized Bed ◽

Bubble Velocity ◽

Bubble Frequency ◽

Bubbling Fluidized Bed ◽

Bed Expansion

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A Method for Reduction in the Start-Up Time of a Bubbling Bed Boiler Combustor

Journal of Energy Resources Technology ◽

10.1115/1.4002135 ◽

2010 ◽

Vol 132 (3) ◽

Cited By ~ 3

Author(s):

Vijay Jain ◽

Prabir Basu ◽

Dominic Groulx

Keyword(s):

Fluidized Bed ◽

Internal Heat ◽

Peak Temperature ◽

Fuel Oil ◽

Start Up ◽

Bubbling Fluidized Bed ◽

Bed Materials ◽

The Mean ◽

Rate Of Heating ◽

Good Agreement

A study on the heating of inert bed solids in a bubbling fluidized bed by means of an over-bed start-up oil burner is presented in this paper. Experiments carried out in a 160 mm diameter bed shows that the bed heats up nonlinearly with time. The rate of heating and the peak temperature reached by the bed solids depend on the bed depth, the mean particle size, and the superficial velocity through the bed. It was further noted that premixing a certain amount of biomass with the inert bed solids accelerates the rate of heating, as well as increase the peak temperature attained. The internal heat generation in the biomass is found to start at temperatures as low as 200°C. Thus, premixing some biomass with inert bed materials could reduce the combustion start-up time of a fluidized bed boiler, reducing at the same time the start-up cost by saving on consumption of expensive fuel oil in the burner. Experimental data in the present laboratory-scale unit shows good agreement with those obtained earlier in an industrial fluidized bed tested with waste-coal.

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Numerical Study of the Influence of Horizontal Tube Banks on the Hydrodynamics of a Dense Gas-Solid Bubbling Fluidized Bed

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1042 ◽

2003 ◽

Vol 1 (1) ◽

Cited By ~ 2

Author(s):

Sanjib K. Das Sharma ◽

Ratan Mohan

Keyword(s):

Fluidized Bed ◽

Solid Phase ◽

Numerical Study ◽

Horizontal Tube ◽

Particle Interactions ◽

Tube Bank ◽

Bubbling Fluidized Bed ◽

Tube Banks ◽

Fluidizing Medium ◽

Good Agreement

Numerical study of the influence of tube-bank on the hydrodynamics of a freely bubbling fluidized bed is relatively less reported in the literature. In this paper, results obtained from CFD study of a two dimensional gas-solid fluidized beds with horizontal tube-bank are compared with the published experimental data (Hull et. al., 1999). A 2-D bed, 1 m high and 0.2 m wide with tubes of diameter 0.026 m was taken for the calculations. Two different tube arrangements of staggered and inline pitch with center-to-center distance of 0.05 m were considered. Air was used as the fluidizing medium and ballotini glass (diameter: 230 mm and density: 2723 kg/m3) was the fluidized material. Air velocities used were 0.15 m/s and 0.187 m/s. The Eulerian-Eularian Two-Fluid CFD model was employed for modeling the momentum equations for both the gas and the solid phase with kinetic theory modification for the solid phase to account for the inter-particle interactions. Hydrodynamic features, such as, bubble size and bubble rise velocity and their variation with height within and outside the tube bank showed good agreement with the data of Hull et al.(1999)

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Numerical study of mixing and heat transfer of SRF particles in a bubbling fluidized bed

Journal of Thermal Analysis and Calorimetry ◽

10.1007/s10973-019-09135-2 ◽

2019 ◽

Vol 142 (2) ◽

pp. 1087-1096

Author(s):

Mohamed Sobhi Alagha ◽

Botond Szucs ◽

Pal Szentannai

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Fluidized Bed ◽

Present Model ◽

Numerical Study ◽

Sand Particle ◽

Particle Sizes ◽

Proposed Model ◽

Bubbling Fluidized Bed ◽

Good Agreement

AbstractIn this article, numerical investigations on mixing and heat transfer of solid refused fuel (SRF) particles in a bubbling fluidized bed are carried out. The numerical model is based on the Eulerian–Eulerian approach with empirical submodels representing gas–solid and solid–solid interactions. The model is verified by experimental data from the literature. The experimental data include SRF vertical distribution in SRF–sand mixtures of different sand particle sizes ($$d_{\mathrm{pm}} = 654,810$$ d pm = 654 , 810 and 1110 $$\upmu$$ μ m) at different fluidization velocities ($$u/u_{\mathrm{mf}} = 1.2$$ u / u mf = 1.2 –2.0). We proposed magnification of drag force exerted by the gas on SRF particles based on Haider and Levenspiel (Powder Technol 58(1):63–70, 1989) drag coefficient. The proposed model shows good agreement with the experimental data at high fluidization velocities ( $$u/u_{\mathrm{mf}} = 1.5$$ u / u mf = 1.5 –2.0) and poor predictions at low fluidization velocities ($$u/u_{\mathrm{mf}} = 1.2$$ u / u mf = 1.2 –1.5). Heat transfer results showed that the present model is valid and gives good agreement with the experimental data of wall–bed heat transfer coefficient.

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3-D Modeling of Liquid Injection into Fluidized Beds

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1178 ◽

2004 ◽

Vol 2 (1) ◽

Cited By ~ 7

Author(s):

Joachim Werther ◽

Stefan Bruhns

Keyword(s):

Fluidized Bed ◽

Flow Structure ◽

Three Dimensional ◽

Fluidized Bed Reactors ◽

Three Dimensional Model ◽

Liquid Injection ◽

Bubbling Fluidized Bed ◽

Solids Mixing ◽

Semi Empirical ◽

Bubble Splitting

A three-dimensional model has been developed to describe the injection of liquid reactants into fluidized bed reactors operating in the bubbling fluidized bed regime. The model considers the processes of liquid transport and evaporation in the vicinity of the point of injection. The underlying idea, which is supported by previous measurements, is that the particles in the dense suspension phase are wetted by the liquid or gas-liquid spray. The wetted particles are subsequently dried while they are following the gross solids circulation within the bed. The model considers the flow structure of the bubbling fluidized bed and the solids mixing with the aid of a hybrid model which combines semi-empirical models for bubble growth by coalescence and for bubble splitting with a CFD approach for the continuous emulsion phase surrounding the bubbles. Submodels for heat and mass transfer are used to describe the temperature and concentration fields in the vicinity of the injection nozzle and the drying process of the wetted particles with the resulting release of the vaporized injection liquid. The model was validated separately against flow structure measurements, solids tracer measurements and experiments with the injection of water and ethanol, respectively, into beds of FCC particles.

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