Hydrodynamic characteristics of fine particles in the riser and standpipe of a circulating fluidized bed

In this work carbon combustion efficiencies in circulating fluidized bed combustion (CFBC) when co-firing biomass and coal mixtures were studied. Experimental results were obtained from the combustion of two kind of coals with a forest residue (Pine bark) in a CBF pilot plant (0.3MWth) with 20-cm i.d. and 6.5-m height. The effect of operating conditions such as percentage of biomass in the feed, temperature, excess air, air velocity and percentage of secondary air on carbon combustion efficiency was studied. A mathematical model for the co-combustion of coal and biomass in a circulating fluidized bed boiler has been developed. The riser is divided in three zones with different hydrodynamic characteristics: bottom, splash and freeboard. The bottom bed has a constant voidage, determined by a modified two-phase theory. The solids are considered in perfect mixing and the gas in plug flow. The voidage in the splash region follows an exponential decay model. In the freeboard region, the solids and the gas are in plug flow, and a core-annulus structure is considered. Devolatilization of solid fuels is modeled with a particle reaction model which allows to determine the volatiles generation rate as a function of time and operating conditions. Kinetics of char combustion is modeled with the shrinking particle model with mixed control by chemical reaction and gas film diffusion, assuming that the ashes separate once formed. To consider that the char particles are a mixture of coal and biomass char particles, a weighted average combustion rate is defined taking into account the individual combustion rates. Population balances of char particles in the different regions were developed to calculate carbon concentrations. The developed model can predict the different gas concentrations along the riser, such as oxygen, SO2, CO, CH4, etc..., and the carbon combustion efficiency. The experimental results of carbon combustion efficiencies and gas emissions were compared with those predicted by the model and a good correlation was found for all the conditions used.

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Novel multistage solid–liquid circulating fluidized bed: Hydrodynamic characteristics

Particuology ◽

10.1016/j.partic.2017.08.003 ◽

2018 ◽

Vol 38 ◽

pp. 134-142 ◽

Cited By ~ 2

Author(s):

Prakash V. Chavan ◽

Manjusha A. Thombare ◽

Sandip B. Bankar ◽

Dinesh V. Kalaga ◽

Veena A. Patil-Shinde

Keyword(s):

Fluidized Bed ◽

Circulating Fluidized Bed ◽

Hydrodynamic Characteristics ◽

Solid Liquid

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CFD Modeling and Simulation of the Hydrodynamics Characteristics of Coarse Coal Particles in a 3D Liquid-Solid Fluidized Bed

Minerals ◽

10.3390/min11060569 ◽

2021 ◽

Vol 11 (6) ◽

pp. 569

Author(s):

Jian Peng ◽

Wei Sun ◽

Haisheng Han ◽

Le Xie

Keyword(s):

Experimental Data ◽

Fluidized Bed ◽

Fine Particles ◽

Particle Density ◽

Cfd Modeling ◽

Hydrodynamic Characteristics ◽

Model Parameters ◽

Low Density ◽

Coal Particles ◽

Simulation Results

In this study, a Eulerian-Eulerian liquid-solid two-phase flow model combined with kinetic theory of granular flow was established to study the hydrodynamic characteristics and fluidization behaviors of coarse coal particles in a 3D liquid-solid fluidized bed. First, grid independence analysis was conducted to select the appropriate grid model parameters. Then, the developed computational fluid dynamics (CFD) model was validated by comparing the experimental data and simulation results in terms of the expansion degree of low-density fine particles and high-density coarse particles at different superficial liquid velocities. The simulation results agreed well with the experimental data, thus validating the proposed CFD mathematical model. The effects of particle size and particle density on the homogeneous or heterogeneous fluidization behaviors were investigated. The simulation results indicate that low-density fine particles are easily fluidized, exhibiting a certain range of homogeneous expansion behaviors. For the large and heavy particles, inhomogeneity may occur throughout the bed, including water voids and velocity fluctuations.

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Hydrodynamic Characteristics of a Novel Circulating Fluidized Bed Steam Reformer Operating in the Fast Fluidization Regime

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.2778 ◽

2011 ◽

Vol 9 (1) ◽

Author(s):

Moataz Bellah M. Mousa ◽

Seif-Eddeen K. Fateen ◽

Essam A. Ibrahim

Keyword(s):

Fluidized Bed ◽

Circulating Fluidized Bed ◽

Numerical Approach ◽

Hydrodynamic Characteristics ◽

Two Phase ◽

Radial Segregation ◽

Fluidization Regime ◽

Computational Fluid Dynamics Cfd ◽

Model Equations ◽

Steam Reformers

Circulating Fluidized Bed Steam Reformers (CFBSRs) represent an important alternative for the production of syngas for the Fisher-Tropsch (FT) process and for hydrogen production. Most research regarding this novel CFBSRs did not consider its hydrodynamic characteristics. In this work, the riser Computational Fluid Dynamics (CFD) simulations were investigated using two phase Eulerian-Eulerian approach coupled with kinetic theory of granular flow with k-epsilon model to describe the turbulence of each phase. The model equations were solved via the commercial CFD package FLUENT, which uses the finite volume numerical approach. Cold flow simulations were carried out under the fast fluidization regime and results were validated qualitatively against available experimental data. The radial segregation of the catalyst, the velocity distribution of both phases and other characteristics of the flow were captured by the simulation. This work showed that for operation under high density and high flux conditions, solids flux should be higher than 300 kg/m2s and inlet void fraction lower than 85%.

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