Bubble behaviors of geldart B particle in a pseudo two-dimensional pressurized fluidized bed

Pressurized fluidized beds have been developed in quite a few industrial applications because of intensified heat and mass transfer and chemical reaction.The bubble behaviors under elevated pressure,strongly influencing the fluidization and reaction conversion of the whole system,are of great research significance.In this work,the bubble behaviors of Geldart B particle in a pseudo two-dimensional(2D)pressurized fluidized bed were experimentally studied based on digital image analysis technique.The effects of pressure and fluidization gas velocity on the general bubble behaviors(i.e.,size,shape and spatial distribution)and the dynamic characteristics,such as the time-evolution of voidage distribution and local flow regimes,were comprehensively investigated.Results show that increasing pressure re-duces the stability of bubbles and facilitates gas passing through the emulsion phase,resulting in the"smoother"fluidization state with smaller bubbles and declined bubble fraction and standard deviation.The equivalent bubble diameter and bubble aspect ratio increase with the increasing gas velocity while decrease as pressure rises.The elevated pressure reduces bubbles extension in the vertical direction,prohibits the"short pass"of fluidization gas in large oblong bubbles/slugs and benefits the gas-solid interaction.The flow regimes variation with gas velocity is affected by the elevated pressure,and demonstrates different features in different local positions of the bed.

Numerical study on hydrodynamics of gas-solids circulating fluidized bed with L-valve

L-valve is often used as a non-mechanical valve for the circulation of solids in gas-solids fluidized bed(GSFB)due to its advantages in simple construction and easy control.The information on solids circu-lation rate as well as the hydrodynamics performance of the CFB with L-valve is of great importance for its better control and design.This paper proposes a Eulerian-Eulerian approach based numerical model integrating the computational fluid dynamics(CFD)with turbulent model,the kinetic theory of granular flow(KTGF)and the drag model,thus the solids circulation rate and the local phase velocity as well as solids volume fraction can be predicted simultaneously.With this model,the hydrodynamics perfor-mance of the full loop GSCFB with a L-valve is analyzed in detail.It is found that the drag model affects the simulation significantly and the(energy minimization multiscale)EMMS method shows good per-formance in the full-loop simulation of GSCFB.

Optimal design of gas distributor in fluidized bed for synthesis of silicone monomer

The structure of the gas distributor is closely related to the production efficiency of organosilicon monomers.To improve the production efficiency of organosilicon monomers,this study uses Eulerian-Eulerian two fluid model and proposes a design formula for the gas distributor to optimize the gas distributor.It is proposed that the pressure drop of the gas distributor,the velocity nonuniformity coefficient,the relative standard deviation of the solid holdup,and the solid particle dispersion coefficient are used to evaluate the performance of the gas distributor.The results show that the performance of the gas distributor is significantly improved when the opening ratioΦ=0.53%is optimized toΦ=0.18%,in which the relative standard deviation of the solid holdup is reduced by 22%,and the solid particle dispersion coefficient is reduced by 40%.On this basis,this article studies the influence of different arrangements of vent holes on gas-solid fluidization characteristics.The results show that the circular arrangement of vent holes is helpful to the mixing of gas and solid.

PIV MEASUREMENT OF THE GAS-SOLID FLOW PATTERN IN A CFB RISER

Particle Imaging Velocimetry (PIV) is a valuable measuring tool for studyingmultiphase flows, such as liquid-gas and gas-solid flow. It can be used to carry out manyhydrodynamic studies, in particular, to determine accurately the gas solid flow structure in CFB(Circulating Fluidized Beds). In this paper, the technique characteristics was described in applyingthe PIV to measure the gas-solid flow in circulating fluidized beds. A primary experiment wascomple-ted on a CFB unit with the PIV, yielding the velocity vector fields of high-density particlesfor different gas-solid superficial velocities and solid recycle rates. Velocities of thetransported particles were calculated with cross-correlation method. The major factors influencingthe successful measurement of particle velocity with the PIV technique were also described.