Flow Characteristic Of The Particle Agglomerates Of The Meso-scale Flow Structure In A Emulsion Phase Gas-solid Fluidized Bed

The emulsion phase gas-solid fluidized bed reactor has the advantages of simple structure,high heat and mass transfer efficiency.The multiphase flow in a gas-solid fluidized bed is a non-linear and non-uniform gas-solid two-phase flow system,which presents a comlex multi-scale structure.At present,the research of this system was mostly conducted in the high superficial gas velocity bed.And the research of the emulsion bed is less.With the further study,the mesoscale flow structure in the bubbling bed and turbulent bed can not be accurately characterized due to the limitation of the bubbling phase and the emulsion phase.In this paper,experiments were made in a cold model of the fluidized bed apparatus.The FCC and the FCC particles with 20% volume fraction were used as the medium.By analyzing the transient solid holdup signals measured by optical fiber probe(PV-6D),it was found that the two types of the probability density curve of the signal bimodal distribution,which are correspond to the bubble and emulsion phase.The third moment(skewness)analysis method was employed to select boundary value(threshold)of the bubble and emulsion phase.It's found that the threshold value of FCC particles was calculated in the range of 0.26-0.35 and the threshold value of FCC particles after adding 20% fine powder was changed within 0.40-0.45 range.In the middle of the fluidized bed,The third moment(skewness)analysis method has a good effect on the probability density curve fitting,and the fitting error,less than 7%.In the side wall,the fitting error is larger.In this paper,a new method is proposed to the fitting of the boundary wall.Besides,a simplification of the third moment(skewness)analysis method is proposed.The simplified method can be used to calculate the bubble phase threshold easily,and the probability density curve fitting presents well.It can be used to the simple calculation of data threshold.It also can be as the initial setting value for the hird moment(skewness)analysis method.Combined with the threshold value by the third moment(skewness)analysis method,the transient solid holdup signal was analyzed deeply by the Matlab software and got the mean holdup of the bubble phase,the emulsion phase and the particle aggregates,the frequency,residence time,velocity and the size of particle aggregates along with the different operating gas velocities and positions.Comparing the structural parameters of two mediums,it's found that the structure parameters of FCC particles after adding fine powder are greatly affected by the operation gas velocity.This particles are easier to cluster and the size of the cluster is larger.