Flow Characteristic Of The Particle Agglomerates In A Dense Gas-solid Fluidized Bed

The dense phase gas-solid fluidized bed reactor has the advantages of simple structure,high heat and mass transfer efficiency,which has been widely used in petrochemical industry.At present,the research of the gas-solid fluidized bed reactor is focused on the industrial application of the macroscopic hydrodynamics and mass and heat transfer characteristics.But the meso-scale two-phase flow structure in the reactor lacks deeper understanding,which greatly limits the structure optimization and design of the gas-solid fluidized bed reactors.Therefore,it is important to study the mesoscale two-phase flow structure characteristics further.In this paper,experiments were made in a cold model of the fluidized bed apparatus and FCC and sand particles were used as the medium.By analyzing the transient solid holdup signals measured by optical fiber probe,it was found that the distribution of the probability density curve of the signal displayed bimodal,and the two peaks correspond to the dilute and dense phase.First,using the peak method,standard deviation method and statistical method respectively to select boundary value(threshold)of the dilute and dense phase,and found that the statistical method based on skewness got the minimum fitting error,less than 5%.On this basis,the transient solid holdup signal was analyzed deeply and got the frequency,residence time,velocity and chord length distribution of particle aggregates along with the different operating gas velocities and positions,and establish correlation with the average solid holdup respectively.Then,pressure fluctuation signals were collected and decoupled using methods suggested by Bi and Van der Schaaf.In bubbling fluidization regime,mean bubble size of the fluidized bed increased with increasing ug,but decreased with increasing ug for turbulent fluidization regime.With the increase of the height,mean bubble size increased in bubbling fluidization regime and increased modestly in turbulent fluidization regime.Finally,this paper used EMMS model and simplified it based on strict derivation.The experience model was established by introducing the correction coefficient,which successfully predicted the size of the particle agglomerates in the dense phase gas-solid fluidized bed,and was in good agreement with experimental values.