Study On Fluidization Behavior Of Geldart-B Particles

Fluidized bed is one of the most important production equipment in modern industry.It is widely used in industries such as chemical,petroleum,metallurgy and atomic energy.The research on fluidization technology has developed from the study of the overall traits of fluidized beds in the late 1940s to the application of two-phase fluid mechanics,rheology,statistics and computer technology to further study the internal traits of the bed.Fluidization behavior research is necessary for designing a fluidized bed reactor and building a new process.In this paper,the fluidization behavior of Geldart-B particles in gas-solid fluidized bed and three-phase fluidized bed with gas phase as continuous phase is studied.Geldart-B particles exhibit distinct fluidization characteristics due to their large particle size and density.The bed is clearly divided into a bubble phase and a dense phase.The gas velocity passing through the dense phase is substantially constant.The bubble appears at the beginning of fluidization.These properties are the basis for analyzing the fluidization behavior of Geldart-B particles.Firstly,through the combination of theoretical derivation and empirical formula,the general formula for solving the expansion ratio R of Geldart-B particle fluidized bed is proposed,and a convergent R iteration formula is constructed in the whole value range.Verification of fluidization experiments on different particles showed that the model predicted R well.The relationship between R and bubbling fluidization flow state is discussed further,and the value of the critical expansion ratio R_tris given.Then,using the three-phase fluidized bed in super-condensed mode as a sample,a probability model describing the stability of the system was developed based on the three-particle collision theory.The probability criterion of the stability model is obtained by analyzing the interactions in the particle collision,the relative velocity distribution and the energy transfer.The model well predicts the Geldart-B particle fluidization system with a solid-liquid contact angle of less than 40°,and gives semi-quantitative results for other systems.