A Study Of Particle Diffusion Coefficient Within MTO Fluidized BED

Methanol to olefins technology has become an important route of olefins production. However the particle diffusion within MTO reactors is closely related to the non-uniform structures such as bubble and particle agglomerate, which affect the residence time distribution of the catalyst and thus has an important influence on the regulation of the amount of carbon deposition of the catalyst and the improvement of the selectivity of production. Hence the study of the particle diffusion within the MTO reactor is an important basis for the design and optimization of methanol to olefins reactor.Turbulent fluidized bed reactor is commonly used in MTO plants. Based on random walk theory, this article establishes a novel image-based method of the research of particle diffusion coefficient within turbulent fluidized bed, combining image processing technology and fiber-optical imaging technology with the calculation of particle diffusion coefficient. This method obtains average particle diffusion coefficient from the particle displacement calculated by the image processing technology based on cross-correlation theory and random walk theory of particle dispersion.Two-dimensional and three-dimensional cold turbulent fluidized bed are designed and built for MTO SAPO-34 catalyst. Firstly, non-contact image acquisition method is used in a two-dimensional turbulent bed for the image acquisition of particles near the wall so as to verify the feasibility of the particle diffusion coefficient research method based on non-contact image method. Then optical fiber is employed for the collection of particle images inside three-dimensional cold turbulent fluidized bed, and the feasibility of research method of particle diffusion coefficient fiber-optical image method is verified. Two methods complement each other, by studying the particle diffusion at different locations within the turbulent bed and therefore build a research method particle diffusion coefficient based on image acquisition and processing.By changing the gas velocity and particle size, as well as the usage of three kinds of SAPO-34 particles with diameters of 70?m,80?m, and 100?m, the impact of gas velocity and particle diameters on particle diffusion coefficient has been studied. By comparison with other documents, the feasibility of image-based method of the research of particle diffusion coefficient within turbulent fluidized bed is proved. The average axial diffusion coefficient of the particles within turbulent bed calculated by the experiment rank generally from 10-2m2/s to 10-1m-2/s, while the average particle radial diffusion coefficients rank generally from 10-3m2/s to 10-2m2/s. As the gas velocity increases, axial and radial solids diffusion coefficients increase in the turbulent fluidized bed. Under the same operating conditions, particles with smaller size mix and spread more intensely, compared to those with larger size. Both the result and the tendency have been in agreement with other articles.Compared with other methods, image-based method for the research of particle diffusion coefficient is simple, feasible and highly accurate, therefore has good research value and bright application prospects.