Fluid Dynamic Characterization of Circulating Fluidized Bed Riser Reactors
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Beschreibung
The objective of the presented work consists in developing an improved understanding of the fluid dynamics in circulating fluidized bed (CFB) reactors by combined consideration of experimental investigations and modeling techniques.
Owing to their characteristic properties such as intense mixing of fluid and solids, excellent heat and mass transfer conditions as well as high mobility of solids, CFBs are an attractive reactor system for fluid-solid reactions in various fields of the process industry. With the aim of gaining an improved understanding of the fluid dynamics in CFB reactors, experimental investigations are carried out in a pilot plant scale CFB unit. Differential pressure measurements are used to derive the axial distribution of the solid volume fraction in the riser and downer section of the CFB. To investigate local flow patterns, an X-ray computer tomography unit is installed in the riser section of the plant. Beyond that, capacitance probes are used to investigate the velocity at which clusters of solids move within the riser under different operating conditions.
By means of force balance analysis, the measured radial distribution of the solid volume fraction is used to study the shear stress distribution in the flow field. Further analysis is devoted to the momentum transfer between the fluid and the solids passing the riser in the form of clusters.
The results of the radial flow pattern analysis are implemented into a fluid dynamic model, which allows for computing a steady-state diagram. The obtained diagram can be used to predict the pressure drop and the solids entrainment rate from a riser reactor for a given solids holdup and superficial gas velocity. Moreover, the drag coefficient and heterogeneity index is derived for flow conditions ranging from dilute to high-density fluid-solid flow.
Eventually, a methodological approach is presented for the design of circulating fluidized beds as a reactor system for fluid-solid reactions.
Autor*in
Timo Hensler
Themen in »Fluid Dynamic Characterization of Circulating Fluidized Bed Riser Reactors«
Circulating Fluidized Beds Fluid-solid flow Drag coefficient