Experimental Measurement And Numerical Simulation Of Novel Riser

Circulating fluidized bed riser reactor has been widely employed in petroleum refiningindustry, which played a vital role being treated as high efficient reactor. It is significant tounderstand the gas-solids flow behaviors in riser reactor from the respects of research andengineering. The experiments were conducted in a high-density, high-flux circulatingfluidized bed (CFB) riser with expanding diameter structure to examine its flow dynamics.Axial and radial solids holdup profiles in different height sections were comparatively studiedin various operating conditions. In addition to that, gas-solids flow dynamics were furtherdiscussed by CFD method to model relevant flow behaviors in expanding diameter riser inorder to explore corresponding model parameters. Finally, the advantages of novel expandingdiameter riser with internals compared with traditional riser were interpreted in detail.The results showed that a good linear relationship of solids fluxes versus both totalpressure drop and superficial velocity can be found. Flow dynamics in high densitycirculating fluidized bed have features:‘S’ shaped axial solids holdup profiles indicated thatsolids holdup decreases from the bottom to the top of the riser and remains nearly constant infull development region; traditional core-annulus structure was found for radial solids holdupprofiles, which meant lower solids holdup is in the center of the riser and solids aggregate inthe wall region. Operating conditions affect the flow behavior to some extent especially interms of superficial velocity and solids fluxes. Average solids holdup in one height sectiondeclines and radial solids holdup profiles remain relatively uniform with the increase ofsuperficial velocity. On the other hand, enhancing solids fluxes improve the solids holdup andpromote its axial profiles.A Eulerian multiphase model with the kinetic theory of granular flow (KTGF) wasstudied for modeling the hydrodynamic behaviors of high-flux circulating fluidized beds(HFCFBs) in a bench scale experiment. Commercial code FLUENT was used in the researchand a suitable model was developed. As a result, a group of suitable models and modelingparameters-i.e.,Gidaspow shear viscosity model, Gidaspow drag model, Johnson-Jacksonboundary conditions, a specularity coefficient of φ=0, a particle-particle restitution coefficientof e=1-proposed for modeling FCC particle flow in HFCFB risers.The simulation results arein good agreement with the experimental values in the center area, and there are significantvariances in wall area. Reasons of calculation deviation are discussed in this article.3D simulation of gas-solid flow in the expanding diameter riser and traditional riser wasstudied. As a result, there is an obvious bias phenomenon with the actual unilateral feed in both risers; when the fluid enters the expanding diameter section, the bias phenomenongradually disappears as the height increassd, and solids holdup profiles remain relativelyuniform; the internal jet compared with traditional nozzle not only improves the turbulenceand mix of gas-solid flow, but also reduces the collision of particles. On the whole, novelexpanding diameter riser with internals improve gas-solids contact efficiency and solidsholdup profiles.