Experimental Investigation of solids concentration and velocity profiles in fluidized bed riser using optical fiber probe and validation using CFD

P, Suman and Mangadody, Narasimha (2019) Experimental Investigation of solids concentration and velocity profiles in fluidized bed riser using optical fiber probe and validation using CFD. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

Study of hydrodynamics is very important for design and optimization of fluidized bed reactor. They are several intrusive and non-intrusive techniques available for characterizing hydrodynamics in multi-phase flow systems such as electrical capacitance tomography, Gamma ray tomography, sampling probe, capacitance probe and Gamma density probe etc. Out of these optical fiber probe stands out as a potential tool with its advantages over other measurement techniques. Optical fiber probe, an intrusive technique measures both the local solids concentration and velocity simultaneously. In this work, dual sensor optical probe is employed for hydrodynamic study of fluidized bed riser. The main objective of the study is to understand the effect of superficial velocity, bed height and particle size on the hydrodynamic behavior in different regimes of fluidization experimentally using optical fiber probe and validating these experimental results with the standard granular CFD Models. Experiments were conducted with fabricated riser having 105 mm internal diameter and 1000 mm height. A series of experiments were run for Geldart A and Geldart AB mixture at 123mm and 200mm bed height pertaining to bubbling and turbulent regimes. With Geldart AB particles, high solids concentration was found near the wall region, where as diluted bed observed in the central zone. Bubbling bed behavior was observed for both Geldart A and AB particles immediately after the minimum fluidization. 2D CFD granular model validation is initially pursued for the experimental results available in literature. A Eulerian-Eulerian two fluid model integrating kinetic theory of granular flow with Gidaspow drag correlation is employed for this purpose. After validating, the same CFD model is used for further validation of the current experimental results obtained. A series of CFD simulations run at which the optical probe measurements conducted for. Time average Solids concentration and particle velocity variation with radius and height from the CFD simulations are compared with experimental results found them in similar trends. Further fine tuning of CFD parameters and appropriate gas input strategies are required for improved simulations.

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