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Numerical investigation of the gas/spray jet interaction with fluidized beds Li, Tingwen


In many industrial fluidized bed reactors, for example fluid catalytic cracking units, coaters and fluid cokers, the reactant feed is introduced into the system in the form of a gas jet or spray for different purposes. A good understanding of the interaction between the feed injection and the bed can lead to improved reactor design and operation. Despite the fact that numerical models and simulations have been used extensively to investigate fluidization processes, still little is known about the interactions of the jet/spray with fluidized beds. In this thesis, gas jets and liquid spray in several gas-solid systems are numerically studied. The Eulerian-Eulerian multi-fluid model with appropriate closure correlations is employed, and two- and three-dimensional numerical simulations are performed accordingly. The numerical simulations can be divided into two groups: two-phase (gas-solid) and three-phase (gas-liquid-solid) simulations. First, a three-dimensional numerical simulation of a single gas jet injection in a cylindrical bubbling fluidized bed is performed and is compared favorably to available experimental data and empirical correlations. After that, the injection of multiple gas jets into a small bubbling fluidized bed is numerically investigated. The influence of the secondary gas injection on the flow hydrodynamics, as well as interactions between the gas jet and the surrounding gas, solids, bubbles, and other jets is studied numerically, and the mixing of the secondary gas with the bed materials is also analyzed. To study the liquid spray in gas-solid systems, several three-phase systems of the low-flow-rate bottom spray into a flat-based spouted bed with a draft tube (DTSB), an evaporating gas-liquid spray into a uniform gas-solid crossflow, and an evaporative water spray into a hot riser are simulated, respectively. Appropriate models are chosen to describe the interactions between spray droplets and particles, as well as the inter-phase heat and mass transfer. While implementing the models in the numerical code, careful comparison with the available experimental data is performed. General features of the spray are properly predicted, and the interaction of the liquid spray with the gas-solid flows is investigated.

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