Numerical Simulation On Flow Characteristic And Denitration Reaction In A Fluidized Bed

Fluidization is widespread in nature, and gradually it catches people’sattention. Based on the research of fluidization technology, the advantage ofgood mixing characteristics and high efficiency of heat and mass transfer in thefluidized bed has been fully reflected. Fluidized bed is widely used in industrysuch as petroleum, chemistry, biomass burning, nuclear fuel reprocessing and soon. With the development of computer technology, researchers have begun tosimulate the fluidized beds. Plenty of numerical models have been proposedincluding continuum model, discrete particle model, discrete bubble model andLattice Boltzmann model. According the Geldart-particle classification and thegas velocity, it is a bubble fluidized bed.In this thesis, an Euler-Euler two-fluid model has been used to simulate themovement of particles in a fluidized bed. The standard k-model is used tosimulate the gas turbulence, and the Kinetic Theory of Granular Flow is used toprovide the closure laws for the Continuum Model. When the concentration ofparticles is beyond0.5, a friction model is added. The Huilin-Gidaspow model isused to represent the drag coefficient. A reaction model is established, and thesource term is added in the continuity and momentum equations. The speciestransport equation is used to control the mass exchange caused by reaction.Arrhenius rate is used for the heterogeneous reaction.The results show that with increasing the gas velocity or decreasing theparticle diameter, the height of bed materials becomes higher, and otherparameters have effects on different zones of the bed. In a bubbling fluidized bed,small bubbles produce from the fluidized bed at the bottom, rise and merge intobig bubbles, ultimately break at surface of the bed. Particles are pulled by thebubbles and move upward. When the bubbles break, particles return to the bedunder the influence of gravity. New bubbles produce, rise and merge.The simulation results of reaction show that the gas uranyl nitratedecomposes rapidly after entering the fluidized bed. The mass fraction of theproduction, NO2, is great near the nozzle. Under the affection of fluidizing gasand particle movement, NO2flows into the bed. With the reaction proceeding, the production has a negative affection on the particle movement.