UBC Theses and Dissertations
Modeling and simulation of a novel internal circulating fluidized bed reactor for selective catalytic reduction of nitrogen oxides Cheng, Xingxing
The internal circulating fluidized bed (i-CFB) reactor exhibits an ability to overcome the negative impact of excessive O₂ present in the flue gas on selective catalytic reduction of NOx with hydrocarbons as the reductant (HC-SCR) by decoupling NOx adsorption and reaction into two separate zones. A mathematical model has been developed in this study, which includes three sub-models: hydrodynamics, adsorption and reaction kinetics. Each sub-model was developed separately and validated by experimental data before they were integrated into the i-CFB model. For the hydrodynamics of i-CFB, solids circulation rates, which were later used for model parameter fitting, were measured using optical fibre probe. The hydrodynamics model was then developed based mass and pressure balance. Adsorption isotherm and deNOx reaction kinetics were developed based on a series of fixed bed experimental data: O₂ adsorption, NOx adsorption and NOx reaction. The kinetic model was further evaluated by fluidized bed adsorption and reaction experiments. The simulation results of the integrated i-CFB model showed good agreement with the experimental data. It is observed from the model that the performance of the current laboratory scale i-CFB reactor was dominated by the catalyst reactivity, rather than the catalyst adsorption rate, because of too short a solids residence time in the reduction zone for the deNOx reaction. Simulation results for i-CFBs with different cross sectional areas of the adsorption and reduction zones showed that a large reduction zone could significantly enhance the overall deNOx efficiency, and there existed an optimal reduction zone to adsorption zone area ratio at which NOx conversion is maximized at a given operating condition. It was also observed that the performance of i-CFB reactors with a larger reduction zone is less sensitive to gas bypass from reduction zone to adsorption zone. Overall, the i-CFB model developed in this study can be used as a tool to assist reactor design and scale up, and to provide guidance on how to further improve the NOx reduction efficiency. The simulation results showed that it is possible to achieve a higher deNOx efficiency higher while avoiding the negative effects of flue gas O₂.
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