Catalytic NOx Reduction in a Novel i-CFB Reactor: I. Kinetics Development and Modeling of Reduction Zone

Abstract

A model was developed for the hydrocarbon selective catalytic reduction (HC-SCR) of NOx in a fluidized bed reactor. For the kinetics, the reaction was divided into two submodels: (i) NO oxidation and adsorption; (ii) hydrocarbon oxidation and NOx reduction. The kinetic parameters were obtained from fitting a fixed bed model to fixed bed experimental data. Mass transfer between solids and gas phases was also considered in this fixed bed model with the reaction term being embedded into the solids phase mass balance equation. Comparing with fixed bed experimental data, the model showed an average error of about 7% for NOx conversion and about 5% for HC conversion. The fitted kinetics was then incorporated into a fluidized bed reactor model, which included gas flow in the bubble phase, gas flow in the dense phase and solids flow in the dense phase. The fluidized bed reactor model was compared to the fluidized bed experimental data. The model showed acceptable agreement with measured NOx conversion, but poor agreement with observed HC conversion data. Suggestions were proposed to further improve the model and experimental data. The fluidized bed model was then applied to simulate NOx reduction in the reduction zone of the internal circulating fluidized bed (i-CFB) reactor. The simulation results showed that NOx conversion could be improved if NOx is fed into the reactor via the solids phase, the same as what happens in the reduction zone of an i-CFB reactor. Also, for the reduction zone of the i-CFB reactor, a higher solids circulation rate is preferred if NOx feed rate is kept at a constant. These simulations could provide good suggestions for the i-CFB design and operation.