Catalytic NO_x 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 NO x in a fluidized bed reactor. For the kinetics, the reaction was divided into two submodels: (i) NO oxidation and adsorption; (ii) hydrocarbon oxidation and NO x 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 NO x 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 NO x 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 NO x reduction in the reduction zone of the internal circulating fluidized bed (i-CFB) reactor. The simulation results showed that NO x conversion could be improved if NO x 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 NO x feed rate is kept at a constant. These simulations could provide good suggestions for the i-CFB design and operation.

Catalytic Performance of NO Reduction by CO over Activated Semicoke Supported Fe/Co Catalysts

“…However, reactor design is a possible way to overcome the oxygen inhibition effect. For example, in the internal circulating fluidized bed (i-CFB) proposed by Yang and Bi, − NO x adsorption and reduction were set into two different zones by separating the gas streams of flue gas and reducing gas. Thus, reducing gas will not get in touch with oxygen in the flue gas and the negative effect of oxygen could be avoided.…”

Catalytic NOx Reduction in a Novel i-CFB Reactor: II. Modeling and Simulation of i-CFB Reactors

“…10 A freeboard region above the annulus and draft tube is considered in the model since it plays an important role for the deNO x reaction in fluidized beds. 13 Therefore, solids and gas flows above the dense bed reaction zone of the annulus and draft tube are very complex. For a first approximation, it is assumed for flow pattern b that gases in the annulus and draft tube are well mixed right above the dense bed region, which is located beneath the draft tube top.…”

“…The solids fraction in the freeboard is treated in the same way as a regular fluidized bed, as shown in Part I. 13 3.2. Governing Equations.…”

“…Governing Equations. As the fluidized bed reactor model developed in Part I, 13 fluidized bed consists of two phases, bubble phase and dense phase. Mass transfer of NO x in the fluidized bed occurs not only between the bubble phase and dense phase but also between the gas phase and particles.…”

“…12 Similarly, reaction kinetics of the catalyst was developed from fixed bed reaction experimental data and then evaluated by the fluidized bed performance data in Part I. 13 Finally, the hydrodynamics, adsorption, and reaction kinetics models are integrated to simulate the performance of i-CFB reactors in this paper. Adsorption and reaction over the Fe/ZSM-5 catalyst are modeled in both the adsorption zone (annulus) and reduction zone (draft tube) of the i-CFB.…”