Abstract
An SCR system with a porous media coated by MnO2-V2O5-WO3/TiO2 for reducing NOx in diesel combustors is being developed from experimental study by authors. In this study, a three-dimensional model of the SCR system is developed to simulate the selective catalytic reduction process of NO with ammonia as a reducing agent. The purpose of this study is to analyze the effects of interfacial heat transfer between the solid and gas phases inside the porous medium, velocity and temperature on the NOx reduction rate of an SCR system by computational fluid dynamic (CFD). The standard porous medium modeling capability which considers the displacement and resistance effects of a distributed material on a gas phase permeating the porous solid is applied to predict the flow field inside the SCR reactor. The chemical reactions inside the SCR reactor and the heat transfer to, from and within the porous solid are considered by the modification of the source terms in a commercial CFD package. Diesel exhaust gas is simulated by solving the three-dimensional Navier-Stokes, mass conservation, chemico-thermal enthalpy and species transport equations coupled with the themophysical equations for mixture properties. The results show that there is no significant effect of the interfacial heat transfer in a steady-state simulation on NOx reduction rate of an SCR system if there is no heat generation in the solid phase. It is also shown that at different space velocities, temperatures below 673 K are observed as a temperature-limited process and temperatures above 673 K are observed as a concentration-limited process.
Keywords: SCR System, NOx Emissions, Porous Medium Approach, CFD Simulation, Chemical Modeling, Solid- Gas Heat Transfer