High Temperature and High Concentration SCR of NO with NH3 for the Oxyfuel Combustion Process : Fitting of Kinetics to Data from a Laboratory Reactor Experiment

This study shows the result of a simulation of a proposed kinetic reaction scheme of high-concentration (5000 ppm NO) and high-temperature (570–800 K) selective catalytic reduction of NO with NH3 on a commercial vanadia based catalyst at a system pressure of 2.2 bar. The simulations are performed with COMSOL Multiphysics ver. 5.1. Experimental data from a catalytic flow reactor can be nicely fitted to a system of kinetic expressions for the selective catalytic reduction (SCR) reaction and its side reactions. Especial attention is given to the formation of N2O. All reaction rate expressions contain an ammonia adsorption term. The value for its pre-exponential factor is 9e−9 and its activation energy is −139 kJ/mol. The fastest reaction is the standard SCR reaction with a pre-exponential factor of 5.28e7 s−1 and an activation energy of 85 kJ/mol. This reaction is affected by internal diffusion limitations. The oxidation of NH3 to NO is the second fastest reaction with parameters 5e12 mol/m3s and 200 kJ/mol. The NSCR of NH3 to N2O is the third fastest reaction with values of 7.5e5 s−1 and 110 kJ/mol. The oxidation of NH3 to N2O has the parameters 8e11 mol/m3/s and 190 kJ/mol. At 640 K inlet temperature the rate of the SCR reaction is about 1.3 mol/m3/s. The oxidation of NH3 to NO is 4.7e−4 mol/m3/s. The rate of the NSCR producing N2O is 1.63e−4 mol/m3/s. The rate of the direct oxidation of NH3 to N2O is 3.7e−5 mol/m3/s. Thus the rate of the SCR reaction is about 35,000 faster than the high temperature production of N2O at this temperature