Experimental and modeling study of the effect of CO and H2 on the urea DeNOx process in a 150 kW laboratory reactor

An experimental and modeling investigation has been performed to study the effect of process additives, H2 and CO on NOx removal from flue gases by a selective non-catalytic reduction process using urea as a reducing agent. Experiments were performed with a flow reactor in which flue gas was generated by the combustion of propane in air at 3% excess oxygen and the desired levels of initial NOx (500 ppm) were achieved by doping the flame with ammonia. Experiments were performed throughout the temperature range of interest i.e. from 850 to 1200 oC for investigation of the effects of the process additives on the performance of aqueous urea DeNOx. Subsequently, computational kinetic modeling with SENKIN code was performed to analyze the performance of urea providing a direct comparison of modeling prediction with experimental measurements. With CO addition, a downwards shift of 215 oC in the peak reduction temperature from 1125 to 910 oC was observed during the experimentation while the kinetic modeling suggests it to be 150 oC i.e. from 1020 to 870 oC. The addition of H2 impairs the peak NOx reduction but suggests a low temperature application of the process. A downward shift of 250 oC in the peak reduction temperature, from 1020 to 770 oC, was observed during kinetic modeling study. The kinetic modeling shows a good qualitative agreement with the experimental observations and reveals additional information about the process.