Effect of oxygenated liquid additives on the urea based SNCR process

Abstract

An experimental investigation was performed to study the effect of oxygenated liquid additives, H 2O 2, C 2H 5OH, C 2H 4(OH) 2 and C 3H 5(OH) 3 on NO x removal from flue gases by the selective non-catalytic reduction (SNCR) process using urea as a reducing agent. Experiments were performed with a 150 kW pilot scale reactor in which a simulated flue gas was generated by the combustion of methane operating with 6% excess oxygen in flue gases. The desired levels of initial NO x (500 ppm) were achieved by doping the fuel gas with ammonia. Experiments were performed throughout the temperature range of interest, i.e. from 800 to 1200 °C for the investigation of the effects of the process additives on the performance of aqueous urea DeNO x. With H 2O 2 addition a downward shift of 150 °C in the peak reduction temperature from 1130 to 980 °C was observed during the experimentation, however, the peak reduction efficiency was reduced from 81 to 63% when no additive was used. The gradual addition of C 2H 5OH up to a molar ratio of 2.0 further impairs the peak NO x reduction efficiency by reducing it to 50% but this is accompanied by a downward shift of 180 °C in the peak reduction temperature. Further exploration using C 2H 4(OH) 2 suggested that a 50% reduction could be attained for all the temperatures higher than 940 °C. The use of C 3H 5(OH) 3 as a secondary additive has a significant effect on the peak reduction efficiency that decreased to 40% the reductions were achievable at a much lower temperature of 800 °C showing a downward shift of 330 °C.