Experimental and modeling study of the effect of CH_4 and pulverized coal on selective non-catalytic reduction process

摘要

The reduction of nitric oxide using ammonia combined with methane and pulverized coal additives has been studied in a drop tube furnace reactor. Simulated flue gas with 1000 ppm NO_x and 3.4% excess oxygen was generated by cylinder gas. Experiments were performed in the temperature range of 700-1200 ℃ to investigate the effects of additives on the DeNO_x performance. Subsequently, a kinetic mechanism was modified and validated based on experimental results, and a computational kinetic modeling with CHEMKIN was conducted to analyze the secondary pollutants. For both methane and pulverized coal additives, the temperature window is shifted towards lower temperatures. The appropriate reaction temperature is shifted to about 900 and 800 ℃, respectively with 1000 ppm methane and 0.051 g min~(-1) pulverized lignite coal. The addition of methane and pulverized coal widens the temperature window towards lower temperature suggesting a low temperature application of the process. Furthermore, selective non-catalytic reduction (SNCR) reaction rate is accelerated evidently with additives and the residence time to complete the reaction is shortened distinctly. NO_x reduction efficiency with 80% is achieved in about 0.3 s without additive at 1000 ℃. However, it is achieved in only about 0.2 s with 100 ppm methane as additive, and only 0.07 and 0.05 s are needed respectively for the cases of 500 and 1000 ppm methane. The modified kinetic modeling agrees well with the experimental results and reveals additional information about the process. Investigation on the byproducts where NO_2 and N_2O were analyzed by modeling and the others were investigated by experimental means indicates that emissions would not increase with methane and pulverized coal additions in SNCR process and the efficacious temperature range of SNCR reaction is widened approximately with 100 ℃.