Experimental Study On The Effects Of Additives On Selective Non-Catalytic Reduction Denitrification At Moderate Temperatures

The growth of NOx emission from power plants has led to more serious environmental pollution. The selective non-catalytic reduction (SNCR) technology is a kind of simple and economic NOx control technology. It has the advantage of easy for transform and short construction period. In addition, it can combine with other NOx control technologies to achieve high denitration efficiency. Therefore, SNCR technology is suitable for new coal-fired power plants and the transformation of the existing power plants. However, SNCR technology requires high temperature and is sensitive to temperature conditions. When the boiler runs with low load, the temperation in the aera of reducing agent injection goes off the best denitration temperature window, which causes that denitration efficiency decreases obviously and can’t meet the NOx emission standards.This problem has become the main impediment for its large-scale popularization and application. Therefore, in order to spread SNCR technology in power plants, it is important to research the influence of boiler low-load running parameters and different flue gas components on SNCR process, as well as improve the denitration efficiency at moderate temperature.Firstly, the NH3-SNCR denitration experiments were performed in a tubular flow reactor with simulated flue gas (NO、O2、CO2、SO2、N2) at 650-950℃. The influences of process parameters (temperature, NSR) and main flue gas components (O2, SO2) on denitration efficiency and pollutant emission (ammonia escape, tail N2O, NO2) were explored. These results are beneficial to better understanding the SNCR reaction characteristic at moderate temperature and guiding the further research on SNCR additives.Secondly, based on the SNCR experiment in simulated flue gas, three kinds of additives (H2, CO, CH4) were studied in the tubular flow reactor. The results show that with the increase of β (Add/NH3), the temperature window of SNCR denitration moved to low temperature and the offset of optimum denitration temperature Topt ranked CO<H2<CH4, the N2O conversion rate inceased and its peak value also moved to low temperature. Compared comprehensively, CH4 and H2 have better performance of improving the SNCR denitration efficiency at moderate temperature:in 700～900℃, the denitration efficiency η can exceed 50% when β (Add/NH3)≥ 0.8; but η is still lower (about 27%) when the temperature was 650℃.Finally, the NH3-SNCR denitration experiments with real coal-fired flue gas were conducted in the 6 kW CFB circulating fluidized bed (CFB) experimental apparatus.The influwences of NSR and flue gas temperature on denitration efficiency, the ammonia escape and N2O emission concentration were explored. The results showe that with no CH4 and NSR=1.5, the denitration efficiency η was less than 17% when the temperature was below 680℃ while η increased to 70% when the temperature was 810℃. With β (CH4/NH3) increased, η increased in 630-680℃. When the temperature was higher than 680℃, the facilitation of CH4 weakened, η was about 50%. At 810℃, CH4 had inhibitory effect on η. In addition, when NSR or β (CH4/NH3) increased, the N2O emission concentration (N2O) increased slightly. Ammonia escape is about 4.7ppm and had no obvious change.