Study On Distribution Characteristics Of Reducing Agent On Hybrid SNCR-SCR Process

According to the air pollutants emission standard of thermal power plant promulgated in2011, NOx emitted from existing coal-fired boilers in key areas must be limited to100mg/m3. To meet such requirements, hybrid SNCR-SCR technologies is widely used in low-capacity boilers in China. However, for tangentially coal-fired utility boilers, reducing agent slipped from SNCR reaction was distrubuted uniformily before the catalyst, thus affecting the denitration efficiency of SCR process.To solve this problem, plenty of numerical simulations were conducted to study the distribution characteristics of ammonia in different cases. Results showed increasing the number of spray layer and the jet velocity or employing the flat-fan injecting method can improve the uniformity of reducing agent, the De-NOx efficiency of SNCR and SCR process achieved46.2%and23.1%, respectively.In order to improving the denitration efficiency of SCR process, a cold test bench was built based on the real boiler with a scale of1:10. In this experiment, two kinds of ammonia supplementary programs were designed and measurements were conducted to analyze the trends and standard deviation of concentration distribution of reducing agent in different cases. Results showed the standard deviation factor decreased from62%to43%which indicated the uniformity of reducing agent was obviously improved.After that, a denitrification test with injection of urea solution into the real boiler was carried out. When applying optimized ammonia injection procedure ever gotten, the standard deviation of concentration distribution of reducing agent before SCR catalyst was only28%, at this moment, the De-NOx efficiency of SNCR and SCR process reached43%and66%, respectively. Moreover, the total efficiency of combined De-NOx process attached80%with low ammonia slip(<5ppm). For further verification, another test was conducted after one month. When the boiler load was190t/h and250t/h, the total denitrification efficiency was all above75%with ammonia slip under5ppm.