Experimental Study on the Effect of Urea and Additive Injection for Controlling Nitrogen Oxides Emissions

摘要

Selective noncatalytic reduction (SNCR) for nitrogen oxides (NOx) abatement, using urea (the NOxOUT process)nas an N-agent was conducted experimentally on a multifunctional combustion facility. Results showed that thenNOxOUT process resulted in 90.1% NO reduction at 1,273K if the N-agent-to-NO mole ratio (NSR) variednbetween 1.5 and 2. Also, oxygen concentration of the inlet gas clearly impacted the process. NOx reduction wasnreduced by 17.1% when oxygen concentration was increased from 2.7 to 3.6%. If the concentration was increasednfurther, decline of NOx reduction would become smooth. At the same time, ample residence time must benguaranteed, and a minimum value of 1.2 s was required for a thorough NOx reduction. The temperatures wheren90% of the maximum reductions are achieved in low and high temperature zones are seen as the lower andnupper limit temperature, respectively. The range between the lower and upper limit temperature is defined as an‘‘temperature window.’’ Different reagents lead to different maximum reductions and the ‘‘temperature win-ndow’’ changes accordingly. Based on these findings, synergistic effect of additives was studied to broaden thennarrow ‘‘temperature window’’ of SNCR. Sodium carbonate, ethanol, glycerol, and acetic acid, with a concen-ntration of 200 ppm, respectively, were selected as additives, and the ‘‘temperature window’’ was broadened byn40–80K. Different additives presented different characteristics. Sodium carbonate simultaneously broadened then‘‘temperature window’’ toward low and high temperature zones and slightly compromised the maximum NOxnreduction. The organic compounds mainly showed effect in low temperature zone and reduced the maximumnNOx reduction by 11–14%. This investigation is performed from operating parameters to additive injection,nwhich makes the effect of additive obvious. It is hoped that the conclusions of this work could further ascertainnthe NOxOUT process and make a contribution to the industrialization of the SNCR technology.