Research On The No Removal Process And The Generating Characters Of N₂O In The SNCR Process Using Urea As The Reducing Agent

SNCR technology is wildly used in NO removing, mainly regarding ammonia,isocyanate and urea as the reducing agent. Urea has been widely used due to itssafety and convenient storage. SNCR process using urea as the reductant(Urea-SNCR) has a high temperature window and N2O emission thanammonia(NH3-SNCR). SNCR technology,which is usually applied with lownitrogen combustion technology, can achieve high denitration efficiency with lowcost. Low nitrogen combustion technology will increase the CO concentration influe gas, and will have influence on the Urea-SNCR process. Studies on theinfluencet mechanism are less, therefore, making the mechanism clear can provideengineering guidance for the Urea-SNCR process with the existence of CO.Firstly, the paper investigated the decomposition process of urea withChemkin4.1code, based on the urea decomposition and HNCO hydrolyzationmechanism in Urea2000.Compared with the experiment result, the calculated resultusing urea decomposition reactions of Urea2000was consistent with theexperiment best. The paper also studied the influence of temperature and oxygenconcentration on urea decomposition process. It’s found that urea decompositionrate increased as the temperature rising; with the presence of oxygen, when thetemperature was above950K, the system would produce NO and N2O, and thehigher oxygen content was, the more the generating of these two substances were.Then the paper had studied the Urea-SNCR process, and the main reason for itstemperature window higher than NH3-SNCR was that HNCO exists in the ureadecomposition products. N2O formation in the Urea-SNCR process had beenstudied, the N2O production of Urea-SNCR was between the HNCO-SNCR processand the NH3-SNCR process, and it’s found that the formation of N2O mainly camefrom the urea decomposition product HNCO, and in theory there is44%nitrogenconverted into N2O in the HNCO-SNCR process. And then the influence of vapourconcentration and oxygen concentration on the Urea-SNCR process and thegeneration of N2O were studied. The paper found that, when the temperature washigher than1200K, the NO removal efficiency of Urea-SNCR process decreasedwith the increasing of vapour concentration, and the temperature window shifted tothe lower direction slightly; the higher the vapor concentration was, the lower theN2O production was; the oxygen concentration had a big influence on theUrea-SNCR process,, the temperature window moved to the lower temperaturedirection with the rising of oxygen concentration, at the same time, the generating of N2O was also increased.CO can make the temperature window of the Urea-SNCR process moving inthe direction of low temperature by promoting OH generation. When thetemperature was higher than1325K, the existence of CO would not change the N2Oformation rule; when temperature is lower than1325K, N2O generation increasedas the concentration of CO increasing.This paper also studied the influence ofammonia nitrogen ratio (NSR) and oxygen concentration on the Urea-SNCRprocess with the existence of CO, and found that, when the CO concentration was300μmol/mol, and the temperature was higher than1100K, with the increase ofNSR, the denitration efficiency of Urea-SNCR process was also on the rise; andwhen the temperature was between950K and1075K, with the increase of NSR,the denitration efficiency of Urea-SNCR decreased, and the N2O generation alsodecreased, when the temperature was higher than1200K, the N2O generation risedwith the NSR increasing; whether CO existed or not would not affect the influenceof oxygen on the Urea-SNCR process.