Influence of CaO on urea pyrolysis in the selective non-catalytic reduction deNOx process.

CaO affects urea pyrolysis when coalescing with melting urea, which decreased the performance of urea-SNCR deNO x process. The influence of CaO on urea pyrolysis was studied with a thermogravimetric analyzer, a fixed bed reactor, and DRIFTS. The mechanism of CaO was also analyzed. Experimental results showed that CaO decreased the pyrolysis rate of urea, especially in the presence of O 2 . NH 3 production in urea pyrolysis was not influenced by CaO, whereas HNCO in the gaseous products disappeared and CO 2 production was increased remarkably. NO, N 2 O, and CO were also produced in the presence of O 2 . DRIFTS experiments showed that Ca(NCO) 2 and CaCN 2 were produced and the composition of the solid products varied with the atmosphere. Mechanism analysis showed that CaO initially reacted with melting urea and biuret to produce Ca(NCO) 2 and release NH 3 and H 2 O. Ca(NCO) 2 decomposed to CaCN 2 and CO 2 with increasing temperature, and CaCN 2 can exist stably in the absence of O 2 because of its high thermostability. In the presence of O 2 , Ca(NCO) 2 can be oxidized to N 2 O, CO 2 , and N 2 , whereas CaCN 2 can be oxidized to NO, CO, and N 2 . [ABSTRACT FROM AUTHOR]