N2O and NO evolution influenced by NH3 and HCN from coal pyrolysis

NH3 and HCN formation mechanisms during coal pyrolysis, as well as N2O and NO formation and inhibition mechanisms influenced by NH3 and HCN, are crucial for N2O and NO synergistic control in CFB. They were revealed by experimental and DFT studies. The results indicate that HCN and NH3 primarily originate from the direct hydrogenation of Coal-N and the secondary pyrolysis of N-containing tar. The concentration of H radicals is a critical determinant of NH3 and HCN yields. A sufficient amount of H radicals will lead to more NH3 release, whereas an insufficient amount will result in more HCN release, and homogeneous hydrogenation of HCN to NH3 is difficult to occur. Furthermore, the formation reaction energy barriers of NH3 and HCN also affect the release ratio of NH3 and HCN. Ca reduces NH3 formation energy barrier from 180.8 kJ/mol to 163.7 kJ/mol and increases HCN release energy barrier from 212.8 kJ/mol to 283.8 kJ/mol, and finally promotes NH3 release but inhibits HCN release. O2 preferentially oxidizes HCN over NH3, and NO directly originates from HCN and NH3 oxidation by O2, but N2O and N2 are the products of NO reduction by HCN and NH3. The homogeneous reduction of NO proceeds sequentially from NO to N2O and then to N2. This study will promote the development of N2O and NO synergistic control technologies.