Evolution behaviors of the nitrogen-containing species and SO2 from coal fast pyrolysis

The nitrogen-containing species and SO2 generated during coal pyrolysis lead to environmental problems. This paper investigated the evolution behaviors of four identified nitrogen-containing species including hydrogen cyanide (HCN), ammonia (NH3), nitric oxide (NO), nitrogen dioxide (NO2), and sulfur dioxide (SO2) from fast pyrolysis of four different types of coal in a fixed bed reactor in the 600-1200( ?)C temperature range. Results show that HCN yield increases as the temperature increasing while the NH3 maximum yield exists a transition tem-perature ranging from 800 to 1000 ?C that depends on coal category. The impact of pyrolysis temperature on the SO(2 )yield is not linear. To further quantify the NH3 formation source, a mathematical method was proposed to divide the NH3 evolution profile into gas-gas reaction and gas-solid reaction two categories. The gas-solid re-action predominates the NH3 formation with a ratio up to 75% in 1200( ?)C high temperature condition. In low temperature condition, which path is predominant depends on the coal category. In addition, the oxynitride including both NO and NO(2 )were observed in pyrolysis process. Moreover, enhancing temperature can boost NO(2 )yield and restrain NO yield. The NO and NO(2 )come from the combination of nitrogen and oxygen functional group which are both directly split off the parent coal. In addition, the elements liberation sequence from fast to slow is carbon > sulfur > nitrogen. To be further, the liberation sequence of pyrolysis species from fast to slow is CO > SO2 > NO > NO2 > HCN > NH3, which can supply guides to remove pollutants in industry.