Evaluation on nitrogen conversion during biomass torrefaction and its blend co-combustion with coal

Abstract

In this work, biomass torrefaction was combined with coal co-combustion to illustrate the differences in biomass performance and the mechanisms of migration and transformation of nitrogen over the entire course of thermal treatments. XPS analysis illustrated that torrefaction in CO2 suppressed the conversion of pyrrole-N (N-5) to quaternary-N (N-Q), whereas the trend for an O2 atmosphere moved in the opposite direction. During co-combustion, the impact on NO emission reduction shifted from positive to negative as the pretreatment temperature was raised, which is closely related to the six elementary reactions involving the intermediacy of NCO and NH, as well as to heterogeneous reduction of NO with char. In addition, torrefaction in a N2/O2 atmosphere at a lower temperature of 250 °C improved the properties of biomass and achieved the lowest NO emission during co-combustion, which provides the supporting theory needed for using effluent in power plants as a torrefaction medium.