Time dependent production of NO from combustion of large biomass char particles

Abstract

In this study, the NO release during the char combustion of single biomass particles was investigated. Cylindrical biomass particles of spruce bark, short rotation coppice (SRC) poplar, Danish straw, and torrefied wood were combusted in a single particle reactor of quartz glass operating between 1073 and 1323K and with 3–19vol.% O2. The initial diameter of the particles was 8mm. Molar fractions of NO and CO2 were measured at the outlet of the reactor system. During the char combustion stage, the measured molar fractions were converted into time resolved release of NO and carbon from the char particle. To model the NO release from the single char particles, the char-N was assumed to be oxidized to NO proportionally to the experimental carbon release rate. The NO reduction reactions are lumped together such that the reduction rate is modeled as a function of an apparent activation energy, pre-exponential factor, and reaction order. The results showed good agreement between the modeled and experimental NO release rates. Initially most of the formed NO was reduced inside the char particle. As the conversion proceeded, the NO release from the char particles increased although the mass and the diameter of the particle decreased. This is attributed that the fraction of char-N being released as NO increased significantly during conversion. In the final conversion stage, all char-N was released as NO.