Biomass Char Nitrogen Oxidation - Single Particle Model

In this study, the release of NO during the combustion of single char particles of spruce bark was investigated. Modeled NO release rates were compared to experimentally determined NO rates from a single particle reactor of quartz glass. The operating conditions were between 1073 and 1323 K with 3-19 vol % O-2 and with 0% NO in the surrounding gas. The NO release rates from the single particles were determined from measured molar fractions of NO at the outlet from the reactor system. In the model, the char-N is assumed to be oxidized proportionally to the char-C oxidation rate, which is measured. The formed NO is assumed to be reduced as a function of the local NO concentration inside the particle. The NO concentration profile inside the char particle is numerically calculated by taking into account the transport of NO inside and outside the particle and the reduction rates of NO inside the char particle. The modeled NO release rates were in good agreement with the measurements. The results show that the fractional conversion of char-N to NO increases as functions of decreasing particle size and conversion. The most likely explanation for this is that the formed NO diffuses away at an increasing rate as the particle decreases in size. Further, a suggested analytical model for the fractional conversion of char-N to NO is tested.