Importance of solid fuel properties to nitrogen oxide formation through HCN and NH3 in small particle combustion

Formation of HNCO, HCN, and NH3 from the pyrolysis of bark and nitrogen-containing model compounds

“…The HCN/NH 3 ratio under pyrolysis conditions was found to be a function of the fuel's O/N ratio in a study involving the bark from three different kinds of wood, four kinds of peat, one German brown coal, and one Colombian bituminous coal [8]. In a followup study with different model compounds of pyridine type, pyrrole type, and amino type, no such correlation could be found [28].…”

“…In this study, proteins are the main nitrogen functionalities in every fuel, and though the amino acid composition may vary between the fuels used, the variations in amino acid composition between natural proteins are normally not too profound, and therefore the HCN/NH 3 ratio is not greatly affected by this. In the previous study [8], in which the correlation between HCN/NH 3 ratio and fuel O/N ratio was established, the fuel O/N ratio was thought not to have any strong correlation with fuel N functionality. However, biomass has mainly protein nitrogen (believed to be pyrrolic nitrogen in [8]), and peat has high proportions of fuel nitrogen in protein and amino functionalities [29].…”

“…However, during the past 10 years, the idea that most of the nitrogen in biomass is in the form of proteins has been seriously questioned. Instead it has been suggested that all nitrogen in biomass should be in heterocyclic aromatic structures [8][9][10], but as outlined in previous work [6,7], the evidence for nitrogen being in heterocyclic structures are not conclusive. In contrast, all available data support the view that proteins are the main source of nitrogen in wood and other biomass [6,7].…”

“…The formation of HNCO had not been expected previously, which is reflected by the fact that the analysis method usually used [8,9,22] to quantify NH 3 (i.e., wet chemical analysis) converts HNCO into ammonia so that the measured concentrations of NH 3 in fact are the sum of the concentrations of NH 3 and HNCO [23].…”

“…Secondary reactions in the gas phase have also been suggested to have an impact on the distribution between HCN and NH 3 . The fuel's O/N ratio has been suggested to be a measure of the fuel's tendency to take part in such secondary reactions [8]. That hypothesis was tested by including three more fuels in this study.…”