Nitrogen in Biomass Char and Its Fate during Combustion: A Model Compound Approach

Abstract

The emission of nitrogen oxide (NO x ) from biomass combustion is still a concern, even though the nitrogen content of biomass in general is relatively small. To elucidate the pathways of fuel N conversion during combustion processes, many studies have focused on the pyrolysis of amino acids and/or model compounds. In contrast, the model compound char nitrogen and its fate during combustion have not been investigated. The partitioning of nitrogen between the volatiles and char and the type of nitrogen species released during char combustion are very important, because volatile N is better controlled by low NO x burners than the nitrogen retained in the char. In this study, low heating rate biomass model chars were prepared from a combination of either cellulose or glucose and five of the amino acids most commonly found in terrestrial biomass: L-proline, Lglutamine, L-histidine, L-asparagine, and L-tryptophan. The chars were characterized by X-ray photoelectron spectroscopy (XPS), and the partitioning of nitrogen was also calculated. Furthermore, the impact of protein nitrogen on emissions of nitrogen species from combustion processes was investigated by thermogravimetric analysis−mass spectrometry (TGA−MS) combustion tests, which were used to calculate the char combustion kinetics and conversion of char nitrogen to different nitrogen-containing species. Results indicate that there may be a correlation between the proportion of pyridinic N and pyrrolic N (and/or possibly some quaternary N) in the char and the N precursor. However, further correlations to the N species formed during the char combustion to the N functionalities in the chars were not obtained and merit further investigation. Finally, the char yields obtained and N partitioning of the model chars are comparable to those reported in the literature for biomass chars.

Combustion kinetic study of woody and herbaceous crops by thermal analysis coupled to mass spectrometry

“…Protein decomposition leads to the formation of volatile cyclic amides which, due to cracking reactions, produces HCN among other components [41]. The second peak stood out for the early apparition of NO 2 followed by the NO emission at higher temperatures for all samples except for W. These results agree well with those reported by Darvell et al (2012) [5] who found two stages for the combustion of different biomass char model samples. These stages were characterized by the release of NO at higher temperatures and the presence of sharper peaks.…”

“…In spite of the environmental advantages, some aspects concerning the release of contaminants during biomass combustion must be taken into account. In this regard, NO x and SO x emissions depend on raw biomass composition, which usually is variable [5]. The control of NO x and SO x from biomass combustion can contribute to decrease the emissions of these pollutants in Canada which are around 0.7 and 1.2 million tons per year for NO x (as NO 2 ) and SO 2 , respectively [6].…”

Life cycle assessment of swine and dairy manure: Pyrolysis and combustion processes

“…One stage was related to the release of amines and NO 2 , which was attributed to the decomposition of proteins (Darvell et al, 2012). In the second one, NO 2 was only detected and attributed to the oxidation of the retained N 2 in the char (Darvell et al, 2010).…”

Some Aspects of Modeling NOx Formation Arising from the Combustion of 100% Wood in a Pulverized Fuel Furnace

“…In bituminous coal combustion, the heterocyclic N-compounds form mainly HCN, but in biomass, fuel-N can exist both as heterocyclic compounds and as amino acid groups in proteins. Hence, NO can be formed from the HCN intermediate produced from the heterocyclic compounds, while the protein nitrogen can be converted into both HCN and NH3 intermediates and ultimately NO together with some HNCO (Darvell et al, 2012;Hansen and Glarborg, 2010;Hansson et al, 2003aHansson et al, , 2003bRen et al, 2011;Stubenberger et al 2008). The protein nitrogen content of wood has been estimated to be in the range of 70-90 wt.% of the total nitrogen, and therefore a combination of both the HCN and NH 3 routes has to be considered.…”