Enhanced ignition of biomass in presence of NOx |
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Affiliation: | 1. School of Engineering and Information Technology, Murdoch University, 90 South Street, Murdoch WA 6150, Australia;2. Dyno Nobel Asia Pacific Pty Ltd, Mt Thorley, NSW 2330, Australia;3. Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695-7905, USA;1. beth.weckman@uwaterloo.ca & ejweckman@uwaterloo.ca;2. atrouve@umd.edu;3. luke.bisby@icloud.com;4. Bart.Merci@UGent.be;1. Department of Architecture, Faculty of Science and Engineering, Tokyo University of Science, 2641 Yamasaki, Noda 278-8510, Japan;2. Department of Architecture and Architectural Engineering, Kyoto University, C1-4-482, Kyoto University Katsura campus, Nishikyo-ku, Kyoto 615-8540, Japan;3. Department of Architecture, Okayama University of Science, Ridaicho, Kita-ku, Okayama-shi 700-0005, Japan;1. Fire Safety Engineering Group, University of Greenwich, London SE10 9LS UK;2. Western Norway University of Applied Sciences, 5528 Haugesund, Norway |
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Abstract: | Accumulation of combustible biomass residues on hot surfaces of processing machineries can pose fire hazards. In addition, the presence of nitrogen oxides (NOx) from plant equipment alters the local conditions, aggravating the propensity for low temperature ignition risks. This study presents an experimental study on a relative effect of NOx on ignition temperature of morpholine, an important surrogate of biomass, to reveal the sensitising role of NOx in ignition of biomass fuels and to gain mechanistic insights into the chemical aspect of this behaviour in fire. The experiments employed a flow-through tubular reactor, operated at constant pressure and residence time of 1.01 bar and 1.0 s, respectively, and coupled with a Fourier-transform infrared spectroscope. For a representative fuel-rich condition (Φ=1.25), the concentration of NOx as small as 0.06% lowers the ignition temperature of morpholine by 150 °C, i.e., from approximately 500 °C to 350 °C. The density functional theory (DFT) calculations performed with the CBS-QB3 composite method, that comprises a complete basis set, characterised the dynamics and energies of the elementary nitration reactions. We related the observed reduction in ignition temperature to the formation of unstable nitrite and nitrate adducts, as the result of addition of NOx species to morphyl and peroxyl radicals. Furthermore, the reaction of NOx with low-temperature hydroperoxyl radical leads to the formation of active OH species that also propagate the ignition process. The present findings quantify the ignition behaviour of biomass under NOx–doped atmospheres. The result is of great importance in practical applications, indicating that safe operation of wood-working plants requires avoiding trace concentration of NOx within the vicinity of biomass residues. This can be facilitated by proper (and separate) venting of engine exhausts. |
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Keywords: | Fire chemistry Sawmill Explosion Ignition Biomass Wood Dust Morpholine Sensitisation Nitration reaction Nitrosation reaction Density functional theory (DFT) |
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