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Experimental study of smouldering in wood pellets with and without air draft
NTNU Norwegian University of Science and Technology, Norway.
NTNU Norwegian University of Science and Technology, Norway.
RISE Research Institutes of Sweden, Safety and Transport, Fire Technology. Western Norway University of Applied Sciences, Norwaay; Otto von Guericke University Magdeburg, Germany.ORCID iD: 0000-0003-0979-2369
RISE Research Institutes of Sweden, Safety and Transport, Fire Technology.ORCID iD: 0000-0002-4831-7563
2020 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 264, article id 116806Article in journal (Refereed) Published
Abstract [en]

Dry wood pellets (diameter 8 mm) of mixed Norwegian spruce and pine were tested in samples of 1.25 kg (1.7 l) in configurations with and without air draft from below. The pellets were placed in a vertical 15 cm diameter cylinder on top of a hot plate. Air draft inlet, when allowed, came through narrow openings in the cylinder bottom periphery. The bulk void of 36% formed channels for gas flows within the pellets bed. Initially, the samples were heated externally from below for 6 h. Time series of distributed temperatures were recorded, together with values of the mass. Smouldering with air draft was observed with two distinct behaviours: Type 1, where the sample after the period of external heating cooled down for several hours, and then increased in temperature to intense smouldering, and Type 2, where the sample went into intense smouldering before the end of external heating. Without draft airflow from below, the sample cooled down after external heating, before developing into intense smouldering about 20 h later. In all cases, the intense period lasted for 2 h. Typical temperatures were in the range 300–450 °C, while higher temperatures occurred in the intense period. Draft flow caused fast oxidation spreading, while slow without draft. Indications of oxidation spreading as a distriäbuted reaction were seen. Circulating air motions in the irregular void between individual pellets is discussed as an explanation for the behaviour. Uneven access to oxygen, with possibilities of locally excess air, can explain the peak temperatures observed. © 2019 The Author(s)

Place, publisher, year, edition, pages
Elsevier Ltd , 2020. Vol. 264, article id 116806
Keywords [en]
Buoyancy, Combustion, Fire, Internal air motion, Poros media, Smolder, Cylinders (shapes), Fires, Air motion, External heating, Fast oxidation, Norwegian spruce, Peak temperatures, Wood pellet, Pelletizing
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-43389DOI: 10.1016/j.fuel.2019.116806Scopus ID: 2-s2.0-85076701167OAI: oai:DiVA.org:ri-43389DiVA, id: diva2:1390369
Note

Funding details: 238329; Funding text 1: Analysis of the fuel was provided by the group of Professor Ulrich Krause at the Department of Process Safety and Environmental Engineering at Otto von Guericke University Magdeburg, Germany. Funding: The first author conducted the work as an Erasmus exchange student from the Technical University of Madrid, Spain. The third author was funded by the Research Council of Norway , Project No. 238329: Emerging Risks from Smoldering Fires (EMRIS).

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-01-31Bibliographically approved

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Fjellgaard Mikalsen, RagniSteen-Hansen, Anne

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