Experimental study of smouldering in wood pellets with and without air draft

FUEL

卷:264

Article

Rebaque, Virginia¹  Ertesvag, Ivar S.¹  Mikalsen, Ragni Fjellgaard^2,3,4  Steen-Hansen, Anne² 

[1] NTNU Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, NO-7491 Trondheim, Norway

[2] RISE Fire Res, Tillerbruvegen 202, NO-7092 Tiller, Norway

[3] Western Norway Univ Appl Sci, Bjornsonsgate 45, NO-5528 Haugesund, Norway

[4] Otto von Guericke Univ, Univ Platz 2, DE-39106 Magdeburg, Germany

关键词: Smolder;    Fire;    Combustion;    Poros media;    Buoyancy;    Internal air motion;   

DOI  :  10.1016/j.fuel.2019.116806

来源: Elsevier

【 摘 要 】

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 degrees 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 distriabuted 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.

【 授权许可】

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