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Experimental correlation of "MIT in oven" in layer with self-heating cubic basket tests

Abstract : In some industrial situations, such as the drying of agricultural or food materials, the products are commonly processed as dust layers in a hot air stream. The experimental conditions of the measurement of the minimum ignition temperature (MIT) in layer, which are described in EN 50281-2-1 standard are unfortunately not representative of these conditions: this test is performed on a hot plate in a ambient temperature and still environment. The use of an oven rather than a simple hot plate in open environment allows for testing and assessing the influence of different experimental conditions. Indeed, on a hot plate, the test temperature is settled on the floor surface of the layer, but the surrounding air is heated only by convection and radiation. On the contrary, in a forced convection temperature-controlled oven, the temperature may be considered homogeneous in the oven. A study aiming to correlate the results of “MIT in oven” in products layer with results of self-heating tests for same products in cubic baskets was conducted. The “MIT in oven” of layers of 5, 10 and 15 mm of thickness were experimentally determined for nine organic products, representative of products used in industrial dryers. In the case of the layer of 5 mm, comparative tests were carried out on two different plates: i) a metal plate, and ii) an insulating ceramic plate. These results were then compared with the standard MIT in 5 mm thick layer values experimentally measured. Finally, the experimental “MIT in oven” in layer were compared with values resulting from cubic basket test modelling, using the shape factor suitable for plate storage. This confirmed the quality of the Frank-Kamenetskii model used, in so far as modelling is in agreement with the experimental results. The assumptions included in this model correspond to "MIT in oven" tests performed on an insulating plate. They are representative for example of the storage of a material in a plate shape storage silo, on the ground. By contrast, the implementation of materials in equipment such as dryers or spray towers corresponds to the tests performed in an oven on a metal plate. They allow to obtain lower ignition temperatures of 0 to 15 °C to the temperatures measured on the insulating plate in the same other conditions. This is why the Frank-Kamenetskii model usually implemented can be used to determine the operating temperatures of equipment provided that a safety margin of at least 20 °C is retained from actual calculations. The use of standardized MIT in layer, measured on a hot plate in ambient conditions, should be avoided for this application.
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Contributor : Gestionnaire Civs <>
Submitted on : Monday, August 6, 2018 - 3:16:23 PM
Last modification on : Tuesday, August 7, 2018 - 1:08:03 AM

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  • HAL Id : ineris-01854180, version 1

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Agnès Janes, Douglas Carson. Experimental correlation of "MIT in oven" in layer with self-heating cubic basket tests. 15. International Symposium on Loss Prevention and Safety Promotion in the Process Industry, Jun 2016, Freiburg, Germany. ⟨ineris-01854180⟩

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