Influence of the size distribution and concentration on wood dust explosion: Experiments and reaction modelling S. Calle ´ * , L. Klaba, D. Thomas, L. Perrin, O. Dufaud Laboratory for Chemical Engineering Science, LSGC-CNRS, 1 rue Grandville BP 451, 54001 Nancy cedex 01, France Accepted 4 May 2005 Available online 20 June 2005 Abstract The explosion ability of wood dust was characterized by a 20 L explosion sphere (Ku ¨ hner). The overpressure inside the sphere is recorded during the explosion. The results show that the violence of the explosion is all the more important that the particle size is low. A model based on balances on chemical reaction, kinetics and thermodynamics leads to the representation of the pressure change during the explosion. There is a good agreement between the calculations and the experiments. D 2005 Elsevier B.V. All rights reserved. Keywords: Explosion; Dust; Overpressure; Combustion 1. Introduction A lot of combustible powders can cause explosion when they are mixed with an oxidant like O 2 and if the mixture is ignited with an energy source (electrical discharge for example). We can find these powders in the food-processing industry (flour, sugar, etc.), in the mechanical engineering industries (Aluminium, etc.) and in the chemical engineering industries (fertilizer, plastic, pulverulent waste, etc.). One explosion per day occurs on average in France [1]. The reasons are the increase of storage capacity and of handling flows of powders which present lower and lower sizes [2]. The hazard is then linked to the transport and the storage of pulverulent materials. Only the knowledge of the parameters which quantify the explosion ability of powders and the control of their environment can help the risk prevention. Cashdollar [3] said that the form and the size of powders have a strong influence on their explosion. As a matter of fact these physical parameters are linked to the particles volumic surface which plays a role in the combustion kinetics. Moreover large size particles (> 500 Am) do not significantly participate in the flame propagation because of the sedimen- tation. The fine fraction of the size distribution controls then the explosion due to its large volumic surface and its ability to stay in suspension. These conclusions were supported with experimental results on aluminium and coal powders [4]. In each case maximum overpressure and maximum rate of pressure rise decrease when the particle size increases. This result was also observed by Soundararajan and al. [5] on ferrous materials. Authors also present results of explosion tests of mixed powders of different sizes which lead to the inhibition of the explosion mechanism. One condition is that one of the two powders is inert and the other is combustible [6,7]. These works show that the lower the inert particle size is, the lower is the amount of these particles necessary to prevent the explosion. Finally Sweiss and Sinclair [8] measured the maximum admissible O 2 concentration to prevent dust explosion as a function of particle size. They obtained the following result: the lower the particle size, the lower the maximum admissible O 2 concentration. The aim of the present work is first to characterize experimentally the explosion of wood dust of different 0032-5910/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2005.05.021 * Corresponding author. Tel.: +33 3 83 17 52 24. E-mail address: sandrine.calle@ensic.inpl-nancy.fr (S. Calle ´). Powder Technology 157 (2005) 144 – 148 www.elsevier.com/locate/powtec