Flame propagation mechanisms in dust explosionsby Wei Gao, Toshio Mogi, Jianliang Yu, Xingqing Yan, Jinhua Sun, Ritsu Dobashi

Journal of Loss Prevention in the Process Industries

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Available online xxx

Keywords:

Dust explosion

Particle thermal characteristics

Particle size distributions

Flame propagation mechanisms rtic combining high-speed photography and a band-pass filter. Two obviously different flame propagation liquefied particles coexist. The region is heterogeneous medium, where particles undergo heating, vaporization/pyrolysis, mixing with oxidizer, ignition, burning, and flame extinction. In addition, the flame propagation process is always unsteady and numerous factors govern the initiation and subsequent propagation of the ent countries have opagation in dust and simulations. detto et al., 2010) rticle size on the rnal, external heat ved. A two-phase combustion model was developed by Slezak et al. (Slezak et al., 1985) to describe the fundamental coal dust flame propagation phenomena under rich fuel conditions. Seshadri et al. (Seshadri et al., 1992) divided the dust flame into a preheat vaporization zone, a reaction zone and a convection zone to analyze the structure of the premixed flames propagating in uniformly distributed volatile particles. Based on Seshadri's theoretical model, Bidabadi et al. (Bidabadi and Rahbari, 2009) described the flame propagation process during organic dust explosions using the supposed * Corresponding author. School of Chemical Machinery, Dalian University of

Technology, Dalian, Liaoning 116024, PR China.

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Journal of Loss Prevention w.

Journal of Loss Prevention in the Process Industries xxx (2015) 1e9E-mail address: gaoweidlut@dlut.edu.cn (W. Gao).propagation mechanisms in this phenomenon. As yet no unified theory exists covering the entire flame process from pre-flame reaction to the final state of the combustion products due to two major problems facing flame propagation research in dust explosions. One is the complexity of the dust cloud of the combustion processes. During dust flame propagation, the flame propagates in the region where combustible particles and vaporized gas and/or

Despitemany difficulties, researchers in differ been investigated the factors affecting flame pr explosions by theoretical analysis, experiments

For theoretical analysis, Benedetto et al. (Bene developed a model to quantify the effect of pa deflagration index, inwhich devolatilization, inte transfer and volatiles combustion were involTo take appropriate measures preventing accidental dust explosions, it is necessary to sufficiently understand the flame particles, moisture, oxygen concentration, the initial pressure, and the initial turbulence intensity.1. Introductionhttp://dx.doi.org/10.1016/j.jlp.2014.12.021 0950-4230/© 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Gao, W., e

Industries (2015), http://dx.doi.org/10.1016/mechanisms were observed in the experiments: kinetics-controlled regime and devolatilizationcontrolled regime. Kinetics-controlled regime was characterized by a regular shape and spatially continuous combustion zone structure, which was similar to the premixed gas explosions. On the contrary, devolatilization-controlled regime was characterized by a complicated structure that exhibited heterogeneous combustion characteristics, discrete blue luminous spots appeared surrounding the yellow luminous zone. It was also demonstrated experimentally that the flame propagation mechanisms transited from kinetics-controlled to devolatilization-controlled while decreasing the volatility of the materials or increasing the size of the particles. Damk€ohler number was defined as the ratio of the heating and devolatilization characteristic time to the combustion reaction characteristic time, to reflect the transition of flame propagation mechanisms in dust explosions. It was found that the kineticscontrolled regime and devolatilization-controlled regime can be categorized by whether Damk€ohler number was less than 1 or larger than 1. © 2014 Elsevier Ltd. All rights reserved. dust flames, such as the physical and chemical properties of the fuel, the average size, shape, concentration and distribution of the28 December 2014

Accepted 29 December 2014Received 18 July 2014

Received in revised form tributions, on flame propagation mechanisms during dust explosions clearly, the flame structures of dust clouds formed by different materials and particle size distributions were recorded using an approachFlame propagation mechanisms in dust

Wei Gao a, b, *, Toshio Mogi b, Jianliang Yu a, Xingqi a School of Chemical Machinery, Dalian University of Technology, Dalian, Liaoning 1160 b Department of Chemical System Engineering, School of Engineering, The University of c State Key Laboratory of Fire Science, University of Science and Technology of China, H a r t i c l e i n f o

Article history: a b s t r a c t

To reveal the effects of pa journal homepage: wwt al., Flame propagation mec j.jlp.2014.12.021plosions

Yan a, Jinhua Sun c, Ritsu Dobashi b

R China yo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan

Anhui 230027, PR China le characteristics, including particle thermal characteristics and size disin the Process Industries elsevier .com/locate/ j lphanisms in dust explosions, Journal of Loss Prevention in the Process n instructure composed of a preheat zone, vaporization zone, reaction zone, and post flame zone. Li (Li, 2012) conducted a detailed theoretical study to understand the transient flame propagation process and the flame-speed oscillation phenomenon in a carbon dust cloud. Based on the radiation heat exchange between particles,

Hanai et al. (Hanai et al., 2000) established a model to clarify the mechanism of the pulsating flame propagation in the PMMA particle cloud. Ogle et al. (Ogle et al., 1984) established a thermalmodel of laminar premixed dust flame propagation. Scott et al. (Scott and

Ali, 2013) analyzed a premixed dusteair flame under conditions where a homogeneous gas-phase reaction front could exist.

Although somemodels were developed recently, theywere only for specific dusts and might not be applicable generally. Identities of the important flame process particularly the controlling regimes of the flame propagation process are still in doubt.