Effects of holding geometry on spontaneous combustible dust ignition are studied. Spontaneous ignition of coal dust deposited on a flat hot surface (1D case) and trapped between two hot surfaces (2D geometry), forming the shape of a wedge, is analyzed using lab-scale experiments and a mathematical model. The solution is obtained by assuming a temperature polynomial of third (one-dimensional) and fifth order (two-dimensional), in the energy conservation equation where the source term is defined using a 1-step Arrhenius type equation. The angle in wedge configuration is varied from 10°to 150°in steps of 10°. The results predicted by the mathematical model compare well with the trends shown by the experimental data. Consequent safety measures associated with dust layers trapped in corners or wedges are discussed. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Vasudevan Raghavan

Department of Mechanical Engineering

1-D case

ARRHENIUS-TYPE EQUATION

COMBUSTIBLE DUST

DUST DEPOSITS

DUST LAYER

Energy conservation equations

HOT SURFACE

Safety measures

Source terms

SPONTANEOUS IGNITION

WEDGE CONFIGURATION

COAL DUST

Deposits

Mathematical models

Polynomials

SPONTANEOUS COMBUSTION

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IIT Madras

Proceedings of the Combustion Institute

Ignition of coal dusts deposited over sufficiently hot surfaces represents a common industrial hazard. If these surfaces are above a minimum threshold temperature, then the heat transfer from them and the associated chemical heat release can cause spontaneous ignition. This ignition front can be an ignition site for nearby combustibles as well, which depends on the location of ignition and the corresponding surface temperature attained by the coal dust. A comprehensive numerical study of ignition process of coal dust layers in different configurations, by solving the coupled Navier-Stokes and energy equations, provides a clear insight of the thermal field in the coal layer as well as the flow field over the coal surface. Such study will also provide quantitative information about the convective heat transfer coefficient, which varies for different cases. In this study, ignition phenomena of coal dusts deposited over a flat plate, wedges of different angles and a 3D corner, have been analyzed using a comprehensive numerical model. The governing equations are solved using Ansys FLUENT and user defined functions. The model has been validated using experimental results and is used to study the effect of wedge angles and the direction of gravity vector on the ignition process. © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Comprehensive numerical modeling of ignition of coal dust layers in different configurations

Ignition behavior of bituminous coal dust deposited between two hot surfaces forming wedges of 60°, and 90° is experimentally studied. Three thermocouples placed along the symmetry plane of the wedge cross-section at various heights from the apex (lowermost, middle and top) are used to record the transient temperature data. Results show that ignition always occurs around the region surrounding the top thermocouple in the case of 60° wedge and both the top and the middle regions in the case of 90° wedge. The trends are explained by investigating three parameters affecting the ignition behavior, namely, the heat transfer from the hot plate to the coal dust, the subsequent chemical heat release, and the heat transfer between different regions within the coal dust. Furthermore, an experimental setup, similar to the standard ASTM E 2021 test, is used to determine the minimum ignition temperatures of coal layers of various thicknesses and to assess the ignition scenario in the wedge configuration using an effective length scale. Measured quantities such as minimum hot plate temperature that causes ignition and the ignition time, as well as the transient heat release rate and heat conducted between various zones, calculated based on the temperature data are used to quantify the three parameters and their effects on ignition behavior. © 2011 The Combustion Institute.

Combustion and Flame

An experimental study of coal dust ignition in wedge shaped hot plate configurations

Journal of Hazardous Materials

A means to estimate thermal and kinetic parameters of coal dust layer from hot surface ignition tests

Fuel

On the role of times to ignition in the thermal safety of transportation of bituminous coals

Laboratory instrumentation modernization at the WPI Nuclear Reactor Facility

Coal Preparation

The Effect of Drying Heat and Moisture Content on the Maximum Temperature Rise During Spontaneous Heating of a Moist Coal Pile

Influence of confinement geometry on ignition behavior of dust deposits

Journal	Proceedings of the Combustion Institute
ISSN	15407489
Open Access	No