Effect of Weathering of Coal and Organic Dusts on Their Spontaneous Ignition
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Fire Technology, 49, 843–856, 2013 2012 Springer Science+Business Media, LLC. Manufactured in The United States DOI: 10.1007/s10694-012-0292-7
Effect of Weathering of Coal and Organic Dusts on Their Spontaneous Ignition Kulbhushan Joshi and Ali S. Rangwala*, Department of Fire Protection Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, USA V. Raghavan, Department of Mechanical Engineering, Indian Institute of Technology, Chennai, India Received: 11 April 2012/Accepted: 11 August 2012
Abstract. Weathering of coal and other cellulosic dusts occur due to the process of wetting and subsequent drying, or by subjecting them to a temperature higher than the ambient temperature for prolonged time periods. The first type of weathering occurs in a wetted storage. The second type of weathering occurs when a dust processing unit stores and maintains the dust deposit at an elevated temperature. As a result of weathering, the physical and thermal properties of the dust may change. Therefore, the weathered dust sample is expected to ignite at a different hot plate temperature as compared to that of a fresh sample, when tested in a standard test method (ASTM E 2021). In this study, three dust samples namely, wheat flour, Pittsburgh seam coal and powder river basin coal, are tested. These dust samples are subjected to one or both types of weathering. Thermogravimetric analysis and standard ignition tests are carried out with both fresh and weathered dust samples. Estimation of the activation energies and reactivity, and measurement of the minimum surface temperature for the onset of ignition have been carried out for all the cases. The implications of the observed results on industrial safety related to combustible dust layers are discussed. Keywords: Spontaneous ignition, Weathering, Coal, Organic dust, Activation energy, Reactivity Nomenclature a b A Ea M m0 m¥ n Q R T t
Conversion degree Heating rate (K/s) Pre-exponential factor (1/s) Activation energy (kJ/mol) Mass (kg) Initial mass (kg) Final mass (kg) Reaction order Heat of combustion (kJ) Gas constant = 8.314 J/mol-K Temperature (K) Time (s)
* Correspondence should be addressed to: Ali S. Rangwala, E-mail: [email protected]
844 f(a) g(a) p(a)
Fire Technology 2013 Kinetic model reaction function Integral of the kinetic model reaction function Exponential integral
Abbreviations PRB PSC
Powder river basin coal Pittsburgh seam coal
1. Introduction Industrial process safety design depends on the physical, chemical, and thermodynamic properties of the substances handled by the facility. When the substance is a fine particulate solid matter, or solid dust, the facility should be designed for dust explosion protection to avoid layer ignition of dust deposited over hot surfaces. This safety design procedure becomes challenging if the properties of the dust change due to weathering. Weathering is generally a natural process that occurs independent of human activities. It can take place in stockpiles, in-seam, refuse dumps and ponds, abandon
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