Effect of mineral matter on coal self-heating rate B. Basil Beamish a , Ahmet Arisoy b, * a School of Engineering, The University of Queensland, Brisbane Queensland 4072, Australia b Faculty of Mechanical Engineering, Istanbul Technical University, Gu ¨mu ¨s ßsuyu, 34437 Istanbul, Turkey Received 27 April 2006; received in revised form 27 March 2007; accepted 28 March 2007 Available online 21 May 2007 Abstract Adiabatic self-heating tests have been conducted on subbituminous coal cores from the same seam profile, which cover a mineral mat- ter content range of 11.2–71.1%. In all cases the heat release rate does not conform to an Arrhenius kinetic model, but can best be described by a third order polynomial. Assessment of the theoretical heat sink effect of the mineral matter in each of the tests reveals that the coal is less reactive than predicted using a simple energy conservation equation. There is an additional effect of the mineral mat- ter in these cases that cannot be explained by heat sink alone. The disseminated mineral matter in the coal is therefore inhibiting the oxidation reaction due to physicochemical effects. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Coal; Spontaneous combustion; Mineral matter; Non-Arrhenius kinetics 1. Introduction Coal self-heating, leading to spontaneous ignition, con- tinues to be a hazard that must be managed by coal mines to create a safe work environment [1]. Spontaneous com- bustion management plans (SCMPs) should contain data that can be used to assess the inherent propensity of the coal to self-heat. This usually involves obtaining results from small-scale laboratory tests. One such test that is fre- quently used by the Australian coal industry is the adia- batic oven R 70 self-heating rate test, which can also be used to study and quantify the factors that affect coal inherent self-heating propensity [2–6]. The test measures the average self-heating rate between 40 °C and 70 °C, known as the R 70 self-heating rate index [7]. The higher the R 70 value, the higher the propensity of coal for self- heating. Tests of this genre have been criticized in the past on the grounds that they disregard different thermal diffu- sivities of the coals tested. These tests also provide a full temperature history of the self-heating process through to thermal runaway at temperatures up to 160 °C and the data can be used to define the reactivity of coal. One important factor that affects coal reactivity and hence self-heating propensity is the mineral matter content of the coal. However, little is known about mineral matter effects on coal self-heating, other than brief investigations by Humphreys et al. [7], Smith et al. [8] and Beamish and Blazak [4]. Smith et al. [8] looked at the heat sink effect of adding different minerals and inorganic constituents to coal as a possible solution to inhibiting coal self-heating. Humphreys et al. [7] added differing amounts of coal ash to the same coal sample to test a mineral matter free correc- tion equation for the R 70 self-heating rate. Beamish and Blazak [4] and Beamish et al. [9] showed a strong negative correlation exists between ash content and R 70 self-heating rate of both low and high rank coals. Such a relationship is not accounted for in most models of coal spontaneous combustion. This paper presents a more detailed kinetic analysis of the self-heating rate data obtained by Beamish and Blazak [4] from subbituminous coal cores. The effects of mineral matter in the coal are clearly defined by means of mathe- matical modelling of the heat sink effect over the entire 0016-2361/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2007.03.049 * Corresponding author. Tel.: +90 212 252 9587; fax: +90 212 245 0795. E-mail address: arisoyah@itu.edu.tr (A. Arisoy). www.fuelfirst.com Available online at www.sciencedirect.com Fuel 87 (2008) 125–130