Low rank coals are more reactive at low temperatures than high rank coals, which leads to spontaneous combustion if not controlled. Due to the increased use of low rank coals, preventing spontaneous combustion during storage and size reduction has become an important issue in power plants. The present study evaluates the low-temperature reactivity for various coals in terms of their rank and country of origin. The experimental method determined the temperature and its gradient for coals in a small fixed bed at the point surpassing that of input oxygen, which were defined as the crossing-point temperature (CPT) and slope (CPS), respectively. Combining the two parameters, a low-temperature reactivity index (LTR index) was proposed. The method tested 17 coals collected from a power plant that yielded CPTs ranging between 168-190 oC and CPSs between 0.862-1.228 oC/min. The LTR index for the coals was calculated to be 0.696 to 1.542. The LTR index was positively correlated with the moisture content and volatile matter/fixed carbon (VM/FC) ratio, and inversely correlated with the ash content. The ignition temperature, measured by thermogravimetric tests, also exhibited a positive relationship with the LTR index. However, no single property of coal was sufficiently correlated with the self-heating propensity for all the coals tested, illustrating the complex mechanisms involved.

Cross Point Temperature Ignition Temperature Low Rank Coal Low Temperature Reactivity Self-heating Spontaneous Combustion

International Energy Agency (IEA), Key world energy statistics (2012).
Korea Energy Economics Institute, Yearbook of energy statistics 2012. Ministry of Knowledge Economy, Uiwang, Korea (2012).
Dong NS, Utilisation of low rank coals, CCC/182, IEA Clean Coal Center (2011).
Moon C, Sung Y, Ahn S, Kim T, Choi G, Kim D, Appl. Therm. Eng., 54, 111 (2013)
Carpenter AM, Coal quality assessment - the validity of empirical tests, IEA CCC/63. IEA Clean Coal Centre (2002).
Nalbandian H, Propensity of coal to self-heat, CCC/172, IEA Clean Coal Center (2010).
Carras JN, Young BC, Prog. Energy Combust. Sci., 20, 1 (1994)
Xuyao Q, Wang D, Zhong X, Gu J, Tao X, Mining Sci. Technol., 20, 0372 (2010)
Wang HH, Dlugogorski BZ, Kennedy EM, Prog. Energy Combust. Sci., 29(6), 487 (2003)
Mao JD, Schimmelmann A, Mastalerz M, Hatcher PG, Li Y, Energy Fuels, 24, 2536 (2010)
Jo W, Choi H, Kim S, Yoo J, Chun D, Rhim Y, Lim J, Lee S, Korean J. Chem. Eng., 30(5), 1034 (2013)
Dou G, Xin H, Wang D, Qin B, Zhong X, Korean J. Chem. Eng., 31(5), 801 (2014)
Beamish BB, Int. J. Coal Geol., 64(1-2), 139 (2005)
Beamish BB, Arisoy A, Effect of intrinsic coal properties on self-heating rates, 12th U.S./North American Mine Ventilation Symposium, 149-153 (2008).
Stracher GB, Geology of Coal Fires: Case Studies from Around the World, The Geological Society of America, 2007, Boulder, Colorado, USA.
Akgun F, Essenhigh RH, Fuel, 80(3), 409 (2001)
Kim CJ, Sohn CH, Fuel Process. Technol., 100, 73 (2012)
Sen R, Srivastava SK, Singh MM, Indian J. Chem. Technol., 16(2), 103 (2009)
Xuyao Q, Wang D, Milke JA, Zhong X, Mining Sci. Technol., 21, 255 (2011)
Garcia-Torrent J, Ramirez-Gomez A, Querol-Aragon E, Grima-Olmedo C, Medic-Pejic L, J. Hazard. Mater., 213-214, 230 (2012)
Beamish BB, Barakat MA, St George JD, Thermochim. Acta, 362, 1 (2000)
Beamish BB, Int. J. Coal Geol., 64(1-2), 139 (2005)
Ohm TI, Chae JS, Lim JH, Moon SH, J. Mech. Sci. Technol., 26, 1299 (2012)
Clemens AH, Matheson TW, Fuel, 75, 891 (1996)