4.2 Naturally Occurring Spontaneous Combustion
115
and relatively low maturation as indicated by reflectance of vitrinite as well as by
fluorescence of liptinites, also indicates that this coal has not generated methane. It
is evident that the low bitumen content in the Huaibei coal is the by-product of only
light oil generation from liptinites and some vitrinites. The oils migrated out of the
coal seams.
Any significant quantities of methane encountered within the coal seams of
Huaibei are likely to have been sourced from coals deeper in the basin where the
coal seams attained higher maturation.
This methane is routinely drained from the mines.
4.3 Methods Used in Evaluation of Coals in Their
Susceptibility to Spontaneous Combustion
The various methods and techniques used to predict the propensity of coals to spontaneous combustion have been outlined by Cotterell (1997). In the last 20 years or so
a large number of papers have been published presenting variations on the methods
already in use, and suggested new techniques (Kaymakci and Didari 2002; Avila
et al. 2014; Saffari et al. 2019; Onifade et al. 2019). The most trusted method used
in predicting the susceptibility of a coal to spontaneously combust was developed
by Saxena et al. (1990). Their study of the Raniganj coals in India pointed out the
possible relationship between coal rank and spontaneous combustion. Samples were
taken and the coal rank was established by vitrinite reflectance. The other parameter of importance recognised by the researchers was the maceral composition of
the coals. The coals were heated and the lowest temperature at which the exothermic reaction could be observed to be self-propellent was taken as a parameter for
measuring the spontaneous combustion propensity of the coals. This was termed the
crossing point (Fig. 4.1); namely the point where the temperature reached crosses
coal rank (designated by volatile matter content and/or vitrinite reflectance). In other
words, the point of ignition. However, this method is based on coal rank as a major
factor.
Saxena et al. (1990) using the crossing point experiment found that samples
with lowest volatile matter and highest vitrinite reflectance were seen to obtain the
highest cross-points, while samples with highest volatile matter and lowest vitrinite
reflectance were seen to ignite at lower temperatures. The conclusion of this study
was that as coalification increased, the susceptibility of the coal to spontaneous combustion decreased. Saxena et al.’s study also concluded that vitrinite-rich coals were
more susceptible to spontaneous combustion than inertinite-rich coals.
Later studies (Cloke and Lester 1994; Cotterell 1997) found that the maceral
composition factor in predicting spontaneous combustion is important but not straight
115
and relatively low maturation as indicated by reflectance of vitrinite as well as by
fluorescence of liptinites, also indicates that this coal has not generated methane. It
is evident that the low bitumen content in the Huaibei coal is the by-product of only
light oil generation from liptinites and some vitrinites. The oils migrated out of the
coal seams.
Any significant quantities of methane encountered within the coal seams of
Huaibei are likely to have been sourced from coals deeper in the basin where the
coal seams attained higher maturation.
This methane is routinely drained from the mines.
4.3 Methods Used in Evaluation of Coals in Their
Susceptibility to Spontaneous Combustion
The various methods and techniques used to predict the propensity of coals to spontaneous combustion have been outlined by Cotterell (1997). In the last 20 years or so
a large number of papers have been published presenting variations on the methods
already in use, and suggested new techniques (Kaymakci and Didari 2002; Avila
et al. 2014; Saffari et al. 2019; Onifade et al. 2019). The most trusted method used
in predicting the susceptibility of a coal to spontaneously combust was developed
by Saxena et al. (1990). Their study of the Raniganj coals in India pointed out the
possible relationship between coal rank and spontaneous combustion. Samples were
taken and the coal rank was established by vitrinite reflectance. The other parameter of importance recognised by the researchers was the maceral composition of
the coals. The coals were heated and the lowest temperature at which the exothermic reaction could be observed to be self-propellent was taken as a parameter for
measuring the spontaneous combustion propensity of the coals. This was termed the
crossing point (Fig. 4.1); namely the point where the temperature reached crosses
coal rank (designated by volatile matter content and/or vitrinite reflectance). In other
words, the point of ignition. However, this method is based on coal rank as a major
factor.
Saxena et al. (1990) using the crossing point experiment found that samples
with lowest volatile matter and highest vitrinite reflectance were seen to obtain the
highest cross-points, while samples with highest volatile matter and lowest vitrinite
reflectance were seen to ignite at lower temperatures. The conclusion of this study
was that as coalification increased, the susceptibility of the coal to spontaneous combustion decreased. Saxena et al.’s study also concluded that vitrinite-rich coals were
more susceptible to spontaneous combustion than inertinite-rich coals.
Later studies (Cloke and Lester 1994; Cotterell 1997) found that the maceral
composition factor in predicting spontaneous combustion is important but not straight