Burn

• During the burning process, overburden rock is baked.

• This produces a thermally-altered rock referred to as red dog, scoria, burn, and, most commonly, clinker (Pictures 1 and 2).

• An understanding of the origin of clinker provides insight on the extent of mineable coal and clinker resources and helps in resource estimation and design of efficient mine development plans.

Origin of Burn• The ignition of coal seams is principally by

spontaneous combustion, lightning strikes, and fires (Picture 3).

• Lignite and subbituminous coals have high inherent moisture and oxygen content and are most susceptible to self-heating. Spontaneous combustion rate depends on the self-heating tendency of the coal and desorption of volatiles.

• Coal and overburden thickness, water saturation, coal lithology, coal morphology, rank, and composition of the coal are geological factors that affect the ignition of coal seams (Goodarzi and Gentzis, 1991).

• The self-heating temperature(temperature at which an exothermic reaction is sustained) for lignite and subbituminous coal is as low as 30° C (86° F), and bituminous coal can be as low as 60° C (140° F) (Kuchta et al., 1980).

• Self-heating is significantly greater in moist air (2.5 times greater) than in dry air. The free moisture in coal can lead to a catalytic type of reaction referred to as “heat of wetting”. The rise in temperature caused by the “heat of wetting” reaction facilitates and accelerates the chemical process of oxidation (Kuchta et al., 1980).

Exploration for Mining Limits

Burn Impacts on Mining