Abstract

Coal burns of recent age are commonly found along the coal outcrops of the Upper Cretaceous Blackhawk Formation within the Wasatch Plateau of east-central Utah. It is not uncommon to find burned coal extending 200 ft (61 m) in from the outcrop. Coal mining has intersected clinker beds of burned coal in numerous mines in the past, but normally the temperature of the strata adjacent to the burned coal is 55° F (12.8° C).

In 1981, exploration drilling at the southern end of East Mountain intersected strata with temperatures above 180° F (82° C). Subsequent exploration and mining have identified the extent of high temperatures and the approximate volume of burned coal. Approximately 83 percent of the energy liberated from the burning of the coal has dissipated into the surrounding rock and atmosphere and only 17 percent remains stored in the rock.

Laboratory work has shown that the existing in-place coal will sustain an exothermic reaction when raised above 140° F (60° C) in the atmosphere, suggesting that at the present time the coal, where exposed to the atmosphere, is oxidizing and giving off additional heat. The recognition of: current oxidation of the coal is also supported by the fact that in-mine drilling has intersected gasses produced by the oxidation of the coal. Inspection of the outcrop in the field and the use of infrared scanners and satellite imagery do not indicate an active burn.

An extensive investigation of the high temperature strata has enabled longwall mining to be completed in strata with temperatures up to 120° F (49° C). Data collected prior to and during mining are useful in understanding the inactive burn and the oxidation characteristics of the coal when exposed to elevated temperatures and the atmosphere.