The overland conveyor moves the coal up to the secondary crusher and from there into the silos which feed the on-site power plants. Each power plant has a different coal reserve. If the silos were full and the mine stopped delivering coal, the Wyodak I plant could operate for about 60 hours.

Coal at the Wyodak mine includes two "seams." The lower seam contains coal that tends to burn hotter and contains less sulfur. Each Wyodak customer has different requirements for sulfur and ash content. These requirements are met by mixing coal from the upper and lower seams. Coal quality is controlled by the amount of each seam being delivered to the secondary crusher.

Spontaneous combustion is common in the mine pit. Moisture is needed for this to occur. It is common when the sun heats the coal after a rain or heavy dew and consequently occurs more often in spring and summer.

© 1996 Black Hills Corporation

This page last modified 10/11/96.