The use of hog fuel in the earlier era was generally for fuel in the boilers of sawmills.
Later, some was burned in Tee Pee burners along with shavings and sawdust, though shavings became useful for animal bedding.
Hog fuel was typically bark and sapwood fiber that was collected during the process of debarking logs as they entered the mills or further collected at the edger.
Most wood chips at a mill are from the pieces of the ends of the logs that are collected as they are bucked to length after debarking.
Today, most hog fuel is further refined for what we now know as beauty bark.