This section is from the book "An Elementary Outline Of Mechanical Processes", by G. W. Danforth. Also available from Amazon: An elementary outline of mechanical processes.
In handling coal at the mine, a considerable quantity becomes pulverized. In this form it is known commercially as screenings. This is now used in mechanical stokers fitted to steam boilers, and some of it is made into briquettes by mixing it with tar or crude oil and pressing it into cakes by a machine for that purpose. Some grades of screenings must be washed to remove mineral matter.