The present invention relates to a ball mill having a substantially horizontal axis of rotation and including a drum supported by two trunions having the same axis of rotation and situated at respective ends of the drum, raw coal being conveyed by substantially vertical pipework to the vicinity of a cylinder having the same axis of rotation and disposed within each trunion so as to open out into the drum, with the space lying between each trunion and its cylinder being connected to a pulverized coal outlet duct via a separator. A raw coal guide member is disposed beneath the pipework, conveying coal under gravity into the inside of the cylinder which includes a rigid Archimedes' screw on its inside surface, a main air feed being provided on said pipework upstream from the separator, all of said air being channeled towards the inside of the cylinder.