Thermal power ball race mill performance improvement Power Stations Coal Milling Balls Large. Coal mill pulverizer in thermal power plants to rpm rpm 1000 rpmType Ball tube Bowl Hammer mill Ball race mill ball mills in thermal power stations power stations coal milling balls large .Aug 01, 2011 Dipak K. Sarkar, in Thermal Power Plant, 2015 4.6.1 Low-speed mill. Mills operating below 75 rpm are known as low-speed mills.Low-speed units include ball or tube or drum mills, which normally rotate at about 15–25 rpm.Other types of mills, e.g., ball-and-race and roll-and-race mills, that generally fall into the medium-speed category may also be included in this category provided their.