Themal power plant NTPC | PDF SlideShare
Primary air fan(PAF): Primary air fan sucks air from atmosphere pressurizes it and sends it to coal mill through primary air pre heater which heats up this pressurized air. Seal air fan(saf): As coal mill is of heavy mass ball bearings are not used but slew bearings are used. To prevent the damage of slew bearing of coal mill seal air fan is used.