While passing through the fan mill beater wheel, coal particles are mutually ground both by collision and friction. Having left the beater wheel, under the influence of transport fluid flow in the mill chamber spiral, the path of coal particles turns towards the spirals exit, providing that the collision with the chamber armoured plates occur under the low angle. The process of the coal grinding inside the fan mill is relatively rough, therefore the coal powder separator should be installed behind the mill. The efficiency of after-grinding process in the fan mills may be increased after the installed fixed, hoop-shaped barriers, into the chamber spiral, around the beater wheel. The increase in the hoop's transparency coefficient, which depends on the number and size of barriers, as well as reciprocal value of the mean hoop's diameter, may influence the increase of the grinding efficiency. The barrier's shape and it's installment angle towards the beating wheel also make a significant influence on the grinding quality. As the consequence of the hoop installment there appears the decrease in ventilating efficiency of the corresponding fan mull. They may complete the coal grinding process without coal powder separators because of the increased rate of the grinding quality.