This is not an easy question and is really for a "bearings" person.  Most of the power is taken up in the friction of the shaft on the bearings.  There are three that consume most of the power:

• Thrust – caused by the torque of the material;
• Pilot – main support near the motor;
• Support – those bearings that are in contact with the material. 

If the conveyor is less than one-third full (recommended design), there is little added power from moving the material unless the solids are pinched between the blade and wall.  That later value must be determined experimentally. Power goes up significantly when the conveyor is over half full.  The pulverizer is really an experimental value. I don't know much about bearings and rely on the suppliers to suggest the motor size.