pulverizer mills
In a pulverizer mill that uses the impact principal, the coal remains in suspension during the entire pulverizing process. FIG.26 shows an impact pulverizer design where all moving parts rotate on a single shaft that is held in place by two bearings mounted externally on separate bearing pedestals. This design has no metal-to-metal contact between pulverizing elements and requires no adjustments to compensate for wear. The pulverizer operates with only a small inventory of coal and therefore provides fast response rates and short startup and shutdown times.
Raw coal and primary air enter the crusher-dryer section (see Fig.26) where hammers propel the coal against a grid. The grid openings reduce the coal size to 1/4 in or less. Tramp iron and other no crushable foreign materials are rejected to an area for easy removal. When the coal passes through the grid section of the crusher-dryer, it enters the pulverizing section, where rapid attrition takes place. Attrition, the impact of coal on coal, as well as on moving and stationary parts, reduces coal particles to the proper size for combustion. 
As shown in Fig.27, fan wheels with abrasion-resistant alloy blades are mounted on the pulverizer shaft. Coal is transported by this integral fan from the pulverizing section directly to the burners. This pulverizer design does not require a separate primary air fan because of this integral fan. The coal feed from the coal bunker and the primary airflow are regulated by adjusting the feeder speed and the primary air discharge damper. (Refer to Fig.2) these types of pulverizers are designed for capacities ranging from about 4 to 27 tons/h.
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