A machine which reduces a solid fuel to a fineness suitlble for burning in suspension. Types used are:

1. High speed:(over 800 r/min)

a. Impact pulverizer: A machine in which the major portion of the reduction in particle size of the fuel to be pulverized is effected by fracture of larger sizes by sudden shock, impingement, or collision of the fuel with rotating memebers and casing.

b. Attrition pulverizer: A machine in which the major portion of the reduction on particle size is by abrasion, either by pulverizer parts on coal or by coal on coal.

2. Medium speed:(between 70 and 300 r/min)

a. Roller pulverizer: A machine having grinding elements consisting of conical or cylindrical rolls and a bowl, bull-ring mating rings, or table, any of which may be the rotating memeber, the fuel to be pulverized being reduced in size by crushing and attrition between the rolls and the rings.

b. Ball pulverizer: A machine in which the grinding elements consist of one or more circular rows of metal balls arranged in suitable raceways, wherein the fuel to be pulverized is reduced in size by crushing and attrition between the balls and raceways.

3. Low speed:(under 70 r/min)

a. Ball or tube pulverizer: A machine having a rotating cylindrical or conical casing charged with metal ball or slugs and the fuel to be pulverized, with reduction in particle size being effected by crushing and attrition resulting from continuous relative movement of the charge on rotation of the casing.

The Speed of Pulverizer