Pulverizer Design and Operation

Pulverizer Design and Operation The three types of coal pulverizers used in the United States are:(1)ball tube mills.(2)bowl mills(also called roller-race mills or vertical spindle mills),and(3)hammermills.

Ball tube mills are rotating horizontal cylinders containing steel or special alloy balls. Coal intermingled with the balls is crushed by the impact and grinding action of the balls as the mill rotates. Hot air flowing through the ball mill carries coal particles to classifiers situated at both ends of the mill (Fig.1). Large particles rejected in the classifiers are returned to the grinding zone for further size reduction. Small particles passing through the classifier exit the mill through piping leading to burners in direct fired systems and to cyclone collectors in indirect fired (storage bin) systems.

Bowl mills are vertical cylinders containing a rotating bowl in contact with two or more spring-loaded rollers. Coal enters the top of the mill and falls through a central feed pipe leading to the bowl (Fig.2) centrifugal force displaces the raw coal toward the outer perimeter where it is crushed between the rollers and a grinding ring in the bowl.

Bowl-type Pulverizer The pulverizer shown in Fig:1 has grinding elements consisting of stationary rollers and a powerdriven bowl in which pulverization takes place as the coal passes between the sides of the bowl and the rollers. A primary air fan draws a stream of heated air though the mill,carrying the fine particles of coal into a two-stage classifier located on the top of the pulverizer. The vanes of the classifier return the coarse particles of coal through the center cone to the bowl for further grinding, while the coal that has been pulverized to the desired fineness passes out of the mill, through the fan, and into the burner lines. The automatic control changes the supply of coal to the bowl of the mill by adiusting the feeder speed and the flow of primary air by regulating a damper in the line from the pulverizer to the fan. This arrangement of primary air fan has the advantage of having a cleaner facility because the mill is under suction rather than being pressurized, thereby eliminating coal leakage. However, the fan now must handle a coal-air mixture and, therefore, its design must incorporate additional preventivewear features to offset the erosion caused by the coal-air mixture.

Fig.1 Bowl-type Pulverizer

Fig.2 Bowl-type Pulverizer Pulverized coal may be radily transported through a pipe by means of a high-velocity stream of air, but the coal will not be equally distributed through the cross section of the pipe. This causes difficulty when two burners are supplied from one pulverizer mill.the distributor (Fig.2) divides the cross section of the main pipe into several narrow strips. The mixture of pulverized coal and air that enters these strips is directed into the two burner pipes in order to obtain equal amounts of coal to the burners.

Pulverizer related articles • • • • • • • • • •

What is a pulverizer? The features of the pulverizer pulverizer mills basic design The principle of pulverizer Pulverizer Design Coal pulverizing and Crushing The Types Of Plastic Pulverizer The Features Of Herbal Pulverizer Pneumatic Pulverizer The Working Principle Of Pulverizer