In coal grinding, various types of mills are commonly used to pulverize and dry coal before it is used as fuel in power plants or industrial boilers. Here are some of the commonly used mills in coal grinding:
- Ball Mills: Ball mills are cylindrical devices with horizontal or vertical rotating chambers that contain grinding media (such as steel balls or rods) inside. Coal is fed into the mill, and the grinding media crush and grind the coal particles. The pulverized coal is then carried out of the mill by the air flow and classified by a classifier, which separates the fine particles and returns the coarse ones for further grinding.
- Bowl Mills: Bowl mills, also known as Raymond mills or vertical spindle roller mills, use a rotating bowl or table and rollers to pulverize coal. The coal is fed into the center of the rotating bowl or table, and the rollers crush and grind the coal against the bowl or table. The pulverized coal is then carried out of the mill by the air flow and classified by a classifier.
- Vertical Roller Mills (VRM): VRMs are increasingly being used in coal grinding applications. They consist of a rotating table or bowl and rollers that apply pressure to the coal bed. The coal is fed into the mill and is ground between the rotating table or bowl and the rollers. The pulverized coal is carried out of the mill by the air flow and classified by a classifier.
- Hammer Mills: Hammer mills are used for the preliminary crushing of coal before it is pulverized in other grinding mills. They consist of rotating hammers that impact the coal and break it into smaller particles. The pulverized coal can then be further processed in other mills.
These are some of the commonly used mills in coal grinding. The choice of mill depends on various factors such as the desired fineness of the pulverized coal, the moisture content of the coal, the coal hardness, and the specific requirements of the application. Different mills may be used in combination to achieve the desired grinding and drying characteristics.