A coal mill is also called a coal pulverizer or coal grinder. It is a mechanical device used to grind raw coal into pulverized coal powders. The most used coal mills in cement plants are air-swept ball mills and vertical roller mills.
At present, most cement plants use coal as the main fuel in the clinker production process. The standard coal consumed by the new dry process for producing 1 ton of cement clinker is usually between 100 kg and 130 kg, and the fuel cost accounts for about 15% of the cement production cost.
Calcining high-quality cement clinker needs a stable coal powder supply. Therefore, coal powder preparation has become an important part of cement production, and the coal mill has also become one of the important pieces of equipment in cement plants. The coal mill in a cement plant should be reliable and should be operated with great care, or it is easy to cause safety accidents In the process of grinding, storage, transportation, and burning of pulverized coal, resulting in casualties and equipment damage.
When we manufacture a coal mill, we will comprehensively take into account the production scale, site, raw coal quality, operating conditions, and other aspects of the target project for reasonable design, so as to perfectly match the kiln calcination system and meet the requirements of reliability, efficiency, safety, environmental protection, and automation.
Air-Swept Ball Mill
The ball mill is a traditional coal pulverizer machine, which has been widely used since it was invented. In the cement plant, the new dry process cement manufacturing requires the moisture content of coal powder to be 0.5% ~ 1.5%, while that of raw coal is 1.5% ~ 4.0%. Therefore, the ball mill should have a drying function besides grinding. In order to enhance the drying ability, large ball mills are equipped with drying chambers.
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During the operation of the ball mill, the raw coal first enters the drying chamber through the feed inlet for drying, and the dried raw coal enters the grinding chamber for grinding and second drying. The pulverized coal is taken out of the mill by hot air.
Compared with the vertical roller mill, the advantages of air-swept ball mill are strong adaptability to raw coal quality, simple operation and low investment cost; the disadvantages are high power consumption and high noise.
Vertical Roller Mill
Vertical roller mill is a popular pulverized coal mill in recent years.
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The working principle of vertical mill is as follows: the material is fed into the mill through the inlet on the top center of the mill and falls on the grinding plate, and the grinding rollers which are driven by the rotation of the grinding plate will crush the material. The fine material is taken away by the high-speed hot air from the bottom to the top, and the coarse material continues to be ground on the grinding plate. The fine material taken away by hot air is separated by the separator on the top of the mill. The pulverized coal with acceptable fineness is discharged from the mill with air, and the unqualified pulverized coal is returned to the mill for further grinding.
Compared with ball mill, the advantages of vertical mill include simple operation, high grinding efficiency, low noise, small floor area, strong drying capacity, and low energy consumption.
Ball Mill vs Vertical Roller Mill
|Milling System||Vertical Roller Mill||Ball Mill|
|Feed coal water content (%)||≤15||≤10|
|Coal powder fineness (0.08mm hole sieve residue, %)||8||8|
|Drying capacity||Very High||High|
|Main motor capacity(kW)||630||1250|
|Total installed capacity(kW)||1359||1722|