How to choose coal grinding equipment? What are the basis for coal mill selection?

Coal mill is an important part of the pulverizing system and an important auxiliary power equipment in power plant. Its main task is to break and grind coal into pulverized coal to provide boiler equipment, its configuration will directly affect the safety and economy of the unit. Because the adaptability of different coal mills to different kinds of coal is very different, combined with the actual situation of the uneven distribution of coal products in China, the quality of coal products will directly affect the economy of the pulverizing system. So, how should coal grinding equipment selection be selected? HCM Machinery  as a coal mill manufacturer, will introduce the basis of coal mill selection. There are many types of coal mill, according to the speed of the grinding working parts of the coal mill equipment selection category can be divided into three types, namely: low-speed coal mill, medium-speed coal mill and high-speed coal mill. The following will introduce the selection of these three coal grinding equipment respectively.

Coal mill equipment selection 1: low-speed coal mill

The typical representative of low speed coal mill is the ball mill. The working principle is: the high-power motor through the gearbox to drive this heavy round plate rotation, the steel ball in the simple is rotated to a certain height and then falls down, through the impact of the steel ball on the coal and between the steel ball, between the steel ball and the guard plate, the coal is ground. The over-coarse unqualified coal is separated when it flows through the coarse powder separator at the back of the ball mill, and then sent to the circular plate from the return powder tube for re-grinding. In addition to transporting coal powder, hot air also plays the role of drying coal. Therefore, hot air is also called desiccant in the powder system. The product has the characteristics of long continuous operation time, easy maintenance, stable output and fineness, large storage capacity, rapid response, large operational flexibility, low air-coal ratio, saving spare coal machine, wide range of grinding coal and so on. It is mainly used for hard and medium-hardness coal, especially for coal with high volatile content and strong abrasive property. However, this low-speed ball mill is bulky, has large metal consumption, occupies a lot of land, and has high initial investment. So the ball mill is suitable for full load operation.

Coal mill equipment type 2: medium speed coal mill 

 The medium speed coal mill is also known as the vertical coal mill, which is characterized by the grinding parts composed of two groups of relative motion of the grinding body. The coal is squeezed and ground between the surfaces of the two grinding bodies and is crushed. At the same time, hot air through the mill dries the coal and sends the pulverized coal to the separator at the upper part of the mill area. After separation, the pulverized coal of certain particle size is taken out of the mill with the air flow, and the coarse pulverized coal is returned to the grinding area for regrinding. The medium speed coal mill has the advantages of compact equipment, small footprint, power consumption saving (about 50%~75% of the ball mill), low noise, light and sensitive operation control. But it is not suitable for grinding harder coal.

Coal mill equipment selection 3: high-speed coal mill

The speed of high-speed coal mill is 500~ 1500 r/min, which is mainly composed of high-speed rotor and grinding shell. Common fan grinding and hammer grinding and so on. In the mill, the coal is crushed by the collision between the high-speed impact and the grinding shell and the collision between the coal. This kind of coal mill and pulverized coal separator form a whole, the structure is simple, compact, the initial investment is low, especially suitable for grinding high moisture lignite and high volatile content, easy to grind bituminous coal. However, because the impact plate is directly eroded and worn by the air flow, its service life is generally only about 1000h when grinding lignite, frequent replacement, and the water content of the ground coal should not be too high, which is generally used for direct blown boilers in power plants, and should not be used for blast furnace injection workshops.

The above three kinds of coal grinding equipment selection have advantages and disadvantages, in the selection of coal grinding equipment, it is necessary to consider the overall selection of pulverizing system. The powder system can be divided into two categories: direct blowing type and intermediate storage type (referred to as storage type). In the direct blowing pulverization system, coal is ground into pulverized coal by a coal mill and then blown directly into the furnace for combustion. In the storage pulverization system, the pulverized coal is first stored in the pulverized coal bin, and then according to the needs of the boiler load, the pulverized coal is sent from the pulverized coal bin to the furnace for combustion by the pulverizer. Different pulverizing systems are also suitable for different types of coal and coal grinding equipment selection. According to the pulverization system, we summarized the following basis for coal mill selection:

(1) Steel ball mill in the middle storage bin type hot air powder system: can be used for anthracite (Vsr<9%) and wear in the strong above the coal.

(2) Ball mill middle storage type exhaust gas powder delivery system: mainly used for coal with strong wear and medium volatile (Var-19%~27%) bituminous coal.

(3) Double-in double-out steel ball mill direct blowing system 22-241: for medium-high volatile (Vs.7-27%~40%) bituminous coal.

(4) Medium-speed coal mill direct blowing system: suitable for grinding bituminous coal with high volatile content (Vanr-27%~40%), high moisture content (external moisture Mp≤15%) and strong wear, as well as coal false loss below strong, coal combustion performance is flammable, and pulverized coal fineness meets the requirements of the coal mill.

(5) Fan mill direct blowing system: suitable for lignite erosion wear index Ke≤3.5 and 50 MW and below bituminous coal unit boiler

In the selection of coal mill equipment, it should be considered according to the combustion characteristics, wear and explosion characteristics of coal, the pulverization characteristics of coal mill and the requirements of pulverized coal fineness, combined with the furnace structure and burner structure of the boiler, and consider the investment, the maintenance and operation level of the power plant and the supporting equipment, the supply of spare parts, the source of coal and the debris in coal and other factors. In order to achieve a reasonable match between pulverizing system, combustion device and boiler furnace, to ensure the safe and economic operation of the unit. HCM Machinery is specialized in the production of medium-speed coal mill manufacturers, we produce HLM series of medium-speed coal mill has the following characteristics:

(1) The use of large diameter roller and disk, rolling resistance is small, raw coal inlet conditions are good, thus improving the production capacity, reduce energy consumption.

(2) reducer performance is good, safe and reliable; Low running noise and vibration; The sealing performance is good to ensure that the coal powder does not enter all the rotating mechanical parts.

(3) Suitable for grinding hard coal, uniform grinding force, high grinding efficiency. Stable and reliable operation.

(4) MPS grinding does not exist in non-effective friction parts, and the metal wear is relatively small. If you have the problem of coal mill equipment selection, welcome to contact HCM Machinery for the basis of coal mill selection, contact

Post time: Jan-19-2024