Raw meal grinding is a vital link in the cement raw material preparation process. After the cement raw material is crushed, it will be sent into the raw mill for further grinding until a certain degree of fineness is reached, and then enter the clinker calcination process. From the production experience of many cement plants, the selection of cement equipment, especially raw mill, will directly affect the project investment, production schedule and economic benefits. At present, in order to adapt to the process characteristics of the new dry method cement production line and make full use of the exhaust gas residual heat of the kiln tail preheating decomposition system, we usually adopt the grinding system that merges drying and pulverizing into a single.
AGICO is an experienced Chinese cement equipment manufacturer. We have been in the cement industry for almost 20 years, specializing in cement EPC project exporting and cement making machines exporting, such as cement production line, cement kiln, cement crusher, cement mill cement raw mill, etc. According to the different properties of materials, there are mainly two kinds of grinding systems used in our cement plant.
Cement Ball Mill Grinding System
The cement ball mill manufactured by AGICO can complete the drying and grinding of raw materials at the same time. After entering the ball mill, materials directly contact with the gas with high temperature, so the heat exchange and the water evaporation is fast. Under normal conditions, we usually divide the cement ball mill grinding system into an intermediate discharge circulating grinding system and tail discharge circulating grinding system.
Intermediate Discharge Circulating Grinding System
Intermediate discharge circulating grinding system is a drying form in the cement ball mill. In terms of drying function, this system is the product of the combination of wind swept mill and tail discharge circulating grinding mill. In terms of grinding function, it is equivalent to a secondary closed-circuit grinding system. After classified by the powder concentrator, most of the raw meal will go back to the fine grinding chamber and a small part to the coarse grinding chamber. This is better for the hardness and granularity adaptability of raw materials.
- The feeding particle size of this system can be relaxed to 25 mm, the phenomenon of over-grinding is less and the grinding efficiency is high.
- There is no drying chamber at the front end of this system, the ventilation resistance of the middle discharging grate plate is smaller than that of the tail discharging grinding mill, and the hot air enters the mill from both ends, so it can pass a large number of hot air and has strong drying capacity.
- In this grinding system, 80% ~ 90% of the hot air enters from the head, and a small part of air enters from the tail. The hot air entering from the tail is not only beneficial to remove the residual moisture of the material, but also can improve the discharge temperature of materials in the fine grinding chamber to prevent condensation.
- Because of the middle exhaust, the air speed in the coarse grinding chamber is large and the fine grinding chamber is small, which is more suitable for the distribution of material particle size.
- This grinding system can dry 6% – 7% moisture of raw materials by using 320 ℃ kiln tail gas. If we use the high-temperature gas in another hot blast furnace, the drying capacity will be increased to 14%.
Tail Discharge Circulating Grinding System
The main difference between the tail discharge circulating grinding system and the air swept mill is that materials in the tail discharge grinding system will first pass through a drying chamber before reaching the grinding chamber. Besides, this system adopts the mechanically discharging method. The hot air will be transferred from the head to the tail, and then discharged into the atmosphere after dedusting by the dust collector.
- Due to mechanical unloading, the amount of air passing through the mill is small.
- The discharging grate in the grinding chamber increases the ventilation resistance, and the air speed should not be too high, generally 3-4m / s. Therefore, the drying capacity of this system is inferior to the intermediate discharge circulating grinding system and the vertical mill system.
- If only use the waste gas from the kiln tail, the system can dry less than 5% of the material moisture. If another hot blast furnace is set, only 8% of the moisture content can be dried.
Cement Vertical Mill Grinding System
Cement vertical mill, also called roller mill, is another raw mill commonly used in cement plants. Compared with the cement ball mill, it has a great difference in structure, grinding principle, process layout, automatic control, and energy consumption, which play an important role in the modern cement industry.
- High Grinding Efficiency. The energy consumption of cement vertical mill grinding system is relatively low, which is 10%-30% lower than that of the cement ball mill grinding system. And the decreased value will increase with the rise of raw material moisture.
- Large Drying Capacity. The cement vertical grinding system can make full use of the low-temperature exhaust gas of the preheater, its air speed is up to 60-80m/s, so the drying efficiency is high. If we adopt the hot blast furnace, this grinding system can dry materials that contain 15%-20% water content.
- Large Feeding Particle Size. The feeding particle size of this grinding system is between 50-150mm. The maximum feeding particle size can be calculated as 5% of the roller diameter.
- Small Space Occupying & Small Noise. The cement vertical mill manufactured by AGICO occupies small space and makes low noise. Because it has less equipment, a high operation rate and small land occupation, it can be set in the open without the workshop. Moreover, its unit power consumption of the product and the production cost is quite low, so the market share of vertical mill is rising rapidly.