In the cement production line, raw material preparation is a very important section. In this process, raw materials of different particle sizes will be ground by the grinding mill to reach a uniform fineness, so that they can fully produce chemical reactions with each other in the subsequent calcination. Grinding mill is the core equipment of raw material preparation, which will directly affect the production efficiency and quality of cement. In current cement plants, the vertical roller mill grinding system, roller press grinding system and ball mill grinding system are the most frequently used and most efficient grinding systems. Next, we will analyze the advantages and disadvantages of the cement vertical mill grinding system and the cement roller press grinding system from the aspects of energy consumption, performance and investment in combination with the actual production experience.
Due to the different grindability of raw materials in cement plants, and the difference between product fineness and equipment efficiency, we can’t judge the merits of the two systems simply based on the comparison of the measured power consumption in Table 1 and Table 2. From the perspective of the system installed capacity, the difference between the two systems is only 65kW. From the perspective of the design calculation, the unit raw meal power consumption of the roller press grinding system is about 3.5kwh/t lower than that of the vertical mill, which is equivalent to the clinker power consumption of 5.25kwh/t. While in the table 3, with the passing of time (the production line has been in operation for 16 years), although the fineness of raw materials has been reduced, the grinding capacity of the roller press is still gradually reduced (more than 10%), and the unit power consumption of the system is significantly increased (more than 10%). Of course, there are factors such as the deterioration of raw materials’ grindability, the reduction of equipment efficiency and so on.
Overall, we can conclude the three tables:
- After long-term operation, although unit raw material grinding power consumption of the cement roller press grinding system is still low, the indexes of the vertical roller mill grinding system is very close to it, among which the output power of the vertical mill and the roller press contribute the same value to the unit power consumption, about 7~8kWh/t.
- With the increase of service time, the unit grinding power consumption of roller press is significantly higher than that of vertical mill, but the proportion of circulating fan in unit power consumption of vertical mill grinding system is much larger than that of roller press grinding system (Design calculation: the former is about 2.75 times of the latter. Actual measurement: the former is about 2 times of the latter.), while the change is very small. The motor of the circulating fan in the roller press grinding system has been running at full load, and its unit raw material power consumption in the early and late period has changed greatly (about 34% more than the design calculation).
System investment is one of the most concerned factors when customers choose a solution. For the vertical grinding mill and the cement roller press, there are too many manufacturers, the equipment configuration is different, and the price varies greatly. The following table is priced based on the high configuration equipment (the hydraulic device adopts Rexroth products, the roller surface of the roller press and the roller skin of the vertical mill both adopt the surfacing welding of high wear-resistant alloy material, the service life is over 8000 h).
It can be seen from the above table that the equipment cost of the two systems is equivalent, but the vertical mill system is relatively high by 400000 RMB. In structure, the roller press grinding system needs a smaller area, but the mainframe is high, the frame size is large, the support equipment is heavy, and there is a pit with a depth of 6m below. Besides, the secondary powder concentrator is set on the top floor and the cement roller press is set on the ground inside the frame. Therefore, if the natural foundation is adopted, there is a higher requirement for engineering geology. If the pile foundation is adopted, the cost of civil engineering is relatively high. The layout of the vertical mill grinding system requires a slightly larger area, and its civil cost mainly comes from two frames (the belt conveyor and bucket elevator frame and the cyclone separator frame), vertical roller mill and circulating fan. Although it adopts the light load frame and its size is small, the foundation of a vertical mill is larger than that of roller press. So the cost of the two systems in civil engineering is equal. Overall, the investment of the roller press grinding system is slightly lower than that of the vertical mill grinding system, but the difference is less than 5%.
- When grinding raw meal, the unit power consumption of the vertical roller mill and the roller press is about the same, which is 7-8kWh/t. But the vertical mill is usually slightly higher.
- The system of the vertical grinding mill is simple and stable. It has ideal adaptability to material moisture and can achieve the goal of energy saving on the premise of satisfying various operating conditions and balanced operation. However, its output capacity largely depends on the wind system and the power consumption of the circulating fan accounts for a large proportion of the system power consumption, almost half of the unit product power consumption. So when we choose the air fan, it is necessary to ensure the stability of its performance parameters, especially its efficiency so that keeping the high capacity of the system and reducing the unit power consumption. Moreover, we should reduce the ventilation of the grinding mill and increase the material external circulation.
- The actual unit power consumption and the investment of the roller press grinding system are small, the energy-saving effect is significant and the system is simple. But due to the limitation of material dispersion on material drying capacity and material grinding performance, its application range is greatly limited. Therefore, the system can be used for grinding raw materials with medium or lower-hardness whose moisture content is less than 3%, but it is not suitable for use in cold and rainy areas.
AGICO Cement Vertical Mill
AGICO Cement is one of the cement equipment and cement production line manufacturers in China. The LM and HRM vertical mill grinding system we produced merges drying, grinding, and powder classification into a single. It has the advantages of high efficiency, low cost, easy operation and maintenance and stable product quality. If you are interested in our products, please feel free to contact us.