In the cement production process, a large amount of energy is consumed. According to statistics, there are about 3-4 tons of materials needed to grind for every one-ton cement production. The power consumption of grinding raw materials, coal and cement accounted for 60%-70% of the total power consumption of the cement plant, and the cost of grinding accounted for about 35% of the total cost. Therefore, the pursuit of technological progress in grinding process has always been one of the key contents of technological innovation in cement industry.
In recent years, the tube mill has gradually been replaced by roller mill and other equipment, became the main equipment of cement grinding in cement production line. While in raw meal grinding, with the mature use of vertical mill and roller mill, the power consumption of grinding one ton raw meal has been reduced from 20 to 10 kWh, and even some people claim to be below 10 kWh. In this article, we will briefly introduce and compare the vertical grinding system, tube mill grinding system and the roller mill grinding system.
Common Raw Material Preparation Technology
At present, the most commonly used raw material preparation technologies are tube mill grinding system, vertical mill grinding system and roller mill grinding system. The energy consumption of tube mill system is relatively high, which is about 21.50 kWh/t, while the dry process cement production line usually uses vertical mill to prepare raw material, because its power consumption is l6.50 kWh/t, which is much lower than that of tube mill. As to the roller mill grinding system, it has the characteristic of high grinding efficiency, simple system, and low power consumption. In addition, its energy-saving effect is better than the vertical mill system. The power consumption is about 13.50 kWh/t. In the areas with small annual rainfall and low water content materials, the roller mill grinding system is gradually popularized and applied.
Comparison of Raw Material Preparation Technology
Vertical Raw Material Grinding System
Vertical mill is a kind of air swept mill, which integrates drying, grinding and product classification. It has the characteristics of less system equipment, simple process, low cost, low power consumption and low noise. Beyond that, its particle feeding size is large and the drying capacity is stronger than the tube mill. With the progress of science and technology, breakthroughs have been made in the wear, vibration and structure problems which puzzled the popularization and application. Vertical raw material grinding has been widely used in dry process cement plants.
The raw material preparation system of the 2 500 t/d cement production line can adopt the vertical mill with the disc diameter of 3 400 mm as the main grinding machine. When the grinding particle size is less than 60 mm, the fineness of the finished product is 16%, and the moisture content of the finished product is 0.5%. The grinding capacity of the mill will be 200 t/h, and the annual utilization rate will be 71.90%.
Roller Mill Raw Material Grinding System
The advantages of using the roller mill for raw material grinding have been realized and widely accepted in recent years. The high-pressure extrusion between rollers makes grinding occur in advance among internal particles, thus improving the production efficiency and reducing the energy consumption for grinding particles. Owing to the restriction of drying capacity of the system (the moisture content of materials is less than 3%), in areas with dry climate, small annual rainfall and low moisture content of materials, the roller mill raw material grinding system has been gradually applied and promoted, which belongs to one of the high-efficiency grinding technologies.
A 2 500 t/d cement production line can adopt roller mill as the main raw material grinding machine. Under normal conditions, it will be equipped with the static powder separator (air volume 350 000-450 000 m/h) and dynamic flour separator (air volume 380 000 450 000 m/h) as the auxiliary equipment. When the feed size is less than 55 mm, material moisture will less than 3% and the finished product moisture will less than 0.5%. The weight of screen residue will be 10%, the production capacity will be 210 t/h and the annual utilization rate will be 68.50%.
Tube Mill Raw Material Grinding System
The tube mill and the powder separator together form a circulating grinding system，wherein, the tube mill mainly consists of drying chamber, coarse grinding chamber and fine grinding chamber. The coarse grinding chamber is equipped with some large diameter steel balls. Under the action of lining plate, the material is broken and ground by them. The fine grinding chamber is equipped with steel balls of smaller diameter, which mainly plays the role of further grinding. This grinding system has reasonable technology and strong grinding ability, so it can be well adapted to all kinds of granularity and hardness materials. However, due to the system is complex and difficult to seal, the air leakage will be large and the drying and grinding capacity will also be affected, resulting in high grinding energy consumption. When the grinding particle size is less than 25 mm, the fineness of the finished product is 12%, and the moisture content of the finished product is 0.50%. The grinding capacity of the mill will be 190 t/h and the annual utilization rate will be 75.70%.
Through comprehensive comparison, it can be seen that the energy consumption of the roller mill raw material grinding system is the lowest, the tube mill grinding system is the highest, and the vertical grinding system is in the middle. What‘s more. The vertical mill and roller mill grinding system are both characterized by the simple system, easy operation, simple maintenance and easy management, but the drying capacity of roller mill grinding system is weaker than that of vertical mill grinding system. However, from the perspective of rational use of energy, in the dry climate area with low moisture raw materials, we should give priority to the roller mill. In other areas, the vertical grinding system will be a good choice.