1. Combined grinding system of roller press + ball mill
The power consumption of ball mill grinding is relatively high, and scholars in the industry have long put forward the theoretical guiding ideology of “more breaking and less grinding”. Now the mature roller press technology is matched with the ball mill to form a combined grinding system. When producing P·O42.5 grade cement, the power consumption of the grinding system can reach below 25 kWh/t, and when producing slag fine powder with a specific surface area of about 420 m2/kg, The power consumption of the grinding system can reach below 50 kWh/t. When using this system for slag powder production, the system has the following characteristics:
(1) The roller press gives full play to the high efficiency of the crushing and coarse grinding stages, combined with the excellent grinding performance of the ball mill, to achieve system stability and product stability on the basis of ensuring system energy consumption. At the same time, due to the strong adaptability of the ball mill, the internal structure of the mill is relatively complex, but the optimization and adjustment are convenient and flexible. It can be adapted to the production of a variety of raw materials and high specific surface area (such as 700 m2/kg) micropowder, and the material from the ball mill has good particle morphology, reasonable particle size distribution, good mineral powder quality, easy hydration, and high activity. It is used in cement Or in concrete, more equal amounts of clinker or cement can be replaced.
(2) Slag and other industrial waste residues are usually abrasive, especially steel slag. The current roller surface wear-resistant treatment technology of the roller press can increase the maintenance-free service life of the roller surface to more than 20,000 hours, which greatly reduces the equipment maintenance cycle and cost. At the same time, since the material processed by the roller press is through-type, it is beneficial to set up an efficient iron remover outside to remove the metal in the crushed material in time, and effectively protect the roller surface and the system for long-term continuous operation.
(3) The blast furnace slag with high activity is quenched by water, and the raw material contains a large amount of water, which requires the pre-grinding system of the roller press to be processed and dried. Since the materials in the roller press system are externally circulated, drying, powder selection, iron removal, etc. are all completed on other independent equipment in the system, so the air volume used for drying and powder selection is small, and the corresponding heat There are also fewer losses, so roller press systems generally have much lower drying heat consumption than vertical mill systems.
(4) The roller press is just a crushing equipment, drying and powder selection are all external, requiring many transportation links and a large building, so the process system is more complicated, and the civil construction investment is relatively high.
(5) The combined grinding system of roller press + ball mill has higher power consumption per ton of product than the vertical grinding system, but the difference in comprehensive drying heat consumption is converted into the actual energy consumption per ton of standard coal consumption (including power consumption and coal consumption) is basically the same. However, due to the different drying methods, the drying heat consumption of the vertical mill system is usually about 20% higher than that of the roller press system. Combining these two factors, the difference in energy consumption between the two systems is very small. The resulting quality advantage of the final product is very obvious. Therefore, when choosing a solution, it is recommended to consider the requirements of the product use, rather than simply the difference in power consumption.
2. Final grinding system of vertical mill
The final grinding of the vertical mill is also a relatively efficient system. Because of its low power consumption, and the integration of drying, grinding and powder selection, the process flow is simple, and it is widely used in the preparation of cement raw meal and pulverized coal ( In recent years, due to the pursuit of lower power consumption, the preparation of cement raw meal has been changed to roller press final grinding), and it has been widely promoted in the field of slag grinding. When the vertical mill is used for the production of ultra-fine ore powder, when the specific surface area of the finished product reaches more than 420 m2/kg, the power consumption of the grinding system can be less than 45 kWh/t. Compared with the roller press + ball mill system, the vertical grinding final grinding system has the following characteristics:
(1) The final grinding system of the vertical mill has relatively few equipments, and the technological process is relatively simple. The core equipment, namely the vertical mill itself, integrates drying, grinding and powder selection. The external circulation of materials is less, and the power consumption used for material transportation is small. less, the system uses a large amount of air, which is very suitable for the grinding of high-humidity and viscous materials. Such as wet discharge of fly ash, clay, etc.
(2) Due to the ventilation mode of the vertical mill, it uses a large amount of air, so it has a strong adaptability to the moisture of the raw material, but the system dust collector it is equipped with is also relatively large, which is also the main reason for its high drying heat consumption.
(3) The amount of external circulation of materials in the vertical mill system is very small, which also makes it difficult to discharge the metal separated during the grinding process in time, resulting in increased roller surface wear. Due to the less metal content in ordinary slag, the wear gap is not obvious. However, when grinding materials with high metal content or very hard materials such as steel slag, nickel iron slag, etc., the wear of the roller surface and the grinding disc is very large, which will bring high maintenance costs.
(4) The pressure on the roller surface of the vertical mill is lower than that of the roller press, and the crushing efficiency is also relatively low. However, due to the grinding characteristics of the vertical mill, it can independently complete the preparation of fine powder below 450 m2/kg under the premise of sufficient moisture. When the particle size of the milled material is very uneven or the specific surface area of the finished product needs to be 500 m2/kg or even higher, it is difficult to stabilize the material bed, resulting in large vibration of the vertical mill and it is difficult to run stably.
(5) The vertical grinding mill also uses material bed grinding, and the morphology of the fine powder particles produced by it is also irregular, and due to the characteristics of powder selection while grinding, the particle gradation distribution of the product is relatively narrow, which affects the slag powder. Increased activity and its admixture ratio in cement or concrete.