The slag grinding plant, also known as the ggbs production line, is specially designed to further process granulated blast furnace slag into slag powder. It is the most crucial step in transforming granulated blast furnace slag from waste into a valuable resource. After processing, the slag powder can be sold as a product and applied in various industries.
Grinding machine is the core equipment of a slag grinding plant. It determines the fineness, activity, and output of the slag powder, directly affecting product application performance. In addition, the grinding process has high energy consumption, and the efficiency of the equipment directly impacts production costs. Currently, the grinding machines used in slag grinding plants mainly include ball mill grinding systems, vertical roller mill systems, and roller press grinding systems. What are the advantages and disadvantages of these grinding machines? How can we choose the right grinding machine? Next, we will provide a detailed explanation.
Ball Mill Grinding Systems
Slag ball mill grinding systems can be divided into open-circuit grinding systems and closed-circuit grinding systems.
Open-circuit Ball Mill Grinding System
The open-circuit grinding system generally uses a high-fineness ball mill. Before entering the ball mill, the slag must first be dried, ensuring the moisture content is ≤2%. It is then fed into the ball mill through a feeder for grinding. After being discharged, the ground slag powder is the final product.
Advantages: Low investment, stable running, simple operation, and high equipment utilization rate.
Disadvantages: High power consumption, low efficiency, difficulty in adjusting powder fineness, tendency for over-grinding, and high wear of grinding media.
In addition, as slag powder fineness requirements increase, the grinding time becomes longer, and the specific surface area of the material increases. Consequently, the tendency for fine particles to agglomerate rises, which affects grinding efficiency and further increases power consumption. To prevent slag powder from adhering to the grinding media and liner surfaces, which reduces grinding efficiency, we can add grinding aids to disperse the powder and eliminate electrostatic adsorption. The finer the grinding fineness, the more significant the effect of grinding aids.
Closed-circuit Ball Mill Grinding System
The closed-circuit grinding system typically uses a combination of a regular ball mill and a high-efficiency powder separator. After the slag is ground into powder in the ball mill, it directly enters the separator. The slag powder that meets the fineness requirements is sent by the separator to the storage silo, while the slag powder that does not meet the fineness requirements is sent back to the ball mill for secondary grinding.
Advantages: The fineness of the slag powder is easy to adjust, which helps reduce over-grinding. The grinding efficiency is relatively higher, and the single-machine capacity is increased.
Disadvantages: The system is complex and requires more equipment.
When grinding slag with a ball mill, the grading of the grinding media inside the mill needs to be adjusted. This involves replacing larger balls with smaller ones. The maximum ball size is typically ≤60mm. Besides, it is necessary to appropriately increase the grinding media loading, and move the partition plate forward to lengthen the fine grinding chamber. The power consumption for grinding slag with steel balls is generally ≥70 kWh/t.
Vertical Roller Mill Systems
The vertical roller mill grinding system has been widely praised by customers in recent years for its high efficiency and energy savings. It adopts the material bed grinding principle. In the grinding chamber of the vertical mill, the grinding rollers continuously press the slag on the grinding table to achieve the grinding effect. The movement speed of the grinding rollers is generally around 6 m/s, and the compression angle is approximately 12 degrees, both of which are superior to those of a roller press. During the grinding process, the amount of water sprayed inside the mill can be adjusted to form a stable material bed, keeping mill vibration within the permissible range.
The vertical mill integrates material drying, grinding, classification, and collection into a single system, eliminating the need for separate drying equipment. Even when the moisture content of the slag reaches 13%–15%, the specific surface area of the ground slag powder can still reach over 450 m²/kg, and the powder fineness is adjustable.
The vertical mill has a small footprint and a simple production process. When producing slag powder with the same specific surface area (≥430 m²/kg), the unit grinding power consumption of a vertical mill is similar to that of a roller press but saves more than 40% of electricity compared to a ball mill.
Roller Press Grinding Systems
The roller press grinding systems can be divided into roller press final grinding system and roller press+ball mill combined grinding system.
Roller Press Final Grinding System
After the slag is ground into powder in the roller press, it enters the separator for grading. The slag powder that meets the required particle size is sent to the silo for storage, while the coarse powder is returned to the roller press for regrinding.
Advantages: The grinding efficiency is relatively high, and energy consumption is lower than that of the ball mill grinding system. For slag powder with a specific surface area of 420 m²/kg, the unit power consumption is approximately 50 kWh/t.
Disadvantages: The circulating load is high. The product quality at the same specific surface area is inferior to that of products ground by ball mills and vertical mills.
Roller Press & Ball Mill Combined Grinding System
The slag is fed into the roller press through the feeder, where it is ground into powder. It then enters the powder separator for grading. Coarse particles are returned to the roller press for secondary grinding, while fine powder is sent to the ball mill for further grinding until the product meets the required particle size.
Advantages: The grinding efficiency is high, and energy consumption is lower than that of the ball mill grinding system. For slag powder with a specific surface area of 420 m²/kg, the unit power consumption is approximately 60 kWh/t.
Disadvantages: The process flow is complex, requiring higher skill levels from operators. It also occupies a larger area and involves higher investment compared to the ball mill grinding system and roller press final grinding system.
Comparison
The ball mill grinding system is technically mature, with reliable performance and stable operation. However, it has low energy efficiency and grinding efficiency. Although the investment is relatively lower, it requires a separate purchase of drying equipment. Besides, the entire grinding process is relatively complex and requires a large footprint. When producing slag powder with the same specific surface area, the unit grinding power consumption is higher than that of the vertical mill grinding system and roller press grinding system. With an average power consumption higher by 30 kWh/t, a ball mill grinding system with an annual production capacity of 1 million tons will consume 30 million kWh more electricity than the vertical mill grinding system and roller press grinding system.
Using a vertical mill grinding system or roller press grinding system to produce high-activity slag powder requires a higher initial investment and a longer payback period. However, the long-term benefits are good, with stable product quality, low unit grinding power consumption, and up to 40% electricity savings compared to the ball mill grinding system. The roller press grinding process is slightly more complex than the vertical mill process.
