Publish Time:December 17, 2019
The direct costs of cement production mainly include raw material procurement and transportation costs，fuel procurement and transportation costs, electricity costs, etc. In the current environment of insufficient demand in the cement market, in order to ensure that cement factories have a certain profit, it is necessary to find ways to reduce costs. Therefore, reducing production costs has become a necessity for the daily operation of cement factories.
The current popular direction for cost reduction in sintering systems is to mainly reduce coal consumption by lowering the heat consumption of the sintering system; On the other hand, it is energy-saving by reducing the power consumption of grinding. Coal and electricity costs account for over 70% of cement production costs. In the case of the same installed capacity, most factories usually replace the raw material vertical mill with a roller press. Of course, this requires comprehensive consideration of multiple factors, but the vast majority of the transformation is successful. The vertical mill system is transformed into a roller press grinding system, effectively reducing the power consumption of grinding. The following are the key analysis points for the feasibility of the renovation:
1. Energy consumption and efficiency
Advantages of roller press: Roller press adopts the principle of high-pressure material bed crushing. Compared with the grinding method of vertical mill, the unit power consumption is usually lower (can be reduced by 20% -30%), especially in the treatment of hard materials, the energy-saving effect is significant. Even if the installed capacity is the same, the actual operating energy consumption of the roller press may be lower. This is why some people believe that there is still a need for the same installed capacity.
Characteristics of vertical mill: The vertical mill has the functions of grinding, drying, and powder selection, suitable for materials with high moisture content. If the raw material humidity is high, the vertical mill may be more efficient. The only advantage of a vertical mill over a roller press is that it can dry composite materials with a moisture content of 5%. Generally, a roller press can dry composite materials with a moisture content of no more than 4%, otherwise it will be difficult to form and disperse the material cake, resulting in a decrease in the output of the roller press system.
2. Production volume and product quality
Production increase: Roller press+V-selection+high-efficiency powder selection machine, with higher production capacity than a single independent grinding system, but different from the built-in powder selection machine of the vertical mill, it requires additional equipment (such as dynamic powder selection machine).
Particle size distribution: The finished product of the vertical mill has a relatively uniform particle size and is suitable for direct use in raw material preparation; The discharge of the roller press requires the use of subsequent grading equipment, which slightly increases the complexity of the process.
3. Maintenance and operation costs
Wear and tear parts cost: The grinding rollers and discs of the vertical mill are severely worn, with short replacement cycles and high maintenance costs; The wear of the roller surface of the roller press machine is relatively controllable (the repair cycle of hard alloy welding is long).
Shutdown time: The maintenance frequency of the roller press may be lower than that of the vertical mill, but if the system needs to be retrofitted (such as adding a new powder selection machine), the initial shutdown time will be longer.
4. Investment cost
Renovation cost: If the original mechanical and electrical capacity is retained, the cost of mechanical structure renovation (foundation, conveying equipment, powder selection system, etc.) still needs to be evaluated, which may account for 30% -50% of the total investment.
Return period: The ratio of energy-saving benefits (annual electricity cost savings) to renovation costs needs to be calculated, and a return period of 2-5 years is usually considered reasonable.
5. Applicable scenarios
Suitable for renovation situations: high hardness of raw materials (such as slag, limestone) or high electricity costs;
The existing vertical mill is severely worn and requires frequent maintenance; Capacity needs to be increased and the site allows for the addition of new equipment.
Not recommended for modification: The raw material has high humidity and relies on the vertical mill drying function;
The existing system has poor compatibility and is difficult to transform; Short term financial pressure makes it difficult to bear the initial investment.
6. Case analysis
Actual data reference: After a cement plant converted its vertical mill to a roller press combined grinding system, the power consumption of raw materials decreased from 22 kWh/t to 14 kWh/t, increasing production capacity by 15%. However, the investment payback period is about 3 years.
Therefore, if the following conditions are met, the renovation is necessary:
1. The raw material characteristics are suitable for roller presses (high hardness, low humidity);
2. The energy-saving benefits can cover the renovation costs (with better long-term economic efficiency);
3. The production line has renovation space and supporting conditions.
Otherwise, retaining the vertical mill and optimizing the existing system may be a more secure choice.
Suggest conducting a detailed technical and economic evaluation (including material testing, energy consumption calculation, and investment return analysis), and collaborating with equipment suppliers to develop targeted solutions.