Cement production is a typical high-energy-consuming industry, accounting for about 7% of the world’s total industrial energy consumption. Energy conservation and emission reduction are eternal topics in this industry. In the process of cement production, the grinding unit accounts for over 60% power consumption, which is a pain point for energy saving and consumption reduction. How to save energy and reduce consumption in the grinding unit is key to increasing profit. We have summarized several tips for real practice.
Choose a reasonably designed cement grinding mill
Replace cement ball mills with vertical roller mills, roller press, ultra fine grinding mill, etc, to get higher efficiency and save power consumption at the same time.
Reduce the particle size of the clinker entering the mill
Reduce the particle size of the clinker entering the mill and adopt the “more crushing and less grinding” process. The particle size is not the smaller the better, because power consumption rises as the particle size increases. Based on experience, the optimal grinding size is about 0.005D.
Strictly control the moisture content of materials
The average moisture of grinding material should be 0.5%-1.5%. It is ideal to keep the average number at 1%. When the moisture content is too high, the fine powder is prone to sticking to the grinding media, etc., which reduces efficiency and output. The mill even stops working when the moisture approximates 5%. However, if the moisture content is low, electrostatic effects may appear, which affect the output.
Control the temperature of materials
High-temperature materials greatly affect the outputs, quality, and consumption of the cement mill. The grindability of materials decreases as the temperature increases. Cement will agglomerate due to electrostatic attraction resulting from high temperatures. Cement false setting resulting from gypsum dehydration when the temperature is too high.
If the material is over 50℃， the cement mill will be affected. If it exceeds 80℃， the output will drop 8%-10%. The cement mill bearing lubrication effect reduces as the temperature rises, causing certain thermal stress that may lead to liner bolt cracks, etc.
The high temperature of the cement mill affects the long-term safe operation of the equipment. Some enterprises even experience a grinding mill shutdown and cooling. This not only affects the output but also leads to a decrease in hourly production and an increase in power consumption due to frequent shutdowns.
Material grindability
Clinker’s grindability is influenced by its cooling rate as well as the amount of different mineral components it contains. The clinker cools rapidly, the minerals form fine glassy crystals, the texture is brittle, and the grindability is good when the mineral composition of the clinker is rich in C3S and low in C4AF. However, a high concentration of C2S and C4AF in the clinker mineral composition results in an extremely tough clinker with a low grindability coefficient, making it challenging to grind and requiring a comparatively large amount of electricity. Additionally, the calcination temperature, calcination environment, and heating rate all affect how grindable the clinker is. For instance, the grindability of yellow-core or overburned clinker is comparatively low.
Enhance mill ventilation
Enhancing cement mill ventilation can increase output and reduce electricity consumption, since the fine powder airflow is carried away, over-grinding is reduced, and grinding efficiency is improved.
Enhancing cement mill ventilation can also reduce temperature in the mill, avoiding gypsum dehydration, cement false setting, and reducing equipment wear.
Reasonably determine the specific surface area of the finished product
Finished product residue control or the specific surface area directly decides the quality, output, and costs. A range of specific surface areas should be determined based on the real situation.
Optimize the internal structure of the mill
Set up an efficient forced screening system with a powder selection function in the traditional tube mill to replace the partition device. Large particles will be intercepted and sent back to be crushed by large grinding balls. Qualified materials enter the rear bin. The separation of large and small particles improves the grinding efficiency.
Small-sized grinding balls of large specific surface area are used in the rear bin of the grinding mill to intensify the grinding effect, which greatly improves the productivity, cement strength, and reduces the power consumption.
Maintain proper grinding ball loading
After production starts, check if the grading and loading of grinding media are suitable. Find out if the fineness meets requirements. If not, improvements are needed, and adding grinding media and clearance after a while. The aim is to keep the grinding mill in good operation to realize high and stable output.
Use grinding aids
To achieve high-quality ball milling, energy conservation, and high production, a small amount of additives can be added during the grinding process to eliminate fine powder adhesion and aggregation, speed up the process, improve grinding efficiency, and increase the 3-30μm content by 10-20%. Together, these chemicals are known as “grinding aids.” By increasing ball mill output without altering the manufacturing process, grinding aids can typically improve cement quality, save costs, and produce high-performance, environmentally friendly cement.
Use frequency conversion technology
One of the most important energy-saving technologies is frequency conversion, which can assist in reducing the energy consumption of auxiliary cement manufacturing equipment, such as fans, batching meters, and variable-speed machinery. It also allows for constant speed control by addressing the ball mills’ high starting torque needs and low operating speeds. The motor ensures process control quality and lowers maintenance costs by starting without inrush current, providing adequate starting torque, and having extensive protection features.
Improve the power factor and efficiency of electrical equipment and reduce power consumption
One benefit of using a low-voltage motor with full phase control technology is that it can automatically alter the motor output power when driving heavy and light loads. This allows the motor to operate at its best moments and saves about 15% on energy. The cement company’s power factor has significantly increased, reactive power demand has decreased, and active power losses have been eliminated through the adoption of green lighting systems and other technical measures.
