S Cement Plant is a modern dry-process cement plant. It uses advanced grinding equipment and technology. The plant employs a CKP vertical mill and a ball mill in a closed circuit system. The CKP mill is CKP-170, and the ball mill has dual chambers with specifications of φ3.9m×12m. It features a cyclone separator. The system's capacity is 115t/h×2.
Clinker and gypsum go through a crusher and break down to particles of ≤40mm, which make up over 95%. They are fed into the CKP mill. The material from the CKP mill contains over 95% of particles ≤10mm. About 10% of this material returns to the CKP mill, while roughly 90% moves to the ball mill along with the separator's return. The ball mill's output combines with fly ash and enters the separator. The separator achieves an efficiency of about 60%, with a circulation load rate of approximately 260%. Most of the cement produced is P.O 42.5R, with a small amount of P.II 42.5R. The average power consumption for both types is 39 kWh/t, using a grinding aid that accounts for 0.02% to 0.03% of the cement weight.
Quality Control Methods and Experience in the Cement Grinding Process
1. Quality Control Methods
The plant uses imported German negative pressure sieves to measure the residue at 15μm, 20μm, 32μm, 45μm, and 63μm based on Japanese methods. The German sieves have a sieve size with an inner diameter of 70mm and a sample weight of 1g. This design allows for a larger airflow during operation, preventing clogging of the sieve holes. The device can complete the measurement of 32μm residue in 8-10 minutes and 45μm residue in 4-6 minutes. It has high machining precision, low failure rates, easy operation, short measurement time, and stable, accurate results, making it suitable for routine production control.
Many domestic cement companies use laser particle size analyzers to measure the particle size distribution of cement. This plant conducted parallel tests using both the negative pressure sieve and the laser analyzer on the same sample. The results showed that the laser analyzer yielded consistent results with the negative pressure sieve for particles over 10μm. However, for particles under 10μm, the laser analyzer's results were slightly higher. This difference occurs because very fine particles tend to agglomerate due to van der Waals forces, making them difficult to disperse in negative pressure sieving. While the laser analyzer is suitable for periodic checks, its complexity, longer operation time, and higher failure rates make it unsuitable for routine quality control.
2. Quality Control Experience
2.1 Fineness
The plant uses the 32μm residue as a routine control basis for the grinding process. When the 32μm residue is within the target control range, the 80μm residue is stable at 0.2% to 0.4%. However, due to equipment failure, the 32μm residue occasionally fluctuated from the target of 16% to 20%. Testing this batch of cement showed a 28-day compressive strength drop of about 4MPa, indicating that the 80μm residue does not effectively reflect the grinding condition. Therefore, using 32μm or 45μm residue as quality control indicators is appropriate.
2.2 Specific Surface Area
Although the plant measures the specific surface area every 4 hours, these measurements serve only as reference points and do not guide routine control. Statistical analysis reveals no strong correlation between strength and specific surface area. Thus, using specific surface area as a control basis is too rough.
2.3 Particle Distribution
The particle size distribution of cement is closely related to its physical properties, especially strength. Experience shows that using 32μm or 45μm residue effectively reflects particle distribution and should be included in routine control.
2.4 Grinding Aids
The plant adds a grinding aid that accounts for 0.02% to 0.03% of the cement weight during grinding. This addition proves effective. There was a brief interruption of the grinding aid, and although the 32μm residue remained within control limits, the particle distribution changed significantly, leading to a noticeable drop in strength.
Conclusion
1.The cement grinding equipment and technology are suitable. The cement's particle distribution is close to the ideal, resulting in improved strength.
2.Particle distribution significantly affects cement's physical properties, particularly strength. Using 32μm or 45μm residue as quality control indicators is appropriate.
3.The combination of vertical and ball mills is an effective cement grinding solution, producing high-quality products with reasonable power consumption.
4.Proper use of grinding aids improves the cement's particle distribution and reduces the quantity of particles smaller than 3μm.
5.Compared to laser particle size analyzers, negative pressure sieves are more suitable for routine quality control.
If you have any questions or needs regarding cement grinding, please feel free to contact us. We look forward to collaborating with you to advance the development and progress of the cement industry!
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