Although the semi-finish grinding has a better effect on the system output increase,

by cctdale3 on 2010-04-17 18:15:00

Abstract: In recent years, with the process of cement industrialization and continuous upgrading of production technology and process control technology, cement grinding technology and equipment have evolved from mainly ball mills to a variety of new types of grinding equipment such as high-efficiency vertical mills and roller presses. The combination of several devices is developing towards larger-scale grinding equipment and intelligent process control technology to meet the requirements of large-scale and modernized cement production. The roller press material bed grinding technology is an advanced and mature grinding technology. Among various roller press grinding processes, the combined grinding system consisting of V-type static separators and roller presses has particularly comprehensive advantages in terms of quality, high output, and low consumption.

Keywords: roller press, new type grinding, combined grinding, grinding system, cement quality, grinding efficiency, comprehensive advantages

1. Combined grinding production advantages

1.1 Energy-saving, environmental protection, ensuring cement quality

Grinding plays a very important role in the cement manufacturing process. Whether it's raw materials (semi-finished products) or cement (finished products), they need to be ground to obtain the desired properties. To produce one ton of cement, approximately 3.5 tons of various materials need to be ground, consuming about 100-110 kW.h of electricity, with 60%-70% of the energy consumed during the grinding process. Especially in the cement grinding system, more energy is consumed compared to the raw material grinding system. This is because when the quality of cement clinker is poor, and the content of dicalcium silicate in the clinker is high, it becomes harder to grind, significantly reducing grinding efficiency and increasing energy consumption. Considering the hydration and hardening reactions, effective utilization of cementitious properties, strength especially early strength, finer grinding of cement is better. This also improves its bleeding and workability characteristics while considering the particle size distribution of the product to achieve energy savings, environmental protection, and ensure cement quality.

1.2 Achieving grand goals

Energy conservation is one of the keys to promoting sustainable socio-economic development and achieving the grand goal of building a moderately prosperous society in all respects. Industry is a major consumer of energy and raw materials, and the cement industry is an energy-intensive sector. Therefore, energy conservation and emission reduction are long-term and important tasks for China's cement industry. The key to achieving this goal lies in improving grinding efficiency and reducing the power consumption of grinding operations. In practical production, the pre-grinding system represented by roller presses dominates material bed grinding. Pre-grinding is divided into circulating pre-grinding, mixed grinding, combined grinding, and semi-final grinding. Compared to the first-stage closed-circuit grinding process using ball mills, combined grinding and semi-final grinding processes have significant system advantages. Although semi-final grinding has better results in terms of system output increase, its energy-saving effect is slightly lower than that of combined grinding, and there are certain restrictions during equipment selection. Therefore, in practical engineering design, the combined grinding process is more widely used, especially in production renovation projects. Due to the limitation of existing equipment capacity (especially insufficient capacity of existing separators), the application of the semi-final grinding process is limited, while the circulating pre-grinding and combined grinding processes have greater feasibility. Among these, the combined grinding process can achieve better energy-saving and output-increasing effects.

2. Key methods for combined grinding to increase output and reduce energy consumption

2.1 Average particle size of cement

In the cement grinding process, it is not an average single particle but a group of particles containing different particle sizes. Therefore, when discussing cement fineness, if only the sieve residue is used as a simple representation method, more than 90% of the cement particles pass through the sieve holes and become undersize material. However, the particle size of these undersize materials is unclear, so even if the sieve residue is the same, there may be a significant difference in specific surface area. The average particle size of cement particles is an important geometric parameter characterizing the cement particle system, but the amount of particle size characteristic information it provides is very limited. Two groups of particles with the same average particle size may have completely different particle size compositions (particle grading).

2.2 Cement specific surface area

Most foreign cement standards specify the specific surface area index, which is generally measured using a Blaine specific surface area apparatus. China's national standards for Portland cement and clinker are now consistent with foreign standards. There is a good relationship between the specific surface area of cement and its performance. The specific surface area of cement finished products has a good correlation with its physical and mechanical strength. Due to the special nature of the closed-circuit grinding process and factors such as the grading precision of the separator and the grinding media grading, the specific surface area of the finished product is generally not very high, limiting the expression of hydration activity. In actual production, the following technical measures can be adopted to increase the specific surface area of cement to above 350 m²/kg.