Important knowledge of new dry process cement - Two

Principle of Raw Material Homogenization

Answer:

The principle of raw material homogenization mainly relies on air mixing and gravity-induced "funnel effect." As raw meal powder falls, it cuts through multiple layers of material, promoting mixing. At the same time, under the influence of different fluidizing airflows, varying degrees of fluidization and expansion occur along the material surface within the silo. Partial fluidization in certain areas causes the material surface to form a radial tilt, facilitating radial mixing and homogenization.

Selection Principles for Raw Material Homogenization Silos

Answer:

① The design must meet the requirements of the production process.

② The selection of the homogenization silo should be based on raw material fluctuations and the capacity of the pre-homogenization yard.

③ Fluctuations in raw material exiting the mill-both in magnitude and frequency-should be minimized. This can be achieved through effective pre-homogenization, mill feeding control, and scheduling to create favorable conditions for homogenization.

④ The raw material preparation system should be properly integrated to form a well-functioning "homogenization chain."

Common Factors Affecting Homogenization Effectiveness

Answer:

① Issues with the feeding device such as leakage, blockage, or uneven air distribution.

② Inconsistencies between raw material properties and design parameters (e.g., changes in moisture content or particle size).

③ Inadequate compressed air pressure or high water content in the air supply.

④ Electromechanical failures in homogenization equipment.

⑤ Uncontrollable external factors such as storage conditions, flow rate of material entering and exiting the silo, and fluctuating composition of incoming raw materials.

Basic Principle of Grinding

Answer:

Grinding is the process in which materials are broken down into fine powder through the application of external forces such as impact, compression, and abrasion. These forces overcome the internal crystalline structure and cohesion between crystals, reducing large particles into smaller ones and eventually into fine powder.

Part of the grinding energy is used to create new surface areas on the particles, converting into surface free energy. However, the majority of the energy is dissipated as heat into the surrounding environment.

Key Features in the Development of Modern Raw Milling Technology

Answer:

① Drying and grinding operations are integrated. Drying-crushing mill systems are widely used, and with improvements in design and materials, roller mills have undergone significant development.

② Mills are now equipped with high-efficiency classifiers and modern conveying equipment, forming advanced dry closed-circuit grinding systems that enhance grinding efficiency and the effective use of grinding power.

③ Equipment is increasingly large-scale, simplifying the process flow and better matching the requirements of large rotary kilns.

④ Electronic quantitative feeders, X-ray fluorescence analyzers, γ-ray analyzers, and computer-based automatic control systems are used to regulate raw material dosing, ensuring a uniform and stable chemical composition of the materials entering the kiln.

⑤ Automation in mill operation has replaced manual controls, with automatic adjustment circuits and computerized systems being widely adopted to maintain stable and efficient production.

Advantages of the Roller Mill

Answer:

① The roller mill uses a thick-bed grinding method, where materials are subjected to compression, shearing, and impact forces. This method is efficient, and the strong airflow quickly removes fine particles, preventing over-grinding. The material residence time in the mill is typically only 2–4 minutes, resulting in higher grinding efficiency and lower energy consumption.

② Hot air enters through a ring around the mill, providing high wind speed and a large ventilation cross-section. This reduces internal resistance, enhances airflow, and improves drying efficiency.

③ The roller mill allows larger input particle sizes, which can eliminate the need for secondary crushing and reduce capital investment.

④ It is equipped with an integrated classifier, eliminating the need for external circulating devices and reducing maintenance costs.

⑤ The short residence time enables fast response to production changes, making it easy to adjust and control material composition and fineness-facilitating automation.

⑥ It has strong adaptability, capable of handling coarse-fine mixed materials and those containing metal impurities.

⑦ Its compact layout requires less building space and can be installed outdoors or in simple sheds, reducing both equipment and civil construction costs.

⑧ The mill features a well-designed structure and grinding mechanism with good overall sealing, low noise, and reduced dust emissions-supporting environmental protection efforts.

Regulation and Control of the Raw Milling System

Answer:

Automatic control of the raw milling system mainly includes five aspects:

① Adjustment of raw material ratios: Ensures that the chemical composition of the milled product meets specified requirements.

② Control of total feed rate: Regulates the total amount of materials fed into the mill to maintain optimal and stable grinding conditions, thereby improving grinding efficiency.

③ Temperature control: Adjusts the temperature of the milling system to ensure proper drying and grinding conditions, and to meet the required product moisture content.

④ Pressure regulation: Maintains proper pressure and ventilation within the mill system to support efficient drying and grinding operations.

⑤ Automated startup and feeding program: Controls the start-up sequence and feeding procedures of the mill system to implement full-process automatic control of raw milling operations.

Function and Significance of Cement Grinding

Function: The main function is to grind cement clinker (along with retarders, performance-adjusting materials, etc.) to the appropriate particle size and form a certain particle gradation. This increases the hydration area and accelerates the hydration rate to meet the cement slurry's setting and hardening requirements.

Significance: Although the heat consumption of cement clinker production has been greatly reduced, the comprehensive power consumption of cement production has remained high for a long time. Through improvements and breakthroughs in grinding technology-such as replacing impact grinding technology with extrusion grinding technology-the utilization rate of grinding power can be improved, reducing the comprehensive power consumption of cement production. Therefore, innovation in cement grinding technology is of great significance for improving cement product quality, saving energy, reducing costs, and making new dry-process cement production more economically competitive.

The characteristics of the development of modern cement grinding technology:

① Achieving large-scale operation in ball mill systems, while innovatively researching and developing extrusion grinding technology and equipment.
② Using high-efficiency powder processing equipment.
③ Employing new high-performance wear-resistant materials to improve the durability of mill components.
④ Adding grinding aids to enhance grinding efficiency.
⑤ Reducing the temperature of the cement to improve grinding efficiency and enhance cement quality.
⑥ Realizing automated operation.
⑦ Taking other technical measures such as reducing the particle size of the material to be ground, ensuring reasonable particle grading of the finished cement product, selecting the appropriate specific surface area according to product standards, improving batching processes, choosing reasonable mineral compositions of clinker, and reducing the moisture content of the material to be ground.
⑧ Developing new equipment for powder conveying.

Several Roller Press Cement Grinding Process Solutions

Answer: Its application generally adopts five process flows: roller press pre-grinding, mixed grinding, combined grinding, semi-final grinding, and final grinding.

When using a roller press for final cement grinding compared to using a ball mill, three major problems may arise:

Higher water demand

Shorter setting time

Lower early strength

Reasons:

Narrow particle size distribution of the cement

Irregular particle morphology

Incomplete dispersion of the compressed cake

Presence of cracks in the particles

Influence of C₃A content and activity

Incomplete dehydration of the sulfate carrier

Insufficient fineness and dispersion of the sulfate carrier

O-SEPA Type High-Efficiency Powder Separator Features

Answer:

① Accurate separation of material particle sizes with high powder selection efficiency.

② Capable of controlling product fineness over a wide range and improving particle size distribution, which helps enhance cement quality.

③ Able to handle high concentrations of dusty gases; uses separation airflow for dust-laden gases without affecting powder separation performance.

④ Allows strong ventilation in the mill, and a large amount of cold air can be introduced into the separator, which helps reduce system temperature and improve efficiency.

⑤ Produces low product temperatures, eliminating the need for a cement cooler and simplifying the process.

⑥ Compact structure, low wear rate of blades and rotor, space-saving layout, and easy maintenance.

⑦ Can increase mill output by 22%–24% and save energy by 8%–20%.

Closed-Circuit Steel Ball Mill System:

Consists of a tube mill, elevator, powder separator, fan, and other major equipment. During the grinding process, coarse-grained materials pass through the mill multiple times. This setup helps reduce over-grinding, prevents particle agglomeration, silo clogging, and mill sticking. It is conducive to producing high-fineness cement, allows flexibility in producing different types of cement, and improves the efficiency of the powder separator.