Ring die pellet mills serve as core feed processing machinery for producing pellet feed, with their performance directly determining feed processing output and occupying a crucial position in the entire feed processing workflow. With increasing environmental awareness, pellet-type biofuels have gradually become widely used renewable energy sources, with production showing a year-on-year increasing trend. By 2008, the global biomass pellet fuel production had reached 11.6 million tons. However, China's current ring die pellet mills still face issues such as non-compliance with production quality standards, low production efficiency, and short service life, which largely constrain the further development of China's ring die pellet mill industry.

Technical Development Bottlenecks

• Production quality is difficult to consistently meet standards
• Production efficiency needs improvement
• Equipment service life is relatively short
• Energy consumption control requires optimization

The ring die pellet mill consists of five core components: conditioner, feeder, pellet manufacturing unit, adjustment structure, and lubrication system. The conditioner includes transmission structure, housing, motor, coupling, reducer, spiral housing, spiral shaft, and bearings, with the core component being the screw conveyor. During operation, powder material undergoes circumferential and axial motion under the agitation of paddles, completing the task of conveying powder material to the pelletizing chamber.

Core Component Analysis

The roller and ring die of the ring die pellet mill are important parts determining pelletizing quality and work efficiency. Ring die pellet mills have high requirements for ring dies, and factors such as ring die diameter, shape, opening rate, and manufacturing materials should be carefully considered during production. At the same time, ring die speed must be strictly controlled during operation; the most suitable ring die speed can effectively improve production efficiency and product quality while reducing wear.

During operation, the ring die rotates clockwise, and the already conditioned raw materials enter the pelletizing chamber, entering the working area. The roller rotates clockwise under the influence of friction. As the die and roller rotate, the raw materials in the working area naturally move forward at high speed, increasing in quantity and experiencing increased inter-particle compression force. When the compression force increases to a certain extent, it overcomes friction, and the raw materials enter the ring die holes. As the roller and die continue to rotate, raw materials continuously enter, and the materials in the ring die holes are compressed and extruded out of the holes after forming, then cut to create the required product.

Working Area Division

Since the 1980s, China has focused on researching biomass solid forming fuel technology. In recent years, with the rapid development of China's economic level, domestic mechanical standards have significantly improved compared to before. Additionally, with the world's emphasis on environmental protection, ring die pellet mill development has encountered good opportunities. As the economy develops, people's requirements for pellet product quality are increasingly high, providing ring die pellet mills with a great opportunity for improvement and innovation.

International Technical Advantages

Some countries have relatively complete technical systems in ring die pellet technology. Developed countries have basically formed a complete ring die pellet equipment technology system, capable of providing various high-quality production equipment, practical production solutions, and problem-solving approaches. Leading enterprises in the ring die pellet field mainly come from foreign developed regions, which started their research in this field earlier and have achieved good results, forming a complete system.

Domestic Research Progress

Domestic universities and research institutes are conducting increasingly in-depth research on biomass forming equipment, mainly in three directions: first, finite element analysis of key components of ring die pellet mills to optimize structure and parameters; second, studying the wear or fatigue mechanisms of key components to solve roller and ring die wear problems; third, analyzing the application of biofuels or equipment. These studies provide theoretical basis and data support for the design and optimization of domestic biomass pellet mills.

Straw should be processed into biomass pellets because biomass pellets contain fewer harmful substances, burn more completely, have usage effects no worse than traditional fuels, cause less environmental pollution, and better align with green industrial concepts. Therefore, ring die pellet mill-produced biomass pellets should be comprehensively popularized in various fields. Currently, only a small portion of straw processing is made into pellets, with pellet-making raw materials often being bamboo, wood, and other materials that can cause pollution.

Market Application Fields

• Hot air furnace fuel replacement
• Boiler fuel application
• Biomass gasification furnace fuel
• Industrial heating systems
• Residential heating equipment

Pellet mills play an important role in waste recycling utilization. If pellets can replace fuels such as coal, it would greatly benefit environmental improvement. Pellet mill work efficiency, product quality, and energy consumption are all commendable, and their products are also environmentally friendly. In European and American markets, pellet fuel has almost replaced coal as a cleaner and more efficient fuel. However, in China, pellet fuel is only promoted in a few fields such as hot air furnaces, boilers, and biomass gasification furnaces, and has not yet been popularized for daily household use. With China's further emphasis on environmental protection and further development of ring die pellet mills, pellet fuel replacing traditional fuels is just around the corner.

Modern ring die pellet mills not only use active rollers but also more commonly use active ring dies. The ring die process relies on main shaft transmission for rotation, typically having 2-3 rollers inside. During operation, the rollers press the powder into the ring die holes, which are then extruded into small cylindrical shapes and immediately cut into pellet form. Ring die pellet mills do not generate additional friction during operation, resulting in lower functional consumption, higher production efficiency, and better product quality.

Technical Development Directions

Although domestic development has been very rapid in recent years, there is still a certain gap due to foreign countries mastering large amounts of advanced technology and professional talent. Currently, China not only lacks high-power equipment with larger ring die diameters, but the service life of key components such as ring dies is far behind that of other countries. Additionally, there is also a gap in agricultural machinery talent. Therefore, China can consider introducing advanced foreign technology and equipment, completing ring die pellet mill research and development with an attitude of taking the essence and discarding the dross, striving to catch up and even surpass as soon as possible.

Ring die pellet mills were initially formed in the 1930s, and have been continuously optimized and innovated over decades of development. To this day, both domestic and international research on granular compressed materials has established a certain foundation, with extensive experiments conducted and future development prospects forecasted based on experimental data. However, research experience on ring dies, the key component for particle forming, remains relatively scarce.

Future Research Directions

• In-depth study of ring die wear failure mechanisms
• New ring die structure design and optimization
• Application of materials science in key components
• Development of intelligent control systems
• Energy consumption optimization technology research

Most research only assumes boundary conditions and conducts numerical simulation analysis of ring die stress and strain, with equipment optimization design being merely simple simulation comparisons and analysis. In the future, through ring die pellet failure research, the structural compensation of ring dies during wear failure processes should be explored to provide a basis for attempting new ring die structure designs, promoting overall industry technological advancement.