Powder is a general term for powder solid bulk materials, which is an aggregate of particles. Pneumatic conveying of powder and granule generally refers to the method of using air flow to transport the powder and granule in the pipeline, and also includes the method of using compressed air to transport the powder and granule in the air conveying chute.
The pneumatic conveying technology of powder and granule began in the late 19th century. After more than 100 years of development and practice, great progress has been made in technology and equipment. Compared with the powder and granule conveying methods of conveyors and transport vehicles, it has the advantages of system sealing, dustproof and environmental protection, so it is widely used in various industries of national economic construction, including chemical industry, petrochemical industry, light industry, Grain, food, medicine, electricity, building materials, transportation, metallurgy, mining and environmental engineering, etc.

Due to the wide range of industries involved in the treatment of powder and granular materials, the material properties are quite different, and the technological processes are various, so there may be ill-considered phenomena in the industrial production process.

Because the pneumatic conveying of powder and granules not only involves powder technology, but also involves fluid mechanics. The actual conveying process is a very complex and changeable process. Although the pneumatic conveying technology is becoming more and more popular, in-depth basic theoretical research is still needed to make the pneumatic conveying device or system technologically advanced, economical and reasonable, and meet the requirements of environmental impact. and guidance from practical experience.
The properties of the material are closely related to pneumatic conveying. Even for the same material, the conveying performance will be far different due to different particle sizes or different moisture contents, such as phosphate rock powder, calcium carbonate precipitates, etc. Due to the increase of the rate, the pneumatic conveying cannot be carried out. When conveying materials with strong abrasiveness, the equipment requires wear-resistant materials and suitable structural types. For brittle and fragile materials and materials whose quality is degraded due to breaking, special consideration must be given to the selection of wind speed; At a certain concentration and temperature, flammable and explosive materials should be considered when pneumatic conveying, the temperature of the material should not exceed the ignition point, otherwise the use of inert gas should be considered.

In short, the characteristics of pneumatic conveying and conveying materials are closely related.

At present, pneumatic conveying has been used more and more widely as a relatively advanced conveying technology, and its research and experiments have become more and more in-depth. I believe that with the continuous deepening of scientific experiments and related engineering practices, pneumatic conveying technology will definitely further development and improvement.

The basic theory of pneumatic conveying
Pneumatic conveying is a technology that uses air flow as a carrier medium to convey granular and powdery materials under certain conditions. At present, the most popular pneumatic conveying methods are suction type and pressure type. Their main mechanism is based on the action of the air flow with a certain speed on the material particles. According to many experimental analyses, the pro-flow motion is the main movement mode of the air and material mixture, that is, the tie flow determines the entire interaction between the air flow and the material particles, or the air flow is in a laminar flow state, and it is impossible to transport the material. . At present, the mainstream conveying methods are positive pressure conveying and negative pressure conveying, also called pressure conveying and suction conveying.
The material particles in the airflow are transported by the total force of the air, and the total force must reach a certain amount. For example, the resultant force and the combined moment acting on the particles in the vertical pipe must make the particles in a suspended state, and the material can be made in the horizontal pipe. The particles move along the bottom of the tube.

According to production practice, the selected airflow velocity can make the material particles in a suspended state in the vertical pipe, and the condition of the material moving along the bottom of the pipe can also be satisfied in the horizontal pipe. Due to the complex motion state of the two-phase flow in the horizontal tube, there is still a lack of sufficient calculation data. At present, the air velocity is selected based on the suspension velocity in the vertical tube.

Features of pneumatic conveying
Pneumatic conveying can not only convey powdery, granular and fibrous materials, such as phosphate rock, coal powder, cement, carbon black, polyethylene, polypropylene, grain, cotton, etc., but also small-sized materials such as coal, rocks, etc. . Pneumatic conveying can be so widely used, mainly because it has the following advantages:
1. The material is transported in a closed pipeline, which is not easy to cause dust pollution to the environment. At the same time, the environment will not cause pollution to the material and make it damp, which can ensure the quality of the conveyed material.
2. The conveying line can be arranged flexibly, occupies a small area, and can make full use of the space. For complex terrain and crowded workshops in the renovation of old factories, the arrangement of conveying pipelines has great adaptability and flexibility.
3. While conveying materials, various production processes can be completed, such as cooling, heating, drying, wetting and purification of materials.
4. Fewer mechanical transmission parts, simple structure, convenient operation and management, few wearing parts and low maintenance cost.
5. It can achieve quantitative transportation, which is convenient for production scheduling and management.
6. It can carry out long-distance decentralized or centralized transportation.
7. The chemically unstable materials can be transported by inert gas protection.
Pneumatic conveying also has some shortcomings, its main disadvantages are:
1. The power consumption is large.
2. The components in the conveying pipeline that are in contact with the air flow and the material wear a lot, especially when conveying abrasive materials, the wear may be more serious. Honggong has summarized the methods to avoid pipeline wear, you can click to understand.

3. There are certain conditions for conveying materials. For example, for brittle and fragile materials, pneumatic conveying cannot be used due to the quality degradation or unqualified products due to crushing; for fine materials or materials that are easy to absorb moisture and agglomerate During the conveying process, it is easy to block the pipe and should not be used; the materials that are easily oxidized should be transported with inert gas protection; and the materials with a block size greater than 50mm and a high density should not be used.