What are the effects of material characteristics on the selection of pneumatic conveying systems?
- Categories:Industry dynamics
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- Time of issue:2021-07-16
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(Summary description)Material characteristics are the basis for the selection of pneumatic conveying systems. According to different material characteristics, we need to select appropriate system types and components to achieve the ideal conveying effect. Precautions for the selection of some typical material characteristics.
What are the effects of material characteristics on the selection of pneumatic conveying systems?
What are the effects of material characteristics on the selection of pneumatic conveying systems?
(Summary description)Material characteristics are the basis for the selection of pneumatic conveying systems. According to different material characteristics, we need to select appropriate system types and components to achieve the ideal conveying effect. Precautions for the selection of some typical material characteristics.
- Categories:Industry dynamics
- Author:
- Origin:
- Time of issue:2021-07-16
- Views:0
Information
Material characteristics are the basis for the selection of pneumatic conveying systems. According to different material characteristics, we need to select appropriate system types and components to achieve the ideal conveying effect. Precautions for the selection of some typical material characteristics.
1. Adhesion and adhesion. Viscous materials can stick or block the discharge hopper, feeder, and conveying pipeline. Therefore, the purging type rotary feeder should be preferred in the rotary blade feeder.
2. Flammable and explosive. When transporting flammable and explosive materials such as plastics, chemicals, metal powder and coal powder, safety measures such as explosion-proof valves and automatic fire extinguishing devices should be used.
3. Moisture content. If the amount of fine powder below 50μm in the wet material is less than 10%, most of it can be transported in the traditional pneumatic conveying system. If the moisture content in the wet material is high, the wet fine powder will adhere to the inner wall of the elbow, causing the pipeline to block, then the feeder should be a purge type rotary blade feeder. If the material is not too humid, the problem of sticking can be reduced by heating and conveying the air.
4. Static electricity. The accumulation of material charge will cause adhesion and affect the fluidity of the material. At this time, it can be solved by air online humidification. In dense phase transportation, because the amount of air used is less, the humidification cost is lower.
5. Grinding. In order to reduce the wear of the conveying pipeline and parts, a lower conveying speed should be selected when conveying abrasive materials. Avoid using feeders with moving parts in the dilute phase system, and use short-radius elbows R/D=2～3, cast iron T-shaped pipes with one end blocked, and ceramic-steel composite pipes made by self-propagating high-temperature synthesis technology And other measures to extend the service life of the pipeline.
6. Fragility. During the transportation process, most of the material damage occurs in feeders such as elbows or screw pumps. Therefore, when designing the system, elbows should be used less and the use of feeders for fragile and brittle materials such as screw pumps should be avoided.
7. Granularity. Top discharge bin pumps and ordinary rotary vane feeders are not suitable for conveying granular materials. The latter will cut granular materials, and the offset rotary blade feeder can avoid this phenomenon.
8. Hygroscopicity. The problems caused by hygroscopic materials can be avoided by conveying air dry. Use freezing method or desiccant to keep the material dry. Sometimes, if the moisture absorption is not large, the materials can also be transported in dense phase with undried air.
9. Low melting point. When the high-speed particles with low melting point and 150°C softening temperature collide with the inner wall of the pipe and the elbow, local melting may occur. For most materials with low melting points, low-speed conveying can eliminate this phenomenon.
10. Fineness. Micron or sub-micron fine powder will be coated on the inner wall of the pipeline during the transportation process, thereby reducing the cross-sectional area of the pipeline and reducing the transportation volume. Usually, a bin pump and a flexible tube that can be regularly beaten in the pipeline are used to solve this problem.
11. Gas permeability and retention ability. Dilute phase transportation is characterized by low pressure, high speed, and uniform distribution of materials on the cross section of the transportation pipeline. Therefore, the transportation process is basically determined by the properties of individual particles that affect the surrounding airflow. The dense phase transportation is characterized by high pressure, low speed and strict separation of two-phase flow. The conveyed materials mainly flow in bundles at the bottom of the pipeline, and occasionally there are sand dunes, irregular agglomerations or plugs that fill the cross section of the pipeline. This conveying process is affected by the overall flow properties of the material rather than the characteristics of individual granular materials. Therefore, the gas permeability and retention capacity of the material have a greater impact on the dense phase system, while the impact on the dilute phase system is less.
When the air retention capacity of the material is high (that is, the gas permeability is poor), only a small amount of air is sufficient to fluidize the material and reduce the internal friction angle. When the air flow stops, the flow process can continue for a certain period of time, and the friction angle in this stage is usually smaller than the wall friction angle. In the dense phase conveying system, the clumps and plugs of this kind of materials are easily broken up, and the materials basically flow in the form of fluidized bundles at the bottom of the pipeline. In dense-phase plug transportation, their critical plug length is relatively short. In addition, the critical plug length allowed by the thicker material with higher air permeability, that is, the lower air retention capacity, will be longer than the pipe diameter, and the stability of the material plug is proportional to the ratio of the length of the plug to the diameter of the pipe. . This kind of material is easy to agglomerate and become clogged in dense phase transportation, and it is easy to cause blockage. It should be used as little as possible or not used in dense phase systems.
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What are the effects of material characteristics on the selection of pneumatic conveying systems?
Material characteristics are the basis for the selection of pneumatic conveying systems. According to different material characteristics, we need to select appropriate system types and components to achieve the ideal conveying effect. Precautions for the selection of some typical material characteristics.
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