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Integration And Application Of Korean Pneumatic Conveying System In Automated Production Line

Introduction to Pneumatic Conveying System Design
In the past 50 years, pneumatic conveying has become increasingly popular compared to other conveying systems due to its flexible layout, containment capabilities, automation potential, low maintenance, and ability to handle dangerous materials by replacing air with an inert gas. According to the definition, pneumatic conveying is the transportation of bulk materials through a gas stream under either negative or positive pressure.

When designing and troubleshooting these systems, it is important to carefully select and design key components like the gas mover, solids feeder, conveying line, and gas-solids separator. It is also crucial to consider the system requirements, conduct experimental tests, and utilize empirical correlations. Although many materials can be conveyed pneumatically, it is most suitable for non-abrasive, non-fibrous, non-friable, and free-flowing materials. Flow regimes can be categorized as either dilute-phase or dense-phase in pneumatic conveying systems.

Dilute Phase Conveying
In dilute-phase conveying, particles are transported within a gas stream at velocities exceeding the saltation (horizontal orientation) and choking (vertical orientation) velocities of the solids. This results in full suspension of the particles during transport. While a variety of bulk solids can be conveyed using this method, it’s important to consider the effects of pipeline wear, particle attrition, and high power consumption.

If these factors are a concern, dense-phase flow conveying may be a better alternative. Dilute-phase systems typically operate with low solids loading ratios (less than 15 kg solids / 1 kg gas), lower system pressures (<1 bar g), and higher gas velocities (15-25 m/s).

Dense Phase Conveying
Dense phase conveying has a solid loading that is higher (20-150 kg / 1 kg gas) than dilute phase, and this occurs when the particles are below the saltation velocity. It can be operated in two flow modes, plug/piston flow or moving bed flow, with material characteristics dictating which mode is best suited. Generally, plug/piston flow is recommended for coarse and permeable materials, while moving bed flow is preferred for fine and air retentive materials.

In plug/piston flow, the material is conveyed as slugs separated by air gaps, while in moving bed flow, the material is conveyed in dunes along the pipeline’s bottom. Examples of materials suitable for these flow modes include coffee beans, plastic pellets, cement, and baking flour. Dense phase conveying usually operates at higher pressures (>2 bar g) and lower gas velocities (3-10 m/s), with three classifications of systems: pressure, vacuum (negative pressure), or a combination of both.

Limitations of pneumatic conveying
Additional instructions provided by the merchant may warn of limitations associated with pneumatic conveying systems, including high specific power consumption, particle attrition, and wear. Pneumatic conveying systems may not be suitable for transporting materials over long distances or at high capacities compared to other means of conveying, such as belt conveyors. Attempting to transport heavy materials, like iron ore, over long distances and at high rates using pneumatic conveying systems may result in economic impracticality due to the energy required.

Poor design can lead to issues such as insufficient capacity, plugging, product build-up, and segregation, while wear may occur over a longer period and may not be immediately apparent to new designers during commissioning.

Considerations for Pneumatic Conveying System Design
Considerations for Designing a Pneumatic Conveying System While pneumatic conveying may not be suitable for all materials, it can be beneficial if designed properly. With its ability to fit into a small space and navigate your processing plant, it can effectively meet your material transfer needs. However, it’s not uncommon to encounter problems with pneumatic conveying equipment, often due to a lack of understanding or a trial-and-error approach to troubleshooting.

This can lead to lost time, reduced revenue, and potential safety risks. To address these issues, it is important to take a systematic approach to both design and troubleshooting. When designing your pneumatic conveying system, it is crucial to consider the system as a whole. Follow the outlined approach for optimal results.

Gain a thorough understanding of the material characteristics, such as particle size, distribution, shape, cohesion, and hardness, as these variables play a crucial role in the design process (3). Consider the impact of velocity on pipe wear when dealing with larger and heavier particles, especially towards the end and bends of the pneumatic lines. For materials that are easily degraded, a low velocity system may be more appropriate.

Keep in mind that fine particles can cause issues with hopper flow, such as arching, ratholing, and flow restrictions, which can affect material flow into the conveying line. It is essential to have a solid understanding of material characteristics in order to make well-informed design decisions. The system should be classified as either batch or continuous operation, which will help determine equipment selection, as well as the type of feeder and gas mover needed.

Will there be multiple pick up or discharge points? This will influence the decision to use a pressure, vacuum, or combination system for material conveyance.

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