How does a pneumatic conveying system work in industry?

A pneumatic conveying system transfers powdery and granular bulk materials in a closed pipeline using compressed air or another carrier gas. The system is suitable for industrial processes where traditional mechanical conveying cannot meet the requirements set by dusting, hygiene, or layout. In this article, we will cover the key operating principles of pneumatic conveying, different system types, and the factors that influence system selection and energy efficiency.

If you wish to explore pneumatic conveying solutions further, Read more about pneumatic conveying and assess how the system fits with your own process.

Pneumaattinen kuljetus eroaa mekaanisesta kuljetuksesta siinä, että pneumaattinen kuljetus käyttää ilman virtausta kaikenlaisten aineiden kuljettamiseen, kun taas mekaaninen kuljetus käyttää fyysisiä laitteita, kuten hihnoja, ruuveja tai suuttimia.

Pneumatic conveying transports material in a closed pipeline using the flow of gas, while mechanical conveying relies on physical moving parts such as screws, chains, or elevators. The most important practical difference is that a pneumatic system is completely enclosed, almost entirely eliminating material loss and dust generation.

Mechanical conveyors are well-suited for short, straight routes and high capacities, but their construction limits route planning. The piping must be built almost straight, and differences in elevation require separate equipment. Pneumatic piping, on the other hand, can be routed freely through differences in elevation, bends, and confined spaces without additional equipment.

The low number of moving parts is a significant advantage in terms of operational reliability. In mechanical systems, wear parts such as bearings, chains, and screws require regular maintenance and cause unplanned downtime. In a pneumatic system, the critical wear points are mainly limited to pipe bends and feeders, the maintenance of which is predictable.

Pneumatic conveying is particularly suitable for processes where material purity, a closed environment, or process automation are important. Mechanical conveying, on the other hand, is often a more competitive option when the materials to be conveyed are coarse, very heavy, or when capacity requirements are very high relative to the conveying distance.

What is the difference between underpressure and overpressure transport systems?

A positive pressure conveying system pushes material into a pipeline using compressed air, whereas a negative pressure conveying system draws material into a pipeline by creating a vacuum. Positive pressure conveying is suitable for long transfer distances and high capacities, while negative pressure conveying is suitable for situations where material is collected from several different points to a single destination.

Pressure conveying

In pressure conveying, a compressor or blower generates the necessary pressure to feed material into the pipeline via a feeder. The system is capable of transporting material over long distances, typically from tens of metres to several hundred metres. The pressure can be adjusted according to the material's properties, and higher pressures achieve both longer distances and greater capacities.

Pressure transport is the most common solution in industrial processes with one or a few feed points and one or more receiving points. It is well suited for applications in the energy, metallurgy, and mineral industries, where the materials being transported can be abrasive or resistant to high temperatures.

Transport of litter

In vacuum conveying, the fan unit is located at the end of the pipeline and creates a suction force that pulls material from multiple feed points into the pipeline. This makes vacuum conveying a practical solution when material needs to be collected from several different locations, such as multiple silos or process points, into a single receiving vessel.

A benefit of vacuum conveying is that any leaks in the pipeline will not release material into the environment, as the pressure is always lower than the ambient air pressure. This makes it particularly suitable for situations where environmental emissions or material loss are critical factors. A limitation of vacuum conveying is the shorter transfer distance and capacity compared to pressure conveying.

Several factors influence the energy consumption of a pneumatic system. These include: * **Compressed air leaks:** Leaks are a significant source of energy loss in pneumatic systems. Even small leaks can lead to considerable wasted energy over time. * **Pressure settings:** Operating the system at a higher pressure than necessary increases energy consumption. Optimising pressure levels to meet the demands of the application is crucial. * **Air treatment:** The processes of filtering, water separation, and lubrication all require energy. Inefficient or unnecessary air treatment can contribute to higher consumption. * **Cylinder and actuator efficiency:** The design and condition of pneumatic cylinders and actuators affect their efficiency. Friction, internal leakage, and incorrect sizing can all lead to increased energy use. * **Control valves:** The type, size, and responsiveness of control valves influence how efficiently compressed air is directed. Inefficient valve operation can lead to air wastage. * **Piping and hose losses:** The size, length, and number of bends in the piping and hoses can create resistance to airflow, increasing the pressure drop and requiring the compressor to work harder, thus consuming more energy. * **Compressor efficiency:** The efficiency of the air compressor itself is a primary factor. Different compressor types have varying efficiencies, and older or poorly maintained compressors are generally less efficient. * **Duty cycle:** The amount of time the system is actively operating (the duty cycle) will naturally affect the overall energy consumption. * **Temperature:** The temperature of the compressed air can impact its density and thus its energy content. * **Air consumption patterns:** Fluctuations in demand and the timing of air usage can influence how efficiently the compressor operates. Addressing these factors through regular maintenance, system design optimisation, and careful operation can significantly reduce the energy consumption of a pneumatic system.

The energy consumption of a pneumatic conveying system is most affected by the mode of transport, the gas velocity in the pipeline, the length of the conveying distance, and the material properties. Of these, gas velocity is often the most significant single factor, as energy consumption increases with the square of the velocity.

Dilute phase transport uses a high gas velocity that keeps the material suspended in the pipeline. This requires more energy but is suitable for light and easily flowing materials. Dense phase transport, such as dense phase conveying, uses a lower gas velocity and larger quantities of material in the pipeline. This significantly reduces energy consumption and is particularly advantageous for long transfer distances.

The following factors directly affect the energy efficiency of the system:

• Gas velocity Lower speed in dense phase conveying significantly reduces energy consumption compared to dilute phase conveying.
• Pipework geometry Bends, vertical sections and a long overall distance increase pressure losses and therefore energy requirements.
• Material properties Dense, coarse, or damp material requires more energy for transfer than light and dry material.
• Suspended solids load ratio The more material relative to the amount of air, the more efficiently energy is utilised.
• System sizing An oversized compressor or incorrectly selected pipe diameter leads to unnecessary energy waste.

Careful system sizing is the most effective way to manage energy consumption. In practice, this means that the transmission method, pipeline diameter, pressure, and gas velocity are optimised for the specific material and process. Post-installation optimisation is always more expensive than initial sizing performed correctly.

Would you like to know how pressure conveyors work in practice? Discover pressure conveyors and see how different applications are implemented in demanding industrial processes.

When is a pneumatic conveying system worth choosing for a process?

A pneumatic conveying system should be chosen when the process requires dust-free and enclosed material transfer, when the layout is challenging, or when the material is sensitive to contamination or mechanical stress. It is also a justifiable choice when the transfer route passes through confined spaces or involves differences in elevation.

Pneumatic conveying is a particularly strong option in the following situations:

1. Materiaali on jauhemaista tai rakeista. and its dusting causes safety or environmental risks
2. The transfer route is complex. and requires several changes of direction or altitude
3. The process requires automation and integration into the plant control system
4. The material is susceptible to mechanical wear the structure must not break during the transfer
5. The process has ATEX requirements and other strict security standards
6. Minimising maintenance is important and unplanned downtime causes significant production losses

Mechanical conveying can be a better option when the material is very coarse or large, when capacity requirements are exceptionally high, or when the transfer distance is short and the route is straight. In these situations, a mechanical solution can be simpler and more cost-effective to implement.

The decision between pneumatic and mechanical conveying is always made on a case-by-case basis. The most important assessment criteria are the material properties, process capacity requirements, layout constraints, operating environment safety requirements, and overall life-cycle costs. The purchase price alone does not tell the whole story, as energy efficiency, maintenance needs, and operational reliability significantly impact total costs in the long term.

Kopar has been designing and delivering pneumatic conveying systems for demanding industrial processes for almost 50 years. Our experience covers applications in the energy, metallurgy, mineral, and chemical industries, and we continuously test materials in our own test facility to ensure that every solution is correctly dimensioned. Explore pneumatic conveying or Get in touch Okay, and tell us about your process requirements.