Dense phase conveyance and dilute phase conveyance are two pneumatic conveying methods operating on different principles. The main difference is the gas velocity and the behaviour of the material in the pipeline: in dilute phase conveyance, the material travels quickly along with the air flow, whereas in dense phase conveyance, it travels more slowly and in denser batches. The right choice depends on the properties of the material, the conveying distance and the process requirements.
Now we will go through the operating principle, suitable materials, and differences in energy efficiency of both methods so that you can evaluate which solution is best suited to your own process. If you want to familiarise yourself with pneumatic conveying solutions already now, Read more about pneumatic conveying.
How do plug and levitation transport systems work differently?
In suspension flow, material travels inside piping along with a high air velocity (typically over 15 m/s) evenly suspended or in suspension. In plug conveying, the gas velocity is significantly lower, around 7-10 m/s, and the material moves inside the piping as dense plugs or layers rather than floating freely in the air stream.
In pneumatic conveying, the pressure is generally low and the velocity high. This means that the material is in constant motion throughout the pipeline and does not stop at any stage. The system is simple in structure and is well suited to short transfer distances and materials that can withstand mechanical stress.
In plug conveyance, especially in the pulse plug conveyance method, air divides the material into smaller plugs that move along the pipeline into the receiving silo. The low material velocity significantly reduces pipeline wear and material degradation. The system operates at a higher pressure but with a smaller volume of air than dilute-phase conveyance.
The practical difference is also visible in system control: pig transport is fully automated and can be integrated directly into the plant control system (DCS), making it easy to use in daily production.
When is slug flow transportation better than suspension flow transportation?
Plug flow conveying is better suited than suspension conveying when the material is susceptible to degradation, abrasive or heavy, the transport distance is long, or the process requires low operating costs and minimal pipe wear. It is a particularly justified choice in demanding industrial processes, such as metallurgy, the mining and minerals industry, and power generation.
The advantages of bulb transport are:
- Low material speed protects sensitive or coarse-grained materials from degradation
- Wear and tear on piping and components is significantly reduced, which extends the service life of the equipment
- Well suited for long transfer distances, up to 300 metres
- Lower air consumption relative to the amount of material conveyed keeps operating costs low
- A closed system minimises dust emissions and material waste
Dense-phase conveying, on the other hand, is best suited for situations where the material is light and free-flowing, the quantities to be moved are small or moderate, and keeping investment costs low is important. Short transfer distances and simple processes are the strongest area of dilute-phase conveying.
It is worth noting that the choice is not always black and white. A well-designed system can be implemented in such a way that the same equipment can be used with either method if necessary with minor software modifications, which gives the process flexibility for changing production requirements.
What materials can be transported by either method?
Suspension flow conveying is best suited to light, fine and free-flowing materials, such as powders and dust-like substances, that can withstand high speeds without breaking down. Plug conveying, on the other hand, is suitable for a wider range of materials, particularly abrasive, granular or delicate materials that cannot be exposed to high velocity forces.
Typical materials for magnetic levitation transport
- Fine powdery substances, such as ash and dust
- Light pellets that float easily in the airflow
- Materials with a small particle size and low density
Materials typical for plug transport
- Consumable materials, such as sand, minerals and metallic powders
- Coarse-grained or heavy materials that break down easily at high speeds
- Fragile granules whose shape or structure is important to preserve during transport
- Materials with a high solids loading ratio (µ greater than 15)
In practice, many industrial processes, such as power generation, metallurgy and the chemical industry, handle materials that are better suited to slug flow transport. Accurate evaluation of material properties before selecting a system is important, as the wrong method can lead to excessive pipeline wear, material loss or process disruptions. Discover pressure conveyors and assess whether plug transport suits your own process.
Which system consumes less energy?
Plug flow conveyance generally consumes less energy than suspension flow conveyance when considering energy relative to the amount of material transferred. Plug flow conveyance uses less compressed air because the low gas velocity and high solids-to-air ratio mean that more material is moved with a given volume of air.
In suspension flow, high air velocity requires maintaining a larger airflow throughout the transfer. This increases the energy consumption of the compressor, particularly in long pipelines and at high capacities. The longer the transfer distance and the larger the material volume, the more pronounced the energy efficiency difference becomes in favour of plug flow.
Energy efficiency is also affected by the overall system design, pipeline routing, pressure losses and material properties. A carefully sized plug conveyor, in which the pressure vessel, fluidisation system and piping are optimised according to the process, can yield significant savings in operating costs over the years.
From an energy-efficiency perspective, it is also important to note that the lower gas velocity of plug flow reduces wear and tear on the pipeline and components. This means less frequent maintenance needs and fewer shutdowns, which improves overall process availability and reduces indirect costs.
In summary: if your process requires continuous, high-capacity material transfer in demanding conditions, plug conveying offers better energy efficiency and lower total costs. Kopar has supplied hundreds of pneumatic conveying systems for demanding industrial processes with nearly 50 years of experience. Explore pneumatic conveying solutions or Get in touch, and we will help you choose the solution that best suits your process.
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