Pneumatic Conveying System: Which One Does Your Industry Need?

What Is Dilute Phase Pneumatic Conveying and How Does It Work?

Dilute phase pneumatic conveying, also known as lean phase conveying, is the most widely used form of pneumatic material transport. The system uses a high velocity air stream, typically between 18 and 35 metres per second, to suspend individual particles and carry them through the pipeline in a state of continuous suspension. Because each particle is kept airborne throughout the journey, the material to air ratio is low, generally between 1 and 15 kilograms of material per kilogram of air.

The system operates at relatively low pressure, typically 0.1 to 0.8 bar gauge on the pressure side, or at vacuum levels of 0.3 to 0.8 bar absolute when configured as a vacuum conveying system. A roots blower or rotary compressor provides the motive air, and a bag filter or cyclone separator recovers the material at the destination.

Dilute phase systems are straightforward to design and relatively low in capital cost. They work extremely well for free flowing granular materials, plastic pellets, ground minerals, grain, and any product that is not fragile, not highly abrasive, and does not absorb moisture readily.

What Is Dense Phase Pneumatic Conveying and How Does It Work?

Dense phase pneumatic conveying moves material through the pipeline in a fundamentally different manner. Rather than suspending particles in a fast air stream, the system pushes material in compact slugs or a moving bed at high pressure and very low velocity, typically between 1 and 10 metres per second. The material to air ratio is correspondingly high, between 30 and 150 kilograms of material per kilogram of air, and the operating pressure at the inlet is typically between 1.5 and 5 bar gauge.

There are two common modes within dense phase conveying: plug flow, where discrete slugs of material are pushed through the pipe separated by air gaps, and fluidised moving bed, where material flows continuously in a densely packed layer along the bottom of the pipeline. Both modes achieve the same fundamental objective of moving material gently at low velocity.

Because velocity is low, particle degradation is minimal. Friable tablets, whole spices, coffee beans, sugar crystals, activated carbon pellets, and abrasive powders such as alumina or silicon carbide can all be conveyed in dense phase mode without the breakage, attrition, or surface damage that high velocity dilute phase conveying would cause.

Side by Side Comparison: Dense Phase vs Dilute Phase Conveying

Which Industries Use Dilute Phase Pneumatic Conveying Systems?

Dilute phase or lean phase pneumatic conveying systems are standard in applications where the material can withstand the velocity without damage and where volume throughput is more important than gentle handling. Key industries and applications include:

• **Cement and fly ash handling** in ready mix plants, silos, and power stations where high tonnage throughput is required over moderate distances
• **Plastic pellet conveying** in injection moulding, extrusion, and film blowing plants where pellets are robust and free flowing
• **Grain and seed transfer** in flour mills, feed mills, and grain storage where whole grains are conveyed between silos and processing equipment
• **Sand and mineral powder conveying** in foundries, glass plants, and ceramic manufacturers for raw material supply
• **PVC powder and resin conveying** in pipe extrusion and compound manufacturing where coarse powders flow freely

Which Industries Use Dense Phase Pneumatic Conveying Systems?

Dense phase systems are the preferred pneumatic conveying solution for high value or structurally sensitive materials where product integrity directly affects quality or regulatory compliance. Key industries include:

• **Pharmaceutical manufacturing** where active pharmaceutical ingredients, excipient powders, and granules must be transferred without attrition that could affect dissolution rate, particle size distribution, or blend uniformity

• **Food processing** where whole spices, dried fruit, coffee beans, nuts, and fragile pasta shapes need to arrive at the destination unchanged in size and appearance
• **Chemical plants** where abrasive powders such as titanium dioxide, alumina, and soda ash would rapidly erode a dilute phase pipeline
• **Carbon black and pigment conveying** where particle size distribution is critical and contamination from pipeline wear must be avoided
• **Specialty polymers and engineering plastics** where pellet surface finish and dimensional accuracy affect downstream processing

How Does Operating Humidity and Temperature Affect System Selection?

Hygroscopic materials, which readily absorb moisture from air, present a particular challenge in dilute phase systems because the high volume of moving air carries more moisture into contact with the product. In dense phase systems, the low air to material ratio dramatically reduces moisture exposure. Hygroscopic powders such as sodium carbonate, certain pharmaceutical excipients, and sugar in fine form are therefore almost always conveyed in dense phase mode.

Temperature is also relevant. In high temperature applications above 80 degrees Celsius, the air delivery equipment and pipeline insulation requirements differ significantly between the two modes. Dense phase systems generally handle hot conditions more easily because the lower air volumes generate less thermal stress on seals and filter media.

What Air Supply Equipment Does Each Mode Require?

For dense phase systems, a high pressure rotary compressor delivering 2 to 5 bar gauge is required. Screw compressors or reciprocating compressors are used at the higher end of the pressure range, while Acme’s tri lobe rotary compressors cover the 1.5 to 3 bar range for medium pressure dense phase applications. In both cases, an air receiver and pressure regulation system are essential to maintain stable conveying conditions.