Dilute-phase pneumatic conveying is one of the most widely used systems for industrially moving powdered and granular solid materials. Characterized by moving particles in suspension within the airflow — at high velocity and low solids concentration — dilute-phase pneumatic conveying offers simple installation, versatility, and a lower initial cost, making it a suitable choice for a wide range of materials and plant configurations.

What Is Pneumatic Conveying and How Do the Systems Differ

Pneumatic conveying is a fully enclosed system that moves solid materials via airflow, from an origin point to a destination within the industrial plant. There are two main systems with distinct operating principles: dilute phase and dense phase.

The choice between the two depends on the material’s physical and chemical characteristics, the distance traveled, the required capacity, and the product’s fragility. Incorrect sizing results in clogging, material degradation, and higher-than-expected energy consumption.

Dilute-Phase Pneumatic Conveying

In dilute-phase pneumatic conveying, solids are transported in suspension within the airflow at speeds generally between 25 and 50 m/s and a low material concentration in the line. The system uses large volumes of air to move relatively smaller amounts of solids — resulting in a solid-to-air ratio significantly lower than in dense-phase systems.

This system is recommended for materials with the following characteristics:

• Particles that aren’t too fragile — able to withstand high transport speeds without degradation
• Granular or crystalline characteristics
• Low or no abrasiveness
• A wide range of particle densities and sizes

Positive- and Negative-Pressure Dilute-Phase Conveying

Dilute-phase pneumatic conveying can be operated under positive or negative (vacuum) pressure, depending on the plant configuration and process needs.

Positive-Pressure Dilute Phase

In positive-pressure dilute phase, a blower located at the start of the line “pushes” the air/material mixture to its destination. This is the most widely used method for dry, non-abrasive particles. Ideal for plants with one origin point and multiple discharge destinations.

Negative-Pressure (Vacuum) Dilute Phase

In negative-pressure dilute phase, a vacuum pump connected to a filter/receiver at the destination “pulls” the mixture along the line. This is the most suitable method for plants with multiple collection points and a single destination — such as unloading raw material from trucks or containers into storage silos — and for materials that compact when pressurized.

Advantages of Dilute-Phase Pneumatic Conveying

The main characteristic of dilute-phase pneumatic conveying is its operational and installation simplicity. Key benefits include:

• Lower initial cost: the lower complexity compared to dense phase results in reduced acquisition and installation investment.
• Material versatility: accepts virtually any type of material, regardless of size, shape, or density — as long as it isn’t excessively fragile or abrasive.
• Ease of maintenance: fewer precision components mean simpler maintenance and less downtime.
• Layout flexibility: easily adapts to different configurations, with multiple origin or destination points within the same plant.

Limitations of Dilute-Phase Pneumatic Conveying

Dilute-phase pneumatic conveying has limitations that must be taken into account during sizing. The high transport speed increases the risk of degrading fragile materials — such as granules, pellets, or crystals — and causes greater pipe wear with abrasive materials. Energy consumption is also higher than in dense phase, due to the larger volume of air moved.

For fragile, heat-sensitive, or highly abrasive materials, dense-phase systems are usually more suitable. According to parameters widely adopted in process engineering, the correct selection between systems should always consider the mixing ratio, transport speed, and the material’s physical properties — in line with technical guidelines from ISO standards for industrial conveying systems.

Globe Systems: Dilute-Phase Pneumatic Conveying Sizing

At Globe Systems, the sizing of dilute-phase pneumatic conveying systems is carried out by our engineering team based on the specific characteristics of each process: material type and particle size, required flow rate, conveying distance, plant configuration, and the sector’s sanitary requirements.

To fully understand the differences between the available systems, also check out our article on pneumatic conveying concepts and applications.