The Basics of Dilute Phase Pneumatic Conveying: An Overview

Pneumatic conveying systems generally fall into one of two broad categories: dense phase or dilute phase. While both types of systems perform the same function, the different ways in which they do so give each one particular benefits. Figuring out which is most suitable for your products and needs is the key to achieving maximum efficiency and productivity at minimal cost.

In a previous blog, we discussed the basics of dense phase pneumatic conveying. So now let’s turn our attention to dilute phase conveying. Here, we look at how dilute phase systems work, their benefits and drawbacks, and whether they’re right for you.


What is dilute phase pneumatic conveying?

Dilute phase pneumatic conveying is a method of transferring dry bulk solids between silos through enclosed, airtight pipes using gas. In this system, materials are constantly metered into the airstream using a rotary airlock or similar component.

Unlike dense phase systems, which use only a small weight of air, dilute phase systems are characterized by high-velocity airstreams. This keeps the materials suspended rather than dragging them along the bottom of the pipe or tube. As such, dilute phase pneumatic conveying systems are best suited to transporting lightweight, low-density materials.


Types of dilute phase pneumatic conveying


Dilute phase pressure conveying

In a dilute phase pressure conveying system, a blower or compressor is placed at the start of the line to supply a high volume of low-pressure air. When bulk materials are introduced, they enter the airstream and are pushed through the pipes at high speeds. Once they reach their destination, the materials are separated from the airstream using a filter receiver or cyclone.

This type of dilute phase system is typically used when there’s just one pickup point but multiple destinations. Dilute phase pressure conveying systems are an excellent choice for conveying non-abrasive, non-fragile materials with a bulk density of less than 62 lb/ft3.


Dilute phase vacuum conveying

In contrast to a pressure system, a dilute phase vacuum conveying system features a suction device at the end of the line. This creates negative pressure – a vacuum – within the pipes, which pulls materials to their destination within the airstream.

Vacuum systems are popular in facilities with multiple pickup points but only one destination area. They’re especially useful for conveying materials that tend to pack or compress under pressure, such as wood shavings. And since they enable tight control of hazardous particles, dilute phase vacuum systems are ideal for moving toxic materials that must not leak.


What materials can a dilute phase system convey?

Dilute phase pneumatic conveying systems are designed to move particles at high speeds while suspended in a powerful airstream. Therefore, they should be used to convey lightweight, non-abrasive materials. That includes those with fine or granular particles and those with a low bulk density.

Common materials that are processed using a dilute phase pneumatic conveying system include:

  • Bleaching earth
  • Cement
  • Chemical powders
  • Coffee beans
  • Flour
  • Fly ash
  • High-density polyethylene (HDPE) powders
  • Lime
  • Pellets
  • Pigments
  • Resins
  • Soda ash
  • Starch
  • Sugar
  • Talc
  • Wood shavings


Benefits of dilute phase pneumatic conveying

  • Highly versatile: These systems can easily adapt to materials with a wide range of product-flow characteristics, such as particle size and bulk density. They can successfully convey most materials, making them the default option for many manufacturers.
  • Long-distance conveying: The powerful airstreams of dilute phase conveyors means they can move material over distances of up to 200 meters. Dense phase systems, on the other hand, generally don’t convey over more than 100 meters.
  • Easy to operate and install: Dilute phase is a much older form of conveying compared to dense phase. As such, many more vendors can provide repairs and servicing. This makes it easier and cheaper to keep your dilute phase pneumatic conveying system in top condition.
  • Easy to clean and maintain: Dense phase systems require much higher pressures than dilute phase systems. That means they need to be built to withstand these pressures and meet codes set by the American Society of Mechanical Engineers (ASME). The extra flanges, bolts, and fasteners they require make dense phase systems very difficult to take apart for inspection, cleaning, and maintenance. Dilute phase systems, on the other hand, are very easy to disassemble. That makes cleaning and maintenance simple.
  • Lower capital investment: Since dilute phase systems aren’t as heavy-duty as dense phase systems, they’re typically cheaper to install. The high number of vendors also lets you compare quotes to get the best price.


Drawbacks of dilute phase pneumatic conveying

  • Risk of product degradation: The high velocities at which materials travel in a dilute phase system can lead to greater attrition or the breakage of powder. This can reduce the quality and saleable quantity of your conveyed product. Therefore, it’s recommended to use this type of conveying in applications in which material degradation isn’t a concern.
  • Higher abrasive wear: If you convey abrasive products in a dilute phase system, the high-volume airstream will increase abrasive wear on your elbows and other components. That means you’ll need to replace your parts more often, leading to increased downtime and maintenance costs. However, you can protect against excessive wear by installing abrasion-resistant components like our ultra-hard Ceram-Back® elbows.
  • Greater power consumption: Approximately half the power of a dilute phase system goes toward moving the conveying gas through the pipeline. This drives up power consumption, which can increase operating costs over time.
  • Materials segregation: In a high-velocity airstream, some materials will move more quickly than others. This can lead to material segregation. Dilute phase conveying is unsuitable for mixed-batch products or for conveying after a mixer.


Build a profitable dilute phase system with industry-leading components

If you convey lightweight, non-abrasive particles with low bulk density, dilute phase pressure or vacuum conveying could help maximize your productivity. These systems can handle a wide range of materials, and they’re very easy to operate, clean, and maintain.

However, a pneumatic conveying system is only as good as the parts used to build it. So if you want to run a highly efficient, productive, and profitable facility, you need durable, cost-effective, wear-resistant parts.

At Progressive Products Inc., we’ve spent more than 40 years designing and developing high-performance components that optimize your system. Our ultra-tough elbows, fittings, and couplings remain in your system much longer, reducing the need for downtime and replacement. That means you can fulfill higher customer demands more quickly and build a reputation for quality.

Explore our range of industry-leading pneumatic conveying components now to build an efficient and profitable system.

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