Pneumatic conveying is a great and efficient way to move bulk materials from one place to another over distances that range from just a few to hundreds of meters.
At the same time, there is also a wide range of materials that can be transported this way and there is no one-size-fits-all solution for how best to do that. Some have to be moved more carefully to ensure that they are not damaged and others can be moved more quickly and a greater volume.
The three phases of pneumatic material conveying systems
There are three ways in which different materials can be moved through pipelines and hoses when using the pneumatic conveying process. These are commonly referred to as phases.
First, there is the dilute phase where a blower or low-pressure compressor is used to send the material through the pipeline as though it is floating without any of it accumulating at the bottom of that pipeline. Because the dilute phase allows material to be moved at a high speed, it is a great way to transport a lot of it in a short time.
The dilute phase has many benefits and is most commonly used. It is highly flexible, easy to design, install, expand, modify, operate and disassemble for cleaning.
It is also very versatile and can handle a wide range of materials and flow characteristics.
In addition, the dilute phase only requires an air pressure of up to 2.5 bar – and often much lower – which means a low-pressure compressor or blower can be used. This reduces both investment and operating costs.
However, the dilute phase also has disadvantages that have to be taken into account when choosing a pneumatic material conveying system. Because of the velocity with which the material moves, abrasive particles could damage the pipeline.
In addition, fragile products can break or be crushed when being transported at such high speeds.
Next, there is the dense phase. Here, the material is pushed (or sucked in the case of negative conveying) through the pipeline. That means it moves more slowly and requires a higher pressure. A common misconception is that conveying in the dense phase requires a pressure as of 1 bar, while it is actually requires a pressure above 2.5 bar. While a low-pressure compressor may work in some cases, a medium-pressure compressor is usually the better solution.
The dense phase is more complex, more expensive and requires more energy. However, it also minimizes wear corrosion of the system piping and its components. It also protects delicate bulk goods from taking damage during pneumatic conveying and prevents the segregation of blended materials.
Finally, there is the transient phase, which is the stage in-between the dilute and dense phases. Some of the material is “flying” through the pipeline and some of it is moved along the sides.