Identifying the correct phase to be used in your pneumatic conveying system is crucial to successfully move your material. In order to narrow the choices down to a single phase, we need to assess your material’s characteristics.
- Particle Size & Shape has an enormous influence on the conveyance phase, since it determines the flowability and how much air is required to move the material. This refers to the shape of each individual particle.
- Bulk Density is the material in its bulk form and helps determine the design of the pneumatic system and what is required to move the bulk from one place to another.
- Moisture Content can affect flowability and is an important consideration when designing a pneumatic system. Moisture can cause materials to pack and clog lines.
- Friability refers to how easily material crumbles or becomes pulverized. Many materials can break when coming into contact with surfaces. If this is a concern for you, lower velocities should be used to minimize particle degradation,
- Cohesiveness means that the material will adhere to itself under pressure and agglomerate, causing problems within the conveyance lines.
- Hygroscopicity is the ability of material easily absorbs moisture in the air. These materials can coat the walls of a conveyance line and cause blockages. Using dried air may help to reduce moisture in the lines.
Three Pneumatic Phases
Once you determine what type of material you are conveying, you need to consider the three basic categories of conveying. Understanding these phases will help determine the best phase for your application.
- Dense: Dense phase pneumatic conveying uses a low speed system. The material is not suspended in the air stream and there is much less wear and tear on the material and system. Friable materials need this type of system for its low velocity to reduce damage to the particles. Materials that are slightly hygroscopic will also likely not require the use of air drying equipment.
- Semi-Dense: Only a portion of the material is suspended in the air stream for a semi-dense phase. This system is ideal for use with products that are in an aeratable state, such as cement or fly ash. This phase should not be used with larger particles, long convey distances or material with high moisture, since they are prone to packing in the line.
- Dilute: This is a high-velocity system where the material is constantly suspended in the air stream. Material will not accumulate at the bottom of the convey line at any point. It is best with non-abrasive, non-fragile material with a light density, such as flour or cornstarch. Larger materials require much higher airflow to keep the particles suspended, and degradation for friable material can be an issue due to the velocity.
How Should You Convey It?
There are several other concerns to keep in mind when deciding on a pneumatic conveyance system. Static charge can be reduced by grounding the convey line and system equipment. In addition, toxic materials should be used with vacuum systems to prevent leakage from escaping into the environment. Finally, some materials can form explosive mixtures when exposed to air, and alternate gasses can be used in the conveyance system.
To determine the best pneumatic conveying phase for your material and unique application, we encourage you to download our new infographic, How Should You Convey It? To obtain your copy, simply click here or select the button below.
If you have additional questions, please contact us today to let us show you how we can help meet all of your material handling needs.