How Pneumatic Conveying Systems Work: Design & Applications

A pneumatic conveying system is a process by which dry bulk materials or powders are transported or carried utilizing a gas from a source to a destination. The bulk materials or granules are transferred through an enclosed conveying pipeline by the collective force of pressure and the gas used (commonly air). The pressure and air flow used to convey the materials is generated by air movers such as positive displacement blowers or vacuums. Therefore, by manipulating the pressure differential and air flow, the system can effectively convey materials over certain distances.

Well created pneumatic conveying systems are much more reasonable and cost-effective than other mechanical systems because they are completely enclosed, can be modified easily and can be reasonably controlled. They also have been known to be much more environmentally sound than other mechanical systems because of their enclosed feature, keeping the materials conveyed clean and protected from harmful, foreign matters.

The two types of pneumatic conveying systems that are commonly used are dilute phase and dense phase conveying. These types can be distinguished specifically by their operating principle. Also, each type can convey materials by either a pressure or a vacuum method. Next, we will explain each phase more thoroughly.

Dilute Phase Conveying

Dilute phase pneumatic conveying is described as the process of pushing (pressure) or pulling (vacuum) particles suspended in air from one location to another. The air-suspended particles are transferred continuously at a low pressure and high velocity. As stated, there are two main types of dilute phase conveying. These types are listed and described below:

• Dilute-phase pressure conveying – This method is the most commonly used process of conveying dry materials that are nonabrasive and resilient with a light bulk density over great distances. Some examples of the materials used in this method are plastic grains, sugar and flour.

How it works: In this type, an air mover, commonly a positive displacement blower, is fixed at the start of the system to supply a high volume of low-pressure air. Placed next in line to the blower is a feeder and rotary airlock valve that methodically “feeds” the materials into the line. As the materials enter the line, air stream supplied by the blower pushes and suspends the particles from where they enter to another destination quickly. The method is commonly used to convey materials from a single destination to multiple locations.

• Dilute-phase vacuum conveying – This method is used to convey materials that compact or compress together under pressure. Some examples of these pressure sensitive materials are wood shavings and fibers. Dilute-phase vacuum conveying is commonly utilized in central vacuum cleaning systems that need many pipes to convey materials to a single location or collection point. In fact, this method is used to convey materials from multiple trucks and rail cars to a single location or silo.

How it works: Dilute-phase vacuum conveying works in the exact opposite way than pressure conveying, in that a positive displacement vacuum provides negative pressure in order to pull material from a storage hopper. The vacuum pump is placed at the opposite end of the line to supply the suction in order to pull material from one location to the next. The negative pressure in the system is controlled by a vacuum relief valve to ensure the right amount of material reaches its destination or multiple locations.

Dense Phase Conveying

Dense phase pneumatic conveying is described as the process of pushing (pressure) or pulling (vacuum) particles that aren’t suspended in the conveying air. The densely transported materials are transferred at high pressure and low velocity or speed. The two main types of dense phase conveying are listed and described below:

• Dense-phase pressure conveying – This method is commonly used to convey abrasive or fragile materials over long distances at extremely low speeds. Materials commonly transferred in this method are hazelnuts, cocoa beans, cereal, candies and glass particles. This system is known for the benefit of stopping or starting with the conveying line full of material.

How it works: Material conveyed by this type of method is first loaded into a pressure vessel or blow pot. Once the blow pot is completely filled, the material vent and inlet valve are closed and compressed air is pushed into the vessel. The compressed air forces the material out of the vessel into the conveying line to the destination. Upon completion of the transfer of all the material in the vessel and line, the process is started again. It is common for air injectors or jets to be fixed over the length of the conveying line to help boost the material.

• Dense-phase vacuum conveying – This type is used to convey abrasive or fragile materials over short distances at low speeds. Dense-phase vacuum conveying is commonly used to unload materials from rail cars and trucks in a fluidized state. It has also been used for pharmaceutical and food applications.

How it works: These types of systems use vacuum pumps to convey material from a silo or hopper to a receiving vessel known as a vacuum hopper. When the vacuum hopper is full the material is then expelled to a destination silo. Once all the material is conveyed from a silo or hopper the process repeats.

Pneumatic conveying is an extremely effective method of transporting materials and is used by a variety of industries to ensure their resources and products are safely transferred. If you have any questions regarded pneumatic conveying system design please contact us today! We also have a variety of PD Blower packages that can be engineered and designed to your pneumatic conveying specifications.

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• How Pneumatic Conveying Systems Work: Design & Applications