PNEUMATIC CONVEYING SYSTEMS
Pneumatic systems are used wherever the transport distance is long and includes many directional changes Since they contain virtually no mechanical and moving parts they are considered to be extremely reliable, safe, low maintenance and resistant to wear.
An optimal design always considers the overall conveying system, its interface points with other systems or equipment, and the corresponding control and safety systems.
We differentiate between two basic designs: the low-pressure or low-density conveying system which uses a radial fan and the high-pressure or high-density conveying system which uses a rotary piston blower.
The Low-Pressure Conveying System with three Design Options:
1. Closed loop without separator:
Recommended for smaller amounts of material and shorter transport distances. The exhaust air is reused as transport air. The advantages of this design are the low investment costs, the absence of exhaust air which eliminates the need for a filter and direct injection of material into the silo or container. Isolation is necessary for safety reasons.
2. Closed loop with centrifugal separator and rotary valve:
This system is used for larger quantities of material and short transport distances. It has the same advantages as the previous design. In addition, isolation is achieved by using a rotary valve.
3. With separator:
The most economical system for large amounts of material and long distances. Filter options include either a static silo filter where housing strength must correspond to the silo’s interior pressure or a bag filter with a rotary valve for isolation. While the first type has the advantage of lower investment costs and the disadvantage of overpressure in the silo, the second type features an isolated discharge system and a normal pressure level in the silo.
The High-Pressure Conveying System:
As transport distances and material loads increase, a high-pressure system is the preferred option. The most important components in this design are the rotary piston blower which has a high operating efficiency and low energy cost as well as the valve designs used. Even with large amounts of material the injectors ensure a low energy consumption. Thick-walled steel pipes and bends provide for a long service life.
High-pressure systems are commonly used for the transport of materials in the range of 1 – 100 t/h (2,200 – 220,000 lbs/h), conveying systems of up to 1,500 meters (5000 ft) in length, and nominal pipe sizes between 88 and 500 millimeters (3.5 – 20 in). They are usually designed as positive pressure units and are implemented for vacuum operation only when transporting materials with a low specific weight (e.g. fibers or insulating materials with density < 30 kg/m³ / 1.87 lb/ft³)