Pressure Conveying of Raw Materials

To silos and storage bins over long distances

Raw material conveying by means of pressure conveying

The advantage of pneumatic pressure conveying systems is the much higher pressure loss Δp which may be achieved in the conveying lines. On the other hand, the disadvantage is that a leaky systems may cause a very dusty work environment within a very short time. Limits given in vacuum conveying are void in pressure conveying. So are conveying pressures of > 3 bar possible, which means that our Δp can reach from several 100 mbar up to several bar in the pipelines with increasing diameters. This allows conveying materials for much longer distances (> 120 m) and much higher quantities.

Due to less physical restrictions pressure conveying systems are often much larger than vacuum conveying systems. Pressure conveyors generally are used to convey materials from one distribution point to several receiving silos which can be bigger than 100 m³ in volume. A typical application is filling of silos.

Typical applications for pressure conveying systems for raw materials

  • Conveying from one feeding point to several delivery points, for example outdoor or indoor silos as well as day consumption storage bins
  • When conveying of raw material is required over a long distance > 120, for example from a central warehouse to the production line
  • When very high throughputs have to be achieved by the raw material conveying system

Limitations of pneumatic pressure conveying

Because of the needed compression work the air inlet temperatures may reach up to 100 °C in certain cases which requires the implementation of coolers to protect products from thermic destruction. This leads to a higher energy consumption of a pressure conveying system. Higher pressure further needs more power in order to meet the need of increased compression work. Therefore, in terms of energy consumption pressure conveying systems are mostly less economic than vacuum conveying systems.

Pressure dilute phase conveying or suspension conveying

Dilute phase conveying systems are using a pressure blower and a rotary valve or an air lock under a product intake such as a dumping station or a raw material storage bin. This conveying method is, even more than in vacuum conveying, suitable for resistant and non-abrasive products. Pressure dilute phase conveying is especially suitable for raw materials of bigger particle size; it might still be suitable for fine abrasive powders due to complete air suspension.

According the ideal gas law; a pressure loss of one bar will already double the gas velocity in a pipeline. Long distance conveying of abrasive materials in pressure conveying systems will therefore cause pipeline damages quickly. A higher wear and tear could be the result. Pressure dilute phase conveying system using a rotary valve

Discontinuous pressure dilute phase conveying of raw material using an air lock

Semi-dense pressure conveying of raw materials

Semi-dense phase and dense phase conveying using compressed air or direct pressure blowers is in terms of the reduced air consumption, and therefore reduced energy requirements, more interesting than to convey in suspension mode, dilute phase. Further, it allows keeping gas velocities at a level which is gentler for most products. Unfortunately, dense phase conveying systems are reaching a much higher pressure loss per meter pipe length than a dilute phase conveying system. The result is a shorter possible conveying distance. Semi-dense phase conveying can be reached using rotary valves or pressure vessels as product intake systems, whereas for dense phase conveying it is mostly, in terms of controls, easier to use a pressure vessel as material intake equipment.

Semi-dense phase pressure conveying of raw material using a pressure vessel
Dense phase pressure conveying of raw material using a pressure vessel

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