This article discusses:

  • Advantages and disadvantages of pneumatic transport
  • The four types of pneumatic transport
  • Calculations for pneumatic transport systems

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Advantages and disadvantages of pneumatic transport

Pneumatic transport has been used since the end of the 19th century. Initially for the transport of grain, and over the years it has spread more and more in the industry thanks to the various innovations in the field of pneumatic transport. Pneumatic transport is currently used in food, dairy, pet food, feed and chemicals. A wide variety of dry powders, granules and granulates are transported with pneumatic transport. Examples of products that are pneumatically transported are: cocoa, coffee, flour, milk powder, salt, sugar, silica, corn starch, animal feeds, premixes and soap. However, this is only a brief summary of products that are pneumatically transported in daily practice. Usually air is used for the pneumatic conveying of products. Depending on product characteristics, this air can be conditioned. The air is cooled and / or dried. This happens when products smear when they get too hot or are hygroscopic. In addition, there may be specific circumstances, such as ATEX risks or specific product properties, that require a different type of gas. In this case, nitrogen is used to pneumatically transport the product. In general, pneumatic transport is not applicable to break-sensitive products, very large product particles and to greasy, sticky and hygroscopic products. This is because there is a risk that the pipes will clog up. This problem is exacerbated in blow transport because the air is heated by compression.

Some advantages of pneumatic transport are:

  • Low maintenance and low labor costs,
  • Dust-free transport of a wide variety of products,
  • Both horizontal and vertical transport possible,
  • Great freedom in the routing of transport lines,
  • Suitable for transporting substances with an ATEX risk or risk of oxidation.

However, there are also disadvantages of pneumatic transport such as:

  • Energy consumption,
  • Wear of pipework and other installation parts as a result of the abrasiveness of products,
  • Chance of product breakage,
  • Contamination between different batches,
  • Limited distances depending on the applied concept.
Pneumatisch Transport 1.JPG

Pneumatic transport

The four types of pneumatic transport

Pneumatic transport can be divided into four different types:

  • dense phase,
  • pulse phase,
  • dune flow,
  • dilute phase.

The properties of the product to be transported must be leading in the choice of the transport type, flow rate, absolute pressure and pipe diameters in the system. Ultimately, all this together determines the maximum length over which the product can be transported. In addition, process properties are relevant in the choice that is made. Breakage caused by the system, product heating causing smearing or ATEX risks in the process are all examples of things that must be assessed and taken into account in the final design.

Another way of classifying pneumatic transport is the way in which the product is transported. This can be done by means of overpressure, underpressure or a closed loop system. The advantage of an overpressure system is that it can bridge greater distances. The disadvantage is that there is a greater chance of product leakage. The advantage of a negative pressure system is that it is easier to create multiple entry points and that there is less chance of product leakage. A disadvantage is that less long distances can be bridged.

The choice of suction or blow transport is usually determined by:

Suction transport:

  • Multiple recording points are possible. For example with several locks in a row,
  • Leakage air from locks is less critical, but must be included in the calculation,
  • The distance is limited due to maximum pressure difference of approx. 500 mbar,
  • A larger pipe diameter is required due to lower airtightness,
  • The permitted bulk density of the product to be transported is limited.

Blow conveyance:

  • Entry point is an airtight intake point,
  • Airtight construction of the system is very important,
  • Leakage air at locks is very critical in a blow transport,
  • The blower should be chosen larger when using locks because of the leakage air,
  • Long distances are possible,
  • Higher bulk weights are possible.

The foundation of a pneumatic system always consists of four main components:

  1. The driving force. This can be a fan, blower, vacuum pump, or compressor.
  2. A product feeder. This is used to introduce the product into the pneumatic transport system.
  3. Piping. This includes pipes, bends, switches, diverters, and couplings.
  4. Separator. Here, the gas must be separated from the product again.
pneumatic conveying system.jpg

Pneumatisch transport system

Pneumatic conveying has been used since the end of the 19th century

In de onderstaande tabel zijn de verschillende vormen van pneumatisch transport naast elkaar uitgezet

Type of conveyingType of air displacementSystem pressureMaximum distanceAdvantagesDisadvantages
Dilute phasepositive pressure (blowing)max. 800 mBar150 meter
  • Suitable for greater distances (>100M)
  • Greater risk of product damage
  • Greater risk of dust emission
  • Air leakage can cause problems
  • Greater risk of segregation
Dilute phasenegative pressure (vacuum)Min. -500 mBar100 meter
  • No dust emission
  • Multiple entry points are possible
  • Greater risk of product damage
  • Lower maximum distance
  • Thicker pipes
  • More risk of segregation 
Dense Phasepositive pressure (blowing)1 Bar - 5 Bar200 meter
  • Suitable for greater distances (>100M)
  • Less product damage
  • Less chance of segregation 
  • Greater risk of dust emission
Dense Phasenegative pressure (vacuum)Min. -900 mBar100 meter
  • Less product damage
  • Multiple entry points are possible
  • Less chance of segregation
  • Lower maximum distance

Calculation of pneumatic transport

When conveying product particles by means of gas, the gas has a certain speed. Contrary to what men would initially expect, the speed of the particles is not equal to the speed of the gas. Because the particles experience friction in the air flow, as a result of gravity and collide with the walls of pipes, they will have a lower speed than the speed of the air flow. The difference in speed is called the slip factor. To calculate the slip factor you can use this formula shown here.

$F_{slip}\ =\frac{V_{lucht}}{V_{deeltje}}$
$F_{slip}\ =\ slipfactor$
$V_{lucht}\ =\ luchtsnelheid\ in\ het\ leidingwerk\ \left(m/sec\right) $
$V_{deeltje}\ =\ deeltjessnelheid\ in\ het\ leidingwerk\ \left(m/sec\right)$
Juul Jenneskens

Name: Juul Jenneskens
Advisor

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