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Friday, September 15, 2017

Airslides provide some of the most efficient and practical methods of conveying bulk powder material. All we need is some low pressure air, an aeration bed and a small incline (gravity) and we can convey hundreds of tonnes of products over long distances.

Airslides are used extensively in conveying homogenous dry powder in many industries including   minerals and mining where it is used in cement, lime and flyash. The Food industry use airslides on flour and many powders in the chemical industry are ideally suited to airslides.  

Airslides have no moving parts and are often a far better solution than using screw conveyors, drag chains and belt conveyors.

Knowing the basic air slide conveyor features

These are some of the basic features of an air slide conveyor system:
  • Typical airslide section width and height of the aeration bed dictates the conveying rate
  • Turning box (pots) are used to divert the flow from one direction to another.
  • The aeration cloth which is generally woven permeable polyester 
  • Fan or Blower to provide the aeration air through the aeration cloth
  • Weir plates that are used to adjust the depth of aeration bed.
  • Air control valves that can be used to adjust the amount of aeration air being used.
  • Inspection ports that provide access to visually inspect inside the airslide section.
  • Dust collection vents to remove the spent air that is expended from the product during the conveying.
  • A typical airslide installation in a cement depot will convey material from a silo discharge some distance where it finally discharges cement via a loading chute into a cement tanker.
  • Pneuvay airslides unlike many other suppliers install a perforated metal support sheet under the aeration cloth which provides stability and less movement of the fabric while conveying which will extend the life of the cloth.

Sample air slide conveyor system
This is an example of an air slide conveyor system

How does an airslide system work?

On a permanent equilibrium, the angle of repose of bulk materials naturally achieves a constant slope from the horizontal plane as shown in the figure below. 

Angle of repose of bulk materials
Angle of repose of bulk materials

To properly allow the transported material to flow, it was necessary to draw conveyor systems with a slope greater than the angle of repose of the material. However, these has resulted to more complications. Thus the invention of fluidised conveying systems otherwise known as air slide systems or air gravity conveyors. 

How to make the airslide system work?

Air slide systems use a technique that maintains the aerated condition of a the bulk material as shown and explained in this video below:

This is implemented from the time this is introduced into the upper end of the channel to the point where it is unloaded. 

How is this possible?

The air slide is a metal box divided into 2 parts:
  The upper part where the fluidized powder material is located
  The lower part where the air is at a pressure between 250 and 500 mmH2O
A porous fabric membrane is located between the two parts of the housing.

Parts of an air slide conveyor metal box
Parts of an air slide conveyor metal box

The air thus passes through a false bottom, or a membrane made of a suitable porous material (polyester), which extends over the entire length of the air slide as shown in the illustration below:

Material flow inside an air slide conveyor system

Operating principle behind the airslide system

The principle of operation behind an airslide system is illustrated below:
The fluidizing air, after passage through the bed of material sliding over the membrane, flows on top of the bed of material and is discharged through a suitable filtration unit.
Since the material is maintained by means of the regular air flow, it flows freely down the slope, even when the inclination angle is relatively small.

The amount of air used is kept to the minimum necessary to reduce the interparticle force and the frictional forces between particles and surfaces of the inner channels, sufficient to allow the flow of material.

How are the dimensions of an airslide system calculated?

An airslide system dimensions include:
  • Width
  • Length
  • Angle of inclination

These are calculated as follow:
The width of an airslide system is calculated based on the capacity and the material density of the powder transported. 

The angle of inclination may vary depending on the type of material being conveyed. It is based on the principle that the more fluid the material is, the lesser the air slide is needed to be inclined.

As for the length of the air slide system, there is no limitation to it. 

Air slide systems: The preferred choice of industries

Air slide system is the preferred choice of many businesses because it is:
  • Reliable
  • Relatively economical
  • Very promising substantial development potential  

This makes it an ideal choice for the following applications:
  • Distribution from bucket elevators to storage silos
  • Gathering under baghouses / precipitators
  • Feed to process
  • Feed to other conveyors
  • Loadout from bulk silos to trucks, railcars or barges
  • In-plant conveying
  • Storage silo / bin withdrawal

How to find the perfect airslide system for your company needs?

The design and installation of air slide systems can be complicated. It requires meticulous and exact calculations. Thus the need for a pneumatic conveying company with years of experience that can deliver the results you wanted.

Below are links to some of the projects we have completed through the years:

Queensland Alumina Ltd

This project included a complete airslide AS500 package for Queensland Alumina Ltd project, all of which were manufactured in Melbourne. Read more.

Queensland Alumina Air Slide Conveyor System Project
Queensland Alumina Air Slide Conveyor System Project

Blue Circle Southern Cement 

Pneuvay supplied Blue Circle Southern Cement (BCSC) a complete set of AS400 and AS300 airslides for their Waurn Ponds Cement Mill for a more efficient power consumption for the company. Read more.

Blue Circle Southern Cement Air Slide Conveyor System Project
Blue Circle Southern Cement Air Slide Conveyor System Project

Do you need help conveying bulk materials like cement, asphalt and grains? We design, manufacture and install air slide systems. Talk to us, today.

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