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        Airslides
           
      1   Introduction
        - The air slides are a transport system well adapted to the powdered materials.
        - They are found in all sectors of a cement plant and particularly in a grinding installation,
          especially around the separator.
        - It is a reliable means of transportation, relatively economical and has a substantial development potential.
        - Here below a picture of an airslide:
         
     
           
      2   System History
        - The fluidized air transport system is a solution to the problems encountered with gravity transport systems.
        - Indeed, when we wanted to move the material from a point A to a point B, we faced the angle of repose of the
          material.
        - The angle of repose is the angle obtained when the material is in permanent equilibrium.
          That is to say, when the material naturally takes a constant slope from the horizontal plane.
          This is known as natural side slope, often noted Δ angle.
        - See the figure here below:
         
     
        - Materials angle of repose:
         
     
        - To solve the problem of flow, it was necessary to draw conveyors with a slope greater than the angle of repose
          of the material, which complicated the implementation.
        - It is for this reason that fluidized conveying systems were invented.
        - As seen in the table above, the angle of repose of cement has greatly decreased when aerated!
          This is illustrated here below:
         
     
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      3   Operating principle
        - The technique for making the transport is therefore essentially to maintain an aerated condition of the bulk material,
          from the time it is introduced into the upper end of the channel to the point where it is unloaded.
        - 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.
        - 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.
        - The principle of operation 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.
        - The requested amount of air remains very reasonable.
           
      4   Sizing elements
        - The technical literature on air slides is quite rare.
        - Very little information is available about the design of these systems.
        - An empirical formula for the width of the air slide is:
         
     
          With:
          l is width in mm
          P is the capacity t/h
          ρ is the material density in kg/m3
        - We do not find this formula very satisfactory.
        - The airslides suppliers usually give the dimensions (width, height) of the box according to the required
          capacity in volume (m3/h).
          We must therefore pay attention to the density to be considered when choosing.
        - The calculator of the website is based on data from a manufacturer.
        - Regarding the length, there is no limitation.
        - The inclination of airslides is between 2 and 13 depending on the type of material to be moved.
        - More the material is fluid and less the air slide needs to be inclined.
        - As already mentioned, the pressure in the chamber is between 250 and 500 mmH2O or mbar.
        - The amount of air needed varies between 2 and 3 m3/m2.h (we speak of the cross section of the box).
        - Here an example of a chart with dimensions offered by a manufacturer:
         
     
        - Manufacturers are testing on site to determine the operating parameters:
          * speed
          * Amount of air required
           
      5   Conclusion
        - Always request the opinion of the expert for sizing an airslide system!
           
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