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      Separators in the cement industry              
      4   Dynamic separators:                
          - Dynamic separators are  classified in three categories (*), the first, second and third generation.    
          - In first generation separators, the air flow is generated by a fan within the body of the classifier.    
          - In second generation, the air flow is generated by an external fan and there are cyclones.      
          - And finally, the third generation has a rotating cage which replace the counterblades.      
            (*) We are waiting a fourth generation              
          - Comparison of efficiencies:              
                          Click on the picture to enlarge
      5   First generation separators:              
      5.1   Introduction:                  
          - Also called: Turbo separators or conventional separators.          
          - The material to be classified is dispersed in the area where the separation is created by a distribution plate.  
          - The air flow required for the separation is produced by a fan located inside the separator itself.    
          - The separator material feed is carried out mechanically by means of suitable continuous conveyors.    
          - Separators can have one or two motors, gear reducers and shaft (one for the main fan and the second one  
            for the distribution plate and the conterblades).            
          - Here a non-exhaustive list of conventional separators:           
            - Heyd (Ch.Pfeiffer)              
            - Sturtevant Whirwind Air Classifier            
            - Turbopol (Polysius)              
            - Schmidt                
            - Raymond                
            - Escher Wyss                
            - CV (F.L.Smidth)              
            - Hischmann                
          - These separators are used for both raw material and cement.          
      5.2   Advantages of 1st generation dynamic separators:            
          - Possibility of mechanical adjustments              
          - Possibility of very large flow rates              
          - Flexibility to produce products of different qualities          
      5.3   Disadvantages of 1st generation dynamic separators:            
          - Bad efficiency especially with high circulating loads due to: poor distribution of the material in the cross section,  
            poor dispersion of the material in the separating air and large quantities of fine material are recirculated in the air,  
            increasing the amount of fines coming with the tails.          
          - No (or little) possibility of cooling or drying the material       
      5.4   Principle of operation:                
          - The main fan produces a stream of air circulating within the separator.        
          - The fan blades pull air from inside the inner cone and push it into the outer cone.      
          - The material is generally fed on the top of the separator (in some cases, it is laterally).      
          - The feed material falls over the dispersion plate, which gives sufficient centrifugal force to the particles to arrive  
             in the separation zone.                
          - Radial slats welded on the distribution plate prevent the displacement of the material which must be separated.  
          - The air with dispersed particles flows up and passes the rotating counterblades.      
          - The separation is mainly realized by two forces: the centrifugal force and the drag force. The drag force produced by the
            airflow on a particle is proportional to the cross-sectional area of the particle, on the other hand the centrifugal force
            is proportional to the mass (volume) of the particle.          
          - Coarse particles are centrifuged and hits the inner wall of the separator. After hitting the wall the coarse fraction gets
             collected into cone.                
          - As a certain number of fines particles are entrained downwards with coarse particles, the air flow returning to the separating
            area has a second chance to pick up any fines in the rejects.          
          - The air with fines flows through the fan to the fines chamber. From there, the fine particles are separated from the  
            conveying air and collected in the outer cone.            
          - The air  with some amount of fine material is going back to the separating zone through the air vanes.    
          - Separators can also have some air inlet and outlet for cooling or drying purposes.      
          - See the figure below:                
            Click on the picture to enlarge        
      5.5   Possibilities of adjustments:              
          Main adjustments:                
          - Control valves: Adjustment of the control valves modifies the opening area for the air to go in the main fan area.  
            When this opening area is reduced, the fineness is increasing (for example Sturtevant)      
          - Position of the counterblades: If the position is closer of the inner body, the opening area for the air to go  
            in the main area will be reduced and the fineness will increase (for example Schmidt).      
          - Counterblades and distribution plate rotation: In some cases where there are 2 motors and two shafts, it is possible  
            to modify the speed of rotation of the counterblades and the distribution plate. If the speed of rotation increase,  
            the fineness increases (for example Heyd).            
          Other possible adjustments:              
          - To increase the main fan speed.              
          - To remove counterblades.              
          - To increase the distribution plate diameter.            
          - To decrease the distance between the distribution plate and the counterblades.      
          Summary of the adjustments and consequences:            
      5.6   Parameter of dimensioning:              
          - The parameter widely accepted is the specific separator load:          
            The values depend from a supplier to an other one:          
      5.7   Different designs:                
          - Turbopol:                  
          - Heyd:                  
          - Sturtevant:                  
          - Raymond:                  
      5.8   First generation separators data sheet:              
          - The data sheet allows to have a good idea of the first generation separators efficiency.      
          - The different data are explained herebelow:            
                    Click on the picture to enlarge      
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