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      Separators in the cement industry              
      6   Second generation separators:              
      6.1   Introduction:                  
          - Also called: Cyclones separators.              
          - As the 1st generation, 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 an external fan.        
          - The separator material feed is carried out mechanically by means of suitable continuous conveyors.    
          - Fines are conveyed in external cyclones.            
          - Fresh air entry and air exit to filter.              
          - The fan that moves the air is a more efficient design and has a considerably reduced dust loading.    
          - These separators have a better separation efficiency due to the external fan and the cyclones.    
          - Comparison between cyclones and conventional separators:          
            The diagram here below shows the specific surface (Blaine) produced        
            in order to achieve a certain percentage of residue on 30µm (From Duda Cement Data Book).    
          - For example, to get 20% residue on 30µm, a turbo separator needs to produce a cement at 3200-3900 Blaine and a  
            separator with cyclones 3000-3600 Blaine.            
            Click on the picture to enlarge  
          - Here a non-exhaustive list of cyclones separators:             
            - Wedag ZUB (KHD)              
            - Cyclopol (Polysius)              
            - SKET (ZAB Co.)              
            - FCB cyclones              
            - Other copies from former Eastern Europe          
      6.2   Advantages of 2nd generation dynamic separators:            
          - Possibility of mechanical adjustments              
          - Possibility of very large flow rates              
          - Flexibility to produce products of different qualities          
          - Better efficiency than the conventional separators             
          - Less power consumption                
          - Reduced wear on the separator internals (especially the fan)          
      6.3   Disadvantages of 2nd generation dynamic separators:            
          - More space needed                
          - Less efficient than cage separators         
      6.4   Principle of operation:                
          - The material is fed at the top of the separator.            
          - Material falls and is dispersed in the circulating air by the distribution plate.        
          - The air stream is generated by an external fan and recirculated. Possibly, there is a regulated fresh air inlet  
            in the part of the duct going to the separator.             
          - There is an exit where air is removed to a dedusting filter in order to maintain a constant underpressure  
            inside the system.                
          - The coarse material is separated by aspiration inside the main casing and goes out via the bottom conical device.  
          - 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 some amount of fine material is going back to the separating zone through the air vanes.    
          - The fine material exits by the top of the separator and the air flow enters into the cyclones through the gas pipe.   
          - The material is separated in the cyclones and exits through the bottom of these.      
          - The cleaned air (the dust content is generally less than 15 g/m³) is recirculated via the fan.      
          - It has been observed that the air flow speed in 2nd generation separators is in the order of 30% of the    
            air speed for conventional separators.              
          - See the figure below:                
            Click on the picture to enlarge  
      6.5   Possibilities of adjustments:              
          Main adjustments:                
          - Speed of counterblades                
          - Fan speed                  
          - Fan damper                  
          Other possible adjustments:              
          - To remove or increase the counterblades number            
          - To increase the distribution plate diameter            
          - To decrease the distance between the distribution plate and the counterblades      
          Summary of the adjustments and consequences:            
      6.6   Parameter of dimensioning:              
          - The Specific Separator load              
            The values depend from a supplier to an other one:          
      6.7   Different designs:                
          - Wedag ZUB (KHD):                
          - Cyclopol (Polysius):                
          - SKET (ZAB):                  
      6.8   Second generation separators data sheet:            
          - The data sheet allows to have a good idea of the second generation separators efficiency.      
          - The different data are explained herebelow:            
                    Click on the picture to enlarge      
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