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      Mill Ventilation and Mill Fan Sizing      
      (only for cement mills)          
                 
      Date        
      Society/Cement plant
      Mill N°      
      Mill diameter m      
      Volume load % (of chamber 2 for mill with 2 compartments,  
      of chamber 3 if mill with 3 compartments)        
      Air velocity in the free section of the mill (above the ball charge):    
      Usual values in open circuit: between 0,8 and 1,2 m/sec      
      Usual values in closed circuit: between 1,2 and 1,5 m/sec      
      Air velocity
    m/sec (choose)    
      Mill output t/h      
      Cement temperature °C (at mill outlet)    
      Recommended temperature: 105°C        
      Air quantity m3/h (inside the mill)    
      Air quantity in Nm3/kg Nm3/kg (of cement)    
      Usual values: between 0,30 and 0,45 Nm3/kg        
      Other air velocities:          
      Air temperature °C (at mill inlet)      
      Inlet trunnion diameter m (taking the screw into account)  
      Mill inlet air velocity m/sec  
      Usual values: between 20 and 25 m/sec        
      Velocity in the intermediate (s) diaphragm (s)      
      (can be calculated with the drawings of the diaphragm)        
      Usual values: between 15 and 20 m/sec        
      Velocity in the outlet diaphragm        
      (can be calculated with the drawings of the diaphragm)        
      Usual values: between 15 and 20 m/sec        
      Outlet trunnion diameter m (in function of the outlet configuration)  
      Mill outlet air velocity m/sec  
      Usual values: between 20 and 25 m/sec        
      False air at mill outlet:          
      This value is directly proportional to the outlet configuration and condition  
      Usual values for mills with lateral drive(s): between 7,5 and 10%    
      Usual values for mills with central drive: between 15 and 20%      
      Usual values for mills with central discharge: between 30 and 40%    
      All these values are relevant for good condition mills      
      False air
    % (choose)      
      Total air quantity m3/h   at °C (cement T° - 3)  
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      Pressure drops in the circuit:        
      Mill pressure drop mmH2O      
      Usual values for small mills with diameter < 2,8m : between 120 and 160mmH2O  
      Usual values for medium mills with diameter from 3 to 3,8m : between 150 and 200mmH2O  
      Usual values for big mills with diameter > 4m : between 180 and 250mmH2O  
      For Monochamber mills, remove the pressure drop of 1 diaphragm, i.e ±60-75mmH2O  
      Other pressure drops in the circuit:        
      Static separator mmH2O      
      Usual value: ±100mmH2O          
      Cyclone mmH2O      
      Usual value: ±80mmH2O          
      Bag filter mmH2O      
      Usual value: ±150mmH2O          
      Electroprecipitator mmH2O      
      Usual value: ±40mmH2O          
      Dynamic pressure mmH2O      
      Usual value: ±20mmH2O          
      Ducts mmH2O      
      Usual value: ±80mmH2O          
      Total pressure drop mmH2O or Pa
                 
      Mill Fan Sizing          
      Reference temperature °C      
      Security coefficient
    (for the air quantity, choose)     
      New air quantity m3/h   at °C  
      Security coefficient
    (for the pressure drop, choose)    
      New pressure drop mmH2O or  Pa
      The majority of the fans in the cement industry are:  centrifugal fans backward  
      curved blades          
      Fan efficiency
    %      
      Fan power kW      
      Transmission loss
    %      
      Fan motor power kW or  HP
                 
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    All rights reserved © 2012-2016 The Cement Grinding Office