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      Pre-grinding systems        
                   
      3   Roller Press (suite 5)        
         3.11 Elements of sizing considerations (suite):        
         3.11.4 Specific power of the press        
        - The specific power is always in kWh/t.        
        - It is this parameter which is important when we want to make energy savings.    
        - One first defines the specific power corresponding to the total flow which passes through the press.
        - The formula is as follows:        
         
     
           
                 
                 
          With:        
          Q is the specific power relative to the flow passing through the press in kWh/t    
          P is the power consumption of the press in kW      
          T is the flow rate passing through the press (throughput) in t/h      
        - The usual values generally accepted for Q are:      
         
     
           
                 
                 
                 
                 
        - The specific power is then defined, corresponding to the output of the system.    
        - The real output equals the fresh feed that enters in the circuit and also equals the finished product coming out
          of the circuit.        
        - The formula is as follows:        
         
     
           
                 
                 
          With:        
          QU is the specific power corresponding to the output of the installation in kWh/t    
          P is the power consumption of the press in kW      
          T is the throughput of the press in t/h        
          c is the circulation factor        
        - Example of calculation:        
          * Output U = 160 t/h        
          * Circulation factor c = 2,5        
          * Absorbed power P = 1058 kW        
          Calculation and result:        
          * Output T = 160.2,5 = 400 t/h        
         
     
           
                 
                 
         
     
           
                 
                 
         3.12 Main dimensions of the roller press:        
        - All the informations here below were collected in the technical brochures of the suppliers and are available on Internet.
        - Ratio roller width / diameter of the roller:        
         
     
           
                 
                 
                 
                 
        - Diameter of the rollers:        
         
     
           
                 
                 
                 
                 
        - Width of the rollers:        
         
     
           
                 
                 
                 
                 
        - Installed power:        
         
     
           
                 
                 
                 
                 
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         3.13 Determine the increase of production:        
        - From experience, we know that for 1 kWh / t spent by the roller press, we made a saving of 2 kWh/t to the ball mill.
        - The above assumption can be a basis for calculating the increase in production possible.  
        - One can also use the diagram here below which gives the production increase in % according the specific power
          of the roller press:        
         
     
     
           
           
           
           
           
           
           
           
           
           
           
           
           
           
        - This diagram is only for a RP in open circuit and a RP with recirculation of cakes.    
        - Generally speaking, possible production increases are shown in the table here below:  
         
     
         
               
               
               
               
               
               
        - The increase of production therefore depends:      
          * The client's wishes        
          * The current situation        
          * The proposed system        
          * The type of material to grind        
        - Roller press suppliers have of course laboratory equipments for performing the necessary tests to size and give
          guarantees of increase.        
        - In our opinion, these tests are the reference and them alone!      
         3.14 Comparison of the situations before / after modification:      
        - When we want to compare the results before and after installation of a roller press, we must realize a sheet
          like the one (example) here below:        
         
     
           
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
        - This comparison clearly shows the gain in production and energy savings.    
        - Another table shows the gains concerning the quality of cement, see example here below:  
         
     
     
           
           
           
           
           
           
           
           
           
           
           
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