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      Cement Mill Circuit Sampling Points and Procedure (Part 1)  
      1. Introduction  
        - Periodic sampling campaigns in a ball mill grinding circuit are essential in order:  
          * to follow the installation in terms of fineness and mass balances  
          * to find existing problems and solve them  
          * to improve the performance of the installation.  
          * to reach the desired cement quality  
        - Schedule a sampling campaign every 3 months.  
      2. Before the sampling campaign  
        - The grinding circuit must be in steady condition at least 2-3 hours before the beginning of the sampling campaign.
        - All the production data must be taken just before the beginning of the sampling campaign.  
        - These data vary from an installation to the other one but basically, we need at least:  
          * Type of cement produced  
          * Production (t/h)  
          * Composition  
          * Fineness target and production target (residue and Blaine)  
          * Last fineness data (residue and Blaine)  
          * Separator tails flow rate (t/h) if existing  
          * Cement temperature at mill outlet  
          * Water injection quantity if existing  
          * Grinding aid quantity if existing  
          * Absorbed power of the ball mill and other main equipments (for the mill, take the absorbed power directly  in the electrical room,
          it is more reliable)  
          * Other data like fans dampers position, pressure at mill outlet, separator speed...etc  
      3. Equipment and tools required  
        - Big bags for the fresh feed samples (clinker, gypsum, limestone...), for example 50kg cement bags is a good option.
        - A shovel to take the fresh feed samples on weighfeeders.  
        - Smallest bags for the separator, filter, product samples.  
        - These bags must be resistant to high temperature (up to 140°C).  
        - Scoop(s) to take circuit samples.  
        - Regarding the circuit samples, the way to collect the sample may be different from an installation to an other.
        - Generally, we have the following items:  
          * Mill outlet: airslide or sampling point  
          * Separator feed: airslide or sampling point  
          * Separator rejects: airslide, sampling point or impact flowmeter opening  
          * Separator fines: airslide or sampling point (cyclones)  
          * Filters product: inside screw sampling point  
        - Various kinds of scoops are existing.  
        - Maybe a special handmade scoop is necessary.  
        - Examples of scoops:  
        - Before the sampling, it is better to check if the sample location has some segregation such as from an air slide!
      4. Example for a classical ball mill circuit  
        - Flow-sheet below:  
        - List of sampling points:  
          1. Clinker sample (*)  
          2. Gypsum sample (*)  
          3. Limestone sample (*)  
          4. Other sample (*)  
          5. Mill outlet  
          6. Static tails sample  
          7. Feed separator sample  
          8. Tails separator sample  
          9. Fines separator sample (**)  
          10. Separator filter sample  
          11. Mill filter sample (***)  
          12. Finished product  
          (*) The sample is generally taken on the feed belt conveyor. It must be taken over the entire width of the belt   
          in order to have a representative sample (preferably just after a crash stop).  
          (**) If there are cyclones, some people take a sample for every cyclone in order to realize a mass balance.   
          (***) Warning: in some cases, the sample must be taken in an endless screw box conveyor. It is dangerous!  
    All rights reserved © 2012-2016 The Cement Grinding Office