You will find some of the CVD's most commonly asked questions below. If you find your question is not answered, please complete the CVD RFI form and one of Knelons CVD technicians will contact you.

1. What is the difference between a batch machine and a CVD?
   • Answer: There are in fact more similarities than differences. Both machines have fluidized rings that allow heavy metals or minerals to be recovered under the influence of enhanced gravitational force. The main difference is the way the concentrate is removed from the fluidized rings. The batch machine goes off line periodically to allow the concentrate to be flushed, while the CVD ejects concentrate every few seconds through pinch valves located at the base of the rings.
   • Learn more on the differences of the batch and continuous concentrators and view the movie online of how they both work.

    

2. I keep hearing the term "mass yield" when a CVD application is discussed. What does this mean?
   • Answer: Mass yield is quite simply the amount of concentrate expressed as the % of feed to the machine. For example, a mass yield of 20%, on a 100 ton per hour machine, means that 20 tons per hour goes to concentrate.
   • Example:

    

3. What applications would be most suitable for the CVD as compared to the batch machine?
   • Answer: Potential applications include...
     • Tantalite
     • Cassiterite
     • Ilmenite/Rutile
     • Fine iron
     • Chromite recovery
     • Gold sulphides
     • Ferroalloy (alloy from slag)
     • Pre-concentration of mineral sands
     • Pre-concentration and de-sliming of heavy minerals

      

4. The specification sheets on the CVD show the tonnage ratings as application specific, yet the batch machines have tonnage ratings, why is that?
   • Answer: There are three factors to consider here, tonnage rating, volumetric rating, and metallurgical result.

     Both the batch machines and the CVD have a tonnage and a volumetric rating. Generally you will reach the tonnage ratings ahead of the volumetric rating if your feeding the machine high percent (%) solids. The reverse is true for low solids applications.

     When the batch machines tonnage is rated, it's generally assumed the batch concentrator will be used in a gold or PGM application on cyclone underflow or mill discharge, and that these streams are in the 55-75% solids range. It's rare batch machines are in low solids applications, thus applying a tonnage rating to them that covers 99% of the operating machines is not misleading.
     The CVD has a much wider range of applications, and may just as easily be installed in a flotation concentrate stream, with perhaps 15 or 20% solids, thus it may reach the volumetric rating long before the tonnage rating, so for that specific application, the tonnage rating may be less than the "nominal" rating.

   Another factor to consider is the metallurgical result desired. As feed rate goes up, at some point either batch or continuous concentrators will reach a point where metallurgical recovery will be traded off with increased feed rate. Within a circulating load, it's less important to obtain high unit recoveries, in fact independent testwork, as well as mathematical modeling and in plant studies have shown a metallurgical benefit by maximizing the feed to a Knelson Concentrator within a re-circulating load, even at the expense of per pass recovery. If either machine is in single pass rather than within a circulating load, then it's desired to maximize the per pass recovery so the overall best metallurgical result may be at a lower tonnage rating.

   Since batch machine applications are overwhelmingly in high solids applications within circulating loads, Knelson can comfortably apply a tonnage rating that cover almost all of the operating machines. The CVD wide variety of applications in streams of vastly varying densities, it's preferred to give clients case-by-case expectations.

5. How long have CVD machines been in operation?
   • Answer: Commercial CVD concentrators have been operating since June 2000. This was originally the prototype machine that was replaced by an updated version in December 2000.

    

6. What are the typical maintenance costs of the CVD?
   • Answer: Commercial CVD history has shown in general, parts costs such as bearings, drive belts, wear cones, etc., are expected to be the same or less as the Knelson batch series concentrators. A 1997 batch concentrator survey showed the Knelson average operational spare parts cost per tonne was $0.0045 and an average abrasion spare parts cost per tonne of $0.0029. These results are excellent considering the batch series operate in very high solids environments with the presence of coarse material while most CVD applications are of much lighter duty.

     The only additional costs expected with the CVD over the batch machines are the periodic replacement of pinch valve sleeves.. Overall, costs in the $0.012 per tonne are likely typical for the Continuous Variable Discharge concentrator.

      7.    How do find out if the CVD concentrator is applicable for my requirements?

• Answer: Complete the CVD RFI form and one of Knelson's CVD technicians will contact you. 
  
  
   

      8.    What are the minimum requirements for the CVD Knelson Concentrators?

• Answer: Details about Knelson Concentrator Air Requirements can be found here.

Did you not find the answer to your question? Send your question to Knelson to have a representative contact you with your answer.