ASTEC Double RAP Dryer

The Double RAP dryer separates the drying process from the mixing process, thereby providing a very reliable plant to be used for the purpose of recycling reclaimed asphalt pavement (RAP). The concept allows for RAP to be pre-conditioned through the external part of the Double RAP dryer, flashing off moisture in the drum, thus eliminating the problems associated with scavenger systems.

With a Double RAP dryer the virgin aggregate passes through the inner drum and the RAP and baghouse fines are introduced into the outer drum where it is mixed with the already-heated virgin aggregate. As the RAP's bitumen softens, the baghouse fines evenly coat the RAP. The bitumen is not added at this point. Instead, the aggregate, fines, and RAP mixture passes out of the Double RAP dryer and moves into a mixing chamber (which can either be a pugmill or rotary mixer). This is where the bitumen is added.

With the addition of the Green Pac™ option, the Double RAP dryer produces warm mix asphalt.

Advantages of the Double RAP dryer:

  • The plant can process HMA mixes with up to 40% RAP content while maintaining zero opacity at the stack.
  • The bitumen only enters at the mixing chamber, so virtually no build-up is produced in the dryer.
  • The hottest part of the drum is surrounded with the insulated mixing chamber, thereby providing the benefit of energy savings.
  • The producer has a choice of using either a rotary mixer (for large, abrasive aggregates) or a twin-shaft pugmill (which offers both compact size and efficient operation).


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