• Why needs reverse circulation drilling?
    • When drilling the hole of diameter >250mm, which the annular area between the drill pipe and inner surface of borehole is very big.
    • If using direct circulation drilling method, it needs very powerful compressor with high air flow(even 2 – 3 compressors) to get enough flushing speed to below all the cuttings out of hole.
    • Otherwise, the cutting will stay in the hole and stuck the drilling. Therefore it can make hole drilling very costly. In this case, the reverse circulation drilling(RC drilling) will be the better choice.
  • Hardrok DTH Reverse Circulation Principle
    • It is opposite from DTH direct circulation drilling method.
    • Air go to hammer via the annular area between outer pipe and inner pipe and take the cuttings out of hole through the area of inner pipe.
    • Due to the smaller annular area and inner pipe area for air go through, it can get very high flushing speed with low air flow from compressor.
    • In this way, it can save cost for drilling
Hardrock RC Drilling System
  • Example of reverse circulation compared and DTH direct circulation method
    • By DC Drilling:
    • Hole Size: 300 mm
    • Drill Pipe Dia. 114 mm
    • Annular area between pipe and wall: 0.06 m2
    • Needed flushing speed: 20 m/s
    • Needed air flow: 72 m3/min.
    • Conclusion: it need 2 air compressors and each one with 36 m3/min air flow
    • By RC Drilling
    • Hole Size: 300 mm
    • Dual drill Pipe Outer Dia. 114 mm
    • Dual drill Pipe Inner Diameter: 60 mm
    • Annular Area between inner and out wall of Dual pipe: 0.00324 m2
    • Needed flushing speed: 20 m/s
    • Needed flushing speed: 20 m/s
    • Needed air flow: 4 m3/min
  • Conclusion: it only need 1 air compressors with 4 m3/min air flow is good enough
  • From above calculation, we can see that by RC drilling it needs much lower air flow and can save the cost for compressor. This is reason why Reverse Circulation is widely used in borehole drilling industry
  • Hardrock Drills Reverse Circulation Accessories
    • RC Drilling Rig
    • Air Compressor
    • Air Inlet Swivel
    • Dual Wall Pipe
    • Special RC Connector
    • RC Hammer
    • RC Hammer Bit
    • Cutting Collectors

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