ECONOMICS OF ROTARY VS. DTH DRILLING
Research output: Thesis › Master's Thesis (University Course)
Surface Mining is a common way to extract valuable minerals from the earth. An important process for surface mining is the drilling and blasting. There are 3 types of bench holes including spilt-hole and buffer-hole for wall control and blasthole for production. There are 3 main bench drilling methods including Top Hammer (TH), Down The Hole (DTH) and rotary drilling. Both TH and DTH belong to the percussive drilling methods. Rotary is using a high pulldown weight on the rotary bit to crush the rock. TH is typically for small diameter hole drilling, DTH is for medium range hole sizes, and rotary can drill medium to large diameter blastholes. For the medium range hole sizes, there is an overlap between rotary and DTH application. This report is comparing the economics of these two drilling methods. DTH is using high pressure air to drive the percussive hammer striking the bit, thus the compressed air is the key factor affecting the drilling performance. The new technology for hammer drilling is that the machine can deliver high air pressure (34 bar) and the tools can handle it. Rotary is using constant high pulldown weight and high rotary torque on bit, thus the pulldown is the key factor affecting the drilling performance. The larger drills can provide more than 30 tons (135,000 pounds) pulldown weight, and the sealed bearing bit can handle higher weight on bit than an air bearing bit. Rotary drills require a heavier machine weight compared to DTH drills. The weight adds cost, but also extends service life of the machine. The major drill suppliers are developing the medium range drills which combining rotary and DTH application. The drills are equipped with a switched compressor which can deliver high air pressure and low volume for DTH application and low pressure and high volume for rotary application. The common application for DTH is at the rock hardness (uniaxial compressive strength) between 80 and 350 MPa and hole sizes between 112 mm and 229 mm. The common application range for rotary is at the rock hardness (uniaxial compressive strength) between 10 and 500 MPa and hole sizes between 171 mm and 406 mm. Rotary bits get higher bit life than hammer bit on all rock type applications. Rotary achieves high rate of penetration (ROP) on the soft formation. DTH achieves higher ROP on the medium to hard rock formations. Rotary is offering lower total drilling cost per bank cubic meters (BCM) by rock hardness based on the mines surveyed in this report. The drilling cost is getting higher for both rotary and DTH drilling when the rock is getting harder and more difficult to drill, which will consume more tools and energy. The total drilling cost per BCM is decreasing for both rotary and DTH when the blasthole size gets larger. Because the larger blasthole will have loose drilling pattern (big burden and space) which means less drilling meters are required for the same amount volume of rock moving. The scenario of economic of drilling method comparison between DTH with 203 mm hole size and Rotary with 406 mm hole size for the same volume of material drilling on the hard rock application, suggests that fewer of rotary drills are required than DTH. The start-up cost for rotary is higher than DTH because large rotary drills are more expensive, but in return, the total drilling cost is less than DTH for the same volume of BCM drilling.
|Translated title of the contribution||ECONOMICS OF ROTARY VS. DTH DRILLING|
|Publication status||Published - 2015|