One of the major energy demanding processes underground is the production drilling of blast holes. The Swedish mining company LKAB has made a major energy cost saving by replacing their air-powered drilling with water-powered drilling in their underground mines.
The conclusion for the energy part of the drilling process is very clear; Wassara is saving both energy and money. A lot of it.
Drilling underground
Keeping energy costs low is an essential part of sustainable mining. One of the major energy demanding processes underground is the production drilling of blast holes. This is particularly true when the boreholes are 30 m (100 ft.) or longer.
Powering Wassaras water-powered DTH hammer
Wassaras drilling technology uses high pressure water. To power a 4½” Down-The-Hole (DTH) Wassara hammer in LKAB, a high pressure pump is delivering water at 200 bar. The energy consumption for each high pressure pump in LKAB mines is merely 110 kWh. Pumping water is much more energy effective compared to compressing air as water cannot be compressed.
Powering an air-powered DTH hammer
Traditional DTH requires compressed air to operate. In underground mining with 4½” blast holes, a booster compressor, normally at 20 bar, is required. A typical energy consumption for one is 240 kWh. This is more than double the energy demand of a Wassara DTH hammer!
The lower energy consumption described above is actually just a small part of the total energy savings that drilling with Wassara DTH enables. The comparison above is between the booster compressor and the high pressure pump, but the picture is a bit more complex.
Multiplying the cost savings
Air-powered drilling requires compressors that delivers the compressed air to the booster compressor. As for LKAB, it was not possible to install power cables of the appropriate size to run a large compressor down in the mine. Hence, the first compressor (delivering 7 bar) was placed at surface and the compressed air was supplied through a piping network all the way to the booster compressor, placed close to the drill rig.
The estimated length of piping to the 1 000 m (3 340 ft.) level is well over 5 000 m (16840 ft.), from surface to the drill rig. That is 5 km (3.1 miles) of piping with joints, bends and some small leaking points here and there. All together it gave a massive pressure loss before the compressed air finally reached the booster compressor.
A very moderate assumption indicates that the first compressor needs to be as large as the booster compressors combined, in order to deliver the compressed air at 7 bar to each of the booster compressors. This shows that the comparison between air-powered and water-powered drilling is as high as 2 × 240 = 480 kW, compared to 110 kW for the high-pressure water pump.
This indicates that the energy demand of an air-powered DTH drilling is 4.36 times higher than Wassaras DTH drilling. Depending on the state of the piping in the network for the compressed air, this factor may be multiplied even further.
More factors
In this case we are assuming that air-powered and water-powered drilling is equally fast. The largest speed factor is the drilling direction (upwards, downwards, horizontal). Another factor is the cost for water, and in what degree the water can be recirculated in the mine. All these factors are unique for each mine and are not easily compared.
One example from real life
It becomes obvious that the difference in energy consumption between an air-powered DTH and Wassara is severe. The Swedish mining company LKAB implemented the water-powered drilling in their two underground mines, Kiruna and Malmberget, back in 1995. Today LKAB have a total of 18 drill rigs that is constantly drilling with the Wassara DTH hammer.
| Number of drill rigs in LKAB | Kiruna | Malmberget |
| Sandvik DL 520 W | 8 rigs | |
| Atlas Copco WL6C | 3 rigs | 7 rigs |
Every day, the drill rigs operate with full pressure (200 bar) for about 12 hours. The rigs have maintenance stops scheduled 8 hours every second week and 5 extra days yearly. If we calculate 18 rigs × 12 hours × 365 days minus (18 rigs × 8 hours × 26 days + (18 rigs × 12 hours × 5 days)), we will get 74 016 operating hours, at full pressure, for a year.
The difference in energy consumption per year
By using the Wassara hammer, LKAB is lowering the energy consumption from the drilling process alone with 27 385 920 kWh per year. The average energy consumption for a modern European household is 10 000 kWh. In other words, the energy savings every year in LKAB just from the drilling process alone equals the energy consumptions for 2 738 households for an entire year.
With a current cost of €25 / MWh, the lower energy consumption is lowering
the costs with € 684 648 / year.
LKAB have used Wassara for their production drilling during the last 20 years. The life of mine of these mines are well over 100 years. By looking at the coming 30 years alone, LKAB will save 821 577 MWh from the drilling process alone. This equals an energy cost saving of € 20 539 440, or the energy consumption for a city with 82 158 households for a whole year.
Energy consumption for the coming 30 years
The conclusion for the energy part of the drilling process is very clear; Wassara is saving both energy and money. A lot of it.