Going for gold: water hydraulic drilling

UK-developed hydraulic drilling technology could be vital for the future of South Africa’s mining industry. Stephen Harris reports

Power stations are everywhere in South Africa’s Mpumalanga region. Cooling towers are dotted across the horizon and huge trains delivering truck after truck of coal make their way across the plains. The area’s vast coal deposits provided the country with ultra-low-cost electricity for years – something its mining industry took great advantage of as it maintained the title of largest gold producer in the world.

Then, four years ago, crisis struck. Failure to build enough new power stations to keep up with demand led to countrywide rolling blackouts. The mining industry was asked to cut its energy usage by 10 per cent just as China knocked South Africa off the top spot for gold production for the first time in more than 100 years. Although the blackouts only lasted a few months, power stations are still under strain and prices are soaring – hitting the gold-mining sector particularly hard.

But two Scottish engineers think they may have a solution that could halt the decline of South Africa’s gold mines. For more than 20 years, Douglas Barrows and his son Alan have been working on technology to vastly reduce the amount of electricity and water consumed during mining, lowering its environmental impact while increasing productivity. Now, their company, Peterstow Aquapower, has opened a factory in South Africa’s tiny neighbour, Swaziland, to deliver their concept to the world.

’This technology will cut the cost of mining by a significant amount, making it very much more safe and very much more ecologically friendly,’ said Douglas, chairman of Peterstow and a determined engineer who began working on the idea in 1985.

The basis for these bold claims is the use of closed-loop water hydraulics, where continuously recycled high-pressure water transfers power to a drill instead of the much more inefficient medium of compressed air. It does this with components that fit together so precisely they do not need oil to lubricate them and so can operate on water alone.

With the specialised drill, water and air do not need to be pumped continuously down to the mine and back to the surface, saving electricity. ’Compressed air is probably the most inefficient use of energy I’ve ever come across,’ said Douglas. ’The very act of compressing air is only about eight per cent mechanically efficient to begin with – the other 90-odd per cent of the energy primarily manifests itself as heat.’

Conventionally, a giant energy-intensive compressor pressurises the air and pipes from the surface to the mine face. It is cooled along the way with chilled water that also has to be transported down, while more water is sprayed around the mine to further lower the temperature, before it is all pumped back up.

Following a few months of blackouts in South Africa, power stations are under strain and prices are soaring

Peterstow replaces this extensive network of pipes and pumps with a self-contained drill and a power pack about the size of a small fridge. Although other water hydraulic drills do exist, they require their own constant supply of high-pressure water brought from the surface and expelled into the mine. Peterstow’s drill, on the other hand, has a built-in pressurising system and the water travels only around 30m in a constant loop.

This technology could cut total energy usage by as much as a third, according to mining industry veteran Ian Cockerill, an adviser to Peterstow and executive chairman of South African mining company Petmin.

’You’re using less than one per cent of the energy that goes into a compressor to get the same result out of the Peterstow drill,’ he said. ’And it’s all to do with the efficiency of the generation and utilisation of energy. The application of a force to water gets much more efficiently transmitted than through air.’

On top of the energy saving, the system uses just two tonnes of water for every tonne of ore mined, as opposed to the five or six associated with existing technology. Water found naturally in the mine is used to cool the surroundings and the drill head, and to remove the rock from the drill hole. The water in the drill is constantly filtered and reused.

This also makes things better for the miners; instead of a blast of dust and hot air infused with lubricating oil, all that emerges from the drill hole is a flow of slurry. No oil means no pollutants are getting into the rock or water. Plus it reduces the ear-splitting noise of conventional drills.

In the 1980s, when Douglas first began working on his idea, the technology to make it a reality did not exist. He had to develop each individual part, working closely with his production engineer son Alan and Danish company Danfoss, which held patents on water hydraulics that originated at the former National Engineering Laboratory in Scotland.

’The key to water hydraulics is the right combination of materials and their interaction, coupled with precision engineering,’ said Alan, Peterstow’s executive director, who oversees the Swaziland factory. The firm uses aluminium, steel, ceramics and various coatings to create components that slide past each other using water instead of oil as lubrication. As water is so runny, parts have to be manufactured to between two and five microns for maximum efficiency.

“Compressed air is probably the most inefficient use of energy I’ve ever come across.”

Douglas Barrows, Peterstow Aquapower

Peterstow’s other major development is the closed-loop system, where water is pressurised inside the drill instead of by gravity as it is piped from the surface. As water enters the drill, it compresses nitrogen gas held behind a rubber diaphragm. When the gas can no longer be compressed, the water is fired at high pressure down the drill to power a piston and rotary motor. This happens around 1,900 times per minute, with the water recycled through the rest of the system at normal pressure.

Almost 80 per cent of the manufacturing process takes place at the £6.5m plant in Ngwenya, Swaziland, which provides easy access to South Africa’s gold-mining region, while creating jobs in one of the world’s poorest countries. Since becoming fully operational 12 months ago, Peterstow has supplied drills to mines in Uganda and Norway, with the biggest number going to Germany for use under water in repairing port facilities.

But the most obvious market remains South Africa, which still has around 50 per cent of the world’s gold reserves. As well as tackling the energy problem, Peterstow’s system works 10 times faster than conventional equipment.

Cockerill thinks this could be enough to arrest South Africa’s gold-mining decline. ’Because this is much more productive, it means your unit cost of production is going to be less, and that means you can start looking at mining areas that previously were marginal.’

Although the drill itself is more expensive, the company said that, without the need for an air compressor or a network of underground pipes, it could cut the capital costs of equipping a new mine by up to 60 per cent. And with mines set to increase from a maximum depth of around 3.2km to more than 5km, such savings could be vital for the future of the industry.

the data
know the drill

The specialised equipment improves the energy efficiency of gold mining

Vital statistics

  • Weight: 29kg
  • Water flow: 36 litres per minute at 110bar pressure
  • Energy consumption: 9kw/hr (drill and rig)
  • Blow frequency : 1,950 blows per minute

For every 1,000 drills, a mine could:

  • Reduce monthly power usage from 6,000,000kWh to just 45,000kWh (based on a six-hour daily operating cycle)
  • Cut annual water usage by more than 20 million tons
  • Reduce capital costs to around $18,500,000 compared with $40,170,000 for the equivalent in pneumatic drills and necessary infrastructure