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A flexible dewatering solution

May 10, 2023

When a gold mine expansion in PNG proved challenging due to major water problems, Crusader Hose was instrumental in providing a solution.

Newcrest's Lihir gold mine is one of the largest gold mines in Papua New Guinea and, indeed, the world. It is expected to produce in excess of one million ounces over 10 years following the second half of 2024.

Upgrades and strategic planning have helped to maintain its projected output. However, the site's location, coupled with mother nature, hasn't always made it easy.

The open-pit mine is located within one of the island's large volcanic calderas and is adjacent to the Luise Harbour. Although the volcano is considered extinct, it remains geothermally active.

Resultant hydrothermal activity reaching up to 200°C, a high water table, the pooling of rainfall and regular seepage of seawater through the crater rim into the pit all contribute to major water issues. A strategic dewatering system was needed before expansion plans could continue.

The prime contractor for the project was a large pumping company from New South Wales. This known expert in designing mine dewatering systems was entrusted with devising a customised dewatering system that was safe and efficient.

The company elected to use submersible pumps in the pit as a means to extract the water. However, the complexity of the situation meant using fibreglass risers was an impossibility due to handling risks.

As a flexible riser was safer to use and better suited to the challenge, Crusader Hose's Flexibore became the system of choice.

The final design included a dewatering system that used three 350-kilowatt (kW) submersible bore pumps suspended from an eight-inch Flexibore hose inside an angled poly pipe casing.

Each pump was driven by a separate generator and connected to a platform, which cantilevered over the pit wall.

To construct the angled bore casing, 900mm diameter poly pipe sections were welded together to form an insulation sleeve, resting at an angle along the pit slope. The length of poly pipe into the pit was 175m, and the water level was bout 45m below the headworks. The bore casing was securely anchored from the headworks, which incorporated a concrete-padded, steel-framed platform, surrounded with safety rails.

Once the bore casing had been secured, the installation of the submersible pumps could commence. As gravity alone could not guarantee a successful installation, a sliding apparatus was devised to protect the pumps from possible damage and to maintain the cables’ integrity.

Each 350kW stainless steel submersible pump was skilfully mounted on a skate that could slide within the casing. These skates allowed the pumps to be lowered inside the poly pipe and acted as a centraliser.

The pumps were connected to the Flexibore risers, which suspended each pump under its own weight as it was lowered 175m into the pit.

Flexibore was chosen for the project because it has excellent tensile strength capabilities, allowing for easy installation of the pumps over a roller while clamped from a crane.

"The woven textile reinforcement of the PU-extruded hose acts like a lifting sling, allowing a high tensile load of up to 16 tonnes to be suspended from it," Crusader Hose managing director Francois Steverlynck said.

"The eight-inch Flexibore also has a burst pressure of 440m, which was well within the design pressure for the project. We know that bores are getting deeper, and the desired pressure capabilities must be maintained.

"Through vigorous research and development, we have also developed a stronger riser with a burst pressure of 700m and a tensile load of 30 tonnes. Our Flexibore flexible riser now has high burst pressures similar or equivalent to fibreglass."

With the submersible pumps safely lowered inside the poly pipe casing, they were then connected to the diesel generators via the power cables attached to the Flexibore hose. Settings and flow rates were controlled until each pump attained a flow rate of 168L per second.

Taranis Power of Western Australia supplied the CAT diesel generators.

Gabriel Hoascar, the engineer from Taranis who connected the pump cables and fired up the generators, said the application of Flexibore proved to be the perfect solution.

"As I realised, it's quite versatile," Hoascar said. "The hose is flexible and supplied in one continuous length. It's easier to handle than fibreglass.

"I was impressed at how efficiently the system worked. Our company will look to supply more systems using Flexibore hose, especially the new high-pressure version for deeper iron ore mines."

Crusader Hose has been manufacturing flexible layflat hose solutions for over 37 years.

"And we’ve been manufacturing and upgrading Flexibore for over 20 years. It's world-standard," Steverlynck said.

"We strongly support and encourage the mining industry to consider the benefits of using a flexible riser for all dewatering projects, simple or complex. Our technical experts can help consultants and engineers with finding the Flexibore system best suited to their project."

Flexibore 250, 300 and 400 can accommodate deep, super-deep and ultra-deep bores.

Wound onto reels or in flatpacks, Flexibore is easy to transport and has a small footprint compared to rigid pipe. The system is quick and easy, requiring less labour and equipment to install. Retrieving, moving and reinstalling Flexibore is also possible, saving time, energy and resources.

Crusader Hose has a large warehouse in its factory in Bayswater, Victoria, and can despatch urgent orders within two days.

This feature appeared in the June 2023 issue of Australian Mining.