McArthur River Mine 

Electricity for powering the mine’s operations was previously produced by a dedicated gas-fired power plant owned by global independent power producer Energy Developments Ltd (EDL). But with the long-term power purchase agreement (PPA) due to expire soon, Glencore decided to issue a tender for a new gas-fired power plant that could satisfy the new power requirements.

The tender for the PPA went out to a number of suppliers. Following a full technical evaluation, Wärtsilä’s solution was shown to be the best technical and economical solution – offering the highest fuel efficiency and the lowest levelised cost of electricity over 20 years. Under an equipment delivery contract, Wärtsilä supplied six Wärtsilä 20V34SG gas engines – including the engine hall, associated exhaust stacks, radiators, control system and related engineering services. The plant has a total output of 53 MW at site conditions.

Wärtsilä also signed a 10-year maintenance agreement with EDL. The agreement provides technical expertise and support as well as online condition monitoring and maintenance planning to ensure maximum plant availability. There were several key benefits that attracted EDL to Wärtsilä’s solution. 

The plant is located in an area where temperatures can hit a scorching 45°C. This, together with demand for high fuel efficiency and lowest levelised cost of electricity, meant gas turbine technology was not even considered an option. Unlike gas turbines, Wärtsilä's internal combustion engines (ICEs) do not suffer significant derating at high ambient temperature. Also, the use of multiple units means the plant can follow load variations while maintaining maximum overall efficiency.

The expanded mine uses a ball mill – a large rotating mill containing steel balls for crushing and grinding rocks into a fine powder. The mill is driven by two electric motors each of about 6 MW capacity. Both motors are started simultaneously to get the ball mill into motion. The high load acceptance requirement presents a demanding challenge for the gas engines in the power plant.

“On a 12 MW ball mill with soft-starting capability, the starting current is typically 150% of the nominal current. Wärtsilä gas engines have high load acceptance capability with numerous proven operating references," says Raymond Vinton, General Manager, Sales at Wärtsilä Australia. 

Wärtsilä was able to demonstrate to EDL with software modelling and simulations that the gas engines were capable of meeting the stringent requirements of frequency and voltage drop during starting of the ball mill.

The Wärtsilä 34SG is a four-stroke, medium-speed, spark-ignited gas engine that works according to the Otto process and the lean-burn principle. Its efficiency is one of the highest of any spark-ignited gas engines currently available.

“The technology we use to control our engines puts them streaks ahead of the competition,” notes Vinton. As an expansion project in the McArthur River Mine, the new digital control system had to be interfaced with the old analogue controls of the existing plant – a task that EDL was confident Wärtsilä could execute based on its previous experience with Wärtsilä engines and control system.

Wärtsilä had worked with EDL in the past and proved it had the capability to manage and deliver projects on time and to budget. With a fast-track schedule of just 12-14 months, the ability to work to a tight deadline at McArthur River was an important consideration. Once again, Wärtsilä proved it was able to honour its commitments resulting in a satisfied customer. With commissioning completed in early 2014, EDL can now provide reliable and low-cost power to Glencore, which will help maintain its position as the number one zinc mining company in the world.