Robert Sheldon, Cummins Power Generation, USA.
With the largest mineral resources of any country in the Gulf region, Saudi Arabia is a land rich in gold and other precious metals, as well as crude oil. However, most of the gold deposits are located in remote areas far from the country’s electric grid. This makes the mining and processing of the ore at these sites dependent on on-site power generation.
The Bulghah gold mine began production in late 2002 as one of the resources surrounding the existing Al-Sukhaybarat gold mine – thought to be part of the fabled King Solomon’s Mines. Located 550 km northwest of Riyadh, the Bulghah gold mine generates all of its electric power using remote power (RP) units from Cummins Power Generation.
The seven remote power units that supply 7 MW to the gold mine
Operating 24 hours a day and 365 days a year, the Bulghah gold mine relies on self-generated electricity to power a vast array of pumps, conveyor systems and crushers, as well as lighting and miscellaneous electric equipment at the site. Bulghah is an open-pit mine and uses the “heap leach” method of gold extraction. An elaborate electric-powered conveyor system transports the crushed gold ore to a plastic-lined pit to create a large pile of crushed ore.
A solution of chemicals that dissolves the gold in the ore is pumped over the heap and allowed to filter down through the pile where the solution is collected and further refined to produce pure gold. Using this method, the mine produces approximately 82 000 ounces of gold annually. It has been estimated that the mine contains some 36 million tonnes of ore that will yield 1.05 grams of pure gold per tonne.
Supplying electricity to this massive operation is a power system composed of seven CP1250-D6 containerized PowerCommand RP units. Each RP unit is prime-rated at 1000 kW for a 7 Mw total system capacity.
Depending on the electrical load, only five or six of the RP units operate at any given time. This allows at least one unit to be offline for maintenance, or in a standby mode, thus guaranteeing a higher level of reliability for a power system that is designed to run continuously, sometimes under adverse environmental conditions.
If one of the operating generators happens to fail for any reason, the standby generator set can be automatically started and paralleled with the remaining units in as little as ten seconds. “
The owner of the mine did not want to undertake the day-to-day operation of the power system, so they contracted with our distributor in Saudi Arabia to install, commission and operate the system,” says Don Watson, rental director for Cummins Power Generation in Europe, the Middle East and Africa. “The station has been operating for over three years already without a single loss of power or interruption of the mining or processing.”
Everything under control
Each RP unit is equipped with a digital PowerCommand control system that offers superior reliability in the difficult desert environmental conditions of high ambient temperatures and blowing dust and sand. Digital controls are also less vulnerable to vibration than conventional analogue controls and significantly improve system reliability.
The digital controls provide an automatic voltage regulator that is integrated with the engine speed governor to maintain precise output voltage and frequency during changing loads. The controls also feature AmpSentry, a system that protects the electrical integrity of the alternator from the effects of over-current, over/under voltage, under-frequency and overload conditions.
The PowerCommand control system also facilitates quick and easy paralleling with the other generators when units are put back online after maintenance. The digital controls and associated switchgear make for smooth paralleling that reduces transients and mechanical stress on the engine and alternator components.
Under the operating agreement, General Contracting Company, the Cummins Power Generation distributor in Saudi Arabia, operates the system and performs all the necessary maintenance.
A tough environment
Local environmental conditions can be harsh. Blowing dust and sand can clog air filters, radiators and alternator cooling ports, often requiring daily inspection and cleaning. The high summertime temperatures that sometimes reach 55ºC (131ºF) require additional de-rating of each generator set of about ten per cent.
Up to ambient temperatures of 45ºC the generator sets can produce their full prime-rated power of about 1250 kW each, but to prevent any engine or alternator overheating during extreme operating conditions, it is prudent and more economical to de-rate them slightly to 1000 kW.
Fuel economy can also be adversely affected by high ambient heat. As ambient heat increases beyond the design optimum temperature of 45ºC, fuel economy begins to fall unless the generator is de-rated to compensate for the high temperature effects. Fuel economy is critical because fuel is by far the largest factor in the cost of operating a prime power system. Each RP unit is designed with onboardfuel storage capacity to run up to 31 hours at its prime rating before refuelling.
Another generator set component that is vulnerable to overheating in high ambient temperature conditions is the alternator. The RP units feature Stamford alternators that are designed and built by Cummins Power Generation. They are oversized for their capacity for improved motor starting and low temperature-rise in prime and continuous load applications.
This is important at this mining site because so much of the electric load is used to operate large motors that run the ore crushers, pumps and conveyor system. The alternators also feature permanent magnet excitation for improved performance as motors cycle on and off.
Lucky seven gensets
The seven generator sets are powered by the Cummins KTA50-G3 engine, a 50-litre diesel engine used in thousands of power generation installations worldwide ranging from on-site prime power to emergency standby power for critical applications. Operating at 1800 rpm and producing electricity at 60 Hz, the generator sets are easy to start, parallel and run due to the digital PowerCommand control systems on each generator set.
All-digital controls improve reliability under extreme operating conditions by significantly reducing analogue components and single points of failure. In addition to frequent inspections to check for dust and sand accumulation, the starting batteries require special attention in the high ambient desert heat to make sure the electrolyte solution is up to specifications.
Oil and filter changes are made after every 250 hours of operation, which is standard for continuous power diesel applications. To perform the oil changes, the generator set is taken offline during a time of low power demand, or when one of the extra generator sets has been started up and synchronized to take its place. Engine overhauls are typically anticipated after approximately 30 000 hours of operation or about once every four years. When they become necessary, the overhauls will be done in such a way as to prevent them from affecting power generation.
The enclosures for the RP units are purpose-built 12 m high-cube ISO containers that are easy to transport to the site. Each enclosure provides optimal protection from the elements while producing a minimal footprint. They are also designed with 100 per cent fluid containment capacity to prevent oil and fuel spillage from contaminating the environment. Vertical cooling air and engine exhaust paths help minimize sound levels adjacent to the container. Each enclosure is equipped with both 120 VAC and 24 VDC lighting to facilitate maintenance.
Pleasing the customer
The power system is installed as a long-term equipment rental for a period of ten years that includes an operating and maintenance agreement with the Cummins Power Generation distributor in Saudi Arabia. The Saudi government has spearheaded development of its mining sector as part of a programme of diversification away from petroleum.
The remote power units supply the power that runs the gold mine’s massive conveyor system
The government’s objectives for the mining sector include establishing industries for extracting and processing minerals, and developing the transportation infrastructure. Saudi Arabia has close to 20 million tonnes of recoverable gold ore and, according to a government web site, non-oil mineral activity is expected to grow at a rate of nine per cent annually.
The operators of the Bulghah gold mine have largely been satisified so far with the reliable operation of their 7 MW prime power system. It is one of the ways that the US company is helping other companies worldwide to operate efficiently and economically in areas outside the reach of today’s power grid.