Power — a driving force at Drummond’s Mina Pribbenow
Mining companies have experienced tremendous growth in recent years as they expand to meet the global demand for materials. That rapid growth can lead to some significant obstacles — like the need to provide the clean, reliable power necessary to support the massive requirements of mining operations.
Such was the situation facing leading coal producer Drummond Ltd. (DLTD) at its Mina Pribbenow open-pit coal mine, located in the Cesar Coal Basin near La Loma, Colombia. The mine’s challenges included access to power, the allocation of power between the mine and its support facilities, large and regular fluctuations in load, regenerative power, generator set availability and fuel quality. Drummond turned to Caterpillar for guidance and technical support to overcome these barriers.
The Drummond operation
The DLTD Colombian operation includes Mina Pribbenow; Puerto Drummond, an ocean port on the Caribbean Sea near Santa Marta; as well as coal transportation and handling facilities. DLTD transports the coal from the mine 193 kilometers (120 miles) by railcar on the renovated portion of the Colombian National Railroad System to Puerto Drummond on the northern coast for export.
La Loma coal meets worldwide sulfur regulations, and is one of the lowest sulfur and ash coals currently exported from Colombia. As emissions regulations are becoming increasingly stringent in many parts of the world, this coal, producing comparatively low levels of NOx, is desirable to utilities that are required to meet new emissions standards.
Investing heavily into production infrastructure in the last few years, DLTD has experienced significant growth at Mina Pribbenow. Shipments of Colombian coal from Mina Pribbenow have increased from 9.1 million tonnes (10 million short tons) in 2000 to 23 million tonnes (25.3 million short tons) in 2007, a growth of 253 percent, with 26 million tonnes (28.6 million short tons) expected for 2008.
Current Reserves at the Mina Pribbenow Complex stand at 561.2 million tonnes (618.6 million short tons). With El Descanso reserves of 1,763 million tonnes (1,943 million short tons) and total DLTD reserves in Colombia exceeding 2,333 million tonnes (2,572 million short tons), DLTD expects to reach 40 million metric tons of annual production within the next five years and anticipates a bright future. The innovative use of a conveyance system and apron feeders to move coal and overburden at the Colombian mine has enabled this growth.
Access to commercial electric power was not available when DLTD began this operation — and still is not available in the Cesar Coal Basin; therefore, DLTD has been responsible for generating all of its own power. A total of 21 diesel-fueled generator sets, including both Caterpillar® 3516 and 3516B models, are installed at Mina Pribbenow to provide prime and standby power.
Stan Grise, assistant superintendent of diesel power plants and maintenance department product support for DLTD, explains how the corporate and electrical engineering departments compared the options. “They looked at several different alternatives including smaller turbines as well as large diesel and natural gas engines,” he says. “Every analysis brought us back to the 2,628-horsepower engine of the Cat® 3516 and 2 MW Generator. We couldn’t find anything that would get us even close to the sheer rotating mass and kW/hp ratio they would generate. Even though the generator sets are designed to carry a constant load, they have performed unbelievably well with the cyclic loads of the Marion 8750 dragline.”
The reciprocating mass of this engine and generator combination are important when dealing with the regenerative power from a dragline. Even with the resistive load bank used to dissipate the regenerative power from the dragline, some of the negative kW is still absorbed by the generator and engine. In a complete dig cycle under extreme digging conditions, the dragline has logged peaks of 90" Boost 135 GPH & 2 MW Output and then back to 0 Boost, 0 GPH, and 0 kW on these Gen Sets (27 MW peak demand).
Division of power
La Loma has two main power sites, with 15 generator sets housed at a new power facility located adjacent to the new gas turbine plant and two kept at the former facility for back-up emergency power for the coal load-out facility — where coal is separated and prepared to meet the different quality needs of DLTD customers. Two Cat XQ2000 trailer-mounted power modulars provide back-up emergency power for the camp and as the motivator on one of the KRUPP Conveyor System Spreaders. An additional five 3516B Gen Sets will be installed for the start-up at El Descanso until a 110,000 volts High Line is completed.
As mine power requirements grew, so did the diesel generator plant. The original plant started operation in July 1998 with two gen sets, with an additional 16 units added between 1999 and 2000. As of March 2008, the Cat 3516 generator sets have generated 493 million kWh @ 12.18 kWh/Gal average LTD. Between 1998 and August 2004, the 3516 gen sets were the sole source of electric power for Mina Pribbenow operations, generating a record high of 86 million kWh and 117,000 operated hours in 2003.
In August 2004, DLTD brought online Phase 1 of a 58 MW capacity duel fuel (compressed natural gas and diesel) gas turbine plant. This addition was necessary to provide power required for 21 apron feeders and the first of three in-pit conveyor systems that went into production in 2006 and 2007. In October 2006, the company completed Phase 2 by installing an additional two LM6000 turbine units. This addition gives DLTD a total installed capacity of 196 MW. To date, the power plant has recorded 98 MW demand with all systems operating along with the apron feeders, electric shovels, dragline and dewatering pumps.
In January 2005, DLTD initiated the relocation of 15 gen sets to the new facility adjacent to the new gas turbine plant. The construction of the new diesel plant was necessary with the installation of the turbine plant and 110,000 volts substation and high line encompassing the entire Pribbenow Mine Complex. The diesel gen sets are 4160 volt boosted to 22,900 volts, then up to 110,000 volts and combined with the turbine plant power at a substation.
“Turbines will not operate under cyclic loads or absorb regenerative power, like those produced by the dragline,” explains Grise. “To be able to continue operating the dragline, the gen sets must be online and provide the power required for the cyclic and regenerative conditions of the dragline.”
One of the most important mining methods used at Mina Pribbenow is now powered 60 percent by Cat generator sets: the Marion 8750 Dragline with an 87.9 bank-cubic-meter (115-cubic-yard) capacity bucket. Requiring a considerable amount of the power generated at the site and representing the largest piece of mining equipment in Colombia, the dragline utilizes up to eight Cat 3516B generator sets, each rated at 1,825 kW (prime) and 2,000 kW (standby). In January 2008, the dragline began stripping river alluvium by direct loading apron feeders, averaging 59,000 bank cubic meters (77,000 cubic yards) per day of production. The process has been so successful, the company is currently disassembling a BE 2570 Dragline with an 87.9 bank-cubic-meter (115-cubic-yard) bucket located in Alabama to use at the El Descanso Mine in Colombia. With the addition of the second dragline, the demand from the Cat gen sets will again increase.
“The dragline is critical to the mining operation,” says Sergio Maury Benedetti, onsite project manager with General de Equipos de Colombia, S.A. (GECOLSA) — La Loma, Colombia’s Cat dealer. “It is very important to maintain a steady, stable source of power to keep it working.”
Regeneration and harmonics
Regenerative power is another challenge presented — and overcome — at the Mina Pribbenow power station on a routine basis. “The electrical load on the power station varies greatly, and often abruptly,” explains Joe Rad, Caterpillar Global Mining commercial manager for Latin America. “This is due largely in part to the operating profile of the dragline.”
“As the dragline digs, swings and dumps throughout its work cycle, the 3516B-driven power station needs to quickly respond by delivering the electric power required by each cycle, routinely in block-load fashion,” Rad continues. “Design and application considerations were given to the 3516B generator sets and power station controls to ensure optimal power quality is delivered to the dragline, mine site and campsite.”
As outlined in a white paper by Drummond’s Larry Casson at a meeting of the Western Mining Electrical Association, electronic controls play a major role in the operation of the dragline. “The Marion 8750 dragline is capable of regenerating up to 60 percent of peak motoring power. To account for this, a six-stage resistive load bank was installed to absorb regenerative power not being utilized by other mine equipment. The diesel generators can absorb a small amount of regenerative power, but the load bank is required to absorb larger amounts of regenerative power,” wrote Casson.
“Generator control is accomplished by using a combination of load share modules and programmable logic controllers (PLCs),” Casson added. The load share modules control load share (kW), and voltage control (kVAR/PF) between generators as well as provide synchronizing control when bringing on additional generators.
The programmable logic controllers serve as the system master control and provide controls for the following areas:
- Control the number of generator sets that are running, including maintaining the minimum number of generators online and increasing the minimum number when pit conditions require more than the preset number
- Control the load bank to prevent excessive frequency resulting from regenerative power that cannot be absorbed by the engines
- Provide an alarm system for maintenance to identify issues before they become a problem
- Monitor and take automatic action on all controls such as service switches, fault relays, alarm relays, analog power data, etc.
The schedule for bringing generator sets online is programmed in advance, but the central PLC in the control room is monitored carefully and variances are made if needed. “We can isolate depending on the load and modify based on increases or decreases in power requirements,” says Maury.
The installation of electronic controls has saved the mine a significant amount of diesel fuel. “In the past, the engines would run whether they were loaded or not, but now if there isn’t any power consumption in over 10 minutes, it starts shutting the generator sets down,” explains Grise. “In addition, there is a radio signal from the dragline to the power plant that tells us when the generator sets need to be shut down or started up. Lowering our fuel consumption has resulted in significant savings for us.”
Grise and Casson discussed the monitoring, testing and different modes of operation, and agreed they wanted the new facility to be able to monitor all engine and generator parameters from the control room as well as use the Caterpillar Customer Communication system and Allan Bradley RS Logix 500 to monitor all PLC and System functions. The plant also has the capability to load bank test any of the gen sets on site; can base-load as many generators at any kW to supplement the turbines without affecting the gen sets that are operating the dragline, or operate the entire mine in the event the turbine plant is shut down for some reason.
Maintaining for maximum availability
In addition to the project manager, one electrical technician and two mechanical technicians from GECOLSA maintain the machinery for maximum performance and efficiency. Important information from the generator sets is sent to the PLC to alert the team when maintenance is required beyond the regular schedule. For example, these reports will indicate when various filters need changing and if anything is out of adjustment in the engine or generator. “Because the loads on generator sets are always changing it is important to rely on the reports generated,” says Maury.
A laptop computer with Caterpillar Electronic Technician software is connected to the generator sets at least twice a day to download data that is reviewed. “We check parameters like fuel consumption, fuel and air restriction, fault alarms, fuel and hourmeter readings — which are exported into a program that tells me how many hours the engine ran in a shift and how many gallons it consumed per hour,” says Grise. “If consumption increases, we know we need to do more testing and make adjustments.”
“All of the generator set maintenance between overhauls is handled onsite,” Grise explains. When the engine requires an overhaul, the engine is sent to GECOLSA’s Cat-certified Component Rebuild Center in Barranquilla, Colombia. “We do all of the scheduled maintenance and testing and adjustments to the engines and generators per Caterpillar guidelines, and it’s made a big difference.”
Grise says the company has experienced excellent results over the years. “We now average about 4,500 operating hours per month on the 19 generator sets engaged in prime power. In previous years we have operated as high as 9,700 hours per month,” he says. Caterpillar calculates when an engine should be ready for replacement based on the number of gallons of fuel consumed by an engine. For this site, that number was set at 2.8 million liters (750,000 gallons), and they are still going strong at almost 3.4 million liters (900,000 gallons), surpassing 26,000 operated hours.
Quality of fuel plays a major role in the availability of power. The fuel may come from refineries in Colombia or be imported from international refineries. “We found that the fuel quality was never the same from one tanker to the next,” says Grise.
Several factors can affect diesel quality, which if not addressed, can be a detriment to the engines. “With average temperatures of 38 degrees C (100 degrees F) and very high humidity, condensation is always an issue. With the amount of equipment we currently operate, our monthly fuel consumption averages 5 million gallons; you better have a good fuel filtration system,” Grise says.
DLTD has procedures in place to ensure the quality of fuel received, and also has developed a bulk fuel filtration system. First, fuel is filtered when it is offloaded from the tankers into two 1.8-million-liter (476,000-gallon) or three 420,000-liter (111,000-gallon) fuel storage tanks. “At our high-flow filter stations we can unload the fuel at approximately 2,270 liters (600 gallons) per minute,” says Grise. As the fuel is off-loaded from the tankers, it is filtered at 25-micron micronic and 25-micron coalescer. Second, the filtering systems at both storage facilities are set up with a second set of high flow filters that are used periodically to polish the fuel. This is accomplished by continuously pumping the fuel in the tanks through the filters back into the tank for several hours. The time required to accomplish a thorough polishing depends on the amount of fuel in the tank (from four to 24 hours). Finally, fuel is filtered as it is dispensed from the storage tanks.
Fuel from the storage facilities is dispensed in several different ways. Tanker trucks are used to transport fuel to satellite fuel stations located around the mine for the overburden truck fleet. Fuel trucks are filled to service the track equipment in the pit. Underground fuel lines are used to dispense fuel to the coal loadout facility to fill the coal haul trucks, dozer and RTD fleet. Each of these fuel stations utilizes 5-micron micronic and 5-micron coalescer filter elements in their vessels prior to dispatching as well. DLTD uses only high quality fuel filters in all of the fuel storage and pumping stations.
A dedicated group of DLTD employees take care of all of the fuel tanks including draining the water every morning from all the fuel storage tanks and filter vessels, replacing the filter elements, maintaining the pressure differential gauges and fuel pumps, and periodically calibrating the fuel meters.
“Now that we have this advanced filtering system, we can maintain a substantial reserve on the mine site,” says Grise. “Even when the refinery is down or barriers to transportation arise, our work continues because we have a steady source of fuel for all of our equipment — including the generator sets.”
The relationship between Caterpillar and Drummond Company began more than 73 years ago in the United States, when Caterpillar dealer Thompson Tractor Company provided a new coal mining customer, H.E. Drummond, with machines, replacement parts and service to start up his open-pit operations in Alabama. “When operations shifted to a greenfield open-pit mine in Colombia, it was natural that Drummond wanted to involve Caterpillar with their operation from day one,” says Keith Malison, Cat Global Mining marketing manager in Latin America. A partnership between Thompson Tractor and GECOLSA quickly developed to meet all of Drummond’s needs. Sales, service and support are now handled solely in Colombia.
Grise is proud of the quality of his onsite technicians. “I’ve got some excellent men,” he says. “I’d put them up against any power generation mechanic or electrician anywhere. In previous years when there were as many as 16 of 18 units on line 24/7, these men did several complete stripped-to-the-bare-block overhauls here at the power plant as fast as the CRC could do them with excellent results.”
Drummond has made a number of modifications to the Cat gen sets to fit its application as well as increase the life of the engine and generator. “We sit down with the electricians and mechanics from GECOLSA, explain what we want the generator sets to do, they draw it out, and together we make it happen,” Grise says. “Most of these guys have worked for me for the last seven years and they’re like family to me.”
More than 95 percent of the mobile equipment and engines used at the mine and port facilities bear the Caterpillar name. “In fact, one of the largest populations of 850-hp Cat D11R tractors and 240-ton Cat 793D trucks are at work in Mina Pribbenow and Drummond’s expansion project,” Malison says. Grise says the company has 76 Cat D11Rs — more than any company in the world. By the end of 2008, the company will have 145 793B, 793C and 793D Cat trucks.