Through a multi-year process, FLSmidth has now successfully delivered numerous pieces of equipment to the Toromocho Mine located in the peaks of the Andes Mountains. Among the engineering feats accomplished are some of the largest mills in the world, as well as a seemingly impossible overland conveyor system.
It has been a several-year process, but commissioning of the Toromocho Copper Mine in Peru is now considered complete. The commissioning is being deemed a success for the FLSmidth supplied equipment. This is a great accomplishment for several different divisions because FLSmidth provided numerous pieces of equipment at Toromocho. This equipment includes four in-plant conveyors, a three-conveyor overland circuit, two belt feeders, two steel ball handling conveyors, two ball mills, one SAG mill, one primary crusher and two pebble crushers, as well as Pneumapress® filters in the hydromet area of the process plant.
The Toromocho mine is located in the peaks of the Andes Mountains about 140 km from the capital city of Lima. The elevation of the process plant is approximately 4,550 meters above sea level, and the highest point of the overland conveyor is just slightly less than 5,000 meters. This extreme elevation, severe terrain and adverse weather made engineering and construction a difficult task.
Largest mills in the world
The mills are the largest ever engineered and constructed in the world. The SAG mill is a 40-foot-diameter mill with a 28-Megawatt ABB wraparound motor that is designed for 5,250 MTPH of throughput. While there are other 40-foot SAG mills currently installed around the world, the motor power and throughput on the Toromocho SAG mill are the largest in the world. The two ball mills are 28 feet in diameter each with 22-Megawatt ABB wraparound motors. They are each designed for 1,575 MTPH of throughput. The shell diameter, motor power and throughput of these ball mills are all the largest in the world.
Severe rain and lightning storms, which occur nearly every day on site, as well as periodic snow and ice storms, caused numerous delays throughout the construction of the mine. To help make up time in the schedule, it was decided to assemble the 470-metric tonne ball mill shells on the ground and then lift them into their cradles on the foundations. According to FLSmidth Field Service Engineer Troy Matter, who was on site during the construction of the mills, this is thought to be the first time an entire mill shell of this size has ever been hoisted into place as one piece.
Nearly impossible overland conveyor
The overland conveyor is thought to be one of the most complex conveyors ever created. The goal of the overland conveyor was to create a single flight conveyor to take 10,000 tons per hour of copper ore from the primary crusher area to the stockpile at the process plant, a distance of about 5.2 kilometers. This sounds fairly routine for an overland conveyor, but when this is coupled with difficult terrain of the area and the elevation, it became a very challenging task. The loading point of the conveyor is located at 4,700 meters above sea level. From there the conveyor climbs 250 meters very quickly to 4,950 meters at the peak and then drops 333 meters back to 4,617 meters at the head of the conveyor. In addition to the severe uphill and downhill portions of the conveyor, the terrain demanded several vertical and horizontal curves. Seven vertical curves, three horizontal curves and two compound curves were needed to transport the copper ore from the crusher area to the stockpile.
There are several benefits to engineering with a single flight versus multiple flights, including significantly less transfer area maintenance as fewer transfers are needed, and significantly less drive maintenance as fewer drives and drive stations are needed.
While designing a single flight conveyor had several benefits, it also presented its fair share of challenges. One of the largest problems was developing a control system that could handle the large swing of power from full demanded to full regenerative. When loading the conveyor up the first hill, 9 MW of power are demanded. When unloading the conveyor, as low as 4 MW of regenerative power are required to keep the belt from running down the hill. In addition to the large power swings, another design hurdle was controlling belt tension for the multiple curves to prevent material spillage, as well as damage to idlers and the belt. This was solved by placing the drive station near the highest point of the conveyor and using a tripper booster drive. The drive system can pull the material up the first hill while holding back the load as it drops down the other side of the mountain. Also, an active take-up winch near the head was installed with a load cell and its own independent control system. The location of the take-up allowed for active tension control at the lowest tension point of the system. The choice of a winch for the take-up mechanism was determined through dynamic analysis. The winch allows the take-up pulley to be locked during an uncontrolled stop (emergency or power failure) creating a dampening effect for the belt tension wave associated with the uncontrolled stop.
Two other design issues that needed to be addressed were the potential for bearing skidding in the reducers and belt installation. First, many reducer companies become concerned with bearing skidding when the expected running power of the conveyor will be 25% or less of installed power. When fully loaded, the overland conveyor is expected to run at approximately 7% of its installed power. Most traditional reducer manufacturers wanted to stay away from this conveyor for that reason. FLSmidth was able to count on Dodge and their controlled start transmission (CST) product line to solve this problem. The CST incorporates a planetary gearbox with a clutch and input shaft brake which can completely eliminate the bearing skidding issue. With drives that can be disengaged and the motor rotation stopped, it allows the mine site to run the conveyor with less than the four installed drives when the conveyor is operating at a full steady state tonnage.
Second, the belt installation required careful consideration. It was decided that the belt installation would start at one of the highest points on the conveyor and gravity would be used to feed the belt onto the conveyor. Special belt clamping stations were designed along the length of the conveyor to help this process.
A special note of thanks is given to the construction team that installed and aligned the overland conveyor. From the first run of the conveyor, the belt aligned well throughout all the curves. This would not have been possible without a properly and accurately installed system.
The Toromocho Mine was a great project for the FLSmidth team. All indications point to success for the company. Designing a conveyor such as the Toromocho overland, as well as installing the three largest mills in the world with rave reviews from Jacobs Engineering, the engineering, procurement and construction (EPC) management team, shows that the FLSmidth team is capable of handling just about any mineral processing or material handling need.
CONTACT: Brad Tensen