More Than Just “from A to B,” Siemens Specializes in Innovative Bulk Material Handling Solutions
By Norbert Becker, Siemens AG
Despite high initial investment costs, in day-to-day operations and especially in the face of increasing energy price no other transportation medium comes close to the cost effectiveness of belt conveyors for transporting large amounts of bulk material over long distances.
In recent years, system designs have become more complicated than ever through increasing length between the axes on long-distance belt conveyors, higher belt speeds, and more challenging routes with horizontal and vertical curves. To ensure that belt conveyors maintain their cost effectiveness well into the future, a robust design is needed that allows for high levels of plant availability, high productivity, low training costs and a long service life. Further considerations include a low-wear design to extend service intervals and reduce costs associated with spare parts and operation.
Siemens’ answer to these demands is Simine CON, the collective name for the company’s drive-system solutions for conveyors, encompassing both mechanical and electrical systems for outstanding overall conveyor performance with both fixed-speed and variable-speed drives. Automation control is also part of the package.
Leaving Nothing to Chance
Only a good design can ensure system longevity. This is why design plays such a pivotal role at Siemens for new conveyor systems as well as for refurbishing existing conveyors. New technical expertise as well as extensive past experience of Siemens engineers flow into the design process. This begins with determining the optimal width of the belt, depending on conveyor inclination, the weight and size of the bulk material, and the speed.
Dimensioning in accordance with DIN 22101 is the basis for the planning of a belt conveyor. But this is only the first step in the design process. All conveyors designed by Siemens—whether for use in an open-pit mine, a complex stockyard or for long-distance uphill or downhill conveyors—are analyzed and optimized using computer simulation. In the case of more complex installations, the simulation also serves as a basis to predict dynamic behavior. This feature is valuable when seeking the right settings for the technology controller. For a mechatronic solution, the system’s full potential can be provided only when the drives and the mechanical system are perfectly aligned.
When it comes to analyzing the process chain, the individual process steps and their interaction are examined with regard to economic and technical feasibility. The resulting model is the basis for optimization according to the methods of Operational Research. These methods have been successfully applied in countless sectors. Dispatcher decision-making duties are supported through recommended optimized scenarios and the system is able to take over automation tasks via an online service. Simulation performed ahead of time ensures reliable operation, especially of complex belt conveyors that operate at a positive or negative incline or with vertical and horizontal curves.
Using fully developed and realistic dynamic simulation models, the configuration of the belt drives is tested so that all start and stop periods are mastered. Special attention is paid to safety-related operating conditions. This could include conveyor performance during emergency stops; out-of-norm conditions for the drives, gears and belt; demonstration of sufficient braking power; and an assessment of safety considerations.
Altogether, simulation enables all possible operating scenarios to be tested and is therefore a very important method for designing innovative belt conveying systems in a short period of time. This greatly minimizes the chance of unpleasant surprises during actual conveyor operations.
Siemens experts use the simulation as the basis for basic and detailed engineering. In the framework of detailed engineering, the exact components as defined in the simulation are added to the bill of material. In contrast to classic OEMs, Siemens uses a high proportion of equipment—converters, motors, gears, drives, automation systems, switch gear and transformers—that it designs and builds. All other components, including drums, rolls, belts and steel structures are procured in the market.
Coal to Power
In Saxony, Germany, as general contractor to Vattenfall, Siemens is supplying a 13.5-km-long belt conveyor. Upon completion in mid-2010, the system will transport raw brown coal from the Reichwalde open-cast mine to the Boxberg power station. Vattenfall, as the fifth-largest producer of electricity and the leading generator of heat in Europe, extracts approximately 60 million mt/ of brown coal every year. The coal is consumed at the Jänschwalde, Schwarze Pumpe and Boxenberg power stations. At Boxenberg, another power station will be connected to the power grid, possibly in 2011. In order to secure the long-term supply of coal to the Boxenberg facility, coal mining will be restarted in the Reichwalde open-cast mine. Using Simine CON, an optimal design was developed and is now being executed to meet the operation’s start-up scheduled for mid-2010.
The belt width is 2,000 mm and, with a total of six conveyor belts, the system will be able to move 6,000 mt/h of coal. The total drive power is 19,350 kW and is distributed between three drive stations, each with an output of 3 x 1,250 kW, and three other stations, each with an output of 3 x 900 kW. Four of the conveyor belts are stationary, while two bench belt conveyors are movable and the associated drive stations are fitted with crawler tracks. The underlying technical design of all the drive stations and deflecting stations is uniform. The scope of the project also includes two water take-off stations and a feeder unit that transfers the coal to an already existing conveyor. Siemens is responsible for engineering the entire system as well as for manufacture, delivery and installation of the equipment. After commissioning, the Siemens service center in Vattenfall’s neighboring Nochten open-cast mine will service and support the new equipment.
Vattenfall, in selecting Siemens for this role, will benefit from having one partner who is responsible for the entire project, from planning to commissioning, as well as from fewer management and technical interfaces; a consistently integrated technological solution; reduced training efforts and times—with integrated training efforts kept to a minimum; and less diversity of spare parts and subsequent savings. Vattenfall also can be assured that they are receiving a product that adheres to ISO 9001 and Siemens’ own quality-management system. At defined points, called Quality Gates, the project results achieved are quantified, evaluated and approved.
The Long-term Picture
There is more to successful supply than just getting the system up and running. Lifecycle services provided by Siemens ensure that high-performance levels are maintained across the conveyor’s entire life cycle. Through a program of timely maintenance, the conveyor can be kept at the cutting edge of technology.
An outstanding example of this constant upgrade capability is the downhill conveyor system at Minera Los Pelambres in Chile. At the Los Pelambres mine, 200 km north of Santiago, Chile, copper ore is extracted at an altitude of 3,200 m ASL. The belt conveyor system, which is 12.7 km long and 1.8 m, wide connects the crushing plant at an altitude of 3,000 m with the beneficiation plant located at an elevation of 1,600 m. Due to the steep incline and the rough surroundings, the electrical and mechanical components are exposed to considerable stress. The system generates about 17 MW electric power during operation with nominal load.
Siemens initially designed and erected the conveyor system in 1999. Back then, the scope included transportation of up to 7,000 mt/h ore at a speed of 6 m/sec. Eight motors with output of 2,500 kW each operated the belts.
In 2006, drive system power had to be increased to match an expansion of beneficiation plant capacity. Two of the three conveyor belts were each fitted with an additional drivetrain to raise system capacity to accommodate the increased ore requirement of the mill. Each drivetrain consisted of a motor, a converter, a transformer and medium-voltage switching devices. The belt drive output was increased from 20 MW to 25 MW, and the conveying system now can transport 8,700 mt/h of material instead of 7,000 mt/h. Traveling at 6 m/sec, crushed ore’s trip to the processing plant takes 35 minutes. Because of the steep slope, which averages 10%, there is a risk of uncontrolled belt slippage. But in an emergency 13 disc brakes, each with a diameter of 2.5 m, can stop the entire belt system within 70 seconds.
A special feature of the conveyor system at Los Pelambres is the ability to generate energy during operation with nominal load. This means that the ten drive motors associated with the belt consume power only if the belt is carrying less than 800 tons of ore. Otherwise, they generate up to 17 MW of power. At 90 million kWh, output in 2007 represented about 15% of the mine’s power needs, reducing energy costs and cutting carbon dioxide output by more than 50,000 mt/y. In 2005, the Chilean Ministry of Economics awarded Minera Los Pelambres the National Prize for Power Efficiency for this technology.
From the beginning of this project in 1999 Siemens has provided Minera Los Pelambres with preventative and corrective maintenance services for the entire conveyor system at its open-cast copper mine high up in the Andes. Los Pelambres has renewed this contract several times; the most recent agreement was signed in 2007 and expires in 2011.
Siemens is responsible for all mechanical and electrical equipment, automation systems and instrumentation, as well as for materials and spare-parts management. An on-site Siemens service team handles maintenance of the entire conveyor system, from the rollers to the belt and the motors.
A fiber optic network links all parts of the installation where sensors monitor critical status parameters on various components. This enables the installation to be monitored around the clock, irrespective of where service personnel are stationed. Faults can be detected at a very early stage and via the Internet, experts can examine the conveyor belt system and its peripheral equipment from anywhere in the world. Any faults detected can thus be analyzed and the installation can be restarted, if necessary, as well. Payment for this maintenance service includes performance-related components: the level of success is measured in price per ton, which is trend-setting in the mining industry, and on the basis of key performance indicators such as availability, reliability and asset condition. Moreover, Siemens and Los Pelambres agree on a maintenance budget each year with Siemens taking responsibility for adherence to this budget
Because a conveyor system is so expensive, it pays to have a low-maintenance solution that boasts high uptime. Innovative maintenance models from Siemens are helping customers get the most from their investment and avoid unforeseen costs.
Norbert Becker is vice president for process solutions, Mining Technologies, Siemens AG,