Conveyor Systems & Trucks Both Have Their Place
It’s an age-old question in the mining industry: Which is better, trucks or conveyor systems? Are fabrication services for trucks needed?
Truck-and-shovel operations are currently the most common method employed by the world’s surface mining operations. But they’re also more labor intensive, less energy efficient and less safe.
Each truck requires approximately seven operating and maintenance staff for a 24/7 operation. And about one-third of all fatal accidents in surface mines are vehicle-related.
On the other hand, trucks and shovels can be purchased off-the-shelf for significantly less upfront capital than conveyor systems. They also allow for flexibility in mine planning. For instance, they can take into consideration any geological variance or volatile commodity price cycles.
Batch vs. Continuous Systems
Truck/shovel systems are considered “batch” mining systems with variable cycle times. This cycle time variance inherently causes certain inefficiencies. (Examples would be shovels waiting for trucks or trucks queuing up to dump their load).
“Continuous” mining systems, on the other hand (such as conveyors), eliminate most of these delays. Conveyors can take a more direct path and do a better job of negotiating rough terrain.
They are also more energy efficient, since trucks carry empty loads half the time. (Did you know, a truck weighing several hundred tons will burn more than 60 gallons of diesel fuel per hour, regardless of its load?)
Both systems are still very expensive, with trucks costing multi-million dollars each, and conveyors costing thousands of dollars per meter. (For example, Brazilian mining giant Vale SA is investing $20 billion dollars in its new 23-mile conveyor system.)
In-Pit Crushing and Conveying
A traditional problem with conveyors, aside from the exorbitant upfront costs, is that they can only accept material in fine particles. This made them impractical for hard-rock mines, until recently.
The solution to this dilemma is “in-pit crushing and conveying systems,” or IPCCs.
The IPCC is ideal technology for large open-pit mines with high outputs. Although the idea for IPCC systems was originally developed in the 1970’s, it’s only in the last few years that these systems have begun to change the face of mining.
The IPCC utilizes a crushing component, such as a gyratory crusher, inside the mine or pit. The crushed material is then sent to the conveyor via truck, rope shovel or hydraulic excavator. At the discharge end of the conveyor, a stacker (for ore or coal) or spreader (for waste) is employed.
The IPCC can be used to achieve either full or partial replacement of trucks both within and outside the mine.
The video below shows how one company, Swedish conglomerate Sandvik, has developed a semi-mobile IPCC concept to reduce the number of mining trucks on site while still maintaining mine flexibility:
One important variable which mining executives must keep in mind when considering conveyor systems is the expected life of the mine (LOM). If the LOM is short, there likely is insufficient time to recover the capital costs of the system. (For example, the general rule is that the LOM should exceed 10 years for an IPCC system to be economically worthwhile.)
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Types of Conveyors
Most surface mine operations utilize some form of bridge conveyor system. Bridge conveyor systems typically consist of mobile bridge sections, which are mounted on tracks or wheels and which carry the chain or rubber belt conveying decks. The mobile bridge sections are typically short and self-propelled. Bridge segments are linked together using chain conveyors.
consist of four basic units: a breaker car module, a conveyor bridge module, a mobile bridge module, and a rigid haulage system. The particular configuration and number of these units depends on the individual mine’s production requirements.
With pipe conveyors, on the other hand, the conveyed material is completely enclosed, protecting it from external influences and spillage. A stretchable rubber belt is driven by multiple friction rollers acting on a vertical drive strip.
One particular type of pipe conveyor is called a tear drop conveyor. With this type, the conveyor belt is suspended from above and pulled into a tear-drop shape for much of its travel. The “pouch” remains closed and dust-tight, protecting both the material conveyed and the environment.
The tear drop conveyor offers significantly greater maneuverability, and can handle much tighter curves and turns than conventional conveyors.
Another type of conveyor system, often used in coal mining, is a vacuum conveyor. This system involves the use of air injector pumps to generate the vacuum, a separation hopper to remove the coal from the air stream, plastic pipe for haulage and flexible loading tubes.
The vacuum action of the system loads the coal directly in the conveyor at the face of the mine. Vacuum conveying systems are ideal for coal mining, as the coal can be loaded from several points to a common storage hopper.
McShane Provides Fabrication Services for Trucks
McShane’s heavy industrial fabrication services routinely exceed customer’s specialized fabrication needs for their heavy industrial projects and field-site locations. Whether on-site or shop fabricated, we deliver premium quality components and manufacturing for things such as furnaces, large ductwork, bulk storage, structural steel, and holding tanks. McShane’s goal is to create long-term relationships as a convenient, single-point-of-contact to save you time and energy as we communicate the process through each phase of production.