The A To Z Of IPCC

Figure 1. Mobile conveyor bridge operating across benches in a coal mine in China.

Boris Frankenreiter, thyssenkrupp Mining Technologies GmbH, Germany, outlines some of the best operational practices for in-pit crushing and conveying (IPCC) operations.

Bulk materials, whether coal, ores or rock, still play a major role in the extraction of natural resources. Today more than ever, the shortage of certain raw materials on the world market highlights the demand that is to be met.

Many deposits are located just below the earth’s surface, which makes extraction from the vicinity of an opencast mine a sensible option.

Product transport and related materials handling

In opencast mine operations, once crushed to the required size, the product must be transported to the next downstream process step. The scope of this article is focused on the crushing interface to mining, and hence only the features relating directly to the immediate transport of materials are considered.

In the case of higher throughputs and coarser particle size product, it is often a requirement to have a product vault or pocket under the crusher that has the capacity to hold approximately two to three truck payloads. Material is then drawn away from the vault by a feeder that discharges onto a main conveyor belt.

On the largest scale, the materials handling of the product requires a range of equipment, including belt wagons, bridge conveyors, and, in some cases, custom systems. Belt wagons (Figure 3) are essentially mobile transfer conveyors, mostly used to provide a connection between mobile crushing plant and a fixed bench conveyor. In most cases, belt conveyors are statically located at the mining face, but are designed to be shiftable. The utilisation of a belt wagon enhances the flexibility during operation of the crushing plant in combination with the belt conveyors and, additionally, the amount of shifting procedures can be reduced.

Flexibly bridging the gap

An even more flexible solution for the material transfer between a crushing plant and a mine face conveyor is formed by mobile conveyor bridges. Principally, they are a further development of belt wagons with the advantage of further improved flexibility. Conveyor bridges, as shown in Figure 1, can operate across one or more mine benches, and further optimise travelling and shifting of the crushing plant and the face conveyors, in order to minimise system downtimes.

Beyond these specialised units for in-pit crushing and conveying (IPCC), conveyors in general form the arteries of the system. Although, these can be deployed as fixed installations in some instances, there is also the need to move the conveyors to optimise material movement. The main movement options for such conveyors are usually referred to as portable, shiftable, or semi-fixed. Portable conveyors are mostly wheel-based and are often designed in a traditional grasshopper style. Shiftable conveyors are designed to be moved periodically, so they are often skid-mounted and have attachment points to allow dragging via dozers. Semi-fixed conveyors are modular, mostly mounted on concrete sleepers, and relocation involves disassembly and movement of the modules.

For the extraction of various mineral resources in mining operations throughout the world, depending on the thickness of the material to be extracted, the movement of smaller or larger quantities of overburden is necessary. This becomes more lucrative the larger the deposits of natural resources are in the mine, located under layers of soil. Once the location and size of the raw material to be extracted have been determined by test drilling, it becomes necessary to remove the overburden layers before extraction of the resources. The overburden is commonly dumped at a suitable location in the mine, at a distance from the extraction site. In many smaller mine activities, the simple truck and shovel method is still useful, as this method is easily scalable. A small fleet of mine trucks, driving the overburden from the excavation face to the overburden dump, often represents the basic

Figure 2. Spreader and tripper car in high capacity application.

Figure 3. Belt wagon application in China.

equipment of a small or medium mining operation.

Mobile mining machines: the gentle giants

In the event of an increase in mine activities, for example due to the increase of production rates or to move larger quantities of overburden, the use of specialised machinery for continuous transportation and dumping becomes economically more favourable. After crushing the overburden into a product size, which can be handled by conveyors at the mine face, the material is transported by belt conveyors to the overburden dump area where tripper cars and spreaders are used in the dumping process. Often, the conveyors at the beginning and at the end of the complete conveyor line are designed as relocatable or shiftable. This way, the specific single conveyors can be moved close to the operation radius of the mining and dumping machinery, thus optimising travel and handling times of excavators and dumping equipment.

Many worldwide mining applications in medium and large scale rely on semi-mobile or fully-mobile crushing

Figure 4. Spreader and tripper car, with tripper car on crawlers. plants at the beginning of the conveying line. The dumping equipment itself is independent from the type machinery used at the mine face. Tripper cars are the first unit of dumping machinery and are used to receive the overburden from the dump conveyors. Therefore, tripper cars are equipped with travel mechanisms either of the rail-type, or – more rarely – the crawler-type. They travel along the relocatable dump conveyor and lift off the belt to a specific transfer point, where the material is transferred to the spreaders. The spreaders form the last member of the conveying chain and dump the overburden in a controlled manner at the designated area. To achieve a maximised flexibility in operation and

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minimise shifting-downtimes, spreaders are commonly designed as two-flight units with travel mechanisms consisting of crawlers. Capacities of spreaders and tripper cars may vary between 3000 m³/hr up to 18 000 m3/hr (Figure 2), and in special cases even more.

Especially in operations where spreaders and tripper cars are intended to drive on freshly filled ground, the crawler–based travel mechanisms of the spreaders are a proven, state of the art technology. Due to the lower weight of the tripper cars, their travel mechanism often consists of a travelling system on rails, which are attached to the dump conveyor, as they always are centred over the conveyor. Special applications with the demand of a very high flexibility also incorporate tripper cars on crawlers, combining with an additional discharge boom with a conveyor (Figure 4), while the spreader is equipped with a support car for the receiving of the conveyor boom. For the application of continuous dumping equipment in smaller mines, a single operating tripper car on crawlers or on rails can also form a standalone solution without a spreader.

Advantages for budget and the environment

Low energy consumption and carbon dioxide reduction are becoming more and more important, even in the mining business. With this in mind, thyssenkrupp has worked to make sure its products are operated entirely electrically.

While discontinuous transport systems are based on a large number of individual transport units like haul trucks, a continuous system minimises the number of operators. While in truck transport systems, each vehicle is operated by at least one person, combined with multiple work shifts per day, a continuous system can be operated by fewer personnel during the same time. A significant increase in operational safety and economic savings is the result of the innovative control and monitoring systems. Implementing these solutions on a large scale optimises the number of personnel needed for safe and economic operation of the transport system even further.

Casestudy: An IPCC system for overburden in an opencast coal mine

The continuous mining equipment recently installed in an opencast mine, located in Bulgaria, is the latest state-of-the-art technology designed for operations. After initial mine planning activities, conducted by thyssenkrupp Mining Technologies, the optimal combination of equipment has been installed inside the mine. The technical solutions adopted for the engineering of the specified continuous mining equipment operations have prioritised the stability and safety of the equipment, whilst maintaining a high degree of robustness to ensure easy and secure operations, as well as good accessibility to the components of the equipment in the event of maintenance.

The complete system, which is designed for a capacity of 3000 tph of overburden, consists of the following equipment: n Semi-mobile crushing plant of the type 63 x 89 in., fed by apron feeder, up to 150 t truck class. n Multiple stationary belt conveyors leading from the crushing plant to one shiftable dump conveyor in the dumping area – total length approximately 3200 m. n Tripper car on rails and spreader on crawlers –

ARs 1600 50+70/17 – forming the dumping equipment with a maximum capacity of 5000 tph.

In normal operations, the system is interlocked and runs in an automatic mode, controlled by programmable logic controllers.

Since commissioning in 2011, the complete IPCC system, as shown in Figure 5, is in continuous operation and has proven to be a reliable, high-performance transport system.

Figure 5. IPCC system in Bulgaria.

Conclusion

When comparing the benefits of a continuous transport system with the characteristics of using trucks, the advantages are obvious: improved capacity, reliability, lower maintenance costs, increased safety in operation, and, not to be overlooked, better environmental prospects. The operation of mobile machines with belt conveyors becomes more economical the larger the mine grows and the larger the quantities that are transported.