Hard rock mines Introduction

Hard rock mines in germany

Hard rock mines in germany

Since the 1940s continuous mining and haulage with bucket wheel excavators and conveyors has been the predominant methodology for high capacity coal or lignite production and overburden removal of soft rock in open pit mining.

In hard rock mines conventional truck and shovel operation is still the most prevalent mining method. It is very flexible and the equipment population can be adjusted to changing mining capacities. But both ecological and economical reasons become an increasingly challenge and restriction for truck and shovel operation.

The development and innovation of crushing technology, semi-mobile but especially of fully mobile crushing systems in the last years enable continuous mining and haulage in medium hard and hard rock applications. The essential part of the in-pit crushing and conveyor systems (IPCC) is the crusher, which basically reduces the lump material after blasting to conveyable size.

In general IPCC utilises the same equipment for continuous haulage and dumping as used in soft rock mining. Only the loading device, the bucket wheel excavator in lignite applications, is replaced by a hydraulic excavator or rope shovel which loads onto a fully mobile crusher. Shovel and mobile crusher follow continuously the face development. In semi-mobile IPCC systems additional trucks are used to shuttle between the shovel or excavator at the face and the semi-mobile crushing station in the pit.

In many studies IPCC was found to be a superior economic alternative to truck and shovel operation in new “green field”, expansions but also as alternative in existing mine operations.

Mine management is usually very quickly convinced of the opportunity and benefit of IPCC whereas mine planning and mine operation need more efforts in accepting the new methodology, because processes and equipment are different and likely unknown.

The following reflections may help to better understand IPCC especially with fully mobile crushing systems.

Continuous Mining and Haulage in Open Pit Lignite Mines

A continuous mining and haulage system in “soft rock” application, i.e. open pit lignite or coal mines comprises basically bucket wheel excavators, conveyor bridges or belt wagons, conveyor systems and the waste dump system for the overburden.

The Rhineland Lignite mines, Hambach, Garzweiler and Inden, are the largest open pit mine in Europe and are operated by RWE Power AG. In approx. 350 m deep pits the mines produce annually around 100 mln tons lignite and 450 mln m3 overburden, which means an stripping ratio of about 4.5. Around 266 km conveyors are used with belt width of 2000 mm to 2800 mm for haulage of lignite and coal. Spreaders are used for the waste dump.

Crusher Selection

The crusher is the key component in medium hard and hard rock applications and so also in IPCC systems. The selection of the crusher type depends mainly on the rock properties, the throughput capacity and the required size distribution. Figure 3 shows indicative the capacity and rock strength for the most common crusher types. At present largest capacities are beyond 10,000 t/h. Gyratory crushers are used for very hard rock, whereas the compact sizers in softer rock are used. Double roll crushers are larger in design and focus on medium hard rock. The hybrid crusher is nearly as compact as sizers but are designed for harder rock material.

Gyratory crusher

Gyratory crusher

Gyratory crushers are predominant in hard rock applications and high capacity operations and are commonly used in fix or semi mobile crushing stations. The throughput is influenced by both rock strength and the fragmentation of the feed. Relocation of the three to four crusher modules is commonly made by transport crawlers. Trucks are either unloading the rock into a rock pocket or into the hopper of the semi-mobile crushing station. An apron feeder transfers the rock into the gyratory crusher. Hopper and apron feeder can be dropped when trucks are directly unloading into the receiving hopper above the gyratory crusher. This so called direct feed is cheaper than the hopper and apron feeder version.

Due to the large size and the dynamics gyratory crushers have not yet been built onto track mounted fully mobile crusher stations.

Double roll crusher

Double roll crushers are used for medium hard rock up to rock strengths of typically 70 MPa. The crushing mechanism is mainly by high pressure which is provided by two rollers with comparable large diameters. All Ciros double roll crushers are equipped with hydraulic gap adjustment for overload protection.

Sizer

The rollers are smaller than in double roll crushers and are equipped with cutting picks. The crushing mechanism in sizers are mainly shear forces which are generated by high roller torques at lower circumferential speed (see Figure 6). The compact design of sizers supported the development of fully mobile crushing solutions

Hybrid Crusher

The hybrid crusher of Ciros’s CR 800 series is a robust and compact roller type crusher combining the advantages of a sizer and double roll crusher. Flywheels at the crusher shafts enable the economic crushing of rock with higher compressive than sizers. The hybrid crushers are designed for rock strength beyond 50 to 70 MPa. The reduction ratio of the hybrid crushers is 1:4 to 1:8 .

Like the double roll crushers all Ciros hybrid crushers are equipped with the hydraulic gap adjustment which ensures optimal product size and throughput even at varying feed size distribution and adjusting to roller wear.

The gap adjustment operates also a quick response overload protection even if such load occurs asymmetrically. When e.g. a shovel bucket tooth gets into the rock material, the crusher quickly opens the gap for release of the tooth and returns thereafter to normal operation mode without stop.

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2 Responses to “ Hard rock mines mining ”

  1. Demand:excavator crusher | Materials:Gold mine | Mike Ernst from USA Says:

    Looking for info on excavator bucket crushers for 20 ton excavator thanks Mike

  2. Demand:Excavator Mobile Crusher | Materials: Hard rock mines | Customer from New Zealand Says:

    Price in $NZ dollars for supply and freight to NZ excavator crusher suitable to fit a 20 ton excavator.

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