12/11/2012 | Author / Editor: Stefan Hinterholzer * / Marcel Dröttboom
Mátra Kraftwerk, Hungary, mines some 8 to 8.5 million tonnes of lignite each year, most of which is used to generate electricity in the company’s own power plant. To expand the capacities of its Bükkábrány open-cast mining sites, the company ordered a compact bucket wheel excavator with a capacity of 6700 cubic metres per hour.
The PE100-1600/1.5x20 Bucket Wheel Excavator made by Sandvik – by virtue of its design and size the world’s largest compact bucket wheel excavator to date – with an overall weight of 1650 tonnes, is designed to handle 6700 lm3/h or an annual capacity of 12 million bm3+t. The complete supply for Bükkábrány (Hungary) consisted of a bucket wheel excavator and a belt wagon, as shown in Figs. 1 and 2.
With some 10 million inhabitants and an area of 93.000 square kilometres, Hungary is relatively small European state. With regard to energy, it is highly dependent on imports. About 70 percent of Hungary’s primary energy requirements are covered by imports. Natural gas, mostly imported from Russia, comprises the largest share in primary energy consumption. That’s why great importance is attached to the extraction and utilisation of domestic energy carriers – not least for reasons of security of supply. Mátra Kraftwerk G.AG is currently making a significant contribution to this. Mátra Kraftwerk G.AG mines some 8 to 8.5 million tonnes of lignite each year, most of which is used to generate electricity in the company’s own power plant at the Visonta location. Mátra covers more than 10 percent of Hungarian electricity requirements, making it the second largest power producer behind the Paks nuclear power plant.
To meet power plant coal requirements, Mátra Kraftwerk G.AG is operating two opencast mine and the Visonta opencast mine (Fig. 5).
The initial plans for expanding the capacities of the Bükkábrány open-cast mining sites were already drawn up in 2005. The overburden equipment used in the mine at that time (3 × SRs/H/-401) was not able to excavate the required quantities of overburden on its own despite continuous increases in capacity and maximum utilization and had to be assisted by cost-intensive shovel and truck operation with an annual capacity of 4 to 5 million cubic metres. The “Bükkábrány Compact Excavator” project was initiated to ensure the long-term handling of overburden in all anticipated coal requirement scenarios, to reduce the costly shovel-and-truck-operation to a technically required minimum and, finally, significantly improve the productivity of its own large-scale equipment capacities.
Following a work-intensive phase of detailed studies, technical specifications, profitability analyses and contract negotiations the order for supplying a compact excavator unit (excavator and belt wagon) was awarded to Sandvik Mining and Construction Materials Handling GmbH in the summer of 2007.
The equipment unit is to be used on the first bench of the Bükkábrány opencast mine. It will have to implement cut heights of up to 50 metres. The compact bucket wheel excavator will implement these cut heights in high cut, in places on a high bench and low bench, and in exceptional cases in low cut operation. It should be able to implement the following operating modes: excavator directly onto feed hopper car, excavator via belt wagon onto feed hopper car dumping operation with/without belt wagon. The device geometry will be dimensioned based on this. Fig. 6 shows an example of when the equipment is in use.
The equipment unit is to achieve a capacity of 6700 Im3/h and an annual effective output of 12 million bm3+t. This output is required to reduce the cost-intensive overburden stripping by subcontractors used in the Bükkábrány opencast mine today to the technologically required minimum. The compact bucket wheel excavator will mainly be used in abrasive and partly cohesive materials. Transfer substations, buckets and teeth had to be designed accordingly to protect them against wear. Optionally, temporary coal extraction is to be possible; this had to be taken into account as well in designing the excavator. Depending on the future coal need scenarios, the unit is to be operated for up to 40 years. Thus its fatigue strength was designed according to DIN 22261 specifications.
Its design and dimensions make this compact bucket wheel excavator the largest one in the world to date. The excavators used in the Bükkábrány so far achieve an annual output of approx. 6 million bm3 per year, meaning that the new device has about double their capacity. With respect to operating weight, driving power at the bucket wheel and travel gear load, this device enters new, challenging dimensions.
The most important technical data of the compact bucket wheel excavator and belt wagon is listed in Tables 1 and 2.
The compete calculation of the equipment unit was carried out in accordance with DIN 22261 specifications for the calculation, design and manufacture of excavators, spreaders and ancillary equipment used in lignite opencast mines. These specifications were systematically implemented for the first time when constructing compact excavators. Finite element models (FEM) were used for all supporting structural steel components and main mechanical components (e.g. the bucket wheel gear). To evaluate fatigue strength, we calculated the corresponding utilisation rates (the ratio between the actual and the admissible stress repetition). As a result, we were able to prove the required fatigue strength for a service life of 50 years for the most important components.
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