Also the mining operations are hindered by the presence of hard intercalations. A WIRTGEN Surface Miner, type 3500 SM, with a theoretical production rate 1,050 m3/h (bank) and a working depth of 470 mm was recommended for the selective mining of the lignite and dirt bands to increase the heating value and reduce the ash content of the ROM lignite. The 3500 SM WIRTGEN Surface Miner went into operation at this mine in MAY 1990.
The coal and spoil are seperately extracted by the WIRTGEN Surface Miner with a high degree of selective in layers of up to approx. 470 mm in thickness, and then transported by truck to the power plant or to the dump as appropriate. Furthermore this machine extracts hard layers without any noticeable restrictions to production.
| Bench geometry: | - length >1,000 m |
| - width >30 m |
During the concluding performance tests, the following results were achieved:
| Production rates: | Coal (UCS 90 kg/cm2) 595 m3/h(bank) |
| Marl (UCS 75 kg/cm2) 800 m3/h(bank) |
| Pick consumption measured after 500 h: | approx. 100 pcs. |
| Total mining output after 500 h: | 392,500 t lignite |
The mined mineral - coal or waste material, correctly sized for conveying is being loaded to dump truck.
The WIRTGEN Surface Miner 3500 SM produces appr. 40% of the required coal.
The average heating value of the coal excavated by the WIRTGEN 3500 SM is 33% higher than the coal excavated by the bucket - wheel excavator. The ash content dropped by 45% when using the WIRTGEN Surface Miner.
The WIRTGEN 3500 SM at Gacko is now the key coal production machine. Since the WIRTGEN 3500 SM has been in operation an improvement of appr. 20% of electricity per t of lignite was realized!
The Gacko 300 MW power plant is coal-fired with lignite which is extracted from an open-cast mine located next door. The annual requirement amounts to 2,400,000 t lignite with an average thermal value of 8,000 kJ/kg (ROM).
The lignite deposite dips in the mining direction at an angle of approx. 5° to 4° (average 10°). The top seam is approx. 12 m to 14 m thick and is interspersed with marl layers of up to 1.0 m in thickness.
The majority of the overburden and the lignite are mined by means of bucket - wheel excavators and transported via mobile transfer conveyors (belt wagons) and a shiftable belt conveyor to the power plant at a production rate fo 1,250 m3/h (loose).
However mining the above mentioned top seam with excavators result in the marl layers being extracted and intermined with the lignite. this reduces the thermal value of the lignite from 11,500kJ/kg ROM in situ to 7,300 kJ/kg. Because of this reduction the power plant has to be shut down several times a year for claiming of the firing equipment.