The Mount Thorley Mine, located in the Hunter Valley region NSW, Australia currently produce 5.2 million t/year ROM coal. The high quality coal is exported.
Appr.4.5% of the cold has to be mined from the Wambo, Whynot and Blakefield coal seams, which take the from of "multiple seams". The coal seams and dirt bands are between 0.1 and 0.2 m thick and horizontally stratified (angle of inclination approx. 4°).
The current method of extraction means that the thinner dirt bands are removed together with the coal so that the unwanted material then has to be washed out in the coal preparation plant.
This means that of the 5.2 millions t "run of mine" coal, approx. 73% remains after washing, i.e. 3,756,00 t of saleable coal, of whith one third is employed as coking coal and 2/3 is used as power plant coal.
The aim is to increase this overall yield figure from 73% to 75%
In order to achieve the desired improvement in the yield level, it was decided by on site management that a WIRTGEN Surface Miner type 4200 SM should be employed for extracting the top seams occuring in the form of "multiple seams".
This unit would be expected to remove 75% of the coal and non-coal material located in the top seams. It is envisaged that employment of the WIRTGEN Surface Miner will bring an improvement in mining accuracy (tolerance of the digging and cutting depth) from the current 5 cm to 10 cm achieved with front end loaders, to 2.5 cm to 5 cm. The resultant improvements expected are as follows:
1. Increase in coal recovery per m2 of deposit surface area.
2. Improvement in the yield level of the coal preparation plant accompanied by a reduction in the ash content.
3. Reduction of mining costs. Both the pure mining costs and also the improvement in coal quality (reduced ash content) have been taken into account.
4. There is also a reduction in the transport costs for transferring the residues from the preparation plant to the dump.
With the WIRTGEN Surface Miner 4200 SM the following results have been reached:
- The material mined by the WIRTGEN Surface Miner had a 4% lower ash content.
- The throughput in the preparation plant was siginficantly higher:
1,100 t/h of coal mined by the WIRTGEN Surface Miner versus 600 t/h of conventionally mined coal.
The WIRTGEN Surface Miner 4200 SM was commissioned in November/December 1990.
Since August 1991 the machine is working 3 shifts a day, 6 days a week.
Instantaneous production measurements gave the following results: Coal: 1,800 t/h, Shale: 1,300 t/h
These production figures take into consideration downtimes for truck changing (average 30 sec) and turning at the pit end (appr. 2.5 to 5.0 min.). Truck size has been 150 t to 190 t loading capacity.
In terms of productivity the WIRTGEN Surface Miner cuts coal at a rate of 16,000 to 20,000 t/day.
In thinner sections the output will be closer to the lower figure. But recovering 0.4 to 0.5 m thick seams it will reach the production of 20,000 t/day in a three shift operation.
Only 0.083 cutting tools/h have been used in an average.
Besides the quality improvement also the recovery of coal from the deposit could be increased.
With the WIRTGEN Surface Miner 4200 SM, it has been possible to extract thin coal seams that would previously have been considered non-recoverable by using conventional methods.