Mine operators have been increasingly turning to an alternative to conventional rip-and-stack or drill-and-blast coal mining – the use of surface miners.
Diverse studies and tests show that surface miners offer considerable advantages in terms of both economic efficiency and the final product.
Road and mineral processing industries solutions provider Wirtgen supplies surface miners in a variety of performance classes for the selective mining of commodities such as coal, limestone, bauxite, gypsum, salt and phosphate.
In addition to mining, these machines can also carry out routing operations for constructing roads and railway tracks, rehabilitating roadways and installing tunnel floors. The range of applications further includes the precision cutting of ditches and channels as well as surface levelling.
Wirtgen conducted a study in collaboration with RWTH Aachen University, in a black coal mine in Queensland, Australia.
The Wirtgen 4200 SM surface miner was integrated into an ongoing operation for the selective mining of coal and interburden. Previously defined targets were checked regularly to determine if they were being met. The production rates of the surface miner were compared with that of the previously used rip-and-stack method over a period of four months based on various performance indicators.
The conventional mining system comprises two supersize dozers for ripping and stacking the material and a large wheel loader for loading it to dump trucks with payloads of between 130 t and 190 t.
Health and Safety
Compared with the three mining machines used at the mine previously, using a surface miner significantly reduced noise emissions.
Mining with the 4200 SM also has a positive impact on dust emissions. In contrast to the dozers and wheel loader – all of which generate considerable quantities of dust that impact on the work environment – the dust produced by a surface miner is contained in the cutting drum housing. A dust suppression system comprising an integrated water spray system also helps to additionally reduce and bind the dust.
An analysis of the two mining methods further demonstrated that fuel consumption is about 79% lower – and, therefore, also carbon dioxide emissions – with surface miners than when using the conventional method. The lower number of machines in use additionally has a positive effect on risk management, because fewer machines mean a reduced risk of accident at the mine.
The surface miner’s anti-vibration cabin offers better ergonomics and optimised working conditions for the machine operator.
Coal seams are generally of varying thickness and separated by interburden layers. Precisely separating the various materials is of tremendous importance if coal is to be mined as cost-efficiently as possible, because it significantly reduces processing costs. Another major cost driver is the percentage of fines, because they are more costly to process than coarse material.
For the study, 100 samples were analysed during operation of the surface miner to determine the particle size distribution. The samples were compared with similar samples taken from the conventional mining equipment and identical mining fields. Significant advantages emerged when working with the surface miner, which produced 14% fewer fines at grain sizes of less than 2 mm, compared with the conventional mining system.
The portion of fines to be processed dropped by 22% at grain sizes of less than 1 mm and by 36% at grain sizes of less than 0.5 mm. Further savings were achieved by significantly reducing the quantity of oversize material. For example, only 17% of the material mined by the surface miners had to be crushed, compared with 26% for the dozers.
Further, working with a surface miner reduced coal mining losses and dilution of coal in the mine. This leads to more product, therefore increased turnover and an improved exploitation of the deposit and thus, a better stripping ratio.
Moreover, Wirtgen surface miners can cut, crush and directly load material onto trucks or dumpers in a single operation, which saves time and the additional cost of purchasing machinery and fuel.
With surface miners, drilling and blasting can be eliminated, therefore commodities located near residential areas, public roads or other infrastructure can be effectively mined. Further, mine operators no longer need to spend time obtaining the required permits, hiring certified blast personnel or compiling the associated documentation.
The use of a surface miner also has a positive effect on water management at an opencast mine. The cut surfaces are levelled and can be cut at an angle. Drainage is further improved as water seepage into the ground is reduced.
In recent years, Wirtgen has conducted several large-scale field tests on particle size distribution and run-of-mine material degradation. In these studies, coal and sedimentary ore from eight different pits were analysed to determine their particle size distribution. About 8 000 t of material were screened to compare the material produced by surface miners with that extracted by conventional mining methods.
All the studies illustrate that using Wirtgen surface miners delivers compelling improvements in final product quality, cost efficiency, environmental protection and safety.
In order to fully exploit the surface miners’ profit potential, an analysis should be conducted when starting the planning of a mining project.