Open Cut » Coal Extraction
This project has developed guidelines for the use of dozers in coal seam preparation operations with particular emphasis on minimising the generation of coal fines by optimising dozer operations. The project also investigated the use of dozers in waste pushing.
The efficiency of coal processing is strongly related to fines generation at the initial stages of coal mining. Increased fines content in ROM feed leads to higher handling and processing costs, low yields, increased product moisture content, and in many cases a reduced product value. Coal fines are generated in all stages of mining but the scope of the current study is limited to fines generation during coal seam preparation with dozers.
An industry-wide review was conducted, covering a major proportion of the open cut mining industry. The review was primarily aimed at understanding the way coal seam preparation with dozers is planned, conducted, measured and analysed, and also to identify potential trial sites. A report detailing this review was distributed to the participating sites.
The project determined that dozers are frequently used with little planning, measurement or analysis. The methods adopted are not responsive to variations in mining conditions such as seam structure and hardness, working block geometry or available equipment. Although the importance of fines, its downstream implications and the role of dozers in fines generation are well recognised, not enough resources are allocated to quantify and address the problem.
There are three main schools of thought:
- Rip and leave
- Rip and push
- A combination of the above.
The rip and leave technique is a quality driven approach, whereas the rip and push technique is driven by loader productivity and is more widely accepted. Combinations of these two techniques are also used to a much lesser degree. The choice of a technique is rarely based on an economic evaluation but rather on a status quo or at best on a simple seam thickness related judgement .
A number of site trials were conducted within this project in order to benchmark the current practices and to develop and test practical methods to reduce fines generation while maintaining the same equipment fleet and working conditions. The field testing program set out to demonstrate the impact of simple changes to the dozing pattern on fines as well as to gather data for the models. The techniques developed at each site were not optimised for prevailing seam and mining conditions at the sites. This is best done by the mine's own personnel following the guidelines developed and using appropriate tools provided as part of the project.
A reduction of 6-19% in fines content, after the rotary breaker was achieved by simply switching from the rip and push technique to the rip and leave technique and by altering the rip spacing. The loader productivity decreased by 10-18% while dozer productivity dramatically increased by 100-200%. These improvements are significant by any standards. More significant gains will flow from further optimisation work.
The final report and accompanying software ( Dozing Workbook ), provide the base tools to assist mine operators find the balance between dozer cost, loader efficiency and fines generation.