Underground » Mining Technology and Production
The aim of this project was to provide the Australian underground coal mining industry with an up to date, state of the art summary of the Longwall Top Coal Caving (LTCC) mining system and its potential for application in Australia. In supporting the project, ACARP requested that the project focus on "summarising the status of the LTCC system and highlight advantages and the problems that must be considered when adopting this mining method in Australia."
The major perceived benefits of the LTCC method for Australia include:
- Operating Cost Reductions: The LTCC method enables potentially double (or greater) the longwall recoverable tonnes, per metre of gateroad development, thereby reducing the development cost/tonne significantly, and reducing the potential for development rate shortfalls leading to longwall production disruption. In addition, other factors such as electrical power and maintenance costs on face equipment are significantly reduced, on a cost per tonne basis.
- Resource Recovery and Mine Financial performance: The LTCC method offers a viable means of extracting up to 75% to 80% of seams in the 5m - 9m thickness range, which constitutes over 50% of Australia's measured and indicated underground minable thick seam resources. Single pass longwall is considered to be limited to an upper height of 6m, and is currently only operating at or below 5m. Improved resource recovery also translates into improved 'life of mine' financial performance through the ability to defray major project infrastructure costs and financing over a larger mineable reserve, hence extended mine life.
- Mine Safety: Lower face heights (relative to high reach single pass longwall) result in improved face control, smaller and less expensive equipment and improved spontaneous combustion control in thick seams, through removal of the majority of top coal from the goaf.
- Some other relevant issues for LTCC are as follows:
- Operationally tested and proven in Chinese mining industry (ie: relatively mature technology).
- The latest Australian resource database shows in excess of 6.4 billion tonnes of underground thick seam coal (>4.5m) in the "measured resource" category, rising to 17.5 billion tonnes when "indicated resources" are included.
In the light of the extent of these resource figures, a controlled, staged program of research into thick seam mining was considered to represent a sound investment in what will ultimately be the future of underground mining in Australia. This current project was an essential first step in such a staged approach.
UNSW and CSIRO have jointly developed a relationship with the Yankuang Group in China, which is one of the leading operators of the LTCC method. The Chinese industry already has many faces operating with this method and has now routinely achieved +5MTPA from the top performing face at Dongtan Colliery (Yankuang Group) in recent years. In June, 2000, representatives from the earlier ACARP thick seam mining UNSW/CMTE project team, together with Mr Bruce Robertson from Anglo Coal Australia, visited China to inspect both multi-slice longwall (MSL) and LTCC operations. CSIRO and ACARP representatives have also visited the Yankuang operations on several occasions over the past five years. All groups have returned with very favourable impressions and views about prospects for the method in Australia.
A hurdle to be overcome before this method is adopted in Australia is providing a potential operator (and investor) with the confidence that the potential incremental economic gain available can be realised, against a perception of risk associated with using different equipment and a different mining method. It is hoped that this status report will provide updated information on the method and applicable Australian reserves, together with operational performance parameters and an economic model to demonstrate the LTCC method potential.
Project Objectives The specific objectives of this project were to prepare a summary of the status of the LTCC system and highlight the advantages and the problems that must be considered when adopting this mining method for Australian application. In particular, this project final report addresses the following issues:
- Update of previously developed Australian thick seam database.
- Provision of a literature review on the method and a critical evaluation of current published information on both the technology and the operational performance data for the method.
- The critical issues associated with the method, identified through a risk assessment approach, are highlighted and evaluated in terms of defining the problems and evaluating appropriate elimination or control strategies (eg immediate face/roof control, periodic weighting, impact of face retreat rate on performance, coal fragmentation, dilution, rear AFC/support maintenance, gate end design, spontaneous combustion management, dust).
- The relative economics of an LTCC operation compared to a 4.5m high single pass longwall are developed through an operational and economic model.
In terms of equipment innovation, the more recent Chinese developments have relocated the top coal draw points to the rear of the longwall supports. The Chinese equipment has a pivoting supplementary goaf or tail canopy behind the support. Beneath this is a retractable second AFC. With the rear AFC extended and the rear canopy lowered/retracted, caved top coal can be loaded onto the rear AFC, whilst production continues conventionally in front of the supports. In the retracted rear AFC position with the rear canopy raised, the supports and face operation can function conventionally.
The Chinese industry reports averages of 15,000 to 20,000 tpd from an LTCC face; up to 75% recovery of 8m+ thick seams using a 3m operating height longwall; and +5 MTPA face production. There are now over 70 LTCC faces in China. A new semi-automated 300m long LTCC face was installed at the Xinglongzhuang Colliery of the Yankuang Group, in Shandong Province, in August, 2001. This is heading towards producing 7 MTPA in 2002/2003.