Published in September 2005 Australian Longwall Magazine

Success for LTCC at the New South Wales mine will lead to broad use of the technology in thick seam mines and launch a new era of longwall mining in Australia and possibly the world.

While triumph will usher in a new era, failure could prove some sceptics right, with some suggesting Australian conditions aren’t suited to the Chinese LTCC technology. So what is DBT doing to ensure success?

Firstly, the OEM has spent the last three years focusing on developing and introducing Yankuang Corp’s LTCC technology to Australia This work unfolded in conjunction with a major research project into LTCC undertaken by CSIRO and the University of NSW. The Austar mine (formerly Southland) recently placed an order for a complete longwall system.

Yanzhou selected DBT to manufacture the LTCC shields, together with a completely integrated longwall system. Significantly, this will be the first time LTCC technology will be designed, manufactured and used outside China.

DBT and Yankuang Group, the technology owner and Austar’s parent company, recently signed an agreement for an exclusive licence for DBT to develop the LTCC technology for Australian and South African markets.

Development of the project began in Germany in May this year and the LTCC is scheduled to commence production mid-2006. Initial production will be 2.5 million tonnes per annum, but capacity is expected to be well in excess of this figure.

LTCC technology has been successfully developed in China with several of Yankuang’s current LTCC mines producing up to 10Mtpa. In China nearly 80% of a thick seam is extracted using LTCC technology, compared to Australian longwall mines which currently extract about 30-40% of the seam.

LTCC incorporates a conventional longwall shearer typically mining at a height of about 3m. LTCC can be used in seam heights from 4.5-12.5m.

Special shields have an elongated gob shield with a retractable flipper caving at the back that allows the coal in the roof to come in behind the shields. This coal is collected by a second chain conveyor located behind the shields. Both chain conveyors dump coal onto the stageloader.

Top coal caving is not performed all the way along the face, stopping 15m short of the gateroads to ensure roof integrity.

The process has been developed in China over the past 20 years, with 80 LTCC faces currently in operation. The majority of the supports in China are currently four-leg, though one mine has updated to two-leg shields in the last six months with substantial improvement in roof integrity.

The risks for the project are big – “Everyone knows there are risks involved in introducing this technology into Australia,” says DBT Australia vice president Andrew Richmond, but “risks are minimised by good equipment design and management rules”

Austar is rated as one of the most challenging mines in Australia and LTCC technology has not been proven outside of China. Perhaps the biggest test is that the entire system must be approved by the New South Wales Department of Mines.

DBT - together with Austar -- is undertaking a detailed risk analysis of the operation, equipment design and management requirements.

For the Australian experience, it has been suggested two operational methods are developed, depending on site-specific geological conditions. DBT is also looking at developing roof support setting and design requirements for optimum set and yield pressures for the most favourable caving conditions.

Thicker seams in Australia are renowned for slabbing problems. This issue in part is solved by the lower extraction height and the small window the coal must fall through to enter the rear conveyor. Large slabs of coal can be crushed by the caving door before falling onto the rear conveyor.

Geotechnical considerations in gateroad control require a quite complex face and gate-end shield arrangement.

Some Australian critics have suggested the LTCC could slow down the rate of advance – which of course can lead to roof problems in heavy roof conditions. In these conditions, DBT said the rear caving could be halted to speed up the rate of advance, minimise stoppages, and regain stable face conditions.

Over the next six months all risks will be identified, analysed, and either designed out and/or suitable management systems put in place. Already the equipment that has been designed to date has significant differences to that currently in operation.

Between now and the start of coaling in June 2006, there will be numerous opportunities to review the equipment layout, ergonomics and safety through prototype inspections, compatibilities and factory minibuild.

DBT said the project ethos was to get it right before it went underground. “The challenge is there, but the reward, the ability to reliably and safely mine thick seams, is also there.”