A new technology in longwall mining will be introduced into Australia shortly, when the first application of a Chinese-developed system of top coal caving is installed in NSW.
The former Southland underground coal mine near Cessnock in the Hunter Valley (formerly owned by Gympie Gold) was closed following a fire. It was subsequently put on care and maintenance under Thiess, which had previously purchased a 10% stake.
The mine, which is the last mining the sought after Greta seam coal, was then purchased 100% in October for $32m by Yanzhou Coal Mining Company of China, and renamed Austar Coal Mine.
Yanzhou is one of the four largest Chinese coal miners in eastern China, with six underground mines in Shandong Province producing more than 40Mtpa of coal, over 90% using the top coal caving method.
The Jining 3 mine produces 10Mtpa, the Dongtan mine is at 8.5Mtpa, and the Zingiongzhuang mine is also at 8.5Mtpa.
Top coal caving was developed originally in France more than 20 years ago but has been further refined in China for dealing with thick seams.
While top slicing has been used elsewhere, the efficiencies are not as high as with top coal caving.
As well, the Chinese government has decreed that at least 85% of a seam must be extracted, rather than the usual Australian practice of going for the sweet spot and often sterilising millions of tonnes of coal that could still be used for things like power generation.
The top coal caving method uses a dual clearance system. While the front looks like a normal longwall system, with a shearer and AFC, a second AFC runs behind the base of the supports to clear coal that subsequently falls from the roof once the chocks have moved forward.
A flap in the base of the rear of each shield is raised to allow the roof coal to cave into the second AFC.
While there are issues with caving control, the effect on support capacity and characteristics, spontaneous combustion and dust, the top coal caving method is considered suitable for seams of 8-9m thickness, as a study by CSIRO Exploration and Mining showed.
Austar Coal Mine will use a top coal caving face built by German longwall supplier DBT under license.
This will be 220m wide with a conventional EL2000 shearer on the main AFC cutting to 2.8m.
The balance of the height of the Greta seam, which ranges from 4.5 to 7.5m, will be handled by the rear AFC (see illustrations for the two AFCs in a typical Chinese configuration at the Yankuang Group).
The system has enabled the Chinese company to produce major amounts of coal in its homeland, with once face alone producing 6Mtpa of raw coal, but at the Austar mine there are constraints of clearance and washery capacity.
It is anticipated that Austar will produce at the rate of 2.5 to 3Mtpa for at least 20 years.
The aim is for production using the top coal caving method to start in mid 2006.
Thiess assisted Austar to mobilise and develop the project that, according to deputy managing director of Yancoal Australia, Boyun Xu, is now owner operated.
According to Xu, speaking to a Mining Equipment and Services Council of Australia briefing in the Hunter Valley, together with Austar Coal Mine general manager Graeme Duncan, the current activities include recruitment of staff and mine workers, training, finalisation of the development start-up plan for longwall A1 and underground pre-development preparation.
Also underway are maintenance and upgrading of the coal clearance system and finalisation of the mine ventilation plan. The company says its objectives are to operate the mine safely, productively and profitably and to become a “shining” example of Chinese-Australian business relationships.
The top coal caving face will also become a working example of a technique that it says has much wider application in Australia, especially among thicker seams.