A Chinese longwall method designed to maximise recovery from thick seams has proven its credentials. Now the technology is about to be adapted for introduction into Australia.
Will Australian coal miners be prepared to examine something rather radical and unusual? Consider the possibility of mining a 9m seam underground and achieving 85% recovery. It may sound too good to be true but in China a method of doing just that has been developed and perfected over the past 15 years.
Called "top coal caving", the method was developed in response to a government edict which demands of miners recovery rates of 85%. The method is very simple conceptually. Coal is first taken conventionally from the seam at a 3m cutting height and loaded with a shearer and front AFC. The remaining top thickness of coal, typically 3-9m, is allowed to cave into the rear AFC. A flipper on the rear of the chock controls the flow of coal into the back AFC.
One of the leading proponents of this method is China's leading coal producer, Yankuang, which is listed on the Shanghai, Hong Kong and New York Stock Exchanges. In 1999 the company produced 26 million tonnes from six mines with eight longwall faces. All faces utilise the top coal caving method. The highest producing face delivered 5Mt in 1999 and a new semi-automated 300m long face is budgeted to produce between 6-7Mt in 2001.
In September 1999, Yankuang's president, Zhao Jingche, accompanied Chinese Premier, Yiang Zemin, on his Australian visit. Zhao signed a letter of intent with the Australian Government to facilitate making a coal mining investment in Australia. Yankuang hopes that an investment in the Australian coal sector will culminate in an improvement in the efficiency and competitiveness of underground thick seam mining in Australia by the application of the top caving method.
A technical delegation from Yankuang has since visited five Australian mine sites which mine in thick seam conditions. Michael Kelly, coal mining co-ordinator, CSIRO exploration and mining, accompanied the delegation. Kelly said the initial response of the technical team was that it would be feasible to introduce the top coal caving method in all but one of the mines visited.
Yankuang has decided to progress to an examination of the method's applicability in Australia. An agreement between Yankuang and CSIRO was signed in March to commence a detailed study of the application of the method in Australia.
Kelly, who has seen the method in China, believes it has tremendous potential in Australia where thick seam resources (classed as over 4.5m in thickness) of around 6 billion tonnes exist.
"It provides an economic way of accessing thick underground deposits. In fact it makes economic sense on its own. I think it could allow people to look at marginal areas differently and would allow them to go underground earlier," he said. Sustainability of coal production for future generations was also another major issue.
The method has many advantages, including increased coal recovery. Because equipment is sized to cut at 3m, face control is improved, gear is easier to handle and less expensive. Kelly said other advantages are lower operating costs through increasing the ratio of extracted tonnes per metre of development roadways. Lower height roadways are also a benefit.
Kelly said Chinese research into this method had been sophisticated and had been conducted at several substantial laboratories. Specially designed chocks, for instance, had undergone up to seven generations of development. Similar methods have been attempted in Europe, but have not reached the productivity levels achieved by the Yankuang group.
In Australia, Kelly felt that dust suppression, spontaneous combustion and levels of subsidence were some of the technical issues that may need some focus. In addition, certain aspects of the process would need to be automated because of the differing labour cost structure in the two countries.
He added that over the coming months CSIRO and Yankuang would focus on assessing the characteristic conditions in China and comparing those with Australian conditions. Certain development requirements may then be undertaken which will address differences in the statutory and geotechnical environments.
By conducting initial R&D, Kelly said benefits to CSIRO will be the opportunity to transmit the technology into the wider industry in the future. "In the current economic and safety environment any technological or mining process must show a quantum benefit to industry above and beyond the incremental change currently being sought by all stakeholders," he said. "The top coal caving mining method has the potential to deliver such a change and should be investigated with an open mind."
