Published in September 2006 Australian Longwall Magazine

Chinese low-seam underground mines are finding fantastic success with DBT’s automated plow systems, with one Chinese producer now looking to install its fourth system.

Mining of thin seams in China is big business. More than 25% of all proven coal reserves are below 1.5m thick and according to Chinese regulations, lower thicker coal seams must not be mined first at the risk of sterilising the higher, thinner seams. Most of the lower thicker seams also contain high methane, which means the upper thin seam must be mined first as a so-called “protective seam” to release the high methane from the thicker seam, according China’s safety regulations.

Thin seams offer producers higher-grade coal – which in China is in high demand as a standalone product or for blending.

While the plow offers great productivity in China, safety is also the paramount reason the country’s operations have turned to DBT’s plow.

“Removal of the coal face worker from the coal extraction process, particularly in the thin seams, is considered a major advantage in the efforts to improve the coal miner’s environment,” DBT international sales vice president Harry Martin said.

“The automated plow longwall system is seen as a potential solution and to this end a number of such systems have been acquired and established. Six such systems are in operation, with two more committed and a further number in various stages of project process.”

With the plow, no operators are required on the face. Plow drives are also located in the entries and the only type of breakdown requiring work on the face would be something like a broken chain, but with the use of DBT’s maintenance-friendly load sensing and overload protection features, this is unlikely, and the highest levels of system availability are achieved.

The plow has neither trailing cables due to drives being static and located in the entries, nor trailing dust suppression hoses because a water curtain automatically triggered by the plow location provides adequate dust suppression. Plus, the plow takes much thinner slices each pass than a shearer and because the cutting motion is not a grinding type, less fines are produced and ventilation does not have to take into account the step caused by the relative wide web of the shearer.

According to Martin, not one accident has occurred to date on a Chinese automated plow face.

The Chinese Tiefa Coal Mining Company now operates two systems, with the third currently being delivered and a fourth project underway. Click here to view plow records .

The plow system was attempted in China in the early 1990s but enjoyed only limited success due to a number of inherent operational weaknesses associated with manual operation.

“The need for personnel on the face working in extremely restricted and confined places for horizon control/adjustment, face alignment, plow advance and shield lower, advance and set resulted in limiting the full potential of the plow,” Martin said.

In 1998, Tiefa adopted a different approach and looked at applying a fully automated system after learning of such attempts in the United States and Germany.

Tiefa decided to import a complete automated plow system from DBT with shields from BMJ (operated by DBT controls), thus minimising capital outlay and financial risk.

“In addition to the eight systems currently purchased from DBT, a number of current users are budgeting for additional systems plus new potential customers in the thinner coal fields of southern China,” Martin said.

Despite the successes of automated plows in recent years, DBT has already developed and supplied the next-generation Gleithobel plow system GH 42 with double cutting horsepower (2 x 800kW) utilising a 42mm chain.

This system commenced production at DSK’s Prosper-Haniel mine in Germany in September 2003 on a panel width of 400m in extremely hard coal.

This system is expected to allow the high production figures realised in the softer coal, to be achieved from the very hard coals as found in some of the German mines as well as in other mines around the world. The results are that the cutting depth has been doubled.

Martin said to keep development in front of the plow, operations use roadheaders with a single entry configuration.

Horizon control on the plow is manual but is generally checked by operations once a week. The plow is steered by bottom sensors that can sense the difference between rock and coal and transfer this information to the shields to adjust.

Martin said the capital cost between a plow and shearer system was very little.

“By being able to double the installed plow power, harder coals in seam rock and larger cutting depths are possible, resulting in the plow becoming an even better solution for the mining of thin coal seams without the need to mine unwanted and costly-to-handle rock,” Martin said.