by Jeremy Busfield, principal mining engineer, Australian Mine Consulting Services

Based on First quarter 2000 production stats.

Longwall systems are rated by their AFC capacity which, over the last twenty years, have steadily increased in line with technological advancement. Current Australia longwall systems range in capacity from 1,000tph up to the three most recent installations at 4,500tph.

Therefore when comparing longwall productivity, it makes sense to compare mines with similar capacity longwalls. This analysis also assists in determining whether the higher rated systems are actually delivering higher productivities.

Of course AFC capacity is not the sole determinant of productivity. Numerous other factors play a part, such as panel width, seam thickness, working roster, equipment availability, etc. However an analysis purely based on AFC capacity provides some interesting results.

The twelve highest rating longwall systems are analysed and grouped according to their AFC capacity (2,500, 3,000, 3,500 and 4,500tph). The average daily longwall production over the last 12 months is calculated and then multiplied by the typical number of operating days available in a year. Assuming a seven day roster and an allowance for one longwall changeout per year (35 days) this then indicates the productive potential of each longwall system.

The average productivity of Australian longwalls based on AFC capacity is:

2,500tph 4.1Mtpa

3,000tph 3.2Mtpa

3,500tph 4.9Mtpa

4,500tph 5.0Mtpa

A productivity increase is evident based on AFC capacity however the difference is not as uniform as could be expected. Notable exceptions are the 3,000tph and 4,500tph systems.

Little difference is noted between the 3,500 and 4,500tph systems which is due in part to the early teething problems at the new mines. It is expected that with time, the average productivity of the 4,500tph systems will increase towards 6Mtpa as Moranbah North and Oaky Creek North get back into full production.

The 3,000tph longwall systems are notably separated from the rest. The suspected reasons are due to the specific mining difficulties at each of the mines of Kenmare, North Goonyella and Dartbrook.

In summary, the top performing mines, among their peers, are Oaky Creek # 1, Crinum and Newlands.