Originally designed by South African-based consulting firm, Mining Consultancy Services (MCS*), the cycle aims to minimise the web cycle time, regulate cutting speed to avoid overloading the AFC, and reduce the duty cycle forces on the shearer.

 

Speaking at the Yeppoon longwall conference in March, Matla general manager, Jock Nel, outlined the method. Matla has used both the conventional “Bi Di and “Half Face” web cutting cycles but have found major benefits in using the OPTI cycle.

 

The web cycle time of OPTI cycle cutting is around 22 minutes per web, compared with the web cycle time for Bi Di cutting of 26 minutes per web.

 

“The OPTI cycle is therefore approximately 15% more productive, for a seam height of 4m in the 4 seam at Matla, however the productivity differential increases to approximately 30% for a seam height of 5.5m as proposed on Matla’s 2 seam shortwall,” Nel said.

 

The OPTI cycle extracts the web in two passes of the face with a half face snaking system with a bottom bench or top and bottom benches left to be extracted on the second pass. The web cycle time is minimized by eliminating the double shuffle process and regulating coal output over the cycle to eliminate peaks.

 

Because the face is extracted in two passes the shearer can cut at a higher haulage speed. The same applies on the second pass, except the shearer is cutting to a free face. Bench height is determined by seam height and drum diameter; coal clearance capacity; maximum cutting speed of the shearer; and spalling propensity from the floor or roof bench.

 

Matla’s face output is currently limited by the belt conveyors to 2500tph. This means, at a web of 1000mm and 95% web factor, the speed of the shearer is limited to 7m/min when cutting full seam height towards main gate.

 

Other advantages to the OPTI cycle have been found to be a reduced power requirement on the AFC.

 

The peak loading rate generated with bi di reduces from 2600tph to 2270tph. Average loading rate over a cycle increases from 1500tph to 1773tph due to the shorter web cycle time.

 

When extracting thick seams combined with hard cutting conditions, one of the challenges is the cutting reaction forces and the stability of the shearer. The OPTI cycle addresses these issues and consequently improves the duty cycle on the shearer.

 

* Mining Consultancy Services (MCS) are represented in Australia by managing director, Chris Wilkinson, who is also heading up the newly opened division of John T Boyd in Brisbane.