Published in June 2007 Australian Longwall Magazine
Story by: Angie Bahr
Photography by: Judi Graphics
The slow-developing grass tree grows 1 centimetre of trunk per year – but once matured is a stunning plant synonymous with the Australian landscape. Anglo Coal’s Grasstree longwall mine shares some attributes with its namesake.
Work began on the development project in 2001 with intentions to start longwall mining in 2005. After some hurdles, the mine actually began cutting coal with the longwall in September 2006 and finished its first block in April.
While the time it took to get the mine up and running went a little longer than originally anticipated, the operation is now breaking away from its namesake and plans to accelerate its growth to produce 4.5 million tonnes this year.
Grasstree is located in Queensland’s central Bowen Basin and extracts coking coal from the 2.3-2.7m German Creek seam. The lease holds reserves of 40Mt, extending out the mine’s life for 11 years. The operation has been designed as a high capacity, low seam mine – with ambitions to produce in excess of 5Mtpa.
The mine, 250m below the surface, is serviced via a shaft/winder system for transportation of personnel and equipment. Grasstree’s shaft system is quite unique, being one of two mines in Queensland with this system. While the ride down is a windy one with the intake air blasting through, it doesn’t take too much time to hit pit bottom.
At the time of Australian Longwall’ visit in May, Grasstree had just finished its first longwall move and had commissioned the face. As first moves go, it was reasonably successful for the crew. The team broke chain on April 17 and was back on coal May 12 – making it a nudge over three weeks for the entire move.
The move for Grasstree has been made easier with a second set of face gear, including shearer, which is set up and tested before the team moves the shields and other equipment to the new panel. This also allows the major components not being used to be brought to the surface for maintenance.
Longwall coordinator Scott Barwick said many of the crew are inexperienced (six out of nine in the longwall crew), with many of the experienced staff sourced from the German Creek Central and Southern collieries. He hopes that in time the mine will get move time down significantly. “For this first move, 80 percent of our crew had never done a move before and it was the first one for many people in their current positions. We learnt a lot and aim to get the move down to two weeks in the future.”
Part of the improvement will be seeing how US coal giant Arch Coal does its longwall moves, particularly at the highly productive Sufco mine in Utah, under a improvement/sharing deal struck between Anglo and Arch.
Working the second panel’s face until the next move, projected for November, will be an Eikhoff SL300 DERDS shearer, which features a brand-new set of Kennametal drums. The new 2m drums will allow the 1150kW shearer to better clean up across the face.
Also working at the 300m face is 170 2-leg DBT shields, with a yield load of 1152t, 1.4-3.4m working range and PM4 controls. The armoured face conveyor, beam stage loader and coal crusher is also DBT. The coal clearance capacity is not a problem for Grasstree, rated at 3500tph out of the bin. The operation also utilises a 600m Macquarie Manufacturing monorail.
The electrical package has been supplied by Ampcontrol and includes a 6.25mva 3300/1100v IP66 transformer, 7-outlet IP66 pump DCB, 8-outlet FLP P66 combined face DCB and control and monitoring enclosure and Ampcontrol voice communications and iMAC face lockout system.
The second block currently being worked is shorter than planned after it pulled up short when development encountered a 3m fault. Barwick said the development crew are now trying to mine through to extend the length of panel 804. The original mine plan had shown longer blocks, which means less moves, making for up to 5.5-6Mtpa production, but at this stage the fault has not been mined through to lengthen the blocks to the original plan.
When mining the first panel, the Grasstree crew had its work cut out with an intrusion along 150m of the tailgate. This slowed the longwall and wore down numerous picks. Hopefully, with the second block the longwall crew won’t encounter similar challenges. Barwick said there was one dyke in the panel but “would not cause too much drama”, and there had been some seismic identified but their impact will not be known until encountered.
With these few geological issues, the longwall crew has still produced some impressive results. Their best week to date has been 147,000t. They mined the first block of 2.2Mt in 26 weeks. On the first week of production on the second block, the crew mined 52,000t and plans to ramp up to 120,000t a week.
On this second panel, Grasstree will start to use automation under supply by CSIRO as a commercially funded project. While already up and running at Beltana and Broadmeadow longwalls, its deployment at Grasstree will be another step forward for the CSIRO team.
According to CSIRO Exploration and Mining principal research engineer Dr David Reid, the Grasstree automation is important to show the broad applicability of the technology across multiple equipment manufacturers and mining operations.
Grasstree operates an Eikhoff shearer and DBT shields. The initial automation focus will be on horizon control.
The automation technology is presently installed on the Grasstree shearer. This provides three-dimensional information about the shearer path, which will be displayed to the operators so they can see the face alignment and horizon control.
The next commissioning stage is to provide the shearer with horizon adjustments from the automation system and observe the shearer control system response. Under closed-loop control, the automation system will provide regular horizon adjustment updates to the shearer to ensure the desired in-seam horizon is maintained.
For Barwick, he has seen no apprehension on the longwall crew’s part in using automation. “Everyone’s supportive and keen to get it in. Once the guys see the advantages, they will be more than happy to use it,” he said.
In other new technology, Grasstree has ordered a complete tracking and two-way messaging cap lamp system from NLT Australia. The order includes IS tracking for all of the supplied cap lamps and underground vehicles, which monitors and locates personnel and equipment throughout the underground workings and can assist in managing an emergency situation. The tracking system operates on the same fibre backbone as the Messenger and does not require a separate network infrastructure to be installed.
The Messenger cap lamps will use NLT’s newest IS-approved LED headpiece, which will eliminate the need for bulbs and therefore all bulb replacement costs.
“The ability for workers to send messages back to the surface has huge implications for safety – not only during rescue operations, but during daily operations as well,” NLT Australia managing director Tim Haight said. “For the first time, workers will be able to send emergency alerts to central control rooms or other networked computers, call for help or simply verify their status.”
In other safety matters, like the grass tree plant, the mine has to be well-drained to thrive. Grasstree has pre-drained the panels using well-proven medium radius drilling (MRD) techniques and in-seam pre-drainage to control gas. They have also utilised post-drainage goaf bore holes and ventilation and tailgate sealing strategies.
With pre-drainage, much of the existing water is also drained from the seam, which leads to some dust issues on the face. To combat this, the operation is trying various methods, including water infusion via inseam boreholes. A trial is currently being conducted where the longwall will intersect the infused part of the seam about mid-June, where they will see the results.
The mine is also looking into water additives for the sprays on the face, and are also trialling different spray positions for maximum dust reduction.
Grasstree’s safety and emergency response mettle will be tested this year with a Level 1 emergency exercise. “We genuinely want to have our guys ready – not just because there is going to be a level 1 – but it certainly gives us a good incentive,” Barwick said.
Grasstree has trained several of its employees in mine emergency management system, which it plans to put into practice during the level 1. The operation is also putting its entire workforce through a Dupont safety course focused on improving safety leadership at the mine.
