Moranbah North's world first

THE world’s biggest powered roof supports have arrived at Anglo Coal’s Moranbah North mine in Queensland.

Angie Tomlinson

Published in September 2008 Australian Longwall Magazine

Moranbah has taken delivery of 35 by 1750-tonne, 2m-wide Joy Mining Machinery roof supports as the first part of its onsite mini-build and compatibility testing as it prepares to head underground for installation in the second quarter of next year.

The roof supports, the biggest in the world, will be part of Moranbah’s new 151 shield face which it hopes will combat the yielding and roof fall incidents it has suffered in the Goonyella Middle seam.

The installation will be carefully watched by the longwall industry worldwide as Moranbah rises to the challenges of installing, operating and moving the massive supports. But most importantly, the industry watches to see if the powerful supports will combat the strata issues at the mine.

“I can assure you for what it is worth there are a lot of sceptics out there because they can’t understand why you need a longwall that big. They can have their view and we will see. We can’t do any more than what we have tried,” said Anglo Coal Australia’s regional engineering and maintenance manager Peter Van De Ven, who has been an integral part of the extensive design and specification team for the powerful supports.

Strata issues in the Goonyella Middle seam are nothing new for the mine or other adjacent mines operating in the seam. Moranbah North started extracting from the seam in 1999.

The depth of cover at the mine varies significantly as the seam dips down into the 100 series panels. With the increase in depth has come significant yield problems for the roof supports with cavities forming on the face and resultant roof falls.

“The present face suffers from being in yield far too often and it was getting progressively worse the deeper the mine got,” Van De Ven said.

He said with the 980t-rated supports the face was yielding 40-50% of the time with support leaning issues, equipment damage and recovery operations.

“We knew we had an issue with the capacity of the existing face. It’s a catch 22 – because the slower the face goes through the ground, the more load it attracts, the worse conditions become.”

In the face of this issue Moranbah in 2004 purchased 25 by 1200t-rated supports which were initially installed at the mid-face. While a “localised” improvement was noticed compared to the previous supports, the 1200t supports had limited overall impact. Van De Ven estimated the supports reduced yield time from 40-50% to 10-15% – still an unacceptable level.

“As project investigation/justification work progressed through 2005 and 2006, the inadequate PRS capacity was recognised as a major issue,” Van De Ven told delegates at the Australian Longwall Mining Summit in June this year.

“We then went and asked how much bigger do we have to go? And that’s how we came up with a 1750-tonne, 2 metre-wide support.”

Anglo adopted a wide-ranging process to determine the Powered Roof Support (PRS) or shield capacity. They looked at historical databases for similar conditions and equipment, and spoke to original equipment manufacturers for their expertise.

The team used strata interpretation and computer modelling techniques, looking at ground reaction curves (FE analysis) and displacement modelling and the Citect and Optimate Faceguard interpretation. Underground face cavity mapping was also used, together with other expert’s opinions.

During the review process consultants – Australian Mining Consultants and Mining Consultancy Services – were used to do the modelling work and the PRS review. Interpretation work was also done to attempt to predict how the roof and supports would behave in future panels, and the Citect data with 3D modelling to confirm the requirements and assessment. Optimate’s Faceguard software was used to validate the modelling.

According to Moranbah North general manager Tim Hobson, members of the workforce were also involved with the design of the supports.

The final specifications for the Joy supports were determined at 1750t yield rated, 2050mm centres with 480mm leg cylinders. The roof supports each weigh 61t, with the gate end supports coming in at 64t.

The supports have a height range of 2.4m to 5m and are controlled by Joy’s RS20s control system. Inner and outer sprag plates were also specified.

Van De Ven said consultants WBM were brought in to carry out a full finite analysis review of Joy’s design. The supports were put through a 90,000 cycle testing and while there were some initial issues at testing stage, the final design of the supports passed the test program.

The new face has been made MDG41 with hydraulic hoses sleeved, individually tagged and the high-pressure hoses restrained. Other enhancements include RS20s control system for the supports and the use of JOY’s FACEBOSS system and the LASC automation system.

Along with the 151 roof supports (72 expected in October and 42 in January) for the 308m Moranbah North face, Anglo has also placed orders for two Joy 7LS6 shearers with LASC automation capability; two matching Joy 2.05m-wide AFCs rated at 4500 tonnes per hour with 50mm Broadband chain. The AFC will be powered by three 1000-kilowatt maingate and tailgate drives.

Van de Ven said the shearers, being manufactured at Joy’s US facilities, will arrive in September this year.

The new equipment will be mated with recently purchased Joy Mining BSL/Crushers and a pair of Longwall Hydraulics pump stations.

Moranbah North Powered Roof Support project manager Johan Laubscher said the mini-build started onsite mid-year when 34 supports were used with the new maingate, tailgate and panline.

“The final assembly of the drive components are currently in progress and connecting the supports to the AFC is the next task. Once the shearer arrives in September it will be assembled and put on the panline.

“The next step after this is to obtain the BSL, DCB, CMU, pump station and more that is currently being used underground in LW201 after the longwall move is completed and assemble this with the new equipment to complete the longwall system.

“Compatibility testing will then commence with completion scheduled by end of December 2008. The training of the crews will start in December and be completed by February 2009 on the mini-build equipment,” Laubscher said.

Hobson said installation would commence in March with the aim of a walk-on, walk-off scenario where the new longwall is fully commissioned before the previous old longwall is completed.

Laubscher added once the new face is up and working, its performance will be monitored through CITECT, plus the mine will look at the availability and utilisation of the equipment.

Van De Ven said the only additional purchase the mine is currently investigating is for a monorail.

To move the massive supports, Moranbah was required to buy a special longwall move fleet, capable of hauling the 64t supports. Currently the largest shield haulers on the market handle up to about 50t.

Industrea Mining Equipment (formerly Boart-Longyear) secured the contract to supply the dedicated fleet, which includes five purpose-built 70t roof support carriers, two 70t mine dozers and two 70t electric retrievers.

Laubscher said the manufacturing of the transport equipment was progressing well with the first of the five carriers on wheels late in August and undergoing initial testing. All five carriers will be delivered to site in January 2009 and fitted with an additional lifting plate arrangement. The first dozer is expected at the end of January 2009 and the second to arrive in April. The two retrievers have a scheduled delivery of June 2009.

On an operational level with the new longwall Laubscher said the biggest challenges will be installation and retrieval of the supports and catering the roadways, intersections and the install and take-off roads for the bigger supports.

“Maintaining the big supports will be the issue when it comes to change out of components like the legs, which weigh almost 4 tonnes each. Training packages are put together which will include videos to show how these special tasks need to be performed. There are also provisions made on the shearer to have a special carry arrangement, and specific lifting points were designed into the support’s canopy to cater for the heavy lifts,” Laubscher said.

The existing 980/1200t longwall at Moranbah North is currently operating in the relatively shallow 200 panels instead of the deep 100 panels.

“We are extracting four short panels in the 200 series, so the mine has a bit of a free kick for a little while we wait for the new longwall to arrive,” Van De Ven said.

When the new equipment is installed it will operate in the deeper 108 panel and then alternate North-South with the deep 600 panels. The old longwall equipment will continue operating in the shallow 200 series panels.

With the two faces, the mine plans to operate a walk-on, walk-off schedule, where the new and old faces alternate operation with the crew simply switching panels once completed.

“We will plan to commission the new face ahead of finishing the previous face but they will not generally run at the same time as the belt system won’t allow two faces together. We will go from multi-week changeovers to walk-on, walk-off,” Van De Ven said.

He said this process will continue for the next three to four years until the 200 series panels are completed and the old face is retired.