Speaking at the 5th Underground Coal Operators conference, held in February, BHP Billiton Illawarra Manager - Special Projects, Peter Whittall, outlined the planning involved in establishing the new mine.

BHP Billiton announced its intention to conduct a feasibility study into establishing the new mine in July 2000. The mine was needed to replace the 1Mtpa of clean coking coal mined by the Elouera mine from the Wongawilli Seam.

Numerous options were reviewed to establish the optimum scenario for this future supply, ranging from a low tonnage operation of around 1.5 million tonnes per annum utilising pillar extraction and longwall techniques to a world class well equipped mine with a minimum capacity of 4.5Mtpa.

A robust pre-feasibility mine plan was developed in the early stages of the project which allowed the project to progress to feasibility.

Laying out the mine plan was one of the project’s major challenges because of geological and surface infrastructure constraints. These included surrounding colliery workings of Kemira, Elouera, and Mt Kembla, the overlying Cordeaux Dam; igneous intrusions and large structures.

Numerous options were evaluated to take into account the presence of these structures and zones and to accommodate the Cordeaux dam on the surface.

“The restricted mining areas has meant that geophysical parameters such as stress direction, roof strength variability and coal quality variations, have, for all intents and purposes, had to be dealt with as outcomes of the chosen mine layout rather than drivers of it,” said Peter Whittall.

The outcome was the development of three distinct areas. Mining will begin in Area 1, which contains two 240m longwall panels. This was originally three 180m blocks but has been reduced in the current plan, saving one set of gateroads and providing a better subsidence profile. Area 1 is oriented in what would normally be deemed to be the worst stress direction for both the gate roads and the longwall retreat. A mine schedule was modelled whereby Area 1 was bypassed and Area 2 mined first but start-up costs before longwall coal were prohibitive.

In 2008 operations would move to Area 2 when the Longwall would be extended to 250 metres and run-of-mine production increased to 4.5 million tonne per annum. On completion of Area 2 in 2011 the Longwall will be moved to Area 3 and again extended to a width of 300m. The blocks have been lengthened to 5200m and production increased to average 5Mtpa.

Area 3 is the only area which has been laid out for optimisation of stress orientation. Mining to date has supported these stress predictions

The first three years of development will be in strata conditions which require reasonably intensive primary support of between 6 and 8 by 2.4m fully encapsulated roof bolts as well as 1.2 to 1.8m rib bolts every metre of advance; rib protection is essential in Wongawilli seam operations. Existing ABM20’s available within Illawarra Coal have been upgraded to ABM20 Mark IIIs with ABM25 conveyor and loader blade.

Other development gear is also second hand, including shuttle cars, PJBs, Eimco 915s and EJ130, MPV, trailers, DCBs, auxiliary fans, monorail, pumps, compressor and the TG conveyor system (which won’t be used for longwall extraction). All of the equipment has been overhauled to support the tasks required.

During mine scheduling mine plan layouts were run on an expected best, expected and expected worse case. Longwall continuity was kept at +100 days in all scenarios for all layouts.

Input into the mine scheduling also derived from the engineering model to determine equipment sizing for the mine (developed by Australian Coal Mining Consultants). This model was used to determine maximum outputs from the longwall to achieve project tonnages and was used in the conveyor design model, in turn used to determine stockpile parameters and design.

The conveyor system was supplied by Continental Conveyors in partnership with Walter Construction Group and consists of the following:

Trunk belts are 1800mm wide, rated at 4500 tph capacity (6000tph peak). Drive units are a combination of up to four 375KW and 450KW units. Gateroad belts are 1500mm wide, rated at 3500tph (4200 tph peak). According to Whittall it was decided to maintain gateroad structure at 1500mm because of man-handling and ergonomic issues.

The system design uses Voith PKL fluid couplings with PLC controlled fluid fill providing variable speed. Whittal said VVVF drives were investigated during feasibility but were discounted because of reliability issues.

“The PKL couplings give creep speed for inspections and slow startup to reduce load spikes. Half speed during development only is achieved using a different gearbox ratio,” he said.

To date the conveyor installations have been successful and are performing as planned.

Part 2 of the Dendrobium report outlines the mine’s ventilation requirements while part 3 looks at the shaft construction project.