According to estimates Sumatra hosts one-third of Indonesia’s coal reserves – some 96% of it lignite. Until recently, development of the Sumatran brown coal reserves has been stymied by the difficulty of transporting lignite – with its renowned self-combustion capacity – over long distances. Also, it’s an economic issue: lignite miners and their customers have to move more of the material for the same end-use energy output than “ordinary” coals.

Now, hopes are being pinned on a twin 600MW power station proposal at the Musi Rawas mine project in south Sumatra, being driven by US-based power company AES Corp and Indonesia’s PT PLN (Persero). They joined up last November for the $US1.5 billion proposal, with Japan’s Sojitz Corp and Indonesia’s PT Triaryani (mining concession owner), to develop the project just 10km from the Musi Rawas mine in Sumatra’s Rawas Ilir district.

The first stage of the twin generating station project is expected to be completed within two years, tapping its fuel from the 1000-hectare Sungaimalam lignite deposit, which is reported to host sufficient reserves for 4200MW of power generation on a 30-year life.

The project is well situated for power station cooling water from the Rawas and Musi rivers that flow along the southern border of the site – and which will accommodate equipment transport barges of up to 500 deadweight tons.

PLN has signed up to take the project’s electricity output for distribution to the 275kV South Sumatra transmission grid, about 30km west of the site, with excess power to be exported to Java via the proposed Java–Sumatra interconnection line that is planned for completion in 2009.

The Musi Rawas exploration concession, DU 1427, the source of the coal to be supplied to the power project, contains an estimated total coal resource of 585 million tonnes, with 90Mt under an overburden with a strip ratio of 1:1.

Six coal seams have been identified, several correlating with seams mined at the nearby Air Laya mine operated by PT Bukit Asam, which has been supplying fuel coal to Suralaya power station in Java for more than 15 years.

The Indonesian Government has approved an environmental impact assessment for the project, which involves an average overburden ratio of 1:6 and an average coal resource dip of 5–10 degrees, making the project ideal for openpit mining.

Musi Rawa coal has 40% moisture, low ash (3–4%), low sulfur (0.2% maximum) and a heat value of 3960kcal/kg, with expectations that natural dewatering will improve the coal characteristics significantly.

Differential thermal analysis and thermo gravimetry evaluation indicates the coal has excellent combustion, performing at the same level as bituminous medium, and has a low possibility of slagging or fouling in the boiler. Nitrogen oxides (NOx) emission levels were found to be 60% of those of standard bituminous coal.

Initially, mine output is expected to be about 4.5Mtpa from the 30m thick Seam IV on the southeast outcrop, progressing south and west. Options in the future could see an increase in power station capacity to 4200MW requiring 15.75Mtpa of coal.

The consortium plans conventional mining, using excavators with 14 cubic metre buckets to load 85t trucks to haul the overburden to external dumps. Calculated strip ratios will start at 1:1, rising to 5:1 by year 11 of the mine’s operation. Coal will be hauled to the power station in 50t side-tipper trucks along a 15km dedicated haul road.

The consortium proposes that as mining progresses along the outcrop, an east-west face will be established across the deposit from top to the base of the coal, opening the way for cross-pit mining blocks to progress north in 200m increments.

Dumping of overburden will continue until year 14, but backfilling of the mine will start as soon as technically feasible, with all waste expected to be back in the pit by year 16. By that stage in the mine life, 34cu.m shovels will be in use to load 240t trucks, the coal being conveyed directly to power station stockpiles. –John O’Neil

Article courtesy specialist coal consultancy and information provider Barlow Jonker, Coalportal.com