Indonesian coals are generally low in ash and sulphur, but on account of their low rank, they have a high content of volatile matter and moisture. The run-of-mine coal does not generally require preparation and simple crushing and screening suffices to produce a marketable product. The coal has nil or minimal coking properties, and thus with few exceptions, can only be used as steaming coal. Only some higher-ranking types are also suitable as pulverised injection coal (PCI). The qualities for export generally have a 37–47% share of volatile matter, with 1–10% ash and mostly 15–22% moisture. The sulphur content is below 1% and, in extreme cases, as low as 0.1%. The high moisture translates into a relatively low calorific value; mostly well below 6,000kcal/kg (net as received). One impediment to the coal’s use in power plants is its high grinding hardness of 40–50 HGI.
The country is increasingly producing and exporting lower quality coal grades as high quality grades are exploited.
In our last report, Indonesia had 5.4 billion tonnes (Bt) of coal reserves. The country’s total coal resources were recently estimated to be 38.8 Bt by the Directorate-General for Mining, including approximately 17 Bt in Sumatra and 21.1 Bt in Kalimantan. 58.6% are lignite, 26.6% are sub-bituminous, 14.4% are bituminous and 0.4% anthracite.
However, these figures have since been increased to 20.69 bilion tons of mineable reserves and 104.76 billion tons of potential reserves. Most of this is low rank coal providing an opportunity for low-rank coal-fired power plant development.