A thermal coal product database was developed containing a wide range of coal quality data and aims to represent the coal quality of the top 6 coal exporting countries. This blogs looks at some of the characteristics of the database.
A comparison of ASTM rank parameters for coal quality in the product database is shown in the chart below. Calorific value and fixed carbon, determined at specific bases, are used to determine rank according to the ASTM standard D388-18. The product database contains coals ranging from sub-bituminous through to anthracite. A couple of coals are close to the lignite classification, but still fall into the sub-bituminous category. All Australian coals fall into the bituminous or higher category. Indonesian coals are spread between the sub-bituminous and bituminous ranks. It must be noted that technically the ASTM classification doesn’t apply to Indonesian coals as the properties do not meet the criteria in the standard. Many of the Indonesian coals are actually classified as lignite coals using the IEA rank classification system (calorific value ( < 4777 kcal/kg moist, ash free).
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Calorific value, ash content and moisture are key coal quality parameters and are important in coal pricing. The figure below compares calorific value of coal in the products database with ash+moisture (ar basis). The ash content is added to the moisture content as the total represents material in the coal that should reduce calorific value. This relationship is shown in the figure, which shows a strong linear relationship between the coal energy and ash+moisture (all on an as-received basis). The bubble size indicates the export tonnage for each mine with larger bubbles exporting more coal than smaller bubbles.
All Australian coals except for 2 coals are shown to have high energy with ash+moisture levels less than 30%. A wide range of values are shown by Indonesian coals. A couple of very large mines export coal with ash+moisture levels of around 30-35%. All Russian, Colombia and South African coals showed ash + moisture levels less than 30% (except for 1 Russian coal). The figure shown a wide range of energy and ash+moisture levels are exported by the top 6 coal exporting countries.
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Power plants limit ash and moisture levels in the coals they purchase due plant operational limits e.g. milling capacity is exceeded using high moisture coals, or ash handling limits are exceeded using high ash coals. The figure below compares ash and moisture levels for coals in the products database. The bubble size indicates the energy content of the coal and consequently larger bubbles sizes are expected for coals located in the low ash and low moisture region. The figure shows the export coals do not have high moisture and high ash contents e.g. moisture above 20% and ash above 15%. This is logical as these coals would have very low energy contents and would not be competitive in the international coal trading market.
Indonesian coals tend to have medium to high moisture levels with ash contents up to 20%. Australian coals however, tend to have moisture levels less than 20% and ash contents up to 25%. There are significantly more small bubble Indonesian coals (low energy content) than Australian coals. South African coals tended to be similar to Australian coals, Many Russian coals have very low moisture levels resulting in very high energy contents.
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The thermal coal products database contains a variety of coal quality data including moisture, proximate analysis, ultimate analysis, energy, total sulfur, HGI, ash fusion temperatures, ash chemistry and trace elements. The figure below compares the distributions of a variety of coal quality parameters for different coal quality databases. The first category, Prod CQ, refers to the product database where every mine exports the same tonnage. The Export category refers to the product database where the mine exports are as they were in 2015. The part CQ category refers to the product database where the mine exports, for mines with partial coal quality availability, are adjusted such that the total exports for each country match the IEA estimates. The full CQ category refers to the product database where the mine exports, for mines with full coal quality availability, are adjusted such that the total exports for each country match the IEA estimates. The MM CQ is a coal quality database with a variety of coals around the world. This database has been filtered to account for thermal export coals from the top 6 exporting countries.
The parameter distributions are shown as boxplots, density chart and the empirical cumulative distribution function plot. These charts all highlight the distributions of the underling coal quality data. The density plots for different parameters clearly shows variations in the coal quality data for different categories e.g. for ash, large spikes of coal quality data are shown by the databases utilising mine export data. Large Indonesian coal mines exporting very low ash products contributes to the spikes shown in the distributions.
The boxplots tend to hide some of the variations. If the average sulfur was only considered, then the difference between the MM CQ database and the Export database is only 0.06%. The distributions as shown by the density plots are significantly different. The distribution of sulfur values for the MM CQ database resembles a normal distributions whereas the other distributions do not.
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The distribution of coal quality results, when adjusted for mine exports varies from simply using a selection of coal quality results. Consequently the developed coal products database simulates the coal quality available in the market better than other methods and will be ideal for ranking different coals in the market.
My next blog will look at different ways of ranking coals with other coals in the market…