These methods are used primarily to determine the suitability of coal for coking, power generation or for iron ore smelting in the manufacture of steel.
It represents the bulk mineral matter after carbon, oxygen, sulfur and water (including from clays) has been driven off during combustion.
Analysis is fairly straightforward, with the coal thoroughly burnt and the ash material expressed as a percentage of the original weight.
Knowledge of the density of each coal play is necessary to determine the properties of composites and blends.
To determine in-place coal tonnages however, it is important to preserve the void space when measuring the specific gravity.
It is necessary to know these data before coal is mined, so that suitable crushing machinery can be designed to optimise the particle size for transport and use.
This removes high-ash value particle and increases the saleability of the coal as well as its energy content per unit volume.
Float-Sink testing is achieved on crushed and pulverised coal in a process similar to metallurgical testing on metallic ore. Abrasion is the property of the coal which describes its propensity and ability to wear away machinery and undergo autonomous grinding.
Coal which has ash that fuses into a hard glassy slag known as clinker is usually unsatisfactory in furnaces as it requires cleaning.
The ash, in the form of a cone, pyramid or cube, is heated steadily past 1000 °C to as high a temperature as possible, preferably 1,600 °C (2,910 °F).
This involves heating a small sample of coal in a standardised crucible to around 800 degrees Celsius (1500 °F).
After heating for a specified time, or until all volatiles are driven off, a small coke button remains in the crucible.