Introduction
The expansion of coal is an important factor influencing its combustion properties, especially those properties which determine the value of the coal in those uses, and those properties which are important in the determination of the occurrence, persistence and intensity of smoke and coal dust in the power generating plant and their emission into the atmosphere. The expansion of coal, in particular its behaviour at elevated temperatures is of great importance for those plants which use coal for their fuel. Expansion tests provide some insight into the behaviour of pulverised coals when subjected to heat.
Theory
Coal expansion is the change or amount of increase in the volume of coal upon a certain degree of heating, expressed as a percentage or fraction of the original volume. In general, coal swells as it is heated and the temperature at which severe swelling occurs is a measure of its coking property. The swelling of coal is a complex phenomenon but its essential basis is the liberation of gases such as CO2 and CH4 at high temperatures and the expansion, or enlargement, of the coal matrix due to the production or recombination of molecules of coal particles.
Results
It has been observed that coal expanding increases both with increasing temperature and with increasing pressure. At atmospheric pressure and low temperatures, the expansion of coal is quite insignificant. However, at high temperatures and pressures, the expansion may be considerable. The magnitude of this expansion is dependent on the properties of the coal, including its rank and composition as well as the conditions under which the coal is heated. Expansion tests may hence be used to give an indication of how a coal will behave when subjected to heat.
Experimental Setup
The experimental setup used to measure the expansion of coal is known as a high volume expansion apparatus (HVEA) and is capable of accurately measuring the volume change of coal over a temperature range of 30°C to up to 600°C under both dynamic loading and static loading. The HVEA is able to quantify the endothermic and exothermic behaviour of coal during thermal expansion.
Discussion
It has been observed that the expansion of coal is a complex phenomenon and is highly dependent on the condition of the coal and the reaction mechanism. Expansion tests may be used to provide an insight into the behaviour of pulverized coals when subjected to heat. The results of this test can be used to determine the coking property of a coal, as well as its combustibility and reactivity characteristics.
Conclusion
In conclusion, the expansion of coal is an important factor influencing its combustion properties. Expansion tests may be used to provide an insight into the behaviour of pulverized coals when subjected to heat, and the results of this test can be used to determine the coking property of a coal, as well as its combustibility and reactivity characteristics.
