Proximate Analysis

The proximate analysis of coal is carried out to determine its behaviour when heated. It gives the percentage of fixed carbon, volatile matter, moisture content, and ash content. This analysis is sufficient for commercial purposes.

The following procedures are adopted to estimate the various contents of coal:

1. Moisture content: One gram sample of coal is heated to a temperature of about 105°C for a period of one hour. The loss in weight gives the moisture content of the coal.
2. Volatile matter: One gram sample of coal is placed in a covered platinum crucible and heated to 950°C. This temperature is maintained for about seven minutes. There is a loss in weight due to vapourisation of moisture and volatile matter. Since the moisture content has already been calculated, the volatile matter can be obtained asVolatile matter = total loss in weight – moisture content
3. Ash content: One gram sample of coal in an uncovered crucible is heated to a temperature of about 720°C until the coal is completely burned. Complete combustion of coal is ascertained by repeated weighing of sample. This ensures that there is only ash remaining in the crucible.
4. Fixed carbon: Fixed carbon can be obtained asFixed carbon = (100% by mass of coal) – (moisture content + volatile matter + ash) However, this difference does not represent all the carbon present in the coal, because some of the carbon in the form of hydrocarbons may have been lost while estimating the volatile matter.