The system in release of volatiles from coal and char - II : slow heating process

The relation between the quantity of volatiles released by a coal and the applied temperature is not directly applicable in slow heating process whereby the full amounts of volatiles are not available. This reduced yield of volatiles or increase of fixed carbon value by coals under delayed heating has been studied in the laboratory. It shows that slow thermal treatment mainly lowers the quantity of residual volatiles in 600ºC char and affects caking and swelling properties of coals. It shows that the extent of fixed carbon enrichment is much dependent on the techniques of pyrolysis. For example, in Gray-King low temperature carbonization, fixed carbon enrichment in coal is about 2 per cent (d.m.f. coal basis) on average. The phenomenon is considered to be a re-arrangement in the coal structure towards yielding more fixed carbon. The change starts quite earlier at temperatures below 100ºC and continues up to 350-450ºC. The starting temperature can be obtained from the F.C. enrichment curve drawn from the temperature of pre-treatment and total volatiles delivered by the coal at 900ºC. Some low or medium volatile coals which show higher values for V.M. figures calculated from their H/C values than the observed figures, are considered to have suffered sudden rise of temperature due to folding of strata or remote igneous activities and this rise also has been estimated from the curve. A method for assessing the effects of severe action of intrusives, e.g., F.C. enrichment, loss of volatiles, rise of temperature in a section of affected coal and the nature of parent coal, has been proposed in this connexion