Self-ignition and mechanisms of interaction of coal with oxygen at low temperatures. 2. Changes in weight and thermal effects on gradual heating of coal in air in the range 20–300 °C

The interaction of lignite, brown and black coal with molecular oxygen was studied by simultaneous TG and DTA. The experiments were carried out in air. Two programs of controlled heating were used. The thickness of the fuel powder layer was varied from run to run in a ratio 1:2:4:20 (see Table 2). The course of TG and DTA curves depends on the rate of heating and the layer thickness. Self-ignition occurs only in thick layers. The free surface remaining the same, an equal relative loss in weight of lignite and of brown coal powders respectively was found in the range 200–280 °C for layers of different thickness when self-ignition does not occur. Endothermic zones were established in the oxidation of thin layers. In thicker layers the oxidative dehydrogenation proceeds at lower temperatures and in a narrow temperature range. Some evidence was obtained that the interaction occurs by concurrent reactions the rate of which is controlled by the composition of the gas phase enclosed in the layer. Reactions of elimination and hydrogen peroxide formation are held responsible for the endothermicity in some stages of interaction.