Thermal Analysis of Coals from Kazakhstan Deposits

Abstract—

Coals from the Ekibastuz, Maikuben, and Karazhyra deposits in Kazakhstan were subjected to thermal analysis for determining the temperature ranges suitable for producing high-calorific gaseous fuel with optimal characteristics. Thermal experiments were performed using the thermogravimetric (TG and DTG) and differential thermal analysis (DTA) methods in oxidizing (air) and inert (helium) media in the temperature range from room temperature to 700–900°С at a linear heating rate of approximately 10°С/min. The results obtained from the TG, DTA, and DTG analyses made it possible to identify three main thermal decomposition intervals of the studied coals in air and in oxygen-free medium: at a temperature below 120–140°С (in air) and below 130–160°С (in helium flow), the water adsorbed in the coal is removed from it; at 280–480°С, low-molecular volatile coal pyrolysis products release and burn (in oxygen-containing medium); the temperature range 340–530°С corresponds to the stage of primary or rapid pyrolysis of coal (in inert medium); the char derived from coal burns (in oxygen-containing medium) at temperatures higher than 480°С; and temperatures above 510°С correspond to the stage of secondary or slow pyrolysis of coals (in inert medium). The maximum yield of volatile products (16.2%) is obtained from the pyrolysis of coal from the Maikuben deposit, and their minimum yield (7.1%) is obtained from the pyrolysis of Ekibastuz coal. The reactions of intensive release of volatile products at the rapid pyrolysis stages of the studied coals end with exothermic (500–550°С) and endothermic (at approximately 650°С) condensation of emerging aromatic structures and formation of char residues. The data presented in the article can be used in searching for raw coal material most suitable for obtaining high-calorific fuel and for selecting the conditions for its industry-grade devolatization.