Mechanical and gaseous properties of coal briquettes in terms of outburst risk

Scientific research often require application of samples with repeatable properties. This demand is difficult to fulfill especially in case of experiments concerning coals. Therefore, a necessity occurs to use a material which stands for coal and is characterized with properties similar to coal. Authors of this article suggest, in required situations, the use of coal briquette as a research material. Huge advantage of coal briquettes application is the fact that in many aspects their properties are similar to the structurally deformed coal (altered coal) which presence, according to recent research, is closely related to areas of increased outburst risk. Authors have conducted studies of mechanical and gaseous properties of coal briquettes. The experimental part of the presented studies included the preparation of coal briquettes of a various porosity (from 13.5% to 33%) and determination of their mechanical parameters: uniaxial compressive strength and Protodiakonov coefficient as well as determination of their gaseous parameters: desorption intensity and adsorption capacity. The properties of coal briquettes were analyzed and referenced to the properties of normal coal and altered coal, characterized by mechanical and gaseous properties specific for coals that are hazardous and prone to outbursts. Dependences between the determined uniaxial compressive strength Rc and porosity, Protodiakonov coefficient f and porosity as well as the relationship between Rc and f for the studied coal briquettes were expressed mathematically. Threshold value of f (equal to 0.3), introduced for Polish outburst prevention, corresponded to 18.5% porosity of coal briquette. Changeover of coal briquette’s porosity provides a prospect of obtaining a coal material which have Rc and f parameters typical for coals occurring in natural conditions. Coal briquette of experimentally determined porosity may replicate the mechanical properties of normal or altered coal. Adsorption capacity of different coal samples (briquette, normal, altered) depended on the coal microstructure and the grinding level of coal. The relationship between the 2 min desorption intensity and the methane saturation pressure for different coal samples (briquette, normal, altered) showed that if the grains constituting the grain fraction were larger the amounts of methane desorbed (for the studied time interval) were smaller. A correlation between coal briquette’s porosity and amount of methane released during 2 min desorption test was not found. Grinding level of coal material creates a new distribution of grain size and it determines diffusion and seepage rate of gas releasing from the inside area of the pores. It was shown in this work that mechanical and gaseous properties of coal briquettes predispose them to conduct representative outburst research. A proper method of coal material preparation for the briquetting process is a key point for future properties of coal briquettes.