Effects of degassing temperature and particle size on pore structure characterization of anthracite coal

Abstract

In low-temperature nitrogen adsorption (LTNA) tests, the specific surface area (SSA) and pore structure characteristics of high-metamorphic anthracite coal are influenced by degassing temperature and particle size. Altered pore structures can further impact the sample adsorption capacity. Studies have shown significant variations in SSA between soft and hard coals although from the same coal seam with similar methane content. This study focuses on elucidating the mechanism of SSA and pore structure alteration under various degassing temperatures and particle sizes using LTNA method. The results obtained from soft and hard anthracite coal samples collected from Guhanshan Coalmine, China indicate: (1) The primary elements around hard coal pores are O, Al and Si. The micro pores below 2 nm and mesopores from 2 to 10 nm contribute to the main pore surface and volume for soft coal when the degassing temperature is below 250 °C. When the degassing temperature is 250 °C, total pore volume (PV) with a size smaller than 10 nm increases, enhancing adsorption capacity. (2) Adsorption capacity, PV and surface area increased when the particle size used for the test reduced to 300–500 mesh. Smaller particles enhance adsorption by increasing the total number of micropores (<2 nm) and mesopores (10-100 nm) for hard coal samples. The primary PV is from 10 to 100 nm pores. When increasing the particle size to 60–80 mesh, surface area of micro pores (<2 nm) significantly increases. (3) Optimal degassing temperatures of 250 °C for soft coal and 300 °C for hard coal are proposed, with the particle size of 60–80 mesh.