Non-destructive characterization of coal samples from China using microfocus X-ray computed tomography

This paper demonstrates capabilities of microfocus X-ray computed tomography (µCT) in characterizing the development of coal porosity and fractures. For the investigated coals, the CT number of minerals, pores and coal matrix are approximately 3000, < 600 and 1000–1600 Hounsfield unit (HU), respectively. The total CT number of analyzed coals mainly relate to the density, coal maceral composition, and proportion of minerals and pores. Although the estimated porosities by segmentation method show some uncertainty, the results correlate well with the analyzed porosities by helium gas method and water-saturated method. The aperture, spacing and spatial distribution of fractures, and mineral morphology are semi-quantitatively evaluated by µCT using a computer-aided design. The slicing analyses of coals demonstrated that distributions of porosity in coals are highly anisotropic. The spatial disposition of pores, fractures and minerals is the most important factor that influences coal porosity and permeability. In spite of the limitation of low spatial resolution (70 μm) and some ring artifacts of X-ray, µCT has major advantages in non-destructive detection and 3D visualized characterization of pores, fractures and minerals compared to traditional methods.