The effect of megascopic texture on swelling of a low rank coal in supercritical carbon dioxide

• Swelling experiments have been conducted on two types of Miocene low rank coals.
• Non-banded coal lithotypes tend to have isotropic swelling.
• Banded coal lithotypes have anisotropic swelling.

Swelling experiments in supercritical CO2 have been conducted on two groups of samples of Miocene low rank coal with different megascopic textures (non-banded and banded) to address the different swelling behaviors. A block sample (30 × 10 × 10 mm) from core samples was used and a strain gauge was attached to the long axis of the sample block to measure the length of change. The actual maceral group compositions between these samples were similar and high in huminite. However, there is a subtle difference in suberinite and corpohuminite maceral where banded samples consistently have higher compositions compared to non-banded ones. The experimental results showed that banded coal samples tend to have anisotropic linear swelling where swelling perpendicular to bedding plane was always greater than that parallel. In contrast, non-banded samples showed more isotropic behavior without much preference to bedding plane orientation. The ratio of perpendicular to parallel swelling was around 1.28 and 1.05 for banded and non-banded coal samples, respectively. The difference in swelling characteristics was concluded as a result of different megascopic textures of coal samples with respect to bedding orientation.