Assessing the potential for CO₂ adsorption in a subbituminous coal, Huntly Coalfield, New Zealand, using small angle scattering techniques

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• 作者：Tennille E. Mares ; Andrzej P. Radliń ; ski ; Tim A. Moore ; David Cookson ; P. Thiyagarajan ; Jan Ilavsky ; Jü ; rgen Klepp
• 关键词：Small Angle Scattering ; Pore size distribution ; Specific surface area ; Subbituminous coal ; New Zealand ; Carbon dioxide
• 刊名：International Journal of Coal Geology
• 出版年：2009
• 出版时间：7 January 2009
• 年：2009
• 卷：77
• 期：1-2
• 页码：54-68
• 全文大小：1470 K

文摘

Small angle scattering techniques (SAXS and SANS) have been used to investigate the microstructural properties of the subbituminous coals (R_max 0.42–0.45 % ) from the Huntly Coalfield, New Zealand. Samples were collected from the two thick (> 5 m) coal seams in the coalfield and have been analysed for methane and carbon dioxide sorption capacity, petrography, pore size distribution, specific surface area and porosity.

Specific surface area (SSA) available for carbon dioxide adsorption, extrapolated to a probe size of 4 Å, ranged from 1.25 × 10⁶ cm^− 1 to 4.26 × 10⁶ cm^− 1 with total porosity varying from 16 % to 25 % . Porosity was found to be predominantly composed of microporosity, which contributed the majority of the available SSA. Although considerable variation was seen between samples, the results fit well with published rank trends.

Gas holding capacity at the reservoir pressure (approximately 4 MPa) ranged from 2.63 to 4.18 m³/t for methane on a dry, ash-free basis (daf) and from 22.00 to 23.72 m³/t daf for carbon dioxide. The resulting ratio of CO₂:CH₄ ranged from 5.7 to 8.6, with an average of 6.7:1.

Holding capacities for both methane and carbon dioxide on a dry ash free basis (daf) were found to be correlated with sample microporosity. However, holding capacities for the two gases on an as analysed (aa) basis (that is including mineral matter and moisture), showed no such correlation. Carbon dioxide (aa) does show a negative correlation with both specific surface area and microporosity. As the coals have low inorganic matter content, the reversal is thought to be related to moisture which is likely concentrated in the pore size range 12.5–125 Å. Methane holding capacity, both daf and aa, correlates with macroporosity, thus suggesting that the holding capacity of micropores is diminished by the presence of moisture in the pores.