Fractal characterization of adsorption-pores of coals from North China; an investigation on CH4 adsorption capacity of coals

Yanbin Yao, Dameng Liu, Dazhen Tang, Shuheng Tang, Wenhui Huang

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

To better understand the characteristics of adsorption-pores (pore diameter < 100 nanometers) and their influence on CH 4 adsorption capacity of coals, we have conducted fractal analysis for 13 fresh coal samples (R o from 0.79 to 4.24%) in North China. Isotherms of N 2 gas adsorption/desorption analyses indicate that coals have different adsorption characteristics at relative pressure of 0-0.5 and 0.5-1. On this basis, two fractal dimensions D 1 and D 2 (at relative pressure of 0-0.5 and 0.5-1, respectively) were obtained using the fractal Frenkel-Halsey-Hill (FHH) method, in which both proposed fractal exponents, '(D - 3) / 3' and '(D - 3)' were investigated. The results show that the fractal exponent '(D - 3)' provides more realistic results than fractal dimensions calculated from (D - 3) / 3. The two fractal dimensions, D 1 and D 2, have different correlations with CH 4 adsorption capacity of coals. The CH 4 adsorption capacity does not vary with increasing fractal dimension D 1 up to about 2.5, but thereafter increases with D 1. In contrast, the CH 4 adsorption capacity varies negatively with D 2 within the entire data range. Further investigation indicates that D 1 represents fractals from pore surface area generated by surface irregularity of coals, while D 2 characterizes fractals related to pore structures that are controlled by the composition (e.g., ash, moisture, carbon) and pore parameter (e.g., pore diameter, micropores content) of coals. Higher fractal dimension D 1 correlates to more irregular surfaces that provide more space for CH 4 adsorption. Higher fractal dimension D 2 represents higher heterogeneity of pore structure and higher liquid/gas surface tension that reduce CH 4 adsorption capacity. Therefore, more irregular coal surface and more homogeneous pore structure indicate higher CH 4 adsorption capacity of coals.

Original languageEnglish (US)
Title of host publicationTSOP 2006: Papers from the 23rd Annual Meeting of TSOP
EditorsShifeng Dai, Chen-Lin Chou
PublisherElsevier
Pages27-42
Number of pages16
Edition1
DOIs
StatePublished - Jan 7 2008
Event2006 Annual Meeting of the Society for Organic Petrology - Beijing, China
Duration: Sep 15 2006Sep 22 2006
Conference number: 23

Publication series

NameInternational Journal of Coal Geology
PublisherElsevier
ISSN (Print)0166-5162

Conference

Conference2006 Annual Meeting of the Society for Organic Petrology
Abbreviated titleTSOP 2006
Country/TerritoryChina
CityBeijing
Period9/15/069/22/06

Keywords

  • ISGS
  • North China
  • N gas adsorption method
  • Coalbed methane (CBM)
  • Fractal dimension
  • Adsorption capacity

ASJC Scopus subject areas

  • Economic Geology
  • Geology
  • Fuel Technology
  • Stratigraphy

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