Thermal stress analysis on small-scale model experiment for development of underground coal gasification

Ryosuke Naka, Takuto Tatekawa, Jun ichi Kodama, Takayuki Sugawara, Ken ichi Itakura, Akihiro Hamanaka, Gota Deguchi

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

Abstract

Underground Coal Gasification is expected to be efficient technique for coal energy recovery from deep or complex coal seam since directional drilling technique is advancing in these days. Authors have been performing small-scale UCG model tests to clear gasification and combustion process in UCG. Then, we found that radial cracks were initiated from the cavity formed in the artificial coal seam. Understanding mechanism of the crack initiation is important for clarification of the detail process of combustion and gasification and assessment for environmental risks. In this study, thermal stress analysis was performed on the small-scale UCG model tests to consider the initiation mechanism of the cracks by assuming that combustion and gasification of coal were progressing through the following three processes which are often observed in coal carbonization: (A) thermal expansion, (B) softening and melting and (C) thermal contraction. It was found that tensile stress was induced in the vicinity of the cavity in the tangential direction in process C. Direction of principal stress in the coal was almost parallel to tangential or radial direction of the cavity and the magnitude of it exceeded coal tensile strength. It was also found that tensile stress zone was extended into deeper coal seam with increase in temperature and time and compressive stress zone was formed outside of the tensile stress zone. It can be considered that the radial cracks initiated at the surface of the cavity since tangential tensile stress exceeded tensile strength of coal. Then, radial cracks were arrested at the boundary of tensile stress zone and compressive stress zone after they were propagating in coal seam.

Original languageEnglish
Title of host publicationISRM International Symposium - 10th Asian Rock Mechanics Symposium, ARMS 2018
PublisherInternational Society for Rock Mechanics
ISBN (Electronic)9789811190032
Publication statusPublished - Jan 1 2018
Event10th Asian Rock Mechanics Symposium, ARMS 2018 - Singapore, Singapore
Duration: Oct 29 2018Nov 3 2018

Publication series

NameISRM International Symposium - 10th Asian Rock Mechanics Symposium, ARMS 2018

Conference

Conference10th Asian Rock Mechanics Symposium, ARMS 2018
CountrySingapore
CitySingapore
Period10/29/1811/3/18

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology
  • Geophysics

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