Rock Engineering

[3305-12-03] Effect of Induced Oxidation on the Mechanical Properties of Lignite by using Hydrogen Peroxide in the SCG Method

○AKM Badrul Alam¹, Noritaka Aramaki ¹, Shuji Tamamura¹, Akio Ueno¹, Takuma Murakami¹, Satoshi Tamazawa¹, Yoshiaki Fujii², Katsuhiko Kaneko¹ (1. Horonobe Research Institute for the Subsurface Environment, Northern Advancement Center for Science & Technology, 5-3 Sakae-machi, Horonobe-cho, Teshio-gun, Hokkaido, 098-3221, Japan, 2. Rock Mechanics Laboratory, Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University, North 13 West 8, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan)

Chairman: Takahiro Funatsu (Kyushu university)

Keywords:Induced oxidation, SCG method, Mechanical properties of lignite, Hydrogen peroxide, Biomethane

The lignite resource of the Tempoku coal field in Hokkaido, Japan is under consideration at our institute for production of biomethane from lignite using the subsurface cultivation and gasification method. The first stage of the method is important and involves dissolved organic carbon (DOC) formation by induced oxidation of lignite using H₂O₂ solution. The subsequest stages involve methanogen cultivation by the organic carbon as substrates to produce biomethane and the the last stage is gas recovery. To obtain more insight into the important first stage, changes in mechanical properties of lignite by induced oxidation were investigated in this research. These properties are important from a groung control standpoint. Lignite core specimens 30 mm in diameter and 60 mm in height were immersed into a 1 wt.% H₂O₂ solution having a liquid/solid ratio of 5:1 to induce oxidation at atmospheric pressure and room temperature. P-wave velocity and density were measured before and after immersion. A series of uniaxial compression tests and the Brazilian tests were performed on both the induced-oxidized (H₂O₂-immersed) and unoxidized (H₂O-immersed) specimens. Intense oxidation was observed at most parts of the exposed surface of lignite specimens, whereas slight oxidation was expected to occur in inner parts, at the specified experimental condition. The induced oxidation of lignite produced DOC, resulting in a decrease of 1.79% and 0.54% in the average P-wave velocity and average density respectively. The P-wave velocity of lignite showed positive correlations with the strength, static tangent modululs, dynamic Young's modulus, and tensile strength regardsless of the oxidation of lignite. Although the P-wave velocity and density decreased slightly in post DOC production by the induced oxidation, the damage of the lignite caused by H₂O₂ can be ignored during the design of SCG reactors at the given experimental condition.