Structural changes in coal at elevated temperature pertinent to underground coal gasification: A review

Akbarzadeh, Hossein; Chalaturnyk, Richard J.

doi:10.1016/j.coal.2014.06.009

Cited by 82 publications

(41 citation statements)

References 50 publications

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“…The pore volume increment can react to pore size distribution [36], when the aperture of a large pore volume increment is illustrated by the aperture ratio of the total pore space. The relationship between the pore diameter and pore volume increment is shown in Figure 13b.…”

Section: Discussionmentioning

confidence: 99%

Coupling Effect of Intruding Water and Inherent Gas on Coal Strength Based on the Improved (Mohr-Coulomb) Failure Criterion

Zhou

et al. 2016

Minerals

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When employing hydraulic processes to increase gas drainage efficiency in underground coal mines, coal seams become a three-phase medium, containing water intruding into the coal pores with the inherent occurrence of gas. This can change the stress state of the coal and cause instability. This work studied the mechanical properties of coal containing water and gas and derived an appropriate failure criterion. Based on mixture theory of unsaturated porous media, the effective stress of coal, considering the interaction of water and gas, was analyzed, and the failure criterion established by combining this with the Mohr-Coulomb criterion. By introducing the stress factor of matrix suction and using fitted curves of experimentally determined matrix suction and moisture content, the relationships between coal strength, gas pressure, and moisture content were determined. To verify the established strength theory, a series of triaxial compression strength tests of coal containing water and gas were carried out on samples taken from the Songzao, Pingdingshan, and Tashan mines in China. The experimental results correlated well with the theoretical predictions. The results showed a linear decrease in the peak strength of coal with increasing gas pressure and an exponential reduction in peak strength with increasing moisture content. The strength theory of coal containing water and gas can become an important part of multiphase medium damage theory.

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Section: Discussionmentioning

confidence: 99%

Coupling Effect of Intruding Water and Inherent Gas on Coal Strength Based on the Improved (Mohr-Coulomb) Failure Criterion

Zhou

et al. 2016

Minerals

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“…Coal contains organic and inorganic solids, moisture and volatile matter, and cleat (fracture) network. According to Akbarzadeh and Chalaturnyk [16], thermal deformation of coal is a resultant response of multiple constituents of the coal to heating.…”

Section: Thermal Deformation Under Isotropic Confining Stressmentioning

confidence: 99%

Influence of High Pressure and Temperature on the Mechanical Behavior and Permeability of a Fractured Coal

Kasani

Chalaturnyk

2017

Energies

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Understanding mechanical behavior and permeability of coal at ambient and high temperature is key in optimizing high-temperature in-situ processes such as underground coal gasification. The main objectives of this study were to characterize thermal deformation, stress-strain behavior, and gas permeability of coal samples acquired from the Genesee coal mine in Central Alberta, Canada under various temperatures and confining stresses. These measurements were conducted in a high-pressure high-temperature triaxial apparatus. Initial thermal expansion of the coal was followed by contraction in both axial and lateral directions at about 140 • C. This temperature corresponds to occurrence of pyrolysis in the coal. All specimens showed brittle behavior during shear while forming complex shear planes. The specimens exhibited compressional volumetric strain responses at all temperatures. Deformation localization initiated at various stage during shearing. Specimens sheared at 200 • C showed higher peak stresses and larger axial strains compared to those tested at room temperature (24 • C). Fluctuations of permeability were observed with confining stress and temperature. Permeability dropped at 80 • C due to thermal expansion of coal and closure of initial fractures; however, it increased at 140 and 200 • C due to a combined response of thermal expansion and pyrolysis. Small axial strain during shear was observed to reduce permeability.

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“…The Hoe Creek II test was conducted for 58 days and consumed a similar amount of coal as the Hanna II Phase 2 one, also using a LVW configuration with an identical well distance [54]. Cross-sections following the Hanna II and Hoe Creek II field tests, taking into account operational monitoring data and post-burn coring show reactor growths up into the coal seam roof [25,57,58], whereby roof collapse particularly occurred at the Hoe Creek II site. As a consequence of the operational procedure and hydrogeological boundary conditions, product gases migrated from the Hoe Creek II reactor into adjacent aquifers, which became contaminated with UCG by-products such as tars and organic compounds [54].…”

Section: Field-tests Hanna II and Hoe Creek Iimentioning

confidence: 99%

“…Next to mechanical stress changes triggered by coal excavation, thermal stresses also induce permeability changes in the reactor's close vicinity [19,[23][24][25][26]. Furthermore, permeability affects natural convection that transports fluids along with heat and potential UCG by-products into the overburden.…”

Section: Introductionmentioning

confidence: 99%

Prediction of Steam Jacket Dynamics and Water Balances in Underground Coal Gasification

Otto

Kempka

2017

Energies

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Underground coal gasification (UCG) converts coal to a high-calorific synthesis gas for the production of fuels or chemical feedstock. UCG reactors are generally operated below hydrostatic pressure to avoid leakage of UCG fluids into overburden aquifers. Additionally, fluid flow out of and into the reactor is also determined by the presence of the steam jacket, emerging in close reactor vicinity due to the high temperatures generated in UCG operation. Aiming at improving the understanding of the substantial role of the steam jacket in UCG operations, we employ numerical non-isothermal multiphase flow simulations to assess the occurring multiphase fluid flow processes. For that purpose, we first validate our modeling approach against published data on the U.S. UCG field trials at Hanna and Hoe Creek, achieving a very good agreement between our simulation and the observed water balances. Then, we discuss the effect of coal seam permeability and UCG reactor pressure on the dynamic multiphase flow processes in the reactor's vicinity. The presented modeling approach allows for the quantification and prediction of time-dependent temperature and pressure distributions in the reactor vicinity, and thus steam jacket dynamics as well as reactor water inand outflows.

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Structural changes in coal at elevated temperature pertinent to underground coal gasification: A review

Cited by 82 publications

References 50 publications

Coupling Effect of Intruding Water and Inherent Gas on Coal Strength Based on the Improved (Mohr-Coulomb) Failure Criterion

Coupling Effect of Intruding Water and Inherent Gas on Coal Strength Based on the Improved (Mohr-Coulomb) Failure Criterion

Influence of High Pressure and Temperature on the Mechanical Behavior and Permeability of a Fractured Coal

Prediction of Steam Jacket Dynamics and Water Balances in Underground Coal Gasification

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