A coupled thermal-mechanical numerical model of underground coal gasification (UCG) including spontaneous coal combustion and its effects

Ekneligoda, Thushan Chandrasiri; Marshall, Alec M.

doi:10.1016/j.coal.2018.09.015

Cited by 26 publications

(22 citation statements)

References 27 publications

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“…The propagation of cracks in coal leads to gas desorption and flow and accelerates the progressive failure process. 11 − 13 Many scholars have carried out numerous studies with respect to the changes due to stress evolution. 14 , 15 Medhurst and Brown 16 conducted conventional triaxial compression experiments on coal samples and reported that the peak strength of coal is proportional to the confining pressure.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Coal Porosity Changes before and after Triaxial Compression Shear Deformation under Different Confining Pressures

Wang

Pan

et al. 2022

ACS Omega

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It is important to explore the changes in coal pores in response to triaxial compression and shear deformation for coal mine gas drainage and efficient coalbed methane mining. To study the variation in coal pores depending on stress, first, a mechanical analysis was carried out, and then the characteristics of coal samples before and after triaxial compression were quantitatively analyzed combined with low-temperature nitrogen adsorption experiments. The compressive strength of the coal samples with a high elastic modulus is significantly greater than that of coal samples with a low elastic modulus. Sihe coal samples with a larger elastic modulus experienced higher peak stress and strain during compression than those from the Chengzhuang Mine with a smaller elastic modulus. With the exception of the coal sample from the Chengzhuang Mine with a confining pressure of 15 MPa, the peak strength and axial strain of the coal samples gradually increased with an increase in confining pressure. The larger the elastic modulus, the greater the axial strain. After triaxial compression, pores with diameters ranging from 2 to 5 nm exhibited a significant change. After the compression of coal with a high elastic modulus, the pore volume and pore specific surface area decreased with the increase in confining pressure, by 60.7 and 59.7%, respectively (compared with raw coal). The complex pore structure consisting of mesopores and macropores (>11 nm) became simpler. The volume and specific surface area of the pores of the coal samples with a low elastic modulus first increased, then decreased, and then increased again with the increase in confining pressure, and after compression, the roughness and complexity of macropores of coal samples are greater than those of micropores. The changes induced in the coal samples of the two mining areas in response to compression differ, which are related to the mechanical properties of the coal bodies.

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Section: Introductionmentioning

confidence: 99%

Characteristics of Coal Porosity Changes before and after Triaxial Compression Shear Deformation under Different Confining Pressures

Wang

Pan

et al. 2022

ACS Omega

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“…12 However, the variation of thermo-mechanical properties of coal with temperature becomes meaningless in UCG. 8 Solid components such as dry coal and char would be consumed owing to pyrolysis and the heterogeneous chemical reactions with the injected oxidants such as oxygen (O 2 ), air, and steam and the produced syngas. 16,17 Inert material, that is, ash is left in the cavity after gasification.…”

Section: 22mentioning

confidence: 99%

“…Although UCG demonstrates great potential in mitigating the world energy demand and advantages over traditional utilization of coal resource, there is a long way to go before its commercialization 3 . One of the main ongoing research interests is the ground deformation, especially subsidence induced by the process of UCG 4–8 . During the process of UCG, the geomechanical response of the gasification coal seam and its surrounding strata could be significant due to substantial variations in temperature, porosity, and pressure 7 .…”

Section: Introductionmentioning

confidence: 99%

“…For the numerical modelings that coupled the flow model and the geomechanical model, 6,7,15 the computation cost would be high. In response, a coupled thermo‐mechanical (T‐M) model including spontaneous coal combustion was proposed by Ekneligoda and Marshall 8 . In the model, the gasification process of coal was simulated by modifying the energy balance equation with an additional term related to the calorific value of coal as a source and the cavity was simulated by removing the gasified zone from the calculation after a specific time.…”

Section: Introductionmentioning

confidence: 99%

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Insights into ground response during underground coal gasification through thermo‐mechanical modeling

Gao

Zagorščak

Thomas

2021

Num Anal Meth Geomechanics

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This paper presents a coupled thermo-mechanical model to investigate the ground response during underground coal gasification (UCG). The model incorporated the temporal and spatial development of temperature, the gradual growth of the cavity, and temperature-dependent material properties. Model verification was made against two benchmarks to acquire the confidence for the predictive purpose. The first exercise demonstrated the correctness of the model implemented in COMPASS. The second exercise showed that using the ash-filled cavity to represent null or empty zones is a good option in the numerical modeling and provided highly comparable results to other models. Based on the Hanna UCG trial, different cases were simulated to investigate the effects of the cavity size in the coal seam and the thermal expansion coefficient of the caprock and base rock on key features that take place during the process of UCG. A maximum temperature in the range of 1200-1500 °C was induced by the gasification of coal, and a cavity with a maximum length of 13.5 m was formed after 30 days of simulation. Meanwhile, small vertical displacement in the range of -5-12 mm took place near the cavity because of the thermal expansion of the geologic materials and the reduction of the overall weight with the creation of the cavity. In addition, it was found the thermal expansion coefficients can influence the thermo-mechanical response of geologic materials, but the effects were insignificant when its order of magnitude was smaller than 10 -6 K -1 .

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“…− dust and air pollution at the time of production, − populated areas are not suitable for research, − delayed redevelopment of the area, the threat of uncontrolled extension of groundwater contamination [23,24]. At present, the most significant Slovakian lignite deposits are in Novaky, Handlova and Cigel, located in the Upper Nitra Basin in the upper strata of Baden.…”

Section: Risk Analysis -Environmental Impact Of Ucg On the Populationmentioning

confidence: 99%

Analysis of Risk Factors for Underground Coal Gasification

Škvareková

Tomašková

Wittenberger

et al. 2019

Management Systems in Production Engineering

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The purpose of this article is to determine the environmental impacts of underground gasification on the population and to analyze the risk of underground coal gasification (UCG) activities using selected risk assessment methods. Coal gas is a regular part of coal deposits and its extraction also allows the use of coal deposits that cannot be extracted by traditional methods. These technologies bring both positive and negative aspects. The paper points out the risk analysis, hazard identification and assessment during the operation of UCG technology using a risk graph and a risk matrix. Identified risks to workers that cannot be reduced should be taken into consideration and appropriate safeguard should be used. For each risk, it is necessary to inform employees about regular education and training. From worldwide experience with this technology, it is possible to analyze risks in Slovakia. Actual gasification produces polluting gases such as carbon dioxide, carbon monoxide, hydrogen sulphide, hydrogen sulphide, nitrogen oxides, tar and ash, and creates a risk that may occur on and under the surface of the site depending on the geological and hydrogeological structure of the deposits. Possible measures to mitigate the adverse effects are proposed for the implementation of this technology. Coal is still one of the main domestic primary energy sources. Currently, only 5 out of 19 deposits in the Slovak Republic are used. Underground gasification could increase the use of Slovak coal and brown coal deposits.

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A coupled thermal-mechanical numerical model of underground coal gasification (UCG) including spontaneous coal combustion and its effects

Cited by 26 publications

References 27 publications

Characteristics of Coal Porosity Changes before and after Triaxial Compression Shear Deformation under Different Confining Pressures

Characteristics of Coal Porosity Changes before and after Triaxial Compression Shear Deformation under Different Confining Pressures

Insights into ground response during underground coal gasification through thermo‐mechanical modeling

Analysis of Risk Factors for Underground Coal Gasification

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