Deep Ground and Energy: Carbon Sequestration and Coal Gasification

Thomas, Hywel Rhys; Hosking, Lee J.; Sandford, Richard J.; Zagorščak, Renato; Chen, M.; An, Ni

doi:10.1007/978-981-13-2221-1_2

Cited by 4 publications

(5 citation statements)

References 59 publications

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“…One of the technologies that offer a prospect towards the transition in the low-carbon future is the Underground Coal Gasification (UCG) through which deep coal deposits can be utilised for the in-situ production of a synthetic gas predominantly consisting of hydrogen, methane, carbon monoxide and carbon dioxide [5,6]. As the coal reserves significantly exceed those of oil and gas, and less than one sixth of the world's coal is economically accessible, UCG offers a possibility to utilise such reserves in a more environmentally safer way than the conventional mining techniques by eliminating mine safety issues, surface damage and solid waste at the surface [7].…”

Section: Introductionmentioning

confidence: 99%

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Experimental study of underground coal gasification (UCG) of a high-rank coal using atmospheric and high-pressure conditions in an ex-situ reactor

Zagorščak

Sadasivam

Thomas

et al. 2020

Fuel

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This paper presents the results of an extensive experimental analysis of underground coal gasification (UCG) using large bulk samples in an ex-situ reactor under atmospheric and high-pressure (30 bar) conditions. The high-rank coal obtained from the South Wales (UK) coalfield is employed for that purpose. The aim of this investigation is to define the gas production rates, gas composition, gas calorific value, process energy efficiency and temperature changes within the UCG reactor during the gasification process based on the pre-defined reactants and flow rates. Two UCG trials, each lasting 105 hours, consisted of six stages where the influences of oxygen, water, air and oxygen enriched air (OEA) under different flow conditions on the gasification process were investigated. Based on the results of two multi-day experiments, it is demonstrated that the gasification under high pressure conditions produces syngas with higher average calorific value (8.49 MJ/Nm 3 ) in comparison to syngas produced at atmospheric pressure conditions (6.92 MJ/Nm 3 ). Hence, the overall energy efficiency of the high-pressure experiment is higher compared to the atmospheric pressure test, i.e. 57.67% compared to 51.72%. This is related to the fact that the high-pressure gasification produces more methane (11.97 vol.%) than the atmospheric pressure gasification (2.30 vol.%). Under elevated pressure, the temperatures recorded in the roof strata are about 100°C higher compared to the UCG process under atmospheric pressure conditions. This work provides new insights into the gasification of carbon-rich coals subject to different gasification regimes and pressures.

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Section: Introductionmentioning

confidence: 99%

“…Fig.1. Scheme of the ex-situ high-pressure UCG installation: (1) compressed reagents, (2) pressure reactor, (3) wet scrubber for gas cleaning, (4) air cooler,(5,6) gas separators, (7) thermal combustor, (8) gas treatment module prior to GC analysis.…”

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confidence: 99%

Experimental study of underground coal gasification (UCG) of a high-rank coal using atmospheric and high-pressure conditions in an ex-situ reactor

Zagorščak

Sadasivam

Thomas

et al. 2020

Fuel

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“…Bulk modulus of rock, (GPa) 6.9 [1] Poisson' ratio of rock, (-) 0.21 [1] Density of rock, (kg/m 3 ) 2450 [1] Specific heat capacity of rock ,(J/K/kg) 898 [2] Thermal conductivity of rock, λ (W/m/K) 0.65 [2] Thermal expansion coefficient of rock, α (1/K) 3 × 10 −5 [3] Bulk modulus of coal, (GPa) 2.18 [1] Poisson's ratio of coal, (-) 0.35 [1] Bulk modulus of coal matrix, (GPa) 7.65 [4] Initial permeability of fracture system, 0 (m 2 ) 3.6 × 10 −15 [1] Initial porosity of coal matrix, 0 (-) 0.045 [5] Initial porosity of fracture, 0 (-) 0.018 [5] Gas viscosity, (Pa•s) 1.84 × 10 −5 [6] Thermal conductivity of CO2, λ (W/m/K) 0.0246 [7] Density of coal, (kg/m 3 ) 1470 [1] Thermal conductivity of coal, λ s (W/m/K) 0.33 [7] Specific heat capacity of coal, (J/K/ m 3 ) 1250 [7] Thermal expansion coefficient of coal, α (1/K) 9 × 10 −5 [7] Maximum adsorption capacity, (mol/kg) 0.91 [1] Temperature-independent Langmuir constant, ∞ (1/MPa) 0.89 [1] Interaction energy, (J/mol) 1197 [8] Surface stress parameter, (mol/m 3 Universal gas constant, (J/mol/K) 8.314 -Matrix block length, (m) 0.01 [6]…”

Section: Materials Parameters Value Referencementioning

confidence: 99%

“…CO2 capture, utilisation and sequestration (CCUS) comprises a broad set of actions intended to reduce greenhouse gas emissions and mitigate climate change. Among the CCUS options is coal seam sequestration [1,2], which provides storage security by taking advantage of coal's preference to adsorb CO2 and can also enhance coalbed methane (CBM) recovery, either for electricity generation or as a feedstock for hydrogen production. Clearly the use of CBM should not lead to additional CO2 emissions, which in most cases requires further CCUS.…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis of dual porosity coupled thermo-hydro-mechanical behaviour during CO2 sequestration in coal

Hosking

Chen

Thomas

2020

International Journal of Rock Mechanics and Mining Sciences

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This study presents a coupled dual porosity thermal-hydraulic-mechanical (THM) model of nonisothermal gas flow during CO2 sequestration in coal seams. Thermal behaviour is part of the disturbed physical and chemical condition of a coal seam caused by CO2 injection, and must be understood for accurate prediction of CO2 flow and storage. A new porosity-permeability model is included for consideration of the fracture-matrix compartment interaction. The new model is verified against an analytical solution and validated against experimental measurements, before being used to analyse coupled THM effects during CO2 sequestration in coal. A simulation of CO2 injection at a fixed rate shows the development of a cooling region within the coal seam due to the Joule-Thomson effect, with the temperature in the vicinity of the well declining sharply before recovering slowly. The temperature disturbance further from the well is more gradual by comparison. Under the simulation conditions studied, CO2 injection increases coal matrix porosity and decreases the porosity and permeability of the natural fracture network, especially in the vicinity of the injection well, due to adsorption-induced coal swelling. Compared with the effects of gas pressure and temperature, the matrix-fracture compartment interaction plays an important role in changes of porosity and permeability. Considering the temperature disturbance caused by CO2 injection under the set of representative conditions studied, the coupled model can provide an insight into the associated effects on CO2 flow and storage during its sequestration in coal seams.

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“…Škvareková et al [19] noted that gas or tar leakage from the cavity to subsurface is one of the main risks during UCG operation. During such leakage, the fracture network in the roof rock contributes the majority of the effort by fluid channel [13,[20][21][22]. Therefore, the fracture network in the confining rock of UCG poses a threaten to the environmental safety and the UCG production.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Evolution of Stratum Fracture during the Cavity Expansion of Underground Coal Gasification

Dong

Zhao

et al. 2022

Energies

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The evolution of fracture zone controls the safety of underground coal gasification (UCG) in terms of gas emission and water leakage. In order to understand the fracture propagation in the confining rock of a UCG cavity with various influence factors, this paper implemented a set of numerical models based on different geological and operating conditions. Analysis was implemented on the mechanism of fracture propagation and its evolution characteristics, suggesting that (a) continuum expansion of the cavity leads a near-field fracture circle in confining rock initially, followed by the roof caving and successive propagation of shear band. (b) The key observed influence factors of fracture propagation are the grade of confining rock, overburden pressure, dimension of the cavity and gasifying pressure, the linear relationships between them, and the fracture height. Additionally, the fracture depth in the base board was mainly caused by tensile fracture. (c) A model was proposed based on the evolution of fracture height and depth in roof and base board, respectively. Validation of this model associated with orthogonal tests suggests a good capacity for predicting fracture distribution. This paper has significance in guiding the design of the gasifying operation and safety assessment of UCG cavities.

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Deep Ground and Energy: Carbon Sequestration and Coal Gasification

Cited by 4 publications

References 59 publications

Experimental study of underground coal gasification (UCG) of a high-rank coal using atmospheric and high-pressure conditions in an ex-situ reactor

Experimental study of underground coal gasification (UCG) of a high-rank coal using atmospheric and high-pressure conditions in an ex-situ reactor

Numerical analysis of dual porosity coupled thermo-hydro-mechanical behaviour during CO2 sequestration in coal

Investigation of the Evolution of Stratum Fracture during the Cavity Expansion of Underground Coal Gasification

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