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Titel |
Do we have to consider temperature-dependent material properties in large-scale environmental impact assessments of underground coal gasification? |
VerfasserIn |
Christopher Otto, Thomas Kempka |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250101613
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Publikation (Nr.) |
EGU/EGU2015-791.pdf |
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Zusammenfassung |
Underground coal gasification (UCG) can increase the world-wide coal reserves by
utilization of coal deposits not mineable by conventional methods. The UCG process
involves combusting coal in situ to produce a high-calorific synthesis gas which
can be applied for electricity generation or chemical feedstock production. Apart
from its high economic potentials, UCG may induce environmental impacts such
as ground subsidence associated with groundwater pollution due to generation of
hydraulic connectivities between the UCG reactor and adjacent aquifers. These changes
overburden conductivity may introduce potential migration pathways for UCG
contaminants such as organic (phenols, benzene, PAHs and heterocyclics) and inorganic
(ammonia, sulphates, cyanides, and heavy metals) pollutants. Mitigation of potential
environmental UCG impacts can be achieved by improving the understanding of coupled
thermo-hydro-mechanical processes in the rocks surrounding the UCG reactor. In the present
study, a coupled thermo-mechanical model has been developed to carry out a parameter
sensitivity analysis and assess permeability changes derived from volumetric strain
increments in the UCG reactor overburden. Our simulation results demonstrate that
thermo-mechanical rock behavior is mainly influenced by the thermal expansion
coefficient, tensile strength and elastic modulus of the surrounding rock. A comparison of
temperature-dependent and temperature-independent simulation results indicates high
variations in the distribution of total displacements in the UCG reactor vicinity related to
thermal stress, but only negligible differences in permeability changes. Hence,
temperature-dependent thermo-mechanical parameters have to be considered in the
assessment of near-field UCG impacts, while far-field models can achieve a higher
computational efficiency by using temperature-independent thermo-mechanical
parameters. Considering the findings of the present study in the large-scale assessment of
potential environmental impacts of underground coal gasification, representative
coupled simulations based on complex 3D large-scale models become feasible. |
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