Applied stress reduces swelling of coal induced by adsorption of water
article
This paper investigates whether or not applied stress reduces swelling of coal upon water adsorption,
and, if so, what mechanisms are responsible. With this aim, thermodynamic models were developed
addressing the effect of a general applied stress on water adsorption capacity and associated swelling
behaviour of coal matrix material, assuming monolayer, multilayer and mixed mono/multilayer adsorption
mechanisms. These all predict applied stress reduces water adsorption capacity and hence swelling.
Experiments were performed on both a solid disc and on pre-compacted powders of Brzeszcze high
volatile bituminous coal at a constant temperature (40 ◦C), using a uniaxial compaction apparatus. The
mechanical response of the samples to stepwise axial loading was determined under both evacuated and
water-exposed conditions. The evacuated samples showed reversible, elastic behaviour. Water-exposed
samples exhibited elastic deformation, time-dependent reversible deformation, plus plastic strains with
time-dependent processes. Axial swelling strains upon introduction of distilled water at a constant fluid
pressure (0.1 MPa) were also measured for samples subjected to fixed axial stresses (25–100 MPa).
The results demonstrated the applied stress reduces swelling upon water adsorption. Comparison with
predictions made using the three models shows that stress-driven reduction in sorption-induced swelling
is caused by the combined effects of (a) permanent time-dependent (compressive) deformation (creep),
(b) the thermodynamic effect of a stress-driven reduction in water sorption capacity and (c) stress-driven
closure of transport paths within the coal matrix. Nonetheless, our results show the above effects of
stress on the swelling response of (Brzeszcze) high volatile bituminous coal to water are minor at typical
in-situ stresses (10–30 MPa). This suggests the large shrinkage effect of the coal upon drying that has been
observed in unconfined experiments is not changed by in-situ stresses.
and, if so, what mechanisms are responsible. With this aim, thermodynamic models were developed
addressing the effect of a general applied stress on water adsorption capacity and associated swelling
behaviour of coal matrix material, assuming monolayer, multilayer and mixed mono/multilayer adsorption
mechanisms. These all predict applied stress reduces water adsorption capacity and hence swelling.
Experiments were performed on both a solid disc and on pre-compacted powders of Brzeszcze high
volatile bituminous coal at a constant temperature (40 ◦C), using a uniaxial compaction apparatus. The
mechanical response of the samples to stepwise axial loading was determined under both evacuated and
water-exposed conditions. The evacuated samples showed reversible, elastic behaviour. Water-exposed
samples exhibited elastic deformation, time-dependent reversible deformation, plus plastic strains with
time-dependent processes. Axial swelling strains upon introduction of distilled water at a constant fluid
pressure (0.1 MPa) were also measured for samples subjected to fixed axial stresses (25–100 MPa).
The results demonstrated the applied stress reduces swelling upon water adsorption. Comparison with
predictions made using the three models shows that stress-driven reduction in sorption-induced swelling
is caused by the combined effects of (a) permanent time-dependent (compressive) deformation (creep),
(b) the thermodynamic effect of a stress-driven reduction in water sorption capacity and (c) stress-driven
closure of transport paths within the coal matrix. Nonetheless, our results show the above effects of
stress on the swelling response of (Brzeszcze) high volatile bituminous coal to water are minor at typical
in-situ stresses (10–30 MPa). This suggests the large shrinkage effect of the coal upon drying that has been
observed in unconfined experiments is not changed by in-situ stresses.
Topics
TNO Identifier
867782
Source
Geomechanics for Energy and the Environment, 16, pp. 45-63.
Pages
45-63
Files
To receive the publication files, please send an e-mail request to TNO Repository.