Transcript CO2 storage and gas diffusivity properties of coals from Sydney

International Journal of Coal Geology , 70, 240–254
CO2 storage and gas diffusivity
properties of coals from Sydney Basin,
Australia
A. Saghafi, M. Faiz , D. Roberts
報告者 : 藍一平
指導老師 : 蔡龍珆 老師
日期 : 2011/05/26
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OUTLINE
Introduction
Objectives
Literature Review
Methods
Result and Discussion
Conclusions
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INTRODUCTION
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Exploration of boreholes involves investigations on factors
affecting CO2 storage and injection, in particular the
adsorption and diffusivity properties of coal.
One particularity of Australian coalfields is the occurrence of
large amounts of CO2 in many coal seams.
extraction well
(http://www.zybsh.cn/zs/ytgk/index.htm)
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Clayton (1998) listed four sources for CO2 gas in coal seams:
Decarboxylation
reactions
Mineral
reactions
Bacterial
oxidation
Magmatic
intrusion
CO2 in Sydney Basin coals is mainly derived from magmatic
sources as the high CO2 content areas generally have
isotopic compositions of δ13C of about −7‰. (Smith and Gould,
1980; Smith et al., 1985)
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Study Area
150 Mt / year of coal
Hunter Coalfiled
Newcastle Coalfiled
Hunter, Newcastle,
Western and Southern
coalfield
Western Coalfiled
Permian-Triassic
Southern Coalfiled
Medium to high volatile
bituminous
Open-cut mining
Fig. 1. The major coalfield in Sydney Basin, NSW
(http://www.csmenergy.com.au/operations.html)
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OBJECTIVES
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The aim of the present investigation is to characterize
Sydney Basin coals according to two parameters
(adsorption and diffusivity), particularly for CO2.
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LITERATURE REVIEW
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adsorbed
phase
In-situ coal
contains gas
• micro-pore
• Langmuir equation
(Langmuir, 1918)
• macro-pores
free
phase
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Convection
Pressure gradient
Macro-pores and Fractures
Diffusion
Concentration gradient
Micro-pores
Sorption
(Remner et al., 1984)
IUPAC
Macroporous
> 50 nm
Mesoporous
2~50 nm
Microporous
< 2 nm
(Saghafi et al., 1987)
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METHODS
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Adsorption isotherm
The technique developed to measure adsorption isotherms is
based on a gravimetric method. (Saghafi, 2003)
Fig. 2. Schematic diagram of gravimetric adsorption
measurement apparatus.
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Measurement method for gas diffusivity
Fick's equation :
Ψd the gas diffusive flux
De
the effective diffusion coefficient
c
the gas concentration
x
the space dimension
P1 = P2
C1,1 > C2,1
Fig. 3. Schematic diagram of measurement
apparatus for gas diffusivity in coal.
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RESULT AND DISCUSSION
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Coal sampling and measuring conditions
Contact
metamorphosed
R0 (max, %)
0.66~1.45
Moisture(%)
0.4~7.9
VM (daf, %)
21~43
Ash(%)
5~34
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Adsorption isotherm measurements (1)
Fig. 5. Relative error (r) in using a Langmuir type
equation for determining CO2 adsorption for all coals
studied.
Fig. 4. Measured adsorbed volume versus Langmuir
estimated volume for CO2 adsorption.
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Adsorption isotherm measurements (2)
Fig. 6. CO2 Langmuir volume VL for the Sydney Basin coals in
relation to volatile matter content (VM).
no clear relationship
Fig. 8. CO2 adsorption capacity of the Sydney
Basin coals according to the rank
Fig. 7. Langmuir pressure (PL) in relation to volatile matter content.
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Adsorption isotherm measurements (3)
C0=30.1 m3/t
h0=400 m
a=0.56
Fig. 9. CO2 storage capacity of the Sydney Basin
coals at in-situ pressure
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Diffusivity and porosity measurements
no clear relationship
Fig. 10. CO2 diffusivity and coal
porosity according to depth.
Fig. 11. CO2 diffusivity and porosity
according to volatile matter content
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Comparison of properties of main seam gases
CO2/CH4 : 1.8
CO2/N2 : 5.9
Fig. 12. Adsorption of pure CO2, CH4 and
N2 on coal (coal17).
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CONCLUSIONS
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The highest adsorptive capacity corresponds to the deepest,
highest rank coal, the lowest corresponds to a shallower coal
but not necessarily the lowest rank coal.
For these samples, no clear relation between the diffusivity
and the depth or rank of coals.
The CO2 storage capacity is about twice that of CH4 and six
times that of N2. The diffusivity of CO2 in coal is about twice
that of CH4.
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Thanks for Your Attention!
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