ARTICLE pubs.acs.org/IECR
Displacement Behavior of Methane Adsorbed on Coal by CO2 Injection Dengfeng Zhang,†,‡ Songgeng Li,*,† Yongjun Cui,§ Wenli Song,† and Weigang Lin† †
State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China ‡ Graduate University, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China § Beijing Research Institute of China Shenhua Coal to Liquid and Chemical Co. Ltd., Beijing 100011, People’s Republic of China ABSTRACT: The displacement behavior of methane adsorbed on coals by CO2 injection has been experimentally studied. With the assumption of the additive property of the adsorbed-phase volume, a novel data processing method is established to obtain the absolute adsorption amount of methane and CO2 as well as the amount of methane recovery. The results show that the adsorption of CO2 on low-rank Bulianta coal initially saturated with methane is higher than that on high-rank Qinshui coal. For comparison, the adsorption isotherms of pure methane and CO2 on coal without initial methane saturation have been conducted. It is found that, for the coal sample without methane saturation, the CO2 adsorption capacity of high-rank Qinshui coal is superior to that of low-rank Bulianta coal. A conceptual model is proposed to give the explanation. It is indicated that for carbon dioxide sequestration on coal with enhanced coal bed methane recovery (CO2ECBM), it would be better to inject CO2 after partial desorption of methane by depressurizing in order to improve CO2 storage. The selectivity ratio of CO2 and effects of operation parameters such as pressure and temperature have been discussed. On the basis of the results, a recommended depth of CO2 sequestration in coal seams has been put forward.
1. INTRODUCTION Geological carbon dioxide (CO2) sequestration is a promising technology in a portfolio of options for stabilizing CO2 concentration in the atmosphere, which includes depleted oil and gas reservoirs, use of CO2 in enhanced oil and gas recovery, deep saline formations, and deep unmineable coal seams.1 Among them, CO2 sequestration in coal seams, also known as CO2 enhanced coal bed methane recovery (CO2ECBM), has received much attention in the past decade.2 It is estimated that the storage capacity of CO2 in coal seams all over the world is between 300 and 964 Gt,3 which can simultaneously recover 1.45 1013 m3 of coal bed methane.2 The major advantages of this process are the deep unmineable coal seams are capable of sequestrating CO2 mainly by adsorption in geologic time scale and recovery of methane can partially offset the sequestration cost. Hitherto, numerous laboratory works and several field tests have been conducted, which confirm the feasibility of the CO2ECBM process.4,5 Characteristics and behaviors of single or binary adsorption of methane and CO2 have been extensively studied.68 In comparison, studies on the displacement behavior of methane adsorbed on coal by injecting CO2 are less although studies on this aspect may more benefit the development of the CO2ECBM process. In the published reports, most of the work has been performed at relatively low CO2 injection pressure and the experimental data on high pressures are rare.9,10 Moreover, there are contradictory points of view on the rank of coal seams suitable to the CO2ECBM process. Reeves et al.11 indicated that ECBM operations were more favorable in low-permeability, high-rank coals. Jackson12 asserted that the ECBM process was more beneficial in undersaturated, low-rank, high-permeability r 2011 American Chemical Society
coals. A fundamental cause for the different views is that the mechanism of methane adsorbed on coal displaced by CO2 has not been fully understood. China has abundant coal and coal bed methane resources. However, the permeability of most of the coal seams in China is low (permeability of 70% of coal seams e 0.001 μm2),13 which results in the low recoverable amount of coal bed methane. Compared with normal methods for methane recovery, the CO2ECBM process can generate a high flow rate and a total recovery amount of methane.14 Liu et al.15 have estimated that the amounts of recoverable methane and CO2 sequestration in 39 coal basins (3001500 m) of China can reach as high as 1.632 1012 m3 and 120.78 108 t, respectively. Hence, applying the ECBM process in China may have great potential. In this work, the results of laboratory studies on the displacement behavior of methane adsorbed on coals exploited from two representive coal seams in China by CO2 injection have been presented. Variables such as operation parameters (temperature and CO2 injection pressure) and coal rank have been examined by introducing an iteration algorithm to generate the absolute adsorption amount of methane and CO2 at the equilibrium state of the displacement process. A conceptual model is proposed in an attempt to describe the microscopic mechanism of the displacement behavior. Received: January 4, 2011 Accepted: June 2, 2011 Revised: May 3, 2011 Published: June 02, 2011 8742
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Table 1. Proximate, Ultimate, and Petrographic Composition Analyses of Coal Samples analysis
Bulianta
Qinshui
Proximate (wt %, ad) moisture
7.00
1.82
ash volatile matter
4.55 31.66
5.77 4.70
fixed carbon
56.79
87.71
Ultimate Analysis (wt %, ada) carbon
72.09
88.17
hygrogen
4.85
2.86
nitrogen
0.59
0.56
sulfur
0.19
0.32
oxygen
17.73
2.32
Maceral Composition (vol %, mmfb) vitrinite
82.30
liptinite
0.00
93.80 0.00
inertinite
17.70
6.20
R0,max c (%)
0.47
4.06
a
Air-dried basis. b Mineral matter free basis. c Maximum vitrinite reflectance coefficient.
2. EXPERIMENTAL SECTION 2.1. Samples. Two coal samples, Bulianta coal (Shangwan coal mine located in Ordos basin, drilled at a depth of about 200 m) and Qinshui coal (Jincheng coal mine located in Qinshui basin, drilled at a depth between 200 and 300 m), were used in this study. Characterization of the coals was conducted in our laboratory. The proximate and petrographic analyses were performed following the standard procedures described in National Standards GB/T 212-2008 and GB/T 16773-2008 of China, respectively. The ultimate analyses were carried out using a CE-440 elemental analyzer for C, H, and N and a KZDL-8 rapid S cube for S. The content of oxygen was determined by subtracting C, H, N, and S. The analysis results of all the samples are presented in Table 1. In comparison with Qinshui coal, the main characteristic of Bulianta coal is of high volatile matter and low fixed carbon. Also worth noting is its relatively low R0,max, which is an indicator of coal rank. Accordingly, Bulianta coal is classified as bituminous coal. Qinshui coal is categorized into anthracite. All of the coal samples were preserved in sealed plastic bags with helium preventing oxidation-related change of the coal structure. The samples were crushed and sieved to obtain particles with diameter between 180 and 250 μm. Before adsorption, samples were dried at 105 °C for 24 h under vacuum proposed by Ottiger et al.16 2.2. Experimental Apparatus and Procedure. The experimental apparatus basically consists of a reference cell (RC) and a sample cell (SC), between which a valve is placed for isolation. The sample cell is equipped with a filter to prevent fine particles from entering the valve. All cells, the associated tubings, and valves are placed in a temperature-regulated air bath to keep the temperature within the fluctuation range of 0.1 °C toward the set point. High-precision temperature and pressure transducers (0.1 °C and 0.689 KPa) are used to ensure the measurement accuracy. The purities of methane and CO2 used in the experiments are 99.99%. In this work, a volumetric method is adopted
to determine the adsorption isotherms of pure methane and CO2. Void volumes of the sample cell (containing coal sample, VV) and the reference cell were calibrated using “nonadsorbing” gas, He. A detailed procedure of volume calibration can be found in the literature.17 The procedures of measurement of the isotherms of pure methane and CO2 are as follows: the sample cell is sealed at atmospheric pressure, and the equilibrium pressure (P1) is recorded at the setting temperature (T); the reference cell is charged with an appropriate amount of adsorbate (P2); the isolation valve is opened, and adsorbate is transferred from the reference cell to the sample cell; the isolation valve is kept open in the adsorption test; and the pressures of the reference cell (P3) and the sample cell (P4) at the adsorption equilibrium are recorded. Theoretically, P3 is equivalent to P4 when the adsorption process reaches final equilibrium. However, two separate pressure transducers were used to measure the pressures of reference and sample cells in our experiment, respectively. Thus, different subscripts are used to represent the final equilibrium pressures of reference and sample cells. On the basis of the real gas law, the Gibbsian surface excess adsorption amount (GSE)18 of methane and CO2 can be calculated by 1 P2 VRC P1 VV P3 VRC P4 VV ΔGSE ¼ + ð1Þ RmT Z2 Z1 Z3 Z4 where R is the universal gas constant (J 3 mol1 3 K1); m is the mass of the coal sample (g); T is the isothermal temperature (K); and Z1, Z2, Z3, and Z4 are methane or CO2 compressibility factors corresponding to P1, P2, P3, and P4 at T, respectively. Previous investigations have shown that the choice of the compressibility factor strongly affects the accuracy of GSE.17 In this work, three equations of state (EoSs) of high predictive accuracy are selected to obtain the compressibility factors of He, methane, and CO2, which are listed in Table 2. To generate the isotherm, the above procedures of GSE determination were repeated for incrementally increasing the pressure of the adsorbate. Thus, the total amount of the adsorbed gas at the end of the nth step is determined from GSEn ¼
n
∑ ΔGSEi i¼1
ð2Þ
With regard to the displacement experiment, the procedure is as follows: (1) The isolation valve between the sample cell and the reference cell is closed; the reference cell is charged with an appropriate amount of methane, and the isolation valve is opened; and the adsorption process begins. (2) When methane adsorption on coal attains equilibrium, the isolation valve is closed; the reference cell is evacuated, and it is charged with an appropriate amount of CO2. (3) The isolation valve is opened carefully, and CO2 is allowed to release into the sample cell driven by the pressure gradient; and the valve is closed in a timely manner when the pressure of the sample cell is close to that of the reference cell. (4) When reaching complete equilibrium for the displacement in step 3, a gas sample is collected from the sample cell via the microvolume valve; and the gas sample is analyzed with GC/TCD. It should be pointed out that in step 3, most work reported in the literature keeps the isolation valve open until the equilibrium pressure is reached.9,10 In that case, when the pressure in the sample cell is equal to that in the 8743
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Table 2. EoSs Selected To Calculate Compressibility Factors of Helium, Methane, and Carbon Dioxide fluid
a
T (°C)
EoS
P (MPa)
AADa (%)
biasb (%)
MADc (%)
reference
CO2
Span and Wagner EoS
50
0.110
0.055
0.002
0.135
19
He
Kaplun and Meshalkin EoS
50
0.15.3
0.121
0.043
0.214
20
methane
Wagner and Span EoS
76.85
0.120
0.029
0.008
0.071
21
Average absolute deviation. b Bias and. c Maximum absolute deviation calculation can be referred to in refs 22 and 23.
Table 3. Experimental Conditions of Methane Displaced by CO2 Injection T a (°C) Pini b (MPa)
35 5
50 10
65 15
Pinj c (MPa)
8, 13, 18
13, 18
27
a
Adsorption temperature. b Initial methane equilibrium pressure. c CO2 injection pressure.
Figure 2. Iteration algorithm of calculation of nabs of methane and CO2 at displacement equilibrium.
Figure 1. Schematic diagram of displacement equilibrium of methane and CO2.
reference cell, methane in the sample cell will disperse into the reference cell, which leads to the decrease of partial pressure of methane in the sample cell. This will result in partial desorption of methane and hence overestimation of methane recovery. In this work, the isolation valve was closed as the pressure in the reference cell is close to that in the sample cell (the pressure in the reference cell remains a little higher than that in the sample cell) to avoid methane entering into the reference cell. Analyses of the gas sample obtained from the reference cell show that no methane is found in the reference cell. In our experiments, both adsorption and displacement experiments proceed for 24 h, which is considered satisfactory enough to reach equilibrium. Pressure fluctuations within the range of 3.45 KPa plus 8 h duration are taken as criteria of the equilibrium state. A Shimadzu GC-2010ATF with micro-thermal conductivity detector (TCD) was used to determine the concentrations of methane and CO2 in the sample cell. Each gas sample was analyzed three times, and the average value was designated as the final concentration of each component. The GSE of methane and CO2 after displacement can be calculated with the free space volume, total pressure, and gas composition. The experimental conditions of the displacement experiments are shown in Table 3. It is necessary to point out that the adsorption of methane and CO2 can result in coal swelling, which may affect the void volume calibration.24 In this work, the alternation of the coal sample
volume caused by methane or CO2 swelling is ignored to simplify the calculation of GSE.
3. COMPUTATION OF NABS OF METHANE AND CO2 FOR DISPLACEMENT PROCESS Currently, researchers attempt to use multicomponent adsorption models to describe the displacement behaviors. Their results show that the displacement behavior cannot be welldescribed.9 In essence, multicomponent competitive adsorption cannot be equivalent to the displacement, which is even more complicated. Thus, a novel data processing method has been proposed in this work instead of the multicomponent adsorption models to calculate the adsorption of methane and CO2 for the displacement process. The schematic diagram of the displacement equilibrium of methane and CO2 and related nomenclature are given in Figure 1. Note that the excess adsorption does not represent the actual adsorbed amount since it ignores the volume of the gas in the adsorbed phase. The actual adsorbed amount is given by the absolute adsorption amount (nabs). The relationship between GSE and nabs is given as24 nabs ¼ GSE +
nabs F Fads gas
ð3Þ
According to eq 3, the absolute adsorption of binary components can be written as nabs, mix ¼ GSEmix + 8744
nabs, mix F Fads, mix gas, mix
ð4Þ
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Table 4. Experimental Results of the Methane Displaced by CO2 sample
a
T (°C) Pini (MPa) Pinj (MPa) Pta (MPa) nCH40 b (mmol/g) nabs,CH4 (mmol/g) nabs,CO2 (mmol/g) nabs,mix (mmol/g) nr,CH4 (mmol/g) η (%)
Bulianta
35
5.24
8.133
7.208
0.842
0.577
1.209
1.786
0.265
31.47
Bulianta
35
5.27
13.145
8.004
0.868
0.520
1.423
1.943
0.348
40.09
Bulianta
35
5.22
18.226
8.418
0.859
0.528
1.736
2.264
0.331
38.53
Qinshui
35
5.46
8.289
7.426
1.582
1.062
0.986
2.048
0.520
32.87
Qinshui
35
5.49
13.067
7.951
1.577
0.865
1.475
2.340
0.712
45.15
Qinshui
35
5.44
18.207
8.440
1.575
0.801
1.478
2.279
0.774
49.14
Bulianta
50
10.37
13.213
11.475
0.941
0.632
0.446
1.078
0.309
32.84
Bulianta Qinshui
50 50
10.39 10.54
18.147 14.500
12.532 11.785
0.892 1.570
0.501 1.207
0.761 0.359
1.262 1.566
0.391 0.363
43.83 23.12
Qinshui
50
10.45
19.084
12.636
1.571
1.100
0.493
1.593
0.471
29.98
Bulianta
65
14.96
27.226
17.579
1.066
0.592
0.826
1.418
0.474
44.47
Qinshui
65
14.93
27.222
17.462
1.735
1.270
0.495
1.765
0.465
26.80
Total equilibrium pressure after displacement. b Initial absolute adsorption of methane.
The nabs of component i in the adsorption system is expressed as18 nabs, mix nabs, i ¼ GSEi + F yi ð5Þ Fads, mix gas, mix Numerous works25,26 have indicated that the adsorbed phase of methane and CO2 can be considered as pseudo-liquid state. Thus, the volume of the binary adsorbed phase is assumed to possess additive property. Accordingly, eq 6 can be obtained, 2
∑ wads, i =Mi i¼1 Fads, mix
¼
2
ads, i ∑ M F i i¼1 ads, i
w
ð6Þ
in which wads, i ¼
xi ¼
x i Mi 2
∑ x i Mi i¼1
nabs, i nabs, mix
ð7Þ
ð8Þ
Mi is the mole mass of component i. On the basis of the assumption of the adsorbed-phase state, the adsorbed-phase densities of methane and CO2 are designated as 26.31 26 and 27.89 kmol/m3 25 (liquid density at the boiling point under atmospheric pressure), respectively. In combination of eq 4 to eq 8, the absolute adsorption amount of methane and CO2, can be obtained through iteration algorithm. The flowchart for solving these equations is shown in Figure 2.
4. RESULTS AND DISCUSSION 4.1. Absolute Adsorption of Methane and CO2. Table 4 presents the displacement results for injecting CO2 to displace the adsorbed methane. It is shown that methane initially adsorbed on coals is partially desorbed due to CO 2 injection. The amount of methane recovery (n r,CH4, nr,CH4 = nCH40 nabs,CH4) and nabs of CO2 both increase with increasing CO 2 injection pressure. The yield of methane recovery (denoted as η, η = nr,CH4/nCH40 ) varies between 23.12 and 49.14% under the experimental conditions. The yield of methane recovery
according to our experiments is much lower than the results of Shimada et al.9 Shimada et al. found that nearly 90% of the adsorbed methane was displaced when the CO2 injection pressure was 6 MPa. The above contradictive results are probably due to the discrepancy of procedures of the displacement experiments as previously mentioned. From Table 4, it can be seen that nabs of CO2 on Bulianta coal saturated with methane is higher than that on Qinshui coal. However, for the coal sample without methane saturation, the CO2 adsorption capacity of high-rank Qinshui coal is superior to that of low-rank Bulianta coal, which is shown in Figure 3. This phenomenon can be explained by the following conceptual adsorption model shown in Figure 4. Coal is first saturated with methane molecules, which occupy some active sites on the coal surface (stage 1). Injected CO 2 is preferentially adsorbed on the vacancies that are not preoccupied by methane molecules since these vacancies have greater adsorption potential (stage 2). This is evidenced by the results of Prusty et al.,10 which show that CO2 is initially adsorbed on coal without release of methane. After the occupation of the vacancies, CO2 starts to grab the active sites occupied by methane (stage 3). Then methane is displaced by CO2. As shown in Table 4, the initial methane adsorption on Qinshui coal is higher than that on Bulianta coal. This may indicate that the number of the vacancies left on Qinshui coal is less than that on Bulianta coal. As mentioned above, the adsorption on the vacancies is much easier than the adsorption on preoccupied active sites. Thus, Qinshui coal saturated with methane has lower nabs of CO2 compared with Bulianta coal. This finding may infer that, for the CO2ECBM process, it would be better to inject CO2 after partial desorption of methane by depressurizing. This kind of operation mode may be beneficial to improve CO2 storage and methane recovery in the target coal seams. In comparison with CO2 absolute adsorption isotherm at 50 and 65 °C (Figure 3b,c), it is interesting to note that the CO2 adsorption at 35 °C is nearly invariable when the pressure is above 9 MPa (Figure 3a). This phenomenon is probably related to the properties of CO2 around its critical point. By rearrangement of eq 3, the absolute adsorption amount (nabs) can be expressed as eq 9. As shown in Figure 5, the extents of variation of GSE and Fgas are almost identical when the pressure is above 9 MPa, but they vary toward an opposite direction. Thus, 8745
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Figure 4. Conceptual model of CO2 sequestration on coal with enhanced coal bed methane recovery.
Figure 5. GSE and bulk density of CO2 at 35 °C (selected EoS is listed in Table 2).
Figure 3. Absolute adsorption isotherms of pure methane and CO2.
the absolute isotherm of CO2 is nearly invariable at pressures above 9 MPa according to nabs ¼
GSE 1 ðFgas =Fads Þ
ð9Þ
In general, the nabs,mix of methane and CO2 increase with the CO2 injection pressure. For Qinshui coal, it is shown that the nabs,mix at 18.21 MPa (2.279 mmol/g) is a little lower than that at 13.07 MPa (2.340 mmol/g). This is probably attributed to experimental errors. In combination with Figure 3, it also can be seen that the value of nabs,mix is between pure methane and
CO2 adsorption amounts at the same equilibrium pressure. It is widely known that CO2 has a stronger affinity to coal than methane. The preferential adsorption of pure CO2 to methane (ratio of nabs) varies between 1.45 and 2.40 for the coals examined under all experimental conditions. Thus, the value of nabs,mix is lower than that of pure CO2 and higher than that of pure methane. 4.2. Selectivity Ratio of CO2. To express the relative adsorption of methane and CO2, the selectivity ratio of CO2 in relation to methane (RCO2) is defined as27 RCO2 ¼
xCO2 =xCH4 yCO2 =yCH4
ð10Þ
The CO2 selectivity ratios under different injection conditions are illustrated in Table 5. The selectivity ratio of CO2 on Bulianta coal is higher than that on Qinshui coal. It is known that methane and CO2 cannot adsorb on the pore surface but also absorb in a coal matrix. The CO2-induced swelling in low-rank coal is more evident than that in high-rank coal.28 Strong swelling is observed for the adsorption of CO2 rather than that of methane.29 Thus, the selectivity ratio of CO2 on Bulianta coal is higher. Additionally, the selectivity ratio is also related to the morphology characteristic of the coal sample. Clarkson et al.30 found that mesopores could also influence CO2 adsorption and do not have 8746
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Table 5. CO2 Selectivity Ratio under Different Injection Conditions RCO2 T (°C) 35
50 65
Pinj (MPa)
Bulianta
Qinshui
8
1.82
0.95
13
1.63
1.45
18 13
1.57 2.25
1.19 0.86
18
2.28
0.68
27
2.63
0.75
an important effect on methane, and their contribution to CO2 decreases with rank. Therefore, the total meso and larger pore volumes of two samples were determined using N2 adsorption data at P/P0 ≈ 1 (P and P0 are equilibrium pressure and saturated vapor pressure of N2, respectively) (Autosorb 1, Quantachrome Instruments). The analysis results show that the total meso and larger pore volume of Bulianta coal is larger than that of Qinshui coal (1.056 102 and 7.300 104 cm3/g, respectively). These two above explanations are consistent with the conclusion that low-rank coals have a higher preferential adsorption ratio of CO2 to methane. The mole fractions of methane and CO2 in bulk phase at temperatures of 35 and 50 °C are presented in Figure 6. It is shown that the mole ratio of methane to CO2 decreases with CO2 injection pressure elevated. This illustrates that although increasing CO2 injection pressure is helpful to enhance methane recovery, the rate of increase of methane is lower than that of CO2 accumulation in the bulk phase due to the increase of CO2 injection pressure. 4.3. Analyses of Geologic Sequestration of CO2. With the depth increasing, both temperature and pressure increase. An increase in pressure will require higher injection pressure of CO2 and hence increase CO2 storage and methane recovery. Temperature increasing has an opposite effect.31 Therefore, there is an optimum depth for the CO2ECBM process. Theoretically, the geothermal gradient of local coal mines shows positive correlation to the depth. The depths corresponding to the tested temperatures are shown in Table 6. From Table 4 and Table 6, it can be seen that higher sequestration depth does not mean higher adsorption amount of CO2. Take Bulianta coal as an example. At a temperature of 35 °C and a injection pressure of 8 MPa, the adsorption amount of CO2 is about 1.209 mmol/g; at a temperature of 50 °C and an injection pressure of 13 MPa, the adsorption amount is only 0.446 mmol/g; in the case of 65 °C, the sequestration amount of CO2 decreases to 0.826 mmol/g despite the high injection pressure of 27 MPa. All of the data show that the dependence of CO2 adsorption on temperature is significantly stronger than that on pressure. Considering the adsorption behaviors of the coals, we may conclude that the optimum depths of CO2 sequestration on Bulianta coal and Qinshui coal are 849.06 and 781.25 m, respectively. The depths happen to be in the optimum depth window recommended in the literature.1 It is reported that, the best choices will be at depths below 8001000 m for geologic sequestration of CO2, where the density of CO2 is high enough (500700 kg/m3) to limit the storage volume required. Determination of the optimum depth of CO2 sequestration in a coal seam is
Figure 6. Methane and CO2 mole composition in the bulk phase. 8747
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Table 6. Sequestration Depth Corresponding to the Test Temperature h c (m) T0 a sample
coal mine
(°C)
Bulianta Shangwan 12.5 32 Qinshui Qinshui
12.5
34
3T b (°C/(100 m)) 35 °C
50 °C
65 °C
2.33.0 33
849.06 1415.09 1981.13
1.793.85 35
781.25 1302.08 1822.92
Notes: a Average annual surface temperature. b Average geothermal gradient. c Sequestration depth. complex. Besides the adsorption behaviors of coals, factors such as reservior porosity, economy, and environmental benefits should be considered.
5. CONCLUSIONS Major conclusions from the test results can be summarized as follows: (1) Both CO2 adsorption and methane recovery increase with the increasing CO2 injection pressure. (2) The adsorption of CO2 on Bulianta coal saturated with methane is higher than that on Qinshui coal. The adsorption of CO2 on the coals without initial methane saturation has an inverse trend. A conceptual model for describing the displacement behavior has been proposed to explain this phenomenon, which indicates that, for the CO2ECBM process, it would be better to inject CO2 after partial desorption of methane by depressurizing in order to improve CO2 storage. (3) The selectivity ratio of CO2 on low-rank Bulianta coal is higher than that on high-rank Qinshui coal. (4) Considering the adsorption behaviors of coals, the recommended depth for CO2 storage is 781 m for the Qinshui coal seam and 849 m for the Bulianta coal seam. ’ AUTHOR INFORMATION Corresponding Author
*Tel.: +86(10)82544815. Fax: +86(10)82544817. E-mail: sgli@ home.ipe.ac.cn.
’ ACKNOWLEDGMENT This work was financially sponsored by the National Natural Science Foundation of China (Grant No. 40672100) and Hundred Talent Project of Chinese Academy of Sciences. The authors acknowledge Mrs. Xia Zhou, Mr. Zeng-Ming Lun, and Mr. Hai-Tao Wang from Exploration and Production Research Institute, SINOPEC, for their assistance in experimental apparatus setup. ’ REFERENCES (1) Orr, F. M., Jr. Onshore Geologic Storage of CO2. Science 2009, 325, 1656. (2) White, C. M.; Smith, D. H.; Jones, K. L.; Goodman, A. L.; Jikich, S. A.; LaCount, R. B.; DuBose, S. B.; Ozdemir, E.; Morsi, B. I.; Schroeder, K. T. Sequestration of Carbon Dioxide in Coal with Enhanced Coalbed Methane Recovery—A Review. Energy Fuels 2005, 19, 659. (3) Kuuskraa, V. A.; Boyer, C. M.; Kelafant, A. Hunt for Qualify Basins Goes Abroad. Oil Gas J. 1992, 90, 49.
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