Moisture removal mechanism of low-rank coal by hydrothermal dewatering: Physicochemical property analysis and DFT calculation

Wu, Ji; Wang, Jie; Liu, Jianzhong; Yang, Yongrong; Cheng, Jun; Wang, Zhihua; Zhou, Junhu; Cen, Kefa

doi:10.1016/j.fuel.2016.09.071

Cited by 97 publications

(29 citation statements)

References 49 publications

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“…This result indicates that the moisture softening of coal could be significant. The wetting action of water molecules weakens the link between coal particles, which will weaken the mechanical properties of coals (Yu et al, 2013;Wu et al, 2017). Meanwhile, the water in the pores and fractures will produce pressure (Su et al, 2017), which will also reduce the elastic modulus of coals and improve the deformation ability, leading to easy compression deformation of the coal…”

Section: Effects Of Macerals and Minerals On Coal Matrix Compressibilitymentioning

confidence: 99%

Insights into matrix compressibility of coals by mercury intrusion porosimetry and N2 adsorption

Cai

Liu

et al. 2018

International Journal of Coal Geology

126

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Matrix compressibility and pore properties (pore size distribution) of a rank range of coals was investigated using mercury intrusion porosimetry (MIP) on coal cores with the pore size distribution also being determined using low temperature at 77 K nitrogen adsorption/desorption isotherms for crushed samples. The coal matrix compressibility is significant when the pressure of MIP is from 0.0074-35 MPa. Mathematical models were developed (based on MIP and nitrogen adsorption/desorption isotherms) to establish the porosity/pore size distribution relationships with matrix compressibility. For coal ranks, the matrix compressibility was between 0.2410-4 to 13.5610-4 MPa-1 , and had a negative exponential relationship with the vitrinite reflectance (R o,m %). Lignites have the maximum matrix compressibility due to their structural open structure having limitied compaction during coalification. In addition to the pore structure relationship the composition, moisture, and ash yields impacts on compressibility were also examined. Inertinite-rich coals however had a low matrix compressibility across the rank range, which may be due to the interinhibitive relationships between the mesopores, macropores and minerals. The wetting action of high moisture (water molecules) weakens the link between the coal particles of the lignites and the subbituminous coals, which causes abnormally high compressibility. Observations here relate to hydrofracturing or CO 2 injection behaviors during enhancing coalbed methane (CBM) recovery.

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Section: Effects Of Macerals and Minerals On Coal Matrix Compressibilitymentioning

confidence: 99%

Insights into matrix compressibility of coals by mercury intrusion porosimetry and N2 adsorption

Cai

Liu

et al. 2018

International Journal of Coal Geology

126

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“…Based on the experimental results, the cluster size was estimated at seven water molecules. Compared with OFGs, nonpolar functional groups, such as alkanes and benzene rings, have much weaker interactions with water 24 and only acted as a “chemical environment” for n H 2 O@lignite in this study.…”

Section: Introductionmentioning

confidence: 91%

Water Clusters in Lignite and Desorption Energy Calculation by Density Functional Theory

He¹,

Xiao²,

Miao³

et al. 2019

ACS Omega

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The interaction of water and hydrophilic sites with hydroxyl, carboxyl, and multiple oxygen-containing functional groups (OFGs) in lignite molecules was studied by density functional theory. The adsorption of water molecules on the lignite surface initially resulted in the formation of hydrogen bond-driven stable rings by three to four water molecules, followed by the formation of three-dimensional water clusters like a ″patchwork″. Aqueous layer thickness obtained from the water cluster size was 0.4–0.6 nm, which was consistent with the experimental data. Thus, pore-filling water beyond this range was less affected by the OFGs on the surface. Calculation of the adsorption energy predicts that the water clusters were primarily formed in the hydrophilic sites with three OFGs (site 1, including a carbonyl group, an alcoholic hydroxyl group and an etheroxy group in tetrahydropyran), then in COOH, and in O–H. For isolated hydroxyl groups, the interaction between the hydroxyl group and water molecules was weaker than that between the water molecules. When the water cluster was located at the hydrophilic sites with two or more OFGs, the adsorption energy of lignite–water interaction was higher than that of water–water interaction. Investigating the thermodynamics of the adsorption process at a molecular scale will help in understanding both drying and resorption process of dried lignite during industrial production.

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“…The pressure is regarded as the initial pore pressure. During the water-driven-methane process, pressure water will flow along the pore channel [21][22][23][24]. This breaks the original mechanical equilibrium in the coal sample, and the stress is redistributed again.…”

Section: Geofluidsmentioning

confidence: 99%

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

Huang

2018

Geofluids

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The existence of the water-driven-methane effect in gassy coal has been verified by field tests and laboratory experiments. However, a water-driven-methane mathematical model that considers methane adsorption and desorption has not yet been established. Based on the water-driven-methane process, a fluid-solid coupling mathematical model of methane driven by water is established. The model’s reliability is verified by the results of a water-driven-methane physical experiment and by using a solution of the COMSOL Multiphysics software. The space-time distribution regularities of the pore pressure, water-methane two-phase saturation, and pore pressure gradient in the water-driven-methane process are analysed. The results reveal the following. (1) The water-driven-methane fluid-solid coupling mathematical model for porous coal is reliable. (2) In the water-driven-methane process, there is an increasing zone and a decreasing zone of pore pressure in the coal sample. The increasing zone of pore pressure is closest to the side of the water inlet, and its area gradually decreases. The decreasing zone of pore pressure is closest to the side of the methane outlet, and its area gradually increases. Over time, the methane pressure in the increasing zone of pore pressure first increases and then decreases, and the methane pressure in the decreasing zone of pore pressure continuously decreases. The change (increase or decrease) rate of the methane pressure gradually decreases from both ends towards the middle of the coal sample. (3) The curve of the water saturation over time changes from a lower concave curve to a straight line, while the curve of the methane saturation with time changes from an upper convex curve to a straight line. The methane saturation in the decreasing zone of pore pressure is greater than that in the increasing zone of pore pressure. Over time, the water saturation of a specific point in space continuously increases while its methane saturation continuously decreases. Both of the increase rate of the water saturation and the decrease rate of the methane saturation gradually reduce over time. (4) The pore pressure gradient along the driving direction first decreases and then increases. The decreasing zone of the pore pressure gradient is located in the increasing zone of pore pressure, and the increasing zone of the pore pressure gradient is located in the decreasing zone of pore pressure. Over time, the pore pressure gradient at the side of the water inlet increases, and its increase rate decreases. The pore pressure gradient at the side of the methane outlet decreases, and its decrease rate decreases. The rate of increase in the pore pressure gradient at the side of the water inlet is greater than the rate of decrease in the pore pressure gradient at the side of the methane outlet.

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Moisture removal mechanism of low-rank coal by hydrothermal dewatering: Physicochemical property analysis and DFT calculation

Cited by 97 publications

References 49 publications

Insights into matrix compressibility of coals by mercury intrusion porosimetry and N2 adsorption

Insights into matrix compressibility of coals by mercury intrusion porosimetry and N2 adsorption

Water Clusters in Lignite and Desorption Energy Calculation by Density Functional Theory

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

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