Removal behaviors of moisture in raw lignite and moisturized coal and their dewatering kinetics analysis

Wen, Yinglin; Liao, Junjie; Liu, Xiao; Wei, Fanjing; Chang, Liping

doi:10.1080/07373937.2016.1160246

Cited by 31 publications

(11 citation statements)

References 26 publications

(41 reference statements)

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“…Based on the activation energy values and R 2 , models with g (α) = −(ln(1 – α)) 1/2 were optimum for the increasing-rate and constant-rate stages and models with g (α) = −ln(1 – α) were optimum for the decreasing-rate stage. We referenced the activation energy values of brown coal drying in other studies. , If the R 2 was very high, but the activation energy was too big or small compared with that in references, then the model would not be used. The acceptable range of activation energies could be 15–45 kJ/mol.…”

Section: Resultsmentioning

confidence: 99%

“…The apparent diffusion coefficient was calculated by Fick’s second law. The details of the calculation process were presented by our previous study. , where D eff is the effective diffusion coefficient (m 2 /s); L , which represents the diameter of coal particle, was taken as 8.6 × 10 –4 m. The value was estimated by that the percentage of coal particle size smaller than 0.75 mm was approximately 85 wt %. The percentage of coal particle size smaller than 0.75 mm was analyzed by a 200-mesh sieve.…”

Section: Methodsmentioning

confidence: 99%

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Correlation between Drying Behaviors of Brown Coal and Its Pore Structures

et al. 2019

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Drying behaviors of brown coal are affected by internal water diffusion, which is controlled by pore structures. To diminish the effect of functional groups on drying, drying behaviors and pore structures of only one kind of coal dried at different heating rates and atmospheres were investigated. The final drying temperature was kept constant. The relationships between pore structures, including specific surface area (S BET), volume of mesopores (V meso), volume of macropores (V macro), volume of total pores (V total), and two fractal dimensions (D I and D II), and drying characteristics, including maximum drying rate (v max), activation energy of drying surface water (E 1), activation energy of drying pore water (E 2), apparent diffusion coefficient surface water (D eff‑1), and apparent diffusion coefficient pore water (D eff‑2), were correlated. The relationship between basic pore parameters and fractal dimensions was examined. For coals dried in N2, the S BET was confirmed as one of the key factors influencing D I. The v max increased with heating rates, resulting from the higher temperature at the same drying time and larger S BET and V macro. The E 1 was higher at faster heating rates, because of the higher temperature gradient and the bigger D I. The E 2 increased as heating rates increased from 3 to 20 °C/min and then decreased for flash drying (directly dried at 200 °C). The increase could be also due to the higher temperature gradient at higher heating rates. The decrease could be because of the effect of V macro on D eff‑2. For coals dried in different atmospheres, the higher E 1 and E 2 in air were due to oxidation reaction. The relatively large heat conductivity of N2 led to the lower E 1. The small molecular diameter of CO2 led to the lower E 2. There was no consistent relationship between S BET and D I and between pore structures and drying characteristics for coals dried in different atmospheres.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Correlation between Drying Behaviors of Brown Coal and Its Pore Structures

et al. 2019

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“…Feng et al investigated the effect of the Mechanical Thermal Expression on the structure of lignite and determined changes in volume of pores between the raw lignite and lignites dried at drying temperatures between 120 • C and 150 • C under pressures of 10 MPa and 30 MPa respectively [10]. Wen et al investigated the drying kinetics of raw and re-moisturised lignite and determined the drying rate of the former was slower in comparison to the latter [11]. Moreover, the study found the effective diffusion coefficient for the moisturised lignite to be higher than a corresponding value for a raw lignite [11].…”

Section: Drying Of Lignitementioning

confidence: 99%

“…Wen et al investigated the drying kinetics of raw and re-moisturised lignite and determined the drying rate of the former was slower in comparison to the latter [11]. Moreover, the study found the effective diffusion coefficient for the moisturised lignite to be higher than a corresponding value for a raw lignite [11].…”

Section: Drying Of Lignitementioning

confidence: 99%

Drying of Lignite of Various Origins in a Pilot Scale Toroidal Fluidized Bed Dryer using Low Quality Heat

et al. 2019

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An experimental study was carried out for lignites of different places of origin, i.e., Poland, Greece, Romania and Australia, using a toroidal bed dryer. The effect of the temperature on the drying efficiency, including the loss of moisture content over time under fixed drying conditions was the subject of the investigation. The main goal was to confirm the possibility of the use of a toroidal bed as a base for a drying system that could utilize low quality heat from sources such as flue gases from a boiler and determine the optimum parameters for such a system. The conducted study has conclusively proven the feasibility of the use of low temperature heat sources for drying lignite in a toroidal bed. A moisture content of 20% could be achieved for most of the tested lignites, using the toroidal bed, with reasonably short residence times (approx. 30 min) and an air temperature as low as 60 °C. Moreover, the change of the particle size distribution, to some degree, affected the final moisture content due to the entrainment of wet, fine particles. The study also determined that the in-bed attrition of the particles is partially responsible for the generation of fines.

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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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Removal behaviors of moisture in raw lignite and moisturized coal and their dewatering kinetics analysis

Cited by 31 publications

References 26 publications

Correlation between Drying Behaviors of Brown Coal and Its Pore Structures

Correlation between Drying Behaviors of Brown Coal and Its Pore Structures

Drying of Lignite of Various Origins in a Pilot Scale Toroidal Fluidized Bed Dryer using Low Quality Heat

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

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