A Review of Microwave Coal Processing

Binner, Eleanor; Lester, Edward; Kingman, S.W.; Dodds, Chris; Robinson, John P.; Wu, Tao; Wardle, Peter; Mathews, Jonathan P.

doi:10.1080/08327823.2014.11689870

Cited by 57 publications

(29 citation statements)

References 88 publications

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“…However, lignite has low dielectric properties for its high organic compounds, which can lead to weak absorbing ability to microwave energy [17]. To improve the microwave [19] for the effects of additive (activated carbon) on the temperature of oil palm shell at drying stage during microwave pyrolysis process (2450 MHz, 1000 W), had presented that the sample temperature increased with the addition of the activated carbon at blending ratios of 10-25%, but the temperature increased slightly with the further increasing of the activated carbon over 25% blending ratio.…”

Section: Introductionmentioning

confidence: 99%

Combined effects of additives and power levels on microwave drying performance of lignite thin layer

Chen

Huang

et al. 2016

Drying Technology

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The microwave drying performance of lignite thin layer in a bench-scale setup was highlighted in terms of three additives with 10% dosage. The dielectric loss for dried lignite, raw lignite, lignite/coal fly ash, lignite/Na 2 SO 4 and lignite/Na 2 CO 3 at 2450 MHz were 0.06, 0.13, 0.14, 0.15 and 0.18. In comparison with raw lignite, the average temperature rising of the thin layer at 385 W for lignite blending with sodium carbonate, sodium sulfate and coal fly ash was about 10, 7 and 2 °C. The apparent activation energies of both falling rate periods for lignite blending with three additives were less than that of raw lignite. Sodium carbonate among three additives could be preferable one, followed by sodium sulfate and coal fly ash. The energy efficiency increased with the addition of sodium carbonate, sodium sulfate and coal fly ash. The required electricity energy for lignite/Na 2 CO 3 blend at 385 W was reduced by about one half in compared with the raw lignite.

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Section: Introductionmentioning

confidence: 99%

Combined effects of additives and power levels on microwave drying performance of lignite thin layer

Chen

Huang

et al. 2016

Drying Technology

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“…Previous investigations of microwave pyrolysis of coal were mainly focused on three areas: the effect of microwave pyrolysis on physicochemical properties such as coal grindability and dryness (Ge et al 2013;Lester et al 2005;Marland et al 2000); dielectric properties, interaction mechanisms, and enhancement of coal pyrolysis using microwave absorbers (Liu et al 2016;Monsef-Mirzai et al 1995;Peng et al 2012Peng et al , 2017; and the properties of pyrolysis products such as gaseous material, tar, and char (Abdelsayed et al 2018;Reddy et al 2019;Reddy and Vinu 2016). Researchers also considered microwave reactors and their scale-up (Binner et al 2014;Salema and Ani 2012). It was demonstrated that microwave pyrolysis showed more gaseous and less tar, high quality liquid fuels and more energy-efficient than conventional pyrolysis (Abdelsayed et al 2018;Reddy and Vinu 2016).…”

Section: Introductionmentioning

confidence: 99%

Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis

Jiang

Meng

et al. 2020

Int J Coal Sci Technol

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This study examined an isothermal CO2 gasification of four chars prepared via two different methods, i.e., conventional and microwave-assisted pyrolysis, by the approach of thermogravimetric analysis. Physical, chemical, and structural behaviours of chars were examined using ultimate analysis, X-ray diffraction, and scanning electronic microscopy. Kinetic parameters were calculated by applying the shrinking unreacted core (SCM) and random pore (RPM) models. Moreover, char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency (CGE). The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure, but the smallest gasification reactivity. Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars, and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s−1, respectively. In addition, a compensation effect was noted during gasification. Finally, the microwave-derived char exhibits better thermodynamic performances than the conventional chars, with the highest CGE and CO molar concentration of 1.30% and 86.18%, respectively. Increasing the pyrolysis temperature, gasification temperature, and CO2-to-carbon molar ratio improved the CGE.

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“…In microwave field, materials can be divided into insulators, conductors, and absorbers. Dipolar molecules in lignite, such as water, have a high dielectric constant and loss factor compared with dry lignite, can absorb microwave energy quickly and turn into thermal energy while the dry lignite particle maintain a low microwave absorbability [14]. Therefore, heat is transferred from the core to the surface of the lignite in microwave heating and the direction is identical with the moisture migration [15].…”

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confidence: 99%

Effect of Temperature and Microwave Power Levels on Microwave Drying Kinetics of Zhaotong Lignite

Zhao

Liu

et al. 2019

Processes

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Microwave drying is a promising and effective way to drying and upgrading lignite. The influence of temperature (100-140 • C) and microwave power levels (500-800 W) on thin-layer drying characteristics of Zhaotong lignite under microwave irradiation were investigated. Fourteen thin-layer drying models were used to analyze the microwave drying process while six thin-layer drying models were used to analyze the hot-air drying process. The microwave drying processes at all temperature (100-140 • C) or low microwave power levels (500-700 W) exhibited four periods: a warm-up period, a short constant period, the first and second falling rate period, while one falling rate period was found during hot-air drying. The effective diffusion coefficient of lignite were calculated and it increases with increasing temperature and microwave power levels. During microwave drying, the two-term exponential model is the most suitable model for all applied conditions, while the Modified Page model is the most suitable model to describe the hot-air drying experiments. The apparent activation energy were determined from Arrhenius equation and the values for the first and second falling rate period are 3.349 and 20.808 kJ·mol −1 at different temperatures, while they are 13.455 and 19.580 W·g −1 at different microwave power levels. This implies the apparent activation energy is higher during the second falling rate period, which suggest that the dewatering of absorbed water is more difficult than capillary water. The value of apparent activation energy in hot-air drying is between the first and second falling rate period of microwave drying. Results indicate that microwave drying is more suitable to dewatering free water and capillary water of lignite.Processes 2019, 7, 74 2 of 18 high reactivity, and low pollution impurities [3], it will be used more widely in the future. Thus, moisture removal is the first essential step to improve the quality of lignite by drying technologies in downstream utilization, such as pyrolysis, gasification, liquefaction, and combustion.Various lignite dehydration technologies have been developed and researched by evaporation or non-evaporation methods [4]. Solar drying [5], steam-fluidized bed drying [6], and flue gas drum drying [7] are based on evaporation drying, while mechanical thermal expression [8,9] and hydrothermal dewatering [10,11] are based on non-evaporation drying. In traditional drying technologies, heat is transferred from the surface to the interior of the material by convection and conduction while the moisture transferred from the inside of the material to the surface. Most of thermal drying process are operated with combustion gas or superheated water vapor and the configuration of the drying reactor are complicated, which induces high costs of construction. In addition, traditional methods will lead to heating inhomogeneity, which is not beneficial for lignite upgrade. Among these dehydration technologies, microwave drying of low-rank coal is a very promising method due to its unique he...

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A Review of Microwave Coal Processing

Cited by 57 publications

References 88 publications

Combined effects of additives and power levels on microwave drying performance of lignite thin layer

Combined effects of additives and power levels on microwave drying performance of lignite thin layer

Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis

Effect of Temperature and Microwave Power Levels on Microwave Drying Kinetics of Zhaotong Lignite

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