The Relationship between Functional Groups and Gaseous Productions and Micropore Structures Development of Coal Oxidized at Low Temperature under Methane-Diluted Atmospheres

Cai, Jiawen; Yang, Shengqiang; Hu, Xincheng; Xu, Qin; Zhou, Baoxue; Zhang, Zhicheng

doi:10.1080/00102202.2018.1527324

Cited by 19 publications

(7 citation statements)

References 41 publications

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“…the main functional groups of different metamorphic coals during low-temperature oxidation, and the critical temperature for coal spontaneous combustion was determined 15 . Wang et al analysed the mechanism of weight gain in the process of coal low-temperature oxidation through TG-FTIR 16 .…”

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confidence: 99%

Experimental Study on the Physisorption Characteristics of O2 in Coal Powder are Effected by Coal Nanopore Structure

Tan¹,

Cheng²,

Zhu³

et al. 2020

Sci Rep

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Bo tan , Gang cheng ✉ , Xiaoman Zhu & Xianbing Yang coal is a porous medium. oxygen molecules in the air penetrate through the pores of coal and are adsorbed on the coal surface. Low-temperature oxidation of coal then occurs, by which coal spontaneous combustion is promoted. Given this process, the authors analysed the physisorption characteristics of o 2 in pulverized coal from the perspective of nanopore structure. In this study, five different kinds of coal samples (two lignites, one bituminous coal, and two anthracites) were selected, and the surface morphology, pore structure parameters and oxygen physisorption capacity of the pulverized coals were determined by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and oxygen adsorption with chromatography (OAC), respectively. The experimental results of SEM and MIP show that with the development of coal, the surface folds increase, and the pores increase in number and shrink, which leads to the nanopores of anthracite and bituminous coal being smaller and more complex than those of lignite. The experimental results of OAC show that adsorbed oxygen is physisorbed by pulverized coal in the order lignite > bituminous coal > anthracite. Analysis of the oxygen desorption curves shows that the oxygen desorption rates of the anthracites and bituminous coal are slower than those of the lignites. The results show that the amount of oxygen physisorbed by pulverized coal is proportional to the fractal dimension of the coal pores, proportional to the pore volume of the nanoscale pores, and inversely proportional to the number of closed pores in the coal. Based on the results of the analyses mentioned above, it is important to analyse the process of coal-oxygen chemisorption and the mechanism for low-temperature oxidation of coal to prevent coal spontaneous combustion. The confirmed worldwide reserves of coal stood at approximately 1,055 billion tons in 2018. The United States, Russia, Australia and China together accounted for 66.1% of the world's coal reserves 1. During mining, storage and transportation, coal can undergo spontaneous combustion, resulting in a huge waste of resources and economic losses in the United States and China per annum. The initial stage of coal spontaneous combustion involves coal low-temperature oxidation, in which oxygen permeates into the coal through pores, then physisorbs and chemisorbs with the functional groups on the coal surface, and adsorption heat is generated and accumulated 2,3 , as shown in Fig. 1. Coal is a porous medium, and the pore structure of coal varies with coal development 4 ; therefore, oxygen diffusion in coal pores and adsorption on coal surfaces are also different 5. The significance of the coal low-temperature oxidation mechanism in the physisorption, chemisorption and diffusion of oxygen in coal nanopores has been studied. In this paper, all oxygen adsorption involved physisorption. Scholars from various countries have performed much work on the influencing factors of coal low-temperature oxidati...

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confidence: 99%

Experimental Study on the Physisorption Characteristics of O2 in Coal Powder are Effected by Coal Nanopore Structure

Tan¹,

Cheng²,

Zhu³

et al. 2020

Sci Rep

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“…Comparing the relationship between temperature and saturated adsorption capacity and residual adsorption capacity, it is found that as temperature increases, the saturated adsorption capacity of different coal ranks shows a decreasing trend, but its influence on the residual adsorption capacity is more complicated. The temperature can not only affect the activity of gas molecules but also change the pore structure and surface properties of coal. − The change in residual adsorption capacity with temperature is actually the superposition of the abovementioned two effects, and the effect of temperature on the pore structure and surface properties of middle- and high-rank coals is more complicated than that of lower rank coals.…”

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confidence: 99%

Study for the Effect of Temperature on Methane Desorption Based on Thermodynamics and Kinetics

Gao

Chen

et al. 2020

ACS Omega

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Desorption hysteresis is important for primary gas production. Temperature may cause serious changes in the methane adsorption/ desorption behaviors. In order to study the mechanism of methane desorption and desorption hysteresis, three sets of samples of long-flame coal, coking coal, and anthracite were collected, and experiments such as microscopic composition determination, liquid nitrogen adsorption, and isothermal adsorption/desorption were performed. From the perspectives of desorption kinetics, desorption thermodynamics, and methane occurrence state, the differences in methane and methane desorption characteristics and the desorption hysteresis mechanism are discussed. The results show that at the same temperature, anthracite (SH3#) has the largest saturated adsorption capacity and residual adsorption capacity, followed by coking coal (SGZ11#), and long-flame coal (DFS4#) has the smallest. As the temperature increases, the theoretical desorption rate and residual adsorption capacity of anthracite (SH3#) and coking coal (SGZ11#) will increase first and then decrease. Temperature and methane desorption do have positive effects, but temperature may have a threshold for promoting methane desorption. It is necessary to comprehensively consider the influence of temperature on the activation of gas molecules and the pore structure of coal. Under the premise of a certain temperature, as the pressure increases, the desorption hysteresis rate changes in a logarithmic downward trend, the methane desorption hysteresis rate in the low-pressure stage (P < 4 MPa) is large, and the methane desorption hysteresis rate in the highpressure stage (P > 4 MPa) is lower; during the isobaric adsorption process, the adsorption capacity of anthracite (SH3#) increases the fastest, followed by SGZ11#, and that of DFS4# is the smallest. In the low-pressure stage (P < 4 MPa), the adsorption capacity increases significantly with the increase in pressure, but in the high-pressure stage (P > 4 MPa), the adsorption capacity does not change significantly with pressure, instead gradually stabilizes. Under the same pressure, the molecular free path of methane increases with temperature. Under the premise of constant temperature, in the low-pressure stage (0 < P < 4 MPa), when the pressure continues to decrease, the free path of methane molecules increases significantly, resulting in a decrease in diffusion capacity. In the high-pressure stage (4 < P < 8 MPa), when the pressure continues to decrease, the free path of methane molecules does not change significantly; the sample desorption process of three sets of samples DFS4#, SGZ11#, and SH3# occurs, and the intermediate adsorption heat is greater than the isometric adsorption heat during the adsorption process, indicating that the desorption process needs to continuously absorb heat from outside the system. The energy difference produced in the process of adsorption and desorption causes the desorption hysteresis effect. The greater the difference in the isometric heat value of adsorption, the...

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“…Comparing the relationship between temperature and saturated adsorption capacity and residual adsorption capacity, it is found that as temperature increases, the saturated adsorption capacity of different coal ranks shows a decreasing trend, but its influence on the residual adsorption capacity is more complicated. Temperature can not only affect the activity of gas molecules, but also change the pore structure and surface properties of coal (Ahamed et al 2019;Cai et al 2019). The change of residual adsorption capacity with temperature is actually the superposition of the above two effects, and the effect of temperature on the pore structure and surface properties of middle and high rank coals is more complicated than that of lower rank coals.…”

Section: 2adsorption/desorption Experiments Resultsmentioning

confidence: 99%

Study the Effect of Temperature on Methane Desorption Based on Thermodynamics and Kinetics

Gao

Chen

et al. 2020

Preprint

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Desorption hysteresis is important for primary gas production. Temperature may cause serious change in the methane adsorption/desorption behaviors. In order to study the mechanism of methane desorption and desorption hysteresis, three sets of samples of long flame coal, coking coal, and anthracite were collected, and experiments such as microscopic composition determination, liquid nitrogen adsorption, and isothermal adsorption/desorption were performed. From the perspectives of desorption kinetics, desorption thermodynamics and methane occurrence state, the differences in methane and methane desorption characteristics and the desorption hysteresis mechanism are discussed. The results show that at the same temperature, anthracite (SH3#) has the largest saturated adsorption capacity and residual adsorption capacity, followed by coking coal (SGZ11#), and long -flame coal (DFS4#) is the smallest. As the temperature rises, the theoretical desorption rate and residual adsorption capacity of anthracite (SH3#) and coking coal (SGZ11#) will increase first and then decrease. Temperature and methane desorption are not completely positive effects, and temperature may have a threshold for promoting methane desorption. It is necessary to comprehensively consider the influence of temperature on the activation of gas molecules and the pore structure of coal. Under the premise of a certain temperature, as the pressure increases, the desorption hysteresis rate changes in a logarithmic downward trend, and the methane desorption hysteresis rate in the low pressure stage (P 4MPa) is large, and the methane desorption hysteresis rate in the high-pressure stage (P>4MPa) is lower; During the isobaric adsorption process, the adsorption capacity of anthracite (SH3#) increases the fastest, followed by SGZ11#, and DFS4# is the smallest. In the low-pressure stage (P 4MPa), the adsorption capacity increases significantly with the increase of pressure, but in the high pressure stage (P 4MPa), the adsorption capacity does not change significantly with pressure, but gradually stabilizes. Under the same pressure, the molecular free path of methane increases with temperature. Under the premise of constant temperature, in the low-pressure stage (0<P<4MPa), when the pressure continues to decrease, the free path of methane molecules increases significantly, resulting in a decrease in the diffusion capacity. In the high-pressure stage (4<P<8MPa), when the pressure continues to decrease, the free path of methane molecules does not change significantly; DFS4#, SGZ11#, SH3# sample desorption process of three sets of samples, the intermediate adsorption heat is greater than the isometric adsorption heat during the adsorption process, indicating that the desorption process needs to continuously absorb heat from outside the system. The energy difference produced in the process of adsorption and desorption causes the desorption hysteresis effect. The greater the difference in the isometric heat value of adsorption, the more significant the hysteresis.

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The Relationship between Functional Groups and Gaseous Productions and Micropore Structures Development of Coal Oxidized at Low Temperature under Methane-Diluted Atmospheres

Cited by 19 publications

References 41 publications

Experimental Study on the Physisorption Characteristics of O2 in Coal Powder are Effected by Coal Nanopore Structure

Experimental Study on the Physisorption Characteristics of O2 in Coal Powder are Effected by Coal Nanopore Structure

Study for the Effect of Temperature on Methane Desorption Based on Thermodynamics and Kinetics

Study the Effect of Temperature on Methane Desorption Based on Thermodynamics and Kinetics

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