Damage caused by freeze‐thaw treatment with liquid nitrogen on pore and fracture structures in a water‐bearing coal mass,Energy Science & Engineering

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Damage caused by freeze‐thaw treatment with liquid nitrogen on pore and fracture structures in a water‐bearing coal mass
Energy Science & Engineering ( IF 3.5 ) Pub Date : 2020-03-10 , DOI: 10.1002/ese3.623
Haifei Lin _{1,

2} , Jinliang Li _{1,

2} , Min Yan _{1,

2} , Shugang Li _{1,

2} , Lei Qin _{1,

2} , Yizhen Zhang _{1,

2}

Affiliation

The purpose of the study was to explore the microscopic and mesoscopic damage mechanisms of water‐bearing coal mass in the freeze‐thaw process with liquid nitrogen. For this purpose, by using a Zeiss microscope, a nonmetal ultrasonic velocity detector and a nuclear magnetic resonance (NMR) spectrometer, the changes in the structures of surface fractures and pores before and after coal masses with different moisture contents when subjected to freeze‐thaw treatment with liquid nitrogen (FTTLN) were tested. The result showed that under the freeze‐thaw effect of liquid nitrogen, the structures of surface fractures and internal pores of coal mass were both changed. Upon increasing the moisture content of the coal, the width of surface fractures increased; the surface fractures showed significant fractal characteristics: The higher the moisture content of the coal, the greater the rate of change of fractal dimension after FTTLN; the ultrasonic wave velocity in the coal mass gradually decreased after FTTLN, and the greater the moisture content, the more significant the decrease in ultrasonic wave velocity; under the freeze‐thaw effect of liquid nitrogen, the pore structure in the coal mass was transformed from micropores and small pores to mesopores and macropores and certain new micropores and small pores were generated. Upon increasing the moisture content of the coal mass, the peak area of micropores and small pores and their proportion decreased at first and then increased (reaching the minimum at 9.12% of moisture content); the peak area, peak area proportion, and porosity of mesopores and macropores always increased. The damage factor attained based on the width of fractures, longitudinal wave velocity, fractal dimension of surface fractures, and porosity was favorably correlated with the moisture content: With increasing moisture content, the coal mass became more severely damaged.

中文翻译：

液氮冻融处理对含水煤体孔隙和裂缝结构的破坏

研究的目的是探讨液态氮冻融过程中含水煤团的微观和介观破坏机理。为此，通过使用蔡司显微镜，非金属超声速度检测器和核磁共振（NMR）光谱仪，对具有不同水分含量的煤块进行冻融前后，表面裂缝和孔隙结构的变化测试了液氮处理（FTTLN）。结果表明，在液氮的冻融作用下，煤体的表面裂缝和内部孔隙结构均发生了变化。随着煤中水分含量的增加，表面裂缝的宽度增加。表面裂缝显示出明显的分形特征：煤中的水分含量越高，FTTLN后的分形维数变化率越大；FTTLN后，煤体中的超声波速度逐渐降低，含水率越大，超声波速度的降低越明显。在液氮的冻融作用下，煤团的孔隙结构由微孔和小孔转变为中孔和大孔，并产生了一些新的微孔和小孔。随着煤块含水量的增加，微孔和小孔的峰面积及其比例先减小然后增大（在含水量的9.12％时达到最小值）。中孔和大孔的峰面积，峰面积比例和孔隙率始终在增加。

更新日期：2020-03-10

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