Characteristics and mechanism of coal rock breaking by liquid nitrogen assisted water jet impacts

IF 4.6 2区工程技术 Q2 ENGINEERING, CHEMICAL

Powder Technology Pub Date : 2025-06-20 DOI:10.1016/j.powtec.2025.121300

Yabin Gao , Junyu Hong , Shaoqi Zhang , Mengbo Li , Gaojie Hou , Ziwen Li , Jinggang Liu

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引用次数: 0

Abstract

To improve the effectiveness of existing water jet-based coal rock breaking, this study proposes a novel approach: liquid nitrogen assisted water jet (LNAWJ) impact breaking. This method effectively destroys the target coal by utilizing the combined effects of low-temperature liquid nitrogen fracturing and the erosive power of the water jet. It also improves the pore and fissure structure of the coal and increases the permeability of coal seams. Using the water jet impact experimental system, a liquid nitrogen assisted water jet impact experiment was conducted to analyze the effects of varying liquid nitrogen cold impact time, rewarming time, and water jet pressures on the fracturing of coal. The study aimed to reveal the characteristics and mechanisms of LNAWJ fracturing by examining the liquid nitrogen fracturing process, the form of coal and rock fracturing, the morphology of crushing pits, and the surface strain characteristics. The results show that liquid nitrogen fracturing, combined with the strong erosive action of the water jet, effectively fractures the coal. The results show that the evolution process of liquid nitrogen fracturing in coal rock can be divided into two stages: the liquid nitrogen cold impact stage and the room temperature thermal impact stage. Both stages effectively fracture the coal. As the liquid nitrogen cold impact time and room temperature thermal impact time increase, the uniaxial compressive strength of the coal decreases, while the total length of the coal sample, fissure area, and porosity increase. Compared to single water jet impact, LNAWJ impact leads to the formation of more irregular impact holes along the fractures in the coal rock. The impact holes are more irregular in shape, and multiple main fracture surfaces form along the crushing pit, extending outward. These fracture surfaces are uneven, secondary cracks develop, and the overall crushing degree of the coal samples is higher. With an increase in liquid nitrogen cold impact time and water jet pressure, the impact of the liquid nitrogen assisted water jet is enhanced. This results in a higher number of fracture surfaces, larger impact pits, and greater crushing of the coal. Specifically, after 60 min of liquid nitrogen cold impact, the depth of the crushing pits increases by 44.44 %, and the area of the pits increases by 125.98 %, compared to a single water jet impact. Additionally, when the jet pressure is increased to 16 MPa, compared to 8 MPa, the crater depth and area increase by 65.21 % and 360.80 %, respectively. During the LNAWJ impact, the destruction of the coal rock occurs in five stages: the liquid nitrogen cold impact initiation, induced crack micro-generation, room temperature thermal impact, water jet impact, and coal crushing. Among these, the induced cracks created during the liquid nitrogen cold impact process provide pathways for the water jet to further fracture the coal, significantly increasing the cracking path and improving the overall crushing of the coal.

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液氮辅助水射流破岩特性及机理

为了提高现有水射流破碎煤岩的有效性，本研究提出了一种新的方法：液氮辅助水射流（LNAWJ）冲击破碎。该方法利用低温液氮压裂和水射流侵蚀力的联合作用，有效地破坏了靶煤。它还改善了煤的孔隙和裂隙结构，增加了煤层的渗透率。利用水射流冲击实验系统，进行液氮辅助水射流冲击实验，分析不同液氮冷冲击时间、复温时间和水射流压力对煤的压裂效果的影响。通过对液氮压裂过程、煤岩破裂形态、破碎坑形态及表面应变特征的研究，揭示LNAWJ压裂特征及机理。结果表明：液氮压裂结合水射流的强冲蚀作用，对煤进行了有效的破裂；结果表明：煤岩液氮压裂演化过程可分为液氮冷冲击阶段和室温热冲击阶段。这两个阶段都有效地破坏了煤。随着液氮冷冲击时间和室温热冲击时间的增加，煤的单轴抗压强度降低，煤样总长度、裂隙面积和孔隙率增加。与单一水射流冲击相比，LNAWJ冲击导致煤岩沿裂隙形成更多不规则冲击孔。冲击孔形状更加不规则，沿破碎坑形成多个主断裂面，并向外延伸。这些断裂面不均匀，次生裂缝发育，煤样整体破碎程度较高。随着液氮冷冲击时间和水射流压力的增加，液氮辅助水射流的冲击作用增强。这导致更多的断裂面，更大的冲击坑，更大的破碎煤。其中，液氮冷冲击60 min后，破碎坑深度比单次水射流冲击增加44.44%，破碎坑面积增加125.98%；此外，当喷射压力增加到16 MPa时，坑深和坑面积分别比8 MPa增加65.21%和360.80%。在LNAWJ冲击过程中，煤岩的破坏分为液氮冷冲击起爆、诱导裂纹微产生、室温热冲击、水射流冲击和煤破碎五个阶段。其中，液氮冷冲击过程中产生的诱导裂纹为水射流进一步破坏煤提供了通道，显著增加了开裂路径，提高了煤的整体破碎程度。

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来源期刊

Powder Technology 工程技术-工程：化工

CiteScore

9.90

自引率

15.40%

发文量

1047

审稿时长

46 days

期刊介绍： Powder Technology is an International Journal on the Science and Technology of Wet and Dry Particulate Systems. Powder Technology publishes papers on all aspects of the formation of particles and their characterisation and on the study of systems containing particulate solids. No limitation is imposed on the size of the particles, which may range from nanometre scale, as in pigments or aerosols, to that of mined or quarried materials. The following list of topics is not intended to be comprehensive, but rather to indicate typical subjects which fall within the scope of the journal's interests: Formation and synthesis of particles by precipitation and other methods. Modification of particles by agglomeration, coating, comminution and attrition. Characterisation of the size, shape, surface area, pore structure and strength of particles and agglomerates (including the origins and effects of inter particle forces). Packing, failure, flow and permeability of assemblies of particles. Particle-particle interactions and suspension rheology. Handling and processing operations such as slurry flow, fluidization, pneumatic conveying. Interactions between particles and their environment, including delivery of particulate products to the body. Applications of particle technology in production of pharmaceuticals, chemicals, foods, pigments, structural, and functional materials and in environmental and energy related matters. For materials-oriented contributions we are looking for articles revealing the effect of particle/powder characteristics (size, morphology and composition, in that order) on material performance or functionality and, ideally, comparison to any industrial standard.