低温循环冻融过程不同煤阶煤体传热-变形特征分析
Heat transfer and deformation characteristics of different rank coals in low-temperature cyclical freeze-thaw process
秦雷 1王伟凯 1林海飞 1周斌 1王瑞哲 1罗荣卫 1李树刚1
作者信息
- 1. 西安科技大学安全科学与工程学院,陕西西安 710054;西安科技大学西部矿井开采及灾害防治教育部重点实验室,陕西西安 710054
- 折叠
摘要
明确不同煤阶煤层高效液氮致裂方式是一个紧迫的问题.为分析不同煤阶煤体液氮循环冻融过程中的传热、变形损伤特征,本试验采用饱水、干燥状态褐煤、烟煤、无烟煤为对象,通过温度-应变监测系统探究煤体传热、变形演化规律,采用核磁共振系统分析煤体致裂前后孔隙度演变.结果表明:经循环冻融后,饱水状态各煤样孔隙度均呈上升趋势,干燥试样则均降低.针对冻融过程煤体温度演化,饱水状态3种煤阶试样温降/升速率绝对值整体为:无烟煤＞褐煤＞烟煤;干燥试样温降速率为褐煤＞无烟煤＞烟煤,温升速率则与煤阶呈正相关.饱水、干燥试样冻融过程体积应变演化结构近乎相同,说明2种状态煤样在冻结过程中均形成一定密闭空间,且随煤阶增加,密闭空间完全形成时间缩短.通过分析循环冻融煤体应变演化幅值,发现对于干燥试样,煤阶越高冻融过程应变演化结构愈发简约,变形幅值越小;饱水煤样变形幅值则由裂隙水、煤阶共同决定.本研究明确了液氮循环冲击煤体冻融特征,对液氮煤岩致裂研究具有借鉴意义.
Abstract
Identifying an efficient method for liquid nitrogen(LN2)fracturing in coal layers of different ranks is an urgent issue.To analyze the heat transfer and deformation damage charac-teristics during the LN2 freeze-thaw cycle in coal bodies of various ranks,this experiment used saturated and dry states of lignite,bituminous coal,and anthracite as subjects.The heat trans-fer and deformation evolution laws of coal bodies were investigated using a temperature-strain monitoring system,and the evolution of porosity before and after coal body fracturing was ana-lyzed using a nuclear magnetic resonance system.The results show that:After cyclic freeze-thaw,the porosity of each coal sample in a saturated state generally increases,while that of dry samples decreases.Regarding the temperature evolution during the freeze-thaw process,the absolute values of the rate of temperature decrease/increase for saturated samples of the three coal ranks are in the order of anthracite＞lignite＞bituminous coal;for dry samples,the rate of temperature decrease is lignite＞anthracite＞bituminous coal,and the rate of temperature increase is positively correlated with coal rank.The volume strain evolution struc-ture during the freeze-thaw process is nearly identical for both saturated and dry samples,indi-cating that a certain closed space is formed during the freezing process in both states,and the complete formation time of the closed space shortened with the increase in coal rank.By analy-zing the amplitude of strain evolution during the cyclic freeze-thaw of the coal body,it is found that for dry samples,the higher the coal rank,the more simplified the strain evolution struc-ture during the freeze-thaw process,and the smaller the deformation amplitude;for saturated coal samples,the deformation amplitude is determined by both fissure water and coal rank.This study clarifies the freeze-thaw characteristics of coal bodies under LN2 cyclic impact and has reference significance for the study of LN2 fracturing of coal rock.
关键词
液氮致裂/煤阶/温度演化/变形破坏/密闭空间Key words
LN2 fracturing/coal rank/temperature evolution/deformation damage/sealed spaces引用本文复制引用
基金项目
国科协青年人才托举工程项目(2022QNRC001)
陕西省青年人才托举计划项目(20220437)
陕西省青年科技新星项目(2022KJXX-59)
国家自然科学基金项目(51904237)
出版年
2024
NETL
NSTL
万方数据