使用可视化和恒定体积气体-固体耦合测试系统使用 CO2轴承煤的单轴压缩实验
Summary
该协议演示如何准备一个煤块样品,并使用可视化且恒定的气体-固体耦合测试系统,对不同CO2压力下的风险进行单轴压缩实验。研究还旨在研究CO2吸附引起的煤物理和机械性能的变化。
Abstract
将二氧化碳(CO2)注入煤层深处,对于降低大气中温室气体的浓度,提高煤层气的回收率具有重要意义。本文介绍了一种可视化的恒量气固耦合系统,以探讨CO2吸附对煤炭物理和机械性能的影响。该系统能够保持恒定的体积并使用摄像机监控样品,为提高仪器精度和采用分形几何方法分析断裂演化提供了潜力。本文提供了使用气固耦合测试系统在不同CO2压力下对煤块样品进行单轴压缩试验的所有步骤。由原煤和胡配钠水泥冷压的煤壳被装在高压CO2中,并使用相机实时监测其表面。然而,煤层与原煤的相似性仍有待改进,甲烷(CH4)等可燃气体不能注入试验。结果表明,CO2吸附导致煤块的峰值强度和弹性模量减少,在失效状态下,煤块的断裂演化表明分形特性。强度、弹性模量和分形维数都与CO2压力相关,但与线性相关无关。可视化和恒量气固耦合试验系统可作为考虑多场耦合效应的岩石力学实验研究平台。
Introduction
大气中CO2浓度的增加是造成全球变暖效应的直接因素。由于煤的吸附能力强,煤层中CO2的封存被认为是减少全球温室气体排放的实用、环保手段。同时,注入的CO2可以取代CH4,在煤层气回收(ECBM)4、5、6中促进天然气生产。CO2封存的生态和经济前景最近引起了全世界研究人员以及不同国际环保团体和政府机构的关注。
煤是一种异构的、结构上各向异性岩石,由毛孔、断裂和煤基质组成。孔隙结构具有较大的特定表面积,可吸附大量气体,在气体固存中起着至关重要的作用,断裂是自由气流7、8的主要路径。这种独特的物理结构为CH4和CO2带来了巨大的气体吸附能力。 矿井瓦斯以几种形式沉积在煤层中:(1)吸附在微孔和较大孔隙的表面;(2)吸收在煤分子结构中;(3)作为裂缝和大孔隙中的游气;(4)溶解在沉积水中。煤对CH4和CO2的吸附行为引起基质膨胀,进一步研究表明,这是一个异质过程,与煤石型9、10、11有关。此外,气体吸附可导致煤12、13、14的构成关系受损。
原煤样品一般用于煤和CO2耦合实验。具体来说,从煤矿工作面切割一大块原煤,准备样品。然而,由于煤层中天然孔隙和裂缝的随机空间分布,原煤的物理和机械性能不可避免地具有较高的分散度。此外,含气煤柔软,难以改造。根据正交实验方法的原理,用原煤粉和水泥重组的煤层,被认为是15、16号煤吸附试验的理想材料。由于金属模具的冷压,其强度可以通过调整水泥量来预设并保持稳定,有利于单变量效应的比较分析。此外,虽然煤层样品的孔隙度是+4-10倍,但在实验研究17、18中,已经发现了原煤样品的孔隙度、类似的吸附和解吸特性以及应力应变曲线。,19,20.本文采用了一种类似的含气煤材料方案,以制备煤层21。原煤取自中国安徽省淮南市新庄子煤矿4671B6工作面。煤层位于地下约450米,海平面以下360米,下降约15°,厚度约1.6米。煤块样品的高度和直径分别为100毫米和50毫米,这是国际岩石力学学会(ISRM)22建议的大小。
以前在实验室条件下进行气载煤实验的单轴或三轴载荷试验仪器存在一些不足和局限性,以研究员23、24、25、26提出 ,27、28:(1)在装载过程中,容器体积随活塞移动而减小,引起气体压力波动和气体吸附干扰;(2)样品的实时图像监测,以及高气压环境下的圆周变形测量,难以进行;(3) 它们仅限于刺激预加载样品的动态负载扰动,以分析其机械响应特性。为了提高气固耦合条件下的仪器精度和数据采集,开发了可视化且恒定体积的测试系统29(图1),包括(1)一个可视化装载容器,恒定体积室,这是核心组件;(2) 带真空通道、两个加注通道和释放通道的气体加注模块;(3) 由电动液压伺服通用测试机和控制机组成的轴向载荷模块;(4) 数据采集模块,由圆周位移测量装置、气体压力传感器和可视化装载容器窗口处的摄像头组成。
核心可视化容器(图2) 是专门设计的,以便两个调节油缸固定在上板上,其活塞与装载器通过梁同时移动,并且装载活塞的截面面积等于调整油缸的总和。流经内孔和软管,将容器中的高压气体和两个气缸连接在一起。因此,当容器装载活塞向下移动并压缩气体时,该结构可以抵消体积的变化并消除压力干扰。此外,在测试过程中防止了对活塞施加的巨大气体感应反作用力,大大提高了仪器的安全性。窗户装有钢化硼硅酸盐玻璃,位于容器的三面,为拍摄样品提供了直接途径。该玻璃已成功测试,并证明具有低膨胀率、高强度、透光性和化学稳定性,可抵抗高达10MPa气体。
本文介绍了使用新的可视化和恒量气固耦合测试系统对CO2轴承煤进行单轴压缩试验的过程,其中包括所有准备煤块的部件的描述样品使用原煤粉和酸钠,以及连续步骤注入高压CO2和进行单轴压缩。使用摄像机监控整个样品变形过程。该实验方法为量化分析含气煤的吸附性损伤和断裂演化特性提供了另一种方法。
Protocol
1. 样品制备 从新庄子煤矿的4671B6工作面收集原煤块。请注意,由于结构强度低和松散,原煤破碎,并可能与杂质混合。为了避免这些内部和外部因素的影响,以及尽可能减少煤的不均匀性,选择大型煤块(长约15厘米,宽10厘米,高10厘米)。 使用钳子去除煤中混合的杂质,用吸水棉和乙醛擦洗破碎机室。 用钳口破碎机将煤块粉碎成小块,并把它们放在装有6和16个网的标准屏幕的筛摇网中?…
Representative Results
煤块样品的平均质量为230克,根据工业分析,煤灰的含水量为4.52%,灰分含量为15.52%。此外,挥发性含量约为31.24%。由于从煤中提取了胡酸钠,煤块的成分与原煤相似。物理特征显示在表 2中。 表3显示了原煤和煤层机械性能的比较,等温吸附试验证明了其气体吸附能力(图6)。试验中使用?…
Discussion
考虑到高压气体的危险,在测试过程中,一些关键步骤非常重要。应定期检查和更换阀门和 O 环,实验室内不得使用任何点火源。使用手动调压阀时,实验者应缓慢扭动阀门,使可视化容器内的压力逐渐增大。在测试期间不要拆解容器。实验完成后,在高压气体完全释放后,应打开容器的后门;否则,有受伤的危险。使用真空吸尘器从容器中取出所有煤块,以免在下次测试中影响气体吸附量。
<p class="jove_cont…Divulgations
The authors have nothing to disclose.
Acknowledgements
这项工作得到了中国国家重大科学仪器开发项目(第51427804号)和山东省国家自然科学基金(授权号51427804)的支持。ZR2017MEE023)。
Materials
| 3Y-Leica MPV-SP photometer microphotometric system | Leica,Germany | M090063016 | Used for vitrinite reflectance measurement |
| Automatic isotherm adsorption instrument | BeiShiDe Instrument Technology (Beijing)CO.,Ltd. | 3H-2000PH | Isothermal adsorption test |
| Electro hydraulic servo universal testing machine | Jinan Shidaishijin testing machine CO.,Ltd | WDW-100EIII | Used to provide axial pressure |
| Gas pressure sensor | Beijing Star Sensor Technology CO.,LTD | CYYZ11 | Gas pressure monitoring |
| Gas tank(carbon dioxide/helium) | Heifei Henglong Gas.,Ltd | Gas resource | |
| high-speed camera | Sony corporation | FDR-AX30 | Image monitoring |
| Incubator | Yuyao YuanDong Digital Instrument Factory | XGQ-2000 | Briquette drying |
| jaw crusher | Hebi Tianke Instrument CO.,Ltd | EP-2 | Coal grinding |
| Manual pressure reducing valve | Shanghai Saergen Instrument CO.,Ltd | R41 | Outlet gas pressure adjustment |
| Proximate Analyzer | Changsha Kaiyuan Instrument CO.,Ltd | 5E-MAG6700 | Coal industrial analysis |
| Resistance strain gauge | Jinan Sigmar Technology CO.,LTD | ASMB3-16/8 | Poisson ratio measurement |
| Sieve shaker (6,16mesh) | Hebi Tianguan Instrument CO.,Ltd | GZS-300 | Coal powder shelter |
| Soft pipe | Jinan Quanxing High pressure pipe CO.,Ltd | Inner diameter=5 mm maximal pressure=30 MPa |
|
| Standard rock sample circumferential deformation test apparatus | Huainan Qingda Machinery CO.,Ltd | Circumferential deformation acquisition |
|
| Strain controlled direct shear apparatus |
Beijing Aerospace Huayu Test Instrument CO.,LTD | ZJ-4A | Tensile strength, cohesion, internal friction angle measurement |
| Vaccum pump | Fujiwara,Japan | 750D | Used to vaccumize the vessel |
| Valve | Jiangsu Subei Valve Co.,Ltd | S4 NS-MG16-MF1 | Gas seal |
| Visual loading vessel | Huainan Qingda Machinery CO.,Ltd | Instrument for sample loading and real-time monitoring |
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Citer Cet Article
Hou, W., Wang, H., Wang, W., Liu, Z., Li, Q. A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System. J. Vis. Exp. (148), e59405, doi:10.3791/59405 (2019).