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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

This protocol demonstrates how to prepare a briquette sample and conduct a uniaxial compression experiment with a briquette in different CO2 pressures using a visualized and constant-volume gas-solid coupling test system. It also aims to investigate changes in terms of coal’s physical and mechanical properties induced by CO2 adsorption.

Abstract

Injecting carbon dioxide (CO2) into a deep coal seam is of great significance for reducing the concentration of greenhouse gases in the atmosphere and increasing the recovery of coalbed methane. A visualized and constant-volume gas-solid coupling system is introduced here to investigate the influence of CO2 sorption on the physical and mechanical properties of coal. Being able to keep a constant volume and monitor the sample using a camera, this system offers the potential to improve instrument accuracy and analyze fracture evolution with a fractal geometry method. This paper provides all steps to perform a uniaxial compression experiment with a briquette sample in different CO2 pressures with the gas-solid coupling test system. A briquette, cold-pressed by raw coal and sodium humate cement, is loaded in high-pressure CO2, and its surface is monitored in real-time using a camera. However, the similarity between the briquette and the raw coal still needs improvement, and a flammable gas such as methane (CH4) cannot be injected for the test. The results show that CO2 sorption leads to peak strength and elastic modulus reduction of the briquette, and the fracture evolution of the briquette in a failure state indicates fractal characteristics. The strength, elastic modulus, and fractal dimension are all correlated with CO2 pressure but not with a linear correlation. The visualized and constant-volume gas-solid coupling test system can serve as a platform for experimental research about rock mechanics considering the multifield coupling effect.

Introduction

The increasing concentration of CO2 in the atmosphere is a direct factor causing the global warming effect. Due to the strong sorption capacity of coal, CO2 sequestration in a coal seam is regarded as a practical and environment-friendly means to reduce the global emission of greenhouse gas1,2,3. At the same time, the injected CO2 can replace CH4 and result in gas production promotion in coalbed methane recovery (ECBM)4,5,6. The ecological ....

Protocol

1. Sample preparation

  1. Collect raw coal blocks from the 4671B6 working face from the Xinzhuangzi coal mine. Note that, due to the low strength and looseness of the structure, the raw coal is broken and probably mixed with impurities. To avoid the influence of these internal and external factors, as well as reduce the inhomogeneity of coal as much as possible, select large coal blocks (about 15 cm long, 10 cm wide, and 10 cm high).
  2. Use a tweezer to remove impurities mixed in the coal and scrub the cru.......

Representative Results

The average mass of the briquette sample was 230 g. Depending on the industrial analysis, the briquette exhibited a moisture content of 4.52% and an ash content of 15.52%. Furthermore, the volatile content was approximately 31.24%. As the sodium humate was extracted from the coal, the components of the briquette were similar to raw coal. The physical characteristics are displayed in Table 2.

The comparison of th.......

Discussion

Considering the danger of high-pressure gas, some critical steps are important during the test. The valves and O rings should be inspected and replaced regularly, and any source of ignition should not be allowed in the laboratory. When using the manual pressure-regulating valve, the experimenter should twist the valve slowly to make the pressure in the visualized vessel increase gradually. Do not disassemble the vessel during the test. When the experiment is finished, the back door of the vessel should be opened after th.......

Acknowledgements

This work was supported by the China National Major Scientific Instruments Development Project (Grant No. 51427804) and the Shandong Province National Natural Science Foundation (Grant No. ZR2017MEE023).

....

Materials

NameCompanyCatalog NumberComments
3Y-Leica MPV-SP photometer microphotometric systemLeica,GermanyM090063016Used for vitrinite
reflectance measurement
Automatic isotherm adsorption instrumentBeiShiDe Instrument Technology (Beijing)CO.,Ltd.3H-2000PHIsothermal adsorption test
Electro hydraulic servo universal testing machineJinan Shidaishijin testing machine CO.,LtdWDW-100EIIIUsed to provide
axial pressure
Gas pressure sensorBeijing Star Sensor Technology CO.,LTDCYYZ11Gas pressure monitoring
Gas tank(carbon dioxide/helium)Heifei Henglong Gas.,LtdGas resource
high-speed cameraSony corporationFDR-AX30Image monitoring
IncubatorYuyao YuanDong Digital Instrument FactoryXGQ-2000Briquette drying
jaw crusherHebi Tianke Instrument CO.,LtdEP-2Coal grinding
Manual pressure reducing valveShanghai Saergen Instrument CO.,LtdR41Outlet gas pressure adjustment
Proximate AnalyzerChangsha Kaiyuan Instrument CO.,Ltd5E-MAG6700Coal industrial analysis
Resistance strain gaugeJinan Sigmar Technology CO.,LTDASMB3-16/8Poisson ratio measurement
Sieve shaker (6,16mesh)Hebi Tianguan Instrument CO.,LtdGZS-300Coal powder shelter
Soft pipeJinan Quanxing High pressure pipe CO.,LtdInner diameter=5 mm
maximal pressure=30 MPa
Standard rock sample circumferential deformation test apparatusHuainan Qingda Machinery CO.,LtdCircumferential deformation
acquisition
Strain controlled
direct shear apparatus
Beijing Aerospace Huayu Test Instrument CO.,LTDZJ-4ATensile strength, cohesion, internal friction
angle measurement
Vaccum pumpFujiwara,Japan750DUsed to vaccumize the vessel
ValveJiangsu Subei Valve Co.,LtdS4 NS-MG16-MF1Gas seal
Visual loading vesselHuainan Qingda Machinery CO.,LtdInstrument for sample
loading and real-time monitoring

References

  1. Mazzotti, M., Pini, R., Storti, G. Enhanced coalbed methane recovery. Journal of Supercritical Fluids. 47 (3), 619-627 (2009).
  2. Litynski, J., et al. U.S. Department of Energy’s Regional Carbon Sequestration Partnership P....

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