Failure Mechanism of Coal after Cryogenic Freezing with Cyclic Liquid Nitrogen and Its Influences on Coalbed Methane Exploitation

Lei Qin, Cheng Zhai, Shimin Liu, Jizhao Xu, Zongqing Tang, Guoqing Yu

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

This study explores how liquid nitrogen (LN2) freezing affects the physical pore and fracture structure of coal. Under lab-controlled conditions, coal specimens were frozen with LN2 under different conditions and thawed, and then the uniaxial compressive strengths, acoustic emissions, and ultrasonic wave velocities of the different specimens were compared. After 60 min of freezing for one set of specimens and 30 freeze-thaw cycles for another set, the elastic moduli of the coal specimens decreased by 47.8% for the 60 min freezes and by 76.2% for the 30 cycles. For the tested two sets of the same specimens, the uniaxial compressive strengths and longitudinal wave velocities dropped by 13.4% and 40.2% and by 47.8% and 76.2%, respectively. At the same time, the coal porosities and Poisson's ratios increased by 17.5% and 68.1% and by 7.14% and 28.6%, respectively. Owing to the reduction of the coal's mechanical strength, the elastically straining stage was shortened and the peak yield point and the plastic deformation were accelerated. By establishing a relational model for an elastic modulus based damage variable D and the LN2 freezing conditions, it was found that variable D increased to and stabilized at 0.12 with the single freezing experiments. However, the damage to the coal caused by cyclic freezing and thawing was continuous and damage accelerated after 20 freeze-thaw cycles. By modeling the state of stress in fractures of LN2 treated coal, the theoretical governing equations for the tension in a single fracture were derived. In addition, the expression regarding the volumetric strain of ice under the effect of tension for a single fracture was obtained. The results showed that the proposed model and expressions were in good agreement with the experimentally obtained data.

Original languageEnglish (US)
Pages (from-to)8567-8578
Number of pages12
JournalEnergy and Fuels
Volume30
Issue number10
DOIs
StatePublished - Oct 20 2016

Fingerprint

Coal
Liquid nitrogen
Freezing
Cryogenics
Compressive strength
Elastic moduli
Ultrasonic velocity
Thawing
Ice
Poisson ratio
Acoustic emissions
Coal bed methane
Strength of materials
Plastic deformation
Porosity

All Science Journal Classification (ASJC) codes

  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology

Cite this

Qin, Lei ; Zhai, Cheng ; Liu, Shimin ; Xu, Jizhao ; Tang, Zongqing ; Yu, Guoqing. / Failure Mechanism of Coal after Cryogenic Freezing with Cyclic Liquid Nitrogen and Its Influences on Coalbed Methane Exploitation. In: Energy and Fuels. 2016 ; Vol. 30, No. 10. pp. 8567-8578.
@article{0eec75ddfd9f495aae1726d0e3522400,
title = "Failure Mechanism of Coal after Cryogenic Freezing with Cyclic Liquid Nitrogen and Its Influences on Coalbed Methane Exploitation",
abstract = "This study explores how liquid nitrogen (LN2) freezing affects the physical pore and fracture structure of coal. Under lab-controlled conditions, coal specimens were frozen with LN2 under different conditions and thawed, and then the uniaxial compressive strengths, acoustic emissions, and ultrasonic wave velocities of the different specimens were compared. After 60 min of freezing for one set of specimens and 30 freeze-thaw cycles for another set, the elastic moduli of the coal specimens decreased by 47.8{\%} for the 60 min freezes and by 76.2{\%} for the 30 cycles. For the tested two sets of the same specimens, the uniaxial compressive strengths and longitudinal wave velocities dropped by 13.4{\%} and 40.2{\%} and by 47.8{\%} and 76.2{\%}, respectively. At the same time, the coal porosities and Poisson's ratios increased by 17.5{\%} and 68.1{\%} and by 7.14{\%} and 28.6{\%}, respectively. Owing to the reduction of the coal's mechanical strength, the elastically straining stage was shortened and the peak yield point and the plastic deformation were accelerated. By establishing a relational model for an elastic modulus based damage variable D and the LN2 freezing conditions, it was found that variable D increased to and stabilized at 0.12 with the single freezing experiments. However, the damage to the coal caused by cyclic freezing and thawing was continuous and damage accelerated after 20 freeze-thaw cycles. By modeling the state of stress in fractures of LN2 treated coal, the theoretical governing equations for the tension in a single fracture were derived. In addition, the expression regarding the volumetric strain of ice under the effect of tension for a single fracture was obtained. The results showed that the proposed model and expressions were in good agreement with the experimentally obtained data.",
author = "Lei Qin and Cheng Zhai and Shimin Liu and Jizhao Xu and Zongqing Tang and Guoqing Yu",
year = "2016",
month = "10",
day = "20",
doi = "10.1021/acs.energyfuels.6b01576",
language = "English (US)",
volume = "30",
pages = "8567--8578",
journal = "Energy & Fuels",
issn = "0887-0624",
publisher = "American Chemical Society",
number = "10",

}

Failure Mechanism of Coal after Cryogenic Freezing with Cyclic Liquid Nitrogen and Its Influences on Coalbed Methane Exploitation. / Qin, Lei; Zhai, Cheng; Liu, Shimin; Xu, Jizhao; Tang, Zongqing; Yu, Guoqing.

In: Energy and Fuels, Vol. 30, No. 10, 20.10.2016, p. 8567-8578.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Failure Mechanism of Coal after Cryogenic Freezing with Cyclic Liquid Nitrogen and Its Influences on Coalbed Methane Exploitation

AU - Qin, Lei

AU - Zhai, Cheng

AU - Liu, Shimin

AU - Xu, Jizhao

AU - Tang, Zongqing

AU - Yu, Guoqing

PY - 2016/10/20

Y1 - 2016/10/20

N2 - This study explores how liquid nitrogen (LN2) freezing affects the physical pore and fracture structure of coal. Under lab-controlled conditions, coal specimens were frozen with LN2 under different conditions and thawed, and then the uniaxial compressive strengths, acoustic emissions, and ultrasonic wave velocities of the different specimens were compared. After 60 min of freezing for one set of specimens and 30 freeze-thaw cycles for another set, the elastic moduli of the coal specimens decreased by 47.8% for the 60 min freezes and by 76.2% for the 30 cycles. For the tested two sets of the same specimens, the uniaxial compressive strengths and longitudinal wave velocities dropped by 13.4% and 40.2% and by 47.8% and 76.2%, respectively. At the same time, the coal porosities and Poisson's ratios increased by 17.5% and 68.1% and by 7.14% and 28.6%, respectively. Owing to the reduction of the coal's mechanical strength, the elastically straining stage was shortened and the peak yield point and the plastic deformation were accelerated. By establishing a relational model for an elastic modulus based damage variable D and the LN2 freezing conditions, it was found that variable D increased to and stabilized at 0.12 with the single freezing experiments. However, the damage to the coal caused by cyclic freezing and thawing was continuous and damage accelerated after 20 freeze-thaw cycles. By modeling the state of stress in fractures of LN2 treated coal, the theoretical governing equations for the tension in a single fracture were derived. In addition, the expression regarding the volumetric strain of ice under the effect of tension for a single fracture was obtained. The results showed that the proposed model and expressions were in good agreement with the experimentally obtained data.

AB - This study explores how liquid nitrogen (LN2) freezing affects the physical pore and fracture structure of coal. Under lab-controlled conditions, coal specimens were frozen with LN2 under different conditions and thawed, and then the uniaxial compressive strengths, acoustic emissions, and ultrasonic wave velocities of the different specimens were compared. After 60 min of freezing for one set of specimens and 30 freeze-thaw cycles for another set, the elastic moduli of the coal specimens decreased by 47.8% for the 60 min freezes and by 76.2% for the 30 cycles. For the tested two sets of the same specimens, the uniaxial compressive strengths and longitudinal wave velocities dropped by 13.4% and 40.2% and by 47.8% and 76.2%, respectively. At the same time, the coal porosities and Poisson's ratios increased by 17.5% and 68.1% and by 7.14% and 28.6%, respectively. Owing to the reduction of the coal's mechanical strength, the elastically straining stage was shortened and the peak yield point and the plastic deformation were accelerated. By establishing a relational model for an elastic modulus based damage variable D and the LN2 freezing conditions, it was found that variable D increased to and stabilized at 0.12 with the single freezing experiments. However, the damage to the coal caused by cyclic freezing and thawing was continuous and damage accelerated after 20 freeze-thaw cycles. By modeling the state of stress in fractures of LN2 treated coal, the theoretical governing equations for the tension in a single fracture were derived. In addition, the expression regarding the volumetric strain of ice under the effect of tension for a single fracture was obtained. The results showed that the proposed model and expressions were in good agreement with the experimentally obtained data.

UR - http://www.scopus.com/inward/record.url?scp=84992322948&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84992322948&partnerID=8YFLogxK

U2 - 10.1021/acs.energyfuels.6b01576

DO - 10.1021/acs.energyfuels.6b01576

M3 - Article

AN - SCOPUS:84992322948

VL - 30

SP - 8567

EP - 8578

JO - Energy & Fuels

JF - Energy & Fuels

SN - 0887-0624

IS - 10

ER -