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Nondestructive natural gas hydrate recovery driven by air and carbon dioxide.

Kang H, Koh DY, Lee H - Sci Rep (2014)

Bottom Line: Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases.Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH.The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea.

ABSTRACT
Current technologies for production of natural gas hydrates (NGH), which include thermal stimulation, depressurization and inhibitor injection, have raised concerns over unintended consequences. The possibility of catastrophic slope failure and marine ecosystem damage remain serious challenges to safe NGH production. As a potential approach, this paper presents air-driven NGH recovery from permeable marine sediments induced by simultaneous mechanisms for methane liberation (NGH decomposition) and CH₄-air or CH₄-CO₂/air replacement. Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases. Then spontaneous melting proceeds until the chemical potentials become equal in both phases as NGH depletion continues and self-regulated CH4-air replacement occurs over an arbitrary point. We observed the existence of critical methane concentration forming the boundary between decomposition and replacement mechanisms in the NGH reservoirs. Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH. The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

No MeSH data available.


Related in: MedlinePlus

NGH production method using air and CO2/air.(a) Schematic illustration of the described air (or CO2/air) driven NGH production method composed of two distinct steps: NGH decomposition caused by injected air (or CO2/air); subsequent decomposition driven guest exchange process. (b) Discovery of the concept of critical methane concentration (CMC) depending on the molar ratio between CH4 and injected air and CO2/air. (c) Methane hydrate at 288.15 K and 200 bar before air injection (top), and mixed hydrate crystals coexist with water at 288.15 K after air injection above the critical concentration (bottom).
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f1: NGH production method using air and CO2/air.(a) Schematic illustration of the described air (or CO2/air) driven NGH production method composed of two distinct steps: NGH decomposition caused by injected air (or CO2/air); subsequent decomposition driven guest exchange process. (b) Discovery of the concept of critical methane concentration (CMC) depending on the molar ratio between CH4 and injected air and CO2/air. (c) Methane hydrate at 288.15 K and 200 bar before air injection (top), and mixed hydrate crystals coexist with water at 288.15 K after air injection above the critical concentration (bottom).

Mentions: In this work, we demonstrate an NGH production method using air and CO2/air. Air is abundant and is available at any time and at any location, which makes it the most attractive element for practical production of NGH. It is known that N2 and O2 gases can play a role in breaking down methane hydrates because of the chemical potential difference (Δμ) between their gas and solid phases161718. Earlier such methods for replacement and dissociation were only considered for use in systems with very dilute methane hydrates131415161718. Accordingly, a continuous supply of fresh air into the NGH can make it melt completely. However, the methane concentration in the recovered gas becomes quite small, requiring additional separation facilities. The use of pure air contributes to methane production by NGH melting, but the key issue arises as to whether replacement can occur when we further extend the systems with concentrated methane hydrates or injection of CO2-enriched air (CO2/air). To address in detail the process of releasing methane from NGH using air or CO2/air, we defined the new variable ‘critical methane concentration' (CMC), which consists of the number of methane and injected molecules, and performed experiments to reveal the mechanisms involved (Fig. 1a).


Nondestructive natural gas hydrate recovery driven by air and carbon dioxide.

Kang H, Koh DY, Lee H - Sci Rep (2014)

NGH production method using air and CO2/air.(a) Schematic illustration of the described air (or CO2/air) driven NGH production method composed of two distinct steps: NGH decomposition caused by injected air (or CO2/air); subsequent decomposition driven guest exchange process. (b) Discovery of the concept of critical methane concentration (CMC) depending on the molar ratio between CH4 and injected air and CO2/air. (c) Methane hydrate at 288.15 K and 200 bar before air injection (top), and mixed hydrate crystals coexist with water at 288.15 K after air injection above the critical concentration (bottom).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4196106&req=5

f1: NGH production method using air and CO2/air.(a) Schematic illustration of the described air (or CO2/air) driven NGH production method composed of two distinct steps: NGH decomposition caused by injected air (or CO2/air); subsequent decomposition driven guest exchange process. (b) Discovery of the concept of critical methane concentration (CMC) depending on the molar ratio between CH4 and injected air and CO2/air. (c) Methane hydrate at 288.15 K and 200 bar before air injection (top), and mixed hydrate crystals coexist with water at 288.15 K after air injection above the critical concentration (bottom).
Mentions: In this work, we demonstrate an NGH production method using air and CO2/air. Air is abundant and is available at any time and at any location, which makes it the most attractive element for practical production of NGH. It is known that N2 and O2 gases can play a role in breaking down methane hydrates because of the chemical potential difference (Δμ) between their gas and solid phases161718. Earlier such methods for replacement and dissociation were only considered for use in systems with very dilute methane hydrates131415161718. Accordingly, a continuous supply of fresh air into the NGH can make it melt completely. However, the methane concentration in the recovered gas becomes quite small, requiring additional separation facilities. The use of pure air contributes to methane production by NGH melting, but the key issue arises as to whether replacement can occur when we further extend the systems with concentrated methane hydrates or injection of CO2-enriched air (CO2/air). To address in detail the process of releasing methane from NGH using air or CO2/air, we defined the new variable ‘critical methane concentration' (CMC), which consists of the number of methane and injected molecules, and performed experiments to reveal the mechanisms involved (Fig. 1a).

Bottom Line: Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases.Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH.The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea.

ABSTRACT
Current technologies for production of natural gas hydrates (NGH), which include thermal stimulation, depressurization and inhibitor injection, have raised concerns over unintended consequences. The possibility of catastrophic slope failure and marine ecosystem damage remain serious challenges to safe NGH production. As a potential approach, this paper presents air-driven NGH recovery from permeable marine sediments induced by simultaneous mechanisms for methane liberation (NGH decomposition) and CH₄-air or CH₄-CO₂/air replacement. Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases. Then spontaneous melting proceeds until the chemical potentials become equal in both phases as NGH depletion continues and self-regulated CH4-air replacement occurs over an arbitrary point. We observed the existence of critical methane concentration forming the boundary between decomposition and replacement mechanisms in the NGH reservoirs. Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH. The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

No MeSH data available.


Related in: MedlinePlus