Dispersion analysis of the unignited flare gas in an LNG-FPSO vessel
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A liquid natural gas floating production, storage, and offloading (LNG-FPSO) unit is a floating vessel used as an offshore plant in order to liquefy and store natural gas until it is offloaded onto an LNG carrier. LNG-FPSOs are incorporated with the new concept of LNG value chain formation, which can be more economical than conventional methods for the development of small- or medium-scale gas fields. A typical approach is implemented for large-scale gas fields by establishing a direct connection between an existing offshore platform and an onshore LNG plant using a pipeline. However, because the facilities required for all processes are designed within a confined space on the vessel, the structure of this vessel may be fundamentally charged with a higher risk of fire or explosion due to the dispersion of flammable gas, which results from accidental leaks of LNG. For the safety design, therefore, quantitative evaluation of the LNG-FPSO is required for understanding the major potential hazards imposed on the personnel, assets, and environment. In this study, a numerical analysis on the dispersion characteristics of the unignited flare gas ejected from a vent mast was performed as a part of quantitative risk assessment (QRA) in the front-end engineering and design (FEED) stage. The results for the selected scenarios showed that the extents of flammable limits evaluated by the concentration distributions of flammable gas released from the vent mast could be acceptable for the helideck, including accommodation as well as all topsides on the basis of CAP 437 Safety Regulation. In the next stage for EPC, a detailed analysis reflecting the variation of environmental conditions will be further required to determine the design specification of flare towers.
Abstract
A liquid natural gas floating production, storage, and offloading (LNG-FPSO) unit is a floating vessel used as an offshore plant in order to liquefy and store natural gas until it is offloaded onto an LNG carrier. LNG-FPSOs are incorporated with the new concept of LNG value chain formation, which can be more economical than conventional methods for the development of small- or medium-scale gas fields. A typical approach is implemented for large-scale gas fields by establishing a direct connection between an existing offshore platform and an onshore LNG plant using a pipeline. However, because the facilities required for all processes are designed within a confined space on the vessel, the structure of this vessel may be fundamentally charged with a higher risk of fire or explosion due to the dispersion of flammable gas, which results from accidental leaks of LNG. For the safety design, therefore, quantitative evaluation of the LNG-FPSO is required for understanding the major potential hazards imposed on the personnel, assets, and environment. In this study, a numerical analysis on the dispersion characteristics of the unignited flare gas ejected from a vent mast was performed as a part of quantitative risk assessment (QRA) in the front-end engineering and design (FEED) stage. The results for the selected scenarios showed that the extents of flammable limits evaluated by the concentration distributions of flammable gas released from the vent mast could be acceptable for the helideck, including accommodation as well as all topsides on the basis of CAP 437 Safety Regulation. In the next stage for EPC, a detailed analysis reflecting the variation of environmental conditions will be further required to determine the design specification of flare towers.
참고문헌 (13)
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