Abstract
Onshore LNG Plant development projects start from the “Concept Definition” phase, where financial feasibility is first estimated and major conditions such as site location and development area extent are decided. Current industrial practice applies “risk” for the evaluation of design options once detailed design data is available. Due to the limited flexibility for “change” during the detailed design phase, safety measures tend towards the application of active safeguarding systems (such as automated depressuring by fire and gas detection). Consequently, it is difficult to apply ideal inherently safer design, e.g., separation distances, during the “Design” phase of a project.
Further, modularized LNG plants require large, complex structures (modules) to support LNG process equipment and to allow sea and land transportation. This results in excessive congestion and the existence of large voids under the module-deck, which are confined by large girders. As such, in the event of leakage, it is critical for plant safety to install adequate ventilation to reduce the accumulation of flammable gas and potential for subsequent explosions. In order to reduce the potential of such hazards, it is important to consider an inherently safer layout to enhance ventilation, e.g., direction or separation.
Implementation of an inherently safer layout during the early design phase requires a strategic approach, such as setting targets for accidental event sizes which avoid escalation events via the separation distance and/or pre-defining the separation distances themselves.
This paper proposes a strategy for the implementation of inherently safer design in the plant overall plot plan and pre-defined separation distances for modules within the process train, based on the evaluation of layout options in view of Air-Fin-Cooler induced air flow in modularized LNG plants by quantifying its effects as Air Change per Hour (ACH) and flammable gas cloud volumes through Computational Fluid Dynamics (CFD) analysis.
