Inherent Safety Design Considering Forced Ventilation Effect by Air-Fin-Cooler in Modularized Onshore LNG Plant

Abstract

Onshore LNG Plant development project starts from Concept Definition phase, where financial feasibility is estimated and major conditions, such as site location and development area extent. It becomes difficult to set ideal inherent safety design, e.g., separation distance, in this phase due to unavailability of design data and priority on financial feasibility. Further, the LNG plant modularized approach requires large, complex structures (modules) for supporting the LNG process equipment and for allowing sea and land transportation. This results in additional congestion of the plant and large voids under module-deck, which are confined by large girders. Thus, in case of leaks, the proper ventilation to reduce the accumulation of gas is critical for the safety. Therefore, the inherently safe layout consideration to enhance ventilation is important in order to reduce potential of flammable gas accumulation and subsequent explosion, e.g., orientation and separation distance. Many base load onshore LNG plants use large number of Air-Fin-Coolers normally mounted on the center pipe rack of the LNG process train. This paper evaluates the Air-Fin-Cooler induced air flow in modularized LNG plants to quantify the effect as Air Change per Hour (ACH) using Computational Fluid Dynamics (CFD) analysis. The results of this evaluation show that the ventilation of the Air-Fin-Cooler induced air flow is influenced by the process train orientation. Further, a moderate increase is observed in specific design conditions or areas, such as shorter separation distances between modules. Based on the results of this evaluation, the inherent safety design measures, which should be taken into consideration in the Concept Definition phase, are proposed to optimize the use of Air-Fin-Cooler, such as train orientation against prevailing wind direction and separation distance between modules.