Last developments in Rapid Phase Transition knowledge and modeling techniques

Abstract

Abstract An incident during the transfer of LNG between a shore or offshore structure (FPSO, GBS) and an LNG carrier can result in a spillage of LNG onto water. A leakage inside a Submerged Combustion Vaporizer can also lead to LNG/water contacts. Under certain conditions, these situations can produce LNG vaporization rates so high that physical explosions, termed Rapid Phase Transitions (RPTs), can occur. These RPTs can generate air and underwater blast pressures, which could damage adjacent plants or structures and lead to serious accidents through an escalation process. Therefore, RPT phenomenon is part of the safety context of LNG facilities and must be taken into account from the design stage. Beginning with the performance of large-scale LNG/water RPT tests by Gaz de France in 1981, considerable research work has been done on this subject within successive partnership agreements. After a series of exploratory studies where numerous large-scale events have been produced and the main parameters identified, a phase of fundamental studies has been performed to select the physics involved. Then, research models have been developed while validation experiments with idealized geometry have been performed to validate them. In order to develop a simple and reliable prediction tool from the research models, a last JIP has been set up, at the end of the year 2000, by Gaz de France with the financial support of TotalFinaElf, Mitsubishi Heavy Industries and one anonymous partner. As a result of this recently completed program, it is possible to provide an insight into the possible hazards presented by RPT events and a quantified estimation, expressed in term of TNT equivalence, of the risks associated. For scenarios selected by the JIP, or other similar scenarios, the risk assessment is also possible through the use of the prediction tool. The communication describes these last developments and the potential of the available tool. 1. Introduction There is a need to assess the safety of, and the potential hazards posed by, both existing and planned import, export and storage facilities for liquefied natural gas (LNG). These safety assessments must necessarily consider the consequences of an accidental spillage of LNG. An incident during the LNG transfer between an onshore or offshore structure (FPSO, GBS) and an LNG carrier can result in an LNG spillage onto water. A leakage inside a Submerged Combustion Vaporizer can also lead to LNG/water contacts. These situations and all the other cases where LNG and water are mixed together can produce, under certain conditions, LNG vaporization rates so high that physical explosions, termed Rapid Phase Transitions (RPTs), can occur. Large-scale experiments in which LNG has been deliberately spilled onto water have shown that RPTs can produce severe, but localized, damage. Should such damage produce further loss of integrity in a real incident, then there is the possibility of an escalation leading to a serious accident, with the risk of large spillage from the bulk storage and associated consequences. Therefore, RPT phenomenon is part of the safety context of LNG facilities and must be taken into account from the design stage.