浮式LNG平台串靠卸载泄漏后果影响分析

Leakage consequence analysis of the marine surface floating LNG platform with the tandem off-loading

浮式LNG生产储卸装置(FLNG)作为新兴的深海气田生产装置,集天然气生产、液化、储存和装卸功能于一身,其卸载方式主要有旁靠卸载和串靠卸载2种,其中串靠卸载因能适应恶劣海况而备受深海作业欢迎,但串靠卸载的泄漏后果和影响尚不明确,因此研究恶劣海况下LNG串靠卸载的泄漏风险及后果尤为迫切和重要。考虑海上极端气象条件,采用DNV公司的PHAST软件,定量计算FLNG串靠卸载方式在卸载臂发生小孔、中孔、大孔泄漏及全尺寸破裂时,LNG泄漏后产生的具有火灾爆炸危险性的蒸汽隔离区域,根据伤害阈值明确LNG导致人员低温冻伤和窒息的最小距离,并对可能发生的喷射火、池火和蒸汽云爆炸等恶劣事故造成的后果进行预测。

This paper is devoted to a study of the LNG leakage risk and the consequence of the tandem offloading under the severe marine conditions by building up a FLNG tandem offloading model.According to the said model,the likely-to-be-confronted risk consequences have been quantified based on a quantitative risk assessment software from DNV,which has been widely adopted as a new apparatus in the deep water gas field,though its offloading leakage risk remains unknown.For the research purpose,the paper has chosen the vapor dispersion exclusion distance,the asphyxiation and cryogenic hazard distance,and the fire and explosion damage area as the principal parameters to estimate the LNG leakage accident consequence in accordance with the domestic and foreign standards and some international protocols.To make more precise assessment of the LNG leakage accident consequence,it is necessary to take into account the two extreme weather conditions in doing the calculation.One of the aforementioned extreme weather conditions refers to the most unfavorable weather condition for the diffusion of the steam,namely,the atmospheric stability F due to the slow wind speed,say,1.5 m/s,whereas the other implies the maximum wind speed,say,21 m/s,whose loading arms have to be able to sustain the atmospheric stability D.Additionally speaking,it is also necessary to take into account the leak with different hole sizes(small,medium,large holes in addition to the catastrophic rupture)as the leakage accident scenarios.The results of our research prove that the vapor or steam dispersion exclusion zone is most likely to be badly affected part by the leakage altitude and the atmospheric stability.It has also been found that the vapor dispersion exclusion zone would be the greatest,in case the leakage takes place at the marine level with the atmospheric stability F.As compared with the simulated data with the critical data that may lead to the cryogenic and asphyxiation hazard,it has been discovered that even the smallest leakage may likely lead to asphyxiation deaths near the spilled point or section,whereas the serious leakage may lead to terrible asphyxiation deaths distance.Besides,the liquid phase spill can be more hazardous than the gas phase one.What is more disastrous is that,the jet fires damage area turns to be very insensitive to the altitude of the leakage source,which ought to be closely related to the leakage size.The actual situation may be:when there happens to be a great leakage,the target would receive greater thermal radiant flux.In such a situation,whether the LNG pool on the marine surface were hit by or not depends on the heat absorbed by the droplets in the process of falling.If there occurs a pool fire on the sea surface,the radiation heat of the fire would be likely to spoil and eventually destroy the lower structure of FLNG device and produce a great pressure against the cargo tank.If it is not ignited,the leakage LNG vaporizes into great gas,and the gas only explodes when it is diffused to the upper deck with a higher level of congestion and the force of explosion can destroy both FLNG and LNG carrier.Seeing such a disastrous risk,the FLNG should be made to face the upwind direction of the LNG carrier during the offloading operation.