Research On The Leakage Diffusion Mechanism And Evolution Of LNG Port Transport And Storage System

Energy is one of the important resources in the world progress. Environment isthe basic condition of human being. These two problems are worldwide for humanitytoday. To solve them, people should not only develop new energy sources but alsoprotect the environment from pollution. LNG is one kind of clean and efficient energy,and it is rich in sources. Reasonable development and utilization of LNG is theimportant way to solve the environment and energy problems in the future, to whichpeople have paid great attention at home and abroad. The amount of use of LNG inour country is considerably large. A large number of LNG is imported from abroad byLNG carriers, and is stored in LNG tank through pipeline. Such dangers as fire,explosion, Rapid Phase Transition (RPT), low temperature, suffocation, etc. willhappen in the process of transport and storage. These dangers can severely affect thesafety of person and property.The research object in this dissertation is LNG transport and storage system,which is composed of LNG carrier, LNG pipeline and LNG tank. Considering the riskof LNG transport and storage system, the leak diffusion mechanism of LNG vessels,storage tanks and pipeline, the formation and evolution of LNG liquid pool, thediffusion of vapor cloud are studied on the basis of domestic and foreign researchresults. So the concrete research contents in this dissertation are as follows:(1) Considering the transport and storage part as one whole system, the reason ofLNG leakage, initial leakage rate, leak location and other factors of carrier in theloading place are studied in this dissertation. The mathematical model of initialleakage rate is developed after analyzing a variety of failure factors of the LNGcarrier dissipation accidents. A double-hull membrane-type LNG carrier, as onediffusion example case, is used to calculate and predict the leakage and diffusion ofLNG based on the initial leakage rate model. The model has certain adaptability, asthe leakage will eventually reach one state of balance for either only the outer hull orboth the hull and tank, when the leakage outlet is below the water surface.(2) The leakage risk of the tank field and pipeline, LNG vaporization rate androllover phenomenon inside the tank is researched in the dissertation. The measures to eliminate stratification and rollover are provided with the research results of therollover phenomenon. By separate storage or internal mixing filling, there is nodensity and temperature difference, so it can prevent LNG stratification and rollover.The evaporation rate model of the LNG pipeline is set up to theoretically predict therate supposing the entire rupture when LNG is transported to the tank through thepipeline. The energy transfer and heat transmission with different surface substratesare researched during the process of LNG leakage and the model can reflect the LNGevaporation considering the thermodynamic characteristics of different surfacesubstrates.(3) The evolution and its model, evaporation of liquid pool, law of heat fluxchange and liquid pool fire are also studied in the dissertation. When LNG transportand storage system is breached, jet flow may occur and will split into fog droplets,which will be partly or completely evaporated in the process of falling. LNG poolwill be formed if the jet flow is worse, and the stability will be broken when thethickness of LNG pool exceed the minimum value to maintain its stability. Eventuallythe pool will reach the maximum as it evaporates. The density of boiling bubbles isalso increasing with the rate of evaporation. Nuclear boiling will stop when thetemperature is high enough. The boiling becomes relatively stable, and it will becometransition boiling as the temperature continues to increase. Transition boiling will turninto film boiling when the heat flux reaches the minimum value. There is hardly anyboiling temperature change at the beginning of leakage, the component of steam isneither any change at the late stage of evaporation, but the boiling temperature risesdramatically. A simplified model of pool fire for the large LNG liquid pool burning isestablished to reflect the characteristics of the flame and the development tendencywhen the wind is in different directions.(4) The model of diffusion process of LNG evaporation cloud and distance ofdiffusion are established. The plume will spread in the downwind direction. There is abalance between plume and surrounded air, which will prevent the rapid reduce ofdensity with plume. The maximum distance model of LNG evaporation in thedownwind direction is established, which has a good adaptability after consideringwind speed, atmospheric stability, surface roughness, obstacles, local terrain factors,etc. (5) Accidents prevention and emergency response plan of the LNG transport andstorage system are researched. The ultimate aim to research the leakage diffusionmechanism and evolution of LNG transport and storage system is to prevent theaccident and reduce the losses. Accident prevention measures and formulation ofemergency plan are researched in the dissertation on the basis of the leakage diffusionmechanism of LNG transport and storage system.