A Study On The Thermal Response Dynamic Process Of Liquefied Gas Tanks Subjected To Fire Environment

The explosion of pressurized liquefied gas (PLG) tanks is a general accident in the production, storage and transportation of PLG. This type of accident used to lead to serious damage of property and loss of life. The fire exposure is one of important reasons of accident which will be caused by the increasing of pressure in the tank, so it is essential to study the thermal response of PLG tanks exposed to fire, which can provide theoretical instruction for prevention and control of PLG tank accident. In this thesis, the researches for this topic are conducted as followings.As a basis of the research, the research of fundamental property calculation for liquefied petroleum gas (LPG) and oil fuel involved in this research is firstly carried out. In view of the characteristic of multi-components for LPG and oil fuel, relations for calculation thermal and transport properties for single component and the mixed regulation for multi-components are recommended respectively. For LPG different ways are adopted to calculating properties of liquid and gas respectively. The calculation method for the liquid superheat limit of LPG in high pressure is studied by using RK state equation.The experimental research on thermal response of LPG tank exposed to fire is carried out. A experimental apparatus to simulate real accident of LPG tank is designed and manufactured. A series of experiments for different fill levels, different type of tanks subjected to different type of fires are performed with this apparatus. From the results of the experiments, the obvious stratification of temperature in the ladings of the tank is observed. And the pressure is increased due to the stratification. Thermal response of the LPG is affected by various factors such as fire type, tank type and fill level etc.. The liquid could be superheated or sub-cooled in fire exposure situation. The pressure can be fitted to time by cube polynomial equation.The numerical simulation for fire environment of PLG tank is studied. The model for diffusion combustion is used, and the product of combustion and temperature field are simulated by probability density function (PDF). Discretetransport radiation model (DTRM) and k-g turbulence model are used to simulate radiation and flow field respectively. The cases of horizontal tank, vertical tank and spherical tank exposed to pool fire under wind or windless conditions, jet fire are simulated respectively. The radiation and total surface heat flux to target tanks are calculated.The models of thermal response of PLG tanks subjected to fire are set up. A more accurate physical model is described without using hypotheses of former researchers. The model of thermal response for liquid phase and vapor phase are set up respectively, the bubble growing and rising in the liquid phase is considered.The numerical simulations of thermal response of LPG tank exposed to pool fire and jet fire are carried out. Comparison of the simulating results to the experiment ones shows good agreement. Influence of various conditions on the thermal response of tanks is simulated. The simulating results show that the pressure and temperature of the ladings , the temperature of tank wall can be fitted to time with polynomial. The constants are determined by initial conditions, fire types, tank types and fill levels etc.. Jet fire is more dangerous for PLG tanks than pool fire, and in this situation, the pressure and wall temperature increase more rapidly. The sizes of tanks, fill levels and tank types also affect the response of tanks. The smaller the tanks and the more the fill levels are, the more rapidly the pressure increase. The pressure in vertical tank increases more rapidly than that in horizontal tank.Failure analysis for exploded tanks in the experiment is carried out. From the analysis it can be showed that plastic deformation is obvious before the tank failure occurs, the failure manner is ductile fracture, the first rupture starts at the position of seriously thinned wall of the tanks. After the initial failure of tanks, the tank could fail in three manner, ie. rapid BLEVE, slow BLEVE and jet release. Criterion of tank failure is set up. When the strength of seriously thinned wall is less than the strength limit of tank material at high temperature, the tank failure occurs. The formula for predicting the bursting pressure of the tanks exposed to fire is suggested. The failure time is predicted by simulating results and failure criterion which shows better agreement with experiment results. The prevention and control countermeasures ofPLG tank accident are suggested, and the simulating method for safety design is put forward. The safe distance of LPG tank accident is calculated.