On Vapor Explosion Critical Condition Analysis And Simulation Of The Pressure Vessel

Liquefied gases, many of which are inflammable, explosive or toxic substances, are usually contained in pressure vessels. Once leakage occurs, these substances will gasify and spread rapidly and form a wide range of dangerous area in a while. It can lead to heavy, big fires and explosive accidents when facing fire hazard. After leaking of the pressure vessel, in which liquefied gases or high temperature liquids over normal boiling point are loaded, the internal substances explode due to its pressure loss, overheating (it is also called BLEVE), and lead to internal overpressure. Large overpressure can make the split expand, and it can even cause local big scope or the overall failure, leading to more accidents.This thesis studies the pressure vessel BLEVE phenomenon in critical condition by using thermodynamics principle, explosion mechanics principle; it analyzes the pressure of cracking tip and the simulation under the critical condition after leaking by using fracture mechanics theory.It analyzes the internal intensity of pressure changing situation during the leakage in the pressure vessel when it explosives by using thermodynamics theory. According to the gas phase space saturated steam specific volume and quality formula and compressed gas leak velocity formula, and the changing relations between ideal gas state equation volume and density, we establish a specific volume and leakage time model, and also a exploding stagnation time model for liquefied gases or high temperature liquid over the normal boiling point.The critical area calculating model of BLEVE is established by using an established specific volume and leakage time model, stagnation time model and vapor explosion overpressure formula.By using the thermodynamics theory, it gets the model formula between the critical area of BLEVE phenomenon and internal gas phase volume, intensity of pressure, leakage speed, liquid surface height, and liquid density in pressure vessel. We can judge whether BLEVE phenomenon occurs in existing crack under the certain intensity of pressure according to the formula of the internal gas phase volume, intensity of pressure, leakage speed, liquid surface height, and liquid density in pressure vessel, as a judgment basis of the BLEVE phenomenon.Through the high temperature and high pressure hot water leakage experiment and the experimental results by references, we verify that the calculation results in established models are basically in accordance with the actual results.On the basis of above research, we analyze the critical temperature, critical intensity of pressure, and critical area when BLEVE phenomenon occurs in normal working pressure and under the highest pressure in the 2000m3 liquid ammonia ball pressure vessel. The hazard of leakage when in BLEVE critical condition in 2000m3 liquid ammonia sphere pressure vessel is simulated by adopting environmental Risk assessment system software (Risk System).