Study On Dynamic Of Flammable VCE Process In Special Operation Conditions And Analysis Of Accidental Consequence

Flammable gases are widely used in industries especially in chemical or petroleum chemical industry. Explosion accidents of gas cloud caused by leakage of gas often cause severe person injuries and great property loss.Research on its explosive regulation is of important application value. Particularly, under condition of industrial production, vapor cloud explosion is danger than unconfined vapor cloud explosion as the process unit connection, pipelining and complication.At present, the application scope of TNT Equivalency method and TNO Multi-energy model are the largest in vapor cloud explosion of accident consequence assessment. However, the TNT Equivalency method, an empirical model, is limited to make a rough estimation for far field of explosion. The TNO Multi-energy needs too much subjective judgment during application despite of its reasonability. Numerical simulation is used for solving the equations of fluid mechanics, and there are still other problems unanswered such as chemical reaction dynamics, turbulence equation near barriers.The typical accident reason of vapor cloud explosion in Domestic and foreign are classified and analyzed. The vapor cloud explosion pattern is determined according to that statistical analysis result, and special operation conditions are used as the research object.The explosion flame-propagation regulation and air Blast Pressure in vapor cloud explosion is studied. It includes:(1) explosion propagation regulation of vapor cloud explosion in a unitThe obstacle-induced disturbance at the flame front is negligible at the early-ignited stage of the flammable gas. When the flame propagates near the obstacles, the change of flame front happens obviously. With the enhancement of height of obstacles, the flame front is pulled and distorted strongly, which results in the rapid increase of flame velocity. And with the increase of the number of obstacles, the flame front that pulled farther will cause the raise of flame velocity, too. The positive feedback mechanism of mutual acceleration among obstacle, turbulent flow and flame is explained.(2) explosion propagation regulation of vapor cloud explosion between units Overpressure-time curve of mix vapor cloud at various separation distances is simulated.If an extended flammable vapor cloud at a chemical plant site extends over more than one process unit, which are separated by lanes of sufficient width, the vapor cloud explosion on ignition develops the same number of separate blasts. If, on the other hand, the separation between the units is insufficient, the vapor cloud explosion develops one big blast. Considering vapor cloud explosion of ethylene-air station, the critical separation distance appeared to be larger than 0.25 times the donor size. Under condition of existing connecting pipe rack between units, the critical separation is reduced because of the flame acceleration.(3) research on regulation of interaction between shock wave and obstaclesThe shock wave is brought from blast wall response to vapor cloud field. Conclusions are: In process of the interaction between shock wave and obstacles, exists not only reflection, but also the phenomenon of diffraction similar to mountain climbing. Overpressure in the surface of obstruction with the positive side exist discrepancies. The maximal difference is that the overpressure distribution is great in the corner of back while it is small in the center. According to the phenomenon of the diffraction for shock wave, the types of barrier wall are designed. The effect of using "T" shape to reducing shock wave overpressure is the most distinct.Contrasting with all kinds of typically representative meaningful engineering methods to carry on the analysis and the research and tally up the regulations, inquire into the path of combining the CFD method with other engineering experienced method.(1) Accident consequence fatalness is quantitative calculated by the associated method of TNT equivalency method and TNO Multi-energy model. Evaluation method which is the combination TNT method (calculation of fatal distance value) with TNO model (calculation of explosive total equivalency value) is obtained.(2) Based on the method of CFD, the accident case is simulated and the overpressure is calculated. At the same time, combined with the TNO model, evaluation approach is gained on the basis of combination CFD simulation method (calculation of explosive overpressure value) with TNO model (confirming of gas quality which participates explosive).