| There are many deflagration accidents resulting from combustion gas leakage and diffusion in large tank area, which causing huge economic loss and casualties. Although there are a lot of research reports about combustible gas diffusion and deflagration in tank area, However, existing research only focuses on combustible gas leakage diffusion regularity or deflagration intensity of combustible gas in open or restricted space, which have not been combined the deflagration intensity of irregular shape of gas cloud due to combustible gas leakage and diffusion, resulting in research achievements cannot provide clear technical guidance for accident model that deflagration comes from combustible gas leakage diffusion.In this paper, the CFD model was adopted to study the law of combustible gas leakage and diffusion in storage tank area and the formation regularity of irregular shape combustible gas cloud from leakage has been paid attention. The main research contents and conclusions of this paper are as follows:(1) The numerical simulation model of combustible gas leakage diffusion and deflagration in large spherical tank area was established. The geometric model was meshed and mesh independent solution was determined for diffusion model. At last, the model effectiveness validations were made on diffusion and deflagration model.(2) The leakage diffusion regularity of combustible medium was studied in tank area. Two parameters is presented in this paper, namely the horizontal maximum distance Lmax and height direction maximum diameter Dmaxto evaluate the range size of combustible gas cloud from gas leak quantitatively. Results show that, when storage tank pressure is IMPa and150mm diameter circular leak hole located spherical tank equator without considering wind speed, methane concentration is symmetry along horizontal direction when gas diffuses and the horizontal maximum distance Lmax is10.95m and remains stable when leakage time is1s, at2s, the height direction maximum diameter Dmax is8.8m reaching stable. The diffusion regularity of methane, hydrogen, propane were compared, it shows that, the risk of hydrogen is greater than the methane and propane.(3) The influence of tank pressure, leakage aperture size and location, wind speed on the range of combustible gas cloud due to methane diffusion were researched respectively. Results show that, tank pressure has little effect on combustible gas flammable range. The Lmax and Amax measuring combustible gas cloud range increases with increasing of leakage diameter, the horizontal maximum distance Lmax and height direction maximum diameter Dmax are17.14m and13.5m respectively on the condition of leakage diameter is200mm, the risk of deflagration becomes bigger when leakage aperture is set at the bottom of tank. Lmax and Dmax decreases with increasing of wind speed and Lmax and Dmax are8.71m and1.53m when wind speed is12m/s.(4) Based on the methane flammable range, the maximum diameter method, actual diffusion area method, center of gravity height sphere method and equal volume ball method were adopted to research maximum deflagration overpressure of irregular gas cloud from methane leakage and diffusion. The results showed that, when storage tank pressure is1MPa and150mm diameter circular leak hole located spherical tank equator without considering wind speed, the maximum overpressure are230kPa,151kPa,125kPa and130kPa respectively corresponding to the four kinds of simplified methods. The explosion overpressure obtaining from equal volume ball method is most close to the actual overpressure of combustible gas cloud, so equal volume ball method can be chose to evaluate the irregular gas cloud explosion intensity(5) The equal volumetric ball method is used to evaluate the deflagration intensity after methane leakage and diffusion under different aperture leakage and wind speed. The results show that, deflagration intensity increases as leakage aperture diameter increases and wind speed decreases. |
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