The hottest Han Technology in preventing BLEVE acc

2022-10-20
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Engineering practice of Han Technology in preventing BLEVE accidents of LPG spherical tanks

1 BLEVE phenomenon and the possibility of harm. The main danger in LPG storage (an accident with low probability but serious consequences) is boiling liquid expanding vapor explosions (abbreviated as BLEVE). When the high-pressure storage tank encounters an exposed fire, the pressure in the tank will rise, At the same time, due to the formation of bubbles on the tank wall (violent boiling) on the fire facing surface in the tank and the dry tank wall above the liquid level until the fault is eliminated, and the metal strength of the dry tank wall will be reduced due to excessive heating, resulting in an increase in internal pressure and a decrease in external strength. Due to the creep of metal at high temperature, it is easy to cause container fracture and explosion. The conditions of BLEVE accident are shown in Figure 1. Three 1000m3 spherical tanks and various oil tank areas in the tank farm of CNOOC (Group) gas company form a "super large dangerous goods warehouse area". The distance from PS raw material storage tank farm to the outer wall of LPG spherical storage tank is 60m, which is less than the requirement of 100m fire prevention distance in code for fire protection design of crude oil and natural gas engineering (gb50183). According to the site conditions, the following situations should be prevented to cause BLEVE accidents in four cooperation projects between spherical tanks and Jilin Province, covering many aspects. Fig. 1 conditions of BLEVE occurrence ⑴ flame spewing due to leakage between spherical tanks; ⑵ high concentration of explosive gas accumulates on the ground; ⑶ the leakage of large aboveground storage tanks leads to the spread of ground flames. 2 basis for implementing Han technical transformation on LPG spherical tanks 2.1 foreign research report Figure 2 and figure 3 are a group of photos. Figure 2 implements Han technical transformation, and figure 3 does not implement transformation. The result is that it burns in the same fire. Those who implement Han transformation maintain the tank structure, and those who do not implement transformation break due to the weakening of metal strength. Figure 2 fire condition of tank body with Han Technology Transformation Figure 3 fire condition of tank body without Han technology transformation experiment shows that Han technology changes the thermal conductivity of LPG, making the heat transfer between liquid layers become the heat transfer between liquid and metal. Due to the huge heat transfer area and the increase of thermal conductivity of Han materials, the heat transfer rate is greatly changed. Similarly, the tank wall heat of the gas phase part (dry tank wall) above the liquid level is quickly transferred to the Han material in the tank, and through the Han material to the liquid phase, the tank wall temperature of the dry tank wall part is reduced, and the strength of the metal material of the tank wall is maintained. 2.2 results of model experiment Figure 4 and figure 5 are a group of comparative experiments. The burner is used as the heat source, and the vessel is made of low carbon steel with a wall thickness of 8mm, which contains 30 # mechanical oil as the heat receiver. One group is equipped with Han material on the ring wall, and the other group is not equipped with Han material. The experimental device is composed of heat source, heat conduction and heat reception. The test results are as follows: the inner wall without Han material is locally red, the machine oil is smoking, and the temperature rise rate of heat conduction and heat radiation of the machine oil is 02 ℃/min. After adding Han material, the machine oil does not smoke, and the temperature rise rate of heat conduction and heat radiation of the machine oil itself is 1.0 ℃/min. That is to say, the heat transfer rate of the tank wall to the tank is increased by 5 times, which greatly changes the over heating of the dry tank wall. The experiment is carried out after changing the thickness of Han material. With the increase of the thickness of Han material, the transfer efficiency does not increase linearly in the process of heating and cooling, and there is an obvious inflection point, so as to determine the best thickness of Han material ring space installation. 3. The plan of taking measures to prevent BLEVE accident of spherical tank is ring space installation method, as shown in Figure 6. 4 Determination of the optimal thickness of Han material ⑴ domestic and foreign studies have shown that under a certain thermal radiation intensity, the relationship between the heat conduction efficiency (heating rate) and the thickness of Han material is shown in Figure 7, so the optimal thickness of Han material can be determined according to the flame radiation intensity. Fig. 4 change of dry and wet tank wall temperature before transformation Fig. 5 change of dry and wet tank wall temperature after Han transformation Fig. 6 installation of Han material in spherical tank annulus to prevent BLEVE Fig. 7 Relationship between temperature rise rate and Han material thickness ⑵ for 1000m3 LPG storage tank of Ocean Group, under the radiation intensity of 65000w/m2-70000 w/M2 on one side, the installation thickness of Han material in annulus, the average calculated value is 500mm, and the actual installation is determined to be 700mm. The thickness of Han material is determined to ensure that the heat of the tank wall of the gas phase part is transferred to the liquid phase and prevent the tank wall of the gas phase part 12.70 from overheating. At the same time, the cost is comprehensively considered. 5. The principle of Han Technology to prevent BLEVE. See Figure 4 for the change curve of dry and wet tank wall temperature before Han transformation. See Fig. 5 for the change curve of dry and wet tank wall temperature after Han transformation. The curve of tank wall yield strength versus time before and after Han reconstruction is shown in Figure 8. The effect of temperature on the properties of low carbon steel is shown in Figure 9. Fig. 8 curve of tank wall yield strength with time before and after Han transformation 5.1 external heating of metal tank wall of LPG spherical tank ⑴ when the temperature reaches 45 ℃, the corresponding internal pressure of LPG rises to 1600kpa. Generally, the opening of safety valve is determined at 1800 kPa, and the corresponding temperature is 55 ℃. When the temperature of LPG reaches 96 ℃, it will reach the critical point (97 ℃, 4200

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