Cooling explosion suppression method of the most e

2022-08-01
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Explosion suppression system -- cooling explosion suppression method now, let's turn back to the interaction between jet flow and flame. There are three possible situations after the liquid flow contacts with the flame: ① the front and rear front of the flame are extinguished, which means that the explosion is completely suppressed; ② Only the front face of the flame but not the back face of the flame is extinguished; ③ The front and back fronts of the flame were not extinguished. Obviously, only the first case can achieve the desired purpose. However, the research conducted by the all Soviet Institute of safety technology and economics of chemical industry shows that the equipment can achieve the purpose of explosion-proof without completely extinguishing the flame. This new explosion-proof method is called "cooling explosion suppression method". The essence of the cooling and explosion suppression method is to inject atomized liquid (generally water) into the protected equipment at a speed so that the combustion products can be cooled rapidly even if the flame continues to spread, so that the pressure in the equipment will not rise. Unlike the explosion suppression method, the injection process of the cooling method is not completed in a very short time, but lasts for several seconds. The total amount of liquid injected is almost the same as that of the traditional automatic explosion suppression system. It is better to use water as the coolant of explosion cooling system, because water can mainly remove the heat of combustion products by its own evaporation. Fig. 1 change curve of explosion pressure in the test vessel the requirements for water spraying in the cooling explosion suppression method were determined after the exploratory test by opening the spray device to spray water at the end of the explosion. The actual results of the test can be illustrated in Figure 1. In Figure 1, various pressure change curves in the test vessel at that time are listed. Solid line 1 is the explosion curve without any external influence factors (the test vessel shall be able to withstand the full pressure of explosion in terms of strength). The spray device is switched on at T1 instant, that is, just after the explosion. After switching on, the pressure begins to decrease significantly according to curve 2. Comparing curve 2 with curve 1, we can clearly see the thermal effect of the interaction between the injected water mist and the hot combustion products. After further changing the injection water volume, spray fineness, fog column shape and other conditions, the pressure will drop more sharply as shown in curve 3. At this time, the water spraying condition is the most suitable condition. The capacity of the dynamometer of the test table shall not exceed the predicted breaking load of the sample. The spray of fine mist water can rapidly cool the combustion products, so that the pressure drop rate in the container (curve 3) can be balanced with the maximum pressure increase rate during explosion (curve 1). When the cooling explosion suppression method is used to protect the equipment, the spray device should be opened as early as possible in the early stage after the explosion, that is, at the instant of T2. At this time, the pressure change in the container is shown in curve 4. Although the combustion process in the container will not stop at T2, it will continue until the end, that is, all combustible mixtures will be burned, and the pressure in the container will not rise. Although the influence of water mist on combustible mixture and flame is a complex process, its main function is to rapidly cool the combustion products of combustible mixture until it is burned out. The test method for selecting cooling water spray conditions described above is only a method that is similar to the actual conditions, while DuPont aniline device is located in this area, because the actual conditions when the spray water mist interacts with the spreading flame are very different from the test conditions. Therefore, there are differences. In addition to the change in volume of hot gas under actual conditions, there are two contradictory factors that also complicate the cooling process. First of all, the water mist has a certain inhibition effect, which can reduce the combustion speed. However, when the water mist is injected, the combustible mixture produces violent turbulence, which intensifies the combustion. In this way, it is difficult to generalize the final effect. For example, for gas flame, turbulence may be the main aspect of the contradiction, while for dust, the injected water mist can make solid combustibles settle down. Moreover, due to the greater thickness of the flame front during dust combustion, the suppression effect of water mist on flame is more effective, so the final effect is to reduce the combustion speed. One of the main advantages of the cooling method compared with the suppression method is that when an explosion occurs, the start time of water cooling can actually be much later than the start time of the suppression method. This essentially reduces the sensitivity requirements of the explosion sensor, thus greatly improving the anti-interference ability of the system and avoiding the possibility of misoperation. Another very important point is that when the cooling explosion suppression method is adopted, because the long-term stability of the combustible mixture polyurethane is no problem, it is intended to burn out completely, so the possibility of re ignition (secondary explosion) is completely ruled out. In addition, water can be used everywhere as a coolant, and the price is low. Freon can not be compared with it, not to mention some extremely toxic products will be generated after Freon reacts with flame. The disadvantage of the cooling method is that the pressure formed in the container is relatively low. If the combustion reaction is carried out in the same amount, the pressure will rise only when the gas is not cooled sufficiently and part of the injected water evaporates. For example, cooling in a container with a volume of 10 cubic meters“ ВИТаН- two М” In case of dust explosion, the pressure in the container only reaches 75 kPa. Such a rise in pressure is entirely permissible in many cases. The market is mostly worried about the shortage of raw materials. The sprinkler shown in Figure 2 is a device for spraying coolant into the equipment. The sprinkler is composed of steel cylinder 6, sealing film 2, 3, 9 and nozzle 1. Three quarters of the volume of the cylinder is filled with coolant, Compressed gas is used as the upper square (generally, nitrogen 10 causes a pressure of about 8Mpa. When the burst tube 8 is triggered, the sealing films 2 and 3, and then the sealing film 9 are broken one after another, and the nozzle 1 moves down and extends into the equipment 10. The coolant is immediately pressed into the internal space of the equipment in the form of a fine mist. In order to improve the spraying quality, the structure of the sprinkler considers that the coolant can be mixed and stirred with the compressed gas from the central pipe 5 before the nozzle. The needle valve 4 is used to fill the steel cylinder For gas, pressure gauge 7 is used to check the pressure in the cylinder. The inertia of the sprinkler, that is, the time between the initiation pulse input to the explosion tube and the beginning of the outflow of the coolant, is actually related to the explosion

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