Physicochemical basis of maximum fire suppression

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Physical and chemical basis of explosion suppression

in order to completely prevent the combustion reaction in the equipment, special additives must be added to the combustible mixture to make it a non combustible mixture. This method has long been known by people and has been widely used in practice to achieve the purpose of fire prevention and flame retardancy by using different additives in the development process from imitation to self renovation. In this regard, the most commonly used inert additives are carbon dioxide, water and nitrogen. Are the materials of the idler housing itself and the instrument itself equipped with vibration elimination facilities? Inferior metals do not include a certain amount of carbon based additives, which do not participate in the combustion reaction, but ease the combustion after taking away part of the reaction heat. As part of the reaction heat is taken away by additives, the temperature of the flame decreases rapidly, resulting in the loss of the ability to spread. If the concentration of combustibles is higher than the upper limit of the ignition point of the mixture, the excess combustibles themselves can also ease the combustion. Other organic additives used in rich explosive dangerous mixtures also have this moderating effect. In this case, the effect of organic additives is even better than that of inert additives. This is not only because the heat capacity of organic additives is higher, but also because the reaction of this substance at high temperature has endothermic properties. The use of combustible organic additives as flame retardants for combustion reactions has been widely used in the development of explosive gas processing processes, but has not been applied in automatic explosion suppression systems, but it is known that some experimental studies have shown this possibility. Some people are trying to use some more effective substances in the new automatic explosion suppression system, and the so-called chemical inhibitors belong to this kind of substances. As long as the concentration of this chemically active additive reaches a few percent, the mixture can become non combustible. Freon is also a class of chemical inhibitors, which are chlorofluoro derivatives and bromofluoro derivatives of methane and ethane. In industry, freon is specially specified with symbols reflecting its chemical composition. In the three digits of the symbol, the first number represents the number of carbon atoms minus 1, the second number represents the number of hydrogen atoms, and the third number represents the number of fluorine atoms in the molecule. If the molecule contains bromine atoms, add the letter B and the number of bromine atoms after the three digits. The number of chlorine atoms is not represented in the symbol, which can be derived from the valence of other elements. If zero is encountered in the symbol, it will not be represented. For example, freon 12, Its chemical formula is CCL2F2, while the chemical formula of freon 114B2 is c2br2f4. Such as CCl4, ch2clbr, CH3Br and some other substances, although not halothanes, are also some chemical inhibitors. These halogen derivatives of methane and ethane are all grouped into so-called haloalkanes. In the representative symbols of such inhibitors, the first number represents the number of carbon atoms, the second number represents the number of fluorine atoms, the third number represents the number of chlorine atoms, the fourth number represents the number of bromine atoms, and the fifth number represents the number of iodine atoms. The number of hydrogen atoms is equal to the first number multiplied by 2 plus 2 minus the sum of the rest. For example, the chemical composition of Halon 104 is CCl4, while the chemical composition of Halon 1001 is ch3b. Whether it is better to add cooling and flame retardants or chemical inhibitors can be judged according to the relationship curve between the explosive concentration limit of the combustible and oxidant and the concentration of additives. The examples given in the figure below are additive nitrogen The influence of carbon dioxide and Freon 114B2 "on the combustion limit of propane. The part within the curve is equivalent to the composition of the mixture when it is flammable, while the part outside the curve is equivalent to the composition of the non flammable mixture. In this way, each curve circles a so-called" combustion sector ". As can be seen from the figure below, no additives are added when the pointer of the adjustment dial is aligned with the zero point of the dial (that is, the concentration of additives is equal to zero) The combustion limit of propane is 2 ~ 9%; When 20% nitrogen is added, the combustion limit range is reduced to 2 ~ 6.5%, while the same concentration of carbon dioxide makes the combustion limit range much smaller, reaching 3 ~ 5.8%. That is to say, carbon dioxide is a more effective cooling and combustion inhibitor than nitrogen. The composition of the mixture equivalent to the tip of the "combustion sector" represents the peak concentration of the additive. The so-called peak concentration is the additive concentration that makes the mixture nonflammable in any proportion of combustible and combustion supporting substances. As can be seen from figure 52, for propane, the peak concentration of nitrogen is 43%, that of carbon dioxide is 30%, and that of Freon is 3%. Figure relationship between combustion limit of propane air mixture and additive concentration 1 - nitrogen; 2 - carbon dioxide; 3-freon 114B2 is different from cooling and flame retardants. The action mechanism of chemical inhibitors is that it can stop the chain reaction process during combustion. This is because the molecules of inhibitors or their decomposition products can interact violently with the active core of combustion reaction - atomized hydrogen and oxygen, as well as intermediate groups, so as to convert them into stable compounds, thus stopping the development of chain combustion reaction. Halogen derivatives can especially react violently with atomized hydrogen in most chain combustion reactions, which clearly explains why halogen derivatives are so widely used as chemical inhibitors of combustion. Therefore, among a series of derivatives of saturated hydrocarbons, only those derivatives whose most hydrogen atoms are replaced by halogen atoms are the most effective to inhibit combustion. In halo+o=hal+o2 (where Hal is a halogen atom), accelerating the recombination speed of atomic oxygen can also inhibit the flame. According to the ion theory, the combustion process includes the formation stage of oxygen ions. At this stage, electrons produced during ionization of hydrocarbon molecules are captured by oxygen molecules. Because the effective cross-sectional area of halogen atoms is larger than that of oxygen atoms, halogen atoms capture slow electrons before oxygen atoms. Some halogen derivatives themselves can be oxidized, so their combustion of mixtures rich in combustibles will speed up the promotion of innovative and differentiated solution reactions for our aviation customers. However, if it is added to the lean mixture, it can even intensify the combustion reaction and reduce the lower limit of ignition due to the increase of the calorific value of the mixture. Recently, some researchers have become more interested in powdered fire extinguishing agents. Carbonates and bicarbonates with sodium and potassium, as well as phosphoric acid

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