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Main characteristics of combustion processes
Solid, liquid and gaseous substances that are formed during the combustion of a substance are called combustion products. The composition and properties of combustion products depend on the composition of the combustible substance and the conditions of its combustion.
Carbon, hydrogen, sulfur and phosphorus, which are part of combustible substances of organic and mineral origin, oxidize during combustion and form carbon monoxide and carbon dioxide (CO and CO2), water vapor (H20), sulfur dioxide (SO2) and phosphoric anhydride(P205). All these products, with the exception of carbon monoxide, can no longer burn.
Combustion can be complete or incomplete depending on the air flow conditions. Complete combustion takes place with a sufficient amount of air. With a lack of air, incomplete combustion occurs. Organic combustible substances under conditions of incomplete combustion are characterized by the release of not only the products listed above, but also various kinds organic compounds(alcohols, ketones, aldehydes, acids).
Combustion products, especially emitted under conditions of incomplete combustion or in the event of thermal decomposition of various kinds of polymer compounds, pose a serious threat to human life and health. For example, inhalation of 0.4% carbon monoxide is fatal, 8-10% concentration of dioxide carbon is also life-threatening. Thermal decomposition products of various kinds are even more dangerous. chemical substances: phosgene, hydrogen chloride, hydrocyanic acid, etc. No less danger to health and human life is the heat released during a fire. Inhalation under fire conditions of air with a temperature of 60 ... 70 ° C, within a few minutes, causes irreversible physiological changes in the human body that end in death.
The amount of heat released during a fire and the temperature environment largely depend on the heat of combustion of the combustible substance. The heat of combustion of a substance depends on its properties and composition: for hydrocarbons, oil and petroleum products it is 39900 ... 46200 J / kg, for coal-8400 ... ... 31500 J / kg, and for wood and cotton - 8400 ... ... 16800 J / kg. The heat released during a fire also has a destructive effect on equipment and building structures of buildings, promotes the spread of fire in the direction of adjacent rooms and buildings, and also interferes with actions aimed at extinguishing the fire.
The actual combustion temperature of a substance is always lower than the theoretical one, since combustion occurs with a large lack of air and with significant heat losses. So, for example, the theoretical combustion temperature of wood is on average 1600 ° C, and the actual temperature does not exceed 1100 ° C; for gasoline, these temperatures are 1700 and 1200 ° C, respectively, and for natural gas, 2000 and 1500 ° C.
To assess the nature of temperature changes during a fire, taking into account different conditions combustion, the concept of temperature is accepted, which should be understood as a change in time average temperature in room. In particular, the generalization of numerous data on fires in residential buildings and public buildings led to the introduction of the concept of standard temperature regime, in the conditions of which the fire resistance is checked building structures in the USSR and a number of foreign countries.

Main characteristics of combustion processes
Solid, liquid and gaseous substances that are formed during the combustion of a substance are called combustion products. The composition and properties of combustion products depend on the composition of the combustible substance and the conditions of its combustion.
Carbon, hydrogen, sulfur and phosphorus, which are part of combustible substances of organic and mineral origin, oxidize during combustion and form carbon monoxide and dioxide (CO and CO2), water vapor (H20), sulfur dioxide (SO2) and phosphoric anhydride (P205 ). All these products, with the exception of carbon monoxide, can no longer burn.
Combustion can be complete or incomplete depending on the air flow conditions. Complete combustion takes place with a sufficient amount of air. With a lack of air, incomplete combustion occurs. Under conditions of incomplete combustion, organic combustible substances are characterized by the release of not only the products listed above, but also various kinds of organic compounds (alcohols, ketones, aldehydes, acids).
Combustion products, especially emitted under conditions of incomplete combustion or in the event of thermal decomposition of various kinds of polymer compounds, pose a serious threat to human life and health. For example, inhalation of 0.4% carbon monoxide is fatal, 8-10% concentration of dioxide carbon is also life-threatening. An even greater danger is presented by the products of thermal decomposition of various kinds of chemical substances: phosgene, hydrogen chloride, hydrocyanic acid, etc. No less danger to the health and life of people is the heat released during a fire. Inhalation under fire conditions of air with a temperature of 60 ... 70 ° C, within a few minutes, causes irreversible physiological changes in the human body that end in death.
The amount of heat released during a fire and the ambient temperature largely depend on the heat of combustion of the combustible substance. The heat of combustion of a substance depends on its properties and composition: for hydrocarbons, oil and petroleum products it is 39900 ... 46200 J / kg, for coal -8400 ... ... 31500 J / kg, and for wood and cotton - 8400 ... ... 16800 J / kg. The heat released during a fire also has a destructive effect on equipment and building structures of buildings, promotes the spread of fire in the direction of adjacent rooms and buildings, and also interferes with actions aimed at extinguishing the fire.
The actual combustion temperature of a substance is always lower than the theoretical one, since combustion occurs with a large lack of air and with significant heat losses. So, for example, the theoretical combustion temperature of wood is on average 1600 ° C, and the actual temperature does not exceed 1100 ° C; for gasoline, these temperatures are 1700 and 1200 ° C, respectively, and for natural gas, 2000 and 1500 ° C.
To assess the nature of the temperature change during a fire, taking into account various combustion conditions, the concept of temperature regime is adopted, which should be understood as the change in time of the average temperature in the room. In particular, the generalization of numerous data on fires in residential buildings and public buildings led to the introduction of the concept of a standard temperature regime under which the fire resistance of building structures in the USSR and a number of foreign countries is checked.

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Phosphoric anhydride P4Oyu (tetraphosphoric decaoxide) is formed when phosphorus is burned in conditions of free air access.

Phosphoric anhydride P40yu (tetraphosphoric decaoxide) is formed when phosphorus is burned in conditions of free air access.

The formation of phosphorus oxides, which easily occurs due to the combustion of phosphorus in air and oxygen, is much more difficult due to complex oxygen compounds. Water at ordinary temperatures is not decomposed by phosphorus; when heated with water white phosphorus begins to react only in the presence of air. At temperatures above the boiling point of water, red phosphorus interacts very inactively with its vapors. Experience has shown that white phosphorus is capable of dissolving in liquid sulfur dioxide, but no interaction between them is observed.

Combustion of a smoldering torch, phosphorus, sulfur in nitrous oxide; combustion of phosphorus and hot coal in nitrogen oxide.

Phosphorus trioxide P4O6 (phosphorous anhydride, tetraphosphorhex oxide) is formed when phosphorus is burned in conditions of limited access of oxygen or air.

Phosphorus trioxide P40v (phosphorous anhydride, tetraphosphorhex-oxide) is formed when phosphorus is burned in conditions of limited access of oxygen or air.

Atomized sludge is introduced into the fire reactor together with the air necessary for the combustion of phosphorus.

For intensive cooling of gases, approximately in the middle of the tower height (below the phosphorus combustion zone), 10 nozzles are installed, into which acid of the same concentration is supplied as in the overflow bowl. Below the zone where the nozzles are located, heat exchange between gas and acid occurs not only on the side surface, but also in the bulk. According to the accepted classification Bottom part The incineration tower operates in the main spray absorber mode. The droplets formed when the acid is sprayed have a high velocity corresponding to the speed of the jet from which they were formed.

Indeed, there is no reason to think that heat accompanying the combustion of phosphorus, changes the mechanism of its oxidation, excluding the formation of Н2О2 or ozone, accompanying the slow oxidation of the same phosphorus. It is more natural to think that in all kinds of combustion, depending on the conditions, both ozone and HsO2 and unstable peroxides are formed; they are not observed only because they immediately decompose, splitting off oxygen. It is easy to be convinced from experience that this is indeed the case. By directing the flame of a hydrogen-oxygen burner onto a piece of ice, it is then easy to detect hydrogen peroxide in the melted water. Obviously, under these experimental conditions, hydrogen peroxide, due to rapid cooling, does not have time to disintegrate in time and, thus, elude observation, as in the usual experiment of burning hydrogen with the collection of the combustion product under the bell; in this case, we observe only the final product of the reaction - water.

Indeed, there is no reason to think that the high temperature accompanying the combustion of phosphorus changes the mechanism of its oxidation, excluding the formation of Н2О2 or ozone, which accompanies the slow oxidation of the same phosphorus. It is more natural to think that in all kinds of combustion, depending on the conditions, both ozone and H2O2 and unstable peroxides are formed; they are not observed only because they immediately decompose, splitting off oxygen. It is easy to be convinced from experience that this is indeed the case. By directing the flame of a hydrogen-oxygen-oxygen gargle on a piece of ice, it is not difficult to then detect hydrogen peroxide in the melt water. Obviously, under these experimental conditions, hydrogen peroxide, due to rapid cooling, does not have time to decompose in time and, thus, elude observation, as in the usual experiment of burning a voaerod with collecting the combustion product under the bell; in this case, we observe only the final preduct of the reaction — water.