Examination: combustion and explosion theory. The theory of combustion of gas mixtures. Pressure when the explosion rate of pressure increases during explosion

The study of the combustion processes of combustible mixtures by Russian and foreign scientists has given the opportunity to theoretically substantiate many phenomena, accompanying the combustion process, including the rate of flame propagation. Studying the rate of propagation of a flame in gas mixtures allows you to determine the safe velocities of gas-entertainment in the pipelines of the ventilation, recovery, aspiration and pipelines of other installations, which are transported by gas and dusty mixtures.

In 1889, Russian scientists V.A. Michelson reviewed two limit cases of flame propagation during normal or slow burning and during detonation.

Further development the theory of normal spread of the flame and detonation received in the works of N.N. Semenova, K.I. Schelkina, D.A. Frank-Kamenetsky, L.N. Chitrina, A.S. Sokolika, V.I. Skobelkin and other scientists, as well as foreign scientists B. Lewis, Elbe, and others. As a result, the theory of ignition of explosive mixtures was created. However, attempts to interpret the phenomena of the spread of the flame as diffusion of active centers or explain the limits of the spread of flames with the conditions of circuit breakdowns are not convincing enough.

In 1942, the Soviet scientist Ya.B. Zeldovich formulated the provisions of the theory of burning and detonation of gases. The combustion theory gives an answer to the main questions: there will be a mixture of this composition of combustion, what will be the burning speed of an explosive mixture, what features and forms of the flame should be expected. The theory argues that the explosion of the gas or steam mixture is not instantaneous. When an ignition source is introduced into a combustible mixture, a fuel oxidation reaction with an oxidizing agent in the ignition source zone begins. The speed of the oxidation reaction in some elementary volume of this zone reaches the maximum - burning arises. The burning on the boundary of the elementary volume with the medium is called the flame front. Flame front has the type of sphere. Flame front thickness, by calculations Ya.B. Zeldovich, equal to 1 - 100 μm. Although the thickness of the combustion zone and is small, but sufficient to flow the combustion reaction. The flame front temperature due to heat of the combustion reaction is 1000 - 3000 0 C and depends on the composition of the combustible mixture. Near the front of the flame, the temperature of the mixture also increases, which is due to heat transmission with thermal conductivity, diffusion of heated molecules and radiation. On the outer surface of the flame front, this temperature is equal to the temperature of self-ignition combustion mixture. The change in the temperature of the mixture along the axis of the pipe at the time of time is graphically shown in Fig. 4.1. Layer Gaza QC 1.which increases the temperature of the mixture, is the front of the flame. With increasing temperature, the flame front expands (up to KK 2.) on the side of the terminal walls of the pipe BUT and M., shifting at some speed unlawful mixture towards the wall M., and burnt gas in the side of the wall BUT. After the flamm of the combustible mixture, the spherical shape of the flame is very quickly distorted and is increasingly stretched in the direction of a non-flammable mixture. Pulling the front of the flame and the rapid increase in its surface is accompanied by an increase in the speed of movement

the central part of the flame. This acceleration lasts until the flame is touched by the pipe walls or, in any case, will not get closer to the pipe wall. At this point, the flame size decreases sharply, and only a small part remains from the flame, overlapping the entire section of the pipe. Extracting the front of the flame and its intensive acceleration immediately after the ignition is sparking, when the flame has not yet reached the pipe walls, are caused by an increase in the volume of combustion products. Thus, in the initial stage of the process of formation of the flame front, regardless of the degree of flammability of the gas mixture, there is an acceleration and subsequent braking of the flame, and this braking will be the greater the greater the speed of the flame.

Fig. 4.1. Temperature change before and behind the flame front: 1 - zone

combustion products; 2 - Flame Front; 3 - zone of self-ignition;

4 - preheating zone; 5 - Source mixture

The process of the development of subsequent burning stages has an influence of the length of the pipe. The lengthening of the pipe leads to the appearance of vibrations and the formation of the cellular structure of the flame, shock and detonation waves.

Consider the width of the warm-up zone before the front of the flame. In this zone, the chemical reaction does not proceed and heat is not allocated. The width of the heating zone l.(in cm) can be determined from the dependence:

where but -Caffetrium temperature; v. - Flame spread rate.

For the methane-air mixture, the width of the heating zone is 0.0006 m, it is significantly less for the hydrogen-air mixture (3 microns). The subsequent combustion occurs in the mixture, the state of which has already changed as a result of thermal conductivity and diffusion of components from adjacent layers. Mixing the reaction products no specific catalytic effect on the rate of displacement of the flame does not provide.

Consider now the speed of moving the front of the flame on the gas mixture. Linear movement speed v. (in m / s) can be determined by the formula

where is the mass rate of burning, g / (cm × m 2), p is the density of the initial combustible mixture, kg / m 3.

The linear speed of moving the flame front is not constant, it changes depending on the compositions of the mixture and impurities of inert (non-combustible) gases, the temperature of the mixture, the diameter of the pipes, etc. The maximum flame propagation rate is observed not at the stoichiometric concentration of the mixture, and in the mixture with an excess of fuel. When introduced into a combustible mixture of inert gases, the rate of propagation of the flame is reduced. It is explained by a decrease in the combustion temperature of the mixture, since part of the heat is consumed for heating not involved in the reaction of inert impurities. The speed of the flame is influenced by the heat capacity of the inert gas. The greater the heat capacity of the inert gas, the greater it reduces the combustion temperature and the stronger reduces the rate of flame propagation. So, in a mixture of methane with air, diluted carbon dioxide, the flame propagation rate is approximately three times less than in a mixture diluted with argon.

With the pre-heating of the mixture, the rate of flame propagation increases. It has been established that the rate of flame propagation is proportional to the square of the initial temperature of the mixture.

With increasing pipe diameter, the flame propagation rate grows unevenly.

With an increase in the diameter of pipes up to 0.10 - 0.15 m, the speed grows quite quickly; With a further increase in pipe diameter, it continues to increase, but to a lesser extent. The increase in temperature occurs until the diameter reaches some limit diameter, above which the increase in speed does not occur. With a decrease in the pipe diameter, the rate of flame propagation decreases, and at a small diameter, the flame in the pipe does not apply. This phenomenon can be explained by increasing thermal losses through the walls of the pipe.

Consequently, to stop the spread of the flame in a combustible mixture, it is necessary to lower the temperature of the mixture in one way or another, the cooling vessel (in our example, the pipe) from the outside or diluting the mixture with cold inert gas.

The normal speed of flame propagation is relatively small (no more than dozen meters per second), but in some conditions the flame in the pipes spreads at a huge speed (from 2 to 5 km / s) exceeding the speed of the sound in this environment. This phenomenon was called detonation. Distinctive features of detonation are as follows:

1) constant burning rate independently of the diameter of the pipe;

2) the high pressure of the flame caused by the detonation wave, which may exceed 50 MPa, depending on the chemical nature of the combustible mixture and the initial pressure; Moreover, due to the high speed of combustion, the developing pressure does not depend on the shape, capacity and tightness of the vessel (or pipe).

Consider the transition of rapid burning into detonation in a long pipe of constant section when the mixture is ignited by the closed end. Under the pressure of the front of the flame in a combustible mixture there are compression waves - shock waves. In the shock wave increases the temperature of the gas up to the values \u200b\u200bat which the mixture itself occurs far in front of the flame front. This combustion regime is called detonation. With the movement of the front of the flame, the movement of the layers adjacent to the wall is braked and the mixture is accelerated accordingly in the center of the pipe; Distribution of

the cross section becomes uneven. The jets of gas mixtures appear, whose speed of which is less than the average gas mixture rate with normal burning, and the jet moving faster. Under these conditions, the speed of movement of the flame is rising relative to the mixture, the amount of gas burning per unit increases, and the movement of the flame front is determined by the maximum speed of the gas jet.

As the flame is accelerated, the amplitude of the shock wave is growing, the compression temperature reaches the temperature of self-ignition of the mixture.

The increase in the total amount of gas burning per unit is due to the fact that in a stream with a variable in cross section, the flame front bend; As a result, its surface increases and the amount of combustible substance increases in proportion.

One of the ways to reduce the combustion rate of combustible mixtures is an effect on the flame of inert gases, but due to their small efficiency, chemical combustion inhibition is currently used, adding halogenated hydrocarbons to the mixture.

Combustible gas mixtures have two theoretical combustion temperatures - with a constant volume and at constant pressure, the first is always higher than the second.

The method of calculating the calorimetric combustion temperature at constant pressure is considered in section 1. Consider the methodology for calculating the theoretical temperature of combustion of gas mixtures at a constant volume, which corresponds to an explosion in a closed vessel. The basis for calculating the theoretical combustion temperature at a constant volume is the same conditions specified in the subdrade. 1.7.

When burning gas mixtures in a closed volume, combustion products do not work; The energy of the explosion is consumed only on the heating of the explosion products. In this case, the total energy is defined as the sum of the internal energy of the explosive mixture Q VN.Men.cm and the heat of burning of this substance. The value of Q VN.Eng.cm is equal to the amount of products of the heat capacity of the components of the explosive mixture at a constant volume on the initial temperature of the mixture

Q vn.an.cm \u003d C 1 t + with 2 t + ... + with n t,

where C 1, C 2, C n is the specific heat capacity of the components constituting the explosive mixture, KJ / (kg × K); T - the initial temperature of the mixture, K.

The value of the value of Q VN.N. MSM can be found on reference tables. The temperature of the explosion of gas mixtures with a constant volume is calculated by the same method as the combustion temperature of the mixture at a constant pressure.

In the temperature of the explosion, the explosion pressure is found. The pressure during the explosion of the gas-air mixture in a closed volume depends on the temperature of the explosion and the ratio of the number of molecules of combustion products to the molecules in the explosive mixture. In the explosion of the gas-air mixture, the pressure usually does not exceed 1.0 MPa if the initial pressure of the mixture was normal. When replacing air in an explosive mixture with oxygen, the explosion pressure sharply increases, since the combustion temperature increases.

In an explosion of even a stoichiometric gas-air mixture, a significant amount of heat is spent on the heating of nitrogen in the mixture, therefore the temperature of the explosion of such mixtures is much lower than the temperature of the explosion with oxygen blends. So, the pressure of the explosion of a stoichiometric mixture of methane, ethylene, acetone and methyl ehi

the oxygen RA is 1.5 - 1.9 MPa, and the stoichiometric mixtures of them with air 1.0 MPa.

The maximum explosion pressure is used in the calculations of the explosiveness of the equipment, as well as in the calculations of the safety valves, explosive membranes and the shells of blasting electrical equipment.

The pressure of the explosion of the river (in MPa) gas-air mixtures are calculated by the formula

where p 0 is the initial pressure of the explosive mixture, MPa; T 0 and T ads - the initial temperature of the explosive mixture and the temperature of the explosion, K; - the number of molecules of gases of combustion products after the explosion; - The number of molecules of gases of the mixture to the explosion.

Example 4.1. . Calculate the pressure during the explosion of a mixture of ethyl alcohol and air vapor.

P 0 \u003d 0.1 MPa; T take \u003d 2933 K; T 0 \u003d 273 + 27 \u003d 300 K; \u003d 2 + 3 + 11.28 \u003d 16.28 mol; \u003d 1 + 3 + 11.28 \u003d 15.28 mol.

Federal Agency for the Education of the Russian Federation

State Educational Institution of Higher Professional Education

"Ufa State Oil Technical University"

Department "Industrial safety and labor protection"

Examination on the subject:

Theory of burning and explosion

1. Theoretical Issues of Blast

In technological processes associated with the production, transportation, processing, receipt, the storage and use of combustible gases (GG) and flammable liquids (LVZ), there is always a risk of formation of explosive gas and steady mixtures.

The explosive medium can form a mixture of substances (gases, vapors, dust) with air and other oxidizing agents (oxygen, ozone. Chlorine, nitrogen oxides, etc.) and substances inclined to explosive transformation (acetylene, ozone, hydrazine, etc.).

The causes of the explosions most often is the violation of the rules of safe operation of equipment, gases leakage through looseness in compounds, overheating of devices, excessive pressure increase, lack of proper control over the technological process, gap or breakage of equipment parts, etc.

The source of initiation of the explosion is:

open flame, burning and hot bodies;

electrical discharges;

Thermal manifestations of chemical reactions and mechanical impacts;

sparks from impact and friction:

shock waves;

Electromagnetic and other radiation.

According to PB 09-540-03, the explosion is:

I.Procession of the vehicle release of potential energy associated with a sudden change in the state of the substance and accompanied by a pressure jump or shock wave.

2. Short-term release of internal energy that creates overpressure

The explosion can occur with the burning (oxidation process) or without it.

Parameters and properties characterizing the explosiveness of the medium:

Flash temperature;

Concentration and temperature limits of ignition;

Self-ignition temperature;

Normal flame propagation rate;

Minimal explosive oxygen content (oxidizing agent);

Minimum ignition energy;

Sensitivity to mechanical exposure (impact and friction). Dangerous and harmful factors affecting working

as a result of the explosion, are:

Shock wave, in front of which pressure exceeds the allowable value;

Crossing structures, equipment, communications, buildings and structures and their split parts;

The harmful substances that were formed during the explosion and (or) harmful substances, the content of which in the air of the working area exceeds the maximum permissible concentrations.

The main factors characterizing the danger of the explosion:

Maximum pressure and explosion temperature;

The rate of increase in the explosion;

Pressure at the front of the shock wave;

Crossing and fugasic properties of an explosive environment.

In the explosion, the initial potential energy of the substance is converted, as a rule, into the energy of heated compressed gases, which, in turn, enters the energy of movement, compression, heating the medium. Part of the energy remains in the form of internal (thermal) energy of expanded gases.

The total amount of energy elected during explosion determines the general parameters (volume, area) of destruction. The concentration of energy (energy in a unit of volume) determines the intensity of the destruction in the focus of the explosion. These characteristics in turn depend on the rate of energy release by an explosive system, which causes an explosive wave.

The explosions most common in the practice of the investigation can be divided into two main groups: chemical and physical explosions.

Chemical explosions include the processes of chemical transformation of the substance manifested by burning and characterized by the release of heat energy in a short period of time and in such a volume that pressure waves apply to the source of the explosion are formed.

Physical explosions include processes leading to an explosion and non-chemical transformations of the substance.

The cause of random explosions is most often combustion processes. The explosions of this kind are most often occurring during storage, transportation and manufacture of explosives (explosives). They take place:

When handling ventures and explosive substances of the chemical and petrochemical industries;

When leaks of natural gas in residential buildings;

in the manufacture, transportation and storage of volatile or liquefied combustible substances;

when washing tanks for storing liquid fuel;

in the manufacture, storage and use of combustible dust systems and some self-spinning solids and liquid substances.

Features of the chemical explosion

There are two main types of explosions: an explosion of condensed explosive and a bulk explosion (explosion of vapor dustless mixtures). The explosions of condensed explosives are caused by all solid explosives and a relatively minor number of liquid explosives, including nitroglycerin. Such explosions typically have a density of 1300-1800 kg / m3, but the primary explosives containing lead or mercury have much large density.

Reaction decomposition:

The easiest case of the explosion is the process of decomposition with the formation of gaseous products. For example, decomposition of hydrogen peroxide with a large thermal effect and formation of water vapor and oxygen:

2N2O2 → 2N2O2 + O2 + 106 kJ / mole

Hydrogen peroxide is dangerous, starting with a concentration of 60%.

Decomposition by friction or impact of lead azide:

Pb (N3) 2 → PB 3N2 + 474 kJ / mol.

Trinitrotrololol (TNT) is a substance with "oxygen deficiency" and therefore, one of the main products of its decay is carbon, which contributes to the formation of smoke with the explosions of TNT.

Substances inclined to explosive decomposition almost always contain one or more characteristic chemical structures responsible for the sudden development of the process with the allocation of a large amount of energy. These structures include the following groups:

NO2 and NO3 - in organic and inorganic substances;

N \u003d n-n - in organic and inorganic azides;

Nx3, where X is a haloid,

N \u003d c in fulminata.

Based on the laws of thermochemistry, it is possible to identify compounds, the decomposition process of which may be explosive. One of the decisive factors determining the potential danger of the system is the prevalence of its internal energy in the initial state compared to the final state. Such a condition is performed at the absorption of heat (endothermic reaction) in the process of formation of matter. An example of the relevant process is the formation of acetylene from the elements:

2C + H2 → CH \u003d CH - 242 kJ / mol.

Not hazardous substances that lose heat in the formation of formation (exothermic reaction) include, for example, carbon dioxide

C + O2 → CO2 + 394 kJ / mol.

It should be borne in mind that the use of the laws of thermochemistry allows only to identify the possibility of an explosive process. Its exercise depends on the rate of reaction and the formation of volatile products. For example, the reaction of paraffin candles with oxygen, despite its high exothermic, does not lead to an explosion due to its low speed.

Reaction 2Al + 4As2O2 → AL2O3 + 2FE in itself, despite the high exothermic, also does not lead to an explosion, since gaseous products are not formed.

Redox reactions that constitute the basis of combustion reactions, for the indicated reason, can lead to an explosion only in conditions of conducive to achieving high reaction rates and pressure growth. The combustion of strongly dispersed solids and liquids can lead in conditions of closed volume to an increase in overpressure up to 8 bar relatively rarely, for example, in liquid air systems, where the aerosol is a fog of oil droplets.

In the polymerization reactions, accompanied by an exothermic effect, and the presence of a flying monomer is often achieved by a stage at which a hazardous increase in pressure may occur, for some substances such as ethylene oxide, polymerization can begin at room temperature. Especially when the initial compounds are contaminated with substances accelerating polymerization. Ethylene oxide may also be isomerized in acetaldehyde exothermal:

CH2SN2O - CH3NS \u003d O + 113,46 kJ / mol

The condensation reactions are widely used in the production of paints, varnishes and resins and due to the exothermic of the process and the presence of volatile components are sometimes brought to the explosions.

To clarify the general conditions conducive to the occurrence of combustion and its transition to an explosion, consider the graph (Figure 1) of the dependence of the temperature developed in the combustible system, if there is volumetric heat generation with it, due to the chemical reaction and heat loss.

If you present the temperature T1 on the chart as a critical point at which there is a combustion in the system, it becomes obvious that in conditions when there is an excess of heat loss over the thermal exploration, such combustion may not occur. This process begins only when the equality is reached between the heat generation rates and heat loss (at the point of touching the corresponding curves) and then it is capable of accelerating with increasing temperature and. Thereby pressing the explosion.

Thus, in the presence of conditions conducive to thermal insulation, the flow of an exothermic reaction in a combustible system can lead not only to the burning, but also to the explosion.

The emerging uncontrollable reactions, favorable explosion, are due to the fact that the heat transfer rate, for example, and vessels is a linear function of the temperature difference between the reaction mass and the cooler, while the speed of the exothermic reaction and, thereby, the flow of heat from it is growing in power, the law with An increase in the initial concentrations of reagents and rapidly increases with increasing temperature as a result of the exponential dependence of the chemical reaction rate on temperature (Arrhenius law). These patterns cause the smallest combustion speeds of the mixture and the temperature at the lower concentration limit of ignition. As the concentration of fuel and oxidant approaches the stoichiometric, the combustion rate and temperature increase to maximum signs.

The gas concentration of stoichiometric composition is a combustible gas concentration in a mixture with an oxidative medium, in which the chemical interaction of the fuel and oxidant of the mixture is fully ensured.

3. Features of the physical explosion

Physical explosions tend to bind to explosions of vessels from pressure of vapors and grooves. Moreover, the main reason for their formation is not a chemical reaction, but a physical process due to the release of the internal energy of compressed or liquefied gas. The strength of such explosions depends on the internal pressure, and the destruction is caused by a shock wave of expanding gas or fragments of a burst vessel. The physical explosion can occur in the case of, for example, the falling of the portable cylinder with a gas under pressure and a breakdown of the valve lowering the pressure. The pressure of liquefied gas rarely exceeds 40 bar (critical pressure of most ordinary liquefied gases).

Physical explosions also include the phenomenon of the so-called physical detonation. This phenomenon occurs when mixing hot and cold liquids, when the temperature of one of them significantly exceeds the boiling point of the other (for example, the pouring of the molten metal into the water). In the resulting pair-like mixture, evaporation can flow explosive due to the developing processes of thin phlegmatization drops of the melt, the rapid heat sink from them and overheating of the cold liquid with its strong vaporization.

Physical detonation is accompanied by a shock wave with excess pressure in the liquid phase, reaching in some cases more than a thousand atmospheres. Many liquids are stored or used in conditions when the pressure of their vapors significantly exceeds atmospheric. Such liquids include: liquefied combustible gases (for example, propane, butane) liquefied ammonia refrigerants or freon, stored at room temperature, methane, which should be stored under reduced temperature, overheated water in steam boilers. If the container with overheated liquid is damaged, there is a pair of expiration into the surrounding space and the rapid partial evaporation of the fluid. With a fairly fast expiration and expansion of steam in the environment, explosive waves are generated. The causes of explosions of vessels with gases and pressure pairs are:

Disorders of the housing integrity due to breakdowns of any node, damage or corrosion with improper operation;

Overheating of the vessel due to disorders in electrical heating or mode of operation of the filling device (in this case, the pressure inside the vessel is increased, and the strength of the case is reduced to the state at which damage occurs);

Explosion vessel when exceeding the allowable pressure.

The explosions of gas containers followed by combustion in the atmosphere based on its own the same causes that are described above and are characteristic of physical explosions. The main difference is to form a fiery ball in this case, the size of which depends on the amount of gaseous fuel thrown into the atmosphere. This amount depends, in turn, from the physical condition in which gas is in the container. When the content of fuel in a gaseous state, its amount will be much smaller than in the case of storage in the same container in liquid form. The explosion parameters that determine its consequences are mainly determined by the nature of the energy distribution in the explosion region and its distribution as the explosive wave spreads from the source of the explosion.

4. Energy potential

The explosion has a great destructive ability. The most important characteristic of the explosion is the total energy of the substance. This indicator is called the energy potential of explosion hazard, it enters all parameters characterizing the scope and effects of the explosion.

In emergency depressurization of the apparatus, its full disclosure (destruction);

The spiring area of \u200b\u200bthe liquid is determined on the basis of the design solutions of the buildings or the external installation site;

The time of evaporation is accepted not more than 1 hour:

E \u003d EII1 + EII2 + EII1 + EII2 + EII3 + EII4,

explosion fire room danger

where EI1 is the sum of the energies of the adiabatic expansion and combustion of the vapor phase (PGFH directly in block, KJ;

EI2 - the combustion energy of the GPF, which entered the depressurized area from adjacent objects (blocks), KJ;

EII1- Energy of the combustion of GTHF, which is generated due to the energy of the superheated fry of the block under consideration and received from the adjacent KJ objects;

EII2 - the combustion energy of the PGF, which is generated from the liquid phase (SHA) due to the heat of exothermic reactions that do not stop during depressurization, KJ;

EII3 - Energy of combustion of PGF. formed from the external coolant for heat transfer from external coolants, KJ;

EII4 - The combustion energy of the PGF, formed from the spilled on the solid surface (floor, pallet, soil, etc.) of the exhaustion by heat transfer from the environment (from the solid surface and air, to the liquid on its surface), KJ.

According to the values \u200b\u200bof the total energy potentials of explosion and the values \u200b\u200bof the above mass and relative energy potential characterizing the explosion hazard of technological blocks are determined.

The above mass is the total mass of combustible vapors (gases) of an explosive vapor-gas cloud, which is reduced to a single combustion energy equal to 46000 kJ / kg:

The relative energy potential of the explosiveness of a combination of a technological unit, which characterizes the total combustion energy and may be the calculated method according to the formula:

where E is the total energy potential of the explosive of the technological unit.

According to the values \u200b\u200bof the relative energy potentials of the transmission mass of the vapor, the technological blocks are categorized. The indicators of the explosive category of technological blocks are shown in Table 1.

Table No.

Explosioning category	OV	m.
I.	>37	>5000
II.	27 − 37	2000−5000
III	<27	<2000

5. TROTIL EQUIVAL. Overpressure at the front of the shock wave

To assess the level of exposure to random and intentional in the breakdowns, the method of evaluation through the TNT equivalent is widely used. Under this method, the destruction destruction is characterized by a TNT equivalent, which determine the mass of trotyl, which is required to cause this level of destruction. Chemically unstable compounds, calculated by formulas:

1 for vapor

q / - specific heat combustion of the vapor-gas environment, kg kg,

qt - the specific energy of the explosion of TNT KJ / kg.

2 for solid and liquid chemically unstable compounds

where WK is the mass of solid and liquid chemically unstable compounds; QK- The specific energy of the explosion of solid and liquid chemically unstable compounds. At the production of a gas-air, steam-air mixture or dust, a shock wave is formed. The degree of resolution of building structures, equipment, machinery and communications, as well as the defeat of people depends on overpressure in the front of the shock wave ΔРФ (the difference between the maximum pressure at the shock wave front and normal atmospheric pressure before this front).

Calculations for estimating the effect of combustible chemical gases and liquids are reduced to the determination of overpressure in the front of the shock wave (ΔРФ) during the explosion of the gas-air mixture at a certain distance from the tank, in which a certain amount is stored in an explosive mixture.

6. Calculation by definition of excessive explosion pressure

The calculation of excessive explosion pressure for combustible gases, vapors of flammable and combustible liquids is made according to the method described in the NPB 105-03 "Definition of categories of premises, buildings and external installations in the explosion and fire hazard."

Task: Determine the excess pressure of the explosion of hydrogen sulfide indoors.

Source conditions

A mode is constantly in a 20 m3 apparatus. The device is located on the floor. The total length of pipelines with a diameter of 50 mm, limited by valves (manual), mounted on the supply and discharge plots of pipelines, is 15 m. The consumption of hydrogen sulfide in pipelines 4 · 10-3 m3 / s. Premises size - 10x10x4 m.

Indoors have emergency ventilation with multiplicity of air exchange 8 h-1. Emergency ventilation is provided with backup fans, automatic starting when exceeding the maximum allowable explosive concentration and power supply on the first category of reliability (PUE). Devices for removing air from the room are located in close proximity to the place of the possible accident.

The main building structures of the building reinforced concrete.

Justification of the estimated option

According to the NPB 105-03, the most unfavorable option of the accident should be taken as the calculated accident, in which the largest amounts of substances are most dangerous in relation to the effects of the explosion.

And as the calculated version, a variant of the depressurization of the container with hydrogen sulfide is adopted and the yield from it and input and the reducing hydrogen sulfide pipelines into the size of the room.

1) Excessive explosion pressure for individual combustible substances consisting of atoms C, H, O, N, CL, BR, I, F, is determined by the formula

(1)

where is the maximum pressure of the explosion of a stoichiometric gas-air or steam-air mixture in a closed volume, determined experimentally or on reference data in accordance with the requirements of P.3 NPB -105-03. In the absence of data it is allowed to take equal to 900 kPa;

Initial pressure, kPa (allowed to take equal to 101 kPa);

The mass of combustible gas (GG) or vapors of flammable (LVZ) and flammable liquids (GZH), which came out as a result of an accident room, kg;

The coefficient of combustible participation in the explosion, which can be calculated on the basis of the nature of the distribution of gases and vapors in the size of the room under the annex. It is allowed to make a value in Table. 2 NPB 105-03. I take 0.5;

Free space;

For the calculated temperature, the maximum absolute air temperature for G.Ufu is taken (according to SNiP 23-01-99 "Construction climatology").

Below is the calculation of the values \u200b\u200bnecessary to determine the excess pressure of the explosion of hydrogen sulfide indoors.

Density of hydrogen sulfide at the calculated temperature:

where M is the molar mass of hydrogen sulfide, 34.08 kg / kmol;

v0 is a molting volume equal to 22,413 m3 / kmol;

0.00367- The coefficient of temperature expansion, hail -1;

tP - Calculated temperature, 390s (absolute maximum air temperature for Ufa).

The stoichiometric concentration of hydrogen sulfide is calculated by the formula:

;

where β is the stoichiometric coefficient of oxygen in the combustion reaction;

nC, NN, N0, NX, - the number of atoms with, n, o and halides in the fuel molecule;

For hydrogen sulfide (H2S) nc \u003d 1, nn \u003d 4, n0 \u003d 0, nx \u003d 0, therefore,

We substitute the value of β, we obtain the value of the stoichiometric concentration of hydrogen sulfide:

The size of the hydrogen sulfide of the premises received at the calculated accident, consists of a gas volume that came out of the apparatus, and the volume of gas released from the pipeline to the closure of the valves and after closing the valves:

where Va is the volume of gas published from the device, m3;

V1T - the volume of gas published from the pipeline before it is turned off, m3;

V2T - the volume of gas released from the pipeline after it is turned off, m3;

where quantity of fluid flow, determined in accordance with the technological regulations, M3 / s;

T - the duration of gas flow into the size of the room, determined by paragraph 38 of the NPB 105-03 C;

where D is the inner diameter of pipelines, m;

Ln - length of pipelines from the emergency apparatus to valves, m;

Thus, the size of the hydrogen sulfide entered the room under the version of the accident:

Mass of hydrogen sulfide indoors:

In the case of referenceing combustible gases, flammable or combustible gases, flammable or combustible liquids in determining the mass value, it is allowed to take into account the operation of emergency ventilation, if it is provided with backup fans, automatic starting when the maximum allowable explosion-proof concentration and power supply on the first category of reliability is exceeded (PUE ), subject to the location of the devices for removing air from the room in the immediate vicinity of the location of the possible accident.

In this case, the mass of flammable gases or vapors of flammable or combustible liquids heated to the flash temperature and above, which entered the volume of the room should be divided into the coefficient determined by the formula

where - the multiplicity of air exchange created by emergency ventilation, 1 / c. In this room there is ventilation with multiplicity of air exchange - 8 (0.0022c);

The duration of the flow of combustible gases and vapors of flammable and combustible liquids into the size of the room, C, accepting equal to 300 seconds. (P.7 NPB 105-03)

The mass of the hydrogen sulfide, located in the room under consideration of the accident:

Explosion calculation results

Option number	Combustible gas	Value, kpa

Hydrogen sulfide		5	Medium damage to buildings

Table. Maximum allowable overpressure during the combustion of gas, vapor or dusty mixtures in rooms or in open space

The source and calculated data are reduced to Table 2.

Table 2 - source and calculated data

No. p / p	Name	Designation	Value
1	Substance, its name and formula	Hydrogen sulfide	H2s.
2	Molecular weight, kg · kmol-1	M.	34,08
3	Fluid density, kg / m3	ρzh.	-
4	Gas density at calculating temperature, kg / m3	ρG.	1,33
5	Medium temperature (air to explosion), 0С	T0.	39
6	Pressure of saturated vapor, kPa	PH	28,9
7	Stoichiometric concentration,% vol.	CST	29,24
8	Room size - Length, m - Width, m - Height, m
9	Pipeline sizes: - diameter, m -Tlin, M.
10	Heptane consumption in pipeline, m3 / s	q.	4 · 10-3.
11	Closing time valves, with	t.	300
12	Emergency ventilation multiplicity, 1 / hour	A.	8
13	Maximum explosion pressure, kPa	Pmax.	900
14	Initial pressure, kpa	P0.	101
15	The coefficient of leakage and non-adhesion	KN	3
16	Fuel participation ratio in the explosion	Z.	0,5

According to the NPB 105-2003, the rooms of the premises on the explosion and fire hazard are accepted in accordance with Table 4.

Category of premises	Characteristics of substances and materials located (applying) indoors
And the explosion	Combustible gases, flammable fluids with an outbreak temperature of no more than 28 ° C in such a quantity, which can form explosive steam outdoor mixtures, with the ignition of which the calculated excessive pressure of the explosion in the room develops., Exceeding 5 kPa. Substances and materials capable of exploding and burning when interacting with water, air oxygen or each other in such a quantity that the calculated excessive excess explosion pressure in the room exceeds 5 kPa.
explosion-dangerous	Combustible dust or fibers, flammable fluids with an outbreak temperature of more than 28 ° C, combustible fluids in such a quantity that can form explosive dusty or steam-air mixtures, with the ignition of which the calculated excessive pressure of the explosion in a room exceeds 5 kPa.
B1-B4 Fire hazardous	Combustible and hard-scale fluids, solid combustible and hard-burning substances and materials (including dust and fibers), substances and materials. Capable when interacting with water, air oxygen or with each other only to burn under the condition that the rooms in which the rooms in which are They are available or appeal, do not belong to categories A or B.
G.	Non-combustible substances and materials in hot, red or molten state, the processing process of which is accompanied by the release of radiant heat, sparks and flames; Combustible gases, liquids and solids that are burned or disposed of fuel.
D.	Non-combustible substances and materials in cold condition,

Conclusion: The room refers to the category A, since it is possible a fuel gas yield (hydrogen sulfide) in such a quantity, which can form explosive steam outdoor mixtures, with the ignition of which the calculated excessive pressure of the explosion explosion is developing exceeding 5 kPa.

8. Determining the values \u200b\u200bof the energy indicators of the explosion hazard of the technological unit during the explosion

The energy potential of the explosion supply E (CJ) of the unit is determined by the total combustion energy of the vapor phase in the block, taking into account the magnitude of its adiabatic expansion, as well as the magnitude of the total combustion of the evaporated fluid from the maximum possible area of \u200b\u200bits strait, and it is considered:

1) in emergency depressurization of the device, its complete disclosure (destruction) occurs;

2) the spiring area of \u200b\u200bthe liquid is determined on the basis of the design solutions of the buildings or the exterior site;

3) Evaporation time is taken no more than 1 h:

The sum of the energies of adiabatic expansion A (CJ) and the combustion of the PGF, which is in the block, KJ:

q "\u003d 23380 KJ / kg - the specific heat of the combustion of the PGF (hydrogen sulfide);

26.9 - Fuel Gas Mass

For practical determination of the energy of adiabatic expansion of PHF, you can use the formula

where B1 can be accepted by table. 5. If the adiabudes is indicated K \u003d 1,2 and the pressure of 0.1 MPa is 1.40.

Table 5. The value of the coefficient B1, depending on the indiabating indicator of the medium and pressure in the technological unit

Indicator	Pressure in the system, MPa
adiabat	0,07-0,5	0,5-1,0	1,0-5,0	5,0-10,0	10,0-20,0	20,0-30,0	30,0-40,0	40,0-50,0	50,0-75,0	75,0-100,0
k \u003d 1,1	1,60	1,95	2,95	3,38	3,08	4,02	4,16	4,28	4,46	4,63
k \u003d 1,2	1,40	1,53	2,13	2,68	2,94	3,07	3,16	3,23	3,36	3,42
k \u003d 1,3.	1,21	1,42	1,97	2,18	2,36	2,44	2,50	2,54	2,62	2,65
k \u003d 1,4.	1,08	1,24	1,68	1,83	1,95	2,00	2,05	2,08	2,12	2,15

0 KJ - Energy of the combustion of the PGF, which received a depressurized area from adjacent objects (blocks), KJ. There are no adjacent blocks, so this component is zero.

0 KJ is the combustion energy of the PGF, which is generated due to the energy of the superheated fry of the block under consideration and received from adjacent objects during Ti.

0 KJ - the energy of the combustion of the PGF, which is generated from the exothermal reactions due to the heat of exothermic reactions that are not stopped during depressurization.

0 KJ - the combustion energy of the PGF, which is generated from the external coolant from the external coolant.

0 KJ - Energy of the combustion of the PGF, formed from the spilled on a solid surface (floor, pallet, soil, etc.) of the exhaustion, due to heat transfer from the environment (from the solid surface and air to the liquid along its surface.

The energy potential of the explosion of the block is equal to:

E \u003d 628923,51 kJ.

According to the values \u200b\u200bof the total energy potentials of explosiveness e, the values \u200b\u200bof the above mass and relative energy potential characterizing the explosion hazard of technological blocks are determined.

The total mass of combustible vapors (gases) of the explosive vapor-gas cloud T given to the single specific combustion energy equal to 46,000 kJ / kg:

The relative energy potential of the explosion hazard of the technological unit is the estimated method according to the formula

According to the values \u200b\u200bof the relative energy potentials of the QB and the above mass of the vapor-gas medium, the technological blocks are categorized. Category indicators are given in Table. five.

Table 4. Indicators of explosion categories of technological blocks

Explosioning category	QB	m, kg.
I.	> 37	> 5000
II.	27 - 37	2000 - 5000
III	< 27	< 2000

Conclusion: The room belongs to the III of the explosion hazard category, since the total weight of the explosive hydrogen-sulfide vapor cloud is reduced to a single specific combustion energy, equal to 16.67 kg, the relative energy potential of the explosion is 5.18.

9. Calculation of the explosive concentration of the gas-air mixture indoors. Definition of a class of premises for the explosion hazard

We define the volume of explosive concentration of hydrogen sulfide indoors:

where T is the mass of the steam-air mixture in the room, kg,

NKPV - lower concentration limit of ignition, g / m3.

The concentration of the steam-air mixture in the room will be:

where VCM is the volume of the explosive concentration of hydrogen sulfide indoors, M3, VC6 - free space, m3.

The calculation results are presented in Table 6.

Table 6. Results of calculating the concentration of a gas-air mixture

According to the Pue, the premises under consideration refers to the class B-Ia - zones located in the premises in which, with normal operation, explosive mixtures of combustible gases (regardless of the lower limit of ignition) or vapors of the LVZ with air are not formed, and are only possible as a result of accidents and malfunctions.

10. Determination of explosion destruction zones. Classification zones of destruction

The radii zones of destruction during the explosion of the gas-air mixture was determined according to the procedure set out in Appendix 2 of PB 09-540-03.

The mass of the vapor-gas substances (kg) participating in the explosion is determined by the work

where Z is the proportion of the above mass of sulfide, participating in the explosion (for GG is 0.5),

t - Mass of hydrogen sulfide indoors, kg.

To assess the level of exposure to the explosion, a TROTIL equivalent can be applied. Trotyl equivalent of the explosion of the vapor-gas medium WT (kg) is determined by the conditions of the nature of the nature and degree of destruction in the explosions of the vapor-gas clouds, as well as solid and liquid chemically unstable compounds.

For the vapor-gas media, the TROTIL EQUIVALE OF THE BRAIN CALLES:

where 0.4 is the proportion of the energy of the explosion of the vapor-gas medium, spent directly on the formation of the shock wave;

0.9 - the proportion of energy of the trinitrotoloole explosion (TNT), spent directly on the formation of the shock wave;

q "-Fimal heat combustion of the vapor-gas environment, KJ / kg;

qt - the specific energy of the explosion of TNT, KJ / kg.

The destruction zone is considered to be the area with the boundaries defined by the R radius, the center of which is considered the technological unit or the most likely place of depressurization of the technological system. The boundaries of each zone are characterized by the values \u200b\u200bof excess pressures along the front of the shock wave of the AR and, accordingly, a dimensionless coefficient K. The classification of the destruction zones is provided in Table 6.

Table 7. The level of possible destruction with an explosive transformation of clouds of fuel-air mixtures

Class of destruction zone	ΔP, kpa	TO	Zone of destruction	Characteristics of the lesion zone
1	≥100	3,8	full	Destruction and collapse of all elements of buildings and structures, including basements, percentage of people survival; For administrative household buildings and buildings of the management of ordinary versions - 30%; For production buildings and constructions of ordinary performances - 0%.
2	70	5,6	strong	The destruction of parts of the walls and overlaps of the upper floors, the formation of cracks in the walls, the deformation of the overlaps of the lower floors. It is possible to limit the use of the preserved basements after clearing the inputs. People survival percentage: For administrative household buildings and buildings management of ordinary versions - 85%: For production buildings and constructions of ordinary performances - 2%
3	28	9,6	middle	Destruction is mainly secondary elements (roofs, partitions and door fills). Overlapping, as a rule, do not collapse. Part of the premises is suitable for use after clearing the debris and works of repair. The percentage of people survival: -For administrative buildings and buildings of the management of ordinary performances - 94%.
4	14	28	weak	Destruction of window and door fills and partitions. The basements and lower floors are fully saved and suitable for temporary use after cleaning the garbage and sealing openings. The percentage of people survival: - for administrative household buildings and buildings of the management of ordinary performances - 98%; Production buildings and constructions of ordinary performances - 90%
5	≤2	56	disposals	Destruction of glass fillings. Percentage of surviving people- 100%

The radius of the zone of destruction (M) is generally determined by the expression:

where K is a dimensionless coefficient characterizing the impact of an explosion to the object.

The results of the calculation of radii zones of destruction during the explosion of the fuel and air mixture in the room are presented in Table 7.

Table 7 - Results of calculation of radii areas of destruction

List of sources used

1. Beschens M.V. Industrial explosions. Evaluation and warning. - M. Chemistry, 1991.

2. Safety of vital activity, safety of technological processes and industries (labor protection): studies, manual for universities / P.P. Kukin, V.L. Lapin, N, L. Ponomarev and others - m. ,: Higher. Shk.t 2001,

3. PB 09-540-03 "General rules of explosion safety for explosion hazardous chemical, petrochemical and oil refineries."

4. GOST 12.1,010-76 * explosion safety

5. NPB 105-03 "Definition of categories of premises and buildings, external installations for the explosive and fire danger."

6. Snip 23 -01-99 Construction climatology.

7. Firelessness of the substances and materials and their extinguishing means. Ed. A "N. Baratova and A. Ya. Korolchenko. M., Chemistry, 1990. 8. Rules of the device of electrical installations. Ed. 7th.

Flame Movement for Gas Mix called flame spread. Depending on the rate of propagation of the flame, the combustion may be declated at a speed of several m / s, explosive - the speed of about tens and hundreds of m / s and detonation - thousands of m / s.
For delaning or normal combustion The heat transfer from the layer to the layer is characteristic, and the flame arising in heated and diluted with active radicals and the reaction products of the mixture is moved towards the initial combustible mixture. This is explained by the fact that the flame, as it were, becomes a source that distinguishes a continuous flow of heat and chemically active particles. As a result, the front of the flame and moves towards the combustible mixture.
Delagrament burningdivided into laminar and turbulent.
Laminar burning is inherent in the normal rate of flame propagation.
The normal speed of the flame spread, according to GOST 12.1.044 of the SSBT, is called flame Front Travel Speed Regarding the unburned gas, in the direction, perpine-dicular to its surface.
The value of the normal flame propagation rate, being one of the indicators of fire and explosive substances, characterizes the risk of industries related to the use of liquids and gases, it is used in calculating the rate of increasing the explosive pressure of gas, steam-air mixtures, critical (quenching) diameter and when developing events , providing fire and explosion safety of technological processes in accordance with the requirements of GOST 12.1.004 and GOST 12.1.010 of the SSBT.
Normal flame propagation rate is a physico-chemical constant of the mixture - depends on the composition of the mixture, pressure and temperature and is determined by the rate of chemical reaction and molecular thermal conductivity.
The temperature relatively poorly increases the normal rate of flame propagation, the inert impurities reduce it, and the increase in pressure leads either to an increase or to a decrease in speed.
In laminar gas stream Gas velocities are small, and the combustible mixture is formed as a result of molecular diffusion. The combustion rate in this case depends on the rate of formation of a combustible mixture. Turbulent flames It is formed with an increase in the rate of flame propagation, when the laminarness of its movement is disturbed. In a turbulent flame, gas jet curling improves mixing of reacting gases, since the surface increases through which the molecular diffusion occurs.
As a result of the interaction of the combustion substance with the oxidizer, combustion products are formed, the composition of which depends on the initial compounds and the conditions of the combustion reaction.
In full combustion of organic compounds, CO 2, SO 2, H 2 O, N 2 are formed, and during the combustion of inorganic compounds - oxides. Depending on the melting point, the reaction products can either be in the form of a melt (AL 2 O 3, TIO 2), or rise into the air in the form of smoke (P 2 O 5, NA 2 O, MGO). Melted solid particles create flame luminosity. When burning hydrocarbons, the strong luminosity of the flame is ensured by the luminescence of carbon black particles, which is formed in large quantities. Reducing the maintenance of carbon black as a result of its oxidation reduces the luminosity of the flame, and the decrease in temperature makes it difficult to oxidation of carbon black and leads to the formation of a soot.
In order to interrupt the combustion reaction, it is necessary to disrupt the conditions for its occurrence and maintenance. Usually, there is a violation of the two main conditions of the stable state - a decrease in temperature and movement of gases.
Reducing temperature It can be achieved by inventive substances that absorb a lot of heat as a result of evaporation and dissociation (for example, water, powders).
Mode Movement Gas It can be changed by reducing and eliminating the inflow of oxygen.
Explosion, according to GOST 12.1.010 " Explosion safety", I would like the transformation of the substance (explosive burning), accompanied by the release of energy and the formation of compressed gases capable of producing work.
The explosion, as a rule, leads to an intensive pressure growth. In the environment, a shock wave is formed and distributed.
Shock wave It has a devastating ability if the former pressure in it is above 15 kPa. It applies to the gas in front of the flame front with sound speed - 330 m / s. In the explosion, the initial energy is converted into the energy of heated compressed gases, which goes into the energy of movement, compression and heating of the medium. Various types of the initial explosion energy are possible - electrical, thermal, elastic compression energy, atomic, chemical.
The main parameters characterizing the danger of an explosion in accordance with GOST 12.1.010 - pressure on the front of the shock wave, the maximum pressure of the explosion, the average and maximum pressure rate of the explosion, crushing or fugasic properties of the explosive medium.
The overall action of the explosion It is manifested in the destruction of equipment or premises caused by a shock wave, as well as in the selection of harmful substances (explosion products or contained in the equipment).
Maximum explosion pressure (P MAX) - the greatest pressure arising in the deflagration explosion of the gas, vapor or dusty mixture in the closed vessel with the initial pressure of the mixture of 101.3 kPa.
Explosion rate of explosion(DR / DT) - an aqueous pressure of the explosion in time on the ascending section of the dependence of the pressure of the explosion of the gas, steam, dusty mixture in a closed vessel from time. At the same time, the maximum and average rate of increase in the explosion is distinguished. When setting the maximum speed, the pressure is used in the straight line of the pressure of the explosion from time to the rectilinear section, and when the average speed is determined, the area between the maximum explosion pressure and the initial pressure in the vessel to the explosion.
Both of these characteristics are important factors to provide explosion protection. They are used in the establishment of the category of rooms and buildings in the explosive and fire hazard, when calculating safety devices, when developing measures for fire and explosion safety of technological processes.
Detonation There is a process of chemical transformation of the oxidizer system - a reducing agent, which is a totality of a shock wave propagating at a constant speed and exceeding the speed of the sound, and the front of the zone of the chemical transformations of the source substances. Chemical energy, emitted in the detonation wave, feeds the shock wave without letting it fade. The speed of the detonation wave is the characteristic of each specific system.

The theory argues that the imaging and the steam-air mixture is not instant. When an ignition source is introduced into a combustible mixture, a fuel oxidation reaction with an oxidizing agent in the ignition source zone begins. The speed of the oxidation reaction in some elementary volume of this zone reaches the maximum - burning arises. The combustion of the elementary volume with the medium is called the front of the flame. Flame front has the type of sphere. Flame front thickness, by calculations Ya.B. Zeldovich , equal to 1-100 μm. Although the thickness of the combustion zone and is small, but sufficient to flow the combustion reaction. The temperature of the flame front due to heat of the combustion reaction is 1000-3000 ° C and depends on the composition of the combustible mixture.

When the flame front is moving, the temperature of the unlawful part of the combustible mixture increases, since the pressure of the mixture increases. Near the flame front temperature of the mixture also rises, due to
Processing heat with thermal conductivity, diffusion of heated molecules and radiation. On the outer surface of the flame front, this temperature is equal to the temperature of self-ignition combustion mixture.

After the flamm of the combustible mixture, the spherical shape of the flame is very quickly distorted and is increasingly stretched in the direction of a non-flammable mixture. Stretching the flame front and the rapid increase in its surface is accompanied by an increase in the speed of movement of the central part of the flame. This acceleration lasts until the flame is touched by the pipe walls or, in any case, will not get closer to the pipe wall. At this point, the flame size decreases sharply, and only a small part remains from the flame, overlapping the entire section of the pipe. Flame front pull
And its intensive acceleration immediately after the ignition is sparking, when the flame has not reached the pipe walls, is caused by an increase in the volume of combustion products. Thus, in the initial stage of the process of formation of the flame front, regardless of the degree of flammability of the gas mixture, there is an acceleration and subsequent braking of the flame, and this braking will be the greater the greater the speed of the flame.

The width of the heating zone (in cm) can be determined from the dependence

1 \u003d a / v

where but- temperature coefficient; v.- Flame spread rate.

Linear movement speed v.(in m / s) can be determined by the formula

V \u003d V T /

where V T. - mass combustion rate, g / (with m 3); - density of the initial combustible mixture, kg / m 3.

The linear speed of moving the front of the flame is inconstant, it changes depending on the compositions. Mixtures and impurities of inert (non-combustible) gases, temperature of the mixture, diameter of pipes, etc. The maximum rate of flame propagation is observed not at the stoichiometric concentration of the mixture, but in a mixture with an excess of fuel. When introduced into a combustible mixture of inert gases, the rate of propagation of the flame is reduced. It is explained by a decrease in the combustion temperature of the mixture, since part of the heat is consumed for heating not involved in the reaction of inert impurities.

With increasing pipe diameter, the flame propagation rate grows unevenly. With an increase in the diameter of pipes to 0.1-0.15 m, the speed grows pretty quickly. The increase in temperature occurs until the diameter reaches some limit diameter,
above which the increase in speed does not occur. With a decrease in the pipe diameter, the rate of flame propagation decreases, and at a small diameter, the flame in the pipe does not apply. This phenomenon can be explained by the increase in thermal losses through the walls.
Pipes.

1) constant burning rate independently of the diameter of the pipe;

As the flame is accelerated, the amplitude of the shock wave is growing, the compression temperature reaches the temperature of self-ignition of the mixture.

An increase in the total amount of gas combining per unit is explained by the fact that in the jet with a variable in cross section, the front of the flame is bent, as a result of this, its surface increases and the amount of the combustible substance increases in proportion.

When burning gas mixtures in a closed volume, combustion products do not work; The energy of the explosion is consumed only on the heating of the explosion products. In this case, the total energy is defined as the sum of the internal energy of the explosive mixture Q VN.M.Sm. And the heat of burning of this substance ΔQ. The value of Q VN.N.M. equal to the amount of the heat capacity of the components of the explosive mixture at a constant volume on the initial temperature
Perats of the mixture

Q VN.Eng.Sm. \u003d C 1 t + with 2 t + ... + with p t

where C 1, C 2, C n is the specific heat capacity of the components constituting
explosive mixture, kJ / (kg k); T -the initial temperature of the mixture, K.

The temperature of the explosion of gas mixtures with a constant volume is calculated by the same method as the combustion temperature of the mixture at a constant pressure.

In the temperature of the explosion, the explosion pressure is found. The pressure during the explosion of the gas-air mixture in a closed volume depends on the temperature of the explosion and the ratio of the number of molecules of combustion products to the molecules in the explosive mixture. When the gas-air blending explosion, the pressure usually does not exceed 1.0 MPa if the initial pressure of the mixture was normal. When replacing air in an explosive mixture with oxygen, the explosion pressure sharply increases, since the combustion temperature increases.

Pressure of the explosion of stoichiometric mixtures of methane, ethylene, acetone and
Oxygen methyl ether is 1.5 - 1.9 MPa, and the stoichiometric mixtures of them with air 1.0 MPa.

r TIS \u003d.

where p 0.- the initial pressure of the explosive mixture, MPa; T 0.and T rv - the initial temperature of the explosive mixture and the temperature of the explosion, K;

Number of molecules of gases of combustion products after an explosion;
- The number of molecules of gases of the mixture to the explosion.