The combustion stage is preceded by the stage of fuel ignition, associated with its heating. This stage does not require oxygen and during its occurrence the fuel itself is a consumer of heat. The faster the fuel temperature rises, the more intense the ignition occurs. Obviously, the factors that delay ignition are: high fuel moisture, increased ignition temperature, small heat-receiving surface of the fuel, low initial temperature of the fuel and the supply of unpreheated air to the firebox.
The combustion stage is the main consumer of air. At this stage, the main part of the fuel heat is released and the highest temperatures develop. The more volatile substances the fuel emits, the more intense the combustion and the more concentrated the air must be supplied. The afterburning stage requires some air; Accordingly, little heat is generated here.
The hydrogen burning stage is the longest in the life of a star. The photon luminosity of stars on the main sequence, where hydrogen burns, is, as a rule, less than at subsequent stages of evolution, and their neutrino luminosity is much lower, due to the fact that central temperatures do not exceed - 4 107 K. Therefore, main sequence stars are the most common stars in the Galaxy and throughout the universe (see Chap.
The hydrogen burning stage in the core takes up most of the star's life, with stars of about solar mass remaining on the main sequence for about 1010 years. The corresponding stage for stars with mass 20 MQ lasts only 106 years, while stars with mass 0 3M0 are expected to spend 3 1011 years at this stage, which is 30 times the age of the Galaxy.
The combustion stage of gaseous fuels and coke is accompanied by the release of heat, which provides an increase in temperatures necessary to accelerate coke oxidation reactions.
During the combustion stage, the bulk of the air is consumed and the bulk of the heat of the fuel is released. Temperatures at this stage of the process reach highest values. The combustion of volatile substances occurs most quickly, which therefore requires a concentrated air supply and great attention to ensuring rapid and complete mixture formation.
The combustion stage includes the combustion of volatiles, coke at temperatures above 1000 C, accompanied by the consumption of most of the required air and release of the main amount of heat. The combustion stage is characterized by the highest temperature. Combustion of volatiles occurs quickly, so it is extremely important to supply a sufficient amount of air in a concentrated manner under conditions of complete mixture formation. Coke burns more slowly, and the reaction of carbon with oxygen occurs on the surface of the coke particles. The intensity of coke combustion is higher, the finer the fuel is crushed. The final stage of combustion solid fuel is afterburning, which requires less air and is accompanied by less heat release. The development of this stage is delayed due to the enveloping of coke particles with ash, which impedes air access to them, especially for fuels with low-melting ash.
Secondly, the stage of combustion of coke residue turns out to be the longest of all stages and can take up to 90% of the total time required for combustion.
The combustion stages discussed above liquid fuel- heating, evaporation and pyrogenetic decomposition of atomized particles of fuel often do not proceed efficiently enough, in addition, they are not sufficiently controllable, which led to the appearance of burner nozzles with preliminary gasification of liquid fuel.
At the beginning of the combustion stage, immediately after the moment of ignition of the fuel, the temperature is not yet very high. Accordingly, the burning rate is low. Therefore, rapid ignition of the fuel and rapid rise in process temperature are very important. Further, in the main part of the combustion stage, the temperature level in the boiler furnaces is already quite high. Accordingly, the rate of reaction of carbon with oxygen on the surface of coke particles is also high. Therefore, the rate of coke burnout is limited in the main part of the coke combustion stage not by this factor, but by the diffusion processes of oxygen supply to the burning particles, which proceed relatively more slowly. At proper organization In the initial part of the combustion stage, it is these processes that in most cases serve as the main factor regulating the intensity of coke combustion in boiler furnaces.
| Dependence of the ratio of the radius of the glow zone to the initial radius of an aluminum-magnesium alloy particle on its relative combustion time fl. |
Combustion is the process of interaction of fuel with an oxidizer, accompanied by the release of heat and sometimes light. In the vast majority of cases, oxygen in the air plays the role of an oxidizing agent. Any combustion involves, first of all, close contact between the molecules of the fuel and the oxidizer. Therefore, for combustion to occur, this contact must be ensured, i.e., it is necessary to mix fuel with air. Consequently, the combustion process consists of two stages: 1) mixing of fuel with air; 2) fuel combustion. During the second stage, first ignition occurs, and then combustion of the fuel occurs,
During the combustion process, a flame is formed in which combustion reactions of the fuel components occur and heat is released. In technology, when burning gaseous, liquid and solid pulverized fuels, the so-called flare combustion method is used. The torch is special case flame, when fuel and air enter the working space of the furnace in the form of jets, which are gradually mixed with one another. Therefore, the shape and length of the torch are usually quite definite.
In the case of flaring fuel combustion, which is the most common in metallurgy and mechanical engineering, the aerodynamic basis of the process is made up of jet flows, the study of which is based on the application of the principles of the theory of free turbulence to various cases. Since during flare combustion the nature of the jet movement can be laminar and turbulent, molecular and turbulent diffusion play a large role in mixing processes. In practice, when creating devices for burning fuel (burners, nozzles), various design techniques are used (directing jets at an angle to each other, creating swirling jets, etc.) in order to organize mixing as necessary for a specific case of fuel combustion.
There are homogeneous and heterogeneous combustion. With homogeneous combustion, heat and mass transfer occur between bodies that are in the same state of aggregation. Homogeneous combustion occurs in volume and is characteristic of gaseous fuel.
During heterogeneous combustion, heat and mass transfer occur between bodies in different states of aggregation (the gas and the surface of fuel particles are in a state of exchange). Such combustion is characteristic of liquid and solid fuels. True, during the combustion of liquid and solid fuels, due to the evaporation of droplets and the release of volatiles, there are elements of homogeneous combustion. However, in a heterogeneous process, combustion mainly occurs from the surface.
Homogeneous combustion can occur in the kinetic and diffusion regions.
During kinetic combustion, complete mixing of fuel with air is carried out in advance, and a pre-prepared fuel-air mixture is supplied to the combustion zone. In this case, the main role is played chemical processes associated with the occurrence of fuel oxidation reactions. With diffusion homogeneous combustion, the processes of mixing and combustion are not separated and occur almost simultaneously. In this case, the combustion process is determined by mixing, since the mixing time is much longer than the time required for the chemical reaction to occur. Thus, full time the course of the combustion process consists of the time of mixture formation (τ cm) and the time of the chemical reaction itself (τ x), i.e.
During kinetic combustion, when the mixture is pre-prepared
With diffusion combustion, on the contrary, the mixing time is immeasurably longer than the time of the chemical reaction.
In heterogeneous combustion of solid fuels, kinetic and diffusion response regions are also distinguished. The kinetic region occurs when the rate of diffusion in the pores of the fuel significantly exceeds the rate of the chemical reaction; the diffusion region occurs when the ratio of the rates of diffusion and combustion is inverse.
From the point of view of mixture formation, carried out using gas burner devices, the organization of fuel combustion processes in air flow can be carried out on the basis of three principles: diffusion, kinetic and mixed.
The appearance of a flame
The occurrence of a flame (ignition of the fuel) can only occur after the necessary contact between the fuel molecules and the oxidizer has been achieved. Any oxidation reaction occurs with the release of heat. At first, the oxidation reaction proceeds slowly with the release of a small amount of heat. However, the heat released helps to increase the temperature and speed up the reaction, which in turn leads to a more energetic release of heat, which again has a beneficial effect on the development of the reaction. Thus, there is a gradual increase in the reaction rate until the moment of ignition, after which the reaction proceeds at a very high speed and has an avalanche character. In oxidation reactions, the mechanism of the chemical reaction and thermal characteristics oxidation process. The primary factor is the chemical reaction and the secondary factor is the release of heat. Both of these phenomena are closely related and influence each other.
It has been established that ignition is possible both under isothermal conditions and with increasing temperature. In the first case, the so-called chain ignition occurs, in which the reaction rate increases as a result of an increase in the number of active centers that arise only as a result of chemical interaction. More often, ignition occurs under non-isothermal conditions, when an increase in the number of active centers occurs as a result of both chemical interaction and thermal effects. IN practical conditions Usually they resort to artificial ignition of fuel, introducing a certain amount of heat into the combustion zone, which leads to a sharp acceleration of the moment of achieving ignition.
The ignition temperature is not a physicochemical constant determined only by the properties of the mixture; it is determined by the conditions of the process, i.e., the nature of heat exchange with the environment (temperature, shape of the vessel, etc.).
Flash points various fuels are given in Table 5.
Table. 5 - Ignition temperatures in air at atmospheric
spheral pressure.
In addition to temperature, the concentration of the combustible component in the mixture has a great influence on the process of fuel ignition. There are minimum and maximum concentrations of the combustible component, below and above which forced ignition cannot occur. Such limiting concentrations are called lower and upper flammability limits; their values for some gases are given in Table 6.
Table 6 - Flammability limits in air and oxygen mixtures at atmospheric pressure and temperature 20 o C
| Flammable gas | Chemical formula | Concentration limits ignition in air mixtures, % gas by volume | Concentration limits of ignition in oxygen mixtures, % gas by volume | ||
| Hydrogen Carbon monoxide Methane Ethane Propane Butane Pentane Hexane Heptane Octane Ethylene Acitylene Benzene Methyl alcohol Ethyl alcohol Carbon disulfide Hydrogen sulfide Water gas Coke gas Natural gas Blast gas | H 2 CO CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12 C 6 H 14 C 7 H 16 C 8 H 18 C 2 H 4 C 2 H 2 C 6 H 6 CH 3 OH CH 5 OH CS H 2 S - - - - | 12,5 3,22 2,37 1,86 1,4 1,25 1,0 0,95 3,75 2,5 1,41 6,72 3,28 1,25 4,3 6,0 5,6 5,1, | 74,2 74,2 12,45 9,5 8,41 7,8 6,9 6,0 - 29,6 6,75 36,5 18,95 50,0 45,50 28-30,8 12,1-25 65-73,9 | 4,65 15,5 5,4 4,1 2,3 1,8 - - - - 2,9 3,5 2,6 - - - - - - - - | 93,9 93,9 59,2 50,5 - - - - 79,9 89,4 - - - - - - - - |
To set flammable limits industrial gases, which are a mixture of various flammable components, use Le Chatelier’s rule, according to which
Fuel combustion is a process of oxidation of combustible components that occurs at high temperatures and is accompanied by the release of heat. The nature of combustion is determined by many factors, including the combustion method, furnace design, oxygen concentration, etc. But the conditions, duration and final results of combustion processes largely depend on the composition, physical and chemical characteristics of the fuel.
Fuel composition
Solid fuels include hard and brown coal, peat, oil shale, and wood. These types of fuels are complex organic compounds formed mainly by five elements - carbon C, hydrogen H, oxygen O, sulfur S and nitrogen N. The fuel also contains moisture and non-flammable minerals, which after combustion form ash. Moisture and ash are the external ballast of the fuel, and oxygen and nitrogen are the internal ballast.
The main element of the combustible part is carbon; it causes the release of the greatest amount of heat. However, the greater the proportion of carbon in a solid fuel, the more difficult it is to ignite. Hydrogen, when burned, releases 4.4 times more heat than carbon, but its share in solid fuels is small. Oxygen, not being a heat-generating element and binding hydrogen and carbon, reduces the heat of combustion, and therefore is an undesirable element. Its content is especially high in peat and wood. The amount of nitrogen in solid fuel is small, but it can form oxides harmful to the environment and humans. Sulfur is also a harmful impurity; it produces little heat, but the resulting oxides lead to corrosion of the boiler metal and air pollution.
Technical characteristics of fuel and their influence on the combustion process
The most important technical characteristics fuels are: calorific value, yield of volatile substances, properties of non-volatile residue (coke), ash content and moisture content.
Heat of combustion of fuel
Heat of combustion is the amount of heat released during complete combustion of a unit of mass (kJ/kg) or volume of fuel (kJ/m3). There are higher and lower calorific values. The highest includes the heat released during the condensation of vapors contained in combustion products. When fuel is burned in boiler furnaces, the exhaust flue gases have a temperature at which the moisture is in a vapor state. Therefore, in this case, a lower calorific value is used, which does not take into account the heat of condensation of water vapor.
The composition and lower calorific value of all known coal deposits are determined and given in the calculated characteristics.
Release of volatile substances
When heating solid fuel without air access under the influence high temperature First, water vapor is released, and then thermal decomposition of the molecules occurs, releasing gaseous substances called volatile substances.
The release of volatile substances can occur in the temperature range from 160 to 1100 °C, but on average - in the temperature range of 400-800 °C. The temperature at which volatiles begin to emerge, the amount and composition of gaseous products depend on the chemical composition of the fuel. The chemically older the fuel, the lower the yield of volatiles and the higher the temperature at which they begin to emit.
Volatile substances ensure earlier ignition of the solid particle and have a significant effect on fuel combustion. Young fuels - peat, brown coal - ignite easily, burn quickly and almost completely. On the contrary, fuels with a low volatile yield, such as anthracite, are more difficult to ignite, burn much more slowly and do not burn completely (with increased heat loss).
Properties of non-volatile residue (coke)
The solid part of the fuel remaining after the release of volatiles, consisting mainly of carbon and mineral parts, is called coke. The coke residue can be, depending on the properties of the organic compounds included in the combustible mass: sintered, slightly sintered (destroyed upon exposure), powdery. Anthracite, peat, brown coals produce a powdery non-volatile residue. Most coals are sintered, but not always strongly. Cohesive or powdery non-volatile residue produces coals with a very high yield of volatiles (42-45%) and with a very low yield (less than 17%).
The structure of the coke residue is important when burning coal in grate furnaces. When flaring in power boilers, the characteristics of coke are not of great importance.
Ash content
Solid fuel contains the largest amount of non-combustible mineral impurities. This is primarily clay, silicates, iron pyrites, but may also include ferric oxide, sulfates, carbonates and silicates of iron, oxides of various metals, chlorides, alkalis, etc. Most of them fall during mining in the form of rocks between which coal layers lie, but there are also mineral substances that have passed into the fuel from coal-forming agents or in the process of converting its original mass.
When fuel is burned, mineral impurities undergo a series of reactions, resulting in the formation of a solid, non-combustible residue called ash. The weight and composition of the ash are not identical to the weight and composition of the mineral impurities of the fuel.
The properties of ash play a big role in organizing the operation of the boiler and furnace. Its particles, carried away by combustion products, abrade heating surfaces at high speeds, and are deposited on them at low speeds, which leads to a deterioration in heat transfer. Ash carried into chimney, can cause harm environment, to avoid this, the installation of ash collectors is required.
An important property of ash is its fusibility; a distinction is made between refractory (above 1425 °C), medium-melting (1200-1425 °C) and low-melting (less than 1200 °C) ash. Ash that has passed the melting stage and turned into a sintered or fused mass is called slag. The temperature characteristic of ash fusibility is of great importance to ensure reliable operation firebox and boiler surfaces, right choice gas temperatures near these surfaces will eliminate slagging.
Moisture is an undesirable component of fuel; along with mineral impurities, it acts as ballast and reduces the content of the combustible part. In addition, it reduces the thermal value, since additional energy is required for its evaporation.
Moisture in fuel can be internal or external. External moisture is contained in capillaries or retained on the surface. With chemical age, the amount of capillary moisture decreases. The smaller the fuel pieces, the greater the surface moisture. Internal moisture enters organic matter.
Methods of fuel combustion depending on the type of firebox
Main types of combustion devices:
- layered,
- chamber.
Layer furnaces are designed for burning large-piece solid fuel. They can be with a dense and fluidized layer. When burning in a dense layer, the combustion air passes through the layer without affecting its stability, that is, the gravity of the burning particles exceeds the dynamic pressure of the air. When burning in a fluidized bed, due to the increased air speed, the particles go into a “boiling” state. In this case, active mixing of the oxidizer and fuel occurs, due to which the combustion of the fuel is intensified.
In chamber furnaces, solid pulverized fuels, as well as liquid and gaseous ones, are burned. Chamber furnaces are divided into cyclone and flare. When flaring, coal particles should be no more than 100 microns; they burn in the volume of the combustion chamber. Cyclonic combustion allows larger size particles, under the influence of centrifugal forces they are thrown onto the walls of the furnace and completely burn out in a swirling flow in a high-temperature zone.
Fuel combustion. Main stages of the process
In the process of combustion of solid fuel, certain stages can be distinguished: heating and evaporation of moisture, sublimation of volatiles and the formation of coke residue, combustion of volatiles and coke, and formation of slag. This division of the combustion process is relatively arbitrary, since although these stages occur sequentially, they partially overlap each other. Thus, the sublimation of volatile substances begins before the final evaporation of all moisture, the formation of volatiles occurs simultaneously with the process of their combustion, just as the beginning of the oxidation of coke residue precedes the end of the combustion of volatiles, and the afterburning of coke can occur even after the formation of slag.
The duration of each stage of the combustion process is largely determined by the properties of the fuel. The coke combustion stage lasts the longest, even for fuels with a high volatile yield. A variety of operating factors and design features fireboxes
1. Preparing fuel before ignition
The fuel entering the furnace is heated, as a result of which, in the presence of moisture, it evaporates and the fuel dries. The time required for heating and drying depends on the amount of moisture and the temperature at which the fuel is supplied to the combustion device. For fuels with a high moisture content (peat, wet brown coals), the heating and drying stage is relatively long.
Fuel is supplied to layered furnaces at a temperature close to the environment. Only in winter time if coal freezes, its temperature is lower than in the boiler room. For combustion in flare and vortex furnaces, fuel is subjected to crushing and grinding, accompanied by drying with hot air or flue gases. The higher the temperature of the incoming fuel, the less time and heat is needed to heat it to the ignition temperature.
Drying of fuel in the furnace occurs due to two heat sources: convective heat of combustion products and radiant heat of the torch, lining, slag.
In chamber furnaces, heating is carried out mainly due to the first source, that is, mixing combustion products into the fuel at the point of its input. Therefore, one of the important requirements for the design of devices for introducing fuel into the furnace is to ensure intensive suction of combustion products. A higher temperature in the furnace also contributes to a reduction in heating and drying time. For this purpose, when burning fuels with the beginning of the release of volatiles at high temperatures (more than 400 ° C), incendiary belts are made in chamber fireboxes, that is, they are closed screen pipes fireproof thermal insulation material to reduce their heat perception.
When burning fuel in a bed, the role of each type of heat source is determined by the design of the furnace. In fireboxes with chain grates, heating and drying are carried out primarily radiant heat torch. In fireboxes with a fixed grate and fuel supply from above, heating and drying occur due to combustion products moving through the layer from bottom to top.
During heating at temperatures above 110 °C, thermal decomposition of organic substances included in the fuel begins. The least durable compounds are those that contain a significant amount of oxygen. These compounds decompose at relatively low temperatures with the formation of volatile substances and a solid residue consisting mainly of carbon.
Young by chemical composition fuels containing a lot of oxygen have a low temperature at which gaseous substances begin to emerge and produce a higher percentage of them. Fuels with a low content of oxygen compounds have a low volatile yield and a higher ignition temperature.
The content of molecules in solid fuel that are easily decomposed when heated also affects the reactivity of the non-volatile residue. First, the decomposition of the combustible mass occurs mainly on the outer surface of the fuel. As the fuel heats up further, pyrogenetic reactions begin to occur inside the fuel particles, the pressure in them increases and the outer shell ruptures. When burning fuels with a high volatile yield, the coke residue becomes porous and has a larger surface area compared to the dense solid residue.
2. The process of combustion of gaseous compounds and coke
The actual combustion of fuel begins with the ignition of volatile substances. During the fuel preparation period, branched chain reactions of oxidation of gaseous substances occur; at first, these reactions occur at low speeds. The generated heat is perceived by the surfaces of the firebox and is partially accumulated in the form of energy of moving molecules. The latter leads to an increase in the rate of chain reactions. At a certain temperature, oxidation reactions proceed at such a rate that the released heat completely covers the heat absorption. This temperature is the ignition temperature.
The ignition temperature is not a constant, it depends both on the properties of the fuel and on the conditions in the ignition zone, on average it is 400-600 ° C. After ignition of the gaseous mixture, further self-acceleration of oxidation reactions causes an increase in temperature. To maintain combustion, a continuous supply of oxidizer and combustible substances is required.
Ignition of gaseous substances leads to enveloping the coke particle in a fire shell. Coke combustion begins when volatile combustion comes to an end. The solid particle is heated to a high temperature, and as the amount of volatile substances decreases, the thickness of the boundary burning layer decreases, oxygen reaches the hot surface of the carbon.
Coke combustion begins at a temperature of 1000 °C and is the longest process. The reason is that, firstly, the oxygen concentration decreases, and secondly, heterogeneous reactions proceed more slowly than homogeneous ones. As a result, the duration of combustion of a solid fuel particle is determined mainly by the combustion time of the coke residue (about 2/3 of the total time). For fuels with a high volatile yield, the solid residue is less than ½ of the initial mass of the particle, so their combustion occurs quickly and the possibility of underburning is low. Chemically old fuels have a dense particle, the combustion of which takes almost the entire time spent in the firebox.
The coke residue of most solid fuels consists mainly, and for some types, entirely of carbon. Combustion of solid carbon produces carbon monoxide and carbon dioxide.
Optimal conditions for heat release
Creation optimal conditions for the carbon combustion process - the basis for the correct construction of a technological method for burning solid fuels in boiler units. The achievement of the greatest heat release in the furnace can be influenced by the following factors: temperature, excess air, primary and secondary mixture formation.
Temperature. Heat release during fuel combustion depends significantly on temperature regime fireboxes At relatively low temperatures In the core of the torch, there is incomplete combustion of flammable substances; carbon monoxide, hydrogen, and hydrocarbons remain in the combustion products. At temperatures from 1000 to 1800-2000 °C, complete combustion of fuel is achievable.
Excess air. Specific heat release reaches its maximum value with complete combustion and excess air ratio, equal to one. As the excess air ratio decreases, the heat release decreases, since the lack of oxygen leads to the oxidation of less fuel. The temperature level decreases, reaction rates decrease, which leads to a sharp decrease in heat generation.
Increasing the excess air coefficient above unity reduces heat generation even more than the lack of air. In real conditions of fuel combustion in boiler furnaces, the limiting values of heat release are not achieved, since there is incomplete combustion. It largely depends on how the mixture formation processes are organized.
Mixture formation processes. In chamber furnaces, primary mixture formation is achieved by drying and mixing fuel with air, supplying part of the air (primary) to the preparation zone, creating a wide-open flame with a wide surface and high turbulence, and using heated air.
In layered fireboxes, the task of primary mixture formation is to supply required quantity air in different zones burning on the grate.
In order to ensure the afterburning of gaseous products of incomplete combustion and coke, secondary mixture formation processes are organized. These processes are facilitated by: the supply of secondary air at high speed, the creation of such aerodynamics that a uniform filling of the entire furnace with a torch is achieved and, consequently, the residence time of gases and coke particles in the furnace increases.
3. Slag formation
During the oxidation of the combustible mass of solid fuel, significant changes occur in mineral impurities. Low-melting substances and alloys with low melting points dissolve refractory compounds.
A prerequisite for the normal operation of boiler units is the uninterrupted removal of combustion products and the resulting slag.
During layer combustion, slag formation can lead to mechanical undercombustion - mineral impurities envelop unburnt coke particles, or viscous slag can block air passages, blocking oxygen access to the burning coke. To reduce underburning, various measures are used - in fireboxes with chain grates, the time spent by the slag on the grate is increased, and frequent drilling is carried out.
In layer furnaces, slag is removed in dry form. In chamber furnaces, slag removal can be dry or liquid.
Thus, fuel combustion is complex physical and chemical process, which is influenced by a large number of different factors, but all of them must be taken into account when designing boilers and combustion devices.
The main combustion conditions are: the presence of a flammable substance, the entry of an oxidizer into the zone chemical reactions and the continuous release of heat necessary to maintain combustion.
Combustion zone
Heat affected zone
smoke zone the space adjacent to the combustion zone is impossible for people to enter without respiratory protection
A - initial stage fire - from the occurrence of an uncontrolled local combustion to the complete engulfment of the room in flames. The average room temperature is low, but in and around the combustion zone local temperatures can reach significant levels.
(
C - Fire extinction stage - the intensity of combustion processes in rooms begins to decrease due to the consumption of the bulk of combustible materials in the room or exposure to extinguishing agents.
6. Factors characterizing the possible development of a fire (list and give explanations). Fire zones and stages. Stages of fire development, their features.
Combustion zone part of the space in which the process of chemical decomposition and evaporation occurs
Heat affected zone there is a process of heat exchange between the surface and the flame, between the enclosed structure and the combustible material itself
Smoke zone the space adjacent to the combustion zone does not allow people to enter without respiratory protection
In the process of fire development there are 3 stages:
A - initial stage fire– from the emergence of an uncontrolled local combustion source to complete engulfment of the room in flames. The average room temperature is low, but in and around the combustion zone, local temperatures can reach significant levels.
B - Stage of full development of the fire ( or a fire that completely engulfs the building). All flammable substances and materials in the room burn. The intensity of heat release from burning objects reaches a maximum, which leads to a rapid increase in temperature in the room to maximum (up to 1100C)
C - Fire extinction stage - the intensity of combustion processes in rooms begins to decrease due to the consumption of the bulk of combustible materials in the room or exposure to extinguishing agents.
7. Indicators of fire and explosion hazard of substances and materials (list the main ones, give definitions, characterize their applicability depending on their state of aggregation).
indicators of fire and explosion hazard of substances and materials - a set of properties of substances (materials) characterizing their ability to initiate and spread combustion. They are distinguished by their state of aggregation:
gases - substances whose saturated vapor pressure at a temperature of 25°C and a pressure of 101.3 kPa exceeds 101.3 kPa;
liquids - substances whose saturated vapor pressure at a temperature of 25°C and a pressure of 101.3 kPa is less than 101.3 kPa; Liquids also include solid melting substances whose melting or dropping point is less than 50°C;
solid substances (materials) - individual substances and their mixed compositions with a melting or dropping point greater than 50°C, as well as substances that do not have a melting point (for example, wood, fabrics, etc.);
dust - dispersed solids (materials) with a particle size of less than 850 microns.
8. Define and explain the following concepts: flammability; fire; fireproof materials; flame retardant materials; combustible materials. List the main methods for determining the flammability of solid materials (without a detailed explanation of their essence).
Flammability – ability of substances and materials to ignite.
Fire – the beginning of combustion under the air of an ignition source.
Start of combustion – start of selection heat in the island river, accompanied by glow, etc.
Tendency to excite– the ability of materials to self-contain, ignite/smolder for various reasons.
Based on flammability, substances and materials are divided into 3 groups:
non-flammable (non-combustible)- under the influence of fire/high. t o do not ignite, do not smolder and do not char (natural and artificial organic materials used in construction), high-grade materials and materials that are not capable of burning in air. Non-flammable substances m/b air defense (for example, oxides or airborne substances that release flammable products upon interaction with water, atmospheric oxygen, or others);
flame retardant (hard to burn)– under the influence of fire/high. t o is difficult to ignite, smolders and chars and continues to burn/smoulder only in the presence of an ignition source (vapors and materials consisting of flammable and non-flammable: polymeric materials);
flammable (combustible)– ignite, smolder and continue to burn after removing the ignition source (all organic materials that do not meet the requirements for non-combustible and difficult-to-burn materials); When determining a group of materials using the calorimetry method as a definition, use. flammability level, i.e. the ratio of the amount of heat released by the sample during combustion to the amount of heat released by the ignition source. Nesgor. m., cat. k0.1, difficult to burn. m. k=0.1-0.5, combustion. m. k=2.1.
Used for classification. substances and materials for flammability; when determining the category of premises according to VP and PO in accordance with the requirements of technological standards. design; when developing measures to ensure food safety.
