Classification of combustible gases

For the gas supply of cities and industrial enterprises, various combustible gases are used, differing in origin, chemical composition and physical properties.

By origin, combustible gases are divided into natural, or natural, and artificial, produced from solid and liquid fuels.

Natural gases are extracted from wells of purely gas fields or oil fields along with oil. The gases of oil fields are called associated gases.

The gases of pure gas fields mainly consist of methane with a small content of heavy hydrocarbons. They are characterized by the constancy of composition and calorific value.

Associated gases, along with methane, contain a significant amount of heavy hydrocarbons (propane and butane). The composition and calorific value of these gases vary widely.

Artificial gases are produced in special gas plants - or obtained as a by-product from the combustion of coal in metallurgical plants, as well as in oil refineries.

Gases produced from coal are used in our country for urban gas supply in very limited quantities, and their specific gravity is constantly decreasing. At the same time, the production and consumption of liquefied hydrocarbon gases, obtained from associated petroleum gases at gas-gasoline plants and oil refineries during oil refining, is growing. Liquid hydrocarbon gases used for urban gas supply consist mainly of propane and butane.

Composition of gases

The type of gas and its composition largely predetermine the scope of gas, the scheme and diameters of the gas network, the design solutions for gas burners and individual gas pipeline units.

Gas consumption depends on the calorific value, and hence the diameters of gas pipelines and the conditions for gas combustion. When using gas in industrial installations, the combustion temperature and flame propagation speed and the constancy of the gas fuel composition are of great importance. The composition of gases, as well as their physico-chemical properties, primarily depend on the type and method of obtaining gases.

Combustible gases are mechanical mixtures of various gases<как го­рючих, так и негорючих.

The combustible part of the gaseous fuel includes: hydrogen (H 2) - a gas without color, taste and smell, its lower calorific value is 2579 kcal / nm 3 \ methane (CH 4) - a colorless, tasteless and odorless gas, is the main combustible part of natural gases, its lower calorific value is 8555 kcal / nm 3; carbon monoxide (CO) - a colorless, tasteless and odorless gas, obtained from the incomplete combustion of any fuel, very toxic, lower calorific value 3018 kcal / nm 3; heavy-hydrocarbons (C p N t), By this name<и формулой обозначается целый ряд углеводородов (этан - С2Н 6 , пропан - С 3 Нв, бутан- С4Н 10 и др.), низшая теплотворная способность этих газов колеблется от 15226 до 34890 kcal/nm*.

The non-combustible part of the gaseous fuel includes: carbon dioxide (CO 2), oxygen (O 2) and nitrogen (N 2).

The non-combustible part of gases is called ballast. Natural gases are characterized by high calorific value and complete absence of carbon monoxide. At the same time, a number of fields, mainly gas and oil, contain a very toxic (and corrosive gas) - hydrogen sulfide (H 2 S). Most artificial coal gases contain a significant amount of highly toxic gas - carbon monoxide (CO). The presence of oxide in the gas carbon and other toxic substances is highly undesirable, since they complicate the production of operational work and increase the danger when using gas.In addition to the main components, the composition of gases includes various impurities, the specific value of which is negligible in percentage terms.However, given that thousands and even millions of cubic meters of gas, then the total amount of impurities reaches a significant value.Many impurities fall out in gas pipelines, which ultimately leads to a decrease in their throughput, and sometimes to a complete cessation of gas flow.Therefore, the presence of impurities in gas must be taken into account both in the design of gas pipelines , as well as during operation.

The amount and composition of impurities depend on the method of production or extraction of gas and the degree of its purification. The most harmful impurities are dust, tar, naphthalene, moisture and sulfur compounds.

Dust appears in gas during production (extraction) or during gas transportation through pipelines. Resin is a product of thermal decomposition of fuel and accompanies many artificial gases. In the presence of dust in the gas, the resin contributes to the formation of tar-mud plugs and blockages in gas pipelines.

Naphthalene is commonly found in artificial coal gases. At low temperatures, naphthalene precipitates in pipes and, together with other solid and liquid impurities, reduces the flow area of ​​gas pipelines.

Moisture in the form of vapors is contained in almost all natural and artificial gases. It enters natural gases in the gas field itself due to the contacts of gases with the water surface, and artificial gases are saturated with water during the production process. The presence of moisture in the gas in significant quantities is undesirable, since it reduces the calorific value of the gas. In addition, it has a high heat capacity of vaporization , moisture during gas combustion carries away a significant amount of heat together with combustion products into the atmosphere.A large moisture content in gas is also undesirable because, condensing when the gas is cooled in the "burden of its movement through pipes, it can create water plugs in the gas pipeline (in lower points) to be deleted. This requires the installation of special condensate collectors and pumping them out.

Sulfur compounds, as already noted, include hydrogen sulfide, as well as carbon disulfide, mercaptan, etc. These compounds not only adversely affect human health, but also cause significant corrosion of pipes.

Other harmful impurities include ammonia and cyanide compounds, which are found mainly in coal gases. The presence of ammonia and cyanide compounds leads to increased corrosion of pipe metal.

The presence of carbon dioxide and nitrogen in combustible gases is also undesirable. These gases do not participate in the combustion process, being a ballast that reduces the calorific value, which leads to an increase in the diameter of gas pipelines and a decrease in the economic efficiency of using gaseous fuel.

The composition of gases used for urban gas supply must meet the requirements of GOST 6542-50 (Table 1).

Table 1

The average values ​​of the composition of natural gases of the most famous fields in the country are presented in Table. 2.

From gas fields (dry)

Calorific value of gases

The amount of heat released during the complete combustion of a unit amount of fuel is called the calorific value (Q) or, as it is sometimes called, the calorific value, or calorific value, which is one of the main characteristics of the fuel.

The calorific value of gases is usually referred to as 1 m 3, taken under normal conditions.

In technical calculations, normal conditions are understood as the state of the gas at a temperature equal to 0 ° C, and, at a pressure of 760 mmHg Art. The volume of gas under these conditions is denoted nm 3(normal cubic meter).

For industrial gas measurements in accordance with GOST 2923-45, the temperature of 20 ° C and pressure of 760 are taken as normal conditions mmHg Art. The volume of gas referred to these conditions, in contrast to nm 3 we will call m 3 (cubic meter).

Calorific value of gases (Q)) expressed in kcal/nm e or in kcal / m 3.

For liquefied gases, the calorific value is referred to 1 kg.

There are higher (Q in) and lower (Q n) calorific value. The gross calorific value takes into account the heat of condensation of water vapor formed during the combustion of fuel. The net calorific value does not take into account the heat contained in the water vapor of the combustion products, since water vapor does not condense, but is carried away with the combustion products.

The concepts Q in and Q n apply only to those gases, during the combustion of which water vapor is released (these concepts do not apply to carbon monoxide, which does not give water vapor during combustion).

When water vapor condenses, heat is released equal to 539 kcal/kg. In addition, when the condensate is cooled to 0°C (or 20°C), heat is released, respectively, in the amount of 100 or 80 kcal/kg.

In total, due to the condensation of water vapor, heat is released more than 600 kcal/kg, which is the difference between the gross and net calorific value of the gas. For most gases used in urban gas supply, this difference is 8-10%.

The values ​​of the calorific value of some gases are given in table. 3.

For urban gas supply, gases are currently used, which, as a rule, have a calorific value of at least 3500 kcal / nm 3. This is explained by the fact that in the conditions of cities gas is supplied through pipes over considerable distances. With a low calorific value, it is required to supply a large amount. This inevitably leads to an increase in the diameters of gas pipelines and, as a result, to an increase in metal investments and funds for the construction of gas networks, and, subsequently, to an increase in operating costs. A significant disadvantage of low-calorie gases is that in most cases they contain a significant amount of carbon monoxide, which increases the danger when using gas, as well as when servicing networks and installations.

Gas with calorific value less than 3500 kcal/nm 3 most often used in industry, where it is not required to transport it over long distances and it is easier to organize incineration. For urban gas supply, it is desirable to have a constant calorific value of gas. Fluctuations, as we have already established, are allowed no more than 10%. A greater change in the calorific value of the gas requires a new adjustment, and sometimes a change in a large number of unified burners for household appliances, which is associated with significant difficulties.

Substances of organic origin include fuel, which, when burned, releases a certain amount of thermal energy. Heat generation should be characterized by high efficiency and the absence of side effects, in particular, substances harmful to human health and the environment.

For ease of loading into the furnace, wood material is cut into individual elements up to 30 cm long. To increase the efficiency of their use, firewood should be as dry as possible, and the combustion process should be relatively slow. In many respects, firewood from such hardwoods as oak and birch, hazel and ash, hawthorn is suitable for space heating. Due to the high resin content, increased burning rate and low calorific value, conifers are significantly inferior in this regard.

It should be understood that the density of wood affects the value of the calorific value.

It is a natural material of plant origin, extracted from sedimentary rock.

This type of solid fuel contains carbon and other chemical elements. There is a division of material into types depending on its age. Brown coal is considered the youngest, followed by hard coal, and anthracite is the oldest of all other types. The age of the combustible substance also determines its moisture content, which is more present in the young material.

In the process of burning coal, the environment is polluted, and slag is formed on the grate of the boiler, which, to a certain extent, creates an obstacle to normal combustion. The presence of sulfur in the material is also an unfavorable factor for the atmosphere, since this element is converted into sulfuric acid in the air space.

However, consumers should not be afraid for their health. Manufacturers of this material, taking care of private customers, seek to reduce the sulfur content in it. The calorific value of coal can differ even within the same type. The difference depends on the characteristics of the subspecies and the content of minerals in it, as well as the geography of production. As a solid fuel, not only pure coal is found, but also low-enriched coal slag pressed into briquettes.

Pellets (fuel pellets) is a solid fuel created industrially from wood and plant waste: shavings, bark, cardboard, straw.

The raw material crushed to the state of dust is dried and poured into the granulator, from where it already comes out in the form of granules of a certain shape. To add viscosity to the mass, a vegetable polymer, lignin, is used. The complexity of the production process and high demand form the cost of pellets. The material is used in specially equipped boilers.

The types of fuel are determined depending on what material they are processed from:

• round timber of trees of any species;
• straw;
• peat;
• sunflower husk.

Among the advantages that fuel pellets have, it is worth noting the following qualities:

• environmental friendliness;
• inability to deform and resistance to fungus;
• ease of storage even outdoors;
• uniformity and duration of burning;
• relatively low cost;
• the possibility of using for various heating devices;
• suitable pellet size for automatic loading into a specially equipped boiler.

Briquettes

Briquettes are called solid fuel, in many respects similar to pellets. For their manufacture, identical materials are used: wood chips, shavings, peat, husks and straw. During the production process, the raw material is crushed and formed into briquettes by compression. This material also belongs to environmentally friendly fuel. It is convenient to store it even outdoors. Smooth, uniform and slow burning of this fuel can be observed both in fireplaces and stoves, and in heating boilers.

The varieties of environmentally friendly solid fuels discussed above are a good alternative to generating heat. Compared to fossil sources of thermal energy, which adversely affect the environment during combustion and are, moreover, non-renewable, alternative fuels have clear advantages and relatively low cost, which is important for certain categories of consumers.

At the same time, the fire hazard of such fuels is much higher. Therefore, some precautions must be taken regarding their storage and the use of fire-resistant wall materials.

Liquid and gaseous fuels

As for liquid and gaseous combustible substances, the situation is as follows.

Gas fuel is divided into natural and artificial and is a mixture of combustible and non-combustible gases containing a certain amount of water vapor, and sometimes dust and tar. The amount of gas fuel is expressed in cubic meters under normal conditions (760 mm Hg and 0 ° C), and the composition is expressed as a percentage by volume. Under the composition of the fuel understand the composition of its dry gaseous part.

natural gas fuel

The most common gas fuel is natural gas, which has a high calorific value. The basis of natural gas is methane, the content of which is 76.7-98%. Other gaseous hydrocarbon compounds are part of natural gas from 0.1 to 4.5%.

Liquefied gas is a product of oil refining - it consists mainly of a mixture of propane and butane.

Combustible gases include: hydrogen H 2, methane CH 4, Other hydrocarbon compounds C m H n, hydrogen sulfide H 2 S and non-combustible gases, carbon dioxide CO2, oxygen O 2, nitrogen N 2 and a small amount of water vapor H 2 O. Indices m and P at C and H characterize compounds of various hydrocarbons, for example, for methane CH 4 t = 1 and n= 4, for ethane С 2 Н b t = 2 and n= b etc.

Composition of dry gaseous fuel (in percent by volume):

CO + H 2 + 2 C m H n + H 2 S + CO 2 + O 2 + N 2 = 100%.

The non-combustible part of dry gaseous fuel - ballast - is nitrogen N and carbon dioxide CO 2 .

The composition of the wet gaseous fuel is expressed as follows:

CO + H 2 + Σ C m H n + H 2 S + CO 2 + O 2 + N 2 + H 2 O \u003d 100%.

The heat of combustion, kJ / m (kcal / m 3), 1 m 3 of pure dry gas under normal conditions is determined as follows:

Q n s \u003d 0.01,

where Qco, Q n 2 , Q with m n n Q n 2 s. - heat of combustion of individual gases that make up the mixture, kJ / m 3 (kcal / m 3); CO, H 2, Cm H n , H 2 S - components that make up the gas mixture, % by volume.

The calorific value of 1 m3 of dry natural gas under normal conditions for most domestic fields is 33.29 - 35.87 MJ/m3 (7946 - 8560 kcal/m3). Characteristics of gaseous fuel is given in table 1.

Example. Determine the net calorific value of natural gas (under normal conditions) of the following composition:

H 2 S = 1%; CH 4 = 76.7%; C 2 H 6 = 4.5%; C 3 H 8 = 1.7%; C 4 H 10 = 0.8%; C 5 H 12 = 0.6%.

Substituting into formula (26) the characteristics of gases from Table 1, we obtain:

Q ns \u003d 0.01 \u003d 33981 kJ / m 3 or

Q ns \u003d 0.01 (5585.1 + 8555 76.7 + 15 226 4.5 + 21 795 1.7 + 28 338 0.8 + 34 890 0.6) \u003d 8109 kcal / m 3.

Table 1. Characteristics of gaseous fuel

The process of gasification of solid fuel is shown in a laboratory experiment (Fig. 1). Having filled the refractory tube with pieces of charcoal, we heat it up strongly and let oxygen pass through the gasometer. Let the gases coming out of the tube pass through a lime water washer and then set it on fire. Lime water becomes cloudy, the gas burns with a bluish flame. This indicates the presence of CO2 dioxide and carbon monoxide CO in the reaction products.

The formation of these substances can be explained by the fact that when oxygen comes into contact with hot coal, the latter is first oxidized into carbon dioxide: C + O 2 \u003d CO 2

Then, passing through hot coal, carbon dioxide is partially reduced by it to carbon monoxide: CO 2 + C \u003d 2CO

PHYSICAL AND CHEMICAL PROPERTIES OF NATURAL GASES

Natural gases have no color, smell or taste.

The main indicators of natural gases include: composition, heat of combustion, density, combustion and ignition temperature, explosive limits and explosion pressure.

Natural gases from pure gas fields mainly consist of methane (82-98%) and other hydrocarbons.

Combustible gas contains combustible and non-combustible substances. Combustible gases include: hydrocarbons, hydrogen, hydrogen sulfide. Non-flammables include: carbon dioxide, oxygen, nitrogen and water vapor. Their composition is low and amounts to 0.1-0.3% CO 2 and 1-14% N 2 . After extraction, toxic hydrogen sulfide gas is extracted from the gas, the content of which should not exceed 0.02 g/m3.

The calorific value is the amount of heat released during the complete combustion of 1 m3 of gas. The heat of combustion is measured in kcal/m3, kJ/m3 of gas. The calorific value of dry natural gas is 8000-8500 kcal/m 3 .

The value calculated by the ratio of the mass of a substance to its volume is called the density of the substance. Density is measured in kg/m3. The density of natural gas depends entirely on its composition and is within c = 0.73-0.85 kg/m3.

The most important feature of any combustible gas is the heat output, i.e. the maximum temperature achieved with complete combustion of the gas, if the required amount of air for combustion exactly matches the chemical formulas of combustion, and the initial temperature of the gas and air is zero.

The heat capacity of natural gases is about 2000 -2100 °C, methane - 2043 °C. The actual combustion temperature in furnaces is much lower than the heat output and depends on the combustion conditions.

The ignition temperature is the temperature of the air-fuel mixture at which the mixture ignites without an ignition source. For natural gas, it is in the range of 645-700 °C.

All combustible gases are explosive, capable of igniting with an open flame or spark. Distinguish lower and upper concentration limit of flame propagation , i.e. the lower and upper concentrations at which an explosion of the mixture is possible. The lower explosive limit of gases is 3÷6%, the upper limit is 12÷16%.

Explosive limits.

Gas-air mixture containing the amount of gas:

up to 5% - does not burn;

from 5 to 15% - explodes;

more than 15% - burns when air is supplied.

The pressure during the explosion of natural gas is 0.8-1.0 MPa.

All combustible gases can cause poisoning of the human body. The main toxic substances are: carbon monoxide (CO), hydrogen sulfide (H 2 S), ammonia (NH 3).

Natural gas has no smell. In order to determine the leak, the gas is odorized (i.e., they give it a specific smell). Carrying out odorization is carried out by using ethyl mercaptan. Carry out odorization at gas distribution stations (GDS). When 1% of natural gas enters the air, its smell begins to be felt. Practice shows that the average rate of ethyl mercaptan for the odorization of natural gas supplied to city networks should be 16 g per 1,000 m3 of gas.

Compared to solid and liquid fuels, natural gas wins in many ways:

Relative cheapness, which is explained by an easier way of extraction and transport;

No ash and removal of solid particles into the atmosphere;

High heat of combustion;

No preparation of fuel for combustion is required;

The work of service workers is facilitated and the sanitary and hygienic conditions of their work are improved;

Facilitates the automation of work processes.

Due to possible leaks through leaks in gas pipeline connections and fittings, the use of natural gas requires special care and caution. The penetration of more than 20% of the gas into the room can lead to suffocation, and if it is present in a closed volume from 5 to 15%, it can cause an explosion of the gas-air mixture. Incomplete combustion produces toxic carbon monoxide CO, which even at low concentrations leads to poisoning of the operating personnel.

According to their origin, natural gases are divided into two groups: dry and fatty.

Dry gases are gases of mineral origin and are found in areas associated with present or past volcanic activity. Dry gases consist almost exclusively of methane alone with an insignificant content of ballast components (nitrogen, carbon dioxide) and have a calorific value Qн=7000÷9000 kcal/nm3.

fatty gases accompany oil fields and usually accumulate in the upper layers. By their origin, fatty gases are close to oil and contain many easily condensable hydrocarbons. Calorific value of liquid gases Qн=8000-15000 kcal/nm3

The advantages of gaseous fuels include the ease of transportation and combustion, the absence of moisture ash, and the significant simplicity of boiler equipment.

Along with natural gases, artificial combustible gases are also used, obtained during the processing of solid fuels, or as a result of the operation of industrial plants as exhaust gases. Artificial gases consist of combustible gases of incomplete combustion of fuel, ballast gases and water vapor and are divided into rich and poor, having an average calorific value of 4500 kcal / m3 and 1300 kkam3, respectively. Composition of gases: hydrogen, methane, other hydrocarbon compounds CmHn, hydrogen sulfide H 2 S, non-combustible gases, carbon dioxide, oxygen, nitrogen and a small amount of water vapor. Ballast - nitrogen and carbon dioxide.

Thus, the composition of dry gaseous fuel can be represented as the following mixture of elements:

CO + H 2 + ∑CmHn + H 2 S + CO 2 + O 2 + N 2 \u003d 100%.

The composition of the wet gaseous fuel is expressed as follows:

CO + H 2 + ∑CmHn + H 2 S + CO 2 + O 2 + N 2 + H 2 O \u003d 100%.

Heat of combustion dry gaseous fuel kJ / m3 (kcal / m3) per 1 m3 of gas under normal conditions is determined as follows:

Qn \u003d 0.01,

Where Qi is the calorific value of the corresponding gas.

The heat of combustion of gaseous fuel is given in table 3.

Blast furnace gas formed during iron smelting in blast furnaces. Its yield and chemical composition depend on the properties of the charge and fuel, the operating mode of the furnace, methods of intensifying the process, and other factors. The gas output ranges from 1500-2500 m 3 per ton of pig iron. The proportion of non-combustible components (N 2 and CO 2) in blast-furnace gas is about 70%, which causes its low thermal performance (the lowest calorific value of gas is 3-5 MJ/m 3).

When burning blast-furnace gas, the maximum temperature of the combustion products (excluding heat losses and heat consumption for the dissociation of CO 2 and H 2 O) is 400-1500 0 C. If the gas and air are heated before combustion, the temperature of the combustion products can be significantly increased.

ferroalloy gas formed during the smelting of ferroalloys in ore reduction furnaces. The exhaust gas from closed furnaces can be used as fuel SER (secondary energy resources). In open furnaces, due to the free access of air, the gas burns on the top. The yield and composition of ferroalloy gas depends on the grade of the smelted

alloy, charge composition, furnace operation mode, its power, etc. Gas composition: 50-90% CO, 2-8% H 2 , 0.3-1% CH 4 , O 2<1%, 2-5% CO 2 , остальное N 2 . Максимальная температура продуктов сгорания равна 2080 ^0 C. Запылённость газа составляет 30-40 г/м^3 .

converter gas formed during steel smelting in oxygen converters. The gas consists mainly of carbon monoxide, its yield and composition during melting change significantly. After purification, the composition of the gas is approximately as follows: 70-80% CO; 15-20% CO 2 ; 0.5-0.8% O 2 ; 3-12% N 2. The heat of combustion of the gas is 8.4-9.2 MJ/m 3 . The maximum combustion temperature reaches 2000 0 C.

coke oven gas formed during the coking of coal charge. In ferrous metallurgy, it is used after the extraction of chemical products. The composition of coke oven gas depends on the properties of the coal charge and coking conditions. Volume fractions of components in the gas are within the following limits, %: 52-62H 2 ; 0.3-0.6 O 2 ; 23.5-26.5 CH 4 ; 5.5-7.7 CO; 1.8-2.6 CO 2 . The heat of combustion is 17-17.6 MJ / m ^ 3, the maximum temperature of the combustion products is 2070 0 С.

Every day, turning on the burner on the stove, few people think about how long ago they began to produce gas. In our country, its development was started in the twentieth century. Before that, it was simply found when extracting oil products. The calorific value of natural gas is so high that today this raw material is simply irreplaceable, and its high-quality counterparts have not yet been developed.

The calorific value table will help you choose the fuel for heating your home

Feature of fossil fuel

Natural gas is an important fossil fuel that occupies a leading position in the fuel and energy balances of many states. In order to supply fuel, cities and all kinds of technical enterprises consume various combustible gases, since natural gas is considered dangerous.

Ecologists believe that gas is the purest fuel; when burned, it releases much less toxic substances than wood, coal, and oil. This fuel is used daily by people and contains such an additive as an odorant, it is added at equipped installations in a ratio of 16 milligrams per 1,000 cubic meters of gas.

An important component of the substance is methane (approximately 88-96%), the rest is other chemicals:

• butane;
• hydrogen sulfide;
• propane;
• nitrogen;
• oxygen.

In this video, we will consider the role of coal:

The amount of methane in natural fuel directly depends on its field.

The described type of fuel consists of hydrocarbon and non-hydrocarbon components. The natural fossil fuel is primarily methane, which includes butane and propane. In addition to the hydrocarbon components, nitrogen, sulfur, helium and argon are present in the described fossil fuel. Liquid vapors are also found, but only in gas and oil fields.

Deposit types

Several types of gas deposits are noted. They are divided into the following types:

• gas;
• oil.

Their distinguishing feature is the hydrocarbon content. Gas deposits contain approximately 85-90% of the presented substance, oil fields contain no more than 50%. The remaining percentages are occupied by substances such as butane, propane and oil.

A huge disadvantage of oil generation is its flushing from various kinds of additives. Sulfur as an impurity is exploited at technical enterprises.

Natural gas consumption

Butane is consumed as a fuel at gas stations for cars, and an organic substance called "propane" is used to fuel lighters. Acetylene is highly flammable and is used in welding and cutting metal.

Fossil fuel is used in everyday life:

• columns;
• gas stove;

This kind of fuel is considered the most budgetary and harmless, the only drawback is the emission of carbon dioxide during combustion into the atmosphere. Scientists all over the planet are looking for a replacement for thermal energy.

Calorific value

The calorific value of natural gas is the amount of heat generated with sufficient burnout of a unit of fuel. The amount of heat released during combustion is referred to one cubic meter, taken under natural conditions.

The thermal capacity of natural gas is measured in the following terms:

• kcal / nm 3;
• kcal / m 3.

There is a high and low calorific value:

1. High. Considers the heat of water vapor that occurs during the combustion of fuel.
2. Low. It does not take into account the heat contained in water vapor, since such vapors do not lend themselves to condensation, but leave with combustion products. Due to the accumulation of water vapor, it forms an amount of heat equal to 540 kcal / kg. In addition, when the condensate cools, heat from 80 to one hundred kcal / kg is released. In general, due to the accumulation of water vapor, more than 600 kcal / kg are formed, this is the distinguishing feature between high and low heat output.

For the vast majority of gases consumed in an urban fuel distribution system, the difference equates to 10%. In order to provide cities with gas, its calorific value must be more than 3500 kcal/Nm 3 . This is explained by the fact that the supply is carried out through the pipeline over long distances. If the calorific value is low, then its supply increases.

If the calorific value of natural gas is less than 3500 kcal / Nm 3, it is more often used in industry. It does not need to be transported for long distances, and it becomes much easier to carry out combustion. Serious changes in the calorific value of the gas require frequent adjustment and sometimes replacement of a large number of standardized burners of household sensors, which leads to difficulties.

This situation leads to an increase in the diameter of the gas pipeline, as well as an increase in the cost of metal, laying networks and operation. The big disadvantage of low-calorie fossil fuels is the huge content of carbon monoxide, in connection with this, the level of danger increases during the operation of the fuel and during the maintenance of the pipeline, in turn, as well as equipment.

The heat released during combustion, not exceeding 3500 kcal/nm 3 , is most often used in industrial production, where it is not necessary to transfer it over a long distance and easily form combustion.