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Gas fuel. gaseous fuel

5. THERMAL BALANCE OF COMBUSTION

Consider methods for calculating the heat balance of the combustion process of gaseous, liquid and solid fuels. The calculation is reduced to solving the following problems.

· Determination of heat of combustion (calorific value) of fuel.

· Determination of the theoretical combustion temperature.

5.1. HEAT OF BURNING

Chemical reactions are accompanied by the release or absorption of heat. When heat is released, the reaction is called exothermic, and when it is absorbed, it is called endothermic. All combustion reactions are exothermic, and combustion products are exothermic compounds.

Released (or absorbed) during the course chemical reaction heat is called the heat of reaction. In exothermic reactions it is positive, in endothermic reactions it is negative. The combustion reaction is always accompanied by the release of heat. Heat of combustion Q g(J / mol) is the amount of heat that is released during the complete combustion of one mole of a substance and the transformation of a combustible substance into products of complete combustion. The mole is the basic SI unit for the amount of a substance. One mole is such an amount of a substance that contains as many particles (atoms, molecules, etc.) as there are atoms in 12 g of the carbon-12 isotope. The mass of an amount of a substance equal to 1 mole (molecular or molar mass) numerically coincides with the relative molecular weight of a given substance.

For example, the relative molecular weight of oxygen (O 2) is 32, carbon dioxide(CO 2) is equal to 44, and the corresponding molecular weights will be equal to M =32 g/mol and M =44 g/mol. Thus, one mole of oxygen contains 32 grams of this substance, and one mole of CO 2 contains 44 grams of carbon dioxide.

In technical calculations, not the heat of combustion is often used Q g, and the calorific value of the fuel Q(J / kg or J / m 3). The calorific value of a substance is the amount of heat that is released during the complete combustion of 1 kg or 1 m 3 of a substance. For liquid and solid substances, the calculation is carried out per 1 kg, and for gaseous substances, per 1 m 3.

Knowledge of the heat of combustion and the calorific value of the fuel is necessary to calculate the combustion or explosion temperature, explosion pressure, flame propagation speed, and other characteristics. Calorific value fuel is determined either experimentally or by calculation. In the experimental determination of the calorific value, a given mass of solid or liquid fuel is burned in a calorimetric bomb, and in the case of gaseous fuel, in a gas calorimeter. These devices measure the total heat Q 0 , released during the combustion of a sample of fuel weighing m. Calorific value Q g is found according to the formula

Relationship between heat of combustion and
fuel calorific value

To establish a relationship between the heat of combustion and the calorific value of a substance, it is necessary to write down the equation for the chemical reaction of combustion.

The product of complete combustion of carbon is carbon dioxide:

C + O 2 → CO 2.

The product of complete combustion of hydrogen is water:

2H 2 + O 2 → 2H 2 O.

The product of complete combustion of sulfur is sulfur dioxide:

S + O 2 → SO 2.

At the same time, nitrogen, halides and other non-combustible elements are released in a free form.

combustible gas

As an example, we will calculate the calorific value of methane CH 4, for which the heat of combustion is equal to Q g=882.6 .

Let's define molecular weight methane in accordance with its chemical formula (CH 4):

М=1∙12+4∙1=16 g/mol.

Determine the calorific value of 1 kg of methane:

Let's find the volume of 1 kg of methane, knowing its density ρ=0.717 kg/m 3 under normal conditions:

Determine the calorific value of 1 m 3 of methane:

The calorific value of any combustible gases is determined similarly. For many common substances, the calorific values and calorific values have been measured with high accuracy and are given in the relevant reference literature. Here is a table of calorific values of some gaseous substances(Table 5.1). Value Q in this table it is given in MJ / m 3 and in kcal / m 3, since 1 kcal = 4.1868 kJ is often used as a unit of heat.

Table 5.1

Calorific value of gaseous fuels

Substance			Acetylene
Q
Q

combustible liquid or solid

As an example, we will calculate the calorific value of ethyl alcohol C 2 H 5 OH, for which the heat of combustion Q g= 1373.3 kJ/mol.

Determine the molecular weight of ethyl alcohol in accordance with its chemical formula (C 2 H 5 OH):

М = 2∙12 + 5∙1 + 1∙16 + 1∙1 = 46 g/mol.

Determine the calorific value of 1 kg of ethyl alcohol:

The calorific value of any liquid and solid combustibles is determined similarly. In table. 5.2 and 5.3 show the calorific values Q(MJ/kg and kcal/kg) for some liquid and solid substances.

Table 5.2

Calorific value of liquid fuels

Substance	Methyl alcohol	Ethanol	Fuel oil, oil
Q
Q

Table 5.3

Calorific value of solid fuels

Substance	wood fresh	wood dry	Brown coal	Peat dry	Anthracite, coke
Q
Q

Mendeleev's formula

If the calorific value of the fuel is unknown, then it can be calculated using the empirical formula proposed by D.I. Mendeleev. To do this, you need to know the elemental composition of the fuel (the equivalent formula of the fuel), that is, the percentage of the following elements in it:

Oxygen (O);

Hydrogen (H);

Carbon (C);

Sulfur (S);

Ashes (A);

Water (W).

The combustion products of fuels always contain water vapor, formed both due to the presence of moisture in the fuel, and during the combustion of hydrogen. Waste products of combustion leave the industrial plant at a temperature above the dew point temperature. Therefore, the heat that is released during the condensation of water vapor cannot be usefully used and should not be taken into account in thermal calculations.

The net calorific value is usually used for the calculation. Q n fuel, which takes into account heat losses with water vapor. For solid and liquid fuels, the value Q n(MJ / kg) is approximately determined by the Mendeleev formula:

Q n=0.339+1.025+0.1085 – 0.1085 – 0.025, (5.1)

where the percentage (mass %) content of the corresponding elements in the fuel composition is indicated in parentheses.

This formula takes into account the heat of exothermic combustion reactions of carbon, hydrogen and sulfur (with a plus sign). Oxygen, which is part of the fuel, partially replaces the oxygen in the air, so the corresponding term in formula (5.1) is taken with a minus sign. When moisture evaporates, heat is consumed, so the corresponding term containing W is also taken with a minus sign.

Comparison of calculated and experimental data on the calorific value of different fuels (wood, peat, coal, oil) showed that the calculation according to the Mendeleev formula (5.1) gives an error not exceeding 10%.

Net calorific value Q n(MJ / m 3) of dry combustible gases can be calculated with sufficient accuracy as the sum of the products of the calorific value of individual components and their percentage in 1 m 3 of gaseous fuel.

Q n= 0.108[Н 2 ] + 0.126[СО] + 0.358[CH 4 ] + 0.5[С 2 Н 2 ] + 0.234[Н 2 S ]…, (5.2)

where the percentage (vol.%) content of the corresponding gases in the mixture is indicated in parentheses.

The average calorific value of natural gas is approximately 53.6 MJ/m 3 . In artificially produced combustible gases, the content of CH 4 methane is negligible. The main combustible components are hydrogen H 2 and carbon monoxide CO. In coke oven gas, for example, the content of H 2 reaches (55 ÷ 60)%, and the net calorific value of such gas reaches 17.6 MJ/m 3 . In the generator gas, the content of CO ~ 30% and H 2 ~ 15%, while the net calorific value of the generator gas Q n= (5.2÷6.5) MJ/m 3 . In blast-furnace gas, the content of CO and H 2 is less; magnitude Q n= (4.0÷4.2) MJ/m 3 .

Consider examples of calculating the calorific value of substances using the Mendeleev formula.

Let us determine the calorific value of coal, the elemental composition of which is given in Table. 5.4.

Table 5.4

Elemental composition coal

Let's substitute given in tab. 5.4 data in the Mendeleev formula (5.1) (nitrogen N and ash A are not included in this formula, since they are inert substances and do not participate in the combustion reaction):

Q n=0.339∙37.2+1.025∙2.6+0.1085∙0.6–0.1085∙12–0.025∙40=13.04 MJ/kg.

Let us determine the amount of firewood required to heat 50 liters of water from 10 ° C to 100 ° C, if 5% of the heat released during combustion is spent on heating, and the heat capacity of water With\u003d 1 kcal / (kg ∙ deg) or 4.1868 kJ / (kg ∙ deg). The elemental composition of firewood is given in Table. 5.5:

Table 5.5

Elemental composition of firewood

Let's find the calorific value of firewood according to Mendeleev's formula (5.1):

Q n=0.339∙43+1.025∙7–0.1085∙41–0.025∙7= 17.12 MJ/kg.

Determine the amount of heat spent on heating water when burning 1 kg of firewood (taking into account the fact that 5% of the heat (a = 0.05) released during combustion is spent on heating it):

Q 2=a Q n=0.05 17.12=0.86 MJ/kg.

Determine the amount of firewood needed to heat 50 liters of water from 10° C to 100° C:

kg.

Thus, about 22 kg of firewood is required to heat water.

What is fuel?

This is one component or a mixture of substances that are capable of chemical transformations associated with the release of heat. Different types fuels differ in the quantitative content of the oxidizing agent in them, which is used to release thermal energy.

AT broad sense fuel is an energy carrier, that is, a potential type of potential energy.

Classification

Currently, fuels are divided according to their state of aggregation into liquid, solid, gaseous.

To hard natural look include stone and firewood, anthracite. Briquettes, coke, thermoanthracite are varieties of artificial solid fuel.

Liquids include substances that contain substances of organic origin. Their main components are: oxygen, carbon, nitrogen, hydrogen, sulfur. Artificial liquid fuel will be a variety of resins, fuel oil.

It is a mixture of various gases: ethylene, methane, propane, butane. In addition to them, gaseous fuels contain carbon dioxide and carbon monoxide s, hydrogen sulfide, nitrogen, water vapor, oxygen.

Fuel indicators

The main indicator of combustion. The formula for determining the calorific value is considered in thermochemistry. allocate " reference fuel”, which implies the calorific value of 1 kilogram of anthracite.

Domestic heating oil is intended for combustion in heating devices of low power, which are located in residential premises, heat generators used in agriculture for drying fodder, canning.

The specific heat of combustion of fuel is such a value that it demonstrates the amount of heat that is formed during the complete combustion of fuel with a volume of 1 m 3 or a mass of one kilogram.

To measure this value, J / kg, J / m 3, calorie / m 3 are used. To determine the heat of combustion, use the calorimetry method.

With an increase specific heat combustion of fuel, the specific fuel consumption decreases, and the coefficient useful action remains the same value.

The heat of combustion of substances is the amount of energy released during the oxidation of a solid, liquid, gaseous substance.

It is determined by the chemical composition, as well as the state of aggregation of the combustible substance.

Features of combustion products

The higher and lower calorific value is associated with the state of aggregation of water in the substances obtained after the combustion of fuel.

The gross calorific value is the amount of heat released during the complete combustion of a substance. This value includes the heat of condensation of water vapor.

The lower working calorific value is the value that corresponds to the release of heat during combustion without taking into account the heat of condensation of water vapor.

The latent heat of condensation is the value of the energy of condensation of water vapor.

Mathematical relationship

The higher and lower calorific value are related by the following relationship:

Q B = Q H + k(W + 9H)

where W is the amount by weight (in %) of water in the combustible substance;

H is the amount of hydrogen (% by mass) in the combustible substance;

k - coefficient of 6 kcal/kg

Calculation methods

The higher and lower calorific value is determined by two main methods: calculated and experimental.

Calorimeters are used for experimental calculations. First, a sample of fuel is burned in it. The heat that will be released in this case is completely absorbed by the water. Having an idea about the mass of water, it is possible to determine the value of its heat of combustion by changing its temperature.

This technique is considered simple and effective, it assumes only the knowledge of technical analysis data.

In the calculation method, the highest and lowest calorific value is calculated according to the Mendeleev formula.

Q p H \u003d 339C p + 1030H p -109 (O p -S p) - 25 W p (kJ / kg)

It takes into account the content of carbon, oxygen, hydrogen, water vapor, sulfur in the working composition (in percent). The amount of heat during combustion is determined taking into account the reference fuel.

The heat of combustion of gas allows you to make preliminary calculations, to identify the efficiency of the use of a particular type of fuel.

Features of origin

In order to understand how much heat is released during the combustion of a certain fuel, it is necessary to have an idea of its origin.

In nature there is different variants solid fuels, which differ in composition and properties.

Its formation is carried out through several stages. First, peat is formed, then brown and hard coal is obtained, then anthracite is formed. The main sources of solid fuel formation are leaves, wood, and needles. Dying, parts of plants, when exposed to air, are destroyed by fungi, forming peat. Its accumulation turns into a brown mass, then brown gas is obtained.

At high pressure and temperature, brown gas turns into coal, then the fuel accumulates in the form of anthracite.

In addition to organic matter, there is additional ballast in the fuel. Organic consider that part that was formed from organic substances: hydrogen, carbon, nitrogen, oxygen. In addition to these chemical elements, it contains ballast: moisture, ash.

Furnace technology involves the allocation of working, dry, as well as combustible mass of burned fuel. The working mass is called the fuel in its original form, supplied to the consumer. Dry weight is a composition in which there is no water.

Compound

The most valuable components are carbon and hydrogen.

These elements are found in any type of fuel. In peat and wood, the percentage of carbon reaches 58 percent, in black and brown coal - 80%, and in anthracite it reaches 95 percent by weight. Depending on this indicator, the amount of heat released during the combustion of fuel changes. Hydrogen is the second most important element of any fuel. Contacting with oxygen, it forms moisture, which significantly reduces the thermal value of any fuel.

Its percentage ranges from 3.8 in oil shale to 11 in fuel oil. Oxygen, which is part of the fuel, acts as ballast.

It is not heat generating chemical element, therefore, negatively affects the value of the heat of combustion. Combustion of nitrogen contained in free or bound form in combustion products, is considered harmful impurities, so its amount is clearly limited.

Sulfur is included in the composition of the fuel in the form of sulfates, sulfides, and also as sulfur dioxide gases. When hydrated, sulfur oxides form sulfuric acid, which destroys boiler equipment, negatively affects vegetation and living organisms.

That is why sulfur is the chemical element, the presence of which in natural fuel is highly undesirable. When getting inside the working room, sulfur compounds cause significant poisoning of the operating personnel.

There are three types of ash depending on its origin:

primary;
secondary;
tertiary.

The primary form is formed from the mineral substances contained in plants. Secondary ash is formed as a result of ingestion of plant residues by sand and earth during formation formation.

Tertiary ash turns out to be part of the fuel in the process of extraction, storage, and also its transportation. With a significant deposition of ash, there is a decrease in heat transfer on the heating surface of the boiler unit, reduces the amount of heat transfer to water from gases. Great amount ash negatively affects the operation of the boiler.

Finally

A significant influence on the combustion process of any type of fuel is exerted by volatiles. The larger their output, the larger the volume of the flame front will be. For example, coal, peat, easily catch fire, the process is accompanied by insignificant heat losses. The coke that remains after the removal of volatile impurities contains only mineral and carbon compounds. Depending on the characteristics of the fuel, the amount of heat varies significantly.

Depending on the chemical composition There are three stages in the formation of solid fuels: peat, lignite, coal.

Natural wood is used in small boiler plants. Mostly wood chips, sawdust, slabs, bark are used, firewood itself is used in small quantities. Depending on the type of wood, the amount of heat released varies significantly.

As the calorific value decreases, firewood acquires certain advantages: rapid flammability, minimal ash content, and the absence of traces of sulfur.

Reliable information about the composition of natural or synthetic fuels, their calorific value, is an excellent way to conduct thermochemical calculations.

At present, there is a real opportunity to identify those main options for solid, gaseous, liquid fuels that will be the most efficient and inexpensive to use in a particular situation.

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 to the city and all kinds of technical enterprises consume various combustible gas, since natural is considered dangerous.

Ecologists believe that gas is the cleanest fuel; when burned, it releases much less toxic substances than firewood, coal, oil. This fuel is used daily by people and contains an additive such as an odorant, which 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.

Them hallmark 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 different kind 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 organic matter, called "propane", is used to refuel 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:

High. Considers the heat of water vapor that occurs during the combustion of fuel.
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 need frequent adjustment and sometimes replacement a large number 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.

PHYSICAL AND CHEMICAL PROPERTIES OF NATURAL GASES

At natural gases there is no color, smell, 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. Maximum temperature achieved with complete combustion of the gas, if the required amount of air for combustion exactly corresponds to 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 average rate ethyl mercaptan for the odorization of natural gas that enters the 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 more the easy way mining 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 negligible 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 fuel include the ease of transportation and combustion, the absence of ash moisture, 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 waste 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 share 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 ovens due to free access air 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.

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.

During the combustion of 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.