Lower calorific value of gas kcal m3. Gaseous fuel

To substances organic origin refers to fuel that, when burned, releases a certain amount of thermal energy. Heat production must be characterized by high efficiency and absence of side effects, in particular, substances harmful to human health and the environment.

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

It should be understood that the value of the calorific value is affected by the density of wood.

This is a natural material 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 older than all other types. The age of a combustible substance also determines its moisture content, which is more present in young material.

During the combustion of coal, environmental pollution occurs, and slag is formed on the boiler grates, 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 in the air space this element is converted into sulfuric acid.

However, consumers should not fear for their health. Manufacturers of this material, taking care of private customers, strive to reduce the sulfur content in it. The heating value of coal can vary even within the same type. The difference depends on the characteristics of the subspecies and the content in it minerals, 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 granules) are solid fuels created industrially from wood and plant waste: shavings, bark, cardboard, straw.

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

Types of fuel are determined depending on the material from which they are processed:

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;
easy storage even outdoors;
uniformity and duration of combustion;
relatively low cost;
Possibility of use for various heating devices;
suitable granule size for automatic loading into a specially equipped boiler.

Briquettes

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

The types of environmentally friendly solid fuel discussed above are a good alternative for generating heat. In comparison with fossil sources of thermal energy, which have an unfavorable effect on combustion environment and, in addition, being 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, it is necessary to take some safety measures regarding their storage and the use of fire-resistant materials for walls.

Liquid and gaseous fuels

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

The heat of combustion is determined by the chemical composition of the combustible substance. The chemical elements contained in a flammable substance are indicated by accepted symbols WITH , N , ABOUT , N , S, and ash and water are symbols A And W respectively.

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The heat of combustion can be related to the working mass of the combustible substance Q P (\displaystyle Q^(P)), that is, to the flammable substance in the form in which it reaches the consumer; to the dry weight of the substance Q C (\displaystyle Q^(C)); to a flammable mass of substance Q Γ (\displaystyle Q^(\Gamma )), that is, to a flammable substance that does not contain moisture and ash.

There are higher ( Q B (\displaystyle Q_(B))) and lower ( Q H (\displaystyle Q_(H))) heat of combustion.

Under higher calorific value understand the amount of heat that is released during complete combustion of a substance, including the heat of condensation of water vapor when cooling the combustion products.

Lower heating value corresponds to the amount of heat that is released during complete combustion, without taking into account the heat of condensation of water vapor. The heat of condensation of water vapor is also called latent heat of vaporization (condensation).

The lower and higher calorific values are related by the relation: Q B = Q H + k (W + 9 H) (\displaystyle Q_(B)=Q_(H)+k(W+9H)),

where k is a coefficient equal to 25 kJ/kg (6 kcal/kg); W is the amount of water in the flammable substance, % (by mass); H is the amount of hydrogen in a combustible substance, % (by mass).

Calculation of calorific value

Thus, the higher calorific value is the amount of heat released during complete combustion of a unit mass or volume (for gas) of a combustible substance and cooling of the combustion products to the dew point temperature. In thermal engineering calculations, the higher calorific value is taken as 100%. The latent heat of combustion of a gas is the heat that is released during the condensation of water vapor contained in the combustion products. Theoretically, it can reach 11%.

In practice, it is not possible to cool combustion products until complete condensation, and therefore the concept of lower calorific value (QHp) has been introduced, which is obtained by subtracting from the higher calorific value the heat of vaporization of water vapor both contained in the substance and those formed during its combustion. The vaporization of 1 kg of water vapor requires 2514 kJ/kg (600 kcal/kg). The lower calorific value is determined by the formulas (kJ/kg or kcal/kg):

Q H P = Q B P − 2514 ⋅ ((9 H P + W P) / 100) (\displaystyle Q_(H)^(P)=Q_(B)^(P)-2514\cdot ((9H^(P)+W^ (P))/100))(for solid matter)

Q H P = Q B P − 600 ⋅ ((9 H P + W P) / 100) (\displaystyle Q_(H)^(P)=Q_(B)^(P)-600\cdot ((9H^(P)+W^ (P))/100))(For liquid substance), Where:

2514 - heat of vaporization at 0 °C and atmospheric pressure, kJ/kg;

H P (\displaystyle H^(P)) And W P (\displaystyle W^(P))- content of hydrogen and water vapor in the working fuel, %;

9 is a coefficient showing that the combustion of 1 kg of hydrogen in combination with oxygen produces 9 kg of water.

Heat of combustion is the most important characteristic fuel, as it determines the amount of heat obtained by burning 1 kg of solid or liquid fuel or 1 m³ of gaseous fuel in kJ/kg (kcal/kg). 1 kcal = 4.1868 or 4.19 kJ.

The lower calorific value is determined experimentally for each substance and is a reference value. It can also be determined for solid and liquid materials, with a known elemental composition, by calculation in accordance with the formula of D.I. Mendeleev, kJ/kg or kcal/kg:

Q H P = 339 ⋅ C P + 1256 ⋅ H P − 109 ⋅ (O P − S L P) − 25.14 ⋅ (9 ⋅ H P + W P) (\displaystyle Q_(H)^(P)=339\cdot C^(P)+1256\ cdot H^(P)-109\cdot (O^(P)-S_(L)^(P))-25.14\cdot (9\cdot H^(P)+W^(P)))

Q H P = 81 ⋅ C P + 246 ⋅ H P − 26 ⋅ (O P + S L P) − 6 ⋅ W P (\displaystyle Q_(H)^(P)=81\cdot C^(P)+246\cdot H^(P) -26\cdot (O^(P)+S_(L)^(P))-6\cdot W^(P)), Where:

C P (\displaystyle C_(P)), H P (\displaystyle H_(P)), O P (\displaystyle O_(P)), S L P (\displaystyle S_(L)^(P)), W P (\displaystyle W_(P))- content in the working mass of fuel of carbon, hydrogen, oxygen, volatile sulfur and moisture in% (by weight).

For comparative calculations, the so-called conventional fuel is used, which has a specific heat of combustion equal to 29308 kJ/kg (7000 kcal/kg).

In Russia thermal calculations(for example, calculating the thermal load to determine the category of a room for explosion and fire hazard) is usually carried out according to lower heat combustion, in the USA, Great Britain, France - at the highest level. In the UK and USA before the introduction of the metric system of measures specific heat combustion was measured in British thermal units (BTU) per pound (lb) (1Btu/lb = 2.326 kJ/kg).

Substances and materials	Lower heating value Q H P (\displaystyle Q_(H)^(P)), MJ/kg
Petrol	41,87
Kerosene	43,54
Paper: books, magazines	13,4
Wood (blocks W = 14%)	13,8
Natural rubber	44,73
Polyvinyl chloride linoleum	14,31
Rubber	33,52
Staple fiber	13,8
Polyethylene	47,14
Expanded polystyrene	41,6
Cotton loosened	15,7
Plastic	41,87

Every day, turning on the burner on the kitchen stove, few people think about how long ago gas production began. In our country, its development began in the twentieth century. Before this, it was simply found during the extraction of petroleum products. Calorific value natural gas so great that today this raw material is simply irreplaceable, and its high-quality analogues have not yet been developed.

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

Features of fossil fuels

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

Environmentalists believe that gas is the cleanest fuel; when burned, it emits much less toxic substances than firewood, coal, oil. This fuel is used daily by people and contains an additive such as an odorant; it is added in equipped installations in a ratio of 16 milligrams per 1 thousand 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 look at the role of coal:

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

The described type of fuel consists of hydrocarbon and non-hydrocarbon components. Natural fossil fuels are primarily methane, which includes butane and propane. Apart from the hydrocarbon components, the described fossil fuel contains nitrogen, sulfur, helium and argon. Liquid vapors are also found, but only in gas oil fields.

Types of deposits

There are several types of gas deposits. They are divided into the following types:

gas;
oil.

Their distinctive feature is the hydrocarbon content. Gas deposits contain approximately 85-90% of the present 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 production is its flushing from various kinds additives Sulfur is used as an impurity in technical enterprises.

Natural gas consumption

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

Fossil fuels are used in everyday life:

columns;
gas stove;

This type of fuel is considered the most inexpensive and harmless; the only drawback is the release of carbon dioxide into the atmosphere when burned. 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 when a unit of fuel is sufficiently burned. The amount of heat released during combustion is referred to as one cubic meter taken in natural conditions.

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

kcal/nm 3 ;
kcal/m3.

There is high and low calorific value:

High. Considers the heat of water vapor generated during fuel combustion.
Low. Does not take into account the heat contained in water vapor, since such vapors do not condense, 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 comes out from 80 to one hundred kcal/kg. In general, due to the accumulation of water vapor, more than 600 kcal/kg is formed, this is the distinguishing feature between high and low heat output.

For the vast majority of gases consumed in the urban fuel distribution system, the difference is equal 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 a 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 over long distances, and combustion becomes much easier. Serious changes in the calorific value of gas require frequent adjustment and sometimes replacement large quantity standardized burners of household sensors, which leads to difficulties.

This situation leads to an increase in gas pipeline diameters, as well as increased costs for metal, network installation and operation. Big disadvantage low-calorie fossil fuels is huge content carbon monoxide, in connection with this, the level of threat during fuel operation and pipeline maintenance, in turn, as well as equipment, increases.

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 cause combustion.

Gas fuel is divided into natural and artificial and is a mixture of flammable and non-flammable gases containing a certain amount of water vapor and sometimes dust and tar. The amount of gas fuel is expressed in cubic meters at normal conditions(760 mmHg and 0°C), and the composition is expressed as a percentage by volume. The composition of the fuel is understood as 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 comprise natural gas from 0.1 to 4.5%.

Liquefied gas petroleum product - consists mainly of a mixture of propane and butane.

Natural gas (CNG, NG): methane CH4 more than 90%, ethane C2 H5 less than 4%, propane C3 H8 less than 1%

Liquefied gas (LPG): propane C3 H8 more than 65%, butane C4 H10 less than 35%

The composition of flammable gases includes: hydrogen H2, methane CH4, Other hydrocarbon compounds CmHn, hydrogen sulfide H2S and non-flammable gases, carbon dioxide CO2, oxygen O2, nitrogen N2 and a small amount of water vapor H2O. Indexes m And n at C and H characterize compounds of various hydrocarbons, for example for methane CH 4 t = 1 and n= 4, for ethane C 2 N b t = 2 And n= b, etc.

Composition of dry gaseous fuel (percentage 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 gas fuel - ballast - consists of nitrogen N and carbon dioxide CO 2.

The composition of 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 = 100%.

The heat of combustion, kJ/m (kcal/m3), 1 m3 of pure dry gas under normal conditions is determined as follows:

Q n s = 0.01,

where Qso, Q n 2, Q c m n n Q n 2 s. - heat of combustion of individual gases included in the mixture, kJ/m 3 (kcal/m 3); CO, H 2, Cm H n, H 2 S - components that make up 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 are given in Table 1.

Example. Determine the lower 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 the characteristics of gases from Table 1 into formula (26), we obtain:

Q ns = 0.01 = 33981 kJ/m 3 or

Q ns = 0.01 (5585.1 + 8555 76.7 + 15 226 4.5 + 21 795 1.7 + 28 338 0.8 + 34 890 0.6) = 8109 kcal/m3.

Table 1. Characteristics of gaseous fuel

Gas	Designation	Heat of combustion Q n s
Gas	Designation	KJ/m3	Kcal/m3
Hydrogen	N,	10820	2579
Carbon monoxide	CO	12640	3018
Hydrogen sulfide	H 2 S	23450	5585
Methane	CH 4	35850	8555
Ethane	C 2 H 6	63 850	15226
Propane	C 3 H 8	91300	21795
Butane	C 4 H 10	118700	22338
Pentane	C 5 H 12	146200	34890
Ethylene	C 2 H 4	59200	14107
Propylene	C 3 H 6	85980	20541
Butylene	C 4 H 8	113 400	27111
Benzene	C 6 H 6	140400	33528

DE type boilers consume from 71 to 75 m3 of natural gas to produce one ton of steam. The cost of gas in Russia as of September 2008. is 2.44 rubles per cubic meter. Therefore, a ton of steam will cost 71 × 2.44 = 173 rubles 24 kopecks. The real cost of a ton of steam at factories is for boilers DE is at least 189 rubles per ton of steam.

DKVR type boilers consume from 103 to 118 m3 of natural gas to produce one ton of steam. The minimum estimated cost of a ton of steam for these boilers is 103 × 2.44 = 251 rubles 32 kopecks. The real cost of steam at factories is no less than 290 rubles per ton.

How to calculate the maximum natural gas consumption for a DE-25 steam boiler? This technical specifications boiler 1840 cubes per hour. But you can also calculate. 25 tons (25 thousand kg) must be multiplied by the difference between the enthalpies of steam and water (666.9-105) and all this divided by the boiler efficiency of 92.8% and the heat of combustion of the gas. 8300. and that's it

Artificial gas fuel

Artificial combustible gases are a fuel of local importance because they have a significantly lower calorific value. Their main combustible elements are carbon monoxide CO and hydrogen H2. These gases are used within the production where they are obtained as fuel for technological and power plants.

All natural and artificial flammable gases are explosive and can ignite in an open flame or spark. There are lower and upper explosive limits of gas, i.e. its highest and lowest percentage concentration in the air. The lower explosive limit of natural gases ranges from 3% to 6%, and the upper limit - from 12% to 16%. All flammable gases can cause poisoning to the human body. The main toxic substances of flammable gases are: carbon monoxide CO, hydrogen sulfide H2S, ammonia NH3.

Natural flammable gases and artificial ones are colorless (invisible) and odorless, which makes them dangerous if they penetrate into the interior of the boiler room through leaks in gas pipeline fittings. To avoid poisoning, flammable gases should be treated with an odorant - a substance with an unpleasant odor.

Production of carbon monoxide CO in industry by gasification of solid fuel

For industrial purposes, carbon monoxide is produced by gasification solid fuel, i.e. converting it into gaseous fuel. This way you can get carbon monoxide from any solid fuel - fossil coal, peat, firewood, etc.

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 strongly and let oxygen pass through from the gasometer. We pass the gases coming out of the tube through a washer with lime water and then set it on fire. The limewater becomes cloudy and 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 = CO 2

Then, passing through hot coal, carbon dioxide is partially reduced to carbon monoxide: CO 2 + C = 2CO

Rice. 1. Production of carbon monoxide (laboratory experiment).

IN industrial conditions Gasification of solid fuel is carried out in furnaces called gas generators.

The resulting mixture of gases is called generator gas.

The gas generator device is shown in the figure. It is a steel cylinder with a height of about 5 m and a diameter of approximately 3.5 m, lined inside with refractory bricks. The gas generator is loaded with fuel from above; From below, air or water vapor is supplied by a fan through the grate.

Oxygen in the air reacts with carbon in the fuel to form carbon dioxide, which, rising through the layer of hot fuel, is reduced by carbon to carbon monoxide.

If only air is blown into the generator, the result is a gas that contains carbon monoxide and air nitrogen (as well as a certain amount of CO 2 and other impurities). This generator gas is called air gas.

If water vapor is blown into a generator with hot coal, the reaction results in the formation of carbon monoxide and hydrogen: C + H 2 O = CO + H 2

This mixture of gases is called water gas. Water gas has a higher calorific value than air gas, since its composition, along with carbon monoxide, also includes a second flammable gas - hydrogen. Water gas (synthesis gas), one of the products of gasification of fuels. Water gas consists mainly of CO (40%) and H2 (50%). Water gas is a fuel (heat of combustion 10,500 kJ/m3, or 2730 kcal/mg) and at the same time a raw material for synthesis methyl alcohol. Water gas, however, cannot be obtained for a long time, since the reaction of its formation is endothermic (with heat absorption), and therefore the fuel in the generator cools down. To keep the coal hot, the injection of water vapor into the generator is alternated with the injection of air, the oxygen of which is known to react with the fuel to release heat.

IN lately Steam-oxygen blasting began to be widely used for fuel gasification. Simultaneous blowing of water vapor and oxygen through the fuel layer allows the process to be carried out continuously, significantly increasing the productivity of the generator and obtaining gas from high content hydrogen and carbon monoxide.

Modern gas generators are powerful devices of continuous operation.

To prevent flammable and toxic gases from penetrating into the atmosphere when fuel is supplied to the gas generator, the loading drum is made double. While fuel enters one compartment of the drum, fuel is poured into the generator from another compartment; when the drum rotates, these processes are repeated, but the generator remains isolated from the atmosphere all the time. Uniform distribution of fuel in the generator is carried out using a cone, which can be installed at different heights. When it is lowered, the coal falls closer to the center of the generator; when the cone is raised, the coal is thrown closer to the walls of the generator.

Removal of ash from the gas generator is mechanized. The cone-shaped grate is slowly rotated by an electric motor. In this case, the ash is displaced towards the walls of the generator and, using special devices, is dumped into the ash box, from where it is periodically removed.

The first gas lamps were lit in St. Petersburg on Aptekarsky Island in 1819. The gas used was obtained by gasification of coal. It was called illuminating gas.

The great Russian scientist D.I. Mendeleev (1834-1907) first expressed the idea that gasification of coal can be carried out directly underground, without lifting it out. The tsarist government did not appreciate this proposal from Mendeleev.

The idea of underground gasification was warmly supported by V.I. Lenin. He called it “one of the great victories of technology.” Underground gasification was carried out for the first time by the Soviet state. Already before the Great Patriotic War, underground generators were operating in the Donetsk and Moscow Region coal basins in the Soviet Union.

An idea of one of the methods of underground gasification is given in Figure 3. Two wells are laid into the coal seam, which are connected below by a channel. Coal is set on fire in such a channel near one of the wells and blast is supplied there. Combustion products, moving along the channel, interact with hot coal, resulting in the formation of combustible gas as in a conventional generator. Gas comes to the surface through the second well.

Producer gas is widely used for heating industrial furnaces - metallurgical, coke ovens and as fuel in cars (Fig. 4).

Rice. 3. Scheme of underground gasification of coal.

A number of organic products are synthesized from hydrogen and carbon monoxide in water gas, for example liquid fuel. Synthetic liquid fuel is a fuel (mainly gasoline) obtained by synthesis from carbon monoxide and hydrogen at 150-170 degrees Celsius and a pressure of 0.7 - 20 MN/m2 (200 kgf/cm2), in the presence of a catalyst (nickel, iron, cobalt ). The first production of synthetic liquid fuel was organized in Germany during the 2nd World War due to a shortage of oil. Synthetic liquid fuel has not become widespread due to its high cost. Water gas is used to produce hydrogen. To do this, water gas mixed with water vapor is heated in the presence of a catalyst and as a result, hydrogen is obtained in addition to that already present in the water gas: CO + H 2 O = CO 2 + H 2