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 are substances that contain substances 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, hydrogen sulfide, nitrogen, water vapor, oxygen.
Fuel indicators
The main indicator of combustion. Formula to determine calorific value considered in thermochemistry. emit "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.
Specific heat fuel combustion - this is such a value that 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 in the specific heat of 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 state of aggregation 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 carry out preliminary calculations, to identify the effectiveness of the application a certain kind 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.
Apart from organic matter, there is additional ballast in the fuel. An organic part is that part that was formed from organic matter: 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 hard 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 quantity is strictly 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 view is formed from minerals that are found 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
Volatile substances have a significant impact on the combustion process of any type of fuel. 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, three stages of the formation of solid fuels are distinguished: 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 fuel, its calorific value, is great way carrying out thermochemical calculations.
At present, there is a real opportunity to identify those main variants of solid, gaseous, liquid fuel, which will be the most effective and inexpensive to use in a particular situation.
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. Quantity gas fuel expressed in cubic meters under normal conditions (760 mm Hg and 0 ° C), and the composition - 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.
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%
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 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
|
Gas |
Designation |
Heat of combustion Q n s |
|
|
KJ/m3 |
kcal/m3 |
||
| Hydrogen | H, | 10820 | 2579 |
| carbon monoxide | SO | 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 |
Boilers of the DE type consume from 71 to 75 m3 of natural gas to produce one ton of steam. The cost of gas in Russia in September 2008 is 2.44 rubles per cubic meter. Consequently, 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 DE boilers at least 189 rubles per ton of steam.
Boilers of the DKVR type 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 for plants is at least 290 rubles per ton.
How to calculate the maximum consumption of natural gas for a steam boiler DE-25? it 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 gas. 8300. and all
Artificial gas fuel
Artificial combustible gases are fuel local importance because they have a much lower calorific value. Their main combustible elements are carbon monoxide CO and hydrogen H2. These gases are used within the limits of the production where they are obtained as fuel for technological and power plants.
All natural and artificial combustible gases are explosive, capable of igniting on an open flame or spark. There are lower and upper explosive limits of gas, i.e. the highest and lowest percentage concentrations in the air. Lower explosive limit natural gases ranges from 3% to 6%, and the top - from 12% to 16%. All combustible gases can cause poisoning of the human body. The main toxic substances of combustible gases are: carbon monoxide CO, hydrogen sulfide H2S, ammonia NH3.
Both natural combustible gases and artificial ones are colorless (invisible), odorless, which makes them dangerous when they penetrate into interior boiler room through leaks in gas pipeline fittings. To avoid poisoning, combustible gases should be treated with an odorant - a substance with an unpleasant odor.
Obtaining carbon monoxide CO in industry by gasification of solid fuel
For industrial purposes, carbon monoxide is obtained by gasification of solid fuel, i.e., its transformation into gaseous fuel. So 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 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 partially reduced to carbon monoxide: CO 2 + C \u003d 2CO
Rice. 1. Obtaining carbon monoxide (laboratory experience).
Under industrial conditions, gasification of solid fuels is carried out in furnaces called gas generators.
The resulting mixture of gases is called producer 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. From above, the gas generator is loaded with fuel; From below, air or water vapor is supplied by a fan through the grate.
Oxygen in the air reacts with the carbon of the fuel, forming carbon dioxide, which, rising up through a layer of hot fuel, is reduced by carbon to carbon monoxide.
If only air is blown into the generator, then a gas is obtained, which in its composition contains carbon monoxide and nitrogen of the air (as well as a certain amount of CO 2 and other impurities). This generator gas is called air gas.
If, however, water vapor is blown into the generator with hot coal, then carbon monoxide and hydrogen are formed as a result of the reaction: C + H 2 O \u003d 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 combustible 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 (calorific value 10,500 kJ/m3, or 2730 kcal/mg) and at the same time raw material for the synthesis of methanol. Water gas, however, cannot be obtained long time, since the reaction of its formation is endothermic (with the absorption of heat), and therefore the fuel in the generator cools down. In order to keep the coal in a hot state, the injection of water vapor into the generator is alternated with the injection of air, the oxygen of which, as is known, reacts with the fuel with the release of heat.
AT recent times steam-oxygen blast began to be widely used for fuel gasification. Simultaneous blowing of water vapor and oxygen through the fuel layer makes it possible to carry out the process continuously, significantly increase the performance of the generator and obtain gas with high content hydrogen and carbon monoxide.
Modern gas generators are powerful devices of continuous action.
So that when fuel is supplied to the gas generator, combustible and toxic gases do not penetrate into the atmosphere, the loading drum is made double. While fuel enters one compartment of the drum, fuel is poured out of the other compartment into the generator; when the drum rotates, these processes are repeated, while the generator remains isolated from the atmosphere all the time. Uniform distribution fuel in the generator is carried out using a cone, which can be installed at different heights. When it is lowered, the coal lies 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 to the walls of the generator and is thrown into the ash box with special devices, from where it is periodically removed.
The first gas lamps were lit in St. Petersburg on Aptekarsky Island in 1819. The gas that was used was obtained by gasification hard coal. It was called light gas.
The great Russian scientist D. I. Mendeleev (1834-1907) was the first to express the idea that the gasification of coal can be carried out directly underground, without lifting it out. The tsarist government did not appreciate Mendeleev's proposal.
The idea of underground gasification was warmly supported by V. I. Lenin. He called it "one of the great triumphs of technology." Underground gasification was carried out for the first time Soviet state. Already before the Great Patriotic War, underground generators were operating in the Donetsk and Moscow region coal basins in the Soviet Union.
Figure 3 gives an idea of one of the methods of underground gasification. Two wells are laid in the coal seam, which are connected at the bottom with 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. The gas comes to the surface through the second well.
Generator gas is widely used for heating industrial furnaces - metallurgical, coke and as a fuel in cars (Fig. 4).
Rice. 3. Scheme of underground gasification of coal.
A number of organic products, such as liquid fuels, are synthesized from hydrogen and carbon monoxide of water gas. Synthetic liquid fuel - 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 fuels was organized in Germany during the 2nd World War due to the shortage of oil. Synthetic liquid fuels have not received wide distribution due to their high cost. Water gas is used to produce hydrogen. To do this, water gas in a mixture 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 water gas: CO + H 2 O \u003d CO 2 + H 2
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 according to GOST 2923-45 for normal conditions assumed temperature 20°C and pressure 760 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 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 to long distances and easier to organize burning. 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 a large number standardized burners for household appliances, which is associated with significant difficulties.
The tables present the mass specific heat of combustion of fuel (liquid, solid and gaseous) and some other combustible materials. Fuels such as: coal, firewood, coke, peat, kerosene, oil, alcohol, gasoline, natural gas, etc. are considered.
List of tables:
At exothermic reaction fuel oxidation, its chemical energy is converted into thermal energy with the release of a certain amount of heat. The emerging thermal energy called the heat of combustion of the fuel. It depends on its chemical composition, humidity and is the main one. The calorific value of fuel, referred to 1 kg of mass or 1 m 3 of volume, forms the mass or volumetric specific calorific value.
The specific heat of combustion of fuel is the amount of heat released during the complete combustion of a unit mass or volume of solid, liquid or gaseous fuel. AT international system units, this value is measured in J / kg or J / m 3.
The specific heat of combustion of a fuel can be determined experimentally or calculated analytically. Experimental Methods definitions of calorific value are based on the practical measurement of the amount of heat released during the combustion of fuel, for example in a calorimeter with a thermostat and a combustion bomb. For a fuel with a known chemical composition, the specific heat of combustion can be determined from Mendeleev's formula.
There are higher and lower specific heats of combustion. The gross calorific value is equal to the maximum number heat released during complete combustion of the fuel, taking into account the heat spent on the evaporation of the moisture contained in the fuel. Net calorific value less value higher by the value of the heat of condensation, which is formed from the moisture of the fuel and the hydrogen of the organic mass, which turns into water during combustion.
To determine fuel quality indicators, as well as in heat engineering calculations usually use the lowest specific heat of combustion, which is the most important thermal and operational characteristic of the fuel and is given in the tables below.
Specific heat of combustion of solid fuel (coal, firewood, peat, coke)
The table shows the values of the specific heat of combustion of dry solid fuel in the unit of MJ/kg. The fuel in the table is arranged by name in alphabetical order.
Of the considered solid fuels, coking coal has the highest calorific value - its specific heat of combustion is 36.3 MJ/kg (or 36.3·10 6 J/kg in SI units). In addition, high calorific value is characteristic of coal, anthracite, charcoal and brown coal.
Fuels with low energy efficiency include wood, firewood, gunpowder, freztorf, oil shale. For example, the specific heat of combustion of firewood is 8.4 ... 12.5, and gunpowder - only 3.8 MJ / kg.
| Fuel | |
|---|---|
| Anthracite | 26,8…34,8 |
| Wood pellets (pillets) | 18,5 |
| Firewood dry | 8,4…11 |
| Dry birch firewood | 12,5 |
| gas coke | 26,9 |
| blast-furnace coke | 30,4 |
| semi-coke | 27,3 |
| Powder | 3,8 |
| Slate | 4,6…9 |
| Oil shale | 5,9…15 |
| Solid rocket fuel | 4,2…10,5 |
| Peat | 16,3 |
| fibrous peat | 21,8 |
| Milling peat | 8,1…10,5 |
| Peat crumb | 10,8 |
| Brown coal | 13…25 |
| Brown coal (briquettes) | 20,2 |
| Brown coal (dust) | 25 |
| Donetsk coal | 19,7…24 |
| Charcoal | 31,5…34,4 |
| Coal | 27 |
| Coking coal | 36,3 |
| Kuznetsk coal | 22,8…25,1 |
| Chelyabinsk coal | 12,8 |
| Ekibastuz coal | 16,7 |
| freztorf | 8,1 |
| Slag | 27,5 |
Specific heat of combustion of liquid fuel (alcohol, gasoline, kerosene, oil)
The table of specific heat of combustion of liquid fuel and some other organic liquids is given. It should be noted that fuels such as gasoline, diesel fuel and oil are characterized by high heat release during combustion.
The specific heat of combustion of alcohol and acetone is significantly lower than traditional motor fuels. In addition, liquid propellant has a relatively low calorific value and, with the complete combustion of 1 kg of these hydrocarbons, an amount of heat equal to 9.2 and 13.3 MJ, respectively, will be released.
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| Acetone | 31,4 |
| Gasoline A-72 (GOST 2084-67) | 44,2 |
| Aviation gasoline B-70 (GOST 1012-72) | 44,1 |
| Gasoline AI-93 (GOST 2084-67) | 43,6 |
| Benzene | 40,6 |
| Winter diesel fuel (GOST 305-73) | 43,6 |
| Summer diesel fuel (GOST 305-73) | 43,4 |
| Liquid propellant (kerosene + liquid oxygen) | 9,2 |
| Aviation kerosene | 42,9 |
| Lighting kerosene (GOST 4753-68) | 43,7 |
| xylene | 43,2 |
| High sulfur fuel oil | 39 |
| Low-sulfur fuel oil | 40,5 |
| Low sulfur fuel oil | 41,7 |
| Sulphurous fuel oil | 39,6 |
| Methyl alcohol (methanol) | 21,1 |
| n-Butyl alcohol | 36,8 |
| Oil | 43,5…46 |
| Oil methane | 21,5 |
| Toluene | 40,9 |
| White spirit (GOST 313452) | 44 |
| ethylene glycol | 13,3 |
| Ethyl alcohol (ethanol) | 30,6 |
Specific heat of combustion of gaseous fuel and combustible gases
A table of the specific heat of combustion of gaseous fuel and some other combustible gases in the dimension of MJ/kg is presented. Of the considered gases, the largest mass specific heat of combustion differs. With the complete combustion of one kilogram of this gas, 119.83 MJ of heat will be released. Also, a fuel such as natural gas has a high calorific value - the specific heat of combustion of natural gas is 41 ... 49 MJ / kg (for pure 50 MJ / kg).
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| 1-Butene | 45,3 |
| Ammonia | 18,6 |
| Acetylene | 48,3 |
| Hydrogen | 119,83 |
| Hydrogen, mixture with methane (50% H 2 and 50% CH 4 by mass) | 85 |
| Hydrogen, mixture with methane and carbon monoxide (33-33-33% by weight) | 60 |
| Hydrogen, mixture with carbon monoxide (50% H 2 50% CO 2 by mass) | 65 |
| Blast Furnace Gas | 3 |
| coke oven gas | 38,5 |
| LPG liquefied hydrocarbon gas (propane-butane) | 43,8 |
| Isobutane | 45,6 |
| Methane | 50 |
| n-butane | 45,7 |
| n-Hexane | 45,1 |
| n-Pentane | 45,4 |
| Associated gas | 40,6…43 |
| Natural gas | 41…49 |
| Propadien | 46,3 |
| Propane | 46,3 |
| Propylene | 45,8 |
| Propylene, mixture with hydrogen and carbon monoxide (90%-9%-1% by weight) | 52 |
| Ethane | 47,5 |
| Ethylene | 47,2 |
Specific heat of combustion of some combustible materials
A table is given of the specific heat of combustion of some combustible materials (, wood, paper, plastic, straw, rubber, etc.). It should be noted materials with high heat release during combustion. These materials include: rubber various types, expanded polystyrene (styrofoam), polypropylene and polyethylene.
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| Paper | 17,6 |
| Leatherette | 21,5 |
| Wood (bars with a moisture content of 14%) | 13,8 |
| Wood in stacks | 16,6 |
| Oak wood | 19,9 |
| Spruce wood | 20,3 |
| wood green | 6,3 |
| Pine wood | 20,9 |
| Kapron | 31,1 |
| Carbolite products | 26,9 |
| Cardboard | 16,5 |
| Styrene-butadiene rubber SKS-30AR | 43,9 |
| Natural rubber | 44,8 |
| Synthetic rubber | 40,2 |
| Rubber SCS | 43,9 |
| Chloroprene rubber | 28 |
| Polyvinyl chloride linoleum | 14,3 |
| Two-layer polyvinyl chloride linoleum | 17,9 |
| Linoleum polyvinylchloride on a felt basis | 16,6 |
| Linoleum polyvinyl chloride on a warm basis | 17,6 |
| Linoleum polyvinylchloride on a fabric basis | 20,3 |
| Linoleum rubber (relin) | 27,2 |
| Paraffin solid | 11,2 |
| Polyfoam PVC-1 | 19,5 |
| Polyfoam FS-7 | 24,4 |
| Polyfoam FF | 31,4 |
| Expanded polystyrene PSB-S | 41,6 |
| polyurethane foam | 24,3 |
| fibreboard | 20,9 |
| Polyvinyl chloride (PVC) | 20,7 |
| Polycarbonate | 31 |
| Polypropylene | 45,7 |
| Polystyrene | 39 |
| High density polyethylene | 47 |
| Low-pressure polyethylene | 46,7 |
| Rubber | 33,5 |
| Ruberoid | 29,5 |
| Soot channel | 28,3 |
| Hay | 16,7 |
| Straw | 17 |
| Organic glass (plexiglass) | 27,7 |
| Textolite | 20,9 |
| Tol | 16 |
| TNT | 15 |
| Cotton | 17,5 |
| Cellulose | 16,4 |
| Wool and wool fibers | 23,1 |
Sources:
- GOST 147-2013 Solid mineral fuel. Determination of the higher calorific value and calculation of the lower calorific value.
- GOST 21261-91 Petroleum products. Method for determining the gross calorific value and calculating the net calorific value.
- GOST 22667-82 Combustible natural gases. Calculation method for determining the calorific value, relative density and Wobbe numbers.
- GOST 31369-2008 Natural gas. Calculation of calorific value, density, relative density and Wobbe number based on component composition.
- Zemsky G. T. Flammable properties of inorganic and organic materials: reference book M.: VNIIPO, 2016 - 970 p.
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 extracted from wells 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 on 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 specific gravity they are decreasing all the time. 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 the gas, the scheme and diameters gas network, Constructive decisions gas burners and individual units of gas pipelines.
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 very significant. Composition of gases, as well as physiochemical properties they 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 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)
| Western Ukraine. . . | 81,2 | 7,5 | 4,5 | 3,7 | 2,5 | - . | 0,1 | 0,5 | 0,735 | |
| Shebelinskoye .............................. | 92,9 | 4,5 | 0,8 | 0,6 | 0,6 | ____ . | 0,1 | 0,5 | 0,603 | |
| Stavropol region. . | 98,6 | 0,4 | 0,14 | 0,06 | - | 0,1 | 0,7 | 0,561 | ||
| Krasnodar region. . | 92,9 | 0,5 | - | 0,5 | _ | 0,01 | 0,09 | 0,595 | ||
| Saratov ............................... | 93,4 | 2,1 | 0,8 | 0,4 | 0,3 | Traces | 0,3 | 2,7 | 0,576 | |
| Gazli, Bukhara region | 96,7 | 0,35 | 0,4" | 0,1 | 0,45 | 0,575 | ||||
| From oil and gas fields (associated) | ||||||||||
| Romashkino ............................... | 18,5 | 6,2 | 4,7 | 0,1 | 11,5 | 1,07 | ||||
| 7,4 | 4,6 | ____ | Traces | 1,112 | __ . | |||||
| Tuymazy ............................... | 18,4 | 6,8 | 4,6 | ____ | 0,1 | 7,1 | 1,062 | - | ||
| Ashy....... | 23,5 | 9,3 | 3,5 | ____ | 0,2 | 4,5 | 1,132 | - | ||
| Bold.......... ............................. . | 2,5 | . ___ . | 1,5 | 0,721 | - | |||||
| Syzran-oil ............................... | 31,9 | 23,9 - | 5,9 | 2,7 | 0,8 | 1,7 | 1,6 | 31,5 | 0,932 | - |
| Ishimbay ............................... | 42,4 | 20,5 | 7,2 | 3,1 | 2,8 | 1,040 | _ | |||
| Andijan. ............................... | 66,5 | 16,6 | 9,4 | 3,1 | 3,1 | 0,03 | 0,2 | 4,17 | 0,801 ; | |
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 of a large number of unified burners for household appliances, which is associated with significant difficulties.
