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 is a product of petroleum 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%
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(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 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 |
|
|
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 DE boilers no less than 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 area 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 obtained by gasification of 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.
Gasification process solid fuel 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. Let's 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 maintain 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 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 ignited 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, such as liquid fuel, are synthesized from hydrogen and carbon monoxide in water gas. 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 ). First production of synthetic liquid fuel 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
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 their quantitative content of oxidizer, which is used to release thermal energy.
In a broad sense, fuel is an energy carrier, that is, a potential type of potential energy.
Classification
Currently, fuel types are divided according to their state of aggregation into liquid, solid, and gaseous.
Stone, firewood and anthracite are considered hard natural materials. Briquettes, coke, thermoanthracite are types of artificial solid fuel.
Liquids include substances that contain substances organic origin. Their main components are: oxygen, carbon, nitrogen, hydrogen, sulfur. Artificial liquid fuel will be a variety of resins and fuel oil.
It is a mixture of various gases: ethylene, methane, propane, butane. In addition to them, gaseous fuel contains carbon dioxide and carbon monoxide, hydrogen sulfide, nitrogen, water vapor, oxygen.
Fuel indicators
The main indicator of combustion. Formula for determining calorific value considered in thermochemistry. highlight " standard fuel", which implies the heat of combustion of 1 kilogram of anthracite.
Household 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 feed, canning.
Specific heat fuel combustion is such a value that demonstrates the amount of heat that is generated 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/m3, calorie/m3 are used. To determine the heat of combustion, the calorimetry method is used.
With an increase in the specific heat of combustion of fuel, the specific fuel consumption decreases, and the coefficient useful action remains unchanged.
The heat of combustion of substances is the amount of energy released during the oxidation of a solid, liquid, or 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 values are related to the state of aggregation of water in the substances obtained after combustion of fuel.
The higher calorific value is the amount of heat released during complete combustion of a substance. This value also includes the heat of condensation of water vapor.
The lowest working heat of combustion 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 amount of energy of condensation of water vapor.
Mathematical relationship
The higher and lower calorific values are related by the following relationship:
QB = QH + k(W + 9H)
where W is the amount by weight (in %) of water in a flammable substance;
H is the amount of hydrogen (% by mass) in the combustible substance;
k - coefficient equal to 6 kcal/kg
Methods for performing calculations
The higher and lower calorific values are determined by two main methods: calculation and experimental.
Calorimeters are used to carry out experimental calculations. First, a sample of fuel is burned in it. The heat that will be released is completely absorbed by the water. Having an idea of the mass of water, you can determine by the change in its temperature the value of its heat of combustion.
This technique is considered simple and effective; it only requires knowledge of technical analysis data.
In the calculation method, the higher and lower calorific values are calculated using the Mendeleev formula.
Q p H = 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 equivalent fuel.
The heat of combustion of gas allows for preliminary calculations and identification of the efficiency of use certain type fuel.
Features of origin
In order to understand how much heat is released when a certain fuel is burned, it is necessary to have an idea of its origin.
In nature there is different options solid fuels, which differ in composition and properties.
Its formation occurs through several stages. First, peat is formed, then brown and hard coal are obtained, then anthracite is formed. The main sources of solid fuel formation are leaves, wood, and pine needles. When parts of plants die and are exposed to air, they are destroyed by fungi and form peat. Its accumulation turns into a brown mass, then brown gas is obtained.
At high blood pressure and temperature, brown gas turns into coal, then the fuel accumulates in the form of anthracite.
In addition to organic matter, the fuel contains additional ballast. Organic is considered to be the part that is formed from organic matter: hydrogen, carbon, nitrogen, oxygen. In addition to these chemical elements, it contains ballast: moisture, ash.
Combustion technology involves the separation of the working, dry, and combustible mass of burned fuel. The working mass is the fuel in its original form supplied to the consumer. Dry mass is a composition in which there is no water.
Compound
The most valuable components are carbon and hydrogen.
These elements are contained 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 fuel combustion changes. Hydrogen is the second most important element of any fuel. When it binds 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. The oxygen contained in the fuel acts as ballast.
It is not heat generating chemical element, therefore has a negative impact on the value of its heat of combustion. The combustion of nitrogen, contained in free or bound form in combustion products, is considered harmful impurities, therefore its quantity is clearly limited.
Sulfur is included in 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 a chemical element whose presence in natural fuel is extremely undesirable. If sulfur compounds get inside the work area, they cause significant poisoning of operating personnel.
There are three types of ash depending on its origin:
- primary;
- secondary;
- tertiary
The primary view is formed from minerals, which are found in plants. Secondary ash is formed as a result of plant residues entering sand and soil during formation.
Tertiary ash appears in the composition of fuel during extraction, storage, and transportation. With significant ash deposition, a decrease in heat transfer on the heating surface of the boiler unit occurs, reducing the amount of heat transfer to water from gases. A huge amount of ash negatively affects the operation of the boiler.
In conclusion
Volatile substances have a significant influence on the combustion process of any type of fuel. The greater their output, the larger the volume of the flame front will be. For example, coal and peat ignite easily, the process is accompanied by minor heat losses. The coke that remains after removing volatile impurities contains only mineral and carbon compounds. Depending on the characteristics of the fuel, the amount of heat changes significantly.
Depending on the chemical composition, there are three stages of solid fuel formation: peat, lignite, and coal.
Natural wood is used in small boiler installations. They mainly use wood chips, sawdust, slabs, bark, and the firewood itself is used in small quantities. Depending on the type of wood, the amount of heat generated varies significantly.
As the heat of combustion 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 in a great way carrying out thermochemical calculations.
Currently appearing real opportunity identifying those main options for solid, gaseous, liquid fuels that will be the most effective and inexpensive to use in a certain situation.
The tables present the mass specific heat of combustion of fuel (liquid, solid and gaseous) and some other combustible materials. The following fuels were considered: coal, firewood, coke, peat, kerosene, oil, alcohol, gasoline, natural gas, etc.
List of tables:
During the exothermic reaction of fuel oxidation, its chemical energy is converted into thermal energy with the release of a certain amount of heat. The resulting thermal energy is usually called the heat of combustion of fuel. It depends on its chemical composition, humidity and is the main one. The heat of combustion of fuel per 1 kg of mass or 1 m 3 of volume forms the mass or volumetric specific heat of combustion.
The specific heat of combustion of a fuel is the amount of heat released during the complete combustion of a unit mass or volume of solid, liquid or gaseous fuel. IN 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 for determining calorific value are based on practical measurement of the amount of heat released when a fuel burns, for example in a calorimeter with a thermostat and a combustion bomb. For fuel with a known chemical composition, the specific heat of combustion can be determined using the periodic formula.
There are higher and lower specific heats of combustion. The higher calorific value is maximum number the heat released during complete combustion of the fuel, taking into account the heat expended on the evaporation of moisture contained in the fuel. Lower heating value less than value higher by the amount of heat of condensation, which is formed from the moisture of the fuel and hydrogen of the organic mass, which turns into water during combustion.
To determine fuel quality indicators, as well as in thermal calculations usually use lower specific heat of combustion, which is the most important thermal and performance characteristic of the fuel and is shown in the tables below.
Specific heat of combustion of solid fuels (coal, firewood, peat, coke)
The table presents the values of the specific heat of combustion of dry solid fuel in the dimension MJ/kg. Fuel in the table is arranged by name in alphabetical order.
The highest calorific value of those considered hard species Coking coal has a fuel - its specific heat of combustion is 36.3 MJ/kg (or in SI units 36.3 10 6 J/kg). In addition, high calorific value is characteristic of coal, anthracite, charcoal and brown coal.
Fuels with low energy efficiency include wood, firewood, gunpowder, milling peat, and oil shale. For example, the specific heat of combustion of firewood is 8.4...12.5, and that of gunpowder is only 3.8 MJ/kg.
| Fuel | |
|---|---|
| Anthracite | 26,8…34,8 |
| Wood pellets (pellets) | 18,5 |
| Dry firewood | 8,4…11 |
| Dry birch firewood | 12,5 |
| Gas coke | 26,9 |
| Blast 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 |
| Milled 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)
A table is given of the specific heat of combustion of liquid fuel and some other organic liquids. It should be noted that fuels such as gasoline, diesel fuel and oil have high heat release during combustion.
The specific heat of combustion of alcohol and acetone is significantly lower than traditional motor fuels. Moreover, relatively low value Liquid rocket fuel has a calorific value and - with complete combustion of 1 kg of these hydrocarbons, an amount of heat will be released equal to 9.2 and 13.3 MJ, respectively.
| 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 rocket fuel (kerosene + liquid oxygen) | 9,2 |
| Aviation kerosene | 42,9 |
| Kerosene for lighting (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 |
| Methane oil | 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 fuels and combustible gases
A table is presented of the specific heat of combustion of gaseous fuel and some other combustible gases in the dimension MJ/kg. Of the gases considered, it has the highest mass specific heat of combustion. The complete combustion of one kilogram of this gas will release 119.83 MJ of heat. Also, 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 gas it is 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 weight) | 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 weight) | 65 |
| Blast furnace gas | 3 |
| Coke Oven Gas | 38,5 |
| Liquefied hydrocarbon gas LPG (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 |
| Propadiene | 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 provided of the specific heat of combustion of some combustible materials (wood, paper, plastic, straw, rubber, etc.). Materials with high heat release during combustion should be noted. These materials include: rubber various types, expanded polystyrene (foam), polypropylene and polyethylene.
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| Paper | 17,6 |
| Leatherette | 21,5 |
| Wood (bars with 14% moisture content) | 13,8 |
| Wood in stacks | 16,6 |
| Oak wood | 19,9 |
| Spruce wood | 20,3 |
| Wood green | 6,3 |
| Pine wood | 20,9 |
| Capron | 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 SKS | 43,9 |
| Chloroprene rubber | 28 |
| Polyvinyl chloride linoleum | 14,3 |
| Double-layer polyvinyl chloride linoleum | 17,9 |
| Polyvinyl chloride linoleum on a felt basis | 16,6 |
| Warm-based polyvinyl chloride linoleum | 17,6 |
| Fabric-based polyvinyl chloride linoleum | 20,3 |
| Rubber linoleum (Relin) | 27,2 |
| Paraffin paraffin | 11,2 |
| Polystyrene foam PVC-1 | 19,5 |
| Foam plastic FS-7 | 24,4 |
| Foam plastic FF | 31,4 |
| Expanded polystyrene PSB-S | 41,6 |
| Polyurethane foam | 24,3 |
| Fiberboard | 20,9 |
| Polyvinyl chloride (PVC) | 20,7 |
| Polycarbonate | 31 |
| Polypropylene | 45,7 |
| Polystyrene | 39 |
| High pressure polyethylene | 47 |
| Low pressure polyethylene | 46,7 |
| Rubber | 33,5 |
| Ruberoid | 29,5 |
| Channel soot | 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 higher calorific value and calculation lower heat combustion.
- GOST 21261-91 Petroleum products. Method for determining the higher calorific value and calculating the lower calorific value.
- GOST 22667-82 Natural flammable gases. Calculation method for determining the calorific value, relative density and Wobbe number.
- 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 flammable gases
For gas supply to cities and industrial enterprises They use various flammable gases that differ in origin, chemical composition and physical properties.
Based on their origin, combustible gases are divided into natural, or natural, and artificial, produced from solid and liquid fuels.
Natural gases extracted from wells of pure gas fields or oil fields along with oil. Gases from oil fields are called associated gases.
Gases from pure gas fields mainly consist of methane with a small content of heavy hydrocarbons. They are characterized by a constant composition and calorific value.
Associated gases Along with methane, they contain a significant amount of heavy hydrocarbons (propane and butane). The composition and calorific value of these gases vary widely.
Artificial gases are produced at special gas plants - or obtained as by-product when burning coal in metallurgical plants, as well as in oil refining plants.
In our country, gases produced from coal are used in very limited quantities for urban gas supply, and their specific gravity is constantly decreasing. At the same time, the production and consumption of liquefied hydrocarbon gases obtained from associated petroleum gases at gas-gasoline plants and at 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 determine the scope of gas application, the layout and diameters of the gas network, constructive solutions gas burner devices and individual gas pipeline units.
Gas consumption depends on the calorific value, and hence the diameters of gas pipelines and gas combustion conditions. When using gas in industrial installations, the combustion temperature and flame propagation speed and the constancy of the composition of the gas fuel are very important. Composition of gases, as well as physical and chemical 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 gaseous fuel includes: hydrogen (H 2) - a colorless, taste and odorless gas, its lower calorific value is 2579 kcal/nm 3\ methane (CH 4) - a gas without color, taste and smell, 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, produced by incomplete combustion of any fuel, very toxic, lower calorific value 3018 kcal/nm 3 ; heavy-hydrocarbons (S p N t), 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 gaseous fuel includes: carbon dioxide (CO 2), oxygen (O 2) and nitrogen (N 2).
The non-combustible part of gases is usually called ballast. Natural gases are characterized by high calorific value and a complete absence of carbon monoxide. At the same time, a number of deposits, 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 oxides in the gas carbon and other toxic substances are highly undesirable, since they complicate 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. However, if you consider that thousands of gases are supplied through gas pipelines. 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 passage. Therefore, the presence of impurities in gas must be taken into account when designing gas pipelines. , and during operation.
The amount and composition of impurities depend on the method of gas production or extraction and the degree of its purification. The most harmful impurities are dust, tar, naphthalene, moisture and sulfur compounds.
Dust appears in gas during the production process (extraction) or during gas transportation through pipelines. Resin is a product of thermal decomposition of fuel and accompanies many artificial gases. If there is dust in the gas, the resin contributes to the formation of tar-mud plugs and blockages of gas pipelines.
Naphthalene is commonly found in man-made 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 vapor is contained in almost all natural and artificial gases. It gets into natural gases in the gas field itself due to contacts of gases with the surface of water, 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 along with combustion products into the atmosphere. A high moisture content in the gas is also undesirable because, condensing when the gas is cooled during its movement through the pipes, it can create water plugs in the gas pipeline (at lower levels). points) that need 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 have a harmful effect on 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 flammable gases is also undesirable. These gases do not participate in the combustion process, being 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 from 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 | |
| Shebelinskoe......................................... | 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 | ||
| Saratovskoe............................... | 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 gas and oil 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 | - | ||
| Fat........ ................................ . | 2,5 | . ___ . | 1,5 | 0,721 | - | |||||
| Syzran-neft................................... | 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 complete combustion of a unit amount of fuel is called calorific value (Q) or, as is sometimes said, calorific value, or calorific value, which is one of the main characteristics of fuel.
The calorific value of gases is usually referred to as 1 m 3, taken under normal conditions.
In technical calculations, normal conditions mean the state of the gas at a temperature of 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, temperature 20°C and Pressure 760 are taken as normal conditions mmHg Art. The volume of gas assigned to these conditions, as opposed to nm 3 we'll call m 3 (cubic meter).
Calorific value of gases (Q)) expressed in kcal/nm e or in kcal/m3.
For liquefied gases, the calorific value is referred to as 1 kg.
There are higher (Qc) and lower (Qn) calorific values. Gross calorific value takes into account the heat of condensation of water vapor generated during fuel combustion. The lower calorific value does not take into account the heat contained in the water vapor of the combustion products, since the water vapor does not condense, but is carried away with the combustion products.
The concepts Q in and Q n refer only to those gases whose combustion releases water vapor (these concepts do not apply to carbon monoxide, which does not produce water vapor upon 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 in the amount of 100 or 80, respectively. kcal/kg.
In total, more than 600 heat is released due to the condensation of water vapor. kcal/kg, which is the difference between the higher and lower calorific value of the gas. For most gases used in urban gas supply, this difference is 8-10%.
The calorific values of some gases are given in table. 3.
For urban gas supply, gases are currently used that, as a rule, have a calorific value of at least 3500 kcal/nm 3 . This is explained by the fact that in urban areas gas is supplied through pipes over considerable distances. When the calorific value is low, a large quantity must be supplied. This inevitably leads to an increase in the diameters of gas pipelines and, as a consequence, 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 calorific value less than 3500 kcal/nm 3 most often used in industry, where it is not necessary to transport it over long distances and it is easier to organize combustion. 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 larger change in the calorific value of gas requires new adjustments and sometimes replacement of a large number of standardized burners of household appliances, which is associated with significant difficulties.
