What is fuel?
It is one component or a mixture of substances that are capable of chemical transformations associated with the release of heat. Different types Fuels are distinguished by the quantitative content of an oxidizer in them, which is used to release thermal energy.
V broad sense fuel is an energy carrier, that is, a potential type of potential energy.
Classification
At present, the types of fuel are subdivided according to their state of aggregation into liquid, solid, and gaseous.
To solid natural species include stone and firewood, anthracite. Briquettes, coke, thermoanthracite are varieties of artificial solid fuel.
Substances that contain substances of organic origin are classified as liquids. 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, the composition gaseous fuel there is 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. allocate " equivalent fuel", Which means the calorific value of 1 kilogram of anthracite.
Domestic heating oil is intended for combustion in low-power heating devices that are located in residential premises, heat generators used in agriculture for drying feed, canning.
Specific heat of combustion of fuel is such a value that demonstrates the amount of heat that is formed during complete combustion of fuel with a volume of 1 m 3 or a mass of one kilogram.
To measure this value, use J / kg, J / m 3, calorie / m 3. Calorimetry is used to determine the calorific value.
With an increase in the specific heat of combustion of the 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, 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 highest and lowest heat of combustion is associated with the state of aggregation of water in the substances obtained after fuel combustion.
The highest calorific value is the amount of heat released during the 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.
Latent heat of condensation is the value of the energy of condensation of water vapor.
Mathematical relationship
The highest and lowest calorific values are related by the following relationship:
Q B = Q H + k (W + 9H)
where W is the amount by weight (in%) of water in a combustible substance;
H is the amount of hydrogen (% by mass) in the combustible substance;
k is a factor of 6 kcal / kg
Calculation Methods
The highest and lowest heat of combustion is determined by two main methods: calculated 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 in this case is completely absorbed by the water. Having an idea of the mass of water, it is possible to determine by the change in its temperature, the value of its heat of combustion.
This technique is considered simple and effective, it only assumes the possession of information about the data of technical analysis.
In the calculation method, the highest and lowest heat of combustion is 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 reference fuel.
The heat of combustion of gas allows preliminary calculations to be made, to reveal the efficiency of using a certain type of fuel.
Features of origin
In order to understand how much heat is released during the combustion of a certain fuel, it is necessary to have an idea of its origin.
There is in nature 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 bituminous coal is obtained, then anthracite is formed. The main sources of solid fuel formation are leaves, wood, and pine needles. Dying off, parts of plants when exposed to air are destroyed by fungi and form peat. Its accumulation turns into a brown mass, then brown gas is obtained.
At high pressure and temperature, brown gas turns into coal, then the fuel accumulates in the form of anthracite.
In addition to organic matter, there is additional ballast in the fuel. The part that was formed from organic matter: hydrogen, carbon, nitrogen, oxygen. In addition to these chemical elements, it contains ballast: moisture, ash.
Furnace technology assumes the release 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 mass is a composition in which there is no water.
Composition
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 bituminous and brown coal - 80 percent, 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 in any fuel. By binding 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, it is considered harmful impurities, therefore, its amount is clearly limited.
Sulfur is included in the fuel in the form of sulfates, sulfides, and also as sulfurous gases. When hydrated, sulfur oxides form sulfuric acid, which destroys boiler equipment, negatively affects vegetation and living organisms.
That is why sulfur is that chemical element, the presence of which in natural fuels is extremely undesirable. If it gets inside the working room, sulfur compounds cause significant poisoning of the maintenance personnel.
There are three types of ash, depending on its origin:
- primary;
- secondary;
- tertiary.
The primary species is formed from minerals that are found in plants. Secondary ash is formed as a result of the ingress of plant residues by sand and earth during formation.
Tertiary ash is included in the composition of the fuel during extraction, storage, and transportation. With a significant deposition of ash, there is a decrease in heat transfer on the heating surface of the boiler unit, reducing the amount of heat transfer to water from gases. Great amount ash negatively affects the operation of the boiler.
Finally
A significant effect on the combustion process of any type of fuel is exerted by volatiles... The larger their output, the larger the volume of the flame front will be. For example, coal, peat, easily ignite, the process is accompanied by insignificant heat losses. The coke, which remains after the removal of volatile impurities, contains only mineral and carbon compounds. Depending on the characteristics of the fuel, the amount of heat varies significantly.
Depending on the chemical composition, there are three stages of solid fuel formation: peat, brown coal, coal.
Natural wood is used in small boiler plants. They mainly use chips, sawdust, slabs, bark, the firewood itself is used in small quantities. Depending on the type of wood, the amount of heat released varies significantly.
As the heat of combustion decreases, firewood acquires certain advantages: quick flammability, minimal ash content, and the absence of traces of sulfur.
Reliable information about the composition of natural or synthetic fuels, their calorific value, is an excellent way to carry out thermochemical calculations.
Currently, there is a real opportunity to identify those main options for solid, gaseous, liquid fuels that will become the most effective and inexpensive to use in a particular situation.
The tables show 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 an exothermic oxidation reaction of fuel, its chemical energy is converted into thermal energy with the release of a certain amount of heat. The emerging thermal energy it is customary to call the heat of combustion of the 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.
Specific heat of combustion of fuel is the amount of heat released during the complete combustion of a unit of mass or volume of solid, liquid or gaseous fuel. In the International System of Units, this value is measured in J / kg or J / m 3.
The specific heat of combustion of the fuel can be determined experimentally or calculated analytically. Experimental methods for determining the 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 fuel with a known chemical composition, the specific heat of combustion can be determined using the Mendeleev formula.
Distinguish between higher and lower specific heats of combustion. The highest calorific value is maximum number the heat released during the complete combustion of the fuel, taking into account the heat spent on the evaporation of 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 is converted 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 performance characteristic of the fuel and is shown 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 terms of MJ / kg. The fuel in the table is sorted alphabetically by name.
The highest calorific value of the considered solid fuels is possessed by coking coal - its specific heat of combustion is 36.3 MJ / kg (or in SI units 36.3 · 10 6 J / kg). In addition, high heat of combustion is characteristic of coal, anthracite, charcoal and brown coal.
Fuels with low energy efficiency include wood, firewood, gunpowder, milling peat, 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 (pellets) | 18,5 |
| Dry firewood | 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 |
| Combustible 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 |
| Hard 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 heats of combustion of liquid fuel and some other organic liquids is given. It should be noted that such fuels as gasoline, diesel fuel and oil are distinguished by high heat release during combustion.
The specific heat of combustion of alcohol and acetone is significantly lower than traditional motor fuels. Moreover, regarding low value The heat of combustion is possessed by liquid rocket fuel 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 |
| Diesel fuel winter (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 |
| 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 |
| 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 fuel and combustible gases
The table of specific heats of combustion of gaseous fuel and some other combustible gases in terms of MJ / kg is presented. Of the gases considered, 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, such a fuel as natural gas has a high calorific value - the specific heat of combustion of natural gas is 41 ... 49 MJ / kg (for a 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 mass) | 60 |
| Hydrogen mixed with carbon monoxide (50% H 2 50% CO 2 by mass) | 65 |
| Blast furnace gas | 3 |
| Coke oven gas | 38,5 |
| Liquefied petroleum gas (LPG) (propane-butane) | 43,8 |
| Isobutane | 45,6 |
| Methane | 50 |
| n-Bhutan | 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 mass) | 52 |
| Ethane | 47,5 |
| Ethylene | 47,2 |
Specific heat of combustion of some combustible materials
There is a table of specific heats of combustion of some combustible materials (wood, paper, plastic, straw, rubber, etc.). Of note are materials with high combustion heat. These materials include: rubber different types, expanded polystyrene (polystyrene), 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 |
| The wood is green | 6,3 |
| Pine wood | 20,9 |
| Nylon | 31,1 |
| Carbolite products | 26,9 |
| Cardboard | 16,5 |
| Styrene-butadiene rubber SKS-30AR | 43,9 |
| Natural rubber | 44,8 |
| Synthetic rubber | 40,2 |
| SKS rubber | 43,9 |
| Chloroprene rubber | 28 |
| Linoleum, polyvinyl chloride | 14,3 |
| Two-layer polyvinyl chloride linoleum | 17,9 |
| Felt-based PVC linoleum | 16,6 |
| Linoleum, polyvinyl chloride on a warm basis | 17,6 |
| Linoleum, polyvinyl chloride on a fabric basis | 20,3 |
| Linoleum rubber (relin) | 27,2 |
| Paraffin wax | 11,2 |
| Polyfoam PVC-1 | 19,5 |
| Styrofoam FS-7 | 24,4 |
| Foam FF | 31,4 |
| Expanded polystyrene PSB-S | 41,6 |
| Polyurethane foam | 24,3 |
| Fiber board | 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 |
| Roofing material | 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 gross calorific value and calculation lower heat combustion.
- GOST 21261-91 Petroleum products. Method for determining the gross calorific value and calculating the net calorific value.
- GOST 22667-82 Natural combustible 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.
- Zemskiy G.T.
The amount of heat released during the complete combustion of a unit of the amount of fuel is called the calorific value (Q) or, as they sometimes say, 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 1 m 3, taken under normal conditions.
In technical calculations, normal conditions mean the state of the gas at a temperature equal to 0 ° C, and, at a pressure of 760 mmHg Art. The gas volume under these conditions is denoted nm 3(normal cubic meter).
For industrial gas measurements in accordance with GOST 2923-45, the normal conditions are taken as a temperature of 20 ° C and a Pressure of 760 mmHg Art. The volume of gas attributed to these conditions, in contrast to nm 3 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.
Distinguish between higher (Q in) and lower (Q n) calorific value. The gross calorific value takes into account the heat of condensation of water vapor generated during fuel combustion. The net calorific value does not take into account the heat contained in the water vapor of the combustion products, since water chests do not condense, but are carried away with the combustion products.
The concepts of Q in and Q n refer only to those gases, the combustion of which emits water vapor (these concepts do not apply to carbon monoxide, which does not produce water vapor during combustion).
During condensation of water vapor, heat is released, equal to 539 kcal / kg. In addition, when the condensate is cooled to 0 ° C (. Or 20 ° C), respectively, heat is released in the amount of 100 or 80 kcal / kg.
In total, more than 600 heat is released due to condensation of water vapor. 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 calorific values 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 urban conditions gas is supplied through pipes over considerable distances. If the calorific value is low, a large amount must be fed. 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 in the following: and to an increase in operating costs. A significant disadvantage of low-calorie gases is that in most cases they contain significant amount carbon monoxide, which increases the danger when using gas, as well as when servicing networks and installations.
Gas with a heating value of 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. Fluctuations, as we have already established, are allowed no more than 10%. Bigger change the calorific value of the gas requires a new adjustment, and sometimes a change a large number unified burners of household appliances, which is associated with significant difficulties.
Combustible gas classification
For gas supply to cities and industrial enterprises various combustible gases are used, differing in origin, chemical composition and physical properties.
By origin, combustible gases are divided into natural, or natural, and artificial, produced from solid and liquid fuels.
Natural gases are extracted from wells of purely gas fields or oil fields along the way with oil. Gases from oil fields are called associated gases.
Gases from pure gas fields are mainly methane with a small content of heavy hydrocarbons. They are characterized by a constant 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 factories-or obtained as a by-product of coal combustion at metallurgical plants, as well as at oil refineries.
Gases produced from coal are used in our country for urban gas supply in very limited quantities, and their proportion is constantly decreasing. At the same time, the production and consumption of liquefied hydrocarbon gases, obtained from associated petroleum gases at gas-petrol plants and at oil refineries during oil refining, is growing. Liquid hydrocarbon gases used for urban gas supply are composed mainly of propane and butane.
Gas composition
The type of gas and its composition largely determine the field of gas application, the scheme and diameters of the gas network, the design solutions of gas burners and individual gas pipeline units.
Gas consumption depends on the calorific value, and hence the diameters of gas pipelines and the conditions for gas combustion. When gas is used in industrial installations, the combustion temperature and flame propagation speed and the constancy of the composition are very important. gas fuel The composition of gases, as well as physicochemical 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) -gas without color, taste or smell, its net calorific value is 2579 kcal / nm 3 \ methane (CH 4) is a colorless, tasteless and odorless gas that is the main combustible part of natural gases, its net calorific value is 8555 kcal / nm 3; carbon monoxide (CO) is a gas without color, taste or smell, it turns out due to incomplete combustion of any fuel, it is very poisonous, net calorific value 3018 kcal / nm 3; heavy-hydrocarbons (C p H 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 usually called ballast. Natural gases are characterized by a high heating value and a complete absence of carbon monoxide. At the same time (a number of fields, mainly gas-oil fields, contain a very poisonous (and corrosively 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 are 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. even millions of cubic meters of gas, the total amount of impurities reaches a significant value. , and 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 when transporting gas through pipelines. Tar is a product of thermal decomposition of fuel and is associated with many artificial gases. In the presence of dust in the gas, the resin contributes to the formation of tar-mud plugs and blockages of 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 vapor is found in almost all natural and artificial gases. It enters natural gases in the gas field itself as a result of gas contacts with the water surface, and artificial gases are saturated with water during the production process. The presence of moisture in the gas in significant quantities is undesirable, since it lowers the calorific value of the gas. , moisture during gas combustion carries away a significant amount of heat along with combustion products into the atmosphere. points) to be deleted. This requires the installation of special condensate traps and their evacuation.
Sulfur compounds, as already noted, include hydrogen sulfide, as well as carbon disulfide, mercaptan, etc. These compounds not only have a detrimental effect on human health, but also cause significant corrosion of pipes.
Among other harmful impurities, ammonia and cyanide compounds should be noted, which are found mainly in coal gases. The presence of ammonia and cyanide compounds leads to increased corrosion of the 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 ballast that reduces the calorific value, which leads to an increase in the diameter of gas pipelines and to 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 | |
| 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 | ||
| 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 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 | - | ||
| Ash ....... | 23,5 | 9,3 | 3,5 | ____ | 0,2 | 4,5 | 1,132 | - | ||
| Fat .......... ............................. | 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 of the amount of fuel is called the calorific value (Q) or, as they sometimes say, 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 1 m 3, taken under normal conditions.
In technical calculations, normal conditions mean the state of the gas at a temperature equal to 0 ° C, and, at a pressure of 760 mmHg Art. The gas volume under these conditions is denoted nm 3(normal cubic meter).
For industrial gas measurements in accordance with GOST 2923-45, the normal conditions are taken as a temperature of 20 ° C and a Pressure of 760 mmHg Art. The volume of gas attributed to these conditions, in contrast to nm 3 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.
Distinguish between higher (Q in) and lower (Q n) calorific value. The gross calorific value takes into account the heat of condensation of water vapor generated during fuel combustion. The net calorific value does not take into account the heat contained in the water vapor of the combustion products, since water chests do not condense, but are carried away with the combustion products.
The concepts of Q in and Q n refer only to those gases, the combustion of which emits water vapor (these concepts do not apply to carbon monoxide, which does not produce water vapor during combustion).
During condensation of water vapor, heat is released, equal to 539 kcal / kg. In addition, when the condensate is cooled to 0 ° C (. Or 20 ° C), respectively, heat is released in the amount of 100 or 80 kcal / kg.
In total, more than 600 heat is released due to condensation of water vapor. 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 calorific values 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 urban conditions gas is supplied through pipes over considerable distances. If the calorific value is low, a large amount must be fed. 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 in the following: and to an increase in operating costs. A significant disadvantage of low-calorific 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 a heating value of 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. Fluctuations, as we have already established, are allowed no more than 10%. A large change in the calorific value of a gas requires a new adjustment, and sometimes a change in a large number of standardized burners of household appliances, which is associated with significant difficulties.
