Calorific value of petroleum gas. gaseous fuel
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 the water vapor does not condense, but is carried away with the combustion products.
The concepts of 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 in a large number of unified 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:
In an exothermic fuel oxidation reaction, its chemical energy is converted into thermal energy with the release of a certain amount of heat. The resulting thermal energy is 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. In the International System of 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 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 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 amount of heat released during complete combustion of the fuel, taking into account the heat spent on the evaporation of the moisture contained in the fuel. The lower calorific value is less than the higher value 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 propellant | 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. Such materials include: rubber of various 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 |
| 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 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.
Substances of organic origin include fuel, which, when burned, releases a certain amount of thermal energy. Heat generation should be characterized by high efficiency and the absence of side effects, in particular, substances harmful to human health and the environment.
For ease of loading into the furnace, wood material is cut into individual elements up to 30 cm long. To increase the efficiency of their use, firewood should be as dry as possible, and the combustion process should be relatively slow. In many respects, firewood from such hardwoods as oak and birch, hazel and ash, hawthorn is suitable for space heating. Due to the high resin content, increased burning rate and low calorific value, conifers are significantly inferior in this regard.
It should be understood that the density of wood affects the value of the calorific value.
It is a natural material of plant origin, extracted from sedimentary rock.
This type of solid fuel contains carbon and other chemical elements. There is a division of material into types depending on its age. Brown coal is considered the youngest, followed by hard coal, and anthracite is the oldest of all other types. The age of the combustible substance also determines its moisture content, which is more present in the young material.
During the combustion of coal, the environment is polluted, and slag is formed on the grate of the boiler, which, to a certain extent, creates an obstacle to normal combustion. The presence of sulfur in the material is also an unfavorable factor for the atmosphere, since this element is converted into sulfuric acid in the air space.
However, consumers should not be afraid for their health. Manufacturers of this material, taking care of private customers, seek to reduce the sulfur content in it. The calorific value of coal can differ even within the same type. The difference depends on the characteristics of the subspecies and the content of minerals in it, as well as the geography of production. As a solid fuel, not only pure coal is found, but also low-enriched coal slag pressed into briquettes.
Pellets (fuel pellets) is a solid fuel created industrially from wood and plant waste: shavings, bark, cardboard, straw.
The raw material crushed to the state of dust is dried and poured into the granulator, from where it already comes out in the form of granules of a certain shape. To add viscosity to the mass, a vegetable polymer, lignin, is used. The complexity of the production process and high demand form the cost of pellets. The material is used in specially equipped boilers.
The types of fuel are determined depending on what material they are processed from:
- round timber of trees of any species;
- straw;
- peat;
- sunflower husk.
Among the advantages that fuel pellets have, it is worth noting the following qualities:
- environmental friendliness;
- inability to deform and resistance to fungus;
- ease of storage even outdoors;
- uniformity and duration of burning;
- relatively low cost;
- the possibility of using for various heating devices;
- suitable pellet size for automatic loading into a specially equipped boiler.
Briquettes
Briquettes are called solid fuel, in many respects similar to pellets. For their manufacture, identical materials are used: wood chips, shavings, peat, husks and straw. During the production process, the raw material is crushed and formed into briquettes by compression. This material also belongs to environmentally friendly fuel. It is convenient to store it even outdoors. Smooth, uniform and slow burning of this fuel can be observed both in fireplaces and stoves, and in heating boilers.
The varieties of environmentally friendly solid fuels discussed above are a good alternative to generating heat. Compared to fossil sources of thermal energy, which adversely affect the environment during combustion and are, moreover, non-renewable, alternative fuels have clear advantages and relatively low cost, which is important for certain categories of consumers.
At the same time, the fire hazard of such fuels is much higher. Therefore, some precautions must be taken regarding their storage and the use of fire resistant wall materials.
Liquid and gaseous fuels
As for liquid and gaseous combustible substances, the situation is as follows.
The heat of combustion is determined by the chemical composition of the combustible substance. The chemical elements contained in the combustible substance are designated by the accepted symbols With , H , O , N , S, and ash and water are symbols BUT and W respectively.
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The heat of combustion can be related to the working mass of the combustible Q P (\displaystyle Q^(P)), that is, to a combustible substance in the form in which it enters the consumer; to dry matter Q C (\displaystyle Q^(C)); to the combustible mass of matter Q Γ (\displaystyle Q^(\Gamma )), that is, to a combustible substance that does not contain moisture and ash.
Distinguish higher ( Q B (\displaystyle Q_(B))) and lower ( Q H (\displaystyle Q_(H))) heat of combustion.
Under higher calorific value understand the amount of heat that is released during the complete combustion of a substance, including the heat of condensation of water vapor during cooling of the combustion products.
Net calorific value corresponds to the amount of heat that is released during complete combustion, without taking into account the heat of condensation of water vapor. The heat of condensation of water vapor is also called latent heat of vaporization (condensation).
The lower and higher calorific value are related by the ratio: Q B = Q H + k (W + 9 H) (\displaystyle Q_(B)=Q_(H)+k(W+9H)),
where k is a coefficient equal to 25 kJ/kg (6 kcal/kg); W - the amount of water in the combustible substance,% (by weight); H is the amount of hydrogen in the combustible substance, % (by mass).
Calculation of heat of combustion
Thus, the higher calorific value is the amount of heat released during the complete combustion of a unit mass or volume (for gas) of a combustible substance and cooling the combustion products to the dew point temperature. In heat engineering calculations, the gross calorific value is taken as 100%. The latent heat of combustion of gas is the heat that is released during the condensation of water vapor contained in the combustion products. Theoretically, it can reach 11%.
In practice, it is not possible to cool the combustion products to complete condensation, and therefore the concept of net calorific value (QHp) is introduced, which is obtained by subtracting from the higher calorific value the heat of vaporization of water vapor both contained in the substance and formed during its combustion. 2514 kJ/kg (600 kcal/kg) is spent on vaporization of 1 kg of water vapor. The net calorific value is determined by the formulas (kJ / kg or kcal / kg):
Q H P = Q B P − 2514 ⋅ ((9 H P + W P) / 100) (\displaystyle Q_(H)^(P)=Q_(B)^(P)-2514\cdot ((9H^(P)+W^ (P))/100))(for solid)
Q H P = Q B P − 600 ⋅ ((9 H P + W P) / 100) (\displaystyle Q_(H)^(P)=Q_(B)^(P)-600\cdot ((9H^(P)+W^ (P))/100))(for a liquid substance), where:
2514 - heat of vaporization at 0 °C and atmospheric pressure, kJ/kg;
H P (\displaystyle H^(P)) and W P (\displaystyle W^(P))- the content of hydrogen and water vapor in the working fuel,%;
9 is a coefficient showing that when 1 kg of hydrogen is burned in combination with oxygen, 9 kg of water is formed.
The calorific value is the most important characteristic of a fuel, as it determines the amount of heat obtained by burning 1 kg of solid or liquid fuel or 1 m³ of gaseous fuel in kJ/kg (kcal/kg). 1 kcal = 4.1868 or 4.19 kJ.
The net calorific value is determined experimentally for each substance and is a reference value. It can also be determined for solid and liquid materials, with a known elemental composition, by calculation in accordance with the formula of D. I. Mendeleev, kJ / kg or kcal / kg:
Q H P = 339 ⋅ C P + 1256 ⋅ H P − 109 ⋅ (O P − S L P) − 25.14 ⋅ (9 ⋅ H P + W P) (\displaystyle Q_(H)^(P)=339\cdot C^(P)+1256\ cdot H^(P)-109\cdot (O^(P)-S_(L)^(P))-25.14\cdot (9\cdot H^(P)+W^(P)))
Q H P = 81 ⋅ C P + 246 ⋅ H P − 26 ⋅ (O P + S L P) − 6 ⋅ W P (\displaystyle Q_(H)^(P)=81\cdot C^(P)+246\cdot H^(P) -26\cdot (O^(P)+S_(L)^(P))-6\cdot W^(P)), where:
C P (\displaystyle C_(P)), H P (\displaystyle H_(P)), O P (\displaystyle O_(P)), S L P (\displaystyle S_(L)^(P)), W P (\displaystyle W_(P))- the content of carbon, hydrogen, oxygen, volatile sulfur and moisture in the working mass of fuel in% (by mass).
For comparative calculations, the so-called Conventional Fuel is used, which has a specific heat of combustion equal to 29308 kJ/kg (7000 kcal/kg).
In Russia, thermal calculations (for example, calculating the heat load to determine the category of a room for explosion and fire hazard) are usually carried out according to the lowest calorific value, in the USA, Great Britain, France - according to the highest. In the United Kingdom and the United States, prior to the introduction of the metric system, calorific value was measured in British thermal units (BTU) per pound (lb) (1Btu/lb = 2.326 kJ/kg).
Substances and materials Net calorific value Q H P (\displaystyle Q_(H)^(P)), MJ/kg Petrol 41,87 Kerosene 43,54 Paper: books, magazines 13,4 Wood (bars W = 14%) 13,8 Natural rubber 44,73 Polyvinyl chloride linoleum 14,31 Rubber 33,52 Staple fiber 13,8 Polyethylene 47,14 Styrofoam 41,6 Cotton loosened 15,7 Plastic 41,87 Every day, turning on the burner on the stove, few people think about how long ago they began to produce gas. In our country, its development was started in the twentieth century. Before that, it was simply found when extracting oil products. The calorific value of natural gas is so high that today this raw material is simply irreplaceable, and its high-quality counterparts have not yet been developed.
The calorific value table will help you choose the fuel for heating your home
Feature of fossil fuel
Natural gas is an important fossil fuel that occupies a leading position in the fuel and energy balances of many states. In order to supply fuel, cities and all kinds of technical enterprises consume various combustible gases, since natural gas is considered dangerous.
Ecologists believe that gas is the purest fuel; when burned, it releases much less toxic substances than wood, coal, and oil. This fuel is used daily by people and contains such an additive as an odorant, it is added at equipped installations in a ratio of 16 milligrams per 1,000 cubic meters of gas.
An important component of the substance is methane (approximately 88-96%), the rest is other chemicals:
- butane;
- hydrogen sulfide;
- propane;
- nitrogen;
- oxygen.
In this video, we will consider the role of coal:
The amount of methane in natural fuel directly depends on its field.
The described type of fuel consists of hydrocarbon and non-hydrocarbon components. The natural fossil fuel is primarily methane, which includes butane and propane. In addition to the hydrocarbon components, nitrogen, sulfur, helium and argon are present in the described fossil fuel. Liquid vapors are also found, but only in gas and oil fields.
Deposit types
Several types of gas deposits are noted. They are divided into the following types:
- gas;
- oil.
Their distinguishing feature is the hydrocarbon content. Gas deposits contain approximately 85-90% of the presented substance, oil fields contain no more than 50%. The remaining percentages are occupied by substances such as butane, propane and oil.
A huge disadvantage of oil generation is its flushing from various kinds of additives. Sulfur as an impurity is exploited at technical enterprises.
Natural gas consumption
Butane is consumed as a fuel at gas stations for cars, and an organic substance called "propane" is used to fuel lighters. Acetylene is highly flammable and is used in welding and cutting metal.
Fossil fuel is used in everyday life:
- columns;
- gas stove;
This kind of fuel is considered the most budgetary and harmless, the only drawback is the emission of carbon dioxide during combustion into the atmosphere. Scientists all over the planet are looking for a replacement for thermal energy.
Calorific value
The calorific value of natural gas is the amount of heat generated with sufficient burnout of a unit of fuel. The amount of heat released during combustion is referred to one cubic meter, taken under natural conditions.
The thermal capacity of natural gas is measured in the following terms:
- kcal / nm 3;
- kcal / m 3.
There is a high and low calorific value:
- High. Considers the heat of water vapor that occurs during the combustion of fuel.
- Low. It does not take into account the heat contained in water vapor, since such vapors do not lend themselves to condensation, but leave with combustion products. Due to the accumulation of water vapor, it forms an amount of heat equal to 540 kcal / kg. In addition, when the condensate cools, heat from 80 to one hundred kcal / kg is released. In general, due to the accumulation of water vapor, more than 600 kcal / kg are formed, this is the distinguishing feature between high and low heat output.
For the vast majority of gases consumed in an urban fuel distribution system, the difference equates to 10%. In order to provide cities with gas, its calorific value must be more than 3500 kcal/Nm 3 . This is explained by the fact that the supply is carried out through the pipeline over long distances. If the calorific value is low, then its supply increases.
If the calorific value of natural gas is less than 3500 kcal / Nm 3, it is more often used in industry. It does not need to be transported for long distances, and it becomes much easier to carry out combustion. Serious changes in the calorific value of the gas require frequent adjustment and sometimes replacement of a large number of standardized burners of household sensors, which leads to difficulties.
This situation leads to an increase in the diameter of the gas pipeline, as well as an increase in the cost of metal, laying networks and operation. The big disadvantage of low-calorie fossil fuels is the huge content of carbon monoxide, in connection with this, the level of danger increases during the operation of the fuel and during the maintenance of the pipeline, in turn, as well as equipment.
The heat released during combustion, not exceeding 3500 kcal/nm 3 , is most often used in industrial production, where it is not necessary to transfer it over a long distance and easily form combustion.