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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.
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. She depends on him chemical composition, humidity and is the main . 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 number heat released during complete combustion of the fuel, taking into account the heat spent on the evaporation of the moisture contained in the fuel. Net calorific value less value higher by the value of the heat of condensation, which is formed from the moisture of the fuel and the hydrogen of the organic mass, which turns into water during combustion.
To determine fuel quality indicators, as well as in thermotechnical calculations usually use the lowest specific heat of combustion, which is the most important thermal and operational characteristic 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 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.
The specific heat of combustion of alcohol and acetone is significantly lower than traditional motor fuels. In addition, liquid rocket fuel 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 mass) | 60 |
| Hydrogen, mixture with carbon monoxide (50% H 2 50% CO 2 by mass) | 65 |
| Blast Furnace Gas | 3 |
| coke oven gas | 38,5 |
| LPG liquefied hydrocarbon gas (propane-butane) | 43,8 |
| Isobutane | 45,6 |
| Methane | 50 |
| n-butane | 45,7 |
| n-Hexane | 45,1 |
| n-Pentane | 45,4 |
| Associated gas | 40,6…43 |
| Natural gas | 41…49 |
| Propadien | 46,3 |
| Propane | 46,3 |
| Propylene | 45,8 |
| Propylene, mixture with hydrogen and carbon monoxide (90%-9%-1% by weight) | 52 |
| Ethane | 47,5 |
| Ethylene | 47,2 |
Specific heat of combustion of some combustible materials
A table is given of the specific heat of combustion of some combustible materials (, wood, paper, plastic, straw, rubber, etc.). It should be noted materials with high heat release during combustion. These materials include: rubber various types, expanded polystyrene (styrofoam), polypropylene and polyethylene.
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| Paper | 17,6 |
| Leatherette | 21,5 |
| Wood (bars with a moisture content of 14%) | 13,8 |
| Wood in stacks | 16,6 |
| Oak wood | 19,9 |
| Spruce wood | 20,3 |
| wood green | 6,3 |
| Pine wood | 20,9 |
| Kapron | 31,1 |
| Carbolite products | 26,9 |
| Cardboard | 16,5 |
| Styrene-butadiene rubber SKS-30AR | 43,9 |
| Natural rubber | 44,8 |
| Synthetic rubber | 40,2 |
| Rubber SCS | 43,9 |
| Chloroprene rubber | 28 |
| Polyvinyl chloride linoleum | 14,3 |
| Two-layer polyvinyl chloride linoleum | 17,9 |
| Linoleum polyvinylchloride on a felt basis | 16,6 |
| Linoleum polyvinyl chloride on a warm basis | 17,6 |
| Linoleum polyvinylchloride on a fabric basis | 20,3 |
| Linoleum rubber (relin) | 27,2 |
| Paraffin solid | 11,2 |
| Polyfoam PVC-1 | 19,5 |
| Polyfoam FS-7 | 24,4 |
| Polyfoam FF | 31,4 |
| Expanded polystyrene PSB-S | 41,6 |
| polyurethane foam | 24,3 |
| fibreboard | 20,9 |
| Polyvinyl chloride (PVC) | 20,7 |
| Polycarbonate | 31 |
| Polypropylene | 45,7 |
| Polystyrene | 39 |
| High density polyethylene | 47 |
| Low-pressure polyethylene | 46,7 |
| Rubber | 33,5 |
| Ruberoid | 29,5 |
| Soot channel | 28,3 |
| Hay | 16,7 |
| Straw | 17 |
| Organic glass (plexiglass) | 27,7 |
| Textolite | 20,9 |
| Tol | 16 |
| TNT | 15 |
| Cotton | 17,5 |
| Cellulose | 16,4 |
| Wool and wool fibers | 23,1 |
Sources:
- GOST 147-2013 Solid mineral fuel. Determination of the higher calorific value and calculation of the lower calorific value.
- GOST 21261-91 Petroleum products. Method for determining the gross calorific value and calculating the net calorific value.
- GOST 22667-82 Combustible natural gases. Calculation method for determining the calorific value, relative density and Wobbe numbers.
- GOST 31369-2008 Natural gas. Calculation of calorific value, density, relative density and Wobbe number based on component composition.
- Zemsky G. T. Flammable properties of inorganic and organic materials: reference book M.: VNIIPO, 2016 - 970 p.
What is fuel?
This is one component or a mixture of substances that are capable of chemical transformations associated with the release of heat. Different types fuels differ in the quantitative content of the oxidizing agent in them, which is used to release thermal energy.
AT broad sense fuel is an energy carrier, that is, a potential type of potential energy.
Classification
Currently, fuels are divided according to their state of aggregation into liquid, solid, gaseous.
To hard natural look include stone and firewood, anthracite. Briquettes, coke, thermoanthracite are varieties of artificial solid fuel.
Liquids include substances that contain substances of organic origin. Their main components are: oxygen, carbon, nitrogen, hydrogen, sulfur. Artificial liquid fuel will be a variety of resins, fuel oil.
It is a mixture of various gases: ethylene, methane, propane, butane. In addition to them, gaseous fuels contain carbon dioxide and carbon monoxide, hydrogen sulfide, nitrogen, water vapor, oxygen.
Fuel indicators
The main indicator of combustion. The formula for determining the calorific value is considered in thermochemistry. emit "reference fuel", which implies the calorific value of 1 kilogram of anthracite.
Domestic heating oil is intended for combustion in heating devices of low power, which are located in residential premises, heat generators used in agriculture for drying fodder, canning.
The specific heat of combustion of fuel is such a value that it demonstrates the amount of heat that is formed during the complete combustion of fuel with a volume of 1 m 3 or a mass of one kilogram.
To measure this value, J / kg, J / m 3, calorie / m 3 are used. To determine the heat of combustion, use the calorimetry method.
With an increase in the specific heat of combustion of fuel, the specific fuel consumption decreases, and the efficiency 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 higher and lower calorific value is associated with the state of aggregation of water in the substances obtained after the combustion of fuel.
The gross calorific value is the amount of heat released during the complete combustion of a substance. This value includes the heat of condensation of water vapor.
The lower working calorific value is the value that corresponds to the release of heat during combustion without taking into account the heat of condensation of water vapor.
The latent heat of condensation is the value of the energy of condensation of water vapor.
Mathematical relationship
The higher and lower calorific value are related by the following relationship:
Q B = Q H + k(W + 9H)
where W is the amount by weight (in %) of water in the combustible substance;
H is the amount of hydrogen (% by mass) in the combustible substance;
k - coefficient of 6 kcal/kg
Calculation methods
The higher and lower calorific value is determined by two main methods: calculated and experimental.
Calorimeters are used for experimental calculations. First, a sample of fuel is burned in it. The heat that will be released in this case is completely absorbed by the water. Having an idea about the mass of water, it is possible to determine the value of its heat of combustion by changing its temperature.
This technique is considered simple and effective, it assumes only the knowledge of technical analysis data.
In the calculation method, the highest and lowest calorific value is calculated according to the Mendeleev formula.
Q p H \u003d 339C p + 1030H p -109 (O p -S p) - 25 W p (kJ / kg)
It takes into account the content of carbon, oxygen, hydrogen, water vapor, sulfur in the working composition (in percent). The amount of heat during combustion is determined taking into account the reference fuel.
The heat of combustion of the gas allows preliminary calculations, identify the efficiency of the use of a particular 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.
In nature there is different variants solid fuels, which differ in composition and properties.
Its formation is carried out through several stages. First, peat is formed, then brown and hard coal is obtained, then anthracite is formed. The main sources of solid fuel formation are leaves, wood, and needles. Dying, parts of plants, when exposed to air, are destroyed by fungi, forming peat. Its accumulation turns into a brown mass, then brown gas is obtained.
At high pressure and temperature, brown gas turns into coal, then the fuel accumulates in the form of anthracite.
In addition to organic matter, there is additional ballast in the fuel. An organic part is that part that was formed from organic matter: hydrogen, carbon, nitrogen, oxygen. In addition to these chemical elements, it contains ballast: moisture, ash.
Furnace technology involves the allocation of working, dry, as well as combustible mass of burned fuel. The working mass is called the fuel in its original form, supplied to the consumer. Dry weight is a composition in which there is no water.
Compound
The most valuable components are carbon and hydrogen.
These elements are found in any type of fuel. In peat and wood, the percentage of carbon reaches 58 percent, in black and brown coal - 80%, and in anthracite it reaches 95 percent by weight. Depending on this indicator, the amount of heat released during the combustion of fuel changes. Hydrogen is the second most important element of any fuel. Contacting with oxygen, it forms moisture, which significantly reduces the thermal value of any fuel.
Its percentage ranges from 3.8 in oil shale to 11 in fuel oil. Oxygen, which is part of the fuel, acts as ballast.
It is not a heat-generating chemical element, therefore it negatively affects the value of its combustion heat. The combustion of nitrogen contained in free or bound form in combustion products is considered to be harmful impurities, so its amount is clearly limited.
Sulfur is included in the composition of the fuel in the form of sulfates, sulfides, and also as sulfur dioxide gases. When hydrated, sulfur oxides form sulfuric acid, which destroys boiler equipment, negatively affects vegetation and living organisms.
That is why sulfur is the chemical element, the presence of which in natural fuel is highly undesirable. When getting inside the working room, sulfur compounds cause significant poisoning of the operating personnel.
There are three types of ash depending on its origin:
- primary;
- secondary;
- tertiary.
The primary form is formed from the mineral substances contained in plants. Secondary ash is formed as a result of ingestion during formation plant residues sand and earth.
Tertiary ash turns out to be part of the fuel in the process of extraction, storage, and also its transportation. With a significant deposition of ash, there is a decrease in heat transfer on the heating surface of the boiler unit, reduces the amount of heat transfer to water from gases. Great amount ash negatively affects the operation of the boiler.
Finally
Volatile substances have a significant impact on the combustion process of any type of fuel. The larger their output, the larger the volume of the flame front will be. For example, coal, peat, easily catch fire, the process is accompanied by insignificant heat losses. The coke that remains after the removal of volatile impurities contains only mineral and carbon compounds. Depending on the characteristics of the fuel, the amount of heat varies significantly.
Depending on the chemical composition, three stages of the formation of solid fuels are distinguished: peat, lignite, coal.
Natural wood is used in small boiler plants. Mostly wood chips, sawdust, slabs, bark are used, firewood itself is used in small quantities. Depending on the type of wood, the amount of heat released varies significantly.
As the calorific value decreases, firewood acquires certain advantages: rapid flammability, minimal ash content, and the absence of traces of sulfur.
Reliable information about the composition of natural or synthetic fuel, its calorific value, is great way carrying out thermochemical calculations.
At present, there is a real opportunity to identify those main options for solid, gaseous, liquid fuels that will be the most efficient and inexpensive to use in a particular situation.
An important thermotechnical characteristic of fuel is its specific heat of combustion.
Specific heat of combustion of fuel
Distinguish between specific higher and lower calorific value. The specific heat of combustion of the working fuel, taking into account the additional heat that is released during the condensation of water vapor located in the combustion products, is called higher specific calorific value of working fuel. This additional amount of heat can be determined by multiplying the mass of water vapor generated from the evaporation of fuel moisture /100 and from the combustion of hydrogen 9 /100 , for the latent heat of condensation of water vapor, equal to approximately 2500 kJ / kg.
Specific lower heating value of fuel – the amount of heat that is released in ordinary practical conditions, i.e. when water vapor does not condense, but is released into the atmosphere.
Thus the relationship between higher and lower specific heat of combustion can be expressed by the equation - = =25(9 ).
64. Conditional fuel.
fuel is any substance that, during combustion (oxidation), releases a significant amount of heat per unit mass or volume and is available for mass use.
Natural and derivative organic compounds in solid, liquid and gaseous states are used as fuel.
Any organic fuel consists of carbon, hydrogen, oxygen, nitrogen, volatile sulfur, and solid and liquid fuels- from ash (mineral residues) and moisture.
An important thermotechnical characteristic of fuel is its specific heat of combustion.
Specific heat of combustion of fuel is the amount of heat that is released during the complete combustion of a unit amount of fuel substance.
The lower the specific heat of combustion of the fuel, the more it is consumed in the boiler unit. For comparison various kinds fuel, according to their thermal effect, the concept of conventional fuel was introduced, the specific heat of combustion of which was taken = 29.3 MJ / kg.
The ratio of Q N R of this fuel to Q sp of standard fuel is called the equivalent of E. Then the conversion of the consumption of natural fuel V N into standard fuel V UT is carried out according to the formula: 
Conditional fuel- the unit of accounting for fossil fuels, that is, oil and its derivatives, natural and specially obtained during the distillation of shale and coal, gas, peat, adopted in calculations, which is used to calculate the useful action of various types of fuel in their total accounting.
In the USSR and Russia per unit reference fuel(cf) the calorific value of 1 kg of coal = 29.3 MJ or 7000 kcal was taken. International Energy Agency ( IEA) took the unit of oil equivalent, usually denoted by the abbreviation TOE(English . Tonne of oil equivalent). One tonne of oil equivalent equals 41.868 GJ or 11.63 MWh. The unit is also used - a barrel of oil equivalent ( BOE).
65. Excess air coefficient.
The number showing how many times the actual air flow is greater than the theoretically required amount of air is called excess air coefficient, i.e. actual air flow L (in kg/kg) or V (m 3 / m 3) is equal to its theoretically required amount L o or V o > multiplied by the coefficient of excess air a
V= aV 0 .
It is known that the source of energy used in industry, transport, agriculture, and households is fuel. These are coal, oil, peat, firewood, natural gas, etc. When fuel is burned, energy is released. Let's try to figure out how energy is released in this case.
Let us recall the structure of the water molecule (Fig. 16, a). It consists of one oxygen atom and two hydrogen atoms. If a water molecule is divided into atoms, then it is necessary to overcome the forces of attraction between atoms, i.e., to do work, and therefore to expend energy. Conversely, if atoms combine to form a molecule, energy is released.
The use of fuel is based precisely on the phenomenon of energy release when atoms combine. For example, the carbon atoms contained in the fuel are combined with two oxygen atoms during combustion (Fig. 16, b). In this case, a molecule of carbon monoxide - carbon dioxide - is formed and energy is released.
Rice. 16. Structure of molecules:
a - water; b - connection of a carbon atom and two oxygen atoms into a carbon dioxide molecule
When designing engines, an engineer needs to know exactly how much heat the fuel being burned can release. To do this, it is necessary to determine experimentally how much heat will be released during the complete combustion of the same mass of fuel of different types.
The physical quantity showing how much heat is released during the complete combustion of a fuel weighing 1 kg is called the specific heat of combustion of the fuel.
The specific heat of combustion is denoted by the letter q. The unit of specific heat of combustion is 1 J/kg.
The specific heat of combustion is determined experimentally using rather complex instruments.
The results of the experimental data are shown in Table 2.
table 2
This table shows that the specific heat of combustion, for example, of gasoline is 4.6 10 7 J / kg.
This means that with the complete combustion of gasoline weighing 1 kg, 4.6 10 7 J of energy is released.
The total amount of heat Q released during the combustion of m kg of fuel is calculated by the formula
Questions
- What is the specific heat of combustion of fuel?
- In what units is the specific heat of combustion of fuel measured?
- What does the expression “specific heat of combustion of fuel equal to 1.4 10 7 J / kg” mean? How is the amount of heat released during the combustion of fuel calculated?
Exercise 9
- How much heat is released during the complete combustion of charcoal weighing 15 kg; alcohol weighing 200 g?
- How much heat will be released during the complete combustion of oil, the mass of which is 2.5 tons; kerosene, the volume of which is 2 liters, and the density is 800 kg / m 3?
- With the complete combustion of dry firewood, 50,000 kJ of energy were released. How much firewood burned?
Exercise
Using Table 2, build a bar chart for the specific heat of combustion of firewood, alcohol, oil, hydrogen, choosing the scale as follows: the width of the rectangle is 1 cell, the height of 2 mm corresponds to 10 J.
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. because of high content resin, increased burning rate and low calorific value coniferous trees are significantly inferior in this respect.
It should be understood that the density of wood affects the value of the calorific value.
it natural material plant origin, extracted from sedimentary rock.
This type of solid fuel contains carbon and other chemical elements. There is a division of material into types depending on its age. The youngest is considered brown coal, followed by stone, and older than all other types - anthracite. 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 manufacturing 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 with fossil sources of thermal energy, which adversely affect the combustion of environment and being, in addition, 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.
