Composition and main characteristics of various types of fuel. Conditional fuel

Fuel composition. conditional fuel.

All existing types of fuel are divided into solid, liquid, gaseous. For heating, the thermal effect of electric current and pulverized fuel are also used. Some groups of fuels, in turn, are divided into two subgroups, of which one is the fuel as it is mined, which is natural fuel; another subgroup is fuel, which is obtained by processing natural fuel, and it is called artificial.

solid fuel:

BUT). natural – firewood, coal, anthracite, peat.

B). artificial – charcoal, coke and pulverized, which is obtained from crushed parts.

Liquid fuel:

BUT). natural – oil.

B). artificial – gasoline, kerosene, fuel oil, resin.

Gaseous fuel:

BUT). natural – natural gas.

B). artificial – generator gas obtained during the gasification of various types of fuel (peat, firewood, coal and others), coking and other gases.

All fuels are made up of the same elements. The difference between fuels is that these elements are contained in the fuel in different quantities. The elements are divided into two groups. The first group includes those elements that burn themselves or support combustion. These include carbon, hydrogen, and oxygen. To the second group belong those which themselves do not burn and do not contribute to combustion; these include nitrogen and water. Sulfur stands out from the named elements. It is a combustible substance and generates heat during combustion, but its presence in the fuel is undesirable, since sulfur dioxide is released during the combustion of sulfur, which passes into the heated metal and worsens its mechanical properties.

The amount of heat released by fuel during combustion is measured in calories. Each fuel releases a different amount of heat when burned. The amount of heat that is released during the complete combustion of 1 kg of solid or liquid fuel or during the combustion of 1 m³ of gaseous fuel is called the calorific value. The calorific value has wide limits. For example, for fuel oil, the calorific value is about 10,000 kcal / kg, for high-quality coal – 7,000 kcal / kg. The higher the calorific value of the fuel, the more valuable it is, since less is required to produce the same amount of heat. To compare the thermal value of fuel, a common unit of measurement is used. Fuel with a calorific value of 7000 kcal/kg (29.31 MJ/kg) is accepted as such a unit. This unit is called conventional fuel. Some countries use different units. For example, in France it is a fuel that has either a lower calorific value of 27.3 MJ/kg (6500 kcal/kg) or a higher calorific value of 28.3 MJ/kg (6750 kcal/kg).

solid fuel.

1. Firewood has a relatively low heat output (specific heat of combustion 10.2 MJ / kg), high humidity and light weight. It is unprofitable to transport them over a long distance, so firewood is mainly local fuel.

Firewood is convenient because it contains little ash (1-2%), easily catches fire and gives a long flame. This makes them one of the most suitable fuels for firing bricks in all batch kilns, in particular floor kilns, in which a long flame contributes to a more uniform firing along the height of the chamber.

The moisture content of freshly cut firewood, which is approximately 45-46%, depends on the type of tree, its age and time of felling. The younger the tree, the more moisture it contains. In winter and autumn, trees contain less moisture than in spring and summer, so the forest must be cut at this time.

Dense heavy types of firewood burn more slowly, releasing a large amount of heat and developing a higher temperature in the furnaces. Lighter types of firewood burn quickly and give a longer flame, so they are more suitable for even firing.

Firewood is the only source of energy that completely absorbs its own gaseous combustion products and does not lead to the greenhouse effect.

2. Peat is a valuable natural biological material. This is the youngest deposit of all types of fuel, which was formed naturally: by the decomposition of dead parts of trees, shrubs, grasses. This occurs with high humidity and limited access to oxygen.

Peat as a biofuel is most often used in agriculture, animal husbandry, medicine, biochemistry and energy. Thanks to modern technologies for the development of production, highly productive soils began to be obtained, both for growing food, and for fertilizers, insulating and packaging materials, carbon reducing metal, etc.

Peat is used as a fuel due to its composition. This includes high carbon content (50-60%), low sulfur content, harmful non-combustible residues and impurities. In fact, peat is young coal.

But peat also has disadvantages. This is lower energy calorific value than coal and the difficulty of combustion due to the high moisture content (up to 65%). But the advantages of peat are nothing more than ecological cleanliness of combustion and low production costs.

Peat contains:

– plant fibers that improve the water-air condition of the soil;

– humic acids that activate plant growth;

– trace elements – nitrogen, potassium, phosphorus, calcium, iron, magnesium.

The most important characteristic is the ash content, which is determined during its combustion and shows the percentage of mineral components. The higher their content, the more fertile the peat. Ash content can vary from 1% in high-moor peat to 50% in lowland peat.

By origin, peat happens:

– lowland and transitional. They consist of rotted remains of woody herbaceous vegetation. They are characterized by high ash content, low calorific value, medium and slightly acid reaction of the medium, high content of nutrients, richness of microelements;

– riding. Consists of the remains of sphagnum mosses, cotton grass, wild rosemary. It is characterized by low ash content, high calorific value, high moisture capacity (from 600 to 1200%), high acidity, low degree of decomposition.

The calorific value of peat is 24 MJ/kg.

3. Coal has the best heat and power characteristics, therefore it is a favorite of consumer demand. Hard coal contains: carbon 75-95%, hydrogen 1.5-5.7%, oxygen 1.5-15%, nitrogen up to 1.5%, sulfur 0.5-4%, ash 3-4.5%, moisture up to 12%, as well as up to 32% volatile substances. The calorific value reaches 7000 kcal/kg, and 1 kg of hard coal makes it possible to obtain 6.67 kW/h of thermal energy.

Coal is one of the least environmentally friendly types of fuel, since when it is burned, a large amount of harmful emissions is released into the atmosphere.

The use of coal is very diverse and wide. It is used to generate electricity at thermal power plants, and is also burned for other energy purposes; coke is obtained from it for metallurgical production, and about 300 different industrial products are made during chemical processing.

The heat of combustion is 29.3 MJ/kg.

4. Anthracite is the oldest fossil coal. According to its characteristics and properties, it is more similar to coal. Their difference lies in the fact that anthracite contains more carbon (more than 90%). That is, it means that anthracite is more combustible than the coal that is commonly used.

Anthracite burns only with strong air draft. Moreover, it burns either almost without a flame, or without a flame at all. It is also odorless and smoke free.

Anthracite is harder than coal and has the following characteristics: density 1500-1700 kg / m², calorific value 33.8-35.2 MJ / kg, composition in the combustible mass of 9% volatile substances.

5. Charcoal is a solid, porous, high-carbon product (84% carbon), formed by heating wood without access (or with little access) to air in furnaces and retorts (sometimes even in fires). Depending on the type of wood, 140-180 kg of coal, 280-400 kg of liquid products and about 80 kg of combustible gases are obtained from 1 m³. The heat of combustion is 31 MJ/kg (7000-8100 kcal/kg). The density of birch charcoal is 380 kg/m³, less dense charcoal is produced by pine (300 kg/m³) and spruce (260 kg/m³). The large porosity of charcoal determines its high adsorption properties. Charcoal has the ability to combine with atmospheric oxygen at ordinary temperatures; this explains the cases of its spontaneous combustion. When unloading from furnaces and retorts, its moisture content is 2-4%, during storage it rises to 7-15%. The ash content of coal should be no more than 3%, the content of volatile substances – no more than 20%. A feature of charcoal is its low content of impurities such as phosphorus and sulfur, which makes it essential for some metallurgical processes.

6. Coke – artificial solid fuel of increased strength; obtained by heating to high temperatures without access to air, natural fuels or products of their processing. Depending on the type of raw material, coal, electrode pitch and petroleum coke are distinguished. The main amount of coke is produced from hard coal.

Coal coke is elongated pieces of gray color.

Relative density 1.8-1.95 g/m³, average porosity is about 50%. Bulk weight of coke 400-500 kg/m³. the calorific value is about 29MJ/kg (about 7000 kcal/kg), and its combustible mass is about 33MJ/kg (about 8000 kcal/kg).

The carbon content in the combustible mass of coke is above 96%, the yield of volatile substances is 0.8-1%. The moisture content during dry quenching does not exceed 0.5%, and when wet – usually 2-4%; sulfur 0.4-1.9%. Ash content should be no higher than 9-10.5%.

7. Pulverized fuel . At present, pulverized coal heating is increasingly used for heating heating, in particular forging furnaces. It is especially advantageous to use it at those plants where there is no gas, but there is local fuel (coal) that cannot be gasified.

Coal burned in forging furnaces in the form of dust should have no more than 15-20% ash, no less than 20% volatile. The less coal has ash, the better its dust burns. An important factor to consider when using pulverized coal is the melting point of the ash. The best coal is the one whose ash is refractory (above 1300°C).

The more volatile coal contains, the better the dust prepared from it ignites; the torch of combustion of dust turns out to be shorter. When the volatile content is less than 17%, the dust is burned unstable, the flame is attenuated, the furnace works intermittently. Therefore, dust from coke and anthracite is unsuitable for heating furnaces.

Liquid fuel

The technological properties of liquid fuel, as well as natural gas, are significantly better than solid fuel: it does not contain ash and slag, it does not require special devices to prepare it for combustion, it has a high calorific value and allows you to get a high temperature in the furnace.

Liquid fuel consists almost entirely of hydrocarbons (96-98%), and the mass content of carbohydrate is 80-90%, and hydrogen 8-14%. Also, liquid fuels often contain free and bound sulfur 0.5-3%, a small amount of bound oxygen and nitrogen, and water.

1. Oil is a natural oily combustible liquid, consisting of a complex mixture of hydrocarbons and other organic compounds. Today, oil is one of the most important minerals for mankind.

The density of oil is 0.65-1.05 g/cm³ and depends on temperature and pressure. It contains a large number of different organic substances and therefore is characterized not by the boiling point, but by the initial boiling point of liquid hydrocarbons (usually > 28 ° C, less often ≥ 100 ° C) and fractional composition – the yield of individual fractions distilled first at atmospheric pressure, and then under vacuum within certain temperature limits.

Specific heat capacity 1.7-2.1 kJ / kg.

Specific heat of combustion 43.7-46.2 MJ/kg.

Oil is a mixture of about 1000 individual substances, of which most are liquid hydrocarbons (80-90%) and heteroatomic organic compounds (4-5%), mainly sulfurous (≈ 250 substances), nitrogenous (> 30 substances) and oxygen ( ≈ 85 substances), as well as organometallic compounds; the remaining components are dissolved hydrocarbon gases, water, mineral salts, solutions of salts of organic acids and other mechanical impurities (particles of sand, limestone).

Oil is unique in its combination of qualities: high energy density, easy to transport, it is easy to get a lot of products from it (motor fuel, solvent, raw materials for the chemical industry, etc.). The depletion of oil resources, the rise in oil prices and other reasons have caused an intensive search for substitutes for liquid fuels.

2 . Gasoline is a combustible mixture of light hydrocarbons with a boiling point of 30 to 200°C. Density ≈ 0.75 g/cm³. Calorific value ≈ 10500 kcal/kg. The freezing point is below -60°C.

Gasoline is obtained by distillation and selection of oil fractions that boil away within certain temperature limits.

Gasoline vapors are highly toxic to humans and their inhalation can cause both acute and chronic poisoning.

3 . Kerosene is a mixture of hydrocarbons that boils away in the temperature range of 150-250 ° C, a transparent, slightly oily to the touch, combustible liquid obtained by direct distillation or rectification of oil.

Density 0.78-0.85 g/cm³ (at 20°C), viscosity 1.2-4.5 mm²/s (at 20°C), flash point 28-72°C; calorific value is about 43 MJ/kg.

Kerosene is used as a jet fuel, a combustible component of liquid rocket fuel, a fuel for firing glass and porcelain products, for household heating and lighting devices, in metal cutting machines, as a solvent, a raw material for the oil refining industry. It is allowed to add up to 20% of kerosene to summer diesel fuel to reduce the pour point without degrading performance.

4. Fuel oil is a dark brown liquid product, the residue after the separation of gasoline, kerosene or gas oil fractions from oil or its secondary processing products, boiling up to 350-360 °.

Fuel oil is a mixture of hydrocarbons, petroleum resins, asphaltenes, carbenes, carboids and organic compounds containing metals (V, Ni, Fe, Mg, Na, Ca). Physical and chemical properties depend on the chemical composition of the original oil and are characterized by the following data:

-viscosity 8-80 mm²/s (at 100°С);

-density 0.89-1 g/cm³ (at 20°C);

– pour point 10-40°C;

– sulfur content 0.5-3.5%;

– ash content up to 0.5%;

– lower calorific value 39.4-40.7 MJ / mol.

Fuel oils are used as fuel for steam boilers, boiler plants and industrial furnaces, for the production of marine fuel oil, heavy motor fuel for crosshead diesels and bunker fuel.

The output of fuel oil is about 50% by weight based on the original oil.

gaseous fuel

Compared to other types of gaseous fuel, it has the following advantages:

-burns in the theoretical amount of air, which ensures high thermal efficiency and boiling point;

– when burned, it does not form undesirable products of dry distillation and sulfur compounds, soot and smoke;

-relatively easily supplied through gas pipelines to remote objects of consumption and can be stored centrally;

-Easily ignites at any ambient temperature;

-requires significantly lower production costs, which means it is a cheaper type of fuel compared to other fuels;

– can be used in compressed and liquefied form for internal combustion engines;

– does not form condensate during combustion, which provides a significant reduction in wear of engine parts, etc.;

At the same time, gaseous fuel also has certain negative properties, which include: a toxic effect, the formation of explosive mixtures when mixed with air, easy flow through leaky joints, etc. Therefore, when working with gaseous fuel, careful observance of the relevant safety regulations is required.

1. Natural gas – a mixture of gases formed in the bowels of the earth during the anaerobic decomposition of organic substances (methane fermentation).

Natural gas belongs to minerals. In reservoir conditions (conditions of occurrence in green subsoil), it is in a gaseous state – in the form of separate accumulations (gas deposits) or in the form of a gas cap of oil and gas fields, or in a dissolved state in oil or water. It can also be in a crystalline state in the form of natural gas hydrates.

The main part of natural gas is methane – from 92 to 98%. The composition may also include heavier hydrocarbons: ethane – up to 6%, propane – up to 1.5%, butane – up to 1%; as well as other non-carbohydrate substances: hydrogen, hydrogen sulfide, carbon dioxide, nitrogen, helium.

Pure natural gas is colorless and odorless. In order to be able to determine the leak by smell, a small amount of substances with a strong unpleasant odor – odorants – is added to the gas. The most commonly used odorant is ethyl mercaptan.

To facilitate the transportation and storage of natural gas, it is liquefied by cooling at elevated pressure.

Approximate physical characteristics:

-density – from 0.68 to 0.85 kg/m³ of relative air (dry, gaseous), from 400 kg/m³ (liquid);

– self-ignition temperature 650°С;

– explosive concentrations of a mixture of gas with air – from 5 to 15% by volume;

– specific heat of combustion 28-46 MJ/m³;

– octane number when used in internal combustion engines 120-130;

– 1.8 times lighter than air, therefore, when leaking, it does not collect in the lowlands, but rises up.

2. Generator gas – a gas mixture containing carbon monoxide (CO) and molecular hydrogen (H₂).

It is obtained by passing air over hot coal or coke in special furnaces – gas generators. Output from coke 4.65 m³/kg. Further, carbon monoxide is mixed with water vapor and the hydrogen component of the generator gas CO + H₂O = = H₂ + CO₂ is obtained.

The calorific value is 800-1000 kcal / m³, and the replacement of air with oxygen during its production leads to a significant increase in the proportion of carbon monoxide and, accordingly, to an increase in calorific value.

Generator gas is used as a fuel in the metallurgical, glass, ceramic industries, for internal combustion engines.

3. Coke oven gas is a combustible gas formed in the process of coal coking, that is, when it is heated without air access to 900-1100°C. Contains many valuable substances. In addition to hydrogen, methane, carbon oxides, it contains vapors of coal tar, benzene, ammonia, hydrogen sulfide, etc.

Raw coke oven gas is successively purified from ammonia and hydrogen sulfide, washed with absorption oil, sulfuric acid. Purified gas (14-15% of the mass of coal) is used as a fuel for heating the battery of coke ovens and for other purposes.

Typical indicators:

-hydrogen 50%, methane 35%, carbon monoxide 10%, ethylene 5%;

– the amount of volatile products up to 25% by weight of coal;

– calorific value 10000-20000 kJ/m³.

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