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organic fuel. Liquid fuel and its characteristics Classification of fuel according to the method of production

Fuel- These are combustible substances that release a significant amount of heat during combustion, which is used directly in technological processes or converted into other forms of energy. These include minerals of organic origin - coal, combustible gases, oil shale, oil, peat, as well as wood and plant waste.

In nuclear energy, the concept of nuclear fuel is used- a substance whose nuclei are divided under the action of neutrons, while releasing energy mainly in the form of the kinetic energy of fission fragments of nuclei and neutrons.

Conventional chemical fuel, in contrast to the nuclear one, is called organic, and it is currently the main source of heat.

To analyze the thermal characteristics of fuels, determine the composition of gases and other calculations, it is necessary to know the chemical structure of each type of fuel. The organic part of solid and liquid fuels consists of a large number of complex chemical compounds, which mainly include five chemical elements: carbon FROM, hydrogen H, oxygen ABOUT, sulfur S and nitrogen N. In addition, the fuel contains mineral impurities BUT and moisture W representing together the external fuel ballast.

The chemical composition of solid, liquid and gaseous fuels is determined not by the number of compounds, but by the total mass of chemical elements (as a percentage per 1 kg or 1 cubic meter of fuel), i.e. determine the elemental composition of the fuel. There are three main elemental fuel compositions:

1) working mass of fuel C+H+O+N+S+A+W=100%;

2) dry weight of fuel C+H+O+N+A=100%;

3) combustible mass of fuel C+ H+O+N=100%.

The working mass is considered to be the mass of fuel in the form in which it enters the enterprise.

If the fuel is heated to 102-105ºС, then moisture will evaporate, then a dry mass of fuel will be obtained. The name of the combustible mass is conditional; since it contains nitrogen and oxygen are not combustible elements and constitute the internal fuel ballast. Nitrogen and oxygen contribute to the combustion process of fuel.

Combustible fuel elements are carbon, hydrogen and sulfur.. Carbon is the main, combustible element of fuel. It has a high calorific value (33,600 kJ/kg) and makes up the bulk of the working mass of the fuel (50-75% for solid fuels and 80-85% for fuel oils). Hydrogen has a high calorific value (about 130,000 kJ/kg), but its amount in solid fuels is small ( H= 2-6%) and somewhat more in liquid (about 10%). This makes the calorific value of liquid fuels higher than solid ones.

Sulfur has a low calorific value (9000 kJ/kg). Its content in fuels is low ( S\u003d 0.2-4%), therefore sulfur, as a combustible component, is not valued.

The presence of sulfur oxides in combustion products at certain concentrations is dangerous for organisms and plants and requires certain measures and means to capture or disperse it in the atmosphere.

FUEL TYPES. FUEL CLASSIFICATION

According to the definition of D.I. Mendeleev, “fuel is a combustible substance deliberately burned to produce heat.”

Currently, the term "fuel" covers all materials that serve as a source of energy (for example, nuclear fuel).

Fuel by origin is divided into:

Natural fuels (coal, peat, oil, oil shale, wood, etc.)

Artificial fuel (motor fuel, generator gas, coke, briquettes, etc.).

According to its state of aggregation, it is divided into solid, liquid and gaseous fuels, and according to its purpose when used, it is divided into energy, technological and household. The highest requirements apply to energy fuels, while the minimum requirements apply to household fuels.

Solid fuel - wood and vegetable mass, peat, shale, brown coal, coal.

Liquid fuel - products of oil refining (fuel oil).

Gaseous fuel - natural gas; gas produced during oil refining, as well as biogas.

Nuclear fuel - fissile (radioactive) substances (uranium, plutonium).

Fossil fuel, i.e. coal, oil, natural gas, make up the vast majority of all energy consumption. The formation of organic fuel is the result of thermal, mechanical and biological influence over many centuries on the remains of flora and fauna deposited in all geological formations. All of these fuels are carbon-based, and energy is released from them primarily through the formation of carbon dioxide.

SOLID FUEL. MAIN CHARACTERISTICS

solid fuel . Fossil solid fuels (with the exception of slates) are a product of the decomposition of the organic matter of plants. The youngest of them - peat - is a dense mass , formed from the decayed remains of marsh plants. Next in "age" are brown coals- an earthy or black homogeneous mass, which, during prolonged storage in air, is partially oxidized (“weathered”) and crumbles into powder. Then come coals, which, as a rule, have increased strength and less porosity. The organic mass of the oldest of them - anthracites - has undergone the greatest changes and consists of 93% carbon. Anthracite has a high hardness.

The world's geological reserves of coal, expressed in standard fuel, are estimated at 14,000 billion tons, of which half are reliable (Asia - 63%, America - 27%). The United States and Russia have the largest coal reserves. Significant reserves are available in Germany, England, China, Ukraine and Kazakhstan.

The entire amount of coal can be represented as a cube with a side of 21 km, from which a “cube” with a side of 1.8 km is annually withdrawn by a person. At this rate of consumption, coal will last about 1000 years. But coal is a heavy, inconvenient fuel that has a lot of mineral impurities, which complicates its use. Its reserves are distributed extremely unevenly. The most famous coal deposits: Donbass (coal reserves 128 billion tons), Pechora (210 billion tons), Karaganda (50 billion tons), Ekibastuz (10 billion tons), Kuznetsk (600 billion tons) , Kansk-Achinsk (600 billion tons). Irkutsk (70 billion tons) basins. The world's largest coal deposits are Tungusskoye (2300 billion tons - more than 15% of world reserves) and Lenskoye (1800 billion tons - almost 13% of world reserves).

Coal mining is carried out by the mine method (from a depth of hundreds of meters to several kilometers) or in the form of open pit mining. Already at the stage of coal mining and transportation, using advanced technologies, it is possible to achieve a reduction in transportation losses. Reducing the ash content and moisture content of shipped coal.

Renewable solid fuel is wood. Its share in the energy balance of the world is now extremely small, but in some regions wood (and more often its waste) is also used as fuel.

As solid fuel briquettes can also be used - a mechanical mixture of coal and peat fines with binders (bitumen, etc.), compressed under pressure up to 100 MPa in special presses.

LIQUID FUEL. MAIN CHARACTERISTICS

Liquid fuel. Almost all liquid fuels are still obtained by refining oil. Oil, a liquid fossil fuel, is a brown liquid containing gaseous and volatile hydrocarbons in solution. It has a peculiar resinous smell. During the distillation of oil, a number of products of great technical importance are obtained: gasoline, kerosene, lubricating oils, as well as vaseline, used in medicine and perfumery.

Crude oil is heated to 300-370 °C, after which the resulting vapors are dispersed into fractions that condense at different temperatures tª: liquefied gas (about 1% yield), gasoline (about 15%, tª=30 - 180°C). Kerosene (about 17%, tª=120 - 135°С), diesel (about 18%, tª=180 - 350°С). The liquid residue with an initial boiling point of 330-350°C is called fuel oil. Fuel oil, like motor fuel, is a complex mixture of hydrocarbons, which mainly include carbon (84-86%) and hydrogen (10-12%).

Fuel oil obtained from oil from a number of fields may contain a lot of sulfur (up to 4.3%), which greatly complicates the protection of equipment and environment when it is burned.

The ash content of fuel oil should not exceed 0.14%, and the water content should not exceed 1.5%. The composition of the ash includes compounds of vanadium, nickel, iron and other metals, so it is often used as a raw material for obtaining, for example, vanadium.

In boilers of boiler houses and power plants, fuel oil is usually burned, in domestic heating installations - household heating oil (a mixture of medium fractions).

World geological oil reserves are estimated at 200 billion tons, of which 53 billion tons. constitute reliable reserves. More than half of all proven oil reserves are located in the countries of the Middle and Near East. In the countries of Western Europe, where there are highly developed industries, relatively small oil reserves are concentrated. Explored oil reserves are increasing all the time. The increase occurs mainly due to the sea shelves. Therefore, all estimates of oil reserves available in the literature are conditional and characterize only an order of magnitude.

The total reserves of oil in the world are lower than those of coal. But oil is a more usable fuel. Especially in a revised form. After rising through the well, the oil is sent to consumers mainly through oil pipelines, railways or tankers. Therefore, the transport component has a significant part in the cost of oil.

GAS FUEL. MAIN CHARACTERISTICS

gaseous fuel. Gaseous fuels primarily include natural gas. This is gas produced from pure gas fields, associated gas oil fields, condensate field gas, mine methane, etc. Its main component is methane CH 4; in addition, gas from different fields contains small amounts of nitrogen N 2 , higher hydrocarbons СnНm , carbon dioxide CO 2 . During the extraction of natural gas, it is purified from sulfur compounds, but some of them (mainly hydrogen sulfide) may remain.

When oil is extracted, the so-called associated gas is released, which contains less methane than natural gas, but more higher hydrocarbons and therefore releases more heat during combustion.

In industry and especially in everyday life, liquefied gas obtained during the primary processing of oil and associated petroleum gases is widely used. They produce technical propane (at least 93% C 3 H 8 + C 3 H 6), technical butane (at least 93% C 4 H 10 + C 4 H 8) and mixtures thereof.

World geological gas reserves are estimated at 140-170 trillion m³.

Natural gas is located in deposits, which are "domes" of a waterproof layer (clay type), under which gas, consisting mainly of methane CH 4, is under pressure in a porous medium (sandstone). At the exit from the well, gas is cleaned from sand suspension, condensate drops and other inclusions and is fed to main gas pipeline with a diameter of 0.5 - 1.5 m and a length of several thousand kilometers. The gas pressure in the gas pipeline is maintained at 5 MPa using compressors installed every 100-150 m. The compressors rotate gas turbines consuming gas. The total gas consumption for maintaining pressure in the gas pipeline is 10-12% of the total pumped. Therefore, the transport of gaseous fuel is very energy-intensive.

IN Lately In a number of places, biogas, a product of anaerobic fermentation (fermentation) of organic waste (manure, plant residues, garbage, sewage, etc.), is increasingly being used. In China, more than a million biogas factories are already operating on a variety of waste (according to UNESCO, up to 7 million). In Japan, biogas sources are landfills of pre-sorted household waste. "Factory", with a capacity of up to 10-20 m³ of gas per day. Provides fuel for a small power plant with a capacity of 716 kW.

Anaerobic digestion of waste from large livestock complexes allows solving the extremely acute problem of environmental pollution with liquid waste by converting it into biogas (about 1 cubic meter per day per unit of cattle) and high-quality fertilizers.

Very perspective view fuel, which has three times the specific energy intensity compared to oil, is hydrogen, scientific and experimental work to find cost-effective ways of industrial transformation of which is currently being actively conducted both in our country and abroad. Hydrogen reserves are inexhaustible and are not associated with any region of the planet. Hydrogen in a bound state is contained in water molecules (H 2 O). When it is burned, water is formed that does not pollute the environment. Hydrogen is conveniently stored, distributed through pipelines and transported at low cost.

Currently, hydrogen is mainly obtained from natural gas, in the near future it will be possible to obtain it in the process of coal gasification. To obtain the chemical energy of hydrogen, the process of electrolysis is also used. The latter method has a significant advantage, as it leads to the enrichment of oxygen in the environment. The widespread use of hydrogen fuel can solve three urgent problems:

Reduce consumption of organic and nuclear fuel;

Satisfy growing energy needs;

Reduce environmental pollution.

NUCLEAR FUEL. CLASSIFICATION AND APPLICATION

Nuclear fuel. The only natural type of nuclear fuel is the heavy nuclei of uranium and thorium. Energy in the form of heat is released under the action of slow neutrons during the fission of the isotope 235 U, which is 1/140 part in natural uranium. 238 U and 239 Th can be used as raw materials, which, when irradiated with neutrons, are converted into new nuclear fuel - 239 Pu and 239 U, respectively. When fission of all nuclei contained in 1 kg of uranium, energy is released 2 10 7 kWh, which equivalent to 2.5 thousand tons of high-quality hard coal with a calorific value of 35 MJ/kg (8373 kcal/kg).

Nuclear fuel is divided into two types:

Natural uranium, containing fissile nuclei 235 U, as well as raw materials 238 U, capable of forming plutonium 239 Pu upon neutron capture;

Secondary fuel that does not occur in nature, including 239 Pu obtained from fuel of the first type, as well as 233 U isotopes formed during the capture of neutrons by 232 Th thorium nuclei.

By chemical composition, nuclear fuel can be:

Metal, including alloys;

Oxide (for example, UO 2);

Carbide (e.g. PuC 1-x)

nitride

Mixed (PuO 2 + UO 2)

Application. Nuclear fuel is used in nuclear reactors, where it is usually located in hermetically sealed fuel elements (TVELs) in the form of pellets a few centimeters in size.

Nuclear fuel is subject to high requirements for chemical compatibility with fuel rod claddings, it must have a sufficient melting and evaporation temperature, good thermal conductivity, a small increase in volume during neutron irradiation, and manufacturability.

Metallic uranium is relatively rarely used as a nuclear fuel. Its maximum temperature is limited to 660 °C. At this temperature, a phase transition occurs in which the crystal structure of uranium changes. The phase transition is accompanied by an increase in the volume of uranium, which can lead to the destruction of the fuel element cladding. With prolonged irradiation in the temperature range of 200-500°C, uranium is subject to radiation growth. This phenomenon is that the irradiated uranium rod is elongated. An increase in the length of the uranium rod by one and a half times was observed experimentally.

The use of metallic uranium, especially at temperatures above 500 °C, is difficult due to its swelling. After nuclear fission, two fission fragments are formed, the total volume of which is greater than the volume of a uranium (plutonium) atom. Part of the atoms - fission fragments are gas atoms (krypton, xenon, etc.). Gas atoms accumulate in the pores of uranium and create an internal pressure that increases with increasing temperature. Due to a change in the volume of atoms in the process of fission and an increase in the internal pressure of gases, uranium and other nuclear fuels begin to swell. Swelling is understood as the relative change in the volume of nuclear fuel associated with nuclear fission.

The swelling depends on the burnup and temperature of the fuel rods. The number of fission fragments increases with burnup, and the internal pressure of the gas increases with burnup and temperature. The swelling of nuclear fuel can lead to the destruction of the fuel element cladding. Nuclear fuel is less prone to swelling if it has high mechanical properties. Metallic uranium just does not apply to such materials. Therefore, the use of metallic uranium as a nuclear fuel limits burnup, which is one of the main estimates of the economics of nuclear energy.

The radiation resistance and mechanical properties of the fuel are improved after uranium alloying, during which small amounts of molybdenum, aluminum and other metals are added to uranium. Doping additives reduce the number of fission neutrons per neutron capture by nuclear fuel. Therefore, alloying additions to uranium tend to be chosen from materials that weakly absorb neutrons.

Good nuclear fuels include some refractory compounds of uranium: oxides, carbides and intermetallic compounds. The most widely used ceramics - uranium dioxide UO 2 . Its melting point is 2800 ° C, density - 10.2 t / m 3. Uranium dioxide has no phase transitions and is less prone to swelling than uranium alloys. This allows you to increase burnout up to several percent. Uranium dioxide does not interact with zirconium, niobium, stainless steel and other materials at high temperatures. The main disadvantage of ceramics is low thermal conductivity - 4.5 kJ/(m·K), which limits the specific power of the reactor in terms of melting temperature. Thus, the maximum heat flux density in VVER reactors running on uranium dioxide does not exceed 1.4 10 3 kW/m 2 , while the maximum temperature in fuel rods reaches 2200 °C. In addition, hot ceramics are very brittle and can crack.

Plutonium is a low-melting metal. Its melting point is 640 °C. Plutonium has poor plastic properties, so it is almost impossible to machine. The technology for manufacturing fuel rods is further complicated by the toxicity of plutonium. For the preparation of nuclear fuel, plutonium dioxide, a mixture of plutonium carbides with uranium carbides, and alloys of plutonium with metals are usually used.

Dispersion fuels have high thermal conductivity and mechanical properties, in which small particles of UO 2 , UC, PuO 2 and other uranium and plutonium compounds are placed heterogeneously in a metal matrix of aluminum, molybdenum, stainless steel, etc. The matrix material determines the radiation resistance and thermal conductivity of the dispersion fuel. fuel. For example, the dispersion fuel of the First NPP consisted of particles of an alloy of uranium with 9% molybdenum filled with magnesium.

CONDITIONAL FUEL

conditional fuel. Different types of energy resources have different quality, which is characterized by the energy intensity of the fuel. Specific energy intensity is the amount of energy per unit mass of the physical body of an energy resource.

To compare different types of fuel, total accounting its reserves, assessing the efficiency of using energy resources, comparing the indicators of heat-using devices, the unit of measurement is adopted - conventional fuel. Conditional fuel is such fuel, during the combustion of 1 kg of which 29309 kJ, or 700 kcal of energy, is released. For comparative analysis 1 ton of reference fuel is used.

1 t.t = 29309 kJ = 7000 kcal = 8120 kWh.

This figure corresponds to good low-ash coal, which is sometimes called coal equivalent.

Abroad, reference fuel with a calorific value of 41,900 kJ/kg (10,000 kcal/kg) is used for analysis. This figure is called the oil equivalent. The table below shows the values of specific energy intensity for a number of energy resources in comparison with conventional fuel.

CONCLUSION

Thus, on the basis of the above material, the following conclusions can be drawn:

Fuel is a combustible substance used to produce heat.

By origin, fuel is natural and artificial.

According to the state of aggregation, solid, liquid and gaseous fuels are distinguished.

According to its intended use, fuel can be energy, technological and household.

As an independent species, nuclear fuel is also isolated.

For comparison various kinds of fuel according to their calorific value, the unit of measurement "conditional fuel" is used.

Conventional fuel - conventionally accepted fuel with a calorific value of 7000 kcal / kg (for liquid and solid fuels) and 7000 kcal / Nm 3 (for gas different types fuel).

LIST OF USED SOURCES

Occupational safety and the basics of energy saving: Proc. allowance /

EM. Krachenya, R.N. Kozel, I.P. Svirid. - 2nd ed. - Minsk: TetraSystems, 2005. - 156-161,166-167 p.

Wikipedia is the free encyclopedia [ Electronic resource] / Nuclear fuel. Access mode: http://ru.wikipedia.org/ Access date: 04.10.2009.

3. Energy Efficiency Department State Committee on standardization of the Republic of Belarus [Electronic resource] / Regulations. Guidelines for the preparation of feasibility studies for energy-saving measures. Access mode: http://energoeffekt.gov.by/doc/metodika_1.asp. Access date: 03.10.2009

APPENDIX A

Table 1: Specific energy intensity of energy resources

Fuel types

specific energy consumption,

Conditional fuel

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Fuel- this is a combustible substance that releases a significant amount of heat during combustion, which is used directly in technological processes and for heating, or is converted into other types of energy.

According to the state of aggregation, fuels of organic origin are divided into solid, liquid and gaseous (gaseous).

By origin, organic fuels are divided into natural (natural) and artificial, obtained by various methods.

Table 1.1

Fossil fuel classification

Depending on the nature of the use, organic fuel can be divided into energy (for obtaining thermal and electrical energy) and industrial (for high-temperature heat-technological installations and systems). Energy and industrial fuels are also defined by the term “boiler and furnace fuel”.

Elementary composition and technical characteristics of organic fuel

The composition of fossil fuels includes various compounds of combustible and non-combustible elements. Solid and liquid fuels contain combustible substances such as carbon C, hydrogen H, volatile sulfur S l, and non-combustible substances - oxygen O, nitrogen N, ash A, moisture W. Volatile sulfur consists of organic S op and pyrite S k compounds: S l \u003d S op + S k. Organic fuel is characterized by:

Working weight;

Dry weight ;

combustible mass;

organic mass.

Sulfur of the organic mass does not contain pyrites. You can recalculate the fuel composition from one mass to another using the appropriate coefficients (Table 1.2)

Table 1.2

Recalculation of fuel composition from one mass to another

Target weight	Desired mass
Target weight	organic
organic

Gaseous fuels are usually reduced to dry mass in volume fractions:

The most important technical characteristics of the fuel are the calorific value, heat output, ash and moisture content, the content of harmful impurities that reduce the value of the fuel, the yield of volatile substances, the properties of coke (non-volatile residue).

Heat of combustion(calorific value) of fuel - the amount of heat released during the complete combustion of a unit of mass (kJ / kg) or volume (kJ / m 3) of fuel. The heat of combustion is a characteristic that determines the fuel consumption for the operation of fuel-using equipment. There are higher and lower calorific values of fuel. When designing boilers and technological units that do not use the latent heat of condensation of water vapor contained in the combustion products of fuel, calculations are traditionally carried out according to net calorific valuecapabilities fuel.

In cases where the latent heat of condensation of water vapor is used in the units, the calculations include gross calorific value fuel.

The lower calorific value of a fuel can be determined by knowing the higher calorific value

The heat of combustion of fuel is determined experimentally in a calorimetric bomb or in a gas calorimeter. The principle of operation of calorimeters is based on the fact that they burn a precisely measured mass or volume of fuel, the released heat of which is transferred to water, the initial temperature and mass of which are known. Knowing the mass of water, and measuring the increase in its temperature, determine the amount of heat released and the calorific value of the fuel. With a known fuel composition, the heat of combustion can be calculated analytically. The working lower calorific value of solid and liquid fuels can be approximately determined by the formula of D.I. Mendeleev, kJ/kg

where

- the heat of combustion of each gas that is part of the fuel, MJ / m 3; C m H n,H 2 S,CO,H 2 - the content of individual gases in the fuel, % vol.

The heat of combustion of individual gases that make up the gaseous fuel is given in table. 1.3.

The heat of combustion of various types of fuel varies over a very wide range. To compare different types of fuel in determining consumption rates, reserves, fuel economy, the concept of conventional fuel has been introduced. Conventional fuel is called fuel, the lower calorific value of which is equal to Q c.t = 29310 kJ/kg (7000 kcal/kg).

To recalculate the consumption of any type of natural fuel into conventional fuel and vice versa, the heat equivalent is used, which is the ratio of the lower calorific value of the working mass of natural fuel to the calorific value of conventional fuel

FUEL TYPES. FUEL CLASSIFICATION

According to the definition of D.I. Mendeleev, “fuel is a combustible substance deliberately burned to produce heat.”

Currently, the term "fuel" covers all materials that serve as a source of energy (for example, nuclear fuel).

Fuel by origin is divided into:

Natural fuels (coal, peat, oil, oil shale, wood, etc.)

Artificial fuel (motor fuel, generator gas, coke, briquettes, etc.).

Solid fuel - wood and vegetable mass, peat, shale, brown coal, coal.

Liquid fuel - products of oil refining (fuel oil).

Gaseous fuel - natural gas; gas produced during oil refining, as well as biogas.

Nuclear fuel - fissile (radioactive) substances (uranium, plutonium).

SOLID FUEL. MAIN CHARACTERISTICS

solid fuel . Fossil solid fuels (with the exception of slates) are a product of the decomposition of the organic matter of plants. The youngest of them - peat - is a dense mass , formed from the decayed remains of marsh plants. The next in “age” are brown coals - an earthy or black homogeneous mass, which, during long-term storage in air, is partially oxidized (“weathered”) and crumbles into powder. Then come coals, which, as a rule, have increased strength and less porosity. The organic mass of the oldest of them - anthracites - has undergone the greatest changes and consists of 93% carbon. Anthracite has a high hardness.

Renewable solid fuel is wood. Its share in the energy balance of the world is now extremely small, but in some regions wood (and more often its waste) is also used as fuel.

Briquettes can also be used as solid fuel - a mechanical mixture of coal and peat fines with binders (bitumen, etc.), compressed under pressure up to 100 MPa in special presses.

LIQUID FUEL. MAIN CHARACTERISTICS

Fuel oil obtained from oil from a number of fields may contain a lot of sulfur (up to 4.3%), which greatly complicates the protection of equipment and the environment during its combustion.

In boilers of boiler houses and power plants, fuel oil is usually burned, in domestic heating installations - household heating oil (a mixture of medium fractions).

GAS FUEL. MAIN CHARACTERISTICS

gaseous fuel. Gaseous fuels primarily include natural gas. These are gas produced from pure gas fields, associated gas from oil fields, gas from condensate fields, coal mine methane, etc. Its main component is methane CH 4; in addition, the gas from different fields contains small amounts of nitrogen N 2 , higher hydrocarbons СnНm , carbon dioxide CO 2 . During the extraction of natural gas, it is purified from sulfur compounds, but some of them (mainly hydrogen sulfide) may remain.

When oil is extracted, the so-called associated gas is released, which contains less methane than natural gas, but more higher hydrocarbons and therefore releases more heat during combustion.

World geological gas reserves are estimated at 140-170 trillion m³.

Natural gas is located in deposits, which are "domes" of a waterproof layer (clay type), under which gas, consisting mainly of methane CH 4, is under pressure in a porous medium (sandstone). At the exit from the well, the gas is cleaned from sand suspension, condensate drops and other inclusions and is fed to the main gas pipeline with a diameter of 0.5 - 1.5 m and a length of several thousand kilometers. The gas pressure in the pipeline is maintained at 5 MPa by means of compressors installed every 100-150 m. The compressors are rotated by gas turbines that consume gas. The total gas consumption for maintaining pressure in the gas pipeline is 10-12% of the total pumped. Therefore, the transport of gaseous fuel is very energy-intensive.

Recently, biogas, a product of anaerobic fermentation (fermentation) of organic waste (manure, plant residues, garbage, sewage, etc.), has been increasingly used in a number of places. In China, more than a million biogas factories are already operating on a variety of waste (according to UNESCO, up to 7 million). In Japan, biogas sources are landfills of pre-sorted household waste. "Factory", with a capacity of up to 10-20 m³ of gas per day. Provides fuel for a small power plant with a capacity of 716 kW.

A very promising type of fuel, which has three times the specific energy intensity compared to oil, is hydrogen, scientific and experimental work to find economical ways of industrial transformation of which is currently being actively conducted both in our country and abroad. Hydrogen reserves are inexhaustible and are not associated with any region of the planet. Hydrogen in a bound state is contained in water molecules (H 2 O). When it is burned, water is formed that does not pollute the environment. Hydrogen is conveniently stored, distributed through pipelines and transported at low cost.

Reduce consumption of organic and nuclear fuel;

Satisfy growing energy needs;

Reduce environmental pollution.

NUCLEAR FUEL. CLASSIFICATION AND APPLICATION

Nuclear fuel is divided into two types:

Natural uranium containing fissile nuclei 235 U, as well as raw materials 238 U, capable of forming plutonium 239 Pu upon neutron capture;
Secondary fuel that does not occur in nature, including 239 Pu obtained from fuel of the first type, as well as 233 U isotopes formed during the capture of neutrons by 232 Th thorium nuclei.

According to the chemical composition, nuclear fuel can be:

Metal, including alloys;
Oxide (for example, UO 2);
Carbide (e.g. PuC 1-x)
nitride
Mixed (PuO 2 + UO 2)

Application. Nuclear fuel is used in nuclear reactors, where it is usually stored in hermetically sealed fuel elements (FELs) in the form of pellets a few centimeters in size.

Good nuclear fuels include some refractory compounds of uranium: oxides, carbides and intermetallic compounds. The most widely used ceramics - uranium dioxide UO 2 . Its melting point is 2800 ° C, density - 10.2 t / m 3. Uranium dioxide has no phase transitions and is less prone to swelling than uranium alloys. This allows you to increase burnout up to several percent. Uranium dioxide does not interact with zirconium, niobium, stainless steel and other materials when high temperatures. The main disadvantage of ceramics is low thermal conductivity - 4.5 kJ/(m·K), which limits the specific power of the reactor in terms of melting temperature. Thus, the maximum heat flux density in VVER reactors running on uranium dioxide does not exceed 1.4 10 3 kW/m 2 , while the maximum temperature in fuel rods reaches 2200 °C. In addition, hot ceramics are very brittle and can crack.

Dispersion fuels have high thermal conductivity and mechanical properties, in which small particles of UO 2 , UC, PuO 2 and other uranium and plutonium compounds are placed heterogeneously in a metal matrix of aluminum, molybdenum, of stainless steel Matrix material and determines the radiation resistance and thermal conductivity of the dispersion fuel. For example, the dispersion fuel of the First NPP consisted of particles of an alloy of uranium with 9% molybdenum filled with magnesium.

CONDITIONAL FUEL

To compare different types of fuel, to summarize its reserves, to assess the efficiency of using energy resources, to compare the indicators of heat-using devices, the unit of measurement is conventional fuel. Conditional fuel is such fuel, during the combustion of 1 kg of which 29309 kJ, or 700 kcal of energy, is released. For comparative analysis, 1 ton of standard fuel is used.

1 t.t = 29309 kJ = 7000 kcal = 8120 kWh.

This figure corresponds to good low-ash coal, which is sometimes called coal equivalent.

CONCLUSION

Thus, on the basis of the above material, the following conclusions can be drawn:

Fuel is a combustible substance used to produce heat.

By origin, fuel is natural and artificial.

According to the state of aggregation, solid, liquid and gaseous fuels are distinguished.

According to its intended use, fuel can be energy, technological and household.

As an independent species, nuclear fuel is also isolated.

To compare different types of fuel in terms of their calorific value, the unit of measurement "reference fuel" is used.

Conventional fuel is conventionally accepted fuel with a calorific value of 7000 kcal/kg (for liquid and solid fuels) and 7000 kcal/Nm 3 (for gaseous fuels).

LIST OF USED SOURCES

1. Occupational safety and the basics of energy saving: Proc. allowance /

EM. Krachenya, R.N. Kozel, I.P. Svirid. - 2nd ed. - Minsk: TetraSystems, 2005. - 156-161,166-167 p.

2. Wikipedia - the free encyclopedia [Electronic resource] / Nuclear fuel. Access mode: http://ru.wikipedia.org/ Access date: 04.10.2009.

3. Energy Efficiency Department of the State Committee for Standardization of the Republic of Belarus [Electronic resource] / Regulatory documents. Guidelines on drawing up feasibility studies for energy-saving measures. Access mode: http://energoeffekt.gov.by/doc/metodika_1.asp. Access date: 03.10.2009

APPENDIX A

Table 1: Specific energy intensity of energy resources

Aggregate condition	Origin of fuel
Aggregate condition	Natural	artificial
		gasoline, kerosene, diesel fuel, fuel oil, alcohol, benzene, resins (coal, peat, shale)
gaseous	natural and oil field	Generator, water, light, coke, semi-coke, blast furnace, refinery gases
	fossil coals, oil shale, peat,	Coal coke and semi-coke, briquetted and pulverized fuel, charcoal

Fuel consists of combustible and non-combustible parts. The combustible part of the fuel is a combination of various organic compounds, which include carbon, hydrogen, oxygen, nitrogen, and sulfur. The non-combustible part (ballast) consists of mineral impurities, including ash and moisture.

Carbon C is the main combustible part of the fuel. With an increase in its content, the thermal value of the fuel increases. For various fuels, the carbon content ranges from 50 to 97%.

Hydrogen H is the second most important combustible component of the fuel. The hydrogen content in the fuel reaches 25%. However, when hydrogen is burned, four times more heat is released than when carbon is burned.

Oxygen O, which is part of the fuel, does not burn and does not release heat, therefore it is the internal ballast of the fuel. Its content, depending on the type of fuel, ranges from 0.5 to 43%.

Nitrogen N does not burn and is the internal fuel ballast. Its content in liquid and solid fuels is not high and amounts to 0.5 - 1.5%.

Sulfur S, during the combustion of which a certain amount of heat is released, is a highly undesirable component of the fuel, since its combustion products - sulfurous SO 2 and sulfuric SO 3 anhydrides cause severe gas or liquid corrosion of metal surfaces. The sulfur content in solid fuels is up to 8%, and in oil from 0.1 to 4%.

Ash A is a non-combustible solid component, the amount of which is determined after complete combustion of the fuel. It is an undesirable and even harmful impurity, since in its presence abrasive wear increases, the operation of various units becomes more complicated. Fuel with a high ash content has a low heat of combustion and ignition.

Moisture W is a highly undesirable admixture of fuel, since, taking part of the heat for evaporation, it reduces the heat and temperature of fuel combustion, complicates the operation of plants (especially in winter), and contributes to corrosion.

Mineral impurities (ash and moisture) are usually divided into external and internal. The former enter the fuel from the environment during its extraction, transportation or storage, while the latter are included in its chemical composition.

The fuel that comes to the consumer in its natural state, and contains, in addition to the combustible part, ash and moisture, is called working. To determine the dry weight of the fuel, it is dried at a temperature of 105°C to remove moisture.

The composition of gaseous fuels is very diverse: its combustible part includes hydrogen H, carbon monoxide CO, methane CH 4 and other gaseous hydrocarbons (CnHm) with the number of hydrocarbon atoms up to 4 inclusive.