Liquid fuel and its characteristics. Fossil fuel Main types of fuels and their classification

Basic definitions, classification and origin of fossil fuels. Elemental and technical composition of fuel. The heat of combustion of fuel and methods for its determination. solid fuel. Liquid fuel. gaseous fuel. Conditional fuel.

Fuel is a substance that can enter into a rapid oxidative process with atmospheric oxygen - combustion, while releasing a significant amount of heat. Fuel is a complex organic compound of combustible elements included in its composition, ballasted with non-combustible components that have a significant impact on its quality.

Its main types are organic fuels: peat, oil shale, coal, natural gas, oil refinery products.

By way of getting Distinguish between natural and artificial fuels. TO

natural include natural fuels: coal, shale, peat, oil, natural gases. Of solid fuels, artificial ones include coke, coal briquettes, charcoal. From liquid - fuel oil, gasoline, kerosene, solar oil, diesel fuel. From gas - blast-furnace, generator, coke gases. Peat, brown coals, bituminous coals and anthracites were formed in the process of sequential coalification of dead plant mass.

Further classification of each group can be made according to their state of aggregation for solid, liquid and gaseous fuels.

The composition and quality of the fuel is determined by chemical and technical analysis. For this, the so-called average sample of a given batch of fuel is taken, which should most correctly reflect the properties and composition of the entire batch or formation from which the fuel is extracted. The selection of the middle batch is carried out in accordance with specially developed instructions.

Fuel extracted from the bowels, from the surface of the earth and delivered to the consumer is called working fuel. The composition of the working fuel includes: carbon (C), hydrogen (H), volatile sulfur (S l), which, when burned, emit a certain amount of heat, oxygen (O) and nitrogen (N), which are the internal fuel ballast, and, finally , ash (A) and moisture (W) that make up the external ballast of the fuel. All of the above elements that make up the fuel are given as a percentage by weight. The fuel in the form in which it enters the consumer is called working, and the substance that makes it up is called the working mass. Its elemental chemical composition is expressed as follows:

C p + H p + O p + N p + S p + A p + W p =100%

Mineral impurities and humidity of the same type of fuel in different areas of its deposit and various places may be different, and may also change during transportation and storage. More constant is the composition of the combustible mass of fuel. With this circumstance in mind, for a comparative thermal assessment of various types of fuel, the conditional concepts of dry, combustible and organic mass were introduced, the components of which, expressed as a percentage, are indicated by the same symbols as the working mass, but, respectively, with the indices "s", "g ” and “o” instead of the working mass index, “p”.

Moisture. The moisture content in solid fuels varies widely - from 5% to 60%. The moisture content of liquid and gaseous fuels is low. Fuel moisture is divided into external (mechanical) W ext,%, and internal (hygroscopic) W gr,%. Their sum is the operating humidity

W p \u003d W ext + W gr, [%]

External moisture is removed from the fuel during its natural drying at room temperature. The reduction in the weight of the fuel will stop when there is an equilibrium between the pressure of water vapor in the fuel and the partial pressure of water vapor in the ambient air.

Internal moisture is retained in the pores of the fuel due to the presence of capillary forces and is removed from it only by heating the fuel. In a drying cabinet up to 105 0 C. The content of internal moisture in solid fuel reaches 10%. However, the total moisture found in this way turns out to be less than the moisture actually in the fuel, because a number of solid fuels contain crystallization or hydrate moisture associated with some mineral components of the fuel: clay, silicates, organic matter. This moisture can be removed from the fuel only at a temperature of 800 0 C.

The presence of moisture in the fuel adversely affects its quality, and, consequently, the operation of the boiler plant, since due to moisture, the amount of combustible substances in the fuel decreases, and, of course, the amount of heat released during its combustion decreases. In addition, part of the heat goes to the evaporation of moisture, and then leaves the boiler plant together with the vapors, lowering its efficiency. It should also be noted that it is difficult to ignite fuel containing moisture, an increase in the volume of flue gases, which in turn increases the consumption of electricity by smoke exhausters. At low flue gas temperatures, the presence of water vapor in them causes the risk of condensation of the latter and the occurrence of corrosion of metal heating surfaces and chimneys.

Ash. The solid non-combustible residue resulting from the completion of the transformations in the mineral part of the fuel during its combustion is called ash. The yield of the gasified part of the impurities reduces the mass of ash in relation to the initial mineral impurities of the fuel, and some reactions, for example, the oxidation of iron pyrites, lead to its increase. Usually, the mass of ash is slightly less than the mass of mineral impurities in the fuel, only in oil shale due to the decomposition of the ash carbonates contained in them.

it turns out much less in comparison with the mass of mineral impurities.

There is no ash as such in the original fuel. It arises as a result of fuel combustion as a dry residue. In solid fuels, the ash content ranges from 2% to 60%. In liquid and gaseous fuels, the ash content is extremely low.

Ash is a mixture of various minerals that have entered the fuel. Ash is divided into three types. Primary ash enters the source material - wood - in the form of dissolved salts together with soil water and is evenly distributed in it. Secondary ash also enters the fuel from the outside with groundwater or as a result of mountain-forming processes that took place in prehistoric times. Both types of this ash cannot be separated from the fuel. Tertiary ash is a random impurity in the form of rock captured during the extraction of fuel and separated from it as a result of enrichment.

In the combustion chamber at high temperatures, part of the ash is melted,

forming a solution of minerals, which is called slag. Slags are removed from the furnace in a liquid or granular state. To assess the degree of contamination of the combustible mass of fuel, the ash content is referred to its dry mass, expressing it as a percentage. The ash content is determined by burning a pre-dried fuel sample of a certain weight in a platinum crucible and calcining to constant weight (solid fuels at a temperature of 800±25°C, and liquid fuels - 500°C). The ash content of the fuel varies from fractions of a percent in fuel oil and wood to 40-60% in shale.

The ash formed during the combustion of fuel at high temperatures and a short residence time in the combustion chamber differs in its chemical and mineralogical composition from the ash formed during the analysis of ash content by burning fuel in laboratory conditions.

Important properties of ash are its abrasiveness and fusibility characteristics. Ash with high abrasiveness causes severe wear of the convective heating surfaces of heat generators.

The fusibility of the ash is determined by heating a trihedral pyramid in a special furnace in a semi-reducing gaseous medium. standard sizes 13 mm high and the length of its base edge 6 mm, made from a crushed test ash sample (GOST 2057-49).

The following characteristics of ash fusibility are distinguished:

t 1 - the temperature of the beginning of deformation, at which the pyramid is bent or its top is rounded;

t 2 - the temperature of the beginning of softening, at which the top of the pyramid

leans to its base or the pyramid turns into a ball;

t 3 - the temperature of the beginning of the liquid-melting state, at which the pyramid

spreads on a stand;

t 0 - the temperature of the beginning of a truly liquid state, at which the melt

slag obeys Newton's laws on the flow of a true fluid.

According to the fusibility characteristics of ash, thermal coals are divided into three groups: with low-melting ash t 3<1350 °С, с золой средней плавкости

1350< t 3 <1450 °С и с тугоплавкой золой t 3 >1450 °C.

The presence of ash in the fuel significantly reduces its value and causes difficulties in the process of its combustion. Fly ash carried into the gas ducts of the boiler abrades and contaminates the heating surfaces, worsening the heat transfer coefficient. The ash and slag that has fallen in the boiler units require special measures to remove them.

Carbon. Carbon is one of the most essential components of each fuel and is included in its composition not in a free state, but in the form of complex organic compounds with hydrogen, oxygen, sulfur and nitrogen. During combustion, pure carbon releases 8130 kcal/kg (34.4 MJ/kg) and is the main source of fuel calorific value. The carbon content in some solid fuels reaches 95%.

Hydrogen. Another important component of the fuel is hydrogen, the content of which in the combustible mass of solid and liquid fuels ranges from 2 to 10%. A lot of hydrogen is contained in natural gas, fuel oil and oil shale, least of all in anthracite. In terms of calorific value, hydrogen is almost 4 times higher than carbon and its calorific value in water vapor is 10.8 MJ / m 3 (2579 kcal / m 3).

Sulfur. The sulfur content in solid fuels, with the exception of shale, is low. When burned, sulfur releases a small amount of heat. There are three types of sulfur in fuel. Organic sulfur S 0 and pyrite Sk make up the so-called combustible volatile sulfur:

S l \u003d S 0 + Sk [%]

The third type of sulfur is sulfate sulfur - S a, which is already oxidized and therefore cannot emit heat, as a result of which it is included in the fuel ash in the form of mineral compounds with iron and calcium. The total sulfur content in the fuel is

Sob \u003d Sl + Sa [%]

Organic sulfur is a part of complex high-molecular organic fuel compounds. Pyrite sulfur is its compounds with metals, more often with iron (FeS_2 - iron pyrite), and is included in the mineral part of the fuel. Organic and pyrite sulfur S l _when fuel is burned, it is oxidized with the release of heat. Sulfate sulfur enters the mineral part of the fuel in the form of sulfates CaS0 4 and FeS0 4 and therefore does not undergo further oxidation during combustion. Sulfate compounds of sulfur turn into ash during combustion. The combustible mass of fuel includes S o and S k, which, during the combustion of the fuel, pass into gaseous SO 2 compounds, and in a small amount into SO 3.

The sulfur content in solid fuels is usually low. In oil, sulfur is part of inorganic compounds, in natural gases it is practically absent, in the associated gases of some oil fields there is a little sulfur in the form of hydrogen sulfide H 2 S and sulfur dioxide SO 2. Sulfur dioxide formed during the combustion of fuel and especially sulfuric gas SO 3 accompanying it in a small amount cause corrosion of metal parts of heat generators and poison the surrounding area. Due to the low calorific value of 9.3 MJ/kg (2220kcal/kg), the presence of sulfur reduces the calorific value of the fuel. Therefore, sulfur is a harmful and undesirable fuel impurity.

nitrogen and oxygen refer to internal fuel ballast. Nitrogen is an inert gas. Its content in solid fuel is 1-2% and during the combustion of fuel it is released in a free state.

The oxygen content in the fuel varies widely, reaching 40%. It is generally accepted that all the oxygen in the fuel is bound to hydrogen and forms water vapor when the fuel burns. In addition, oxygen, being in combination with hydrogen or carbon of the fuel, converts some of the fuel into an oxidized state and reduces its heat of combustion. The oxygen content is high in wood and peat. Nitrogen does not oxidize when fuel is burned in air and passes into the combustion products in a free form.

Fuels are combustible substances, the main component of which is carbon, used to obtain thermal energy by burning them.

Classification. According to the physical state, fuel can be solid, liquid, gaseous. Glass melting furnaces operate on liquid and gaseous fuels.

A number of requirements are imposed on the fuel used for glass melting furnaces: during combustion, it must emit a significant amount of heat per unit of its mass or volume, it must not emit gases that are harmful to human health, as well as adversely affecting the materials of furnaces and furnaces, it must be convenient for transportation and burning.

The main characteristic of the fuel is its calorific value Q. The calorific value of the fuel is the amount of heat released during the complete combustion of a unit mass or volume of fuel (1 kg of liquid fuel or 1 m 3 of gaseous fuel). Calorific value is measured in kcal / kg or kcal / m 3 (in SI - kJ / kg, kJ / m 3).

The calorific value of various types of fuel varies widely - from 1000 to 10,000 kcal/kg.

By origin, fuel is divided into natural and artificial. The latter is obtained as a result of the processing of natural fuel. In table. 3 shows the classification of industrial fuels.

In industry, solid, liquid and gaseous fuels are used. Distinguish between natural fuel, extracted on the surface of the earth or in its bowels, and artificial, obtained by processing natural.

The main requirements for process fuel include: low cost of production, low cost of transportation, ease of use, the possibility of using it with a high efficiency, low content of harmful impurities.

Different types of fuel (solid, liquid and gaseous) are characterized by general and specific properties. General fuel properties include calorific value and humidity, specific properties include ash content, sulfur content (sulfur content), density, viscosity and other properties.

Heat of combustion- the amount of heat that is released during the complete combustion of 1 kg or 1 m 3 of fuel. The energy value of fuel is primarily determined by its heat of combustion.

Distinguish between higher and lower calorific value. The lower calorific value differs from the higher amount of heat spent on the evaporation of moisture contained in the fuel and formed during the combustion of hydrogen. The net calorific value is taken into account to calculate the need for fuel and its cost when compiling heat balances and determining the efficiency of installations using fuel. When comparing different types of fuel, the concept of reference fuel is used, which is characterized by a lower calorific value of 29 MJ / kg.

Humidity(moisture content) of the fuel reduces its heat of combustion due to increased heat consumption for the evaporation of moisture and an increase in the volume of combustion products (due to the presence of water vapor).

Ash content- the amount of ash formed during the combustion of mineral substances contained in the fuel. The mineral substances contained in the fuel reduce its calorific value due to a decrease in the content of combustible components (the main reason) and an increase in heat consumption for heating and melting the mineral mass.

sulfur content(sulfur content) refers to the negative factor of the fuel, since when it is burned, sulfur dioxide gases are formed that pollute the atmosphere and destroy the metal. In addition, the sulfur contained in the fuel partially passes into the smelted metal, welded glass mass, reducing their quality. For example, for the melting of crystal, optical and other glasses, fuel containing sulfur cannot be used, since sulfur significantly reduces the optical properties and color of the glass.

Fuel composition. Fuels of various types, deposits and mines differ in their composition. When considering solid and liquid fuels, it is customary to distinguish between the following components: carbon, hydrogen, sulfur, oxygen, nitrogen, ash, and moisture. In relation to gaseous fuel, the composition is understood mainly as: carbon monoxide, hydrogen, methane, ethane, propane, butane, ethylene, benzene, hydrogen sulfide, etc. Oxygen and nitrogen included in the fuel are classified as internal organic fuel ballast, and ash and moisture - to the outside.

The composition of solid and liquid fuels is expressed as a percentage by weight, gaseous - as a percentage by volume.

Solid and liquid fuels consist of combustible and non-combustible parts. The combustible part of the fuel includes carbon, hydrogen, oxygen, nitrogen and sulfur. Oxygen and nitrogen do not burn; they are included in the composition of the combustible mass conditionally. Therefore, the combustible part of the fuel is called conditionally combustible mass. The non-combustible part of the fuel - ballast - consists of moisture and ash. The organic mass of the fuel is carbon, oxygen and nitrogen.

The fuel in the form in which it enters the furnaces for combustion is called the working fuel. Due to the fact that the moisture content in it can vary widely, the composition of the fuel is often characterized by its dry weight.

To designate the composition to which the content of one or another element in the fuel belongs, the indices o, g, c and p are used, which are read respectively: o - organic mass; g - combustible mass; c - dry fuel; p - working fuel. For example, CO is the carbon content in the organic mass; Sr - sulfur content in the conditionally combustible mass; Ac - content, ash in dry fuel; Wp is the moisture content of the working fuel.

Energy fuels are combustible substances that are economically feasible to use to produce heat and electricity. According to the state of aggregation, fuels are divided into solid, liquid and gaseous. By origin - natural, formed from the remains of plant and animal origin for a long time, and artificial, obtained as a result of the processing of natural fuels. The former include coal, oil, natural gas. The second category includes coke, briquettes, coal preparation waste, diesel fuel, fuel oil, blast furnace, coke oven and generator gases.

Fuel consists of combustible and mineral parts and moisture. The composition of the combustible part includes carbon C, hydrogen H and sulfur S, which are in complex compounds with oxygen O and nitrogen N. An important characteristic of the fuel is the heat of combustion. The heat of combustion is the amount of heat released during the complete combustion of fuel. Distinguish between lower and higher calorific value.

Carbon is the main part of the fuel. The more it is in the composition, the higher the heat of combustion of the fuel. The carbon content by mass in solid fuels ranges from 25% (shale and peat) to 70% (anthracite). Hydrogen is contained in the fuel in a small amount of 2-10%. Its heat of combustion is 4 times greater than that of carbon. Oxygen is included in the composition of the fuel in the form of various compounds, including those with combustible elements, which reduces the amount of heat released during fuel combustion. Therefore, oxygen is referred to as fuel ballast. Nitrogen is also referred to as fuel ballast. Its content is low (in solid fuel up to 3% by weight). During combustion, most of the nitrogen in the fuel is converted into toxic oxides N0 and N0*.

Sulfur, depending on the type of compound in which it is included, is divided into organic S0 if it is associated with carbon, hydrogen, nitrogen and oxygen; pyrite SK - a compound with iron (usually iron pyrite); sulfate Sc, which is in the form of compounds FeSO4, MgSO4, CaSO4. Sulfur, which is part of organic and pyrite compounds, participates in the combustion process, releasing heat and forming sulfur dioxide.

S02 and sulfuric S03 anhydrides. Therefore, organic and pyrite sulfur is often called volatile fuel.

Sulfur, which is part of FeS04, MgS04, CaS04, etc., does not burn, so, when burning fuel, sulfates practically do not decompose. In solid fuel, the sulfur content reaches 5%, in liquid fuel 3.5%. The presence of sulfur in the fuel is undesirable, since the oxides S02 and S03 formed during the combustion of sulfur in the presence of moisture give solutions of sulfurous and sulfuric acids, which cause corrosion of the pipes of the heating surfaces of the convective shaft of the boiler and have a harmful effect on environment.

Under the mineral part of the fuel understand non-combustible impurities. Their number depends on the origin of the fuel and the technology of its extraction. Distinguish between internal mineral impurities formed during the formation of a coal deposit, and external mineral impurities that got into the fuel during its extraction from adjacent rock layers. Internal mineral impurities, unlike external ones, are fairly evenly distributed in the fuel and therefore practically cannot be separated from the combustible mass.

When fuel is burned, ash A is formed from mineral impurities. It characterizes the mineral part of the fuel. The content of ash A in the fuel is determined by the amount of solid residue obtained after burning a pre-dried fuel sample of a certain mass in a platinum crucible and subsequent calcination to a constant mass value at a temperature of 800 °C. When designing boilers, and primarily their furnaces, the temperature characteristic of ash fusibility is of great importance. It depends on the composition of the ash and its surrounding gaseous medium. Evaluation of fusibility is carried out according to the temperatures of three states of ash: U - the beginning of deformation; t2 - the beginning of softening; t3 - liquid-melting state:

To take measures to prevent contamination of the heating surfaces located behind the furnace, it is important to know the solidification temperature of the ash. Usually this temperature is 50 °C below t2. During the combustion of fuel in the furnace in the zone of high temperatures, partial or complete melting of the ash occurs. Some of it is carried away with the products of combustion from the furnace. The rest of the ash, partially decomposed, is fused or sintered into slag, which is then removed in a liquid or solid state from the bottom of the furnace. Under the action of high temperatures, the oxides contained in the slag together with other substances form multicomponent compounds, and the melting point of the slag differs from the temperature ts of the liquid state of the ash. In furnaces with liquid slag removal, for free flow of slag from the furnace, its temperature must be higher than the temperature ts of the liquid-melting state of the ash. This temperature is called the temperature /nzh of normal liquid ash removal, it is determined by 22

The chemical composition of the slag. As a rule, \u003d ta + (100-4-200) ° С.

Moisture W, like the mineral part, is the fuel ballast. It reduces its heat of combustion. In addition, part of the heat of the burnt fuel is spent on its evaporation. The moisture contained in the fuel is divided into external and internal (hygroscopic). External moisture enters the fuel during its extraction, transportation and storage. Its quantity fluctuates over a wide range of 1-40%. External moisture can be removed from the fuel when it is dried. Internal moisture is associated with both the organic part of the fuel and the mineral part. It includes colloidal and hydrated moisture. Colloidal moisture forms gels with fuel. Its amount depends on the nature and composition of the fuel, content / moisture in the atmospheric air. Hydrate moisture is chemically bound with mineral fuel impurities. Its content is small. When the fuel is dried, part of the colloidal moisture evaporates, while the content of hydrated moisture does not change.

Wet solid fuels lose moisture in air, while dried ones acquire it. These processes occur until an equilibrium is reached between the partial pressure of water vapor in air and fuel. Fuel with moisture obtained in this way is called air-dry. If air-dry fuel is heated at atmospheric pressure to a temperature of 105 ° C, then all moisture from the fuel will be practically removed. The amount of moisture removed from an air-dry fuel is called the hygroscopic moisture WrH.

The composition of the fuel in the form in which it enters the TPP, expressed as a set of individual elements and components (by weight for solid and liquid fuels), is called the working mass of the fuel:

TOC o "1-3" h z cp + № + Sp 4-Op + Np + Wp + Ap = 100%. (one)

If external and internal moisture is removed from the fuel, then the dry mass has the following composition:

Cc-j-Hc-fSc + Oc-fNc+Ac = 100 o/0. (2)

Excluding ash from the dry mass, we obtain a combustible mass of fuel

Cr + Hr + Sr + Or-f No. = 100%. (3)

If pyrite sulfur is isolated from the combustible mass, then the remaining mass of fuel is called organic mass

Cr + Hg + Og + No = 100%. (4)

The composition of the working and dry masses of the same fuel, depending on the conditions of extraction and the weather, can vary within a fairly wide range. The composition of the combustible mass of fuel is constant. Therefore, it is used for conversion to dry and working weights. Formulas for recalculating the composition, for example, from a working

2. The conversion factor for the composition of solid and liquid fuels from one mass to another

Target weight	Desired mass
		organic






organic

Dry masses are easy to obtain, since 1 kg of working mass contains (100-Nr) / 100 (kg) dry mass of fuel. Therefore,

CP + Hp + Sp + O "+ Np + W" H - A "_ 100 ~

C + ns -) - sc + oc + ne + ac 100 - w "100 100"

Cp \u003d Cs (100- Wp) / 100: HP \u003d HC (100-Wp) / 100

The conversion factor (100 -Wp)/100 is constant for all fuel elements. The conversion factors for the composition of solid and liquid fuels from one mass to another are given in Table. 2.

If the fuel is heated without access to air, then volatile substances are released from it as a result of thermal separation of unstable oxygen-containing hydrocarbon compounds and a solid non-volatile residue remains. The yield of volatiles and the properties of the solid residue are important thermal characteristics of solid fuels.

Volatile yield V is determined by the decrease in the combustible mass of fuel when it is heated for 7 minutes without air access at a temperature of 850 ° C and is expressed in% of the combustible mass of fuel. The composition of volatiles usually includes hydrogen, hydrocarbons, carbon monoxide and carbon dioxide. The value of the release of volatiles and the temperature of the 4th beginning of their release depend on the age of the fuel. The higher the yield of volatiles and the lower the temperature of the beginning of their release, the easier the fuel ignites. The highest yield of volatile and most - 24

Young fuels have a lower temperature at the beginning of their exit: for peat, Vrn = 70%, *out = 100-g - PO °C; in brown coal. Utya \u003d "40-1-65%; W 130-i-170 °С.

The solid residue that remains after the release of volatiles from the fuel can be sintered, slightly sintered and powdery. Only some bituminous coals give a dense sintered 1 residue with a large number of pores, called coke.

The heat of combustion of fuel is determined empirically. The amount of heat released depends on the final state of the combustion products and, in particular, on the state of aggregation of moisture (in the form of steam or water). In this regard, a distinction is made between the highest Qb and the lowest calorific value.

The difference between Qjj and Ql is that the former takes into account the heat that is released during the condensation of water vapor (moisture in the combustion products is in the form of water), while the latter does not take this heat into account. Since the temperature of the combustion products in the boiler is high enough and water vapor does not condense, the heat spent on the evaporation of moisture is lost. Therefore, in thermal calculations, the lower calorific value of the working fuel is used. If Qb is known, then = Ql - 25.2 (Wp/100 + 9H7100),

Where 25.2 (Wp / 100 + 9N/100) is the amount of heat spent on the evaporation of moisture (Wp / 1000) contained in the fuel and water (9НР / 100) formed during the combustion of hydrogen, kJ / kg;

25.2 MJ/kg - the value of the latent heat of vaporization for water at a pressure of 0.1 MPa.

In the absence of experimental data, an approximate value for solid fuel and fuel oil can be found using the formula proposed by D. N. Mendeleev,

QS \u003d 0.339CP + 1.03HP - 0.109 (Or - Sp) - 0.259WP.

To compare different fuels, the concept of reference fuel is used, i.e., fuel whose calorific value is equal to

29.3 MJ/kg. The concept of reference fuel is used in determining various fuel resources, comparing specific fuel consumption per unit of generated energy, and conducting technical and economic calculations. In a comparative assessment of the quality of fuels, the characteristics of fuels reduced to the lowest calorific value % kg/MJ are convenient:

Wn = Wp/Qp„; Ap = Ap/Qp; Sn = SP/QH-

The given characteristics of fuels Wn, A "and S" show how much moisture, ash and sulfur fall on 1 MJ of the lower calorific value, in% of the working mass of the fuel. Depending on the reduced humidity, it is customary to consider fuels: low-moisture with W "= 0.7% - kg / MJ, medium-moisture with Wn = 0.7h - 1.89% kg / MJ, high-moisture with Wn\u003e 1.89% ■ kg /MJ.

Solid fuel is characterized by abrasiveness - the property, when in contact with other materials, to cause wear of the latter, which depends on the amount of pyrite, ash and its composition contained in it. This characteristic of the fuel is important for the choice of equipment for the pulverizing system.

The hardness of a solid fuel and its resistance to grinding (grinding) are characterized by the grinding ability coefficient &lo (the ratio of the specific energy consumption spent on grinding anthracite to the specific energy consumption required for grinding the fuel in question). The softer the fuel, the greater the kno value. This fuel indicator is taken into account when designing pulverizing systems and, first of all, when choosing the type and capacity of grinding equipment.

Density of solid fuel (in kg/m3), as one of its characteristics, is widely used in calculations of systems for loading, storing and supplying fuel to pulverizing systems. There are apparent and bulk density. Apparent density is the mass per unit volume of a piece of fuel with internal pores filled with air and moisture. Bulk density is the mass of fuel contained in a unit volume filled with pieces of fuel, i.e., it also takes into account the volume of air between the pieces of fuel.

Fossil solid fuels are divided into peat, brown, hard coal and anthracite. Peat is geologically the youngest solid fuel. It is characterized by a low degree of decomposition of organic residues and a relatively low calorific value, an increased content of volatiles (U "l yes 70%), hydrogen (Hg \u003d \u003d 5h-6%), oxygen (Og\u003e 30%) and nitrogen (Nr \u003d 2-^ 2.5%) Peat is characterized by very high hygroscopicity and humidity (Wp = 35-=-60%).

Brown coals (grade B) include coals with a higher calorific value of the deashed working mass Q | l00 / (l00 - Ar)< < 23,9 МДж/кг. По геологическому происхождению они близки к торфу. В бурых углях достаточно велико содержание летучих (К = 65-М0 %), водорода (Нг = 4-f-6,5 % и более) и кислорода (Ог = 15ч-30 %). Они отличаются высокой гигроскопичностью и влажностью, содержание углерода достаточно велико (Сг = = 55-^78 %), а количество слаборазложившихся растительных остатков мало. По влажности бурые угли классифицируют: Б1 - с влажностью более 40 %; Б2 - с влажностью 30-40 % и БЗ - с влажностью менее 30 %.

; Hard coals include coals, in which 100 / (100 - Ar)\u003e\u003e 23.9 MJ / kg. They are characterized by high carbon content (75-97%), density and heat of combustion. As the carbon content increases, the proportions of oxygen, hydrogen, and volatiles in the fuel decrease. By volatile output, taking into account the ability 26

Sintering of the solid residue, the following classification of coals is adopted: long-flame (D), gas (G), gas fat - h (GZh), fatty (L), coke fat (KZh), coke (K), enriched sintering (OS), weakly caking (SS), lean (T). As the transition from coal grade D to T, the volatile yield changes from 36% or more (D) to 9-17% (T), and the humidity, respectively, from 14 to 5%.

Semi-anthracites (PA) and anthracites (A) include coals with QE 100 / (100 - Ar) > 23.9 MJ / kg and a volatile yield of less than 9% They contain 89-f-92.5% Cr, 2-b3 .6% Hr, 0.8-fl.3% Nr, 2.2-5% Or, 0.64-0.9% Sr.

Semi-anthracites have a volatile yield of more than 5% and a higher calorific value than anthracites. PA and A are high grade fuels; their waste is used in power boilers.

According to the size of the pieces obtained during the extraction, coal is classified as follows: plate (P), large (K), walnut (O), small (M), seed (C), shtyb (W) and ordinary (P). The size of the pieces of coal from class K to class W decreases from 50-100 to 6-13 mm. In class Sh, the pieces of coal are smaller than 6 mm, and in class P, the size of the pieces is unlimited and can be 0-200 (300) mm. In table. 3 shows the characteristics of solid fuels of some deposits.

Liquid fuels are characterized by conventional viscosity and pour and flash points. It is customary to express the conditional viscosity in conditional degrees (VU). It is defined as the ratio of the outflow time of a certain volume (2-10-4 m3) of liquid fuel to the outflow time of the same volume of water at a temperature of 20 °C.

The nominal viscosity of liquid energy fuel (fuel oil) is usually included in its labeling. So, the numbers after the letter M, in brands of fuel oil (for example, M 40 and M 200) - conditional viscosity at a temperature of 50 ° C (40 and 200 ° VU, respectively). Relative viscosity strongly depends on temperature:

° VU, \u003d ° VUBO (50 / g) p,

Where °Byj - conditional viscosity of liquid fuel at temperature °VU50 - conditional viscosity at t = 50 °С; p - exponent, depending on the value of °VU50.

Below are the values of the relative viscosity °VU50 at various p

"VUy .............................. 2 5 10 15 twenty

I. ................................................ .1.8 2.3 2.6 2.75" 2.86

For high-quality atomization and reliable transportation of liquid fuel through pipelines, its viscosity should not exceed 2-3 °VU. To fulfill this condition, preheating of the fuel is necessary. Heating oil heating temperature depends on its brand and is 80-140 °C.

3. Characteristics of solid fuel

Fuel deposit			Elemental composition (working weight), %

Donetsk

Kuznetsk
Karaganda
Ekibastuz
Podmoskovnoe

Babaevskoe
Kizelovskoe
Chelyabinsk,
Kansko-Achinsk
Nazarovskoye
Irsha-Borodin-

Azeya

The pour point is the minimum temperature at which the fluid loses its fluidity, and it becomes impossible to drain and pump it. For fuel oil, this temperature depends on the brand and is 5-25 °C.

Flash point - the temperature at which liquid fuel vapors in a mixture with air flare up when in contact with a flame. For fuel oil, the flash point is 80-140 °C. At open system fuel oil heating, its temperature should be lower than the flash point by 10-15 °C.

As an artificial liquid fuel in boilers, fuel oil of three grades is used: M40, Ml00 and M200 - a heavy residue of oil distillation resulting from the separation of light fractions from it (gasoline, kerosene, legroin, etc.). Fuel oil is a low-ash and almost anhydrous fuel. It is classified by the content of sulfur compounds in it and by viscosity. According to the number of sulfur-containing compounds, fuel oil is divided into low-sulfur (Sc< 0,5 %), сернистый (Sc = 0,5-2 %) и высокосернистый (Sc >2%). The "Guidelines for the economic and social development of the USSR for 1986-1990 and for the period up to 2000" indicate the need for a significant reduction in the use of fuel oil as a fuel, primarily at thermal power plants.

Gaseous fuel is a mixture of combustible (hydrogen H2, hydrocarbons of the methane series, heavy hydrocarbons CHa, hydrogen sulfide H2S and carbon monoxide CO), a small amount of non-combustible gases (oxygen Oa, nitrogen Na, dioxide 28

Temperature	Volatiles	Heat of combustion	Coefficient of spreadability cl0	The volume of air and combustion at a	Products = 1 m"/kg

carbon CO2 and water vapor H20). Its composition is recorded in the form of its constituent compounds (in% by volume). All calculations are carried out on the basis of a unit volume of dry gas taken under normal conditions (pressure 0.1 MPa and temperature 20 ° C)

CH4 + С2Нв + С3Н8 + ■ ■+ Н2 + H2S + CO + N2 + С02 +

The heat of combustion of gaseous fuel under normal conditions and a known content of gases included in its composition,

QM = 0.01)

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