Volatile substances of coal. Great encyclopedia of oil and gas

Laboratory work No. 3

Determination of the heat of combustion of coals based on their moisture content,

ash content and volatile matter yield

Goal of the work- become familiar with the methods for determining the main indicators of the technical analysis of coal, acquire practical skills in working with the appropriate laboratory equipment and study in practice the basics of the accelerated method for assessing coal.

Laboratory work is complex. It is based on the determination of three main indicators of coal - moisture, ash content and the release of volatile substances on the basis of which the lower calorific value is calculated working mass coal, which is the most important indicator of the quality of coal as an energy fuel.

The heat of combustion, usually denoted by the symbol, is the amount of thermal energy (hereinafter referred to as heat, or heat) released when the combustible components of the fuel are completely oxidized by oxygen gas. In this case, it is accepted that higher oxides are formed as a result of oxidation reactions And sulfur oxidizes only to , and fuel nitrogen is released in the form of molecular nitrogen. Heat of combustion is a specific characteristic. In hard and liquid fuels referred to a unit of mass, that is, 1 kg(specific heat of combustion), and for gaseous fuels - to a unit volume (volumetric heat of combustion) under normal physical conditions, that is, at R = P 0 = 760 mmHg Art. = 1 atm =101325 Pa And
T = T 0 = 273.15 TO (t = t 0 = 0°C). Due to this m 3 under these conditions it received the name “ normal cubic meter " and the recommended designation " no. m 3" Thus, gaseous fuels are classified as 1 no. m 3. Units of measurement accepted in technical literature: “ kJ/kg» (« kJ/no. m 3") or " MJ/kg» (« MJ/no. m 3"). In the old technical literature, the units of measurement were " kcal/kg» (« kcal/no. m 3"). When converting them into modern units of measurement, it should be remembered that 1 kcal = 4,1868 kJ.

The amount of heat that went into heating the products of complete combustion 1 kg or 1 no. m 3 fuel, provided that these products contain condensed water vapor, that is, water, is called higher calorific value of fuel . This heat is denoted as .

If during fuel combustion water vapor is not condensed, then a smaller amount of released heat will be consumed to heat the combustion products by the amount of the latent heat of condensation of water vapor (latent heat of evaporation of water) . In this case, heat was called lower heating value of fuel and is denoted as . Thus, the determination does not take into account the heat spent on evaporating the moisture of the fuel itself and the moisture formed during the combustion of hydrogen in the fuel. Accordingly, the value is related to how .

The composition of coal, like any other solid fuel, is expressed as a percentage by weight (wt.%). In this case, the following are most often taken as 100%:

· composition of the fuel in working condition (composition of its working mass), indicated by the superscript “ r »:

· composition in the analytical state (composition of the analytical mass), indicated by the superscript “ A »:

· dry composition (dry mass composition), indicated by the superscript “ d »:

· composition in a dry, ash-free state (composition of the dry, ash-free mass), indicated by the superscript “ daf »:

where the mass fractions in the corresponding mass of coal are carbon, hydrogen, combustible sulfur, oxygen, nitrogen, total and analytical moisture, wt. %; A – ash content of the corresponding mass of coal, wt. %.

To determine the heat of combustion of coals, a single standard method is used - the method of combustion in a calorimetric bomb. With this method, a weighed portion of an analytical coal sample weighing 0.8...1.5 G burned in an atmosphere of compressed oxygen in a hermetically sealed metal vessel - a calorimetric bomb, which is immersed in a certain volume of water. By increasing the temperature of this water, the amount of heat released during combustion of the sample is determined. This gives the fuel combustion heat for the bomb. Due to the fact that fuel combustion occurs in quite specific

Rice. Schematic diagram of a classic calorimeter for determining the heat of combustion of solid fuels

1 – calorimetric bomb; 2 – stirrer; 3 – thermostat cover; 4 – system for igniting the hitch; 5 – thermometer or a device replacing it; 6 – calorimetric vessel; 7 – thermostat.

conditions (atmosphere of pure oxygen, oxidation of combustible sulfur to SO 3 with the subsequent formation of nitric acid in the condensed moisture, and so on), the value is recalculated using the following formula:

where is the heat of formation of sulfuric acid from SO 2 and dissolving it in water, numerically equal to 94.4 kJ based on 1% sulfur; - sulfur content “in the bomb wash” is the amount of sulfur converted into sulfuric acid during combustion, based on the initial sample of coal, wt. % (may be used instead of the total sulfur content in the analytical mass of coal, if , A
); a - coefficient taking into account the heat of formation and dissolution of nitric acid, equal to 0.001 for lean coals and anthracites and 0.0015 for all other fuels.

Knowing , first determine the higher calorific value of the working mass of fuels:

, (2)

Where =kJ/kg or kJ/norm.m 3; =
= wt. %.

Coefficient 24.62 in (3) reflects the heat of heating water from
t 0 = 0°C to t = 100°C and its evaporation at P 0 = 101325 Pa based on
1 wt. % water.

The value calculated for the operating state of the fuel corresponds to the actual heat released during its combustion in furnaces, and therefore is widely used in thermal engineering calculations. is an integral indicator of the quality of fuels and largely determines their consumer properties.

One of the main features of fossil coals is the ability to decompose (destruct) their organic mass when heated without air access. With such heating, gas and vapor decomposition products called volatiles are formed. After removing volatile substances from the heating zone, a residue remains called coke residue, or coke residue. Since volatile substances are not contained in coals, but are formed when they are heated, they speak of the “yield of volatile substances”, and not about their content in coals.

The yield of volatile substances is understood as the relative mass of volatile substances, expressed as a percentage, formed during the thermal decomposition of coal under standard conditions. The release of volatiles is indicated by the symbol V , and the non-volatile (coke) residue is N.V. .

The vaporous part of volatile substances consists of condensable hydrocarbons, which are a group of oily and resinous substances that are the most valuable chemical product.

The gaseous part of volatile substances consists of hydrocarbon gases of the saturated and unsaturated series ( CH 4 , C m H n and so on), carbon monoxide and dioxide ( CO , CO 2 ), hydrogen ( H 2 ) and so on.

The composition of the non-volatile residue consists mainly of carbon and mineral impurities in the form of ash.

The yield of volatile substances is one of the main classification parameters of fossil coals. Based on the volatile yield values ​​and the characteristics of the coke residue, the suitability of coals for coking and the behavior of coals in processing and combustion processes are assessed.

The essence of the standard method for determining the yield of volatile substances is to heat a sample of an analytical coal sample weighing 1±0.1 g without access to air at t = 900±5 °C within 7 min. The yield of volatile substances is determined by the loss of mass of the initial sample, taking into account the moisture content in the fuel.

The release of volatiles from an analytical sample is calculated using the formula

(4)

Where = wt. %; - weight loss of a sample of coal after the release of volatile substances, G; - weight of the initial sample of coal, G; - moisture content in the initial portion of the analytical coal sample, wt. %;

- the yield of non-volatile residue from the analytical sample of the tested coal, %, is calculated using the formula

IN laboratory work coals will be used
wt % , therefore, methods for determining quantities and not considered in laboratory work.

The yield of volatile substances in the dry, ash-free state of coal is determined as follows:

. (6)

The permissible differences between the results of two parallel determinations in absolute values ​​should not exceed 0.3 wt. % at wt.%; 0.5 wt. % at wt. %;1.0 wt. % at wt. % .

One of the most important thermal characteristics of fuels is the volatile yield and the properties of the coke residue. When solid fuels are heated, thermally unstable complex oxygen-containing hydrocarbon compounds of the combustible mass decompose with the release of flammable gases: hydrogen, hydrocarbons, carbon monoxide and non-combustible gases - carbon dioxide and water vapor. The yield of volatile substances is determined by heating a sample of air-dry fuel in an amount of 1 g without access of air at a temperature of 850°C for 7 minutes. The volatile yield, defined as the decrease in the mass of the test fuel sample minus the moisture contained in it, is referred to as the combustible mass of the fuel. Different fuels have different composition and heat of combustion of volatile substances. As the chemical age of the fuel increases, the content of volatile substances decreases and their release temperature increases. At the same time, due to a decrease in the amount of inert gases, the heat of combustion of volatile substances increases. For shale, the volatile yield is 80-90% of the combustible mass; peat - 70%; brown coals - 30-60%, hard coals of grades G and D - 30 - 50%, for lean coals and anthracites the volatile yield is low and, accordingly, equals I -13 and 2-9%. Therefore, the content of volatile substances and their composition can be taken as signs of the degree of carbonization of the fuel and its chemical age. For peat, the release of volatiles begins at a temperature of approximately 100°C, brown and fatty coals - 150-170°C, oil shale - 230°C, lean coals and anthracites ~400°C and ends at high temperatures - 1100-1200°C. After distillation of volatile substances from the fuel, a so-called coke residue is formed. When coal contains bituminous substances, which when heated turn into a plastic state or melt, a powdered sample of coal tested for volatile content can cake and swell. The ability of a fuel to form more or less strong coke during thermal decomposition is called sinterability. Peat, brown coals and anthracite produce powdered coke. Hard coals with a volatile yield of 42-45% and lean coals with a volatile yield of less than 17% produce powdery or sticky coke residue. Coals that form a caked coke residue are a valuable technological fuel and are used primarily for the production of metallurgical coke. Coke in the form of a sintered or fused residue is obtained by heating coal crushed to sizes of 3-3.5 mm at a temperature of 1000°C without access to air. The properties of coke depend on the composition of organic compounds of the combustible mass of fuel and the content of volatile substances in it.

Definition release of volatile substances. When heated without access to air, coal decomposes, releasing gas and vapor products called volatile substances.

Depending on the heating temperature, after removal of volatile substances, a solid residue (crust), coke or semi-coke remains. Volatiles are not contained in free form in the fuel, but are formed during heating, so they do not talk about the content of volatiles, but about their yield.

The yield of volatile substances depends not only on the type of fuel, but also on the conditions of its heating (dry distillation of coal). Exit volatile substances and at the same time the determined sintering ability are general indicators, by which the Properties and composition of coal can be approximately predicted.

The composition of volatile substances includes valuable substances that are widely used in the national economy. For example, the volatile substances of coal contain benzene, toluene, ammonia, hydrogen, methane, etc. The volatile substances formed during the dry distillation of wood contain methane, carbon monoxide, acetic acid, methyl alcohol, etc.

Type of coal Volatile yield - % Carbon content - C,% True density - 4, g/cm 413

Determination of volatile matter yield is classical method coal analysis. In almost all existing classifications of coals, volatile yield is one of the main indicators.

In Fig. the dependence of expansion pressure on release of volatiles weight of coal. From Fig. Some correlation is already visible, but when the release of volatile substances is more than 21-22%, it weakens and becomes clearer when heterogeneous coals are excluded (about 0.20).

For coals whose volatile matter yield is in the range of 17-21%, no correlation is observed at all. However, it is possible to delineate a zone that includes heterogeneous coals (curve with a dashed line), which give insignificant expansion pressure. This obviously means that any homogeneous coal with a volatile matter yield of 19-24% is not included397

The coke obtained according to such a technological scheme has fairly good physical and mechanical properties. Thus, the molded coke used for the first experimental blast furnace smeltings had the following quality indicators (at the charge yard of the metallurgical plant) M40 = 89.9%, MIO = 6%, the content of pieces with a size of 40-80 mm is 86% When calcined to 0 C in an inert atmosphere, this coke does not separate fines, does not fall apart, but, on the contrary, becomes denser and mechanically stronger. The porosity of this coke, depending on the requirements of the consumer, can be adjusted by changing the process from 35 to 60% when coking the same coal. The yield of volatile substances from commercial molded coke is 1.6-2.5%

What is coking of coals, volatile yield

Name and symbol Coal grades Output volatile substances Y,% Coke yield, % Lump sizes, mm Characteristics of non-volatile residue (coke)

Types of coals Volatile matter yield, % and organic mass Composition, % 337

After 9-10 months of storage in stacks of different Donetsk coal output volatile substances from OS grade coals increases by 2-3%, T grade - by 1.39%, while for Zh grade coals it changed within 1.18-0.54%; in general, the change in the yield of volatile substances is relatively small .
The yield of volatile substances and the heat of combustion as a result of the oxidation of coals change differently depending on the degree of metamorphism and the molecular structure of the organic mass of coal. Release of volatile substances during long-term storage47

The yield and quality of chemical coking products depend on a number of factors, the degree of metamorphism, the petrographic composition of coals, the release of volatile substances, humidity, temperature regime coking, etc.10

Coal designation Volatile yield (Parr recalculation), % Bulk weight(converted to dry weight), g/ls 306

The bake depends on the properties of the coal charge (the nature of the coal, the yield of volatile substances) and the coking temperature. The burning temperature for Donbass coals is 1.0-2.6% (Donbass), and for coals from the Eastern regions of Russia it is 1.5-3.0%.85

Anthracite coal (AS) is coal particles up to 13 mm in size, screened out in mines when producing ordinary anthracite. When sorting dry anthracite for coals of class ASh, the size of the pieces is set to less than 3 mm.

For hard coal grades D, G and anthracite, when supplied to power plants for combustion in a pulverized state, also at high humidity, a class has been established with a piece size of less than 13 mm, conventionally designated DSSh, GSSH and ASH (seed with a piece). AS has the lowest volatile yield of all coal grades, which makes it difficult to ignite. Ash ash consists mainly of silicon oxide and aluminum. A small part of the ash consists of calcium, magnesium, potassium and sodium oxide.15

In the near future, the international classification of hard coals will become widespread. It is based on three very important parameters of coal: the release of volatile substances, caking and coking properties.12

The difference in the scope of analysis for bituminous and brown coals is determined by the different values ​​of the volatile yield for them. The volatile yield of bituminous coals can fluctuate greatly; here, together with the characteristics of the coke residue, it determines their grade and hydrogen content. For oxidized bituminous coals, the characteristics of the coke residue, and often the yield of volatiles change according to changes in the calorific value and humidity of the air-dry sample. For brown coals, the yield of volatiles varies -

What is the reason for the gap between the practical and calculated coke yield, or coke burn, as it is sometimes incorrectly called? The calculations are based on the value of the yield of volatile substances during crucible testing, which is identified with the practical coke yield in furnaces. However, it is known that the yield of volatile substances depends on the rate of temperature rise; with the acceleration of coal heating, the yield of volatile substances increases, which corresponds to a decrease in the yield of coke. Comparing the rate of temperature rise during crucible coking (approximately 400-500 °C per minute) and in coke ovens (about 1 °C per minute), one can see the complete discrepancy between these processes; obviously, in coke ovens the coke residue should be greater than with crucible coking testing. In addition, with an increase in the yield of volatile substances in the charge and an increase in the coking rate, the formation of graphite increases due to the pyrolysis of coke oven gas hydrocarbons.437

Replacing the classifications based on elementary analysis with a classification based on two parameters - the yield of volatile substances in relation to the combustible mass and physical properties - showed that the results obtained are quite convergent and the coals are also arranged in approximately the same sequence as in the classification based on elementary analysis. From a review of a large number of industrial classifications from different countries, it is clear that the yield of volatile substances is the most important characteristic, which is included in almost all technical classifications of hard coals. There are reasons for this, because the chemical nature of coal and its chemical age greatly affect the yield of volatile substances. As the chemical age of coals increases, the yield of volatile substances continuously decreases.569

Coal production from the Chernogorsk deposit increased in 8 compared to 0 from 1 to 2.9 million. In terms of quality, coal from the Minusinsk basin is close to gas and long-flame coals. The yield of volatile substances per combustible mass is 35-42%, the thickness of the plastic layer y = O-7 mm.

Type of coal Volatile matter yield, and Color Trait Gloss Hardness (Mohs scale) Specific gravity20

If coals consist only or predominantly of microcomponents of the vitrinite group, then the change in their properties depending on the degree of their metamorphism is well expressed by the yield of volatile substances, recalculated to the combustible mass, with an increase in the degree of metamorphism of coals, the yield of volatile substances from them decreases. This is the basis for various classifications of coals, which are especially applicable to claren-type coals, i.e., to coals with a predominant content of vitrinite (for example, coals of the Donetsk basin).8

Coal grade Technological group of coal Volatile yield, % Thickness of plastic-21

Fuel Coal grade Volatile yield per combustible mass UD v7o Lowest caloric content per combustible mass in kcal/kg Coefficient of conversion to standard fuel Calorific value of working fuel 0 in kcal/kg650

Coal grade Volatile matter yield 0/ /0 Intumescence according to AFNOR Expansion temperature, °C International dilatometry (dilatation) International classification

Pattaisky and Teichmüller 24, studying the relationship between the carbon content in humus coals and the release of volatile substances, found that with an increase in carbon content, the yield of volatile substances from coals decreases unequally at different stages of metamorphism. Thus, in brown and poorly metamorphosed hard coals, the yield of volatile substances is poorly consistent with changes in carbon content. In this case, the degree of metamorphism of coals is more clearly characterized by carbon content than by the release of volatile substances.

According to Storch and staff 11, p. 30, the elementary structural formula of carbon substance consists of indene trimers linked by ether bridges. They provide a number of evidence in favor of this structure related to the elemental composition of coal, the release of volatile substances, mechanical properties, etc. However, this formula must also be rejected, since it does not correspond to the results obtained during the oxidation of coal and its decomposition by metallic sodium.

Research by E. A. Shapatina showed that the main factor determining the decomposition, and therefore the loss of volatile coal during high-speed heating, is not the residence time, but the heating temperature field. Based on the example of studying the process of releasing volatiles from pulverized (micron-sized) gas coal (volatile yield in the original coal is 38.8%) when it is quickly (in 0.45 s) heated to various temperatures in the range of 390-600 ° C with exposure at 71

As the particle heats up, it is heated, dried, and then sublimation of the fuel begins. The higher the content of volatiles in the fuel, the more intense their release. The release of volatiles begins at higher temperatures, the older the fuel.

From the brown ones coal output volatiles begin at a temperature of about °C, from gas coal - about °C, from PG - about °C, from lean coals - about 320 °C, from anthracite - about 380 °C L. 46. The release of volatiles continues up to temperatures of the order 800-1000°С.341

Coking ability is influenced by the petrographic composition, the degree of metamorphism of coal, the release of volatile substances, as well as the nature of changes during heating - the transition to a partial state, the degree of viscosity and the temperature range of this state, sintering, and the dynamics of gas evolution19

The gas and vapor products formed during the thermal destruction of coal undergo various transformations, which are associated with both the sintering process and the decomposition process during their evacuation. The decomposition process is influenced by the technological and thermal regimes of coking. The yield and quality of the chemical products of coking depend on a number of factors. degree of metamorphism, petrographic composition of coals, release of volatile substances, humidity, coking temperature, etc.78

To characterize the plastic properties and gas release, Bunte and Imhof tested the following German coals using this method: 1) non-expanding (sticking) coal from Upper Silesia 2) non-expanding caking coals from the Saar basin 3) Saar coal, which in properties occupies an intermediate position between the first two coals 4-5 ) two intumescent caking coals, one from Upper Silesia, the other from the Wurm deposit. For the listed five coals, the yield of volatile substances per combustible mass was respectively equal to 38.6 33.8 34.2 27.8 19.0%. Coal 1 showed a maximum pressure at 420° of only about 8 jas of water. Art. For coal 2, the maximum pressure was about 1000 mm of water. Art. at 420°, both with a sample of 10 g and 5 g. The maximum pressure for the 3rd coal was equal to 450 lsh at 440° for the 4th coal - 340 lsh at 480° and for the 5th coal - 550 ML1 at 490°.

It is known that entrainment from pulverized coal furnaces consists of a mixture of combustible particles and fly ash. The content of the latter ranges from 75 7o when burning anthracite to 99.5% in the case of burning brown coal.

As it turned out, with such a small content of combustibles in the drift, it is impossible to achieve objective results when analyzing the technical, elemental and fractional composition of the flammable part of the drift. In table

Figure 2 shows the yield of volatile substances from the entrainment of industrial pulverized coal furnaces burning various grades of coal, as well as from samples of Nazarovo brown coal taken along the length of the torch. Before analysis, the entrainments were dispersed into fractions.

It can be seen that the yield of volatile substances in the entrainment often exceeds that of the original coal. The yield of volatile substances in fine fractions is especially high.

In samples from a flare of Nazarovo brown coal, the yield of volatiles per combustible mass was 65% with a combustible content of 50% and >100% in all fractions with a combustible content of 6.61%. All this indicates that fly ash is not a completely inert material.

Apparently, during analyzes associated with high heat entrainment, ash undergoes a number of changes, interacting with flammable residues and gaseous products of their thermal decomposition. The presence of a flammable part of the entrainment creates a reducing atmosphere. Metal oxides contained in fly ash can be partially or completely reduced by reacting with carbon, as well as with gaseous products of thermal decomposition of the combustible part of the fly ash.82

The quality of coals from the Tunguska and Lena basins is very diverse and is represented by various groups of coalification - from anthracite to brown coal. Release of volatile substances from various groups coal content ranges from 5 to 59% 25.

Some regularity has been established in the distribution of coals over the basin area. Anthracite and graphite are located in the west of the basin.

In its middle part along the meridian there are coals with a significant release of volatile substances, and in the east there are predominantly brown coals. It is noted that as one moves from east to west, the release of volatile substances in coals decreases 25.

A test for coking ability of coals from the Angarsk region showed that they have fairly good caking ability. 25 When using Tunguska coals for coking, their enrichment will be required, since the coals of the identified reserves have an ash content of up to 15%. The sulfur content of the studied coals does not exceed 1.5%. in connection with which they can be classified as low- and medium-sulfur coals.

Sandor coked briquettes of Yorkshire coal (output volatile substances 32.5%), compressed under a pressure of 698 kg/cm, when heated in a nitrogen atmosphere at a rate of 5° per minute. up to 690 and 800°. The resulting cokes were kept at the final temperature for two hours and then cooled.

The electrical resistance values ​​measured on coke blocks produced in this way during repeated heating and cooling of the latter gave curves that coincided with each other. Electrical resistance was measured in an air atmosphere in a vacuum and in nitrogen. The electrical resistance of samples stored in air increased slightly after a few days compared to the initial one. The curves of the dependence of electrical resistance on temperature, in vacuum and in nitrogen, in the temperature range -50° - -360° obeyed the equation

Similar experiments carried out on a production scale were published in the American press. In American experiments, a significant improvement in the quality of coke (Table 64) was obtained by coking coal from coal (volatile yield 38.5/about) with semi-coke from the same coal in an industrial furnace.

It has been established that, along with a decrease in the content of carbon and hydrogen, the yield of volatile substances in coals increases, the calorific value, the amount of extracted substances, etc. decrease.

During the oxidation of reduced coals, the same pattern is observed in the change in the yield of volatile substances in young and more mature coals as in the original coal that has not been subjected to hydrogenation, i.e., in gas coal, the yield of volatile substances decreases, and in lean, although it decreases, does not decrease below the output. volatile compounds in the original coal.

During the oxidation of reduced coals, a decrease in the yield of volatile substances is observed in all types of coals without exception, i.e., the oxidation process of reduced coals proceeds in the direction of a more complex molecule. However, it should be noted that for gas coal the yield of volatile substances after oxidation becomes less than that of the original coal, for coke coal it changes little, and for lean coal with a plastic layer equal to zero, it remains significantly higher than the yield of the original coal.

The Hilt rule in the Irkutsk basin is not confirmed with an increase in the stratigraphic depth of coal seams, the yield of volatile substances does not decrease, but, on the contrary,. At the same time, the content of hydrogen and sulfur in coals increases and, accordingly, the content of carbon and acid decreases.

White Charcoal Binchotan from Vietnam

Categories

in the coals - in-va. released from fossil coals when heated. Composition of the drug: volatile organic. parts of coal, decomposition products of certain minerals. Contents of L. v. in coals ranges from 50% (brown coals) to 4% (anthracite). The solid mass that remains after the removal of the drug is called. coke residue. L.v. influence the caking ability of coals: coke bakes well only in coking coals, which give 18 - 35% l.v., and remains powdery in coals with the yield of l.v. above 42% and below 10%.

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• - in the coals - in-va. released from fossil coals when heated. Composition of the drug: volatile organic. parts of coal, decomposition products of certain minerals. Contents of L. v. in coals ranges from 50% to 4%...

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