INTRODUCED by Gosstandart of Russia

2. ADOPTED by the Interstate Council for Standardization, Metrology and Certification (Minutes No. 6-94 of October 21, 1994)

3. This International Standard is the complete authentic text of ISO 7404-5-85 Bituminous and anthracite coal. Methods of petrographic analysis. Part 5. Method for the microscopic determination of vitrinite reflectance indices" and contains additional requirements that reflect the needs of the national economy

4. REPLACE GOST 12113-83

Introduction date 1996-01-01

This International Standard applies to brown coals, hard coals, anthracites, coal mixtures, solid diffuse organics and carbonaceous materials and specifies a method for determining reflectance values.

The vitrinite reflectance index is used to characterize the degree of metamorphism of coals, during their prospecting and exploration, development of deposits and classification, to establish the thermogenetic transformation of scattered solid organic matter in sedimentary rocks, as well as to determine the composition of coal mixtures during enrichment and coking.

Additional requirements reflecting the needs of the national economy are in italics.

1. PURPOSE AND SCOPE

This International Standard specifies a method for determining the minimum, maximum and arbitrary reflectance values ​​using a microscope in immersion oil. and in the air on polished surfaces polished section of briquettes and polished pieces vitrinite component of coal.

GOST 12112-78 Brown coals. Method for determining the petrographic composition

GOST 9414.2-93 Hard coal and anthracite. Methods of petrographic analysis. Part 2. Method for preparing coal samples

3. ESSENCE OF THE METHOD

The essence of the method lies in the measurement and comparison of electric currents arising in a photomultiplier tube (PMT) under the influence of a light flux reflected from the polished surfaces of macerals or submacerals of the test sample and standard samples (etalons) with a set reflection index.

4. SAMPLING AND SAMPLE PREPARATION

4.1. Sampling for the preparation of polished briquettes is carried out according to GOST 10742.

4.2. Polished briquettes are made according to GOST 9414.2.

From the samples intended for measuring the reflection indices with the construction of reflectograms, two polished briquettes with a diameter of at least 20 mm are made.

4.3. For the preparation of polished briquettes from rocks with inclusions of solid dispersed organic matter, the crushed rock is preliminarily enriched, for example, by flotation, by the method of chemical decomposition of the constituent inorganic part of the rocks, and others.

4.4. To prepare polished pieces of coal, samples are taken from the main bed-forming lithotypes with a size of at least 30–30–30 mm. When taking samples from the core of boreholes, it is allowed to take samples with a size of 20 × 20 × 20 mm.

4.5. To prepare polished pieces from rocks with inclusions of solid dispersed organic matter, samples are taken in which inclusions of solid organic matter are visible microscopically or their presence can be assumed by the type of deposits. The size of the samples depends on the possibility of sampling (natural outcrops, mine workings, cores from boreholes).

4.6. The preparation of polished pieces consists of three operations: impregnation in order to give the samples strength and solidity for subsequent grinding and polishing.

4.6.1. Synthetic resins, carnauba wax, rosin with xylene, etc. are used as impregnating agents.

For some types of coals and rocks with inclusions of solid dispersed organic matter, it is sufficient to immerse the sample in an impregnating substance.

If the sample has sufficient strength, the surface perpendicular to the layering plane is lightly ground.

Samples of weakly compacted sandy-clayey rocks containing small scattered organic inclusions are dried in an oven at a temperature of 70 °C for 48 hours before soaking in rosin with xylene.

The samples are tied with wire, to the end of which a label with a passport is attached, and placed in one layer in a porcelain cup, rosin is poured into it, crushed into grains ranging in size from 3 to 7 mm, and xylene is poured (3 cm 3 per 1 g of rosin) so that so that the samples are completely covered with the solution.

Impregnation is carried out in a fume hood when heated on a closed tile for 50 - 60 min until the xylene is completely evaporated. The samples are then removed from the cup and cooled to room temperature.

4.6.2. Grind two mutually parallel planes of the impregnated sample, perpendicular to the layering, and polish one of them.

Grinding and polishing is carried out in accordance with GOST R 50177.2 and GOST 12113.

4.7. In the study of long-term stored polished briquettes and polished pieces, as well as previously measured samples, it is necessary to grind them down by 1.5 - 2 mm before measuring the reflection index and polish them again.

5. MATERIALS AND REAGENTS

5.1. Calibration standards

5.1.1. Reflection index standards, which are samples with a polished surface, meet the following requirements:

a) are isotropic or represent the main section of uniaxial minerals;

b) durable and corrosion resistant;

c) maintain a constant reflectance for a long time;

e) have a low absorption rate.

5.1.2. The standards must be more than 5 mm thick or have the shape trihedral prism (30/60°) to prevent more light from entering the lens than that reflected from its upper (working) surface.

A polished edge is used as a working surface to determine the reflection index. Base and sides of the standard covered with opaque black varnish or placed in a strong opaque frame.

The path of the beam in a wedge-shaped standard inserted into black resin during photometric measurements of the reflectance is shown in Figure 1.

5.1.3. When carrying out measurements, at least three standards are used with reflection indices that are close or overlap the measurement area of ​​the reflection indices of the samples under study. To measure the reflectance of coal equal to 1.0%, standards with reflectances of approximately 0.6 should be used; 1.0; 1.6%.

The average refractive and reflective indices for commonly used standards are shown in Table 1.

5.1.4. The true values ​​of the reflection index of standards are determined in special optical laboratories or calculated from the refractive index.

Knowing the refractive index n and the absorption rate? (if it is significant) of the reference at a wavelength of 546 nm, you can calculate the reflectance ( R) as a percentage according to the formula

If the refractive index is not known, or it is assumed that the surface properties may not accurately correspond to the nominal basic properties, the reflectance is determined by careful comparison with a standard with a known reflectance.

5.1.5. The zero standard is used to eliminate the influence of the dark current of the photomultiplier tube and scattered light in the optical system of the microscope. Optical glass K8 can be used as a zero standard or a polished briquette made of coal with a particle size of less than 0.06 mm and having a recess in the center with a diameter and a depth of 5 mm filled with immersion oil.

Figure 1 - Beam path in a wedge-shaped standard inserted into black resin,
in photometric measurements of the reflectance

Table 1

Average refractive indices of reflection for commonly used standards

5.1.6. When cleaning standards, care must be taken not to damage the polished surface. Otherwise, it is necessary to re-polish its working surface.

5.2. Immersion oil meeting the following requirements:

non-corrosive;

non-drying;

with a refractive index at a wavelength of 546 nm 1.5180 ± 0.0004 at 23 °C;

with temperature coefficient dn/dt less than 0.005 K -1 .

The oil must be free of toxic components and its refractive index must be checked annually.

5.3. Rectified spirit,

5.4. Absorbent cotton wool, fabric for optics.

5.5. Slides and plasticine for fixing the studied samples.

6. EQUIPMENT

6.1. Monocular or a binocular polarizing microscope with a photometer to measure the index in reflected light. The optical parts of the microscope used to measure the reflectance are shown in Figure 2. The constituent parts are not always arranged in the specified sequence.

6.1.1. Light source BUT. Any light source with stable emission can be used; a 100W quartz halogen lamp is recommended.

6.1.2. Polarizer D- polarizing filter or prism.

6.1.3. Aperture for adjusting light, consisting of two variable apertures, one of which focuses light on the rear focal plane of the lens (illuminator IN), the other - on the surface of the sample (field aperture E). It must be possible to center with respect to the optical axis of the microscope system.

6.1.4. Vertical illuminator - Berek prism, coated plain glass plate or Smith illuminator (combination of mirror with glass plate W). The types of vertical illuminators are shown in Figure 3.

6.1.6. Eyepiece L - two eyepieces, one of which is provided with a crosshair, which may be scaled so that the total magnification of the objective, the eyepieces and in some cases the tube is between 250° and 750°. A third eyepiece may be required M on the path of light to the photomultiplier.

BUT- lamp; B- converging lens IN- aperture of the illuminator; G- thermal filter;
D- polarizer; E- field diaphragm; F- focusing lens of the field diaphragm;
W- vertical illuminator; AND- lens; R - sample; TO- table; L- eyepieces;
M - third eyepiece; H- measuring aperture, ABOUT- 546 nm interference filter;
P- photomultiplier

Figure 2 - Optical parts of a microscope used to measure the reflectance

6.1.7. A microscope tube having the following attachments:

a) measuring aperture H, which allows you to adjust the light flux reflected into the photomultiplier from the surface of the sample R, area less than 80 microns 2 . The aperture should be centered with the cross hairs of the eyepiece;

b) devices for optical isolation of eyepieces to prevent excess light from entering during measurements;

c) the necessary blackening to absorb scattered light.

NOTE With care, part of the light flux can be diverted to the eyepiece or TV camera for continuous observation when measuring the reflectance.

6.1.8. Filter ABOUT with a bandwidth maximum at (546 ± 5) nm and a bandwidth half-width of less than 30 nm. The filter should be located in the light path directly in front of the photomultiplier.

BUT- filament; B- converging lens IN - aperture of the illuminator (position of reflection of the filament);
G- field diaphragm; D- focusing lens of the field diaphragm; E- Berek prism;
F- reverse focal plane of the lens (the position of the image of the filament and the aperture of the illuminator);
W- lens; AND- sample surface (image position of the field of view);

but- vertical illuminator with Berek prism; b- illuminator with a glass plate; in- Smith's illuminator

Figure 3 - Scheme of vertical illuminators

6.1.9. Photomultiplier P, fixed in a nozzle mounted on a microscope and enabling the light flux through the measuring aperture and the filter to enter the photomultiplier window.

The photomultiplier should be of the type recommended for measuring light fluxes of low intensity, should have sufficient sensitivity at 546 nm and low dark current. Its characteristic should be linear in the measurement region, and the signal should be stable for 2 hours. Usually, a direct multiplier with a diameter of 50 mm is used with an optical input at the end, having 11 diodes.

6.1.10. microscope stage TO, capable of rotating 360° perpendicular to the optical axis, which can be centered by adjusting the stage or lens. The rotating stage is connected to the preparation driver, which ensures the movement of the sample, with a step of 0.5 mm in the directions X And Y, equipped with a device that allows for slight adjustment of movements in both directions within 10 microns.

6.2. DC stabilizer for light source. Characteristics must satisfy the following conditions:

1) lamp power should be 90 - 95% of the norm;

2) fluctuations in lamp power should be less than 0.02% when the power source changes by 10%;

3) ripple at full load less than 0.07%;

4) temperature coefficient less than 0.05% K -1.

6.3. DC voltage stabilizer for photomultiplier.

Characteristics must satisfy the following conditions:

1) voltage fluctuations at the output must be at least 0.05% when the voltage of the current source changes by 10%;

2) ripple at full load less than 0.07%;

3) temperature coefficient less than 0.05% K -1;

4) changing the load from zero to full should not change the output voltage by more than 0.1%.

Note - If during the measurement period the voltage of the power supply drops by 90%, an autotransformer should be installed between the power supply and both stabilizers.

6.4. Indicating device (display), consisting of one of the following devices:

1) a galvanometer with a minimum sensitivity of 10 -10 A/mm;

2) recorder;

3) digital voltmeter or digital indicator.

The instrument shall be adjusted so that its full scale response time is less than 1 s and its resolution is 0.005% reflectance. The device must be equipped with a device for removing the small positive potential that occurs when the photomultiplier is discharged and due to the dark current.

Notes

1. The digital voltmeter or indicator must be able to clearly distinguish the values ​​of the maximum reflectance when the sample is rotated on the stage. Individual values ​​of the reflectance can be stored electronically or recorded on magnetic tape for further processing.

2. A low noise amplifier can be used to amplify the photomultiplier signal when applied to the indicating instrument.

6.5. fixture to give the polished surface of the test sample or reference position parallel to the glass slide (press).

7. MEASUREMENTS

7.1. Equipment preparation (in 7.1.3 and 7.1.4, the letters in parentheses refer to Figure 2).

7.1.1. Initial Operations

Make sure that the room temperature is (23 ± 3) °C.

Include current sources, lights and other electrical equipment. Set the voltage recommended for this photomultiplier by its manufacturer. To stabilize the equipment, it is kept for 30 minutes before the start of measurements.

7.1.2. Microscope adjustment for reflectance measurement.

If an arbitrary reflectance is measured, the polarizer is removed. If the maximum reflectance is measured, the polarizer is set to zero when using a glass plate or Smith illuminator, or at an angle of 45° when using a Berek prism. If a polarizing filter is used, it is checked and replaced if it shows significant discoloration.

7.1.3. Lighting

A drop of immersion oil is applied to the polished surface of the polished briquette mounted on a glass slide and leveled and placed on the microscope stage.

Check the correct adjustment of the microscope for Koehler illumination. Adjust the illuminated field using the field diaphragm ( E) so that its diameter is about 1/3 of the entire field. Illuminator aperture ( IN) are adjusted so as to reduce glare, but without unduly reducing the intensity of the luminous flux. In the future, the size of the adjusted aperture is not changed.

7.1.4. Adjustment of the optical system. Center and focus the image of the field diaphragm. Center the lens ( AND) but relative to the axis of rotation of the object stage and adjust the center of the measuring aperture ( H) so that it coincides either with the cross hairs or with a given point in the field of view of the optical system. If the image of the measuring aperture cannot be seen on the sample, a field containing a small shiny inclusion, such as a pyrite crystal, is selected and aligned with the cross hairs. Adjust the centering of the measuring aperture ( H) until the photomultiplier gives the highest signal.

7.2. Reliability testing and hardware calibration

7.2.1. Hardware stability.

The standard with the highest reflectance is placed under the microscope, focused in immersion oil. The voltage of the photomultiplier is adjusted until the display reading matches the reflectance of the standard (for example, 173 mV corresponds to a reflectance of 173%). The signal must be constant, the change in reading must not exceed 0.02% within 15 minutes.

7.2.2. Changes in readings during rotation of the reflectance standard on the stage.

Place a standard with an oil reflectance of 1.65 to 2.0% on the stage and focus in the immersion oil. Rotate the stage slowly to ensure that the maximum change in readings is less than 2% of the reflectance of the sample taken. If the deviation is higher than this value, it is necessary to check the horizontal position of the standard and ensure its strict perpendicularity to the optical axis and rotation in the same plane. If after this the fluctuations do not become less than 2%, the manufacturer must check the mechanical stability of the stage and the microscope geometry.

7.2.4. Linearity of the photomultiplier signal

Measure the reflectance of the other standards at the same constant voltage and the same light aperture setting to verify that the measurement system is linear within the measured limits and that the standards are consistent with their design values. Rotate each standard so that the readings are as close as possible to the calculated value. If the value for any of the standards differs from the calculated reflectance by more than 0.02%, the standard should be cleaned and the calibration process repeated. The standard must be polished again until the reflection index differs from the calculated one by more than 0.02%.

If the reflectance of the standards does not give a linear diagram, check the linearity of the photomultiplier signal using standards from other sources. If they don't give a line graph, test the signal again for linearity by applying several neutral density calibration filters to reduce the light flux to a known value. If non-linearity of the photomultiplier signal is confirmed, replace the photomultiplier tube and carry out further testing until signal linearity is obtained.

7.2.5. Hardware calibration

Having established the reliability of the apparatus, it is necessary to ensure that the indicating instrument gives the correct readings for the zero standard and the three reflection standards of the test coal, as indicated in 7.2.1 to 7.2.4. The reflectance of each standard shown on the display should not differ from the calculated one by more than 0.02%.

7.3. Vitrinite reflectance measurement

7.3.1. General provisions

The method for measuring the maximum and minimum reflectance values ​​is given in 7.3.2, and for an arbitrary one in 7.3.3. In these subclauses, the term vitrinite refers to one or more submacerals of the vitrinite group.

As discussed in Section 1, the choice of submacerals to be measured determines the result, and therefore it is important to decide which submacerals to measure the reflectance and note them when reporting the results.

7.3.2. Measurement of maximum and minimum vitrinite reflectance in oil.

Install the polarizer and check the apparatus according to 7.1 and 7.2.

Immediately after calibration of the equipment, a leveled polished preparation made from the test sample is placed on a mechanical stage (preparation) that allows measurements to be made starting from one corner. Apply immersion oil to the surface of the sample and focus. Slightly move the specimen with the driver preparation until the cross hairs are focused on a suitable surface of the vitrinite. The surface to be measured must be free from cracks, polishing defects, mineral inclusions or relief and must be at some distance from the boundaries of the maceral.

Light is passed through a photomultiplier and the table is rotated 360° at a speed of not more than 10 min -1 . Record the largest and smallest values ​​of the reflection index, which is noted during the rotation of the table.

NOTE When the slide is rotated 360°, ideally, two identical maximum and minimum readings can be obtained. If the two readings are very different, the cause should be determined and the error corrected. Sometimes the cause of the error can be air bubbles in the oil getting into the measured area. In this case, the readings are ignored and air bubbles are eliminated by lowering or raising the microscope stage (depending on the design). The front surface of the objective lens is wiped with an optical cloth, a drop of oil is again applied to the surface of the sample and focusing is performed.

The sample is moved in the direction X(step length 0.5 mm) and take measurements when the crosshairs hit a suitable surface of the vitrinite. In order to be sure that the measurements are made on a suitable site of the vitrinite, the sample can be moved by the slider up to 10 µm. At the end of the path, the sample moves to the next line: the distance between the lines is at least 0.5 mm. The distance between the lines is chosen so that the measurements are distributed evenly on the surface of the section. Continue to measure the reflectance using this testing procedure.

Every 60 min, recheck the calibration of the apparatus against the standard closest to the highest reflectance (7.2.5). If the reflectance of the standard differs by more than 0.01% from the theoretical value, discard the last reading and perform them again after recalibrating the apparatus against all standards.

Reflectance measurements are made until the required number of measurements is obtained. If the polished briquette is prepared from coal of one layer, then from 40 to 100 measurements and more are made (see table 3 ). The number of measurements increases with the degree of vitrinite anisotropy. In each measured grain, the maximum and minimum values ​​of the count are determined and during the rotation of the microscope stage. The average maximum and minimum reflectance values ​​are calculated as the arithmetic mean of the maximum and minimum reports.

If the sample used is a mixture of coals, then 500 measurements are made.

On each polished specimen, 10 or more vitrinite areas should be measured, depending on the degree of anisotropy of the test sample and the objectives of the study.

Before starting measurements, the polished specimen is set so that the layering plane is perpendicular to the incident beam of the optical system of the microscope. At each measured point, the position of the maximum reading is found, and then readings are recorded every 90° of the microscope stage rotation when it is rotated 360°.

Maximum and minimum reflectance (R 0,max and R 0, min) calculated as the arithmetic mean of the maximum and minimum readings, respectively.

7.3.3. Measurement of an arbitrary vitrinite reflectance in immersion oil (R 0, r)

Use the procedure described in 7.3.2, but without polarizer and sample rotation. Perform calibration as described in 7.2.5

Measure the vitrinite reflectance until the required number of measurements is recorded.

On each polished briquette, it is necessary to perform from 40 to 100 or more measurements (table 3 ) depending on the homogeneity and degree of anisotropy of the test sample.

The number of measurements increases with an increase in heterogeneity in the composition of the huminite and vitrinite group, as well as with a pronounced anisotropy of hard coals and anthracites.

The number of measurements for samples containing solid dispersed organic matter is determined by the nature and size of these inclusions and can be significantly lower.

To establish the composition of coal mixtures from reflectograms, it is necessary to carry out at least 500 measurements on two samples of the coal sample under study. If the participation of coals of various degrees of metamorphism, which are part of the charge, cannot be established unambiguously, another 100 measurements are carried out and in the future until their number is sufficient. Limit number of measurements - 1000.

On each polished piece, up to 20 measurements are performed in two mutually perpendicular directions. To do this, the polished piece is set so that the layering plane is perpendicular to the incident beam of the optical system of the microscope. The sites for measurements are chosen so that they are evenly distributed over the entire surface of the vitrinite of the studied polished specimen.

Arbitrary reflection index (R 0, r ) is calculated as the arithmetic mean of all measurements.

7.3.4. Reflection measurements in air.

Definitions of the maximum, minimum and arbitrary reflection indices (R a, max , Ra, min And R a, r) ​​may be carried out for a preliminary assessment of the stages of metamorphism.

Measurements in air are carried out similarly to measurements in immersion oil at lower values ​​of aperture stop, illuminator voltage, and PMT operating voltage.

On the studied polished briquette, it is necessary to perform 20 - 30 measurements, polished - 10 or more.

8. PROCESSING THE RESULTS

8.1. Results can be expressed as a single value or as a series of numbers in 0.05% reflectance intervals (1 / 2 V-step) or at intervals of 0.10% of the reflection index ( V-step). The average reflectance and standard deviation are calculated as follows:

1) If individual readings are known, then the average reflectance and standard deviation are calculated using formulas (1) and (2), respectively:

(2)

where ?R- average maximum, average minimum or average arbitrary reflection index, %.

Ri- individual indication (measurement);

n- number of measurements;

Standard deviation.

2) If the results are presented as a series of measurements in 1 / 2 V-step or V-step, use the following equations:

where R t- average value 1 / 2 V-step or V-step;

X- number of reflectance measurements in 1 / 2 V-step or V-step.

Register vitrinite submacerals, which include values ?R no matter which reflectance was measured, the maximum, minimum or arbitrary, and the number of measurement points. Percentage of vitrinite for each 1/2 V-step or V-step can be represented as a reflectogram. An example of expressing the results is given in Table 2, the corresponding reflectogram is in Figure 4.

Note - V-step has a range of 0.1 reflectance, and 1/2 has a range of 0.05%. To avoid overlapping reflectance values ​​expressed to the second decimal place, the ranges of values ​​are presented, for example, as follows:

V- step - 0.60 - 0.69; 0.70 - 0.79 etc. (incl.).

1 / 2 V- steps: 0.60 - 0.64; 0.65 - 0.69 etc. (incl.).

The average value of the series (0.60 - 0.69) is 0.645.

The average value of the series (0.60 - 0.64) is 0.62.

8.2. Optionally, an arbitrary reflection index (R 0, r ) is calculated from the average values ​​of the maximum and minimum reflectance values ​​according to the formulas:

for polished ore R 0, r = 2 / 3 R 0, max + 1 / 3 R 0, min

for polished briquette

Value occupies an intermediate position between R 0, max and R 0, min And associated with the grain orientation in the polished briquette.

8.3. As an additional parameter, the reflection anisotropy index (AR) is calculated using the formulas:

8.4. The processing of measurement results in ordinary and polarized light in air on polished briquettes and polished pieces is carried out similarly to the processing of measurement results in immersion oil (8.1 ).

Figure 4 - Reflectogram compiled according to the results of table 2

table 2

Measured reflectance arbitrary

Submacerals of vitrinitis telocollinitis and desmocollinitis

Total number of measurements n = 500

Average reflectance ?R 0, r = 1.32%

Standard deviation? = 0.20%

9. PRECISION

9.1. Convergence

Convergence of the definitions of the mean values ​​of the maximum, minimum or arbitrary reflectance is the value by which two separate readings differ, taken with the same number of measurements by the same operator on the same slide using the same apparatus at a confidence level of 95%.

Convergence is calculated by the formula

where? t- theoretical standard deviation.

Convergence depends on a number of factors including:

1) limited calibration accuracy with reflectance standards (6.2.5);

2) allowable calibration drift during measurements (6.3.2);

3) the number of measurements made and the range of values ​​of the reflectance index for vitrinite of one coal seam.

The overall effect of these factors can be expressed as a standard deviation of the average reflectance of up to 0.02% for a sample of one individual coal from one seam. This corresponds to a convergence of up to 0.06%.

9.2. Reproducibility

The reproducibility of determinations of the average values ​​of the maximum, minimum or arbitrary indicators is the value by which the values ​​​​of two determinations performed with the same number of measurements by two different operators on two different preparations made from the same sample and using different equipment differ with a confidence probability 95%.

Reproducibility is calculated by the formula

where? 0 is the actual standard deviation.

If operators are adequately trained to identify vitrinite or the corresponding submacerals, and the standard reflectance is reliably known, the standard deviations of mean reflectance determinations by different operators in different laboratories are 0.03%. The reproducibility is thus 0.08%

9.3. Permissible discrepancies between the results of the average values ​​of the reflection indicators of the two definitions are indicated in the table 3 .

Table 3

10. TEST REPORT

The test report must include:

2) all details necessary to identify the sample;

3) total number of measurements;

4) the type of measurements made, i.e. maximum, minimum or an arbitrary reflection index;

5) the type and ratio of vitrinite submacerals used in this definition;

6) the results obtained;

7) other features of the sample noticed during the analysis and which may be useful in the use of the results.

Of all the OM microcomponents, vitrinite is the best in terms of indicativeness in studying the degree of catagenetic transformation. The fact is that, for reliable diagnostics, a microcomponent is needed, which must have a regular change in properties during the transformation process, at the same time it must be widely distributed in the OM. Vitrinite meets all the above requirements, unlike other microcomponents of coals and DOM. Which either merge with the total organic mass of coal already at the middle stages of catagenesis (leuptinite), or weakly and unevenly react to changes in environmental parameters (fusinite). And only vitrinite changes its properties naturally gradually and is very easy to diagnose.

It is on the basis of the reflectivity of vitrinite that most of the scales for determining the degree of catagenesis are built. In addition to it, other microcomponents of DOM are also used, but to a lesser extent. The method is based on the pattern of increase in gloss during catagenesis. This can be easily seen visually if we consider the change in the brilliance of coals in the process of changing them. No special instruments are required to notice that the brilliance of anthracite, for example, is much higher than that of brown coal. Reflectivity is closely related to the internal structure of a substance, namely, the degree of packing of particles in a substance. That's what she depends on. Of course, the study of the degree of catagenesis by reflectance is carried out using special equipment, for example, the POOS-I device consists of a polarizing microscope, an optical attachment, a photomultiplier tube (PMT) and a recording device. When conducting a study, photocurrents caused by light reflected from the surface of the sample and the standard are compared.

So, vitrinite, or rather its reflectivity, was taken as the standard for research. It is measured using various photometers and standards in air and immersion medium with strictly perpendicular light incidence on a well-polished sample surface. Measurements are carried out only in a narrow wavelength range: from 525 to 552 nm. This limitation is due to the technical characteristics of the device. A wavelength of 546.1 nm is taken as the standard, but small fluctuations around this value have practically no noticeable effect on the measurement value. The sample is fixed on the microscope stage and stopped so that its surface is perpendicular to the axis of the optical attachment. As mentioned above, we measure the intensity of the reflected light alternately at the sample and the standard using a PMT. By definition, reflectivity is the ability to reflect some of the light that hits a surface. If we translate this into numerical language, then this is the ratio of reflected light to incident.

Which can be written as:

Where I1 is the reflected light intensity and I2 is the incident light intensity. In practice, when carrying out measurements, the formula is used

Here R is the desired reflection index, d is the reading of the device when measuring the test substance, and R1, respectively, is the reflectance of the standard and d1 is the reading of the device when measuring the standard. If you set the receiver device to zero for the reference, then the formula simplifies to R=d.

In addition to vitrinite, other OM microcomponents are also used for measurements. Some of them have the property of reflectivity anisotropy. Three measurement parameters are usually used: Rmax Rmin Rcp. The increase in vitrinite anisotropy during catagenesis is mainly due to the process of gradual ordering of aromatic humic micelles associated with an increase in pressure with increasing immersion depth. Measurements in the case of an anisotropic preparation are conceptually no different from the measurement of a homogeneous sample, but several measurements are carried out. The microscope stage rotates 360? at intervals of 90?. Two positions with the maximum reflectivity and two with the minimum are always detected. The angle between each of them is 180?. Measurements are made for several rock fragments and the average value is calculated later. As the arithmetic mean of the averages of the maximum and minimum measurements:

You can immediately determine the average value by choosing a rotation angle of 45? from the maximum or minimum value, but this measurement is valid only when studying a weakly transformed OF.

When conducting research, there are several problems associated with the technology. For example, if we have a rock with a low total content of organic matter, then there is a need for special processing of the sample and its conversion into the form of concentrated polished sections-briquettes. But in the process of obtaining concentrates, the original organic matter is subjected to chemical treatment, which cannot but affect the optical properties of the substance. In addition, information about the structure of the organic matter of the rock is lost. Distortions in the measurements can also be introduced by the fact that the technology of the drug preparation process is not standardized and the readiness of the sample is usually determined visually. The problem is also the physical properties of the rocks, such as strong mineralization or brittleness of coal, in this case it is necessary to study the reflectivity on the surface area that was obtained. If the area is chosen correctly, then the surrounding defects practically do not affect the measurements. But fundamentally, the quantitative values ​​of errors practically do not affect the determination of the stage of catagenesis.

Samples are studied, usually under normal air conditions, it is easy, fast. But if you need a detailed study under high magnification, immersion media are used, usually cedar oil. Both measurements are correct and each of them is used, but each in its own specific case. The advantages of measurements in an immersion medium are that they allow one to study particles with a small dimension; in addition, sharpness increases, which makes it possible to diagnose the degree of catagenesis in more detail.

An additional difficulty in research is the diagnosis of OM microcomponents, since they are usually determined in transmitted light. While the reflectivity is obviously in the reflected. That's why. Usually, two methods are combined in the research process. That is, transmitted and reflected light are alternately used to study the same DOM fragment. For this, polished sections are usually used on both sides. In them, after viewing and determining the microcomponent in transmitted light, the illumination is switched and measurements are taken in reflected light.

Vitrinite can be used not only to determine the degree of transformation of organic matter, but also to determine its relationship to the rock. In syngenetic vitrinite, the fragments are usually elongated, the particles are parallel to the bedding planes, and usually have a cellular structure. If we are dealing with vitrinite particles of a rounded, rounded shape, then most likely this is a redeposited substance.

Grade A (anthracite).
Anthracites combine coal with a vitrinite reflectance of more than 2.59%. With a volatile matter yield of less than 8%, anthracites also include coals with a vitrinite reflectance of 2.2 to 2.59%. The bulk of anthracite is used for energy purposes. Medium and large classes of them serve as smokeless fuel in the domestic sector. Part of the anthracites is sent to the production of thermoanthracite, which, in turn, is used as the main carbonaceous filler in the manufacture of cathode blocks for electrolyzers in the aluminum industry. Anthracites are also used for the production of silicon carbide and aluminum carbide.

Mark D (long-flame).
Long-flame coal are coals with a vitrinite reflectance of 0.4 to 0.79% with a volatile matter yield of more than 28-30% with a powdery or slightly caking non-volatile residue. Long-flame coals do not sinter and are classified as thermal coals. Directions for the use of these coals are energy and municipal fuels, therefore their most significant characteristic is the heat of combustion. When moving to the next brand of DG calorific value coal increases significantly. Studies have shown that long-flame coal with a low ash content can serve as a good raw material for the production of synthetic liquid fuel and chemical products, production of molded coke and spherical absorbents, low-temperature (up to 700 degrees) coking.

Brand DG (long-flame gas).
Long-flame gas coals are coal with a vitrinite reflectance of 0.4 to 0.79% with a volatile matter yield of more than 28-30% with a powdery or slightly caking non-volatile residue. These coals are transitional between coals of grades D and G. They differ from long-flame coals in the presence of sintering (the thickness of the plastic layer is 6-9 mm, and from gas coals with similar sintering properties - more insignificant brittleness and increased mechanical strength. The latter circumstance determines the predominance of coarse coals among such coals). DG grade coal is also referred to the group of power-generating coals, they are not suitable for participation in coke charges, because the formed coke is characterized by low mechanical strength and increased reactivity.

Mark G (gas).
Coal gas has two technological groups. Vitrinite coals (vitrinite reflectance from 0.5 to 0.89%) with a volatile matter yield of 38% or more, with a plastic layer thickness of 10 to 12 mm form group 1G, vitrinite and inertinite coals with a vitrinite reflectance of 0.8 - 0.99%, the yield of volatile substances is 30% and above and the thickness of the plastic layer is from 13 to 16 mm form group 2G. . Gas coals are mainly used as energy and domestic fuels. Group 2G coal with a plastic layer thickness of more than 13 mm is used for coking. The limited possibility of using gas coals in the charges of coking plants producing metallurgical coke is due to the fact that during layered coking they cause the formation of microcracks in the coke, which significantly reduce its strength. Gas coal with a plastic layer thickness of 8-12 mm is used for the production of molded coke and spherical absorbents, and coals with a plastic layer thickness of less than 8 mm are used for gasification and semi-coking. Vitrinite low-ash coal grade G with a volatile matter yield of more than 42% is a good raw material for the production of synthetic liquid fuels.
Mark B (Brown).
Brown coal is characterized by low vitrinite reflectance (less than 0.6%) and high volatile matter (more than 45%). Brown coals are divided depending on the humidity into technological groups: 1B (moisture over 40%), 2B (30-40%), 3B (up to 30%). Brown coals of the Kansk-Achinsk coal basin are mainly represented by group 2B and partially - 3B (vitrinite reflection index 0.27-0.46%), brown coals of the Moscow Region basin belong to group 2B, coals of the Pavlovsky and Bikinsky deposits (Primorsky Territory) belong to group 1B. Brown coal is used as an energy fuel and chemical raw material.

GZhO brand (gas fat lean).
Fatty gas coals, lean in terms of the yield of volatile substances and the thickness of the plastic layer, occupy an intermediate position between coals of grades G and GZh. There are two technological groups. Technological group 1GZhO includes coal with a vitrinite reflection index of less than 0.8% and a volatile matter yield of less than 38%, with a plastic layer thickness of 10 to 16 mm. Group 2GZhO includes coals with a vitrinite reflectance of 0.80-0.99%, a yield of volatile substances less than 38%, with a plastic layer thickness of 10-13 mm, as well as coals with a vitrinite reflectance of 0.80-0.89% with the yield of volatile substances is 36% or more with a plastic layer thickness of 14-16mm. Humidity grade GZhO fluctuates within 6-8%, ash content - 6-40%. The carbon content varies within 78-85%, hydrogen - from 4.8 to 6.0%, sulfur 0.2-0.8%. GZhO brand coal is characterized by a wide variation in properties, which does not allow us to recommend any one direction for their use. Coal of the 1GZhO group with a plastic layer thickness of less than 13 mm can make up no more than 20% of the charges of coking plants, and only on condition that the rest of the charge contains well-caking coals with a vitrinite reflection index of 1 to 1.5%. Group 2GZhO coal is a good raw material for coking (especially with a vitrinite reflectance of at least 0.85%) and can make up more than half of the charge. Fusinite coal of group 1GZhO (subgroup 1GZhOF) is completely unsuitable for the production of metallurgical coke, and can be used in the domestic (large classes) or energy (small classes) sectors.

Brand GZH (gas fat).
Fatty gas coals occupy an intermediate position between grades of G and Zh coals and are divided into two groups. Group 1GZh combines coal with a vitrinite reflectance of 0.5-0.79%, a volatile matter yield of 38% or more, and a plastic layer thickness of more than 16 mm. The 2GZh group combines coal with a vitrinite reflectance of 0.8-0.99%, a volatile matter yield of 36% or more, and a plastic layer thickness of 17-25 mm. Grade GZh differs from gas coals in a higher sintering capacity, and from coals of Zh grade - in a higher yield of volatile substances. GZh grade coals are mainly used in the coking industry and are included in the group of coal grades especially valuable for coking. In most cases, they can completely replace fat coals in the charge of coking plants. It is advisable to use GZh grade coal concentrates with an ash content of less than 2% as a binder in the production of electrode and carbon-graphite products; GZh grade coals are also suitable for the production of synthetic liquid fuels.

Mark J (bold).
Fatty coals are divided into two groups. The first group (1G) includes coal with a vitrinite reflectance of 0.8–1.19%, a volatile matter yield of 28–35.9%, and a plastic layer thickness of 14–17 mm. The second group (2G) includes coals with a vitrinite reflectance of 0.8-0.99%, a volatile matter yield of 36% or more, with a plastic layer thickness of 26 mm or more. The same group includes coals with the same values ​​of the vitrinite reflectance index, but with the release of volatile substances from 30 to 36% with a plastic layer thickness of 18 mm and more. Also, group 2G includes coal with a vitrinite reflectance of 1-1.19% with a volatile matter yield of at least 30% with a plastic layer thickness of at least 18 mm. Coal grade Zh is a particularly valuable coking coal and is used mainly in the coke industry, accounting for 20 to 70% of the coke charge. Coke obtained from Zh grade coals has high structural strength.

Brand KZh (coke fat).
Fat coke coals stand out as coal with a vitrinite reflectance of 0.9-1.29%, a plastic layer thickness of 18 mm, with a volatile matter yield of 25-30%. The main consumer of KZh grade coal is the by-product coke industry. Of all the grades of coal used to produce coke, they have the highest coking capacity. High-quality metallurgical coke is obtained from them without mixing with coals of other grades. In addition, they are able to accept up to 20% of filler coal grades KO, KS and OS without changing the quality of coke.

Mark K (Coke).
Coke coal is characterized by a vitrinite reflection index from 1 to 1.29%, as well as good sintering properties. The thickness of the plastic layer is 13-17 mm for coals with a vitrinite reflectance of 1.0-1.29% and 13 mm and higher with a vitrinite reflectance of 1.3-1.69%. The yield of volatile substances is in the range of 24-24.9%. Without mixing them with coals of other grades, they provide conditioned metallurgical coke. The quality of coke can significantly increase when coal grade K is mixed with 20-40% coal grades Zh, GZh and KZh.

Brand KO (coke lean).
Coal lean coke is a coal with a yield of volatile substances close in value to coke coal, but with a thinner plastic layer - 10-12 mm. The reflection index of vitrinite is 0.8-0.99%. Coal grade KO is mainly used for the production of metallurgical coke as one of the filler coals for grades GZh and Zh.

KSN brand (coke weakly caking low metamorphosed).
Low-caking, low-metamorphosed coke coals are characterized by a vitrinite reflection index from 0.8 to 1.09%. When coking without mixing with other coals, they give mechanically low strength, highly abrasive coke. They are used both in the coke industry, and in the power industry and the domestic sector. KSN grade coal can also be used to produce synthetic gas.

Grade KS (Coke weakly caking).
Low-caking coking coals are characterized by low sintering (the thickness of the plastic layer is 6-9 mm with a vitrinite reflection index of 1.1-1.69%. Coal of the KS grade is used mainly in the coke industry as a lean component. Part of the coal is used for layer combustion in industrial boilers Low-caking coke coals are characterized by low caking ability (plastic layer thickness 6-9 mm with vitrinite reflectance index 1.1-1.69%. used for stratified combustion in industrial boiler houses and in the domestic sector.

Brand OS (lean sintering).
The lean coals sintering have vitrinite reflection indices from 1.3 to 1.8% and the yield of volatile substances is not more than 21.9%. The thickness of the plastic layer for the 2OS group is 6-7 mm, and for the 1OS group it is 9-12 mm with a vitrinite composition and 10-12 mm with a fusinite composition. Humidity of mined coal grade OS does not exceed 8-10%. Ash content ranges from 7 to 40%. The sulfur content in the Kuznetsk basin does not exceed 0.6%, sometimes it reaches 1.2% in the Karaganda basin, and 1.2-4.0% in the Donbass. The carbon content is 88-91%, hydrogen 4.2-5.%. The main consumer of OS grade coal is the by-product coke industry; these coals are one of the best lean components in coke blends. Some coals of the OS grade even without mixing with coals of other grades give high-quality metallurgical coke; but during coking, they develop a large bursting pressure on the walls of coke ovens, coke is issued from the ovens with with great difficulty, which leads to a rapid failure of the furnaces. Therefore, OS grade coal is usually coked in a mixture with G and GZh coals, which have a high degree of shrinkage.

Brand TS (skinny slightly caking).
Lean low-caking coals are characterized by a volatile matter yield of less than 22% and very low sintering (the plastic layer thickness is less than 6 mm. The moisture content of mined coal of the TS grade is low - 4-6%. The ash content is in the range of 6-45%. The carbon content is 89-91%, hydrogen 4.0-4.8%. Sulfur content in coals of Kuzbass 0.3-0.5%, Donbass 0.8-4.5%. mainly in the power industry; large-medium classes of coals of this brand are good smokeless fuel for small boilers and individual domestic use.

Grade SS (low caking).
Weakly caking coals are characterized by a vitrinite reflection index in the range of 0.7-1.79%, a plastic layer thickness of less than 6 mm, and a release of volatile substances, which is characteristic of well-coking coals of Zh, KZh, K, KS and OS grades. Humidity of the mined coal reaches 8-9%. Ash content ranges from 8 to 45%. The sulfur content usually does not exceed 0.8%. The carbon content ranges from 74 to 90%, hydrogen from 4.0 to 5.0%. They are mainly used in large power plants, in industrial boiler houses and in the domestic sector. In a limited amount, certain varieties of SS grade coals are used in batches of coking plants.

Mark T (skinny).
Lean coal is characterized by the release of volatile substances from 8 to 15.9% with a vitrinite reflection index from 1.3 to 2.59%; sintering is absent. They are mainly used in the electric power industry and in the domestic sector; under the condition of low ash content, they can be used to obtain carbonaceous fillers in electrode production.

Vitrinite group: a - colinite (homogeneous gray) with cutinite (black). reflected light. Immersion b - colinitis (homogeneous gray), corpocolinitis (dark gray oval body on the left), thelinitis (uneven stripe in the center). White spherulites - pyrite. reflected polarized light. State of extinction; c - vitrodetrinitis. reflected light. Immersion g - colinitis (top), thelinitis (bottom).

Telinite (gray), rubberite (black). reflected light. Immersion.

Crushed fragments of a vitrinite character are very often found in bituminous coal. They form the desmocolinite groundmass of clarite and trimacerite. As a rule, when examined in normal reflected light using oil immersion, these fragments cannot be distinguished from each other. In this case, they are combined under the name "desmocolinitis". Only iodide-methylene immersion makes it possible to clearly distinguish them in coal with a high yield of volatile substances. In reflected light using oil immersion, vitrodetrinite particles can only be seen when they are surrounded by components having a different reflectivity (for example, clay minerals in carbonaceous shales or inertinite in sham).

Knowledge of the basics of coal formation processes and the conditions for the applicability of solid fuels in metallurgy allows flexible control technological processes and economic efficiency of iron and steel production.

The use of fossil fuels in metallurgy goes back one hundred years. The source material and conditions for the formation of fossil fuels have become the reason for their species diversity. Modern metallurgy places high demands on the quality of raw materials, incl. to coke and injected additives. Knowledge of the fundamentals of coal formation processes and the conditions for the applicability of solid fuels in metallurgy makes it possible to flexibly control technological processes and the economic efficiency of iron and steel production.

Composition and structure of the original plant material

The current theory of coal formation implies the origin of fossil fuels from plant matter that has undergone a certain metamorphism over a long period of time.

A variety of plants, from unicellular algae to trees, took part in the formation of the starting material for all fossil fuels. By modern ideas in the structure of plants, substances of the following chemical groups are distinguished: fats, waxes, resins, carbohydrate complexes (celluloses and pectins), lignin, proteins.

Fats are widely distributed in plants: they contain about 1700 different types of fats. By chemical composition, fats are esters of a trihydric alcohol - glycerol - and saturated and unsaturated fatty acids (monocarboxylic, with a normal carbon chain and an even number of carbon atoms). Fats are insoluble in water, but easily soluble in diethyl ether, carbon disulfide, gasoline, aromatic hydrocarbons.

Waxes- these are esters of higher monocarboxylic acids and higher primary monohydric alcohols of a normal structure. Waxes in plants cover the stems, leaves, and spore shells with a thin layer, protecting them from external influences. Waxes have a high melting point for organic materials (70...72 °C). They are extremely stable substances and, due to their stability, are almost always present in coals.

resins. Plant resins are a mixture of various organic compounds (acids, esters, alcohols, phenols and hydrocarbons). Resins are inherent in higher plants, in which they are found in solutions of essential oils (balms). In plants, resin passages are filled with balms. When the plant is damaged, resin concentrates are abundantly released, which quickly thicken in air as a result of the evaporation of essential oils, as well as due to the partial polymerization of resin substances. Such clots of solid resin reach us in the form of resin nodules embedded in the organic part of the coal.

Cellulose(С6Н10О5) - the main construction material plant tissues, giving plants mechanical strength.

Hemicelluloses(heteropolysaccharides) are complex organic compounds, the hydrolysis of which produces the simplest sugars (pentoses, hexoses, etc.).

pectin substances- perform a supporting function in the walls of plant cells, young fruits and tissues.

lignin is an aromatic polymer. Participates in the formation of plant cell walls. The formation of lignin is typical only for vascular plants. During the period of evolution (the emergence of plants on land), vascular plants acquired the ability to produce enzymes capable of forming lignin from carbohydrates. Lignin plays the role of a cementing agent that glues bundles of cellulose fibers, and thus constitutes the main part of wood. The approximate content of lignin in some plants (% wt.) is: beech - 22, spruce - 27, tree-like alfalfa - 23, club moss - 37, cuckoo flax - 38, sphagnum (a special kind of moss) - 4.5.

Squirrels- natural products of a macromolecular structure, which are converted during hydrolysis into alpha-amino acids. One of the most important properties of proteins, which is absent in other plant chemical groups, is specificity.

The elemental composition of coal formers is given in Table. one:

Table 1. Elemental composition of coal formers

The quantitative content of chemical groups of substances in various types plants are given in table. 2.

Table 2. Content in plants of the main groups chemical substances, % (wt.)

Initial plant material and its transformations during coal formation processes

Depending on the composition of the initial plant material, coals are divided into humus, sapropelite, liptobiolite and mixed.

Humus coals derived from land plants.

Liptobiolite coals They are also formed from terrestrial vegetation, but from the most persistent plant components under natural conditions - integumentary tissues (cuticles, bark, resins, spores, pollen).

Sapropelite coals are formed exclusively from clusters of algae - green, blue-green.

mixed coals are a product of joint transformations of various terrestrial and aquatic vegetation.

Along with the source material, the composition and properties of coals are also influenced by the physical and geographical conditions under which the accumulation of plant material took place. This concept covers the landscape environment, subdivided into lake, marsh, sea, lagoon, etc., and its physicochemical (hydrochemical and microbiological) features, including salinity, flow, stagnation, etc.

The most important condition for the formation of hard coal is the lack of access to the source material of oxygen from the air. Formation conditions and types of coals are given in Table. 3.

Table 3. Formation conditions and types of coals

Only humic, banded coals can be coking, i.e. claren coals:

• claren (lat. clarus - brilliant) - coal, which is composed of components rich in carbon and microimpurities: vitren, micrinite and fuzen.
• vitren, vitrite, vitrinite (lat. vitrum - glass) - black shiny, rich in hydrocarbons plant tissue- the main carrier of sintering properties. Forms "lenses" and "layers" in the bulk of the coal.
• micrinite is a black matte component from plant spores.
• fusin, fusinite (French fusain - lens) - black powdery, similar to charcoal with a silky sheen.

Classification of coals according to the degree of metamorphism

Differences in the source material, the degree of watering of peatlands, the chemical composition of the environment, and the facies conditions of sedimentation and peat accumulation, which determine the direction and intensity of the oxidation and reduction microbiological processes, created the basis for the formation of various genetic types of coals in the peat stage. Peat formation and peat accumulation ended with the overlapping of the peat bog by sediments forming roof rocks. The diagenetic (compaction, dehydration of sediments, gas release) and biochemical processes of a reducing nature, which took place at relatively low temperatures and pressure, led to the transformation of peat into brown coal.

Coals, including weakly decomposed woody residues cemented by earthy coals, are called lignites.

brown coals- one of the varieties of coal - are widely used. The share of brown coal and lignite reserves in the world coal reserves is 42%. The shallow occurrence and large thickness of coal seams make it possible to widely use open way development, the economic and technical advantages of which largely compensate for the relatively low quality of raw materials.

As a result of prolonged exposure to elevated temperatures and pressure, brown coals are converted into hard coals, and the latter into anthracites. The irreversible process of gradual change in the chemical composition (primarily in the direction of carburization), physical and technological properties of organic matter in transformations from peat to anthracite is called coalification. Coalification at the stages of transformation of brown coals into hard coals and the latter into anthracites, due to the processes occurring in the earth's crust, is called coal metamorphism. There are three main types of coal metamorphism:

• regional, caused by the influence of the internal heat of the Earth and the pressure of the overlying rock strata when coals sink into the depths of the earth's crust;
• thermal - under the influence of heat released by igneous bodies that overlapped or intruded into the coal-bearing stratum, or into its underlying deposits;
• contact - under the influence of heat of igneous rocks that have intruded into coal seams or crossed them directly; It is problematic that coal metamorphism is recognized as possible due to an increase in temperatures in the areas of manifestation of tectonic compressive and shearing forces - dynamometamorphism.

Structural and molecular rearrangement of organic matter during the metamorphism of coals is accompanied by a consistent increase in their relative carbon content, a decrease in oxygen content, and the release of volatile substances; The hydrogen content, heat of combustion, hardness, density, brittleness, optical, electrical, and other physical properties of coals change in certain patterns with extreme values ​​at the middle stages of coalification. To determine these stages, the following are used: the yield of volatile substances, carbon content, microhardness, and other features of the chemical composition and physical properties of coals. The most effective method for determining the stage of coalification is by the reflectivity of vitrinite.

hard coals at the middle stages of metamorphism, they acquire sintering properties - the ability of gelified and lipoid components of organic matter to pass, when heated under certain conditions, into a plastic state and form a porous monolith - coke. The relative amount of coal reserves with high caking ability is 10...15% of the total coal reserves, which is associated with a higher intensity of organic matter transformation at the middle stages of metamorphism. Sintering coals occur at temperatures from about 130 to 160...180 °C with a general temperature range that determines the course of coal metamorphism, from 70...90 °C for long-flame coals to 300...350 °C for anthracites. The highest quality sintering coals were formed in basins that experienced regional metamorphism during deep subsidence of the coal-bearing strata. During thermal and contact metamorphism, due to a sharp change in temperature and low pressure, the transformation of organic matter proceeds unevenly and the quality of coals is characterized by uneven technological properties. The rocks of coal-bearing formations, along with the metamorphism of coals, experience catagenetic transformations.

In zones of aeration and active action of groundwater near the Earth's surface, coals undergo oxidation. In terms of its effect on the chemical composition and physical properties of coals, oxidation has an opposite direction compared to metamorphism: coals lose their strength properties (before they turn into a sooty substance) and sintering properties; in them, the relative content of oxygen increases, the amount of carbon decreases, the humidity and ash content increase, and the heat of combustion sharply decreases. The depth of coal oxidation, depending on the modern and ancient relief, the position of the groundwater table, the nature of climatic conditions, the material composition and metamorphism of coals, ranges from 0 to 100 m vertically.

Differences in the material composition and degree of metamorphism led to a large differentiation in the technological properties of coals. To establish a rational direction for the industrial use of coal, they are divided into grades and technological groups; This subdivision is based on parameters that characterize the behavior of coals in the process of thermal action on them. The boundary between brown and hard coals is the highest calorific value of the working mass of ashless coal, equal to 5700 kcal/kg (23.86 MJ).

The leading indicator for the use of coal for energy purposes - the lower calorific value - in terms of working fuel ranges from (kcal / kg): 2000 ... 5000 (8.372 ... 20.930 MJ) for brown, 4100 ... 6900 (17.162 ...28.893 MJ) for bituminous coals and 5700...6400 (23.86...26.79 MJ) for anthracites. The reduced value of this indicator for brown coals is explained by the low degree of coalification of organic matter, weak compaction of the material and, accordingly, their high natural moisture content, which varies within 15 ... 58%. According to the content of working moisture, brown coals are divided into technological groups: B1 with Wp\u003e 40%, B2 with Wp 30 ... 40% and B3 with Wp< 30%.
The industrial labeling of hard coals is based on indicators characterizing the results of their high-temperature dry distillation (coking): the yield of volatile substances formed during the decomposition of organic matter (partially inorganic material - sulfides, carbonates, hydrated minerals), and the characteristic of the ashless combustible residue - coke by sintering . The weight yield of volatile substances from coals consistently decreases with an increase in the degree of coalification from 45 to 8% for hard coals and up to 8 ... 2% for anthracites.

In the USSR, the sintering ability of coals is determined in a laboratory apparatus by the plastometric method proposed in 1932 by Soviet scientists L. M. Sapozhnikov and L. P. Bazilevich, by the thickness of the plastic layer formed during heating (y), taking into account shrinkage (x), expressed in mm. The greatest sintering ability is characterized by coals of the middle stages of coalification with a plastic layer thickness of 10 ... 35 mm (grades K and Zh). With a decrease and increase in the degree of metamorphism, the caking capacity of coals decreases. Coals of grades D and T are characterized by weakly sintered powdery non-volatile residue. In table. 4 shows the values ​​of the main indicators of the quality of coals on various stages coalification in relation to grades according to GOST.

Table 4. Main indicators of the quality of graded coals

In addition to those indicated in the table, intermediate grades are distinguished in some basins: gas fat (GZh), coke fat (KZh), coke second (K2), weakly caking (SS). Coal grades G, GZh, Zh, KZh, K and OS are divided into technological groups according to caking capacity; to indicate technology group to letter designation mark, a number is added indicating the lowest value of the thickness of the plastic layer (y) in these coals, for example, G6, G17, KZh14, etc. For coals of specific basins, the values ​​of classification indicators (VG and y) are regulated by GOST. To obtain metallurgical coke, a mixture of various grades of coal is used - a charge, the main component of which is coals with high sintering properties.

The subdivision of coals into brown, black and anthracites is accepted in most European countries (in some - with the release of additional lignites). The International Coal Classification System, adopted in 1956 by the United Nations Economic Commission for Europe, is also based on the yield of volatile substances for coals with V>33% - the higher calorific value of the wet ash-free mass, caking ability, and coking capacity. The type of coal is indicated by a three-digit code number, the first digit of which indicates the class of coal (according to volatile or calorific value), the second - the group (according to caking ability, determined by the Rog method or the swelling index in the crucible), the third - the subgroup (according to coking, determined by the Odiber- Arnoux or Gray King). In the US and some other countries, coals are classified into lignites, sub-bituminous, bituminous coals and anthracites; classification parameters are as follows: for lignites, subbituminous and bituminous (with volatile >31%) coals - the calorific value of ash-free mass, for bituminous with volatile<31% и антрацитов – выход летучих веществ и содержание связанного углерода.

Marking of coals, reflecting a complex of certain technological properties of coal varieties, is used as the main criterion in the practice of industrial use of coals. For specific areas of consumption, additional technical requirements are established. A sharp decrease in the thermal effect of coal combustion and economic indicators of their use due to ballast (ash and moisture) determines the need for briquetting coals with high natural moisture and preliminary enrichment of high-ash coals. The maximum ash content of coals sent for layer combustion should not exceed 20 ... 37%, for pulverized combustion - 45%.

For coking, low-ash (enriched) sintering bituminous coals are used, in which the content of sulfur and phosphorus is limited. For semi-coking, gasification, production of liquid fuels, mountain wax, and other areas of consumption, sintering, sulfur content, ash content, lumpiness, thermal stability, tar, bitumen content, and other quality indicators are standardized.

The main coal basins of the Russian Federation - sources of coking coal

Donetsk basin. One of the largest European coal basins. On the territory of the Rostov region, only the extreme eastern part of the basin is located, where anthracites are predominantly distributed. Coking coals are found in three out of seven districts - Kamensko-Gundorovsky, Belokalitvensky, Tatsinsky - and are characterized by light and medium washability. The coals of the Donets Basin are characterized by a high sulfur content.

Kuznetsk basin. It is located on the territory of the Kemerovo and Novosibirsk regions and covers an area of ​​27 thousand km2 (110 x 350 km). Of the 25 geological and industrial regions, coking coals are developed in 20. Coal washability is light and medium with a concentrate yield of 70 to 90%. The coals of the Kuznetsk basin are characterized by low sulfur content. All grades of coking coal are mined in the basin. Favorable mining and geological conditions for the occurrence of coals, a small depth of their mining make the use of these coals economically feasible practically throughout Russia.

Pechora basin. It is part of the Northern District and is located on the territory of the Komi Republic and the Nenets Autonomous Okrug of the Arkhangelsk Region. The area of ​​the basin is 90 km2. Coking coals are common in the Vorkuta, Vorgashor and Khalmeryu deposits. The coals are mostly moderately enriched (the concentrate yield is from 70 to 85% (wt.), the coals of the GZhO, K, Zh grades are easily enriched (the concentrate yield is 85-93% wt.). Fatty and gaseous fatty coals of the Vorkuta and Vorgashor deposits are able to take in as a lean additive to 50% of lean coals with a significant increase in coke strength Coals of grade K of the Khalmeryu deposit during coking produce strong metallurgical coke of high quality.

Karaganda basin. It is a source of coking coal for enterprises in the East of Russia, located in Central Kazakhstan on the territory of the region of the same name. Its area is 3000 km2 (30 x 100 km). Hard coals, because mineral components are very finely distributed in the organic mass of coal. The output of the concentrate is from 15 to 65% (wt.).

Quality indicators of coking coals

The quality of coals is determined by their technological and petrographic parameters.

Volatile matter (V)- products, with the exception of moisture, released from coal in the form of gas and steam. They are formed during the decomposition of coal under heating conditions without air access. They are determined for dry (dry - Vd) or dry ash-free state (dry ash free - Vdaf). Together with sinterability, it determines the suitability of coals for coking. It is this indicator that is the key one when compiling a coal charge and considering the possibility of replacing coal in a charge.

Ash content (A) is the content of non-combustible inorganic material in coal. It is defined as the residue formed when coal is heated as a result of the combustion of the entire combustible mass. Determined for dry condition (dry - Ad).

Sulfur (S)– sulfur content in coal. It is contained in the form of sulfides, sulfates, organic compounds and elemental sulfur. Determined for dry condition (dry - Sd).

Vitrinite (Vt)- one of the types of organic matter (macerals), which forms a mass of coal. In addition to vitrinitis, there are liptinitis and inertinitis. Vitrinite is the most valuable maceral.

Vitrinite reflectance index (R0)- the reflectivity of vitrinite is an indicator of the degree of metamorphism of coals (the more, the older the coal). To characterize the degree of coalification, the average reflectance of vitrinite in ordinary monochromatic light is determined.

Plastic layer thickness (y)- one of the main indicators of coal sintering, characterizing the assessment of the quality of coking coals. It is defined as the maximum distance between the interfaces "coal - plastic mass - semi-coke", determined during plastometric tests.

Fixed carbon (FC)- part of the carbon remaining when coal is heated in a closed vessel until the volatile substances are completely removed (i.e. this is the non-volatile part minus ash).

Total Moisture (TM)- moisture contained in fossil coals, including free, surface and bound. During coking, moisture adversely affects the bulk density of the coal charge, the consumption of electricity for crushing and heat for coking; with a moisture content of more than 8%, it is difficult to transport the charge in coal preparation shops.

Gray King coking index– this indicator is the main characteristic of coal coking ability; the type of coke according to Gray-King is determined by the reference scale: A, B, C, D, E, F, G1, G2,...,G12; type of coke "A" indicates that the coal does not coke, types "B", "C", "D" indicate low coking,..., types "G5" - "G12" indicate high coking properties of coals, moreover, the higher the number, the better the coking.

Free Swelling Index (Crucible Swelling Number (CSN)/Free Swelling Index (FSI))- the main characteristic by which the sintering ability of coals is estimated throughout the world; Caking is one of the most important classification indicators for coals used for coking; The sinterability of the coal charge must be sufficient to ensure high strength of the coke substance (as a rule, the higher the CSN value, all other things being equal, the better).

Gieseler Max Fluidity- well-sintering coals are determined by the Gieseler method; this parameter is very important for coking coals, because low-flowing coals are not able to independently participate in the coking process (they require the addition of high-flowing coals for binding); to compare this parameter, a logarithmic (ordinal scale) is used.

Grindability Index (Hardgrove Index) is the empirical index achieved as a result of grinding the coal sample. Grinding of narrowly classified coal weighing 50 g is carried out in an annular ball mill for 60 revolutions. The index is determined on the basis of the granulometric composition of crushed coal.

Classification of coking coals

In Russia and the CIS there is a Unified classification of coals in accordance with GOST 25543-88. According to this classification, coal is divided into the following grades:

• B - brown;
• D - long-flame;
• DG - long-flame gas;
• G - gas;
• GZhO - gas fat lean;
• GJ - gas fatty;
• F - fatty;
• QOL - coke fat;
• K - coke;
• KO - coke lean;
• KSN - coke sintering low metamorphosed;
• KS - coke weakly caking;
• OS - lean sintering;
• TS - skinny sintering;
• SS - weakly caking;
• T - skinny;
• A is anthracite.

The world classification divides coals into Hard Coking Coal (HCC), Semi-soft Coking Coal (SSCC), Pulverised Coal for Injection (PCI), Thermal Coal/Steam Coal (Fig. 1):

Figure 1 - World classification of coals

The ratio of world reserves of coals and the direction of their use, depending on the content of carbon and moisture, is shown in fig. 2:

Figure 2 - Ratio of world coal reserves

PUT - pulverized coal fuel

The history of the development of pulverized coal injection technology

The technology of blast-furnace smelting using pulverized coal fuel has been known since 1831. The industrial application of the technology of injection of pulverized coal began only in the middle of the 20th century, and this technology became widespread in the 80s of the 20th century. The protracted period of development of the PCF technology can be explained by the need to develop complex and expensive equipment for the preparation and injection of PCB, as well as successful competition from fuel oil and natural gas.

The first patent for blowing crushed solid fuel into a blast furnace through lances was issued in England in 1831. A similar patent was issued in Germany in 1877. Data on the beginning of the practical use of PUT vary: according to some sources, the first attempts at blowing were made in 1840, according to to others, the first blowing of crushed coal into a shaft furnace was carried out in Canada during the smelting of blister copper in 1911.

Large-scale experimental work on injection of PUT began in the 50s-60s of the 20th century in the USA. At that time, fuel oil played a leading role in fuel injection technology.
In 1955, in the USSR at the metallurgical plant named after. Dzerzhinsky, experiments were carried out on blowing coal dust through a tuyere into a blast furnace with a volume of 427 m3 during the smelting of ferrosilicon. These experiments laid the foundation for research into the blast furnace process using pulverized fuel in industrial blast furnaces in the USSR.

It was only after the energy crisis in the 1970s that attention was paid to coal as a more reasonable economic alternative. The practice of injection of fuel oil and other oil derivatives used in the 1970s ensured coke consumption at the level of 400 kg/t of pig iron. The second oil crisis made it necessary to abandon the injection of liquid agents and sharply increased the consumption of coke.

The 1980s saw a period of rapid growth in the construction of pulverized carbon injection plants around the world, mainly in Europe and Asia. In North America, the injection of natural gas together with other types of liquid and solid fuels has become popular. By the end of the 1980s, the injection of PUT significantly replaced other types of fuel in the United States as well.

Due to the opposite direction of the impact of the processes of injection of pulverized coal and natural gas on the blast furnace run, it became obvious to combine the injection of these fuels for a milder effect on the run of the furnace. In the United States, this technology has become widely used (Table 5):

Table 5. Use of various injected additives in US blast furnaces

The popularity of this solution is explained by the fact that the combination of two materials provides, under less stringent conditions, the greatest possible savings in coke.
To date, as a result of improvement, the technology of injection of PUT has found wide practical application. The use of pulverized coal injection technology makes it possible to reduce the specific consumption of coke to 325...350 kg/t of pig iron. The Netherlands is the leader in terms of specific consumption of PU (Fig. 3, ). Recently, the technology has been actively developed in China ().

Figure 3. Inflation rate of IUT

Necessary Conditions for Successful Implementation of the PUT Injection Technology

To introduce the technology of injection of pulverized coal into blast-furnace smelting, it is necessary to carry out a set of the following measures:

• improve the quality of coke in terms of CSR to 62% or more;
• reduce the ash content of the charge for coking to 7.5%;
• ensure high stability of the quality indicators of the charge for coking;
• use for PUT coals with an ash content of 6.0-8.5% and a sulfur content of less than 0.5%;
• to ensure the stability of the quality indicators of coals used for PUT;
• to ensure the stability of the quality of the components of the iron ore charge;
• reduce the content of fines in iron ore to 3...5%;
• increase the blast temperature to 1200...1250 °C;
• increase the oxygen content in the blast to 28...33%.

Parallel to the reduction of coke consumption when large amounts of pulverized coal are injected, the requirements for coke quality first of all increase ( see section "Download/Supplementary Literature"), since coke is the only solid material below the blast furnace cohesion zone and is consumed here at a slower rate, i.e. exposed to longer exposure to high temperatures and the weight of the charge column. In this regard, the coke must be physically stronger and more resistant to chemical attack in order to ensure high gas permeability of the charge.

The coke stretch reactivity (CSR) is largely dependent on the chemical composition of the ash, which affects the reactivity of the coke.

The composition of the blast-furnace slag also has an effect on the efficiency of the injection of PCB - the researchers found a significant deterrent effect on the increase in pressure losses resulting from the use of iron ore raw materials with a low content of Al2O3.

Peculiarities of combustion of coal dust in the tuyere hearths of a blast furnace

The most important defining requirement of the new technology is to ensure complete combustion of the fuel within the tuyere zone of the blast furnace. The release of pulverized coal particles outside the tuyere zone causes a decrease in the coke replacement ratio, a deterioration in the viscosity of the slag and the gas permeability of the lower part of the blast furnace.
The complete combustion of coal dust particles in tuyere chambers is determined by the fractional composition of coal, the content of volatiles, the temperature of the tuyere zone, and the oxygen content in the blast.

On the basis of theoretical and practical studies, it has been shown that within the tuyere zones, particles smaller than 200...100 µm can completely burn out. The negative side of reducing the size of injected coal is a significant increase in the cost of preparing pulverized coal, a decrease in the productivity of grinding equipment, an increase in coal losses, etc.
The combustion process of coal particles can be divided into three stages:

1. heating and release of volatile substances;
2. ignition of volatile substances and degassing;
3. combustion of carbonaceous residue and melting of inorganic elements of coal.

The first stage involves the heating of a coal particle from ambient temperature to 450 °C, proceeds almost instantly and takes no more than 5% of the total burning time of the particle. The heating time is directly proportional to the particle diameter and inversely proportional to the temperature around the particle. Moreover, the influence of the particle diameter on the heating rate is more significant.

In reality, the process of degassing and the third stage - the combustion of the carbonaceous residue - do not take place strictly sequentially, but overlap each other. That is, the combustion of the carbonaceous residue begins before the completion of the degassing process. The burning time is determined by the formula:

where ρ is the particle density, g/cm3; d—particle diameter, mm; β is the substance transfer number (cm/s), determined by the Rantz and Marshall equation; C_O2 is the oxygen concentration in the gas space, mol/cm3. The combustion of the coke residue occupies a significant part of the process, and the combustion time is directly proportional to the particle diameter, inversely proportional to the oxygen content, and at this stage does not depend on the ambient temperature.

The presented description gives a qualitative description of the process of combustion of coal particles in the tuyere hearth. In reality, the combustion process of particles is more complex - during combustion, the particles change their speed relative to the flow, the size and shape of the particles change, and the coefficients of heat and thermal diffusivity change. The temperature of the gas medium and the oxygen content in it are also variables.

It should be noted that in the tuyere hearth of a blast furnace, the conditions for the combustion of coal dust are more favorable:

• dust is fed into a hot blast stream with a temperature of 1100...1250 °C, moving at a high speed, as a result of which the dust warms up well and disperses;
• there is a significant space in front of the tuyeres of the blast furnace with a low concentration of circulating pieces of coke and a high concentration of oxygen - in this volume, the flare process of burning coal dust is developed;
• unburned dust particles, falling on pieces of heated coke with a melt film, can stick to them and, returning to the tuyere zone, burn out.

However, even under such conditions, some of the coal dust may not burn. Reducing the size of the coal particles and increasing the temperature shortens the time required for complete combustion. In this case, an increase in temperature has a greater effect on the completeness of the process than the particle size.

The performed calculations show that when particles of 100 µm in size are blown into the tuyere zone and the blast temperature is 1000 °C, about 60... the rest will reach the boundaries of the zone in the form of degassed particles. The further behavior of unburned particles can develop according to one of the following scenarios:

• secondary gasification of dust carbon with CO2;
• oxidation of coal dust carbon with liquid phase oxides (FeO, SiO2, MnO, etc.);
• capture of particles by charge with transition to the lower layers of a blast furnace with subsequent combustion in tuyere hearths.

According to calculations, regardless of the consumption of injected coal, 66% of all unburned coal is carried out through the top, 23% is consumed in the carbon gasification reaction, and the remaining 11% enters the central zone of the hearth of a blast furnace.

The study of the composition of the flue dust for the carbon content of coke and blown coal showed that in dry dust the carbon content is about 55%, of which 90% is coke carbon, and 10% is semi-coke carbon from coal dust. Based on the total removal of blast furnace dust, the removal of coal dust through the blast furnace is about 1% of the blown coal.

Coal reactivity, low ash content, low flash point and low volatile content are the most favorable combination. The content of sulfur and phosphorus is limited by the specific melting conditions and the requirements for the content of these elements in cast iron. Thus, in relation to the quality characteristics of pulverized coal and parameters of a blast furnace, the efficiency of its injection is determined by the following fundamental features:

• application of low-ash coals for PUT (5...14%);
• crushing of PUT up to 22...75 microns;
• acceptable coal grindability index (HGI);
• uniform supply of pulverized coal into the tuyeres of the blast furnace (non-uniformity ±4...10%).

World practice of using coal for PUT

The characteristics of the coals used as PUT are given in Table. 6.

Table 6. Characteristics of coals for PUT

For injection purposes, coals with low coking properties are used - CSN index less than 4 units, fluidity within 200 ddpm. Sulfur content is limited to 0.6%, ash content - no more than 10%.

It should be noted that coals with a high content of volatiles (32...38%) and coals with low volatiles (15...20%) are mainly used for injection:

Figure 4 - The content of volatile substances in coals for PUT

Coals with a low volatile content are characterized by a high carbon content, which greatly increases the coke replacement ratio. At the same time, high volatile coal has a low coke replacement ratio but good combustion efficiency. In addition, the use of coals with a high content of volatile substances for injection promotes the reduction reaction due to the higher hydrogen content in such coals.

In many cases, in order to improve the technological controllability of the process, coal mixtures of high and low volatile coals are used in order to control the content of volatile substances and the ash content of injected PUT. In addition, with the joint injection of pulverized coal and natural gas, for economic efficiency, it is possible to increase the proportion of high-volatility coals in mixtures during periods of increasing natural gas prices. This makes it possible to partially compensate for the reducing ability of the resulting gases due to the hydrogen of volatile substances.

On the curve of the relationship between coal type and plastic properties, coals for injection as PCI occupy the extreme positions:

Figure 5 - Relationship between coal type and plastic properties

Such position of coals for PUT is directly reflected in their price. PCI coal is a category of coal not suitable for coking. This coal is inferior in price to premium brands of coking coal (-31% on average per year). But the use of pulverized coal injection technology saves expensive coke, which results in price superiority over coking coals of the Semi Soft category (+12% on average per year). The dynamics of price changes is shown in fig. 6.

Figure 6 - The ratio of metallurgical coal quotations

Implementation of the technology of injection of PUT in the Russian Federation

Despite the fact that the first experiments on injection of PUT in the USSR date back to the middle of the 20th century, this technology has not yet found wide application in Russian enterprises. Causes:

• the presence of excess reserves of natural gas;
• complex infrastructure for the preparation, storage and supply of ICT;
• unresolved problems with the supply of pulverized coal to blast furnaces (tuyere design, distribution uniformity);
• the need for parallel investment in improving the quality of coke and iron ore.

The last attempt to implement the technology of injection of pulverized coal in the Russian Federation was the implementation of the project at Tulachermet in 1992-1993. During the experiment, it was not possible to solve the issues related to the supply of PUT to the blast furnace.

Until now, the interest in the technology of injection of PUT has been of an academic nature. But the changed economic conditions led to a revision of the strategy for the development of domestic metallurgy. The current trend of increasing the cost of natural gas for industrial enterprises prompted the leading metallurgical companies of the Russian Federation to implement projects for the injection of pulverized coal (NLMK, Evraz ZSMK, Evraz NTMK). Considering the more complex technical and technological conditions of Russian enterprises (Table 7, see section "Download/Supplementary Literature") and the quality of the domestic coal base, the implementation of projects for the injection of pulverized coal will be fraught with certain difficulties, and it is unlikely to achieve high rates in terms of the amount of injected pulverized coal and the coke replacement ratio.

Table 7. Technological conditions of blast furnaces

However, the transition to a new technology is an obvious step towards optimizing the cost of pig iron through a combination of various technological substitutes for coke.

If we talk about the coal base for PUT in the Russian Federation, then it seems possible to use coals with low coking properties (GZhO, SS, TS) and thermal coal grades bordering on coking grades (G, T) for these purposes. The combination of high volatility (G, GZhO) and low volatility (SS, TS, T) grades will make it possible to create controlled coal mixtures for use as pulverized coal.

The quality and uses of coal are largely determined by the composition of the original plant material and the degree of metamorphism. The description of the main qualitative characteristics of metallurgical coals is given. A special place is occupied by coals for use as pulverized coal fuel (PCF). The requirements for the successful implementation of the technology of injection of pulverized coal are listed, the features of combustion of pulverized coal in a blast furnace and the specifics of the implementation of the technology of injection of pulverized coal in the Russian Federation are reflected. The requirements for coals for use as PUT are given and the grades of coal for use as PUT are listed.

• pulverized coal fuel
• coal quality for PUT
• PUT price
• ITB requirements

Main literature:

Supporting literature:

• Injection of PUT at the threshold of a new century ("NChMZR" 02.2001)
• Improving the quality of raw materials during the injection of pulverized coal ("NChMZR" 03.2001)
• Requirements for the quality of coke for BF with high consumption of pulverized coal ("Steel" 06.2009)
• Prospects for the use of PUT in the DCs of Ukraine and Russia ("Stal" 02.2008)