RU2707276C1 - Preparation method of pulverized coal fuel for combustion - Google Patents

Abstract

FIELD: heat power engineering.

SUBSTANCE: invention relates to heat engineering, namely to technology of burning hydrocarbon fuels, including low quality. Described is a method for preparation of pulverized coal fuel for combustion, which consists in drying and crushing crude coal, wherein said coal is coated with oxides and/or hydroxides of iron in the form of a suspension or dry powder spray, wherein concentration (amount) of deposited iron oxides and/or iron hydroxides should not exceed 0.4 % of the weight of the coal. Iron oxides and/or hydroxides are also applied on coal in the form of suspension in modified liquid glass, in which they make not more than 5 %.

EFFECT: reduction of average time of release of volatile substances, increase of rate of coagulation of magnetic particles, reduction of slagging of walls of boilers due to introduction of additive from iron oxides on surface of dust particles in a hammer coal mill, and also reduction of emission of ash aerosols into atmosphere.

7 cl, 5 dwg, 1 tbl, 9 ex

Description

The invention relates to a power system, and in particular, to a technology for burning hydrocarbon fuels, including low quality.

One of the main problems of the operation of large pulverized coal boilers is the accumulation of slag deposits on the walls of the boilers. This problem is especially aggravated when the boiler switches to a new type of fuel, for which this boiler was not originally designed for. This approach to the use of another type of fuel, often with poorer performance, is observed everywhere throughout the world. The reasons for this approach can be both economic and the depletion of stocks of high-quality readily available type of coal fuel.

Deposits on the walls can be divided into soft and hard. Solid - difficult to separate from the walls by conventional methods, withstand large shock loads and have a large magnetization. The microprobe analysis of slag deposits on the boiler walls shows the presence of a significant proportion of magnetic particles in hard, solid (non-loose type) deposits that are fixed on the boiler walls. It was found that this mixture consists mainly of iron oxides such as magnetite. After some time, a complete stop of the boiler is required to clean the boiler walls from these deposits.

The analysis of the literature on magnetic particles in boilers showed that the fraction of iron oxides in these particles increases tenfold (http://earchive.tpu.ru/bitstream/11683/30400/1/TPU211194.pdf).

Magnetic particles are formed during the combustion of a coal dust particle in high-temperature flares of large boilers due to the early emission of volatile particles from such a particle, with the removal of particles containing iron from the body of the coal matrix. Oxidation of iron occurs already in the combustion shell around such a particle in the zone of entry of an external oxidizing agent - oxygen. In this case, the particles of magnetic iron are small in size (less than 1 micron), therefore, when attracted to the forming precipitate on the walls of the boiler, they harden it to a concrete state.

To reduce the deposition of particles on the wall, it is necessary to increase the aggregates into which magnetic particles are collected. It is due to the magnetic dipole interaction. Then these aggregates begin to sediment (precipitate) down, the pores of the sediment (like small particles) do not clog on the walls, as a result of which the sediment on the wall should become loose and fall down into the boiler hopper. The deposition of particles suspended in hot gases on the cold walls of boilers and heat exchangers is undesirable. The resulting layer has low thermal conductivity, which leads to a deterioration in the thermal characteristics of the apparatus. The density of the sediment on the wall of the boiler largely depends on how new particles are embedded in this precipitate.

From aerosol physics it is known that the process of deposition of particles on a colder surface from a hotter gas is very efficient by the thermophoretic mechanism.

The thermophoretic force (it weakly depends on the particle size in the size range up to 5-10 microns) drives the particles out of the stream in the boiler (with a diameter of more than 1-6 meters). Modern boilers are large in size, which is important for estimating how many particles reach the wall of the boiler, how many will fall down or rise up the next turns in the boiler. And already at a distance of several millimeters or less, magnetic attraction between the iron-containing particles takes effect, compacting the sediment. For example, the parameters of the CHPP-5 boiler, Novosibirsk, where we carried out part of the experiments, are described here (http://scbist.com/scb/uploaded/kotly/4-parovye-kotly.htm).

With an increase in the thickness of the precipitate on the cooling pipes (approximately 300 ° C of the water temperature inside these pipes, and in the boiler plume in the center of 1200-1600 ° C), the precipitate (deposition) begins to warm up to 800 ° C and above. It begins to sinter, condense and very tightly fit the cooling pipes. What forces to stop a copper and to bring down a deposit manually with special hammers. In areas in which the maximum growth of boiler deposits on the walls occurs (the upper third of the boiler for Novosibirsk TPP-5, for example), the gas temperature is about 1600 ° C.

The heating of the precipitate leads to sintering of relatively fusible particles with iron oxides (and calcium, for brown coal, for example) and the formation of a very hard hard precipitate.

Our analysis (numerical and study of samples) showed that it is also necessary to take into account the sedimentation forces and the structure (fractality) of aerosol particles [S.E. Pashchenko, K. K. Sabelfeld, Atmospheric and technogenic aerosol: kinetic, electron-probe and numerical methods of investigation, Volume 1, Computing Center SB RAS 1992; patent RU 2282742 - Method for burning solid rocket fuel, 2004].

In those conditions when magnetic forces are not determining, precipitation on the boilers is loose and fall down themselves in the mode of operation of the boiler without stopping it. To do this, there are cold pallets at the bottom of the boiler with the desired angle of inclination, along which such loose sediment rolls into the external dump.

The closest analogue is the technical solution described in patent RU 2678310 dated 02.11.2018, in which a modified liquid glass (MZH) is applied to the coal before grinding, which has a high wetting coefficient of the surface of coal dust generated during coal grinding.

MFZ fills cracks (gaps) in coal particles formed during the grinding process, then when such a particle is heated in a flare at the initial stage of heating, MFZ in the crack turns into a high-temperature silica gel, and prevents the emission of volatiles.

Surface active agents (SAS) can serve as modifiers in liquid glass. For example, sodium stearate C17H35COONa can be used - this component is cheap and non-toxic.

But the specified technical solution is aimed at ensuring, when using it, efficient burning of pulverized coal fuel with the formation of an environmentally cleaner high-temperature flame with a decrease in emissions of nitrogen oxides, as well as a reduction in dust formation and explosion hazard.

The objective of the invention is to develop a method of burning coal, which minimizes or eliminates the formation of solid magnetic deposits on the walls of the boilers, which will reduce the downtime of the boilers under cleaning and avoid damage to the walls of the tubes of the boiler during rough mechanical cleaning of deposits, and will also expand the range of coals that have a large slag ratio (but cheap).

To solve the problem, it is necessary to convert the particles of ash sediment on the walls of the boilers and in the emissions from the boilers in front of the electric filters into the optimal structures, hardness and fractality in size. To solve the problem, it is necessary to learn how to control the properties of the dispersed phase (aerosols of the mineral residue) in the boiler volume (size and fractality, friability) to minimize the rate of wall overgrowth. Physically, this is achieved by accelerating dozens of times the process of aerosol coagulation.

Thus, it is necessary:

- change the combustion modes of single dust particles; due to the presence on their surface of additional magnetic particles, which, when heated by a dusty coal particle, block the process of opening primary gaps (as in the prototype), but also additionally intercept the gaps of iron oxide particles from the coal matrix during subsequent opening. These particles of iron oxides are always formed during the combustion of coal dust particles, since coal always has a mineral admixture of iron oxides of various types. But the addition to the surface of dust particles introduced in a hammer mill should accelerate their coagulation above the surface of a burning particle, increase their size, and change their shape. Which, as mentioned above, leads to the formation of fractal particles and to loose sediment on the walls of the boilers. The loose sediment then falls down into the hopper under the action of gravity.

- increase the size of dust particles for more efficient sedimentation in cold and (or) hot ash collectors;

- increase the efficiency of charging particles in electrostatic precipitators to increase the efficiency of electrostatic precipitators; when we increase the fractal particle size, the electron diffusion charge in the electrostatic precipitator will be faster, which means that the degree of purification will be higher.

The main technical result of the claimed invention is to reduce the average time for the emission of volatiles, increase the rate of coagulation of magnetic particles, reduce slagging of the boiler walls by introducing an additive of iron oxides onto the surface of dust particles in a hammer coal mill, and also reduce the emission of ash aerosols into the atmosphere.

The technical result is achieved by a method of preparing pulverized coal fuel for combustion, including drying and crushing of raw coal, and on this coal is applied oxides and (or) hydroxides of iron in the form of a suspension or dry powder spray, while the concentration (amount) of supported iron oxides and (or ) iron hydroxides should be no more than 0.4% by weight of coal.

At the same time, iron oxides and / or iron hydroxides are applied to coal before crushing in the form of a suspension with a content by weight of iron oxides from 10 to 50%.

According to the method, oxides and / or hydroxides of iron are applied to coal in the form of a dry powder spray at the inlet or outlet of a hammer mill with a particle size of no more than 0.5 μm in the spray stream.

Oxides and / or hydroxides of iron are also applied to coal in the form of a suspension in modified liquid glass, in which they make up no more than 5%.

In the method, iron oxides and hydroxides are heated before being deposited on coal until the appearance of magnetite.

In this case, iron oxides and hydroxides are heated in a magnetic field before being applied to coal until the magnetization of all iron-containing compounds is achieved.

An aqueous suspension of iron oxides and hydroxides is intensively saturated with oxygen (bubbling).

We give estimates for boilers 6 TPE-214 / A TPP-5, Novosibirsk. This technique will allow, with proper operation of the boiler, to increase the fall in deposits in the lower bunker from 5-7% for CHPP-5 today on brown coal, to 60-70%. This dramatically reduces the load on electrostatic precipitators and the release of aerosols into the CHPP-5 pipe into the atmosphere.

When grinding on the initial piece of coal with a size of less than a few centimeters, a multiple powerful effect occurs on the grinding surface. It is known that under such loads, the surface and volume of coal pass through the process of sharp formation of gaps (for example, nucleating in dislocation growth). These gaps, in turn, generate an emission of small particles of coal (from nanometers to 1-2 microns).

When heated, iron compounds in coal pass into the gas phase and into the aerosol phase (they are much more volatile than the oxides of silicon and aluminum, the main components of the coal ash sediment).

According to the invention, in the mode of grinding coal in hammer mills, iron oxides and hydroxides are introduced, both in the form of a suspension (wet spray) and in the form of a dry powder spray. For example, iron (II-III) ferroadditives are introduced into the hopper before grinding in the form of a highly dispersed aerosol through a dry air nozzle.

As our model and bench laboratory studies show, iron oxides are concentrated in the field of fresh activation gaps during grinding. And when a dust particle with such a modified surface reaches the beginning of the torch in a coal boiler (particle size fraction of the order of 100 microns), heating of its surface begins. When heated, particles of iron oxides on the surface of a coal particle at the base of the boiler plume transform into 5-15 nm ferromagnetic particles. An exchange spin mechanism arises in the regime of creating supermagnetism, small particles turn into a single magnetized domain, in which all the spins of the iron oxide molecules are directed in the same direction. This leads to a strong dipole magnetic field near such a particle, and hence to effective capture by another of the same particle. If the particles are initially large - more than 50-100 nm, several domains will appear inside them, which will dampen the general magnetic field due to their random orientation in space. This is bad for our task. Thus, we set requirements for the sizes of introduced particles of iron oxides in a hammer mill. For, we repeat, a sharp increase in the strength of the magnetic dipole-dipole attraction of such particles. Which leads to an increase in the rate of their coagulation processes in the combustion zone of each pulverized-coal particle.

As a result of this specific coagulation of magnetic domain (single-domain) particles, not only fast coagulation occurs, but also the magnetic particles are linked north-south by polarities. This leads to the formation of chains that are locked into polyhedra at steps 5–6 (on 5–6–7 sides, almost flat). Such a structure is extremely loose in itself. At the same time, its basis is the structure of magnetite, the Curie point of which is high enough to conduct the coagulation process near the combustion surface of a dust particle of 50-100 μm coal dust particles.

These small 3-6 nm magnetite particles are so porous that they easily capture the bulk of particles of silicon and aluminum oxides that escape from the particle at a later stage of combustion (for example, coke combustion) by the fractal filter mechanism. Such mixed particles are easily observed under an electron microscope, since the density of iron oxides is more than 5 g / cm ³ and significantly exceeds the density of aluminum and silicon oxides.

Such a precipitate is visible in the form of loose gray-yellow deposits. It easily falls off the walls (as mentioned above).

We studied samples taken at CHPP-5 when working on brown coal - fallen deposits, coal before grinding, coal after grinding, ash trapped by particle electrostatic precipitators, their magnetic properties, microwave response, and precipitation hardness were determined.

In FIG. 1 and FIG. Figure 2 shows the structure of the real sediment from TPP-5.

Model experiments with ground brown coal from CHPP-5 were carried out - the modes of deposition of iron oxides and hydroxides in model laboratory ball mills were substantiated.

In FIG. 3 shows a magnetic agglomerate that has formed in the volume of a model boiler. In FIG. 4 shows the result of the deposition of such magnetic agglomerates on the walls of the boiler (in this case, a 600 micron needle made of boiler steel). High porosity and friability of the sediment due to magnetic coagulation of particles are visible.

In FIG. 5 image in the reflected and in the light rays of a fragment of magnetic deposition with a finely dispersed phase on the surface of primary pulverized-coal particles.

Observation and determination of the process of delaying the ignition of a coal particle (the beginning of the emission of volatiles) due to the modification of the combustion surface with various additives was carried out using a plasma torch to ignite primary particles with a size of about 50-150 μm and laser illumination to visualize highly dispersed aerosols.

At the base of the torch of a model gas burner, up to 10 cm in length and 2 cm in diameter, coal particles were introduced from above (injection or drop in a gravitational field). Particles were picked up by the torch stream, moved in it, heated up, and began to burn. Everything was recorded on a high-speed camera, both in its own glow and in the strobe-illumination mode with a frequency of 200-1000 Hz. When the release of volatiles and their ignition begins, this can be seen in the gas halo of glow around the particle trajectory. After the termination of the emission of volatile gas, the gas halo disappears, and a bright (white contrast), clear and narrow trace of the particle is seen in the heterogeneous combustion mode. That is, only the process of oxygen oxidation of the carbon residue.

Thus, in one experiment, three main phases can be distinguished. The first is heating, the second is the combustion of volatiles, the third is the burning of coke residue.

Example 1 - input of dry powder.

An iron oxide powder was prepared from a ferric iron solution. Dried at 50 ° C for 40 hours. Moreover, several samples were dried in a magnetic field of about 500 Oe (4000 A / m), which is approximately 100 times stronger than the Earth’s average field. The powders were finely dispersed, with a particle size of less than 0.1 μm, since they were made in solution by bubbling microbubbles of an external oxidizer (oxygen).

Dry input was carried out in a small ball mill at the same time as grinding primary brown coal (Borodinsky open pit, CHPP-5, September 2018).

After that, powder coated coal was used in standard combustion tests, as described above and in the main prototype. The ratio of coal to dry powder of iron oxides (hydroxides) varied over a wide range of ratios (100 to 1, 100 to 0.1, and 100 to 0.01). The uniformity of the application was controlled by burning in a model burner and by tracking the intensity of the yellow-brown cloud of glow along the ignition and combustion paths of coal dust particles.

Example 2 - input in the form of a suspension.

Injection in the form of a suspension was distinguished by the fact that the solutions of iron oxides were not dried, but only partially sedimentally enriched by draining the upper part of the solutions after turning off the blowing with air bubbles (up to 90-95% of the initial concentration).

The remaining part was applied through a spray directly to coal before grinding (or after grinding on already ground). The main requirement is uniformity of application, which was achieved by mixing coal under a spray jet. Concentrations varied in a range, as in example 1 above.

Testing of coatings was carried out by the method of model combustion in model burners (described above). The method of suspensions is more moody in terms of the preparation of samples of coal with ferrous compounds, although faster because of the absence of a long drying process of the samples.

Example 3 - input with liquid glass.

This method is based largely on the technologies and methods described by us in the prototype. The main action is the introduction into the solution with iron oxides and hydroxides of a small fraction of the usual type of liquid glass. Input is carried out in different proportions.

After intensive bubbling with an oxidizing agent (air) for at least 30 minutes (complete mixing 10 times), you can either dry the solution or prepare a suspension, as described above. The application to coal particles does not differ from those described above, however, care must be taken that the temperature of the substances does not exceed 60-70 ° C. This is necessary in order to avoid premature formation of silicon oxides during the drying of liquid glass to complete grinding or complete mixing of coal in the coal preparation process.

Example 4

Coated particles with and without coating were burned in a gas burner, the exhaust of which was included in a metal container with a volume of 60 liters of rectangular cross section. The resulting particles were selected by vacuum sampling and studied in optical and electron microscopes. Primary particles have a size of the order of the characteristic for the coagulation limit in such a regime of burning coal dust. This is about 80-120 nm. With a width of the distribution spectrum of about 1.3 σg. (σg is the parameter of the lognormal distribution).

The proportion of agglomerates for burning coal dust particles without coating is not more than 5% percent of the total number of particles. The number of primary particles in such agglomerates is 3-5 pieces. These are typical characteristics when burning different particles about 100 microns in size under conditions of high capacity.

When applied to primary coal particles of iron oxides, as proposed in this application, the spectrum of the selected particles and their type, composition, were completely different. 90-95% of the particles were in the composition of agglomerates. Agglomerates consisted of dozens, sometimes up to hundreds of primary particles. Moreover, these were not three-dimensional spherical agglomerates, but elongated chains or planar formations. Their porosity, or the so-called fractal dimension, were small.

Evaluation of electron microscopic photographs by density contrast gives the density of such particles at the level of 0.3-0.8 grams per cm ³ . Measurements of the deposition of such fractal agglomerates in magnetic fields showed their magnetic moment. As a result, coagulation is accelerated due to the interaction of magnetic dipoles of primary particles, when they are combined in a boiler flame (capacity).

Example 5

We carried out burning in the described metal container (boiler model) coal dust particles without coating and coated with iron oxides of sufficiently large quantities (up to 500 grams). In order to create a deposit on the metal walls that mimic the real surface of the boiler (wall material). Then the container was cooled, the precipitate from the walls and bottom was taken by special methods, weighed, and its characteristics were examined using optical electron microscopes.

In nine experiments on burning equal amounts of coated pulverized-coal particles, the sediment at the bottom (mostly at the walls) exceeded from 4 to 7 times the weight of the sediment at the bottom of unmodified coal particles. Accordingly, the total weight of the precipitate on the walls of the microcottle from the combustion of particles with a shell was just as less than when burning ordinary coal particles. In both cases, the primary particles of coal were prepared from grinding in a brown coal hammer mill at TPP-5.

Morphological analysis of the sediment (color, particle shape, hardness of attachment to the wall, etc.) showed that coated carbon particles give a friable sediment of a light brown type. The sediment is easily separated, cut with a scalpel. And with vibrations of the boiler wall, it simply crumbles down to the bottom by 30-70% of its primary mass.

When burning simple coal particles in a number of places, dense, blackish deposits are formed on the walls of the boiler, which are magnetic in themselves. And on which it is impossible to apply significant scratches with a scalpel. The hardness of such deposits strongly depends on the location on the wall of the micro-boiler. And maximum in areas of turbulent rotation of the jet and high torch temperatures.

Our studies show that the mechanism of formation of deposits of different densities and hardness depends on the density of the primary fractal agglomerates, which approach the wall and are fixed on it or on the surface of an already growing deposit. We indicated in the example above that particles with an additional magnetic dipole moment have a much lower density (3-8 times) during coagulation.

Example 6

The method of dry spraying of magnetic oxides on the primary brown coal of the Borodino section and processing the mixture in a small ball mill yielded pulverized coal particles.

5%, 2%, 1%, 0.5%, 0.1%, 0.05%, 0.01% by weight of brown coal were deposited. The criterion was microscopic studies of the obtained modified particles and the combustion rate of such particles in the photo-recording mode of gas combustion and coke residue combustion (described above). Additionally, the magnetic properties of the resulting particles were studied using the methods of a point magnetic probe (5-10 μm localization) and the method of suspension mobility.

At 5%, 2%, and 1%, an excess fraction of particles of iron oxides on the surface of the pulverized-coal particles of the prepared fuel was detected by color contrast. Their size was more than 1-2 microns, the color was dark orange, and when burning in the burner they gave additional burning tracks with a greenish tint. That is, they did not participate useful in the process of magnetic passivation of the cracks of pulverized-coal particles.

When studying a mixture with 0.01% iron oxides by our methods, we did not observe significant changes in the morphology and combustion conditions in the tracks. This is the limit of sensitivity of our experimental methods.

When studying a mixture with 0.05%, excess particles of dark orange iron oxides on the surface of pulverized-coal particles were still observed, although 90-95% of the tracks were classical combustion with a delay in gas combustion, as indicated in the table above.

When studying a mixture with 0.1%, the number of useful tracks with a delay of gas ignition was about 30-50%.

As is clear from a theoretical consideration of this process of crushing the mixture into dusty coal particles in hammer mills, the result of the coating efficiency will depend on the degree of grinding of the particles (function of their size distribution) and the impact load on the fracture of particles with a new gap formation on their surface. However, in practice, control of such characteristics is very laborious, and part production is not possible.

Thus, we propose to take a generalized criterion of 0.4% or less in terms of the content of iron oxides based on the mass of coal being milled.

Example 7

In a number of production situations, it is convenient to apply iron and hydroxide oxides in the form of a suspension at the CHPP when working with different coals. This provides a more uniform application. There are two criteria for this application. There should not be much water, but there should be enough water to obtain a homogeneous primary suspension and for the absence of a phase of water coagulation of glandular magnetized particles.

Aqueous solutions (suspensions) in a mixture with a powder of ferrous particles were taken from 80, 60, 50, 30, 10, 5, and 1%. Percentage refers to the mass fraction of glandular particles.

At 80, 60%, the spray in the nozzles is difficult, the nozzle nozzle quickly clogs. Especially if iron oxides have primary magnetization.

When spraying a 5 and 1% solution, analysis of the surface of the primary coal particle showed that when the droplet dries from spraying the solution, the oxide particles are pulled together in separate lines on the surface of the primary coal particle. That is, subsequent crushing leads to significant inhomogeneities in the coating of dust particles. Which affects the heterogeneity of the ignition tracks.

Therefore, the proportion of oxides in the solution from 10% to 50% allows us to satisfy the signs of optimal passivation of coal particles to the stage of grinding.

Example 8

In some production processes it may be advantageous to apply particles of iron oxides to the prepared pulverized coal particles before they enter the burners of powerful boilers. In this case, the application is proposed to be carried out with a dry gas nozzle, using, for example, secondary air paths or additional injection along the nozzle perimeters. The main condition is that the particles of iron oxides must be dusty, that is, less than 0.5 microns. This size allows you to create a homogeneous aerosol cloud and enter it into the burners. The maximum size is determined by the size of the cracks in the pulverized-coal particles, which must be magnetically passivated. As shown by electron microscopic studies, the spray particles have a sufficient diffusion mobility (0.001 cm ² / s) in the region of small sizes, which allows them to reach gaps in the dust-coal particles, and to be fixed on their geometric irregularities due to Van der Waals forces over time being in the dust ducts before injection into the torch.

Dry spray particles with an average size of 1, 0.1 and 0.02 μm were investigated. The spread of the lognormal size distribution function was 0.5–0.9 σg.

For 1 μm particles, the inertia forces began to play the role of atomization during atomization, and more than 60% by weight of such particles were deposited on the details of atomizer designs.

For particles of about 0.01 μm, the Van der Waals forces with respect to their mass are significant, which led to their almost uniform deposition on the surface of pulverized-coal particles. This means that the passivation of cracks accounted for less than 10% of their mass.

The most optimal sizes are about 0.1 μm. Both in terms of the mass entering the gap and the efficiency of diffusion to it near the surface. Additionally, the thermophoretic force begins to act for such particles (the difference between the injection temperatures and the particle surface temperature). The deposition on the surface takes on a structure that largely reflects the structure of the cracks and stresses on the pulverized-coal particle before entering the torch.

Example 9

In patent 2678310 (prototype), we applied modified liquid glass to cracks in pulverized-coal particles.

It was experimentally shown in model plants that the introduction of liquid iron into the primary powder of iron oxides at a level of no more than 5% allows all operations to introduce Fe-liquid iron to crushers and nozzles. At a higher percentage, problems begin, since the viscosity of liquid glass is significant and problems begin to clump the iron powder in the spray nozzles even at still low temperatures in the air duct. For example, at 10% FS, the particles of oxides irreversibly coalesce by weight of iron oxides, and when crushed with coal in model ball mills, at the points of increase in local temperatures above 130 ° C, pulverized-coal particles simply begin to ceramize.

According to the literature, as well as our experiments, it is possible to sharply increase the magnetism of iron oxides and hydroxides if they are heated to temperatures above 180-250 ° C depending on the size of the primary particles.

If the glandular particles are heated in a magnetic field, the magnetization of such particles can be increased. When sprayed, they lose adhesion to each other, and therefore move like ordinary particles (preferably about 0.1 microns in size). However, when the first particles are fixed on the surface due to Van der Waals forces, subsequent particles will be attracted (or repelled) due to the interaction of their magnetic moments. That allows you to ultimately adjust their structure, the density of the bridge of sediment between the particles of primary combustion (5-100 microns). At the same time, it is the density of glandular deposits on the walls of large boilers that is most important from the point of view of their fastening strength in the boiler (Alekhnovich A.N. Effect of fineness of coal grinding on slagging of boilers - Electrical stations, 2015, No. 10; Alekhnovich A.N. slagging as an indicator of slagging properties: determination and application (part 1) - Electrical stations, 2014, No. 3, pp. 16-24).

Our experiments show that heating the primary powder of glandular oxide particles and heating in a magnetic field significantly increase the magnetization (or magnetic susceptibility) by tens of times.

Claims (7)

1. A method of preparing pulverized coal fuel for combustion, including drying and crushing of raw coal, characterized in that the iron is deposited with iron oxides and / or hydroxides in the form of a suspension or dry powder spray, the concentration of supported iron oxides and / or iron hydroxides be no more than 0.4% by weight of coal. 2. The method according to p. 1, characterized in that iron oxides and / or iron hydroxides are applied to the coal before crushing in the form of a suspension with the content by weight of iron oxides from 10 to 50%. 3. The method according to p. 1, characterized in that the oxides and / or hydroxides of iron are applied to the coal in the form of a dry powder spray at the inlet or outlet of a hammer mill with a particle size of no more than 0.5 microns in the spray stream. 4. The method according to p. 1, characterized in that the oxides and / or hydroxides of iron are applied to the coal in the form of a suspension in a modified liquid glass, in which they make up no more than 5%. 5. The method according to p. 1, characterized in that the oxides and hydroxides of iron before applying to coal are heated to the phase of the appearance of magnetite. 6. The method according to claim 5, characterized in that the iron oxides and hydroxides are heated in a magnetic field before being deposited on coal until the magnetization of all iron-containing compounds is achieved. 7. The method according to p. 5, characterized in that the aqueous suspension of iron oxides and hydroxides is intensively saturated with oxygen (bubbling).

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