RU2493240C2 - Method of directed introduction of reagent to control slag forming as result of combustion of coal with increased content of iron and/or calcium - Google Patents

Abstract

FIELD: machine building.SUBSTANCE: invention refers to a method of reduction of cohesive properties of slag and/or its adhesion ability to surface of a furnace chamber and thus reducing degree of contamination. The above method involves combustion of slag-forming coal in combustion zone; coal with increased iron content exceeding approximately 15% is used considering weight of ash and expressed as FeOand/or calcium content exceeding 5% considering weight of ash and expressed as CaO, at total excess oxygen; removal of gaseous combustion products through heat-exchange equipment under conditions providing cooling of the slag formed at fuel combustion; and introduction to combustion zone of the furnace chamber till contact with the above heat-exchange equipment, to gaseous combustion products of aqueous aluminium trihydroxide in the amount, with drop size and in the concentration forming nanoparticles with the size of less than 200 nm in hot gaseous combustion products, which are optimum to reduce contamination degree and to improve friable properties of the obtained slag. The invention also refers to a method for removal of slag deposits from a furnace chamber and a furnace chamber cleaning and maintenance method.EFFECT: effective slag control; higher operating efficiency of a furnace chamber.8 cl, 2 dwg, 2 ex

Description

Priority Statement

The submitted application claims priority on the preliminary description of US invention No. 61/080,004, registered July 11, 2008 and fully incorporated into this application.

State of the art

[0001] The presented invention relates to a method for increasing the productivity of a combustion chamber, when burning coal with a high content of iron and / or calcium, by reducing the tendency to slag formation on heat exchange surfaces, changing the basic properties of slag to facilitate its removal and actual removal of slag .

[0002] The burning of coal, like any other fossil fuel, is inevitably less efficient than required, and it can also become a source of pollution. Ensuring a high level of productivity in the operation of combustion chambers and controlling the composition of emissions is an important aspect of the energy supply necessary for the development of the economy, while maintaining the quality of the ambient air is necessary for our survival. Since performance and emissions are interrelated parameters, some technical solutions cope with one task to the detriment of another, while not simultaneously achieving both goals. The issue of economical operation of power plants and waste incinerators is socially significant, and the development of new technologies is important to solve this problem.

[0003] The choice of fuel plays an important role in reducing some environmental pollution problems, but cannot completely eliminate them. Some types of coal, such as tar coal of the Illinois and Appalachian coal basins, occupy a significant place in the consumption of many power plants designed for those types of coal, the use of which solves the issue of saving to the detriment of other issues. For decades, the subject of special attention of heat engineers and operators of power plants has been the tendency to slag formation, as well as the properties of slag from such types of coal with a high iron content. There are a number of factors that affect the physical and chemical properties of slag. See, for example, “Energy Production from Combustion of Fossil Fuels,” ed. Certified Engineer Joseph G. Singer, 1991: Chapter 3, Heat Engineering. One way or another, with the current state of industry, there is a trade-off between the choice of cheap coal and the actual economic component of electricity production, for which slag formation becomes a problem. The accumulation of slag is a problem, as it leads to a decrease in heat transfer and often requires long periods of downtime for cleaning equipment.

[0004] A problem associated with the use of coal is the formation of large quantities of ash and fine particles, requiring collection and disposal. In the field of technology, it has become common practice to use additives to control the formation of slag and its properties, but additives can adversely affect the overall parameters of particulate capture systems. Accordingly, the optimal organization of slag control has often been limited, since particulate capture systems do not provide the necessary complete capture of particulate matter. This is especially a problem for long-running power plants where it is not possible to increase the capacity of particulate collection equipment.

[0005] Even more complicating the problem is that coal, depending on its composition, reacts differently to various additives. In general, a formula is not yet known that allows correlating various coal compositions with suitable additives and their amount to ensure the efficient operation of particulate capture equipment. The study of specific coal compositions and the modes of use of additives has attracted the attention of many researchers because of their desire to provide cheap electricity with economically viable emission control measures.

[0006] There is a need for an improved method that would provide more efficient control of slag, especially when using problematic fuels, such as coal with a high sulfur content, which in particular causes slag formation, as well as coal with a high content of iron and / or calcium, thereby increasing the efficiency of operation of boiler equipment and improving economic performance.

Disclosure of the invention

[0007] An object of the invention is to provide an improved method for controlling slag generated in combustion chambers operating on fuels with a tendency to slag formation.

[0008] Another objective is to propose a method for controlling slag produced by burning coal with a high content of iron and / or calcium, with a reduction in the use of chemicals.

[0009] It is also an object of the present invention to provide a method for removing slag from heat exchanging surfaces of boilers generated by burning coal with a high content of iron and / or calcium, while reducing the use of chemicals.

[0010] Another more specific objective is to propose a method for more efficient control of slag by reducing downtime necessary to remove slag.

[0011] An even more specific objective of some embodiments of the present invention is to achieve the above objectives while improving the efficiency of the combustion chamber.

[0012] These and other objectives are achieved within the framework of the present invention, at least in its preferred embodiments, by proposing an improved method for controlling slag in combustion chambers in which slag-forming types of coal with a high content of iron and / or calcium are burned.

[0013] In accordance with one embodiment of the invention, there is provided a method of reducing the cohesive properties of slag and / or its adhesion to the surface of the combustion chamber and thereby reducing the degree of pollution, including: burning slag-forming coal with a high content of iron and / or calcium, with a total excess oxygen; removal of the resulting flue gases through heat exchange equipment under conditions that ensure cooling of the slag formed during the combustion of coal; and also the introduction, before contact with the specified heat exchange equipment, of an aqueous solution of aluminum trihydroxide in an amount, with droplet size and concentration, optimal to reduce the degree of contamination, and, preferably, to increase the fragility of the resulting slag.

[0014] In one of the preferred embodiments of the invention, aluminum trihydroxide is introduced in the form of an aqueous solution, and to determine the values of the flow rate and the choice of the rate of introduction of the reagent, to determine the point (s) of the introduction of the reagent, the concentration of the reagent, the size of the drops of the reagent and / or the kinetic energy of the reagent use the principles of computational fluid dynamics.

[0015] In another preferred embodiment, magnesium hydroxide in the form of an aqueous suspension is added together with a suspension of aluminum trihydroxide.

[0016] According to another embodiment, the invention provides a method for cleaning surfaces of furnaces with slag deposits by introducing an aqueous solution of aluminum trihydroxide in an amount, droplet size, and concentration optimal for contact with small particles formed when the suspension dries, in order to contact existing slag deposits.

[0017] In another embodiment, the invention provides a method for cleaning and maintaining the combustion chamber, comprising an initial dosage of aluminum trihydroxide of about 3 to 6 pounds per ton of coal and about 1 to 2 pounds of Mg (OH) ₂ per ton of coal for time sufficient to reduce slag formation, followed by a reduction in dosage from about 10 to about 50% of the initial values to ensure cleanliness and efficiency of operation of the combustion chamber.

[0018] Other preferred embodiments of the present invention and their advantages are described below.

Brief Description of the Drawings

[0019] The accompanying drawings provide a better understanding of the presented invention and show the advantages of its use.

[0020] Figure 1 is a diagram of one embodiment of the invention.

[0021] Figure 2 is a photograph of a slag sample obtained after a 24-hour cycle of introducing aluminum trihydroxide into the combustion chamber, in which coal with a high iron content was burned, as described below in Example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0022] First, refer to Figure 1, which schematically shows one embodiment of the invention. Figure 1 conventionally depicts a large-sized combustion chamber 10 of the type used to generate steam in the production of electricity, process steam, heating or burning waste. Coal is fed through burners 20 and 20a and burns with air in the combustion zone 21. An advantage of the invention is that coal with a high iron content is used (for example, the iron content exceeds about 15%, for example, from about 20 to 35%, taking into account the weight ash and expressed as Fe ₂ O ₃ ) and / or calcium (for example, the calcium content exceeds about 5%, for example, from about 10 to 25%, taking into account the weight of the ash and expressed as CaO). Another advantage of the invention is that it is possible to effectively control slag for types of coal with a significant sulfur content, for example, about 1% and in the range of about 3 to about 5%. Hereinafter in the text of the description, all fractions and percentages given are given relative to weight.

[0023] The combustion air supplied by the fan 22 and the duct 24 is preferably preheated by gas-gas heat exchangers (not shown) that transfer heat from the duct (not shown) to the outlet of the combustion chamber. Hot flue gases rise and pass through heat exchangers 26, which transfer the heat of the flue gases to water to form steam. Depending on the design of a particular boiler, other heat exchangers can be added to the circuit, including a heat exchanger (downstream, not shown). Untreated slag will tend to form on these heat transfer surfaces located inside a specific combustion chamber in accordance with the design decisions made for the placement of equipment. An advantage of the present invention is that modeling methods, in particular the principles of computational fluid dynamics, are used to determine the initial direction of input chemicals (especially those that are considered effective for specific types of coal in the framework of the present invention) and the optimal placement of their feed devices to reduce and / or control of slag deposits and ensuring the efficient operation of the boiler.

, а датчики температуры (например, 44) - стандартным обозначением

. Оба клапана 42 и датчики температуры 44 соединены с блоком управления 46 посредством электрических кабелей (например, 48), показанных пунктирной линией. Указанные клапаны, датчики температуры и кабели изображены только для иллюстрации концепции, при этом квалифицированный же рабочий, руководствуясь изложенными здесь принципами, сможет оптимально их расположить для надлежащего контроля сигналов и ответных действий оборудования. Блоком управления 46 может быть универсальный компьютер, запрограммированный в соответствие с определенным режимом управления с контурами прямой и обратной связи.[0024] A number of suitable nozzles are provided, preferably with pneumatic spraying, installed in two groups 30 and 30a for introducing only aluminum trihydroxide or aluminum trihydroxide with a suspension of magnesium hydroxide from reservoirs 40 and 40a, respectively. Preferred is the aqueous base of both aluminum trihydroxide and magnesium hydroxide, administered as suspensions and / or solutions, as the case may be. The supply lines (e.g. 41) are represented by a double line in the drawing. Valves (e.g. 42) are represented by the standard designation

and temperature sensors (e.g. 44) with the standard designation

. Both valves 42 and temperature sensors 44 are connected to the control unit 46 via electrical cables (e.g., 48) shown by a dashed line. The indicated valves, temperature sensors and cables are shown only to illustrate the concept, while a skilled worker, guided by the principles set forth here, will be able to optimally position them for proper control of signals and equipment responses. The control unit 46 may be a universal computer programmed in accordance with a specific control mode with direct and feedback loops.

[0025] Aluminum trihydroxide (Al (OH) ₃ ), which the present invention is recognized to be effective in significantly reducing the formation of slag deposits or cleaning slag deposits resulting from the burning of problematic types of coal, is also known as aluminum hydroxide and aluminum hydroxide. Regardless of the type of feed, aluminum trihydroxide is preferred to be mixed with water to be introduced from reservoir 40 through connected lines 41, with or without chemical stabilizers, in concentrations optimal for storage and use, for example, at least about 25%, and preferably not less than 65% solids by weight.

[0026] As will be described later, the concentration and flow rate will be initially determined by simulation methods to ensure that the proper amount of chemicals is supplied to the right place in the combustion chamber and in the right physical form in order to achieve the desired results in reducing slag formation and ease of cleaning. For use in the present method, the substance is dissolved by a method determined, for example, using the principles of calculated hydrodynamics in the range from about 0.1 to about 10%, more strictly, from about 1 to about 5%. When an aqueous solution of aluminum trihydroxide comes into contact with hot gases in the combustion chamber, it is assumed that it consists of very small particles, for example, nanoparticles with a size of, for example, less than 200 nanometers, and more preferably about less than 100 nanometers. An average particle size of from 50 to about 150 nanometers is preferred for the process of the present invention. To ensure this size, it is necessary that aluminum trihydroxide is introduced with water. Small particles are believed to destroy conventional crystalline or glassy structures forming slag. Regardless of the mechanism used, a clear advantage of the invention is that the resulting slag is extremely fragile and can easily be destroyed by brushing, and can also be broken by hand.

[0027] A significant advantage of the invention is an increase in the fragility of the slag, which facilitates its removal. The implementation of the invention also slows down or eliminates the process of deposition of slag. An advantage is also that when introduced in large doses, the method proposed by the invention can practically ensure the removal of already formed slag. The term "increase in brittleness of the slag" means that after processing it takes less effort per unit area to destroy the formed slag compared to the efforts to break the slag formed, ceteris paribus, but without the proposed treatment. The term "slag removal" means that the weight of the slag adhered to the surfaces of the boiler, especially to the heat exchange surfaces, is reduced compared to the original values due to the processing proposed by the present invention. There are also several additional and concomitant advantages of the invention, including a decrease in the amount of SO ₃ for coal with a high sulfur content, a decrease in the pressure drop on the heat exchange equipment, the possibility of using cheaper fuel, a decrease in the formation of CO, a decrease in the formation of CO ₂ due to an increase in the burned fuel, improved heat transfer, reduced downtime, increased productivity, the possibility of rapid cleaning, high purity of heat transfer surfaces, the possibility of complete cleaning and a combustion chamber, as well as the ability to operate equipment with greater efficiency in all modes.

[0028] For most types of coal, the best way is to share aluminum trihydroxide and magnesium hydroxide. Although some types of coal, for example, with a low content of silica salts, can burn, causing fewer problems associated with the formation of slag, nevertheless, the use of magnesium hydroxide, at least in the initial stages, is preferred. It is preferable to prepare magnesium hydroxide from saline solutions containing calcium and other salts, in the General case, from underground salt water or from sea water. Dolomite lime is mixed with these solutions to form a solution of calcium chloride and magnesium hydroxide, which precipitates and is filtered out of the solution. Thus obtained magnesium hydroxide can be mixed with water with or without stabilizers, in concentrations optimal for storage and use, for example, from 25 to 65% solids by weight. For use in the present method, the substance is dissolved by a method determined using the principles of computational fluid dynamics in the range from 0.1 to 10%, more strictly from 1 to 5%. When it comes into contact with a gas stream in a combustion chamber, it is assumed that it consists of nanoparticles of a size of, for example, less than 200 nanometers, and more preferably less than about 100 nanometers. An average particle size of from about 50 to about 150 nanometers is preferred for the method of the present invention. If necessary or depending on preferences, other types of MgO can be used, for example, white magnesia or caustic magnesite, based on the available composition of the substance, providing the required particle size range.

[0029] In order to better achieve the described effect, the invention involves using the advantages of modeling in computational fluid dynamics in mudflows to determine the initial levels of flow rate and to select the initial values of the rate of introduction of the reagent, determine the point (s) of the introduction of the reagent, the concentration of the reagent, the size of the reagent droplets and kinetic energy reagent. Computational fluid dynamics has a transparent scientific apparatus, and in this case it allows you to use all its advantages in terms of supplying a minimum amount of chemicals to ensure maximum effect.

[0030] It is extremely important that the amount of chemicals be a substoichiometric value in terms of the effect on the melting temperature of the slag, which is often recognized as the determining factor for controlling the slag. In accordance with the present invention, there is convincing evidence that the result from the implementation of the present invention is achieved not only due to the relatively small amount of reagent used, but also due to the physical prevention of slag formation with possible borderline chemical and kinetic effects not described in the literature.

[0031] The experiment showed that the initial values of the feed rate, determined by the methods of computational fluid dynamics, can achieve good efficiency with subsequent adjustment depending on the observed results. As a guide for determining feed rates, you can specify that up to about 6 pounds of aluminum trihydroxide (dry active aluminum trihydroxide) or 8 pounds (as 65 -70% suspension) per tonne of coal. For example, when a preferred 70% suspension is added, an amount of about 1 to about 6 pounds of suspension will be effective (more strictly, for example, about 2 to about 3 pounds of suspension). It is also preferable to use up to about 2 pounds of a suspension of Mg (OH) ₂ (at a concentration of about 50-60% solids) per tonne of coal. For example, when a 60% suspension is preferably added, an amount of from about 0.5 to about 2 pounds of Mg (OH) ₂ may be used per suspension per ton of coal, for example from about 0.7 to about 1 pound of Mg (OH) ₂ suspend per ton of coal. Suspensions, if necessary, are diluted, usually to a particle concentration of about 5%, for more local tasks, to about 35% or more.

[0032] The weight of the slag adhered to the surfaces of the combustion chamber, especially to the heat transfer surfaces, is significantly reduced compared to the original values due to the treatment proposed by the present invention, especially when using aluminum trihydroxide and Mg (OH) ₂ at elevated concentrations in the above ranges for example, from about 3 to 6 pounds of aluminum trihydroxide per ton of coal, and from about 1 to 2 pounds of Mg (OH) ₂ per ton of coal. This ability to remove slag provides the ability to clean and maintain modes with a specified initial dosage to remove slag, followed by a reduction in dosage to from about 10 to about 50% of the initial dosage to ensure cleanliness and efficient operation of the combustion chamber.

[0033] It is significant that, for optimal slag removal according to the present invention, calculations of the correct initial concentrations, feed rates and introductions are required to ensure the effective physical appearance of aluminum trihydroxide with the addition, as a preferred option, of magnesium hydroxide introduced into the hot flue gases into the chamber 20 in order to achieve the desired effect of the use of chemicals. The principles of computational fluid dynamics can be used as described in US Pat. No. 7,162,960 to Smirniotis et al. Particle removal equipment (not shown) can be used until the gas stream reaches the chimney.

[0034] In another alternative embodiment of the invention, combustion catalysts and / or chemicals for treating the gas stream may be added to the fuel, to the combustion zone, or by other methods, as described, for example, in US Pat. No. 7,162,960 to Smirniotis et al.

[0035] The following examples are provided to further explain and illustrate the invention, and under no circumstances should be construed as limiting the implementation of the present invention. Unless otherwise indicated, all fractions and percentages are by weight.

Example 1

[0036] This example illustrates the introduction of aluminum trihydroxide into a furnace in which 540 tons of coal are burned per day. Coal is a mixture of tarry coals of the Illinois and Appalachian coal basins, with the following characteristics according to the analysis:

Sample one 2 3 Humidity% 11.28 10.85 10.19 Ash content,% 14.91 13.63 13.91 Volatiles, % 36.03 35.04 Bound carbon% 39.49 40.86 Total, % one hundred one hundred Sulfur,% 3.95 4.44 Highest calorific value, BTU / lb 10742 10730

Coal test analysis is given in the following table: Ash composition: SiO ₂ % 41.44 44.74 42.19 Al ₂ O ₃ % 28.96 09/22 19.9 Fe ₂ O ₃ % 23.16 25.33 30.4 Cao % 1.17 1.74 1.64 MgO % 0.8 0.8 0.74 Na ₂ O % 0.25 0.3 0.25 K ₂ O % 2.37 2.22 2.14 TiO ₂ % 0.96 0.9 0.85 SO ₃ % 0.52 1.4 1.63 P ₂ O ₅ % 0.19 0.04 0.01 Sro % 0.06 0.04 0.03 Bao % 0.07 0.18 0.06 Mn ₃ O ₄ % 0.05 0.04 0.04 Unknown % 0.18 0.12 Total % one hundred one hundred one hundred

Thus, coal having iron in the content of about 15%, based on (based on) the weight of the ash and expressed as Fe ₂ O ₃ and / or calcium in the content of more than 5%, based on (based on) the weight of the ash and expressed as CAO.

[0037] For the experiment, Al (OH) ₃ (suspension of aluminum trihydroxide suspension) was supplied at a concentration of 70% by weight of the aqueous suspension at a rate of 5 pounds of suspension per ton of coal from air-cooled nozzles arranged in two groups of three nozzles in each, the wall opposite the two groups of pulverized coal burners - one group at a level between two burners and one group at a level above the uppermost pulverized coal burners. The suspension is diluted to a concentration of 35% aluminum trihydroxide by weight. The density of the aluminum trihydroxide slurry prior to dilution was approximately 14 pounds per gallon, corresponding to a feed rate of approximately 193 gallons per day (approximately 5 pounds per tonne of coal) of the aluminum trihydroxide slurry. The size of the coal and the concentration forming the nanoparticles with a size of less than 200 nm in hot gaseous products of combustion are optimal for reducing the degree of contamination and increasing the fragility of the resulting slag.

[0038] Based on the described experiment, it was found that effective for this particular combustion chamber is a level of about 1 to about 6 pounds of suspended aluminum trihydroxide per ton of coal, for example, about 2 to about 3 pounds per ton.

Example 2

[0039] This example illustrates the benefits of introducing Mg (OH) ₂ (magnesium hydroxide) into a furnace burning 540 tons of coal per day, in addition to introducing aluminum trihydroxide (see Example 1). Coal was a mixture of tarry coals of the Illinois and Appalachian coal basins, as described in Example 1.

[0040] Magnesium hydroxide was supplied as a suspension in an amount of 2 pounds of suspension in a concentration of from 50 to 60% by weight per ton of coal consumed. The density of the suspension of magnesium hydroxide was approximately 12 pounds per gallon. Thus, the feed rate of the Mg (OH) ₂ slurry was about 90 gallons per day. As in the case described above, we introduced a suspension of aluminum trihydroxide in an amount of about 5 pounds of suspension per ton of coal consumed. The density of aluminum trihydroxide was approximately 14 pounds per gallon, and the feed rate of aluminum trihydroxide was approximately 193 gallons per day. The size of the coal and the concentration forming the nanoparticles with a size of less than 200 nm in hot gaseous products of combustion are optimal for reducing the degree of pollution and increasing the fragility of the resulting slag.

[0041] Based on this experiment, we estimate the optimal (economic performance for this particular combustion chamber) feed rate as about 0.5 to about 2 pounds of Mg (OH) ₂ slurry per ton of coal (for example, about 1 pound per ton ) plus about 1 to about 6 pounds of aluminum trihydroxide suspension per ton (e.g., about 2 to about 3 pounds per ton). Figure 2 with a photograph of a slag sample obtained after a 24-hour cycle of the introduction of only aluminum trihydroxide. The slag was unexpectedly fragile.

[0042] The above description is sufficient for a person skilled in the art to implement the invention. It does not aim at a detailed description of explicit modifications and changes that will become apparent to a qualified person after reading the present description. However, the present description aims to indicate such explicit modifications and changes as are included in the scope of the present invention, which is disclosed in the following claims. It is envisaged that the claims include all objects of the invention and technological steps, the use of which in an arbitrary sequence ensures the achievement of the stated goals, unless the context clearly indicates otherwise.

Claims (8)

1. A method of reducing the cohesive properties of slag and / or its adhesion to the surface of the combustion chamber and thereby reducing the degree of contamination, including:
- burning slag-forming coal in the combustion zone, using coal with a high iron content exceeding about 15%, taking into account the weight of the ash, and expressed as Fe ₂ O ₃ , and / or a calcium content exceeding 5%, taking into account the weight of the ash, and expressed as CaO, with a total excess of oxygen;
- removal of gaseous products of combustion through heat exchange equipment under conditions providing cooling of the slag formed during the combustion of fuel; and
- introduction into the combustion zone of the combustion chamber, before contact with the specified heat exchange equipment, in the gaseous products of combustion of aqueous aluminum trihydroxide in an amount, with droplet size and in a concentration forming nanoparticles of a size less than 200 nm in hot gaseous products of combustion, optimal to reduce the degree of pollution and increase the friability of the resulting slag. 2. The method according to claim 1, in which the principles of calculated hydrodynamics are used to determine the initial values of the rate of introduction of the reagent, determine the point (s) of introduction, concentration, droplet size and kinetic energy. 3. The method according to claim 1, characterized in that the treatment further includes the introduction of an aqueous solution of magnesium hydroxide in an amount, with droplet size and in a concentration that allows the formation of nanoparticles with a size of less than 200 nm, optimal to reduce the degree of contamination. 4. The method according to claim 3, characterized in that the treatment includes the introduction of up to about 6 pounds of aqueous aluminum trihydroxide per ton of coal and up to about 2 pounds of Mg (OH) ₂ per ton of coal. 5. A method for removing slag deposits from a combustion chamber in which coal is burned with an increased iron content exceeding about 15%, taking into account the weight of the ash, and expressed as Fe ₂ O ₃ , and / or a calcium content exceeding 5%, taking into account the weight of the ash , and expressed as CaO, including:
the introduction into the gaseous products of combustion formed in the combustion chamber of aqueous aluminum trihydroxide in an amount, with droplet size and in a concentration forming nanoparticles less than 200 nm in size, optimal for removing slag deposits. 6. The method according to claim 5, characterized in that the treatment further includes the introduction of an aqueous solution of magnesium hydroxide in an amount, with droplet size and concentration, optimal to reduce the degree of contamination. 7. The method according to claim 6, characterized in that the treatment includes the introduction of up to about 6 pounds of aqueous aluminum trihydroxide per ton of coal and up to about 2 pounds of Mg (OH) ₂ per ton of coal. 8. A method of cleaning and maintaining a combustion chamber for burning coal with an increased iron content exceeding about 15%, taking into account the weight of the ash, and expressed as Fe ₂ O ₃ , and / or a calcium content exceeding 5%, taking into account the weight of the ash, and expressed as CaO, which includes an initial dosage of aqueous aluminum trihydroxide from about 3 to 6 pounds per ton of coal and about 1 to 2 pounds of an aqueous solution of magnesium hydroxide per ton of coal for a time sufficient to reduce slag formation, and then reduce the dosage to from about 10 to about 50% of the initial values to ensure the purity and efficiency of operation of the combustion chamber, while aqueous aluminum trihydroxide and an aqueous solution of magnesium hydroxide are presented in the form of droplets with a size and concentration sufficient to form nanoparticles smaller than 200 nm in size to reduce the degree of slag pollution.

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