Boiler fire coal additive and preparation method thereof

Abstract

The invention discloses a boiler fire coal additive and a preparation method thereof. The fire coal additive is composed of the following components in parts by weight: 30-60 parts of an oxidant; 15-40 parts of an alloy phase change material; 0.1 to 2 parts of an adhesive; 1-5 parts of a permeation auxiliary agent; 40-80 parts of a dispersion carrier; the preparation method of the boiler fire coal additive comprises the following steps: carrying out powder coating on an oxidant by using an alloy phase change material and an adhesive, and then uniformly mixing the coated powder with a permeation auxiliary agent and a dispersion carrier to obtain the boiler fire coal additive. The fire coal additive realizes circular decoking, and generates positive economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of coal additives, specifically relating to a boiler coal additive and its preparation method that improves coal combustion efficiency and efficient coke removal by coating an oxidant with an alloy phase change material. Background Technology

[0002] In modern power generation, power plant boilers are core equipment, and their stable and efficient operation is crucial for power supply. However, boiler coking problems occur frequently, causing many adverse effects on boiler operation. For example:

[0003] Heat transfer deterioration: The flue gas temperature at the furnace outlet rises, causing the superheater and reheater to overheat, and the desuperheating water volume increases significantly, directly resulting in water and energy waste or even tube rupture.

[0004] Reduced output: When the coking thickness of the water-cooled wall is too thick, it will lead to a decrease in boiler evaporation, and in severe cases, the unit will be forced to reduce load or shut down.

[0005] Safety accidents: Large coke blocks (such as those weighing hundreds of kilograms) suddenly fall, damaging the water-cooled wall of the cold ash hopper, causing a sudden drop in furnace pressure, fire extinguishing, or even personal injury or death; there have been reports of casualties and significant economic losses due to this in China.

[0006] Economic considerations: Literature reports that for every 15°C increase in flue gas temperature, coal consumption for power generation increases by approximately 1 g / (kW·h); induced draft fan current increases by 10–25%, increasing the production and operating costs of power companies.

[0007] The industry has reached a basic consensus on the causes of coking in power plant boilers: (I) Fuel characteristics: The composition and characteristics of fuel are key intrinsic factors affecting coking in power plant boilers. The ash content, ash melting point, and volatile matter content of fuel directly determine the likelihood and extent of coking during combustion. In addition, the volatile matter content of fuel plays a crucial role in the stability of the combustion process. Incomplete combustion can create localized high-temperature zones in the furnace, making it easier for ash to melt and adhere under high temperatures, thus promoting coking. (II) Other factors: Parameters such as the aerodynamic field distribution, combustion method, and flame temperature during combustion; the parameter settings during boiler operation all have a direct and significant impact on coking.

[0008] To address this issue, Qin Yun of Ningxia Coal Industry Co., Ltd., a subsidiary of the State Energy Group, published "Analysis of Causes and Preventive Measures for Coking in Pulverized Coal Boilers in Power Plants" in the 2025 issue (Volume 7, Issue 13) of *Water Resources and Hydropower Technology and Application*. The article provides the following solutions: co-firing of coal and adjusting furnace temperature; controlling the fuel-air mixing ratio and optimizing burner injection angle; strengthening soot blowing and coking removal; adjusting the fineness and uniformity of pulverized coal; and strengthening boiler operation monitoring and data analysis. While these measures can reduce the risk of boiler coking to some extent, they are all preventative measures and do not provide effective solutions for problems that have already occurred during boiler operation.

[0009] Patent CN112779072 B discloses a decoking agent and its preparation method. The auxiliary agent used in the raw material components is a compound mixed acid of hydrochloric acid, hydrofluoric acid and nitric acid. Although strong acid has a good decoking effect on the coke layer, it will inevitably cause some corrosion to the boiler equipment, resulting in a reduction in the service life of the boiler.

[0010] Patent CN105542902 B discloses a decoking agent for waste incinerators and its preparation method. Although this decoking agent can remove ash and some coke in the incinerator, it poses a risk of unstable gas pressure during the decoking process and is not very efficient at removing thick, hard coke.

[0011] Patent CN115491240 B discloses an additive for power plant boilers and its application. It uses a compound of oxides, sodium / potassium salts, and nitrates, relying on sublimation and explosion at temperatures ≥800℃ to loosen and peel off the coke layer. However, its temperature window is narrow, requiring repeated additions. The residual alkali metals exacerbate high-temperature corrosion, and the instantaneous gas generation during the peeling process poses a risk of boiler collapse. Furthermore, this coking removal method fails to change the chemical properties of the ash slag, and coking still recurs.

[0012] In light of the current state of the industry, it is essential to develop an additive for boiler coal that can efficiently and environmentally improve coal efficiency and reduce production safety risks through cyclic coking removal. Summary of the Invention

[0013] Given that boiler coking is widely considered a complex and important issue in the industry, the inventors of this invention have conducted in-depth analysis of the causes of coking. Based on their long-term experience in the research and development and production of coal additives, combined with scientific experimental research, they have creatively discovered that through the specific formula and coating process of this invention, not only can coking be removed, but the components in the formula can also change the chemical properties of the ash, increase the melting point of the ash, and prevent subsequent low-temperature melting and cyclic coking.

[0014] This invention is achieved through the following means:

[0015] This invention provides a boiler coal additive, which involves coating an oxidant with a controlled particle size using a binder and an alloy phase change material with a controlled particle size at a certain mass ratio, and then mixing it with other components.

[0016] On one hand, the present invention provides a boiler coal additive, which, by weight, comprises the following components:

[0017] 30-60 parts of oxidant;

[0018] 15-40 parts of alloy phase change material;

[0019] 0.1-2 parts adhesive;

[0020] 1-5 parts of penetration enhancer;

[0021] 40-80 parts of dispersion carrier;

[0022] Furthermore, the mass ratio of oxidant to alloy phase transformation material is 1:0.5-0.75.

[0023] Preferably, its component composition, by weight parts, is as follows:

[0024] 45 parts of oxidizing agent;

[0025] 27 parts of alloy phase change material;

[0026] 1 part adhesive;

[0027] 3 parts of penetration enhancer;

[0028] 60 portions of dispersion carrier;

[0029] Furthermore, the mass ratio of oxidant to alloy phase transformation material is 1:0.6.

[0030] To achieve other purposes with boiler coal additives, other components can be added. For example, a catalyst can be added to accelerate the oxidation rate of carbon, carbon monoxide, volatile matter, etc., in the coal. A sulfur-fixing agent can be added to react with sulfur in the coal during combustion to form stable solid sulfates, thus "fixing" sulfur in the ash and reducing sulfur dioxide (SO2) emissions. A leavening agent can be added to address the varying structures of coal fuel layers or ash layers from different coal mines, making them more porous and loose, increasing permeability, and preventing caking.

[0031] Furthermore, the oxidant is at least one selected from potassium nitrate, sodium nitrate, potassium chlorate, and sodium chlorate, and has a particle size of 10-60 μm. Preferably, the oxidant is potassium nitrate, which has the characteristics of stable oxygen supply during decomposition and moderate decomposition temperature, providing efficient and continuous oxidation catalysis for the activation reaction of alloy phase change materials, and can effectively promote the chemical modification of ash slag.

[0032] Furthermore, the alloy phase transformation material is preferably at least one of Al-Si alloy powder and Al-Mg alloy powder, with a particle size of 5-30 μm. Preferably, this alloy material has a low eutectic phase transformation point, and the released active aluminum, silicon, or magnesium elements have the highest reactivity with coking components such as iron and sodium in coal ash, which can generate mineral phases, making it a direct material for altering the chemical properties of ash slag.

[0033] Furthermore, the adhesive is at least one selected from polyethylene glycol 4000, polyethylene glycol 6000, gum arabic, sodium alginate, hydroxypropyl methylcellulose, polyvinylpyrrolidone, and sodium carboxymethyl cellulose. Preferably, the adhesive is polyethylene glycol 6000 or hydroxypropyl methylcellulose, which has suitable adhesive strength and thermal decomposition characteristics, enabling it to effectively coat the oxidant in the alloy material at low temperatures and completely decompose and vaporize in the high-temperature stage without affecting combustion or the contact between the alloy material and ash.

[0034] Furthermore, the penetration aid is at least one of nano-sized hydrophobic silica, nano-sized alumina, nano-sized titanium dioxide, and nano-sized graphene microflakes. Preferably, the penetration aid is nano-sized hydrophobic silica, whose ultrafine particle size and hydrophobic properties allow it to penetrate the cracks when the phase change material in the coal additive absorbs and releases heat on the surface of the coke, causing thermal stress and cracks. After the phase change material becomes liquid, it has low viscosity and high fluidity, allowing it to continue penetrating the cracks under the guidance of the penetration aid, achieving "deep delivery." This effectively solves the problem of breaking up thicker coke blocks and reduces the amount of coal additive used.

[0035] Furthermore, the dispersion carrier is at least one of expanded perlite powder, hollow glass microspheres, diatomaceous earth powder, and ultrafine zeolite powder. Preferably, the dispersion carrier is expanded perlite powder, which has a porous structure, low density, and good flowability. It can not only uniformly disperse the oxidant, but also has a skeletal structure at high temperatures. When combined with ash and slag, it can provide a loose supporting effect, making the ash and slag layer easier to detach.

[0036] On the other hand, the present invention also provides a method for preparing the above-mentioned boiler coal additive, which is prepared by the following steps:

[0037] S1: Powder coating

[0038] Oxidizing agents are coated with powder using alloy phase change materials and binders to obtain coated powder with a particle size of 10-200μm.

[0039] S2: Finished product mixing

[0040] The coating powder in S1 is uniformly mixed with the penetrating agent and the dispersing carrier to obtain the boiler coal additive.

[0041] Preferably, the mixing equipment selected is a three-dimensional motion mixer, a hopper mixer, or a V-type mixer, which has good mixing uniformity and a gentle mixing process, effectively avoiding damage to the coated powder caused by high-intensity mixing.

[0042] Furthermore, the powder coating can be rotary coating, dry mechanical coating, or fluidized bed coating. As the most preferred embodiment, the preparation method using a rotary coating process includes the following steps:

[0043] S11: Preheating

[0044] Add the oxidant into the rotary coating pan, start the pan, control the rolling speed to 10-30 r / min, and preheat with hot air at 40-60℃.

[0045] S12: Package

[0046] The adhesive is prepared into an aqueous solution with a mass concentration of 3%-8%, and sprayed onto the oxidant in the rolling process using an atomizing nozzle with a nozzle diameter of 0.2-1.0 mm, a spray pressure of 0.1-0.3 MPa, and an atomization pressure of 0.3-0.5 MPa. At the same time, alloy phase change material powder is spread, and the mass ratio of spray volume to powder volume is controlled to be 1:5-15.

[0047] S13: Drying

[0048] Continue rolling and keeping the powder dry with hot air for 10-30 minutes to obtain the coated powder.

[0049] Preferably, the preheating speed is 20 r / min and the preheating temperature is 50℃; the adhesive concentration is 5% and the nozzle diameter is 0.6 mm, the spray pressure is 0.2 MPa and the atomization pressure is 0.4 MPa; the mass ratio of spray volume to powder amount is 1:10; and the drying time is 15 min.

[0050] Furthermore, the powder coating is a dry mechanical coating, comprising the following steps:

[0051] S11: Feeding

[0052] Oxidant, alloy phase change material, and binder powder are added into a mechanical stirring mill, and zirconium oxide balls with a particle size of 3-5 mm are added at the same time. The mass ratio of material to ball is controlled to be 5-8:1.

[0053] S12: Grinding

[0054] Start the stirred mill and control the speed at 300-500 r / min. Grind and coat for 10-20 minutes to make the alloy phase transformation material adhere tightly to the oxidant surface through mechanical force.

[0055] S13: Screening

[0056] After grinding, the particles are graded and sieved using an air jet sieve with 10μm and 200μm double-layer screens to collect particles with a diameter of 10-200μm, thus obtaining the coated powder.

[0057] Preferably, the grinding balls have a particle size of 4mm, and the material to ball ratio is 6:1; the grinding speed is 400r / min, and the grinding and coating time is 15min.

[0058] Furthermore, the powder coating is a fluidized bed coating, comprising the following steps:

[0059] S11: Fluidization, Preheating

[0060] The oxidant is introduced into the fluidized bed coating machine, the fluidizing air is turned on, and the fluidizing air velocity is controlled at 0.8-1.5 m / s, the inlet air temperature is 60-80℃, and the outlet air temperature is 50-70℃, so that the oxidant forms a fluidized state.

[0061] S12: Spray Coating

[0062] Prepare an aqueous solution with a mass concentration of 15%-30% by mixing the adhesive and alloy phase change material. Add 2000-mesh talc powder (1% by mass of the aqueous solution) to the anti-clogging gun. After stirring evenly, inject the solution into the spray system and spray it onto the surface of the oxidant at an atomization pressure of 0.3-0.6 MPa and a spray rate of 5-15 mL / min.

[0063] S13: Drying

[0064] After the spraying is finished, keep the fluidizing air velocity and inlet air temperature constant, and continue fluidizing and drying for 10-30 minutes to obtain the coated powder.

[0065] Preferably, the fluidization air velocity during fluidization and preheating is 1.2 m / s, the inlet air temperature is 70℃, and the outlet air temperature is 60℃; the atomization pressure during spray coating is 0.45 MPa, and the spray rate is 10 mL / min; the fluidization drying time during drying is 15 min.

[0066] The beneficial effects of this invention compared to the prior art are as follows:

[0067] 1. Achieved cyclic decoking

[0068] Most existing decoking technologies (such as strong acid cleaning and alkali metal blasting) are essentially one-time stripping methods, and their core flaw is that they cannot change the chemical properties of the ash. Low-melting-point minerals in coal ash, such as iron and sodium aluminosilicates, will remelt and act as "binders," leading to repeated coking. However, the specific formulation of this invention can chemically react the active metals released by the alloy phase change material with the fusible components in the coal ash, such as iron oxide and alkali metal compounds, to generate stable new mineral phases, thus eliminating the stickiness. This breaks the cycle of coking and achieves a cyclic decoking effect.

[0069] 2. Highly efficient penetration, capable of breaking down hard, thick coke deposits.

[0070] When the alloy phase transformation material in the additive comes into contact with the surface of the high-temperature coke, the phase transformation process can instantly generate a thermal shock effect, causing a dense crack network to form on the surface of the coke due to intense thermal stress, thus achieving initial peeling and embrittlement of the coke. Simultaneously, driven by the penetrating aid, the molten alloy material penetrates deep into the coke along the newly formed cracks. This process, which allows the additive to penetrate to the core of the coke, not only improves the initial peeling effect but also enables deep penetration and structural destruction of thick, hard coke layers, thereby achieving decoking of hard, thick layers.

[0071] 3. Overall application effect: economical and safe

[0072] The coal additive of this invention prevents coking at the source, reduces the frequency and large amount of coal additives needed, improves the energy efficiency of boiler units, reduces the need for load reduction or shutdown for coking removal due to coking, ensures continuous and safe operation of the unit, and generates positive economic benefits. Attached Figure Description

[0073] Figure 1 Scanning electron microscope (SEM) images of ash residue from the experimental group in Example 2.

[0074] Figure 2 Scanning electron microscope (SEM) image of ash residue from control group 2 in Experimental Example 2.

[0075] Figure 3 X-ray diffraction pattern of ash slag in Experimental Group 2.

[0076] Figure 4 The image shows the X-ray diffraction pattern of the ash residue in the control group 2 of Experimental Example 2. Detailed Implementation

[0077] The following description illustrates exemplary embodiments of the present invention, including various details to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions, operations, and structures are omitted in the following description.

[0078] Unless otherwise defined, the technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. While similar or identical methods and materials may be applied in experimental or practical applications, the present invention describes materials and methods hereinafter. In case of conflict, the definitions included herein shall prevail.

[0079] Example 1: Preparation of Coal Additives by Roll Coating

[0080] 1. Formula

[0081]

[0082] 2. Preparation method

[0083] S1: Powder coating (roll coating)

[0084] S11: Preheating: Add the potassium nitrate powder, after air jet milling, into the rotary coating pan. Start the pan and control the rotation speed to 20 r / min. Introduce 50℃ hot air and preheat the material for 10 minutes to ensure uniform temperature.

[0085] S12: Coating: Hydroxypropyl methylcellulose is dissolved in purified water to prepare a 5% (w / w) adhesive solution. The spray system (nozzle diameter 0.6 mm) is activated, and the adhesive solution is uniformly sprayed onto the rotating potassium nitrate powder in an atomized form at a spray pressure of 0.2 MPa and an atomization pressure of 0.4 MPa. Simultaneously, Al-Si alloy powder is fed into the pan at a constant rate using a precision screw feeder, controlling the mass ratio of adhesive spray solution to alloy powder to be 1:10. During this process, the mechanical force of the rotation causes the wet potassium nitrate particles to continuously adhere to the alloy powder, forming a wet-coated powder with potassium nitrate as the core, Al-Si alloy as the shell, and hydroxypropyl methylcellulose as the outer shell.

[0086] S13: Drying: After spraying and powdering, keep the pan rotating at 20 r / min and continue to circulate 50℃ hot air for 15 minutes. After drying, the coated powder is obtained.

[0087] S2: Finished product mixing

[0088] The coated powder, nano-hydrophobic silica, and expanded perlite powder prepared above are fed into a three-dimensional motion mixer. The mixer speed is set to 15 r / min, and the mixture is mixed for 40 minutes until the components are evenly distributed, thus obtaining the boiler coal additive product of the present invention.

[0089] Example 2: Dry mechanical coating preparation of coal additives

[0090] 1. Formula

[0091] Same as Example 1.

[0092] 2. Preparation method

[0093] S1: Powder coating (dry mechanical coating)

[0094] S11: Feeding: Add potassium nitrate powder, Al-Si alloy powder, and hydroxypropyl methylcellulose powder together into a vertical mixing mill. At the same time, add zirconia grinding balls with a particle size of 4mm, controlling the ratio of grinding balls to the total mass of materials (ball-to-material ratio) to be 6:1.

[0095] S12: Grinding and Coating: Close the grinding chamber and start the equipment. Control the stirring shaft speed to 400 r / min and grind continuously for 15 minutes at room temperature. During this process, the strong impact and shearing of the grinding balls and the mutual friction between materials cause the low-hardness alloy powder and the binder to be firmly embedded, pressed, or coated on the surface of potassium nitrate under mechanical force, forming tightly bonded composite particles.

[0096] S13: Sieving: After grinding, discharge the material and sieve to remove the zirconia balls. Then, use an air jet sieve with 10μm and 200μm screens to classify the material. Collect the coated powder with a particle size between 10-200μm, and discard excessively fine powder (<10μm) and incompletely coated coarse particles (>200μm).

[0097] S2: Finished product mixing

[0098] The coated powder, nano-hydrophobic silica, and expanded perlite powder prepared above are fed into a hopper mixer. The mixer speed is set to 20 r / min, and the mixture is mixed for 30 minutes until the components are evenly distributed, thus obtaining the boiler coal additive product of the present invention.

[0099] Example 3: Preparation of Coal Additives via Fluidized Bed Coating

[0100] 1. Formula

[0101] Same as Example 1.

[0102] 2. Preparation method

[0103] S1: Powder coating (fluidized bed coating)

[0104] S11: Fluidization and Preheating: Place potassium nitrate powder into the fluidization chamber of the fluidized bed coating machine (bottom spray type). Turn on the fan and adjust the fluidization velocity to 1.2 m / s. Set the inlet air temperature to 70℃ and the outlet air temperature to be stable at around 60℃, so that the potassium nitrate powder forms a stable and uniform fluidized state in the chamber, and preheat for 10 minutes.

[0105] S12: Spray Coating: Hydroxypropyl methylcellulose and Al-Si alloy powder are added to purified water and stirred to disperse, preparing a homogeneous suspension with a mass concentration of 20%. 1% (by mass) of 2000-mesh talc powder is added to the suspension as an anti-blocking agent, and the mixture is stirred until homogeneous. The suspension is pumped at a rate of 10 mL / min using a peristaltic pump to an atomizing nozzle located at the bottom of the fluidized bed. Under an atomization pressure of 0.45 MPa, the suspension is atomized and sprayed onto the surface of the fluidized potassium nitrate powder. The droplets rapidly spread, wet, and adhere to the alloy powder; subsequently, the moisture evaporates rapidly in the hot air stream, achieving coating.

[0106] S13: Drying: After the spraying is completed, keep the fluidization air speed and inlet air temperature constant, and continue fluidization drying for 15 minutes to remove the moisture on the particle surface and obtain a dry, loose coated powder.

[0107] S2: Finished product mixing

[0108] Mix the finished product from Example 1.

[0109] Examples 4-6: Preparation of Coal Additives with Different Dosage Forms

[0110] 1. Formula

[0111]

[0112] 2. Preparation method

[0113] Same as Example 1.

[0114] Example 7 Preparation of Coal Combustion Additives with Different Oxidants

[0115] The only difference between this embodiment and Example 1 is that the oxidant is replaced by sodium chlorate instead of potassium nitrate. The other components, dosages, and preparation methods are the same as in Example 1.

[0116] Alternative Note: Sodium chlorate (NaClO3) is used as the oxidant. Sodium chlorate decomposes at high temperatures, releasing oxygen and chlorine. Its decomposition temperature (starting at approximately 250-300°C) differs from that of potassium nitrate, providing an alternative oxidizing environment for the alloy phase change material. In this embodiment, 50g of sodium chlorate is used. Industrial-grade sodium chlorate with a purity ≥99.0% is recommended, with a particle size D90 controlled at approximately 30μm after air jet milling to ensure compatibility with the coating process.

[0117] Example 8 Preparation of Coal Additives for Different Alloy Phase Change Materials

[0118] The only difference between this embodiment and Embodiment 1 is that the alloy phase change material is replaced by Al-Mg alloy powder instead of Al-Si alloy powder. The other components, dosages, and preparation methods are the same as in Embodiment 1.

[0119] Alternative method: Al-Mg alloy powder (i.e., aluminum-magnesium alloy, containing approximately 5 wt% magnesium) is used as the phase change material. In this embodiment, the amount of Al-Mg alloy powder used is 30 g. The purity is ≥99%, and the particle size D90 is controlled at 20 μm to ensure its reactivity and coating effect.

[0120] Example 9 Preparation of Coal Combustion Additives with Different Permeation Aids

[0121] The only difference between this embodiment and Example 1 is that the penetration aid is replaced by nano-hydrophobic silica with nano-alumina. The other components, dosages, and preparation methods are the same as in Example 1.

[0122] Alternative Note: γ-phase nano-alumina (γ-Al₂O₃) is used as a penetration aid. Nano-alumina possesses an extremely high specific surface area and good flowability, which facilitates the dispersion and penetration of active ingredients. Furthermore, alumina itself is a high-temperature refractory material and may act as a skeletal support in ash and slag. In this embodiment, the amount of nano-alumina used is 3g. A product with a specific surface area between 150-250 m² / g is used.

[0123] Example 10 Preparation of Coal Additives with Different Dispersion Carriers

[0124] The only difference between this embodiment and Example 1 is that the dispersion carrier is replaced by hollow glass microspheres instead of expanded perlite powder. The other components, dosages, and preparation methods are the same as in Example 1.

[0125] Alternative Description: Hollow glass microspheres are used as the dispersion carrier. These are tiny, hollow, smooth spherical particles with a low true density (approximately 0.2-0.6 g / cm³), excellent flowability, and the ability to uniformly disperse and carry active ingredients. At high temperatures, their stable glassy structure maintains the looseness of the ash residue. In this embodiment, 80 g of hollow glass microspheres are used.

[0126] Example 11: Preparation of Coal Additive from High-Content, Large-Particle-Size Coated Powder of Phase Change Material

[0127] 1. Formula

[0128]

[0129] 2. Preparation method

[0130] S1: Powder coating (roll coating)

[0131] S11: Preheating: Add the potassium nitrate powder, after air jet milling, into the rotary coating pan. Start the pan and control the rotation speed to 30 r / min. Introduce hot air at 55℃ and preheat the material for 15 minutes to ensure uniform temperature.

[0132] S12: Coating: Hydroxypropyl methylcellulose is dissolved in purified water to prepare a 5% (w / w) adhesive solution. The spray system (nozzle diameter 1.0 mm) is activated, and the adhesive solution is uniformly sprayed onto the rotating potassium nitrate powder in an atomized form at a spray pressure of 0.25 MPa and an atomization pressure of 0.35 MPa. Simultaneously, Al-Si alloy powder is fed into the pan at a constant rate using a precision screw feeder, controlling the mass ratio of adhesive spray solution to alloy powder to be 1:7. During this process, the mechanical force of the rotation causes the wet potassium nitrate particles to continuously adhere to the alloy powder, forming a wet-coated powder with potassium nitrate as the core, Al-Si alloy as the shell, and hydroxypropyl methylcellulose as the outer shell.

[0133] S13: Drying: After spraying and powdering, keep the pan rotating at 20 r / min and continue to circulate hot air at 55℃ for 30 minutes. After drying, the coated powder is obtained.

[0134] S2: Finished product mixing

[0135] Same as Example 1.

[0136] Example 12: Preparation of Coal Additive for Low-Content, Small-Particle-Size Phase Change Material Coated Powder

[0137] 1. Formula

[0138]

[0139] 2. Preparation method

[0140] S1: Powder coating (roll coating)

[0141] S11: Preheating: Add the potassium nitrate powder, after air jet milling, into the rotary coating pan. Start the pan and control the rotation speed to 10 r / min. Introduce 45℃ hot air and preheat the material for 10 minutes to ensure uniform temperature.

[0142] S12: Coating: Hydroxypropyl methylcellulose is dissolved in purified water to prepare a 5% (w / w) adhesive solution. The spray system (nozzle diameter 0.2 mm) is activated, and the adhesive solution is uniformly sprayed onto the rotating potassium nitrate powder in an atomized form at a spray pressure of 0.15 MPa and an atomization pressure of 0.5 MPa. Simultaneously, Al-Si alloy powder is fed into the pan at a constant rate using a precision screw feeder, controlling the mass ratio of adhesive spray solution to alloy powder to be 1:15. During this process, the mechanical force of the rotation causes the wet potassium nitrate particles to continuously adhere to the alloy powder, forming a wet-coated powder with potassium nitrate as the core, Al-Si alloy as the shell, and hydroxypropyl methylcellulose as the outer shell.

[0143] S13: Drying: After spraying and powdering, keep the pan rotating at 10 r / min and continue to circulate 40℃ hot air for 10 minutes. After drying, the coated powder is obtained.

[0144] S2: Finished product mixing

[0145] Same as Example 1.

[0146] Comparative Example 1: Preparation of Coal Combustion Additive by Direct Mixing

[0147] 1. Formula

[0148] Same as Example 1.

[0149] 2. Preparation process

[0150] Potassium nitrate, Al-Si alloy powder, hydroxypropyl methylcellulose, nano-hydrophobic silica, and expanded perlite powder from the formula were all added into a three-dimensional motion mixer. The mixer speed was set to 15 r / min, and the mixture was mixed for 120 minutes until all components were evenly distributed, thus obtaining the boiler coal additive product of Comparative Example 1.

[0151] Comparative Example 2: Coal Additive Prepared According to Patent CN 115491240 B

[0152] 1. Formula:

[0153]

[0154] 2. Preparation process

[0155] 1. Weigh the metal oxide, nitrate, dispersant, leavening agent, and binder, mix the above components, heat and stir, raise the temperature to 100℃, and maintain for 30 minutes.

[0156] 2. Cool to room temperature, add sodium carbonate, potassium nitrate, sodium chloride and quartz sand, mix until uniform, and dry to obtain a solid powder.

[0157] Experimental Example 1: Particle Size Determination of Coated Powder

[0158] Measurement method: Laser diffraction (dry method) was used for measurement.

[0159] Instrument: Baxter BT-2001 Dry Laser Particle Size Analyzer

[0160] Dispersion medium: compressed air

[0161] Distributed pressure: 0.05MPa

[0162] Vibration feed speed: 5 Hz

[0163] Light blocking rate range: 0.5%-5%

[0164] Feed nozzle height: 6mm

[0165] Measurement results:

[0166]

[0167] in conclusion:

[0168] The results show that coal additives with different particle sizes can be prepared by selecting materials of different particle sizes and combining different process parameters. Furthermore, different amounts of oxidant and alloy phase change material can meet the application requirements under different conditions.

[0169] For working conditions with poor coal quality and a tendency to coke, additive products with a high proportion of alloy phase change materials can be selected. The higher content of alloying elements can act more fully and continuously on the coke at high temperatures. Through their phase change heat absorption and promotion of mineral phase reconstruction, they can effectively increase the ash melting point and reduce the viscosity of ash slag, thereby inhibiting and loosening coke formation.

[0170] For cases with a thick coke layer, additives with smaller particle sizes can be selected. The smaller particle size gives them better permeability, allowing them to diffuse and penetrate deeper into the interface and interior of the thick coke block, effectively intervening in deep coking and improving the overall coking removal effect.

[0171] Experimental Example 2: Microstructure Analysis of Ash and Slag

[0172] Experimental objective:

[0173] The aim was to simulate the combustion process of adding excessive amounts of different coal additives to prepare ash residue. The effects of DSC thermal analysis, scanning electron microscopy, and X-ray diffraction analysis on improving the performance of ash residue by promoting the formation of high-temperature stable mineral phases were verified.

[0174] Experimental procedure:

[0175] Basic coal sample: Select typical bituminous coal with high ash content and high slagging tendency, grind it and pass it through a 100-mesh standard sieve.

[0176] Experimental group: 5% by weight of the coal additive prepared in Example 1 was incorporated, and homogeneity was achieved by mixing with coal powder, sieving, and then remixing.

[0177] Control group 1: The coal additive prepared in Comparative Example 1 was added at a weight ratio of 5%, and the mixture was mixed with coal powder, sieved, and then mixed again to achieve uniformity.

[0178] Control group 2: The coal additive prepared in Comparative Example 2 was added at a weight ratio of 5%, and the mixture was mixed with coal powder, sieved, and then mixed again to achieve uniformity.

[0179] Detection method:

[0180] Differential scanning calorimetry: Samples from the experimental group, control group 1, and control group 2 that had not undergone combustion were directly used. A programmed temperature rise test was conducted in air, with the temperature increased from 30℃ to 1100℃ at a constant rate of 10℃ / min.

[0181] Experimental results:

[0182] Differential scanning calorimetry:

[0183] Experimental group: an exothermic peak appeared in the 300-500℃ range, a sharp endothermic peak appeared at 577℃, and a broad peak appeared in the 700-900℃ range.

[0184] Control group 1: Exothermic peaks appeared in the 300-500℃ range, the intensity of the endothermic peak at 577℃ decreased, and the broad peak in the 700-900℃ range was weaker than that of the experimental group.

[0185] Control group 2: Exothermic peaks appeared in the 300-500℃ range, no endothermic peaks were observed near 580℃, and no significant additional exothermic effect was observed in the 700-900℃ high-temperature range.

[0186] The above results show that, using the coal additive of the present invention, at approximately 577°C, the Al-Si eutectic alloy undergoes a molten phase transformation, and in the range of 700-900°C, the molten alloy and the coal ash components undergo a violent exothermic chemical reaction to generate a mineral phase.

[0187] Combustion ash: Each group of samples was placed in a muffle furnace and heated programmatically from room temperature to 600°C at a rate of 5°C / min, and held at that temperature for 30 minutes. The temperature was then increased from 600°C to 1100°C at a rate of 5°C / min and held at that temperature for 120 minutes. After the program was completed, the samples were allowed to cool naturally to room temperature in the furnace, lightly ground in an agate mortar, and then passed through a 100-mesh sieve.

[0188] Detection method:

[0189] Morphological observation: Field emission scanning electron microscopy was used. First, the overall morphology was observed at low magnification, and then local micro-areas were observed in detail at high magnification.

[0190] Diffraction analysis: X-ray diffractometer, Cu-Kα radiation, scanning range 10-60° (2θ), continuous scanning mode.

[0191] Experimental results:

[0192] Electron micrographs:

[0193] Experimental group: The overall structure is loose and porous, with numerous well-developed columnar or nearly spherical crystals visible (typical mullite morphology). See the instruction manual for details. Figure 1 .

[0194] Control group 1: The overall structure is loose and porous, with a small number of well-formed columnar or near-spherical crystals.

[0195] Control group 2: The overall structure is loose and porous, with almost no columnar or near-spherical crystals. See the instruction manual for details. Figure 2 .

[0196] Diffraction analysis:

[0197] Experimental group: Sharp, high-intensity diffraction peaks appeared at approximately 16.4°, 26.3°, and 35.0°. See the instruction manual for details. Figure 3 .

[0198] Control group 1: Diffraction peaks appeared at the same positions, but the intensity was much lower than that of the experimental group.

[0199] Control group 2: A very sharp, strong peak appears at approximately 26.6°. See the instruction manual for details. Figure 4 .

[0200] The above results show that the alloy powder in the configuration of this invention can promote complete crystal development, resulting in sharp X-ray diffraction peaks. According to the standard diffraction card (PDF card), the strongest mullite diffraction peaks at 2θ angles are 26.27°, 35.97°, and 16.47°, corresponding to the experimental group results; however, no characteristic mullite peaks were observed in the control group. The sharp peak with a count of approximately 600 at around 26° may be due to crystalline quartz inherent in the coal or introduced by additives (such as a small number of spherical objects seen in SEM).

[0201] Experiment 3 Performance Testing

[0202] The coal additive of the present invention was mass-produced according to the formulation and preparation method of Example 1, and the Xi'an Thermal Power Research Institute was commissioned to conduct combustion tests on the batch samples of the production scale.

[0203] Test objective:

[0204] The slag removal effect of the coal additive of the present invention was determined by slag formation test.

[0205] Combustion characteristic tests were conducted to determine the effect of the coal additive of the present invention on the ignition and burnout characteristics of coal.

[0206] Testing process:

[0207] The experiment was conducted in two phases, with each phase lasting 72 hours.

[0208] The first phase of the experiment did not add any coal additives and only burned the test coal.

[0209] In the second phase of the experiment, the coal additive of the present invention was added to the test coal (equivalent to adding the coal additive of the present invention once every 8 hours in actual application, with a dosage of one ten-thousandth of the coal consumption).

[0210] The test items are the same in each stage, and the results of the two stages are compared with each other.

[0211] The test coal samples were collected from the Shenfu-Dongsheng coalfield, and practical application showed that this type of coal has a serious tendency to slagging.

[0212] Test results:

[0213] Slagging test:

[0214] Comparison of slag samples from two stages of testing

[0215]

[0216] Ignition and burnout tests:

[0217] The temperature distribution of the flame along the test furnace was measured, and the temperature in the second stage of the test furnace was 50-100℃ higher than that in the first stage.

[0218] Burnout rates were measured by sampling coal samples from the experimental furnace. A burnout distribution chart was plotted with the residence time of pulverized coal in the furnace (s) on the x-axis and the burnout rate (%) on the y-axis, under different residence times. The burnout rate in the first 0-3 seconds of the second stage was higher than that in the first stage, and the final burnout rates were basically the same.

[0219] Test conclusion:

[0220] 1. The coal additive of the present invention can loosen the slag sample and alleviate and remove slag formation in the furnace, thereby improving the boiler thermal efficiency and the safety of equipment operation.

[0221] 2. The coal additive of the present invention can advance the ignition of Shenhua coal and improve the early combustion rate of coal, thereby enhancing the heat exchange in the furnace and having certain economic value.

Claims

1. A boiler coal additive, characterized in that, It consists of the following components in parts by weight: 30-60 parts of oxidant; 15-40 parts of alloy phase change material; 0.1-2 parts adhesive; 1-5 parts of penetration enhancer; 40-80 parts of dispersion carrier; Furthermore, the mass ratio of oxidant to alloy phase transformation material is 1:0.5-0.

75.

2. The boiler coal additive according to claim 1, characterized in that, The oxidant is at least one of potassium nitrate, sodium nitrate, potassium chlorate, and sodium chlorate, and has a particle size of 10-60 μm.

3. The boiler coal additive according to claim 1, characterized in that, The alloy phase transformation material is at least one of Al-Si alloy powder and Al-Mg alloy powder, and the particle size is 5-30 μm.

4. The boiler coal additive according to claim 1, characterized in that, The adhesive is at least one of polyethylene glycol 4000, polyethylene glycol 6000, gum arabic, sodium alginate, hydroxypropyl methylcellulose, polyvinylpyrrolidone, and sodium carboxymethyl cellulose.

5. The boiler coal additive according to claim 1, characterized in that, The penetration aid is at least one of nano-hydrophobic silica, nano-alumina, nano-titanium dioxide, and nano-graphene microflakes.

6. The boiler coal additive according to claim 1, characterized in that, The dispersion carrier is at least one of expanded perlite powder, hollow glass microspheres, diatomaceous earth powder, and ultrafine zeolite powder.

7. A method for preparing the boiler coal additive as described in claim 1, characterized in that, Includes the following steps: S1: Powder coating Oxidizing agents are coated with powder using alloy phase change materials and binders to obtain coated powder with a particle size of 10-200μm. S2: Finished product mixing The coating powder in S1 is uniformly mixed with the penetrating agent and the dispersing carrier to obtain the boiler coal additive.

8. The method for preparing boiler coal additive according to claim 7, characterized in that, The powder coating is a rotary coating, which includes the following steps: S11: Preheating Add the oxidant into the rotary coating pan, start the pan, control the rolling speed to 10-30 r / min, and preheat with hot air at 40-60℃. S12: Package The adhesive is prepared into an aqueous solution with a mass concentration of 3%-8%, and sprayed onto the oxidant in the rolling process using an atomizing nozzle with a nozzle diameter of 0.2-1.0 mm, a spray pressure of 0.1-0.3 MPa, and an atomization pressure of 0.3-0.5 MPa. At the same time, alloy phase change material powder is spread, and the mass ratio of spray volume to powder volume is controlled to be 1:5-15. S13: Drying Continue rolling and keeping the powder dry with hot air for 10-30 minutes to obtain the coated powder.

9. The method for preparing boiler coal additive according to claim 7, characterized in that, The powder coating is a dry mechanical coating, which includes the following steps: S11: Feeding Oxidant, alloy phase change material, and binder powder are added into a mechanical stirring mill, and zirconium oxide balls with a particle size of 3-5 mm are added at the same time. The mass ratio of material to ball is controlled to be 5-8:

1. S12: Grinding Start the stirred mill and control the speed at 300-500 r / min. Grind and coat for 10-20 minutes to make the alloy phase transformation material adhere tightly to the oxidant surface through mechanical force. S13: Screening After grinding, the particles are graded and sieved using an air jet sieve with 10μm and 200μm double-layer screens to collect particles with a diameter of 10-200μm, thus obtaining the coated powder.

10. The method for preparing boiler coal additive according to claim 7, characterized in that, The powder coating is a fluidized bed coating, comprising the following steps: S11: Fluidization, Preheating The oxidant is introduced into the fluidized bed coating machine, the fluidizing air is turned on, and the fluidizing air velocity is controlled at 0.8-1.5 m / s, the inlet air temperature is 60-80℃, and the outlet air temperature is 50-70℃, so that the oxidant forms a fluidized state. S12: Spray Coating The adhesive and alloy phase change material are prepared into an aqueous solution with a mass concentration of 15%-30%. 2000-mesh talc powder is added to the anti-clogging gun at a mass ratio of 1% of the aqueous solution. After stirring evenly, the solution is injected into the spray system and sprayed onto the surface of the oxidant at an atomization pressure of 0.3-0.6MPa and a spray rate of 5-15mL / min. S13: Drying After the spraying is finished, keep the fluidizing air velocity and inlet air temperature constant, and continue fluidizing and drying for 10-30 minutes to obtain the coated powder.

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