A doping modification and granulation preparation method for improving combustion heat value of iron powder

Abstract

The application discloses a kind of doping modification and granulation preparation methods for improving iron powder combustion heat value, belong to new energy storage and zero-carbon fuel technical field.The method is abandoned light and wind power electrolytic hydrogen as reducing agent, hydrogen reduction is prepared to millimeter level fuel particle with ignition temperature ≤600°C after iron oxide raw material is reduced to metal iron powder, through doping aluminum powder, silicon iron powder, magnesium powder and boron powder and other high heat value metal powder, combination binder granulation and surface passivation treatment, heat value ≥18 MJ / kg.The application significantly improves the combustion heat value of iron powder (50-100% higher than pure iron powder), reduces the ignition temperature, improves the storage stability and combustion characteristics, and the combustion products can be magnetically separated and recycled for use, and the remaining components can be sold as building material raw materials, constructing a zero-carbon energy recycling system of "green electricity hydrogen production-hydrogen reduction-iron powder combustion-product recovery", providing a technically feasible and economically reasonable solution for replacing coal-fired power generation.

Description

Technical Field

[0001] This invention belongs to the field of new energy storage and zero-carbon fuel technology, specifically relating to a doping modification and granulation preparation method for improving the combustion calorific value of iron powder, and a zero-carbon energy cycle system based on this method. Background Technology

[0002] Coal, as a traditional fossil fuel, still occupies an important position in my country's energy structure, but the CO2 emissions from its combustion are one of the main causes of the greenhouse effect. Therefore, developing zero-carbon or low-carbon alternative fuels to achieve a clean replacement of coal is of great significance for promoting the transformation of the energy structure.

[0003] Metal fuels (especially iron powder) are considered potential zero-carbon fuels because they do not directly produce CO2 during combustion, and the byproducts can be magnetically separated and reduced by renewable hydrogen. However, the calorific value of pure iron powder is only about 7–8 MJ / kg (lower range) / about 11 MJ / kg (higher range), and its powdered form has a high ignition temperature, poor flowability, and is easily oxidized during storage, limiting its direct replacement of coal in industrial boilers. Existing technologies have addressed this by using ball milling to improve reactivity, but this introduces energy consumption and dust safety risks; other methods improve combustion by adding nitrogen- or sulfur-containing oxidants, but introduce new emissions and byproduct impurities. Overall, there is still a lack of an integrated, engineerable solution that couples "doping to increase calorific value and lower ignition temperature," "powder → millimeter-scale granulation to improve flow / transportation," "surface passivation to ensure storage stability and controllable ignition," and "green electrolysis for hydrogen production → hydrogen reduction → product recycling." This invention addresses this technical problem.

[0004] However, pure iron powder has the following technical bottlenecks as a fuel: (1) The calorific value of combustion is low (the calorific value of pure iron powder is about 11.3 MJ / kg), which is much lower than that of coal (about 20-30 MJ / kg), resulting in insufficient energy density; (2) The ignition temperature is high (about 700-800°C for pure iron powder), making ignition difficult and unfavorable for practical applications; (3) Iron powder has a large specific surface area, making it easy to oxidize and resulting in poor storage stability; (4) Iron powder is in powder form, with poor flowability, which is unfavorable for transportation and combustion control.

[0005] Currently, some research has focused on improving the combustion performance of iron powder. For example, some existing technologies improve reactivity through ball milling, but this suffers from high energy consumption and susceptibility to spontaneous combustion; others improve combustion performance by adding oxidants, but this introduces nitrogen- and sulfur-containing components, which are detrimental to environmental protection. Furthermore, systematic methods for preparing iron powder fuel, particularly comprehensive solutions for improving calorific value, reducing ignition temperature, improving storage stability, and recycling combustion products, are still lacking in existing technologies.

[0006] Meanwhile, Northwest my country is rich in wind and solar energy resources, but due to the limited grid absorption capacity, the phenomenon of "wind and solar curtailment" is serious, resulting in a large waste of clean energy. How to utilize the curtailed wind and solar power to produce hydrogen, and use the hydrogen to reduce iron oxide to produce metallic iron powder, thereby developing high-performance iron-based fuels and constructing a complete zero-carbon energy cycle system, is the core technical problem that this invention aims to solve. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a doping modification and granulation preparation method to improve the combustion calorific value of iron powder. By doping with high-calorific-value metal powder, bonding granulation and surface passivation treatment, the combustion calorific value of iron powder fuel is significantly improved, the ignition temperature is reduced, the storage stability is improved, and a zero-carbon energy cycle system of "green electricity to hydrogen production - hydrogen reduction - iron powder combustion - product recovery" is constructed.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for doping modification and granulation preparation to improve the calorific value of iron powder includes the following steps:

[0010] (1) Raw material preparation: Using hydrogen gas obtained by electrolysis of abandoned solar and wind power as a reducing agent, the iron oxide raw material is reduced in a hydrogen reduction furnace to obtain metallic iron powder;

[0011] (2) Doping modification: The iron powder obtained in step (1) is mechanically mixed with one or more of aluminum powder, ferrosilicon powder, magnesium powder and boron powder to obtain a doped mixed powder;

[0012] (3) Binder granulation: Add binder to the doped mixed powder obtained in step (2) and granulate it using a granulation device to obtain millimeter-sized particles;

[0013] (4) Surface passivation: The millimeter-sized particles obtained in step (3) are subjected to surface passivation treatment to obtain the fuel particles prepared by the doping modification and granulation preparation method for improving the calorific value of iron powder combustion.

[0014] Preferably, in step (1), the iron oxide raw material is one or more of hematite, magnetite, ferric oxide, or iron-containing waste slag from steel plants.

[0015] Preferably, in step (1), the hydrogen reduction reaction temperature is 400-800°C, the reaction time is 1-6 hours, the hydrogen flow rate is 0.5-5 L / min, and the reaction pressure is 0.1-0.5 MPa.

[0016] Preferably, in step (2), the components are as follows by mass percentage: 50-80% iron powder, 5-20% aluminum powder, 3-15% ferrosilicon powder, 2-10% magnesium powder, and 1-5% boron powder.

[0017] Preferably, in step (3), the binder is one or more of polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), starch, epoxy resin or phenolic resin, and the amount of binder used is 2-10% of the mass of the mixed powder.

[0018] Preferably, in step (3), the granulation equipment is a disc granulator, a roller granulator or an extrusion granulator, and the granulation particle size is 1-10 mm.

[0019] Preferably, in step (4), the surface passivation treatment is as follows: the granulated particles are placed in an oxygen-containing atmosphere and subjected to surface oxidation treatment at 50-150°C for 0.5-4 hours to form a dense oxide film with a thickness of 10-100 nm on the particle surface.

[0020] Preferably, in step (4), the surface passivation treatment is: using the sol-gel method to coat the particle surface with a silicon dioxide or aluminum oxide passivation layer with a thickness of 20-200 nm.

[0021] The present invention also provides a fuel pellet prepared by the above method, wherein the fuel pellet has a calorific value ≥18 MJ / kg, an ignition temperature ≤600°C, a particle size of 1-10 mm, and a bulk density of 1.5-3.0 g / cm³.

[0022] The present invention also provides the application of the above-mentioned fuel particles, which are used as zero-carbon fuel for combustion and power generation in coal-fired power plant boilers. The combustion products are recycled for hydrogen reduction in step (1) after magnetic separation to recover iron oxide. The remaining components are sold as building material raw materials.

[0023] This invention also provides a zero-carbon energy recycling system, comprising: a hydrogen production unit from curtailed solar and wind power electrolysis, a hydrogen reduction unit, a doping and modification granulation unit, a combustion power generation unit, a product recovery unit, and a waste residue sorting and sales unit; wherein, the hydrogen production unit from curtailed solar and wind power electrolysis produces hydrogen by electrolyzing water using curtailed solar and wind power, the hydrogen is used as a reducing agent in the hydrogen reduction unit to reduce iron oxide to metallic iron powder, the metallic iron powder is used in the doping and modification granulation unit to prepare fuel particles, the fuel particles are used in the combustion power generation unit to generate electricity, the combustion products are used in the product recovery unit to recover iron oxide through magnetic separation and are then recycled to the hydrogen reduction unit, and the remaining components are used in the waste residue sorting and sales unit to be sold as building material raw materials.

[0024] The beneficial effects of this invention are:

[0025] (1) Significantly improves the calorific value of combustion: By doping with high-calorific-value metal powders such as aluminum powder (calorific value of about 31 MJ / kg), ferrosilicon powder, magnesium powder (calorific value of about 24.7 MJ / kg) and boron powder, the calorific value of the fuel particles prepared by this invention can reach 18-25 MJ / kg, which is 50-100% higher than that of pure iron powder (11.3 MJ / kg), approaching or reaching the calorific value level of coal, and meeting the combustion requirements of coal-fired power plant boilers.

[0026] (2) Significantly reduced ignition temperature: The doped aluminum, magnesium and other metal powders have a lower ignition temperature and form a micro-battery effect with the iron powder, which promotes local heating and reduces the ignition temperature of the fuel particles to 500-600°C, which is 100-200°C lower than that of pure iron powder, thus improving ignition performance and combustion stability.

[0027] (3) Improve storage stability: Through surface passivation treatment, a dense nano-scale oxide film or ceramic coating layer is formed on the particle surface, which effectively isolates the contact between air and internal metal, prevents spontaneous combustion and oxidation, and the activity does not decrease significantly after being stored at room temperature for more than 6 months.

[0028] (4) Optimize combustion characteristics: Granulation process transforms powdered iron powder into millimeter-sized particles, improving fluidity and facilitating transportation and metering; the doped metal inside the particles forms a uniformly distributed composite structure with iron, generating a synergistic exothermic effect during combustion and improving combustion efficiency.

[0029] (5) Construct a zero-carbon circular system: Hydrogen is produced by electrolysis of abandoned wind and solar power as a reducing agent. No fossil energy is consumed and no CO2 emissions are generated in the whole process. Iron oxide in the combustion products can be efficiently recovered and recycled through magnetic separation. The remaining components (mainly aluminum oxide, silicon oxide, magnesium oxide, etc.) can be sold as high-quality building material raw materials to achieve full utilization of resources.

[0030] (6) High economic feasibility: Hydrogen production using curtailed wind and solar power has extremely low electricity costs (as low as RMB 0.1 / kWh); iron oxide raw materials are widely available, including steel plant slag or low-grade iron ore; combustion products are recycled, reducing raw material costs; the overall system has good economic benefits. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the doping modification and granulation preparation method for improving the combustion calorific value of iron powder according to the present invention;

[0032] Figure 2 This is a schematic diagram of the zero-carbon energy cycle system described in this invention;

[0033] Figure 3 This is a comparison curve of TG-DSC thermal analysis between Example 1 and Comparative Example 1 of the present invention;

[0034] Figure 4 This is a flowchart of the magnetic separation and recovery process of the combustion products of the fuel particles prepared in Example 1 of the present invention.

[0035] Explanation of reference numerals in the attached diagrams: 1. Hydrogen production unit from curtailed solar and wind power electrolysis; 2. Hydrogen storage tank; 3. Hydrogen reduction furnace; 4. Iron oxide raw material silo; 5. Iron powder collector; 6. Doping mixer; 7. Aluminum powder silo; 8. Ferrosilicon powder silo; 9. Magnesium powder silo; 10. Boron powder silo; 11. Binder storage tank; 12. Granulator; 13. Surface passivation furnace; 14. Fuel pellet finished product silo; 101. Hydrogen production unit from curtailed solar and wind power electrolysis; 102. Hydrogen reduction unit; 103. Doping and modification granulation unit; 104. 105. Combustion power generation unit; 106. Product recovery unit; 107. Waste residue sorting and sales unit; 108. Iron oxide circulation pipeline; 109. Building material raw material output pipeline; 300. DSC curve of Example 1; 301. DSC curve of Comparative Example 1; 302. TG curve of Example 1; 303. TG curve of Comparative Example 1; 404. Combustion product collector; 405. Magnetic separator; 406. Iron oxide recovery bin; 407. Non-magnetic component bin; 408. Building material processing equipment. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1

[0037] (like Figure 1 A method for doping modification and granulation preparation to improve the calorific value of iron powder includes the following steps:

[0038] (1) Raw material preparation: Hydrogen produced by electrolyzing water from abandoned wind and solar power in Northwest China (electricity price 0.08 yuan / kWh) was used as a reducing agent. Iron-containing waste slag from steel plants (main component is Fe2O3, content 85%) was placed in a hydrogen reduction furnace and reduced for 4 hours under the conditions of hydrogen flow rate 2 L / min, reaction temperature 600°C and reaction pressure 0.2 MPa to obtain metallic iron powder with a purity of 96.5% and a particle size of 50-100 μm.

[0039] (2) Doping modification: Weigh 65% iron powder, 15% aluminum powder, 10% ferrosilicon powder, 7% magnesium powder and 3% boron powder by mass percentage, place them in a V-type mixer, and mix at 30 rpm for 2 hours to obtain doped mixed powder.

[0040] (3) Bonding and granulation: Add 5% by mass of polyvinyl alcohol (PVA) aqueous solution (PVA concentration 10%) to the doped mixed powder, and granulate using a disc granulator to control the granulation particle size to 3-5 mm to obtain wet particles.

[0041] (4) Surface passivation: The wet particles are placed in a fluidized bed, dried at 80°C in an air atmosphere and surface oxidized for 2 hours to form a dense Fe2O3 oxide film with a thickness of about 50 nm on the particle surface, thus obtaining the finished fuel particles.

[0042] Tests showed that the fuel pellets prepared in this embodiment had a calorific value of 21.5 MJ / kg, an ignition temperature of 550°C, a bulk density of 2.3 g / cm³, and an activity retention rate of >95% after 6 months of storage at room temperature. Example 2

[0043] (like Figure 2 A method for doping modification and granulation preparation to improve the calorific value of iron powder includes the following steps:

[0044] (1) Raw material preparation: Hydrogen gas produced by electrolysis of abandoned wind and solar power was used as a reducing agent. Hematite powder (Fe2O3 content 92%) was placed in a hydrogen reduction furnace and reduced for 3 hours under the conditions of hydrogen flow rate 3 L / min, reaction temperature 700°C and reaction pressure 0.3 MPa to obtain metallic iron powder with a purity of 98.2% and a particle size of 30-80 μm.

[0045] (2) Doping modification: Weigh 70% iron powder, 12% aluminum powder, 8% ferrosilicon powder, 6% magnesium powder and 4% boron powder by mass percentage, place them in a three-dimensional motion mixer, and mix at 25 rpm for 3 hours to obtain doped mixed powder.

[0046] (3) Adhesive granulation: Add 3% sodium carboxymethyl cellulose (CMC) aqueous solution (CMC concentration 8%) to the doped mixed powder, and granulate using a roller granulator to control the granulation particle size to 5-8 mm to obtain wet granules.

[0047] (4) Surface passivation: The wet particles are placed in an oven and dried at 120°C in an air atmosphere and surface oxidized for 1 hour to form a dense oxide film with a thickness of about 30 nm on the particle surface, thus obtaining the finished fuel particles.

[0048] Tests showed that the fuel pellets prepared in this embodiment had a calorific value of 19.8 MJ / kg, an ignition temperature of 580°C, a bulk density of 2.1 g / cm³, and an activity retention rate of >93% after 6 months of storage at room temperature. Example 3

[0049] (like Figure 4 A method for doping modification and granulation preparation to improve the calorific value of iron powder includes the following steps:

[0050] (1) Raw material preparation: Hydrogen gas produced by electrolysis of abandoned wind and solar power was used as a reducing agent. Magnetite powder (Fe3O4 content 88%) was placed in a hydrogen reduction furnace and reduced for 5 hours under the conditions of hydrogen flow rate 1.5 L / min, reaction temperature 500°C and reaction pressure 0.15 MPa to obtain metallic iron powder with a purity of 95.8% and a particle size of 40-120 μm.

[0051] (2) Doping modification: Weigh 55% iron powder, 20% aluminum powder, 12% ferrosilicon powder, 8% magnesium powder and 5% boron powder by mass percentage, place them in a double cone mixer, and mix at 20 rpm for 4 hours to obtain doped mixed powder.

[0052] (3) Bonding and granulation: Add 8% starch aqueous solution (12% starch concentration) to the doped mixed powder, and granulate using an extrusion granulator to control the granulation particle size to 2-4 mm to obtain wet granules.

[0053] (4) Surface passivation: The wet particles are coated using the sol-gel method: The particles are immersed in a tetraethyl orthosilicate (TEOS) ethanol solution and reacted at 60°C for 4 hours to form a SiO2 coating layer with a thickness of about 100 nm on the particle surface. After drying, the fuel particles are obtained.

[0054] Tests showed that the fuel pellets prepared in this embodiment had a calorific value of 23.2 MJ / kg, an ignition temperature of 520°C, a bulk density of 2.5 g / cm³, and an activity retention rate of >97% after 6 months of storage at room temperature. Example 4

[0055] A method for doping modification and granulation preparation to improve the calorific value of iron powder includes the following steps:

[0056] (1) Raw material preparation: Hydrogen gas produced by electrolysis of abandoned wind and solar power was used as a reducing agent. Iron oxide powder (Fe2O3 content 99%) was placed in a hydrogen reduction furnace and reduced for 2 hours under the conditions of hydrogen flow rate 4 L / min, reaction temperature 750°C and reaction pressure 0.4 MPa to obtain metallic iron powder with a purity of 99.1% and a particle size of 20-60 μm.

[0057] (2) Doping modification: Weigh 75% iron powder, 8% aluminum powder, 5% ferrosilicon powder, 5% magnesium powder and 2% boron powder by mass percentage, place them in a high-speed mixer, and mix at 800 rpm for 30 minutes to obtain doped mixed powder.

[0058] (3) Bonding and granulation: Add 4% by mass of epoxy resin acetone solution (epoxy resin concentration 15%) to the doped mixed powder, and granulate using a disc granulator to control the particle size to 6-10 mm to obtain wet particles.

[0059] (4) Surface passivation: The wet particles are placed in an oven and dried at 100°C in an air atmosphere and surface oxidized for 1.5 hours to form a dense oxide film with a thickness of about 40 nm on the particle surface, thus obtaining the finished fuel particles.

[0060] Tests showed that the fuel pellets prepared in this embodiment had a calorific value of 18.6 MJ / kg, an ignition temperature of 600°C, a bulk density of 2.0 g / cm³, and an activity retention rate of >94% after 6 months of storage at room temperature. Comparative Example 1 (e.g.) Figure 3 )

[0061] The iron powder (purity 96.5%) obtained in step (1) of Example 1 was directly granulated and surface passivated without adding any doped metal powder, and the other conditions were the same as in Example 1.

[0062] Tests showed that the pure iron powder particles prepared in the comparative ratio had a calorific value of 11.5 MJ / kg, an ignition temperature of 720°C, a bulk density of 2.8 g / cm³, and an activity retention rate of <85% after 3 months of storage at room temperature. Comparative Example 2

[0063] The doped metal powder in Example 1 was replaced with an equal mass of iron oxide powder, and the other conditions were the same as in Example 1.

[0064] Tests showed that the granules prepared in the comparative sample had a calorific value of 9.8 MJ / kg and an ignition temperature >800°C, making them almost impossible to burn normally. Application examples

[0065] The fuel pellets (calorific value 21.5 MJ / kg) prepared in Example 1 were mixed with thermal coal (calorific value 22 MJ / kg) at a blending ratio of 50% and a combustion test was conducted in a 300 MW coal-fired power plant boiler. The results showed that the fuel pellets ignited stably, burned completely, and had a uniform furnace temperature distribution. NOx emissions were reduced by about 15% compared to pure coal combustion. After separation by a magnetic separator, the iron oxide recovery rate of the combustion products reached 92%, and the recovered iron oxide was returned to the hydrogen reduction unit for recycling. The non-magnetic components (mainly Al2O3, SiO2, MgO, etc.) met the standard of GB / T 18046-2017 "Granulated Blast Furnace Slag Powder for Cement and Concrete" and can be sold as high-quality slag powder.

[0066] Economic analysis shows that using low-cost electricity from wind and solar power curtailment to produce hydrogen, combined with recycling processes, can effectively control raw material and manufacturing costs, making it feasible for industrial-scale promotion.

[0067] The following power plant co-firing data and cost calculations are based on a low-price power scenario of wind and solar curtailment in Northwest China during a certain period and the operating boundary of a specific 300 MW unit. They are for illustrative verification only and do not constitute a limitation on the essential technical features of this invention.

Claims

1. A method for preparing iron-based composite fuel particles, characterized in that, This includes the following steps performed sequentially: (1) Hydrogen reduction: Using hydrogen as a reducing agent, the iron oxide-containing raw material is reduced at 400–800°C and 0.1–0.5 MPa for 1–6 h to obtain metallic iron powder; (2) Doping and mixing: The obtained iron powder is mechanically mixed with a dopant to obtain a doped powder; the dopant comprises, by weight of the total doped powder: 5-20% aluminum powder, 3-15% ferrosilicon powder, 2-10% magnesium powder, 1-5% boron powder, with the balance being iron powder and ≤3% unavoidable impurities, and the total amount of the dopant added is controlled at 20-50%; (3) Binder granulation: A binder is added to the doped mixed powder, and wet particles with a particle size of 1–10 mm are formed by a disc granulator, a roller granulator or an extrusion granulator; the amount of binder is 2–10% of the mass of the doped mixed powder, and the binder is selected from one or more of PVA aqueous solution, CMC aqueous solution, starch paste, epoxy resin acetone solution or phenolic resin solution. (4) Surface passivation: The wet particles are subjected to surface passivation treatment to form a dense passivation layer with a thickness of 10–200 nm on the surface, thereby obtaining the iron-based composite fuel particles.

2. The preparation method according to claim 1, characterized in that, The iron oxide-containing raw material mentioned in step (1) is selected from one or more of hematite, magnetite, Fe2O3, and iron-containing waste slag from steel plants; the hydrogen flow rate is 0.5–5 L / min.

3. The preparation method according to claim 1, characterized in that, The granulation particle size in step (3) is controlled at 2–8 mm.

4. The preparation method according to claim 1, characterized in that, The surface passivation described in step (4) is carried out by atmospheric oxidation passivation: the granulated particles are placed in an oxygen-containing atmosphere and treated at 50–150°C for 0.5–4 h to grow a dense oxide film mainly composed of Fe3O4 / Fe2O3 on the particle surface with a film thickness of 10–100 nm.

5. The preparation method according to claim 1, characterized in that, The surface passivation described in step (4) is sol-gel coating passivation: the granulated particles are contacted with an alcohol solution containing silicon or aluminum source, reacted at 50–80°C and dried / calcined at low temperature to form a coating layer mainly composed of SiO2 or Al2O3 on the surface of the particles, with a coating layer thickness of 20–200 nm.

6. The preparation method according to any one of claims 1–5, characterized in that, The hydrogen is derived from wind power curtailment, solar power curtailment, or renewable electricity electrolysis water production units.

7. An iron-based composite fuel pellet prepared by the method according to any one of claims 1–5, characterized in that: The particles have a particle size of 1–10 mm, a bulk density of 1.5–3.0 g / cm³, and a passivation layer with a thickness of 10–200 nm on the surface. The dry composition of the particles, by mass fraction, includes: 50–80% metallic iron, 2–15% Al, 1–8% Si, 0.5–6% Mg, 0.1–3% B, with the remainder being oxygen and process impurities. In a TG-DSC test at 10 K / min in an air atmosphere, the ignition onset temperature is ≤620°C, and the high calorific value of the oxygen bomb method is ≥17 MJ / kg.

8. The iron-based composite fuel pellets according to claim 7, characterized in that: The passivation layer is a surface oxide film or a SiO2 / Al2O3 ceramic coating layer.

9. The use of the iron-based composite fuel pellets according to claim 7 or 8, characterized in that: The particles are used as solid fuel and are fed into a coal-fired boiler for combustion and power generation at a blending ratio of 10–80 wt% with thermal coal. After the combustion products are separated by magnetic separation, the iron oxides obtained are returned to the hydrogen reduction process, and the remaining solid components can be used as building material raw materials or disposed of in landfills.

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