Coal-based carburant with high fixed carbon content and preparation method thereof

Abstract

This application discloses a coal-based carbon raiser with high fixed carbon content and its preparation method. The carbon raiser is prepared from raw materials comprising at least coal-based powder, biomass tar, and pitch through a mixing, granulation, graphitization, and calcination process, wherein the mass ratio of the coal-based powder, biomass tar, and pitch is 100:20–40:10–20. The carbon raiser of this application exhibits outstanding fixed carbon content, excellent mechanical strength, and high carbon raising efficiency.

Description

Technical Field

[0001] This application relates to the field of carbon raisers, and in particular to a coal-based carbon raiser with high fixed carbon content and its preparation method. Background Technology

[0002] Carbon raisers, as a key metallurgical auxiliary material, play an indispensable role in the iron and steel smelting and casting industries. Their main purpose is to compensate for insufficient carbon content caused by chemical reactions and oxidation losses during high-temperature smelting by adding high-carbon materials to molten metal, ensuring that the carbon content of the final product meets the expected standards, thereby guaranteeing the performance stability and mechanical strength of the metal materials.

[0003] The carbon raw materials used in the preparation of carbon raisers are diverse, commonly including graphite, petroleum coke, metallurgical coke, and coal. Graphite-based carbon raisers use natural or artificial graphite as the main raw material, and are produced through processes such as crushing, screening, and mixing. They possess high carbon purity and good high-temperature stability, and are easily dissolved and uniformly distributed in molten metal. Petroleum coke-based carbon raisers use petroleum coke as the raw material, and are produced through high-temperature roasting, grinding, and molding processes. They have a high fixed carbon content and low ash and sulfur content, making them suitable for the production of high-quality castings sensitive to impurities. Coal-based carbon raisers are obtained from anthracite, lignite, and other coal-based raw materials through high-temperature heat treatment and crushing and grading, and are relatively low in cost.

[0004] my country has abundant coal resources at relatively low prices, meeting market demands for both environmental friendliness and economic efficiency. However, coal-based carbon raisers generally have low mechanical strength, making them prone to breakage during transportation and use. They are also susceptible to oxidation and loss due to the high temperatures of smelting during addition, and the broken particles can cause dust pollution and low carbon raising efficiency. Summary of the Invention

[0005] To improve the mechanical strength and performance of coal-based carbonitriding agents, this application provides a coal-based carbonitriding agent with high fixed carbon content and its preparation method.

[0006] In a first aspect, this application provides a coal-based carbon raiser with high fixed carbon content, which is prepared by mixing, granulating, graphitizing and calcining raw materials including at least coal-based powder, biomass tar and pitch through a process. The mass ratio of the coal-based powder, biomass tar and pitch is 100:20 to 40:10 to 20.

[0007] Preferably, the D50 particle size of the coal-based powder is less than or equal to 3 mm.

[0008] Preferably, the asphalt is coal tar pitch and / or petroleum asphalt.

[0009] Preferably, the biomass tar is selected from one or more of wood tar, straw tar, rice husk tar, and algae tar.

[0010] Preferably, at a temperature of 20–25°C, the viscosity of the biomass tar is 50,000–300,000 cP.

[0011] Preferably, the graphitization calcination temperature is 2300–2800°C.

[0012] In this application, coal-based powder is used as the main carbon raw material, biomass tar is used as a binder, and pitch is used as a reinforcing agent for mixing and granulation. The resulting granules are then subjected to high-temperature graphitization calcination, which gradually transforms the carbon material within the granules into graphitized microcrystals. These microcrystals have a compact and ordered crystal structure, exhibiting excellent mechanical strength and melt dissolution rate, resulting in outstanding carbon-adding efficiency. Simultaneously, the high-temperature calcination allows for the full release of ash, volatile matter, and impurities such as hydrogen, nitrogen, and sulfur from the raw materials, effectively increasing the fixed carbon content in the carbon-adding agent.

[0013] It should be noted that the viscosity range selected for the biomass tar mentioned above gives it good adhesion, promoting the adhesion of coal-based raw materials to form granules. At the same time, this viscosity does not affect the penetration and diffusion capacity of the biomass tar.

[0014] Preferably, the coal-based powder is prepared according to the following method:

[0015] First roasting: The coal-based raw material is crushed and screened, and the screened powder is placed in an oxygen-free negative pressure environment and roasted at a low temperature of 400-800℃ for 2-4 hours to obtain a porous product.

[0016] Secondary roasting: The coal-based raw material is placed in a slightly aerobic environment and roasted at a low temperature of 230-300℃ for 1-3 hours to obtain oxidized coal-based powder; the oxygen volume percentage in the slightly aerobic environment is 0.2-0.7%.

[0017] Preferably, the coal-based raw material is one or more of anthracite, sub-bituminous coal, lignite, and bituminous coal.

[0018] Preferably, the vacuum degree of the oxygen-free negative pressure environment is -0.01 to -0.1 MPa.

[0019] The aforementioned stepwise roasting process can form a microporous channel structure on coal-based powder, which, in conjunction with biomass tar, forms a network reinforcement structure within the recarburizer during graphitization and calcination, effectively improving the mechanical strength of the recarburizer. Specifically, the primary roasting is carried out under oxygen-free negative pressure and high temperature. These conditions allow the organic volatiles in the coal-based raw material to escape rapidly, forming a microporous channel structure along the escape path. This channel allows biomass tar to permeate and diffuse, filling the interlaced channels and forming hard and continuous solid coke during graphitization and calcination. This results in a network-like reinforcement structure within the recarburizer, significantly improving its mechanical strength. Furthermore, the primary roasting requires temperature control to regulate the volatile matter release rate, which is beneficial for controlling pore size.

[0020] Furthermore, the secondary roasting is carried out in a slightly aerobic environment at low temperature. The presence of oxygen can, on the one hand, increase the internal defects of the coal-based powder and promote the formation of pore structures on the coal-based powder. On the other hand, the slightly aerobic environment can introduce polar oxygen-containing groups on the surface and in the pores of the carbonizer, which can enhance the wettability of the weakly polar biomass tar to the carbonizer, promote the penetration performance of biomass tar, and ensure the formation of the aforementioned network reinforcement structure.

[0021] Secondly, this application provides a method for preparing a coal-based recarburizing agent with high fixed carbon content, which adopts the raw material ratio of any of the above-mentioned recarburizing agents and includes the following steps:

[0022] Mixed granulation: Coal-based powder, asphalt and biomass tar are mixed and granulated. After granulation, the mixture is screened to remove particles with a diameter greater than 8 mm, and mixed granules are obtained.

[0023] Graphitization and calcination: The mixed granules are placed in an oxygen-free environment at 2300-2800℃ for graphitization treatment, and then cooled down after treatment to obtain the final product;

[0024] Preferably, the granulation is performed using rolling granulation or fluidized bed granulation.

[0025] Preferably, the graphitization process takes 5 to 8 days.

[0026] Preferably, before graphitization and calcination, the mixed granules are immersed in liquid carbon dioxide for 1 to 3 minutes, and then the granules are taken out and heated at 180 to 300°C to sublimate the liquid carbon dioxide; after sublimation, graphitization is carried out.

[0027] The mixed granules are immersed in liquid carbon dioxide. The micropores and defects formed by the secondary roasting of the coal-based powder can absorb a suitable amount of liquid carbon dioxide. After heating and sublimation, a large amount of gas is generated, creating gas pressure within the pores. This gas pressure causes the gas to expand and escape. On the one hand, this forms a pore structure in the mixed granules that complements the coal-based powder, giving the carburizer a porous structure overall. This is beneficial for improving the dissolution rate of the carburizer obtained after graphitization and calcination in the melt, thus increasing the carburizing efficiency. On the other hand, it also facilitates the full diffusion of biomass tar, further strengthening the network reinforcement structure.

[0028] It is important to note that the sublimation temperature used after soaking should not exceed 300℃. Excessively high temperatures not only easily lead to excessively rapid biochemical expansion, resulting in larger and uneven pore sizes, affecting the strength of the carbon raiser, but also easily cause combustion reactions, resulting in carbon loss and affecting carbon raising efficiency and mechanical strength. Conversely, the temperature should not be too low, as a slow sublimation expansion rate makes it difficult to form a uniform and fine microporous structure, thus affecting carbon raising efficiency.

[0029] In summary, this application has the following beneficial effects:

[0030] 1. This application uses coal-based powder, biomass tar and pitch as raw materials for mixing, granulation, graphitization and calcination, which is beneficial to improve the graphitization degree and fixed carbon content of the carbon raiser, and improve mechanical strength and carbon raising efficiency.

[0031] 2. This application employs a two-stage roasting process to pretreat coal-based powder. On the one hand, it forms a rich microporous channel structure in the particle structure; on the other hand, it introduces polar oxygen-containing groups on the particle surface and in the channels, thereby effectively coordinating the full diffusion of biomass tar into the channel structure. During graphitization and calcination, a hard and continuous network reinforcement structure is formed, which significantly improves the mechanical strength of the carburizing agent. At the same time, this channel structure can increase the contact area with molten steel and improve the dissolution and absorption efficiency of the carburizing agent (carburizing efficiency).

[0032] 3. Liquid carbon dioxide is adsorbed through the micropores formed by coal-based powder. Then, by heating, the liquid carbon dioxide sublimates rapidly within the pores, generating a large amount of gas. The expansion and escape caused by the gas pressure promotes the formation of porous structures on the carbon raiser, thereby improving carbon raising efficiency and further enhancing its mechanical strength. Detailed Implementation

[0033] Preparation Example

[0034] Preparation Example 1

[0035] Coal-based powder is prepared according to the following steps:

[0036] First roasting: Anthracite is added to a crusher for circulating crushing, the crushed powder is screened to remove particles larger than 3mm, the screened powder is placed in a nitrogen environment with a vacuum of -0.05MPa and roasted at 550±5℃ for 3h to obtain a porous product.

[0037] Secondary roasting: The coal-based raw material is placed in an environment with an oxygen volume percentage of 0.5% and roasted at a low temperature of 270±5℃ for 2 hours to obtain oxidized coal-based powder.

[0038] Preparation Example 2

[0039] Coal-based powder is prepared according to the following steps:

[0040] First roasting: Anthracite is added to a crusher for circulating crushing, the crushed powder is screened to remove particles larger than 3mm, the screened powder is placed in a nitrogen environment with a vacuum of -0.02MPa and roasted at a low temperature of 700±5℃ for 3h to obtain a porous product.

[0041] Secondary roasting: The coal-based raw material is placed in an environment with an oxygen volume percentage of 0.3% and roasted at a low temperature of 240±5℃ for 3 hours to obtain oxidized coal-based powder.

[0042] Preparation Example 3

[0043] Coal-based powder is prepared according to the following steps:

[0044] First roasting: Anthracite is added to a crusher for circulating crushing, the crushed powder is screened to remove particles with a diameter greater than 3mm, the screened powder is placed in a nitrogen environment with a vacuum degree of -0.1MPa, and roasted at a low temperature of 450±5℃ for 4h to obtain a porous product.

[0045] Secondary roasting: The coal-based raw material is placed in an environment with an oxygen volume percentage of 0.5% and roasted at a low temperature of 290±5℃ for 2 hours to obtain oxidized coal-based powder.

[0046] Preparation Example 4

[0047] Coal-based powder is prepared according to the following steps:

[0048] First roasting: The coal-based raw material is placed in an environment with an oxygen volume percentage of 0.7% and roasted at a low temperature of 290±5℃ for 2 hours to obtain oxidized coal-based powder.

[0049] Secondary roasting: Anthracite is added to a crusher for circulating crushing, and the crushed powder is screened to remove particles with a diameter greater than 3mm. The screened powder is placed in a nitrogen environment with a vacuum degree of -0.1MPa and roasted at a low temperature of 450±5℃ for 4h to obtain a porous product.

[0050] Preparation Example 5

[0051] The coal-based powder differs from that in Preparation Example 1 in that it was not roasted once. The specific operation is as follows:

[0052] Anthracite is added to a crusher for circulating crushing. The crushed powder is then screened to remove particles larger than 3 mm. The screened powder is then placed in an air environment and calcined at a low temperature of 270±5℃ for 2 hours to obtain oxidized coal-based powder.

[0053] Preparation Example 6

[0054] The coal-based powder differs from the preparation example 1 in that it is not subjected to secondary roasting; the porous product obtained from primary roasting is the coal-based powder.

[0055] Example

[0056] The coal tar pitch used in this example is Shenhua coal tar pitch, with a softening point of 150–160℃, a coking value of over 60%, an ash content of 12–13%, and a sulfur content of 1.8%. Petroleum asphalt has a softening point of 100–110℃ and a density of 1.082 kg / m³. 3 Ash content: 0.016%, Sulfur content: 2.2%.

[0057] Example 1

[0058] A coal-based carbon raiser with high fixed carbon content is prepared according to the following steps:

[0059] Mixed granulation: Take 1000g of the coal-based powder obtained in Preparation Example 1, mix it with 120g of coal tar pitch and 300g of wood tar (viscosity about 100000cP), add it to a rotary granulator for rolling granulation, and then sieve it to remove particles with a diameter greater than 8mm to obtain mixed granules.

[0060] Graphitization calcination: The mixed granules are placed in a graphite furnace and graphitized at a high temperature of 2500℃ in a nitrogen atmosphere. After 6 days, they are taken out and cooled down to obtain the final product.

[0061] Example 2

[0062] A coal-based carbon raiser with high fixed carbon content is prepared according to the following steps:

[0063] Mixed granulation: Take 1000g of the coal-based powder obtained in Preparation Example 1, mix it with 100g of coal tar pitch and 380g of wood tar (viscosity about 50000cP), add it to a rotary granulator for rolling granulation, and then sieve it to remove particles with a diameter greater than 8mm to obtain mixed granules.

[0064] Graphitization calcination: The mixed granules are placed in a graphite furnace and graphitized at a high temperature of 2500℃ in a nitrogen atmosphere. After 8 days, they are taken out and cooled down to obtain the final product.

[0065] Example 3

[0066] A coal-based carbon raiser with high fixed carbon content is prepared according to the following steps:

[0067] Mixed granulation: Take 1000g of the coal-based powder obtained in Preparation Example 1, mix it with 180g of coal tar pitch and 240g of wood tar (viscosity about 250000cP), add it to a rotary granulator for rolling granulation, and then sieve it to remove particles with a diameter greater than 8mm to obtain mixed granules.

[0068] Graphitization calcination: The mixed granules are placed in a graphite furnace and graphitized at a high temperature of 2700℃ in a nitrogen atmosphere. After 5 days, they are taken out and cooled down to obtain the final product.

[0069] Example 4

[0070] A coal-based carbon raiser with high fixed carbon content is prepared according to the following steps:

[0071] Mixed granulation: Take 1000g of the coal-based powder obtained in Example 1, mix it with 150g of coal tar pitch and 280g of straw tar (viscosity about 80000cP), add it to a rotary granulator for rolling granulation, and then sieve it to remove particles with a diameter greater than 8mm to obtain mixed granules.

[0072] Graphitization calcination: The mixed granules are placed in a graphite furnace and graphitized at a high temperature of 2400℃ in a nitrogen atmosphere.

[0073] Example 5

[0074] A coal-based carbon raiser with high fixed carbon content differs from Example 1 in that wood tar with a viscosity of 30,000 cP is used instead of wood tar with a viscosity of 100,000 cP.

[0075] Example 6

[0076] A coal-based carbon raiser with high fixed carbon content differs from Example 1 in that wood tar with a viscosity of 400,000 cP is used instead of wood tar with a viscosity of 100,000 cP.

[0077] Example 7

[0078] A coal-based carbon raiser with high fixed carbon content, which differs from Example 1 in that an equal amount of coal-based powder obtained in Preparation Example 4 is used to replace the coal-based powder obtained in Preparation Example 1.

[0079] Example 8

[0080] A coal-based carbon raiser with high fixed carbon content, which differs from Example 1 in that an equal amount of coal-based powder obtained in Preparation Example 5 is used to replace the coal-based powder obtained in Preparation Example 1.

[0081] Example 9

[0082] A coal-based carbon raiser with high fixed carbon content, which differs from Example 1 in that an equal amount of coal-based powder obtained in Preparation Example 6 is used to replace the coal-based powder obtained in Preparation Example 1.

[0083] Example 10

[0084] A coal-based carbon raiser with high fixed carbon content is prepared according to the following steps:

[0085] Mixed granulation: The coal-based powder obtained in Preparation Example 1 was mixed with coal tar pitch and wood tar (viscosity about 100,000 cP) and added to a rotary granulator for rolling granulation. After granulation, the mixture was screened to remove particles with a diameter greater than 8 mm, and mixed granules were obtained.

[0086] Graphitization calcination: The mixed granules are immersed in liquid carbon dioxide for 3 minutes, the granules are filtered out and heated at 260±5℃ to make the liquid carbon dioxide sublimate rapidly; when no gas escapes from the granules, the granules are placed in a graphite furnace and graphitized at 2500℃ in a nitrogen atmosphere. After 6 days, they are taken out and cooled to obtain the final product.

[0087] Example 11

[0088] A coal-based carbon raiser with high fixed carbon content is prepared according to the following steps:

[0089] Mixed granulation: The coal-based powder obtained in Preparation Example 1 was mixed with coal tar pitch and wood tar (viscosity about 100,000 cP) and added to a rotary granulator for rolling granulation. After granulation, the mixture was screened to remove particles with a diameter greater than 8 mm, and mixed granules were obtained.

[0090] Graphitization calcination: The mixed granules are immersed in liquid carbon dioxide for 1 minute, the granules are filtered out and heated at 200±5℃ to make the liquid carbon dioxide sublimate rapidly; when no gas escapes from the granules, the granules are placed in a graphite furnace and graphitized at 2500℃ in a nitrogen atmosphere. After 6 days, they are taken out and cooled to obtain the final product.

[0091] Comparative Example

[0092] Comparative Example 1

[0093] A coal-based carbon raiser with high fixed carbon content differs from Example 1 in that an equal amount of coal tar pitch is used to replace wood tar.

[0094] Comparative Example 2

[0095] A coal-based carbon raiser with high fixed carbon content differs from Example 1 in that an equal amount of wood tar is used to replace coal pitch.

[0096] Comparative Example 3

[0097] Commercially available graphite powder carbon raiser.

[0098] Performance testing

[0099] Experiment 1: Basic Indicator Test

[0100] The ash content, fixed carbon content, moisture content, and volatile matter content of the recarburizer were tested in accordance with the provisions of YBT192-2015 "Carburizing Agents for Steelmaking".

[0101] Experiment 2: Mechanical Strength Test

[0102] The compressive strength of the carbon raiser was determined in accordance with the provisions of JB / T8133.8-2013 "Test Methods for Physicochemical Properties of Electrocarbon Products - Part 8: Compressive Strength".

[0103] Experiment 3: Determination of apparent porosity of carbon raiser

[0104] The test was conducted in accordance with the provisions of YB / T908-1997 "Determination of Apparent Porosity of Carbon Materials".

[0105] Table 1. Test Results

[0106]

[0107] Analysis of experimental results:

[0108] First, it should be noted that the above compressive strength is used to characterize the mechanical strength of the carbon recarrier, while apparent porosity refers to the content of open pores in the carbon recarrier. The higher the content, the higher the specific surface area under the same particle size, and the carbon recarrier efficiency is also improved accordingly.

[0109] (1) As can be seen from Examples 1-11 and Comparative Examples 1-3, and Table 1, this application uses coal-based powder as the main carbon raw material, biomass tar as a binder, and pitch as a reinforcing agent for mixing, granulation, and graphitization calcination to obtain a carbon recharger with high fixed carbon content and good mechanical strength. This may be because graphitization calcination allows ash, volatile matter, and impurities such as hydrogen, nitrogen, and sulfur in the raw materials to be fully released, effectively increasing the fixed carbon content in the carbon recharger. It also promotes the orderly arrangement and recombination of carbon atoms, gradually forming graphite crystals, thus resulting in a carbon recharger with high mechanical strength and high fixed carbon content.

[0110] (2) As can be seen from Examples 1 and 7-9 and Table 1, this application adopts a stepwise roasting process, successively subjecting the coal-based raw materials to high-temperature negative pressure anaerobic roasting and low-temperature micro-aerobic roasting, which significantly improves the mechanical strength and apparent porosity of the obtained carbon raiser. The reason may be that the high-temperature negative pressure anaerobic roasting process allows volatiles and moisture in the coal-based raw materials to escape, thereby forming a rich microporous channel structure in the coal-based powder; while the low-temperature micro-aerobic roasting can introduce oxygen-containing groups into the surface channels of the powder, giving it weak polarity, thereby improving the compatibility between the coal-based powder and biomass tar, which is conducive to the wetting and penetration of biomass tar into the coal-based powder. When it penetrates into the aforementioned microporous channels, it can form hard and continuous solid coke in the graphitization calcination process, forming a strong true network structure, which greatly improves the mechanical strength of the carbon raiser.

[0111] It is evident that both primary and secondary calcination affect the reinforcing effect of the resulting network structure. Furthermore, the order of primary and secondary calcination also influences the distribution of polar groups and the morphology and quantity of the pore structure, thus affecting the reinforcing effect.

[0112] (3) Combining Examples 1 and 5-6 with Table 1, it can be seen that the viscosity of biomass tar affects both the mechanical strength and apparent porosity of the final carbon raiser. This may be because excessively high viscosity affects the penetration and wetting effect of biomass tar, hindering the formation of the network structure; while excessively low viscosity affects the cohesive effect on coal-based raw materials, hindering the improvement of the compactness of coal-based powder. Both factors affect the mechanical strength of the carbon raiser.

[0113] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A coal-based carburizer with high fixed carbon content, characterized in that, The carbon additive is prepared by mixing and granulating raw materials including coal-based powder, biomass tar and pitch in a mass ratio of 100:20-40:10-20, and then graphitizing and calcining the mixed granules. The coal-based powder is prepared by the following method: Primary roasting: the coal-based raw material is crushed and sieved, and the sieved powder is placed in an oxygen-free negative pressure environment and roasted at a low temperature of 400-800℃ for 2-4h to obtain a porous product; Secondary roasting: the coal-based raw material is placed in a micro-oxygen environment and roasted at a low temperature of 230-300℃ for 1-3h to obtain oxidized coal-based powder; the oxygen volume percentage in the micro-oxygen environment is 0.2-0.7%.

2. The carburant according to claim 1, characterized in that, The D50 particle size of the coal-based powder is less than or equal to 3mm.

3. The carburant according to claim 1, characterized in that, The pitch is coal pitch and / or petroleum pitch.

4. The carburant according to claim 1, characterized in that, The biomass tar is selected from one or more of wood tar, straw tar, rice husk tar and algal tar.

5. The carburant according to claim 1, characterized in that, The viscosity of the biomass tar is 50000-300000cP at a temperature of 20-25℃.

6. The carburant according to claim 1, characterized in that, The coal-based raw material is a combination of one or more of anthracite, subanthracite, lignite and bituminous coal.

7. The carburant according to claim 1, characterized in that, The vacuum degree of the oxygen-free negative pressure environment is -0.01 to -0.1MPa.

8. A method for producing a coal-based carbon increaser having a high fixed carbon content, characterized by, The raw material ratio of the carbon additive is as claimed in any one of claims 1-7, and the method comprises the following steps: Mixing and granulating: the coal-based powder, pitch and biomass tar are mixed and granulated, and the granules with a particle size greater than 8mm are sieved out to obtain mixed granules; Graphitizing and calcining: the mixed granules are placed in an oxygen-free environment at 2300-2800℃ for graphitization treatment, and then cooled to obtain the carbon additive; The granulation is performed by rolling or fluidized bed granulation; the graphitization treatment time is 5-8 days.

9. The preparation method of claim 8, wherein before the roasting step, the mixed granules are immersed in liquid carbon dioxide for 1-3min, then taken out and heated at 180-300℃ to make the liquid carbon dioxide sublimate; after sublimation, the graphitization treatment is performed.

Images