High-strength biomass carbon-containing pellet and preparation method and application thereof

Abstract

This invention discloses a high-strength biomass carbon-containing pellet, its preparation method, and its application, relating to the field of blast furnace ironmaking technology. The pellet comprises the following raw materials by mass fraction: 70%–85% iron ore, 4%–15% binder, 5%–11% biochar, and 1%–3% basic flux. The high-strength biomass carbon-containing pellet of this invention exhibits high strength and good wear resistance. Its high thermal detonation temperature and low thermal detonation index effectively reduce powder generation after entering the blast furnace. The high-strength biomass carbon-containing pellet exhibits superior reducibility, reductive expansion, and low-temperature reductive pulverization performance compared to traditional sintered ore, pelletized ore, and lump ore. It can be directly used as blast furnace feedstock, reducing the amount of coke used in blast furnace smelting, thereby reducing ironmaking costs and CO2 emissions, resulting in significant economic, social, and ecological benefits.

Description

Technical Field

[0001] This invention relates to a blast furnace ironmaking technology, and particularly to a high-strength biomass carbon-containing pellet, its preparation method, and its application. Background Technology

[0002] Traditional blast furnace burdens mainly consist of sintered ore and pellets, which undergo iron oxide reduction and slag-iron separation processes within the blast furnace. This process ensures high porosity and gas permeability in the blast furnace's bulk zone, facilitating stable and smooth blast furnace operation. However, both sintering and pelletizing processes require high temperatures, consuming large amounts of fossil fuels and emitting significant pollutants. Therefore, finding a new type of burden that can replace sintered ore and pellets is crucial for achieving green, low-carbon, and sustainable development in blast furnace ironmaking.

[0003] Cold-bonded carbon-containing pellets are a type of ore pellet with added carbonaceous reducing agents. Compared to traditional sintered ore and oxide pellets, carbon-containing pellets expand the interface of the carbon-oxygen reduction reaction, reduce gas diffusion at the solid-phase reaction interface, and allow for direct contact between carbon and oxygen. Furthermore, the diffusion of gases generated during the reduction reaction also inhibits the oxidation of oxidizing gases. Carbon-containing pellets are an effective means of reducing the coke ratio and fuel ratio, and improving production efficiency in blast furnace smelting.

[0004] Compared with sintered ore and traditional oxide pellets, cold-consolidated pellets do not require high-temperature sintering or roasting. They have the advantages of simple equipment, short process flow, low construction investment cost, and low CO2 and pollutant emissions. In particular, cold-consolidated pellets can be made by briquetting iron ore powder and coal powder reducing agent together to prepare iron-containing materials with a certain carbon content, which is difficult to achieve with traditional sintered ore and oxide pellets.

[0005] Traditional cold-bonded pellets generally use binders as the main measure to improve pellet strength. However, this method has problems such as high cost of binders, large usage, low consolidation strength, reduced iron grade, and high content of harmful elements. How to improve the strength of cold-bonded pellets has become the key issue for its successful application in blast furnace ironmaking production.

[0006] The related technology discloses a carbon-containing pellet for blast furnaces, which uses sintering machine head electrostatic precipitator ash, blast furnace gas mud, furnace front ore bin dust and calcium-free slag as raw materials, and adds bentonite and hydrated lime as binders to prepare carbon-containing pellets, realizing the resource recycling of waste. However, the pellets have a high content of harmful elements and a compressive strength of only 96.82 N / piece, making it difficult to apply to blast furnace ironmaking production.

[0007] The related technology discloses a method for preparing hot-pressed carbon-containing iron ore pellets and ironmaking raw materials. Iron ore powder, coal powder and flux are uniformly mixed and heated for hot pressing. The hot-pressed pellets are then subjected to long-term heat treatment at high temperature to produce pellets with a compressive strength greater than 2000N / piece and a drop strength greater than 4 times / piece. However, this process requires hot pressing, which places relatively stringent requirements on the forming equipment. In addition, the high-temperature heat treatment process consumes a large amount of heat and emits pollutants, making it difficult to meet the current requirements for green and low-carbon steel production. Summary of the Invention

[0008] The purpose of this invention is to provide a high-strength biomass carbon-containing pellet to solve at least one aspect of the problems and defects mentioned in the background art.

[0009] The present invention also provides a method for preparing the above-mentioned high-strength biomass carbon-containing pellets.

[0010] This invention also provides applications of the aforementioned high-strength biomass carbon-containing pellets.

[0011] Specifically, the first aspect of this invention discloses a high-strength biomass carbon-containing pellet, comprising the following raw materials by mass fraction:

[0012] 70%–85% iron ore, 4%–15% binder, 5%–11% biochar, 1%–3% alkaline flux. The binder is used to improve the room temperature and high temperature strength of the carbon-containing pellets, the biochar is a reducing agent for iron ore, and the alkaline flux improves the high temperature metallurgical properties of the carbon-containing pellets.

[0013] According to one technical solution of the high-strength biomass carbon-containing pellet technology of the present invention, it has at least the following beneficial effects:

[0014] The high-strength biomass carbon-containing pellets of the present invention can partially replace sintered ore, pellets and lump ore in blast furnace ironmaking production, reducing CO2 and pollutant emissions from ironmaking production.

[0015] The biomass carbon-containing pellets of the present invention have the characteristics of high compressive strength and good wear resistance. They do not crack, pulverize or deteriorate during production, transportation, storage and use, reduce the return ore rate, improve the permeability of the blast furnace block zone, and are conducive to improving the economic and technical indicators of blast furnace ironmaking.

[0016] According to some embodiments of the present invention, the iron ore includes at least one of hematite, magnetite and limonite.

[0017] According to some embodiments of the present invention, the iron ore powder has a particle size of less than 0.074 mm, accounting for more than 50% by mass.

[0018] According to some embodiments of the present invention, the adhesive includes at least one selected from cement, bentonite, aluminum dihydrogen phosphate, water glass, gelatinized starch, sodium carboxymethyl cellulose, and phenolic resin.

[0019] According to some embodiments of the present invention, the adhesive has a particle size of less than 0.1 mm and accounts for more than 12% by mass.

[0020] According to some embodiments of the present invention, the biochar includes at least one of straw pyrolysis char and waste wood pyrolysis char.

[0021] According to some embodiments of the present invention, the volatile matter content of the biochar is less than 25%.

[0022] According to some embodiments of the present invention, the biochar has a particle size of less than 0.074 mm accounting for more than 60% by mass.

[0023] According to some embodiments of the present invention, the alkaline flux includes at least one of limestone, dolomite, quicklime, calcined dolomite, hydrated lime, serpentine, and forsterite.

[0024] According to some embodiments of the present invention, the mass proportion of the alkaline flux with a particle size of less than 0.074 mm is more than 50%.

[0025] According to some embodiments of the present invention, the compressive strength of the high-strength carbon-containing pellets is greater than 2000 N / pellet.

[0026] According to some embodiments of the present invention, the high-strength carbon-containing pellets have a drop strength greater than 10 times on a 2-meter cement floor.

[0027] According to some embodiments of the present invention, the wear index of the high-strength carbon-containing pellets is less than 10%.

[0028] According to some embodiments of the present invention, the thermal bursting temperature of the high-strength carbon-containing pellets is greater than 800°C.

[0029] According to some embodiments of the present invention, the thermal bursting index of the high-strength carbon-containing pellets is less than 2%.

[0030] According to some embodiments of the present invention, the reducing power of the high-strength carbon-containing pellets is greater than 80%.

[0031] According to some embodiments of the present invention, the reduction expansion index of the high-strength carbon-containing pellets is less than 7%.

[0032] According to some embodiments of the present invention, the low-temperature reduction pulverization index of the high-strength carbon-containing pellets is greater than 91%.

[0033] A second aspect of this invention provides a method for preparing the above-mentioned high-strength biomass carbon-containing pellets, comprising the following steps:

[0034] S1. The raw materials and water are mixed to obtain a water-containing homogeneous material;

[0035] S2. High-pressure molding of the water-containing mixed material followed by heat treatment;

[0036] The heat treatment temperature is 200℃~700℃.

[0037] According to one technical solution of the preparation method of the present invention, at least the following beneficial effects are achieved:

[0038] The heat treatment temperature of this invention is between 200℃ and 700℃, which can promote the rapid curing of the high-temperature binder, enhance the compressive strength and drop strength of the pellets, improve the wear resistance of the pellets, and meet the quality requirements of the raw materials in the transportation, storage and use process of blast furnace smelting.

[0039] This invention uses a high-pressure heat treatment method to prepare high-strength biomass carbon-containing pellets. Compared with traditional sintering and oxidation pelletizing processes, it has the advantages of shorter process flow, less equipment investment, lower heating temperature, lower energy consumption, and less pollutant and CO2 emissions, which meets the strategic needs of current green and low-carbon metallurgical development.

[0040] According to some embodiments of the present invention, the heat treatment time is 10 min to 100 min.

[0041] According to some embodiments of the present invention, the heat treatment time is 20 min to 60 min.

[0042] According to some embodiments of the present invention, the temperature of the heat treatment is 300°C to 500°C.

[0043] According to some embodiments of the present invention, the high-pressure forming is one of a roller briquetting machine and a hydraulic forming machine.

[0044] According to some embodiments of the present invention, biomass carbon-containing pellets are obtained after high-pressure molding.

[0045] According to some embodiments of the present invention, the biomass carbon-containing pellets have a drop strength of more than 3 times when dropped from a height of 0.5m.

[0046] According to some embodiments of the present invention, the heating method of the heat treatment is at least one of electric heating, gas combustion heating and microwave heating.

[0047] According to some embodiments of the present invention, the heat treatment apparatus includes one of a chain grate machine, a rotary kiln, a tunnel kiln, a vertical shaft furnace, and a belt conveyor.

[0048] According to some embodiments of the present invention, the mass ratio of the raw materials to the water is 100:7 to 9.

[0049] The third aspect of this invention provides the application of the above-mentioned high-strength biomass carbon-containing pellets in blast furnace ironmaking production. Detailed Implementation

[0050] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0051] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0053] This invention provides a method for preparing high-strength biomass carbon-containing pellets, which are obtained by the following method:

[0054] S1) Iron ore powder, binder, biochar, and alkaline flux are mixed in a mass ratio of 70%–85% iron ore powder, 4%–15% binder, 5%–11% biochar, and 1%–3% alkaline flux.

[0055] S2) The mixture obtained in step S1 is fed into a high-power mixer for mixing. During the mixing process, 7% to 9% water is added to obtain a water-containing mixed material. The mixed material is then loaded into a pressure molding equipment for high-pressure molding to obtain biomass carbon-containing pellets.

[0056] S3) The biomass carbon-containing pellets prepared in step S2) are fed into a heating furnace, and the heating temperature is controlled at 200℃~700℃. After heating for 10min~100min, the strength of the pellets is improved, and high-strength biomass carbon-containing pellet products are obtained.

[0057] By adopting the above technical solution, iron ore powder, binder, biochar and flux are mixed into a mixture, which is then fed into a high-intensity mixer for homogenization. The homogenized mixture is then fed into a briquetting machine for high-intensity briquetting. The pressure-formed briquettes are then fed into a heating furnace for medium and low temperature heating treatment to improve the strength of the briquettes, resulting in high-strength carbon-containing briquette products.

[0058] The high-strength carbon-containing pellets prepared in the embodiments of the present invention have the characteristics of high compressive strength, excellent wear resistance and good reducibility. They can be used as substitutes for sinter, pellets and lump ore in blast furnace ironmaking, direct reduction ironmaking and smelting reduction ironmaking. They can reduce the emission of CO2 and pollutants in the ironmaking process and have good environmental and economic benefits.

[0059] Furthermore, the iron ore powder in S1) includes a mixture of one or more iron ores, such as hematite, magnetite, and limonite.

[0060] Furthermore, the proportion of iron ore powder with a particle size of less than 0.074 mm is more than 50%.

[0061] Furthermore, the binder in S1) includes one or a mixture of several binders selected from cement, bentonite, aluminum dihydrogen phosphate, water glass, gelatinized starch, sodium carboxymethyl cellulose, and phenolic resin.

[0062] Furthermore, the proportion of adhesive particles smaller than 0.1 mm is more than 12%.

[0063] Furthermore, the biochar in S1) includes one or a mixture of several of the following: straw pyrolysis char and waste wood pyrolysis char.

[0064] Furthermore, the volatile matter content of the biochar is less than 25%, and the proportion of particles smaller than 0.074 mm is more than 60%.

[0065] Furthermore, the alkaline flux in S1) includes a mixture of several alkaline fluxes selected from limestone, dolomite, slaked lime, lightly calcined dolomite, quicklime, serpentine, and forsterite.

[0066] Furthermore, the proportion of alkaline flux particles smaller than 0.074 mm is more than 50%.

[0067] Furthermore, the pressure forming equipment in S2) includes a roller briquetting machine and a hydraulic forming machine, and the prepared biomass carbon-containing pellets have a drop strength of more than 3 times at 0.5m.

[0068] Furthermore, the heating furnace in S3) includes one or more of the following combinations: chain grate machine, rotary kiln, tunnel kiln, vertical furnace, and belt conveyor.

[0069] Furthermore, the heat source for the heating furnace can be a combination of several heating methods, including electric heating, gas combustion heating, and microwave heating.

[0070] Furthermore, the heating temperature is between 300℃ and 500℃, and the heating time is between 20 minutes and 60 minutes.

[0071] Furthermore, the high-strength biomass carbon-containing pellets in S3 have a compressive strength greater than 2000N / pellet, a drop strength of more than 10 times on a 2-meter cement floor, an abrasion index of less than 5%, a thermal bursting temperature greater than 800℃, a thermal bursting index of less than 2%, a reducibility of more than 80%, a reduction expansion index of less than 7%, and a low-temperature reduction pulverization index of more than 91%.

[0072] Furthermore, the high-strength biomass carbon-containing pellets in S3 can partially or even completely replace sinter, pellet frames, and lump ore in blast furnace ironmaking, direct reduction ironmaking, and molten reduction ironmaking, reducing CO2 and pollutant emissions from ironmaking production.

[0073] Example 1

[0074] This embodiment is a high-strength biomass carbon-containing pellet, composed of the following raw materials by mass fraction:

[0075] 72% iron ore powder, 15% high-temperature binder, 11% biochar (cotton straw charcoal), 2% alkaline flux.

[0076] In this embodiment, the iron ore powder is hematite powder, which is pulverized by a ball mill. The mass proportion of the pulverized particles smaller than 0.074mm is more than 60%. The ball mill is a φ900×1800 type equipment manufactured by Zhonghui Machinery.

[0077] In this embodiment, the biochar is cotton stalk char. The biochar is pulverized using a medium-speed mill, and the mass percentage of the pulverized particles smaller than 0.074 mm is more than 65%.

[0078] In this embodiment, the high-temperature binder uses bentonite and aluminum dihydrogen phosphate, wherein the mass percentage of bentonite is 55%, the mass percentage of aluminum dihydrogen phosphate is 45%, and the mass percentage of particles with a size of 0.1 mm is more than 60%.

[0079] In this embodiment, the alkaline flux is slaked lime, and the slaked lime has a particle size of less than 0.074 mm and a mass ratio of more than 55%.

[0080] The method for preparing high-strength biomass carbon-containing pellets in this embodiment consists of the following steps:

[0081] S1. Iron ore powder, high-temperature binder, biochar and alkaline flux are mixed into a mixture. The mixture is loaded into a cylindrical mixer for homogenization. During the homogenization process, 7% by mass of water is added (the mass ratio of the mixture to water is 100:7).

[0082] S2. The material mixed in step S1 is shaped using a roller briquetting machine. The maximum linear pressure of the roller briquetting machine is 11t / cm, and the size of the shaped pellets is 22mm×25mm×28mm, thus obtaining wet pellets.

[0083] S3. Add the wet pellets to the electric rotary kiln and heat at 400°C for 20 minutes under an oxygen-free atmosphere. After heating, cool under a nitrogen atmosphere.

[0084] In this embodiment, the wet pellet formed in step S2 has a drop strength of 6 times at 0.5m.

[0085] The cooled biomass-containing carbon pellets were subjected to metallurgical performance tests according to GB / T14201-1993-Method for Determining the Compressive Strength of Iron Ore Pellets and GB / T10322.6-2004-Method for Determining the Hot Cracking Index of Iron Ore. The results showed that the cold compressive strength reached 2100 N / pellet, the drop strength on a 2-meter cement floor was 13 times, the abrasion index was 6.37%, the hot cracking index was 1.8%, the reducibility was 82.3%, the reduction expansion index was 6.27%, and the low-temperature reduction pulverization index was 92.1%.

[0086] The high-strength biomass carbon-containing pellets prepared in this embodiment exhibit high strength and good wear resistance. Their high thermal detonation temperature and low thermal detonation index effectively reduce powder generation after entering the blast furnace. The high-strength biomass carbon-containing pellets demonstrate superior reducibility, reductive expansion, and low-temperature reductive pulverization properties compared to traditional sintered ore, pellets, and lump ore. They can be directly used as blast furnace feedstock, reducing the amount of coke used in blast furnace smelting, thereby lowering ironmaking costs and CO2 emissions, resulting in significant economic, social, and ecological benefits.

[0087] Example 2

[0088] This embodiment is a high-strength biomass carbon pellet, which differs from Embodiment 1 in that cotton straw charcoal is replaced with soybean straw charcoal.

[0089] The amount of raw materials used and the method for preparing high-strength biomass carbon-containing pellets were carried out in accordance with Example 1.

[0090] Example 3

[0091] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Embodiment 1 in that cotton straw charcoal is replaced with corn straw charcoal.

[0092] The amount of raw materials used and the method for preparing high-strength biomass carbon-containing pellets were carried out in accordance with Example 1.

[0093] Example 4

[0094] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Embodiment 2 in that hematite is replaced with magnetite.

[0095] The amount of raw materials used and the method for preparing high-strength biomass carbon-containing pellets were carried out in accordance with Example 1.

[0096] Example 5

[0097] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Embodiment 4 in that soybean straw charcoal is replaced with wheat straw charcoal.

[0098] The amount of raw materials used and the method for preparing high-strength biomass carbon-containing pellets were carried out in accordance with Example 1.

[0099] Example 6

[0100] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Embodiment 2 in that hematite is replaced with limonite.

[0101] The amount of raw materials used and the method for preparing high-strength biomass carbon-containing pellets were carried out in accordance with Example 1.

[0102] The types of iron ore powder and biochar used in Examples 2-6 are shown in Table 1; Table 2 shows the metallurgical properties of the biomass carbon-containing pellets prepared in Examples 2-6.

[0103] Table 1. Types of iron ore powder and biochar in Examples 2-6

[0104] Example Iron ore powder Biochar Example 2 Hematite Soybean straw charcoal Example 3 Hematite Corn stalk charcoal Example 4 magnetite Soybean straw charcoal Example 5 magnetite Wheat straw charcoal Example 6 goethite Soybean straw charcoal

[0105] Table 2 Performance of Biomass Carbon-Containing Pellet Preparations in Examples 2-6

[0106]

[0107] As shown in Table 2, the wet high-strength biomass carbon-containing pellets prepared in Examples 2-6 all exhibited a 0.5m drop strength exceeding 5 times, meeting the performance requirements for subsequent heating and strengthening processes in the furnace. After heat treatment, the cold compressive strength exceeded 2030 N / pellet, the 2m drop strength exceeded 11 times, the abrasion index was less than 6.62%, the thermal burst temperature was greater than 800℃, the thermal burst index was less than 2%, the reducibility was greater than 80.6%, the reduction expansion index was less than 6.4%, and the low-temperature reduction pulverization index was greater than 91.8%. Therefore, these pellets can be used as alternative raw materials for blast furnace smelting of sintered ore and pellets.

[0108] When using the same iron ore powder as raw material, different choices of carbon reducing agents result in different properties in the prepared carbon-containing pellets. Among them, the cold compressive strength of high-strength carbon-containing pellets prepared with cotton straw charcoal as the carbon reducing agent is significantly higher than that of carbon-containing pellets prepared with soybean straw charcoal and corn straw charcoal as reducing agents. The main reason is that the bulk density of soybean straw charcoal and corn straw charcoal is lower than that of cotton straw charcoal. Under the same addition amount, soybean straw charcoal and corn straw charcoal have a larger volume, which reduces the amount of binder in the unit volume of pellets when the amount of binder is constant, thus affecting the compressive strength of the high-strength biomass carbon-containing pellets obtained after heat treatment.

[0109] Similarly, due to the highest density of magnetite and the lowest density of limonite, carbon-containing pellets made from magnetite and cotton straw charcoal have the highest drop strength and compressive strength under the same biochar conditions. Wheat straw charcoal has the lowest bulk density compared to soybean straw charcoal, corn straw charcoal, and cotton straw charcoal, and carbon-containing pellets made from magnetite and wheat straw charcoal also have low strength.

[0110] Examples 2-6 also show that the best reduction was achieved with carbon-containing pellets prepared from magnetite and wheat straw charcoal. This is mainly because wheat straw charcoal has good reactivity and can undergo a reduction reaction with iron ore powder at relatively low temperatures. However, it can also be seen that the carbon-containing pellets prepared from wheat straw charcoal have the highest reduction expansion index. This is mainly because wheat straw charcoal can undergo a reduction reaction with iron ore powder at relatively low temperatures. The large amount of gaseous products generated during the diffusion of these products to the outside of the pellets increases internal stress, thus increasing the expansion index. At the same time, wheat straw charcoal has a high content of alkali metal (K) elements, which easily generates a liquid phase during the reduction process. The uneven diffusion of the liquid phase also leads to the expansion of the pellet volume.

[0111] As can be seen from Table 2, the metallurgical properties of high-strength biomass carbon-containing pellets prepared under different conditions vary to some extent, but they can all meet the requirements of blast furnace smelting and can be directly used as blast furnace feedstock, reducing the amount of coke used in blast furnace smelting, thereby reducing ironmaking costs and CO2 emissions, and having significant economic, social and ecological benefits.

[0112] Example 7

[0113] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Example 4 in that the mass fraction of the raw materials used in its preparation is different.

[0114] In this embodiment, the high-strength biomass carbon-containing pellets are composed of the following raw materials by mass fraction:

[0115] 76% iron ore powder, 13% high-temperature binder, 9% biochar (cotton straw charcoal), 2% alkaline flux.

[0116] The preparation method was carried out in accordance with Example 4.

[0117] Example 8

[0118] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Example 4 in that the mass fraction of the raw materials used in its preparation is different.

[0119] In this embodiment, the high-strength biomass carbon-containing pellets are composed of the following raw materials by mass fraction:

[0120] 75% iron ore powder, 14% high-temperature binder, 9% biochar (soybean straw charcoal), 2% alkaline flux.

[0121] The preparation method was carried out in accordance with Example 4.

[0122] Example 9

[0123] This embodiment is a high-strength biomass carbon-containing pellet, composed of the following raw materials by mass fraction:

[0124] 75% iron ore powder, 13% high-temperature binder, 10% biochar (soybean straw charcoal), 2% alkaline flux.

[0125] In this embodiment, the iron ore powder is magnetite powder, which is pulverized by a ball mill. The mass proportion of the pulverized particles smaller than 0.074 mm is more than 60%.

[0126] In this embodiment, the biochar is cotton stalk char. The biochar is pulverized using a medium-speed mill, and the mass percentage of the pulverized particles smaller than 0.074 mm is more than 65%.

[0127] In this embodiment, the high-temperature binder uses bentonite and aluminum dihydrogen phosphate, wherein the mass percentage of bentonite is 55%, the mass percentage of aluminum dihydrogen phosphate is 45%, and the mass percentage of particles with a size of 0.1 mm is more than 60%.

[0128] In this embodiment, the alkaline flux is slaked lime, and the slaked lime has a particle size of less than 0.074 mm and a mass ratio of more than 55%.

[0129] The method for preparing high-strength biomass carbon-containing pellets in this embodiment consists of the following steps:

[0130] S1. Iron ore powder, high-temperature binder, biochar and alkaline flux are mixed into a mixture. The mixture is loaded into a cylindrical mixer for homogenization. During the homogenization process, 7% by mass of water is added (the mass ratio of the mixture to water is 100:7).

[0131] S2. The material mixed in step S1 is shaped using a roller briquetting machine. The maximum linear pressure of the roller briquetting machine is 11t / cm, and the size of the shaped pellets is 22mm×25mm×28mm, thus obtaining wet pellets.

[0132] S3. Add the wet pellets to the electric rotary kiln and heat them at 500°C for 15 minutes under an oxygen-free atmosphere. After heating, cool them under the exhaust gas of the hot blast stove.

[0133] Example 10

[0134] This embodiment is a high-strength biomass carbon-containing pellet, composed of the following raw materials by mass fraction:

[0135] 74% iron ore powder, 14% high-temperature binder, 10% biochar (soybean straw charcoal), 2% alkaline flux.

[0136] In this embodiment, the iron ore powder is magnetite powder, which is pulverized by a ball mill. The mass proportion of the pulverized particles smaller than 0.074 mm is more than 60%.

[0137] In this embodiment, the biochar is cotton stalk char. The biochar is pulverized using a medium-speed mill, and the mass percentage of the pulverized particles smaller than 0.074 mm is more than 65%.

[0138] In this embodiment, the high-temperature binder uses bentonite and aluminum dihydrogen phosphate, wherein the mass percentage of bentonite is 55%, the mass percentage of aluminum dihydrogen phosphate is 45%, and the mass percentage of particles with a size of 0.1 mm is more than 60%.

[0139] In this embodiment, the alkaline flux is slaked lime, and the slaked lime has a particle size of less than 0.074 mm and a mass ratio of more than 55%.

[0140] The method for preparing high-strength biomass carbon-containing pellets in this embodiment consists of the following steps:

[0141] S1. Iron ore powder, high-temperature binder, biochar and alkaline flux are mixed into a mixture. The mixture is loaded into a cylindrical mixer for homogenization. During the homogenization process, 7% by mass of water is added (the mass ratio of the mixture to water is 100:7).

[0142] S2. The material mixed in step S1 is shaped using a roller briquetting machine. The maximum linear pressure of the roller briquetting machine is 11t / cm, and the size of the shaped pellets is 22mm×25mm×28mm, thus obtaining wet pellets.

[0143] S3. Add the wet pellets to the electric rotary kiln and heat at 500°C for 20 minutes under an oxygen-free atmosphere. After heating, cool under a nitrogen atmosphere.

[0144] Example 11

[0145] This embodiment is a high-strength biomass carbon-containing pellet, and the raw materials used in its preparation are the same as those in Example 4.

[0146] The preparation method differs from that in Example 4 in that:

[0147] S3. Add the wet pellets to the electric rotary kiln and heat at 500°C for 20 minutes under an oxygen-free atmosphere. After heating, cool under a nitrogen atmosphere.

[0148] Example 12

[0149] This embodiment is a high-strength biomass carbon-containing pellet, and the raw materials used in its preparation are the same as those in Example 4.

[0150] The preparation method differs from that in Example 4 in that:

[0151] S3. Add the wet pellets to the electric rotary kiln and heat at 400°C for 30 minutes under an oxygen-free atmosphere. After heating, cool under a nitrogen atmosphere.

[0152] The amounts of biochar, high-temperature binder, and heat treatment temperatures used in Examples 7-12 are shown in Table 3. Table 4 shows the metallurgical properties of the high-strength biomass carbon-containing pellets prepared in Examples 7-12.

[0153] Table 3 Preparation parameters of Examples 7-12

[0154]

[0155] Table 4. Properties of high-strength carbon-containing pellets prepared in Examples 7-12

[0156]

[0157] As shown in Table 4, the high-strength biomass carbon-containing wet pellets prepared in Examples 7-12 exhibited a 0.5m drop strength of 6-7 times, a cold compressive strength of 2061-2211 N / pellet, a 2m drop strength of 12-15 times, an abrasion index of 3.16%-3.81%, a thermal burst temperature greater than 800°C, a thermal burst index less than 2%, a reducibility of 80.3%-81.6%, a reduction expansion index of 4.7%-5.1%, and a low-temperature reduction pulverization index of 92.5%-93.6%.

[0158] The slight differences in strength between samples prepared in different embodiments are mainly due to the fact that, with the same carbon reducing agent content, the increased amount of high-temperature binder leads to a stronger skeleton formed during heat treatment, resulting in increased strength of the high-strength carbon-containing pellets. Conversely, when the amount of high-temperature binder remains constant, the increased amount of carbon reducing agent causes an increase in pellet volume, making it difficult to form a high-strength solidified skeleton during heat curing, thus leading to a decrease in the strength of the carbon-containing pellets.

[0159] Meanwhile, the strength of high-strength carbon-containing pellets is also affected by heat treatment temperature and time. Bentonite maintains good bonding effect at room temperature and lower temperatures, while aluminum dihydrogen phosphate is a high-temperature binder. As the heat treatment temperature increases, the consolidation effect improves, and the strength of the prepared carbon-containing pellets increases. The reducibility of high-strength carbon-containing pellets is mainly affected by the type of carbon reducing agent. Under the same reducing agent conditions, the reducibility of the pellets remains basically stable. The reduction expansion and low-temperature reduction pulverization properties are greatly affected by the pellet strength. As the pellet strength increases, the reduction expansion index decreases, while the low-temperature reduction pulverization index increases, thus improving the reduction expansion and low-temperature reduction pulverization properties of high-strength carbon-containing pellets.

[0160] As can be seen from Table 4, the metallurgical properties of high-strength biomass carbon-containing pellets produced under different conditions vary to some extent, but they can all meet the requirements of blast furnace smelting and can be directly used as blast furnace feedstock, reducing the amount of coke used in blast furnace smelting, thereby reducing ironmaking costs and CO2 emissions, and having significant economic, social and ecological benefits.

[0161] Example 13

[0162] This embodiment is a high-strength biomass carbon-containing pellet, composed of the following raw materials by mass fraction:

[0163] 76% iron ore powder, 12% high-temperature binder, 10% biochar (soybean straw charcoal), 2% alkaline flux.

[0164] In this embodiment, the iron ore powder is magnetite powder, which is pulverized by a ball mill. The mass proportion of the pulverized particles smaller than 0.074 mm is more than 60%.

[0165] In this embodiment, the biochar is cotton stalk char. The biochar is pulverized using a medium-speed mill, and the mass percentage of the pulverized particles smaller than 0.074 mm is more than 65%.

[0166] In this embodiment, the high-temperature binder is composed of 70% asphalt analogue, 20% phenolic resin, and 10% sodium carboxymethyl cellulose by mass, with a particle size of 0.1 mm accounting for more than 60% by mass.

[0167] In this embodiment, the alkaline flux is slaked lime, and the slaked lime has a particle size of less than 0.074 mm and a mass ratio of more than 55%.

[0168] The preparation method in this embodiment is the same as that in Example 4.

[0169] Example 14

[0170] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Example 13 in the mass fraction of the raw materials used in its preparation.

[0171] In this embodiment, the high-strength biomass carbon-containing pellets are composed of the following raw materials by mass fraction:

[0172] 75% iron ore powder, 13% high-temperature binder, 10% biochar (soybean straw charcoal), 2% alkaline flux.

[0173] Example 15

[0174] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Example 13 in the mass fraction of the raw materials used in its preparation.

[0175] In this embodiment, the high-strength biomass carbon-containing pellets are composed of the following raw materials by mass fraction:

[0176] 74.5% iron ore powder, 14% high-temperature binder, 10% biochar (soybean straw charcoal), 1.5% alkaline flux.

[0177] Example 16

[0178] This embodiment is a high-strength biomass carbon-containing pellet, which differs from Example 13 in the mass fraction of the raw materials used in its preparation.

[0179] In this embodiment, the high-strength biomass carbon-containing pellets are composed of the following raw materials by mass fraction:

[0180] 73.5% iron ore powder, 15% high-temperature binder, 10% biochar (soybean straw charcoal), 1.5% alkaline flux.

[0181] The specific values ​​for the types of binders, binder usage, types of alkaline flux, and amounts of alkaline flux used in Examples 13-16 are shown in Table 5 (asphalt analogue: No. 30 asphalt produced by Hunan Xinyue Asphalt Co., Ltd.; phenolic resin: Type 2402 produced by Shandong Maofa Chemical Co., Ltd.). Table 6 shows the metallurgical properties of the biomass carbon-containing pellets prepared in Examples 13-16.

[0182] Table 5. Types and amounts of adhesives used in Examples 13-16

[0183]

[0184] Table 6. Properties of high-strength carbon-containing pellets prepared in Examples 13-16

[0185]

[0186] As shown in Table 6, the high-strength biomass carbon-containing pellets prepared in Examples 13-16 can meet the requirements of blast furnace smelting. Compared with Example 4, it can be seen that the binder of 70% asphalt analog + 20% phenolic resin + 10% sodium carboxymethyl cellulose can significantly improve the 0.5m drop strength of wet pellets, with values ​​exceeding 8. The main reason is that the room temperature bonding performance of sodium carboxymethyl cellulose is superior to that of bentonite. Its colloidal particles or polymer molecules are interconnected to form a framework and a spatial network structure. When the gel loses or reabsorbs the dispersion medium, its shape and volume will not change. Even if the content of sodium carboxymethyl cellulose in the binder is only 10%, its bonding effect still exceeds that of bentonite in Example 4. Meanwhile, the high-strength biomass carbon-containing pellets after furnace heat treatment exhibit a cold compressive strength greater than 2230 N / pellet and a drop strength greater than 16 times from 2m. The main components are water glass and phenolic resin. During heat treatment, the water glass solidifies, binding the iron ore powder particles together to enhance pellet strength. Phenolic resin, being thermosetting, strengthens the cohesion between ore powder particles under heating conditions. At 400℃, the cohesion formed by water glass and phenolic resin is stronger than that formed by bentonite and aluminum dihydrogen phosphate, resulting in higher compressive and drop strengths in the carbon-containing pellets prepared in Examples 13-16. Furthermore, it can be seen that the type and amount of alkaline flux have little impact on the metallurgical properties of the pellets, mainly because the proportion of alkaline flux in the pellets is relatively low.

[0187] As can be seen from Table 6, the metallurgical properties of high-strength biomass carbon-containing pellets produced under different conditions vary to some extent, but they can all meet the requirements of blast furnace smelting and can be used directly as blast furnace feedstock, reducing the amount of coke used in blast furnace smelting, thereby reducing ironmaking costs and CO2 emissions, and having significant economic, social and ecological benefits.

[0188] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-strength biomass carbon-containing pellets, characterized in that, Includes the following steps: S1. Prepare a water-containing homogeneous material by mixing the raw materials and water. The raw materials for preparation, by mass fraction, include: 72%~85% iron ore powder, 4%~15% binder, 5%~11% biochar, and 1%~3% alkaline flux; The binder includes at least one of cement, bentonite, aluminum dihydrogen phosphate, water glass, gelatinized starch, sodium carboxymethyl cellulose and phenolic resin; the biochar is at least one of straw pyrolysis char and waste wood pyrolysis char, the volatile matter content of the biochar is less than 25%, and the mass percentage of the biochar with a particle size less than 0.074 mm is more than 60%. S2. After high-pressure molding of the water-containing homogenized material, heat treatment is performed. The heating atmosphere for heat treatment is an oxygen-free atmosphere. The heat treatment temperature is 300~500℃ and the heat treatment time is 10min-100min.

2. The preparation method according to claim 1, characterized in that, The iron ore powder includes at least one of hematite, magnetite, and limonite.

3. The preparation method according to claim 1, characterized in that, The alkaline flux includes at least one of limestone, dolomite, slaked lime, lightly calcined dolomite, quicklime, serpentine, and forsterite.

4. A high-strength biomass carbon-containing pellet prepared by the preparation method according to any one of claims 1-3, characterized in that, The high-strength biomass carbon-containing pellets have a compressive strength greater than 2000N / pellet.

5. The application of the high-strength biomass carbon-containing pellets as described in claim 4 in blast furnace ironmaking production.

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