A method for preparing converter metallized pellets by using converter slag and iron and zinc-containing dust sludge

Abstract

The application discloses a method for preparing converter metallized pellets by using converter steel slag and iron and zinc-containing dust sludge, which comprises the following steps: 1) mixing and ball milling the converter steel slag and biomass fuel according to a proportion; then mixing the iron and zinc-containing dust sludge and CDQ powder of dry quenching dust removal ash of a coking plant, and stirring to make the mixture uniform; 2) roller compacting the mixture at room temperature to form green pellets, and naturally curing; 3) feeding the green pellets into a rotary hearth furnace for step-by-step high-temperature reduction and cooling, thereby obtaining the converter metallized pellets. The converter metallized pellets are prepared by using the converter steel slag, biomass fuel, CDQ powder and iron and zinc-containing dust sludge as main raw materials, and by combining the roller compacting and step-by-step high-temperature reduction processes, so that the mechanical strength of the obtained metallized pellets can be effectively ensured, and the metallization rate of the metallized pellets can be improved; and the preparation method is simple, low in energy consumption and cost, high in metallization rate, and suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of furnace smelting materials technology, specifically relating to a method for preparing re-converter metallized pellets using converter steel slag and iron-zinc dust. Background Technology

[0002] Converter slag is a byproduct of the steelmaking process, accounting for approximately 15% of crude steel production. Typically, converter slag is crushed, screened, and magnetically separated to recover metals before becoming waste slag tailings. However, the current comprehensive utilization rate of steel slag is less than 30%, and long-term stockpiling not only occupies land but also adversely affects the surrounding environment, necessitating the search for effective utilization methods.

[0003] Iron-zinc dust and sludge are also a challenge for the resource utilization of solid waste in steel enterprises. The conventional disposal method is to directly return it to sintering for reuse, but the Zn content is high, which will continuously increase the zinc load on the blast furnace in the long run, seriously affecting the smooth operation and longevity of the blast furnace.

[0004] Currently, steel companies are widely adopting rotary hearth furnaces for centralized treatment of iron-zinc dust and sludge. The dust and sludge are mixed with carbon powder to ensure reduction efficiency and bentonite to ensure pellet strength. Green pellets are then subjected to high-temperature Zn removal and carbon reduction to produce metallized pellets, which are then reused in previous processes. However, this preparation method requires excessive amounts of carbon powder, resulting in significant energy consumption. Furthermore, the addition of bentonite to ensure pellet strength increases the operating costs of the rotary hearth furnace, and its main components, silica and alumina, reduce the metallization rate of the metallized pellets. This also increases steelmaking operating costs when the pellets are recycled. Summary of the Invention

[0005] The main objective of this invention is to provide a method for preparing metallized pellets from converter steel slag and iron-zinc dust, which can effectively solve the problem of resource utilization of metallurgical solid waste such as steel slag and iron-zinc dust, reduce the raw material batching cost of rotary hearth furnace production, and effectively ensure the mechanical strength of the obtained metallized pellets and improve the metallization rate of the metallized pellets. Moreover, the preparation method involved is relatively simple, energy-saving, low-cost, and has a high metallization rate, making it suitable for widespread application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0008] 1) Mix converter slag and fruit shell biomass fuel in a certain proportion, ball mill them to prepare a powder mixture of less than 100 mesh; then mix it with iron-zinc dust and CDQ powder, and stir it to make it evenly mixed to form a mixture.

[0009] 2) Roll press the obtained mixture at room temperature to form green pellets, and then allow them to cure naturally;

[0010] 3) The obtained green pellets are sent to a rotary hearth furnace for stepwise high-temperature reduction and then cooled to obtain the rotary hearth metallized pellets.

[0011] In the above scheme, the raw materials used for the metallization pellets in the converter include the following by weight: 8-12 parts of converter steel slag, 2-8 parts of biomass fuel, 2-8 parts of CDQ powder, and 78-82 parts of iron-zinc dust.

[0012] In the above scheme, the converter slag is subjected to magnetic separation before use; wherein, the main components (dry basis) and their mass percentages include: TFe 18-22%, CaO 40-48%, SiO2 8-12%, Mn 2-4%, MgO 3-5%, Al2O3 1-2%, P 0.5-1.5%, S 0.05-0.1%, Zn 0-2%; and its particle size is 0-5mm.

[0013] In the above scheme, the iron-zinc dust is a mixture of various iron-containing dusts from iron and steel metallurgy. Its main chemical components (dry basis) and their mass percentages include: TFe 30-50%, Zn 2-6%, CaO 5-18%, SiO2 2-8%, C 4-25%, as well as O, H, and N elements combined with Fe, Zn, and other elements, and unavoidable small amounts of other impurity elements; its particle size characteristic is that particles below 100 mesh account for ≥90% of the total particle size.

[0014] In the above scheme, the shell biomass fuel can be selected from one of walnut shells, peanut shells, and chestnut shells; its particle size is 0-5cm.

[0015] In the above scheme, the CDQ powder is dust from the dry quenching environment of a coking plant, wherein the main components (dry basis) and their mass percentage include: C≥75%.

[0016] In the above scheme, the roller pressing step uses a high-pressure roller briquetting machine to press oval-shaped green pellets with a particle size ≤4cm and a compressive strength ≥1500N.

[0017] In the above scheme, the natural maintenance time is 12-24 hours.

[0018] In the above scheme, the stepwise (four-stage) high-temperature reduction step includes: first, raising the temperature from 35-50℃ to 190-210℃ over a heating time of 2.5-3.5 minutes; then raising the temperature to 365-375℃ over a heating time of 4-5 minutes; then raising the temperature to 1150-1215℃ over a heating time of 4.5-5.5 minutes; and finally raising the temperature to 1340-1360℃ over a heating time of 1.5-2.5 minutes, and holding at that temperature for 12-15 minutes.

[0019] The rotary kiln metallized pellets prepared according to the above scheme have a green pellet compressive strength ≥1500N, a dezincification rate ≥93%, a metallization rate ≥68%, and a metallized pellet compressive strength >3000N.

[0020] The principle of this invention is as follows:

[0021] This invention uses converter steel slag, biomass fuel, CDQ powder, and iron-zinc dust as main raw materials. First, the converter steel slag and nutshell biomass are mixed and ground, which effectively improves the grinding efficiency of the nutshell biomass and stimulates the cementing properties of the steel slag, resulting in a uniformly mixed powder mixture. Then, it is mixed with iron-zinc dust and CDQ powder to prepare green pellets, which undergo stepwise high-temperature reduction: In the first stage, the moisture content of the pellets is reduced to below 1%; in the second stage, the volatile substances of the nutshell biomass are released and burned, providing a heat source for the next heating step and promoting the formation of micropores in the metal pellets to facilitate the entry of reducing gases into the pellets; in the third stage, the volatile substances of the biomass inside the nutshells are completely released, and the metal reduction reaction temperature of the pellets is increased; in the fourth stage, ZnO in the pellets is reduced to metallic Zn, which is then volatilized with the flue gas and collected by a bag filter dust collection system to produce metallized pellets.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] I. This invention utilizes the cementitious activity of converter steel slag to replace traditional raw materials such as bentonite, thereby improving the strength of green pellets while recovering Fe and CaO, which can be recycled back to the converter with the pellets, reducing the amount of limestone added during steelmaking and lowering C emissions.

[0024] II. This invention utilizes fruit shell biomass to replace traditional carbon powder in the formulation, which reduces C emissions and allows the green pellets to form micropores during the heating process. This facilitates the entry of CO gas into the green pellets for reduction reactions, effectively improving the dezincification rate and metallization rate.

[0025] Third, this invention mixes and ball-mills steel slag and nutshell biomass, which can effectively improve the ball milling efficiency of biomass and stimulate the cementing activity of steel slag.

[0026] Fourth, the preparation process involved in this invention is simple, requires no additional equipment on the basis of existing processes, and can realize the efficient resource utilization of various solid wastes, with significant economic and environmental benefits. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the preparation process of metallized pellets according to one embodiment of the present invention. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] In the following examples, the converter steel slag used was magnetically separated before use; the main components (dry basis) and their mass percentages included: TFe 19-21%, CaO 43-47%, SiO2 9-11%, Mn 2.5-3.5%, MgO 3.5-4.5%, Al2O3 1.2-1.8%, P 0.7-1.3%, S 0.08-0.09%, Zn 0.8-1%; its particle size was 0-5mm. Fruit shell biomass fuel could be selected from walnut shells, peanut shells, or chestnut shells, with a particle size of 0-5mm. CDQ powder was dust collected from the dry quenching environment of a coking plant, and its main components (dry basis) and their mass percentages included: C ≥ 75%. The iron-zinc dust used is a mixture of various iron-containing dusts from iron and steel metallurgy. Its main chemical components (dry basis) and their mass percentages include: TFe 45-47%, Zn 4-5%, CaO 10-12%, SiO2 3-5%, C 15-20%, as well as O, H, and N elements combined with Fe, Zn, and other elements, and unavoidable small amounts of other impurities; its particle size characteristic is that particles below 100 mesh account for ≥90% of the total mass.

[0030] In the following embodiments, a high-pressure roller briquetting machine was used to press green pellets with a compressive strength of ≥1500N and a diameter of 2.5*2.5*1.5cm.

[0031] Example 1

[0032] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0033] 1) Weigh the raw materials according to the proportions. The weight percentages of each raw material are as follows: 10 parts of converter steel slag, 2 parts of biomass fuel, 8 parts of CDQ powder, and 80 parts of iron-zinc dust.

[0034] 2) Weigh out the converter steel slag and walnut shells and put them into a ball mill to mix and grind them into a fine powder mixture with a mesh size of less than 100 mesh;

[0035] 3) Mix the obtained powder mixture with iron-zinc dust and CDQ powder, and stir in a forced mixer for 5 minutes until uniformly mixed to form a mixture;

[0036] 4) The resulting mixture is fed into a roller press and pressed into green pellets at room temperature, and then cured under natural conditions for 12 hours;

[0037] 5) The obtained green pellets are fed into a rotary hearth furnace for stepwise high-temperature reduction. In the first stage, the temperature is increased from 50°C to 200°C in 2.5 minutes. In the second stage, the temperature is increased to 370°C in 5 minutes. In the third stage, the temperature is increased to 1200°C in 4.5 minutes. In the fourth stage, the temperature is increased to 1350°C in 1.5 minutes and held for 13 minutes to obtain metallized pellet products.

[0038] 6) The metallized pellets are cooled and then returned to the converter for reuse.

[0039] Example 2

[0040] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0041] 1) Weigh the raw materials according to the proportions. The weight percentages of each raw material are as follows: 8 parts converter steel slag, 4 parts biomass fuel, 6 parts CDQ powder, and 82 parts iron-zinc dust.

[0042] 2) Weigh out the converter steel slag and chestnut shells and put them into a ball mill to mix and grind them into a fine powder mixture with a mesh size of less than 100 mesh;

[0043] 3) Mix the obtained powder mixture with iron-zinc dust and CDQ powder, and stir in a forced mixer for 7 minutes until uniformly mixed to form a mixture;

[0044] 4) The resulting mixture is fed into a roller press and pressed into green pellets at room temperature, and then cured under natural conditions for 16 hours;

[0045] 5) The obtained green pellets are fed into a rotary hearth furnace for stepwise high-temperature reduction. In the first stage, the temperature is increased from 50°C to 200°C in 3.5 minutes. In the second stage, the temperature is increased to 370°C in 4 minutes. In the third stage, the temperature is increased to 1200°C in 5.5 minutes. In the fourth stage, the temperature is increased to 1350°C in 2.5 minutes and held for 15 minutes to obtain metallized pellet products.

[0046] 6) The metallized pellets are cooled and then returned to the converter for reuse.

[0047] Example 3

[0048] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0049] 1) Weigh the raw materials according to the proportions. The weight percentages of each raw material are as follows: 12 parts of converter steel slag, 8 parts of biomass fuel, 2 parts of CDQ powder, and 78 parts of iron-zinc dust.

[0050] 2) Weigh out the converter steel slag and peanut shells and put them into a ball mill to mix and grind them into a fine powder mixture with a mesh size of less than 100 mesh;

[0051] 3) Mix the obtained powder mixture with iron-zinc dust and CDQ powder, and stir in a forced mixer for 6 minutes until the mixture is uniform.

[0052] 4) The resulting mixture is fed into a roller press and pressed into green pellets at room temperature, and then cured under natural conditions for 24 hours;

[0053] 5) The obtained green pellets are fed into a rotary hearth furnace for stepwise high-temperature reduction. In the first stage, the temperature is increased from 50°C to 200°C in 3 minutes. In the second stage, the temperature is increased to 370°C in 5 minutes. In the third stage, the temperature is increased to 1200°C in 5 minutes. In the fourth stage, the temperature is increased to 1350°C in 2 minutes and held for 12 minutes to obtain metallized pellet products.

[0054] 6) The metallized pellets are cooled and then returned to the converter for reuse.

[0055] Comparative Example 1

[0056] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0057] 1) Weigh the raw materials according to the proportions. The weight percentages of each raw material are as follows: 10 parts bentonite, 10 parts CDQ powder, and 80 parts iron-zinc dust.

[0058] 2) Weigh out the converter steel slag and bentonite, put them into a ball mill, mix and grind them into fine powder with a mesh size of less than 100 mesh;

[0059] 3) Mix the obtained powder mixture with the iron-zinc dust in a forced mixer for 6 minutes until a uniform mixture is formed;

[0060] 4) The resulting mixture is fed into a roller press and pressed into green pellets at room temperature, then cured under natural conditions for 24 hours;

[0061] 5) The obtained green pellets are fed into a rotary hearth furnace for stepwise high-temperature reduction. In the first stage, the temperature is increased from 50°C to 200°C in 3 minutes. In the second stage, the temperature is increased to 370°C in 5 minutes. In the third stage, the temperature is increased to 1200°C in 5 minutes. In the fourth stage, the temperature is increased to 1350°C in 2 minutes and held for 12 minutes to obtain metallized pellet products.

[0062] 6) The metallized pellets are cooled and then returned to the converter for reuse.

[0063] Comparative Example 2

[0064] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0065] 1) Weigh the raw materials according to the proportions. The weight percentages of each raw material are as follows: 10 parts of converter steel slag, 10 parts of CDQ powder, and 80 parts of iron-zinc dust.

[0066] 2) Weigh out the converter steel slag and CDQ powder and put them into a ball mill to mix and grind them into a powder mixture of less than 100 mesh;

[0067] 3) Mix the obtained powder mixture with the iron-zinc dust in a forced mixer for 6 minutes until a uniform mixture is formed;

[0068] 4) The resulting mixture is fed into a roller press and pressed into green pellets at room temperature, then cured under natural conditions for 24 hours;

[0069] 5) The obtained green pellets are fed into a rotary hearth furnace for stepwise high-temperature reduction. In the first stage, the temperature is increased from 50°C to 200°C in 3 minutes. In the second stage, the temperature is increased to 370°C in 5 minutes. In the third stage, the temperature is increased to 1200°C in 5 minutes. In the fourth stage, the temperature is increased to 1350°C in 2 minutes and held for 12 minutes to obtain metallized pellet products.

[0070] 6) The metallized pellets are cooled and then returned to the converter for reuse.

[0071] Comparative Example 3

[0072] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0073] 1) Weigh the raw materials according to the proportions. The weight percentages of each raw material are as follows: 10 parts bentonite, 10 parts biomass fuel, and 78 parts iron-zinc dust.

[0074] 2) Weigh out the converter steel slag and biomass fuel and put them into a ball mill to mix and grind them into a powder mixture with a mesh size of less than 100 mesh;

[0075] 3) Mix the obtained powder mixture with the iron-zinc dust in a forced mixer for 6 minutes until a uniform mixture is formed;

[0076] 4) The resulting mixture is fed into a roller press and pressed into green pellets at room temperature, and then cured under natural conditions for 24 hours;

[0077] 5) The obtained green pellets are fed into a rotary hearth furnace for stepwise high-temperature reduction. In the first stage, the temperature is increased from 50°C to 200°C in 3 minutes. In the second stage, the temperature is increased to 370°C in 5 minutes. In the third stage, the temperature is increased to 1200°C in 5 minutes. In the fourth stage, the temperature is increased to 1350°C in 2 minutes and held for 12 minutes to obtain metallized pellet products.

[0078] 6) The metallized pellets are cooled and then returned to the converter for reuse.

[0079] Comparative Example 4

[0080] A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust includes the following steps:

[0081] 1) Weigh the raw materials according to the proportions. The weight percentages of each raw material are as follows: 12 parts of converter steel slag, 8 parts of biomass fuel, 2 parts of CDQ powder, and 78 parts of iron-zinc dust.

[0082] 2) Weigh out the converter steel slag and biomass fuel and put them into a ball mill to mix and grind them into a powder mixture with a mesh size of less than 100 mesh;

[0083] 3) Mix the obtained powder mixture with iron-zinc dust and CDQ powder in a forced mixer for 6 minutes until a uniform mixture is formed;

[0084] 4) The resulting mixture is fed into a roller press and pressed into green pellets at room temperature, and then cured under natural conditions for 24 hours;

[0085] 5) The obtained green pellets are fed into a rotary hearth furnace for stepwise high-temperature reduction. In the first stage, the temperature is increased from 50°C to 200°C in 3 minutes. In the second stage, the temperature is increased to 1200°C in 8 minutes. In the third stage, the temperature is increased to 1350°C in 2 minutes and held for 12 minutes to obtain metallized pellet products.

[0086] 6) The metallized pellets are cooled and then returned to the converter for reuse.

[0087] The metallized pellets obtained in Examples 1-3 and Comparative Examples 1-4 were subjected to tests on mechanical properties and metallization rate, and the results are shown in Table 1.

[0088] Table 1. Performance test results of the metallized pellets obtained in Examples 1-3 and Comparative Examples.

[0089]

[0090] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for preparing recycled converter metallized pellets using converter steel slag and iron-zinc dust, characterized in that, Includes the following steps: 1) Mix converter steel slag and nutshell biomass fuel in a certain proportion, ball mill them to prepare a powder mixture of less than 100 mesh; then mix it with iron-zinc dust and CDQ powder, and stir it to make it evenly mixed to form a mixture. 2) Roll press the obtained mixture at room temperature to form green pellets, and then allow them to cure naturally; 3) The obtained green pellets are sent to a rotary hearth furnace for stepwise high-temperature reduction and then cooled to obtain the rotary hearth metallized pellets. The aforementioned shell-based biomass fuel is one of walnut shells, peanut shells, or chestnut shells; its particle size is 0-5 cm. The stepwise high-temperature reduction process includes: first, raising the temperature from 35-50℃ to 190-210℃ over a heating time of 2.5-3.5 minutes; then raising the temperature to 365-375℃ over a heating time of 4-5 minutes; next, raising the temperature to 1150-1215℃ over a heating time of 4.5-5.5 minutes; and finally raising the temperature to 1340-1360℃ over a heating time of 1.5-2.5 minutes, and holding at that temperature for 12-15 minutes.

2. The method according to claim 1, characterized in that, The raw materials used for the metallization pellets in the converter and their respective weight proportions include: 8-12 parts converter steel slag, 2-8 parts biomass fuel, 2-8 parts CDQ powder, and 78-80 parts iron-zinc dust.

3. The method according to claim 1, characterized in that, The main components of the converter steel slag and their mass percentages include: TFe 18-22%, CaO 40-48%, SiO 28-12%, Mn 2-4%, MgO 3-5%, Al2O3 1-2%, P 0.5-1.5%, S 0.05-0.1%, Zn 0-2%; its particle size is 0-5mm.

4. The method according to claim 1, characterized in that, The main chemical components and their mass percentages of the iron-zinc dust sludge include: TFe 30-50%, Zn 2-6%, CaO 5-18%, SiO2 2-8%, C 4-25%; particles smaller than 100 mesh account for ≥90% of the total mass.

5. The method according to claim 1, characterized in that, The C content in the CDQ powder is ≥75wt%.

6. The method according to claim 1, characterized in that, The natural curing time is 12-24 hours.

7. Rotary metallized pellets prepared by the method according to any one of claims 1 to 6.

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