Method for secondary dust removal of rotary hearth furnace using steelmaking

Abstract

The present invention discloses a method for utilizing secondary dust removal ash from steelmaking in a rotary hearth furnace. By adopting hydrocarbon-based vascular materials as supports and reducing agents, the secondary dust removal ash from steelmaking is used in a rotary hearth furnace to prepare metallized products and then reused in the converter, thereby realizing the reuse of the secondary dust removal ash from steelmaking in the steel production process, avoiding waste of resources and protecting the environment.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste resource utilization, and in particular relates to a method for utilizing secondary dust removal ash from steelmaking in a rotary hearth furnace. Background Art

[0002] In recent years, steel enterprises have widely adopted the centralized treatment process of iron-containing and zinc-containing dust such as rotary hearth furnace, and recycled the iron in the dust mud in the form of metallized pellets in the iron-making and sintering processes, while removing the zinc in the dust mud, reducing the problem of zinc enrichment in blast furnaces caused by the reuse of iron-containing and zinc-containing dust mud, and ensuring the smooth operation and longevity of blast furnaces. Secondary dust removal ash from steelmaking is iron-containing and zinc-containing dust produced by environmental dust removal in smelting processes such as molten iron pretreatment, converter, refining, and tundish in steelmaking plants, and is a typical target for rotary hearth furnace treatment. Due to the large use of auxiliary materials such as alkaline flux in the steelmaking process, secondary dust removal ash from steelmaking is highly alkaline and contains a large amount of free CaO. When using steelmaking dust removal ash to prepare pellets for rotary hearth furnaces, in the raw ball stage, the volume expansion of Ca(OH)2 produced by the hydration of free CaO can easily cause expansion, breakage, and pulverization of raw balls after ball formation, affecting the quality of the pellets. The problem of raw ball powdering can be avoided by pre-digesting the free CaO in the steelmaking dust before batching. However, since the temperature of the rotary hearth furnace can reach 1250-1300°C, Ca(OH)2 is dehydrated again to produce free CaO during the heating process. When the reduced metallized pellets are cooled and encounter water vapor in the air, the free CaO is regenerated into Ca(OH)2 and expands, resulting in the powdering of the metallized pellets.

[0003] The addition of dust or clay materials rich in SiO2 and Al2O3 can reduce the basicity of the rotary hearth furnace mixture, and generate stable calcium silicate and calcium aluminate with free calcium oxide at high temperature, thereby reducing the powdering of metallized pellets. However, elements such as silicon and aluminum reduce the TFe quality of the pellets, form slag in the blast furnace, and increase energy consumption. The method of using red iron oxide or hematite rich in Fe2O3 to participate in the batching can ensure the quality of the pellets, and generate calcium ferrite and other substances to stabilize free CaO at high temperature. However, due to the reducing atmosphere of the rotary hearth furnace, Fe2O3 loses its ability to stabilize free CaO after being reduced to metallic Fe. Summary of the invention

[0004] Aiming at the technical problems that the existing secondary dust removal ash from steelmaking has high alkalinity and much free CaO, which leads to much pulverization of metallized pellets in rotary hearth furnace, the present invention provides a method for utilizing secondary dust removal ash from steelmaking in a rotary hearth furnace for producing high-quality metallized pellets.

[0005] To achieve the above object, the present invention provides a method for removing dust from a rotary hearth furnace using secondary steelmaking dust removal, comprising the following steps:

[0006] 1) Dry distilling the hydrocarbon-based vascular material precursor at 400-600° C. for 30-60 min in a nitrogen atmosphere;

[0007] 2) cooling the material obtained in step 1) to room temperature under a N2 atmosphere, crushing the material to less than 5 mm to obtain hydrocarbon-based vascular material, and further grinding the material to less than 0.1 mm to obtain hydrocarbon-based vascular material powder;

[0008] 3) mixing hydrocarbon-based vascular material powder and steelmaking secondary dust removal ash in a weight ratio of 1:1-2 to form a mixture, and then adding water and a binder to further mix evenly to form a blank, wherein the water accounts for 10-15% of the weight of the mixture and the binder accounts for 2-3% of the weight of the mixture;

[0009] 4) Use a double-roll ball press to make the blank into 20-25 mm green balls;

[0010] 5) Send the green pellets into the chain grate dryer, heat to 250-350℃, and keep it for 10-15 minutes;

[0011] 6) The dried green balls are sent to a rotary hearth furnace for staged heating reduction. The first stage is heated to 400-600°C and maintained for 5-8 minutes. The second stage is heated to 900-1000°C and maintained for 10-15 minutes. The third stage is heated to 1200-1300°C and maintained for 20-25 minutes to obtain a metallized product.

[0012] 7) The metallized product is cooled in a N2 atmosphere and then returned to the rotary kiln for reuse.

[0013] Furthermore, in the step 1), the dimensions of the hydrocarbon-based vascular material precursor are: 40 to 120 cm in length, 10 to 20 cm in width, and 1 to 3 cm in thickness.

[0014] Furthermore, in the step 2), the hydrocarbon-based vascular material contains tubular voids, and the diameter of the tubular voids is 10 to 100 μm.

[0015] Furthermore, in the step 2), the chemical composition of the hydrocarbon-based vascular material powder includes, by weight percentage, 50.0%≤C≤70.0%, 5.0%≤H≤10.0%, S≤0.2%, CaO≤1.0%, MgO≤1.0%, SiO2≤1.0%, Al2O3≤1.0%, and the remainder is the O element combined with the C, H, and S elements and other inevitable impurity elements; its particle size characteristics are: the number of particles with a particle size of 0.01 to 0.1 mm is 80 to 99%.

[0016] Furthermore, in the step 3), the chemical composition of the secondary dust ash from steelmaking includes, by weight percentage, 30.0%≤TFe≤40.0%, 25.0%≤CaO≤35.0%, 5.0%≤MgO≤10.0%, SiO2≤10.0%, Al2O3≤5.0%, K2O≤1.0%, Na2O≤1.0%, S≤1.0%, P2O5≤0.5%, 1.0%≤Zn≤5.0%, C≤2.0%, and moisture≤1.0%; the remainder is O, H, N elements combined with Fe, Zn, S, P and other elements and other inevitable impurity elements; the particle size characteristic of the secondary dust ash from steelmaking is: the residue on a 100-mesh sieve is ≤15.0%.

[0017] Furthermore, in the step 2), the binder is one or a mixture of methyl cellulose, water glass, epoxy resin or phenolic resin.

[0018] Furthermore, in the step 1), the high temperature carbonization is 500-600° C. and the carbonization time is 45-60 min.

[0019] Furthermore, in the step 5), the heating temperature is 300-350°C.

[0020] Furthermore, in step 6), the second stage heating temperature is 950-1000°C, and the third stage heating temperature is 1250-1300°C.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] 1) After being crushed and ground, the hydrocarbon-based vascular material still retains its own structural void characteristics. After being mixed with steelmaking dust removal ash, it can effectively resist the hydration expansion effect of free CaO in both the green ball and metallized product stages, avoiding the pulverization and breakage of the pellets.

[0023] 2) The oxidation and heat release of C element in the oxidizing atmosphere of the converter is beneficial to increase the temperature of molten steel and promote the smelting of large scrap ratio in the converter. CaO is an essential substance for converter smelting, which can absorb various impurities in molten steel and improve the purity of molten steel. The present invention uses steelmaking secondary dust removal ash and hydrocarbon-based vascular materials to prepare metallized products with high C and CaO content, which is conducive to recycling for steelmaking.

[0024] 3) The present invention returns the secondary dust removal ash from steelmaking to production for utilization, thus avoiding waste of resources and protecting the environment.

[0025] 4) The process of the present invention is simple, based on the existing rotary hearth furnace process, with small investment and high technical and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the cross section of the hydrocarbon-based vascular material of the present invention;

[0027] Figure 2 The present invention is a schematic flow chart of a method for utilizing secondary dust removal in steelmaking of a rotary hearth furnace. DETAILED DESCRIPTION

[0028] The process of the present invention will be further described below in conjunction with the embodiments.

[0029] (1) Technical Principle of the Invention

[0030] The main chemical reactions for the conversion of free CaO in secondary dust removal during steelmaking are shown in Equations 1 to 2.

[0031] CaO+H2O=Ca(OH)2 Formula 1

[0032] Ca(OH)2=CaO+H2O↑ Formula 2

[0033] As shown in Formula 1, the volume expansion of CaO during digestion to generate Ca(OH)2 is about 110-120%, which leads to increased stress in the pellets, which are easy to break and pulverize. The pre-digestion method used in the pelletizing stage to convert CaO into Ca(OH)2 can avoid the problem of breakage and pulverization of the green balls. However, due to the high heating temperature of the rotary hearth furnace, Ca(OH)2 is decomposed and converted into CaO again at high temperature. After the pellets are cooled, CaO is converted again in the air according to Formula 1, and there is still an expansion problem. Therefore, the conventional pre-digestion method in the pelletizing stage cannot solve the expansion problem of free CaO in the secondary dust removal ash of steelmaking.

[0034] The hydrocarbon-based vascular material is made by dry distillation of its precursor and has a large number of microscopic voids in the structure. Crushing and grinding will not destroy its microscopic voids. Therefore, after the secondary dust removal ash from steelmaking is mixed with the hydrocarbon-based vascular material powder to form pellets, there will be a large number of microscopic voids in the pellets. During the CaO digestion and expansion process of the secondary dust removal ash from steelmaking, these voids have a certain toughness, which can offset the internal stress generated by the digestion of CaO to generate Ca(OH)2, and solve the problems of pellet breakage and pulverization.

[0035] like Figure 2 The method for removing dust from a rotary hearth furnace using secondary steelmaking dust removal comprises the following steps:

[0036] 1) Dry distilling the hydrocarbon-based vascular material precursor at 400-600° C. (preferably 500-600° C.) for 30-60 min (preferably 45-60 min) under N2 atmosphere; the dimensions of the hydrocarbon-based vascular material precursor are: 40-120 cm in length, 10-20 cm in width, and 1-3 cm in thickness;

[0037] 2) The material obtained in step 1) is cooled to room temperature under a N2 atmosphere, crushed to less than 5 mm to obtain a hydrocarbon-based vascular material, and further ground to less than 0.1 mm to obtain a hydrocarbon-based vascular material powder; the hydrocarbon-based vascular material contains a pipe-like void inside, and the void diameter is 10 to 100 μm, such as Figure 1 As shown;

[0038] The chemical composition of the hydrocarbon-based vascular material powder includes, by weight percentage, 50.0%≤C≤70.0%, 5.0%≤H≤10.0%, S≤0.2%, CaO≤1.0%, MgO≤1.0%, SiO2≤1.0%, Al2O3≤1.0%, and the remainder is the O element combined with the C, H, S elements and other inevitable impurity elements; the particle size characteristics are: the number of particles with a particle size of 0.01-0.1 mm is 80-99%; the binder is one or a mixture of methyl cellulose, water glass, epoxy resin or phenolic resin;

[0039] 3) mixing hydrocarbon-based vascular material powder and steelmaking secondary dust removal ash in a weight ratio of 1:1-2 to form a mixture, and then adding water and a binder to further mix evenly to form a blank, wherein the water accounts for 10-15% of the weight of the mixture and the binder accounts for 2-3% of the weight of the mixture;

[0040] The chemical composition of the secondary dust removal ash from steelmaking includes 30.0%≤TFe≤40.0%, 25.0%≤CaO≤35.0%, 5.0%≤MgO≤10.0%, SiO2≤10.0%, Al2O3≤5.0%, K2O≤1.0%, Na2O≤1.0%, S≤1.0%, P2O5≤0.5%, 1.0%≤Zn≤5.0%, C≤2.0%, and moisture≤1.0% by weight; the remainder is O, H, N elements combined with Fe, Zn, S, and P elements and other inevitable impurity elements; the particle size characteristics of the secondary dust removal ash from steelmaking are: the residue on a 100-mesh sieve is ≤15.0%;

[0041] 4) Use a double-roll ball press to make the blank into 20-25 mm green balls;

[0042] 5) Send the green pellets into a chain grate dryer, heat to 250-350°C (preferably 300-350°C), and keep for 10-15 minutes;

[0043] 6) The dried green balls are sent to a rotary hearth furnace for staged heating reduction, wherein the first stage is heated to 400-600° C. and maintained for 5-8 minutes, the second stage is heated to 900-1000° C. (preferably 950-1000° C.) and maintained for 10-15 minutes, and the third stage is heated to 1200-1300° C. (preferably 1250-1300° C.) and maintained for 20-25 minutes to obtain a metallized product;

[0044] 7) The metallized product is cooled in a N2 atmosphere and then returned to the rotary kiln for reuse.

[0045] Example 1

[0046] 1) Dry distilling the hydrocarbon-based vascular material precursor at 420° C. for 35 min under a nitrogen atmosphere;

[0047] 2) cooling the material obtained in step 1) to room temperature under a N2 atmosphere, crushing the material to less than 5 mm to obtain hydrocarbon-based vascular material, and further grinding the material to less than 0.1 mm to obtain hydrocarbon-based vascular material powder;

[0048] 3) mixing hydrocarbon-based vascular material powder and steelmaking secondary dust removal ash in a weight ratio of 1:1 to form a mixture, and then adding water and a binder to further mix evenly to form a blank, wherein the water accounts for 12% by weight of the mixture and the binder accounts for 2.2% by weight of the mixture;

[0049] 4) Use a double-roll ball press to make the blank into 20-25 mm green balls;

[0050] 5) Send the green pellets into the chain grate dryer, heat to 270°C and keep it for 10 minutes;

[0051] 6) The dried green balls are sent to a rotary hearth furnace for staged heating reduction, with the first stage heated to 420°C and maintained for 5 minutes, the second stage heated to 910°C and maintained for 11 minutes, and the third stage heated to 1230°C and maintained for 20 minutes to obtain a metallized product;

[0052] 7) The metallized product is cooled in a N2 atmosphere and then returned to the rotary kiln for reuse.

[0053] Example 2

[0054] 1) Dry distilling the hydrocarbon-based vascular material precursor at 500° C. for 45 min in a N2 atmosphere;

[0055] 2) cooling the material obtained in step 1) to room temperature under a N2 atmosphere, crushing the material to less than 5 mm to obtain hydrocarbon-based vascular material, and further grinding the material to less than 0.1 mm to obtain hydrocarbon-based vascular material powder;

[0056] 3) mixing hydrocarbon-based vascular material powder and steelmaking secondary dust removal ash in a weight ratio of 1:1.5 to form a mixture, and then adding water and a binder to further mix evenly to form a blank, wherein the water accounts for 12% by weight of the mixture and the binder accounts for 2.5% by weight of the mixture;

[0057] 4) Use a double-roll ball press to make the blank into 20-25 mm green balls;

[0058] 5) Send the green pellets into the chain grate dryer, heat to 300℃ and keep it for 12 minutes;

[0059] 6) The dried green balls are sent to a rotary hearth furnace for staged heating reduction. The first stage is heated to 500°C and maintained for 7 minutes. The second stage is heated to 950°C and maintained for 12 minutes. The third stage is heated to 1260°C and maintained for 22 minutes to obtain a metallized product.

[0060] 7) The metallized product is cooled in a N2 atmosphere and then returned to the rotary kiln for reuse.

[0061] Example 3

[0062] A method for removing dust from a rotary hearth furnace using secondary steelmaking dust removal comprises the following steps:

[0063] 1) Dry distilling the hydrocarbon-based vascular material precursor at 590° C. for 55 min under a nitrogen atmosphere;

[0064] 2) cooling the material obtained in step 1) to room temperature under a N2 atmosphere, crushing the material to less than 5 mm to obtain hydrocarbon-based vascular material, and further grinding the material to less than 0.1 mm to obtain hydrocarbon-based vascular material powder;

[0065] 3) mixing hydrocarbon-based vascular material powder and steelmaking secondary dust removal ash in a weight ratio of 1:2 to form a mixture, and then adding water and a binder to further mix evenly to form a blank, wherein the water accounts for 15% of the weight of the mixture and the binder accounts for 3% of the weight of the mixture;

[0066] 4) Use a double-roll ball press to make the blank into 20-25 mm green balls;

[0067] 5) Send the green pellets into the chain grate dryer, heat to 340℃ and keep it for 15 minutes;

[0068] 6) The dried green balls are sent to a rotary hearth furnace for staged heating reduction. The first stage is heated to 600°C and maintained for 8 minutes. The second stage is heated to 1000°C and maintained for 15 minutes. The third stage is heated to 1290°C and maintained for 24 minutes to obtain a metallized product.

[0069] 7) The metallized product is cooled in a N2 atmosphere and then returned to the rotary kiln for reuse.

[0070] Comparative Example

[0071] Comparative Examples 1, 2, and 3 use the same steelmaking secondary dust removal ash as in Examples 1, 2, and 3, and use an equal amount of anthracite powder to replace the hydrocarbon-based vascular material in the examples, and prepare metallized products according to the same process as in each example. The pulverization rate and strength of the obtained metallized pellets are shown in Table 1. It can be seen that the method of the present invention can effectively avoid the expansion problem caused by the hydration of free CaO in the steelmaking secondary dust removal ash, reduce the pulverization rate of the product, and improve the strength.

[0072] Table 1. Comparison of metallized product quality between the examples and the comparative examples

[0073] Powdering rate / % Strength / kN Example 1 21％ 2792 Comparative Example 1 49％ 1963 Example 2 19％ 2953 Comparative Example 2 43％ 2277 Example 3 15％ 3378 Comparative Example 3 39％ 2542

[0074] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A method for removing dust from a rotary hearth furnace using secondary steelmaking dust removal, characterized in that: The steps include: 1) Dry distilling the hydrocarbon-based vascular material precursor at 400-600° C. for 30-60 min in a nitrogen atmosphere; 2) Cooling the material obtained in step 1) to room temperature under N2 atmosphere, crushing to less than 5 mm to obtain hydrocarbon-based vascular material, and further grinding to less than 0.1 mm to obtain hydrocarbon-based vascular material powder; the chemical composition of the hydrocarbon-based vascular material powder includes 50.0%≤C≤70.0%, 5.0%≤H≤10.0%, S≤0.2%, CaO≤1.0%, MgO≤1.0%, SiO2≤1.0%, Al2O3≤1.0%, and the remainder is O element combined with C, H, S elements and other inevitable impurity elements; its particle size characteristics are: the number of particles with a particle size of 0.01-0.1 mm is 80-99%; the hydrocarbon-based vascular material contains pipe-shaped voids inside, and the void diameter is 10-100 μm; 3) mixing hydrocarbon-based vascular material powder and steelmaking secondary dust removal ash in a weight ratio of 1:1-2 to form a mixture, and then adding water and a binder to further mix evenly to form a blank, wherein the water accounts for 10-15% of the weight of the mixture and the binder accounts for 2-3% of the weight of the mixture; 4) Using a double-roll ball press to make the blank into 20-25 mm green balls; 5) Send the green pellets into the chain grate dryer, heat to 250-350℃, and keep it for 10-15 minutes; 6) The dried green balls are sent to a rotary hearth furnace for staged heating reduction. The first stage is heated to 400-600°C and maintained for 5-8 minutes. The second stage is heated to 900-1000°C and maintained for 10-15 minutes. The third stage is heated to 1200-1300°C and maintained for 20-25 minutes to obtain a metallized product. 7) The metallized product is cooled in a N2 atmosphere and then returned to the rotary kiln for reuse.

2. The method for secondary dust removal of a rotary hearth furnace using steelmaking according to claim 1, characterized in that: In the step 1), the dimensions of the hydrocarbon-based vascular material precursor are: 40 to 120 cm in length, 10 to 20 cm in width, and 1 to 3 cm in thickness.

3. The method for secondary dust removal of a rotary hearth furnace using steelmaking according to claim 1, characterized in that: In the step 3), the chemical composition of the secondary dust removal ash from steelmaking includes, by weight percentage, 30.0%≤TFe≤40.0%, 25.0%≤CaO≤35.0%, 5.0%≤MgO≤10.0%, SiO2≤10.0%, Al2O3≤5.0%, K2O≤1.0%, Na2O≤1.0%, S≤1.0%, P2O5≤0.5%, 1.0%≤Zn≤5.0%, C≤2.0%, and moisture≤1.0%; the remainder is O, H, N elements combined with Fe, Zn, S, and P elements and other inevitable impurity elements; the particle size characteristic of the secondary dust removal ash from steelmaking is: the residue on a 100-mesh sieve is ≤15.0%.

4. The method for secondary dust removal of a rotary hearth furnace using steelmaking according to claim 1, characterized in that: In the step 2), the binder is one or a mixture of methyl cellulose, water glass, epoxy resin or phenolic resin.

5. The method for secondary dust removal of a rotary hearth furnace using steelmaking according to claim 1, characterized in that: In the step 1), the high temperature dry distillation is 500-600° C. and the dry distillation time is 45-60 min.

6. The method for secondary dust removal of a rotary hearth furnace using steelmaking according to claim 1, characterized in that: In the step 5), the heating temperature is 300-350°C.

7. The method for secondary dust removal of a rotary hearth furnace using steelmaking according to claim 1, characterized in that: In the step 6), the second stage heating temperature is 950-1000°C, and the third stage heating temperature is 1250-1300°C.

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