Steelmaking slag former produced by utilizing iron-containing dust and mud and use method of steelmaking slag former

Abstract

The invention discloses a steelmaking slag former produced by using iron-containing dust and a use method thereof, and aims to solve the problems of low utilization rate of iron-containing dust in iron and steel enterprises, difficulty in slagging in low-silicon molten iron / semi-steel steelmaking, poor dephosphorization effect and the like. The steelmaking slag former is prepared by uniformly mixing iron-containing dust and mud with limestone powder or lime powder according to a ratio, directly feeding the mixture into a kiln or roasting the mixture at 800-1250 DEG C in a ball-pressing manner, and ingredients containing SiO2 or SiO2 and Al2O3 can be added as required. Iron resources and various beneficial components in the iron-containing dust sludge are fully utilized, the low-melting-point pre-melting slag former is formed after roasting, the slag former has the advantages of being high in slag forming speed, good in dephosphorization effect, small in converter blowing temperature drop and the like, metallurgical lime can be partially or completely replaced, and the slag former is suitable for different blowing scenes such as normal molten iron, low-silicon molten iron and semisteel; and the additional value of the iron-containing dust mud is remarkably improved, the smelting cost is reduced, the metal loss and splashing phenomena are reduced, and good industrial application value is achieved.

Description

Technical Field

[0001] This invention relates to the field of iron and steel, and more specifically to the utilization of iron-containing dust and sludge in the steelmaking process. Background Technology

[0002] Iron-containing dust and sludge from steel enterprises include converter dust and sludge, electric furnace dust and sludge, sintering machine head dust and sludge generated in the sintering process, blast furnace dust and sludge generated in the ironmaking process, and iron oxide scale generated in the rolling process. The composition of some dust and sludge from a certain plant is detailed in Table 1.

[0003] Table 1. Chemical composition analysis (%) of various dust collector ash.

[0004]

[0005] As shown in the table above, some dust and sludge contain as much as 40-65% iron, as well as CaO, Zn, C, and other components. Currently, steel plants are using converter dust ash as a coolant or slagging agent by pressing it into pellets. For example, the patent application "Production process for recovering iron by adding sludge pellets to the converter (CN202310045305.3)" describes pressing converter sludge, dust, and iron oxide scale into sludge pellets using a binder for use as a slagging agent in steelmaking. Due to the high CaO content, converter dust and sludge are prone to bursting when the pellets are mixed in large proportions.

[0006] The patent “A method for cold-forming pellets and its preparation and use” (CN201910310194.8) uses blast furnace ash, converter ash, lime powder, iron concentrate, and binder to form pellets as a steelmaking coolant or slag-forming agent.

[0007] Sintering machine head ash, also known as sintering machine dust, contains impurities such as Fe2O3, CaO, K, Na, Zn, Pb, and Cl. Because it easily accumulates, it causes blast furnace nodules, equipment corrosion, and the dust is too fine and large to be directly returned to sintering. Sintering machine head ash usually needs to be washed with water, i.e., wet or pyrometallurgical processes, to remove harmful impurities. After impurity removal, the remaining Fe2O3 and other components are either sent to sintering or directly to the blast furnace.

[0008] When the Zn content in blast furnace bag ash is less than 1%, it can be returned to the sintering batch for use. However, most steel plants have blast furnace bag ash with a Zn content of more than 1%. If it is returned to the sintering process for continued use, it will cause Zn enrichment in the sinter, leading to excessive Zn load in the blast furnace. This can easily result in problems such as reduced coke strength, erosion of refractory bricks, formation of furnace nodules, and damage to tuyeres.

[0009] Currently, zinc extraction from blast furnace baghouse ash is mostly achieved using rotary kiln technology. However, some steel companies have low slag metallization rates, and slag utilization is problematic. Some slag is sold externally, while others are processed into pellets and returned to the converter for steelmaking, as seen in the patent "Method for Preparing Steelmaking Furnace Charges from Zinc Extraction Slag from Blast Furnace Ash" (202010042578.9).

[0010] Steel sheet from rolled steel can be used as a coolant in converter steelmaking.

[0011] The converter steelmaking process is essentially a slag-forming process, requiring early and effective slag formation. In the early stages of converter blowing, the temperature is low, resulting in a high phosphorus distribution ratio between the slag and iron, making the early blowing stage more suitable for dephosphorization. While the low temperature in the early stages of converter blowing leads to a high dephosphorization equilibrium coefficient and easier dephosphorization, the low temperature also makes slag formation difficult. Often, by the time the lime has fully hardened, the molten pool temperature has already risen, reducing the dephosphorization effect and increasing the risk of re-drying during the blowing process.

[0012] Normal molten iron has a [Si] content of 0.4-0.6%, and metallurgical lime is generally added during the blowing process. For low-silicon molten iron with [Si] < 0.4%, in the early stage of blowing, due to the low mass fraction of silicon in the molten iron, the silicon and manganese elements in the molten iron are oxidized within 1-2 minutes. The molten iron has little chemical exothermic reaction, the molten pool heats up slowly in the early stage, the content of acidic oxide SiO in the slag is low, and the amount of lime added is small and difficult to melt, which leads to missing the favorable opportunity for dephosphorization at low temperature.

[0013] The low silicon content in the molten iron allows it to enter the carbon-oxygen reaction stage earlier during blowing. At this stage, the decarburization rate is very high, and both the blown-in oxygen and the iron oxide in the slag participate in the decarburization reaction, resulting in the lowest possible FeO content in the slag. This reduced FeO content causes the high-melting-point phase to coat the lime, making it difficult to melt. The resulting slag volume is small, and the slag layer cannot adequately cover the molten steel. The exposed molten steel and slag are highly susceptible to problems such as oxygen lance sticking and fume hood sticking under the influence of the oxygen jet, further exacerbating the mid-stage drying process.

[0014] As the decarburization reaction continues, the molten pool temperature rises, the carbon content in the steel gradually decreases, and the (FeO) content in the slag increases. In the later stages of blowing, the decarburization reaction slows down, the stirring in the molten pool weakens, and the rising temperature melts the lime, but before it can fully react, the blowing process reaches its end. The resulting high-basicity, high-oxidizing slag, due to its small volume, has insufficient dephosphorization capacity, easily leading to highly oxidizing slag at the end of the process.

[0015] To compensate for the deficiency of low-silicon molten iron, a patented method for converter smelting of low-silicon molten iron (CN202210817710.8) involves adding 15-25% high-silicon molten iron containing 1.6-1.9% [Si] to the low-silicon molten iron to make up for the lack of [Si] in the low-silicon molten iron. A patented method for solving the difficulty of slag formation in converter smelting of ultra-low-silicon molten iron (CN202310578009.X) involves adding intermediate ladle slag with acidic components of SiO2 and Al2O3 in the early stage of blowing.

[0016] The patent application “A method for smelting low-phosphorus steel from high-phosphorus and low-silicon molten iron” (CN202410792975.6) utilizes silicon-killed steel LF refining slag to increase the SiO2 content in the slag.

[0017] After vanadium extraction, the semi-steel produced contains traces of [Si] and 0.30-3.8% [C]. Therefore, the semi-steel smelting process produces less acidic slag-forming material, a later initial slag formation time, and insufficient chemical heat generated by the molten iron. This makes steelmaking with semi-steel more difficult than steelmaking with low-silicon molten iron, resulting in a lower dephosphorization rate.

[0018] Due to the lack of elements such as [Si] and [Mn] in semi-steel, the slag formation rate in the early stage of the converter is slow, with an average formation time of about 4 minutes. When the initial slag is discharged in the early stage of the converter, the initial slag has just formed and has not yet fully participated in the dephosphorization reaction. When the dephosphorization period ends, it is the period of intense carbon-oxygen reaction, and the slag foaming is serious, making it difficult to pour the slag. During the slag pouring process, there is a serious loss of metallic iron. Due to the large heat loss in the vanadium extraction process, the steelmaking of semi-steel is not hot enough. The slag discharge in the early stage of the converter further increases the heat loss.

[0019] Both the patented method for slag formation in semi-steel (CN201410250194.0) and the patented method for reducing the consumption of auxiliary materials in semi-steel smelting (CN201810177350.3) involve adding ferrosilicon alloy to semi-steel to increase the content of acidic oxides (SiO2) in the slag and raise the temperature of the molten pool. However, this process has high smelting costs.

[0020] In addition, for high-phosphorus molten iron and low-phosphorus or ultra-low-phosphorus steel, more slag material is often required to achieve deep dephosphorization, and slag is repeatedly formed.

[0021] The calcination of metallurgical active lime also has very strict requirements on raw materials and production processes. Summary of the Invention

[0022] In view of the current situation of iron-containing dust and sludge treatment and utilization in steel enterprises and the different blowing conditions of low-silicon low-temperature molten iron, semi-steel and normal silicon-containing molten iron in various steel enterprises, this invention aims to develop a steelmaking slag-forming agent that uses iron-containing dust and sludge to produce slag-forming agent with good dephosphorization effect in the early stage of converter blowing, so as to replace or partially replace the current metallurgical lime slag-forming steelmaking.

[0023] The present invention relates to a steelmaking agent produced using iron-containing dust and sludge, characterized in that the iron-containing dust and sludge are mixed with limestone powder or lime powder in a certain proportion, formed into balls, and then placed into a kiln for calcination, or the mixed material is directly placed into a kiln for calcination.

[0024] Furthermore, the iron-containing dust and sludge is one or more of the following: converter sludge, mill head sludge, blast furnace dust removal sludge, rolled steel scale, and other iron oxide-containing waste materials.

[0025] Furthermore, the iron-containing dust and sludge are mixed with limestone powder or lime powder at a ratio of 100:0-70 or 100:0-60.

[0026] Furthermore, the iron-containing dust and sludge are mixed with limestone powder or lime powder at a ratio of 100:15-60 or 100:10-50.

[0027] Furthermore, depending on the needs, appropriate amounts of SiO2 or SiO2 and Al2O3 ingredients may be added to the mixture of iron-containing dust and limestone powder or lime powder.

[0028] Furthermore, the SiO2-containing ingredients are one of silicon-killed steel slag, yellow sand, and quartz sand.

[0029] Furthermore, the SiO2 and Al2O3-containing ingredients are clay.

[0030] Furthermore, the lime powder includes CaO-containing dust.

[0031] Furthermore, the furnace roasting temperature is 800-1250℃.

[0032] A method for using a steelmaking slagging agent produced from iron-containing dust and sludge, characterized in that it can be used throughout the entire steelmaking process, especially in the initial stage of blowing.

[0033] The principle of the technical solution of this invention is as follows: Iron-containing dust and sludge contains up to 40-60% iron, and some contain components such as CaO, SiO2, and Al2O3. The slag TFe grade of the kiln slag after the blast furnace ash fire treatment or the zinc extraction of the bag filter ash in the rotary kiln is low, and it contains a small amount of acidic substances such as SiO2 and Al2O3 and impurities such as Zn. It has low value for sintering and is sold cheaply.

[0034] This invention involves adding an appropriate amount of limestone powder or lime to iron-containing dust and sludge, and calcining it at 800-1250℃. This allows the kiln slag formed from FeO or Fe2O3 (melting point 1369℃ or 1565℃), SiO2 (melting point 1713℃), Al2O3 (melting point 2054℃), and CaO (2572℃) in the dust and lime powder or limestone powder mixture to become a low-melting-point (1150-1450℃) pre-melting steelmaking slag-forming agent, mainly composed of dicalcium silicate 2CaO·SiO2 (with dissolved MgO) (melting point around 2000℃), CaO·2Fe2O3 (melting point 1226℃), 2CaO·Fe2O3 (melting point 1430℃), 3CaO·Fe2O3, and calcium aluminate Ca2(Al,Fe)2O (melting point around 1400℃).

[0035] The roasting temperature is controlled at 800-1250℃. Sufficient lime powder or limestone powder is added so that the CaO introduced can form 2CaO·SiO2 with the SiO2 in the mixed material. The excess CaO will not continue to form 3CaO·SiO2, but will gradually form a pre-melted slag-forming agent with CaO·2Fe2O3, 2CaO·Fe2O3, 2CaO·Fe2O3 or Ca2(Al,Fe)2O, CaO·Fe2O3 as the main phase. Among them, CaO·2Fe2O3 is conducive to slag formation, 2CaO·Fe2O3 and 2CaO·Fe2O3 are conducive to dephosphorization, 2CaO·Fe2O3 and 2CaO·SiO2 are conducive to dephosphorization and phosphorus fixation, and Ca2(Al,Fe)2O is a dephosphorization and desulfurization agent. The kiln slag contains reduced metallic iron and a small amount of residual carbon, which is returned to the converter as part of the slag-forming agent. This reduces the consumption of steelmaking materials, and the residual carbon can generate heat to smelt iron and increase gas recovery. It is especially suitable for dephosphorization and slag-forming blowing of low-silicon molten iron and semi-steel. The Al2O3 in the slag-forming agent not only facilitates slag formation, reduces mid-blowing drying, and reduces splashing, but also increases the metallic iron content in the final slag of medium and high carbon steel, improves steel yield, and enhances the effect of slag splashing for furnace protection.

[0036] Since the blast furnace ash and blast furnace head ash contain certain chloride salts, they are conducive to the gasification and recovery of elements such as Zn, K, Na, and Pb.

[0037] Depending on the SiO2 content in the iron dust, lime powder, or limestone powder, and the raw material conditions of each steel plant, i.e., the silicon content of molten iron or semi-steel, the choice is made whether to add SiO2-containing raw materials. The production of slag-forming dephosphorizing agents for steelmaking requires slag-forming agents with corresponding dicalcium silicate content and melting point.

[0038] With the continued use of the steelmaking additive produced by this invention, the CaO content in converter dust will continue to decrease, and the addition of limestone powder or lime powder will gradually increase.

[0039] Beneficial effects

[0040] This invention discloses a technical solution for producing steelmaking slag-forming agents using iron-containing dust and sludge. The process involves batching, mixing, or calcining iron-containing dust and sludge with low-cost limestone or lime powder from steel plant lime kilns, along with other iron-containing and CaO-containing waste materials, to produce a pre-melted steelmaking slag-forming agent. This significantly increases the added value of the iron-containing dust and sludge. It can completely or partially replace metallurgical lime in slag-forming steelmaking, resulting in rapid slag formation, good dephosphorization, and minimal temperature drop during converter blowing. It is particularly suitable for low-silicon, low-temperature molten iron and semi-steel blowing, thus enhancing the iron resource recovery value of the iron-containing dust and sludge. Furthermore, this process can also transform kiln slag into pre-melted steelmaking slag during the extraction of zinc and impurities from blast furnace dust or sintering machine head ash. Detailed Implementation

[0041] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0043] Table 2 Main components of iron-containing dust, sludge, and lime, etc.

[0044]

[0045] Example 1

[0046] Based on the ratio of converter ash to limestone powder in Table 1 (100:80), the required amount of limestone powder is 191.5 kg (385 kg) per 1000 kg of converter mud. After mixing, the mixture is pressed into 10 mm lumps, dried, and then placed in a kiln and fired at 1200℃ for 50 minutes to form balls.

[0047] Ca2(Fe,Al)2O5: 34.8%

[0048] Ca(Fe,Al)₂O₄: 45.1%

[0049] Ca2SiO4: 9.8%

[0050] Other: Balance

[0051] Example 2

[0052] Based on the formula in Table 1, the amount of limestone powder to be added to the converter mud (dry basis) and lime powder mixture is calculated according to the formula nCaO=2nSiO2+2n(1 / 2Fe2O3)+1 / 2n(1 / 2Fe2O3): 151kg (385kg) of limestone powder is required for 1000kg of converter mud. After mixing, the mixture is pressed into 10mm small balls, dried, and then placed in a kiln and fired at 1250℃ for 40 minutes to form balls.

[0053] Ca2(Fe,Al)2O5: 32.8%

[0054] Ca(Fe,Al)₂O₄: 40.1%

[0055] Ca2SiO4: 7.5%

[0056] Other: Balance

[0057] Example 3

[0058] Converter capacity: 120t. Smelting grade X60 pipeline steel. Slag retention process. Following conventional smelting procedures, 112t of molten iron and 17t of scrap steel were first added to the furnace. After ignition with oxygen blowing for approximately 1 minute, oxygen supply was increased to 15-40%, followed by the addition of 2500kg of slag-forming agent (Example 1 of this invention) and 200kg of magnesium balls. Oxygen supply was increased to 40-90%, and 3200kg of slag-forming agent (Example 1 of this invention) was added in small batches. Slag formation time was 2'20". After blowing for 13'30", the lance was lifted, the furnace was tilted, temperature was measured, samples were taken, and steel was tapped. This furnace produced 128 tons of steel.

[0059] The composition and temperature of the molten iron in this furnace are as follows:

[0060]

[0061] The final steel composition and temperature for this furnace are:

[0062]

[0063] No lime was used in this furnace; the smelting was carried out entirely using the slag-forming agent of this invention. The final converter temperature was 1629℃, the final carbon content was 0.05%, the final phosphorus content was 0.0090%, the dephosphorization rate was 95.0%, the final slag basicity was 3.08, and the TFe content was 16.2%.

[0064] Example 4

[0065] LX82A steel was smelted in a 120t converter. Raw materials: 112t molten iron, 1320℃, 0.05% silicon, 0.14% phosphorus, and 18t scrap steel. Oxygen supply system: Top-blown flow rate controlled at 40000 Nm³ / h during smelting. 3 / h; Oxygen supply 0.35%, lance position 1.50m; Oxygen supply 35-90%, lance position 1.7-2.0m; Oxygen supply 90-100%, lance position 1.3-1.5m; The actual oxygen lance position can be adjusted appropriately according to the slag formation. Bottom blowing regime: From the start of blowing to 90% oxygen supply, the bottom blowing flow rate is 200 Nm³ / h. 3 / h; oxygen supply 90% until the end of blowing, bottom blowing intensity 450Nm 3 / h. Oxygen blowing at 35% temperature, molten pool temperature is 1320℃. Charging schedule: 15-40% oxygen supply, add 2700kg of slagging agent (Example 1 of this invention) and 500kg of magnesium balls; during 40-90% oxygen supply, add 1500kg of lime and 1500kg of slagging agent (Example 1 of this invention) in small batches. The composition and temperature of the molten iron in this furnace are as follows:

[0066]

[0067] The final steel composition and temperature for this furnace are:

[0068]

[0069] This furnace was smelted using lime and the slag-forming agent of this invention via the above method, with a slag formation time of 2′40″. Converter final temperature: 1648℃, final carbon: 0.035%, final phosphorus: 0.007%, dephosphorization rate: 95.0%, final slag basicity: 3.25, TFe: 17.5%.

[0070] Comparative Example

[0071] 120t converter. Smelting X60 pipeline steel.

[0072] The molten iron volume is 113 tons, the molten iron temperature is 1351℃, the silicon content is 0.5%, the phosphorus content is 0.131%, and the scrap steel volume is 15 tons. Oxygen supply system: Top blowing flow rate is controlled at 40000 Nm³ / h during the smelting process; oxygen supply from 0-35% is achieved at a lance position of 1.50m; from 35-90% at a lance position of 1.6-1.90m, oxygen supply from 90-100% at a lance position of 1.3-1.5m, adjusted appropriately according to slag formation. Bottom blowing system: From the start of blowing to 90% oxygen supply, the bottom blowing flow rate is 200 Nm³ / h; from 90% oxygen supply to the end of blowing, the bottom blowing intensity is 462 Nm³ / h. Temperature measurement at 35% oxygen supply indicates a molten pool temperature of 1330℃. For an oxygen supply of 15-40%, add 1500 kg of lime, 1000 kg of iron oxide scale, and 600 kg of magnesium balls; for an oxygen supply of 40-90%, using a small-batch, frequent-batch approach, add another 2000 kg of lime and 1500 kg of iron oxide scale. The composition and temperature of the molten iron in this furnace are as follows:

[0073]

[0074] The final steel composition and temperature for this furnace are:

[0075]

[0076] Slag formation time: 3'50″. Blowing was stopped at 14'53″, the lance was lifted, and samples were taken. Temperature was measured. Final temperature: 1617℃, final carbon: 0.041%, final phosphorus: 0.017%, dephosphorization rate: 86.9%, final slag basicity: 3.4, TFe: 20.1%.

[0077] Compared with Examples 1 and 2, the slag-forming agent of the present invention was not added during the smelting process, resulting in poor slag formation, long slag formation time, long oxygen supply blowing time, high slag basicity, high TFe content, and poor dephosphorization effect.

[0078] As can be seen from the above specific embodiments and comparative examples, the technical solution achieves deep reduction of slag at the blowing endpoint, a significant reduction in iron oxide, no phosphorus return at the molten steel endpoint, a shorter slag splashing operation time, and improved steel slag activity.

[0079] Although the present invention has been described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Any process adjustments made by those skilled in the art based on the principles of the present invention, such as variations in process parameters and details like ingredient proportions, whether pelletization occurs in the kiln, and the firing temperature and time, should fall within the scope of protection of the technical solutions sought by the claims of this invention.

Claims

1. A method for producing steelmaking additives using iron-containing dust and sludge, characterized in that, Iron-containing dust and mud are mixed with limestone powder or lime powder in a certain proportion, formed into balls, and then placed in a kiln for firing, or the mixed material is placed directly into the kiln for firing.

2. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, The iron-containing dust and sludge are mixed with limestone powder or lime powder at a ratio of 100:0-80 or 100:0-60.

3. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, The iron-containing dust and sludge is one or more of the following: converter sludge, machine head sludge, blast furnace dust removal sludge, rolled steel scale, and other iron oxide-containing waste materials.

4. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, The iron-containing dust and sludge are mixed with limestone powder or lime powder at a ratio of 100:15-60 or 100:10-50.

5. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, When the iron-containing dust and sludge are mixed with limestone powder or lime powder, appropriate amounts of SiO2 or SiO2 and Al2O3 ingredients may be added.

6. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, The SiO2-containing ingredients are one of silicon-killed steel slag, yellow sand, and quartz sand.

7. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, The SiO2 and Al2O3-containing ingredients are clay.

8. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, The lime powder includes CaO-containing dust removal ash.

9. The method for producing steelmaking additives using iron-containing dust and sludge as described in claim 1, characterized in that, The furnace roasting temperature is 800-1250℃.

10. A method for using a steelmaking slagging agent produced from iron-containing dust and sludge, characterized in that, It can be used throughout the entire steelmaking process, especially in the early stages of blowing.

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