Efficient utilization method of blast furnace gravity ash in converter steelmaking

Abstract

The invention belongs to the technical field of efficient utilization of solid waste, and particularly relates to an efficient utilization method of blast furnace gravity ash in converter steelmaking. The efficient utilization method comprises the following steps: uniformly mixing the blast furnace gravity ash, the steel rolling process waste and a binder to prepare a mixture; after the mixture is pressed into balls and screened, the balls are conveyed to a baking furnace through a conveying channel for low-temperature baking, and blast furnace gravity ash pressed balls are obtained; the strength of the blast furnace gravity ash pressing balls is larger than or equal to 1200 N, the iron content is larger than or equal to 50 wt%, and the water content is smaller than or equal to 2 wt%; the steel grade for converter steelmaking is low-alloy steel grade, the screened blast furnace gravity ash pressed balls are added into a converter overhead bunker through a conveying belt and added into a converter along with a first batch of cold charge, and the adding amount of the blast furnace gravity ash is 2-7 Kg / t steel. By the adoption of the method, the quality of steel billets and steel smelted by adding the blast furnace gravity ash completely meets the standard requirement, and direct use of the blast furnace gravity ash pressing balls in converter steelmaking is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of efficient utilization of solid waste, and particularly relates to a method for efficiently utilizing blast furnace heavy dust in converter steelmaking. Background Art

[0002] Blast furnace heavy dust contains high-value utilization elements such as about 40% Fe and about 17% C, but also contains relatively high harmful elements such as K, Na, and Zn. Due to the different granulation properties of these harmful elements, the treatment is difficult. The cyclic enrichment of K, Na, and Zn in the blast furnace is highly harmful to the blast furnace, and it is easy to cause adverse effects such as hanging, caving, nodulation, unstable coal gas flow, unsmooth furnace conditions, and increased fuel ratio in the blast furnace. In severe cases, it will affect the stability of the blast furnace.

[0003] At present, the treatment method of blast furnace heavy dust is basically to return it to sintering for use. With the continuous increase in ore prices, the ironmaking cost remains high. In order to reduce production costs and optimize the ore blending structure, the proportion of ore with relatively low price is increased. Since the content of K, Na, and Zn in low-price ore is relatively high, if the blast furnace heavy dust is continuously returned to sintering for use, the content of K, Na, and Zn in the blast furnace will exceed the standard, affecting the stability of the blast furnace. Therefore, it is necessary to reduce the addition ratio of blast furnace heavy dust in sintering burden. According to the requirement of not discharging environmental protection solid waste from the factory, new use channels for blast furnace heavy dust must be opened up to meet the dual requirements of environmental protection indicators and production stability, and ensure the stability of the blast furnace.

[0004] Enterprises with rotary kilns or rotary hearth furnaces will also treat some or all of the blast furnace heavy dust through rotary kilns or rotary hearth furnaces. After zinc extraction and salt extraction treatment of the blast furnace heavy dust, the harmful elements such as K, Na, and Zn in the blast furnace heavy dust are reduced, and it is processed into rotary kiln concentrate powder or homogenized pellets, which are returned to sintering or ironmaking for use. The cost of this process increases significantly. The treatment cost of the rotary kiln is about 380 yuan / ton, and the treatment cost of the rotary hearth furnace is about 800 - 1400 yuan / ton. The treated rotary kiln concentrate powder needs to be sintered and then put into blast furnace ironmaking, and the comprehensive cost such as fuel consumption increases by about 700 yuan / ton in this process. The homogenized pellets can be directly used in blast furnace ironmaking, and the increased cost is about 500 yuan / ton.

[0005] It can be seen that at present, blast furnace heavy dust is mainly recycled in the field of blast furnace smelting. Limited by the alkali metal composition, only a part of the blast furnace heavy dust can be directly returned to sintering for use, and there is still a large amount of blast furnace heavy dust that cannot be directly recycled. Preparing blast furnace heavy dust into rotary kiln concentrate powder or homogenized pellets, on the one hand, is limited by equipment, not all enterprises have rotary kilns or rotary hearth furnaces, and on the other hand, the treatment cost is relatively high. Therefore, there is an urgent need for a new method for utilizing blast furnace heavy dust so that a large amount of blast furnace heavy dust can be recycled to meet the requirement of not discharging environmental protection solid waste from the factory. Summary of the Invention

[0006] The object of the present invention is to provide a method for the low-cost and high-efficiency application of blast furnace gravity ash in the converter steelmaking process. Using the briquettes made from blast furnace gravity ash in converter steelmaking not only realizes the efficient utilization of blast furnace gravity ash, but also effectively solves a series of problems caused by the relatively high content of harmful elements such as K, Na, and Zn in blast furnace gravity ash. If directly returned to sintering for utilization, it will lead to a relatively high content of harmful elements such as K, Na, and Zn in sintered ore, resulting in enrichment when used in the blast furnace, affecting the stability of the blast furnace, or requiring treatment through a rotary kiln or a rotary hearth furnace, with high production costs, high fuel ratios, and impacts on the stability of the blast furnace condition.

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows: An efficient utilization method of blast furnace gravity ash in converter steelmaking includes the following steps:

[0008] Mix blast furnace gravity ash, waste from the rolling process, and a binder evenly to obtain a mixture. The waste from the rolling process is one or a combination of scale and rolling sludge. After the mixture is conveyed to the briquetting machine hopper through a conveyor belt for briquetting and screening, it is conveyed to a baking furnace through a conveying channel for low-temperature baking to obtain blast furnace gravity ash briquettes. Inspect the strength, composition, and moisture content of the blast furnace gravity ash briquettes, and select the blast furnace gravity ash briquettes with a strength ≥ 1200 N, an iron content ≥ 50 wt%, and a moisture content ≤ 2 wt%.

[0009] The steel grade for converter steelmaking is a low-alloy steel grade. When the molten iron temperature is 1390 - 1470 °C, the iron consumption is 810 - 930 Kg / t steel, and the Si content of the molten iron is 0.25 - 0.5 wt%, or when the molten iron consumption is 810 - 850 kg, the molten iron temperature ≥ 1450 °C, and the Si content of the molten iron ≥ 0.35 wt%, or when the molten iron consumption > 850 kg, the molten iron temperature ≥ 1420 °C, and the Si content of the molten iron > 0.25 wt%, add the selected blast furnace gravity ash briquettes to the converter high-level hopper through a conveyor belt and add them to the converter with the first batch of cold materials. The addition amount of the blast furnace gravity ash is 2 - 7 Kg / t steel.

[0010] In the prior art, the converter dust is mainly pelletized and directly applied to the whole process of converter steelmaking. Converter dust is generated during the converter steelmaking process. The dust is rich in iron oxides and alkaline substances, and the carbon content is extremely low (<2%). Blast furnace gravity ash is generated during the blast furnace ironmaking process, mainly from the blast furnace gas gravity dust removal system, and a large amount of carbon is contained in the blast furnace gravity ash. When the carbon content of the pellets added during the converter steelmaking process is too high, it is easy to consume the iron oxide in the slag, resulting in slag drying back, causing adverse effects such as rephosphorization, gun sticking or flue sticking, resulting in a high phosphorus content in the molten steel and affecting the product composition and performance. Therefore, the inertial thinking of those skilled in the art is that the converter dust is pelletized and applied to the converter steelmaking, and the blast furnace gravity ash is pelletized and applied to the blast furnace, and there is no precedent for applying the blast furnace dust to the converter steelmaking.

[0011] In the present invention, blast furnace gravity ash, waste from the rolling process and a binder are prepared into blast furnace gravity ash pellets, and the blast furnace gravity ash pellets meeting the requirements of strength, composition and moisture are screened out and put into the converter as cold materials for smelting low-alloy steel grades. According to the iron consumption, molten iron temperature and actual situation of the steel grade to be smelted, they are added with the first batch of cold materials at a rate of 2-7 Kg per ton of steel. It is found that there are no differences in various indexes such as composition, mechanical properties and metallographic structure between the steel billets and rolled products smelted with the addition of blast furnace gravity ash and those without the addition of gravity ash pellets, and it has no influence on the smelting process and fully meets the standard requirements.

[0012] Further, by weight, in the mixture, the content of blast furnace gravity ash is 60-70%, the content of scale is 25-30%, and the content of the binder is 5-10%.

[0013] Further, by weight, in the mixture, the content of blast furnace gravity ash is 50-60%, the content of rolling sludge is 35-40%, and the content of the binder is 5-10%.

[0014] Further, by weight, in the mixture, the content of blast furnace gravity ash is 50-55%, the content of scale is 20-35%, the content of rolling sludge is 10-25%, and the content of the binder is 5-10%.

[0015] Further, the binder is a liquid binder, such as water glass can be selected.

[0016] Further, the low-temperature baking temperature is 150°C - 190°C, and the time is 1.5 h - 2 h.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] The present invention first proposes the low-cost and high-efficiency application of BF gravity ash in the BOF steelmaking process, which can effectively avoid the enrichment of harmful elements such as K, Na, and Zn in BF gravity ash in the blast furnace, affecting the stability of the blast furnace; it avoids the use after treatment by rotary kiln or rotary hearth furnace process and then returning to sintering or ironmaking, shortens the usage process of BF gravity ash, reduces fuel consumption and energy consumption, avoids risks such as BF hanging, caving, accretion, unstable gas flow, and poor furnace condition, prolongs the BF maintenance time and the service life of refractories, and improves production efficiency.

[0019] In the present invention, the BF gravity ash is pelletized and directly used in BOF steelmaking. Only the pelletizing processing cost (including binder) and the costs of iron scale, rolling line sludge, etc. are required, with a total of about 500 yuan per ton, and the cost reduction effect is remarkable.

[0020] According to the actual situation of iron consumption, hot metal temperature and steel grades to be smelted, the BF gravity ash pellets are added into the BOF with the first batch of cold charge at a rate of 2 - 7 Kg per ton of steel. As cold charge, the BF gravity ash first melts into steel slag at high temperature. Part of it enters the slag and part is converted into molten steel. The C element in the pellets can provide heat during the melting stage of scrap steel, which is beneficial to the recovery of molten iron elements in the pellets at high temperature, reduces iron consumption, and improves the yield. In addition, the reaction of carbon with oxygen or carbon dioxide can generate carbon monoxide, increasing the gas recovery. The results prove that the quality of the steel billets and steel products smelted with the addition of BF gravity ash fully meets the standard requirements, realizing the direct use of BF gravity ash pellets in BOF steelmaking. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The metallographic structure diagram of the steel billet prepared in Example 1, with a magnification of 100 times;

[0022] Figure 2 The metallographic structure diagram of the steel billet prepared in Example 1, with a magnification of 200 times;

[0023] Figure 3 The metallographic structure diagram of the steel billet prepared in Comparative Example 1, with a magnification of 100 times;

[0024] Figure 4 The metallographic structure diagram of the steel billet prepared in Comparative Example 1, with a magnification of 200 times. DETAILED DESCRIPTION OF THE INVENTION

[0025] The following are specific examples of the present invention to further describe the technical solutions of the present invention, but the protection scope of the present invention is not limited to these examples. Any changes or equivalent substitutions that do not deviate from the concept of the present invention are included in the protection scope of the present invention.

[0026] Example 1

[0027] Preparation of briquettes from BF gravity dust by a briquetting company: Since BF gravity dust has fine particle size and low density, to avoid dusting, the gravity dust is transported to the briquetting company by tanker trucks and conveyed into a silo for standby. According to the briquetting ratio and a certain feeding sequence, BF gravity dust, waste from the rolling process, and binder are added to a mixing hopper for strong stirring to make the added materials as evenly mixed as possible. Based on the iron content of BF gravity dust, mill scale, and rolling line sludge respectively, calculations are made according to the final iron content not less than 50%, and different types of combinations are selected for mixed use. The first combination scheme is selected: BF gravity dust, mill scale, and binder (the content of BF gravity dust is 65%, the content of mill scale is 28%, and the content of binder is 7%). The evenly mixed ingredients are conveyed to the briquetting machine hopper through a conveyor belt. The mixed materials are briquetted, screened, and conveyed to a baking furnace through a conveying channel for low-temperature baking. After baking, samples are taken for testing related indicators such as strength, composition, and moisture. The measured indicators of the BF gravity dust briquettes are as follows: strength: 1450 N, Fe: 53 wt%, moisture: 0.8 wt%.

[0028] Application of BF gravity dust in converter steelmaking: The prepared briquettes are added to the converter high-level hopper through a conveyor belt for standby. The steel grade smelted in this furnace is low-alloy steel, the molten iron temperature is 1410 °C, the iron consumption is 850 Kg / t steel, and the Si content of the molten iron is 0.35 wt%. In this heat, BF gravity dust briquettes are added with the first batch of cold materials at a rate of 5 Kg per ton of steel. The whole production process is stable, no phenomenon of steel slag drying back occurs, and all indicators are normal. At the same time, the recovery of ferrite is increased, the ferrite recovery rate of the converter is improved, the steel output is increased, and the comprehensive energy consumption is reduced.

[0029] The steel billets and rolled products smelted with the addition of BF gravity dust are tracked and comprehensively inspected and analyzed. All performance indicators are no different from the composition, mechanical properties, and metallographic structure of those without adding the gravity dust briquettes, and the structure is ferrite and pearlite, fully meeting the requirements of the standard.

[0030] Example 2

[0031] Preparation of briquettes from blast furnace gravity ash by a briquetting company: Since the blast furnace gravity ash has fine particle size and low density, to avoid dusting, the gravity ash is transported to the briquetting company by a tanker truck and conveyed into a silo for standby. The blast furnace gravity ash, waste from the steel rolling process, and binder are added to a mixing hopper according to the briquetting ratio and a certain feeding sequence and vigorously stirred to make the added materials as evenly mixed as possible. According to the iron content of the blast furnace gravity ash, scale, and rolling line sludge respectively, calculations are made based on the final iron content not less than 50%, and different combinations are selected for mixed use. The second combination scheme is selected: blast furnace gravity ash, rolling line sludge, and binder (the content of blast furnace gravity ash is 60 wt%, rolling line sludge is 35 wt%, and binder is 5 wt%). The evenly mixed ingredients are conveyed to the briquetting machine silo through a conveyor belt. The mixed materials are briquetted, screened, and conveyed to a baking furnace through a transfer channel for low-temperature baking. After baking is completed, samples are taken for testing and inspection of relevant indicators such as strength, composition, and moisture. The measured indicators of the briquettes made from blast furnace gravity ash are as follows: strength: 1380 N, Fe: 52 wt%, moisture: 1.2 wt%.

[0032] Application of blast furnace gravity ash in converter steelmaking: The prepared briquettes are added to the converter high-level bin through a conveyor belt for standby. The steel grade smelted in this furnace is low-alloy steel, the molten iron temperature is 1460 °C, the iron consumption is 830 Kg / t steel, and the Si content of the molten iron is 0.40 wt%. In this furnace campaign, blast furnace gravity ash briquettes are added in batches, with a total addition of 2 Kg per ton of steel. The entire production process is stable, all indicators are normal, at the same time, the recovery of ferrite is increased, the ferrite yield of the converter is improved, the steel output is increased, and the comprehensive energy consumption is reduced.

[0033] The steel billets and rolled products smelted with the addition of blast furnace gravity ash are tracked and comprehensively inspected and analyzed. All performance indicators are no different from the composition, mechanical properties, metallographic structure, etc. of those without adding the gravity ash briquettes, fully meeting the requirements of the standards.

[0034] Example 3

[0035] Preparation of briquettes from blast furnace gravity ash by a briquetting company: Since the blast furnace gravity ash has fine particle size and low density, to avoid dusting, the gravity ash is transported to the briquetting company by a tanker truck and conveyed into a silo for standby. The blast furnace gravity ash, waste from the rolling process, and binder are added to a mixing hopper according to the briquetting ratio and a certain feeding sequence and vigorously stirred to make the added materials as evenly mixed as possible. Based on the iron content of the blast furnace gravity ash, mill scale, and rolling line sludge respectively, calculations are made according to the final iron content not less than 50%, and different combinations are selected for mixed use. The third combination scheme is chosen: blast furnace gravity ash, mill scale, rolling line sludge, and binder (the content of blast furnace gravity ash is 55 wt%, mill scale is 22 wt%, rolling line sludge is 15 wt%, and binder is 8 wt%). The evenly mixed ingredients are conveyed to the briquetting machine silo through a conveyor belt. The mixed materials are briquetted, screened, and conveyed to a baking furnace through a conveying channel for low-temperature baking. After baking, samples are taken for testing and inspection of relevant indicators such as strength, composition, and moisture. The measured indicators of the briquettes made from blast furnace gravity ash are: strength: 1420 N, Fe: 52 wt%, moisture: 1.0 wt%.

[0036] Application of blast furnace gravity ash in converter steelmaking: The prepared briquettes are added to the converter high-level silo through a conveyor belt for standby. The steel grade smelted in this furnace is low-alloy steel, the molten iron temperature is 1430 °C, the iron consumption is 900 Kg / t steel, and the Si content of the molten iron is 0.30 wt%. In this heat, blast furnace gravity ash briquettes are added in batches, with a total addition of 7 Kg per ton of steel. The entire production process is stable, all indicators are normal, at the same time, the recovery of ferrite is increased, the ferrite yield rate of the converter is improved, the steel output is increased, and the comprehensive energy consumption is reduced.

[0037] The steel billets and rolled products smelted with the addition of blast furnace gravity ash are tracked and comprehensively inspected and analyzed. All performance indicators are no different from those of the components, mechanical properties, and metallographic structures without adding this gravity ash briquette, fully meeting the requirements of the standards.

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 1 is that blast furnace gravity ash briquettes are not added to the first batch of cold materials, and other smelting processes are exactly the same as those in Example 1.

[0040] The composition test results of the steel billets finally prepared in Example 1 are shown in Table 1:

[0041] Table 1

[0042]

[0043] The composition test results of the steel billets finally prepared in Comparative Example 1 are shown in Table 2:

[0044] Table 2

[0045]

[0046] The steel property test results of the steel prepared in Example 1 are shown in Table 3 as follows:

[0047] Table 3

[0048]

[0049] The steel property test results of the steel prepared in Comparative Example 1 are shown in Table 4 as follows:

[0050] Table 4

[0051]

[0052] The metallographic structure of the steel prepared in Example 1 is as Figure 1 shown, and the metallographic structure of the steel prepared in Comparative Example 1 is as Figure 2 shown.

[0053] The testing methods and testing conditions of the steel in Example 1 and Comparative Example 1 are completely the same. The testing method for the steel composition is based on GB / T 4336-2016, and the testing method for the steel properties is based on GB 1499.2-2024 and the enterprise internal control standards. From the test results in Tables 1 to 4 and Figure 1 , Figure 2 , it can be seen that there are no differences in the composition, mechanical properties, and metallographic structure between the steel finally smelted by adding blast furnace gravity ash briquettes using the method of the present application and the steel smelted without adding blast furnace gravity ash briquettes. Moreover, the structure is ferrite and pearlite, fully meeting the standard requirements. Compared with Comparative Example 1, in Example 1, due to the addition of blast furnace gravity ash briquettes, beneficial effects such as increased recovery of ferrite, improved converter ferrite yield, increased steel production, and reduced comprehensive energy consumption are achieved.

[0054] The present invention is not limited to the above embodiments. Anyone should know that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, all fall within the protection scope of the present invention.

Claims

1. A method for the efficient utilization of BF gravity dust in converter steelmaking, characterized in that It includes the following steps: Mix blast furnace gravity ash, waste from the rolling process, and a binder evenly to obtain a mixed material, where the waste from the rolling process is one or a combination of scale and rolling sludge; After the mixed material is conveyed to the briquetting machine hopper through a conveyor belt for briquetting and screening, it is conveyed to a baking furnace through a transfer channel for low-temperature baking to obtain blast furnace gravity ash briquettes; Inspect the strength, composition, and moisture content of the blast furnace gravity ash briquettes, and screen out blast furnace gravity ash briquettes with a strength ≥ 1200 N, an iron content ≥ 50 wt%, and a moisture content ≤ 2 wt%; The steel grade for converter steelmaking is a low-alloy steel grade. When the hot metal temperature is 1390 - 1470 °C, the iron consumption is 810 - 930 Kg / t steel, and the hot metal Si content is 0.25 - 0.5 wt%, or when the hot metal consumption is 810 - 850 kg, the hot metal temperature ≥ 1450 °C, and the hot metal Si content ≥ 0.35 wt%, or when the hot metal consumption > 850 kg, the hot metal temperature ≥ 1420 °C, and the hot metal Si content > 0.25 wt%, add the screened blast furnace gravity ash briquettes to the converter high-level hopper through a conveyor belt and add them to the converter with the first batch of cold materials. The addition amount of the blast furnace gravity ash is 2 - 7 Kg / t steel.

2. The efficient utilization method according to claim 1, wherein By weight, in the mixed material, the content of blast furnace gravity ash is 60 - 70%, the content of scale is 25 - 30%, and the content of the binder is 5 - 10%.

3. The efficient utilization method according to claim 1, characterized in that By weight, in the mixed material, the content of blast furnace gravity ash is 50 - 60%, the content of rolling sludge is 35 - 40%, and the content of the binder is 5 - 10%.

4. The efficient utilization method according to claim 1, characterized in that By weight, in the mixed material, the content of blast furnace gravity ash is 50 - 55%, the content of scale is 20 - 35%, the content of rolling sludge is 10 - 25%, and the content of the binder is 5 - 10%.

5. The efficient utilization method according to claim 1, characterized in that, The binder is a liquid binder.

6. The efficient utilization method according to claim 1, wherein The binder is water glass.

7. The efficient utilization method according to claim 1, characterized in that, The low-temperature baking temperature is 150 °C - 190 °C, and the time is 1.5 h - 2 h.

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