Method for injecting pickling sludge into blast furnace

Abstract

The present invention discloses a method for injecting pickling sludge into a blast furnace, comprising: (1) drying the pickling sludge to obtain dried pickling sludge; (2) mixing and grinding the dried pickling sludge with injection coal to obtain a mixed fine powder; and (3) using the mixed fine powder in the blast furnace coal injection process. The method of the present invention effectively recycles stainless steel pickling sludge, improves the performance of slag in the blast furnace hearth area, reduces slag viscosity and slag melting point, and promotes the discharge of slag iron. At the same time, the metal elements in the pickling sludge are effectively recovered, achieving the effect of preventing solid waste from leaving the factory and rationally utilizing solid waste.

Description

Technical Field

[0001] The invention relates to the technical field of blast furnace injection and resource recycling, and in particular to a method for injecting pickling sludge into a blast furnace. Background Art

[0002] Stainless steel pickling sludge contains large amounts of heavy metal elements such as Fe, Cr, and Ni. The Fe content is relatively high, followed by Cr, and there is a small amount of Ni, which has a high recycling value. However, the chromium element in pickling sludge mainly exists in the form of hexavalent chromium ions, which poses a serious threat to the ecological environment, food safety, and human health. It is necessary to find effective ways to dispose of pickling sludge. At the same time, the content of S, F, and Cl elements in pickling sludge is also relatively high, and how to effectively control harmful elements will be a more difficult problem. At present, typical resource utilization technologies for stainless steel pickling sludge mainly include: mixing with sintered ore, mixing with pelletized ore, direct reduction, mixing with steelmaking auxiliary materials, wet leaching, and materialization.

[0003] However, these resource utilization technologies cannot achieve the effective recycling of stainless steel pickling sludge. Summary of the Invention

[0004] The object of the present invention is to provide a method for injecting pickling sludge into a blast furnace. By means of this method, the utilization of stainless steel pickling sludge is linked to the blast furnace coal injection technology, the stainless steel pickling sludge is effectively recycled, the performance of the slag in the blast furnace hearth area is improved, the slag viscosity and the slag melting point are reduced, the discharge of slag iron is promoted, and at the same time, the metal elements in the pickling sludge are effectively recovered, so as to achieve the effect of preventing solid waste from leaving the factory and rationally utilizing solid waste.

[0005] Specifically, the present invention is achieved through the following technical solutions:

[0006] A method for injecting pickling sludge into a blast furnace comprises the following steps:

[0007] (1) drying the stainless steel pickling sludge to obtain dry pickling sludge;

[0008] (2) mixing and grinding the dried pickling sludge with the PCI coal to obtain a mixed fine powder;

[0009] (3) The mixed fine powder is used in the blast furnace coal injection process.

[0010] Optionally, in step (1), the water content of the dried pickling sludge is below 4%.

[0011] Optionally, in step (2), the portion of the mixed fine powder with a particle size below 0.074 mm is not less than 70%.

[0012] Optionally, in step (2), the amount of the dried pickling sludge is determined based on the furnace cross-sectional area utilization coefficient.

[0013] Optionally, in step (2), if the furnace cross-sectional area utilization coefficient is ≤55t / m 2 ·d, the amount of dried pickling sludge is 12-15kg / t·molten iron; if 55t / m 2 ·d<the utilization coefficient of the cross-sectional area of the furnace<60t / m 2 ·d, the amount of dried pickling sludge is 9-11kg / t·molten iron; if 60t / m 2 ·d≤ utilization coefficient of the furnace cross-sectional area <70t / m 2 ·d, the amount of the dried pickling sludge is 6-8kg / t·molten iron; if the furnace cross-sectional area utilization coefficient is ≥70t / m 2 ·d, the amount of the dried pickling sludge is ≤5kg / t·molten iron.

[0014] Optionally, in step (2), the proportion of the dried pickling sludge in the mixed fine powder is determined according to the coal ratio.

[0015] Optionally, in step (2), if the coal ratio is ≤110 kg / t, the proportion of the dried pickling sludge is 12% to 15%; if 110 kg / t < the coal ratio <140 kg / t, the proportion of the dried pickling sludge is 8% to 11%; if 140 kg / t ≤ the coal ratio <170 kg / t, the proportion of the dried pickling sludge is 4% to 7%; if the coal ratio is ≥170 kg / t, the proportion of the dried pickling sludge is ≤3%.

[0016] Optionally, in step (2), the proportion of bituminous coal in the mixed fine powder is not less than 25%.

[0017] It can be seen from the above technical solution that the method of injecting pickling sludge into a blast furnace of the present invention has at least the following beneficial effects:

[0018] (1) The method of injecting pickling sludge into a blast furnace of the present invention increases the alkalinity of the tuyere slag, reduces the melting point of the molten acidic slag of the pulverized coal ash, increases the volume of the whirlpool, and improves the liquid permeability of the dead material column.

[0019] (2) The method of injecting pickling sludge into a blast furnace of the present invention can recover the Cr and Ni elements in the pickling sludge into molten iron, which can be directly used for smelting stainless steel, thereby realizing the recycling of the pickling sludge. DETAILED DESCRIPTION

[0020] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0021] In the present invention, "%" means "% by weight" unless otherwise specified.

[0022] Blast furnace ironmaking plays an important role in steel production, and modern blast furnace ironmaking processes mostly utilize coal-fired injection (CPI). However, current CPI technology has issues such as acidic slag in the tuyere area and poor fluidity, which have yet to be effectively addressed.

[0023] On the other hand, stainless steel pickling sludge contains some metal elements with high recovery value, but also contains some harmful elements. Existing methods for utilizing stainless steel pickling sludge are still unable to effectively control harmful elements while recovering valuable metal elements.

[0024] However, the inventors have analyzed and studied the properties of stainless steel pickling sludge. XRD analysis of the pickling sludge after low-temperature drying showed that the main phases were CaSO4 and CaF2. Chemical composition analysis revealed that the CaO content was 25% to 35%, and the SiO2 content was 1.5% to 2.5%, indicating an alkaline substance. Furthermore, the CaF2 content in the pickling sludge was 5% to 10%. Analysis of the softening properties of the pickling sludge revealed a deformation temperature of 1242°C, a softening temperature of 1281°C, a hemispherical temperature of 1291°C, and a flow temperature below 1300°C. The fusibility of fly ash from blast furnace injection coal indicates a flow temperature of 1300°C to 1400°C. Mixing the pickling sludge with pulverized coal will not cause slagging in the spray gun.

[0025] Furthermore, the inventors believe that:

[0026] (1) CaF2 in the stainless steel pickling sludge enters the blast furnace from the tuyere vortex zone and fuses with the slag, which can reduce the melting temperature of the slag, reduce the viscosity of the slag, improve the fluidity of the slag, and facilitate the discharge of slag iron; clean the impurities in the gaps between the coke in the dead material column, improve its liquid permeability and air permeability; at the same time, avoid the erosion of the upper and middle furnace walls of the blast furnace when fluorite is added from the top of the furnace.

[0027] (2) After the stainless steel pickling sludge is dehydrated, it enters the blast furnace tuyere vortex zone along with the pulverized coal. Under high temperature conditions, the CaSO₄ in the pickling sludge rapidly decomposes into CaO and SO₂. The slag in the tuyere area is primarily acidic, so the addition of CaO can improve the slag alkalinity. Alkaline slag has a lower viscosity than acidic slag, which is beneficial to the fluidity of molten iron. Furthermore, the increased CaO activity in the slag enhances the slag's desulfurization capacity and reduces the [S] content in the molten iron. However, the majority of the SO₂ decomposed from the CaSO₄ in the pickling sludge is carried away by the coal gas.

[0028] Based on the inventors' research, the present invention proposes a method for injecting pickling sludge into blast furnaces. This method utilizes the alkaline substances and elements that lower the slag melting point in stainless steel pickling sludge, combined with the blast furnace's operating conditions. Pulverized coal mixed with appropriate pickling sludge is injected through the tuyere, improving the liquid and air permeability of the coke shell in the tuyere area, thereby activating the furnace hearth. Furthermore, the pickling sludge can be effectively recycled.

[0029] Specifically, the method for injecting pickling sludge into a blast furnace of the present invention comprises the following steps:

[0030] (1) Drying the stainless steel pickling sludge to obtain dry pickling sludge.

[0031] The water content of stainless steel pickling sludge is usually 40% to 50%. Therefore, it needs to be dried before use to reduce the water content of the pickling sludge to 4%.

[0032] (2) Mixing and grinding the dried pickling sludge with the PCI coal to obtain a mixed fine powder.

[0033] In the present invention, the proportion of the mixed fine powder having a particle size of -0.074 mm (i.e., below 0.074 mm) is not less than 70%. After the particle size is fine, the combustion rate and reaction rate of the mixed fine powder after entering the tuyere will be significantly improved.

[0034] In the present invention, the composition of the PCI coal may refer to the PCI coal used in the existing blast furnace PCI technology, such as bituminous coal, anthracite and lignite, and the proportion of each substance may also refer to the relevant solutions in the existing technology.

[0035] In the present invention, the proportion of bituminous coal in the mixed fine powder is preferably not less than 25%, so as to improve the combustion efficiency of the coal powder.

[0036] In the present invention, the amount of stainless steel pickling sludge is determined according to the furnace cross-sectional area utilization coefficient, which refers to the daily molten iron output / furnace cross-sectional area, and the unit is t / m 2 ·d.

[0037] Specifically, if the furnace cross-sectional area utilization coefficient is ≤55t / m 2·d, then the amount of dry pickling sludge is 12~15kg / t·molten iron (12~15kg of dry pickling sludge per ton of molten iron); if 55t / m 2 ·d< furnace cross-sectional area utilization coefficient<60t / m 2 ·d, then the amount of dry pickling sludge is 9-11kg / t·molten iron; if 60t / m 2 ·d≤ furnace cross-sectional area utilization coefficient<70t / m 2 ·d, then the amount of dry pickling sludge is 6-8kg / t·molten iron; if the furnace cross-sectional area utilization coefficient is ≥70t / m 2 ·d, then the amount of dry pickling sludge is ≤5kg / t·molten iron.

[0038] Summarized in a table as follows:

[0039] <![CDATA[Cylinder hearth cross-sectional area utilization coefficient (t / m 2 ·d)]]> ≤55 55～60 60～70 ≥70 Stainless steel pickling sludge dosage (kg / t·molten iron) 12～15 9～11 6～8 ≤5

[0040] In the present invention, the standard (dosage) set for stainless steel pickling sludge is related to the viscosity and holdup of the slag iron liquid between the cokes in the tuyere area and the raceway of the blast furnace. It is specifically manifested in the working state of the tuyere area by parameters such as the size of the tuyere raceway, the height of the blast furnace air volume, and the quality of the tuyere state. The dosage of pickling sludge is determined based on the smelting intensity and the amount of pulverized coal injection to eliminate the problem of slag iron stagnation between the tuyere cokes. At the same time, the impact on the blast furnace lining is minimal. After research by the inventors, the stainless steel pickling sludge dosage was selected according to the above table, which can effectively eliminate the problem of slag iron stagnation between the tuyere cokes and reduce the impact on the blast furnace lining to a minimum.

[0041] In the present invention, the proportion of stainless steel pickling sludge in the mixed coal is determined based on different coal ratio levels. The so-called stainless steel pickling sludge proportion refers to the weight percentage of stainless steel pickling sludge (i.e., pickling sludge after drying) in the mixed fine powder (i.e., the sum of stainless steel pickling sludge and PCI coal).

[0042] Specifically, if the coal ratio is ≤110kg / t, the proportion of stainless steel pickling sludge is 12% to 15%; if 110kg / t<coal ratio<140kg / t, the proportion of stainless steel pickling sludge is 8% to 11%; if 140kg / t≤coal ratio<170kg / t, the proportion of stainless steel pickling sludge is 4% to 7%; if the coal ratio is ≥170kg / t, the proportion of stainless steel pickling sludge is ≤3%.

[0043] Summarized in a table as follows:

[0044]

[0045] After research by the inventors, the proportion of stainless steel pickling sludge is determined according to the above table. When a small amount of stainless steel pickling sludge is added, the viscosity of the slag can be effectively reduced, the alkalinity of the slag can be improved, and thus the fluidity of the slag can be improved. At the same time, since the amount of stainless steel pickling sludge added is small, the harmful substances such as SO2 produced by it can be carried away by the blast furnace gas and will not have an adverse effect on the blast furnace.

[0046] Furthermore, by imposing dual constraints on the added stainless steel pickling sludge by the furnace cross-sectional area utilization coefficient and the coal ratio, the beneficial effect brought by the rapid decomposition of CaF2 and CaSO4 in the stainless steel pickling sludge into CaO under high temperature conditions can be fully utilized, and the adverse effects caused by the high-temperature combustion of the stainless steel pickling sludge can be minimized.

[0047] (3) Use the mixed fine powder in the blast furnace coal injection process

[0048] For specific operations, please refer to the relevant solutions in the prior art and will not be described in detail here.

[0049] Example

[0050] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. In the following examples, the experimental methods without specific conditions are based on conventional methods and conditions.

[0051] Example 1:

[0052] The output of a large blast furnace is maintained at about 8800-9000t / d in a certain period. The utilization coefficient of the hearth cross-sectional area is 58-59t / m 2 d. The blast furnace's economic and technical indicators were poor, with the coal ratio maintained at 130 kg / t. The pressure differential within the furnace was high, material collapse and slippage were frequent, and the material line was significantly deviated. The blast furnace's slag and iron discharge was obstructed, manifested in short tapping times, increased tapping frequency, incomplete slag and iron discharge, and poor furnace hearth activity.

[0053] According to the above blast furnace operation situation, the method of injecting stainless steel pickling sludge is adopted to improve the active state of the furnace hearth. The specific technical measures are:

[0054] (1) After the pickling sludge is dried in a medium-temperature rotary kiln, the moisture content is reduced to 3.5%.

[0055] (2) Furnace cross-sectional area utilization coefficient 58-59t / m 2 ·d. The amount of pickling sludge is selected as 11kg / t.

[0056] (3) The coal ratio is 130 kg / t, and the proportion of pickling sludge in the mixed coal is 8.5%.

[0057] (4) The proportion of mixed coal (after adding pickling sludge) with a particle size of -0.074mm is 75%. At the same time, the proportion of bituminous coal is 30%. This will increase the combustion efficiency of the mixed coal.

[0058] (5) The spraying cycle is 15-20 days.

[0059] Effect analysis

[0060]

[0061]

[0062] After a period of operation, the blast furnace hearth condition has significantly improved. Specifically, the pressure differential within the furnace has decreased, the deflection has been reduced, the number of material collapses and slippages has significantly decreased, the iron tapping time has become more reasonable, and the blast furnace operation has improved. This has provided the conditions and prerequisites for increasing blast furnace production. At the same time, the pickling sludge has been digested.

[0063] Example 2:

[0064] 2000m 3 At a certain stage, the output of the blast furnace only reached 3800t / d. The utilization coefficient of the hearth cross-sectional area was less than 55t / m 2 d. Maintain a coal-to-fuel ratio of 110-120 kg / t. High blast pressure within the blast furnace leads to frequent slag surges in the tuyere area, large molten iron temperature deviations, frequent tuyere damage, and an increase in unplanned air shutoffs. Signs of hearth accumulation also appear.

[0065] According to the above blast furnace operation situation, the method of injecting stainless steel pickling sludge is adopted to improve the active state of the furnace hearth. The specific technical measures are:

[0066] (1) After the pickling sludge is dried in a medium-temperature rotary kiln, the moisture content is reduced to 3.2%.

[0067] (2) The furnace cross-sectional area utilization coefficient is less than 55t / m 2 ·d. The amount of pickling sludge is selected as 15kg / t.

[0068] (3) The coal ratio is 110 kg / t, and the proportion of pickling sludge in the mixed coal is 13.6%.

[0069] (4) The proportion of mixed coal (after adding pickling sludge) with a particle size of -0.074mm is 72%. At the same time, the proportion of bituminous coal is 35%.

[0070] (5) The spraying cycle is 12-18 days.

[0071] Effect analysis

[0072]

[0073] After a period of use, the blast furnace's operating conditions improved significantly, with reduced wind pressure, a significant decrease in the number of damaged tuyere ports, and significantly fewer wind stoppages. The blast furnace's economic and technical indicators saw significant improvements.

[0074] Example 3:

[0075] A 4000m 3 The output of the first-class blast furnace was 10,300t / d at a certain stage. The utilization coefficient of the hearth cross-sectional area was 64-66t / m 2 d. The coal ratio is maintained at 145-155 kg / t. The air pressure inside the blast furnace is relatively stable, while the heat load fluctuates frequently. However, the blast furnace maintains good stability. To maintain this condition, stainless steel pickling sludge is injected.

[0076] Specific technical measures include:

[0077] (1) After the pickling sludge is dried in a medium-temperature rotary kiln, the moisture content is reduced to 3.9%.

[0078] (2) The utilization coefficient of the hearth cross-sectional area is between 60-70t / m 2 ·d. The amount of pickling sludge is selected as 7kg / t.

[0079] (3) The coal ratio is 150 kg / t, and the proportion of pickling sludge in the mixed coal is 5%.

[0080] (4) The proportion of mixed coal (after adding pickling sludge) with a particle size of -0.074mm is 76%. At the same time, the proportion of bituminous coal is 28%.

[0081] (5) The spraying cycle is 10-15 days.

[0082] Effect analysis

[0083]

[0084] After a certain period of use, the frequency of fluctuations in the blast furnace's thermal load decreases, which is conducive to stable production of the blast furnace.

[0085] Example 4:

[0086] A 4000m 3 The output of the first-class blast furnace was 11,200t / d at a certain stage. The utilization coefficient of the hearth cross-sectional area was 71-72t / m 2 d. The coal ratio was maintained at 175 kg / t. The air pressure inside the blast furnace was relatively stable, with occasional increases and decreases in air volume. However, the economic and technical indicators of the blast furnace were good. To maintain the condition of the blast furnace, stainless steel pickling sludge was injected.

[0087] Specific technical measures include:

[0088] (1) After the pickling sludge is dried in a medium-temperature rotary kiln, the moisture content is reduced to 3.5%.

[0089] (2) The furnace cross-sectional area utilization coefficient is greater than 70t / m 2 ·d. The amount of pickling sludge is selected as 4kg / t.

[0090] (3) The coal ratio is 175 kg / t, and the proportion of pickling sludge in the mixed coal is 2.5%.

[0091] (4) The proportion of mixed coal (after adding pickling sludge) with a particle size of -0.074mm is 80%. At the same time, the proportion of bituminous coal is 25%.

[0092] (5) The spraying cycle is 5-10 days.

[0093] Effect analysis

[0094]

[0095] After a certain period of use, the blast furnace air volume becomes stable and the blast furnace resistance is enhanced.

[0096] The above embodiments are preferred implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any other substitutions, modifications, combinations, changes, simplifications, etc. that do not deviate from the spirit and principles of the present invention should be considered equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for injecting pickling sludge into a blast furnace, characterized in that: The steps include: (1) Drying the stainless steel pickling sludge to obtain dry pickling sludge; The XRD analysis results of the dried pickling sludge showed that its main phases were CaSO4 and CaF2; (2) Mixing and grinding the dried pickling sludge with PCI coal to obtain a mixed fine powder; The amount of the dried pickling sludge is determined according to the utilization coefficient of the furnace cross-sectional area; the proportion of the dried pickling sludge in the mixed fine powder is determined according to the coal ratio; If the furnace cross-sectional area utilization coefficient is ≤55 t / m 2 ·d, the amount of dried pickling sludge is 12~15 kg / t·molten iron; if 55 t / m 2 · d<the utilization coefficient of the cross-sectional area of the furnace<60 t / m 2 ·d, the amount of dried pickling sludge is 9~11 kg / t·molten iron; if 60 t / m 2 · d≤ utilization coefficient of the furnace cross-sectional area < 70 t / m 2 ·d, the amount of dried pickling sludge is 6~8 kg / t·molten iron; if the furnace cross-sectional area utilization coefficient is ≥70 t / m 2 d. The amount of dried pickling sludge is ≤5 kg / t·molten iron; if the coal ratio is ≤110 kg / t, the proportion of dried pickling sludge is 12%-15%; if 110 kg / t < the coal ratio <140 kg / t, the proportion of dried pickling sludge is 8%-11%; if 140 kg / t ≤ the coal ratio <170 kg / t, the proportion of dried pickling sludge is 4%-7%; if the coal ratio is ≥170 kg / t, the proportion of dried pickling sludge is ≤3%; (3) The mixed fine powder is used in the blast furnace coal injection process.

2. The method for injecting pickling sludge into a blast furnace according to claim 1, wherein: In step (1), the moisture content of the dried pickling sludge is below 4%.

3. The method for injecting pickling sludge into a blast furnace according to claim 1, wherein: In step (2), the portion of the mixed fine powder with a particle size of less than 0.074 mm is not less than 70%.

4. The method for injecting pickling sludge into a blast furnace according to claim 1, wherein: In step (2), the pulverized coal includes bituminous coal, anthracite and lignite, and the proportion of bituminous coal in the mixed fine powder is not less than 25%.

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