Additive for coal injection into blast furnaces

Abstract

This invention discloses a blast furnace pulverized coal additive, which is composed of the following raw materials: 12-18 parts by weight of stearic acid-modified cerium oxide powder, 15-21 parts by weight of pyrolusite powder, 20-30 parts by weight of dolomite powder, 8-12 parts by weight of fluorite powder, and 5-8 parts by weight of calcium nitrate. The stearic acid-modified cerium oxide powder has a particle size between 400-600 mesh, while the particle size of the remaining raw material powders is between 100-200 mesh. This invention uses stearic acid to modify the surface of the cerium oxide powder, changing its surface from hydrophilic to hydrophobic. This results in stronger affinity with coal powder, which also has a hydrophobic surface, improving contact efficiency and thus increasing the utilization rate of the cerium oxide powder.

Description

Technical Field

[0001] This invention belongs to the field of coal powder combustion aids, specifically relating to an additive for assisting the combustion of coal powder used in the pulverized coal injection process of blast furnaces in the steel industry. Background Technology

[0002] Pulverized coal injection (PCI) is a core technology in modern blast furnace ironmaking. It involves injecting pulverized coal into the blast furnace tuyeres to replace some of the expensive and scarce metallurgical coke, thereby reducing pig iron costs, conserving coking coal resources, and improving the smelting process. The PCI process is as follows: First, a coal mill grinds coarse coal particles into pulverized coal with a particle size of approximately 200 mesh (usually requiring a content of pulverized coal smaller than 200 mesh of not less than 80 wt%). Then, a pulverized coal lance continuously injects it into the blast furnace's direct-fired pipe (the temperature at the direct-fired pipe is typically 900-1200℃). The pulverized coal mixes with the high-speed, high-temperature hot air supplied to the direct-fired pipe and enters the tuyeres vortex zone inside the blast furnace for complete combustion, releasing a large amount of heat. Therefore, the temperature in the tuyeres vortex zone can reach as high as 2000-2400℃. The hot air then continues to enter the blast furnace to heat the iron ore.

[0003] The ironmaking industry aims for the highest possible combustion efficiency of pulverized coal in the tuyeres, ideally between 62% and 79% under sufficient oxygen supply, with higher being better but no lower than 50%. Low combustion efficiency leads to several problems: 1. Unburned or incompletely burned pulverized coal (referred to as "unburned pulverized coal" or "unburned residual coal") rises with the airflow, clogging the gaps between coke layers. This significantly increases the resistance of the blast furnace burden to the rising gas, worsening blast furnace permeability, causing "breathing difficulties," increased blast pressure, and even serious accidents such as "difficulty descending the burden" or "burden suspension." 2. Incomplete combustion of pulverized coal releases less heat, resulting in insufficient heat supply to the blast furnace, affecting the full reduction of iron ore and the fluidity of molten iron. 3. A large amount of unburned pulverized coal is carried out of the furnace by the gas, increasing the load on subsequent dust removal equipment and potentially causing blockages and malfunctions.

[0004] To improve pulverized coal combustion efficiency, technicians typically make improvements on the blast furnace side and / or the pulverized coal side. Blast furnace side improvements include oxygen enrichment (increasing oxygen content to promote combustion), high blast temperature (providing more heat to accelerate the reaction), and optimizing the lance structure to improve pulverized coal combustion in the tuyeres. Pulverized coal side improvements can be implemented by controlling pulverized coal particle size (fineer particles are easier to burn) and providing pulverized coal injection additives (adding catalytically active ingredients to promote combustion). Blast furnace side improvements are more suitable for newly installed blast furnaces. For existing blast furnaces, equipment modifications require shutdowns and production losses; therefore, technicians prefer pulverized coal side improvements. Since pulverized coal particle size is limited by existing mills and pulverized coal injection processes and cannot be infinitely fined, pulverized coal injection additives are the most favored improvement method by plant technicians because it only requires adding the additive to the pulverized coal without modifying the existing blast furnace equipment and its auxiliary pulverized coal injection equipment and processes.

[0005] Currently, additives are widely used in industry to promote the combustion of pulverized coal. The main active components of these additives are transition metal oxides such as cerium dioxide, iron oxide, copper oxide, or manganese dioxide. They also contain auxiliary components such as CaO, MgO, fluorite, barium permanganate, calcium nitrate, and auxiliary fuel powder. Among these, cerium oxide is the most preferred transition metal oxide. After being dispersed on the surface of pulverized coal, it acts as an active carrier of oxygen, fixing oxygen from the air and continuously transferring it to carbon atoms in the pulverized coal, thus accelerating the oxidation and combustion reaction of carbon. It is the most indispensable active component in the additive. However, because cerium oxide powder and pulverized coal are physically mixed, the powder particles only contact each other at limited contact points. Furthermore, the additive contains other raw material powders, and the cerium oxide powder randomly contacts the pulverized coal and other raw material powders, without preferentially contacting the pulverized coal (even when it does contact, the contact is weak and may separate again). Therefore, the contact efficiency between cerium oxide powder and pulverized coal is naturally occurring without deliberate control. After the additive is mixed with pulverized coal and then injected into the direct-blowing pipe by compressed air, the compressed air, which serves as the power source, and the high-speed hot air flowing inside the direct-blowing pipe have a strong airflow dispersing effect on the mixed powder. This may cause the cerium oxide powder and pulverized coal to separate again. As a result, the pulverized coal and cerium oxide powder actually undergo thermochemical processes independently in the hot air. The portion of cerium oxide powder that does not come into direct contact with the pulverized coal does not actually play a role in combustion, which reduces the utilization rate of cerium oxide powder.

[0006] The present invention aims to solve the above-mentioned problems. Summary of the Invention

[0007] The first aspect of this invention provides a blast furnace pulverized coal additive, which is composed of the following raw materials: 12-18 parts by weight of stearic acid-modified cerium oxide powder, 15-21 parts by weight of pyrolusite powder, 20-30 parts by weight of dolomite powder, 8-12 parts by weight of fluorite powder, and 5-8 parts by weight of calcium nitrate, wherein the particle size of the stearic acid-modified cerium oxide powder is between 400-600 mesh, and the particle size of the remaining raw material powders is between 100-200 mesh.

[0008] In this invention, the preparation process of the stearic acid-modified cerium oxide powder is as follows: Cerium oxide powder with a particle size between 80-100 mesh is mixed with solid stearic acid at a weight ratio of 1:0.05-0.1, and then placed in a ball mill and ball-milled at a temperature not lower than 70°C for at least 30 minutes, yielding the stearic acid-modified cerium oxide powder. There are no restrictions on the ball milling media used; stainless steel balls, zirconia balls, and ceramic balls are all acceptable. The ball mill speed is typically set above 100 rpm, and the ball mill temperature is controlled by an electrically heated jacket. During ball milling, the following interactions occur between materials: the high-intensity grinding action breaks the cerium oxide powder into smaller particles and creates many fresh surfaces; the stearic acid solid is rolled into a thin film and gradually coated on the surface of the cerium oxide powder as it is blended with the cerium oxide powder at high intensity; stearic acid molecules can also undergo esterification with the hydroxyl groups on the surface of the cerium oxide powder to form chemical bonds, or react directly with the outer surface of the cerium oxide powder to form cerium stearate. These interactions, whether occurring individually or in combination, can add long-chain alkyl groups such as stearic acid groups to the surface of the cerium oxide powder, changing the surface of the cerium oxide powder from hydrophilic to hydrophobic. This facilitates the selective contact and dispersion of cerium oxide powder particles on the surface of coal powder, since the carbonaceous material on the surface of coal powder is naturally hydrophobic.

[0009] Preferably, steam can be introduced during the ball milling process to fumigate the material inside the mill jar. To save costs, atmospheric pressure steam at 100°C is usually sufficient, although higher pressure and temperature steam can also be used. Steam promotes the formation of more surface hydroxyl groups on the fresh surface of the newly generated cerium oxide powder, which facilitates esterification of stearic acid molecules and increases the adhesion of stearic acid to the cerium oxide powder surface.

[0010] Of course, other known methods can be used to surface modify cerium oxide powder with stearic acid, such as the "wet surface modification" most commonly used in the rubber and plastics additive industry, but these are not as simple to operate as the ball milling modification method used in this invention. How to surface modify cerium oxide powder with stearic acid is a mature technology and not the key point of this invention. The key point of this invention is to use stearic acid-modified cerium oxide powder in the new application field of blast furnace pulverized coal additives.

[0011] The method of using the blast furnace pulverized coal additive of the present invention is very simple. It can be added to the raw coal coarse powder in the coal grinding process and ground into fine powder together in a coal mill. The weight ratio of the blast furnace pulverized coal additive of the present invention to the raw coal coarse powder is usually between 0.6wt% and 1.2wt%, preferably between 0.8wt% and 1wt%.

[0012] The functions of each component in this invention are as follows:

[0013] Cerium oxide powder, as the core active ingredient, disperses on the surface of coal powder and plays a catalytic oxidation role. It acts as an active carrier of oxygen, fixing oxygen from the air and continuously transferring it to carbon atoms in the coal powder, thus accelerating the carbon oxidation and combustion reaction. The main component of pyrolusite powder is manganese dioxide (in this invention, lower-grade pyrolusite with a manganese dioxide content of 50 wt% can be used; of course, higher purity is better), which is also a transition metal oxide and can also play a certain catalytic oxidation role. Dolomite powder (in this invention, lower-grade ore with a calcium carbonate and magnesium carbonate content of 60 wt% is usually used; of course, higher purity is better) decomposes into CaO and MgO upon heating for sulfur fixation; fluorite (in this invention, lower-grade ore with a CaF2 content of 35 wt% is usually used; of course, higher purity is better) acts as a flux, combining with ash in the coal powder to improve slag fluidity; calcium nitrate decomposes upon heating, releasing a large amount of highly active oxygen, which can be used to lower the ignition point of the coal powder. The functions of these components are well known in the prior art and will not be elaborated further.

[0014] The second aspect of the present invention relates to the use of stearic acid-modified cerium oxide powder in blast furnace pulverized coal additives, wherein the stearic acid-modified cerium oxide powder becomes hydrophobic on the surface compared to unmodified cerium oxide powder, thereby improving the contact efficiency with coal powder having a hydrophobic surface.

[0015] The advantages of this invention lie in the surface modification of cerium oxide powder with stearic acid, changing its surface from hydrophilic to hydrophobic. Since the surface of coal powder is also hydrophobic, under the energy action of co-grinding during the coal grinding process, the cerium oxide powder is more easily oriented and relatively firmly adheres to the coal powder surface, improving the contact efficiency with the coal powder. Moreover, this microscopic adhesion allows the cerium oxide powder to "bind" or "pair" with the coal powder, resisting the strong dispersing effect of compressed air and hot air to some extent during the injection into the blast furnace direct-fired pipe. This ensures that the cerium oxide powder and coal powder remain in contact and undergo the thermochemical process together in the initial stage of injection into the support pipe. In the high-temperature airflow above 900°C and rich in oxygen, the alkyl chains of stearic acid on the surface of the cerium oxide powder can be instantly burned off without affecting the catalytic effect of the internal cerium oxide, thus more fully utilizing the catalytic oxidation effect of the cerium oxide powder. In addition, in this invention, other raw materials besides cerium oxide can be directly used as lower-grade ore powders without the need for chemically pure reagents, which also reduces costs. Detailed Implementation

[0016] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, the following embodiments are provided for detailed description to facilitate understanding by those skilled in the art.

[0017] Comparative Example 1

[0018] 12 parts by weight of cerium oxide powder (chemically pure, the same below), 15 parts by weight of pyrolusite powder (manganese dioxide content 50wt%, the same below), 20 parts by weight of dolomite powder (calcium and magnesium carbonate content 62wt%, the same below), 8 parts by weight of fluorite powder (CaF2 content 35wt%, the same below), and 5 parts by weight of calcium nitrate powder (chemically pure, the same below) were taken. The initial particle size of the cerium oxide powder was about 80 mesh. It was ball-milled to a particle size of 400 mesh at 70℃ and 100 rpm, but no stearic acid was added for surface modification. The particle size of the remaining raw material powders was about 100 mesh. After the raw materials were fully mixed, the comparative sample 1 was obtained.

[0019] Example 1

[0020] 12 parts by weight of stearic acid-modified cerium oxide powder, 15 parts by weight of pyrolusite powder, 20 parts by weight of dolomite powder, 8 parts by weight of fluorite powder, and 5 parts by weight of calcium nitrate powder were taken. The particle size of the stearic acid-modified cerium oxide powder was approximately 400 mesh, and the particle size of the remaining raw material powders was approximately 100 mesh. After thorough mixing of all raw materials, sample 1 was obtained. The preparation process of stearic acid-modified cerium oxide powder is as follows: Cerium oxide powder with a particle size of approximately 80 mesh and solid stearic acid (chemically pure, the same below) were taken, with a mass ratio of cerium oxide to stearic acid of 1:0.05. The two were put into a ball mill and ball-milled at 70°C and 100 rpm for 30 minutes. After unloading the material, the stearic acid-modified cerium oxide powder was obtained, and its particle size was approximately 400 mesh. The modified powder was gently sprinkled on the water surface, and the powder particles were found to float or be suspended without sinking, indicating that its surface had changed from hydrophilic to hydrophobic.

[0021] Example 2

[0022] Take 12 parts by weight of stearic acid-modified cerium oxide powder, 15 parts by weight of pyrolusite powder, 20 parts by weight of dolomite powder, 8 parts by weight of fluorite powder, and 5 parts by weight of calcium nitrate powder. The stearic acid-modified cerium oxide powder has a particle size of about 400 mesh, and the particle size of the other raw material powders is about 100 mesh. After the raw materials are fully mixed, sample 2 is obtained. The preparation process of stearic acid modified cerium oxide powder is as follows: Cerium oxide powder raw material with a particle size of about 80 mesh and stearic acid solid are taken, and the mass ratio of cerium oxide to stearic acid is 1:0.05. The two are put into a ball mill and ball milled at 70℃ and 100 prm. During the ball milling process, 100℃ atmospheric pressure water steam is intermittently introduced into the ball mill jar to fumigate the material. After the water steam is introduced, the gas atmosphere temperature inside the ball mill will naturally rise to 100℃. However, due to the heat dissipation effect of the metal shell of the ball mill and the large overall heat capacity of the ball mill, the main body temperature of the ball mill will only rise slightly to less than 80℃. When the atmosphere temperature inside the ball mill gradually decreases to about 80℃, 100℃ atmospheric pressure water steam is introduced again. After fumigating and ball milling for 30 minutes, the material was discharged to obtain the stearic acid-modified cerium oxide powder. The powder was dried to remove any entrained condensate. The dried modified powder was then gently sprinkled onto water. The powder particles floated or suspended without sinking, indicating that their surface had changed from hydrophilic to hydrophobic. Testing showed that the particle size of the dried modified powder was approximately 400 mesh.

[0023] Application Examples

[0024] The application experiment was conducted in a small-scale pulverized coal injection simulated blast furnace at the School of Metallurgy, Beijing University of Science and Technology. The pulverized coal used was from a blast furnace of a steel company in Tangshan City, ground to approximately 200 mesh (60wt% anthracite + 40wt% bituminous coal). Each combustion aid sample was added to the pulverized coal at a rate of 0.8wt% of the pulverized coal weight and thoroughly mixed. The pulverized coal was then injected into the direct-fired pipe of the simulated blast furnace using a pulverized coal injection gun. The experimental conditions were as follows: coal ratio 140 kg / t, hot blast temperature in the direct-fired pipe between 990-1110℃, hot blast velocity 160 m / s, and hot blast oxygen enrichment rate 5.2%. The ignition delay time from pulverized coal injection to combustion was monitored (a shorter time indicates easier ignition). Unburned pulverized coal particles discharged with the blast furnace flue gas and collected at the bag filter were also collected. Their ash content was measured to calculate the pulverized coal combustion rate (a higher combustion rate indicates more complete combustion).

[0025] As a baseline for the experiment, a blank experiment was also conducted under the same experimental conditions using only pulverized coal without any additives.

[0026] The experimental results are shown below:

[0027]

[0028] As can be seen, compared with the blank experiment, all control and experimental samples significantly shortened the ignition delay time and improved the pulverized coal combustion rate. However, experimental samples 1 and 2 showed better combustion-supporting effects than control sample 1. This indicates that modifying cerium oxide powder with stearic acid can improve the combustion-supporting effect, and that steam fumigation during the modification process is more conducive to improving the modification effect. The above improvements can be attributed to and indirectly prove that the contact efficiency between cerium oxide powder modified with stearic acid and pulverized coal is improved compared with that before modification.

[0029] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A blast furnace pulverized coal additive, characterized in that, It is composed of the following raw materials: 12-18 parts by weight of stearic acid modified cerium oxide powder, 15-21 parts by weight of pyrolusite powder, 20-30 parts by weight of dolomite powder, 8-12 parts by weight of fluorite powder, and 5-8 parts by weight of calcium nitrate. The particle size of the stearic acid modified cerium oxide powder is between 400-600 mesh, and the particle size of the other raw material powders is between 100-200 mesh.

2. The blast furnace pulverized coal additive according to claim 1, characterized in that, The preparation process of the stearic acid-modified cerium oxide powder is as follows: Cerium oxide powder with a particle size between 80 and 100 mesh is mixed with stearic acid solid at a weight ratio of 1:0.05-0.1, and then placed in a ball mill and ball-milled at a temperature of not less than 70°C for at least 30 minutes before being discharged to obtain the stearic acid modified cerium oxide powder.

3. The blast furnace pulverized coal additive according to claim 2, characterized in that, Steam is introduced during the ball milling process to fumigate the materials.

4. The use of stearic acid-modified cerium oxide powder in blast furnace pulverized coal additives, characterized in that, Compared to unmodified cerium oxide powder, stearic acid-modified cerium oxide powder becomes hydrophobic, thus improving its contact efficiency with coal powder that has a hydrophobic surface.

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