Method for improving blast furnace coal powder preheating and injection performance

Abstract

This invention discloses a method for improving the injection performance of pulverized coal preheating in blast furnaces. A magnetite powder tank and a heating system are installed on the pulverized coal conveying pipeline between the pulverized coal tank and the distributor. Magnetite powder and pulverized coal are separately conveyed by high-pressure nitrogen and mixed in the injection main pipe to form a coal-iron mixture. The high-pressure nitrogen is used to convey the coal-iron mixture to the heating pipes of the heating system, where the mixture is subjected to high-frequency electromagnetic induction heating. This high-frequency electromagnetic induction heating generates eddy currents in the magnetite powder particles, coupled with conductive heating through the heating pipe wall, eddy current heating within the magnetite powder, and induction heating of the pulverized coal material to achieve the heating of the coal-iron mixture. The heated coal-iron mixture is then evenly distributed by the distributor to the injection branch pipes corresponding to each tuyer in the blast furnace. This method achieves extremely rapid and uniform heating of the pulverized coal, significantly improves conveying stability and injection uniformity, promotes rapid combustion of pulverized coal in the blast furnace tuyer zone, and increases the coal-coke replacement ratio.

Description

Technical Field

[0001] This invention relates to the field of blast furnace ironmaking technology, and more specifically to a method for improving the injection performance of pulverized coal by preheating blast furnace coal. Background Technology

[0002] In blast furnace ironmaking, fuel costs account for approximately 32% of the cost of molten iron. To reduce blast furnace fuel costs and improve the competitiveness of molten iron, steel companies generally strive to increase the pulverized coal injection ratio to replace coke, which costs about twice as much. Typically, the coal-coke replacement ratio is around 0.8. For every 1 kg increase in the pulverized coal injection ratio per ton of iron, coke consumption can be reduced by approximately 0.8 kg, thereby lowering the cost of molten iron. However, the increase in the pulverized coal injection ratio also brings two prominent problems: First, the stability of pulverized coal transportation decreases, making it prone to pipe deposition, flow pulsation (flow fluctuation > 15%), and even blockage, affecting the uniformity of injection and the stability of blast furnace conditions. Second, pulverized coal combustion is incomplete in the blast furnace tuyeres, increasing the proportion of unburned pulverized coal (usually 5%~15%), which deposits in the furnace belly and hearth, reducing the permeability of the burden and increasing fuel consumption.

[0003] One major reason for the aforementioned problems is the low temperature of the pulverized coal injected into the blast furnace, typically only 60-80°C. If this temperature is below the ambient water vapor dew point, it can cause the pulverized coal to clump, affecting transport. Simultaneously, the low-temperature pulverized coal burns slowly upon entering the blast furnace, with some entering the reducing atmosphere region before complete combustion, becoming unburned pulverized coal. Therefore, increasing the temperature of the injected pulverized coal is a key approach to improving its transport and combustion performance, thereby achieving stable operation with a high coal-to-gas ratio.

[0004] Existing technologies include several methods for preheating pulverized coal, such as electromagnetic induction heating, high-temperature waste gas heat exchange, and thermal oil heating. However, traditional preheating methods generally suffer from slow heating speeds (e.g., waste gas heating requires more than 3 seconds), low temperature control accuracy (fluctuations can reach ±30℃), complex equipment, or low energy efficiency, making it difficult to meet the high requirements of blast furnaces for stable pulverized coal injection and rapid response. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method for improving the injection performance of pulverized coal preheating in blast furnaces, so as to solve the problem that the pulverized coal conveying and combustion performance decreases under high pulverized coal injection ratio conditions, thereby affecting the smooth operation of the blast furnace and increasing fuel consumption.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for improving the injection performance of pulverized coal preheating in a blast furnace, wherein a magnetite powder tank and a heating system are installed on the pulverized coal conveying pipeline between the pulverized coal tank and the distributor at the pulverized coal injection end of the blast furnace; magnetite powder and pulverized coal are respectively conveyed by high-pressure nitrogen and mixed in the injection main pipe to form a coal-iron mixture; the coal-iron mixture is conveyed to the heating pipe of the heating system by high-pressure nitrogen, and the coal-iron mixture is heated by high-frequency electromagnetic induction heating through the heating system; the high-frequency electromagnetic induction heating achieves the heating of the coal-iron mixture by exciting the magnetite powder microparticles to generate eddy current heating, and coupling three mechanisms: heating tube wall conduction heating, magnetite powder internal eddy current heating, and pulverized coal material induction heating; the heated coal-iron mixture is evenly distributed by the distributor to the injection branch pipes corresponding to each tuyer of the blast furnace, and finally injected into the blast furnace through the pulverized coal injection gun.

[0007] Adding an appropriate amount of magnetite powder to pulverized coal and employing high-frequency electromagnetic induction heating utilizes the eddy currents generated by the movement of magnetite powder in a magnetic field to rapidly raise the temperature of the pulverized coal from 30-60℃ to 150-250℃ within 0.5-0.8 seconds. This improves the conveying and combustion performance of the pulverized coal, reduces clogging at the pulverized coal injection end, increases the coal-coke replacement ratio, and reduces coke consumption and iron production costs. After the heated pulverized coal is injected into the blast furnace tuyeres, the preheating stage before combustion at the tuyeres is reduced, allowing the pulverized coal to burn rapidly and immediately upon entering the furnace. This reduces the proportion of unburned pulverized coal and its impact on permeability, thereby maintaining normal blast furnace production and improving furnace stability.

[0008] In this invention, the temperature of pulverized coal is generally controlled to be no less than 150°C to ensure that the temperature of pulverized coal before it is injected into the blast furnace is no less than the dew point temperature of the water vapor in the injection environment, effectively preventing caking caused by the temperature of pulverized coal being lower than the dew point of the water vapor. In addition, the temperature of pulverized coal is controlled to be no more than 250°C to prevent the decomposition of volatiles and coking of high-volatile coal powder from affecting the normal injection of pulverized coal, and to keep the temperature of pulverized coal below the ignition point temperature of pulverized coal, thus ensuring the system safety at the pulverized coal injection end.

[0009] The incorporation and coupling of magnetite powder achieves a triple function: (a) Utilizing the density of magnetite powder (2.5~3.0 g / cm³) 3 The density is greater than that of pulverized coal (0.5~0.8 g / cm³). 3 Furthermore, magnetite powder has better flowability than coal powder. Adding a small amount of magnetite powder to coal powder helps to loosen and break up clumps of coal powder, thereby improving the coal powder conveying performance. (b) By utilizing the ferromagnetism and extremely high permeability of magnetite powder, eddy current heating is efficiently generated in a high-frequency (20-50kHz) alternating electromagnetic field, which serves as an internal heat source and significantly improves the heating rate of pulverized coal. (c) After being injected into the blast furnace tuyeres along with pulverized coal, the coal undergoes thermal decomposition (Fe3O4→3FeO+1 / 2O2, FeO → Fe +1 / 2O2), releasing oxygen which acts as an oxidant, promoting the combustion of surrounding pulverized coal and increasing the combustion rate. Simultaneously, the generated iron and ferrous oxide enter the furnace, effectively injecting some iron-containing raw materials and improving the blast furnace utilization coefficient. The heating system of this invention achieves synergistic and rapid heating through the coupling of three heat transfer mechanisms: (i) The wall of the heating tube is heated by high-frequency electromagnetic induction, thereby conducting heat to the coal powder close to the tube wall; (ii) The high-frequency electromagnetic field directly and efficiently excites eddy currents inside the magnetite powder microparticles, causing them to heat up rapidly and serve as an internal heat source to efficiently heat the surrounding coal powder. (iii) The high-frequency electromagnetic field produces a certain induction heating effect on the coal powder particles themselves.

[0010] This multi-mode coupled heating system, which combines "tube wall conduction heating + internal eddy current heating + material induction heating," is key to achieving rapid and uniform heating of pulverized coal within 0.5 to 0.8 seconds.

[0011] Furthermore, the magnetite powder is magnetite microparticles, taking into account both flowability and eddy current effect, with a particle size of less than 10 μm; the magnetite powder is Fe3O4, and the proportion is 5%~10% of the coal powder mass. Other ferromagnetic materials with similar magnetic permeability and thermal decomposition characteristics can also be selected as magnetite powder.

[0012] Furthermore, the pulverized coal is transported from the pulverizing end to the pulverized coal tank at the injection end, and then transported to the injection main pipe through the pulverized coal tank valve; the magnetite powder is transported from the magnetite powder tank to the pulverized coal in the injection main pipe through the magnetite powder tank valve.

[0013] Furthermore, the heating tube is installed vertically, and the material flows from top to bottom. Gravity not only prevents coal powder from depositing inside the tube wall, but also fluidizes the coal powder in the pipe, making the coal powder more uniformly heated and further avoiding the risk of blockage caused by local accumulation. One end of the heating tube is connected to the main injection pipe through the heating tube flange, and the other end is connected to the distributor through the distributor valve flange. The heating tube shell is wound with a high-frequency electromagnetic coil, which is evenly wound around the heating tube shell with a pitch of 5-10mm. The high-frequency electromagnetic coil is covered by a protective sleeve, which serves both as insulation and electromagnetic shielding to prevent leakage. A feed thermocouple is arranged at the feed end of the heating tube, and a discharge thermocouple is arranged at the discharge end. The high-frequency electromagnetic coil, feed thermocouple, and discharge thermocouple are all connected to the heating controller. By receiving thermocouple signals, the electromagnetic frequency of the high-frequency electromagnetic coil is adjusted within the range of 20-50kHz. The heating power is changed by adjusting the electromagnetic frequency of the high-frequency electromagnetic coil according to the temperature values ​​of the feed and discharge thermocouples. The coal powder temperature control accuracy can reach ±5℃, which is better than the ±30℃ level of traditional waste gas heating coal powder temperature fluctuation. This provides a guarantee for achieving stable injection and preventing coal powder overheating (controlling the temperature not to exceed 250℃ to prevent premature precipitation of volatiles and coking, and keeping it below the ignition point to ensure safety).

[0014] Furthermore, the heating tube is a wear-resistant alloy-coated steel tube, and its inner wall is sprayed with a ZrO2-Al2O3 composite ceramic layer with a thickness of 40-60 μm, which effectively improves the thermal conductivity and prevents coal powder adhesion. The ZrO2-Al2O3 composite ceramic layer is prepared by atmospheric plasma spraying, wherein the mass ratio of ZrO2 to Al2O3 is (3~5):1, and the bonding strength between the coating and the substrate is ≥15 MPa.

[0015] Furthermore, the distributor is made of wear-resistant alloy steel and has a structure combining a lower conical cavity section and an upper cylindrical cavity section. The number of injection branch pipes corresponds to the number of blast furnace tuyeres, typically 18 to 40. The injection branch pipes are evenly connected to the upper cylindrical cavity section of the distributor, and the inclination angle of the injection branch pipes is similar to or the same as the inclination angle of the upper conical cavity section of the distributor. The top of the upper cylindrical cavity section is a sealing plate, and the distributor valve in the lower conical cavity section is connected to the heating pipe via a flange.

[0016] The structure of the distributor and injection branch pipes allows the high-pressure solid-gas flow to enter the cavity and form a powerful vortex, which evenly distributes the pulverized coal into each injection branch pipe. This effectively reduces resistance loss during pulverized coal transportation and avoids problems such as blockage and uneven wear. It is suitable for pulverized coal transportation needs under various gas-solid ratios (dense phase or dilute phase) in blast furnace pulverized coal injection systems. The transportation process has small pulsations and no vortex, and the pulverized coal injection is uniform, stable and reliable. Under high pulverized coal injection ratios, the error of each branch pipe can be controlled within ±3%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention enhances the fluidity and eddy current heating of pulverized coal by using magnetite powder, combined with multi-mode coupled heating of "pipe wall conduction + internal eddy current + material induction", which significantly improves the conveying stability and injection uniformity, promotes the rapid combustion of pulverized coal in the blast furnace tuyeres, increases the combustion rate by about 3 to 5 percentage points, and improves the coal-coke replacement ratio. Based on the calculation of 170 kg of pulverized coal injected per ton of iron, it is estimated that the cost per ton of iron can be reduced by about 7.14 yuan. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the method for improving the injection performance of pulverized coal preheating according to the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The description herein is merely exemplary and does not constitute a limitation on the scope of protection of the present invention.

[0020] Combination Figure 1 The specific implementation method of a blast furnace pulverized coal preheating method to improve injection performance is as follows: A magnetite powder tank 6 and a heating system 8 are installed on the pulverized coal conveying pipeline between the pulverized coal tank 5 and the distributor 10 at the pulverized coal injection end of the blast furnace. Pulverized coal and magnetite powder are mixed in the injection main pipe 3 with high-pressure nitrogen 1 to form a coal-iron mixture. The coal-iron mixture is transported to the heating pipe 8.3 of the heating system 8 by the high-pressure nitrogen 1 through the nitrogen valve 2. The coal-iron mixture is rapidly heated by the high-frequency electromagnetic coil 8.4 in the heating system 8, so that the temperature of the pulverized coal rises from 30-60℃ to 150-250℃ in 0.5-0.8 seconds. Then, the distributor 10 evenly distributes the heated coal-iron mixture to each injection branch pipe 12, and finally it is injected into the blast furnace by the pulverized coal injection gun 16.

[0021] Powdered coal is transported from the pulverizing end to the powdered coal tank 5 at the injection end, and then conveyed to the injection main pipe 3 through the powdered coal tank valve 4. Magnetite powder is transported from the magnetite powder tank 6 through the magnetite powder tank valve 7 to the powdered coal in the injection main pipe 3 and mixed to form a coal-iron mixture. The magnetite powder is finely granulated magnetite powder with a particle size of less than 10μm, and the magnetite powder is Fe3O4, with an addition ratio of 5% to 10% of the powdered coal mass.

[0022] The heating tube 8.3 is installed vertically. One end of the heating tube 8.3 is connected to the main injection pipe 3 via the heating tube flange 8.1, and the other end is connected to the distributor 10 via the flange of the distributor valve 9. A high-frequency electromagnetic coil 8.4 is wound around the outer shell of the heating tube 8.3, and the high-frequency electromagnetic coil 8.4 is covered by a protective sleeve 8.5. A feed thermocouple 8.2 is arranged at the feed end of the heating tube 8.3, and a discharge thermocouple 8.7 is arranged at the discharge end. The high-frequency electromagnetic coil 8.4, the feed thermocouple 8.2, and the discharge thermocouple 8.7 are all connected to the heating controller 8.6, which receives thermocouple signals and adjusts the electromagnetic frequency of the high-frequency electromagnetic coil 8.4 within the range of 20~50kHz. The heating tube 8.3 is made of wear-resistant alloy coated steel pipe, and the inner wall of the heating tube is sprayed with a ZrO2-Al2O3 composite ceramic layer with a thickness of 40~60μm.

[0023] Specifically: The heating controller 8.6 has a preset temperature control program that receives the initial temperature signal of the pulverized coal from the feed thermocouple 8.2 and the real-time temperature signal from the discharge thermocouple 8.7. Through the built-in PID (proportional-integral-derivative) control algorithm, it calculates the required heating power and outputs a control signal to dynamically adjust the operating frequency (within the range of 20-50kHz) of the high-frequency electromagnetic coil 8.4, thereby stabilizing the temperature of the pulverized coal at the discharge end at the set value (such as a certain value between 150-250℃), with a control accuracy of ±5℃.

[0024] The distributor 10 is made of wear-resistant alloy steel and consists of a lower conical cavity section and an upper cylindrical cavity section. The number of injection branch pipes 12 corresponds to the number of blast furnace tuyeres. The injection branch pipes 12 are evenly connected to the upper cylindrical cavity section of the distributor 10 through branch pipe valves 13. The inclination angle of the injection branch pipes 12 is similar to or the same as the inclination angle of the upper conical cavity section of the distributor (e.g., cone angle 30~45°). The top of the upper cylindrical cavity section is a sealing plate 11, and the distributor valve 9 of the lower conical cavity section is connected to the heating pipe 8.3 through a flange. The injection branch pipes 12 are connected to the pulverized coal injection gun 16 through the flange of the hose valve 15 of the metal hose 14. The pulverized coal injection rate of each branch pipe can be controlled independently through the branch pipe valve 13 and the hose valve 15, meeting the blast furnace's needs for adjusting injection parameters at different tuyeres.

[0025] After pulverized coal is heated and injected into the blast furnace tuyeres, the preheating stage of pulverized coal combustion before the tuyeres is reduced, allowing the pulverized coal to burn rapidly and immediately upon entering the furnace. This reduces the proportion of unburned pulverized coal and its impact on permeability, thereby maintaining normal blast furnace production and improving furnace stability. This effectively reduces the blast furnace fuel ratio and iron production costs. Based on the calculation of injecting 170 kg of pulverized coal per ton of blast furnace iron, increasing the pulverized coal combustion rate by 3 percentage points, it is estimated that the cost per ton of iron can be reduced by 7.14 yuan.

Claims

1. A method for improving the injection performance of pulverized coal in a blast furnace by preheating it, characterized in that, The method is as follows: a magnetite powder tank (6) and a heating system (8) are installed on the coal powder conveying pipeline between the coal powder tank (5) and the distributor (10) at the pulverized coal injection end of the blast furnace. The magnetite powder and coal powder are respectively conveyed by high-pressure nitrogen and mixed in the injection main pipe (3) to form a coal-iron mixture. The coal-iron mixture is conveyed to the heating pipe (8.3) of the heating system (8) by high-pressure nitrogen (1). The coal-iron mixture is heated by high-frequency electromagnetic induction through the heating system (8). The high-frequency electromagnetic induction heating is achieved by stimulating the magnetite powder microparticles to generate eddy current heating, coupled with the heating pipe (8.3) wall conduction heating, the magnetite powder internal eddy current heating and the coal powder material induction heating. The heated coal-iron mixture is evenly distributed by the distributor (10) to the injection branch pipe (12) corresponding to each tuyer of the blast furnace, and finally injected into the blast furnace through the coal injection gun (16).

2. The method according to claim 1, characterized in that, The magnetite powder is magnetite microparticles with a particle size of less than 10 μm; the magnetite powder is Fe3O4, and the proportion of the powder is 5% to 10% of the mass of the coal powder.

3. The method according to claim 1, characterized in that, The pulverized coal is transported from the pulverizing end to the pulverized coal tank (5) at the injection end, and then transported to the injection main pipe (3) through the pulverized coal tank valve (4); the magnetite powder is transported from the magnetite powder tank (6) to the pulverized coal in the injection main pipe (3) through the magnetite powder tank valve (7).

4. The method according to claim 1, characterized in that, The heating tube (8.3) is installed vertically. One end of the heating tube (8.3) is connected to the main jet pipe (3) through the heating tube flange (8.1), and the other end is connected to the distributor (10) through the flange of the distributor valve (9).

5. The method according to claim 1, characterized in that, The heating tube (8.3) has a high-frequency electromagnetic coil (8.4) wound around its outer shell. The high-frequency electromagnetic coil (8.4) is covered by a protective sleeve (8.5). A feed thermocouple (8.2) is arranged at the feed end of the heating tube (8.3), and a discharge thermocouple (8.7) is arranged at the discharge end. The high-frequency electromagnetic coil (8.4), feed thermocouple (8.2), and discharge thermocouple (8.7) are all connected to the heating controller (8.6). The controller receives thermocouple signals and adjusts the electromagnetic frequency of the high-frequency electromagnetic coil (8.4) within the range of 20~50kHz.

6. The method according to claim 1, characterized in that, The heating tube (8.3) is a wear-resistant alloy coated steel tube, and the inner wall of the heating tube is sprayed with a ZrO2-Al2O3 composite ceramic layer with a thickness of 40~60μm.

7. The method according to claim 1, characterized in that, The temperature of the pulverized coal rises from 30-60°C to 150-250°C within 0.5-0.8 seconds.

8. The method according to claim 1, characterized in that, The distributor (10) is made of wear-resistant alloy steel and has a structure that combines a lower conical cavity section and an upper cylindrical cavity section. The number of injection branch pipes (12) corresponds to the number of blast furnace tuyeres. The injection branch pipes (12) are evenly connected to the upper cylindrical cavity section of the distributor (10). The inclination angle of the injection branch pipes (12) is similar to or the same as the inclination angle of the upper conical cavity section of the distributor.

9. The method according to claim 8, characterized in that, The top of the upper cylindrical cavity section is a sealing plate (11), and the distributor valve (9) of the lower conical cavity section is connected to the heating pipe (8.3) through a flange.

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