Iron oxide powder roasting furnace and method for producing low-chlorine low-moisture iron oxide powder

Abstract

The invention provides an iron oxide powder roasting furnace and a method for producing low-chlorine low-moisture iron oxide powder. The iron oxide powder roasting furnace comprises a furnace body, a first heating assembly and a second heating assembly. A furnace chamber is formed in the furnace body; the first heating assembly supplies heat to the furnace chamber at the first heating position, and the second heating assembly supplies heat to the furnace chamber at the second heating position; the first heating position is located between the top and the middle of the furnace chamber, and the second heating position is located between the middle and the bottom of the furnace chamber; a first reaction area is formed between the first heating position and the top of the furnace chamber; a second reaction zone is formed between the second heating position and the bottom of the furnace chamber, and an intermediate reaction zone is formed between the first reaction zone and the second reaction zone; the first reaction zone has ascending airflow in the roasting process, and the second reaction zone has descending airflow in the roasting process. The low-chlorine low-moisture iron oxide powder can be obtained, the problem that the chlorine content of the iron oxide powder exceeds the standard is solved, the moisture of the iron oxide powder is reduced, and the specific surface area of the iron oxide powder is increased.

Description

Technical Field

[0001] This invention relates to the field of iron oxide powder production, and more particularly to an iron oxide powder roasting furnace and a method for producing low-chlorine, low-moisture iron oxide powder. Background Technology

[0002] Waste acid from steel strip pickling, after heating and concentration, mainly contains ferrous chloride. During the heating and concentration process, some ferrous chloride also converts to ferric chloride. After roasting, iron oxide powder is obtained. Currently, the concentrated waste acid is typically injected into the furnace cavity from the top. Inside the furnace, the waste acid reacts with oxygen and water to produce iron oxide powder and furnace gas. Three main gas burners are evenly arranged around the furnace cavity in the waist section of the furnace. These burners inject combustion gas tangentially into the furnace cavity, resulting in a furnace temperature of 600-630℃ in the waist section, 430-450℃ in the top section, and 300-400℃ in the bottom section.

[0003] During the roasting process, the furnace gas spirals upward into the top of the roasting furnace due to the suction of the furnace gas fan and the surrounding blowing of the main gas burner; the iron oxide powder generated in the roasting furnace spirals downward under the combined action of gravity and the surrounding blowing of the main gas burner. Although iron oxide powder can be obtained after roasting waste acid in the above manner, the existing roasting furnace and roasting method make it difficult to simultaneously achieve the desired chlorine content, moisture content, and specific surface area in the iron oxide powder, thus affecting the quality of the iron oxide powder.

[0004] Therefore, it is necessary to provide an iron oxide powder calcination furnace and a method for producing low-chlorine, low-moisture iron oxide powder to solve the technical problem of how to obtain iron oxide powder that balances chlorine content, moisture content, and specific surface area. Summary of the Invention

[0005] The main objective of this invention is to provide an iron oxide powder roasting furnace and a method for producing low-chlorine, low-moisture iron oxide powder, aiming to solve the technical problem of how to obtain iron oxide powder that balances chlorine content, moisture content, and specific surface area, so as to obtain iron oxide powder with low chlorine, low moisture content, and high specific surface area.

[0006] To achieve the above objectives, the present invention provides an iron oxide powder calcining furnace, comprising a furnace body, a first heating component, and a second heating component; the furnace body forms a furnace cavity; the first heating component supplies heat to the furnace cavity at a first heating position, and the second heating component supplies heat to the furnace cavity at a second heating position; the first heating position is located between the top and the middle of the furnace cavity, and the second heating position is located between the middle and the bottom of the furnace cavity; A first reaction zone is formed between the first heating position and the top of the furnace cavity; a second reaction zone is formed between the second heating position and the bottom of the furnace cavity; and an intermediate reaction zone is formed between the first reaction zone and the second reaction zone; the first reaction zone has an upward airflow during the roasting process, and the second reaction zone has a downward airflow during the roasting process.

[0007] Furthermore, both the first heating component and the second heating component inject combustion gas into the furnace cavity in a circulating manner; the rising airflow in the first reaction zone is spiral upward, and the descending airflow in the second reaction zone is spiral downward; the spiral directions of the airflow are opposite in the first reaction zone and the second reaction zone.

[0008] Furthermore, within the first reaction zone, the rising airflow spirals upward in a clockwise direction; within the second reaction zone, the descending airflow spirals downward in a counterclockwise direction.

[0009] Furthermore, during the heating process, the first heating component sprays combustion gas into the furnace cavity in a horizontal direction; The top of the furnace body is provided with a first furnace gas outlet, which is connected to the first reaction zone; the first furnace gas outlet is used to connect to a suction device, and the upward trend of the rising airflow is generated by the suction action of the suction device.

[0010] Furthermore, during the heating process, the second heating component sprays combustion gas obliquely downward into the furnace cavity; the downward trend of the descending airflow is generated by the oblique downward spraying action of the second heating component; the spraying direction of the second heating component forms an angle of 3-15° with the horizontal direction; The bottom of the furnace body is provided with a second furnace gas outlet, which is connected to the second reaction zone to discharge the furnace gas from the bottom of the furnace cavity.

[0011] Furthermore, both the first heating assembly and the second heating assembly include at least three gas burners; In both the first heating assembly and the second heating assembly, each of the gas burners is arranged around the furnace cavity, and the combustion gas injected by each gas burner enters the furnace cavity tangentially, so that the combustion gas injected by the first heating assembly and the second heating assembly has a circulating motion tendency.

[0012] Furthermore, the iron oxide powder roasting furnace also includes a liquid injection assembly disposed on the top of the furnace body, the liquid injection assembly having a liquid nozzle that extends into the furnace cavity.

[0013] The present invention also provides a method for producing low-chlorine, low-moisture iron oxide powder, wherein the iron oxide powder is produced using an iron oxide powder roasting furnace as described above. The method includes: controlling the first heating component and the second heating component to heat the furnace cavity; and spraying liquid material downward from the top of the furnace cavity, the liquid material containing ferrous ions and chloride ions.

[0014] Furthermore, the temperature at the top of the furnace cavity is 420-450℃, the temperature in the middle of the furnace cavity is 620-650℃, and the temperature at the bottom of the furnace cavity is 450-500℃.

[0015] Furthermore, the liquid also contains a surfactant, which includes one or more of anionic and nonionic surfactants.

[0016] Compared with the prior art, the present invention has at least the following advantages: This invention enables the production of low-chlorine, low-moisture iron oxide powder, solving the problem of excessive chlorine content in iron oxide powder, reducing its moisture content, and increasing its specific surface area. By improving the iron oxide powder calcination furnace and incorporating a first and second heating element, forming a first reaction zone, a second reaction zone, and an intermediate reaction zone, this invention resolves the conflict between chlorine content, moisture content, and particle size growth. This not only ensures sufficient reaction of the iron oxide powder, reducing its chlorine and moisture content, but also inhibits grain growth, resulting in a high-quality iron oxide powder product.

[0017] In this invention, the first reaction zone has an upward airflow, the second reaction zone has a downward airflow, and the intermediate reaction zone provides sufficient reaction space and time. Therefore, after the liquid material is sprayed into the first reaction zone, it undergoes a preliminary reaction, forming a large amount of furnace gas and a large number of initially unreacted fine iron oxide powder grains. Under the inertia generated by the spraying force, the initial fine iron oxide powder grains enter the intermediate reaction zone and gradually lose their initial inertia. Due to the relative balance between the buoyancy of the gas and the gravity of the fine iron oxide powder grains in the second reaction zone, and the sufficient reaction space provided by the intermediate reaction zone, the initial fine iron oxide powder grains can fully react in the intermediate reaction zone, achieving relatively complete removal of chlorine and moisture. Once the iron oxide powder grains in the intermediate reaction zone grow, and the gravity exceeds the buoyancy, they fall into the second reaction zone. Since the second reaction zone is close to the furnace bottom and has a downward airflow, the iron oxide powder grains in the second reaction zone will quickly fall to the furnace bottom, reducing the space and time for grain growth and preventing further grain growth. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the iron oxide powder calcining furnace in this invention; Figure 2 This is a schematic diagram showing the distribution of the first heating component in this invention; Figure 3 This is a schematic diagram showing the distribution of the second heating component in this invention; Figure 4 This is a graph showing the chlorine and moisture content of different batches of iron oxide powder in Comparative Example 1 of this invention; Figure 5 This is a graph showing the specific surface area of ​​different batches of iron oxide powder in Comparative Example 1 of the present invention; Figure 6 This is a data graph showing the chlorine content and moisture content of different batches of iron oxide powder in Example 1 of the present invention; Figure 7 This is a data graph showing the specific surface area of ​​different batches of iron oxide powder in Example 1 of the present invention; Figure 8 This is a data graph showing the chlorine content and moisture content of different batches of iron oxide powder in Example 2 of the present invention; Figure 9 This is a data graph showing the specific surface area of ​​different batches of iron oxide powder in Example 2 of the present invention.

[0020] Reference numerals in the attached drawings: 1. Furnace body; 2. Furnace cavity; 3. First heating component; 4. Second heating component; 5. First furnace gas outlet; 6. Second furnace gas outlet; 7. First burner; 8. Second burner; 9. Third burner; 10. Fourth burner; 11. Fifth burner; 12. Sixth burner; 13. Rising airflow; 14. Falling airflow; 15. Liquid injection component; 16. Screw conveyor; 17. Furnace gas collection tank; 18. Double cyclone dust collector.

[0021] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0024] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0025] It is important to understand that existing iron oxide powder roasting furnaces have a vertical cylindrical structure with conical upper and lower ends. The furnace is lined with refractory and acid-resistant bricks and externally wrapped with an insulation layer, designed as a steel-concrete structure with ring support for vertical operation. Generally, the waste acid is first filtered and then pumped to a Venturi pre-concentrator for heating and concentration. The heated and concentrated waste acid is then pressurized and pumped to spray guns on the top of the roasting furnace, where it is sprayed into the furnace. Inside the furnace, the waste acid reacts with oxygen and water to produce iron oxide powder and furnace gas. Three spray guns are installed on the top of the furnace, each with a nozzle at the bottom. When the pressure rises, the spray guns can be pulled out to clean the nozzles, removing any blockages. Inside the furnace, the concentrated waste acid is sprayed into a mist by the spray guns.

[0026] The existing iron oxide powder roasting furnace has three main gas burners arranged circumferentially in the waist section, which enter the furnace tangentially. The furnace temperature in the waist section reaches 600-630℃, while the furnace temperature in the top section reaches 430-450℃, providing a heat source for the reaction and concentration of acid evaporation, forming furnace gas and iron oxide powder. Under the combined action of the furnace gas fan and the tangential entry of combustion gases into the furnace waist, the furnace gas spirals upward into the top of the roasting furnace.

[0027] The iron oxide powder generated in the roasting furnace spirals downwards under the combined effects of gravity and the tangential direction of the combustion gases entering the furnace. During roasting, this spiral downward movement of the iron oxide powder is actually a process of removing chlorine carried by the powder; furthermore, it is also a process of continuous collision, bonding, and crystallization growth of the iron oxide powder. For iron oxide powder, the lower the chlorine content, the higher the quality; the smaller the particle size, the larger the specific surface area, and the higher the quality. The iron oxide powder enters the conical bottom of the roasting furnace, passes through a crusher and a rotary valve, and is then conveyed to a double-screw conveyor. The double-screw conveyor is equipped with a gas burner as a dechlorination device. The heated and dechlorinated iron oxide powder is then drawn into the iron oxide powder silo by the negative pressure generated by the iron oxide powder transport fan, and finally bagged by a bagging machine (located below the iron oxide powder silo).

[0028] The reactions during the roasting process include: 4FeCl2+4H2O+O2= 2Fe2O3+ 8HCl; 2FeCl3 + 3H2O = Fe2O3 + 6HCl

[0029] During the research process, this invention discovered that existing roasting furnaces have at least the following problems: 1. Although the existing roasting furnace has a waist temperature of 600-630℃ and a top temperature of 430-450℃, there is insufficient reaction space and time, which makes it easy for the chlorine content and moisture content of the iron oxide powder to exceed the standard.

[0030] 2. The existing roasting furnace not only lacks sufficient reaction space and time, but also has a furnace bottom temperature of 300-400℃, which requires further enhancement for the evaporation of residual moisture. In addition, if the discharge temperature of the iron oxide powder is low, it will cool down rapidly during the conveying process, making it easier to absorb moisture from the air during the conveying process.

[0031] 3. Existing roasting furnaces not only have poor dechlorination and dehydration effects, but the specific surface area of ​​iron oxide powder also needs further improvement. During the spiral downward process of iron oxide powder at high temperatures, it is often a process of grain growth. Therefore, the smaller the reaction space and time, the smaller the particle size, and the better the particle size and specific surface area. However, once the reaction space and time are reduced, the removal of chlorine and water will be less complete, resulting in a conflict between chlorine removal, water removal and particle size.

[0032] 4. Existing technology sets up a double screw conveyor after the iron oxide powder exits the furnace, and the double screw conveyor is equipped with a gas burner as a dechlorination device, so that the screw conveyor is heated and dechlorinated at the same time; however, this method is not conducive to industrial application.

[0033] The main reasons include: (1) The gas burner installed on the double helix conveyor is an indoor combustion process, which will affect the on-site environment. Once the burner is extinguished, a large amount of gas will flow out, which can easily cause carbon monoxide poisoning; (2) Once the gas burned by the gas burner installed on the double helix conveyor contains chlorine, it will affect the on-site environment and produce a pungent odor; (3) The gas burner installed on the double helix conveyor is actually not evenly burned. The iron powder is conveyed by the spiral conveyor by turning the iron powder to achieve heating. It only heats and dechlorinates the iron oxide powder on the surface, and does not have any effect on the iron powder inside. The dechlorination device installed after the iron oxide powder is discharged from the furnace is actually an ineffective supplementary facility.

[0034] See Figure 1-3 To understand, the present invention provides an iron oxide powder calcining furnace, including a furnace body, a first heating component, and a second heating component; the furnace body forms a furnace cavity; the furnace body has a cylindrical structure, and the furnace body also has an upper end and a lower end, which are conical; the furnace cavity has a cylindrical structure, and the furnace body also has an upper end and a lower end, which are conical.

[0035] The first heating component supplies heat to the furnace cavity at a first heating position, and the second heating component supplies heat to the furnace cavity at a second heating position. The first heating position is located between the top and middle of the furnace cavity, and the second heating position is located between the middle (furnace waist) and the bottom of the furnace cavity. The heating positions of both the first and second heating components correspond to the cylindrical structure of the furnace cavity.

[0036] A first reaction zone is formed between the first heating position and the top of the furnace cavity; a second reaction zone is formed between the second heating position and the bottom of the furnace cavity; and an intermediate reaction zone is formed between the first reaction zone and the second reaction zone; the first reaction zone has an upward airflow during the roasting process, and the second reaction zone has a downward airflow during the roasting process.

[0037] In a preferred embodiment of the present invention, both the first heating component and the second heating component inject combustion gas into the furnace cavity in a circulating manner. In this invention, the combustion gas source includes coal gas and combustion air, and the combustion air is surplus after combustion. The rising airflow in the first reaction zone is a spiral upward airflow, and the descending airflow in the second reaction zone is a spiral downward airflow; the spiral directions of the airflow are opposite in the first and second reaction zones.

[0038] In this invention, within the first reaction zone, the rising airflow spirals upward clockwise; within the second reaction zone, the descending airflow spirals downward counterclockwise. Correspondingly, the first heating component injects combustion gas into the furnace cavity in a clockwise circulating manner, causing the airflow to flow clockwise; correspondingly, the second heating component injects combustion gas into the furnace cavity in a counterclockwise circulating manner, causing the airflow to flow counterclockwise.

[0039] In some embodiments of the present invention, the first heating component injects combustion gas into the furnace cavity in a horizontal direction during the heating process.

[0040] In this invention, a first furnace gas outlet is provided at the top side of the furnace body, and the first furnace gas outlet is connected to the first reaction zone; the first furnace gas outlet is used to connect to a suction device, and the upward trend of the rising airflow is generated by the suction action of the suction device.

[0041] Specifically, the present invention achieves an upward airflow in the first reaction zone by controlling the blowing direction of the first heating component and the suction effect of the suction device. Since the first heating component blows combustion gas horizontally into the furnace cavity during heating, it does not affect the upward flow of the airflow. The suction effect of the suction device allows the airflow to rise. Furthermore, when the first heating component blows combustion gas into the furnace cavity in a circulating manner, the airflow can spiral upward.

[0042] It should be noted that, in this invention, circulation is understood as the tendency of movement flowing around the furnace cavity. The circulation directions of the combustion gases injected by the first heating component and the second heating component are opposite; specifically, the combustion gases injected by the first heating component have a clockwise circulation tendency, and the combustion gases injected by the second heating component have a counterclockwise circulation tendency. In this invention, the circulation direction is correspondingly set by the arrangement of the gas nozzles in the first heating component and the second heating component.

[0043] It should also be noted that although the furnace gas discharged from the first furnace gas outlet will contain some iron oxide powder that has undergone preliminary reaction, a return port will be opened near the middle of the furnace body. After solid-gas separation, the iron oxide powder that has undergone preliminary reaction will enter the intermediate reaction zone through the return port to continue the subsequent reaction. During the implementation process, the furnace gas discharged from the first furnace gas outlet passes through a double cyclone dust collector. Under the action of centrifugal force and gravity, a portion of the iron oxide powder in the double cyclone dust collector is separated. The separated iron oxide powder is sent back to the roasting furnace by the rotary valve at the bottom of the double cyclone.

[0044] In some embodiments of the present invention, during the heating process, the second heating component sprays combustion gas obliquely downward into the furnace cavity; the downward trend of the descending airflow is generated by the oblique downward spraying action of the second heating component; the spraying direction of the second heating component forms an angle of 3-15° with the horizontal direction (not shown in the figure), specifically an angle of 5°.

[0045] Specifically, by controlling the blowing direction of the second heating component to tilt it downwards (not shown in the figure), the present invention can form a descending airflow. Although the suction effect of the suction device still exists, the second heating component is lower than the middle of the furnace cavity, and the second heating component provides a downward blowing force, so it does not affect the formation of the descending airflow. Furthermore, when the second heating component blows combustion gas into the furnace cavity in a circulating manner, the airflow can be spiraled downwards.

[0046] To facilitate the discharge of furnace gas from the furnace cavity and prevent excessive gas pressure, a second furnace gas outlet (slightly higher than the discharge port at the bottom of the furnace) is provided on the side of the bottom of the furnace body. This second furnace gas outlet is connected to the second reaction zone to discharge the furnace gas from the bottom of the furnace cavity. The second furnace gas outlet is also connected to a furnace gas collection tank, which is connected to a silo. It should be noted that the furnace gas discharged from the second furnace gas outlet will contain some iron oxide powder, which can be recovered later.

[0047] In this invention, compared to existing calcining furnaces, a first heating component and a second heating component are provided. The first heating component is higher than the middle of the furnace cavity, providing a heat source for the initial reaction and evaporation of the feed liquid. In the first reaction zone, a large amount of furnace gas and initially unreacted fine iron oxide powder grains are formed (this is only used to describe the reaction state and does not mean that all of them are iron oxide). The intermediate reaction zone is formed between the first heating component and the second heating component, providing sufficient reaction space and time to obtain fully reacted iron oxide powder. The second heating component is lower than the middle of the furnace cavity, and the second reaction zone has a downward airflow, which shortens the time and space for the growth of iron oxide powder grains after complete reaction and effectively controls the BET index of iron powder. The downward airflow drives the fully reacted iron oxide powder to quickly enter the bottom of the furnace, and can also heat the iron oxide powder that has sunk to the bottom of the furnace, further reducing the moisture content.

[0048] Furthermore, the airflow in the first reaction zone spirals upward clockwise, while the airflow in the second reaction zone spirals downward counterclockwise. In the intermediate reaction zone, the mutual cancellation of the clockwise upward airflow and the counterclockwise downward airflow allows the reaction to progress from a preliminary reaction to a complete reaction. Additionally, due to the positioning of the first and second heating components, the intermediate reaction zone is relatively wide, with a broad high-temperature area. Furthermore, the relative balance between the gravity and buoyancy of the iron oxide powder in the intermediate reaction zone further facilitates the reduction of moisture and chlorine content. Once the iron oxide powder grains in the intermediate reaction zone begin to grow, their gravity exceeds buoyancy, causing them to fall into the second reaction zone. Driven by the downward airflow, they quickly enter the furnace bottom, preventing further grain growth. Therefore, this invention, through the placement of the first and second heating positions, forms three distinct reaction zones. This allows for control: a preliminary reaction occurs in the first reaction zone, a full reaction occurs in the intermediate reaction zone, and then the powder rapidly falls in the second reaction zone, utilizing the residual heat from the furnace bottom to further remove excess moisture. The rapid falling airflow and the slow temperature drop of the iron oxide powder further facilitate the removal of excess moisture.

[0049] As an explanation of the first heating component and the second heating component in this invention, both the first heating component and the second heating component include at least three gas burners, specifically three gas burners each; for example, the first heating component has a first burner, a second burner, and a third burner; the second heating component has a fourth burner, a fifth burner, and a sixth burner; the gas source for the gas burners includes coal gas and air. All the gas burners in the first heating component are at the same horizontal position, and all the gas burners in the second heating component are at the same horizontal position.

[0050] In the first heating assembly, each of the gas burners is evenly arranged around the furnace cavity, and the combustion gas injected by each gas burner enters the furnace cavity in a tangential direction, so that the combustion gas injected by the first heating assembly has a circulating motion tendency, thereby forming a spiral upward airflow together with the suction effect of the suction device.

[0051] In the second heating assembly, each of the gas burners is uniformly arranged around the furnace cavity, and the combustion gas injected by each gas burner enters the furnace cavity tangentially, so that the combustion gas injected by the second heating assembly has a circulating motion tendency; furthermore, the second heating assembly injects combustion gas obliquely downward, thereby further forming a spiral downward airflow.

[0052] In this invention, the iron oxide powder calcining furnace further includes a liquid injection assembly disposed on the top of the furnace body. The liquid injection assembly has a liquid nozzle that extends into the furnace cavity and is close to the top of the furnace cavity; the first heating position is located below the liquid nozzle. Further, the liquid injection assembly includes a spray gun, and the liquid nozzle is disposed at the bottom of the spray cavity.

[0053] In the specific implementation process, the liquid feed is sprayed into the first reaction zone through the liquid feed nozzle, and then undergoes a preliminary reaction in the first reaction zone to form a large amount of furnace gas and initial fine iron oxide powder grains; subsequently, based on the inertia brought about by the liquid feed spray, the initial fine iron oxide powder grains enter the intermediate reaction zone for full reaction to achieve full dechlorination and moisture removal; once the iron oxide powder grains in the intermediate reaction zone grow, they will enter the second reaction zone, and then quickly descend to the bottom of the furnace, where the residual heat of the furnace bottom will be used to further remove moisture.

[0054] In this invention, the bottom of the iron oxide powder roasting furnace is connected to a screw conveyor for receiving the iron oxide powder obtained in the roasting furnace; the screw conveyor of this invention is not equipped with an additional dechlorination component.

[0055] In this invention, based on the application scenario, the first heating component is positioned between the top and middle of the furnace cavity, and its position is vertically adjustable; the second heating component is positioned between the middle and bottom of the furnace cavity, and its position is also vertically adjustable. Therefore, the intermediate reaction zone can be wide or narrow, allowing for flexible control of the iron oxide powder quality indicators according to actual needs. To control the chlorine and moisture content, a wide range is selected for the intermediate reaction zone; to control for smaller particle size, a narrow range is selected for the intermediate reaction zone. Adjusting the width of the intermediate reaction zone appropriately achieves a reasonable control method for the quality requirements of iron oxide.

[0056] In some embodiments of the present invention, the furnace height of the iron oxide powder roasting furnace is 20-22 meters, the vertical distance between the first heating position and the liquid feed nozzle is 2-5 meters, the vertical distance between the second heating position and the furnace waist is 2-3 meters, and the liquid feed nozzle extends into the furnace from top to bottom for 1.2-1.8 meters.

[0057] Alternatively, the furnace height of the iron oxide powder calcining furnace can be defined as X, in meters; the vertical distance between the first heating position and the liquid nozzle is (0.15-0.18)X, in meters; and the vertical distance between the second heating position and the furnace waist is (0.1-0.13)X, in meters.

[0058] The present invention also provides a method for producing low-chlorine, low-moisture iron oxide powder, which uses an iron oxide powder roasting furnace as described above to produce iron oxide powder.

[0059] In this invention, the method for producing low-chlorine, low-moisture iron oxide powder includes: controlling the first heating component and the second heating component to heat the furnace cavity; spraying a liquid material downward from the top of the furnace cavity; the liquid material contains ferrous ions and chloride ions, and may further contain ferric ions; specifically, the liquid material contains ferrous chloride with a concentration of 360-420 g / L; it may further contain some ferric chloride; the liquid material is concentrated waste acid, which originates from the hydrochloric acid pickling of steel strip.

[0060] In this invention, the process of controlling the first heating component and the second heating component to heat the furnace cavity includes: the first heating component heating the furnace cavity at the first heating position, and the second heating component heating the furnace cavity at the second heating position to form the first reaction zone, the second reaction zone and the intermediate reaction zone; after the liquid material is sprayed downward from the top of the furnace cavity, it passes through the first reaction zone, the intermediate reaction zone and the second reaction zone in sequence to obtain the iron oxide powder.

[0061] In this invention, the liquid material is sprayed downward from the top of the furnace cavity by nozzle spraying. Specifically, the liquid material is sprayed into the furnace cavity through the liquid material nozzle on the spray gun, so that the liquid material is in the form of a mist.

[0062] In this invention, the top temperature of the furnace cavity is 420-450℃, the middle temperature of the furnace cavity is 620-650℃, and the bottom temperature of the furnace cavity (the temperature of the bottom iron oxide powder) is 450-500℃. Although the top and middle temperatures of the furnace cavity are similar to those of existing roasting methods, this invention forms a first reaction zone, an intermediate reaction zone, and a second reaction zone, which allows the reaction process to proceed sequentially, ensuring the particle size of the iron oxide powder while obtaining low-chlorine and low-moisture iron oxide powder.

[0063] In this invention, the feed solution may also contain surfactants, which include one or more of anionic and nonionic surfactants; the anionic surfactant includes sodium dodecyl sulfate, and the nonionic surfactant includes dodecylphenol polyoxyethylene ether. The concentration of the anionic surfactant in the feed solution can be 5-10 g / L; the concentration of the nonionic surfactant in the feed solution can be 5-10 g / L.

[0064] In this invention, when the feed liquid also contains the surfactant, the surfactant has a segregation and dispersion effect on the concentrated waste acid, making it less likely for the concentrated waste acid to crystallize and clog the supply pipe, thus ensuring unobstructed flow. Furthermore, it can also prevent the feed liquid nozzle from becoming clogged, thereby avoiding affecting the atomization of the feed liquid in the furnace cavity.

[0065] In addition, the surfactant plays a role in dispersing the solute in the liquid uniformly; when the liquid is sprayed in the calcining furnace, it can further ensure the formation of iron oxide powder with uniform particle size, uniform specific surface area, uniform composition, uniform color difference and other physicochemical properties, which has a positive effect on the quality stability of iron oxide powder.

[0066] The following is a description of the technical advantages of this invention: The existing calcining furnace has only three burners arranged in a row on the same plane, which cannot burn the iron oxide powder thoroughly. The iron oxide powder that is not burned thoroughly often has a high chlorine content. Iron oxide powder with high chlorine content is often corrosive, which will affect the equipment and products of downstream enterprises that produce soft and hard magnetic materials. For example, it will cause corrosion of production equipment and the corrosiveness of products will affect the normal operation of components made of iron oxide powder magnetic materials.

[0067] Downstream enterprises have a key control indicator for the chlorine content of iron oxide powder (iron oxide powder, a by-product of cold rolling in steel mills, is used as the base material for the production of electronic components); therefore, taking the first heating component and the second heating component, both of which contain three gas burners, as an example, this invention sets up two planes in the calcining furnace, with three burners on each plane, for a total of six burners, to ensure that the iron oxide powder is thoroughly burned and that the chlorides in the iron oxide powder are fully volatilized.

[0068] Furthermore, the first row of burners is designed to ensure that a large amount of water in the concentrated acid (feed solution) evaporates and some of the raw materials such as ferrous chloride react to generate iron oxide and hydrogen chloride mist. When the iron oxide powder floats down in the calcining furnace, it encounters the heat supplied by the second row of burners. The second row of burners is designed to ensure that the ferrous chloride reacts completely to generate iron oxide and hydrogen chloride mist, as well as that a very small amount of water evaporates, hydrogen chloride completely volatilizes, and surfactants are completely burned. After passing through the second row of burners, the fully reacted iron oxide powder falls quickly, preventing further crystal growth.

[0069] Furthermore, when the concentrated acid is sprayed into the calcining furnace, the nozzles are often blocked by ferrous chloride crystals and impurities, resulting in a straight-line liquid flow instead of a mist. This leads to unstable chlorine content in the generated iron powder. Iron powder produced by a straight-line liquid flow has a higher chlorine content, while iron powder produced by a mist has a lower chlorine content. The residence time of the straight-line liquid flow in the furnace is shorter, while that of the mist is longer, resulting in a longer heating time and a lower chlorine content. The addition of a surfactant in this application can reduce the possibility of ferrous chloride segregation and crystallization; furthermore, the combustion of the surfactant can accelerate the volatilization of chlorides in the iron oxide powder.

[0070] The following is an exemplary description of the present invention: This invention involves installing three gas burners (arranged circumferentially, entering the furnace chamber tangentially) on a plane 2-5 meters below the feed nozzle. The furnace top temperature is controlled at 420-450℃. Combustion gases enter the furnace chamber tangentially, causing the gas flow to enter the furnace horizontally and clockwise. These three gas burners provide the heat source for the initial reaction and the complete evaporation of the concentrated acid, forming a large amount of furnace gas and initially unreacted fine iron oxide powder particles (this is only used to describe the reaction state and does not mean all of them are iron oxide). Due to the combined effect of the furnace gas fan's suction and the tangential entry of the combusted gas into the furnace waist, a large amount of furnace gas spirals upwards into the top of the roasting furnace.

[0071] Three gas burners are installed on a plane 2-3 meters below the furnace waist (three gas burners arranged circumferentially, entering the furnace cavity tangentially). The furnace waist temperature is controlled at 620-650℃. The combustion gas enters the furnace cavity tangentially, and the airflow deviates from the horizontal direction by 5° downwards and counterclockwise into the furnace. These three gas burners provide the heat source for complete reaction and a small amount of concentrated acid to completely evaporate, forming a small amount of furnace gas.

[0072] The downward spiral airflow causes the iron oxide powder, after complete reaction, to quickly sink to the bottom of the furnace and heat the iron oxide powder that has already settled at the bottom of the furnace. The temperature of the iron oxide powder at the bottom of the furnace is 450-500℃, which can reduce the moisture content.

[0073] Between the two flat burners (two rows of burners), an intermediate reaction zone is formed; the upper airflow spirals upward clockwise, and the lower airflow spirals downward counterclockwise. In the intermediate reaction zone, the clockwise and counterclockwise rotations cancel each other out, and the reaction is in the complete reaction stage here. In addition, the high-temperature zone inside the furnace is wider, which is more conducive to reducing the moisture and chlorine content. The generated iron oxide powder is in relative balance with gravity and buoyancy of the airflow here, which is conducive to reducing the chlorine content. Once the iron oxide powder grains grow, gravity exceeds buoyancy and they fall into the lower layer, and due to the spiral downward, they quickly enter the bottom of the furnace.

[0074] The following are specific examples of the present invention: Comparative Example 1 The roasting furnace used in this comparative example is a vertical cylindrical structure with conical upper and lower ends, lined with refractory and acid-resistant bricks, and wrapped with an insulation layer on the outside; diameter: approximately 9.7 meters, height: approximately 21.1 meters.

[0075] The roasting furnace has a first furnace gas outlet at the top side position, which is connected to the furnace gas blower. The top of the roasting furnace is equipped with three spray guns with liquid nozzles at the bottom. The liquid nozzles of the spray chamber extend into the furnace chamber and are used to spray liquid into the furnace chamber from top to bottom. The spray guns extend into the furnace from the top for about 1.5 meters.

[0076] The furnace waist has three main gas burners arranged circumferentially. The combustion gas from the three main gas burners enters the furnace cavity in a clockwise direction along the tangential direction and is heated. The furnace temperature in the waist reaches 600-630℃, the furnace temperature in the top reaches 430-450℃, and the furnace temperature in the bottom reaches 300-400℃.

[0077] During the roasting process, liquid material is sprayed into the furnace cavity through the liquid material nozzle, and then furnace gas and iron oxide powder are formed in the furnace cavity. Due to the combined effect of the furnace gas fan and the combustion gas entering the furnace cavity tangentially, the furnace gas spirals upward into the top of the roasting furnace. After roasting, the iron oxide powder is collected from the discharge port at the bottom of the furnace.

[0078] In this comparative example, the ferrous chloride concentration in the feed solution was 360-420 g / L and contained no surfactant. The ferrous chloride concentration was calculated based on the concentration before heating and concentration and the concentration factor. Although some ferrous chloride will be converted into ferric chloride, this conversion does not need to be considered, and the analysis can be performed based on the calculated ferrous chloride concentration.

[0079] In this comparative example, the detection results of iron oxide powder are shown in Table 1 and... Figure 4-5 As shown; Note: In this invention, the detection results of the chemical component chloride refer only to the chlorine content.

[0080] Table 1. Detection results of iron oxide powder From Table 1 and Figure 4-5 As can be seen from this comparative example, the specific surface area BET(m) 2 The specific surface area (BET value) of iron oxide powder (i.e., the smaller the particle size) corresponds to the chlorine and moisture content. A larger specific surface area (i.e., smaller the particle size) results in a stronger ability to adsorb chlorides and moisture; a higher specific surface area also indicates higher moisture and chlorine content. High-quality iron oxide powder requires a BET value greater than 3.5 μm for its specific surface area. 2 / g, but also requires that the chlorine content and moisture content be as low as possible, which is somewhat contradictory. Traditional methods are not very effective at controlling specific surface area, chlorine content and moisture content.

[0081] Example 1 The roasting furnace used in this embodiment is a vertical cylindrical structure with conical upper and lower ends, lined with refractory and acid-resistant bricks, and wrapped with an insulation layer on the outside; diameter: approximately 9.7 meters, height: approximately 21.1 meters.

[0082] The roasting furnace has a first furnace gas outlet at the top side position, which is connected to the furnace gas blower; the roasting furnace has a second furnace gas outlet at the bottom side position, which is connected to the furnace gas collection tank, which is connected to the silo.

[0083] The top of the roasting furnace is equipped with three spray guns with liquid nozzles at the bottom. The liquid nozzles of the spray guns extend into the furnace cavity and are used to spray liquid into the furnace cavity from top to bottom. The spray guns extend into the furnace from the top for about 1.5 meters.

[0084] Three main gas burners (first row of burners) are arranged in a circle on a plane about 3.5 meters below the spray gun. The combustion gas from the three main gas burners enters the furnace cavity clockwise along the tangential direction and is heated. Three main gas burners (second row of burners) are arranged in a circle on a plane about 2.5 meters below the furnace waist. The combustion gas from the three main gas burners enters the furnace cavity counterclockwise along the tangential direction and is heated, and is inclined downward at 5° off the horizontal direction. The temperature at the top of the furnace cavity is 420-450℃, the temperature in the middle (furnace waist) of the furnace cavity is 620-650℃, and the temperature at the bottom of the furnace cavity is 450-500℃.

[0085] During the roasting process, molten feed is injected into the furnace cavity through feed nozzles. A first reaction zone is formed between the first row of burners and the top of the furnace cavity; a second reaction zone is formed between the second row of burners and the bottom of the furnace cavity; and an intermediate reaction zone lies between the first and second reaction zones. The first reaction zone experiences an upward spiral airflow during roasting, while the second reaction zone experiences a downward spiral airflow. After initial roasting in the first reaction zone, the resulting initial product enters the intermediate reaction zone for complete reaction, then rapidly falls into the second reaction zone, and finally, iron oxide powder is collected from the outlet at the bottom of the furnace.

[0086] In this embodiment, the concentration of ferrous chloride in the feed solution is basically the same as that in Comparative Example 1, and it does not contain surfactants.

[0087] In this embodiment, the detection results of iron oxide powder are shown in Table 2 and Figure 6-7 As shown.

[0088] Table 2 Detection results of iron oxide powder From Table 2 and Figure 6-7 It can be seen that, compared with control example 1, the specific surface area increased, the moisture and chlorine content decreased, and the stability of the indicators improved.

[0089] Example 2 Compared to Example 1, this embodiment also contains sodium dodecyl sulfate and dodecylphenol polyoxyethylene ether in the feed solution. The concentration of sodium dodecyl sulfate is about 10 g / L, and the concentration of dodecylphenol polyoxyethylene ether is about 10 g / L. Other conditions remain unchanged.

[0090] In this embodiment, the detection results of iron oxide powder are shown in Table 3 and Figure 8-9 As shown.

[0091] Table 3. Detection results of iron oxide powder From Table 3 and Figure 8-9 It can be seen that by adding surfactants, the stability of iron oxide powder indicators is further improved, the quality fluctuation is small, and the intervention capability is strong.

[0092] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A calcining furnace for iron oxide powder, characterized in that, The furnace includes a furnace body, a first heating component, and a second heating component; the furnace body forms a furnace cavity; the first heating component supplies heat to the furnace cavity at a first heating position, and the second heating component supplies heat to the furnace cavity at a second heating position; the first heating position is located between the top and the middle of the furnace cavity, and the second heating position is located between the middle and the bottom of the furnace cavity; A first reaction zone is formed between the first heating position and the top of the furnace cavity; a second reaction zone is formed between the second heating position and the bottom of the furnace cavity; and an intermediate reaction zone is formed between the first reaction zone and the second reaction zone; the first reaction zone has an upward airflow during the roasting process, and the second reaction zone has a downward airflow during the roasting process.

2. The iron oxide powder calcining furnace according to claim 1, characterized in that, Both the first heating component and the second heating component inject combustion gas into the furnace cavity in a circulating manner; the rising airflow in the first reaction zone is spiral upward, and the descending airflow in the second reaction zone is spiral downward; the spiral directions of the airflow are opposite in the first reaction zone and the second reaction zone.

3. The iron oxide powder calcining furnace according to claim 2, characterized in that, In the first reaction zone, the rising airflow spirals upward in a clockwise direction; in the second reaction zone, the descending airflow spirals downward in a counterclockwise direction.

4. The iron oxide powder calcining furnace according to claim 1, characterized in that, During the heating process, the first heating component sprays combustion gas into the furnace cavity in a horizontal direction; The top of the furnace body is provided with a first furnace gas outlet, which is connected to the first reaction zone; the first furnace gas outlet is used to connect to a suction device, and the upward trend of the rising airflow is generated by the suction action of the suction device.

5. The iron oxide powder calcining furnace according to claim 1, characterized in that, During the heating process, the second heating component sprays combustion gas obliquely downward into the furnace cavity; the downward trend of the descending airflow is generated by the oblique downward spraying action of the second heating component; the spraying direction of the second heating component forms an angle of 3-15° with the horizontal direction; The bottom of the furnace body is provided with a second furnace gas outlet, which is connected to the second reaction zone to discharge the furnace gas from the bottom of the furnace cavity.

6. The iron oxide powder calcining furnace according to claim 1, characterized in that, Both the first heating assembly and the second heating assembly include at least three gas burners; In both the first heating assembly and the second heating assembly, each of the gas burners is arranged around the furnace cavity, and the combustion gas injected by each gas burner enters the furnace cavity tangentially, so that the combustion gas injected by the first heating assembly and the second heating assembly has a circulating motion tendency.

7. The iron oxide powder calcining furnace according to claim 1, characterized in that, The iron oxide powder roasting furnace also includes a liquid injection assembly disposed on the top of the furnace body, the liquid injection assembly having a liquid nozzle that extends into the furnace cavity.

8. A method for producing low-chlorine, low-moisture iron oxide powder, characterized in that, Iron oxide powder is produced using the iron oxide powder roasting furnace as described in any one of claims 1-7; The method includes: controlling the first heating component and the second heating component to heat the furnace cavity; and spraying liquid material downward from the top of the furnace cavity, the liquid material containing ferrous ions and chloride ions.

9. The method for producing low-chlorine, low-moisture iron oxide powder according to claim 8, characterized in that, The temperature at the top of the furnace cavity is 420-450℃, the temperature in the middle of the furnace cavity is 620-650℃, and the temperature at the bottom of the furnace cavity is 450-500℃.

10. The method for producing low-chlorine, low-moisture iron oxide powder according to claim 8, characterized in that, The liquid also contains surfactants, which include one or more of anionic and nonionic surfactants.

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