A fluidized bed roasting furnace for zinc concentrate and a process for reducing zinc ferrite.

Abstract

This invention discloses a fluidized bed roasting furnace for zinc concentrate and a process for reducing zinc ferrite. The furnace has a hearth area greater than 152 m². 2 During the fluidized bed roasting of zinc concentrate, zinc ferrite formation mainly occurs in a ring-shaped region extending approximately 300 mm from the centerline of the fluidized bed furnace, known as the turbulent deposition layer. As the furnace bed area increases, the ratio of the turbulent deposition zone area to the furnace bed area decreases, reducing the contact area between ZnO and Fe2O3 in the formation of zinc ferrite. This reduces zinc ferrite formation and solves the problem of increased cost per ton of zinc due to excessive zinc ferrite in zinc roasted ore.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to a fluidized bed roasting furnace for zinc concentrate and a process for reducing zinc ferrite. Background Technology

[0002] In zinc concentrate, the total amount of Zn, S, and Fe is 90-95%. Besides the main component, zinc sulfide (ZnS), there are many associated minerals, such as Fe7S8 and FeS2. During roasting, these associated minerals (Fe7S8, FeS2, etc.) not only undergo oxidation reactions of varying degrees like ZnS, but their derivatives can further form various salts. For example, at roasting temperatures above 600℃, sulfide roasting easily results in a solid-solid reaction to form zinc ferrite: ZnO + Fe2O3 = ZnO·Fe2O3. However, during wet leaching, zinc ferrite (ZnO·Fe2O3) is insoluble in dilute sulfuric acid and remains in the residue, causing zinc loss, affecting the leaching efficiency, reducing the direct zinc recovery rate, and increasing the cost per ton of zinc for production enterprises. Even with high-temperature, high-acid leaching and new iron removal processes, the process flow remains complex, inevitably leading to zinc loss.

[0003] Furthermore, the deposition of roasted sand in the expanded section of the furnace during roasting will also lead to the formation of zinc ferrite (ZnO·Fe2O3). Unoxidized sulfides carried by the flue gas during production will also increase the residual sulfur in the roasted sand. Industrially, fluidized bed roasting of zinc concentrate used in pyrometallurgical zinc refining requires low residual sulfur in the roasted sand, generally 0.5% S, and a roasting temperature greater than 1100℃, known as oxidative roasting. Fluidized bed roasting of zinc concentrate used in hydrometallurgical zinc refining requires the roasted sand to retain a certain amount of residual sulfur to reduce acid consumption in wet leaching, generally less than 3% S, and a roasting temperature less than 1000℃, known as acid roasting. Currently, the traditional fluidized bed furnace has a hearth area of ​​48m². 2 110m 2 and 152m 2 In all three furnace types, approximately 6-9% of the zinc in the zinc roasted ore is zinc ferrite, accounting for about 10-13% of the total zinc content. Therefore, the formation of zinc ferrite during the fluidized bed roasting process of zinc concentrate has been a persistent problem for enterprises and a challenge that metallurgists urgently need to solve. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a fluidized bed roasting furnace for zinc concentrate and a process for reducing zinc ferrite, thereby overcoming the problem of increased cost per ton of zinc caused by excessive zinc ferrite in zinc roasted ore.

[0005] The technical solution adopted in this application is as follows:

[0006] A fluidized bed roasting furnace for zinc concentrate, characterized by a hearth area greater than 152 m². 2 .

[0007] The fluidized bed roaster for zinc concentrate is an enlarged-top furnace, meaning the lower part is cylindrical and the upper part is enlarged. The hearth of the fluidized bed roaster is located at the bottom of the cylindrical section, with a radius of R and an area of ​​πR. 2 During the fluidized bed roasting of zinc concentrate, zinc ferrite formation mainly occurs in a ring-shaped area extending approximately 300 mm from the lower inner wall of the fluidized bed furnace towards the furnace centerline, known as the turbulent deposition layer. This is attributed to the influence of heat dissipation and air leakage from the outer wall of the fluidized bed furnace, cooling pipes, various furnace doors, and discharge ports. This area is approximately 50-100°C lower than the furnace interior temperature. Furthermore, the air caps on the outer ring of the tube sheet are some distance from the inner wall, creating dead zones in the fluidized bed and resulting in relatively gentle boiling within the furnace. If the radius of the fluidized bed furnace is R, the ratio of the area of ​​the turbulent deposition zone for zinc ferrite formation to the area of ​​the fluidized bed furnace is: This expression shows that as the furnace bed area increases, i.e., the R value increases, the ratio of the turbulent deposition zone area of ​​zinc ferrite to the furnace bed area decreases. This reduces the contact area between ZnO and Fe2O3 in the formation of zinc ferrite, thereby reducing zinc ferrite formation. Currently, the largest furnace bed area for fluidized bed roasting furnaces is 152 m². 2 When the furnace bed area of ​​the fluidized bed roasting furnace is greater than 152m² 2 When the contact area between ZnO and Fe2O3 decreases, the formation of zinc ferrite can be reduced.

[0008] Preferably, the furnace bed area is 198m². 2 Due to limitations imposed by the structure and materials used in fluidized bed roasting furnaces, the maximum area that can currently be increased to 198m² is [limited / limited]. 2 When the surface area of ​​the fluidized bed furnace increases to 198m² 2 At this time, the zinc ferrite produced during the traditional zinc concentrate fluidized bed roasting process can be reduced from 6-9% to 3-4%, a reduction of up to 50%.

[0009] Furthermore, multiple sets of spatial stepped cooling pipe devices are arranged circumferentially on the furnace wall above the furnace bed. Each set of spatial stepped cooling pipe devices includes two independently detachable cooling circulation pipes, which are arranged vertically along the height of the fluidized bed roasting furnace. The two independently detachable cooling circulation pipes can be controlled separately, thereby homogenizing the temperature and flow fields of the fluidized bed layer in the fluidized bed furnace, ensuring the roasting temperature and height of the fluidized bed layer, and preventing localized high or low temperatures in the fluidized bed layer caused by the complete disassembly of a single cooling circulation pipe, which could disrupt the formation conditions of zinc ferrite.

[0010] Specifically, the number of groups of the spatial tiered cooling buried pipe device is n, where 4 ≤ n ≤ 12.

[0011] Specifically, the cooling circulation pipeline includes multiple horizontally arranged cooling pipe sections, the diameter of which is D, 76mm≤D≤108mm; each cooling pipe section in the spatial stepped cooling buried pipe device is at a different height, and the distance between the centerline of the lowest cooling pipe section and the furnace bed is L1, L1≤220mm.

[0012] Specifically, the spatial tiered cooling buried pipe device also includes an inspection door, which is installed on the furnace wall of the fluidized bed roasting furnace, and all cooling circulation pipes pass through the inspection door.

[0013] Furthermore, an air distribution device is installed on the furnace wall of the expanded section of the fluidized bed roasting furnace. This device includes an air supply pipe and multiple air distribution nozzles, arranged circumferentially along the expanded section. One end of each nozzle is connected to the air supply pipe, and the other end extends through the furnace wall into the furnace. The air source, through the air distribution device, sweeps the inclined surface of the expanded section. Zinc concentrate tends to deposit naturally in the expanded section; the addition of the air distribution device to the furnace wall extends the reaction space, disturbs the upper flow field, and provides favorable combustion conditions for residual sulfur entrained in the flue gas. Simultaneously, it reduces the residence time of ZnO and Fe2O3 deposited in the expanded section at the roasting temperature, thus reducing the formation of zinc ferrite. The air distribution device can be made of cast steel, ceramic, or a combination of metal and non-metal materials.

[0014] Specifically, the distance by which the air distribution nozzle penetrates the furnace wall of the fluidized bed roasting furnace and extends into the furnace is L2, where 20mm≤L2≤25mm.

[0015] Specifically, multiple air distribution nozzles are evenly arranged on the circumference of the expanded section of the fluidized bed roasting furnace, and the included angle between the centers of two adjacent air distribution nozzles is α, where α < 25°; the ends of the air distribution nozzles are provided with multiple air outlets, and the number of air outlets is greater than 3.

[0016] Based on the same inventive concept, this invention also proposes a process for reducing zinc ferrite, employing the aforementioned fluidized bed roasting furnace for zinc concentrate, controlling the roasting temperature of the fluidized bed layer within the furnace to be 950℃~980℃; the air source for the air distribution device is compressed air or oxygen-enriched air, with an oxygen concentration <30%, a pressure P = 10kpa~20kpa, and an air outlet velocity at the end of the air distribution nozzle less than 20m / s. When the roasting temperature of the fluidized bed layer in the furnace reaches 950℃~980℃, the height of the fluidized bed layer can reach 900mm~1000mm. When the furnace bed area of ​​the fluidized bed furnace is greater than 152m²... 2 At the same time, it can reduce the proportion of the turbulent deposition zone that is prone to producing zinc ferrite, and the maximum temperature of boiling roasting can reach 980℃, which can improve the heat collection and temperature stabilization effect of the boiling furnace, so that the production capacity of a single series of wet zinc smelting system can reach 200,000 t / a of electrolytic zinc.

[0017] The beneficial effects of this invention are:

[0018] 1. The zinc concentrate fluidized bed roasting furnace of the present invention adopts an increased furnace bed area, which can reduce the proportion of the turbulent deposition zone that is prone to producing zinc ferrite, reduce the formation of zinc ferrite, improve the heat accumulation and temperature stabilization effect of the fluidized bed furnace, and enable the single-series wet zinc smelting system to reach a capacity of 200,000 t / a of electrolytic zinc.

[0019] 2. The zinc concentrate fluidized bed roasting furnace of the present invention adopts an increased air distribution device, which can effectively extend the reaction space inside the furnace to reduce the formation of zinc ferrite and residual sulfur in the flue dust.

[0020] 3. The zinc concentrate fluidized bed roasting furnace of the present invention adopts a spatial stepped cooling buried tube device, which solves the problem of local high or low temperature in the fluidized bed, further homogenizes the temperature field and flow field of the fluidized bed, and ensures that the roasting temperature of the fluidized bed is 950-980℃ and the height of the fluidized bed is 900-1000mm. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a zinc concentrate fluidized bed roasting furnace according to the present invention;

[0022] Figure 2 for Figure 1 Schematic diagram of the structure of the mid-space stepped cooling buried pipe device along the circumference of the fluidized bed furnace;

[0023] Figure 3 for Figure 1 Enlarged structural schematic diagram of the space-level cooling pipe buried device at point II;

[0024] Figure 4 for Figure 1 Schematic diagram of the mid-space tiered cooling pipe device from direction A;

[0025] Figure 5 for Figure 1 Schematic diagram of the structure of the air distribution device along the circumference of the fluidized bed furnace;

[0026] Figure 6 for Figure 1 Enlarged schematic diagram of the air distribution device at point I.

[0027] In the diagram, 1-discharge port, 2-spatial cascade cooling buried pipe device, 21-cooling circulation pipe, 211-cooling pipe section, 22-inspection door, 3-furnace bed, 4-overflow port, 5-smoke exhaust port, 6-air distribution device, 61-air supply pipe, 62-air distribution nozzle. Detailed Implementation

[0028] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. Unless otherwise specified, all percentages below refer to mass percentages.

[0029] Example 1:

[0030] Zinc concentrate with a moisture content of 7-8% (containing 49% zinc and 7% iron) is fed into the fluidized bed furnace through the feed port 1 using a feeder. Figure 1 As shown, the area of ​​the fluidized bed furnace 3 is 198m². 2 Feed rate (dry material): 56 t / h (6.8 t / m³) 2 ·d). For example Figure 2 As shown, six sets of spatial stepped cooling pipe devices 2 are arranged circumferentially above the fluidized bed furnace 3. Each set of spatial stepped cooling pipe devices 2 includes two sets of independently detachable cooling circulation pipes 21, which are arranged vertically along the height of the fluidized bed furnace. Figure 3 As shown, the cooling circulation pipe 21 includes four horizontally arranged cooling pipe sections 211, each with a diameter D, where 76mm ≤ D ≤ 108mm. Each cooling pipe section 211 in the spatial stepped cooling buried pipe device 2 is at a different height, and the distance between the centerline of the lowest cooling pipe section 211 and the fluidized bed furnace 3 is L1, where L1 ≤ 220mm. Figure 3 and Figure 4 As shown, the spatial stepped cooling buried pipe device also includes an inspection door 22, which is installed on the furnace wall of the fluidized bed furnace, and all cooling circulation pipes 21 pass through the inspection door 22. Figure 1 As shown, an air distribution device 6 is installed in the expanded section of the fluidized bed furnace, and the air source blows the inclined surface of the expanded section of the fluidized bed furnace through the air distribution device 6. Figure 1 and Figure 5 As shown, the air distribution device 6 includes an air supply pipe 61 and twenty air distribution nozzles 62, which are evenly arranged along the circumference of the enlarged section of the fluidized bed furnace. One end of each air distribution nozzle 62 is connected to the air supply pipe 61, and the other end penetrates the furnace wall of the fluidized bed furnace and extends into the furnace by a distance L2, where 20mm ≤ L2 ≤ 25mm. Figure 6 As shown, the end of the air distribution nozzle 62 is provided with multiple air outlets, the number of which is greater than 3. The airflow direction of each air outlet is parallel to the wall of the fluidized bed furnace, and the airflow velocity at each air outlet is less than 20 m / s. The air source is compressed air or oxygen-enriched air, with an oxygen concentration of <30% and a pressure P = 10 kPa to 20 kPa.

[0031] The roasting temperature is controlled at 950℃, the furnace bottom pressure at 15 kPa, and the fluidized bed height at 900 mm. Zinc calcined ore is discharged through overflow port 4, cooled in a cooling cylinder, and then sent to the wet zinc smelting system. The roasting flue gas enters a waste heat boiler, cyclone separator, and electrostatic precipitator through exhaust port 5 for cooling and dust collection. The collected dust is also returned to the cooling cylinder. The cooled and dust-removed flue gas then enters the acid production system. The zinc ferrite in the produced zinc calcined ore contains 4% zinc, and the residual sulfur in the flue gas is 2.45%.

[0032] Example 2:

[0033] The fluidized bed furnace structure in this embodiment is the same as that in Embodiment 1. Zinc concentrate with a water content of 7-8% (containing 49% zinc and 7% iron) is fed into the fluidized bed furnace using a feeder. The feed rate (dry material) is 57 t / h (6.9 t / m³). 2 •d), the roasting temperature is controlled at 980℃, the furnace bottom pressure is 20kpa, the boiling layer height is 1000mm, the zinc content of zinc ferrite in the produced zinc roasted sand is 3%, and the residual sulfur in the flue dust is 2.26%.

[0034] Comparative Example 1:

[0035] The results of zinc concentrate roasting in a conventional fluidized bed roaster under the conditions of Example 1 are shown in the table below:

[0036]

[0037] The comparative examples show that the zinc content in zinc ferrite produced by conventional fluidized bed roasting of zinc concentrate is significantly higher than that of the present invention.

[0038] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A zinc concentrate fluidised bed roaster characterised in that: The hearth (3) of the fluidized bed roaster has an area greater than 152 m 2 ; Multiple sets of spatial ladder cooling buried pipe devices (2) are arranged along the circumferential direction on the furnace wall above the furnace bed (3). Each set of spatial ladder cooling buried pipe devices (2) includes two sets of independently detachable cooling circulation pipes (21). The two sets of cooling circulation pipes (21) are arranged up and down along the height direction of the boiling furnace. The cooling circulation pipe (21) includes multiple horizontally arranged cooling pipe sections (211), and each cooling pipe section (211) in the spatial stepped cooling buried pipe device (2) is at a different height; The distance between the centerline of the lowest cooling pipe section (211) and the fluidized bed furnace (3) is L1, where L1≤220mm.

2. A zinc concentrate fluidised bed roaster according to claim 1 characterised in that: The hearth (3) area is 198 m 2 .

3. A zinc concentrate fluidised bed roaster according to claim 1 characterised in that: The number of groups of the spatial cascade cooling buried pipe device (2) is n, where 4≤n≤12.

4. The zinc concentrate fluidized bed roasting furnace according to claim 1, characterized in that: The diameter of the cooling pipe section (211) is D, 76mm≤D≤108mm.

5. The zinc concentrate fluidized bed roasting furnace according to claim 1, characterized in that: The spatial cascade cooling buried pipe device also includes an inspection door (22), which is installed on the furnace wall of the fluidized bed roasting furnace, and the cooling circulation pipes (21) all pass through the inspection door (22).

6. The zinc concentrate fluidized bed roasting furnace according to any one of claims 1 to 5, characterized in that: An air distribution device (6) is installed on the furnace wall of the expanded section of the fluidized bed roasting furnace. The air distribution device (6) includes an air supply pipe (61) and multiple air distribution nozzles (62). The multiple air distribution nozzles (62) are arranged along the circumferential direction of the expanded section of the fluidized bed roasting furnace. One end of the air distribution nozzle (62) is connected to the air supply pipe (61), and the other end penetrates the furnace wall of the fluidized bed roasting furnace and extends into the fluidized bed roasting furnace.

7. The zinc concentrate fluidized bed roasting furnace according to claim 6, characterized in that: The distance by which the air nozzle (62) extends from the furnace wall of the fluidized bed roasting furnace into the furnace is L2, 20mm≤L2≤25mm.

8. The zinc concentrate fluidized bed roasting furnace according to claim 6, characterized in that: Multiple air distribution nozzles (62) are evenly arranged on the circumference of the expanded section of the fluidized bed roasting furnace. The included angle between the centers of two adjacent air distribution nozzles (62) is α, where α < 25°. The ends of the air distribution nozzles (62) are provided with multiple air outlets, and the number of air outlets is greater than 3.

9. A process for reducing zinc ferrite, characterized in that: Using the fluidized bed roaster for zinc concentrate as described in any one of claims 1 to 8, the ratio of the area of ​​the turbulent deposition zone for zinc ferrite formation to the area of ​​the fluidized bed furnace is: ) 2 ,in R The radius of the fluidized bed furnace is defined as follows: the firing temperature of the fluidized bed in the fluidized roasting furnace is controlled to be 950℃~980℃; an air distribution device (6) is installed on the furnace wall of the expanded section of the fluidized roasting furnace, and the air source of the air distribution device (6) is compressed air or oxygen-enriched air, with an oxygen concentration of <30%, a pressure of P=10kpa~20kpa, and an air outlet velocity of less than 20m / s at the end of the air distribution nozzle (62).

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