Process for reducing the grade of tin in dust from a bag of a tin smelting rotary kiln

Abstract

This invention relates to a process for reducing the tin content of dust in rotary kiln baghouse dust during tin smelting, belonging to the technical field of non-ferrous metal metallurgical equipment and methods. In this invention, various well-mixed materials are placed into a hopper and fed into a rotary kiln through a feed pipe. After high-temperature roasting in the rotary kiln, roasted slag containing ≤1.5% arsenic is produced for processing in top-blown furnaces and electric furnaces. The flue gas enters an electrostatic precipitator from the kiln tail pipe, where valuable metals such as tin are captured and returned to the roasting process. The high-temperature flue gas then enters a baghouse filter through an environmentally friendly duct. The baghouse filter collects dust containing ≤1% tin and ≥73% arsenic, which is then sent to an arsenic treatment system for harmless treatment, achieving true arsenic neutralization and significantly reducing the impact of arsenic on the tin smelting system, thereby improving the economic efficiency of tin smelting.

Description

Technical Field

[0001] This invention belongs to the technical field of non-ferrous metal metallurgical equipment and methods, specifically relating to a rotary kiln roasting and impurity removal system for tin smelting. Background Technology

[0002] The main raw materials for rotary kiln oxidation roasting in tin smelting are centrifugal slag and some raw materials with high arsenic and sulfur content. After high-temperature roasting in the rotary kiln, the resulting roasted slag with lower arsenic and sulfur content is supplied to top-blown furnaces and electric furnaces. The high-temperature flue gas is treated by electrostatic precipitators to recover valuable metals such as tin, and then enters bag filters to enrich arsenic and its compounds. The enriched arsenic slag is then sent to an arsenic treatment system for harmless treatment. If the tin grade entering the bag filters is too high, it will not only cause the loss of valuable metals such as tin, but also cause certain damage to the arsenic slag treatment system, directly affecting the economic and technical indicators of tin smelting. Therefore, controlling the roasting temperature and adjusting the efficiency of electrostatic precipitators to minimize the tin content of the arsenic slag captured by the bag filters is an important prerequisite for improving the technical and economic indicators and economic benefits of tin smelting. This requires rotary kilns to carry out technical research and development to improve the arsenic removal rate of rotary kilns, make full use of the heat of the materials themselves, reduce production and operating costs, tap potential for efficiency improvement, and ensure the realization of the high-quality development goals of tin smelting. Summary of the Invention

[0003] In view of this, the purpose of this invention is to solve the problems existing in the prior art and provide a process method that is easy to operate, has good economic benefits, low safety and environmental risks and management difficulty, and good technical and economic indicators.

[0004] To achieve the above technical objectives, the following technical means are employed:

[0005] Various mixed materials are placed into a hopper and fed into a rotary kiln through a feed pipe. After high-temperature roasting in the rotary kiln, roasted slag containing ≤1.5% arsenic is produced for processing in top-blown furnaces and electric furnaces. The flue gas enters electrostatic precipitators 1, 2, 3, and 4 sequentially from the kiln tail flue. Valuable metals such as tin in the high-temperature flue gas are captured by the electrostatic precipitators and returned to the roasting process. The high-temperature flue gas then enters bag filters 1, 2, and 3 through environmental protection ducts. After bag filter capture, dust containing ≤1% tin and ≥73% arsenic can be collected and sent to the arsenic treatment system for harmless treatment, achieving true arsenic elimination, significantly reducing the impact of arsenic on the tin smelting system, and improving the economic efficiency of tin smelting.

[0006] The specific technical solution is as follows:

[0007] A process for reducing the tin grade in baghouse dust during tin smelting, the process comprising the following steps:

[0008] A. The prepared materials are loaded into the hopper and fed into the rotary kiln through the feed pipe for high-temperature roasting, producing roasted slag with arsenic content ≤1.5% for processing in top blown furnaces and electric furnaces.

[0009] B. After the flue gas with a temperature ≥300℃ comes out of the rotary kiln, it passes through high-temperature electrostatic precipitator box 1, electrostatic precipitator box 2, electrostatic precipitator box 3 and electrostatic precipitator box 4 in sequence. Valuable metals such as tin in the high-temperature flue gas are captured by the electrostatic precipitator and returned to the roasting. After the high-temperature flue gas comes out of electrostatic precipitator box 4, it passes through bag filter box 1, bag filter box 2 and bag filter box 3 in sequence at 160-180℃, and then enters the acid production system at 100-120℃.

[0010] Optionally, in step A, the length, temperature, and high-temperature volatilization time of the high-temperature section of the rotary kiln are adjusted according to the arsenic content of the material during kiln start-up, as follows:

[0011] In the initial stage of kiln operation, materials containing 9-11% arsenic are introduced, with the length of the high-temperature section of the rotary kiln controlled at 5-15 meters and the temperature at 700-850℃ to avoid kiln slagging caused by excessively rapid heating. The high-temperature volatilization time is controlled at 1.5-2.0 hours. In the middle stage of kiln operation, materials containing 15-20% arsenic are introduced, with the length of the high-temperature section controlled at 4-16 meters and the temperature at 850-1000℃. The high-temperature volatilization time is controlled at 2.0-2.5 hours. In the later stage of kiln operation, materials containing 11-15% arsenic are introduced, with the length of the high-temperature section controlled at 3-15 meters and the temperature at 800-900℃. The high-temperature volatilization time is controlled at 1.8-2.2 hours. The prepared materials are loaded into the hopper and fed into the rotary kiln through the feed pipe. The temperature is adjusted according to the arsenic content of the materials throughout the process, resulting in good roasting effect and controlling the arsenic content of the roasted slag below 1.5%.

[0012] It should be noted that this invention uses bidirectional adjustment of kiln speed and kiln negative pressure. The kiln speed is controlled at 20-45% in the initial stage of kiln opening, 45-90% in the middle stage, and 90-98% in the later stage. The length and temperature of the high-temperature section in the kiln can be controlled according to the kiln roasting atmosphere at different kiln opening times. Thermocouples are used to monitor the temperature of each section, and temperature guns are used to measure the temperature of the kiln shell and roasted slag. The temperature of the high-temperature section in the kiln can be kept at the required 750-1000℃. The kiln speed is adjusted based on the arsenic content of the slag, and the high-temperature volatilization time of the material is calculated to ensure that the arsenic content of the roasted slag is below 1.5%.

[0013] Furthermore, the high-temperature section inside the kiln is between 750-1000℃, which ensures that the flue gas temperature entering the electrostatic precipitator is above 300℃, thereby improving the dust collection efficiency of the electrostatic precipitator.

[0014] Optionally, in step B, under the action of the high-temperature electrostatic precipitator, dust containing ≥30% tin is enriched in electrostatic precipitator one, dust containing ≥15% tin is enriched in electrostatic precipitator two, dust containing ≥2% tin is enriched in electrostatic precipitator three, and dust containing <2% tin is enriched in electrostatic precipitator four. The electrostatic precipitator effect is good, and the tin metal balance can reach 99.5%.

[0015] It should be noted that the present invention adjusts the voltage and current in the electrostatic precipitator according to the changes in tin and arsenic content in the flue dust, controls the tin and arsenic content in the flue dust in each electrostatic precipitator, and granulates the recovered tin flue dust for re-roasting in the kiln to improve the metal balance of tin.

[0016] Furthermore, after the high-temperature flue gas exits from the electrostatic precipitator box four, it enters the filter bag one. After being captured by the filter bag one, the tin content of the flue gas in the filter bag one drops to below 1%, while the arsenic content reaches above 76%. After being captured by the filter bags two and three, the tin content of the flue gas in the filter bags two and three drops to below 0.05%, while the arsenic content reaches above 76%.

[0017] Furthermore, when the temperature in the high-temperature section of the kiln reaches above 850℃, the heat from the combustion of arsenic and sulfur in the material is utilized. After the rotary kiln has been running for 3-4 days, external heating is stopped, and the natural gas consumption is reduced by more than 50% compared to when the temperature in the high-temperature section of the kiln is below 850℃.

[0018] It should be noted that the arsenic and sulfur in the material release heat when they burn in the kiln. When the proportion of heat-generating material is ≥35%, the proportion of heat-absorbing material can be adjusted to achieve self-heating of the material to meet the roasting requirements, and the natural gas consumption per unit can be reduced by about 50%.

[0019] Furthermore, when the material is roasted using its own heat, once the natural gas is cut off, there is no longer any moisture produced by the combustion of natural gas, and the electrostatic precipitator and filter bag are not easily corroded.

[0020] As can be seen from the above technical solution, compared with the prior art, the process for reducing tin grade in baghouse dust in rotary kilns for tin smelting provided by the present invention has the following superior effects:

[0021] (1) Easy to operate. Traditional low-temperature roasting processes rely heavily on the experience of operators and lack clear reference data. This invention can be precisely controlled based on thermocouple monitoring data, combined with advanced equipment such as temperature guns and infrared meters, and does not require strict professional skills from operators.

[0022] (2) Good economic benefits. This invention can make full use of the heat of the material itself, and the amount of natural gas used can be reduced by more than 30%, resulting in good economic benefits.

[0023] (3) Low safety and environmental risks and low management difficulty. This invention increases the temperature of the bag filter and electrostatic precipitator, which greatly reduces the probability of dust getting damp in the electric field and bag filter, making the dust collection system less prone to corrosion and reducing the chance of safety and environmental risks. Moreover, this invention only requires operation according to various instruments and operating instructions, and various adjustments are clear and simple, enabling visual management.

[0024] (4) Excellent technical and economic indicators. The arsenic content in the roasting slag produced by this invention can be reduced by more than 20%, the tin loss with arsenic precipitation can be reduced by more than 50%, and the tin metal balance in the rotary kiln can reach more than 99.5%. Attached Figure Description

[0025] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the process for reducing the tin grade of bag dust in a rotary kiln for tin smelting according to the present invention.

[0027] In the diagram: 1 is the hopper, 2 is the rotary kiln, 3 is the first electrostatic precipitator, 4 is the second electrostatic precipitator, 5 is the third electrostatic precipitator, 6 is the fourth electrostatic precipitator, 7 is the first bag filter, 8 is the second bag filter, 9 is the third bag filter, and 10 is the acid production system. Detailed Implementation

[0028] 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 some embodiments of the present invention, and not all embodiments. 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.

[0029] Material Processing: Taking the feed material of a rotary kiln in a tin smelter as the research object, and considering the three stages of kiln operation (initial, middle, and late), the arsenic content (As) in the feed material is controlled at 9-11% in the initial stage, 15-20% in the middle stage, and 11-15% in the late stage. Taking a daily processing capacity of 120 tons of mixed material in the initial stage, 156 tons in the middle stage, and 144 tons in the late stage as an example, by adjusting the kiln temperature and the length of the high-temperature section according to the arsenic content in the feed material, an arsenic removal rate of ≥90% can be achieved while controlling the arsenic content of the roasted slag to <1.5%.

[0030] Example 1

[0031] like Figure 1 This invention provides a process for reducing the tin grade of baghouse dust in tin smelting rotary kilns, specifically including the following steps:

[0032] (1) In the initial stage of kiln opening, the kiln temperature is raised to 750°C and the kiln speed is 30%. The feed rate is 5.0t / h and the arsenic content in the kiln is 9-10%. After feeding, natural gas and the heat released by the roasting of the materials are used to supply the temperature required for arsenic removal. The length of the high-temperature section is 5-15 meters. The temperature in the high-temperature section is controlled at 700-850°C and the electric field inlet is 300-350°C. The kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 30% and 45%. When the kiln speed reaches 45%, the external heating of natural gas is increased and the proportion of heat-generating materials is increased. At the same time, the softening point of the materials is increased and the temperature is raised to enter the middle stage of kiln operation.

[0033] (2) After entering the middle stage of kiln opening, the feed rate is 6.5t / h, the arsenic content in the kiln is 15-17%, the length of the high temperature section is 4-16 meters, the temperature of the high temperature section is 850-1000℃, and the electric field inlet temperature is 300-350℃. When the temperature in the kiln reaches 900℃, the proportion of exothermic materials and high softening point materials is increased. When the temperature in the kiln rises to 950℃, external heating is stopped. The material itself is used to release heat for roasting. The kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 45% and 90%. The arsenic content of the roasted product can be reduced to below 1%, and the tin content of the bag dust can be reduced to below 0.5%. When the kiln speed reaches 90%, the proportion of exothermic materials is reduced, and the negative pressure at the kiln tail is lowered to move the high temperature section forward into the later stage of kiln opening.

[0034] (3) When entering the later stage of kiln opening, the feed rate is 6.0t / h, the arsenic content in the kiln is 11-13%, the length of the high temperature section is 3-15 meters, the temperature of the high temperature section is 800-900℃, when the temperature in the kiln is ≤830℃, the proportion of exothermic material is increased, when the temperature in the kiln is ≥870℃, the proportion of exothermic material is reduced, the electric field inlet is 300-350℃, and the kiln speed is adjusted according to the amount of roasted slag produced, and the kiln speed is controlled between 90%-98%. When the output of roasted slag is ≤100 tons, materials with arsenic content ≤2% are added to cool down. When the kiln tail temperature is ≤120℃, water is poured to cool down, and the kiln is stopped to clean up the kiln sludge.

[0035] This technology can achieve an arsenic removal rate of over 91%, and the arsenic content in the roasting slag can be reduced to below 1.3%.

[0036] Example 2

[0037] like Figure 1 The process for reducing tin grade in baghouse dust during tin smelting provided by this invention specifically includes the following steps:

[0038] (1) In the initial stage of kiln opening, the kiln temperature is raised to 750°C and the kiln speed is 30%. The feed rate is 5.0t / h and the arsenic content in the kiln is 10-11%. After feeding, natural gas and the heat released by the roasting of the materials are used to supply the temperature required for arsenic removal. The length of the high-temperature section is 5-15 meters. The temperature in the high-temperature section is controlled at 700-850°C and the electric field inlet is 300-350°C. The kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 30% and 45%. When the kiln speed reaches 45%, the external heating of natural gas is increased and the proportion of heat-generating materials is increased. At the same time, the softening point of the materials is increased and the temperature is raised to enter the middle stage of kiln operation.

[0039] (2) After entering the middle stage of kiln opening, the feed rate is 6.5t / h, the arsenic content in the kiln is 17-20%, the length of the high temperature section is 4-16 meters, the temperature of the high temperature section is 850-1000℃, and the electric field inlet temperature is 300-350℃. When the temperature in the kiln reaches 900℃, the proportion of exothermic materials and high softening point materials is increased. When the temperature in the kiln rises to 950℃, external heating is stopped. The material itself is used to release heat for roasting. The kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 45% and 90%. The arsenic content of the roasted product can be reduced to below 1.2%, and the tin content of the bag dust can be reduced to below 0.8%. When the kiln speed reaches 90%, the proportion of exothermic materials is reduced, and the negative pressure at the kiln tail is lowered to move the high temperature section forward into the later stage of kiln opening.

[0040] (3) When entering the later stage of kiln opening, the feed rate is 6.0t / h, the arsenic content in the kiln is 13-15%, the length of the high temperature section is 3-15 meters, the temperature of the high temperature section is 800-900℃, when the temperature in the kiln is ≤830℃, the proportion of exothermic material is increased, when the temperature in the kiln is ≥870℃, the proportion of exothermic material is reduced, the electric field inlet is 300-350℃, and the kiln speed is adjusted according to the amount of roasted slag produced, and the kiln speed is controlled between 90%-98%. When the output of roasted slag is ≤100 tons, materials with arsenic content ≤2% are added to cool down. When the kiln tail temperature is ≤120℃, water is poured to cool down, and the kiln is stopped to clean the kiln sludge.

[0041] This technology can achieve an arsenic removal rate of over 90%, and the arsenic content in the roasting slag can be reduced to below 1.5%.

[0042] Examples 1 and 2 demonstrate that when the high-temperature section temperature is 700-850℃ in the initial stage of kiln opening and 850-1000℃ in the middle stage of kiln opening, the arsenic removal rate can reach over 90% by controlling the kiln speed and the length of the high-temperature section during roasting.

[0043] Comparative Example 1: Firing in a kiln at a temperature ≤700℃, with a high-temperature section length of 5-15 meters.

[0044] Specifically, the following steps are included:

[0045] (1) In the initial stage of kiln opening, the kiln temperature is raised to 750℃ and the kiln speed is 30%. The feed rate is 5.0t / h and the arsenic content in the kiln is 9-10%. After feeding, natural gas and the heat released by the roasting of materials are used to supply the temperature required for arsenic removal. The length of the high-temperature section is 5-15 meters. The temperature in the high-temperature section is controlled to be ≤700℃. The electric field inlet is 300-350℃. The kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 30% and 45%. When the kiln speed reaches 45%, the external heating of natural gas is increased and the proportion of heat-generating materials is increased. At the same time, the softening point of the material is increased and the temperature is raised to enter the middle stage of kiln operation.

[0046] (2) After entering the middle stage of kiln opening, the feed rate is 6.5t / h, the arsenic content in the kiln is 15-17%, the length of the high temperature section is 4-16 meters, the temperature of the high temperature section is 700℃, the electric field inlet is 300-350℃, and the kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 45% and 90%, and the arsenic content of the roasted slag can be reduced to below 2.0%, and the tin content of the bag dust can be reduced to below 3.0%. When the kiln speed reaches 90%, the proportion of exothermic materials is reduced, and the negative pressure at the kiln tail is lowered to move the high temperature section forward into the later stage of kiln opening.

[0047] (3) When entering the later stage of kiln opening, the feed rate is 6.0t / h, the arsenic content in the kiln is 10-13%, the length of the high temperature section is 3-15 meters, the temperature of the high temperature section is 700℃, the electric field inlet is 300-350℃, and the kiln speed is adjusted according to the amount of roasted slag produced, and the kiln speed is controlled between 90% and 98%. When the output of roasted slag is ≤100 tons, materials with arsenic content ≤2% are added to cool down. When the kiln tail temperature is ≤120℃, water is poured to cool down, and the kiln is stopped to clean up the kiln sludge.

[0048] This technology can achieve an arsenic removal rate of up to 75%, and the arsenic content in the roasting residue can be reduced to 2.5%.

[0049] Comparative Example 2: The length of the high-temperature section in the middle stage of kiln opening is 5-15 meters, and the length of the high-temperature section in the later stage of kiln opening is 4-15 meters.

[0050] (1) In the initial stage of kiln opening, the kiln temperature is raised to 700℃ and the kiln speed is 30%. The feed rate is 5.0t / h and the arsenic content in the kiln is 9-10%. After feeding, natural gas and the heat released by the roasting of materials are used to supply the temperature required for arsenic removal. The length of the high-temperature section is 5-15 meters. The temperature in the high-temperature section is controlled at 700-850℃ and the electric field inlet is 300-350℃. The kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 30% and 45%. When the kiln speed reaches 45%, the external heating of natural gas is increased and the proportion of heat-generating materials is increased. At the same time, the softening point of the material is increased and the temperature is raised to enter the middle stage of kiln operation.

[0051] (2) After entering the middle stage of kiln opening, the feed rate is 6.5t / h, the arsenic content in the kiln is 15-17%, the length of the high temperature section is 5-15 meters, the temperature of the high temperature section is 850-1000℃, and the electric field inlet temperature is 300-350℃. When the temperature in the kiln reaches 900℃, the proportion of exothermic materials and high softening point materials is increased. When the temperature in the kiln rises to 950℃, external heating is stopped. The material itself is used to release heat for roasting. The kiln speed is adjusted according to the amount of roasted slag produced. The kiln speed is controlled between 45% and 90%. The arsenic content of the roasted product can be reduced to below 1.3%, and the tin content of the bag dust can be reduced to below 1.2%. When the kiln speed reaches 90%, the proportion of exothermic materials is reduced, and the negative pressure at the kiln tail is lowered to move the high temperature section forward into the later stage of kiln opening.

[0052] (3) When entering the later stage of kiln opening, the feed rate is 6.0t / h, the arsenic content in the kiln is 11-13%, the length of the high temperature section is 4-15 meters, the temperature of the high temperature section is 800-900℃, when the temperature in the kiln is ≤830℃, the proportion of exothermic material is increased, when the temperature in the kiln is ≥870℃, the proportion of exothermic material is reduced, the electric field inlet is 300-350℃, and the kiln speed is adjusted according to the amount of roasted slag produced, and the kiln speed is controlled between 90%-98%. When the output of roasted slag is ≤100 tons, materials with arsenic content ≤2% are added to cool down. When the kiln tail temperature is ≤120℃, water is poured to cool down, and the kiln is stopped to clean up the kiln sludge.

[0053] This technology can achieve an arsenic removal rate of up to 80%, and the arsenic content in the roasting residue can be reduced to below 1.8%.

[0054] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A process for reducing the grade of tin in dust from a bag filter of a smelting rotary kiln of tin, characterized by, The process comprises the following steps: A, the prepared material is loaded into the hopper (1), enters the rotary kiln (2) through the discharge pipe, and is high-temperature calcined to produce calcined slag containing arsenic ≤1.5% for top-blown furnace and electric furnace treatment; B, after the temperature ≥300℃ flue gas comes out of the rotary kiln (2), it successively passes through high-temperature electric dust collection box one (3), electric dust collection box two (4), electric dust collection box three (5) and electric dust collection box four (6), and the valuable metals including tin in the high-temperature flue gas are captured and returned to the roasting; then the high-temperature flue gas comes out of the electric dust collection box four (6), passes through bag one (7), bag two (8) and bag three (9) at 160-180℃ in turn, and then enters the acid making system (10) at 100-120℃; In step A, the length, temperature and high-temperature volatilization time of the high-temperature section of the rotary kiln (2) are adjusted according to the arsenic content of the material during the opening of the kiln, as follows: In the initial stage of opening the kiln, the material containing 9-11% arsenic is added, the length of the high-temperature section of the rotary kiln (2) is controlled at 5-15 meters, the temperature of the high-temperature section is controlled at 700-850℃, and the high-temperature volatilization time is controlled at 1.5-2.0h; in the middle stage of opening the kiln, the material containing 15-20% arsenic is added, the length of the high-temperature section is controlled at 4-16 meters, the temperature of the high-temperature section is controlled at 850-1000℃, and the high-temperature volatilization time is controlled at 2.0-2.5h; in the later stage of opening the kiln, the material containing 11-15% arsenic is added, the length of the high-temperature section is controlled at 3-15 meters, the temperature of the high-temperature section is controlled at 800-900℃, and the high-temperature volatilization time is controlled at 1.8-2.2h.

2. The process for reducing tin grade in baghouse dust during tin smelting in rotary kilns according to claim 1, characterized in that, After the high-temperature flue gas comes out of the electric dust collection box four (6), it enters the bag one (7), and after being captured by the bag one (7), the tin content in the bag dust is reduced to below 1%, and then passes through the bag two (8) and the bag three (9) for capture, so that the tin content in the smoke dust is reduced to below 0.05% and the arsenic content reaches above 76%.

3. The process of claim 1-2, wherein the process is characterized by, When the temperature of the high-temperature section in the kiln reaches 850-1000℃, the heat generated by the combustion of arsenic and sulfur in the material is used to supply the heat required for roasting, and the external heat supply is stopped after the rotary kiln is started for 3-4 days.

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