A roasting process and system for deep removal of impurities from zinc concentrates

Abstract

This invention discloses a roasting process and system for deep impurity removal from zinc concentrate, including zinc concentrate blending, zinc concentrate drying, pre-roasting and impurity removal in the front chamber of a fluidized bed furnace, positive and negative oxygen roasting and impurity removal, indirect cooling of roasted sand for heat recovery to produce roasted sand, flue gas treatment, and dust recovery. This invention, by employing a process of periodic fluctuating feeding and zoned control of air injection with different oxygen contents, meets the different impurity removal requirements under low excess oxygen conditions for removing impurities such as lead and cadmium, and under high temperature and high excess oxygen conditions for desulfurization. It can produce superior roasted sand from lower-quality zinc concentrate to meet the requirements of subsequent pyrometallurgical zinc smelting processes such as direct zinc oxide. Furthermore, by adopting an oxygen-enriched process, the heat carried away by the flue gas is reduced, the required heat is also reduced, the sulfur content of the raw material is reduced, and the feed rate is increased, thereby improving the output.

Description

Technical Field

[0001] This invention relates to the field of metal smelting technology, and in particular to a roasting process and system for deep removal of impurities from zinc concentrate. Background Technology

[0002] In pyrometallurgical zinc refining, especially in the direct zinc oxide production process, high-temperature oxidative roasting is used to remove the sulfur content of zinc concentrate to a minimum and to remove as much of the main impurities such as lead and cadmium as possible from the concentrate, in order to obtain roasted ore suitable for subsequent direct zinc oxide production.

[0003] In the high-temperature oxidative roasting process, the main control indicators are temperature and excess oxygen. High temperature and high excess oxygen are beneficial for desulfurization and reducing the sulfur content of roasted ore; high temperature and lower excess oxygen are beneficial for the removal of lead and cadmium because the vapor pressure of lead and cadmium sulfides is significantly higher than that of their oxides. Therefore, it is desirable for lead and cadmium sulfides to volatilize before oxidation to achieve a higher lead and cadmium removal rate. Since the vapor pressure of lead and cadmium sulfides increases with temperature, increasing the roasting temperature is beneficial for the volatilization of lead and cadmium sulfides, thus improving the lead and cadmium removal rate. However, if the temperature is too high, lead and cadmium sulfides are more likely to oxidize and sinter, leading to a decrease in the lead and cadmium removal rate or even furnace failure. Therefore, the oxidative roasting of zinc concentrate presents a contradiction: the excess oxygen coefficient required for desulfurization, lead and cadmium removal, and the high temperature required for desulfurization and lead and cadmium sulfide volatilization versus the requirement that the temperature cannot be too high to avoid oxidation and sintering of lead and cadmium sulfides.

[0004] To address this issue, a roasting process and system for deep impurity removal from zinc concentrate is proposed to solve the problems existing in the current technology. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems by providing a roasting process and system for deep impurity removal from zinc concentrate. This invention employs a process of periodic fluctuating feeding and zoned control of air injection with varying oxygen contents to meet different impurity removal requirements under low excess oxygen conditions for lead and cadmium removal, and high temperature and high excess oxygen conditions for desulfurization. It can produce high-quality roasted ore from lower-quality zinc concentrate, meeting the requirements of subsequent pyrometallurgical zinc smelting processes such as direct zinc oxide. Furthermore, the oxygen-enriched process reduces the heat carried away by the flue gas, thus reducing the required heat and lowering the sulfur content of the raw materials. Simultaneously, the increased feeding rate improves yield. To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: According to one aspect of the present invention, a roasting process for deep removal of impurities from zinc concentrate is provided, comprising the following steps: A. Batching: Zinc concentrates from different mines are mixed and blended to obtain zinc concentrates with zinc, sulfur, lead, cadmium, arsenic and other contents that meet the process requirements.

[0006] B. Drying: The zinc concentrate prepared in step A is fed into an indirect heating drying cylinder and dried to a moisture content of 8-15%.

[0007] C. Pre-roasting of the forecourt: The zinc concentrate dried in step B is fed into the forecourt of the fluidized bed furnace through the feed inlet of the fluidized bed furnace in a periodic fluctuating feeding manner. Conventional air is blown in from the forecourt air chamber at the bottom of the forecourt furnace. The air enters the forecourt pre-roasting through the air distribution plate and air cap. By adjusting the feeding amount and air volume, the forecourt fluidized bed roasting temperature is controlled to be no less than 850°C. By adjusting the air volume, fluidization is ensured and sedimentation is avoided. After pre-purification in a fluidized state, the zinc concentrate enters the main bed of the fluidized bed furnace. D. Positive and Negative Oxygen Roasting and Impurity Removal: The material pre-roasted in step C is fluidized and enters the front main bed of the fluidized bed furnace. Air is blown into the air chamber of the front main bed (or oxygen is supplemented and the oxygen content after supplementation is lower than that of the oxygen-enriched air in the rear main bed) to control the roasting atmosphere of the front main bed with negative oxygen (insufficient oxygen). The roasting temperature of the front main bed is 1100~1230℃. The material in the front main bed enters the rear main bed in fluidized form and continues to be fluidized and roasted in the rear main bed. During the roasting process of the rear main bed, oxygen-enriched air is blown into the rear main bed through the air chamber to control the roasting atmosphere of the rear main bed with positive oxygen (excess oxygen). The roasting temperature of the rear main bed is 0~50℃ higher than that of the front main bed. The roasted sand after roasting in the rear main bed is discharged through the discharge port.

[0008] E. Secondary air roasting: The fluidized bed furnace expansion section is equipped with a secondary air (or oxygen-enriched air) replenishment hole. The unroasted zinc concentrate sulfides and sublimed sulfur contained in the flue gas generated in steps C, D, and E enter the fluidized bed furnace expansion section for further combustion.

[0009] F. Calcined Sand Cooling: The calcined sand obtained in step D is discharged into a calcined sand cooler and cooled to a temperature suitable for safe transportation before being sent downstream to produce products such as zinc oxide.

[0010] G. Flue gas treatment and dust recovery: The flue gas discharged in steps C, D, and E recovers heat and is subjected to gravity dust collection in a waste heat boiler. After the dust in the flue gas is collected by a cyclone dust collector and a deep dust collector, it is sent to the flue gas acid production system to produce sulfuric acid. The dust is returned to the furnace for roasting or sent to the wet zinc smelting process.

[0011] Preferably, in step C, the highest temperature of the forebed refers to the firing temperature in the middle of the forebed during the period when the main bed reaches its highest firing temperature.

[0012] Preferably, in step D, the positive and negative oxygen roasting refers to the positive oxygen roasting where the total amount of oxygen blown into the front bed, the front main bed, and the rear main bed is greater than the amount of oxygen required for zinc concentrate roasting, and the negative oxygen roasting refers to the negative oxygen roasting where the total amount of oxygen blown into the front bed, the front main bed, and the rear main bed is less than the amount of oxygen required for zinc concentrate roasting.

[0013] Preferably, in step D, the excess oxygen in the front main bed is lower than that in the rear main bed, and the pre-baked sand material is roasted in an atmosphere with even less oxygen in the front main bed; the bed layer is the sum of the front bed, the front main bed and the rear main bed, and the excess oxygen coefficient of the bed layer is 0.90~1.10.

[0014] Preferably, in step D, the oxygen concentration of the air in the front main bed air chamber or the oxygen-enriched air after supplementing oxygen is controlled to be ≥ air oxygen content and ≤ 25%, and the oxygen concentration of the oxygen-enriched air in the rear main bed air chamber is controlled to be ≥ air oxygen content and ≤ 35%, so as to obtain a good roasting effect.

[0015] Preferably, in step D, the rear main bed air chamber and the front main bed air chamber are separated.

[0016] Preferably, in step D, the zinc concentrate is characterized by fluctuating feeding, where the material's residence time in the front bed, front main bed, and rear main bed during fluidized bed roasting is 50-90 minutes, i.e., the fluctuation cycle is 50-90 minutes. After completing the fluctuating cycle roasting, the material is discharged from the fluidized bed furnace through the discharge port. During the roasting cycle, the fluidized bed temperature is reduced to the minimum process control index range by reducing the amount of material fed. Pressing is achieved by using a large amount of material fed, and the furnace temperature is restored to the maximum process temperature index range by pressing. Then, the pressing amount and the amount of material fed into the front bed are adjusted accordingly. The airflow and oxygen content in the main bed air chamber and the rear main bed air chamber are maintained within the range of the highest calcination temperature index of the main bed for 40-80 minutes. After that, the feeding is reduced until the calcination temperature drops to the minimum process control temperature index range. During this period, the airflow and oxygen content in the front and rear main bed air chambers are adjusted appropriately to make the calcination temperature of the fluidized bed reach the minimum operating temperature index. The feeding reduction process lasts for 10-20 minutes, and then the pressing process is restarted. The pressing and feeding are periodic cyclic operations.

[0017] Preferably, in step E, the control index of the secondary air is the SO2 concentration at the outlet of the fluidized bed furnace flue gas. By supplementing the secondary air, the SO2 concentration at the outlet of the fluidized bed furnace flue gas is ensured to be no higher than 13.5%, so that the incompletely burned concentrate carried out by the flue gas and the sublimed sulfur generated under negative oxygen conditions are fully burned, avoiding the sublimed sulfur and insufficient oxygen-sulfur ratio from affecting the subsequent flue gas acid production.

[0018] Preferably, in step F, the calcined sand cooler is one or more of a direct cooling cylinder, an indirect cooling cylinder, or a fluidized bed cooler.

[0019] Preferably, in step G, the deep dust collector is one or more multi-stage series of an electrostatic precipitator and a bag filter.

[0020] A roasting system for deep removal of impurities from zinc concentrate includes an ore blending module, a drying and feeding module, a drying module, a roasting and feeding module, a roasting module, and a flue gas heat recovery and dust collection module; the ore blending module, drying and feeding module, drying module, feeding and feeding module, roasting module, and flue gas heat recovery and dust collection module are connected in sequence. The ore blending module includes a silo, a batching crane, a fume hood, a fume duct, a bag filter, and an exhaust stack. The fume hoods at each dust collection point are connected in parallel through the fume duct. The parallel fume hoods, bag filters, and exhaust stacks are connected sequentially through the duct. The drying and feeding module includes a disc feeder with a hopper and a conveying device with smoke collection function. The discharge port of the disc feeder with the hopper is directly connected to the inlet of the first-stage conveying device. The discharge port of the previous-stage conveying device is directly connected to the inlet of the next-stage conveying device. The discharge port of the last-stage conveying device is connected to the drying module and extends into the drying cylinder. Smoke hoods are installed at each dust outlet. The outlets of the smoke hoods and the smoke collection device of the conveying device with smoke collection function are connected to the inlet of the bag filter or the inlet pipe of the bag filter through pipes. The drying module includes a rotary drying cylinder, a flue gas duct, a bag filter, an exhaust stack, and a heating medium duct. The inlet of the rotary drying cylinder is connected to the outlet of the last-stage conveyor of the drying and feeding module, and the outlet of the rotary drying cylinder is directly connected to the inlet of the first-stage conveyor of the feeding submodule of the roasting and feeding module. The heating medium inlet of the rotary drying cylinder is connected to the heating medium supply duct, and the heating medium outlet of the rotary drying cylinder is connected to the heating medium return duct. The flue gas outlet of the rotary drying cylinder is connected to the bag filter through a flue gas duct, and the outlet of the bag filter is connected to the exhaust stack inlet through a flue gas duct. The rotary drying cylinder adopts an indirect heating method, and the indirect heating medium is one or more of steam, hot oil, and high-temperature flue gas. The roasting feeding and feeding module includes a conveying device with smoke collection function, an intermediate silo, and a roasting feeding device; the inlet of the first-stage conveying device with smoke collection function is connected to the outlet of the rotary drying kiln, the outlet of the upper-stage conveying device is directly connected to the inlet of the lower-stage conveying device, and the outlet of the last-stage conveying device is connected to the roasting feeding device, which feeds the material into the fluidized bed furnace. The conveying equipment with smoke collection function is one or more of belt conveyors, bucket elevators, screw conveyors, and chain tube conveyors; the roasting feeding device is one or more of disc feeders with smoke collection function, belt conveyors, screw feeders, and chutes.

[0021] The roasting module is a fluidized bed roasting device with a special structure (referred to as a fluidized bed furnace). The fluidized bed furnace consists of, from bottom to top, a wind chamber, a wind chamber air distribution plate, a wind cap, a roasting section, a transition section, an expansion section, and a flue gas outlet. The roasting section is the fluidized bed roasting layer. In the horizontal direction, the roasting section consists of a feed inlet, a front bed, a front main bed, a rear main bed, and a discharge outlet. The discharge outlet is connected to the inlet of the roasted sand cooling cylinder. After cooling, the roasted sand is a highly purified product roasted sand. The wind chamber is divided into a front bed wind chamber, a front main bed wind chamber, and a rear main bed wind chamber. The front bed wind chamber is independent or forms an integral wind chamber with the front main bed. The rear main bed uses a separate rear wind chamber. The inlet of the front bed wind chamber is connected to the outlet of the furnace bottom fan. The inlet of the front wind chamber is also connected to the outlet of the furnace bottom fan and connected to the oxygen pipeline. The inlet of the rear wind chamber is connected to the outlet of the furnace bottom fan and the oxygen pipeline. The transition section of the fluidized bed furnace is equipped with a secondary air inlet. The secondary air is connected to the outlet pipeline of the furnace bottom fan and the oxygen pipeline.

[0022] The flue gas heat recovery and dust collection module includes a waste heat boiler, one or more cyclone dust collectors in series, a relay fan, and a deep dust collector. The deep dust collector is one or more electrostatic precipitators and bag filters in series. The flue gas outlet at the top or upper part of the fluidized bed furnace is connected to the waste heat boiler. The outlet of the waste heat boiler is connected to the inlet of the cyclone dust collector. The outlet of the last-stage cyclone dust collector is connected to the inlet of the first-stage electrostatic precipitator or bag filter. The outlet of the previous-stage electrostatic precipitator or bag filter is connected to the inlet of the next-stage electrostatic precipitator or bag filter. The outlet of the last-stage electrostatic precipitator or bag filter is connected to the subsequent flue gas acid production system. In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The roasting process and system for deep impurity removal of zinc concentrate described in this invention, by adopting a process of periodic fluctuating feeding and zoned control of blowing in air with different oxygen contents, meets different impurity removal requirements under low excess oxygen conditions for removing impurities such as lead and cadmium, and under high temperature and high excess oxygen conditions for desulfurization. It can produce superior roasted sand from zinc concentrate of poor quality, which can meet the requirements of subsequent pyrometallurgical zinc smelting such as direct zinc oxide. Furthermore, after adopting the oxygen-enriched process, the heat carried away by the flue gas is reduced, the required heat is also reduced, the sulfur content of the raw material is reduced, and at the same time, the feeding amount is increased, thereby increasing the output.

[0023] 2. The roasting process and system for deep impurity removal of zinc concentrate described in this invention introduces oxygen-enriched air into the rear main bed, enhancing the gradient difference between the positive and negative air atmospheres of the front and rear boiling layers. Under the same boiling layer space velocity, the feed rate can be increased, thereby improving the processing capacity. Furthermore, it enhances the conditions for removing different impurities, resulting in roasted ore with lower content of impurities such as lead, cadmium, arsenic, antimony, and sulfur, and better quality roasted ore, which can better meet the requirements of subsequent pyrometallurgical zinc smelting such as direct zinc oxide.

[0024] 3. The roasting process and system for deep removal of impurities from zinc concentrate described in this invention can reduce the sulfur content entering the furnace, reduce the impact of flue gas on the roasting temperature, increase the amount of flue gas (such as boiler dust), and improve the utilization rate of raw materials. In addition, the amount of air used is small, the SO2 concentration in the flue gas is higher, and the amount of flue gas is small, which is beneficial to the subsequent production of acid from flue gas. Lead and cadmium volatilize in the form of sulfides and are enriched and recovered after secondary air oxidation and dust collection, resulting in a high resource recovery rate. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow of the present invention; Figure 2 This is a schematic diagram of the processing system of the present invention; In the attached diagram: 1. Zinc concentrate silo and batching silo; 2. Overhead crane; 3. Disc feeder (including silo); 4. Bag filter; 5. Smoke collector fan; 6. Exhaust stack; 7. Wet ore belt conveyor; 8. Drying kiln; 9. Dry ore belt conveyor; 10. Bucket elevator; 11. Intermediate silo; 12. Belt feeder; 13. Fluidized bed furnace; 13-1. Air chamber; 13-1a. Front bed air chamber; 13-1b. Front main bed air chamber; 13-1c. Rear main bed air chamber; 13-2. Air distribution plate (including air cap); 13- 3. Calcination section; 13-3a. Pre-calcining bed of fluidized bed roasting; 13-3b. Main bed before fluidized bed roasting; 13-3c. Main bed after fluidized bed roasting; 13-4. Discharge port; 13-5. Fluidized bed furnace transition section; 13-6. Secondary air vent (one or more, such as 13-6a and 13-6b); 13-7. Fluidized bed furnace expansion section; 13-8. Fluidized bed furnace flue gas outlet; 14. Furnace bottom fan; 15. Roasted sand cooling cylinder; 16. Boiler; 17. Cyclone dust collector; 18. Relay fan; 19. Electrostatic precipitator. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of the invention, and these aspects of the invention can be achieved even without these specific details.

[0027] Please see Figures 1 to 2 This invention provides a roasting process and system for deep impurity removal from zinc concentrate, the technical solution of which is as follows: Example 1 The roasting process for deep impurity removal from zinc concentrate involves the following steps: A. Batching: Zinc concentrates from different mines are mixed and blended to obtain zinc concentrates with zinc, sulfur, lead, cadmium, arsenic and other contents that meet the process requirements.

[0028] B. Drying: The zinc concentrate prepared in step A is fed into an indirect heating drying cylinder and dried to a moisture content of 10-12%.

[0029] C. Pre-roasting of the forebed: The zinc concentrate dried in step B is fed into the forebed of the fluidized bed furnace in a periodic fluctuating feeding manner. Conventional air is blown in from the forebed air chamber at the bottom of the forebed. In this case, the forebed air chamber is set up separately. The air enters the forebed pre-roasting through the air distribution plate and the air cap. The forebed fluidized bed roasting temperature is controlled at 920~950℃ by changing the feeding amount and the air intake. The air volume is adjusted to ensure fluidization and avoid sedimentation. After pre-roasting and impurity removal in a fluidized state, the zinc concentrate enters the main bed of the fluidized bed furnace.

[0030] D. Positive and Negative Oxygen Calcination and Impurity Removal: The material pre-calcined in step C is fluidized and enters the front main bed of the fluidized bed furnace. Oxygen-infused air with an oxygen content of 22-23% is blown into the front main bed air chamber. The minimum temperature after reducing the material in the front main bed is 1070-1100℃, and the maximum temperature after adding material is 1170-1195℃. Oxygen-enriched air with an oxygen concentration of 28-29% is blown into the rear main bed air chamber. The minimum temperature after reducing the material in the rear main bed is 1100-1120℃, and the maximum calcination temperature after reducing material is 1180-1200℃. The excess oxygen coefficient of the bed layers (front bed, front main bed, and rear main bed combined) is 0.95-1.0. The calcined sand from the rear main bed is discharged through the outlet.

[0031] In step D, the excess oxygen coefficient of the air and oxygen blown into the front bed, front main bed, and rear main bed is 0.98 (oxygen deficiency of 2%). The zinc concentrate fluctuating feeding conditions are as follows: uniform feeding (pressing) for 45 minutes, followed by 15 minutes of reducing the feeding until the temperature of the rear main bed drops to 1100~1120℃, and then feeding at the normal feeding (pressing) rate. The feeding is cyclically fluctuated according to these conditions.

[0032] E. Secondary air roasting: Air is supplied to the secondary air supply hole of the fluidized bed furnace expansion section to control the SO2 concentration at the fluidized bed furnace flue gas outlet to not exceed 12.5%, so that the unroasted zinc concentrate sulfides and sublimed sulfur contained in the flue gas generated in steps C, D and E can enter the fluidized bed furnace expansion section for further combustion.

[0033] F. Cooling of roasted sand: The roasted sand obtained in step D is discharged into an indirect cooling cylinder through a chute and cooled to below 80°C with soft water before being sent downstream to produce products such as direct zinc oxide.

[0034] G. Flue gas treatment and dust recovery: The flue gas discharged in steps C, D, and E is subjected to heat recovery and gravity dust collection in a waste heat boiler. After the dust in the flue gas is collected by a cyclone dust collector and an electrostatic precipitator, it is sent to the flue gas acid production system to produce sulfuric acid. The boiler dust is returned to the ore blending furnace for roasting, and the dust from the cyclone dust collector and the dust from the electrostatic precipitator are sent to the wet zinc smelting process.

[0035] H. Treatment effect; The following are the specifications of a company's first-grade oxidized roasted zinc concentrate and the actual composition of the zinc concentrate fed into the furnace: Table 1. Parameters of Primary Oxidized Roasted Zinc Concentrate and Actual Zinc Concentrate Composition (w, %) of a Certain Company The quality of the calcined sand produced after calcination using this process is shown in the table below: Table 2. Quality Indicators and Quality (w, %) of Oxidized Roasted Sand from a Certain Company As shown in Table 1, the zinc concentrate index and actual blending composition data indicate that the zinc content in the actual blend is lower than the requirements for first-grade oxidized roasted zinc concentrate. Furthermore, the contents of impurities such as sulfur, lead, lead oxide, cadmium, arsenic, and antimony also fail to meet the requirements for first-grade oxidized roasted zinc concentrate. In particular, the absolute value of sulfur content is 1.79 percentage points lower than the target, resulting in a reduction of approximately 6.4% in the calorific value of the zinc concentrate. Table 2 shows the quality index and quality of oxidized roasted calcined ore from a certain company, demonstrating that the roasting process significantly improves all roasting indicators compared to the first-grade roasting standard.

[0036] In this case, 15.4m was used. 2 Fluidized bed furnace, with a foreboard area of ​​1.4m². 2 The front master bed has an area of ​​7m² 2 The rear master bed area is 7m² 2 The original design firing intensity was 7~7.5 t / (m). 2 After 60 days of roasting, the roasting intensity was calculated to be 8.31 t / (m²) based on monthly statistical data. 2 (d) The calcination intensity is about 10% higher than the maximum designed calcination intensity, and this calcination intensity is also more than 10% higher than the calcination intensity before adopting this process.

[0037] Example 2 The roasting process for deep impurity removal from zinc concentrate involves the following steps: A. Batching: Zinc concentrates from different mines are mixed and blended to obtain zinc concentrates with zinc, sulfur, lead, cadmium, arsenic and other contents that meet the process requirements.

[0038] B. Drying: The zinc concentrate prepared in step A is fed into an indirect heating drying cylinder and dried to a moisture content of 11-13%.

[0039] C. Pre-roasting of the forebed: The zinc concentrate dried in step B is fed into the forebed of the fluidized bed furnace in a periodic fluctuating feeding manner. Conventional air is blown in from the forebed air chamber at the bottom of the forebed. In this case, the forebed air chamber is set up separately. The air enters the forebed pre-roasting through the air distribution plate and the air cap. The forebed fluidized bed roasting temperature is controlled at 900~930℃ by changing the feeding amount and the air intake. The air volume is adjusted to ensure fluidization and avoid sedimentation. After pre-roasting and impurity removal in a fluidized state, the zinc concentrate enters the main bed of the fluidized bed furnace.

[0040] D. Positive and Negative Oxygen Calcination and Impurity Removal: The material pre-calcined in step C is fluidized and enters the front main bed of the fluidized bed furnace. Conventional air is blown into the front main bed air chamber. The minimum temperature of the front main bed after material reduction is controlled by feeding, which is 1100~1130℃, and the maximum temperature after feeding is 1190~1210℃. Oxygen-enriched air mixed with oxygen is blown into the rear main bed air chamber. The oxygen concentration of the oxygen-enriched air is 28~29%. The minimum temperature of the rear main bed after material reduction is 1120~1140℃, and the maximum calcination temperature after material reduction is 1200~1220℃. The excess oxygen coefficient of the bed layers (front bed, front main bed and rear main bed combined) is 0.90~0.95. The calcined sand after the rear main bed is discharged through the discharge port.

[0041] In step D, the excess oxygen coefficient of the air and oxygen blown into the front bed, front main bed, and rear main bed is 0.95 (oxygen deficiency of 5%). The zinc concentrate fluctuating feeding conditions are as follows: uniform feeding (pressing) for 45 minutes, followed by 15 minutes of reducing the feeding until the temperature of the rear main bed drops to 1120~1140℃, and then feeding at the normal feeding (pressing) rate. The feeding is cyclically fluctuated under these conditions.

[0042] E. Secondary air roasting: Supplement 30-35% oxygen-enriched air into the secondary air supply hole of the fluidized bed furnace expansion section, and control the SO2 concentration at the flue gas outlet of the fluidized bed furnace to be no higher than 13%, so that the unroasted zinc concentrate sulfides and sublimated sulfur contained in the flue gas generated in steps C, D and E can enter the fluidized bed furnace expansion section for further combustion.

[0043] F. Cooling of roasted sand: The roasted sand obtained in step D is discharged into an indirect cooling cylinder through a chute and cooled to below 80°C with soft water before being sent downstream to produce products such as direct zinc oxide.

[0044] G. Flue gas treatment and dust recovery: The flue gas discharged in steps C, D, and E is subjected to heat recovery and gravity dust collection in a waste heat boiler. After the dust in the flue gas is collected by a cyclone dust collector and an electrostatic precipitator, it is sent to the flue gas acid production system to produce sulfuric acid. The boiler dust is returned to the ore blending furnace for roasting, and the dust from the cyclone dust collector and the dust from the electrostatic precipitator are sent to the wet zinc smelting process.

[0045] H. Treatment effect; The following are the specifications of a company's first-grade oxidized roasted zinc concentrate and the actual composition of the zinc concentrate fed into the furnace: Table 1. Parameters of Primary Oxidized Roasted Zinc Concentrate and Actual Zinc Concentrate Composition (w, %) of a Certain Company The quality of the calcined sand produced after calcination using this process is shown in the table below: Table 2. Quality Indicators and Quality (w, %) of Oxidized Roasted Sand from a Certain Company In this case, given that the zinc concentrate contained excessive levels of lead, lead oxide, cadmium, arsenic, and antimony, but the sulfur content met the standards, the positive and negative oxygen levels during the positive and negative air roasting were increased to effectively reduce the lead, cadmium, arsenic, and antimony content in the roasted ore.

[0046] As shown in Table 1, the primary zinc concentrate index and actual ore blending data indicate that the zinc content in the actual blend is lower than the primary oxidized roasted zinc concentrate index but higher than the secondary oxidized roasted zinc concentrate index. The sulfur content meets the primary and secondary oxidized roasted zinc concentrate indexes, while the contents of impurities such as lead, lead oxide, cadmium, and arsenic do not meet the secondary oxidized roasted zinc concentrate index requirements. Table 2 shows the oxidized roasted calcined ore quality index and calcined ore quality of a certain company. It is evident that after adopting this roasting process, among the various impurity indexes, except for slightly exceeding the standards for sulfur and antimony, the contents of other impurity elements all meet the primary roasting standard.

[0047] In this case, 20m was used. 2 Fluidized bed furnace, with a foreboard area of ​​2m² 2 The front master bed has an area of ​​10m² 2 The rear master bed has an area of ​​10 square meters. 2 The original design firing intensity was 7~7.5 t / (m). 2 After 55 days of roasting, the roasting intensity was calculated to be 8.26 t / (m²) based on monthly statistical data. 2 (d) The calcination intensity is about 10% higher than the maximum designed calcination intensity, and this calcination intensity is also more than 10% higher than the calcination intensity before adopting this process.

[0048] The present invention uses the above-mentioned process and processing system for zinc concentrate oxidative roasting, which can not only produce high-quality roasted sand with deep removal of lead, cadmium, arsenic, antimony and sulfur using lower grade zinc concentrate, but also improve the production capacity of the original equipment and achieve better economic benefits.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A roasting process for deep impurity removal from zinc concentrate, characterized in that, Includes the following steps: A. Batching: Zinc concentrate from different mines is blended to obtain zinc concentrate with zinc, sulfur, lead, cadmium, arsenic and other contents that meet the process requirements; B. Drying: The zinc concentrate prepared in step A is fed into an indirect heating drying cylinder and dried to a moisture content of 8-15%; C. Pre-roasting of the forecourt: The zinc concentrate dried in step B is fed into the forecourt of the fluidized bed furnace through the feed inlet of the fluidized bed furnace in a periodic fluctuating feeding manner. Conventional air is blown in from the forecourt air chamber at the bottom of the forecourt furnace. The air enters the forecourt pre-roasting through the air distribution plate and air cap. By adjusting the feeding amount and air volume, the forecourt fluidized bed roasting temperature is controlled to be no less than 850°C. By adjusting the air volume, fluidization is ensured and sedimentation is avoided. After pre-purification in a fluidized state, the zinc concentrate enters the main bed of the fluidized bed furnace. D. Positive and Negative Oxygen Roasting and Impurity Removal: The material pre-roasted in step C is fluidized and enters the front main bed of the fluidized bed furnace. Air is blown into the air chamber of the front main bed (or oxygen is supplemented and the oxygen content after supplementation is lower than that of the oxygen-enriched air in the rear main bed), and the front main bed is roasted in a negative oxygen (insufficient oxygen) atmosphere. The roasting temperature of the front main bed is 1100~1230℃. The material in the front main bed enters the rear main bed in a fluidized form and continues to be fluidized and roasted in the rear main bed. During the roasting process of the rear main bed, oxygen-enriched air is blown into the rear main bed through the air chamber, and the rear main bed is roasted in a positive oxygen (excess oxygen) atmosphere. The roasting temperature of the rear main bed is 0~50℃ higher than that of the front main bed. The roasted sand after roasting in the rear main bed is discharged through the discharge port. E. Secondary air roasting: The fluidized bed furnace expansion section is equipped with a secondary air (or oxygen-enriched air) replenishment hole. The unroasted zinc concentrate sulfides and sublimed sulfur contained in the flue gas generated in steps C, D, and E enter the fluidized bed furnace expansion section for further combustion. F. Calcined Sand Cooling: The calcined sand obtained in step D is discharged into a calcined sand cooler and cooled to a temperature that allows for safe transportation before being sent downstream to produce products such as zinc oxide. G. Flue gas treatment and dust recovery: The flue gas discharged in steps C, D, and E recovers heat and is subjected to gravity dust collection in a waste heat boiler. After the dust in the flue gas is collected by a cyclone dust collector and a deep dust collector, it is sent to the flue gas acid production system to produce sulfuric acid. The dust is returned to the furnace for roasting or sent to the wet zinc smelting process.

2. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step C, the highest temperature of the forebed refers to the firing temperature in the middle of the forebed during the period when the main bed reaches its highest firing temperature.

3. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step D, the positive and negative oxygen roasting refers to the process where the total amount of oxygen blown into the front bed, the front main bed, and the rear main bed is greater than the amount of oxygen required for zinc concentrate roasting, and the process where the negative oxygen roasting refers to the process where the total amount of oxygen blown into the front bed, the front main bed, and the rear main bed is less than the amount of oxygen required for zinc concentrate roasting.

4. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step D, the excess oxygen in the front main bed is lower than that in the rear main bed, and the pre-baked sand material is roasted in an atmosphere with even less oxygen in the front main bed; the bed layer is the sum of the front bed, the front main bed and the rear main bed, and the excess oxygen coefficient of the bed layer is 0.90~1.

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5. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step D, the oxygen concentration of the air in the front main bed air chamber or the oxygen-enriched air after supplementing oxygen is controlled at ≥ air oxygen content and ≤25%, and the oxygen concentration of the oxygen-enriched air in the rear main bed air chamber is controlled at ≥ air oxygen content and ≤35%, so as to obtain a good roasting effect.

6. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step D, the rear main bed air chamber and the front main bed air chamber are separated.

7. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step D, the zinc concentrate is characterized by fluctuating feeding, where the material stays in the front bed, front main bed and rear main bed for 50 to 90 minutes, that is, the fluctuating cycle is 50 to 90 minutes, and the material is discharged from the fluidized bed furnace through the discharge port after completing the fluctuating cycle roasting. During the roasting cycle, the temperature of the fluidized bed is reduced to the minimum process control range by reducing the amount of material fed. Pressing is done using a large amount of material, and the furnace temperature is restored to the maximum process temperature range by pressing. Then, the amount of material pressed, as well as the airflow and oxygen content in the front and rear main bed air chambers, are adjusted appropriately to maintain the maximum roasting temperature range of the main bed for 40-80 minutes. Afterward, the amount of material fed is reduced until the roasting temperature drops to the minimum process control temperature range. During this period, the amount of material fed, as well as the airflow and oxygen content in the front and rear main bed air chambers, are adjusted appropriately to bring the fluidized bed roasting temperature to the minimum operating temperature range. The material reduction process lasts for 10-20 minutes, and then the pressing process is restarted. The pressing and material reduction are performed in a cyclical manner.

8. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step E, the control index of the secondary air is the SO2 concentration at the outlet of the fluidized bed furnace flue gas. By supplementing the secondary air, the SO2 concentration at the outlet of the fluidized bed furnace flue gas is ensured to be no higher than 13.5%, so that the unburned concentrate carried out by the flue gas and the sublimed sulfur generated under negative oxygen conditions are fully burned, avoiding the sublimed sulfur and insufficient oxygen-sulfur ratio from affecting the subsequent flue gas acid production.

9. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step F, the calcined sand cooler is one or more of a direct cooling cylinder, an indirect cooling cylinder, or a fluidized bed cooler.

10. The roasting process for deep impurity removal from zinc concentrate according to claim 1, characterized in that: In step G, the deep dust collector is one or more multi-stage series of electrostatic precipitators and bag filters.

11. A roasting system for deep impurity removal from zinc concentrate according to any one of claims 1-10, characterized in that, It includes a ore blending module, a drying and feeding module, a drying module, a roasting and feeding module, a roasting module, and a flue gas heat recovery and dust collection module; the ore blending module, the drying and feeding module, the drying module, the feeding and feeding module, the roasting module, and the flue gas heat recovery and dust collection module are connected in sequence; The ore blending module includes a silo, a batching crane, a fume hood, a fume duct, a bag filter, and an exhaust stack. The fume hoods at each dust collection point are connected in parallel through the fume duct. The parallel fume hoods, bag filters, and exhaust stacks are connected sequentially through the duct. The drying and feeding module includes a disc feeder with a hopper and a conveying device with smoke collection function. The discharge port of the disc feeder with the hopper is directly connected to the inlet of the first-stage conveying device. The discharge port of the previous-stage conveying device is directly connected to the inlet of the next-stage conveying device. The discharge port of the last-stage conveying device is connected to the drying module and extends into the drying cylinder. Smoke hoods are installed at each dust outlet. The outlets of the smoke hoods and the smoke collection device of the conveying device with smoke collection function are connected to the inlet of the bag filter or the inlet pipe of the bag filter through pipes. The drying module includes a rotary drying cylinder, a flue gas duct, a bag filter, an exhaust stack, and a heating medium duct. The inlet of the rotary drying cylinder is connected to the outlet of the last-stage conveyor of the drying and feeding module, and the outlet of the rotary drying cylinder is directly connected to the inlet of the first-stage conveyor of the feeding submodule of the roasting and feeding module. The heating medium inlet of the rotary drying cylinder is connected to the heating medium supply duct, and the heating medium outlet of the rotary drying cylinder is connected to the heating medium return duct. The flue gas outlet of the rotary drying cylinder is connected to the bag filter through a flue gas duct, and the outlet of the bag filter is connected to the exhaust stack inlet through a flue gas duct. The rotary drying cylinder adopts an indirect heating method, and the indirect heating medium is one or more of steam, hot oil, and high-temperature flue gas. The roasting feeding and feeding module includes a conveying device with smoke collection function, an intermediate silo, and a roasting feeding device; the inlet of the first-stage conveying device with smoke collection function is connected to the outlet of the rotary drying kiln, the outlet of the upper-stage conveying device is directly connected to the inlet of the lower-stage conveying device, and the outlet of the last-stage conveying device is connected to the roasting feeding device, which feeds the material into the fluidized bed furnace. The conveying equipment with smoke collection function is one or more of belt conveyors, bucket elevators, screw conveyors, and chain tube conveyors; the roasting feeding device is one or more of disc feeders with smoke collection function, belt conveyors, screw feeders, and chutes. The roasting module is a fluidized bed roasting device with a special structure, namely a fluidized bed furnace. The fluidized bed furnace, from bottom to top, consists of a wind chamber, a wind chamber air distribution plate, a wind cap, a roasting section, a transition section, an expansion section, and a flue gas outlet. The roasting section is the fluidized bed roasting layer. Horizontally, the roasting section consists of a feed inlet, a front bed, a front main bed, a rear main bed, and a discharge outlet. The discharge outlet connects to the inlet of the roasted sand cooling cylinder, and the roasted sand is cooled to obtain a highly purified product roasted sand. The wind chamber is divided into a front bed wind chamber, a front main bed wind chamber, and a rear main bed wind chamber. The front bed wind chamber is independent or forms an integral wind chamber with the front main bed, while the rear main bed uses a separate rear wind chamber. The inlet of the front bed wind chamber connects to the outlet of the furnace bottom fan, and the inlet of the front wind chamber also connects to the furnace bottom fan outlet and is connected to an oxygen pipeline. The inlet of the rear wind chamber connects to the furnace bottom fan outlet and an oxygen pipeline. The transition section of the fluidized bed furnace is equipped with a secondary air inlet, and the secondary air connects to the furnace bottom fan outlet pipeline and an oxygen pipeline. The flue gas heat recovery and dust collection module includes a waste heat boiler, one or more cyclone dust collectors in series, a relay fan, and a deep dust collector. The deep dust collector is one or more electrostatic precipitators and bag filters in series. The flue gas outlet at the top or upper part of the fluidized bed furnace is connected to the waste heat boiler, the outlet of the waste heat boiler is connected to the inlet of the cyclone dust collector, the outlet of the last cyclone dust collector is connected to the inlet of the first electrostatic precipitator or bag filter, the outlet of the previous electrostatic precipitator or bag filter is connected to the inlet of the next electrostatic precipitator or bag filter, and the outlet of the last electrostatic precipitator or bag filter is connected to the subsequent flue gas acid production system.

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