A method and system for producing zinc calcined sand from zinc-containing waste based on heat fractionation and flue gas recycling

Abstract

This invention discloses a method and system for producing zinc calcined sand from zinc-containing waste based on calorific value classification and flue gas recycling. First, the zinc-containing hazardous waste is classified according to its calorific value. High-calorific-value raw materials are self-heated and roasted in a fluidized bed roaster (1), while low-calorific-value raw materials are supplemented and roasted in a rotary kiln (2), achieving efficient energy utilization. Then, the zinc-containing flue gas dust and sludge collected through flue gas purification are returned to the rotary kiln (2) for cyclic roasting via a closed conveying device (8). Combined with a multi-stage flue gas purification process involving "dry + wet + deep treatment" (gravity settling chamber (4), scrubbing tower (5), desulfurization device (6), and electrostatic precipitator (7)), efficient zinc recovery and ultra-low emissions are achieved. The total zinc recovery rate of this invention reaches 90%-95%, reducing energy consumption by more than 20% compared to traditional processes, and the particulate matter in the exhaust gas is ≤10mg / m³. 3 SO2 ≤ 35 mg / m³ 3 The products meet industry standards, achieving the unified treatment, resource recycling, and environmental compliance of zinc-containing hazardous waste, and possess significant commercial value and social benefits.

Description

Technical Field

[0001] This invention relates to the fields of non-ferrous metal metallurgy and solid waste resource utilization, specifically to a co-processing system for zinc-containing hazardous waste (including zinc flue ash, zinc ash, zinc oxide, etc.) based on heat grading and closed-loop flue gas recycling, as well as a zinc calcined sand production method and system, which is applicable to the clean recycling and high-value utilization of zinc-containing hazardous waste on an industrial scale. Background Technology

[0002] Zinc-containing waste (such as flue ash from the steel industry, zinc ash from galvanizing, and zinc smelting slag) is a typical hazardous waste with a zinc content of 30%-65%, possessing extremely high recycling value. However, due to its high content of harmful impurities such as fluorine, chlorine, and lead, it is difficult to dispose of. Traditional processes for producing zinc calcined ore from zinc-containing waste have three major pain points:

[0003] Serious energy waste: The difference in calorific value of raw materials is not distinguished. All raw materials are roasted in the same rotary kiln, which requires a large amount of external fuel. The chemical heat of high-calorific-value raw materials is not utilized, resulting in high energy costs.

[0004] Low resource recovery rate: The zinc-containing dust (zinc content 25%-40%) and sludge collected during the flue gas purification process are mostly disposed of as hazardous waste due to their high impurity content, resulting in a total zinc recovery rate of only about 80%, which leads to serious resource waste.

[0005] Environmental compliance is difficult: the flue gas treatment process is simple, mostly using a single wet scrubbing method, which does not completely remove acidic gases and particulate matter, easily causing equipment corrosion, and the exhaust emissions are difficult to meet ultra-low standards, resulting in significant environmental risks.

[0006] Poor system synergy: The lack of integrated design in raw material processing, roasting, purification, and recycling hinders the efficient and coordinated disposal of zinc-containing hazardous waste, failing to balance economic and environmental benefits. Therefore, developing an integrated process and system capable of graded heat utilization, flue gas recycling, and ultra-low emissions is crucial for solving the challenges of zinc-containing hazardous waste disposal, aligning with the industry's green development orientation and market demands. Summary of the Invention

[0007] Purpose of the invention

[0008] To address the shortcomings of existing technologies, the core objective of this invention is to provide a method and system for producing zinc calcined sand from zinc-containing waste based on heat grading and flue gas recycling, achieving: ① graded utilization of raw material calorific value to reduce external fuel consumption; ② construction of a closed-loop flue gas recycling system to increase zinc recovery rate to over 90%; ③ optimization of multi-stage flue gas purification to achieve ultra-low emissions; ④ integrated and collaborative treatment of zinc-containing hazardous waste, balancing commercial value and social benefits.

[0009] Technical Solution and Invention Features: Graded Utilization of Heat; Calcination Process Design Based on Material Characteristics

[0010] One of the core innovations of this invention is "heat classification," which involves designing roasting schemes based on the calorific value of zinc-containing hazardous waste: for high-calorific-value raw materials (mainly zinc-containing flue ash) with a calorific value ≥ 2000 kcal / kg, a fluidized bed roaster (1) is used for self-heating roasting, making full use of its own chemical heat to maintain the roasting reaction without the need for additional fuel; for low-calorific-value raw materials with a calorific value < 2000 kcal / kg, a rotary kiln (2) is used for roasting, and pulverized coal is added by a pulverizer (3) for combustion assistance. This design optimizes energy flow from the source, reducing energy consumption by more than 20% compared to traditional processes. At the same time, by precisely controlling the process parameters of the two roasting devices (wind speed of the fluidized bed roaster (1) (monitored by wind speed monitor (19)) and material layer height (monitored by material layer height sensor (20)); rotation speed of the rotary kiln (2) (controlled by speed regulator (22)) and filling rate), it ensures that zinc is efficiently converted into zinc oxide and impurities are fully volatilized.

[0011] Closed-loop dust recycling: a full-process zinc resource recovery system

[0012] Another core innovation is "dust recycling," which involves constructing a closed-loop recycling system of "roasting-purification-recovery-re-roasting." The zinc-containing dust (coarse particles) collected in the gravity settling chamber (4) and the zinc-containing sludge collected in the wet alkaline scrubbing tower (5) during the flue gas purification process are all returned to the mixer (21) of the rotary kiln (2) for re-roasting via a closed conveying pipeline (30) and a screw conveyor (31), completely breaking the loss path of this part of the zinc in the traditional process. The returned material accounts for 5%-15% of the total zinc material in the system, which not only solves the problem of hazardous waste disposal of dust and sludge, but also increases the total zinc recovery rate from 80%-85% to 90%-95%, maximizing resource utilization. At the same time, after the zinc roasted sand is cooled by the cooler (9) and screened by the vibrating screen (10), the fine powder under the screen is incorporated into the recycling system through the under-screen outlet (10-1), further improving the recovery efficiency. Multi-level synergistic purification: environmental protection guarantee for ultra-low emissions

[0013] The system is equipped with a four-stage flue gas purification system consisting of dry settling, wet alkaline scrubbing, desulfurization, and electrostatic precipitator, forming a synergistic purification logic: the gravity settling chamber (4) first removes coarse particulate matter, reducing the subsequent scrubbing load; the wet alkaline scrubbing tower (5) uses sodium hydroxide solution, and the alkaline solution is automatically replenished through the pH online monitoring instrument (28), efficiently absorbing acidic gases such as HCl and HF; the desulfurization device (6) adopts the limestone-gypsum method, and the slurry is evenly sprayed through the spray layer (6-1) to ensure a desulfurization efficiency of ≥95%; the electrostatic precipitator (7) removes fine particulate matter and acid mist, ultimately achieving particulate matter in the tail gas ≤10mg / m³. 3 SO2 ≤ 35 mg / m³ 3 It is far below the ultra-low emission standard, solving the problem of traditional processes failing to meet environmental protection standards.

[0014] System Integration and Collaboration: A Complete Solution for Hazardous Waste Disposal

[0015] This invention is not an improvement on a single step, but rather the construction of an integrated system of "raw material processing - graded roasting - flue gas purification - flue gas dust circulation - product post-processing". Each unit is closely connected and operates in coordination: the magnetic separator (11) in the raw material pretreatment stage removes iron and recovers iron impurities to the iron impurity recovery bin (17) while avoiding interference from iron impurities; the central control unit (33) realizes real-time control of key parameters such as temperature, wind speed, and pH value to ensure process stability; and the closed conveying pipeline (30) prevents secondary pollution from flue gas dust. The entire system realizes the coordinated disposal of zinc-containing hazardous waste, taking into account the three major goals of resource recovery, energy consumption reduction, and environmental protection compliance, highlighting its systematic nature and practicality. Attached Figure Description

[0016] Figure 1 This is a flowchart of the overall process of the present invention;

[0017] Figure 2 This is a schematic diagram of the raw material processing and classification module;

[0018] Figure 3 This is a schematic diagram of the heat-stage roasting module;

[0019] Figure 4 This is a schematic diagram of the flue gas purification module;

[0020] Figure 5 This is a schematic diagram of the smoke and dust circulation module;

[0021] Figure 6 This is a schematic diagram of the product post-processing module;

[0022] Figure 7 This is a schematic diagram of the control module;

[0023] Figure 8 A comparison chart of parameters for heat-stage roasting;

[0024] Figure 9 This is a graph showing the relationship between zinc recovery rate and the proportion of recycled materials.

[0025] Figure 10 This is a comparison chart of flue gas pollutant emissions. Detailed Implementation

[0026] Example

[0027] Raw material processing and classification: Zinc-containing hazardous waste was selected as zinc flue ash (Zn 45%, calorific value 2600 kcal / kg), zinc ash (Zn 55%, calorific value 750 kcal / kg), and zinc oxide (Zn 60%, calorific value 600 kcal / kg), and mixed in a ratio of 65%:25%:10%, with a zinc content of 43.2%. After iron removal by a 1200mT magnetic separator (11) (iron removal rate 93%), crushing by a crusher (12), and screening by a screening machine (13) to a particle size ≤5mm, it was classified by a calorific value analyzer (14). The zinc flue ash entered the high calorific value raw material silo (15), and the mixed zinc ash and zinc oxide entered the low calorific value raw material silo (16).

[0028] Heat-graded roasting: High-calorific-value raw materials are fed into the fluidized bed roasting furnace (1) through a quantitative feeder (18), with the wind speed controlled at 1.5 m / s (monitored by a wind speed monitor (19)) and the material layer height at 1.0 m (monitored by a material layer height sensor (20)). The self-heating roasting temperature is 1100℃, and the temperature is maintained for 2 hours. Low-calorific-value raw materials are fed into a mixer (21), mixed with circulating materials, and then fed into a rotary kiln (2). Pulverized coal (fixed carbon content 68%) is injected into the kiln by a pulverizer (3) to aid combustion. The rotation speed is controlled at 2 r / min (controlled by a speed regulator (22)), the filling rate is 12%, and the roasting temperature is 1250℃ (monitored by a temperature monitoring device (23)). The temperature is maintained for 2.5 hours.

[0029] Flue gas purification and material collection: The flue gas from the roasting furnace enters the gravity settling chamber (4) (residence time 12s) through the flue gas duct (24), and the flue dust (Zn 32%) is collected to the flue dust collection bin (25); then it enters the wet alkaline scrubbing tower (5), and is sprayed with 10% sodium hydroxide solution (liquid-to-gas ratio 12L / m). 3 The pH is controlled at 9-10 (controlled by an online pH monitor (28), and alkali is replenished through an alkali replenishment system (27)). Zinc-containing sludge (Zn 20%) is collected. The flue gas passes through a desulfurization device (6) (spraying limestone slurry in a spray layer (6-1), with a desulfurization efficiency of 96%) and an electrostatic precipitator (7) (operating voltage 45kV), and is then drawn out by an induced draft fan (29). The particulate matter concentration in the tail gas is 8mg / m³. 3 SO2 concentration 28 mg / m³ 3 .

[0030] Dust collection and post-processing: Dust from the dust collection bin (25) and zinc-containing sludge from the sludge outlet (5-1) of the wet alkaline scrubbing tower (5) are returned to the mixer (21) of the rotary kiln (2) via a closed conveying pipe (30) and a screw conveyor (31). The returned material accounts for 10% of the total zinc material in the system. Zinc calcined sand discharged from the overflow sand outlet (1-1) of the fluidized bed roasting furnace (1) and the kiln head sand outlet (2-1) of the rotary kiln (2) is cooled to room temperature by a cooler (9) and screened by a vibrating screen (10) (5mm screen hole). The undersize material is the finished zinc calcined sand (Zn 56.8%, F 0.016%, Cl 0.023%), which enters the finished product bin (32). The fine powder undersize is returned to the crusher for crushing and then re-enters the vibrating screen for circulation.

[0031] Implementation effect

[0032] The finished zinc calcined sand meets the YS / T883-2013 standard, with a total zinc recovery rate of 93.2%, which is 13 percentage points higher than the traditional process; the system coal consumption is 220 kg / t zinc calcined sand, which is 28% lower; the exhaust gas emission indicators meet the ultra-low standard, realizing the clean, efficient and high-value utilization of zinc-containing hazardous waste.

[0033] Beneficial effects

[0034] Outstanding innovation: The combined design of "heat-stage roasting" and "closed-loop flue gas circulation" has not been disclosed in existing technologies. It solves the technical problems of energy waste, low recovery rate and failure to meet environmental protection standards in traditional processes, and has outstanding substantive features and significant progress.

[0035] Highly efficient resource recycling: The total zinc recovery rate reaches 90%-95%, and valuable elements such as iron and lead are recovered simultaneously, significantly improving resource utilization, reducing production costs, and demonstrating outstanding commercial value.

[0036] Environmentally friendly and ultra-low emission: The four-stage flue gas purification system achieves deep removal of pollutants, and the exhaust emissions are better than the ultra-low standard, with no secondary pollution and significant social benefits;

[0037] Strong system synergy: The integrated design is adapted to the needs of co-processing zinc-containing hazardous waste. The equipment has a high degree of integration and automation, and can be directly applied to industrial-scale production, with broad prospects for promotion. High product quality: The finished zinc calcined sand has low impurity content, meets industry standards, and can meet the downstream needs of high-end hydrometallurgical zinc smelting, with high added value.

Claims

1. A method for producing zinc calcined sand from zinc-containing waste based on heat fractionation and flue gas recycling, characterized in that, Includes the following steps: Raw material calorific value classification and pretreatment: Zinc-containing hazardous waste (containing at least one of zinc flue ash, zinc ash, zinc oxide, and zinc smelting slag, with a zinc content of 30-65%) is subjected to magnetic separation to remove iron (magnetic field strength 1000-1500mT, iron removal rate ≥90%), crushing and screening (particle size ≤5mm), and then classified into high-calorific-value raw materials (≥2000 kcal / kg, mainly zinc flue ash) and low-calorific-value raw materials (<2000 kcal / kg) according to calorific value. Heat-graded roasting: High-calorific-value raw materials are fed into a fluidized bed roasting furnace (1) and roasted using their own calorific value. The furnace wind speed is controlled at 1.2-1.8 m / s and the material layer height is controlled at 0.8-1.2 m. Low-calorific-value raw materials are fed into a rotary kiln (2) and pulverized coal (fixed carbon content ≥65%) is injected through a pulverizer (3) to supplement fuel roasting. The rotary kiln (2) speed is controlled at 1.5-3 r / min and the filling rate is controlled at 8%-15%. Both roasting methods control the temperature at 1000-1300℃ and hold for 1.5-3 h to convert zinc into zinc oxide to form zinc roasted sand. Fluorine, chlorine, lead, and sulfur compounds volatilize and enter the flue gas. Multi-stage flue gas purification and material collection: The flue gas from the fluidized bed roaster (1) and the rotary kiln (2) is combined and sequentially subjected to dry settling (gravity settling chamber (4), residence time ≥10s) and wet alkaline scrubbing (8%-12% sodium hydroxide solution, liquid-to-gas ratio 8-15L / m³). 3 , scrubbing tower (5)), desulfurization (limestone-gypsum method, desulfurization efficiency ≥95%, desulfurization device (6)), electrostatic precipitator (operating voltage 30-60kV, electrostatic precipitator (7)) treatment, and exhaust gas is discharged in compliance with standards; collect dry sedimentation dust (zinc content 25-40%) and wet alkaline washing zinc-containing sludge (zinc content 15-25%); Closed-loop circulation of flue gas: The flue gas collected by the multi-stage purification and material collection process is returned to the rotary kiln (2) batching system through a closed conveying device (8), mixed with fresh low-calorific-value raw materials and then roasted. The returned material accounts for 5%-15% of the total zinc material in the system. Post-processing of the product: The zinc roasted sand discharged from the fluidized bed roasting furnace (1) (overflow sand discharge port (1-1)) and the rotary kiln (2) (kiln head sand discharge port (2-1)) is cooled by the cooler (9) and screened (vibrating screen (10), screen hole 0.15mm). The material on the screen is the finished zinc roasted sand, and the fine powder under the screen is incorporated into the circulating material. The final total zinc recovery rate reaches 90%-95%.

2. The method according to claim 1, characterized in that, In the raw material calorific value classification and pretreatment step, the mixing ratio of zinc-containing hazardous waste is 60-70% zinc flue ash, 20-30% zinc ash, and 5-10% zinc oxide. After mixing, the zinc content is stabilized at 40-45%.

3. The method according to claim 1, characterized in that, In the step-by-step heat-graded roasting, the air distribution plate (1-2) of the fluidized bed roasting furnace (1) is a wind cap structure, and the ventilation uniformity error is ≤10%; the kiln body (2-2) of the rotary kiln (2) has an inclination angle of 3°-5° and is lined with high-temperature refractory material (2-3).

4. The method according to claim 1, characterized in that, In the multi-stage purification of flue gas and material collection process, the pH of the circulating liquid in the wet alkaline scrubbing tower (5) is controlled at 8-10, and sodium hydroxide solution is automatically replenished by the pH online monitoring instrument (28).

5. The method according to claim 1, characterized in that, The finished zinc calcined sand meets the following specifications: Zn≥55%, F≤0.02%, Cl≤0.03%, Pb≤1.5%, which conforms to the YS / T883-2013 standard.

6. A system for implementing the method according to any one of claims 1-5, characterized in that, include: Raw material processing and classification unit: Magnetic separator (11), crusher (12), screening machine (13), calorific value analyzer (14) and dual raw material bins (high calorific value raw material bin (15) and low calorific value raw material bin (16)) are connected in series. Magnetic separator (11) is connected to iron impurity recovery bin (17). Heat classification roasting unit: Fluidized bed roasting furnace (1) and rotary kiln (2) are set in parallel. Fluidized bed roasting furnace (1) is connected to high calorific value raw material bin (15) through quantitative feeder (18) and equipped with wind speed monitor (19) and material layer height sensor (20). Rotary kiln (2) is connected to low calorific value raw material bin (16) through mixer (21) and equipped with pulverized coal injector (3), speed regulator (22) and temperature monitoring device (23). Flue gas multi-stage purification unit: Flue gas merging pipe (24) and gravity settling chamber (4) (bottom) are connected in series along the flue gas flow direction. The system includes a dust collection chamber (25), a wet alkaline scrubbing tower (5) (equipped with a circulating liquid tank (26), an alkaline replenishment system (27), an online pH monitor (28)), a desulfurization device (6), an electrostatic precipitator (7), and an induced draft fan (29); a dust circulation unit including a closed conveying pipeline (30) and a screw conveyor (31), with the dust collection chamber (25), the sludge discharge port (5-1) of the wet alkaline scrubbing tower (5), and the mixer (21) of the rotary kiln (2) respectively at both ends; a product post-processing unit connected in sequence to a cooler (9), a vibrating screen (10), and a finished product silo (32), with the undersize discharge port (10-1) of the vibrating screen (10) connected to the screw conveyor (31) of the dust circulation unit; and a central control unit (33) electrically connected to the monitoring instruments and actuators of each unit to achieve automatic parameter control and equipment linkage.

7. The system according to claim 6, characterized in that, The desulfurization device (6) is a spray tower type structure with three spray layers (6-1) inside, and is equipped with a limestone slurry preparation system (34) and a gypsum dewatering device (35).

8. The system according to claim 2, characterized in that, The sealed conveying pipeline (30) of the dust circulation unit is made of wear-resistant and corrosion-resistant material, and the conveying capacity of the screw conveyor (31) can be dynamically adjusted according to the amount of circulating material.

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