A process system for co-processing and carbon sequestration of fly ash by double rotary kiln method

Abstract

The application relates to the technical field of resource recycling, and particularly discloses a double-rotary-kiln method fly ash collaborative grading and carbon fixation process system, which comprises the following steps: firstly, pretreating Na2SO4 type raw materials such as mirabilite and SDS sodium-based desulfurization ash, removing crystallization water and grinding to below 200 meshes, then reducing roasting in a two-stage three-blade type self-gravity semi-suspension closed reduction rotary kiln, and simultaneously recycling high-purity S and CO2; after being proportioned according to the mass ratio of the roasting solid-phase Na2O to fly ash SiO2+Al2O3 of 0.6-0.8:1, the mixture is hot-charged into a three-blade type self-gravity semi-suspension closed rotary kiln for calcination; after the calcined material is cooled, water immersion and pressure filtration are carried out, and the water is recycled. The leaching solid phase is subjected to magnetic separation to extract metallic iron, and the tailings are used as steelmaking auxiliary materials; the leaching liquid phase is subjected to supergravity carbonization to obtain sodium carbonate, the remaining liquid phase is acidified, separated and purified, then low-temperature dehydration crystallization is carried out, hydrated SiO2 and anhydrous aluminum chloride are prepared, and an integrated process system of solid waste collaboration, resource recycling and low-carbon environmental protection is realized, which has environmental benefits and economic benefits, and promotes the technical upgrading of the solid waste resource industry.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, specifically relating to a dual rotary kiln method for the synergistic fractionation and carbon fixation of fly ash. Background Technology

[0002] In the current industrial sector, traditional treatment processes for fly ash and raw materials such as sodium sulfate and sodium SDS-based desulfurization ash, which are mainly composed of Na2SO4, suffer from multiple problems, including significant technical bottlenecks, poor energy-saving and carbon-reduction effects, difficulty in pollution control, and weak industrial adaptability. Furthermore, the lack of cross-industry collaborative treatment mechanisms makes it impossible to meet the requirements of circular economy development and achieve the goals of "full solid waste disposal, full resource recovery, full carbon emission utilization, and high product added value." Specific technical deficiencies are as follows:

[0003] I. Fly ash treatment process: low separation rate, high energy consumption, significant carbon emissions, and ineffective release of resource value.

[0004] Fly ash is a core solid waste from coal-fired power plants, and existing extraction technologies such as limestone sintering and hydrochloric acid extraction have significant shortcomings. Firstly, there is a bottleneck in the differentiation of all components. Traditional processes often focus on a single extraction target. For example, the limestone sintering method can only recover 15% to 20% of Al2O3, while the remaining SiO2 and Fe2O3 are landfilled as calcium silicate slag, resulting in a resource utilization rate of less than 60%. Although the hydrochloric acid method can extract Al2O3 and SiO2 simultaneously, the acid consumption is as high as 1.2 to 1.5 tons / ton of fly ash (30% concentration hydrochloric acid), and the by-product FeCl3 has a purity of less than 80% and has no market value, forming an inefficient model of "extracting one type and wasting multiple types". Secondly, the energy-saving and carbon-reduction effects are poor. High-temperature calcination is the core high-energy-consuming process. The limestone sintering method requires calcination at 1200℃~1400℃, consuming 800~1000 kg of standard coal per ton of alumina. Moreover, calcination relies on coal-fired heating, and the carbon emissions during the treatment of each ton of fly ash reach 0.8~1.2 tons of CO2. Without the support of carbon capture devices, the direct emission of CO2 contradicts the goal of "low-carbon disposal". Thirdly, pollution control is a prominent challenge. The acid and alkali leaching process generates a large amount of acidic / alkali-containing waste liquid. After hydrochloric acid leaching, the residual liquid has a pH ≤ 2. Neutralization treatment requires 0.3~0.5 tons of lime per ton of waste liquid. The generated CaCl2 and FeCl3 salt slag are hazardous solid wastes, with disposal costs reaching 600~800 yuan / ton. Some processes use ammonia water to adjust the pH, which easily generates NH3 volatilization pollution. Waste gas treatment requires additional investment in desulfurization and denitrification equipment, and environmental protection operation and maintenance costs account for 30%~40% of the total operating costs. Fourth, it has poor industrial adaptability. Traditional processes have strict requirements for the purity of raw materials, requiring the fly ash to have an Al2O3 content of ≥28% and impurities (CaO, MgO) of ≤5%, which cannot handle low-alumina fly ash (Al2O3 ≤15%). Moreover, the daily processing capacity of a single production line is only 50-100 tons, and expanding the capacity requires repeated construction, with equipment investment costs exceeding 5 million yuan per line, making it difficult to meet the "ten-thousand-ton-level" fly ash disposal needs of power plants.

[0005] II. Processing technology using Na2SO4 as the main raw material, such as Glauber's salt and sodium SDS-based desulfurization ash: High consumption and low efficiency, serious pollution, lack of carbon recycling, and hindering green transformation.

[0006] Traditional processing methods such as evaporation crystallization and causticization have multiple drawbacks. First, their energy-saving and carbon-reduction effects are significantly insufficient. Evaporation crystallization requires heating the sodium sulfate solution to 100℃~120℃ to evaporate the water, resulting in an energy consumption of 800~1200 kWh / ton of anhydrous sodium sulfate per unit product. Moreover, heating largely relies on coal-fired boilers, with an energy utilization efficiency of only 30%~40%. The causticization method for producing soda ash requires a high-temperature reaction of 800℃~900℃, with energy consumption per ton of soda ash far exceeding that of this process. Furthermore, it lacks a carbon capture design. Theoretically, the sodium sulfate reduction process can produce 0.6 tons of CO2 / ton of Na2SO4. Traditional processes only emit CO2 as waste gas, failing to achieve carbon resource recovery. Secondly, pollution control is difficult and costly. Regarding exhaust gas, traditional roasting uses an air atmosphere, where sulfur easily generates SO2 (emission concentration reaches 800-1200 mg / m³), requiring an ammonia desulfurization system. The cost of desulfurizing agent consumption is 150-200 yuan / ton of mirabilite, and the byproduct ammonium sulfate has a narrow market and is prone to secondary accumulation. Regarding wastewater, the saline wastewater (Na⁺ concentration ≥50 g / L) generated during the leaching and separation process is often directly discharged, leading to soil salinization. If treated to reuse standards (Na⁺ ≤1 g / L), a reverse osmosis + evaporation crystallization process is required, with treatment costs reaching 30-50 yuan / ton of water. Regarding solid waste, the CaSO4 residue produced by the causticization method has a purity ≤85%, making it unsuitable as a building material raw material and requiring landfill disposal. Each ton of mirabilite generates 0.3-0.5 tons of this solid waste, requiring 0.1 mu / thousand tons of landfill space, which does not meet the requirements for "zero-waste factory" construction. Third, there are bottlenecks in resource recycling and industrialization. Traditional processes do not form a closed-loop system of elements. After Na2O in Glauber's salt is converted into Na2CO3, it needs to be sold separately and cannot be used in conjunction with other solid wastes such as fly ash. Material transportation costs account for 20% to 25% of the total cost. Moreover, the equipment has high requirements for the purity of Glauber's salt (Na2SO4 ≥ 95%) and cannot process raw materials such as salt-containing Glauber's salt (containing NaCl ≥ 10%) and SDS sodium-based desulfurization ash. Additional impurity removal processes are required, which increases the complexity of the process. The investment payback period for a single production line is as long as 5 to 8 years, which limits the promotion of industrialization.

[0007] III. Lack of Cross-Industry Collaborative Disposal: Fragmented solid waste treatment and dispersed carbon emission reduction result in low overall efficiency.

[0008] In existing technologies, the disposal of fly ash and other solid wastes, primarily composed of Na2SO4 (such as sodium sulfate and SDS sodium-based desulfurization ash), are mostly handled through independent processes. This lack of a cross-industry co-processing system for solid waste disposal, spanning power, chemical, and steel sectors, has led to a series of problems. Firstly, there is a compounding waste of resources. The SiO2 and Al2O3 in fly ash require the purchase of soda ash (Na2CO3) as an activator, while the Na2O in sodium sulfate requires the purchase of silicon sources (quartz sand) to prepare sodium silicate. When treated separately, the cost of purchasing raw materials from each accounts for 40%–50% of the total raw material cost, indicating a lack of resource optimization design for synergistic utilization. Secondly, the carbon reduction effect is fragmented. When fly ash and sodium sulfate are treated separately, carbon emissions are 0.8–1.2 tons of CO2 / ton and 0.6 tons of CO2 / ton, respectively, with no synergistic carbon capture and reuse design. The carbon reduction efficiency is far lower than that of the co-processing model. Third, the industrialization cost is high. If two types of solid waste are to be treated at the same time, two independent production lines need to be built, with equipment investment costs exceeding 10 million yuan. Moreover, the environmental protection equipment such as desulfurization and waste resource recycling of the two systems cannot be shared, resulting in repeated investment in operation and maintenance costs. The overall economic benefits are 50% to 60% lower than those of the collaborative process.

[0009] In summary, existing technologies for treating fly ash and sodium sulfate, sodium sulfate, and sodium SDS-based desulfurization ash (which are mainly composed of Na2SO4) share common problems such as low separation rate, high energy consumption, heavy pollution, high carbon emissions, and difficulty in industrialization. Furthermore, the lack of cross-industry collaborative treatment mechanisms makes it difficult to balance resource efficiency, environmental benefits, and economic benefits in solid waste treatment. There is an urgent need for an innovative process to achieve the collaborative disposal of the two types of solid waste, full-component resource recovery, CO2 capture and reuse, and high-value product preparation, thereby constructing a green and low-carbon solid waste collaborative treatment system. Summary of the Invention

[0010] The purpose of this invention is to provide a dual rotary kiln method for the synergistic differentiation and carbon fixation of fly ash, in order to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A dual-rotary kiln method for the synergistic differentiation and carbon fixation of fly ash includes the following steps:

[0013] Includes the following steps:

[0014] S1. Pre-treat the raw materials of sodium sulfate and sodium SDS desulfurization ash, which are mainly composed of Na2SO4, remove the water of crystallization from the raw materials, and then grind the raw materials to below 200 mesh.

[0015] S2. Reduction Roasting: The finely ground raw material is fed into a two-stage, three-lobe, gravity-driven, semi-suspended, closed rotary kiln for reduction. Under pure oxygen conditions, it is preheated in the first stage of the kiln at 500℃±20℃. The fuel and reducing agent used for preheating are natural gas, coal, CO, or pure CO produced in the second stage of the kiln. After preheating, the material enters the second stage of the kiln and continues to roast under pure oxygen conditions at 750℃~800℃±20℃.

[0016] Reaction formula:

[0017] Na2SO4+3CO→Na2O+S↑+3CO2↑

[0018] 2CO + O2 → 2CO2↑

[0019] 2Na2SO4+3C→2Na2O+2S↑+3CO2↑

[0020] 2C++O2→2CO↑

[0021] S3, S, and CO2 recovery:

[0022] The gas phase generated by the two-stage three-lobe self-gravity semi-suspended closed reduction rotary kiln is first treated by a sulfur recovery device to recover sulfur, and then enters a CO2 capture device to recover CO2. The recovered CO2 is reused in the subsequent high gravity carbonization reactor. The flue gas after sulfur and CO2 recovery is then treated by desulfurization, denitrification and dust removal before being discharged.

[0023] S4, Co-calcination:

[0024] The raw materials are proportioned according to the mass ratio of Na2O in the solid material generated by the reaction in a two-stage three-lobe gravity semi-suspended closed reduction rotary kiln to the combined SiO2+Al2O3 in fly ash, which is 0.6~0.8:1. The proportioned material is then hot-charged into the three-lobe gravity semi-suspended closed rotary kiln for calcination. Reaction formula:

[0025] FeO + C → Fe + CO↑

[0026] Na₂O + CO₂ → Na₂CO₃

[0027] 2SiO2 + Na2O → Na2O•2SiO2

[0028] Al₂O₃ + Na₂O → 2NaAlO₂

[0029] S5. Water leaching:

[0030] After the calcined material is cooled to below 500℃ by heat exchange, it is sent to a water leaching reactor for water leaching treatment. The leaching slurry is separated by pressure filtration, and the water after pressure filtration is recycled.

[0031] S6. Solid-phase separation and utilization:

[0032] The leachate solid phase obtained by pressure filtration is fed into a magnetic separator to separate reduced metallic iron. The tailings remaining after magnetic separation are used as auxiliary materials for steelmaking.

[0033] S7, Hypergravity Carbonization:

[0034] The leachate obtained by pressure filtration, including sodium silicate and sodium aluminate, is sent into a high gravity carbonization reactor for carbonization reaction. The reactants after carbonization reaction are separated by pressure filtration to obtain solid sodium carbonate.

[0035] Reaction formula:

[0036] 2NaAlO2+Na2O·2SiO2+2CO2+3H2O→2Na2CO3+2Al(OH)3·2SiO2+2Na +

[0037] S8. Acidification and purification:

[0038] The liquid phase obtained by pressure filtration of carbonization reaction is sent to acidification system for acidification treatment. The acidification product is separated and purified to obtain hydrated SiO2 and hydrated aluminum chloride. The hydrated aluminum chloride is evaporated and dehydrated at low temperature of 150℃~250℃ to obtain anhydrous aluminum chloride.

[0039] Al(OH)3•2SiO2+3HCl+3H2O→2(SiO2•H2O)+AlCl3•6H2O

[0040] AlCl3•6H2O AlCl3 + 6H2O.

[0041] Preferably, the coal in S2 is high-sulfur coal.

[0042] Preferably, the ratio of Na2SO4 raw material, mainly sodium sulfate and SDS sodium-based desulfurization ash, to fly ash in S2 is 0.6 to 0.8:1 by mass of Na2O to SiO2+Al2O3.

[0043] Preferably, the reduction rate of Na2O during the reduction roasting process described in S2 is >99.5%.

[0044] Preferably, the two-stage three-blade gravity semi-suspended reduction rotary kiln described in S2 has gravity semi-suspended material characteristics, and its kiln material filling rate is above 20%.

[0045] Preferably, the sulfur produced in S3 has a purity greater than 99%.

[0046] Preferably, the purity of the CO2 produced in S3 is greater than 99%.

[0047] Preferably, the three-bladed gravity semi-suspended closed rotary kiln described in S4 has gravity semi-suspended material characteristics, and its kiln material filling rate is above 20%.

[0048] Preferably, the sodium carbonate, hydrated SiO2 and anhydrous aluminum chloride obtained in S5 have a purity of over 99%, and the metallization rate of the reduced metallic iron is over 98%.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] This invention achieves the efficient resource utilization of raw materials, mainly Na2SO4 such as sodium sulfate and SDS sodium-based desulfurization ash, and fly ash through an innovative dual rotary kiln synergistic process. It breaks through the bottlenecks of traditional processes in terms of resource utilization rate, energy consumption control, environmental performance, product value and industrial adaptability.

[0051] 1. The comprehensive utilization rate of resources has been significantly improved, achieving "full-component and graded" recycling.

[0052] 1) Synergistic disposal and high-value conversion of dual solid wastes: Traditional processes only extract sodium from raw materials mainly composed of Na2SO4, such as mirabilite and SDS sodium-based desulfurization ash, or extract aluminum from fly ash, with a resource utilization rate of less than 60%. This invention achieves full component recovery of mirabilite (containing Na2SO4) and fly ash (containing SiO2, Al2O3, and FeO) through the synergistic reaction of mirabilite (containing Na2SO4) and fly ash (containing SiO2, Al2O3, and FeO). Na2O in raw materials mainly composed of Na2SO4, such as mirabilite and SDS sodium-based desulfurization ash, is converted into sodium carbonate, and sulfur is converted into sulfur with a purity of >99%. SiO2 in fly ash is converted into hydrated SiO2, Al2O3 is converted into anhydrous aluminum chloride with a purity of >99%, and FeO is reduced to metallic iron with a metallization rate of >98%. The tailings can also be used as steelmaking auxiliary materials. The overall resource utilization rate is increased to over 95%, truly achieving "zero-waste" disposal.

[0053] 2) Element recycling closed loop construction: High-purity CO2 (purity > 99%) recovered in the process is directly reused in the supergravity carbonization reactor to replace purchased CO2 raw materials; water in the water leaching stage is recycled to reduce fresh water consumption; even the pure CO produced by the second stage rotary kiln can be fed back to the first stage as a reducing agent to form a "sodium-sulfur-carbon-water" system internal cycle, reducing dependence on purchased raw materials and further improving resource recycling efficiency.

[0054] 2. Energy consumption is significantly reduced, which aligns with the requirements of green and low-carbon development.

[0055] 1) Double energy saving of pure oxygen roasting + semi-suspension kiln: Traditional raw material processing processes based on Na2SO4, such as sodium sulfate and SDS sodium-based desulfurization ash (e.g., evaporation crystallization, causticization), consume 800-1200 kWh / t of energy per unit, and the high-temperature reaction relies heavily on air atmosphere (nitrogen absorbs heat, wasting energy); This invention uses "pure oxygen roasting" to reduce ineffective nitrogen heat absorption, and is combined with "two-stage three-blade self-gravity semi-suspension rotary kiln" (material filling rate > 20%, heat transfer efficiency improved by 30%), so that the reduction roasting temperature (750℃~800℃) is lower than that of the traditional causticization method (800℃~900℃), and the preparation of anhydrous aluminum chloride only requires low-temperature dehydration at 150℃~250℃, and the overall energy consumption is reduced by 40%~60% compared with the traditional process.

[0056] 2) Hot charging and preheating combined with energy saving: The solid material (high temperature state) generated by the two-stage rotary kiln is directly "hot charged" into the three-lobe rotary kiln for calcination without the need for additional heating, thus reducing heat loss; at the same time, the waste heat of the calcined material is recovered through heat exchange and cooling, further reducing system energy consumption and realizing "energy cascade utilization".

[0057] 3. Environmental risks are controllable, achieving "near-zero emissions".

[0058] 1) Zero pollution discharge of exhaust gas and wastewater: Traditional processes easily generate SO2 exhaust gas (low sulfur utilization rate) and saline / acidic wastewater (direct discharge pollutes water and soil); This invention uses a three-stage treatment of "sulfur recovery device + CO2 capture device + desulfurization, denitrification and dust removal" to ensure that pollutants such as SO2 and NOx in the flue gas meet the standards for discharge, and the sulfur recovery rate is >99% (no SO2 waste); the water leaching process uses recycled water, and there is no discharge of saline wastewater; the acidification system only produces purified products, and there is no accumulation of acidic waste liquid, thus avoiding the risk of secondary pollution from the source.

[0059] 2) Zero solid waste accumulation: The final products of the process are only high-purity products (sulfur, sodium carbonate, hydrated SiO2, anhydrous aluminum chloride, metallic iron) and steelmaking auxiliary tailings. No waste solid slag is generated, which completely solves the solid waste problems of traditional processes such as "landfilling of silicon-calcium slag after aluminum extraction" and "accumulation of salt slag in hydrochloric acid process", and meets the construction requirements of "zero waste factory".

[0060] 4. The products have high added value, resulting in significantly improved economic benefits.

[0061] 1) High-purity products open up high-value markets: Traditional process products are mostly low-value-added basic chemical products (such as sodium sulfate, with a market price of 800~1200 yuan / ton); the sulfur (purity >99%), sodium carbonate (purity >99%), and anhydrous aluminum chloride (purity >99%) produced by this invention are all industrial-grade high-purity raw materials, which can be directly used in fine chemicals, electronic materials and other fields, with prices 5~10 times higher than sodium sulfate; metallic iron (metallization rate >98%) can be directly recycled for steel smelting, and the tailings can also generate additional revenue as steelmaking auxiliary materials, increasing the added value of products from a single production line by 3-5 times.

[0062] 2) Significant cost advantages: On the one hand, the co-treatment of solid waste reduces the cost of individual disposal (e.g., the traditional landfill cost of fly ash is about 50 yuan / ton, while this invention achieves "profit through waste"); on the other hand, the closed-loop resource recycling reduces the cost of raw material procurement (e.g., recycled CO2 replaces external purchases, and self-made CO replaces external purchases of reducing agents), shortening the investment payback period from 5-8 years in traditional processes to 3-4 years, resulting in significant economic benefits.

[0063] 5. It has strong industrial adaptability and is easy to scale up and promote.

[0064] 1) Wide compatibility with raw materials: Traditional processes require high purity of Glauber's salt (≥95%), and cannot process raw materials with low purity sodium sulfate, industrial by-product Glauber's salt, and sodium SDS-based desulfurization ash, which are mainly composed of Na2SO4. This invention, through pretreatment (grinding to below 200 mesh) and synergistic reaction, can directly process raw materials with low purity Glauber's salt, sodium SDS-based desulfurization ash, and other Na2SO4-based raw materials (impurity ≤15%), as well as fly ash with different compositions (SiO2+Al2O3 content fluctuation ±5% can be adapted), without the need for additional impurity removal processes, thus reducing the difficulty of raw material pretreatment.

[0065] 2) High compatibility between equipment and process: Both rotary kilns adopt a "gravity semi-suspended" structure, which has high equipment maturity and low operation and maintenance difficulty; and the process can be connected with existing steel plants (tail slag is used as steelmaking auxiliary material) and chemical plants (products are directly connected to downstream), without the need to build a complete production line separately. The equipment investment cost is reduced by 30% to 50% compared with the traditional "two independent processes", making it easier to achieve large-scale industrial application.

[0066] In summary, this invention not only solves the pain points of "high energy consumption, high pollution, and low utilization" in the traditional treatment of raw materials such as sodium sulfate, sodium SDS-based desulfurization ash, and fly ash, which are mainly composed of Na2SO4, but also constructs an integrated process system of "solid waste synergy - resource recycling - high-value output - low carbon and environmental protection", which has environmental, economic and social benefits, and has important demonstration significance for promoting the technological upgrading of the solid waste resource utilization industry. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of the process system of the present invention. Detailed Implementation

[0068] 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.

[0069] Example 1

[0070] The present invention discloses a dual-rotary kiln method for the synergistic differentiation and carbon fixation of fly ash, comprising the following steps:

[0071] I. Raw Material Preparation and Parameter Setting

[0072] (a) Raw materials used

[0073] The composition of fly ash from a certain power plant is shown in the table below:

[0074]

[0075] The fly ash contains a total SiO2 and Al2O3 content of 75.11% (49.86% + 25.25%) and an Fe2O3 content of 10.15%, which provides the basic conditions for synergistic reaction with Glauber's salt to recover high-value-added elements. No additional purification or pretreatment is required. It only needs to be crushed by a jaw crusher and then ground to 200 mesh (particle size ≤ 75μm) by a ball mill to ensure the reaction activity.

[0076] Glauber's salt specifications: Industrial-grade by-product Glauber's salt (main component is Na2SO4・10H2O) is selected, with Na2SO4 purity ≥92% and stable water of crystallization content (theoretical value 55.9%). The water of crystallization is removed by a multi-effect evaporation dehydration device to convert it into anhydrous Glauber's salt (Na2SO4 content ≥98%), and then it is ground to 200 mesh to avoid heat consumption due to evaporation of water of crystallization during the roasting process.

[0077] Reducing agent and auxiliary medium: The reducing agent is high-sulfur coal (sulfur content 3%~5%, fixed carbon content ≥75%), which is ground to 200 mesh, which reduces costs and utilizes the sulfur element in the coal to assist the reaction; the roasting gas is industrial pure oxygen (purity ≥99.5%) to ensure a stable oxidizing atmosphere and avoid the formation of by-products from Na2O and impurities.

[0078] (II) Calculation of core proportions

[0079] The raw material ratio is calculated according to the core process requirement of "the mass ratio of Na2O in Glauber's salt to SiO2+Al2O3 in fly ash is 0.7:1". The specific steps are as follows:

[0080] Key component mass calculation: Based on 100kg of fly ash, the mass of SiO2 is 100kg × 49.86% = 49.86kg, the mass of Al2O3 is 100kg × 25.25% = 25.25kg, and the total mass of the two is 49.86kg + 25.25kg = 75.11kg.

[0081] Calculation of required Na2O mass: According to the mixing ratio requirements, the required Na2O mass = 75.11kg × 0.7 = 52.577kg.

[0082] Calculation of anhydrous sodium sulfate dosage: The theoretical Na2O content in anhydrous sodium sulfate (Na2SO4) = (62 / 142) × 100% ≈ 43.66%. Considering the actual Na2O conversion rate of 99% in the reaction, the required mass of anhydrous sodium sulfate = 52.577 kg ÷ (43.66% × 99%) ≈ 122.8 kg.

[0083] The dosage of reducing agent is determined as follows: the mass ratio of high-sulfur coal to anhydrous sodium sulfate is 1:8, so the dosage of high-sulfur coal = 122.8kg ÷ 8 ≈ 15.4kg. This ensures that the amount of reducing agent is sufficient and not excessive, and avoids the generation of excess carbon impurities.

[0084] (III) Equipment and process parameter benchmarks

[0085]

[0086] II. Detailed Process Implementation

[0087] (a) S1: Glauber's salt reduction roasting (sodium oxide generation stage)

[0088] Raw material mixing and feeding: 2456 kg of anhydrous sodium sulfate (200 mesh) and 308 kg of high-sulfur coal (200 mesh) are mixed evenly in a double spiral mixer for 15 min to ensure that the material uniformity is ≥95%; then, the material is fed into the first stage rotary kiln at a constant speed through a closed scraper conveyor, and the feeding rate is controlled at 2 t / h to maintain a stable filling state in the kiln.

[0089] Segmented temperature and atmosphere control: The front section (preheating zone) of the rotary kiln is heated to 500℃±10℃ by a natural gas burner, and industrial pure oxygen (purity ≥99.5%) is introduced to initially burn the high-sulfur coal to generate CO (reducing agent); the rear section (roasting zone) is heated to 750℃±10℃ to ensure that the core reaction proceeds fully.

[0090] Main reaction: Na₂SO₄ + 3CO → Na₂O + S↑ + 3CO₂↑ (Na₂O formation rate ≥ 99%)

[0091] Auxiliary reaction: 2Na₂SO₄ + 3C → 2Na₂O + 2S↑ + 3CO₂↑ (Consumes excess carbon and replenishes Na₂O)

[0092] Separation of gas and solid products:

[0093] Gas phase processing: The mixed gas containing S and CO2 generated during roasting first enters a low-temperature condenser (temperature 5℃±2℃). The S vapor is condensed into liquid sulfur, which is then separated by centrifugation to obtain sulfur product with a purity ≥99.2%, and sent to a sulfur storage tank. The remaining CO2-containing gas enters an organic amine CO2 recovery unit to obtain CO2 with a purity ≥99.5%, which is compressed to 0.8MPa and stored in a CO2 storage tank for subsequent carbonization.

[0094] Solid phase collection: Solid products in the kiln (main components: Na2O, FeO, unreacted impurities) are discharged through a closed discharge valve, cooled to below 200°C by a cooler, and directly charged into the second stage rotary kiln.

[0095] (ii) S2: Co-calcination of fly ash (sodium oxide purification and element conversion stage)

[0096] Material mixing and feeding: The solid product collected in S1 (containing about 1050 kg of Na2O) and 2000 kg of fly ash (200 mesh) are mixed evenly by a paddle mixer for 20 minutes to ensure that Na2O is in full contact with SiO2 and Al2O3 in the fly ash; the mixture is fed into the second-stage rotary kiln by a bucket elevator, and the feeding rate is controlled at 2.5 t / h.

[0097] Calcination process control: Industrial pure oxygen (purity ≥99.5%) is introduced into the rotary kiln, and the temperature is maintained at 800℃±15℃ by an electric heating device. The rotation speed is 2~2.5r / min, and the calcination time is 50~55min to promote the reaction between Na2O and the active components in fly ash.

[0098] Na₂O + 2SiO₂ → Na₂O・2SiO₂ (Sodium silicate, soluble)

[0099] Na₂O + Al₂O₃ → 2NaAlO₂ (Sodium aluminate, soluble)

[0100] FeO is partially oxidized to Fe2O3 in a pure oxygen atmosphere, which prepares for subsequent magnetic separation.

[0101] Calcination product processing: After calcination, the material (temperature about 800℃) enters the shell and tube heat exchanger, where it exchanges heat with circulating water to cool down to below 150℃. At the same time, the heat is recovered for preheating the raw materials. After heat exchange, the material is sent to the water leaching reactor.

[0102] (III) S3: Water leaching and multi-element separation

[0103] Water leaching reaction: Add circulating water (from the subsequent pressure filtration stage) to the water leaching reactor, control the solid-liquid ratio to 1:5, stir at 200 r / min, heat to 80℃±5℃, and leach for 30 min to fully dissolve sodium silicate and sodium aluminate; during the leaching process, CaO and MgO in fly ash react with water to generate Ca(OH)2 and Mg(OH)2, which are partially dissolved in the leachate.

[0104] Filtration separation: The leachate slurry is subjected to solid-liquid separation using a plate and frame filter press (filtration pressure 0.6 MPa, filter cloth pore size 0.1 μm) to obtain:

[0105] The filtrate, mainly composed of sodium silicate (concentration approximately 180 g / L), sodium aluminate (concentration approximately 120 g / L), and small amounts of Ca(OH)2 and Mg(OH)2, is sent to a liquid phase storage tank to await carbonization treatment.

[0106] Filter cake: Main components are Fe2O3, FeO, TiO2, and undissolved tailings, with a moisture content of ≤25%, and is temporarily stored in the filter cake storage silo.

[0107] Iron recovery by magnetic separation: The filter cake is fed into a permanent magnet drum separator (magnetic field strength 12000Gs, rotation speed 30r / min) to separate metallized iron (purity ≥98.5%, metallization rate ≥98%), which is sold as raw material for steel plants; the tailings of magnetic separation (main components TiO2, CaO, MgO) are sent to the tailings treatment workshop, and after grinding, they are used as steelmaking auxiliary material (replacing lime) to achieve full utilization.

[0108] (iv) S4: Hypergravity carbonization and preparation of high value-added products

[0109] Carbonization reaction: The filtrate from S3 is pumped into the high-gravity carbonization reactor, and CO2 recovered from S1 is introduced (flow rate 25 m³ / h, pressure 0.8 MPa). The reaction temperature is controlled at 40℃±5℃, the rotation speed at 1900 r / min, and the carbonization time at 22 min. The reaction occurs as follows:

[0110] Na2O·2SiO2+2CO2+H2O→2NaHCO3+2SiO2·H2O↓

[0111] 2NaAlO2+4CO2+6H2O→2NaHCO3+2Al(OH)3·3H2O↓

[0112] Separation of carbonization products: The carbonized slurry was fed into a horizontal screw centrifuge (4000 r / min, separation factor 3000) to obtain:

[0113] Solid phase: Main components are SiO2・H2O (white carbon black) and Al(OH)3・3H2O, with a moisture content of ≤30%. It is sent to the washing tank and washed 3 times with deionized water (liquid-solid ratio of 3:1 each time) to remove residual Na⁺.

[0114] Liquid phase: The main component is NaHCO3 (concentration of about 150g / L), which is fed into an evaporator crystallizer and evaporated and crystallized at 80℃±5℃ and a vacuum of -0.09MPa to obtain industrial-grade sodium carbonate (purity ≥99.3%). Part of it is recycled for process pH adjustment, and the rest is sold externally.

[0115] Preparation of silica and aluminum salt: The washed solid phase is fed into a dryer (150℃±10℃, drying time 2h) to obtain silica product (purity ≥99.1%, particle size 25~30nm, meeting the HG / T3061-2009 high dispersibility standard); the remaining Al(OH)3・3H2O after drying is added to 31% industrial hydrochloric acid (hydrochloric acid to Al(OH)3・3H2O molar ratio 3:1), and reacted at 60℃±5℃ for 30min to generate AlCl3 solution, which is then concentrated by evaporation and dehydrated at low temperature (210℃±10℃, vacuum degree -0.095MPa) to obtain anhydrous aluminum chloride (purity ≥99.0%, meeting the GB / T3959-2004 first-grade standard).

[0116] (v) S5: Recycling and Environmental Protection

[0117] Water resource recycling: Wastewater generated during the filter pressing and washing processes is treated in a sedimentation tank (retention time 2 hours) to remove suspended impurities, and then decolorized by an activated carbon filter (adsorption efficiency ≥95%) to obtain recycled water with a reuse rate ≥92%. Only 8% fresh water is added to meet the process water requirements.

[0118] Exhaust gas treatment: The small amount of unrecovered flue gas discharged from the two-stage rotary kiln is successively treated by an ammonia desulfurization tower (SO2 removal rate ≥98%), an SCR denitrification tower (NOx removal rate ≥95%), and a bag filter (particulate matter removal rate ≥99.9%). The exhaust gas contains SO2 ≤35mg / m³, NOx ≤50mg / m³, and particulate matter ≤10mg / m³, which meets the requirements of GB13223-2011 "Emission Standard of Air Pollutants for Thermal Power Plants".

[0119] Zero solid waste discharge: magnetic separation tailings are fully utilized as steelmaking auxiliary materials, with no process solid waste discharged externally; sulfur, sodium carbonate, precipitated silica, anhydrous aluminum chloride, and metallic iron are all sold as products, achieving "full utilization of raw materials and full added value of products".

[0120] III. Implementation Results Verification

[0121] (a) Resource utilization rate

[0122] Recovery rates of core elements: SiO2 recovery rate of 98.5%, Al2O3 recovery rate of 97.8%, and Fe2O3 recovery rate of 98.2% in fly ash; Na2SO4 conversion rate of 99.1% and Na2O utilization rate of 98.7% in mirabilite; overall resource utilization rate ≥95%, far exceeding traditional fly ash utilization processes (usually ≤70%).

[0123] By-product recovery: Sulfur recovery rate 99.2%, CO2 recovery rate 98.5%, water recycling rate 92%, with no resource waste.

[0124] (ii) Product quality and production capacity

[0125]

[0126] (III) Energy consumption and environmental protection indicators

[0127] Energy consumption level: The energy consumption per unit product (based on 1 ton of anhydrous aluminum chloride) is 850 kWh, which is 43.3% lower than the traditional soda ash decomposition method (1500 kWh / t); due to the "gravity semi-suspended" structure, the gas-solid contact efficiency of the two-stage rotary kiln is increased by 30%, and the calcination time is shortened by 25% compared with traditional equipment.

[0128] Environmental benefits: Based on the annual treatment of 1 million tons of fly ash of this component, it can reduce the stockpiling of mirabilite solid waste by 1.2 million tons, reduce CO2 emissions by 80,000 tons (due to CO2 recycling), and eliminate the discharge of harmful gases such as SO2 and Cl2, with zero wastewater discharge, meeting environmental protection requirements.

[0129] Example 2

[0130] The present invention discloses a dual-rotary kiln method for the synergistic differentiation and carbon fixation of fly ash, comprising the following steps:

[0131] I. Raw material characteristics and proportioning design

[0132] (a) Basic parameters of raw materials

[0133] The main components of fly ash are: SiO2 = 48.5%, Al2O3 = 32.2%, Fe2O3 = 6.8%, and other impurities (CaO, MgO, K2O, etc.) 12.5%; particle size distribution: ≤100μm (D50 = 55μm), specific surface area 380m² / kg. Pretreatment: After impurity removal by air classifier sieving, it can be used directly without additional grinding.

[0134] SDS sodium-based desulfurization ash specifications:

[0135] Chemical formula: Na₂SO₄・10H₂O, Na₂SO₄ purity 86.5% (intermediate value), water of crystallization content 55.9%. Pretreatment: The water of crystallization is removed by a triple-effect evaporation dehydration device (vacuum degree -0.08MPa, temperature 75℃) to convert it into anhydrous sodium sulfate (Na₂SO₄ content ≥98.2%), and then ball-milled to 200 mesh (particle size ≤75μm).

[0136] Performance parameters of high-sulfur coal: Industrial analysis: sulfur content 4.0%, fixed carbon 80%, ash content 8.5%, volatile matter 7.5%. Particle size: ≤80 mesh (180μm), dried to moisture content ≤2% by airflow dryer (inlet temperature 120℃).

[0137] (II) Calculation of core proportions

[0138] Calculated according to the process standard "mass ratio of Na2O in Glauber's salt to SiO2+Al2O3 in fly ash is 0.65:1":

[0139] Key component calculation (based on 1000 kg of fly ash)

[0140] SiO2 mass = 1000kg × 48.5% = 485kg

[0141] Mass of Al2O3 = 1000kg × 32.2% = 322kg

[0142] Total active ingredient mass = 48.5 + 32.2 = 807 kg

[0143] Calculation of Na2O demand: Required Na2O mass = 807kg × 0.65 = 524.55kg

[0144] Anhydrous Glauber's salt dosage conversion:

[0145] The theoretical Na₂O content in anhydrous Na₂SO₄ = (62 / 142) × 100% = 43.66%

[0146] Assuming a 98% conversion rate, the required mass of anhydrous sodium sulfate is approximately 524.55 kg ÷ (43.66% × 98%) ≈ 1248 kg.

[0147] The corresponding mass of original SDS sodium-based desulfurization ash (containing water of crystallization) = 1248kg ÷ 93.5% × (1 + 55.9% / 44.1%) ≈ 3562kg

[0148] The reducing agent is matched with a high-sulfur coal to anhydrous sodium sulfate mass ratio of 1:7.5. Therefore, the amount of high-sulfur coal used is approximately 1248 kg ÷ 7.5 ≈ 166 kg.

[0149] (III) Equipment Parameter Setting

[0150]

[0151] II. Implementation of Process Steps

[0152] (a) S1: SDS sodium-based desulfurization ash reduction roasting (first stage kiln)

[0153] The mixed feed consists of 1248 kg of anhydrous sodium sulfate and 166 kg of high-sulfur coal mixed for 15 min using a twin-shaft paddle mixer (60 r / min), with a mixing uniformity of ≥95%. The mixture is then continuously fed into a first-stage reduction kiln via an airlock feeder at a feed rate of 1.8 t / h.

[0154] Control of reduction reaction:

[0155] Kiln head preheating section (0~15m): The temperature is raised from room temperature to 500℃, and nitrogen is introduced to replace the air (the oxygen content is reduced to below 0.3%).

[0156] In the reaction section of the kiln (15~35m): the temperature is maintained at 720℃, and the core reaction occurs.

[0157] Na₂SO₄ + 3C → Na₂O + S↑ + 3CO↑ (Conversion rate 98.5%)

[0158] 2S + C → CS2↑ (Assisted desulfurization, sulfur recovery rate 99%)

[0159] Kiln tail cooling section (35~45m): The material is cooled to below 300℃, and nitrogen protection is used to prevent Na2O oxidation.

[0160] Gas-solid separation:

[0161] Gas phase: A mixed gas containing S, CO, and CS2 undergoes two-stage condensation (first stage at 120℃ to recover CS2, second stage at 5℃ to recover sulfur) to obtain sulfur with a purity of 99.3% (yield 89 kg / 1000 kg fly ash). The remaining CO is washed and reused as fuel.

[0162] Solid phase: The reduction product (Na2O content 42.3%, residual carbon ≤1.2%) is sent to the second-stage kiln via a closed screw conveyor.

[0163] (ii) S2: Co-oxidative roasting (two-stage kiln)

[0164] The solid products from the first-stage kiln are mixed with 1000 kg of fly ash using a loss-in-weight batching scale in a specific ratio, and then fed into the second-stage oxidation kiln via an elevator. The material is kept in the kiln for 50 minutes.

[0165] Regulation of oxidation reaction:

[0166] Heating section (0~20m): Heating to 600℃ in air atmosphere, Fe²⁺ is oxidized to Fe³⁺.

[0167] Reaction section (20~40m): Temperature 850℃, sodiumization reaction occurs:

[0168] Na₂O + 2SiO₂ → Na₂O・2SiO₂ (soluble sodium silicate, conversion rate 99%)

[0169] Na2O + Al2O3 → 2NaAlO2 (soluble sodium aluminate, conversion rate 98%).

[0170] Cooling section (40~50m): The material is cooled to 250℃ to prevent violent boiling during subsequent water immersion.

[0171] The characteristics of the roasted product are that the discharged material is light gray granules with a particle size of ≤3mm. The water-soluble components (sodium silicate + sodium aluminate) account for 68.5%, and Fe2O3 is uniformly distributed in the form of magnetic particles.

[0172] (III) S3: Water immersion and separation of iron elements

[0173] The product from the water leaching process was fed into a leaching tank, and 80℃ deionized water was added at a solid-liquid ratio of 1:6. The stirring speed was 180 r / min, and the leaching was carried out for 30 min. The leaching endpoint was monitored by an online turbidity meter (turbidity stabilized below 50 NTU).

[0174] Solid-liquid separation:

[0175] The leachate was separated by a plate and frame filter press (filtration pressure 0.5 MPa) to obtain:

[0176] Filtrate: containing sodium silicate (165g / L) and sodium aluminate (132g / L), pH=13.2, is sent to the carbonization stock solution tank.

[0177] Filter cake: moisture content 28%, main components are Fe2O3 (32.5%), TiO2 (8.2%) and undissolved residue.

[0178] The iron-extracting filter cake from the magnetic separation process is crushed by a dispersant and then fed into a wet magnetic separator (35% slurry concentration) for separation under a magnetic field strength of 10000 Gs to obtain:

[0179] Iron concentrate: Fe content ≥65%, yield 67kg / 1000kg fly ash, used as raw material for sintering.

[0180] Tailings: The non-magnetic portion (including TiO2, CaO, etc.) is sent to the building materials workshop to make non-fired bricks.

[0181] (iv) S4: Hypergravity carbonization separation

[0182] The carbonization reaction filtrate is pumped into the high-gravity carbonizer, and CO2 (95% purity) recovered from the kiln tail is introduced, controlled as follows:

[0183] The inlet CO2 partial pressure is 0.6 MPa, and the liquid flow rate is 8 m³ / h.

[0184] The carbonization endpoint occurs at pH 9.5 (adjusted via an online pH meter and CO2 valve).

[0185] Na2O·2SiO2+2CO2+H2O→2NaHCO3+2SiO2·H2O↓

[0186] 2NaAlO2+4CO2+6H2O→2NaHCO3+2Al(OH)3↓

[0187] Hierarchical separation:

[0188] The carbonization slurry was first separated into crude SiO2·H2O (35% water content) by a horizontal centrifuge (3000 r / min), washed three times with deionized water (the conductivity was reduced to below 50 μS / cm), and spray dried (inlet air temperature 200℃) to obtain white carbon black (purity 99.2%, particle size 20~30 nm).

[0189] The centrifuged mother liquor was sent to a settling tank, and 0.1% polyacrylamide flocculant was added. After the Al(OH)3 precipitate was filtered by plate and frame filter (moisture content 30%), it was sent to a rotary dryer (120℃) to obtain aluminum hydroxide (purity 98.5%).

[0190] The sodium salt recovery supernatant (containing NaHCO3=145g / L) was crystallized by multi-effect evaporation (vacuum degree -0.09MPa, final effect temperature 55℃) to obtain industrial grade sodium carbonate (purity 99.1%, conforming to GB210.1-2004 superior grade), with a yield of 478kg / 1000kg fly ash.

[0191] (v) S5: Recycling and Environmental Protection

[0192] Resource recycling:

[0193] Evaporated condensate (conductivity ≤20μS / cm) is recycled in the water immersion process, with a recycling rate of 90%.

[0194] The magnetic separation tailings and a small amount of filter press residue are mixed in a 3:1 ratio, 5% cement is added for curing, and then pressed into non-fired bricks (compressive strength ≥15MPa).

[0195] The flue gas from the kiln is treated by a desulfurization tower (Ca(OH)2 slurry), and the SO2 emission concentration is ≤30mg / m³.

[0196] Key performance indicator control:

[0197] Overall water consumption: 1.2t / t fly ash (advanced industry value).

[0198] Overall energy consumption: 680 kWh / t fly ash (38% lower than traditional processes).

[0199] Zero solid waste discharge: all by-products are utilized as resources.

[0200] III. Implementation Results Verification

[0201] (a) Product yield and quality

[0202]

[0203] (II) Analysis of Technological Advantages

[0204] Resource utilization rate: The recovery rate of SiO2 in fly ash is 98.2%, the recovery rate of Al2O3 is 97.5%, and the conversion rate of Na2SO4 in SDS sodium-based desulfurization ash is 98.5%, which is much higher than that of traditional acid leaching method (SiO2 recovery rate ≤85%).

[0205] Economic efficiency: The comprehensive revenue per ton of fly ash is approximately RMB 420 (after deducting raw material and energy costs), and the investment payback period is 3.5 years.

[0206] Environmental friendliness: It realizes the whole chain transformation of "solid waste-product", reduces CO2 emissions by 860 kg / t fly ash, and achieves zero wastewater discharge.

[0207] The dual rotary kiln device of the present invention includes a two-stage three-blade gravity semi-suspended closed reduction rotary kiln and a three-blade gravity semi-suspended closed rotary kiln. The gas phase outlet of the two-stage three-blade gravity semi-suspended closed reduction rotary kiln is connected in sequence to a sulfur recovery device and a CO2 capture device. The CO2 output end of the CO2 capture device is connected to a supergravity carbonization reactor. The solid phase output end of the two-stage three-blade gravity semi-suspended closed reduction rotary kiln and the fly ash feed end are connected together to the feed end of the three-blade gravity semi-suspended closed rotary kiln. The discharge end of the three-lobe gravity semi-suspended closed rotary kiln is connected to a heat exchange device, and the discharge end of the heat exchange device is connected to a water leaching reactor. The solid-liquid separation end of the water leaching reactor is connected to a magnetic separator and a high-gravity carbonization reactor, respectively. The solid-liquid separation end of the high-gravity carbonization reactor is the output end of sodium carbonate and the feed end of the acidification system, respectively. The discharge end of the acidification system is the output end of hydrated SiO2 and the anhydrous aluminum chloride preparation device, which is a crystallization device adapted for low-temperature evaporation and dehydration at 150℃~250℃. Both the two-stage three-lobe gravity semi-suspended closed reduction rotary kiln and the three-lobe gravity semi-suspended closed rotary kiln are equipped with a pure oxygen inlet device, and the kiln body has a three-lobe structure adapted for gravity semi-suspended materials. The water leaching reactor is connected to a water circulation device, which is connected to the inlet end of the water leaching reactor to achieve water recycling.

[0208] The dual rotary kiln method for synergistic fractionation and carbon fixation of fly ash in this invention and its supporting equipment all involve existing, mature industrial equipment. There is no customized or special-purpose equipment. The models and specifications of the relevant equipment can be conventionally selected and adapted from the existing industrial equipment system according to the actual production capacity and process parameter requirements. Specific details are as follows:

[0209] The multi-effect evaporation dehydration device, ball mill, and jaw crusher in the raw material pretreatment stage are all commonly used raw material processing equipment in the fields of chemical, metallurgical, and solid waste treatment. Their models can be selected according to the raw material processing capacity (such as hourly processing capacity or daily processing capacity) and the general specifications on the market can be selected to meet the process requirements of removing crystal water and grinding materials to below 200 mesh.

[0210] The two-stage three-lobe gravity semi-suspended closed reduction rotary kiln for roasting and calcination is a mature kiln type in the existing industrial kiln field. Its core parameters such as diameter, length, rotation speed, and filling rate can be adapted according to the production scale. The pure oxygen inlet device, temperature control system, and closed unloading device are all standard components for rotary kilns and there are no special customization requirements.

[0211] The sulfur recovery unit (low-temperature condensation + activated carbon adsorption combination unit), CO2 capture unit (organic amine method or improved organic amine method), ammonia desulfurization tower, SCR denitrification tower, and bag filter in the gas-solid recovery and tail gas treatment process are all commonly used gas-solid separation and tail gas treatment equipment in the coal chemical, power, and environmental protection fields. Their models can be conventionally selected according to process parameters such as flue gas volume, sulfur content, and CO2 concentration, as long as they meet the requirements of sulfur purity ≥99%, CO2 purity ≥99%, and tail gas emission standards.

[0212] Tubular heat exchangers, water leaching reactors, plate and frame filter presses, horizontal screw centrifuges, permanent magnet drum / roller magnetic separators, double screw mixers, paddle mixers, enclosed scraper conveyors, and bucket elevators in the solid-liquid separation and material conveying process are all commonly used reaction, separation, and conveying equipment in the chemical and mining industries. Their models can be selected according to the requirements of material quantity, solid-liquid ratio, separation accuracy, etc., and are generally available in the market to meet the process requirements of heat exchange and cooling, leaching reaction, solid-liquid separation, and magnetic separation of iron elements.

[0213] The high-gravity carbonization reactor, acidification system (acid reactor), low-temperature evaporation dehydration crystallization device (vacuum evaporation crystallizer), spray dryer, and rotary dryer in the carbonization and acidification purification process are all existing and commonly used reaction, purification, and drying equipment in the fields of fine chemicals and inorganic materials. Their speed, pressure, and temperature control functions are inherent attributes of the equipment. The model can be conventionally selected according to the material throughput and product purity requirements to meet the process requirements of carbonization reaction, acidification purification, and low-temperature dehydration crystallization.

[0214] The sedimentation tanks, activated carbon filters, booster pumps, various storage tanks, valves, and automated control systems in the water circulation and auxiliary processes are all existing common auxiliary equipment and control components in the industrial production field. They have no special technical requirements and can be selected conventionally according to the process matching needs.

[0215] It should be understood that numerous specific implementation decisions can be made during the development of any practical implementation, such as in any engineering or design project. Such development efforts may be complex and time-consuming, but for those skilled in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0216] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A dual-rotary kiln method for the synergistic fractionation and carbon fixation of fly ash, characterized in that, Includes the following steps: S1. Pre-treat the raw materials of sodium sulfate and sodium SDS desulfurization ash, which are mainly composed of Na2SO4, remove the water of crystallization from the raw materials, and then grind the raw materials to below 200 mesh. S2. Reduction Roasting: The finely ground raw material is fed into a two-stage, three-lobe, gravity-driven, semi-suspended, closed rotary kiln for reduction. Under pure oxygen conditions, it is preheated in the first stage of the kiln at 500℃±20℃. The fuel and reducing agent used for preheating are natural gas, coal, CO, or pure CO produced in the second stage of the kiln. After preheating, the material enters the second stage of the kiln and continues to roast under pure oxygen conditions at 750℃~800℃±20℃. Reaction formula: Na2SO4+3CO→Na2O+S↑+3CO2↑ 2CO + O2 → 2CO2↑ 2Na2SO4+3C→2Na2O+2S↑+3CO2↑ 2C + O2 → 2CO↑ S3, S, and CO2 recovery: The gas phase generated by the two-stage three-lobe self-gravity semi-suspended closed reduction rotary kiln is first treated by a sulfur recovery device to recover sulfur, and then enters a CO2 capture device to recover CO2. The recovered CO2 is reused in the subsequent high gravity carbonization reactor. The flue gas after sulfur and CO2 recovery is then treated by desulfurization, denitrification and dust removal before being discharged. S4, Co-calcination: The raw materials are proportioned according to the mass ratio of Na2O in the solid material generated by the reaction in the two-stage three-lobe gravity semi-suspended closed reduction rotary kiln to the combined SiO2+Al2O3 in the fly ash, which is 0.6~0.8:

1. The proportioned material is then hot-charged into the three-lobe gravity semi-suspended closed rotary kiln for calcination. Reaction formula: FeO + C → Fe + CO↑ Na₂O + CO₂ → Na₂CO₃ 2SiO2 + Na2O → Na2O•2SiO2 Al₂O₃ + Na₂O → 2NaAlO₂ S5. Water leaching: After the calcined material is cooled to below 500℃ by heat exchange, it is sent to a water leaching reactor for water leaching treatment. The leaching slurry is separated by pressure filtration, and the water after pressure filtration is recycled. S6. Solid-phase separation and utilization: The leachate solid phase obtained by pressure filtration is fed into a magnetic separator to separate reduced metallic iron. The tailings remaining after magnetic separation are used as steelmaking auxiliary materials. S7, Hypergravity Carbonization: The leachate obtained by pressure filtration, including sodium silicate and sodium aluminate, is sent into a high gravity carbonization reactor for carbonization reaction. The reactants after carbonization reaction are separated by pressure filtration to obtain solid sodium carbonate. Reaction formula: 2NaAlO2 + Na2O • 2SiO2 + 2CO2 + 3H2O → 2Na2CO3 + 2Al(OH)3 • 2SiO2 + 2Na + S8. Acidification and purification: The liquid phase obtained by pressure filtration of carbonization reaction is sent to acidification system for acidification treatment. The acidification product is separated and purified to obtain hydrated SiO2 and hydrated aluminum chloride. The hydrated aluminum chloride is evaporated and dehydrated at low temperature of 150℃~250℃ to obtain anhydrous aluminum chloride. Al(OH)3•2SiO2+3HCl+3H2O→2(SiO2•H2O)+AlCl3•6H2O AlCl3•6H2O AlCl3+6H2O。 2. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The coal mentioned in S2 is high-sulfur coal.

3. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The ratio of Na2SO4 raw materials, mainly sodium sulfate and SDS sodium-based desulfurization ash, to fly ash in S2 is 0.6 to 0.8:1 by mass of Na2O to SiO2 + Al2O3.

4. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The reduction rate of Na2O during the reduction roasting process described in S2 is >99.5%.

5. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The two-stage three-blade gravity semi-suspended reduction rotary kiln described in S2 has the characteristics of gravity semi-suspended materials, and its kiln material filling rate is above 20%.

6. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The sulfur produced as described in S3 has a purity greater than 99%.

7. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The CO2 produced as described in S3 has a purity greater than 99%.

8. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The three-lobe self-gravity semi-suspended closed rotary kiln described in S4 has the characteristics of self-gravity semi-suspended materials, and its kiln material filling rate is above 20%.

9. The dual-rotary kiln method for synergistic fractionation and carbon fixation of fly ash according to claim 1, characterized in that, The sodium carbonate, hydrated SiO2, and anhydrous aluminum chloride obtained in S5 all have a purity of over 99%, and the metallization rate of the reduced metallic iron is over 98%.

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