A method for source reduction and resource utilization of incineration flue gas sodium-based deacidification and fly ash

Abstract

The present application relates to fly ash resource technology field, the present application discloses a kind of incineration flue gas sodium-based deacidification and fly ash source head reduction resource method, comprising the following steps: S1: sodium bicarbonate is sprayed into flue gas passage to carry out preliminary deacidification, S2: system collects the desulfurization ash generated by reaction, S3: the fly ash collected into water washing dissolution link, fast filtration extract initial stage filtrate, S4: NH4HCO3 is added to the electrodialysis reaction system to carry out electrodialysis metathesis reaction, to obtain NaHCO3 Crystal, ammonium chloride solution or ammonium sulfate solution;Subsection dissolution is used, and initial stage filtrate is introduced into electrodialysis system, to avoid electrodialysis membrane crystallization while reducing electrodialysis processing load and realizing deacidification cycle.The high concentration brine obtained by the way of multi-stage countercurrent water washing system or dry-wet method fixed bed continuous water washing desalination of the end stage filtrate with reduced solid-liquid ratio is removed in vacuum evaporation device to obtain crystallization, so that the processing efficiency of vacuum evaporation device is greatly increased.

Description

Technical Field

[0001] This invention relates to the field of fly ash resource utilization technology, specifically a method for sodium-based deacidification of incineration flue gas and source reduction and resource utilization of fly ash. Background Technology

[0002] Traditional mainstream calcium-based deacidification processes use calcium hydroxide as the core deacidifying agent. While they can achieve basic removal of acidic pollutants, they generally suffer from prominent problems such as low agent utilization, large fly ash generation, and high difficulty in subsequent disposal. The fly ash generated by calcium-based deacidification is mainly composed of insoluble calcium salts. Current disposal methods mainly involve solidification and stabilization landfilling and co-processing in cement kilns. The former consumes a large amount of land resources and poses significant long-term environmental risks, while the latter faces bottlenecks such as limited disposal capacity, easy formation of kiln rings, and difficulty in treating washing wastewater. It is difficult to find a balance between environmental friendliness and economic feasibility, and it cannot meet the needs of high-quality development in the industry.

[0003] The fly ash after flue gas deacidification can be washed with water to obtain valuable soluble salts. When sodium bicarbonate (NaHCO3) is used as the flue gas deacidification agent, the fly ash washing filtrate and ammonium bicarbonate (NH4HCO3) can be introduced into the electrodialysis reaction system to obtain sodium bicarbonate and achieve recycling.

[0004] For example, Beijing generated 135,500 tons of fly ash from municipal solid waste incineration in 2024. Even with the lowest possible liquid-to-solid ratio (1 kg fly ash to 3-10 liters of water), the actual volume of fly ash filtrate produced during fly ash washing is still enormous. While reducing the liquid-to-solid ratio decreases the electrodialysis throughput, the increased salt concentration leads to accelerated crystallization and clogging of the electrodialysis membrane, affecting its lifespan. Reducing the salt concentration would require connecting a large number of electrodialysis modules in series, and the limited throughput would result in excessively long operating times for the electrodialysis process.

[0005] The article "Research on Key Mechanisms and Technologies of Fly Ash Washing and Desalination in Waste Incineration, Author: Li Minjie" proposes to optimize the liquid-solid ratio of the washing process and adopt a fixed-bed continuous washing and desalination method with medium-temperature sintered packing. The liquid-solid ratio was optimized to 0.41 L / kg. Although the liquid-solid ratio was reduced, the salt concentration in the fly ash washing filtrate increased significantly. If electrodialysis is to be applied, water needs to be added to adjust the concentration, which still cannot effectively control the volume of wastewater treated by electrodialysis.

[0006] While vacuum evaporation is highly efficient for removing liquids from highly concentrated brine, it cannot achieve sodium bicarbonate recycling, unlike electrodialysis, thus failing to create an economic cycle.

[0007] Therefore, directly introducing an electrodialysis system during the fly ash washing stage results in large equipment size, frequent electrodialysis maintenance, and a long actual processing time. This further reduces the profit margin for the secondary utilization of valuable materials.

[0008] Lowering the liquid-to-solid ratio and increasing the salt concentration, if vacuum evaporation equipment is used to remove moisture, makes it impossible to achieve deacidifying agent circulation, resulting in poor economic efficiency. Summary of the Invention

[0009] The purpose of this invention is to provide a method for sodium-based deacidification of incineration flue gas and source reduction and resource utilization of fly ash, so as to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash includes: Step S1: Using sodium bicarbonate as a deacidifying agent, sodium bicarbonate is injected into the flue gas channel for preliminary deacidification, converting gaseous acidic pollutants into solid reaction intermediates. Step S2: After the flue gas reacts, the system collects the desulfurization ash generated by the reaction. This fly ash contains soluble sodium salts including Na2SO4 and NaCl. Step S3: The collected fly ash enters the water washing and dissolving stage. Before the soluble sodium salts in the fly ash are completely dissolved, the initial filtrate is quickly filtered and extracted. The remaining solution is further washed and dissolved with water and used as the final filtrate. Step S4: The initial filtrate is purified by solution purification to obtain a purified sodium salt solution. The COD in the solution is reduced by ozone oxidation. Then, the purified sodium salt solution is obtained by a combination of ultrafiltration, nanofiltration and reverse osmosis. The purified sodium salt solution is then fed into the electrodialysis reaction system. NH4HCO3 is added to the electrodialysis reaction system to carry out an electrodialysis metathesis reaction, thereby obtaining NaHCO3 crystals, ammonium chloride solution or ammonium sulfate solution. Step S5: Add fresh dried fly ash to the final filtrate, adjust the liquid-to-solid ratio to 3L / kg, and then introduce it into a multi-stage countercurrent water washing system. After the final filtrate is fully dissolved, filter the insoluble fly ash residue through precipitation solid-liquid separation technology, and then perform solution purification to obtain a purified final sodium salt solution. Finally, introduce the final sodium salt solution into the evaporation system to remove moisture and obtain solid salt.

[0011] Step S6: The separated NaHCO3 is filtered and dried, and then returned to step S1 for recycling as a deacidifying agent; Step S7: The ammonium chloride or ammonium sulfate solution is concentrated by reverse osmosis, evaporated and crystallized, and then sold as agricultural nitrogen fertilizer or industrial-grade ammonium chloride to realize economic value, thereby opening up a green closed-loop process from source reduction to resource recycling.

[0012] As a further embodiment of the present invention: in step S3, the initial water washing and dissolution conditions are set to a liquid-to-solid ratio of 3-5 L / kg and a time of 3-10 minutes, with the filtrate salt concentration in the range of 4%-10%.

[0013] As a further aspect of the present invention: in step S4, the concentration of the sodium salt solution fed into the electrodialysis reaction system is 5%-8%.

[0014] As a further embodiment of the present invention, step S3A, which replaces step S3, involves the following steps: the collected dry fly ash enters the wetting process, water is added to the fly ash, and the initial filtrate is obtained by filtration before the soluble sodium salts in the fly ash are completely dissolved. The fly ash is then used as a wetting packing material for the subsequent fixed-bed continuous water washing and desalination section.

[0015] As a further embodiment of the present invention, step S5A, which replaces step S5, involves using a combination of pre-wetted fly ash as the initial material and dried fly ash as the supplementary material, continuously washing the mixture with water on a fixed bed, and obtaining the filtrate as the final filtrate.

[0016] As a further embodiment of the present invention: both the initial filtrate and the final filtrate are subjected to ozone oxidation to reduce the COD in the solution, and then a purified sodium salt solution is obtained by a combination of ultrafiltration, nanofiltration and reverse osmosis.

[0017] As a further aspect of the present invention: in step S4, the concentration of the sodium salt solution fed into the electrodialysis reaction system is 8%-15%.

[0018] As a further embodiment of the present invention: a concentration detection device is added in steps S3 and S3A, and the initial filtrate is obtained by filtration within the salt concentration range of 8%-15%.

[0019] Compared with the prior art, the beneficial effects of the present invention are: Compared with traditional methods, this invention integrates sodium-based deacidification of incineration flue gas with source reduction and resource utilization of fly ash. Utilizing the readily soluble sodium salt as the product of sodium-based deacidification, a staged dissolution process is employed. The initial filtrate is introduced into the electrodialysis system, preventing crystallization of the electrodialysis membrane, reducing the electrodialysis treatment load, and achieving deacidification recycling. The final filtrate, with a reduced solid-liquid ratio, is desalinated through a multi-stage countercurrent water washing system or a dry-wet fixed-bed continuous water washing method to obtain high-concentration brine. This brine is then crystallized in a vacuum evaporator, significantly increasing the processing efficiency of the vacuum evaporator. This completely solves the problem of the inability to balance the solid-liquid ratio in electrodialysis, avoids water waste caused by brine concentration reduction, simultaneously enables the reuse of the deacidifying agent, and addresses the issues of excessive electrodialysis treatment load and desalinated brine volume, increasing environmental benefits and enhancing the economic value of fly ash disposal. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a process for sodium-based deacidification of incineration flue gas and source reduction and resource utilization of fly ash; Detailed Implementation

[0022] Please see Figure 1 Example 1: Includes: Step S1: Using sodium bicarbonate as a deacidifying agent, sodium bicarbonate is injected into the flue gas channel for preliminary deacidification, converting gaseous acidic pollutants into solid reaction intermediates. Step S2: After the flue gas reacts, the system collects the desulfurization ash generated by the reaction. This fly ash contains soluble sodium salts including Na2SO4 and NaCl. Step S3: The collected fly ash enters the water washing and dissolution stage. Before the soluble sodium salts in the fly ash are completely dissolved, the initial filtrate is rapidly extracted by filtration. The remaining solution is further washed and dissolved with water and used as the final filtrate. During this process, the fly ash can be washed at a ratio of 1 kg of fly ash to more than 3 liters of water. Before the dissolution is complete, the initial filtrate is obtained through mechanical filtration. At this point, the concentration of the initial filtrate is lower than that of the theoretically dissolved filtrate. Due to the tendency of the electrodialysis membrane to crystallize, the initial filtrate obtained at this stage is just sufficient for use in the electrodialysis system to obtain sodium bicarbonate for reuse. Details are as follows: As a further step in this process: In step S3, the initial water washing dissolution conditions are set to a liquid-to-solid ratio of 3-5 L / kg, a time of 3-10 minutes, and a filtrate salt concentration within the range of 4%-10%. Precisely controlling the initial filtrate salt concentration within the 4%-10% range is crucial for creating an optimal operating window for the electrodialysis system that balances high efficiency, low energy consumption, and long-term stability. This concentration range ensures a sufficiently high ion concentration in the feed water, providing a considerable ion migration flux, enabling the electrodialysis unit to operate at high current efficiency, maximizing the capacity per unit membrane area, and making it more economical from a life-cycle cost perspective. Furthermore, this upper limit concentration (≤10%) effectively avoids the risk of increased inorganic salt (such as CaCO3, CaSO4) precipitation on the membrane surface and in the compartment due to excessively high concentrations of scaling ions such as calcium and magnesium. Combined with the inhibitory effect of the electric field on contaminants, this mitigates membrane fouling and significantly extends the cleaning cycle and membrane life. Furthermore, this concentration range makes it easy to maintain the system's operating current density in an optimized range that is close to but does not exceed the "limit current density," which not only ensures the processing rate but also fundamentally avoids operational instability caused by polarization scaling induced by excessively high concentrations. This ensures that the entire electrodialysis process can operate continuously, efficiently, and with low maintenance for a long time.

[0023] The energy consumption of electrodialysis is positively correlated with the salinity of the feed water. When treating low-concentration brine (e.g., 1%-3% salinity), the energy consumption per unit of permeate can be as low as 1.5-2.5 kWh / m³, which is 30%-50% lower than that of reverse osmosis (RO) technology. This can significantly reduce operating costs for treating large volumes of fly ash washing liquid. However, low-concentration brine with a salinity of 1%-3% is not very effective for electrodialysis, so the concentration of brine cannot be reduced solely based on energy consumption. The absolute content of suspended solids, colloids, and organic matter in low-concentration brine is usually low. The electric field formed on the surface of the electrodialysis membrane has a certain inhibitory and destructive effect on organic pollutants and microorganisms. Therefore, treating low-concentration brine can effectively slow down the membrane fouling rate, extend the chemical cleaning cycle and membrane lifespan, and ensure the long-term stable operation of the system.

[0024] Step S4: The initial filtrate is purified by removing impurities to obtain a purified sodium salt solution. Specifically, the COD in the solution is reduced by ozone oxidation. Then, the purified sodium salt solution is obtained by a combination of ultrafiltration, nanofiltration, and reverse osmosis. The purified sodium salt solution is then fed into an electrodialysis reaction system. NH4HCO3 is added to the electrodialysis reaction system to carry out an electrodialysis metathesis reaction, thereby obtaining NaHCO3 crystals, ammonium chloride solution, or ammonium sulfate solution.

[0025] As a further refinement of this step, in step S4, the concentration of the purified sodium salt solution fed into the electrodialysis reaction system is 5%-8%. Precisely limiting the concentration of the electrodialysis feed sodium salt solution to 5%-8% is a core process parameter derived from multi-objective system optimization. Compared to a wider concentration window of 4%-10%, it exhibits significant advantages in energy efficiency, economy, and operational stability. This concentration range, through precise matching of solution conductivity and operating current density, allows the system to operate stably in the high-density region near the limiting current density while avoiding significant aggravation of concentration polarization, thereby maximizing the yield per unit membrane area and further optimizing energy consumption per unit product. In engineering practice, the narrow range control of 5%-8% significantly reduces the system's sensitivity to fluctuations in feed water concentration. This not only simplifies the control difficulty of the upstream washing process and reduces the additional water or energy consumption incurred for concentration adjustment, but also provides a more precise basis for the standardized design and selection of electrodialysis membrane stacks, helping to reduce equipment investment redundancy. Most importantly, tightening the concentration limit from a strict 10% to 8% more effectively suppresses the supersaturation tendency of sparingly soluble salts (such as CaCO3 and CaSO4) at the membrane interface, fundamentally reducing the kinetic driving force of inorganic fouling. Simultaneously, at this concentration, the absolute load of organic matter and colloids remains at a lower level, which, combined with the synergistic antifouling effect of the membrane surface electric field, can significantly slow down the membrane fouling rate. This directly translates to a substantial extension of the chemical cleaning cycle and an effective improvement in the service life of the ion exchange membrane, thereby fundamentally reducing the long-term maintenance costs and operational risks of the system, ensuring the efficient, stable, and sustainable operation of the entire resource recovery process loop.

[0026] A purified sodium salt solution is introduced into the electrodialysis reaction system and undergoes an electrodialysis metathesis reaction with added ammonium bicarbonate (NH4HCO3). Utilizing the selective permeability of the cation exchange membrane and anion exchange membrane, under the drive of a DC electric field, NH4⁺, HCO3⁻, and Na⁺ are exchanged. + Four types of ions, Cl⁻, migrate in a directional manner, and a double decomposition transformation occurs between NH₄HCO₃ and NaCl: sodium bicarbonate (NaHCO₃) crystals precipitate on the desalination side, and ammonium chloride solution is enriched on the concentration side.

[0027] Optional, NH4⁺, HCO3⁻, Na + SO4 2 ⁻ Four types of ions migrate in a directional manner, and a double decomposition transformation occurs between NH4HCO3 and Na2SO4: sodium bicarbonate (NaHCO3) crystals precipitate on the desalination side, and ammonium sulfate solution is enriched on the concentration side.

[0028] Step S5: Add fresh dried fly ash to the final filtrate, adjust the liquid-to-solid ratio to approximately 3 L / kg, and then introduce it into a multi-stage countercurrent water washing system. After the final filtrate is fully dissolved, filter out the insoluble fly ash residue using a sedimentation solid-liquid separation technique. Then, perform solution purification to obtain a purified final sodium salt solution. Finally, introduce the final sodium salt solution into an evaporation system to remove moisture and obtain solid salt.

[0029] Since soluble salts in fly ash are not completely extracted, to further improve economic efficiency, the final filtrate can be washed using a multi-stage countercurrent water washing method. In this case, it is necessary to ensure that the liquid-to-solid ratio of the final filtrate is close to 3 L / kg, which can be achieved by adding fresh fly ash, reducing water waste. Multi-stage countercurrent water washing ensures that the salts in the fly ash are nearly or completely dissolved into the final filtrate. Finally, the liquid is separated using a vacuum evaporation device to obtain solid salts.

[0030] This technical solution employs a dual-washing process, utilizing the salt's dissolution time to obtain low-concentration and high-concentration brine twice. The low-concentration brine is then coupled with electrodialysis, reducing throughput and the burden on the electrodialysis equipment, extending its lifespan, and lowering maintenance costs. Simultaneously, the high-concentration brine is more compatible with vacuum evaporation equipment.

[0031] The solid salt separated by evaporation and crystallization mainly consists of sodium chloride and potassium chloride. After purification, the product salt meets the industrial salt standard GB / T5462-2015 and can be sold as an industrial raw material, generating economic benefits. This directly transforms the disposal cost center into a resource revenue point.

[0032] Additional explanation: The high-purity sodium salt obtained from evaporation can be refluxed to the front-end system as a raw material. For example, in the preparation process of sodium-based deacidifying agent NaHCO3, pure NaCl solution can be used as a sodium source for bipolar membrane electrodialysis or other alkali production processes.

[0033] Step S6: The separated NaHCO3 is filtered and dried and then returned to step S1 as a deacidifying agent for recycling. Alternatively, the concentrated and crystallized NaHCO3 can be directly returned to step S1 as a deacidifying agent for recycling. Step S7: The ammonium chloride or ammonium sulfate solution is concentrated by reverse osmosis, evaporated and crystallized, and then sold as agricultural nitrogen fertilizer or industrial-grade ammonium chloride to realize economic value, thus opening up a green closed-loop process from source reduction to resource recycling.

[0034] Example 2: Includes: Step S1: Using sodium bicarbonate as a deacidifying agent, sodium bicarbonate is injected into the flue gas channel for preliminary deacidification, converting gaseous acidic pollutants into solid reaction intermediates. Step S2: After the flue gas reacts, the system collects the desulfurization ash generated by the reaction. This fly ash contains soluble sodium salts including Na2SO4 and NaCl. Step S3A: The collected dry fly ash enters the wetting process, water is added to the fly ash, and the initial filtrate is obtained by filtration before the soluble sodium salts in the fly ash are completely dissolved. The fly ash is then used as a wetting packing material for the subsequent fixed bed continuous water washing and desalination section. After adding the dried fly ash to water, the fly ash is filtered to obtain the initial filtrate before the salt is completely dissolved. The remaining fly ash is discharged by pressure filtration to disperse most of the liquid and is used as a wet packing material in the fixed bed continuous water washing and desalination section.

[0035] Step S4: The initial filtrate is purified by solution purification to obtain a purified sodium salt solution. The purified sodium salt solution is then introduced into the electrodialysis reaction system. NH4HCO3 is added to the electrodialysis reaction system to carry out an electrodialysis metathesis reaction, thereby obtaining NaHCO3 crystals, ammonium chloride solution, or ammonium sulfate solution.

[0036] Step S5A: Using pre-wetted fly ash as the initial material and dried fly ash as the supplementary material, the mixture is continuously washed with water on a fixed bed, and the resulting filtrate is the final filtrate.

[0037] Since the liquid-to-solid ratio can be as low as 0.41 L / kg in fixed-bed continuous water washing desalination using medium-temperature sintered packing, a liquid-to-solid ratio of 3 L / kg is used for initial dissolution and wetting of fly ash. After the initial filtrate is removed, the combination of wetted fly ash as initial material and dry fly ash as supplementary material, along with continuous water washing on a fixed bed, maximizes water conservation. The resulting high-concentration brine can be directly used for evaporation treatment.

[0038] Step S6: The separated NaHCO3 is filtered and dried, and then returned to step S1 as a deacidifying agent for recycling.

[0039] Step S7: Ammonium chloride or ammonium sulfate solution is concentrated by reverse osmosis, evaporated and crystallized, and then used as agricultural nitrogen fertilizer.

[0040] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash, characterized in that: include: Step S1: Using sodium bicarbonate as a deacidifying agent, sodium bicarbonate is injected into the flue gas channel for preliminary deacidification, converting gaseous acidic pollutants into solid reaction intermediates. Step S2: After the flue gas reacts, the system collects the desulfurization ash generated by the reaction. This fly ash contains soluble sodium salts including Na2SO4 and NaCl. Step S3: The collected fly ash enters the water washing and dissolving stage. Before the soluble sodium salts in the fly ash are completely dissolved, the initial filtrate is quickly filtered and extracted. The remaining solution is further washed and dissolved with water and used as the final filtrate. Step S4: The initial filtrate is purified by solution purification to obtain a purified sodium salt solution. The purified sodium salt solution is then introduced into the electrodialysis reaction system. NH4HCO3 is added to the electrodialysis reaction system to carry out an electrodialysis metathesis reaction, thereby obtaining NaHCO3 crystals, ammonium chloride solution or ammonium sulfate solution. Step S5: Add fresh dried fly ash to the final filtrate, adjust the liquid-to-solid ratio to 3L / kg, and then introduce it into a multi-stage countercurrent water washing system. After fully dissolving, filter the insoluble fly ash residue through precipitation solid-liquid separation technology, and then perform solution purification to obtain a purified final sodium salt solution. Finally, introduce the final sodium salt solution into the evaporation system to remove moisture and obtain solid salt. Step S6: The separated NaHCO3 is filtered and dried, and then returned to step S1 for recycling as a deacidifying agent; Step S7: Ammonium chloride or ammonium sulfate solution is concentrated by reverse osmosis, evaporated and crystallized, and then used as agricultural nitrogen fertilizer.

2. The method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash according to claim 1, characterized in that: In step S3, the initial water washing and dissolution conditions are set as follows: liquid-to-solid ratio of 3-5 L / kg, time of 3-10 minutes, and filtrate salt concentration within the range of 4%-10%.

3. The method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash according to claim 2, characterized in that: In step S4, the concentration of the sodium salt solution sent into the electrodialysis reaction system is 5%-8%.

4. The method for sodium-based deacidification of incineration flue gas and source reduction and resource utilization of fly ash according to claim 1, characterized in that: Step S3A, which includes replacing step S3: The collected dry fly ash enters the wetting process, water is added to the fly ash, and the initial filtrate is obtained by filtration before the soluble sodium salts in the fly ash are completely dissolved. The fly ash is then used as a wetting packing material for the subsequent fixed bed continuous water washing and desalination section.

5. The method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash according to claim 4, characterized in that: Step S5A, which replaces step S5, involves using a combination of pre-wetted fly ash as the initial material and dried fly ash as the supplementary material, continuously washing the mixture with water on a fixed bed, and obtaining the filtrate as the final filtrate.

6. The method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash according to claim 1, characterized in that: In step S6: The concentrated and crystallized NaHCO3 is directly returned to step S1 as a deacidifying agent for recycling.

7. The method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash according to claim 1, characterized in that: Both the initial and final filtrates are treated with ozone oxidation to reduce COD in the solution, and then purified sodium salt solution is obtained through a combination of ultrafiltration, nanofiltration, and reverse osmosis.

8. The method for sodium-based desulfurization of incineration flue gas and source reduction and resource utilization of fly ash according to claim 4, characterized in that: In steps S3 and S3A, a concentration detection device is added, and the initial filtrate is obtained by filtration within the salt concentration range of 8%-15%.

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