Fly ash high-efficiency dechlorination method by convection-mass transfer water washing

Abstract

The present application relates to the technical field of fly ash treatment, and discloses a fly ash convection-mass transfer water washing high-efficiency dechlorination method, wherein a surfactant is added when supercritical carbon dioxide is used to treat fly ash, the surfactant can reduce the surface energy of water in the micropores of the fly ash, the water is micro-emulsified, the flowability of the supercritical carbon dioxide in the pore channels of the fly ash is improved, the contact area between the supercritical carbon dioxide and water is significantly increased, the damage of the supercritical carbon dioxide to the internal lattice structure of the fly ash is significantly improved, the dissolution of the insoluble chlorine is significantly improved, and the chlorine removal rate is significantly improved. Meanwhile, the surfactant can also inhibit the agglomeration of the fly ash, avoid the pore blockage, and improve the mass transfer efficiency.

Description

Technical Field

[0001] This invention relates to the field of fly ash treatment technology, and in particular to a highly efficient dechlorination method for fly ash by convective mass transfer water washing. Background Technology

[0002] Waste incineration fly ash contains a large amount of chloride salts. These chloride salts can cause problems such as corrosion of sintering furnaces, blockage of flues, reduction of building material strength, and corrosion of steel bars when the fly ash is reused. Therefore, fly ash can only be reused after it has been dechlorinated to meet standards. The current traditional method for fly ash dechlorination is water washing, but water washing is not very effective at removing sparingly soluble chloride salts, which means that the fly ash still contains a high content of chloride salts.

[0003] In recent years, those skilled in the art have discovered that using carbon dioxide coupled with water washing can significantly improve the chlorine removal rate in fly ash and remove sparingly soluble chloride salts. For example, CN112275782B discloses a fly ash water washing device and method based on carbon dioxide conditioning. Another example is the prior art "Study on the Influence of Differential Characteristics of Municipal Solid Waste Incineration Fly Ash on Dechlorination and Desalination Effect - Taking Chongqing and Tianjin Fly Ash as Examples." In the above technical solutions, the chloride removal rate can reach 94%. Furthermore, the prior art "Supercritical CO2 coupled with water washing to enhance the removal of chlorine in MSWI flyash together with its carbon sequestration function" uses a treatment method of "supercritical treatment + secondary water washing + supercritical treatment + re-washing." In this technical solution, the residual chlorine content in fly ash is 0.88%, and the chlorine removal rate can reach 96.5%. This technical solution also points out that supercritical carbon dioxide can stabilize heavy metals in fly ash and reduce the concentration of lead and chromium ions leaching from the washing solution. When using the supercritical carbon dioxide coupled with water washing to treat fly ash, this invention found that the supercritical carbon dioxide in the prior art usually requires multiple cycles to achieve a significant dechlorination effect. Moreover, supercritical carbon dioxide treatment can only be carried out under specific temperature and pressure conditions, and multiple cycles consume a lot of energy. Therefore, it is of great significance to develop an energy-saving and efficient water washing dechlorination method. Summary of the Invention

[0004] The purpose of this invention is to improve the chlorine removal rate in supercritical carbon dioxide coupled water washing fly ash treatment.

[0005] This invention optimizes the supercritical carbon dioxide coupled water washing method for fly ash treatment. A surfactant is added during supercritical carbon dioxide treatment of fly ash. The surfactant reduces the surface energy of water in the fly ash micropores, causing water microemulsification, improving the flowability of supercritical carbon dioxide in the fly ash channels, significantly increasing the contact area between supercritical carbon dioxide and water, significantly enhancing the destructive effect of supercritical carbon dioxide on the internal crystal structure of fly ash, significantly increasing the dissolution of sparingly soluble chlorine, and significantly improving the chlorine removal rate. The surfactant also inhibits fly ash agglomeration, avoids pore blockage, and improves mass transfer efficiency.

[0006] The specific technical solution of this invention is as follows: A highly efficient dechlorination method for fly ash via convection-mass transfer water washing includes the following steps: (1) Carbon dioxide, surfactant and fly ash are placed in a reaction device for supercritical carbon dioxide treatment to produce pretreated fly ash. The surfactant is one or more of organosilazane modified alkyl glycoside, polyalkoxy modified heptamethyltrisiloxane (Silwet L-77), sodium dodecyl sulfate (SDS) and linear alkylbenzene sulfonate (LAS). (2) Pretreated fly ash is placed in a water washing device for water washing treatment to obtain dechlorinated fly ash.

[0007] As a preferred option, the conditions for supercritical carbon dioxide treatment include: temperature 30~40℃, pressure 10~15MPa, and treatment time 30~40min.

[0008] Preferably, the carbon dioxide flow rate is 0.05~0.2L / min per gram of fly ash, the water content of the fly ash is 5~10%, and the amount of surfactant added is 0.2~0.3g per gram of fly ash.

[0009] Preferably, the washing process includes primary washing and secondary washing.

[0010] As a preferred method, the conditions for primary water washing include: pH 9-10 and ultrasonication for 5-10 minutes.

[0011] As a preferred option, the conditions for secondary water washing include: a solid-liquid ratio of 1 to 3:1 between the primary water washing residue and pure water, a stirring rate of 200 to 400 r / min, and a time of 30 to 40 min.

[0012] Preferably, the product is washed with water and then filtered and dried at a temperature of 100~120℃.

[0013] Preferably, the pH is adjusted using a citric acid solution with a concentration of 0.1~0.5 mol / L.

[0014] As a preferred embodiment, organosilazane-modified alkyl glycosides are prepared by silane etherification grafting reaction of alkyl glycosides and hexamethyldisilazane.

[0015] Preferably, the conditions for the silane etherification grafting reaction include: temperature 45~60℃, time 3~5h, molar ratio of total hydroxyl groups of alkyl glycoside to hexamethyldisilazane 1:0.6~1.2, iodine as catalyst, and catalyst dosage of 1~1.5% of the total hydroxyl groups of alkyl glycoside.

[0016] Existing supercritical carbon dioxide coupled with water washing methods for treating fly ash suffers from high energy consumption due to multiple cycles. This invention optimizes the existing technology to address this issue. Existing supercritical carbon dioxide coupled with fly ash water washing processes typically require multiple cycles of supercritical carbon dioxide and water washing. Analysis revealed that in existing technologies, the initial treatment is usually supercritical carbon dioxide used to treat dry fly ash. However, dry fly ash has a highly polar surface, while supercritical carbon dioxide has a highly non-polar surface, resulting in poor wettability of supercritical carbon dioxide on dry fly ash and difficulty in penetrating its interior. After the initial cycle, the dry fly ash is washed to form wet fly ash. When supercritical carbon dioxide is used again to treat the wet fly ash, it readily dissolves in water to form carbonic acid, which then enters the fly ash interior through adsorption via the fly ash micropores, gradually dissolving the insoluble chloride ions within the fly ash. Therefore, directly using supercritical carbon dioxide to treat wet fly ash can reduce the number of cycles and lower energy consumption.

[0017] This invention also discovered that adding a surfactant significantly improves the chlorine removal rate of wet fly ash when using supercritical carbon dioxide to treat it. Water in wet fly ash forms a liquid film in the pores, hindering the flow of supercritical carbon dioxide. With the addition of a surfactant, the water in the micropores is microemulsified, forming tiny water pockets that spread evenly on the pore walls. This allows supercritical carbon dioxide to flow smoothly through the pores, significantly increasing the contact area with water. This significantly improves the efficiency of supercritical carbon dioxide dissolving in water to form carbonic acid, better breaking down the calcium aluminum silicate mineral framework and releasing the insoluble chlorine, thereby significantly improving the chlorine removal rate of the fly ash. Furthermore, the surfactant also inhibits fly ash agglomeration, allowing supercritical carbon dioxide to react fully and evenly with the fly ash.

[0018] Compared with the prior art, this application has the following technical effects: (1) Use supercritical carbon dioxide to treat wet fly ash to reduce the number of treatment cycles and reduce treatment energy consumption; (2) When supercritical carbon dioxide is used to treat wet fly ash, a surfactant is added to reduce the surface energy of water in the micropores of fly ash, increase the flowability of supercritical carbon dioxide inside fly ash, inhibit fly ash agglomeration, enhance the destructive effect of supercritical carbon dioxide on the calcium aluminum silicon mineral skeleton of fly ash, significantly increase the dissolution of insoluble chlorine, and significantly increase the chlorine removal rate of fly ash. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments.

[0020] To better understand the content of this invention, further explanation is provided below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of this invention.

[0021] Example 1:

[0022] A highly efficient dechlorination method for fly ash via convection-mass transfer water washing includes the following steps: (1) Add the total hydroxyl groups of alkyl glycoside (APG1214) and hexamethyldisilazane to the reaction vessel at a molar ratio of 1:1, and then add the catalyst (iodine, the amount of catalyst is 1.2% of the total hydroxyl groups of alkyl glycoside). React at 50°C for 4 hours to prepare surfactant (organosilazane modified alkyl glycoside). (2) The fly ash (moisture content of 8% and total chlorine content of 21.24%) and surfactant (addition amount of 0.25g per gram of fly ash) were loaded into the supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 35℃, pressure 12MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.1L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to make pretreated fly ash. (3) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 2:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 105℃ for 8 h to produce dechlorinated fly ash.

[0023] Example 2:

[0024] A highly efficient dechlorination method for fly ash via convection-mass transfer water washing includes the following steps: (1) Add the total hydroxyl groups of alkyl glycoside (APG1214) and hexamethyldisilazane to the reaction vessel at a molar ratio of 1:0.6, and then add the catalyst (iodine, the amount of catalyst is 1% of the total hydroxyl groups of alkyl glycoside). React at 45°C for 3 hours to prepare surfactant (organosilazane modified alkyl glycoside). (2) The fly ash (moisture content of 5% and total chlorine content of 21.24%) and surfactant (addition amount of 0.2g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 30℃, pressure 10MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.05L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to make pretreated fly ash. (3) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 1:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 100℃ for 8 h to produce dechlorinated fly ash.

[0025] Example 3:

[0026] A highly efficient dechlorination method for fly ash via convection-mass transfer water washing includes the following steps: (1) Add the total hydroxyl groups of alkyl glycoside (APG1214) and hexamethyldisilazane to the reaction vessel at a molar ratio of 1:1.2, and then add the catalyst (iodine, the amount of catalyst is 1.5% of the total hydroxyl groups of alkyl glycoside). React at a temperature of 45~60℃ for 5h to prepare surfactant (organosilazane modified alkyl glycoside). (2) The fly ash (moisture content of 10% and total chlorine content of 21.24%) and surfactant (addition amount of 0.3g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 40℃, pressure 15MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.2L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to make pretreated fly ash. (3) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 3:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 100~110℃ for 8 h to produce dechlorinated fly ash.

[0027] Example 4:

[0028] A highly efficient dechlorination method for fly ash via convection-mass transfer water washing includes the following steps: (1) Fly ash (moisture content of 8%, total chlorine content of 21.24%) and surfactant (Silwet L-77, added at 0.25g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 35℃, pressure 12MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.1L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to make pretreated fly ash. (2) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 2:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 105℃ for 8 h to produce dechlorinated fly ash.

[0029] Example 5:

[0030] A highly efficient dechlorination method for fly ash via convection-mass transfer water washing includes the following steps: (1) Fly ash (moisture content of 8% and total chlorine content of 21.24%) and surfactant (SDS, added at 0.25g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 35℃, pressure 12MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.1L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to make pretreated fly ash. (2) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 2:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 105℃ for 8 h to produce dechlorinated fly ash.

[0031] Example 6:

[0032] A highly efficient dechlorination method for fly ash via convection-mass transfer water washing includes the following steps: (1) Fly ash (moisture content of 8% and total chlorine content of 21.24%) and surfactant (LAS, added at 0.25g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 35℃, pressure 12MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.1L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to make pretreated fly ash. (2) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 2:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 105℃ for 8 h to produce dechlorinated fly ash.

[0033] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not use supercritical carbon dioxide treatment, and included the following steps: Fly ash (total chlorine content 21.24%) was added to a washing device. 0.1 mol / L citric acid solution was added to adjust the pH of the washing solution to 9-10. The first-stage washing (ultrasonic treatment) was performed for 5 min. The first-stage washing solution and the first-stage washing residue were separated by filtration. The first-stage washing residue was added to pure water at a liquid-to-solid ratio of 2:1 for a second-stage washing (stirring speed 300 r / min) for 20 min. The second-stage washing solution and the second-stage washing residue were separated by filtration. The second-stage washing residue was dried at 105℃ for 8 h to produce dechlorinated fly ash.

[0034] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses dry fly ash for treatment, including the following steps: (1) Add the total hydroxyl groups of alkyl glycoside (APG1214) and hexamethyldisilazane to the reaction vessel at a molar ratio of 1:1, and then add the catalyst (iodine, the amount of catalyst is 1.2% of the total hydroxyl groups of alkyl glycoside), and react at 50°C for 4 hours to prepare the surfactant. (2) The fly ash (dry fly ash with a total chlorine content of 21.24%) and surfactant (addition amount of 0.25g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 35℃, pressure 12MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.1L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to prepare pretreated fly ash. (3) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 2:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 105℃ for 8 h to produce dechlorinated fly ash.

[0035] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that the fly ash moisture content is too high, including the following steps: (1) Add the total hydroxyl groups of alkyl glycoside (APG1214) and hexamethyldisilazane to the reaction vessel at a molar ratio of 1:1, and then add the catalyst (iodine, the amount of catalyst is 1.2% of the total hydroxyl groups of alkyl glycoside), and react at 50°C for 4 hours to prepare the surfactant. (2) The fly ash (moisture content of 20% and total chlorine content of 21.24%) and surfactant (addition amount of 0.25g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 35℃, pressure 12MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate of 0.1L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to make pretreated fly ash. (3) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 2:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 105℃ for 8 h to produce dechlorinated fly ash.

[0036] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the total hydroxyl groups of the alkyl glycoside were not modified, and the following steps were performed: (1) Fly ash (dry fly ash with a total chlorine content of 21.24%) and surfactant (alkyl glycoside total hydroxyl APG1214, added at 0.25g per gram of fly ash) were loaded into a supercritical carbon dioxide device. The parameters of the supercritical carbon dioxide device were set (temperature 35℃, pressure 12MPa, stirring speed 300r / min). Carbon dioxide (purity 99.999%, flow rate 0.1L / min per gram of fly ash) was introduced and reacted for 30min. After the reaction was completed, the supercritical carbon dioxide was discharged first, and then the fly ash was taken out to prepare pretreated fly ash. (2) Add the pretreated fly ash to the washing device, add 0.1 mol / L citric acid solution to adjust the pH of the washing solution to 9~10, perform first-stage washing (ultrasonic treatment) for 5 min, filter to separate the first-stage washing solution and the first-stage washing residue, add the first-stage washing residue to pure water at a liquid-solid ratio of 2:1 for second-stage washing (stirring rate 300 r / min) for 20 min, filter to separate the second-stage washing solution and the second-stage washing residue, and dry the second-stage washing residue at 105℃ for 8 h to produce dechlorinated fly ash.

[0037] Example of detection: The components of the dechlorinated fly ash and washing solutions prepared in Examples 1-6 and Comparative Examples 1-4 were tested. The total chlorine test method was conducted in accordance with the published content of "HJ 999-2018 Determination of Fluorine and Chlorine in Solid Waste by Alkali Fusion-Ion Chromatography". The contents of Pb and Cr in the dechlorination fly ash leachate were tested according to the content published in "HJ 766-2015 Determination of Metallic Elements in Solid Waste by Graphite Furnace / Inductively Coupled Plasma Mass Spectrometry". The calcium ion concentration in the primary washing solution was tested according to the content published in "HJ 766-2015 Determination of Metallic Elements in Solid Waste by Graphite Furnace / Inductively Coupled Plasma Mass Spectrometry". The test results are shown in Table 1; Table 1 Test Results

[0038] As shown in Table 1, the total chlorine content in the dechlorinated fly ash obtained in Examples 1-6 was 0.03-0.19%, the chlorine removal rate was 99.08-99.83%, the Pb content in the dechlorinated fly ash leachate was 0.351-0.49 mg / L, the Cr content in the dechlorinated fly ash leachate was 0 mg / L, and the calcium ion concentration in the primary washing solution was 34.89-61.94 g / kg. Compared with Comparative Example 1 (which did not use supercritical carbon dioxide), using supercritical carbon dioxide to pretreat fly ash before washing significantly improved the chlorine removal rate, fixed heavy metals in fly ash, reduced the leaching of heavy metals, and fixed calcium ions in fly ash, reducing calcium loss.

[0039] Comparative Example 2 illustrates a technique for directly treating dry fly ash using supercritical carbon dioxide. Compared to Example 1, Comparative Example 2 shows a significantly improved chlorine removal rate, indicating that supercritical carbon dioxide treatment of wet fly ash is significantly more effective at removing chlorine than dry fly ash. Comparative Example 3 addresses a technique for treating wet fly ash with excessive moisture content. Compared to Example 1, Comparative Example 3 shows a decreased chlorine removal rate, demonstrating that a certain amount of water in the fly ash is necessary to significantly improve the supercritical carbon dioxide effect. Both excessively low and high water content in the fly ash will reduce the effectiveness of supercritical carbon dioxide.

[0040] Furthermore, this invention also tested the application effects of different surfactants. The results showed that different surfactants exhibited different characteristics in the supercritical carbon dioxide coupled water washing fly ash treatment process. Silwet L-77 in Example 4 was prone to hydrolysis under alkaline conditions, while SDS and LAS in Example 5 produced a large amount of foam. These surfactants, in scenarios with large processing volumes, affected dispersibility and reduced treatment efficiency. Therefore, this invention also provides organosilazane-modified alkyl glycosides as surfactants. These surfactants produce less foam and are stable in alkaline environments, exhibiting superior application effects compared to other surfactants.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A highly efficient dechlorination method for fly ash via convection-mass transfer water washing, characterized in that, Includes the following steps: (1) Carbon dioxide, surfactant and fly ash are placed in a reaction device for supercritical carbon dioxide treatment to produce pretreated fly ash. The surfactant is one or more of organosilazane modified alkyl glycoside, polyalkoxy modified heptamethyltrisiloxane, sodium dodecyl sulfate and linear alkylbenzene sulfonate. (2) Pretreated fly ash is placed in a water washing device for water washing treatment to obtain dechlorinated fly ash.

2. The method according to claim 1, characterized in that, The conditions for supercritical carbon dioxide treatment include: temperature 30~40℃, pressure 10~15MPa, and treatment time 30~40min.

3. The method according to claim 1, characterized in that carbon dioxide... The feed rate is 0.05~0.2L / min per gram of fly ash, the moisture content of the fly ash is 5~10%, and the amount of surfactant added is 0.2~0.3g per gram of fly ash.

4. The method according to claim 1, characterized in that, The washing process includes primary washing and secondary washing.

5. The method according to claim 4, characterized in that, The conditions for primary water washing include: pH 9-10, and ultrasonication for 5-10 minutes.

6. The method according to claim 4, characterized in that, The conditions for secondary water washing include: a liquid-to-solid ratio of primary water washing residue to pure water of 1 to 3:1, a stirring rate of 200 to 400 r / min, and a time of 30 to 40 min.

7. The method according to claim 1 or 3, characterized in that, After washing, the product is filtered and dried at a temperature of 100~110℃.

8. The method according to claim 5, characterized in that, pH is adjusted using citric acid solution with a concentration of 0.1~0.5 mol / L.

9. The method according to claim 1, characterized in that, Organosilazane-modified alkyl glycosides are prepared by silyl etherification grafting reaction of alkyl glycosides and hexamethyldisilazane.

10. The method according to claim 9, characterized in that, The conditions for the silyl etherification grafting reaction include: temperature 45~60℃, time 3~5h, molar ratio of total hydroxyl groups of alkyl glycoside to hexamethyldisilazane 1:0.6~1.2, iodine as catalyst, and catalyst dosage of 1~1.5% of the total hydroxyl groups of alkyl glycoside.

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