A method for the resource utilization of fly ash by synergistic dissolution of chloride ions with subcritical dimethyl ether-water.

Abstract

This invention relates to the field of fly ash harmless treatment and resource utilization technology, specifically to a method for the resource utilization of fly ash by synergistic dissolution of chloride ions with subcritical dimethyl ether-water. The method involves mixing chloride-containing fly ash with water, additives, and subcritical dimethyl ether, followed by sequential stirring and solid-liquid separation to obtain a solid product. The chloride ion content of the solid product is ≤0.30%, and the water content is ≤20%. This process effectively removes chloride ions from fly ash through a co-dissolution system of dimethyl ether, water, and additives under specific temperature, time, and solid-liquid ratio conditions. Dimethyl ether can be recycled, and the low-chlorine, low-moisture solid product can be used as a substitute raw material for limestone in the production of cement and other building materials. This invention provides a novel fly ash dechlorination technology, which is of great significance for the harmless treatment and resource utilization of hazardous waste, as well as for reducing the exploitation of primary resources, thus meeting the development needs of pollution reduction and carbon reduction.

Description

Technical Field

[0001] This invention relates to the field of fly ash harmlessness and resource utilization technology, specifically to a method for the resource utilization of fly ash by subcritical dimethyl ether-water synergistic dissolution of chloride ions. Background Technology

[0002] With limitations in landfill and land-use disposal technologies, and the implementation of waste sorting policies, solid waste incineration technology has become more widely used. Currently, technologies such as standalone incineration and co-incineration can basically meet the requirements in terms of environmental protection, practicality, and economy. However, as a hazardous waste, incineration fly ash presents a significant challenge due to its large volume and high treatment costs.

[0003] Fly ash is mainly generated in flue gas purification systems and heat recovery systems. After treatment processes such as alkaline washing, its pH is generally between 11 and 13. It contains a large amount of elements such as Cl, Ca, Al, Si, K, and Na, as well as small amounts of heavy metals and some harmful components. Typically, fly ash undergoes solidification pretreatment such as cement solidification and stabilization before being safely landfilled as hazardous waste. However, the large amount of chloride ions and other soluble salts in fly ash hinders hydration during the solidification process, resulting in poor solidification. Traditional water washing processes for fly ash treatment not only generate large amounts of wastewater, but also form highly water-content "sludge" after mixing with water, making subsequent dewatering difficult and energy-intensive. If chloride ions in fly ash can be efficiently removed, the aforementioned safe landfill process can be ensured, and fly ash with low chloride content can be used as a good cement raw material for resource utilization, helping to turn fly ash "waste into treasure." However, current technologies still lack effective means to remove chloride ions from fly ash, making it difficult to guarantee the efficiency of harmless treatment and hindering its resource utilization. Summary of the Invention

[0004] The present invention aims to provide a method for the resource utilization of fly ash by synergistic dissolution of chloride ions by subcritical dimethyl ether-water, in order to solve the technical problem of the lack of effective means to remove chloride ions from fly ash in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for the resource utilization of fly ash by synergistic dissolution of chloride ions by subcritical dimethyl ether-water involves mixing chlorine-containing fly ash with water, additives, and subcritical dimethyl ether, followed by sequential stirring and mixing treatment and solid-liquid separation to obtain a solid product.

[0007] Furthermore, subcritical dimethyl ether is prepared by pressurizing gaseous dimethyl ether at room temperature and pressure to 0.5-1.0 MPa to form liquid subcritical dimethyl ether.

[0008] Furthermore, the mass ratio of the mixture formed by chlorine-containing fly ash, water, and additives is 1:4-10; the mass ratio of water to additives is 1-10:1; and the additives include methanol and / or ethanol.

[0009] Furthermore, the mass ratio of the mixture formed by subcritical dimethyl ether, water, and additives is 1:1-5.

[0010] Furthermore, the stirring and mixing time is 5-30 min, the speed is 300-500 rpm, the temperature is 15-30℃, and the pressure is 0.6 MPa.

[0011] Furthermore, the pore size of the filter screen used in the solid-liquid separation process is 200-300 mesh.

[0012] Furthermore, the chlorine-containing fly ash contains CaO and SiO2; and the chloride ion content is ≥15%.

[0013] Furthermore, the solid product has a chloride ion content of <0.30% and a water content of <20%.

[0014] Furthermore, the liquid product obtained after solid-liquid separation is used for gas-liquid separation to obtain gaseous dimethyl ether; the gaseous dimethyl ether is dried and then pressurized for liquefaction to obtain subcritical dimethyl ether.

[0015] Furthermore, the solid product is used to prepare cement; the chloride ion content of the solid product is ≤0.05%, and the moisture content is ≤8%.

[0016] In summary, the principle and beneficial effects of this technical solution are as follows:

[0017] In this technical solution, chlorinated fly ash is placed in a reactor. A certain amount of water and additives are injected into the reactor through the inlet pipe to dissolve the fly ash. Dimethyl ether is pressurized and liquefied using an air pump and then introduced into the reactor to mix with the fly ash solution. After the subcritical dimethyl ether, water, additives, and fly ash are thoroughly mixed, the valve is opened to separate the solid and liquid phase products. The solid phase product has a chloride ion content of less than 0.30% and a water content of less than 20%. The liquid phase product is mainly a mixture of dimethyl ether and water. The dimethyl ether is recovered through depressurization treatment and can be recycled by drying and repressurizing and liquefying. The separated solid phase product is used as a substitute raw material for cement production and, along with other raw materials, is sent to a cement kiln for cement production, realizing the resource utilization of waste.

[0018] The subcritical dimethyl ether solvent extraction technology used in this scheme is a novel solvent extraction technology that has shown great potential in the dehydration and recovery of useful substances from wastes such as microalgae, sludge, and algal sludge. However, this technology has not yet been used for the resource utilization of fly ash, and it is unknown whether it can effectively remove impurities (such as chloride ions) from fly ash that affect its comprehensive utilization. This invention utilizes the miscibility of subcritical dimethyl ether with water, and improves the solubility of chloride ions in fly ash by adjusting parameters and adding additives, thereby further enhancing solid-liquid separation performance and achieving the goal of harmless treatment and resource utilization of chlorine-containing fly ash.

[0019] This process avoids the problems of complex processes and high energy consumption in existing fly ash washing processes, and improves the removal efficiency of chloride ions in fly ash. Utilizing fly ash as a cement raw material not only saves space and costs associated with fly ash landfill, but also effectively reduces the demand for mining cement raw materials such as limestone, which is of significant importance for pollution reduction and carbon reduction. Furthermore, the subcritical dimethyl ether in this invention can be recycled through a depressurization-purification-pressurization process, which is conducive to further promoting the construction of an environmentally friendly and circular society.

[0020] In summary, the inventors discovered and utilized the highly efficient dissolution and easy separation of chloride ions in fly ash through the co-solution of subcritical dimethyl ether and water. Under specific conditions of temperature, time, and solid-liquid ratio, effective removal of chloride ions from fly ash is achieved through a co-solution system of dimethyl ether, water, and additives. The dimethyl ether can be recycled after vacuum drying, and the low-chlorine, low-moisture solid product can be used as a substitute raw material for limestone in the production of cement and other building materials. This invention provides a novel fly ash dechlorination technology, which is of great significance for the harmless treatment and resource utilization of hazardous waste, as well as for reducing the exploitation of primary resources, thus meeting the development needs of pollution reduction and carbon reduction. Attached Figure Description

[0021] Figure 1 This is the overall process flow diagram for Example 1. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well known to those skilled in the art, and the materials and reagents used can all be obtained commercially.

[0023] Example 1:

[0024] A method for the resource utilization of fly ash through the synergistic dissolution of chloride ions by subcritical dimethyl ether-water, the process is as follows: Figure 1 As shown, the general steps are as follows:

[0025] S1: Chlorine-containing fly ash is placed in a reactor, and a mixture of water and additives (4-10 times the mass of the fly ash) is injected to dissolve the fly ash. The mass ratio of water to additives is 1-10:1; the additives include methanol and / or ethanol, and their function is to improve dissolution and separation performance. Dimethyl ether is gaseous at room temperature and pressure. It is liquefied (forming subcritical dimethyl ether, under which pressure dimethyl ether can form a subcritical state) by pressurizing it to 0.5-1.0 MPa using an air compressor pump and then transported to the reactor. The mass ratio of dimethyl ether to water and additives is 1:1-5. The mixture is stirred and mixed with fly ash and water using a built-in stirring shaft in the reactor for 5-30 minutes, at a speed of 300-500 rpm, at a temperature of 15-30℃, and at a pressure of 0.6 MPa inside the reactor. The fly ash mainly contains CaO, SiO2, and chloride ions, with a chloride ion content of approximately 15%.

[0026] S2: After the dimethyl ether, water, additives, and fly ash in the reactor are fully mixed, open the pressure valve at the bottom of the reactor to reduce the pressure, allowing the solid and liquid phase products to pass through the filter screen (200-300 mesh) at the bottom of the reactor for separation. The solid phase product is retained at the bottom of the reactor, while the liquid phase product is discharged from the reaction system. The chloride ion removal rate of the separated solid phase product can reach 90%-95% compared to the initial fly ash (calculated as (chloride ion content in initial fly ash - chloride ion content in solid phase product) / chloride ion content in initial fly ash × 100%), the chloride ion content in the solid phase product is less than 0.30%, and the final moisture content of the solid phase product is less than 20%.

[0027] S3: The liquid product after solid-liquid separation enters the gas-liquid separator (set temperature 25-30℃, no external pressure required). Dimethyl ether is gaseous at room temperature and pressure, and can therefore be volatilized and recovered from the product. Gaseous dimethyl ether is collected from the gas-liquid separator, dried (to a moisture content of <2%), and then pressurized by an air pump for re-liquefaction and recycling.

[0028] S4: The separated solid products are used as a substitute raw material for limestone in the cement production process. Together with clay, admixtures and other raw materials, they are sent to the cement kiln for high-temperature calcination at a predetermined temperature to produce cement, thereby realizing the resource utilization of waste.

[0029] Perform specific tests according to the above operating procedures, and refer to Table 1 for parameter settings.

[0030] Table 1: Parameter settings for Test 1-.

[0031]

[0032] Comparative Example 1:

[0033] This comparative example is essentially the same as Test 3 in Example 1, except that subcritical dimethyl ether was replaced with an equal amount of methanol (other parameters and conditions were set the same as in Test 3). After treatment, the chloride ion content in the solid product of this comparative example was 11%, the water content was 39%, and the chloride ion removal rate was 25%. It is evident that using methanol as the extraction reagent cannot effectively reduce the chloride ion content in the solid product, and the fly ash is difficult to recycle. Furthermore, the high water content in the solid product requires significant energy expenditure in subsequent steps to remove water and form industrial raw materials with acceptable water content, increasing the number of process steps and production costs.

[0034] Comparative Example 2:

[0035] This comparative example is essentially the same as Test 3 in Example 1, except that subcritical dimethyl ether was replaced with an equal amount of ethanol (other parameters and conditions were set the same as in Test 3). After treatment, the solid product of this comparative example contained 8% chloride ions, 33% water, and a chloride ion removal rate of 47%. Using ethanol as the extraction organic solvent also presents similar problems to methanol. Alcohol solvents showed some effect in removing chloride ions (but the effect was still insufficient), but the water removal effect was very unsatisfactory.

[0036] Comparative Example 3:

[0037] This comparative example is essentially the same as Test 3 in Example 1, except that subcritical dimethyl ether was replaced with an equal amount of acetonitrile (other parameters and conditions were set the same as in Test 3). After treatment, the chloride ion content in the solid product of this comparative example was 14%, the water content was 21%, and the chloride ion removal rate was 8%. Acetonitrile, as an organic solvent with excellent dehydration properties, was not very effective in removing chloride ion impurities under the conditions of this process. Although the use of acetonitrile can reduce the water content in the solid product to some extent (compared to alcohol solvents), the effect is still insufficient.

[0038] In addition to methanol, ethanol, and acetonitrile mentioned in Comparative Examples 1-3, the inventors also extensively experimented with other organic solvents, such as acetone, ethyl acetate, chloroform, toluene, tributyl phosphate, dimethyl sulfoxide, and hexane. None of these organic solvents effectively reduced the chloride ion content and water content in the solid product. Using these organic solvents, the chloride ion content in the solid product ranged from 5% to 15%. After extensive screening, the inventors discovered that subcritical dimethyl ether has a significantly more significant effect on removing chloride ions and reducing water content compared to other organic solvents. The chloride ion content in the solid product can be reduced to below 0.3%, significantly better than other solvents, with a reduction of more than 10 times. This effect was unexpected by the inventors before the experiment. Furthermore, with further parameter optimization, the chloride ion content in the solid product can be reduced to 0.05%, and the water content can be reduced to 8% (refer to Test 3).

[0039] Comparative Example 4:

[0040] This comparative example is essentially the same as Test 3 in Example 1, except that the mixture of water and additives was replaced entirely with an equal amount of water. After treatment, the chloride ion content in the solid product of this comparative example was 0.5%, the water content was 25%, and the chloride ion removal rate was 86%. Comparing this comparative example with Test 3 in Example 1, it was found that without the addition of additives such as ethanol, the mixture of water and additives would have a significant negative impact on the chloride ion removal rate. The chloride ion content in the solid product of this comparative example was nearly 16 times higher than that in Test 3, and the water content was nearly 20% higher. This demonstrates that the addition of ethanol additives plays a crucial role in further improving the process effect (reducing the chloride ion content and water content in the product).

[0041] Comparative Example 5:

[0042] This comparative example is essentially the same as test 3 in Example 1, except that the additive in the mixture of water and additives was replaced with an equal amount of acetonitrile. After treatment, the chloride ion content in the solid product of this comparative example was 13%, the water content was 10%, and the chloride ion removal rate was 12%. The experimental data from this comparative example show that the selection of an appropriate type of additive is crucial to ensuring the quality of the solid product. Acetonitrile, compared to ethanol, did not improve the quality of the solid product (due to the high chloride ion content); moreover, the addition of acetonitrile, compared to its absence, further reduced the quality of the solid product.

[0043] Comparative Example 6:

[0044] This comparative example is essentially the same as test 3 in Example 1, except that the water in the mixture of water and additives was replaced with an equal amount of acetonitrile. After treatment, the chloride ion content in the solid product of this comparative example was 15% (equivalent to virtually no chloride ion removal effect), the water content was 8%, and the chloride ion removal rate was 2%. If the subcritical dimethyl ether extraction environment is replaced with acetonitrile + ethanol, it will have a significant negative impact on the chloride ion removal effect.

[0045] In summary, this method is the first to discover that using subcritical dimethyl ether (DME) for fly ash treatment can effectively remove chloride ions from fly ash and reduce the moisture content in the solid product. Furthermore, the successful implementation of subcritical DME extraction technology requires a specific solution environment; using water and alcohol solvents (such as methanol and ethanol) in conjunction with subcritical DME extraction can effectively enhance the effectiveness of the DME.

[0046] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for the resource utilization of fly ash by synergistic dissolution of chloride ions with subcritical dimethyl ether-water, characterized in that, Its chloride ion removal rate is 90%-95%; the fly ash contains CaO, SiO2, and chloride ion components; Chlorine-containing fly ash was mixed with water, additives and subcritical dimethyl ether, and then subjected to stirring and mixing treatment and solid-liquid separation to obtain a solid product. Subcritical dimethyl ether is prepared by pressurizing gaseous dimethyl ether at room temperature and pressure to 0.5-1.0 MPa to form liquid subcritical dimethyl ether. The additives include methanol and / or ethanol; The solid product has a chloride ion content of ≤0.30% and a moisture content of ≤20%.

2. The method for the resource utilization of fly ash by synergistic dissolution of chloride ions by subcritical dimethyl ether-water according to claim 1, characterized in that, The mass ratio of the mixture of chlorine-containing fly ash, water, and additives is 1:4-10; the mass ratio of water and additives is 1-10:

1.

3. The method for the resource utilization of fly ash by synergistic dissolution of chloride ions with subcritical dimethyl ether-water according to claim 2, characterized in that, The mass ratio of the mixture formed by subcritical dimethyl ether, water, and additives is 1:1-5.

4. The method for the resource utilization of fly ash by synergistic dissolution of chloride ions by subcritical dimethyl ether-water according to claim 3, characterized in that, The mixing time is 5-30 minutes, the speed is 300-500 rpm, the temperature is 15-30℃, and the pressure is 0.6 MPa.

5. The method for the resource utilization of fly ash by synergistic dissolution of chloride ions by subcritical dimethyl ether-water according to claim 4, characterized in that, The filter screen used in the solid-liquid separation process has a mesh size of 200-300.

6. The method for the resource utilization of fly ash by synergistic dissolution of chloride ions by subcritical dimethyl ether-water according to claim 5, characterized in that, The liquid product obtained after solid-liquid separation is used for gas-liquid separation to obtain gaseous dimethyl ether; the gaseous dimethyl ether is dried and then pressurized for liquefaction to obtain subcritical dimethyl ether.

7. The method for the resource utilization of fly ash by synergistic dissolution of chloride ions by subcritical dimethyl ether-water according to claim 6, characterized in that, The solid product is used to prepare cement; the chloride ion content of the solid product is ≤0.05%, and the moisture content is ≤8%.

Images