Method for improving desulfurization activity of slaked lime by using household garbage incineration fly ash

Abstract

The present application belongs to the technical field of desulfurizer preparation, and particularly relates to a method for improving the desulfurization activity of slaked lime by using household garbage incineration fly ash, which comprises the following steps: 1) mixing fly ash with hydrochloric acid and stirring for a period of time to obtain fly ash acid washing slurry; 2) performing pressure filtration dewatering on the fly ash acid washing slurry to obtain fly ash residue and pressure filtrate; 3) performing concentration crystallization on the pressure filtrate to obtain crystalline salt; 4) mixing slaked lime with the fly ash residue and calcining to obtain calcined material; and 5) mixing the calcined material with water, crystalline salt and alcohol additive and aging to obtain slaked lime with improved desulfurization activity. The method can significantly improve the desulfurization activity of slaked lime, thereby being used in a garbage incineration flue gas purification process to improve the acid gas removal rate, and at the same time, the method reasonably utilizes useful components of fly ash to realize the reuse of fly ash, thereby reducing the amount of fly ash entering a landfill.

Description

Technical Field

[0001] This invention belongs to the field of desulfurization agent preparation technology, specifically relating to a method for improving the desulfurization activity of quicklime using fly ash from municipal solid waste incineration. Background Technology

[0002] With societal development, the volume of municipal solid waste collected continues to increase. Incineration technology, due to its ability to effectively address secondary pollution from raw waste, significantly reduce volume, and recover energy, has surpassed landfill to become the most important method for treating municipal solid waste. The rapid development of municipal solid waste incineration technology has led to a growing concern regarding the disposal of the large amounts of fly ash generated during incineration.

[0003] Furthermore, the desulfurization process in waste incineration flue gas purification systems mainly employs a combination of rotary spray semi-dry desulfurization and dry desulfurization processes, with semi-dry desulfurization being the primary process, contributing over 90% of the overall desulfurization. However, with the increasing stringency of flue gas emission standards, the activity of slaked lime used for waste incineration flue gas desulfurization decreases, leading to an increase in the amount of slaked lime used in semi-dry desulfurization and thus increasing the cost of treating municipal solid waste incineration flue gas. Therefore, there is an urgent need to develop a method to improve the desulfurization activity of slaked lime entering waste incineration plants, preparing enhanced slaked lime for the purification of waste incineration flue gas. This is crucial for improving the treatment efficiency of waste incineration flue gas and reducing the production and operating costs of enterprises. Summary of the Invention

[0004] The purpose of this invention is to provide a method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration. The method improves the activity of slaked lime through two stages: first, the calcination stage of slaked lime, which involves calcining slaked lime to obtain quicklime; and second, the dry digestion stage of the calcined quicklime, which involves dry digestion of quicklime with the addition of additives during the digestion process, thereby obtaining slaked lime with stronger activity.

[0005] Specifically, the present invention provides the following technical solution:

[0006] A method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration includes the following steps:

[0007] 1) Mix fly ash with hydrochloric acid and stir for a period of time to obtain fly ash pickling slurry;

[0008] 2) The fly ash pickling slurry is dewatered by pressure filtration to obtain fly ash residue and filtrate;

[0009] 3) The filtrate is concentrated and crystallized to obtain crystalline salt;

[0010] 4) The quicklime and fly ash residue are mixed and then calcined to obtain the calcined material;

[0011] 5) After calcination, the material is mixed with water, crystalline salt, and alcohol additives and then hydrated to obtain quicklime with improved desulfurization activity.

[0012] First, this invention uses slaked lime (calcium hydroxide) as raw material to prepare quicklime through calcination. Compared to calcium carbonate, calcium hydroxide has a decomposition temperature of 510-550℃. In practice, calcium hydroxide begins to decompose when the temperature is heated to 450℃. The calcium oxide after heating and decomposition has higher activity (due to the high temperature of water after reaction). Second, the fly ash pickling solution contains high concentrations of calcium chloride and sodium chloride. After pressure filtration and crystallization, a mixture of crystalline salts containing sodium chloride and calcium chloride is obtained. This invention found that adding the above-mentioned crystalline chloride salts during the dry digestion process of calcium oxide can promote the dissolution of calcium hydroxide (the reaction between calcium hydroxide and sulfur dioxide is most rapid in the ionic state; the more solid calcium hydroxide dissolves into water, the more calcium hydroxide participates in the sulfur dioxide reaction, and the higher the sulfur dioxide removal rate). Furthermore, this invention found that adding alcohol additives during the dry digestion process of quicklime allows the hydroxyl groups to anchor on the surface of calcium hydroxide ions, thereby forming an alcohol molecule coating layer on the surface of calcium hydroxide. This effectively prevents the aggregation of calcium hydroxide particles, thereby increasing the specific surface area of ​​slaked lime and improving desulfurization activity.

[0013] Preferably, in step 1), the hydrochloric acid is 0.1-3 mol / L dilute hydrochloric acid, more preferably 2-3 mol / L dilute hydrochloric acid.

[0014] Preferably, in step 1), the L / S ratio of the hydrochloric acid to fly ash is 3-10, more preferably 3-5. Wherein, L is the volume of the liquid (in liters), and S is the mass of the solid (in kilograms).

[0015] Preferably, in step 1), the stirring time is 60-300 min, more preferably 60-90 min.

[0016] By adopting the above-mentioned preferred pickling conditions, it can be ensured that the fly ash is completely pickled. Otherwise, insufficient pickling will result in a high salt content in the residual filter cake, affecting the amount of filter cake used.

[0017] Preferably, in step 2), a diaphragm filter press is used to dewater the fly ash pickling slurry. The filtration pressure of the diaphragm filter press is 0.4-2.0 MPa (more preferably 0.6-1.0 MPa), the filter cloth is made of polyester, and the moisture content of the fly ash residue obtained after filtration is 35-40%.

[0018] Preferably, in step 3), an MVR evaporator is used to concentrate and crystallize the filtrate. In a preferred embodiment, the heat source for the MVR evaporator comes from a waste incineration plant.

[0019] Preferably, in step 4), the amount of fly ash residue is 5%-20% based on the mass of the slaked lime, more preferably 5-10%. This invention has found that the addition of sulfates to the fly ash residue can lower the calcination temperature of the slaked lime, but the amount of calcium sulfate added must be controlled, as the presence of calcium sulfate impurities will slow down the hydration process of the slaked lime.

[0020] Preferably, in step 4), the calcination temperature is 450-580℃, the time is 12-24h, and the proportion of undecomposed calcium hydroxide after calcination is 10-20%. Experiments have shown that when the calcium hydroxide decomposition rate reaches 80-90%, the calcium oxide obtained at this time has stronger activity.

[0021] More preferably, in step 4), the calcination temperature is 510-550℃, the time is 12-18h, and the proportion of undecomposed calcium hydroxide after calcination is 10-15%.

[0022] Preferably, in step 5), the L / S ratio of the calcined material to water is 0.5-8, and more preferably, the L / S ratio is 2-4.

[0023] In a preferred embodiment, to promote the maturation effect, the initial temperature of the water is 20-60°C, more preferably 40-50°C.

[0024] Preferably, in step 5), the amount of crystalline salt used is 0.1-0.3% based on the mass of the calcined material, more preferably 0.1-0.2%. This invention has found that when the amount of crystalline salt is less than 0.1%, the effect of promoting calcium hydroxide dissolution is not significant; when the amount is greater than 0.3%, excessive impurities are introduced, affecting the quality of the digested calcium hydroxide.

[0025] Preferably, in step 5), the alcohol additive is selected from one or more of isopropanol, triacetamide, and polyethylene glycol;

[0026] Based on the mass of the calcined material, the amount of the alcohol additive is 0.1-2.0%, more preferably 0.1-0.5%. Compared with other alcohols, the above-mentioned alcohol additive has a better effect on preventing the aggregation of calcium hydroxide particles. At the same time, the present invention found that when the amount of alcohol additive is less than 0.1%, the effect of alcohol additive on inhibiting the aggregation of calcium hydroxide particles is not obvious, and when the amount is more than 2.0%, the efficiency of the additive decreases and the preparation cost increases.

[0027] Preferably, in step 5), the aging process is performed three times, with each aging period lasting 40-90 minutes, more preferably 50-60 minutes. The aforementioned amounts of water and alcohol additives are added for each aging process; crystalline salt is added only for the first aging process, and not for the subsequent two.

[0028] The present invention also provides a quicklime, which is prepared by the above method.

[0029] The present invention also provides the application of the above-mentioned quicklime as a desulfurizing agent in the waste incineration flue gas purification process.

[0030] The beneficial effects of this invention are as follows:

[0031] The method provided by this invention can significantly improve the desulfurization activity of quicklime, thereby improving the removal rate of acidic gases in the flue gas purification process of waste incineration. At the same time, the method also makes reasonable use of the useful components of fly ash, realizing the reuse of fly ash and reducing the amount of fly ash entering landfills. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the prior art in the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a process flow diagram of Example 1, which describes the method of improving the desulfurization activity of quicklime using fly ash from municipal solid waste incineration. Detailed Implementation

[0034] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the invention.

[0035] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. All reagents or instruments without specified manufacturers are conventional products that can be purchased through legitimate channels.

[0036] Example 1

[0037] A method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration can be partially referenced. Figure 1 The steps are as follows:

[0038] Fly ash pickling steps: Mix fly ash with dilute hydrochloric acid (3mol / L) with an L / S ratio of 3 and stir continuously for 60 minutes;

[0039] Fly ash filtration process: The fly ash pickling slurry is dewatered using a high-pressure diaphragm filter press at a pressure of 2.0 MPa. Polyester filter cloth is used, and fly ash residue with a moisture content of 40% is obtained after filtration.

[0040] Fly ash filter press leachate concentration and crystallization steps: The fly ash filter press leachate is concentrated and crystallized using an MVR evaporation system. The heat source is from the waste incineration plant, thereby obtaining a mixture of crystalline salts of sodium chloride and calcium chloride.

[0041] Calcination steps of slaked lime: Before calcining slaked lime, add 5% of fly ash residue by weight of slaked lime, mix thoroughly, and calcine at 550℃ for 12 hours, controlling the proportion of unreacted calcium hydroxide in the reaction product to be 10%.

[0042] Dry slaking steps of quicklime: Add water to the calcined quicklime at an L / S ratio of 2, with an initial water temperature of 60℃. Add 0.1% of the mass of the mixed salt of calcium chloride and sodium chloride, and add 0.1% of the mass of polyethylene glycol. Perform three slaking processes, adding the above-mentioned amounts of water and alcohol additives for each slaking process. Only the first slaking process requires the addition of the above-mentioned amounts of crystalline salt; the subsequent two processes do not require it. Stirring is required during the slaking process, and each slaking process lasts for 60 minutes, thus obtaining slaked lime with improved desulfurization activity.

[0043] Table 1 below compares the technical specifications of untreated quicklime (i.e., quicklime delivered to the plant) with those of quicklime prepared by the method shown in Example 1 (i.e., quicklime pro).

[0044] Table 1 Technical Indicators for Improving the Activity of Quicklime

[0045] Serial Number project Factory entry quota Quicklime delivered to the plant quicklime pro 1 Color Appearance White powder White powder White powder 2 <]]> ≥85.0 86.5 93.6 3 <![CDATA[ω[H2O]]]> ≤2.0 1.8 1.2 4 Particle size distribution (45μm sieve pass rate) % ≥85.0 86.2 88.0 5 Bulk density (g / mL) 0.4-0.65 0.52 0.46 6 BET specific surface area (m2 / g) No requirements 15 45 7 Specific pore volume (m³ / g) No requirements 0.06 0.16 8 Dry sulfur dioxide removal efficiency (%) ≥85.0 86.8 95.2 9 Dry removal efficiency of hydrogen chloride (%) ≥90.0 92.5 98.5

[0046] The method for determining the acid gas removal rate is as follows:

[0047] A 0.5 g sample of slaked lime was placed in a reaction tube and heated to 200°C. Separately, a mixture of N2 containing 6000 ppm HCl and 1000 ppm SO2, and 30% relative humidity (RH), was prepared by adding steam. This mixture was also heated to 200°C and passed through the reaction tube at a space velocity of 300 mL / min, allowing the acidic gases to be absorbed by the slaked lime. Unabsorbed HCl gas was collected in a cooling trap, while SO2 gas was collected using hydrogen peroxide solution. The amount of collected acidic gas was measured by NaOH titration, and the percentage of gas absorbed as it passed through the reaction tube was calculated.

[0048] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration, characterized in that, Includes the following steps: 1) Mix fly ash with hydrochloric acid and stir for a period of time to obtain fly ash pickling slurry; 2) The fly ash pickling slurry is dewatered by pressure filtration to obtain fly ash residue and filtrate; 3) The filtrate is concentrated and crystallized to obtain crystalline salt; 4) The quicklime and fly ash residue are mixed and calcined to obtain the calcined material; 5) After calcination, the material is mixed with water, crystalline salt, and alcohol additives and then slaked to obtain quicklime with improved desulfurization activity; In step 1), the hydrochloric acid is 0.1-3 mol / L dilute hydrochloric acid, and the L / S ratio of the hydrochloric acid to fly ash is 3-10; In step 5), the amount of crystalline salt used is 0.1-0.3% based on the mass of the calcined material.

2. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that... In step 1), the hydrochloric acid is a dilute hydrochloric acid with a concentration of 2-3 mol / L.

3. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 1), the L / S ratio of hydrochloric acid to fly ash is 3-5.

4. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 1), the stirring time is 60 min to 300 min.

5. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 4, characterized in that, In step 1), the stirring time is 60-90 minutes.

6. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 2), a diaphragm filter press is used to dewater the fly ash pickling slurry. The filtration pressure of the diaphragm filter press is 0.4-2.0 MPa, the filter cloth is made of polyester, and the moisture content of the fly ash residue obtained after filtration is 35-40%.

7. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 4), the amount of fly ash residue used is 5%-20% based on the mass of the quicklime.

8. The method for improving the desulfurization activity of quicklime using fly ash from municipal solid waste incineration according to claim 7, characterized in that, In step 4), the amount of fly ash residue is 5-10% based on the mass of the quicklime.

9. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 4), the calcination temperature is 450-580℃, the time is 12-24h, and the proportion of undecomposed calcium hydroxide after calcination is 10-20%.

10. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 9, characterized in that, In step 4), the calcination temperature is 510-550℃, the time is 12-18h, and the proportion of undecomposed calcium hydroxide after calcination is 10-15%.

11. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 5), the L / S ratio of the calcined material to water is 0.5-8.

12. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 11, characterized in that, In step 5), the L / S ratio of the calcined material to water is 2-4.

13. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 5), the amount of crystalline salt used is 0.1-0.2% based on the mass of the calcined material.

14. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 1, characterized in that, In step 5), the alcohol additive is selected from one or more of isopropanol, triacetamide, and polyethylene glycol; The amount of alcohol additive used is 0.1-2.0% based on the mass of the calcined material.

15. The method for improving the desulfurization activity of slaked lime using fly ash from municipal solid waste incineration according to claim 14, characterized in that, The amount of alcohol additive used is 0.1-0.5% based on the mass of the calcined material.

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