Calcium-based desulfurizing agent regeneration method and cyclic utilization method

Abstract

The invention relates to a calcium-based desulfurizer regeneration method and a calcium-based desulfurizer recycling method. The calcium-based desulfurizer regeneration method comprises the following steps that S1, desulfurized ash obtained after flue gas dry desulfurization is screened, and desulfurized ash powder A is obtained; s2, adding hydrogen peroxide into the desulfurized ash powder A, and stirring for reaction to obtain desulfurized ash powder B; and S3, mixing the desulfurized ash powder B with an alcohol solvent, adding calcium oxide, grinding, and drying to obtain the regenerated calcium-based desulfurizer. According to the invention, H2O2 and a main component Ca (OH) 2 in the desulfurized fly ash are added to generate calcium peroxide, so that the desulfurization efficiency is effectively improved; the low-boiling-point alcohol solvent is added, the surface of the low-boiling-point alcohol solvent is rich in functional groups such as hydroxyl, agglomeration of fine powder particles can be effectively prevented, and the specific surface area can be increased; and meanwhile, the specific surface area is favorably increased by grinding, so that the regenerated calcium-based desulfurizing agent with high specific surface area is obtained, and the desulfurization efficiency is favorably improved.

Description

Technical Field

[0001] This invention belongs to the field of flue gas treatment, specifically relating to a method for regenerating and recycling a calcium-based desulfurizing agent. Background Technology

[0002] Flue gas desulfurization (FGD) technologies are categorized into wet, semi-dry, and dry FGD technologies. Wet and semi-dry FGD processes significantly reduce flue gas temperature, and subsequent denitrification adds extra energy consumption for raising the flue gas temperature, making them unsuitable for flue gas desulfurization in gas-fired power generation. Dry FGD processes, on the other hand, feature good flue gas adaptability, high reactivity, and no temperature drop during the desulfurization process. Industries such as steel, coking, and building materials all employ dry FGD technology, with sodium bicarbonate and Ca(OH)2 being the primary desulfurizing agents.

[0003] However, sodium bicarbonate desulfurization faces the following problems: 1) The cost of desulfurizing agents is high, and enterprises face great pressure and heavy burden in order to meet the environmental protection requirements of ultra-low emissions; 2) The desulfurization product sodium sulfate is easily soluble in water and difficult to store. In some places, the desulfurization product is identified as hazardous waste, which is difficult to treat and dispose of; 3) It is easy to absorb moisture and caking, which is not conducive to transportation and storage.

[0004] Besides sodium bicarbonate, high-surface-area calcium hydroxide powder exhibits good desulfurization activity and is characterized by its wide availability, low price, and easy processing of desulfurization products. It is considered an excellent alternative to sodium bicarbonate for desulfurization and is widely used in flue gas desulfurization. However, it suffers from a high calcium-to-sulfur ratio; after the reaction, over 70% of the calcium in the desulfurization ash exists as Ca(OH)₂, approximately 5% as CaCO₃, and only about 20% as CaSO₄ or CaSO₃. Currently, the disposal method for high-surface-area calcium hydroxide (desulfurization ash) after desulfurization is to use it in sintering feedstock or transport it to wet desulfurization processes for use as ordinary desulfurization lime. This significantly reduces the utilization value of high-surface-area calcium hydroxide.

[0005] Therefore, it is necessary to provide a method for improving the recycling of calcium-based desulfurizers to enhance the utilization efficiency of high specific surface area calcium hydroxide desulfurizers. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a method for regenerating and recycling calcium-based desulfurizers, thereby solving the technical problem of low utilization efficiency of calcium-based desulfurizers in the prior art.

[0007] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for regenerating a calcium-based desulfurizer, comprising the following steps: S1, sieving the desulfurized ash after dry desulfurization of flue gas to obtain desulfurized ash powder A; S2, adding hydrogen peroxide to desulfurized ash powder A and stirring to react to obtain desulfurized ash powder B; S3, mixing desulfurized ash powder B with an alcohol solvent and adding calcium oxide, then grinding and drying to obtain a regenerated calcium-based desulfurizer.

[0008] Secondly, the present invention provides a method for regenerating and recycling calcium-based desulfurizing agent, comprising the following steps: mixing the above-mentioned regenerated calcium-based desulfurizing agent with fresh calcium-based desulfurizing agent and injecting it into the flue for desulfurization, and collecting the desulfurization ash for recycling.

[0009] Compared with the prior art, the beneficial effects of the present invention include: This invention increases desulfurization efficiency by adding hydrogen peroxide to generate calcium peroxide from Ca(OH)2, the main component of desulfurization ash. Furthermore, the addition of low-boiling-point alcohol solvents, rich in functional groups such as hydroxyl groups, effectively prevents the agglomeration of fine particles, thus increasing the specific surface area. The addition of calcium oxide powder generates Ca(OH)2 while removing water. Simultaneously, grinding also contributes to increasing the specific surface area, resulting in a high-specific-surface-area regenerated calcium-based desulfurizer, which further enhances desulfurization efficiency. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] To address the shortcomings of existing desulfurization technologies using high specific surface area calcium hydroxide in coal gas combustion power generation, which result in a high calcium-to-sulfur ratio and low efficiency, this invention provides a calcium-based desulfurizer regeneration and recycling method that enables the recycling of high specific surface area calcium hydroxide, thereby improving its efficiency.

[0012] In a first aspect, the present invention provides a method for regenerating a calcium-based desulfurizing agent, comprising the following steps: S1, after screening the desulfurization ash from the dry desulfurization of flue gas, desulfurization ash powder A is obtained; S2, add hydrogen peroxide to desulfurized ash powder A and stir to react to obtain desulfurized ash powder B; S3 involves mixing desulfurization ash powder B with an alcohol solvent, then adding calcium oxide powder, followed by grinding and drying to obtain a regenerated calcium-based desulfurizer.

[0013] Preferably, in step S1, the main components of the desulfurization ash include more than 60% calcium hydroxide.

[0014] Preferably, in step S1, the sieving is performed through a 100-mesh sieve. This invention removes large pieces of material through sieving.

[0015] Preferably, in step S2, adding hydrogen peroxide to the desulfurization ash powder A specifically includes: spraying hydrogen peroxide while stirring the desulfurization ash powder A; the mass concentration of hydrogen peroxide is 27-35% (industrial grade); the amount of hydrogen peroxide sprayed is 2-5% of the mass fraction of the desulfurization ash powder A.

[0016] The main component in desulfurization ash is still Ca(OH)2. After adding H2O2, calcium peroxide can be generated. The reaction rate of calcium peroxide with SO2 is much greater than that of Ca(OH)2, which will significantly increase the desulfurization efficiency. By stirring the desulfurization ash powder A while spraying hydrogen peroxide, the small amount of hydrogen peroxide added can be fully mixed with the desulfurization ash powder A, avoiding uneven reaction.

[0017] Preferably, in step S2, the temperature of the stirring reaction is below 60°C, and the time is 5 to 10 minutes; after the reaction is completed, stirring continues for 0 to 5 minutes.

[0018] It is understandable that hydrogen peroxide is sprayed during the stirring reaction. The spraying speed should be controlled to prevent over-reaction, that is, the hydrogen peroxide should be sprayed out within 5 to 10 minutes.

[0019] Preferably, in step S3, the alcohol solvent includes one or more of anhydrous ethanol, ethylene glycol, isopropanol, n-propanol, and tert-butanol.

[0020] More preferably, the alcohol solvent has a boiling point below 200°C.

[0021] When calcium hydroxide and calcium peroxide aggregate in fine powder, they tend to form large-particle calcium hydroxide or calcium peroxide crystals, making it difficult to increase the specific surface area and resulting in low desulfurization efficiency. This invention uses low-boiling-point alcohols such as anhydrous ethanol, ethylene glycol, isopropanol, n-propanol, and tert-butanol, whose surfaces are rich in functional groups such as hydroxyl groups, which can effectively prevent the agglomeration of fine powder particles and help increase the specific surface area. At the same time, grinding also helps to increase the specific surface area.

[0022] Preferably, the alcohol solvent is added to the desulfurization ash powder B by spraying, and the amount of alcohol solvent added is 0.1 to 2% of the mass fraction of the desulfurization ash powder A.

[0023] Preferably, the activity of calcium oxide is ≥380 (mL / min), and the amount added is 4% to 12% of the mass fraction of desulfurization ash powder A.

[0024] Preferably, grinding is carried out using a ball mill or a vertical roller mill, and the grinding time is 20 to 60 minutes.

[0025] Preferably, the drying is carried out at 100–400°C for 20–30 minutes.

[0026] In a further preferred embodiment, during the drying process, the generated flue gas is condensed to recover the alcohol solvent, and the recovered alcohol solvent is recycled.

[0027] Secondly, the present invention provides a method for regenerating and recycling calcium-based desulfurizing agent, comprising the following steps: mixing the above-mentioned regenerated calcium-based desulfurizing agent with fresh calcium-based desulfurizing agent and injecting it into the flue for desulfurization, and collecting the desulfurization ash for recycling.

[0028] Preferably, when the molar ratio of calcium sulfate in desulfurization ash relative to total calcium is ≥50%, 20-50% of the desulfurization ash is discharged externally.

[0029] As the number of cycles increases, the sulfate content in the desulfurization ash rises. When the content exceeds a certain level, the recycling effect decreases. Therefore, the desulfurization ash is periodically discharged in proportion.

[0030] The main mechanism of action and advantages of this invention are as follows: (1) In this invention, the desulfurization ash collected by bag filter after dry desulfurization of high specific surface area calcium hydroxide is used as a regenerated raw material. Its main component is still Ca(OH)2. After sieving, it is transferred to a mixing chamber. Hydrogen peroxide is added while stirring in the mixing chamber to generate calcium peroxide. The specific reaction is as follows: Main reaction: Ca(OH)2 + H2O2 = CaO2 + 2H2O (1) The side reaction is: CaSO3 + H2O2 = CaSO4 + H2O (2) Among them, the reaction rate of calcium peroxide with SO2 is much greater than that of Ca(OH)2, which will significantly increase the desulfurization efficiency; the side reaction is due to the presence of a small amount of calcium sulfite in the desulfurization ash, which further reacts to form calcium sulfate.

[0031] (2) Injecting low-boiling-point alcohols such as anhydrous ethanol, isopropanol, n-propanol, and tert-butanol into the desulfurization ash after reacting with H2O2 can effectively prevent the agglomeration of fine powder particles and improve the specific surface area. At the same time, grinding is also conducive to improving the specific surface area, thereby obtaining a regenerated calcium-based desulfurizer with a high specific surface area, which is beneficial to improving the desulfurization efficiency.

[0032] (3) Add a small amount of fresh calcium oxide to the desulfurization ash after the alcohol is injected, and grind it after stirring to consume the small amount of water (mainly from the water in the injected hydrogen peroxide). Then transfer it to a rotary kiln drying furnace for drying. The flue gas generated after drying is condensed, and the alcohol solvent can be collected. The condensation and recovery process is simple, does not require stepwise condensation, and the obtained alcohol solvent has high purity and can be directly recycled. The calcium oxide drying reaction is as follows: CaO + H₂O = Ca(OH)₂ (3) (4) The regenerated calcium-based desulfurizer (regenerated high specific surface area calcium hydroxide) after grinding and drying can replace part of the fresh high specific surface area calcium hydroxide and be injected into the flue at the same time as the fresh high specific surface area calcium hydroxide, and the following desulfurization reaction occurs: CaO2 + SO2 = CaSO4 (4) Ca(OH)2 + SO2 = CaSO3 + H2O (5) Ca(OH)2+SO2+1 / 2O2=CaSO4+H2O (6) In summary, in the dry desulfurization process using high specific surface area calcium hydroxide, the low utilization rate of the desulfurizing agent leads to a serious waste of high specific surface area calcium hydroxide raw materials. This invention significantly reduces the consumption of high specific surface area desulfurizing agent by regenerating and recycling high specific surface area calcium hydroxide.

[0033] The present invention will be further described in detail below through specific embodiments.

[0034] Example 1 A method for regenerating and recycling a calcium-based desulfurizer includes the following steps: S1, the desulfurization ash from the dry desulfurization of high specific surface area calcium hydroxide flue gas (obtained by bag filter dust collection) is screened in the screening chamber, and desulfurization ash powder A passing through 100 mesh is retained.

[0035] S2, transfer desulfurization ash powder A into the mixing chamber, add hydrogen peroxide (33wt%) while stirring in the mixing chamber, the amount of hydrogen peroxide injected is 3% of the mass fraction of desulfurization ash powder A; the temperature in the mixing chamber is controlled to be below 40℃ by injecting low temperature nitrogen gas; the reaction time is controlled at 10 minutes; stirring is continued during the reaction, and stirring is continued for 5 minutes after the reaction is completed to obtain desulfurization ash powder B.

[0036] S3, desulfurization ash powder B is mixed with an alcohol solvent, and then calcium oxide powder is added. The alcohol solvent is ethylene glycol, which is sprayed into desulfurization ash powder B at a rate of 1% of the mass fraction of desulfurization ash powder A. The amount of calcium oxide powder added is 6.3% of the mass fraction of desulfurization ash powder A. After being stirred evenly in a mixer, the mixture is transferred to a ball mill for grinding under closed conditions for 45 minutes. The ground desulfurization ash is then transferred to a rotary kiln drying oven at a drying temperature of 220℃ for 30 minutes to obtain regenerated calcium-based desulfurizing agent (regenerated high specific surface area calcium hydroxide). The flue gas generated after drying is collected by condensation, and the resulting alcohols are returned to the mixing chamber as surface modifiers for recycling.

[0037] S4, regenerated high specific surface area calcium hydroxide replaces part of the fresh high specific surface area calcium hydroxide, and is injected into the flue gas desulfurization process simultaneously with the fresh high specific surface area calcium hydroxide, so that the flue gas can be emitted in compliance with standards.

[0038] Example 2 The only difference from Example 1 is that in step S2, the amount of hydrogen peroxide injected is 2% of the mass fraction of desulfurization ash powder A, and the amount of calcium oxide powder added is adaptively adjusted to 4.2% of the mass fraction of desulfurization ash powder A; the other steps and conditions are the same as in Example 1.

[0039] Example 3 The only difference from Example 1 is that in step S2, the amount of hydrogen peroxide injected is 5% of the mass fraction of desulfurization ash powder A, and the amount of calcium oxide powder added is adaptively adjusted to 10.4% of the mass fraction of desulfurization ash powder A; the other steps and conditions are the same as in Example 1.

[0040] Example 4 The only difference from Example 1 is that the reaction temperature in step S2 is 20°C; the other steps and conditions are the same as in Example 1.

[0041] Example 5 The only difference from Example 1 is that the reaction temperature in step S2 is 60°C; the other steps and conditions are the same as in Example 1.

[0042] Example 6 The only difference from Example 1 is that in step S2, stirring is no longer performed after the reaction is complete; the other steps and conditions are the same as in Example 1.

[0043] Example 7 The only difference from Example 1 is that all flue gas desulfurization is carried out using regenerated calcium-based desulfurizer, and the desulfurization conditions are the same as in Example 1.

[0044] Comparative Example 1 The only difference from Example 1 is that in step S3, ethyl acetate is used instead of ethylene glycol as the surfactant; the other steps and conditions are the same as in Example 1.

[0045] Comparative Example 2 The only difference from Example 1 is that in step S3, the amount of alcohol solvent injected is 4% of the mass fraction of desulfurization ash powder A; the other steps and conditions are the same as in Example 1.

[0046] Comparative Example 3 All flue gas desulfurization was carried out using desulfurization ash, and the desulfurization conditions were the same as in Example 1.

[0047] Comparative Example 4 Fresh high specific surface area calcium hydroxide was used for flue gas desulfurization, and the desulfurization conditions were the same as in Example 1.

[0048] Performance testing (1) The particle size, specific surface area, average pore volume and average pore size of the desulfurization ash, fresh high specific surface area calcium hydroxide and regenerated calcium-based desulfurizer in Example 1 were tested, and the results are shown in Table 1 below.

[0049] Table 1. Test results of microstructure properties of various powders

[0050] As shown in Table 1, the particle size range and specific surface area of ​​the desulfurization ash are smaller than those of fresh high specific surface area calcium hydroxide. After treatment by the method of this invention, the regenerated calcium-based desulfurizer has a larger specific surface area, which basically reaches the level of fresh high specific surface area calcium hydroxide.

[0051] (2) The desulfurization efficiency of each embodiment and comparative example was tested, and the results are shown in Table 2 below.

[0052] Table 2. Desulfurization efficiency of each embodiment and comparative example.

[0053] As shown in Table 2, the regenerated calcium-based desulfurizers in Examples 1-7 of this invention can achieve the same or even better desulfurization effect as fresh high specific surface area calcium hydroxide (Comparative Example 4). However, in Comparative Example 1, the use of ethyl acetate could not effectively modify the desulfurization process, resulting in a decrease in the desulfurization rate. In Comparative Example 2, the excessive amount of alcohol solvent had an adverse effect on the regeneration effect and reduced the desulfurization rate. In Comparative Example 3, the use of desulfurization ash alone resulted in a low desulfurization rate and unstable desulfurization. This indicates that the regeneration method of this invention can obtain a regenerated calcium-based desulfurizer with a high specific surface area, which is beneficial to improving the desulfurization efficiency.

[0054] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for regenerating a calcium-based desulfurizing agent, characterized in that, Includes the following steps: S1, after screening the desulfurization ash from the dry desulfurization of flue gas, desulfurization ash powder A is obtained; S2, add hydrogen peroxide to the desulfurized ash powder A and stir to react to obtain desulfurized ash powder B; S3, after mixing the desulfurization ash powder B with an alcohol solvent, calcium oxide is added, and the mixture is ground and dried to obtain a regenerated calcium-based desulfurizing agent.

2. The calcium-based desulfurizer regeneration method according to claim 1, characterized in that, In step S1, the main components of the desulfurization ash include more than 60% calcium hydroxide; The sieving process involves passing the material through a 100-mesh sieve.

3. The calcium-based desulfurizer regeneration method according to claim 1, characterized in that, In step S2, adding hydrogen peroxide to the desulfurization ash powder A specifically includes: spraying hydrogen peroxide while stirring the desulfurization ash powder A; The mass concentration of the hydrogen peroxide is 27-35%; The amount of hydrogen peroxide injected is 2 to 5% of the mass fraction of desulfurization ash powder A.

4. The calcium-based desulfurizer regeneration method according to claim 1, characterized in that, In step S2, the temperature of the stirring reaction is below 60°C, and the time is 5 to 10 minutes; after the reaction is completed, stirring continues for 0 to 5 minutes.

5. The calcium-based desulfurizer regeneration method according to claim 1, characterized in that, In step S3, the alcohol solvent includes one or more of anhydrous ethanol, ethylene glycol, isopropanol, n-propanol, and tert-butanol.

6. The calcium-based desulfurizer regeneration method according to claim 1, characterized in that, In step S3, the alcohol solvent is added to the desulfurization ash powder B by spraying, and the amount of alcohol solvent added is 0.1% to 2% of the mass fraction of the desulfurization ash powder A; The amount of calcium oxide added is 4% to 12% of the mass fraction of desulfurization ash powder A.

7. The calcium-based desulfurizer regeneration method according to claim 1, characterized in that, In step S3, the grinding is carried out using a ball mill or a vertical roller mill, and the grinding time is 20 to 60 minutes.

8. The calcium-based desulfurizer regeneration method according to claim 1, characterized in that, In step S3, the drying is performed at 100–400°C for 20–30 minutes.

9. The calcium-based desulfurizer regeneration method according to claim 8, characterized in that, During the drying process, the generated flue gas is condensed to recover the alcohol solvent and then recycled.

10. A method for regenerating and recycling a calcium-based desulfurizing agent, characterized in that, Includes the following steps: The calcium-based desulfurizing agent regenerated by the regeneration method according to any one of claims 1-9 is mixed with fresh calcium-based desulfurizing agent and injected into the flue for desulfurization, and the desulfurization ash is collected for recycling.

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