Method for removing sulfate in ferrous ethylenediaminetetraacetic acid complexed denitration solution by recycling anion resin

Abstract

The application discloses a method for removing sulfate radicals in iron ethylenediaminetetraacetic acid complexed denitration liquid by recycling anion resin, and belongs to the field of chemical industry and environmental protection. The method comprises two parts of removing sulfate ions in the iron ethylenediaminetetraacetic acid complexed recycling denitration liquid by using anion resin and recovering and regenerating the anion resin. The method for removing sulfate ions in the recycling denitration liquid is as follows: after the recycling denitration liquid is filtered, sodium sulfite is added, the pH is adjusted, and heating regeneration is carried out; the pH of the recycling denitration liquid is adjusted, and ion exchange is carried out after cooling; after the ion exchange is completed, citric acid is added to adjust the pH of the denitration liquid to 7.0, and then the denitration liquid is discharged by using a blowing process and enters a denitration procedure. The method can effectively solve the problem that the denitration capacity is reduced due to the accumulation of sulfate salts in the recycling and regeneration process of the denitration liquid, reduces the problem of resin iron and ferrous ion pollution and poisoning, and improves the problem of short service life of the resin by using the resin recovery method.

Description

Technical Field

[0001] This invention belongs to the field of chemical environmental protection and relates to the method of sulfate removal and resin recovery in the recycling process of ferrous chelate complex denitrification liquid in wet denitrification technology. Specifically, it relates to a method for removing sulfate from ferric ethylenediaminetetraacetic acid complex denitrification liquid by recycling anion exchange resin. Background Technology

[0002] As is well known, nitrogen oxides (NOx) are important precursors to photochemical smog and haze. Since GB13223-2011 limited NOx emissions from thermal power plants, my country's denitrification market has been launched on a large scale. Currently, the most widely used technologies in the denitrification field are medium- and low-temperature flue gas denitrification SCR technology and high-temperature flue gas denitrification SNCR technology.

[0003] Selective catalytic reduction (SCR), as the most efficient denitrification technology, has always been the preferred choice for treating flue gas from coal-fired power plants. The widespread use of SCR catalysts has significantly contributed to NOx emission reduction in my country, but it has also brought a series of problems. First, the consumption of denitrification catalysts and denitrification liquids is substantial. However, denitrification catalysts generally deactivate after 24,000 hours of operation. At that time, to meet denitrification emission requirements, the deactivated catalysts need to be replaced. Directly landfilling them would result in a huge waste of resources; therefore, the recycling and regeneration of denitrification catalysts or denitrification liquids is essential. Second, the low-temperature flue gas generated at the end of some kilns cannot meet the basic requirements of SCR technology; its flue gas temperature is mostly below 150℃ or even lower. Considering that the operating temperature window of currently developed low-temperature denitrification technologies is mostly above 180℃, additional preheating / heat exchange devices are often required to supplement the flue gas heat in order to match their operating temperature, leading to high denitrification costs.

[0004] Wet complexation denitrification is an important research direction in integrated desulfurization and denitrification, especially ferrous complexes, which have been widely studied due to their advantages such as fast NO absorption rate, large capacity, and ability to achieve simultaneous desulfurization. EDTA-iron complexation wet denitrification technology has advantages such as efficient removal of nitrogen oxides from flue gas, simultaneous desulfurization, good stability, applicability to various types of flue gas treatment, and low operating and maintenance costs. However, as denitrification proceeds, the denitrification liquid needs to be recycled and regenerated. During multiple regeneration cycles, thermally stable sulfates accumulate, significantly reducing the denitrification capacity of the liquid. When using resins to remove sulfates from the denitrification liquid, the resin is easily contaminated by iron ions, leading to resin poisoning, short service life, frequent replacement, and increased denitrification costs. Summary of the Invention

[0005] The technical problem to be solved by this invention is to remove sulfate ions from the ferric complex denitrification solution, thereby solving the problem of reduced denitrification capacity caused by sulfate accumulation during the denitrification cycle regeneration process, while greatly reducing the problem of iron and ferrous ion pollution and poisoning of the resin, and providing a new method for revitalizing the resin to improve the problem of short resin service life.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex denitrification solution by recycling anion exchange resin, comprising two parts: removing sulfate ions from ethylenediaminetetraacetic acid iron complex circulating denitrification solution by using anion exchange resin and regenerating the anion exchange resin.

[0007] The above-mentioned method for removing sulfate ions from the ferric complex ethylenediaminetetraacetic acid circulating denitrification solution using anion exchange resin includes the following steps:

[0008] A. Filter the ferric complex circulating denitrification solution to be treated, then add sodium sulfite to adjust the pH value, and regenerate it under heating conditions with stirring;

[0009] B. Adjust the pH value of the regenerated circulating denitrification liquid, and after it cools down, pass it into the ion exchange reactor for ion exchange;

[0010] C. After ion exchange, citric acid is added to adjust the pH of the denitrification solution to 7.0. Then, the denitrification solution is discharged using a purging process and enters the denitrification process.

[0011] In step A above, the amount of sodium sulfite added is 5-10 g / L, the pH is adjusted to 7.0-9.0, and the heating temperature is controlled at 85-100℃.

[0012] In step B above, the pH of the regenerated circulating denitrification liquid is adjusted to 7.0, and then its temperature is reduced to 20-30℃ by circulating cooling water; D301 anion exchange resin is used for ion exchange, and the pH of the circulating denitrification liquid is controlled to be <9.0 during the ion exchange process.

[0013] The specific method for the recovery and regeneration of the above-mentioned anion exchange resin includes the following steps:

[0014] a. The anion exchange resin to be revived is rinsed with demineralized water until the effluent is clear, and then rinsed once with revival solution;

[0015] b. The anion exchange resin treated in step a is soaked in hydrochloric acid, and then rinsed twice with water.

[0016] c. The anion exchange resin treated in step b is soaked in NaOH solution, and then rinsed three times with water.

[0017] In step a above, the resuscitation solution is prepared by mixing disodium ethylenediaminetetraacetate, dimercaprol and cysteine ​​in a molar ratio of 2-4:2-4:1-2, the mass fraction of the mixture in the resuscitation solution is 5-10%, and the pH is 7.0-9.0.

[0018] In step a above, a single rinse includes forward rinsing and backwashing. The backwashing time is 20-30 minutes, the forward rinsing time is 30-60 minutes, and the number of alternating cycles of backwashing and forward rinsing is 4-6 times. The inlet water flow rate for forward rinsing is 10-20 m / h, and the inlet water flow rate for backwashing is 30-50 m / h.

[0019] In step b above, the concentration of hydrochloric acid is 4% to 8%, the volume of hydrochloric acid is 2 to 3 times the volume of resin, and the soaking time is 4 to 8 hours.

[0020] In step b above, the secondary rinsing includes forward rinsing and back rinsing. The inlet water flow rate for both forward and back rinsing is 20-30 m / h. The rinsing is stopped when the pH of the rinsed water reaches 6.0.

[0021] In step c above, the concentration of the NaOH solution is 5% to 8%, the volume of the NaOH solution is 2 to 3 times the volume of the resin, and the soaking time is 4 to 8 hours.

[0022] In step c above, the three rinsing steps include forward rinsing and back rinsing. The inlet water flow rate for both forward and back rinsing is 15 m / h. The rinsing is stopped when the pH of the rinsed water reaches 7.0.

[0023] The beneficial effects of this invention are as follows: This invention provides a method for removing sulfate from ferrous ethylenediaminetetraacetic acid (EDTA) chelate denitrification solution. It employs anion exchange resin to remove sulfate from the denitrification solution, and controls the exchange conditions during the resin exchange process. This effectively solves the problem of decreased denitrification performance caused by the accumulation of thermally stable sulfates in the denitrification solution during the combined denitrification process with ferrous chelates and sodium sulfite. This significantly improves the denitrification capacity of the regenerated denitrification solution and is beneficial for the regeneration of wet denitrification circulating solution. This invention proposes a new method for the ion exchange process of ferrous chelate denitrification solution, which is of great significance for promoting the engineering application of ferrous chelate wet denitrification technology. Furthermore, the resin used for sulfate removal in this method is inexpensive and can be recycled and reused multiple times after processing, serving as one of the desalination pathways for denitrification solution recycling. Regarding the resin regeneration problem, this invention uses a self-prepared resuscitator, solving the problem of resin poisoning due to iron ion contamination during repeated regeneration and extending the resin's service life.

[0024] In summary, the process of this invention is simple and easy to implement, providing a guarantee for the recycling of complex denitrification liquid. The ion exchange method for treating sulfate in denitrification liquid can reduce the amount of new liquid input in wet denitrification projects and reduce costs. At the same time, the recovery process used in ion exchange resin can further effectively avoid the problem of resin being easily poisoned by iron ions, improve the service life of the resin, reduce the amount of ion exchange resin used, and achieve good economic and environmental benefits. Detailed Implementation

[0025] The technical solution of the present invention can be implemented in the following manner.

[0026] A method for removing sulfate ions from ethylenediaminetetraacetic acid (EDTA) iron complex denitrification solution by recycling anion exchange resin includes two parts: removing sulfate ions from the EDTA iron complex circulating denitrification solution using anion exchange resin and regenerating the anion exchange resin. The specific steps are as follows.

[0027] (1) The ferric complex ethylenediaminetetraacetic acid circulating denitrification solution to be treated is filtered to remove suspended matter. Sodium sulfite (5-10 g / L) is added to the filtrate to adjust the pH to 7.0-9.0, and the solution is heated to 85-100℃ and stirred for regeneration; wherein:

[0028] ①The purpose of adding sodium sulfite is to reduce the oxidized ferrous ions in the denitrification liquid and to reduce the nitrosyl esters generated by gas absorption in the denitrification liquid under the assistance of heating.

[0029] ② The reason for controlling the pH is that the optimal pH range for Fe(II)EDTA, the main active component of the denitrification solution, is 7.0 to 9.0. Within this range, ferrous iron can effectively form stable complexes. Below this pH value, the stability of the complexes decreases; above this pH value, especially under alkaline conditions, Fe(II) is easily oxidized to Fe(III), leading to a decrease in the denitrification capacity of the denitrification solution. In particular, at pH 7.0, the stability constant (K) of Fe(II)EDTA is very high, reaching the order of 10^15. As the pH value decreases or increases, the stability constant will decrease accordingly.

[0030] (2) Adjust the pH of the regenerated circulating denitrification liquid to 7.0, and then lower its temperature to 20-30℃ using circulating cooling water. Afterward, pass the liquid into an ion exchange reactor and perform ion exchange using D301 anion exchange resin. During the ion exchange process, control the pH of the circulating denitrification liquid to < 9.0; where:

[0031] ① The reason for setting up ion exchange after the denitrification solution regeneration is that sodium sulfite reduces iron ions and nitrosyl ions during the regeneration process, which will generate sulfate ions. Adding an ion exchange system at this time can better remove sulfate ions.

[0032] ② After the addition of sodium sulfite for reduction, the exchange of hydroxide ions in the anion exchange resin with the anions in the solution will cause the pH of the denitrification solution to rise, making some ferrous ions free. Therefore, it is necessary to adjust the pH of the denitrification solution after regeneration to about 7.0 so that the ferrous ions in the denitrification solution can be fully complexed and are not easily adsorbed by the resin.

[0033] ③ The reason for controlling the temperature of the denitrification solution is that temperature has a certain impact on the stability of Fe(II)EDTA. Generally speaking, Fe(II)EDTA is more stable at lower temperatures. As the temperature increases, the stability of the complex decreases because high temperature may promote the oxidation of Fe(II) and the decomposition of the complex, resulting in an increase in free states. This leads to the resin adsorbing ferrous ions, which not only reduces the effective component content of the denitrification solution but also causes ferrous ion poisoning after multiple resin exchanges. Preferably, the temperature range can be autonomously adjusted based on the stability of the complexes of different ferrous ion complexing agents with temperature changes.

[0034] ④ The purpose of controlling the pH of the circulating denitrification liquid in the ion exchanger during the ion exchange process is to prevent the oxidation of ferrous iron in the denitrification liquid, which would reduce the effective components of the denitrification liquid and thus reduce its denitrification capacity.

[0035] ⑤ According to laboratory experimental results, the resin needs to be regenerated after a certain number of exchanges (80-100 times). This is related to the adsorption capacity of the resin and can be determined independently according to the actual treatment volume.

[0036] (3) After the ion exchange is completed, citric acid is added to adjust the pH of the denitrification liquid to 7.0. Then, the denitrification liquid is discharged by purging process. At this time, the denitrification liquid can enter the denitrification process.

[0037] (4) Rinse the anion exchange resin to be revived with demineralized water until the effluent is clear, then rinse it once with revival solution to desorb ferrous and ferric ions from the resin; wherein:

[0038] ① The resuscitation solution is prepared by mixing disodium ethylenediaminetetraacetate, dimercaprol, and cysteine ​​in a molar ratio of 2–4:2–4:1–2. The mass fraction of the mixture in the resuscitation solution is 5–10%. The resuscitation solution can be recycled multiple times, and the pH is controlled at 7.0–9.0. Disodium ethylenediaminetetraacetate, dimercaprol, and cysteine ​​are selected as resin resuscitation agents because these reagents have high complexation constants with iron and ferrous ions, which can effectively elute ferrous and ferric ions from the resin.

[0039] (5) Soak the resin in a 4% to 8% hydrochloric acid solution. The volume of hydrochloric acid is 2 to 3 times the volume of the resin. Soak for 4 to 8 hours. After soaking, rinse the resin twice with water until the pH of the rinse water is 6.0.

[0040] (6) Soak the resin in an alkaline solution of 5% to 8% NaOH solution. The volume of the NaOH solution is 2 to 3 times the volume of the resin. The soaking time is 4 to 8 hours. After the soaking, rinse the resin three times with water until the pH of the rinse water is 7.0.

[0041] The technical solution and effects of the present invention will be further explained below through practical examples.

[0042] Example

[0043] I. Removal of sulfate ions from ferric complex ethylenediaminetetraacetic acid circulating denitrification solution using anion exchange resin

[0044] In Example 1, the circulating denitrification liquid requiring regeneration was filtered. Sodium sulfite was added to the filtrate, controlling the concentration to 6 g / L, and the pH was adjusted to 7.0. Regeneration was then carried out by stirring at 92°C for 20 min. After regeneration, the pH of the circulating denitrification liquid was adjusted to 7.0 and cooled to 20°C. It was then passed to an ion exchange reactor for ion exchange for 30 min, during which the pH of the circulating denitrification liquid in the exchanger was controlled at 7.0. After the exchange, citric acid was added to adjust the pH of the denitrification liquid to 7.0, and then the ion exchange reactor was purged using a purging process before entering the denitrification process.

[0045] Testing revealed that the sulfate content in the circulating denitrification liquid after heating and regeneration was 50 g / L; the sulfate content in the circulating denitrification liquid after ion exchange treatment was 8 g / L, with a sulfate removal rate of 84%. The denitrification efficiency of the circulating denitrification liquid treated in this embodiment can be increased by 55% compared to the untreated circulating denitrification liquid.

[0046] In Example 2, the circulating denitrification liquid requiring regeneration was filtered. Sodium sulfite was added to the filtrate, controlling the concentration to 6 g / L, and the pH was adjusted to 7.0. Regeneration was then carried out by stirring at 92°C for 20 min. After completion, the pH of the circulating denitrification liquid was adjusted to 7.0 and cooled to 25°C. It was then passed to an ion exchange reactor for ion exchange for 30 min, during which the pH of the circulating denitrification liquid in the exchanger was controlled at 7.0. After the exchange, citric acid was added to adjust the pH of the denitrification liquid to 7.0, and then the ion exchange reactor was purged using a purging process before entering the denitrification process.

[0047] Testing revealed that the sulfate content in the circulating denitrification liquid after heating and regeneration was 54 g / L; the sulfate content in the circulating denitrification liquid after ion exchange treatment was 13 g / L, with a sulfate removal rate of 76%. The denitrification efficiency of the circulating denitrification liquid treated in this embodiment can be increased by 48% compared to the untreated circulating denitrification liquid.

[0048] In Example 3, the circulating denitrification liquid requiring regeneration was filtered. Sodium sulfite was added to the filtrate, controlling the concentration to 6 g / L, and the pH was adjusted to 7.0. Regeneration was then carried out by stirring at 92°C for 20 min. After completion, the pH of the circulating denitrification liquid was adjusted to 7.0 and cooled to 30°C. It was then passed to an ion exchange reactor for ion exchange for 30 min, during which the pH of the circulating denitrification liquid in the exchanger was controlled at 7.0. After the exchange, citric acid was added to adjust the pH of the denitrification liquid to 7.0, and then the ion exchange reactor was purged using a purging process before entering the denitrification process.

[0049] Testing revealed that the sulfate content in the circulating denitrification liquid after heating and regeneration was 57 g / L; the sulfate content in the circulating denitrification liquid after ion exchange treatment was 15 g / L, with a sulfate removal rate of 74%. The denitrification efficiency of the circulating denitrification liquid treated in this embodiment can be increased by 45% compared to the untreated circulating denitrification liquid.

[0050] As shown in Examples 1-3, the method of the present invention can effectively remove sulfate from the circulating denitrification solution, improving the denitrification capacity of the regenerated denitrification solution. However, as the resin is used multiple times, its ion exchange capacity gradually deteriorates, showing a negative correlation with the number of exchanges. Analysis of the filtrate of the regenerated resin revealed that the reduced resin exchange capacity was due to iron ion adsorption on the resin. In Examples 4-5 below, a revival solution that can effectively adsorb iron from the resin was used for rinsing to reduce iron poisoning in the resin.

[0051] II. Anion exchange resin regeneration

[0052] The resuscitation solution used in the examples was prepared by mixing disodium ethylenediaminetetraacetate, dimercaprol and cysteine ​​in a molar ratio of 4:4:2, with a mass fraction of 5% and a pH of 7.0.

[0053] Example 4 describes the recovery of D301 resin after 10 ion exchanges in the ion exchange process of the above examples.

[0054] First, the D301 resin to be revived was rinsed with demineralized water, then rinsed with revival solution (backwash for 25 min, forward wash for 45 min, alternating between forward and backwash cycles 5 times; the influent flow rate for forward wash was 20 m / h, and the influent flow rate for backwash was 40 m / h). Next, the resin was soaked in 5% hydrochloric acid for 6 h, followed by rinsing with water (influent flow rate for both forward and backwashes was 20 m / h) until the pH of the rinse water reached 6.0. Finally, the resin was soaked in 5% NaOH solution for 6 h, followed by rinsing with water (influent flow rate for both forward and backwashes was 15 m / h) until the pH of the rinse water reached 7.0.

[0055] The regenerated resin of this embodiment is reused in the ion exchange process of the present invention to remove sulfate ions from the circulating denitrification liquid. The sulfate content in the circulating denitrification liquid after heating regeneration is 50 g / L, and the sulfate content in the circulating denitrification liquid after ion exchange treatment is 10 g / L, with a sulfate removal rate of 80%.

[0056] Example 5 describes the recovery of D301 resin after 20 ion exchanges in the ion exchange process of the above examples.

[0057] First, the D301 resin to be revived was rinsed with demineralized water, then rinsed with revival solution (backwash for 20 min, forward wash for 45 min, alternating between forward and backwash cycles 5 times; the influent flow rate for forward wash was 20 m / h, and the influent flow rate for backwash was 40 m / h). Next, the resin was soaked in 5% hydrochloric acid for 6 h, followed by a second rinse with water (influent flow rate for both forward and backwashes was 20 m / h) until the pH of the rinse water reached 6.0. Finally, the resin was soaked in 5% NaOH solution for 6 h, followed by a third rinse with water (influent flow rate for both forward and backwashes was 15 m / h) until the pH of the rinse water reached 7.0.

[0058] The regenerated resin of this embodiment is reused in the ion exchange process of the present invention to remove sulfate ions from the circulating denitrification liquid. The sulfate content in the circulating denitrification liquid after heating regeneration is 60 g / L, and the sulfate content in the circulating denitrification liquid after ion exchange treatment is 15 g / L, with a sulfate removal rate of 75%.

[0059] As can be seen from Examples 4 and 5, the method of the present invention can effectively revive anion exchange resins. After revival, the resins still have good adsorption capacity and can be recycled.

Claims

1. A method for removing sulfate ions from ethylenediaminetetraacetic acid (EDTA) iron complex denitrification solution by recycling anion exchange resin, characterized in that: The process includes two parts: removing sulfate ions from the ethylenediaminetetraacetic acid iron complex circulating denitrification solution using anion exchange resin and regenerating the anion exchange resin. The specific method for removing sulfate ions from the ethylenediaminetetraacetic acid iron complex circulating denitrification solution using anion exchange resin includes the following steps: A. Filter the ferric complex circulating denitrification solution to be treated, then add sodium sulfite to adjust the pH to 7.0~9.0, and regenerate by stirring under heating conditions at a temperature of 85~100℃; B. Adjust the pH of the regenerated circulating denitrification liquid to 7.0, and then cool it down to 20~30℃ with circulating cooling water before passing it into an ion exchange reactor for ion exchange. D301 anion exchange resin is used for ion exchange. During the ion exchange process, the pH of the circulating denitrification liquid is controlled to be <9.

0. C. After ion exchange, citric acid is added to adjust the pH of the denitrification solution to 7.

0. Then, the denitrification solution is discharged using a purging process and enters the denitrification process. The specific method for regenerating the anion exchange resin includes the following steps: a. The anion exchange resin to be revived is rinsed with demineralized water until the effluent is clear, and then rinsed once with a revival solution; the revival solution is prepared by mixing disodium ethylenediaminetetraacetate, dimercaptopropanol and cysteine ​​in a molar ratio of 2~4:2~4:1~2, the mass fraction of the mixture in the revival solution is 5~10%, and the pH is 7.0~9.0; b. The anion exchange resin treated in step a is soaked in hydrochloric acid, and then rinsed twice with water. c. The anion exchange resin treated in step b is soaked in NaOH solution, and then rinsed three times with water.

2. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex denitrification solution using recycled anion exchange resin according to claim 1, characterized in that: In step A, the amount of sodium sulfite added is 5~10 g / L.

3. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex denitrification solution using recycled anion exchange resin according to claim 1, characterized in that: In step a, a single rinse includes forward rinsing and backwashing. The backwashing time is 20-30 min, the forward rinsing time is 30-60 min, and the number of alternating cycles of backwashing and forward rinsing is 4-6 times. The inlet water flow rate for forward rinsing is 10-20 m / h, and the inlet water flow rate for backwashing is 30-50 m / h.

4. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex denitrification solution by recycling anion exchange resin according to claim 1, characterized in that: In step b, the hydrochloric acid concentration is 4%~8%, the volume of hydrochloric acid is 2~3 times the volume of resin, and the soaking time is 4~8 hours.

5. The method for removing sulfate ions from ethylenediaminetetraacetic acid ferric complex denitrification solution using recycled anion exchange resin according to claim 1, characterized in that: In step b, the secondary rinsing includes forward rinsing and backwashing. The inlet water flow rate for both forward and backwashing is 20~30m / h. The rinsing is stopped when the pH of the rinsed water reaches 6.

0.

6. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex denitrification solution using recycled anion exchange resin according to claim 1, characterized in that: In step c, the concentration of the NaOH solution is 5%~8%, the volume of the NaOH solution is 2~3 times the volume of the resin, and the soaking time is 4~8 h.

7. The method for removing sulfate ions from ethylenediaminetetraacetic acid ferric complex denitrification solution using recycled anion exchange resin according to claim 1, characterized in that: In step c, the three rinsing processes include forward rinsing and back rinsing. The inlet water flow rate for both forward and back rinsing is 15 m / h. The rinsing process is stopped when the pH of the rinsed water reaches 7.0.