CN110124451A - SO in wet type substep removing flue gas2With the method for NO - Google Patents

Abstract

The invention discloses a wet step-by _- step method for removing SO2 and NO in flue gas. The flue gas to be purified is continuously passed into the first-level absorption tower and the second-level absorption tower; in the first-level absorption tower, the SO ₂ is absorbed and removed after contacting the primary absorption liquid. In the secondary absorption tower, NO in the flue gas is absorbed and removed after contacting the secondary absorption liquid, and the purified gas is discharged; the primary absorption liquid absorbs SO ₂ After entering the regeneration tower ①, under the catalysis of the biochar catalyst, the iron-organic complex is transformed; after the secondary absorption liquid complexes and absorbs NO, it enters the regeneration tower ②, where the iron-organic complex is transformed, and the regenerated absorption liquid It then enters the first-stage absorption tower and is recycled in the system. The method of the invention realizes step-by _- step efficient green removal of SO2 and NO in flue gas, the absorbent used can be recycled, and no other desulfurization and denitrification chemicals need to be added in the removal process.

Description

Wet step-by-step removal of SO2 and NO from flue gas

technical field

The invention relates to a flue gas desulfurization or denitrification method, in particular to a flue gas desulfurization and denitrification process integration method, which is applied in the technical fields of waste gas purification and environmental protection engineering.

Background technique

Sulfur oxides (SO _X ) and nitrogen oxides (NO _X ) are the main pollutants that cause air pollution. The man-made emissions of these pollutants mainly come from the combustion process of fossil resources such as coal and fuel oil and the chemical production process. They have the characteristics of large smoke emissions and concentrated pollutant emissions, which can easily cause regional air pollution problems. The sulfur oxides (SO _X ) emitted in the combustion flue gas are mainly sulfur dioxide (SO ₂ ), and the nitrogen oxides (NO _X ) are mainly nitric oxide (NO), accounting for more than 90%. Therefore, the removal of SO ₂ and NO is the focus of combustion flue gas purification.

At present, the commercialized desulfurization and denitrification process mostly adopts the combination process of wet limestone or ammonia method to remove SO ₂ and selective catalytic reduction (SCR) to remove NO; but the process is complicated and requires a large amount of chemicals to remove pollutants , such as CaO, NH ₃ , etc., but also produce a large amount of waste, such as desulfurization gypsum.

The wet simultaneous flue gas desulfurization and denitrification process has the advantages of simple process and low equipment investment. It is still attractive to the desulfurization and denitrification process with a small amount of flue gas. Researchers have also developed a variety of wet desulfurization and denitrification integrated technologies. Craftsmanship and Technology. Simultaneous wet desulfurization and denitrification are mainly divided into oxidation method and complexation absorption method. The oxidation method is to increase the rate of desulfurization and denitrification by adding an oxidant to accelerate the oxidation rate of NO. For example, the patent CN109276987A uses peroxides of alkali metals or alkaline earth metals, oxidizing inorganic salts or organic peroxides to form oxidants and activators composed of soluble bases or salts that can generate weak acid ions in aqueous solution. The absorbent obtained by mixing the absorbent can remove SO ₂ and NO in the industrial tail gas. Patent CN208436644U proposes a process of first converting NO2 in the flue gas into nitric _acid and NO, and then converting the generated NO into NO2 by blowing air, and at the same time, the sulfur _dioxide in the flue gas is absorbed by the water liquid to achieve desulfurization and denitrification. . The operation of the above two methods is very simple, but improper handling is likely to cause secondary pollution, and the cost of reagent use is relatively high.

The complexation absorption method is considered by scholars to be a flue gas simultaneous desulfurization and denitrification technology that is expected to realize industrial application. This technology is to add a complexing agent that can react with NO to the absorption liquid, which can significantly increase the solubility of NO in water, realize the separation of NO in flue gas, and solve the problem of low mass transfer rate of NO in the liquid phase. Ferrous chelation method is one of the most researched methods of liquid phase complexation absorption method. The method uses Fe(II)-EDTA (or Fe(II)-Cit, iron citrate) as the absorbent, and has many advantages such as fast NO absorption rate, high efficiency, stable formation and complexation, and low cost and easy availability. The chemistry involved in this method is as follows:

Fe(II)EDTA(Fe(II)-Cit) solution undergoes a complexation reaction with NO, causing NO with very low solubility to enter the liquid phase and form a ferrous nitrosyl complex, thereby removing NO from the gas:

NO(g)→NO(aq) (1)

NO(aq)+Fe(II)EDTA→Fe(II)EDTA-NO (2)

Due to the presence of 3%-5% oxygen in the flue gas, the ferrous chelating agent will be oxidized to Fe(III)EDTA, lose its activity, and no longer have the ability to bind NO, resulting in a decrease in the NO removal efficiency of the absorbing liquid:

4Fe(II)EDTA+O ₂ +4H ⁺ →4Fe(III)EDTA+2H ₂ O (3)

Therefore, the efficient regeneration of ferrous chelating agent is the key to the continuous operation of the process. To solve this problem, the patent CN104084023A proposes to use ferrous chelating agent to complex absorb NO, and the absorption liquid is reduced to ammonia gas by metal iron to realize denitrification, and then ammonia gas is mixed with ammonia water in the desulfurization section, reacted with sulfur dioxide to obtain ammonium sulfite, and then oxidized The process of obtaining ammonium sulfate and realizing desulfurization is relatively simple, but it needs to consume ammonia and metal iron, which increases the cost of treatment.

In addition, if there is SO ₂ in the flue gas, the SO ₂ in the flue gas is easily absorbed by water and reacts with Fe(II)EDTA-NO to form Fe(II)EDTA(SO ₃ ^2- )NO, which is extremely stable, Difficult to break down, resulting in loss of absorbent.

SO ₂ (g)+H ₂ O→H ⁺ +SO ₃ ^2- (4)

Fe(II)EDTA-NO+SO ₃ ^2- → Fe(II)EDTA(SO ₃ ^2- )NO (5)

Therefore, it is particularly necessary to develop efficient and cheap absorption liquid regeneration and recycling technologies and processes, which has become a technical problem to be solved urgently.

Contents of the invention

In order to solve the problems of the prior art, the purpose of the present invention is to overcome the deficiencies in the prior art, and provide a wet step _- by _- step method for removing SO2 and NO in the flue gas, which can efficiently absorb and remove SO2 and NO in the flue gas, With the goal of reducing the consumption of chemical agents as much as possible, using ferric organic complexes as absorbents, utilizing the efficient absorption of SO2 by _ferric organic complexes, and using the specificity of ferrous organic complexes for NO Absorption, step by step to achieve the removal of two pollutants; at the same time, using the oxidation-reduction properties of SO ₂ and NO itself, using biochar as a catalyst, to accelerate electron transfer, to achieve ferric organic complexes and ferrous organic complexes The high-efficiency conversion between compounds ensures the integration of absorbent regeneration cycle and desulfurization and denitrification.

To achieve the above object, the present invention adopts the following technical solutions:

A wet step-by _- step method for removing SO2 and NO from flue gas. _The flue gas containing SO2 and NO to be purified is successively and continuously passed into a primary absorption tower and a secondary absorption tower;

_In the primary absorption tower, the SO2 in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the flue gas after desulfurization continues to enter the secondary absorption tower. The main component of the primary absorption liquid is ferric organic complexes;

In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged;

There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels;

After the primary absorption liquid absorbs SO2 in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid, and the ferric organic complex in the sulfur-containing solution is Converted into ferrous organic complexes to form a secondary absorption liquid after regeneration, and pump the regenerated secondary absorption liquid into the secondary absorption tower for denitrification process;

After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the ferrous organic complex in the nitrogen-containing solution is It is converted into a ferric organic complex to form a first-level absorption liquid after regeneration, and then pumped into the first-level absorption tower through another pump to replenish the liquid volume of the first-level absorption liquid and perform a desulfurization process; thereby forming an absorption liquid cycle Regeneration and continuous use to realize the integrated process of wet desulfurization and denitrification step by step.

As a preferred technical solution of the present invention, the main component of the primary absorption liquid is at least one ferric organic complex in iron citrate (Fe(III)Cit, Fe(III)EDTA and Fe(III)NTA); In the regeneration tower ①, under the catalysis of biochar, the ferric organic complex in the sulfur-containing solution is converted into at least one of Fe(II)Cit, Fe(II)EDTA and Fe(II)NTA). ferric organic complex, control the residence time of the sulfur-containing solution to 0.5-2min, adjust the pH of the obtained secondary absorption liquid containing ferrous organic complex to 5.0-6.0, and then transport it into the secondary absorption tower , to carry out the denitrification process; in the regeneration tower ②, under the catalysis of biochar, the divalent iron organic complex in the nitrogen-containing solution is transformed into Fe(III)Cit, Fe(III)EDTA and Fe(III) At least one ferric organic complex in NTA), the residence time of the nitrogen-containing solution is controlled to be 1.2-7.2min, and then transported into the primary absorption tower for desulfurization process, thereby forming the absorption liquid to be regenerated and continuously used.

As a further preferred technical solution of the present invention, the biochar is made of biomass as raw material, which is crushed and sieved, and then heated through 300 to 800 °C at a heating rate of not less than 10 °C/min under _N2 atmosphere. ℃ constant temperature pyrolysis method, performing pyrolysis for at least 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, the catalytic activity of the biochar is maintained by supplementing new biochar.

As a preferred technical solution of the present invention, in the regeneration tower 1., a solution of sulfate ions is formed after the regeneration reaction, and after low-temperature crystallization, sodium sulfate crystals are separated out to be separated from the absorption liquid, and used as industrial raw materials, crystallization mother liquor After regeneration, it forms a secondary absorption liquid, which is transported into the secondary absorption tower for continued use.

In the above-mentioned primary absorption tower, it is preferable to control the pH value of the primary absorption liquid to be 4.0-6.0, and preferably to control the liquid-gas ratio to be 4.2-12.0 L/m ³ . In the above-mentioned primary absorption tower, it is further preferred to control the pH value of the primary absorption liquid to 4.5-5.5.

In the above-mentioned secondary absorption tower, it is preferable to control the pH value of the primary absorption liquid to be 5.0-6.0, and preferably to control the liquid-gas ratio to be 2.0-6.0 L/m ³ .

Principle of the present invention is as follows:

A kind of wet step-by _- step removal of SO2 and NO technology in the flue gas of the present invention is that the flue gas to be purified is continuously passed into the first-level absorption tower and the second-level absorption tower; the flue gas continuously flows through the first-level absorption tower and the second-level absorption tower. The second-stage absorption tower is discharged after purification; the absorption liquid takes (Fe(III)Cit) as an example, after passing through the first-stage absorption tower, after absorbing SO ₂ in the flue gas, it enters the absorption liquid regeneration tower ①, and is pumped after regeneration. After the absorption of NO in the flue gas is completed, it enters the absorption liquid regeneration tower ②, and after regeneration, it is pumped into the primary absorption tower for recycling; the specific process flow is shown in Figure 1.

a. Further, the first-stage absorption tower is characterized in that the Fe(III)Cit solution is used as the absorption liquid, the pH is controlled at 4.0 to 6.0, and the SO ₂ in the flue gas is mainly absorbed and removed, and the liquid-gas ratio is controlled at 4.2 to 6.0. 12.0L/m ³ , the specific reaction is as follows:

SO ₂ +H ₂ O→HSO ₃ ^2- +H ⁺ (6)

H ⁺ +Cit ³⁺ →HCit ²⁺ (7)

H ⁺ +HCit ²⁺ →H ₂ Cit ⁺ (8)

The preparation method of the Fe(III)Cit absorption solution described in the above step a is: Fe2( _SO4 ) ₃ and sodium citrate are used in a molar ratio of 1: ( _1-3 ), and the concentration of Fe(III) is 0.01 ~0.03mol/L is dissolved in water.

b. Further, the absorption liquid regeneration tower ① is characterized in that biochar is used as a filler, and the residence time of the absorption liquid is controlled to be 0.5 to 2 minutes, and the following reactions specifically occur:

The biochar described in the above step b is based on biomass (such as corn stalks) as raw material, which is crushed, sieved, and kept at a constant temperature of 300°C to 800°C at a heating rate of 10°C/min under _N2 atmosphere Prepared by pyrolysis for 2 hours.

c. Further, in the second-stage absorption tower, the liquid in the absorption liquid regeneration tower ① is used as the absorption liquid, the pH is controlled at 5.0-6.0, and the NO in the flue gas is mainly absorbed and removed, and the liquid-gas ratio is controlled at 2.0-6.0L/ m3, specifically the following reaction occurs:

NO(g)→NO(aq) (10)

NO(aq)+Fe(II)Cit→Fe(II)Cit-NO (11)

In the presence of oxygen in the flue gas, the following reactions occur

4Fe(II)Cit+O ₂ +4H ⁺ →4Fe(III)Cit+2H ₂ O (12)

d. Further, the mixed solution in the absorption liquid regeneration tower ② is characterized in that biochar is used as a filler, and the residence time of the absorption liquid is controlled to be 1.2 to 7.2 minutes, and the following reactions specifically occur:

The preparation method of the biochar described in the above step d is the same as that of the biochar in the absorption liquid regeneration tower ①.

e. Further, the biochar in the present invention can be supplemented with fresh biochar to maintain the catalytic activity after the catalytic activity is reduced.

f. Further, due to the continuous desulfurization process in the absorption liquid, there will be sulfate accumulation, which can be recycled. The specific method is: filter the absorption liquid to remove solid impurities, use cold water to crystallize to generate NaSO ₄ , and the crystal slurry is passed through Centrifugal dehydration, the separated mother liquor can be returned to the absorption tower for recycling.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

1. The method of the present invention takes the ferric organic complex as the absorption liquid, utilizes the buffering effect of the trivalent ferric organic complex salt _on H ⁺ , efficiently absorbs SO in the gas phase, and uses the SO dissolved in the liquid phase after absorption ₃ ^2- is a reducing agent, under the action of a catalyst, the ferric organic complex is reduced to a ferrous organic complex; and then the ferrous organic complex obtained from the reduction is used to specifically absorb NO, forming a complex of ferrous organic complex-NO; after that, the biochar catalyst catalyzes the decomposition of ferric organic complex-NO to form ferric organic complex and N ₂ to realize the regeneration of the absorption liquid ;

2. The method of the present invention not only realizes the integrated desulfurization and denitrification, but also avoids the failure of the absorbent, ensures the regeneration and recycling of the divalent iron organic complex, and does not require the introduction of other chemicals; catalyzes the ferric organic complex The biochar required for recycling and regeneration of ferrous organic complexes has the characteristics of wide source of raw materials, simple preparation and reusability;

3. The method of the present invention has the advantages of simple technological process, low investment, low operating cost, convenient control and operation, and easy popularization and application.

Description of drawings

Fig. 1 is a schematic diagram of the process flow of wet step-by _- step removal of SO2 and NO from flue gas according to the embodiment of the present invention.

Detailed ways

Below in conjunction with specific implementation example, above-mentioned scheme is described further, and preferred embodiment of the present invention is described in detail as follows:

Embodiment one:

In this embodiment, referring to Fig. 1, an absorption and purification device is set up, including a primary absorption tower, an absorption liquid regeneration tower ①, a secondary absorption tower, and an absorption liquid regeneration tower ② _; the gas containing SO and NO is drawn out by an induced draft fan , enter the first-level absorption tower from the bottom of the tower, and the regenerated absorption liquid is a solution mainly containing Fe(III)Cit. The regenerated absorption liquid enters from the top of the tower after being pressurized by a water pump. The removal of SO ₂ is completed within; the purified flue gas enters the bottom of the secondary absorption tower, and the primary absorption liquid flows into the absorption liquid regeneration tower ① for regeneration. After regeneration, a solution mainly containing Fe(II)Cit is obtained, and the regenerated The secondary absorption liquid is pumped into the top of the secondary absorption tower, and the gas containing NO in the secondary absorption tower is in reverse contact with the absorption liquid to complete the removal of NO; the absorption liquid that has absorbed NO enters the absorption liquid regeneration tower ② for After regeneration, it is pumped into the primary absorption tower for recycling.

In this example, referring to Figure 1, 1 part of Fe ₂ (SO ₄ ) ₃ and 2 parts of Na ₃ Cit·2H ₂ O were weighed to form a solution, and the pH was adjusted to 4.5 with dilute sulfuric acid, as a step-by-step wet removal method. _The absorption liquid of the primary absorption tower in the process of SO2 and NO in flue gas.

In this example, referring to Fig. 1, the biochar is made of corn stalk biomass as raw material, which is crushed and sieved, and then heated at a constant temperature of 800°C at a heating rate of 10°C/min under _N2 atmosphere. In the pyrolysis method, pyrolysis is carried out for 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, the catalytic activity of the biochar is maintained by supplementing new biochar. Activated biochar is prepared from corn stalks and used in the absorption liquid regeneration tower ① and absorption liquid regeneration tower ② to carry out catalytic oxidation-reduction reactions.

In this example, referring to Fig. 1, a wet step-by _- step method for removing SO2 and NO from flue gas, the flue gas containing SO2 and NO to be purified is successively passed into the first-stage absorption tower and the _second -stage absorption tower. absorption tower;

_In the primary absorption tower, the SO in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the flue gas after desulfurization continues to enter the secondary absorption tower. The main component of the primary absorption liquid is iron citrate Fe (III) Cit; the pH value of the control primary absorption liquid is 4.5, and the control liquid-gas ratio is 6.0L/m ³ ;

In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged; the pH value of the secondary absorption liquid is controlled at 5.0, and the liquid-gas ratio is controlled at 4.0L /m ³ ;

There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels;

After the primary absorption liquid absorbs SO in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid. The residence time of the sulfur-containing solution is controlled to be 1.0min, and the sulfur-containing solution is The Fe(III)Cit in the solution is converted into Fe(III)Cit to form a secondary absorption liquid after regeneration. The pH of the regenerated secondary absorption liquid is adjusted to 5.0, and the regenerated secondary absorption liquid is pumped into the The secondary absorption tower performs denitrification process; in the regeneration tower ①, a solution of sulfate ions is formed after the regeneration reaction, and after low-temperature crystallization, sodium sulfate crystals are precipitated, which are separated from the absorption liquid and used as industrial raw materials, crystallization mother liquor As a secondary absorption liquid after regeneration, it is transported into the secondary absorption tower for continued use;

After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the residence time of the sulfur-containing solution is controlled to be 5.0min. The Fe(III)Cit in the solution is converted into Fe(III)Cit, thereby forming a primary absorption liquid after regeneration, adjusting the pH of the regenerated primary absorption liquid to 4.5, and pumping it into the primary absorption tower through another pump, Supplement the liquid volume of the first-stage absorption liquid to carry out the desulfurization process; thereby forming an integrated process of wet desulfurization and denitrification step by step through the cycle regeneration and continuous use of the absorption liquid. In this embodiment, a single complexing agent, ferric citrate (Fe(III) _-Cit ), is used to absorb SO2 and NO in stages to avoid mutual interference, and utilize SO2 and NO's own oxidation _- reduction properties, using biochar as a catalyst, Realize the Fe(III)-Cit regeneration cycle, avoid the chemical consumption of desulfurization and denitrification, and greatly reduce the operating cost. This embodiment efficiently absorbs and removes _SO2 and NO in the flue gas, and aims to reduce the consumption of chemical agents as much as possible. Ferric citrate (Fe(III)Cit) is used as the absorbent to utilize _citrate to efficiently absorb SO2, and The specific absorption of Fe(II)-Cit to NO realizes the removal of the two pollutants step by step; at the same time, the oxidation-reduction properties of SO ₂ and NO are used, and biochar is used as a catalyst to accelerate electron transfer and realize Fe(III) ) efficient conversion between Cit/Fe(II)Cit, so as to ensure the integration of regeneration cycle of absorbent and desulfurization and denitrification.

Experimental test analysis:

In this embodiment, the absorption liquid is fully contacted with the polluted gas in the _{two -} stage swirling plate tower, and the removal of SO and NO is completed respectively. After testing, the removal efficiency of SO can reach 90-95%, and the removal efficiency of NO can reach 82%. %~91%.

In this example, Fe(III)Cit is used as the absorption liquid, and the buffering effect of citrate on H ⁺ is used to efficiently absorb SO ₂ in the gas phase, and the SO ₃ ^2- dissolved in the liquid phase after absorption is used as the reducing agent, and the catalyst Under the action of Fe(III)Cit is reduced to Fe(II)Cit; then use the reduced Fe(II)Cit to specifically absorb NO in the gas phase to form a complex Fe(II)Cit-NO; after that , Fe(II)Cit-NO is decomposed by the biochar catalyst to form Fe(III)Cit and N ₂ to realize the regeneration of the absorption liquid; the present invention not only realizes the integrated desulfurization and denitrification, but also avoids the failure of the absorbent, ensuring The regeneration and recycling of Fe(II)Cit does not require the introduction of other chemicals. The biochar required for catalytic Fe(III)Cit/Fe(II)Cit cycle regeneration has the characteristics of wide source of raw materials, simple preparation, and reusability. The whole process is simple, with low investment and low operating costs.

Embodiment two:

This embodiment is basically the same as Embodiment 1, especially in that:

In this embodiment, an absorption and purification device is set up, including a primary absorption tower, an absorption liquid regeneration tower ①, a secondary absorption tower, and an absorption liquid regeneration tower ② _; Enter the first-stage absorption tower, the regenerated absorption liquid is a solution mainly containing Fe(III)Cit, the regenerated absorption liquid enters from the top of the tower after being pressurized by a water pump, the gas-liquid two-phase flows in reverse, and the SO ₂ is completed in the first-stage absorption tower. removal; the purified flue gas enters the bottom of the secondary absorption tower, and the primary absorption liquid flows into the absorption liquid regeneration tower ① for regeneration. After regeneration, a solution mainly containing Fe(II)Cit is obtained, and the regenerated secondary absorption The liquid is pumped into the top of the secondary absorption tower, and the gas containing NO in the secondary absorption tower is in reverse contact with the absorption liquid to complete the removal of NO; the absorption liquid that has absorbed NO enters the absorption liquid regeneration tower ② for regeneration, and then passes through The pump circulates into the primary absorption tower for recycling.

In this example, 1 part of Fe ₂ (SO ₄ ) ₃ and 2 parts of Na ₃ Cit·2H ₂ O were weighed to form a solution, and the pH was adjusted to 5.5 with dilute sulfuric acid as a wet method to remove SO in flue gas step by step. ₂ and the absorption liquid of the primary absorption tower in the process of NO.

In this example, referring to Fig. 1, the biochar is made of waste sawdust biomass as a raw material, which is crushed and sieved, and then heated at a rate of 10°C/min under _N2 atmosphere, through 500°C and 500°C. A constant temperature pyrolysis method at 800° C. is carried out for 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, the catalytic activity of the biochar is maintained by supplementing new biochar. Activated biochar is prepared from waste sawdust and used in the absorption liquid regeneration tower ① and absorption liquid regeneration tower ② to carry out catalytic oxidation-reduction reactions.

In this embodiment, a wet step _- by _- step method for removing SO2 and NO from flue gas, the flue gas containing SO2 and NO to be purified is successively passed into the primary absorption tower and the secondary absorption tower;

_In the primary absorption tower, the SO in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the flue gas after desulfurization continues to enter the secondary absorption tower. The main component of the primary absorption liquid is iron citrate Fe (III) Cit; the pH value of the control primary absorption liquid is 5.5, and the control liquid-gas ratio is 6.0L/m ³ ;

In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged; the pH value of the secondary absorption liquid is controlled to be 6.0, and the liquid-gas ratio is controlled to be 4.0L /m ³ ;

There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels;

After the primary absorption liquid absorbs SO in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid. The residence time of the sulfur-containing solution is controlled to be 1.0min, and the sulfur-containing solution is The Fe(III)Cit in the solution is converted into Fe(III)Cit to form a secondary absorption liquid after regeneration. Adjust the pH of the regenerated secondary absorption liquid to 6.0, and pump the regenerated secondary absorption liquid into the The secondary absorption tower performs denitrification process; in the regeneration tower ①, a solution of sulfate ions is formed after the regeneration reaction, and after low-temperature crystallization, sodium sulfate crystals are precipitated, which are separated from the absorption liquid and used as industrial raw materials, crystallization mother liquor As a secondary absorption liquid after regeneration, it is transported into the secondary absorption tower for continued use;

After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the residence time of the sulfur-containing solution is controlled to be 5.0min. The Fe(III)Cit in the solution is converted into Fe(III)Cit, thereby forming a primary absorption liquid after regeneration, adjusting the pH of the regenerated primary absorption liquid to 5.5, and pumping it into the primary absorption tower through another pump, Supplement the liquid volume of the first-stage absorption liquid to carry out the desulfurization process; thereby forming an integrated process of wet desulfurization and denitrification step by step through the cycle regeneration and continuous use of the absorption liquid. In this embodiment, a single complexing agent, ferric citrate (Fe(III) _-Cit ), is used to absorb SO2 and NO in stages to avoid mutual interference, and utilize SO2 and NO's own oxidation _- reduction properties, using biochar as a catalyst, Realize the Fe(III)-Cit regeneration cycle, avoid the chemical consumption of desulfurization and denitrification, and greatly reduce the operating cost. This embodiment efficiently absorbs and removes _SO2 and NO in the flue gas, and aims to reduce the consumption of chemical agents as much as possible. Ferric citrate (Fe(III)Cit) is used as the absorbent to utilize _citrate to efficiently absorb SO2, and The specific absorption of Fe(II)-Cit to NO realizes the removal of the two pollutants step by step; at the same time, the oxidation-reduction properties of SO ₂ and NO are used, and biochar is used as a catalyst to accelerate electron transfer and realize Fe(III) ) efficient conversion between Cit/Fe(II)Cit, so as to ensure the integration of regeneration cycle of absorbent and desulfurization and denitrification.

Experimental test analysis:

In this embodiment, the absorption liquid is in full contact with the polluted gas in the _{two -} stage swirling plate tower, and the removal of SO and NO is completed respectively. After testing, the removal efficiency of SO can reach 92-98%, and the removal efficiency of NO can reach 73%. %~84%.

In this example, Fe(III)Cit is used as the absorption liquid, and the buffering effect of citrate on H ⁺ is used to efficiently absorb SO ₂ in the gas phase, and the SO ₃ ^2- dissolved in the liquid phase after absorption is used as the reducing agent, and the catalyst Under the action of Fe(III)Cit is reduced to Fe(II)Cit; then use the reduced Fe(II)Cit to specifically absorb NO in the gas phase to form a complex Fe(II)Cit-NO; after that , Fe(II)Cit-NO is decomposed by the biochar catalyst to form Fe(III)Cit and N ₂ to realize the regeneration of the absorption liquid; the present invention not only realizes the integrated desulfurization and denitrification, but also avoids the failure of the absorbent, ensuring The regeneration and recycling of Fe(II)Cit does not require the introduction of other chemicals. The biochar required for catalytic Fe(III)Cit/Fe(II)Cit cycle regeneration has the characteristics of wide source of raw materials, simple preparation, and reusability. The whole process is simple, with low investment and low operating costs.

Embodiment three:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, an absorption and purification device is set up, including a primary absorption tower, an absorption liquid regeneration tower ①, a secondary absorption tower, and an absorption liquid regeneration tower ② _; Enter the first-stage absorption tower, the regenerated absorption liquid is a solution mainly containing Fe(III)EDTA, the regenerated absorption liquid enters from the top of the tower after being pressurized by a water pump, the gas-liquid two-phase flows in reverse, and the SO ₂ is completed in the first-stage absorption tower. removal; the purified flue gas enters the bottom of the secondary absorption tower, and the primary absorption liquid flows into the absorption liquid regeneration tower ① for regeneration. After regeneration, a solution mainly containing Fe(II)EDTA is obtained, and the regenerated secondary absorption The liquid is pumped into the top of the secondary absorption tower, and the gas containing NO in the secondary absorption tower is in reverse contact with the absorption liquid to complete the removal of NO; the absorption liquid that has absorbed NO enters the absorption liquid regeneration tower ② for regeneration, and then passes through The pump circulates into the primary absorption tower for recycling.

In this example, 1 part of Fe ₂ (SO ₄ ) ₃ and 2 parts of Na ₃ EDTA·2H ₂ O were weighed to form a solution, and the pH was adjusted to 4.5 with dilute sulfuric acid as a wet method to remove SO in flue gas step by step. ₂ and the absorption liquid of the primary absorption tower in the process of NO.

In this example, referring to Fig. 1, the biochar is made of waste sawdust biomass as a raw material, which is crushed and sieved, and then heated at a rate of 10°C/min under _N2 atmosphere, through 700°C and A constant temperature pyrolysis method at 800° C. is carried out for 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, the catalytic activity of the biochar is maintained by supplementing new biochar. Activated biochar is prepared from waste sawdust and used in the absorption liquid regeneration tower ① and absorption liquid regeneration tower ② to carry out catalytic oxidation-reduction reactions.

In this embodiment, a wet step _- by _- step method for removing SO2 and NO from flue gas, the flue gas containing SO2 and NO to be purified is successively passed into the primary absorption tower and the secondary absorption tower;

_In the primary absorption tower, the SO in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the desulfurized flue gas continues to enter the secondary absorption tower. The main component of the primary absorption liquid is Fe(III) EDTA; control the pH value of the primary absorption liquid to 4.5, and control the liquid-gas ratio to 6.0L/m ³ ;

In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged; the pH value of the secondary absorption liquid is controlled at 5.0, and the liquid-gas ratio is controlled at 4.0L /m ³ ;

There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels;

After the primary absorption liquid absorbs SO in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid. The residence time of the sulfur-containing solution is controlled to be 1.0min, and the sulfur-containing solution is The Fe(III)EDTA in the solution is converted into Fe(III)EDTA to form a secondary absorption liquid after regeneration, adjust the pH of the regenerated secondary absorption liquid to 5.0, and inject the regenerated secondary absorption liquid into the The secondary absorption tower performs denitrification process; in the regeneration tower ①, a solution of sulfate ions is formed after the regeneration reaction, and after low-temperature crystallization, sodium sulfate crystals are precipitated, which are separated from the absorption liquid and used as industrial raw materials, crystallization mother liquor As a secondary absorption liquid after regeneration, it is transported into the secondary absorption tower for continued use;

After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the residence time of the sulfur-containing solution is controlled to be 5.0min. The Fe(III)EDTA in the solution is converted into Fe(III)EDTA, thereby forming a primary absorption liquid after regeneration, adjusting the pH of the regenerated primary absorption liquid to 4.5, and pumping it into the primary absorption tower through another pump, Supplement the liquid volume of the first-stage absorption liquid to carry out the desulfurization process; thereby forming an integrated process of wet desulfurization and denitrification step by step through the cycle regeneration and continuous use of the absorption liquid. In this example, a single complexing agent, Fe(III)EDTA, is used to absorb SO2 and NO step by step to avoid _mutual interference. By using the self _- oxidation and reduction properties of SO2 and NO, and using biochar as a catalyst, Fe(III)- The EDTA regeneration cycle avoids the chemical consumption of desulfurization and denitrification, which greatly reduces the operating cost. This embodiment efficiently absorbs and removes _SO2 and NO in the flue gas, and aims to reduce the consumption of chemicals as much as possible. Fe(III)EDTA is used as the absorbent, and the efficient absorption of SO2 by Fe(III)EDTA is used, and Fe( _II ) ) The specific absorption of NO by EDTA realizes the removal of the two pollutants step by step; at the same time, the oxidation-reduction properties of SO ₂ and NO are used, and biochar is used as a catalyst to accelerate electron transfer and realize Fe(III)EDTA/Fe (II) Efficient conversion between EDTA, so as to ensure the integration of regeneration cycle of absorbent and desulfurization and denitrification.

Experimental test analysis:

In this embodiment, the absorption liquid is fully contacted with the polluted gas in the _two -stage swirling plate tower, and the removal of SO and NO is completed respectively. After testing, the removal efficiency of SO can reach _91-95 %, and the removal efficiency of NO can reach 84%. ~93%.

In this example, Fe(III)EDTA is used as the absorbing liquid, and the buffering effect of Fe(III)EDTA on H ⁺ is used to efficiently absorb SO ₂ in the gas phase, and SO ₃ ^2- dissolved in the liquid phase after absorption is used as the reducing agent. Under the action of the catalyst, Fe(III)EDTA is reduced to Fe(II)EDTA; then the reduced Fe(II)EDTA is used to specifically absorb NO in the gas phase to form a complex Fe(II)EDTA-NO ; After that, the biochar catalyst catalyzes the decomposition of Fe(II)EDTA-NO to form Fe(III)EDTA and N ₂ to realize the regeneration of the absorption liquid; the present invention not only realizes integrated desulfurization and denitrification, but also avoids the failure of the absorbent, The regeneration and recycling of Fe(II)EDTA is guaranteed without the introduction of other chemicals. The biochar required for catalytic Fe(III)EDTA/Fe(II)EDTA recycling regeneration has the characteristics of wide source of raw materials, simple preparation, and reusability. The whole process is simple, with low investment and low operating costs.

Embodiment four:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, an absorption and purification device is set up, including a primary absorption tower, an absorption liquid regeneration tower ①, a secondary absorption tower, and an absorption liquid regeneration tower ② _; Enter the first-stage absorption tower, the regenerated absorption liquid is a solution mainly containing Fe(III)EDTA, the regenerated absorption liquid enters from the top of the tower after being pressurized by a water pump, the gas-liquid two-phase flows in reverse, and the SO ₂ is completed in the first-stage absorption tower. removal; the purified flue gas enters the bottom of the secondary absorption tower, and the primary absorption liquid flows into the absorption liquid regeneration tower ① for regeneration. After regeneration, a solution mainly containing Fe(II)EDTA is obtained, and the regenerated secondary absorption The liquid is pumped into the top of the secondary absorption tower, and the gas containing NO in the secondary absorption tower is in reverse contact with the absorption liquid to complete the removal of NO; the absorption liquid that has absorbed NO enters the absorption liquid regeneration tower ② for regeneration, and then passes through The pump circulates into the primary absorption tower for recycling.

In this example, 1 part of Fe ₂ (SO ₄ ) ₃ and 2 parts of Na ₃ EDTA·2H ₂ O were weighed to form a solution, and the pH was adjusted to 5.5 with dilute sulfuric acid to remove SO from flue gas step by step by wet method. ₂ and the absorption liquid of the primary absorption tower in the process of NO.

In this example, referring to Fig. 1, the biochar is made of waste sawdust biomass as a raw material, which is crushed and sieved, and then heated at a rate of 10°C/min under _N2 atmosphere, through 700°C and A constant temperature pyrolysis method at 800° C. is carried out for 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, the catalytic activity of the biochar is maintained by supplementing new biochar. Activated biochar is prepared from waste sawdust and used in the absorption liquid regeneration tower ① and absorption liquid regeneration tower ② to carry out catalytic oxidation-reduction reactions.

In this embodiment, a wet step _- by _- step method for removing SO2 and NO from flue gas, the flue gas containing SO2 and NO to be purified is successively passed into the primary absorption tower and the secondary absorption tower;

_In the primary absorption tower, the SO in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the desulfurized flue gas continues to enter the secondary absorption tower. The main component of the primary absorption liquid is Fe(III) EDTA; control the pH value of the primary absorption liquid to 5.5, and control the liquid-gas ratio to 6.0L/m ³ ;

In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged; the pH value of the secondary absorption liquid is controlled to be 6.0, and the liquid-gas ratio is controlled to be 4.0L /m ³ ;

There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels;

After the primary absorption liquid absorbs SO in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid. The residence time of the sulfur-containing solution is controlled to be 1.0min, and the sulfur-containing solution is The Fe(III)EDTA in the solution is converted into Fe(III)EDTA to form a secondary absorption liquid after regeneration. Adjust the pH of the regenerated secondary absorption liquid to 6.0, and pump the regenerated secondary absorption liquid into the The secondary absorption tower performs denitrification process; in the regeneration tower ①, a solution of sulfate ions is formed after the regeneration reaction, and after low-temperature crystallization, sodium sulfate crystals are precipitated, which are separated from the absorption liquid and used as industrial raw materials, crystallization mother liquor As a secondary absorption liquid after regeneration, it is transported into the secondary absorption tower for continued use;

After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the residence time of the sulfur-containing solution is controlled to be 5.0min. The Fe(III)EDTA in the solution is converted into Fe(III)EDTA, thereby forming a primary absorption liquid after regeneration, adjusting the pH of the regenerated primary absorption liquid to 5.5, and pumping it into the primary absorption tower through another pump, Supplement the liquid volume of the first-stage absorption liquid to carry out the desulfurization process; thereby forming an integrated process of wet desulfurization and denitrification step by step through the cycle regeneration and continuous use of the absorption liquid. In this example, a single complexing agent, Fe(III)EDTA, is used to absorb SO2 and NO step by step to avoid _mutual interference. By using the self _- oxidation and reduction properties of SO2 and NO, and using biochar as a catalyst, Fe(III)- The EDTA regeneration cycle avoids the chemical consumption of desulfurization and denitrification, which greatly reduces the operating cost. This embodiment efficiently absorbs and removes _SO2 and NO in the flue gas, and aims to reduce the consumption of chemicals as much as possible. Fe(III)EDTA is used as the absorbent, and the efficient absorption of SO2 by Fe(III)EDTA is used, and Fe( _II ) ) The specific absorption of NO by EDTA realizes the removal of the two pollutants step by step; at the same time, the oxidation-reduction properties of SO ₂ and NO are used, and biochar is used as a catalyst to accelerate electron transfer and realize Fe(III)EDTA/Fe (II) Efficient conversion between EDTA, so as to ensure the integration of regeneration cycle of absorbent and desulfurization and denitrification.

Experimental test analysis:

In this embodiment, the absorption liquid is fully contacted with the polluted gas in the _{two -} stage swirling plate tower, and the removal of SO and NO is completed respectively. After testing, the removal efficiency of SO can reach 90-94%, and the removal efficiency of NO can reach 79%. ~88%.

In this example, Fe(III)EDTA is used as the absorbing liquid, and the buffering effect of Fe(III)EDTA on H ⁺ is used to efficiently absorb SO ₂ in the gas phase, and SO ₃ ^2- dissolved in the liquid phase after absorption is used as the reducing agent. Under the action of the catalyst, Fe(III)EDTA is reduced to Fe(II)EDTA; then the reduced Fe(II)EDTA is used to specifically absorb NO in the gas phase to form a complex Fe(II)EDTA-NO ; After that, the biochar catalyst catalyzes the decomposition of Fe(II)EDTA-NO to form Fe(III)EDTA and N ₂ to realize the regeneration of the absorption liquid; the present invention not only realizes integrated desulfurization and denitrification, but also avoids the failure of the absorbent, The regeneration and recycling of Fe(II)EDTA is guaranteed without the introduction of other chemicals. The biochar required for catalytic Fe(III)EDTA/Fe(II)EDTA recycling regeneration has the characteristics of wide source of raw materials, simple preparation, and reusability. The whole process is simple, with low investment and low operating costs.

Embodiment 5: This embodiment is basically the same as the foregoing embodiment, and the special features are:

In this embodiment, an absorption and purification device is set up, including a primary absorption tower, an absorption liquid regeneration tower ①, a secondary absorption tower, and an absorption liquid regeneration tower ② _; Enter the first-stage absorption tower, the regenerated absorption liquid is a solution mainly containing Fe(III)NTA, the regenerated absorption liquid enters from the top of the tower after being pressurized by a water pump, the gas-liquid two-phase flows in reverse, and the SO ₂ is completed in the first-stage absorption tower. removal; the purified flue gas enters the bottom of the secondary absorption tower, and the primary absorption liquid flows into the absorption liquid regeneration tower ① for regeneration. After regeneration, a solution mainly containing Fe(II)NTA is obtained, and the regenerated secondary absorption The liquid is pumped into the top of the secondary absorption tower, and the gas containing NO in the secondary absorption tower is in reverse contact with the absorption liquid to complete the removal of NO; the absorption liquid that has absorbed NO enters the absorption liquid regeneration tower ② for regeneration, and then passes through The pump circulates into the primary absorption tower for recycling.

In this example, 1 part of Fe ₂ (SO ₄ ) ₃ and 2 parts of Na ₃ NTA·2H ₂ O were weighed to form a solution, and the pH was adjusted to 4.5 with dilute sulfuric acid as a wet method for stepwise removal of SO from flue gas. ₂ and the absorption liquid of the primary absorption tower in the process of NO.

In this example, referring to Fig. 1, the biochar is made of waste sawdust biomass as a raw material, which is crushed and sieved, and then heated at a rate of 10°C/min under _N2 atmosphere, through 700°C and A constant temperature pyrolysis method at 800° C. is carried out for 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, the catalytic activity of the biochar is maintained by supplementing new biochar. Activated biochar is prepared from waste sawdust and used in the absorption liquid regeneration tower ① and absorption liquid regeneration tower ② to carry out catalytic oxidation-reduction reactions.

In this embodiment, a wet step _- by _- step method for removing SO2 and NO from flue gas, the flue gas containing SO2 and NO to be purified is successively passed into the primary absorption tower and the secondary absorption tower;

_In the primary absorption tower, the SO in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the desulfurized flue gas continues to enter the secondary absorption tower. The main component of the primary absorption liquid is Fe(III) NTA; control the pH value of the primary absorption liquid to 4.5, and control the liquid-gas ratio to 6.0L/m ³ ;

In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged; the pH value of the secondary absorption liquid is controlled at 5.0, and the liquid-gas ratio is controlled at 4.0L /m ³ ;

There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels;

After the primary absorption liquid absorbs SO in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid. The residence time of the sulfur-containing solution is controlled to be 1.0min, and the sulfur-containing solution is The Fe(III)NTA in the solution is converted into Fe(III)NTA to form a secondary absorption liquid after regeneration. Adjust the pH of the regenerated secondary absorption liquid to 5.0, and pump the regenerated secondary absorption liquid into the The secondary absorption tower performs denitrification process; in the regeneration tower ①, a solution of sulfate ions is formed after the regeneration reaction, and after low-temperature crystallization, sodium sulfate crystals are precipitated, which are separated from the absorption liquid and used as industrial raw materials, crystallization mother liquor As a secondary absorption liquid after regeneration, it is transported into the secondary absorption tower for continued use;

After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the residence time of the sulfur-containing solution is controlled to be 5.0min. The Fe(III)NTA in the solution is converted into Fe(III)NTA, thereby forming a primary absorption liquid after regeneration, adjusting the pH of the regenerated primary absorption liquid to 4.5, and pumping it into the primary absorption tower through another pump, Supplement the liquid volume of the first-stage absorption liquid to carry out the desulfurization process; thereby forming an integrated process of wet desulfurization and denitrification step by step through the cycle regeneration and continuous use of the absorption liquid. In this example, a single complexing agent, Fe(III)NTA, is used to absorb SO2 and NO step by step to avoid _mutual interference, and to use biochar as a catalyst to realize Fe(III)NTA by using the self _- redox properties of SO2 and NO. The regeneration cycle avoids the consumption of chemicals for desulfurization and denitrification, which greatly reduces the operating cost. This embodiment efficiently absorbs and removes _SO2 and NO in the flue gas, and aims to reduce the consumption of chemicals as much as possible. Fe(III)NTA is used as the absorbent, and the efficient absorption of SO2 by Fe(III)NTA and Fe( _II ) NTA are used as the goal. ) NTA’s specific absorption of NO to realize the removal of the two pollutants step by step; at the same time, using the oxidation-reduction properties of SO ₂ and NO itself, biochar is used as a catalyst to accelerate electron transfer and realize Fe(III)NTA/Fe (II) High-efficiency conversion between NTA, thus ensuring the integration of regeneration cycle of absorbent and desulfurization and denitrification.

Experimental test analysis:

In this embodiment, the absorption liquid is in full contact with the polluted gas in the _{two -} stage swirling plate tower, and the removal of SO and NO is completed respectively. After testing, the removal efficiency of SO can reach 92-97%, and the removal efficiency of NO can reach 73%. ~82%.

In this example, Fe(III)NTA is used as the absorbing liquid, and the buffering effect of Fe(III)NTA on H ⁺ is used to efficiently absorb SO ₂ in the gas phase, and SO ₃ ^2- dissolved in the liquid phase after absorption is used as the reducing agent. Under the action of the catalyst, Fe(III)NTA is reduced to Fe(II)NTA; then the Fe(II)NTA obtained from the reduction is used to specifically absorb NO in the gas phase to form a complex Fe(II)NTA-NO ; Afterwards, the biochar catalyst catalyzes the decomposition of Fe(II)NTA-NO to form Fe(III)NTA and N ₂ to realize the regeneration of the absorption liquid; the present invention not only realizes integrated desulfurization and denitrification, but also avoids the failure of the absorbent, The regeneration and recycling of Fe(II)NTA is guaranteed without the introduction of other chemicals. The biochar required for catalytic Fe(III)NTA/Fe(II)NTA recycling regeneration has the characteristics of wide source of raw materials, simple preparation, and reusability. The whole process is simple, with low investment and low operating costs.

Embodiment six:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this embodiment, an absorption and purification device is set up, including a primary absorption tower, an absorption liquid regeneration tower ①, a secondary absorption tower, and an absorption liquid regeneration tower ② _; Enter the first-stage absorption tower, the regenerated absorption liquid is a solution mainly containing Fe(III)NTA, the regenerated absorption liquid enters from the top of the tower after being pressurized by a water pump, the gas-liquid two-phase flows in reverse, and the SO ₂ is completed in the first-stage absorption tower. removal; the purified flue gas enters the bottom of the secondary absorption tower, and the primary absorption liquid flows into the absorption liquid regeneration tower ① for regeneration. After regeneration, a solution mainly containing Fe(II)NTA is obtained, and the regenerated secondary absorption The liquid is pumped into the top of the secondary absorption tower, and the gas containing NO in the secondary absorption tower is in reverse contact with the absorption liquid to complete the removal of NO; the absorption liquid that has absorbed NO enters the absorption liquid regeneration tower ② for regeneration, and then passes through The pump circulates into the primary absorption tower for recycling.

In this example, 1 part of Fe ₂ (SO ₄ ) ₃ and 2 parts of Na ₃ NTA·2H ₂ O were weighed to form a solution, and the pH was adjusted to 5.5 with dilute sulfuric acid as a wet method to remove SO in flue gas step by step. ₂ and the absorption liquid of the primary absorption tower in the process of NO.

In this example, referring to Fig. 1, the biochar is made of waste sawdust biomass as a raw material, which is crushed and sieved, and then heated at a rate of 10°C/min under _N2 atmosphere, through 700°C and A constant temperature pyrolysis method at 800° C. is carried out for 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, the catalytic activity of the biochar is maintained by supplementing new biochar. Activated biochar is prepared from waste sawdust and used in the absorption liquid regeneration tower ① and absorption liquid regeneration tower ② to carry out catalytic oxidation-reduction reactions.

In this embodiment, a wet step _- by _- step method for removing SO2 and NO from flue gas, the flue gas containing SO2 and NO to be purified is successively passed into the primary absorption tower and the secondary absorption tower;

_In the primary absorption tower, the SO in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the desulfurized flue gas continues to enter the secondary absorption tower. The main component of the primary absorption liquid is Fe(III) NTA; control the pH value of the primary absorption liquid to 5.5, and control the liquid-gas ratio to 6.0L/m ³ ;

In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged; the pH value of the secondary absorption liquid is controlled to be 6.0, and the liquid-gas ratio is controlled to be 4.0L /m ³ ;

There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels;

After the primary absorption liquid absorbs SO in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid. The residence time of the sulfur-containing solution is controlled to be 1.0min, and the sulfur-containing solution is The Fe(III)NTA in the solution is converted into Fe(III)NTA to form a secondary absorption liquid after regeneration, adjust the pH of the regenerated secondary absorption liquid to 6.0, and pump the regenerated secondary absorption liquid into the The secondary absorption tower performs denitrification process; in the regeneration tower ①, a solution of sulfate ions is formed after the regeneration reaction, and after low-temperature crystallization, sodium sulfate crystals are precipitated, which are separated from the absorption liquid and used as industrial raw materials, crystallization mother liquor As a secondary absorption liquid after regeneration, it is transported into the secondary absorption tower for continued use;

After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the residence time of the sulfur-containing solution is controlled to be 5.0min. The Fe(III)NTA in the solution is converted into Fe(III)NTA, thereby forming a primary absorption liquid after regeneration, adjusting the pH of the regenerated primary absorption liquid to 5.5, and pumping it into the primary absorption tower through another pump, Supplement the liquid volume of the first-stage absorption liquid to carry out the desulfurization process; thereby forming an integrated process of wet desulfurization and denitrification step by step through the cycle regeneration and continuous use of the absorption liquid. In this example, a single complexing agent, Fe(III)NTA, is used to absorb SO2 and NO step by step to avoid _mutual interference. By using the self _- redox properties of SO2 and NO, and using biochar as a catalyst, Fe(III)- The NTA regeneration cycle avoids the consumption of chemicals for desulfurization and denitrification, greatly reducing operating costs. This embodiment efficiently absorbs and removes _SO2 and NO in the flue gas, and aims to reduce the consumption of chemicals as much as possible. Fe(III)NTA is used as the absorbent, and the efficient absorption of SO2 by Fe(III)NTA and Fe( _II ) NTA are used as the goal. ) NTA’s specific absorption of NO to realize the removal of the two pollutants step by step; at the same time, using the oxidation-reduction properties of SO ₂ and NO itself, biochar is used as a catalyst to accelerate electron transfer and realize Fe(III)NTA/Fe (II) High-efficiency conversion between NTA, thus ensuring the integration of regeneration cycle of absorbent and desulfurization and denitrification.

Experimental test analysis:

In this embodiment, the absorption liquid is fully contacted with the polluted gas in the _{two -} stage swirling plate tower, and the removal of SO and NO is completed respectively. After testing, the removal efficiency of SO can reach 91-97%, and the removal efficiency of NO can reach 65%. ~76%.

In this example, Fe(III)NTA is used as the absorbing liquid, and the buffering effect of Fe(III)NTA on H ⁺ is used to efficiently absorb SO ₂ in the gas phase, and SO ₃ ^2- dissolved in the liquid phase after absorption is used as the reducing agent. Under the action of the catalyst, Fe(III)NTA is reduced to Fe(II)NTA; then the Fe(II)NTA obtained from the reduction is used to specifically absorb NO in the gas phase to form a complex Fe(II)NTA-NO ; Afterwards, the biochar catalyst catalyzes the decomposition of Fe(II)NTA-NO to form Fe(III)NTA and N ₂ to realize the regeneration of the absorption liquid; the present invention not only realizes integrated desulfurization and denitrification, but also avoids the failure of the absorbent, The regeneration and recycling of Fe(II)NTA is guaranteed without the introduction of other chemicals. The biochar required for catalytic Fe(III)NTA/Fe(II)NTA recycling regeneration has the characteristics of wide source of raw materials, simple preparation, and reusability. The whole process is simple, with low investment and low operating costs.

The methods of the above-mentioned embodiments of the present invention remove sulfur dioxide (SO ₂ ) and nitrogen monoxide (NO) in the flue gas by wet step by step, and the flue gas to be purified is continuously passed into the primary absorption tower and the secondary absorption tower; _In the tower, the SO2 in the flue gas is absorbed and removed after contacting the primary absorption liquid, and in the secondary absorption tower, the NO in the flue gas is absorbed and removed after contacting the secondary absorption liquid, and the purified gas is discharged; The above-mentioned primary absorption liquid is ferric organic complex solution, and the pH value is controlled between 4.0 and 6.0; the primary absorption liquid enters the regeneration tower ① after absorbing SO ₂ , and under the catalytic action of biochar catalyst, three The valent iron organic complex is transformed into a divalent iron organic complex, adjusted to pH 5.0-6.0, and then enters the secondary absorption tower for use as a secondary absorption liquid; after the secondary absorption liquid complexes and absorbs NO, it enters the regeneration tower ②, under the catalysis of the biochar catalyst, ferric organic complexes are transformed, and the regenerated absorption liquid enters the primary absorption tower and is recycled in the system. The biochar catalyst is obtained by pyrolyzing biomass at 300-800° C. for at least 2 hours under N ₂ atmosphere. The step-by-step and efficient green removal of SO ₂ and NO in the flue gas can be realized. The absorbent Fe(III)Cit used can be recycled, and no other desulfurization and denitrification chemicals need to be added during the removal process.

The embodiment of the present invention has been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiment, and various changes can also be made according to the purpose of the invention of the present invention. The changes, modifications, substitutions, combinations or simplifications should be equivalent replacement methods, as long as they meet the purpose of the present invention, as long as they do not deviate from the technical principle of the method for wet step-by _- step removal of SO2 and NO in flue gas of the present invention and inventive concepts all belong to the protection scope of the present invention.

Claims (7)

1. a kind of wet step-by _- step removal of SO2 and the method for NO in the flue gas, it is characterized in that _: the flue gas that contains SO2 and NO to be purified is successively passed into a primary absorption tower and a secondary absorption tower; _In the primary absorption tower, the SO2 in the flue gas is absorbed and removed after being in contact with the primary absorption liquid, and the flue gas after desulfurization continues to enter the secondary absorption tower. The main component of the primary absorption liquid is ferric organic complexes; In the secondary absorption tower, the NO in the flue gas is absorbed and removed after being in contact with the secondary absorption liquid, and the gas that reaches the standard after denitrification and purification is discharged; There is also a regeneration tower ① and a regeneration tower ②, which can regenerate the absorption liquid in the absorption towers at all levels; After the primary absorption liquid absorbs SO2 in the flue gas in the primary absorption tower, a sulfur _- containing solution is formed, and the sulfur-containing solution enters the regeneration tower ① of the absorption liquid, and the ferric organic complex in the sulfur-containing solution is Converted into ferrous organic complexes to form a secondary absorption liquid after regeneration, and pump the regenerated secondary absorption liquid into the secondary absorption tower for denitrification process; After the secondary absorption liquid in the secondary absorption tower completes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, and the nitrogen-containing solution enters the regeneration tower ② of the absorption liquid, and the ferrous organic complex in the nitrogen-containing solution is It is converted into a ferric organic complex to form a first-level absorption liquid after regeneration, and then pumped into the first-level absorption tower through another pump to replenish the liquid volume of the first-level absorption liquid and perform a desulfurization process; thereby forming an absorption liquid cycle Regeneration and continuous use to realize the integrated process of wet desulfurization and denitrification step by step. 2. according to claim 1 described wet stepwise removal of SO in flue gas _The method of and NO is characterized in that: The main component of the primary absorption liquid is at least one ferric organic complex in iron citrate (Fe(III)Cit, Fe(III)EDTA and Fe(III)NTA); In the regeneration tower ①, under the catalysis of biochar, the ferric organic complex in the sulfur-containing solution is converted into at least one of Fe(II)Cit, Fe(II)EDTA and Fe(II)NTA). ferric organic complex, control the residence time of the sulfur-containing solution to 0.5-2min, adjust the pH of the obtained secondary absorption liquid containing ferrous organic complex to 5.0-6.0, and then transport it into the secondary absorption tower , carry out the denitrification process; In the regeneration tower ②, under the catalysis of biochar, the divalent iron organic complex in the nitrogen-containing solution is converted into at least one of Fe(III)Cit, Fe(III)EDTA and Fe(III)NTA) A ferric organic complex, the residence time of the nitrogen-containing solution is controlled to be 1.2 to 7.2 minutes, and then transported into the first-stage absorption tower for desulfurization process, thereby forming the absorption liquid to be regenerated and continuously used. 3. according to claim ₂ described wet step-by-step removal SO2 and the method for NO in flue gas, it is characterized in that: described biochar is to be raw material with biomass, after crushing, sieving, then in _N2 atmosphere At a heating rate not lower than 10°C/min, carry out pyrolysis at a constant temperature of 300-800°C for at least 2 hours to prepare active biomass; when the catalytic activity of the biochar decreases, supplement The new biochar maintains the catalytic activity of the biochar. 4. according to claim 1 described wet step-by _- step removal of SO in the flue gas and NO method, it is characterized in that: in described regeneration tower 1., form the solution of sulfate ion after regeneration reaction, after low-temperature crystallization , Sodium sulfate crystals are precipitated, which are separated from the absorption liquid. As industrial raw materials, the crystallization mother liquor is used for regeneration to form a secondary absorption liquid, which is transported into the secondary absorption tower for continued use. 5. according to claim 1, the wet step-by _- step removal method of SO2 and NO in the flue gas is characterized in that: in the primary absorption tower, the pH value of the primary absorption liquid is controlled to be 4.0～6.0, and the liquid gas is controlled to The ratio is 4.2 to 12.0 L/m ³ . 6. The method for wet and step-by _- step removal of SO2 and NO from flue gas according to claim 5, characterized in that: in the primary absorption tower, the pH value of the primary absorption liquid is controlled to be 4.5-5.5. 7. The method for removing SO2 and NO in the flue gas according to claim ₁ , characterized in that: in the secondary absorption tower, the pH value of the primary absorption liquid is controlled to be 5.0 to 6.0, and the liquid gas is controlled to The ratio is 2.0 to 6.0 L/m ³ .