CN110124451B

CN110124451B - Wet-type step-by-step SO removal in flue gas2And NO process

Info

Publication number: CN110124451B
Application number: CN201910391806.0A
Authority: CN
Inventors: 於柯言; 胡甜; 刘扬; 刘畅; 刘强
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2019-05-13
Filing date: 2019-05-13
Publication date: 2021-11-05
Anticipated expiration: 2039-05-13
Also published as: CN110124451A

Abstract

The invention discloses a wet-type step-by-step removal method for SO in flue gas₂And NO method, the flue gas to be purified is continuously introduced into a first-stage absorption tower and a second-stage absorption tower; in the first-stage absorption tower, SO in the flue gas₂The NO in the flue gas is absorbed and removed after being contacted with the primary absorption liquid, in the secondary absorption tower, the NO in the flue gas is absorbed and removed after being contacted with the secondary absorption liquid, and the purified gas is discharged; absorbing SO with the first-stage absorption liquid₂Then enters a regeneration tower, and under the catalytic action of a charcoal catalyst, an iron organic complex is converted; and (4) after the second-stage absorption liquid absorbs NO in a complexing way, the second-stage absorption liquid enters a regeneration tower II to generate iron organic complex conversion, and the regenerated absorption liquid enters the first-stage absorption tower again to be recycled in the system. The method realizes SO in the flue gas₂And NO is removed in a step-by-step efficient and green manner, the used absorbent can be recycled, and other desulfurization and denitrification chemical agents are not required to be added in the removing process.

Description

Wet-type step-by-step SO removal in flue gas2And NO process

Technical Field

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

Background

Sulfur Oxides (SO)_X) And Nitrogen Oxides (NO)_X) Is the main pollutant causing air pollution. The artificial emission of the pollutants mainly comes from the combustion process and the chemical production process of fossil resources such as coal, fuel oil and the like, has the characteristics of large smoke emission, concentrated pollutant emission and the like, and is easy to cause the problem of regional atmospheric pollution. Sulfur Oxides (SO) emitted from combustion flue gas_X) Mainly sulfur dioxide (SO)₂) Nitrogen Oxide (NO)_X) It is mainly Nitric Oxide (NO) and the ratio is more than nine. Thus, for SO₂And NO removal is the focus of combustion flue gas cleaning.

At present, the SO removal by a wet limestone or ammonia method is mostly adopted in the commercialized desulfurization and denitrification process₂A combined process for Selective Catalytic Reduction (SCR) for NO removal; however, the process flow is complicated and the removal is carried outThe pollutants require the consumption of large amounts of chemicals, such as CaO, NH₃Etc. while also producing large amounts of waste, such as desulfurized gypsum.

The wet-process simultaneous flue gas desulfurization and denitration process has the advantages of simple process, low equipment investment and the like, still has certain attraction to the desulfurization and denitration process with small flue gas quantity, and researchers also develop various wet-process desulfurization and denitration integrated processes and technologies. The wet-process simultaneous desulfurization and denitrification is mainly classified into an oxidation method and a complex absorption method. The oxidation method is to increase the oxidation rate of NO by adding an oxidant, thereby improving the desulfurization and denitrification rate. For example, patent CN109276987A discloses a method for removing SO in industrial exhaust gas by using an absorbent obtained by mixing an oxidant composed of alkali metal or alkaline earth metal peroxide, inorganic salt or organic peroxide having oxidizing property and an activator composed of soluble alkali or salt having activating effect and capable of generating weak acid radical ions in aqueous solution₂And NO. Patent CN208436644U proposes that NO in smoke is firstly₂Converting into nitric acid and NO, converting the NO produced into NO by blowing air₂Meanwhile, sulfur dioxide in the flue gas is absorbed by water liquid, so that the desulfurization and denitrification process is realized. The two methods are simple in operation, but secondary pollution is easily caused by improper treatment, and the reagent use cost is high.

The complex absorption method is a flue gas simultaneous desulfurization and denitrification technology which is considered by scholars to be expected to realize industrial application. The technology is characterized in that a complexing agent capable of reacting with NO is added into absorption liquid, so that the solubility of NO in water can be remarkably increased, the separation of NO in flue gas is realized, and the problem of low mass transfer rate of NO in a liquid phase is solved. The ferrochelation method is one of the most studied methods of the liquid phase complex absorption method at present. The method adopts Fe (II) -EDTA (or Fe (II) -Cit, ferric citrate) as absorbent, and has the advantages of high NO absorption rate, high efficiency, stable generated complexing, low cost, easy obtaining and the like. The chemical principle involved in the method is as follows:

fe (II) EDTA (Fe (II) -Cit) solution and NO generate complexation reaction, so that NO with low solubility enters into liquid phase to form a ferroconoyl complex, and NO is removed from gas:

NO(g)→NO(aq) (1)

NO(aq)+Fe(II)EDTA→Fe(II)EDTA-NO (2)

because 3% -5% of oxygen exists in the flue gas, the ferrous chelator can be oxidized into Fe (III) EDTA, the activity is lost, the ability of combining NO is not provided, and the NO removal efficiency of the absorption liquid is reduced:

4Fe(II)EDTA+O₂+4H⁺→4Fe(III)EDTA+2H₂O (3)

therefore, efficient regeneration of the ferrous chelator is critical to the process being able to operate continuously. To this problem, patent CN104084023A proposes to adopt the complexing of ferrous chelator to absorb NO, and the absorption liquid is reduced to the ammonia by metallic iron and realizes the denitration, mixes ammonia and the aqueous ammonia of desulfurization section again, reacts with sulfur dioxide and obtains ammonium sulfite, and then the oxidation obtains ammonium sulfate, realizes the desulfurization, and this technology is also comparatively simple, nevertheless needs to consume ammonia and metallic iron for the cost of handling increases to some extent.

Furthermore, if SO is present in the flue gas₂SO in the flue gas₂Is easily absorbed by water and reacts with Fe (II) EDTA-NO to generate Fe (II) EDTA (SO)₃ ^2-) NO, the compound is extremely stable and difficult to decompose, resulting in loss of the absorbent.

SO₂(g)+H₂O→H⁺+SO₃ ^2- (4)

Fe(II)EDTA-NO+SO₃ ^2-→Fe(II)EDTA(SO₃ ^2-)NO (5)

Therefore, it is necessary to develop an efficient and inexpensive technology and process for regenerating and recycling the absorption liquid, which is a technical problem to be solved.

Disclosure of Invention

In order to solve the problems of the prior art, the invention aims to overcome the defects of the prior art and provide a wet type step-by-step removal method for SO in flue gas₂And NO can be efficiently absorbed and removed₂And NO, with the aim of minimizing the consumption of chemical agents, using a ferric organic complex as an absorbent, and using the ferric organic complex for SO₂High efficiency absorption of N using ferrous organic complexesThe specific absorption of O realizes the removal of two pollutants step by step; with simultaneous use of SO₂And the oxidation-reduction property of NO per se, and the biochar is used as a catalyst, so that the electron transfer is accelerated, and the high-efficiency conversion between the ferric iron organic complex and the ferrous iron organic complex is realized, thereby ensuring the integration of the regeneration circulation of the absorbent and the desulfurization and denitrification.

In order to achieve the purpose, the invention adopts the following technical scheme:

wet-type substep desorption SO in flue gas₂And NO, the SO-containing gas to be purified₂The flue gas with NO is sequentially and continuously introduced into a primary absorption tower and a secondary absorption tower;

in the first-stage absorption tower, SO in the flue gas₂The flue gas is absorbed and removed after being contacted with the primary absorption liquid, the desulfurized flue gas continuously enters a secondary absorption tower, and the primary absorption liquid mainly comprises a ferric iron organic complex;

in the secondary absorption tower, NO in the flue gas is absorbed and removed after contacting with secondary absorption liquid, and the gas up to the standard after denitration and purification is discharged;

the device is also provided with a first regeneration tower and a second regeneration tower which can respectively regenerate the absorption liquid in each stage of absorption tower;

the first-stage absorption liquid in the first-stage absorption tower absorbs SO in the flue gas₂Then, forming a sulfur-containing solution, enabling the sulfur-containing solution to enter a regeneration tower of the absorption liquid, converting a ferric iron organic complex in the sulfur-containing solution into a ferrous iron organic complex, thereby forming a secondary absorption liquid after regeneration, and pumping the regenerated secondary absorption liquid into the secondary absorption tower through a pump for carrying out a denitration process;

after the secondary absorption liquid in the secondary absorption tower finishes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, the nitrogen-containing solution enters a regeneration tower of the absorption liquid, a ferrous organic complex in the nitrogen-containing solution is converted into a ferric organic complex, so that a primary absorption liquid is formed after regeneration, and the primary absorption liquid is pumped into the primary absorption tower through another pump to supplement the liquid amount of the primary absorption liquid, and a desulfurization process is carried out; thereby forming the integrated process of the cyclic regeneration and the continuous use of the absorption liquid and realizing the wet-type step-by-step desulfurization and denitrification.

As the preferable technical proposal of the invention, the primary absorption liquid mainly comprises at least one ferric iron organic complex in ferric citrate (Fe (III) Cit, Fe (III) EDTA and Fe (III) NTA); in a regeneration tower, under the catalytic action of biochar, converting a ferric iron organic complex in a sulfur-containing solution into at least one ferrous iron organic complex in Fe (II) Cit, Fe (II) EDTA and Fe (II) NTA), controlling the retention time of the sulfur-containing solution to be 0.5-2 min, adjusting the pH value of the obtained secondary absorption liquid containing the ferrous iron organic complex to be 5.0-6.0, and conveying the secondary absorption liquid into a secondary absorption tower for a denitration process; in the regeneration tower II, under the catalytic action of biochar, a ferrous iron organic complex in a nitrogen-containing solution is converted into at least one ferric iron organic complex in Fe (III) Cit, Fe (III) EDTA and Fe (III) NTA), the retention time of the nitrogen-containing solution is controlled to be 1.2-7.2 min, and then the nitrogen-containing solution is conveyed into a primary absorption tower for desulfurization, so that the absorption liquid is regenerated circularly and continuously used.

As a further preferable technical scheme of the invention, the biochar is prepared by taking biomass as a raw material, crushing, sieving and then carrying out N₂Pyrolyzing for at least 2 hours at a temperature rise rate of not less than 10 ℃/min in a constant temperature pyrolysis method at 300-800 ℃ in an atmosphere to prepare an active biomass; and when the catalytic activity of the biochar is reduced, maintaining the catalytic activity of the biochar by supplementing new biochar.

In the preferred technical scheme of the invention, in the regeneration tower (i), a sulfate ion solution is formed after regeneration reaction, sodium sulfate crystals are separated out after low-temperature crystallization, so that the absorption liquid is separated out and used as an industrial raw material, and a crystallization mother liquor is used as a secondary absorption liquid formed after regeneration and is conveyed into a secondary absorption tower for continuous use.

In the first-stage absorption tower, the pH value of the first-stage absorption liquid is preferably controlled to be 4.0-6.0, and the liquid-gas ratio is preferably controlled to be 4.2-12.0L/m³. In the first-stage absorption tower, the pH value of the first-stage absorption liquid is preferably controlled to be 4.5-5.5.

In the above-mentioned secondary absorption tower, it is preferable to control the primary absorptionThe pH value of the collected liquid is 5.0-6.0, and the liquid-gas ratio is preferably controlled to be 2.0-6.0L/m³。

The principle of the invention is as follows:

the invention relates to a wet-type step-by-step removal method for SO in flue gas₂The process for mixing NO is to continuously introduce the flue gas to be purified into a first-stage absorption tower and a second-stage absorption tower; the flue gas continuously flows through the first-stage absorption tower and the second-stage absorption tower, and is discharged after being purified; the absorption liquid takes (Fe (III) Cit) as an example, and SO in the flue gas is absorbed by the absorption liquid through a first-stage absorption tower₂Then, the flue gas enters an absorption liquid regeneration tower I, is pumped into a secondary absorption tower through a pump after being regenerated, enters an absorption liquid regeneration tower II after the absorption of NO in the flue gas is completed, and is pumped into a primary absorption tower through a pump for recycling after being regenerated; the specific process flow is shown in figure 1.

a. Further, the first-stage absorption tower is characterized in that Fe (III) Cit solution is used as absorption liquid, the pH value is controlled to be 4.0-6.0, and SO in flue gas is mainly absorbed and removed₂The liquid-gas ratio is controlled to be 4.2-12.0L/m³Specifically, the following reaction occurs:

SO₂+H₂O→HSO₃ ^2-+H⁺ (6)

H⁺+Cit³⁺→HCit²⁺ (7)

H⁺+HCit²⁺→H₂Cit⁺ (8)

the preparation method of the Fe (III) Cit absorption liquid in the step a comprises the following steps: mixing Fe₂(SO₄)₃And sodium citrate according to the molar ratio of 1 to (1-3), and the concentration of Fe (III) is 0.01-0.03 mol/L.

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

the biochar in the step b takes biomass (such as corn straws) as a raw material and is crushedSieving, under N₂In the atmosphere, the material is prepared by pyrolysis for 2 hours at the constant temperature of 300-800 ℃ at the heating rate of 10 ℃/min.

c. Further, in the secondary absorption tower, the liquid in the absorption liquid regeneration tower is used as absorption liquid, the pH value is controlled to be 5.0-6.0, NO in the flue gas is mainly absorbed and removed, the liquid-gas ratio is controlled to be 2.0-6.0L/m 3, and the following reactions are specifically carried out:

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+O₂+4H⁺→4Fe(III)Cit+2H₂O (12)

d. Further, the mixed solution in the absorption liquid regeneration tower II is characterized in that biochar is used as a filler, the retention time of the absorption liquid is controlled to be 1.2-7.2 min, and the following reactions are specifically carried out:

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

e. Furthermore, the biochar disclosed by the invention can supplement fresh biochar to maintain the catalytic activity after the catalytic activity is reduced.

f. Further, because the desulfurization process is continuously carried out in the absorption liquid, sulfate is accumulated and can be recycled, and the specific method comprises the following steps: filtering the absorption liquid to remove solid impurities, and crystallizing with cold water to obtain NaSO₄The crystal mush is centrifugally dewatered, and the separated mother liquid can be returned to the absorption tower for recycling.

Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:

1. the method takes a ferric organic complex as an absorption liquid and utilizes ferric organic complex salt to react with H⁺Buffer action of (2) to absorb gas phase efficientlySO₂And with SO dissolved in the liquid phase after absorption₃ ^2-Reducing ferric organic complex into ferrous organic complex under the action of catalyst; then the ferrous iron organic complex obtained by reduction is used for specifically absorbing NO in a gas phase to form a ferrous iron organic complex-NO; then, the divalent iron organic complex-NO is catalyzed to be decomposed to form trivalent iron organic complex and N in the biochar catalyst₂The regeneration of the absorption liquid is realized;

2. the method disclosed by the invention realizes integrated desulfurization and denitrification, avoids the failure of the absorbent, ensures the regeneration and cyclic utilization of the ferrous organic complex, and does not need the introduction of other chemicals; the biochar required by the circulation regeneration of the ferric organic complex and the ferrous organic complex is catalyzed, and has the characteristics of wide raw material source, simple preparation and reusability;

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

Drawings

FIG. 1 shows a wet-type step-by-step removal of SO from flue gas according to an embodiment of the present invention₂And a schematic process flow diagram for NO.

Detailed Description

The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:

the first embodiment is as follows:

in this embodiment, referring to fig. 1, an absorption purification apparatus is constructed, which includes a first-stage absorption tower, an absorption liquid regeneration tower (i), a second-stage absorption tower, and an absorption liquid regeneration tower (ii); will contain SO₂Leading out the gas with NO by a draught fan, entering a first-stage absorption tower from the bottom of the tower, taking the regenerated absorption liquid as a solution mainly containing Fe (III) Cit, pressurizing the regenerated absorption liquid by a water pump, entering from the top of the tower, leading the gas phase and the liquid phase to flow in reverse direction, and finishing SO in the first-stage absorption tower₂Removing; the purified flue gas enters the bottom of a secondary absorption tower, the primary absorption liquid flows into an absorption liquid regeneration tower to be regenerated, a solution mainly containing Fe (II) Cit is obtained after regeneration, and the regenerated secondary absorption tower absorbsPumping the liquid into the top of a secondary absorption tower by a pump, and reversely contacting the NO-containing gas in the secondary absorption tower with the absorption liquid to finish NO removal; the absorption liquid absorbing NO enters an absorption liquid regeneration tower II for regeneration, and then is circularly pumped into a first-stage absorption tower through a pump for recycling.

In this example, referring to FIG. 1, 1 part of Fe was weighed₂(SO₄)₃And 2 parts of Na₃Cit·2H₂Preparing O to form a solution, adjusting the pH to 4.5 by using dilute sulfuric acid, and removing SO in the flue gas step by step as a wet method₂And the absorption liquid of the first-stage absorption tower in the NO process.

In this example, referring to fig. 1, the biochar is prepared from corn stalk biomass as raw material by crushing, sieving, and then adding N₂Pyrolyzing for 2 hours at a temperature rise rate of 10 ℃/min in an atmosphere by a constant temperature pyrolysis method at 800 ℃ to prepare active biomass; and when the catalytic activity of the biochar is reduced, maintaining the catalytic activity of the biochar by supplementing new biochar. The active biochar is prepared from corn straws and is used for carrying out catalytic oxidation-reduction reaction in an absorption liquid regeneration tower I and an absorption liquid regeneration tower II.

In the present embodiment, referring to fig. 1, a wet-type step-by-step removal of SO in flue gas₂And NO, the SO-containing gas to be purified₂The flue gas with NO is sequentially and continuously introduced into a primary absorption tower and a secondary absorption tower;

in the first-stage absorption tower, SO in the flue gas₂The flue gas is absorbed and removed after being contacted with a primary absorption liquid, the desulfurized flue gas continuously enters a secondary absorption tower, and the primary absorption liquid mainly comprises ferric citrate Fe (III) Cit; controlling the pH value of the primary absorption liquid to be 4.5 and controlling the liquid-gas ratio to be 6.0L/m³；

In the secondary absorption tower, NO in the flue gas is absorbed and removed after contacting with secondary absorption liquid, and the gas up to the standard after denitration and purification is discharged; controlling the pH value of the secondary absorption liquid to be 5.0 and controlling the liquid-gas ratio to be 4.0L/m³；

the first-stage absorption liquid in the first-stage absorption tower absorbs SO in the flue gas₂Then, forming a sulfur-containing solution, enabling the sulfur-containing solution to enter a regeneration tower of the absorption liquid, controlling the residence time of the sulfur-containing solution to be 1.0min, converting Fe (III) Cit in the sulfur-containing solution into Fe (III) Cit, thereby forming a secondary absorption liquid after regeneration, adjusting the pH value of the regenerated secondary absorption liquid to be 5.0, and pumping the regenerated secondary absorption liquid into the secondary absorption tower through a pump for carrying out a denitration process; in the regeneration tower I, a sulfate ion solution is formed after regeneration reaction, sodium sulfate crystals are separated out after low-temperature crystallization, so that an absorption liquid is separated out and used as an industrial raw material, and a crystallization mother liquor is used as a secondary absorption liquid formed after regeneration and is conveyed into a secondary absorption tower for continuous use;

after the secondary absorption liquid in the secondary absorption tower finishes the absorption of NO in the flue gas, a nitrogenous solution is formed, the nitrogenous solution enters a regeneration tower of the absorption liquid, the residence time of the sulfur-containing solution is controlled to be 5.0min, Fe (III) Cit in the nitrogenous solution is converted into Fe (III) Cit, so that a primary absorption liquid is formed after regeneration, the pH value of the regenerated primary absorption liquid is adjusted to be 4.5, the regenerated primary absorption liquid is pumped into the primary absorption tower through another pump, the liquid amount of the primary absorption liquid is supplemented, and a desulfurization process is carried out; thereby forming the integrated process of the cyclic regeneration and the continuous use of the absorption liquid and realizing the wet-type step-by-step desulfurization and denitrification. In the embodiment, a single complexing agent ferric citrate (Fe (III) -Cit) is adopted to absorb SO step by step₂And NO, SO as to avoid mutual interference₂And NO is self-oxidation-reduction, and biochar is used as a catalyst, so that Fe (III) -Cit regeneration cycle is realized, the consumption of desulfurization and denitration chemicals is avoided, and the operation cost is greatly reduced. The embodiment efficiently absorbs and removes SO in the flue gas₂And NO, the aim of reducing the consumption of chemical agents as much as possible is to use ferric citrate (Fe (III) Cit) as an absorbent and use citrate to react SO₂The high-efficiency absorption and the specific absorption effect of Fe (II) -Cit on NO realize the removal of two pollutants step by step; with simultaneous use of SO₂And the oxidation-reduction property of NO, and biochar is used as a catalyst to accelerate electron transfer and realize the high-efficiency conversion between Fe (III) Cit/Fe (II) Cit, thereby ensuring the regeneration cycle of the absorbent and desulfurization and desorptionAnd (4) integrating nitre.

Experimental test analysis:

the absorption liquid of the embodiment is fully contacted with the polluted gas in the two-stage cyclone plate tower to respectively complete SO₂And removal of NO, detection of SO₂The removal efficiency can reach 90-95%, and the removal efficiency of NO can reach 82-91%.

In this example, Fe (III) Cit is used as absorption liquid, and citrate is used to react with H⁺The buffer function of the absorption tower can efficiently absorb SO in the gas phase₂And with SO dissolved in the liquid phase after absorption₃ ^2-Reducing Fe (III) Cit to Fe (II) Cit under the action of a catalyst as a reducing agent; then Fe (II) Cit obtained by reduction is used for specifically absorbing NO in a gas phase to form a complex Fe (II) Cit-NO; then, Fe (II) Cit-NO is catalyzed by a biochar catalyst to be decomposed into Fe (III) Cit and N₂The regeneration of the absorption liquid is realized; the invention realizes integrated desulfurization and denitrification, avoids the failure of the absorbent, ensures the regeneration and cyclic utilization of Fe (II) Cit, and does not need the introduction of other chemicals. The biochar required for catalyzing the cyclic regeneration of Fe (III) Cit/Fe (II) Cit has the characteristics of wide raw material source, simple preparation, reusability, simple whole process, low investment and low operating cost.

Example two:

this embodiment is substantially the same as the first embodiment, and is characterized in that:

in the embodiment, an absorption purification device is constructed, which comprises a first-stage absorption tower, an absorption liquid regeneration tower I, a second-stage absorption tower and an absorption liquid regeneration tower II; will contain SO₂Leading out the gas with NO by a draught fan, entering a first-stage absorption tower from the bottom of the tower, taking the regenerated absorption liquid as a solution mainly containing Fe (III) Cit, pressurizing the regenerated absorption liquid by a water pump, entering from the top of the tower, leading the gas phase and the liquid phase to flow in reverse direction, and finishing SO in the first-stage absorption tower₂Removing; the purified flue gas enters the bottom of a secondary absorption tower, the primary absorption liquid flows into an absorption liquid regeneration tower to be regenerated, a solution mainly containing Fe (II) Cit is obtained after regeneration, the regenerated secondary absorption liquid is pumped into the top of the secondary absorption tower by a pump, and NO-containing gas in the secondary absorption towerThe body is in reverse contact with the absorption liquid to complete the removal of NO; the absorption liquid absorbing NO enters an absorption liquid regeneration tower II for regeneration, and then is circularly pumped into a first-stage absorption tower through a pump for recycling.

In this example, 1 part of Fe was weighed₂(SO₄)₃And 2 parts of Na₃Cit·2H₂Preparing O to form a solution, adjusting the pH to 5.5 by using dilute sulfuric acid, and removing SO in the flue gas step by step as a wet method₂And the absorption liquid of the first-stage absorption tower in the NO process.

In this example, referring to fig. 1, the biochar is prepared from waste wood chip biomass as raw material, by crushing, sieving, and then adding N₂Pyrolyzing for 2 hours at a heating rate of 10 ℃/min in a constant temperature pyrolysis method of 500 ℃ and 800 ℃ in the atmosphere to prepare active biomass; and when the catalytic activity of the biochar is reduced, maintaining the catalytic activity of the biochar by supplementing new biochar. The waste wood chips are used for preparing the active biochar which is used for carrying out catalytic oxidation reduction reaction in an absorption liquid regeneration tower I and an absorption liquid regeneration tower II.

In this embodiment, a wet-type step-by-step removal of SO from flue gas₂And NO, the SO-containing gas to be purified₂The flue gas with NO is sequentially and continuously introduced into a primary absorption tower and a secondary absorption tower;

in the first-stage absorption tower, SO in the flue gas₂The flue gas is absorbed and removed after being contacted with a primary absorption liquid, the desulfurized flue gas continuously enters a secondary absorption tower, and the primary absorption liquid mainly comprises ferric citrate Fe (III) Cit; controlling the pH value of the primary absorption liquid to be 5.5 and controlling the liquid-gas ratio to be 6.0L/m³；

In the secondary absorption tower, NO in the flue gas is absorbed and removed after contacting with secondary absorption liquid, and the gas up to the standard after denitration and purification is discharged; controlling the pH value of the secondary absorption liquid to be 6.0 and controlling the liquid-gas ratio to be 4.0L/m³；

the first-stage absorption liquid in the first-stage absorption tower absorbs SO in the flue gas₂After that, sulfur is formedThe solution is prepared by allowing a sulfur-containing solution to enter a regeneration tower of an absorption liquid, controlling the residence time of the sulfur-containing solution to be 1.0min, converting Fe (III) Cit in the sulfur-containing solution into Fe (III) Cit, so as to form a secondary absorption liquid after regeneration, adjusting the pH value of the regenerated secondary absorption liquid to be 6.0, and pumping the regenerated secondary absorption liquid into the secondary absorption tower through a pump for a denitration process; in the regeneration tower I, a sulfate ion solution is formed after regeneration reaction, sodium sulfate crystals are separated out after low-temperature crystallization, so that an absorption liquid is separated out and used as an industrial raw material, and a crystallization mother liquor is used as a secondary absorption liquid formed after regeneration and is conveyed into a secondary absorption tower for continuous use;

after the secondary absorption liquid in the secondary absorption tower finishes the absorption of NO in the flue gas, a nitrogenous solution is formed, the nitrogenous solution enters a regeneration tower of the absorption liquid, the residence time of the sulfur-containing solution is controlled to be 5.0min, Fe (III) Cit in the nitrogenous solution is converted into Fe (III) Cit, so that a primary absorption liquid is formed after regeneration, the pH value of the regenerated primary absorption liquid is adjusted to be 5.5, the regenerated primary absorption liquid is pumped into the primary absorption tower through another pump, the liquid amount of the primary absorption liquid is supplemented, and a desulfurization process is carried out; thereby forming the integrated process of the cyclic regeneration and the continuous use of the absorption liquid and realizing the wet-type step-by-step desulfurization and denitrification. In the embodiment, a single complexing agent ferric citrate (Fe (III) -Cit) is adopted to absorb SO step by step₂And NO, SO as to avoid mutual interference₂And NO is self-oxidation-reduction, and biochar is used as a catalyst, so that Fe (III) -Cit regeneration cycle is realized, the consumption of desulfurization and denitration chemicals is avoided, and the operation cost is greatly reduced. The embodiment efficiently absorbs and removes SO in the flue gas₂And NO, the aim of reducing the consumption of chemical agents as much as possible is to use ferric citrate (Fe (III) Cit) as an absorbent and use citrate to react SO₂The high-efficiency absorption and the specific absorption effect of Fe (II) -Cit on NO realize the removal of two pollutants step by step; with simultaneous use of SO₂And the oxidation-reduction property of NO, and the biochar is used as a catalyst, so that the electron transfer is accelerated, and the high-efficiency conversion between Fe (III) Cit/Fe (II) Cit is realized, thereby ensuring the integration of the regeneration cycle of the absorbent and the desulfurization and denitrification.

Experimental test analysis:

the absorption liquid of the embodiment is fully contacted with the polluted gas in the two-stage cyclone plate tower to respectively complete SO₂And removal of NO, detection of SO₂The removal efficiency can reach 92-98%, and the removal efficiency of NO can reach 73-84%.

Example three:

this embodiment is substantially the same as the previous embodiment, and is characterized in that:

in the embodiment, an absorption purification device is constructed, which comprises a first-stage absorption tower, an absorption liquid regeneration tower I, a second-stage absorption tower and an absorption liquid regeneration tower II; will contain SO₂Leading out the gas with NO by a draught fan, entering a first-stage absorption tower from the bottom of the tower, taking the regenerated absorption liquid as a solution mainly containing Fe (III) EDTA, pressurizing the regenerated absorption liquid by a water pump, entering from the top of the tower, leading the gas phase and the liquid phase to flow in reverse direction, and finishing SO in the first-stage absorption tower₂Removing; the purified flue gas enters the bottom of a secondary absorption tower, the primary absorption liquid flows into an absorption liquid regeneration tower I for regeneration, a solution mainly containing Fe (II) EDTA is obtained after regeneration, the regenerated secondary absorption liquid is pumped into the top of the secondary absorption tower through a pump, and the gas containing NO in the secondary absorption tower reversely contacts with the absorption liquid to complete the removal of NO; the absorption liquid absorbing NO enters into the absorptionAnd a liquid recovery and regeneration tower II performs regeneration, and then the liquid is circularly pumped into a first-stage absorption tower through a pump for recycling.

In this example, 1 part of Fe was weighed₂(SO₄)₃And 2 parts of Na₃EDTA·2H₂Preparing O to form a solution, adjusting the pH to 4.5 by using dilute sulfuric acid, and removing SO in the flue gas step by step as a wet method₂And the absorption liquid of the first-stage absorption tower in the NO process.

In this example, referring to fig. 1, the biochar is prepared from waste wood chip biomass as raw material, by crushing, sieving, and then adding N₂Pyrolyzing for 2 hours at a heating rate of 10 ℃/min under an atmosphere by a constant temperature pyrolysis method of 700 ℃ and 800 ℃ to prepare active biomass; and when the catalytic activity of the biochar is reduced, maintaining the catalytic activity of the biochar by supplementing new biochar. The waste wood chips are used for preparing the active biochar which is used for carrying out catalytic oxidation reduction reaction in an absorption liquid regeneration tower I and an absorption liquid regeneration tower II.

in the first-stage absorption tower, SO in the flue gas₂The flue gas is absorbed and removed after being contacted with the primary absorption liquid, the desulfurized flue gas continuously enters a secondary absorption tower, and the primary absorption liquid mainly comprises Fe (III) EDTA; controlling the pH value of the primary absorption liquid to be 4.5 and controlling the liquid-gas ratio to be 6.0L/m³；

the first-stage absorption liquid in the first-stage absorption tower absorbs SO in the flue gas₂Then, a sulfur-containing solution is formed, and the sulfur-containing solution is introduced into a regeneration tower of an absorption liquid, and the residence time of the sulfur-containing solution is controlled to be 1.0min, converting Fe (III) EDTA in the sulfur-containing solution into Fe (III) EDTA, so as to form a secondary absorption liquid after regeneration, adjusting the pH value of the regenerated secondary absorption liquid to 5.0, and pumping the regenerated secondary absorption liquid into a secondary absorption tower through a pump for denitration process; in the regeneration tower I, a sulfate ion solution is formed after regeneration reaction, sodium sulfate crystals are separated out after low-temperature crystallization, so that an absorption liquid is separated out and used as an industrial raw material, and a crystallization mother liquor is used as a secondary absorption liquid formed after regeneration and is conveyed into a secondary absorption tower for continuous use;

after the secondary absorption liquid in the secondary absorption tower finishes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, the nitrogen-containing solution enters a regeneration tower of the absorption liquid, the retention time of the sulfur-containing solution is controlled to be 5.0min, Fe (III) EDTA in the nitrogen-containing solution is converted into Fe (III) EDTA, so that a primary absorption liquid is formed after regeneration, the pH value of the regenerated primary absorption liquid is adjusted to be 4.5, the regenerated primary absorption liquid is pumped into the primary absorption tower through another pump, the liquid amount of the primary absorption liquid is supplemented, and a desulfurization process is carried out; thereby forming the integrated process of the cyclic regeneration and the continuous use of the absorption liquid and realizing the wet-type step-by-step desulfurization and denitrification. In this example, a single complexing agent Fe (III) EDTA is used to absorb SO in steps₂And NO, SO as to avoid mutual interference₂And NO is self-redox, and biochar is used as a catalyst, so that Fe (III) -EDTA regeneration circulation is realized, the consumption of desulfurization and denitrification chemicals is avoided, and the operation cost is greatly reduced. The embodiment efficiently absorbs and removes SO in the flue gas₂And NO, with the aim of minimizing the consumption of chemicals, using Fe (III) EDTA as absorbent and using Fe (III) EDTA to treat SO₂The high-efficiency absorption and the specific absorption effect of Fe (II) EDTA on NO realize the removal of two pollutants step by step; with simultaneous use of SO₂And the oxidation-reduction property of NO, and the biochar is used as a catalyst, so that the electron transfer is accelerated, and the high-efficiency conversion between Fe (III) EDTA/Fe (II) EDTA is realized, thereby ensuring the integration of the regeneration circulation of the absorbent and the desulfurization and denitrification.

Experimental test analysis:

the absorption liquid of the embodiment is fully contacted with the polluted gas in the two-stage cyclone plate tower to respectively complete SO₂And removal of NO, detection of SO₂The removal efficiency can reach 91-95%, and the removal efficiency of NO can reach 84-93%.

In this embodiment, Fe (III) EDTA is used as absorption liquid to absorb H⁺The buffer function of the absorption tower can efficiently absorb SO in the gas phase₂And with SO dissolved in the liquid phase after absorption₃ ^2-Reducing Fe (III) EDTA into Fe (II) EDTA under the action of a catalyst by using a reducing agent; then Fe (II) EDTA obtained by reduction is used for specifically absorbing NO in a gas phase to form a complex Fe (II) EDTA-NO; then, Fe (II) EDTA-NO is catalyzed by the biochar catalyst to be decomposed into Fe (III) EDTA and N₂The regeneration of the absorption liquid is realized; the invention realizes integrated desulfurization and denitrification, avoids the failure of the absorbent, ensures the regeneration and cyclic utilization of Fe (II) EDTA and does not need the introduction of other chemicals. The biochar required for catalyzing the recycling regeneration of Fe (III) EDTA/Fe (II) EDTA has the characteristics of wide raw material source, simple preparation, reusability, simple whole process, low investment and low operating cost.

Example four:

in the embodiment, an absorption purification device is constructed, which comprises a first-stage absorption tower, an absorption liquid regeneration tower I, a second-stage absorption tower and an absorption liquid regeneration tower II; will contain SO₂Leading out the gas with NO by a draught fan, entering a first-stage absorption tower from the bottom of the tower, taking the regenerated absorption liquid as a solution mainly containing Fe (III) EDTA, pressurizing the regenerated absorption liquid by a water pump, entering from the top of the tower, leading the gas phase and the liquid phase to flow in reverse direction, and finishing SO in the first-stage absorption tower₂Removing; the purified flue gas enters the bottom of a secondary absorption tower, the primary absorption liquid flows into an absorption liquid regeneration tower I for regeneration, a solution mainly containing Fe (II) EDTA is obtained after regeneration, the regenerated secondary absorption liquid is pumped into the top of the secondary absorption tower through a pump, and the gas containing NO in the secondary absorption tower reversely contacts with the absorption liquid to complete the removal of NO; the absorption liquid absorbing NO enters an absorption liquid regeneration tower II for regeneration, and then is circularly pumped into a first-stage absorption tower through a pump for recycling.

In this example, 1 part of Fe was weighed₂(SO₄)₃And 2 parts of Na₃EDTA·2H₂Preparing O to form a solution, adjusting the pH to 5.5 by using dilute sulfuric acid, and removing SO in the flue gas step by step as a wet method₂And the absorption liquid of the first-stage absorption tower in the NO process.

in the first-stage absorption tower, SO in the flue gas₂The flue gas is absorbed and removed after being contacted with the primary absorption liquid, the desulfurized flue gas continuously enters a secondary absorption tower, and the primary absorption liquid mainly comprises Fe (III) EDTA; controlling the pH value of the primary absorption liquid to be 5.5 and controlling the liquid-gas ratio to be 6.0L/m³；

the first-stage absorption liquid in the first-stage absorption tower absorbs SO in the flue gas₂Then, forming a sulfur-containing solution, enabling the sulfur-containing solution to enter a regeneration tower of the absorption liquid, controlling the retention time of the sulfur-containing solution to be 1.0min, and converting Fe (III) EDTA in the sulfur-containing solution into Fe (III) EDTA, thereby forming a secondary absorption liquid after regenerationAdjusting the pH value of the regenerated secondary absorption liquid to 6.0, and pumping the regenerated secondary absorption liquid into a secondary absorption tower through a pump to carry out a denitration process; in the regeneration tower I, a sulfate ion solution is formed after regeneration reaction, sodium sulfate crystals are separated out after low-temperature crystallization, so that an absorption liquid is separated out and used as an industrial raw material, and a crystallization mother liquor is used as a secondary absorption liquid formed after regeneration and is conveyed into a secondary absorption tower for continuous use;

after the secondary absorption liquid in the secondary absorption tower finishes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, the nitrogen-containing solution enters a regeneration tower of the absorption liquid, the retention time of the sulfur-containing solution is controlled to be 5.0min, Fe (III) EDTA in the nitrogen-containing solution is converted into Fe (III) EDTA, so that a primary absorption liquid is formed after regeneration, the pH value of the regenerated primary absorption liquid is adjusted to be 5.5, the primary absorption liquid is pumped into the primary absorption tower through another pump, the liquid amount of the primary absorption liquid is supplemented, and a desulfurization process is carried out; thereby forming the integrated process of the cyclic regeneration and the continuous use of the absorption liquid and realizing the wet-type step-by-step desulfurization and denitrification. In this example, a single complexing agent Fe (III) EDTA is used to absorb SO in steps₂And NO, SO as to avoid mutual interference₂And NO is self-redox, and biochar is used as a catalyst, so that Fe (III) -EDTA regeneration circulation is realized, the consumption of desulfurization and denitrification chemicals is avoided, and the operation cost is greatly reduced. The embodiment efficiently absorbs and removes SO in the flue gas₂And NO, with the aim of minimizing the consumption of chemicals, using Fe (III) EDTA as absorbent and using Fe (III) EDTA to treat SO₂The high-efficiency absorption and the specific absorption effect of Fe (II) EDTA on NO realize the removal of two pollutants step by step; with simultaneous use of SO₂And the oxidation-reduction property of NO, and the biochar is used as a catalyst, so that the electron transfer is accelerated, and the high-efficiency conversion between Fe (III) EDTA/Fe (II) EDTA is realized, thereby ensuring the integration of the regeneration circulation of the absorbent and the desulfurization and denitrification.

Experimental test analysis:

the absorption liquid of the embodiment is fully contacted with the polluted gas in the two-stage cyclone plate tower to respectively complete SO₂And removal of NO, detection of SO₂The removal efficiency can reach 90-94%, and the removal efficiency of NO can reachCan reach 79-88%.

Example five: this embodiment is substantially the same as the previous embodiment, and is characterized in that:

in the embodiment, an absorption purification device is constructed, which comprises a first-stage absorption tower, an absorption liquid regeneration tower I, a second-stage absorption tower and an absorption liquid regeneration tower II; will contain SO₂Leading out the gas with NO by a draught fan, entering a first-stage absorption tower from the bottom of the tower, taking the regenerated absorption liquid as a solution mainly containing Fe (III) NTA, pressurizing the regenerated absorption liquid by a water pump, entering from the top of the tower, leading the gas phase and the liquid phase to flow in reverse direction, and finishing SO in the first-stage absorption tower₂Removing; the purified flue gas enters the bottom of a secondary absorption tower, the primary absorption liquid flows into an absorption liquid regeneration tower to be regenerated, a solution mainly containing Fe (II) NTA is obtained after regeneration, the regenerated secondary absorption liquid is pumped into the top of the secondary absorption tower through a pump, and the gas containing NO in the secondary absorption tower reversely contacts with the absorption liquid to complete the removal of NO; the absorption liquid absorbing NO enters an absorption liquid regeneration tower II for regeneration, and then is circularly pumped into a first-stage absorption tower through a pump for recycling.

In this example, 1 part of Fe was weighed₂(SO₄)₃And 2 parts of Na₃NTA·2H₂O configuration forming solutionAdjusting pH to 4.5 with dilute sulfuric acid, and removing SO from flue gas by wet method₂And the absorption liquid of the first-stage absorption tower in the NO process.

in the first-stage absorption tower, SO in the flue gas₂The flue gas is absorbed and removed after being contacted with the primary absorption liquid, the desulfurized flue gas continuously enters a secondary absorption tower, and the primary absorption liquid mainly comprises Fe (III) NTA; controlling the pH value of the primary absorption liquid to be 4.5 and controlling the liquid-gas ratio to be 6.0L/m³；

the first-stage absorption liquid in the first-stage absorption tower absorbs SO in the flue gas₂Then, forming a sulfur-containing solution, enabling the sulfur-containing solution to enter a regeneration tower of the absorption liquid, controlling the retention time of the sulfur-containing solution to be 1.0min, converting Fe (III) NTA in the sulfur-containing solution into Fe (III) NTA, thereby forming a secondary absorption liquid after regeneration, adjusting the pH value of the regenerated secondary absorption liquid to be 5.0, and pumping the regenerated secondary absorption liquid into the secondary absorption tower through a pump for carrying out a denitration process; in the said regeneration column (r) there is,forming a sulfate ion solution after a regeneration reaction, crystallizing at low temperature, and separating out sodium sulfate crystals so as to separate out absorption liquid as an industrial raw material, wherein a crystallization mother liquor is used as a secondary absorption liquid formed after regeneration and is conveyed into a secondary absorption tower for continuous use;

after the secondary absorption liquid in the secondary absorption tower finishes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, the nitrogen-containing solution enters a regeneration tower of the absorption liquid, the retention time of the sulfur-containing solution is controlled to be 5.0min, Fe (III) NTA in the nitrogen-containing solution is converted into Fe (III) NTA, so that a primary absorption liquid is formed after regeneration, the pH value of the regenerated primary absorption liquid is adjusted to be 4.5, the primary absorption liquid is pumped into the primary absorption tower through another pump, the liquid amount of the primary absorption liquid is supplemented, and a desulfurization process is carried out; thereby forming the integrated process of the cyclic regeneration and the continuous use of the absorption liquid and realizing the wet-type step-by-step desulfurization and denitrification. In this example, SO was absorbed stepwise by using a single complexing agent Fe (III) NTA₂And NO, SO as to avoid mutual interference₂And NO is oxidized and reduced by itself, and biochar is used as a catalyst, so that the regeneration cycle of Fe (III) NTA is realized, the consumption of desulfurization and denitrification chemicals is avoided, and the operation cost is greatly reduced. The embodiment efficiently absorbs and removes SO in the flue gas₂And NO, with the aim of minimizing the consumption of chemical agents, using Fe (III) NTA as absorbent and using Fe (III) NTA for SO₂The high-efficiency absorption and the specific absorption effect of Fe (II) NTA on NO realize the removal of two pollutants step by step; with simultaneous use of SO₂And the oxidation-reduction property of NO, and the biochar is used as a catalyst, so that the electron transfer is accelerated, and the high-efficiency conversion between Fe (III) NTA/Fe (II) NTA is realized, thereby ensuring the integration of the regeneration cycle of the absorbent and the desulfurization and denitrification.

Experimental test analysis:

the absorption liquid of the embodiment is fully contacted with the polluted gas in the two-stage cyclone plate tower to respectively complete SO₂And removal of NO, detection of SO₂The removal efficiency can reach 92-97%, and the removal efficiency of NO can reach 73-82%.

This example uses Fe (III) NTA as absorption liquid, and Fe (III) NTA for H⁺The buffer function of the utility model is high-efficiency suctionCollecting SO in the gas phase₂And with SO dissolved in the liquid phase after absorption₃ ^2-Reducing Fe (III) NTA into Fe (II) NTA under the action of a catalyst by using a reducing agent; then Fe (II) NTA obtained by reduction is used for specifically absorbing NO in a gas phase to form a complex Fe (II) NTA-NO; then, catalyzing Fe (II) NTA-NO to decompose to form Fe (III) NTA and N in a biochar catalyst₂The regeneration of the absorption liquid is realized; the invention realizes integrated desulfurization and denitrification, avoids the failure of the absorbent, ensures the regeneration and the cyclic utilization of Fe (II) NTA, and does not need to introduce other chemicals. The biochar required by catalyzing the recycling regeneration of Fe (III) NTA/Fe (II) NTA has the characteristics of wide raw material source, simple preparation, reusability, simple whole process, low investment and low operating cost.

Example six:

In this example, 1 part of Fe was weighed₂(SO₄)₃And 2 parts of Na₃NTA·2H₂Preparing O to form a solution, adjusting the pH to 5.5 by using dilute sulfuric acid, and removing SO in the flue gas step by step as a wet method₂And the absorption liquid of the first-stage absorption tower in the NO process.

in the first-stage absorption tower, SO in the flue gas₂The flue gas is absorbed and removed after being contacted with the primary absorption liquid, the desulfurized flue gas continuously enters a secondary absorption tower, and the primary absorption liquid mainly comprises Fe (III) NTA; controlling the pH value of the primary absorption liquid to be 5.5 and controlling the liquid-gas ratio to be 6.0L/m³；

the first-stage absorption liquid in the first-stage absorption tower absorbs SO in the flue gas₂Then, forming a sulfur-containing solution, enabling the sulfur-containing solution to enter a regeneration tower of the absorption liquid, controlling the retention time of the sulfur-containing solution to be 1.0min, converting Fe (III) NTA in the sulfur-containing solution into Fe (III) NTA, thereby forming a secondary absorption liquid after regeneration, adjusting the pH value of the regenerated secondary absorption liquid to be 6.0, and pumping the regenerated secondary absorption liquid into the secondary absorption tower through a pump for carrying out a denitration process; in the first regeneration tower, sulfate ion solution is formed after regeneration reaction, sodium sulfate crystal is separated out after low-temperature crystallization, so that absorption liquid is separated out,as an industrial raw material, the crystallization mother liquor is regenerated to form a secondary absorption liquid which is conveyed into a secondary absorption tower for continuous use;

after the secondary absorption liquid in the secondary absorption tower finishes the absorption of NO in the flue gas, a nitrogen-containing solution is formed, the nitrogen-containing solution enters a regeneration tower of the absorption liquid, the retention time of the sulfur-containing solution is controlled to be 5.0min, Fe (III) NTA in the nitrogen-containing solution is converted into Fe (III) NTA, so that a primary absorption liquid is formed after regeneration, the pH value of the regenerated primary absorption liquid is adjusted to be 5.5, the primary absorption liquid is pumped into the primary absorption tower through another pump, the liquid amount of the primary absorption liquid is supplemented, and a desulfurization process is carried out; thereby forming the integrated process of the cyclic regeneration and the continuous use of the absorption liquid and realizing the wet-type step-by-step desulfurization and denitrification. In this example, SO was absorbed stepwise by using a single complexing agent Fe (III) NTA₂And NO, SO as to avoid mutual interference₂And NO is self-redox, and biochar is used as a catalyst, so that Fe (III) -NTA regeneration cycle is realized, the consumption of desulfurization and denitrification chemicals is avoided, and the operation cost is greatly reduced. The embodiment efficiently absorbs and removes SO in the flue gas₂And NO, with the aim of minimizing the consumption of chemical agents, using Fe (III) NTA as absorbent and using Fe (III) NTA for SO₂The high-efficiency absorption and the specific absorption effect of Fe (II) NTA on NO realize the removal of two pollutants step by step; with simultaneous use of SO₂And the oxidation-reduction property of NO, and the biochar is used as a catalyst, so that the electron transfer is accelerated, and the high-efficiency conversion between Fe (III) NTA/Fe (II) NTA is realized, thereby ensuring the integration of the regeneration cycle of the absorbent and the desulfurization and denitrification.

Experimental test analysis:

the absorption liquid of the embodiment is fully contacted with the polluted gas in the two-stage cyclone plate tower to respectively complete SO₂And removal of NO, detection of SO₂The removal efficiency can reach 91-97%, and the removal efficiency of NO can reach 65-76%.

This example uses Fe (III) NTA as absorption liquid, and Fe (III) NTA for H⁺The buffer function of the absorption tower can efficiently absorb SO in the gas phase₂And with SO dissolved in the liquid phase after absorption₃ ^2-Is a reducing agent, under the action of a catalyst,reducing Fe (III) NTA to Fe (II) NTA; then Fe (II) NTA obtained by reduction is used for specifically absorbing NO in a gas phase to form a complex Fe (II) NTA-NO; then, catalyzing Fe (II) NTA-NO to decompose to form Fe (III) NTA and N in a biochar catalyst₂The regeneration of the absorption liquid is realized; the invention realizes integrated desulfurization and denitrification, avoids the failure of the absorbent, ensures the regeneration and the cyclic utilization of Fe (II) NTA, and does not need to introduce other chemicals. The biochar required by catalyzing the recycling regeneration of Fe (III) NTA/Fe (II) NTA has the characteristics of wide raw material source, simple preparation, reusability, simple whole process, low investment and low operating cost.

The method of the embodiment of the invention removes sulfur dioxide (SO) in the flue gas step by step in a wet manner₂) And Nitric Oxide (NO), continuously introducing the flue gas to be purified into the primary absorption tower and the secondary absorption tower; in the first-stage absorption tower, SO in the flue gas₂The NO in the flue gas is absorbed and removed after being contacted with the primary absorption liquid, in the secondary absorption tower, the NO in the flue gas is absorbed and removed after being contacted with the secondary absorption liquid, and the purified gas is discharged; the primary absorption liquid is ferric iron organic complex solution, and the pH value is controlled to be 4.0-6.0; absorbing SO with the first-stage absorption liquid₂Then, the mixture enters a regeneration tower, under the catalytic action of a charcoal catalyst, a ferric organic complex is converted into a ferrous organic complex, the pH value is adjusted to be 5.0-6.0, and the mixture enters a secondary absorption tower to be used as secondary absorption liquid; and (4) after the second-stage absorption liquid absorbs NO in a complexing way, the second-stage absorption liquid enters a regeneration tower II, a ferric iron organic complex is converted under the catalytic action of a charcoal catalyst, and the regenerated absorption liquid enters a first-stage absorption tower and is recycled in the system. The biochar catalyst is prepared from biomass in N₂And pyrolyzing for at least 2 hours at 300-800 ℃ in an atmosphere. Can realize SO in the flue gas₂And NO is removed in a step-by-step efficient and green manner, the used absorbent Fe (III) Cit can be recycled, and other desulfurization and denitrification chemical agents are not required to be added in the removing process.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the embodiments, and various changes can be made according to the objects of the inventionChanges, modifications, substitutions, combinations, or simplifications made without departing from the spirit or principles of the invention are intended to be equivalent substitutions for the purpose of the invention in wet fractional removal of SO from flue gas₂And NO, are within the scope of the invention.

Claims

1. Wet-type substep desorption SO in flue gas₂And NO, characterized in that: containing SO to be purified₂The flue gas with NO is sequentially and continuously introduced into a primary absorption tower and a secondary absorption tower;

2. The wet type step-by-step SO removal method for flue gas according to claim 1₂And NO, characterized in that:

the primary absorption liquid mainly contains at least one ferric iron organic complex selected from ferric citrate (Fe (III) Cit), Fe (III) EDTA and Fe (III) NTA;

in a regeneration tower, under the catalytic action of biochar, converting a ferric iron organic complex in a sulfur-containing solution into at least one ferrous iron organic complex in Fe (II) Cit, Fe (II) EDTA and Fe (II) NTA, controlling the retention time of the sulfur-containing solution to be 0.5-2 min, adjusting the pH value of the obtained secondary absorption liquid containing the ferrous iron organic complex to be 5.0-6.0, and conveying the secondary absorption liquid into a secondary absorption tower for denitration;

in the regeneration tower II, under the catalytic action of biochar, a ferrous iron organic complex in a nitrogen-containing solution is converted into at least one ferric iron organic complex in Fe (III) Cit, Fe (III) EDTA and Fe (III) NTA, the retention time of the nitrogen-containing solution is controlled to be 1.2-7.2 min, and then the nitrogen-containing solution is conveyed into a primary absorption tower for desulfurization, so that the absorption liquid is regenerated circularly and continuously used.

3. The wet type step-by-step SO removal method for flue gas according to claim 2₂And NO, characterized in that: the biochar is prepared by taking biomass as a raw material, crushing, sieving and then adding N₂Pyrolyzing for at least 2 hours at a temperature rise rate of not less than 10 ℃/min in a constant temperature pyrolysis method at 300-800 ℃ in an atmosphere to prepare an active biomass; and when the catalytic activity of the biochar is reduced, maintaining the catalytic activity of the biochar by supplementing new biochar.

4. The wet type step-by-step SO removal method for flue gas according to claim 1₂And NO, characterized in that: in the regeneration tower, a solution of sulfate ions is formed after regeneration reaction, sodium sulfate crystals are separated out after low-temperature crystallization, so that the absorption liquid is separated out and used as an industrial raw material, and crystallization mother liquor is used as a secondary absorption liquid formed after regeneration and conveyedEntering a secondary absorption tower for continuous use.

5. The wet type step-by-step SO removal method for flue gas according to claim 1₂And NO, characterized in that: in the first-stage absorption tower, the pH value of the first-stage absorption liquid is controlled to be 4.0-6.0, and the liquid-gas ratio is controlled to be 4.2-12.0L/m³。

6. The wet type fractional removal of SO from flue gas according to claim 5₂And NO, characterized in that: in the primary absorption tower, the pH value of primary absorption liquid is controlled to be 4.5-5.5.

7. The wet type step-by-step SO removal method for flue gas according to claim 1₂And NO, characterized in that: in the secondary absorption tower, the pH value of the secondary absorption liquid is controlled to be 5.0-6.0, and the liquid-gas ratio is controlled to be 2.0-6.0L/m³。