CN113477055A

CN113477055A - Method for inhibiting secondary release of mercury in seawater desulfurization process

Info

Publication number: CN113477055A
Application number: CN202110737834.0A
Authority: CN
Inventors: 王乐乐; 黄见勋; 苏胜; 王中辉; 雷嗣远; 向军; 陈逸峰; 尹子俊; 马云龙; 鲍强; 姚燕; 何川; 孔凡海; 杨晓宁; 卿梦磊
Original assignee: Xiamen Huaxia International Power Development Co ltd; Huazhong University of Science and Technology; Suzhou Xire Energy Saving Environmental Protection Technology Co Ltd
Current assignee: Xiamen Huaxia International Power Development Co ltd; Huazhong University of Science and Technology; Suzhou Xire Energy Saving Environmental Protection Technology Co Ltd
Priority date: 2021-06-30
Filing date: 2021-06-30
Publication date: 2021-10-08

Abstract

The invention relates to a method for inhibiting secondary mercury release in a seawater desulfurization process, which comprises a plurality of or all of the following steps: adding NH into raw coal entering a furnace₄Cl, and/or NH₄Br solid; spraying an oxidant into the SCR denitration device; spraying a solid adsorbent into the dust removal device; spraying an oxidant into the seawater wet desulphurization device, and adding a stabilizer and/or a curing agent into an aeration tank; and adjusting the pH value of the desulfurization wastewater in the aeration tank to be between 6 and 7. According to the invention, the proper oxidant is added to promote the oxidation of mercury in the flue gas, and the proper stabilizer/curing agent is added to inhibit the secondary release of mercury in the desulfurization wastewater, so that the demercuration efficiency of the system is improved, and Hg is effectively reduced⁰The secondary release amount of (4).

Description

Method for inhibiting secondary release of mercury in seawater desulfurization process

Technical Field

The invention relates to the field of flue gas purification and pollutant control, in particular to a method for inhibiting secondary mercury release in a seawater desulfurization process.

Background

Mercury in coal combustion flue gas exists mainly in 3 forms: elemental mercury (Hg)⁰) Ionic mercury (Hg)²⁺) And particulate mercury (Hg)^p). At present, the mercury removal method of the coal power plant mainly focuses on 2 aspects: sorbent injection technology and the use of existing pollutant control devices in conjunction with mercury removal technology. Although the adsorbent injection technology has higher demercuration efficiency, the cost is high, the subsequent treatment of the adsorbent is difficult, and the secondary pollution is easily caused by improper treatment. The utilization of the existing pollutant control equipment in cooperation with the mercury removal technology has relatively great advantages, and is the mercury removal technology mainly adopted by most of the coal-fired power plants at present. At present, most coal-fired power plants in China adopt limestone-gypsum wet flue gas desulfurization devices, and a small part of coastal power plants adopt seawater wet desulfurization devices. However, the high mercury removal efficiency is difficult to achieve only by using a wet flue gas desulfurization device, and the main reason for the low removal efficiency is that gaseous mercury in flue gas generated by coal burning is mainly elemental mercury Hg⁰And Hg²⁺In the form of Hg²⁺Is easy to dissolve in water, and 70-95% of Hg in flue gas can be used as absorbent in WFGD system no matter limestone or seawater is used as absorbent²⁺Removal of, but not water-insoluble Hg⁰The catching effect is not significant. In addition, due to changes in environmental conditions (temperature) and some residual reducing ions in the desulfurized slurry (Such as SO₃ ^2-、HSO₃ ^-、Fe²⁺And Mn²⁺Etc.) of the sulfur-containing gas, Hg absorbed in the desulfurization slurry²⁺Will be in Hg⁰Is released into the atmosphere again to form a secondary release of mercury, which can significantly reduce the demercuration efficiency of the WFGD system and cause serious pollution and harm to the environment.

Chinese patent with publication number CN106693980A discloses a flue gas mercury oxidation catalyst which can effectively oxidize Hg in flue gas⁰Oxidation to Hg²⁺And thus removed by the desulfurization unit, without taking into account Hg in the desulfurized slurry⁰The system demercuration efficiency is still low due to the secondary release problem.

At present, researches on inhibition of secondary mercury release of a seawater wet desulphurization device are relatively few, so that development of synergistic mercury removal and inhibition of secondary mercury release in desulphurization wastewater in the existing seawater wet flue gas desulphurization device has important practical value and theoretical significance.

Disclosure of Invention

The invention aims to provide a method for inhibiting secondary mercury release in a seawater desulfurization process.

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

a method for inhibiting secondary release of mercury in the process of seawater desulfurization,

the treatment of the flue gas generated by the combustion of raw coal in the boiler comprises the following steps: adopting an SCR denitration device for denitration, adopting a dust removal device for dust removal of the flue gas after denitration, adopting a seawater wet desulphurization device for desulphurization and then discharging the flue gas after dust removal, adopting an aeration tank for aeration of the desulphurization wastewater generated by the seawater wet desulphurization device and then discharging the flue gas,

the method includes many or all of the following:

1) adding NH into raw coal entering the furnace₄Cl, and/or NH₄Br solid;

2) spraying an oxidant into the SCR denitration device;

3) spraying solid adsorbent into the dust removal device to adsorb Hg in the flue gas⁰And Hg^P；

4) Injecting oxidant into a seawater wet desulphurization device to further remove Hg in the flue gas⁰Oxidation to Hg²⁺；

5) Adding a stabilizer and/or a curing agent into the aeration tank to further reduce Hg⁰The secondary release of (2);

6) adjusting the pH value of the desulfurization wastewater in the aeration tank to 6-7 to further inhibit Hg²⁺Reduction of Hg to reduce Hg⁰The second release.

Preferably, the method also comprises 7) symmetrically arranging a plurality of aeration fans at equal intervals (interval of 5 m) in the aeration tank, controlling the flow rate of the aeration fans in the aeration tank to be not more than 2L/min, controlling the aeration time to be 5-10 min, and adjusting the aeration flow rate and the aeration time to ensure that SO in the desulfurization wastewater is ensured₃ ^2-All converted to SO₄ ^2-To inhibit SO₃ ^2-With Hg²⁺Reaction of Hg²⁺Reduction to Hg⁰。

Preferably, in: NH (NH)₄Cl, and/or NH₄The addition amount of Br solid is 0.3-0.5% of the mass of raw coal fed into the furnace, and NH is added₄Cl、NH₄Br can be rapidly decomposed into NH at the temperature of 300-450 DEG C₃HCl and HBr, NH₃Can be used in SCR denitration process, and HCl and HBr can promote Hg in flue gas⁰Oxidation to Hg²⁺。

Preferably, in 2): the oxidant is KMnO₄、NaClO₂、O₃The total injection amount of the oxidant is 150-200 ug/m³Flue gas.

Preferably, in 2): the injection point of the oxidant is arranged at the inlet of the SCR denitration device, so that the injected oxidant can be fully contacted with the flue gas, and Hg in the flue gas is ensured⁰Fully oxidized into Hg²⁺。

Preferably, in 3): the solid adsorbent is selected from one or more of montmorillonite, diatomite and natural zeolite powder, and the total injection amount of the solid adsorbent is 150-300 mg/m³Flue gas.

Preferably, in 3): the injection point of the solid adsorbent is set at the inlet of the dust removing device.

Preferably, in 4): the oxidizing agent is selected from H₂O₂、KMnO₄、NaClO₂The total concentration of the oxidizing agent is 0.05-0.15mmol/L when H is₂O₂、KMnO₄、NaClO₂When one is selected, the total concentration is the concentration of a single addition amount; when H is present₂O₂、KMnO₄、NaClO₂When a plurality of oxidants are selected, the total concentration is the sum of the concentrations of all the oxidants in single addition amount.

Further preferably, when the oxidant is selected from H₂O₂And KMnO₄The adding proportion of the two is 1: 0.8-1: 1.2; when the oxidant is KMnO₄With NaClO₂The adding proportion of the two is 1: 0.85-1: 1.15; when the oxidant is selected from H₂O₂With NaClO₂The adding proportion of the two is 1: 0.8-1: 1.2; when the oxidant is selected from H₂O₂、KMnO₄And NaClO₂The adding proportion of the three is 1: 0.8: 0.8.

preferably, in 5): the stabilizer is selected from BMIMCl, NaCl, FeCl₂、FeSO₄、CuSO₄The total amount of the stabilizer is 0.05-0.1 mmol/L, if two or more stabilizers are added and mixed in equal proportion, the total amount of the stabilizer is kept unchanged, and the stabilizer is added into an aeration tank after being uniformly mixed.

Preferably, in 5): the curing agent is Na₂And if two or more curing agents are added and mixed in equal proportion, the total addition amount is kept unchanged, and the curing agents are uniformly mixed and added into an aeration tank.

Preferably, in 6): introducing the seawater at the inlet of the 1/4-1/3 seawater wet desulphurization device into an aeration tank to adjust the pH value of the desulphurization wastewater, so that the Cl content in the desulphurization wastewater is increased^-Content of effective in inhibiting Hg²⁺Reduction to Hg⁰Thereby reducing Hg⁰The second release.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

according to the invention, the oxidation of mercury in flue gas is promoted by adding a proper oxidant, and the secondary release of mercury in the desulfurization wastewater is inhibited by adding a proper stabilizer/curing agent:

(1) adding NH into raw coal entering the furnace₄Cl、NH₄Br solid, decomposing it into NH by high temp. of furnace₃HCl and HBr, the ammonia spraying amount of the SCR denitration device is reduced, and meanwhile, Hg in the flue gas can be sprayed by the decomposed HCl and HBr⁰Oxidation to Hg²⁺The mercury removal efficiency of the system is improved;

(2) further reducing Hg in flue gas by adding an oxidant to the SCR device⁰Oxidation to Hg²⁺The mercury is absorbed by a seawater wet desulphurization device, so that the mercury removal efficiency of the system is improved;

(3) effectively removing Hg in the flue gas by spraying the solid adsorbent to the dust removal device^PWhile being capable of adsorbing part of Hg⁰And solve Hg⁰The problem of difficult dissolution in the subsequent seawater wet desulphurization device is effectively reduced⁰The secondary release amount of (a);

(4) effectively fixing Hg in the desulfurization wastewater by adding a proper stabilizer/curing agent into an aeration tank²⁺Inhibition of Hg²⁺Reduction to Hg⁰Thereby effectively reducing Hg⁰The secondary release improves the mercury removal efficiency of the system.

Drawings

FIG. 1 is a schematic diagram of the process of this example;

FIG. 2 is a schematic diagram of a system for implementing the method of the present embodiment.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

A method for inhibiting secondary release of mercury during seawater desulfurization, wherein: the method is based on a flue gas treatment device as shown in figure 2: the method comprises the following steps:

the system comprises a raw coal bin 1, a boiler 2 communicated with the raw coal bin 1, an SCR denitration device 3 communicated with the boiler 2, a flue gas cooling device 4 communicated with the SCR denitration device 3, an electrostatic dust removal device 5 communicated with the flue gas cooling device 4, a seawater wet desulphurization device 6 communicated with the electrostatic dust removal device 5, a heat exchanger 7 communicated with the seawater wet desulphurization device 6 and an aeration tank 8.

The treatment of the flue gas generated by the combustion of the raw coal in the boiler 2 by adopting the device comprises the following steps: denitration, cooling the flue gas after denitration, performing electrostatic dust removal on the cooled flue gas, performing desulfurization heat exchange on the flue gas after dust removal, and discharging the desulfurization wastewater generated by seawater wet desulfurization after aeration.

As shown in fig. 1: the method comprises the following steps:

1) adding a certain proportion of NH into raw coal entering the furnace₄Cl、NH₄Br solid;

wherein NH₄Cl/NH₄The addition amount of Br solid is 0.3-0.5% of the mass of raw coal fed into the furnace, and NH is added₄Cl、NH₄Br can be rapidly decomposed into NH at the temperature of 300-450 DEG C₃HCl and HBr, NH₃Can be used in SCR denitration process, and HCl and HBr can promote Hg in flue gas⁰Oxidation to Hg²⁺。

2) Injecting a certain amount of oxidant into the SCR denitration device to remove Hg in the flue gas⁰Oxidation to Hg²⁺；

Wherein, oxidant injection site arranges in SCR denitrification facility entrance, and the oxidant of injection fully contacts with the flue gas, guarantees with the Hg in the flue gas⁰Fully oxidized into Hg²⁺The oxidant is KMnO₄、NaClO₂、O₃One or more mixtures of (a); the preferred oxidant is O₃The spraying concentration is 150-200 ug/m³Flue gas.

3) Injecting a certain amount of solid adsorbent to the inlet of the electrostatic dust collection device to adsorb Hg in the flue gas⁰And Hg^P(ii) a The solid adsorbent is one or more of montmorillonite, diatomite and natural zeolite; the preferable adsorbent is montmorillonite, and the injection amount is 150-300 mg/m³Flue gas.

4) Spraying a certain amount of oxidant into a seawater wet desulphurization device to further remove Hg in flue gas⁰Oxidation to Hg² ⁺；

Wherein the oxidant is injected as H₂O₂、KMnO₄、NaClO₂One or more of (a); the preferred oxidant is H₂O₂And NaClO₂The total concentration of the additive is 0.1mmol/L, and the addition ratio is 1: 0.8-1: 1.2.

5) adjusting the aeration flow and the aeration time to remove SO in the desulfurization wastewater₃ ^2-Oxidation to SO₄ ^2-To inhibit Hg²⁺Reduction of (2); simultaneously introducing part of seawater at the inlet of the desulfurizing tower to improve the pH value and Cl of the desulfurization wastewater in the aeration tank^-The content further inhibits Hg²⁺Reduction of Hg to reduce Hg⁰The secondary release of (2);

wherein the optimal aeration flow is 1-2L/min, the aeration time is 5-10 min, and SO in the desulfurization wastewater is ensured₃ ^2-All converted to SO₄ ^2-To inhibit SO₃ ^2-With Hg²⁺Reaction of Hg²⁺Reduction to Hg⁰(ii) a Meanwhile, the seawater at the inlet of the 1/4-1/3 desulfurizing tower is introduced to increase the pH value of the desulfurization wastewater in the aeration tank to 6-7, and improve the Cl content in the desulfurization wastewater^-Content of effective in inhibiting Hg²⁺Reduction to Hg⁰Thereby reducing Hg⁰The second release.

6) Adding a certain mass of stabilizer/curing agent into the aeration tank to further reduce Hg⁰The secondary release of (2);

wherein the stabilizer is BMIMCl, NaCl, FeCl₂、FeSO₄、CuSO₄One or more mixtures of (a); the curing agent is Na₂One or more of S, NaHS, CaS, FeS and CuS. The preferred stabilizer is a mixture of BMIMCl and NaCl, with a total concentration of additives of 0.1mmol/L, and a ratio of 1: 1; the preferred curing agent is Na₂The mixture of S and NaHS has the total additive concentration of 0.2mmol/L and the addition ratio of 1: 1.

in connection with the system as shown in fig. 2: by NH₄Cl/NH₄Adding a certain proportion of NH4Cl/NH into the raw coal bin 1 by the Br injection system 9₄Br solid, mercury in raw coal will release large amount of Hg during combustion⁰、Hg²⁺And Hg^P(ii) a And NH added₄Cl/NH₄The decomposition temperature of Br is 300-450 ℃, and the Br can be rapidly decomposed into NH at the high temperature of the boiler 2₃HCl and HBr, NH formed₃Can be used in the subsequent SCR denitration process, and the HCl and HBr can promote Hg in the flue gas⁰Oxidation to Hg²⁺。

The flue gas at the tail part of the boiler 2 still contains a large amount of Hg before entering the SCR device⁰In order to reduce Hg⁰The oxidant injection device 10 is arranged at the inlet of the SCR denitration device 3, and Hg in the flue gas is injected by injecting a proper amount of oxidant⁰Further oxidized to Hg²⁺So as to be absorbed by the subsequent electrostatic dust collection device 5 and the seawater wet desulphurization device 6.

The flue gas contains gaseous mercury (Hg) in the flue gas⁰) In addition, the mercury-containing coating also contains granular mercury (Hg)^P) In order to remove Hg^PThe solid adsorbent injection device 11 is generally arranged at the inlet of the electrostatic dust collection device 5, and Hg in the flue gas can be effectively adsorbed by injecting some active porous substances^PAnd can adsorb partial Hg⁰And is removed by the electrostatic dust collector 5 together with the fly ash in the flue gas.

When the flue gas flows through the seawater wet desulphurization device 6, most Hg in the flue gas²⁺Is absorbed by seawater and transferred into the desulfurization wastewater, but Hg⁰Is difficult to dissolve in water and can not be absorbed by seawater, so that a certain amount of oxidant is sprayed into the flue gas by the oxidant spraying device 12 in the seawater wet desulphurization device 6 to further remove Hg in the flue gas⁰Oxidation to Hg²⁺So as to be absorbed by seawater and improve the mercury removal efficiency of the system.

The desulfurized wastewater after the completion of desulfurization flows into the aeration tank 8, Hg in which²⁺Instability, environmental conditions (temperature) and residual reducing ions (such as SO) in the desulfurization waste water₃ ^2-、HSO₃ ^-、Fe²⁺And Mn²⁺Etc.) of absorbed Hg²⁺Will be in Hg⁰Is released again into the atmosphere, forming a secondary release of mercury, thereby significantly reducing the mercury removal efficiency of the system. To suppress Hg⁰The appropriate amount of stabilizer/curing agent is added into the aeration tank 8 to react with the absorbed Hg²⁺The reaction generates more stable compound/complex compound, which is fixed in the desulfurization wastewater; or with absorbed Hg²⁺The precipitate generated by the reaction is removed from the aeration tank, thereby effectively inhibiting Hg²⁺Reduction of Hg to reduce Hg⁰The second release.

Example (b):

the details are explained by taking a certain 300MW unit of a power plant as an example, and the unit is arranged with the system shown in figure 2. Hg in SCR inlet flue gas at 300MW load^TThe concentration is 55ug/m³，Hg²⁺The concentration is 33.8ug/m³，Hg⁰The concentration is 12.2ug/m³，Hg^PThe concentration is 9ug/m³；SO₂The concentration is 900 ppm, the NOx concentration is 400 ppm.

Table 1: the addition conditions are as follows:

table 2: the mercury removal effect is as follows:

the above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for inhibiting secondary release of mercury in the process of seawater desulfurization,

the method is characterized in that: the method includes many or all of the following:

1) adding NH into raw coal entering the furnace₄Cl, and/or NH₄Br solid;

2) spraying an oxidant into the SCR denitration device;

3) spraying a solid adsorbent into the dust removal device;

4) spraying an oxidant into a seawater wet desulphurization device;

5) adding a stabilizer and/or a curing agent into the aeration tank;

6) and adjusting the pH value of the desulfurization wastewater in the aeration tank to be 6-7.

2. The method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: the method also comprises 7) controlling the flow rate of an aeration fan in the aeration tank to be not more than 2L/min, wherein the aeration time is 5-10 min.

3. The method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: in 1): NH (NH)₄Cl, and/or NH₄The addition amount of Br solid is 0.3-0.5% of the mass of raw coal fed into the furnace.

4. The method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: in 2): the oxidant is KMnO₄、NaClO₂、O₃The total injection amount of the oxidant is 150-200 ug/m³Flue gas.

5. The method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: in 3): the solid adsorbent is selected from one or more of montmorillonite, diatomite and natural zeolite powder, and the total injection amount of the solid adsorbent is 150-300 mg/m³Flue gas.

6. The method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: in 4): the oxidizing agent is selected from H₂O₂、KMnO₄、NaClO₂The total concentration of the oxidizing agent is 0.05-0.15 mmol/L.

7. The method of claim 6The method for inhibiting the secondary release of mercury in the seawater desulfurization process is characterized by comprising the following steps: when the oxidant is selected from H₂O₂And KMnO₄The adding proportion of the two is 1: 0.8-1: 1.2; when the oxidant is KMnO₄With NaClO₂The adding proportion of the two is 1: 0.85-1: 1.15; when the oxidant is selected from H₂O₂With NaClO₂The adding proportion of the two is 1: 0.8-1: 1.2; when the oxidant is selected from H₂O₂、KMnO₄And NaClO₂The adding proportion of the three is 1: 0.8: 0.8.

8. the method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: in 5): the stabilizer is selected from BMIMCl, NaCl, FeCl₂、FeSO₄、CuSO₄One or more of the stabilizer, wherein the total adding amount of the stabilizer is 0.05-0.1 mmol/L.

9. The method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: in 5): the curing agent is Na₂One or more of S, NaHS, CaS, FeS and CuS, and the total amount of the curing agent is 0.1-0.2 mmol/L.

10. The method for inhibiting secondary release of mercury during seawater desulfurization as recited in claim 1, wherein: in 6): introducing the seawater at the inlet of the 1/4-1/3 seawater wet desulphurization device into an aeration tank to adjust the pH value of the desulphurization wastewater.