Photoelectric synergistic catalytic oxidation and wet absorption integrated mercury nitrate removal system and method

Abstract

The present invention discloses a photoelectric coordinated catalytic oxidation and wet absorption integrated mercury nitrate removal system and method, which can simultaneously remove elemental mercury and nitrogen oxides in coal-fired flue gas, and uses two devices to respectively perform photoelectric coordinated catalytic oxidation of elemental mercury and wet absorption removal of mercury and nitrogen elements. The present invention arranges an atomizing nozzle in the flue gas duct, sprays a hydrogen peroxide solution containing hexahydrated ferrous sulfate, and efficiently converts elemental mercury into divalent mercury soluble in water under the action of the electrode plate electric field and ultraviolet light, and then the flue gas enters the subsequent wet denitrification device, which can realize the simultaneous absorption and removal of mercury and nitrogen elements in the flue gas. This system can be modified on the existing wet denitrification process, with a simple process flow, low investment cost, high removal efficiency, and high economic value and practical production significance.

Description

Technical Field

[0001] The present invention relates to a method for efficiently removing mercury and nitrogen from coal-fired flue gas, and in particular to a photoelectric coordinated catalytic oxidation and wet absorption mercury nitrate integrated removal system and method. Background Art

[0002] Mercury is a heavy metal element. Both its simple substance and its compounds are highly biologically toxic and cause various direct or indirect harms to humans, plants and animals. The international environmental and health communities have paid increasing attention to the hazards of mercury. The sources of mercury pollution to the environment mainly include two aspects: natural release and human emissions. Among them, the proportion of mercury emissions from coal combustion accounts for about one-third. In the process of wet desulfurization, adjusting various operating parameters, using H2S and adding a small amount of ethylenediaminetetraacetic acid (EDTA) reagent can significantly increase the mercury capture efficiency of the desulfurization system. The selective catalytic reduction denitrification device (SCR) can not only convert NO x It is reduced to nitrogen N2 and also to elemental mercury Hg 0 It also has a certain oxidation effect. However, these flue gas purification devices have limited ability to remove mercury, especially elemental mercury Hg in coal-fired flue gas. 0 , which is extremely volatile, can usually pass through conventional flue gas purification devices without being captured. 0 The control of mercury is the key to controlling total mercury emissions. There are many control technologies for high-concentration mercury sources, but these technologies are difficult to work on low-concentration mercury in coal-fired power plants and are relatively expensive. At present, post-combustion flue gas mercury removal technologies mainly include dry removal (injection of adsorbents) and wet removal (addition of oxidants). Dry demercuration has limited efficiency, high cost, and will affect the internal flow field of the boiler. Therefore, wet demercuration is a better choice, and a strong oxidizing solution can be used to remove elemental mercury Hg 0 Oxidized to ionic mercury Hg 2+ The latter is retained in the oxidant solution. In order to avoid secondary pollution of mercury, the divalent mercury solution is properly treated. However, a set of wet mercury removal equipment is difficult to accept for new power plants and existing power plants in terms of construction site and investment.

[0003] At present, the construction cost of independent forced oxidation mercury removal equipment is very high. Therefore, it is necessary to propose a wet mercury removal method with high efficiency and economic requirements, and to be able to utilize the existing equipment of the power plant to simultaneously remove mercury and other pollutants to meet the increasingly stringent emission standards for pollutants in the flue gas of coal-fired power plants. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a photoelectric synergistic catalytic oxidation and wet absorption mercury nitrate integrated removal system and method, which is a method for efficiently removing mercury and nitrogen oxides from coal-fired flue gas. It uses forced oxidation + solution absorption, which is a relatively reliable and efficient method for removing gaseous Hg 0 and nitrogen oxides methods.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A photoelectric synergistic catalytic oxidation and wet absorption integrated mercury nitrate removal system, consisting of a flue gas pipeline 1, a solution nozzle 2, an electrode plate 3, an ultraviolet light source 4, positive and negative electrodes 5, an electrochemical enrichment cell 6, a check valve 7, a circulation pump 8, and a spray device 9;

[0007] The flue gas pipe 1 is the main body and attachment of the whole system, which is a section of inlet straight pipe connected to an intermediate vertical pipe section. The bottom of the intermediate vertical pipe section is sealed to leave a rectangular area as an electrochemical enrichment tank 6. The top of the intermediate vertical pipe section is connected to the outlet straight pipe section. The solution nozzle 2 is installed on the upper wall of the inlet straight pipe section of the flue gas pipe 1; the electrode plate 3 is installed on the upper and lower walls of the inlet straight pipe section of the flue gas pipe 1, and the electrode plate 3 is located behind the solution nozzle 2; the ultraviolet light source 4 is installed on the upper electrode of the electrode plate 3. The positive and negative electrodes 5 are mounted on the two side walls at the bottom of the middle vertical pipe section of the flue gas duct 1, and the positive and negative electrodes 5 are in the electrochemical enrichment tank 6; the outlet of the electrochemical enrichment tank 6 is connected to the inlet of the circulation pump 8 via the check valve 7, and the outlet of the circulation pump 8 is connected to the spray device 9, and the spray device 9 is located at the upper part of the middle vertical pipe section of the flue gas duct 1; the solution nozzle 2 sprays a hydrogen peroxide solution containing ferrous sulfate hexahydrate into the flue gas duct 1, and the electrochemical enrichment tank 6 contains an oxidant.

[0008] Solution nozzle 2 sprays the hydrogen peroxide solution containing ferrous sulfate hexahydrate evenly into the pipeline. 0 The flue gas containing NO and the liquid particles formed by atomization continue to move forward, flow through the electric field arranged by the electrode plate 3 behind the solution nozzle 2, and are irradiated by the ultraviolet light source 4. The elemental mercury is catalytically oxidized to divalent mercury by high efficiency; then the flue gas enters the middle vertical pipe section of the flue gas pipeline 1 for wet denitrification: in the electrochemical enrichment cell 6, Hg 2+ The enriched mercury is uniformly treated at the cathode and can be directly electrolyzed to generate elemental mercury for recovery; the cheap oxidant solution in the electrochemical enrichment cell 6 is transported to the spraying device 9 through the check valve 7 and the circulating pump 8, and is sprayed from top to bottom on the upper part of the middle vertical pipe section of the flue gas pipeline 1, and the Hg-containing mercury is further treated. 2+ and NO2 and the remaining small amount of Hg 0The flue gas containing NO and the oxidant liquid particles formed by atomization move in opposite directions, and after removal, they return to the electrochemical enrichment tank 6. After the photoelectric synergistic catalytic oxidation of elemental mercury and the wet absorption removal of mercury and nitrogen elements, mercury and nitrogen elements are processed at the same time and remain in the liquid phase, and finally the purified flue gas is obtained.

[0009] Under the combined effect of the electric field formed by the electrode plates 3 and the irradiation of the ultraviolet light source 4, the oxidant catalytically oxidizes elemental mercury, namely, photoelectric synergistic catalytic oxidation.

[0010] The intensity of the ultraviolet light source 4 is 300-3000 μW / cm according to the concentration of elemental mercury in the purified flue gas. 2 Choose between.

[0011] The electrochemical enrichment cell 6 contains an oxidant Ca(ClO)2 solution with a pH value of 4-6.

[0012] The pH value of the hydrogen peroxide solution containing ferrous sulfate hexahydrate is 3-4.

[0013] In order to ensure uniform dispersion of liquid particles in the flue gas duct and sufficient gas-liquid absorption reaction, the solution nozzle 2 should use a type with a large spray angle and small atomized particles.

[0014] The operation method of the integrated photoelectric catalytic oxidation mercury nitrate removal system is a combination of photoelectric catalytic oxidation of elemental mercury and wet absorption removal of mercury and nitrogen elements in a single system, which is specifically as follows:

[0015] Photocatalytic oxidation:

[0016] After desulfurization, Hg 0 The flue gas containing NO enters the flue gas duct 1. At this time, there are still unremoved elemental mercury and nitrogen oxides in the flue gas, which enter the inlet straight pipe section of the flue gas duct 1.

[0017] At the front end of the electrode plate 3, a solution nozzle 2 is arranged at the top center of the inlet straight pipe section of the flue gas duct 1, and a hydrogen peroxide solution containing hexahydrated ferrous sulfate is sprayed into the flue gas duct to contact the flue gas, so that the elemental mercury in the flue gas is oxidized to divalent mercury. After adding hexahydrated ferrous sulfate (II) ammonium (i.e., Fe(NH4)2·(SO4)2·6H2O) to hydrogen peroxide, a Fenton solution is formed, which has strong oxidizing properties, and the reaction equation is as follows:

[0018]

[0019] The ferrous ion catalyzes the decomposition of H2O2 mainly through Fe 2+ with Fe 3+ Among them, when the pH is about 3, the trivalent iron ion is mainly in the form of Fe(OH)2+ Exist in the form of complex ions;

[0020] After the solution nozzle 2, the electrode plates 3 arranged above and below the inlet straight pipe section of the flue gas duct 1 generate an electric field with an electric field strength of about 0.1 to 100 kV / cm. Tiny droplets are easily affected by the electrostatic field and charge separation occurs. By utilizing this effect, under the action of the electrostatic field, two ions of different charges will converge in different directions, and the ion concentration in the middle will decrease, promoting the reversible reaction. The chemical equilibrium moves toward the direction of dissociating more ·OH, generating more active oxidizing particles ·OH. That is, the electrostatic field can strengthen the dissociation of H2O2, thereby helping the H2O2 dissociation reaction to proceed faster and more thoroughly. Since the role of the electric field at this time is only to help the dissociation of H2O2 in the solution to generate ·OH, rather than ionizing O2 to generate ozone O3, the voltage and power consumption are low, and the energy consumption is lower than that of the ionization oxidation method. The intensity of the electric field can be adjusted during use by detecting the removal efficiency. If the removal rate of elemental mercury is low, increase the electric field strength. This can not only ensure the full utilization of the substance, but also reduce energy consumption;

[0021] A short-wave continuous ultraviolet light source 4 is installed at the inlet straight pipe section of the flue gas duct 1. The ultraviolet light can promote the decomposition of H2O2 to produce OH. The ultraviolet light and Fe 2+ There is a synergistic effect on the catalytic decomposition of H2O2, that is, the decomposition rate of H2O2 at this time is much greater than that of Fe 2+ The simple addition of the decomposition rates of H2O2 under catalysis or UV light excitation is due to the fact that the hydroxy complex of trivalent iron can undergo photosensitization reaction to generate OH. The reaction equation is:

[0022]

[0023] OH has strong oxidizing properties and can capture gaseous Hg on the surface of droplets 0 And an oxidation reaction occurs:

[0024] 2OH·+Hg→Hg 2+ +2OH -

[0025] In the above reaction, the insoluble zero-valent mercury Hg 0 Forced oxidation to water-soluble Hg 2+ , thereby achieving complete capture of mercury;

[0026] Hg content after desulfurization 0 and NO flue gas, and the injected H2O2 / Fe 2+ After the solutions are mixed, a forced oxidation reaction occurs under the combined action of ultraviolet light and electric field, which removes most of the Hg 0 and NO to Hg 2+and NO2, so far the photoelectric cooperative catalytic oxidation part is completed, and most of the mercury is removed;

[0027] Wet absorption:

[0028] After the flue gas flows out through the electrode plate 3, wet denitrification is carried out. A mature wet process can be used to ensure the removal of NOx. A cheap oxidant Ca(ClO)2 solution can be used in the electrochemical enrichment tank 6 at the bottom of the middle vertical pipe section of the flue gas duct 1. The mass concentration is controlled at 25-35%, which is more economical. In order to ensure the denitrification efficiency, the pH is controlled at 4-6, and the capture of mercury can also be achieved.

[0029] In the wet denitrification process, positive and negative electrodes 5 can be arranged on both sides of the lower part of the electrochemical enrichment cell 6 as an electrolysis device to achieve the reduction and recovery of mercury at the cathode through electrolysis of the absorption liquid: liquid Hg 2+ and NO3 - In the enrichment tank, Hg 2+ The mercury is concentrated at the cathode for unified treatment. It can be directly electrolyzed to generate elemental mercury for recycling, or it can be solidified by adding sulfur. It will not be discharged into the environment with coal ash or desulfurization gypsum, thus avoiding secondary pollution.

[0030] The solution in the electrochemical enrichment tank 6 is transported to the spray device 9 located at the upper part of the middle vertical pipe section of the flue gas pipeline 1 through the check valve 7 and the circulation pump 8, and the oxidant Ca(ClO)2 solution is sprayed into the middle vertical pipe section of the flue gas pipeline 1, so that the Hg-containing 2+ and NO2 and the remaining small amount of Hg 0 The flue gas containing NO and the Ca(ClO)2 liquid particles formed by atomization move in opposite directions, increasing the reaction area and reaction kinetics of wet absorption removal, thereby removing Hg that has not been completely oxidized in the flue gas. 0 / NO undergoes further oxidation absorption.

[0031] Compared with conventional independent forced oxidation mercury removal equipment, the photoelectric synergistic catalytic oxidation and wet absorption mercury nitrate integrated removal system of the present invention combines photoelectric synergistic catalytic oxidation of elemental mercury and wet absorption removal of mercury and nitrogen elements, and can use the existing equipment of the power plant to remove mercury and other pollutants at the same time, meet the increasingly stringent emission standards for pollutants in the flue gas of coal-fired power plants, and is expected to achieve significant energy saving and economic benefits, and can achieve the following

[0032] Beneficial effects:

[0033] (1) The present invention utilizes the three effects of "iron ion catalysis", "ultraviolet light excitation" and "enhancement of electrostatic field" to dissociate H2O2 to generate more active oxidative particles

[0034] OH contributes to the removal of elemental mercury.

[0035] (2) The present invention utilizes a mature wet denitrification process to simultaneously oxidize and absorb elemental mercury and NO in the flue gas, i.e., synergistically remove the two pollutants, mercury and nitrogen, and adopts an electrolysis process to achieve mercury recovery and reuse.

[0036] (3) The present invention can adjust the oxidant injection amount, light intensity, and electric field strength online according to the concentration of pollutants in the flue gas and the emission requirements, thereby regulating the operating energy consumption, and has a good advantage in energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the structure of the system of the present invention. DETAILED DESCRIPTION

[0038] like Figure 1 As shown, a photoelectric synergistic catalytic oxidation and wet absorption integrated mercury nitrate removal system is composed of a flue gas pipeline 1, a solution nozzle 2, an electrode plate 3, an ultraviolet light source 4, positive and negative electrodes 5, an electrochemical enrichment cell 6, a check valve 7, a circulation pump 8, and a spray device 9;

[0039] The flue gas pipe 1 is the main body and attachment of the whole system, which is a section of inlet straight pipe connected to an intermediate vertical pipe section. The bottom of the intermediate vertical pipe section is sealed to leave a rectangular area as an electrochemical enrichment tank. The top of the intermediate vertical pipe section is connected to the outlet straight pipe section. The shape is as follows: Figure 1 As shown; the solution nozzle 2 is installed at the upper wall of the inlet straight pipe section of the flue gas duct 1; the electrode plate 3 is installed on the upper and lower walls of the inlet straight pipe section of the flue gas duct 1, and the electrode plate 3 is located after the solution nozzle 2; the ultraviolet light source 4 is installed on the upper electrode plate of the electrode plate 3; the positive and negative electrodes 5 are installed on the two side walls at the bottom of the middle vertical pipe section of the flue gas duct 1, and the positive and negative electrodes 5 are in the electrochemical enrichment tank 6; the electrochemical enrichment tank 6 is located at the bottom of the middle vertical pipe section of the flue gas duct 1, and the outlet of the electrochemical enrichment tank 6 is connected to the inlet of the circulation pump 8 via the check valve 7, and the outlet of the circulation pump 8 is connected to the spray device 9, and the spray device 9 is located at the upper part of the middle vertical pipe section of the flue gas duct 1. The solution nozzle 2 sprays a hydrogen peroxide solution containing hexahydrated ferrous sulfate into the flue gas duct 1, and the electrochemical enrichment tank 6 contains an oxidant.

[0040] The present invention utilizes the three effects of "iron ion catalysis", "ultraviolet light excitation" and "enhancement of electrostatic field" to contribute to the removal of elemental mercury by dissociating H2O2 to generate more active oxidizing particles OH, and in addition to the mature wet denitrification process, it simultaneously oxidizes and absorbs elemental mercury and NO in the flue gas, that is, the synergistic removal of mercury and nitrogen pollutants, and adopts an electrolysis process to achieve mercury recycling. The method can adjust the oxidant injection amount, light intensity, and electric field intensity online according to the concentration of pollutants in the flue gas and emission requirements, thereby regulating the operating energy consumption, and has a good advantage in energy saving and emission reduction.

[0041] The operating method of the integrated photoelectric catalytic oxidation mercury nitrate removal system of the present invention adopts the combination of photoelectric catalytic oxidation of elemental mercury and wet absorption removal of mercury and nitrogen elements in a single system. The specific operating method is as follows:

[0042] Photocatalytic oxidation:

[0043] Desulfurization finished containing Hg 0 The flue gas containing NO and NH3 enters the flue gas duct 1. At this time, there is still elemental mercury and nitrogen oxides in the flue gas that have not been removed, and they enter the inlet straight pipe section of the flue gas duct 1.

[0044] At the front end of the electrode plate 3, a solution nozzle 2 is arranged at the top center of the inlet straight pipe section of the flue gas duct 1, and a hydrogen peroxide solution (pH value is about 3-4) containing hexahydrated ferrous sulfate is sprayed into the flue gas duct to contact with the flue gas, so that the elemental mercury in the flue gas is oxidized to divalent mercury. After adding hexahydrated ferrous sulfate (II) ammonium (i.e., Fe(NH4)2·(SO4)2·6H2O) to hydrogen peroxide, a Fenton solution is formed, which has strong oxidizing properties, and the reaction equation is as follows:

[0045]

[0046] The ferrous ion catalyzes the decomposition of H2O2 mainly through Fe 2+ with Fe 3+ Among them, when the pH is about 3, the trivalent iron ion is mainly in the form of Fe(OH) 2+ Exist in the form of complex ions;

[0047] To ensure uniform dispersion of liquid particles in the pipeline and sufficient gas-liquid absorption reaction, solution nozzle 2 should use a type with a larger spray angle and smaller atomized particles;

[0048] After the solution nozzle 2, the inlet straight pipe section of the flue gas duct 1 is provided with electrode plates 3 of suitable size above and below. The device generates a reasonable electric field with an electric field strength of about 0.1 to 100 kV / cm. Tiny droplets are easily affected by the electrostatic field and charge separation occurs. By utilizing this effect, under the action of the electrostatic field, two ions of different charges converge in different directions, and the ion concentration in the middle is reduced, promoting the reversible reaction. The chemical equilibrium moves toward the direction of dissociating more ·OH, generating more active oxidizing particles ·OH. That is, the electrostatic field can strengthen the dissociation of H2O2, thereby helping the H2O2 dissociation reaction to proceed faster and more thoroughly. Since the role of the electric field at this time is only to help the dissociation of H2O2 in the solution to generate ·OH, rather than ionizing O2 to generate ozone O3, high voltage and power consumption are not required, and the energy consumption is lower than that of the ionization oxidation method. The strength of the electric field can be adjusted during use by detecting the removal efficiency. If the removal rate of elemental mercury is low, the electric field strength is increased. This can not only ensure the full utilization of the substance, but also reduce energy consumption;

[0049] A short-wave continuous ultraviolet light source 4 is installed at a suitable position of the inlet straight pipe section of the flue gas pipe 1. Ultraviolet light can promote the decomposition of H2O2 to produce OH, so the ultraviolet light source should be installed at a suitable position of the pipe behind the solution nozzle 2 and on the upper plate of the electrode plate 3. Ultraviolet light and Fe 2+ There is a synergistic effect on the catalytic decomposition of H2O2, that is, the decomposition rate of H2O2 at this time is much greater than that of Fe 2+ The simple addition of the decomposition rates of H2O2 under catalysis or UV light excitation is due to the fact that the hydroxy complex of trivalent iron can undergo photosensitization reaction to generate OH. The reaction equation is:

[0050]

[0051] OH has strong oxidizing properties and can capture gaseous Hg on the surface of droplets 0 And an oxidation reaction occurs:

[0052] 2OH·+Hg→Hg 2+ +2OH -

[0053] In the above reaction, the insoluble zero-valent mercury Hg 0 Forced oxidation to water-soluble Hg 2+ Therefore, an ultraviolet light source 4 is provided to promote the oxidation reaction of elemental mercury, and the intensity of the ultraviolet light (300 to 3000 μW / cm 2 ) can be adjusted through the detection of removal efficiency to ensure the needs of energy conservation and emission reduction;

[0054] Hg content after desulfurization 0and NO flue gas, and the injected H2O2 / Fe 2+ After the solutions are mixed, a forced oxidation reaction occurs under the combined action of ultraviolet light and electric field, which removes most of the Hg 0 and NO to Hg 2+ and NO2. At this point, the photoelectric synergistic catalytic oxidation part is completed and most of the mercury is removed.

[0055] Wet absorption:

[0056] After the flue gas flows out through the electrode plate 3, wet denitrification is carried out. A mature wet process can be used to ensure the removal of NOx. A cheap oxidant Ca(ClO)2 solution can be used in the electrochemical enrichment tank 6 at the bottom of the middle vertical pipe section of the flue gas duct 1. The mass concentration is controlled at about 30%, which is more economical. In order to ensure the denitrification efficiency, the pH is controlled at about 5, and the capture of mercury can also be achieved.

[0057] In the wet denitrification process, positive and negative electrodes 5 can be arranged on both sides of the lower part of the electrochemical enrichment tank 6 as an electrolysis device, with the positive electrode on the left and the negative electrode on the right. Through the electrolysis of the absorption liquid, the reduction and recovery of mercury element is realized at the cathode: liquid Hg 2+ and NO3 - In the enrichment tank, Hg 2+ The enriched mercury is uniformly treated at the cathode. It can be directly electrolyzed to generate elemental mercury for recovery, or it can be solidified by adding sulfur. It will not be discharged into the environment with coal ash or desulfurization gypsum, thus avoiding secondary pollution.

[0058] The solution in the electrochemical enrichment tank 6 is transported to the spray device 9 located at the upper part of the middle vertical pipe section of the flue gas pipeline 1 through the check valve 7 and the circulation pump 8, and the oxidant Ca(ClO)2 solution is sprayed into the middle vertical pipe section of the flue gas pipeline 1, so that the Hg-containing 2+ and NO2 and the remaining small amount of Hg 0 The flue gas containing NO and the Ca(ClO)2 liquid particles formed by atomization move in opposite directions, increasing the reaction area and reaction kinetics of wet absorption removal, thereby removing Hg that has not been completely oxidized in the flue gas. 0 / NO undergoes further oxidation absorption.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A photoelectric synergistic catalytic oxidation and wet absorption integrated mercury nitrate removal system, characterized in that: It is composed of a flue gas pipeline (1), a solution nozzle (2), an electrode plate (3), an ultraviolet light source (4), positive and negative electrodes (5), an electrochemical enrichment cell (6), a check valve (7), a circulation pump (8), and a spray device (9); The flue gas pipe (1) is the main body and attachment of the entire system, and is a section of inlet straight pipe connected to an intermediate vertical pipe section. The bottom of the intermediate vertical pipe section is sealed to leave a rectangular area as an electrochemical enrichment tank (6). The top of the intermediate vertical pipe section is connected to the outlet straight pipe section. The solution nozzle (2) is installed on the upper wall surface of the inlet straight pipe section of the flue gas pipe (1); the electrode plate (3) is installed on the upper and lower walls of the inlet straight pipe section of the flue gas pipe (1), and the electrode plate (3) is installed behind the solution nozzle (2); the ultraviolet light source (4) is installed on the upper electrode plate of the electrode plate (3). The positive and negative electrodes (5) are installed on the two side walls at the bottom of the middle vertical pipe section of the flue gas duct (1), and the positive and negative electrodes (5) are located in the electrochemical enrichment tank (6); the outlet of the electrochemical enrichment tank (6) is connected to the inlet of the circulation pump (8) via a check valve (7), and the outlet of the circulation pump (8) is connected to the spray device (9), and the spray device (9) is located at the upper part of the middle vertical pipe section of the flue gas duct (1); the solution nozzle (2) sprays a hydrogen peroxide solution containing ferrous sulfate hexahydrate into the flue gas duct (1), and the electrochemical enrichment tank (6) contains an oxidant.

2. The photoelectric coordinated catalytic oxidation and wet absorption integrated mercury nitrate removal system according to claim 1, characterized in that: The solution nozzle (2) sprays the hydrogen peroxide solution containing ferrous sulfate hexahydrate evenly into the flue gas duct. 0 The flue gas containing NO and the liquid particles formed by atomization continue to move forward, flowing through the electric field arranged by the electrode plate (3) behind the solution nozzle (2), and being irradiated by the ultraviolet light source (4), the elemental mercury is catalytically oxidized to divalent mercury with high efficiency; the flue gas then enters the middle vertical pipe section of the flue gas duct (1) for wet denitrification: in the electrochemical enrichment tank (6), the Hg 2+ The enriched mercury is uniformly treated at the cathode and can be directly electrolyzed to generate elemental mercury for recovery; the cheap oxidant solution in the electrochemical enrichment cell (6) is transported to the spraying device (9) through the check valve (7) and the circulating pump (8), and is sprayed from top to bottom on the upper part of the middle vertical pipe section of the flue gas duct (1), so that the Hg-containing 2+ and NO2 and the remaining small amount of Hg 0 The flue gas containing NO and the atomized oxidant liquid particles move towards each other and return to the electrochemical enrichment cell (6) after removal.

3. The photoelectric synergistic catalytic oxidation integrated mercury nitrate removal system device according to claim 1, characterized in that: Under the combined action of the electric field arranged on the electrode plate (3) and the irradiation of the ultraviolet light source (4), the elemental mercury is catalytically oxidized by the oxidant, that is, photoelectric coordinated catalytic oxidation.

4. The photoelectric coordinated catalytic oxidation and wet absorption integrated mercury nitrate removal system according to claim 1, characterized in that: The electrochemical enrichment cell (6) contains an oxidant Ca(ClO)2 solution with a pH value of 4-6.

5. The photoelectric coordinated catalytic oxidation and wet absorption integrated mercury nitrate removal system according to claim 1, characterized in that: The pH value of the hydrogen peroxide solution containing ferrous sulfate hexahydrate is 3-4.

6. The photoelectric coordinated catalytic oxidation and wet absorption integrated mercury nitrate removal system according to claim 1, characterized in that: The solution nozzle (2) is of a type that has a large spray angle and small atomized particles.

7. The photoelectric coordinated catalytic oxidation and wet absorption integrated mercury nitrate removal system according to claim 1, characterized in that: The intensity of the ultraviolet light source (4) is 300 to 3000 μW / cm according to the concentration of elemental mercury in the purified flue gas. 2 Choose between.

8. The operation method of the photoelectric coordinated catalytic oxidation integrated mercury nitrate removal system according to any one of claims 1 to 7, characterized in that: The photoelectric synergistic catalytic oxidation of elemental mercury and the wet absorption removal of mercury and nitrogen are combined in a single system as follows: Photocatalytic oxidation: After desulfurization, Hg 0 The flue gas containing NO and Hg enters the flue gas duct (1). At this time, the flue gas still contains elemental mercury and nitrogen oxides that have not been removed, and enters the inlet straight pipe section of the flue gas duct (1); A solution nozzle (2) is arranged at the center of the top of the inlet straight pipe section of the flue gas duct (1) at the front end of the electrode plate (3), and a hydrogen peroxide solution containing hexahydrated ferrous sulfate is sprayed into the flue gas duct to contact the flue gas, so that the elemental mercury in the flue gas is oxidized to divalent mercury; after adding hexahydrated ferrous sulfate (II) ammonium, i.e., Fe(NH4)2·(SO4)2·6H2O, to the hydrogen peroxide, a Fenton solution is formed, which has strong oxidizing properties, and the reaction equation is as follows: In the formula, (·) represents free radicals, ·OH and HO· both represent hydroxyl radicals; The ferrous ion catalyzes the decomposition of H2O2 mainly through Fe 2+ with Fe 3+ The conversion between the two is carried out; among them, when the pH is 3-4, the trivalent iron ion is mainly in the form of Fe(OH) 2+ Exist in the form of complex ions; After the solution nozzle (2), the electrode plates (3) arranged above and below the inlet straight pipe section of the flue gas duct (1) generate an electric field with an electric field strength of 0.1 to 100 kV / cm; the tiny droplets are easily affected by the electrostatic field and charge separation occurs. By utilizing this effect, under the action of the electrostatic field, two ions of different charges converge in different directions, and the ion concentration in the middle is reduced, promoting the reversible reaction. The chemical equilibrium moves toward the direction of more dissociated ·OH, generating more active oxidized particles ·OH; that is, the electrostatic field can strengthen the dissociation of H2O2, thereby helping the H2O2 dissociation reaction to proceed faster and more thoroughly; since the role of the electric field at this time is only to help the dissociation of H2O2 in the solution to generate ·OH, rather than ionizing O2 to generate ozone O3, the voltage and power consumption are low, and the energy consumption is lower than that of the ionization oxidation method; the intensity of the electric field is adjusted by detecting the removal efficiency during use. If the removal rate of elemental mercury is low, the electric field intensity is increased, which can not only ensure the full utilization of the material, but also reduce energy consumption; A short-wave continuous ultraviolet light source (4) is installed at the inlet straight pipe section of the flue gas duct (1). The ultraviolet light can promote the decomposition of H2O2 to produce ·OH. The ultraviolet light and Fe 2+ There is a synergistic effect on the catalytic decomposition of H2O2, that is, the decomposition rate of H2O2 at this time is much greater than that of Fe 2+ The simple addition of the catalytic or UV-excited H2O2 decomposition rates is due to the photosensitization reaction of the hydroxy complex of trivalent iron to generate OH. The reaction equation is: OH has strong oxidizing properties and captures gaseous Hg on the surface of the droplets 0 And an oxidation reaction occurs: 2·OH+Hg→Hg 2+ +2OH - In the above reaction, the insoluble zero-valent mercury Hg 0 Forced oxidation to water-soluble Hg 2+ , thereby achieving complete capture of mercury; Hg content after desulfurization 0 and NO flue gas, and the injected H2O2 / Fe 2+ After the solutions are mixed, a forced oxidation reaction occurs under the combined action of ultraviolet light and electric field, which removes most of the Hg 0 and NO to Hg 2+ and NO2, so far the photoelectric cooperative catalytic oxidation part is completed, and most of the mercury is removed; Wet absorption: After the flue gas flows out through the electrode plate (3), wet denitrification is carried out. A wet process is adopted to ensure the removal of NOx. A cheap oxidant Ca(ClO)2 solution with a mass concentration controlled at 25-35% is used in the electrochemical enrichment tank (6) at the bottom of the middle vertical pipe section of the flue gas pipeline (1), and mercury is also captured at the same time. In the wet denitrification process, positive and negative electrodes (5) are arranged on both sides of the lower part of the electrochemical enrichment tank (6) as an electrolysis device to achieve the reduction and recovery of mercury at the cathode through electrolysis of the absorption liquid: liquid Hg 2+ and NO3 - In the enrichment tank, Hg 2+ The mercury is collected at the cathode for unified treatment, directly electrolyzed to generate elemental mercury for recycling, or solidified by adding sulfur, instead of being discharged into the environment with coal ash or desulfurization gypsum, thus avoiding secondary pollution. The solution in the electrochemical enrichment tank (6) is transported to the spray device (9) located at the upper part of the middle vertical pipe section of the flue gas pipeline (1) through the check valve (7) and the circulating pump (8), and the oxidant Ca(ClO)2 solution is sprayed into the middle vertical pipe section of the flue gas pipeline (1), so that the Hg-containing 2+ and NO2 and the remaining small amount of Hg 0 The flue gas containing NO and the Ca(ClO)2 liquid particles formed by atomization move in opposite directions, increasing the reaction area and reaction kinetics of wet absorption removal, thereby removing Hg that has not been completely oxidized in the flue gas. 0 / NO undergoes further oxidation absorption.

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