CN111514712B

CN111514712B - Novel method for denitration of flue gas by cooperation of anode and cathode electrocatalysis

Info

Publication number: CN111514712B
Application number: CN202010370894.9A
Authority: CN
Inventors: 江波; 徐灿程; 关雨欣; 牛庆赫; 刘树梁; 孟宪哲; 刘奕捷
Original assignee: Qingdao University of Technology
Current assignee: Qingdao University of Technology
Priority date: 2020-05-06
Filing date: 2020-05-06
Publication date: 2021-10-01
Anticipated expiration: 2040-05-06
Also published as: CN111514712A; WO2021223249A1

Abstract

The invention discloses a novel anode-cathode electrocatalysis synergistic flue gas denitration method, and belongs to the technical field of atmospheric treatment. The method of the invention utilizes the active matter produced by anodic oxidation to oxidize NO in the flue gas into high valence NOx which is easy to be dissolved in water, the NOx absorbed by water phase is converted into nitrite and nitrate, meanwhile, the dissolved nitrate nitrogen can be converted into nitrogen or ammonium radical on the cathode through catalytic reduction, and the produced ammonium radical can be finally oxidized into nitrogen by hypochlorous acid produced by anodic electrolysis. According to the system, the solution is lifted to the top of the reaction device by using the lifting pump, and spray is formed by the spraying device, so that the contact time and the contact area of NO and the solution are further increased, and the treatment efficiency is improved.

Description

Novel method for denitration of flue gas by cooperation of anode and cathode electrocatalysis

Technical Field

The invention belongs to the technical field of atmospheric treatment, and particularly relates to a novel method for denitration of flue gas by cooperation of anode and cathode electrocatalysis.

Background

The energy structure of China is mainly coal, smoke generated in the combustion process of the coal contains a large amount of NOx, 90-95% of the NOx is insoluble NO, and a series of environmental problems such as ozone layer cavities, photochemical smog, acid rain, haze and the like can be caused. Therefore, in recent years, flue gas desulfurization and denitration are strategic points in the field of energy and environment in China, and especially have important environmental and social significance for treating haze pollution which is currently concerned.

The control technology of NOx starts relatively late, and at present, there are two main types: one is to reduce the NOx emission concentration to some extent by using low NOx combustion techniques, such as air staged combustion techniques. However, as the environmental protection requirements become stricter, the environmental protection requirements cannot be met by singly adopting the technology; the other method is to remove NOx from the combusted flue gas, and the main methods comprise dry flue gas denitration and wet flue gas denitration. At present, the dry flue gas denitration for large-scale commercial application mainly comprises the following steps: selective Catalytic Reduction (SCR) and selective non-catalytic reduction (SNCR). SCR denitration principle: under the action of certain temperature and catalyst, with NH₃、CO、H₂Etc. as reducing agent, which can selectively react with NOx in the flue gas to reduce the NOx into pollution-free N₂And H₂And O. The method has the main advantages of high denitration efficiency, low reaction temperature and no secondary pollution to the environment caused by the product. On the other hand, the SCR method has the disadvantages of easy catalyst deactivation, narrow operating temperature range, ammonia slip, high investment cost, and the like. In SNCR, urea or ammonia compounds as reducing agents convert NOx to non-polluting N₂. The denitration process of the selective non-catalytic reduction method is finished in a boiler combustion chamber, and due to the high-temperature environment, a catalyst is not needed, a flue is not needed to be reformed, the investment is low, and the operation of a unit is not influenced. But the denitration efficiency is low, the operation temperature is high, and ammonia is easy to leak. The wet flue gas denitration technology mainly utilizes acid or alkali and other oxidants to remove NO_xThe nitrogen oxides are removed by oxidation and absorption. The common methods are as follows: nitric acid absorption, complex absorption, oxidation absorption, lye absorption, acid absorption, and the like. The wet flue gas denitration technology has the advantages of simple equipment and flow, easy operation, labor cost saving and the like, but the problems of absorption liquid regeneration and denitration efficiency reduction after regeneration of the method are difficult problems of the technology. Strong NOx oxidizers, represented by ozone, potassium permanganate, hydrogen peroxide, and hypochlorous acid, are limited in their application because of the large reagent consumption and the increased subsequent treatment of the waste stream.

Disclosure of Invention

According to the defects of the prior art, the invention aims to provide the method for denitration of the flue gas by cooperation of the electrocatalysis of the anode and the cathode, the method is operated at normal temperature and normal pressure, is easy to operate, can be applied to the treatment of NOx at normal temperature and low concentration, has high denitration efficiency, does not add chemical reagents in the process, does not have secondary pollution, and has low cost, low consumption and high safety performance.

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

the utility model provides a novel method of flue gas denitration is in coordination with positive and negative electrode electro-catalysis, set up the negative and positive electrode in the reactor, use NaCl solution as the electrolyte, treat the flue gas of denitration through micropore aeration device, from the entering solution of reactor bottom, strong oxidizing nature hydroxyl free radical and active chlorine that anodic oxidation produced oxidize the NOx in the flue gas into the NOx of the high valence state of easily dissolving in the water, NOx by aqueous phase absorption turns into nitrite and nitrate, dissolved nitrate nitrogen can be turned into nitrogen gas or ammonium through catalytic reduction on the negative pole simultaneously, the ammonium radical that produces can finally be oxidized into nitrogen gas by the hypochlorous acid that anode electrolysis generated, accomplish electrocatalysis denitration reaction with this.

On the basis of the scheme, the working current density in the electrocatalytic denitration reaction is 1-50mA/cm²(ii) a The input voltage waveform is direct current or pulse.

On the basis of the scheme, the anode is a ruthenium-iridium electrode, lead oxide or Sb-SnO₂One kind of (1).

On the basis of the scheme, the cathode is a nitrate-nitrogen reduction catalyst, and preferably, the cathode is one of noble metal or cheap metal and oxide thereof; more preferably, the cathode is one of Pd, P, copper, indium, cobalt or an oxide thereof.

On the basis of the scheme, the electrode distance between the anode and the cathode is 1-10 cm.

On the basis of the scheme, the concentration of the NaCl solution is 0.001-1.0M.

On the basis of the scheme, the microporous aeration device is one of a diaphragm type microporous aerator, a tubular aerator, a disc type aerator and a microporous ceramic aerator.

On the basis of the scheme, the top of the reactor is also provided with a spraying device, and part of electrolyte is lifted to the spraying device through a lifting pump to form spray and absorb and degrade part of overflowed NO.

The principle of the technical scheme of the invention is as follows: NO enters the solution from the inlet hose 9 at the bottom of the reactor through the micropore aeration of the micropore aeration disc 12. NaCl solution as electrolyte, Cl^-Will oxidize at the anode 10 to generate Cl radicals and ClO^-The NO in the flue gas is oxidized into high-valence NOx which is easily dissolved in a water body by utilizing anodic oxidation, the NOx absorbed by a water phase is converted into nitrite and nitrate, meanwhile, the dissolved nitrate nitrogen can be converted into nitrogen or ammonium radical on a cathode 7 through catalytic reduction, and the generated ammonium radical can be finally oxidized into nitrogen by hypochlorous acid generated by anodic electrolysis and overflows from a gas outlet 2 at the top of the device. The system utilizes the lift pump to lift the solution to the top of the reaction device, and spray is formed by the spray nozzle 3 of the spray device, so that the contact time and the contact area of NO and the solution are further increased, and the treatment efficiency is improved. The chemical (ionic) equation for the reaction is:

NO+HClO→NO₂+HCl 3NO₂+H₂O→2HNO₃+NO

NO₂+H₂O→HNO₃+HNO₂ HNO₂+HClO→HNO₃+HCl

NO₃ ^-+2e^-+2H⁺→NO₂ ^-+3H₂O NO₂ ^-+6e^-+8H⁺→NH₄ ⁺+2H₂O

2NO₂ ^-+10e^-+12H⁺→N₂+6H₂O 2NH₄ ⁺+3HOCl→N₂+3H₂O+3Cl^-+5H⁺

the invention has the advantages that:

(1) by using the synergistic treatment of anodic oxidation and cathodic reduction on NOx, NOx (mainly NO) is converted into nontoxic and harmless N₂Simple and convenient, and high pin removal efficiency.

(2) The technology operates at normal temperature and normal pressure, can be applied to the treatment of NOx at normal temperature and low concentration, and has the advantages of no addition of chemical reagents, no secondary pollution, low cost, low consumption and high safety performance in the process.

Drawings

FIG. 1 is a schematic view of a denitration reactor according to the present invention, wherein: 1-outlet hose, 2-gas outlet, 3-spray nozzle, 4-flange, 5-circulation hose, 6-cathode electric connection port, 7-cylinder cathode, 8-circulation water opening, 9-inlet hose, 10-anode, 11-anode electric connection port and 12-microporous aeration disc.

Detailed Description

Terms used in the present invention have generally meanings as commonly understood by one of ordinary skill in the art, unless otherwise specified.

The present invention will be described in further detail with reference to the following data, with reference to specific examples. The following examples are intended to illustrate the invention and are not intended to limit the scope of the invention in any way.

Example 1

By using Ti/IrO₂-RuO₂Is an anode, metal copper is a cathode, and the distance between the electrodes is 5 cm. 0.05M NaCl was used as electrolyte and the initial pH was adjusted to 7. The NO concentration was 500ppm and the solution was passed through a membrane microaeration chamber at a flow rate of 1L/min. The electrolyte is sprayed from a spraying device at the top by a lift pump, and part of the gas overflowing from the solution is brought back into the solution again. The treated gas overflows from the top of the reactor and is introduced into a gas cylinder, and the concentration of the treated gas is measured by using a flue gas analyzer to monitor the treatment degree of NOx in real time.

The working current density is 20mA/cm²At this time, the NO conversion was 90%.

Example 2

The lead oxide electrode is used as an anode, the metal Pd coating is used as a cathode, and the electrode distance is 5 cm. 0.07M NaCl was used as the electrolyte and the initial pH was adjusted to 7. The NO concentration was 500ppm and the solution was passed through a membrane microaeration chamber at a flow rate of 1.2L/min. The electrolyte is sprayed from a spraying device at the top by a lift pump, and part of the gas overflowing from the solution is brought back into the solution again. The treated gas overflows from the top of the reactor and is introduced into a gas cylinder, and the concentration of the treated gas is measured by using a flue gas analyzer to monitor the treatment degree of NOx in real time.

The working current density is 25mA/cm²At this time, the NO conversion was 92%.

Example 3

By using Sb-SnO₂The electrode is an anode, the metal cobalt is a cathode, and the distance between the electrodes is 6 cm. 0.08M NaCl was used as electrolyte and the initial pH was adjusted to 7. The NO concentration was 500ppm and the solution was passed through a membrane microaeration chamber at a flow rate of 1.3L/min. A spraying device is not adopted, the treated gas overflows from the top of the reactor and is introduced into a gas cylinder, a flue gas analyzer is used for measuring the concentration of the treated gas, and the treatment degree of NOx is monitored in real time.

The working current density is 30mA/cm²At this time, the NO conversion was 80%.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. A novel method for denitration of flue gas by cooperation of anode and cathode electro-catalysis is characterized in that anode and cathode electrodes are arranged in a reactor and Ti/IrO is adopted₂-RuO₂Is an anode, metal copper is a cathode, and the distance between the electrodes is 5 cm; 0.05M NaCl is adopted as electrolyte, and the initial pH value is adjusted to 7; enabling the flue gas to be denitrated to pass through a diaphragm type microporous aerator at the flow rate of 1L/min, enabling the flue gas to enter a solution from the bottom of the reactor, enabling an electrolyte to form spray from a spraying device at the top through a lifting pump, and bringing part of gas overflowing the solution back to the solution again; the strong oxidizing hydroxyl free radical and active chlorine generated by anodic oxidation oxidize NO in the flue gas into high-valence NOx which is easily dissolved in water, and the NOx absorbed by the water phase is converted into nitrite and nitrateMeanwhile, the dissolved nitrate nitrogen can be converted into nitrogen or ammonium radicals on the cathode through catalytic reduction, and the generated ammonium radicals can be finally oxidized into nitrogen by hypochlorous acid generated by anode electrolysis so as to finish the electrocatalytic denitration reaction;

the working current density in the electrocatalytic denitration reaction is 20mA/cm²(ii) a The input voltage waveform is direct current or pulse.

2. A novel method for denitration of flue gas by cooperation of anode and cathode electro-catalysis is characterized in that anode and cathode electrodes are arranged in a reactor, a lead oxide electrode is used as an anode, a metal Pd coating is used as a cathode, and the electrode distance is 5 cm; 0.07M NaCl is adopted as electrolyte, and the initial pH value is adjusted to 7; enabling the flue gas to be denitrated to pass through a diaphragm type microporous aerator at the flow rate of 1.2L/min, enabling the flue gas to enter a solution from the bottom of the reactor, enabling an electrolyte to form spray from a spraying device at the top through a lifting pump, and bringing part of gas overflowing from the solution back to the solution again; the strong oxidizing hydroxyl free radical and active chlorine generated by anodic oxidation oxidize NO in the flue gas into high-valence NOx which is easily dissolved in water, the NOx absorbed by a water phase is converted into nitrite and nitrate, meanwhile, the dissolved nitrate nitrogen can be converted into nitrogen or ammonium on a cathode through catalytic reduction, and the generated ammonium can be finally oxidized into nitrogen by hypochlorous acid generated by anodic electrolysis so as to finish electrocatalysis denitration reaction;

the working current density in the electrocatalytic denitration reaction is 25mA/cm²(ii) a The input voltage waveform is direct current or pulse.

3. A novel method for denitration of flue gas by cooperation of anode and cathode electrocatalysis is characterized in that anode and cathode are arranged in a reactor and Sb-SnO is adopted₂The electrode is an anode, the metal cobalt is a cathode, and the distance between the electrodes is 6 cm; 0.08M NaCl is adopted as electrolyte, and the initial pH value is adjusted to 7; enabling the flue gas to be denitrated to pass through a diaphragm type microporous aerator at the flow rate of 1.3L/min, enabling the flue gas to enter a solution from the bottom of the reactor, enabling an electrolyte to form spray from a spraying device at the top through a lifting pump, and bringing part of gas overflowing from the solution back to the solution again; strongly oxidizing hydroxyl radical and activity generated by anodic oxidationThe NO in the flue gas is oxidized into high-valence NOx which is easily dissolved in a water body by chlorine, the NOx absorbed by a water phase is converted into nitrite and nitrate, meanwhile, the dissolved nitrate nitrogen can be converted into nitrogen or ammonium on a cathode through catalytic reduction, and the generated ammonium can be finally oxidized into nitrogen by hypochlorous acid generated by anode electrolysis so as to finish the electrocatalytic denitration reaction;

the working current density in the electrocatalytic denitration reaction is 30mA/cm²(ii) a The input voltage waveform is direct current or pulse.