CN104190226B - Complexing absorption and aerobic denitrification combined smoke denitration process - Google Patents

Abstract

The invention discloses a flue gas denitrification process combined with complexation absorption and aerobic denitrification. The NO in the flue gas is absorbed by an alkaline absorption liquid added with an oxygen-resistant cobalt complexing agent Co ^II (L) in an absorption tower. In this process, the residual O ₂ in the flue gas is used as an oxidant, and the cobalt complex is used as a catalyst to realize the catalytic oxidation of NO to NO ₂ ^- , and the NO ₃ ^- is dissolved in the liquid phase and regenerated into a cobalt complex for recycling. After the flue gas is purified to meet the standard, the tail liquid is absorbed into the aerobic bioreactor, and under neutral conditions, the aerobic denitrifying bacteria degrade NO ₂ ^‑ and NO ₃ ^‑ into gaseous reduction products to completely eliminate nitrogen pollution. This process uses cobalt complexes as liquid-phase catalysts to realize NO complex absorption and catalytic oxidation simultaneously, and completely eliminate nitrogen pollution through the action of microorganisms. The method is reasonable in process, low in energy consumption, less in investment and operating costs, and less in secondary pollution, and is an ideal flue gas denitrification process.

Description

A complexation absorption combined with aerobic denitrification flue gas denitrification process

technical field

The invention belongs to the technical field of flue gas purification, and relates to a flue gas denitrification process combined with complexation absorption and aerobic denitrification.

Background technique

NO _x includes N ₂ O, NO, NO ₂ , N ₂ O ₃ , N ₂ O ₄ , N ₂ O ₅ , which mainly come from natural sources such as volcanic eruptions, lightning, bacterial activities, industry, transportation, and fossil fuel combustion, etc. Man-made sources of human activities, NO _x can form photochemical smog with hydrocarbons, produce acid rain, acid fog, damage vegetation, endanger human health, and NO _x can also destroy the ozone layer. In view of this, it is very important to take certain measures to reduce or eliminate _NOx emissions.

The flue gas denitration technologies that are widely used in industry are selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), but the catalyst is easily deactivated, the equipment investment is large, the operating cost is high, and secondary pollution is generated. The problem makes it more difficult to apply in flue gas denitrification. Therefore, it is particularly urgent to develop an economical and environmentally friendly flue gas denitrification technology. As a new flue gas denitrification method, microbial flue gas denitrification technology has gradually attracted people's attention due to its advantages of simple equipment, low investment and operation costs, and less environmental pollution.

NO accounts for about 95% of the NO _x emitted with coal-fired flue gas, and NO is insoluble in water and cannot enter the liquid medium for transformation and utilization by microorganisms. Moreover, the adsorption capacity of the surface of microorganisms is very poor, which makes the actual removal of NO The efficiency is very low, so there is a big limitation in completely using microbial technology to remove NO _x . Developed in the 1980s, complexation absorption combined with biological transformation to remove NO _x technology (i.e. BioDeNO _x process), organically combined chemical absorption (Fe ^II (EDTA), etc.) complexation absorption and biological denitrification technology, not only The gas-liquid mass transfer is enhanced, the solubility of NO in the liquid phase is increased, and the complexing absorbent can be regenerated under the action of microorganisms to realize the recycling of the complexing agent. Although the BioDeNO _x technology has solved the gas-liquid mass transfer problem of NO well, the actual coal-fired flue gas contains 3%-8% O ₂ , and it is easy to oxidize the Fe ^II complexing agent widely used in this process to Fe ^III thus loses the complexing ability, and the presence of _O2 will affect the denitrification performance of traditional anaerobic/facultative denitrifiers. The solution to the problem of oxygen interference can be considered from the two processes of complexation absorption and microbial reduction in this process.

First of all, researchers have done a lot of research on the screening of oxygen-tolerant and denitrification complexing agents. Long, Xin et al. (Environmental Science, 2005,26(1):20-23. East China Electric Power, 2010,38(3):408-413. Chemical Engineering, 2011,39(6):8-11.) It was found that the cobalt complexing agent can complex and remove NO in the presence of oxygen, and the removal mechanism includes the following process: after the exhaust gas containing NO and _O2 passes through the cobalt complexing agent, NO and _O2 are complexed and absorbed by the cobalt complexing agent, Formation of complexed NO and complexed O ₂ . The complexed O ₂ complexed by dinuclear dioxygen bridge complexes with strong oxidative properties will oxidize the complexed NO to NO ₂ . NO ₂ dissolves in water to generate NO ₃ ^- and NO ₂ ^- . In addition, Chinese patents with application numbers 200910216259.9, 01105698.3, 01105004.7, _02110646.0 ^, and _{201210167859.2} all mention the use ^of cobalt complexing agents for denitrification of exhaust gas. There is a risk of secondary pollution in the discharge.

On the other hand, in the 1980s, Robertson (Archives of Microbiology, 1984, 139 (4): 351-354.Applied and Environmental Microbiology, 1988, 54 (11): 2812-2818.) and others studied the combination of microorganisms Thiosphaerapantotropha (Pantotrophic thiococcus, now renamed Paracoccus denitrificans) found that it can simultaneously use nitrate and _O2 as the final electron acceptor for cooperative respiration, and this phenomenon is defined as aerobic denitrification.

Oxygen will be dissolved in the absorption liquid during the absorption process of complex denitrification, the characteristic of aerobic denitrification bacteria that can denitrify in the presence of oxygen can avoid the NO ₃ ^- and NO ₂ ^- produced by dissolved oxygen on denitrification. Therefore, aerobic denitrifying bacteria show its advantages in complexation absorption combined with denitrification flue gas denitrification process.

Contents of the invention

The purpose of the present invention is to propose a method for complexation absorption combined with biotransformation to remove nitrogen oxides in flue gas, which is different from the traditional _BioDeNOx process, which can utilize the combined action of complexing agents and microorganisms under aerobic conditions Convert _NOx into nitrogen and completely eliminate nitrogen pollution.

Technical scheme of the present invention is as follows:

Put the alkaline absorption liquid containing cobalt complexing agent Co ^II (L) in the absorption tower to complex absorb NO and _O2 in the flue gas, transfer NO and _O2 from the gas phase to the liquid phase, and the cobalt complex The complexing agent and O ₂ are complexed to form a binuclear dioxygen bridge complex (complexed O ₂ ), the cobalt complexing agent is complexed with NO to form a complex NO; the cobalt complexing agent is complexed with O ₂ to form a dinuclear dioxygen The formula complex oxidizes the complexed NO to complexed NO ₂ , and the complexed NO ₂ forms NO ₂ ^- and NO ₃ ^- in the above-mentioned alkaline absorption liquid, and at the same time regenerates the cobalt complexing agent to purify the standard flue gas emission;

The alkaline absorption solution containing NO ₂ ^- and NO ₃ ^- formed above is placed in an aerobic bioreactor. Under neutral conditions, aerobic denitrifying bacteria degrade NO ₂ ^- and NO ₃ ^- into N ₂ , Thereby completely eliminating nitrogen pollution.

The remaining treatment liquid from the aerobic denitrifying bacteria treatment enters the sedimentation tank. After the sedimentation, the activated sludge is refluxed or discharged, and the separated liquid containing Co ^II (L) is directly returned to the flue gas absorption tower as a denitrification absorption liquid for recycling.

The cobalt complexing agent Co ^II (L) is prepared from an inorganic cobaltous salt and a ligand. Inorganic cobaltous salts are mainly one or more mixtures of cobaltous chloride, cobaltous sulfate and cobaltous nitrate; the ligands are ethylenediaminetetraacetic acid (EDTA), citric acid (Cit), nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethyltriaminepentaacetic acid (DTPA) or a mixture of two or more.

The pH value in the aerobic bioreactor is controlled at 6.0-9.0, the temperature is controlled at 25-35°C, the residence time is controlled at 6-36h, and COD _cr :N:P=(100-200):5:1.

The absorption tower is a kind of packed tower, spray tower, bubble tower or sieve plate tower. The aerobic bioreactor adopts the treatment method of aerobic suspension growth system (activated sludge method, oxidation pond method, etc.) or aerobic attachment growth Systematic treatment methods (biological filter, biological turntable, biological contact oxidation, etc.).

The carbon source added in the process of aerobic microbial degradation treatment is sodium lactate, sodium acetate, sodium propionate, sodium succinate, sodium citrate or solid organic matter rich in cellulose such as cotton and wheat straw, and the phosphorus source is phosphoric acid, phosphoric acid diphosphate hydrogen salt or hydrogen phosphate di-salt.

Effect and benefit of the present invention are:

This method has made some changes on the basis of the traditional BioDeNO _x process, changing the widely used ferrous complexing agent into a cobalt complexing agent, and at the same time converting the anaerobic/facultative denitrifying bacteria The aerobic biological denitrification process is changed to an aerobic denitrification denitrification process dominated by aerobic denitrifying bacteria. The method can not only tolerate the residual oxygen in the flue gas, but also completely eliminate nitrogen pollution by utilizing the metabolic process of microorganisms, and the complexed cobalt denitrification absorbent can be recycled. In addition, the method has reasonable process, low energy consumption, low investment and operation costs, and little secondary pollution.

Description of drawings

The accompanying drawing is a process flow chart of the flue gas denitrification process of complexation absorption combined with aerobic denitrification of the present invention.

In the figure: 1 booster fan; 2 absorption tower; 3 demister; 4 outlet flue; 5 absorption liquid delivery pump;

6. Aerobic bioreactor; 7. Settling tank; 8. Circulating liquid delivery pump.

detailed description

The specific implementation manners of the present invention will be described in detail below in conjunction with the technical solutions and accompanying drawings, but the present invention is not limited to the following examples.

The flue gas is sent into the lower part of the absorption tower 2 through the booster fan 1 provided in the process, and the initial absorption liquid is an alkaline solution adding a cobalt complexing agent Co ^II (L). The NO and O ₂ in the flue gas are complexed by Co ^II (L), and the complexed O ₂ further oxidizes the complexed NO to complexed NO ₂ , and the complexed NO ₂ forms NO ₂ ^- ,NO ₃ ^- , and regenerate the cobalt complexing agent at the same time, the purified flue gas enters the demister 3 on the upper part of the absorption tower, removes the moisture in the flue gas, enters the flue gas discharge channel 4, and then discharges to control a certain amount of flue gas The residence time in the absorption tower can obtain better denitrification efficiency.

The absorption liquid is discharged from the bottom of the absorption tower, and then sent to the absorption tower 2 by the absorption liquid delivery pump 5 for recycling. During the circulation of the absorption liquid, part of the absorption liquid is sent to the aerobic bioreactor 6 . In the aerobic bioreactor 6, NO ₂ ^- , NO ₃ ^- is reduced to gaseous reduction product N ₂ by aerobic denitrifying bacteria, thereby completely eliminating nitrogen pollution.

The treatment liquid after aerobic microbial conversion treatment enters the sedimentation tank 7, and the separation liquid containing the cobalt complexing agent Co ^II (L) is transported by the circulating liquid delivery pump 8 and returned to the absorption tower circulation system for recycling as the denitrification absorption liquid.

Example 1

For an 80t/h coal-fired thermal electric boiler, the flue gas flow rate is 100,000 Nm ³ /h, the NO content is 500mg/Nm ³ , and the flue gas temperature is 130°C. According to the process of the present invention, when leaving the absorption tower, the NO content is 100mg/Nm ³ , the denitrification efficiency is 80%.

The absorption tower is a sieve plate tower with a diameter of 3.5m and a height of 22m. The liquid-gas ratio is 10L/Nm ³ . The residence time of the absorption liquid in the circulating reaction tank is 5min. The denitrification complexing agent in the absorption process is Co ^II (EDTA).

The aerobic bioreactor adopts biofilter, the pH value is controlled at 7.0, the temperature is controlled at 30°C, and the residence time is 30h. The carbon source is sodium lactate, the phosphorus source is potassium dihydrogen phosphate, and the absorption solution COD _cr :N:P=200:5:1.

Example 2

A 200t/h coal-fired thermal electric boiler, the flue gas flow rate is 250,000 Nm ³ /h, the NO content is 400mg/Nm ³ , and the flue gas temperature is 150°C. According to the process of the present invention, when leaving the absorption tower, the exhaust gas is absorbed The NO content is 80mg/Nm ³ , and the denitrification efficiency is 80%.

The absorption tower is a packed tower with a diameter of 6m and a height of 25m. The liquid-gas ratio is 10L/Nm ³ . The residence time of the absorption liquid in the circulating reaction tank is 5min. The denitrification complexing agent in the absorption process is Co ^II (Cit).

The aerobic bioreactor adopts the activated sludge process aerobic bioreactor, the pH value is controlled at 7.0, the temperature is controlled at 30°C, and the residence time is 28h. The carbon source is sodium acetate, the phosphorus source is potassium dihydrogen phosphate, and the absorption solution COD _cr :N:P=150:5:1.

Claims (1)

1. A complexation absorption combined with aerobic denitrification flue gas denitrification process is characterized in that the alkaline absorption liquid containing cobalt complexing agent is placed in the absorption tower for complexation and absorption of NO and O in the flue gas _2. Transfer NO and O ₂ from the gas phase to the liquid phase, the cobalt complexing agent complexes with O ₂ to form a binuclear dioxygen bridge complex, and the cobalt complexing agent complexes with NO to form a complex NO; the binuclear dioxygen bridge complex The complex oxidizes the complexed NO to complexed NO ₂ , and the complexed NO ₂ forms NO ₂ ^- and NO ₃ ^- in the above-mentioned alkaline absorption liquid, and at the same time regenerates the cobalt complexing agent to purify the standard flue gas emission; Put the above-mentioned alkaline absorption solution containing NO ₂ ^- and NO ₃ ^- in an aerobic bioreactor, under neutral conditions, aerobic denitrifying bacteria degrade NO ₂ ^- and NO ₃ ^- into N ₂ , completely eliminate nitrogen pollution; After being treated by aerobic denitrifying bacteria, the remaining treatment liquid enters the sedimentation tank, and after sedimentation, the activated sludge is refluxed or discharged, and the separated liquid containing cobalt complexing agent is directly returned to the absorption tower as a denitrification absorption liquid for recycling; The cobalt complexing agent is prepared from an inorganic cobaltous salt and a ligand; the inorganic cobaltous salt is a mixture of one or more of cobaltous chloride, cobaltous sulfate, and cobaltous nitrate; the The ligands mentioned above are one or more mixtures of ethylenediaminetetraacetic acid, citric acid, nitrilotriacetic acid, hydroxyethylethylenediaminetriacetic acid and diethyltriaminepentaacetic acid; The pH value in the aerobic bioreactor is controlled at 6.0-9.0, the temperature is controlled at 25-35°C, the residence time is controlled at 6-36h, and COD _cr :N:P=(100-200):5:1.