CN105561755B - A kind of clean flue gas biological desulphurization method of denitration and device - Google Patents

Abstract

The invention belongs to the field of environmental biology technology, in particular, the invention relates to a clean flue gas biological desulfurization and denitrification method and device. The present invention collects and directly converts sulfur oxides in flue gas into high-purity sulfur through four biological reactions of denitrification, sulfate reduction, methanation, and sulfur oxidation to produce elemental sulfur, combined with sulfide stripping/hydrogen sulfide absorption. Nitrogen oxides are converted into nitrogen, and the absorption liquid is regenerated, saving the consumption of alkali and water. In addition, the treatment process does not produce solid waste and waste water, and does not produce secondary pollution.

Description

A clean flue gas biological desulfurization and denitrification method and device

technical field

The invention belongs to the field of environmental biology technology, in particular, the invention relates to a clean flue gas biological desulfurization and denitrification method and device.

Background technique

The flue gas produced by the combustion of coal and other fuels contains a large amount of sulfur oxides and nitrogen oxides, which are the main pollutants in the atmosphere. The country has listed flue gas sulfur oxides and nitrogen oxides as the main monitoring indicators for air pollution control. At present, people have proposed a variety of flue gas desulfurization and denitrification methods, and some methods have achieved industrial application. However, these methods still have serious secondary pollution problems, and produce a large amount of difficult-to-treat waste liquid and waste solids, such as high-sulfate wastewater and calcium sulfate solids. In actual production, due to the high cost of treatment or the inability to deal with them, these wastes are often only disposed of by simple methods such as stacking and landfilling. Air pollution urgently needs to develop a clean and non-secondary pollution flue gas desulfurization and denitrification process.

Since sulfur oxides in flue gas are easy to react with water to form sulfuric acid, see Reaction Formula 1-2, so water washing, alkali washing and other methods are often used for flue gas desulfurization, among which limestone-gypsum method is the most mature method for flue gas sulfur oxide removal , the most widely used method. The principle of the limestone-gypsum method is to use the solid calcium sulfate (gypsum) generated by the reaction of limestone and sulfur oxides to generate sulfuric acid and sulfurous acid, see reaction formula 3. The desulfurization gypsum produced by the calcium salt method of flue gas desulfurization is calcium sulfate hydrate, which is significantly different from natural gypsum in properties, and it is difficult to reuse and high cost. In most cases, it is disposed of by stacking.

SO ₂ +H ₂ O→H ₂ SO ₃ (1)

SO ₃ +H ₂ O→H ₂ SO ₄ (2)

The limestone-gypsum method uses lime slurry to absorb sulfur oxides, which is very easy to scale and block, which affects the continuous operation of the equipment. To overcome this problem, the double-alkali method represented by the sodium-alkali double-alkali method has been developed. The sodium-alkali double-alkali method uses NaOH or Na ₂ CO ₃ solution to absorb SO _x in the flue gas, and then treats the absorption solution with limestone or lime to regenerate NaOH or Na ₂ CO ₃ , see formulas 4 and 5. Although the double-alkali method represented by the sodium-alkali double-alkali method solves the scaling problem of the limestone-gypsum method, it still produces a large amount of calcium sulfate hemihydrate, which needs to be treated to produce gypsum, and the cost of solid waste treatment is even higher. high. The problem of large amounts of desulfurized gypsum produced by flue gas desulfurization remains unresolved.

Studies have shown that the most effective way to solve the difficult treatment of desulfurized gypsum is to convert sulfate and sulfite into elemental sulfur through biological reactions and recover them. The principle is that sulfate and sulfite are first reduced to sulfide by sulfate-reducing bacteria, and then It is oxidized to elemental sulfur by sulfur-oxidizing bacteria, see formulas 6 and 7.

2HS ^- +O ₂ →2S ⁰ +OH ^- (7)

Based on the above principles, the flue gas biological desulfurization method has been developed. First, organic wastewater is used to absorb sulfur oxides, and sulfur oxides are converted into sulfates and sulfites. Salt and sulfite are reduced to sulfide, and sulfide-containing effluent enters the aerobic reactor and is oxidized to elemental sulfur by sulfur-oxidizing bacteria (CN 2010105553188, CN200510076816). However, there are two significant problems in the above-mentioned flue gas biological desulfurization process: 1. High sulfate wastewater is one of the most difficult wastewater to treat and is a research hotspot in the field of wastewater treatment. The sulfide produced by sulfate reduction has a strong effect on anaerobic digestion. Inhibition, the sulfur oxides in the flue gas are absorbed into the wastewater, which increases the difficulty and cost of wastewater treatment. For example, Chinese patents CN201220477214 and CN201110133900 have proposed solutions to the problem of difficult treatment of high sulfate wastewater. Moreover, due to the limitation of sulfate content in wastewater, the gas-liquid ratio absorbed by flue gas sulfur oxides is low, the amount of absorbent is large, and the energy consumption is high. 2. The wastewater treatment system contains a large amount of organic matter. In the process of aerobic sulfur oxidation, not only elemental sulfur is produced, but also a large amount of sludge is produced, forming a mixture of sulfur and sludge. The sulfur content is low and the recovery cost is low. For example, Chinese patent CN200910077456 proposes a method for extracting sulfur with halogenated hydrocarbons, alkyl or aryl disulfides, or alkylnaphthalene and liquid petroleum hydrocarbons. However, this method not only has the problem of high cost, but also produces difficult-to-handle Wastewater containing organic solvents. Due to the low economic value of sulfur, the sulfur sludge mixture with low sulfur content has no recycling value. Therefore, the existing flue gas biological desulfurization methods cannot achieve economical and effective sulfur recovery.

In addition, flue gas biological desulfurization is significantly different from sulfate wastewater treatment. The flue gas pollutants are gaseous sulfur oxides and do not contain organic matter. Ideally, flue gas biological desulfurization should convert sulfur oxides into elemental sulfur without producing any waste water and waste gas. Since sulfate-reducing bacteria need electron donors to complete the sulfate reduction reaction, organic matter should be added to flue gas biological desulfurization, but the type and quantity of organic matter can be selected and controlled. The absorption liquid of flue gas biological desulfurization should be renewable and recyclable, so as to reduce the water consumption of flue gas biological desulfurization, avoid waste water discharge, and avoid secondary pollution. The difference between flue gas biological desulfurization and sulfate wastewater treatment lies in , the absorption solution will contain nitrate nitrogen, while sulfate wastewater contains ammonium nitrogen.

In the process of flue gas biological desulfurization, while sulfur oxides are absorbed, nitrogen oxides will also be absorbed, which can realize flue gas biological simultaneous desulfurization and denitrification. Thus, an absorption solution containing sulfate and nitrate nitrogen is formed, and there is a substrate competition relationship between anaerobic denitrification and sulfate reduction. The flue gas biological desulfurization process needs to consider the synergistic treatment of sulfate and nitrate nitrogen. Through process design, the problem of competition between denitrification and sulfate reduction can be solved, and the simultaneous biological desulfurization and denitrification of flue gas can be established.

Contents of the invention

The purpose of the present invention is in order to provide a kind of clean flue gas biological desulfurization and denitrification process, in order to realize this technical goal, the present invention adopts following technical scheme:

The clean flue gas biological desulfurization and denitrification method of the present invention comprises the following steps:

(1) Flue gas biological desulfurization co-production of elemental sulfur:

(1-1) Absorb sulfur oxides and nitrogen oxides in the flue gas with a weak alkali solution to form an acidic absorption rich solution;

(1-2) Adding organic matter to the acidic absorption rich solution in step (1-1) to form an acidic mixed solution, acidifying with the acidic mixed solution, the sulfide is blown off and converted into hydrogen sulfide;

(1-3) The hydrogen sulfide gas produced by stripping is absorbed by the lye, and the sulfide-containing rich liquid produced is converted into elemental sulfur through a biological sulfur oxidation reaction;

(2) Denitrification combined with sulfate reduction:

(2-1) supplementing the carbon source in the absorbing rich liquid after the hydrogen sulfide is blown off in the step (1-2), and reducing the nitrate nitrogen in the absorbing rich liquid to nitrogen through facultative denitrification reaction;

(2-2) the absorption rich liquid after step (2-1) denitrification undergoes anaerobic sulfate reduction reaction, and the sulfate and sulfite therein are reduced to sulfide;

(2-3) making step (2-2) waste water after sulfate reduction pass through anaerobic methanogenesis reaction, and remaining organic matter is converted into methane;

(2-4) The waste water after the anaerobic methanogenesis reaction in step (2-3) undergoes an aerobic reaction to remove the carbon source.

Specifically, the clean flue gas biological desulfurization and denitrification method of the present invention comprises the following steps:

(1) Flue gas biological desulfurization co-production of elemental sulfur:

(1-1) Absorb sulfur oxides and nitrogen oxides in the flue gas with a weak alkali solution to form an acidic absorption rich solution;

(1-2) Adding organic matter to the acidic absorption rich solution in step (1-1) to form an acidic mixed solution, the acidic mixed solution enters the sulfide stripping tower, and is acidified by the acidic mixed solution, and the sulfide is stripped and converted into hydrogen sulfide;

(1-3) The hydrogen sulfide gas produced by stripping is absorbed by the hydrogen sulfide absorption tower containing soda liquor, and the sulfide-containing rich liquid produced is sent into the biological sulfur oxidation reactor to be converted into elemental sulfur;

(2) Denitrification combined with sulfate reduction:

(2-1) The absorption rich liquid after the hydrogen sulfide is blown off in the step (1-2) enters the facultative denitrification reactor, supplements the carbon source, and reduces the nitrate nitrogen in the absorption rich liquid to nitrogen;

(2-2) The absorption rich liquid after step (2-1) denitrification enters the anaerobic sulfate reduction reactor, and sulfate and sulfite are reduced to sulfide;

(2-3) making step (2-2) the waste water after the sulfate reduction enters the anaerobic methanogenic reactor for processing, and the remaining organic matters are converted into methane;

(2-4) The waste water after the anaerobic methanogenesis reaction in step (2-3) enters the aerobic aeration tank to remove the carbon source.

The invention absorbs sulfur oxides and nitrogen oxides in flue gas with weak alkaline solution to form acidic absorption rich liquid. In order to add an appropriate amount of organic matter to the absorption rich liquid, the nitrate nitrogen in the absorption rich liquid is first converted into nitrogen, and then the sulfate in it is reduced to sulfide. Utilize acidic absorption rich liquid acidification to convert sulfide into hydrogen sulfide, transfer the converted hydrogen sulfide to the gas phase by gas stripping, absorb hydrogen sulfide with pure alkali solution and convert it back to sulfide, and complete the separation and purification of sulfide. Separation of sulfide and organic matter. The purified sulfide is converted into elemental sulfur by chemoautotrophic biosulfur oxidizing bacteria, and biosulfur is obtained by sedimentation and centrifugation. Since the sulfide does not contain impurities, the recovered sulfur has high purity and can meet the requirements of commercial sulfur without treatment. The absorbed rich liquid is treated with denitrification and sulfate reduction, and the nitrate nitrogen and sulfate formed by the absorption of nitrogen oxides and sulfur oxides are completely removed. However, neither denitrification nor sulfate reduction can completely degrade organic matter, so anaerobic methanogenesis treatment is required to completely degrade the remaining organic matter into methane and carbon dioxide. The three reactions of denitrification, sulfate reduction and methane production will all produce alkali, and the flue gas absorption liquid can be regenerated and recycled, greatly reducing the consumption of flue gas biological desulfurization and denitrification water and alkali.

According to the clean flue gas biological desulfurization and denitrification method of the present invention, in order to realize the recycling of intermediate products and achieve the environmental protection purpose of clean flue gas, preferably, the nitrogen gas produced in the step (2-1) enters the gas collection and treatment system , after being purified and pressurized, it is used as an inert circulating carrier gas between step (1-2) hydrogen sulfide stripping and step (1-3) hydrogen sulfide absorption. The step (1-2) of returning the sulfide-containing wastewater after the anaerobic sulfate reduction reaction in the step (2-2) participates in the conversion of hydrogen sulfide. The waste water after the aerobic reaction in (2-4) enters the buffer tank and is used as weak lye in step (1-1) to absorb sulfur oxides and nitrogen oxides in the flue gas.

According to the method for biological desulfurization and denitrification of clean flue gas of the present invention, the weak alkali solution in step (1-1) is 0.2-0.5M NaHCO ₃ solution.

In the step (1-1), in the process of absorbing sulfur oxides and nitrogen oxides, it is necessary to control the gas-liquid ratio to reduce the pH value of the acidic absorption rich liquid to 4.0-5.0. The absorption of sulfur oxides to form sulfuric acid and sulfurous acid will lower the pH value, and the pH value of the rich solution will be reduced to 4.0-5.0 by controlling the absorption of sulfur oxides, which is conducive to the stripping of sulfides.

According to the clean flue gas biological desulfurization and denitrification method of the present invention, the organic matter added in step (1-2) is one or more of ethanol, lactic acid or lactate, or glucose.

The lye in the step (1-3) of the present invention is NaHCO ₃ with a concentration of 0.2-0.5M. The elemental sulfur generated in step (1-3) can be further processed into finished sulfur with a purity ≥ 99% after precipitation and centrifugation.

The carbon source in step (2-1) of the present invention is one or more of ethanol, lactic acid or lactate, and glucose.

The pH value of the aerobic reaction in step (2-4) of the present invention is >7.0. The waste water produced by sulfate reduction enters the aerobic pool for treatment after blowing off. The influent of the aerobic tank contains residual sulfides stripped and residual carbon sources from sulfate reduction. These substances are oxidized to produce acid, which will reduce the pH value of the aerobic tank, and alkali supplementation is required to keep the pH of the aerobic tank stable. In addition, the effluent from the aerobic pool is directly used for the absorption of sulfur oxides in the flue gas, and maintaining a high pH value is conducive to absorption.

The biological sulfur oxidation reaction, facultative denitrification reaction, anaerobic sulfate reduction reaction and methanogenic reaction described in the present invention can all use the existing bacterial strains that can carry out the above-mentioned reaction, and preferably use the anaerobic and facultative denitrification reaction of municipal sewage plant. and aerobic activated sludge.

The device based on the above-mentioned clean flue gas biological desulfurization and denitrification method provided herein includes a flue gas biological desulfurization co-production elemental sulfur system and a denitrification combined sulfate reduction system;

The flue gas biological desulfurization co-production elemental sulfur system includes a flue gas absorption tower 1, a mixing tank 2, a sulfide stripping tower 7, a hydrogen sulfide absorption tower 8 and a biological sulfur oxidation reactor 9;

The denitrification combined sulfate reduction system includes a facultative denitrification reactor 3, an anaerobic sulfate reduction reactor 4, an anaerobic methanogenesis reactor 5 and an aerobic aeration tank 6;

The flue gas absorption tower 1 is sequentially connected to the mixing tank 2, the sulfide stripping tower 7, the hydrogen sulfide absorption tower 8 and the biological sulfur oxidation reactor 9;

The facultative denitrification reactor 3 and the sulfide stripping tower 7 are connected to the anaerobic sulfate reduction reactor 4, the anaerobic methanogenesis reactor 5 and the aerobic aeration tank 6 in sequence.

According to the clean flue gas biological desulfurization and denitrification device of the present invention, preferably, a gas circulation circuit is provided between the sulfide stripping tower 7 and the hydrogen sulfide absorption tower 8; the facultative oxygen denitrification reactor 3 is further connected with gas collection and The treatment system 12, the connecting gas collection and treatment system 12 is connected to the gas circulation circuit between the sulfide stripping tower 7 and the hydrogen sulfide absorption tower 8 .

Further preferably, the anaerobic sulfate reduction reactor 4 is connected to the mixing tank 2 .

Further preferably, the aerobic aeration tank 6 is connected to the flue gas absorption tower 1 through a buffer tank 14 .

The biological sulfur oxidation reactor 9 of the present invention is further connected in sequence with a sulfur sedimentation tank 10 and a sulfur centrifuge 11 for purifying sulfur.

The advantages of the present invention are: compared with the prior art, the process provided by the present invention converts sulfur oxides in flue gas into elemental sulfur, and high-purity elemental sulfur can be obtained through simple physical methods, truly realizing sulfur recovery ; Utilize biological denitrification, anaerobic sulfate reduction and methanogenic reaction to generate alkali to realize the regeneration and recycling of the absorption liquid; the sulfur oxides and nitrogen oxides in the flue gas are converted into elemental sulfur and nitrogen respectively, and the sulfur The recovery rate is higher than 90%, which completely solves the secondary pollution problem of flue gas desulfurization and denitrification, and realizes biological desulfurization and denitrification of clean flue gas.

Description of drawings

Fig. 1 is a flow chart of the clean flue gas biological desulfurization and denitrification process of the present invention.

Figure 2 shows the processing results of simulated flue gas with different concentrations of sulfur oxides.

Figure 3 shows the treatment results of simulated flue gas with different ratios of sulfur oxides and nitrogen oxides.

Figure 4 shows the processing results of real flue gas.

reference sign

1. Flue gas absorption tower 2. Mixing tank 3. Facultative oxygen denitrification reactor

4. Anaerobic sulfate reduction reactor 5. Anaerobic methanogenesis reactor

6. Aerobic aeration tank 7. Sulfide stripping tower 8. Hydrogen sulfide absorption tower

9. Biological sulfur oxidation reactor 10. Sulfur sedimentation tank 11. Sulfur centrifuge

12. Gas collection and treatment system 13. Biogas recovery system 14. Buffer pool

Detailed ways

The present invention will be further described in detail below in conjunction with the examples, but the embodiments of the invention are not limited thereto.

Example 1 Clean flue gas biological desulfurization and denitrification process flow

As shown in Figure 1, the clean flue gas biological desulfurization and denitrification integrated process of the present invention is mainly composed of flue gas absorption, sulfide stripping/hydrogen sulfide absorption, facultative denitrification, anaerobic sulfate reduction, anaerobic methanogenesis, micro It is composed of oxygen sulfur oxidation to produce elemental sulfur, sulfur recovery and aerobic aeration tank. The specific process is as follows:

1) Using 0.2-0.5M NaHCO ₃ as the absorption liquid, absorb the sulfur oxides and nitrogen oxides in the flue gas that has been dedusted and cooled in the absorption tower 1, and absorb the rich liquid by controlling the gas-liquid ratio. The pH value drops to 4.0-5.0.

2) Absorb the rich liquid and anaerobic sulfate reduction reactor 4 backflow and mix in the mixing tank 2 to form an acidic mixed liquid, and the mixed liquid enters the sulfide stripping tower 7, the sulfide is stripped and converted into hydrogen sulfide, and the pH rises to 5.5-6.0.

3) The hydrogen sulfide-containing gas produced by stripping is absorbed by the hydrogen sulfide absorption tower 8, and the generated sulfide-containing rich liquid is sent to the biological sulfur oxidation reactor 9 to be converted into elemental sulfur. The generated elemental sulfur is prepared into finished sulfur with a purity of ≥99% through precipitation (sulfur sedimentation tank 10) and centrifugation (sulfur centrifuge 11). The waste liquid produced by centrifugation returns to the biological sulfur oxidation reactor 9. The sulfide produced by anaerobic sulfate reduction is finally converted into elemental sulfur through sulfide stripping/hydrogen sulfide absorption, chemoautotrophic sulfur-oxidizing bacteria oxidation.

4) The absorbed rich liquid that has been stripped off enters the facultative denitrification reactor 3, supplements ethanol, lactic acid, glucose and other carbon sources, stirs and mixes, and the nitrate nitrogen in the absorbed rich liquid is reduced to nitrogen gas, and the nitrogen gas enters the gas collection and treatment The system 12 is used as an inert cycle carrier gas between sulfide stripping and hydrogen sulfide absorption after purification and pressurization; the gas collection and treatment system 12 may include a gas cabinet, a filter device and a pressurization device, etc.

5) Absorbed rich liquid after denitrification treatment enters the anaerobic sulfate reduction reactor 5, sulfate and sulfite are reduced to sulfide, and waste liquid containing sulfide enters the external circulation of the anaerobic sulfate reduction reactor, and returns to the anaerobic sulfate reduction reactor. to step 2).

6) Since the anaerobic sulfate reduction cannot completely degrade the carbon source, the effluent from the anaerobic sulfate reduction enters the anaerobic methanogenic reactor 5 for treatment to convert the remaining organic matter into methane, and the generated methane enters the biogas recovery system 13 .

7) After denitrification, anaerobic sulfate reduction and methanogenic reaction, the sulfate and nitrate nitrogen in the absorbed rich solution are completely removed, and the additional carbon source is completely consumed. Since the above three biological reactions all produce alkali, the pH value of the effluent from anaerobic methanogenic reactor 5 rises to about 7.0.

8) The circulating liquid after denitrification, anaerobic sulfate reduction and methanogenic reaction treatment enters the aerobic aeration tank 6 to remove a small amount of additional carbon source that may remain, and NaHCO ₃ solution is added as needed to adjust the pH value to 7.5.

9) The circulating fluid treated with aerobic aeration is regenerated, enters the buffer tank 14, and is used as the flue gas absorption liquid again, and is pumped into the flue gas absorption tower to enter the next cycle.

The pH detection points of this system: the absorption rich liquid of the flue gas absorption tower 1, the sulfide stripping tower 7 and the hydrogen sulfide absorption tower 8, the facultative denitrification reactor 3 and the aerobic aeration tank 6, the anaerobic sulfate The effluent of reduction reactor 4 and anaerobic methanogenesis reactor 5.

The pH adjustment point of this system is the aerobic aeration tank 6 .

The principles of sulfur oxide absorption, hydrogen sulfide stripping, and hydrogen sulfide absorption are acid-base neutralization, and the absorption richness of the aerobic aeration tank 6, flue gas absorption tower 1, sulfide stripping tower 7, and hydrogen sulfide absorption tower 8 is detected. The pH value of the solution can not only control the absorption or stripping, but also indirectly calculate the absorption or stripping of sulfur oxides and hydrogen sulfide. The facultative denitrification reactor 3, the anaerobic sulfate reduction reactor 4, and the anaerobic methanogenesis reactor 5 are the three main reactions of the present invention, and the biological activity is greatly affected by the pH value, so online detection of the pH value is required.

The waste water produced by sulfate reduction enters the aerobic pool for treatment after blowing off. The influent of the aerobic tank contains residual sulfides stripped and residual carbon sources from sulfate reduction. These substances are oxidized to produce acid, which will reduce the pH value of the aerobic tank, and alkali supplementation is required to keep the pH of the aerobic tank stable. In addition, the effluent from the aerobic pool is directly used for the absorption of sulfur oxides in the flue gas, and maintaining a high pH value is conducive to absorption. Therefore, the pH adjustment point of the system is set in the aerobic aeration tank.

Example 2 The treatment effect of the present invention on simulated flue gas with different concentrations of sulfur oxides

Simulated flue gas: SO _x concentration (calculated as SO ₂ ) is 500, 1000, 2000, 3000, 4000mg/Nm ³ (Stage1～5).

Gas flow rate: 1.0 Nm ³ /h.

Absorption of poor solution: adjust the pH to 7.5 with 0.2M NaHCO ₃ solution.

Hydrogen sulfide absorption liquid: Na ₂ CO ₃ solution.

Supplementary carbon source: The control system automatically adds ethanol according to the pH difference between the absorbed poor solution and the rich solution.

What kind of strain is the biological sulfur oxidation reactor? The denitrifying bacteria were taken from the denitrification sludge of the municipal sewage treatment plant and inoculated in the facultative denitrification reactor; the anaerobic sludge of the municipal sewage treatment plant was inoculated in the anaerobic sulfate reduction reactor and the methanogenesis reactor respectively.

Adjust the gas-liquid ratio and control the pH of the absorbed rich liquid to be 4.0-5.0.

The remaining experimental conditions are set with reference to Example 1.

The experimental results are shown in Figure 2. After the simulated flue gas is treated, the SO _x removal rate is >99%, and the SO _x concentration is reduced to <40mg/Nm ³ . Sulfur recovery rate (recovery ratio in the form of elemental sulfur) >90%. After determination, the purity of sulfur is >99%. The COD concentration of the effluent from the aerobic aeration tank is <20mg/m ³ . After calculation, the average alkali consumption (calculated as NaOH) is 43.5g/kg SO ₂ , which is 3.5% of the theoretical consumption.

This example shows that the present invention can efficiently remove sulfur oxides, most of which are converted into elemental sulfur and effectively recovered. The external drainage produced during the treatment process not only has a small amount of water, but also has a COD concentration lower than the discharge standard, so it can be discharged directly. Alkali consumption is only 3.5% of theoretical consumption. It can be seen that the present invention is a clean flue gas desulfurization process that does not produce secondary pollution, saves water and chemicals.

Example 3 The treatment effect of the present invention on simulated flue gas with different ratios of sulfur oxides and nitrogen oxides

Simulated flue gas: SO _x concentration (calculated as SO ₂ ) 2000mg/Nm ³ , NO _x concentration (calculated as NO ₂ ) 50, 100, 200, 400 mg/Nm ³ (Stage 1～4).

Other processing conditions are identical with embodiment 2.

The experimental results are shown in Figure 3. After the simulated flue gas is treated, the SO _x concentration is reduced to <10mg/Nm ³ , and the SO _x removal rate is >99%. Since NO _x includes NO that is poorly soluble in water, the removal rate of NO _x is as low as 50-70%. After the flue gas is treated with biological desulfurization and denitrification, the concentration of NO _x is reduced to below 200mg/Nm ³ , and the removal rate of nitrate nitrogen generated after nitrogen oxides are absorbed is 100%. Indexes such as sulfur recovery rate, sulfur purity, and effluent COD are similar to those in Example 2, being >90%, >98%, and <20mg/m ³ respectively.

This example shows that the present invention has a certain denitrification ability while desulfurizing the flue gas. Although the _NOx removal rate is not high, it can still be used for flue gas treatment with low _NOx content and achieve standard emission. In the process of flue gas desulfurization and denitrification, it still has the characteristics of no secondary pollution, water saving and chemical saving. The invention is a clean flue gas biological desulfurization and denitrification process.

Example 4 Using different carbon sources as electron donors to simulate the operation effect of flue gas biological desulfurization and denitrification

Simulated flue gas: SO _x concentration (calculated as SO ₂ ) is 2000 mg/Nm ³ , and NO _x concentration (calculated as NO ₂ ) is 500 mg/Nm ³ .

Ethanol, lactic acid, sodium lactate, glucose, and mixed carbon sources were used as additional carbon sources.

Mixed carbon source: ethanol: lactic acid: glucose = 5:2:1

Other processing conditions are identical with embodiment 2.

The experimental results show that ethanol, lactic acid, sodium lactate, and glucose can all be used as carbon sources for flue gas biological desulfurization and denitrification, see Table 1. Taking carbon source consumption as an index, the ethanol experimental group had the least consumption per 1Nm ³ simulated flue gas. Taking the influent of the aerobic pool as the index, the effluent COD concentration of the mixed carbon source experimental group was the lowest.

Table 1 Consumption of different carbon sources and COD of aerobic pond influent

This example illustrates that in the present invention, one of ethanol, lactic acid, sodium lactate, and glucose can be selected as the carbon source, and a mixed carbon source composed of ethanol, lactic acid, and glucose can also be used. Ethanol single and mixed carbon sources worked best.

Example 5 Treatment effect of clean flue gas biological desulfurization and denitrification process on real flue gas

Flue gas: SO _x concentration (calculated as SO ₂ ) is 1,000-2,000 mg/Nm ³ , NO _x concentration (calculated as NO ₂ ) is 400-500 mg/Nm ³ , and has been treated with cooling and dust removal.

Mixed carbon source: ethanol: lactic acid: glucose = 5:2:1

Other processing conditions are identical with embodiment 2.

The experimental results are shown in Figure 4. After treatment, the concentration of SO _x in the flue gas is <20mg/Nm ³ , and the concentration of NO _x (calculated as NO ₂ ) is <180 mg/Nm ³ . The removal rates of SO _x and NO _x are >95% and >62%, respectively. The COD concentration in the outflow of the aerobic aeration tank is less than 30mg/L, and the total nitrogen is less than 10mg/L to meet the direct discharge standard. The average alkali consumption (calculated as NaOH) is 45.2g/kg SO ₂ , which is 3.6% of the theoretical consumption.

After calculation, the sulfate removal rate of the absorbed rich solution is >95%, the sulfur recovery rate is >90%, and the sulfur purity is >95%. The removal rate of nitrate nitrogen in absorbing rich solution is 100%.

This embodiment shows that the present invention can be used in actual flue gas desulfurization and denitrification, and the treated flue gas meets the national emission standard. More importantly, sulfur oxides are converted into high-purity elemental sulfur and recovered through a series of biological reactions, and nitrogen oxides are converted into nitrogen. The use of biological reactions to regenerate the absorption liquid saves more than 95% of the alkali consumption and reduces the consumption of chemicals and water. No solid waste is generated during the treatment process, and the COD and total nitrogen concentrations in the generated wastewater are lower than the most stringent national discharge standards. Therefore, the present invention is a clean flue gas biological desulfurization and denitrification process with water saving, alkali saving and no secondary pollution.

Of course, the present invention can also have various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the disclosure of the present invention without departing from the spirit and essence of the present invention. All changes and deformations should belong to the protection scope of the appended claims of the present invention.

Claims (14)

1. A clean flue gas biological desulfurization and denitrification method, comprising the following steps: (1) Flue gas biological desulfurization co-production of elemental sulfur: (1-1) Absorb sulfur oxides and nitrogen oxides in the flue gas with a weak alkali solution to form an acidic absorption rich solution; (1-2) Adding organic matter to the acidic absorption rich solution in step (1-1) to form an acidic mixed solution, which is acidified by using the acidic mixed solution, and the sulfide is blown off and converted into hydrogen sulfide; (1-3) The hydrogen sulfide gas produced by stripping is absorbed by the lye, and the sulfide-containing rich liquid produced is converted into elemental sulfur through a biological sulfur oxidation reaction; (2) Denitrification combined with sulfate reduction: (2-1) supplementing the carbon source in the absorbing rich liquid after the hydrogen sulfide is blown off in the step (1-2), and reducing the nitrate nitrogen in the absorbing rich liquid to nitrogen through facultative denitrification reaction; (2-2) the absorption rich liquid after step (2-1) denitrification undergoes anaerobic sulfate reduction reaction, and the sulfate and sulfite therein are reduced to sulfide; (2-3) making step (2-2) waste water after sulfate reduction pass through anaerobic methanogenesis reaction, and remaining organic matter is converted into methane; (2-4) The waste water after the anaerobic methanogenesis reaction in step (2-3) undergoes an aerobic reaction to remove the carbon source. 2. The clean flue gas biological desulfurization and denitrification method according to claim 1, characterized in that the nitrogen produced in the step (2-1) enters the gas collection and treatment system, and is used in the step (1) after being purified and pressurized -2) Inert circulating carrier gas between hydrogen sulfide stripping and step (1-3) hydrogen sulfide absorption. 3. The clean flue gas biological desulfurization and denitrification method according to claim 1, characterized in that, after the step (2-2) anaerobic sulfate reduction reaction, the sulfide-containing waste water reflux step (1-2) participates in sulfidation hydrogen conversion. 4. The clean flue gas biological desulfurization and denitrification method according to claim 1, characterized in that, the waste water after the (2-4) aerobic reaction enters the buffer pool as the weak lye in the step (1-1) , Absorb sulfur oxides and nitrogen oxides in flue gas. 5. The method for biological desulfurization and denitrification of clean flue gas according to claim 1, characterized in that the weak alkali solution in step (1-1) is 0.2-0.5M NaHCO ₃ solution. 6 . The method for biological desulfurization and denitrification of clean flue gas according to claim 1 , characterized in that, in the step (1-1), the pH value of the acidic absorption rich liquid is reduced to 4.0-5.0 by controlling the gas-liquid ratio. 7. The method for biological desulfurization and denitrification of clean flue gas according to claim 1, characterized in that the organic matter added in step (1-2) is one or more of ethanol, lactic acid or lactate, or glucose. 8. The method for biological desulfurization and denitrification of clean flue gas according to claim 1, characterized in that the carbon source in step (2-1) is one or more of ethanol, lactic acid or lactate, and glucose. 9. The method for biological desulfurization and denitrification of clean flue gas according to claim 1, characterized in that the pH value of the aerobic reaction in step (2-4) is 7.0-7.5. 10. A device based on the clean flue gas biological desulfurization and denitrification method according to claim 1, characterized in that it comprises a flue gas biological desulfurization co-production elemental sulfur system and a denitrification combined sulfate reduction system; The flue gas biological desulfurization co-production elemental sulfur system includes a flue gas absorption tower (1), a mixing tank (2), a sulfide stripping tower (7), a hydrogen sulfide absorption tower (8) and a biological sulfur oxidation reactor ( 9); The denitrification combined sulfate reduction system includes a facultative denitrification reactor (3), an anaerobic sulfate reduction reactor (4), an anaerobic methanogenesis reactor (5) and an aerobic aeration tank (6); The flue gas absorption tower (1) is sequentially connected to a mixing tank (2), a sulfide stripping tower (7), a hydrogen sulfide absorption tower (8) and a biological sulfur oxidation reactor (9); The facultative denitrification reactor (3) is connected with the sulfide stripping tower (7), and is connected with the anaerobic sulfate reduction reactor (4), the anaerobic methanogenesis reactor (5) and the aerobic aeration reactor in sequence. Air pool (6). 11. The device according to claim 10, characterized in that, a gas circulation loop is provided between the sulfide stripping tower (7) and the hydrogen sulfide absorption tower (8); the part-oxygen denitrification reactor (3) A gas collection and treatment system (12) is further connected, and the gas collection and treatment system (12) is connected to the gas circulation circuit between the sulfide stripping tower (7) and the hydrogen sulfide absorption tower (8). 12. The device according to claim 10, characterized in that the anaerobic sulfate reduction reactor (4) is connected to the mixing tank (2). 13. The device according to claim 10, characterized in that the aerobic aeration tank (6) is connected to the flue gas absorption tower (1) through a buffer tank (14). 14. The device according to claim 10, characterized in that, the biological sulfur oxidation reactor (9) is further connected to a sulfur sedimentation tank (10) and a sulfur centrifuge (11) in sequence.