METHOD FOR SIMULTANEOUSLY REMOVING HIGH-LOAD SULFUR DIOXIDE AND NITROGEN OXIDE IN WASTE GAS

Abstract

A method for simultaneously removing high-load sulfur dioxide and nitrogen oxide in waste gas, relating to the technical field of industrial waste gas purification by biological methods. According to the method, the waste gas is led into a simultaneous desulfurization and denitrification packing tower and removed, microbial floras for simultaneously removing the sulfur dioxide and the nitrogen oxide are loaded on fillers of the packing tower, and the molar concentration ratio of the sulfur dioxide to the nitrogen oxide in the waste gas is (0.76˜1.06):1.

Claims

1. A method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas, characterized by: the method comprising introducing waste gas into a packed biotrickling-filter (BF) to synchronously desulfurize and denitrify the waste gas, packings in the BF are loaded with microbial flora for synchronous removal, and a molar concentration ratio of sulfur dioxide and nitrogen oxides in the waste gas is (0.76˜1.06): 1.

2. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 1, wherein the microbial flora includes: Arthrobacter, Nitrospira, Flavobacterium, Pseudomonas, Rhodococcus, Ralstonia, Hyphomicrobium, Pseudomonas, Rhodococcus, Bacillus, Acinetobacter, Candidatus Acinetobacter, Zoogloea, Hyphomicrobium, Dietzia, Burkholderia, Mycobacterium, Pseudomonas, Rhodococcus and Paenibacillus.

3. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 1, wherein the source of the microbial flora for simultaneously removing sulfur dioxide and nitrogen oxides includes biological sludge.

4. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 3, wherein a concentration of sulfur dioxide in the waste gas is 2700-3600 mg/m3.

5. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 4, wherein a concentration of nitrogen oxides in the waste gas is 1680-2300 mg/m3.

6. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 3, wherein the packings loaded in the BF includes acid resistant porous granular materials.

7. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 6, wherein a diameter of the packings is 50-200 mm.

8. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 1, wherein the method specifically comprising the following steps: a) adding nutrient solution into the BF; b) mixing the waste gas with air and passing it into the BF for treatment, controlling operating temperature of the BF; c) spraying the nutrient solution from the upper side of the BF, the nutrient solution flows out from the bottom, and then flows back to the upper side of the BF through a peristaltic pump for circulating spraying; d) discharging gas treated by the BF system through a gas outlet on the top of the BF.

9. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 8, wherein the operating temperature of the BF in step b) is 25˜35 oC.

10. The method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas according to claim 9, wherein reagents contained in the nutrient solution include FeSO4.7H.sub.2O, K2HPO4.3H.sub.2O, KCl, Ca (NO3)2.4H.sub.2O, CH3COONa.3H2O and MgSO4.7H2O, and a pH value of the nutrient solution is 2.5.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is the structural diagram of the BFs used in example 1;

[0032] FIG. 2 shows the change in SO.sub.4.sup.2− concentration in BFs (R1 and R2) in example 5;

[0033] FIG. 3 shows the change in NO.sub.3.sup.− and NO.sub.2.sup.− concentration in BFs (R1 and R3) in example 5;

[0034] FIG. 4 shows the change in pH value in BFs (R1, R2 and R3) in example 5;

[0035] FIG. 5 shows the SO.sub.2 removal level of BF (R1) in example 5;

[0036] FIG. 6 shows the NO.sub.x removal level of BF (R1) in example 5;

[0037] FIG. 7 shows the SO.sub.2 removal level of BF (R2) in example 5;

[0038] FIG. 8 shows the NO.sub.x and SO.sub.2 removal level of BF (R3) in example 5;

[0039] FIG. 9 shows the microbial community level in BFs (R1, R2 and R3) in example 5.

[0040] In FIGS., 1. air inlet; 2. flowmeter; 3. air inlet pipeline; 4. packing container; 5. spraying device; 6. air outlet; 7. nutrient solution inflow pipeline; 8. peristaltic pump; 9. nutrient solution storage container; 10. nutrient solution outflow pipeline.

DETAILED DESCRIPTION

[0041] The invention will be further described in combination with specific examples.

Example 1

[0042] The waste gas in this example comes from the simulated flue gas generated by the gas generation device. Before entering the synchronous desulfurization and denitrification BF for treatment, the simulated flue gas is first introduced into the mixing device to mix the simulated flue gas and air.

[0043] As shown in FIG. 1, the air inlet 1, gas flowmeter 2, air inlet pipeline 3, packing container 4, nutrient solution spraying device 5, air outlet 6, nutrient solution inflow pipeline 7, peristaltic pump 8, nutrient solution storage container 9 and nutrient solution outflow pipeline 10 of the BF for simultaneous removal of high load sulfur dioxide and nitrogen oxides are disclosed in this example.

[0044] The waste gas can enter the BF through the air inlet 1, and enter the packing container 4 of the BF through the air inlet pipeline 3. In this process, the gas flow is regulated by the gas flowmeter 2, and the generated gas is discharged through the top of the packing container 4. A nutrient solution spraying device 5 is placed at the upper end of the packing container 4, and used for evenly spraying the nutrient solution. During the operation, the nutrient solution is sprayed from the upper end, passes through the biofilm packing area of the packing container 4 and flows out from the bottom. The outflow nutrient solution flows into the nutrient solution storage container 9 through the nutrient solution inflow pipeline 7. The nutrient solution inflow pipeline 7 is placed between the nutrient solution storage container 9 and the nutrient solution spraying device 5, and a peristaltic pump 8 is installed on the nutrient solution inflow pipeline 7. Therefore, the nutrient solution in the nutrient solution storage container 9 can be pumped back to the nutrient solution spray device 5, and repeatedly sprayed and utilized during the operation of the BF. Baffles are respectively arranged at the lower end and the middle part of the packing container 4 for fixing the packings loaded with microorganisms.

[0045] The packings in this example are ceramsite particles with a diameter of 5 mm, on which 10 g of sludge from the biotreatment tank of the sewage system is inoculated, and the sludge provides microorganisms for the BF to simultaneously remove sulfur dioxide and nitrogen oxides.

[0046] In this example, the method for simultaneously removing high load sulfur dioxide and nitrogen oxides in waste gas specifically includes the following steps:

[0047] 1) The nutrient solution is added into the BF, and the waste gas to be treated is introduced into the BF system. In this example, the molar concentration ratio of sulfur dioxide and nitrogen oxides in the waste gas is (0.76˜.06): 1, the concentration of sulfur dioxide at the air inlet 1 is 2700˜3600 mg/m.sup.3, and the concentration of nitrogen oxides is 1680˜2300 mg/m.sup.3.

[0048] 2) In the example, the desulfurization and denitrification treatment is carried out in an aerobic environment, the aerobic environment is provided by air, the oxygen concentration in the air is 20%, the air flow rate is kept at 0.1m.sup.3/h, the gas residence time is 100 seconds, and the liquid-gas ratio is 30 L/m.sup.3.

[0049] 3) During the operation of the BF, the reaction temperature of the BF is controlled to be 25° C., and the nutrient solution is sprayed at the rate of 8L/h. After collecting at the bottom, the nutrient solution is returned to the nutrient solution spraying device 5 through the peristaltic pump 8 for circulating spraying, and the nutrient solution is replenished 20% every week and refreshed every two weeks.

[0050] The preparation process of the nutrient solution is as follows: setting the solution volume to be 1.0 L, adding chemical reagents by weight and adjusting the pH to 2.5 with dilute sulfuric acid, the chemical reagents include FeSO.sub.4.7H.sub.2O, K.sub.2HPO.sub.4.3H.sub.2O, KCl, Ca (NO.sub.3).sub.2.4H.sub.2O, CH.sub.3COONa.3H.sub.2O and MgSO.sub.4.7H.sub.2O, wherein the mass concentration of FeSO.sub.4.7H.sub.2O in the nutrient solution is 0.23 g/L; The mass concentration of K.sub.2HPO.sub.4.3H.sub.2O is 0.655 g/L; The mass concentration of KCl is 0.1 g/L; The mass concentration of Ca (NO.sub.3).sub.2.4H.sub.2O is 0.01 g/L, and the mass concentration of CH.sub.3COONa.3H.sub.2O is 0.498 g/L; The mass concentration of MgSO.sub.4.7H.sub.2O is 0.5 g/L.

[0051] After two cycles of operation, the concentrations of sulfur dioxide and nitrogen oxides at the air outlet 6 were detected: the concentration of sulfur dioxide was less than 100 mg/m.sup.3, with an average of 2 mg/m.sup.3, the removal rate was 99%˜100%, with an average of 99.9%; the concentration of nitrogen oxides ranged from 160 mg/m.sup.3 to 615 mg/m.sup.3, with an average of 415 mg/m.sup.3, the removal rates ranged from 66% to 92%, with an average of 77.5%.

Example 2

[0052] This example is basically the same as example 1, with the difference that:

[0053] In this example, the concentration of sulfur dioxide at the air inlet 1 range from 2850 to 3050 mg/m.sup.3, nitrogen oxides 2150 to 2230 mg/m.sup.3, and the molar concentration ratio of sulfur dioxide to nitrogen oxides in the waste gas is 0.76:1.

[0054] The packings are ceramsite particles with a diameter of 200 mm, the desulfurization and denitrification treatment in step 2) is carried out in an aerobic environment, the aerobic environment is provided by air, the oxygen concentration in the air is 20%, the air flow rate is kept at 0.2 m.sup.3/h, the gas residue time is 110 seconds, and the liquid gas ratio is 40 L/m.sup.3.

[0055] The operating temperature of the BF is 35° C.

[0056] After two cycles of operation, the concentrations of sulfur dioxide and nitrogen oxides in the waste gas at the air outlet 6 were detected: the concentration of sulfur dioxide ranged from 0 to 30 mg/m.sup.3, the removal rate ranged from 99% to 100%, with an average of 99.9%; the nitrogen oxide 160 to 390 mg/m.sup.3, the removal rate ranged from 80% to 92%, with an average of 85.4%.

Example 3

[0057] This example is basically the same as example 1, with the difference that:

[0058] In this example, the concentration of sulfur dioxide at the air inlet 1 range from 2930 to 3000 mg/m.sup.3, nitrogen oxides 1680 to 2000 mg/m.sup.3, and the molar concentration ratio of sulfur dioxide to nitrogen oxides in the waste gas is 1.06:1.

[0059] The packings are made of porous acid resistant plastic with a diameter of 100 mm, the desulfurization and denitrification treatment in step 2) is carried out in an aerobic environment, the aerobic environment is provided by air, the oxygen concentration in the air is 20%, the air flow rate is kept at 0.2 m.sup.3/h, the gas residence time is 110 seconds, and the liquid gas ratio is 40 L/m.sup.3.

[0060] The operating temperature of the BF is 30° C.

[0061] After two cycles of operation, the concentrations of sulfur dioxide and nitrogen oxides in the waste gas at the air outlet 6 were detected: the concentration of sulfur dioxide ranged from 0 to 80 mg/m.sup.3, the removal rate ranged from 98% to 100%, with an average of 99.5%; the nitrogen oxide ranged from 260 to 300 mg/m.sup.3, the removal rate 78% to 85%, with an average of 81.0%.

Example 4

[0062] This example is basically the same as example 1, with the difference that:

[0063] In this example, the concentration of sulfur dioxide at the air inlet 1 is 2700˜3600 mg/m.sup.3, the concentration of nitrogen oxides is 1800˜2300 mg/m.sup.3, and the molar concentration ratio of sulfur dioxide and nitrogen oxides in the waste gas is 0.9:1.

[0064] After two cycles of operation, the concentrations of sulfur dioxide and nitrogen oxides in the waste gas at the air outlet 6 were detected: the concentration of sulfur dioxide ranged from 0 to 30 mg/m.sup.3, the removal rate ranged from 99% to 100%, with an average of 99.9%; the nitrogen oxide ranged from 190 to 600 mg/m.sup.3, the removal rate 66% to 89%, with an average of 75.4%.

Comparative example 1

[0065] This example is basically the same as example 1, with the difference that:

[0066] In this example, the molar concentration ratio of sulfur dioxide and nitrogen oxides in the waste gas is (0.66˜0.76):1, the concentration of sulfur dioxide at the air inlet 1 is between 2500˜3450 mg/m.sup.3, and the concentration of nitrogen oxides is between 2250˜2650 mg/m.sup.3.

[0067] After two cycles of operation, the concentrations of sulfur dioxide and nitrogen oxides in the waste gas at the air outlet 6 were detected: the concentration of sulfur dioxide ranged from 0 to 20 mg/m.sup.3, with an average of 1.3 mg/m.sup.3, the removal rate ranged from 99% to 100%, with an average of 99.9%; the nitrogen oxide ranged from 600 to 910 mg/m.sup.3, with an average of 791 mg/m.sup.3, the removal rate 62% to 74%, with an average of 68.1%.

Comparative example 2

[0068] This example is basically the same as example 1, with the difference that:

[0069] In this example, the molar concentration ratio of sulfur dioxide and nitrogen oxides in the waste gas is (1.06˜1.56): 1, the concentration of sulfur dioxide at the air inlet 1 is between 2450 to 3450 mg/m.sup.3, and the nitrogen oxides between 1000 to 1750 mg/m.sup.3.

[0070] After two cycles of operation, the concentrations of sulfur dioxide and nitrogen oxides in the waste gas at the air outlet 6 were detected: the concentration of sulfur dioxide ranged from 0 to 223 mg/m.sup.3, with an average of 103 mg/m.sup.3, the removal rate ranged from 93% to 100%, with an average of 97.0%; the nitrogen oxides ranged from 200 mg/m.sup.3 to 787 mg/m.sup.3, with an average of 448 mg/m.sup.3, and the removal rate ranged from 36% to 82%, with an average of 65.2%.

[0071] Table 1 shows the results of simultaneous removal of sulfur dioxide and nitrogen oxides in the examples and comparative examples.

TABLE-US-00001 TABLE 1 Results of simultaneous removal of sulfur dioxide and nitrogen oxides in example 1 and comparative examples the the concentration concentration the molar of SO.sub.2 at the the average of NOx at the the average concentration ratio inlet removal rate inlet removal Name of SO.sub.2 and NOx (mg/m.sup.3) of SO.sub.2 (mg/m.sup.3) rate of NOx Example 1 (0.76~1.06):1 2700~3600 99.9% 1680~2300 77.5% Example 2 0.76:1 2850~3050 99.9% 2150~2230 85.4% Example 3 1.06:1 2930~3000 99.5% 1680~2000 81.0% Example 4 0.9:1 2700~3600 99.9% 1800~2300 75.4% Comparative (0.66~0.76):1 2500~3450 99.9% 2250~2650 68.1% Example 1 Comparative (1.06~1.56):1 3000~3600 97.0% 1000~1750 65.2% Example 2

[0072] According to table 1, when the molar concentration ratio of SO.sub.2 and NO.sub.x is set to (0.76 1.06): 1, the average SO.sub.2 removal rate of the system reaches ˜100%, and the average NO.sub.x removal rate reaches >76%, which significantly improves the synchronous removal efficiency. When the ratio is greater than or less than the range, the NO.sub.x removal rate of the system decreases.

Example 5

[0073] The invention verifies the mechanism of simultaneous removal of sulfur dioxide and nitrogen oxides from flue gas. In this example, a series of BFs (3 BFs)were settled up, and parallelly operated, in which R1 is the simultaneous removal BF, R2 is the denitrification BF, and R3 is the desulfurization BF.

[0074] The simulated flue gas containing nitrogen oxides and sulfur dioxide is introduced into the BFs respectively for treatment under aerobic environment. The microbial flora has the functions of nitrification, denitrification, sulfidation and desulfurization, in which nitrification and denitrification are the main mechanisms for removing nitrogen oxides, and sulfidation is the main mechanism for removing sulfur dioxide.

[0075] The invention studies the reaction mechanism of nitric acid and sulfuric acid produced by oxidation of nitrogen oxide and sulfur dioxide with or without microbial mediation under aerobic conditions, as well as the main microbial community types that mediate the reaction.

[0076] By monitoring the concentration of sulfur dioxide, nitrogen dioxide and nitric oxide in the inlet and outlet gas of the reactor, the concentration of nitrate and sulfate in the circulating nutrient solution of the reactor and the pH value, the reaction mechanism of nitric acid and sulfuric acid produced by the oxidation of nitrogen oxides and sulfur dioxide mediated by microorganisms was studied. Then, high-throughput sequencing technology was used to study the microbial molecular mechanisms of simultaneous and separate removal of NO.sub.x and SO.sub.2 from simulated flue gas.

[0077] 1) Study on BF R1

[0078] In R1, the average outlet gas concentration of SO.sub.2 is kept at less than 100 mg/m.sup.3, the concentration of NO.sub.x is between160 to 620 mg/m.sup.3, including 108-463 mg/m.sup.3 NO and 22-187 mg/m.sup.3 NO.sub.2. Among them, the concentration of SO.sub.2 is far lower than the limit value of SO.sub.2 emission concentration (400 mg/m.sup.3) in China's boiler air pollutant emission standard (GB 13271-2014), which meets the emission requirements.

[0079] After the third cycle of stable operation of the reactor, the removal of SO.sub.2 and NO.sub.x in R1 showed a significant correlation (r.sup.2=0.33, p<0.05) during the third to seventh cycle, and the molar ratio of synergistic removal was 1.06:1 (Formula 1). However, the concentrations of SO.sub.4.sup.2− and NO.sub.3.sup.− in the nutrient solution of R1 showed different increasing trends:

[0080] a) at the initial stage (day 2-4 of the 3rd cycle), SO.sub.4.sup.2− and NO.sub.3.sup.− in R1 increased linearly;

[0081] b) from day 4 to day 7, the growth of SO.sub.4.sup.2− and NO.sub.3.sup.− slowed down or even stopped;

[0082] c) the concentration of SO.sub.4.sup.2− and NO.sub.3.sup.− increased in S-form after about 20% nutrient solution supplement on the 7th day, and accumulated to 23.07 g/L and 15.93 g/L respectively before complete nutrient solution replacement (day 12-14 of the 3rd cycle). The concentrations of SO.sub.4.sup.2− and NO.sub.3.sup.− in the nutrient solution were highly significantly correlated (r.sup.2=0.87, p<0.001), showing a synergistic effect. The molar concentration ratio of SO.sub.4.sup.2− and NO.sub.3.sup.− in the solution was 1.30:1, accounting for 81.0% and 81.7% of the total amount of N and S eliminated from the gas, respectively.

[0083] A portion (about 15%) of SO.sub.4.sup.2− and NO.sub.3.sup.− may be retained in the packings' pores by adsorption, which also leads to the emergence of plateau period and the rapid recovery of SO.sub.4.sup.2− and NO.sub.3.sup.− concentration after the nutrient solution supplement. However, compared with our study of simultaneous removal of SO.sub.2 and NO.sub.x at low load (1500˜2700 mg/m.sup.3 and 950˜1700 mg/m.sup.3 respectively), the concentration of NO.sub.3.sup.− in the solution was significantly higher (77.8% in low load solution, p<0.05), and the relative abundance of denitrifying microorganisms Pseudomonas and Rhodococcus decreased significantly (Pseudomonas decreased from 52.7% to 1.0%, Rhodococcus decreased from 19.2% to 0.6%), while the relative abundances of nitrifying microorganisms, such as Arthrobacter, Nitrospira, Flavobacterium and Hypomicrobium increased to 1%˜2% of the total microbial abundances, indicating that the nitrogen oxide removal reaction reduced the denitrification, but increased the nitrogen oxide oxidation.

[0084] In the reaction system of the invention, there is a denitrifying nitrogen removal reaction due to the existence of denitrifying microorganisms.

10e.sup.−+2NO.sub.3.sup.−+12H.sup.+.fwdarw.N.sub.2+6H.sub.2O   Formula 1

[0085] The concentration of SO.sub.4.sup.2− was significantly lower (p<0.05) than that of low load solution (84.8%). The appearance of desulfurizing microorganism Paenibacillus indicated that part of SO.sub.4.sup.2− entering the solution was utilized by microorganisms, reduced to sulfur and stored in cells, which was also consistent with the sulfur color on the surface of packings. Therefore, in the reaction system of the invention, there is a sulfate reduction reaction:

##STR00001##

[0086] Therefore, under the microbial catalytic system of the invention, the simultaneous removal reaction of nitrogen oxide and sulfur dioxide is carried out according to the reaction formula 3

##STR00002##

[0087] FIG. 2 is a comparison of the SO.sub.4.sup.2− concentration in the circulating nutrient solution of R1 and R2 in this example; FIG. 3 is a comparison of the NO.sub.3.sup.− and NO.sub.2.sup.− concentrations in the circulating nutrient solution of R1 and R3; FIG. 4 is a comparison of the pH values in R1, R2 and R3 in this example.

[0088] 2) Study on independently desulfurization R2 or denitrification R3

[0089] In the other two bioreactors, the SO.sub.2 emission concentration of R2 is 0-1151 mg/m.sup.3; the NO.sub.x emission concentration of R3 is 536˜810 mg/m.sup.3, including 275˜643 mg/m.sup.3 NO and 135˜422 mg/m.sup.3 NO.sub.2.

[0090] There was no significant difference in the inlet concentration between R1 with R2, or R1 with R3. The performance of R1, i.e. the removal rates of SO.sub.2 and NO.sub.x (99.9% and 77.5%) were significantly better than those of R2 (81.9%, SO.sub.2) or R3 (67.7%, NO.sub.x ) (p<0.05),

[0091] FIG. 5 shows the SO.sub.2 removal rate of R1 in example 5; FIG. 6 shows the removal rate of NO.sub.x of R1 in example 5; FIG. 7 shows the SO.sub.2 removal rate of R2 in example 5; FIG. 8 shows the NO.sub.x removal rate of R3 in example 5.

[0092] In the invention, the microorganism includes nitrifying microorganism, denitrifying microorganism and sulfurizing microorganism. Specific microbial species are nitrification or nitrite oxidation function, denitrification function, sulfurization function and desulfurization function. FIG. 9 shows the difference of microbial community level in R1, R2 and R3.

[0093] In FIG. 9, the microbial species with nitrification or nitrite oxidation function include Arthrobacter, Nitrospira, Flavobacterium, Pseudomonas, Rhodococcus, Ralstonia and Hypomicrobium, and the denitrification microbes include Pseudomonas, Rhodococcus, Bacillus, Acinetobacter, Candida Acinetobacter, Zoogloea and Hypomicrobium; the microbial species with sulfurization function include Dietzia, Burkholderia, Mycobacterium, Pseudomonas, Rhodococcus, and the desulfurization microbes include Paenibacillus.

[0094] Table 2 shows the comparison of removal efficiency of different BFs.

TABLE-US-00002 TABLE 2 Comparison of removal efficiency of different BFs Outlet SO.sub.2 Outlet NOx Inlet SO.sub.2 SO.sub.2 Removal Inlet NOx NOx Removal BF (mg/m.sup.3) (mg/m.sup.3) Rate (mg/m.sup.3) (mg/m.sup.3) Rate R1 2700~3300 0~100 99.9% 1700~2300 160~615 77.5% R2 2500~3100 0~1151 81.9% — — — R3 — — — 1900~2650 488~810 67.7%

[0095] The present invention and its examples have been described above, and the description is not restrictive. Therefore, it shall be within the protection scope of the invention if ordinary technical personnel in the art are inspired by the invention to design a structure and an example similar to the technical solution without creatively departing from the creative purpose of the invention.