CN101279185B - Gas phase oxidation-liquid phase reduction method for absorbing and removing nitrous oxides in exhaust air - Google Patents
Gas phase oxidation-liquid phase reduction method for absorbing and removing nitrous oxides in exhaust air Download PDFInfo
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- CN101279185B CN101279185B CN2007103072406A CN200710307240A CN101279185B CN 101279185 B CN101279185 B CN 101279185B CN 2007103072406 A CN2007103072406 A CN 2007103072406A CN 200710307240 A CN200710307240 A CN 200710307240A CN 101279185 B CN101279185 B CN 101279185B
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- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 claims description 2
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- IMNIMPAHZVJRPE-UHFFFAOYSA-N triethylenediamine Chemical compound C1CN2CCN1CC2 IMNIMPAHZVJRPE-UHFFFAOYSA-N 0.000 description 4
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Abstract
The invention provides a gas-phase oxidation/liquid-phase reduction method for absorbing and removing NOx. The method utilizes O2 in waste gases as an oxidizer; after be processed by non-catalyst oxidization or catalyzed oxidation by modified active carbon materials, NOx waste gas with low oxidization degree reacts with an alkaline reducing solution fully to remove NOx. After going through multi-grade oxidization, reduction and absorption, the NOx in waste gases can fully meet the emission standard. The method of the invention has the advantages of being able to realize up-to-standard emission of NOx waste gas with low oxidization degree, simple technique, small cost and high removing efficiency.
Description
(1) technical field
The present invention relates to the method for a kind of gas phase oxidation-liquid phase reduction absorbing and removing nitrogen oxides of exhaust gas (NOx).
(2) background technology
Have nitrated, nitrosation reaction in the production processes such as fine chemistry industry process such as pharmaceutical factory, NOx content is higher in the combustion gas, forms " Huanglong " phenomenon, is one of important pollutant that causes at present atmosphere pollution.NOx not only forms photochemical fog in atmosphere, form acid rain, acid mist, also closely related with the destruction of ozone layer, and also the serious harm mankind's is healthy, therefore the important topic of environmental area is not only in the processing of NOx, also is the inevitable requirement that realizes China's sustainable economic development.The removal methods of nitrogen oxide mainly is divided into dry method and wet method two classes: the SCR method is widely used in Europe, the United States in the dry method, but it requires flue-gas temperature generally more than 300 ℃, is fit to the processing of coal-fired flue-gas; And wet method relatively is fit to the industrial production treatment of waste gas, to oxidizability (NO
2/ (NO
2+ NO) concentration ratio) high NOx exhaust-gas treatment effect is better.
The almost discharging at normal temperatures and pressures of NOx waste gas generally contains steam, oxygen etc. in the industrial production, and wherein oxygen content is higher, and is identical with air sometimes, is not suitable for using the SCR method and handles.Simultaneously, the main component among the NOx is NO, and oxidizability is very low ,～10～20%, because the low solubility of NO in absorption liquids such as water, alkali lye makes conventional wet absorption liquid very low to this type of NOx removal efficiency, be difficult to reach emission request.At present, the liquid Absorption Study shows that to reduce the denitration effect of absorption process better, when the off-gas oxidizing degree greater than 50% the time, can obtain denitration efficiency [Yang Yang nitrogen oxide emission-reduction technology and denitrating flue gas engineering 2007 metallurgical industry publishing houses more than 90%], therefore utilize oxidant that NO in the waste gas is oxidized to NO
2, improving the off-gas oxidizing degree is one of effective way that removes this type of NOx.
Patent 200610012414.1,200610051721.0,200710052129.7,200610012525.2,200610051737.1,200510062185.X, 200710067082.1,200710061515.2 Deng utilizing chloric strong oxidant (sodium chlorite, clorox etc.), hydrogen peroxide, ozone oxidation and photochemical catalytic oxidation mode are carried out oxidation to the NO in the waste gas, these mode of oxidizing separately or be used in combination the bigger NOx removal efficiency that improved, but owing to used extra oxidant, investment, running cost strengthens, in, small enterprise uses difficulty and strengthens, and there is certain problem in the photochemical catalytic oxidation application when NOx exhaust-gas treatment amount is big; Patent 01105698.3,02110646.0 is an oxidant with airborne oxygen, triethylenediamine cobalt solution liquid phase oxidation NO, can realize the qualified discharge of NOx, but the use of triethylenediamine cobalt will increase the exhaust-gas treatment cost, and aspect Engineering Control, may also have some problems in the commercial plant; Patent 200510062296.0,200510062297.5 is passed through to Fe
IIAdd the complexed absorption of effective additive realization in the EDTA solution, when the reaction time is 20-30s, can make the NOx removal efficiency reach 65-95% NOx, but the increasing of the cost input of absorption liquid, and absorb back component of effluent complexity, more difficult.
Young Sun Mok[Absorption-reduction technique assisted by ozoneinjection and sodium sulfidefor NOx removal from exhaust gas, ChemicalEngineering Journal, 2006] with 300ppm NO through ozone oxidation, Na
2After the aqueous slkali of S absorbed, removal efficiency can reach more than 95%; CN101036851A will contain the waste gas of NOx after ozone oxidation, polyethylene glycol absorb, and almost reach 100% removal efficiency.But ozone generating-device investment is big, cost is higher, in, that small enterprise uses difficulty is bigger.[Oxidation of NOinto NO such as Isao Mochida
2Over Active Carbon Fibers, Energy﹠amp; Fuels 1994,8:1341-1344] utilize the NACF (ACF) of modification at room temperature to carry out the oxidation experiment of NO (400ppm).Conversion ratio is 73% under 25 ℃ of drying conditions, but the conversion of NO that had severe inhibition of steam in the waste gas, conversion ratio only is 21% under the saturation vapour, the existence of high-load steam has seriously hindered the application of ACF catalytic oxidation NO in the visible industrial waste gas.
Therefore, how to remove nitrogen oxides from exhaust gas low-costly and efficiently, prior art still has improved space.
(3) summary of the invention
The object of the invention provides a kind of method of the suboxides degree NOx nitrogen oxides of exhaust gas that contains saturation vapour of gas phase oxidation-liquid phase reduction absorbing and removing industrial discharge, has guaranteed to contain the reasonable discharging of NOx waste gas under situation cheaply.
The technical solution used in the present invention is:
A kind of method of gas phase oxidation-liquid phase reduction absorbing and removing nitrogen oxides of exhaust gas, described nitrogen oxide are NO and NO
2Mixture, described method is as follows: the waste gas of nitrogen-containing oxide through non-catalytic oxidation or catalytic oxidation, is made NO carry out gaseous oxidation and is converted into NO
2After, the liquid-phase reduction through the reproducibility absorption liquid absorbs again, removes the oxynitrides in the waste gas; The off-gas oxidizing degree of described nitrogen-containing oxide is lower than 50%; Can contain in the described waste gas or moisture vapor not; Described non-catalytic oxidation or catalytic oxidation process use in the waste gas contained oxygen itself to be oxidant; Described reproducibility absorption liquid is the mixed aqueous solution of reducing agent and alkali, and described reducing agent is one of following: 1. urea, 2. vulcanized sodium, 3. sodium sulfite, 4. sodium thiosulfate, 5. ammonium sulfite; Described alkali is NaOH or potassium hydroxide; In the described mixed aqueous solution, the mass content of reducing agent is 0.02～20%, the mass content of alkali is 0.01～20%.
Described non-catalytic oxidation step is as follows: under the normal temperature, the waste gas of nitrogen-containing oxide is fed in the oxidizing tower, utilize oxygen in the waste gas with the NO oxidation.
Described catalytic oxidation step is as follows: as catalyst, with steam waste gas is heated to 20～100 ℃ with the active carbon of fixed-bed oxidation reactor filling modification or NACF, the oxygen in the waste gas is reacted with NO; The active carbon of described modification is prepared by following method: with the aqueous slkali soaking 18～24h of active carbon with 0.5～2.0M; be washed till neutrality with deionized water; 400～1000 ℃ of roasting 1h (being preferably 600～800 ℃) under dry back nitrogen or the hydrogen shield; heating rate 10K/min obtains the active carbon of modification.
Described liquid-phase reduction is absorbed in the bubble tower and carries out, and waste gas enters at the bottom of by tower, by bubbling and reproducibility absorption liquid reaction back, discharged by cat head.
Perhaps, described liquid-phase reduction is absorbed in the packed tower and carries out, waste gas enters at the bottom of by tower, with the reverse haptoreaction of reproducibility absorption liquid after, discharge by cat head.Used filler typically refers to granular pattern filler or structured packing in the packed tower, and the granular pattern filler mainly is meant Pall ring, Raschig ring, arc saddle, intalox saddle, and material can be plastics or pottery; Structured packing mainly is meant screen waviness packings or grid packing, and the screen waviness packings material can be plastics or carbon fiber, and grid packing can be plastics or wood.
Described gaseous oxidation and liquid-phase reduction absorb and can hocket.For realizing the qualified discharge of NOx, gaseous oxidation and liquid-phase reduction absorb the reaction of high order that can hocket, and the order of reaction is determined by actual conditions, generally adopts 1～4 grade.Also can earlier NOx be absorbed after 1 grade of oxidation again under the equal conditions, but this moment, the oxidizing tower volume was bigger, catalyst amount is big, does not generally adopt.For common industrial waste gas, general 2～3 grades of processing can reach the emission request of NOx.
After the present invention carries out gaseous oxidation by the suboxides degree NOx that adopts oxidant cheaply will contain saturation vapour at normal temperatures and pressures, the oxidizability of NOx can reach more than 50% in the waste gas, absorbs through liquid-phase reduction, can realize the qualified discharge of NOx, and technology is simple, and is easy to operate.
Characteristics of the present invention are:
(1) adopt oxidation technology that unmanageable NO is oxidized to tractable NO
2, adopt reproducibility alkali lye to handle NOx, guarantee the waste gas qualified discharge;
(2) make full use of the oxygen in the waste gas, need not to use in addition oxidant, reduced the waste gas pollution control and treatment cost;
(3) use the modified activated carbon material to be catalyst, the catalysqt deactivation of effectively having avoided the water vapour in the waste gas to cause has improved oxidation effectiveness;
(4) alkali lye and reducing agent synergy has been accelerated the NOx absorption rate, reduces equipment size, reduces equipment investment;
(5) reducing agent is reduced to harmless nitrogen with NOx, reduced the consumption of alkali, reduced the processing cost that absorbs waste liquid on the one hand, reduced the concentration of the salt that forms in the absorption liquid on the other hand, prevented that effectively packed absorber from may stop up because of salting out the absorption tower that causes;
(6) carry out exhaust-gas treatment at normal temperatures and pressures, cut down the consumption of energy;
(7) can before the absorption waste liquid goes wastewater treatment, the salt recovery system be set,, reduce the waste gas pollution control and treatment cost, also reduce the treating waste liquid expense to reclaim salts such as useful sodium nitrate and natrium nitrosum.
Beneficial effect of the present invention is mainly reflected in: can show the qualified discharge of suboxides degree NOx waste gas under low-cost condition, and technology is simple; Make full use of the oxygen in the waste gas, need not additionally to add oxidant, the NO that will be difficult to handle is converted into easy-to-handle NO
2, the efficient height.
(4) description of drawings
Fig. 1 is the flow chart of the method for the embodiment of the invention 1; Wherein 1 for containing NOx waste gas, and 2 is sample tap, and 3 is oxidizing tower, and 4 is the absorption tower, and 5 are the reduction absorption liquid, and 6 is exhaust port, and 7 is discard solution discharge port.
Fig. 2 is the flow chart of the method for the embodiment of the invention 4; Wherein 1 for containing NOx waste gas, and 2 is sample tap, and 8 is beds, and 9 is oxidation reactor, and 4 is the absorption tower, and 5 are the reduction absorption liquid, and 6 is exhaust port, and 7 is discard solution discharge port.
Fig. 3 is the flow chart of the method for the embodiment of the invention 10; Wherein 1 for containing NOx waste gas, and 2 is sample tap, and 3 is oxidizing tower, and 10 is packed tower, and 11 is reservoir, and 12 is fresh reproducibility absorption liquid inlet, and 6 is exhaust port, and 7 is discard solution discharge port.
(5) specific embodiment
The present invention is described further below in conjunction with specific embodiment, but protection scope of the present invention is not limited in this:
Embodiment 1:
NOx waste gas feeds oxidizing tower 3 through O
2After the oxidation, enter the absorption tower by 4 bottoms, absorption tower and reduce absorption reaction by bubbling and absorption liquid 5, reaction back gas is discharged by cat head, and waste gas absorbs processing through tertiary oxidation-reduction, and tail gas is through exhaust port 6 emptyings.Oxidizing tower 3 diameter 40mm, high 300mm, total oxidation volume 2.0L, bubble absorbing tower 4 diameter 40mm, high 600mm.Waste gas contains 1907ppmvNOx, saturation vapour and about 20% O under the normal temperature
2, reduction absorption liquid 5 additions are 200ml, its composition is 4% (W/W) NaOH and 8% (W/W) CO (NH
2)
2Gas flow: 0.08m
3/ h, normal temperature and pressure be reaction down, import and export NOx concentration by flue gas analyzer (testo350-XL) in sample tap 2 check and analysis.
Embodiment 2:
Reactor and operating condition contain NOx1330ppmv with embodiment 1 in the waste gas, saturation vapour and about 20% O under the normal temperature
2, reduction absorption liquid 5 additions are 200ml, its composition is 4% (W/W) NaOH and 8% (W/W) CO (NH
2)
2, gas flow: 0.08m
3/ h, normal temperature and pressure is reaction down, and import and export NOx concentration is by flue gas analyzer (testo 350-XL) check and analysis.
Embodiment 3:
Waste gas at oxidizing tower 3 through O
24 reactions of the laggard absorption tower of oxidation absorb through stair oxidation, reduction and to handle, absorb back tail gas after testing, handle the back emptying.Oxidizing tower 3 diameters are 80mm, and height is 600mm (oxidation volume 3.0L), bubble absorbing tower 4 diameter 40mm, high 600mm.Contain 1785ppmvNOx in the waste gas, saturation vapour and about 20% O under the normal temperature
2, reduction absorption liquid 5 additions are 300ml, contain 1% (W/W) NaOH and 8% (W/W) CO (NH
2)
2, gas flow: 0.08m
3/ h, normal temperature and pressure be reaction down, import and export NOx concentration by flue gas analyzer (testo350-XL) in sample tap 2 check and analysis.
Embodiment 4:
Fixed-bed oxidation reactor 9 filling modified activated carbons are heated to the waste gas 1 of suitable temperature through steam, by the O in fixed-bed oxidation reactor 9 and the waste gas
2Oxidation reaction takes place, and reaction back gas 4 is reduced absorption through the absorption tower, waste gas after secondary catalysis, oxidation by exhaust port 6 emptyings.Oxidation reactor 9 internal diameter Φ 9.0mm, high 140mm, bubble absorbing tower 4 diameter 40mm, high 600mm.The modified activated carbon preparation method: commercial active carbon is 20～30 orders through grinding screening, after the KOH of 1M solution soaks 24h, is washed till neutrality with deionized water, and dry back is in H in baking oven
2Protection is 800 ℃ of roasting 1h in resistance furnace down, heating rate 10K/min.
The waste gas main component is: 845ppmvNOx, 20 ℃ of following saturated steams, 20% left and right sides O
2Oxidation reactor 9 temperature: 50 ℃, absorption liquid 5 additions are 300ml, contain 0.5% (W/W) NaOH and 2% (W/W) CO (NH
2)
2, gas flow: 0.12m
3/ h, in sample tap 2 check and analysis, wherein waste gas NOx oxidizability after oxidation reactor 9 oxidations is 50% to import and export NOx concentration by flue gas analyzer (testo 350-XL).
Embodiment 5:
The waste gas that contains saturated steam (20 ℃) utilizes modified activated carbon and airborne O by integration fixed-bed oxidation reactor 9 after steam is heated to uniform temperature
2Oxidation reaction takes place, utilize flue gas analyzer (testo 350-XL) constantly to detect oxidation import and export NOx change in concentration and reach stable state until reaction, outlet waste gas is through exhaust port 6 emptyings.Oxidation reactor 9 internal diameter Φ 9.0mm, high 140mm, modified activated carbon quality 4.5g, reaction temperature is 50 ℃, and the reaction time is 2s, and the preparation method of modified activated carbon is with embodiment 4.
Embodiment 6:
Reactor and operating condition are carried out the one-level catalytic oxidization-reduction with NOx waste gas 1 and are absorbed processing with embodiment 4.Contain NOx 741ppmv in the waste gas, 20 ℃ of saturated steams and 20% left and right sides O
2Waste gas is by modified activated carbon and O
2The gas cyaniding degree is 52% after the generation oxidation reaction, and reduction absorption liquid 5 additions are 300ml, contain 0.5% (W/W) NaOH and 2% (W/W) Na
2SO
3
Embodiment 7:
Reactor and operating condition are carried out the one-level catalytic oxidization-reduction with NOx waste gas 1 and are absorbed processing with embodiment 4.Contain NOx 662ppmv in the waste gas, 20 ℃ of saturated steams and 20% left and right sides O
2Waste gas is by modified activated carbon and O
2The gas cyaniding degree is 52% after the generation oxidation reaction, and reduction absorption liquid 5 additions are 300ml, contain 0.5% (W/W) NaOH and 1% (W/W) Na
2S
2O
3
Embodiment 8:
Reactor and operating condition are carried out the one-level catalytic oxidization-reduction with NOx waste gas 1 and are absorbed processing with embodiment 4.Contain NOx 771ppmv in the waste gas, 20 ℃ of saturated steams and 20% left and right sides O
2Waste gas is by modified activated carbon and O
2The gas cyaniding degree is 5 1% after the generation oxidation reaction, and reduction absorption liquid 5 additions are 300ml, contain 0.5% (W/W) NaOH and 1% (W/W) Na
2S.
Embodiment 9:
Reactor and operating condition are carried out the secondary catalytic oxidization-reduction with NOx waste gas 1 and are absorbed processing with embodiment 4.Contain NOx 783ppmv in the waste gas, 20 ℃ of saturated steams and 20% left and right sides O
2Waste gas is by modified activated carbon and O
2The gas cyaniding degree is 50% after the generation oxidation reaction, and reduction absorption liquid 5 additions are 300ml, and composition is 0.5% (W/W) NaOH and 2% (W/W) (NH
4)
2SO
3
Embodiment 10:
Under the normal temperature and pressure, waste gas is through entering packed tower 10 at the bottom of by tower after oxidizing tower 3 oxidations (oxidation volume 3.05L), absorption liquid is sprayed into tower by tower top by circulating pump, carry out after backward reaction absorbs with NOx, enter reservoir 11 by the discharge of tower bottom, discharged by cat head through the gas after absorbing, waste gas carries out secondary oxidation, reduction absorption reaction, and tail gas is through exhaust port 6 emptyings.Oxidizing tower 3 diameter 900mm, high 1100mm, packed tower 10 diameter 400mm, high 1500mm, filler floor height 750mm wherein, filler are Dg25 plastics Pall ring (Ningbo great abundant chemical industry Co., Ltd).Contain 1540ppmvNOx in the waste gas, saturation vapour and 20% left and right sides O under the normal temperature
2, absorption liquid contains 1% (W/W) NaOH and 6% (W/W) CO (NH
2)
2Gas flow: 0.5m
3/ h, liquid spraying density 15m
3/ m
2H, import and export NOx concentration is by flue gas analyzer (testo 350-XL) check and analysis.
The treatment effect of NOx sees Table 1 under each embodiment different condition.
Table 1: the treatment effect of NOx under the different condition
| Numbering | Experiment process | Import | Outlet | Removal efficiency or conversion ratio/% | ||
| NOx /ppmv | Oxidizability/% | NOx /ppmv | Oxidizability/% | |||
| 1 | The oxidation of tertiary oxidation tower, three grades of absorptions | 1907 | 20.1 | 429 | 6.85 | 77.5 |
| 2 | The oxidation of tertiary oxidation tower, three grades of absorptions | 1330 | 14.8 | 410 | 4.49 | 69.2 |
| 3 | One-level absorbs after the oxidation of stair oxidation tower | 1785 | 18.2 | 372 | 20.2 | 79.0 |
| 4 | Secondary catalytic oxidation-urea alkali lye absorbs | 845 | 4.14 | 160 | 16.5 | 81.1 |
| 5 | The modified activated carbon catalytic oxidation | 740 | 5.00 | 337 | 54.0 | 55.0 |
| 6 | Sodium sulfite alkali lye absorbs behind the catalytic oxidation | 741 | 6.48 | 263 | 25.5 | 64.5 |
| 7 | The thiosulfuric acid soda lye absorbs behind the catalytic oxidation | 662 | 4.83 | 279 | 6.10 | 58.0 |
| 8 | Catalytic oxidation after cure soda lye absorbs | 771 | 3.58 | 241 | 6.64 | 69.0 |
| 9 | Secondary catalytic oxidation-ammonium sulfite alkali lye absorbs | 783 | 4.47 | 201 | 5.47 | 74.3 |
| 10 | Secondary oxidation tower oxidation-absorption | 1540 | 22.5 | 210 | 37.8 | 86.4 |
Annotate: numbering is corresponding with the embodiment sequence number in the table, and every group of test concrete operations step seen each related embodiment; Among the embodiment 1～9, except that embodiment 4, liquid absorbs and all carries out in bubble absorbing tower, and embodiment 10 absorption tests are carried out in packed tower.
Claims (4)
1. the method for a gas phase oxidation-liquid phase reduction absorbing and removing nitrogen oxides of exhaust gas, described nitrogen oxide is NO and NO
2Mixture, described method is as follows: the waste gas of nitrogen-containing oxide through non-catalytic oxidation or catalytic oxidation, is made NO carry out gaseous oxidation and is converted into NO
2After, the liquid-phase reduction through the reproducibility absorption liquid absorbs again, removes nitrogen oxides from exhaust gas; Described reproducibility absorption liquid is the mixed aqueous solution of reducing agent and alkali, and described reducing agent is one of following: 1. urea, 2. vulcanized sodium, 3. sodium sulfite, 4. sodium thiosulfate, 5. ammonium sulfite; Described alkali is NaOH or potassium hydroxide; In the described mixed aqueous solution, the mass content of reducing agent is 0.02～20%, the mass content of alkali is 0.01～20%; Described non-catalytic oxidation step is as follows: under the normal temperature, the waste gas of nitrogen-containing oxide is fed in the oxidizing tower, utilize oxygen in the waste gas with the NO oxidation; Described catalytic oxidation step is as follows: as catalyst, with steam waste gas is heated to 20～100 ℃ with the active carbon of fixed-bed oxidation reactor filling modification or NACF, the oxygen in the waste gas is reacted with NO; The active carbon of described modification is prepared by following method: with the aqueous slkali soaking 18～24h of active carbon with 0.5～2.0M, be washed till neutrality with deionized water, 400～1000 ℃ of roasting 1h under dry back nitrogen or the hydrogen shield obtain the active carbon of modification.
2. the method for claim 1, it is characterized in that: described liquid-phase reduction is absorbed in the bubble tower and carries out, and waste gas enters at the bottom of by tower, by bubbling and reproducibility absorption liquid reaction back, discharged by cat head.
3. the method for claim 1, it is characterized in that: described liquid-phase reduction is absorbed in the packed tower and carries out, waste gas enters at the bottom of by tower, with the reverse haptoreaction of reproducibility absorption liquid after, discharge by cat head.
4. the method for claim 1 is characterized in that: described gaseous oxidation and liquid-phase reduction absorb and hocket.
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