CN113117493A - Method for flue gas desulfurization and denitration by using mixed reducing agent - Google Patents
Method for flue gas desulfurization and denitration by using mixed reducing agent Download PDFInfo
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- CN113117493A CN113117493A CN201911406654.3A CN201911406654A CN113117493A CN 113117493 A CN113117493 A CN 113117493A CN 201911406654 A CN201911406654 A CN 201911406654A CN 113117493 A CN113117493 A CN 113117493A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/75—Multi-step processes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/54—Nitrogen compounds
- B01D53/56—Nitrogen oxides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/60—Simultaneously removing sulfur oxides and nitrogen oxides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
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- B01D2251/10—Oxidants
- B01D2251/106—Peroxides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2251/00—Reactants
- B01D2251/20—Reductants
- B01D2251/206—Ammonium compounds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D2251/00—Reactants
- B01D2251/30—Alkali metal compounds
- B01D2251/304—Alkali metal compounds of sodium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/02—Other waste gases
- B01D2258/0283—Flue gases
Abstract
The invention discloses a method for performing flue gas desulfurization and denitrification by using a mixed reducing agent. Contacting a 15-35 wt% hydrogen peroxide aqueous solution with the pretreated flue gas in a flue gas pipeline to react to obtain flue gas I; introducing the flue gas I into an absorption tower, spraying absorbent dry powder and mixed reducing agent dry powder into the absorption tower, and contacting the absorbent dry powder and the mixed reducing agent dry powder with the flue gas I to perform desulfurization and denitrification reaction so as to form flue gas II; wherein the mixed reducing agent is a mixture of sodium sulfite, sodium bisulfite and ammonium bisulfite; the molar ratio of the sodium sulfite to the sodium bisulfite to the ammonium bisulfite is (1.3-2.9) to (0.9-1.1) to 1; and the molar ratio of nitric oxide contained in the pretreated flue gas introduced in unit time to tetravalent sulfur element contained in the mixed reducing agent dry powder added in unit time is 1: 3.0-4.5. The invention has high desulfurization efficiency and denitration efficiency.
Description
Technical Field
The invention relates to a method for performing flue gas desulfurization and denitrification by using a mixed reducing agent.
Background
The main pollution source of the current atmospheric environmental pollution is coal-fired flue gas which is discharged in large quantity. The coal-fired flue gas contains a large amount of harmful gases of nitrogen oxides such as sulfur dioxide, nitric oxide and the like. Among them, nitrogen oxides are highly harmful. How to effectively remove sulfur dioxide and nitrogen oxides in flue gas, especially effective removal of NO is the focus of research.
The traditional flue gas treatment technical method with single function (single desulfurization or single denitration), such as SCR, SNCR, SDA and the like, has already been popularized and applied to a certain extent. However, how to realize integrated desulfurization and denitrification is more and more emphasized. If only simply combine individual desulfurization technique and individual denitration technique, not only can increase equipment area, still can increase investment running cost. And the denitration efficiency is still to be improved. In addition, some denitration technologies also use ammonia gas, so that the ammonia escape phenomenon exists and certain danger exists.
CN106422772A discloses an aqueous ammonia gasification system for SCR flue gas denitration, is used for aqueous ammonia gasification and ammonia injection process of SCR flue gas denitration technology. The system comprises an ammonia water tank, an ammonia water pump, an ammonia water metering control device and a plurality of ammonia water spray guns which are connected in sequence. During operation, the aqueous ammonia in the aqueous ammonia groove is sent to aqueous ammonia measurement controlling means after through the ammonia water pump pressure boost, send to the aqueous ammonia spray gun after the flow and the pressure of aqueous ammonia are adjusted to aqueous ammonia measurement controlling means, aqueous ammonia in the aqueous ammonia spray gun sprays into former flue gas flue with the atomizing form under the promotion of compressed air in the compressed air jar, under the heat effect of the former flue gas of denitration, the aqueous ammonia after the atomizing gasifies completely, after the aqueous ammonia after the gasification mixes with the former flue gas of denitration, provides ammonia flue gas mist for the denitration reaction. Although this patent document hardly causes the ammonia slip phenomenon, it is difficult to ensure the degree of mixing with the flue gas after the ammonia water injected in this patent document is gasified, and the denitration efficiency and the utilization rate of the reducing agent are affected.
CN102997697A discloses a sinter waste heat utilization process based on sintering flue gas purification, which provides that high-temperature hot sinter is used for directly heating desulfurized sintering flue gas to enable the temperature of the sintering flue gas to reach the window temperature of selective catalytic reduction above 380 ℃, and then SCR denitration is carried out. The process solves the problems that the sintering flue gas temperature is low and the temperature of an SCR denitration window cannot be met, but the problems of high energy consumption, high catalyst cost, easy catalyst poisoning and the like still exist in the subsequent sintering flue gas SCR denitration process.
CN108722134A discloses a flue gas desulfurization and denitrification process, which proposes to use a flue gas from a combustion deviceThe flue gas is mixed with a denitrifier for denitration, the main component of the denitrifier is reduced sulfur, and a product in the process of desulfurization and denitration is N2And SO2And then SO generated by absorption of a desulfurizing agent is utilized2. The process increases SO in the flue gas2The content of (b) leads to an increased desulfurization burden, resulting in an increased cost.
CN104941430B discloses a method for oxidizing NO in flue gas by combining a gas-phase oxidizing agent and a liquid-phase oxidizing agent, wherein the gas-phase oxidizing agent is ozone, and the liquid-phase oxidizing agent is hydrogen peroxide; then the alkaline absorbent is used for carrying out the integrated absorption and removal of sulfur dioxide and nitrogen oxide. In the process, two oxidants are respectively sprayed to ensure the oxidation effect of NO, but ozone is used as the oxidant, and the oxidant has many defects, such as high price, difficult transportation, strict requirements on smoke dust amount of flue gas, complex process, certain danger in the operation process and the like. In addition, the oxidation efficiency and denitration efficiency in the method are still to be improved.
Disclosure of Invention
The invention aims to provide a method for performing flue gas desulfurization and denitrification by using a mixed reducing agent. According to the invention, hydrogen peroxide is used as an oxidant, absorbent dry powder (calcium hydroxide dry powder and/or calcium oxide dry powder) and mixed reducing agent dry powder (a mixture of sodium sulfite, sodium bisulfite and ammonium bisulfite) are used for integrated desulfurization and denitrification of flue gas in an absorption tower, and the denitrification efficiency is further improved.
The invention adopts the following technical scheme to achieve the aim.
The invention provides a method for performing flue gas desulfurization and denitrification by using a mixed reducing agent, which comprises the following steps of:
(1) contacting a 15-35 wt% hydrogen peroxide aqueous solution with the pretreated flue gas in a flue gas pipeline to react to obtain flue gas I;
(2) introducing the flue gas I into an absorption tower, spraying absorbent dry powder and mixed reducing agent dry powder into the absorption tower, and contacting the absorbent dry powder and the mixed reducing agent dry powder with the flue gas I to perform desulfurization and denitrification reaction so as to form flue gas II;
wherein the mixed reducing agent is a mixture of sodium sulfite, sodium bisulfite and ammonium bisulfite; the molar ratio of the sodium sulfite to the sodium bisulfite to the ammonium bisulfite is (1.3-2.9) to (0.9-1.1) to 1; and the molar ratio of nitric oxide contained in the pretreated flue gas introduced per unit time in the step (1) to tetravalent sulfur element contained in the mixed reducing agent dry powder added per unit time in the step (2) is 1: 3.0-4.5.
According to the method provided by the invention, preferably, the molar ratio of nitric oxide contained in the pretreated flue gas introduced per unit time in the step (1) to tetravalent sulfur element contained in the mixed reducing agent dry powder added per unit time in the step (2) is 1: 3.2-4.2.
According to the method, the molar ratio of the sodium sulfite, the sodium bisulfite and the ammonium bisulfite in the mixed reducing agent is preferably (1.5-2.5): 1:1.
According to the method of the present invention, preferably, in the step (2), the absorbent dry powder is one or two selected from calcium oxide dry powder and calcium hydroxide dry powder; and the molar ratio of the absorbent dry powder added per unit time in the step (2) to the sulfur dioxide contained in the pretreated flue gas introduced per unit time in the step (1) is a calcium-sulfur ratio which is 1.1-2.1: 1.
According to the method provided by the invention, preferably, in the step (2), the contact time of the absorbent dry powder and the mixed reducing agent dry powder with the flue gas I is 5-30 s; in the step (2), the flow speed of the flue gas I in the absorption tower is 1-8 m/s.
According to the method of the present invention, preferably, in the step (2), when the absorbent dry powder and the mixed reducing agent dry powder are sprayed into the absorption tower, water is sprayed into the absorption tower through the second spraying device, so as to humidify the absorbent dry powder and the mixed reducing agent dry powder; wherein the second spraying equipment is a humidifier.
According to the method of the invention, preferably, the nitric oxide contained in the pretreated flue gas introduced per unit time in the step (1) and the H in the aqueous hydrogen peroxide solution added per unit time2O2The molar ratio of (A) to (B) is 1: 1.1-4.1.
According to the method of the invention, preferably, in the step (1), the aqueous hydrogen peroxide solution is sprayed into the flue gas pipeline through the first spraying device and is contacted with the pretreated flue gas to carry out oxidation reaction; wherein the first spraying equipment is an atomizing nozzle; the contact time of the aqueous hydrogen peroxide solution and the pretreated flue gas is 1-20 s.
According to the method provided by the invention, preferably, in the step (1), the flow speed of the pretreated flue gas in the flue gas pipeline is 5-15 m/s.
According to the method of the invention, preferably, in the step (1), the raw flue gas is pretreated by an electric precipitator to obtain pretreated flue gas; in the step (2), the absorption tower is a dense-phase dry tower.
The invention adopts hydrogen peroxide to oxidize NO in the flue gas into high-valence nitrogen oxide, and removes the nitrogen oxide and SO in an absorption tower (dense phase dry tower) by using mixed reducing agent dry powder (mixture of sodium sulfite, sodium bisulfite and ammonium bisulfite) and absorbent dry powder2Nitrogen, sodium sulfate, ammonium sulfate and calcium sulfate are generated, and secondary pollution is avoided. The desulfurization efficiency of the invention can reach 99.6%, and the denitration efficiency can reach more than 96%. Compared with a wet process, the method has the advantages that the water consumption is low, the by-product is a powdery product, the water consumption is reduced, the process steps of crystallizing and purifying the by-product can be saved, and the process cost is low.
Drawings
FIG. 1 is a schematic structural diagram of an integrated desulfurization and denitrification apparatus according to the present invention.
1-an absorbent bin; 2-sodium sulfite storage; 3-sodium bisulfite storage; 4-ammonium bisulfite storage; 5-a mixing agitator; 6-oxidant storage tank; 7-an atomizing nozzle; 8-an electric dust remover; 9-dense phase dry tower; 10-a humidifier; 11-bag dust collector; 12-ash bin; 13-chimney.
Detailed Description
The present invention will be further described with reference to the following specific examples, but the scope of the present invention is not limited thereto.
"wt%" of the present invention is a weight percentage.
The process comprises a pretreatment step, an oxidation reaction step and a desulfurization and denitrification reaction step. Optionally, a dust removal step and a recycling step are also included. The method is suitable for treating the flue gas containing sulfur dioxide and nitric oxide, such as coal-fired boilers, steel sintering machines, pellets, industrial kilns and the like. As described in detail below.
< pretreatment step >
And (3) pretreating the raw flue gas by an electric precipitator to obtain pretreated flue gas. According to an embodiment of the invention, the pretreatment is performed by a wet electrostatic precipitator. Through the pretreatment step, larger and tiny particles in the flue gas can be removed. The dust content in the original flue gas is 80-220 mg/Nm3Preferably 90 to 180mg/Nm3More preferably 100 to 160mg/Nm3. The dust content in the pretreated flue gas is 5-20 mg/Nm3Preferably 6 to 18mg/Nm3More preferably 7 to 16mg/Nm3. The pre-dedusting efficiency can reach more than 90%. This facilitates more complete reaction of the hydrogen peroxide with the Nitric Oxide (NO) in the flue gas and formation of NO2、N2O5And the high-valence nitrogen oxides are beneficial to the next desulfurization and denitrification reaction.
The temperature of the raw flue gas before pretreatment can be 90-150 ℃, preferably 100-130 ℃, and more preferably 110-120 ℃. The moisture content of the original flue gas is 5-15%, and preferably 5-12%. The temperature and humidity of the flue gas are controlled within the range, so that the hydrogen peroxide aqueous solution is more favorable for forcibly oxidizing NO into NO2、N2O5And the nitrogen oxides with high valence states are beneficial to improving the denitration efficiency.
The oxygen content in the raw flue gas before pretreatment is 5-25 vol%, preferably 8-20 vol%. When the oxygen content in the flue gas is in the range, the hydrogen peroxide aqueous solution can react with NO in the flue gas more fully to form NO2、N2O5And high valence nitrogen oxides.
The sulfur content of the raw flue gas before pretreatment is 500-5000 mg/Nm3Preferably 600 to 4500mg/Nm3More preferably 600 to 4000mg/Nm3. The sulfur-containing substances in the original flue gas are mainly sulfur dioxide. Nitrogen oxides of raw flue gasesNOxThe concentration is 180-650 mg/Nm3Preferably 220 to 550mg/Nm3. The nitrogen oxides in the original flue gas are mainly NO. This facilitates the forced oxidation of NO to NO by hydrogen peroxide2、N2O5And the high-valence nitrogen oxides are beneficial to improving the denitration efficiency.
In the invention, the NO content in the pretreated flue gas in unit time is basically the same as the NO content in the original flue gas in unit time; pretreatment of SO in flue gas in unit time2Content and SO in original flue gas in unit time2The contents were substantially the same.
< Oxidation reaction step >
And (3) contacting a 15-35 wt% hydrogen peroxide aqueous solution with the pretreated flue gas in the flue gas pipeline to react to obtain the flue gas I. This is advantageous for sufficient oxidation of NO in the flue gas.
Hydrogen peroxide oxidizes Nitric Oxide (NO) in flue gas to nitrogen dioxide (NO)2) Dinitrogen pentoxide (N)2O5) And high valence nitrogen oxides. The oxidation principle of oxidizing NO with hydrogen peroxide is as follows:
NO+H2O2→NO2+H2o (Main)
2NO+3H2O2→N2O5+3H2O (Main)
2NO+3H2O2→2HNO3+2H2O (vice)
2NO+H2O2→2HNO2(vice)
The concentration of the aqueous hydrogen peroxide solution may be 15 to 35 wt%, preferably 20 to 35 wt%, more preferably 27.5 wt% or 35 wt%, still more preferably 27.5 wt%. This is advantageous for both the oxidation effect and the saving of aqueous hydrogen peroxide.
Nitric oxide contained in the pretreated flue gas introduced in unit time and H in the aqueous hydrogen peroxide solution added in unit time2O2The molar ratio of (a) to (b) is 1:1.1 to 4.1, preferably 1:1.1 to 3, and more preferably 1:1.2 to 2.1. Thus being beneficial to fully oxidizing NO in the smoke and saving peroxideHydrogen peroxide aqueous solution, and then be favorable to improving denitration efficiency.
And spraying the aqueous hydrogen peroxide solution into the flue gas pipeline through the first spraying equipment, and contacting with the pretreated flue gas to perform an oxidation reaction. The first spraying equipment is an atomizing nozzle. This facilitates the contact of the aqueous hydrogen peroxide solution with the pre-treated flue gas to carry out the oxidation reaction.
The contact time of the hydrogen peroxide aqueous solution and the pretreated flue gas is 1-20 s, preferably 1-10 s, and more preferably 1-3 s. The flow velocity of the pretreated flue gas in the flue gas pipeline is 5-15 m/s, preferably 9-13 m/s, and more preferably 10-12 m/s. Thus, the method is favorable for fully oxidizing NO in the flue gas, and further improves the denitration efficiency.
In the present invention, the aqueous hydrogen peroxide solution is supplied from the oxidizing agent tank. Supplying the hydrogen peroxide aqueous solution to first spraying equipment by an oxidant storage tank, spraying the hydrogen peroxide aqueous solution into a flue gas pipeline through the first spraying equipment, and then contacting and reacting with the pretreated flue gas in the flue gas pipeline to form flue gas I.
In the present invention, the oxidation step is carried out in the flue gas duct before the absorption tower. With first equipment setting that sprays in the flue before the flue gas gets into the absorption tower, can increase the contact time of hydrogen peroxide aqueous solution and flue gas like this to promote the quick oxidation reaction of hydrogen peroxide to low valence nitrogen oxide (mainly be NO), and then be favorable to improving denitration efficiency.
< desulfurization/denitration reaction step >
And introducing the flue gas I into an absorption tower, spraying absorbent dry powder and mixed reducing agent dry powder into the absorption tower, and contacting the absorbent dry powder and the mixed reducing agent dry powder with the flue gas I to perform desulfurization and denitrification reaction so as to form flue gas II, namely the desulfurization and denitrification flue gas. Thus being beneficial to improving the desulfurization efficiency and the denitration efficiency, having no secondary pollution and being more environment-friendly.
The mixed reducing agent is a mixture of sodium sulfite, sodium bisulfite and ammonium bisulfite; and the molar ratio of the sodium sulfite to the sodium bisulfite to the ammonium bisulfite is (1.3-2.9): 0.9-1.1): 1, preferably (1.5-2.5): 1:1, and more preferably (1.7-2.2): 1:1. The invention finds that the ratio of the sodium sulfite, the sodium bisulfite and the ammonium bisulfite is controlled in the range, which is very beneficial to improving the denitration effect. The particle size of the dry powder of the mixed reducing agent is 100-400 meshes, preferably 150-350 meshes, and more preferably 200-300 meshes. This is favorable to improving denitration efficiency.
Nitric oxide contained in the pretreated flue gas introduced per unit time in the step (1) and tetravalent sulfur element (SO) contained in the mixed reducing agent dry powder added per unit time in the step (2)3 2-Or HSO3 2-) The molar ratio of (a) to (b) is 1:3.0 to 4.5, preferably 1:3.2 to 4.2, and more preferably 1:3.3 to 3.8. Thus being beneficial to improving the denitration efficiency and not influencing the desulfurization efficiency. If the dosage of the mixed reducing agent dry powder is too small, the denitration efficiency is low; if the dosage of the mixed reducing agent dry powder is too much, the denitration efficiency is not greatly improved, but the cost is increased; moreover, too much dry powder of the mixed reducing agent can influence the absorption of the dry powder of the absorbent and reduce the desulfurization efficiency.
The absorbent dry powder is one or two of calcium oxide dry powder and calcium hydroxide dry powder, preferably, the absorbent dry powder is calcium hydroxide dry powder. The molar ratio of the absorbent dry powder (calcium oxide or calcium hydroxide) added per unit time in the step (2) to the sulfur dioxide contained in the pretreated flue gas introduced per unit time in the step (1) is a calcium-sulfur ratio, which can be 1.1-2: 1, preferably 1.1-1.8: 1, and more preferably 1.1-1.5: 1. This is advantageous in improving the desulfurization efficiency.
Calcium hydroxide is also known as slaked or hydrated lime. The particle size of the calcium oxide dry powder or the calcium hydroxide dry powder is 100-400 meshes, preferably 150-350 meshes, and more preferably 200-250 meshes. This is advantageous in improving the desulfurization efficiency.
The contact time of the absorbent dry powder, the mixed reducing agent dry powder and the flue gas I in the absorption tower is 5-30 s, preferably 6-15 s, and more preferably 9-12 s. The flow speed of the flue gas I in the absorption tower is 1-8 m/s, preferably 2-5 m/s, more preferably 3-5 m/s, such as 4 m/s. Thus, the dry powder of the mixed reducing agent and the nitrogen oxide can fully react, and the desulfurization efficiency and the denitration efficiency can be improved.
In the present invention, the absorbent dry powder is supplied from the absorbent bin. The dry powder of the mixed reducing agent comprises dry sodium sulfite powder, dry sodium bisulfite powder and dry ammonium bisulfite powder. The sodium sulfite dry powder is supplied from a sodium sulfite storage bin. The sodium bisulfite dry powder is supplied from a sodium bisulfite storage bin. The ammonium bisulfite dry powder is supplied from an ammonium bisulfite storage bin. And (3) respectively conveying the three reducing agents in the sodium sulfite storage bin, the sodium bisulfite storage bin and the ammonium bisulfite storage bin to a mixing stirrer according to the molar ratio, uniformly mixing, and then spraying into the absorption tower through a pump.
In the invention, chain type stirring equipment is preferably arranged in the absorption tower, and the chain type stirring equipment in the absorption tower can generate strong turbulence around the absorption tower, so that the process of desulfurization, denitrification and mass transfer can be enhanced, the contact time of the absorbent and the mixed reducing agent with the flue gas I is prolonged, and the desulfurization efficiency and the denitrification efficiency are improved.
According to one embodiment of the invention, the absorption column is a dense phase dry column. The dense phase dry column used in the present invention is an absorption column commonly used in the art.
And when the absorbent dry powder and the mixed reducing agent dry powder are sprayed into the absorption tower, water is sprayed into the absorption tower through the second spraying equipment, so that the absorbent dry powder and the mixed reducing agent dry powder are humidified. The second spraying equipment is a humidifier. Thus, the desulfurization efficiency and the denitration efficiency are improved, the water consumption is low, and the obtained by-product is powdery solid, so that the subsequent treatment is facilitated.
According to one embodiment of the invention, flue gas I is introduced into a dense-phase drying tower, absorbent dry powder and mixed reducing agent dry powder are sprayed into the dense-phase drying tower, water is sprayed into the dense-phase drying tower through a second spraying device, so that the absorbent dry powder and the mixed reducing agent dry powder are humidified, and the absorbent dry powder and the mixed reducing agent dry powder are contacted with the flue gas I in the absorption tower and subjected to desulfurization and denitrification reactions, so that flue gas II is formed. According to one embodiment of the invention, the second spraying device is a humidifier.
In the present invention, as described in the oxidation reaction step, the products obtained by oxidizing NO in the pretreated flue gas with hydrogen peroxide include: NO2、N2O5、HNO3、HNO2And H2O, and obtaining the flue gas I.
Then, the mixed reducing agent dry powder of sodium sulfite, sodium bisulfite and ammonium bisulfite and the absorbent dry powder are contacted with the flue gas I and are subjected to full desulfurization and denitrification reaction, and the principle is as follows:
4Na2SO3+2NO2→N2+4Na2SO4(Main)
5Na2SO3+N2O5→N2+5Na2SO4(Main)
4NaHSO3+2NO2→N2+2Na2SO4+2H2SO4(Main)
10NaHSO3+2N2O5→2N2+5Na2SO4+5H2SO4(Main)
4NH4HSO3+2NO2→N2+2(NH4)2SO4+2H2SO4(Main)
10NH4HSO3+2N2O5→2N2+5(NH4)2SO4+5H2SO4(Main)
5Na2SO3+2HNO3→N2+5Na2SO4+H2O (vice)
3Na2SO3+2HNO2→N2+3Na2SO4+H2O (vice)
4Na2SO3+2NO+O2→N2+4Na2SO4(vice)
10NaHSO3+4HNO3→2N2+5Na2SO4+5H2SO4+2H2O (vice)
6NaHSO3+4HNO2→2N2+3Na2SO4+3H2SO4+2H2O (vice)
4NaHSO3+2NO+O2→N2+2Na2SO4+2H2SO4(vice)
10NH4HSO3+4HNO3→2N2+5(NH4)2SO4+5H2SO4+2H2O (vice)
6NH4HSO3+4HNO2→2N2+3(NH4)2SO4+3H2SO4+2H2O (vice)
4NH4HSO3+2NO+O2→N2+2(NH4)2SO4+2H2SO4(vice)
SO2+H2O→H2SO3(Main)
3H2SO3+2Ca(OH)2→Ca(HSO3)2+CaSO3+4H2O (Main)
Ca(HSO3)2+2CaSO3+2O2+Ca(OH)2→4CaSO4+2H2O (Main)
NO+NO2+Ca(OH)2→Ca(NO2)2+H2O (vice)
Ca(NO2)2+O2→Ca(NO3)2(vice)
N2O5+Ca(OH)2→Ca(NO3)2+H2O (vice)
HNO2+HNO3+1/2O2+Ca(OH)2→Ca(NO3)2+2H2O (vice)
H2SO4+Ca(OH)2→CaSO4+2H2O
According to one embodiment of the invention, the method for performing flue gas desulfurization and denitration by using the mixed reducing agent comprises the following specific steps:
(1) pretreating raw flue gas by an electric precipitator to obtain pretreated flue gas; introducing the pretreated flue gas into a flue gas pipeline; supplying 15-35 wt% aqueous hydrogen peroxide solution from an oxidant storage tank to first spraying equipment, spraying the aqueous hydrogen peroxide solution into a flue gas pipeline through the first spraying equipment, and contacting the aqueous hydrogen peroxide solution with the pretreated flue gas to perform an oxidation reaction to obtain flue gas I; wherein the first spraying equipment is positioned in the flue gas pipeline; the first spraying equipment is an atomizing nozzle;
(2) introducing the flue gas I into an absorption tower, spraying the absorbent dry powder and the mixed reducing agent dry powder into the absorption tower, and spraying water into the absorption tower through second spraying equipment, so as to humidify the absorbent dry powder and the mixed reducing agent dry powder, and contacting the absorbent dry powder and the mixed reducing agent dry powder with the flue gas I in the absorption tower to perform desulfurization and denitrification reaction, thereby forming flue gas II; wherein the absorption tower is a dense-phase dry tower; the second spraying equipment is a humidifier; the absorbent dry powder is supplied from an absorbent bin; and respectively conveying sodium sulfite, sodium bisulfite and ammonium bisulfite from a sodium sulfite storage bin, a sodium bisulfite storage bin and an ammonium bisulfite storage bin to a mixing stirrer according to a molar ratio, uniformly mixing to obtain mixed reducing agent dry powder, and then spraying the mixed reducing agent dry powder into an absorption tower through a pump.
< step of removing dust >
And carrying out dust removal treatment on the flue gas II through dust removal equipment to obtain purified flue gas. According to one embodiment of the invention, the dust removal device is a bag-type dust remover. And filtering by a filter bag to obtain the purified flue gas meeting the dust emission requirement. The purified flue gas is discharged through an exhaust device, and the exhaust device is a chimney. The particles intercepted on the filter bag are blown to a dust hopper of the dust remover, and one part of the particles is sent to the dust bin. Mainly discharging byproducts such as calcium sulfate, sodium sulfate, ammonium sulfate and the like into the ash bin.
< circulation step >
Recycling the absorbent dry powder and the mixed reducing agent dry powder which are not completely reacted to the absorption tower. Specifically, the absorbent dry powder and the mixed reducing agent dry powder which are not completely reacted may be circulated to the absorption tower by a circulation device.
According to one embodiment of the present invention, the incompletely reacted absorbent dry powder and the mixed reducing agent dry powder are fed into the absorption tower from the bottom of the absorption tower or a dust collector hopper through a circulation device.
Example 1
FIG. 1 shows a schematic diagram of an apparatus used in a method for desulfurization and denitrification of flue gas by using a mixed reducing agent according to the present invention. As can be seen from the figure, the flue gas desulfurization and denitrification apparatus of the present invention comprises: the device comprises an absorbent bin 1, a sodium sulfite bin 2, a sodium bisulfite bin 3, an ammonium bisulfite bin 4, a mixing stirrer 5, an oxidant storage tank 6, an atomizing nozzle 7, an electric dust remover 8, a dense phase drying tower 9, a humidifier 10, a bag-type dust remover 11, an ash bin 12 and a chimney 13.
(1) The raw flue gas from the sintering machine is subjected to removal of particulate matter by an electric precipitator 8 to obtain pretreated flue gas, and the pretreated flue gas is introduced into a flue gas pipeline. Supplying an aqueous solution of hydrogen peroxide having a concentration of 27.5% by weight to an atomizing nozzle 7 located in the flue gas duct through an oxidant storage tank 6; then the aqueous hydrogen peroxide solution is sprayed into the flue gas pipeline through the atomizing nozzle 7 and contacts with the pretreated flue gas in the flue gas pipeline to carry out oxidation reaction, thereby forming the flue gas I.
(2) Introducing the flue gas I into a dense-phase drying tower 9, spraying the calcium hydroxide dry powder and the mixed reducing agent dry powder into the dense-phase drying tower 9, spraying water into the dense-phase drying tower 9 through a humidifier 10, humidifying the calcium hydroxide dry powder and the mixed reducing agent dry powder, and contacting the calcium hydroxide dry powder and the mixed reducing agent dry powder with the flue gas I for 10s and reacting to form the flue gas II. Wherein, the calcium hydroxide dry powder is supplied by the absorbent bin 1. Sodium sulfite, sodium bisulfite and ammonium bisulfite in set proportion are respectively conveyed into a mixing stirrer 5 by a sodium sulfite storage bin 2, a sodium bisulfite storage bin 3 and an ammonium bisulfite storage bin 4 and are uniformly mixed to obtain the dry powder of the mixed reducing agent. The raw flue gas (inlet flue gas) parameters and process parameters are shown in table 1.
And (3) carrying out dust removal treatment on the flue gas II by adopting a bag-type dust remover 11 to obtain purified flue gas. The cleaned flue gases are discharged through a stack 13. The unreacted absorbent dry powder and the mixed reducing agent dry powder are sent into a dense phase drying tower 9 for recycling, and byproducts calcium sulfate, sodium sulfate, ammonium sulfate and the like enter an ash bin 12. Desulfurization efficiency and denitration efficiency are shown in table 2.
TABLE 1
TABLE 2
| Item | Numerical value | Unit of |
| Efficiency of desulfurization | 99.6 | ％ |
| Denitration efficiency | 96.2 | ％ |
Example 2
The process parameters were the same as in example 1, except that the process parameters of the mixed reducing agent were different. See table 3 for process parameters of the dry powder of mixed reductants of this comparative example. The desulfurization efficiency and the denitration efficiency are shown in Table 4.
TABLE 3
TABLE 4
| Item | Unit of | Numerical value |
| Efficiency of desulfurization | ％ | 99.5 |
| Denitration efficiency | ％ | 96.7 |
Comparative example 1
The process parameters were the same as in example 1, except that the process parameters of the mixed reducing agent were different. See table 5 for process parameters of the dry powder of mixed reductants of this comparative example. The desulfurization efficiency and the denitration efficiency are shown in Table 6.
TABLE 5
TABLE 6
| Item | Unit of | Numerical value |
| Efficiency of desulfurization | ％ | 99.5 |
| Denitration efficiency | ％ | 89.6 |
Comparative example 2
The process parameters were the same as in example 1 except that the dry powder of the mixed reducing agent was different. See table 7 for process parameters of the dry powder of mixed reductants of this comparative example. The desulfurization efficiency and the denitration efficiency are shown in Table 8.
TABLE 7
TABLE 8
| Item | Unit of | Numerical value |
| Efficiency of desulfurization | ％ | 99.5 |
| Denitration efficiency | ％ | 93.5 |
The present invention is not limited to the above-described embodiments, and any variations, modifications, and substitutions which may occur to those skilled in the art may be made without departing from the spirit of the invention.
Claims (10)
1. A method for performing flue gas desulfurization and denitrification by using a mixed reducing agent is characterized by comprising the following steps:
(1) contacting a 15-35 wt% hydrogen peroxide aqueous solution with the pretreated flue gas in a flue gas pipeline to react to obtain flue gas I;
(2) introducing the flue gas I into an absorption tower, spraying absorbent dry powder and mixed reducing agent dry powder into the absorption tower, and contacting the absorbent dry powder and the mixed reducing agent dry powder with the flue gas I to perform desulfurization and denitrification reaction so as to form flue gas II;
wherein the mixed reducing agent is a mixture of sodium sulfite, sodium bisulfite and ammonium bisulfite; the molar ratio of the sodium sulfite to the sodium bisulfite to the ammonium bisulfite is (1.3-2.9) to (0.9-1.1) to 1; and the molar ratio of nitric oxide contained in the pretreated flue gas introduced per unit time in the step (1) to tetravalent sulfur element contained in the mixed reducing agent dry powder added per unit time in the step (2) is 1: 3.0-4.5.
2. The method according to claim 1, wherein the molar ratio of nitric oxide contained in the pretreated flue gas introduced per unit time in the step (1) to tetravalent sulfur contained in the mixed reducing agent dry powder added per unit time in the step (2) is 1: 3.2-4.2.
3. The method according to claim 1, wherein the molar ratio of the sodium sulfite, the sodium bisulfite and the ammonium bisulfite in the mixed reducing agent is (1.5-2.5): 1:1.
4. The method according to claim 1, wherein in the step (2), the absorbent dry powder is one or two selected from calcium oxide dry powder and calcium hydroxide dry powder; and the molar ratio of the absorbent dry powder added per unit time in the step (2) to the sulfur dioxide contained in the pretreated flue gas introduced per unit time in the step (1) is a calcium-sulfur ratio which is 1.1-2.1: 1.
5. The method of claim 1, wherein:
in the step (2), the contact time of the absorbent dry powder and the mixed reducing agent dry powder with the flue gas I is 5-30 s;
in the step (2), the flow speed of the flue gas I in the absorption tower is 1-8 m/s.
6. The method according to claim 1, wherein in the step (2), when the absorbent dry powder and the mixed reducing agent dry powder are sprayed into the absorption tower, water is sprayed into the absorption tower through a second spraying device, so that the absorbent dry powder and the mixed reducing agent dry powder are humidified; wherein the second spraying equipment is a humidifier.
7. The method according to claim 1, wherein the nitric oxide contained in the pretreated flue gas introduced per unit time in step (1) and the H in the aqueous hydrogen peroxide solution added per unit time2O2The molar ratio of (A) to (B) is 1: 1.1-4.1.
8. The method of claim 1, wherein:
in the step (1), spraying aqueous hydrogen peroxide into a flue gas pipeline through first spraying equipment, and contacting with pretreated flue gas to perform oxidation reaction; wherein the first spraying equipment is an atomizing nozzle;
in the step (1), the contact time of the aqueous hydrogen peroxide solution and the pretreated flue gas is 1-20 s.
9. The method according to claim 1, wherein in the step (1), the flow velocity of the pretreated flue gas in the flue gas pipeline is 5-15 m/s.
10. The method according to any one of claims 1 to 9, wherein:
in the step (1), the raw flue gas is pretreated by an electric precipitator to obtain pretreated flue gas;
in the step (2), the absorption tower is a dense-phase dry tower.
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