CN108744926A - It is a kind of to remove flue gas NO simultaneouslyxAnd SO2Oxidative absorption method - Google Patents

Abstract

The invention discloses an oxidation absorption method for simultaneously removing flue gas NO _x and SO ₂ , belonging to the field of flue gas pollution control. In this method, the flue gas to be purified is passed into the reaction device, and the SO ₂ and NO _x in the flue gas are fully contacted with the oxidation absorption liquid to undergo an oxidation absorption reaction, and finally discharged after purification. The oxidation absorbing liquid is a solution composed of calcium peroxide and persulfate, and the molar ratio of persulfate and calcium peroxide in the solution is 0.15-1.5. The method for absorbing NO _x and SO ₂ by wet oxidation has strong oxidation and strong alkaline absorption capabilities, and can achieve 100% SO ₂ removal efficiency and more than 70% NO _x removal efficiency, even up to 95%. _The invention can realize the simultaneous removal of SO2 and _NOx in the same wet scrubbing device, and has the characteristics of high removal efficiency, no secondary pollution, recyclable resources, low cost and the like.

Description

An Oxidative Absorption Method for Simultaneously Removing NOx and SO2 from Flue Gas

technical field

_The invention relates to an oxidation absorption method for simultaneously removing _NOx and SO2 in flue gas, and belongs to the subfield of flue gas pollution control in the technical field of environmental protection.

Background technique

my country's primary energy is mainly coal. With the continuous development and utilization of clean energy such as natural gas, solar energy, and wind energy, the proportion of coal demand has declined, but it still accounts for more than 60%. Gaseous pollutants such as SO ₂ and NO _x emitted from coal combustion will cause a series of environmental problems such as acid rain, photochemical smog, and eutrophication of water bodies. In the face of increasingly serious environmental pollution, the Chinese government has proposed that coal-fired boilers meet gas emission standards, that is, near-zero emissions (under the premise that the O ₂ concentration is 6%, the maximum emission limits for smoke, SO ₂ and NO _x values should be lower than 10, 35 and 50 mg/m ³ respectively). At present, for the control of SO ₂ and NO _x , coal-fired boilers generally adopt the "1+1" desulfurization and denitrification technology, that is, the combination of separate desulfurization equipment and separate denitration equipment. The equipment has the problems of large floor area and high investment cost. For coal-fired boilers in China, it is urgent to develop a simultaneous desulfurization and denitrification technology with low investment, low operating cost and high efficiency to achieve simultaneous removal of SO ₂ and NO _x in the same equipment.

Oxidative absorption method has high removal efficiency, low operating cost and low investment, and can simultaneously remove SO ₂ and NO _x in the same wet scrubber, and has broad application prospects. Publication No. CN106731631A and Publication No. _102989273A disclose two methods for oxidatively absorbing NO _x and SO ₂ using chlorine-containing compounds. Although high removal efficiency can be achieved, chlorine _- containing compounds will Chlorine-containing gas is produced, causing secondary pollution to the environment. In addition, chlorine-containing oxidants will cause equipment corrosion. Publication No. CN103157358A discloses a flue gas denitrification method based on advanced oxidation technology, using low-cost, non-polluting dual oxidants composed of H ₂ O ₂ and Na ₂ S ₂ O ₈ to oxidize and absorb NO through active free radicals generated by thermal excitation _x , this method can achieve high _NOx removal efficiency without secondary pollution, but the instability of H ₂ O ₂ will cause ineffective decomposition, which makes the utilization rate of H ₂ O ₂ low, and when H _{2 O2} can explode in excess.

Contents of the invention

The object of the present invention is to provide a method for simultaneously removing NOx and SO ₂ in flue gas by using persulfate and calcium peroxide (CaO ₂ ) as an oxidation absorbent, wherein CaO ₂ is not only used as a solid source of H ₂ O ₂ , Simultaneous hydrolysis produces alkaline absorbent Ca(OH) ₂ .

The present invention is achieved through the following technical solutions:

An oxidation absorption method for simultaneously removing flue gas NO _x and _SO , said method comprising:

Fill the oxidation absorption liquid in the wet scrubbing device, and the oxidation absorption liquid is a mixed solution of persulfate and calcium peroxide;

_Passing the flue gas containing _NOx and SO2 into the wet scrubbing device, making the flue gas contact and react with the oxidation absorption liquid so that the _NOx and SO2 in the flue gas are absorbed by the oxidation absorption liquid at the same time _;

The flue gas that has been absorbed and removed by the oxidation absorption liquid to remove NO _x and SO ₂ is discharged from the wet scrubbing device for further purification treatment;

After contacting and reacting with the flue gas, the oxidation absorbing liquid is separated by filtration and then returned to the wet scrubbing device.

In the above technical solution, the molar ratio of the persulfate to calcium peroxide is 0.15-1.5.

In the above technical solution, the persulfate includes one or more mixtures of potassium hydrogen persulfate, ammonium persulfate and sodium persulfate.

In the above technical solution, the pH value of the oxidation absorption liquid is 9.5-11.5, which is adjusted by adding acid and/or alkali.

In the above technical scheme, sulfuric acid and sodium hydroxide are selected for use as the acid and the alkali respectively.

In the above technical solution, the concentration of the sulfuric acid is 0.1-5 mol/L, and the concentration of the sodium hydroxide is 0.1-1 mol/L.

In the above technical solution, the reaction temperature of the oxidation absorption liquid is 50-55°C.

In the above technical solution, the wet scrubbing device includes any one or combination of bubble towers, packed towers, spray towers or sieve tray towers.

In the above technical solution, when the oxidation absorption liquid in the wet scrubbing device is sprayed, the flue gas containing NO _x and SO ₂ is passed into the wet scrubbing device to flow countercurrently with the oxidation absorption liquid. contact.

In the above technical solution, when the wet scrubbing device adopts a bubble tower, the flue gas enters the wet scrubbing device through the air distribution device, and the flue gas forms bubbles to contact and react with the absorption liquid.

The present invention has the following advantages and outstanding effects: ① The method has both strong oxidation and strong absorption capabilities, and can simultaneously remove SO ₂ and NOx in flue gas with a set of wet scrubbing equipment, and has high desulfurization and denitrification efficiency. ②This method adopts an environment-friendly oxidation absorption liquid, which is low in cost, does not produce secondary pollution, and the reaction product can be recycled.

Detailed ways

The specific structure, principle and implementation of the present invention will be further described below in conjunction with specific examples.

The invention relates to a method for simultaneously removing _NOx and SO from coal _- fired flue gas, the method comprising:

Fill the oxidation absorption liquid in the wet scrubbing device, and the oxidation absorption liquid is a mixed solution of persulfate and calcium peroxide;

_Passing the flue gas containing _NOx and SO2 into the wet scrubbing device, making the flue gas contact and react with the oxidation absorption liquid so that the _NOx and SO2 in the flue gas are absorbed by the oxidation absorption liquid at the same time _;

The flue gas that has been absorbed and removed by the oxidation absorption liquid to remove NO _x and SO ₂ is discharged from the wet scrubbing device for further purification treatment;

After contacting and reacting with the flue gas, the oxidation absorbing liquid is separated by filtration and then returned to the wet scrubbing device.

Persulfates include one or more mixtures of potassium hydrogen persulfate, ammonium persulfate and sodium persulfate. Usually, the molar ratio of persulfate to calcium peroxide is 0.15~1.5.

In order to achieve the ideal simultaneous removal effect, the pH value of the oxidation absorption solution is 9.5~11.5, which is adjusted by adding acid and/or alkali. Sulfuric acid and sodium hydroxide are used as acid and alkali respectively, the concentration of sulfuric acid is 0.1~5 mol/L, and the concentration of sodium hydroxide is 0.1~1 mol/L.

The flue gas is usually above 120°C, so the reaction temperature of the oxidation absorption liquid passed into the flue gas is 50~55°C.

The above-mentioned wet scrubbing device includes any one or a combination of bubble towers, packed towers, spray towers or sieve tray towers.

When the oxidation absorption liquid in the wet scrubbing device is sprayed, the wet scrubbing device usually uses any one or a combination of packed towers, spray towers or sieve tray towers. After the oxidation absorption liquid is filled in the wet scrubbing device, the oxidation absorption liquid is sprayed down from the spray layer, and the flue gas containing NO _x and SO ₂ is passed into the lower part of the wet scrubbing device to make it flow upwards and the oxidation absorption liquid countercurrent type touch. After the reaction, the oxidation absorption solution is precipitated from the bottom, separated, filtered and collected, or recycled, or recycled in other ways.

When the wet scrubbing device adopts a bubble tower, the flue gas enters the wet scrubbing device through the air distribution device, and the flue gas forms bubbles to contact and react with the absorption liquid. The absorbed liquid after the reaction is either replaced in sequence batches, or gradually discharged from the device through continuous flow. The oxidation absorption liquid discharged after the reaction is collected by precipitation, separation, filtration, or recycled, or recycled by other means.

The oxidation absorbing liquid of the present invention has both strong oxidizing ability and alkaline absorbing ability, and is composed of calcium peroxide and persulfate mixed solution, and the molar ratio is 0.15-1.5. The reaction mechanism is shown below.

Free radical chain reaction:

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Oxidative absorption reaction:

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It is characterized in that CaO ₂ generates H ₂ O ₂ and Ca(OH) ₂ through hydrolysis, and Na ₂ S ₂ O ₈ is excited by H ₂ O ₂ and ^OH- to generate SO ₄ ^•− at a low temperature of 50-55 °C. •Active free radicals such as OH and O ₂ ^•− , under the action of free radicals and Ca(OH) ₂ , NO and SO ₂ are finally transformed into NO ₃ ^-- , SO ₄ ^2- and CaSO ₄ ·2H ₂ O. Thereby _realizing the simultaneous removal of NOx and SO2 in the same wet scrubbing device.

Example 1:

For a 35 t boiler, the flue gas volume is 35000 m ³ /h, the flue gas temperature is 120 ℃, and the concentrations of NO _x and SO ₂ in the flue gas are 200 mg/m ³ and 1000 mg/m ³ respectively. L sodium persulfate and 0.2 mol/L calcium peroxide uniformly mixed turbid mixed liquid is used as an oxidation absorbent for wet simultaneous desulfurization and denitrification, and it is in full reverse contact with flue gas in the spray tower, with a liquid-gas ratio of 10-20. The reaction temperature is 50°C, and the denitrification efficiency and desulfurization efficiency can be achieved by 80% and 100%, respectively, by testing the purified flue gas.

The industrial prices of sodium persulfate and 70% calcium peroxide are 6,500 yuan/t and 6,000 yuan/t, respectively. The cost of wet simultaneous desulfurization and denitrification operation for one day is equivalent to an increase of 40 yuan for 1 ton of fuel.

Example 2:

For a 35 t boiler, the flue gas volume is 35000 m ³ /h, the flue gas temperature is 120 ℃, and the concentrations of NO _x and SO ₂ in the flue gas are 200 mg/m ³ and 1000 mg/m ³ respectively. L ammonium persulfate and 0.2 mol/L calcium peroxide uniformly mixed turbid mixture is used as an oxidation absorbent for simultaneous wet desulfurization and denitrification, and it is in full reverse contact with the flue gas in the spray tower, with a liquid-gas ratio of 10-20. The reaction temperature is 50°C, and the denitrification efficiency and desulfurization efficiency can be achieved by 70% and 100%, respectively, by testing the purified flue gas.

The industrial prices of ammonium persulfate and 70% calcium peroxide are 4,500 yuan/t and 6,000 yuan/t, respectively. The cost of wet simultaneous desulfurization and denitrification operation for one day is equivalent to the cost of 1 ton of fuel increased by about 30 yuan.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a kind of removing flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that the method includes：

Oxidative absorption liquid is filled in wet scrubbing device, the oxidative absorption liquid is that persulfate and calper calcium peroxide mixing are molten Liquid；

NO will be contained_xAnd SO₂Flue gas be passed through in the wet scrubbing device, make flue gas and the oxidative absorption liquid haptoreaction So that the NO in flue gas_xAnd SO₂It is absorbed simultaneously by the oxidative absorption liquid；

It will be by oxidative absorption liquid absorbing and removing NO_xAnd SO₂Flue gas the wet scrubbing device is discharged；

Oxidative absorption liquid after being reacted with smoke contacts continues to be returned to the wet scrubbing device after being separated by filtration.

2. one kind described in accordance with the claim 1 removes flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that it is described The molar ratio of persulfate and calper calcium peroxide is 0.15 ~ 1.5.

3. removing flue gas NO simultaneously according to one kind as claimed in claim 1 or 2_xAnd SO₂Oxidative absorption method, which is characterized in that institute It includes one or more mixtures in potassium hydrogen peroxymonosulfate, ammonium persulfate, sodium peroxydisulfate to state persulfate.

4. one kind described in accordance with the claim 1 removes flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that it is described The pH value of oxidative absorption liquid is 9.5 ~ 11.5, is adjusted by the way that acid and/or alkali is added.

5. a kind of according to claim 4 remove flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that it is described Soda acid selects sulfuric acid and sodium hydroxide respectively.

6. removing flue gas NO simultaneously according to a kind of described in claim 5_xAnd SO₂Oxidative absorption method, which is characterized in that the sulphur A concentration of 0.1 ~ 5 mol/L, a concentration of 0.1 ~ 2 mol/L of the sodium hydroxide of acid.

7. one kind described in accordance with the claim 1 removes flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that it is described The reaction temperature of oxidative absorption liquid is 50 ~ 55 DEG C.

8. one kind described in accordance with the claim 1 removes flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that it is described Wet scrubbing device includes bubble tower, packed tower, spray column or the combination of sieve-plate tower any one or more of.

9. a kind of according to claim 8 remove flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that work as institute When stating oxidative absorption liquid selection spray mode in wet scrubbing device, contain NO by described_xAnd SO₂Flue gas be passed through the wet method In wash mill with the oxidative absorption liquid is reverse-flow contacts.

10. a kind of according to claim 8 remove flue gas NO simultaneously_xAnd SO₂Oxidative absorption method, which is characterized in that work as institute When stating wet scrubbing device selection bubble tower, flue gas enters wet scrubbing device by air-distribution device, and flue gas forms bubble and inhales Receive liquid haptoreaction.