CN105771652A - Flue gas denitration method by taking manganese oxide as cyclic absorption medium - Google Patents

Abstract

The invention discloses a flue gas denitrification method using manganese oxide as a circulating absorption medium, heating manganese nitrate to generate nitrogen dioxide gas and manganese dioxide solid; passing nitrogen dioxide gas into the desulfurized flue gas, using Alkaline absorbent absorbs SO ₂ and NO _x gases in the desulfurization flue gas to generate sulfate and nitrite; use an acidic solution containing manganese dioxide as the absorbent to absorb and Manganese dioxide solids together with man-made _NOx gas, generate manganese nitrate. The present invention uses alkaline absorbents with wide sources and cheap prices as raw materials and recycles manganese oxide working medium, which can effectively remove nitrogen oxide NOx toxic gases in flue gas. After absorption treatment, sulfur dioxide SO ₂ in flue gas is ≤1PPM, NOx ≤ 50PPM, low-cost by-products of high value-added nitrite, especially calcium nitrite, can help enterprises to have economic benefits while protecting the environment, and completely change the current heavy economic burden on related enterprises.

Description

A flue gas denitrification method using manganese oxide as a circulating absorption medium

technical field

The invention belongs to the technical field of denitrification, and relates to all industries and fields in which nitrogen oxide NOx needs to be removed from the flue gas produced by burning fossil fuels such as coal, oil, and natural gas in a fixed burner, and specifically relates to a manganese oxide cycle Flue gas denitrification method with absorption medium.

Background technique

After coal, oil, natural gas and other fossil fuels are burned at high temperature, the flue gas contains acidic substances such as sulfur dioxide SO ₂ and nitrogen oxide NOx, which have caused great damage to the atmosphere and human living environment for many years. The existing technologies at home and abroad use limestone and magnesium oxide as desulfurizers, which can remove sulfur _dioxide SO2 in the flue gas to 100-200PPM; ) and strictly control the amount of addition, the NOx in the flue gas can be removed by 50-60%. Although the SNCR method requires less investment, its operating temperature is high (900-1200°C), its elasticity is small, and its high ammonia escape rate is likely to cause secondary pollution. The management of storing liquid ammonia or ammonia water is also more troublesome. At present, the SCR method commonly used in large-scale power plants at home and abroad also uses reducing agents such as ammonia to selectively reduce NOx to harmless nitrogen and water in the temperature range of 250-400 ° C, using catalysts and the presence of oxygen. . The denitrification rate of the SCR method can reach more than 90%. The disadvantage is that the fluid velocity, temperature and concentration in the catalytic bed need to be strictly controlled. The design requirements of the catalytic bed structure are high, and ammonia storage system, purging system and catalyst need to be imported from abroad, which are expensive, easy to age, and easy to cause secondary pollution during regeneration. The denitrification process has no products and no direct benefits. Therefore, the SCR law has caused a heavy economic burden to many domestic enterprises. There are research results that adding ozone in the gas phase and adding hydrogen peroxide, chlorate, high-valent metal salts and metal complexes in the liquid phase can achieve a high denitrification effect, which greatly increases the operating cost and most of them are not mature enough in technology .

In the prior art, Chinese patent CN101982419 discloses a method of leaching pyrolusite with nitrogen oxide gas under pressure to prepare manganese nitrate solution. Due to the limited resources of pyrolusite, this method cannot be directly applied to a wider field of flue gas denitrification.

Therefore, the market urgently needs a new method with low investment, low operating cost, stable operation, effective removal of toxic gases such as nitrogen oxides NOx in flue gas, and by-products with value-added products, helping enterprises to protect the environment while maintaining economic efficiency. income.

Contents of the invention

In view of the technical problems of limited pyrolusite resources and high denitrification cost in the prior art, the purpose of the present invention is to provide a flue gas denitrification method using manganese oxide as a circulating absorption medium.

The technical scheme that the present invention takes is:

A method for flue gas denitrification using manganese oxide as a circulating absorption medium, comprising the steps of:

Pyrolysis of manganese nitrate; heating manganese nitrate to generate nitrogen dioxide gas and manganese dioxide solid;

Primary denitrification: Nitrogen dioxide gas is introduced into the desulfurized flue gas, and alkaline absorbent is used to absorb SO ₂ and NO _x gases in the desulfurized flue gas to generate sulfate and nitrite;

Secondary denitrification: use an acidic solution containing manganese dioxide as an absorbent to absorb the NO _x gas artificially added together with manganese dioxide solids in the flue gas after the first denitrification, and generate manganese nitrate.

Further, the manganese nitrate in the step of pyrolyzing manganese nitrate is the manganese nitrate generated in the secondary denitration.

Further, the nitrogen dioxide gas in the first denitrification step is nitrogen dioxide gas obtained by pyrolyzing manganese nitrate.

Furthermore, the nitrogen dioxide gas fed in the first denitration step is such that the NO ₂ /NO molar ratio in the mixed gas before the first denitration is ≤1.

Further, the sulfate and nitrite generated in the first denitrification step are filtered to remove the solid phase, and the liquid phase is evaporated to produce a nitrite product.

Furthermore, calcium oxide or calcium hydroxide slurry is used to absorb SO in the desulfurization flue in the first denitrification step and _NOx gas, generate calcium _sulfate and calcium nitrite, filter out calcium sulfate, evaporate and concentrate calcium nitrite solution , made into calcium nitrite products, used as steel and cement corrosion inhibitors;

Further, in the step of pyrolyzing manganese nitrate, the manganese nitrate aqueous solution is directly sprayed into the side line medium-temperature flue gas or heated air, so that it is decomposed at 200-350° C. to generate nitrogen dioxide and manganese dioxide.

Further, the alkaline absorbent in the primary denitration step is set to be any one of NaOH, Mg(OH) ₂ , Fe(OH) ₃ , CaO or Ca(OH) ₂ .

Further, the acidic solution of manganese dioxide in the second denitrification step adopts a mixed solution containing manganese dioxide and nitric acid, wherein the concentration of manganese dioxide is 0.1%-5%, the concentration of nitric acid is 0-10%, and the operating temperature is Set to 15-60°C.

Furthermore, the operating temperature is set at 30-55°C.

A denitrification device used in a flue gas denitrification method using manganese oxide as a circulating absorption medium, including a manganese nitrate pyrolyzer, a first denitrification tower and a second denitrification tower:

Manganese nitrate pyrolyzer: the top is fed with side line medium-temperature flue gas, and the bottom is connected with a gas-solid separation component. Part of the gas from the gas-solid separation component is passed into the first denitrification tower through a gas mixer, and the remaining gas and solids are separated by gas-solid separation. The component outlet enters the second denitrification tower;

Denitration Tower ₁ : The top is fed into the alkaline absorbent in the alkali circulation tank to absorb SO2 and NOx gas in the desulfurization flue gas, the bottom is fed into the mixed gas from the gas mixer, and the gas-solid Part of the nitrogen dioxide gas separated by the separation module is directly passed into the bottom of the second denitrification tower from the outlet gas of the first denitrification tower;

The second denitrification tower: the top is passed into the acidic solution containing manganese dioxide in the manganese circulation tank, and the bottom is passed into the flue gas leaving the first denitrification tower and another part of nitrogen dioxide gas and manganese dioxide solids remaining in the gas-solid separation component. The manganese circulation tank is connected with the manganese nitrate pyrolyzer.

Further, the alkali circulation tank is connected with the calcium nitrite evaporator, the calcium sulfite is oxidized to calcium sulfate by the oxygen in the flue gas and filtered out, and the calcium nitrite evaporator evaporates the calcium nitrite into a concentrated solution, which is further produced into nitrous acid calcium products.

The beneficial effects of the present invention are:

1. The present invention uses manganese oxide as the working medium, and the denitrification product manganese nitrate produces nitrogen dioxide gas and manganese dioxide solid after thermal decomposition, and the self-produced nitrogen _dioxide NO can strengthen the absorption of insoluble gas NO, and manganese dioxide The solid can oxidize the denitrification product nitrite to nitrate to ensure the continuous absorption of nitrogen oxide gas NO _X and generate reusable manganese nitrate. The invention makes full use of the thermal price change technology of nitrogen and manganese compounds, only consumes the heat of thermal decomposition of manganese nitrate, and can realize high-efficiency recovery and utilization of nitrogen oxides.

2. The present invention uses alkaline absorbents with wide sources and cheap prices as raw materials, and recycles manganese oxide working media, which can effectively remove nitrogen oxides NO _X toxic gases in flue gas, and obtain low-cost by-products and high value-added products such as Nitrate can efficiently remove harmful components of SO ₂ and NO _x in the flue gas without adding additional reducing agents, catalysts or oxidants, and the denitrification solution can be concentrated and processed into nitrite products.

3. In the present invention, the nitrogen dioxide gas is artificially passed into the first denitrification tower and the NO ₂ /NO (molar ratio) in the mixed gas is ≤1. The absorbent is preferably calcium oxide CaO or calcium hydroxide Ca(OH) ₂ , the absorption liquid obtained after recycling can be concentrated and processed into calcium nitrite products. As a corrosion inhibitor for reinforced concrete, the market sales of by-products have broad prospects and bring huge economic benefits.

4. The present invention supplements NO ₂ gas into the desulfurization gas, which is beneficial to the absorption of NO in the flue gas; introducing MnO ₂ into the denitrification absorption liquid can convert the nitrite in the absorption liquid into corresponding nitrate in time, and strengthen the The absorption process takes place. NO ₂ , MnO ₂ , which enhance NO gas absorption and nitrite conversion, are thermal decomposition products of by-product Mn(NO ₃ ) ₂ . After secondary absorption treatment, sulfur dioxide SO ₂ in the flue gas is ≤1PPM, NOx≤50PPM, no waste water discharge during the cycle absorption process, low investment, low operating cost, and stable operation.

5. The method for producing nitrogen dioxide gas and manganese dioxide solid in the present invention is to directly spray the concentrated solution of Mn(NO ₃ ) ₂ into the mixed gas of high-temperature flue gas and air so that the temperature is between 200-350°C. Heating and decomposing to produce nitrogen dioxide gas and manganese dioxide solid circulation are used to strengthen the flue gas denitrification process, make full use of the heat of high-temperature flue gas, consume only part of the heat, and can greatly reduce the cost of flue gas denitrification.

6. This method is applicable to the desulfurization and denitrification of various fossil fuel combustion waste gases and the treatment of nitric acid tail gas. It can help enterprises to have economic benefits while protecting the environment, and completely change the current heavy economic burden on related enterprises.

Description of drawings

Fig. 1 is a schematic diagram of the overall process flow of the denitrification device in the present invention.

Among them, 1. Denitration tower; 2. Alkali circulation tank; 3. Calcium circulation pump; 4. Calcium evaporator; 5. Gas mixer; 6. Manganese nitrate decomposer; 7. Gas-solid separation component; 8. Denitration Second tower; 9. Manganese circulation tank; 10. Manganese circulation pump; 11. Manganese nitrate evaporator; 12. Concentrated manganese pump.

detailed description

In order to make denitrification of the present invention, calcium nitrite manufacture and manganese oxide regeneration and produce nitrogen dioxide NO _The chemical principle and the realization of gas have further understanding, special explanation is as follows:

Example 1

A method for flue gas denitrification using manganese oxide as a circulating absorption medium, comprising the steps of:

Pyrolysis of manganese nitrate; heating manganese nitrate to generate nitrogen dioxide gas and manganese dioxide solid;

Primary denitrification: nitrogen dioxide gas is introduced into the desulfurized flue gas, and calcium oxide or calcium hydroxide is used as an absorbent to absorb SO ₂ and NO _x gases in the desulfurized flue gas to generate calcium sulfate and calcium nitrite;

Secondary denitrification: use an acidic solution containing manganese dioxide as an absorbent to absorb the NO _x gas artificially added together with manganese dioxide solids in the flue gas after the first denitrification, and generate manganese nitrate.

Further, the manganese nitrate in the step of pyrolyzing manganese nitrate is the manganese nitrate generated in the secondary denitration.

Further, the nitrogen dioxide gas in the first denitrification step is nitrogen dioxide gas obtained by pyrolyzing manganese nitrate.

Furthermore, the nitrogen dioxide gas fed in the first denitration step is such that the molar ratio NO ₂ /NO in the mixed gas before the first denitration is ≤1.

Using manganese oxide as the working medium, the denitrification product manganese nitrate is thermally decomposed to produce nitrogen dioxide gas and manganese dioxide solid. The self-produced nitrogen dioxide NO ₂ can strengthen the absorption of insoluble gas NO, and the manganese dioxide solid can denitrify The product nitrite is oxidized to nitrate, which ensures the continuous absorption of nitrogen oxide gas and generates reusable manganese nitrate. By making full use of the thermal price conversion technology of nitrogen and manganese compounds, nitrogen can be realized by only consuming the heat of thermal decomposition of manganese nitrate. Efficient recycling of oxides.

Further, calcium sulfate is filtered out in the first denitrification step, and calcium nitrite is evaporated to produce calcium nitrite product, which is used as a corrosion inhibitor for reinforced concrete.

Further, in the step of pyrolyzing manganese nitrate, the manganese nitrate aqueous solution is directly sprayed into the side line medium-temperature flue gas or heated air, so that it decomposes at 200-350°C to produce nitrogen dioxide and manganese dioxide, and decomposes to produce nitrogen dioxide and manganese dioxide. Nitrogen oxide gas and manganese dioxide solid circulation are used to strengthen the flue gas denitrification process, make full use of the heat of high-temperature flue gas, consume only part of the heat, and greatly reduce the cost of flue gas denitrification.

Further, the alkaline absorbent in the first denitrification step is set to any one of NaOH, Mg(OH) ₂ , Fe(OH) ₃ , CaO or Ca(OH) ₂ to obtain low-cost by-products and high additional The value product nitrite can efficiently remove harmful components of SO ₂ and NO _x in the flue gas without adding additional reducing agents, catalysts or oxidants, and the denitrification solution can be concentrated and processed into nitrite products.

Furthermore, the alkaline absorbent is preferably calcium oxide CaO or calcium hydroxide Ca(OH) ₂ , which can concentrate and process the absorption liquid obtained after recycling into calcium nitrite products, which can be used as steel cement corrosion inhibitors and by-products The sales volume in the market has a broad prospect and brings huge economic benefits.

Further, the acidic solution of manganese dioxide in the second denitrification step adopts a mixed solution containing manganese dioxide and nitric acid, wherein the concentration of manganese dioxide is 0.1%-5%, the concentration of nitric acid is 0-10%, and the operating temperature is Set it at 15-60°C, and introduce MnO ₂ into the denitrification absorption liquid, which can convert the nitrite in the absorption liquid into corresponding nitrate in time, and strengthen the absorption process. NO _{2 ,} MnO ₂ , which enhance NO gas absorption and nitrite conversion, are thermal decomposition products of by-product Mn(NO ₃ ) ₂ . After secondary absorption treatment, sulfur dioxide SO ₂ in the flue gas is ≤1PPM, NOx≤50PPM, no waste water discharge during the cycle absorption process, low investment, low operating cost, and stable operation.

Furthermore, the operating temperature is set at 30-55°C.

Further illustrate technical scheme in the present invention below in conjunction with chemical reaction equation:

A flue gas denitrification method using manganese oxide as a circulating absorption medium, specifically comprising the following steps:

(1) After adding some nitrogen dioxide gas to the desulfurized flue gas, it enters the first denitrification tower, absorbs SO2 and NOx gases in the desulfurized flue gas with calcium _oxide or calcium hydroxide slurry, and generates calcium sulfite Ca(SO ₃ ) ₂ and calcium nitrite Ca(NO ₂ ) ₂ aqueous solution:

Ca(OH) ₂ +SO ₂ →CaSO ₃ +H ₂ O

CaSO ₃ +1/2O ₂ →CaSO ₄ ↓

Ca(OH) ₂ +NO+NO ₂ →Ca(NO ₂ ) ₂ +H ₂ O

Filter out calcium sulfate CaSO ₄ , evaporate and concentrate calcium nitrite solution to make calcium nitrite product, which is used as corrosion inhibitor for reinforced concrete;

(2) The flue gas leaving the first denitrification tower enters the second denitrification tower together with part of the nitrogen dioxide gas and manganese dioxide solid produced by pyrolysis of manganese nitrate, and is absorbed by the acidic suspension containing manganese dioxide:

NO+NO ₂ +H ₂ O→2HNO ₂

HNO ₂ +HNO ₃ +MnO ₂ →Mn(NO ₃ ) ₂ +H ₂ O

2NO ₂ +H ₂ O→HNO ₂ +HNO ₃

(3) The flue gas after leaving the second denitrification tower is discharged directly or after being heated. After the Mn(NO ₃ ) ₂ in the circulating absorption liquid exceeds 10%, take out the concentrated solution concentrated into 30-55%; introduce the concentrated manganese nitrate solution into Heating and decomposing in 200-350°C high-temperature airflow, the chemical reaction of the cyclic regeneration of the cyclic absorption medium is as follows:

Mn(NO ₃ ) ₂ ＝MnO ₂ +2NO ₂ ↑

Through the gas-solid separation combination equipment, part of the NO ₂ mixed gas without manganese dioxide enters the first denitrification tower together with the desulfurization gas, and part of the NO ₂ mixed gas containing manganese dioxide enters the second denitrification tower.

Example 2

A denitrification device used in a flue gas denitrification method using manganese oxide as a circulating absorption medium, including a manganese nitrate pyrolyzer, a first denitrification tower and a second denitrification tower:

Manganese nitrate pyrolyzer: the top end is fed with the side line medium-temperature flue gas, and the bottom end is connected to the gas-solid separation component. A part of the gas outlet of the gas-solid separation component is passed into the first denitrification tower through the gas mixer, and the other part of the gas-solid separation component is and the solid outlet are passed into the second denitrification tower;

Denitration Tower ₁ : The top is fed into the alkaline absorbent in the alkali circulation tank to absorb SO2 and NOx gas in the desulfurization flue gas, the bottom is fed into the mixed gas from the gas mixer, and the gas-solid Part of the nitrogen dioxide gas separated by the separation module is directly passed into the bottom of the second denitrification tower from the outlet gas of the first denitrification tower;

The second denitrification tower: the top is passed into the acidic solution containing manganese dioxide in the manganese circulation tank, and the bottom is passed into the flue gas leaving the first denitrification tower and another part of nitrogen dioxide gas and manganese dioxide solids remaining in the gas-solid separation component. The manganese circulation tank is connected with the manganese nitrate pyrolyzer.

Further, the alkali circulation tank is connected to the calcium nitrite evaporator, the calcium sulfite is oxidized to calcium sulfate by the oxygen in the flue gas and filtered out, the calcium nitrite solution is evaporated and concentrated by the calcium nitrite evaporator, and further made into calcium nitrite product.

The denitration system formed by the denitration device in the present invention will be further described below through the connection relationship between the various components.

A flue gas denitration device using manganese oxide as a circulating absorption medium, including a denitrification tower, an alkali circulation tank, a calcium circulation pump, a calcium evaporator, a gas mixer, a manganese nitrate decomposer, a gas-solid separation component, and a denitrification second Tower, manganese circulation tank, manganese circulation pump, manganese nitrate evaporator and concentrated manganese pump, the top of the first denitrification tower is connected to the second denitrification tower through a flue gas pipeline, and the bottoms of the first denitrification tower and the second denitrification tower are respectively equipped with alkali circulation tanks One end of the alkali circulation tank is connected to the upper end of the first denitration tower through a calcium circulation pump, and the other end of the alkali circulation tank is connected to the calcium evaporator through a pipeline; one end of the manganese circulation tank is connected to the upper end of the second denitration tower through a manganese circulation pump, and the manganese circulation The other end of the tank is connected to the manganese nitrate evaporator, and the manganese nitrate evaporator is connected to the manganese nitrate decomposer through a concentrated manganese pump. One end of the gas-solid separation component is connected to the lower end of the second denitrification tower, the other end of the gas-solid separation component is connected to a gas mixer, one end of the gas mixer is fed with flue gas, and the other end of the gas mixer is connected to the lower end of the first denitrification tower.

In the present invention, through the gas-solid separation combination equipment, part of the NO mixed gas without manganese _dioxide enters the first denitrification tower together with the desulfurization gas, and part of the mixed gas containing manganese dioxide NO2 enters the _second denitrification tower, and the flue gas containing nitrogen oxides NOx The flue gas and part of the self-produced nitrogen dioxide NO ₂ pass into the first denitrification tower, and react with the alkaline absorbent in the absorption liquid to form nitrite (when the alkaline absorbent is calcium oxide or calcium hydroxide slurry , react with calcium hydroxide in the absorption liquid to form calcium nitrite); the flue gas leaving the first denitrification tower still contains a small amount of nitrogen oxide NOx, which is mixed with self-produced nitrogen dioxide and manganese dioxide and enters the second denitrification tower together. The circulating absorption liquid in the tower is an acidic aqueous solution mixed with manganese dioxide. Under acidic conditions, manganese dioxide oxidizes the denitrification product nitrous acid into nitric acid and simultaneously generates manganese nitrate. Concentrated manganese nitrate solution is obtained by evaporation and concentration; the concentrated manganese nitrate solution is sprayed into the side stream flue gas at 200-350°C to generate self-produced nitrogen dioxide gas and manganese dioxide solid, which are circulated into the first and second denitrification towers. After secondary absorption treatment, the sulfur dioxide SO ₂ in the flue gas is ≤1PPM, and the NOx is ≤50PPM.

Example 3

Taking the denitrification system composed of the first denitrification tower (lower tower) and the second denitrification tower (upper tower) arranged side by side as an example, the flue gas denitrification method in the present invention will be further described.

The total height of the denitrification packed tower is 2000mm, the upper and lower parts are 1000mm, and the diameter is 50mm; the operating temperature is 35°C, and 5L/min of simulated mixed gas containing _NO350ppm , NO2 450ppm, _O26 . Add 2% Ca(OH) ₂ suspension, liquid-gas ratio (L/G)=6.5. Measure NO87ppm and NO2 _62ppm in the outlet gas of the lower tower. Directly pass the gas from the outlet of the lower tower to the bottom of the upper tower, sprinkle the suspension of 1‰MnO ₂ and 3% HNO ₃ into the top of the tower, the liquid-gas ratio (L/G)=10, measure NO28ppm, NO ₂ 21ppm.

Example 4

Taking the denitrification system composed of the first denitrification tower and the second denitrification tower arranged in parallel left and right as an example, the flue gas denitrification method in the present invention will be further described.

As shown in Figure 1, the first denitrification tower and the second denitrification tower are packed towers with a height ^of 5000mm and a diameter of 1000mm. Mix them and pass them into the bottom of the first denitrification tower. The measured gas composition is SO ₂ 72ppm, NO378ppm, and NO ₂ 502ppm. Sprinkle 2% Ca(OH) ₂ suspension into the top of the first tower, and the liquid-gas ratio (L/G)= 3.5. Measure NO71ppm and NO ₂ 42ppm in the outlet gas of the first tower. The outlet gas of the first denitrification tower is passed directly to the bottom of the second denitrification tower, and the suspension of 1‰MnO ₂ and 2% HNO ₃ is sprinkled on the top of the tower, the liquid-gas ratio (L/G)=6, and the NO21ppm in the outlet gas of the upper tower is measured , NO ₂ 16ppm, SO ₂ 2ppm.

After continuously supplementing Ca(OH) ₂ and running continuously for 48 hours, the denitrification liquid in the first denitrification tower contains 6.8% Ca(NO ₃ ) ₂ , which is evaporated and concentrated into a calcium nitrite product with a content of 95%.

After 96 hours of continuous operation, the denitrification liquid of the second denitrification tower containing 5.3% Mn(NO ₃ ) ₂ was evaporated into a 50% concentrated solution, sprayed into the side stream gas at 320°C, and the decomposition rate of Mn(NO ₃ ) ₂ was measured to be 89% , the newly generated NO ₂ gas and the side stream mixed gas are introduced into the first denitration tower and the second denitration tower after gas-solid separation, and the circulation strengthens the absorption of NO _X gas in the flue gas and the conversion of nitrite in the absorption liquid into nitrate.

The above is not a limitation of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the essential scope of the present invention, some changes, modifications, additions or substitutions can also be made, these Improvements and changes should also be regarded as the protection scope of the present invention.

Claims (10)

1. the flue gas method of denitration that a kind is cyclic absorption medium with manganese oxide, it is characterised in that comprise the steps:

Pyrolysis manganese nitrate；Heating manganese nitrate generates nitrogen dioxide gas and manganese dioxide solid；

Denitration: pass into nitrogen dioxide gas in the flue gas after desulfurization, uses the SO in alkaline absorbent Absorption Desulfurization flue gas₂And NO_xGas, generates sulfate and nitrite；

Secondary denitration: use the acid solution containing manganese dioxide as absorbent, absorb NO that is in a denitration rear pass gas and that artificially add together with manganese dioxide solid_xGas, generates manganese nitrate.

2. according to claim 1 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterised in that manganese nitrate in described pyrolysis manganese nitrate step adopts the manganese nitrate generated in secondary denitration.

3. according to claim 1 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterised in that nitrogen dioxide gas in a described denitrification step adopts the nitrogen dioxide gas that pyrolysis manganese nitrate obtains.

4. according to claim 1 or 3 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterised in that the nitrogen dioxide gas passed in a described denitrification step is to make its NO carried out before a denitration in mixing gas₂/ NO mol ratio≤1.

5. according to claim 1 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterised in that the sulfate generated in a described denitrification step and nitrite, filter out solid phase, evaporation liquid phase makes nitrite product.

6. according to claim 1 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterized in that, in described pyrolysis manganese nitrate step, manganese nitrate aqueous solution it is injected directly in side line temperature flue gas or adds in hot-air so that it is decomposing between 200-350 DEG C and produce nitrogen dioxide and manganese dioxide.

7. according to claim 1 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterised in that the alkaline absorbent in a described denitrification step is set to NaOH, Mg (OH)₂、Fe(OH)₃, CaO or Ca (OH)₂In any one.

8. according to claim 1 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterized in that, in described secondary denitrification step, the acid solution of manganese dioxide adopts the mixed solution containing manganese dioxide and nitric acid, wherein, manganese dioxide concentration is 0.1%-5%, concentration of nitric acid is 0-10%, and operation temperature is set to 15-60 DEG C.

9. according to claim 8 a kind of be cyclic absorption medium with manganese oxide flue gas method of denitration, it is characterised in that described operation temperature is set to 30-55 DEG C.

10. according to claim 1 a kind of be cyclic absorption medium with manganese oxide the denitrification apparatus that adopts of flue gas method of denitration, it is characterised in that include manganese nitrate pyrolysis apparatus, denitration one tower and denitration two tower:

Manganese nitrate pyrolysis apparatus: top passes into temperature flue gas in side line, and bottom connects gas solid separation assembly, and the portion gas of this gas solid separation assembly passes in denitration one tower by gas mixer, remaining gas and solid are entered in denitration two tower by gas solid separation module outlet；

Denitration one tower: top passes into the alkaline absorbent in alkali circulating slot, the SO in Absorption Desulfurization flue gas₂With NOx gas, bottom passes into the mixing gas come in gas mixer, passes into the part nitrogen dioxide gas that gas solid separation components apart goes out in gas mixer, and the exit gas of denitration one tower is passed directly into denitration two tower bottom；

Denitration two tower: top passes into the acid solution in manganese circulating slot containing manganese dioxide, bottom passes into out remaining another part nitrogen dioxide gas and manganese dioxide solid in the flue gas of denitration one tower and gas-solid separation assembly, described manganese circulating slot and manganese nitrate pyrolysis apparatus and connects.