CN101632897A - Method for simultaneously removing sulfur oxides and nitric oxides in flue gas - Google Patents

Abstract

A method for simultaneously removing sulfur oxides and nitrogen oxides in flue gas belongs to the technical field of flue gas purification. The method is that the flue gas from the combustion equipment enters the fluidized bed reactor through the flue, and water or steam is sprayed into the flue gas flue before the flue gas enters the fluidized bed reactor, and the flue gas in the flue contains O _2. H ₂ O, SO ₂ and NOx gas components, and control the flue gas temperature in the range of 90°C to 200°C; then inject fresh absorbent CaO and/or Ca(OH) ₂ directly into the flue to oxidize NO ; The temperature of the fluidized bed reactor is controlled between 50°C and 90°C, and the flue gas is desulfurized and denitrified in the fluidized bed reactor. In the method, by adjusting the process steps and controlling the reaction conditions, simultaneous desulfurization and denitrification can be realized in the same system. When the calcium-sulfur-nitrogen molar ratio Ca/(S+0.5N) is 1.3, the _SO2 removal rate can reach over 85%, and the NO removal rate can reach over 60%.

Description

A method for simultaneously removing sulfur oxides and nitrogen oxides from flue gas

technical field

The invention relates to a desulfurization and denitrification method for fossil fuel combustion flue gas, belonging to the technical field of flue gas purification.

Background technique

Today, due to the large-scale use of fossil fuels, more than 20 million tons of sulfur oxides (mainly _SO2 ) and more than 10 million tons of nitrogen oxides (mainly NO) are discharged into the atmosphere every year, causing Serious acid rain pollution. At present, technologies for controlling sulfur dioxide emissions that have been applied on a large scale include limestone-gypsum method and semi-desulfurization flue gas desulfurization technology (spray drying method and flue gas circulating fluidized bed method), which are characterized by high desulfurization efficiency, but Unable to denitrify. Especially for the semi-dry flue gas desulfurization technology, when CaO or Ca(OH) ₂ is used as the absorbent, although the finer the absorbent particles, the higher the reactivity, but the calcium-sulfur molar ratio (relative to the SO ₂ in the inlet flue gas ) actually exceeds 1.3 in order to achieve a higher desulfurization efficiency. The more mature technologies for reducing nitrogen oxide emissions in flue gas include SCR (selective catalytic reduction) and SNCR (selective non-catalytic reduction), both of which use ammonia or urea to reduce nitrogen oxides in flue gas to The advantage of SCR is high denitrification efficiency, but the disadvantage is high cost, especially the cost of catalyst, which is difficult for users to accept, and has high requirements for operation and maintenance. The cost of SNCR is relatively low, but the denitrification efficiency It is also low, and has strict requirements on the temperature of the injection point. Both require the reducing agent to be mixed with the flue gas evenly, otherwise part of the reducing agent will escape and cause secondary pollution. The above desulfurization and denitrification technologies implement separate control of sulfur dioxide and nitrogen oxides, and the investment in equipment is relatively large.

Contents of the invention

The purpose and task of the present invention is to provide a method for simultaneously removing sulfur oxides and nitrogen oxides in flue gas for the deficiencies and defects of the prior art. In the case of molar ratio, through reasonable control of process steps and operating parameters, simultaneous desulfurization and denitrification can be realized in one system, thereby further saving equipment investment and achieving good desulfurization and denitrification effects.

Technical scheme of the present invention is as follows:

A method for simultaneously removing sulfur oxides and nitrogen oxides in flue gas, characterized in that the method comprises the steps of:

1) The flue gas from the combustion equipment enters the fluidized bed reactor through the flue, and water or steam is sprayed into the flue gas flue before the flue gas enters the fluidized bed reactor, and the flue gas in the flue contains O _2. H ₂ O, SO ₂ and NOx gas components, and control the flue gas temperature in the range of 90°C to 200°C; then directly inject one or both of the fresh absorbent CaO and Ca(OH) ₂ into the flue gas In the pipeline, it first participates in the oxidation process of NO in the flue gas, and controls the calcium-sulfur-nitrogen molar ratio Ca/(S+0.5N) between 1.0 and 2.5 to realize partial desulfurization and denitrification functions;

2) The flue gas is desulfurized and denitrified in the fluidized bed reactor. By spraying water into the fluidized bed reactor, the temperature of the fluidized bed reactor is controlled between 50°C and 90°C. Operate at a temperature of 5°C to 25°C with a dew point;

3) The flue gas after desulfurization and denitrification enters the separator through the pipeline, and part of the separated solid particles in the separator returns to the fluidized bed reactor or is sprayed into the original flue gas flue and enters the fluidized bed reactor with the flue gas. Part of it is discharged from the system to maintain the material balance of the whole system; the purified flue gas is discharged from the flue.

The technical feature of the present invention is also that: the volume fraction of water vapor in the flue gas at the point where the absorbent is injected is between 5% and 25%, and the volume fraction of _O2 is between 1% and 15%. Control the molar ratio of calcium, sulfur and nitrogen Ca/(S+0.5N) between 1.0 and 2.5. Preferably, the flue gas temperature at the injection point of the absorbent is controlled between 100 and 150°C. The average particle diameter d ₅₀ of the absorbent is preferably 2 μm to 50 μm, and the R ₉₀ is less than 10%. In the fluidized bed reactor, the gas flow rate is controlled to be 3m/s-10m/s, and the average particle content is controlled to be 1kg/m ³ -10kg/m ³ . The separator is an inertial separator, an electrostatic precipitator or a bag filter.

Compared with the prior art, the present invention has the following advantages and outstanding effects:

When the temperature of the absorbent injection point is 100-150°C, the volume fraction of oxygen in the flue gas is in the range of 1-15% (dry flue gas), the volume fraction of water vapor is between 5-30%, and the molar ratio of calcium, sulfur and nitrogen When Ca/(S+0.5N) is 1.3, the removal rate of SO ₂ can reach more than 85%, and the removal rate of NO can reach more than 60%. When using the same calcium-sulfur molar ratio as the traditional semi-dry flue gas desulfurization technology, its desulfurization effect is significantly improved. While achieving high-efficiency desulfurization, it can also remove NO in the flue gas, so that sulfur dioxide in the conventional flue gas Within the range of concentration and nitrogen oxide concentration, sulfur oxide and nitrogen oxide emissions can meet the national environmental protection requirements.

Another outstanding effect of the present invention is to achieve the purpose of simultaneous desulfurization and denitrification in one system. According to the characteristics of the flue gas composition, through reasonable control of the process steps and operating parameters, the nitrogen monoxide is first catalyzed and oxidized to nitrogen dioxide, and then absorbed by the absorbent Ca(OH) ₂ or CaO together with sulfur dioxide to achieve a good The effect of desulfurization and denitrification greatly saves equipment investment, and it is not necessary to establish two sets of control devices because of the difference between sulfur oxides and nitrogen oxides, which effectively reduces the control cost of flue gas pollutant emissions.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

1-original flue gas flue; 2-fluidized bed reactor; 3-steam or water injection pipe; 4-absorbent storage tank; 5-water spray pipe; 6-fluidized bed reactor outlet flue; 7-separator; 8-return pipe; 9-ash outlet; 10-clean flue gas flue

Detailed ways

The principle and technical process of the present invention will be further described below with the aid of the accompanying drawings.

Fig. 1 is a process flow diagram of the present invention. The flue gas from the combustion equipment enters the fluidized bed reactor 2 through the original flue gas flue 1, and before the flue gas enters the fluidized bed reactor, water or steam is injected into the flue gas through the steam or water injection pipe 3 Flue gas, the flue gas in the flue contains O ₂ , H ₂ O, SO ₂ and NOx gas components, and the temperature of the flue gas is controlled within the range of 90 ° C to 200 ° C, while ensuring that the volume fraction of water vapor in the flue gas is 5 %～25%. Then one or both of the fresh absorbents CaO and Ca(OH) ₂ are directly injected into the flue from 4 channels of the storage box, fully mixed with the flue gas, and first participate in the oxidation process of NO in the flue gas to control the calcium-sulfur _The nitrogen molar _ratio Ca/(S+0.5N) is between 1.0 and 2.5; on the one hand, it participates in the desulfurization _reaction ; reaction to achieve the purpose of denitrification. Since some SO ₂ and NOx are not removed in time in the flue, after entering the fluidized bed reactor 2, they further react with the unreacted absorbent quicklime CaO or slaked lime Ca(OH) ₂ to make most of the SO ₂ and NOx was captured. In order to ensure a high desulfurization and denitrification efficiency in the fluidized bed reactor, the amount of water sprayed is controlled through the water spray pipe 5 to ensure that the temperature in the fluidized bed reactor is between 50°C and 90°C and is 5°C higher than the dew point ~15°C range work. The flue gas after desulfurization and denitrification carries the removal products through the outlet flue 6 of the fluidized bed reactor and enters the separator 7. The solid materials separated by the separator mainly contain CaO or Ca(OH) ₂ and desulfurization products CaSO ₄ and CaSO ₃ , denitrification products Ca(NO ₃ ) ₂ , Ca(NO ₂ ) ₂ and other substances, in order to improve the utilization rate of the absorbent, part of the separated solid materials will be recycled and directly returned to the fluidized bed reactor through the return pipeline 8 , to re-participate in the chemical reaction process of simultaneous desulfurization and denitrification. Part of the solid material is discharged from the ash discharge port 9 to maintain the solid material balance of the entire system, and the dust-removed flue gas is discharged from the clean flue gas flue 10 .

In addition, part of the solid material returned from the return pipe 8 can also be directly injected into the original flue gas flue 1, and enter the circulating fluidized bed reactor with the flue gas, thereby prolonging the contact between the absorbent and the pollutants _SO2 and NOx time, increase the oxidation rate of nitric oxide, and enhance the effect of desulfurization and denitrification. The gas velocity in the fluidized bed reactor 7 is about 3m/s to 5m/s, the solid material mass in the fluidized bed reactor 7 is 6kg/m ³ on average, and the gaseous pollutants SO ₂ , SO ₃ , NO, NO ₂ and HCl are largely absorbed in the fluidized bed reactor 7 by the fine-grained active absorbent. This method can also remove HCl in the flue gas, and the hygroscopic CaCl ₂ formed by the reaction with the absorbent helps to improve the efficiency of desulfurization and denitrification.

The principle of simultaneous desulfurization and denitrification is: in addition to the pollutants _SO2 and NO in the flue gas, the flue gas at the point where the absorbent is injected must simultaneously contain 1% to 15% of oxygen and 5 to 30% of water vapor. SO ₂ in the flue gas can be removed directly by reacting with CaO and (or) Ca(OH) ₂ , it can also be removed together with oxygen and water vapor in the flue gas in the absorbent quicklime CaO or slaked lime Ca(OH) ) ₂ in the presence of catalyzed NO oxidation into NO ₂ , which then reacts with CaO or Ca(OH) ₂ to achieve the purpose of reducing SO ₂ and NOx in the flue gas. In the temperature range of the present invention, when _the absorbent is CaO or Ca(OH) ₂ , the SO in the flue gas can be directly removed in the form of sulfate or sulfite, while water vapor, Under the joint action of oxygen, SO ₂ and Ca(OH) ₂ or CaO, NOx in flue gas can be removed in the form of nitrate or nitrite. The main desulfurization and denitrification reaction equation is:

Ca(OH) ₂ +SO ₂ →CaSO ₃ +H ₂ O (1)

CaO+SO ₂ →CaSO ₃ (2)

Under the co-catalysis of SO ₂ , O ₂ , water vapor and CaO or Ca(OH) ₂ , the reaction of NO being oxidized to NO2 is:

NO+1/2O ₂ ←→NO ₂ (3)

Additionally, the following responses are included

2NO ₂ (g)←→N ₂ O ₄ (g) (4)

NO(g)+NO ₂ (g)←→N ₂ O ₃ (g) (5)

N ₂ O ₃ (g)+H ₂ O←→2HNO ₂ (g) (6)

N ₂ O ₄ (g)+H ₂ O(g)←→HNO ₂ (g)+HNO ₃ (g) (7)

HNO ₂ (g)+Ca(OH) ₂ ←→Ca(NO ₂ ) ₂ +H ₂ O (8)

HNO ₃ (g)+Ca(OH) ₂ ←→Ca(NO ₃ ) ₂ +H ₂ O (9)

HNO ₂ (g)+CaO←→Ca(NO ₂ ) ₂ (10)

HNO ₃ (g)+CaO←→Ca(NO ₃ ) ₂ (11)

In addition to the above separate desulfurization and denitrification reactions, there is also a chemical reaction that promotes each other between desulfurization and denitrification, thereby significantly improving the desulfurization rate and denitrification rate. The specific general package reaction equation is as follows:

2NO ₂ +CaSO ₃ →Ca(NO ₂ ) ₂ +CaSO ₄ (12) makes the desulfurization reactions (1) and (2) proceed to the right, thus ensuring that the desulfurization and denitrification process is more effective than the conventional semi-dry desulfurization process. High desulfurization efficiency. Moreover, the effect is good when the average particle size d ₅₀ of the absorbent is 2 μm to 20 μm. The fluidized bed reactor operates at a temperature of 5°C to 25°C higher than the dew point, and the gas velocity in the fluidized bed reactor is controlled at 4m/s to 6m/s, the average solid residence time is controlled at 30min, and the average solid When the content is controlled at 6kg/ ^m3 , the method according to the present invention can reliably maintain high desulfurization and denitrification efficiency. Under these conditions, even with high _SO2 content in the exhaust gas, the _SO2 removal efficiency in the flue gas can be reliably maintained greater than 85%, and the NOx removal efficiency is greater than 60%.

Specific process steps: Combustion flue gas containing SO ₂ , NO, water vapor, oxygen, carbon dioxide and nitrogen enters the fluidized bed reactor from the original flue gas flue, and by spraying water or water vapor, on the one hand, the flue gas temperature is controlled at In the range of 90°C to 200°C, at the same time, ensure that the volume fraction of water vapor in the flue gas is between 5% and 25%. Then, one or both of the fresh absorbents CaO and Ca(OH) ₂ can be directly sprayed into the flue with a flue gas temperature of 90°C to 200°C and fully mixed with the flue gas. The absorbent is mixed with SO ₂ , water vapor, Oxygen together catalyzes the oxidation of NO to NO ₂ , and NO ₂ and SO ₂ are simultaneously absorbed by the absorbent. The gaseous pollutants SO ₂ and NOx that have not been removed in time enter the circulating bed reactor with the flue gas and further react with the absorbent, so that most of the SO ₂ and NOx are captured. In order to ensure a high desulfurization and denitrification efficiency in the fluidized bed reactor, the amount of water sprayed is controlled through the water spray pipe 5 to ensure that the temperature in the fluidized bed reactor is between 50°C and 90°C and is 5°C higher than the dew point ~ 25 ℃ range work. The flue gas after desulfurization and denitrification enters the separator with the removed products, and part of the separated solid materials are discharged from the ash discharge port to maintain the solid material balance of the whole system. The flue gas after dust removal is discharged from the flue gas flue 10 . The materials separated by the separator mainly contain CaO or Ca(OH) ₂ and desulfurization products CaSO ₄ , CaSO ₃ , denitrification products Ca(NO ₃ ) ₂ and Ca(NO ₂ ) ₂ and other substances. In order to improve the utilization rate of the absorbent, some of the separated materials are recycled and directly returned to the fluidized bed reactor through the return pipeline to re-participate in the chemical reaction process of simultaneous desulfurization and denitrification. In addition, part of the solid material returned from the return pipe can also be directly injected into the original flue gas flue, and enter the circulating fluidized bed reactor with the flue gas, thereby prolonging the contact time between the absorbent and pollutants SO ₂ and NOx, and improving The oxidation rate of nitric oxide enhances the effect of desulfurization and denitrification. The gaseous pollutants SO ₂ , SO ₃ , NO and NO ₂ are efficiently absorbed by the absorbent in the flue and the fluidized bed reactor. This method can also remove HCl in the flue gas, which reacts with the absorbent to form hygroscopic CaCl ₂ , which helps to improve the efficiency of desulfurization and denitrification. The finer the particle size of the absorbent, the better the primary desulfurization and denitrification effect. Quicklime (CaO) or slaked lime (Ca(OH) ₂ ) with an average particle size d ₅₀ of the absorbent of less than 100 μm has a better desulfurization effect. The products discharged from the flue gas cleaning system can be recycled.

The present invention is illustrated below with several specific examples:

Embodiment 1: adopt slaked lime (as absorbent, average particle size d ₅₀ is 20 μ m, R ₉₀ is less than 10%, calcium sulfur nitrogen molar ratio (Ca/(S+0.5N)) is 1.3, and absorbent injects point flue gas The temperature is 110°C, the temperature inside the fluidized bed reactor is 80°C, the temperature difference above the dew point is 20°C, the volume fraction of oxygen in the flue gas is 5%, the volume fraction of water vapor is 20%, the NO is 400ppm, the _SO2 is 800ppm, and the desulfurization efficiency is 85 %, the denitrification efficiency is 60%.

Example 2: quicklime is used as the absorbent, the average particle size _d50 of the absorbent is 50 μm, the _R90 is less than 10%, the molar ratio of calcium, sulfur and nitrogen Ca/(S+0.5N) is 1.1, and the flue gas temperature at the injection point of the absorbent 150°C, the volume fraction of oxygen in the flue gas is 3%, the volume fraction of water vapor is 20%, the temperature inside the fluidized bed reactor is 60°C, the temperature difference above the dew point is 15°C, the NO is 400ppm, the _SO2 is 800ppm, and the desulfurization efficiency is 80% , The denitrification efficiency is 50%.

Example 3: quicklime is used as the absorbent, the average particle size _d50 is 20 μm, the _R90 is less than 10%, the calcium sulfur nitrogen molar ratio (Ca/(S+0.5N)) is 2.5, and the flue gas temperature at the injection point of the absorbent 120°C, the volume fraction of oxygen in the flue gas is 8%, the volume fraction of water vapor is 30%, the temperature inside the fluidized bed reactor is 70°C, the temperature difference above the dew point is 15°C, the NO is 400ppm, the _SO2 is 800ppm, and the desulfurization efficiency is 95% , The denitrification efficiency is 75%.

Example 4: Using slaked lime as the absorbent, the average particle size d ₅₀ is 80 μm, the R ₉₀ is less than 20%, the calcium sulfur nitrogen molar ratio (Ca/(S+0.5N)) is 1.2, and the flue gas temperature at the injection point of the absorbent 100°C, the volume fraction of oxygen in the flue gas is 3%, the volume fraction of water vapor is 5%, the temperature inside the fluidized bed reactor is 90°C, the temperature difference above the dew point is 25°C, the NO is 400ppm, the _SO2 is 800ppm, and the desulfurization efficiency is 70% , The denitrification efficiency is 45%.

Claims (7)

1. a method that removes flue gas sulphur oxide and nitrogen oxide simultaneously is characterized in that this method comprises the steps:

1) enters in the fluidized-bed reactor by flue from the flue gas in the combustion apparatus, before flue gas enters fluidized-bed reactor, water or water vapour are sprayed into the flue gas flue, contain O in the flue gas in the flue ₂, H ₂O, SO ₂With the NOx gas componant, and the control flue-gas temperature is in 90 ℃～200 ℃ scopes; Then with fresh absorbent CaO and Ca (OH) ₂In one or both be directly injected in the flue, participate in earlier the oxidizing process of NO in the flue gas, control calcium sulphur nitrogen mol ratio Ca/ (S+0.5N) realizes the desulfurization and the denitration function of part between 1.0～2.5;

2) flue gas carries out desulphurization denitration in fluidized-bed reactor, and by spraying water in fluidized-bed reactor, the temperature of control fluidized-bed reactor is between 50 ℃～90 ℃, and fluidized-bed reactor moves under the temperature conditions that is higher than 5 ℃～25 ℃ of dew points;

3) flue gas behind the desulphurization denitration enters separator by pipeline, a separated solid particle part of getting off is returned fluidized-bed reactor or is sprayed into flue and enters fluidized-bed reactor with flue gas again in the separator, another part is discharged from system, to keep the material balance of whole system; Discharge from the flue pipeline through the flue gas that purifies.

2. according to the described a kind of method that removes flue gas sulphur oxide and nitrogen oxide simultaneously of claim 1, it is characterized in that: absorbent sprays into the volume fraction of steam in the flue gas between 5～25%, O ₂Volume fraction between 1～15%.

3. according to the described a kind of method that removes flue gas sulphur oxide and nitrogen oxide simultaneously of claim 1, it is characterized in that: control calcium sulphur nitrogen mol ratio Ca/ (S+0.5N) is between 1.0～2.5.

4. according to claim 1,2 or 3 described a kind of methods that remove flue gas sulphur oxide and nitrogen oxide simultaneously, it is characterized in that: the flue-gas temperature in the described flue is controlled between 100～150 ℃.

5. according to the described a kind of method that removes flue gas sulphur oxide and nitrogen oxide simultaneously of claim 4, it is characterized in that: the average grain diameter d of absorbent ₅₀Be 2 μ m～100 μ m, R ₂₀₀Less than 10%.

6. according to the described a kind of method that removes flue gas sulphur oxide and nitrogen oxide simultaneously of claim 1, it is characterized in that: gas flow rate is controlled to be 3m/s～10m/s in fluidized-bed reactor, and the average content of particle is controlled to be 1kg/m ³～10kg/m ³

7. according to the described a kind of method that removes flue gas sulphur oxide and nitrogen oxide simultaneously of claim 1, it is characterized in that: described separator adopts inertia separator, electric cleaner or sack cleaner.

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