JP5230900B2 - Denitration method of exhaust gas - Google Patents

Description

  The present invention relates to a denitration method for exhaust gas, and more particularly to a denitration method for reductively removing nitrogen oxides in exhaust gas discharged from ships, power generation diesel engines, and the like.

  In recent years, there has been a great interest in reducing particulate matter and nitrogen oxides emitted from automobile diesel engines such as buses and trucks. Similarly, exhaust gases from ships and diesel engines for power generation, boiler exhaust gases, Removal of harmful substances in plant off-gas is also an important issue. However, while diesel engines for automobiles use light oil with a low sulfur content as fuel, ships and diesel engines for power generation use fuels with a high sulfur content such as A heavy oil or C heavy oil. For this reason, the exhaust gas contains a large amount of sulfur oxides, which is a major obstacle in removing harmful substances.

  Generally, as a denitration method for exhaust gas, a non-catalytic denitration method and a selective reduction catalyst method (SCR method) are known. As the non-catalytic denitration method, a denitration method using a nitrogen-based reducing agent such as ammonia or urea is widely known, but high activity cannot be obtained unless the exhaust gas temperature is a high temperature state of 900 to 1000 ° C. (for example, Patent Documents). 1 and 2)), and relatively low temperature exhaust gas of about 250 to 450 ° C. discharged from ships, diesel engines for power generation, etc., because it is necessary to heat the exhaust gas to raise the temperature, etc. The increase in cost caused the application to be difficult.

  Patent Document 3 proposes a method for reducing and decomposing nitrogen oxides in exhaust gas by using a pyrolytic agent such as ammonia thermally decomposed by an afterburner. However, in this method, a reducing agent such as ammonia is mixed and burned in the fuel gas of the afterburner used for thermal decomposition, so that ammonia burns or amine radicals obtained by thermal decomposition disappear. There was a problem that the denitration rate was low.

  On the other hand, in Patent Document 4, as one of the SCR methods, a part of nitric oxide in exhaust gas is oxidized to nitrogen dioxide, and then a nitrogen-based reducing agent such as ammonia or urea is added to add a vanadium-titania catalyst. It is proposed to reduce the contact. However, this SCR method is inferior to the non-catalytic denitration method in that a large amount of SCR catalyst is used. Further, when the exhaust gas temperature is 300 ° C. or lower, if the sulfur dioxide in the exhaust gas is oxidized to sulfur trioxide, etc., ammonia To produce ammonium sulfate, which is deposited on the SCR catalyst, reducing its catalytic activity. For this reason, the SCR method has only been adopted for a high temperature state of 300 ° C. or higher where sulfur dioxide is difficult to oxidize or an exhaust gas having a sulfur oxide concentration of about 1 ppm or less.

  In addition, the SCR method using hydrocarbons with low reactivity to sulfur oxides as the reducing agent can also be denitrated in the presence of sulfur oxides, but at the same time as catalyst degradation occurs, the reactivity of nitrogen oxides In order to improve this, it is necessary to operate in a high temperature state where the exhaust gas temperature is 350 ° C. or higher, so that it has not been put into practical use (see, for example, Patent Documents 4 and 5).

Therefore, in the non-catalytic denitration method and the SCR method, the nitrogen oxide in the exhaust gas which is a relatively low temperature of about 250 to 450 ° C. discharged from a ship or a diesel engine for power generation and contains sulfur oxides, There has not yet been established a denitration method that efficiently removes sulfur oxides without being affected by sulfur oxides.
US Pat. No. 6,066,303 JP 2002-136837 A JP 54-99076 A JP 2001-525902 A JP 2002-349248 A

  An object of the present invention is a denitration method for efficiently removing nitrogen oxides in exhaust gas containing a sulfur oxide at a low temperature without being affected by the sulfur oxides. Is to provide.

An exhaust gas denitration method that achieves the above object is a denitration method that reductively removes nitrogen oxides in exhaust gas containing nitrogen monoxide and sulfur dioxide, and oxidizes a part of the nitrogen monoxide in the exhaust gas. A first step of generating nitrogen dioxide, a second step of separately adding a nitrogen compound and a hydrocarbon compound to the high temperature region to generate an amine radical, the nitric oxide discharged from the amine radical and the first step, and A third step of mixing an exhaust gas containing nitrogen dioxide, and in the first step, the exhaust gas is a catalyst having an active metal supported on a support containing titanium, the active metal being a vanadium compound, a niobium compound , A contact treatment with an oxidation catalyst that is at least one selected from a molybdenum compound and a tungsten compound, or a plasma irradiation treatment to convert nitric oxide into a diacid Characterized in that it is oxidized to nitrogen.

  The exhaust gas denitration method of the present invention increases the reactivity of nitrogen oxides in the exhaust gas by oxidizing a part of nitrogen monoxide in the exhaust gas to generate nitrogen dioxide in the first step, and the downstream third step. Can be easily reduced and decomposed. Further, in the second step, a nitrogen compound and a hydrocarbon compound are added to a high temperature region, and an amine radical is efficiently generated by a reaction between the hydroxy radical generated from the hydrocarbon compound and the nitrogen compound, and an unreacted nitrogen compound Is less likely to remain. Furthermore, in the third step, the amine radical and the exhaust gas containing nitrogen monoxide and nitrogen dioxide discharged from the first step can be immediately mixed to reduce and decompose nitrogen oxides in the exhaust gas. Therefore, even if the exhaust gas temperature is low, since the reactivity of both nitrogen oxides and amine radicals is high, it is possible to efficiently remove nitrogen oxides, and no reduction catalyst is used. Even if it contains sulfur oxide, ammonium sulfate or the like is not generated and the denitration efficiency is not lowered.

The present invention is described in detail below.
FIG. 1 is a block flow diagram showing an example of a process in the exhaust gas denitration method of the present invention. In FIG. 1, exhaust gas 31 discharged from the diesel engine 1 has a portion of nitric oxide in the first step 2. Nitric oxide and nitrogen dioxide are reduced and decomposed in the third step 4 by the amine radicals 33 generated in the second step 3 in the third step 4.

  The diesel engine 1 to which the denitration method of the present invention is applied is not particularly limited and is preferably a marine vessel or a power generation diesel engine, but may be an automobile diesel engine. Further, the present invention is not limited to diesel engines, and can be applied as a denitration method for boilers and various plant off-gases.

  Further, the fuel 30 of the diesel engine 1 is not particularly limited, and light oil, A heavy oil, C heavy oil, DME, or the like can be used. Among these, in order to take advantage of the characteristics of the denitration method of the present invention, it is preferable to use a fuel containing sulfur, and A heavy oil or C heavy oil is preferably used. A heavy oil is stipulated in the JIS standard (JIS K2205) as 1 type 1 sulfur content 0.5 mass% or less, 1 type 2 sulfur content 2.0 mass% or less, C heavy oil type 3 type 1 The sulfur content is specified as 3.5% by mass or less. Among these, A heavy oil used for diesel engines such as ships and diesel generators mainly has a sulfur content of 0.2% by mass or less, and C heavy oil mainly has a sulfur content of 3.5% by mass or less. .

  In the denitration method of the present invention, the exhaust gas 31 to be treated is not particularly limited as long as it contains nitrogen monoxide and sulfur dioxide, exhaust gas from ships and power generation diesel engines, exhaust gas from automobile diesel engines, boilers. It may be exhaust gas or plant off gas. In general, the exhaust gas 31 contains harmful substances such as particulate matter, nitrogen oxides and sulfur oxides. The particulate matter is mainly in the form of soot, and the nitrogen oxides are mainly used as nitric oxide. In many cases, sulfur oxides are mainly contained as sulfur dioxide. The concentration of the sulfur oxide containing sulfur dioxide in the exhaust gas 31 is preferably 50 ppm or more, more preferably 100 ppm or more, and particularly preferably 500 ppm or more because the effectiveness of the present invention becomes more remarkable.

  Further, the exhaust gas 31 from the ship and the diesel engine for power generation is relatively low temperature, and as it is, it has been difficult to treat by the conventional non-catalytic denitration method. However, the denitration method of the present invention heats and raises the exhaust gas 31. This makes it possible to perform denitration with high efficiency without requiring a treatment for performing a temperature treatment. In the present invention, even if the temperature of the exhaust gas 31 is preferably about 250 to 450 ° C., particularly about 250 to 300 ° C., the denitration reaction can be performed on the exhaust gas.

  In the denitration method of the present invention, the first step 2 is a treatment step for generating nitrogen dioxide by oxidizing a part of nitrogen monoxide in the exhaust gas 31. Here, it is not always necessary to oxidize all of the nitric oxide in the exhaust gas, and at least a part of it needs to be oxidized to nitrogen dioxide. The oxidation treatment may be performed so that the ratio of nitrogen dioxide to nitrogen oxides in the exhaust gas is preferably 40% by weight or more, more preferably 50% by weight or more, and the ratio of nitrogen dioxide is within the above range. By doing so, the reductive decomposition of nitrogen oxides in the third step of the latter stage can be further effectively advanced, which is preferable.

A method of oxidizing the nitric oxide is a method or a plasma irradiation method is contacted with an acid catalyst. Without oxidizing sulfur dioxide in the exhaust gas 31, since only it is possible to selectively oxidize nitrogen monoxide, a method of contacting the oxide catalyst, into a plasma irradiation method. In general, when exhaust gas is oxidized, not only nitric oxide but also sulfur dioxide is oxidized, making it difficult to remove particulate matter, or reacting with ammonia during the subsequent denitration reaction to produce ammonium sulfate. Although was made is likely to occur adverse effects or, oxidation treatment of the exhaust gas in the present invention is to contact treatment or plasma irradiation treatment with an acid catalyst, and a selective nitric oxide as it is oxidized to nitrogen dioxide, dioxide Sulfur is hardly oxidized and the above-mentioned adverse effects can be prevented.

  In the first step, when the oxidation rate of nitric oxide is Nc and the oxidation rate of sulfur dioxide is Sc, the ratio Sc / Nc of the oxidation rate of sulfur dioxide to the oxidation rate of nitrogen monoxide Nc is preferably 0.01 to 0.2, more preferably 0.01 to 0.1, and still more preferably 0.01 to 0.05. By making the ratio Sc / Nc of the oxidation rate within the above range, the oxidation of nitrogen monoxide to nitrogen dioxide is selectively advanced to increase the reactivity of nitrogen oxides, while sulfur dioxide is converted to sulfur trioxide and the like. It is preferable because it can suppress harmful effects caused by oxidation.

  In the oxidation treatment used in the present invention, the oxidation rate Nc of nitric oxide is preferably 30% or more, more preferably 40% or more, and further preferably 50% or more. By setting the oxidation rate Nc within the above range, nitrogen dioxide can be generated more effectively, which is preferable. Further, the oxidation rate Sc of sulfur dioxide is preferably 5% or less, more preferably 2% or less, and further preferably 1% or less. By setting the oxidation rate Sc within the above range, generation of sulfur trioxide and the like can be advantageously suppressed.

  In the present invention, the oxidation rate Nc of nitrogen monoxide and the oxidation rate Sc of sulfur dioxide are calculated by measuring the nitrogen oxide concentration and the sulfur oxide concentration of each of the exhaust gas 31 and the oxidation treatment gas 32. is there.

  In the present invention, the plasma irradiation treatment is not particularly limited as long as it selectively oxidizes nitric oxide, but preferably includes atmospheric pressure low temperature plasma irradiation treatment, for example, microwave discharge, AC discharge, etc. (For example, pulse discharge or analog discharge), or direct current discharge (for example, spark discharge, arc discharge, glow discharge, or corona discharge).

  The atmospheric pressure low temperature plasma irradiation means preferably has a plasma generating electrode capable of generating plasma by atmospheric pressure pulse discharge, and generates and emits plasma in a state where exhaust gas is always flowing. And nitric oxide can be efficiently oxidized. As such a plasma generating electrode, for example, a coaxial structure having stainless steel, steel, Kanthal, Inconel or the like as a core wire can be cited as a suitable example. Such a plasma generating electrode can oxidize nitric oxide to nitrogen dioxide with low energy.

  On the other hand, when nitric oxide in exhaust gas is oxidized to nitrogen dioxide by contact treatment with an oxidation catalyst, it is preferable to oxidize the exhaust gas by passing it through a catalyst layer having an oxidation catalyst. The substrate of the catalyst layer is not particularly limited as long as it supports the oxidation catalyst and can be in contact with the exhaust gas. For example, a stainless steel metal honeycomb filter, a ceramic honeycomb filter, a wire mesh filter, a ceramic A filtration filter substrate and the like can be preferably mentioned, and a stainless steel metal honeycomb filter is particularly preferable.

In the present invention, the oxidation catalyst is a catalyst obtained by supporting an active metal on a carrier containing titanium, active metal, vanadium compound, niobium compound, in at least which is one oxidation catalyst selected from molybdenum compounds and tungsten compounds In particular, vanadium compounds and tungsten compounds are more preferable. These oxidation catalysts perform a catalytic function of selectively oxidizing nitrogen monoxide to nitrogen dioxide while suppressing oxidation of sulfur dioxide to sulfur trioxide or the like. In addition, the oxidation catalyst having these active metals is less poisoned by sulfur trioxide or the like in the exhaust gas, and it is possible to maintain the selective oxidation function of nitric oxide for a long time.

  The oxidation rate of nitric oxide in the oxidation catalyst having these active metals may be lower than the oxidation rate in a platinum catalyst which is a general oxidation catalyst. However, the low oxidation rate can be compensated by increasing the amount of active metal used. That is, these active metals can be obtained at a lower cost than platinum catalysts, and the amount of nitrogen dioxide produced can be made equivalent to that of platinum catalysts by increasing the amount used.

  In the present invention, the active metal constituting the oxidation catalyst is at least one metal compound selected from vanadium, niobium, molybdenum, and tungsten. For example, vanadium such as vanadium oxide, vanadyl sulfate, vanadyl nitrate, vanadium chloride, etc. Preferred examples include compounds, niobium compounds such as niobium oxide, niobium sulfate and niobium chloride, molybdenum compounds such as molybdenum oxide, molybdenum sulfate and molybdenum chloride, and tungsten compounds such as tungsten oxide, tungsten sulfate and tungsten chloride. it can. Of these, vanadium oxide, tungsten oxide, molybdenum oxide, and niobium oxide can be more preferably used as the active metal. These active metals may be used alone, but two or more active metals among the above may be used in combination.

  In particular, it is preferable to use a vanadium compound and a tungsten compound in combination as the active metal because a more remarkable effect can be obtained. Specifically, vanadium oxide and tungsten oxide, vanadium oxide and molybdenum oxide, and vanadium oxide and niobium oxide can be preferably exemplified. In particular, it is preferable to use vanadium oxide and tungsten oxide as active metals because the oxidation rate of sulfur dioxide can be suppressed while increasing the oxidation rate of nitric oxide.

In the present invention, a carrier for supporting the active metal can be preferably exemplified a carrier T iO _2. Also, the carrier, TiO ₂ and SiO ₂ in combination Awa Seno so on, and _{TiO 2, Al 2 O 3,} SiO 2, a combination of any one of ZrO ₂ may be a carrier obtained by blending. The support for coating the catalyst support may be a general catalyst support other than the support composition such as a metal support base, cordierite or carbon composite. The composition of the support is not particularly limited, and the combination thereof is not limited by the elements constituting the catalyst carrier.

In the present invention, the active metal is supported on a carrier containing titanium . That is, it is preferably supported on TiO ₂ . The use of TiO ₂ in the carrier, while maintaining the oxidation rate of nitrogen monoxide, Ru can be suppressed oxidation rate of sulfur dioxide.

Therefore, the object of the present invention is achieved by using an oxidation catalyst used in the treatment method of the present invention in which vanadium oxide and tungsten oxide are supported on TiO ₂ or in which vanadium oxide is supported on TiO _2. Most preferred above.

  In the present invention, these active metals are powdered, granular, honeycomb-shaped, coated on a wire filter, coated on a ceramic paper roll, coated on a filter cloth, or dip-coated on a honeycomb carrier. Form may be sufficient. Moreover, an active metal can be prepared and used by a well-known method, and can also be used selecting it suitably from commercial products. In addition, the carrier constituting the oxidation catalyst can be prepared and used by a known method, or can be appropriately selected from commercially available products. Therefore, the oxidation catalyst obtained by supporting the active metal on the carrier can be prepared and used by a known method, or can be appropriately selected from commercially available products.

  In the present invention, the oxidation treatment gas 32 exiting the first step preferably has a nitrogen dioxide ratio in the nitrogen oxide of preferably 40% by weight or more, more preferably 50% by weight or more. The reactivity of the oxide increases, and reductive decomposition is facilitated in the next third step. Further, the temperature of the oxidation treatment gas 32 may be 250 ° C. or higher, and even if the exhaust gas temperature is 250 to 450 ° C., a sufficient denitration effect can be obtained. Therefore, the entire exhaust gas is reheated for the purpose of increasing the denitration efficiency. It is not always necessary. Therefore, even a relatively low temperature exhaust gas discharged from a diesel engine or the like can be treated as it is.

  The second step 3 is a treatment step for generating a reducing gas independently of the first step for oxidizing exhaust gas, that is, a treatment for generating amine radicals by adding a nitrogen compound and a hydrocarbon compound to a high temperature region. It is a process. The high temperature region in the second step is preferably a high temperature region of 700 to 1000 ° C. formed around the flame of the burner or the electric heater.

In the high temperature region, for example, when ammonia is used as the nitrogen compound, the following reaction occurs, and an amine radical is generated. The amine radical is composed of nitrogen monoxide, nitrogen dioxide, and the like in the downstream third step. Used for reductive decomposition of nitrogen oxides.
(1) Hydroxyl radicals (OH *) are generated during the combustion reaction of hydrocarbon compounds.
(2) Hydroxy radicals act on ammonia to produce amine radicals (NH ₂ *).
NH ₃ + OH * → H ₂ O + NH ₂ *

  In the second step of the present invention, amine radicals are efficiently generated by the reaction of hydroxy radicals generated from hydrocarbon compounds and nitrogen compounds, and unreacted nitrogen compounds are less likely to remain in the reducing gas. Therefore, it is preferable.

  FIG. 2 is an explanatory view showing an example of a device configuration used in the exhaust gas denitration method of the present invention, and particularly shows a configuration example of the second step including a burner.

  In FIG. 2, a burner 10 is provided in a pipe portion 5 that communicates with an exhaust gas flue 20 and is formed at a substantially right angle, and a nitrogen compound is directed toward a high temperature region 22 formed at a downstream end of a flame 21 of the burner. 36 and hydrocarbon compound 37 are added from nozzles 8 and 9. In the high temperature region 22, reducing gas 33 (amine radical) is generated and immediately supplied to the third step 4 to reduce and decompose nitrogen oxides in the exhaust gas 32 by denitration reaction.

  In the present embodiment, the high temperature region 22 employs an outer cylinder method formed in the pipe portion 21 communicating with the flue 20, but the high temperature region 22 can also be formed inside the flue 20. . The outer cylinder method is preferable because the reducing gas 33 can be generated without being affected by the flow rate of the exhaust gas.

  The nitrogen compound 36 is not particularly limited as long as it can generate an amine radical, but ammonia, urea, cyanuric acid, amines, nitriles, etc. can be used, and in particular, ammonia, urea, cyanuric acid are used. It is preferable to do. As the hydrocarbon compound 37, methane, propane, butane, light oil, heavy oil, gasoline, or the like can be used, and methane, propane, butane, light oil, heavy oil is particularly preferable.

In the present embodiment, the nitrogen compound 36 and the hydrocarbon compound 37 are separately blown toward the high temperature region 22 formed at the downstream end of the flame 21 of the burner 10 . This is because an excellent denitration effect can be obtained as compared with the case where the nitrogen compound 36 and the hydrocarbon compound 37 are mixed and blown into the flame 21 or burned in the flame 21 of the burner 10.

  The burner 10 plays a role as a heating means for forming at least the local high-temperature region 22. For such a heating means, an electric heater, a heat exchanger, or the like can be used in addition to the burner 10. It is preferable to use a burner or an electric heater. In particular, the burner 10 can easily form a local high-temperature region with a simple configuration, can easily control the size, position, temperature, etc. of the high-temperature region 22, and generates a gas flow with combustion. The reducing gas 33 thus obtained can be promptly sent to the third step in the joining region of the flue 20 and the pipe part 5, which is preferable.

  The burner 10 burns the supplied fuel gas 38 and air 39 to form a flame 21. Further, air 39 may be introduced from the peripheral portion of the burner 10 in order to promote combustion of the hydrocarbon compound 37 and the flame 21 as necessary.

  It is preferable that the nozzle 8 as the first blowing nozzle for blowing in the nitrogen compound and the nozzle 9 as the second blowing nozzle for blowing in the hydrocarbon compound are arranged so as to protrude from the inner wall surface of the pipe portion 5. In the present embodiment, it is preferable that the nozzle 8 and the nozzle 9 are provided so as to be able to blow obliquely at a predetermined angle toward the direction of the flue 20 at a position facing each other across the high temperature region 22. The embodiment of FIG. 2 is an example in which the blowing angle of the nozzle 8 and the blowing angle of the nozzle 9 are set equal, but it is not always necessary to set both at the same angle. For example, in order to precede the generation of hydroxy radicals, the nozzle 9 which is a hydrocarbon compound blowing nozzle has a larger blowing angle, that is, the center line of the nozzle 9 with respect to the center line of the tube portion 5. The angle formed by the nozzle 8 is preferably set to be larger than the angle formed by the center line of the nozzle 8.

  Further, the installation positions of the nozzle 8 and the nozzle 9 and the burner 10 are an example of an arrangement in which the embodiment of FIG. 2 is equidistant, but it is not always necessary to be equidistant. That is, for the same reason as described above, it is preferable that the nozzle 9 which is a hydrocarbon compound blowing nozzle is disposed at a position closer to the burner 10.

  The installation positions and blowing angles of the nozzles 8 and 9 are preferably adjusted according to the distance of the burner 10 to the flame 21. That is, the nitrogen compound 36 and the hydrocarbon compound 37 are each blown into the high temperature region 22 formed at the downstream end of the flame 21, and the reducing gas 33 containing the generated amine radicals easily enters the flue 20. It is preferable to arrange and adjust the nozzle 8 and the nozzle 9 as described above.

  In the present invention, the temperature of the high temperature region 22 is preferably 700 to 1000 ° C, more preferably 800 to 900 ° C. By making the temperature of the high temperature region 22 within the above range, compared with the case where ammonia is directly burned by a burner, the decomposition of the hydrocarbon compound into a hydroxy radical and the decomposition of the nitrogen compound into an amine radical are efficiently performed, And since it advances stably, it is preferable. That is, by blowing a hydrocarbon compound and a nitrogen compound into the high temperature region 22, it is possible to advantageously generate the reducing gas 33 and increase the denitration efficiency.

  Moreover, it is also possible to form the high temperature region 22 by using an electric heater or the like instead of the burner. In addition, after heating a nitrogen compound and a hydrocarbon compound separately with an electric heater etc., a nitrogen compound and a hydrocarbon compound can also be separately blown into the pipe part 5, respectively. In this case, the collision and confluence region of the blown nitrogen compound and hydrocarbon compound plays the same role as the high temperature region 22.

  In the present invention, the distance from the wall surface of the flue 20 to the high temperature region 22 is preferably set to such a distance that the generated amyl radical does not disappear before reaching the flue 20. Specifically, in the high temperature region 22, the position of the intersection of the center line of the nitrogen compound blowing nozzle 8 and the center line of the tube portion 5 is preferably set to about 0 cm to 15 cm from the wall surface of the flue 20.

  In the denitration method of the present invention, in the third step 4, the reducing gas 33 containing the amine radical generated in the second step 3 and the oxidation treatment gas 32 containing nitrogen monoxide, nitrogen dioxide and the like processed in the first step. Is a non-catalytic denitration method in which nitrogen oxides are immediately mixed to reduce and decompose nitrogen oxides.

  In the third step, the nitrogen oxides of the exhaust gas to be treated contain nitrogen dioxide, so that the reactivity can be increased compared to the case of only nitrogen monoxide, and the amine radical is highly reactive to reducing gas. Therefore, even if the exhaust gas temperature is low, it is possible to remove nitrogen oxides advantageously, and since no reduction catalyst is used, even if the exhaust gas contains sulfur oxides, ammonium sulfate Etc. are not generated and the denitration efficiency is not lowered.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited by these Examples.

  Using the test apparatus shown in FIG. 3, the nitrogen oxide concentration and the sulfur oxide concentration in the denitration process of the exhaust gas were measured.

  In FIG. 3, the exhaust gas from the diesel engine 1 is drawn out to the flue 20 and the bypass line 7, and the first step 2 and the third step 4 made of oxidation treatment means are arranged in the flue 20. The second step 3 including the high temperature region was arranged by direct connection. The high temperature region of the second step was formed at the downstream end of the burner flame. The size of the pipe used and the gas flow rate in the pipe were as shown in Table 1.

Further, a measurement point 52a upstream of the first step 2, a measurement point 52b intermediate between the first step 2 and the third step 4, and a measurement point 52c downstream of the third step 4 are provided, and a NOx meter, SO ₂ meter and thermometer are provided. 51 was installed, and the nitrogen oxide concentration, sulfur dioxide concentration and gas temperature at each measurement point were measured.

Further, the SO ₂ injection unit 53 is provided upstream of the measurement point 52a, and to be able to prepare the SO ₂ in the flue gas to a predetermined concentration. The exhaust gas at the measurement point 52a was configured such that the NOx concentration was 860 ppm, the SO ₂ concentration was 540 ppm, and the exhaust gas temperature was 300 ° C.

  In the second step 3, the angle between the center line of the nozzle 8 and the nozzle 9 and the center line of the pipe part 5 is 45 degrees, and the center line of the nozzle 8 and the nozzle 9 and the center line of the pipe part 5 are Are set so that both are located at a distance of 10 cm from the inner wall surface of the flue 20. In addition, the position of the burner and the strength of the flame were adjusted so that the temperature in the vicinity of the intersection was 800 to 900 ° C.

[Example 1]
In the denitration method described above, as a first step oxidation treatment means, a pulsed plasma generator was used to evaluate a denitration method in which a part of nitrogen monoxide in exhaust gas was oxidized to nitrogen dioxide. The nitrogen compound blown from the nozzle 8 was ammonia, and the hydrocarbon compound blown from the nozzle 9 was propane gas.

The NOx concentration and the SO ₂ concentration at the measurement points 52b and 52c in the denitration process were measured. The obtained results are shown in Table 2. Note that the oxidation rate Nc of nitric oxide at the measurement point 52b was 51%, and the ratio Sc / Nc of the oxidation rate of sulfur dioxide to Nc was 0.04.

[Comparative Example 1]
In the denitration method of Example 1, the denitration method was evaluated in the same manner as in Example 1 except that the plasma generator was turned off and the exhaust gas was not oxidized. The obtained results are shown in Table 2. Note that the oxidation rate Nc of nitric oxide at the measurement point 52b was 6%, and the ratio Sc / Nc of the oxidation rate of sulfur dioxide to Nc was 0.

[Comparative Example 2]
In the denitration method of Example 1, the denitration method was evaluated in the same manner as in Example 1 except that nitrogen gas was blown from the nozzle 9 instead of propane gas. The obtained results are shown in Table 2. Note that the oxidation rate Nc of nitric oxide at the measurement point 52b was 51%, and the ratio Sc / Nc of the oxidation rate of sulfur dioxide to Nc was 0.04.

  As is apparent from the results in Table 2, Example 1 in which a portion of nitric oxide in the exhaust gas was oxidized to generate nitrogen dioxide, and ammonia and propane gas were added to the high temperature region to generate amine radicals. Although the exhaust gas temperature was as low as 300 ° C., the NOx removal rate was about 72%, which was an excellent result. On the other hand, Comparative Example 1 in which the exhaust gas was not subjected to oxidation treatment and treated without catalyst was not necessarily sufficient with a NOx removal rate of about 43%, and instead of hydrocarbon compounds (propane gas) when amine radicals were generated. It was confirmed that the denitration rate of Comparative Example 2 to which nitrogen gas was added was as low as about 3%.

It is a block flow figure showing an example of a process in a denitration method of exhaust gas of the present invention. It is explanatory drawing which shows an example of the apparatus structure used for the denitration method of the waste gas of this invention. It is explanatory drawing which shows the outline | summary of the test apparatus used for the Example.

Explanation of symbols

1 Diesel engine 2 1st process (NO oxidation means)
3 Second Step 4 Third Step 5 Pipe 6 Loader 7 Bypass Line 8 Nozzle 9 Nozzle 10 Burner 20 Flue 21 Flame 22 High Temperature Region 30 Fuel 31 Exhaust Gas (NO)
32 Oxidation gas (NO + NO ₂ )
33 Reducing gas (amine radical)
34 Purified gas 35 Exhaust gas 36 Nitrogen compound 37 Hydrocarbon compound 38 Fuel gas 39 Air 51 NOx meter, SO ₂ meter and thermometer 52a, 52b, 52c Measurement point 52 SO ₂ injection part

Claims (7)

A denitration method for reductively removing nitrogen oxides in exhaust gas containing nitrogen monoxide and sulfur dioxide, the first step of generating nitrogen dioxide by oxidizing a part of nitrogen monoxide in the exhaust gas, nitrogen A second step of separately adding a compound and a hydrocarbon compound to the high temperature region to generate amine radicals, and a third step of mixing the amine radicals and exhaust gas containing nitrogen monoxide and nitrogen dioxide discharged from the first step And in the first step, the exhaust gas is a catalyst in which an active metal is supported on a support containing titanium, and the active metal is at least one selected from a vanadium compound, a niobium compound, a molybdenum compound, and a tungsten compound. A denitration method for exhaust gas in which nitric oxide is oxidized into nitrogen dioxide by contact treatment with an oxidation catalyst or plasma irradiation treatment. 2. The exhaust gas denitration method according to claim 1, wherein, in the first step, a ratio Sc / Nc of an oxidation rate Sc of sulfur dioxide to an oxidation rate Nc of nitric oxide is 0.01 to 0.2. The exhaust gas denitration method according to claim 1 or 2 , wherein the high temperature region is formed around a flame of a burner or an electric heater. The exhaust gas denitration method according to any one of claims 1 to 3 , wherein the high temperature region has a temperature of 700 to 1000 ° C. The exhaust gas denitration method according to any one of claims 1 to 4 , wherein the nitrogen compound is any one of ammonia, urea, and cyanuric acid. The exhaust gas denitration method according to any one of claims 1 to 5 , wherein the hydrocarbon compound is any one of methane, propane, butane, light oil, and heavy oil. The exhaust gas denitration method according to any one of claims 1 to 6 , wherein the exhaust gas is exhaust gas of a diesel engine using A heavy oil or C heavy oil as fuel.

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