JP2005254093A - Method and apparatus for denitrification - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a denitrification technique achieving an excellent denitrification rate even for exhaust gas containing a sulfur content in a high concentration, e.g. exhaust gas from diesel engines. <P>SOLUTION: In a radical-generating section 51, ammonia is blown from a nozzle 20, and propane is blown from a nozzle 30 into the heating zone near the tip of the flame of a burner 13 to generate hydroxy and amine radicals. Exhaust gas which is passing through a flue 50 is introduced with the amine radicals from the radical-generating section 51 to denitrify nitrogen oxides in the gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a denitration technique for treating nitrogen oxides in exhaust gas discharged from a ship or a relatively large diesel engine for power generation.

  As a method for treating nitrogen oxides in exhaust gas, a selective reduction denitration (SCR) method using ammonia and its compounds and a vanadium-titania catalyst has been established. In this selective reduction denitration, when the exhaust gas temperature is 300 ° C. or lower, ammonia reacts with sulfur oxides in the exhaust gas to produce ammonium sulfate (ammonium sulfate) and deposit on the catalyst. It is used for exhaust gas in the region (350 ° C or higher) or low sulfur oxide concentration (10 ppm or lower).

  In the catalytic denitration method using hydrocarbons that do not react with sulfur oxides, denitration in the presence of sulfur oxides is also possible, but the condition is that the reactivity is low and the exhaust gas temperature is 400 ° C. or higher.

  On the other hand, as a non-catalytic denitration method, a method of injecting ammonia into exhaust gas and applying pulse discharge or plasma to convert it to amine radicals to react with nitrogen oxides has been developed, but this method requires a large amount of power. Therefore, it is not an economical process.

  As another example of the non-catalytic denitration method, when ammonia and hydrogen peroxide are added to a nitrogen oxide-containing gas to reduce nitrogen oxide, hydrogen peroxide is added at the same time as ammonia addition or thereafter. (For example, patent document 1) is proposed. However, since the reaction temperature of this method is as high as 400 ° C. or higher (preferably 500 to 1200 ° C.) and the denitration rate is low, it cannot be applied to low-temperature diesel engine exhaust gas below 300 ° C.

  Furthermore, a method for reducing and decomposing nitrogen oxides in exhaust gas using a pyrolyzing agent of a reducing agent such as ammonia has been proposed (for example, Patent Document 2 and Patent Document 3). However, in this method, since a reducing agent such as ammonia is mixed in the fuel gas of the burner used for thermal decomposition and burned, the ammonia is burned or the disappearance of amine radicals proceeds and the denitration rate is low. There was a problem.

JP 54-56976 A JP 54-99076 A JP 54-119370 A

  Accordingly, it has been demanded to provide a denitration technique that can obtain an excellent denitration rate even with respect to exhaust gas from a diesel engine or the like that contains a high concentration of sulfur and has a relatively low temperature.

  In order to solve the above-described problem, a first aspect of the present invention is a denitration method for reductively removing nitrogen oxides in exhaust gas, which is provided in an exhaust gas flue or a heating region in a room communicating with the flue. Therefore, the denitration method is characterized in that the nitrogen compound and the hydrocarbons are blown separately or mixed.

  According to the first aspect, the heating region is formed in the exhaust gas flue and the room communicating with the flue, and the nitrogen compounds and the hydrocarbons are blown toward the heating region, whereby the hydrocarbons are burned. An amine radical is generated by a reaction between the generated hydroxy radical and a nitrogen compound, and nitrogen oxide in exhaust gas can be efficiently denitrated by the generated amine radical.

  In addition, since it is a method capable of non-catalytic denitration, it is not affected by sulfur oxides in the exhaust gas, and sulfur oxides of 500 to 1000 ppm or more like diesel engine exhaust gas discharged from ships, power plants, etc. It is also effective for an exhaust gas containing nitrile, and denitration can be performed without producing ammonium sulfate. Furthermore, since denitration is possible at a relatively low exhaust gas temperature of 200 to 500 ° C., it is not necessary to reheat the exhaust gas, and energy consumption may be small.

  The second aspect of the present invention is a denitration method for reductively removing nitrogen oxides in exhaust gas, wherein a burner is installed in the exhaust gas flue or a room communicating with the flue, and the burner is used. A denitration method is characterized in that a nitrogen compound and hydrocarbons are blown toward a heating region.

  According to this second aspect, in addition to the same effects as the first aspect, a simple burner is provided in the exhaust gas flue and the like, and nitrogen compounds and hydrocarbons are blown to produce by combustion of hydrocarbons. An amine radical is generated by a reaction between the hydroxy radical and a nitrogen compound, and the generated amine radical can efficiently denitrate nitrogen oxides in the exhaust gas. Here, amine radicals can be generated with minimal energy by flame heating nitrogen compounds and hydrocarbons.

  Moreover, the 3rd aspect of this invention is a denitration method characterized by the temperature of the said heating area | region being 700-1000 degreeC in the 1st aspect or the 2nd aspect. In the heating range of 700 to 1000 ° C., propane combustion and thermal decomposition of ammonia proceed rapidly. By blowing propane and ammonia into this region, hydroxy radicals and amine radicals are efficiently generated, and denitration efficiency is improved. Can be improved.

  In addition, a fourth aspect of the present invention is the denitration method according to any one of the first to third aspects, wherein the exhaust gas temperature in the exhaust gas flue is 200 to 500 ° C. In the present invention, since nitrogen compounds and hydrocarbons are supplied toward a local heating region (preferably a region of 800 to 900 ° C.) in the vicinity of the flame of the burner, the temperature of the entire exhaust gas is about 200 to 500 ° C. Sufficient denitration performance can be obtained even at relatively low temperatures. Therefore, it is not necessary to reheat the entire exhaust gas, and energy consumption and operating cost can be kept low.

  In addition, according to a fifth aspect of the present invention, in any one of the first to fourth aspects, the nitrogen compound is ammonia gas or urea water, and the hydrocarbons are methane, propane, butane, or light oil. This is a denitration method. According to the fifth aspect, an excellent denitration effect can be obtained by using a specific nitrogen compound and hydrocarbons in combination.

  According to a sixth aspect of the present invention, there is provided a denitration device for reductively removing nitrogen oxides in exhaust gas, wherein at least a local heating region is provided in the exhaust gas flue or a room communicating with the flue. A denitration apparatus comprising: a heating means for making; and one or a plurality of blowing nozzles for blowing nitrogen compounds and hydrocarbons separately or mixed toward the heating region. is there. The denitration apparatus according to the sixth aspect is an apparatus suitable for carrying out the denitration method according to the first aspect, and the same effects as those of the first aspect can be obtained.

  Further, a seventh aspect of the present invention is a denitration apparatus for reductively removing nitrogen oxides in exhaust gas, the exhaust gas flue or a burner installed in a room communicating with the flue, A denitration apparatus comprising one or a plurality of blowing nozzles that blow nitrogen compounds and hydrocarbons separately or in a mixed manner toward a heating region by a flame. The denitration apparatus according to the seventh aspect is an apparatus suitable for carrying out the denitration method according to the second aspect, and the same effect as the second aspect can be obtained.

  According to the present invention, by heating the nitrogen compound and hydrocarbons, amine radicals can be generated with less energy, and the denitration reaction can proceed efficiently.

  Further, since it can be denitrated without using a catalyst, it can also treat exhaust gas (including high-concentration sulfur oxide) from a diesel engine or the like using a high-sulfur fuel as a raw material.

  Furthermore, since nitrogen compounds and hydrocarbons are supplied toward a local heating region (preferably a region of 800 to 900 ° C.) by a burner or the like, the temperature is about 200 to 500 ° C. However, sufficient denitration performance can be obtained without reheating the whole, which is particularly advantageous for low-temperature exhaust gas having a temperature of about 200 to 300 ° C.

Next, embodiments of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a principle diagram showing an outline of a non-catalytic denitration apparatus 10 according to a preferred embodiment of the present invention, and FIG. 2 is an enlarged view of a main part of the radical generator 51 in FIG. The non-catalytic denitration apparatus 10 of the present embodiment has, as main components, a radical generation part 51 as a “room” that is formed and communicated with the flue 50 of the exhaust gas substantially at right angles, a burner 13, and a nitrogen compound. And a nozzle 20 as a second blowing nozzle for blowing hydrocarbons, and these are integrally provided in the middle of the flue 50.

  In the present embodiment, the radical generating unit 51 as a “room” is configured by the tube unit 11 communicating with the flue 50 as shown in FIG. 1 and adopts an outer cylinder method. Although it is possible to form a heating region directly in the flue without providing a room, the outer cylinder method is preferable because radicals can be generated without being affected by the flow rate of exhaust gas. A part of the flue 50 may constitute a part of the non-catalytic denitration device 10.

The exhaust gas to be treated by the non-catalytic denitration apparatus 10 of the present invention is not particularly limited, but for example, exhaust gas discharged from a relatively large diesel engine or the like used for ships or power generation can be targeted. In general, high-sulfur fuel containing a large amount of sulfur compounds is often used for marine or power generation diesel engines. Therefore, not only nitrogen oxides (NO _x ) but also high concentrations are contained in the exhaust gas discharged. Sulfur oxide (SO _x ) is often included. In the case of such exhaust gas, desulfurization using a catalyst is difficult because sulfur oxide becomes a catalyst poison, and non-catalytic denitration without using a catalyst is more advantageous.

  The target exhaust gas temperature may be a temperature exceeding 500 ° C. However, in the present invention, a sufficient denitration effect can be obtained if it is about 200 to 500 ° C. Therefore, it is necessary to reheat the entire exhaust gas for the purpose of increasing the denitration efficiency. Not necessarily required. Therefore, even a relatively low temperature exhaust gas discharged from a diesel engine or the like can be treated as it is.

The nitrogen compound used in the present invention is not particularly limited as long as it can generate an amine radical. Examples thereof include ammonia gas and urea water that generates ammonia by hydrolysis. Examples of hydrocarbons include methane, propane, butane, and light oil. In the present embodiment, nitrogen compounds and hydrocarbons are blown separately toward the heating region of the burner 13 by the flame. By injecting nitrogen compounds and hydrocarbons toward a high-temperature reaction field (heating region), it is superior to the case where they are mixed and burned in the burner 13 as shown in the examples below. Denitration performance can be obtained.
The radical generator 51 can be formed of a branch pipe made of the same material as the pipe forming the flue 50. In the present embodiment, a small burner 13 is disposed in the innermost part of the radical generator 51 (the part farthest from the flue 50).

  The burner 13 functions as a “heating means” that creates at least a local heating region. As the heating means, for example, an electric heater, a heat exchanger, or the like can be used in addition to the burner. In addition, although it is possible to employ a configuration in which the entire radical generation unit 51 is heated, the burner 13 is advantageous because a local heating region can be easily created with a simple configuration. The burner 13 is supplied with a combustion gas (for example, a mixed gas of propane and air) and burns.

  It is possible to introduce “oxygen-containing gas” into the radical generator 51 for the purpose of promoting combustion of hydrocarbons and the burner 13. As the gas containing oxygen, a gas containing oxygen, nitrogen, and water vapor is preferable. For example, air can be used. As illustrated in FIG. 2, air introduction portions 15 a and 15 b may be provided in the vicinity of the burner 13 as necessary, and air may be separately introduced from here.

A nozzle 20 as a first blowing nozzle that blows in a nitrogen compound and a nozzle 30 as a second blowing nozzle that blows in hydrocarbons are arranged so as to protrude into the radical generator 51. In the present embodiment, the nozzle 20 and the nozzle 30 are provided so as to be able to blow obliquely at a predetermined angle toward a position facing each other and in the direction of the flue 50 with the radical generator 51 therebetween. .
In the present embodiment, the nozzle 20 and the nozzle 30 are both provided at equidistant positions on the innermost side (the burner 13 side) of the radical generator 51 with respect to the wall of the flue 50. The arrangement of the nozzle 20 and the nozzle 30 need not necessarily be equidistant with respect to the flue 50. For example, considering that the generation of hydroxy radicals is preceded, it is possible to satisfy B ₃₀ > B ₂₀ .

In the present embodiment, blowing angle theta ₂₀ of the nozzle _20, and are set equal to blowing angle theta ₃₀ of the nozzle 30, it is also possible to vary the theta ₂₀ and theta _30.

The installation positions (distances B ₂₀ and B ₃₀ ) and the blowing angles (θ ₂₀ and θ ₃₀ ) of the nozzles 20 and 30 are preferably adjusted according to the distance of the burner to the flame. That is, it is preferable that the nozzle 20 and the nozzle 30 are arranged at an angle at which the blown nitrogen compound and hydrocarbon collide in the heating region by the flame and easily enter the flue 50.

  The positions of the nozzle 20 and the nozzle 30 so that nitrogen compounds and hydrocarbons can be blown into the heating region at a temperature of 700 to 1000 ° C. (preferably 800 to 900 ° C.) in the heating region by the flame of the burner. It is desirable to determine the angle. In the heating region at a temperature of 700 to 1000 ° C., the combustion of hydrocarbons supplied from the nozzle 30 and the thermal decomposition of the nitrogen compound supplied from the nozzle 20 are more stable and stable than when ammonia is burned by a burner. Since it proceeds, it becomes possible to efficiently generate hydroxy radicals and amine radicals. Therefore, the NOx removal efficiency can be improved by providing the nozzle 20 and the nozzle 30 so that hydrocarbons and nitrogen compounds can be blown into this region.

  Further, the nitrogen compound and hydrocarbons blown from the nozzle 20 and the nozzle 30 collide in the radical generation unit 51 at the intersection point on the extended line of the nozzle 20 and the nozzle 30 in the blowing direction. The distance A from the wall surface of the flue 50 to this intersection is preferably set to such a distance that the generated amine radicals do not disappear before reaching the flue 50. Although it depends on the diameter, it is preferably set to about several centimeters to several tens of centimeters.

  In the non-catalytic denitration apparatus 10 having the above configuration, the exhaust gas passes through the flue 50 in the direction indicated by the white arrow in FIG. In the radical generator 51, nitrogen compounds are blown from the nozzle 20 and hydrocarbons are blown from the nozzle 30 into the heating region near the flame tip of the burner 13, and hydroxy radicals and amine radicals are generated according to the reaction mechanism described later. To do. Amine radicals are mixed in the exhaust gas in the middle of passing through the flue 50 from the radical generator 51, and a denitration reaction of nitrogen oxides in the exhaust gas occurs. The denitrated purified gas flows through the flue 50 toward a discharge port (not shown) on the atmosphere side and is discharged.

<Action>
In this invention, the radical production | generation part 51 is provided in the middle of the exhaust gas flue 50, and an amine radical is generated by blowing a nitrogen compound and hydrocarbons toward a high temperature reaction field (heating area). The generated amine radicals are immediately mixed in the exhaust gas, react with nitrogen oxides, and generate nitrogen through a reductive denitration reaction to make it harmless. In the vicinity of the flame by the burner 13, for example, the following reaction occurs, amine radicals are generated, and the generated amine radicals are used for reduction of nitrogen oxides (NO and the like).
(1) During the combustion reaction (HC + O ₂ ) of hydrocarbons, hydroxy radicals (OH ^* ) are generated.
(2) Hydroxy radicals act on ammonia to produce amine radicals.
NH ₃ + OH ^* → NH ₂ ^* + H ₂ O
(3) Reaction between amine radicals and nitrogen oxides (NO) occurs to generate nitrogen.
NO + NH ₂ ^* → N ₂ + H ₂ O
That is, in the present invention, by adding hydrocarbons in addition to nitrogen compounds and generating hydroxy radicals, it is possible to promote the generation of amine radicals and obtain high denitration performance.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by this.
When the test apparatus 100 shown in FIG. 3 is used to mix and burn ammonia with propane for burner (Comparative Example 1), when ammonia and nitrogen are blown separately (Comparative Example 2), ammonia and propane gas are mixed. The denitration test was performed under three conditions when blown separately (Example 1). For ammonia and propane, almost the same amount of nitrogen was mixed for the purpose of increasing the flow rate.
The size of the pipe used and the gas flow rate in the pipe are as shown in Table 1.

  The test apparatus 100 pulled out a bypass line 53 from the exhaust gas flue 50 of the diesel engine 70, and the non-catalytic denitration apparatus 10 was arranged in the bypass line 53. The configuration of the non-catalytic denitration apparatus 10 is the same as that shown in FIGS. Measurement point a and measurement point b were provided upstream and downstream in the gas flow direction, and a NOx meter, SOx meter, and thermometer were installed so that the non-catalytic denitration apparatus 10 was interposed. Further, an SOx injection portion 55 is provided in the vicinity of a branch point from the flue 50 to the bypass line 53 so that the concentration of SOx in the exhaust gas can be adjusted to a predetermined level.

In this test, in the radical generator 51, the ammonia nozzle 20 and the propane nozzle 30 are both installed at the same distance from the flue 54 of the bypass line 53, and the angles θ ₂₀ and θ ₃₀ are All were 45 degree | times. The distance A from the flue 54 of the bypass line 53 to the intersection (the collision point between the injected ammonia gas and propane gas) on the extended line of both nozzles was set to 10 cm. Further, the position of the burner 13 and the strength of the flame were adjusted so that the temperature near the intersection was 800 to 900 ° C. Table 2 shows the exhaust gas conditions before denitration measured at the position a in FIG.

  Table 3 shows the results of measuring the NOx concentration of the exhaust gas at the position b in FIG.

  From Table 3, Comparative Example 1 in which ammonia was mixed with propane, which is the fuel gas of the burner 13, has a very low NOx removal rate. This is because the combustion of ammonia and the disappearance of amine radicals progressed in the flame by performing mixed combustion. It is thought that it is because it ends. Further, in Comparative Example 2 in which ammonia and nitrogen were blown separately, it is considered that a low denitration rate was obtained as a result of insufficient radical generation.

  On the other hand, in Example 1 in which ammonia and propane were separately supplied to a high-temperature reaction field, a high denitration rate was obtained. This is considered to be the result of the efficient generation of amine radicals from ammonia by generating hydroxyl radicals by directly blowing ammonia and propane into the 800 ° C to 900 ° C region.

  The present invention has been described above with reference to various embodiments. However, the present invention is not limited to the above embodiments, and can be applied to other embodiments within the scope of the invention described in the claims. It is.

  For example, in the embodiment shown in FIG. 1 and FIG. 2, the radical generation unit 51 serving as a room communicating with the flue 50 is provided in the middle of the flue 50 of the exhaust gas. It is good also as a structure which installs the burner 13, the nozzle 20, and the nozzle 30 in the direct flue 50, and introduce | transduces a nitrogen compound and hydrocarbons.

  In the embodiment shown in FIG. 2, the nitrogen compound and the ammonia compound are blown from separate nozzles (separate blow positions). For example, as shown in FIG. 4, the burner 13 is fed from one blow nozzle 40. The mixed nitrogen compound and hydrocarbons may be blown toward the heating region.

  INDUSTRIAL APPLICABILITY The present invention can be used for denitration of exhaust gas from diesel engines such as ships and power generation facilities.

1 is a principle diagram showing an outline of a non-catalytic denitration apparatus according to an embodiment of the present invention. It is a principal part enlarged view of FIG. It is drawing explaining the outline | summary of a test apparatus. It is a principal part enlarged view of the non-catalyst denitration apparatus which concerns on another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Non-catalytic denitration apparatus 11 Pipe part 13 Burner 15 (15a, 15b) Air introduction part 20 Nozzle 30 Nozzle 40 Nozzle 50 Flue 51 Radical generation part 53 Bypass line 54 Bypass line flue 55 SOx injection part 60 Flame 70 Diesel engine 100 test equipment

Claims (7)

A denitration method for reductively removing nitrogen oxides in exhaust gas,
A denitration method, wherein nitrogen compounds and hydrocarbons are blown separately or mixed toward an exhaust gas flue or a heating region in a room communicating with the flue. A denitration method for reductively removing nitrogen oxides in exhaust gas,
A burner is installed in an exhaust gas flue or a room communicating with the flue, and nitrogen compounds and hydrocarbons are blown separately or mixed toward the heating area by the burner. Denitration method.   3. The denitration method according to claim 1, wherein the temperature of the heating region is 700 to 1000 ° C. 4.   4. The denitration method according to claim 1, wherein an exhaust gas temperature in the exhaust gas flue is 200 to 500 ° C. 5.   5. The denitration method according to claim 1, wherein the nitrogen compound is ammonia gas or urea water, and the hydrocarbons are methane, propane, butane, or light oil. A denitration device for reductively removing nitrogen oxides in exhaust gas,
Heating means for creating at least a localized heating area in the flue gas flue or in a room communicating with the flue;
One or a plurality of blowing nozzles that blow nitrogen compounds and hydrocarbons separately or mixed toward the heating region,
A denitration apparatus, characterized in that A denitration device for reductively removing nitrogen oxides in exhaust gas,
An exhaust flue or a burner installed in a room communicating with the flue;
One or a plurality of blowing nozzles that blow nitrogen compounds and hydrocarbons separately or mixed toward the heating region by the burner;
A denitration apparatus, characterized in that

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