JPH0751536A - Denitration of combustion exhaust gas - Google Patents

Abstract

PURPOSE:To remove NOX in combustion exhaust gas with high denitration efficiency by performing the ammonia denitration of NOX-containing combustion exhaust gas and subsequently reducing the denitrated gas with hydrocarbon to oxidize the remaining NOX and unreacted NH3 before decomposing and removing NOX. CONSTITUTION:At first, the NOX-containing combustion exhaust gas from a boiler 1 is guided to a dry denitration device 4-1 using NH3 as a reducing agent to be denitrated. Next, the denitrated gas is guided to a hydrocarbon denitration device 4-2 using hydrocarbon as a reducing agent and the remaining NOX and NOX generated by oxidation of unreacted NH3 are decomposed and removed. By this constitution, NH3 leaked to the gas to be treated is made zero and NOX in the combustion exhaust gas can be removed within a wide temp. range with high denitration efficiency of 90% or more.

Description

Detailed Description of the Invention

[0001]

The invention denitration process of the NOx-containing flue gas BACKGROUND OF THE, more particularly a high denitrification rate of a combination of a dry denitration apparatus for the dry denitration apparatus and hydrocarbons and NH ₃ as a reducing agent and a reducing agent Regarding denitration method.

[0002]

2. Description of the Related Art A method for removing NOx in combustion exhaust gas and
Then, as shown in FIG. 8 and FIG. ₃As a reducing agent
A method using a dry denitration device is generally used. Figure 8 and Figure
In 9, 1 is a boiler, 2 is a gas turbine, 3 is NH
₃Injection nozzle, 4-1 is NH₃Denitration device, 6 is air preheating
Vessel, 7 is an exhaust gas boiler, 8 is a chimney, 9 is combustion air, 1
0 represents a economizer. With this method, a high denitration rate was obtained.
Excess NH in order to₃It is necessary to add
Unreacted NH₃Leak NH₃Discharged into the process gas as
Is coming. Moreover, leak NH₃Amount of 5-10pp
Excess NH to reach m₃Can still be achieved by adding
The effective denitration rate was about 80 to 90%. Also, combustion exhaust
SOx in gas, especially SO₃If included,
NH in the space₃Acid remains to form acidic ammonium sulfate
To do. Therefore, the equipment on the downstream side of the exhaust gas (air preheater,
In the low temperature part of the exhaust gas boiler)
There is a possibility of trouble due to the adhesion of um.
Leakage NH as much as possible₃Under conditions that reduce
The reality is that they are being driven.

[0003]

When the dry denitration apparatus using NH ₃ as a reducing agent is used alone as described above,
If the amount of leak NH ₃ is to be suppressed to 10 ppm or less, a denitrification rate of 90% or more cannot be expected, and when applied to exhaust gas containing SOx, it is necessary to take measures against acidic ammonium sulfate in the downstream equipment. It was The present invention solves the above-mentioned problems of the prior art, achieves a denitrification rate of 90% or more while keeping the amount of leak NH ₃ low, and even when it is applied to exhaust gas containing SOx, it is used in equipment on the downstream side. It is an object of the present invention to provide a method for denitration of combustion exhaust gas that does not require any special measures against ammonium ammonium sulfate.

[0004]

According to the present invention, combustion exhaust gas containing NOx is first introduced into a dry denitration device (hereinafter abbreviated as NH ₃ denitration device) using NH ₃ as a reducing agent for denitration and then carbonization. Remaining NOx led to a dry denitration device (hereinafter abbreviated as hydrocarbon denitration device) using hydrogen as a reducing agent
And a method for denitrifying combustion exhaust gas, characterized by decomposing and removing NOx generated by oxidizing unreacted NH ₃ .
The combustion exhaust gas denitration method of the present invention includes the following methods as preferred embodiments. (1) The temperature of the combustion exhaust gas in the combustion exhaust gas path is 200 to
An exhaust gas denitration method in which an NH ₃ denitration device and a hydrocarbon denitration device are installed in a position such that the temperature is within a range of 600 ° C. (2) An exhaust gas denitration method in which the amount of NH ₃ added to the combustion exhaust gas in the NH ₃ denitration device is equal to or less than equimolar to NOx in the exhaust gas. (3) A method for denitration of exhaust gas in which both NH ₃ and hydrocarbon added as a reducing agent to the combustion exhaust gas are added to the combustion exhaust gas on the upstream side of the NH ₃ denitration device. (4) An exhaust gas denitration method in which an unreacted hydrocarbon is decomposed and removed by providing an oxidation catalyst layer near the exhaust gas outlet of the hydrocarbon denitration apparatus.

The denitration method of the present invention is characterized in that NOx is reduced to some extent in the NH ₃ denitration apparatus in the first stage, and a hydrocarbon denitration apparatus is installed in the second stage to decompose the remaining NOx. With such a structure, a high denitration rate can be obtained without the problem of leak NH ₃ .

In the NH ₃ denitration apparatus, NOx reacts with NH _{3 in} the presence of a denitration catalyst and is decomposed according to the following reaction formula. 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1) The denitration catalyst used here is not special, and titanium oxide used in ordinary NH ₃ denitration equipment is used as a carrier to support active metal components such as vanadium and tungsten. A supported catalyst may be used.

In a hydrocarbon denitration apparatus, NOx is a hydrocarbon (represented by CH ₂ ) or an oxygen-containing hydrocarbon (represented by CH ₂ O) produced from hydrocarbon in the presence of a denitration catalyst.
And is decomposed according to the following reaction formula. CH ₂ + 1 / 2O ₂ → CH ₂ O (2) 2NO + CH ₂ O → N ₂ + CO + H ₂ O (3) CH ₂ O + 1 / 2O ₂ → H ₂ O + CO (4) CO + 1 / 2O ₂ → CO ₂ (5) where The hydrocarbon is not particularly limited and, for example, ethylene, propylene, butadiene, benzene and the like which can be easily handled may be used. Further, as the denitration catalyst here, a Cu ion-exchange metallosilicate catalyst, a catalyst in which a platinum group element such as iridium is supported on a crystalline silicate, and the like can be used. Further, the unreacted NH ₃ mixed in the exhaust gas from the NH ₃ denitration device is oxidized into NOx according to the following equation, and is decomposed and removed together with NOx in the exhaust gas. 2NH ₃ + 5 / 2O ₂ → 2NO + 3H ₂ O (6) 2NO + CH ₂ O → N ₂ + CO + H ₂ O (7) CO + 1 / 2O ₂ → CO ₂ (8)

FIG. 1 shows an embodiment in which the denitration method of the present invention is applied to exhaust gas treatment of a boiler plant, and FIG. 2 shows an embodiment in which it is applied to a gas turbine plant. 1 and 2, 1 is a boiler, 2 is a gas turbine, 3 is an NH ₃ injection nozzle, 4-1 is an NH ₃ denitration device, 4-2 is a hydrocarbon denitration device, 5 is an injection nozzle for hydrocarbons, etc., 6 is an air preheater, 7 is an exhaust gas boiler (a heat exchanger in the exhaust gas boiler is not shown), 8 is a chimney, 9 is combustion air, and 10 is a economizer. In the case of a boiler plant, the denitration device is installed between the economizer 10 of the boiler 1 and the air preheater 6, but the exhaust gas temperature at this position is 2 if the operational load of the boiler is taken into consideration.
It becomes about 00 to 450 ° C. Further, in the case of a gas turbine plant, the denitration device is installed in front of or inside the exhaust gas boiler 7, but the exhaust gas temperature in this case is 20
It is about 0 to 600 ° C.

[0009] and NH ₃ denitration method of the NH ₃ and the reducing agent, the relation between the NOx removal efficiency and the processing gas temperature at the hydrocarbon denitration method using hydrocarbon as a reducing agent, the reducing agent and the type of the denitration catalyst, the process gas Although it depends on the concentration, the gas flow conditions, etc., as can be seen from the test results shown in FIGS. 3A and 3B, both methods show good denitration activity in the temperature range of 200 to 600 ° C. Therefore, it can be said that these methods are denitration methods suitable for the exhaust gas treatment of the above-mentioned boiler plant or gas turbine plant.

Next, the relationship between the molar ratio of NH _{3 to} NOx in the NH ₃ denitration method, the denitration rate and the amount of slag NH ₃ is as shown in FIG. This relationship also varies slightly depending on the type of catalyst and gas treatment conditions, but as shown in FIG. 4, there is a condition where the leak NH ₃ is several ppm or less and the denitration rate exceeds 80%. Under such conditions, NH ₃ denitration is performed,
Then, the remaining NOx is decomposed and N
By decomposing H ₃ , a high denitration rate can be achieved,
There is almost no leak NH _{3, and} even when applied to a gas containing SOx, it is possible to configure a denitration system that does not require measures against ammonium ammonium sulfate.

In the NH ₃ denitration apparatus, hydrocarbons are discharged as they are, with little involvement in the reaction. Thus, in the embodiment of FIG. 1 and 2, although injected NH ₃ and hydrocarbons in front of each NH ₃ denitration apparatus and hydrocarbons denitrator, NH ₃ and hydrocarbons as shown in FIGS. 6 and 7 Alternatively, the NH ₃ and hydrocarbons may be simultaneously injected from the injection nozzle 11 in front of the NH ₃ denitration device in the previous stage.

In the hydrocarbon denitration apparatus, an excess amount of hydrocarbon is injected in order to allow the denitration reaction to proceed efficiently.
Therefore, unreacted hydrocarbons flow out into the process gas.
When such unreacted hydrocarbon is unfavorable,
A layer of a Pt-based or Pd-based oxidation catalyst is installed near the outlet of the hydrocarbon denitration apparatus, and oxidation treatment is performed. This oxidation catalyst layer may be installed integrally with the hydrocarbon denitration device,
Alternatively, it may be separately provided on the downstream side.

[0013]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples. The following tests were carried out by using an NH ₃ denitration apparatus in which titanium oxide as a carrier was loaded with a catalyst supporting vanadium and tungsten as active metals and a hydrocarbon denitration apparatus in which a crystalline silicate was loaded with a catalyst supporting iridium. went. The test conditions in Examples 1 to 4 were as follows. Sample gas: NO of 100 ppm and 1% of O ₂ and the rest are N ₂ , CO ₂ and H ₂ O Gas amount: 200 Nm ³ / H SV value in each denitration apparatus: 10000H ^-1 (Example 1) First, 1.0 for NO in sample gas
NH ₃ molar ratio (100 ppm) was added to 200-6
It was passed through an NH ₃ denitration apparatus at 00 ° C., and the relationship between the treatment temperature and the denitration rate was investigated. The results are shown in Fig. 3 (a). Next, the sample gas was added with C ₂ H ₄ (100 p
pm) and 0.34 molar ratio of C ₃ H ₆ (34 ppm) were added and the mixture was passed through a hydrocarbon denitration apparatus at 200 to 600 ° C. to examine the relationship between the treatment temperature and the denitration rate. The results are shown in Fig. 3 (b). From FIG. 3A and FIG. 3B, the process gas temperature 200
It can be seen that a high denitration rate of 60% or more is obtained in the range of up to 600 ° C.

(Embodiment 2) First, NO is added to the sample gas.
To each of 0.8, 0.9, 1.0, 1.1, and 1.2 molar ratios of NH ₃ , respectively, and added at a temperature of 380 ° C.
₃ Through a denitration device, changes in the denitration rate and the leak NH ₃ amount were examined. The results are shown in the graph of FIG. 4, and it can be seen that a denitration rate of more than 90% is obtained from an NH ₃ molar ratio of around 1.0, but the amount of leaked NH ₃ also increases and exceeds 10 ppm.

Next, 1.0 is added to the sample gas for NO.
When C ₂ H ₄ (100 ppm) in a molar ratio and C ₃ H ₆ (34 ppm) in a 0.34 molar ratio were added and denitration was performed at 380 ° C. through a hydrocarbon denitration device, the denitration rate was about 90%.
(Dotted line in FIG. 3B). Furthermore, the sample gas was added with 1.0 molar ratio of NH ₃ (100 ppm).
Is added, and denitration is performed by passing it through an NH ₃ denitration device to obtain 90% N
O is removed, and 1.0 is applied to NO remaining in the processing gas.
Add a molar ratio of C ₂ H ₄ (10 ppm) and a 0.34 molar ratio of C ₃ H ₆ (3.4 ppm), and add 200 to 600 ° C.
Fig. 5 (a) shows the result of decomposing the remaining NO through the hydrocarbon denitration equipment, and the total denitration rate is 99%.
As described above, the leak NH ₃ was 5 ppm or less.

Example 3 NH ₃ (80 ppm) in a 0.8 molar ratio to NO was added to the sample gas to produce NH ₃
Denitration is performed through a denitration device (NH ₃ /NO=0.8 in FIG. 4).
Point), 10 ppm relative to NO remaining in the processing gas
C ₂ H ₄ and 3.4 ppm C ₃ H ₆ were added, 20
NO remaining after passing through a hydrocarbon denitration device at 0-600 ° C
The result of decomposing is shown in FIG. 5 (b), and the overall glass rate reached 98%, and the leak NH ₃ could be made almost zero. If proper conditions are selected in this way, NH ₃ at the outlet of the denitration device can be made almost zero, and S
It can be seen that even if Ox is included, measures for acidic ammonium sulfate in subsequent devices can be eliminated.

Example 4 To the sample gas, 1.0 molar ratio of NH ₃ , 0.1 molar ratio of C ₂ H ₄ and 0.034 molar ratio of C ₃ H ₆ were added, and the mixture was heated at 380 ° C. NH _{3 at} temperature
As a result of denitration through the denitration equipment and passing the treated gas through the hydrocarbon denitration equipment to decompose the remaining NOx, the total denitration rate is 99% or more, and the leak NH ₃ is 5 p
It was pm or less, and the same effect as that of the example of FIG. From this, it can be seen that only NH ₃ reacts effectively in the NH ₃ denitration device, hydrocarbons do not react and flow out downstream, and react in the hydrocarbon denitration device. Therefore, as shown in FIGS. 6 and 7, NH ₃ as a reducing agent and hydrocarbon can be injected at the same time, so that a space for sufficiently diffusing and mixing can be obtained, and the injection nozzle space may be one place. , The device becomes compact.

(Example 5) Test conditions Sample gas: NO of 100 ppm and 1% of O ₂ with the balance being N ₂ , CO ₂ and H ₂ O gas amount: 200 Nm ³ / H Gas temperature: 380 ° Hydrocarbon denitration SV value in the apparatus and oxidation catalyst layer: 10
000H ^-1 1.0 molar ratio to NO in the sample gas (100 pp
m) C ₂ H ₄ and 0.34 molar ratio (34 ppm) C
₃ H ₆ was added, and the mixture was passed through a hydrocarbon denitration apparatus for denitration treatment. As a result, as shown in Fig. 3 (b), about 90%
Although denitration rate is obtained, the processing gas C ₂ H ₄ and C
20 ppm and ₃ ppm of ₃ H ₆ were respectively discharged.

Next, an oxidation catalyst layer made of a Pt catalyst was installed in the downstream of the hydrocarbon denitration apparatus, and when the above-mentioned soot gas was passed, C ₂ H ₄ and C ₃ H ₆ became almost zero. From this, it can be seen that by combining the NH ₃ denitration device, the hydrocarbon denitration device, and the oxidation catalyst layer, NH ₃ and hydrocarbons in the process gas can be made almost zero, and a high denitration rate can be achieved.

[0020]

According to the method of the present invention, a high denitration rate can be obtained.
And is economically advantageous, but leak NH ₃There is a problem of N
H₃In addition to denitration equipment and NOx, NH₃Of disassembling
By combining the hydrocarbon denitration equipment that can
Leakage into the natural gas NH₃Is set to almost zero, and 200 to 60
High denitration rate of 90% or more in a wide temperature range of 0 ℃
Thus, NOx in the combustion exhaust gas can be removed. Well
Leakage into the processing gas NH₃Because there is almost no
Measures against acidic ammonium sulfate in equipment installed downstream of the denitration equipment are also not
It is important. Furthermore, by installing an oxidation catalyst layer,
The outflow of hydrocarbons into the process gas can also be prevented.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing one embodiment in which the method of the present invention is applied to a boiler plant.

FIG. 2 is a schematic explanatory view showing one embodiment in which the method of the present invention is applied to a gas turbine plant.

FIG. 3 is a graph showing the relationship between the treatment gas temperature and the denitration rate in the NH ₃ denitration method and the hydrocarbon denitration method.

FIG. 4 is a graph showing the relationship between the molar ratio of NH ₃ and NOx, the denitration rate, and the amount of leaked NH ₃ in the NH ₃ denitration method.

FIG. 5: Denitration rate and leak NH ₃ with respect to process gas temperature when continuously passing through an NH ₃ denitration device and a hydrocarbon denitration device
A graph showing the relationship with the amount of.

FIG. 6 is a schematic diagram showing a method of applying the method of the present invention to a boiler plant,
Schematic explanatory drawing which shows one embodiment which injects ₃ and hydrocarbon simultaneously.

FIG. 7 is a schematic explanatory view showing an embodiment in which the method of the present invention is applied to a gas turbine plant and NH ₃ and hydrocarbon are simultaneously injected.

FIG. 8 is a schematic explanatory view showing a conventional technique in which an NH ₃ denitration device is applied to a boiler plant.

FIG. 9 is a schematic explanatory view showing a conventional technique in which an NH ₃ denitration device is applied to a gas turbine plant.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Serizawa 1-1 1-1 Atsunoura-machi, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard Co., Ltd.

Claims (5)

[Claims] 1. A combustion exhaust gas containing NOx is first converted to NH.
DeNOx by introducing it to a dry denitration device using ₃ as a reducing agent, and then introducing it to a dry denitration device using hydrocarbon as a reducing agent to decompose and remove residual NOx and NOx generated by oxidation of unreacted NH _3. A method for denitration of combustion exhaust gas, characterized by: 2. A dry denitration device using NH ₃ as a reducing agent and a dry denitration device using hydrocarbon as a reducing agent are installed at a position in the combustion exhaust gas passage where the temperature of the combustion exhaust gas is in the range of 200 to 600 ° C. The method for denitrifying combustion exhaust gas according to claim 1, wherein _{3. The} dry denitration apparatus using NH ₃ as a reducing agent, wherein the amount of NH ₃ added to the combustion exhaust gas is equal to or less than equimolar to NOx in the exhaust gas. A method for denitrifying combustion exhaust gas according to the description. 4. N added as a reducing agent to combustion exhaust gas
Both the H ₃ and the hydrocarbon are added to the combustion exhaust gas at the upstream side of the dry denitration apparatus using NH ₃ as a reducing agent, and the combustion exhaust gas according to any one of claims 1 to 3, wherein Denitration method. 5. An oxidation catalyst layer is provided in the vicinity of the exhaust gas outlet of a dry denitration apparatus using hydrocarbon as a reducing agent to decompose and remove unreacted hydrocarbons. A method for denitrifying combustion exhaust gas according to the description.