JP3524652B2 - Exhaust gas denitration method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas denitration method capable of removing nitrogen oxides (NOx) in exhaust gas with high efficiency.

[0002]

2. Description of the Related Art Conventionally, as a method of treating nitrogen oxides in exhaust gas, a NOx removal catalyst is installed upstream of the exhaust gas flow to reduce and remove nitrogen oxides by catalytic reduction with ammonia, and then an NH ₃ decomposition catalyst on the flow side. A denitration method for decomposing excess NH ₃ by disposing a catalyst and a method for further denitrification catalyst installed downstream of the NH ₃ decomposition catalyst to reduce nitrogen oxides generated in the NH ₃ decomposition step are proposed. An example of the denitration apparatus in these methods is shown in FIGS. 4 and 5. FIG NH ₃ decomposing catalyst layer NH ₃ injection nozzle 1 in order from the upstream side, the denitration catalyst layer denitration catalyst-filled 2 and NH ₃ decomposing catalyst is filled denitration apparatus 5 which exhaust gas 6 is introduced in the apparatus 4 In the apparatus of FIG. 5, the second denitration catalyst layer 7 is further provided on the downstream side.

In the former method, more than the reaction equivalent of NH ₃ is added to the NOx to be removed, high-efficiency denitration is performed in the upstream denitration catalyst layer, and unreacted NH ₃ is decomposed in the NH ₃ decomposition catalyst layer. It is intended to NOx and NH ₃ concentrations of target, the latter with the addition of NH ₃ addition of a large amount than the former, perform denitration at a high efficiency close to 100% in the upstream of the denitration catalyst layer, NH ₃ decomposition catalyst Unreacted NH ₃ is decomposed in the layer. When decomposing the NH ₃ by NH ₃ decomposition catalyst some NO is produced by the following reaction formula.

## STR1 ## 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O In this method, the generated NO is reacted with NH ₃ remaining in the NH ₃ decomposition catalyst layer to treat NOx.
A second denitration catalyst layer is installed on the downstream side of the H ₃ decomposition catalyst layer.

As the denitration catalyst in the above method, a conventionally used TiO ₂ -based denitration catalyst containing vanadium, tungsten, molybdenum or the like as an active component can be used.

NH₃Decomposition catalyst is dehydrated
At (1.0 ± 0.6) R₂O ・ [aM₂O₃・ BAl₂
O₃] ・ CMeO ・ ySiO₂(In the formula, R: Alkali gold
Group ion and / or hydrogen ion, M: VII of the periodic table
Group I elements, rare earth elements, titanium, vanadium, chromium,
Selected from the group consisting of niobium, antimony and gallium
One or more elements, Me: alkaline earth element, a + b =
1.0, a ≧ 0, b ≧ 0, c ≧ 0, y / c> 12, y>
X) having the chemical composition of 12) and shown in Table 1 below.
Crystalline silicate with line diffraction pattern, γ-Al₂
O₃, Θ-Al ₂O₃, TiO₂, ZrO₂, TiO₂
・ ZrO₂, SiO₂・ Al₂O₃, Al₂O₃・ Ti
O₂, SO_Four/ ZrO₂, SO_Four/ ZrO₂・ Ti
O₂, Y-type zeolite, X-type zeolite, A-type zeolite
, Mordenite and silicalite
One or more types of porous materials used as carriers and white as the active metal
Gold, palladium, rhodium, ruthenium and iridium
A catalyst having at least one noble metal selected from the group consisting of
Can be used.

[0006]

[Table 1]

[0007]

As can be seen from the relationship between the SV value and the NH ₃ decomposition catalyst layer outlet NOx and NH ₃ concentrations shown in FIG. 2, the NH ₃ decomposition catalyst used in the above-mentioned denitration device has a small SV value. If so, the decomposition rate of NH ₃ is improved, but the amount of NOx produced is increased, and the exhausted NOx is discharged.
Will exceed the required value, or NOx concentration >> NH ₃ concentration at the outlet of the NH ₃ decomposition catalyst layer, and NH ₃
There is no point in installing a denitration catalyst layer at the outlet of the decomposition catalyst layer. In a boiler plant or gas turbine plant, the amount of gas decreases as the load decreases, and SV
The value becomes small. Normally, the maximum amount of gas is 100% at the denitration equipment in boiler plants and gas turbine plants.
Since the load is the design point, when an NH ₃ decomposition catalyst is used, the exhausted NOx may increase at low load, and measures must be taken.

In view of the above-mentioned prior art, the present invention is to provide a denitration method in which the NOx concentration at the outlet of the denitration device does not increase even when the boiler plant or the gas turbine plant is in a low load state.

[0009]

The present invention includes the following inventions (1) to (3). (1) An exhaust gas containing nitrogen oxides, an NH ₃ injection nozzle in order from the upstream side, a denitration catalyst layer filled with a denitration catalyst for catalytically reducing nitrogen oxides using NH ₃ as a reducing agent,
In NH ₃ decomposing catalyst denitration method in which nitrogen oxides are reduced and removed through a denitration apparatus provided with the NH ₃ decomposing catalyst layer filled with, a gas flow path between the denitration catalyst layer and the NH ₃ decomposing catalyst layer By providing a gas flow area control means for adjusting the size of the cross-sectional area and cutting off a part of the gas flow path, NH
_{3 A} method for denitration of exhaust gas, characterized in that the volume of a portion of the decomposition catalyst layer through which exhaust gas passes is controlled according to the load of exhaust gas.

(2) An exhaust gas containing nitrogen oxides, in order from the upstream side, an NH ₃ injection nozzle, a NOx removal catalyst layer filled with a NOx removal catalyst for catalytically reducing nitrogen oxides using NH ₃ as a reducing agent, NH ₃ decomposing catalyst and NH ₃ decomposing catalyst layer filled with nitrogen oxides catalytically reducing denitration catalyst through a denitration apparatus provided with a second denitration catalyst layer filled NOx and NH ₃ as a reducing agent In the denitration method for reducing and removing substances, a gas flow area control means for adjusting the size of the cross-sectional area of the gas passage is provided between the upstream denitration catalyst layer and the NH ₃ decomposition catalyst layer, A method for denitration of exhaust gas, which comprises controlling the volume of a portion of the NH ₃ decomposition catalyst layer through which the exhaust gas passes according to the load of the exhaust gas by shutting off a part.

(3) The above-mentioned (1) or (2) is characterized in that the gas flow area control means controls the cutoff ratio of the gas passage to be γ represented by the following equation (1).
Exhaust gas denitration method.

## EQU2 ## 1-γ = G (x) / (V _CA × SV _L ) ... (1) SV _L : NH ₃ decomposition catalyst limit SV value (NH _{3 at} the outlet of the NH ₃ decomposition catalyst layer) Limit SV value where the concentration is equal to or higher than the NOx concentration G (x): amount of treated gas per unit time at exhaust gas load (x) V _CA : NH ₃ decomposition catalyst layer capacity γ: gas flow path cutoff ratio

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas denitration method of the present invention, exhaust gas containing nitrogen oxides generated in various boiler plants, gas turbine plants, etc. is passed through a denitration catalyst layer and NH.
_{3 When} performing denitration processing using a denitration device having a decomposition catalyst layer or a second denitration catalyst layer, the denitration catalyst layer and NH
₃ provided gas flow area control means for adjusting the flow area of the gas between the decomposition catalyst layer, operating conditions of the boiler plant and gas turbine plants, i.e., for adjusting the flow area of the gas in accordance with the increase or decrease of the process gas volume I am trying.

A gas cut-off damper is generally used as a means for controlling the gas flow area. A plurality of dampers are installed vertically to the gas flow path, and a required number of dampers are opened according to the fluctuation of the gas flow rate. By closing the rest, the flow velocity of the gas is controlled to be constant.

(Function) NH₃At the inlet of the decomposition catalyst layer
The gas flow rate and NH ₃Decomposition catalyst
It is possible to control the volume of the portion of the bed through which the processing gas passes.
it can. That is, boiler plant and gas turbine
Even if the amount of gas decreases due to low load operation
₃SV value of gas in the decomposition catalyst layer is not less than a predetermined value
Can be held at. This will show you in Figure 3.
As the load decreases and the gas amount decreases, NH₃Decomposition catalyst
The NOx concentration at the layer outlet is NH₃Keep below the same concentration
be able to.

[0015]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples. In this example, a denitration apparatus having the configuration shown in FIG. 1 is used, and as the denitration catalyst, a catalyst in which vanadium and tungsten are supported as active metals on titanium oxide,
As the NH ₃ decomposition catalyst, a crystalline silicate supported with platinum as an active metal was used.

In the denitration apparatus of FIG. 1, an NH ₃ injection nozzle 1, a denitration catalyst layer 2, a gas blocking damper 4, an NH ₃ decomposition catalyst layer 3 and a second denitration catalyst layer 7 are arranged in this order from the upstream side where the exhaust gas 6 is introduced. is set up. In this device, a louver damper that can freely control the gas distribution area is used as the gas cutoff damper 4. This damper is a combination of a plurality of louvers that can be opened and closed individually, and is installed in a shape perpendicular to the gas flow path. The gas distribution area can be controlled by adjusting the opening and closing of each louver. The cutoff ratio γ of the gas flow area by the cutoff damper 4 is determined by the equation (1).

A denitration test of exhaust gas containing NOx was conducted by using the test apparatus having this structure. Changing the flow rate of the exhaust gas 6, for the case with and without using the gas blocking damper 4, NH ₃ and NO at the outlet of the NH ₃ decomposing catalyst layer 3
The result of measuring the concentration of x is shown in FIG. From FIG. 3, when the gas shut-off damper 4 is not used, the gas load is about 7
When the concentration becomes 5% or less, the NOx concentration exceeds the NH ₃ concentration, but by adjusting the gas flow area using the gas blocking damper 4, the NOx concentration at the outlet of the NH ₃ decomposition catalyst layer 3 is adjusted.
It can be seen that the concentration can be suppressed to be equal to or lower than the NH ₃ concentration. The test conditions are as shown in Table 2, and the shutoff ratio of the shutoff damper 4 is based on the conditions in Table 2 and the above formula (1) is used.
It was determined by the value calculated from.

[0018]

[Table 2]

[0019]

According to the method of the present invention, the NH ₃ decomposition catalyst can be made to function effectively not only when the exhaust gas source such as a boiler or a gas turbine is at 100% load but also under a partial load condition. It is possible to improve the efficiency of the denitration device, and it is possible to eliminate the risk that the NOx concentration at the outlet of the denitration device will rise.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a denitration device according to an embodiment of the present invention.

FIG. 2 SV value and outlet NO in the NH ₃ decomposition catalyst layer
₃ is a graph showing the relationship between x and NH ₃ concentration.

FIG. 3 is a graph showing the measurement results of the concentrations of NH ₃ and NOx at the outlet of the NH ₃ decomposition catalyst layer in the example.

FIG. 4 is an explanatory diagram showing the configuration of an example of a conventional denitration device.

FIG. 5 is an explanatory diagram showing the configuration of another example of the conventional denitration device.

Claims (3)

(57) [Claims] 1. An NH ₃ injection nozzle for exhaust gas containing nitrogen oxides from the upstream side, a NOx removal catalyst layer filled with a NOx removal catalyst for catalytically reducing nitrogen oxides using NH ₃ as a reducing agent, and an NH _{3. In} a denitration method of reducing and removing nitrogen oxides by passing through a denitration device provided with an NH ₃ decomposition catalyst layer filled with a ₃ decomposition catalyst, a gas flow path is disconnected between the denitration catalyst layer and the NH ₃ decomposition catalyst layer. It is possible to control the volume of the portion of the NH ₃ decomposition catalyst layer through which the exhaust gas passes according to the load of the exhaust gas by providing a gas flow area control means for adjusting the size of the area and blocking a part of the gas flow path. Characteristic exhaust gas denitration method. 2. The exhaust gas containing nitrogen oxides is supplied to the upstream side.
NH in order₃Injection nozzle and NH₃As a reducing agent
Denitrification catalyst packed with denitrification catalyst for catalytically reducing elemental oxides
Medium layer, NH₃NH filled with decomposition catalyst₃Decomposition catalyst layer
And NH₃Is used as a reducing agent to catalytically reduce nitrogen oxides
Denitration equipment provided with a second denitration catalyst layer filled with denitration catalyst
The denitration method of reducing and removing nitrogen oxides through a storage
And the denitration catalyst layer on the upstream side and NH₃Between cracking catalyst layer
Gas flow area control to adjust the cross-sectional area of the gas flow path
By providing a control means and blocking a part of the gas flow path
NH ₃Exhaust the volume of the portion of the decomposition catalyst layer through which the exhaust gas passes.
Of exhaust gas, which is characterized by controlling according to the load of the exhaust gas.
Glass method. 3. The exhaust gas according to claim 1 or 2, wherein the gas flow area control unit controls the gas flow path cutoff ratio to be γ represented by the following formula (1). Denitration method. [Number 1] 1-γ = G (x) / (V CA × SV L) ··· (1) SV L: NH 3 in the exit of the NH ₃ decomposing catalyst usage limit SV value (NH ₃ decomposing catalyst layer Limit SV value where the concentration is equal to or higher than the NOx concentration G (x): amount of treated gas per unit time at exhaust gas load (x) V _CA : NH ₃ decomposition catalyst layer capacity γ: gas flow path cutoff ratio