JP3462580B2 - Exhaust gas denitration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to nitrogen oxides in exhaust gas.
Exhaust gas that can remove (NOx) with high efficiency
A denitration method. [0002] 2. Description of the Related Art Removal of NOx contained in flue gas
The method is NH_ThreeCatalytic reduction method using urea as reducing agent
Has been widely put to practical use mainly in thermal power plants. As a catalyst
Activated vanadium, tungsten, and molybdenum
A titanium oxide-based catalyst is mainly used. [0003] SUMMARY OF THE INVENTION In recent years, NOx emission regulations have been
It is becoming increasingly severe, especially in metropolitan areas.
Regulations are being implemented, and power plants adjacent to urban areas
When expanding power generation equipment in response to growing power demand,
High efficiency denitration is required. A conventional denitration method is NH_ThreeContact with a reducing agent
In the reduction method, NOx is converted to N_TwoMinute
Understood. Embedded image 4NO + 4NH_Three+ O_Two  → 4N_Two+ 6H_TwoO From the reaction equation, theoretically, the equimolar amount of N
H_ThreeIf it is added, 100% of NOx can be removed.
You. However, in reality, NH_ThreeAnd NOx
It is impossible to mix them completely uniformly, and highly efficient denitration
NH to do _ThreeNeed to be added in excess of NOx
is there. Unreacted NH_ThreeAre emitted at a significant rate
There were drawbacks. [0005] In view of the state of the art, the present invention is based on the prior art.
Eliminate the disadvantages and unreacted NH_ThreeEmissions to the atmosphere as much as possible
Exhaust gas denitration method that can perform high-efficiency denitration
It is intended to provide. [0006] The present invention is as follows.
You. (1) Exhaust gas containing nitrogen oxides
Reactor, using ammonia as a reducing agent and contacting nitrogen
In the method for removing an oxide, a first gas is provided upstream of a gas flow.
A denitration catalyst layer is installed, and exhaust gas is introduced at the entrance of the first denitration catalyst layer.
Addition of ammonia over the reaction equivalent of the nitrogen oxides,
NOx concentration in the outlet gas of the first denitration catalyst layer is set to 0 to 10 pp
m, NH_ThreeAdjust the concentration to the range of 10 to 30 ppm, and
Oxidatively decomposes ammonia into nitrogen and nitrogen oxides downstream of
Installed an ammonia decomposition catalyst layer
NH in exhaust gas at outlet of near cracking catalyst layer_ThreeConcentration and NOx concentration
0 <NH_Three(Ppm) -NOx (ppm) <3
(Ppm) range, and a second denitration after that.
The catalyst layer is installed, and NO in the exhaust gas at the outlet of the second denitration catalyst layer
x concentration 0.1 ppm or less, NH_ThreeConcentration less than 3ppm
Adjust toAnd the ammonia decomposition catalyst is
(1.0 ± 0.6) R _Two O ・ [aM _Two
O _Three ・ BAl _Two O _Three ] ・ CMeO ・ ySiO _Two (R: A
Lucari metal ion and / or hydrogen ion, M: periodic table
Group VIII elements, rare earth elements, titanium, vanadium, black
, Niobium, antimony and gallium
At least one element, Me: alkaline earth metal element,
a + b = 1, a ≧ 0, b ≧ 0, c ≧ 0, y / c> 12,
y> 12) and having the formula shown in Table 1 below.
A crystalline silicate having a line diffraction pattern as a carrier,
Platinum, palladium, ruthenium and iridium as active metals
Contains one or more metals selected from the group consisting of indium
An exhaust gas denitration method characterized by being a catalyst. [0007] [Table 1]                VS: Very strong (X-ray source: Cu)                   S: Strong                   M: Intermediate                   W: weak It is. [0008] Hereinafter, one embodiment of the present invention will be described with reference to FIG.
Clarify the effect. First desorption at the uppermost stream of exhaust gas flow
A nitrate catalyst layer is added to the_ThreeFurther cracking catalyst layer
A second denitration catalyst layer is installed downstream of the first denitration catalyst layer.
NH more than the reaction equivalent to NOx_ThreeAnd add
90% or more denitration is performed in the first denitration catalyst layer, and the first denitration catalyst
Unreacted NH flowing out of the medium layer_ThreeTo NH_ThreeDecomposition catalyst layer
NOx, N at the downstream second denitration catalyst layer inlet
H_ThreeAdjust the concentration to reduce NOx at the outlet of the second denitration catalyst layer.
0.1 ppm or less, NH_ThreeTo a level of 3 ppm or less
You. The upstream and downstream first and second denitration catalyst layers have V,
TiO containing W, Mo, etc. as active ingredients_TwoConventional practical use of the system
The known catalyst can be used. In the above embodiment of the present invention, NH_ThreeDisassembly
As the catalyst used for the medium layer, select nitrogen as defined below
It is desirable that the rate% is 70% or more. (Equation 1) Nitrogen selectivity% = [1- ｛Ammonia decomposition catalyst outlet NO_x
(Ppm) -NO for ammonia decomposition catalyst inlet_x(Ppm)｝/｛ Ammonia decomposition catalyst inlet NH_Three(Ppm) -Ammonia decomposition catalyst outlet NH_Three(Ppm)｝] × 10
0 That is, the nitrogen selection of the ammonia decomposition catalyst as defined above
If the selectivity is small, NH_Three0 <NH at the outlet of the cracking catalyst layer
_Three(Ppm) -NO_x(Ppm) <3 (ppm)
The operating range of the plant that can be trawled becomes narrower and wider
It is necessary to control the amount of processing gas and temperature conditions
Therefore, the nitrogen selectivity should be at least 70% or more.
Is preferred. NH having the above nitrogen selectivity_ThreeCracking catalyst
As (1.0 ± 0.6) R_Two
O ・ [aM_TwoO_Three・ BAl_TwoO_Three] ・ CMeO ・ ySi
O_Two(R: alkali metal ion and / or hydrogen ion,
M: Group VIII element of the periodic table, rare earth element, titanium, banana
From zium, chromium, niobium, antimony and gallium
At least one element selected from the group consisting of: Me: alkaline earth
A class metal element, a + b = 1, a ≧ 0, b ≧ 0, c ≧ 0, y
/ C> 12, y> 12) and the above Table 1
Crystalline silicate having X-ray diffraction pattern shown in
With platinum, palladium, ruthenium as active metals
At least one member selected from the group consisting of
Catalysts containing metals are preferred. Excess NH in the first denitration catalyst layer_ThreeIs supplied
NOx: 0 to 10 ppm, N
H_Three: 10 to 30 ppm.
_ThreeIn the cracking catalyst layer, NH_ThreeIs reduced to NH_ThreeCracking catalyst layer
NH at exit_ThreeThe difference between the concentration and the NOx concentration is 0 <NH_Three(P
pm) -NOx (ppm) <3 (ppm)
Then, the exhaust gas having the composition is denitrated in the second denitration catalyst layer,
NOx concentration in exhaust gas from the outlet of the second denitration catalyst layer: 0.
1 ppm or less, NH_ThreeConcentration: 3ppm or less
it can. On the other hand, the conventional denitration catalyst layer alone
NH_ThreeTo remove NOx in the exhaust gas
NOx concentration in steel: 0.1ppm or less
Then, at least 10 ppm or more of NH is contained in the exhaust gas._Three
Is inevitable. [0013] The following examples further illustrate the method of the present invention.
Explain physically. (Example 1) (Preparation of denitration catalyst): Titania (TiO_Two) Pentic acid as carrier
Vanadium (V_TwoO_Five4% by weight, tungsten trioxide
Ten (WO_Three) Was supported in an amount of 3.3 wt.
mm pitch, 0.5mm wall thickness
This catalyst was used as a denitration catalyst. (NH_ThreePreparation of decomposition catalyst) Water glass No. 1
(SiO_Two: 30%): 5616 g to water: 5429 g
After dissolution, this solution was designated as solution A. On the other hand, water: 4175
g of aluminum sulfate: 718.9 g, ferric chloride: 1
10 g, calcium acetate: 47.2 g, sodium chloride
262 g and concentrated hydrochloric acid: 2020 g
This solution was designated as solution B. Solution A and Solution B
And a precipitate is formed, sufficiently stirred, and pH = 8.
A slurry of 0 was obtained. 20 liters of this slurry
Charged in a clave and added tetrapropyl ammonium
Add 500 g of bromide, and add water at 160 ° C for 72 hours.
Perform thermal synthesis, wash with water, dry after synthesis, and further 500
C. for 3 hours to obtain crystalline silicate 1. This result
Crystalline silicate 1 is in the molar ratio of oxides (water of crystallization is omitted)
It is represented by the following composition formula.
It was displayed in. Embedded image 0.5Na_TwoO ・ 0.5H_TwoO · [0.8Al
_TwoO_Three・ 0.2Fe_TwoO_Three・ 0.25CaO] ・ 25S
iO_Two The above crystalline silicate 1 is converted to 4N NH_FourCl aqueous solution 40
Stir for 3 hours at_FourIon exchange was performed. Io
After washing and drying at 100 ° C for 24 hours,
Baking at 00 ° C. for 3 hours to obtain H-type crystalline silicate 1
Was. Each of the H-type crystalline silicates 1
Platinic acid aqueous solution, palladium nitrate aqueous solution, ruthenium chloride
Aqueous solution, impregnated with iridium chloride aqueous solution, evaporated to dryness,
The powder was fired at 500 ° C. for 3 hours to obtain a powder catalyst. The resulting powder
Powder: Alumina sol as binder for 100 g:
3 g, silica sol: 55 g (SiO_Two: 20 wt%)
Water: Add 200g to make slurry, for cordierite
Monolith substrate (grid shape per 30 cells square inch)
200g / m per substrate surface^Twoof
It was carried at the coating amount. The resulting catalyst is converted to NH_ThreeCracking catalyst 1
To 5. The properties are shown in Table 2 below. [0017] [Table 2] The above NH_ThreeIn the method for preparing the cracking catalyst, the salt
Cobalt chloride: 112 g instead of ferric chloride, titanium chloride
: 105 g, vanadium chloride: 10 g, chromium chloride:
107 g, niobium chloride: 135 g, antimony chloride: 1
55g, gallium chloride: 119g
H-type crystalline silicates 2, 3, 4, 5,
6, 7 and 8 were prepared, and each of these H-type crystalline silicates was prepared.
Operation similar to the above preparation method using chloroplatinic acid aqueous solution
The platinum is supported on each H-type crystalline silicate by
Operate in the same manner as in
200g / m per substrate surface area^TwoNo
The amount supported. The resulting catalyst is converted to NH_ThreeDecomposition catalyst 6-1
It was set to 1. The properties are shown in Table 3 below. [0019] [Table 3](Denitration reaction test) 40 mm × 50 mm × 4
Three 00 mmL denitration catalysts, 42 mm x 50 mm x
500 mmL of the NH_ThreeOne cracking catalyst and the denitration catalyst
Two media were arranged in series and tested under the following conditions. [0021] [Table 4] Table 5 shows the results of this test. Conventional
NO at the outlet of the first denitration catalyst layer on the upstream side corresponding to the nitrification method
x is extremely high denitration rate of 0.02-0.03ppm
What is made ゝ NH_ThreeIs a large amount of 10 to 20 ppm
On the other hand, in the method of the present invention, the second denitration on the downstream side is performed.
NOx: 0.02-0.1 ppm, NH at the catalyst layer outlet
_Three<3 ppm or less, NOx, NH_ThreeBoth sides
It has been confirmed that both emissions have achieved low levels
Was. [0023] [Table 5][0024] According to the denitration method of the present invention, the reducing agent
NH_ThreeEmissions at a low level,
Rate NOx removal can be performed.

[Brief description of the drawings] FIG. 1 is an explanatory view of one embodiment of the exhaust gas denitration method of the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshiaki Obayashi, Inventor 4-62-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Inventor Takako Kobayashi 2-5-2 Marunouchi, Chiyoda-ku, Tokyo No. 1 Mitsubishi Heavy Industries, Ltd. Head Office (72) Inventor Akira Serizawa 1-1, Akunouramachi, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (56) References JP-A-63-87521 (JP, A) JP-A-2-293022 (JP, A) JP-A-51-84771 (JP, A) JP-A-56-108516 (JP, A) JP-A-53-132465 (JP, A) JP-A-53-108065 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/00 B01D 53/86

Claims (1)

(57) [Claim 1] In a method for removing an oxide of nitrogen by contacting an exhaust gas containing nitrogen oxide to a reactor filled with a catalyst and using ammonia as a reducing agent, the method comprises the steps of: A first denitration catalyst layer is installed on the upstream side of the flow, ammonia is added to the inlet of the first denitration catalyst layer at a reaction equivalent of or more than the reaction equivalent of nitrogen oxides in the exhaust gas, and the NOx concentration in the first denitration catalyst layer outlet gas is reduced. 0 to
10 ppm, the NH ₃ concentration was adjusted in the range of 10 to ₃₀ ppm, and an ammonia decomposition catalyst layer having a function of oxidizing and decomposing ammonia into nitrogen and nitrogen oxides was installed in the subsequent stream. the difference between the ₃ concentration and NOx concentration _{0 <NH 3 (ppm) -NOx} (p
pm) <3 (ppm), and further, a second denitration catalyst layer is installed downstream of the denitration catalyst layer. The NOx concentration in the exhaust gas at the outlet of the second denitration catalyst layer is 0.1 ppm or less, and the NH ₃ concentration is 3 ppm.
ppm consists in adjusting below, the ammonia partial
With the decatalyst dehydrated, (1.0 ± 0.6) R ₂ O
・ [ AM ₂ O ₃ ・ bAl ₂ O ₃ ] ・ cMeO ・ ySiO
₂ (R: alkali metal ion and / or hydrogen ion,
M: Group VIII element of the periodic table, rare earth element, titanium, banana
From zium, chromium, niobium, antimony and gallium
At least one element selected from the group consisting of: Me: alkaline earth
A class metal element, a + b = 1, a ≧ 0, b ≧ 0, c ≧ 0, y
/ C> 12, y> 12) and the details of the invention
X-ray diffraction pattern shown in Table 1 described in the detailed description section
Crystalline silicate with a carrier as active metal
Consists of platinum, palladium, ruthenium and iridium
A catalyst containing at least one member selected from the group
Exhaust gas denitration method.