JPH0775720A - Treatment of waste gas and catalyst for removing nitrogen oxide and dioxin - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen oxides and dioxins in a waste gas with one kind of a catalyst at the same time by cooling the waste gas to a specific temp. and after collecting dust, heating again up to a specific temp. and bringing the gas into contact with a specific catalyst with a reducing agent for denitration. CONSTITUTION:The waste gas containing nitrogen oxide and toxic chlorine compounds such as dioxins is cooled to 100-180 deg.C. The cooled waste gas is, after introduced into a bag filter to capture dust containing solid dioxins, heated again to 200-249 deg.C. Next, the waste gas is brought into contact with the honeycomb shaped catalyst, which is composed of 70-95wt.% at least one kind of oxides of Ti and Si and 1-20wt.% at least one kind of oxides of W and V and 3-7mm in aperture equivalent diameter, with the reducing agent for denitration such as ammonia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simultaneously removing nitrogen oxides (NO _x ) and dioxins (DXN) in exhaust gas, and a nitrogen oxide / dioxin removing catalyst used in this method.

[0002]

2. Description of the Related Art NO _x , SO _x , HCl are contained in exhaust gas generated from an incinerator for incinerating municipal solid waste or industrial waste.
In addition to toxic substances such as, for example, dioxins, which are highly toxic, and organic chlorine compounds such as PCB are contained in a small amount.
For NO _x , SO _x, etc., the removal technology has been put to practical use, but the dioxin removal technology has not reached the level of practical use.

Conventionally, the following method has been proposed as a technique for removing dioxins in exhaust gas. (1) As described in JP-A-2-35914, at least one of titanium oxide, vanadium oxide, tungsten oxide, platinum, and palladium is used as a catalyst.
A method of decomposing aromatic chlorine compounds in exhaust gas of an incinerator at 150 ° C. or higher using seeds. (2) A method of decomposing dioxin in exhaust gas of an incinerator into HCl, H ₂ O, and CO ₂ by a general-purpose oxidation catalyst as described in JP-A-3-4920. (3) As described in JP-A-3-8415, as a catalyst, an A component selected from Ti, Si and Zr and Pt, Pd, Ru, Mn, Cu, Cr and Fe are selected. And a component B, and an organochlorine compound such as dioxin is used as a honeycomb structure having a catalyst through-hole having an equivalent diameter of 2 mm or more and an opening ratio of 50% or more at a temperature of 2
50 ° C or higher, space velocity (SV) 50000 h ^-1 or less, gas amount (AV) per 1 m ^{2 of} catalyst surface area 250 m ³ / hr · m ²
(At temp.) A method of removing under the following conditions.

(4) As described in JP-A-3-12221, the chlorine-based polymer compound in the exhaust gas of the incinerator is removed by using the catalyst having the same composition and shape as the above (3), and thereafter. , Method of introducing dust to the dust collecting part to remove dust. (5) as described in JP-A-4-200722, NO _x, the DXN (dioxin), incinerator exhaust gas containing NH _3, and is brought into contact with the denitrification catalyst at 200 to 500 ° C., first NO _x And then removing DXN by contacting with a de-DXN catalyst at 200 to 500 ° C. One or more oxides of Ti, Si, Al and Zr are used as the substrate of the DXN-free catalyst, and Pt,
It is described that at least one metal selected from Pd, Ru, Mn, Cu, Cr and Fe or an oxide thereof is used. Also, as the base, 3Al ₂ O ₃ .2SiO
₂ is used for the surface coating of TiO ₂ , and as a substrate, TiO ₂ —SiO ₂ , TiO ₂ —ZrO ₂ , TiO _{2
2 -SiO 2 -Al 2 O 3,} TiO 2 -SiO 2 -Zr
It is stated that O ₂ is used.

(6) As described in Japanese Examined Patent Publication No. 4-63288, after incinerating exhaust gas containing SO _x , NO _x , CO, dust, etc., it is gradually dusted, and then platinum is added to the ceramic honeycomb structure. A method of contacting a supported catalyst at 300 to 500 ° C. to remove dioxin in exhaust gas. (7) As described in JP-A-4-265122, Pt and P are formed on the surface of a substrate made of at least one oxide selected from Ti, Si, Al and Zr.
a catalyst supporting at least one metal selected from d, Ru, Mn, Cu, Cr and Fe, or an oxide thereof,
150 to 340 incinerator exhaust gas added with ammonia
A method of removing NO _x and an organic chlorine compound by contacting at ℃.

[0006]

[Problems to be Solved by the Invention] The above (1) to (7)
The method described in this publication has the following differences compared with the present invention. (1) Removes only aromatic chlorine compounds, NO
_x and dioxin (DXN) are not treated at the same time. Moreover, the corresponding catalyst composition ratio of the present invention is not described. (2) Removes only dioxin, NO _x , D
It does not remove XN at the same time. Further, the catalyst uses a general-purpose oxidation catalyst, and the catalyst composition is not described. (3) Only DXN is removed, and NO _x and DXN are not simultaneously processed. Also, the catalyst composition is different. (4) Removes only chlorine-based polymer compounds, NO
_x and DXN are not processed simultaneously. Also, the process and catalyst composition are different. (5) the denitrification and de DXN performs in different catalysts and different processes, not the NO _x · DXN simultaneous treatment with one type of catalyst. Also, the catalyst composition is different. (6) Only DXN is removed, and NO _x and DXN are not simultaneously processed. Also, the catalyst composition is different. (7) Although it removes NO _x and DXN at the same time, it does not contain an oxide of W or an oxide of V, and the constituent materials and proportions of the catalyst are different.

In view of the above points, the inventors of the present invention are diligently researching a method for efficiently removing dioxins in exhaust gas, and a catalyst for NO _x reduction decomposes dioxins in exhaust gas. It was found to have a function. The present invention was made by focusing on the fact that dioxin in exhaust gas exists in both gaseous and solid forms based on the above findings, and the object of the present invention is to use one type of catalyst,
An object of the present invention is to provide a method for efficiently removing NO _x and dioxins simultaneously and a catalyst therefor.

[0008]

In order to achieve the above object, the method for treating exhaust gas of the present invention comprises cooling exhaust gas containing toxic chlorine compounds such as nitrogen oxides and dioxins to 100 to 180 ° C. Then, this cooling exhaust gas is introduced into a bag filter to collect dust containing solid dioxins, and then reheated to 200 to 249 ° C., and then this exhaust gas is mixed with an oxide of Ti and an oxide of Si. 70 to 95 wt% of at least one of W oxide and V
1 to 20% by weight of at least one of the oxides mentioned above is brought into contact with a honeycomb-shaped catalyst having an equivalent opening diameter of 3 to 7 mm together with a reducing agent for denitration such as ammonia, and toxic chlorine such as nitrogen oxides and dioxins. The feature is that compounds are decomposed and removed at the same time. As the denitration reducing agent, ammonia gas, urea water, ammonia water, or the like is used.

The cooling temperature of the exhaust gas is 100 to 180 ° C, preferably 110 to 150 ° C. If the content is lower than this range, there is concern that corrosion due to chloride and deterioration of dust filter efficiency of the bag filter may occur. On the other hand, if it is higher than this range, the removal performance of HCl and SO _x of the temperature-reducing reactor tends to deteriorate, and the dioxin removal performance of the bag filter tends to deteriorate. The reheating temperature is 200 to 249.
However, considering the denitration and dedioxin performance and the steam generation conditions in the refuse incineration facility, it is 210-2
The temperature is preferably 20 ° C. Below this range,
The denitration performance and the dioxin removal rate tend to decrease, while if it is higher than this range, decomposed dioxin may be resynthesized. The opening diameter of the honeycomb catalyst is 3 to 7 mm, but it is preferably 4 to 6 mm. If it is smaller than this range, there is a concern that clogging due to incinerated dust or acidic ammonium sulfate may occur. on the other hand,
When it is larger than this range, the amount of processing gas per unit volume of catalyst is decreased and the required amount of catalyst is increased.

In the above method, it is preferable that powdered activated carbon is blown into the upstream side of the bag filter to adsorb dioxins in the exhaust gas to the powdered activated carbon, and then the powdered carbon is collected by the bag filter. Further, it is preferable to add at least one of ozone and hydrogen peroxide to the exhaust gas before contacting with the catalyst. Further, it is preferable to use a catalyst to which 0.01 to 3 wt% of at least one of Pt, Pd, Ru and Rh is further added.

According to the above-mentioned method of the present invention, in addition to dioxins, PCB as a dioxin-related substance, especially coplanar PCB (Copla PCB) as shown in Chemical Formula 1
nar PCB) can be removed.

[0012]

[Chemical 1]

[0013] NO _x · dioxin removal catalyst of the present invention includes at least one 70 to 95 wt% of the oxide of the oxide and Si of Ti as a first component, W as the second component
1 to 20 of at least one of the oxides of V and V
wt%, and is characterized by. As the first component, TiO ₂ alone, SiO ₂ alone, TiO ₂ and SiO
A mixture of _2, or a composite oxide of TiO ₂ -SiO ₂ can be used.

Further, NO _x · dioxin removal catalyst of the present invention is an oxide of at least one and 70 to 95 wt%, W as the second component of the oxide of the oxide and Si of Ti as a first component and At least one of V oxides 1
~ 20 wt% and Pt, Pd, Ru and R as third component
At least one kind of h is 0.01 to 3% by weight.

The content of the first component is 70 to 95% by weight, preferably 80 to 90% by weight. Of these, the Si oxide content is preferably 0 to 10 wt% and the Ti oxide content is 70 to 90 wt% from the viewpoints of moldability of the catalyst and maintenance of the catalytic action environment. The content of the second component is 1 to 20 wt.
%, But from the viewpoint of denitration and dedioxin, it is preferable that W oxide is 3 to 15 wt% and V oxide is 4 to 10 wt%. Further, the content of the third component is 0.01 to 3
Although it is wt%, it is preferably 0.1 to 1 wt%. If it is less than this range, the decomposition performance of dioxin tends to decrease, while if it is more than this range, the denitration performance tends to decrease.

Hereinafter, examples of processing steps of the method of the present invention will be described with reference to FIGS.
It will be described with reference to FIG. First, as shown in FIG. 1, the exhaust gas containing NO _x , SO _x , HCl, dioxins, dust, and the like discharged from the incinerator 10 is cooled by the temperature reduction reactor 12
Will be introduced to. In the dehumidifying reactor, water is sprayed to reduce the temperature, and desalting and desulfurizing agents such as slaked lime and quick lime are injected for desalting and desulfurizing. The exhaust gas cooled to 100 to 180 ° C. is introduced into the bag filter 14 to collect dust containing dioxins. Next, the exhaust gas is reheated to 200 to 249 ° C. by the reheater 16 and introduced into the denitration / DXN device 18, where NO _x and dioxins are decomposed and removed, and then discharged from the chimney 20. In addition, the reducing agent for denitration such as ammonia is
It is added to the XN device 18 or the upstream side thereof. Denitration / D removal
The XN device 18 includes at least one of 70 to 95 wt% of Ti oxide and Si oxide, W oxide and V oxide.
1 to 20 wt% of at least one of the oxides of the above-mentioned, and a honeycomb-shaped catalyst having an opening equivalent diameter of 3 to 7 mm is housed. In addition to the above catalyst, Pt, Pd, Ru and Rh
In some cases, a catalyst containing 0.01 to 3 wt% of at least one of them may be used.

As described above, by collecting solid dioxins with the bag filter 14, denitration / DX removal is performed.
It is possible to reduce the burden on the honeycomb catalyst in the N device 18, prevent deterioration of the catalyst and clogging of the catalyst, and extend the life of the catalyst.

In addition, as shown in FIG.
In some cases, powder activated carbon is blown in front of (4) (upstream side) to adsorb dioxins in the exhaust gas to the powder activated carbon, and then trapped by a bag filter. In this case, there is an advantage that the effect of removing dioxins is improved. Other configurations are similar to those in the case of FIG.

Further, as shown in FIG. 3, ozone, hydrogen peroxide, or both of them are added to the exhaust gas before contact with the catalyst, that is, in the exhaust gas upstream of the NOx removal / DXN device 18. Sometimes. In this case, there is an advantage that the reaction proceeds further and the effect of removing dioxins is improved. Other configurations are similar to those in the case of FIG.

Further, as shown in FIG. 4, powdered activated carbon is blown in front of the bag filter 14, and denitration and denitration are performed.
It may be configured to add ozone or / and hydrogen peroxide before the XN device 18. Other configurations are similar to those in the case of FIG.

[0021]

EXAMPLES Hereinafter, examples and experimental examples of the present invention will be described. Experimental Example 1 TiO ₂ 72 wt%, V ₂ O ₅ 7 wt%, WO ₃ 5 wt
% Of catalyst was prepared. On the other hand, as an alternative substance for dioxins, orthochlorophenol 10ppm, NO _x 12
Prepare a gas containing 0 ppm and add ammonia to this gas.
After the H ₃ / NO _x molar ratio of 1.0 was added, the catalyst was brought into contact with a honeycomb structure having an opening equivalent diameter of 6 mm, and the space velocity (SV) was 3100 h ⁻¹ , 4100 h.
^-1 , 6,200 h ^-1 , 12500 h ^-1 in case of N
The O _x and removal performance of orthochlorophenol was measured. The relationship between the temperature and the removal rate at this time was as shown in FIG. From this, the temperature range in which the exhaust gas is brought into contact with the catalyst is preferably 190 to 400 ° C,
~ 320 ° C is more effective. However, since the temperature of the exhaust gas introduced into the bag filter is as low as 100 to 180 ° C,
Reheating to a too high temperature is not preferable from the viewpoint of re-synthesis of dioxin and economical efficiency, and is 200 to 249 ° C.
The degree is enough.

Experimental Example 2 TiO ₂ 73 wt%, V ₂ O ₅ 5 wt%, WO ₃ 5 wt%
%, Pd 0.5 wt% was prepared, and the measurement was performed under the same conditions as in Experimental Example 1 except for the above. The result was as shown in FIG.

Experimental Example 3 In a honeycomb structure having the same composition and shape as the catalyst used in Experimental Example 1, 100 ppm of NO _x and dioxins (PCDD) were added.
+ PCDF) Ammonia is added at a ratio of NH ₃ / NO _x molar ratio of 0.6 to the dust incinerator exhaust gas after dust removal containing 1.2 to 12 ng / Nm ³ , and the space velocity (SV) 2500
Contacted at h ^-1 . The relationship between the temperature and the removal rate at this time was as shown in FIG.

Experimental Example 4 A honeycomb structure having the same composition and shape as the catalyst used in Experimental Example 2 was used, and the measurement was carried out under substantially the same conditions as in Experimental Example 3. The result was as shown in FIG.

Experimental Example 5 An exhaust gas containing 100 ppm of NO _x and 10 ppm of benzene was brought into contact with a honeycomb structure having the same composition and shape as the catalyst used in Experimental Example 1 at a temperature of 250 ° C. and SV3100 h ⁻¹ , and was removed by gas chromatography. The performance was measured. The results were as shown in FIGS. 9 and 10. At the catalyst outlet, no peak was observed around 0.79 minutes, which is the retention time for benzene analysis (Fig. 10), indicating that benzene was almost decomposed.

Experimental Example 6 A honeycomb structure having the same composition and shape as the catalyst used in Experimental Example 1 was used. NO _x 100ppm, coplanar PCB
A gas containing 0.02 ng / Nm ³ was prepared, and this gas was heated to 210 to 220 ° C.
The H ₃ / NO _x molar ratio of 0.4 was added to bring the mixture into contact with the above honeycomb structure, and AV (gas flow rate per 1 m ^{2 of} contact surface area) m ³ / m ² · hr and coplanar PCB removal rate were obtained. The relationship was measured. The result was as shown in FIG.

Example 1 Waste incinerator exhaust gas containing 96 ppm of NO _x and 10 ng / Nm ^{3 of} dioxins was cooled to about 150 ° C. in a water spray type desuperheater, and this cooled exhaust gas was introduced into a bag filter to remove dioxins. After collecting the contained dust, it was reheated to 210 ° C with a tube-type steam heater, and NH ₃ / NO _x was added to this gas.
NH ₃ was injected at a molar ratio of 0.8 and then TiO 2.
_{2 72wt%, V 2 O 5} 7wt%, WO 3 5wt%, was measured removal performance of the NO _x and dioxins in contact with the honeycomb catalyst of the eye opening 6 mm. As a result, NO _{x at the} outlet of the catalytic reactor was 19 ppm and dioxins were 0.07 ng.
The result was / Nm ³ . The dioxin concentration at the bag filter outlet was 0.6 ng / Nm ³ .

Example 2, Comparative Example 1 Powdered activated carbon corresponding to 1.5% of fly ash was blown into the exhaust gas of a refuse incinerator at 170 ° C. containing 120 ppm of NO _x and 4.3 ng / Nm ^{3 of} dioxins, followed by post-treatment. Was collected by a bag filter of No. 3 and the removal performance of DXNs was measured. As a result, the dioxin concentration at the bag filter outlet was 0.42 ng / Nm ³ . When powdered activated carbon was not blown in, the dioxin content at the bag filter outlet was 0.85 ng / Nm ³ . From the above results, it was found that the removal rate was improved by about 10% as compared with the case where activated carbon was not blown.

[0029]

Since the present invention is configured as described above, it has the following effects. (1) NO _x and dioxins can be efficiently decomposed and removed simultaneously with one type of catalyst, so that the exhaust gas treatment device can be made compact. (2) The catalyst of the present invention is C ₆ H ₅ Cl, C ₆ H ₅ ClO.
Not only dechlorination of dioxin precursors such as benzene ring, but also decomposes benzene ring, so dioxin, coplanar PC
Generation and resynthesis of B can be suppressed. (3) Since solid dioxin is collected in advance by the bag filter, the burden on the honeycomb catalyst in the downstream desulfurization / deDXN device can be reduced, and deterioration and clogging of the catalyst can be prevented. The life of the catalyst can be extended.

[Brief description of drawings]

FIG. 1 is a process chart showing an example of a flow for carrying out an exhaust gas treatment method of the present invention.

FIG. 2 is a process drawing showing another example of the flow for carrying out the exhaust gas treatment method of the present invention.

FIG. 3 is a process chart showing another example of a flow for carrying out the exhaust gas treatment method of the present invention.

FIG. 4 is a process drawing showing still another example of the flow for carrying out the exhaust gas treatment method of the present invention.

FIG. 5 is a graph showing the measurement results in Experimental Example 1, showing the removal performance of NO _x and orthochlorophenol which is a dioxin substitute.

FIG. 6 is a graph showing the measurement results in Experimental Example 2, showing the removal performance of NO _x and orthochlorophenol which is a dioxin substitute.

FIG. 7 is a graph showing the measurement results in Experimental Example 3 and showing actual measurement data of the removal performance of NO _x and dioxins in the exhaust gas of a refuse incinerator.

FIG. 8 is a graph showing the measurement results in Experimental Example 4 and showing the actual measurement data of the removal performance of NO _x and dioxin in the exhaust gas of a refuse incinerator.

FIG. 9 is a graph showing the measurement results in Experimental Example 5 and showing the retention time of benzene in the analysis of exhaust gas.

FIG. 10 is a graph showing the measurement results in Experimental Example 5 and showing the benzene removal performance.

FIG. 11 is a graph showing the measurement results of Experimental Example 6 and showing the removal performance of coplanar PCB.

[Explanation of symbols]

 10 Incinerator 12 Dehumidifying Reactor 14 Bag Filter 16 Reheater 18 Denitration / Dedioxin (DXN) Device 20 Chimney

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/30 ZAB A 8017-4G B01D 53/36 102 B (72) Inventor Takashi Mori Kobe city center 3-1-1 Higashikawasaki-cho, Kawasaki, inside the Kobe factory (72) Inventor Tadashi Maruyama 1-1, Kawasaki-cho, Akashi-shi, Hyogo Inside the Akashi factory, Kawasaki Heavy Industries (72) Inventor Yoshihiro Ide Kobe-shi Chuo-ku Higashikawasakicho 1-3-3 Kawasaki Heavy Industries, Ltd. Kobe Head Office (72) Inventor Kenichi Kashiwara 1-3 Higashikawasakicho Chuo-ku, Chuo-ku Kawasaki Heavy Industries Ltd. Kobe Headquarters (72) Inventor Keiro Morimoto 1-3-3 Higashikawasaki-cho, Chuo-ku, Kobe Inside Kawaju Environmental Engineering Co., Ltd.

Claims (6)

[Claims] 1. An exhaust gas containing toxic chlorine compounds such as nitrogen oxides and dioxins is cooled to 100 to 180 ° C., and the cooled exhaust gas is introduced into a bag filter to collect dust containing solid dioxins. After doing 200-2
The exhaust gas is reheated to 49 ° C., and at least one of Ti oxide and Si oxide is added to 70 to 95 wt.
% And at least one of W oxide and V oxide of 1 to 20 wt%, and a honeycomb-shaped catalyst having an opening equivalent diameter of 3 to 7 mm is brought into contact with a denitration reducing agent such as ammonia, and nitrogen is added. An exhaust gas treatment method characterized by simultaneously decomposing and removing toxic chlorine compounds such as oxides and dioxins. 2. The method for treating exhaust gas according to claim 1, wherein powdered activated carbon is blown into the upstream side of the bag filter, dioxins in the exhaust gas are adsorbed by the powdered activated carbon, and then collected by the bag filter. . 3. The method for treating exhaust gas according to claim 1 or 2, wherein at least one of ozone and hydrogen peroxide is added to the exhaust gas before contact with the catalyst. 4. The exhaust gas treatment method according to claim 1, wherein a catalyst further containing 0.01 to 3 wt% of at least one of Pt, Pd, Ru and Rh is used. 5. A first component of at least one of Ti oxide and Si oxide of 70 to 95 wt%, and a second component of at least one of W oxide and V oxide of 1 to 20 wt%. %, A catalyst for removing nitrogen oxides / dioxins. 6. A first component of at least one of Ti oxide and Si oxide of 70 to 95 wt%, and a second component of at least one of W oxide and V oxide of 1 to 20 wt%. %, And 0.01 to 3 wt% of at least one of Pt, Pd, Ru and Rh as a third component, a catalyst for removing nitrogen oxides and dioxins.