JP3868705B2 - Combustion exhaust gas treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention, BurningIt relates to a method for treating fired exhaust gas. Specifically, it can decompose chlorinated organic compounds such as dioxin with high efficiency at low temperatures.The lawThe present invention relates to a method for treating flue gas used under specific conditions.
[0002]
[Prior art]
Combustion exhaust gas discharged from incinerators that treat municipal waste and industrial waste contains various harmful components, but chlorinated organic compounds such as highly toxic dioxins and their precursors, aromatic chlorine compounds. Removal of nitrogen oxides, which are causative agents of compounds and photochemical smog, is particularly important.
[0003]
Various methods are known as a method for removing chlorinated organic compounds from combustion exhaust gas. In particular, catalytic cracking is an excellent method for decomposing chlorinated organic compounds under conditions of 500 ° C. or less. By the way, the catalytic decomposition of a chlorinated organic compound is required to be performed at a temperature of 250 ° C. or lower because dioxins once decomposed are regenerated at a decomposition temperature of 300 ° C. or higher.
[0004]
Furthermore, in recent years, in city garbage incineration facilities, power is generated by steam obtained for the purpose of recovering heat generated at the time of garbage incineration, and electric power is supplied to the city garbage incineration facility and surplus power is sold. By the way, when the above steam is used to maintain the reaction temperature of the catalyst layer for chlorinated organic compound decomposition, there is a disadvantage that a larger amount of steam is consumed as the reaction temperature is higher. Therefore, from such a viewpoint, operation at a reaction temperature as low as possible, specifically, a reaction temperature of 200 ° C. or less is required.
[0005]
On the other hand, catalytic decomposition of chlorinated organic compounds is considered an oxidation reaction, and the reaction rate inevitably decreases as the reaction temperature decreases. Therefore, when an attempt is made to obtain a predetermined decomposition rate by performing catalytic cracking at a lower temperature, it is necessary to increase the amount of catalyst or decrease the amount of processing gas per unit time. However, in the municipal waste incineration facility, since it is difficult to reduce the amount of processing gas, there is a problem that the processing apparatus becomes enormous.
[0006]
On the other hand, as a catalyst carrier, TiO 2 is generally used.₂, SiO₂, Al₂O_Three, ZrO₂In the case of a catalyst for decomposing chlorinated organic compounds, SO₂Is often contained, so SO₂Resistant to TiO₂Is commonly used. For example, in Japanese Patent No. 2633316, TiO₂Active ingredient V on carrier₂O_FiveAnd WO_ThreeIn US Pat. No. 2,916,259, the dispersibility of the active component is improved by using a binary or ternary composite oxide of Ti, Si, and Zr as a carrier, thereby improving the catalyst performance. We are trying to improve.
[0007]
In Japanese Patent No. 2633316, a reaction temperature of 270 to 290 ° C. is adopted. However, such a temperature is not sufficiently low, and in Japanese Patent No. 2916259, the temperature is 200 ° C. And SV is 2000hr^-1These reaction conditions are employed, and it is necessary to use a large amount of catalyst.
[0008]
As described above, none of the conventional catalysts for decomposing chlorinated organic compounds is sufficiently satisfactory for use in a low-temperature condition and a compact processing apparatus.
[0009]
[Problems to be solved by the invention]
  The present invention has been made in view of the above circumstances, and the purpose thereof is 250 ° C. or lower (preferably from the viewpoint of the problem of resynthesis of dioxins and the reduction of the amount of steam used as a heating source of the catalyst layer). Is a method for decomposing chlorinated organic compounds, which can employ a reaction temperature of 200 ° C. or less)Is a method for treating combustion exhaust gas using specific conditions, and further, the acidic ammonium sulfate produced by ammonia introduced into the exhaust gas for the decomposition of nitrogen oxides and sulfur dioxide in the exhaust gas is applied to the catalyst surface. Combustion exhaust gas treatment method improved to prevent precipitationIs to provide.
[0011]
[Means for Solving the Problems]
As a result of various studies, the present inventor has obtained the following various findings. That is, WO_ThreeIs highly dispersed in the crystal lattice, WO_Three-TiO₂A catalyst in which an active component is supported on a binary composite oxide support is pure TiO.₂WO as active ingredient in carrier_ThreeCompared to a catalyst on which is supported, decomposition performance of chlorinated organic compounds is high. As a carrier, WO_Three-TiO₂By using the binary composite oxide, the heat resistance is improved, for example, the decrease in the catalyst performance due to the decrease in the specific surface area that inevitably occurs in the calcination step of the catalyst production is suppressed, and the catalyst performance is relatively improved. The knowledge that it improves is obtained. Furthermore, if two types of catalysts having specific performance are used under specific conditions, precipitation of acidic ammonium sulfate on the catalyst surface can be prevented.
[0013]
  The present invention has been completed based on the above findings.Is a method for treating a combustion exhaust gas containing a chlorinated organic compound, sulfur dioxide and nitrogen oxide, which satisfies the following conditions (a) to (d): Lies in the way.
[0014]
(A) As a catalyst, vanadium (V) oxidation as an active ingredient on a carrierThing isA low oxidation performance catalyst (X) supported and having a chlorinated organic compound resolving power and a nitrogen oxide resolving power in the presence of ammonia and having a sulfur dioxide oxidative conversion of 1.3% or less as defined below; WO₃-TiO₂Vanadium (V) oxidation as an active ingredient on binary composite oxide supportThing isThe supported catalyst has a ratio of the carrier to the total amount of the catalyst of 70% by weight or more, and has a chlorinated organic compound resolving power and a sulfur dioxide oxidative conversion rate defined below of 3.0% or more. Two types of catalyst with high oxidation performance catalyst (Y) are used.
[0015]
<Oxidation conversion rate of sulfur dioxide>
Pressure: normal pressure, temperature: 250 ° C., SV (space velocity): 1850 Hr^-1, Catalyst amount: O under conditions of 450 ml₂10% dry volume, SO₂500ppm, H₂O: 10% by volume, N₂A gas having a balanced amount is supplied to the reaction tube filled with the catalyst, and the SO_ThreeConcentration and total SO_XThen, the oxidation conversion rate (%) of sulfur dioxide is calculated by the following formula.
[0016]
[Expression 2]
(Exit SO_ThreeConcentration / Outlet total SO_X) × 100
[0017]
(B) Each contact process with combustion exhaust gas, a low oxidation performance catalyst, and a high oxidation performance catalyst is performed in an arbitrary order and in a temperature range of 100 to 250 ° C.
[0018]
(C) When the contact step with the low oxidation performance catalyst is preceded, ammonia is introduced into the combustion exhaust gas flowing into the contact step with the low oxidation performance catalyst, the amount of which is ammonia in the combustion exhaust gas flowing out from the step The amount is adjusted to 20 ppm or less.
[0019]
(D) When the contact step with the high oxidation performance catalyst is preceded, ammonia is introduced into the combustion exhaust gas flowing into the contact step with the low oxidation performance catalyst.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
  First, according to the present inventionUsed in combustion exhaust gas treatment methodsA method for decomposing chlorinated organic compounds will be described. thisDisassembly method, As a catalyst for decomposing chlorinated organic compounds, WO₃-TiO₂A catalyst in which an active component is supported on a binary composite oxide support and the ratio of the support to the total amount of the catalyst is 70% by weight or more is used.
[0021]
WO_Three-TiO₂Binary composite oxide support is TiO₂Hydrous titanic acid with a content of 20 to 50% by weight (TiO₂Hydrate), a soluble tungsten compound is added and dehydrated, and then calcined. WO_Three-TiO₂Binary composite oxide support is TiO₂WO_ThreeHas a highly dispersed structure, crystallization by heating and rutile TiO₂Have the property of suppressing the transfer of. Such a feature provides the following significant advantages.
[0022]
That is, in the production of the catalyst, a water-soluble salt is used as a raw material in order to highly disperse the active ingredient in the carrier, but in order to finally form a stable oxide, a firing treatment is always performed. Furthermore, when it is set as a molded body, it is fired to improve its strength. In addition, heat treatment is always performed when the catalyst is used (contact reaction). In this way, heat treatment is unavoidable for the catalyst, whereby crystallization of the support proceeds. When the crystallization of the carrier proceeds, condensation of the active component occurs, the dispersion state deteriorates, and the catalyst performance is lowered. However, WO_Three-TiO₂As described above, the binary composite oxide support is suppressed from being crystallized by heating, that is, a decrease in catalyst performance. In other words, the catalyst performance is relatively improved. Such an effect is particularly remarkable when the temperature of the catalytic reaction is low.
[0023]
TiO₂WO_ThreeWhether or not is highly dispersed can be confirmed by X-ray diffraction as described below.
[0024]
In the X-ray diffraction spectrum, the peak intensity is WO_ThreeVaries depending on the content of_ThreeWhen crystals are present, a peak appears at a position of 2θ = 23.5 °. Conversely, WO_ThreeEven if there is a large amount of_ThreeTiO, not alone₂High dispersion
WO_ThreeAs a result, a peak does not appear at the position of 2θ = 23.5 °, and the reagent special grade anatase TiO₂A peak appears only at the same position. Therefore, in the X-ray diffraction spectrum, WO_ThreeThe peak intensity of 2θ = 23.5 °, which is the peak of the anatase type TiO₂If the value is 1/100 or less with respect to the peak intensity of 2θ = 25.3 °, which is a peak of γ, it can be sufficiently judged that the dispersion is highly dispersed.
[0025]
In addition, WO_ThreeEnters the space of the crystal lattice so that TiO₂The crystal lattice expands in a certain direction. That is, WO_Three-TiO₂The binary composite oxide support is pure anatase TiO.₂X-ray diffraction spectrum and lattice spacing is anatase TiO₂Further, the angle becomes larger by 0.05 ° or more at 2θ, and the (2, 0, 0) plane and the (2, 1, 1) plane expand.
[0026]
WO_Three-TiO₂WO in binary composite oxide support_ThreeIs usually 1 to 20% by weight, preferably 5 to 15% by weight. WO_ThreeIf the percentage of the content is less than 1% by weight,_ThreeIf the above-mentioned effect due to high dispersion of the resin is not expressed and exceeds 20% by weight, WO_ThreeHigh dispersion becomes difficult.
[0027]
  In the present invention, the active component of the chlorinated organic compound decomposition catalystIsVanadium (V) oxidationWith thingsis there. Vanadium (V) oxide is preferably used because it is inexpensive and has a high decomposition rate of chlorinated organic compounds.
[0028]
Although it does not restrict | limit especially as a raw material of said vanadium oxide, Vanadium pentoxide (V₂O_Five) Or ammonium metavanadate (NH_FourVO_Three) Is preferably used. These raw materials are usually dissolved in an oxalic acid aqueous solution or a monoethanolamine aqueous solution and used as a raw material solution. The content of vanadium oxide in the chlorinated organic compound decomposition catalyst is not only used alone as an active ingredient, but also varies depending on the method of using the catalyst, etc., but is usually 0.1 to 30% by weight, preferably 0.1 to 20% by weight. %.
[0029]
  When using the above-mentioned metal active ingredient, the catalyst is prepared by a method in which the aqueous solution of the active ingredient and the carrier are mixed well and then molded, or calcined after impregnating the molded carrier base material with the aqueous solution of the active ingredient. To prepare.
[0030]
The shape and size of the catalyst are appropriately selected depending on the presence / absence of dust in the chlorinated organic compound-containing gas, the amount of treatment gas, the size of the reactor, and the like. Examples of the shape of the catalyst include a honeycomb shape, a columnar shape, a spherical shape, and a plate shape.
[0031]
As a method for producing a honeycomb-shaped catalyst in which an active component is supported on a carrier, (a) the carrier component and the active component or its raw material are kneaded together with a molding aid, and then shaped into a honeycomb shape by an extrusion molding method or the like. And (b) a method of impregnating and supporting a carrier component and an active component on a honeycomb-shaped substrate. The following method is illustrated as an example of the manufacturing method (a) described above.
[0032]
(1) Dissolve ammonium metavanadate in an aqueous solution of about 10% by weight monoethanolamine.
(2) A titanium sulfate solution is hydrolyzed to obtain a metatitanic acid slurry.
(3) After adjusting the pH by adding 15 wt% ammonia water to the metatitanic acid slurry, reflux treatment is performed for 1 hour or more.
(4) Ammonium paratungstate is added, and further reflux treatment is performed for 1 hour or more.
(5) The obtained slurry is filtered, and the obtained cake is dried at a temperature of 50 to 150 ° C. for 3 to 50 hours, then baked at a temperature of 400 to 650 ° C., and pulverized after cooling.
(6) The obtained powdery WO_Three-TiO₂The binary composite oxide support and the aqueous solution prepared in the above (1) are kneaded with a kneader.
[0033]
(7) (i) A kneaded product further kneaded with a molding aid is extruded and dried at a temperature of 50 to 150 ° C. for 3 to 50 hours, and then SV100 to 2000 Hr.^-1Or (ii) the kneaded product is dried at a temperature of 50 to 150 ° C. for 3 to 50 hours and fired at a temperature of 450 to 650 ° C. To form.
[0034]
Moreover, the following method is illustrated as an example of the above-mentioned manufacturing method (b). That is, a carrier component prepared in the above (2) to (5) is coated on a base material having a desired shape such as a columnar shape, a spherical shape, a honeycomb shape, a plate shape, and the aqueous solution prepared in the above (1). It is applied and impregnated with the active ingredient, dried at 50 to 150 ° C. for 3 to 50 hours, and then fired at a temperature of 450 to 650 ° C.
[0035]
In the case of a catalyst formed on a substrate, the substrate is TiO₂And SiO₂And Al₂O_ThreeEtc. are used alone or in combination. WO_Three-TiO₂The amount of the binary composite oxide (carrier component) is usually 70 to 99% by weight with respect to the total amount of the carrier component and the active component. The total amount of the carrier component and the active component is usually 5 to 70% by weight, preferably 10 to 50% by weight, based on the total amount of the base material, the carrier component and the active component.
[0036]
When all of the added raw materials are active components as in the kneading / forming method, the catalyst composition is estimated from the added amount, assuming that the raw material components such as the respective metal salts have changed to the corresponding metal oxides. When the catalyst is produced by an impregnation method, the catalyst is treated with hydrofluoric acid, melted with ammonium sulfate, and the catalyst composition is measured by a plasma emission analysis method (ICP-AES analysis method).
[0037]
saltMethod for decomposing elemental organic compoundsInBrings the chlorinated organic compound-containing gas into contact with the catalyst. Examples of the chlorinated organic compound-containing gas include dioxins represented by 2,3,7,8-tetrachlorodibenzodioxin and 2,3,4,7,8-pentachlorodibenzofuran, and 3,3 ′, 4. Coplanar PCBs typified by 4,4 ', 5-pentachlorobiphenyl are about 0.1 to 200 ng / m³(N.T.P) (toxic equivalent conversion value), which is a precursor substance of dioxins, chlorobenzenes such as monochlorobenzene and trichlorobenzene, chlorophenols such as O-chlorophenol and trichlorophenol, A gas containing chlorobenzofuran or the like, specifically, an exhaust gas when burning municipal waste, industrial waste, or the like in a method for treating a combustion exhaust gas described later is used. Such a chlorinated organic compound-containing gas contains oxygen together with moisture, and the content thereof is usually 0.5 to 25 vol%, preferably 1 to 21 vol%.
[0038]
The chlorinated organic compound-containing gas as described above is usually introduced into the contact process after removing dust and heavy metals through a bag filter. If necessary, the acid gas may be removed by treatment with a slaked lime reaction tower before treatment with the bag filter.
[0039]
The contact temperature between the chlorinated organic compound-containing gas and the catalyst is usually 100 to 250 ° C, preferably 100 to 200 ° C. When the contact temperature exceeds 250 ° C., the decomposition rate of the chlorinated organic compound increases, but it is disadvantageous from the viewpoint of saving steam for heating the catalyst layer as well as the problem that the decomposed dioxins are re-synthesized. When the contact temperature is less than 100 ° C., condensation causing trouble in operation is caused. The pressure of the catalyst layer is usually −0.05 to 0.9 MPa, preferably −0.01 to 0.5 MPa as a gauge pressure. The space velocity (SV) is usually 100 to 50000 Hr.^-1, Preferably 1000-20000Hr^-1It is.
[0040]
  Next, the method for treating combustion exhaust gas according to the present invention will be described. In the present invention, as a catalyst,Vanadium (V) oxide is supported as an active ingredient on the carrier, andA low oxidation performance catalyst (X) having a chlorinated organic compound resolution and a nitrogen oxide resolution in the presence of ammonia and having an oxidation conversion rate of sulfur dioxide of 1.3% or less as defined below; WO₃-TiO₂Active ingredient in binary complex oxide supportVanadium (V) oxide asAnd a ratio of the carrier with respect to the total amount of the catalyst is 70% by weight or more, and has a chlorinated organic compound resolving power and an oxidation conversion rate of sulfur dioxide defined below is 3.0% or more. Two types of high oxidation performance catalyst (Y) are used.
[0041]
<Oxidation conversion rate of sulfur dioxide>
Pressure: normal pressure, temperature: 250 ° C., SV (space velocity): 1850 Hr^-1, Catalyst amount: O under conditions of 450 ml₂10% dry volume, SO₂500ppm, H₂O: 10% by volume, N₂A gas having a balanced amount is supplied to the reaction tube filled with the catalyst, and the SO_ThreeConcentration and total SO_XThen, the oxidation conversion rate (%) of sulfur dioxide is calculated by the following formula.
[0042]
[Equation 3]
(Exit SO_ThreeConcentration / Outlet total SO_X) × 100
[0043]
The low oxidation performance catalyst (X) defined as described above is composed of ammonia and sulfur dioxide (actually sulfur oxide SO_XAnd H₂SO) in the presence of O)₂Or SO_ThreeAlthough it is physically adsorbed, it has a feature of hardly producing acidic ammonium sulfate. By the way, a catalyst having a low oxidative conversion of sulfur dioxide usually has a low ability to decompose chlorinated organic compounds. Therefore, when only the low oxidation performance catalyst (X) is used, a large amount of catalyst is required for a high removal rate of the chlorinated organic compound, resulting in poor efficiency.
[0044]
  Therefore, in the present invention, by using the high oxidation performance catalyst (Y) defined as described above, that is, a catalyst having high decomposition performance of the chlorinated organic compound, in other words,The aboveUtilize decomposition methods of chlorinated organic compounds under specific conditions (The aboveBy using a catalyst for decomposing chlorinated organic compounds by modifying the oxidation conversion rate of sulfur dioxide to 3.0% or more), a high removal rate of chlorinated organic compounds can be achieved with a relatively small amount of catalyst as a whole. Yes. In the case of a high oxidation performance catalyst (Y), if ammonia and sulfur dioxide are present in the exhaust gas, acidic ammonium sulfate is generated and adhered to the catalyst surface at a temperature of 100 to 250 ° C., causing a decrease in performance. Therefore, the high oxidation performance catalyst (Y) is used under the condition that the ammonia concentration in the combustion exhaust gas is 20 ppm or less, as will be described later.
[0045]
The oxidation conversion rate of sulfur dioxide of the low oxidation performance catalyst (X) is preferably 0.8% or less from the viewpoint of more reliably preventing the formation of acidic ammonium sulfate, and the oxidation conversion rate of sulfur dioxide of the high oxidation performance catalyst (Y). Is preferably 5% or more, more preferably 6% or more from the viewpoint of further increasing the removal rate of the chlorinated organic compound.
[0046]
  Different oxidative conversions of the above sulfur dioxide can be achieved by using catalysts having different compositions and types. For example, V ₂O₅When the content is 2.5% by weight or less, the low oxidation performance catalyst (X) is obtained, and when the content is 3.5% by weight or more, the high oxidation performance catalyst (Y) is obtained.
[0047]
First, the low oxidation performance catalyst (X) will be described. This catalyst is usually formed by supporting an active ingredient on a carrier. The carrier is not particularly limited, but SO_XTiO with excellent acid resistance from the viewpoint of treatment of contained flue gas₂Are preferably used. TiO₂TiO₂-SiO₂TiO₂-SiO₂-ZrO₂TiO₂-WO_Three-SiO₂Or a complex oxide such as
[0048]
  As the active component of the catalyst, the same components as in the above-mentioned decomposition method of chlorinated organic compoundsIs mentioned.A catalyst containing vanadium oxide is particularly preferable because it is inexpensive, has a high decomposition rate of chlorinated organic compounds, and can decompose nitrogen oxides in the presence of ammonia. The amount of vanadium oxide supported isDisassembly methodSimilarly, it is usually 0.1 to 30% by weight, preferably 0.1 to 20% by weight.
[0049]
Further, as the low oxidation performance catalyst (X), a catalyst similar to the above-mentioned catalyst for decomposing chlorinated organic compounds can be used as long as the above-mentioned conditions for the oxidative conversion of sulfur dioxide are satisfied. The shape and size of the catalyst, the method for preparing the catalyst, and the like are the same as in the case of the catalyst for decomposing chlorinated organic compounds.
[0050]
Next, the high oxidation performance catalyst (Y) will be described. As described above, this catalyst is obtained by modifying the above-mentioned catalyst for decomposing chlorinated organic compounds to a sulfur dioxide oxidation conversion rate of 3.0% or more.
[0051]
Next, the method for treating combustion exhaust gas of the present invention will be described. In this invention, each contact process with a combustion exhaust gas, a low oxidation performance catalyst, and a high oxidation performance catalyst is performed in an arbitrary order and a temperature range of 100-250 degreeC. The condition where the contact temperature is 250 ° C. or lower is a condition defined from the viewpoint of preventing the regeneration of the decomposed dioxin or the like as described above, and the condition where the contact temperature is 100 ° C. or more hinders the operation of the apparatus. This is a condition defined from the viewpoint of reliably preventing condensation. The pressure during the contact treatment is usually -0.05 to 0.9 MPa, preferably -0.01 to 0.5 MPa as a gauge pressure. SV is usually 100 to 50000 Hr.^-1, Preferably 1000-20000Hr^-1It is.
[0052]
The combustion exhaust gas targeted by the treatment method of the present invention is a chlorinated organic compound, usually NO of 0.1 ppm or more._xUsually, SO of 0.1 ppm or more_xExhaust gas containing, for example, exhaust gas from burning municipal waste or industrial waste. Such combustion exhaust gas contains 0.1 to 200 ng / m of dioxins and coplanar PCBs together with moisture and oxygen.^Three(NTP) (toxic equivalent equivalent value) is included. Furthermore, as described above, various chlorinated organic compounds that are precursors of dioxins are also included.
[0053]
The combustion exhaust gas is usually introduced into the contact process after removing dust and heavy metals through a bag filter. If necessary, the acid gas may be removed by treatment with a slaked lime reaction tower before treatment with the bag filter.
[0054]
In the present invention, when the contact step with the low oxidation performance catalyst is preceded, ammonia is introduced into the combustion exhaust gas flowing into the contact step with the low oxidation performance catalyst, the amount of which is in the combustion exhaust gas flowing out from the step The amount of ammonia is adjusted to 20 ppm or less.
[0055]
That is, in the above case, the contact step with the low oxidation performance catalyst, which is the first step, is performed in the presence of ammonia for decomposition of nitrogen oxides. At this time, acidic ammonium sulfate is hardly generated because the catalyst has low oxidizing properties. Therefore, simultaneously with the decomposition of nitrogen oxides, the chlorinated organic compound is decomposed at a high level according to the ability of the low oxidation performance catalyst. The amount of ammonia introduced into the combustion exhaust gas is determined so that nitrogen oxides can be highly decomposed under the above conditions. The consumption amount of ammonia in the combustion exhaust gas is determined by the temperature and processing amount of the combustion exhaust gas, the amount of catalyst used, the gas contact area, and the like. The chlorinated organic compound remaining in the combustion exhaust gas flowing out from the first step is decomposed by the contact step with the high oxidation performance catalyst which is the second step. At this time, acidic ammonium sulfate is hardly generated because the ammonia concentration in the combustion exhaust gas is suppressed to 20 ppm or less.
[0056]
On the other hand, in the method for treating combustion exhaust gas according to the present invention, when the contact step with the high oxidation performance catalyst is preceded, ammonia is introduced into the combustion exhaust gas flowing into the contact step with the low oxidation performance catalyst.
[0057]
That is, in the above case, the contact step with the high oxidation performance catalyst, which is the first step, is performed in the absence of ammonia because the chlorinated organic compound is decomposed and the nitrogen oxide is not substantially decomposed. When ammonia is introduced into the incinerator for partial decomposition of nitrogen oxides, the amount of ammonia introduced into the incinerator is adjusted so that the ammonia concentration in the combustion exhaust gas is 20 ppm or less. Nitrogen oxides in the combustion exhaust gas flowing out from the first step are decomposed by the contact step with the low oxidation performance catalyst which is the second step. At this time, acidic ammonium sulfate is hardly generated because the catalyst has low oxidizing properties. Therefore, the amount of ammonia introduced into the combustion exhaust gas flowing into the contact step with the low oxidation performance catalyst (the effluent gas from the first step) is arbitrarily determined so that the nitrogen oxides can be decomposed at a high level. The
[0058]
The size and shape of the reactor in each of the above contact steps can be arbitrarily selected without departing from the object of the present invention. Moreover, each catalyst may be filled into a separate reactor or may be filled as a different layer in the same reactor.
[0059]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by a following example, unless the summary is exceeded. In addition, the catalysts (A) to (H) used in the following examples were prepared as follows.
[0060]
<WO_Three-TiO₂Preparation of binary complex oxide>
The titanium sulfate solution obtained from the production process of titanium oxide by the sulfuric acid method is thermally hydrolyzed to obtain metatitanic acid, which is taken out as titanium oxide, 7550 g, charged into a stirring tank equipped with a reflux, and 4700 g of 15 wt% aqueous ammonia is added thereto. In addition, the pH was adjusted to 9.5, followed by heat aging at 95 ° C. with sufficient stirring for 1 hour. Next, 1070 g of ammonium paratungstate was added, and further, heat aging under the same conditions as described above was performed for 1 hour. Thereafter, the slurry was cooled and taken out, filtered and dehydrated, and the obtained cake was dried at 100 ° C. for 20 hours, then heated to 600 ° C. at a rate of 75 ° C./Hr, and kept at the same temperature for 5 hours. And after cooling, it grind | pulverized to the appropriate particle size.
[0061]
<Preparation of catalyst>
Preparation of catalyst (A):
A raw material liquid (1) was prepared by dissolving 643 g of ammonium metavanadate in 6000 g of a 10 wt% monoethanolamine aqueous solution heated to 80 ° C. Raw material liquid (1) and the above-mentioned WO_Three-TiO₂8500 g of the binary composite oxide powder and 1000 g of the forming aid were kneaded for 2 hours with a double-arm kneader, and the obtained kneaded product was formed into a honeycomb structure with a diameter of 5 mm by an extruder. The resulting molding was dried at a temperature of 130 ° C. for 24 hours, and then SV100Hr^-1And calcining for 3 hours under the condition of a temperature of 500 ° C. to obtain the catalyst (A) shown in Table 1.
[0062]
Preparation of catalyst (B):
In the preparation of the catalyst (A), the catalyst (B) shown in Table 1 was obtained in the same manner as the preparation of the catalyst (A) except that the calcination temperature was changed to 600 ° C.
[0063]
Preparation of catalyst (C):
In the preparation of the catalyst (A), the catalyst (C) shown in Table 1 was obtained in the same manner as the preparation of the catalyst (A) except that the calcination temperature was changed to 700 ° C.
[0064]
Preparation of catalyst (D):
In the preparation of the catalyst (A), the amount of ammonium metavanadate used is 129 g, and the WO_Three-TiO₂A catalyst (D) shown in Table 1 was obtained in the same manner as the preparation of the catalyst (A) except that the amount of the binary composite oxide powder was changed to 8900 g.
[0065]
Preparation of catalyst (E):
In the preparation of the catalyst (A), 1070 g of ammonium paratungstate was added to the raw material liquid (1), and this was added to commercially available TiO.₂A catalyst (E) shown in Table 1 was obtained in the same manner as the preparation of the catalyst (A), except that 7550 g of powder and 1000 g of molding aid were mixed and molded.
[0066]
Preparation of catalyst (F):
In the preparation of the catalyst (A), 1070 g of ammonium paratungstate was added to the raw material liquid (1), and this was added to commercially available TiO.₂A catalyst (F) shown in Table 1 was obtained in the same manner as in the preparation of the catalyst (A) except that 7550 g of powder and 1000 g of molding aid were mixed and molded, and the calcination temperature was changed to 600 ° C.
[0067]
Preparation of catalyst (G):
In the preparation of the catalyst (A), 1070 g of ammonium paratungstate was added to the raw material liquid (1), and this was added to commercially available TiO.₂A catalyst (G) shown in Table 1 was obtained in the same manner as in the preparation of the catalyst (A) except that 7550 g of powder and 1000 g of molding aid were mixed and molded, and the calcination temperature was changed to 700 ° C.
[0068]
Preparation of catalyst (H):
A raw material liquid (2) was prepared by dissolving 516 g of ammonium metavanadate in 6000 g of a 10 wt% monoethanolamine aqueous solution heated to 80 ° C. 1070 g of ammonium paratungstate is added to the raw material liquid (2), and this is added to commercially available TiO.₂7650 g of powder and 1000 g of molding aid were mixed and kneaded for 2 hours with a double-arm kneader, and the resulting kneaded product was molded into a honeycomb structure with a diameter of 5 mm by an extruder. The resulting molding was dried at a temperature of 130 ° C. for 24 hours, and then SV100Hr^-1And calcining at 500 ° C. for 3 hours to obtain the catalyst (H) shown in Table 1.
[0069]
<Measurement of sulfur dioxide oxidation conversion>
Of the catalysts described above, (A), (D) and (H) were each processed into a sample of 450 ml (honeycomb structure having 6 holes in the vertical and horizontal directions and a height of 500 mm). A glass reaction tube was filled. Next, the reaction tube was placed in a tubular electric furnace, and the temperature of the catalyst was maintained at 250 ° C. while allowing a predetermined amount of nitrogen gas and oxygen gas to flow. Next, H to achieve a predetermined concentration₂O and SO₂Gas was added. The gas composition is O₂10% dry volume, SO₂500ppm, H₂O10 vol%, N₂It was the balance amount, and the gas preparation amount (rate) was 835 L / Hr (at 0 ° C., 101.325 KPa).
[0070]
The gas is passed through the reaction tube for 70 hours, after which the gas at the outlet of the reaction tube is sampled and SO_ThreeConcentration was measured. Next, the gas at the outlet of the reaction tube is again sampled and the total SO_XConcentration was measured. SO_ThreeSampling using a spiral collection tube_XOf SO_ThreeOnly by collecting. And the collected SO_ThreeWas washed with water and analyzed by the precipitation titration method of JIS K 0103. Total SO_XThe sampling and analysis were performed according to the method of JIS K 0103. The oxidation conversion rate of sulfur dioxide was determined by the following equation.
[0071]
[Expression 4]
(Exit SO_ThreeConcentration / Outlet total SO_X) × 100
[0072]
[Table 1]
[0073]
<X-ray diffraction>
Measurement was performed on the catalyst (A). As the X-ray diffractometer, “RINT1500” manufactured by Rigaku Corporation was used. The measurement conditions were a Cu tube, a voltage of 40 KV, a current of 250 mA, a sampling width of 0.020 °, and a scanning speed of 4.000 ° / min. The light emitting slit was 1 °, the scattering slit was 2 °, and the light receiving slit was 1 °. The measurement result of X-ray diffraction is shown in FIG.
[0074]
<Surface spacing measurement>
Measurement was performed on the catalyst (A). 0.5 g of silicon was mixed with 2.5 g of the crushed sample to form a measurement sample. As the X-ray diffractometer, “RINT1500” manufactured by Rigaku Corporation was used. The measurement conditions were a measurement range of 52 to 58 °, a scanning speed of 0.2 ° / min. The other conditions were the same as above. The mixed silicon is used as an internal standard substance, and the difference between the measured value of the silicon and the JCPDS file value is defined as “the difference generated by the X-ray diffractometer”.₂The measurement error due to the device was eliminated by subtracting the difference between the measured value and the literature value. The results are shown in Table 2.
[0075]
[Table 2]
[0076]
<Characteristics of catalyst (A)>
Catalyst (A) contains 9.5% by weight of WO_Three1 and no peak is observed at 2θ = 23.5 ° in FIG. 1, and as shown in Table 2, anatase TiO₂From the JCPDS data, the 0.09 ° peak on the (2, 0, 0) plane and the 0.08 ° peak on the (2, 1, 1) plane move to the lower angle side, and 2θ becomes smaller. That is, the surface interval is widened. From these, the catalyst (A) is 9.5% by weight of WO_ThreeHighly dispersed TiO₂It was confirmed that the catalyst was based on the catalyst.
[0077]
<Activity test>
A glass reactor was filled with 30 ml of each of the above catalysts, and the activity test was performed in an atmospheric pressure fixed bed flow reactor. The dimensions of the catalyst fixed bed were 28 mm in length, 28 mm in width, and 38 mm in height. The raw material gas composition is o-chlorophenol (OCP) 100 ppm, O₂10 vol%, H₂O10 vol%, N₂It was the composition of the balance amount. SV of raw material gas is 5000Hr^-1Met. After holding at 160 ° C., 180 ° C., and 200 ° C. for 5 hours, the gas passing through the reactor was sampled with a microsyringe and analyzed by gas chromatography. The analysis was performed by the absolute calibration curve method.
[0078]
  Reference example1-3
  Activity tests were performed using catalysts (A) to (C). The results are shown in Table 3.
[0079]
  referenceComparative Examples 1-3
  Activity tests were performed using catalysts (E)-(G). The results are shown in Table 3.
[0080]
[Table 3]
[0081]
  As is clear from Table 3, WO₃-TiO₂Binary composite oxide support was usedReference exampleThe catalyst is pure TiO₂The resolution of chlorinated organic compounds is higher than that of catalysts of the same composition using a support. Such a difference in decomposition performance was due to the high calcination temperature during catalyst preparation.Reference example3 (Catalyst (C): calcination temperature 700 ° C.)referenceThis is remarkable in comparison with Comparative Example 3 (catalyst (G): calcination temperature 700 ° C.), and the difference in heat resistance of the catalyst is clear. In addition, WO₃-TiO₂Binary composite oxide support was usedReference exampleThis catalyst has a high resolution of chlorinated organic compounds even at 160 ° C. where the reaction temperature is low.
[0082]
  Example1
  Three glass reactors having an inner diameter of 5 cm and a length of 60 cm filled with a catalyst having a honeycomb structure of 3 cm × 3 cm × 50 cm are connected in series, and placed in a thermostat having a longitudinal inner diameter of 80 cm, a lateral inner diameter of 80 cm, and a height of 1.5 m. installed. The front two reactors were filled with catalyst (D), and the last one reactor was filled with catalyst (A) to assemble an atmospheric pressure fixed bed flow reactor. And using this apparatus, the treatment test of the model exhaust gas of the municipal waste incinerator was conducted as follows.
[0083]
Temperature 200 ° C, SV5000Hr^-1While adding ammonia with an average concentration of 80 ppm to the above-mentioned conditions, an average concentration of 1 ng-TEQ / m was added to the above apparatus.^Three(N.T.P) dioxins and SO with an average concentration of 30 ppm₂And NO with an average concentration of 85 ppm_xA gas containing was passed. The amount of ammonia added was adjusted so that the ammonia concentration immediately before the catalyst (A) (immediately after the previous two reactors) was measured and the value thereof was 20 ppm or less.
[0084]
Analysis of exhaust gas after treatment is performed by gas chromatography mass spectrometry in accordance with “Dioxin Standard Measurement and Analysis Manual for Waste Treatment” (Environmental Maintenance Division, Water Environment Department, Ministry of Health and Welfare (February 1997)) It was. The analysis was performed 2 weeks and 4 months after passing the gas. The evaluation results are shown in Table 4.
[0085]
  Example2
  Example1When assembling the atmospheric pressure fixed bed flow reactor, the front one was filled with the catalyst (A) and the rear two were filled with the catalyst (D). The ammonia addition position is immediately before the catalyst (D) (immediately after the previous one), and the ammonia addition amount is the average NO._xMolar ratio (NO_x/ NH₃), Except for 11In the same way, a treatment test was conducted for model exhaust gas from a municipal waste incinerator. The evaluation results are shown in Table 5.
[0086]
  Comparative example1
  Example1, Except that the atmospheric pressure fixed bed flow reactor assembled using the catalyst (H) in all three was used, and the ammonia addition amount was not adjusted based on the measurement results of the ammonia concentration immediately after the previous two. Example1A model exhaust gas treatment test was conducted in the same manner as above. The evaluation results are shown in Table 6.
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[Table 4]
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[Table 5]
[0089]
[Table 6]
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【The invention's effect】
  According to the present invention described aboveIfWO₃-TiO₂A catalyst using a binary composite oxide carrier can decompose chlorinated organic compounds such as dioxin with high efficiency at a lower temperature. Moreover, according to the present invention, once decomposed dioxins and the like are not regenerated. Furthermore, according to the present invention, since the deterioration of the catalyst over time is suppressed by minimizing the acidic ammonium sulfate produced from the sulfur oxides, chlorinated organic compounds such as dioxins and nitrogen oxides in combustion exhaust gas Can be removed with high efficiency.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction chart of a catalyst (A) according to the present invention.

Claims (1)

A method for treating combustion exhaust gas containing a chlorinated organic compound, sulfur dioxide, and nitrogen oxide, wherein the following conditions (a) to (d) are satisfied:
(A) As a catalyst, vanadium (V) oxide is supported as an active component on a support, and has a chlorinated organic compound resolving power and a nitrogen oxide resolving power in the presence of ammonia, and oxidation of sulfur dioxide as defined below. A catalyst having a low oxidation performance catalyst (X) having a conversion rate of 1.3% or less and a catalyst in which vanadium (V) oxide is supported as an active component on a WO ₃ —TiO ₂ binary composite oxide support A high oxidation performance catalyst (Y) having a ratio of the carrier to the total amount of 70% by weight or more, having a chlorinated organic compound resolving power and a sulfur dioxide oxidation conversion rate of 3.0% or more as defined below. Two types are used.
<Oxidation conversion rate of sulfur dioxide>
Pressure: normal pressure, temperature: 250 ° C., SV (space velocity): 1850 Hr ⁻¹ , catalyst amount: 450 ml, O ₂ 10 dry volume%, SO ₂ 500 ppm, H ₂ O: 10 volume%, N ₂ balance An amount of a composition gas is supplied to a reaction tube filled with a catalyst, SO ₃ concentration at the outlet of the reaction tube and total SO _X concentration are obtained, and the oxidation conversion rate (%) of sulfur dioxide is calculated by the following equation.
(B) Each contact process with combustion exhaust gas, a low oxidation performance catalyst, and a high oxidation performance catalyst is performed in an arbitrary order and in a temperature range of 100 to 250 ° C.
(C) When the contact step with the low oxidation performance catalyst is preceded, ammonia is introduced into the combustion exhaust gas flowing into the contact step with the low oxidation performance catalyst, the amount of which is ammonia in the combustion exhaust gas flowing out from the step The amount is adjusted to 20 ppm or less.
(D) When the contact step with the high oxidation performance catalyst is preceded, ammonia is introduced into the combustion exhaust gas flowing into the contact step with the low oxidation performance catalyst.