JP2005125275A - Device for treating diesel exhaust gas and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for treating a diesel exhaust gas capable of reducing the discharge amount of PM, NOx and SO<SB>3</SB>in the exhaust gas as much as possible, by effectively removing these materials without poisoning a denitration catalyst and to provide a method therefor. <P>SOLUTION: In the device for treating the diesel exhaust gas provided with dust and soot removing means (2 and 3) which catch particle matters (PM) in the exhaust gas, incinerate and eliminate them in an exhaust gas flow passage 10 of a diesel engine 1, a nitrogen oxide removing device 4 and a sulfur oxide removing device 6 are provided in this order in the exhaust gas flue 10 of the next stream to the dust and soot removing means (2 and 3), and the sulfur oxide removing device 6 is a sulfur oxide absorbing agent layer of which the absorbing component is an alkaline salt. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a diesel exhaust gas treatment device and a treatment method, and in particular, removes sulfur oxides in diesel exhaust gas emitted from a mobile diesel engine such as an automobile or a stationary small diesel engine such as a generator. The present invention relates to a diesel exhaust gas treatment apparatus and a treatment method.

  Particulate matter (hereinafter referred to as PM) discharged from diesel vehicles may have a carcinogenic effect, and there are concerns about adverse effects on public health. That is, in recent years, it has become an urgent task to reduce particulate matter and nitrogen oxides emitted from automobiles and to improve air pollution. Therefore, regulations on environmental pollutants emitted from automobiles will be strengthened, and the "Automobile NOx / PM Law" that regulates nitrogen oxides (NOx) and PM has been enacted, and stricter regulations than ever have been implemented. That is scheduled. Under these circumstances, engine combustion has been energetically improved, but there is a trade-off relationship between reducing fuel consumption and increasing PM generation when attempting to reduce NOx generation. Development of post-treatment technology for purifying pollutants in exhaust gas is being actively promoted.

  On the other hand, not only mobile diesel engine equipment such as automobiles, but also stationary diesel engine equipment, that is, power generation equipment, distributed power equipment installed in buildings, hospitals, etc. are increasing, and these exhaust gas regulations have been strengthened. ing.

  Various techniques for treating diesel exhaust gas discharged from various facilities having such a diesel engine have been proposed and implemented. FIG. 6 shows a flow of a diesel exhaust gas treatment apparatus that is currently mainstream. In FIG. 6, this apparatus includes an oxidation catalyst layer 2, a diesel particulate filter (DPF) 3, a reduction catalyst, which are sequentially provided in the exhaust pipe or exhaust gas duct 10 as the exhaust gas flow path of the diesel engine 1 along the gas flow direction. An agent injection device 5 and a denitration catalyst layer 4 are provided.

PM in the exhaust gas is collected by, for example, DPF 3 made of a honeycomb carrier with alternately filled eyes, and NO ₂ generated by oxidation of NO in accordance with the following equation (1) by the preceding oxidation catalyst layer 2 (2) It is burned off according to the formula.
NO + 1 / 2O ₂ → NO ₂ (1)
NO ₂ + C → CO ₂ + 1 / 2N ₂ (2)
The exhaust gas from which PM has been removed flows into the downstream denitration catalyst layer 4, and nitrogen oxides in the exhaust gas are selectively catalytically reduced and decomposed by, for example, urea or hydrocarbons injected from the reducing agent injection device 5. The
JP-A-60-235620

The exhaust gas treatment technology for collecting and burning the PM is an excellent method for obtaining a high PM removal rate, but has the following problems.
That is, in diesel engines, for example, light oil, heavy oil, etc. are used as fuel, and these fuels contain sulfur (S) content, and this S content is sulfur oxide, mainly SO ₂ from the engine. It is discharged and causes air pollution.

Here, according to a detailed examination by the present inventor, when a treatment method in which PM in diesel exhaust gas is collected by DPF, oxidized and burned is adopted, about 60% of SO ₂ contained in the exhaust gas is oxidized. It was found that the catalyst layer was oxidized according to the following formula (3) to produce sulfur trioxide (SO ₃ ).

SO ₂ + 1 / 2O ₂ → SO ₃ (3)
Since sulfur oxides adversely affect the human body, especially the respiratory tract, it is not preferable to exhaust it to the atmosphere as it is. In addition, it has been found that SO ₃ is more harmful than SO ₂ and has a great influence on the human body even at several ppm. Therefore, in recent years, in order to reduce the amount of sulfur oxides emitted, there is a tendency to use low S content diesel oil as the fuel for diesel engines. However, even if the S content in the fuel is reduced to, for example, 50 ppm, It is inevitable that several ppm of sulfur oxide is mixed, and SO ₃ emitted from diesel vehicles traveling in urban areas is a major problem.

  On the other hand, in stationary diesel engines used for cogeneration etc., it is said that A heavy oil having an S content of about 500 ppm is mainly used as fuel, and the concentration of sulfur oxides in exhaust gas is several tens of ppm. Since most of such cogeneration facilities are installed in the suburbs of the city, there is a concern that the sulfur oxide contained in the diesel exhaust gas may adversely affect the human body.

By the way, when treating diesel exhaust gas, NOx treatment is usually performed using a denitration catalyst simultaneously with removal of PM. However, since SO ₃ has a higher adsorption power to the denitration catalyst than SO ₂ , SO _{3 in the} inside causes a significant decrease in the performance of the denitration catalyst. Therefore, when diesel exhaust gas is treated by an apparatus containing an oxidation catalyst, a secondary problem arises in that NOx is exhausted out of the system without being sufficiently treated due to the reduced performance of the denitration catalyst poisoned by SO ₃ . There is a fear.

An object of the present invention shows the above-mentioned solution to the problems of the prior art, SOx in exhaust gas, particularly poisoning of a denitration catalyst by diesel exhaust gas treatment apparatus and processing method, and SO ₃ can be reduced as much as possible the emission of SO ₃ An object of the present invention is to provide a diesel exhaust gas treatment device and a treatment method capable of absorbing and removing SO ₃ in exhaust gas while preventing the above.

The above problem can be solved by providing a sulfur oxide (SOx) removing means in the exhaust gas flue of the diesel engine. That is, in order to solve the above problems, the invention claimed in the present application is as follows.
(1) In a diesel exhaust gas treatment apparatus provided with dust removal means for collecting and removing particulate matter in exhaust gas in the exhaust gas flow path of a diesel engine, sulfur oxide removal means is provided in the exhaust gas flue. A diesel exhaust gas treatment apparatus characterized by that.
(2) The diesel exhaust gas treatment apparatus as described in (1) above, wherein the sulfur oxide removing means is provided downstream of the dust removing means.
(3) The sulfur oxide removing means is a sulfur oxide absorbent layer containing at least one of alkali metal, alkaline earth metal and rare earth element salts or oxides, and iron oxide as an absorbing component. The diesel exhaust gas treatment device according to (1) or (2) above.
(4) A nitrogen oxide removing means and a sulfur oxide removing means are sequentially provided downstream of the dust removing means, and the sulfur oxide removing means is a salt or oxide of alkali metal, alkaline earth metal and rare earth element. The diesel exhaust gas treatment device according to any one of (1) to (3), wherein the sulfur oxide absorbent layer has at least one of them as an absorption component.
(5) Sulfur oxide removal means and nitrogen oxide removal means are sequentially provided downstream of the dust removal means, and the sulfur oxide removal means is a sulfur oxide absorbent layer containing iron oxide as an absorption component. The diesel exhaust gas treatment apparatus according to any one of (1) to (3) above, wherein
(6) The sulfur oxide absorbent is obtained by carrying the absorbent component on a catalyst carrier, and the carrying amount is 50 to 200 g / l. The diesel exhaust gas treatment apparatus according to any one of the above.
(7) The diesel exhaust gas treatment apparatus according to any one of (1) to (6), wherein the dust removal means is a combination of an oxidation catalyst layer and a filter or a filter with an oxidation catalyst.
(8) The diesel as described in (4) or (5) above, wherein the nitrogen oxide removing means is a denitration catalyst layer that selectively reduces and removes nitrogen oxides in the presence of a reducing agent. Exhaust gas treatment equipment.
(9) Diesel engine exhaust gas is introduced into a dust removal means having an oxidation catalyst layer, particulate matter in the exhaust gas is collected, burned and removed by NO ₂ or O ₂ generated by oxidation of NO, and then nitrogen Sulfur oxide absorbent layer which is introduced into oxide removing means to decompose and remove nitrogen oxide, and then uses at least one of alkali metal, alkaline earth metal and rare earth element salts or oxides as an absorbing component A diesel exhaust gas treatment method characterized in that it is introduced into and absorbs and removes sulfur oxides in the exhaust gas.
(10) Diesel engine exhaust gas is introduced into a dust removal means having an oxidation catalyst layer, particulate matter in the exhaust gas is collected, burned and removed by NO ₂ or O ₂ generated by oxidation of NO, and then oxidized It is introduced into the sulfur oxide absorbent layer using iron as an absorption component to absorb and remove sulfur oxide in the exhaust gas, and then introduced into the nitrogen oxide removing means to decompose and remove nitrogen oxide. Diesel exhaust gas treatment method.

According to the invention described in claim 1 of the present application, it is possible to prevent not only PM in exhaust gas but also emission of SO ₃ that is a causative substance of environmental pollution and has a great adverse effect on the human body.
According to the invention described in claim 2 of the present application, not only the PM in the exhaust gas but also SO ₃ produced by the oxidation of SO _{2 in} the oxidation catalyst layer which is a part of the dust removal means is effectively absorbed and separated. The discharge to the outside of the system can be avoided.

According to the invention described in claim 3 of the present application, in addition to the effects of the above invention, SO ₃ can be chemically absorbed or adsorbed to prevent its discharge out of the system.
According to the invention described in claim 4 of the present application, since the sulfur oxide removing means is installed downstream of the nitrogen oxide removing means, even if an alkaline salt is used as an absorbing component, the denitration catalyst is covered with the alkali salt. Poison and deterioration can be prevented, whereby PM and SO ₃ can be efficiently removed by combustion or collected, and NOx can be prevented from being discharged outside the system due to deterioration of the denitration catalyst.

According to the invention described in claim 5 of the present application, since the exhaust gas after SO ₃ is absorbed and removed flows into the denitration catalyst layer, poisoning and deterioration of the denitration catalyst due to SO ₃ are prevented. It is possible to effectively prevent not only PM and SO ₃ but also NOx from flowing out of the system.
According to the invention described in claim 6 of the present application, in addition to the effect of the above-described invention, it is possible to extend the replacement interval of the absorbent and to prevent the clogging of the carrier and to sufficiently exhibit the sulfur oxide absorption effect. it can.

According to invention of Claim 7 of this application, in addition to the effect of the said invention, the particulate matter in waste gas can be effectively collected, burned, and removed.
According to invention of Claim 8 of this application, in addition to the effect of the said invention, the nitrogen oxide in waste gas can be decomposed | disassembled and removed effectively.

According to the invention described in claim 9 of the present application, in addition to PM and NOx contained in diesel exhaust gas, SO ₃ oxidized by SO ₂ is effectively separated while preventing denitration catalyst poisoning by alkaline salt. Can be removed.
According to the invention of claim 10 of the present application, SO ₃ in which SO ₂ is oxidized in addition to PM and NOx contained in diesel exhaust gas is effectively separated while preventing the denitration catalyst from being poisoned by SO _3. Can be removed.

  FIG. 1 is an explanatory diagram showing a flow of a diesel exhaust gas treatment apparatus according to an embodiment of the present invention. In FIG. 1, this apparatus includes an SOx absorbent layer as a sulfur oxide (SOx) removal means on an exhaust pipe 10 which is an exhaust gas flow path of a diesel engine 1 provided with a dust removal means comprising an oxidation catalyst layer 2 and a DPF 3. 6 and the SOx absorbent layer 6 is disposed downstream of the oxidation catalyst layer 2 and the DPF 3 as dust removal means. That is, the apparatus shown in FIG. 1 is arranged in the exhaust pipe 10 of the diesel engine 1 in order along the gas flow direction with the oxidation catalyst layer 2 and the DPF 3 and the denitration catalyst layer 4 and the SOx absorbent layer as nitrogen oxide (NOx) removal means. 6 is provided. Reference numeral 5 denotes an apparatus for injecting a reducing agent into the upstream side of the denitration catalyst layer 4 of the exhaust pipe 10.

In such a configuration, the exhaust gas discharged from the diesel engine 1 flows through the exhaust pipe 10 and flows into the oxidation catalyst layer 2, where nitrogen monoxide (NO) in the exhaust gas is oxidized according to the above-described equation (1). While being oxidized to nitrogen (NO ₂ ), hydrocarbons (HC) are combusted to produce CO ₂ and H ₂ O. At the same time, a part of SO _{2 in} the exhaust gas is oxidized to SO ₃ according to the above-described equation (3). The exhaust gas at the outlet of the oxidation catalyst layer 2 then flows into the DPF 3 where PM contained in the exhaust gas is collected, oxidized by the NO ₂ generated in the oxidation catalyst layer 2 according to the above equation (2), and burned. To CO ₂ . The DPF 3 outlet exhaust gas flows into the downstream denitration catalyst layer 4, where NOx in the exhaust gas is reduced to nitrogen by a denitration reaction using a reducing agent injected from the reducing agent injection device 5, for example, urea. . The exhaust gas at the outlet of the denitration catalyst layer 4 flows into the downstream SOx absorbent layer 6 containing, for example, calcium carbonate as an absorption component, where SO ₃ in the exhaust gas reacts with calcium carbonate and is fixed as calcium sulfate. The exhaust gas from which PM, NOx, and SOx have been removed in this way is discharged out of the system as treated exhaust gas.

  In the present invention, the exhaust gas flow path of the diesel engine is an exhaust gas such as an exhaust pipe or a duct through which the exhaust gas discharged from the diesel engine circulates regardless of a stationary type such as a power generation facility of a building or a mobile type such as an automobile. Includes all flow paths.

In the present invention, the SOx removing means is, for example, an SOx absorbent layer, and at least one selected from, for example, alkali metal, alkaline earth metal and rare earth element salts or oxides, and iron oxide is applied as the absorbing component. . The absorption component may be any as long as it reacts with SO ₃ to form a sulfate, such as an alkali metal carbonate such as sodium carbonate or potassium carbonate, an alkali metal such as calcium carbonate, magnesium carbonate, or barium carbonate. Earth metal carbonates, alkali metal oxides such as sodium oxide, alkaline earth metal oxides such as calcium oxide, magnesium oxide and barium oxide, rare earth element oxides such as cerium oxide and lanthanum oxide, calcium hydroxide, water Alkaline earth metal hydroxides such as magnesium oxide and barium hydroxide, iron oxide and the like are preferably used. Moreover, what carried | supported iron on carriers, such as a titanium oxide, is used suitably. Those containing iron as an absorption component have a denitration performance, so that a higher denitration effect can be obtained. Such absorption components may be used alone or in combination. Further, a binder such as a binder can be added to facilitate molding.

The absorbent component can be used by coating a carrier such as cordierite and alumina, particularly a honeycomb carrier. The amount of loading on the carrier is not particularly limited, but is preferably 50 to 200 g / l. Since the absorbent absorbs SO ₃ and is gradually sulfated, and its SOx absorption capacity is lost, it is desirable to replace it at regular intervals. However, if the amount of the absorbent component supported is less than 50 g / l, the replacement period will be longer. If it becomes faster and exceeds 200 g / l, it becomes difficult to carry the absorbing component due to clogging or the like. The absorbent component or the absorbent on which the absorbent component is supported is molded into a shape that can be installed in the exhaust pipe, for example, a particulate shape or a honeycomb shape.

The SO ₃ absorption reaction when carbonate is used as the absorption component is shown in equation (4).
MCO ₃ + SO ₃ → MSO ₄ ↓ + CO ₂ M: Metal (4)
In the present invention, the dust removing means refers to, for example, a device that collects soot and burns and removes it. In the presence of an oxidation catalyst in which a noble metal such as platinum is supported on a catalyst carrier such as alumina, silica, titania or ceria, NO is produced by oxidation of NO according to the formulas (1) and (2). A device for burning and removing according to ₂ is mentioned. Here, in the present invention, in order to remove SO ₃ oxidized from SO _{2 that} is generated simultaneously with combustion of soot, the SOx absorbing means is installed at the subsequent stage of the soot removing means.

In the present invention, as the NOx removal means, a catalytic reduction method using an ammonia precursor such as ammonia or urea, a catalytic reduction method using hydrocarbon as a reducing agent, which is generally used as a boiler exhaust gas treatment apparatus for power plants, etc. And those utilizing the Nox occlusion catalyst method and the like. The NOx removing means may be of any type, and even if the NOx removing means is omitted, it is possible to reduce the SOx concentration, particularly the SO ₃ concentration in the exhaust gas.

  In the present invention, either of the NOx removal means and the SOx removal means may basically be disposed upstream, but an SOx removal means that uses an absorber having an alkaline salt as an absorbing component is used, and the NOx removal means is a NOx removal catalyst. When using a layer, it is preferable to arrange the SOx absorber in the downstream of the denitration catalyst layer. Alkaline salts are poisoning components of denitration catalysts, and even if they are small amounts, there is a possibility that the denitration activity may be significantly reduced. By placing the SOx absorber downstream of the denitration catalyst device, poisoning of the denitration catalyst can be prevented. is there.

On the other hand, depending on the type of denitration catalyst, SOx becomes a catalyst poison, and the denitration performance is reduced. Therefore, it may be preferable to provide SOx absorption means before the NOx removal means to remove SOx before contacting the NOx removal catalyst. In the present invention, when iron oxide is used as the sulfur oxide absorption component, it is preferable to arrange the SOx absorption device upstream of the denitration catalyst layer. This is because the absorbent containing an acid as a component does not poison the denitration catalyst, and since it itself exhibits denitration activity, the denitration performance can be further enhanced.
In the present invention, the DPF is a flow-through filter that is alternately clogged as described above, and the soot in the exhaust gas flowing in from the inlet portion is captured by the filter wall, and only the gas flows out. Yes.

  A diesel engine 1 with an output of 25 kw is used, an oxidation catalyst layer 2 with a cell number of 300 cpsi, a porosity of 30%, a volume of 1.2 L cordierite carrier loaded with a noble metal, and a DPF3 with a cell number of 300 cpsi. Using a cordierite support with a porosity of 70% and a volume of 2.5 L, a Ti-WV catalyst component is supported on a cordierite support with a cell number of 400 cpsi, a porosity of 30% and a volume of 2.5 L as a denitration catalyst layer 4. In the apparatus of FIG. 1, the SOx absorbent layer 6 is a cordierite carrier having a cell number of 400 cpsi, a porosity of 30%, and a volume of 0.5 L, coated with calcium carbonate at 100 g / l. When the diesel engine 1 was operated at a load of 100% using light oil of 50 ppm S as fuel, the exhaust gas at about 380 ° C. discharged was treated as follows.

That is, the exhaust gas of the diesel engine 1 flows through the exhaust gas flue 10 and flows into the oxidation catalyst layer 2, where a part of NO in the exhaust gas is oxidized to NO ₂ by the oxidation action of the noble metal component, While carbon (HC) is burned, for example, a part of SO ₂ having a concentration of ₂ to ₃ ppm is oxidized to SO _3, and the SO ₃ concentration at the entrance of the oxidation catalyst layer 2 is 0.1 ppm or less is, for example, 1 to 2 ppm. To increase. The exhaust gas whose SO ₃ concentration has increased through the oxidation catalyst layer 2 flows into the downstream DPF ₃ , where PM is collected on the filter wall. At this time, the PM is oxidized and burned by the NO ₂ generated by the oxidation of NO in the oxidation catalyst layer 2 according to the above-described equation (2) to become CO ₂ . After the PM is removed and the exhaust gas that has passed through the DPF 3 flows into the denitration catalyst layer 4, NOx in the exhaust gas is catalytically reduced by, for example, a 35 wt% urea aqueous solution injected from the reducing agent injection device 5. The exhaust gas from which NOx is decomposed and removed then flows into the SOx absorbent layer 6, where SO ₃ in the exhaust gas reacts with calcium carbonate as an absorption component and is fixed as calcium sulfate, and the concentration of SO _{3 in} the exhaust gas Is reduced to 0.1 ppm or less.

According to the present embodiment, by providing the SOx absorbent layer 6 on the downstream side of the dust removal means comprising the oxidation catalyst layer 2 and the DPF 3, not only PM and NOx can be treated, but also generated by oxidation of SO ₂ . SO ₃ can be effectively absorbed and separated to prevent its emission outside the system. Further, by providing the SOx absorbent layer 6 using an alkaline salt as an absorbent in the downstream of the denitration catalyst layer 4, it is possible to avoid poisoning of the denitration catalyst due to the alkaline salt.

FIG. 2 is an apparatus system diagram showing another embodiment of the present invention. This exhaust gas treatment apparatus is different from the apparatus of FIG. 1 in that the denitration catalyst layer 4 and the reducing agent injection device 5 are eliminated. In this apparatus, exhaust gas discharged from a diesel engine 1 flows into the oxidation catalyst layer 2, wherein a portion of NO is oxidized to NO _2, SO ₂ is oxidized with hydrocarbon (HC) is burned As a result, SO ₃ is generated. The exhaust gas flowing out of the oxidation catalyst layer 2 flows into the downstream DPF, where PM is collected and burned and removed by NO ₂ generated by the oxidation of NO. The exhaust gas from which PM has been removed by combustion flows into the downstream SOx absorbent layer 6 where the SO ₃ is absorbed and removed.
Also in the present embodiment, SO ₃ generated by the oxidation of SO ₂ can be effectively absorbed and removed, and emission to the atmosphere can be avoided as much as possible.

FIG. 3 is an apparatus system diagram showing another embodiment of the present invention. 3, this apparatus is provided with a DPF 7 with an oxidation catalyst in place of the oxidation catalyst layer 2 and the DPF 3 in FIG.
Also in this embodiment, PM in exhaust gas can be collected and removed by combustion, and SO ₃ produced by SO ₂ oxidation can be absorbed and removed by the SOx absorbent layer 6 to avoid release to the outside of the system. it can.
In this embodiment, as the DPF with an oxidation catalyst, for example, a cordierite carrier having a cell number of 300 cpsi, a porosity of 70%, and a volume of 17 L and carrying an oxidation catalyst component such as a noble metal is used.

FIG. 4 is an apparatus system diagram showing still another embodiment of the present invention. In FIG. 4, this apparatus is provided with a DPF 7 with an oxidation catalyst instead of the DPF 3 in FIG.
According to the present embodiment, since the oxidation catalyst component is supported on both the oxidation catalyst layer 2 and the DPF 7 with the oxidation catalyst, the amount of the catalyst is relatively increased. For example, the same conditions with a load of 100% and a catalyst temperature of 380 ° C. Then, the soot burning ability becomes higher than the other embodiments. At the same time, the oxidation rate of SO ₂ to SO ₃ is high, for example, about 80%, but SO ₃ is absorbed and removed by the downstream SOx absorbent layer 6, thus preventing its discharge out of the system. be able to.
In this embodiment, since the conversion rate of SO ₂ to SO ₃ becomes high, it is preferable that the amount of the absorbent in the SOx absorbent layer 6 is larger than that in other embodiments, for example, the first embodiment. In this embodiment, the amount of absorbent loaded is, for example, 100 g / l, and the volume is, for example, 4 L.

FIG. 5 is an apparatus system diagram showing still another embodiment of the present invention. 5, this apparatus, as an absorbent for SO ₃ absorber layer 6, for example, using iron-bearing titanium oxide cordierite carrier (cell number 400 cpsi, a porosity of 30%) was obtained by coating, this SO ₃ The absorbent layer 6 is disposed upstream of the denitration catalyst layer 4.
Also in this embodiment, SO ₃ generated by oxidation of SO ₂ can be effectively absorbed and removed from the system, as in the other embodiments. Further, by using an iron component as the sulfur oxide absorbent, even if the SO ₃ absorbent layer 6 is provided upstream of the denitration catalyst layer 4, the denitration catalyst is not poisoned, and the denitration performance is improved. Can be achieved. Furthermore, since SO ₃ in the exhaust gas is absorbed and removed before flowing into the denitration catalyst layer, poisoning of the denitration catalyst by SO ₃ can be prevented.

Next, the de-SO ₃ effect of the SO ₃ absorbent in the present invention will be described using specific experimental examples.
Experimental example 1
300 g of iron hydroxide (FeO (OH), manufactured by Kishida Chemical Co., Ltd.) is suspended in 700 g of water, and the resulting slurry is applied to a flow-through cordierite honeycomb (400 cpsi, 100 mm sq.-50 mm length) by the wash coat method. Loading and drying were repeated, and firing was performed at 500 ° C. for 2 hours to obtain an SO ₃ absorbent having a loading amount of 150 g / l as iron oxide.
Experimental example 2
Dissolved iron nitrate _{(Fe (NO 3) 2 ·} 9H 2 O) 362g of water, titanium oxide (MCH, manufactured by Ishihara Sangyo Kaisha, Ltd.) were mixed heated on putting 1kg sand bath, dried, air stream 500 ° C. And then pulverized with a hammer mill to obtain a catalyst powder. The resulting powder 300g and water 700g are mixed to make a slurry, impregnated into a flow-through type alumina honeycomb (400cpsi, 100mm square -100mm length), dried and then fired at 500 ° C for 2 hours to form iron oxide An SO ₃ absorbent having a loading time of 9 g / l was obtained.
Experimental example 3
Dissolve 1 kg of sodium hydroxide (NaOH, manufactured by Kishida Chemical Co., Ltd.) in water to prepare a 40 wt% sodium hydroxide aqueous solution, and impregnate it into a flow-through type alumina honeycomb (400 cpsi, 100 mm square -100 mm length). After drying, it was calcined at 500 ° C. for 2 hours to obtain an SO ₃ absorbent having a loading amount as sodium carbonate of 100 g / l.
Experimental Example 4
1 kg of calcium carbonate (CaCO ₃ , manufactured by Kishida Chemical Co., Ltd.), 100 g of colloidal silica (OS sol, manufactured by Nissan Chemical Co., Ltd.) and water were mixed to obtain a slurry having a calcium carbonate concentration of 30 wt%. This slurry was supported on a flow-through cordierite honeycomb (400 cpsi, 100 mm sq.-50 mm long) by the wash coat method, dried repeatedly, fired at 500 ° C for 2 hours, and the amount of calcium carbonate supported was 150 g / l. An SO ₃ absorbent was obtained.
Experimental Example 5
1 kg of cerium oxide (Ce ₂ O ₃ , manufactured by Kishida Chemical Co., Ltd.), 100 g of alumina sol (alumina sol 520, manufactured by Nissan Chemical Co., Ltd.) and water are mixed to prepare a slurry with a cerium oxide concentration of 30 wt%. A cordierite honeycomb (400 cpsi, 100 mm sq.-50 mm long) supported by the wash coat method, repeatedly dried, fired at 500 ° C. for 2 hours, and an SO ₃ absorbent with a loading time of 200 g / l as cesium oxide Obtained.

  Separately, alumina sol (alumina sol 520, manufactured by Nissan Chemical Co., Ltd.) and water are mixed, and 1 liter of an aqueous solution containing 15% alumina is prepared. Dinitrodiammine was applied to the carrier obtained by dipping, impregnating 100 mm (50 mm length), draining with air blow twice, drying in air at 150 ° C for 5 hours, and baking at 500 ° C for 2 hours. Impregnated with an aqueous solution of platinum (Tanaka Kikinzoku), drained by air blow, dried in air at 150 ° C for 5 hours, and then calcined at 550 ° C for 2 hours. The amount of platinum supported per volume was 2g / An liter of oxidation catalyst was obtained.

Using a flow-type test device, the above prepared oxidation catalyst was cut and installed upstream of the reaction tube, and the SO ₃ absorbent obtained in Experimental Examples 1 to 5 was cut and installed in the subsequent flow. the sO ₂ and sO ₃ concentration in the reaction tube inlet and outlet were measured under the conditions, the sO ₃ absorption capacity than not including the sO ₃ absorber as compared with Comparative example 1 was operated in the same manner as this sO ₃ absorber It was measured. The SO ₃ concentration was measured according to JIS standards.

  The results of Test Examples 1 to 5 and Comparative Example 1 are summarized in Table 2.

From the results of Comparative Example 1, it can be seen that approximately 60% of SO ₂ is oxidized to SO ₃ in the oxidation catalyst layer outlet. It can be seen that when the absorbents of Experimental Examples 1 to 5 are installed downstream of the oxidation catalyst layer, the generated SO ₃ is almost completely removed, and the SO ₃ concentration in the outlet gas is remarkably reduced. Thus, by applying the present invention, it is possible to effectively remove SO ₃ that adversely affects the human body and prevent environmental pollution.

When an oxidation catalyst layer and DPF or DPF with an oxidation catalyst are used as a means for removing dust in diesel exhaust gas discharged from diesel engine equipment, SO ₂ in the exhaust gas is oxidized to SO ₃ by the oxidation catalyst, causing air pollution. Although it is a cause, by applying the present invention, not only PM but also SO ₃ emissions can be significantly reduced, so it is possible to prevent environmental pollution caused by diesel exhaust gas and adverse effects on the human body. .

The figure which shows the system | strain of the diesel exhaust gas processing apparatus which is one Example of this invention. Explanatory drawing which shows the other Example of this invention. Explanatory drawing which shows another Example of this invention. Explanatory drawing which shows the further another Example of this invention. Explanatory drawing which shows another Example of this invention. Explanatory drawing which shows a prior art.

Explanation of symbols

1 ... diesel engine, 2 ... oxidizing catalyst layer, 3 ... DPF, 4 ... denitration catalyst layer, 5 ... reductant injector, 6 ... sulfur oxides (SO ₃₎ absorbent layer, 7 ... oxidation catalyzed DPF, 10 ... Exhaust pipe.

Claims (10)

A diesel exhaust gas treatment apparatus provided with dust removal means for collecting and removing particulate matter in exhaust gas in an exhaust gas flow path of a diesel engine, wherein sulfur oxide removal means is provided in the exhaust gas flue Diesel exhaust gas treatment equipment. The diesel exhaust gas treatment device according to claim 1, wherein the sulfur oxide removing means is provided in the downstream of the dust removing means. The sulfur oxide removing means is a sulfur oxide absorbent layer containing at least one of alkali metal, alkaline earth metal and rare earth element salts or oxides, and iron oxide as an absorbing component. Item 3. The diesel exhaust gas treatment apparatus according to Item 1 or 2. A nitrogen oxide removing means and a sulfur oxide removing means are sequentially provided downstream of the dust removing means, and the sulfur oxide removing means is at least a salt or oxide of alkali metal, alkaline earth metal and rare earth element. The diesel exhaust gas treatment apparatus according to any one of claims 1 to 3, wherein the sulfur oxide absorbent layer includes one type of absorbent component. A sulfur oxide removing unit and a nitrogen oxide removing unit are sequentially provided downstream of the dust removing unit, and the sulfur oxide removing unit is a sulfur oxide absorbent layer containing iron oxide as an absorption component. The diesel exhaust gas treatment apparatus according to any one of claims 1 to 3. 6. The diesel according to claim 3, wherein the sulfur oxide absorbent is obtained by carrying the absorbent component on a catalyst carrier, and the carrying amount is 50 to 200 g / l. Exhaust gas treatment equipment. The diesel exhaust gas treatment apparatus according to any one of claims 1 to 6, wherein the dust removal means is a combination of an oxidation catalyst layer and a filter or a filter with an oxidation catalyst. The diesel exhaust gas treatment apparatus according to claim 4 or 5, wherein the nitrogen oxide removing means is a denitration catalyst layer that selectively reduces and removes nitrogen oxides in the presence of a reducing agent. Diesel engine exhaust gas is introduced into dust removal means with an oxidation catalyst layer to collect particulate matter in the exhaust gas, burned and removed with NO ₂ or O ₂ generated by NO oxidation, and then removed with nitrogen oxides It is introduced into the means to decompose and remove nitrogen oxides, and then introduced into a sulfur oxide absorbent layer using at least one of alkali metal, alkaline earth metal and rare earth element salts or oxides as an absorbing component. A method for treating diesel exhaust gas, comprising absorbing and removing sulfur oxides in the exhaust gas. Diesel engine exhaust gas is introduced into dust removal means with an oxidation catalyst layer to collect particulate matter in the exhaust gas, burned and removed by NO ₂ or O ₂ generated by NO oxidation, and then absorbed iron oxide Diesel that is introduced into a sulfur oxide absorbent layer used as a component to absorb and remove sulfur oxides in exhaust gas, and then introduced into nitrogen oxide removing means to decompose and remove nitrogen oxides Exhaust gas treatment method.

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