JP3767040B2 - Engine exhaust gas purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a purification device for exhaust gas discharged from an engine, particularly a vehicle engine.
[0002]
[Prior art]
As a catalyst that efficiently purifies nitrogen oxides (NO _x ), carbon monoxide (CO), and hydrocarbons (HC), which are harmful components in exhaust gas discharged from engines, particularly automobile engines such as automobiles, as a catalyst. A heat-resistant porous carrier such as light is based on one or two kinds of noble metals such as platinum (Pt), palladium (Pd), rhodium (Rh), and oxidation of nickel (Ni), cobalt (Co), etc. as necessary. A three-way catalyst having a catalyst added as a catalyst component is widely used.
[0003]
However, the above three-way catalyst can efficiently remove harmful components in the operation region near the so-called theoretical air-fuel ratio where the oxygen concentration in the exhaust gas is approximately 1% or less, but the oxygen concentration in the exhaust gas is several times. %, I.e., exhaust gas discharged from a lean combustion region of an Otto cycle engine and a diesel engine operating in an essentially oxygen-excess state has a disadvantage that the purification efficiency of harmful components is remarkably low.
[0004]
Therefore, NO _x and HC can be purified even in the above lean combustion region where the oxygen concentration in the exhaust gas is high by loading a transition metal on a substance having a molecular sieve structure such as various natural zeolites or synthetic zeolites. Catalysts such as those generally called zeolite catalysts have been developed. A catalyst in which a transition metal is supported on a substance of this type of molecular sieve structure (hereinafter, this type of catalyst is sometimes referred to as a molecular sieve structure catalyst) is obtained by a reaction using CO or HC contained in exhaust gas as a reducing agent. NO _x can be effectively removed.
[0005]
However, the molecular sieve structure catalyst occurs a change in crystal structure by the presence of a small amount of water, it is known that the rejection performance of the NO _x in the exhaust gas is significantly reduced, thus, at least the water in the exhaust gas 5 % or less, preferably without providing a means for reducing to less than 1%, be located within the exhaust gas passage molecular sieve structure catalyst alone can not be expected excellent nO _x reduction effect.
[0006]
In order to solve the above problems, a molecular sieve structure catalyst, for example, a water gas reaction catalyst arranged in an exhaust gas passage on the upstream side of a zeolite catalyst is disclosed in Japanese Patent Laid-Open No. 4-300631. However, in this proposed exhaust gas purification device, when water is removed by the water gas reaction catalyst, CO and HC in the exhaust gas are used as a reducing agent, so the downstream molecular sieve structure catalyst has a NO _x removal function. There is an inconvenience that the amount of the reducing component in the exhaust gas necessary for exhibiting it is insufficient, and a sufficient NO _x removal effect cannot be obtained.
[0007]
[Problems to be solved by the invention]
The present invention was devised in view of the above circumstances, and is a necessary condition for a molecular sieve structure catalyst to effectively remove NO _x , which is a reduction in moisture in exhaust gas and a sufficient amount of CO, HC, etc. An object of the present invention is to provide an exhaust gas purifying apparatus for an engine that can be compatible with the presence of a reducing agent.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a catalyst in which a transition metal is supported on a substance having a molecular sieve structure disposed in an exhaust passage of an engine, and an exhaust passage on the upstream side of the catalyst. a water treatment device and the exhaust gas purifying apparatus of the engine in which a consisting of water decomposition means for decomposing the water released from the water removal means and the water removing means for absorbing moisture to produce a reducing hydrogen, Two branch passages that are disposed in an exhaust passage on the upstream side of the catalyst and are selectively supplied with exhaust gas by a switching valve, a moisture treatment device disposed in each of the branch passages, and exhaust gas are supplied. A control unit that operates the switching valve to supply exhaust gas to the other branch passage when moisture storage saturation of the water removal means in the water treatment device in one branch passage is detected; In addition, the moisture removal means in the one branch passage where the supply of exhaust gas is stopped by the switching valve releases the stored moisture, and the hydrogen decomposition means generates reductive hydrogen and supplies the exhaust gas. The present invention proposes an exhaust gas purifying apparatus for an engine, characterized in that the moisture removing means in the other branch passage is configured to occlude moisture in the exhaust gas.
[0009]
In the present invention, the upper Symbol water decomposition means preferably by irradiation of ultraviolet rays to decompose the water is a photocatalyst to generate a reducing hydrogen.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Reference numeral 10 in the figure is a conceptually shown engine, for example, an engine for a vehicle such as an automobile. The engine 10 is generated in an intake manifold 12 that takes in outside air via an air cleaner (not shown) and the engine 10. An exhaust manifold 14 for discharging combustion gas to the outside air is provided, and the exhaust manifold 14 forms an exhaust passage 16 of the engine 10 together with an exhaust pipe connected to an exhaust end thereof.
[0011]
A catalytic converter generally indicated by reference numeral 18 is interposed downstream of the exhaust passage 16, and a molecular sieve structure catalyst 20 is accommodated inside the catalytic converter 18. Two branch passages 22 a and 22 b are provided between the exhaust passage 16 on the downstream side of the exhaust manifold 14 and the exhaust passage 16 on the upstream side of the catalytic converter 18. A switching valve 26 is provided in the upstream junction 24 of the branch passages 22a and 22b, and a valve control lever 30 is fixed to a valve shaft 28 of the switching valve 26.
[0012]
The valve control lever 30 is pivotally connected to an output end of an operating rod 34 driven by an actuator 32. The actuator 32 may be an arbitrary actuator such as an electromechanical actuator including an electromagnetic actuator, a compressed air-operated air cylinder device, a pinion driven by an electric motor, and a rack bar meshing with the pinion. it can. In addition, a moisture sensor 36 for detecting moisture contained in the exhaust gas is provided in the exhaust passage 16 between the downstream side joining portions of the branch passages 22a and 22b and the catalytic converter 18, and the moisture sensor 36 A signal or information indicating the detected moisture content Ew in the exhaust gas is supplied to the control unit 38 that controls the actuator 32.
[0013]
The branch passages 22a and 22b are provided with moisture treatment devices generally indicated by reference numerals 40a and 40b, respectively. The moisture treatment device 40a includes moisture removal means 42a for absorbing and storing moisture in the exhaust gas. , And a water decomposing means 44a disposed downstream thereof. Similarly, the moisture treatment apparatus 40b includes a moisture removing unit 42b that occludes moisture in the exhaust gas, and a moisture decomposing unit 44b disposed on the downstream side thereof. The moisture removing means 42a and 42b have substantially the same structure, and the moisture decomposing means 44a and 44b have substantially the same structure.
[0014]
The moisture removing means 42a and 42b are ceramics such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), which can withstand high temperature exhaust gas, and have excellent corrosion resistance and chemical stability. Porous moisture occlusion bodies 46a and 46b made of materials and having innumerable micropores, and heating devices 48a and 48b for releasing the occluded moisture by heating the moisture occlusion bodies 46a and 46b. Yes.
The moisture decomposing means 44a and 44b include photocatalysts 50a and 50b, respectively, and ultraviolet irradiation devices 52a and 52b that cause the photocatalysts 50a and 50b to have activity.
[0015]
The catalyst 20 in which the transition metal is supported on the substance having the molecular sieve structure is generally called zeolite, the main components are silica and alumina, the Si / Al ratio is about 5 to 100, the crystal structure is X-type, Y Type, ZSM type metallosilicates, etc., and these zeolites and metallosilicates are ion-exchanged with transition metals.
[0016]
The photocatalysts 50a and 50b are made of a carrier made of alumina, cordierite or the like, titania (TiO ₂ ) as a main agent, and iron oxide (Fe ₂ O ₃ ), copper oxide (Cu ₂ O), nickel oxide as necessary. What carried 1 type, or 2 or more types of additives, such as (NiO), can be employ | adopted advantageously. Further, the ultraviolet irradiation devices 52a and 52b include a lamp that generates ultraviolet rays having a wavelength λ of about 300 nm, which is housed in a quartz glass container that can withstand high temperatures of exhaust gas and has improved impact resistance. Furthermore, the specific shape structure of the carriers of the photocatalysts 50a and 50b and the relative arrangement of the ultraviolet irradiation devices 52a and 52b are arbitrary.
[0017]
FIG. 1 shows a state in which the branch passage 22a is closed by the switching valve 26, the branch passage 22b is opened, and the exhaust gas of the engine 10 flows into the branch passage 22b. While the exhaust gas passes through the moisture occlusion body 46b of the moisture removing means 42b provided in the branch passage 22b, the contained moisture is effectively absorbed, and the moisture content is 5% or less, preferably 1% or less. And flows through the resting water decomposition means 44b to the catalytic converter 18 and contacts the molecular sieve structure catalyst 20 stored in the converter. Since the moisture in the exhaust gas is low and reducing components such as CO and HC are not lost in the middle, NO _x is effectively reduced even in an excess atmosphere where more oxygen exists than in the stoichiometric air-fuel ratio state. At the same time, CO and HC are purified.
[0018]
The moisture content Ew in the exhaust gas detected by the moisture sensor 36 is lower than the set value until the moisture occlusion body 46b in the moisture removing means 42b in the branch passage 22b is saturated. 32 is de-energized, the switching valve 26 is held in the switching position indicated by the solid line in the figure, and the heating device 48b of the moisture removing means 42b is also de-energized. Further, since the ultraviolet irradiation device 52b of the moisture decomposing means 44b is also deactivated, the photocatalyst 50b is deactivated and does not act.
[0019]
On the other hand, the heating unit 48a in the moisture removing means 42a in the branch passage 22a is energized by the control unit 38, and the ultraviolet irradiation device 52a of the moisture decomposing unit 44a is energized. Moisture stored in 46a is released by heating and decomposes in contact with the activated photocatalyst 50a to produce reducing hydrogen H and OH.
The reducing hydrogen H and OH, as well as low moisture content of the exhaust gas from the branch passage 22b described above, flows into the catalytic converter 18, so enhancing the reducing atmosphere required for _the NO _x purification of the molecular sieve structure catalyst 20 Further improvement in NO _x purification efficiency is achieved.
[0020]
As time passes, when the moisture storage body 46b in the branch passage 22b is saturated or nearly saturated and the water absorption capacity is reduced to a certain limit, the moisture in the exhaust gas flowing through the branch passage 22b gradually increases. Therefore, the controller 38 energizes the actuator 32 based on the signal or information in which the moisture content Ew of the moisture sensor 36 is detected. Due to the urging of the actuator 32, the operating rod 34 is displaced upward in the figure, and the switching valve 26 is switched to the position indicated by the dotted line via the valve control lever 30. As a result, the exhaust gas of the engine 10 flows into the branch passage 22a, and the inflow to the branch passage 22b is blocked.
[0021]
At the same time, the heating device 48a in the moisture removing means 42a of the branch passage 22a is deactivated, the moisture occlusion body 46a begins to occlude moisture in the exhaust gas, and the ultraviolet irradiation device 52a of the moisture decomposing means 44a is deactivated. As a result, the photocatalyst 50a is deactivated, and the exhaust gas passes through the photocatalyst 50a and is supplied to the catalytic converter 18.
[0022]
On the other hand, since the heating device 48b in the moisture removing means 42b of the blocked branch passage 22b is energized, the moisture occluded in the moisture occlusion body 46b starts to be released. At the same time, the ultraviolet irradiation device 52b of the water decomposing means 44b is energized, so that the photocatalyst 50b is activated, and the water released from the water occlusion body 46b comes into contact with the photocatalyst 50b and decomposes, thereby reducing hydrogen. H and OH are generated and supplied to the catalytic converter 18. As a result, in the same manner as described above, NO _{x in} the exhaust gas is effectively purified, and CO and HC are purified.
[0023]
In the above embodiment, the moisture removing means 42a and 42b and the moisture decomposing means 44a and 44b constituting the moisture treatment devices 40a and 40b are shown as separate devices, but the moisture is contained in a common casing. The removing means 42a and the moisture decomposing means 44a can be accommodated, and similarly the moisture removing means 42b and the moisture decomposing means 44b can be accommodated.
[0024]
【The invention's effect】
As described above, an exhaust gas purification apparatus for an engine according to the present invention includes a catalyst in which a transition metal is supported on a substance having a molecular sieve structure disposed in an exhaust passage of an engine, and an exhaust passage on the upstream side of the catalyst. A moisture treatment device comprising a moisture removal means for storing moisture in the exhaust gas and a moisture treatment device for decomposing moisture released from the moisture removal means to produce reductive hydrogen , upstream of the catalyst Two branch passages which are disposed in the exhaust passage on the side and are selectively supplied with exhaust gas by a switching valve, a moisture treatment device respectively disposed in the branch passage, and one branch passage where exhaust gas is supplied A control unit that operates the switching valve to supply exhaust gas to the other branch passage when moisture storage saturation of the water removing means in the water treatment device is detected, and the switching valve The water removal means in the one branch passage where the supply of exhaust gas has been further stopped releases the stored moisture, and reductive hydrogen is generated by the water decomposition means, and the other branch passage is supplied with the exhaust gas. The internal moisture removal means is characterized in that the moisture in the exhaust gas is occluded, and is an oxygen-excess state, and harmful components in the exhaust gas of the engine containing a large amount of moisture, especially NO which is usually difficult to remove. There is an advantage that _x can be effectively purified. In addition, there is an advantage that the exhaust gas can be continuously and effectively purified during the continuous operation of the engine, regardless of the limited water storage capacity of the water removing means.
[0025]
Further, in the present invention, the upper Symbol water decomposition unit, by a photocatalyst to generate a reducing hydrogen by decomposing water by irradiation of ultraviolet rays, molecular sieve structure catalyzed by small energy consumption required to ultraviolet radiation NO _x There is an advantage that reducible hydrogen effective for purification can be generated and purification efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a preferred embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Engine, 14 ... Exhaust manifold, 16 ... Exhaust passage, 18 ... Catalytic converter, 20 ... Catalyst, 22a and 22b ... Branch passage, 26 ... Switching valve, 32 ... Actuator, 36 ... Moisture sensor, 38 ... Control unit, 40a And 40b ... moisture treatment device, 42a and 42b ... moisture removal means, 44a and 44b ... moisture decomposition means, 46a and 46b ... moisture storage, 48a and 48b ... heating device, 50a and 50b ... photocatalyst, 52a and 52b ... UV irradiation apparatus.

Claims (2)

A catalyst in which the transition metal is supported on a substance having a molecular sieve structure disposed in the exhaust passage of the engine, and a moisture removing means disposed in the exhaust passage on the upstream side of the catalyst and storing moisture in the exhaust gas. a decompose exhaust gas purifying apparatus of the engine provided with a water treatment apparatus comprising a moisture separation means for generating a reducing hydrogen released moisture from the means,
Two branch passages which are arranged in an exhaust passage on the upstream side of the catalyst and are selectively supplied with exhaust gas by a switching valve, a moisture treatment device respectively disposed in the branch passage, and exhaust gas are supplied A control unit that operates the switching valve to supply exhaust gas to the other branch passage when moisture storage saturation of the water removal means in the water treatment device in one branch passage is detected. In the water removal means in the one branch passage where the supply of water is stopped, the stored moisture is released, reducing hydrogen is generated by the water decomposition means, and the exhaust gas is supplied in the other branch passage. An exhaust gas purification apparatus for an engine, characterized in that the moisture removal means is configured to occlude moisture in the exhaust gas. It said water decomposition means, the exhaust gas purification apparatus for an engine according to claim 1, characterized in that the photocatalyst to produce a reducing hydrogen by decomposing water by irradiation of ultraviolet rays.

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