JP6251933B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus including a reduction device using plasma and a chemical oxidation catalyst.

  2. Description of the Related Art Conventionally, an exhaust gas purification device that purifies exhaust gas exhausted from an engine using plasma is known (see, for example, Patent Document 1).

  JP2011-12559A

  In Patent Document 1, a plurality of plate-like electrode structures are stacked via exhaust gas passages, that is, a plurality of electrode structures are arranged along the direction in which the exhaust gas flows. Accordingly, the cross-sectional area of the exhaust gas passage is reduced, the amount of exhaust gas activated by plasma is small, and it is difficult to efficiently purify the exhaust gas. Increasing the passage cross-sectional area of the exhaust gas passage leads to an increase in the size of the exhaust gas purification device.

In addition, the exhaust gas purification device incinerates particulate matter in the exhaust gas by oxidation reaction, but effectively purifies the main harmful substances (HC, CO, NOx) in the exhaust gas. Is desired.
Furthermore, since the above oxidation reaction does not proceed easily when the exhaust gas temperature is low, such as when the engine is started, it is difficult to purify the exhaust gas, and it is desirable to raise the exhaust gas temperature early.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an exhaust gas purification device capable of effectively purifying exhaust gas.

In order to solve the above-described problems, the present invention provides a plasma reduction device having a NOx reduction action disposed upstream in an exhaust pipe body, a metal oxidation catalyst device disposed downstream in the exhaust pipe body, and the plasma reduction The apparatus includes at least a pair of electrodes of an anode and a cathode, and each electrode is planar and arranged with a predetermined space in the flow direction of the exhaust gas, and the exhaust gas passes through each electrode surface and the space. Each electrode surface is orthogonal to the exhaust gas flow, a pulse current supplied to the anode and cathode is generated by an SI thyristor, and the frequency of the pulse current is 100,000 Hz or more .

  According to this configuration, by making the anode and cathode electrode surfaces orthogonal to the exhaust gas flow, plasma can be generated efficiently based on the exhaust gas passing through the electrodes, and the exhaust gas passage cross-sectional area can be further increased. Since it can be enlarged, exhaust gas can be purified efficiently. In addition, NOx is reduced by the plasma reduction device, and oxygen and heat generated by this reduction action are used to quickly raise the temperature of the downstream metal oxidation catalyst device, while the metal oxidation catalyst device reduces HC and CO. The exhaust gas can be purified by oxidation, and the exhaust gas can be effectively purified. The metal oxidation catalyst device is heated at an early stage at the time of cold start, and the effect of exhaust gas purification by oxidation is increased.

In the above configuration, the high-frequency pulse is generated by the SI thyristor , the plasma that activates the exhaust gas and promotes the reduction action can be generated, and the reduction efficiency can be improved.

Further, in the above configuration, the heat generated during the generation of the plasma and the heat generated during the reduction reaction can suppress heat release from the exhaust gas when the temperature of the exhaust gas rises, and is supplied to the downstream metal oxidation catalyst device. The temperature of the exhaust gas can be further increased. Thereby, the purification | cleaning effect | action of the exhaust gas by a catalyst can be improved.

  Further, in the above configuration, the cathode is arranged at one end of the tubular ceramic body, the anode is arranged at the other end to form a plasma reduction unit, and the plasma reduction unit is assembled in the exhaust pipe body. Also good. According to this configuration, the cathode and the anode can be easily arranged at a predetermined interval inside the exhaust pipe main body.

  In the above configuration, the anode may be insulated by the ceramic body, and the cathode may be grounded to the exhaust pipe body by a fixing ring. According to this configuration, the ceramic body can support the anode and the cathode and insulate the anode, thereby reducing the number of parts.

  Further, in the above configuration, the metal oxidation catalyst device may be a metal honeycomb catalyst device or a wire knit catalyst device. According to this configuration, it is possible to increase the catalyst surface area by making the metal foil serving as a carrier thinner in the metal honeycomb catalyst device and making the wire material serving as the carrier thinner in the wire knit catalyst device. Moreover, since the temperature rises easily, the purification performance of the exhaust gas activated by the plasma reduction device can be further enhanced.

  In the present invention, a plasma reduction device having NOx reduction action is disposed upstream, a metal oxidation catalyst device is disposed downstream, and the plasma reduction device includes at least a pair of electrodes of an anode and a cathode, and each electrode is planar. Since the exhaust gas passes and each electrode surface is orthogonal to the exhaust gas flow, it is possible to efficiently generate plasma based on the exhaust gas passing through the electrode, and to further increase the exhaust gas passage cross-sectional area. Therefore, exhaust gas can be purified efficiently. In addition, NOx is reduced by the plasma reduction device, and oxygen and heat generated by this reduction action are used to quickly raise the temperature of the downstream metal oxidation catalyst device, while the metal oxidation catalyst device reduces HC and CO. The exhaust gas can be purified by oxidation, and the exhaust gas can be effectively purified.

  It is sectional drawing which shows the exhaust-gas purification apparatus which concerns on this invention.   It is sectional drawing which shows a plasma reduction unit.   It is a front view which shows a plasma reduction unit.   It is an operation | movement figure explaining an effect | action of a plasma reduction apparatus.   It is a graph which shows the relationship between the electric power capacity in a semiconductor element, and an operating frequency.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, “upstream” and “downstream” indicate upstream and downstream of the flow of exhaust gas.
FIG. 1 is a cross-sectional view showing an exhaust gas purification device 10 according to the present invention.
The exhaust gas purification device 10 includes an exhaust pipe 14 connected to a cylinder head of the engine, and a plasma reduction device 11 and a catalyst device 12 provided in the exhaust pipe 14 for purifying exhaust gas exhausted from the engine. Has been.
The exhaust pipe 14 includes a connection pipe 21 connected to the cylinder head, an upstream taper pipe 22 connected at one end to the connection pipe 21, a straight pipe 23 connected to the other end of the upstream taper pipe 22, and a straight pipe. It consists of a downstream taper tube 24 connected to the downstream end of the tube 23. The downstream taper pipe 24 is connected to, for example, another exhaust pipe, a silencer, or the like.

The connecting pipe 21 includes a flange portion 26 in which bolt holes 26 a and 26 a are opened when the exhaust gas purification device 10 is attached to the cylinder head with a bolt, and a pipe portion 27 attached to the flange portion 26. The upstream tapered tube 22 includes a small-diameter tube portion 22a attached to the outer peripheral surface of the tube portion 27 of the connecting tube 21, a large-diameter tube portion 22b attached to the inner peripheral surface of the straight tube 23, a small-diameter tube portion 22a, It comprises a tapered portion 22c that integrally connects the large-diameter pipe portions 22b.
The straight pipe 23 is a cylindrical member and is grounded. The downstream tapered tube 24 includes a large-diameter tube portion 24a attached to the inner peripheral surface of the straight tube 23, a small-diameter tube portion 24b formed with a smaller diameter than the large-diameter tube portion 24a, a large-diameter tube portion 24a, and a small-diameter tube portion 24a. It consists of the taper part 24c which connects each of the pipe parts 24b integrally.

The plasma reduction device 11 includes a plasma reduction unit 15 disposed in the straight pipe 23 and a power supply device 33 that supplies power to the plasma reduction unit 15. The plasma reduction unit 15 includes a pair of electrodes of an anode 31 disposed on the downstream side of the exhaust gas and a cathode 32 disposed on the upstream side of the anode 31.
Discharging by applying a pulse voltage between the anode 31 and the cathode 32 generates plasma (non-equilibrium plasma) in the exhaust gas flowing in the exhaust pipe 14.
The anode 31 is connected to a connection terminal 34 of a conductive wire extending from the power supply device 33, and the cathode 32 is grounded via the straight pipe 23. The power supply device 33 is a device that generates a high-frequency pulse voltage, and supplies a positive voltage from one output terminal to the anode 31, and the other output terminal is grounded.
The plasma reduction unit 15 is fixed in the straight pipe 23 by a fixing unit 36 included in the plasma reduction device 11.

  The fixing portion 36 includes an insulating material 37 that sandwiches the straight pipe 23 between the plasma reduction unit 15 side, a washer 38 applied to the insulating material 37, an end of the plasma reduction unit 15, the insulating material 37, and the washer 38. 23 and a bolt 41 and a nut 42 to be fastened. The bolt 41 passes through the end of the plasma reduction unit 15, the insulating material 37, and the washer 38. A connection terminal 34 is attached between the washer 38 and the nut 42.

The pulse power source incorporates an SI thyristor (electrostatic induction thyristor). Conventionally, as shown in FIG. 5, a semiconductor device that realizes a switching operation frequency of 100,000 Hz or more has been confirmed by a recent study to be capable of switching operation of an SI thyristor at a frequency of 100,000 Hz or more. ing. In the plasma reduction device 11 of this embodiment, a pulse current having a pulse frequency of at least 100,000 Hz is generated by the high-speed switching operation of the SI thyristor, and this pulse current is supplied to the plasma reduction unit 15.
It is known that when the pulse frequency is 100,000 Hz or more, radicals that are highly reactive with NOx (for example, N radicals) increase, and it is possible to improve the reduction performance and promote the following reduction reaction. Have gained.
_{2NOx + 2N → 2N 2 + xO} 2

The catalyst device 12 is a chemical oxidation catalyst attached to the straight pipe 23 via a holding member 43. The catalyst device 12 is a ceramic honeycomb in which a metal catalyst such as Pt (platinum), Rh (rhodium), or Pd (palladium) is supported on a ceramic carrier or metal carrier made of ceramic or metal and having numerous pores formed. It is composed of a catalyst or a metal honeycomb catalyst. The catalytic device 12 mainly purifies by oxidizing HC and CO.
Alternatively, the catalyst device 12 is composed of a wire knit catalyst in which a metal wire is knitted to form a net, the metal catalyst is supported on the net, and the net is overlapped and wound or folded. The The wire-knit catalyst can increase the surface area of the metal catalyst, and since the turbulent flow tends to occur in the gas flow path between the wires, the volume in contact with the metal catalyst can be increased. It is possible to improve.

FIG. 2 is a cross-sectional view showing the plasma reduction unit 15.
The plasma reduction unit 15 is electrically connected to the cylindrical ceramic body 45, the anode 31 and the cathode 32 attached to both ends of the ceramic body 45, the electrode terminal 46 electrically connected to the anode 31, and the cathode 32. The unit includes a fixing ring 47 that is connected and fixes the cathode 32 to the ceramic body 45. The unit is inserted into the straight pipe 23 and fixed.

The anode 31 and the cathode 32 are members formed into a planar shape by assembling or knitting a plurality of wires. In the state where the plasma reduction unit 15 is assembled to the straight pipe 23, the anode 31 and the cathode 32 are arranged so as to be orthogonal to the flow direction of the exhaust gas, and the exhaust gas is effectively formed on the anode 31 and the cathode 32. Go through the eyes of the interval. In this way, by making the anode 31 and the cathode 32 orthogonal to the direction of the exhaust gas flow, for example, compared with the case where the electrodes are arranged along the flow of the exhaust gas, plasmaization of the exhaust gas is further promoted. The knowledge that is effective for radical generation has been obtained.
The ceramic body 45 is a member that insulates the anode 31 and the cathode 32 and keeps them at a predetermined interval, and projects in the axial direction of the cylindrical portion 45a integrally with the cylindrical portion 45a and one end surface of the cylindrical portion 45a. It consists of a protruding end 45b. In the protruding end 45b, the electrode terminal 46 is disposed on the inner surface 45d, the concave portion 45f is formed on the outer surface 45e, and the convex portion 37a of the insulating material 37 is fitted into the concave portion 45f. Therefore, after inserting the plasma reduction unit 15 into the straight tube 23, the convex portion 37 a of the insulating material 37 is inserted into the concave portion 45 f of the ceramic body 45 through the through hole 23 a formed in the straight tube 23. The plasma reduction unit 15 is positioned with respect to the axial direction and the circumferential direction of the straight pipe 23.

The electrode terminal 46 is a member having an L-shaped cross section in which the contact portion 46a and the fastening portion 46b are integrally formed. The contact portion 46a is electrically connected to the anode 31 and the bolt insertion hole 46c formed in the fastening portion 46b. Bolt 41 is passed through.
The fixing ring 47 is fitted and fixed to an annular step 45g formed on the outer peripheral surface of one end of the ceramic body 45. The outer peripheral surface 47a of the fixing ring 47 is press-fitted into the inner peripheral surface 23b of the straight pipe 23, and the fixing ring 47 and the straight pipe 23 are electrically connected.

FIG. 3 is a front view showing the plasma reduction unit 15.
The anode 31 includes a plurality of straight linear members 51 extending radially and a plurality of circular wire members 52, 53, 54, and 55 concentrically attached to the respective straight straight members 51. Between the adjacent straight straight members 51 and 51 and between the adjacent circular wires 52 and 53, circular wires 53 and 54, and circular wires 54 and 55, eyes through which exhaust gas passes are formed. The cathode 32 (see FIG. 2) also has the same structure as the anode 31.

Next, the operation of the plasma reduction apparatus 11 described above will be described.
FIG. 4 is an operation diagram for explaining the operation of the plasma reduction device 11.
As indicated by an arrow A in the exhaust pipe 14, a high frequency (100,000 Hz or higher) pulse voltage is applied between the anode 31 and the cathode 32 of the plasma reduction unit 15 from the power supply device 33 while the exhaust gas is flowing. Then, discharge occurs between the anode 31 and the cathode 32, and non-equilibrium plasma is generated in the exhaust gas.
In the non-equilibrium plasma, various radicals (active species) are generated. For example, N radicals in the radicals reduce NOx in the exhaust gas to generate N ₂ and O ₂ . Such a reaction is successively performed in the exhaust gas passing through the cathode 32 and the anode 31 as indicated by an arrow B.

Then, as shown by arrow C, when the plasma exhaust gas passes through the catalyst device 12, HC and CO in the exhaust gas are oxidized by O ₂ or the like generated during the NOx reduction reaction, and The reaction is accelerated by the heat generated during the reduction reaction of NOx, and becomes H ₂ O, CO ₂ . This oxidation reaction is also promoted by radicals in the plasma. The purified exhaust gas is discharged out of the exhaust pipe 14 as indicated by an arrow D.

  For example, when a chemical catalyst such as a three-way catalyst is used to oxidize CO and HC, the catalyst is not sufficiently activated and the purification performance is low when the exhaust gas temperature is low, such as when the engine is started. Become. For this reason, it is necessary to devise so as to reach the catalyst activation temperature at an early stage, which may increase the cost. In the present embodiment, the plasma reduction device 11 generates a non-equilibrium plasma from a relatively low temperature of the exhaust gas, thereby reducing NOx and promoting heat generation by the reduction action. The catalyst device 12 on the downstream side is a metal oxidation catalyst device and is heated at an early stage, which is advantageous in terms of both temperature and oxygen concentration. Since the plasma reduction unit 15 and the catalyst device 12 are arranged in the same exhaust pipe 14, more specifically, in the same straight pipe 23, the plasma reduction unit 15 and the catalyst device 12 are close to each other. The effect of oxygen concentration becomes even more pronounced. Therefore, by employing the plasma reduction device 11 of the present embodiment, an extra exhaust gas heat retention device or the like is unnecessary, and a significant cost reduction is possible.

  Further, in the conventional chemical catalyst, the catalytic metal is expensive, and Pt used for the reduction of Nox is particularly expensive. On the other hand, Pd and Rh used for the oxidation of HC and CO are relatively inexpensive. In this embodiment, the cost of the exhaust gas purification device 10 can be reduced by using the plasma reduction device 11 for NOx reduction and the chemical oxidation catalyst carrying Pd and Rh for oxidation of HC and CO. Furthermore, since the plasma reduction device 11 activates not only the reduction of NOx but also other components, the amount of the metal catalyst of the chemical oxidation catalyst can be reduced and the size can be reduced. In this respect, the cost can be suppressed.

FIG. 5 is a graph showing the relationship between power capacity and operating frequency in a semiconductor device. The vertical axis of the graph represents power capacity (unit: VA), and the horizontal axis represents operating frequency (unit: Hz). As semiconductor elements, an SI thyristor and an IGBT (insulated gate bipolar transistor) are shown.
The SI thyristor operates within a range indicated by a one-dot chain line, and can operate at a frequency of 100,000 Hz or more. The IGBT operates within the range indicated by the broken line, and the operating frequency is lower than 100,000 Hz.

  As shown in FIGS. 1, 2, and 3, the metal oxidation in which the plasma reduction device 11 having the NOx reduction action is arranged upstream, and a catalyst such as Pt, Rh, Pd is supported on a metal carrier. A catalyst device 12 as a catalyst device is disposed downstream, and the plasma reduction device 11 includes at least a pair of electrodes of an anode 31 and a cathode 32, and each electrode is formed in a planar shape by assembling a wire so that exhaust gas passes therethrough. Each electrode surface was made orthogonal to the exhaust gas flow.

  According to this configuration, by making the electrode surfaces of the anode 31 and the cathode 32 orthogonal to the exhaust gas flow, non-equilibrium plasma can be efficiently generated based on the exhaust gas passing through the anode 31 and the cathode 32, and Since the exhaust gas passage sectional area can be further increased, the exhaust gas can be purified efficiently. In addition, NOx is reduced by the plasma reduction device 11, and using the oxygen and heat generated by this reduction action, a catalyst device 12 as a metal oxidation catalyst device provided with a metal carrier disposed on the downstream side. The catalyst device 12 can oxidize HC and CO to purify the exhaust gas while raising the temperature early, and the exhaust gas can be effectively purified.

Further, the plasma reduction device 11 generates a pulse current supplied to the anode 31 and the cathode 32 by an SI thyristor and sets the frequency of the pulse current to 100,000 Hz that can reduce at least NOx. Therefore, a high frequency pulse is generated by the SI thyristor. It is possible to generate non-equilibrium plasma that can be generated and the activation of the exhaust gas is further increased, and the reduction efficiency can be improved.
In addition, the cathode 32 is disposed at one end of the tubular ceramic body 45 and the anode 31 is disposed at the other end to form the plasma reduction unit 15 and the plasma reduction unit 15 is assembled in the exhaust pipe 14. The anode 31 and the cathode 32 can be easily arranged at a predetermined interval inside the tube 14.

  Further, since the anode 31, the cathode 32, and the catalyst device 12 are accommodated in the same exhaust pipe 14, heat is released from the exhaust gas when the temperature of the exhaust gas rises due to heat generated when the plasma is generated and heat generated during the reduction reaction. The temperature of the exhaust gas supplied to the downstream side catalyst device 12 can be further increased. Thereby, the purification | cleaning effect | action of the exhaust gas by a catalyst can be improved.

In addition, since the anode 31 is insulated by the ceramic body 45 and the cathode 32 is grounded to the exhaust pipe 14 by the fixing ring 47, the anode 31 and the cathode 32 are supported by the ceramic body 45 and the anode 31 is insulated, so that Can be reduced.
Further, when the catalyst device 12 is a metal honeycomb catalyst device or a wire knit catalyst device, the metal honeycomb catalyst device has a thinner metal foil as a carrier, and the wire knit catalyst device has a wire material as a carrier. Since the surface area of the metal catalyst can be increased and the temperature is easily raised, the purification performance of the exhaust gas activated by the plasma reduction device 11 can be further enhanced.

The above-described embodiment is merely an aspect of the present invention, and can be arbitrarily modified and applied without departing from the gist of the present invention.
For example, in the above embodiment, as shown in FIG. 2, the exhaust gas purification apparatus 10 is provided with a pair of electrodes of the anode 31 and the cathode 32. However, the present invention is not limited to this, and a plurality of anodes 31 and cathodes 32 are provided. May be.
As shown in FIG. 3, the anode 31 and the cathode 32 (see FIG. 2) are composed of a plurality of straight straight members 51 and a plurality of circular wires 52, 53, 54, 55. It may be configured by knitting or knitting vertical and horizontal wires. Or you may comprise with the board (punching plate) which has innumerable holes.
In this embodiment, the catalyst device 12 as a metal oxidation catalyst device is disposed downstream of the plasma reduction device 11. However, the present invention is not limited thereto, and the catalyst is supported on a ceramic carrier downstream of the plasma reduction device 11. A ceramic oxidation catalyst device may be arranged.

10 Exhaust gas purification device 11 Plasma reduction device 12 Catalytic device (metal oxidation catalyst device)
14 Exhaust pipe (exhaust pipe body)
15 Plasma reduction unit 31 Anode 32 Cathode 45 Ceramic body 47 Fixing ring

Claims (4)

A plasma reduction device having NOx reduction action is arranged upstream in the exhaust pipe body, a metal oxidation catalyst device is arranged downstream in the exhaust pipe body ,
The plasma reduction device includes at least a pair of electrodes of an anode and a cathode, and each electrode is planar and is arranged with a space at a predetermined interval in the flow direction of the exhaust gas. Exhaust gas , wherein each electrode surface is orthogonal to the exhaust gas flow, a pulse current supplied to the anode and cathode is generated by an SI thyristor, and the frequency of the pulse current is 100,000 Hz or more. Gas purification device.   The cathode is disposed at one end of a tubular ceramic body, and the anode is disposed at the other end to form a plasma reduction unit,
  The exhaust gas purification device according to claim 1, wherein the plasma reduction unit is assembled in the exhaust pipe main body.   Insulating the anode with the ceramic body;
  The exhaust gas purification device according to claim 2, wherein the cathode is grounded to the exhaust pipe body by a fixing ring.   The exhaust gas purification device according to any one of claims 1 to 3, wherein the metal oxidation catalyst device is a metal honeycomb catalyst device or a wire knit catalyst device.

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