JP2013170482A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of uniformly dispersing ammonia in exhaust gas.SOLUTION: An injection member 10 includes a first circulation path 11 and a second circulation path 12 provided in an upstream side and a downstream side, respectively, with respect to a direction where exhaust gas circulates. The first circulation path 11 is connected to a branch pipe 20, while the second circulation path 12 is connected to an ammonia supply pipe 7. The lower end face 10a of the injection member 10 is formed to be linearly recessed from an upstream end point 10a1 located at the most upstream side and from a downstream end point 10a2 located at the most downstream side, toward the center line 10a3 of the lower end face 10a, the center line perpendicular to the longitudinal direction of an exhaust pipe 2, and the cross section of the lower end face 10a is formed in a V-shape. Opening ends 11a and 12a of the first circulation path 11 and the second circulation path 12 are located on slopes from the upstream end point 10a1 and from the downstream end point 10a2 toward the center line 10a3, respectively, and thereby the opening ends are sloped in directions opposing to each other.

Description

  The present invention relates to an exhaust gas purification device, and more particularly, to an exhaust gas purification device that selectively reduces nitrogen oxide (NOx) using ammonia as a reducing agent.

  In order to reduce NOx contained in exhaust gas of a diesel engine, a urea SCR (Selective Catalytic Reduction) system has been developed. In the conventional urea SCR system, the urea water added to the exhaust pipe is hydrolyzed into ammonia by the heat of the exhaust gas flowing through the exhaust pipe and flows into the SCR catalyst. Therefore, it is sufficient that the temperature of the exhaust gas does not increase. There is a problem that it is not possible to obtain a proper purification performance. In order to obtain a sufficient purification performance in a state where the temperature of the exhaust gas is not high, it is necessary to heat the urea water with external power, and in this case, there is a problem that power consumption increases. On the other hand, as described in Patent Document 1 and the like, a technique for adding ammonia as a reducing agent directly into an exhaust pipe has been developed.

JP 2006-76877 A

  However, when ammonia is added directly into the exhaust pipe, it corresponds to a NOx concentration on the order of ppm relative to the exhaust gas flow rate in order to reduce the amount of ammonia slipping the SCR catalyst without being used for NOx purification. A very small amount of ammonia has to be added, i.e. from 1 / 1,000,000 to 1 / 10,000 for an exhaust gas flow of several g / sec to several hundred g / sec. In this case, in order to uniformly disperse the added ammonia in the exhaust gas, there has been a problem that the distance from the point where ammonia is added to the exhaust gas to the SCR catalyst has to be increased.

  The present invention has been made to solve such problems, and an object thereof is to provide an exhaust gas purifying apparatus capable of uniformly dispersing ammonia in exhaust gas.

An exhaust gas purification apparatus according to the present invention includes an SCR catalyst provided in an exhaust pipe through which exhaust gas discharged from an internal combustion engine flows, and ammonia and ammonia in the exhaust pipe on the upstream side of the SCR catalyst in the direction in which the exhaust gas flows. An injection member for injecting carrier gas, an ammonia supply source for supplying ammonia to the injection member, and a carrier gas supply source for supplying carrier gas to the injection member are provided, and the injection member has a first flow path and a second flow A path is provided, ammonia flows through one of the first flow path and the second flow path and carrier gas flows through the other, and the ammonia and carrier gas flowing through the first flow path and the second flow path are: It is injected towards each other in the exhaust pipe. Ammonia and carrier gas injected into the exhaust pipe from the first flow path and the second flow path of the injection member collide with each other and mix.
The first circulation path and the second circulation path may be arranged in a positional relationship such that they are on the upstream side and the downstream side in the direction in which the exhaust gas flows.
Each of the first circulation path and the second circulation path may have an opening end that opens into the exhaust pipe, and each opening end may be inclined in a direction toward each other. Alternatively, each of the first distribution path and the second distribution path may be inclined in a direction toward each other.
The carrier gas supply source is a branch pipe that branches from the exhaust pipe on the upstream side of the injection member with respect to the direction in which the exhaust gas flows in the exhaust pipe. The carrier gas is an exhaust gas that flows through the branch pipe. Of the first distribution path and the second distribution path, the first distribution path and the second distribution path may be connected to a direction in which ammonia does not flow.
In the exhaust pipe, a DPF may be provided upstream of the branch pipe in the direction in which the exhaust gas flows.
The ammonia supply source may include an ammonia raw material tank that stores the ammonia raw material, and a hydrolysis catalyst that hydrolyzes the ammonia raw material supplied from the ammonia raw material tank into ammonia.

  According to the present invention, the ammonia and the carrier gas injected into the exhaust pipe from the first flow path and the second flow path of the injection member collide with each other and mix to generate an air-fuel mixture, and then the exhaust gas in the exhaust pipe Since they are mixed, ammonia can be uniformly dispersed in the exhaust gas.

1 is a schematic configuration diagram of an exhaust gas purification device according to an embodiment of the present invention. It is an expanded sectional view of the injection member of the exhaust-gas purification apparatus concerning this embodiment. It is an expanded sectional view of the modification of the injection member of the exhaust-gas purification apparatus which concerns on this embodiment.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIG. 1, an oxidation catalyst 3, a diesel particulate filter (DPF) 4, and NOx are selectively passed through an exhaust pipe 2 through which exhaust gas discharged from a diesel engine 1 that is an internal combustion engine flows. An SCR catalyst 5 to be reduced and an ASC (Ammonia Slip Catalyst) catalyst 6 to oxidize ammonia as a reducing agent that has passed through the SCR catalyst 5 are provided. The exhaust pipe 2 is provided with an injection member 10 between the DPF 4 and the SCR catalyst 5 for injecting ammonia and exhaust gas that is a carrier gas described later.

  One end of an ammonia supply pipe 7 is connected to the injection member 10. The other end of the ammonia supply pipe 7 is connected to an ammonia supply source 8. The ammonia supply source 8 includes a urea water tank 13 (ammonia raw material tank) that stores urea water that is an ammonia raw material, and a hydrolysis catalyst for hydrolyzing the urea water supplied from the urea water tank 13 to generate ammonia. 14. Further, a branch pipe 20 that branches from the exhaust pipe 2 downstream of the DPF 4 and upstream of the injection member 10 is also connected to the injection member 10. Here, the branch pipe 20 constitutes a carrier gas supply source for collecting a part of the exhaust gas flowing through the exhaust pipe 2 and supplying the exhaust gas as the carrier gas to the injection member 10.

  As shown in FIG. 2, the injection member 10 includes therein a first flow path 11 and a second flow path 12 provided on the upstream side and the downstream side in the direction in which the exhaust gas flows. The first distribution path 11 is connected to the branch pipe 20. The second distribution path 12 is connected to the ammonia supply pipe 7. The lower end surface 10a of the injection member 10 passes through the center of the lower end surface 10a from the upstream end point 10a1 located on the most upstream side and the downstream end point 10a2 located on the most downstream side, and is perpendicular to the direction in which the exhaust gas flows. The lower end surface 10a has an inverted V-shaped cross section. The lower end surface 10a is linearly recessed toward the center line 10a3. Since the opening end portions 11a and 12a of the first distribution path 11 and the second distribution path 12 are located on the inclined surfaces from the upstream end point 10a1 and the downstream end point 10a2 to the center line 10a3, respectively, they go toward each other. Inclined in the direction.

Next, the operation of the exhaust gas purifying apparatus according to this embodiment will be described with reference to FIGS.
After starting the diesel engine 1, the exhaust gas flows through the exhaust pipe 2. As the exhaust gas flows through the oxidation catalyst 3, a part of the nitrogen monoxide (NO) in the exhaust gas is oxidized to nitrogen dioxide (NO ₂ ). Subsequently, exhaust gas flows through the DPF 4 so that particulate matter (PM) in the exhaust gas is captured by the DPF 4. The exhaust gas flowing out from the DPF 4 flows into the SCR catalyst 5. By the operation described later, ammonia is injected from the injection member 10 and flows into the SCR catalyst 5 together with the exhaust gas flowing out from the DPF 4. In the SCR catalyst 5, ammonia reacts with NOx in the exhaust gas to form nitrogen and water. Ammonia remaining without being consumed in the SCR catalyst 5 is oxidized in the ASC catalyst 6. The exhaust gas from which NOx has been purified in this way flows through the exhaust pipe 2 and is exhausted to the atmosphere.

Next, the operation in which ammonia is injected from the injection member 10 will be described.
In the ammonia supply source 8, urea water is supplied from the urea water tank 13 to the hydrolysis catalyst 14, and is hydrolyzed to produce ammonia. The ammonia produced by the ammonia conveying means (not shown) flows through the ammonia supply pipe 7, then flows through the second flow path 12 in the injection member 10, and is injected into the exhaust pipe 2 from the opening end 12 a. The ammonia conveying means may be a pump, or a means for controlling the pressure of ammonia relative to the pressure of the exhaust gas in the exhaust pipe 2 by controlling the amount of ammonia to be hydrolyzed. On the other hand, part of the exhaust gas flowing out from the DPF 4 flows through the branch pipe 20, then flows through the first flow path 11 in the injection member 10, and is injected into the exhaust pipe 2 from the opening end portion 11 a.

  At this time, since the opening end portions 11a and 12a are inclined in the direction toward each other, the exhaust gas and ammonia injected from the opening end portions 11a and 12a are injected toward each other, and as a result, collide with each other. Mix together. Further, the exhaust gas and ammonia are mixed with the exhaust gas flowing through the exhaust pipe 2, and the ammonia is uniformly dispersed in the exhaust gas. If ammonia is uniformly dispersed in the exhaust gas, ammonia acts on all catalyst active points in the SCR catalyst 5 and the NOx purification reaction occurs uniformly, so that NOx is efficiently purified.

  Thus, since the exhaust gas and ammonia injected into the exhaust pipe 2 from the first flow path 11 and the second flow path 12 of the injection member 10 collide with each other and mix, the ammonia is uniformly dispersed in the exhaust gas. Can be made. If the ammonia is simply dispersed in the exhaust gas in the exhaust pipe 2, an extremely small amount of ammonia is added to the exhaust gas flow rate, so that it is difficult to uniformly disperse the ammonia. However, in this embodiment, after colliding with the exhaust gas that has passed through the first flow path 11 to generate a uniform mixture of exhaust gas and ammonia, it is dispersed into the exhaust gas in the exhaust pipe 2. Therefore, since a larger amount of the above air-fuel mixture is dispersed with respect to the exhaust gas flow rate in the exhaust pipe 2 than when ammonia is simply injected, the dispersibility of ammonia is improved.

  In this embodiment, the exhaust gas circulates in the first circulation path 11 and the ammonia circulates in the second circulation path 12. However, the present invention is not limited to this mode, and ammonia circulates in the first circulation path 11. In addition, the exhaust gas may flow through the second flow path 12.

  In this embodiment, the exhaust air flowing through the first flow path 11 and the second flow path 12 is formed by inclining the opening end portions 11a and 12a of the first flow path 11 and the second flow path 12 in the direction toward each other. Although gas and ammonia were injected toward each other, the present invention is not limited to this mode. As shown in FIG. 3A, the lower end surface 10a has a flat shape, and the first flow path 11 and the second flow path 12 may be inclined in directions toward each other. Moreover, it is not limited to the 1st distribution path 11 and the whole 2nd distribution path 12 inclining, As FIG.3 (b) shows, the direction where the opening edge part 11a and 12a vicinity go to each other at least As long as it is tilted. Further, as shown in FIG. 3C, the second distribution path 12 is a double pipe structure surrounded by the first distribution path 11, and a portion in the vicinity of the opening end portion 11 a of the first distribution path 11. May be configured to be inclined in a direction toward the second distribution path 12.

  In this embodiment, the urea water tank 13 and the hydrolysis catalyst 14 are used as the ammonia supply source 8. However, the present invention is not limited to this embodiment. A tank for storing pure ammonia or an ammonia storage cylinder may be used as the ammonia supply source 8 to supply ammonia directly to the injection member 10. Even when the urea water tank 13 and the hydrolysis catalyst 14 are used as the ammonia supply source 8, the ammonia raw material is not limited to urea water. An aqueous solution of an arbitrary substance can be used as long as it is a substance that generates ammonia by a hydrolysis reaction. For example, an aqueous solution of ammonium carbamate, isocyanate, ammonium carbonate, or the like may be used.

In this embodiment, exhaust gas is used as the carrier gas, and the carrier gas supply source is the branch pipe 20. However, the present invention is not limited to this embodiment. The carrier gas may be any gas that does not cause a chemical reaction with ammonia, and may be air, for example. When the carrier gas is air, a pump or the like that collects air from the atmosphere and supplies it to the injection member 10 constitutes a carrier gas supply source. Further, a cylinder filled with an arbitrary carrier gas may be mounted and supplied to the injection member 10 with a pump or the like. In this case, the cylinder and the pump constitute a carrier gas supply source. However, if the exhaust gas is used as the carrier gas, the amount of gas flowing into the SCR catalyst 5 does not increase. Therefore, according to the configuration of this embodiment, the configuration after the SCR catalyst 5 does not need to be increased in size.
In this embodiment, one each of the first distribution path 11 and the second distribution path 12 are provided, but a plurality of them may be provided, and the first distribution path 11 and the second distribution path 12 may not be the same number. It suffices if they are arranged so as to collide with each other. Further, the first flow path 11 and the second flow path 12 may have different channel cross-sectional areas.

  In this embodiment, the branch pipe 20 branches from the exhaust pipe 2 downstream of the DPF 4 and upstream of the injection member 10, but the present invention is not limited to this form. As long as it is upstream from the injection member 10, it may be branched from any position, and may be branched between the oxidation catalyst 3 and the DPF 4 or upstream from the oxidation catalyst 3. However, since the exhaust gas flowing out from the DPF 4 contains almost no PM because the PM is captured by the DPF 4, according to the configuration of this embodiment, the risk of contaminating or blocking the injection member 10 is reduced. can do.

  DESCRIPTION OF SYMBOLS 1 Diesel engine (internal combustion engine), 2 exhaust pipe, 4 DPF, 5 SCR catalyst, 8 ammonia supply source, 10 injection member, 11 1st flow path, 11a (1st flow path) opening edge part, 12 2nd flow Path, 12a (second flow path) open end, 13 urea water tank (ammonia raw material tank), 14 hydrolysis catalyst, 20 branch pipe (carrier gas supply source).

Claims (7)

An SCR catalyst provided in an exhaust pipe through which exhaust gas discharged from the internal combustion engine flows;
An injection member for injecting ammonia and a carrier gas into the exhaust pipe on the upstream side of the SCR catalyst with respect to the direction in which the exhaust gas flows;
An ammonia supply source for supplying the ammonia to the injection member;
A carrier gas supply source for supplying the carrier gas to the injection member;
The injection member is provided with a first flow path and a second flow path, the ammonia flows through one of the first flow path and the second flow path, and the carrier gas flows through the other, The exhaust gas purifying apparatus in which the ammonia and the carrier gas flowing through the first flow path and the second flow path are injected toward each other in the exhaust pipe.   2. The exhaust gas purification device according to claim 1, wherein the first circulation path and the second circulation path are arranged in a positional relationship so as to be upstream and downstream in a direction in which the exhaust gas flows.   The said 1st distribution path and the said 2nd distribution path each have an opening edge part opened in the said exhaust pipe, and each opening edge part inclines in the direction which goes mutually, The Claim 1 or 2 Exhaust gas purification device.   The exhaust gas purification device according to claim 1 or 2, wherein each of the first flow path and the second flow path is inclined in a direction toward each other. The carrier gas supply source is a branch pipe that branches from the exhaust pipe on the upstream side of the injection member with respect to the direction in which the exhaust gas flows in the exhaust pipe,
The carrier gas is an exhaust gas flowing through the branch pipe;
The exhaust gas purification device according to any one of claims 1 to 4, wherein the branch pipe is connected to one of the first flow path and the second flow path where the ammonia does not flow.   The exhaust gas purification apparatus according to any one of claims 5 to 6, wherein a DPF is provided in the exhaust pipe upstream of the branch pipe in a direction in which the exhaust gas flows. The ammonia supply source is
An ammonia raw material tank for storing ammonia raw material;
The exhaust gas purification apparatus according to any one of claims 1 to 6, further comprising a hydrolysis catalyst that hydrolyzes the ammonia raw material supplied from the ammonia raw material tank into ammonia.

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