JP4273011B2 - SCR muffler - Google Patents

Description

  The present invention relates to an SCR muffler equipped with an SCR catalyst for selectively reducing and purifying nitrogen oxide (NOx) contained in exhaust gas.

  In recent years, particulate matter (PM) and nitrogen oxides (NOx) contained in exhaust gas discharged from internal combustion engines such as diesel engines have been purified from environmental pollution problems such as acid rain and photochemical smog. The necessity is high.

  Therefore, conventionally, in an SCR muffler provided with a selective reduction SCR (= Selective Catalytic Reduction) catalyst in an exhaust system of an internal combustion engine, urea water or the like is reduced or reduced by a reducing agent supply nozzle from the upstream side. There is a technique in which nitrogen oxide (NOx) contained in exhaust gas is selectively reduced and purified by an SCR catalyst by spraying and supplying an agent precursor to exhaust gas (see, for example, Patent Document 1).

Among such techniques, in particular, there is a technique in which a vent hole such as a punching hole is provided in the exhaust pipe in order to disperse and equalize the flow of the exhaust gas (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 2001-20724 Japanese Utility Model Publication No. 2-115912

  However, in the conventional technology, since the exhaust gas flow is poor, the nitrogen oxide (NOx) purification efficiency during transient operation or the like is low, and the nitrogen oxide (NOx) purification efficiency in the entire low temperature to high temperature region is low. There was a problem of being low.

  In particular, when urea water is supplied as a reducing agent precursor, the flow of exhaust gas is poor, so urea is deposited in an exhaust pipe or the like located upstream of the SCR catalyst, and purification efficiency of nitrogen oxides (NOx) There was a problem that the remarkably deteriorated.

  Therefore, an object of the present invention is to provide an SCR muffler that can improve the flow of exhaust gas and improve the purification efficiency of nitrogen oxide (NOx) contained in the exhaust gas.

In order to solve the above problems, the present invention provides an SCR catalyst for selectively reducing and purifying nitrogen oxide (NOx) contained in exhaust gas, an exhaust pipe for allowing the exhaust gas to flow into the SCR catalyst, In an SCR muffler comprising a reducing agent or the like supply means for supplying a reducing agent or a reducing agent precursor to the exhaust gas , a vent hole is provided in a side portion of the exhaust pipe, and the reducing agent etc. supply means A plate having vent holes for dispersing and equalizing the flow of exhaust gas is provided downstream and upstream of the SCR catalyst, and the plate is attached so as to block the downstream end of the exhaust pipe. And the vent hole provided in the plate has a diameter larger than that of the exhaust pipe, and is disposed only in a region having a diameter larger than that of the exhaust pipe, and in the region of the plate that blocks the downstream end. , the exhaust pipe Wherein the convex portions having a cross section tapering toward the upstream side.

The present invention also provides an SCR catalyst for selectively reducing and purifying nitrogen oxide (NOx) contained in the exhaust gas, and an exhaust gas having a vent hole in the muffler insertion portion, the exhaust gas flowing into the SCR catalyst. a tube, in SCR muffler and a reducing agent, such as a supply means for supplying a reducing agent or a reducing agent precursor to the exhaust gas, with the plate having no vent hole, only the exhaust pipe has peeling infarction, The plate has a cross-sectional shape that is convex toward the upstream side in the exhaust pipe.

  According to the present invention, in the SCR muffler, the flow of exhaust gas can be improved, and the purification efficiency of nitrogen oxides (NOx) contained in the exhaust gas can be improved.

The best mode for carrying out the SCR muffler of the present invention will be described below with reference to the accompanying drawings. The present invention described in claim 1 corresponds to FIG. 4B, and the present invention described in claim 2 corresponds to FIG. Other figures are reference figures of the present invention.

FIG. 1 is a basic model diagram of an SCR muffler .
As shown in FIG. 1, the SCR muffler includes an SCR catalyst 1 for selectively reducing and purifying nitrogen oxide (NOx) contained in exhaust gas, an exhaust pipe 2 for allowing the exhaust gas to flow into the SCR catalyst 1, A reductant supply unit 3 for supplying a reductant or a reductant precursor to the exhaust gas, and the flow of the exhaust gas is dispersed and uniformized downstream of the reductant supply unit 3 and upstream of the SCR catalyst 1 For this purpose, a plate 4 having a vent hole 5 is provided.

  Although FIG. 1 shows the exhaust pipe 2 inserted into the muffler, the exhaust pipe 2 and the muffler are integrally formed without the exhaust pipe 2 being inserted into the muffler. Also good. Moreover, forms, such as a serial type | mold, a parallel type | mold, a round shape, and a cylinder shape, are not ask | required.

Further, in FIG. 1, the plate 4 having air holes 5 (more specifically, the downstream end opening of the exhaust pipe 2) exhaust pipe 2 and are illustrated those which closes both the muffler, the invention is It is not restricted to such a form. That is, in the present invention, the plate 4 having air holes 5, also good in the form of Ru provided downstream end opening of the exhaust pipe 2 adjacent to the SCR catalyst 1, as other forms, such as supply means 3 reducing agent If it is downstream and upstream of the SCR catalyst 1, the plate 4 having the vent holes 5 may be provided in the middle of the exhaust pipe 2, or may be provided in the muffler itself without being provided in the exhaust pipe 2.

Furthermore, as shown in FIG. 2, when the exhaust pipe 2 is inserted into the muffler and has a vent hole in the insertion portion, only the exhaust pipe 2 may be closed with a plate 4 having no vent hole. .

In the SCR muffler having such a configuration, the exhaust gas passes through the exhaust pipe 2 and flows from the upstream side to the downstream side and flows into the SCR catalyst 1.
The exhaust gas, which contain toxic substances discharged from an internal combustion engine such as a diesel engine, specifically, unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen monoxide (NO) or Ru Tei contains nitrogen dioxide (NO ₂₎ nitrogen oxides such as (NOx) is.

  Such exhaust gas is supplied with the reducing agent or the reducing agent precursor by the reducing agent supply means 3 until it flows into the SCR catalyst 1.

  The reducing agent or reducing agent precursor includes not only the reducing agent itself but also a reducing agent precursor such as a substance that liberates the reducing agent, and includes hydrocarbons, cyanuric acid, ammonia, ammonium carbonate, ammonium carbamate, Any substance such as urea may be used, or a plurality of substances may be combined. Further, such a reducing agent or reducing agent precursor may be in any state of solid, liquid, and gas, and a plurality of them may be combined.

For example, the reducing agent, such as a supply unit 3, ammonia itself may be configured to supply as a reducing agent but, ammonia has a strong odor, relatively high due to the high toxicity at concentrations less toxic urea water reducing agent What is spray-fed as a precursor is preferable. When the urea water is sprayed and supplied as a reducing agent precursor in this way, urea in the urea water is brought into contact with the exhaust gas in the exhaust pipe and thermally decomposed or hydrolyzed to release ammonia as a reducing agent. In the SCR muffler described above, through the addition nozzle, it is set to be sprayed for supplying urea water from the exhaust pipe outside the exhaust gas in the exhaust pipe.

  Thereafter, the exhaust gas further flows in the exhaust pipe in the downstream direction, and reaches the plate 4 having the vent holes 5 on the upstream side of the SCR catalyst 1.

Figure 3 is a cross-sectional view of a plate 4 having air holes 5, in the center for closing the exhaust pipe 2 is not placed vents 5, only in the peripheral portion of the region which is larger in diameter than the exhaust pipe outlet, concentric A plurality of circular ventilation holes 5 are arranged in a staggered pattern.

Here, the shape of the vent hole 5 may be any of a circular shape, an elliptical shape, a long hole shape, a fan shape, and other polygonal shapes, but is preferably a punching hole shape. Also good. The size and number of the vent holes 5 may be large or small. The vent holes 5 are preferably arranged in a uniform and contrasting manner, and are preferably arranged only in a region having a larger diameter than the exhaust pipe.

Furthermore , the plate 4 may have any shape such as a circle, an ellipse, a square, and other polygons, and may have any shape such as a flat shape and a convex shape. Moreover, the cross-sectional shape which becomes the convex of the convex plate may be a semicircular shape, a triangular pyramid or the like, and the direction thereof may be a downstream direction, but is preferably an upstream direction. The size of the plate 4 is preferably large enough to close the exhaust pipe 2 and the muffler tube opening, and more preferably larger than the exhaust pipe 2 as described above. Further, the number of the plates 4 may be one or more.

Thus, since the exhaust pipe 2 is completely closed at the center of the plate 4 where the vent hole 5 is not disposed, the exhaust gas flowing through the exhaust pipe and reaching the plate 4 directly passes through the plate 4. Cannot be blocked by the plate surface. For this reason, the exhaust gas passes through the vent hole of the muffler insertion portion of the exhaust pipe 2 and flows out of the exhaust pipe, and then flows through the gap between the muffler and the exhaust pipe 2 and reaches the plate 4 again. Thereafter, the exhaust gas flowing out of the exhaust pipe passes through the peripheral portion of the plate 4 where the vent holes 5 are disposed, and flows into the SCR catalyst 1 on the downstream side thereof. Wherein the nitrogen oxides contained in the exhaust gas (NOx) are adsorbed on the SCR catalyst 1.

The SCR (= Selective Catalytic Reduction) catalyst 1 includes titanium dioxide (TiO ₂ ), vanadium pentoxide (V ₂ O ₅ ), tungsten trioxide (WO ₃ ), molybdenum trioxide (MoO ₃ ), and silicon dioxide (SiO 2). ₂ ), any one of sulfates, zeolites, etc., may be combined. Further, the SCR catalyst 1 may be caged or supported on a catalyst carrier having a honeycomb structure.

  By such an SCR catalyst 1, nitrogen oxide (NOx) contained in the exhaust gas is selectively reduced and purified, and converted into environmentally friendly nitrogen and water.

  Here, the nitrogen oxide (NOx) purification efficiency is affected by the flow of exhaust gas flowing into the SCR catalyst 1.

  FIG. 4 is a diagram showing the flow of exhaust gas flowing into the SCR catalyst 1 in the present embodiment. FIG. 4A shows the flow of exhaust gas when the flat plate 4 having the vent holes 5 is provided. On the other hand, FIG. 4B shows the flow of exhaust gas when the convex plate 4 having the vent holes 5 is provided.

  As shown in FIG. 4, since the exhaust pipe 2 is blocked by the central portion of the plate 4 without the vent hole 5, the exhaust gas cannot pass through the plate 4 directly and passes through the vent hole of the exhaust pipe 2. Then, it flows out of the exhaust pipe, passes through the peripheral portion of the plate 4 with the vent holes 5, and flows into the SCR catalyst 1.

  At this time, the flow of the exhaust gas is dispersed and uniformed by the vent holes 5 of the plate 4, and the flow of the exhaust gas flowing into the SCR catalyst 1 is improved. Note that in FIG. 4B, the flow of exhaust gas is more dispersed and uniform in FIG. 4B than in FIG.

  FIG. 5 is a diagram showing the flow of exhaust gas when only the exhaust pipe 2 is closed with the plate 4 having no air holes, as shown in FIG.

  Also in this case, since the exhaust gas is blocked by the central portion of the plate 4 having no vent hole, it passes through the vent hole of the exhaust pipe 2 and flows out of the exhaust pipe, but the gap between the muffler and the exhaust pipe 2 Is not blocked by the plate 4, the exhaust gas flows into the SCR catalyst 1 without being blocked. For this reason, as shown in FIG. 4, the flow of the exhaust gas is not dispersed and uniformed by the vent holes of the plate, but flows into the SCR catalyst 1 as compared with the case where the plate 4 is not provided. The flow of exhaust gas is improved.

  Thus, when the flow of the exhaust gas flowing into the SCR catalyst 1 is improved, the adsorption rate of the nitrogen oxide (NOx) contained in the exhaust gas to the SCR catalyst 1 is increased, and the purification efficiency of the nitrogen oxide (NOx) is increased. Will improve.

It is a basic model figure (reference figure) of an SCR muffler. It is a model figure (reference drawing) of the SCR muffler when only the exhaust pipe 2 is closed with a plate having no air holes. It is sectional drawing (reference drawing) of the plate 4 which has the vent hole 5. FIG. FIG. 3 is a diagram showing the flow of exhaust gas flowing into the SCR catalyst 1. It is a figure which shows the flow of the exhaust gas which flows in into the SCR catalyst 1 at the time of plugging only the exhaust pipe 2 with the plate 4 which does not have a vent hole.

Explanation of symbols

1 SCR catalyst 2 Exhaust pipe 3 Reducing agent supply means 4 Plate 5 Ventilation hole

Claims (2)

An SCR catalyst for selectively reducing and purifying nitrogen oxide (NOx) contained in exhaust gas;
An exhaust pipe for allowing the exhaust gas to flow into the SCR catalyst;
Supply means such as a reducing agent for supplying a reducing agent or a reducing agent precursor to the exhaust gas;
SCR muffler with
A vent is provided in the side of the exhaust pipe,
A plate having vent holes for dispersing and homogenizing the flow of exhaust gas is provided on the downstream side of the reducing agent supply means and the upstream side of the SCR catalyst,
The plate is attached so as to block the downstream end of the exhaust pipe, and has a larger diameter than the exhaust pipe,
The vent hole provided in the plate is disposed only in a region having a larger diameter than the exhaust pipe,
An SCR muffler characterized in that a convex portion having a cross-sectional shape convex toward the upstream side in the exhaust pipe is provided in a region of the plate that covers the downstream end portion . An SCR catalyst for selectively reducing and purifying nitrogen oxide (NOx) contained in exhaust gas;
An exhaust pipe for causing the exhaust gas to flow into the SCR catalyst and having a vent hole in a muffler insertion portion;
Supply means such as a reducing agent for supplying a reducing agent or a reducing agent precursor to the exhaust gas;
SCR muffler with
A plate having no vent hole, only the exhaust pipe has peeling infarction,
The SCR muffler characterized in that the plate has a cross-sectional shape that is convex toward the upstream side in the exhaust pipe.

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