JP2008180202A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accelerate diffusion of a liquid reducer or its precursor supplied by injection into exhaust gas. <P>SOLUTION: A reducer injection nozzle 14 for properly supplying by injection an urea water solution stored in a reducer tank 24 and an air injection nozzle 32 for properly supplying by injection compressed air stored in an air reservoir 30 toward the urea water solution are respectively disposed on an exhaust upstream side of a NOx reduction catalyst 16 which reduces and controls emission of nitrogen oxides (NOx) by using the urea water solution as the precursor of the liquid reducer. The compressed air supplied by injection from the air injection nozzle 32 is made to collide against the urea water solution supplied by injection from the reducing agent injection nozzle 14. With this, urea is inhibited from being separated out on the inner wall of an exhaust pipe 10 while facilitating atomization and diffusion of the urea water solution and its mixing with exhaust gas and improving efficiency of NOx emission control. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust purification apparatus that reduces and purifies nitrogen oxides (NOx) in exhaust using a reducing agent, and particularly relates to a technique for promoting diffusion of a liquid reducing agent injected into the exhaust or its precursor. .

As a catalyst purification system for removing NOx in engine exhaust, an exhaust purification device described in Japanese Patent Laid-Open No. 2000-27627 (Patent Document 1) has been proposed. Such an exhaust purification device injects and supplies a liquid reducing agent or a precursor thereof according to the engine operating state to the exhaust upstream of the NOx reduction catalyst disposed in the exhaust pipe, so that NOx in the exhaust in the NOx reduction catalyst can be reduced. A catalytic reduction reaction with a reducing agent is performed to purify NOx into harmless components.
JP 2000-27627 A

  However, in the conventionally proposed technology, if the liquid reducing agent or its precursor does not diffuse substantially uniformly in the exhaust gas, the concentration of the reducing agent supplied to the NOx reduction catalyst becomes uneven, so that the NOx purification efficiency only decreases. However, the reducing agent may be released into the atmosphere as it is. Further, depending on the engine operating state, it is also assumed that only the solvent evaporates from the liquid reducing agent or its precursor adhering to the inner wall of the exhaust pipe, and the solute of the liquid reducing agent or its precursor is precipitated. If the solute of the liquid reducing agent or its precursor is deposited on the inner wall of the exhaust pipe, the exhaust flow is hindered, which may cause problems such as increased exhaust pressure and reduced fuel consumption.

  Therefore, in view of the conventional problems as described above, the present invention causes the liquid reducing agent or its precursor to collide with the liquid reducing agent or its precursor injected and supplied upstream of the exhaust of the NOx reduction catalyst. An object of the present invention is to provide an exhaust purification device that promotes diffusion of precursors and suppresses NOx purification efficiency reduction and solute precipitation.

  Therefore, in the first aspect of the present invention, a reduction catalyst that is disposed in the exhaust pipe and reduces and purifies nitrogen oxides using a reducing agent, and a liquid reducing agent or a precursor thereof is injected upstream of the reduction catalyst. A reducing agent injection nozzle to be supplied; and an air injection nozzle for supplying and supplying compressed air toward the liquid reducing agent injected from the reducing agent injection nozzle or a precursor thereof. To do.

The invention according to claim 2 is characterized in that a diffusion plate is disposed in an exhaust pipe located between the reducing agent injection nozzle and the air injection nozzle and the reduction catalyst.
According to a third aspect of the present invention, the reducing agent injection nozzle injects and supplies the liquid reducing agent or a precursor thereof in a direction that makes an acute angle with respect to the exhaust circulation direction, and the air injection nozzle is in the exhaust circulation direction. Compressed air is injected and supplied in a direction that forms an acute angle.

According to a fourth aspect of the present invention, the air injection nozzle injects and supplies compressed air toward a liquid reducing agent or a precursor thereof from a position facing the reducing agent injection nozzle.
The invention according to claim 5 is characterized in that the reducing agent injection nozzle injects and supplies only a liquid reducing agent or a precursor thereof.

  According to the first aspect of the present invention, since the compressed air is injected and supplied toward the liquid reducing agent or the precursor thereof injected and supplied upstream of the exhaust of the reduction catalyst, the liquid reducing agent or the precursor thereof and the compressed air Impinges and promotes atomization, diffusion and mixing with exhaust. For this reason, the nonuniformity of the reducing agent concentration supplied to the reduction catalyst is reduced, and the purification efficiency of nitrogen oxides can be improved while suppressing the reducing agent release. Moreover, since the absolute amount of the liquid reducing agent or its precursor adhering to the inner wall of the exhaust pipe is drastically reduced, solute deposition of the liquid reducing agent or its precursor on the inner wall of the exhaust pipe can be suppressed.

According to the invention of claim 2, since the exhaust gas containing the reducing agent is diffused substantially uniformly by the diffusion plate, the unevenness of the reducing agent concentration supplied to the reduction catalyst is drastically reduced, while reducing the reducing agent release, Nitrogen oxide purification efficiency can be further improved.
According to the third aspect of the present invention, the liquid reducing agent or its precursor and the compressed air are each injected and supplied in a direction that forms an acute angle with respect to the exhaust flow direction, so that the exhaust flow in the exhaust pipe is prevented from being hindered. it can.

According to invention of Claim 4, since compressed air is injected and supplied from the position facing the injection supply direction of the liquid reducing agent or its precursor, the atomization, diffusion, and mixing with exhaust are performed effectively. be able to.
According to the invention described in claim 5, since the consumption of compressed air is suppressed, for example, it is possible to reduce the size of an air reservoir that supplies compressed air.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an overall configuration of an exhaust purification apparatus that uses a urea aqueous solution as a precursor of a liquid reducing agent and reduces and purifies NOx contained in engine exhaust by a catalytic reduction reaction.
The engine exhaust pipe 10 includes a nitrogen oxidation catalyst 12 that oxidizes nitric oxide (NO) into nitrogen dioxide (NO ₂ ) along the exhaust flow direction, and urea in a direction that forms an acute angle with the exhaust flow direction. A reducing agent injection nozzle 14 that injects and supplies an aqueous solution, an NOx reduction catalyst 16 that reduces and purifies NOx using ammonia obtained by hydrolyzing an aqueous urea solution, and an ammonia oxidation that oxidizes ammonia that has passed through the NOx reduction catalyst 16 A catalyst 18 is provided. The reducing agent injection nozzle 14 is stored in a reducing agent tank 24 via a reducing agent addition device 22 electronically controlled by a reducing agent addition control unit (hereinafter referred to as “reducing agent addition ECU”) 20 having a built-in computer. An aqueous urea solution is supplied. The reducing agent addition ECU 20 is connected to an engine control unit (hereinafter referred to as “engine ECU”) 26 via an in-vehicle network such as a CAN (Controller Area Network) in order to appropriately read the engine rotation speed Ne and the fuel injection amount Q. The Further, an exhaust temperature sensor 28 for detecting an exhaust temperature T is attached to the exhaust pipe 10 positioned between the nitrogen oxidation catalyst 12 and the reducing agent injection nozzle 14.

In such an exhaust purification device, the urea aqueous solution injected and supplied from the reducing agent injection nozzle 14 is hydrolyzed by the exhaust heat and water vapor in the exhaust, and converted into ammonia. It is known that the converted ammonia undergoes a reduction reaction with NOx in the exhaust gas in the NOx reduction catalyst 16 and is converted into water (H ₂ O) and nitrogen (N ₂ ). At this time, in order to improve the NOx purification efficiency by the NOx reduction catalyst 16, NO is oxidized to NO ₂ by the nitrogen oxidation catalyst 12, improvements to what ratio between NO and NO ₂ in the exhaust gas suitable for catalytic reduction reaction Is done. On the other hand, ammonia that has passed through the NOx reduction catalyst 16 is oxidized by the ammonia oxidation catalyst 18 disposed downstream of the exhaust gas, so that ammonia is prevented from being released into the atmosphere as it is.

  As a feature of the present invention, as shown in detail in FIG. 2, the exhaust pipe 10 at a position facing the reducing agent injection nozzle 14 is supplied to the air reservoir 30 toward the urea aqueous solution injected from the reducing agent injection nozzle 14. An air injection nozzle 32 for supplying the stored compressed air is provided. As with the reducing agent injection nozzle 14, the air injection nozzle 32 injects and supplies compressed air in a direction that forms an acute angle with respect to the exhaust flow direction. Further, in order to control the flow rate of the compressed air supplied and supplied from the air injection nozzle 32, an electromagnetic opening and closing electronically controlled by the reducing agent addition ECU 20 is connected to the pipe 34 that connects the air reservoir 30 and the air injection nozzle 32. A valve 36 is interposed. Further, a diffusion plate 38 as shown in FIG. 3 is disposed in the exhaust pipe 10 located between the reducing agent injection nozzle 14 and the air injection nozzle 32 and the NOx reduction catalyst 16 in order to diffuse the fluid substantially uniformly. Is done.

FIG. 4 shows the contents of a control program that is repeatedly executed every predetermined time in the reducing agent addition ECU 20 when the engine is started.
In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the engine speed Ne is read from the engine ECU 26.
In step 2, the fuel injection amount Q is read from the engine ECU 26.

In step 3, the exhaust temperature T is read from the exhaust temperature sensor 28.
In step 4, the urea aqueous solution addition amount corresponding to the engine rotational speed Ne, the fuel injection amount Q, and the exhaust temperature T is referred to with reference to a map in which the urea aqueous solution addition amount corresponding to the engine rotational speed, the fuel injection amount, and the exhaust temperature is set. Is calculated.
In Step 5, it is determined whether or not the urea aqueous solution addition amount is larger than 0, that is, whether or not the urea aqueous solution should be added. If the urea aqueous solution addition amount is greater than 0, the process proceeds to step 6 (Yes), while if the urea aqueous solution addition amount is 0, the present processing is terminated (No).

In step 6, a control signal corresponding to the urea aqueous solution addition amount is output to the reducing agent adding device 22 in order to inject and supply the urea aqueous solution from the reducing agent injection nozzle 14.
In step 7, a control signal is output to the on-off valve 36 in order to inject and supply compressed air from the air injection nozzle 32. Here, it is desirable that the control signal output to the on-off valve 36 is a control signal corresponding to the urea aqueous solution addition amount so as to suppress the consumption amount of compressed air as much as possible.

  According to such a control program, a urea aqueous solution corresponding to the engine operating state is injected and supplied to the exhaust pipe 10, and compressed air is injected and supplied toward the urea aqueous solution. For this reason, the urea aqueous solution injected and supplied from the reducing agent injection nozzle 14 collides with the compressed air, the atomization, diffusion and mixing with the exhaust are promoted, and hydrolysis to ammonia is efficiently performed. At the same time, the absolute amount of the urea aqueous solution adhering to the inner wall of the exhaust pipe 10 is drastically reduced, and precipitation of urea as the solute is suppressed. At this time, since the urea aqueous solution and the compressed air are intermittently injected and supplied according to the engine operating state, the consumption can be suppressed as much as possible. Further, since the exhaust gas containing ammonia as the reducing agent is diffused substantially uniformly by the diffusion plate 38, the unevenness of the ammonia concentration supplied to the NOx reduction catalyst 16 is drastically reduced, and the NOx purification efficiency is suppressed while suppressing ammonia release. Can be improved.

  Since the reducing agent injection nozzle 14 and the air injection nozzle 32 inject and supply the urea aqueous solution and the compressed air in directions that form an acute angle with respect to the exhaust circulation direction, the exhaust flow in the exhaust pipe 10 is not hindered. Moreover, since the air injection nozzle 32 injects and supplies compressed air toward the urea aqueous solution from a position facing the reducing agent injection nozzle 14, the atomization, diffusion and mixing with the exhaust can be performed efficiently. .

Note that the present invention is not limited to a spray that supplies a mixture of urea aqueous solution and compressed air from the reducing agent injection nozzle 14 but can be applied to only a urea aqueous solution in a droplet state. In the case where only the urea aqueous solution is injected and supplied, the amount of compressed air consumed is further suppressed, and therefore, for example, the air reservoir can be downsized.
In addition, the reducing agent is not limited to the urea aqueous solution as a precursor, but an ammonia aqueous solution is used, or alcohol, light oil or the like mainly containing hydrocarbons is used according to the NOx reduction mechanism in the NOx reduction catalyst 16. be able to.

  Furthermore, it goes without saying that the present invention is applicable not only to an internal combustion engine such as an engine but also to an external combustion engine such as a boiler and a turbine.

The block diagram which shows an example of the exhaust gas purification device which actualized this invention The main part of this invention is shown, (A) is a longitudinal cross-sectional view of an exhaust pipe, (B) is the cross-sectional view. A perspective view showing an example of a diffusion plate Flow chart showing processing contents of control program

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exhaust pipe 14 Reducing agent injection nozzle 16 NOx reduction catalyst 32 Air injection nozzle 38 Diffusion plate

Claims (5)

A reduction catalyst disposed in the exhaust pipe for reducing and purifying nitrogen oxides using a reducing agent;
A reducing agent injection nozzle that injects and supplies a liquid reducing agent or a precursor thereof upstream of the exhaust of the reduction catalyst;
An air injection nozzle for supplying and supplying compressed air toward the liquid reducing agent supplied from the reducing agent injection nozzle or a precursor thereof;
An exhaust emission control device comprising:   The exhaust emission control device according to claim 1, wherein a diffusion plate is disposed in an exhaust pipe located between the reducing agent injection nozzle and the air injection nozzle and the reduction catalyst. The reducing agent injection nozzle injects and supplies a liquid reducing agent or a precursor thereof in a direction that forms an acute angle with respect to the exhaust flow direction,
The exhaust emission control device according to claim 1 or 2, wherein the air injection nozzle injects and supplies compressed air in a direction that forms an acute angle with respect to an exhaust flow direction.   The said air injection nozzle injects and supplies compressed air toward the liquid reducing agent or its precursor from the position facing the said reducing agent injection nozzle, The any one of Claims 1-3 characterized by the above-mentioned. Exhaust gas purification device described in 1.   The exhaust emission control device according to any one of claims 1 to 4, wherein the reducing agent injection nozzle injects and supplies only a liquid reducing agent or a precursor thereof.

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