JP2010144632A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To promote hydrolysis of a urea aqueous solution by colliding water vapor to the urea aqueous solution injected and supplied to the exhaust upstream side of a NOx reduction catalyst. <P>SOLUTION: In this exhaust emission control device including the NOx reduction catalyst 18 disposed in the exhaust pipe 14 of an engine 10 reducing and cleaning NOx in exhaust gas by using ammonia formed from the urea aqueous solution by hydrolysis, a urea aqueous solution injection nozzle 22 injecting and supplying the urea aqueous solution to the exhaust upstream side, and a urea aqueous solution supply device 26 for atomizing and supplying the urea aqueous solution to the urea aqueous solution injection nozzle 22 according to the engine operation state, the water vapor generated in a water vapor generation device 30 is injected and supplied to the exhaust upstream side of the NOx reduction catalyst 18 from a water vapor injection nozzle 24. The water vapor is made to collide to the urea aqueous solution spray injected and supplied from the urea aqueous solution injection nozzle 22, hydrolysis is performed in a moisture-rich atmosphere, and fission and dispersion of the urea aqueous solution by the collision of the water vapor is promoted to promote hydrolysis. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device that reduces and purifies nitrogen oxides (NOx) in exhaust gas using ammonia generated from an aqueous urea solution by hydrolysis.

As a catalyst purification system for removing NOx contained in engine exhaust, an exhaust purification device described in Japanese Patent Laid-Open No. 2000-27627 (Patent Document 1) has been proposed. This exhaust purification device injects and supplies a urea aqueous solution according to the engine operating state upstream of the NOx reduction catalyst disposed in the exhaust pipe. Then, by using ammonia produced by hydrolysis, NOx in the exhaust gas is selectively reduced by the NOx reduction catalyst to purify NOx into harmless components.
JP 2000-27627 A

  However, if the hydrolysis of the urea aqueous solution does not proceed sufficiently, ammonia corresponding to the engine operating condition is not generated, and the concentration of ammonia in the exhaust gas becomes dark, so that the NOx purification efficiency in the NOx reduction catalyst is only reduced. In addition, unreacted ammonia that has passed through the NOx reduction catalyst may be released into the atmosphere. Furthermore, during the transitional period of engine operation, the urea aqueous solution injection flow rate is large relative to the exhaust temperature and exhaust flow rate, and the hydrolysis does not proceed sufficiently, and only the solvent (water) evaporates. Further, urea crystals may be deposited on the nozzles, and clogging may occur in the nozzle holes of the injection nozzle. If urea crystals are excessively precipitated in the exhaust pipe, the exhaust flow is hindered, leading to an increase in exhaust pressure and a decrease in fuel consumption.

  Therefore, in view of the conventional problems as described above, the present invention provides an exhaust purification device that promotes hydrolysis of urea aqueous solution by colliding water vapor with urea aqueous solution injected and supplied upstream of the NOx reduction catalyst. The purpose is to provide.

  For this reason, in the present invention, the exhaust purification device is disposed in the engine exhaust pipe and uses ammonia produced from the urea aqueous solution by hydrolysis to reduce and purify NOx in the exhaust, upstream of the exhaust. A urea aqueous solution injection nozzle that injects and supplies urea aqueous solution, a urea aqueous solution supply device that atomizes urea aqueous solution according to engine operating conditions and supplies the urea aqueous solution injection nozzle to the urea aqueous solution injection nozzle, and a urea aqueous solution spray that is injected and supplied from the urea aqueous solution injection nozzle A water vapor collision device that collides with water vapor.

  According to the present invention, since the water vapor collides with the urea aqueous solution spray supplied from the urea aqueous solution injection nozzle, the urea aqueous solution spray and the water vapor are mixed, and the urea aqueous solution is hydrolyzed in an atmosphere rich in moisture. . Moreover, since water vapor collides with the urea aqueous solution spray, the division and diffusion of the urea aqueous solution are promoted. These synergistic effects promote the hydrolysis of the urea aqueous solution, and suppress the reduction of NOx purification efficiency in the reduction catalyst, the release of unreacted ammonia, and the increase in exhaust pressure and fuel consumption due to urea crystal precipitation. Can do.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a first embodiment of an exhaust emission control device.
An exhaust pipe 14 connected to the exhaust manifold 12 of the engine 10 includes a nitrogen oxidation catalyst 16 that oxidizes nitrogen monoxide (NO) into nitrogen dioxide (NO ₂ ) along the exhaust circulation direction, and urea by hydrolysis. A NOx reduction catalyst 18 that selectively reduces and purifies NOx using ammonia generated from an aqueous solution, and an ammonia oxidation catalyst 20 that oxidizes ammonia that has passed through the NOx reduction catalyst 18 are arranged in this order. The exhaust pipe 14 positioned between the nitrogen oxidation catalyst 16 and the NOx reduction catalyst 18 has a urea aqueous solution injection nozzle 22 for supplying and supplying a urea aqueous solution, and a water vapor injection nozzle for supplying and supplying water vapor that promotes hydrolysis of the urea aqueous solution. 24, respectively. The attachment position of the water vapor injection nozzle 24 may be either upstream or downstream of the urea aqueous solution injection nozzle 22 as long as it is upstream of the NOx reduction catalyst 18.

  The urea aqueous solution injection nozzle 22 is connected to a urea aqueous solution tank 28 that stores the urea aqueous solution via an urea aqueous solution supply device 26 that incorporates an electric pump that sucks and pumps the urea aqueous solution and a flow rate control valve that controls the injection supply flow rate. Communication connection. In addition, the water vapor injection nozzle 24 heats water with an electric heater and generates a water vapor through a water vapor generator 30 that generates water vapor and a flow rate control valve 32 that controls a supply flow rate of the generated water vapor. The water tank 34 which stores the water to be communicated is connected. The urea aqueous solution supply device 26 pumps the urea aqueous solution sucked from the urea aqueous solution tank 28 to the urea aqueous solution injection nozzle 22 while atomizing.

  A temperature sensor 36 for measuring the exhaust temperature is attached to the exhaust pipe 14 positioned between the nitrogen oxidation catalyst 16 and the urea aqueous solution injection nozzle 22. The output signal of the temperature sensor 36 is input to a reducing agent addition control unit (hereinafter referred to as “reducing agent addition ECU”) 38 having a built-in computer. The reducing agent addition ECU 38 is, for example, an engine control unit (hereinafter referred to as “engine ECU”) 40 that electronically controls the engine 10 via, for example, a CAN (Controller Area Network) to read the engine rotation speed and the fuel injection flow rate as appropriate. Connected. The reducing agent addition ECU 38 controls the urea aqueous solution supply device 26 and the flow rate control according to the engine operating state (engine rotational speed, fuel injection flow rate and exhaust temperature) according to a control program stored in a ROM (Read Only Memory) or the like. Each valve 32 is electronically controlled.

  Note that the water vapor injection nozzle 24 and the water vapor generation device 30 constitute a water vapor collision device. In addition, the flow control valve 32 and the reducing agent addition ECU 38 constitute a flow control device.

In such an exhaust purification device, the urea aqueous solution spray injected and supplied from the urea aqueous solution injection nozzle 22 into the exhaust pipe 14 is hydrolyzed by the exhaust heat and the water vapor in the exhaust to generate ammonia. This ammonia is selectively reduced with NOx in the exhaust gas in the NOx reduction catalyst 18 and purified to harmless water (H ₂ O) and nitrogen (N ₂ ). At this time, in order to improve the NOx purification efficiency by the NOx reduction catalyst 20, NO is oxidized to NO ₂ by the nitrogen oxidation catalyst 16, and the ratio of NO to NO ₂ in the exhaust gas is improved to be suitable for the reduction reaction. The Further, the ammonia that has passed through the NOx reduction catalyst 18 is oxidized by the ammonia oxidation catalyst 20 disposed downstream of the exhaust gas, so that the ammonia is prevented from being released into the atmosphere as it is.

  Here, since the water vapor injected from the water vapor injection nozzle 24 collides with the urea aqueous solution spray supplied from the urea aqueous solution injection nozzle 22, the urea aqueous solution spray and the water vapor are mixed, and the moisture is rich. The urea aqueous solution is hydrolyzed in the atmosphere. Further, since the water vapor collides with the urea aqueous solution spray, the division and diffusion of the urea aqueous solution are promoted, and the mixing of the urea aqueous solution and the exhaust is promoted. These synergistic effects promote the hydrolysis of the urea aqueous solution, lower the NOx purification efficiency in the NOx reduction catalyst 18, release of unreacted ammonia that could not be treated with the ammonia oxidation catalyst 20, and exhaust due to urea crystal precipitation. An increase in pressure and a decrease in fuel consumption can be suppressed.

FIG. 2 shows a second embodiment of the exhaust purification device. In addition, about the same structure as previous 1st Embodiment, the description is abbreviate | omitted or simplified by attaching | subjecting the same code | symbol.
In the present embodiment, instead of injecting and supplying the steam generated by the steam generator 30 to the exhaust upstream of the NOx reduction catalyst 18, as shown in FIG. And supply the spray. In this way, since the water vapor collides with the urea aqueous solution spray in the internal space of the urea aqueous solution supply device 26 having a smaller cross-sectional area than the exhaust pipe 14, the division and diffusion can be further promoted. Since other operations and effects are the same as those in the first embodiment except for the promotion of mixing of the urea aqueous solution and the exhaust gas, refer to the description thereof.

  By the way, in the water vapor generator 30, water is heated by an electric heater to generate water vapor. In order to reduce the energy required for steam generation, it is desirable to provide a preheating device that preheats the water supplied from the water tank 34 to the steam generation device 30 with the heat of the engine 10. As an example of this preheating device, for example, a pipe connecting the water tank 34 and the water vapor generating device 30 may be routed around the engine to exchange heat with the engine 10.

Overall configuration diagram showing a first embodiment of an exhaust purification device Whole block diagram which shows 2nd Embodiment of exhaust gas purification device Sectional drawing of the principal part of the urea aqueous solution supply apparatus in 2nd Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 14 Exhaust pipe 18 NOx reduction catalyst 22 Urea aqueous solution injection nozzle 24 Water vapor injection nozzle 26 Urea aqueous solution supply device 28 Urea aqueous solution tank 30 Water vapor generation device 32 Flow control valve 34 Water tank 38 Reductant addition ECU

Claims (4)

A reduction catalyst that is disposed in the engine exhaust pipe and reduces and purifies nitrogen oxides in the exhaust gas using ammonia generated from the aqueous urea solution by hydrolysis;
A urea aqueous solution injection nozzle for supplying an aqueous urea solution to the exhaust upstream of the reduction catalyst;
A urea aqueous solution supply device that atomizes a urea aqueous solution according to the engine operating state and supplies the urea aqueous solution to the urea aqueous solution injection nozzle;
A water vapor collision device for making water vapor collide with the urea aqueous solution spray supplied from the urea aqueous solution injection nozzle;
An exhaust emission control device comprising: The water vapor collision device is:
A water vapor injection nozzle that injects water vapor upstream of the reduction catalyst;
A steam generator for heating water with an electric heater to generate steam;
A flow rate control device for controlling a flow rate of water vapor supplied from the water vapor generation device to the water vapor injection nozzle according to an engine operating state;
Comprising
The exhaust gas purification apparatus according to claim 1, wherein the water vapor sprayed from the water vapor spray nozzle collides with the urea water spray sprayed from the urea aqueous solution spray nozzle. The water vapor collision device is:
A steam generator for heating water with an electric heater to generate steam;
A flow rate control device for controlling the flow rate of water vapor supplied from the water vapor generation device according to the engine operating state;
Comprising
The exhaust gas purification apparatus according to claim 1, wherein water vapor whose flow rate is controlled by the flow rate control device collides with the urea aqueous solution spray inside the urea aqueous solution supply device.   The exhaust emission control device according to claim 2 or 3, further comprising a preheating device for preheating water supplied to the water vapor generating device with heat of an engine.

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