WO2006061943A1

WO2006061943A1 - Exhaust gas purification apparatus

Info

Publication number: WO2006061943A1
Application number: PCT/JP2005/018292
Authority: WO
Inventors: Yuji Yajima
Original assignee: Nissan Diesel Motor Co., Ltd.
Priority date: 2004-12-07
Filing date: 2005-10-03
Publication date: 2006-06-15
Also published as: JP2006161672A; JP4290114B2

Abstract

This invention provides an exhaust gas purification apparatus characterized by having such a structure that comprises a nozzle for jetting a liquid reducing agent toward the upstream of exhaust gas in a reducing catalyst provided in an exhaust system, a jetting amount control valve for regulating the jetting amount of the liquid reducing agent jetted from the nozzle, and a pressure device for supplying the liquid reducing agent supplied from a storage tank to a jetting amount control valve after exposure to a high-pressure gas having a pressure above the atmospheric pressure. A larger amount of gas is dissolved in a liquid reducing agent under a higher pressure, and, upon jetting into the exhaust gas, a pressure drop and a temperature rise cause rapid separation of the dissolved gas. In this case, atomization of the liquid reducing agent is accelerated by the expansion power, and the atomized reducing agent is homogeneously dispersed in the exhaust gas.

Description

Specification

Exhaust purification equipment

Technical field

The present invention relates to an exhaust purification device that removes nitrogen oxides (NOx) contained in exhaust gas, and more particularly to an exhaust purification device that employs selective catalytic reduction (SCR).

Background art

[0002] As an exhaust purification device that removes NOx contained in exhaust gas, an exhaust purification device employing SCR as disclosed in Patent Document 1 has been proposed.

In this exhaust purification device, a reduction catalyst is disposed in the exhaust system, and a reducing agent is injected from the nozzle upstream of the reduction catalyst and added to cause a catalytic reduction reaction between NOx in the exhaust and the reducing agent. NOx is treated as a harmless component. The reduction reaction uses ammonia that has good reactivity with NOx, and as a reducing agent therefor, an aqueous urea solution or aqueous ammonia solution that easily generates ammonia by hydrolysis with exhaust heat and water vapor in the exhaust. Alternatively, a liquid reducing agent such as HC is used.

Patent Document 1: Japanese Patent Laid-Open No. 2003-293740

Disclosure of the invention

Problems to be solved by the invention

[0003] In the exhaust gas purification apparatus as in the above prior art, when the liquid reducing agent is injected into the exhaust gas by the nozzle and the injected liquid reducing agent is not evenly dispersed in the exhaust gas, the liquid reducing agent in the exhaust gas Due to unevenness in concentration, it is not possible to obtain sufficient reducing agent utilization efficiency and NOx reduction efficiency in the reduction catalyst.

Accordingly, an object of the present invention is to provide an exhaust purification device having a structure in which a liquid reducing agent can be well dispersed in exhaust gas.

Means for solving the problem

[0004] An exhaust emission control device according to the present invention is provided in an exhaust system, and reduces and purifies nitrogen oxides in exhaust gas with a liquid reducing agent, and injects the liquid reducing agent upstream of the exhaust of the reducing catalyst. And an injection amount control for adjusting the injection amount of the liquid reducing agent injected from the nozzle. And a pressurizing device that sends the liquid reducing agent sent from the storage tank to the injection amount control valve after being exposed to a high-pressure gas having a pressure higher than atmospheric pressure. It is characterized by that.

[0005] Normally, the atmospheric pressure in the tank for storing the liquid reducing agent is maintained at atmospheric pressure by a breather. Therefore, the liquid reducing agent sent to the storage tank force injection amount control valve is a gas under atmospheric pressure. Is dissolved. In the present invention, focusing on this point, if more gas is dissolved in the liquid reducing agent at a higher pressure, when the liquid reducing agent is injected into the exhaust gas, the pressure decreases and the temperature increases. The idea was that rapid precipitation of the dissolved gas occurred and the expansion force promoted the fine particles of the liquid reducing agent and allowed it to be evenly dispersed in the exhaust. Therefore, a pressurizing device is provided so that the liquid reducing agent is exposed to a high-pressure gas having a pressure higher than the atmospheric pressure, so that more gas is dissolved and sent to the injection amount control valve. When high pressure is applied, more gas dissolves in the liquid reducing agent. Henry's law (at constant temperature, the mass of a gas dissolved in a certain amount of solvent is proportional to the pressure, and the volume of the gas is independent of the pressure. The component of the gas mixture is dissolved in proportion to the partial pressure).

[0006] The high-pressure gas may be generated by taking in air and compressing it. However, in the present invention, the high-pressure gas contains a large amount of carbon dioxide having good solubility in a liquid as the high-pressure gas. Recalling the use of exhaust. In other words, the pressurizing device can pressurize the exhaust gas after purification into a high-pressure gas.

Such a pressurizing apparatus includes a compressor that takes in and compresses gas, a high-pressure tank that stores the gas sent out from the compressor, and a pressure-feed pump that sends a liquid reducing agent into the high-pressure tank. And good. More preferably, since the solubility of gas generally becomes smaller as the temperature becomes higher, in order to reduce the temperature in the high-pressure tank as much as possible, a high-pressure gas cooler that cools the gas compressed by the compressor may be provided. When exhaust is used as a good gas, the exhaust may be cooled by an exhaust cooler before the exhaust is taken into the compressor. In order to maintain cleanliness, it is also preferable that the compressor take in gas through a filter.

[0007] Further, the pressurizing device includes a pressure sensor that detects the atmospheric pressure in the high-pressure tank, and a pressure controller that controls the compressor according to the output of the pressure sensor to keep the atmospheric pressure in the high-pressure tank constant. It can also be provided. In addition to this, a level sensor that detects the liquid level of the liquid reducing agent in the high-pressure tank, and according to the output of the level sensor, controls the pressure feed pump to keep the amount of liquid reducing agent in the high-pressure tank constant. A liquid level controller. As a result, the amount of dissolved gas can be stabilized by keeping the gas pressure and the amount of liquid reducing agent constant in the high-pressure tank.

The invention's effect

[0008] According to the exhaust gas purification apparatus provided with the pressurizing device of the present invention, the liquid reducing agent in which a large amount of gas is dissolved by pressurization is injected from the nozzle, so the liquid reducing agent injected from the nozzle into the exhaust gas The pressure drop and the temperature rise force cause rapid precipitation of dissolved gas, and the expansion force promotes atomization of the liquid reducing agent. As a result, the liquid reducing agent can be evenly dispersed in the exhaust gas, and the reducing agent utilization efficiency and NOx reduction efficiency in the reduction catalyst can be further improved.

Brief Description of Drawings

FIG. 1 is a schematic view showing a first embodiment of an exhaust emission control device according to the present invention.

FIG. 2 is a control flowchart of the pressure controller.

FIG. 3 is a control flowchart of the liquid level controller.

FIG. 4 is a schematic view showing a second embodiment of the exhaust gas purification apparatus according to the present invention. Explanation of symbols

[0010] 20 Pressurizing device

21 Compressor

22 High pressure tank

23 Pressure pump

24 Huinoleta

25 High pressure gas cooler

26 Pressure sensor

27 Level sensor

28 Pressure controller

29 Liquid level controller 30 Exhaust cooler

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] FIG. 1 shows a first embodiment of an exhaust purification apparatus according to the present invention. The illustrated exhaust purification system is composed of an oxidation catalyst 1, a NOx reduction catalyst 2 and an NH slip catalyst interposed in the exhaust system.

Three

It has three. The NOx reduction catalyst 2 causes the NOx in the exhaust gas to undergo a catalytic reduction reaction with the liquid reducing agent, and the liquid reducing agent is injected from the nozzle 4 and added to the upstream side of the NOx reduction catalyst 2 exhaust. An injection amount control valve 5 for supplying an appropriate amount of liquid reducing agent to the nozzle 4 is provided. The injection amount control valve 5 is provided with an exhaust temperature detected by the exhaust temperature sensors 6 and 7, and an engine rotation obtained from the ECU 8 of the engine. It is controlled by ECU9 according to the speed.

Various liquid reducing agents as described above, such as urea aqueous solution, are stored in a tank 10, and the inside of the tank 10 is maintained at atmospheric pressure by a breather 11.

The pressurizing device 20 of the first embodiment includes a compressor 21, a high-pressure tank 22, and a pumping pump 23. Further, a filter 24 is interposed at the gas inlet of the compressor 21, and a high-pressure gas cooler 25 is interposed between the compressor 21 and the high-pressure tank 22.

[0013] The compressor 21 of the present embodiment takes in air as gas through the filter 24, compresses it, and sends out compressed air at a predetermined pressure. The compressed air sent out from the compressor 21 is cooled by the high-pressure gas cooler 25 and then sent to the high-pressure tank 22 in order to suppress the temperature rise. On the other hand, the pressure pump 23 sucks out the liquid reducing agent stored in the tank 10 and sends it out into the high-pressure tank 22. Since the inside of the high-pressure tank 10 is maintained at a pressure higher than the atmospheric pressure, the liquid reducing agent is injected by applying pressure by the pressure feed pump 23.

[0014] The liquid reducing agent that has entered the high-pressure tank 22 is exposed to the high-pressure gas inside it, so that more air is dissolved, and is sent to the injection amount control valve 5 through the pipe P. Injected into force exhaust. When the liquid reducing agent is injected into the exhaust gas, the dissolved air abruptly precipitates due to the pressure drop and temperature rise, and the expansion force promotes atomization of the liquid reducing agent. .

A pressure sensor 26 and a level sensor 27 are installed in the high pressure tank 22 of the spherical pressure vessel of this embodiment, and each output thereof is input to the pressure controller 28 and the liquid level controller 29, respectively. Has been. The pressure controller 28 and the liquid level controller 29 maintain the atmospheric pressure and the amount of liquid reducing agent in the high-pressure tank 22 at a constant level, and control the amount of air dissolved in the liquid reducing agent.

[0015] The pressure controller 28 plays a role of maintaining the atmospheric pressure in the high-pressure tank 22 constant by executing the control flow shown in FIG. In other words, after the initialization is started when the idling switch is turned on, the compressor 21 is turned off at step S1, and it is confirmed whether the engine is operated at step S2. As a result, if the engine is not yet operated, the process returns to step S1 and the process is repeated. On the other hand, if the engine is operated, the process proceeds to step S3, and it is checked from the output value of the pressure sensor 26 whether the atmospheric pressure in the high pressure tank 22 has reached the specified value. As a result, if the atmospheric pressure exceeds the specified value, the process returns to step S1 to turn off the compressor 21 so that the tank atmospheric pressure does not become higher than necessary. On the other hand, if the air pressure is not more than the specified value, the process proceeds to step S4 to operate the compressor 21, and the process returns to step S3 and remains ON until the atmospheric pressure reaches the specified value.

[0016] The liquid level controller 29 controls the liquid reducing agent liquid level in the high-pressure tank 22 to a constant level by executing the control flow shown in FIG. 3, thereby keeping the amount of liquid reducing agent in the tank constant. maintain. That is, after the initial switch is started when the idling switch is turned on, the pumping pump 23 is turned off at step S10, and it is confirmed whether the engine is operated at step S11. As a result, if the engine is not yet operated, the process returns to step S10 and the process is repeated. On the other hand, if the engine is operated, the process proceeds to step S12, and the level sensor 27 detects whether the level of the liquid reducing agent in the high-pressure tank 22 is detected by the level sensor 27 from the output value of the level sensor 27. Check if the liquid level has reached the 27 position. As a result, if it is detected, the process returns to step S10 to turn off the pressure pump 23 so that the amount of reducing agent in the tank does not increase more than necessary. On the contrary, if the liquid level is not sensed, the process proceeds to step S13 to operate the pressure feed pump 23, and the process returns to step S12 to keep it on until the liquid level is detected.

[0017] In the first embodiment described above, air is compressed and used as a high-pressure gas, but it is also possible to use, as a gas, exhaust gas that contains a larger amount of carbon dioxide that is easily dissolved in a liquid. is there. A second embodiment using this exhaust is shown in FIG. The second embodiment shown in FIG. 4 has the same configuration as that of the first embodiment, except that in the pressurizing device 20, the exhaust gas is sent to the compressor 21 via the filter 24.

The pressurizing device 20 of the second embodiment takes in the exhaust gas that has passed through the NH slip catalyst 3 and cools it.

Three

An exhaust cooler 30 is provided. Then, the exhaust gas after being cooled by the exhaust cooler 30 is sent to the compressor 21 through the filter 24. Since the exhaust gas is hot as it is, it is preferable to cool it with the exhaust cooler 30 and send the power to the compressor 21 as well, but since it has a high-pressure gas cooler 25, it does not cool the exhaust gas through the filter 24. A configuration to capture is also possible.

Since other configurations are the same as those of the first embodiment, description thereof is omitted.

Claims

The scope of the claims

[1] A reduction catalyst that is disposed in the exhaust system and reduces and purifies nitrogen oxides in the exhaust with a liquid reducing agent;

A nozzle for injecting the liquid reducing agent upstream of the exhaust of the reduction catalyst;

The injection amount control valve for controlling the injection amount of the liquid reducing agent injected from the nozzle and the liquid reducing agent sent from the storage tank are exposed to a high-pressure gas having a pressure higher than atmospheric pressure. A pressurizing device to be sent to the injection amount control valve later;

An exhaust emission control device comprising:

[2] The pressurizing device includes: a compressor that takes in and compresses gas; a high-pressure tank that stores the gas sent from the compressor; and a pressure-feed pump that sends a liquid reducing agent into the high-pressure tank. The exhaust emission control device according to claim 1.

3. The exhaust purification apparatus according to claim 2, wherein the pressurizing device further includes a high-pressure gas cooler that cools the gas compressed by the compressor.

4. The exhaust gas purification apparatus according to claim 2, wherein the compressor takes in gas through a filter.

[5] The pressurizing device includes a pressure sensor that detects an atmospheric pressure in the high-pressure tank, a pressure controller that controls the compressor according to an output of the pressure sensor, and maintains the atmospheric pressure in the high-pressure tank constant. The exhaust purification apparatus according to claim 2, further comprising:

[6] The pressurizing device includes a level sensor that detects a liquid level of the liquid reducing agent in the high-pressure tank, and controls the pumping pump according to an output of the level sensor to control the amount of the liquid reducing agent in the high-pressure tank. The exhaust emission control device according to claim 2, further comprising a liquid level controller that keeps the pressure constant.

7. The exhaust emission control device according to claim 2, wherein the pressurizing device uses exhaust gas cooled by an exhaust cooler as the gas compressed by the compressor.