WO2006003868A1

WO2006003868A1 - Exhaust purifying device

Info

Publication number: WO2006003868A1
Application number: PCT/JP2005/011776
Authority: WO
Inventors: Kiminobu Hirata
Original assignee: Nissan Diesel Motor Co., Ltd.
Priority date: 2004-07-02
Filing date: 2005-06-28
Publication date: 2006-01-12
Also published as: JP4290081B2; JP2006017043A

Abstract

Disclosed is an exhaust purifying device comprising a NOx reduction catalyst which is disposed in an engine exhaust pipe for reducing NOx with a liquid reducer such as an aqueous urea solution, a hot plate arranged in the lower part of the exhaust pipe in the exhaust upstream of the NOx reduction catalyst, an electrothermal heater built in the hot plate, a reducer-adding device for supplying the liquid reducer to the upper surface of the hot plate, and a control unit or thermostat for controlling the electrothermal heater so that the temperature of the hot plate is set at least the melting point of the reducer component or higher. By actively vaporizing and hydrolyzing the liquid reducer supplied to the upper surface of the hot plate, the reducer component can be effectively used while being prevented from precipitation.

Description

Exhaust purification equipment

Technical field

[0001] The present invention relates to an exhaust gas purification apparatus that reduces and purifies nitrogen oxides (NOx) in exhaust gas using a liquid reducing agent, while preventing precipitation of the reducing agent component (solute) and effectively It is about technology to plan utilization.

Background art

[0002] An exhaust purification device disclosed in Japanese Patent Laid-Open No. 2000-27627 (Patent Document 1) has been proposed as a catalyst purification system for removing NOx in engine exhaust. The exhaust purification system is designed to inject NOx and liquid reductant in the exhaust gas by injecting and supplying a liquid reductant according to the engine operating condition to the exhaust upstream of the reduction catalyst installed in the engine exhaust pipe. The catalyst is subjected to a catalytic reduction reaction to purify NOx as a harmless component. Here, the reduction reaction is NO

Ammonia, which has good reactivity with X, is used. As the liquid reducing agent, an aqueous urea solution that generates ammonia by hydrolysis with exhaust heat and water vapor in the exhaust is used. Patent Document 1: JP 2000-27627 A

Disclosure of the invention

Problems to be solved by the invention

Incidentally, it is known that a part of the urea aqueous solution injected and supplied upstream of the reduction catalyst exhaust adheres to the inner wall of the exhaust pipe. Since the exhaust pipe is heated by exhaust heat, moisture (solvent) may evaporate from the urea aqueous solution adhering to the inner wall, and urea as a reducing agent component may be deposited. If the engine load is high, the exhaust pipe temperature rises above the melting point of urea as the exhaust temperature rises, and urea is dissolved and removed. However, if the engine load is low, such as the idling state, for a long time, the exhaust pipe temperature will not rise above the melting point of urea, and the urea deposition will gradually increase!]. Further, when the urea accumulation amount force S increases to some extent, the exhaust resistance increases, and there is a possibility that the fuel consumption and the output decrease due to the increase of the exhaust pressure.

[0004] Therefore, in view of the above-described conventional problems, the present invention provides a hot pop having a built-in electric heater. The liquid reducing agent is supplied to the upper surface of the rate, and the electric heater is controlled so that the hot plate temperature is at least equal to or higher than the melting point of the reducing agent component, thereby preventing precipitation of the reducing agent component and effective use thereof. An object of the present invention is to provide an exhaust purification apparatus.

Means for solving the problem

[0005] Therefore, an exhaust emission control device according to the present invention is provided in an engine exhaust pipe, and a reduction catalyst that reduces and purifies nitrogen oxides with a liquid reducing agent, and a lower part of the exhaust pipe that is located upstream of the reduction catalyst exhaust A hot plate, an electric heater that heats the hot plate, a reducing agent supply device that supplies a liquid reducing agent to the upper surface of the hot plate, and a control unit or thermostat that controls the operation of the electric heater. It is composed of

The invention's effect

[0006] According to the exhaust gas purification apparatus according to the present invention, the liquid reducing agent supplied to the upper surface of the hot plate receives heat from the hot plate heated by the electric heater, and the temperature is equal to or higher than the melting point of the reducing agent component. Raise the temperature. For this reason, since the liquid reducing agent is heated to a temperature higher than the melting point, vaporization and hydrolysis are promoted, and the liquid reducing agent is led to the reduction catalyst while being diffused almost uniformly in the exhaust pipe. On the other hand, the nitrogen oxides in the exhaust gas led to the reduction catalyst through the exhaust pipe are released into the atmosphere as harmless components by the catalytic reduction reaction. Therefore, by actively vaporizing and hydrolyzing the liquid reducing agent supplied to the upper surface of the hot plate, effective use can be achieved while preventing the precipitation of the reducing agent component.

Brief Description of Drawings

FIG. 1 is an overall configuration diagram showing an example of an exhaust purification apparatus to which the present invention is applied.

FIG. 2 is a detailed explanatory view of a hot plate.

FIG. 3 is a flowchart of a control program for controlling the electric heater.

FIG. 4 is an explanatory diagram of a heater output map.

FIG. 5 is a flowchart of a diagnostic program for diagnosing deterioration of the electric heater. Explanation of symbols

[0008] 10 engines 14 Exhaust pipe

18 Additive nozzle

20 NOx reduction catalyst

24: Pioneer Rounoru

26 Reducing agent addition equipment

28 Hot plate

30 plate temperature sensor

32 Electric heater

34 Rotational speed sensor

36 Load sensor

38 Reducing agent temperature sensor

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 shows the overall configuration of an exhaust purification system that uses an aqueous urea solution as the liquid reducing agent and purifies NOx in the engine exhaust by a catalytic reduction reaction.

An exhaust pipe 14 connected to the exhaust manifold 12 of the engine 10 includes an oxidation catalyst 16 that oxidizes nitric oxide (NO) to nitrogen dioxide (NO) along the exhaust circulation direction, and urine.

2

An addition nozzle 18 that drops or sprays the aqueous solution from above to add downward, a NOx reduction catalyst 20 that reduces and purifies NOx with ammonia obtained by hydrolyzing the urea aqueous solution, and a NOx reduction catalyst 20 And an ammonia acid catalyst 22 that acidifies the ammonia that has passed through the catalyst. The addition nozzle 18 is supplied with a urea aqueous solution from a reducing agent container (not shown) via a reducing agent adding device 26 controlled by a control unit 24 having a built-in computer according to the engine operating state. Here, the reducing agent supply device is configured by the cooperation of the reducing agent container, the addition nozzle 18, the control unit 24, and the reducing agent addition device 26.

[0010] In addition, the exhaust pipe 14 positioned below the addition nozzle 18 receives the urea aqueous solution dropped or injected from the addition nozzle 18 and heats it to a melting point temperature (about 132 ° C) or higher. Hot plate made of metal with excellent thermal conductivity that promotes its vaporization and hydrolysis 2 8 is arranged. As shown in FIG. 2, the hot plate 28 includes a plate temperature sensor 30 and an electric heater 32 for detecting the plate temperature Thp.

[0011] As a control system for the electric heater 32 built in the hot plate 28, in addition to the plate temperature sensor 30, a rotational speed sensor 34 for detecting the rotational speed Ne of the engine 10 and a load sensor 36 for detecting the engine load Q And a reducing agent temperature sensor 38 for detecting the urea aqueous solution temperature Tu supplied from the addition nozzle 18 is provided. Here, as the engine load Q, intake air flow rate, intake negative pressure, accelerator opening, throttle opening, fuel injection amount, etc. can be used. The signals of the plate temperature sensor 30, the rotation speed sensor 34, the load sensor 36, and the reducing agent temperature sensor 38 are respectively input to the control unit 24 and are electrically heated by a control program stored in the ROM (Read Only Memory). Heater 32 is controlled.

FIG. 3 shows the contents of a control program that is repeatedly executed at predetermined time intervals in the control unit 24.

In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the rotational speed Ne is read from the rotational speed sensor 34.

In step 2, it is determined whether or not the engine 10 has been started based on the rotational speed Ne, that is, whether or not the rotational speed Ne is greater than 0 (Ne> 0). And if engine 10 starts and goes to step 3 (Yes), engine 10 starts and / or, otherwise NOx in the exhaust does not need to be purified. The process is terminated to avoid excessive energy consumption (No).

[0013] In step 3, the plate temperature Thp of the hot plate 28 is read from the plate temperature sensor 30.

In step 4, it is determined whether or not the plate temperature Thp is less than a predetermined value T. here

0

The predetermined value τ is a temperature slightly higher than the melting point temperature of urea, in other words, at least

0

What is necessary is just to make it more than melting | fusing point temperature. If the plate temperature Thp is less than the predetermined value T,

0

Proceed to step 5 (Yes). On the other hand, if the plate temperature Thp is equal to or higher than the predetermined value T, the step

0

Proceed to step 9 (No), and stop the operation of the electric heater 32 that stops the heating of the hot plate 28. In step 5, the urea aqueous solution temperature Tu is read from the reducing agent temperature sensor 38.

In step 6, the engine load Q is read from the load sensor 36.

In step 7, the heater output according to the urea aqueous solution temperature Tu, the rotational speed Ne, and the engine load Q is calculated with reference to the heater output map as shown in FIG. Here, in the heater output map, a heater output capable of generating heat to compensate for the decrease in the plate temperature Thp when the urea aqueous solution is supplied to the hot plate 28 is set. Further, since the heater output is calculated with reference to the heater output map, the control load required for the heater output calculation can be kept low. When the heater output is set discretely, it is desirable to perform the interpolation calculation using a well-known interpolation technique for improving the control accuracy.

[0015] In step 8, the electric heater 32 is operated based on the calculated heater output.

According to the exhaust gas purifier, the electric heater 32 operates when the plate temperature T hp of the hot plate 28 is lower than the predetermined value T, while the plate temperature Thp is higher than the predetermined value T.

Stop at 0 0. At this time, since the operation of the electric heater 32 is controlled based on the heater output corresponding to the urea aqueous solution temperature Tu, the rotational speed Ne, and the engine load Q, a relatively low temperature urea aqueous solution is supplied to the upper surface of the hot plate 28. However, the plate temperature Thp can be maintained at a predetermined value T or more with the minimum necessary energy. Also, the hot plate 28

0

Since the operation of the electrothermal heater 32 is controlled so that the rate temperature Thp is at least a predetermined value that is the melting point temperature of urea, the urea aqueous solution supplied to the hot plate 28 is reliably and efficiently vaporized and hydrolyzed. Can be decomposed.

[0016] The exhaust gas of the engine 10 is introduced into the NOx reduction catalyst 20 through the exhaust manifold 12, the exhaust pipe 14, and the oxidation catalyst 16. On the other hand, the urea aqueous solution supplied from the addition nozzle 18 to the upper surface of the hot plate 28 is maintained at a temperature equal to or higher than the melting point of urea because the plate temperature Thp of the hot plate 28 is maintained above the melting point of urea. -Is introduced into the NOx reduction catalyst 20 disposed downstream of the exhaust gas. NOx reduction catalyst 20 uses ammonia as a reducing agent, and NOx in the exhaust gas is water (H 2 O) and harmless.

2

It is reduced and purified to a simple gas (nitrogen N, etc.). At this time, NOx purification by NOx reduction catalyst 20

2

NO oxidation into NO by the oxidation catalyst 16 that improves the rate of NO and N in the exhaust The ratio with O is improved to be suitable for the catalytic reduction reaction. In addition, NOx reduction catalyst 20

2

The excess ammonia is acidified by the ammonia acid catalyst 22 disposed downstream of the exhaust gas, so that it is possible to prevent ammonia that emits a strange odor from being released into the atmosphere as it is.

[0017] It should be noted that fins and throttles may be provided around the hot plate 28 to promote diffusion of vaporized and hydrolyzed ammonia. The hot plate 28 preferably has a certain heat capacity so that the plate temperature Thp does not easily decrease even when a relatively low temperature urea aqueous solution is supplied. Furthermore, by making the hot plate 28 detachable from the exhaust pipe 14, it is recommended that when urea is precipitated, it should be removed by washing.

FIG. 5 shows a diagnostic program that is executed repeatedly in parallel with the control program shown in FIG. 3 for diagnosing deterioration of the electric heater 32.

In step 11, the rotational speed Ne is read from the rotational speed sensor 34.

In step 12, it is determined whether or not the engine 10 is started based on the rotational speed Ne. Then, if the engine 10 has been started, the process proceeds to step 13 (Yes), while if the engine 10 has started! /, If not, the process is terminated (No).

In step 13, the engine load Q is read from the load sensor 36.

In step 14, it is determined whether the engine 10 is idling based on the rotational speed Ne and the engine load Q. If it is in the idling state, the process proceeds to step 15 (Yes), but if it is not in the idling state, the process ends (No). Whether the engine is idling or not may be determined based on the opening degree of the throttle valve installed in the intake pipe or the output of the idling switch attached to the throttle valve.

[0020] In step 15, it is determined whether or not the idling state has continued for a predetermined time. If the idling state continues for a predetermined time, the process proceeds to step 16 (Yes), while if the idling state does not continue for the predetermined time, the process ends (No).

In step 16, the plate temperature Thp of the hot plate 28 is read from the plate temperature sensor 30.

In Step 17, it is determined whether or not the plate temperature Thp is less than a predetermined value T. And

0

If the plate temperature Thp is less than the predetermined value T, proceed to Step 18 (Yes), Activating a warning device such as a warning light to notify that the sensor 32 has deteriorated. On the other hand, if the plate temperature Thp is equal to or higher than the predetermined value T, the process is terminated (No).

0

According to the powerful diagnostic program, it is possible to indirectly diagnose whether the electric heater 32 built in the hot plate 28 is deteriorated or not through its function. That is, when the engine 10 is in an idling state, the exhaust temperature is lowered, so that the plate temperature Thp of the hot plate 28 is gradually lowered. However, if the deterioration of the electric heater 32 is small, the plate temperature Thp of the hot plate 28 is maintained at a predetermined value T or more by the control program shown in FIG.

0, the plate temperature Thp remains below T even if the idling state continues for a predetermined time.

0 never. Therefore, if the plate temperature Thp of the hot plate 28 is lower than the predetermined value T when the idling state continues for a predetermined time, the electric heater 32 is deteriorated.

0

It can be diagnosed that the amount of heat has decreased. When the electric heater 32 is deteriorated, it is possible to prompt the inspection and maintenance of the exhaust emission control device by notifying this by a warning device such as a warning light.

In order to control the plate temperature Thp of the hot plate 28, a thermostat that automatically turns off 0 N / OFF at a temperature slightly higher than the melting point of urea may be used instead of software processing by the control unit 24. Yeah!

In addition, the present invention is not limited to an exhaust gas purification apparatus that uses an aqueous urea solution as a liquid reducing agent, but can also be applied to those that use gasoline, light oil, alcohol, or the like mainly containing hydrocarbons as a liquid reducing agent. It ’s ugly! /

Claims

The scope of the claims

[1] A reduction catalyst disposed in the engine exhaust pipe for reducing and purifying nitrogen oxides with a liquid reducing agent;

A hot plate disposed in a lower portion of an exhaust pipe located upstream of the exhaust of the reduction catalyst, an electric heater for heating the hot plate,

A reducing agent supply device for supplying a liquid reducing agent to the upper surface of the hot plate; a control unit for controlling the operation of the electric heater;

An exhaust emission control device comprising:

[2] A plate temperature sensor for detecting the plate temperature of the hot plate is provided,

The control unit controls the operation of the electric heater so that the plate temperature force detected by the plate temperature sensor is at least a predetermined value that is a melting point of the reducing agent component. Exhaust purification equipment.

[3] a reducing agent temperature sensor for detecting a liquid reducing agent temperature;

A rotational speed sensor for detecting the engine rotational speed;

A load sensor for detecting engine load;

With

The control unit controls the output of the electric heater based on the liquid reducing agent temperature, the engine rotation speed, and the engine load detected by the reducing agent temperature sensor, the rotation speed sensor, and the load sensor, respectively. The exhaust emission control device according to claim 2.

4. The control unit calculates an output of the electric heater with reference to a map in which a heater output corresponding to a liquid reducing agent temperature, an engine rotation speed, and an engine load is set. 3. The exhaust emission control device according to 3.

[5] The control unit determines whether or not the engine is idling for a predetermined time, and determines that the plate temperature sensor detects the plate temperature when the idling state has continued for a predetermined time. 3. The exhaust emission control device according to claim 2, wherein if it is less than a predetermined value, it is diagnosed that the electric heating heater has deteriorated.

[6] When the control unit diagnoses that the electric heater has deteriorated, 6. The exhaust emission control device according to claim 5, further comprising a notification device for notification.

7. The control unit determines whether or not the engine has started, and controls the operation of the electric heater only when it is determined that the engine has started and started! The exhaust emission control device according to 1.

8. The exhaust emission control device according to claim 1, wherein fins or throttles are provided around the hot plate.

9. The hot plate is characterized in that the exhaust pipe force can also be removed.

The exhaust emission control device according to 1.

[10] A reducing catalyst disposed in the engine exhaust pipe for reducing and purifying nitrogen oxides with a liquid reducing agent;

A reducing agent supply device for supplying a liquid reducing agent to the upper surface of the hot plate; and a thermostat for controlling the operation of the electric heater so that the plate temperature of the hot plate is equal to or higher than the melting point of the reducing agent component;

An exhaust emission control device comprising: