JP2006046287A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of clogging in an injection nozzle due to crystals of urea. <P>SOLUTION: In this exhaust emission control device, a selective reduction type catalyst 4 is provided in the middle of an exhaust pipe 3, and urea water 8 as reducer is added to the upstream side of the selective reduction type catalyst 4 through the injection nozzle 5, so that NOx is reduced. Between a urea water supply pipe 7 to introduce urea water 8 from a urea water tank 6 to the injection nozzle 5 and a drain pipe 12 for condensation water 11 from an air conditioner 10 to flow down to be discharged to outward of a car, nozzle cleaning piping 13 is provided to introduce condensation water 11 to reach a lower position of the urea water supply pipe 7 by using level difference from an upper position of the drain pipe 12. An opening valve 14 is provided close to a terminal end of the nozzle cleaning piping 13 to be normally closed, and opened when a starter switch is off. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device applied to an engine such as a diesel engine.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas circulates. A required amount of reducing agent is added upstream of the catalyst so that the reducing agent undergoes a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. Since it is difficult to ensure safety with respect to traveling with ammonia itself, in recent years, the use of non-toxic urea water as a reducing agent has been studied (see, for example, Patent Document 1). .
JP 2002-161732 A

That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water in the exhaust gas is thermally decomposed into ammonia and carbon dioxide gas according to the following formula, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. NOx is reduced and purified well by ammonia.
[Chemical 1]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

  However, in this type of exhaust gas purification apparatus using urea water as a reducing agent, the injection nozzle for adding urea water is exposed to high-temperature exhaust gas in the exhaust pipe. There is a risk that moisture will evaporate and urea crystals may be deposited in the injection nozzle. Repeating such precipitation several times will clog the injection nozzle, and the amount of urea water injection will vary, resulting in quantitative accuracy. There is a concern that problems may occur such as damage to the water or the injection of urea water becomes difficult.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust emission control device capable of preventing the possibility of clogging of an injection nozzle due to urea crystals.

  The present invention provides an exhaust emission control device equipped with a selective reduction catalyst in the middle of an exhaust pipe and reducing and purifying NOx by adding urea water as a reducing agent to the upstream side of the selective reduction catalyst via an injection nozzle. In this case, there is a difference in height from the upper position of the drain pipe between the urea water supply pipe that guides the urea water from the urea water tank to the injection nozzle and the drain pipe that causes the air-conditioner condensate to flow down to be discharged outside the vehicle. A nozzle cleaning pipe that guides air-conditioner condensate to the lower position of the urea water supply pipe is provided, and a first on-off valve that is normally closed and opened when the starter switch is off is provided near the end of the nozzle cleaning pipe. It is characterized by that.

  Thus, in this way, even when moisture is evaporated from the remaining urea water and urea crystals are precipitated in the injection nozzle, the first time when the starter switch is turned off and the engine is stopped. The air-conditioner condensate collected in the nozzle cleaning pipe flows into the urea water supply pipe to dissolve the urea crystals in the injection nozzle, and the inside of the injection nozzle is washed with water.

  On the other hand, in the operating state where the starter switch is on, the air conditioner condensate led from the drain pipe is gradually stored in the nozzle cleaning pipe because the first on-off valve is closed. When the nozzle cleaning pipe is filled with the air-conditioner condensate due to the continuous operation over the period, the air-conditioner condensate overflowing from the nozzle cleaning pipe flows down to the normal drain pipe and is discharged to the outside as it is.

  Furthermore, in the present invention, an inverted U-shaped loop pipe portion is formed on the upstream side of the first opening / closing valve in the nozzle cleaning pipe, and the nozzle cleaning pipe branches downward to the upstream side of the loop pipe portion. It is also possible to provide a branch pipe for opening the air-conditioner condensed water to the outside of the vehicle, and to provide a second opening / closing valve that is normally closed and opened when the starter switch is turned off.

  In this way, when the starter switch is turned off and the engine is stopped, the first and second on-off valves are opened, and the air conditioner condensation accumulated from the first on-off valve to the vicinity of the top of the loop pipe section. Only water is guided to the injection nozzle and used to dissolve urea crystals, and the remaining air-conditioner condensate is discharged from the branch pipe to the outside of the vehicle.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, even if urea crystals are precipitated in the injection nozzle, the air-conditioner condensate is introduced from the nozzle cleaning pipe when the engine is stopped. Since the urea crystals in the injection nozzle can be dissolved with the air-conditioner condensed water, the possibility that the injection nozzles may be clogged with the urea crystals can be prevented, and the injection amount of urea water Can be reliably avoided by avoiding inconveniences such as fluctuations in the accuracy of quantitative measurement and the difficulty in injecting urea water itself.

  (II) According to the invention described in claim 2 of the present invention, the spray nozzle is washed with water using only the air-conditioner condensed water accumulated between the first opening / closing valve and the vicinity of the top of the loop pipe portion. Therefore, it is possible to avoid the possibility that an excessive amount of air-conditioner condensate is introduced into the exhaust pipe.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes an engine that is a diesel engine, and an exhaust pipe 3 through which exhaust gas 2 discharged from each cylinder of the engine 1 flows. In the middle of this, a selective reduction catalyst 4 having the property of selectively reacting NOx with ammonia even in the presence of oxygen is equipped, and an injection nozzle 5 is installed upstream of the selective reduction catalyst 4. A urea water supply pipe 7 is connected between the spray nozzle 5 and a urea water tank 6 provided at a required place.

  A supply pump 9 is provided in the middle of the urea water supply pipe 7 so that the urea water 8 (reducing agent) in the urea water tank 6 can be injected into the exhaust pipe 3 from the injection nozzle 5. Connected between the pump 9 and the injection nozzle 5 is a nozzle cleaning pipe 13 that branches from an upper position of a drain pipe 12 through which the condensed water 11 from the air conditioner 10 flows down and is discharged to the outside of the vehicle.

The nozzle cleaning pipe 13 is branched from the drain pipe 12 at a height H ₂ higher than the height H ₁ from the road surface G of the injection nozzle 5 and extends to a position below the urea water supply pipe 7 in a descending gradient. Thus, the condensed water 11 from the drain pipe 12 can be guided to the injection nozzle 5 by using the height difference, and the nozzle cleaning pipe 13 is normally closed and opened when the starter switch is turned off. An on-off valve 14 is provided.

  Here, when the condensed water 11 is guided from the drain pipe 12 to the nozzle cleaning pipe 13, a filter or the like (not shown) is disposed upstream from the branching location in the drain pipe 12 so that foreign matter can be collected in advance. And good.

  In FIG. 1, 15 indicates a cab and 16 indicates a loading platform. The nozzle cleaning pipe 13 described above is routed in the cab 15 as much as possible in order to avoid freezing in winter, and the temperature in the pipe is below freezing. It is preferable not to become.

  Thus, if the exhaust emission control device is configured in this way, even if water is evaporated from the remaining urea water 8 and urea crystals are precipitated in the injection nozzle 5, the starter switch is turned off and the engine is turned off. 1 is stopped, the open / close valve 14 is opened, and the condensed water 11 accumulated in the nozzle cleaning pipe 13 flows into the urea water supply pipe 7 to melt the urea crystals in the injection nozzle 5, and the inside of the injection nozzle 5 is washed with water. Will be.

  On the other hand, in the operation state in which the starter switch is turned on, the open / close valve 14 is closed, so that the condensed water 11 led from the drain pipe 12 is gradually stored in the nozzle cleaning pipe 13. When the nozzle cleaning pipe 13 is filled with the condensed water 11 due to the continuous operation over a period of time, the condensed water 11 overflowing from the nozzle cleaning pipe 13 flows down to the normal drain pipe 12 and is discharged to the outside as it is. become.

  Therefore, according to the above embodiment, even if urea crystals are precipitated in the injection nozzle 5, the condensed water 11 is introduced from the nozzle cleaning pipe 13 when the engine 1 is stopped to wash the inside of the injection nozzle 5 with water. Since the urea crystals in the injection nozzle 5 can be dissolved by the condensed water 11, it is possible to prevent the possibility that the injection nozzle 5 is clogged by the urea crystals, and the injection amount of the urea water 8 can be reduced. It is possible to maintain the normal injection of the urea water 8 by reliably avoiding problems such as fluctuations that impair the quantitative accuracy or make the injection of the urea water 8 difficult.

  FIG. 2 shows another embodiment of the present invention, in which an inverted U-shaped loop pipe portion 17 is formed on the upstream side of the on-off valve 14 in the nozzle cleaning pipe 13, and the lower side is formed on the upstream side of the loop pipe portion 17. A branch pipe 18 that branches in the direction and opens the condensed water 11 in the nozzle cleaning pipe 13 to the outside of the vehicle is provided, and a second open / close valve 19 that is normally closed and opened when the starter switch is turned off is provided in the branch pipe 18. It has become a thing.

Here, the height H ₃ of the loop pipe portion 17 from the road surface G is set to be lower than the height H ₂ of the branch portion of the drain pipe 12 and higher than the height H ₁ of the injection nozzle 5.

  Thus, in this way, when the starter switch is turned off and the engine 1 is stopped, the first and second on-off valves 14 and 19 are opened, respectively, from the on-off valve 14 to the vicinity of the top of the loop pipe portion 17. Only the condensed water 11 accumulated during this period is guided to the injection nozzle 5 and used to dissolve urea crystals, and the remaining condensed water 11 is discharged from the branch pipe 18 to the outside of the vehicle.

  Therefore, in the case of such a configuration example, it is possible to perform water washing of the injection nozzle 5 using only the condensed water 11 accumulated between the opening / closing valve 14 and the vicinity of the top of the loop pipe portion 17. The possibility that an excessive amount of condensed water 11 is introduced into the exhaust pipe 3 can be avoided in advance.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment, and a washing water tank may be separately provided for emergency so that the spray nozzle can be appropriately washed with water. Of course, various modifications can be made without departing from the scope of the present invention.

It is a systematic diagram schematically showing an example of an embodiment for carrying out the present invention. It is a systematic diagram schematically showing another embodiment of the present invention.

Explanation of symbols

3 Exhaust pipe 4 Selective reduction catalyst 5 Injection nozzle 6 Urea water tank 7 Urea water supply pipe 8 Urea water 10 Air conditioner 11 Condensed water (air conditioner condensed water)
12 Drain pipe 13 Nozzle cleaning pipe 14 Open / close valve (first open / close valve)
17 Loop pipe section 18 Branch pipe 19 Open / close valve (second open / close valve)

Claims (2)

  An exhaust emission control device equipped with a selective reduction catalyst in the middle of an exhaust pipe and reducing and purifying NOx by adding urea water as a reducing agent to the upstream side of the selective reduction catalyst via an injection nozzle, Between the urea water supply pipe for introducing urea water from the urea water tank to the injection nozzle and the drain pipe for allowing the air-conditioner condensate to flow down and discharging it outside the vehicle, the difference in height from the upper position of the drain pipe is utilized. A nozzle cleaning pipe that guides air-conditioner condensate to a position below the urea water supply pipe is provided, and a first on-off valve that is normally closed and opened when the starter switch is off is provided near the end of the nozzle cleaning pipe. Exhaust gas purification device.   An inverted U-shaped loop pipe portion is formed on the upstream side of the first opening / closing valve in the nozzle cleaning pipe, and the air-conditioner condensate in the nozzle cleaning pipe is branched to the downstream side upstream of the loop pipe portion. 2. The exhaust emission control device according to claim 1, wherein a branch pipe that is opened is provided, and a second opening / closing valve that is normally closed and opened when the starter switch is turned off is provided on the branch pipe.

Images