JP2007182803A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of positively decomposing urea water into ammonia to obtain an excellent NOx reducing effect from an exhaust temperature lower than the conventional one even in a vehicle of such an operating form that an operating state at a low exhaust temperature continues for a long time. <P>SOLUTION: An ultrasonic irradiation tank 14 having an inflow port 14a and an outflow port 14b of urea water 12 is disposed as an ultrasonic irradiation means 13 for irradiating urea water 12 with ultrasonic wave. A urea water supply line 15 is connected to the inflow port 14a of the ultrasonic irradiation tank 14 serving as the ultrasonic irradiation means 13, and an addition nozzle 16 leading the urea water 12 irradiated with ultrasonic wave, into an exhaust pipe 9 upstream of an selective reduction type catalyst 10 is connected to the outflow port 14b of the ultrasonic irradiation tank 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  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 flows, and the selective reduction catalyst A required amount of a reducing agent is added to the upstream side 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 an exhaust purification device.

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. In the case of a purification apparatus, 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 (for example, patents). Reference 1).

That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water will be (NH ₂ ) ₂ .CO + H ₂ O → 2NH ₃ + CO ₂ in the exhaust gas.
Is thermally decomposed into ammonia and carbon dioxide by the chemical reaction formula shown below, and NOx in the exhaust gas is favorably reduced and purified by ammonia on the selective catalytic reduction catalyst.
JP 2002-161732 A

  However, in the case of an exhaust gas purification apparatus using such urea water as a reducing agent, an exhaust temperature of about 200 [° C.] or higher is required to obtain sufficient catalytic activity during the reduction reaction. NOx reduction rate because the decomposition from urea water to ammonia does not proceed when the low operating condition (generally, the low exhaust temperature range extends to the low load operating range) that is below 200 [° C] There is a problem that it does not increase easily. For example, in the case of a vehicle that travels on a congested road such as an urban route bus, driving at a predetermined temperature or higher does not continue for a long time. The rate remained low and a good NOx reduction effect could not be obtained.

  Moreover, in the conventional case, urea water is simply injected directly into the exhaust pipe, so that the heat transfer efficiency from exhaust gas exhaust heat to urea water is low, especially when the exhaust temperature is low, the amount of ammonia produced is small. Therefore, the amount of ammonia necessary for NOx reduction cannot be supplied to the selective reduction catalyst, and the NOx reduction effect is significantly reduced.

  In view of such circumstances, the present invention is capable of actively decomposing urea water into ammonia even when the vehicle is in an operation mode in which an operation state with a low exhaust temperature continues for a long time. It is an object of the present invention to provide an exhaust purification device that can provide a good NOx reduction effect.

The present invention is 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 upstream of the selective reduction catalyst,
The present invention relates to an exhaust emission control device comprising ultrasonic irradiation means for irradiating the added urea water with ultrasonic waves.

  According to the above means, the following operation can be obtained.

  When ultrasonic waves are applied to the urea water added as a reducing agent upstream of the selective catalytic reduction catalyst during operation, bubbles are generated by cavitation, and when the bubbles collapse due to the cavitation, the lifetime is short. The high temperature and high pressure local field (hot spot) is formed, and the CN bond portion having a low binding energy in the urea molecule is cut. Therefore, even if the exhaust temperature is low, the ultrasonic wave The urea water irradiated with ultrasonic waves in the irradiation means is efficiently decomposed into ammonia and carbon dioxide gas, and the amount of ammonia produced increases, so it is different from simply injecting urea water directly into the exhaust pipe as in the past. , The amount of ammonia required for NOx reduction can be supplied to the selective catalytic reduction catalyst, and the ammonia is effectively combined with NOx in the exhaust gas on the selective catalytic reduction catalyst. The reaction was, NOx in the exhaust gas is satisfactorily reduced and purified from lower than a conventional exhaust temperature.

  In the exhaust gas purification apparatus, the ultrasonic irradiation means can be configured by an ultrasonic irradiation tank that irradiates and discharges the urea water introduced by vibrating the entire tank with a vibrator.

  Further, in the exhaust purification apparatus, the ultrasonic irradiation means can be constituted by an ultrasonic irradiation tank that irradiates and discharges the urea water introduced by vibrating the horn by a vibrator.

  According to the exhaust emission control device of the present invention, urea water can be actively decomposed into ammonia even when the vehicle is in an operation mode in which an operation state with a low exhaust temperature continues for a long time. An excellent effect of obtaining a good NOx reduction effect can be obtained.

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

  1 to 4 show an example of an embodiment of the present invention. In the illustrated diesel engine 1, a turbocharger 2 is provided, and the air 4 guided from an air cleaner 3 passes through an intake pipe 5. The air 4 sent to the compressor 2a of the turbocharger 2 and pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and the air 4 is led from the intercooler 6 to an intake manifold (not shown). Thus, it is introduced into each cylinder of the diesel engine 1.

  Exhaust gas 7 discharged from each cylinder of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 driving the turbine 2b is discharged outside the vehicle through the exhaust pipe 9. It is supposed to be.

  In addition, a selective reduction catalyst 10 is held by a casing 11 in the middle of an exhaust pipe 9 through which the exhaust gas 7 flows. The selective reduction catalyst 10 is flow-through as shown in FIG. It is formed as a honeycomb structure of the type, and has the property that NOx can be selectively reacted with ammonia even in the presence of oxygen.

  And as the ultrasonic irradiation means 13 for irradiating the urea water 12 with ultrasonic waves (frequency is about 20 [kHz] to several [MHz]), the ultrasonic irradiation having the inlet 14a and the outlet 14b of the urea water 12 is performed. A tank 14 is provided, a urea water supply line 15 is connected to an inlet 14a of an ultrasonic irradiation tank 14 as the ultrasonic irradiation means 13, and ultrasonic waves are supplied to an outlet 14b of the ultrasonic irradiation tank 14. An addition nozzle 16 for guiding the irradiated urea water 12 into the exhaust pipe 9 on the upstream side of the selective catalytic reduction catalyst 10 is connected.

  Here, in the ultrasonic irradiation tank 14, for example, as shown in FIG. 3A, a vibrator 17 is embedded at the bottom thereof, and the whole tank is vibrated by the vibrator 17 so that ultrasonic waves are applied to the urea water 12. An irradiating type is adopted, or as shown in FIG. 3B, a horn 18 for transmitting the vibration from the vibrator 17 is disposed therein, and the horn 18 is vibrated by the vibrator 17. A method of irradiating urea water 12 with ultrasonic waves can be employed. The vibrator 17 of the ultrasonic irradiation tank 14 is activated and stopped by turning on and off a power source 19 (see FIG. 1).

  The urea water supply line 15 extends from a urea water tank 20 in which the urea water 12 is stored, and a supply pump 21 that pumps the urea water 12 in the urea water tank 20 in the middle of the urea water supply line 15. The regulator 22 for adjusting the pressure of the urea water 12 pumped by the supply pump 21 and the urea water 12 whose pressure has been adjusted by the regulator 22 are added via the ultrasonic irradiation tank 14 as the ultrasonic irradiation means 13. An injector 23 for injecting from the nozzle 16 is provided.

  On the other hand, the control device 24 outputs a drive command signal 21 a to the supply pump 21, outputs a pressure adjustment command signal 22 a to the regulator 22, and outputs a valve opening command signal 23 a to the injector 23. The addition amount of the urea water 12 is appropriately controlled by the valve opening operation of the injector 23, and the injection pressure required at the time of the addition is appropriately obtained by driving the supply pump 21 and the operation of the regulator 22. At the same time, when the urea water 12 is added, a control command signal 19a is output to the power source 19 in conjunction with the urea water 12 so that the urea water 12 to be added is irradiated with ultrasonic waves.

  In the control device 24, the rotational speed and load of the diesel engine 1 are exchanged with an unillustrated engine control computer (ECU: Electronic Control Unit). The amount of NOx generated is estimated based on the current operating state, the amount of urea water 12 added corresponding to the estimated amount of NOx generated is calculated, and the addition of the necessary amount of urea water 12 and ultrasonic irradiation are executed. It has come to be.

  Next, the operation of the illustrated example will be described.

  During operation, the supply pump 21, the regulator 22, and the injector 23 are actuated by the drive command signal 21 a, the pressure regulation command signal 22 a, and the valve opening command signal 23 a from the control device 24, so that a necessary amount of urea water 12 is urea. The water supply line 15 is introduced into the ultrasonic irradiation tank 14 through the inlet 14a, and the power supply 19 is turned on by the control command signal 19a from the control device 24 to operate the vibrator 17 of the ultrasonic irradiation tank 14. Then, the urea water 12 is irradiated with ultrasonic waves in the ultrasonic irradiation tank 14.

  When the urea water 12 is irradiated with ultrasonic waves in the ultrasonic irradiation tank 14, bubbles are generated by cavitation, and when the bubbles are collapsed by the cavitation, a short-lived high-temperature and high-pressure local field (hot spot) is formed. As a result, the C—N bond portion having a low binding energy in the urea molecule is cut, so that the urea water 12 irradiated with ultrasonic waves in the ultrasonic irradiation tank 14 even when the exhaust temperature is low. Is efficiently decomposed into ammonia and carbon dioxide gas, and the amount of ammonia produced increases, so that the amount of NOx required for NOx reduction is different from that in which the urea water 12 is simply injected directly into the exhaust pipe 9 as in the prior art. Ammonia can be supplied to the selective catalytic reduction catalyst 10, and the ammonia effectively reacts with NOx in the exhaust gas 7 on the selective catalytic reduction catalyst 10, and the exhaust gas 7 NOx is to be satisfactorily reduced and purified from lower than a conventional exhaust gas temperature.

  In fact, according to the results of experiments conducted by the present inventors, as shown in the graph of FIG. 4, the ammonia decomposed by irradiating the urea water 12 with ultrasonic waves in the above-described apparatus configuration of the illustrated example. When comparing the case X added to the upstream side of the selective catalytic reduction catalyst 10 and the conventional case Y in which the urea water 12 is added directly to the upstream side of the selective catalytic reduction catalyst 10 without performing such ultrasonic irradiation. In the conventional case Y, in order to obtain a high NOx reduction rate, the bed temperature (incoming exhaust temperature) of the selective catalytic reduction catalyst 10 is required to be approximately 200 [° C.] or higher, whereas in the case X, selective reduction is performed. It was actually confirmed that a high NOx reduction rate can be obtained if the bed temperature (inlet side exhaust gas temperature) of the type catalyst 10 is about 140 [° C.].

  In this way, even in a vehicle having an operation mode in which an operation state with a low exhaust temperature continues for a long time, the urea water 12 can be actively decomposed into ammonia, and a favorable NOx reduction effect can be obtained from a lower exhaust temperature than before. It is done.

  It should be noted that the exhaust emission control device of the present invention is not limited to the illustrated examples described above, and it is needless to say that various modifications can be made without departing from the scope of the present invention.

It is the schematic which shows an example of the form which implements this invention. FIG. 2 is a perspective view showing a part of the selective catalytic reduction catalyst of FIG. It is a schematic sectional drawing which shows the ultrasonic irradiation tank of FIG. 1, (a) is a figure of the system which vibrates the whole tank with a vibrator | oscillator, and irradiates an ultrasonic wave to urea water, (b) is a horn with a vibrator | oscillator. It is a figure of the system which vibrates and irradiates an ultrasonic wave to urea water. It is a graph which shows the relationship between selective reduction type | mold catalyst bed temperature (inlet side exhaust gas temperature), and NOx reduction rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 7 Exhaust gas 9 Exhaust pipe 10 Selective reduction type catalyst 11 Casing 12 Urea water 13 Ultrasonic irradiation means 14 Ultrasonic irradiation tank 15 Urea water supply line 16 Addition nozzle 17 Vibrator 18 Horn 19 Power supply 20 Urea water tank 21 Supply Pump 22 Regulator 23 Injector

Claims (3)

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 upstream of the selective reduction catalyst,
An exhaust emission control device comprising ultrasonic irradiation means for irradiating the added urea water with ultrasonic waves.   The exhaust emission control device according to claim 1, wherein the ultrasonic irradiation means is configured by an ultrasonic irradiation tank that irradiates and discharges the urea water introduced by vibrating the entire tank with a vibrator.   The exhaust emission control device according to claim 1, wherein the ultrasonic irradiation means is constituted by an ultrasonic irradiation tank that irradiates and discharges the urea water introduced by vibrating the horn with a vibrator.

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