JP2007182805A - 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 injection port 14 of urea water 13 is arranged toward the lower reaches inside a chamber 12 upstream of a selective reduction type catalyst 10, and a heater 15 serving as a heating device 16 is disposed downstream thereof. An exhaust temperature detector 22 detecting the temperature of exhaust gas 7, and a heating device temperature detector 23 detecting the temperature of the heater 15 are provided, and a control device 24 outputs a control signal 16a for applying a current to the heater 15 to generate heat so that the actual heating device temperature based on a detection signal 23a from the heating device temperature detector 23 is an appropriate temperature under the condition that the actual exhaust temperature based on a detection signal 22a from the exhaust temperature detector 22 is about 200°C or less. <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 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.

  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,
A heating device for heating the added urea water to decompose it into ammonia;
An exhaust gas temperature detector for detecting the temperature of the exhaust gas guided to the selective catalytic reduction catalyst;
A heating device temperature detector for detecting the temperature of the heating device;
Control that outputs a control signal to the heating device based on the exhaust gas temperature detected by the exhaust gas temperature detector and the heating device temperature detected by the heating device temperature detector so that the added urea water is decomposed into ammonia. The present invention relates to an exhaust emission control device comprising the device.

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

  During operation, the temperature of the exhaust gas is detected by an exhaust temperature detector, and if the exhaust temperature does not reach a temperature sufficient to efficiently thermally decompose urea water into ammonia and carbon dioxide, When urea water is added in a state where the heating device is operated by the control signal and the heating device temperature detected by the heating device temperature detector becomes an appropriate temperature, the urea water is heated and ammonia and carbon dioxide gas are added. The resulting ammonia efficiently reacts with the NOx in the exhaust gas on the selective catalytic reduction catalyst, and the NOx in the exhaust gas is reduced and purified well from the lower exhaust temperature than before. .

In the exhaust emission control device, the urea water injection port is arranged in the exhaust pipe toward the downstream side thereof, and
A heating device can be configured by disposing a heater that generates heat by energization downstream of the urea water injection port.

  In this case, it is preferable to fill the urea water flow passage portion in the heater with a metal fiber member for increasing the contact area of the urea water with the heater in order to heat the urea water more efficiently.

In the exhaust purification device, the urea water injection port is connected to the exhaust pipe,
A heater can also be configured by arranging a heater that generates heat by energization on the outer periphery of the urea water injection port.

  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.

  FIG. 1 is a first example of an embodiment of the present invention. In the illustrated diesel engine 1, a turbocharger 2 is provided, and air 4 guided from an air cleaner 3 is introduced into the turbocharger via an intake pipe 5. The air 4 sent to the compressor 2a of the charger 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). 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.

  A chamber 12 is provided in the exhaust pipe 9 upstream of the casing 11, and an injection port 14 for urea water 13 (reducing agent) is disposed inside the chamber 12 toward the downstream side, and the urea A heating device 16 is configured by disposing a heater 15 that generates heat by energization downstream of the jet port 14 of the water 13.

  The injection port 14 for the urea water 13 is provided at the tip of a urea water supply line 18 extending from the urea water tank 17, and the urea water 13 in the urea water tank 17 is pumped in the middle of the urea water supply line 18. A supply pump 19, a regulator 20 for adjusting the pressure of the urea water 13 pumped by the supply pump 19, and an injector 21 for injecting the urea water 13 whose pressure has been adjusted by the regulator 20 from the injection port 14 are provided. It is like that.

  On the other hand, an exhaust temperature detector 22 for detecting the temperature of the exhaust gas 7 is provided on the inlet side of the chamber 12, and the heater 15 serving as the heating device 16 has a heating device temperature for detecting the temperature of the heater 15. A detector 23 is provided, and a detection signal 22 a from the exhaust gas temperature detector 22 and a detection signal 23 a from the heating device temperature detector 23 are input to the control device 24.

  Further, the control device 24 outputs a drive command signal 19 a to the supply pump 19, outputs a pressure adjustment command signal 20 a to the regulator 20, and outputs a valve opening command signal 21 a to the injector 21. The addition amount of the urea water 13 is appropriately controlled by the valve opening operation of the injector 21, and the injection pressure required at the time of addition is appropriately obtained by driving the supply pump 19 and the operation of the regulator 20. It is supposed to be.

  Here, 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, and the amount of urea water 13 that matches the estimated amount of NOx generated is calculated, and the required amount of urea water 13 is added. ing.

  And in the said control apparatus 24, on condition that the measured exhaust gas temperature based on the detection signal 22a from the said exhaust gas temperature detector 22 is about 200 [degreeC] or less, it is from the said heating apparatus temperature detector 23. A control signal 16a for generating heat by energizing the heater 15 serving as the heating device 16 is outputted so that the actually measured heating device temperature based on the detection signal 23a becomes an appropriate temperature. It is heated and efficiently decomposed into ammonia and carbon dioxide.

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

  During operation, the temperature of the exhaust gas is detected by the exhaust temperature detector 22, and the control device 24 indicates that the exhaust temperature is about 200 [° C.] or less based on the detection signal 22 a from the exhaust temperature detector 22. When the control signal 24 is confirmed, the control signal 24a is output from the control device 24 to the heater 15 as the heating device 16, the energization of the heater 15 is executed, and heating is performed based on the detection signal 23a from the heating device temperature detector 23. Control is performed so that the apparatus temperature becomes an appropriate temperature.

  As a result, even when the temperature of the exhaust gas 7 does not reach a temperature sufficient for thermally decomposing the urea water 13 into ammonia and carbon dioxide (about 200 [° C.]), the heater 15 in the chamber 12 generates heat by energization. Therefore, a necessary amount of urea water 13 is supplied to the heater 15 that has generated heat by the drive command signal 19a, the pressure regulation command signal 20a, and the valve opening command signal 21a from the control device 24. When the injector 21 is operated to be injected from the injection port 14, the injected urea water 13 is heated by the heater 15 as the heating device 16 and is efficiently thermally decomposed into ammonia and carbon dioxide gas. Ammonia effectively reacts with NOx in the exhaust gas 7 on the selective catalytic reduction catalyst 10, and the NOx in the exhaust gas 7 is good from the lower exhaust temperature than before. It will be reduced and purified on.

  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 13 can be actively decomposed into ammonia, and a good NOx reduction effect can be obtained from a lower exhaust temperature than before. It is done.

  FIG. 3 is a second example of an embodiment of the present invention. In the drawing, the same reference numerals as those in FIG. 1 denote the same components, and the basic configuration is the same as that shown in FIG. However, as shown in FIG. 3, the feature of the illustrated example is that the contact area of the urea water 13 with respect to the heater 15 is increased in the flow passage portion of the urea water 13 in the heater 15 as the heating device 16. Therefore, the metal fiber member 25 such as stainless steel wool is filled.

  In the illustrated example, the diameter of the chamber 12 and the diameter of the heater 15 are made narrower than in the first example shown in FIG.

  In the second example shown in FIG. 3, as in the first example shown in FIG. 1, the temperature of the exhaust gas is detected by the exhaust temperature detector 22 during operation, and the detection signal 22a from the exhaust temperature detector 22 is detected. When the control device 24 confirms that the exhaust temperature is about 200 [° C.] or less based on the control signal 24a, a control signal 16a is output from the control device 24 to the heater 15 as the heating device 16, and the heater 15 Then, control is performed so that the heating device temperature becomes an appropriate temperature based on the detection signal 23a from the heating device temperature detector 23. In this state, a necessary amount of urea water is supplied to the heater 15 that has generated heat. 13 is operated by the drive command signal 19a, the pressure regulation command signal 20a, and the valve opening command signal 21a from the control device 24 to operate the supply pump 19, the regulator 20, and the injector 21. When jetted from the jet port 14, the jetted urea water 13 is heated by a heater 15 as a heating device 16 and is efficiently thermally decomposed into ammonia and carbon dioxide, and the ammonia generated thereby is selectively reduced catalyst 10. The NOx in the exhaust gas 7 reacts effectively with the above, and the NOx in the exhaust gas 7 is reduced and purified well from an exhaust temperature lower than before, but the urea water 13 flows in the heater 15 as the heating device 16. Since the road portion is filled with a metal fiber member 25 such as stainless steel wool, the contact area of the urea water 13 with the heater 15 is increased, and the urea water 13 injected from the injection port 14 is heated more efficiently. It becomes possible to do.

  Thus, in the case of the second example shown in FIG. 3, as in the case of the first example shown in FIG. Therefore, it can be decomposed into ammonia, and a good NOx reduction effect can be obtained from a lower exhaust temperature than before.

  FIG. 4 shows a third example of an embodiment of the present invention. In the figure, the same reference numerals as those in FIGS. 1 and 3 denote the same components, and the basic configuration is shown in FIGS. 3 is the same as that shown in FIG. 3 except that the urea water 13 injection port 14 is connected to the exhaust pipe 9 and the urea water 13 injection port 14 as shown in FIG. The heating device 16 is configured by disposing a heater 15 that generates heat when energized.

  In the third example shown in FIG. 4, as in the first example shown in FIG. 1 and the second example shown in FIG. 3, the exhaust gas temperature is detected by the exhaust gas temperature detector 22 during operation. When it is confirmed by the control device 24 that the exhaust gas temperature is about 200 [° C.] or less based on the detection signal 22a from the detector 22, the control signal 16a is sent from the control device 24 to the heater 15 as the heating device 16. Is output, energization of the heater 15 is executed, and control is performed so that the heating device temperature becomes an appropriate temperature based on the detection signal 23a from the heating device temperature detector 23. The urea pump 13 is operated by the drive command signal 19a, the pressure regulation command signal 20a, and the valve opening command signal 21a from the control device 24 to operate the supply pump 19, the regulator 20, and the injector 21. When the more injected from the injection port 14, the urea water 13, which is the injection, after being heated directly by the heater 15 which is disposed on the outer periphery of the injection port 14, the shape to be supplied into the exhaust pipe 9.

  In this way, if the injected urea water 13 is directly heated by the heater 15 disposed on the outer peripheral portion of the injection port 14 and then supplied into the exhaust pipe 9, the temperature of the exhaust gas 7 is temporarily set to the urea water. 13 does not reach a temperature sufficient to thermally decompose 13 into ammonia and carbon dioxide (about 200 [° C.]), but even at a very low temperature, the very low temperature exhaust gas 7 There is no fear that the urea water 13 injected from the injection port 14 is cooled, and it is possible to reliably perform thermal decomposition of the urea water 13 into ammonia and carbon dioxide gas. It effectively reacts with NOx in the exhaust gas 7 on the catalyst 10, and the NOx in the exhaust gas 7 is reduced and purified well from an exhaust temperature lower than before.

  Thus, in the case of the third example shown in FIG. 4 as well, as in the case of the first example shown in FIG. 1 and the second example shown in FIG. However, the urea water 13 can be actively decomposed into ammonia, and a good NOx reduction effect can be obtained from a lower exhaust temperature than before.

  The exhaust emission control device of the present invention is not limited to the above-described illustrated examples. For example, the heating device 16 shown in each of the first and second examples is combined in the exhaust pipe 9. A third example in which the heating device 16 is configured by arranging the heater 15 that generates heat by energization on the outer peripheral portion of the injection port 14 of the urea water 13 may be provided in series. Needless to say, various modifications may be made without departing from the gist of the present invention, such as a combination with the first and second examples.

It is the schematic which shows the 1st 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 the schematic which shows the 2nd example of the form which implements this invention. It is the schematic which shows the 3rd example of the embodiment which implements this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 7 Exhaust gas 9 Exhaust pipe 10 Selective reduction type catalyst 11 Casing 12 Chamber 13 Urea water 14 Injection port 15 Heater 16 Heating device 16a Control signal 17 Urea water tank 18 Urea water supply line 19 Supply pump 20 Regulator 21 Injector 22 Exhaust Temperature detector 22a Detection signal 23 Heating device temperature detector 23a Detection signal 24 Control device 25 Metal fiber member

Claims (4)

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,
A heating device for heating the added urea water to decompose it into ammonia;
An exhaust gas temperature detector for detecting the temperature of the exhaust gas guided to the selective catalytic reduction catalyst;
A heating device temperature detector for detecting the temperature of the heating device;
Control that outputs a control signal to the heating device based on the exhaust gas temperature detected by the exhaust gas temperature detector and the heating device temperature detected by the heating device temperature detector so that the added urea water is decomposed into ammonia. And an exhaust emission control device. While arranging the urea water injection port toward the downstream side inside the exhaust pipe,
The exhaust emission control device according to claim 1, wherein a heater is configured by disposing a heater that generates heat upon energization downstream of the urea water injection port.   The exhaust emission control device according to claim 2, wherein the urea water flow passage portion of the heater is filled with a metal fiber member for increasing the contact area of the urea water with the heater. While connecting the urea water injection port to the exhaust pipe,
The exhaust emission control device according to claim 1, wherein a heater is configured by disposing a heater that generates heat by energization on an outer peripheral portion of the urea water injection port.

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