JP2010261331A - Exhaust purification device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the problem wherein ammonia of high concentration slips from a selective reduction type catalyst by the sudden temperature rise in the selective reduction type catalyst during forced regeneration of a particulate filter. <P>SOLUTION: This exhaust purification device has a temperature adjusting means 30 for holding a temperature rise in the selective reduction type catalyst 5 in a set gradient so that the ammonia concentration in exhaust gas 3 flowing in the selective reduction type catalyst 5 becomes the concentration suitable for reducing and eliminating NOx in the exhaust gas 3 when forcibly regenerating the particulate filter 14, and balances an NOx quantity and an ammonia quantity in the selective reduction type catalyst 5. <P>COPYRIGHT: (C)2011,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 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.

  That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is thermally decomposed into ammonia and carbon dioxide gas in the exhaust gas, and NOx in the exhaust gas is converted into the selective catalytic reduction catalyst. It is reduced and purified well by ammonia (see, for example, Patent Document 1).

  In addition, when purifying exhaust gas from a diesel engine, it is not enough to remove NOx in the exhaust gas, and particulate matter (particulate matter) contained in the exhaust gas is also collected through the particulate filter. However, when this type of particulate filter is employed, it is necessary to regenerate the particulate filter by appropriately burning and removing the particulate before the exhaust resistance increases due to clogging.

  For this reason, a flow-through type oxidation catalyst is attached to the preceding stage of the particulate filter, and fuel is added to the exhaust gas upstream of the oxidation catalyst when the amount of particulate accumulation increases. It is considered to forcibly regenerate the curate filter.

  In other words, if fuel is added to the exhaust gas upstream of the oxidation catalyst, the added fuel (HC) undergoes an oxidation reaction while passing through the preceding oxidation catalyst. The catalyst bed temperature of the particulate filter immediately after that is raised, the particulates are burned out, and the particulate filter is regenerated.

  In general, as a specific means for performing the fuel addition as described above, the post-injection is executed at the timing of non-ignition later than the compression top dead center following the main injection of fuel performed near the compression top dead center. It is considered that the fuel is added to the exhaust gas, but in order to efficiently utilize the added fuel for forced regeneration and oxidize the added fuel before the temperature of the exhaust gas drops as much as possible, It is considered preferable to dispose the particulate filter and the preceding oxidation catalyst upstream of the selective reduction catalyst.

JP 2003-155914 A

  However, if the particulate filter is forcibly regenerated before the selective catalytic reduction catalyst, the heat generated by the oxidation reaction of the added fuel at the preceding oxidation catalyst and the particulates collected in the particulate filter burn. There is a problem that the temperature of the exhaust gas on the outlet side of the particulate filter rapidly rises to, for example, about 500 ° C. or more due to the heat generated by.

  FIG. 7 shows the adsorption characteristic A, which is the relationship between the catalyst temperature of the selective reduction catalyst and the amount of adsorption by which the selective reduction catalyst adsorbs ammonia. The selective catalytic reduction catalyst simultaneously adsorbs and desorbs ammonia, and as shown in FIG. 7, the ammonia adsorption amount shows a behavior that rapidly decreases as the catalyst temperature increases. Therefore, when the catalyst temperature rapidly rises from the state where it is operated at the predetermined temperature in FIG. 7, the adsorbed ammonia comes off from the selective catalytic reduction catalyst all at once.

  FIG. 8 shows an ideal state of the catalyst temperature of the selective catalytic reduction catalyst and the ammonia concentration in the selective catalytic reduction catalyst. The catalyst temperature B is an active temperature (central value) at which the selective catalytic reduction catalyst has a high activity. Although the target temperature is set in the vicinity, the actual catalyst temperature varies depending on the operating conditions. Further, the ammonia concentration C in the exhaust gas in the selective reduction catalyst due to the adsorption and desorption with respect to the selective reduction catalyst is an ammonia concentration (balance concentration) suitable for reducing and purifying NOx in the exhaust gas. The amount of urea water is adjusted so that the amount of ammonia in the exhaust gas in the selective catalytic reduction catalyst and the amount of NOx are substantially balanced, thereby removing NOx.

  FIG. 9 shows the relationship between the catalyst temperature B and the ammonia concentration C in the catalyst during forced regeneration of the particulate filter. The forced regeneration of the particulate filter is normally performed after the vehicle is stopped. For this reason, the forced regeneration is performed from a state where the catalyst temperature is lower than the target temperature. For example, when the particulate filter is forcibly regenerated by adding fuel to the exhaust gas, the exhaust gas temperature rapidly rises. Therefore, the catalyst temperature B in FIG. 9 rapidly rises as shown by B ′. To come. As shown in FIG. 7, the ammonia held in the selective catalytic reduction catalyst is released at a stroke as a result of such a rapid increase in the catalyst temperature. For this reason, the ammonia concentration C in the catalyst is increased by the amount of hatching. It increases rapidly like C ′. Here, since the amount of NOx in the exhaust gas slightly increases during the forced regeneration of the particulate filter, a part of the increased ammonia is consumed by the increased NOx. Therefore, the increased amount C ′ of ammonia becomes excessive and slips (discharges) from the selective catalytic reduction catalyst to the outside at once. In addition, it is considered that an ammonia oxidation catalyst 15 is provided after the selective catalytic reduction catalyst 5 to remove the slipping ammonia. However, as described above, when high-concentration ammonia slips, the treatment is performed. There was a problem of being discharged outside without being exhausted.

  As described above, the conventional exhaust gas purification apparatus has a problem that exhaust gas generates an ammonia odor due to slipping of high-concentration ammonia.

  The present invention has been made in view of the above circumstances, and prevents the problem that high concentration of ammonia slips from the selective catalytic reduction catalyst due to a rapid temperature rise of the selective catalytic reduction catalyst during forced regeneration of the particulate filter. An object of the present invention is to provide an exhaust emission control device.

  The exhaust purification apparatus of the present invention is equipped with a selective reduction catalyst in the middle of an exhaust pipe of an engine, and NOx is reduced and purified by adding urea water as a reducing agent upstream of the selective reduction catalyst. A purification device and a particulate filter disposed upstream of the urea water addition position with an oxidation catalyst attached to the upstream stage; and raising the exhaust temperature at the particulate filter inlet to raise the particulate filter An exhaust purification device that burns the particulates collected in the exhaust gas to perform forced regeneration of the particulate filter, wherein ammonia in exhaust gas flowing in the selective catalytic reduction catalyst during forced regeneration of the particulate filter In order to maintain the temperature increase of the selective catalytic reduction catalyst at a set gradient so that the concentration becomes a concentration suitable for reducing and purifying NOx in exhaust gas. And a temperature control means for balancing the NOx amount and the ammonia amount in the selective catalytic reduction catalyst.

  Thus, in the exhaust purification apparatus of the present invention, the ammonia concentration in the exhaust gas flowing through the selective catalytic reduction catalyst reduces and purifies NOx in the exhaust gas by the temperature adjusting means during forced regeneration of the particulate filter. The increase in the temperature of the selective catalytic reduction catalyst is maintained at a set gradient so that the concentration is suitable for the NOx amount and the amount of ammonia in the selective catalytic reduction catalyst is balanced, and a high concentration of ammonia from the selective catalytic reduction catalyst. Is prevented from slipping.

  The exhaust purification apparatus of the present invention is equipped with a selective reduction catalyst in the middle of the exhaust pipe of the engine, and urea water is added as a reducing agent upstream of the selective reduction catalyst to reduce and purify NOx. And an exhaust pipe upstream of the urea water addition position and a particulate filter arranged with an oxidation catalyst attached to the preceding stage, and the exhaust temperature at the inlet of the particulate filter is increased to increase the particulates. An exhaust gas purification apparatus configured to burn particulates collected by a curative filter and perform forced regeneration of the particulate filter, and in exhaust gas flowing through the selective catalytic reduction catalyst during forced regeneration of the particulate filter NOx amount increasing means for increasing the NOx amount in the engine exhaust gas so that the ammonia in the exhaust gas is consumed by NOx in the exhaust gas And the NOx amount and the ammonia amount in the selective catalytic reduction catalyst are balanced.

  Thus, in the exhaust purification apparatus of the present invention, during forced regeneration of the particulate filter, ammonia in the exhaust gas flowing through the selective catalytic reduction catalyst is consumed by NOx in the exhaust gas by the NOx amount increasing means. Thus, since the NOx amount in the engine exhaust gas is increased, the NOx amount and the ammonia amount in the selective catalytic reduction catalyst are balanced, and the high concentration ammonia is prevented from slipping from the selective catalytic reduction catalyst.

  Further, during forced regeneration of the particulate filter, selective reduction is performed by the temperature control means so that the ammonia concentration in the exhaust gas flowing through the selective catalytic reduction catalyst becomes a concentration suitable for reducing and purifying NOx in the exhaust gas. In the exhaust gas of the engine so that the ammonia in the exhaust gas flowing through the selective catalytic reduction catalyst is consumed by the NOx in the exhaust gas by maintaining the temperature rise of the type catalyst at a set gradient and increasing the amount of NOx. By simultaneously increasing the NOx amount, the NOx amount and the ammonia amount in the selective catalytic reduction catalyst are balanced, and it is possible to prevent high concentration ammonia from slipping from the selective catalytic reduction catalyst.

  In the above exhaust purification apparatus, the temperature adjusting means may be a post injection controller that commands an injection amount of post injection to a fuel injection controller that controls main injection and post injection to the engine. .

  In the exhaust purification apparatus, the temperature adjusting means may be a fuel addition device for adding fuel upstream of the oxidation catalyst, and a fuel addition controller for controlling a fuel addition amount by the fuel addition device.

  In the exhaust purification apparatus, the temperature adjusting means may be a burner device provided upstream of the oxidation catalyst and a burner controller for controlling the amount of fuel added by the burner device.

  Further, in the above exhaust purification apparatus, the NOx amount increasing means instructs the fuel injection controller that controls main injection and post injection to the engine to retard the main injection and controls the NOx amount in the exhaust gas. The injection angle controller may be increased.

  Further, in the exhaust purification device, the NOx amount increasing means includes an exhaust gas recirculation device for recirculating engine exhaust gas to the intake air, and commands to reduce the exhaust gas recirculation amount by the exhaust gas recirculation device. An exhaust gas recirculation amount controller that increases the amount of NOx may be used.

  According to the exhaust gas purification apparatus of the present invention, the ammonia concentration in the exhaust gas flowing through the selective catalytic reduction catalyst is changed in the exhaust gas by the temperature adjusting means during forced regeneration of the particulate filter that raises the exhaust temperature by the exhaust temperature raising means. Since the increase in the temperature of the selective catalytic reduction catalyst is maintained at a set gradient so as to obtain a concentration suitable for reducing and purifying NOx, the amount of NOx in the selective catalytic reduction catalyst and the amount of ammonia are balanced, There is an effect that it is possible to prevent the problem of slipping of high-concentration ammonia from the selective catalytic reduction catalyst, and to prevent generation of ammonia odor due to exhaust gas.

  Further, according to the exhaust purification apparatus of the present invention, the ammonia in the exhaust gas flowing through the selective catalytic reduction catalyst is exhausted by the NOx amount increasing means during the forced regeneration of the particulate filter that raises the exhaust temperature by the exhaust temperature raising means. Since the amount of NOx in the engine exhaust gas is increased so that it is consumed by the NOx in the exhaust gas, the amount of NOx and the amount of ammonia in the selective catalytic reduction catalyst are balanced, and a high concentration is obtained from the selective catalytic reduction catalyst. There is an effect that the problem of ammonia slipping can be prevented and the generation of ammonia odor due to exhaust gas can be prevented.

  Further, during forced regeneration of the particulate filter that raises the exhaust gas temperature by the exhaust gas temperature raising means, the temperature control means reduces and purifies NOx in the exhaust gas by the ammonia concentration in the exhaust gas flowing through the selective catalytic reduction catalyst. The ammonia in the engine exhaust gas flowing in the selective reduction catalyst is kept in the engine exhaust gas by maintaining the temperature increase of the selective reduction catalyst at a set gradient so that the concentration is suitable for the NOx amount and by the NOx amount increasing means. By simultaneously increasing the amount of NOx in the exhaust gas so that it is consumed by NOx, the amount of NOx in the selective catalytic reduction catalyst and the amount of ammonia are balanced, resulting in a high concentration from the selective catalytic reduction catalyst. This prevents the problem of ammonia slip and prevents the generation of ammonia odor caused by exhaust gas.

1 is an overall schematic configuration diagram of an exhaust emission control device as an example of an embodiment for carrying out the present invention. It is a whole schematic block diagram which shows the other example of the temperature control means shown in FIG. It is a whole schematic block diagram of the exhaust gas purification apparatus as another example of the embodiment for carrying out the present invention. FIG. 4 is an overall schematic configuration diagram showing another example of the NOx amount increasing means shown in FIG. 3. It is a graph which shows the example which raises the temperature of a selective reduction type catalyst along a setting gradient by the form of FIG. 1, FIG. 5 is a graph showing an example in which the NOx concentration in the selective catalytic reduction catalyst is increased according to the modes of FIGS. 3 and 4. It is a graph which shows the relationship between the catalyst temperature of a selective reduction catalyst, and the adsorption amount which a selective reduction catalyst adsorbs ammonia. It is a graph which shows the ideal state of the catalyst temperature of a selective reduction catalyst, and the ammonia concentration in a selective reduction catalyst. It is a graph which shows the change of the catalyst temperature at the time of forced regeneration of a particulate filter, and the ammonia concentration in a catalyst.

  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. The exhaust purification apparatus shown in FIG. 1 is in the middle of an exhaust pipe 4 through which exhaust gas 3 discharged from a diesel engine 1 through an exhaust manifold 2 flows. The selective reduction catalyst 5 having the property of selectively reacting NOx with ammonia even in the presence of oxygen is provided.

  An injection nozzle 6 is installed on the inlet side of the selective reduction catalyst 5, and urea water supply including a urea water injection valve 8 is provided between the injection nozzle 6 and a urea water tank 7 provided at a required place. The urea water 11 (reducing agent) in the urea water tank 7 is connected to the selective catalytic reduction catalyst 5 via the urea water injection valve 8 by driving a supply pump 10 connected in the middle of the urea water supply line 9. The urea water adding device 12 is configured by the injection nozzle 6, the urea water tank 7, the urea water injection valve 8, the urea water supply line 9, and the supply pump 10.

  Further, the exhaust pipe 4 upstream of the urea water 11 addition position (opening position of the injection nozzle 6) by the urea water addition device 12 is equipped with an oxidation catalyst 13 in the preceding stage, and the oxidation catalyst is integrated with itself. A particulate filter 14 supported on the catalyst is provided, and immediately after the selective reduction catalyst 5, an ammonia oxidation catalyst 15 for oxidizing excess ammonia as a countermeasure against leaked ammonia is provided.

  A turbocharger 16 driven by the exhaust gas 3 is provided in the middle of the exhaust pipe 4 of the diesel engine 1. The air taken in from the air cleaner 17 and compressed by the turbocharger 16 is cooled by the intercooler 18, and then the intake manifold The engine is supplied to each cylinder of the diesel engine 1 through 19.

  Further, in the diesel engine 1, an exhaust gas recirculation device in which a part of the exhaust gas 3 is taken out by the EGR pipe 20 and cooled by the EGR cooler 21 and then supplied to the intake manifold 19 through the EGR valve 22. 23 is provided.

  Further, the accelerator of the driver's seat (not shown) is provided with an accelerator sensor 24 (load sensor) that detects the accelerator opening as a load of the diesel engine 1, and the rotational speed is set at an appropriate position of the diesel engine 1. A rotation sensor 25 for detection is equipped, and the accelerator opening signal 24a from the acceleration sensor 24 and the rotation sensor 25 and the rotation speed signal 25a are an engine control computer (ECU: Electronic Control Unit) including fuel injection control. It is input to a certain control device 26.

  The control device 26 supplies fuel to the solenoid valve of each injector of the fuel injection device 27 that injects fuel into each cylinder according to the current operating state determined from the accelerator opening signal 24a and the rotational speed signal 25a. A fuel injection controller 28 is provided for instructing a fuel injection signal 28a for main injection and a post injection signal 28b for instructing post injection following the main injection.

  The fuel injection controller 28 determines and outputs the fuel injection signal 28a in the normal mode based on the accelerator opening signal 24a and the rotation speed signal 25a, while the particulate filter 14 needs to be forcibly regenerated. Is switched from the normal mode to the regeneration mode, followed by the non-ignition timing (starting from a crank angle of 90 ° to 90 °) after the main injection of fuel performed near the compression top dead center (crank angle 0 °). The post-injection signal 28b for performing the post-injection in a range of 130 ° is determined and output.

  That is, when post-injection is performed at a non-ignition timing later than the compression top dead center following main injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 3 by this post-injection. The unburned fuel undergoes an oxidation reaction while passing through the oxidation catalyst 13 in the preceding stage of the particulate filter 14, and the particulate filter 14 immediately after the inflow of the exhaust gas 3 heated by the reaction heat. Thus, the catalyst bed temperature is raised and the particulates are burned and removed.

  Here, the control device 26 extracts the fuel injection amount determined from the output values of the rotational speed signal 25a and the fuel injection signal 28a of the diesel engine 1, and generates particulates based on the rotational speed and the injection amount. The basic generation amount of particulates based on the current operating state of the diesel engine 1 is estimated from the map, and this basic generation amount is multiplied by a correction coefficient considering various conditions related to the generation of particulates and The final generated amount is obtained by subtracting the particulate processing amount in the operating state of this, and the final generated amount is accumulated momentarily to estimate the particulate deposited amount, and the accumulated amount is a predetermined target value. When it is estimated that the value has reached, the fuel injection controller 28 switches from the normal mode fuel injection signal 28a to the post injection signal 28b. It has become to so that.

  In the form shown in FIG. 1, when the particulate filter 14 is forcibly regenerated, the temperature of the exhaust gas 3 rises, so that the temperature of the selective catalytic reduction catalyst 5 also rises, and the ammonia adsorbed on the selective catalytic reduction catalyst 5 is released. As a result, the ammonia concentration in the exhaust gas flowing in the selective catalytic reduction catalyst 5 increases, so that the ammonia concentration in the selective catalytic reduction catalyst 5 has a concentration suitable for reducing and purifying NOx in the exhaust gas. Thus, the control device 26 is provided with a temperature adjusting means 30 for maintaining the temperature increase of the selective catalytic reduction catalyst 5 at a set gradient.

  The temperature adjusting means 30 includes a post injection controller 31, and the post injection controller 31 includes a relationship between the post injection amount and the temperature of the selective catalytic reduction catalyst 5 during forced regeneration of the particulate filter 14. The relationship between the temperature of the selective catalytic reduction catalyst 5 and the ammonia concentration in the selective catalytic reduction catalyst 5 is obtained in advance from experience values and inputted. When a forced regeneration start signal 32 is input to the post-injection controller 31, the post-injection controller 31 determines that the ammonia concentration in the exhaust gas flowing through the selective catalytic reduction catalyst 5 is the NOx in the exhaust gas. In order to increase the temperature of the selective catalytic reduction catalyst 5 along the set gradient α in FIG. 5 so as to obtain a concentration suitable for reduction and purification, a post injection amount command 31a is output to the fuel injection controller 28, The post injection amount is controlled. Further, a thermometer 29 for detecting the exhaust gas temperature at the inlet of the selective catalytic reduction catalyst 5 is provided, and the detected temperature signal 29a from the thermometer 29 is input to the post injection controller 31 to select the selective catalytic reduction catalyst 5. The temperature is corrected by feedback.

  Thus, in the form of FIG. 1, during normal operation of the diesel engine 1, the fuel injection amount is controlled by the fuel injection signal 28 a from the fuel injection controller 28, and the exhaust gas from the exhaust pipe 4 is controlled. 3 is selective reduction in the presence of ammonia vaporized by adding urea water 11 by the urea water adding device 12 operated by the urea water addition signals 8a and 10a after the particulates are removed by the particulate filter 14; NOx is removed by the mold catalyst 5 and the exhaust gas 3 is purified.

  During forced regeneration of the particulate filter 14, the fuel injection controller 28 performs control to switch from the fuel injection signal 28a for performing the main injection at the normal time to the post injection signal 28b for performing the post injection following the main injection. At this time, the fuel addition controller 40, to which the start signal 32 is input, sets the fuel so that the temperature of the selective catalytic reduction catalyst 5 raised in temperature by the addition of the fuel 38 increases along the set gradient α shown in FIG. A fuel addition command 40a is output to the adding device 39 to control the amount of fuel 38 added.

  During the forced regeneration of the particulates, the addition of the urea water 11 by the urea water adding device 12 is stopped.

  As described above, the post-injection controller 31 increases the temperature of the selective catalytic reduction catalyst 5 along the set gradient α shown in FIG. 5, so that the NOx amount in the selective catalytic reduction catalyst 5 is equalized. Only a slight increase C ′ occurs, and for this reason, the NOx amount and the ammonia amount in the selective catalytic reduction catalyst 5 are substantially balanced. Therefore, the problem of high-concentration ammonia slipping from the selective catalytic reduction catalyst 5 is prevented, and ammonia odor due to exhaust gas is not generated. Further, as described above, ammonia having a slight increase amount C ′ can be processed by the ammonia oxidation catalyst 15 provided at the subsequent stage of the selective catalytic reduction catalyst 5.

  FIG. 2 shows another example of the temperature adjusting means 30 of FIG. 1, and the temperature adjusting means 30 of FIG. 2 is provided upstream of the oxidation catalyst arranged in the front stage of the particulate filter 14. The addition nozzle 33 and a fuel tank 34 provided at a required place are connected by a fuel addition line 36 provided with an addition valve 35, and the fuel pump 34 provided in the middle of the fuel addition line 36 is driven to drive the fuel tank 34. The fuel addition device 39 is provided so that the fuel 38 can be added to the upstream side of the oxidation catalyst 13 upstream of the particulate filter 14 via the addition valve 35.

  On the other hand, a fuel addition controller 40a that outputs a fuel addition command 40a for controlling the amount of fuel added by the fuel addition device 39 when the forced regeneration start signal 32 is input to the control device 26. 40 is provided. The fuel addition controller 40 includes a relationship between the amount of fuel added by the fuel addition device 39 and the temperature of the selective catalytic reduction catalyst 5 during forced regeneration of the particulate filter 14, and the temperature of the selective catalytic reduction catalyst 5 and the selective catalytic reduction type. The relationship with the ammonia concentration in the catalyst 5 is obtained in advance from experience values and inputted. The fuel addition controller 40 is supplied with a detected temperature signal 29a from a thermometer 29 that detects the exhaust gas temperature at the inlet of the selective catalytic reduction catalyst 5.

  2 shows a case where the fuel injection controller 28 outputs only the fuel injection signal 28a by the main injection in the normal mode to the diesel engine 1, but simultaneously with the fuel addition by the fuel addition device 39, As shown in FIG. 1, the post-injection signal 28b may be output to the diesel engine 1 to perform post-injection simultaneously.

  Further, although not shown in the drawing, the temperature adjusting means 30 includes a burner device upstream of the oxidation catalyst disposed in the previous stage of the particulate filter 14, and further burner control for controlling the amount of fuel added by the burner device. In this case, combustion by the burner device and post-injection by the post-injection signal 28b shown in FIG. 1 may be performed simultaneously.

  Thus, in the form of FIG. 2, when the particulate filter 14 is forcibly regenerated, the fuel addition command 39 from the fuel addition controller 40 causes the fuel addition device 39 to supply the fuel 38 to the inlet of the oxidation catalyst 13 in the upstream stage of the particulate filter 14. At this time, the fuel addition controller 40 adds the fuel so that the temperature of the selective catalytic reduction catalyst 5 raised in temperature by the addition of the fuel 38 increases along the set gradient α shown in FIG. A fuel addition command 40a is output to the device 39 to control the amount of fuel 38 added.

  As described above, since the temperature of the selective catalytic reduction catalyst 5 is raised along the set gradient α shown in FIG. 5 by the fuel addition device 39 and the fuel addition controller 40, the amount of NOx in the selective catalytic reduction catalyst 5 is increased. Only occurs with a slight increase C ′ that is equalized. For this reason, the amount of NOx and the amount of ammonia in the selective catalytic reduction catalyst 5 are substantially balanced. The problem of ammonia slippage is prevented, and ammonia odor due to exhaust gas is not generated.

  FIG. 3 shows another embodiment of the present invention. At the time of forced regeneration of the particulate filter 14, the temperature of the selective reduction catalyst 5 rises as the temperature of the exhaust gas 3 rises, and the selective reduction catalyst. Therefore, the ammonia concentration in the exhaust gas flowing in the selective catalytic reduction catalyst 5 increases due to the ammonia adsorbed on the gas 5 being separated. Therefore, even if the ammonia concentration in the selective catalytic reduction catalyst 5 rapidly increases in this way, the NOx amount increases for increasing the NOx amount in the engine exhaust gas so that the ammonia is consumed by the NOx in the exhaust gas. Means 41 are provided.

  The NOx amount increasing means 41 shown in FIG. 3 has an injection angle controller 42, and the injection angle controller 42 includes the temperature of the selective reduction catalyst 5 and the selective reduction during the forced regeneration of the particulate filter 14. The relationship between the ammonia concentration in the type catalyst 5 and the relationship between the retard angle of the main injection and the NOx concentration in the exhaust gas 3 are obtained in advance from experience values and inputted. When the forced regeneration start signal 32 is input to the injection angle controller 42, the injection angle controller 42 sends the NOx concentration D in the exhaust gas flowing in the selective catalytic reduction catalyst 5 as shown in FIG. The retard control command 42a is output to the fuel injection controller 28 so that the increase amount D ′ of the exhaust gas consumes the increase amount C ′ of the ammonia concentration C that increases in the selective catalytic reduction catalyst 5 during forced regeneration. The delay control of the main injection is performed. A detected temperature signal 29 a from a thermometer 29 that detects the exhaust gas temperature at the inlet of the selective catalytic reduction catalyst 5 is input to the injection angle controller 42. Note that the forced regeneration of the particulate filter 14 may be performed by increasing the exhaust gas temperature by the post injection signal 28b from the fuel injection controller 28, as shown in FIG. 1, or as shown in FIG. The exhaust gas temperature may be raised by the fuel addition device 39 and the fuel addition controller 40.

  Thus, in the embodiment shown in FIG. 3, when the particulate filter 14 is forcibly regenerated, for example, the fuel injection controller 28 performs post injection following the main injection from the fuel injection signal 28a by the main injection at the normal time. At this time, the injection angle controller 42 to which the forced regeneration start signal 32 is input outputs a retard angle control command 42a to the fuel injection controller 28 so as to retard the main injection. Therefore, as shown in FIG. 6, the NOx concentration D in the selective catalytic reduction catalyst 5 increases as an increase amount D ′.

  As described above, the NOx concentration D in the exhaust gas 3 is increased as shown in FIG. 6 by the control by the injection angle controller 42 during forced regeneration of the particulate filter 14 as shown in FIG. Even if the ammonia concentration C increases as the increase amount C ′, the ammonia increase amount C ′ is consumed by the increase amount D ′ of the NOx concentration D. At this time, NOx of the exhaust gas at the outlet of the tail pipe 5a is stable without increasing. Therefore, the problem of high-concentration ammonia slipping from the selective catalytic reduction catalyst 5 is prevented, and ammonia odor due to exhaust gas is not generated.

  FIG. 4 shows another example of the NOx amount increasing means 41 in FIG. 3. The NOx amount increasing means 41 in FIG. The exhaust gas recirculation amount controller 43 is configured to reduce the exhaust gas recirculation amount by the device 23. The exhaust gas recirculation amount controller 43 includes a relationship between the temperature of the selective catalytic reduction catalyst 5 and the ammonia concentration in the selective catalytic reduction catalyst 5 during the forced regeneration of the particulate filter 14, and exhaust gas recirculation by the exhaust gas recirculation device 23. The relationship between the circulation amount and the NOx concentration in the exhaust gas 3 is obtained in advance from experience values and input. When the forced regeneration start signal 32 is input to the exhaust gas recirculation amount controller 43, the exhaust gas recirculation amount controller 43 outputs a recirculation amount decrease command 43a to the EGR valve 22 to thereby reduce the exhaust gas recirculation amount. Thus, the amount of NOx in the exhaust gas 3 is increased. The exhaust gas recirculation amount controller 43 is supplied with a detected temperature signal 29a from a thermometer 29 for detecting the exhaust gas temperature at the inlet of the selective catalytic reduction catalyst 5. For forced regeneration of the particulate filter 14, as shown in FIG. 1, the exhaust gas temperature is raised by the post injection signal 28b from the fuel injection controller 28, or as shown in FIG. In addition, the exhaust gas temperature may be raised by the fuel addition device 39 and the fuel addition controller 40.

  Thus, in the embodiment of FIG. 4, when the particulate filter 14 is forcibly regenerated, for example, the fuel injection controller 28 performs post injection following the main injection from the fuel injection signal 28a by the main injection at the normal time. At this time, the exhaust gas recirculation amount controller 43, to which the forced regeneration start signal 32 is input, outputs a recirculation amount decrease command 43a to the EGR valve 22 to reduce the exhaust gas recirculation amount. Since the control is performed to decrease, the NOx concentration D in the selective catalytic reduction catalyst 5 increases as shown by an increase amount D ′ as shown in FIG.

  As described above, the NOx concentration D in the exhaust gas 3 is increased as shown in FIG. 6 by the control by the exhaust gas recirculation amount controller 43 during the forced regeneration of the particulate filter 14 as shown in FIG. Even if the ammonia concentration C increases as the increase amount C ′ at the time of regeneration, the ammonia increase amount C ′ is consumed by the increase amount D ′ of the NOx concentration D. The problem of high concentration of ammonia slipping from the type catalyst 5 is prevented, and ammonia odor due to exhaust gas is not generated.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment, and the temperature adjusting means and the NOx amount increasing means may be based on systems other than the illustrated example. Of course, various changes can be made without departing from the scope of the present invention.

1 Diesel engine (engine)
DESCRIPTION OF SYMBOLS 3 Exhaust gas 4 Exhaust pipe 5 Selective reduction type | mold catalyst 12 Urea water addition apparatus 13 Oxidation catalyst 14 Particulate filter 23 Exhaust gas recirculation apparatus 28 Fuel injection controller 28b Post injection signal 29 Thermometer 29a Detection temperature signal 30 Temperature control means 31 Post Injection controller 31a Post injection amount command 39 Fuel addition device 40 Fuel addition controller 40a Fuel addition command 41 NOx amount increasing means 42 Injection angle controller 42a Delay angle control command 43 Exhaust gas recirculation amount controller 43a Recirculation amount decrease command

Claims (8)

  A NOx purification device equipped with a selective reduction catalyst in the middle of the exhaust pipe of the engine and adding urea water as a reducing agent upstream of the selective reduction catalyst to reduce and purify NOx; and addition of urea water A particulate filter disposed upstream of the position with an oxidation catalyst attached to the front stage, and the particulates collected by the particulate filter by raising the exhaust temperature at the particulate filter inlet. An exhaust gas purification apparatus configured to burn and forcibly regenerate a particulate filter, wherein the concentration of ammonia in the exhaust gas flowing through the selective catalytic reduction catalyst converts NOx in the exhaust gas during forced regeneration of the particulate filter. A temperature adjusting means is provided for maintaining the temperature increase of the selective catalytic reduction catalyst at a set gradient so that the concentration is suitable for reduction and purification. An exhaust emission control device characterized by balancing the amount of NOx and the amount of ammonia in a selective catalytic reduction catalyst.   A NOx purification device equipped with a selective reduction catalyst in the middle of the exhaust pipe of the engine and adding urea water as a reducing agent upstream of the selective reduction catalyst to reduce and purify NOx; and addition of urea water A particulate filter disposed upstream of the position with an oxidation catalyst attached to the preceding stage, and raising the exhaust temperature at the particulate filter inlet to collect particulates collected by the particulate filter. An exhaust gas purification apparatus that combusts and performs forced regeneration of a particulate filter, wherein ammonia in exhaust gas flowing through the selective catalytic reduction catalyst is consumed by NOx in the exhaust gas during forced regeneration of the particulate filter. The NOx in the selective catalytic reduction catalyst is provided with a NOx amount increasing means for increasing the NOx amount in the engine exhaust gas. An exhaust emission control device characterized in that the x amount and the ammonia amount are balanced.   A NOx purification device equipped with a selective reduction catalyst in the middle of the exhaust pipe of the engine and adding urea water as a reducing agent upstream of the selective reduction catalyst to reduce and purify NOx; and addition of urea water A particulate filter disposed upstream of the position with an oxidation catalyst attached to the preceding stage, and raising the exhaust temperature at the particulate filter inlet to collect particulates collected by the particulate filter. An exhaust gas purification apparatus configured to burn and forcibly regenerate a particulate filter, wherein the concentration of ammonia in the exhaust gas flowing through the selective catalytic reduction catalyst converts NOx in the exhaust gas during forced regeneration of the particulate filter. Temperature control means for keeping the temperature increase of the selective catalytic reduction catalyst at a set gradient so that the concentration is suitable for reduction and purification, and selection A NOx amount increasing means for increasing the NOx amount in the engine exhaust gas so that ammonia in the exhaust gas flowing in the reduction catalyst is consumed by NOx in the exhaust gas. An exhaust emission control device characterized in that the NOx amount and the ammonia amount are balanced.   The exhaust according to claim 1 or 3, wherein the temperature adjusting means is a post-injection controller configured to instruct an injection amount of post-injection to a fuel injection controller that controls main injection and post-injection for the engine. Purification equipment.   The exhaust emission control device according to claim 1 or 3, wherein the temperature adjusting means is a fuel addition device that adds fuel upstream of the oxidation catalyst, and a fuel addition controller that controls a fuel addition amount by the fuel addition device.   The exhaust emission control device according to claim 1 or 3, wherein the temperature adjusting means is a burner device provided upstream of the oxidation catalyst and a burner controller for controlling the amount of fuel added by the burner device.   The NOx amount increasing means is an injection angle controller for instructing a fuel injection controller that controls main injection and post injection to the engine to increase the NOx amount in the exhaust gas by instructing a retard control of the main injection. The exhaust emission control device according to claim 2 or 3.   The NOx amount increasing means includes an exhaust gas recirculation device that recirculates engine exhaust gas to intake air, and an exhaust gas recirculation device that increases the NOx amount in the exhaust gas by commanding a decrease in the exhaust gas recirculation amount by the exhaust gas recirculation device. The exhaust emission control device according to claim 2 or 3, wherein the exhaust gas purification device is a circulation amount controller.

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