JP2005248823A - Reducing agent supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To take a countermeasure against freezing of reducing agent such as urea water to be added to selective reduction type catalyst at as low cost as possible without necessitating large amount of pressurized air. <P>SOLUTION: This reducing agent supply device for adding urea water 5 (reducing agent) to the selective reduction type catalyst 4 is provided with a tank 6 storing urea water 5, a scooping-out pipe 9 with an electric heater 16 inserted into the tank 6 downward from above, an addition line 7 for leading the urea water 5 onto the upstream side more than the selection reduction type catalyst 4 in an exhaust pipe 3, a pump 8 for feeding the urea water 5 onto an exhaust pipe 3 side from a tank 6 side, an air purge line 22 with an opening and closing valve 21 connected with the uppermost stream part of the addition line 7 to lead pressurized air 14 from an air tank 12, and a one-way valve 23 for blocking a flow passage going toward a tank 6 side by air pressure between a join position of the air purge line 22 for the addition line 7 and an upper end of the scooping-out pipe 9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reducing agent supply apparatus.

  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. In recent years, it has been difficult to ensure the safety of traveling with ammonia itself, and 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 decomposed into ammonia and carbon dioxide under a temperature condition of about 170 ° C. or higher, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. The NOx contained therein is reduced and purified well by ammonia.

  FIG. 4 shows an example of a conventional apparatus for adding urea water to the upstream side of the selective catalytic reduction catalyst. In the example shown here, an exhaust pipe 3 through which exhaust gas 2 from the engine 1 circulates is shown. The selective catalytic reduction catalyst 4 is equipped, and this selective catalytic reduction catalyst 4 is formed as a flow-through type honeycomb structure or the like, and has the property of selectively reacting NOx with ammonia even in the presence of oxygen. doing.

  The inlet side of the selective catalytic reduction catalyst 4 is connected to a tank 6 provided at a required place and storing urea water 5 by an addition line 7, and is installed in the middle of the addition line 7. By driving the pump 8, the urea water 5 in the tank 6 is sucked up through the suction pipe 9 and the filter 10.

  On the other hand, an addition valve 11 is provided on the downstream side of the pump 8 of the addition line 7, and an addition air line 15 that leads the pressurized air 14 from the air tank 12 through the protection valve 13 is connected to the addition valve 11. The addition valve 11 allows the urea water 5 to accompany the flow of the pressurized air 14 from the addition air line 15 and be introduced to the inlet side of the selective catalytic reduction catalyst 4 by blowing air.

  Here, the air tank 12 is conventionally mounted on a vehicle such as a bus or a truck, and stores pressurized air 14 pressurized by an engine-driven air compressor (not shown) after removing moisture through a dryer. It is what I did.

  However, in the case where the urea water 5 is used as the reducing agent in this way, the urea water 5 is frozen at −13.5 ° C. or lower. Is indispensable.

  Therefore, conventionally, an electric heater 16 is attached to the suction pipe 9 inserted into the tank 6, and the electric heater 16 is energized to generate heat, whereby the urea frozen in and around the suction pipe 9. The water 5 can be thawed, and the water jacket 17 holds a path from the upper end of the suction pipe 9 to the addition valve 11, and the engine 1 is cooled around the water jacket 17. The water 18 is circulated through the circulation line 19 so that the urea water 5 frozen in the path from the upper end of the suction pipe 9 to the addition valve 11 is defrosted.

  In addition, since the illustrated example is air blowing in the route after the addition valve 11 in the addition line 7, the urea water 5 does not remain when the engine 1 is stopped. Therefore, it is not particularly necessary to take measures against freezing of the urea water 5.

  FIG. 5 shows another example of a conventional apparatus for adding urea water 5 to the upstream side of the selective catalytic reduction catalyst 4. In the example shown here, an injector is provided at the most downstream portion of the addition line 7. 20 is provided so that the urea water 5 introduced from the tank 6 by this injector 20 can be directly injected into the inlet side of the selective catalytic reduction catalyst 4 under the pressure of the pump 8.

  As a countermeasure against freezing of the urea water 5 in such a conventional apparatus, an air purge that guides the pressurized air 14 from the air tank 12 through the protection valve 13 and the on-off valve 21 between the pump 8 and the injector 20 in the addition line 7. The line 22 is connected, and when the engine 1 is stopped, the on-off valve 21 is opened, and the urea water 5 in the addition line 7 is air purged to the tank 6 side and the exhaust pipe 3 side by the pressurized air 14 from the air tank 12. As a countermeasure against freezing, the urea water 5 does not remain in the system by sweeping out (as a countermeasure against freezing of the urea water 5 in the tank 6, an electric heater 16 is attached to the suction pipe 9 as in FIG. 4. is there).

As prior art document information related to measures against freezing of an apparatus for adding a reducing agent to this type of selective reduction catalyst, for example, the following Patent Document 1 has already been proposed.
JP 2000-27627 A

  However, in the former conventional apparatus shown in FIG. 4, the water jacket 17 is required, and the system of the cooling water 18 becomes complicated, resulting in a significant increase in cost. On the other hand, in the latter conventional apparatus shown in FIG. 5, the pressurized air 14 is distributed to the two systems of the tank 6 side and the exhaust pipe 3 side and the effect of the air purge is weakened. There was a problem that a large amount of pressurized air 14 was required to remove all the urea water 5 remaining in the system, which could not be efficiently swept into the system.

  The present invention has been made in view of the above circumstances, and realizes a countermeasure for freezing of a reducing agent such as urea water to be added to the selective catalytic reduction catalyst at an inexpensive cost and without requiring a large amount of pressurized air. The purpose is to get.

  The present invention relates to a tank for storing a reducing agent, a suction pipe with an electric heater inserted downward from above into the tank, and an appropriate position upstream of the selective reduction catalyst of the upper end of the suction pipe and the exhaust pipe. An addition line that connects between the two, a pump that is installed in the addition line and feeds a reducing agent from the tank side to the exhaust pipe side, and is connected to the most upstream part of the addition line to guide pressurized air from the air tank An air purge line with an open / close valve, and a one-way valve that, between the joining position of the air purge line with respect to the addition line and the upper end of the suction pipe, block the flow path toward the tank side with air pressure when the pressurized air is introduced. The reducing agent supply apparatus characterized by the above.

  Thus, if the open / close valve of the air purge line is temporarily opened for a predetermined time when the engine is stopped, the pressurized air from the air tank is introduced into the most upstream part of the addition line, and the air pressure causes the one-way valve to The closed air flows only in one direction toward the exhaust pipe, and the reducing agent in the addition line is efficiently pushed out to the exhaust pipe.

  That is, the reducing agent is pushed out by acting in one direction of the addition line without impairing the effect of the air purge by the pressurized air introduced from the air tank, so that the remaining reducing agent to be substantially swept out of the system remains. If there is a minimum amount of pressurized air suitable for the amount, the reducing agent remaining in the addition line is efficiently removed out of the system.

  Furthermore, even if a slight amount of reducing agent that cannot be air purged remains between the joining position of the air purge line with respect to the addition line and the one-way valve, the one-way valve is used when the air pressure in the system returns to normal pressure after the air purge is completed. Open, and the reducing agent flows down the suction pipe by gravity and is collected in the tank.

  On the other hand, when the reducing agent in the tank has been frozen, the electric heater of the suction pipe is energized to generate heat, and the urea water frozen in and around the suction pipe may be thawed.

  In the present invention, an addition valve is provided on the downstream side of the pump of the addition line, and an addition air line for introducing pressurized air from an air tank is connected to the addition valve, and the addition valve is connected to the addition air line. The flow of pressurized air is accompanied by a reducing agent and guided to the upstream side of the selective catalytic reduction catalyst. Alternatively, an injector is provided at the most downstream portion of the addition line, and is guided from the tank by the injector. The reducing agent may be injected as it is upstream of the selective catalytic reduction catalyst.

  According to the above-described reducing agent supply apparatus of the present invention, the reducing agent remaining in the addition line with the minimum amount of pressurized air can be efficiently processed without requiring a water jacket or a complicated cooling water system. In addition, the remaining reducing agent that cannot be fully purged with air can be finally collected through the one-way valve, flowing down the suction pipe, and collected in the tank. Since the frozen reducing agent can be thawed by the electric heater of the suction pipe, the countermeasure for freezing the reducing agent to be added to the selective catalytic reduction catalyst is realized at the lowest possible cost and without requiring a large amount of pressurized air. It is possible to achieve an excellent effect of being able to.

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

  1 and 2 show an example of an embodiment for carrying out the present invention, and portions denoted by the same reference numerals as those in FIG. 4 represent the same items.

  As shown in FIG. 1, in this embodiment, the water jacket 17 and the circulating line 19 for the cooling water 18 in the conventional apparatus shown in FIG. 4 are not required, and the pressurized air 14 is introduced from the air tank 12 to the addition valve 11. An air purge line 22 is branched in the middle of the air line 15, and the tip of the branched air purge line 22 is connected to the most upstream portion of the addition line 7 via an on-off valve 21, and the air purge line 22 is connected to the addition line 7. A one-way valve 23 is provided between the joining position and the upper end of the suction pipe 9 to block the flow path toward the tank 6 with air pressure when the pressurized air 14 is introduced.

  The details of the one-way valve 23 are as shown in FIG. 2 in an enlarged manner. When the on-off valve 21 composed of an electromagnetic valve is opened and the pressurized air 14 is introduced from the air purge line 22, it is always opened by a spring 24. The held valve body 25 is pushed down against the resilience of the spring 24 by air pressure and is landed on the valve seat 26, whereby the flow path toward the tank 6 is closed. Yes.

  As shown in FIG. 2, the suction pipe 9 equipped with the electric heater 16 can be configured as a heat rubber pipe in which the electric heater 16 (electric heating wire) is embedded.

  Thus, for example, if the control logic is incorporated in an engine control computer (ECU: Electronic Control Unit) so that the on-off valve 21 of the air purge line 22 is temporarily opened for a predetermined time when the engine 1 is stopped, Pressurized air 14 is introduced into the most upstream portion of the addition line 7, and the one-way valve 23 is closed by the air pressure, and the pressurized air 14 flows only in one direction toward the exhaust pipe 3, and the urea water 5 in the addition line 7. Is efficiently pushed to the exhaust pipe 3 side.

  That is, the urea water 5 is pushed out by acting in one direction of the addition line 7 without impairing the effect of the air purge by the pressurized air 14 guided from the air tank 12, so that it should be substantially swept out of the system. If there is a minimum amount of pressurized air 14 corresponding to the remaining amount of the urea water 5, the urea water 5 remaining in the addition line 7 is efficiently removed from the system.

  Furthermore, even if a slight amount of urea water 5 that cannot be air purged remains between the joining position of the air purge line 22 with respect to the addition line 7 and the one-way valve 23, the air pressure in the system returns to normal pressure after the air purge is completed. At this time, the one-way valve 23 is pushed up and opened by the resilience of the spring 24, and the urea water 5 flows down the suction pipe 9 by gravity and is collected in the tank 6.

  On the other hand, when the urea water 5 in the tank 6 is frozen, the electric heater 16 of the suction pipe 9 is energized to generate heat, and the urea water 5 frozen in and around the suction pipe 9 is thawed. You can do it.

  Therefore, according to the above-described embodiment, urea remaining in the addition line 7 with the minimum amount of pressurized air 14 without requiring a water jacket 17 or a complicated cooling water 18 (see FIG. 4) system. The water 5 can be efficiently removed out of the system, and the urea water 5 remaining slightly without being purged of air can finally be recovered through the one-way valve 23 to flow down the suction pipe 9 into the tank 6. Furthermore, since the urea water 5 frozen in the tank 6 can be thawed by the electric heater 16 of the suction pipe 9, it is possible to reduce the freezing measures of the urea water 5 to be added to the selective catalytic reduction catalyst 4 as much as possible. This can be realized at a low cost and without requiring a large amount of pressurized air 14.

  FIG. 3 shows another embodiment of the present invention, where the same reference numerals as those in FIG. 5 denote the same components. In this embodiment, the air purge line 22 in the conventional apparatus of FIG. Is connected to the most upstream portion of the addition line 7 via an on-off valve 21, and between the joining position of the air purge line 22 with respect to the addition line 7 and the upper end of the suction pipe 9, the configuration shown in FIGS. The same one-way valve 23 as in the example is provided.

  Thus, even in this case, the method of adding the urea water 5 to the selective catalytic reduction catalyst 4 is not air blowing, and is the same as in the case of the embodiment shown in FIGS. The action and effect can be obtained, and the countermeasure against freezing of the urea water 5 to be added to the selective catalytic reduction catalyst 4 can be realized at the lowest possible cost and without the need for a large amount of pressurized air 14.

  The reducing agent supply apparatus of the present invention is not limited only to the above-described embodiments. The reducing agent is not limited to urea water, and various other modifications are made within the scope not departing from the gist of the present invention. Of course you get.

It is the schematic which shows an example of the form which implements this invention. It is sectional drawing which expands and shows the principal part of FIG. It is the schematic which shows another form example of this invention. It is the schematic which shows a prior art example. It is the schematic which shows another prior art example.

Explanation of symbols

3 Exhaust pipe 4 Selective reduction catalyst 5 Urea water (reducing agent)
6 Tank 7 Addition Line 8 Pump 9 Suction Pipe 11 Addition Valve 12 Air Tank 14 Pressurized Air 15 Addition Air Line 16 Electric Heater 20 Injector 21 Open / Close Valve 22 Air Purge Line 23 One Way Valve

Claims (3)

  Connection between a tank for storing the reducing agent, a suction pipe with an electric heater inserted downward from above into the tank, and an appropriate position upstream of the selective reduction catalyst of the exhaust pipe and the upper end of the suction pipe An addition line that is connected to the addition line, a pump that supplies the reducing agent from the tank side to the exhaust pipe side, and an on-off valve that is connected to the most upstream part of the addition line and guides pressurized air from the air tank. An air purge line, and a one-way valve that, between the joining position of the air purge line with respect to the addition line and the upper end of the suction pipe, include a one-way valve that blocks the flow path toward the tank side when the pressurized air is introduced. Reducing agent supply device.   An addition valve is provided on the downstream side of the pump of the addition line, and an addition air line for introducing pressurized air from the air tank is connected to the addition valve so that the addition valve can flow the pressurized air from the addition air line. 2. The reducing agent supply apparatus according to claim 1, wherein a reducing agent is accompanied and led to the upstream side of the selective catalytic reduction catalyst.   2. The apparatus according to claim 1, wherein an injector is provided at the most downstream portion of the addition line, and the reducing agent guided from the tank by the injector is directly injected to the upstream side of the selective catalytic reduction catalyst. Reducing agent supply device.

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