JP4166655B2 - Engine exhaust purification system - Google Patents

Description

TECHNICAL FIELD The present invention relates to an engine exhaust purification device (hereinafter referred to as “exhaust purification device”) that reduces and removes nitrogen oxide (NOx) in exhaust using an aqueous urea solution , and in particular, when a storage tank that stores an aqueous urea solution is opened and closed. The present invention relates to a technique for reducing generated bad odor.

As a catalyst purification system for removing NOx contained in engine exhaust, an exhaust purification device disclosed in Japanese Patent Laid-Open No. 2000-27627 (Patent Document 1) has been proposed.
Such an exhaust purification device has a reduction catalyst disposed in an exhaust system of an engine, and injects and supplies a reducing agent upstream of the exhaust of the reduction catalyst to cause a catalytic reduction reaction between NOx in the exhaust and the reducing agent, thereby reducing NOx. It purifies to harmless components. The reducing agent is stored in a storage tank in a liquid state at room temperature, and a necessary amount corresponding to the engine operating state is injected and supplied from the injection nozzle. The reduction reaction uses ammonia having good reactivity with NOx, and as the reducing agent, an aqueous urea solution that is easily hydrolyzed by exhaust heat and water vapor in the exhaust to generate ammonia is used.
JP 2000-27627 A

By the way, according to the above-described conventional exhaust purification device, when the storage tank becomes hot as the ambient temperature changes or the like, the urea aqueous solution stored in the storage tank causes a chemical reaction to become ammonia-based gas, and the upper space of the storage tank. Will be full. When an operator removes the injection cap of the storage tank, for example, when replenishing the urea aqueous solution, the filled ammonia-based gas leaks to the outside, and there is a possibility that a bad odor may be generated .

Therefore, in view of the conventional problems as described above, the present invention is an engine that suppresses malodors that occur when the storage tank is opened and closed by returning the ammonia-based gas in the upper space of the storage tank to the intake system or the exhaust system. An object is to provide an exhaust emission control device.

Therefore, according to the first aspect of the present invention, the reduction catalyst that is disposed in the engine exhaust system and reduces and purifies nitrogen oxides with ammonia , and the ammonia that is disposed downstream of the reduction catalyst and passes through the reduction catalyst. and ammonia oxidation catalyst for oxidizing the an injection nozzle disposed in the exhaust upstream of the reduction catalyst, a storage tank for storing urea aqueous solution converted to the ammonia, the injected urea aqueous solution stored in said storage tank A reducing agent supply device for supplying to the nozzle , a forced discharge means for forcibly discharging the ammonia gas in the upper space of the storage tank to an intake system or an exhaust system upstream of the ammonia oxidation catalyst , and the ammonia oxidation catalyst a temperature detecting means for detecting the temperature of the temperature detected by the temperature detecting means is equal to or higher than the activation temperature of the ammonia oxidation catalyst In, and characterized in that an exhaust gas purifying apparatus for an engine including a control means for actuating said forced discharge means.

The invention according to claim 2 is characterized in that the control means operates the forced discharge means for a predetermined time.
According to a third aspect of the present invention, the forcible discharge means is an electric fan interposed in a pipe connecting the upper space of the storage tank and an intake system or an exhaust system upstream of the ammonia oxidation catalyst. Features.

According to a fourth aspect of the present invention, the pipe is provided with a check valve that opens only in a direction of discharging the ammonia-based gas in the upper space of the storage tank to the intake system or the exhaust system. And
According to a fifth aspect of the present invention, the forced exhaust means communicates a venturi provided in an intake system or exhaust system upstream of the ammonia oxidation catalyst , and an upper space of the storage tank and the intake system or exhaust system. And an opening / closing valve interposed in a pipe that performs the opening / closing operation when the temperature detected by the temperature detection means is equal to or higher than the activation temperature of the ammonia oxidation catalyst. The valve is opened.

In the invention of claim 6, wherein said temperature detecting means, through the upstream side of the exhaust temperature of the ammonia oxidation catalyst, characterized in that to indirectly detect the temperature of the ammonia oxidation catalyst.

According to the first aspect of the present invention, nitrogen oxides contained in the exhaust of the engine are reduced and purified by the reduction catalyst using ammonia obtained by hydrolyzing the urea aqueous solution stored in the storage tank . Further, the ammonia that has passed through the reduction catalyst is oxidized by an ammonia oxidation catalyst disposed downstream thereof, converted into a harmless substance, and then discharged into the atmosphere.
On the other hand, when the temperature in the storage tank rises with a change in ambient temperature or the like, a part of the urea aqueous solution chemically reacts or vaporizes to become ammonia-based gas and fills the upper space of the storage tank. Then, as a result of the engine operating state changing and the exhaust temperature rising, when the temperature of the ammonia oxidation catalyst becomes equal to or higher than its activation temperature, the ammonia-based gas in the upper space of the storage tank is changed to the intake system upstream of the ammonia oxidation catalyst or It is forcibly discharged into the exhaust system. The ammonia-based gas discharged to the intake system or the exhaust system contributes to the reduction and purification reaction in the reduction catalyst , is oxidized in the ammonia oxidation catalyst and converted into a harmless substance, and then discharged into the atmosphere. For this reason, the ammonia concentration in the upper space of the storage tank is greatly reduced, and even if the injection cap is removed to fill the storage tank with the urea aqueous solution , it becomes difficult for the operator to feel the smell of ammonia. The malodor which generate | occur | produces can be reduced.

According to the second aspect of the present invention, the ammonia-based gas in the upper space of the storage tank is forced to the intake system or the exhaust system for a predetermined time when the temperature of the ammonia oxidation catalyst becomes equal to or higher than its activation temperature. Discharged. For this reason, in order to forcibly discharge the ammonia-based gas in the upper space of the storage tank to the intake system or the exhaust system, even if an electric fan or the like that requires driving energy is used, by setting the predetermined time appropriately, While ensuring the effects of the present invention, battery consumption and the like can be suppressed.

According to the third aspect of the present invention, the ammonia gas in the upper space of the storage tank is forcibly discharged to the intake system or the exhaust system by the electric fan. For this reason, even if it does not have a complicated mechanism, the effect of the present invention can be enjoyed only by controlling the operation of the electric fan.
According to the fourth aspect of the present invention, the pipe connecting the upper space of the storage tank and the intake system or the exhaust system is reversely opened only in the direction of discharging the ammonia-based gas in the upper space of the storage tank. Since the stop valve is interposed, it is possible to prevent the fluid flowing through the intake system or the exhaust system from flowing backward even when the electric fan is not operating.

According to the fifth aspect of the present invention, when the temperature of the ammonia oxidation catalyst becomes equal to or higher than the activation temperature, the piping that connects the upper space of the storage tank and the intake system or the exhaust system is opened and passes through the venturi to be negative. The ammonia-based gas in the upper space of the storage tank is forcibly discharged to the intake system or the exhaust system by the intake air or the exhaust gas under pressure. For this reason, energy for driving an electric fan or the like for forcibly discharging ammonia-based gas becomes unnecessary, and battery consumption and the like can be suppressed.

According to the sixth aspect of the present invention, instead of detecting the temperature of the ammonia oxidation catalyst directly, via the exhaust gas temperature on the upstream side with its temperature and closely related, to indirectly detect the temperature of the ammonia oxidation catalyst be able to. For this reason, it is not necessary to perform temperature detection at a thermally disadvantageous position, and thermal obstacles such as a temperature sensor can be reduced.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows the configuration of an exhaust emission control device embodying the present invention.
The exhaust of the engine 10 passes from the exhaust manifold 12 toward the downstream through an exhaust pipe 20 in which an oxidation catalyst 14, a NOx reduction catalyst 16, and a slip-type ammonia oxidation catalyst 18 ( ammonia oxidation catalyst ) are respectively disposed. Discharged inside. Further, the urea aqueous solution stored in the storage tank 22 is injected and supplied together with air to the upstream side of the exhaust of the NOx reduction catalyst 16 via the reducing agent supply device 24 and the injection nozzle 26 .

  In addition, an electric fan 28 for forcibly discharging the gas (ammonia-based gas) in the upper space is attached to the top wall of the storage tank 22 and an injection cap 30 for replenishing the urea aqueous solution is detachable. It is attached. The discharge port of the electric fan 28 is interposed between the oxidation catalyst 14 and the NOx reduction catalyst 16 via a pipe 34 provided with a check valve 32 that opens only in the direction of discharging from the storage tank 22. The exhaust pipe 20 is connected in communication.

  On the other hand, as a control system for the reducing agent supply device 24 and the electric fan 28, the exhaust pipe 20 between the oxidation catalyst 14 and the NOx reduction catalyst 16 and upstream of the position where the pipe 34 from the storage tank 22 is connected. On the side, a temperature sensor 36 (temperature detection means) for detecting the exhaust temperature is attached to indirectly detect the temperature of the slip type ammonia oxidation catalyst 18. If the temperature sensor 36 has sufficient heat resistance, the temperature of the slip type ammonia oxidation catalyst 18 may be directly detected. The exhaust temperature signal from the temperature sensor 36 is input to a control device 38 having a built-in computer, and when the exhaust temperature becomes equal to or higher than the activation temperature (for example, 200 ° C.) of the slip type ammonia oxidation catalyst 18, the electric fan 28. Is operated for a predetermined time. Further, the control device 38 controls the reducing agent supply device 24 in accordance with the engine operating state such as the engine rotation speed and the fuel injection amount.

In the control device 38, control means is realized by a control program stored in a ROM (Read Only Memory). Further, a forced discharge means is configured including the electric fan 28 and the pipe 34.
Next, the operation of the exhaust emission control device having such a configuration will be described.
Exhaust gas from the engine 10 is guided to the oxidation catalyst 14 through the exhaust manifold 12 and the exhaust pipe 20. The oxidation catalyst 14 oxidizes a portion of the nitrogen monoxide (NO) in the exhaust gas to convert it into nitrogen dioxide (NO ₂ ) in order to improve the NOx purification efficiency in the NOx reduction catalyst 16 located downstream thereof. . Exhaust gas in which the composition ratio of NO and NO ₂ is improved by the oxidation catalyst 14 is guided to the NOx reduction catalyst 16 through the exhaust pipe 20. On the other hand, urea aqueous solution corresponding to the engine operating state is injected and supplied from the injection nozzle 26 located upstream of the NOx reduction catalyst 16 together with air, and is hydrolyzed by the exhaust heat and water vapor in the exhaust to become ammonia, together with the exhaust. It is supplied to the NOx reduction catalyst 16. In the NOx reduction catalyst 16, NOx purification is performed by converting NOx in the exhaust into water and harmless gas by a reduction reaction using ammonia. Further, the ammonia that has passed through the NOx reduction catalyst 16 is converted into a harmless substance even if released into the atmosphere by the slip ammonia oxidation catalyst 18 located downstream of the NOx reduction catalyst 16.

  On the other hand, when the temperature in the storage tank 22 rises due to a change in ambient temperature or the like, the aqueous urea solution undergoes a chemical change to become ammonia-based gas, and the upper space of the storage tank 22 is filled with ammonia-based gas. When the engine operating state changes and the exhaust temperature becomes equal to or higher than the activation temperature of the slip type ammonia oxidation catalyst 18, the electric fan 28 operates for a predetermined time. For this reason, the ammonia-based gas in the upper space of the storage tank 22 is forcibly discharged by the electric fan 28 and discharged to the exhaust upstream of the NOx reduction catalyst 16 through the pipe 34. The ammonia-based gas discharged upstream of the NOx reduction catalyst 16 contributes to the reduction reaction in the NOx reduction catalyst 16 and is oxidized in the slip-type ammonia oxidation catalyst 18 located downstream thereof. Since the check valve 32 is interposed in the pipe 34 that connects the electric fan 28 and the exhaust pipe 20 in communication, the exhaust flowing through the exhaust pipe 20 is stored even when the electric fan 28 is not operating. Backflow to the tank 22 can be prevented.

  Therefore, every time the slip type ammonia oxidation catalyst 18 becomes higher than the activation temperature, the ammonia gas in the upper space of the storage tank 22 is forcibly discharged to the upstream side of the NOx reduction catalyst 16, so that the ammonia remaining there Concentration is greatly reduced. For this reason, even if the injection cap 30 is removed in order to replenish the urea aqueous solution, the ammonia concentration is low, so that it is difficult for the operator to feel the ammonia odor, and the bad odor generated when the storage tank 22 is opened and closed can be reduced.

  Instead of the electric fan 28 in the above embodiment, as shown in FIG. 2, a venturi 40 is provided in the exhaust pipe 20 upstream of the NOx reduction catalyst 16, and the ammonia gas in the upper space of the storage tank 22 is provided here. May be discharged. In this case, a normally closed electromagnetic opening / closing valve 42 may be interposed in the pipe 34 so that the electromagnetic opening / closing valve 42 is opened at the timing when the electric fan 28 is operated. In this way, the ammonia gas in the upper space of the storage tank 22 is forcibly discharged by the exhaust gas that has passed through the venturi 40 and has a negative pressure, so that energy for driving the electric fan 28 is increased. This eliminates the need for battery consumption.

  Further, in the above embodiment, the configuration in which the ammonia-based gas in the upper space of the storage tank 22 is discharged upstream of the NOx reduction catalyst 16 is adopted, but if it is upstream of the slip type ammonia catalyst 18, the intake system and You may make it discharge | emit ammonia-type gas to the arbitrary places of an exhaust system.

1 is a configuration diagram of a first embodiment of an exhaust emission control device embodying the present invention. The block diagram of 2nd Embodiment of the exhaust gas purification device which actualized this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 16 NOx reduction catalyst 18 Slip-type ammonia oxidation catalyst 20 Exhaust pipe 22 Storage tank 24 Reducing agent supply apparatus
26 Injection nozzle 28 Electric fan 32 Check valve 34 Piping 36 Temperature sensor 38 Control device 40 Venturi 42 Electromagnetic on-off valve

Claims (6)

A reduction catalyst disposed in the engine exhaust system for reducing and purifying nitrogen oxides with ammonia ;
An ammonia oxidation catalyst disposed downstream of the reduction catalyst and oxidizing the ammonia that has passed through the reduction catalyst;
An injection nozzle disposed upstream of the exhaust of the reduction catalyst;
A storage tank for storing an aqueous urea solution that is converted to ammonia ;
A reducing agent supply device for supplying an aqueous urea solution stored in the storage tank to the injection nozzle ;
Forcibly discharging means for forcibly discharging the ammonia gas in the upper space of the storage tank to an intake system or an exhaust system upstream of the ammonia oxidation catalyst ;
Temperature detecting means for detecting the temperature of the ammonia oxidation catalyst ;
Control means for operating the forced discharge means when the temperature detected by the temperature detection means is equal to or higher than the activation temperature of the ammonia oxidation catalyst ;
An exhaust emission control device for an engine characterized by comprising:   2. The engine exhaust gas purification apparatus according to claim 1, wherein the control means operates the forced exhaust means for a predetermined time. The said forced discharge means is an electric fan interposed in a pipe connecting the upper space of the storage tank and an intake system or an exhaust system upstream of the ammonia oxidation catalyst. Item 3. An exhaust emission control device for an engine according to Item 2. 4. The engine according to claim 3, wherein the pipe is provided with a check valve that opens only in a direction in which ammonia-based gas in the upper space of the storage tank is discharged to an intake system or an exhaust system. Exhaust purification equipment. The forced exhaust means is an open / close unit interposed in a pipe connecting the venturi provided in the intake system or exhaust system upstream of the ammonia oxidation catalyst and the upper space of the storage tank and the intake system or exhaust system. And a valve,
The said control means opens the said on-off valve when the temperature detected by the said temperature detection means becomes more than the activation temperature of the said ammonia oxidation catalyst , The open / close valve is characterized by the above-mentioned. Engine exhaust purification system. Said temperature detecting means, through the upstream side of the exhaust temperature of the ammonia oxidation catalyst, any one of claims 1 to 5, characterized in that to indirectly detect the temperature of the ammonia oxidation catalyst The engine exhaust gas purification apparatus as described.

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