JP4166656B2 - 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 oxides (NOx) in exhaust using a reducing agent, and in particular, when a storage tank that stores the reducing agent 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 required 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. Such malodors are generated not only when a urea aqueous solution is used as a reducing agent, but also when an ammonia aqueous solution, light oil mainly containing hydrocarbons, or the like is used.

  Therefore, in view of the above-described conventional problems, the present invention appropriately discharges the gas in the upper space of the storage tank while oxidizing it with an oxidation catalyst, thereby suppressing the exhaust of the engine that suppresses bad odor generated when the storage tank is opened and closed. An object is to provide a purification device.

Therefore, in the first aspect of the present invention, the reduction catalyst is disposed in the engine exhaust system and reduces and purifies nitrogen oxides with a reducing agent, the storage tank for storing the reducing agent, and the storage tank stored in the storage tank. A reducing agent supply device that supplies the reducing agent to the reduction catalyst, a forced exhaust device that forcibly exhausts the gas in the upper space of the storage tank, and a gas that is exhausted by the forced exhaust device is temporarily adsorbed. An adsorbing device, an oxidation catalyst for oxidizing the gas separated from the adsorbing device, a reducing agent temperature detecting means for detecting a reducing agent temperature in the storage tank, and a reducing agent temperature detected by the reducing agent temperature detecting means And an operation control means for operating the forcible exhaust device when it is equal to or greater than a first predetermined value .

In the invention of claim 2, catalyst temperature detection means for detecting the catalyst temperature of the oxidation catalyst, and catalyst activation means for activating the oxidation catalyst based on the catalyst temperature detected by the catalyst temperature detection means; , Provided.

In a third aspect of the invention, the apparatus includes a heating device that heats the oxidation catalyst, and the catalyst activation means is configured such that the catalyst temperature detected by the catalyst temperature detection means is equal to or higher than the activation temperature of the oxidation catalyst. The heating device is controlled.
According to a fourth aspect of the present invention, there is provided heating stop means for stopping the operation of the heating device when the catalyst temperature detected by the catalyst temperature detection means is equal to or higher than a second predetermined value. .

The invention according to claim 5 is characterized in that the adsorption device is mordenite, cobalt-supported mordenite, or activated carbon.
The invention according to claim 6 is characterized in that the oxidation catalyst is an electrothermal honeycomb catalyst.

  According to the first aspect of the present invention, the nitrogen oxide contained in the exhaust of the engine is reduced and purified by the reduction catalyst using the reducing agent supplied from the storage tank by the reducing agent supply device to become a harmless substance. After that, it is 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 reducing agent chemically reacts or vaporizes to become gas and fills the upper space of the storage tank. The gas in the upper space of the storage tank is forcibly discharged from the storage tank by the forced discharge device and is temporarily adsorbed by the adsorption device. The gas adsorbed by the adsorption device is gradually separated when a predetermined condition is satisfied, is oxidized in the oxidation catalyst and converted into a harmless substance, and then released into the atmosphere.

  Therefore, even in a situation where gas is generated from the reducing agent in the storage tank, the gas in the upper space is forcibly discharged, so that the concentration of the gas remaining there is greatly reduced. For this reason, even if the injection cap is removed in order to replenish the storage tank with the reducing agent, it becomes difficult for the operator to feel the odor of the reducing agent, and the bad odor generated when the storage tank is opened and closed can be reduced. In addition, the gas forcedly discharged from the upper space of the storage tank is temporarily adsorbed by the adsorption device and then gradually desorbs and is oxidized in the oxidation catalyst, so that a gas odor may drift around the storage tank. Is prevented.

At this time, the forced discharge device is activated only when the reducing agent temperature in the storage tank is equal to or higher than the first predetermined temperature, that is, when there is a possibility that gas is generated from the reducing agent. The operation of the discharge device is prevented. For this reason, the operation sound of the forced discharge device and the energy required for the operation can be suppressed to the minimum necessary.
According to the second aspect of the present invention, since the activation is performed based on the catalyst temperature of the oxidation catalyst, the oxidation of the gas generated from the reducing agent can be prevented from becoming insufficient.

According to the third aspect of the invention, since the heating device for heating the oxidation catalyst is controlled so that the catalyst temperature of the oxidation catalyst becomes equal to or higher than the activation temperature, the oxidation catalyst can be reliably maintained in the active state. it can.
According to the invention of claim 4 , when the catalyst temperature of the oxidation catalyst is equal to or higher than the second predetermined value, that is, the temperature at which the oxidation catalyst is sufficiently activated, the operation of the heating device is stopped. While suppressing the energy consumed by the heating device, it is possible to prevent thermal damage caused by the temperature of the oxidation catalyst being increased more than necessary.

According to invention of Claim 5, the gas forcedly discharged from the upper space of the storage tank can be adsorb | sucked efficiently by making an adsorption | suction apparatus into mordenite, cobalt carrying | support mordenite, or activated carbon .
According to the sixth aspect of the invention, by using the electrocatalytic honeycomb catalyst as the oxidation catalyst, the heating device can be easily configured while suppressing an increase in the flow resistance of the gas generated from the reducing agent.

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 from the engine 10 is exhausted from the exhaust manifold 12 to 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 are respectively disposed. . Further, the liquid reducing agent 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. Here, as the liquid reducing agent, a urea aqueous solution that easily generates ammonia by hydrolysis is used as the liquid reducing agent. However, in response to the reduction reaction of the NOx reduction catalyst 16, a light oil containing hydrocarbon as a main component is used. May be used.

  Further, an injection cap 28 for replenishing the urea aqueous solution is detachably attached to the top wall of the storage tank 22 and a forced fan such as an electric fan for forcibly discharging the gas (ammonia-based gas) in the upper space. A discharge device 30 is attached. Further, on the discharge side of the forced exhaust device 30, an adsorption device 32 such as mordenite, cobalt-supported mordenite or activated carbon that temporarily adsorbs the forced exhaust gas, and an oxidation catalyst that oxidizes the gas separated from the adsorption device 32. 34 are arranged in this order. Here, as the oxidation catalyst 34, it is desirable to use an electrothermal honeycomb catalyst in which a catalytic metal or the like is wash-coated on a honeycomb carrier having a low flow resistance and a heating device such as an electric heater for promoting the activation is incorporated. Note that the heating device is not limited to the configuration built in the oxidation catalyst 34, and may be configured to be provided in addition thereto.

  On the other hand, as a control system of the exhaust purification device, a reducing agent temperature sensor 36 (reducing agent temperature detecting means) that detects the urea aqueous solution temperature in the storage tank 22 and a catalyst temperature sensor 38 (catalyst) that detects the catalyst temperature of the oxidation catalyst 34. Temperature detecting means) and a control device 40 incorporating a computer. Then, the control device 40 controls the reducing agent supply device 24 according to the engine operating state such as the engine speed and the fuel injection amount by a control program stored in a ROM (Read Only Memory), and the reducing agent temperature sensor. Based on the temperature signals from 36 and the catalyst temperature sensor 38, the heating device for activating the forced discharge device 30 and the oxidation catalyst 34 is controlled. The control device 40 realizes an operation control means, a catalyst activation means, and a heating stop means.

FIG. 2 is a flowchart showing the control contents repeatedly executed at predetermined time intervals in the control device 40 after the engine is started.
In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the urea aqueous solution temperature is read from the reducing agent temperature sensor 36.
In step 2, whether the urea aqueous solution temperature is a predetermined value above T _1, i.e., whether or not reached slightly lower first predetermined temperature than the temperature (e.g. 80 ° C.) of ammonia-based gas is generated from the urea aqueous solution Is determined. If the urea aqueous solution temperature is equal to or higher than the predetermined value T ₁ , the process proceeds to step 3 (Yes), while if the urea aqueous solution temperature is lower than the predetermined value T ₁ , the process is ended (No).

In step 3, the urea aqueous solution temperature in the storage tank 22 is a predetermined value above T _1, i.e., since the ammonia-based gas has reached a temperature slightly lower than the temperatures generated to actuate the forced discharge device 30 a predetermined time, the storage tank The ammonia gas in the upper space of 22 is forcibly discharged.
In addition, a series of processes in step 1 to step 3 correspond to the operation control means.
In step 4, the catalyst temperature of the oxidation catalyst 34 is read from the catalyst temperature sensor 38.

In step 5, the catalyst temperature of the oxidation catalyst 34 is equal to or less than a predetermined value T _2, i.e., the catalyst temperature is whether reached the activation temperature of the oxidation catalyst 34 (for example, 200 ° C.) is determined. Since the catalyst temperature oxidation catalyst 34 equal to or less than a predetermined value T ₂ is in a non-active, the process proceeds to step 6 (Yes), the energization is started the heating device. On the other hand, the catalyst temperature goes to step 7 is higher than a predetermined value T ₂ (No).

In step 7, whether or not the catalyst temperature of the oxidation catalyst 34 is equal to or higher than a predetermined value T _3, that is, whether or not the oxidation catalyst 34 is equal to or higher than a second predetermined value (for example, 400 ° C.) that is sufficiently activated. Is determined. If the catalyst temperature is equal to or higher than the predetermined value T ₃ , the oxidation catalyst 34 is sufficiently activated, so the process proceeds to step 8 (Yes), and the energization to the heating device is stopped to suppress unnecessary power consumption. Let On the other hand, if the catalyst temperature is lower than the predetermined value T ₃ , the current to the heating device is increased or decreased according to the catalyst temperature at that time in order to maintain the catalyst temperature at the predetermined values T _{2 to} T ₃ .

A series of processes in Step 4 to Step 9 corresponds to the catalyst activation means, and a series of processes in Step 4, Step 7 and Step 8 correspond to the heating stop means.
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, surplus ammonia that has not contributed to the reduction reaction and has passed through the NOx reduction catalyst 16 is made harmless even if released into the atmosphere by the slip-type ammonia oxidation catalyst 18 located downstream of the NOx reduction catalyst 16. Converted.

On the other hand, when the temperature in the storage tank 22 rises due to a change in ambient temperature or the like, the urea aqueous solution undergoes a chemical change to become ammonia-based gas, which fills the upper space of the storage tank 22. At this time, since the urea aqueous solution temperature becomes a predetermined value above T _1, forcible discharge device 30 is operated for a predetermined time by the control unit 40. For this reason, the ammonia gas in the upper space of the storage tank 22 is forcibly discharged by the forced discharge device 30 and temporarily adsorbed by the adsorption device 32. The ammonia-based gas adsorbed by the adsorption device 32 is gradually separated when a predetermined condition is satisfied, is oxidized in the oxidation catalyst 34 and converted into a harmless substance, and then released into the atmosphere.

  Therefore, under the situation where ammonia-based gas is generated from the urea aqueous solution in the storage tank 22, the ammonia-based gas in the upper space is forcibly discharged, so that the concentration of ammonia remaining therein is greatly reduced. For this reason, even if the injection cap 28 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. Further, the ammonia-based gas forcibly discharged from the upper space of the storage tank 22 is temporarily adsorbed by the adsorption device 32 and then gradually desorbed and is oxidized in the oxidation catalyst 34. Ammonia odor can be prevented from drifting.

In addition, since the heating device is controlled so that the catalyst temperature of the oxidation catalyst 34 is maintained within a predetermined temperature range equal to or higher than the activation temperature, the oxidation catalyst 34 is kept in an active state while suppressing unnecessary power consumption. can do. In particular, when the catalyst temperature of the oxidation catalyst 34 is equal to or higher than the predetermined temperature T ₃ , that is, when the oxidation catalyst 34 is sufficiently activated, the operation of the heating device is stopped, so that the oxidation catalyst 34 is heated more than necessary. No heat damage can be prevented.

Configuration diagram of an exhaust emission control device embodying the present invention Flow chart showing control contents executed by control device

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 16 NOx reduction catalyst 20 Exhaust pipe 22 Storage tank 24 Reducing agent supply apparatus 30 Forced discharge apparatus 32 Adsorption apparatus 34 Oxidation catalyst 36 Reducing agent temperature sensor 38 Catalyst temperature sensor 40 Control apparatus

Claims (6)

A reduction catalyst disposed in the engine exhaust system for reducing and purifying nitrogen oxides with a reducing agent;
A storage tank for storing the reducing agent;
A reducing agent supply device for supplying the reducing agent stored in the storage tank to the reduction catalyst;
A forced discharge device for forcibly discharging the gas in the upper space of the storage tank;
An adsorption device for temporarily adsorbing the gas discharged by the forced discharge device;
An oxidation catalyst for oxidizing the gas separated from the adsorption device;
Reducing agent temperature detecting means for detecting the reducing agent temperature in the storage tank;
An operation control means for operating the forced discharge device when the reducing agent temperature detected by the reducing agent temperature detecting means is equal to or higher than a first predetermined value;
An exhaust emission control device for an engine characterized by comprising: Catalyst temperature detecting means for detecting the catalyst temperature of the oxidation catalyst;
Catalyst activation means for activating the oxidation catalyst based on the catalyst temperature detected by the catalyst temperature detection means;
The exhaust emission control device for an engine according to claim 1, further comprising: A heating device for heating the oxidation catalyst;
The engine exhaust according to claim 2, wherein the catalyst activating means controls the heating device so that the catalyst temperature detected by the catalyst temperature detecting means becomes equal to or higher than the activation temperature of the oxidation catalyst. Purification equipment. The engine exhaust according to claim 3 , further comprising a heating stop means for stopping the operation of the heating device when the catalyst temperature detected by the catalyst temperature detecting means is equal to or higher than a second predetermined value. Purification equipment. 5. The engine exhaust gas purification apparatus according to claim 1, wherein the adsorption device is mordenite, cobalt-supported mordenite, or activated carbon . The engine exhaust purification apparatus according to any one of claims 1 to 5, wherein the oxidation catalyst is an electrothermal honeycomb catalyst .

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