JP6733352B2 - Oxidation catalyst and exhaust gas purification system - Google Patents

Description

The present invention relates to an exhaust gas purification system and an exhaust gas purification method for purifying nitrogen oxides in exhaust gas of an internal combustion engine mounted on a vehicle.

An internal combustion engine mounted on a vehicle is equipped with an exhaust gas purification system that combines an oxidation catalyst device, a collection filter device for purifying particulate matter, a selective reduction catalyst device (SCR catalyst device) for purifying nitrogen oxides, and the like. , Purifying exhaust gas. This selective reduction catalyst device purifies nitrogen oxides in exhaust gas by using ammonia generated by hydrolysis of urea water supplied from the urea water supply device on the upstream side as a reducing agent. There is.

At the time of purifying this nitrogen oxide, the catalyst temperature of the selective reduction catalyst or this selection is selected with the intention of properly controlling the injection amount of the reducing agent such as urea water to maintain a high NOx reduction rate. The injection amount of urea water is controlled according to the exhaust temperature on the upstream side of the reduction catalyst (see, for example, Patent Documents 1 and 2).

JP, 2006-46289, A JP, 2010-71227, A

On the other hand, exhaust gas purification systems are often equipped with a collection filter device in addition to a selective reduction catalyst device, so that the exhaust gas is forced to rise before the amount of trapped particulate matter reaches saturation. Forced regeneration control is performed to burn and remove the particulate matter that is warmed and collected. During this forced regeneration control, the temperature of the exhaust gas passing through the selective reduction catalyst device may rise to a high temperature of about 350° C. to 400° C., which deteriorates the exhaust gas purification rate and is irreversible with the selective reduction catalyst device. There is a problem that the deterioration may occur.

An object of the present invention is to prevent the temperature of the selective reduction catalyst device from becoming excessively high even during forced regeneration control of the collection filter device, and to cause irreversible destruction of the selective reduction catalyst device with structural damage. To provide an exhaust gas purifying system and an exhaust gas purifying method capable of maintaining a high purifying performance while achieving a long service life of a selective reduction catalyst device while avoiding any significant deterioration.

An exhaust gas purification system of the present invention for achieving the above object is a collection filter device that collects and purifies particulate matter, a selective reduction type catalyst device that purifies nitrogen oxides, and the selective reduction type. In the exhaust gas purification system comprising a reducing solution supply device that supplies a reducing solution into the exhaust gas on the upstream side of the catalyst device, and a control device that controls the supply amount of the reducing solution, the control device is At the time of controlling the supply amount of the reducing solution, during the forced regeneration control of the collection filter device, the catalyst solution temperature of the selective reduction type catalyst device is supplied from the reducing solution supply device so as not to exceed a preset upper limit temperature. And a urea water increase control for increasing the supply amount of the reducing solution supplied above the minimum amount necessary for reducing the nitrogen oxides in the exhaust gas, and cooling the selective reduction catalyst device with the reducing solution. When the forced regeneration control is terminated during the urea water increase control, the supply amount of the reducing solution supplied from the reducing solution supply device is lower than the minimum necessary amount capable of reducing nitrogen oxides in exhaust gas. Urea water reduction control to reduce the amount, the cumulative amount of the reduction amount of the reducing solution in the urea water reduction control, when the amount corresponding to the cumulative amount of the increasing amount of the reducing solution in the urea water increasing control, the reduction The urea solution normal control is performed so that the supply amount of the reducing solution supplied from the solution supply device is the minimum amount necessary to reduce the nitrogen oxides in the exhaust gas. A characteristic exhaust gas purification system.

Further, the exhaust gas purifying method of the present invention for achieving the above object, when purifying exhaust gas of an internal combustion engine, collects and purifies particulate matter with a trapping filter device, and supplies a reducing solution. In the exhaust gas purification method for purifying nitrogen oxides in a selective reduction catalyst device using a reducing solution supplied to the exhaust gas in the device, the selective reduction catalyst is controlled during forced regeneration control of the collection filter device. The supply amount of the reducing solution supplied from the reducing solution supply device is set so that the catalyst temperature of the device does not become higher than a preset upper limit temperature than a necessary minimum amount capable of reducing nitrogen oxides in exhaust gas. Also, the selective reduction type catalyst device is cooled by this reducing solution, and when the forced regeneration control is completed while the reducing solution is being increased, the reducing solution is supplied from the reducing solution supply device. The amount is reduced below the minimum amount required to reduce the nitrogen oxides in the exhaust gas, and the cumulative amount of reduction of the reducing solution in this reduction is calculated as When the amount corresponding to the cumulative amount is reached, the supply amount of the reducing solution supplied from the reducing solution supply device is set to the minimum amount necessary to reduce the nitrogen oxides in the exhaust gas. Exhaust gas purification method.

According to the exhaust gas purifying system and the exhaust gas purifying method of the present invention, during the forced regeneration control of the trapping filter device, the catalyst temperature of the selective reduction catalyst device is reduced so as not to exceed the preset upper limit temperature. Since the selective reduction type catalyst device is cooled by increasing the supply amount of the solution above the minimum amount required to reduce the nitrogen oxides in the exhaust gas, the selective reduction type catalyst device is cooled even during the forced regeneration control of the collection filter device. Since the catalyst temperature of the catalytic converter can be maintained at a temperature lower than the upper limit temperature, irreversible deterioration that accompanies structural destruction of the selective catalytic reduction apparatus is avoided and the life of the selective catalytic reduction apparatus is extended. While maintaining high purification performance.

It is a figure which shows typically the structure of the exhaust gas purification system of embodiment which concerns on this invention. It is a figure which shows an example of the control flow of the exhaust gas purification method of embodiment which concerns on this invention. It is a figure which shows typically the structure of arrangement|positioning different from FIG. 1 in the exhaust gas purification system of embodiment which concerns on this invention. It is a figure which shows typically the structure of the exhaust gas purification system as a comparative example.

Hereinafter, an exhaust gas purification system and an exhaust gas purification method according to embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, an exhaust gas purification system 1 according to an embodiment of the present invention includes an oxidation catalyst device (DOC) 20 in an exhaust passage 11 through which exhaust gas G discharged from an engine (internal combustion engine) 10 passes. , A collection filter device (DPD) 30 that collects and purifies PM (particulate matter), and an SCR catalyst device (selective reduction catalyst device: SRC) 40 that purifies NOx (nitrogen oxide) in the exhaust gas G And a urea water supply device (reduction solution supply device) 41 that supplies urea water (reduction solution) U into the exhaust gas G on the upstream side of the SCR catalyst device 40, and the supply amount of the reduction solution is controlled. An exhaust gas purification system including a control device 50.

Then, the oxidation catalyst device 20 uses oxygen (O ₂ ) in the exhaust gas G to oxidize hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gas G, and to include them in PM. It is an exhaust gas purification device that oxidizes SOF (unburned combustible substance) that is converted into water (H ₂ O) and carbon dioxide (CO ₂ ), and is composed of ceramics such as cordierite. The full-throw type honeycomb structure 21 is configured to carry a precious metal such as platinum (Pt), palladium (Pd), and rhodium (Rh) as an oxidation catalyst.

The trapping filter device 30 is for trapping PM in the exhaust gas G, and is, for example, a monolith honeycomb type in which the inlets and outlets of cells (channels) of a honeycomb of porous ceramic are alternately plugged. It is composed of wall flow type filters. Then, the exhaust gas G flows from the inlet of the unsealed cell of the collection filter device 30 and the PM outlet cell wall formed at the boundary between the adjacent outlet and the unsealed cell. It passes through and exits the adjacent exit from the exit of the unsealed cell. When the exhaust gas G passes through the cell wall, PM contained in the exhaust gas G is collected on the cell wall.

Since the amount of collected PM that can be collected is limited in this collection filter device 30, the temperature of the exhaust gas G passing through the collection filter device 30 is raised before the amount of collected PM is saturated. The forced regeneration control for burning and removing the collected PM is regularly performed.

In this forced regeneration control, the fuel F is directly injected into the exhaust pipe of the ventilation passage 11 from the fuel injection nozzle 31 provided in the exhaust passage 11, or the post injection of the cylinder fuel injection of the engine 10 is performed. , The fuel F is supplied into the exhaust gas G. As a result, the unburned fuel in the exhaust gas G is increased, the unburned fuel is oxidized by the catalytic reaction in the oxidation catalyst device 20, and the temperature of the exhaust gas G is raised by the heat generated by this oxidation. At the same time, nitric oxide (NO) in the exhaust gas G is oxidized to nitrogen dioxide (NO ₂ ) to bring the NO:NO ₂ ratio in the exhaust gas G close to 1:1. The temperature increase and the change in the ratio of NOx promote the combustion of PM in the collection filter device 30 and, at the same time, promote the purification of NOx in the SCR catalyst device 40.

Further, the SCR catalyst device 40 is one in which catalytic zeolite such as iron ion-exchange aluminosilicate is carried on a carrier such as a ceramic honeycomb, and urea injected by a urea water supply device 41 provided in the exhaust passage 11 on the upstream side thereof. Ammonia (NH ₃ ) generated by hydrolysis of water U by the heat of exhaust gas G is used as a reducing agent, and NOx contained in exhaust gas G is purified to nitrogen (N ₂ ) and water (H ₂ O). It is a device. In the reduction of NOx, ammonia is adsorbed by the SCR catalyst device 40, and then NOx is reduced by a catalytic reaction. This NOx purification method using an SCR catalyst has the advantages that the NOx reduction rate is high and there is little adverse effect on fuel efficiency.

In the present invention, the SCR catalyst device 40 is composed of an upstream first SCR catalyst device 40A and a downstream second SCR catalyst device 40B, and the first SCR catalyst device 40A is installed in the engine 10. It is configured to have a catalyst carrying amount and a device capacity capable of sufficiently reducing NOx in the exhaust gas G with the supply amount Wu of the urea water U corresponding to the NOx generated in the entire operating state. ..

On the other hand, the second SCR catalyst device 40B is formed by hydrolysis of the urea water U when the urea water increase control is performed to increase the supply amount Wu of the urea water U from the urea water supply device 41 described later. Ammonia cannot be completely consumed by the first SCR catalyst 40A and flows out from the first SCR catalyst 40A. Therefore, the amount of catalyst carried and the capacity of the device that can sufficiently adsorb this outflowing ammonia and suppress the outflow to the downstream side can be provided. Configured to have. In the second SCR catalyst device 40B, it is desired that the catalyst composition has a large ammonia adsorption amount, for example, silicoaluminophosphate type zeolite (SAPO).

Further, in order to improve the cooling effect of the urea water Un on the first SCR catalyst 40A, a cooling accelerating rotary blade 42 is provided between the urea water supply device 41 and the first SCR catalyst 40A to provide the urea water supply device. With the jet flow of the urea water U supplied from 41, the cooling-promoting rotary blades 42 are rotated on the upstream side to blow air to the first SCR catalyst 40A to accelerate the cooling of the first SCR catalyst 40A. It is preferable to configure.

In addition, the distribution of the urea water U flowing into the first SCR catalyst 40A and the amount of exhaust gas in the flow passage cross section is adjusted by the cooling accelerating rotary blades 42, so that the temperature of the first SCR catalyst 40A is likely to increase. It is preferable to configure such that a large amount of urea water U flows in. Even when the cooling promotion rotary vane 42 is not provided, the injection distribution of the urea water U supplied from the urea water supply device 41 is adjusted to increase the urea water in a portion of the first SCR catalyst 40A that is likely to reach a high temperature. It is preferable to configure so that U flows in.

The exhaust gas purification system 1 also includes an exhaust gas temperature sensor 51 for detecting or estimating the catalyst temperature Tc in the SCR catalyst device 40. In the configuration shown in FIG. 1, the exhaust gas temperature sensor 51 is arranged on the downstream side of the SCR catalyst device 40 and detects the temperature Tgd of the exhaust gas G flowing out to the SCR catalyst device 40. Alternatively, the exhaust gas temperature sensor 51 may be arranged upstream of the SCR catalyst device 40 to detect the temperature Tgu of the exhaust gas G flowing out from the SCR catalyst device 40.

Further, the exhaust gas purification system 1 includes NOx concentration sensors 52 and 53 in order to control the supply amount Wu of the urea water U. The first NOx concentration sensor 52 is arranged on the upstream side of the SCR catalyst device 40, detects the NOx concentration C1 of the exhaust gas G flowing into the SCR catalyst device 40, and the second NOx concentration sensor 53 is the SCR catalyst. The NOx concentration C2 of the exhaust gas G flowing out from the SCR catalyst device 40 is detected by being arranged on the downstream side of the device 40. Further, a differential pressure sensor 54 for detecting the differential pressure ΔP across the collection filter device 30 is provided.

In the present invention, the control device 50 that controls the supply amount Wu of the urea water U detects the temperature sensor 51 during the forced regeneration control of the collection filter device 30 when controlling the supply amount Wu of the urea water U. The supply amount Wu of the urea water U supplied from the urea water supply device 41 is set to NOx in the exhaust gas G so that the catalyst temperature Tc of the SCR catalyst device 40 estimated from the temperature Tgd does not exceed a preset upper limit temperature Tu. Is increased beyond the minimum necessary amount Wb that can reduce the urea water, and the urea water increase control for cooling the SCR catalyst device 40 with this urea water U is performed.

Although it is preferable to directly measure the catalyst temperature Tc of the SCR catalyst device 40, it is generally difficult to measure the temperature Tgd of the exhaust gas G after passing through the SCR catalyst device 40 by the exhaust gas temperature sensor 51. The catalyst temperature Tc of the SCR catalyst device 40 is estimated from the detected temperature Tg. As a simple method, the detection temperature Tgd is set to the catalyst temperature Tc.

Further, the preset upper limit temperature Tu is a temperature in which the temperature Ts at which the irreversible deterioration of the SCR catalyst device 40 starts has a margin, and is preferably within a temperature range in which the purification performance of the SCR catalyst device 40 does not deteriorate. It is the temperature on the high temperature side, and is the temperature set in advance by experimental results and the like. For example, a temperature in the range of 350°C to 400°C is adopted. The upper limit temperature Tu is a temperature corresponding to the catalyst temperature Tc, but when the temperature Tgd of the exhaust gas G is adopted, the difference between the temperature Tgd of the exhaust gas G and the catalyst temperature Tc is taken into consideration. It is set as a temperature corresponding to the temperature Tgd. Further, it is more preferable that the upper limit temperature Tu is a temperature at which the catalyst temperature Tc of the SCR catalyst device 40 can be maintained in a high purification performance.

Further, the minimum necessary amount Wb of urea water U capable of reducing NOx in the exhaust gas G is the engine operating state Ec set by the engine speed Ne and the load Q (or the fuel injection amount q) of the engine 10. On the other hand, the amount of urea water U that can generate the amount of ammonia that can reduce NOx discharged from the engine 10 in the engine operating state Ec by a chemical reaction from the engine operating state Ec at the time of control, in other words, the discharge amount The amount of urea water that has a chemical equivalent relationship with the NOx that is stored.

Further, the ammonia that is excessively generated by the excessive injection of the urea water U during the urea water increase control is adsorbed to the new second SCR catalyst device 40B that is installed downstream of the first SCR catalyst device 40A and has a large ammonia adsorption amount. Let That is, by arranging the second SCR catalyst device 40B having a large amount of adsorbed ammonia, the purging performance is maintained and the outflow (slip) of extra ammonia is suppressed.

Further, by performing the urea water reduction control in which the supply amount Wu of the urea water U after the forced regeneration control of the collection filter device 30 is finished is reduced by the amount increased during the forced regeneration control, The ammonia adsorbed by the SCR catalyst device 40B is used for purification of NOx. This urea water reduction control is performed to reduce the amount ΔWu of the urea water U corresponding to the amount ΔWu increased by the urea water increase control during the forced regeneration control, and thereafter, the normal urea water control is resumed.

Next, an exhaust gas purification method according to an embodiment of the present invention will be described. In this exhaust gas purification method, when purifying the exhaust gas of the engine 10, the collection filter device 30 collects and purifies PM, and the urea water supply device 41 supplies urea water U into the exhaust gas G. Is a method for purifying NOx in the SC catalyst device 40 by using the exhaust gas purifying method. In this exhaust gas purification method, the catalyst temperature Tc of the SCR catalyst device 40 is set in advance during forced regeneration control of the collection filter device 30. In order to prevent the temperature from becoming higher than the upper limit temperature Tu, the supply amount Wu of the urea water U supplied from the urea water supply device 41 is increased above the minimum necessary amount Wb capable of reducing NOx in the exhaust gas G, and this urea is supplied. This is a method of cooling the SCR catalyst device with water U.

More specifically, this method can be performed by control according to the control flow of FIG. The control flow of FIG. 2 is shown as a control flow that is started by being called from the advanced control flow when the engine 10 is started, and returns to the advanced control flow when the engine 10 is stopped and ends. When this control flow starts, it is determined in step S10 whether the forced regeneration control of the collection filter device 30 is being performed.

If it is determined in step S10 that the forced regeneration control is not being performed, the process proceeds to step S20, and the urea water normal control for NOx purification is performed for a preset control time Δt. This normal urea water control is control for supplying the urea water supply device 41 into the exhaust gas G with the amount Wb of urea water U necessary and sufficient for purifying NOx discharged in the engine operating state Ec.

As the urea water supply control from the urea water supply device 41, the NOx emission amount is estimated from the engine operating state Ec, and the necessary and sufficient supply amount Wb of the urea water U corresponding to the NOx emission amount is calculated, Feed-forward control for supplying the urea water U with this supply amount Wb, and feedback for controlling the supply amount Wu of the urea water U so that the detection values C1, C2 of the NOx concentration sensors 52, 53 become the purification target NOx concentration. Control or the like can be used.

If the forced regeneration control is being performed in the determination in step S10, the process proceeds to step S30, and urea water increase control is performed. In this urea water increase control, the exhaust gas temperature sensor 51 is used for the amount (the minimum necessary amount) Wb of the urea water U that is necessary and sufficient for purifying NOx discharged from the engine 10 in the engine operating state Ec. The catalyst temperature Tc is estimated from the temperature Tgd of the exhaust gas G detected in 1. and the supply amount Wu of the urea water U is increased so that the catalyst temperature Tc of the SCR catalyst device 40 becomes equal to or lower than the upper limit temperature Tu.

This increase amount ΔWu is calculated as follows when the exhaust gas temperature sensor 51 is arranged on the downstream side of the SCR catalyst device 40. Since the flow rate Wg of the exhaust gas G and its specific heat can be estimated from the engine operating state Ec, from the temperature difference ΔTug between the upper limit temperature Tu and the temperature Tg of the exhaust gas G, the specific heat of the exhaust gas G and the amount Wg of the exhaust gas G. The heat quantity Qg for lowering the temperature of the exhaust gas G and the heat quantity Qc for lowering the temperature of the exhaust gas purifying apparatus 40 can be calculated from the temperature difference ΔTug and the specific heat of the SCR catalyst device 40, and both heat quantities (Qg+Qc) can be calculated. Since it is possible to calculate the increase amount ΔWu of the urea water U necessary for deprivation, it is possible to control the supply amount Wu of the urea water U by feedforward control so that the SCR catalyst device 40 does not exceed the upper limit temperature Tu. it can.

Alternatively, the exhaust gas temperature sensor 51 arranged on the downstream side of the SCR catalyst device 40 may perform feedback control of the supply amount Wu of the urea water U so that the detected temperature Tgd does not exceed the upper limit temperature Tu.

On the other hand, this increase amount ΔWu is calculated as follows when the exhaust gas temperature sensor 51 is arranged on the upstream side of the SCR catalyst device 40. Since the flow rate Wg of the exhaust gas G and its specific heat can be estimated from the engine operating state Ec, the temperature difference ΔTgu (=Tg−Tu) between the upper limit temperature Tu and the temperature Tg of the exhaust gas G, the specific heat of the exhaust gas G, and the exhaust gas Since the increase amount ΔWu of the urea water U necessary for lowering the temperature of the exhaust gas G can be calculated from the amount Wg of G, the feed-forward control controls the supply amount Wu of the urea water U so that the SCR catalyst device 40 has the upper limit. It is possible to prevent the temperature from becoming equal to or higher than Tu.

Alternatively, the supply amount Wu of the urea water U may be feedback-controlled so that the detected temperature Tgd of the exhaust gas temperature sensor 51 arranged on the downstream side of the SCR catalyst device 40 does not exceed the upper limit temperature Tu.

That is, during the forced regeneration control of the collection filter device 30, when the SCR catalyst device 40 is likely to be exposed to the high temperature exhaust gas G, the urea water increase control for increasing the urea water U is performed to perform the exhaust gas G. The urea water U is injected into the exhaust gas G in excess of the amount Wb of the normal urea water U capable of reducing NOx therein, and control is performed to lower the catalyst temperature Tc of the SCR catalyst device 40.

The urea water increasing control of step S30 is performed for the control time Δt, and it is determined whether or not the forced regeneration control of step S31 is completed. If the determination has not ended, the urea water increase control in step S30 is repeated.

The extra ammonia produced by the excessive injection of the urea water U is adsorbed by the new second SCR catalyst device 40B, which is installed downstream of the normal first SCR catalyst device 40A and has a large ammonia adsorption amount. This suppresses the outflow (slip) of excess ammonia while maintaining the purification performance.

Then, if the forced regeneration control is completed in the determination in step S31, the process goes to the urea water reduction control in step S40, and in this step S40, the urea is supplied at the supply amount Wu which is smaller than the normal urea water U amount Wb by the decrease amount ΔWd. The urea water reduction control for supplying the water U is performed for the control time Δt, and in step S41, the cumulative amount ΣΔWu of the increase amount ΔWu of the urea water U in step S30 and the cumulative amount of the decrease amount ΔWd of the urea water U in step S40. ΣΔWd is compared, and if the cumulative amount ΣΔWd of the decrease amount ΔWd is less than the cumulative amount ΣΔWu of the increase amount ΔWu, the process returns to step S40, and the urea water reduction control of step S40 is repeated. Then, in step S41, if the cumulative amount ΣΔWd of ΔWd is equal to or larger than the cumulative amount ΣΔWu of the increased amount ΔWu, the process returns to step S10.

After that, from step S10, the urea water normal control of step S20, or the urea water increase control of step S30 and the urea water decrease control of step S40 are repeatedly performed, and the operation of the engine 10 is stopped and a high-level control flow is performed. Returning to this, the control flow of FIG. 2 is also ended together with the end of this advanced control flow.

Then, the urea water reduction control for reducing the supply amount Wu of the urea water U after the forced regeneration control of the collection filter device 30 is finished from the normal amount Wb of the urea water U by the preset reduction amount ΔWd, The ammonia adsorbed by the second SCR catalyst device 40B is used for purification of NOx by performing the process until the cumulative amount ΣΔWu of the amount ΔWu increased during the forced regeneration control. By performing this urea water reduction control, the supply amount Wu of the urea water U is reduced until the amount corresponding to the accumulated amount ΣΔWu of the amount ΔWu increased by the urea water increase control during the forced regeneration control is reached. Return to control.

In the exhaust gas purification system 1 of this embodiment shown in FIG. 1, the temperature Tgu of the exhaust gas G flowing into the SCR catalyst device 40 during the forced regeneration control of the collection filter device 30 is determined by the collection filter device 30. Since the heat of oxidation generated by the combustion of the PM trapped in the PM tends to increase, the trapping filter device 30 has been described by exemplifying the configuration on the upstream side of the SCR catalyst device 40. The collection filter device 30 shown in FIG. 4 can also be applied to the exhaust gas purification system 1A on the downstream side of the SCR catalyst device 40.

Then, according to the exhaust gas purification system 1 and the exhaust gas purification method having the above-described configurations, the catalyst temperature Tc of the SCR catalyst device 40 does not exceed the preset upper limit temperature Tu during the forced regeneration control of the collection filter device 30. As described above, since the supply amount Wu of the urea water U is increased to cool the SCR catalyst device 40, it is possible to prevent the catalyst temperature Tc of the SCR catalyst device 40 from becoming excessively high even during the forced regeneration control of the collection filter device 30. It is possible to prevent the irreversible deterioration that accompanies the structural destruction of the SCR catalyst device 40 and realize the long life of the SCR catalyst device 40, while maintaining the high purification performance.

That is, as in the exhaust gas purification system 1X of the comparative example shown in FIG. 4, the SCR catalyst device 40 becomes a high temperature of about 400° C. during the forced regeneration control of the collection filter device 30, and the exhaust gas purification rate deteriorates. In contrast to the problem that the structure of the SCR catalyst device 40 exposed to high temperature is destroyed and irreversible deterioration occurs and the life of the SCR catalyst device 40 is shortened, the second SCR catalyst of the present invention is used. By arranging the device 40B and the urea water increase control and the urea water decrease control, it is possible to prevent irreversible deterioration of the SCR catalyst device 40 while maintaining high purification performance more efficiently, and to extend the life of the catalyst. Can be realized, which can provide a solution that can lead to long-term cost savings.

1 Exhaust Gas Purification System 10 Engine (Internal Combustion Engine)
11 Exhaust passage 20 Oxidation catalyst device (DOC)
30 Collection filter device (DPD)
31 Fuel injection nozzle 40 SCR catalyst device (SCR)
40A 1st SCR catalyst device 40B 2nd SCR catalyst device 41 Urea water supply device (reduction solution supply device)
42 Cooling promotion rotary vanes 50 Control device 51 Exhaust gas temperature sensor 52 NOx concentration sensor

Claims (3)

A collection filter device that collects and purifies particulate matter, a selective reduction catalyst device that purifies nitrogen oxides, and a reduction that supplies a reducing solution into the exhaust gas on the upstream side of the selective reduction catalyst device. Solution supply device, and an exhaust gas purification system comprising a control device for controlling the supply amount of the reducing solution,
The control device is
At the time of controlling the supply amount of the reducing solution, during the forced regeneration control of the collection filter device, the catalyst solution of the selective reduction type catalyst device is supplied from the reducing solution supply device so as not to exceed a preset upper limit temperature. And a urea water increase control for increasing the supply amount of the reducing solution supplied above the minimum amount necessary for reducing the nitrogen oxides in the exhaust gas, and cooling the selective reduction catalyst device with the reducing solution. ,
When the forced regeneration control is terminated during the urea water increase control, the supply amount of the reducing solution supplied from the reducing solution supply device is reduced below the necessary minimum amount capable of reducing nitrogen oxides in the exhaust gas. Urea water reduction control to
When the cumulative amount of the reduction amount of the reducing solution in the urea water reduction control reaches an amount corresponding to the cumulative amount of the increasing amount of the reducing solution in the urea aqueous solution increase control, the reducing solution is supplied from the reducing solution supply device. An exhaust gas purification system, which is configured to perform a urea water normal control in which a supply amount of a reducing solution is set to a minimum amount necessary for reducing nitrogen oxides in exhaust gas. The exhaust gas purification system according to claim 1, wherein a second selective reduction catalyst device is disposed downstream of the selective reduction catalyst device. When purifying exhaust gas from an internal combustion engine, a particulate filter is used to collect and purify particulate matter, and a reducing solution supply device uses the reducing solution supplied into the exhaust gas for selective reduction. In an exhaust gas purification method for purifying nitrogen oxides with a catalyst device, during the forced regeneration control of the collection filter device, the catalyst temperature of the selective reduction catalyst device does not exceed a preset upper limit temperature, the reduction The supply amount of the reducing solution supplied from the solution supply device is increased beyond the minimum amount required to reduce nitrogen oxides in the exhaust gas, and the selective reduction catalyst device is cooled by this reducing solution. ,
When the forced regeneration control is finished while increasing the amount of the reducing solution, the supply amount of the reducing solution supplied from the reducing solution supply device is lower than the minimum necessary amount capable of reducing nitrogen oxides in the exhaust gas. Lose weight,
When the cumulative amount of the reduced amount of the reducing solution in this reduced amount corresponds to the cumulative amount of the increased amount of the reducing solution during the increasing amount of the reducing solution, the reducing solution supplied from the reducing solution supply device. The exhaust gas purification method is characterized in that the supply amount of is reduced to the minimum amount necessary for reducing nitrogen oxides in the exhaust gas.

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