KR20220131689A - Control method of exhaust gas purification device - Google Patents

Abstract

The present invention relates to a control method of an exhaust gas purifying apparatus. According to the present invention, a differential pressure and a nitrogen oxide (NO_x) emission concentration at a front end and a rear end of an sDPF measured in an exhaust gas purifier composed of a diesel oxidation catalyst (DOC) and the sDPF are compared with set values to determine whether the sDPF is regenerated. In addition, when it is determined that regeneration of the sDPF is progressing, injection of a reducing agent is stopped and a regeneration reaction for removing PM and an ammonium salt accumulated inside the sDPF is performed. In addition, when the sDPF regeneration is completed, the control method of the exhaust gas purifying apparatus recalculating an injection amount of the reducing agent is performed to secure back pressure stability and NO_x removal efficiency of the exhaust gas purifying apparatus. In addition, operation stability is improved by maintaining a proper reducing agent injection condition. The control method of the exhaust gas purifying apparatus of the present invention comprises: a measurement step; a judgment step; and a regeneration step.

Description

CONTROL METHOD OF EXHAUST GAS PURIFICATION DEVICE

The present invention relates to a control method of an exhaust gas purification device for improving the exhaust gas purification efficiency and operation safety of the exhaust gas purification device for a diesel engine.

Compression ignition diesel engines have higher emission concentrations of air pollutants such as nitrogen oxides (NOx) and particulate matter (PM) compared to gasoline engines. In order to minimize the emission of air pollutants, diesel oxidation catalyst (Diesel Oxidation Catalyst, DOC), nitrogen oxide removal catalyst (DeNOx Catalyst), diesel particulate filter (Diesel Particulate Filter, DPF), and diesel particulate filter (DPF) are optional The exhaust gas purification system is composed of complex processes such as sDPF (SCR coated DPF), a catalytic filter that can simultaneously remove nitrogen oxides (NOx) and particulate matter (PM) by coating with a reduction catalyst (SCR). It is widely used.

In the method of regenerating particulate matter (PM) in an exhaust gas purification system using sDPF, a chemical reaction of nitrogen dioxide (NO ₂ ) and particulate matter (PM) generated from diesel oxidation catalyst (DOC) using diesel oxidation catalyst (DOC) There is a natural regeneration method in which particulate matter (PM) is continuously removed through the evaporator, and a forced regeneration method in which the particulate matter (PM) is burned by increasing the exhaust gas temperature by using a burner, heater, fuel post-injection, etc. However, in the case of the forced regeneration method, additional equipment such as a burner is required, and since a heat source and fuel must be used continuously, installation and operating costs are high, and it is difficult to apply to a large-capacity diesel engine exhaust gas purification system of MW or higher.

Therefore, the exhaust gas purification system composed of Diesel Oxidation Catalyst (DOC) and sDPF to which the natural regeneration method is applied has the most simple and economical advantage. SCR reaction of NOx (NO, NO ₂ ) and ammonia (NH ₃ ) and natural regeneration reaction between nitrogen dioxide (NO ₂ ) and particulate matter (PM) on the sDPF of the exhaust gas purification system composed of a diesel oxidation catalyst (DOC) and sDPF This will happen at the same time.

In general, the NH ₃ -SCR reaction can be represented by Schemes 1 to 3 below, Scheme 1 is a general standard SCR reaction, Scheme 2 is a fast SCR reaction, and Scheme 3 is a nitrogen dioxide (NO ₂ ) SCR reaction.

[Scheme 1]

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

[Scheme 2]

NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O

Scheme 3 is a NO ₂ SCR reaction.

[Scheme 3]

2NO ₂ + 4NH ₃ + O ₂ → 3N ₂ + 6H ₂ O

The particulate matter (PM) regeneration reaction reacts carbon (C), which is the main component of particulate matter (PM), with nitrogen dioxide (NO ₂ ) as shown in Schemes 4 and 5 below to generate carbon dioxide (CO ₂ ) or carbon monoxide (CO) Oxidation of particulate matter (PM) occurs.

[Scheme 4]

C+NO ₂ → CO + NO

[Scheme 5]

C + 2NO ₂ → CO ₂ + 2NO

In the sDPF phase, since nitrogen dioxide (NO ₂ ) is competitively used for the SCR reaction and the natural regeneration reaction, a higher nitrogen dioxide (NO ₂ ) amount than that used for the natural regeneration of particulate matter (PM) on the DPF is required, and an appropriate amount of reducing agent is injected is important

When the natural regeneration performance of particulate matter (PM) of sDPF decreases due to excessive ammonia (NH ₃ ) injection as a reducing agent in the exhaust gas purification system composed of diesel oxidation catalyst (DOC) and sDPF and changes in engine exhaust conditions due to external factors, sDPF Particulate matter (PM) and ammonium salts (Ammonium nitrate, Ammonium sulfate, etc.) caused by excess ammonia (NH ₃ ) accumulate inside, thereby increasing the back pressure of the exhaust gas purification device, and the accumulation of the particulate matter inhibits the reaction of the SCR catalyst. As a result, a reduction in nitrogen oxide (NOx) removal efficiency may occur at the same time.

Therefore, in order to secure the performance and operation stability of the exhaust gas purification system composed of Diesel Oxidation Catalyst (DOC) and sDPF to which the natural regeneration method is applied, inactivating factors such as particulate matter (PM) and ammonium salt accumulated in the sDPF are removed, and the introduced reducing agent It is essential to apply a control method that can optimally control the amount.

Korean Patent No. 10-0959318

The present invention in consideration of the above points is the differential pressure of the sDPF, the NOx emission concentration, the back pressure reduction rate of the sDPF, and the increase in the NO ₂ concentration measured at the rear end of the sDPF in an exhaust gas purification device for a diesel engine composed of a diesel oxidation catalyst (DOC) and sDPF. By comparing the measured speed with a preset value, a regeneration reaction to remove particulate matter (PM) and ammonium salt accumulated inside the sDPF is performed, and a control method to readjust the injection of reducing agent is performed to stabilize the back pressure of the exhaust gas purification device An object of the present invention is to provide a control method for an exhaust gas purification system that improves operation stability by securing and NOx removal efficiency and maintaining an appropriate reducing agent injection condition.

In order to achieve the above object, the control method of the exhaust gas purification device of the present invention comprises the steps of (a) measuring the differential pressure of the sDPF and the nitrogen oxide concentration at the rear end of the sDPF in the exhaust gas purification device for a diesel engine, (b) Comparing the differential pressure of the sDPF measured in step (a) and the nitrogen oxide concentration set value to determine whether to proceed with sDPF regeneration, (c) (b) if it is determined that sDPF regeneration proceeds in step (b) sDPF The step of regenerating the sDPF by stopping the reducing agent injection, (d) calculating the lower back pressure value of sDPF, (e) comparing the lower back pressure lower limit value of the sDPF with the differential pressure of the sDPF re-measured after step (c) to determine whether to re-inject the reducing agent, (f) if it is determined that the reducing agent is re-injected in step (e), measuring the nitrogen oxide concentration at the rear end of the sDPF to re-calculate the reducing agent injection amount, and (g) the ( It may include the step of injecting a reducing agent to the injection amount of the reducing agent recalculated in step f).

In step (b), when the nitrogen oxide concentration is equal to or greater than the set concentration and the differential pressure of the sDPF is equal to or greater than the set differential pressure, it is determined that sDPF regeneration is in progress.

In the step (b), when the nitrogen oxide concentration is higher than or equal to the set concentration or the differential pressure of the sDPF is less than the set differential pressure, the reducing agent injection amount can be controlled to inject the reducing agent into the exhaust gas purification device for the diesel engine.

In step (c), it is preferable to perform sDPF regeneration until the back pressure reduction rate of the sDPF becomes less than or equal to a set value.

In step (d), the lower limit of the back pressure of the sDPF is calculated through the amount of ash accumulated in the sDPF.

The step (e) is a first determination step of determining whether the reducing agent is re-injected at the rate of increasing the back pressure decrease rate or the nitrogen dioxide (NO ₂ ) concentration of the sDPF, and the re-measured differential pressure of the sDPF and the lower limit value of the back pressure of the sDPF are compared Including a second determination step of determining whether or not to re-inject the reducing agent can be determined to proceed with the re-injection of the reducing agent.

In the first determination step of the step (e), the back pressure reduction rate of the sDPF or the nitrogen dioxide (NO ₂ ) concentration measured at the rear end of the sDPF is less than the preset value, and the re-measured value of the sDPF in the second determination step When the differential pressure is less than or equal to the lower limit of the back pressure of the sDPF, it may be determined that the re-injection of the reducing agent proceeds.

On the other hand, when the re-measured differential pressure of the sDPF in step (e) is less than the lower limit of the back pressure of the sDPF, it is determined that the exhaust gas purification device is checked.

In the control method of the exhaust gas purification device of the present invention, the nitrogen oxide (NOx) removal efficiency is reduced in the exhaust gas purification device composed of a diesel oxidation catalyst (DOC) and sDPF, and when the differential pressure of sDPF occurs, the exhaust gas purification device After stopping the injection of the reducing agent, performing the natural regeneration method of sDPF, and then periodically re-evaluating the reducing agent injection conditions through the control method to re-evaluate the reducing agent injection conditions, the control method to restore exhaust gas purification by re-injecting the reducing agent again This has the effect of increasing the NOx removal efficiency of the exhaust gas purification device and securing the back pressure stability, thereby securing the long-term operation stability of the exhaust gas purification device.

1 shows the configuration of an exhaust gas purification device for a diesel engine of the present invention.
2 and 3 are flowcharts of a control method of an exhaust gas purification apparatus according to an embodiment of the present invention.
4 is a graph showing the differential pressure of the sDPF according to the operating time of the exhaust gas purification device and NOx and NO ₂ concentrations measured at the rear end.

The present invention stops the injection of the reducing agent when the differential pressure between the front and rear ends of the sDPF and the emission concentration of nitrogen oxides reaches a preset condition in an exhaust gas purification device for a diesel engine composed of a diesel oxidation catalyst (DOC) and sDPF. It relates to a control method of an exhaust gas purification device to secure the efficiency of the exhaust gas purification device and the operation stability of the exhaust gas purification device by removing the particulate matter (PM) and ammonium salt accumulated in the will be.

Hereinafter, the control method of the exhaust gas purification apparatus of the present invention will be described in detail with reference to the accompanying exemplary drawings. This is not necessarily limited to what is described herein, since it may be implemented in various different forms by those of ordinary skill in the art to which the present invention pertains as an example.

1 shows the configuration of an exhaust gas purification device for a diesel engine.

As shown in FIG. 1 , the exhaust gas purification device 100 for a diesel engine is configured in the order of a diesel oxidation catalyst (DOC) 20 and sDPF 30 at the rear end of the diesel engine 10 .

The diesel oxidation catalyst 20 removes unburned hydrocarbons discharged from the diesel engine, and oxidizes nitrogen monoxide (NO) to generate nitrogen dioxide (NO ₂ ) necessary for natural regeneration of sDPF.

The sDPF (30) is a diesel particulate filter installed at the rear end of the diesel oxidation catalyst (20) and coated with a selective reduction catalyst for collecting particulate matter (PM) contained in exhaust gas, and on the sDPF (30), injected from the front end SCR reaction of reducing agent and nitrogen oxide (NOx) and natural regeneration reaction of NO ₂ and PM occur competitively.

The sDPF 30 may use a vanadium pentoxide (V ₂ O ₅ )-based catalyst and a zeolite-based catalyst as a catalyst, and the vanadium pentoxide (V ₂ O ₅ )-based catalyst is vanadium pentoxide (V ₂ O ₅ ) may be composed of a composition containing tungsten trioxide (WO ₃ ) and titanium dioxide (TiO ₂ ) as an active material, and a transition metal such as cerium dioxide (CeO ₂ ) may be used as a co-catalyst, and also the zeolite (Zeolite) )-based catalyst may preferably be a zeolite-based ceramic catalyst substituted with an element such as copper (Cu) or iron (Fe).

In the exhaust gas purification apparatus for a diesel engine, a reducing agent injection port 41 for injecting a reducing agent may be formed between the rear end of the diesel oxidation catalyst 20 and the front end of the sDPF 30 .

The reducing agent injected into the exhaust gas purification device through the reducing agent injection port 41 is ammonia (NH ₃ )-based precursors such as NH ₃ (g), NH ₃ (aq), urea(aq), urea(s). Can be used. have.

The sDPF pressure is measured by the pressure sensors 51 and 52 that measure the pressure at the front and rear end of the sDPF to calculate the differential pressure, and the nitrogen oxide sensor 60 installed at the rear end of the sDPF is nitrogen oxide (NOx) in the exhaust gas discharged through the sDPF. By measuring the concentration, it continuously audits whether the exhaust gas purification system is operating properly.

2 and 3 are flowcharts of a control method of an exhaust gas purification apparatus according to an embodiment of the present invention. In the exhaust gas purification apparatus for a diesel engine as shown in FIG. 1, the purification efficiency of nitrogen oxide (NOx) is reduced and sDPF When the differential pressure of the sDPF is regenerated by stopping the reducing agent injection, the control method for re-assessing the reducing agent injection conditions is shown.

2, (a) measuring the differential pressure of sDPF and the nitrogen oxide concentration at the rear end of the sDPF in the exhaust gas purification device for a diesel engine (S110), (b) the measured differential pressure of the sDPF and the nitrogen oxide concentration Comparing with the set value, determining whether the regeneration reaction of the sDPF is progressing (S120), (c) If it is determined that the sDPF regeneration reaction is proceeding, stopping the reducing agent injection to regenerate the sDPF (S130), (d) Calculating the lower back pressure limit of the sDPF (S140), (e) comparing the lower back pressure of the sDPF with the re-measured differential pressure of the sDPF to determine whether to re-inject the reducing agent (S150), (f) re-injecting the reducing agent When it is determined that the reduction agent injection amount is recalculated (S160), and (g) the operation of the exhaust gas purification apparatus can be controlled in the order of the step (S170) of injecting the reducing agent with the recalculated reducing agent injection amount.

The step (a) (S110) is a step of acquiring information on the differential pressure of sDPF and nitrogen oxide concentration in the exhaust gas purification device for a diesel engine for determining whether the regeneration reaction of the exhaust gas purification device for a diesel engine is performed. The differential pressure, which is a pressure difference, is measured at the front and rear ends of the sDPF 30 with the pressure sensors 51 and 52 located at the front and rear ends of the sDPF 30, and a nitrogen oxide sensor installed at the rear end of the sDPF 30 ( 60), the nitrogen oxide (NOx) concentration value of the exhaust gas emitted through the sDPF 30 is measured.

The (b) step (S120) is performed by comparing the differential pressure of the sDPF and the nitrogen oxide concentration measured in the (a) step (S110) with the preset differential pressure and the nitrogen oxide concentration of the sDPF, the differential pressure of the sDPF and the nitrogen oxide concentration When it reaches more than a preset value, it is determined whether or not to stop injecting the reducing agent and start the regeneration reaction of sDPF. Here, the regeneration reaction is a natural regeneration method using a chemical reaction of particulate matter (PM) composed mainly of nitrogen dioxide (NO ₂ ) and carbon (C).

As shown in FIG. 3 , (b) step (S120) is performed when the nitrogen oxide concentration measured in step (a) (S110) is greater than or equal to the set concentration (k1) and the differential pressure of the sDPF is greater than or equal to the set differential pressure (k2), sDPF The sDPF regeneration reaction is judged to be in progress by judging the performance degradation due to the accumulation of particulate matter (PM) inside.

However, when the nitrogen oxide concentration is higher than the set concentration (k1) or the differential pressure of the sDPF is less than the set differential pressure (k2), it is determined that the injection amount of the reducing agent is insufficient in the exhaust gas purification device, and the reducing agent is injected more at the reducing agent injection port 41 The reducing agent injection amount is adjusted as much as possible (S121).

In the (c) step (S130), when it is determined that the sDPF regeneration reaction proceeds in the (b) step (S120), the reducing agent injection is stopped and the sDPF regeneration reaction is performed, and the (c) step (S130) performs the sDPF regeneration reaction at a rate at which the differential pressure of the sDPF decreases until the rate of decrease of the back pressure of the sDPF reaches the set pressure (k3) or less.

The step (d) (S140) is a step of calculating the lower limit value of the back pressure (k4) of the sDPF through the amount of ash accumulated in the sDPF as a calculated value for determining whether or not to re-inject the reducing agent. Here, the ash accumulation in the sDPF is calculated by calculating the ash accumulation using the ash generation conditions such as the accumulated operating time of the diesel engine and the amount of engine oil used to calculate the lower back pressure lower limit value (k4) of the sDPF. do.

(e) step (S150) compares the lower limit value (k4) of the back pressure of the sDPF in step (S140) and the differential pressure of the sDPF re-measured through the pressure sensors 51 and 52 to determine whether or not to re-inject the reducing agent do.

Specifically, the determination of whether to re-inject the reducing agent in (e) step (S150) is a first determination of the rate of increase in back pressure or nitrogen dioxide (NO ₂ ) concentration of sDPF, and the (d) calculation in step (S140). A second determination is made as to whether or not to re-inject the reducing agent using the lower limit value (k4) of the back pressure of the sDPF.

As shown in FIG. 3 , as the rate at which the differential pressure of the sDPF decreases, the rate of decrease of the back pressure of the sDPF is compared with the set pressure value (k3). To complete the first determination of re-injection of the reducing agent (S151).

Then, when the differential pressure of the sDPF re-measured through the pressure sensors 51 and 52 is below the lower back pressure lower limit value (k4) of the sDPF in step (d) (S140), the second determination of re-injection of the reducing agent to restart the reducing agent injection is performed (S152).

As another reducing agent re-injection judgment, based on the nitrogen dioxide (NO ₂ ) concentration of the exhaust gas measured at the rear end of the sDPF, when the nitrogen dioxide (NO ₂ ) concentration increase rate is less than the set value, when the differential pressure of the sDPF is less than the lower limit of the back pressure of the sDPF Alternatively, it can be used in the control method of the exhaust gas purification device by recalculating the injection amount of the reducing agent.

If the re-measured differential pressure of the sDPF in step (S150) is less than the lower back pressure lower limit of the sDPF, and the sDPF differential pressure does not reach the lower back pressure lower limit value (k4) of the sDPF, check the exhaust gas purification device It is determined as (S153).

In the inspection (S153) of the exhaust gas purification value, a separate inspection of the exhaust gas purification device is performed, such as removing ash in the sDPF, checking the normal operation of the back pressure gauge, and checking the catalyst deactivation by sending a check necessary signal to the user.

In the (f) step (S160), when it is determined that the reducing agent is re-injected in the (e) step (S150), the nitrogen oxide at the rear end of the sDPF measured at the regeneration completion point when the sDPF differential pressure is equal to or less than the lower back pressure lower limit value (k4) of the sDPF. This is the step of re-calculating the amount of reducing agent injected to satisfy the emission limit of nitrogen oxides by sensing the (NOx) concentration value.

(g) step (S170) controls the injection of the reducing agent injected from the reducing agent injection port with the reducing agent injection amount recalculated in the (f) step (S160).

It is possible to continuously operate by repeatedly performing the exhaust gas purification device control method of steps (a) to (g) as described above.

Figure 4 is a graph showing the nitrogen oxide (NOx) and nitrogen dioxide (NO ₂ ) concentrations measured at the differential pressure and the rear end of the sDPF according to the operating time of the exhaust gas purification device.

As shown in FIG. 4 , the emission concentration of nitrogen oxide (NOx) is about 90 to 100 ppm after the operation of the exhaust gas purification device, and the differential pressure of the sDPF rises rapidly from 15 mbar to 25 mbar.

When the injection of the reducing agent is stopped after 8 hours of operation of the exhaust gas purification device, the nitrogen dioxide (NO ₂ ) concentration measured at the rear end of the sDPF according to the stop of the injection of the reducing agent rapidly rises from about 20 ppm to 130 ppm. Thereafter, as the natural regeneration proceeds as a regeneration reaction in which the particulate matter (PM) accumulated inside the sDPF is oxidized by nitrogen dioxide (NO ₂ ), the consumption of nitrogen dioxide (NO ₂ ) decreases and nitrogen dioxide (NO ₂ ) measured at the rear end of the sDPF ) concentration increases gradually. However, as the nitrogen dioxide (NO ₂ ) concentration increases and particulate matter accumulated inside the sDPF is removed as a heat source of the exhaust gas, the nitrogen dioxide (NO ₂ ) value measured at the rear end of the sDPF after the sDPF regeneration reaction is completed does not change and remains constant.

And the differential pressure of sDPF continuously decreases during the sDPF regeneration reaction, which is the time to stop the inflow of reducing agent. As shown in FIG. 4, when the back pressure reduction rate of sDPF reaches 0.3 mbar/h after 8 hours of stopping the injection of the reducing agent, the lower limit of the back pressure of the sDPF at this time is 16 mbar or less, and the injection of the reducing agent is restarted. Here, the back pressure reduction rate of the sDPF is the differential pressure of the sDPF that is decreased per unit time, and it means the differential pressure rate of the sDPF that is decreased during the reducing agent inflow stop time.

After the regeneration reaction is completed, the reducing agent injection conditions are recalculated based on the nitrogen oxide (NOx) concentration measured at the rear end of the sDPF before the reducing agent injection and the engine operating conditions, etc. .

Here, the re-injection of the reducing agent is performed by checking whether the sDPF back pressure lower limit is reached when the back pressure decrease rate of the sDPF or the NO ₂ concentration increase rate measured at the rear end of the sDPF is less than the set value.

Through the above process, it can be confirmed that the NOx emission concentration is 20 ppm and the back pressure is stably operated without a sharp increase in the range of 17 to 20 mbar.

As described above, through the control method of the exhaust gas purification device of the present invention, the back pressure stability and nitrogen oxide (NOx) removal efficiency of the exhaust gas purification device are secured, and operation stability is improved by maintaining an appropriate reducing agent injection condition into the exhaust gas purification device. elevate

10: diesel engine
20: DOC
30: sDPF
41: reducing agent nozzle
51, 52: pressure sensor
60: nitrogen oxide sensor
100: exhaust gas purification device

Claims (11)

(a) measuring the differential pressure of the sDPF and the nitrogen oxide concentration at the rear end of the sDPF in an exhaust gas purification device for a diesel engine;
(b) determining whether sDPF regeneration proceeds by comparing the differential pressure of the sDPF measured in step (a) and the nitrogen oxide concentration set value; and
(c) stopping the reducing agent injection when it is determined that sDPF regeneration proceeds in step (b) sDPF, and regenerating the sDPF until the back pressure reduction rate of the sDPF becomes less than or equal to a set value; Control method of an exhaust gas purification device comprising a. According to claim 1,
In the step (b), when the nitrogen oxide concentration is greater than or equal to a preset concentration and the differential pressure of the sDPF is greater than or equal to a preset differential pressure, it is determined that sDPF regeneration proceeds. According to claim 1,
In the step (b), when the nitrogen oxide concentration is higher than or equal to a preset concentration or the differential pressure of the sDPF is less than a preset differential pressure, the exhaust gas purification device, characterized in that the reducing agent injection amount is controlled to inject the reducing agent into the exhaust gas purification device for the diesel engine control method. According to claim 1,
After the step (c), (d) calculating a lower limit value of the back pressure of the sDPF; the control method of the exhaust gas purification apparatus comprising the. 5. The method of claim 4,
The step (d) is a control method of an exhaust gas purification apparatus, characterized in that calculating the lower limit value of the back pressure of the sDPF through the amount of ash (Ash) accumulated in the sDPF. 5. The method of claim 4,
After step (d), (e) determining whether to re-inject the reducing agent by comparing the lower limit value of the back pressure of the sDPF and the re-measured differential pressure of the sDPF; Control method of an exhaust gas purification apparatus comprising: . 7. The method of claim 6,
Step (e) is,
A first determination step of determining whether to re-inject the reducing agent at the rate of decreasing back pressure or nitrogen dioxide (NO ₂ ) concentration of sDPF; and
and a second determination step of determining whether to re-inject the reducing agent by comparing the re-measured differential pressure of the sDPF with the lower limit of the back pressure of the sDPF. 8. The method of claim 7,
In the first determination step, the back pressure decrease rate of the sDPF or the nitrogen dioxide (NO ₂ ) concentration measured at the rear end of the sDPF is less than the preset value, and the differential pressure of the re-measured sDPF in the second determination step is the back pressure of the sDPF If the lower limit value or less, the control method of the exhaust gas purification device, characterized in that it is determined that the re-injection of the reducing agent. 7. The method of claim 6,
When the differential pressure of the sDPF re-measured in the step (e) is less than the lower limit of the back pressure of the sDPF, the control method of the exhaust gas purification device, characterized in that it is determined as an inspection of the exhaust gas purification device. 7. The method of claim 6,
After the step (e), (f) when it is determined that the reducing agent is re-injected in the step (e), measuring the nitrogen oxide concentration at the rear end of the sDPF to re-calculate the reducing agent injection amount; Exhaust comprising a; Control method of gas purifier. 11. The method of claim 10,
After step (f), (g) injecting a reducing agent at the injection amount of the reducing agent recalculated in step (f); Control method of an exhaust gas purification apparatus comprising the.

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