KR101558675B1 - Method and system for regenerating of lnt catalyst - Google Patents

Abstract

The present invention relates to a method for measuring a lambda value and a lambda value, comprising: measuring a first lambda value and a second lambda value through a first lambda sensor and a second lambda sensor provided at the front end and the rear end of an NT catalyst; A rich control step of controlling the concentration of the reducing agent in the exhaust gas flowing into the LNT catalyst to be richer than the steady state in order to remove the harmful oxide occluded in the LNT catalyst; And a normal regulating step of regulating the reducing agent concentration in the exhaust gas to a steady state by using the difference between the first lambda value and the second lambda value measured by the first lambda sensor and the second lambda sensor. Wherein when the difference between the first lambda value and the second lambda value is less than or equal to a reference value, the reducing agent concentration is adjusted to a steady state. In the normal regulating step, Further comprising the step of estimating the degree of deterioration of the LNT catalyst through the cumulative value of the difference between the first lambda value and the second lambda value to add a time for controlling the concentration of the reducing agent to be more concentrated than the normal state, Wherein the adding step accumulates the difference value continuously until the difference value between the first lambda value and the second lambda value reaches the reference value from the time when the concentration of the reducing agent is adjusted to be richer than the steady state, ; And setting the additional time for adjusting the concentration of the reducing agent to be richer than the steady state according to the calculated cumulative value.

Description

TECHNICAL FIELD The present invention relates to a regeneration system for a LNT catalyst,

The present invention relates to an LNT catalyst, and more particularly, to an apparatus and a method for regenerating an LNT catalyst capable of reducing NOx and SOx purification performance by optimizing a concentration control time of a reducing agent when removing harmful oxides using an LNT catalyst, System and method.

NOx Trap is called various names such as lean NOx Trap (LNT), NOx adsorber, NOx storage / reduction catalyst (NSRC) and NOx adsorber catalyst (NAC).

This NOx trap has the conventional three-way catalytic function at the stoichiometric air-fuel ratio, and adsorbs and stores NOx in the lean region. When the air-fuel ratio is rich, the NOx trap is purified and the NOx trap function is restored.

Ba, Sr, and K are used as the NOx trap materials. NO in the lean area is converted into NO ₂ by Pt and stored in the NOx trap, and NOx stored in the NOx trap is reduced to N ₂ when the air-fuel ratio is high.

In addition, the NOx trap has an advantage of high temperature durability, but there is a problem that the sulfur component in the fuel is poisoned. Currently, the concentration of SOx gas contained in the exhaust gas is not measured because there is no SOx sensor.

Therefore, it is determined that the sulfur concentration of EU6 diesel oil is below 10 ppm, and the DeSOx point is determined and DeSOx control is performed.

However, the conventional NOx trap is a passive regeneration method that does not consider the poisoning state of the catalyst. When the deterioration degree of the catalyst is high, the detoxification performance of the harmful oxides such as NOx and SOx is reduced and also the CO / HC The slip amount is increased.

On the other hand, a "desulfurization method of a nitrogen oxide storage catalyst system" of Korean Patent Laid-Open Publication No. 10-2013-0017957 has been conventionally introduced.

However, even with this method, regeneration control can not be appropriately performed depending on the degree of poisoning and deterioration of the catalyst, and there is a limit to the improvement of the detoxification performance of the harmful oxide.

It should be understood that the foregoing description of the background art is merely for the purpose of promoting an understanding of the background of the present invention and is not to be construed as an admission that the prior art is known to those skilled in the art.

KR 10-2013-0017957A

The present invention has been made in order to solve the conventional problems as described above, and it is an object of the present invention to improve the NOx and SOx purifying performance by optimizing the concentration control time of the reducing agent when removing harmful oxides using the LNT catalyst, And to provide a regeneration system and method for an LNT catalyst.

According to another aspect of the present invention, there is provided a method of measuring a lambda value, comprising: measuring a first lambda value and a second lambda value through a first lambda sensor and a second lambda sensor installed at a front end and a rear end of an LNT catalyst;
A rich control step of controlling the concentration of the reducing agent in the exhaust gas flowing into the LNT catalyst to be richer than the steady state in order to remove the harmful oxide occluded in the LNT catalyst; And
A normal regulating step of regulating the reducing agent concentration in the exhaust gas to a steady state by using the difference between the first lambda value and the second lambda value measured by the first lambda sensor and the second lambda sensor;
, ≪ / RTI &
Wherein when the difference between the first lambda value and the second lambda value is less than or equal to a reference value, the reducing agent concentration is adjusted to a steady state,
In the normal regulating step, the deterioration degree of the LNT catalyst is estimated through the accumulation value obtained by adding the difference values of the first lambda value and the second lambda value in the rich regulating step, Further comprising:
Wherein the adding step accumulates the difference value continuously until the difference value between the first lambda value and the second lambda value reaches the reference value from the time when the concentration of the reducing agent is adjusted to be richer than the steady state, A calculation step of calculating; And setting the additional time for adjusting the concentration of the reducing agent to be richer than the steady state according to the calculated cumulative value.
In the setting step, the additional time is set shorter as the accumulated value is larger, and the additional time is set longer as the accumulated value is smaller.
The additional time is set within a range of a reference regeneration time from the time when the concentration of the reducing agent is adjusted to the reference value on the basis of the new LNT catalyst until the difference between the first lambda value and the second lambda value reaches the reference value .

It is an object of the present invention to provide a fuel cell system and a fuel cell system that maximize DeNOx and DeSOx performance while minimizing the CO / HC slip, .

Particularly, the deterioration degree of the catalyst is determined by the sum of the difference in lambda value of the upstream / downstream lambda sensor, and the regeneration time is further controlled in accordance with the deterioration degree, thereby improving the Nox / CO purification rate through the highly accurate regeneration control There is also an effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a regeneration system for an LNT catalyst according to the present invention; FIG.
FIG. 2 is a view for explaining a reproduction end point based on the difference in lambda value according to the reproduction method of the present invention and a reproduction end point in consideration of the deterioration degree of the catalyst; FIG.
3 is a view showing a comparison between the regeneration cumulative value and regeneration time of a new LNT catalyst and a deteriorated LNT catalyst according to the present invention.
4 is a view sequentially showing the regeneration method of the LNT catalyst according to the present invention.
5 is a view showing a regeneration control flow in the regeneration method of the LNT catalyst according to the present invention.
6 is a graph showing NOx and CO purification rates according to additional regeneration times of the LNT catalyst according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a view schematically showing the regeneration system of the LNT catalyst according to the present invention. FIG. 2 is a view showing a regeneration end point of the LNT catalyst according to the present invention, FIG. 3 is a view showing a comparison between the regeneration cumulative value and the regeneration time of the new LNT catalyst and the deteriorated LNT catalyst according to the present invention, and FIG. 4 is a graph showing a regeneration method of the LNT catalyst according to the present invention FIG. 5 is a view showing a regeneration control flow of the regeneration method of the LNT catalyst according to the present invention, and FIG. 6 is a graph showing the NOx and CO purifying rate according to the regeneration time of the LNT catalyst according to the present invention to be.

The regeneration system of the LNT catalyst of the present invention mainly comprises an LNT (Lean NOx Trap) catalyst 1, a first lambda sensor 3 and a second lambda sensor 5, and a control unit 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an LNT catalyst 1 is disposed on an exhaust line. A first lambda sensor 3 and a second lambda sensor 5 installed at the front end and the rear end of the LNT catalyst 1 to measure the lambda value of the exhaust gas; And the concentration of the reducing agent in the exhaust gas flowing into the LNT catalyst (1) to be richer than the steady state in order to detoxify the harmful oxide occluded in the LNT catalyst (1), wherein the first lambda sensor (3) And a control unit (13) for adjusting the concentration of the reducing agent in the exhaust gas to a steady state when the difference between the first lambda value and the second lambda value measured by the lambda sensor (5) is less than or equal to a reference value.

Here, the harmful oxide stored in the LNT catalyst 1 may be NOx and SOx, and the reducing agent may be HC and CO contained in the exhaust gas. A method of controlling the concentration of the reducing agent in the control unit 13 may be a method of adjusting the air-fuel ratio or separately supplying a reducing agent at the front end of the LNT catalyst 1. Alternatively, another known reducing agent concentration The control method may be applied.

That is, when NOx and SOx are removed using the LNT catalyst 1, the first lambda value of the first lambda sensor 3 and the second lambda sensor 5 provided at the front end and the rear end of the LNT catalyst 1, The control to control the concentration of the reducing agent to a rich level based on the point where the values coincide with each other is terminated.

Therefore, at the time of removing NOx and SOx, it is possible to maximize the DeNOx and DeSOx performance, minimize the CO / HC slip, and improve the fuel efficiency by optimally controlling the time for the reducing agent to be controlled in a rich manner.

In addition, the LNT catalyst 1 adsorbs / occludes NOx in the LNT under lean conditions during normal operation, periodically sets the concentration of the reducing agent to a rich condition, and stores / And purifies adsorbed NOx. In addition, the LNT catalyst (1) adsorbs / stores not only NOx but also Sox (sulfur oxide), so that it regenerates the Sox which was occluded in the LNT by repeatedly regulating the concentration of the reducing agent at high temperature To perform DeSOx.

A DPF (Diesel Particulate Filter) 7 may be installed downstream of the LNT catalyst 1. Temperature sensors 9 and 11 may be installed at the front end and the rear end of the LNT catalyst 1.

That is, the DPF 7 located at the rear end of the LNT catalyst 1 collects PM (particulate matter) discharged from the engine at the time of traveling, and the engine periodically performs post-injection to increase the temperature of the exhaust gas, It is possible to remove the PM trapped in the exhaust gas, thereby further improving the purification performance of the exhaust gas.

On the other hand, as a method of regenerating by using the regeneration system of the LNT catalyst 1 of the present invention, there is a method of regenerating the LNT catalyst 1 through the first lambda sensor 3 and the second lambda sensor 5 provided at the front end and the rear end of the LNT catalyst 1 1) measuring a lambda value and a second lambda value; (S20) for controlling the concentration of the reducing agent in the exhaust gas flowing into the LNT catalyst (1) to be richer than the steady state in order to remove the harmful oxide occluded in the LNT catalyst (1); And a normal regulating step of regulating the reducing agent concentration in the exhaust gas to a steady state by using the difference between the first lambda value and the second lambda value measured by the first lambda sensor 3 and the second lambda sensor 5 S30). ≪ / RTI >

Here, the normal regulating step S30 may adjust the reducing agent concentration to a steady state when the difference between the first lambda value and the second lambda value is less than the reference value.

In the normal regulating step S30, it is preferable that the temperature of the LNT catalyst 1 is higher than the reference temperature for activation of the LNT catalyst 1.

2, when the concentration of the reducing agent provided toward the LNT catalyst 1 is adjusted to be richer than the steady state, NOx and SOx occluded in the LNT catalyst 1 under the lean condition are reduced, . At this time, the first lambda value of the first lambda sensor 3 provided at the front end of the LNT catalyst 1 is measured to be a relatively rich value, and the second lambda value of the second lambda sensor 5 provided at the rear stage of the LNT catalyst 1 The second lambda value is measured as a relatively lean value through regeneration by the catalyst.

Subsequently, when the detoxification of the harmful oxide occluded in the LNT catalyst 1 is completed after a predetermined regeneration time, the reducing action of the reducing agent passing through the LNT catalyst 1 is greatly reduced, and the second lambda value Converges to the first lambda value of the front end, and the difference between the first lambda value and the second lambda value is reduced to a reference value (for example, 0.04) or less. At this time, the regeneration is terminated by regulating the concentration of the reducing agent to the normal state. Here, it is appropriate to adjust the concentration of the reducing agent to the steady state to a lean condition for the occlusion of NOx and SOx in the LNT catalyst 1.

Therefore, it is possible to optimize the time for controlling the concentration of the reducing agent optimally, thereby increasing the DeNOx and DeSOx efficiency, maintaining a high HC / CO purification rate, minimizing the HC / CO slip, reducing the fuel consumption rate, .

In the normal regulating step S30, the degree of deterioration of the LNT catalyst 1 is estimated based on the accumulation value obtained by adding the difference between the first lambda value and the second lambda value in the rich control step S20, And a further step of adding a time to make the concentration richer than the steady state.

The additional step may be configured to include a calculation step and a setting step.

Specifically, the adding step continuously accumulates the difference value until the difference between the first lambda value and the second lambda value reaches the reference value from the time when the concentration of the reducing agent is adjusted to be richer than the steady state A calculation step of calculating an accumulated value; And setting the additional time for adjusting the concentration of the reducing agent to be higher than the normal state differently according to the calculated accumulated value.

In addition, in the setting step, the additional time is set shorter as the accumulated value is larger, and the additional time may be set longer as the accumulated value is smaller.

In addition to the above steps, the regeneration time is inversely proportional to the degree of deterioration of the catalyst.

That is, in the case of a catalyst having a high degree of deterioration, the regeneration time is shortened, and in the case of a catalyst having a low degree of deterioration, the regeneration time is relatively long.

The deterioration factor of the catalyst is mainly heat and sulfur poisoning. Degradation due to sulfur poisoning can be reversibly reversed depending on the sulfur concentration of the fuel, and toxicity can be removed through deSOx and recovery of activity can be restored.

Therefore, it is necessary to grasp the poisoning state of the LNT catalyst 1 and to adjust the concentration of the reducing agent to a necessary amount at the time of controlling the reducing agent concentration for DeNOx and DeSOx.

Depending on the deterioration state of the LNT catalyst 1, the additional time for adjusting the concentration of the reducing agent is preferably variable and a certain range of values should be selected (eg, 0 ≦ additional time (t) ≦ 5).

The graph at the top in FIG. 3 shows the performance of the new LNT catalyst 1 during DeNOx. From the point of time when the concentration of the reducing agent is adjusted to the rich level, the difference between the first lambda value and the second lambda value becomes equal The cumulative cumulative value is 6.0.

? (Second lambda value at the rear end - first lambda value at the front end) = 6.0

3 shows the DeNOx performance of the deteriorated LNT catalyst 1. From the point of time when the concentration of the reducing agent is adjusted to the rich level, the first lambda value and the second lambda value become equal to each other The accumulated value of the difference value is 2.8.

Σ (second lambda value at the rear end - first lambda value at the front end) = 2.8

That is, in the case of the degraded LNT catalyst 1 at the lower end where the degree of deterioration of the LNT catalyst 1 is large, applying the same additional time (additional regeneration time after matching the upstream / downstream lambda sensor) with the new LNT catalyst 1 Is ineffective in terms of NOx / CO / HC purification of the LNT catalyst 1.

Therefore, in the case of the new LNT catalyst 1 shown in Fig. 3, since there is not much deterioration, it is not necessary to give much additional time. On the contrary, in the case of the bottom deterioration LNT catalyst 1, In order to maintain a certain level of NOx / CO / HC purification performance, it is necessary to give as much additional time as possible. That is, the catalyst having a lower degree of deterioration is provided with a relatively small amount of additional time, and the catalyst having a higher degree of deterioration has a relatively increased amount of additional time.

However, if an excessively long time is applied, the CO / HC slip is generated without improving the purification performance of the NOx, and it is necessary to control the optimization of the additional time according to the deterioration degree of the catalyst.

Specifically, the additional time is determined based on the new LNT catalyst 1, from the point of time when the concentration of the reducing agent is adjusted to a rich level, to the point at which the difference between the first lambda value and the second lambda value reaches the reference value It can be set within the range of the reproduction time.

For example, if the regeneration time of the new LNT catalyst 1 is 10 seconds and the regeneration time of the deteriorated LNT catalyst 1 being used is 5 seconds, the additional time is the regeneration time of the new LNT catalyst 1 of 10 It can be set within 5 seconds so as not to exceed the second.

FIGS. 4 and 5 are diagrams showing the regeneration control flow of the regeneration method of the LNT catalyst 1 according to the present invention.

4 and 5, NOx and SOx occluded in the LNT catalyst 1 are removed by adjusting the concentration of the reducing agent to be richer than the steady state in order to perform DeNOx and DeSOx using the LNT catalyst 1. [

In this case, the first lambda value and the second lambda value are measured from the first lambda sensor 3 and the second lambda sensor 5 provided on the front and rear sides of the LNT catalyst 1. The concentration of the reducing agent is richer than the normal state The accumulation value is calculated by accumulating the difference between the first lambda value and the second lambda value until the first lambda value becomes equal to the second lambda value at the time of adjustment.

Then, the cumulative value is compared with the set value to determine the additional time for adjusting the concentration of the reducing agent to be richer than the steady state.

A, b, c, d, and e shown in FIG. 5 are positive numbers. (A> b> c> d> e)

The additional times t1, t2, t3, t4 and t5 are zero or more, and the larger the accumulated value, the shorter the additional time. (T5>t4>t3>t2> t1)

That is, if the cumulative value exceeds the value b and is equal to or smaller than the value a, the reproduction time by t1 is added, the cumulative value exceeds the c value, the value is below the value b, the reproduction time by t2 is added, If the value exceeds the d value and is equal to or smaller than the value c, the playback time of t3 is added.

Thus, in order to secure a high purification rate of NOx / CO / HC, additional regeneration time is added after the regeneration time at which the first lambda value and the second lambda value become equal to each other, The NOx purification rate can be maintained. However, in the case of a catalyst having a relatively small deterioration, even if the additional time is short, the deterioration of the purification performance due to deterioration is small, and thus the purification performance is high.

6 is a graph showing the NOx and CO purifying ratios according to the additional regeneration times of the LNT catalyst 1 according to the present invention, wherein the purifying ratios of NOx / CO are shown on the basis of the aged LNT catalyst 1 of 160 k equivalent will be.

As shown in the figure, it can be confirmed that the conditions for giving additional time of 3t to 4t are optimal conditions for maintaining the high NOx / CO purifying performance. As the additional time is increased, the NOx purification rate is increased. However, when the NOx purification rate is higher than a certain level, the NOx purification rate is saturated and the CO purification rate is deteriorated.

In addition, when the cumulative value is large, the catalyst activity is high. Therefore, when the aggressive addition time is applied, the NOx purification rate is increased, but the additional fuel injection is performed under the regulated satisfaction condition, . Therefore, it is confirmed that setting the additional time according to the deterioration degree of the LNT catalyst 1 after determining the degree of progress of the catalyst deterioration through the cumulative value is more effective in terms of NOx / CO purifying performance and fuel efficiency.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limited to the specific embodiments set forth herein; rather, .

1: LNT catalyst 3: first lambda sensor
5: second lambda sensor 7: DPF
S10: Measurement step S20: Enrichment step
S30: normal regulation step

Claims (10)

delete delete delete A measuring step of measuring a first lambda value and a second lambda value through a first lambda sensor and a second lambda sensor installed at the front end and the rear end of the LNT catalyst;
A rich control step of controlling the concentration of the reducing agent in the exhaust gas flowing into the LNT catalyst to be richer than the steady state in order to remove the harmful oxide occluded in the LNT catalyst; And
A normal regulating step of regulating the reducing agent concentration in the exhaust gas to a steady state by using the difference between the first lambda value and the second lambda value measured by the first lambda sensor and the second lambda sensor;
, ≪ / RTI &
Wherein when the difference between the first lambda value and the second lambda value is less than or equal to a reference value, the reducing agent concentration is adjusted to a steady state,
In the normal regulating step, the deterioration degree of the LNT catalyst is estimated through the accumulation value obtained by adding the difference values of the first lambda value and the second lambda value in the rich regulating step, Further comprising:
Wherein the adding step accumulates the difference value continuously until the difference value between the first lambda value and the second lambda value reaches the reference value from the time when the concentration of the reducing agent is adjusted to be richer than the steady state, A calculation step of calculating; And setting an additional time for adjusting the concentration of the reducing agent to be higher than the steady state according to the calculated accumulated value. delete delete delete The method of claim 4,
In the setting step,
The additional time is set shorter as the cumulative value is larger,
Wherein the additional time is set longer as the cumulative value is smaller. The method of claim 4,
The additional time,
And the reference lambda value is set within a range of a reference regeneration time from the time when the concentration of the reducing agent is adjusted to the reference value on the basis of the new LNT catalyst until the difference value between the first lambda value and the second lambda value reaches the reference value LNT catalyst regeneration method.
delete

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