KR20150133407A - Exhaust gas processing device and method - Google Patents

Abstract

The present invention relates to a device and a method for processing the exhaust gas of a vehicle, and aims to provide a device and a method for processing the exhaust gas, which can maximize the reduction of NOx by using a lambda sensor and a temperature sensor without using a NOx sensor. To achieve this purpose: a lean NOx trap (LNT), a selective catalytic reduction (SCR) catalyst, and an oxygen storage catalyst including an oxygen storage material and a jewel are placed in order in the flow direction of the exhaust gas; a front end lambda sensor is placed on the side of the top flow of the LNT; a rear end lambda sensor is placed on the side of the bottom flow of the oxygen storage catalyst; and a temperature sensor is placed to measure the exhaust gas temperature.

Description

[0001] EXHAUST GAS PROCESSING DEVICE AND METHOD [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas processing apparatus and method for a vehicle, and more particularly, to an exhaust gas processing apparatus and method capable of maximizing NOx reduction performance by using a lambda sensor and a temperature sensor without using a NOx sensor.

DeNOx catalyst technologies such as LNT (Lean NOx Trap) and SCR (Selective Catalytic Reduction) are applied as a post-treatment device for reducing NOx (nitrogen oxides) in the exhaust gas as the exhaust gas regulation of the vehicle is strengthened .

The DeNOx catalyst is a type of catalytic converter that removes NOx contained in exhaust gas. When a reducing agent such as urea, ammonia (NH ₃ ), carbon monoxide (CO), hydrocarbon (HC) NOx is reduced through an oxidation-reduction reaction with a reducing agent.

In recent years, LNT is used as a post-treatment device for removing NOx from exhaust gas components generated during operation of the lean-burn engine. The LNT adsorbs or occludes NOx contained in the exhaust gas in a lean atmosphere, When operated in a rich atmosphere, it desorbs adsorbed or occluded NOx.

The SCR system is capable of effectively reducing NOx by supplying a reducing agent to the SCR catalyst. It supplies a reducing agent to the exhaust gas unlike the EGR (exhaust gas recirculation system) which reduces NOx by recirculating the exhaust gas to lower the combustion temperature of the combustion chamber A method of reducing NOx is adopted.

SCR systems are termed selective catalytic reduction in the sense that reducing agents such as urea (UREA), ammonia, carbon monoxide, hydrocarbons, etc. react better with NOx in oxygen and NOx.

In addition, technologies such as DOC (Disel Oxidation Catalyst), DPF (Diesel Particulate Filter) and CPF (Catalyzed Particulate Filter) technologies have been developed as post-treatment technologies for reducing particulate matter (PM) .

In recent years, an SCP on Diesel Particulate Filter (SDPF) having a particulate matter collecting function and a NOx abatement function has been developed and used.

SDPF is coated with an SCR catalyst in the pore DPF by reacting NOx from NH ₃ and the exhaust gas on the SCR catalyst traps particulate matter in the exhaust gas purification of water and N _2, and in addition through a filter, that is, DPF function.

Prior art documents relating to the above-described exhaust gas treating apparatus for a vehicle include Korean Patent Publication No. 2012-0008521 (2012. 30.), Japanese Patent Publication No. 2009-540189 (2009.11.19), Japanese Patent Publication 2007-527314 (2007.9.27), Japanese Unexamined Patent Application Publication No. 2003-286827 (Oct. 10, 2003), and Japanese Unexamined Patent Publication No. 2009-291764 (Dec. 17, 2009).

On the other hand, as a method of determining the degree of deterioration of the SCR catalyst and the SDPF catalyst, a NOx sensor is mounted on the upstream side and the downstream side of the SCR or SDPF, and NOx is measured through the NOx sensor. When the purification performance of the SCR or SDPF is low, .

Although this method is a direct deterioration measurement method and a high precision method, since the price of the NOx sensor is 10 times as high as that of the temperature sensor, it is an expensive system when the NOx sensor is mounted on the upstream side and the downstream side of the catalyst.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an exhaust gas processing apparatus and method capable of maximizing NOx reduction performance by using a lambda sensor and a temperature sensor without using a NOx sensor. have.

According to an aspect of the present invention, there is provided an exhaust gas purifying catalyst comprising: an oxygen storage catalyst including an LNT (Lean NOx Trap) catalyst, an SCR (Selective Catalytic Reduction) catalyst, Placed in turn; An upstream lambda sensor disposed upstream of the LNT, a downstream lambda sensor disposed downstream of the oxygen storage catalyst, and a temperature sensor for measuring an exhaust gas temperature. to provide.

According to another aspect of the present invention, there is also provided an exhaust gas purifying catalyst comprising: an oxygen storage catalyst, which comprises an LNT (Lean NOx Trap) catalyst, an SCR (Selective Catalytic Reduction) catalyst, and an oxygen storage material; An upstream lambda sensor disposed upstream of the LNT, a downstream lambda sensor disposed downstream of the oxygen storage catalyst, and a temperature sensor for measuring an exhaust gas temperature; And NH ₃ generated in the LNT and NO x in the exhaust gas react in the SCR catalyst during rich operation to remove NO x.

Therefore, according to the exhaust gas processing apparatus and the control method thereof of the present invention, the NOx reduction performance can be maximized by using the lambda sensor and the temperature sensor without using the NOx sensor.

FIG. 1 schematically shows a configuration of an exhaust gas treating apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the structure of an integral 'SDPF + ceria catalyst' in the constitution of the embodiment shown in FIG.
3 is a view schematically showing a configuration of an exhaust gas treating apparatus according to another embodiment of the present invention.
FIG. 4 is a view showing a 'SCR catalyst + ceria catalyst' of the zone coating type in the embodiment shown in FIG.
5 is a view for explaining the NH ₃ generation mechanism in the LNT in the present invention.
6 is a diagram showing the NH ₃ generation temperature region in the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains.

The present invention relates to an exhaust gas treating apparatus and method capable of coping with the EU6 exhaust gas regulation, which is basically composed of an LNT, an SCR catalyst and an oxygen storage catalyst.

FIG. 1 is a view schematically showing a configuration of an exhaust gas treating apparatus according to an embodiment of the present invention. Referring to FIG. 1, an exhaust gas purifying apparatus according to an embodiment of the present invention includes a lean NOx trap , A nitrogen oxide storage catalyst), an SCR (Selective Catalytic Reduction) catalyst, and an oxygen storage catalyst.

The LNT is a catalyst coated with a hot storage material such as Ba or the like and adsorbs or occludes NOx contained in the exhaust gas under a lean atmosphere (lean operation) (Rich operation), NH ₃ is produced as a reaction by-product.

Also, in the present invention, the SCR catalyst may be an SCP on Diesel Particulate Filter (SDPF) having both a trapping function of particulate matter (PM) and a NOx abatement function.

The SDPF is formed by coating an SCR catalyst material on a multi-pore filter (DPF) for capturing particulate matter of a diesel exhaust gas. The NOx in the exhaust gas is reacted with NH ₃ on the SCR catalyst to purify it with water and N ₂ , Function, that is, the DPF function, collects the particulate matter in the exhaust gas.

This combination of the LNT and SDPF is passive (passive) to be configured to the SCR catalyst system, when the DeNOx in rich the NOx that is occluded in the LNT atmosphere produce a NH ₃ as reaction by-products, and NH ₃ and the exhaust generated in the LNT NOx in the gas is purified by reacting with SDPF.

The oxygen storage catalyst may be a ceria catalyst containing cerium oxide (CeO ₂ ), which is an oxide of cerium, also called ceria, as an oxygen storage material.

In a preferred embodiment, the SDPF and the ceria catalyst may be constructed integrally using a single multi-pore filter.

FIG. 2 is a cross-sectional view showing the structure of an integral 'SDPF + ceria catalyst' in the constitution of the embodiment shown in FIG. 1, which comprises a multi-pore filter for collecting particulate matter in the diesel exhaust gas, A selective catalytic reduction (SCR) catalyst layer 12, and a ceria catalyst layer 13 coated on the exhaust gas outlet side of the filter and containing ceria and a noble metal.

Here, the SCR catalyst layer 12 may be a coating layer containing a zeolite catalyst, and the ceria catalyst layer 13 may be formed of a noble metal impregnated with ceria.

The filter is constituted by a plurality of filter walls 11 in which a layer is disposed, and the plurality of filter walls 11 have a structure in which an inlet side and an outlet side are formed by mutually opposing faces, .

More specifically, an SCR catalyst layer (zeolite type) 12 is coated on one surface of a multi-pore filter, and then a ceria catalyst layer 13 containing ceria (oxygen storage material) and a noble metal is coated on the other surface.

At this time, the ceria catalyst layer 13 is formed by coating the inlet side surface of the DPF filter with the SCR catalyst layer 12, and then coating the ceria catalyst layer 13 carrying the noble metal on the ceria with the outlet side surface of the DPF filter. It is also possible to form the ceria catalyst layer on the outlet side of the DPF filter before coating the ceria catalyst layer 13 and further coating the ceria catalyst layer carrying the precious metal.

A multi-pore filter for trapping particulate matter of the diesel exhaust gas is used as a base. A SCR catalyst layer 12 is provided on the exhaust gas inlet side of the filter and a ceria catalyst layer 13 is provided on the exhaust gas outlet side of the filter Coating to form an integral 'SDPF + ceria catalyst'.

The filter is constituted by a plurality of filter walls 11 in which the layer layers are spaced apart at regular intervals so that the faces of the plurality of filter walls 11 facing each other form an exhaust gas inlet side and an outlet side, Are formed alternately.

At this time, by providing the plug 14 between the filter walls 11 for blocking the rear end of each inlet side and the front end of each outlet side, the rear end of each inlet side is blocked by the plug 14, So that only the rear end of each outlet is opened in a state in which the front end of each outlet is clogged by the plug 14.

In the embodiment of FIG. 1, lambda sensors L1 and L2 for detecting the oxygen concentration in the exhaust gas are provided on the upstream side of the LNT and the downstream side of the oxygen storage catalyst, respectively. The upstream lambda sensor (Hereinafter referred to as " downstream lambda sensor ") L2 is provided on the downstream side of the LNT as well as on the upstream side of the LNT, Downstream side, that is, downstream of the 'SDPF + ceria catalyst' in which the SDPF and the ceria catalyst are integrally formed using one multi-pore filter.

Temperature sensors T1 and T2 are provided on the upstream side of the SDPF (on the downstream side of the LNT) and on the downstream side of the ceria catalyst. In the embodiment of FIG. 1, the upstream and downstream sides of the 'SDPF + ceria catalyst' The sensors T1 and T2 are installed.

FIG. 3 is a schematic view of a configuration of an exhaust gas processing apparatus according to another embodiment of the present invention. In FIG. 3, the exhaust gas flow direction of the LNT, DPF (H ₂ S reduction), an SCR catalyst, and an oxygen storage catalyst.

In the embodiment of FIG. 3, a separate DPF for performing H ₂ S reduction function is disposed between the LNT and the SCR catalyst, that is, the downstream side of the LNT and the upstream side of the SCR catalyst, and the SCR catalyst and the oxygen storage catalyst are sequentially disposed downstream of the DPF .

Here, the oxygen storage catalyst may be a ceria catalyst.

The SCR catalyst and the ceria catalyst may be coated with a ceria catalyst material comprising a SCR catalyst material, a noble metal and a ceria on the surface of a carrier through which exhaust gas is allowed to pass.

At this time, the SCR catalyst and the ceria catalyst can be used as one catalyst using one carrier. The carrier is divided into two sections, and one portion of the SCR catalyst material, the other portion of the noble metal and ceria (All " SCR catalyst + ceria catalyst ") coated with a ceria catalyst material,

That is, the SCR catalyst material and the ceria catalyst material are coated on the front side region and the rear side region of the carrier by a zone coating method, respectively. As shown in FIG. 4, the front side is used as an SCR catalyst (zeolite type) And the back side is used as a ceria catalyst having a catalyst layer carrying noble metal on ceria.

Alternatively, a two-brick configuration may be applied in which the catalyst is in the form of a two-brick catalyst prepared by coating each carrier with an SCR catalyst material and a ceria catalyst material, that is, a combination of a separate SCR catalyst and a ceria catalyst.

3, the lambda sensors L1 and L2 are provided on the upstream side of the LNT and on the downstream side of the oxygen storage catalyst, respectively. The upstream lambda sensor (hereinafter referred to as the " shear lambda sensor & ) Is provided on the upstream side of the LNT, and a downstream lambda sensor (hereinafter referred to as " downstream lambda sensor ") L2 is also provided on the downstream side of the LNT on the downstream side of the ceria catalyst serving as the oxygen storage catalyst.

Further, temperature sensors T1, T2, and T3 are provided on the upstream side of the DPF (on the downstream side of the LNT), on the downstream side, and on the downstream side of the ceria catalyst, respectively.

As described above, the configuration of the exhaust gas processing apparatus according to the embodiment has been described with reference to Figs. 1 to 3. In the exhaust gas processing apparatus according to the embodiment, the engine air-fuel ratio control (lambda control) is performed in order to reduce NOx stored in the LNT By creating a periodic rich atmosphere (rich operation), NOx can be efficiently removed from the SCR catalyst using NH ₃ generated in the LNT.

That is, when NOx is stored in the LNT in a lean atmosphere (period of lean operation), and NH ₃ is generated in the LNT by the reaction in the periodically rich atmosphere, NH ₃ and NOx react with each other in the SCR catalyst, The ceria catalyst carrying a small amount of noble metal will purify CO and HC which are excessively rich.

At this time, in order to effectively generate a sufficient amount of NH ₃ , it is necessary to exhaust the oxygen in the LNT by a rich atmosphere and further maintain a rich atmosphere for several seconds.

In order to maintain the additional rich atmosphere, an SCR catalyst is placed on the downstream side of the LNT and an oxygen storage catalyst (ceria) is disposed on the downstream side of the SCR catalyst so that additional rich atmosphere can be maintained by the signal of the downstream lambda sensor And a downstream lambda sensor L2 is mounted on the downstream side of the oxygen storage catalyst so that the oxygen of the downstream oxygen storage catalyst is not exhausted even if the oxygen in the rich LNT is exhausted, It is determined that the oxygen on the upstream side is not exhausted from the oxygen sensor, so that the rich time can be further extended.

As a result, the additional rich atmosphere can be maintained, thereby increasing the amount of NH ₃ generated in the LNT, thereby increasing the overall NOx purification performance.

Of course, NH ₃ generated in the LNT reacts with NO x in the SCR catalyst, and NH ₃ is used to purify NO x in the SCR catalyst.

In the present invention, a ceria catalyst having an oxygen storage material and a small amount of noble metal is disposed on the downstream side of the SCR catalyst to artificially increase the rich time. In order to maintain the rich atmosphere, a lambda sensor L2), it is possible to increase the rich time, to induce efficient generation of NH ₃ effectively, to purify NH ₃ + NO x from the SCR catalyst, and to remove CO and HC from the ceria catalyst carrying the noble metal do.

FIG. 5 is a view for explaining the mechanism of NH ₃ generation in the LNT, in which the horizontal axis represents time and the vertical axis represents (a) the lambda value, (b) temperature, and (c) the concentration of NH ₃ and CO in the exhaust gas .

5 (a), when the lambda breakthrough time point at which the lambda value of the Lambda upstream sensor Lambda sensor (lane lambda sensor) L1 and the Lambda sensor downstream of the LNT sensor become the same, Breakthrough Point '.

Here, the lambda sensor downstream of the LNT should be distinguished from the downstream lambda sensor L2, that is, the lambda sensor L2 installed on the downstream side of the ceria catalyst, which is an oxygen storage catalyst, Means a side lambda sensor (upstream of the SCR catalyst (SDPF) in Fig. 1, upstream of the DPF in Fig. 3).

Hereinafter, the Lambda downstream sensor and the downstream Lambda sensor will be described separately. Here, the Lambda sensor downstream of the LNT means a lambda sensor installed on the downstream side of the LNT immediately downstream of the LNT, Means a lambda sensor of the present invention installed at the downstream end of a ceria catalyst as an oxygen storage catalyst.

In the conventional case, the rich control is terminated at the time of occurrence of the lambda breakthrough in which the lambda value of the Lambda upstream side lambda sensor and the Lambda downstream side lambda sensor become equal to each other, that is, the 'Breakthrough Point' shown in FIG.

 In (b), the exhaust gas temperature (exhaust temperature), which is the temperature of the LNT downstream temperature sensor T1, is shown.

Referring to (c), when the lambda value of the Lambda sensor upstream from the LNT upstream side and the Lambda sensor downstream of the LNT become equal to the 'Breakthrough Point', the time from the start of the rich operation is set to 't _bt ' Respectively.

When the rich atmosphere (Lambda, λ) <1) is created through engine control, the reductive chemical equation (NOx reduction and rich NOx reduction chemical reaction formula) before the lambda breakthrough is as shown in the following reaction formula .

_{Ba (NO 3) 2 + 3CO} → 2NO + 2CO 2 + BaCO 3

_{2NO + 2CO → N 2 + 2CO} 2

When lowering the oxygen concentration in the exhaust gas in a rich atmosphere to increase the reducing agent components, such as CO, HC, nitrate which has been inserted in the high-temperature storage material such as Ba is desorbed as reduced by the reducing agent component, such as CO, HC nitrogen (N ₂ ).

In addition, the reaction formula after the occurrence of lambda breakthrough is as follows.

CO + H ₂ O → CO ₂ + H ₂ (Water / Gas-Shift)

HC ₃ + 3H ₂ O → 3CO + 6H ₂ (Steam Reforming)

5H ₂ + 2NO? 2NH ₃ + 2H ₂ O

From the time stored in the oxygen storage material is stored in the oxygen and NOx occlusion material quality NOx is consumed is not located in the LNT began to an NH ₃ occurs in the LNT, and with H ₂ in the rich sustained condition after exhaustion of NOx and O ₂ NO (which is desorbed from the LNT or fed from the exhaust gas) reacts to generate NH ₃ .

Also the region in which NH ₃ occurs most frequently in the 5 (c) is t _bt and for α hours (after the rich control LNT upstream-side and downstream-side time that the lambda value is equal to the lambda sensor), after t _bt further α If the rich atmosphere is maintained for a period of time, the amount of generated NH ₃ can be increased.

In the conventional case, the rich control is terminated at the 'breakthrough point' at which the lambda value of the LNT upstream lambda sensor and the LNT downstream lambda sensor are equal to each other. However, in the present invention, the shear lambda sensor (LNT upstream lambda sensor) The effect that the rich control is terminated at the time when the lambda value of the sensor L2 becomes equal and the additional rich control for the alpha time is further maintained after the existing t _bt is obtained.

If α is set too short, the amount of NH ₃ generated decreases. If α is set too long, the amount of NH ₃ generated increases, but the amount of CO increases excessively, adversely affecting the fuel efficiency. Do.

The additional rich time α (for example, within five seconds) is the oxygen storage of the downstream catalyst, that is the amount of ceria catalyst ceria or may be increased according to the oxygen storage amount, the additional rich continued excess NH ₃ generated by .

Further, NH ₃ , which is increased in amount of generated by the additional rich time, is reacted with NO x through the SCR catalyst on the downstream side of the LNT to reduce NO x in the exhaust gas, and CO and HC, which are increased during the additional rich time, To further reduce it.

Also, it is preferable that the exhaust gas temperature, exhaust gas flow rate, catalyst aging degree, t _bt, etc., which are engine / catalyst conditions, are the main factors affecting NH ₃ generation, and the shorter the t _bt , the shorter the α.

In this way, the rich atmosphere for DeNox is immediately terminated after the time t _{bt in the} conventional case. However, in the present invention, the rich atmosphere is maintained for a further α time period after t _bt for DeNox to effectively generate a large amount of NH ₃ , Thereby further reducing NOx in the exhaust gas in the SCR catalyst.

FIG. 6 is a view showing an NH ₃ generation temperature region. NH ₃ starts to be produced at a low temperature of about 200 ° C., and a maximum amount is generated at about 300 ° C., and is generated even at 350 ° C. or higher.

The amount of NH ₃ generated depends on the lambda value, the exhaust gas flow rate, and the concentration.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments. Forms are also included within the scope of the present invention.

11: Filter wall
12: SCR catalyst layer
13: ceria catalyst layer
14: Plug
L1: Shear lambda sensor
L2: downstream lambda sensor
T1, T2, T3: Temperature sensor

Claims (19)

Disposing an LNT (Lean NOx Trap) catalyst, an SCR (Selective Catalytic Reduction) catalyst, and an oxygen storage catalyst, including an oxygen storage material and a noble metal, along the exhaust gas flow direction;
An upstream lambda sensor disposed upstream of the LNT, a downstream lambda sensor disposed downstream of the oxygen storage catalyst, and a temperature sensor for measuring an exhaust gas temperature.
The method according to claim 1,
Wherein the oxygen storage catalyst is a ceria catalyst containing ceria as an oxygen storage material.
The method according to claim 1,
Wherein the SCR catalyst is formed by coating an SCR catalyst layer on a multi-pore filter capable of collecting particulate matter in diesel exhaust gas.
The method according to claim 1,
The SCR catalyst and the oxygen storage catalyst are composed of an integrated catalyst using one multi-pore filter,
The above-
Multi - pore filter;
An SCR catalyst layer coated on the exhaust gas inlet side of the filter; And
And an oxygen storage material catalyst layer coated on the exhaust gas outlet side of the filter and containing an oxygen storage material and a noble metal.
The method of claim 4,
Wherein the filter is a multi-pore filter capable of collecting particulate matter in diesel exhaust gas.
The method of claim 4,
Characterized in that the filter is constituted by a plurality of filter walls in which a layer is arranged and the plurality of filter walls have a structure in which the inlet side and the outlet side are formed so that the inlet side and the outlet side alternate with each other, Gas processing device.
The method according to claim 1,
And a DPF (Diesel Particulate Filter) is disposed between the LNT and the SCR catalyst.
The method of claim 7,
Wherein the SCR catalyst and the oxygen storage catalyst are composed of an integral catalyst using a single carrier, and the integrated catalyst comprises an SCR catalyst layer, an oxygen storage material catalyst layer containing an oxygen storage material and a noble metal in a zone coating manner on the front region and the rear region of the carrier Wherein the catalyst layer is formed by coating.
The method according to claim 4 or 8,
Wherein the oxygen storage material is a ceria.
The method of claim 1, claim 3, claim 4 or claim 8,
Wherein the SCR catalyst layer of the SCR catalyst is a coating layer comprising a zeolite catalyst.
The method according to claim 1,
Wherein the rich operation is maintained until a lambda value of the front end lambda sensor and the rear end lambda sensor becomes equal after starting rich operation for removing NOx occluded in the LNT.
Disposing an LNT (Lean NOx Trap) catalyst, an SCR (Selective Catalytic Reduction) catalyst, and an oxygen storage catalyst, including an oxygen storage material and a noble metal, along the exhaust gas flow direction;
An upstream lambda sensor disposed upstream of the LNT, a downstream lambda sensor disposed downstream of the oxygen storage catalyst, and a temperature sensor for measuring an exhaust gas temperature;
NH ₃ generated in the LNT and NO x in the exhaust gas react in the SCR catalyst during rich operation to remove NO x.
The method of claim 12,
So that CO and HC in the exhaust gas are removed by the noble metal contained in the oxygen storage catalyst.
The method of claim 12,
Wherein rich operation is maintained until a lambda value of the front end lambda sensor and the rear end lambda sensor become equal after starting rich operation for removing NOx occluded in the LNT.
15. The method of claim 14,
( _Tbt ) from the start of the rich operation to the point at which the lambda values of the dedicated lambda sensor and the downstream lambda sensor become equal to each other and the exhaust gas temperature measured by the temperature sensor. Gas treatment method.
The method of claim 12,
Wherein the oxygen storage catalyst is a ceria catalyst containing ceria as an oxygen storage material.
The method of claim 12,
Wherein the SCR catalyst is formed by coating an SCR catalyst layer on a multi-pore filter capable of collecting particulate matter in a diesel exhaust gas.
The method of claim 12,
And a DPF (Diesel Particulate Filter) is disposed between the LNT and the SCR catalyst.
The method according to claim 12 and claim 17,
Wherein the SCR catalyst layer of the SCR catalyst is a coating layer comprising a zeolite catalyst.

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