CN216172386U

CN216172386U - SCR-LNT catalyst and aftertreatment system for reducing nitrogen oxide emission

Info

Publication number: CN216172386U
Application number: CN202122721716.9U
Authority: CN
Inventors: 刘世龙
Original assignee: Great Wall Motor Co Ltd
Current assignee: Great Wall Motor Co Ltd
Priority date: 2021-11-08
Filing date: 2021-11-08
Publication date: 2022-04-05
Anticipated expiration: 2031-11-08

Abstract

The utility model belongs to the technical field of engine tail gas treatment, and particularly relates to an SCR-LNT catalyst and a post-treatment system for reducing nitrogen oxide emission, wherein the SCR-LNT catalyst comprises a catalyst carrier, an LNT catalyst layer coated on the catalyst carrier, and an SCR catalyst layer arranged on the LNT catalyst layer; wherein the LNT catalyst layer is perovskite powder La_0.7Sr_0.3CoO₃The SCR catalyst layer comprises a copper powder coating and Al₂O₃Coating; the aftertreatment system comprises the SCR-LNT catalyst, a DPF device and a controller. The combination of the SCR catalyst layer, the LNT catalyst layer and the SCR-LNT catalytic device greatly improves the NOx conversion efficiency, can solve the problem of eliminating high-concentration NOx discharged by a rich-combustion engine of a heavy-duty diesel vehicle, and widens the active temperature window of the catalytic coating to a certain extent.

Description

SCR-LNT catalyst and aftertreatment system for reducing nitrogen oxide emission

Technical Field

The utility model belongs to the technical field of engine tail gas treatment, and particularly relates to an SCR-LNT catalyst and an aftertreatment system for reducing nitrogen oxide emission.

Background

Diesel vehicles include light-duty diesel vehicles and heavy-duty diesel vehicles, which emit nitrogen oxides at a high concentration, and in order to convert them into pollution-free gases such as carbon dioxide, water and nitrogen, exhaust gas exhaust aftertreatment systems are constructed using various catalyst systems in the exhaust system of the vehicle.

At present, the catalytic technology applied to the exhaust emission system of the heavy-duty diesel vehicle mainly comprises NH₃-SCR (selective catalytic reduction) technology, HC-SCR technology and LNT (diesel lean NOX trap) -SCR technology. Wherein NH₃The SCR technique is NH₃For the selective reduction of NOx by a reductant over a catalyst to form non-toxic N₂And H₂O; the HC-SCR technology is a technology for selective catalytic reduction of NOx using some of the hydrocarbons present in exhaust gas as a reducing agent; LNT-SCR technology generally includes an LNT device, a DPF device (soot particulate supply), and an SCR connected in seriesProvided is a device.

In the above-mentioned catalytic system, NH₃SCR requires, in practice, a urea tank and a precisely controlled urea injection system for the motor vehicle load, NH being present in complex vehicle conditions₃Leakage and secondary pollution. The HC-SCR technology has the problems that the catalyst activity is not high enough, the temperature window is narrow, and finally the NOx conversion efficiency is low. The LNT device in the LNT-SCR technology is a post-treatment technology for periodic adsorption-catalytic reduction by utilizing the concentration change of engine mixed gas, and catalytic generation of NH can exist₃Instability problem and adsorption of NH by SCR systems₃Mainly depends on the acidity of the surface of the catalyst, but the acidity of the catalyst is weakened by the high temperature generated during the regeneration of the front DPF, so that the conversion performance of NOx is reduced, and the high-concentration NO generated by a heavy diesel engine is finally influenced_xThus, from a practical point of view, heavy duty diesel engines have a high NO concentration_xThe elimination techniques of (a) have yet to be further improved.

SUMMERY OF THE UTILITY MODEL

The embodiment of the utility model provides an SCR-LNT catalyst and an aftertreatment system for reducing nitrogen oxide emission, and aims to solve the problem that an engine emits high-concentration NO_xLow conversion efficiency and narrow temperature window of catalytic coating activity.

In order to achieve the purpose, the utility model adopts the technical scheme that: on one hand, the SCR-LNT catalyst is provided and comprises a catalyst carrier, an LNT catalyst layer coated outside the catalyst carrier and an SCR catalyst layer arranged outside the LNT catalyst layer; wherein the LNT catalyst layer is perovskite powder La_0.7Sr_0.3CoO₃The SCR catalyst layer comprises a copper powder coating and Al₂O₃And (4) coating.

In one possible implementation manner, a first temperature detection device is disposed on the LNT catalyst layer, and a second temperature detection device is disposed on the SCR catalyst layer.

Optionally, the first temperature detection device or the second temperature detection device adopts a K-type thermocouple.

In one possible implementation, a heat insulating layer is further disposed between the SCR catalyst layer and the LNT catalyst layer.

Optionally, the heat insulation layer is a quartz cotton layer, wherein the thickness of the quartz cotton layer is 12-18 μm.

Optionally, the copper powder coating is provided on Al₂O₃The outer layer of the coating layer, the thickness of the copper powder coating layer is 25-40 mu m, and the Al is₂O₃The thickness of the coating is 20-60 mu m.

In one embodiment, the catalyst carrier is a copper-based molecular sieve having a pore size of 1 to 2mm × 1 to 2 mm.

On the other hand, the utility model also provides an aftertreatment system for reducing nitrogen oxide emission, which comprises the SCR-LNT catalytic device, wherein the SCR-LNT catalytic device is provided with an inlet and an outlet which are used for being communicated with an exhaust system of a rich-combustion engine, and the SCR-LNT catalytic device is filled with the SCR-LNT catalyst;

and a DPF device provided with an inlet communicated with the outlet of the SCR-LNT catalytic device and an exhaust gas discharge port.

In one embodiment, the catalyst is not densely packed in the SCR-LNT catalytic device, wherein the catalyst has a cylindrical structure.

In some embodiments, a first NOx concentration sensor is provided at an inlet of the SCR-LNT catalytic device, a second NOx concentration sensor is provided at an inlet of the DPF device, and a differential pressure sensor is connected between the inlet of the DPF device and an exhaust gas discharge port.

In one embodiment, the aftertreatment system further comprises a controller, wherein the output ends of the first temperature detection device, the second temperature detection device, the first NOx concentration sensor, the second NOx concentration sensor and the differential pressure sensor are respectively connected to the corresponding input ends of the controller.

Compared with the prior art, the SCR-LNT catalyst and the aftertreatment system for reducing nitrogen oxide emission provided by the utility model have the following advantages:

coating with copper powder and Al₂O₃The SCR catalyst layer formed by the coating can be at 300-350 ℃ and C₃H₆The selective catalytic reduction catalyst shows optimal NO reduction activity when being used as a reducing agent, enables the SCR catalyst layer to selectively and catalytically reduce partial NOx by utilizing carbon ammonia compounds contained in tail gas with high efficiency, reduces the storage reduction pressure of the LNT catalyst layer, can reduce the escape of NOx on the LNT catalyst layer by reducing the concentration of the NOx entering the LNT catalyst layer, enables the storage efficiency of the LNT catalyst layer on the NOx in a lean burn stage and the reduction efficiency of the NOx in a rich burn stage to be improved, and improves the storage efficiency of the LNT catalyst layer on the NOx in the lean burn stage and the reduction efficiency of the NOx in the rich burn stage through non-noble metal perovskite powder La_0.7Sr_0.3CoO₃LNT catalyst layer formed of coating layer capable of being coated with C₃H₆When the catalyst is used as a reducing agent, almost NO N0 is generated, and the optimal NO conversion performance is shown at 300-400 ℃, so that the conversion efficiency of a catalytic system is maximized. Therefore, the combination of the SCR catalyst layer, the LNT catalyst layer and the SCR-LNT catalytic device greatly improves the NOx conversion efficiency, can solve the problem of eliminating high-concentration NOx emitted by a rich-burn engine of a heavy-duty diesel vehicle, and widens the active temperature window of the catalytic coating to a certain extent.

Drawings

FIG. 1 is a schematic cross-sectional view of an SCR-LNT catalyst;

FIG. 2 is a schematic longitudinal cross-sectional view of an SCR-LNT catalyst;

FIG. 3 is a schematic illustration of an aftertreatment system for reducing nitrogen oxide emissions;

description of reference numerals:

11-a catalyst support; 12-LNT catalyst layer; 13-a layer of quartz wool; 14-an SCR catalyst layer; 15-first temperature detection means; 16-a second temperature detection device;

21-a first NOx concentration sensor; 22-SCR-LNT catalytic system; 23-a second NOx concentration sensor; 24-DPF device; 25-differential pressure sensor; 26-control unit.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit the utility model.

Referring to fig. 1, the SCR-LNT catalyst provided by the present invention will now be described. The SCR-LNT catalyst in this embodiment includes a catalyst carrier 11, an LNT catalyst layer 12 coated outside the catalyst carrier, and an SCR catalyst layer 14 coated outside the LNT catalyst layer; wherein the LNT catalyst layer 12 is perovskite powder La_0.7Sr_0.3CoO₃Coating, the SCR catalyst layer 14 comprises a copper powder coating and Al₂O₃And (4) coating.

In this example, diesel engine exhaust enters the SCR-LNT device and some of the NOx is in the copper powder coating and Al in the SCR catalyst layer₂O₃Catalytic reaction of the coating with NH₃Generating N₂And H₂O reduces the concentration of NOx entering the LNT catalyst layer 12, and the other part of NOx is in the LNT catalyst layer 12, calcium titanium mineral powder La_0.7Sr_0.3CoO₃Under the catalytic action of the coating, with C₃H₆When the catalyst is used as a reducing agent, almost NO N0 is generated, and the optimal NO conversion performance is shown at 300-400 ℃, so that the conversion efficiency of a catalytic system is maximized.

The SCR-LNT catalytic system provided by the utility model is composed of a copper powder coating and Al₂O₃The SCR catalyst layer 14 formed by the coating can be at 300-350 ℃ and C₃H₆The catalyst shows the optimal NO reduction activity when being used as a reducing agent, so that the SCR catalyst layer 14 can selectively catalyze and reduce partial NOx by utilizing carbon ammonia compounds contained in exhaust gas with high efficiency, the storage reduction pressure of the LNT catalyst layer 12 is reduced, the NOx concentration entering the LNT catalyst layer 12 is reduced, the NOx escape on the LNT catalyst layer 12 can be reduced, the NOx storage efficiency of the LNT catalyst layer 12 in a lean combustion stage and the NOx reduction efficiency of the LNT catalyst layer 12 in a rich combustion stage are improved, and the non-noble metal perovskite La_0.7Sr_0.3CoO₃ LNT catalyst layer 12 formed of a coating layer, which can be formed of C₃H₆When the catalyst is used as a reducing agent, almost NO N0 is generated, and the optimal NO conversion performance is shown at 300-400 ℃, so that the conversion efficiency of a catalytic system is maximized. Therefore, through the utility modelThe novel combination of the SCR catalyst layer 14 and the LNT catalyst layer 12 greatly improves the NOx conversion efficiency, can solve the problem of eliminating high-concentration NOx discharged by a heavy diesel engine, and widens the active temperature window of the catalytic coating to a certain extent.

In one embodiment, the LNT catalyst layer is provided with a first temperature detection device 15, and the SCR catalyst layer is provided with a second temperature detection device 16.

Alternatively, the first temperature detection device 15 and the second temperature detection device 16 may use a K-type thermocouple. The high-precision and high-sensitivity K-type thermocouple is used for monitoring the temperature of the SCR-LNT catalytic device 23 to achieve the optimal catalytic temperature of the catalyst, so that nitrogen oxides are reduced more thoroughly.

In order to ensure that the SCR catalyst layer 14 and the LNT catalyst layer 12 are reacted in the respective optimum reaction temperature ranges, a heat insulating layer is further provided between the SCR catalyst layer and the LNT catalyst layer.

In one embodiment, the thermal insulation layer is a quartz cotton layer 13, wherein the thickness of the quartz cotton layer 13 is 12 to 18 μm.

In order to realize efficient and stable partial NOx elimination, the copper powder coating is arranged on Al₂O₃The outer layer of the coating layer, the thickness of the copper powder coating layer is 25-40 mu m, and the Al is₂O₃The thickness of the coating is 20-60 mu m.

In one embodiment, the catalyst carrier 11 is a copper-based molecular sieve having a pore diameter of 1 to 2mm × 1 to 2mm, and the pore diameter of the molecular sieve enables the SCR-LNT catalyst to pass through pores of the molecular sieve linearly without blocking the pores.

In a second aspect, referring to FIG. 2, an aftertreatment system for reducing NOx emissions in accordance with the present invention is now described. In another embodiment, an aftertreatment system for reducing nitrogen oxide emissions includes the SCR-LNT catalytic device 22, the SCR-LNT catalytic device 22 has an inlet for communicating with an exhaust system of a rich-burn engine and an outlet, and the SCR-LNT catalytic device 22 is filled with the SCR-LNT catalyst; and a DPF device 24, wherein the DPF device 24 is provided with an inlet communicated with an outlet of the SCR-LNT catalytic device 22 and an exhaust gas outlet.

The aftertreatment system for reducing nitrogen oxide emission provided by the utility model firstly improves the conversion efficiency of NOx in engine exhaust to the maximum extent through the SCR-LNT catalytic device 22, then reduces smoke particles in the exhaust through the DPF device 24, and ensures the efficient operation of the SCR-LNT catalytic device 22 and the DPF device 24 through the control unit, so that the exhaust can meet the emission requirement after passing through the aftertreatment system.

Illustratively, the catalyst is not densely packed in the SCR-LNT catalytic device, wherein the catalyst has a cylindrical structure.

Alternatively, a first NOx concentration sensor 21 is provided at the inlet of the SCR-LNT catalytic device, a second NOx concentration sensor 23 is provided at the inlet of the DPF device, and a differential pressure sensor 25 is connected between the inlet of the DPF device and the exhaust gas discharge port.

In one embodiment, the aftertreatment system further comprises a controller 26, wherein the output ends of the first temperature detecting device 15, the second temperature detecting device 16, the first NOx concentration sensor 21, the second NOx concentration sensor 23 and the differential pressure sensor 25 are respectively connected to corresponding input ends of the controller 26.

Determining the adsorption amount of the SCR device in the SCR-LNT catalytic device 22 from the concentration signal of the first NOx concentration sensor 21, and determining the adsorption amount of the LNT device in the SCR-LNT catalytic device 22 from the concentration signal of the second NOx concentration sensor 23; the controller 26 may be capable of collecting sensor signals, monitoring the operating state of the SCR-LNT catalytic device 22, and transmitting data remotely.

In summary, the SCR-LNT catalyst and the aftertreatment system for reducing nitrogen oxide emission provided by the embodiments of the present invention pass the copper powder coating layer of the SCR catalyst layer in the SCR-LNT catalytic device and Al for the gas emitted from the outlet of the heavy diesel engine₂O₃Coating and LNT catalytic layer calcium titanium mineral powder La_0.7Sr_0.3CoO₃Catalytic reaction of catalytic coating, solving the problem of eliminating heavy diesel vehiclesThe problem of high concentration NOx discharged by the rich-burning engine is solved, and the smoke dust particles are removed through the DPF to obtain the finally discharged gas, so that the method has wide use space.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the utility model, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. The SCR-LNT catalyst is characterized by comprising a catalyst carrier, an LNT catalyst layer coated outside the catalyst carrier, and an SCR catalyst layer arranged outside the LNT catalyst layer; wherein the LNT catalyst layer is perovskite powder La_0.7Sr_0.3CoO₃A coating layer, the SCR catalyst layer comprises a copper powder coating layer and Al₂O₃And (4) coating.

2. The SCR-LNT catalyst of claim 1, wherein a first temperature detection device is disposed on the LNT catalyst layer, and a second temperature detection device is disposed on the SCR catalyst layer.

3. The SCR-LNT catalyst of claim 2, wherein the first temperature detecting means or the second temperature detecting means employs a type K thermocouple.

4. The SCR-LNT catalyst of claim 1, further comprising a thermal insulation layer disposed between the SCR catalyst layer and the LNT catalyst layer.

5. The SCR-LNT catalyst of claim 4, wherein the thermal insulation layer is a quartz wool layer having a thickness of 12-18 μm.

6. The SCR-LNT catalyst of any of claims 1 to 5, wherein the copper powder coating is on Al₂O₃Of coatingsAn outer layer, wherein the thickness of the copper powder coating is 25-40 mu m, and the Al is₂O₃The thickness of the coating is 20-60 mu m.

7. The SCR-LNT catalyst of claim 1, wherein the catalyst support is a copper-based molecular sieve with a pore size of 1-2 mm x 1-2 mm.

8. An aftertreatment system for reducing nitrogen oxide emissions, comprising:

the SCR-LNT catalytic device is provided with an inlet and an outlet which are used for being communicated with an exhaust system of a rich-combustion engine, and the SCR-LNT catalytic device is filled with the SCR-LNT catalyst according to any one of claims 1-7;

and the DPF device is provided with an inlet communicated with the outlet of the SCR-LNT catalytic device and an exhaust outlet.

9. The aftertreatment system of claim 8, wherein the catalyst is non-densely packed within the SCR-LNT catalytic device, wherein the catalyst is of a cylindrical structure.

10. The aftertreatment system of claim 8, wherein a first NOx concentration sensor is installed at an inlet of the SCR-LNT catalytic device, a second NOx concentration sensor is installed at an inlet of the DPF device, and a differential pressure sensor is connected between the inlet of the DPF device and an exhaust gas exhaust port.

11. The aftertreatment system of claim 10, wherein a first temperature sensing device is disposed on the LNT catalyst layer and a second temperature sensing device is disposed on the SCR catalyst layer, the aftertreatment system further comprising a controller, wherein outputs of the first temperature sensing device, the second temperature sensing device, the first NOx concentration sensor, the second NOx concentration sensor, and the differential pressure sensor are coupled to respective inputs of the controller.