CN111219236A

CN111219236A - Diesel engine tail gas aftertreatment system

Info

Publication number: CN111219236A
Application number: CN201811404556.1A
Authority: CN
Inventors: 汪利峰
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-11-23
Filing date: 2018-11-23
Publication date: 2020-06-02

Abstract

The invention relates to the technical field of diesel engine emission control, and discloses a diesel engine tail gas aftertreatment system which comprises an engine supercharger outlet, wherein a diesel engine particle trap, a selective reduction catalyst unit and an ammonia leakage catalyst unit are sequentially connected with the engine supercharger outlet, a urea solution spraying unit is arranged between the diesel engine particle trap and the selective reduction catalyst unit, and a diesel oxidation catalyst is integrated in the diesel engine particle trap. The invention integrates the DOC unit into the CSF, reduces the system volume and reduces the system cost.

Description

Diesel engine tail gas aftertreatment system

Technical Field

The invention relates to the technical field of emission control of diesel engines, in particular to a diesel engine tail gas aftertreatment system.

Background

The current diesel engine tail gas emission regulation requires CO/HC brought by insufficient combustion and PM and NO generated in the total combustion process_xIt is desirable to control their emissions using an aftertreatment system. The conventional approach is to use a Diesel Oxidation Catalyst (DOC) to control CO/HC emissions and to produce NO₂To satisfy the subsequent passive regeneration of a diesel particulate trap (CSF) and the reaction of a selective reduction catalyst (SCR). Or combusting fuel to provide sufficient temperature for active regeneration of CSF. Wall flow catalyst coated CSF for particulate treatment and SCR for NO_xAnd (4) discharging. In the regeneration of trapped Particulate Matter (PM) in CSF, the classification can be generally as NO₂For oxidation ofPassive regeneration of agents and with O₂Is the active regeneration of the oxidant. As previously mentioned, DOC is used to generate NO₂Either for passive regeneration of the CSF or for combustion of fuel to provide sufficient temperature for active regeneration. Ammonia Slip Catalyst (ASC) to prevent NH carry over during urea over spray₃And (4) leakage.

Referring to fig. 1, in a conventional diesel exhaust aftertreatment system, a DOC unit, a CSF, an SCR unit and an ASC unit are sequentially connected from an outlet of an engine supercharger, a urea solution spraying unit is disposed between the CSF and the SCR unit, and the ASC unit is integrated on the SCR unit. Referring to fig. 2, the ASC unit may also be a separate catalyst unit.

Disclosure of Invention

The invention aims to solve the problems and provides a diesel engine tail gas aftertreatment system, wherein a DOC unit is integrated into a CSF (CSF), so that the system volume is reduced and the system cost is reduced.

The technical scheme adopted by the invention is as follows:

the utility model provides a diesel engine exhaust's aftertreatment system, characterized by includes that engine supercharger export connects gradually diesel particulate filter, selective reduction catalyst unit and ammonia reveal catalyst unit, set up urea solution between diesel particulate filter and the selective reduction catalyst unit and spout the unit, integrated diesel oxidation catalyst in the diesel particulate filter.

Further, a diesel oxidation catalyst metal carrier is installed before the outlet of the engine supercharger and the diesel particulate trap, and the volume of the diesel oxidation catalyst metal carrier is less than 0.4 times of the engine displacement.

Further, the catalyst of the selective reduction catalyst unit includes V-W-TiO₂Predominantly V-based catalysts.

Further, the catalyst of the selective reduction catalyst unit comprises a Fe-based and Cu-based catalyst based on zeolite, which is one or more of Beta, FAU, MFI, ZSM5, CHA, SAPO, AEI, AFX structures.

Further, the diesel particulate filter is formed by coating precious metal slurry on a wall-flow diesel particulate filter carrier, wherein the content of the precious metal in each cubic foot of honeycomb carrier is 1-25g, and the precious metal is any one or both of Pt and Pd.

Further, the noble metal is present in an amount of 3 to 15g per cubic foot of the honeycomb support.

The invention has the beneficial effects that:

(1) the functions of the DOC unit are integrated into the CSF, so that a separate DOC unit is not needed, and the functions of reducing the volume of the system and the cost of the system are achieved;

(2) under the condition of the same precious metal content, the system has lower system back pressure and higher PM passive regeneration speed;

(3) the system of the present invention has similar NO oxidation capacity and outlet NO as the existing system with a separate DOC unit₂/NO_xAnd (4) proportion.

Drawings

FIG. 1 is a schematic diagram of a prior art processing system with an ASC unit integrated into an SCR unit;

FIG. 2 is a schematic diagram of a prior art ASC unit independent processing system architecture;

FIG. 3 is a schematic view of a processing system of the present invention with an ASC unit integrated into an SCR unit;

FIG. 4 is a schematic diagram of an independent processing system of the ASC unit of the present invention;

FIG. 5 is a schematic illustration of the addition of DOC metal carriers to FIG. 3;

FIG. 6 is a schematic illustration of the addition of DOC metal carriers to that of FIG. 4;

FIG. 7 is a schematic diagram of the placement and station location of a comparative experimental system;

FIG. 8 is a graph of the system back pressure and the resulting change in back pressure of the system during passive regeneration of PM;

FIG. 9 shows the system outlet NO when the system backpressure and PM are being passively regenerated₂/NO_xAnd (5) a result chart.

Detailed Description

The following describes in detail an embodiment of the diesel exhaust aftertreatment system of the present invention with reference to the accompanying drawings.

Referring to fig. 3, the after-treatment system for diesel exhaust includes an engine supercharger, an outlet of which is sequentially connected to a diesel particulate trap (CSF), a selective reduction catalyst unit (SCR unit) and an ammonia slip catalyst unit (ASC unit), a urea solution spray unit is disposed between the CSF and the SCR unit, and a diesel oxidation catalyst unit (DOC unit), which is simply represented as CSF + SCR + ASC, is integrated in the CSF. The ASC unit is here integrated in the SCR unit, which is divided into two parts, one part arranged separately and one part integrated with the ASC unit.

Referring to fig. 4, the ASC unit may also be a separate catalyst unit, disposed after the two SCR units.

Referring to fig. 5, a metal-supported DOC is added after the outlet of the engine supercharger and before CSF to treat long-chain hydrocarbons in exhaust emission. Its volume is less than 0.5 times the engine displacement. The other units are the same as in fig. 3.

Referring to fig. 6, similar to fig. 5, the ASC unit may also be a separate catalyst unit, disposed after both SCR units.

The SCR catalyst in the system includes but is not limited to V-W-TiO₂Predominantly V-SCR, predominantly zeolite Fe-based and Cu-based SCR, wherein zeolites include, but are not limited to, Beta, FAU, MFI, ZSM5, CHA, SAPO, AEI, AFX structures.

The technical effects of the present invention will be described below by comparing experimental data with the experimental results of the DOC + CSF combination of the prior art and the single CSF of the present invention.

Experimental samples: Pt/Al on Corning 10.5X 8 (diameter X length, unit: inch), 200/12 (mesh/wall thickness) blank DPF support₂O₃Coating of catalyst slurry, wherein the total content of noble metal was 3.02 g. After coating, calcining for 500-1 h. The total precious metal content is from 1 to 25g, preferably from 3 to 15g, per cubic foot of volume on the DPF support.

Comparison sample: DOC is Corning 10.5X 4 (diameter X length, unit: inch), 400/4 (mesh/wall thickness)) Carrier of (3), carrying Pt/Al₂O₃Catalyst slurry having a noble metal content of 1.89 g. CSF is Corning 10.5X 8 (diameter. times. length, unit: inch), 200/12 (mesh/wall thickness) carrier, coated with Pt/Al₂O₃Catalyst slurry, noble metal content 1.13 g. The total precious metals in the system was 3.02 g. After coating, calcining for 500-1 h.

Aging conditions are as follows: the calcined catalyst was aged in a muffle furnace at 550 ℃ for 200 hours.

Bench test: the experimental sample was single CSF, the comparative sample was a combination of DOC + CSF, and the total precious metal amount for both systems was 3.02 g.

Referring to fig. 7, carbon loading was performed using a 13L national fifth engine to test the system for soot backpressure, passive regeneration rate and NO oxidation capacity.

The experimental procedure was as follows:

1) the system is loaded with 4g/L PM (based on CSF volume), then a cyclic test is carried out by a fixed engine road spectrum, the change of the system back pressure is observed, and if the system back pressure continuously drops and finally stabilizes, the system has better PM passive regeneration capacity. Wherein the number of cycles required to reach steady state compression indicates the rate of passive regeneration of PM. A smaller number of cycles means a faster passive regeneration rate.

2) Meanwhile, when the road spectrum cycle test of the engine is carried out, the NO/NO of the inlet and the outlet of the system is carried out by using Horiba MEXA 7500_xConcentration test to calculate NO at the outlet of the system₂/NO_xA ratio. NO₂/NO_xA higher ratio of (d) means a higher NO oxidizing ability of the system.

The experimental results are as follows:

referring to fig. 8, the system back pressure and the change in back pressure of the system during passive regeneration of PM are shown. At the start of the test, the CSF system had less backpressure than DOC + CSF, about 0.5KPa lower. The results show that the CSF system results in less system backpressure due to the fewer DOC fraction than the DOC + CSF system.

After 3 road spectrum circulations, the back pressure of the CSF system is stabilized to 2.0KPa, and after 5-6 circulations, the DOC + CSF system reaches the stable system back pressure of 2.2 KPa. The results demonstrate that the new CSF system has superior PM passive regeneration capability over the DOC + CSF system.

See FIG. 9 for NO at the system outlet₂/NO_xAnd (6) obtaining the result. The new CSF system and the old DOC + CSF system have similar system outlet NO₂The results indicate that both systems have similar NO oxidation capabilities, which also provides for the SCR conversion efficiency of the system.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. An after-treatment system of diesel engine tail gas which characterized in that: the diesel particulate filter is characterized in that an outlet of an engine supercharger is sequentially connected with a diesel particulate filter, a selective reduction catalyst unit and an ammonia leakage catalyst unit, a urea solution spraying unit is arranged between the diesel particulate filter and the selective reduction catalyst unit, and a diesel oxidation catalyst is integrated in the diesel particulate filter.

2. The diesel exhaust aftertreatment system of claim 1, wherein: installing a diesel oxidation catalyst metal carrier before an engine supercharger outlet and a diesel particulate trap, wherein the volume of the diesel oxidation catalyst metal carrier is less than 0.4 times of the engine displacement.

3. The diesel exhaust aftertreatment system of claim 1, wherein: the catalyst of the selective reduction catalyst unit comprises V-W-TiO₂Predominantly V-based catalysts.

4. The diesel exhaust aftertreatment system of claim 1, wherein: the catalyst of the selective reduction catalyst unit comprises Fe-based and Cu-based catalysts with zeolite as a main component, and the zeolite is one or more of Beta, FAU, MFI, ZSM5, CHA, SAPO, AEI and AFX structures.

5. The diesel exhaust aftertreatment system of claim 1, wherein: the diesel particulate trap is formed by coating precious metal slurry on a wall-flow diesel particulate trap carrier, wherein the content of the precious metal in each cubic foot of the carrier is 1-25g, and the precious metal is any one or both of Pt and Pd.

6. The diesel exhaust aftertreatment system of claim 5, wherein: the noble metal is present in an amount of 3 to 15 grams per cubic foot of support.