KR20170006162A - Exhaust gas post-processing device and method - Google Patents

Abstract

An objective of the present invention is to provide an exhaust gas post-treatment device which reduces mileage degradation of an engine and a burden of the engine, secures a high a denitrification rate, and has denitrification performance in a low temperature condition. According to an embodiment of the present invention, the exhaust gas post-treatment device comprises: an exhaust pipe to distribute exhaust gas of an engine; a hydrocarbon selective catalytic reduction (HC-SCR) disposed on the exhaust pipe to remove nitrogen oxide contained in exhaust gas; a lean nitrogen oxide trap (LNT) to remove nitrogen oxide remained in exhaust gas passing through the hydrocarbon selective catalytic reduction; and a reformer connected to the exhaust pipe in front of the hydrocarbon selective catalytic reduction to reform fuel to produce and supply a reducing agent of hydrogen and a hydrocarbon (HC) species.

Description

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

The present invention relates to an exhaust gas post-treatment apparatus and a method for simplifying a post-treatment system of an exhaust gas.

As environmental regulations have been strengthened, various exhaust gas aftertreatment devices have been proposed. The small and medium sized vehicles are equipped with a nitrogen oxide trap (LNT) or a selective catalytic reduction (Urea SCR) to remove nitrogen oxides (NOx) contained in the exhaust gas of the engine. .

However, in order to cope with more stringent regulations such as EURO VI or later exhaust gas control, especially real driving emissions (RDE), it is necessary to construct a system capable of additionally removing NOx from existing technologies Needs to be.

For example, it is necessary to construct a system with low NOx removal rate as low as urea selective reduction catalyst (Urea SCR) and a simple structure even in medium and large vehicles.

The nitrogen oxide storage catalyst (LNT) occludes NOx in the lean burn condition of the engine, and periodically forms a rich burn condition in the engine to reduce desorbed NOx.

In the super-rich combustion condition, the fuel may be additionally injected into the LNT by injecting the fuel after the equivalence ratio combustion in the engine, or a separate fuel injector may be installed in the exhaust pipe and the fuel may be injected as a reducing agent in front of the LNT. In the case of applying the nitrogen oxide storage catalyst (LNT), the fuel consumption may be lowered and the engine burden may be caused by the frequent super-rich combustion condition of the engine.

Urea SCR has high denitrification (De-NOx) performance but it has low NOx treatment efficiency at low temperature because it has denitrification performance at high temperature of 220 ~ 230 ° C.

Separate Urea tanks and urea injectors are required and hydrolysis reactors may be required to separate ammonia (NH ₃ ) from the urea water, as the case may be. When the urea number selective reduction catalyst (Urea SCR) is applied, the complexity of the system can increase the price of the apparatus and increase the installation space of the apparatus in the vehicle.

It is an object of the present invention to provide an exhaust gas aftertreatment apparatus having a reduction in fuel consumption of an engine, a burden on an engine, securing a high denitration rate, and denitrating performance even under low temperature conditions.

It is another object of the present invention to provide an exhaust gas post-treatment method for treating nitrogen oxide contained in exhaust gas by using the exhaust gas post-treatment apparatus.

An exhaust gas after-treatment apparatus according to an embodiment of the present invention includes an exhaust pipe for circulating exhaust gas of an engine, a hydrocarbon selective reduction catalyst (HC SCR) provided in the exhaust pipe to remove nitrogen oxides contained in the exhaust gas, A nitrogen oxide storage catalyst (LNT) for removing nitrogen oxide remaining in the exhaust gas via the selective reduction catalyst, and a reforming catalyst connected to the exhaust pipe in front of the hydrocarbon selective reduction catalyst to reform the fuel to produce hydrogen and hydrocarbon (HC) species ) ≪ / RTI > reducing agent.

The hydrocarbons may have a carbon number of C1 to C5.

A method for post-treatment of an exhaust gas according to an embodiment of the present invention includes a first step of producing a large amount of hydrocarbon (HC) species and hydrogen by reforming a fuel by supplying fuel and air to a reformer under lean- A second step of supplying hydrogen and hydrocarbon species onto a hydrocarbon selective reduction catalyst (HC SCR) for circulating exhaust gas, a nitrogen oxide storage catalyst (LNT) disposed behind a hydrocarbon selective reduction catalyst (HC SCR) A third step of passing exhaust gas via the hydrocarbon selective reduction catalyst, and a fourth step of switching to a rich combustion condition after a lapse of a predetermined period of time under lean burn conditions and then switching to a lean burn condition after engine operation.

In the first step, the partial oxidation or decomposition of light oil may produce hydrogen which functions as a reducing agent, hydrocarbons (HC) of C1 to C5, and hydrogen.

In the second step, after the hydrocarbon selective reduction catalyst (HC SCR) is activated, the produced hydrogen and hydrocarbon species act as a reducing agent on the hydrocarbon selective reduction catalyst (HC SCR), and nitrogen oxides ) Can be reduced to nitrogen (N ₂ ).

In the third step, the nitrogen oxide contained in the exhaust gas may be occluded in the nitrogen oxide storage catalyst (LNT) before the hydrocarbon selective reduction catalyst (HC SCR) is activated.

As described above, an embodiment of the present invention is characterized in that a hydrocarbon selective reduction catalyst (HC SCR) and a nitrogen oxide storage catalyst (LNT) are sequentially provided in an exhaust pipe and a reducing agent of hydrogen and hydrocarbon species reformed in the reformer is introduced into a hydrocarbon selective reduction catalyst HC SCR) to remove nitrogen oxide, which can reduce the fuel consumption of the engine and reduce the burden on the engine.

That is, in one embodiment, the hydrocarbon selective reduction catalyst (HC SCR) is activated during the normal operation to reduce the nitrogen oxide discharged from the engine, and only the residual nitrogen oxide that is not reduced in the hydrocarbon selective reduction catalyst (HC SCR) (HC SCR) is not activated as in the case of the cold start condition, the nitrogen oxide storage catalyst can be decomposed into nitrogen It is possible to provide a means capable of absorbing oxides and removing nitrogen oxides in the exhaust gas under any conditions. That is, the denitration performance can be ensured even under a low temperature condition.

Through this process, the fuel efficiency of the engine is improved and the burden on the engine is reduced as compared with the existing oxide removal apparatus.

1 is a configuration diagram of an exhaust gas post-treatment apparatus according to an embodiment of the present invention.
2 is a cross-sectional view of the reformer applied to Fig.
3 is a flowchart of an exhaust gas after-treatment method according to an embodiment of the present invention.
4 is a graph comparing the lean and hyper-rich combustion conditions according to the prior art and one embodiment of the present invention.
FIG. 5 is a graph comparing the denitration performance according to the prior art and one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

1 is a configuration diagram of an exhaust gas post-treatment apparatus according to an embodiment of the present invention. 1, an exhaust gas post-treatment apparatus according to an embodiment includes an exhaust pipe 20 for circulating exhaust gas of an engine 10, a hydrocarbon selective reduction catalyst (HC SCR) 30 provided in an exhaust pipe 20, , A nitrogen oxide storage catalyst (LNT) 40, and a reformer 50.

A hydrocarbon selective reduction catalyst (HC SCR) 30 is installed in the exhaust pipe 20 and is configured to remove nitrogen oxides contained in the exhaust gas. The nitrogen oxide storage catalyst (LNT) 40 is disposed in the exhaust pipe 20 behind the hydrocarbon selective reduction catalyst (HC SCR) 30, and is made of nitrogen oxide (NOx) remaining in the exhaust gas via the hydrocarbon selective reduction catalyst 30. [ .

The nitrogen oxide storage catalyst (LNT) 40 further increases the denitration rate of the hydrocarbon selective reduction catalyst (HC SCR) 30 and expands the denitable temperature range in the exhaust gas aftertreatment apparatus as a whole.

The reformer 50 is configured to reform the fuel to produce a reducing agent of hydrogen and hydrocarbon (HC) species and is connected to the exhaust pipe 20 in front of the hydrocarbon selective reduction catalyst 30. Therefore, the reducing agent of the hydrogen and hydrocarbon (HC) species produced in the reformer 50 is supplied to the hydrocarbon selective reduction catalyst (HC SCR) 30 together with the exhaust gas. For example, hydrocarbons produced in the reformer 50 may have a carbon number of C1 to C5.

2 is a cross-sectional view of the reformer applied to Fig. Referring to FIG. 2, the reformer 50 generates plasma to generate a reducing agent as a fuel and supplies it to the exhaust pipe 20 and the hydrocarbon selective reduction catalyst 30, so that the NOx contained in the exhaust gas . ≪ / RTI > That is, the reformer 50 may be formed of a plasma device.

The reformer 50 may be configured to generate a rotating flow arc plasma. For example, the reformer 50 includes a housing 41 connected to the exhaust pipe 20, an electrode 42 embedded in the housing 41 and forming a discharge gap G between the inner surface of the housing 41, .

When the housing 41 is electrically grounded and a voltage HV is applied to the electrode 42, a rotating fluid arc is generated by using the oxidant as a discharger at the discharge gap G. By supplying fuel to the rotating flow arc, the fuel is reformed with a reducing agent of hydrogen and hydrocarbon (HC) species and is ejected out of the housing 41.

One side of the housing 41 is closed through an insulating member 43, and an electrode 42 is provided on the insulating member 43. Therefore, the insulating member 43 electrically insulates the housing 41 from the electrode 42, thereby enabling generation of an arc in the discharge gap G.

The housing 41 has an oxidant supply port 44 for supplying an oxidant between the insulating member 43 and the discharge gap G and a surge chamber 45 connected to the oxidant supply port 44, (44).

The oxidant supply port 44 is formed in a tangential direction from the housing 41 toward the electrode 42 to induce a rotational flow of the oxidant supplied into the housing 41 (not shown). The surge chamber 45 temporarily stores the supplied oxidizing agent so that the amount of the oxidizing agent supplied to the plurality of oxidizing agent supply openings 44 is uniform.

The housing 41 also has a fuel supply port 46 in a cylinder corresponding to the end portion of the electrode 42. The fuel supply port 46 may supply a part of the fuel supplied to the engine 10. [

The reformer 50 reforms the fuel supplied to the fuel supply port 46 by the plasma reaction by the rotational flow arc of the oxidizing agent supplied to the oxidizing agent supply port 44 to produce a reducing agent of hydrogen and hydrocarbon (HC) species.

Since the housing 41 of the reformer 50 is connected to the exhaust pipe 20, the generated reducing agent of hydrogen and hydrocarbon (HC) species is supplied to the hydrocarbon selective reduction catalyst 30 through the exhaust pipe 20 to reduce NOx do.

3 is a flowchart of an exhaust gas after-treatment method according to an embodiment of the present invention. Referring to FIG. 3, the exhaust gas after-treatment method of one embodiment includes a first step (ST1) to a fourth step (ST4).

In the first step ST1, fuel and air are supplied to the reformer 50 under lean-burn conditions to reform the fuel to produce a large amount of hydrocarbons (HC) species and hydrogen. The first step (ST1) can produce hydrocarbons (HC) of C1 to C5 carbon atoms and hydrogen which function as a reducing agent by partially oxidizing or cracking light oil.

The second step (ST2) supplies the produced hydrogen and hydrocarbon species onto a hydrocarbon selective reduction catalyst (HC SCR) for circulating the exhaust gas.

The reformed hydrocarbon species and hydrogen are supplied to the hydrocarbon selective reduction catalyst 30 through the exhaust pipe 20 and denitrified at the hydrocarbon selective reduction catalyst 30. [

That is, in the second step ST2, after the hydrocarbon selective reduction catalyst (HC SCR) 30 is activated, the produced hydrogen and hydrocarbon species act as a reducing agent on the hydrocarbon selective reduction catalyst 30, Reduce oxides (NOx) to nitrogen (N ₂ ).

The third step ST3 allows the exhaust gas passing through the hydrocarbon selective reduction catalyst 30 to flow from the nitrogen oxide storage catalyst (LNT) 40 disposed behind the hydrocarbon selective reduction catalyst (HC SCR)

That is, the third step ST3 stores the nitrogen oxide contained in the exhaust gas in the nitrogen oxide storage catalyst (LNT) 40 before the hydrocarbon selective reduction catalyst (HC SCR) 30 is activated. The nitrogen oxide storage catalyst 40 stores NOx while the hydrocarbon selective reduction catalyst (HC SCR) 30 is not denitrified or the residual nitrogen oxide (NOx) that has not been subjected to the fresh reduction in the hydrocarbon selective reduction catalyst Thereby reducing the denitrification performance of the hydrocarbon selective reduction catalyst (HC SCR) 30.

Therefore, in order to remove the nitrogen oxide stored in the nitrogen oxide storage catalyst 40 at a high temperature, the cycle of the rich combustion condition for the nitrogen oxide storage catalyst 40 implementing the rich combustion condition can be remarkably prolonged. That is, the time for driving the engine in the rich combustion condition is shortened, and the time for driving in the lean-burn condition becomes long.

The fourth step (ST4) is switched to the rich combustion condition at the lapse of the set time in the lean burn condition, and is switched to the lean burn condition after the engine operation.

4 is a graph comparing the lean and hyper-rich combustion conditions according to the prior art and one embodiment of the present invention. Referring to FIG. 4, during the same operation time of the engine 10, the conventional art on the left side shows a shortened rich combustion period for removing nitrogen oxides from the nitrogen oxide storage catalyst.

On the other hand, in the embodiment on the right side, the rich combustion period for removing nitrogen oxide from the nitrogen oxide storage catalyst 40 is very long. Therefore, in one embodiment, the fuel consumption of the engine 10 can be improved, and the burden on the engine 10 can be alleviated.

FIG. 5 is a graph comparing the denitration performance according to the prior art and one embodiment of the present invention. Referring to FIG. 5, the hydrocarbon selective reduction catalyst (HC SCR) and the urea water selective reduction catalyst (Urea SCR) of the prior art have excellent denitrification performance at a relatively high temperature and low denitrification performance at a low temperature.

In contrast, one embodiment has excellent denitrification performance corresponding to the prior art at high temperature, and at the same time, excellent denitrification performance at low temperature (L1). That is, under the same operating temperature conditions, one embodiment removes a greater amount of nitrogen oxides than the prior art.

That is, one embodiment stores nitrogen oxides in the nitrogen oxide storage catalyst (LNT) 40 before activating the hydrocarbon selective reduction catalyst (HC SCR) 30, so that it can have a high denitration performance as a whole.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And it goes without saying that the invention belongs to the scope of the invention.

10: engine 20: exhaust pipe
30: Hydrocarbon selective reduction catalyst (HC SCR) 40: Nitrogen oxide storage catalyst (LNT)
41: housing 42: electrode
43: Insulation member 44:
45: Surge chamber 46: Fuel supply port
50: Reformer G: Discharge gap

Claims (6)

An exhaust pipe through which the exhaust gas of the engine flows;
A hydrocarbon selective reduction catalyst (HC SCR) provided in the exhaust pipe to remove nitrogen oxides contained in the exhaust gas;
A nitrogen oxide storage catalyst (LNT) for removing nitrogen oxide remaining in the exhaust gas via the hydrocarbon selective reduction catalyst; And
A reformer connected to the exhaust pipe in front of the hydrocarbon selective reduction catalyst to reform the fuel to produce and supply a reducing agent of hydrogen and hydrocarbon (HC) species;
And the exhaust gas after-treatment apparatus. The method according to claim 1,
The hydrocarbon
And has a carbon number of C1 to C5. A first step of producing a large amount of hydrocarbon (HC) species and hydrogen by reforming the fuel by supplying fuel and air to the reformer under lean burn conditions;
A second step of supplying the produced hydrogen and hydrocarbon species onto a hydrocarbon selective reduction catalyst (HC SCR) for circulating exhaust gas;
A third step of flowing exhaust gas via the hydrocarbon selective reduction catalyst in a nitrogen oxide storage catalyst (LNT) disposed behind a hydrocarbon selective reduction catalyst (HC SCR); And
The fourth step of switching to the rich combustion condition at the lapse of the set time in the lean burn condition and switching to the lean burn condition after the engine operation
And the exhaust gas after treatment. The method of claim 3,
The first step
A method for post-treatment of an exhaust gas which produces partial hydrogenation or decomposition of light oil, hydrogen (HC) functioning as a reducing agent, hydrocarbons (HC) having a carbon number of C1 to C5, and hydrogen. 5. The method of claim 4,
The second step
After the hydrocarbon selective reduction catalyst (HC SCR) is activated,
Wherein the produced hydrogen and hydrocarbon species act as a reducing agent on the hydrocarbon selective reduction catalyst (HC SCR) to reduce nitrogen oxides (NOx) contained in the exhaust gas to nitrogen (N ₂ ). The method of claim 3,
In the third step,
Before the hydrocarbon selective reduction catalyst (HC SCR) is activated,
And the nitrogen oxide contained in the exhaust gas is occluded in the nitrogen oxide storage catalyst (LNT).

Images