FR3049005A1 - DEVICE FOR TREATING EXHAUST GAS - Google Patents

Abstract

An exhaust gas treatment device of an internal combustion engine, comprising: - at least one ammonia treatment unit arranged to be placed in series along an exhaust line, comprising a gas inlet, exhaust and an exhaust gas outlet, characterized in that the treatment device further comprises: - at least one recirculation loop arranged to withdraw exhaust gas downstream of the outlet of said at least one unit of ammonia treatment and reinject them into the exhaust line, upstream of the inlet of said at least one ammonia treatment unit.

Description

DEVICE FOR TREATING EXHAUST GAS

[001] The present invention generally relates to an exhaust gas treatment device of an internal combustion engine such as a diesel engine for reducing an ammonia present in the exhaust gas, and to equip an exhaust line mounted on a motor vehicle.

[002] WO2015093603 (A1) discloses an exhaust gas treatment system, which comprises a selective catalytic reduction unit, or "SCR" for "Selective Catalytic Reduction" in English, which consists of reducing NOx by introducing a reducing agent (or a precursor of such a reducing agent) into the exhaust gas by catalyzed reactions. It may for example be a urea solution, the decomposition of which will make it possible to obtain ammonia which will serve as a reducing agent. Downstream of this SCR unit is an ammonia leak treatment unit which is a catalyst for treating NH3 ammonia leakage or excess by oxidation of ammonia to nitrogen oxides NOx and then the reduction of said NOx to less nitrogen N2, which we can in the rest of this text refer to as unit ASC. "ASC" is the acronym in English for the term "Ammonia Slip Catalyst" or catalyst for ammonia leaks in French.

[003] However, this ammonia leakage treatment unit or AUC unit has a large volume and must provide adequate space under floor to accommodate such a unit ASC. In addition, it is possible that in some severe engine operation scenarios (towing, mountain slope ...), there is a lot of unused ammonia leaving the SCR unit, and the ASC unit may not be able to completely treat this ammonia which will then be released into the atmosphere. Providing a sufficiently large ASC unit for all cases would increase costs and / or would result in modifying the vehicle chassis to accommodate such a unit in an exhaust line tunnel for example.

An object of the present invention is to meet the disadvantages of the documents of the prior art mentioned above and in particular, first of all, to propose an effective exhaust gas treatment device for treating the entire environment. ammonia present, without increasing the volume and / or overall cost of the device.

[005] For this, a first aspect of the invention relates to an exhaust gas treatment device of an internal combustion engine, comprising: at least one ammonia treatment unit arranged to be placed in series along an exhaust line, comprising an exhaust gas inlet and an exhaust gas outlet, (it is for example able to transform between the exhaust gas inlet and the exhaust gas outlet ammonia present in the exhaust gas in at least one other substance, especially at least partially nitrogen, or possibly at least temporarily store it) such that the treatment device further comprises: - at least one recirculation loop arranged to withdraw exhaust gas downstream of the outlet of said at least one ammonia treatment unit and reinject them into the exhaust line, upstream of the inlet of said at least one unit of ammo treatment niac.

[006] It is thus possible to pass the exhaust several times in the ammonia treatment unit, to increase a rate of oxidation or catalytic conversion of ammonia to nitrogen and water. This can also make it possible to heat up the ammonia treatment unit more quickly at the beginning of operation of the engine, because a recirculation then makes it possible to transfer more heat from the exhaust gases to the ammonia treatment unit.

[007] In other words, the invention proposes to recirculate exhaust gas specifically in the ammonia treatment unit. In its simplest definition, the recirculation loop includes only the ammonia treatment unit, and not several elements of the exhaust line.

[008] Advantageously, the exhaust gas treatment device comprises a valve arranged downstream of the exhaust gas outlet of said at least one ammonia treatment unit, for opening or closing at least partially said at least one ammonia treatment unit. a recirculation loop. Such a valve makes it possible to regulate the recirculation rate, from no recirculation to a recirculation rate which may be 50% of the total flow, for example.

[009] The term "valve" in the broad sense is understood to mean any means of passive or controllable closure of said recirculation loop. In the case where it is controllable, it is connected at least to an on-board computer on the vehicle, itself connected to one or more sensors.

Advantageously, the exhaust gas treatment device comprises at least one probe for measuring an ammonia level in the exhaust gas downstream of the exhaust gas outlet of the at least one unit. ammonia treatment. Such an ammonia measurement sensor makes it possible to check whether the ammonia level is below a value such as 10 ppm, for example, and to decide whether or not to regulate the recirculation rate.

Advantageously, the valve is arranged between the ammonia measuring probe, and the ammonia treatment unit.

Advantageously, the exhaust gas treatment device comprises at least one Venturi tube upstream of the exhaust gas inlet, and wherein the recirculation loop is connected at the level of the Venturi tube to reinject the exhaust gases in the exhaust line. Such a Venturi tube will accelerate the exhaust at its neck, and thus create a vacuum that can suck the exhaust gas of the recirculation loop.

Advantageously, the Venturi tube comprises a deflector upstream of a connection with the recirculation loop. Such a deflector can increase the Venturi effect, limiting the risk of reflux. The deflector, as well as the connection with the recirculation loop are located at the neck of the Venturi tube.

Advantageously, the exhaust gas treatment device comprises a fresh air supply line under pressure and connected to the recirculation loop to increase a recirculation speed. Such a pressurized air supply line, injected into the exhaust line, can create or increase a Venturi effect and thus suck up the gases from the recirculation loop, upstream of the ammonia treatment unit.

Advantageously, the fresh air supply line is connected upstream to a motor cooling zone or an intake manifold of the engine powered by a turbocharger. The invention proposes to use advantageously existing pressurized air sources under hood (a cooling zone directly supplied by scoops or openings in the facade is pressurized as soon as the vehicle is in motion).

Advantageously, the exhaust gas treatment device comprises a control valve arranged to regulate a flow of fresh air in the fresh air supply line. Air is injected into the exhaust line only if there is a need to recirculate exhaust.

[0017] Advantageously, the exhaust gas treatment device comprises a turbine arranged to increase a recirculation speed in the recirculation loop.

Advantageously, the turbine is driven by exhaust gas from the exhaust line.

Another aspect of the invention is an exhaust line of a heat engine comprising at least one exhaust gas treatment device according to the first aspect of the invention. Advantageously, the exhaust line optionally comprises a device for treating the nitrogen oxides (NO, NO 2,...) Upstream of said exhaust gas treatment device. The invention makes it possible to efficiently treat the ammonia present in the exhaust gas, which would not have reacted completely with nitrogen oxides.

Another aspect of the invention is a motor vehicle comprising at least one exhaust gas treatment device according to the first aspect of the invention.

[0021] Another aspect of the invention is an exhaust gas treatment process comprising the steps of: - at least partially converting ammonia into nitrogen in an ammonia treatment unit placed in series in a vehicle exhaust line, - withdrawing exhaust gases downstream from the ammonia treatment unit, - reinjecting upstream of the ammonia treatment unit the exhaust gas removed.

Advantageously, the exhaust gas treatment method comprises a step consisting in measuring an ammonia level in the exhaust gas, and in which the steps consisting in taking the exhaust gases and injecting them are not carried out. performed only if the ammonia level is above a predetermined value, such as 10 ppm. According to the invention, the quantity of the desired exhaust gas is taken, if necessary, by controlling the opening and closing means of the valve-type recirculation loop (for example of the all-or-nothing type or preferably, progressive type).

Other features and advantages of the present invention will appear more clearly on reading the following detailed description of an embodiment of the invention given by way of non-limiting example and illustrated by the accompanying drawings, in which: Figure 1 shows a schematic view of an exhaust line of an internal combustion engine, comprising an exhaust gas treatment device according to the invention; FIG. 2 represents a detail of the exhaust line of FIG.

FIG. 1 represents a very simplified exhaust line connected to an internal combustion engine 100 of the diesel engine type, and which comprises in particular, from upstream to downstream: a urea injection unit 40; a unit for reducing NOx or SCR unit, a probe for measuring a NOx level, an ammonia treatment unit or an ASC unit,

an exhaust gas recirculation loop 10 in parallel with the ASC unit; a probe 20 for measuring an ammonia level.

The exhaust line can of course include other elements, such as temperature probes, a turbine driving a turbo, an exhaust gas recirculation valve (EGR type) to reinject gas from the engine. exhaust in an intake manifold of the engine 100, a particulate filter, a silencer ... it is also possible to provide an SCR unit providing a particulate filter function.

As already mentioned, the urea injection unit 40 and the NOx reduction unit or SCR unit, are used to reduce NOx nitrogen oxides produced during operation of the engine 100.

In particular, the SCR unit processes the nitrogen oxides. The principle of reducing these NOx by SCR can be broken down into two main steps: 1> Formation of the reducing agent (NH3) from Adblue ® which is a mixture of 32.5% urea and water injected into the exhaust line through the injection unit 40: - (NH2) 2CO -> NH3 + HNCO (R1) thermolysis of urea - HNCO + H20 -> NH3 + CO2 (R2) hydrolysis of isocyanic acid

The decomposition of the urea, injected by the injection unit 40 into a mixing box upstream of the SCR unit can be done in two steps: a first called "thermolysis" which forms a molecule of NH3 and a molecule of isocyanic acid (HNCO) and a second which forms the second molecule of NH3 from the hydrolysis of isocyanic acid. This step makes it possible to form the reducer essential for the operation of the SCR reduction. 2> Selective catalytic reduction of NOx by NH3 by the SCR coatings of the SCR unit: - 4 NO + 02 + 4 NH3 4 N2 + 6 H20 (R3) Standard SCR - NO + N02 + 2 NH3 -> 2 N2 + 3 H20 (R4) SCR with fast kinetics - 6 N02 + 8 NH3 -> 7 N2 + 12 H2O (R5) SCR with slow kinetics Several reactions can take place (R3 to R5), but the optimal and sought conversion of NOx is obtained thanks to the reaction (R4) whose kinetics is the fastest.

The catalyst of the SCR unit may be based on zeolites exchanged with iron, such as zeolites β, iron ferrierite, ZSM5, The substrate of SCR unit 6 may be rather cordierite.

Downstream of the SCR unit is the ammonia treatment unit or ASC unit. In the example discussed, a unit of the ASC type, the structure of which has two impregnation layers, is chosen: a layer C2 which performs the oxidation function of the NH 3 to NO x and a layer C1 which performs the function of reducing the NOx by NH3 to nitrogen N2.

The composition of the ASC unit is thus as follows: the layer C1 (that which is in contact with the exhaust gas) corresponds to a catalytic coating of SCR type and the lower layer C2 (the one that is in contact with the walls of the catalytic substrate) contains precious metals (preferably palladium (Pd) in a very small amount, between 0.5 and 5 g / ft 3, ie between 0.5 g and 5 g per volume of 38.48 cm 3, ( ideally from 1g to 2g) deposited on Alumina The operation of the ASC unit is as follows: the residual ammonia enters the layer C1 and stores itself in this layer in part The rest of the ammonia passes through this layer C1 and penetrates into the layer C2 whose precious metals (Pd) promote the oxidation of ammonia NH3 to NOx.When the NOx emerge from the catalytic oxidation coating of the layer C2, they necessarily pass through the layer C1 where is stored the NH3, the NOx reduction reaction by the NH3 can then take place and the NOx are converted to nitrogen (N2) before emerging from this ASC unit.

Exit the exhaust line, so there is no, or almost no risk of ammonia emissions into the atmosphere with this unit ASC.

However, in case of severe use of the engine 100, it may be that the ASC unit can not process all the ammonia entering the ASC unit. In order to avoid a volume increase of the ASC unit, the invention proposes to implement an exhaust gas recirculation loop 10 in parallel with the ASC unit. Indeed, such exhaust gas recirculation in the ASC unit will help to oxidize most of the ammonia present in the exhaust gas.

A recirculation valve 11 may be provided downstream of the unit ASC, in the exhaust line to force (for example closing up to 50% of the section of the exhaust line) part of Exhaust gas to go into the recirculation loop 10, and thus be redirected to the input of the ASC unit. It is advantageous to operate this recirculation only if necessary, that is to say if there is an excess of ammonia in the exhaust gas leaving the unit ASC, and for this purpose, The invention proposes to implant a measurement probe 20 of an ammonia level, downstream of the ASC unit. This ammonia measurement probe 20 and the recirculation valve 11 may be connected to an engine control unit to at least partially open the recirculation loop 10 only when the level of ammonia released into the atmosphere exceeds a given threshold, for example a rate of 10 ppm.

FIG. 2 shows in detail the environment of the ASC unit, and in particular the options of the invention which can improve the recirculation of the exhaust gases in the recirculation loop 10. In fact, the valve of recirculation 11 regulates the flow in the recirculation loop 10, but because of the counter pressures that it may cause, the recirculation flow may not be sufficient.

A first option may be to implant a Venturi tube 12 just upstream of the entrance of the ASC unit. Thus, the average velocity V1 of the exhaust gas will locally be increased up to V2 at the neck of the Venturi tube 12, which decreases the pressure there, and connecting the recirculation loop 10 will cause suction exhaust gas from the downstream of the UPS unit to the neck of the Venturi tube 12 via the recirculation loop 10.

One can provide a deflector in the Venturi tube neck 12, or just upstream thereof to ensure the connection of the recirculation loop 10 and avoid the reflux phenomena in the latter. Such a deflector may be a sheet in the Venturi tube 12 which occupies only an angular portion of the cross section of the duct.

A second option may be to inject air under pressure via a fresh air supply line 13, regulated by a booster valve 14. The fresh air supply line 13 can very well take from the fresh air at a place under the hood where there is a dynamic pressure (as downstream of a bailer on the front of the vehicle), or in an intake manifold of the engine 100, downstream of a compressor or turbo. This injection of air under pressure can be performed at the junction between the recirculation loop 10 and the exhaust line and will cause the exhaust gas passing through the recirculation loop 10. As shown in Figure 2, this Fresh air supply line 13 can also be connected to the neck of the Venturi tube 12, but this is not mandatory.

A third option may be to integrate a turbine 15 in the recirculation loop 10 to increase the flow rate of recirculation of the exhaust gas. Very advantageously, the turbine 15 is motorized by the exhaust gas passing through the exhaust line.

Of course, the makeup valve 14, the recirculation valve 11, the turbine 15 can be controlled by a computer, depending on the ammonia content that measures the measurement probe 20 of a level of ammonia .

In conclusion, the recirculation loop 10 keeps a low volume for the ASC unit, while increasing the efficiency of the treatment of ammonia by this unit.

It will be understood that various modifications and / or improvements obvious to those skilled in the art can be made to the various embodiments of the invention described in this description without departing from the scope of the invention defined by the appended claims. In particular, reference is made to an ASC unit for treating the ammonia still present in the exhaust gas, but the invention is not limited to this technology. The invention can be used to recirculate exhaust gases on any type of ammonia treatment unit.

Claims (10)

An exhaust gas treatment device of an internal combustion engine, comprising: - at least one ammonia treatment unit (ASC) arranged to be placed in series along an exhaust line, comprising an exhaust gas inlet and an exhaust gas outlet, characterized in that the treatment device further comprises: - at least one recirculation loop (10) arranged to withdraw exhaust gas downstream of the output of said at least one ammonia treatment unit (ASC) and reinject them into the exhaust line, upstream of the inlet of said at least one ammonia treatment unit (ASC). 2. exhaust gas treatment device according to the preceding claim, comprising a valve (11) arranged downstream of the exhaust gas outlet of said at least one ammonia treatment unit (ASC), to open or at least partially closing said at least one recirculation loop (10). 3. Exhaust gas treatment device according to one of the preceding claims, comprising at least one sensor (20) for measuring the ammonia content in the exhaust gas downstream of the exhaust gas outlet. exhausting said at least one ammonia treatment unit (ASC). 4. Exhaust gas treatment device according to the preceding claim, in its dependence on claim 2, wherein the valve (11) is arranged between the ammonia measurement probe and the ammonia treatment unit ( CSA). An exhaust gas treatment device according to one of the preceding claims, comprising at least one Venturi tube (12) upstream of the exhaust gas inlet, and wherein the recirculation loop (10). is connected at the level of the Venturi tube (12) to reinject the exhaust gases into the exhaust line. 6. exhaust gas treatment device according to the preceding claim, wherein the venturi tube (12) comprises a deflector upstream of a connection with the recirculation loop (10). An exhaust gas treatment device according to one of the preceding claims, comprising a fresh air supply line (13) under pressure and connected to the recirculation loop (10) to increase a recirculation speed. 8. exhaust gas treatment device according to one of the preceding claims, comprising a turbine (15) arranged to increase a recirculation rate in the recirculation loop (10). 9. exhaust line of a heat engine, characterized in that it comprises the device according to one of the preceding claims. A method of treating exhaust gas comprising the steps of: - at least partially converting ammonia into an ammonia treatment unit (ASC) placed in series in a vehicle exhaust line; exhaust gas downstream of the ammonia treatment unit (ASC), - reinjecting upstream of the ammonia treatment unit (ASC) said exhaust gas removed.