DE102017130702B4 - Method and arrangement for reducing the NOx content of exhaust gas - Google Patents

Abstract

Method for reducing the NOx content of exhaust gas from an internal combustion engine, which flows to an outlet at least via a particle filter (14) and at least one catalytic converter (22, 24) downstream thereof, the exhaust gas flowing into the exhaust gas path upstream of the at least one catalytic converter ( 22, 24) arranged at least one heat exchanger (40) having condensation stage (18) only flows completely through when the dew point temperature T _T or approximately dew point temperature T _{T of} the exhaust gas is reached on the heat exchanger (40).

Description

The invention relates to a method for reducing the NOx content of exhaust gas from an internal combustion engine, which flows to an outlet at least via a particle filter and at least one catalytic converter arranged downstream thereof.

Furthermore, the invention relates to an arrangement for reducing the NOx content in the exhaust gas of an internal combustion engine with at least one particle filter arranged in the flow path of the exhaust gas and at least one catalyst downstream of this and a condensation stage with condensate drain arranged upstream of the at least one catalyst.

Efforts are increasing to remove soot particles from diesel exhaust gases. For this purpose, it is known that a diesel particle filter and at least one catalytic converter are arranged in the exhaust gas flow of a diesel engine. Frequently, several catalysts such as electrically heated catalysts and SCR catalysts are connected in series.

Depending on the devices that remove the soot particles, however, the engine has to use more power so that the exhaust gas is expelled.

The DE 10 2004 004 939 A1 an exhaust device for exhaust gases from internal combustion engines can be found, in which a heat exchanger is integrated. The heat exchanger can be connected upstream or downstream of the exhaust.

A disadvantage of the corresponding device is that there is still a high level of soot at the start of starting the engine.

The US 2015/0322833 A1 is a device for removing SOx and NOx from the exhaust gas of a motor vehicle. For this purpose, a condenser is provided, which is arranged in the flow path of the particle filter and catalyst required for exhaust gas purification.

The EP 3 009 635 A1 refers to an internal combustion engine in which cleaned exhaust gas flows through a condenser.

With an exhaust system after DE 10 2004 032 287 A1 exhaust gas flows through a condenser until the engine has warmed up.

The present invention is based on the object of developing a method and an arrangement of the type mentioned at the outset such that the NOx content in the exhaust gas is reduced, in particular already when the internal combustion engine is started. Furthermore, it should be avoided that the flow resistance is noticeably increased during ongoing operation, even if the NOx content is reduced in comparison to known arrangements.

To achieve the object, on the one hand, a method is proposed for reducing the NOx content of exhaust gas from an internal combustion engine, which flows to an outlet at least via a particle filter and at least one catalytic converter arranged downstream thereof, the exhaust gas at least one arranged in the exhaust gas path upstream of the at least one catalyst only flows through a condenser stage having heat exchanger when the dew point temperature T _T or approximately the dew point temperature T _{T of} the exhaust gas is reached on the heat exchanger.

In particular, it is provided that a valve device is arranged upstream of the condensation stage or integrated therein, by means of which exhaust gas is at least partially kept away from the condensation stage at the heat exchanger before the dew point temperature T _T is reached. In particular, the exhaust gas is then passed through a further particle filter.

For this purpose, it is provided in particular that the exhaust gas is guided past the condensation stage via a bypass before the dew point temperature T _T is reached. Another particle filter can be provided in the bypass.

According to the invention, it is provided in particular that the soot particles are already reduced at the start of starting an internal combustion engine by switching on a further particle filter which, if the dew point for the exhaust gas has not yet been reached at the heat exchanger, bypasses the condensation stage. After reaching the dew point temperature T _T on the heat exchanger, the further particle filter is no longer flowed through, so that an additional resistance cannot build up during continuous operation by collecting soot particles, so the performance of the engine is not adversely affected.

The cooling in the condensation stage takes place by means of the heat exchanger, with direct evaporation or indirect cooling being possible by switching the heat exchanger into a brine circuit.

In a further development of the invention, it is provided that the condensation stage is arranged after the particle filter and before the catalytic converter in the flow path of the exhaust gas.

In particular, the exhaust gas in the condensation stage should be cooled to a temperature TA of at least 80 ° C., in particular to a temperature T _A between 50 ° C. and 80 ° C.

The condensate accumulating in the condensation stage is drained off via a drain that can be heated in order to ensure, even at low temperatures, that the outflow is not impeded by condensate from the condensation stage.

In particular, the condensation stage is designed such that a flow direction is forced on the exhaust gas flowing through the condensation stage, which runs along the driving surface of a vehicle having the internal combustion engine, that is to say in particular a horizontally running flow direction.

However, the invention is also achieved by an arrangement for reducing the NOx content in the exhaust gas of an internal combustion engine with at least one particle filter arranged in the flow path of the exhaust gas and at least one catalyst downstream of this and a condensation stage with condensate drain arranged upstream of the at least one catalyst, parallel to or in the condensation stage there is an exhaust gas-carrying bypass, through which the exhaust gas can flow when the temperature of the heat exchanger in the condensation stage is greater than the dew point temperature T _T or approximately the dew point temperature T _{T of} the exhaust gas.

In particular, the invention provides that the secondary path, which can be designed as a bypass running parallel to the condensation stage, has or is a further particle filter.

In the condensation stage, the temperature TK can be set to TK ≅ T _T = dew point temperature of the exhaust gas by direct evaporation or by indirect cooling of the heat exchanger.

Furthermore, the invention provides that a valve device is arranged upstream of the condensation stage, by means of which exhaust gas can be fed to the condensation stage or to the bypass depending on the temperature TK prevailing at the heat exchanger in the condensation stage. This has the particular advantage that when the heat exchanger has a temperature which is equal to the dew point temperature T _{T of} the exhaust gas, the exhaust gas bypass can be shut off, so that the exhaust gas flows exclusively through the condensation stage.

The condensation stage can have, in particular, a cuboid housing that has condensate guides on the bottom, which can be formed by beads.

The condensate can also be drained off via a heatable outlet opening, so that it is ensured that the condensate can flow out of the housing even at low temperatures.

The invention is explained in more detail below with the aid of the following description of preferred exemplary embodiments.

• 1 eine Prinzipdarstellung einer Abgasreinigung,
• 2 eine erste Ausführungsform einer Vorreinigungsstufe,
• 3 einen Ausschnitt aus der 2,
• 4 eine zweite Ausführungsform einer Vorreinigungsstufe,
• 5 eine Prinzipdarstellung eines Gehäuses einer Kondensationsstufe im Querschnitt,
• 6 das Gehäuse gem. 5 im Längsschnitt,
• 7 ein Detail des Abflusses aus dem Gehäuse gemäß 5 und 6,
• 8 eine Prinzipdarstellung der Kühlung der Kondensationsstufe und
• 9 eine weitere Prinzipdarstellung einer weiteren Ausführungsform zum Kühlen der Kondensationsstufe

Show it:

• 1 a schematic diagram of exhaust gas purification,
• 2 a first embodiment of a pre-cleaning stage,
• 3 a section of the 2 .
• 4 a second embodiment of a pre-cleaning stage,
• 5 a schematic representation of a housing of a condensation stage in cross section,
• 6 the housing acc. 5 in longitudinal section,
• 7 a detail of the drain from the housing according to 5 and 6 .
• 8th a schematic diagram of the cooling of the condensation stage and
• 9 a further schematic representation of a further embodiment for cooling the condensation stage

In the present invention, the exhaust gas aftertreatment systems of engines that are already in use are used to reduce the NOx emissions, which is generally referred to as “fine dust”, which can be caused by the oxidation during the combustion process in engines with diesel and gasoline fuels.

The teaching according to the invention results in an exhaust gas volume reduction by means of a thermal process to approximately 60%, nitrogen oxide compounds being eliminated by a simultaneous condensation process (NOx reduction), in fact approximately up to 30%.

Based on 1 the exhaust gas purification section of an internal combustion engine, such as a diesel engine, is described purely in principle, without the invention being restricted thereby.

The exhaust gas coming from the diesel engine (arrow 10 ) overflows in the exemplary embodiment a diesel oxidation catalyst 12 and a particle filter 14 , Then there is a pre-cleaning stage according to the invention 16 provided that from a condensation stage 18 and another particle filter 20 consists. The pre-cleaned exhaust gas then flows over an electrically heated catalytic converter 22 , an SCR catalytic converter 24 and a silencer 26 to then be expelled. There is also a urea tank 28 provided with control. To control the urea supply, NOx sensors 30, 32 are provided, which inject urea into the electrically heated catalyst 22 and the SCR catalyst 24 Taxes. In this regard, reference is also made to the well-known technology; the core of the invention is the pre-cleaning stage 16 that mentioned a condensation level 18 and in particular a particle filter 20 includes.

Through the pre-cleaning stage according to the invention 16 the exhaust gases are dried, which reduces the catalytic reaction and reduction and thus the ammonia produced. Thus, the pre-cleaning stage 16 downstream components such as the catalysts 22 . 24 relieved.

The pre-cleaning stage according to the invention 16 is based on the 2 to 4 explained in more detail.

The pre-cleaning stage 16 has a two-way valve 34 on to the exhaust gas (connection 36 ) optionally the condensation level 18 or the particle filter 20 supply. The condensation level 18 and the particle filter 20 can in a box-like cuboid housing 38 be arranged, the dimensions of z. B. 1100 mm x 800 mm x 180 mm, without thereby limiting the invention. The housing 38 is fully insulated and can have a double wall that delimits a vacuum cavity in which there is insulation.

Inside the case 38 are z. B. fins to form a heat exchanger 40 available, which are shown in principle. A coolant flows through the fins. This is in the upper area of the housing 38 a connection 42 and an outlet at the opposite end in the floor area 44 provided, as in principle the 5 and 6 can be seen. In the 6 is also the exhaust gas inlet 46 and the exhaust gas outlet 48 shown.

In the bottom area of the housing 38 are bead-shaped condensate guides 50 provided that purely in principle 5 are indicated. About the guides 50 can do that in the condensation stage 18 precipitated condensate to the drain 52 are supplied according to the 7 is heatable (symbol 54 ). The 7 is also the insulation of the double wall of the housing 38 refer to. Heating is required to ensure that condensate does not freeze at low temperatures, causing it to drain out of the interior of the housing 38 would be hindered.

In the embodiment of the 2 is inside the housing 38 the particle filter 20 that according to 4 but also in a bypass line 56 can be arranged parallel to the condensation stage 18 to the housing 38 runs. In the feeder 46 is the two-way valve 34 to selectively exhaust the particulate filter 20 or the heat exchanger 40 having condensation level 18 supply.

As can be seen from the figures, the exhaust gas flows at a temperature of e.g. B. about 600 ° C in the pre-cleaning stage 16 , either in the particle filter 20 or the condensation level 18 , The position of the two-way valve 34 depends on the temperature at the heat exchanger 40 in the condensation stage 18 occurs. If the temperature is above the dew point of the exhaust gas, the two-way valve gives 34 the way to the particle filter 20 free, so that as a result the 2 only part of that in the housing 38 arranged heat exchanger 40 is flowed through, whereas when using the bypass line 36 the heat exchanger 40 is not applied. Is the temperature at the heat exchanger 40 equal or approximately equal to the dew point temperature T _{T of} the exhaust gas, so the two-way valve 34 switched ( 3 ), so that the exhaust gas only through the condensation stage 18 flows.

The temperature at the heat exchanger 40 z. B. by means of at least one temperature sensor 39 determined. Based on 2 it can also be seen that a regulation is made to the heat exchanger 40 to the desired temperature.

Through the pre-cleaning stage 16 The advantage is that the exhaust gas volume can be reduced to approx. 60%, and at the same time up to 30% of nitrogen oxide compounds can be eliminated by the condensation that takes place.

The following calculation should clarify the volume reduction. Average consumption values for a diesel engine are assumed: 5 1 diesel fuel according to DIN EN 590 per hour. The amount of exhaust gas is about 1.3 m ³ / min and thus 78 m ³ / h.

If the density at 600 ° C. of the exhaust gas is approximately 0.404 kg / m ³ , a volume of approximately 28 m would result at an outlet temperature of approximately 50 ° C. at which the exhaust gas has a density of 1.120 kg / m ^{3 3} , so that the reduction in exhaust gas volume is approximately 64%. The amount of condensation is about 4 kg / h. Taking the amount of exhaust gas and the temperature reduction into account, there is a cooling requirement of around 7.0 KW.

The cooling of the heat exchanger can take place directly or indirectly, as on the basis of the 8th and 9 is made clear.

In 8th the generation of refrigeration by direct evaporation is shown in principle. You can see the heat exchanger 40 , which is arranged in a refrigeration cycle in which there is a compressor in the usual way 58 , a condenser 60 and an expansion valve 62 are located. According to 9 indirect cooling can be carried out in a brine circuit 64 used to the heat exchanger 40 to the desired temperature. The brine cycle 64 is by means of a heat exchanger 66 cooled, which is in a cycle that the 8th corresponds, so that the same reference numerals are used for the same elements.

At the heat exchanger 40 it is in particular a lamella arrangement. The housing 38 is flowed through horizontally, in particular through the 6 should be clarified.

Claims (14)

Method for reducing the NOx content of exhaust gas from an internal combustion engine, which flows to an outlet at least via a particle filter (14) and at least one catalytic converter (22, 24) downstream thereof, the exhaust gas flowing into the exhaust gas path upstream of the at least one catalytic converter ( 22, 24) arranged at least one heat exchanger (40) having condensation stage (18) only flows completely through when the dew point temperature T _T or approximately dew point temperature T _{T of} the exhaust gas is reached on the heat exchanger (40). Procedure according to Claim 1 , characterized in that exhaust gas is passed through a further particle filter (20) before the dew point temperature Tr is reached. Procedure according to Claim 1 or 2 , characterized in that a valve device (34) is arranged upstream of the condensation stage (18) or integrated therein, by means of which an at least partial flow around the heat exchanger (40) present in the condensation stage (18) is made possible. Procedure according to Claim 2 , characterized in that before the dew point temperature T _{T is reached,} the exhaust gas is fed to the further particle filter (20) via a bypass (56). Method according to at least one of the preceding claims, characterized in that the exhaust gas in the condensation stage (18) is cooled to a temperature TK of at least 80 ° C, in particular to a temperature T _K between 50 ° C and 80 ° C. Method according to at least one of the preceding claims, characterized in that condensate accumulating in the condensation stage (18) is discharged via a heatable condensate drain (52). Method according to at least one of the preceding claims, characterized in that the exhaust gas flowing through the condensation stage (18) is forced into a flow direction which runs along a driving surface of a vehicle having the internal combustion engine. Arrangement for reducing the NOx content in the exhaust gas of an internal combustion engine with at least one particle filter (14) arranged in the flow path (10) of the exhaust gas and at least one catalyst (22, 24) downstream thereof and one in the flow path (10) the at least one catalyst (22 , 24) upstream condensation stage (18) with condensate drain (52), parallel to the condensation stage (18) is an exhaust gas-carrying bypass, through which the exhaust gas can flow when there is a temperature at the heat exchanger (40) present in the condensation stage (18) , which is greater than the dew point temperature T _{T of} the exhaust gas. Arrangement after Claim 8 , characterized in that the exhaust gas bypass has or is a further particle filter (20). Arrangement after Claim 8 or 9 , characterized in that the temperature in the heat exchanger (40) can be adjusted in the condensation stage (18) by direct evaporation or by indirect cooling. Arrangement according to at least one of the Claims 8 to 10 , characterized in that the condensation stage (18) has a housing (38) in which the heat exchanger (40) is arranged. Arrangement according to at least one of the Claims 8 to 11 , characterized in that a valve device (34) is arranged upstream of the condensation stage (18), by means of which, depending on the temperature prevailing at the heat exchanger (40), the exhaust gas can either be fed exclusively to the exhaust gas bypass or flows completely through the heat exchanger (40). Arrangement after Claim 11 , characterized in that the housing (38) has guides (50) on the bottom, such as beads, for condensate to be discharged. Arrangement according to at least one of the Claims 8 to 13 , characterized in that the condensate can be discharged via a heatable outlet opening or line (52).

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