EP1626797A1

EP1626797A1 - Device for clearing a supply pipe of a reducing agent that has previously gone from a first phase to a second phase then back to the first phase

Info

Publication number: EP1626797A1
Application number: EP04728227A
Authority: EP
Inventors: Martin Havers
Original assignee: HJS Fahrzeugtechnik GmbH and Co KG
Current assignee: HJS Fahrzeugtechnik GmbH and Co KG
Priority date: 2003-05-26
Filing date: 2004-04-19
Publication date: 2006-02-22
Also published as: BRPI0409743A; US20060048503A1; WO2004103529A1; KR20060004985A; JP2007501357A

Abstract

The invention relates to a device for clearing a supply pipe (10) of a reducing agent that has previously gone from a first phase to a second phase then back to the first phase, wherein the pipe is used to supply the reducing agent in the second phase to an SCR catalytic converter inserted into the exhaust line of a diesel engine. The device is a valve (12) for metering the reducing agent in the second phase. The fixed valve seat or the movable valve surface (16) engaging same and bearing thereagainst when the valve (12) is in the closed position is in the form of a condenser element controlled by a controller and intended to act as a cryogenic well inserted into the supply pipe (10) when controlled accordingly. The condenser element or the valve element matching same is heatable under the control of a controller.

Description

Device for releasing a reducing agent which has been reformed into a first phase and which leads a reducing agent brought from a first phase into a second phase

The invention relates to a device for releasing a reducing agent that has been reformed into the first phase of a supply line leading a reducing agent brought from a first phase into a second phase for supplying the reducing agent in the second phase to an SCR catalytic converter that is switched into the exhaust line of a diesel internal combustion engine ,

In addition to carbon monoxide (CO), particles and hydrocarbons (HC), nitrogen oxides (NO _x ) in particular are among the environmentally hazardous, directly emitted primary pollutants that arise during the operation of internal combustion engines, especially diesel engines. The use of three-way catalytic converters, such as those used in gasoline engines and gas engines, cannot be used in the diesel engine exhaust due to an excess of oxygen. For this reason, selectively working SCR catalysts (Selective Catalytic Reduction Catalysts) were developed to reduce nitrogen oxide emissions in diesel engines, in which the nitrogen oxides emitted are reduced to the air's own N ₂ and H ₂ O with an added reducing agent, namely ammonia (NH ₃ ) ,

A device for feeding ammonia in its gaseous phase into the exhaust line of an internal combustion engine of a motor vehicle is known from DE 197 20 209 C 1. This includes a gas-tight and pressure-resistant converter in which there is a thermolytically NH ₃ -releasing substance or a thermolytically NH ₃ -releasing substance mixture - a so-called NH ₃ precursor. Ammonium carbamate present as a solid, for example, can be provided as the NH ₃ precursor. The converter is connected to the exhaust line of a diesel engine via a supply line, the supply line opening into the exhaust line in the flow direction of the exhaust gas in front of the input side of an SCR catalytic converter. A cycle valve is provided as the metering device, which is controlled by a control unit so that the required amount of NH ₃ can be injected into the exhaust gas flow depending on certain engine operating characteristics. The converter essentially consists of a pressure-resistant reaction container, which is surrounded by a heating device designed as a coil of heat. The heating device is integrated into the cooling water circuit of the diesel engine via a supply line and a discharge line.

By heating the ammonium carbamate used, for example, as an NH ₃ precursor, it decomposes into NH ₃ and CO2, as a result of which the reducing agent has been brought from a first, here solid phase to a second, here gaseous phase. This gas mixture accumulates in the pressure-resistant reaction vessel until a corresponding internal pressure is built up. When a certain internal pressure is reached in the reaction vessel, a state of equilibrium is established, so that further ammonium carbamate is not decomposed. Under operating conditions of the engine, in which the cooling water flowing through the heating device generally has a temperature between 80 and 100 ° C., the pressure in the reaction vessel corresponds to the equilibrium state, which is about 3-4 bar for ammonium carbamate. So that a sufficient amount of NH ₃ can be provided for injection into the exhaust gas stream during dynamic operation of the diesel engine, the converter also serves as a reaction gas storage device in order to store a certain amount of reaction gas or the NH ₃ contained therein as a reducing agent.

The reaction vessel is usually located at a certain distance from the exhaust line. It has been shown that the reaction gas mixture can, depending on the. \ IH ₃ precursors used, re-form into its solid form again when the temperatures drop. In the worst case, this can lead to the supply line becoming blocked. The same applies to the valves arranged within the supply line, for example the timing valve described above as a metering device. Ultimately, the clogging of the supply line, and in particular of the clock valve switched on therein, when the internal combustion engine is taken out of operation with some reducing agents, such as when using ammonium carbamate not excessively problematic, since when starting up again, the NH ₃ precursor deposited in the supply line and in particular in the valve or valves decomposes again when starting up again with increasing temperatures and the supply line and the valve or valves are then free. In order to accelerate the restarting of the supply line, it has already been proposed to heat the supply line and the valves switched on therein. Depending on the distance of the reaction container from the exhaust line, the realization of such a heating device for heating the entire supply line including the clock valve switched on therein is considerable.

On the basis of this prior art discussed, the invention is therefore based on the object of proposing a device with which the problems outlined above of a regression of NH ₃ precursors within the feed line are countered.

This object is achieved according to the invention by a generic device mentioned at the outset in that the device is a valve for metering the reducing agent in the second phase, in which the fixed valve seat or the movable valve surface interacting with the fixed valve seat, which in the closed position Position of the valve on the valve seat is present as a condenser element that can be controlled by a control unit to form a cold trap switched into the supply line if the condenser element is controlled accordingly, and the condenser element designed as a valve seat or valve surface or the complementary valve element can be controlled by a control unit are heated.

This device, which is designed as a metering valve, comprises a capacitor element for forming a cold trap. The capacitor element is connected to a control device and, as such, is operated with appropriate control when the internal combustion engine is shut down and / or when the valve is closed. Switching on the capacitor element can also be tied to other operating parameters, for example the current temperature of the valve and / or the feed line. By switching on the capacitor element, its temperature is reduced to form the cold trap, with the result that reducing agent located in the second phase in the vicinity of the capacitor element reverts to its first phase (for example when ammonium carbamate is used) or to an intermediate phase. In this process, in particular the reducing agent present in the vicinity of the cold trap and in its second phase is drawn to the cold trap and also reduced in the first phase or in an intermediate phase. As a result of this effect, any reducing agent present in the second phase is pulled out of the feed line and, if appropriate, further valves, couplings or the like switched on therein to the cold trap formed by the condenser element. As a result of this measure, reducing agent present in its second phase at a defined point in the feed line is collectively reduced. When the supply line for supplying reducing agent to the SCR catalytic converter switched into the exhaust line of the internal combustion engine is started up again, only the area of the capacitor element needs to be freed from the reducing agent which has been reformed into the first phase or into an intermediate phase by appropriate heating. For this reason, the valve also has a heating device in order to feed the reducing agent which has been regenerated in the valve by driving the capacitor element into the second phase for supplying the same to the SCR catalytic converter which is connected to the exhaust line of the internal combustion engine.

The capacitor element is expediently assigned either to the valve seat or to the movable valve surface interacting with the fixed valve. The heating device is assigned either to the same valve element or to the complementary valve element.

The advantage of this device is that it is simultaneously designed as a metering valve.

An embodiment is preferred in which the movable valve surface of the valve is designed as a heatable condenser element, so that this part of the valve is used both for forming the cooling case and for the Dissolving the reduced reductant is responsible. It is expedient to use one or more Peltier elements which can cool or heat depending on their control. It is advantageous if the movable valve surface itself is the heat-exchanging surface of the Peltier element or elements.

An embodiment is expedient in which the fixed valve seat has two connection openings arranged adjacent to one another, which can be closed together by the movable valve surface. The valve surface acting as a condenser element, which closes both connection openings in the closed position of the valve, leads to the formation of a cold trap associated with each connection line, as a result of which, in its second phase, reducing agent still present in the respective supply line branch is particularly effective he follows. One of these connection openings is connected to a container storing the reducing agent or a reducing agent precursor, while the other connection opening of the valve is connected to the exhaust line.

The procedure described above is particularly suitable for switching on in such a feed line through which gaseous reducing agent flows, which has been formed from an NH ₃ precursor present in the solid phase by thermolytic cleavage. Ammonium carbamate is particularly suitable for this purpose as an NH ₃ precursor. This device can also be used in connection with a system in which urea (urea) is used as an NH ₃ precursor.

The invention is described below using an exemplary embodiment with reference to the accompanying figures. Show it:

1: a schematic representation of a device for supplying ammonia as a reducing agent to an SCR catalytic converter switched on in the exhaust line of an internal combustion engine with a valve switched on in the supply line in its open position and

Fig. 2: the valve of Figure 1 in its closed position. A device for supplying ammonia (NH ₃ ) to a reduction catalytic converter which is connected to the exhaust line of a diesel engine of a motor vehicle is identified overall in FIG. 1 by reference number 1. This device 1 comprises a container 2 for generating ammonia (NH ₃ ) by thermolytic decomposition of an NH ₃ precursor, an ammonium carbamate compact ₃ being used as the NH ₃ precursor in the exemplary embodiment shown. The ammonium carbamate compact 3 is designed as a cylindrical body and is brought into the shape shown in the figure by pressing powdered ammonium carbamate. The ammonium carbamate compact 3 has a round cross-sectional area. A heating device, generally designated by the reference number 4, is arranged in the container 2. The heating device 4 is designed as a radiant heater.

In the exemplary embodiment shown, the radiant heater is formed from three individual heating elements 5, 5 ', 5 ", each of which represents an Archimedean spiral. The individual heating elements 5, 5', 5" of the heating device 4 can be controlled independently of one another, so that depending on the number of the heating elements 5, 5 ', 5 "which are energized, the heat output produced and / or the course of a heating phase can be controlled. The heating device 4 is located in a lower part of the container 2 below the heating elements 5, 5 ', 5 "thermal insulation 6 is arranged. Above and at a short distance from the radiant heater is a heating plate 7 as a further part of the heating device 4. In the exemplary embodiment shown, the heating plate 7 consists of a transparent glass-ceramic material which is permeable to the heat radiation generated by the heating device 4. The side of the heating plate 7 facing the ammonium carbamate compact 3 is structured by knobs. A pipe section 8 is molded onto the heating plate 7, pointing towards the lower end of the container 2. This includes a connection channel 9. The connection channel 9 is connected to a feed line, generally designated by the reference number 10. Ultimately, the connection duct 9 forms part of the feed line 10. FIG. 1 shows the device 1 and in particular the container 2 with the ammonium carbamate compact 3 located therein before initial start-up, but with the feed line 10 open. For this reason, the lower end face of the ammonium carbamate compact 3 rests on the top of the knob structure of the heating plate 7. After the device 1 has been started up for the first time by actuating the heating device 4, a certain amount will have decomposed thermolytically from the end face of the ammonium carbamate compact 3. As a result, the knobs press into the ammonium carbamate compact 3 and fix it.

The heating device 4 is designed such that, on the side of the heating plate 7 facing the ammonium carbamate compact 3, at most only those temperatures arise which are lower than the decomposition temperature of the reaction gas or mixture formed during the thermolysis of the ammonium carbamate. This is not largely achieved by the glass ceramic heating plate 7. Therefore, in the heating device 4, the advantages of radiant heating with regard to rapid reactivity and the associated spontaneous decomposition of ammonium carbamate are combined with advantages of those heating devices which are obtained, for example, when using contact heating.

A roller piston 11 is arranged in the container 2 and divides the interior of the container into a first container section and into a second container section. The roller piston 11 separates the two container sections in a gas-tight manner. The heating device 4 and the ammonium carbamate compact 3 as well as the outlet formed by the connection channel 9 are located in the first container section. The other container section is connected to a compressed air system D. Via the compressed air system D, which also includes a compressor for providing the necessary air pressure in the system, a pressure is built up in this container section for providing the desired contact pressure between the ammonium carbamate compact 3 and the top of the heating plate 7.

The ammonium carbamate compact ₃ , which is in solid form, is stored in the container 2 as an NH ₃ precursor. When energizing the Heating device 4 is thermolytically decomposed ammonium carbamate lying on the heating plate 7, so that the NH ₃ precursor is brought into a second phase - the gaseous phase. This gaseous reducing agent is supplied to the exhaust line or the SCR catalytic converter via the connecting duct 9 and the supply line 10.

A valve 12 is switched on in the feed line 10. The valve 12 is shown in Figure 1 in its open position. The valve 12 comprises a Peltier element 13 as a movable element, which can be brought into its open position via an actuator 14. The actuator 14 can be, for example, an electromagnet. The valve 12 can be brought into its closed position shown in FIG. 2 by moving the pelter element 13 by the energy stored in the force of a compression spring 15. With its surface 16, the Peltier element 13 forms the movable valve surface and thus the actuating element of the valve 12. A membrane 17 seals the valve chamber 18 circumferentially.

In the open position of the valve 12, reaction gas formed by thermolysis in the container 2 flows through the valve chamber 18 into the supply line 10 connecting the valve 12 to the exhaust line in order to supply the gaseous reducing agent to the SCR catalytic converter. If the valve 12 is closed, as shown in FIG. 2, the Peltier element 13 is simultaneously energized in order to cool its heat-exchanging surface 16. The surface 16 of the Peltier element 13 bears against the connection opening assigned to the connection channel 9 and on of those for connecting the valve 12 to the exhaust line, which both connection openings are sealed by seals 19 with respect to the valve surface formed by the surface 16, and by the condenser effect which occurs due to the cooling, the reducing agent gas located in the two branches of the supply line 10 becomes the then drawn cold surface 16, which serves as a cold trap in this situation. As a result, the lines 10 are kept clear after the heating device 4 has been switched off, so that the risk of ammonium carbamate regressing from the gaseous reducing agent within the feed line 10 is largely avoided. When opening or just before opening the valve 12, the Peltier element 13 is energized in such a way that it acts as a heating element serves, as a result of which the ammonium carbamate formed as a result of the cold trap function decomposes rapidly and then the valve 12 is intended to be conventional and thus movable and functional.

In the exemplary embodiment described in the figures, the two outlet openings of the valve 12 forming the valve seat with their seals 19 are arranged next to one another. In this embodiment, both exit openings are therefore closed at the same time by the surface 16 of the Peltier element 13 serving as a movable valve surface. The Peltier element 13 is advantageously energized only shortly after the valve 12 is closed in order to provide its cold trap function.

Ammonium carbamate is the preferred NH ₃ precursor material for operating the described device. An advantage of using ammonium carbamate is that its thermolytic decomposition starts to a significant extent at temperatures above 70 ° C. This relatively low thermolysis temperature has the advantage that even at relatively low temperatures, the ammonium carbamate collected therein during the cold trap function of the valve can be freed from the ammonium carbamate re-formed in its first phase by decomposing it into its reaction gases with low energy in order to free the valve.

LIST OF REFERENCE NUMBERS

contraption

container

Ammoniumcarbamatpressling

heater

heating element

thermal insulation

heating plate

pipe section

connecting channel

feed

rolling piston

Valve

Peltier element

actuator

compression spring

top

membrane

valve chamber

poetry

Compressed air system

Claims

claims

1. Device for freeing a feed line leading a reducing agent brought from a first phase into a second phase

(10) for supplying the reducing agent in the second phase to an SCR catalytic converter, which is switched into the exhaust line of a diesel internal combustion engine, of reducing agent reformed into the first phase, characterized in that the device has a valve (12) for metering the in the second

Phase is the reducing agent, in which the fixed valve seat or the movable valve surface (16) which interacts with the fixed valve seat and which, when the valve (12) is in the closed position, bears against the valve seat as a condenser element which can be controlled by a control unit Forming a cold trap switched into the supply line (10) is formed if the condenser element is controlled accordingly, and the condenser element designed as a valve seat or valve surface or the complementary valve element can be heated by a control unit.

2. Device according to claim 1, characterized in that the movable valve surface (16) of the valve is designed as a heatable capacitor element.

3. Device according to claim 2, characterized in that the movable valve surface (16) is formed by the heat-exchanging surface of one or more Peltier elements (13).

4. Device according to eircem of claims 1 to 3, characterized in that the fixed valve seat has two connection openings arranged adjacent to one another, one of which has a connection opening that stores the reducing agent or a reducing agent precursor and brings the reducing agent into its second phase and the other Connection opening is connected to the exhaust line.

5. The device according to claim 4, characterized in that in the closed position of the valve (12) both connection openings of the valve seat are closed by the movable valve surface (16).

6. Device according to one of claims 1 to 5, characterized in that the valve (12) on the outlet side of a container (2) for storing a precursor (3) which is split off under the supply of heat NH ₃ , from the reaction gas or reaction gas mixture thereof after a NH ₃ - cleavage as the temperature drops, a solid, in particular the precursor material regresses, and a heating device (4) for bringing about a thermolytic NH ₃ cleavage of the NH ₃ precursor (3) within the container (2) is connected.

Apparatus according to claim 6, characterized in that the NH ₃ precursor stored in the container (2) is an ammonium carbamate compact (3).