JP2007501357A - Apparatus for removing reducing agent returned to first phase from supply pipe for introducing reducing agent transferred from first phase to second phase - Google Patents

Abstract

From the supply pipe 10 for leading the reducing agent transferred from the first phase to the second phase and supplying the reducing agent in the second phase to the SCR-catalytic converter incorporated in the exhaust system of the diesel engine, An apparatus for removing a reducing agent that has returned to a first phase is provided. The device is provided as a valve 12 for metering the reducing agent in the second phase. In order for the fixed valve seat or the movable valve surface 16 that cooperates with the fixed valve seat to abut the valve seat in the closed position of the valve 12 to form a cool trap in the supply pipe 10, Acts as a condenser element operable by a control unit. The condenser element formed as this valve seat or valve face, or a valve element that complements this element, is actuated and heated by the control unit.

Description

  The present invention provides a reductant that has been transferred from a first phase to a second phase and supplies the reductant in the second phase to an SCR-catalytic converter that is incorporated into the exhaust system of a diesel engine. The present invention relates to an apparatus for removing a reducing agent that has returned to a first phase from a tube.

In addition to carbon monoxide (CO), particulate matter and hydrocarbons (HC), primary harmful substances that are generated when operating internal combustion engines, especially diesel engines, and are released directly and pose a danger to the environment, There is nitrogen oxide (NOx). Three-way catalytic converters used in gasoline engines and gas engines cannot be used because the exhaust gas from diesel engines is excessive in oxygen. For this reason, selectively operating SCR-catalytic converters have been developed to reduce emissions of nitrogen oxides from diesel engines. In this catalytic converter, a reducing agent, that is, ammonia (NH ₃ ) is supplied, and nitrogen oxides discharged are reduced to generate N ₂ and H ₂ O originally present in the air.

A device for supplying gaseous ammonia to the exhaust system of an internal combustion engine of a motor vehicle is known from DE 197 20 209 C1. This device is equipped with an airtight and pressure-resistant supply mechanism that contains a substance that separates NH ₃ by thermal decomposition or a mixture of substances that separate NH ₃ by thermal decomposition—so-called NH ₃ precursors. Has been. As this NH ₃ precursor, for example, ammonium carbamate existing as a solid can be used. The supply mechanism is coupled to the exhaust system of the diesel engine via a supply pipe, and this supply pipe is connected to the exhaust system in front of the inlet side of the SCR-catalytic converter when viewed in the direction of the exhaust gas flow. As the metering device, a pulse valve actuated by the control unit is provided, so that a required amount of NH ₃ can be blown into the exhaust gas stream according to the engine operating parameters. The supply mechanism is mainly composed of a pressure-resistant reaction vessel, and this reaction vessel is surrounded by a heating serpentine tube. The heater is incorporated in the cooling water circulation system of the diesel engine through a supply pipe and a discharge pipe.

For example, ammonium carbamate used as an NH ₃ precursor decomposes into NH ₃ and CO ₂ when heated. Thereby, the reducing agent is transferred from the first phase, which in this case is a solid phase, to the second phase, which in this case is a gas phase. This gas mixture is collected in a pressure-resistant reaction vessel and forms an internal pressure corresponding thereto. When the reaction vessel reaches a specific internal pressure, an equilibrium state occurs, so that the ammonium carbamate does not decompose any more. Under engine operating conditions where the temperature of the cooling water flowing through the heater is usually 80 to 100 ° C., the pressure corresponding to the equilibrium state dominates the inside of the reaction vessel. This pressure is about 3-4 bar for ammonium carbamate. This supply mechanism is also used as a reaction gas reservoir so that when the diesel engine is driven, a sufficient amount of NH ₃ is obtained to be blown into the exhaust gas stream, a certain amount of reaction gas or NH ₃ contained therein is contained. Is stored as a reducing agent.

This reaction vessel is usually provided at a certain distance from the exhaust system. It has been found that when the temperature drops inside the feed system, the reaction gas mixture may return to the solid form (solid phase) again, depending on the NH ₃ precursor used. In disadvantageous cases, this can cause the supply system to become clogged. The same applies to valves arranged inside the supply system, for example the pulse valves already described as metering devices. The addition of some reducing agent, such as ammonium carbamate, to this supply line, particularly the pulse valve incorporated therein, is not unduly problematic when shutting down the internal combustion engine. This is because the NH ₃ precursor deposited on the supply pipe, particularly one or more valves, will decompose again when the temperature rises at the start of operation, so that the supply pipe and one or more valves are then opened. This is because that. It has already been proposed to heat the supply pipe and the valve incorporated therein in order to accelerate the start-up of the supply pipe. In realizing this type of heater that heats the entire supply system and the pulse valve incorporated therein, the distance between the reaction vessel and the exhaust system is greatly affected.

In view of the above background art, an object of the present invention is to propose an apparatus that addresses the above-described problem of reforming the NH ₃ precursor in the supply pipe.

  The present invention solves this problem by providing a device having a valve as described below for metering the reducing agent in the second phase. That is, in the valve according to the present invention, the fixed valve seat or the movable valve surface cooperating with the fixed valve seat functions as a condenser element operable by the control unit. The valve surface is in close contact with the valve seat when the valve is closed. The condenser element can also be actuated to form a cool trap in the supply tube. Then, the condenser element formed as a valve seat or valve face, or a valve element that complements this condenser element, can be actuated and heated by the control element.

  This device, which is configured as a metering valve, comprises a condenser element that forms a cool trap. This condenser element is connected to a control device. And when the internal combustion engine is shut down and / or when the valve is closed, it is actuated and operated accordingly. Activation of the condenser element can be performed in relation to other operating parameters, such as the current temperature of the valves and / or supply lines. By activating the condenser element, its temperature drops and a cool trap is formed. As a result, the reducing agent in the second phase returns to the first phase (for example when using ammonium carbamate) or to the intermediate phase within the environment of the condenser element. In this process, the reducing agent, particularly around the cool trap and in the second phase, is also attracted to the cool trap and returns to the first or intermediate phase as well. By this action, the reducing agent in the second phase existing in these mechanical elements is drawn to the cool trap formed by the condenser element from the supply pipe and the valve or coupling incorporated in the supply pipe. Based on such an action, the reducing agent in the second phase is collected at a predetermined site in the supply pipe and returned to the original phase. In order to supply the reducing agent to the SCR-catalyst converter incorporated in the exhaust system of the internal combustion engine by operating the supply pipe anew, the corresponding heating is performed and the reducing agent returned to the first phase or the intermediate phase is supplied. It only has to be removed from the area of the condenser element. For this purpose, the valve is also provided with a heater. The reducing agent that has returned to the original phase in the valve by the operation of the condenser element is heated by the heater, so that it is transferred again to the second phase, and this reduction is applied to the SCR-catalytic converter incorporated in the exhaust system of the internal combustion engine. Supply agent.

  As a reasonable method, the condenser element shall be assigned to the valve seat or to a movable valve face cooperating with a fixed valve seat. The heater is assigned to this valve element or to a complementary valve element.

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

  In a preferred embodiment, the movable valve face of the valve is configured to function as a heatable condenser element. As a result, the movable valve surface of the valve can be used for forming a cool trap and for decomposing the returned reducing agent. A suitable method is to use one or more Peltier elements that can be cooled or heated, depending on their mode of operation. In this case, the movable valve surface itself is preferably the heat exchange surface of one or more Peltier elements.

  In a suitable embodiment, it is assumed that the fixed valve seat comprises two adjacent connection ports, which can be closed together by a movable valve surface. The valve face functioning as a condenser element will close both connections at the closed position of the valve, forming a cool trap around each connection. This makes it possible to attract the reducing agent in the second phase existing in each supply system particularly effectively. One connection port is connected to a container for storing a reducing agent or a reducing agent precursor. The other connection port of the valve is connected to the exhaust system.

The method described above is particularly suitable for use with a supply tube as described below. That is, it is a supply pipe through which a gas phase reducing agent flows, and this reducing agent is obtained by separation from NH ₃ precursor existing in a solid phase by thermal decomposition. For this, in particular ammonium carbamate is suitable as NH ₃ precursor. This device can also be used for systems that use urea as the NH ₃ precursor.

  Hereinafter, the present invention will be described by way of examples with reference to the accompanying drawings.

The whole apparatus for supplying ammonia (NH ₃ ) to a reduction catalytic converter incorporated in an exhaust system of an automobile diesel engine is denoted by reference numeral 1 in FIG. The apparatus 1 includes a container 2 for thermally decomposing an NH ₃ precursor to generate ammonia (NH ₃ ). In the illustrated embodiment, ammonium carbamate cake 3 is used as the NH ₃ precursor. This ammonium carbamate cake 3 is formed in a cylindrical shape and takes a form as shown in the figure by compressing powdered ammonium carbamate. This ammonium carbamate cake 3 has a round cross section. A heater 4 is provided in the container 2 so as to face the whole. The heater 4 is a radiation type heater.

  This radiation heater is in the illustrated embodiment formed from three independent heater elements 5, 5 ′, 5 ″ arranged in an intricate manner, each in the form of an Archimedean spiral. 5, 5 ′, 5 ″ can operate independently of each other, so that depending on the number of heater elements 5, 5 ′, 5 ″ energized from time to time, the resulting heat output and / or transition of the heating stage can be varied. The heater 4 is installed in the lower part of the container 2. A heat insulating material 6 is provided below the heater elements 5, 5 ', 5 ". A heater plate 7 is installed as another part of the heater 4 at a slight interval above the radiation type heater. In the illustrated embodiment, the heater plate 7 is made of a transparent glass ceramic material. This material is transparent to the heat rays generated from the heater 4. A plurality of protrusions are formed on the surface of the heater plate 7 facing the ammonium carbamate cake 3. A tube 8 is connected to the heater plate 7 toward the lower end of the container 2. This pipe 8 surrounds the connection flow path 9. The connection flow path 9 is connected to a supply pipe denoted by reference numeral 10 as a whole. The connection flow path 9 forms a part of the supply pipe 10.

  FIG. 1 shows a device 1 and in particular a container 2. This container accommodates the ammonium carbamate cake 3 in its interior before the start of the first operation. Since the supply pipe 10 is open, the bottom surface portion of the ammonium carbamate cake 3 contacts the top surface of the protrusion structure of the heater plate 7. After the first operation of the apparatus 1 by the operation of the heater 4 is started, the bottom portion of the ammonium carbamate cake 3 is thermally decomposed to some extent. Thereby, the protrusion of the heater plate 7 is pushed into the ammonium carbamate cake 3 to fix the ammonium carbamate cake 3.

  The heater 4 is designed as described below. That is, the temperature generated on the heater plate 7 on the side facing the ammonium carbamate cake 3 is configured to be at most lower than the decomposition temperature of the reaction gas or reaction gas mixture generated during the thermal decomposition of the ammonium carbamate. . Such characteristics are effectively realized by the heater plate 7 made of glass ceramic. Therefore, the heater 4 has the advantages of a radiation heater such as quick reactivity and spontaneous decomposition of ammonium carbamate, and a heater obtained when, for example, a contact heater is used in combination with the heater plate 7. The advantage of can also be obtained.

  The container 2 is provided with a bellows piston 11. Thereby, the inside of a container is divided into the 1st container part and the 2nd container part. By means of the bellows piston 11, both container parts are separated from one another in an airtight manner. The first container portion is provided with a heater 4, an ammonium carbamate cake 3, and an outlet provided as a connection channel 9. The second container part is connected to the compressed air system D. The compressed air system D is accompanied by a compressor for obtaining the air pressure required for this system. Through this system, a pressure is generated on the second container portion, and thus a desired pressing force can be applied between the ammonium carbamate cake 3 and the surface of the heater plate 7.

In the container 2, an ammonium carbamate cake 3 present in solid form is stored as an NH ₃ precursor. When the heater 4 is energized, the ammonium carbamate in contact with the heater plate 7 is thermally decomposed, so that the NH ₃ precursor is transferred to the second phase, that is, the gas phase. This gaseous reducing agent is supplied to the exhaust system or the SCR-catalytic converter via the connection flow path 9 and the supply pipe 10.

  A valve 12 is incorporated in the supply pipe 10. The valve 12 is shown in the open position in FIG. The valve 12 includes a Peltier element 13 as a movable element. The Peltier element 13 can be arranged in the open position by operating the actuator 14. For example, an electromagnet can be used as the actuator 14. By displacing the Peltier element 13 with the elastic energy accumulated in the compression spring 15, the valve 12 can be arranged in the closed position shown in FIG. The surface 16 of the Peltier element 13 functions as a movable valve surface and forms the actuator of the valve 12. The diaphragm 17 seals the valve chamber 18 over a wide range.

  In the open position of the valve 12, the reaction gas formed by thermal decomposition in the container 2 flows through the valve chamber 18 to the supply pipe 10 connecting the valve 12 and the exhaust system, and the gaseous reducing agent is supplied to the SCR−. Supply to the catalytic converter. As shown in FIG. 2, when the valve 12 is closed, the Peltier element 13 is energized simultaneously, and the heat exchange surface 16 of this element is cooled. The surface 16 of the Peltier element 13 contacts the connection port assigned to the connection flow path 9 and the connection port that connects the valve 12 to the exhaust system. Both these connections are sealed against the valve surface formed by the surface 16 by a seal 19 and cooled by the condenser effect. Due to the contact described above, the reducing agent gas present in the supply pipes 10 on both sides is attracted to the low temperature surface 16, and the surface 16 functions as a cool trap in this state. Thereby, after the heater 4 is stopped, the inside of the supply pipe 10 becomes lean, so that the risk that the reducing agent in the supply pipe 10 returns to ammonium carbamate is greatly reduced. The Peltier element 13 is energized when opening the valve 12 or immediately before opening the valve 12. Since the Peltier element 13 functions as a heater element, the ammonium carbamate formed as a result of the cool trap function is rapidly decomposed. Following this, the valve 12 becomes operable and the ammonia supply device becomes operable.

  In the case of the illustrated embodiment, in the valve 12, two outlet openings composed of a valve seat and its seal 19 are arranged side by side. Thus, in this embodiment, both outlet openings are simultaneously sealed by the surface 16 of the Peltier element 13 which functions as a movable valve surface. The energization of the Peltier element 13 for obtaining the cool trap function is preferably performed immediately after the valve 12 is closed.

Ammonium carbamate is a preferred NH ₃ precursor for operation of the apparatus. The advantage of using ammonium carbamate is that if the temperature exceeds 70 ° C., thermal decomposition is initiated at a sufficient level. Such a relatively low pyrolysis temperature has the following advantages. The ammonium carbamate that has already been collected by the cool trap function of the valve is decomposed at a relatively low temperature, that is, with a small amount of energy, and released again into the reaction gas, so that the ammonium carbamate returned to the first phase is recovered. The advantage is that it can be removed from the valve.

It is a figure which shows the apparatus which supplies ammonia as a reducing agent to the SCR-catalyst converter integrated in the exhaust system of the internal combustion engine. FIG. 2 shows the valve of FIG. 1 in a closed position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus 2 Container 3 Ammonium carbamate cake 4 Heater 5 Heater element 6 Heat insulating material 7 Heater plate 8 Pipe material 9 Connection flow path 10 Supply pipe 11 Bellows piston 12 Valve 13 Peltier element 14 Actuator 15 Compression spring 16 Surface 17 Diaphragm 18 Valve chamber 19 Seal D Compressed air system

Claims (7)

  Supply pipe (10) for directing the reducing agent transferred from the first phase to the second phase and supplying the reducing agent in the second phase to the SCR-catalyst converter incorporated in the exhaust system of the diesel engine From the apparatus for removing the reducing agent returned to the first phase, the apparatus is a valve (12) for metering the reducing agent in the second phase, the fixed valve seat, or the fixed A movable valve surface (16) that cooperates with the valve seat and abuts the valve seat in the closed position of the valve (12) is operable by the control unit to form a cool trap in the supply pipe (10). A condenser element that functions as a condenser element and is formed as said valve seat or valve face, or that complements this element, can be actuated and heated by the control unit. And wherein the.   2. A device according to claim 1, characterized in that the movable valve face (16) of the valve is formed as a heatable condenser element.   Device according to claim 2, characterized in that the movable valve face (16) is formed by a heat exchange surface of one or more Peltier elements (13).   The fixed valve seat has two connection ports adjacent to each other, one connection port connected to a container for storing the reducing agent or reducing agent precursor and transferring the reducing agent to the second phase, The apparatus according to any one of claims 1 to 3, wherein the connection port is connected to an exhaust system.   5. Device according to claim 4, characterized in that, in the closed position of the valve (12), both connections of the valve seat are sealed by a movable valve face (16). The NH ₃ is separated under heat supply, and when the temperature falls after the NH ₃ separation, the precursor (3) formed by returning the reaction gas or the reaction gas mixture to the solid phase is stored, and one of the valves (12) is stored. The container (2) is connected to the opening of the heater, and the container (2) is provided with a heater (4) for causing separation of NH ₃ by thermal decomposition of the precursor (3). The device according to claim 1, wherein the device is a device. The device according to claim 6, characterized in that the NH ₃ precursor stored in the container (2) is an ammonium carbamate cake (3).

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