DE102004025965A1 - Flue gas purification equipment for use in motor vehicle, has exhaust gas catalytic converters in flue gas pipeline of internal combustion engine, and two reactant preheated layers heating reactant on two temperature levels - Google Patents

Abstract

The equipment has exhaust gas catalytic converters (23, 23`) in a flue gas pipeline of an internal combustion engine. Oxygen and fuel of the engine is supplied to a catalytic fuel reformer (1) which supplies hydrogenous reformer gases at an inlet side of the converter. Two reactant preheated layers (2`, 2) heat the reactant on two temperature levels, where latter level is higher than former level.

Description

The The invention relates to an emission control system for cleaning a Exhaust gases of an internal combustion engine having the features of the preamble of Claim 1.

In the published patent application DE 102 10 367 A1 is described an exhaust gas purification system with an arranged in an exhaust pipe of an internal combustion engine exhaust gas catalyst and a catalytic fuel reformer for generating a hydrogen-containing reforming gas from fuel and a partial exhaust gas flow of the internal combustion engine. In this exhaust gas purification system, the reforming gas produced by the fuel reformer can be fed to the exhaust gas line on the input side and to the fuel reformer a controllable heating device for heating the reformer and / or the partial exhaust gas flow.

Out Hydrocarbon produced reforming gas is in many ways usable in motor vehicles. Due to its high hydrogen and carbon monoxide content is the reforming gas for cold start purposes, and in particular as a reducing agent for the exhaust gas cleaning can be used. An important aspect of use a fuel reformer for onboard generation of a hydrogen-containing Reforming gas from fuel concerns the heat management of the reformer, especially when it is operated discontinuously.

task The invention is therefore an exhaust gas purification system with a Reformer for generating a hydrogen-containing reforming gas indicate fuel in which the reformer with high efficiency is operable.

These Task is by an emission control system with the features of claim 1.

The Emission control system according to the invention is characterized by the fact that a first Eduktvorheizstufe for Eduktaufheizung to a first temperature level and one of the first Eduktvorheizstufe downstream second Eduktvorheizstufe downstream Eduktaufheizung on the other hand higher second Temperature level are provided. As educts fed to the reformer come mainly fuel, Oxygen and optionally water into consideration. Preferably one for the fuel used in the operation of the internal combustion engine such as Diesel fuel as a starting material for used in the reformer expiring reforming reactions. These include a partial oxidation of the fuel, where as important and preferred products hydrogen and carbon monoxide are formed, the for support the catalytic emission control can be used. As an oxygen source preferably serves ambient air. However, it can also be oxygenated Internal combustion engine exhaust gas can be used as starting material. That in the exhaust contained water can thereby improve the hydrogen yield used in the reforming process.

The two-stage according to the invention Eduktvorheizung allows on the one hand, a particularly good preparation of the educt mixture fed to the reformer, which improves its performance. On the other hand, through Use of reformer waste heat In the Eduktaufheizung efficiency-reducing heat losses are avoided. By the preheating stages located at different temperature levels can be obtained during the reforming process at different temperature levels Process waste heat effectively use for Eduktvorheizung. Remain in this way big parts the waste heat in the process, what the thermal efficiency of the reformer operation improved accordingly.

In Embodiment of the invention takes place in the first Eduktvorheizstufe a heat release of the reformed gas discharged from the fuel reformer. As the reforming process preferably takes place in a temperature range between 800 ° C and 1000 ° C, contains the reforming gas a comparatively high heat energy. This is due to partial release of an educt to the reforming process fed again. The first Eduktvorheizstufe is preferred as an air heater educated. The heating of the air or the oxygen-containing Feed gas is preferably carried out at a temperature level, which is a Evaporation of the reformer supplied fuel allows.

In Another embodiment of the invention is the second Eduktvorheizstufe in heat transfer contact with the fuel reformer. In this case, a construction is preferred in the case of a high proportion of heat delivered by the reformer in the form of radiant heat to the starting materials becomes. This becomes inertia the system decreases, causing a rapid adjustment of a thermal Equilibrium allows. By the heat emission is the reformer cooled, so that its overheating due to the released heat of reaction in the partial oxidation of the fuel is avoided.

In a further embodiment of the invention, the second Eduktvorheizstufe is designed as a fuel evaporator. In the second Eduktvorheizstufe the liquid operating fuel of Brennkraftmaschi ne, preferably injected finely distributed. The energy necessary for evaporation is supplied on the one hand by the air heated in the first educt preheating stage and on the other hand by the reformer. At the same time, further heating takes place to a temperature level which is higher than the first Eduktvorheizstufe.

In Another embodiment of the invention is the fuel reformer annular executed. Preference is given to an elongated form with Edukteintritt a ring end and product outlet at the other ring end. From the Ring structure results in a big one Surface volume ratio and thus an improved heat transfer, for example, to the second Eduktvorheizstufe. The comparatively large surface of the Ring structure reduces additionally the thermal inertia of the system.

In Another embodiment of the invention surrounds the second Eduktvorheizstufe the fuel reformer annular or it is surrounded annularly by the fuel reformer. This allows a Space-saving construction, for example as a tube-in-tube arrangement with highly effective heat transfer.

In Another embodiment of the invention is the reforming catalyst as a corrugated iron structure or as a wire mesh or as a metal foam executed. These metallic according to the invention catalyst support have improved thermal properties over one conventional honeycomb carrier structure on.

In Further embodiment of the invention surrounds the fuel reformer the exhaust pipe at least partially. This allows a particularly compact Structure of the emission control system according to the invention.

advantageous embodiments are shown in simplified form in the drawings and in the following Description closer explained. It is understood that the above and the following yet to be explained Features not only in the specified combination, but also usable in other combinations or alone are without departing from the scope of the invention.

It demonstrate:

1 a schematic block diagram representation of an arrangement of an internal combustion engine and associated emission control system,

2 a schematic block diagram representation of an advantageous embodiment of the emission control system and

3 a schematic sectional view of an advantageous embodiment of the fuel reformer with associated components.

The schematic representation of 1 shows a diesel engine 20 , whose exhaust gases via an oxidation catalyst 21 and a downstream particle filter 22 are guided. The exhaust gases are further via a nitrogen oxide storage catalyst 23 and a downstream SCR catalyst 24 guided. The emission control system also has a fuel reformer 1 on, whose reforming gas line 10 upstream of the nitrogen oxide storage catalyst 23 flows into the exhaust pipe. Here are the fuel reformer 1 to carry out the fuel reforming air and fuel fed. This is in the 1 shown greatly simplified. The inventively provided Eduktvorheizstufen or heat exchangers will be discussed in more detail below. The reformer 1 Feedable diesel fuel is that for the supply of the diesel engine 1 provided fuel tank 25 removable. Other for the operation of the diesel engine and the exhaust gas purification system provided units such as control units, sensors or control devices are not shown for clarity.

The operation of the exhaust gas cleaning system according to the invention will be described below., It being assumed that the optional switching element 11 is not provided.

The diesel engine 20 discharged exhaust gases are first from the oxidation catalyst 21 largely purified from oxidizable constituents such as carbon monoxide and hydrocarbon. Subsequently, in the particle filter 22 the removal of exhaust particles such as soot particles. The exhaust gases continue to the nitrogen oxide storage catalyst 23 fed in which they in lean operation of the diesel engine 20 be largely removed from the exhaust gas by adsorption. Subsequently, the exhaust gas through the SCR catalyst 24 in which the remaining nitrogen oxides contained in the exhaust gas by selective reduction with in the SCR catalyst 24 Cached ammonia can be reduced. Is the absorption capacity of the nitrogen oxide storage catalyst 23 depleted of nitrogen oxides, so the operation of the diesel engine 20 switched to an approximately stoichiometric or rich operation, and at the same time the exhaust gas from the reformer hydrogen-containing reforming gas via the reforming gas 10 fed. As a result, hydrogen enriched, reducing exhaust gas passes into the nitrogen oxide storage catalyst 23 , As a result, the nitrogen oxides adsorbed there are reduced, causing the nitrogen oxide Speicherkata lyst 23 is regenerated. In particular, due to the high proportion of hydrogen in the exhaust gas arise in the regeneration of the nitrogen oxide storage catalyst 23 comparatively large amounts of ammonia. These are in turn adsorbed in the downstream SCR catalyst and are available for the regeneration following lean operation of the diesel engine as a reducing agent for nitrogen oxides available. With the exhaust gas purification system according to the invention thus an effective reduction of the essential pollutants is possible.

If no intermediate storage for reforming gas is provided, the abovementioned embodiments of the exhaust gas purification system require a predominantly discontinuous operation of the reformer 1 , This disadvantage can be achieved by a double-flow exhaust system, as shown schematically in 2 is shown avoided. Here are in the in 2 shown further advantageous embodiment of the emission control system according to the invention, the components, as far as they are with the parts of 1 match, identified by the same reference numerals.

2 shows as cleaning components of the exhaust system only the nitrogen oxide storage catalyst, but here a first nitrogen oxide storage element 23 and a second nitrogen oxide storage element 23 ' in two parallel exhaust gas flows. The nitrogen oxide storage elements 23 . 23 ' can depending on the position of an inserted into the exhaust pipe switching element 11 alternately be acted upon with exhaust gas or with reforming gas. For this purpose, the switching element 11 Exhaust via the exhaust pipe 9 and reforming gas via the reforming gas line 10 supplied and the switching element 11 operated accordingly. In the position shown receives the nitrogen oxide storage element 23 Reformiergas and is therefore in a regeneration mode with ammonia formation, while the nitrogen oxide storage element 23 ' receives lean, nitrogen oxide-containing exhaust gas and is therefore in the adsorption mode. With this embodiment, a permanently lean operation of the diesel engine and a predominantly continuous operation of the fuel reformer 1 allows.

The fuel reformer 1 is like in 2 represented according to the invention a first heat exchanger 12 and a second heat exchanger 14 and a Eduktheizheizstufe 3 assigned. The first heat exchanger 12 includes a heat-emitting side 2 and a heat receiving side 2 ' , which as the first Eduktvorheizstufe the reformer 1 supplied air heats up to a first temperature level. The heat-emitting side 2 of the first heat exchanger 12 is in thermal contact with that of the reformer 1 produced hot reforming gas. The transition from the reforming gas to the air heat flow is with a double arrow 7 characterized. In the usual operating conditions, this indicates the reformer 1 leaving reforming gas at a temperature of about 900 ° C. By constructive measures it is achieved that cooled by the heat transfer, the reforming to, for example, about 800 ° C and from the first heat exchanger 12 outflowing and into the second Eduktvorheizstufe 3 incoming air is heated to a temperature of preferably about 200 ° C.

The second Eduktvorheizstufe 3 is preferably designed as a fuel evaporator. For evaporation of the fuel and for further heating of the reformer 1 supplied educts is a heat transfer contact the second Eduktvorheizstufe 3 with the reformer 1 intended. It is envisaged that the heat transfer by radiation and / or convection takes place. The heat transfer from the reformer 1 on the second Eduktvorheizstufe is doing with the double arrow 6 characterized. In this way, the reformer can 1 a substantially single-phase air-fuel mixture of preferably about 350 ° C are supplied. At this temperature, hardly any pre-reactions of the fuel are to be expected, so that the reforming controlled in the reformer 1 can expire.

By means of the preferably provided for the exhaust gas purification system second heat exchanger 14 is in about 800 ° C hot reforming gas contained heat energy to the exhaust gas of the diesel engine upstream of the nitrogen oxide storage catalyst 23 . 23 ' transfer. The heat transfer is with the double arrow 8th characterized. With the heat transfer, even at low engine load with correspondingly low exhaust gas temperatures, an improved effect of the storage element located in the storage mode 23 . 23 ' reached. Instead of the heat transfer from the reforming to the exhaust gas, however, a heat output from the reforming can be provided to the coolant of the diesel engine.

The fuel reformer 1 is preferably designed as a catalytic reformer for carrying out a partial oxidation of the diesel fuel used here. Preferably, it is supplied with an air-fuel mixture having an air ratio λ of about 0.35. This means that the air-fuel mixture contains an oxygen content that is 35% of the proportion required for complete oxidation of the fuel. Thus, on the one hand, a high hydrogen yield is achieved, and on the other hand, the partial oxidation takes place above the soot limit. The catalyst used is preferably a catalytically coated catalyst support. This can be designed as a honeycomb body. Due to the improved heat conduction properties, however, is a corrugated metal or wire knit catalyst support. Particularly preferred is a metal foam carrier.

The function of the fuel reformer 1 consists in the illustrated embodiments of the exhaust gas purification system mainly therein, the for the ammonia production in the nitrogen oxide storage catalyst 23 stored nitrogen oxides provide important hydrogen. It is understood, however, that of the reformer 1 also produced hydrogen for other purposes such as to improve the onset of the oxidation catalyst 21 especially when cold starting the diesel engine 20 can be used. Due to the reactivity of the reforming gas whose oxidation is possible even at relatively low catalyst temperatures, so that the heat of reaction liberated the catalyst 21 heated quickly and thus it is brought quickly to its normal operating temperature. Exhaust gas heating by oxidation of reforming gas may also assist in soot regeneration of the particulate filter 22 be used. The generation of the necessary for Rußabbrand high exhaust gas temperatures is thus facilitated.

In 3 is a preferred embodiment of the reformer and the associated components shown in a schematic sectional view, wherein the components, as far as those of 1 respectively. 2 correspond, are provided with the same reference numerals. As shown, a circular ring shape is for both the reformer 1 as well as for the first heat exchanger 12 intended. A particularly compact embodiment of the exhaust gas purification system is achieved when the circular ring structure is arranged around an exhaust pipe section. Although the reformer designed as an annular gap 1 here inwardly with respect to the second Eduktvorheizstufe 3 is executed, the arrangement can of course be carried out the other way round. This applies analogously to the execution of the first heat exchanger 12 ,

When operating the reformer 1 air becomes the heat-receiving side made in the manner of an annular gap 2 ' of the heat exchanger 12 fed. It is advantageous to provide by design measures a spiral flow guide for the air to be heated. In an analogous way, the heat-emitting side 2 of the heat exchanger 12 or the second Eduktvorheizstufe 3 be executed. It is advantageous for the heat exchanging components 2 . 2 ' . 3 also an embodiment in the form of a tube bundle arrangement, wherein the gas-carrying pipe sections are arranged in a circle.

The in the first Eduktvorheizstufe 2 ' heated to about 200 ° C air is further in the immediately following second Eduktvorheizstufe 3 forwarded. The second Eduktvorheizstufe 3 In addition, diesel fuel is supplied. Due to the heat transfer from the reformer 1 and the Wämeinhalts the supplied air takes place in the second Eduktvorheizstufe 3 an evaporation of the diesel fuel and a further heating of the formed air-fuel mixture to about 350 ° C. This is by deflection in the adjacent annular reformer 1 directed. In this runs at about 1000 ° C, the catalytically assisted partial oxidation of the diesel fuel, the diesel fuel is converted predominantly to hydrogen and carbon monoxide. The released heat of reaction is partly to the second Eduktvorheizstufe 3 transferred and used for Eduktaufheizung.

The generated reforming gas has at its exit from the reformer 1 Typically, a temperature of about 900 ° C and is in the directly to the reformer 1 subsequent first heat exchanger 12 directed. There takes place as described a heat transfer to the reformer supplied air.

By the illustrated embodiment of the components 1 . 2 . 2 ' . 3 as standing in heat transfer contact annular gap cylinder a particularly favorable ratio of surface area to volume and thus a particularly good heat transfer is achieved. This advantageously reduces the thermal inertia of the overall system, allowing a rapid response of the system to changing operating conditions.

For an advantageous response, it may also be provided, two axially successive zones of the reformer 1 provide with different sized thermal masses. To improve the cold start properties, it is advantageous to provide a zone with low thermal mass in the entrance area. It is advantageous, this in turn nachzuschalten a zone with a comparatively large thermal mass. This improves the thermal behavior in a batch operation of the reformer. For the cold start or for the ignition of the air-fuel mixture can be further provided, a heated by a glow plug vortex chamber the reformer 1 upstream or in the entrance area of the reformer 1 to arrange what is not shown in detail. It is understood that components whose intended temperature is above the ambient temperature, may be provided with a corresponding thermal insulation.

Claims (8)

Emission control system for cleaning a Exhaust gases of an internal combustion engine ( 20 ), with - one in an exhaust pipe of the internal combustion engine ( 1 ) arranged exhaust gas catalyst ( 23 ; 23 ' ) and - a catalytic fuel reformer ( 1 ) for producing a hydrogen-containing reforming gas, - wherein the fuel reformer ( 1 ) an oxygen and fuel of the internal combustion engine ( 20 ) comprehensive Eduktgemisch can be fed, and the reforming gas on the input side of the catalytic converter ( 23 ; 23 ' ) can be supplied to the exhaust gas line, characterized in that a first Eduktvorheizstufe ( 2 ' ) to Eduktaufheizung to a first temperature level and one of the first Eduktvorheizstufe ( 2 ' ) downstream second Eduktvorheizstufe ( 3 ) are provided for Eduktaufheizung to a contrast higher second temperature level. Exhaust gas purification system according to claim 1, characterized in that in the first Eduktvorheizstufe ( 2 ' ) a heat output of the fuel reformer ( 1 ) is discharged reforming gas. Exhaust gas purification system according to claim 1 or 2, characterized in that the second Eduktvorheizstufe ( 3 ) in heat transfer contact with the fuel reformer ( 1 ) stands. Exhaust gas purification system according to one of claims 1 to 3, characterized in that the second Eduktvorheizstufe ( 3 ) is designed as a fuel evaporator. Emission control system according to one of claims 1 to 4, characterized in that the fuel reformer ( 1 ) is annular. Exhaust gas purification system according to one of claims 1 to 5, characterized in that the second Eduktvorheizstufe ( 3 ) the fuel reformer ( 1 ) annularly surrounds or from the fuel reformer ( 1 ) is surrounded annularly. Emission control system according to one of claims 1 to 6, characterized in that the reforming catalyst as a corrugated iron structure or is designed as a wire mesh or as a metal foam. Emission control system according to one of claims 1 to 6, characterized in that the fuel reformer ( 1 ) at least partially surrounds the exhaust pipe.