DE102012203574A1 - Exhaust gas purification device for reducing nitrogen oxides in the exhaust gas stream of internal combustion engines - Google Patents

Abstract

An exhaust gas cleaning device for reducing nitrogen oxides in the exhaust gas flow of an internal combustion engine (10) is described. The exhaust gas purification device comprises (a) a catalyst reactor unit (51) with a reactor housing (52) which has a plurality of inlet and outlet openings (53, 54) and with a plurality of inlet openings (53) arranged in the reactor housing (52) and attached to the inlet openings (53 ) subsequent raw gas cascades (60) and with a large number of clean gas cascades (80) arranged in the reactor housing (52) and connected to the outlet openings (54) and (b) a bed (90) introduced into the reactor housing (52) through which the exhaust gas flow can flow ) of catalyst elements, the catalyst elements having a support made of a foam metal and a catalytic coating for the selective catalytic reduction (SCR) of nitrogen oxides. Furthermore, an exhaust system comprising the exhaust gas cleaning device and a method for operating the exhaust system are described.

Description

The invention relates to an exhaust gas purification device with a bed of catalyst elements for the reduction of nitrogen oxides in the exhaust stream of an internal combustion engine.

A variety of catalysts have been proposed in the past to purify environmentally relevant substances such as nitrogen oxides in various oxidation states (NO, NO ₂ , N ₂ O ₄ , N ₂ O ₅ and N ₂ O) emitted from internal combustion engines , These are controlled or uncontrolled catalysts, oxidation catalysts, three-way conversion catalysts (TWC catalysts), NO _x storage catalysts and SCR (selective catalytic reduction) catalysts.

In addition to sulfur oxides, nitrogen oxides (NO _X ) are among the limited exhaust gas components in shipping that arise during combustion processes and whose permissible emissions are being lowered ever further. Marine propulsion engines operated on board are 4-stroke engines or 2-stroke, slow-speed engines, both of which operate on IFO180, IFO380, MDO and MGO heavy fuel oils and distillates. In these engines, due to the high combustion temperatures of greater than 1600 ° C, the so-called thermal NO _X , which by means of an operating according to the principle of selective catalytic reduction SCR catalyst, an input reductant (usually NH ₃ or a precursor compound (precursor ) is converted by this and oxygen (O _2). A detailed description of such procedures on the basis of SCR catalysts, the DE 34 28 232 A1 be removed.

The structure of an SCR system varies according to the technical requirements and is adapted to this individually. The basic principle is based on the following structure: The reducing agent is added to the still polluted exhaust gas and mixed homogeneously with it. In most cases, the reducing agent is ammonia (NH ₃ ), ammonia water or urea. Subsequently, the reduction of the nitrogen oxides takes place on the catalyst. The NO _x- free exhaust gas leaves the catalyst as possible without NH ₃ -slip.

This general principle can be extended by additional components depending on requirements. For example, arrangements with an oxidation catalyst, ammonia blocking catalyst or hydrolysis catalyst, if the reducing agent is to be formed from dry urea, are conceivable. These can optionally be combined with the SCR catalyst by upstream or downstream.

By means of the SCR catalyst, the resulting in the internal combustion engine, such as a diesel engine, nitrogen oxides are reduced in the presence of the reducing agent to nitrogen (N ₂ ) and water (H ₂ O). The reducing agent is either added directly to the exhaust gas or a precursor of the reducing agent is added, which releases the reducing agent only in the exhaust aftertreatment system. As a reducing agent, ammonia (NH ₃ ) can be supplied in gaseous form or as an aqueous solution. It is also known to supply urea as a precursor to the exhaust gas stream, which is then thermolytically and hydrolytically converted to NH ₃ , H ₂ O and CO ₂ .

The first applications of SCR technology in the maritime sector have shown that the adaptation of land-based technologies is problematic as the mobility of ships presents problems with vibration, vibration, heeling, stability, etc. Also, the exhaust gas composition, especially the high sulfur content, presents a particular challenge that has not been satisfactorily solved.

For the catalyst reactors used in the prior art for heterogeneous catalysis, a construction variant has prevailed so far, namely the so-called honeycomb catalyst. In a housing (Canning or module) is a carrier material, is used for the extruded ceramic or a metal sheet. The carrier forms parallel channels through which the exhaust gas flows. Already here it is attempted to provide the exhaust gas with as large a surface as possible, with which it can interact, so that the channels are made as fine as possible. The so-called cell density indicates the number of channels per area (square inches). The designs used in the art here range from 25 to 400 cpsi (cells per square inch) as a typical value for ceramics and up to 1200 cpsi for high cell, high performance versions with metallic supports. Here, the wall thickness is often just 30 microns. The limiting factor here is the tolerable pressure drop. The carrier component is demanded high thermal and mechanical strength, since it is often exposed to strong temperature fluctuations and shocks. A heat-resistant metal grid or a ceramic mat around the honeycomb body therefore ensures the fixation in the housing and the absorption of vibrations.

Catalytic converters, which are generally used in the automotive industry and in power plant technology, usually have a honeycomb honeycomb structure with a high heat and impact resistance as a carrier material. Cordierite, a magnesium-aluminum-silicate material (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) is characterized by a high temperature resistance and a large porosity of 20 to 40 vol .-%, which consists mainly of macropores with average diameters of a few micrometers, from.

For large-scale systems, which include marine engines here, larger units are assembled in modular design from many, usually cuboid monoliths. The practical application on board ships has shown that such catalysts can only be operated to a limited extent with the fuel quality HFO. Also, the mechanical stresses (temperature fluctuations, shocks, vibrations) that occur during ship operation, significantly higher than in stationary operation.

Honeycomb catalysts, such as. B. the publications DE 102 55 612 A1 . EP 1 063 396 A2 . EP 1 713 584 A1 and EP 1 920 834 A1 are distinguished by a large number of cells per square centimeter and have wall thicknesses between 0.2 and 1.5 mm, wherein wall thicknesses between 0.2 to 0.3 mm are preferred. The disadvantage of these small wall thicknesses is that mechanical stresses, such as pressure surges through the so-called "soot bubbles", can cause damage. This process of cleaning the honeycomb catalysts by means of pressure surges is necessary because large engines, especially marine engines powered by residual oils, release particulate matter, soot, metal ashes, metals and sulphates. These deposit in the honeycomb of the honeycomb catalyst and lead to a decrease in the catalytic activity of the catalyst and to an increase in the pressure loss.

Another disadvantage of the honeycomb catalysts is that the exhaust gas flow in the honeycomb channels over the length of the channels from turbulent to laminar and the mass transfer between gas phase and catalytically active surface decreases sharply, resulting in a decrease in the catalyst activity.

The invention is therefore based on the object to provide an exhaust gas purification device whose properties meet the requirements of the engine and in particular the large engine industry for use as Abgasentstickung in heavy oil fired diesel engines.

According to the invention this object is achieved by an exhaust gas purification device for reducing nitrogen oxides in the exhaust stream of an internal combustion engine. The exhaust gas purifying apparatus comprises a catalyst reactor unit having a reactor housing having a plurality of inlet and outlet ports and a plurality of raw gas cascades arranged in the reactor housing and adjacent to the inlet ports and having a plurality of clean cascades disposed in the reactor housing and adjacent to the outlet ports. In addition, the exhaust gas purification device comprises a, introduced in the reactor housing, from the exhaust gas stream durchströmmbare bed of catalyst elements, the catalyst elements having a support of a foam metal and a catalytic coating for selective catalytic reduction (SCR) of nitrogen oxides.

This exhaust gas purification device is characterized by a significantly smaller volume of construction than conventional honeycomb catalysts offer. This makes it much easier to subsequently integrate an exhaust gas purification device in the exhaust system of a ship. By the bulk of the loose catalyst elements known from monolithic catalysts voltage problem is solved, creating a catalyst is created specifically for the requirements of shipping. The support made of foam metal are characterized by their insensitivity to thermal expansion and mechanical stress. Preferably, the bed is flow-optimized and is flowed around during operation of the exhaust stream of the internal combustion engine usually turbulent constantly and flows through.

The foam metal of the catalyst elements preferably comprises iron, iron oxide, chromium, aluminum and / or nickel or alloys thereof or preferably consists thereof.

Further preferably, the catalyst elements have the geometric shape of a sphere, a hemisphere, a ring, a tube, a Raschid ring, a half-tube, a plate, a cylinder or a cube.

Furthermore, the catalyst elements preferably have a length or a diameter of 0.5 to 30 mm, preferably 1 to 15 mm and particularly preferably 2 to 8 mm.

Furthermore, the foam metal of the catalyst elements has a specific surface area of 8,000 to 25,000 m ² / m ³ , in particular 11,000 to 18,000 m ² / m ³ .

According to a preferred embodiment of the invention, the foam metal has pores with a pore diameter of 100 to 3200 .mu.m, in particular from 400 to 1200 microns.

Theoretically, it is also possible to use a ceramic carrier, preferably cordierite, instead of the foam metal. However, you would have to doing without the benefits of a support made of a foam metal.

The catalytic coating preferably comprises a catalytically active material in the form of at least one oxide of a transition metal with the atomic number 21 to 30, 39 to 48, 57 to 80 and 89 to 112 and / or at least one alkali and / or alkaline earth metal compound and / or at least one Compound of the third main group or subgroup of the periodic table and / or at least one rare earth metal or zinc compound or in the form of mixtures of these.

Further preferably, the catalytic coating comprises an NH ₃ -storing material, in particular aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO) or a zeolite of the type X, Y and / or ZSM-5. The alumina (Al ₂ O ₃ ), the zirconia (ZrO) or the zeolite forms the basic structure of the coating on which the catalytically active material is present in free distribution.

Preferably, the catalytic coating comprises a catalytically active material for the conversion of hydrocarbons (HC). These hydrocarbons may, for example, C1 to C10 hydrocarbons, particularly CH ₄ to C ₁₀ H ₂₂ (alkanes) to be. The catalytically active material is usually a combination of suitable noble metals.

The coating of the foam metal support with catalysts, as well as with the NH ₃ -stichernden material is usually carried out by a washcoat process, as is also known for conventional honeycomb-shaped metal or ceramic support.

The NH ₃ -speichernde material preferably has a BET surface area of at least 300 m ² / g, especially at least 400 m ² / g and particularly preferably of at least 500 m ² / g. Furthermore, the material storing NH ₃ preferably has a particle size of at most 0.9 μm, in particular of at most 0.6 μm and particularly preferably of not more than 0.3 μm. Furthermore, the NH _3- storing material preferably has an average pore size of 0.4 to 1 nm, more preferably 0.7 to 0.8 nm.

According to a preferred embodiment of the invention, the crude gas and / or the pure cascade comprise in the flow direction (ie axially) extending elements. As a result of this configuration, the raw gas can also be transported into the regions of the catalyst unit which are opposite the inlet openings and / or can be discharged from the regions opposite the outlet opening. This allows an equally distributed flow through the bed.

Furthermore, the elements of the crude gas and / or pure-gas cascades extending in the direction of flow preferably have a roof-like shape. The roof-like shape designates a molding, which is closed at the top and open at the bottom. Through the roof-like shape of extending in the direction of flow elements of the crude gas and / or pure cascade channels form by filling the catalyst reactor unit with the bed, which upwardly from the extending in the direction of flow, roof-like elements of the raw and / or pure cascade and be limited to the bottom of the bed. As a result, the raw and / or clean gas can freely flow within the crude and / or pure cascade and be distributed within the catalyst reactor.

Particularly preferably, an element extending in the direction of flow has a cross-sectionally normal shape to the flow direction in the form of a second limb. The intersection of the two legs shows in the assembled state of the exhaust gas purification device upwards. Thus, the extending in the direction of flow elements of the crude gas and / or pure cascade are arranged as two angularly arranged, preferably flat surfaces, the cutting line forms the highest point of the raw gas and / or the pure cascade.

Preferably, the two legs of the extending in the direction of flow elements of the crude gas and / or pure cascade a leg length of 5 to 30 cm, in particular from 10 to 20 cm, and / or an angle of 15 ° to 110 °, in particular from 20 ° to 90 °, preferably from 45 ° to 75 °, on. These embodiments allow a flow-favorable cross section of the channels formed by the roof-like elements extending in the direction of flow.

Preferably, the crude gas and / or the pure cascade cascades are arranged at a distance of 10 to 50 cm, in particular from 15 to 35 cm, to each other. This distance represents a good compromise flow resistance as it flows through the bed and the effective catalytic surface.

According to a preferred embodiment of the invention, the reactor housing of the catalyst reactor unit has discharge means for discharging spent or contaminated catalyst elements. Austragungsmittel are in particular a rotary valve, a screw conveyor or a double pendulum flap. By these embodiments, for. B. contaminated with soot catalyst elements from the catalyst reactor unit discharged and, for example, purified or treated outside the catalyst reactor unit.

Furthermore, an exhaust system for an internal combustion engine, comprising an exhaust gas purification device according to the invention is provided. The exhaust system usually includes at least one inlet and outlet, which direct the raw gas to the exhaust gas purification device and away from the exhaust gas purification device.

Preferably, the exhaust system further comprises a metering device arranged upstream of the exhaust gas purification device for metering a reducing agent into the exhaust gas flow, in particular of ammonia (NH ₃ ) or a precursor compound therefrom. The metering device allows insertion, z. As an injection of the reducing agent or its precursor compound in the exhaust stream.

According to a further preferred embodiment of the invention, the exhaust system further comprises a burner arranged upstream of the exhaust gas purification device for increasing the exhaust gas temperature. The burner can furthermore preferably be operated with liquid or gaseous fuels, in particular with a boil-off of a liquid-gas tank.

Furthermore, a method for operating an exhaust system according to the invention is provided. The method comprises a first step of providing an exhaust system according to the invention. Furthermore, the method comprises a second step of introducing the exhaust gas flow into the catalyst reactor unit through the inlet openings and at least partially through the raw gas cascades. Moreover, the method comprises a third step of passing the exhaust gas flow through the bed of catalyst elements. Furthermore, the method comprises a fourth step of diverting the exhaust gas stream from the catalyst reactor unit at least partially through the clean-water cascade and through the outlet openings.

Preferably, in a discontinuous procedure, a subset of the catalyst elements is discharged from the device upon reaching a predetermined pressure loss and / or a predetermined NO _x -Regas concentration threshold and replaced by not yet acted catalyst elements. As a result, a uniform operation of the catalyst over the operating time can be ensured. Nevertheless, a continuous discharge and replenishment of catalyst elements is possible.

Further preferably, the reducing agent required for the catalytic reduction is metered only when a defined temperature is reached. As a result of this embodiment, flooding of the catalyst reactor unit with reducing agent can be prevented, as long as a minimum temperature necessary for the catalytic reaction has not yet been reached.

Preferably, in addition to nitrogen oxides and C1 to C10 hydrocarbons, particularly CH ₄ reduced catalytically to C ₁₀ H _22, for which the coating of the catalyst elements comprising as catalytically active material suitable noble metals.

According to a preferred embodiment of the invention, a pyrolysis of the urea metered in upstream of the exhaust gas purification device takes place in a crude gas hood of the exhaust gas purification device, which adjoins the reactor housing on the input side. The exhaust gas flow is passed through the raw gas hood, which distributes the exhaust gas flow to the inlet openings.

In general, the exhaust gas purification device will operate in overpressure, which is due to the flow resistance of the catalyst reactor unit and the pressure of the exhaust gas flow from the internal combustion engine. However, the exhaust gas purification device is preferably operated under reduced pressure, which is generated by means of a fan arranged downstream of the catalyst reactor unit.

Preferably, the control of the dosage of the reducing agent in dependence on an operating point of the internal combustion engine, for which in particular a characteristic value from the engine control unit is used. The characteristic value from the engine control unit represents a quantity leading the exhaust gas flow, whereby the dosage of the reducing agent can be adjusted before the exhaust gas flow arrives at the metering device.

Further preferred embodiments of the invention are specified in the subclaims or to be taken from the following description of the figures.

The invention will be explained in more detail with reference to a drawing and the description below. Show it:

1 an exhaust system according to the invention and

2 a cross section through an exhaust system.

1 is a schematic view of an exhaust system according to the invention according to a preferred embodiment. An exhaust gas purification device of the exhaust system comprises a catalyst reactor unit 51 , with within one reactor housing 52 arranged raw gas cascades 60 and pure-case cascades 80 , The raw and clean cascades 60 . 80 can be arranged as shown in parallel to each other and in the flow direction of the exhaust stream. The crude gas cascades 60 as shown already before the entrance openings 53 opposite side of the reactor housing 52 end, or even adjoin them. Likewise, the pure cascade can 80 as shown already before the exit openings 54 opposite side of the reactor housing 52 end, or even adjoin them. The reactor housing 52 is with a fill 90 filled by catalyst elements. The catalyst elements comprise a support of foam metal, as well as a catalytic coating for the selective catalytic reduction (SCR) of nitrogen oxides. In an upper area of the reactor housing 52 is a storage silo 70 arranged while in a lower region of the reactor housing 52 a means of discharge 120 is arranged.

The crude gas cascades 60 are above entrance openings 53 fluidically with a raw gas hood 40 connected and pure-case cascades 80 are above exit openings 54 fluidically with a clean cover 100 connected. The crude gas hood 40 serves as a distributor for dividing the exhaust gas flow into the inlet openings 53 while the clean-up hood 100 as a collector for collecting the exhaust gas flow from the outlet ports 54 serves. Upstream of the raw gas hood is an exhaust gas supply line 50 arranged, which the supply of the exhaust gas stream from an internal combustion engine 10 in the raw gas hood 40 serves. At the exhaust gas supply line 50 are a first NO _x probe 20 , a metering device 30 and a first pressure sensor 150a arranged. An exhaust gas discharge 110 closes downstream of the clean cover 100 at. At the exhaust gas outlet 110 are a second pressure sensor 150b , a temperature sensor 130 and a second NO _x probe 140 arranged.

2 shows a view of a sectional plane AA through the catalyst reactor unit 51 the exhaust system. Inside the reactor housing 52 are in the vertical direction alternately Rohgaskaskaden 60 and pure-case cascades 80 arranged. The viewing direction is in the flow direction through the raw and pure cascade 60 . 80 and through that, to the pure cascade 80 subsequent exit openings 54 , The raw and clean cascades 60 . 80 include roof-like, extending in the flow direction elements, which are the raw and clean cascade 60 . 80 Limit to the top and can have a two-limb shape in cross-section. Through the roof-like, extending in the direction of flow elements of the raw and Reingaskaskaden 60 . 80 Form during filling of the reactor housing 51 with the bed 90 essentially bulk-free channels of the raw and pure cascade 60 . 80 below the roof-like, extending in the direction of flow elements.

Through the flow-free channels of the raw gas cascades 60 can the exhaust gas streams in the flow direction in the catalyst reactor unit 51 then penetrate through the bed 90 through to the pure cascade 80 to stream. By this construction, a uniform loading of the bed 90 with the exhaust gas flow 90 ensures and also reduces the flow of exhaust gas opposite flow resistance.

The in the 1 and 2 shown exhaust system shows the following operation:
The internal combustion engine 10 , which has a variety of cylinders, operates on the 2-stroke or the 4-stroke principle and burns fuel of different quality (residual oils, marine diesel MDO or marine gas oil MGO). Potentially used for internal combustion engines have compared with internal combustion engines of road vehicles usually relatively large displacement larger 5 Liters per cylinder, preferably larger 10 Liters per cylinder, but more preferably from larger 20 Liters per cylinder. The exhaust gas leaves the cylinders and enters an exhaust manifold. The exhaust manifold is connected to the exhaust gas supply line 50 connected.

As shown schematically by arrows, the exhaust gas flow passes or flows in sequence through the exhaust gas supply line 50 and the raw gas hood 40 , in which the exhaust gas flow in the form of several partial exhaust gas streams to the inlet openings 53 the crude gas cascade 60 is distributed. The partial exhaust gas streams flow at least partially through the raw gas cascades 60 and then from the raw gas cascades 60 through the bed 90 from catalyst elements to the pure cascade 80 , The exhaust partial streams of the pure cascade 80 then be in the clean cover 100 summarized and reach downstream in the exhaust gas discharge 110 , Subsequently, the purified exhaust gas flow can be supplied to a further use by heat extraction or discharged through a chimney to the atmosphere.

The reducing agent required for the selective catalytic reduction of nitrogen oxides is used as ammonia water or as an aqueous urea solution by means of the metering device 30 supplied to the exhaust gas stream. The upstream of the metering device 30 arranged first NO _x probe 20 determines the NO _x concentration of the exhaust gas. From the NO _x concentration, the required amount of reducing agent is calculated by means of the metering device 30 is metered into the exhaust stream. Alternatively, there is also the option of the required Determine the amount of reducing agent based on a characteristic value from the engine control unit.

The temperature sensor 130 , which at the exhaust gas discharge 110 installed, determines the temperature of the exhaust gas. Upon reaching a desired minimum temperature is started with the dosage of the reducing agent. The minimum temperature may be between 140 ° C and 270 ° C, depending on the exhaust gas composition. The operating temperature of the exhaust gas purification device may be between 140 ° C and 500 ° C.

The reducing agent in the form of an aqueous urea solution is thermolyzed in the exhaust stream and hydrolyzed, while the urea is degraded by means of chemical reaction to ammonia (NH ₃ ): (NH ₂ ) ₂ CO → NH ₃ + HNCO HNCO + H ₂ O → NH ₃ + CO ₂

This pyrolysis of urea takes place partially or even mainly in the raw gas hood 40 instead of. The exhaust gas mixed with the reducing agent becomes in the raw gas hood 40 further mixed and evenly through the raw gas cascades 60 the catalyst reactor unit 51 fed to the selective catalytic reduction. The exhaust gas leaves the raw gas cascades 60 and flows in turbulent form through the bed consisting of catalyst elements 90 in which the desired selective catalytic reaction occurs, which proceeds, for example, according to the following reaction equations: 4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O 4NH ₃ + 2NO ₂ + 2NO → 4N ₂ + 6H ₂ O 8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O

Excess ammonia is intermediately stored in the NH ₃ storing components of the coating of the catalyst elements.

Denitrification by an SCR causes deliberate and unwanted reactions, as there is no chemical reaction that is 100% selective. That is, there are also side reactions, some of which are desirable. Thus, the NO _X can be implemented in various ways in the catalyst. These different reactions compete with each other. Whichever prevails depends on different factors. Dwell time of the gas in the reactor, substance concentrations, the nature of the catalyst and above all the temperature are the determining factors. A theoretical assessment of which reaction predominates for a given catalyst at a given temperature is difficult. It is not always clear which mechanism (Eley-Rideal, Longmuir-Henschelwood) exists. In practice, equations for the reaction kinetics are usually determined empirically and their evaluation provides information about a possible reaction mechanism.

The catalyst elements of the bed 90 usually contain at least one oxide of a transition metal with atomic number 21 to 30, 39 to 48, 57 to 80 and 89 to 112, an alkali or alkaline earth metal compound and / or a compound of the third main or subgroup of the Periodic Table and / or a Rare earth metal or zinc compound or mixtures thereof.

The catalyst elements of the bed 90 have a length or diameter of z. B. 1 to 30 mm, preferably 2 to 8 mm, in the geometric shape of a tube, a Raschid ring, a ball, a cube of a cylinder or a plate, which consists of a foam metal, for. B. of iron oxide or nickel and a large porosity in the form of pores with a diameter of z. B. 100 to 2000 microns, preferably 400 to 1200 microns, and a large specific surface area of z. B. 8000 to 25000 m ² / m ³ , preferably 11000 to 18000 m ² / m ³ , have.

After the catalytically purified exhaust gas, the bed 90 , Leaves from catalyst elements, it passes downstream through the pure cascade 80 and the exit openings 54 in the clean cover 100 and from there into the exhaust gas discharge 110 ,

The second NO _X probe 140 connected to the exhaust pipe 110 is mounted, determines the NO _x concentration of the purified exhaust gas flow and provides the measured value as a further controlled variable of the metering device 30 available to minimize any NH ₃ slip or NO _X slip.

The cleaned exhaust gas passes through the exhaust pipe 110 to possibly further downstream exhaust treatment facilities, a device for heat extraction or through a chimney into the atmosphere.

In case of contamination of the catalyst elements 90 by accumulation of dusts, salts or metal ashes which may be formed in the engine during the combustion process, resulting in a decrease in catalyst activity, the contaminated catalyst elements from the catalyst reactor may be removed by means of a discharge means 120 , z. B. a rotary valve and discharged by slipping catalyst elements from the storage silo 70 be replaced. The decrease in activity is due to the second NO _x probe 140 determined.

In addition, by means of the pressure sensors 150a and 150b the total pressure loss of the exhaust gas purification device determined. If the total pressure loss exceeds a permissible value, commissioning of the discharge medium will start 120 a part of the bed consisting of catalyst elements 90 discharged and by slipping catalyst elements from the storage silo 70 replaced.

LIST OF REFERENCE NUMBERS

10

 engine

20

first NO _X probe

30

 metering

40

 Rohgashaube

50

 exhaust lead

51

 Catalyst reactor unit

52

 reactor housing

53

 entry ports

54

 exit ports

60

 Rohgaskaskaden

70

 storage silo

80

 Clean gas cascade

90

 Bed of catalyst elements

100

 Clean gas cap

110

 Flue gas discharge

120

 discharge means

130

 temperature sensor

140

second NO _X probe

150a

 first pressure sensor

150b

 second pressure sensor

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 3428232 A1 [0003]
• DE 10255612 A1 [0011]
• EP 1063396 A2 [0011]
• EP 1713584 A1 [0011]
• EP 1920834 A1 [0011]

Claims (16)

Exhaust gas purification device for reducing nitrogen oxides in the exhaust gas flow of an internal combustion engine ( 10 ) comprising (a) a catalyst reactor unit ( 51 ) with a reactor housing ( 52 ), which has a plurality of inlet and outlet openings ( 53 . 54 ), and a plurality in the reactor housing ( 52 ) and to the entrance openings ( 53 ) subsequent crude gas cascade ( 60 ) and a plurality in the reactor housing ( 52 ) and to the outlet openings ( 54 ) subsequent pure cascade ( 80 ) and (b) one, in the reactor housing ( 52 ) introduced by the exhaust gas stream through-flowing bed ( 90 ) of catalyst elements, wherein the catalyst elements comprise a support of a foam metal and a catalytic coating for the selective catalytic reduction (SCR) of nitrogen oxides. Exhaust gas purification device according to claim 1, characterized in that the foam metal of the catalyst elements comprises or consists of iron, iron oxide, chromium, aluminum and / or nickel or alloys thereof. Exhaust gas purification device according to one of the preceding claims, characterized in that the catalyst elements have a length or diameter of 0.5 to 30 mm, preferably 1 to 15 mm and particularly preferably 2 to 8 mm. Exhaust gas purification device according to one of the preceding claims, characterized in that the catalytic coating comprises at least one oxide of a transition metal with the atomic number 21 to 30, 39 to 48, 57 to 80 and 89 to 112 and / or at least one alkali and / or alkaline earth metal compound and / or at least one compound of the third main or subgroup of the periodic table and / or at least one rare earth metal or zinc compound or mixtures of these. Exhaust gas purification device according to one of the preceding claims, characterized in that the catalytic coating comprises a NH ₃ -sticherndes material, in particular aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO) or a zeolite of the type X, Y and / or ZSM-5. Exhaust gas purification device according to one of the preceding claims, characterized in that the catalytic coating comprises a catalytically active material for the conversion of hydrocarbons (HC). Exhaust gas purification device according to one of the preceding claims, characterized in that the crude gas and / or the pure cascade ( 60 . 80 ) comprise elements extending in the direction of flow. Exhaust gas purification device according to claim 7, characterized in that extending in the direction of flow elements of the crude gas and / or pure-hydrogen cascade ( 60 . 80 ) have a roof-like shape. Exhaust gas purification device according to one of the preceding claims, characterized in that the reactor housing ( 52 ) the catalyst reactor unit ( 51 ) Discharge funds ( 120 ) for discharging spent or contaminated catalyst elements, in particular a rotary valve, a screw conveyor or a double pendulum flap. Exhaust system for an internal combustion engine ( 10 ), comprising an exhaust gas purification device according to any one of the preceding claims. Exhaust system according to claim 10, further comprising a metering device arranged upstream of the exhaust gas purification device ( 30 ) for the metered addition of a reducing agent in the exhaust stream, in particular of ammonia (NH ₃ ) or a precursor compound thereof. Exhaust system according to one of claims 10 to 11, further comprising a burner disposed upstream of the exhaust gas purification device for increasing the exhaust gas temperature, which can be operated with a liquid or gaseous fuel, in particular with a boil-off of a liquid-gas tank. A method of operating an exhaust system according to any one of claims 10 to 12, comprising the following steps: I) providing an exhaust system according to any one of claims 10 to 12; II) introducing the exhaust gas stream into the catalyst reactor unit ( 51 ) through the entrance openings ( 53 ) and at least partially by the raw gas cascades ( 60 ); III) passing the exhaust gas flow through the bed ( 90 ) of catalyst elements; IV) discharging the exhaust gas stream from the catalyst reactor unit ( 51 ) at least partially by the pure cascade ( 80 ) and through the exit openings ( 54 ). A method according to claim 13, characterized in that a subset of the catalyst elements upon reaching a predetermined pressure drop and / or a predetermined NO _x -Renchaskonzentrationsschwelle from the device is discharged and replaced by not yet acted catalyst elements. Method according to one of claims 13 to 14, characterized in that the reducing agent required for the catalytic reduction is metered only when reaching a defined temperature. Method according to one of claims 13 to 15, characterized in that a pyrolysis of the urea metered in upstream of the exhaust gas purification device in a raw gas hood ( 40 ) of the exhaust gas purification device, which input side to the reactor housing ( 52 ).

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