DE19822591C2 - Denitrification device for internal combustion engines and method for denitrification of exhaust gases - Google Patents

Description

The present invention relates to a denitrification device for burning voltage motors according to the preamble of claim 1 and a method for Denitrification of exhaust gases from internal combustion engines according to the preamble of Claim 13.

The emission of nitrogen oxides from internal combustion engines represents a significant environmental pollution. In particular, internal combustion engines or Mo gates of motor vehicles used in road traffic have one large proportion of environmental pollution. Therefore, the emission of Nitrogen oxides increasingly restricted by the relevant laws.

The well-known three-way catalytic converters with a fuel-air mixture from Lamda = 1 operate significantly to reduce emissions contributed. Gasoline engines with such a three-way catalyst mostly the current regulations. However, this is essential for the ver more economical diesel and lean engines are not the case. The reason for that lies in the high excess of air during combustion.

NO _x storage catalytic converters for lean-burn petrol engines are known which initially store the nitrogen oxides in ma geren operation, a rich operation for regeneration of the storage catalytic converter then taking place. Especially in diesel engines that always work with excess air (λ <1), this would lead to an increase in fuel consumption. In addition, a high Oxidationswär me would result from the high oxygen content of the diesel exhaust gases, which lead to damage or destruction of the catalyst.

DE 196 26 837 A1 shows a NO _x accumulator through which the exhaust gas flow flows and which is separated from the exhaust gas flow for regeneration. The NO _x storage be for this purpose in a branch of the exhaust system, which can be closed by a flap. This branch is blocked off by a controller in order to regenerate the NO _x store. The exhaust gas is then passed through a second branch. A further NO _x store can be arranged in the second branch, which can be closed by a further flap.

However, a complex flap control is necessary to control the exhaust gas alternately through the various branches. In addition, is a double-flow system required, which leads to increased costs. Also the design a system with several flaps is complex.

JP 6-257426 A in Patent Abstract of Japan, Sect. M, Vol. 18 (1994) No. 660, describes a rotating NO _x accumulator which is divided into passages through which flow can pass, a cover element being provided on its input side in order to separate individual passages from the flow and to introduce a reducing agent there. However, there is a high consumption of reducing agent, with excess reducing agent being released into the atmosphere.

So-called Denox catalysts are also known, but only one Degree of conversion of max. Reach 50%. In addition, one Exhaust gas purification device for motor vehicles work reliably and free of Weak points must be in order to enable series production.

It is therefore the object of the present invention to provide a device and a Specify procedures whereby the emission of nitrogen oxides from Internal combustion engines, in particular of Otto and lean engines and Diesel engines, effective, inexpensive and can be reduced with little effort, a low consumption of reducing agent is possible.

This object is achieved by the denitrification device according to claim 1 and the method for denitrification of exhaust gases according to claim 13. Further  advantageous features, aspects and details of the invention result from the dependent claims, the description and the drawings.

The denitrification device for internal combustion engines according to the invention comprises: a Storage for the absorption of nitrogen oxide from a duct passed through the storage Exhaust gas flow, and a device for reducing and / or removing the nitrogen oxide from a region of the store which is separate from the exhaust gas stream, the store in flowable segments is divided and a cover element on its input side has, the segments by a relative movement between the cover and the memory are separable from the exhaust gas flow, and wherein the cover element as Cover is designed, which encloses an area of the memory, the Segments in the separated state form part of a gas cycle.

This effectively reduces the emission of nitrogen oxides, especially in the case of Diesel and lean engines, with the effort to manufacture and control the System is low.

Preferably, the memory is a rotatably mounted roller and the cover z. B. a cover for covering part of the input side or end face of the roller. The memory and the cover element are preferably rotatable relative to one another and the Segments can be operated alternately or one after the other and / or cyclically be covered and released again. Preferably the ratio between that covered part of the entrance side and the gas flow area 1% to 30%, preferably 1% to 10%.

A reducing agent is advantageously introduced into the separated section introduced. The nitrogen oxide can also be used with others Methods are reduced, for example by plasma chemical methods or by the use of microwaves. There is also the possibility of nitrogen oxides in the to desorb covered areas or segments again, e.g. B. by Heating with a microwave, and then returning it to the combustion. A double flow System is no longer necessary.  

The memory is advantageously provided with at least one alkaline element Nitrogen oxides absorbed, coated. Elements of the alkali group, the alkaline earth group or the rare earths used, whereby barium as has proven particularly suitable. Preference is also still precious metal, such as. B. Pt, Ru, Pa, Rh etc., in the coating. This makes it particularly effective Absorption of nitrogen oxides reached.

The reducing agent is advantageously also circulated, which is an advantage has that no excess reducing agent is released into the atmosphere.

A small opening in the separating device is preferably used to drive the gas circuit, e.g. B. attached to the exhaust gas flow side. This can make a small one Proportion of the exhaust gas flow drive the gas circuit.

According to a further aspect of the invention, a method for denitrification is proposed Created exhaust gases from internal combustion engines, comprising the steps of: driving one Exhaust gas flow through a memory to remove nitrogen oxide from the exhaust gas flow; Reduce and / or remove nitrogen oxide from a separate one from the exhaust gas flow Area of the memory, with segments of the memory due to a relative movement be separated from the exhaust gas flow between the memory and a cover element, and wherein a gas cycle is generated by the segments separated from the exhaust gas flow.

The memory can rotate relative to the cover, and in or out A reducing agent is preferably introduced in areas separated from the exhaust gas flow. In particular, the reducing agent can be conducted in a closed gas cycle become.

A preferred embodiment of the invention is described below with reference to the drawings described in which

Fig. 1 is a view of the denitrizer according to the invention shows a rotary absorber as a preferred embodiment; and

Fig. 2 shows a longitudinal section through the rotary absorber according to the invention.

Fig. 1 shows a view of the denitrification device with a rotary absorber 1 as a preferred embodiment of the invention. The NO _x accumulator or absorber 1 consists of a cylindrical body, which has a ceramic honeycomb or carrier structure 11 in its interior, and a housing, which is not shown in the figure. The absorber 1 has a low pressure loss geometry, ie gas can easily flow through it. Instead of the ceramic honeycomb body, wound or corrugated steel sheet can also be used to build up the memory or absorber 1 . The absorber 1 is segmented or divided into an individual flowable sub-areas or segments 11 a, which are formed in the support structure 11 . The cylindrical absorber 1 has an end face 12 which forms an input side through which the exhaust gas flow in the direction of Pfei les A reaches the absorber 1 . The exhaust gas flow is released again through a rear side 14 of the absorber 1 . At the input or end face 12 of the absorber 1 , a plate-shaped cover 2 is arranged, which covers a portion of the exhaust gas inlet side end face or end face 12 and the surface of which is aligned parallel to the end face. Thus, the covered part with the segments 11 a lying behind the cover 2 cannot be traversed by the exhaust gas. The cover 2 is firmly connected to the housing of the absorber 1 and forms a separating device.

The absorber 1 is rotatably supported about its longitudinal axis, so that with a rotation of the cylindrical absorber 1 always other segments 11 a are covered or opened again. Instead of the rotatable mounting of the absorber 1 , it is also possible to make the cover 2 movable, so that in each case under different areas of the input side 12 are covered. That is, in this case the absorber 1 is fixed and the cover 2 rotates about an axis that runs parallel to the longitudinal axis of the absorber 1 . In the preferred embodiment shown here, however, the cover 2, together with the housing (not shown in the figure), is immovable, while the cylindrical body is rotatable about its longitudinal axis, as shown by arrow B.

The carrier structure 11 is coated on the inside with at least one alkaline element which absorbs nitrogen oxides. Elements of the alkali group, the alkaline earth group or the rare earth group are advantageous here. Zeolites or silver can also be used. There is also a precious metal, such as. B. Pt, Ru, Pd, Rh, etc., in the coating 13th In the embodiment described here, the cylindrical support structure 11 is coated with barium, which is particularly suitable for the absorption of nitrogen oxides.

Behind the cover 2 there is an injector or a nozzle (not shown in FIG. 1) through which a reducing agent is introduced into the covered partial areas 11 a. It can be used as a reducing agent, for. As fuel, ammonia, urea, hydrogen and the like can be used. Furthermore, a partial fraction from the fuel is also suitable as a reducing agent. The reducing agent first ensures that the atmosphere is reducing. As a result, the nitrogen oxide absorbed or stored in the coated carrier structure 11 can be reduced to nitrogen.

In operation, the exhaust gas flows through the support structure 11 of the absorber 1 . In this case, the exhaust gas flow enters the absorber 1 at the end face 12 or input side, the exhaust gas not flowing through the part of the absorber 1 covered by the cover 2 . After the exhaust gas has flowed through the absorber 1 , it emerges again at its rear side 14 . While the exhaust gas flows through the absorber 1 , it is rotated about its longitudinal axis. When oxygen-containing exhaust gas flows through the absorber 1 from the internal combustion engine, nitrogen oxide is absorbed and bound in the carrier structure 11 . As a result, the nitrogen oxide is stored in the carrier. In addition to absorption, the nitrogen oxide can also be stored by adsorption or by a chemical bond, e.g. B. by nitrate formation. Mixed forms are also possible.

When flowing through, no exhaust gas gets into the covered segments of the absorber 1 . However, the rotary movement B ensures that the entire carrier or memory is loaded with nitrogen oxide. In addition, the parts of the support structure 11 which were previously loaded with nitrogen oxide, that is to say when flowing through them, reach the covered filling area. This separates the segments 11 a from the exhaust gas stream A.

Now the reducing agent described above is introduced via the nozzle arranged behind the screen or cover 2 . Thereby, the information stored in the substrate structure were Trä 11 nitrogen oxide in the separated portions or segments 11 a is reduced to nitrogen. After the reduction, these segments 11 a are flowed through again by the exhaust gas in order to again absorb nitrogen oxide in their walls.

The system is adjusted by a suitable choice of the segment size, the rotational speed of the carrier 11 or the absorber 1 and the amount of the reducing agent used so that the stored nitrogen oxide is converted almost completely into nitrogen with the least possible use of the reducing agent. It has been found that a particularly effective reduction takes place if the ratio of the covered area to the gas-flow area is between 1% and 10%. Generally a ratio between 1% and 30% is advantageous.

Fig. 2 shows a longitudinal section through a denitrification device, which is a further preferred embodiment of the invention. On the rotary absorber or storage 1 , a cover 20 is arranged as a separating or cover element, which is designed so that a closed gas circuit is maintained within the cover 20 during operation. For this purpose, the cover 20 covers a segment 11 a of the rotary absorber 1 over its entire length. In this case, an intermediate space 40 is formed between the enclosed areas of the absorber 1 and the cover 20 , through which the gas within the cover 20 after flowing through the covered segments 11 a is guided back to the input side 12 in order to enter the absorber 1 again to enter. The direction of flow of this closed gas circuit is indicated in FIG. 2 by the arrows C. The reducing agent flowing through the device or nozzle 3 for supplying the reducing agent into the interior of the cover 20 is circulated through this construction. This has the advantage that no excess reducing agent reaches the atmosphere or that there is only a small consumption of reducing agent.

At the front 20 a of the cover 20 , which faces the exhaust gas flow, there is a small opening 21 . This allows a small proportion of the exhaust gas flow A to enter the interior of the cover 20 , whereby the gas circuit C is driven within the cover 20 . On the abgasabge side 20 b there is another opening 22 through which escape of excess gas from the interior of the cover 20 is made possible. The drive of the gas circuit C can also in other ways, for. B. done by a fan.

In a further embodiment of the invention, which is not shown in the figures is, the nitrogen oxide is reduced by the use of microwaves. It can However, other methods can also be used, for example plasma chemical methods.

In a still further embodiment of the invention, a device for Microwave generation arranged on the denitrification device, whereby the nitrogen oxides in the covered segment by heating with the microwave be desorbed thermally. Then they become the Ver combustion supplied, d. H. exhaust gas recirculation takes place. This too design has the advantage that no double-flow system is required because the Separation of the gas spaces by the rotating roller by means of a cover Segment happens.

The present invention enables an effective and reliable Ent embroidery of exhaust gases from internal combustion engines, especially gasoline Lean engines and diesel engines. Through the configuration according to the invention a double-flow system can be avoided for the denitrification device, which reduces effort, increases reliability and reduces costs be wrested.

Claims (20)

1. denitrification device for internal combustion engines, with a store ( 1 ) for receiving nitrogen oxide from an exhaust gas flow guided through the store ( 1 ), and a device ( 3 ) for reducing and / or removing the nitrogen oxide from an area of the store separate from the exhaust gas flow ( 1 ), wherein the memory ( 1 ) is divided into flowable segments ( 11 a) and has a cover element ( 20 ) on its input side ( 12 ), and wherein the segments ( 11 a) by a relative movement between the cover element ( 20 ) and the store ( 1 ) can be separated from the exhaust gas flow, characterized in that the cover element ( 20 ) is designed as a cover which encloses an area of the store ( 1 ), the segments ( 11 a) forming part of a gas circuit in the separated state. 2. denitrification device according to claim 1, characterized in that the memory ( 1 ) and / or the cover member ( 20 ) are rotatable relative to each other, wherein the segments ( 11 a) are alternately and / or cyclically covered and released again during operation. 3. denitrification device according to claim 1 or 2, characterized in that the memory ( 1 ) is a rotatably mounted roller and the cover element ( 20 ) covers a portion of the input side ( 12 ). 4. denitrification device according to one of the preceding claims, characterized in that the ratio between the covered portion of the input side ( 12 ) and the gas flow area is between 1% and 30%, preferably between 1% and 10%. 5. denitrification device according to one of the preceding claims, characterized in that the reducing device ( 3 ) for supplying a reducing agent in the separated from the exhaust gas segments ( 11 a) is used. 6. denitrification device according to one of the preceding claims, characterized characterized in that the reducing device generates microwaves and / or for plasma chemical reduction serves. 7. denitrification device according to one of the preceding claims, characterized characterized in that the reducing / removal device is a heating device for includes thermal desorbing. 8. denitrification device according to any one of the preceding claims, further characterized by an exhaust gas recirculation device, in particular for recirculation of desorbed nitrogen oxides for combustion. 9. denitrification device according to one of the preceding claims, characterized in that the memory ( 1 ) has a carrier structure ( 11 ) with a coating ( 13 ) which comprises at least one alkaline element which absorbs nitrogen oxides, the alkaline element preferably from the alkali group , the alkaline earth group or from the group of rare earths, in particular barium. 10. denitrification device according to claim 9, characterized in that the coating ( 13 ) further comprises a noble metal, preferably Pt, Ru, Pd, and / or Rh. 11. Denitrification device according to one of the preceding claims, characterized in that an intermediate space ( 40 ) is formed between the enclosed region of the store ( 1 ) in order to return gas to the inlet side ( 12 ). 12. Denitrification device according to claim 11, characterized in that the cover ( 20 ) has an opening ( 21 ) for supplying part of the exhaust gas flow into the gas circuit. 13. A process for the denitrification of exhaust gases from internal combustion engines, comprising the steps:
Guiding an exhaust gas flow through a store ( 1 ) in order to remove nitrogen oxide from the exhaust gas flow;
Reducing and / or removing nitrogen oxide from an area of the store ( 1 ) which is separate from the exhaust gas flow;
segments ( 11 a) of the accumulator ( 1 ) being separated from the exhaust gas flow by a relative movement between the accumulator ( 1 ) and a cover element ( 20 ), characterized in that a gas circuit is generated by the segments ( 11 a) separated from the exhaust gas flow. 14. The method according to claim 13, characterized in that the memory ( 1 ) rotates relative to the cover element ( 20 ). 15. The method according to claim 13 or 14, characterized in that the cover element ( 20 ) covers part of the input side ( 12 ) of the memory ( 1 ) and sweeps over the input side ( 12 ). 16. The method according to any one of claims 13 to 15, characterized in that the memory ( 1 ) rotates while the cover element ( 20 ) is fixed, so that the segments ( 11 a) separated from the exhaust gas stream by rotation of the memory ( 1 ) be released again. 17. The method according to any one of claims 13 to 16, characterized in that a reducing agent is introduced into the segments ( 11 a) separated from the exhaust gas stream. 18. The method according to any one of claims 13 to 17, characterized in that the gas circuit is driven by the segments separated from the exhaust gas flow ( 11 a) by the exhaust gas flow. 19. The method according to any one of claims 13 to 18, characterized in that the Reduction / removal of nitrogen oxide by microwaves, plasma chemical reduction and / or by thermal desorbing. 20. The method according to any one of claims 14 to 19, characterized in that the Rotation speed and / or the amount of reducing agent supplied is controlled.