SK24693A3 - Device for catalytic reduction of nitrogen oxides - Google Patents

Abstract

The appts. has a redn. catalyst (5), in an oxygen-contg. exhaust gas pipe, and an urea container (7) connected to a spray nozzle (9) for finely spraying urea soln. onto an evaporator (3). The evaporator (3) is in the form of a flow mixer. Pref. the flow mixer acts as a hydrolysis catalyst comprising a support structure coated with a 90-10:10-90 wt. ratio mixt. of Al2O3 and TiO2, SiO2, ZrO2 and/or H-zeolite.

Description

Equipment for catalytic reduction of NOx

Technical field

The invention relates to an apparatus for the catalytic reduction of NOx in combustion products.

which contain oxygen. using urea.

with a reduction catalyst contained in the flue gas exhaust, as well as a urea tank.

which is connected by means of the supply device to the flue gas stream.

In this case, the feed device has a spray nozzle through which the liquid urea solution can be finely sprayed onto the evaporator.

BACKGROUND OF THE INVENTION

The use of urea as a reducing agent for the reduction of nitric oxide by selective catalytic oxygen-containing products is known, for example, from DE-OS.

045. Held et ol, UAE 900

496 (1990), pages 13-19.

Urea minimizes the use of toxic and intense ammonia and thereby transporting and storing ammonia that require appropriate precautions.

In the known processes, the urea solution is preheated under direct spraying conditions into the flue gas line upstream of the reduction catalyst. These processes produce unexpected reduction products. In urea thermolysis, urea disintegrates to form non-fusible cyanidic acid to form a gas such as carbon dioxide and ammonia. when heated to a temperature above the melting point, i.e. 133 ° C. When the urea is heated to 130 ° C to 250 ° C, HNCO sublimes under partial decomposition to ammonia and reactive isocyanic acids. The rest remains biuret.

acid to cyanide and amelide. Formation of cyanide acid.

amelide and other substances are very detrimental to the gasification of urea.

because solid urea is first of all liquid urea.

then again solid non-fusible substances.

According to DE 40 38 054, the solution consists in this. that the urea is finely atomized through a nozzle onto the hydrolysis catalyst. This results in the hydrolysis of the urea to ammonia and carbon dioxide through a temperature range of 180 [deg.] C. to 550 [deg.] C. important for reduction catalysis.

SUMMARY OF THE INVENTION

The object of the invention is to further develop a device according to DE 40 38 054. in order to reduce the space requirement of the flue gas treatment plant necessary for installation in a vehicle, consisting of an evaporator, hydrolysis and a reduction catalyst, ensuring the urea decomposition into ammonia and carbon dioxide.

Qualitative decay means a degree of efficiency above

99.9%, the following unexpected side effects are significantly reduced:

depositing urea at the inlet of the catalyst;

a coating on the controlled reduction catalyst, i. uncontrollable accumulation effects:

- urea penetration and generation of urea particles.

The object is solved by the features of the invention according to the main claim.

The invention is based on knowledge. that the degree of urea decomposition efficiency by the use of an evaporator or by hydrolysis in indirect channels exceeds 99.9% and thus the incidence of the above-mentioned side effects may be reduced.

According to the invention, the evaporator is provided with thin indirect channels which are interconnected through grooves and small openings in a flow connection. By this embodiment, the urea solution nebula emerging from the nozzle is divided into a plurality of jet filaments which are inverted within the evaporator, partially joined together and separated again. This ensures that the droplets of the solution are brought into contact with the hot-water channel wall as quickly as possible. Connection between the channels also permits partially transverse flows due to pressure differences within adjacent channels. The cross-flow ensures an even distribution of the solution stream or vapor throughout the cross-section of the evaporator and the associated reduction catalyst.

This division can be promoted by splitting the mainstream evaporator into two or more portions when the portions are spaced one behind the other. By spacing between them, intensely perpendicular flow components can be induced when the evaporator covers differently in cross section.

The evaporator arrangement described above is successfully avoided.

that the drops of urea solution flow through the evaporator without contact with the channel walls and thus do not evaporate.

The evaporator preferably consists of a metal having a high thermal conductivity, the channels being separated from each other by a very thin metal wall having grooves or cross-flow openings.

The metal walls allow a rapid heat supply to the solution distribution point and thus evaporate the droplets. A cold passage such as that found in ceramics is avoided.

Such an evaporator is preferably made of a suitable profiled, thin metal foil having inter alia grooves or openings. The foil is rolled in one in spirals or at larger diameters in several turns to form the evaporator and covered with a cylindrical sheath. The profiles are designed so. that after rolling, they form essentially axial channels but which do not run straight but have turns. which occur as quickly as possible at short distances of 5 to 10 mm.

The channels and also the grooves or holes preferably have a diameter in the range of a few millimeters, in particular between 0.5 and 2 mm.

According to another embodiment of the invention, the walls of the evaporator ducts are overlaid with an absorbent material. which is porous due to surface enlargement. Such a catalytic overlay captures drops of solution and causes a quantitative conversion of the urea solution to ammonia and carbon dioxide and avoids an unexpected side effect.

Sufficient acceleration of evaporation with hydrolysis and inhibition of unexpected by-products is applied to all of the urea water mist on the components. with particular contact with the support structure of the fine inorganic oxide catalyst. Inorganic oxides must be resistant to flue gases from diesel engines at temperatures up to 700 ° C and their porous structure must remain stable for many thousands of working hours.

Therefore, alumina mixtures are used. titanium dioxide, silica, zirconia and / or H-zeolite in a weight ratio between alumina and other oxides of 90: 10 to 10 90.

The use of a mixture of metal oxides containing H-zeolite provides the catalyst with sufficient activity for selective catalytic reduction of NOx with ammonia, thus reducing the volume of the reduction catalyst to 10-30 X. H-mordenite has proven to be H-zeolite resistant to flue gas from a diesel engine. H-ZSM5 and an aluminum-free cracking catalyst containing silicon.

The fine particle metal oxides introduced in the claim are particularly effective, but may still be supplemented with the following carriers, alone or in admixture; niobium pentoxide, tantalobium pentoxide. tungsten oxide, aluminum silicate and other zeolites such as aluminum-free cracking catalysts.

The evaporator or catalyst is preferably located in the flue gas outlet where it is fixed downstream of the reduction catalyst. This has the advantage that the heat from the flue gas stream is used directly for evaporation and hydrolysis. The flue gas, which also flows through the evaporator, ensures the transport of the urea mist. The evaporator preferably occupies the entire cross-section of the flue gas outlet. However, it is also possible to design a smaller evaporator. allow a partial flow of flue gas to flow around it in order to achieve a homogenous temperature.

In order to further reduce pollutants, an oxidation catalyst can also be placed in the flow direction in addition to the reduction catalyst. According to another embodiment of the invention, the evaporator and the catalysts can be combined into a single housing in which at least one absorption evaporator is also integrated. The absorbent evaporator can be technically simple to be threaded and can be provided with a passage through which the gas can reach the expansion space filled with absorbent material, for example mineral wool or metal wool, when the flue gas oscillates. This evaporator is arranged downstream of the catalysts. Preferably, the sleeve already has a mixing device in the region of the flue gas inlet, i.e. before mixing the flue gases and the urea solution.

When the evaporator is positioned over the entire flue gas cross-section, spiral disks are formed on one side of the flue gas inlet to distribute the mist of the solution with the urea preferably supported in the evaporator cross-section.

For example, the spiral disk may be so constructed.

wherein the flue gas stream is vortexed into the urea solution stream.

so that there is already a vigorous mixing before the evaporator and thus a good distribution of solution drops into the evaporator.

As a spray nozzle, a pressure spray nozzle is provided which is connected to an inlet duct, at the other end of which a pressurized air duct and a urea solution inlet duct, i.e. a pressurized air duct flows into the urea solution duct as close as possible to the storage tank. solution. In this way, a further gas / solution mixture can be achieved before exiting the nozzle, which promotes the finest possible dispersion of the solution. The inlet duct, which is filled with compressed air and urea solution, uniformises the solution unevenness due to the dosing, so that a uniform flow of solution is ensured in the pressure spray nozzle.

The urea solution storage tank is preferably a pressure vessel which can be connected to the same pressure network.

I

- 6 air.

By means of a pulse solenoid valve, the supply of urea solution can be dosed more precisely in conjunction with the pressure tank.

Measures against crystallization of urea are not necessary.

in addition, an indirectly controlled pump is not necessary. The control of the urea solenoid solenoid valve is dependent on the load and speed of the flue gas-fired combustion machine.

Thereby, the need for the urea solution can be adapted to the operating conditions and the NOx concentration of the flue gas, so that ammonia build-up of the released urea solution on the reduction catalyst is prevented and thus the operation of the reduction catalyst is ensured without further conditions.

Dosing can take place in the presence of the NOx sensor proportionally to the mass flow in the flue gas.

The urea solution is incompletely decomposed at low temperature.

Come

160 ° C. with formation of their ammonia and carbon dioxide products.

It is therefore advisable to override the temperature control, which, if the temperature of the flue gas in the region of the catalyst exceeds the set value, makes it impossible to supply the urine solution.

The spray nozzles are also preferably optionally integrated in the evaporator housing. In order to reduce the deposition of urea crystals t inside the casing and the components present therein, at least the circuit coming into contact with the urea solution is provided with a thermally conductive solution retaining cover, droplets coming into contact with the walls rapidly causing evaporation and hydrolysis.

Description of the drawings

The drawings show schematically exemplary embodiments of the invention. Here it shows:

Fig. 1 shows a flue gas system of an internal combustion machine with a first embodiment of FIG. 2 shows a detail of FIG. 1 shows another embodiment of FIG. 4 and 5 show another exemplary embodiment in cross-section or longitudinal section of FIG. 6 and 7, another example of FIG. 6A. B detail according to FIG. 6 fig. 7A is a detail of an embodiment of the input.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 shows a combustion machine 1 with a corresponding exhaust gas outlet 2. To reduce NOx, a reduction catalyst 5 is included in the flue gas outlet 2.

The reducing agent used is ammonia, which is obtained by the decomposition of the urea solution 6. The urea solution 6 is located in the pressure tank 7 and is transformed within the flue gas exhaust 2 using the flue gas heat 12, evaporation and hydrolysis to ammonia and carbon dioxide. This gas is mixed with the flue gas 12 into the reduction catalyst 5.

For the reaction of the urea solution 6, according to FIG. 1, an evaporator 3 and a hydrolytic catalyst 4 are provided upstream of the reduction catalyst 2 in the exhaust gas outlet 2. The evaporator 3 is formed from two parts 3a, 3b, both parts of which adhere to the gaps 8 arranged behind the reduction catalyst.

3a. 3b of the evaporator are with each other.

they consist of a thermally conductive co-forming sheet which is a mixture so that they can cause radial and / or flowing inside. This will be as fast as possible and

Parts 3a, shaped

3b on the evaporator 3 of the torque component with the most perfect heat transfer to the urea solution. In addition, the same distribution of the urea solution and of the resulting gases over the entire cross-section of the evaporator 3 and the hydrolytic catalyst must be achieved with the possibility of cross-flow. The gap 8 between the two parts of the evaporator 3a and 3b also contributes to the homogeneous distribution.

In FIG. 2, an embodiment of the evaporator 3 is shown in detail. The evaporator 3 consists of a plurality of substantially longitudinally extending channels 20 with a small diameter of about 1 or 2 mm. As shown in detail in section, the channels 20 do not run straight. but with turns 21 that follow at short intervals. The walls 22 of the ducts 20 consist of thin sheets which are provided with openings or bores 23 allowing partial flow from one duct 20 to the adjacent duct 20. The bores 23 shown in FIG. 2 on the straight section of the ducts 20 can also be formed in the turn 21, whereby the separation of the fibers at one location and the connection of the gas fibers at another location can be even more efficient.

Evaporator 3, preferably catalytically overlayed, as described above, must be prevented that first, droplets of solution from the evaporator 3 can enter the evaporator 3 and that, secondly, the uneven distribution of the solution at the inlet of evaporator 3 continues through the entire evaporator 3. rolled, profiled sheet equipped with suitable bores 23.

The conversion beginning with the urea thermolysis in the evaporator 3 is completed on the hydrolytic catalyst 4. The hydrolytic catalyst 4 formed with a number of thin channels or in the evaporator 3 embodiment contains as active components mixtures with fine particles of metal oxides such as alumina with titanium dioxide, silicon dioxide. zirconium dioxide and / or H-zeolite, wherein the weight ratio between alumina and other oxides may vary from 90: 10 to 10: 90, achieving a layered support structure at a concentration of 40 to 220 g / l and preferably 60 to 160 g / 1 mixtures of metal oxides per carrier volume. The active component is used at a spatial velocity above 30,000 h ^-1 at least between 240 and 650 ° C.

To reduce the space requirement, the evaporator 3 and hydrolytically

catalyst 4 produced preferably than building part 34. as is illustrated on the Fig. Third Onto It was can be used evaporator 3 created than jet mix . than shows Fig. 2

the channel walls 22 are provided with a catalytically active metal oxide overlay. as mentioned earlier. A porous overlay promotes a hydrolytic process.

The action of the separated or combined hydrolytic catalysts 4 occurs when the urea solution 6 enters the apparatus as a fine mist, i.e. with very small droplets. For this, the component 34 is equipped with a pressure spray nozzle

9. Compressed air and urea solution 6 enter inlet 10. The compressed air line 11 opens into the inlet conduit 10 as close to the pressure tank 7 as possible, thereby ensuring sufficient mixing of the compressed air with the urea solution 6. From the compressed air line 11, a second compressed air line 11 'is separated with a pressure control valve 13 for the pressure tank 7.

Essential for the quantitative conversion of urea solution 6 to ammonia and carbon dioxide while reducing by-product formation is the very rapid heating of solution 6 to about 350 ° C and rapid hydrolysis. This can, in addition to the measures described above, be favorably ensured by further measures by suitably mixing the flue gas 12 into the mist from the urea solution 6.

Fig. 1 shows a simple embodiment in which the pressure spray nozzle 9 is arranged in the middle of the straight flue gas outlet 2 and is bypassed with the flue gas 12. The mist of the solution is entrained by the flue gas flow 12 and carried to the evaporator 3.

In FIG. 3, another arrangement is shown which allows the flue gas to be mixed with the mist solution prior to entering the evaporator 13 or component 34. The component 34 is located in the housing 30. an inlet conduit 10 protrudes from its front side 31 from its pressure spray nozzle 9 in the pre-chamber. In this case, the flue gas 12 is introduced into the pre-chamber 32 in a tantalizing manner. The flue gas flow 12 thus generated is intensified by the rotating disc 33 in the second region of the antechamber 32. The flue gas 12 then flows through the rotating disc 33 in the second periphery of the antechamber 32 in which the pressure spray nozzle 9 is located. and mixed with the flue gas 12. This mixture then enters the component 34.

In the housing 30 is located behind the component 34 a reduction catalyst 5 and also a sequential oxidation catalyst 35. In addition, an absorber evaporator 366, which is designed as a funnel inlet tube 37, provided with openings 38, is integrated in the housing 30, Expansion space 50 may be filled with a steel string 51, for example. The cleaned flue gas 12 '* is discharged through a clean pipe section 2' 'or freely discharged. The cross-section of this clean section 2 '‘corresponds to the cross-section of the flue gas outlet 2. Prior to mixing the flue gas 12 with the urea solution 6, sound insulation may also be performed. For this purpose, the anterior chamber 32 is lined with a soundproofing lining.

The flue gas 12 with ammonia and carbon dioxide is introduced from the component 34 into a reduction catalyst 5 in which the NOx is reduced in a known manner.

In order to ensure the operability of the described reduction system ΝΟχ, it is necessary to release the reduction catalyst 5 from the excess ammonia. For this purpose, the system is provided with a regulator 15 which regulates the dosing of the urea solution feed 6 by means of the solenoid valve 16, depending not only on the engine speed, but also on its load. This feeds the urea solution 6 corresponding to the need, i.e. the NOx content of the flue gas 12, so that the ammonia released by the hydrolysis is completely introduced into the reduction process. The control procedure is also provided by signals from two temperature sensors 17 and 18 which monitor the temperature of the flue gas 12 in the pollutant conversion area. If the temperature sensors 17, 18 signal a temperature below a set value. when a complete conversion of the urea solution to ammonia is not possible, the supply of the urea solution 6 is prevented until the desired temperature in the flue gas system is reached again.

Another measure that supports trouble-free operation of the system.

is an overlay of the antechamber 32 which comes into contact with the urea solution. material.

which, by thermal conductivity and active components according to claims 9 and 10, prevents settling of the urine crystals even by their early evaporation and hydrolysis.

Thermal insulating measures may also be provided on the housing 30 and the pressure spray nozzle 9 and / or other part may be heated. Heating of the inlet conduit 10 and the pressure spray nozzle 9 is prevented. in particular, small urea crystals deposit in the nozzle 9.

Breakthrough of ammonia through the reduction catalyst 5 is possible under prolonged operation below 300 ° C. since the active ammonia storage centers are overloaded. How auxiliary measures are =

(1) Discharge of the entire catalytic converter design so that also the short-term phases of the engine acceleration highly heat the reduction catalyst 5 above the minimum temperature required for ignition,

2) stop dosing of the urea solution 6 by control until the minimum traffic temperature is reached.

In FIG. 4 and 5, a further embodiment of gas mixing is provided by a conical guide plate 40, on which the pressure spray nozzle 9 protrudes on its narrow side and around which the flue gas 12 flows. fed to the housing 30 through a flue gas outlet 2. Between the internal pressure P2 and the external pressure pi a pressure drop p = Pi - P2 occurs. which moves the beam of flue gas 12 at a speed V _and flue gas. The individual rays of flue gas 12 enter the spray cone 44 of the urea with air and mixing takes place. By selecting the diameter and distance of the wall openings as well as the distribution between the pressure spray nozzle 9 and the hydrolytic catalyst 4, the mixing of the urea into the flue gas 12 can be controlled.

variant for it is shows FIG. and 6. na which my mixing equipment 60 three rows guide slots 61 until 63rd which are regularly divided into districts areas m. n.

By means of the guide grooves 61, 63, the flue gas 12 acquires a rotational movement which in the first region m and in the third region o supports the flue gas particles 64, 65 in the direction of the inlet rotation. whereas the second guide groove 62 causes a reversal of the rotational movement in the second region n of the mixing device 60. In FIG. 6A shows a cross-section through a second region ⁱⁿ which the second guide grooves 62 distributed at the periphery cause the flow of the third beam 66 of the flue gas particles to be reversed. In the first and third regions m, o, the guide grooves 61, 63 are directed such that the flue gas particle beams 64, 65 retain their current flow direction.

By reversing the rotary motion, a strong turbulent flow is produced in the region between the pressure spray nozzle 9 and the hydrolytic catalyst 4. This leads to mixing of the mist of the urea solution 6 into the flue gas stream 12. By repeatedly reversing the rotary movement, the mixing process can be intensified.

Another variant is shown in FIG. 7, in which the funnel-shaped mixer 70 is provided with a plurality of inlets 71 having a plurality of manifold plates 72 that provide rotational movement of the incoming individual flue gas streams 73. The distribution plates 72 are arranged in a bow-like manner, so that a plurality of individual flue gas streams 73 flow in the inner region 74 of the mixer 70 and provide a strong turbulent flow which causes good mixing of the flue gas 12 and the mist of the urea solution 6.

Combinations may also be used for guide plates 72 accelerated and / or circulating. as they move rapidly according to FIG. 7th

it is the division of flue gases into numerous partial streams. Here, some of the partial streams 5 and others can be introduced into a rotary one

The reaction of the urea solution to ammonia and carbon dioxide is described in more detail below by means of two exemplary embodiments.

t3

Example 1

In the heated quartz tube, the metal support honeycomb of the groove type with transverse flow generation according to FIG. 2. length 43 mm, covered with metal oxides of composition A according to the table

1. Spray from adjustable pump-driven micro-jet. 18.8 ml / h of urea solution at a concentration of 32.5% by weight, while the O2 gas mixture flows through the catalyst. HC (200 ppm Ci). CO (100 ppm), CO2 (20 ppm) and water vapor (£ 5). The gas mixture velocity (2480 l / h) is 60,000 h ^-1 . The gaseous mixture flows for analysis on a long path cell (optical path length 2 m) heated to 110 ° C. The spectrum shows the formation of ammonia (2000 ppm) and carbon dioxide (1000 ppm) with a molar ratio of 2: 1, corresponding to complete hydrolysis of urea according to the equation:

C0 (NH2) 2 * H2O in the temperature range of 160 ° C to h at 200, 300 and 400 ° C of catalyst through a condenser and condensate with quantitatively all temperatures from 5 to 10 conversion of urea 51 99.97

-> 2NH3 + CO2

600 [deg.] C. In a long-term experiment of 8, the gas mixture is passed after leaving the sublimate at the inlet to the condenser and analyzed. Sublimate consists of mg urea. This can be realized

Comparative Example 1a

Example 1 is repeated. A metal support honeycomb of a conventional type with parallel channels of 43 mm in length shall be used. Overlaid with metal oxide mixtures, composition A in Table 1 ä, experiments for catalytic hydrolysis of urea are repeated under almost identical conditions. The molar ratio of NH3 / CO2 2 ^: 1 is also observed in the spectrometer on the other hand. 6

Comparative Example 1b

Example 1 is repeated. An uncoated metal layer of a honeycomb of the conventional type with parallel channels extending 43 mm in length is used. In addition to NH3 and CO2, the spectrum shows the occurrence of HNCO. There is a massive return to urea. At 200 ° C 68 300 ° C 79%, 400 ° C 83%.

Examples 2 to 7

In a further series of experiments, 2000 ppm NO is added to the gas mixture under nearly the same conditions. While the catalysts having an A to C overlay according to Examples 7 to 9 provide NOx reduction of at most from 10¾. The catalysts with overlapping D and E according to Examples 10 and 11, depending on the NO temperature, produce a reduction of between 15 ¾ at 300 ° C and 35 µl at 500 ° C.

Example 12

The 12-liter six-cylinder diesel engine with optimally adjusted diesel fuel consumption with a sulfur content of 0.045 ¾ and conventional commercial engine oil is used for flue gas production. The engine is operated in a 13-stage test according to 88/55 / EVG. The aim of the experiment was to reduce the limit pollutants by 11 g NDx / kVh, 3.5 g CO / kVh and 1.1 g HC / kVh by at least 70 *. As a reducing agent, a 32.5 ¾ solution of urea in water is sprayed with the dosing device shown in FIG. 1 for the catalyst system of FIG. 3. The following catalysts were used:

1) Hydrolysis catalyst. RG 90 000 h ^-1 , active components:

a mixture of metal oxides of composition A according to Table 1. carrier: metal honeycomb according to FIG. Second

2) Reduction catalyst, RG 30 000 h ^-1 , active components:

V2 O5 / VO3 / T and O2 on metal honeycomb.

3) Oxidation catalyst, RG 90,000 h ^-1 . active components:

platinum on a metal honeycomb stabilized with alumina.

As a result of flue gas treatment, it was found: 3.2 g ΝΟχ / kVh (71 *). 0.9 CO / kVh (74%). 0.22 g HC / kVh (80%). Extraction of the particles with hot HaO / isopropanol and gravimetric determination of urea show a penetration of 2 mg / kVh of urea. This small value indicates that urea penetration cannot cause a measurable increase in particle weight. No deposits of urea or urea products were found in the catalyst inlet region. Reducing the reducing agent. which is an aqueous urea solution, occurs above a flue gas temperature of 250 ° C. with an amount of urea solution 75% equivalent for NOx removal.

Example 13

Engine test test conditions. as described in Example 12 is repeated with the ^following catalyst: ........

1) Hydrolytic catalyst RG 90,000 h ^-1 , active components according to composition D according to Table 1. Carrier: metal honeycomb according to FIG. Second

2) Reduction catalyst, RG 366,000 h ^-1 , active components and support as in Example 12.

3) Oxidation catalyst as in Example 12.

As a result of the flue gas treatment, 3.2 g ΝΟχ / kVh (71 fc) was found. 0.9 g CO / kVh (74%) and 0.24 g HC / kVh (22. Urea penetration was 2.5 mg / kVh).

Table 1

Active components of hydrolysis catalysts in g / l.

Al2O3 T1O2 SiO2 Zr02 H-modern H-ZSM-5 A 120 - 40 10 - - B 90 60 10 '- - - C 30 110 10 - - - D 70 - - - 70 - E 70 - - - 70

Examples A to C correspond to the prior art, examples D and E correspond to claim 9.

Examples of hydrolysis catalyst production

Metal honeycomb 0 35 mm. the length of 43 mm is shortened in an aqueous suspension of 25% by weight. Al 2 O 3, SiO 2 and ZrCl 2, weight ratio = 4 = 1. Composition A and excess excess material is blown off by overpressure. It is dried at 120 ° C and calcined for 5 hours at 700 ° C. Compositions B to E are analogous.

Claims (22)

PATENT CLAIMS 1) Apparatus for catalytic reduction of ΝΟχ in oxygen-containing products using urea, with a reduction catalyst contained in the flue gas exhaust, as well as a urea tank connected via an inlet device, for example consisting of an inlet line and a solenoid valve, to a spray nozzle The liquid urea solution is finely sprayed into the evaporator, characterized in that the evaporator (3, 34) is designed as a flow mixer. Device according to claim 1, characterized in that. The evaporator (3, 34) is adapted to divide the stream of the urea solution (6) into the flow fibers, to reverse them, divide them and join them. 3) Device according to claim 1 or 2, characterized in that the evaporator (3 or 3a, 3b) is formed in two or more parts in the flow direction, and a gap (8) is formed between two successive evaporator parts (3a, 3b). Device according to any one of the preceding claims, characterized in that the evaporator (3, 34) is made of metal and consists of channels (20) running substantially in the direction of flow, which are interconnected within the evaporator (3, 34). . Device according to claim 4, characterized in that. The channels (20) are provided with a turn (21) and the walls (22) of these channels (20) are provided with bores (23). which are formed at least in part perpendicular to the main flow direction. f / 6) Device according to claims 4 or 5, characterized in that 7) channels (20) mi 1m, The devices characterized by the boreholes (23), in particular, have a cut below 2 mm. Some of the walls overlap with a diameter in the region of their previous units and claims. (22) evaporator channels (20) (3) with both fine and particulate organic oxides. 8) Device according to one of the preceding claims. characterized by. that the evaporator (3) is constructed as a building 9) part (34) p Equipment hydrocata with lysator. according to claim 7, 8th characterized in that the overlaying of the component (34) is carried out by a mixture of alumina with titanium dioxide. silicon dioxide. zirconium dioxide and / or Wherein the weight ratio between aluminum oxide and the other components i is 90: Device according to claim 9, characterized in that. wherein the overlay of the component (34) is carried out at a concentration of 40 to 220 gl ^-1, preferably 60 to 160 gl ^-1 , of the oxide mixture per volume of the component (34). Apparatus according to claim 9, characterized in that the lamination of the component (34) is carried out by an H-containing oxide mixture. Device according to one of the preceding claims, characterized in that the evaporator (3) or the component (34) is located in the flue gas outlet (2) downstream of the reduction catalyst (5). 13) Device according to claim 9, characterized in that. The process according to claim 1, characterized in that an oxidation catalyst (J5) is arranged downstream of the editorial catalyst (5) in the flow direction i and the flue gas (12). Device according to claim 10, characterized in that. 3. The method according to claim 1, characterized in that a reduction catalyst (5) and possibly an oxidation catalyst (35) and an absorber evaporator (36) are integrated in the housing (30) for the component (35). A device according to any one of the preceding claims, characterized in that. The rotating discs (33) are formed on one side of the stream upstream of the evaporator (3) or the component (34). Device according to any one of the preceding claims, characterized in that. The spray nozzle (9) is designed as a pressure nozzle and is connected to the reservoir (7) by an inlet line (10) and a solenoid valve (16), the compressed air line (11) entering the inlet line (10) as close as possible to the tank (7). ). Device according to claim 13, characterized in that. The solenoid valve (16) is pulse controlled. Device according to claim 14, characterized in that. The solenoid valve (16) is connected to an apparatus for determining the load and speed of the internal combustion engine and optionally the NΟχ sensor. 19) Device according to claims 14, characterized by. The solenoid valve (16) is connected via a regulator (15) to the thermal sensors (17, 18). It is preferably provided before entering the evaporator (3) and leaving the reduction catalyst (5). Device according to one of the preceding claims, characterized in that. The spray nozzle (9) is integrated in the jacket (30) of the evaporator (3) or component (34). wherein the inner walls of the shell (30) are provided at least in the area in contact with the urea solution with a porous overlay, preferably of inorganic oxides. Device according to one of the preceding claims. characterized by. that it is equipped with a mixing device (33. 40. 60. 70) to split the flue gas (12) into partial streams (64, 65). and conversion. which is located in the flue gas outlet (2) in front of the mixing point of the mist of solution (12). (66) urea into flue gas Device according to one of the preceding claims, characterized in that the catalysts (34, 5, 35) are thermally insulated by an air gap (53).