AT507105A1 - METHOD AND DEVICE FOR CLEANING EXHAUST GASES INVOLVED IN COMBUSTION PROCESSES - Google Patents

Description

The invention relates to a process for the purification of exhaust gases obtained in combustion processes with a dust content of> 5 g / m 3 and nitrogen oxides NOX, wherein the exhaust gases are catalytically de-nitrogenized in a catalyst with several parallel flow channels and dedusted before discharge into the atmosphere.

The present invention also relates to an apparatus for purifying exhaust gases obtained in combustion processes with a dust content of> 5 g / m 3 and nitrogen oxides NOX, with a catalyst having a plurality of parallel flow passages for catalytic denitrification of the exhaust gases and at least one filter stage arranged downstream of the catalytic converter for dedusting the exhaust gases Exhaust gases before exiting into the atmosphere.

In a number of combustion processes, exhaust gases accumulate, which contain a high dust content and nitrogen oxides N0X.

For example, in the cement clinker production, the raw materials, especially limestone, clay and silica are burned in an oven to cement clinker and then ground and filled into appropriate containers. For firing the raw materials so-called rotary kilns are preferably used, which are heated to temperatures of 1350 to 1700 ° C, which are required for the cement clinker formation. The raw materials are usually preheated in a preheating tower consisting of several consecutively arranged cyclones before they enter the rotary kiln. The exhaust gases flow through the production process in countercurrent to the material flow and, after leaving the last cyclone heat stage, are fed to an exhaust gas purification system. In the denitrification, which is part of the exhaust air purification, with so-called SCR (Selective Catalytic Reduction) catalysts by adding ammonia or ammonia releasing compounds, such as. Ammonia water or urea, achieved at optimal operating temperature, a cleavage of nitrogen oxides NOx in the exhaust gases in environmentally neutral nitrogen N2 and water H20. After a possible cooling or heat recovery, the exhaust gases finally reach a filter stage, where they are dedusted before they escape into the atmosphere. The filter stage before the exit of the exhaust gases into the atmosphere can be formed for example by electric or bag filters.

The relatively high dust content of the exhaust gases leads to a rapid clogging of the catalysts, which is why they are often ····················· ···

- 2 • · ♦ must be cleaned, maintained or replaced. In order to extend the exchange intervals of the catalysts, for example, catalysts with relatively large cross-sections of the flow channels are used. However, this again requires a larger volume for the catalyst. For example, EP 863 790 Bl describes such a catalyst in which the flow channels have a minimum cross section of 10 mm. Even with these catalysts are not yet satisfactory service life of the catalyst to achieve.

The object of the present invention is therefore to provide an abovementioned method and device for cleaning exhaust gases resulting from combustion processes, in which the service life of the catalytic converter is increased and thus the maintenance intervals can be extended. The method and the device should be feasible or producible as inexpensively as possible. Disadvantages of known methods and devices should be avoided or at least reduced.

The object of the invention is achieved by a method mentioned above, in which the exhaust gases are flowed through the catalyst from top to bottom and in only one layer parallel flow channels formed by tubes of round cross-section, tubes with a cross section with at least five corners whose corner angle > 90 °, or parallel plates are catalytically de-embroidered. By the flow direction of the catalyst from top to bottom and the use of only one layer of parallel flow channels, the clogging of the catalyst can be delayed. The use of catalysts designed in this way also reduces the clogging of the catalyst by the dust constituents of the exhaust gases.

Preferably, the exhaust gases are catalytically de-nitrogenized in only one layer of parallel flow channels having a length of at least 1.5 m. Since the blockage of the flow channels of the catalyst takes place mainly at the beginning of the flow channels of each layer of flow channels, it is advantageous to use only one layer of parallel flow channels. However, in order nevertheless to achieve the surfaces of the flow channels required for the catalytic denitrification, these are designed to be particularly long. To keep the cost of such catalysts low, the flow channels are as simple as possible. *** ····· ··· ······· ········· ··· ··· ·· - 3 -

Geometries, which are relatively easy to produce even in a length of at least 1.5 m.

Preferably, the exhaust gases are coarsely dedusted before the catalytic Entsti-ckung to 50 to 95%. By dedusting the exhaust gases before the catalytic denitrification, the dust content before entering the catalyst can be reduced accordingly and thus the clogging of the catalyst can be further delayed. On the other hand, the effort can be kept low by deliberately coarse dedusting. Since the exhaust gases after exiting the rotary kiln usually have relatively high temperatures of usually 350 to 400 ° C, some filters for such coarse dedusting, such. Bag filter, off.

Preferably, therefore, the exhaust gases are dedusted mechanically or electrically before the catalytic denitrification.

In order to minimize the expense of coarse dedusting of the exhaust gases, the exhaust gases are dedusted before the catalytic denitrification up to a dust content of 1 to 20 g / m3. These values can be achieved with relatively simple filter systems and already cause significant extensions of the service life of the catalyst, as it is not clogged so quickly.

According to a further feature of the invention it is provided that the flow channels of the catalyst are cleaned. The cleaning can be carried out periodically or as required, for example by compressed air, sound, mechanical cleaning or the use of appropriate cleaning fluids.

After the catalytic denitrification, the exhaust gases are preferably cooled. As a result of this cooling, filter stages which only withstand lower temperatures, such as, for example, dust removal from the exhaust gases, can be used. Bag filter, are used. The thermal energy obtained by the cooling can be used for heating the factory building, but also for preheating the raw material in the cement production or the like, whereby the energy balance can be improved.

The object of the invention is also achieved by a device mentioned above, wherein the catalyst from top to bottom of the exhaust gases is flowed through and the catalyst consists of only one layer of parallel flow channels, which flow channels through tubes round cross-section, tubes with a cross section with at least five Corners whose corner angles are> 90 ° or plates arranged in parallel. As already mentioned above, such arranged and thus formed catalysts do not clog so easily, so that their service life can be increased.

In order to achieve a sufficient catalytic effect even in a position of flow channels in the catalyst, the flow channels are formed with a length of at least 1.5 m.

Preferably, the flow channels are formed by parallel tubes of round cross-section or bundles of such tubes. Tubes of round cross-section can also be made in the above-mentioned lengths of at least 1.5 m relatively easily and inexpensively. Moreover, round cross-section tubes have no corners which would facilitate clogging of the flow channels of the catalyst.

Likewise, the flow channels can be formed by parallel tubes polygonal, in particular hexagonal, cross-section. The more corners the cross section of the parallel tubes has, the larger the resulting inner angles and the more difficult the clogging of the flow channels due to the corners. However, the production costs increase with increasing number of corners of the polygonal cross-sections also.

Another optimal embodiment of the catalysts can also be achieved in that the flow channels are formed by parallel plates, which are held by laterally arranged spacers. By parallel plates, the flow channels of the catalysts can be relatively easily and inexpensively manufactured. The spacers, which are preferably arranged only in the side region, promote the blockage of the flow channels of the catalyst only to a small extent.

The plates can be flat in the simplest case.

If the plates zigzag-shaped, trapezoidal or wavy, an enlargement of the catalytic surface over a flat embodiment of the plates can be achieved at the same height of the flow channels.

Preferably, in front of the at least one catalytic converter, at least one of the catalytic converters is at least one catalytic converter.

at least one filter is provided for coarse dedusting to 50 to 95% of the exhaust gases. As already mentioned above, the cost of such a filter can be kept relatively low due to the coarse dedusting and still the life of the catalyst can be significantly increased.

The at least one filter for dedusting can be formed by a centrifugal separator, in particular a cyclone or multicyclone. Such mechanical filters are relatively robust and also suitable for exhaust gases of higher temperatures.

Likewise, the at least one filter for dedusting can be formed by an electrostatic precipitator. In Elekrofiltern the dust particles are electrically charged so that they adhere to an electrode, the so-called collecting electrode.

By regularly cleaning the dust layer on the collecting electrode, the dust can be removed from the exhaust gas flow.

According to a further feature of the invention, it is provided that the at least one filter for dedusting for the purification of the exhaust gases is formed up to a dust content of 1 to 20 g / m3. By such a relatively low dedusting the cost of such a filter can be kept low before the catalyst and also relatively high Abreinigungsintervalle be achieved for the filter.

According to a further feature of the invention, a device for purifying the catalyst is provided. This cleaning device is used for regular or on-demand cleaning of the flow channels of the catalyst. Due to the inventively achieved higher service life of the catalyst, however, a purification of the catalyst is required only in longer maintenance intervals.

After the catalyst, a device for cooling the dedusted and de-nitrogenized exhaust gases is preferably provided. By cooling the exhaust gases, filters which are only suitable for lower exhaust gas temperatures can be used before they are released into the atmosphere, and furthermore the heat of the exhaust gases can be recovered for a better energy balance and used further.

The present invention will be explained in more detail with reference to the accompanying drawings. Show:

1 is a schematic representation of a plant for Ze- ········ ··

·· ·· ·· - 6 - ··· ·· prior art cement clinker preparation;

Fig. 2 is a schematic view of a cement clinker manufacturing plant according to the present invention;

3 shows a further embodiment of a plant for cement clinker production with a single-layered catalyst; and

4 to 9 different embodiments of the flow channels of the catalyst.

Fig. 1 shows a schematic view of a device for cement clinker production according to the prior art. The device for cement clinker production consists of a furnace 1, in particular a rotary kiln, in which the raw materials for the production of cement clinker are fired. Usually, the raw materials in a preheating tower 2, which may consist of a plurality of superimposed cyclones 3, preheated. For this purpose, the raw materials are placed on a material task 4 in the preheating tower 2. According to the counter-stomper principle, the raw material enters the furnace 1, whereas the exhaust gases A flow through the preheating tower 2 against the flow of the raw material. After the preheating tower 2, the exhaust gases A, which contain both nitrogen oxides N0X and dust, pass into a catalyst 5. In the catalyst 5, flow channels 6 are formed by appropriately arranged elements, through which the exhaust gases A flow, whereupon the nitrogen oxides are converted by appropriate catalytic reactions N0X be partly converted into nitrogen N2 and water H20. The denitrated exhaust gases A pass through a possible cooling device 7, on the one hand to lower the exhaust gases A to a temperature which are suitable for the subsequent filter stage 8 for dedusting the exhaust gases A. On the other hand, by such a cooling device 7, the heat contained in the exhaust gases A recovered and used, for example, for heating a factory building, but also for preheating the components in the cement clinker production. After the filter stage 8, which may be formed by bag filter or electrostatic precipitator, the exhaust gases A pass through a chimney 9 into the atmosphere. After the catalyst 5, the fired raw material of cement clinker carried with the exhaust gases A passes into a mill 10 where it is ground to a desired size prior to filling.

Since the exhaust gases A have a relatively high dust content before entering the catalyst 5, the catalysts clog ······ ··· ·

Are relatively fast and have a relatively short life.

Since the exhaust gases A before entering the catalyst 5 also have a relatively high temperature, which is also required for the catalytic effect, a number of measures for reducing the dust content before the catalyst 5 are ruled out. So far, therefore, no steps have been taken to dedust the exhaust A before the catalyst 5.

Fig. 2 shows an embodiment of the invention, in which a catalyst 5 is used with only one layer of flow channels 6. Such a single-layer catalyst 5 has lower clogging rates and thus a longer service life. It is also important for a lower blockage rate that the catalyst 5 is flowed through from top to bottom with the exhaust gases A, and the flow channels 6 have as few elements as possible, which promote a blockage. These include corners with a corner angle of> 90 ° or also elements to which the dust of the exhaust gases A can adhere. Since the blockage of the flow channels 6 of the catalysts 5 takes place predominantly in the inlet region of the flow channels 6, the blockage in a single-layer catalyst 5 is relatively lower than in the case of multi-layer catalysts 5. For regular or on-demand cleaning of the flow channels 6 of the catalyst 5, a corresponding device 12 can be provided be provided for purifying the catalyst 5.

Fig. 3 shows a further embodiment of the subject invention, in which before the single-layer catalyst 5 is additionally provided a filter 11 for coarse dedusting of the exhaust gases A. In order to keep the cost of such dedusting low and keep the cost of such a filter 11 low, deliberately only a rough dedusting of the exhaust gases A is made to 50 to 95%. Such a coarse dedusting up to a dust content of preferably 1 to 20 g / m3 is possible with relatively little effort and causes a significant extension of the service life of the catalyst. 5

Since the temperatures of the exhaust gases A are relatively high before entering the catalyst 5 and may not be lowered too much for optimum catalytic effect, mechanical filters, such as centrifugal, for coarse dedusting before the catalyst 5 are particularly suitable. The centrifugal separators may be formed, for example, by cyclones, multisks, ... ····························································································. «··· ··························

Cyclones or Umlenkabscheider be formed. Such filters 11 are particularly cheap and mechanically very simple.

Pre-dedusting up to 80% can be achieved with such centrifugal separators.

Alternatively, electrostatic precipitators can also be used as filters 11 for the pre-separation. Although such electrostatic precipitators are more expensive than centrifugal separators and have relatively low efficiency at high temeratures, they are also optimally applicable for coarse pre-dedusting of only 50 to 95%.

Combinations of centrifugal separators and electrostatic precipitators are also conceivable, the centrifugal separators being used for coarse dedusting and the electrostatic precipitators for fine dedusting. However, in such a combination, the production price for such a filter 11 also increases.

Theoretically, even at the relatively high temperatures bag filters are possible, instead of textile tubular fabric metal mesh are used. Such filters are relatively expensive.

The following FIGS. 4 to 9 show various preferred embodiments of the flow channels 6 of the catalyst 5 according to the invention.

According to FIG. 4, the flow channels 6 are formed by tubes 13 with a round cross-section. The tubes 13 can be combined into tube bundles. The length L of the flow channels 6 of the catalyst 5 is preferably at least 1.5 m. In this way, the required surfaces for a catalytic effect in the catalyst 5 can be achieved. Tubes 13 of round cross section can also be made relatively easily in such long lengths L.

According to FIG. 5, the flow channels 6 of the catalytic converter 5 are formed by tubes of polygonal cross-section, in particular by hexagonal tubes 14. Also, such hexagonal tubes 14 can be assembled into a tube bundle.

According to Fig. 6, the flow channels 6 can also be formed by parallel plates 15, which are held by corresponding spacers 16 in the desired position. While the plates 15 according to FIG. 6 are essentially planar, the plates according to FIG. 7 may also be wavy or, according to FIG. 8, trapezoidal or, according to FIG. 9, ········································· • • • • • • • • # ♦ • • 9 9 • • • • 9 ·· * · 9 • 99 - 9 - ·· be zig-zag shaped. As a result, the area of the plates 15 and thus the catalytically active surface of the catalyst 5 is increased.

The figures show only some of the possible embodiments for the flow channels 6 of the catalyst 5, all of which clog more severely than previously used catalysts of the prior art.

By the method and the apparatus according to the present invention, the service life of the catalyst 5 can be increased and thus the maintenance interval of the catalyst 5 can be extended. The additional cost is relatively low, whereby a wide application is possible.

Although the illustrated embodiments are directed to an apparatus for cement production, applications of the subject invention are also conceivable in exhaust gases, which arise in other combustion processes and are characterized by a high dust and nitrogen oxide content.

Claims (23)

············································································································································································································ ································································································································································································ 5 g / m3 and nitrogen oxides (N0X), wherein the exhaust gases (A) in a catalytic converter (5) with a plurality of parallel flow channels (6) are catalytically entstickt and dedusted before leaving the atmosphere, characterized in that the exhaust gases (A) from top to bottom through the catalyst (5) and in only one layer of parallel flow channels (6) formed by tubes (13) of round cross-section, tubes (14) having a cross-section with at least five corners whose corner angles are> 90 ° , or parallel plates (15) are catalytically de-embroidered. 2. The method according to claim 1, characterized in that the exhaust gases (A) in a single layer of parallel flow channels (6) with a length (L) of at least 1.5 m are entecktisch catalytically. 3. The method according to claim 1 or 2, characterized in that the exhaust gases (A) are dedusted before the catalytic denitrification to 50 to 95%. 4. The method according to claim 3, characterized in that the exhaust gases (A) are dedusted mechanically before the catalytic denitrification. 5. The method according to claim 3 or 4, characterized in that the exhaust gases (A) are dedusted before the catalytic denitrification. 6. The method according to any one of claims 3 to 5, characterized in that the exhaust gases (A) are dedusted before the catalytic denitrification up to a dust content of 1 to 20 g / m3. 7. The method according to any one of claims 1 to 6, characterized in that the flow channels (6) of the catalyst (5) are cleaned. 8. The method according to any one of claims 1 to 7, characterized ·························································. 11 shows that the exhaust gases (A) are cooled after the catalytic denitrification. 9. Apparatus for purifying exhaust gases (A) with a dust content occurring in combustion processes> 5 g / m3 and nitrogen oxides (NOX), with a catalyst (5) having a plurality of parallel flow channels (6) for the catalytic denitrification of the exhaust gases (A), and at least one after the catalyst (5) arranged filter stage (8) for dedusting the exhaust gases (A) before leaving the atmosphere, characterized in that the catalyst (5) from top to bottom of the exhaust gases (A) is flowed through, and that the catalyst (5) consists of only one layer of parallel flow channels (6) which are flow channels (6) through tubes (13) of round cross-section, tubes (14) with a cross-section with at least five corners, whose corner angles are> 90 °, or parallel plates (15) are formed. 10. The device according to claim 9, characterized in that the flow channels (6) have a length (L) of at least 2 m. 11. The device according to claim 9 or 10, characterized in that the flow channels (6) by parallel tubes (13) are formed round cross-section. 12. The device according to claim 9 or 10, characterized in that the flow channels (6) by parallel tubes (14) polygonal, in particular hexagonal, cross-section are formed. 13. The apparatus of claim 9 or 10, characterized in that the flow channels (6) by parallel plates (15) are formed, which are held by laterally arranged spacers (16). 14. The apparatus according to claim 13, characterized in that the plates (15) are flat. 15. The apparatus according to claim 13, characterized in that the plates (15) are zigzag-shaped. «· ···« ··· «# ························· ···················· · ··· it ·· · ♦ ·· ·· - 12 - 16. The apparatus according to claim 13, characterized in that the plates (15) are trapezoidal. 17. The apparatus according to claim 13, characterized in that the plates (15) are formed wave-shaped. 18. Device according to one of claims 9 to 17, characterized in that before the catalyst (5) at least one filter (11) for coarse dedusting to 50 to 95% is provided. 19. The apparatus according to claim 18, characterized in that the at least one filter (11) for dedusting by a centrifugal separator, in particular a cyclone or multi-cyclone, is formed. 20. Device according to claim 18 or 19, characterized in that the at least one filter (11) for preliminary dedusting is formed by an electrostatic precipitator. 21. Device according to one of claims 18 to 20, characterized in that the at least one filter (11) for dedusting to clean the exhaust gases (A) is formed to a dust content of 1 to 20 g / m3. 22. Device according to one of claims 9 to 21, characterized in that a device (12) for cleaning the catalyst (5) is provided. 23. Device according to one of claims 9 to 22, characterized in that after the catalyst (5) means (7) for cooling the dedusted and de-nitrogenized exhaust gases (A) is provided. GH / jd / dp