WO2011018322A1

WO2011018322A1 - Method and system for the reduction of nitrogen oxides in dust-containing exhaust gases by means of an scr catalytic converter

Info

Publication number: WO2011018322A1
Application number: PCT/EP2010/060706
Authority: WO
Inventors: Sebastian Frie; Melanie Tribowski; Mark Colberg; Luis Lagar Garcia; Timo Stender
Original assignee: Polysius Ag
Priority date: 2009-08-11
Filing date: 2010-07-23
Publication date: 2011-02-17
Also published as: EP2315621A1; DE102009036948A1

Abstract

In the method according to the invention for the reduction of nitrogen oxides in dust-containing exhaust gases by means of an SCR catalytic converter, the exhaust gases, before they enter into the catalytic converter, are conditioned by means of the agglomeration of dust particles to a minimum size which is such that the dust particle agglomerates conducted through the catalytic converter neither block nor deactivate the porous surface of the catalytic converter.

Description

Process as well as a plant for the reduction of nitrogen oxides of dusty exhaust gases by means of an SCR catalytic converter

The invention relates to a method and a plant for the reduction of nitrogen oxides (NOχ) dust-containing exhaust gases by means of an SCR catalyst. such

Exhaust gases are obtained, for example, in furnaces for cement or minerals as well as in power plant technology.

The SCR process for NOχ reduction requires a reasonable use of vanadium and precious metals due to the sometimes high sulfur loads in the exhaust gases reaction temperatures of about 280 ⁰ C. In cement kilns, it is therefore usually necessary to place the catalyst directly behind the cyclone preheater , since process-related temperatures of about 300 to 380 ° C are present here. Unfortunately, however, the exhaust gases at this point on an extremely high dust load in the order of 50 to 150 g / Nm ³ . These high

Dust loads lead to operating problems due to blockages on the catalytic converter; they may also deactivate the porous surface of the catalyst. Since the catalyst is usually fixedly mounted in the reactor, there are limited opportunities to clean it in operation and reactivate.

In order to remove dust deposits on the surface of high-dust catalysts, the use of compressed air blowers is known (DE 10037499). To support the cleaning performance of these dust blowers has also been proposed an additional acoustic cleaning of the catalysts with sonic horns, which loosen up the accumulated dust before it is removed with the dust blowers (DE 102005039997).

In practice, however, it has been found that these known processes do not guarantee the desired cleaning effect in many cases, especially in the production of cement clinker.

A process is also known for the purification of gases, in which dust particles contained in the gas stream are first agglomerated by sonication and separated by means of a porous cross-flow filter before it reaches such dust-free clean gas, for example, a catalyst bed is supplied (US 4,319,891 and US 4,378,976). In a similar method, the deposition of the dust agglomerates formed by the application of sound takes place directly in the sound chamber, from which a dust-free gas stream is drawn off and fed to a catalyst (US Pat. No. 5,419,877).

The invention is based on the object to provide a method and a system that allow a particularly effective and operationally reliable reduction of nitrogen oxides dust-containing exhaust gases by means of an SCR catalyst.

This object is achieved in the method according to the invention in that the exhaust gases are conditioned before entering the catalyst by agglomeration of dust particles to such a minimum size, in which passed through the catalyst dust particle agglomerates clog the catalyst nor disable its porous surface. The plant according to the invention is accordingly characterized by a conditioning stage upstream of the catalyst for agglomeration of dust particles contained in the exhaust gases to the said minimum size. As the experiments underlying the invention showed the danger of a

Clogging of the catalyst and deactivation of its porous surface are very closely related to the size of the dust particles. Provided therefore, according to the invention for a certain minimum size of the dust particle agglomerates, they can be performed without operating problems usually through the catalyst, since they clog neither the catalyst nor disable its porous surface. In this way, a very effective and operationally reliable reduction of nitrogen oxides of dust-containing exhaust gases by means of the SCR catalyst is made possible. Depending on the type of SCR catalyst and the temperature, the dust content and the

Volume flow of dusty exhaust gases is the desired average Particle size of the dust particle agglomerates at least 5 microns, preferably 8 to 15 microns.

The agglomeration of dust particles can be brought about acoustically by generating ultrasonic waves in a dusty exhaust gas flow.

Another possibility is to cause the agglomeration electrostatically by at least two dust-containing exhaust gas streams are charged electrostatically in opposite directions and then brought together for the purpose of agglomeration of dust particles.

These and other details of the invention are the subject of the dependent claims and will be explained in more detail in connection with the description of some exemplary embodiments.

In the drawing show:

Fig. 1 is a schematic representation of a first exemplary embodiment (with acoustic agglomeration), from which the increasing with the size of the formed dust particle agglomerates reducing their

Oscillation amplitude is apparent,

2 is a schematic representation of the first exemplary embodiment for explaining the pressure drop occurring in the flow shadow of the agglomerates,

3 shows a flow chart of a system according to the invention with acoustic agglomeration, FIG. 4 shows a schematic diagram of a further exemplary embodiment with acoustic agglomeration, Fig. 5 is a schematic representation of an embodiment with electrostatic agglomeration. In the first embodiment shown schematically in FIGS. 1 and 2, the agglomeration of dust particles in the exhaust gas flow is acoustically brought about. For this purpose, dust-containing exhaust gases 3 are fed to a conditioning stage 1 for the agglomeration of dust particles contained in the exhaust gases 3.

The conditioning stage 1 is formed by an example horizontally oriented flow tube, in which near the entrance of the dust-containing exhaust gases 3, a sound source 2 is arranged. The sound source 2 acts on the conditioning stage 1 with sound or ultrasonic waves whose frequency is at least 18 kHz, preferably at least 20 kHz, and whose sound level is at least 120 dB, preferably 140 to 160 dB. These ultrasonic waves generate a relative movement between the dust particles and the fluid carrying them, which leads to collisions between the dust particles and to a dust particle agglomeration.

The carrier gas 4, i. The gas component of the dust-containing exhaust gases 3, is offset due to its low density of the ultrasonic waves in a vibration with the largest amplitude. Small dust particles oscillate almost synchronously and with approximately the same amplitude as the carrier gas 4. With increasing diameter of the forming dust particle agglomerates 5, the effect of inertia becomes increasingly noticeable; the oscillation amplitude of the forming agglomerates 5 is now lower. With increasing distance from the sound source 2 and correspondingly longer exposure time of the ultrasonic waves, the diameter of the agglomerates 5 becomes larger, the different vibration amplitudes supporting the desired collision of the dust particles and thus their agglomeration.

The illustration of the four oscillations of different amplitude in FIG. 1 is to understand quite schematically and to illustrate the relationship between the amplitude of vibration and the size of the forming agglomerates and the space-time growth of the agglomerates. As illustrated in FIG. 2, the vibrations of the dust particles and the forming dust particle agglomerates also lead to pressure gradients. Thus, the particle A generates behind it a flow shadow, which has a pressure gradient result: the pressure p2 behind the particle A is smaller than the pressure pl in front of the particle A .. The lower pressure p2 in the flow shadow of the particle A leads there to a higher Velocity v2 as before the particle A (vi). The pressure drop behind a particle A causes the particle B following in the flow shadow of the particle A to oscillate more rapidly and therefore additionally increases the collision rate and the agglomeration. In order to achieve high agglomeration rates, a balance between the dust load of the exhaust gases and the propagation of the sound waves in the conditioning stage is required. The acoustic agglomeration is preferably carried out with a dust loading between 3 and 30 g / Nm ³ , preferably between 5 and 20 g / Nm ³ .

Extremely high dust loads of the exhaust gases, for example between 50 and 150 g / Nm ³ , can occur, for example, in the cement industry on the gas outlet side of the preheater. Here it is advisable to reduce the dust load of the exhaust gases before the dust agglomeration by first dedusting to a suitable level for the dust agglomeration. As an aid to such

Pre-dedusting are especially suitable cyclones because of their simple structure and their low susceptibility to interference. An existing anyway Zyklonvorwärmer the cement kiln can therefore be extended by an additional level for the purpose of the dedusting of the exhaust gases. On the market there are SCR catalyst types with plate and honeycomb geometries as well as with different channel diameters. At high dust sensitivity of the catalyst, as is usually the case especially for small dimensions of the flow channels of the catalyst, it may be appropriate to the dust content of the exhaust gases after the dust agglomeration, but before feeding the

Exhaust gases to the catalyst to reduce by deposition of at least a portion of the dust particle agglomerates formed to a suitable value for the SCR catalyst. The pre- and post-dedusting of the exhaust gases with cyclones increase the

Total pressure loss of a system and increase the system cost. The dedusting by a cyclone can be dispensed with, depending on the required purity, even in the case of dust-sensitive catalysts, if the dust particle agglomerates formed in the conditioning stage are at least partly already deposited at the outlet of the conditioning stage.

Fig. 3 shows schematically the gas path of a plant for the reduction of nitrogen oxides dust-containing exhaust gases by means of an SCR catalyst, wherein the exiting the preheater tower of a cement combustion exhaust gases are subjected to an acoustic Staubagglomeration before they get into the catalyst. A

Pre-dedusting of the exhaust gases before the dust agglomeration as well as subsequent dedusting in a dedusting unit between acoustic agglomeration and entry into the SCR catalytic converter are optionally provided. 4 shows a schematic diagram of a system in which an acoustically induced agglomeration takes place in the conditioning stage and subsequently a separation of formed dust particle agglomerates.

The dust-containing exhaust gas 3 enters the conditioning stage 1 on the left, which is designed as an approximately horizontally arranged tube. The sound sources 2a, 2b, 2c are in upper area or above the conditioning stage 1 arranged horizontally next to each other.

The agglomeration of dust particles in the conditioning stage 1 leads due to gravity to a decrease in the formed dust particle agglomerates. As a result, a partial dedusting of the exhaust gas is already achieved in the conditioning stage 1. In its lower part, preferably near the right end, is the

Conditioner 1 provided with an opening 6 through which sedimented

Dust particle agglomerates are discharged, while the partially dedusted gas 7 is withdrawn separately.

To further improve the deposition of the formed dust particle agglomerates baffles can be provided, for example, in the vicinity of the gas side outlet of the conditioning stage.

Fig. 5 shows an embodiment of an electrostatically induced agglomeration. The dust-containing exhaust gas 3 is in this case divided into at least two partial streams 3a, 3b, which then flow through a device 8 for electrostatic charging. In this, the partial flow 3a becomes electropositive and the partial flow 3b is charged electronegatively. Subsequently, the two partial streams

3a, 3b are brought together again in a zone 9 of the conditioning stage, with oppositely charged dust particles attracting and agglomerating electrostatically.

In contrast to acoustic agglomeration, no dedusting is generally required in this electrostatic agglomeration. Preferably, instead of a Nachentstaubung. The extent to which it occurs depends on the interactions between the dust agglomerates and the catalyst.

Claims

claims:

1. A process for the reduction of nitrogen oxides dust-containing exhaust gases by means of an SCR catalyst, characterized in that the exhaust gases before entering the catalyst by agglomeration of dust particles to such

At least large conditioned, in which passed through the catalyst dust particle agglomerates clog the catalyst nor disable its porous surface.

2. The method according to claim 1, characterized by an average particle size of the dust particle agglomerates formed in the conditioning of the exhaust gases of at least 5 microns, preferably from 8 to 15 microns.

3. The method according to claim 1, characterized by an acoustically induced agglomeration, by in a dusty exhaust gas flow

Ultrasonic waves are generated.

4. The method according to claim 1, characterized by an electrostatically induced agglomeration by at least two dust-containing exhaust gas substreams electrostatically charged in opposite directions and then for the purpose

Agglomeration of dust particles are merged.

5. The method according to claim 3, characterized in that the acoustically induced agglomeration at a dust load of the exhaust gases to be conditioned between 3 and 30 g / Nm ³ , preferably between

5 and 20 g / Nm, takes place.

6. The method according to claim 5 for extremely dusty exhaust gases, in particular of cement kilns, characterized in that the dust loading of the exhaust gases to be conditioned before the Staubagglomeration first by a dedusting to a value between 3 and 30 g / Nm ³ , preferably between 5 and 20 g / Nm ³ , is reduced.

7. The method according to claim 1, characterized in that the dust content of the exhaust gases after the dust agglomeration, but before feeding the exhaust gases to the S CR catalyst, by deposition of a portion of the formed

Dust particle agglomerates is reduced to a value suitable for the catalyst used.

8. The method according to claim 3, characterized in that the sound or

Ultrasonic waves having a frequency of at least 18 kHz, preferably of at least 20 kHz, and a sound level of at least 120 dB, preferably from 140 to 160 dB, are used.

9. System comprising an SCR catalyst for the reduction of nitrogen oxides dust-containing exhaust gases, characterized by a catalytic converter upstream conditioning stage (1) for agglomeration of the exhaust gases (3) contained dust particles to such a minimum size, in the guided through the catalyst dust particles Agglomerates clog the catalyst nor disable its porous surface.

10. Plant according to claim 9, characterized in that the conditioning stage (1) contains at least one acoustic vibration generator (2, 2a, 2b, 2c) for the agglomeration of dust particles.

11. Plant according to claim 9, characterized in that the conditioning stage contains a device (8, 9) for the electrostatic agglomeration of dust particles.

12. Plant according to claim 9, characterized by a SCR catalyst upstream device for the separation of dust particle agglomerates formed in the conditioning stage.

13. Plant according to claims 10 and 12, characterized in that the acoustic vibration generator (2 a, 2 b, 2 c) are arranged in the upper region of the dust-containing exhaust gases (3) in approximately horizontal direction conditioning stage (1) and that at the same time As a device for the separation of dust particle agglomerates formed conditioning stage in its lower part an opening (6) for discharging the deposited dust particle agglomerates.

14. Plant according to claim 9, characterized by a conditioner upstream of the device for dedusting the exhaust gases to a dust load between 3 and 30 g / Nm ³ , preferably between 5 and 20 g / Nm ³ .