WO2011018333A1

WO2011018333A1 - Method and device for the selective catalytic denitrogenization or utilization of dust-containing gases

Info

Publication number: WO2011018333A1
Application number: PCT/EP2010/060905
Authority: WO
Inventors: Sebastian Frie; Detlev Kupper; Melanie Tribowski; Timo Stender; Mark Colberg; Markus Deimel; Alfred Buhl
Original assignee: Polysius Ag
Priority date: 2009-08-13
Filing date: 2010-07-27
Publication date: 2011-02-17
Also published as: DE102009037050A1

Abstract

In the method according to the invention for the selective catalytic denitrogenization or utilization of dust-containing exhaust gases, it is sought to prevent dust accumulations in a treatment device (catalytic converter, waste heat boiler or heat exchanger) through which a dust-containing exhaust gas flows, wherein the treatment device has surface regions which come into contact with the dust-containing exhaust gas. Here, the dust contained in the exhaust gas is electrostatically charged before it flows through the treatment device, and those surface regions which come into contact with the dust-containing exhaust gas are held at a potential with the same polarity as the potential of the charged dust.

Description

Process and device for the selective catalytic denitrification or use of dusty exhaust gases

The invention relates to a method and a device for the selective catalytic denitrification or use of a dusty exhaust gases in one

Treatment facility.

The treatment device is a catalyst for selective catalytic denitrification, for example, of flue gases of the cement and mineral industries act or to a waste heat boiler or heat exchanger for

Use of the exhaust gases.

The SCR process for NO x reduction requires due to the sometimes high sulfur loads in exhaust gas of plants for the production of cement clinker minimum reaction temperatures greater than 260 ⁰ C. Therefore, it is usually necessary to place the catalyst directly behind the cyclone are here for process reasons favorable temperatures from about 300 to 380 ⁰ C ago. Unfavorably, after the last preheater cyclone there are also extremely high dust loads in the order of magnitude of 50 to 150 g / Nm ³ (Nm ³ = standard cubic meter). These high dust loads lead to operational problems

Form of clogging of the catalyst and deactivation of the porous catalyst surface. Obvious therefore is the idea to dedust the exhaust gas at least partially immediately after the preheater to mitigate these problems. In particular, the use of a Heißelektrofϊlters is favorable, which can cause a partial dedusting of the exhaust gas flow without exhaust gas conditioning or cooling at temperatures greater than 300 ⁰ C.

DE 34 35 953 A1 and CA 2,145,111 A1 describe combined methods with electric filters and SCR catalysts. In a field of tension, the dust particles are electronegatively charged by the corona discharge of a spray electrode. On the following electropositive polarized precipitation electrode is the dust is separated. The precipitation electrode is coated with a catalytically active material or is made of catalytically active material. At the collecting electrode thus the dust separation and the NO reduction take place.

However, this method does not provide a solution for dust deposits on the catalyst. Rather, the dust is selectively deposited on the catalyst surface and leads to the known negative consequences: blockage of the pores and deactivation of the active surface.

In addition, an electric filter is described in US 2005/0051028.

The invention is therefore based on the object in the selective catalytic denitrification or the use of dusty exhaust gases in a waste heat boiler or heat exchanger to provide effective protection against dust deposits, which can also be used when very large industrial amounts of exhaust gas, for example from power plants or cement plants to be treated. According to the invention we achieve this object by the features of claims 1, 2, 5 and

6 solved.

In the method according to the invention for the selective catalytic denitrification or use of dust-containing exhaust gases, the treatment device (catalyst, waste heat boiler or

Heat Exchanger) are protected from dust deposits, wherein the treatment device has surface areas that come into contact with the dust-containing exhaust gas. In this case, the dust contained in the exhaust gas is electrostatically charged before flowing through the treatment device and coming into contact with the dusty exhaust gas surface areas on a potential which is rectified to the potential of the charged dust.

In this way, it is ensured that the charged dust particles are repelled from the surface areas of a catalyst, waste heat boiler or heat exchanger.

In the device according to the invention for the selective catalytic denitrification or use of dust-containing exhaust gases at least one means for electrostatic dust charging and a subsequently arranged, perfused by the dusty exhaust gas treatment device (catalyst, waste heat boiler or heat exchanger) is provided, wherein the treatment device with the dust-containing exhaust gas in contact have upcoming surface areas, which are at a potential that is rectified to the potential of the charged dust.

Further embodiments of the invention are the subject of the dependent claims.

According to an embodiment of the invention, a part of the electrostatically charged dust is attracted and discharged from a collecting electrode in the device for electrostatic charge dust, while the remaining dust is supplied together with the exhaust gas of the treatment device. The device for electrostatic dust conditioning has, for example, at least one spray electrode and at least one precipitation electrode. But it can also be designed as an ionizer.

The treatment device through which the dust-laden exhaust gases flow can be formed, for example, by a catalyst which has, in particular, electrically conductive supports on which the catalyst mass is applied. These electrically conductive carriers can then be connected to a voltage source for application of the potential. If the exhaust gas in the treatment facility catalytically entstickt, the exhaust gas is a reducing agent, in particular an ammonia-containing reducing agent, before or after the electrostatic charge of the dust contained in the exhaust gas admit. According to another embodiment of the invention, however, there is also the

Possibility that the surface areas of the treatment device coming into contact with the dusty exhaust gas have a permanently electrostatic property, which is also referred to as electret property. This is an electrically insulating material that contains quasi-permanently stored electrical charges or permanently aligned dipoles and thus generates a quasi-permanent electric field in its environment or in its interior. This property makes it possible to produce an electrostatic-repellent surface without having to apply a permanent voltage. It is possible to apply such an electret as a coating on the surface areas. For a catalyst, the coating would have to be designed so that it does not close the access to the macropores and thus to the important, large inner surface of the catalyst.

A variant consists of applying the electret only in regions on the catalyst. This can be done for example by a network structure that on the

Catalyst is tensioned. Conversely, it is possible to apply the catalyst to a carrier monolith having appropriate electret properties. According to another embodiment of the invention, wherein the

Treatment apparatus is formed by a catalyst, this has catalyst plates and precipitation plates which are arranged alternately to each other, wherein the surface areas, which are at a potential which is rectified to the potential of the charged dust, formed by the catalyst plates and the precipitation plates have opposite potential. The flow cross-section is alternately equipped with catalyst and precipitation plates.

According to a particular embodiment, the catalytically active material is applied to an electrically conductive support, preferably on a wire mesh, as used in conventional plate catalysts. The catalyst material is applied to the electrically conductive wire mesh, that at the ends of an electrical potential can be connected. The connected potential is in the same direction as the charge of the dust. The opposite pole is formed by the precipitation plates, which are not coated with catalyst material and consist of a metallic material which has a low surface roughness and a low adhesion to the dust. Practical experience shows that plates are particularly suitable for this purpose which have an average roughness R _{z of} less than 2 μm. Suitable materials are austenitic stainless steels with Cr contents> 13% (w), preferably X5CrM18-10 / material no. 1.4301.

The Staubaufiadung in the upstream device for electrostatic dust charging experience the dust particles between the plates a strong attraction to non-catalytic precipitation plate and thus effectively kept away from the catalyst plates.

The cleaning of the collecting electrodes in electrostatic precipitators is usually done mechanically by knocking devices. For the inventive design, this variant is unfavorable, because the large number of plates in a catalyst in a mechanical knocking device would lead to a disproportionate effort.

Advantageously, the cleaning of the precipitation plates is therefore also carried out by an electrostatic action. This takes place in the form of impulse cleaning. The usually positively poled precipitation plates are applied for a few milliseconds with a negative voltage. The negative Poled catalyst plates are applied accordingly with a positive potential. This reversal causes a repulsion of the dust deposits. The cleaning can be supported at the same time with a dust blower, which briefly increases the volume flow and thus the gas velocity and supports the removal of the dissolved material via the gas flow, without resulting in an accumulation of dust on the catalyst plates. The polarity reversal takes place for very short time intervals, with a duration of less than 1 second.

Further advantages and embodiments of the invention will be explained in more detail below with reference to the further description and the drawing.

In the drawing show

1 is a block diagram of the device according to the invention,

2 shows a schematic detail view of the treatment device according to a first exemplary embodiment,

Fig. 3 is a schematic detail view of the treatment device according to a second embodiment and

Fig. 4 is a schematic detail view of the treatment device according to a fourth embodiment. The device shown in FIG. 1 for selective catalytic denitrification or

The use of dust-containing exhaust gases consists essentially of a device 2 for electrostatic dust charging and a subsequently arranged, perfused by a dusty exhaust gas treatment device 1 1. The device 2 for electrostatic dust charging has, for example, a spray electrode 2a and a collecting electrode 2b. Depending on

Embodiment, it comes to an exclusive charge of the exhaust gas in the first contained dust, or to a partial deposition of a fraction 3 fraction of the dust.

The device for electrostatic dust charging can be formed in particular by an insufficiently dimensioned Elektrofϊlter, wherein the spray and

Precipitation electrode are connected to a high voltage source. The

Stress field causes a corona discharge between spray and

Precipitation electrode and a full charge of dust particles in the

Gas space. At the collecting electrode 2b, incomplete separation of dust takes place, typically an increase of <10 g / Nm ³ 'but more than 1 g / Nm ³ . The non-separated but charged dust particles get along with the

Exhaust gas in the subsequent treatment device. 5

In another embodiment, however, the counter electrode can also be designed so that it only builds up the high field strengths and does not perform any function in the sense of dust separation. In this case, the dust is charged only electrostatically and not deposited.

If the subsequent treatment device 5 is formed by a catalyst, the injection of an ammonia-containing reducing agent 4 is provided.

In particular, in the case of an intended separation of a partial fraction 3 of the dust, the reducing agent 4 necessary for the SCR reaction is added after the device 2 for the electrostatic charging of dust. Alternatively, an upstream dosage is possible.

In the treatment device 5 designed as a catalyst, the denitrification of the exhaust gas 1 with ammonia or an ammonia-containing substance takes place according to the following reaction equation. 4NO + 4NH ₃ + O ₂ -> 4N ₂ + 6H ₂ O The injection of ammonia increases the conductivity in the device 2 for electrostatic dust charging. At high temperatures (> 300 ⁰ C) but is already a very low dust resistance. Too low dust resistances can promote a back spray of the counter electrode. Therefore, ammonia is preferably injected only after the electric filter / ionizer in order to reduce the risk of re-spraying discharged particles.

In a possibly downstream waste heat boiler or heat exchanger 6, a part of the exhaust gas heat can be transferred to a fluid before the exhaust gas is passed to further process stages 7.

In the context of the invention, the treatment device 5 can be formed by a catalyst, a heat exchanger or a waste heat boiler. Fig. 2 shows a schematic detail view of the catalyst formed

Treatment device 5. The dust-laden and dust-laden ionized gas 1 flows through the channels of the catalyst. The surface areas 8 of the catalyst plates or honeycombs have a surface charge which corresponds to that of the charged dust 9. This results in a repelling effect between dust 9 and the surface areas 8, wherein the surface charge of the catalyst erfϊndungsgemäß can be realized by an electret coating.

FIG. 3 shows a further detailed view of a treatment device 5 embodied as a catalytic converter in an alternative embodiment. The

Surface regions 8 of the catalyst plates are arranged alternately with electrically conductive precipitation plates 10 in the space and in each case connected to the opposite pole of a voltage source 11. Accordingly, an electric field E forms with the field lines 12 between the catalyst plates and the precipitation plates, so that the incoming Dust particles 9 are moved to the collecting electrodes 10 and kept away from the surface areas 8 of the catalyst plates.

The cleaning of the precipitation plates can also be carried out by an electrostatic action. This takes place in the form of impulse cleaning. The usually positively poled precipitation plates are applied for a few milliseconds with a negative voltage. The negatively polarized catalyst plates are applied accordingly with a positive potential. This reversal causes a repulsion of the dust deposits. The cleaning can be supported at the same time with a dust blower, which briefly increases the volume flow and thus the gas velocity and supports the removal of the dissolved material via the gas flow, without causing an accumulation of dust on the catalyst plates. The polarity reversal takes place for very short time intervals, with a duration of less than 1 second.

According to the method described above, the dust load contained in the exhaust gas is not transported to the active surface regions of the catalyst, but prevented by electrostatic forces thereof, so that sufficiently large catalyst surfaces are available in order to realize a significant DeNOx effect can.

The electrostatic charge of the surface regions of a catalyst can, for example, by

Introducing charged particles into the catalyst mass, such as metal particles,

Application on the catalyst surface, for example by means of a gas-permeable electret layer or

• An electrostatic polarization of the ceramic catalyst mass used. SCR catalysts are sometimes equipped with mechanical protective or sacrificial layers to reduce the wear on the front edges of the catalyst by dust erosion and force effects of sootblowers. These layers can be protected by a corresponding polarization on the surface from dust deposits.

Although the illustrated embodiments of the invention are essentially related to an SCR catalyst, the invention can also be applied to other applications in which a treatment device is to be protected from dusting. This is especially in waste heat boilers and

Heat exchangers of the case.

In Fig. 4, an embodiment is shown, in which the treatment device 5 is formed by a heat exchanger having transfer tubes 10, 11 to heat incoming cold air 12 and remove as heated air 12 '.

The dust-containing exhaust gas 1 initially has uncharged dust particles Ia, which are charged in a device 2 upstream of the treatment device 5 for electrostatic charging (for example an ionizer 2a), so that, for example, negatively charged dust particles Ib form. The surface areas of the transfer tubes 10, 11 are kept at the same, here negative potential in order to avoid the accumulation of the charged dust particles Ib. The charging of the transfer tubes 10, 11 can be done by applying a corresponding potential or for example by permanent charges 13. After the heat exchanger designed as a treatment device 5, the dust-containing exhaust gas flows as cooled exhaust gas 1 'from.

A dust deposit on the transfer tubes can also be solved by the charging of the dust and the same direction electrostatic charge of the heat exchanger surfaces.

Claims

claims

1. A process for the selective catalytic denitrification of dust-containing exhaust gases (1) in a treatment device designed as a catalyst (5) having surface areas (8), which come into contact with the dust-containing exhaust gas, wherein the dust contained in the exhaust before flowing through the treatment device (5) is electrostatically charged and the surface areas coming into contact with the dust-laden exhaust gas are kept at a potential which is rectified to the potential of the charged dust to protect against dust deposits.

2. A method for using dust-containing exhaust gases (1) in a formed as a waste heat boiler or heat exchanger treatment device (5) having surface areas (8), which come into contact with the dust-containing exhaust gas, wherein the dust contained in the exhaust before flowing through the

Treatment device (5) is charged electrostatically and the coming into contact with the dust-containing exhaust gas surface areas to protect against dust deposits are kept at a potential that is rectified to the potential of the charged dust.

3. The method according to claim 1 or 2, characterized in that a part of the electrostatically charged dust is attracted by a collecting electrode (2b) and discharged there and the remaining dust is supplied together with the exhaust gas of the treatment device (5).

4. The method according to claim 1, characterized in that the exhaust gas, a reducing agent (4), in particular an ammonia-containing reducing agent, is added before or after the electrostatic charge of the dust contained in the exhaust gas.

5. Device for the selective catalytic denitrification of dust-containing exhaust gases (1) having at least one means (2) for electrostatic dust charging and subsequently arranged by the dusty exhaust gas (1) and through-trained as a catalyst treatment device (5), wherein the catalyst with the dusty exhaust gas coming into contact

Having surface areas (8) that are at a potential that is rectified to the potential of the charged dust.

6. Apparatus for using dusty exhaust gases (1) with at least one device (2) for electrostatic dust charging and subsequently arranged, from the dusty exhaust gas (1) and through-trained as a waste heat boiler or heat exchanger treatment device (5), wherein the treatment device with the dusty exhaust gas has contacting surface areas (8), which are at a potential which is rectified to the potential of the charged dust.

7. Device according to claim 5 or 6, characterized in that the device for electrostatic dust conditioning has at least one spray electrode (2a) and at least one precipitation electrode (2b).

8. Apparatus according to claim 5 or 6, characterized in that the device for electrostatic dust conditioning (2) is formed by an ionizer.

9. The device according to claim 5, characterized in that the catalyst (5) comprises electrically conductive carrier, is applied to the catalyst mass.

10. The device according to claim 9, characterized in that the electrically conductive carrier are connected to a voltage source.

11. The device according to claim 5 or 6, characterized in that the coming into contact with the dusty exhaust gas surface areas (8) of the treatment device (5) have a permanent electrostatic property.

12. The device according to claim 5, characterized in that the catalyst catalyst plates and precipitation plates (10) which are arranged alternately to each other and the surface areas (8) which are at a potential which is rectified to the potential of the charged dust, through the Catalyst plates are formed and the precipitation plates (10) have an opposite potential.

13. The apparatus according to claim 13, characterized in that the catalyst and deposition plates (10) are briefly acted upon during a cleaning phase with respective opposite electrostatic voltage pulses.