AT511939A4 - FILTER - Google Patents

Abstract

The invention relates to a filter for the separation of chromium (VI) compounds from exhaust gases for a decentralized power generation unit. The filter is provided in the exhaust path and includes a first filter unit having a large inner surface provided with a solid acid and a second filter unit having a large inner surface provided with a solid base. In a subsequent white space flaking and dust are collected.

Description

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Vaillant Group Austria GmbH PT 5167 AT

filter

The invention relates to a filter for the separation of chromium (VI) compounds from exhaust gases for a power generation unit and a power generation unit with a filter according to the invention.

In energy production units, such as, for example, decentralized burners, Stirling engines or fuel cell systems, high-temperature-resistant stainless steels and nickel-based alloys are used in components that conduct combustion gas, air and, in particular, exhaust gas. High temperature stainless steels and nickel base alloys contain chromium in large quantities which form a protective oxide topcoat to protect the component from high temperature corrosion. However, this cover layer may be affected by the atmosphere, e.g. be attacked by an increased water vapor partial pressure and chromium compounds can be discharged as chromium hydroxides from the component. Depending on the temperature, of the partial pressure of oxygen and water vapor, metastable gaseous chromium (oxy) hydroxides (chromium evaporation) form from the protective Cr203 top layer. Cyclic thermal stress can also lead to microcracks in the protective covering layer and chromium oxides can flake off and thus be discharged. On the one hand, the protective cover layer is consequently lost. On the other hand, human-toxic and water-polluting chromium compounds can be discharged directly or with the condensate from the energy production unit. φ · · · * ·· * · # # • φ · · Φ »» * «• *« · * · »* * * 2 ..............

Chromium compounds can also enter the flue gas with the fuel, e.g. For example, coal and biogenic fuels can contain larger amounts of chromium. During the combustion process, these chromium compounds are converted into chromium oxides. In this case, chromium (VI) -containing compounds can arise.

While it is known from power plant processes to precipitate these chromium (VI) compounds in scrubbers (e.g., amine scrubbing) and remove them from the flue gas with the wash water. Subsequently, the washing water is purified by means of anion and cation exchangers of the chromium compounds and fed back to the flue gas scrubber. Wet chemical processes usually require a high expenditure on equipment, which is why these methods for use in small decentralized power generation plants can be used only partially or not at all or can not be represented in these costs.

It is therefore an object of the invention to provide a simple apparatus, compact and inexpensive filter for the separation of chromium (VI) compounds from exhaust gases to power plants, especially at small decentralized power plants such as fuel cells, combined heat and power plants with e.g. Stirling engines or burners provide.

This object is achieved according to the features of claim 1. Advantageous embodiments result from the features of the dependent claims. The independent claims describe a power generation unit and a fuel cell with a filter according to the invention.

According to the invention, the filter is provided in the exhaust path and comprises a first filter unit with a first filter body located in the flow path of the exhaust gas. This first filter unit is arranged in the exhaust path, that sets a temperature of 180 ° C to 500 ° C and preferably from 300 ° C to 500 ° C during operation in the first filter unit. This temperature range thermodynamically promotes the conversion of chromium (VI) compounds to chromium (III) compounds.

The first filter body preferably consists of a metal fabric, a metal foam or a ceramic foam. This ensures on the one hand a large effective surface and on the other hand a low flow velocity of the exhaust gas to be filtered and thus a long residence time in the filter.

In a development of the invention, the first filter body contains a solid acid. The acid promotes and accelerates the reduction of the chromium (VI) compound.

The solid acid used is preferably a Bronsted acid, a Lewis acid or tungsten oxide, which is particularly preferably applied as a coating on a support of zirconium or zirconium oxide.

In a further development of the invention, a second filter unit is provided, which is connected downstream of the first filter unit in the exhaust gas stream. In the second filter unit, the harmless chromium (III) compounds converted by the first filter unit are effectively separated. Again, a large specific surface favors adsorption. By means of a basic material, the chromium (III) compounds and possibly still existing chromium (VI) compounds can precipitate or form non-volatile, solid chromium complexes.

Preferably, the second filter body consists of a metal fabric, a metal foam or a ceramic foam. This ensures, on the one hand, a large effective surface area and, on the other hand, a low flow velocity of the exhaust gas to be filtered, and thus a long residence time in the filter. In one variant, the filter body is made of aluminum hexaaluminate.

It is advantageous that the second filter body consists of the solid basic material barium oxide or a coating with barium oxide. In a further development of the invention, a space for receiving chromium oxide flakes from the second filter unit is provided below the second filter unit. In this void, the discharges can collect and be removed as part of a maintenance,

An advantageous design of the exhaust system provides that the gas flow is diverted in the empty space in a direction opposite to gravity, whereby settle dust-like constituents of the exhaust gas and can no longer be discharged with the gas flow.

The power generation unit is preferably a fuel cell, a burner or a combined heat and power plant based on an internal combustion engine, such as a combustion engine. a Stirling engine, an internal combustion engine with internal combustion or a gas turbine, which are each housed decentralized in a residential building or commercial enterprise, etc.

In cases where the power generation unit has an exhaust gas heat exchanger, the filter according to the invention is advantageously provided in front of the exhaust gas heat exchanger to ensure the required temperatures in the filter.

An energy conversion unit according to the invention, preferably a fuel cell according to the invention, has the above-described filter according to the invention.

The invention will now be explained in detail with reference to FIGS. Here are Es represent:

Figure 1: an energy generation unit according to the invention with a erfindungsge MAESSEN filter

Figure 2: in detail an embodiment of the filter according to the invention

FIG. 1 shows a power generation unit 13 according to the invention with the filter 4 according to the invention. The power generation unit 13 is, for example, a decentralized combined heat and power unit based on a fuel cell or a stirring motor or a burner. Air and fuel are supplied via the air supply 11 and the fuel supply 12. In the case of a fuel cell or a Stirling engine 13 power is generated in the power generation unit. In addition, waste heat accumulates, which can be used for heating purposes. Electricity and waste heat are used decentrally. However, the electricity can also be fed into the grid. In the case of a burner, only heat is generated by the power generation unit 13. Via a line 5 unpurified exhaust gas is discharged. The temperature of the exhaust gas is 180 ° C to 500 ° C. This exhaust gas may contain toxic chromium (VI) compounds, which are filtered by the filter 4. The filter 4 consists of a first filter unit 1, a second filter unit 2 and a void 3. The first filter unit 1 contains a sixth

Filter body, which consists for example of a metal fabric, a metal foam or a ceramic foam and on the one hand has a large surface area and on the other hand, a low flow velocity and thus causes a long residence time of the exhaust gas in the first filter unit. Preferably, the first filter unit 1 contains a solid acid such as tungsten oxide. The high temperature of the first filter unit 1 and the acid promote conversion of the toxic chromium (VI) compounds into uncritical chromium (III) compounds. There is a reduction reaction 4 CrO 3 - »2 Cr 2 O 3 + 3 O 2.

Subsequently, the filter 4 has a second filter unit 2, which also contains a filter body with a large surface, which ensures a long residence time of the exhaust gas in the second filter unit. In the second filter unit, a basic material such as barium oxide is introduced. There is an adsorption or precipitation of the chromium (III) compounds in the second filter unit 2. The adsorption or precipitation in the second filter unit 2 can lead to an increase of a chromium layer in the second filter unit 2. If the layer thickness has exceeded a critical layer thickness, it will lead to Chromoxidabplatzungen. Therefore, under the second filter unit 2, a void 3 is provided, in which the flakes can fall down.

The thus purified from the chromium compounds exhaust gases are then passed through an exhaust heat exchanger 7, from which the heat of the exhaust gas is removed by means of a Wärmeauskopp- treatment. The heat can be used for heating purposes, for example. Subsequently, the cooled exhaust gas is discharged via a line 8. The resulting in the heat extraction condensate will also be removed via a line 9.

Figure 2 illustrates in detail an embodiment of the filter 4 according to the invention.

In the empty space 3, the exhaust gas flow is deflected against gravity, so that chrome (lll) dusts and spalling can no longer be discharged with the gas flow.

LIST OF REFERENCE NUMERALS 1 First filter unit 2 Second filter unit 3 Empty space 4 Filter 5 Unpurified exhaust gas line 6 Purified exhaust gas line 7 Exhaust gas heat exchanger 8 Cooled exhaust gas line 9 Condensate line 10 Heat extraction 11 Air supply 12 Fuel supply 13 Energy production unit

Claims (17)

1 1. A filter for separating chromium (VI) compounds from exhaust gases for an energy production unit, wherein the filter is provided in the exhaust gas path, characterized in that the filter has a first filter unit with a first filter body provided in the flow path of the exhaust gas, wherein the first filter unit is connected to the power generation unit that sets in the first filter unit in operation a temperature of 180 ° C to 500 ° C, preferably 300 ° C to 500 ° C. wherein the first filter unit converts the chromium (VI) compounds to chromium (III) compounds. 2. Filter according to claim 1, characterized in that the first Fiiterkörper consists of a metal mesh, a metal foam or a ceramic foam. 3. Filter according to claim 1 or 2, characterized in that the first filter body contains a solid acid. 4. Filter according to claim 3, characterized in that the first filter body is formed from a Brönsted acid or coated with a Bronsted acid. 2 5. Filter according to claim 3, characterized in that the first filter body is formed from a Lewis acid or coated with a Lewis acid 6. Filter according to claim 3, characterized in that the first filter body is formed from tungsten oxide or coated with tungsten oxide. 7. Filter according to claim 6, characterized in that the first filter body consists of tungsten oxide coated zirconium or zirconium oxide 8. Filter according to one of the preceding claims, characterized in that the filter comprises a second filter unit, which is connected downstream of the first filter unit in the exhaust gas stream, and in that the second filter unit has a second filter body with a large specific surface, which is equipped with fixed bases. 9. Filter according to claim 8, characterized in that the second filter body consists of a metal fabric, a metal foam or a ceramic foam. 10. Filter according to claim 8 or 9, characterized in that aluminum hexaaluminate is used as the second filter body. 11. Filter according to one of claims 8 to 10, characterized in that is used as solid bases barium oxide or a coating with barium oxide. 12. Filter according to one of claims 1 to 11, characterized in that a space for receiving Chromoxidabplatzungen is provided below the second filter unit. 3 13. A filter according to claim 12, characterized in that the empty space is designed so that the gas flow is directed in the direction of gravity or directed perpendicular to the force of gravity and is umgeenkt in the void against gravity. 14. Filter according to one of the preceding claims, characterized in that the energy generating unit is a decentralized fuel cell, a decentralized burner or a decentralized combustion engine. 15. The filter according to claim 14, characterized in that the energy generating unit has an exhaust gas heat exchanger for utilizing the exhaust gas heat and that the filter is arranged in the flow direction of the exhaust gas in front of the exhaust gas heat exchanger. 16 decentralized power generation unit, characterized in that the power generation unit comprises a filter according to one of the preceding claims. 17. Fuel cell system, characterized in that the fuel cell system comprises a filter according to one of claims 1 to 16.