DE102018010292A1 - Process for flue gas treatment and flue gas treatment plant - Google Patents

Abstract

The invention relates to a process for the treatment of flue gas, which arises in the combustion of carbonaceous fuels, in particular fossil fuels, in which at least one reactive oxygen species is generated electrochemically and wherein the flue gas is treated with the reactive oxygen species. The invention further relates to a use of an electrochemically generated reactive oxygen species for the chemical reduction of CO, in particular of CO contained in flue gas. The invention further relates to a flue gas treatment plant having a flue gas feed, characterized by a fluidly connected to the flue gas supply electrolysis device for the electrochemical generation of reactive oxygen species.

Description

The invention relates to a method for flue gas treatment and a flue gas treatment plant.

Today, most of the energy needed globally is generated by combustion processes. Particularly important in this context is the combustion of carbonaceous fuels.

Carbonaceous fuels include, in particular, the groups of fossil fuels and biogenic fuels. For example, fossil fuels include oil, natural gas, lignite, black coal and peat and their processed products. Further processing products are in particular gasoline, diesel, heating oil and the like. Biogenic fuels include those derived from renewable raw materials or waste. These are in particular wood, biogas and biofuels.

The product of combustion of such fuels is flue gases. These flue gases predominantly contain solid particles in the form of fly ash, particulate matter, soot and the gases water vapor, nitrogen, carbon dioxide, sulfur dioxide and nitrogen oxide.

Flue gases from power plants, blast furnaces, steel mills and other large combustion plants are freed from solids by flue gas cleaning and in some cases from sulfur dioxide (flue gas desulphurisation) and nitrogen oxide. Previously, they were distributed over large areas by high chimneys, so as not to overburden the surrounding area. In particular, the greenhouse gas carbon dioxide contained in flue gases can not be removed with the known flue gas cleaning process.

Such a method is for example from the AT 507890 A4 known, with which fine dust ≤ 10 microns in diameter can be detected. At the same time gaseous pollutants such as NO _x , SO _x , CFC and methane can be oxidatively eliminated and applied with the wash water. The removal of carbon dioxide is not possible with this method.

Global warming and emissions of climate-relevant gases such as carbon dioxide have been a hot topic of discussion in recent years and decades. Considerable solutions to CO ₂ management are required to meet the goal of global warming of +2 ° C by the European Parliament in 2009 within the next 100 years.

One way to achieve this goal is to reduce CO ₂ emissions per se. At present, this is mainly achieved by focusing on renewable energies and on certain fuels that emit a comparatively small amount of greenhouse gases. Such a fuel is for example natural gas. In contrast, coal, especially lignite, emits comparatively much CO ₂ . In Germany, therefore, more investments are currently being made in gas-fired power plants. On the other hand, coal-fired power plants, especially lignite-fired power plants, are shut down.

This has the adverse geostrategic side effect that the economy depends on foreign raw materials. Germany in particular has comparatively large lignite deposits. However, the natural gas needed to operate gas-fired power plants must be imported from outside the EU, in particular from Russia, Saudi Arabia and Iran.

Irrespective of this, however, the reduction in CO ₂ emissions alone will probably not be enough to achieve the climate goals. In this context, therefore, CO ₂ filters have been developed which are used in industry to reduce CO ₂ emissions to the atmosphere. However, these filters are predominantly CO ₂ storage, which must be laboriously stored, processed or disposed of.

There is therefore a vital economic interest in making carbon dioxide economically useful in itself. In particular, as a raw material for the chemical industry. Industrially reproducible processes for the utilization of CO ₂ are currently unknown.

It is therefore an object of the invention to provide a method by which the CO ₂ contained in the flue gas can be made available for further exploitation.

To solve the problem, the invention proposes a method for the treatment of flue gas, which in the combustion of carbonaceous fuels, in particular fossil fuels, arises in which at least one reactive oxygen species is generated electrochemically and wherein the flue gas is treated with the reactive oxygen species

It has surprisingly been found that reactive oxygen species are capable of chemically reacting with carbon dioxide such that carbon dioxide is almost completely chemically converted to other compounds. This is the sustainable way on the one hand, the CO ₂ Reduced emissions and opened up a new source of raw materials. The carbon of the carbon-containing reaction products preferably has a lower oxidation number than the carbon in the carbon dioxide. Carbon dioxide is thus chemically reduced during the reaction. The starting point is a complex reaction mechanism that has not yet been fully elucidated. What is certain, however, is that CO ₂ undergoes a chemical reaction with the reactive oxygen species, which leads to its conversion with a reduction in the oxidation number of the carbon.

The reaction produces a plurality of reaction products. These are predominantly C ₁ and C ₂ hydrocarbon compounds. These are in particular methanol, ethanol, methane and / or ethane. The invention provides for the first time a possibility for the reduction of CO ₂ from flue gases, which does not simply reduce the CO ₂ emissions by selecting the fuel or CO _{2 is} filtered from the flue gas. Rather, the products obtainable by the process according to the invention can be used as raw materials for industry, in particular the chemical industry. In particular, methane is an important starting material for industrial syntheses of hydrogen, methanol, acetylene, hydrogen cyanide, carbon disulfide and methyl halides. It serves as a starting point for many other organic compounds. Likewise, methanol is an important starting material for syntheses in the chemical industry. Of great importance in terms of quantity are the primary derivatives formaldehyde, acetic acid, MTBE, methyl methacrylate, methyl chloride and methylamine. These are processed into a series of secondary and tertiary derivatives. Known examples are vinyl acetate, acetic anhydride, phenol-formaldehyde resins and melamine resins. In addition, methyl methacrylate is an important raw material in polymer chemistry.

The reaction products are preferably isolated individually or fed as a mixture of substances at least one further separation process. Possible separation processes are in the field of gas separation, in particular membrane separation processes. Further, distillation, preferably fractional distillation, and / or extraction as liquid-based separation processes is preferred.

Another is added. The possibility according to the invention of utilizing CO ₂ on an industrial scale means that in order to reduce the CO ₂ emissions, it is no longer necessary to use fuels whose combustion produces comparatively little CO ₂ . On the contrary, it is even advantageous to use fuels that release comparatively much CO ₂ during combustion. A preferred fuel is therefore lignite. As a result, the production of the reaction products according to the invention is advantageously increased. The invention thus also allows the energy-economic separation of foreign raw materials, in particular natural gas. On the contrary, it is possible to make greater use of proven domestic raw materials, in particular lignite, in energy production. Advantageously, the consistent use of the method according to the invention also jobs in German and European lignite mining can be maintained or even expanded.

According to the invention, a reactive oxygen species is generated. Preferably, as the reactive oxygen species superoxide anion O _{2 •} ^- (former designation: superoxide anion), hydroxyl radical OH •, ozone O ₃ and / or singlet oxygen ¹ O ₂ generated. Preference is given to the generation of reactive oxygen radicals. This group preferably includes the hyperoxide anion and the hydroxyl radical. Hydroxyl radicals are particularly preferably produced. On the one hand, this species can be advantageously produced on an industrial scale. On the other hand, the yield of the chemical reaction between the hydroxyl radical and carbon dioxide is particularly high.

According to the invention, the reactive oxygen species are generated electrochemically. Preferably, the reactive oxygen species is generated by electrolysis. It is preferred that the electrolyte is at least partially formed from an ionic liquid. According to a preferred embodiment of the invention, the reactive oxygen species is generated by means of a diamond electrode. This largely prevents the formation of oxygen during the electrolysis. By using the diamond electrode, 90% of the electrical energy used is used to generate the reactive oxygen species, in particular the hydroxyl radical. Preferably, the diamond electrode is a boron-doped diamond electrode. This improves the conductivity of the electrode.

According to a preferred embodiment of the invention, an electrolysis tank is provided for carrying out the electrolysis. According to the invention, the electrolysis tank can be filled with electrolyte when carrying out the process.

According to the invention, at least one component of the flue gas is treated with the reactive oxygen species. It is conceivable to mix the flue gas and the reactive oxygen species in the gas phase. Preferably, a pressure chamber is provided for this purpose. This is especially possible in those cases where the reactive Oxygen species can be isolated as gas. This is preferably the case with ozone and singlet oxygen.

According to an alternative embodiment of the invention, the flue gas is introduced into the electrolysis tank for treatment with the reactive oxygen species. This has the advantage that treatment of the flue gas can take place directly at the point of generation of the reactive oxygen species, in particular the hydroxyl radicals. This reduces the likelihood of unwanted recombination between radical oxygen species, especially the hydroxyl radicals, for the intended reaction. The electrolysis tank preferably has inlets and outlets for the electrolyte and / or the flue gas. According to a preferred method, the flue gas is continuously introduced into the electrolysis tank, where it is treated with the reactive oxygen species. Subsequently, the reaction product (s) are discharged. Preferably, the electrolyte is continuously exchanged. This advantageously ensures that the production rate of the reactive oxygen species is kept at a constant level. It is preferred if the electrolyte, which is preferably at least partially formed from an ionic liquid, is injected into the flue gas stream before being introduced into the electrolysis tank. This forms an aerosol of flue gas and electrolyte. Through this optimized distribution, the treatment time can be reduced.

Alternatively or additionally, the electrolyte can be introduced in a liquid state into the electrolysis tank. In the event that the electrolyte is used only in the liquid state, it is preferred that the flue gas is introduced into the electrolyte. It is harmless to the reaction that carbon dioxide is present in the electrolyte partly in the gaseous state, partly as dissolved CO ₂ and partly as carbonic acid, bicarbonate and / or carbonate.

According to a preferred feature of the invention, a plurality of gas outlets and / or gas nozzles are provided for introducing the flue gas and / or the flue gas electrolyte aerosol.

According to a preferred embodiment of the invention, the flue gas is subjected to a flue gas purification prior to treatment with the reactive oxygen species. In particular, solid particles, in particular fly ash, fine dust and soot are freed. This prevents unwanted side reactions with the oxygen species. Preferably, the flue gas is supplied to further purification steps before treatment with the reactive oxygen species. In particular, sulfur oxides and / or nitrogen oxides are removed. This also prevents unwanted side reactions.

The method according to the invention can be carried out directly in a combustion plant, in particular a power plant. The directly generated flue gases are fed to the process according to the invention. By implementing such an integrated system, the processes can be optimized and costs can be saved. Alternatively, an independent treatment plant is conceivable. For example, bottled and stored flue gas can be treated in this independent processing plant. This has the advantage of being independent of the location of the incinerator, so that flue gases from a variety of incineration plants can be processed.

The invention further relates to the use of an electrochemically generated reactive oxygen species for the chemical reduction of CO ₂ .

The electrochemically generated reactive oxygen species is preferably a hydroxyl radical.

The invention also relates to a flue gas treatment plant. The flue gas treatment plant according to the invention has a flue gas supply. This can be formed in particular by at least one flue gas pipe. Preferably, the flue gas supply is formed by a flue gas piping system of a plurality of tubes. As a result, the flue gas originating from a flue gas source is fed to the treatment.

According to a preferred feature of the invention, the flue gas treatment plant has at least one flue gas purification device. A flue gas cleaning device is preferably a filter unit for removing solid particles, a flue gas desulphurisation device for removing in particular sulfur oxides, a denitrification device for removing nitrogen oxides and / or an activated carbon filter for removing organic radicals, dioxins and / or heavy metal impurities.

According to the invention, the flue-gas treatment plant has an electrolysis device which is fluidically connected to the flue-gas feed to generate reactive oxygen species, in particular hydroxyl radicals. For this purpose, the electrolysis device preferably has a diamond electrode according to the invention.

The diamond electrode preferably has a base body. The main body is covered with a layer of polycrystalline diamond coated. The layer thickness of the diamond layer is preferably between 2 μm and 25 μm, preferably between 5 μm and 10 μm. The electrode is thus economical to manufacture and operate effectively.

Preferably, the diamond electrode is coated by chemical vapor deposition. For this purpose, the electrode is placed in a vacuum chamber. Subsequently, the electrode is contacted in the vacuum chamber with a gas mixture comprising hydrogen and a carbon source. The carbon source is preferably formed from a hydrocarbon. Particularly preferably, the carbon source is formed from methane. Preferably, the gas mixture is activated before contacting with the body at temperatures above 2000 ° C, preferably at 2800 ° C. The activation preferably takes place on heated tungsten wires. The coating is carried out at elevated temperature and reduced pressure compared to standard chemical conditions. For the purposes of the invention, standard chemical conditions have a temperature of 0 ° C and a pressure of 1 bar. Preferably, the electrode is coated at a temperature between 500 ° C and 1000 ° C, preferably between 600 ° C and 950 ° C. Preferably, the electrode is coated at a pressure between 15 and 30 mbar, preferably at 20 mbar.

According to a preferred embodiment, the diamond electrode is formed as a diamond anode, preferably as a boron-doped diamond anode. As a result, reactive oxygen species, in particular hydroxyl radicals, can be generated directly from water.

The reactive oxygen species formed by the diamond electrode is preferably a hydroxyl radical.

The electrolysis device preferably has an electrolysis container which can be filled with the electrolyte. In the electrolysis tank, the diamond electrode is arranged. Electrolysis tank preferably has gas inlets and / or nozzles for the introduction of the flue gas and / or the flue gas electrolyte aerosol. Preferably, in particular when the electrolyte is used in liquid form, the electrolysis tank is connected to an exchange system for the electrolyte. The exchange system has a pump, a reservoir and connections for fluidic connection with the electrolysis tank. For this purpose, the electrolysis tank has at least one inlet and at least one outlet. As a result, the electrolyte can be replaced continuously.

• 1 eine erfindungsgemäße Rauchgasaufbereitungsanlage in schematischer Darstellung;
• 2 ein Verfahren gemäß der Erfindung in Form eines Flussdiagramms.

The invention will be explained with reference to two embodiments. Show

• 1 a flue gas treatment plant according to the invention in a schematic representation;
• 2 a method according to the invention in the form of a flow chart.

1 shows a flue gas treatment plant according to the invention. The heart of the system is the electrolysis tank 10 comprising cathodes 11 , Channels 9 and one or more diamond anodes 13 ,

The cathodes 11 may be formed in particular of stainless steel or copper. The channels 9 extend inside the electrolysis tank 10 between cathodes 11 and anode 13 , On both sides they have inlets and outlets for a flue gas electrolyte aerosol and for the electrolyte in liquid form. Within the channels 9 the treatment of the flue gas with the electrolyte takes place.

In the present case, the electrolyte is formed from at least one ionic liquid. The flue gas treatment plant has a storage tank 1 for the electrolyte. It also provides a filling line 2 ready to put the reservoir 1 with a liquid container 6 fluidically connects. They are sensors 3 and 5 provided over which the liquid container 6 and at least the reservoir 1 signal technically connected. The task of the sensor is to monitor the level of the electrolyte in the liquid container 6 , If the level falls below a predetermined value, in an automated process electrolyte from the reservoir 1 in the liquid container 6 pumped.

The flue gas treatment plant has a flue gas inlet 4 on. About the smoke gas inlet 4 flue gas, which has already been desulfurized in process steps, not shown here, fed to the treatment according to the invention. According to an optional process step, the flue gas may be pre-scrubbed 24 be subjected. For this purpose, electrolyte from the liquid container 6 by means of a pump 22 a nozzle unit 7 fed. By means of the nozzle unit 7 the electrolyte is injected into the flue gas stream and washed in this way. The flue gas then passes through the nozzle unit 7 wherein an aerosol of flue gas and electrolyte is formed. This aerosol flows into an anteroom 8th one in which the aerosol is collected and from which it then enters the channels 9 is directed. Furthermore, in the anteroom 8th an emergency injection device 25 arranged.

In addition to the flue gas to be treated the channels 9 of the electrolysis tank via the line G liquid electrolyte supplied in the form of at least one ionic liquid. The management G is liquid tank side with a pump 21 fluidically connected.

The electrolysis tank has in cross-section with respect to the plane of the drawing on top and bottom pressure plates 12 , This allows the cross sections of the channels 9 be downsized. The in the channels 9 In this way, guided media are put under pressure and put under pressure.

The diamond anode 13 has a base body. The main body is coated with a layer of polycrystalline diamond. The layer thickness of the diamond layer is presently between 5 .mu.m and 10 .mu.m. The polycrystalline diamond layer is doped with boron in the present case. It can be operated with a current density of 15 mA / cm ² . There can be several anodes 13 be provided. The necessary number can be determined depending on the amount of flue gas to be treated.

To the electrolysis tank 10 joins a collecting unit. The collecting unit has a collecting space 14 for gaseous reaction products of the flue gas treatment, a collecting container 18 for the spent electrolyte and liquid reaction products of the flue gas treatment and a safety flap 15 on.

About the safety flap 15 can in case of malfunction of the plant, the flue gas through an emergency line 16 be discharged from the plant.

The collection room 14 can have a valve 23 , Preferably a gas solenoid valve, the gaseous reaction products are removed and fed to another use.

The collection container 18 can over the valve 20 , preferably a solenoid valve, be emptied. For the automation of this process are sensors 17 . 19 intended. The sensors 17 . 19 are with signaling with the valve 20 connected and control this depending on the level of the collection container 18 ,

2 shows a flue gas treatment process according to the invention in general form. In the method is in the process step V1 Flue gas generated. In the present case, lignite is incinerated in a lignite-fired power station for this purpose.

In process step V2 the flue gas is purified in particular by solid particles, sulfur oxides and nitrogen oxides. To liberate solid particles, the flue gas is passed through a filter system comprising electrostatic precipitator and / or a fabric filter. Subsequently, the freed of solid particles flue gas in a gas scrubbing, in particular flue gas desulfurization, fed. This sulfur oxides and hydrogen chloride are removed from the flue gas. Subsequently, the flue gas is fed to a denitrification device for the removal of nitrogen oxides. Subsequently, the flue gas is passed through an activated carbon filter to remove organic residues, dioxins and heavy metals from the flue gas.

In process step V3 are generated in the course of an electrolysis by means of a boron-doped diamond anode and an electrolyte, which is preferably at least partially formed from at least one ionic liquid, continuously hydroxyl radicals.

In process step V4 The pre-cleaned flue gas is introduced into an electrolysis tank for the purpose of treatment with hydroxyl radicals.

It is preferred to start the generation of the hydroxyl radical prior to the introduction of the flue gas. This ensures that already reactive species at the time of introduction of the flue gas are present in the electrolyte.

In process step V5 the flue gas in the electrolysis tank is treated with the hydroxyl radicals. In this case, a chemical reaction between the hydroxyl radicals and at least the originating from the flue gas CO ₂ takes place. Here, the CO _{2 is} chemically reduced. The originating from the flue gas CO ₂ is in the electrolysis vessel in gaseous form, as dissolved CO ₂ , as carbonic acid, bicarbonate and / or carbonate before. However, this does not change the result.

In process step V6 the reaction products are isolated individually or collected as a mixture of substances. Gaseous reaction products, especially methane, rise after treatment and can be collected and withdrawn. By means of suitable analysis methods, the gaseous constituents can be identified. The use of a GC (gas chromatography) with mass spectrometer is preferred. Liquid and dissolved reaction products accumulate in the electrolyte. Preferably, the electrolyte is continuously circulated in the electrolysis tank. In this case, the electrolyte enriched with reaction products is discharged from the electrolysis tank and replaced by fresh electrolyte. The reaction products can then be removed from the electrolyte by suitable separation techniques. Preferred separation processes are in particular fractional distillation and / or extraction.

The reaction products can then be bottled and stored to allow for their further use as a raw material in due course to the chemical industry. Alternatively, the reaction products, as known from chemical parks, can be directly fed to their further use via pipelines.

LIST OF REFERENCE NUMBERS

1

Storage tank for ionic liquid

2

Filling line for ionic liquid

3

sensor

4

Flue gas inlet

5

sensor

6

liquid container

7

nozzle unit

8th

anteroom

9

channel

10

electrolysis tank

11

cathode

12

printing plate

13

diamond anode

14

staging area

15

flap

16

emergency line

17

sensor

18

Clippings

19

sensor

20

Valve

21

pump

22

pump

23

Valve

24

gas scrubbing

25

Noteinspritzungseinrichtung

G

management

V1

Burning lignite

V2

Flue gas cleaning

V3

Generation of hydroxyl radicals

V4

Introduction of the flue gas into the electrolysis tank

V5

Treatment of the flue gas

V6

Isolation of the reaction products

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• AT 507890 A4 [0006]

Claims (10)

Process for the treatment of flue gas, which is formed in the combustion of carbonaceous fuels, in particular fossil fuels, in which at least one reactive oxygen species is generated electrochemically and wherein the flue gas is treated with the reactive oxygen species. Method according to Claim 1 , characterized in that are generated as reactive oxygen species hydroxyl radicals and / or hyperoxide anions. Method according to one of Claims 1 or 2 , characterized in that the reactive oxygen species is generated electrochemically by means of a diamond electrode, in particular a boron-doped diamond electrode. Method according to Claim 3 , characterized in that the at least one reactive oxygen species in an electrolysis tank comprising the diamond electrode is produced by electrolysis of an at least partially composed of at least one ionic liquid electrolyte. Method according to Claim 4 , characterized in that the flue gas is introduced into the electrolysis tank for treatment with the reactive oxygen species. Method according to one of the preceding claims, characterized by the following method steps: - production of flue gas by combustion of a carbonaceous fuel; - Exemption of the flue gas of solid particles and / or sulfur-containing components and / or nitrogen oxide-containing components; - Generation of hydroxyl radicals in a water-filled electrolysis tank by electrolysis of an at least partially consisting of at least one ionic liquid electrolyte by means of a boron-doped diamond electrode; - Introduction of the flue gas into the electrolysis tank. - Treatment of the gaseous and / or dissolved components of the flue gas with the hydroxyl radicals in the electrolysis tank. Use of an electrochemically generated reactive oxygen species for the chemical reduction of CO ₂ , in particular of CO ₂ contained in flue gas. Use after Claim 7 , characterized in that the reactive oxygen species is formed by hydroxyl radicals. Flue gas treatment plant comprising a flue gas supply, characterized by an electrolytically connected to the flue gas supply electrolysis device for the electrochemical generation of reactive oxygen species. Flue gas treatment plant according to Claim 9 comprising a flue gas cleaning device, which is fluidly connected to the electrolysis device via the flue gas supply, wherein the flue gas cleaning device has at least one filter unit for removing solid particles, at least one flue gas desulfurization device for removing sulfur oxides and / or at least one denitrification device for removing nitrogen oxides, and wherein the electrolysis device an electrolytic container which can be filled with an electrolyte which is at least partially composed of at least one ionic liquid, a diamond anode being arranged in the electrolysis container, the diamond anode having a base body coated with a polycrystalline diamond layer, the diamond layer having a layer thickness between 2 μm and 25 μm having.

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