Method for separating off and immobilizing carbon dioxide and/or carbon monoxide from an exhaust gas

Abstract

The invention relates to a method for separating off and immobilizing carbon dioxide and/or carbon monoxide from an exhaust gas (18). In the method, a stoichiometric ratio of carbon dioxide to hydrogen, and/or of carbon monoxide to hydrogen, which is suitable for a methanation reaction is set by virtue of a corresponding quantity of hydrogen or alternatively carbon dioxide and/or possibly carbon monoxide being supplied, with an auxiliary gas (24), to the exhaust gas (18). Subsequently, a catalytic reaction is performed in which, as starting products, carbon dioxide and/or carbon monoxide and hydrogen are converted into methane and water. The methane is separated off from the product of the catalytic reaction and is subsequently split into carbon and hydrogen, wherein the carbon takes solid form. The split-off carbon is collected and disposed of.

Claims

1. A process for separation and immobilization of carbon dioxide and/or carbon monoxide from an offgas, wherein the offgas is obtained by combustion of fossil fuels in a power plant, as a byproduct in an industrial process or as an extraction gas in the extraction of fossil fuels, comprising the steps of: a) establishing a stoichiometric ratio of carbon dioxide to hydrogen and/or of carbon monoxide and hydrogen which is suitable for a methanization reaction by supplying the offgas with a corresponding amount of hydrogen or alternatively carbon dioxide and/or carbon monoxide by an additive gas, b) performing a catalytic reaction in which the reactants carbon dioxide and/or carbon monoxide and also hydrogen are converted into methane and water, c) separating the methane from the product of the catalytic reaction, wherein remaining residual gases are discharged into the atmosphere, d) cracking the methane into carbon and hydrogen, wherein the carbon is generated as a solid, e) collecting the cracked carbon, and f) landfilling the collected carbon wherein the offgas is a mixture of at least two components, wherein the offgas comprises at least carbon dioxide or carbon monoxide as one component and the offgas comprises at least one inert gas as a further component which remains in the offgas after the separation according to step c), wherein to establish the stoichiometric ratio the proportions of carbon dioxide and/or of carbon monoxide present in the offgas are measured, wherein the proportion of hydrogen present in the offgas is optionally also measured.

2. The process of claim 1, wherein in step a) a stoichiometric ratio of 4 hydrogen molecules to 1 molecule of carbon dioxide and/or 3 hydrogen molecules to 1 molecule of carbon monoxide is established in the offgas, wherein in the case of an excess of hydrogen in the offgas an additive gas containing carbon dioxide and/or carbon monoxide is used and in the case of a deficit of hydrogen an additive gas containing hydrogen is used.

3. The process of claim 1, wherein the separation of the methane is effected by condensation, adsorption, or separation with membranes.

4. The process of claim 1, wherein the cracking of the methane is effected by a pyrolysis process.

5. The process of claim 1, wherein the cracking of the methane produces hydrogen and wherein the energy required for the cracking is provided by partial utilization of the hydrogen.

6. The process of claim 1, wherein the cracking of the methane produces hydrogen and wherein at least a portion of the hydrogen is used as a starting material in the chemical industry or as an energy carrier for the generation of electricity, heat, or as a fuel for vehicles.

7. The process of claim 1, wherein the methane separated in step c) is fed into a gas network and to perform step d) of the process methane is withdrawn from the gas network.

8. The process of claim 1, wherein the offgas is desulfurized, purified of other impurities, and/or dedusted in a pretreatment.

9. The process of claim 1, wherein the hydrogen supplied in step a) is produced by an electrolysis operation, wherein the oxygen likewise generated is supplied to a combustion operation in which the offgas treated with the process is formed.

10. The process of claim 1, wherein the carbon obtained as a solid is mixed with a carrier before the landfilling of step f), wherein the carrier is selected from loam, gravel, building rubble, slags, rocks, wastes, or a combination of two or more of these carrier materials.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Working examples of the invention are shown in the drawings and more particularly elucidated in the description which follows.

(2) FIG. 1 shows a schematic representation of a first embodiment of the process where the offgas comprises an excess of carbon oxides and

(3) FIG. 2 shows a schematic representation of a second embodiment of the process where the offgas comprises an excess of hydrogen.

(4) The following description of the working examples of the invention refers to identical or similar components and elements with identical reference numerals without repeated description of these components and elements in individual cases. The figures are a mere schematic representation of the subject matter of the invention.

(5) FIG. 1 shows a first embodiment of the process in which an offgas 18 rich in carbon oxides, which in the example shown contains CO.sub.2, CO and further components represented by “X” such as nitrogen and argon, is mixed with H.sub.2 as additive gas 24 to establish a stoichiometric ratio of CO.sub.2 to H.sub.2 and CO to H.sub.2 which is optimal for a subsequent methanization reaction. The hydrogen H.sub.2 is produced from water H.sub.2O using electrical energy via an electrolyzer 14. In the example shown, the oxygen O.sub.2 likewise generated in the electrolysis is discharged into the atmosphere. Aternatively, the oxygen O.sub.2 may also be supplied to a combustion operation to form the offgas 18.

(6) The offgas 18 mixed with the hydrogen H.sub.2 is supplied to a reactor 10 in which a catalytic methanization reaction is performed. Carbon dioxide CO.sub.2 and hydrogen H.sub.2 and also carbon monoxide CO and hydrogen H.sub.2 react to afford a methane CH.sub.4 and water H.sub.2O. In a separation apparatus 12, the water H.sub.2O produced in the methanization and the further components X are separated from the methane CH.sub.4. The methane CH.sub.4 is subsequently fed into a natural gas network 16.

(7) At the location where landfilling of carbon black C may be effected, the methane CH.sub.4 is withdrawn from the natural gas network 16 and supplied to a methane cracker 20. In the methane cracker 20, the methane CH.sub.4 is cracked into carbon black C and hydrogen H.sub.2 by pyrolysis. The hydrogen H.sub.2 is subsequently available for further utilization, for example as a starting material for the chemical industry or as an energy carrier.

(8) The carbon generated in the form of carbon black C during the cracking of the methane CH.sub.4 is stored in a carbon landfill 22 and thus permanently removed from the atmosphere.

(9) FIG. 2 shows a schematic representation of a second embodiment of the process. A hydrogen-rich offgas 18, which in the example shown contains CO.sub.2, CO, H.sub.2 and the further components represented by “X”, is mixed with an additive gas 24 containing CO.sub.2 to establish a stoichiometric ratio of CO.sub.2 to H.sub.2 and CO to H.sub.2 which is optimal for a subsequent methanization reaction. The additive gas 24 may contain further components represented by “Y” such as for example H.sub.2O or N.sub.2.

(10) The resulting reaction mixture is supplied to a reactor 10 in which a catalytic methanization reaction is performed. Carbon dioxide CO.sub.2 and hydrogen H.sub.2 and also carbon monoxide CO and hydrogen H.sub.2 react to afford a methane CH.sub.4 and water H.sub.2O. In a separation apparatus 12, the water H.sub.2O produced in the methanization and any further components “X” and “Y” present are separated from the methane CH.sub.4. The methane CH.sub.4 is subsequently fed into a natural gas network 16.

(11) At the location where landfilling of carbon black C may be effected, the methane CH.sub.4 is withdrawn from the natural gas network 16 and supplied to a methane cracker 20. In the methane cracker 20, the methane CH.sub.4 is cracked into carbon black C and hydrogen H.sub.2 by pyrolysis. The hydrogen H.sub.2 is subsequently available for further utilization, for example as a starting material for the chemical industry or as an energy carrier.

(12) The carbon generated in the form of carbon black C during the cracking of the methane CH.sub.4 is stored in a carbon landfill 22 and thus permanently removed from the atmosphere.

(13) The invention is not limited to the presently described embodiments and the aspects highlighted therein. On the contrary, a multiplicity of variations which are within the purview of those skilled in the art is possible within the scope specified by the claims.

LIST OF REFERENCE NUMERALS

(14) 10 Reactor 12 Separating means 14 Electrolyser 16 Natural gas network 18 Offgas 20 Methane cracker 22 Carbon landfill 24 Additive gas