Providing carbon dioxide by means of oxygen-based combustion

Abstract

A method for preparing a carbonaceous product includes providing oxygen, in particular from electrolysis, and providing a fuel. The method also includes combusting the fuel with the oxygen by an oxy-fuel combustion process in order to provide energy, purifying a flue gas produced by the oxy-fuel combustion process, and separating carbon dioxide from the flue gas produced by the oxy-fuel combustion process, wherein energy provided by the oxy-fuel combustion process includes, in particular exclusively, heat which is used as process heat for purifying and/or for synthesising or providing the carbonaceous product. A corresponding system is designed to carry out the described method.

Claims

1. A process for producing a carbon-containing product, comprising: providing oxygen (O2), and a fuel, combusting the fuel by means of the oxygen (O2) in an oxyfuel process to provide energy, purifying a flue gas formed by the oxyfuel process, and separating carbon dioxide (CO2) from the flue gas formed by the oxyfuel process, comprising reacting the oxygen (O2) in the flue gas with hydrogen (H2) to form water (H2O), wherein the energy provided by the oxyfuel process comprises heat which is utilized as process heat for a CO2-based synthesis that produces the carbon-containing product and that comprises an endothermic reaction.

2. The process as claimed in claim 1, wherein hydrogen (H2) is provided and the carbon dioxide (CO2) which has been separated off is reacted with the hydrogen (H2) in the CO2-based synthesis to give the carbon-containing product.

3. The process as claimed in claim 2, wherein the CO2-based synthesis comprises a reverse water gas shift reaction.

4. The process as claimed in claim 1, wherein the carbon-containing product is a secondary energy carrier.

5. The process as claimed in claim 1, wherein the carbon-containing product is methane, methanol, MTBE, DME, OME, kerosene, gasoline, diesel and/or waxes.

6. The process as claimed in claim 1, wherein the fuel is biomass or biomass-based, and/or a standardized fuel present in pressed form or pellet form.

7. The process as claimed in claim 1, wherein the provision of the oxygen (O2) and/or hydrogen (H2) occurs by means of fluctuating renewable energy and the provision of the energy occurs in a nonfluctuating manner.

8. The process as claimed in claim 2, wherein the provision of the oxygen (O2) and/or the provision of the hydrogen (H2) occurs by means of an electrolysis.

9. The process as claimed in claim 8, wherein the electrolysis is carried out under elevated pressure so that the oxygen (O2) and the hydrogen (H2) are likewise present under elevated pressure or the oxygen (O2) and the hydrogen (H2) are provided in compressed form after they have been produced electrolytically.

10. The process as claimed in claim 1, further comprising a further carbon dioxide purification step subsequent to separating the carbon dioxide (CO2) from the flue gas and comprising reacting the oxygen (O2) in the flue gas with hydrogen (H2) to form water (H2O).

11. The process as claimed in claim 1, wherein the energy provided by the oxyfuel process comprises heat which is utilized for subsequent power-heat coupling.

12. The process as claimed in claim 1, wherein the energy provided by the oxyfuel process comprises electric energy which is obtained as nonfluctuating energy.

13. The process as claimed in claim 1, wherein the oxyfuel process is carried out without flue gas recirculation.

14. The process as claimed in claim 1, wherein a fluidized bed is used for the combustion of the fuel.

15. The process as claimed in claim 1, wherein the energy provided by the oxyfuel process comprises exclusively heat.

16. The process as claimed in claim 3, wherein the carbon-containing product comprises methanol.

17. The process as claimed in claim 12, wherein the energy provided by the oxyfuel process comprises electric energy which is obtained as nonfluctuating energy, by means of a steam power process.

18. The process as claimed in claim 1, wherein the fuel is combusted in a minimally superstoichiometric amount that is effective to ensure some of the oxygen (O2) remains unburnt and part of the flue gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows, in simplified form, a process sequence of the process of the invention in the form of a flow or block diagram.

DETAILED DESCRIPTION OF INVENTION

(2) In the working examples and in the FIGURE, identical elements or elements having the same effect can in each case be denoted by identical reference symbols. The elements depicted and their relative sizes are basically not to be regarded as being true to scale, but instead individual elements can be depicted exaggeratedly thick or large for better presentation and/or for better understanding.

(3) FIG. 1 indicates, in simplified form, a process according to the invention for producing or providing carbon dioxide or a carbon-containing product, in particular hydrocarbon-based product, P.

(4) FIG. 1 shows, inter alia, a plant 100. The plant 100 is advantageously equipped for providing a carbon-containing product, for example also pure carbon, or in particular a hydrocarbon-based product. In particular, the plant 100 is advantageously a PtCbF plant (“power-to-carbon-based fuels”), i.e. equipped for providing the abovementioned product, in particular a fuel, from energy provided, for example from renewable sources and/or the oxygen-based combustion of a fuel.

(5) For this purpose, the plant 100 advantageously comprises a combustion apparatus 101. The combustion apparatus 101 is advantageously equipped for oxygen-based combustion of a fuel, advantageously a biomass-based fuel, in particular biomass BM. Accordingly, the combustion apparatus is advantageously an oxyfuel combustion plant.

(6) The combustion apparatus 101 is accordingly advantageously made for the combustion of biomass. As an alternative, the combustion apparatus can also be equipped and designed for combustion of biological fuels or energy carriers, for example bio oils or pyrolytically produced oils.

(7) However, advantage is given to using biomass BM, in particular in pressed and standardized form, for the fuel since this product is, in particular, more readily marketable or producible and more suitable for long-range transport.

(8) In addition, this form of fuel gives more reproducible combustion results and/or products. The abovementioned biomass can, for example, be provided by processes known in the prior art in the form of tablets or pellets which can be provided by means of drying measures, in particular torrefication, tableting and/or pressing (“pelleting”). A particularly high-quality tablet is formed by additional torrefication of the biomass, which can encompass a drying measure at temperatures above 250° C. Corresponding tablets or pellets are typically obtained from wood, wood offcuts or comparable raw materials. Furthermore, these fuels or energy carriers can be burnt or concomitantly burnt in conventional air-based steam power stations.

(9) Depending on the precise shape and composition of the, in particular biomass-based, fuel to be burnt in the oxygen-based combustion, a flue gas formed (in FIG. 1 denoted as “gas”) can, for example, contain waste products such as nitrogen oxides (NO.sub.x), sulfur oxides (SO.sub.x) and/or chlorine (Cl), chlorine compounds or further substances in addition to CO.sub.2 and water.

(10) In the course of the process described, oxygen (O.sub.2) which advantageously originates from an electrolysis, advantageously a PEM electrolysis (see below), to be fed, in particular, as oxidant to a combustion should be burnt in a minimally superstoichiometric amount in the combustion apparatus 101, i.e. so that a small proportion of oxygen can still be present in the flue gas. This is most advantageous and most efficient in view of the difficulty or impossibility of carrying out precisely stoichiometric combustion. Furthermore, this can be necessary or advantageous in order to avoid formation of dioxins and (other) toxic hydrocarbons. This residual oxygen in the CO.sub.2 normally has to be removed by means of complicated purification measures comprising, for example, activated carbon filters or molecular sieves.

(11) The above-described combustion apparatus 101 comprises, for example, a fluidized bed or other means, for example gratings, for holding the fuel in place in the gasification of a fuel possibly provided in solid form (“biomass pellet”). The use of a fluidized bed for the gasification and/or combustion of the fuel is advantageous since it in principle allows a possibly more inefficient flue gas recirculation in the course of the oxyfuel process to be dispensed with or the recirculation to be reduced.

(12) However, the combustion can in principle be carried out with and without CO.sub.2 recirculation.

(13) The plant 100 advantageously further comprises a gas purification 102. The gas purification or gas purification facility 102 can, for example, be equipped so as to purify, and in particular also remove dust from, the flue gas formed by combustion (cf. reference symbol “GR” for the process step of gas purification in FIG. 1).

(14) The plant 100 advantageously further comprises a CO.sub.2 removal device 103. The removal device 103 can, in particular, be equipped for separating waste products which can inherently be present in the fuel, from the carbon dioxide obtained or to be obtained, in particular by condensing out water. The waste materials mentioned can, for example, comprise nitrogen oxides (NO.sub.x), sulfur oxides (SO.sub.x) and/or chlorine or further substances.

(15) A pump or transport device 105 by means of which the carbon dioxide can be fed to a downstream synthesis can also be seen in FIG. 1.

(16) Furthermore, the plant 100 comprises an apparatus 104 for converting carbon dioxide and hydrogen into the carbon-containing product described.

(17) It can also be seen in FIG. 1 that, for example, a further CO.sub.2 purification (CO.sub.2—R) can be carried out subsequent to the gas purification and/or the removal of the CO.sub.2 in order to provide carbon dioxide in high-purity form for the synthesis of the product P.

(18) For the carbon dioxide removal or separation (cf. reference symbol “Sep” for the process step of removal/separation in FIG. 1) or a carbon dioxide purification GR, it is possible, in particular, to react a residual proportion of oxygen O.sub.2, i.e. for example oxygen originating from the superstoichiometric oxyfuel combustion and/or the electrolysis, with provided hydrogen H.sub.2 to form water H.sub.2O (this is indicated by the broken-line arrow and the reference symbol H.sub.2).

(19) The apparatus 104 is, in particular, designed or equipped for the synthesis (cf. reference symbol “Synth” for the process step of the reaction or synthesis in FIG. 1) of the carbon-containing, in particular hydrocarbon-based, product. For example, the apparatus 104 can be designed for reacting, with introduction of hydrogen, in particular from a (or produced by a) PEM electrolysis, the carbon dioxide which has been separated off into the carbon-containing product P. The carbon-containing product P can be methane, methanol, MTBE, DME, OME, kerosene, gasoline, diesel, comparable fuels or additives, products produced or able to be produced by the Fischer-Tropsch synthesis or waxes. The products mentioned are of particular importance industrially or in particular for mobility purposes.

(20) In the conventional methanol synthesis in particular, synthesis gas (for example a mixture of H.sub.2, CO and CO.sub.2) is, for example, used as starting material and reacted under high pressures and at high temperatures. For example, the reaction of hydrogen and the carbon dioxide obtained by the process described can be carried out by means of the Sabatier process.

(21) The reaction or synthesis of the further abovementioned products can be carried out analogously by known methods.

(22) For the provision of the starting materials for the process described, in particular oxygen O.sub.2 and hydrogen H.sub.2, reference is made to the left-hand side of FIG. 1. In the process described, renewable energy sources RES are advantageously employed as energy source or for operating an electrolysis, advantageously a water-based PEM electrolysis. The electrolysis process is denoted by the reference symbol EL in FIG. 1. Electrolysis products formed are, as is known, oxygen O.sub.2 (see upper part of FIG. 1) and hydrogen H.sub.2 (cf. lower part of FIG. 1).

(23) The products oxygen and hydrogen can, for example, be temporarily stored in the case of an undersupply of renewable energy sources, even in advance, by known means, so that the above-described combustion (oxyfuel process) can be carried out predictably and continuously.

(24) The vertical upward-pointing arrow in the upper part of the FIGURE (oxygen path) indicates that oxygen is possibly produced in excess and has to be blown off, or can advantageously be utilized in another way.

(25) In order to convey these substances, in particular make the oxygen available for the combustion, and the hydrogen to the apparatus 104, it is possible to employ a compressor (cf. reference symbol 106 in FIG. 1) or another transport or compression device.

(26) The abovementioned electrolysis, which is, for example, supplied with electric energy EE from the renewable energy sources RES, can optionally be carried out under elevated pressure so that the electrolysis products, oxygen O.sub.2 and hydrogen H.sub.2, are likewise present under elevated pressure. As an alternative or in addition, oxygen O.sub.2 and hydrogen H.sub.2 can be compressed after they have been electrolytically produced. The pressures or gauge pressures mentioned can assume values in the range from 20 to 80 bar or more.

(27) A significant aspect of the process described relates to the embodiment in which the energy E provided by the oxyfuel process comprises, in particular exclusively, heat C which can be made available for further purposes, for example be utilized as process heat for the removal of carbon dioxide CO.sub.2, for the purification and/or for a synthesis or provision of the carbon-containing product P.

(28) A CO.sub.2-based synthesis, e.g. of methanol, could comprise, for example, a reverse CO conversion or reverse water gas shift reaction (RWGS) in a first step. Here, CO.sub.2 is endothermically reacted with H.sub.2 to form CO and H.sub.2O. The actual synthesis could then take place furthermore by conventional means using the resulting mixture of CO and H.sub.2 (corresponds, for example, to a classical synthesis gas). The abovementioned heat from the oxygen-based combustion can advantageously be utilized for the RWGS process described.

(29) The abovementioned heat can likewise be utilized for subsequent power-heat coupling.

(30) As an alternative or in addition to the abovementioned embodiments, the energy E provided by the oxyfuel process can comprise electric energy EE which is obtained as nonfluctuating energy, for example by means of a steam power process.

(31) The invention is not restricted to the working examples by the description of these, but encompasses each new feature and each combination of features. This includes, in particular, any combination of features in the claims, even when this feature or this combination itself is not explicitly indicated in the claims or working examples.