APPARATUS AND METHOD FOR UTILIZING OFF-GASES FROM A POWER-TO-X SYSTEM

Abstract

A power-to-X system for the utilization of off-gases, includes an electrolyzer for generating hydrogen H2 and oxygen O2, a unit, connected to the electrolyzer, for processing the hydrogen H2, for removing any remaining water H2O and oxygen O2 from the generated stream of hydrogen H2, a compressor, connected to the unit for processing the hydrogen H2, for compressing the hydrogen H2, and a chemical reactor, connected to the compressor, for producing a synthesis gas consisting of hydrogen H2 and carbon dioxide CO2 that can be added. An oxy-fuel combustion system to which non-condensable off-gases from the chemical reactor and oxygen O2 from the electrolyzer can be supplied, and carbon dioxide CO2 generated during the combustion of the off-gases in the oxy-fuel combustion system can be returned to the stream of hydrogen H2 downstream of the electrolyzer via a return line.

Claims

1. A power-to-X plant for utilizing off-gases, comprising: an electrolyzer for production of hydrogen H.sub.2 and oxygen O.sub.2, a plant for processing of the hydrogen, connected to the electrolyzer, for separation of remaining oxygen O.sub.2 and water H.sub.2O from a stream of hydrogen H.sub.2 produced, at least one compressor for compression of the hydrogen H.sub.2 or of a mixture of hydrogen H.sub.2 and carbon dioxide CO.sub.2, a chemical reactor for production of alcohols or hydrocarbons, and an oxyfuel combustion plant, to which noncondensable off-gases from the chemical reactor and oxygen O.sub.2 from the electrolyzer are suppliable, and carbon dioxide CO.sub.2 which is formed in the oxyfuel combustion plant as a result of the combustion of the off-gases is recyclable via a return line into the stream of hydrogen H.sub.2 downstream of the electrolyzer.

2. The power-to-X plant as claimed in claim 1, wherein the oxyfuel combustion plant comprises a heat exchanger by which the heat generated during the combustion is dissipatable and is integrable into other parts of the power-to-X plant.

3. The power-to-X plant as claimed in claim 1, wherein biomass and/or processed waste is, alternatively or additionally, suppliable to the oxyfuel combustion plant and/or the oxyfuel combustion plant comprises a heater by which it is electrically heatable using electricity from renewable sources.

4. The power-to-X plant as claimed in claim 1, further comprising: a removal flow line through which synthesis gas from the chemical reactor is suppliable to the oxyfuel combustion plant.

5. The power-to-X plant as claimed in claim 1, wherein a lambda probe is arranged in the return line of the oxyfuel combustion plant, so that, by measurement and regulation of a quantity of oxygen O.sub.2 introduced, complete combustion of the off-gases to form CO.sub.2 is ensured.

6. The power-to-X plant as claimed in claim 1, wherein the compressor for compression of hydrogen H.sub.2 and carbon dioxide CO.sub.2 is a piston compressor designed for operating pressures above 10 bar, and the plant for processing of the hydrogen is a DeOxoDryer.

7. The power-to-X plant as claimed in claim 1, further comprising: a return line for carbon dioxide CO.sub.2 through which the carbon dioxide CO.sub.2 from the oxyfuel combustion plant is suppliable into the stream for hydrogen H.sub.2 upstream of the compressor.

8. The power-to-X plant as claimed in claim 1, further comprising: a contaminant remover which is connected to the oxyfuel combustion plant and in which contaminants produced in the oxyfuel process, such as sulfur, alkali-metal and halogen compounds, and oxygen O.sub.2 are removable, and the purified carbon dioxide CO.sub.2 is suppliable via a return line to the stream of hydrogen H.sub.2 upstream of the compressor.

9. A method for utilizing off-gases in a power-to-X plant, comprising: producing hydrogen H.sub.2 and oxygen O.sub.2 by an electrolyzer, separating remaining water H.sub.2O and oxygen O.sub.2 from the hydrogen H.sub.2 in a plant for processing of the hydrogen, compressing the hydrogen H.sub.2 in a compressor, producing synthesis gas in a chemical reactor from the hydrogen H.sub.2 together with carbon dioxide CO.sub.2, and supplying noncondensable off-gases, contained in the synthesis gas, from the chemical reactor together with oxygen O.sub.2 from the electrolyzer are supplied to an oxyfuel combustion plant, and carbon dioxide CO.sub.2 which is formed as a result of the combustion of the off-gases is recycled into the stream of hydrogen H.sub.2 downstream of the electrolyzer.

10. The method as claimed in claim 9, wherein the oxyfuel combustion plant comprises a heat exchanger by which the heat generated during the combustion is dissipated and is integrated into other parts of the power-to-X plant.

11. The method as claimed in claim 9, wherein biomass and/or processed waste for incineration is, alternatively or additionally, combusted in the oxyfuel combustion plant and/or wherein the oxyfuel combustion plant comprises a heater by which it is electrically heated using electricity from renewable sources.

12. The method as claimed in claim 9, wherein synthesis gas from the chemical reactor is supplied to the oxyfuel combustion plant via a removal flow line.

13. The method according to claim 9, wherein the oxygen concentration in the oxyfuel combustion plant is measured by a lambda probe in a return line, and complete combustion of the mixed gases to form CO.sub.2 is ensured by regulation of the quantity of oxygen O.sub.2 introduced.

14. The method as claimed in claim 9, wherein the compressor is a piston compressor which is operated at a pressure of above 10 bar and wherein the plant for processing of the hydrogen is a DeOxoDryer.

15. The method as claimed in claim 9, wherein the carbon dioxide CO.sub.2 from the oxyfuel combustion plant is supplied through a return line for carbon dioxide CO.sub.2 into the line for hydrogen H.sub.2 upstream of the compressor.

16. The method as claimed in claim 9, wherein contaminants produced in the oxyfuel process, such as sulfur, alkali-metal and halogen compounds, and oxygen O.sub.2 are removed in a contaminant remover, and the purified carbon dioxide CO.sub.2 is supplied into the stream of hydrogen H.sub.2 via a return line upstream of the compressor.

17. The power-to-X plant as claimed in claim 2, wherein the heat generated during the combustion is dissipatable and is integrable into crude methanol processing and/or into auxiliary steam generation for start-up of the chemical reactor.

18. The power-to-X plant as claimed in claim 8, wherein the oxygen O2 in particular is removable cryogenically.

19. The method as claimed in claim 10, wherein the heat generated during the combustion is dissipatable and is integrable into crude methanol processing and/or into auxiliary steam generation for start-up of the chemical reactor.

20. The method as claimed in claim 16, wherein the oxygen O2 in particular is removable cryogenically.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is described in more detail in the text which follows with reference to figures. In the figures:

[0034] FIG. 1 shows a power-to-X plant according to the prior art.

[0035] FIG. 2 shows a power-to-X plant according to a first embodiment of the invention.

[0036] FIG. 3 shows a power-to-X plant according to a further embodiment of the invention.

DETAILED DESCRIPTION OF INVENTION

[0037] FIG. 1 shows a power-to-X plant 1 according to the prior art. It essentially consists of an electrolyzer 2, a plant for processing of hydrogen 3, a compressor 4, and a chemical reactor 5 for methanol synthesis.

[0038] What is supplied to the electrolyzer 2 is regenerative electrical energy 18 which, for example, comes from a wind turbine or photovoltaic system. Moreover, water 19 is supplied to the electrolyzer 2. In the electrolyzer, hydrogen H.sub.2 and oxygen O.sub.2 are produced. The oxygen O.sub.2 is released into the atmosphere and the hydrogen H.sub.2 is conducted into the plant for processing 3 for drying. The hydrogen H.sub.2 is withdrawn from and conducted out of the plant for processing of the hydrogen 3. The hydrogen H.sub.2 dried in the plant 3 is conducted out of the plant 3 and mixed with carbon dioxide CO.sub.2, which is supplied to the power-to-X plant from outside.

[0039] The hydrogen H.sub.2/carbon dioxide CO.sub.2 mixture is also referred to as synthesis gas 22. The synthesis gas 22 is then supplied to the compressor 4 and is compressed therein. The compressed synthesis gas 22 is then conducted into the chemical reactor 5, where it is starting material for the synthesis of methanol. The conversion of synthesis gas 22 into methanol takes place in tubular reactors and is not complete in one step. Downstream of the chemical reactor 5 is a gas-liquid separation plant 20, in which the partially converted product (methanol and water) is withdrawn. The incompletely converted partial stream 21 is recycled into the chemical reactor 5 and thus circulated.

[0040] As a result of the reaction in the chemical reactor 5, what are formed are not only methanol, but also further noncondensable gases, which are concentrated in the chemical reactor 5 owing to the circulation. Major constituents are hydrogen H.sub.2, carbon dioxide CO.sub.2, carbon monoxide CO, methane CH.sub.4 and methanol CH.sub.3OH. These gas mixtures are referred to as off-gases 8, which are discharged from the process continuously or discontinuously in order to avoid excessively high concentration of noncondensable gases in the chemical reactor 5.

[0041] In the prior art, these off-gases 8 are supplied to a combustion plant 23 and combusted under supply of air 24. What is formed here is a combustion gas 25 which predominantly contains carbon dioxide CO.sub.2, water H.sub.2O and nitrogen N.sub.2 and which is released into the atmosphere.

[0042] Leaving the power-to-X plant is synthetically produced methanol CH.sub.3OH.

[0043] FIG. 2 shows a power-to-X plant according to a first embodiment of the invention. In contrast to FIG. 1, the oxygen O.sub.2 produced in the electrolyzer 2 is not released, or not completely released, into the atmosphere, but diverted for use later in the process. In a further difference from the prior art, there is provided a further compressor 26, which is arranged upstream of the plant for processing of the hydrogen 3. The central difference from the prior art is the provision of an oxyfuel combustion plant 7, to which the oxygen O.sub.2 from the electrolyzer 2 and the off-gas 8 from the chemical reactor 5 are supplied.

[0044] In the oxyfuel combustion plant 7, the off-gases 8 are likewise utilized thermally, but with virtually pure oxygen O.sub.2 as an oxidizer that has been removed from the electrolyzer 2 as a by-product. The combustion gas of the oxygen-based combustion consists almost entirely of water vapor and carbon dioxide CO.sub.2. By comparatively simple condensation of the water vapor, the carbon dioxide CO.sub.2 can be obtained in a very pure form and recycled to the production process.

[0045] According to the invention, the combustion gas consisting of virtually pure carbon dioxide CO.sub.2 is recycled via a return line 9 into the stream of hydrogen H.sub.2 downstream of the electrolyzer 2. The recycling is expediently carried out upstream of the compressor 26.

[0046] In order to support the combustion in the oxyfuel combustion plant 7, there is further provided a removal flow line 12 through which synthesis gas from the chemical reactor 5 is suppliable to the oxyfuel combustion plant 7.

[0047] In the power-to-X plant 1 according to FIG. 2, a lambda probe 14 can be arranged in the return line 9 of the oxyfuel combustion plant 7, so that, by measurement and regulation of a quantity of oxygen O.sub.2 introduced, complete combustion of the off-gases to form CO.sub.2 is ensured without, however, supplying oxygen in excess.

[0048] The compressor 4 can be designed as a piston compressor designed for operating pressures above 10 bar. The plant for processing of the hydrogen 3 can be a DeOxoDryer.

[0049] FIG. 3 shows an alternative embodiment of the invention. The essential difference from the embodiment in FIG. 2 is that the oxyfuel combustion plant 7 is an oxyfuel boiler, to which, alternatively or additionally, biomass and/or processed waste 27 is supplied. Alternatively or additionally, what can be provided in the oxyfuel combustion plant 7 is a heater 11 which is electrically heatable using electricity from renewable sources.

[0050] Moreover, there is provided a heat exchanger 10 which is downstream of the oxyfuel combustion plant 7. It is by means of the heat exchanger 10 that the heat generated during the combustion is dissipatable and is integrable into other parts of the power-to-X plant 1. The heat can advantageously be transferred to crude methanol processing and/or to auxiliary steam generation for start-up of the chemical reactor 5.

[0051] Connected to the oxyfuel combustion plant 7 of FIG. 3 is a return line for carbon dioxide CO.sub.2 15 through which the carbon dioxide CO.sub.2 can be conducted out of the oxyfuel combustion plant. Connected into the return line 15 is a contaminant remover 16 which removes contaminants produced in the oxyfuel process, such as sulfur, alkali-metal and halogen compounds, and relatively large quantities of oxygen O.sub.2. The oxygen O.sub.2 in particular is removed cryogenically. The stream of largely pure carbon dioxide CO.sub.2 that has been purified by the remover 16 is supplied via a return line 17 to the stream of hydrogen H.sub.2 upstream of the compressor 4.

[0052] The invention makes it possible to utilize the off-gases which are formed in a power-to-X plant for the process, instead of having to release them into the atmosphere. This makes it possible to reduce the emission of CO.sub.2 from the entire plant while simultaneously utilizing the carbon dioxide CO.sub.2 in the actual process and the oxygen O.sub.2 from the electrolyzer. Compared to conventional off-gas combustion, energy for the air blowers can also be saved as a result.