METHOD FOR THE SYNTHESIS OF GAS-FORMED OR LIQUID ENERGY CARRIERS FROM A SEA STORM POWER PLANT

Description

[0001] The invention relates to a method for producing gaseous or liquid energy carriers according to the preamble of claim 1. In particular, the invention relates to the production of gaseous carbon-containing energy carriers (CxHy) such as methane (CH4) and liquid hydrocarbons such as methanol (CH3OH, hereinafter referred to as MeOH), as well as nitrogen-containing energy carriers such as ammonia (NH3).

[0002] A method and a device for energy storage are known, for example, from WO 2011 / 120706 A1, wherein hydrogen is produced from water by electrolysis and synthesized with at least one other reactant, such as carbon dioxide, to form a product that is introduced into a storage device for intermediate storage, from which it can be extracted for material and / or energy recovery. The electricity for the electrolysis is provided by a solar thermal power plant.

[0003] The synthesis components necessary for the production of carbon-containing energy carriers, hereinafter referred to as syn-gas, consist, according to SdT, of a mixture of carbon monoxide (CO) and hydrogen (H2) with smaller proportions of carbon dioxide (CO2) and water (H2O). On an industrial scale, they are usually produced via steam reforming of natural gas or coal, or via the partial oxidation of natural gas with water as the H2 source. The first patent for the synthesis process known as Fischer-Tropsch was granted in 1925.

[0004] Alternatively, CO2 can also be captured from flue gas, which is produced on a large scale during the combustion of fossil fuels such as natural gas or oil, a process known as "carbon capture" (CC). Another alternative is capture from ambient air, usually abbreviated as DAC (direct air capture).

[0005] In the case of ammonia, the syngas consists of a mixture of N₂ and H₂ as well as other components from steam reforming such as CO, CO₂, and H₂O. N₂ is usually obtained by fractional distillation of liquefied air in air separation plants according to the Linde process. On an industrial scale, NH₃ is produced via the Haber-Bosch process, for which Fritz Haber was granted patent no. 235,421 in 1906.

[0006] Until now, CH4 was readily available in large quantities and at low cost in the form of natural gas, but it can also be produced catalytically from syngas. HS Ellworthy and HW Williamson received the first patents for this process in 1904 / 05, but these have rarely been used on an industrial scale. Today, the industrial production of MeOH is carried out almost exclusively using catalytic processes from syngas. Alternatively, MeOH can also be produced heterogeneously by catalytic hydrogenation of CO2, for which – as claimed in EP03846936A1 – special catalysts made of indium oxide with additions of palladium are used.

[0007] With the exception of the last example, all processes require at least partially high temperatures and also involve complex reaction chemistry. This is because the syn gases, which mostly originate from fossil sources or biomass, have complex compositions, necessitating the consideration of numerous competing reactions within the synthesis process and requiring elaborate downstream purification steps. These processes are characterized by high energy losses at technically limited temperature levels and, due to poor energy efficiency, cause high CO2 emissions. This is primarily because exothermic processes require significant energy for cooling, certain reactions only occur at high temperatures, and the available catalyst materials remain effective only within a narrow but high temperature range.Therefore, it is not sufficient to provide primary energy supply through renewable electricity from wind power, photovoltaics or known ocean thermal energy plants, because even then secondary CO2 releases, for example from distillation or rectification processes, will continue unchanged.

[0008] US patent 4 055 145 A discloses an OTEC process in which the electricity generated is used to operate an electrolyzer for the production of hydrogen, which is synthesized with nitrogen from the air to form ammonia in a downstream synthesis facility, the synthesis facility being located in a lagoon.

[0009] In / HD19 / and / HD20 / methods were investigated to determine how primary energy supply for energy carrier production can be realized using OTEC (Ocean Thermal Energy Conversion) processes and how commercial optimization can be achieved.

[0010] One disadvantage is the low net power output of OTEC production plants. In / HD20 / , the lack of economic viability of OTEC plants according to the current state of the art is attributed to 1. the high energy consumption of auxiliary equipment (pump power requires approximately 80% of the Rankine output), and 2. the low driving temperature difference of the Rankine cycle. / HD20 / investigates how higher driving temperature differences in the OTEC process can be achieved by utilizing diverse additional external heat sources (e.g., solar-assisted combined OTEC cycle), and how the OTEC process can be improved through the "smart integration" of downstream processes. / HD20 / examines, on the one hand, the use of the generated OTEC electricity in downstream processes in process-technically separate plants, and on the other hand, the use of cold deep-sea water as an additional end product to improve the economic viability of the OTEC plant.

[0011] In / HD19 / , an additional energy carrier production process (methanol and ammonia synthesis) is also investigated, which is technically separate from the OTEC process. The subsequent processes following the Rankine cycle of the OTEC process—electrolysis, cryogenic CO2 production, and methanol synthesis—are technically independent of the OTEC process.

[0012] OTEC technologies with a closed cycle - hereinafter referred to as CC-OTEC (Closed Cycle) - have a significantly higher availability of 95% than PV and wind, but even after 50 years of intensive research, it has not yet been possible to prove their economic viability via a demonstrator.

[0013] Reasons for this include: 1. The low efficiency of CC-OTEC is approximately 3%. 2. The differential pressure at the turbine of CC-OTEC plants is too low to achieve satisfactory efficiencies. 3. The working fluid used, NH3, is toxic and requires extensive safety measures. 4. The electricity consumption of auxiliary equipment, e.g., water pumps, drastically reduces the yield of CC-OTEC plants, making their operation uneconomical. 5. Without combination with other heat sources and renewable energy recovery technologies, the design of the high-pressure circuit in wet steam operation is problematic. 6. Since the evaporator and condenser alone must handle the heat exchange, they are very large. 7. Existing and planned OTEC plants lack coupling to (exothermic) downstream processes; consequently, the benefit of heat recovery from downstream processes cannot contribute to optimizing the efficiency and economic viability of CC-OTEC plants. 8.CC-OTEC involves redistributing water and the living organisms and plankton it contains in the ocean. CC-OTEC is not economically viable in the open ocean because the electricity transmission costs and line losses would become too high.

[0014] To solve the CC-OTEC-specific problem (pumping large quantities of water from a depth of 1,000 m to the condenser at the surface), US20070289303 proposes using a low-boiling-point liquid as the working medium. However, this comes at the cost of the turbine, condenser, and evaporator components also being located at a depth of 1,000 m, which makes both the maintenance of the components and the use of waste heat from subsequent processes for the synthesis of the energy carrier according to the invention very difficult or impossible.

[0015] The object of the invention is therefore to disclose a process in which the efficiency of the Rankine process and the energy efficiency of the overall process are optimized, CO2 emissions are largely eliminated, and the production of the energy carrier as well as the energy and resource use are largely self-sufficient.

[0016] The invention solves the problem by means of a method according to claim 1.

[0017] According to the invention, energy carrier synthesis is integrated both thermally and materially (physically) into the Rankine cycle of an ocean thermal energy recovery power plant according to the invention. For this purpose, the temperature gradients in the ocean are used in the Rankine cycle to generate renewable energy (RE) electricity. This electricity is used directly in the plant for the electrolysis of water to produce green hydrogen (H₂), which is added as an additive to the working fluid of the Rankine cycle upstream of the turbine to increase its enthalpy. After the turbine, it is extracted and subsequently serves as the first component of the synthesis gas. As the second component of the synthesis gas, CO₂ or N₂ is combined with the H₂, resulting in an exothermic synthesis reaction to produce the final product. Cooling of this synthesis process is achieved via a heat exchanger from the working fluid of the Rankine cycle, which increases the enthalpy in the Rankine cycle and thus its efficiency.The green oxygen from the electrolysis is used under adiabatic expansion to cool the AM in the Rankine cycle after the turbine, thus allowing a smaller and lower-loss design of the Rankine capacitor.

[0018] This ensures that the reaction enthalpy from electrolysis and energy carrier synthesis, through its integration into the Rankine cycle, increases the efficiency of the Rankine cycle. This maximizes the energy efficiency of energy carrier production and achieves a CO2-free energy supply for the synthesis's auxiliary equipment and the entire plant. Since ocean thermal energy conversion plants are generally known as OTEC (Ocean Thermal Energy Conversion), but the novel process presented here differs fundamentally, the novel ocean thermal energy conversion plant process according to the invention will henceforth be referred to as eOTEC (enhanced Ocean Thermal Energy Conversion).

[0019] To understand the systemic advantages of eOTEC in energy carrier synthesis compared to SdT, it is necessary to examine the reactions of syngas production and energy carrier synthesis in more detail. This will be explained below using natural gas as the raw material for syngas and MeOH or CH4 as an example of the energy carrier.

[0020] Today, the industrial production of (grey) MeOH is almost exclusively carried out using catalytic processes from syngas, a mixture of CO and H₂ in a ratio of approximately 1:2 (see Eq. 4b below). The H₂ and CO required for this process are currently mostly obtained by steam reforming of natural gas (Eq. 2a). Alternatively, as planned for eOTEC, MeOH can also be produced heterogeneously by catalytic hydrogenation of CO₂ (Eq. 6a), whereby the CO₂ is not derived from natural gas but is obtained via DAC.

[0021] One of eOTEC's primary goals is to operate the MeOH synthesis at a pressure where the working fluid, CO2, as the second component of the syngas, evaporates. This pressure is identical to the H2 pressure from electrolysis, the first component of the syngas. A second goal is to ensure that the reaction to the final product proceeds so rapidly that the purge process (recirculation of unreacted syngas into the reactor), which is standard in synthesis, is at least simplified or ideally eliminated. This is facilitated at high pressure, as reaction (6a) shifts towards the MeOH side according to Le Chatelier's principle.

[0022] The catalysts used, as well as the temperature and pressure at which equations (6a) and (6b) take place, also play a significant role. In the currently favored low-pressure process with copper-zinc-aluminum oxide-based catalysts, temperatures range between 200 and 300°C and pressures between 50 and 100 bar, and are therefore both within the range of CO2 evaporation (60...70 bar) and the H2 pressure of the eOTEC process, which, in the case of high-pressure PEM electrolysis, lies between 30 and 120 bar.

[0023] Recent studies show that a considerable increase in the activity and selectivity of the catalyst is possible if the catalysts used today are doped with tiny amounts of zinc oxide, which are in close contact with the copper as nanoparticles, which is an important prerequisite for realizing a heterogeneous catalytic process with a simplified purge process.

[0024] The reactions involved in syngas production can be divided into three groups: 1. Endothermic - with steam: CH 4 + H 2 O ↔ CO + 3 H 2 ; ΔH R = +206 kJ / mol (2a) -CH 2 - + H 2 O ↔ CO + 2 H 2 ; ΔH R = +151 kJ / mol (2b) C + H 2 O ↔ CO + H 2 ; ΔH R = +119 kJ / mol (2c) 2. Exothermic - with oxygen: CH 4 + ½ O2 ↔ CO + 2 H 2 ; ΔH R = -36 kJ / mol (3a) -CH 2 - + ½ O 2 ↔ CO + H 2 ; ΔH R = -92 kJ7mol (3b) C + ½ O 2 ↔ CO ; ΔH R = -123 kJ / mol (3c) 3. Equilibrium reactions: Oxidation / Electrolysis: H₂ + ½ O₂ ↔ H₂O ; ΔH R = -240 kJ / mol (4a) Water-gas shift: CO + H₂O ↔ CO₂ + H₂; ΔH R = +162 kJ / mol (4b) Boudouart equilibrium: C + CO 2 ↔ 2 CO ; ΔH R = -42 kJ / mol (4c)

[0025] Due to the multitude of possible reactions of the cracking products, the chemical composition of the resulting syngas, for which only H₂ and CO₂ or CO are required for the e-gas methane (Eq. 5) and the e-fuel MeOH (Eq. 6), is very complex and also strongly dependent on the position of the chemical equilibria (Eq. 4). This, in turn, has a negative impact on catalyst design, since a catalyst can generally only be optimized for one reaction.

[0026] These and other disadvantages (see below) are eliminated according to the invention by the fact that (I) Reactions (Eq. 3a) to (3c) are suppressed because the precursors CH₄, -CH₂, and C are only formed upon combustion in air; (II) oxygen, which must be obtained from air in pure form to heat the reactor to the temperature of 750–900°C required by the Ni catalyst via CH₄ combustion, is neither present nor necessary, since the MeOH synthesis takes place between 300 and 400°C; and (III) in the equilibrium reactions, reactions (Eq. 4a) and (4c) also do not occur due to the lack of precursors C and O₂. Since water is also produced during the synthesis (Eqs. 5a, 5b, and 6a), only the water-gas shift reaction (Eq. 4b) is possible.

[0027] Two reaction pathways are possible for the synthesis of CH4 and MeOH, and the catalysts and process window (pressure and temperature) must be matched accordingly. This matching is achieved more effectively the fewer reaction pathways exist. I: End product methane (CH4):

[0028] CO2 pathway: CO2 + 4H2 ↔ CH4 + 2H2O; ΔH R = -165 kJ / mol (5a) Path CO: CO + 3 H 2 ↔ CH 4 + H 2 O; ΔH R = -206kJ / mol (5b) II: End product MeOH (CH3OH):

[0029] CO2 pathway: CO2 + 3H2 ↔ CH3OH + H2O; ΔH R = -49.6 kJ / mol (6a) Path CO: CO + 2 H 2 ↔ CH 3 OH; ΔH R = -90.8 kJ / mol (6b)

[0030] In the case of the third end product, ammonia, there is only one path: Path N2: N2 + 3 H 2 ↔ 2 NH 3 ; ΔH R = -92 kJ / mol (7a)

[0031] At eOTEC, the production of MeOH via (Eq. 6a) is preferred over (Eq. 6b) or the production of CH4 via (Eq. 5) for the following reasons: (I) MeOH is liquid and can be transported more easily and cost-effectively over long distances by ship than gaseous CH4, (II) CO2, unlike CO, can be obtained regeneratively from air, (III) The heat of reaction is lower due to the higher calorific value of CO compared to the inert CO2, and (IV) The water produced according to (Eq. 6a) can be used for electrolysis after separation from the MeOH.

[0032] Only through the inventive linking of the sub-processes (A) Production of renewable electricity from the temperature gradients in the sea via the Rankine cycle (with CO2 as the active component) with (B) production of the second component of the syngas from ambient air via DAC, which is possible to achieve 100% renewable electricity by using renewable electricity from (A) and waste heat from electrolysis (C) or MeOH synthesis (D), and (C) use of the electricity from (A) to produce H2 via water electrolysis, (D) obtaining the water required for electrolysis from MeOH synthesis according to (Eq. 6a) or by condensing water in the DAC process or at the condenser, provided it is located in ambient air, and (E) synthesis to the final product MeOH using the CO2 from (B) and H2 from (C), using the (F) waste heat from (C) and (E) to optimize the efficiency of (A). This completes the cycle of a perfect circular economy within a plant. The exothermic synthesis of the final product itself thus contributes to increasing the efficiency of the Rankine cycle that drives this process.

[0033] That the process demonstrated here using the e-gas CH4 and the e-fuel MeOH as examples can also be used in a similar form to produce more complex gaseous or liquid energy carriers, fuels, or chemical base materials is readily apparent to a person skilled in the art. Examples include ammonia synthesis for the production of ammonia using the Haber-Bosch process, Fischer-Tropsch synthesis for the production of linear hydrocarbon chains, and oxo synthesis for the production of, for example, aliphatic aldehydes such as butanol, which requires oxygen, a by-product of eOTEC's electrolysis.

[0034] Today's technical production of grey MeOH from syngas using catalytic processes is not self-sufficient, requires extensive external utilities and media supply, and consumes additional non-renewable energy. This is due, among other things, to the need for additional process steps, such as the purification and, in particular, desulfurization of natural gas or coal, heating before reforming, and subsequent compression.

[0035] In contrast, the process according to the invention is completely self-sufficient and independent of external energy sources, in that all substances required for the synthesis of the energy carrier, such as water (for electrolysis), CO2 or N2 (for the synthesis of the energy carrier) or heat (for regenerating the DAC plant and increasing the efficiency of the overall system), are obtained autonomously on the platform, with only renewable electricity from the eOTEC process being used to operate the required equipment.

[0036] The following explains how the CC-OTEC-specific disadvantages described above can be eliminated. 1: By designing for a different AM (e.g. CO2), the turbine differential pressure, which is important for efficiency, can be significantly increased.

[0037] Based on the usable temperature differences of 20 to 24°C in the equatorial zones of the oceans, the use of CO2 as an additive material (AM) compared to NH3 in CC-OTEC results in a fourfold increase in turbine differential pressure (from 6 bar to approximately 24 bar). However, this advantage over CC-OTEC comes at the cost of higher AM mass flow rates due to the lower volumetric density of CO2. This disadvantage is more than compensated for by the higher pressure differential and the resulting increase in turbine efficiency of approximately 10%, meaning this weakness has no economic impact.

[0038] CO2 is ideally suited for driving gas turbines and has no corrosive properties. Furthermore, since the molar mass of CO2 (44 g / mol) is 2.6 times higher than that of NH3 (17 g / mol), the average momentum transfer ( p = m × v The force applied to the turbine blade is also increased by a factor of 1.6. Therefore, the turbine power output is correspondingly higher – for the same volume flow rate.

[0039] To ensure that eOTEC operates in the preferably supercritical range / Fr17 / with dry steam or at most a negligible wet steam content, process and safety-related risks are further minimized, which has a cost-reducing effect on the safety concept and the approval procedure.

[0040] The preferred CO2 is significantly less corrosive and less toxic than the previous use of NH3, is also non-flammable as a fire extinguishing agent, and furthermore offers another technical refinement which is not investigated here, but can be used as an additional commercial booster. 2: In the eOTEC process, liquid AM is pumped instead of water at different temperatures.

[0041] In eOTEC, energy transport in the form of water at different temperatures is replaced by the transport of material flows in liquid and gaseous states, utilizing the associated latent heat. This drastically reduces pipe cross-sections / RB 18 / and decreases the necessary, efficiency-reducing pumping power from up to 90% to less than 10%. 3: The eOTEC process is designed for the additional use of ST or PVT collectors.

[0042] The locations suitable for eOTEC all offer favorable conditions for solar thermal energy (ST). These include not only higher radiation intensity but also, in equatorial regions, almost perpendicular irradiance year-round, making a horizontal orientation of the collectors optimal. Complex tracking of the collectors using trackers is therefore unnecessary.

[0043] For eOTEC, however, the provision of low-temperature heat by ST in the range of 40°C and above is ideally suited and contributes significantly to increasing efficiency and to the simple and trouble-free operation of the turbine due to the low or very low or no wet gas content.

[0044] As an alternative to solar thermal collectors, photovoltaic-thermal (PVT) collectors can also be used for the simultaneous generation of heat and electricity. This configuration serves both to raise the temperature in the dry steam section of the CO2 turbine and simultaneously to lower the temperature of the PV modules, thus significantly increasing the efficiency of both the solar power system and the Rankine cycle. Since excess renewable energy can also be used for electrolysis, this dual benefit creates a further synergy that also contributes to shortening the amortization period. 4: By using a recuperator between the turbine and the connecting line to the condenser, the AM to be liquefied can be pre-cooled and the AM to be evaporated can be pre-heated.

[0045] As is typical in the ORC process, a recuperator can be installed between the material streams before and after the condenser. This recuperator pre-cools the AM to be liquefied and pre-heats the AM to be evaporated. The recuperator is conveniently located on the eOTEC platform, as it is easily accessible there and the medium from the turbine has not yet cooled down significantly.

[0046] This effect is all the more important and efficient the higher the superheat, because due to the quasi-isothermal expansion, the gas has not yet cooled down significantly, and the temperature of the AM from the turbine is considerably higher than that of the surface water. On the other hand, the AM still has a high wet steam content before entering the evaporator, which decreases in the recuperator, allowing the evaporator and condenser to be designed smaller. 5: The conversion of electricity to H2 at the eOTEC plant site enables the direct use of waste heat from processes such as electrolysis and energy carrier synthesis.

[0047] The coupling of the Rankine cycle to H2 electrolysis improves its efficiency per K by about 2% (see Eq. 8), since the heat resulting from the losses in electrolysis (efficiency approx. 80%) can be excellently fed back into the eOTEC process at a normally unfavorable temperature level of 60...80°C, thus not being lost, but being made available again as electricity and also improving the efficiency of the electrolysis.

[0048] Higher-grade exothermic heat is generated during the synthesis of the energy carrier. This heat can be used to regenerate the CO2 filters of the DAC system, which is possible even at temperatures between 80°C and 100°C. The residual heat – like the low-temperature heat from electrolysis – can be used to increase the superheat and thus the efficiency of the Rankine cycle. 6: The conversion of H2 and CO2 to industrial and chemical P 2< X base products takes place according to the invention in the eOTEC process.

[0049] This creates a highly efficient energy feedback loop between electricity production, electrolysis, and the synthesis of basic industrial chemical products. Instead of electricity, which requires costly and lossy power lines for distribution, a simple and inexpensive end product such as MeOH or NH3 is marketed. 7: By positioning the condenser in situ at the condensation temperature in the sea, the need to pump seawater from great depths and feed it back in near the surface is eliminated.

[0050] In CC-OTEC systems, the condenser, installed on the platform or on land, is fed with cold seawater from a depth of approximately 1,000 m, while the evaporator is supplied with warm surface water. This means that in a 100 MW CC-OTEC plant, approximately 200 m³ / h of cold seawater is heated by 2-3 K in the condenser, and approximately 400 m³ / h of warm seawater (RB18) is cooled by 2-3 K in the evaporator. The water is then returned to the sea at shallow depths via a common manifold. This vertical water transfer results in the following disadvantages: Cold deep water, potentially containing high concentrations of carbonate ions, mixes with warm surface water saturated with CO2. Since the solubility of CO2 decreases exponentially with temperature, CO2 is released into the atmosphere when the partial vapor pressure is exceeded. As with hydroelectric power plants, it is essential to prevent organisms from reaching the surface from great depths, as their viability there is severely limited, and the sudden pressure drop from 100 to 1 bar can lead to irreversible cell damage and death. 8: The condenser and evaporator can be smaller.

[0051] This is achieved through the following innovations: Due to the system efficiency being two to three times higher, the HEX units can be smaller for the same electrical output. The use of a recuperator allows for initial pre-cooling, thereby increasing the wet steam content of the dry steam coming from the turbine, and simultaneously heating, thus increasing the wet steam content of the liquid AM pumped upwards. The recuperator's effect is greater the higher the superheat. Using a HEX unit downstream of the recuperator in the gaseous AM line, in which the O2 coming from electrolysis is expanded and cooled via the Joule-Thomson effect, allows for a second pre-cooling, resulting in a second increase in the wet steam content of the dry steam coming from the turbine. The transport of the warm, gaseous AM via heat-conducting pipes from the turbine to the condenser at a depth of 1,000m further cools the AM. 9: Avoidance of electricity transmission costs through an integrated eOTEC plant concept

[0052] The eOTEC-internal integration of the power generator with the H2 electrolysis process has a significant impact on the plant design according to the invention and the avoidance of parasitic costs. The generated electricity is neither transported via costly routes for external use, nor are alternative strategies for increasing economic efficiency necessary, as proposed for previous ocean thermal energy plants (see, for example, / HD19 / and / HD20 / ).

[0053] Due to CC-OTEC's business model (selling electricity and by-products such as cold seawater for SWAC (Sea Water Air-Conditioning), seawater for fish farming and aquaculture, or desalinated and mineralized seawater as drinking water), CC-OTEC plants were built exclusively on land or near the coast, and cold water from a depth of 1,000m was pumped to land through long pipelines using high-energy-consumption pumps.

[0054] This plant design allows for short power cables, but this comes at the cost of long and expensive water pipes and the limitation that such conditions are only found in regions of mostly volcanic origin, such as islands, where water depths of 1,000m are reached just a few kilometers behind the coast.

[0055] Since the levelized cost of electricity (LCOE) for CC-OTEC increases significantly with increasing distance from the coast, e.g. from $0.07 / kWh @ 10km to $0.22 / kWh @ 400 km / NiO1 / , CC-OTEC cannot compete economically with other renewable energy sources such as solar and wind power on the open sea, despite its high availability of 95%. 10: eOTEC plans to store at least some of the CO2 in the sea.

[0056] At eOTEC, the CO2 required for energy carrier synthesis is to be extracted on-site from the air using DAC, which is why, according to the CO2 color theory, it is a green energy carrier. Since the waste heat from the energy carrier synthesis is also used to regenerate the CO2 filters, this is achieved in an energy-neutral manner, creating a closed-loop system.

[0057] Excess CO2 from the DAC process can be captured due to the design of the Rankine cycle. open cycle process- with inlet and outlet openings for CO2 - released into the sea in a controlled manner at a suitable depth, preferably in situ at the AM condensation temperature of the deep water, where, due to the buffering effect of the seawater, it is converted into sedimenting substances such as carbonate and bicarbonate ions that do not re-enter the atmosphere, or is removed from the reaction equilibrium by competing reactions (for example, the formation of H2CO3). This makes it possible for the first time to produce energy carriers with a negative CO2 footprint. 11: eOTEC eliminates systemic disadvantages of P2X technologies

[0058] The systemic advantages of eOTEC, which result from the inventive linking of electricity generation via the Rankine cycle with the production of green H2 through electrolysis for the consumption of the generated electricity and with P2<X technologies for the conversion of the H2 into more easily transportable and, above all, storable energy carriers, are shown below for (I) MeOH and (II) methane as examples of carbon-containing energy carriers and for (III) ammonia as an example of a nitrogen-containing energy carrier. This can be transferred in a similar form to other hydrocarbons.

[0059] Today, the technical production of (grey) MeOH is carried out almost exclusively using catalytic processes. Syngas , a mixture of CO and H2 in a ratio of approximately 1:2 (Eq. 5b). Alternatively, as planned for eOTEC, MeOH can also be produced heterogeneously catalytically by hydrogenation of CO2 (Eq. 6a).

[0060] Syngas (CO, CO2 and H2) is also produced almost exclusively from fossil fuels today. When coal or lignite is used, this is achieved through coal gasification with steam and air; when natural gas is used, it is achieved through steam reforming or the partial oxidation of natural gas (Eq. 3a).

[0061] The eOTEC process according to the invention is explained in detail below.

[0062] For the sake of simplicity, the invention is explained using the following example: (1) The end product is MeOH as an example of a liquid energy carrier, (2) H2 is the first component of the syn gas, and (3) CO2 is the second component of the syn gas, which is obtained from the air via DAC and is identical to the working fluid (WF). Figures 1 and 2 show: Fig. 1The inventive process for the production of MeOH with a focus on power generation via the Rankine cycle with CO2 as AM including its production via DAC, the pre-cooling, condensation, liquefaction, pre-heating, evaporation and superheating of the AM including its storage in the sea as well as the thermal linking of the heat-requiring processes such as the Rankine cycle and DAC with the heat-generating or exothermic processes electrolysis and MeOH synthesis via heat exchangers (HEX), Fig. 2 The inventive process for the production of MeOH with a focus on the additive H2 optionally introduced into the cycle process, the electrolysis, the storage of the intermediate and end products, the treatment of the purge gas and the linking of the individual processes for the preferably energy- and resource-autonomous production of the energy carrier MeOH from the components RE-electricity, CO2 and water.

[0063] The significance of the in the Fig. 1 and Fig. 2 The arrows and tiles used are explained in the accompanying legends. Fig. 1 and Fig. 2 explained.

[0064] Fig. 1 Figure 1 shows the eOTEC cycle with CO2 as the active material, including the mass, heat, and electricity flows of all components. The energy carrier MeOH is synthesized from the two components H2 and CO2, preferably the only components of the syngas, using catalysts in reactor (14) according to Eq. 6a. The H2 required for the synthesis is obtained as the first component of the syngas via the electrolyzer (11) of water electrolysis. This process utilizes the electricity (17) from generator (4) as well as the water produced during MeOH synthesis in reactor (14) according to Eq. 6a, or during CO2 production via DAC (18), which is drawn from storage (19b).

[0065] The components shown below the water surface (25) – condenser (6), AM pump (7), and discharge device (8b) – are located at a depth of approximately 1,000 m. Unlike the SdT, the condenser is therefore not located above the water surface and, in particular, not on land, but in the water at a depth where the water temperature is below the condensation temperature of the AM at the prevailing pressure. Condensation thus occurs in situ with the water, eliminating the need for a pump to raise the water (approximately 200 m³ / s for a 100 MW system). Since, according to the invention, AM is pumped instead of water, the volume flow rate is also significantly reduced by the latent heat component during the phase transition.

[0066] The components of the Rankine cycle above the water surface, such as the recuperator (5), evaporator (1) and numerous HEX, are advantageously connected to the components at depth via (not shown) pressure-resistant pipes.

[0067] In Fig. 1 In addition to the evaporator (1) and condenser (6), five further HEX components can be identified (HEX#1 (2), HEX#2 (21a), HEX#3 (21b), HEX#4 (22) and HEX#5 (5)), which optimize the overall process in accordance with bullet b of the main claim. This interconnection results in the enormous increase in efficiency and defines the thermodynamic equilibrium conditions under which the entire system operates.

[0068] Overheating of the AM is important for several reasons: 1. Without superheating, the compressed CO2 gas in the turbine would expand exclusively in the wet steam range, which negatively impacts the turbine's efficiency and performance. Superheating is therefore carried out to at least the extent necessary to ensure that the subsequent expansion in the turbine preferentially occurs in the dry steam range, thus preventing condensation in the turbine due to expansion-induced cooling. For CO2 as the active gas, a superheat of approximately 7–12°C is sufficient. 2. Superheating the active gas increases the Carnot efficiency of the turbine according to... η Carnot = T warm − T kalt / T warm where Twarm without superheating is the temperature of the seawater at the surface and Tcold is the temperature of the deep water at a depth of approximately 1,000 m. According to equation (8), the Carnot efficiency of the turbine increases by almost 50% from 6.6% to 9.6% with a superheat of 10 K (e.g., from 25°C to 35°C), thus enabling economical operation of eOTEC compared to OTEC (without superheating). The process is described below, starting with pump (7). The AM is represented differently for the possible states of matter: gaseous (dotted line), wet steam (dashed line), and liquid (solid line).

[0069] In the pump (7), the pressure of the CO2 liquefied in the condenser (6) at approximately 40 bar (corresponding to the vapor pressure of CO2 at a condensation temperature of 5°C) is increased to approximately 65 bar. This corresponds to the pressure at which CO2 evaporates in the evaporator (1) with surface water at 25°C.

[0070] The liquid CO2 first enters the discharge device, consisting of a 3-way valve (20d) and a pump (8b) for further pressure increase, as well as an optional downward-leading pipe (not shown) through which a portion of the CO2 flow is released into the sea at an even greater depth. Through chemical buffering processes, the CO2 is almost completely converted into other chemical compounds, leading to an increase in the concentration of HCO3- in the deep water, and ultimately, CO2 remains far below the solubility limit in the deep water.

[0071] As the liquid CO2 passes through the (not shown) riser pipe, it warms up in the warmer upper layers of the ocean, partially transitioning into wet steam. At the surface, the still-cold CO2 first flows through the recuperator, where it is preheated via HEX#5 (5) by the warmer gaseous counterflow coming from the turbine (3), while simultaneously the downward-flowing gas stream from the turbine is precooled. Ideally (maximum heat transfer), both streams have the same temperature after passing through HEX#5 (5). Due to the change in the enthalpy of the streams in the recuperator, both the condenser (6) and the evaporator (1) can be made smaller.

[0072] The preheated CO2 wet vapor exiting the recuperator enters the evaporator (1), which is supplied via line (10a) with warm, near-surface seawater at 25–30°C. The seawater, cooled by 2–3°C, is then returned to the sea via line (10b). The evaporator and the water flow rates within the evaporator are designed to ensure that the CO2 preferably evaporates completely.

[0073] Alternatively, the evaporator – like the condenser (see below) – can be implemented "in-situ with the seawater." In this case, the seawater pump (10c) for pumping the warm surface water (400 m³ / s for a 100 MW system) is eliminated, further increasing the efficiency of the overall system.

[0074] Part of the vaporized CO2 passes through the 3-way valve (20a) to another 3-way valve (20e), which again divides the AM stream into two partial streams, one of which is fed directly into the reactor (14) and the other part together with H2 from the electrolysis in the reactor (14a) is converted into CO and H2O via the water-gas shift reaction (Eq. 4b), which after combining with the CO2 stream passing through the valve (20e) then forms a syn gas according to SdT, consisting of CO, H2, CO2 and H2O.

[0075] The splitting of some of the CO2 into CO is only intended if, despite recent advances in the development of catalysts, it proves impossible to increase the efficiency of the heterogeneous catalytic synthesis according to (Eq. 6b) to at least the level according to SdT, where the catalyst is optimized for a CO / CO2 mixture with only 1–3% CO2. Using the 3-way valve (20e) and shifting the equilibrium of the water-gas shift reaction (Eq. 4b) towards CO, it should be possible to significantly increase the CO content in the synthesis gas.

[0076] The catalyst is preferably optimized for reaction (Eq. 6a) because the CO pathway (Eq. 6b) is only possible via the water-gas shift reaction (Eq. 4b). However, this reaction is strongly suppressed because, unlike in steam reforming, the syngas contains little CO due to the low process temperatures in reactor (14), and water is only produced stoichiometrically via reaction (Eq. 6a). This results in the intended potential for increasing the efficiency and reducing the cost of MeOH synthesis. Efficiency is increased because, by focusing on only one pathway (Eq. 6a), the catalyst can be designed to be more selective and therefore more efficient. Costs are reduced because the complex workup of unreacted syngas is eliminated, as the catalyst is optimized for CO2, which is kinetically favored anyway, as the dominant reactant. Examples of this are shown in EP03846936A1.

[0077] During a cold start, the catalyst is initially heated with electricity from the generator (4) until the heat of reaction (Eq. 6a) is sufficient to switch off the electric heating and cool the catalyst bed. For the copper-zinc oxide-aluminum oxide catalysts used in low-pressure synthesis, the optimal catalyst temperature is approximately 5–10 K below the recrystallization temperature of copper. The 3-way valve (20a) is preferably controlled so that only the amount of CO₂ required for MeOH synthesis according to (Eq. 6a) enters the reactor, which is stoichiometrically necessary for the conversion of the H₂ produced by electrolysis (11). The water produced during synthesis is stored in the water tank (19b) after purification.

[0078] During MeOH synthesis, the pressure in reactor (14) initially increases due to the temperature rise to 200–300°C and then decreases again in the reactor bed area during synthesis, since, according to equation 6a, four molecules are reduced to two. If the syngas were completely converted, the pressure of the mass flow leaving reactor (14) would therefore change only slightly. However, since syngas can hardly be converted 100% in a single pass in practice, the unreacted syngas is separated from the MeOH in a separation device (25a). This can be achieved by liquefaction, whereby the resulting low-temperature heat is used via the cooling stream (15a / b) to further superheat the AM.While the liquefied crude methanol is stored in the storage tank (16), the cooled and still gaseous purge gas is first compressed via the compressor (25b) and stored in the storage tank (12d) at a pressure approximately equal to the pressure of the syn gas components before they are introduced into the reactor (14). The purge gas is automatically injected into the reactor via the pressure relief valve (13c) as soon as the pressure in the syn gas inlet area falls below a certain threshold.

[0079] The majority of the CO2 mass flow not required for MeOH synthesis is preheated as much as possible – at a temperature close to that of the seawater flowing through the evaporator (1) – via the HEX#2 (21a), which is supplied with warm, pressurized electrolysis oxygen, and then divided again via the 3-way valve (20b): The smaller partial flow passes to the HEX#1 (2), which is preferably integrated into the catalyst bed of the reactor (14) and dissipates the process heat released according to (Eq. 6a), leading to superheating of this partial flow. The 3-way valve (20b) is preferably controlled by a temperature measurement in the catalyst bed so that the temperature always remains within the optimal process window, thus ensuring that the plant is operated optimally with regard to reaction rate, MeOH yield, and catalyst lifetime.

[0080] The cooled O2, still under high pressure, is split into two partial flows via the 3-way valve (20c). One portion is fed to the storage tank (12b) as a potential third component of the syngas or for sale as a by-product. The unused portion is depressurized to ambient pressure via the throttle (23), cooling by approximately 20° K due to the Joule-Thomson effect. This cooling effect is used via the HEX#4 (22) to further cool the CO2 coming from the HEX#5 (5) of the recuperator, which is already pre-cooled, thereby increasing the wet gas fraction.

[0081] The highly superheated AM exiting reactor (14) is combined with the preheated main stream coming from the 3-way valve (20b), resulting in a second superheating of the AM. The combined stream then reaches HEX#3 (21b), which is supplied with warm medium from the cooling processes (15a / b) of the electrolyzer (11) and reactor (14), resulting in a third superheating of the AM.

[0082] Between the HEX#3 (21b) and the turbine (3) is the inlet device (8a) for gaseous CO2, which ensures that the Rankine cycle receives as much CO2 as is consumed for MeOH synthesis and released into the sea via the outlet device (8b). To achieve a circular economy, the CO2 is preferably captured on-site via Direct Air Capture (DAC) and—unlike CO2 from CCUS (Carbon Capture and Usage)—is not gray, but green in the CO2 color coding system. According to the invention, the filters of the DAC system, which must be heated to 80–100°C for regeneration in the case of a solid-state adsorber, are preferably regenerated with the higher-grade waste heat (100–120°C) from a PEM electrolyzer instead of with waste heat from alkaline electrolysis according to the boiling point (SdT), whose temperature is approximately 20°C lower.

[0083] A further advantage of the DAC process, which is preferably based on desorption on solids, is the Fig. 1 The use of the condensate produced during filter loading, which is more than sufficient in quantity to operate the electrolysis process (not shown), is described below. This creates a circular system for the 100% renewable production of energy carriers on offshore platforms. (1) Production of the RE electricity (17) for electrolysis (17a) and for operating the auxiliary equipment (17b) via the turbine from stored marine heat, (2) Production of H2 as the first syn-gas component from the electrolysis of water, (3) Obtaining water for electrolysis via DAC and the MeOH synthesis (Eq. 6a) as by-products and (4) Production of CO2 or N2 as the second syn-gas component from the air via DAC or an air separation plant.

[0084] This means that eOTEC platforms according to the invention can be operated 100% autonomously at sea, since only the end products – energy carriers and electrolysis oxygen – need to be transported away to maintain logistics. Furthermore, if excess CO2 is captured in the sea, even negative CO2 emissions can be achieved.

[0085] In a further step (see Fig. 2 It may be possible to further increase the enthalpy of the AM by adding H2 from the electrolysis as an additive shortly before it enters the turbine (3). This is preferably done at a partial pressure that is slightly higher than the pressure in the CO2 line. If the pressure from the high-pressure electrolysis is insufficient, it may be possible to increase it to the desired level using a compressor (24).

[0086] The AM, enriched with respect to enthalpy in five stages, then flows into the turbine (3), where it expands and cools. The electricity (17) generated by the generator (4) serves to power the entire plant and all process steps, which are preferably all arranged on one platform.

[0087] The AM, cooled by approximately 30K and expanded to approximately 40bar in the turbine (3), is cooled by the following steps before it enters the condenser (6), thereby being converted as far as possible into the wet steam phase in order to make the condenser located at a depth of 1,000m as small as possible: a) In a first step, the AM coming from the turbine (3) is cooled via HEX#5 (5) of the recuperator in a countercurrent process with the cold wet steam pumped upwards by the pump (7), thereby equalizing the temperatures of the material streams at the outlet. b) In a second step, the AM coming from the recuperator and pre-cooled is further cooled in HEX#4 (22), whereby the oxygen gas (Joule-Thomson coefficient µ = 0.27 K / bar), which was previously expanded to 1 bar in the throttle (23) and thereby cooled by 16°C, serves as the cooling gas. The effects (a) and (b) are greater the higher the superheat of the AM at the inlet to the turbine (3). c) In a third step, the gas coming from HEX#4 (22) is further cooled in the approximately 1,000m long connecting line to the condenser (6) which is surrounded by cold seawater, with an increasing wet steam content.

[0088] In the condenser (6), the AM is then completely liquefied. The pressure is then increased again to approximately 65 bar via the pump (7), the liquid AM is fed to the evaporator via the recuperator, after which the cycle begins again.

[0089] If AM NH3 is identical to the energy carrier, the following results: Fig. 1 The following changes: a) The synthesis of the energy carrier is carried out according to Eq. (7a) instead of Eq. (6a). b) The system (18) serves to separate nitrogen (N2) from the air, which is supplied to the reactor (14) either directly or via an intermediate N2 storage tank (not in Fig. 2c) The discharge device (8b) is omitted. d) The 3-way valves (20a) and (20b) and the reactor (14a) are omitted, and the AM stream coming from the evaporator (1) is directed 100% into HEX#2 (21a). e) The 3-way valve (20b) splits the AM stream so that the partial stream in HEX#1 (2) cools the reactor bed sufficiently to prevent damage and to ensure maximum efficiency and yield of energy carrier synthesis, thus avoiding the need for purging the syn gas components if possible.

[0090] Fig. 2 Figure 1 shows the process according to the invention in simplified form with the storage areas for the precursors and end products (hatched), as well as the processes linked via the lines (15a,b) and (17a / b) electrolyzer (11), synthesis reactor (14), air separation (18) and water desalination (19a) with dotted background.

[0091] As with CO2 as an AM, in a preferred embodiment, the H2 from electrolysis can be fed into the Rankine cycle via an H2 inlet valve (13a) upstream of the turbine (3). This ensures that the mass flow and excess heat from electrolysis can be used directly and without loss via an intermediate heater to increase the enthalpy upstream of the turbine. A diffusion lock (13b) downstream of the turbine removes the H2 from the AM, temporarily stores it in the reservoir (12a), and feeds it into the reactor (14) for NH3 synthesis as needed. List of abbreviations used:

[0092] abbreviation Meaning AM Working medium (of an ORC process) CC-OTEC Closed Cycle Ocean Thermal Energy Conversion CCS Carbon Capture and Storage CCUS Cabon Capture, Use and Storage DAC Direct Air Capture eOTEC Enhanced Ocean Thermal Energy Conversion HEX Heat Exchanger MeOH Methanol OTEC Ocean Thermal Energy Conversion P2X Power-to-X PEM Proton Exchange Membrane (Electrolysis) RE Renewable Energy Syngas Synthesis gas (for a P2X process) References:

[0093] HD19A. Hasan, I. Dincer: "A New Integrated Ocean Thermal Energy-Based Trigeneration System for Sustainable Communities"; Journal of Energy Resources Technology. 2019 by ASME, Vol. 192, S. 061301-1 - 061301-9 HD20A- Hasan, I. Dincer: "An Ocean Thermal Energy Conversion Based System for District Cooling, Ammonia and Power Production", International Journal of Hydrogen Energy 345 (2020) 15878 - 15887 Fr17J. Fricke: "Neue CO2-betriebene Gasturbinen können Kraftwerks-Technik revolutionieren", Cluster Energietechnik, 2017 RB18G. Rau, J. Baird: "Negative-CO2-Emissions Ocean Thermal Energy Conversion, Renewable and Sustainable Energy Revisions, 95 (2018), 265-272 # Designation Optional Description or task 1 Evaporator no Conversion of AM from wet steam to gaseous AM by heat exchange with a stream of warm seawater via (10a / b) or in situ with the seawater or in situ with air. 2 HEX #1 no Cooling of the reactor bed and superheating of the partial stream of gaseous AM that enters the reactor (14) via the valve (20b). 3 turbine no Relief of the overheated AM, preferably in the dry steam region. 4 generator no Generation of renewable electricity, which is used for electrolysis (17a) and for operating the auxiliary equipment (17b). 5 HEX #5 Yes Recuperator for the 1st pre-cooling of the dry steam coming from the turbine (3) while simultaneously heating the wet steam coming from the pump (7). 6 capacitor no Liquefaction of the wet steam from HEX #4 (22) of the AM to the boiling line by heat exchange with cold seawater via (9a / b) or in situ with the seawater. 7 pump no Pressure increase of the liquefied AM and pumping to the recuperator (5). 8a Injection device no Compressor for introducing CO2 from the DAC system (18) into the Rankine cycle. If the AM is ammonia, the N2 obtained via the air separation plant (19) is compressed as the 2nd component of the syn gas and fed to storage #5 (N2). 8b Ejection device Yes Pump for removing CO2 from the Rankine cycle into the sea. 9 Cold seawater on / off Yes 9a / b: Supply and discharge of cold seawater via pump (9c) for operation of the condenser (6). (9c) can be omitted if condensation takes place in situ of the seawater. 10 Warm seawater on / off Yes 10a / b: Supply and discharge of warm seawater via pump (10c) for operation of the evaporator (1). (10c) can be omitted if the evaporation takes place in situ of the seawater. 11 electrolyzer no Decomposition of water into hydrogen and oxygen and storage in the storage units (12a) and (12b) respectively after heat removal via HEX #3 (21b) and HEX #2 (21a). 12a Storage #1 no For H2 from electrolysis (11) as the 1st component of the syn gas 12b Storage #2 no For O2 from electrolysis (11) as a possible 3rd component of the syn gas 12c Storage #5 no Storage for the second component of the syn gas (CO2 or N2), which in the case of CO2 comes from the DAC plant (18) or in the case of N2 from an air separation plant (18). 13a ZSS one Yes The additive H2 is injected upstream of the turbine at a pressure that is preferably higher than the pressure of the AM at the injection point; for this reason, high-pressure PEM electrolysis is preferred. 13b ZSS from Yes Diffusion lock of the additive H2 after turbine and introduction into storage tank #1 (12a) 14 Reactor #1 no Synthesis of the energy carrier and use of the exothermic heat to superheat the AM partial flow, which is diverted as a partial flow from the valve (20b) to cool the reactor bed. 14a Reactor #2 Yes Reactor for splitting CO2 and H2 into CO and H2O according to the water-gas shift reaction, should this be necessary for reasons of efficiency in energy carrier synthesis. 15a / b coolant flow no Cooling medium in / out for cooling the electrolysis (11) and transferring the heat to the AM in HEX #3 (21b) to prevent overheating of the same or to regenerate the DAC filters (18d). 16 Storage #3 no For energy carriers from reactor #1 (14). 17a / b RE-Strom no For electrolysis (17a) and auxiliary equipment (17b). 18 Production of the second component of the syngas no (A) CO2: Extraction of CO2 and water for electrolysis (11) from air or (B) N2: Extraction of N2 from air via an air separation plant. Note: In the following, a distinction is made between case A and B. 18a / b Air inlet and air outlet no A: Air inlet or residual air outlet (without CO2) B: Air inlet or residual air outlet (without N2) 18c fan no Intake of outside air 18d CO2 filter no A: Filter regeneration via heat flow 15a / b from electrolysis (11) or energy carrier synthesis (14) B: Filtration is achieved through liquefaction 19a Water desalination plant Yes For electrolysis (11), when water from MeOH synthesis (14) or DAC (18) is insufficient, using RE current (17b) 19b Storage #4 no Water for electrolysis, which is obtained from MeOH synthesis (14), seawater desalination (19a), the DAC process (18) or evaporation of AM in outside air. 20a 3-way valve #1 no Splitting the gaseous AM stream into a main stream to HEX #2 (21a) and a partial stream to valve (20e) 20b 3-way valve #2 no Splitting the gaseous AM main stream coming from HEX #2 (21a) into a main stream to HEX #3 (21b) and a partial stream to HEX #1 (2) for cooling the reactor bed. 20c 3-way valve #3 Yes Division of the O2 stream coming from the electrolyzer (11) into the O2 tank (12b) and the throttle (23) for subcooling the AM expanded in the turbine (3). 20d 3-way valve #4 Yes Division of the liquid AM CO2 stream coming from the pump (7) into a main stream to the recuperator (5) and a partial stream for storage in the ocean. 20e Three-way valve #5 Yes Splitting of the AM partial stream CO2 coming from valve (20a) into two partial streams, one of which leads to reactor #1 (14) and the other to reactor #2 (14a). 21a HEX #2 Yes 1. Overheating of the vaporized AM through heat exchange with the waste heat of the electrolysis oxygen. 21b HEX #3 Yes Heat exchange from waste heat of electrolysis (11) or process heat of energy carrier synthesis (14) and 2. superheating of the AM dry steam. 22 HEX #4 Yes 2. Pre-cooling of the gaseous AM coming from the recuperator (5) and preferably conversion to wet steam. 23 throttle Yes 1. Cooling O2 and 2. Pre-cooling of the gaseous AM coming from the recuperator (5). 24 compressor Yes For H2 from electrolysis (11). This is only necessary if the H2 pressure in the storage tank (12a) is lower than the pressure of the AM before the turbine. 25 Sea surface . / . To visualize the components above and below the sea surface.

Claims

1. Method for producing gaseous or liquid energy carriers from at least two synthesis gas components, the first component of which is hydrogen produced by electrolysis of water, the electricity for the electrolysis being obtained via a turbine (3) of an ocean thermal energy conversion plant integrated into a Rankine cycle which uses a working medium, characterized in that a. the working medium of the Rankine cycle is chemically and physically identical to at least one component of the energy carrier synthesis and a partial flow of the working medium is guided, as the second component of the energy carrier synthesis, into a reactor (14) used for this purpose via a first 3-way valve (20a) of the Rankine cycle, b. process heats from electrolysis and reaction enthalpies from the energy carrier synthesis or other processes necessary for obtaining the working medium and / or another component of the energy carrier synthesis are recycled into the Rankine cycle and thus contribute to increasing the thermodynamic efficiency of the Rankine process and the efficiency of the entire process.

2. Method according to claim 1, characterized in that the other partial flow of the first 3-way valve (20a) is split via another 3-way valve (20b), one of the resulting partial flows being guided, via a heat exchanger (2), to cool a reactor bed of the reactor (14) used for the energy carrier synthesis.

3. Method according to either of the preceding claims, characterized in that the electrolysis takes place in an electrolyzer (11) and the resulting reactants, hydrogen and oxygen, are temporarily stored in a storage facility (12a) or a storage facility (12b), the electrolysis preferably being high-pressure PEM electrolysis, in particular seawater electrolysis.

4. Method according to claim 3, characterized in that the hydrogen from the electrolyzer (11) is added at least partially as an additive to the working medium of the Rankine cycle via a check valve (13a) in order to transfer the waste heat from the electrolysis to the working agent of the Rankine cycle.

5. Method according to claim 4, characterized in that in the electrolyzer (11), the hydrogen partial pressure is greater than the pressure of the working medium at the point of introduction of the hydrogen as an additive into the working medium of the Rankine cycle via the check valve (13a), the additive contained in the working medium preferably being withdrawn from the working medium via a diffusion lock (13b) and stored in the storage facility (12a).

6. Method according to any of the preceding claims, characterized in that a condenser (6) serving as a heat sink of the Rankine cycle is located in the seawater at the height at which the working medium condenses at the temperature of the seawater, the cold seawater at this point serves as a cooling medium for the condensation, and in particular no pumping of cold seawater takes place, as a reault of which an associated efficiency-reducing parasitic pumping power is eliminated, an evaporator (1) serving as a heat source of the Rankine cycle preferably being located at the height of the seawater at which the working medium evaporates at the temperature of the seawater, and the warm seawater at this point serving as a heating medium for the evaporation.

7. Method according to any of claims 1 to 6, characterized in that an evaporator (1) serving as a heat source of the Rankine cycle is located in the ambient air and the ambient air serves as the heating medium for evaporation, water preferably being condensed from the ambient air used as the heating medium at the evaporator (1) and stored in a storage facility (19b).

8. Method according to any of the preceding claims, characterized in that the thermal energy contained in the oxygen produced during the electrolysis is transferred to the gaseous working medium via a heat exchanger (21a) and used for first superheating of the evaporated working medium, the electrolysis preferably taking place in an electrolyzer (11) and the waste heat from the electrolyzer (11) and the reaction enthalpy from the reactor (14) being used in a further heat exchanger (21b) for second superheating of the gaseous working medium.

9. Method according to claim 8, characterized in that due to the overheating of the working medium, the turbine (3) of the Rankine cycle can be operated as a gas turbine in dry steam and thus exhibits improved efficiency and performance.

10. Method according to any of the preceding claims, characterized in that a component of the synthesis gas is CO2 which is obtained via DAC (direct air capture) (18) and is stored in a storage facility (12c), or a component of the synthesis gas is CO2 and / or N2 which is obtained via an air separation plant (18) and is stored in a storage facility (12c).

11. Method according to claim 10, characterized in that the DAC method is based on solid-state adsorption and the energy for desorption of a filter used in this DAC method is taken from the reaction enthalpy of the energy carrier synthesis and / or the process heat from the electrolysis, the water obtained in the DAC method and / or in the energy carrier synthesis preferably being stored in a storage facility (19b) and supplied to an electrolyzer (11) used for the electrolysis.

12. Method according to any of the preceding claims, characterized in that the working medium, after leaving the turbine (3) of the Rankine cycle, is directed through a first heat exchanger (5) which serves as a recuperator and in which the gaseous working medium located on the outlet side of the turbine (3) is subjected to first cooling, and at the same time the liquid working medium flowing toward an evaporator (1) and coming from a working agent pump (7) is preheated, the working medium, after leaving the recuperator (5), preferably being directed through a second heat exchanger (22) in which the oxygen from an electrolyzer (11) used for the electrolysis is expanded and the working medium is subjected to second cooling.

13. Method according to any of the preceding claims, characterized in that a third component of the synthesis gas is oxygen which is guided from a storage facility (12b) into the reactor (14) used for the energy carrier synthesis and is used for the synthesis of oxygen-containing energy carriers.

14. Method according to any of the preceding claims, characterized in that a component of the synthesis gas is CO2, which, before being introduced into the reactor (14) used for the energy carrier synthesis via a 3-way valve (20e), is divided into two partial flows, of which the first partial flow is directed to the reactor (14) and the second partial flow is converted, in a further reactor (14a), into CO and H2O with the addition of H2 via a water gas shift reaction.

15. Method according to any of the preceding claims, characterized in that the working medium is CO2, part of the working medium being released into the ocean via a valve (20d) and being completely dissolved in situ according to the temperature-dependent partial vapor pressure and stored in the seawater.