Abstract
A modular reactor configuration for the production of hydrogen (H.sub.2) by means of electrolysis in its single-stage design and of methane (CH.sub.4) in its two-stage design with optional gas storage and gas utilization in fuel cells, wherein the single-stage design, consisting of the electrolyzer, the fuel cell, the gas storage tanks for separate storage of H.sub.2 and oxygen (O.sub.2), the associated lines, the condenser, the H.sub.2O container, the heat storage tanks and the evaporator, is based on the principles of a reversible product cycle for H.sub.2 according to FIG. 1 and can serve both as electricity storage and for H.sub.2 production as fuel gas, and whose two-stage design, exemplified according to FIG. 5 with the additional components the methanation reactor, the lines and, the heat exchangers and as well as the CH.sub.4 discharge in the H.sub.2O condenser, based on extended reversible reference processes, which describe the possible methanation reactions in this second reactor stage with the reaction equations, which can also run in parallel, and are thermodynamically equivalent to the reverse reaction of the oxidation of CH.sub.4 and thus indicate the best possible structures for further technical implementation.
Claims
1-17. (canceled)
18. A device, comprising: an electrolyzer, an H.sub.2 gas reservoir for storage of H.sub.2 gas, an O.sub.2 gas reservoir for storage of O.sub.2 gas, wherein the electrolyzer supplies the H.sub.2 gas reservoir with H.sub.2 gas produced via electrolysis and supplies the O.sub.2 gas reservoir with O.sub.2 gas produced via electrolysis, an associated H.sub.2 gas line, an associated O.sub.2 gas line, an H.sub.2O container, and an evaporator, wherein the electrolyzer is supplied with vaporous H.sub.2O from the H.sub.2O container via a feed pump, the evaporator, and a vaporous H.sub.2O line, wherein H.sub.2O in the evaporator is supplied with evaporation heat from a heat source, wherein the evaporation heat from the heat source is waste heat from processes or waste heat obtained from the environment.
19. The device according to claim 18, wherein the waste heat used for evaporation is heated by a heat pump to a temperature level required for evaporation.
20. The device according to claim 18, further comprising: a fuel cell, wherein the electrolyzer is arranged for supplying the fuel cell with H.sub.2 gas via the associated H.sub.2 gas line and O.sub.2 gas via the associated O.sub.2 gas line, wherein a device for supplying waste heat of the fuel cell to a first heat accumulator for supplying heat to the electrolyzer, and for conducting the gaseous reaction product H.sub.2O of the fuel cell via a vapor compressor and a condenser, which delivers waste heat to a second heat accumulator, to the H.sub.2O container, and from there, if required, conducting the H.sub.2O via the feed pump and the evaporator supplied by the heat accumulator via the line in the vapor state to the electrolyzer.
21. The device according to according to claim 18, wherein the electrolyzer and the heat source are integrated in an integrated evaporator, which also serves as a steam accumulator, with electrolytic cells protected by cladding tubes and are supplied from a steam dome via a line and flow distributors or a steam space, which is separated from an evaporator section by perforated plates, with vaporous H.sub.2O and the product H.sub.2 gas and O.sub.2 gas are discharged correspondingly either via collectors and or gas chambers, again separated by the perforated plates, via the lines, the H.sub.2O supply being effected via one or more connections.
22. The device according to claim 21, wherein the port or ports are also used for steam supply from a steam network.
23. The device according to claim 21, wherein the heat supply of the heat source is provided by heat emitting fluids or reactions from outside.
24. The device according to claim 20, wherein, in the case of an electricity storage device, fuel cells are used as heat sources.
25. The device according to claim 18, wherein the electrolyzer and the heat source are integrated into an integrated evaporator which also serves as a steam storage, wherein cells of the electrolyzer are arranged directly in an evaporator section without cladding tubes and the steam can flow directly to electrodes of the cells, wherein, in the case of an H.sup.+-conducting electrolyte, an O.sub.2 outlet is provided and H.sub.2 is discharged via a gas space and an H.sub.2 outlet, wherein, in the case of an O.sup.2−-conducting electrolyte, the gases in the outlets are correspondingly interchanged and, accordingly, also the associated connecting lines.
26. The device according to claim 18, further comprising: a methanation reactor for the additional production of methane CH.sub.4 from H.sub.2 and CO.sub.2 or from H.sub.2 and CO or from H.sub.2O and CO, lines, heat exchangers, and a CH.sub.4 discharge in an H.sub.2O condenser, wherein the methanation reactor serves as a heat source for the electrolyzer.
27. The device according to claim 26, wherein the device is arranged for conducting incoming CO.sub.2 via a distribution system or a separated gas space to a CO.sub.2 electrolysis cell for the generation of CO via electrolysis, and for feeding CO generated there via an outlet collector and the conduit after preheating or after mixing with H.sub.2 in the gas space as synthesis gas to the methanation reactor.
28. The device according to claim 26, wherein the H.sub.2 supply for methanation is via an integrated fuel cell with an H.sup.+-conducting electrolyte.
29. The device according to claim 26, wherein the device for storing CH.sub.4 generated in a CH.sub.4 generator in gas storage tanks for use in fuel cells for power and heat generation and for feeding the formed CO.sub.2 via a flue gas condenser and a CO.sub.2 conduction system after compression in a CO.sub.2 compressor to the CO.sub.2 storage tank and from there to the CH.sub.4 generator for renewed CH.sub.4 generation with H.sub.2O, further arranged for the production of H.sub.2 and CO.sub.2 from CH.sub.4 via reforming reactors and supply of the produced CO.sub.2 via the line to the CO.sub.2 storage.
30. The device for producing CH.sub.4 and H.sub.2 according to claim 26, wherein the device is arranged for producing ethene C.sub.2H.sub.4 from H.sub.2 and CO.sub.2 or from H.sub.2O and CO, and/or other hydrocarbons C.sub.nH.sub.m.
31. The device according to claim 26, wherein the methanation reactor is provided with an O.sup.2−-conducting electrolyte which allows O.sub.2 forming during methanation to be removed in situ during the reaction.
32. The device according to claim 26, wherein the methanization reactor is installed in the integrated evaporator, the walls of which are formed of O.sup.2−-conducting electrolytes, whereby the channel is formed with the cladding tube, which channel serves for the discharge of the O.sub.2 produced during the reaction, wherein the methanation reactor is supplied with vaporous H.sub.2O are via a steam dome via a conduit and a steam compartment, which is separated from an evaporator section by perforated plates, or via flow distributors, and wherein the product gases CH.sub.4 and O.sub.2 are discharged correspondingly either via headers or gas compartments, again separated by the perforated plates, via the lines, wherein the H.sub.2O supply and/or steam supply from a steam network is effected via one or more connections, wherein the heat supply is effected by any heat-emitting fluids or reactions from outside.
33. The device according to claim 26, wherein the methanation reactor is additionally supplied with H.sub.2 and/or CO via electrolyzers integrated in the integrated evaporator, wherein H.sub.2 and/or CO, when an O.sup.2−-conducting electrolyte is used, is supplied to the gas compartment via the gas compartment and the line and, when separate H.sub.2 is supplied to the gas compartment, via the gas compartment and the line with the extraction point, and, in the case of separate CO routing, via collectors and the line to the gas compartment, whereby, when an H.sup.+-conducting electrolyte is used, H.sub.2 can be routed separately via the evaporator section, the steam line and the gas compartment, the released O.sub.2 being removed via the gas compartment and CO being routed via collectors and the line to the gas compartment.
34. The device according to claim 26, wherein the heat released at larger temperature differences between methanation and electrolysis is used to evaporate the supplied water.
35. The device according to claim 18, wherein the evaporator can be kept ready for operation even in the event of failure of the heat supply by an external heat supply by electrical heating, direct H.sub.2/O.sub.2 combustion in the steam compartment, or external steam supply.
36. The device according to claim 18, wherein a gas outlet from the electrolysis located directly downstream of the evaporator is provided with separating devices, such as cyclones or condensers, in order to avoid steam outlets with the electrolysis gas.
37. The device according to claim 18, wherein the condenser also serves as a waste heat source of the heat pump.
Description
TASK OF THE INVENTION
[0025] 1. to use the principles of the reversible comparison process according to FIG. 1 to improve the energy efficiency of “power-to-gas” technologies based on H.sub.2 and synthetic hydrocarbons, generally hydrocarbon compounds, as elements of large-scale electricity storage and to use CO.sub.2 as a raw material in closed cycles without releasing CO.sub.2 to the environment; [0026] 2. improving the energy efficiency of H.sub.2 generation using electrolysis through devices to provide H.sub.2O in gaseous state upstream of the electrochemical electrolysis cell, largely independent of the operating temperature; [0027] 3. improvement of thermal integration of upstream electrolysis for H.sub.2 generation and Sabatier exothermic methanation reaction, and utilization of the working potential of this reaction for recovery, thus improving efficiency. [0028] 4. improvement of thermal integration of upstream electrolysis for H.sub.2 generation and exothermic methanation in potential new electrochemical processes. [0029] 5. system integration of the newly developed above gas generators into an electricity storage system and with integrated recycling for CO.sub.2 as a sustainable industrial feedstock. [0030] 6. transfer of the process logic and device to other related process designs.
Solution of the Task
[0031] The elaborated reversible process control of electricity storage with the aid of H.sub.2, as indicated in FIG. 1, can be directly implemented with minor adaptations into a technically realizable device for electricity storage for grid stabilization with high efficiency, the design of which leads directly to the sought-after devices for energy-efficient generation of H.sub.2 and advantageously CH.sub.4 as well as other synthetic hydrocarbons, generally hydrocarbon compounds. Crucial for the transfer of the principles to a device is that the electrolyzer is always provided with the required H.sub.2O only in the gas phase by a suitable heat recovery or use of waste heat, in order to avoid high heat losses due to the necessary H.sub.2O evaporation.
[0032] The technical solution of the electricity storage device, as shown in FIG. 6, differs from this reversible basic structure only in that real occurring temperature and pressure differences are taken into account. For this purpose, the fuel cell (2) is supplied with H.sub.2 and O.sub.2 from the gas accumulators (3a) and (4a) when electricity is required and is operated at a temperature so much higher than the electrolyzer (1) that reliable heat exchange via the heat accumulator (8) is ensured. The pressure of the exhaust steam of the fuel cell (2) is appropriately increased by a steam compressor (18) so that the heat accumulator (7) can be supplied by the condenser (5) with waste heat at a sufficiently high temperature during the condensation of the exhaust steam of the fuel cell, and the condensate is supplied to the H.sub.2O tank (6). When there is a power surplus, the electrolyzer (1) is supplied with steam from the H.sub.2O tank (6) via the feed pump (19), the evaporator (9) and the H.sub.2O line (10), and then refills the two gas reservoirs (3) and (4) with H.sub.2 and O.sub.2. The heat required for this is taken from the heat accumulator (7).
[0033] The amount of heat stored in the heat accumulator (8), which follows from the release of the reaction entropy of the fuel cell, is relatively small at low operating temperatures of the electrolyzer. It is therefore advisable to check here whether the operating conditions of the electrolyzer permit an economical additional storage installation, or whether it is more sensible to compensate for the heat loss by electrical heating or to seek other solutions.
[0034] According to the invention, the evaporation heat from the heat source (22, 27) is waste heat from processes or waste heat obtained from the environment. Waste heat from (industrial) processes is in particular industrial waste heat, preferably with a temperature of maximum 400° C., further preferably maximum 300° C., still further preferably maximum 200° C. Waste heat from processes is advantageously external waste heat, i.e. it is supplied to the device according to the invention from outside and originates, for example, from an external industrial process and not from processes within the device according to the invention, in particular not from the waste heat of a fuel cell in the device according to the invention, unless this heat would otherwise be discharged into the environment as intended. A heat pump can be omitted if the temperature of the waste heat is above the required evaporation temperature.
[0035] A simplified device shown in FIG. 7 with the same mode of operation differs from the basic solution discussed above in that the system of condenser (5), H.sub.2O container (6), heat accumulator (7) and evaporator (9) is replaced by a steam accumulator (20) which supplies the electrolyzer (1) with steam in the event of a power surplus and is recharged by the exhaust steam from the fuel cell via the steam compressor (18) when power is required. To increase the security of supply, the steam accumulator (20) can be equipped with electrical heating for pressure maintenance or a connection to a steam network, if available, or further connected steam accumulators or other heat accumulators and thus be integrated into an industrial sector coupling with a large storage volume.
[0036] The device described can also be used with regenerative fuel cells (1/2), which can also be operated as electrolyzers, as FIG. 8 shows. For this purpose, the steam accumulator (20) is connected to the regenerative fuel cell (1/2) and the steam compressor (18) simultaneously via a three-way valve (21). In fuel cell mode, the three-way valve (21) connects the regenerative fuel cell (1/2) to the steam compressor (18) and the steam accumulator (20) is charged with the vaporous H.sub.2O formed. In electrolysis mode, the three-way valve connects the steam accumulator (20) to the regenerative fuel cell (1/2) which is in electrolysis mode. To increase operational reliability and storage volume, the steam storage tank (20) can also be connected to other steam storage tanks in a steam network and integrated into an industrial sector coupling.
[0037] As already explained on the basis of the extension of the balance boundary of the electrolyzer-fuel cell system as shown in FIG. 20, the possibilities of process improvement shown in FIG. 1 can therefore also be used for open cycles for H.sub.2 production and consequently for CH.sub.4 production and, under certain conditions, also for the production of further hydrocarbons (C.sub.nH.sub.m) or hydrocarbon compounds. Thermodynamically, the reversible process described above can be approximated if the evaporation heat released during H.sub.2 oxidation—whether in a fuel cell or in a combustion reactor—is released to the environment during its condensation due to lack of recuperation capability, if conversely the evaporation heat of the H.sub.2O required for electrolysis can be recovered from the environment. This can be achieved, or at least approximated, as part of a system integration of the electrolysis (1) using a circuit as indicated in FIG. 9. H.sub.2O is fed from the tank (6) via the feed pump (19) to the evaporator (23), where it is supplied with sufficient heat of evaporation from the heat source (22), and the resulting steam is then fed to the electrolyzer (1). In its structural design, the evaporator (23) can integrate the steam accumulator (20) into the evaporator (9). If, for example, the heat source (22) is supplied with solar heat or geothermal heat with evaporation heat, the requirement for a reversible process would be well approximated, since the environment would have (at least approximately) resupplied the evaporator with the entropy given off during H.sub.2 oxidation by this type of heat transfer. Although this ideal case is not always achievable, a setup according to FIG. 9 can always be used to utilize waste heat from various processes, if necessary within the limits of economic viability, with the aid of heat pumps, as already shown in the comparative process according to FIG. 20, to evaporate the H.sub.2O supplied to the electrolyzer in order to significantly reduce the exergy losses of 17% during H.sub.2 production. The advantage of this approach is that in industrial plants steam with low exergy can be used for this purpose in order to save the dissipation of electrical work.
[0038] The device shown in FIG. 10 shows an advantageous installation of an electrolyzer (1) in an integrated evaporator (26), which also serves as a steam accumulator (20) or for steam storage, similar to a shell boiler. Heating can be carried out in various ways using a heat source (27). For example, various heat-emitting fluids can be passed through tubes, or exothermic reactions that need to be cooled can take place there. The heat sources (27) are to be arranged in parallel in such a way that an orderly evaporation process and water circulation in the evaporator section (9) can be ensured. The electrolyzer (1) consists of parallel arranged cell groups (24), which can be plate- or tube-shaped but also micro-process modules, which are surrounded by a cladding tube (25). The steam is directed via the steam dome (28), the steam line (29) to the distributors (30) and then to the cell groups (24) located in the cladding tube (25). The parallel flow distributors (30) connect the cell groups (24) and the associated cladding tubes (25) to the parallel headers (31) and (32). The gases of systems (3) and (4) then exit from headers (31) and (32). If an H.sup.+-conducting electrolyte is used for the cell groups (24), H.sub.2 exits as a gas in (3) and O.sub.2 exits as a gas in (4). When an O.sup.2−-conducting electrolyte is used, H.sub.2 exits as a gas in (4) and O.sub.2 exits as a gas in (3). H.sub.2O is supplied via the inlet connection (33), whereby the entering water should already be preheated to close to the saturated steam temperature. When using the electrolyzer in industrial plants with steam networks, the inlet connection (33) can also be used to feed external steam to maintain the temperature of the system during shutdowns and also, depending on the possibilities of system integration, for steam heating instead of the heat source (27). For start-up and as an emergency supply, electrical heating of the evaporator is also possible. In the case of an integrated H.sub.2 electricity storage system in accordance with the structures discussed in FIG. 7, the individual fuel cell groups (2) are surrounded analogously to the electrolysis cells (24) with or without cladding tubes corresponding to (25) and, while retaining the circuitry indicated in FIG. 7, are simultaneously used as a heat source (27). It should be noted that, in comparison with the design of the electrolyzer (1), the gases involved, H.sub.2 and O.sub.2, enter the fuel cell via two separate flow distributors in the fuel cell process in accordance with the process-related reversal of the flow direction, and the product H.sub.2O is fed to the steam compressor (18) via an outlet collector and is then fed to the integrated evaporator (26) via the inlet (33). One option is for the steam compressor (18) to inject the higher pressure steam not only into the evaporator section (9), but also into the steam chamber (35a). Instead of electrical heating, gas accumulators (3a) and (4a) can also be used to supply heat to maintain the pressure of the integrated evaporator, and thus integrated H.sub.2 burners supplied with O.sub.2 that feed their exhaust gas H.sub.2O directly into the evaporator section (9). In the case of integrated H.sub.2 electricity storage systems corresponding to FIG. 8, the integration of the regenerative fuel cell (1/2) shown here in place of the electrolyzer (1) into the integrated evaporator (26) alone is sufficient, and the latter takes over the tasks of the steam accumulator (20) and the heat accumulator (8). The H.sub.2O exiting the fuel cell (1/2) is returned to the integrated evaporator (26) via the steam compressor (18).
[0039] FIG. 11 shows a variation of the device shown in FIG. 10, in which the flow distributors (30) and the collectors (31) and (32) are replaced by chambers. The flow distributor (30) is replaced by the steam chamber (34), which is separated from the actual evaporator section (9) by a tube sheet (35). Similarly, the two headers (31) and (32) are replaced by the two gas chambers (36) and (37) formed with the tube sheets (35). The flow routing and gas distribution is analogous to what was said for FIG. 10. In the case of an integrated H.sub.2 electricity storage unit according to the variants presented in FIG. 7 or 8, what has been said above in the description of FIG. 10 applies.
[0040] A further simplification of the construction of the device is shown in FIG. 12. The electrolyzer is constructed as in FIGS. 10 and 11 with the difference that the cladding tube (25) is omitted and the cells are arranged directly in the evaporator section (9). This reduces the number of tube sheets (35) to only one and the discharge of the generated gases O.sub.2 and H.sub.2 takes place via the associated outlet nozzles of lines (3) and (4). It is possible that steam is also entrained with the outgoing product gases O.sub.2 or H.sub.2. This effect can be largely reduced with cyclones and, if necessary, by subsequent condensation. Which gases escape at (3) and (4) depends on the electrolyte selected and corresponds to what has already been said above. In the case of an integrated H.sub.2 electricity storage system according to the structures discussed in FIG. 7, the same applies as in the description of FIG. 10.
[0041] As FIGS. 3 and 4 show, the device shown in FIGS. 10 to 12 also fulfills very well the requirements for optimizing devices for CH.sub.4 generation and its thermal integration with the upstream electrolysis. For this purpose, FIG. 13 shows the heating (11) of the integrated evaporator using the example of the variant shown in FIG. 12 by means of an exothermic reaction based on the methanation reaction Eq. (6) instead of or as a supplement to the general heat source (27). At the same time, this also shows the principle structure of the associated further necessary system integration for an integrated CH.sub.4 generator. In principle, all of the systems integration steps given in Eqs. (6) to (10) are exothermic and therefore in principle suitable for heating the evaporator, as already explained for FIG. 4. The basic principles required to design integrated CH.sub.4 generators combining electrolytic H.sub.2 generation with both thermal and possible electrochemical CH.sub.4 methanation reactors have already been presented in FIG. 5. For further clarification of the design principles of a highly integrated CH.sub.4 generator, the reaction control according to Eq. (6) already selected and explained in FIG. 5 is therefore also further used in FIG. 13. As in FIG. 12, the assignment of system (4) to O.sub.2 and of system (3) to H.sub.2 is immediately clear here, because only H.sub.2 and not O.sub.2 is allowed to flow into the methanation reactor (11). The fluid in the piping system (12) is CO.sub.2 and flows to the methanation reactor (11) without upstream electrolysis. The system design corresponds to the formulated rules described in (Wolfgang Georg Winkler: Sustainable product development based on second law of thermodynamics. September 2011. Applied Energy 88(9): 3248-3256 DOI: 10.1016/j.apenergy.2011.03. 020). According to these rules, reactants and products must first be used for heat recovery, taking into account the individual temperature levels of the reactions involved, before additional heat may be added. In the first stage, the products H.sub.2 and O.sub.2 are obtained from the reactant H.sub.2O. In the second reaction stage, CH.sub.4 and H.sub.2O are produced from the reactants H.sub.2 and CO.sub.2 according to Eq. (6). This results in three different temperature levels: ambient, evaporator/electrolyzer and methanation, between which the heat recovery shown here takes place. The CH.sub.4—H.sub.2O mixture is discharged from the methanation reactor (11) via the line (13) according to equation (6). The CH.sub.4—H.sub.2O mixture is then passed through the heat exchangers (16) to the H.sub.2 preheater and the second stage CO.sub.2 preheater (17) and finally to the condenser (15) for separation of CH.sub.4 and H.sub.2O. The condensed H.sub.2O is stored in the tank (6) and the CH.sub.4 is discharged separately (14).
[0042] From the electrolyzer, 4 moles of H.sub.2O are required to produce 1 mole of CH.sub.4, half of which is thus provided by the recirculation and the other from outside. These 4 mol H.sub.2O/mol CH.sub.4 are supplied to the evaporator section (9) via the condenser (15) after preheating via the line (33) and are supplied internally to the electrolyzer (1) as steam. The O.sub.2 leaving the electrolyzer is used via the heat exchanger (17) as the first preheating stage to preheat the incoming CO.sub.2. In this process, the condenser (15) can also serve as a waste heat source for the heat pump.
[0043] Since the electrolytic H.sub.2 generation must also be combined together with the electrolytic generation of CO, FIG. 14 shows a corresponding addition to the system setup of the device shown in FIG. 13. However, the changes in the system only affect the area of the device that comprises the supply line of the CO.sub.2 (12) and the components associated with it. In particular, these relate to the change in preheating associated with the supply and discharge of the process gases CO.sub.2 and CO. The second preheating stage of CO.sub.2 is replaced by a preheating of CO by the CH.sub.4—H.sub.2O mixture in the heat exchanger (42) corresponding to the temperature level. The design options for integrating the CO.sub.2 electrolyzer (39) can be taken from FIGS. 10 and 11 using the example of integrating the H.sub.2O electrolyzer. The solution shown in FIG. 14 is based on FIG. 10. When simultaneously integrating the electrolyzers for the generation of H.sub.2 and CO, special care must be taken to avoid short circuits in the integrated evaporator (26). The CO.sub.2 is fed via the line (12) to the distributor (38) of the CO.sub.2 electrolyzer (39), where it is converted into CO while releasing ½ O.sub.2 into the evaporator section (9) in the same way as for H.sub.2O electrolysis. This is led via the collector (40) and the line (41) to the preheater (42) and from there to the methanation reactor (11). The conception of the treatment of the CH.sub.4—H.sub.2O mixture leaving the methanation reactor (11) remains unchanged compared to FIG. 13.
[0044] Analogous to FIG. 11, this device can be further simplified in terms of design, as shown in FIG. 15. There, the distributor (38) is replaced by a CO.sub.2 inlet chamber (43), which serves to supply gas to the electrolysis cell (39). The CO formed in the electrolysis cell (39) is then fed into the H.sub.2 outlet chamber (36) and the H.sub.2—CO mixture is fed to the methanation reactor (11) via the line (3) after preheating in the heat exchanger (16), as in FIG. 13.
[0045] Another possibility for improving the efficiency of methanation according to Eqs. (6) and (7) results from utilizing the unused potential indicated in FIG. 3 for the recovery of electrical work in these thermal processes. FIG. 16 serves to explain the practical implementation. H.sub.2 and CO.sub.2 flow into the methanation reactor (11) according to Eq. (6) or CO according to Eq. (7). In both cases, additional H.sub.2 alone is needed compared to the CH.sub.4 generation requirement, in order to be able to separate O.sub.2 after oxidation with H.sub.2 by condensation of CH.sub.4. The available potential to supply electric work can be utilized by adding H.sub.2 using an H.sup.+-conducting fuel cell. H.sup.+ ions then emerge from the outer surface of the fuel cell and react with CO.sub.2 and CO, respectively, to form CH.sub.4 and H.sub.2O. In all highly integrated systems according to FIGS. 10 to 16, special care must be taken to ensure that no short circuits can occur between the integrated current-carrying components and that they are excluded by design.
[0046] In the case of direct electrochemical generation of CH.sub.4 using O.sup.2−-conducting electrolytes, already discussed above, the design principles derived above can be adapted to the appropriate devices. FIG. 21, which arises from the design according to FIG. 11, shows as an exemplary example a device for a methanation reaction according to Eq. (5). The electrolysis cells (24) are replaced by methanation reactors (11), the walls of which are formed from O.sup.2−-conducting electrolytes, whereby the channel (37a) is formed with the cladding tube (25a), which serves to discharge the O.sub.2 produced during the reaction. Steam is supplied to the steam chamber (34) via the steam line (29). CO.sub.2 is supplied there through the line (12) after its preheating in the heat exchanger (17), and the mixture of H.sub.2O CO.sub.2 is then fed into the methanation reactor (11). According to the design of the separate gas inlet by means of distributors or chambers according to FIG. 10 or FIG. 11, a separate feed of CO.sub.2 and vaporous H.sub.2O into the methanation reactor can also take place. Depending on the catalysts used, different operating temperatures are possible for such methanation reactors, therefore, due to the possible different operating conditions, reference is made to the already quoted design rules for heat recovery in (Wolfgang Georg Winkler: Sustainable product development based on second law of thermodynamics. September 2011. Applied Energy 88(9): 3248-3256 DOI: and to the presented embodiments in FIGS. 10 to 15.
[0047] Using combinations with the devices for generating H.sub.2 and CH.sub.4 according to Eqs. (6) to (10), the inlet gas concentrations of the methanation reactors (11) can be optimized for different catalysts. For this purpose, the device according to FIG. 21 only has to be supplemented by the installation of H.sub.2O and/or CO.sub.2 electrolysis cells according to the embodiments of FIGS. 10 to 15. If, for example, an admixture of H.sub.2 is desired, the device according to FIG. 21 can be combined with H.sub.2O electrolysis, as FIG. 22 shows using the example of Eq. (9). For this purpose, only the chambers (34, 36, 37) at the inlet and outlet must be divided with a partition (35a) and/or supplemented or replaced with the design of flow distributors (30) and collectors (31), (32). The corresponding division at the outlet results in a chamber (36) for CH.sub.4 and a chamber (36a) for H.sub.2. The construction of the electrolysis section corresponds to FIG. 11 with an O.sup.2−-conducting electrolyte. The H.sub.2 formed is admixed to the CO.sub.2 line (12) via the line (3). Alternatively, the H.sub.2 can also be added on the steam side in the line (29) or in the inlet chamber (34); in this case, an optional H.sub.2 withdrawal is also possible via the branch (3a). A control device (29a) is used to control the amount of steam supplied to the electrolysis (1, 24) and thus the H.sub.2 production. In the same way, the supply of CO and CO.sub.2 to the methanation reactors (11) can be controlled in the required ratio. If only a smaller addition of H.sub.2 is required for methanation, the cladding tube (25) can be dispensed with, following FIG. 12, if an H.sup.+-conducting electrolyte is used, the steam and the H.sub.2 formed being fed to the methanation reactor (11) via the evaporator section (9) and the line (29). The O.sub.2 exiting the electrolyzer (1, 24) is then discharged via the gas compartment (37), and the partition (35a) and gas compartment (36a) are omitted. The installation of a CO.sub.2 electrolyzer (39) is analogous to that of an H.sub.2O electrolyzer (1) with O.sup.2−-conducting electrolytes and accordingly a cladding tube analogous to (25) and with the associated gas chambers (43) and or flow distributors (38) and collectors (40). The pipe (41) conducts the formed CO to the methanation reactor (11). The geometrical arrangement of the individual integrated methanation reactors (11) and the electrolysers (1) and (39) is decisively determined by their influence on the heat and substance concentrations as well as the heat and substance transport and, if necessary, optimized with internals for flow control.
[0048] The further integration of the device of an integrated CH.sub.4 generator (44) designed according to the above mentioned design principles into a sustainable energy system is essential for the sustainability and CO.sub.2 freedom of its operation. Again, the reversible comparative process shown in FIG. 1 represents the theoretical basis of the process control. Accordingly, the CH.sub.4 produced is stored in existing gas storage tanks (45) and used in fuel cells (2) to generate electricity and heat. The resulting flue gas contains only CO.sub.2 and H.sub.2O, and residual heat utilization in a flue gas condenser (46) allows CO.sub.2 and H.sub.2O to be separated. After compression in the CO.sub.2 compressor (47), the resulting CO.sub.2 is fed via a CO.sub.2 piping system (12) to the CO.sub.2 storage (48), which in turn feeds the CH.sub.4 generator (44) again. To improve the sustainability of the energy system and the raw material economy, it is expedient to cover the C.sub.nH.sub.m demand, generally demand for hydrocarbon compounds, of industry and commerce (49) from the gas storage facilities (45). However, since CH.sub.4 synthesis requires CO.sub.2 as a feedstock, this supply relationship of regenerative CH.sub.4 supply inevitably results in the unavoidable need to also recycle CO.sub.2 from plastic waste and return it to the CH.sub.4 generator through the pipeline (12). Since the volumetric energy density of CH.sub.4 is about four times higher than that of H.sub.2, CH.sub.4 can be used to hold significantly more energy to cover seasonal longer severe supply shortages of renewable power than would be possible with H.sub.2. Therefore, it is appropriate to conceptually provide for the possibility of H.sub.2 generation from CH.sub.4 (50) to secure H.sub.2 supply even in the event of prolonged generation shortfalls of renewable electricity generation, thus significantly increasing H.sub.2 supply security. Conversely, hydrogen supply (4) to industry from ongoing hydrogen production (51) is also a useful addition. The H.sub.2O system (10), which is also shown, is intended to illustrate the H.sub.2O demand of the processes described, but in practice this is probably only of interest at highly integrated industrial sites.
[0049] The process control of the devices derived here from the example of CH.sub.4 production and the technical solutions shown here for their plant engineering implementation can also be used, as already indicated several times, for the production of C.sub.2H.sub.4 and other hydrocarbons C.sub.nH.sub.m or hydrocarbon compounds. The prerequisite for this is that the thermodynamics of their process control correspond to the characteristic diagrams of reaction work, reaction heat and O.sub.2 removal in the electrolyzers and in the methanation reactor shown in FIGS. 3 and 4, so that these structures can be used. FIG. 18 shows an example of a compilation of comparable reaction equations for CH.sub.4 and C.sub.2H.sub.4 and the associated methods of O.sub.2 removal.
