Method for operating a combustion furnace and arrangement comprising such a furnace

Abstract

The invention relates to a method for operating a combustion furnace (1) which uses a fuel gas stream to heat and form a combustion product stream, wherein at least a portion of the heat of the combustion product stream is used to form a steam stream. A prerequisite is that at least a portion of the steam stream is subjected to high-temperature electrolysis (2) to form a hydrogen-containing substance stream and an oxygen-containing substance stream, and at least a portion of the hydrogen-containing substance stream is used as the fuel gas stream. A corresponding arrangement (100, 200, 300) is also a subject of the invention.

Description

[0001] The invention relates to a method for operating a combustion furnace, in particular a glass melting furnace, and to an arrangement having such a furnace and an electrolysis device. Prior art

[0002] Combustion furnaces are generally used to provide heat energy, for example, to the material to be processed or for chemical reactions. By burning the fuel with an oxidant, heat energy is released inside the furnace. The operating modes of the furnace can be distinguished based on the oxidant used.

[0003] In the following, reference is mainly made to a glass furnace or glass melting furnace in order to explain the background of the invention and the measures proposed therefrom. However, the invention is also applicable to use in combination with other combustion furnaces, in particular when they operate at a temperature level comparable to that of a glass melting furnace and if they use comparable media, which is the case, for example, in steel furnaces or other melting furnaces.

[0004] For a glass furnace or glass melting furnace, air is usually used as an oxidant. Air, or more precisely, the oxygen in the air, is burned with the fuel inside the glass furnace to form flue gas and supply the energy required to melt the glass. The flue gas extracted from the glass melting furnace usually has a temperature of about 1500°C.

[0005] In glass melting furnaces operated with combustion air, hot flue gases are usually used to preheat the combustion air to up to 1250°C. This preheating is carried out in a discontinuously operated regenerator having at least two regenerator beds. While the hot flue gases heat one regenerator bed during one cycle, the other regenerator bed is cooled by heating the combustion air. As soon as the regenerator bed through which the flue gases are passed has been sufficiently heated, the flow through the bed is switched and the combustion air is directed to the bed that has been previously heated. The regenerator bed that was cooled down in the previous step by heating the combustion air is now passed through by the hot flue gases and heated accordingly.

[0006] If a regenerator is used to recover heat from the flue gases of a glass furnace, only a portion of the waste heat can be recaptured. The waste heat released into the environment by the flue gases escaping from the regenerator is wasted. Depending on the oxidant used in the glass furnace, the temperature of the escaping flue gas stream can exceed 800° C., as described, for example, in EP 0 953 543 B1.

[0007] The operation of a glass melting furnace with (substantially) pure oxygen, which is also possible and in some cases advantageous, makes a significant difference in terms of process technology. Due to the reduced oxygen volume flow compared to the use of combustion air, heat recovery by oxygen heating is usually not implemented. In addition to the energy aspect, this is also due to the lower potential volume flow to be heated (due to the lack of gas nitrogen load) and other reasons, such as technical challenges of the materials used when heating the oxygen in the heat exchanger.

[0008] Regardless of the type of oxidant used, heat recovery from flue gases is relatively inefficient in known methods for operating glass furnaces. In oxygen-operated glass furnaces, heat recovery is often even poorer than in air-operated glass furnaces due to poor preheatable oxygen. This results in heat losses in the form of exhaust gases to the environment. The low energy efficiency ultimately leads to increased consumption of fuel and oxidant, as well as higher environmental impact due to increased emissions.

[0009] Waste heat recovery from the flue gases of a glass furnace can also take the form of cooling the hot flue gases and simultaneously evaporating water, i.e. steam generation. The steam generated in this way can then be used for various purposes, such as heating. However, typically, the operator of the glass furnace does not use the generated steam on site, so that the steam is converted into electricity in a generator driven by a steam turbine. This electricity can then be used for own consumption, or paid to the grid.

[0010] In the case of waste heat being used for steam generation and downstream power generation, the problem is that there are not always suitable customers for this electricity. Especially at low feed-in tariffs, this option may not be economically attractive. This is why the trend in the glass melting industry is now increasingly using electrical energy to melt or further process the glass. The reason for this is that if the operators of glass melting furnaces buy electricity from the grid at certain times of excess electricity, they can buy it very cheaply.

[0011] In theory, the melting enthalpy in a glass furnace could be provided 100% by direct electrical heating and thus using regenerative energy, the CO2 footprint could be almost completely eliminated. However, in practice, only about 80% direct electrical heating is considered possible, as the convective contribution of the flue gases is considered essential for the required uniform temperature distribution of the melt.

[0012] For more details on glass melting furnaces, refer to the relevant technical literature, for example: Wolfgang Trier, : Konstruktion und Betriebsverhalten, Springer-Verlag Berlin, Heidelberg, New York, Tokyo 1984.

[0013] The object of the present invention is to provide an improved possibility of using waste heat from the flue gases of a combustion furnace, in particular a glass melting furnace. Summary of the invention

[0014] Against this background, the present invention proposes a method for operating a combustion furnace, in particular a glass melting furnace, and a corresponding arrangement with a combustion furnace and an electrolysis device, which have the features of the present invention. Advantageous embodiments of the present invention are the subject of the corresponding technical solutions of the present invention and the following description.

[0015] As mentioned above, mainly glass melting furnaces or glass furnaces are mentioned here, but the present invention is also applicable to use in combination with other combustion furnaces. Therefore, the reference to glass melting furnaces or glass furnaces should not be understood as limiting.

[0016] If "oxygen", "hydrogen" or other gases are mentioned below, this is also to be understood as including gas mixtures which contain a major proportion, in particular more than 50%, 60%, 70%, 80%, 90%, 95%, 99% or 99.5%, of the gas specified in each case. In particular, the terms mentioned also refer to so-called "technical" gases with corresponding specifications.

[0017] The invention is based on the finding that an improved utilization of waste heat can be achieved from the flue gases of a glass melting furnace by using this waste heat, for example in the high-temperature electrolysis of water.

[0018] In addition to the chemical conversion of fossil feedstocks into synthesis gas, for example by steam reforming, hydrogen can also be produced by electrochemical conversion of water, where the following overall reaction is observed:

[0019] H2O→H2+0.5O2

[0020] Depending on the electrolyte and separator used, three types of water electrolysis with different half-cell reactions can currently be distinguished. If the water electrolysis is operated with regenerative energy, the production of hydrogen in this way is essentially emission-free.

[0021] In low-temperature electrolysis with a proton-conducting membrane (proton exchange membrane electrolysis, PEMEL), the cathode reaction is the conversion of two protons and two electrons into molecular hydrogen. At the anode, two protons, (mathematically) half an oxygen molecule and two electrons are formed from one water molecule. The charge carriers are the protons transported through the membrane used:

[0022] Cathode: 2H + +2e – →H2

[0023] Anode: H2O→2H + +0.5O2+2e –

[0024] Charge carrier: H +

[0025] In low temperature electrolysis (anion exchange electrolysis, AEL) with an anion exchange separator, two water molecules react with two electrons at the cathode to form a hydrogen molecule and two hydroxide ions. The anode reaction involves the reaction of two hydroxide ions to (mathematically) half an oxygen molecule and a water molecule and two electrons. The hydroxide ion represents the charge carrier:

[0026] Cathode: 2H2O+2e – →H2+2OH –

[0027] Anode: 2OH – →0.5O2+H2O+2e –

[0028] Charge carrier: OH –

[0029] High temperature electrolysis using a solid oxide electrolyzer (SOEC) that conducts oxygen ions involves a cathodic reaction of water molecules with two electrons to form hydrogen molecules and oxygen ions. At the anode, the oxygen ions react to (mathematically) half an oxygen molecule and two electrons. The oxygen ions are charge carriers:

[0030] Cathode: H2O+2e – →H2+O2 –

[0031] Anode: O2 – →0.5O2+2e –

[0032] Charge carrier: O2 –

[0033] While PEMEL and AEL are limited to temperatures below the evaporation temperature of water due to the presence of an aqueous environment, the oxygen conductivity of SOEC is only given above 600° C. The advantageous operating temperature range is between 700° C. and 900° C.

[0034] Conventional high-temperature processes have so far generally been based exclusively on the use of fossil fuels, primarily natural gas, in the case of glass furnaces to provide the melting enthalpy. In addition, the glass produced also has a CO2 footprint, which can lead to reduced profitability in view of the higher CO2 certificate prices. The CO2 footprint can be reduced by improving waste heat utilization and thus reducing fuel consumption, but it cannot be avoided.

[0035] In the case where waste heat is used for steam generation and downstream power generation, as mentioned above, the problem is that there are not always suitable customers for this electricity. Especially when the feed-in tariff is low, this option is not always attractive.

[0036] The main advantage of the present invention is that waste heat, especially from a glass melting furnace, can be used in an advantageous manner to convert water into fuel in the form of hydrogen and oxygen. This is achieved by using energy recovered from the flue gases to evaporate water for high temperature electrolysis and then further heating it to the operating temperature of the SOEC. DETAILED DESCRIPTION

[0037] In general, the invention proposes a method for operating a combustion furnace, in particular a glass melting furnace, which is heated using a fuel gas stream and forms a combustion product stream. The furnace is at least partially heated using a corresponding fuel gas, but in the context of the invention, in particular the corresponding furnace can also be partially heated electrically. As already explained above, in theory 100% of the melting enthalpy can be provided by direct electrical heating, but at present, the practical use of electrical heating is generally possible only to an extent of about 80%, since the convective contribution of the flue gases is essential for the required uniform temperature distribution in the glass melt.

[0038] As is known in this respect from the prior art, in the case of heat recovery when forming the steam stream, the heat from at least a portion of the combustion product stream is also used for the present invention. The "forming" of the steam stream comprises the usual steps known from steam generation, namely preheating water (boiler feed water) from the feed temperature (e.g., about 15° C.) to a temperature just below the evaporation temperature at the pressure used. Typical pressures for preheating boiler feed water are in the range of about 1.5 bar to 2.0 bar, and the preheated water can be about 1.8 bar. For example, the preheating is carried out at a temperature level of about 115° C. All pressure specifications here refer to absolute pressures.

[0039] The preheated water can then be evaporated in the steam generation process, thereby initially forming saturated steam. The saturated steam formed is usually present at a temperature level of, for example, about 115° C. and a pressure level of, for example, about 1.6 bar. By further heating, hot steam or superheated steam can be formed from the corresponding saturated steam, for example at a temperature level of about 750° C. The pressure level at which the corresponding superheated steam is provided is about 1.4 bar. In addition to using waste heat, heating can also include other heating methods at any time, such as electric heaters. However, if, for example, during a startup procedure in a corresponding process, sufficient heat or no heat can be obtained from the combustion product stream, for example, then electric heating or alternative combustion can also be used.

[0040] According to the invention, it is a prerequisite that at least part of the steam stream is subjected to high temperature electrolysis in a corresponding electrolysis device to form a hydrogen-containing stream and an oxygen-containing stream, and at least part of the hydrogen-containing stream is used as a fuel gas stream for heating the furnace.

[0041] Thus, in contrast to the prior art, in which the corresponding steam is usually used to generate electrical energy or for heating purposes, the following invention provides for the electrolysis of steam, in particular using the above-mentioned SOEC. Thus, within the scope of the present invention, waste heat from a glass melting furnace can be used directly to generate hydrogen, which in turn can be used as fuel for burning the furnace.

[0042] By means of the measures proposed according to the invention, the thermal energy contained in the corresponding combustion product stream can be recovered to a greater extent than in the prior art. In particular, in the case of complete combustion of hydrogen, the combustion product stream consisting essentially of steam can be cooled at a slightly above atmospheric pressure level of, for example, about 1.05 bar to a temperature level of, for example, about 105° C. This temperature level is lower than the temperature levels conventionally achieved during the cooling of flue gases from a glass furnace.

[0043] In high-temperature electrolysis, in which an oxygen-containing stream is formed in addition to the hydrogen-containing stream within the scope of the invention, at least a portion of this oxygen-containing stream can be used together with the fuel gas stream (i.e. the oxidant) to heat the corresponding gas furnace. If insufficient oxygen is available here, for example because a more than stoichiometric oxygen supply is required for the safe and complete combustion of the hydrogen, it is also possible to work with excess oxygen. This means that externally supplied oxygen can be added to the process. This can come from known sources, such as air separation or a separate electrolysis.

[0044] Within the scope of the present invention, the "hydrogen-containing stream" formed in the high-temperature electrolysis process generally contains hydrogen and water only in the form of non-electrolysis steam. The same applies to the "oxygen-containing stream" formed in the high-temperature electrolysis process. In the electrolysis process using SOEC, steam is provided both on the cathode side and on the anode side. In this way, if no other fuel gas is used, a corresponding combustion product stream can also be provided that is free of carbon dioxide. In particular, the present invention does not burn fossil fuels to heat the glass furnace.

[0045] In the context of the present invention and in all configurations described herein, steam can therefore be supplied to the high-temperature electrolysis on the cathode side and the anode side, wherein in the context of the present invention, the ratio between the amounts of steam supplied on the anode side and the cathode side can be in particular between 0.1 and 1, in particular also between 0.3 and 0.9, preferably between 0.5 and 0.8. Instead of or in addition to supplying steam to the anode side, air can also be supplied to the anode side. Therefore, in all forms of the invention, the anode side can also be flushed completely or partially with air.

[0046] In all embodiments described herein, the hydrogen-containing stream formed in the high-temperature electrolysis (which is arranged on the cathode side) in the context of the present invention can be fed back to the high-temperature electrolysis on the cathode side at least in part (in particular in an adjustable part). By such adjustments, the hydrogen content can be set specifically to a desired value. It is advantageous to adjust the hydrogen content from 0.1 mol% to 10 mol%, and in particular from 1 mol% to 8 mol%, preferably from 3 mol% to 5 mol%. This will also be explained below with respect to specific embodiments.

[0047] In the context of the present invention and in all embodiments, the high temperature electrolysis is advantageously operated by setting the process conditions used in such a way that the water conversion on the cathode side of the high temperature electrolysis is 60% to 100%, in particular 70% to 95%, preferably 80% to 90%. The percentages are dimensionless and refer to the initial water content.

[0048] As explained above, the formation of the corresponding steam stream includes preheating the water used to form the steam stream, evaporating the preheated water into saturated steam, and superheating or further heating the saturated steam to obtain superheated steam. In return, the cooling of the combustion product stream includes several cooling steps, wherein the combustion product stream is continuously cooled to its condensation temperature. These steps are explained in more detail below from the direction of cooling the combustion product stream from high temperature to low temperature and with reference to different embodiments of the present invention. They are called "heat exchange steps".

[0049] The heat exchange step carried out in the context of the present invention comprises, in a first configuration of the present invention, a first heat exchange step in which the combustion product stream or a portion thereof is cooled from a temperature level of 1400° C. to a temperature level of 900° C. to 1100° C. This cooling is carried out, for example, at a temperature level of about 1500° C. to a temperature level of about 980° C. and at a pressure level slightly above atmospheric pressure, wherein a slight pressure reduction is produced during the cooling. For example, the corresponding pressure level is about 1.05 bar before the first heat exchange step and about 1.0 bar after the first heat exchange step.

[0050] In this first embodiment of the invention, during this first heat exchange step, the saturated steam used to form the steam stream fed to the high-temperature electrolysis can be superheated from a temperature level of, for example, about 100° C. to 120° C. to a temperature level of, for example, about 700° C. to 900° C. For example, the superheating occurs from a temperature level of about 115° C. to a temperature level of about 750° C. In this first embodiment, but also in all other embodiments of the invention, the corresponding superheated steam can optionally be further heated and fed to the high-temperature electrolysis in the form of corresponding partial flows on the cathode side and the anode side (as a purge gas stream). The pressure of the saturated steam before the superheating can, for example, be about 1.4 bar to 1.8 bar, in particular about 1.6 bar. For example, after the corresponding superheating, the pressure of the saturated steam is about 1.2 bar to 1.6 bar, in particular about 1.4 bar. The pressure loss is caused by the lower pressure in the high-temperature electrolysis and the heat exchanger structure.

[0051] In a first form of the invention, in a subsequent second heat exchange step, the combustion product stream or part thereof is further cooled from a temperature level of, for example, about 900° C. to 1100° C., in particular about 980° C., to a temperature level of, for example, about 100° C. to 200° C., in particular about 150° C. Such cooling may be carried out, for example, at atmospheric pressure or slightly above atmospheric pressure of about 1.0 bar to 1.1 bar, for example about 1.0 bar, to a pressure level slightly below atmospheric pressure of about 0.9 bar to 1.0 bar, for example about 0.95 bar. In particular, such a pressure level slightly below atmospheric pressure is caused by the use of a downstream compressor or blower conveying the combustion product stream.

[0052] In this second heat exchange step, in the first configuration of the invention, in return for cooling the combustion product stream, the preheated water is evaporated into saturated steam, for example starting from a temperature level of about 110° C. to 120° C., in particular about 115° C., and about 1.6 bar to 2.0 bar, in particular about 1.8 bar. Compared to the preheated water, the saturated steam is present at a slightly lower pressure level of, for example, about 1.4 bar to 1.8 bar, in particular about 1.6 bar, and at a temperature level comparable thereto. As explained below, only a portion of the preheated water may be evaporated in the second heat exchange step, in particular when, depending on the process conditions, the flue gas enthalpy is insufficient to completely evaporate the feed water. In this case, a portion of the preheated water may be evaporated separately, for example electrically, and then added back to the saturated steam formed in the second heat exchange step.

[0053] Preheating of the water for generating saturated steam is carried out in the first embodiment of the invention, but also in all other forms, in a preceding third heat exchange step, which is explained below, and in which the combustion product stream is further cooled and in particular (partially) condensed.

[0054] In a second embodiment of the invention as an alternative to the first embodiment, the combustion product stream is first used for evaporation and only then can the steam be superheated. However, the corresponding heat exchange steps are given below again from the direction of the combustion product stream from higher temperature to lower temperature.

[0055] The heat exchange step used in the second embodiment of the invention comprises a first heat exchange step in which the combustion product stream is cooled from its initial temperature level, as previously explained, and at the pressure previously explained for the first heat exchange step, to a temperature level of, for example, about 600° C. to 700° C., specifically about 620° C. The first heat exchange step is a heat exchange step in which the combustion product stream is cooled from its initial temperature level, as previously explained, and at the pressure previously explained for the first heat exchange step, to a temperature level of, for example, about 600° C. to 700° C., specifically about 620° C. The second heat exchange step is a heat exchange step in which the combustion product stream is cooled from its initial temperature level, as explained. As previously mentioned, the pressure level will be slightly reduced. However, in the second embodiment of the invention, this first heat exchange step occurs not in connection with the superheating of steam, but in connection with the evaporation of preheated water, which evaporates in this first heat exchange step of the above-described embodiment of the invention to form saturated steam. The water and steam parameters may correspond to those of the above-described first embodiment of the invention.

[0056] In this second embodiment of the invention, the heat exchanging step further comprises a second heat exchanging step, wherein the combustion product stream or a portion thereof is cooled from a temperature level of, for example, about 600° C. to 700° C. to a temperature level of, for example, about 100° C. to 200° C. The heat exchanging step is then used to cool the combustion product stream or a portion thereof. For example, the cooling may be carried out from the mentioned temperature level of about 620° C. to a temperature level of about 150° C., wherein the pressure level may also be reduced from atmospheric pressure to slightly below atmospheric pressure at this point.

[0057] Compared to this second heat exchange step, in the second embodiment of the present invention, the saturated steam generated in the first heat exchange step is superheated from a temperature level of, for example, about 100° C. to 120° C., for example, to a temperature level of about 600° C. to 700° C., specifically about 590° C., while obtaining superheated steam. Therefore, the above embodiment of the present invention is different from the above embodiment of the present invention in the order of the first heat exchange step and the second heat exchange step.

[0058] The second embodiment of the invention can be advantageous because, due to the different sequence of the heat exchange steps, the heat of the combustion product stream can still be sufficient to evaporate the preheated water. Therefore, in this configuration, (electric) evaporators can be saved, which can have a positive impact on plant costs. However, the no longer required power input previously applied by the electric evaporator is not no longer required in this embodiment, but due to the lower temperature of the superheated steam, it must now be provided by one or more corresponding heaters for the superheated steam. Although such heaters are optional or only required during startup in the first embodiment of the invention, they are usually also required in the control operation of the second embodiment.

[0059] In a third embodiment of the invention, again differently, the heat integration in the second heat exchange step no longer takes place to generate superheated steam, but rather (at least primarily) heats a hydrogen-containing stream and / or an oxygen-containing stream which is formed in high-temperature electrolysis.

[0060] In this third configuration, the second heat exchange step comprises cooling the combustion product stream or part thereof from a temperature level of, for example, about 600° C. to 700° C., in particular about 620° C., to a temperature level of (only) for example about 300° C. to 400° C., in particular about 380° C., and in the second heat exchange step, heating the hydrogen-containing stream and / or the oxygen-containing stream formed in the high-temperature electrolysis. The cooling of the combustion product stream or part thereof can be carried out, for example, at a slight pressure reduction from atmospheric pressure to about 0.95 bar. In a further substep of the second cooling step, the correspondingly cooled combustion product stream can be countercurrently cooled again under steam superheating, wherein, however, in this further substep, generally only a slight further cooling of the combustion product stream of, for example, about 30° C. or about 20° C. to 50° C. occurs.

[0061] The advantage of this embodiment is that, due to the possibility of additional pressure increase of the electrolysis product stream with the help of a compressor or a blower, an optimal inlet pressure of the burner can be ensured. This pressure increase is possible because the product streams (i.e. the hydrogen-containing stream and the oxygen-containing stream) can be fed to the pressure increase in the third embodiment of the invention at a lower temperature level. As in other embodiments of the invention, they are obtained from high-temperature electrolysis at a temperature level of 700° C. to 900° C., in particular about 800° C. and a pressure level of, for example, about 1.0 bar to 1.2 bar, in particular about 1.1 bar, and in the third embodiment, they can each be cooled for a saturated steam stream or only slightly superheated steam stream that is then fed to the high-temperature electrolysis on the anode side and cathode side as a superheated steam stream. This cooling enables a problem-free compression.

[0062] For example, at a temperature level of about 140° C. to 160° C., a saturated or alternatively only slightly superheated steam stream is present, since in the third embodiment, no steam superheating (or at least not to the above extent) is performed using the combustion product stream. The superheated steam stream in heat exchange with the hydrogen-containing stream and the oxygen-containing stream may be maintained at a temperature level of, for example, about 600° C. to 800° C., in particular about 750° C. and a pressure level of, for example, about 1.1 bar to 1.5 bar, in particular about 1.2 bar.

[0063] The compressor or corresponding blower used in the third embodiment of the hydrogen-rich stream obtained on the cathode side can simultaneously compress a recycle stream formed by the hydrogen-rich stream, which is advantageously fed back to the cathode side to provide reducing conditions in order to avoid nickel oxidation. It is also advantageous to carry out a corresponding recycle in other embodiments of the invention, but in a different way, for example by simply cooling the stream to be recycled. As mentioned above, compression may not be possible at the high temperatures at the outlet of the high-temperature electrolysis unit.

[0064] In all configurations of the invention described above, the second heat exchange step may be followed by a third heat exchange step, in which the combustion product stream or part thereof is cooled from a temperature level of 100° C. to 200° C. to a lower temperature level and partially condensed. In this third cooling step, for example, cooling may be carried out at a pressure level of, for example, about 1.05 bar to a temperature level of about 105° C. The corresponding condensate may be discharged to the atmosphere and / or separated to provide further boiler feed water.

[0065] In all embodiments of the invention, the flue gas or at least the part thereof subjected to the second cooling step and the third cooling step can be compressed between the second cooling step and the third cooling step, for example to a pressure level of 1.25 bar. During this compression, due to the increase in internal energy, a further temperature increase is carried out, for example to a temperature level of about 180° C. However, a corresponding compression can also be carried out downstream of the third heat exchange step, in particular in the third embodiment of the invention described above. Upstream compression has the advantage that the compression heat can also be used for steam generation.

[0066] In the context of the present invention, some of the energy required for generating steam, in particular some of the energy for evaporation in the first embodiment of the invention, may be provided from a heat source separate from the combustion product stream, as explained above. Details have already been mentioned.

[0067] In the context of the present invention, the hydrogen-containing stream and the oxygen-containing stream formed in the high-temperature electrolysis can be cooled specifically for steam, which is fed to the high-temperature electrolysis. This has been explained before with reference to the third embodiment of the present invention. In particular, this can involve two partial streams of the above-mentioned corresponding steam streams, which are fed to the high-temperature electrolysis on the cathode side or the anode side. The hydrogen-containing stream and the oxygen-containing stream can be compressed after the corresponding heat exchange and then fed to the furnace.

[0068] As already explained several times, in the context of the present invention, the furnace can also be partially electrically heated, wherein the partial energy provided in the context of the present invention by oxidation of hydrogen from high-temperature electrolysis can amount to about 15% to 25%, in particular about 20%, of the energy required for the melting process. The remainder can be provided by direct heating. Depending on the process conditions, high-temperature electrolysis, electric heaters and blowers require between 1.5 and 2.1 MW of electrical energy to provide one MW of thermal energy absorbed by the glass melt.

[0069] In all embodiments of the invention explained above and below, the high temperature electrolysis can be operated at a pressure that does not require compression of the product stream for further use. Thus, the pressure used in the high temperature electrolysis will be suitable for the corresponding application and at least at the required inlet pressure.

[0070] The invention also encompasses an arrangement with a combustion furnace, in particular a glass melting furnace, which in particular can be arranged to carry out the process as previously explained in various embodiments. With regard to further features and advantages of the arrangement proposed according to the invention, explicit reference is made to the explanations above regarding the procedure proposed according to the invention and its preferred embodiments.

[0071] In summary, in its respective embodiments, the present invention enables continuous operation of a combustion furnace, in particular a glass melting furnace, without the use of fossil fuels. When using regeneratively generated electrical energy, the process has no carbon dioxide footprint. The heat of the combustion product stream can be optimally utilized without simultaneously producing outlet steam. The present invention also reduces the formation of thermal nitrogen oxides by providing nitrogen-free fuel and oxidant. The high steam content in the fuel gas also offsets the formation of thermal nitrogen oxides by the external air flow. The present invention allows simplified fuel gas preheating in some of the above-mentioned embodiments, since only the steam must be superheated instead of oxygen and hydrogen, which is technically advantageous.

[0072] The invention is explained below with reference to the accompanying drawings, which illustrate arrangements of embodiments according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 An arrangement according to an embodiment of the invention is shown.

[0074] Figure 2An arrangement according to an embodiment of the invention is shown.

[0075] Figure 3 An arrangement according to an embodiment of the invention is shown.

[0076] Detailed description with drawings

[0077] Figure 1 An arrangement designated 100 according to an embodiment of the present invention is shown. Figure 2 and 3 Another embodiment is shown in , in which they are designated 200 and 300 respectively. Figure 1 The arrangement 100 corresponds at least partially to the first embodiment of the present invention described above, Figure 2 The arrangement 200 in corresponds at least partially to the second embodiment described above, and Figure 3 The arrangement 300 in corresponds at least partially to the third embodiment of the invention described above.

[0078] All arrangements 100 to 300 typically have a glass melting furnace 1 and an electrolysis device 2 having a cathode side 21 and an anode side 22, all arrangements 100 to 300 also provide water (boiler feed water) (W) and finally use it to form two steam streams 111 and 112, which are respectively supplied to the cathode side 21 and the anode side 22 of the electrolysis device 2. The formation of these steam streams 111 and 112 is explained separately for each of the following embodiments.

[0079] Using the electrolysis device, a hydrogen-containing gas stream 121 and an oxygen-containing gas stream 122 are also formed in all embodiments. In addition to hydrogen and oxygen, the gas streams 121 and 122 also contain water in the form of superheated steam. They are fed into the glass melting furnace 1 and burned therein. An external oxygen feed 3 can be provided to cover any additional oxygen demand that may be required. In all forms of the invention, a combustion product stream 131 is extracted from the glass melting furnace 1. The embodiments of the invention shown using arrangements 100 to 300 differ in particular in the order or specific embodiment of heat recovery from the combustion product stream 131, which is explained in detail below.

[0080] In such Figure 1 In the arrangement 100 shown, the combustion product stream 131 is first fed into the heat exchanger X1, where the saturated steam 103 is superheated and superheated steam 104 is formed. The superheated steam is divided into steam streams 111 and 112. After cooling in the heat exchanger X1, the combustion product stream F is fed into the heat exchanger X2, where preheated water is evaporated into saturated steam. The preheated water is supplied in the form of water stream 102 and passes through the heat exchanger X2 in the form of partial stream 102a. Another partial stream 102b is evaporated in the electric heater E1. After evaporation into the saturated steam stream 103, the evaporated partial streams 102a and 102b are combined.

[0081] After cooling in the heat exchanger X2, the combustion product stream 131 is subjected to compression in a compressor or blower C1 and then passes through another heat exchanger X3, which serves to preheat the water stream 101. The water contained in the combustion product stream 131 is at least partially condensed in the heat exchanger X3.

[0082] Figure 1 Additional elements shown in are additional electric heaters E2 and E3 which use steam streams 111 and 112 respectively in the absence or presence of too little waste heat from the combustion product stream 131 .

[0083] exist Figure 2 In the arrangement 200 shown, the combustion product stream 131 first flows through the heat exchanger X1 and is thereby cooled. In the heat exchanger X1, the preheated water (boiler feed water) 102 is evaporated into saturated steam 103. As described above, in this arrangement, the formation of the partial streams 102a and 102b and the use of the electric heater E1 can be dispensed with. After cooling in the heat exchanger X1, the combustion product stream 131 passes through the heat exchanger X2, in which superheated steam 104 is generated. The further arrangement here corresponds essentially to Figure 1 The arrangement shown in , but the electric heaters E2 and E3 are here permanently operated due to the lower degree of superheat in the heat exchanger X2.

[0084] Figure 3 An arrangement according to a further development of the invention is shown and is generally referenced 300. This in turn differs in the use of heat exchangers and in the type of waste heat recovery.

[0085] The combustion product stream 131 passes through heat exchangers X2a and X2b downstream of heat exchanger X1, the use of which corresponds substantially to Figure 2 and the use of arrangement 200, and therefore for heating a hydrogen-containing stream 121 and an oxygen-containing stream 122. These streams 121 and 122 are compressed in compressors C2 and C3, which is possible due to the previous cooling of the gas streams 121 and 122, as described above. This cooling is then carried out in heat exchangers X3a and X3b in countercurrent with steam streams 111 and 112, which are initially provided here in an unheated or only slightly superheated state and, after being superheated in heat exchangers X3a and X3b, are fed to the electrolysis unit 2. Further cooling of the combustion product stream 131 is carried out in heat exchanger X4 by superheating the steam stream 103. As also shown herein, a (particularly adjustable) partial stream 121a of the stream 121 is returned to the high-temperature electrolysis 1, as explained above.

Claims

1. A method for operating a combustion furnace, wherein the combustion furnace uses a fuel gas stream to heat and form a combustion product stream, wherein the heat of at least a portion of the combustion product stream is used to form a steam stream, wherein at least a portion of the steam stream is subjected to high temperature electrolysis to form a hydrogen-containing stream and an oxygen-containing stream, and at least a portion of the hydrogen-containing stream is used as a fuel gas stream, characterized in that The formation of the steam stream comprises a plurality of heat exchange steps to which the combustion product stream or a portion thereof is subjected, wherein water used to form the steam stream and / or steam used to form the steam stream is heated in the heat exchange steps, and wherein the heat exchanging step comprises a first heat exchanging step, wherein the combustion product stream or a portion thereof is cooled from a temperature level of 1400°C to 1600°C to a temperature level of 900°C to 1100°C, and wherein saturated steam used to form the steam stream is superheated from a temperature level of 100°C to 120°C to a temperature level of 700°C to 900°C, and wherein the heat exchanging step comprises a second heat exchanging step, wherein the combustion product stream or a portion thereof is cooled from a temperature level of 900°C to 1100°C to a temperature level of 100°C to 200°C, and wherein water used to form the steam stream is evaporated to form saturated steam; or, wherein the heat exchanging step comprises a first heat exchanging step, wherein the combustion product stream or a portion thereof is cooled from a temperature level of 1400°C to 1600°C to a temperature level of 600°C to 700°C, and wherein water used to form the steam stream is evaporated to form saturated steam, and wherein the heat exchanging step comprises a second heat exchanging step, wherein the combustion product stream or a portion thereof is cooled from a temperature level of 600°C to 700°C to a temperature level of 100°C to 200°C, and wherein the saturated steam used to form the steam stream is superheated from a temperature level of 100°C to 120°C to a temperature level of 700°C to 900°C.

2. The method according to claim 1, wherein in addition, at least a portion of the oxygen-containing stream is also used together with the fuel gas stream to heat the combustion furnace.

3. A method according to claim 1 or 2, wherein the formation of the steam flow includes a plurality of heat exchange steps, the combustion product flow or a portion thereof is subjected to the plurality of heat exchange steps, wherein water used to form the steam flow and / or steam used to form the steam flow is heated in the heat exchange steps.

4. A method according to claim 1 or 2, wherein the formation of the steam flow includes a combined heat exchange step, the combustion product flow or a portion thereof is subjected to the combined heat exchange step, wherein water used to form the steam flow and / or steam used to form the steam flow is heated in the combined heat exchange step.

5. The method according to claim 1, wherein the heat exchange step includes a second heat exchange step, wherein the combustion product stream or a portion thereof is cooled from a temperature level of 600°C to 700°C to a temperature level of 300°C to 400°C, and wherein the hydrogen-containing material stream and / or oxygen-containing material stream formed in the high temperature electrolysis is heated.

6. The method according to claim 1, wherein the heat exchanging step comprises a third heat exchanging step, wherein the combustion product stream or a portion thereof is cooled from a temperature level of 100° C. to 200° C. and thereby partially condensed, and wherein water used to form the steam stream is preheated.

7. The method according to claim 6, wherein the combustion product stream or at least the portion thereof subjected to the second and third heat exchange steps is compressed between the second and third heat exchange steps or after the third heat exchange step.

8. The method of claim 1, wherein a heater operated by a separate heat source is also used to evaporate water.

9. The method according to one of claims 1-2 and 5-8, wherein the hydrogen-containing stream and the oxygen-containing stream formed in the high-temperature electrolysis are cooled against steam supplied to the high-temperature electrolysis.

10. The method according to one of claims 1-2 and 5-8, wherein the combustion furnace is partially heated electrically.

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