Method for treating raw water for use as reactant water in an electrolysis process, and water treatment system for carrying out the method

Abstract

The invention relates to a method for treating raw water (1) for use as reactant water in an electrolysis process, in which method salt-laden raw water (1) is provided and thermal desalination of the raw water (1) is carried out, wherein heat (QIN) is supplied to the raw water (1) and the raw water is evaporated, wherein salt-free water (H2O) is drawn off, which is provided as reactant water (9) and supplied to an electrolysis process in which hydrogen (H2) is generated as product gas, wherein the generated hydrogen (H2) is loaded by subjecting the hydrogen (H2) to an exothermic loading process from which heat (QOUT) is released, wherein released heat (QOUT) is transferred and supplied to the raw water (1) as heating heat (QIN) and used for evaporation. The invention further relates to a water treatment system (11) for carrying out the method.

Description

[0001] 2024PF00693

[0002] Description

[0003] Method for treating raw water for use as feed water in an electrolysis process and water treatment system for carrying out the process

[0004] The invention relates to a method for treating raw water for use as feed water in an electrolysis process, in which salt-laden raw water is provided and thermal desalination of the raw water is carried out. The invention further relates to a water treatment system designed for carrying out the method.

[0005] Hydrogen is currently produced, for example, using proton exchange membrane (PEM) electrolysis or alkaline electrolysis. Electrolyzers use electrical energy to produce hydrogen and oxygen from the supplied water. Hydrogen represents an environmentally friendly and sustainable energy carrier. It has the unique potential to make energy systems, transportation, and large parts of the chemical industry climate-friendly and without carbon dioxide emissions.

[0006] This goal can be achieved if the hydrogen is produced using renewable energies via PEM electrolysis.

[0007] An electrolyzer typically has a large number of electrolysis cells arranged adjacent to each other. Water is split into hydrogen and oxygen in these electrolysis cells via water electrolysis. In a PEM electrolyzer, for example, deionized water is typically supplied as a reactant on the anode side and split into hydrogen and oxygen at a membrane electrode assembly (MEA), consisting of a proton-exchange membrane (PEM), an anode, and a cathode. The water is oxidized to oxygen at the anode. The protons pass through the proton-exchange membrane. Hydrogen is produced on the cathode side.

[0008] 2

[0009] decorated. The water is usually pumped from one underside into the anode compartment and / or cathode compartment.

[0010] Besides PEM electrolysis, other forms of electrolysis are known, such as alkaline electrolysis, in which other ions are transported through a membrane or diaphragm. For the sake of simplicity, the present invention will therefore refer to protons as an example, for instance, using the term "proton-permeable." Current research explores other types of electrolyzers in which other ions, e.g., hydroxide ions, selectively pass through the membrane, thus enabling charge transport for the electrolysis reaction. The general problem underlying the invention can also be applied to these types of electrolyzers. Therefore, the protons mentioned here are to be understood as representative. The term "proton-permeable" is thus to be understood in a significantly broader sense, namely as "permeable to a specific type of ion," particularly through a membrane.

[0011] The electrolysis process takes place in the so-called electrolysis stack, which consists of several electrolysis cells. Highly purified, fully demineralized water is introduced as the reactant into the electrolysis stack, which is under DC voltage. After passing through the electrolysis cells, two fluid streams emerge, consisting of water and gas bubbles (oxygen O2 and hydrogen H2, respectively). The respective separation of the water and gas phases in the fluid streams occurs in gas separators.

[0012] Due to the harsh electrochemical conditions that can always occur during electrolysis, small amounts of H₂O₂ or OH radicals can form within the electrolyzer, for example, in the cells. It is generally known that such species can chemically attack the ionomer or the membrane material of PEM electrolyzers, with the latter potentially causing [2024PF00693]

[0013] 3

[0014] Such degradation releases fluorides as degradation products. This is because the membrane contains fluorine and is made, for example, of PFSA (perfluorosulfuric acid). The membrane is a particularly important element for the functionality of electrolysis cells in PEM electrolysis, so its lifespan and its limitations due to degradation effects are of great importance, especially from an economic perspective. Other degradation products include, for example...

[0015] Metal anions dissolve in aqueous solution through oxidative and corrosive attack on the corresponding water-bearing materials and are thus directly introduced into the process water. Consequently, during the operation of an electrolysis plant, anions and cations increasingly enter the process water as dissolved salts, contaminating it.

[0016] However, the purity of the process water is essential for a long service life of the electrolyzer. As described above, the process water can contain ions that are released as a degradation product from the electrolyzer stack / cell or other parts of the overall system, such as piping or tanks. Therefore, in the ongoing development of PEM electrolyzers aimed at long service life, it is crucial that the process water maintains the highest purity at all times, as the presence of contaminating ions can accelerate the degradation of the stack / cell and the entire system. These effects can cause lasting damage and limit the service life of an electrolyzer, potentially leading to premature failure and even the loss of the electrolyzer.Therefore, it is essential for operations that the ions are removed from the process water as much as possible to ensure a very low ion concentration as the upper limit during operation. For this purpose, the process water must be treated accordingly, i.e., deionized, so that fully demineralized water ("DI water") or deionized water is obtained. High-purity, fully demineralized water is also used in this process (2024PF00693).

[0017] 4

[0018] The process water is continuously replenished to compensate for the water consumption caused by the electrolysis process.

[0019] To remove ions present in the water during operation, water treatment and purification systems are typically used. These systems employ ion exchangers as ion-selective elements, integrated into the process water circuit or the fresh water inlet of the electrolysis plant. Complex purification cycles or stages remove the remaining ions from the process water. However, the exchange capacity of ion exchangers is limited and, until now, can only be determined with considerable effort. Furthermore, malfunctions of the ion exchangers have been observed. A malfunction of the ion exchanger in the water treatment system can lead to significant degradation and reduced performance of the electrolyzer, especially if it is not detected or not detected in time.

[0020] Depending on the plant's location, the primary water supply for an electrolysis plant may necessitate the use of saline water (saltwater) due to freshwater or drinking water scarcity. This is particularly important when procuring and ensuring a continuous supply of raw water as the feedstock. While the salt load of major rivers flowing from continents varies considerably, the overall salt concentration in the world's oceans is remarkably consistent, averaging 35 parts per thousand (‰), or 35 grams of salt per liter of seawater. Consequently, the significantly higher salt content compared to freshwater requires substantial technical and economic resources for the treatment of raw water with high salt concentrations, simply to reduce the salt load considerably.Therefore, concepts for the desalination of raw water, especially seawater, and the provision of ultrapure water as a feedstock for PEM electrolysis are necessary, which are also economically viable. According to the literature, an electrical [2024PF00693] is used for the ultrapure water.

[0021] 5

[0022] Conductivity in the range of < 1.0 pS cm 1 required at the entrance of the PEM electrolysis process, i.e., in the feed to an electrolyzer.

[0023] The invention is therefore based on the objective of providing a method for treating salt-laden raw water, which is specifically designed for use in water electrolysis and is characterized by high energy efficiency. A further objective of the invention is to provide a water treatment system with an electrolyzer, with which the method can be carried out and thus fully demineralized water can be supplied to the electrolyzer as reactant water.

[0024] The problem, which is directed towards a method for treating salt-laden raw water, is solved according to the invention by a method for treating salt-laden raw water for use as feed water in an electrolysis process, in which salt-laden raw water is provided and thermal desalination of the raw water is carried out, wherein heat is supplied to the raw water and it is evaporated, wherein salt-free water is drawn off, which is provided as feed water and supplied to an electrolysis process in which hydrogen is produced as product gas, wherein the produced hydrogen is loaded by subjecting the hydrogen to an exothermic loading process from which heat is released, wherein the released heat is transferred and supplied to the raw water as heating energy and used to evaporate the raw water.

[0025] The invention is based on the understanding that existing concepts for the desalination of raw water and the provision of ultrapure water as feed water for PEM electrolysis are in need of improvement from an efficiency perspective. A particular difficulty and technical-economic burden lies in the continuous procurement, treatment, and provision of fully desalinated feed water for an electrolyzer. Therefore, there are hardly any systems and processes described that employ a systemic approach.

[0026] 6

[0027] The focus is on a comprehensive approach that considers the provision of salt-free water as well as the production, transport, and loading of hydrogen generated in a water electrolysis process, and integrates these aspects into a single solution. According to the literature, a conductivity of <1.0 pS cm⁻¹ is required for the ultrapure water at the inlet of the PEM electrolysis system, which places very high demands on the desalination process and significantly impacts the energy and costs associated with it.

[0028] Furthermore, the invention advantageously considers and takes into account economic aspects in the technical implementation of the process. The economic viability of electrolyzers for the production of renewable hydrogen is largely determined by the price of the required renewable electricity. Electrolyzers are often located in regions where solar and wind power plants can be operated with high efficiency. These are typically sunny countries where, however, drinking water is scarce, so seawater must be used as the feedstock for the electrolysis process. The desalination of seawater or saline inland water to a low conductivity range, ideally less than 1.0 pScur, is therefore necessary. 1This requires the use of significant amounts of energy. The issue also applies in principle to the treatment of raw water with a slightly lower salt concentration than seawater, whereby it can be assumed that the treatment effort increases with increasing salt concentration.

[0029] Another aspect that plays an important role in connection with this invention concerns the transport of the produced renewable hydrogen from the production site to the point of use. Renewable hydrogen is primarily used in industrial centers and densely populated regions. These locations are often far from the production sites, so the produced renewable hydrogen

[0030] 7

[0031] The hydrogen must be transported after production. Various technologies are available for transporting hydrogen. Significant amounts of heat are generated at the hydrogen production site, which is often also the loading point for transport. This heat is not normally used at the loading point and was therefore discarded.

[0032] The invention proposes, for the first time, that the heat released during typical loading processes be utilized by integrating the loading process with the treatment of the salt-laden raw water. This integrated solution has a significant positive impact on the overall process's economic efficiency and, due to its systemic approach, is clearly superior to conventional raw water desalination methods.

[0033] The invention advantageously utilizes the heat released (waste heat) from exothermic processes used to load electrolytically produced hydrogen for transport from the production site to the point of use. The released heat is used and transferred for thermal raw water treatment, specifically supplied to the raw water as heating energy, thereby evaporating the raw water. In this way, the endothermic desalination process for the raw water is thermally coupled to the exothermic loading process for the hydrogen produced from electrolysis as a product gas. This thermal coupling of the desalination and loading processes can be implemented directly or indirectly.The processes can be coupled permanently, for a limited time, or intermittently, depending on requirements, with a corresponding heat transfer of released heat and input as heating energy for the desalination process. This process is superior to previously known methods. 2024PF00693.

[0034] The techniques described in the prior art for desalinating raw water and providing ultrapure water as feed water for PEM electrolysis are typically based on evaporation of the raw water or on reverse osmosis processes. Combinations of both processes are also used. Evaporation yields largely desalinated water distillate as the main product and a highly concentrated brine or salt solution (brine) or suspension as a byproduct. In some cases, the byproduct is even evaporated to dryness because liquid byproduct streams are not permitted. The processes listed require the use of very large amounts of heat; the enthalpy of vaporization of water is approximately 2250 kJ / kg. Evaporation at atmospheric pressure is the simplest variant in terms of equipment.This method has the disadvantage that the water must be evaporated at 100 °C, and no waste heat at this comparatively high temperature level is available in the vicinity of electrolysis plants. The evaporation temperature even increases further, which is detrimental, if a high degree of evaporation of the byproduct is required. The necessary heat of vaporization must currently be generated and supplied using electricity or other means. In any case, heat generation is associated with significant operating costs. If the available waste heat from electrolysis is to be used, it must be considered that, according to the literature, this waste heat is available at temperatures below 80 °C. Consequently, either a heat pump would have to be used or the evaporation would have to be carried out at a significantly reduced pressure, for example, by using an additional vacuum pump.In both cases, additional investment costs for the required equipment and the costs for the required electricity must be taken into account.

[0035] Reverse osmosis processes are also known. Compared to water evaporation, these are characterized by less equipment and consequently lower investment costs; however, unlike 2024PF00693

[0036] 9

[0037] The evaporation process cannot utilize waste heat from the electrolysis plant because reverse osmosis is not a thermal process. It relies on a significant increase in the pressure of the raw water and requires the use of electricity for the pressure booster pump. The electricity needed for pump operation is lost to hydrogen production from the electrolysis process, thus considerably reducing the overall efficiency of the process.

[0038] The invention, however, proposes for the first time an integrated approach for the treatment of salt-laden raw water for electrolysis, offering a significantly improved energy balance. The process of the invention makes particularly advantageous use of the waste heat released during exothermic subprocesses for hydrogen loading. This waste heat is used as usable or heating energy for the thermal treatment of the raw water, which provides ultrapure water for water electrolysis. By utilizing the released heat, it is unnecessary to use electricity or other energy carriers to supply the raw water treatment process with heating energy. Consequently, considerable operating costs are saved, especially compared to reverse osmosis, which requires electricity, and to conventional evaporation processes, which require the generation of heat from electricity or fuels.The temperature level at which the released waste heat is available is higher than the temperature level of the raw water treatment, thus enabling particularly efficient heat transfer without the use of additional heat pumps. This contrasts with conventional methods, which, for example, utilize waste heat from electrolysis, typically only available at a low temperature level of less than 80 °C.

[0039] The process described in the invention allows for the advantageous thermal treatment and desalination of raw water at atmospheric pressure within a temperature range of approximately 100 °C. In particular, no Absen-2024PF00693

[0040] 10

[0041] Control of the water's evaporation temperature is necessary. This is very advantageous compared to conventional methods, as it eliminates the need for an additional vacuum pump.

[0042] In a particularly preferred embodiment of the process, the exothermic hydrogen loading process comprises a catalytic hydrogenation in which hydrogen is absorbed and loaded by a liquid organic hydrogen carrier in a chemical reaction, releasing heat as heat of reaction.

[0043] In this advantageous embodiment of the hydrogen loading process, which involves loading a liquid organic hydrogen carrier (LOHC), heat of reaction is released through the highly exothermic chemical addition of hydrogen to the double bonds of the unloaded LOHC. LOHCs are organic compounds, typically aromatics, that absorb hydrogen through catalytic hydrogenation and, in their loaded state, serve as hydrogen transport vehicles. At the destination, the hydrogen is discharged as needed through catalytic dehydrogenation. The resulting unloaded LOHC can then be transported back, thus closing the material cycle.

[0044] In a preferred embodiment of the process, the loading of the liquid organic hydrogen carrier (LOHC) is carried out in a temperature range between 150°C and 300°C. In particular, the loading takes place at approximately 250°C.

[0045] The released heat is therefore at a temperature level significantly above that typically required for thermal raw water desalination. This heat can thus be transferred to the evaporation process as at least a portion of the heating energy without the use of a heat pump. 2024PF00693

[0046] 11

[0047] Depending on the degree of conversion, the hydrocarbon products formed during loading exhibit no or only a few double bonds. These loaded LOHCs can then be transported relatively safely as liquids. Besides pipeline transport, road or ship transport is also easily possible. Utilizing the heat released during loading for the thermal treatment of raw water, especially seawater, is particularly advantageous because, due to the high exothermicity of hydrogenation, the released heat is normally more than sufficient to enable the complete evaporation of the raw water. Therefore, the heat required for the necessary heating energy for raw water desalination is covered by the released hydrogenation energy.The reaction enthalpy for the exemplary LOHC dibenzyltoluene is -59 kJ / mol H2 and corresponds to approximately 1.5 times the heat requirement for the treatment of the raw water required for the production of the added hydrogen by water evaporation.

[0048] In a particularly advantageous embodiment of the process, the liquid organic hydrogen carrier (LOHC) is selected from unsaturated organic compounds comprising methylcyclohexane, N-ethylcarbazole, dibenzyltoluene or benzyltoluene.

[0049] Liquid organic hydrogen carriers (LOHCs) are organic compounds that can absorb and release hydrogen through chemical reactions. LOHCs can therefore be used as storage media for hydrogen. In principle, any unsaturated compound (organic molecules with C-C double or triple bonds) can absorb hydrogen upon hydrogenation. To absorb hydrogen, the dehydrated form of the LOHC (an unsaturated, usually aromatic compound) reacts with the hydrogen in a hydrogenation reaction. Hydrogenation is an exothermic reaction and is carried out at elevated pressures (approx. 30–50 bar) and temperatures of approx. 150–200 °C in the presence of a catalyst.

[0050] 12

[0051] The corresponding saturated compound is formed, which can be stored or transported under ambient conditions. If the hydrogen is needed again, the now hydrogenated, hydrogen-rich form of the LOHC is dehydrogenated, releasing the hydrogen back from the LOHC. This reaction is endothermic and takes place at elevated temperatures (250–320 °C) in the presence of a catalyst. Before the hydrogen can be used, it may need to be purified of LOHC vapor. To increase efficiency, the heat contained in the hot stream exiting the release unit should be transferred to the cold stream of hydrogen-rich LOHC entering the release unit, thus minimizing the energy required for preheating before the reaction.

[0052] The invention makes efficient use of the heat released during hydrogen uptake in the hydrogenation reaction to provide heating energy for the evaporative desalination of the raw water.

[0053] From a plant engineering perspective, a direct transfer from the hydrogenation reactor to the raw water to be evaporated is possible, which can be achieved, for example, with just one heat exchanger. An indirect transfer via an intermediate heat transfer circuit is also possible, for which at least two heat exchangers are required.

[0054] Evaporation can be carried out at temperatures around 100 °C at atmospheric pressure. As explained above, the use of a vacuum pump is therefore unnecessary. It is possible that for particularly thorough evaporation of the remaining brine—in extreme cases, complete evaporation—temperatures slightly above 100 °C may be required. However, these heating temperatures are still significantly below the temperature level of heat generation resulting from the hydrogenation reaction. 2024PF00693

[0055] 13

[0056] In a particularly preferred embodiment of the process, the exothermic loading process of hydrogen comprises a compression of the hydrogen, whereby hydrogen is compressed, releasing heat as heat of compression.

[0057] This type of exothermic hydrogen loading process can be carried out alternatively or, if necessary, additionally, i.e., in parallel operation, to the exothermic hydrogen loading process via the catalytic hydrogenation described above.

[0058] In this second variant, i.e., hydrogen loading by compression, heat is released during the compression process. Since the compression efficiency is below 100%, some of the electrical energy used is converted into heat (waste heat), which is advantageously transferred to the raw water for thermal treatment. Although hydrogen compression differs in many respects from the chemical addition of H₂ to a LOHC, compression exhibits advantageous properties that also apply similarly to the described case of LOHC loading:

[0059] The heat released during the compression of a certain amount of hydrogen is normally sufficient to thermally treat and desalinate the amount of water required for the electrolytic production of hydrogen.

[0060] In a particularly advantageous embodiment of the process, the hydrogen is compressed to a pressure of more than 300 bar, in particular 700 bar.

[0061] It can be assumed that the hydrogen will be compressed to more than 300 bar, which is very realistic, as hydrogen compressions up to 700 bar are technically possible and typical. 2024PF00693

[0062] 14

[0063] The subsequent transport of the highly compressed hydrogen can be carried out, for example, in a tank or via a pipeline, where the hydrogen is used for its intended purpose. During hydrogen compression, temperatures occur that are significantly higher than the temperature range used to evaporate water at atmospheric pressure for raw water treatment and desalination.

[0064] Due to the characteristics described, the second variant also enables the thermal water treatment system to be supplied with sufficient quantities of heat. A particular advantage is that the use of additional equipment such as a heat pump or a vacuum pump can be avoided.

[0065] In a preferred embodiment of the process, the raw water treatment, the electrolysis process, and the hydrogen loading process are carried out largely synchronously, i.e., continuously and in coordination, during normal operation. This is achieved by considering the balance in normal operation, namely that the production and loading of a specific quantity of hydrogen per unit of time each requires the processing of a corresponding quantity of the raw water input in the same unit of time. Ideally, with perfectly synchronous execution of these subprocesses without any time lag or interruption of any subprocess, the use of thermal or material storage devices, such as gas or water storage tanks, can therefore be dispensed with.In reality, perfectly synchronous operation is only possible in continuous, fluctuation-free operation, but not during load changes, because the treated feed water must first be electrolyzed before the electrochemically produced hydrogen can be loaded. Since the processes do not occur infinitely fast, changes in the throughput of one subprocess require the other subprocesses to be brought up to the new load point. This can be preferably achieved by using the 2024PF00693.

[0066] 15

[0067] heat and / or mass buffers are implemented in the process control.

[0068] To address this problem and take precautions, in a still preferred embodiment of the process, the heat released in the loading process is routed through a heat exchanger and indirectly transferred as heating energy to the raw water, and the raw water is evaporated.

[0069] Furthermore, it is preferable to store the heat released in the exothermic loading process in a heat storage unit.

[0070] It has proven sensible and advantageous for operations to at least partially decouple the subprocesses in the procedure by implementing a certain degree of inertia in the heating system. This can lead to a favorable process design with regard to the heat flow from the heat released during the loading process and the heating energy required for the evaporation of the raw water. Therefore, a heat storage unit is proposed as a buffer, providing a heat reserve that can be accessed as needed, for example, if the exothermic loading process is temporarily interrupted or disrupted.

[0071] Furthermore, in a preferred embodiment of the process, hydrogen obtained from the electrolysis process is temporarily stored in a gas storage facility, with hydrogen being withdrawn from the gas storage facility and fed into the exothermic loading process.

[0072] Furthermore, it has proven useful and advantageous for operations to at least partially decouple the subprocesses in the procedure by implementing a certain degree of inertia into the material system as needed. With regard to hydrogen, this can be achieved by transferring hydrogen obtained from the electrolysis process—for example, a partial stream—into a gas storage tank and storing it there at a storage pressure or for temporary storage. 2024PF00693

[0073] 16

[0074] Therefore, a hydrogen gas storage system is preferably proposed as a buffer, providing a hydrogen supply that can be accessed as needed, for example, if the electrolysis process is temporarily interrupted, disrupted, or operating at partial load, or if hydrogen production is temporarily reduced. Similarly, a storage system with fully demineralized feed water can be provided to allow for adjustments to the current production rate of ultrapure water from the thermal treatment of raw water, as required.

[0075] In a particularly preferred embodiment of the process, thermal evaporation of the raw water is achieved by carrying out a multi-stage flash evaporation.

[0076] Multi-stage flash distillation (MSF) is the most widespread process and is used on a large industrial scale. In addition to this process, solar seawater desalination methods are also used to a lesser extent. This is a thermal process abbreviated as "MSF" (multi-stage flash distillation, evaporation, or desalination). It is the most frequently used method for seawater desalination. Its predecessor was multi-effect distillation. In this process, the supplied seawater is heated to a temperature of 115 °C using the waste heat from a thermal power plant, or in rare cases, a nuclear power plant.The salt water heated in the so-called brine heater evaporates in downstream expansion stages under vacuum; the water vapor condenses within these stages on pipes filled with cooling liquid and is drawn off as salt-free water.

[0077] In a preferred embodiment of the process, an external auxiliary heater is activated, at least temporarily, to evaporate the raw water, by means of which auxiliary heat is provided and transferred to the raw water, particularly in the case of a 2024PF00693

[0078] 17

[0079] Disruption or insufficient supply of released heat from the exothermic loading process.

[0080] This further increases process flexibility, in addition to the heat storage described above, and ensures continuous operation even if, for example, the exothermic loading process or heat transfer is disrupted or insufficient, or if a heat storage system is unavailable. Depending on the expected load profiles, the plant operator decides whether buffer storage should be provided or whether, from an economic perspective, it is more sensible to establish an external auxiliary heat supply, for example, via an electric heater or a fuel-fired burner, which is activated and operated during short periods of insufficient waste heat from the loading process.

[0081] The described processes can therefore be supplemented by auxiliary energy or auxiliary heat if necessary, e.g., in the case of H2 compression to pressures significantly below 300 bar, where insufficient waste heat is generated for raw water treatment. This scenario is still advantageous compared to conventional methods, where all the required heat is generated by using electricity or burning a fuel, and is superior to previously known methods.

[0082] In a preferred embodiment of the process, the brine is separated and drained during thermal desalination, so that fully demineralized feed water is obtained.

[0083] Separating the material streams is important. Due to phase separation resulting from the evaporation process, the salt or brine precipitates from the raw water and can be discharged or rinsed out of the multi-stage evaporation reactor. The salt-free water is drawn off and provided as feed water for the electrolysis process, possibly with the application of a downstream evaporation process.

[0084] 18

[0085] Filter or purification stages as required to ensure low electrical conductivity in the range of < 1.0 pS cm-1 at the input of the PEM electrolysis.

[0086] Another aspect of the invention relates to a water treatment system for carrying out the process. The water treatment system according to the invention for carrying out the process comprises a thermal desalination plant that can be supplied with salt-laden raw water, an electrolyzer to which salt-free water obtained from the desalination plant can be supplied as feed water for the electrolysis process, and a loading device downstream of the electrolyzer that can be loaded with hydrogen obtained from the electrolysis process in an exothermic loading process with the release of waste heat, wherein a heat recovery device is provided which is equipped to transfer waste heat released from the loading process to the desalination plant and to operate the thermal desalination process using the waste heat.

[0087] In a preferred embodiment, the heat recovery device in the water treatment system has a heat flow line that connects the loading device to the thermal desalination plant in terms of heat flow technology.

[0088] The heat transfer system ensures that the heat released during the catalytic loading process (waste heat) is effectively utilized and transferred to the desalination plant via suitable heat exchangers, where it can be used as process heat for evaporation. Such a heat exchanger, for example, has a return line for conveying or directing a heat flow, thus enabling heat transport from the loading facility to the desalination plant. A fluid is advantageously used, such as a heat transfer medium or heat exchanger medium that absorbs and transports heat, for example, water. Direct or indirect heat transfer can be implemented in the system (implement-2024PF00693).

[0089] 19

[0090] be equipped, i.e., heat exchangers can be provided that are operated with a heat exchange medium.

[0091] In a preferred embodiment of the water treatment system, the heat recovery device includes a heat storage unit.

[0092] A thermal storage system allows the heat released during the exothermic charging process to be stored and temporarily retained for its intended use. The thermal storage system can be connected directly to the return line as a buffer or in parallel with it, ensuring that thermal energy is stored and available at a desired temperature level for process control. The thermal storage system is operated with a thermal storage medium, i.e., it is charged and discharged. This medium is typically a pumpable, heat-storing, and heat-transferring fluid such as water. The thermal storage system itself can also consist of a solid or a packed bed as the heat-storing material. The input and output of thermal energy, i.e., the charging and discharging of the thermal storage system, is achieved using a heat-transferring medium or fluid.

[0093] The thermal storage system allows for on-demand discharge and injection into the return line, while also providing a degree of inertia and buffering effect. This means that the subprocesses of desalination, electrolysis, and hydrogen charging do not need to be fully synchronized or strictly coordinated. This feature is particularly advantageous for plant start-up and shutdown, transient operation, and in the event of malfunctions in water treatment system components.

[0094] In a preferred embodiment of the water treatment system, a hydrogen storage system is provided, which supplies the electrolyzer 2024PF00693

[0095] 20

[0096] downstream, whereby the hydrogen storage can be charged with hydrogen obtained from the electrolysis process.

[0097] In addition to a heat storage system, a hydrogen storage system for the produced hydrogen is also advantageous for operation, either additionally or alternatively. The hydrogen storage system is connected to a product gas line leading out of the electrolyzer or branches off in parallel from the hydrogen product gas line with a storage line.

[0098] In principle, it is preferable to operate the raw water treatment, electrolysis, and exothermic charging of the produced hydrogen largely synchronously. With precisely synchronous operation, at least the amount of heat required to process the necessary quantity of raw water into ultrapure water—i.e., to obtain desalinated water for electrolysis—is generated and transferred at any given time. In the case of a fully synchronous operating and plant concept, no heat storage or buffer storage is necessary. However, buffer storage can be advantageously used to compensate for time lags between subprocesses and to partially decouple them, for example, during operational load changes or start-up phases.

[0099] In a particularly advantageous embodiment of the water treatment system, the loading device includes an LOHC reactor with which catalytic hydrogenation can be carried out with the release of waste heat (QOU) as heat of reaction.

[0100] In this way, chemical reaction energy is provided during operation in the LOHC reactor, at a high reaction temperature of 150°C to 300°C, typically 250°C.

[0101] Alternatively or additionally, the loading unit in the water treatment system has a compressor station by means of which water obtained from the electrolysis process-2024PF00693

[0102] 21

[0103] The substance can be compressed by releasing waste heat as heat of compression.

[0104] The compressor station compresses the hydrogen obtained from electrolysis to a working pressure, thereby heating the gas. The heat of compression is released and can be used for the treatment of the raw water, in particular its desalination in the desalination plant. The compressor station has one or more turbo compressors designed for hydrogen compression, achieving a final pressure of up to 700 bar. It is possible and advantageous to compress the hydrogen from the electrolyzer directly as it exits the electrolyzer via the hydrogen product gas line, or to compress it to a pre-pressure. Therefore, the electrolysis plant may already include a compressor station connected to the electrolyzer.

[0105] In a preferred embodiment of the water treatment system, an additional heating system is provided, which can supply additional auxiliary heat that can be transferred to the desalination plant as needed to support the thermal desalination process.

[0106] This has proven to be an advantageous additional option, for example, to continuously maintain the evaporation process in the desalination plant in the event of an operating situation with an insufficient supply or disruption in the production of released heat. The auxiliary heater also offers greater flexibility for transient operating situations. The water treatment system can therefore be equipped with a buffer storage tank for heat and / or fuel storage, or – for the generally short periods of insufficient heat supply – alternatively or additionally provide the possibility of generating auxiliary heat using the auxiliary heater. The auxiliary heater can be electrically operated or combustion-based with a fuel and a combustion chamber (2024PF00693).

[0107] 22

[0108] ner . A fuel cell is also possible to provide the heating energy for an electric auxiliary heater.

[0109] Exemplary embodiments of the invention are explained in more detail with reference to a drawing. This drawing shows, schematically and in a highly simplified manner:

[0110] FIG 1 schematically illustrates the basic principle of the treatment of salt-laden raw water according to the method of the invention;

[0111] FIG 2 shows an embodiment of a water treatment system for obtaining ultrapure water for an electrolyzer with loading device;

[0112] FIG 3 shows an embodiment of a water treatment system with a loading device modified compared to FIG 2;

[0113] FIG 4 shows a water treatment system with LOHC reactor and buffer storage;

[0114] FIG 5 shows a water treatment system with a buffer storage tank that is larger than that shown in FIG 4.

[0115] The same reference symbols have the same meaning in the figures.

[0116] FIG 1 shows a schematic representation of a water treatment system 11, its essential functional elements, and their interaction. The water treatment system 11 integrates various different plant components into a complex, interacting overall system, which includes, among other things, the energy-efficient treatment of saline raw water 1. The water treatment system 11 comprises a thermal desalination plant 13, an electrolyzer 15, and a loading device 17 for the hydrogen H2 produced in the electrolyzer 15. In the thermal desalination plant, the hydrogen H2 is produced in the electrolyzer 15.

[0117] 23

[0118] In salting plant 13, fully demineralized water (H2O) can be obtained from the salt-laden raw water (1). This requires energy in the form of heat (Q). INThis requires heat that is supplied to or coupled into the thermal desalination plant 13 at a temperature of, for example, 250°C. The thermal desalination plant 13 is thus a heat sink and is based on the principle of multi-stage flash evaporation of the salt-laden raw water 1. The loading device 17 itself acts as the heat source, from which heat QOUT is obtained as usable heat or waste heat from the exothermic loading process of hydrogen H2. A heat recovery device 19 is provided for the transfer of heat QOUT, so that a thermal coupling between the heat source at the loading device 17 and the heat sink at the desalination plant 13 is realized. The thermal coupling can be effected, for example, by a heat flow line 21 in which a fluid is transferred as a heat transfer medium from the loading device 17 to the desalination plant 13.

[0119] The salt-free water H2O obtained from the desalination plant 13 can be supplied to the electrolyzer 15 as feed water 9 for the electrolysis process. The loading device 17 downstream of the electrolyzer 15 can be charged with the hydrogen H2 obtained from the electrolysis process in an exothermic loading process, releasing waste heat QOU. The heat recovery device 19 is equipped to transfer at least some of the waste heat QOUT released from the loading process back to the desalination plant 13 as heat Q. INto transfer. The thermal desalination process of the raw water 1 can thus be operated particularly efficiently with extensive use of the waste heat QOUT. Through the thermal coupling of the production site of the hydrogen H2 produced by electrolysis in the electrolyzer 15 with the loading point of the hydrogen H2 via the heat recovery unit 19, a high efficiency gain can be achieved in the provision of fully desalinated water H20 as feed water 9 for water electrolysis. Especially in areas without access to fresh water, but 2024PF00693

[0120] 24

[0121] With sufficient renewable electricity production, the described process can be used to desalinate seawater under much more economically attractive conditions, since an exothermic loading process for the hydrogen H2 is integrated into the water treatment system 11. The brine or salt solution 7 is separated and discharged from the desalination plant 13.

[0122] As shown below, the invention proposes exothermic loading processes for the hydrogen H2 which release sufficient waste heat QOUT to operate the treatment of the salt-laden raw water 1 in the endothermic desalination process.

[0123] Figure 2 shows a water treatment system 11 for producing ultrapure water H₂O for an electrolyzer 15 with a loading device 17 according to a particularly advantageous embodiment of the loading device 17. Here, the loading device 17 includes a LOHC reactor 25 with which a catalytic hydrogenation of a liquid organic hydrogen carrier (LOHC) can be carried out, releasing waste heat QOU as heat of reaction. The liquid organic hydrogen carrier (LOHC) is selected from unsaturated organic compounds comprising, for example, methylcyclohexane, N-ethylcarbazole, dibenzyltoluene, or benzyltoluene. Dibenzyltoluene (DBT) exhibits a reaction enthalpy of approximately -59 kJ / mol upon incorporation of hydrogen H₂, which is available as heat QOU for utilization.Through thermal coupling via the heat recovery device 19, the heat QOUT can be used to operate the desalination plant 13 and transferred to where it is used as process heat QI. N The hydrogen is supplied and introduced into the desalination process. A tank 31A containing unloaded liquid organic hydrogen carrier (LOHC) is connected to the inlet of the LOHC reactor 25. Furthermore, a product gas line 33 leads from the electrolyzer 15 to the LOHC reactor 25, through which hydrogen H2 obtained from electrolysis can be introduced into the LOHC reactor 25. The hydrogen H22024PF00693 in the LOHC reactor 25

[0124] 25

[0125] Liquid hydrogen carrier (LOHC) loaded in an exothermic chemical reaction is transferred to a tank 31B and made available for further purposes, e.g. . transported to an unloading point or place of use for the hydrogen H2 .

[0126] Figure 3 shows a water treatment system 11 for producing ultrapure water H₂O for an electrolyzer 15 with a loading device 17 according to a further advantageous embodiment of the loading device 17. Here, the loading device 17 includes a compressor station 27. The hydrogen H₂ obtained from the electrolysis process is compressed by the compressor station 27, whereby heat of compression is recovered as usable waste heat QOU. In this respect, an exothermic loading process with the hydrogen H₂ is also carried out in this process. The hydrogen H₂ is compressed to a pressure of more than 300 bar, in particular approximately 700 bar, and is thereby heated. The heat of compression QOU released in the loading process is recovered directly or indirectly as heating energy Q by means of the heat recovery device 19. INThe heat is transferred to the raw water 1, where it is evaporated. For indirect thermal coupling, the heat recovery device 19 may have one or more heat exchangers, such that a heat exchange medium or fluid is guided in a heat exchanger, allowing the heating energy Q to be transferred. IN for the operation of the thermal desalination plant 13 is provided there. The embodiments according to FIG. 2 and FIG. 3 differ in principle essentially by the exothermic loading process and the specific plant components required for each in the water treatment system 11.

[0127] Depending on the operating mode and the operator's requirements, it may be advantageous in the further design of the water treatment system 11 to provide buffer storage tanks for various purposes in order to increase operational flexibility. The buffer storage tanks decouple, to a certain extent, the subprocesses of the endothermic desalination of the raw water 1, the 2024PF00693

[0128] 26

[0129] Water electrolysis in the electrolyzer 15 and the exothermic loading of hydrogen H2 in the loading device 17.

[0130] FIG. 4 shows an example of a water treatment system 11 with an LOHC reactor 25 according to FIG. 2 and with an additional buffer storage tank. Here, the buffer storage tank is designed as a heat storage tank 3, i.e., a thermal buffer storage tank, and is integrated into the heat recovery system 19. This can be achieved by connecting the heat storage tank 3 in series with the heat flow line 21, as illustrated in FIG. 4. Alternatively, it is also possible to design a heat storage tank 3 as a heat storage tank branching off from the heat flow line 21 and running in parallel to it, and operated accordingly.

[0131] In contrast, FIG. 5 shows an embodiment of a water treatment system 11 with buffer storage tanks that are even larger than those shown in FIG. 4. In addition to a heat storage tank 3, the water treatment system 11 also includes mass or fluid storage tanks. A gas storage tank 5 is connected to the product gas line 33 for the hydrogen H2. This allows hydrogen H2 obtained from the electrolysis process to be temporarily stored in a gas storage tank 5, from which hydrogen H2 can be withdrawn as needed and fed into the exothermic charging process. This is advantageous in operating situations where hydrogen production is disrupted, temporarily interrupted, or foreseeably reduced. Thus, sufficient hydrogen H2 can be stored in the gas storage tank 5 to continue the subsequent exothermic charging process without interruption. The water treatment system 11 is also equipped with additional buffer storage tanks.A raw water storage tank 23 is set up for the salt-laden raw water 1, as well as a clean water storage tank 29 for receiving fully demineralized water H20 as feed water for operating the electrolysis process in the electrolyzer 15.2024PF00693.

[0132] 27

[0133] As an additional option or for emergency operation, it is possible to activate an external auxiliary heater 35, at least temporarily, to evaporate the raw water 1, by means of which auxiliary heat Q H is provided and transferred to the raw water, particularly in the event of a disruption or insufficient supply of released heat QOU from the exothermic loading process. However, the exothermic loading process is generally preferred in normal operation and implemented as the primary operating function, which is only supplemented temporarily and as a last resort by auxiliary heat Q. Hsupplemented or substituted. The water treatment system 11 shown in FIGS. 4 and 5 has an auxiliary heater 35, with which additional auxiliary heat Q is supplied. H The auxiliary heater 35 can be electrically or fuel-operated and serves to support the thermal desalination process as needed by providing the corresponding auxiliary heat Q. H , which can be transferred to or introduced into the thermal desalination plant ( 13 .

Claims

2024PF00693 28 Patent claims 1. Method for the preparation of raw water (1) for use as feed water in an electrolysis process, wherein salt-laden raw water (1) is provided and thermal desalination of the raw water (1) is carried out, wherein heat (QIN) is supplied to the raw water (1) and it is evaporated, wherein salt-free water (H2O) is withdrawn, which is supplied as feed water (9) and fed to an electrolysis process in which hydrogen (H2) is produced as product gas, wherein the produced hydrogen (H2) is loaded by subjecting the hydrogen (H2) to an exothermic loading process from which heat (QOUT) is released, wherein the released heat (QOU) is transferred and supplied as heating energy (QIN) to the raw water (1) and used for the evaporation of the raw water (1).

2. The method of claim 1, wherein the exothermic loading process of hydrogen (H2) comprises a catalytic hydrogenation in which hydrogen (H2) is absorbed and loaded by a liquid organic hydrogen carrier (LOHC) in a chemical reaction, releasing heat (QOU) as heat of reaction.

3. Method according to claim 2, wherein the loading of the liquid organic hydrogen carrier (LOHC) takes place in a temperature range between 150 °C and 300 °C, in particular at 250 °C.

4. The method of claim 2 or 3, wherein the liquid organic hydrogen carrier (LOHC) is selected from unsaturated organic compounds comprising methylcyclohexane, N-ethylcarbazole, dibenzyltoluene or benzyltoluene.

5. Method according to one of the preceding claims, wherein the exothermic loading process of hydrogen (H2) comprises a compression of the hydrogen (H2), wherein hydrogen2024PF00693 29 (H2) is compressed, releasing heat (QOUT) as heat of compression.

6. The method according to claim 5, wherein the hydrogen (H2) is compressed to a pressure of more than 300 bar, in particular 700 bar.

7. Method according to one of the preceding claims, wherein heat (QOU) released in the loading process is guided in a heat exchanger and indirectly transferred as heating energy (QIN) to the raw water, which is then evaporated.

8. Method according to one of the preceding claims, wherein heat (QOU) released in the exothermic loading process is stored in a heat storage unit (3).

9. Method according to one of the preceding claims, wherein hydrogen (H2) obtained from the electrolysis process is temporarily stored in a gas storage tank (5), wherein hydrogen (H2) is withdrawn from the gas storage tank (5) and supplied to the exothermic loading process.

10. Method according to one of the preceding claims, wherein thermal evaporation of the raw water ( 1 ) is effected by carrying out a multi-stage flash evaporation.

11. Method according to one of the preceding claims, in which an external auxiliary heater (35) is activated at least temporarily for the purpose of evaporating the raw water ( 1 ), by means of which auxiliary heat (Q ) H ) is provided and transferred to the raw water, especially in the event of a disruption or undersupply of released heat (QOUT) from the exothermic loading process.

12. Method according to one of the preceding claims, wherein the brine (7) is separated during thermal desalination. 2024PF00693 30 and is discharged, so that fully demineralized reactant water ( 9 ) is obtained .

13. Water treatment system (11) for carrying out the method according to one of the preceding claims, comprising a thermal desalination plant (13) that can be supplied with salt-laden raw water (1), an electrolyzer (15) to which salt-free water (H2O) obtained from the desalination plant (13) can be supplied as reactant water (9) for the electrolysis process, and a loading device (17) downstream of the electrolyzer (15) that can be loaded with hydrogen (H2) obtained from the electrolysis process in an exothermic loading process with the release of waste heat (QOUT), wherein a heat recovery device (19) is provided which is equipped to transfer waste heat (QOU) released from the loading process to the desalination plant (13) and to the thermal Desalination process using waste heat (QOU) to operate.

14. Water treatment system ( 11 ) according to claim 13, wherein the heat recovery device ( 19 ) has a heat flow line ( 21 ) which connects the loading device ( 17 ) to the thermal desalination plant ( 13) in terms of heat flow.

15. Water treatment system ( 11 ) according to claim 13 or 14, wherein the heat recovery device ( 19 ) comprises a heat storage unit ( 3 ).

16. Water treatment system ( 11 ) according to one of claims 13 , 14 or 15, wherein a hydrogen storage tank ( 5 ) is provided which is downstream of the electrolyzer ( 15 ), wherein the hydrogen storage tank ( 5 ) can be charged with hydrogen (H2) obtained from the electrolysis process .

17. Water treatment system (11) according to one of claims 13 to 16, wherein the loading device (17) comprises an LOHC reactor (25) with which a catalytic hydrogenation 2024PF00693 31 is feasible with the release of waste heat (QOU) as reaction heat.

18. Water treatment system ( 11 ) according to one of claims 13 to 17, wherein the loading device ( 17 ) has a compressor station (27 ) by means of which hydrogen (H2) obtained from the electrolysis process can be compressed with the release of waste heat ( QOU ) as heat of compression .

19. Water treatment system ( 11 ) according to one of claims 13 to 18, wherein an auxiliary heater (35) is provided, with which additional auxiliary heat (Q ) is supplied. H ) is available, which can be transferred to the thermal desalination plant ( 13) as needed to support the thermal desalination process .

Images