Process for production of methanol using waste heat from electrolysis cell

Abstract

The invention relates to a method for producing methanol on the basis of a synthesis gas stream comprising a hydrogen component and a carbon oxide component, wherein at least one component is at least partially produced in an electrolytic cell. The synthesis gas stream is converted to a crude methanol stream over a methanol synthesis catalyst in a reactor arrangement. The methanol is thermally separated from the crude methanol stream by distillation in a distillation unit by evaporation of the methanol-containing stream in a distillation evaporator of the distillation unit. According to the invention, the waste heat generated in the electrolytic cell is transferred by indirect heat transfer to a circulating heat pump medium of the heat pump system, which results in at least partial evaporation of the heat pump medium, then the heat pump medium is compressed, and the heat released by the heat pump medium by at least partial condensation is transferred by indirect heat transfer to the liquid medium, and heat transferred from the heat pump system to the liquid medium is at least partially utilized for evaporating the methanol-containing stream in the distillation evaporator.

Description

Technical Field

[0001] The present invention relates to a process for producing methanol from a synthesis gas stream, wherein the synthesis gas stream comprises a hydrogen component and a carbon dioxide component. The process is characterized in that at least one of the components is at least partially provided by an electrolyzer and the waste heat generated in the electrolyzer is utilized by a heat pump system for thermally separating methanol from crude methanol obtained from methanol synthesis by distillation. Background Art

[0002] The production plant for producing methanol comprises a distillation zone for thermally separating the crude methanol obtained in the methanol synthesis into methanol, water and by-products. For this purpose, heating at a temperature level of greater than 90°C, preferably greater than 120°C, or greater than 150°C is required.

[0003] Some of this heat can be provided in the form of medium-pressure steam, which is generated by boiler feed water on the shell side in the water-cooled methanol reactor in the cooling of the catalyst bed. This medium-pressure steam can be expanded outside the reactor and saturated to a saturated steam pressure corresponding to the temperature required for distillation. However, this steam only covers a portion of the heat requirement for distillation; the remaining heat requirement must be provided in some other way.

[0004] Conventional methanol plants based on fossil fuels (e.g. natural gas) utilize high temperature heat, typically greater than 300° C., from synthesis gas production, which is utilized in the form of steam to provide the missing heat for methanol distillation. Examples of synthesis gas production from fossil fuels are steam reforming (SMR), autothermal reforming (ATR), partial oxidation (POx) and catalytic partial oxidation (CPO) of methane. The steam formed in the synthesis gas production can also be expanded and saturated to a saturated steam pressure corresponding to the temperature required for distillation.

[0005] Different conditions exist in methanol production methods that are not based on the use of fossil fuels to produce synthesis gas. For example, in the so-called methanol synthesis based on carbon dioxide, a carbon dioxide stream, for example from a carbon dioxide separation device, is preferably reacted with hydrogen produced by electrolysis. Therefore, the synthesis gas "production" in this case is simply a combination of the above-mentioned streams. If any, waste heat at high temperature levels only appears to a small extent, which can be used as steam. Since the synthesis gas produced in this way also contains almost or completely no carbon monoxide, the actual methanol formation reaction is carried out with a lower heat formation (exothermicity) than when using a synthesis gas with a high carbon monoxide content. Therefore, on the shell side of the water-cooled reactor involved, the steam generated is less than in the conventional methanol synthesis.

[0006] The above-described method therefore suffers from a lack of available heat from the outset.

[0007] Therefore, heat must be imported from a source external to the plant in question. This is usually done in the form of steam, which can originate from a nearby supply network, an electric steam boiler or heat recovery within the plant generating the carbon dioxide stream. Examples of plants generating carbon dioxide streams are power plants, cement plants, steel mills and chemical production plants.

[0008] Heat input in the form of steam has the following disadvantages and problems, especially for methanol plants:

[0009] • Steam must be provided in sufficient quantity and under suitable conditions (eg pressure of 2 to 6.5 bar; temperature greater than 90° C., greater than 120° C. or greater than 150° C.; saturated or superheated) in the vicinity of the methanol plant.

[0010] • The CO2 footprint of the steam used should not worsen the CO2 footprint of the CO2 based methanol plant, as is often the case, for example, when the input steam is generated from waste heat from a combustion process and / or an oxidation process.

[0011] Regarding the utilization of heat or steam, methanol distillation can compete with a carbon dioxide separation unit which, depending on the technology used, also requires steam. An example of such a technology is the chemical absorption of carbon dioxide on amines. The thermal regeneration of the carbon dioxide-laden amine solution requires steam.

[0012] At certain locations, the only available power comes from renewable energy sources (solar, wind). This renewable energy must therefore be converted into heat, for example with the aid of an electric steam boiler. At such locations, methanol distillation competes with the electrolysis plant for renewable energy sources and thus significantly increases the power consumption and capacity of renewable energy sources.

[0013] Electrolysis plants release large amounts of waste heat in principle, but at such a low temperature level that steam with a temperature that can be used to heat the methanol distillation cannot be generated on this basis. Waste heat in this form is often referred to as low-grade heat. Waste heat from electrolysis cells is therefore often released to the atmosphere or fed into a district heating network with or without low-temperature heat pumps at temperatures of, in particular, less than 90°C.

[0014] Modern electrolyzers require complex cooling systems to release the waste heat formed during the electrochemical water splitting process to the environment. This is achieved, for example, by means of air coolers, cooling water-operated plate heat exchangers and / or cooling towers. The utilization of at least some of the waste heat from the electrolyzer will therefore reduce operating costs (OPEX) and capital costs (CAPEX), as well as the space required for the electrolysis device, in particular its cooling system. This can be achieved, for example, by saving additional water for cooling towers or electricity for air coolers.

[0015] In this regard, US 11,247,955 B2 discloses a method for producing methanol from a carbon dioxide stream and a hydrogen stream, wherein the hydrogen stream is provided by electrolysis of water. Waste heat from the electrolysis system is used as a heat source for a heat pump system, and the heat released by the heat pump system is transferred to steam, which is used, for example, in an evaporator to distill the produced crude methanol. Summary of the invention

[0016] The procedure described in US Pat. No. 11,247,955 B2 has the disadvantage that the heat released by the heat pump system is transferred directly to steam. Steam as a gaseous medium is not conducive to the absorption of heat, because its volumetric specific heat absorption capacity is much lower than that of similar liquids. For example, steam at 5 bar has a specific heat capacity of 2.5 kJ / kg / K, while liquid water at 5 bar has a specific heat capacity of 4.3 kJ / kg / K, so that the amount of steam required to transfer a defined heat flow at a defined temperature difference is higher than the amount of water. In addition, a comparable volume of steam material flow requires a larger pipe diameter than liquid, because the density of steam is several times lower than that of water, for example 2.7 kg / m 3 (Steam) vs.915kg / m 3 (water). Large pipe diameters increase the costs of the pipes involved. If the heat is to be supplied to the consumer in the form of steam, once the heat pump medium has transferred the heat to the heated liquid, a defined amount of waste heat can be utilized by means of a phase change of the heated liquid (for water the specific enthalpy change is, for example, about 2100 kJ / kg) at a significantly lower mass flow or temperature difference in the heat carrier medium than in the case of heat transfer from the heat pump medium to the steam.

[0017] A disadvantage also exists with regard to steam (by definition dry, saturated or superheated) as a heat-absorbing medium, that the heat transfer coefficient α between the heat exchanger wall and the medium is significantly lower and therefore worse than with heated liquids. A corresponding heat exchanger, according to the equation Q=α*A*ΔT, assuming an equal temperature difference ΔT between the wall and the liquid or gaseous medium, requires a relatively high area A to compensate for the lower α. The larger area is directly reflected in the outlay on components.

[0018] Depending on the hydrogen production capacity of the electrolyser required for methanol synthesis, an electrolyser operating on PEM technology at full load has the potential to release several times the heat input required for the methanol plant as waste heat. However, as mentioned before, the problem is that this waste heat is usually provided at a temperature of only 40°C to 60°C (low-grade heat). Therefore, a heat pump system is used to overcome the difference between this electrolyser waste heat temperature and the required temperature for methanol distillation, which is usually above 120°C, with maximum efficiency.

[0019] It is therefore a general object of the present invention to at least partially overcome the disadvantages of the prior art.

[0020] In particular, it is an object of the present invention to utilize the waste heat from an electrolysis plant with maximum efficiency in a distillation plant by means of a heat pump system for separating methanol from a methanol-containing stream.

[0021] The independent claims contribute to at least partially achieving at least one of the above-mentioned objects. The dependent claims provide preferred embodiments that contribute to at least partially achieving at least one of the objects. Preferred embodiments of components according to one category of the invention are, where relevant, also preferably used for the same names or corresponding components of the corresponding other categories of the invention. The expressions "having", "comprising" or "containing" etc. do not exclude the possible presence of other elements, components etc. The indefinite article "a" or "an" does not exclude the possible presence of a plurality.

[0022] The above objects are achieved at least in part by a method for producing methanol, the method comprising the following process steps:

[0023] a) providing a synthesis gas stream comprising at least a hydrogen component and a carbon oxide component, wherein at least one of the components is at least partially provided by an electrolyzer;

[0024] b) converting a synthesis gas stream over a methanol synthesis catalyst in a reactor arrangement to obtain a gaseous crude methanol stream;

[0025] c) producing a liquid crude methanol stream by condensing and separating the crude methanol stream obtained in step b);

[0026] d) thermally separating methanol from a liquid crude methanol stream in a distillation apparatus, wherein the distillation apparatus has at least one distillation column, wherein the methanol-containing stream is evaporated in a distillation evaporator,

[0027] Features

[0028] The waste heat generated in the electrolyzer is transferred to the circulating heat pump medium of the heat pump system by indirect heat transfer, which causes at least partial evaporation of the heat pump medium, the heat pump medium is then compressed, and the heat released by the heat pump medium by at least partial condensation is transferred to the liquid medium by indirect heat transfer, and the heat transferred from the heat pump system to the liquid medium is at least partially utilized for evaporating the methanol-containing stream in the distillation evaporator in step d).

[0029] A methanol-containing stream is a stream which is at least partially in liquid phase, wherein the liquid component of the stream is evaporated, preferably completely evaporated, in a distillation evaporator. With regard to a methanol-containing stream, it is not important whether the stream is partially or completely in liquid phase. It is essential that at least some of the heat released by the heat pump medium is utilized to evaporate the liquid component of the methanol-containing stream.

[0030] The distillation apparatus comprises one or more distillation columns. If the distillation apparatus comprises two or more distillation columns, these distillation columns are preferably arranged in series. Preferably, each distillation column produces an overhead product and a bottom product, wherein the bottom product boils at a lower pressure and / or a lower temperature than the overhead product.

[0031] The liquid crude methanol stream produced in step c) is treated in a distillation unit to separate methanol from the crude methanol stream. The aim here is in particular to obtain a stream of pure methanol. In addition, water and by-products are separated from the crude methanol stream in the distillation unit.

[0032] The methanol-containing stream is the stream which is evaporated in the distillation evaporator of the distillation column. Since the distillation evaporator forms in particular part of the bottom of the respective column, the stream (feed stream) which is fed to the distillation column differs in its composition from the methanol-containing stream. The feed stream of the distillation column can be referred to as the methanol-containing feed stream.

[0033] In the case of the first of the distillation columns arranged in series, or if only one distillation column is present, the methanol-containing feed stream corresponds in terms of its composition to the liquid crude methanol stream. The methanol-containing feed stream may be referred to herein as the first methanol-containing feed stream.

[0034] In one example, in a first distillation column, low-boiling by-products are separated from a first methanol-containing feed stream. The bottom product is fed to a second distillation column as a second methanol-containing feed stream. The top product formed in this second distillation column is essentially pure methanol, while the bottom product essentially contains water, wherein the methanol content is up to 1% by volume. To obtain further methanol, the bottom product from the second distillation column can be fed to a further third distillation column as a third methanol-containing feed stream.

[0035] At least one distillation column of the distillation apparatus can have a side draw of a stream comprising methanol and water.

[0036] Examples of suitable heat pump media are water, methanol, ethanol, hydrocarbons, oxygenates, halogenated or partially halogenated hydrocarbons, or hydrofluoroolefins.

[0037] The compression of the heat pump medium increases its temperature. In one embodiment, the temperature of the heat pump medium can be further increased by additional heating, for example, by an external heat source. The external heat source can be an electric heating device. After compression, the heat pump medium releases heat to the liquid medium via indirect heat transfer, so that the heat pump medium is at least partially condensed. According to the functional principle of the compression heat pump, the pressure of the heat pump medium is reduced after the heat is transferred to the liquid medium. In one embodiment, this is achieved by means of an expansion valve. Subsequently, the cycle begins again, i.e. the heat pump medium absorbs waste heat from the electrolyzer, so that it is at least partially evaporated.

[0038] The combination of heat recovery and heat transfer via the heat pump medium and the use of a liquid as the medium to which the heat from the heat pump medium is transferred is superior to the method taught in US 1 1 ,247,955 B2. The latter proposes using a medium in the form of steam to transfer heat from the heat pump medium to the medium in a heat exchanger.

[0039] The heat transferred from the heat pump system to the liquid medium is at least partially utilized to evaporate the methanol-containing stream in the distillation evaporator according to step d). The fact that this heat is utilized to evaporate the methanol-containing stream does not necessarily mean that the methanol-containing stream is completely evaporated in the distillation evaporator by heat transfer from the heat pump medium. The heat transfer from the heat pump medium increases the enthalpy of the methanol-containing stream in the distillation evaporator, but the methanol-containing stream can at least partially remain in a liquid state. The complete evaporation of the methanol-containing stream can be achieved by a further downstream distillation evaporator, or a distillation evaporator operated in parallel, or by means of another heat exchanger structure in the same distillation evaporator via another heating medium, such as steam.

[0040] The waste heat transfer from the electrolyser to the expanded heat pump medium and the heat transfer from the compressed heat pump medium to the liquid medium can be short-range or long-range. In each case, however, the heat is transferred by indirect heat transfer, i.e. never directly from one medium to another, which results in mixing of the respective liquid or gaseous media.

[0041] Proximate heat transfer (option 1) means in the present invention that there is no further intermediate auxiliary medium for indirect heat transfer. For example, in a heat exchanger, a proximate indirect heat transfer is achieved from one medium to another.

[0042] Remote heat transfer (option 2) in the present invention means indirect heat transfer from the heat pump medium to the auxiliary medium and then from the auxiliary medium to the liquid medium. The indirect heat transfer from the heat pump medium to the auxiliary medium can be achieved by means of a first heat exchanger. The indirect heat transfer from the auxiliary medium to the liquid medium can be achieved by means of a second heat exchanger. In another option, these two steps can be combined in one heat exchanger with two separate heat exchanger structures.

[0043] One advantage of option 1 (close heat transfer) is inherently more efficient heat transfer through fewer and smaller heat exchangers due to the use of smaller amounts of heat carrier medium. Another advantage is the high temperature difference in the heat exchanger, which results in a lower flow rate of the heat pump medium within the heat pump circuit.

[0044] One advantage of option 2 (remote heat transfer) is the increased safety level. For example, in the event of a leak in a heat exchanger, the heat pump medium cannot reach the process side of the electrolyser or the methanol distillation unit. The auxiliary media used for heat transfer can be selected so that they do not damage the respective process side in the event of a small leak. Examples of suitable auxiliary media are water, water-glycol mixtures and thermal oils. Option 2 also brings advantages with regard to the maintenance of the heat pump:

[0045] - waste heat from the electrolyser can be removed more easily, for example by using an air cooler which helps cool the auxiliary medium;

[0046] - The heat required by the distillation evaporator can be temporarily covered by feeding hot liquid or steam into the corresponding heat carrier circuit;

[0047] When boiling water is used as auxiliary medium, the auxiliary medium can be mixed with steam obtained from the shell side of the water-cooled methanol synthesis reactor. In one example, this is low-pressure steam.

[0048] The synthesis gas stream provided comprises at least a hydrogen component and a carbon oxide component. In other words, the synthesis gas stream comprises hydrogen and carbon monoxide and / or carbon dioxide.

[0049] At least one component is at least partially provided by the electrolyzer. In particular, in order to provide a synthesis gas stream,

[0050] - the hydrogen component can be generated at least partly by electrolysis, or

[0051] the carbon oxide component can be at least partly produced electrolytically, in particular electrolytically produced carbon monoxide (CO),

[0052] or

[0053] The hydrogen component and the carbon oxide component can be produced at least partially by electrolysis, in particular hydrogen and carbon monoxide can be produced at least partially by electrolysis.

[0054] In a preferred embodiment, the hydrogen component is provided entirely by an electrolysis cell by electrolysis of an aqueous electrolytic medium. Examples of suitable processes are PEM electrolysis, alkaline electrolysis, AEM electrolysis and high temperature electrolysis with steam as electrolytic medium.

[0055] The method may also include several electrolysis cells, from which waste heat is transferred to the circulating heat pump medium of the heat pump system by indirect heat transfer.

[0056] In a further preferred embodiment, the hydrogen component is provided at least in part by the electrolysis of an electrolyzer by an aqueous electrolytic medium, and the carbon oxide component is provided in the form of a stream with a high carbon dioxide content. In an example, the stream with a high carbon dioxide content contains at least 50% by volume of carbon dioxide, preferably at least 75% by volume of carbon dioxide, further preferably at least 90% by volume of carbon dioxide, further preferably at least 95% by volume of carbon dioxide, further preferably at least 99% by volume of carbon dioxide, further preferably at least 99.5% by volume of carbon dioxide. This type of methanol synthesis is also referred to as methanol synthesis based on CO2. The stream with a high carbon dioxide content can come from, for example, a carbon dioxide separation device, for example, from amine washing, physical washing (e.g., methanol washing), a membrane separation device, or a cryogenic carbon dioxide separation device.

[0057] In a further embodiment, the carbon oxide component of the synthesis gas stream can be provided at least in part by electrolysis of a stream containing carbon dioxide. The electrolysis of carbon dioxide reduces it at least in part to carbon monoxide. The resulting carbon monoxide-containing gas can be used as the carbon oxide component for methanol synthesis.

[0058] In the reactor arrangement, the synthesis gas stream is converted into a gaseous crude methanol stream by a suitable methanol synthesis catalyst, for example a copper-based catalyst. The reactor arrangement may comprise one or more reactors connected in series and / or in parallel. In one embodiment, the reactor arrangement comprises two or more reactors connected in series, wherein the crude methanol stream carries out intermediate condensation in the downstream of each reactor, which means that step c) is carried out in the downstream of each reactor of this reactor cascade. The reactor can be a water-cooled and / or air-cooled reactor in principle, regardless of their arrangement.

[0059] The crude methanol stream contains at least methanol and water.In addition, often unwanted by-products are present in the crude methanol stream, which can also be removed in the thermal separation step d).

[0060] By condensing and separating the gaseous crude methanol stream obtainable in step b), a liquid crude methanol stream is obtained in step c). Uncondensed components may be, for example, unconverted components of the synthesis gas stream which, in the case of a conventional methanol synthesis with a synthesis loop, are fed back to the inlet of the reactor arrangement.

[0061] The thermal separation step d) is particularly used to separate methanol from a liquid crude methanol stream. In particular, this provides at least one crude methanol stream, at least one water stream and at least one by-product stream. For this purpose, the methanol-containing stream is evaporated in a distillation evaporator of at least one distillation column. The one or more distillation columns constitute part of a distillation apparatus. The thermal separation in step d) can therefore comprise two or more separation steps connected in series.

[0062] The heat introduced into the methanol-containing stream during the evaporation is transferred by the distillation process essentially to the top product from the corresponding distillation column, from which the heat is extracted by the coolant. An example of a composition of a methanol-containing stream is

[0063] - stabilized crude methanol at the bottom of the primary column as the first distillation column, i.e. crude methanol from which low-boiling components have been substantially removed, and

[0064] - A mixture having methanol and water as main components at the bottom of the atmospheric column serving as the second distillation column, the methanol content of which is lower than that of the crude methanol stream.

[0065] A preferred embodiment of the process according to the invention is characterized in that the heat released by the heat pump medium is transferred in close proximity in the distillation evaporator by indirect heat transfer to the methanol-containing stream, wherein the methanol-containing stream comprises the liquid medium.

[0066] This preferred embodiment is an example of close transfer of heat released by the heat pump medium to a liquid medium. In this embodiment, the liquid medium is a stream containing methanol, or a liquid component of a stream containing methanol evaporated in a distillation evaporator. In one embodiment, the stream containing methanol is at least partially evaporated in the distillation evaporator by heat transfer from the heat pump medium.

[0067] In one embodiment, the methanol-containing stream is not completely evaporated in the distillation evaporator by heat transfer from the heat pump medium. In the latter embodiment, the methanol-containing stream is partially evaporated by supplying heat via the heat pump medium and then evaporated to completion (in series) by another heat transfer medium, such as steam.

[0068] In a further embodiment, not the entire methanol-containing stream is evaporated in the distillation evaporator by heat transfer from the heat pump medium. In a latter embodiment, that part of the methanol-containing stream that has not yet been heated by means of the heat pump medium is evaporated in another heat exchanger by another heat transfer medium, for example steam.

[0069] In this respect, it is of no importance that the heat transferred by the heat pump medium can also be partly transferred to the gaseous crude methanol. What is essential is that the heat provided by the heat pump medium is at least partly transferred to the methanol-containing stream, which thereby at least partly evaporates.

[0070] The feed stream containing methanol can be a liquid feed stream that has passed through a distillation step. Crucially, the feed stream containing methanol contains methanol and water and / or by-products, so that it may be necessary to further distill and evaporate in a distillation evaporator to obtain a methanol feed stream with a higher purity relative to the methanol content of the feed stream, or to obtain a water feed stream with a higher purity relative to the water content of the feed stream. The feed stream containing methanol can be a feed stream with high methanol content and low water content. In this case, further distillation may be required to obtain a methanol feed stream with a higher purity relative to the methanol content of the feed stream. The feed stream containing methanol can also be a feed stream with high water content and low methanol content. In this case, further distillation may be required to obtain a water feed stream with a higher purity relative to the water content of the feed stream.

[0071] A preferred embodiment of the process according to the invention is characterized in that the heat released by the heat pump medium is transferred to a first auxiliary medium by indirect heat transfer, wherein the first auxiliary medium comprises a liquid medium, and the heat absorbed by the first auxiliary medium is transferred to the methanol-containing stream in the distillation evaporator by indirect heat transfer.

[0072] The transfer of heat in the heat pump medium to the first auxiliary medium can keep the latter in a liquid state, or at least partially evaporate due to heat transfer. The above statement is applicable to the heat transfer from the first auxiliary medium to the feed stream containing methanol in the distillation evaporator. The feed stream containing methanol does not have to evaporate completely. It is crucial for this embodiment that at least some of the heat in the heat pump medium is transferred to the first auxiliary medium, and at least some of the heat absorbed by the first auxiliary medium is transferred to the feed stream containing methanol, so that the heat can be used to evaporate the feed stream containing methanol. The heat absorbed by the first auxiliary medium can also be transferred to several feed streams containing methanol in multiple distillation evaporators.

[0073] In one embodiment, the first auxiliary medium is water with a pressure of at least 3 bar, preferably greater than 5 bar, but not greater than 90 bar. The water can be heated and then sent to the distillation evaporator, or it can be evaporated in a pressure vessel to generate saturated steam. The steam generated in this way is then sent to the distillation evaporator. Optionally, the saturated steam stream thus generated can be compressed and saturated again to increase its temperature and pressure.

[0074] In a further embodiment, the first auxiliary medium is thermal oil.

[0075] A preferred embodiment of the process according to the invention is characterized in that the reactor arrangement comprises a water-cooled reactor and that a steam stream is generated in the cooling system of the water-cooled reactor and that this steam stream is at least partially combined with the first auxiliary medium before the heat absorbed by the first auxiliary medium is transferred to the methanol-containing stream in the distillation evaporator by indirect heat transfer.

[0076] In this preferred embodiment, when the reactor arrangement has at least one water-cooled reactor, the heat integration of the whole system is improved. Usually, boiling boiler feed water is used as a cooling medium for indirectly cooling the catalyst bed in the methanol synthesis reactor to utilize the principle of evaporative cooling. The steam stream generated on the shell side of the reactor, in particular the low-pressure steam stream, can be at least partially combined with the first auxiliary medium before the heat absorbed by the first auxiliary medium is transferred to the methanol-containing stream via indirect heat transfer in the distillation evaporator. In other words, after heat is transferred from the heat pump terminal medium to the first auxiliary medium, the first auxiliary medium is supplemented with the above-mentioned steam stream, and then heat is transferred from the first auxiliary medium to the methanol-containing stream in the distillation evaporator. Not only the heat absorbed by the first auxiliary medium from the heat pump medium is transferred here, but also the heat present in the steam stream is transferred.

[0077] A preferred embodiment of the method according to the invention is characterized in that the waste heat generated in the electrolysis cell is transferred short-range to the heat pump medium by indirect heat transfer from the electrolysis medium.

[0078] This preferred embodiment corresponds to the case in which the waste heat generated in the electrolysis cell is transferred to the heat pump medium over a short distance by indirect heat transfer, which is associated with the advantages set out above.

[0079] The waste heat generated in the electrolyzer is stored in particular in the electrolytic medium, which is discharged from the electrolytic cell stack of the electrolyzer after the electrolysis reaction is completed. The waste heat from this medium is transferred to the heat pump medium by indirect heat transfer, either close or remote, so that the heat pump medium is at least partially evaporated. The transfer of heat in the electrolytic medium, i.e. at least some of the waste heat from the electrolyzer, can be carried out before or after the separation of the product gas from the electrolytic medium, but should preferably be carried out before the electrolytic medium, which has been freed of product gas, enters the electrolytic cell stack again.

[0080] A preferred embodiment of the method according to the invention is characterized in that the waste heat generated in the electrolysis cell is transferred to the second auxiliary medium by indirect heat transfer and the heat absorbed by the second auxiliary medium is transferred to the heat pump medium.

[0081] This preferred embodiment corresponds to the example in which the waste heat generated in the electrolyzer is remotely transferred to the heat pump medium by indirect heat transfer. In this preferred embodiment, the waste heat present in the electrolytic medium is first indirectly transferred to the second auxiliary medium and then indirectly transferred from the second auxiliary medium to the heat pump medium.

[0082] A preferred embodiment of the process according to the invention is characterized in that the reactor arrangement comprises a water-cooled reactor and that a steam stream is generated in the cooling system of the water-cooled reactor and that this steam stream is at least partially combined with the second auxiliary medium before the heat absorbed by the second auxiliary medium is transferred to the heat pump medium.

[0083] In this preferred embodiment, when the reactor arrangement has at least one water-cooled reactor, similar to the above-mentioned embodiment, the heat integration of the whole system is improved. However, here, with respect to the heat transfer to the heat pump medium, this makes the heat pump medium at least partially evaporated. In this embodiment, the steam stream generated on the shell side of the water-cooled reactor, especially the low-pressure steam stream, is at least partially combined with the second auxiliary medium before the waste heat absorbed by the second auxiliary medium from the electrolyzer is transferred to the heat pump medium by indirect heat transfer to make the latter at least partially evaporated. In other words, the second auxiliary medium is supplemented with the above-mentioned steam stream, and then heat is transferred from the second auxiliary medium to the heat pump medium. Here, not only the waste heat generated by the electrolyzer is transferred to the heat pump medium, but also the heat present in the steam stream is transferred.

[0084] A preferred embodiment of the method according to the invention is characterized in that the heat pump medium comprises water, wherein the steam stream is utilized for the compression of the heat pump medium.

[0085] In particular, it is preferred that the reactor arrangement comprises a water-cooled reactor and that the steam stream is generated in the cooling system of the water-cooled reactor and is used at least partly for the compression of the heat pump medium.

[0086] It is further preferred here that the heat pump system comprises a jet pump for compressing a heat pump medium, wherein the jet pump has a suction port, a pressure port and a motive medium connection, and wherein the heat pump medium to be compressed is supplied to the jet pump via the suction port, a steam stream is supplied to it via the motive medium connection, and the compressed heat pump medium is discharged from the jet pump via the pressure port.

[0087] If utilize water or at least one aqueous medium as heat pump medium, steam stream can be used for the compression of at least a portion of heat pump medium.In this case, the electric energy that the compression of this part of heat pump medium needs is seldom (if any), for example by means of piston compressor or turbo compressor.

[0088] For this purpose, preference is given to utilizing at least a portion of the steam stream generated in the cooling system of the water-cooled reactor of the reactor arrangement.

[0089] Further preferably, the compression of at least a portion of the heat pump medium is achieved by means of a steam stream in a jet pump. The jet pump may also be referred to as a power pump alternatively. Since the jet pump has a compression effect in this embodiment, it may also be referred to as an ejector. The jet pump has a power medium connection, a suction port and a pressure port. The steam stream is introduced into the jet pump via the power medium connection, and the expanded heat pump medium is introduced via the suction port. With the help of the steam stream, the pressure of the heat pump medium in the jet pump is increased; thereby the heat pump medium is compressed by the steam stream. The compressed heat pump medium is discharged from the jet pump via the pressure port. The pressure of the power medium connection is higher than the pressure at the pressure port, and the pressure at the pressure port is higher than the pressure at the suction port. Since the amount of the heat pump medium is increased by supplying steam at the power medium connection of the jet pump, a portion of the heat pump medium is preferably separated from the heat pump medium loop upstream of the position where heat is transferred to the liquid medium. Since this is particularly condensed water, it is preferably supplied as cooling water to the cooling system of the water-cooled reactor arranged in the reactor. This completes the loop between the water-cooled reactor and the circulating heat pump medium.

[0090] If water or at least an aqueous medium is utilized as the heat pump medium, the heat pump medium can be compressed by a combination of a jet pump and a compressor. The jet pump and the compressor can be connected in series or in parallel here.

[0091] For this purpose, preference is given to utilizing at least a portion of the steam stream generated in the cooling system of the water-cooled reactor of the reactor arrangement.

[0092] A preferred embodiment of the method according to the invention is characterized in that the heat pump system is designed as a high-temperature heat pump system, in which the compressed heat pump medium is at a temperature of at least 60°C, preferably at a temperature of at least 100°C.

[0093] It is further preferred that the heat pump medium has a temperature of not more than 200°C, preferably not more than 180°C.

[0094] A preferred embodiment of the process according to the invention is characterized in that the carbon oxide component of the synthesis gas stream comprises at least 50 mol % carbon dioxide and in that at least part of the carbon oxide component results from a carbon dioxide separation process.

[0095] Further preferably, the carbon oxide component of the synthesis gas stream comprises at least 75 volume % carbon dioxide, further preferably at least 90 volume % carbon dioxide, further preferably at least 95 volume % carbon dioxide, further preferably at least 99 volume % carbon dioxide, further preferably at least 99.5 volume % carbon dioxide.

[0096] Carbon dioxide deposition methods are understood here to refer to methods for more or less selectively separating carbon dioxide from a gas mixture stream. The separation can be achieved by a cryogenic method comprising condensation of carbon dioxide and optional cryogenic distillation. In addition, such a method may comprise one or more separation steps achieved by a membrane. In addition, the separation may comprise an absorption process comprising at least one physical or chemical absorption step, and a subsequent desorption step. In addition, the separation may comprise an adsorption process comprising an adsorption step on a solid surface and a subsequent desorption step from the surface. In this case, the carbon dioxide itself does not have to be a species that is adsorbently bound to each surface. In addition, the separation may comprise a membrane-based method that produces at least one retentate stream and one permeate stream, wherein at least one stream has a carbon dioxide content higher than the feed stream supplied to the membrane. DETAILED DESCRIPTION

[0097] The present invention is described in detail below through three operating examples and one numerical example. Figures 1 to 3 Description. In the figures, functionally and / or structurally identical or at least similar components are given the same reference numerals. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] Figure 1 A simplified block flow diagram of a first embodiment of the method according to the present invention,

[0099] Figure 2 A simplified block flow diagram of a second embodiment of the method according to the present invention,

[0100] Figure 3 A simplified block flow diagram of a third embodiment of the method according to the present invention,

[0101] Figure 1 A block flow diagram of method 1 according to a first embodiment of the present invention is shown.

[0102] In accordance with Figure 1 In the embodiments, the waste heat transfer from the electrolyzer to the heat pump medium and the condensation heat of the heat pump medium to the methanol-containing stream are both achieved in close proximity by indirect heat transfer, i.e. without an auxiliary heat transfer medium.

[0103] Electrolyzer 10, such as PEM electrolyzer, is supplied with water stream 20 via water reservoir 11, and electric energy is supplied thereto via DC power supply 12. Electrolyzer produces oxygen stream (not shown) and hydrogen stream 23 by electrochemical cracking of water as electrolytic medium. Oxygen stream is released into the atmosphere. Alternatively, oxygen stream can also be released to another point in another process or methanol device. Hydrogen stream 23 is fed into methanol synthesis reactor arrangement 13, which at least comprises water-cooled methanol synthesis reactor, cooler, condenser and separator (details not shown). Carbon dioxide stream 24 from carbon dioxide source 14 is also supplied to methanol synthesis reactor arrangement 13. Carbon dioxide source 14 is a regeneration tower of amine washing unit. In methanol synthesis reactor arrangement 13, hydrogen in hydrogen stream 23 and carbon dioxide in carbon dioxide stream 24 are converted into crude methanol stream on methanol synthesis catalyst. First, crude methanol stream containing at least methanol and water is fed into primary tower, where low boiling point components are removed as top product (not shown). The bottom product from the primary column is fed as methanol-comprising feed stream 25a to a distillation column 15 , in which a methanol stream 26 is produced as top product and also a water stream (not shown) as bottom product.

[0104] The method also includes a heat pump system 9, which includes a heat exchanger 16, a heat exchanger 17, a compressor 18 and a throttle valve 19. The above components are fluidly connected to each other through corresponding conduits so that the heat pump medium can circulate between the mentioned components. The heat exchanger 16 has the function of an evaporator of the heat pump system, and the heat exchanger 17 has the function of a liquefier.

[0105] A stream 21 of hot electrolytic medium is discharged from the electrolyzer 10, the heat of which is partially transferred in the heat exchanger 16 to the liquid heat pump medium 28a entering the heat exchanger 16. The heat pump medium 28a is thus evaporated. The hot electrolytic medium 21 is cooled accordingly, so that a stream 22 of the cooled electrolytic medium is discharged from the heat exchanger 16 and fed back to the electrolyzer. The evaporated heat pump medium 28b is fed to the compressor 18, which increases the temperature and pressure of the evaporated heat pump medium. The compressed heat pump medium 28c is fed to the heat exchanger 17, where the heat pump medium is liquefied (condensed) in heat exchange with the methanol-containing stream 25b discharged from the distillation column 15. The heat exchanger 17 in this case not only constitutes a part of the heat pump system 9, but also constitutes a part of the distillation evaporator of the distillation column 15. In the heat exchanger 17, the methanol-containing stream 25b is partially but not completely evaporated by the transfer of condensation heat from the heat pump medium. For complete evaporation, the partially evaporated methanol-containing stream 25c is fed to a further heat exchanger 39, which likewise forms part of the distillation evaporator of the distillation column 15. The heat exchanger 39 is supplied with a steam stream 27a, which completely evaporates the methanol-containing stream 25c. The completely evaporated methanol-containing stream 25d enters the distillation column 15 in order to be thermally separated therein into a methanol stream 26 and a water stream (not shown). The vapor stream 27a is condensed in the heat exchanger 39 and leaves the heat exchanger 39 as a condensate stream 27b.

[0106] The condensed, cooled heat pump medium stream 28 d is expanded via the throttle valve 19 and fed as expanded heat pump medium stream 28 a to the heat exchanger 16 (evaporator), in which the heat pump medium is evaporated again by absorbing waste heat from the electrolysis cell 10 .

[0107] Figure 2 A block flow diagram of method 2 according to a second embodiment of the present invention is shown.

[0108] In accordance with Figure 2 In the embodiments of the present invention, the transfer of waste heat from the electrolyzer to the heat pump medium and the transfer of condensation heat of the heat pump medium to the methanol-containing feed stream are both achieved remotely by indirect heat transfer, i.e. in each case using an auxiliary heat transfer medium and an intermediate heat exchanger.

[0109] The following is basically related to Figure 1 The difference between the embodiments.

[0110] The waste heat from the electrolysis cell 10 is first transferred in the heat exchanger 32, to which the stream 30b of the cooled second auxiliary medium is supplied. The heat from the hot electrolysis medium stream 21 is transferred to the cooled auxiliary medium stream 30b in the heat exchanger 32. The auxiliary medium stream 30a, which has thus been heated, is discharged from the heat exchanger 32 and has the effect of evaporating the heat pump medium 28a supplied to the heat exchanger in the heat exchanger 16 (evaporator), which is then fed to the compressor 18 as evaporated heat pump medium 28b.

[0111] On the liquefier side of the heat pump system 9, the cooling stream 29a of the first auxiliary medium has the effect of condensing the compressed heat pump medium stream 28c. The resulting heated auxiliary medium stream 29b is combined with a steam stream 37 taken from the cooling system of the water-cooled reactor of the methanol synthesis reactor arrangement 13. The corresponding combined stream of steam and heated first auxiliary medium is fed to the heat exchanger 31, in which the methanol-containing stream 25b is evaporated. The evaporated methanol-containing stream 25a is fed to the distillation column 15 for thermal separation into a methanol stream 26 and a water stream (not shown). The heat exchanger 31 here is the distillation evaporator of the distillation column 15 and does not constitute part of the heat pump system 9.

[0112] Figure 3 A block flow diagram of method 3 according to a third embodiment of the present invention is shown.

[0113] In accordance with Figure 3 In the embodiment of Figure 2 The embodiment of the invention is transferred by means of a second auxiliary medium—first to the second auxiliary medium in the heat exchanger 32 and then from the second auxiliary medium to the expanded heat pump medium 28a in the heat exchanger 16, thus evaporating it.

[0114] In accordance with Figure 3 In the embodiment, the heat pump medium used is water.

[0115] The stream 28b of the evaporated heat pump medium is fed to the jet pump 33 via the suction port 34. The jet pump is also supplied with a steam stream 37 via the power medium connection 36. The steam stream 37 is taken from the cooling system of the water-cooled reactor of the methanol synthesis reactor arrangement 13. The steam stream 37 compresses the vaporous heat pump medium 28b in the jet pump 33 and is discharged from the jet pump 33 via its pressure port 35 as a stream 28c of compressed heat pump medium. The compressed heat pump medium 28c is condensed in the heat exchanger 17 and thus heats the methanol-containing stream 25b, which thus evaporates and enters the distillation column 15 as a gaseous methanol-containing stream 25e.

[0116] From the condensed heat pump medium stream 28d, a substream 38 is separated for mass balance compensation. This substream 38 is fed to the cooling system of the water-cooled reactor of the methanol synthesis reactor arrangement 13 in order to be reused as cooling water.

[0117] The following numerical examples based on simulation data are also intended to illustrate the advantages of the method according to the invention.

[0118] A typical 100 MW PEM electrolyser at full load generates about 20 to 25 MW of heat at about 50° C. A methanol plant producing methanol at a rate of about 220 t of methanol per day at full load based on carbon dioxide and electrolytically produced hydrogen has a heat input requirement of at least about 10 MW at at least about 130° C.

[0119] According to the following embodiment, the electrolyzer transfers its waste heat closely to the heat pump medium of the heat pump system by means of a heat exchanger, and the compressed and heated heat pump medium transfers its heat closely to the liquid crude methanol in the distillation evaporator by means of a heat exchanger.

[0120] Waste heat from the electrolyser can be transferred in the following ways:

[0121] - 10 MW of waste heat from the process medium of the electrolysis cell (electrolysis medium at 60°C) is transferred to the heat pump medium in order to evaporate the latter, which has a temperature of 50°C after evaporation.

[0122] - The evaporated heat pump medium is fed to a compressor, which increases the temperature of the heat pump medium to 130° C. and increases the pressure of the heat pump medium. Taking into account the known high-temperature heat pump curve, the compression of a heat pump medium containing 10 MW requires approximately 3.3 MW of power (e.g. in the form of electricity). The quality factor is therefore 3.

[0123] - The heat pump medium at 130° C. is condensed on the hot side of the methanol distillation column and provides 10 MW in the heat exchanger of the distillation evaporator by the heat of condensation.

[0124] As a comparison: If saturated steam at 130° C. were to be produced from water at 2.7 bar by supplying electrical energy, this would consume the entire 10 MW transferred in the heat exchanger of the distillation evaporator.

[0125] The savings in this case resulting from the use of the invention is 10 MW (full power consumption for heating to generate saturated steam) minus 3.3 MW (power consumption of the heat pump system), which is a saving of 6.7 MW. This power is "saved", meaning that it is not consumed in the form of additional power, but can be provided by utilizing waste heat from the electrolyzer.

[0126] List of Reference Numerals

[0127] 1, 2, 3 Methods

[0128] 9 Heat Pump System

[0129] 10. Electrolyzer

[0130] 11 Water reservoir

[0131] 12 DC power supply

[0132] 13 Methanol Synthesis Reactor Layout

[0133] 14 Carbon dioxide source

[0134] 15 Distillation Tower

[0135] 16 Heat exchanger (evaporator)

[0136] 17 Heat exchanger (liquefier)

[0137] 18 Compressor

[0138] 19 Throttle valve

[0139] 20 water flow

[0140] 21. Thermolysis medium

[0141] 22 Cooling of electrolyte

[0142] 23 Hydrogen Stream

[0143] 24 Carbon dioxide stream

[0144] 25a Feed stream containing methanol

[0145] 25b, 25c, 25d, 25e: methanol-containing stream

[0146] 26 Methanol Stream

[0147] 27a Steam stream

[0148] 27b Condensate stream

[0149] 28a, 28b, 28c, 28d circulating heat pump medium

[0150] 29a, 29b Stream of the first auxiliary medium

[0151] 30a, 30b Stream of the second auxiliary medium

[0152] 31 Heat exchanger for the first auxiliary medium

[0153] 32 Heat exchanger for the second auxiliary medium

[0154] 33. Jet Pump

[0155] 34 suction port

[0156] 35 Pressure port

[0157] 36 Power medium connection

[0158] 37 Steam Stream

[0159] 38 Condensate stream

[0160] 39 Heat exchanger

Claims

1. A method for producing methanol comprising the following process steps: a) providing a synthesis gas stream comprising at least a hydrogen component (23) and a carbon oxide component (24), wherein at least one of the components is at least partially provided by an electrolyser (10); b) converting the synthesis gas stream over a methanol synthesis catalyst in a reactor arrangement (13) to obtain a gaseous crude methanol stream; c) producing a liquid crude methanol stream by condensing and separating the crude methanol stream obtained in step b); d) thermally separating methanol from the liquid crude methanol stream in a distillation apparatus, wherein the distillation apparatus has at least one distillation column (15), wherein a methanol-containing stream (25b) is evaporated in a distillation evaporator (17, 31), Features The waste heat generated in the electrolyzer (10) is transferred to the circulating heat pump medium (28a, 28b, 28c, 28d) of the heat pump system (9) by indirect heat transfer, which causes at least partial evaporation of the heat pump medium, which is then compressed, and the heat released by the heat pump medium by at least partial condensation is transferred to the liquid medium by indirect heat transfer, and the heat transferred from the heat pump system to the liquid medium is at least partially utilized for evaporating the methanol-containing stream (25b) in the distillation evaporator in step d).

2. The method according to claim 1, characterized in that The heat released by the heat pump medium is transferred in a distillation evaporator (17, 31) by indirect heat transfer to the methanol-containing stream (25b), wherein the methanol-containing stream (25b) comprises a liquid medium.

3. The method according to claim 1, characterized in that The heat released by the heat pump medium is transferred to the first auxiliary medium (29a) by indirect heat transfer, wherein the first auxiliary medium (29a, 29b) contains a liquid medium, and the heat absorbed by the first auxiliary medium (29b) is transferred to the methanol-containing stream (25b) by indirect heat transfer in the distillation evaporator (17, 31).

4. The method according to claim 3, characterized in that The reactor arrangement (13) comprises a water-cooled reactor, and a steam stream (37) is generated in the cooling system of the water-cooled reactor and is at least partially combined with the first auxiliary medium (29b) before the heat absorbed by the first auxiliary medium (29b) is transferred to the methanol-containing stream (25b) in the distillation evaporator (17, 31) by indirect heat transfer.

5. A method according to any one of the preceding claims, characterised in that The waste heat generated in the electrolytic cell (10) is transferred to the heat pump medium (28a) over a short distance by indirect heat transfer from the electrolytic medium (21).

6. The method according to any one of claims 1 to 4, characterized in that Waste heat generated in the electrolytic cell (10) is transferred to the second auxiliary medium (30b) through indirect heat transfer, and heat absorbed by the second auxiliary medium (30a) is transferred to the heat pump medium (28a).

7. The method according to claim 6, characterized in that The reactor arrangement comprises a water-cooled reactor, and a steam stream (37) is generated in a cooling system of the water-cooled reactor and is at least partially combined with the second auxiliary medium (29b) before the heat absorbed by the second auxiliary medium (29b) is transferred to the heat pump medium.

8. A method according to any one of the preceding claims, characterised in that The heat pump medium (28a, 28b, 28c, 28d) comprises water, wherein a steam stream (37) is used for compressing the heat pump medium.

9. The method according to claim 8, characterized in that The reactor arrangement (13) comprises a water-cooled reactor, and a steam stream (37) is generated in the cooling system of the water-cooled reactor and is used at least partly for the compression of the heat pump medium (28b).

10. The method according to any one of claims 8 and 9, characterized in that The heat pump system (9) comprises a jet pump (33) for compressing the heat pump medium (28b), wherein the jet pump has a suction port (34), a pressure port (35) and a motive medium connection (36), and wherein the heat pump medium (28b) to be compressed is supplied to the jet pump (33) via the suction port (34), a steam stream (37) is supplied to it via the motive medium connection (36), and the compressed heat pump medium (28c) is discharged from the jet pump (33) via the pressure port (35).

11. A method according to any one of the preceding claims, characterised in that The heat pump system (9) is designed as a high-temperature heat pump system, wherein the compressed heat pump medium (28c) is at a temperature of at least 60°C, preferably at a temperature of at least 100°C.

12. A method according to any one of the preceding claims, characterised in that The carbon oxide component (24) of the synthesis gas stream comprises at least 50 mole percent carbon dioxide, and at least a portion of the carbon oxide component is produced by a carbon dioxide separation process.

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