Production of methanol from biomass and green hydrogen

Abstract

In a method for producing methanol, synthesis gas (25) obtained from biomass (5) is fed to a methanol synthesis plant (80). In a main operating mode in which sufficient current can be used to electrolytically obtain hydrogen, the electrolytically obtained hydrogen (45) is supplied to the methanol synthesis plant (80). In a secondary operating mode in which insufficient current can be used for the electrolytic production of hydrogen (45), a residual gas (26) obtained when the synthesis gas (25) is separated from the biogas (15) obtained from the biomass (5) is fed to the generator (50) in order to thereby provide current to the plant (10, 20, 30, 40, 70, 80) involved in the method.

Description

Technical Field

[0001] The present invention relates to a method for methanol synthesis and a corresponding system. Background Art

[0002] A method for producing biomethanol is known from EP 3 452 438 B1, in which hydrogen obtained by electrolysis and organic waste are transported. In addition, it is known from EP 3 017 015 B1 that a steam cracker is used in the first step of preparing biomass in order to decompose hydrocarbon-containing raw materials into shorter chains. This method and device focus on performing chemical conversion as efficiently as possible from the input materials provided, such as especially biomass and hydrogen. It is typically not considered here that in some cases, the raw materials may not be present sufficiently for conversion, and / or fluctuations in the amount or time of the raw materials may occur. In addition, the demand for non-regeneratively obtained current should be reduced or avoided for the entire system of methanol synthesis. Summary of the invention

[0003] The invention is directed to this problem. The features of the independent claims describe the inventive advantages. Preferred developments are the subject matter of the dependent claims.

[0004] In a method for producing methanol, synthesis gas is obtained from biomass and is supplied to a methanol synthesis plant. Here, in a main operating mode in which sufficient current can be used to electrolytically obtain hydrogen, the hydrogen obtained electrolytically is correspondingly supplied to the methanol synthesis plant. And in a secondary operating mode in which there is not sufficient current available for electrolytically producing hydrogen, the residual gas obtained when the synthesis gas is separated from the biogas obtained from the biomass is supplied to a generator in order to produce current for the equipment involved in the method. Therefore, the residual gas is the difference between the produced biogas and the synthesis gas that is especially separated so that it can be used directly in the methanol synthesis plant. In the secondary operating mode, electrolysis is not operated in particular. The term "current for electrolytically obtaining hydrogen" refers in particular to current that can be generated renewably, such as current from photovoltaics or wind power. However, in principle, other current sources are also included, for example, current sources from atomic energy.

[0005] According to the standard, a methanol synthesis plant is a unit that converts synthesis gas (H2 and CO) into methanol. However, in the special case, CO2 is mainly supplied to the process instead of CO. The synthesis unit works with a recirculation pump / blower, which re-supplies the unconverted output material to the synthesis unit. Methanol and water are produced in the synthesis unit. Because a small amount of harmful gases / exogenous gases or inert gases are always also supplied to the process when feeding the gas, the accumulation of the gas must be avoided by a purge gas flow so as not to impair the efficiency of the synthesis process. The process is exothermic and the heat generated can be used in other parts of the facility (for preheating distillation or HyGas processes). The output gas of the purge gas flow can be used by various components of the system, such as especially generators or oxyfuel burners.

[0006] On the one hand, the amount of biogas in the bioreactor, in particular in the HyGas generator, cannot vary well over time, so that a biogas flow that is largely constant over time is obtained. On the other hand, the amount of photovoltaic current fluctuates depending on the time of day, so that fluctuations in the (daytime) time relationship of the input materials for methanol synthesis occur as a result. Due to the above-mentioned two operating modes of the method of the present invention (in combination with the intermediate stage), it is achieved that the maximum feasible amount of methanol is obtained at any point in time, and at the same time the required amount of non-green electricity is reduced overall. Although the amount of methanol produced in the secondary operating mode, i.e. in the absence of green electricity, is significantly reduced compared to the main operating mode, it is still feasible to carry out the synthesis by conveying the residual gas from the biomass utilization to the generator without having to use non-green electricity.

[0007] Advantageously, at least in the primary operating mode and preferably also in the secondary operating mode, the residual gas obtained when separating the synthesis gas from the biogas produced from the biomass is fed to a treatment device in order to produce additional synthesis gas therefrom, which is also fed to the methanol synthesis plant. The methanol synthesis plant requires simple compounds, such as H2, CO2, which are first separated from the biogas in a first step. In order to obtain a high yield of synthesis gas from the biogas, the remaining components, i.e. the residual gas, are converted in the second step so that they can be used as "additional synthesis gas".

[0008] It is particularly advantageous that in a treatment device, the residual gas is fed to an oxyfuel burner and a converter in a specific ratio, wherein oxidation is performed in the oxyfuel burner, and the oxidized gas is fed to the converter, and the converter uses the gas to perform processing, especially reduction, so that the gas can be fed to a methanol synthesis plant as another synthesis gas. The treatment device can also be used in a secondary operating mode. In particular, an oxyfuel burner is a burner unit that burns hydrocarbons and other gases to generate heat. In the special case, the gas is burned with pure oxygen to avoid the introduction of nitrogen, for example, from the air. The combustion air ratio is substoichiometric to produce an oxygen-free exhaust gas stream, which can be used as a reactant in another process step in itself. Therefore, the converter is a chemical unit that converts hydrocarbons into hydrogen and carbon dioxide / carbon monoxide. This process is endothermic, so that heat must be supplied from the outside.

[0009] It is also advantageous that the switch between the primary operating mode and the secondary operating mode can be made depending on the available green electricity or depending on the available hydrogen (the system is oriented so that the system can carry out the switch), or that a mixture of operating modes can be used, wherein these mixtures differ, for example, in the proportion of residual gas supplied to the generator or to the treatment device. The amount of available green electricity is particularly suitable as a criterion for the switch (or proportional setting or regulation) because it is easy to measure. The amount of hydrogen obtained by electrolysis is proportional to the green electricity, so that the electrolytic hydrogen can also be used as a criterion. But in the end, the total hydrogen present in the system of the methanol synthesis plant is an important criterion for the control / regulation between the two operating modes, which also depends on the synthesis gas that can vary depending on the quality of the raw materials. And because this is also affected by the hydrogen content in the synthesis gas (or multiple synthesis gases), alternatively, the parameter can also be considered as a criterion for the switch.

[0010] In addition, it is advantageous here that the switch between the operating modes or the setting of the ratio of the operating modes takes place automatically as a function of the current available for the electrolysis or the amount of available hydrogen and the C / H ratio of the synthesis gas / biogas, so that an autonomously operating system is formed, in which control personnel generally do not have to intervene. The system is therefore preferably configured such that it can switch between the operating modes (preferably automatically) as a function of the current available for the electrolysis or the amount of available hydrogen.

[0011] It is also advantageous that in the primary and secondary operating modes, biogas is produced from the biomass and that a synthesis gas comprising hydrogen H2 and in particular also carbon dioxide CO2 is separated from the biogas in a hydrogen separator. This describes by way of example how synthesis gas can be obtained from biomass. The hydrogen separator essentially comprises a membrane unit which separates hydrogen (and possibly hydrogen and CO2) from a gas stream. In addition to membrane solutions, other technologies are also conceivable here, such as pressure swing adsorption and the like.

[0012] Furthermore, it is advantageous to conduct the process heat generated by the generator and / or the oxyfuel burner and the methanol synthesis unit to a HyGas generator for producing biogas and / or to a converter and / or to a methanol distillation or methanol synthesis unit. This is advantageous because the components requiring heat are directly supplied with the generated process heat in this way.

[0013] In one development, a reservoir for oxygen is provided, wherein in the primary operating mode, the reservoir is filled with oxygen obtained by electrolysis and the oxygen is used in the secondary operating mode to operate the oxyfuel burner. The oxyfuel burner must usually be operated with pure oxygen. As a result, the oxyfuel burner can also be used efficiently during the auxiliary operation, that is to say in the phases in which no electrolytic oxygen is generated, so that a 24-hour cycle is obtained, via which oxygen can be repeatedly stored and provided for the auxiliary operation.

[0014] In one refinement, a storage for CO2 is provided, wherein in the secondary operating mode, the storage can be filled with CO2 obtained from synthesis gas, and the stored carbon dioxide can be used for methanol synthesis in the main operating mode. As a result, during the main operation, an increased production of hydrogen is achieved in phases with high availability of green electricity (e.g. in the case of strong solar radiation / strong winds). This also results in a 24-hour cycle, over which the carbon dioxide can be repeatedly stored and provided for the main operation.

[0015] In an alternative or additional development, part of the green electricity can be used to generate additional CO2 by separation from ambient air (direct air capture - DAC) by means of a separation device and added to the synthesis gas. Thus, in the H2 excess phase, i.e. in the phase with high availability of green electricity, an increased production of methanol can be achieved.

[0016] In addition, in a development, an H 2 store can be provided in order to achieve further flexibility in the H 2 supply to the methanol synthesis plant even in auxiliary operation.

[0017] Here, a system for producing methanol is also considered, the system having a HyGas generator for feeding a hydrogen separator, the hydrogen separator being configured to separate mainly hydrogen H2, the hydrogen being delivered to a methanol synthesis plant as synthesis gas, wherein the remaining portion from the hydrogen separator being delivered as residual gas to an oxyfuel burner and / or a converter and / or a generator, wherein the system is configured to deliver electrolytic hydrogen to the methanol synthesis plant in a primary operating mode. And no electrolysis occurs in a secondary operating mode. In addition, a control device or a regulating device is provided so that when the delivered electrolytic hydrogen is reduced, the residual gas flow from the hydrogen separator to the converter and in particular also to the oxyfuel burner is correspondingly reduced to start or increase the residual gas flow from the hydrogen separator to the generator. The electrolytic hydrogen is preferably obtained by electrolysis using electric current generated by solar or wind energy. The hydrocarbon flow from the hydrogen separator not only to the oxyfuel burner but also to the converter takes place in a predetermined ratio which is set or regulated such that a mixture of H2, CO and CO2 which is as pure as possible is conducted from the converter to the methanol synthesis plant which is also suitable for synthesis in a stoichiometric manner. The system is configured for carrying out the method according to the claim. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be described exemplarily below.

[0019] Figure 1 A flow chart showing the system in a first embodiment in a main operating mode, wherein the diagram is also used in a mixed form of operating mode,

[0020] Figure 2 A flow chart showing the system in a first embodiment in a secondary operating mode,

[0021] Figure 3 A flow chart showing the system in a second embodiment in a primary operating mode, wherein the diagram is also used in a mixed form of operating modes, and

[0022] Figure 4 A flow chart showing the system in a second embodiment in a secondary operating mode. DETAILED DESCRIPTION

[0023] In the following description of a preferred embodiment of the system for methanol synthesis, a primary operating mode and a secondary operating mode are described, which differ in particular in whether sufficient green electricity is supplied to the device for operating the electrolysis device and its individual components themselves. Green electricity is in particular current obtained by photovoltaics or wind power. Since photovoltaics only work during the day, the primary operating mode can alternatively also be called a "daytime operating mode", so that the secondary operating mode is called a "nighttime operating mode".

[0024] In principle, the two operating modes of the device are also different. That is, in the main operating mode, sufficient (regeneratively generated) current is delivered to achieve maximum methanol synthesis. In the operating mode, in principle, the maximum methanol synthesis is limited by the carbon gas content and / or oxygen content in the biogas 15 described below. In the secondary operating mode, the current generated by the regenerative technology is not delivered to the facility. Because non-regenerative current should preferably not be used, in the secondary operating mode, the system is suppressed so that methanol production is reduced, and instead, the main share of the biogas 15 generates current for the operation of the various components of the system in the generator 50. The term "generator" is a general concept for a variety of technical feasibility for obtaining current from organic matter. In particular, organic matter can be burned in a combustion chamber, whereby the liquid evaporates, thereby generating the desired current in the turbine.

[0025] exist Figure 1 In the diagram of , biomass 5 is fed to a HyGas generator 10 at the top left. The term "biomass" is to be understood as a general term and includes, for example, sewage sludge, but in particular also organic waste, for example biowaste such as green waste or pomace, fermentation residues from biogas plants and manure, but also waste from the food industry. In particular, due to sewage sludge regulations, the burning of sewage sludge is no longer permitted.

[0026] Rather, it even makes sense to refine the contained (or available) raw materials in order to create as much added value as possible, as this happens in the methanol production described below. An apparatus for treating wet organic matter with supercritical water at a pressure of more than 250 bar and a temperature of more than 600° C. is particularly referred to as a HyGas generator 10. Biogas 15 is decomposed here, which is a gas with a high methane-CH4- and hydrogen-H2-content. In addition, other (preferably short-chain) hydrocarbons are contained, such as, in particular, C2H6, but also CO, CO2. The HyGas generator 10 produces water 12 as a by-product, which is used here in part in the electrolysis but is not considered in detail. In particular or alternatively, the HyGas generator 10 can be an anaerobic fermenter.

[0027] The generated biogas 15 is fed to a hydrogen separator 20. There, components directly used in a methanol synthesis plant 80 are separated and fed to the methanol synthesis plant 80 as synthesis gas 25. The synthesis gas 25 is mainly hydrogen H2. For technical reasons, it may also contain a significant portion of carbon dioxide CO2. And if necessary, it may also contain other gases in a certain smaller amount.

[0028] The portion of the biogas 15 that cannot be further conducted as synthesis gas 25 is referred to below as residual gas 26 and is conducted to a regulator or switch 30. The regulator or switch is referred to below in simplified form as a "regulator". In the sense of regulation technology, this can be a control device or a regulation loop. In particular, this is a control device when the available green electricity is considered as a regulating variable. On the other hand, if the total amount of hydrogen supplied to the methanol synthesis plant 80 is considered as a regulating variable, this can be a regulating device, because the amount of hydrogen supplied to the methanol synthesis plant 80 via the converter 70 is changed depending on the regulation position. The regulator 30 divides the supplied residual gas (mass) flow 26 into two partial (mass) flows, wherein the division is different in different operating modes.

[0029] In the main operating mode, the system comprises an electrolysis device 40, which is preferably supplied with regeneratively generated electricity (photovoltaic, wind power) and in which water is decomposed into electrolytic hydrogen 45 and electrolytic oxygen. The electrolytic hydrogen 45 is directed directly to the methanol synthesis device 80. The electrolytic oxygen is supplied to the oxyfuel burner 60 or is derived from the system as required. The methanol synthesis device 80 produces the desired biomethanol and water as a waste product. In addition, residual gas 55 remains, which cannot be used here and is supplied to the generator 50 in the return. The generator 50 burns the gas supplied to it and thereby generates current and heat, which are supplied to different components of the system for their own part, where corresponding requirements exist.

[0030] As already mentioned, in the regulator 30 the supplied residual gas 26 is divided into partial (mass) flows in specific ratios corresponding to its control position. Figure 1 and Figure 2 The width of the arrows schematically indicates the division ratio in the primary operation mode or the secondary operation mode. Figure 1 In the main operating mode of the present invention, a larger portion (in particular, optionally completely 100%) enters the treatment device including the oxyfuel burner 60 and the reformer 70. From the treatment device 60, 70, a corresponding mass flow is conducted as additional synthesis gas 72 to the methanol synthesis device 80. The residual gas 26 conducted to the treatment device 60, 70 is divided between the oxyfuel burner 60 and the reformer 70 in a specific ratio within the treatment device 60, 70. The ratio is determined so that the best possible stoichiometric synthesis of methanol is achieved in the methanol synthesis plant 80. The determination of the ratio can be carried out automatically via a control loop (not shown).

[0031] The oxyfuel burner 60 is operated with pure oxygen, but in a substoichiometric amount, and its output products are, in particular, water and CO2, which are directed to the reformer 70. The reformer 70 also receives a share of the residual gas 26, and a conversion process takes place in the reformer. The endothermic process is supplied with heat from the oxyfuel burner 60 and / or the generator 50. The product gas of the reformer 70 is H2, CO and CO2 and is supplied as further synthesis gas 72 to a methanol synthesis unit 80.

[0032] exist Figure 2 , a secondary operating mode is shown in which no hydrogen is produced from the electrolysis and supplied to the methanol synthesis plant 80. Since the production of methanol in the methanol synthesis plant 80 is thereby reduced, the demand for synthesis gas 25 and 72 is also reduced, wherein the CO2 demand is particularly reduced. Therefore, in particular, a portion of the synthesis gas 25 separated (or separable) in the hydrogen separator 20 is not supplied to the methanol synthesis plant 80, but is introduced into the flow of the residual gas 26. In other words, preferably only a reduced flow of the synthesis gas 25 is separated from the biogas 15. The corresponding portion is derived from the demand of the methanol synthesis plant 80.

[0033] In the secondary operating mode, a larger portion of the residual gas 26, which may be changed in this way, is passed as generator gas 52 to the generator 50, such as by Figure 2 The width of the arrow is shown. There, the generator gas is burned in order to thereby generate current and heat, which are used in the components of the system with corresponding requirements. As a result, the need for non-regeneratively obtained current can be reduced or avoided for the entire system for methanol synthesis. The heat generated here is also directed to the corresponding components of the system in a similar manner to the oxyfuel burner 60.

[0034] Depending on the specific gas composition, it is possible to direct the portion of the residual gas 26 that is to be prepared only to the reformer 70, so that in this case no oxyfuel burner 60 is required. Alternatively, the portion directed to the treatment devices 60, 70 can also be set to zero. The latter occurs when the volume flow of the synthesis gas 25 is sufficient for the methanol synthesis plant 80. The portion of the synthesis gas 25 that is not used for synthesis is supplied to the generator 50 as recirculated gas 55 and is used thermally.

[0035] Thus, the regulator 30 can supply 100% of the residual gas 26 to the generator 50. On the other hand, in the secondary operating mode, there is no state in which 100% of the residual gas 26 is supplied to the processing devices 60, 70. This state, that is to say a state in which the generator 50 is not supplied with residual gas 26, is possibly meaningful in the main operating mode. However, even in the main operating mode, the generator 50 is always used, because the returned gas 55 is used thermally in the generator. The intermediate stage is also (preferably steplessly) adjustable. As an alternative to the intermediate stage, a corresponding complete change of the operating mode is also possible.

[0036] Alternatively, an oxygen reservoir 62 can also be used. When the system is operated in the primary operating mode during the day with photovoltaic current, an excess of electrolytic oxygen is typically produced. The excess is obtained as the difference between the oxygen obtained by electrolysis and the oxygen demand of the oxyfuel burner 60. The excess can be stored in the oxygen reservoir 62 for the secondary operating mode during the night, so that the oxyfuel burner 60 can also be operated at night. That is, the oxyfuel burner 60 must be operated with pure oxygen in order to ensure its functionality and to ensure that no foreign gases, such as nitrogen, are supplied to the methanol synthesis plant 80.

[0037] Figure 3 and Figure 4 A second embodiment of a flow chart showing the primary mode of operation and the secondary mode of operation, respectively. The embodiment differs from the embodiment in only one respect. Figure 1 and Figure 2 , only this aspect is discussed below. According to a further embodiment of the flow diagram, in the case of high availability of green electricity, i.e. for example in the case of strong solar radiation, part of the flow is used in the separation device 64 to separate carbon dioxide from the ambient air (direct air capture) and added to the synthesis gas 25. As a result, the production of excess hydrogen in the methanol synthesis plant 80 can be prevented in the phase of excess green electricity. Alternatively, the excess green electricity can be used to produce additional carbon dioxide in order to maximize the methanol production.

[0038] Alternatively or in addition thereto, a CO2 storage 63 can also be used, which is filled with excess carbon dioxide in the auxiliary operation, which carbon dioxide can be added to the synthesis gas 25 again during the main operation in the excess green electricity phase. In this case, the regulator 30 controls the filling and emptying of the CO2 storage 63 and the supply of green electricity to the separation device 64.

Claims

1. A method for producing methanol, The synthesis gas (25) obtained from the biomass (5) is fed to a methanol synthesis plant (80), wherein In the main operating mode, in which sufficient current is available for the electrolytic production of hydrogen, the electrolytically produced hydrogen (45) is accordingly fed to the methanol synthesis plant (80), And in which, in a secondary operating mode in which insufficient current is available for the electrolytic production of hydrogen (45), residual gas (26) obtained when separating the synthesis gas (25) from the biogas (15) obtained from the biomass (5) is fed to a generator (50) in order to provide current for the devices (10, 20, 30, 40, 70, 80) involved in the method.

2. A method according to claim 1, wherein at least in the main operating mode, and preferably also in the secondary operating mode, the residual gas (26) obtained when separating the synthesis gas (25) from the biogas (15) produced from the biomass (5) is supplied to a processing device (60, 70) in order to generate additional synthesis gas (72) which is also supplied to the methanol synthesis plant (80).

3. A method according to claim 2, wherein in the treatment device, the residual gas (26) is supplied to an oxy-fuel burner (60) and a converter (70) in a specific ratio, wherein oxidation is carried out in the oxy-fuel burner (60), and the oxidized gas is also supplied to the converter (70), and the converter (70) uses the gas to perform processing, i.e., in particular reduction, so that the gas can be supplied to the methanol synthesis plant (80) as additional synthesis gas (72).

4. A method according to any one of claims 1 to 3, wherein a switch is made between the primary operating mode and the secondary operating mode depending on the available green electricity or available hydrogen (45), or a mixed form of operating modes is used, wherein these mixed forms differ in the proportion of residual gas (26) delivered to the generator (50) or the treatment device (60, 70).

5. The method according to any of the preceding claims, wherein the residual gas flow (26) is divided into two partial flows (52, 71), which are directed to the generator (50) or the treatment device (60, 70).

6. The method according to claim 4 or 5, wherein the conversion or division is automatically performed according to the current available for electrolysis or the amount of hydrogen (45) of the methanol synthesis unit (80).

7. A method according to any of the preceding claims, wherein in the primary operating mode and in the secondary operating mode, biogas (15) is produced from biomass (5), and synthesis gas (25) is separated from the biogas (15) in a hydrogen separator (20), the synthesis gas comprising hydrogen H2 and in particular also carbon dioxide CO2.

8. A method according to any of the preceding claims, wherein the process heat generated by the generator (50) and / or the oxyfuel burner (60) is directed to a HyGas generator (10) for producing the biogas (15) and / or to a converter (70).

9. The method according to claim 1 , comprising a reservoir (62) for oxygen, wherein in the primary operating mode the reservoir (62) is filled with oxygen obtained by electrolysis and the oxygen is used in the secondary operating mode for operating the oxyfuel burner (60).

10. A method according to any of the preceding claims, comprising a storage tank (63) for CO2, wherein in the secondary operating mode the storage tank (63) can be filled with CO2 obtained from the synthesis gas (25), and the stored CO2 can be used for methanol synthesis in the main operating mode.

11. The method according to any of the preceding claims, wherein a portion of the green electricity is used to produce additional CO2 by separation from ambient air (direct air capture DAC) by means of a separation device (64) and added to the synthesis gas (25).

12. A system for producing methanol, the system comprising a HyGas generator (10) for feeding a hydrogen separator (20), the hydrogen separator being configured to separate mainly hydrogen H2, which can be supplied as synthesis gas (25) to a methanol synthesis plant (80), wherein the remaining portion from the hydrogen separator (20) can be supplied as residual gas (26) to an oxyfuel burner (60) and / or a converter (70) and / or a generator (50), wherein The system is configured to supply electrolytic hydrogen (45) to the methanol synthesis plant (80) in a main operating mode, and configured to switch to a secondary operating mode in which no electrolytic hydrogen (45) is supplied, It is characterized in that A regulating device (30) is provided, which is configured to start or increase the residual gas flow (26, 52) from the hydrogen separator (20) to the generator (50) by, in particular, correspondingly reducing the residual gas flow (26, 72) from the hydrogen separator (20) to the converter (70) and preferably also to the oxyfuel burner (60) when the hydrogen supplied to the methanol synthesis plant (80), in particular the electrolytic hydrogen (45), is reduced.

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