Methanol production from biomass and green hydrogen

Description

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

[0002] EP 3 452 438 B1 discloses a process for the production of bio-methanol in which electrolytically produced hydrogen and organic waste materials are added. Furthermore, EP 3 017 015 B1 discloses the use of steam crackers in a first step of biomass processing to break down a hydrocarbon-containing feedstock into shorter chains. Such processes and devices focus on carrying out the chemical conversions from provided input materials, such as biomass and hydrogen, as efficiently as possible. Typically, they do not consider that in some cases the feedstocks for the conversions might not be sufficiently available and / or that there may be fluctuations in the quantity or timing of the feedstocks' availability. Furthermore, the aim is to reduce or eliminate the need for non-renewably generated electricity for the overall methanol synthesis system.

[0003] The present invention addresses this problem. The features of the independent claims describe inventive advantages. Preferred embodiments are the subject of the dependent claims.

[0004] In a process for producing methanol, synthesis gas is obtained from biomass and fed into a methanol synthesis unit. In a primary operating mode, when sufficient electricity is available for electrolytic hydrogen production, the resulting electrolytically produced hydrogen is supplied to the methanol synthesis unit. In a secondary operating mode, when insufficient electricity is available for electrolytic hydrogen production, a residual gas, obtained during the separation of the synthesis gas from biogas derived from the biomass, is fed to a generator to produce electricity for equipment involved in the process. This residual gas is therefore the difference between the biogas produced and the synthesis gas, which has been separated in such a way that it can be used directly in the methanol synthesis unit.In secondary operating mode, electrolysis is specifically not carried out. The term "electricity for electrolytic hydrogen production" refers specifically to electricity generated from renewable sources, such as photovoltaics or wind power. However, other electricity sources, such as nuclear power, are also included.

[0005] A standard methanol synthesis unit converts synthesis gas (H₂ and CO) into methanol. In this particular case, however, predominantly CO₂ is fed into the process instead of CO. The synthesis unit operates with a recirculation pump / blower, which returns the unconverted feedstocks to the synthesis. The synthesis produces methanol and water. Since small amounts of contaminants, foreign gases, or inert gases are always introduced into the process along with the feed gases, a purge gas stream is necessary to prevent the accumulation of these gases and thus avoid compromising the efficiency of the synthesis process. The process is exothermic, and the resulting heat can be used in other parts of the plant (for preheating the distillation or the HyGas process). The outgoing gases from the purge gas stream can be used by various components of the system, such as the generator or the oxyfuel burner.

[0006] On the one hand, the amount of biogas in a bioreactor, particularly in a HyGas generator, cannot be easily varied over time, resulting in a largely constant biogas flow. On the other hand, the amount of photovoltaic electricity fluctuates depending on the time of day, leading to fluctuations in the (daily) ratio of these inputs for methanol synthesis. Due to the two operating modes of the inventive process described above (combined with intermediate stages), it is possible to obtain the maximum possible amount of methanol at any given time while simultaneously reducing the overall amount of non-green electricity required.Although the amount of methanol produced in the secondary operating mode, i.e., when there is a shortage of green electricity, is significantly reduced compared to the main operating mode, the supply of residual gas from biomass utilization to the generator still makes it possible to carry out the synthesis without having to resort to non-green electricity.

[0007] It is advantageous if, at least in the main operating mode and preferably also in the secondary operating mode, a residual gas resulting from the separation of synthesis gas from biogas produced from biomass is fed into a processing unit to generate further synthesis gas, which is then also fed into the methanol synthesis plant. The methanol synthesis plant requires simple chemical compounds, such as H₂ and CO₂, which are initially separated from the biogas in a first step. To obtain a high yield of synthesis gas from the biogas, the remaining components, i.e., the residual gas, are converted in the described second step so that it can be used as "further synthesis gas."

[0008] During processing, it is particularly advantageous if the residual gas is fed in a specific ratio to an oxyfuel burner and a reformer. Oxidation is carried out in the oxyfuel burner, and the oxidized gas is fed to the reformer. The reformer then processes these gases, particularly by reducing them, to supply them as the further synthesis gas to the methanol synthesis unit. This processing method can also be used in secondary operation. An oxyfuel burner is, in particular, a burner unit that combusts hydrocarbons and other gases to generate heat. In this specific case, the gas is combusted with pure oxygen to avoid the introduction of, for example, nitrogen from the air. The combustion air-fuel ratio is substoichiometric to produce an oxygen-free exhaust gas stream, which can then be used as a reactant in subsequent process steps.A reformer is a chemical unit that converts hydrocarbons into hydrogen and carbon dioxide / carbon monoxide. The process is endothermic and therefore requires an external heat source.

[0009] Furthermore, it is advantageous if the system can switch between primary and secondary operating modes depending on the available green electricity or hydrogen (the system is designed to perform this switching), or if hybrid operating modes are used, with the hybrid modes differing, for example, in the ratio of residual gas that is fed either to the generator or the processing unit. The amount of available green electricity is particularly suitable as a criterion for switching (or proportionally adjusting or regulating), as it is easy to measure. The amount of electrolytically produced hydrogen is proportional to the green electricity, so this electrolysis hydrogen can also be used as a criterion.Ultimately, the total amount of hydrogen present in the methanol synthesis system is a crucial criterion for controlling the switching between the two operating modes. This control is also dependent on the synthesis gas, which can vary depending on the quality of the feedstock. Since this is also influenced by the hydrogen content in the synthesis gas (or gases), this quantity can alternatively be used as a criterion for switching between modes.

[0010] Additionally, it is advantageous if the switching between operating modes or the adjustment of the ratio between operating modes occurs automatically depending on the electricity available for electrolysis or the amount of available hydrogen, as well as the C / H ratio of the synthesis / biogas, thus creating an autonomously operating system that does not require regular intervention by a control person. Therefore, the system is preferably configured to switch between operating modes (preferably automatically) depending on the electricity available for electrolysis or the amount of available hydrogen.

[0011] It is also advantageous if biogas is produced from biomass in both the primary and secondary operating modes, and synthesis gas, comprising hydrogen (H2) and, in particular, carbon dioxide (CO2), is separated from the biogas in a hydrogen separator. This illustrates how synthesis gas can be obtained from biomass. A hydrogen separator essentially comprises a membrane unit that separates hydrogen (and, if applicable, hydrogen and CO2) from a gas stream. Besides membrane solutions, other technologies such as pressure swing adsorption or similar methods are also conceivable.

[0012] Furthermore, it is advantageously considered that process heat generated by the generator and / or the oxyfuel burner, as well as the methanol synthesis, is directed to a HyGas generator for biogas production and / or to the reformer and / or to the methanol distillation or synthesis. This is advantageous because the components requiring heat are thus directly supplied with the generated process heat.

[0013] In a further training project, an oxygen storage system is provided. During primary operation, the storage system is filled with electrolytically generated oxygen, while during secondary operation, this oxygen is used to power the oxyfuel burner. The oxyfuel burner typically requires pure oxygen for operation. This allows the oxyfuel burner to be used effectively even during secondary operation, i.e., during periods without electrolysis oxygen generation. This results in 24-hour cycles over which the oxygen can be iteratively stored and made available for secondary operation.

[0014] In a further development project, a CO2 storage system is provided. In secondary operating mode, the storage system can be filled with CO2 recovered from synthesis gas, and in primary operating mode, the stored carbon dioxide can be used for methanol synthesis. This allows for increased hydrogen production during periods of high availability of green electricity (e.g., during intense solar radiation or high winds) during primary operation. This also results in 24-hour cycles over which the carbon dioxide can be iteratively stored and made available for primary operation.

[0015] In an alternative or additional training process, a portion of the green electricity can be used to generate additional CO2 by capturing it from the ambient air (Direct Air Capture - DAC) using a capture device and adding it to the synthesis gas. This allows for an increased methanol yield during periods of high H2 surplus, i.e., periods with high availability of green electricity.

[0016] Additionally, a further training course can provide an H2 storage system to generate further flexibility in the H2 supply for methanol synthesis, even during secondary operation.

[0017] This document also considers a system for the production of methanol, featuring a hydrogen gas generator to feed a hydrogen separator designed primarily to separate hydrogen (H₂). This hydrogen is then fed as synthesis gas to a methanol synthesis device. Remaining components from the hydrogen separator are supplied as residual gas to an oxyfuel burner and / or a reformer and / or a generator. The system operates in a primary mode, supplying electrolysis hydrogen to the methanol synthesis device. In a secondary mode, no electrolysis occurs. Furthermore, a control system is provided to initiate or increase the residual gas flow from the hydrogen separator to a generator when the supply of electrolysis hydrogen decreases. This is achieved by correspondingly reducing the residual gas flow from the hydrogen separator to the reformer and, in particular, to the oxyfuel burner.The electrolysis hydrogen is preferably obtained by electrolysis using electricity generated from solar or wind energy. The hydrocarbon flow from the hydrogen separator to both the oxyfuel burner and the reformer occurs in a predetermined ratio, which is set and regulated so that the reformer delivers the purest possible mixture of H₂, CO, and CO₂ to the methanol synthesis apparatus, a mixture that is also stoichiometrically suitable for synthesis. The system is configured to carry out the required processes.

[0018] The invention is described below by way of example. The following are shown. Fig. 1: a flow diagram of the system in a first embodiment of the main operating mode, wherein this diagram is also used for mixed forms of the operating modes, Fig. 2: a flow diagram of the system in a first embodiment of a secondary operating mode, Fig. 3: a flow diagram of the system in a second embodiment of the main operating mode, wherein this diagram is also used for mixed forms of the operating modes, and Fig. 4: a flow diagram of the system in a second embodiment of the secondary operating mode.

[0019] The following description of preferred embodiments of a methanol synthesis system describes a primary and a secondary operating mode, which differ in particular in whether the device is supplied with sufficient green electricity for operation from an electrolysis unit, and in the individual components of the electrolysis unit itself. Green electricity is, in particular, electricity generated by photovoltaics or wind power. Since photovoltaics only operate during the day, the primary operating mode can alternatively be referred to as "daytime operation" and the secondary operating mode consequently as "nighttime operation".

[0020] Basically, two operating modes of the device are distinguished. In the main operating mode, sufficient (regeneratively generated) electricity is supplied to enable maximum methanol synthesis. In this mode, this maximum methanol synthesis is fundamentally limited by the carbon and / or oxygen content in the biogas 15 described below. In the secondary operating mode, no electricity generated by renewable technologies is supplied to the system. Since non-renewable electricity is preferably not used, the system is throttled in the secondary operating mode to reduce methanol production, and instead, a significant portion of the biogas 15 generates electricity in a generator 50 to power the individual components of the system. The term "generator" is a generic term for a variety of technical possibilities for generating electricity from organic substances.In particular, the organic substances can be burned in a combustion chamber, causing a liquid to evaporate and thus generating the desired electricity in a turbine.

[0021] In the top left of the diagram, the Fig. 1Biomass is fed into a HyGas generator 10. The term "biomass" is understood as a general term and includes, for example, sewage sludge, but especially also organic waste, such as organic waste like green waste or pomace, digestate from biogas plants and liquid manure, but also waste from the food industry. Particularly due to the sewage sludge ordinance, it is no longer permitted to incinerate sewage sludge. Rather, it is even more sensible to refine the contained (or recoverable) raw materials in a way that creates added value, as is done in the methanol production described below. HyGas generators 10 are specifically devices that treat a wet organic mass with supercritical water at a pressure of more than 250 bar and a temperature of over 600°C. Biogas 15 is separated in this process, which is a gas with a high methane (CH4) and hydrogen (H2) content.Furthermore, other (preferably short-chain) hydrocarbons are present, such as C₂H₆, but also CO and CO₂. As a byproduct, the HyGas generator 10 produces water 12, which, apart from its partial use in electrolysis, will not be considered in detail here. In particular, or alternatively, the HyGas generator 10 can be an anaerobic fermenter.

[0022] The biogas produced 15 is fed to a hydrogen separator 20. There, components that can be used directly in the methanol synthesis device 80 are separated and fed to the methanol synthesis device 80 as synthesis gas 25. The synthesis gas 25 consists primarily of hydrogen H₂. For technical reasons, it may also contain a significant proportion of carbon dioxide CO₂. Other gases may also be present in certain smaller quantities.

[0023] The portion of the biogas 15 that cannot be further processed as synthesis gas 25 is subsequently referred to as residual gas 26 and is directed to a controller or switch 30. For simplicity, this will be referred to as the "controller" in the following. In terms of control engineering, this can be either a control system or a closed-loop control system. It is a control system, in particular, if the available green electricity is used as the manipulated variable. If, on the other hand, the total amount of hydrogen supplied to the methanol synthesis device 80 is used as the manipulated variable, it can be a control system, since the amount of hydrogen supplied to the methanol synthesis device 80 via a reformer 70 changes depending on the controller setting. The controller 30 divides the supplied residual gas (mass) flow 26 into two partial (mass) flows, with the division differing depending on the operating mode.

[0024] In its main operating mode, the system comprises an electrolysis unit 40, preferably powered by regeneratively generated electricity (photovoltaics, wind power), in which water is split into electrolytic hydrogen 45 and electrolytic oxygen. The electrolytic hydrogen 45 is fed directly to the methanol synthesis unit 80. The electrolytic oxygen is supplied to an oxyfuel burner 60 as needed or discharged from the system. The methanol synthesis unit 80 produces the desired biomethanol and water as a byproduct. Furthermore, residual gases 55 remain, which cannot be used here and are fed back to a generator 50. The generator 50 combusts the supplied gases, thereby generating electricity and heat, which are in turn supplied to various components of the system where there is a corresponding demand.

[0025] As already mentioned, in the regulator 30 the supplied residual gas 26 is divided into partial (mass) flows in a specific ratio according to its control setting. The width of the arrows of the Fig. 1 and 2 This schematically expresses the distribution ratio for the main and secondary operating modes. Accordingly, in the main operating mode, the Fig. 1A larger proportion (optionally 100%) of the gas is fed into a processing unit comprising an oxyfuel burner 60 and a reformer 70. A corresponding mass flow from the processing unit 60, 70 is supplied as a further synthesis gas 72 to the methanol synthesis unit 80. The residual gas 26 fed into the processing unit 60, 70 is divided within the unit between the oxyfuel burner 60 and the reformer 70 in a specific ratio. This ratio is determined to ensure the best possible stoichiometric synthesis of methanol in the methanol synthesis unit 80. The determination of this ratio can be automated via a control loop (not shown).

[0026] The oxyfuel burner 60 is operated with pure oxygen, but substoichiometrically, and its feedstocks are primarily water and CO₂, which are fed to the reformer 70. The reformer 70 also receives a portion of the residual gas 26, and conversion processes take place within it. These endothermic processes are supplied with heat from the oxyfuel burner 60 and / or the generator 50. The product gases of the reformer 70 are H₂, CO, and CO₂, and are fed as further synthesis gas 72 to the methanol synthesis 80.

[0027] In Fig. 2The auxiliary operating mode is shown in which no hydrogen is produced from electrolysis and supplied to the methanol synthesis device 80. Since this reduces methanol production in the methanol synthesis device 80, the demand for synthesis gases 25 and 72 also decreases, particularly the CO₂ demand. Thus, a portion of the synthesis gas 25 separated (or separable) in the hydrogen separator 20 is not supplied to the methanol synthesis device 80, but rather introduced into the residual gas stream 26. In other words, preferably only a reduced stream of synthesis gas 25 is separated from the biogas 15. The respective proportion is determined by the demand of the methanol synthesis device 80.

[0028] In the auxiliary operating mode, a larger proportion of the potentially modified residual gas 26 is directed to the generator 50 as generator gas 52, as indicated by the width of the arrow. Fig. 2As indicated, the fuel is burned to generate electricity and heat, which are then used by the system components that require it. This reduces or eliminates the need for non-renewable electricity in the overall methanol synthesis system. The resulting heat is also transferred to the relevant system components, similar to the Oxyfuel Burner 60.

[0029] Depending on the specific gas composition, it may be possible that the portion of the residual gas 26 to be processed is only directed to the reformer 70, so that the oxyfuel burner 60 is not required in this case. Alternatively, the portion directed to the processing units 60, 70 can be set to zero. The latter occurs when the volume flow of the synthesis gas 25 is sufficient for the methanol synthesis unit 80. Portions of the synthesis gas 25 that are not used for synthesis are fed back to the generator 50 as recycled gases 55 and thermally utilized.

[0030] The regulator 30 can therefore supply 100% of the residual gas 26 to the generator 50. Conversely, in the secondary operating mode, there is no condition where 100% of the residual gas 26 is supplied to the processing unit 60, 70. This condition, i.e., where the generator 50 is not supplied with residual gas 26, is only relevant in the primary operating mode. Even in the primary operating mode, the generator 50 is always used, as the recirculated gases 55 are thermally utilized within it. Intermediate stages are also adjustable (preferably continuously). Alternatively, a complete switch between operating modes is also possible.

[0031] An optional oxygen storage unit 62 can also be used. When the system is operated in its primary operating mode during the day using photovoltaic power, a surplus of electrolysis oxygen is typically generated. This surplus is the difference between the electrolytically produced oxygen and the oxygen demand of the oxyfuel burner 60. This surplus can be stored in the oxygen storage unit 62 for the secondary operating mode during the night, allowing the oxyfuel burner 60 to operate even at night. The oxyfuel burner 60 must be operated with pure oxygen to ensure its proper function and to prevent foreign gases, such as nitrogen, from entering the methanol synthesis device 80.

[0032] Figures 3 and 4Each shows a second embodiment of a flowchart for the main and secondary operating modes. This embodiment differs from the one in the only aspect. Figure 1 and 2 The process flow diagram shown, of which only this aspect will be discussed below. According to the further embodiment of the process flow diagram, when green electricity is highly available, e.g., during intense sunlight, a portion of the electricity is used in a capture device 64 to capture carbon dioxide from the ambient air (direct air capture) and add it to the synthesis gas 25. This prevents an excess of hydrogen from forming in the methanol synthesis device 80 during periods of surplus green electricity. Instead, the surplus green electricity can be used to generate further carbon dioxide in order to maximize the methanol yield.

[0033] Alternatively or additionally, a CO2 storage unit 63 can be used, which is filled with excess carbon dioxide during secondary operation. This excess carbon dioxide can then be added back to the synthesis gas 25 during main operation, in phases of excess green electricity. The controller 30 controls the filling and emptying of the CO2 storage unit 63 and the supply of green electricity to the separation device 64.

Claims

1. Process for producing methanol, in which a synthesis gas (25) that has been recovered from biomass (5) is fed to a methanol synthesis apparatus (80), wherein in a main operating mode in which sufficient electrical power is available for electrolytic hydrogen recovery, correspondingly electrolytically recovered hydrogen (45) is fed to the methanol synthesis apparatus (80), and wherein, in a secondary operating mode in which insufficient electrical power is available for electrolytic production of hydrogen (45), a tail gas (26) that arises from a biogas (15) recovered from the biomass (5) on removal of the synthesis gas (25) is fed to a generator (50) in order to provide electrical power for apparatuses (10, 20, 30, 40, 70, 80) involved in the process.

2. Process according to Claim 1, wherein, at least in the main operating mode, and preferably also in the secondary operating mode, a tail gas (26) that arises from a biogas (15) produced from biomass (5) on removal of the synthesis gas (25) is fed to a processing operation (60, 70) in order thereby to produce further synthesis gas (72) which is also fed to the methanol synthesis apparatus (80).

3. Process according to Claim 2, wherein, in the processing operation, the tail gas (26) is fed in a particular ratio to an oxyfuel burner (60) and a reformer (70), wherein an oxidation is conducted in the oxyfuel burner (60) and the oxidized gas is likewise fed to the reformer (70), and the reformer (70) conducts a processing operation with these gases, namely a reduction in particular, in order to be able to supply it as a further synthesis gas (72) to the methanol synthesis apparatus (80).

4. Process according to any of Claims 1 to 3, wherein the system switches between the main operating mode and secondary operating mode depending on the available green power or the available hydrogen (45), or mixed forms of the operating modes are used, wherein the mixed forms differ in the ratio of the tail gas (26) that is fed either to the generator (50) or to the processing operation (60, 70).

5. Process according to any of the preceding claims, in which the tail gas stream (26) is divided into two substreams (52, 71) that are passed to the generator (50) or a processing operation (60, 70).

6. Process according to Claim 4 or 5, wherein the switchover or division takes place in an automated manner depending on the current available for the electrolysis or the amount of hydrogen (45) from the methanol synthesis apparatus (80).

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

8. Process according to any of the preceding claims, in which process heat which is generated by the generator (50) and / or the oxyfuel burner (60) is passed to a HyGas generator (10) for generation of the biogas (15) and / or to a reformer (70).

9. Process according to any of the preceding claims, having a storage means (62) for oxygen, wherein, in the main operating mode, the storage means (62) is filled with electrolytically recovered oxygen, and the oxygen is used in the secondary operating mode for operation of the oxyfuel burner (60).

10. Process according to any of the preceding claims, having a storage means (63) for CO2, wherein, in the secondary operating mode, the storage means (63) can be filled with CO2 recovered from the synthesis gas (25), and the stored CO2 can be utilized in the main operating mode for methanol synthesis.

11. Process according to any of the preceding claims, wherein a portion of the green power is used to produce additional CO2 by separation from ambient air (direct air capture - DAC) by means of a separation apparatus (64) and to add it to the synthesis gas (25).

12. System for production of methanol, having a HyGas generator (10) for feeding a hydrogen separator (20) set up to separate hydrogen H2 in particular, which is feedable as synthesis gas (25) to a methanol synthesis apparatus (80), wherein remaining fractions from the hydrogen separator (20) may be fed as a tail gas (26) to an oxyfuel burner (60) and / or a reformer (70) and / or a generator (50), wherein the system is set up, in a main operating mode, to feed electrolysis hydrogen (45) to the methanol synthesis apparatus (80), and is set up to switch to a secondary operating mode in which no electrolysis hydrogen (45) is supplied, characterized in that a controller (30) is provided, which is configured to start or to increase a tail gas stream (26, 52) from the hydrogen separator (20) to a generator (50) in the event of a reduction in the hydrogen fed to the methanol synthesis apparatus (80), especially the electrolysis hydrogen (45), especially by correspondingly reducing a tail gas stream (26, 72) from the hydrogen separator (20) to the reformer (70) and preferably also the oxyfuel burner (60).