Process and plant for the production of methanol from a carbon-containing feedstock

Abstract

The invention relates to a process for producing methanol from a carbon-containing feedstock. In a process where efficiency and energy use are optimized, at least the following steps are included: processing of at least one carbon-containing feedstock (2); gasification in a gasifier (3) or pyrolysis in a pyrolysis furnace of the processed carbon-containing feedstock to obtain a crude synthesis gas; processing of the crude synthesis gas (4) to obtain a synthesis gas; methanol synthesis (5) to obtain crude methanol; expansion of the crude methanol in a low-pressure separator (7); distillation of the expanded crude methanol to obtain methanol and an overhead product; extraction of a partial stream from the methanol synthesis (5) and feeding at least a part of the partial stream to the processing of the carbon-containing feedstock.

Description

[0001] The invention relates to a process for producing methanol from a carbon-containing feedstock.

[0002] In addition, the invention relates to a plant for the production of methanol from a carbon-containing feedstock.

[0003] Methanol is produced through an exothermic reaction that uses hydrogen and carbon oxides as reactants, which are fed as a gas stream into a suitable reactor for methanol synthesis. These substances can be obtained from various sources.

[0004] One approach involves subjecting a carbon-containing energy carrier stream to steam reforming or catalytic partial oxidation, resulting in a synthesis gas consisting primarily of hydrogen and carbon oxides. Depending on the type of energy carrier and the synthesis gas production method, different proportions of hydrogen and carbon oxides—and thus different stoichiometry—are achieved in the synthesis gas. The resulting stoichiometry can then be adjusted through various measures, such as a water-gas shift reaction. An advantage of this approach is that the energy carrier itself—e.g., natural gas—can typically be supplied at high pressure, meaning that only a relatively small pressure increase is required after synthesis gas production to reach the pressure necessary for methanol synthesis.

[0005] Another way to provide the reactants for methanol synthesis is to use a gas stream with a high carbon dioxide content and no hydrogen. Such a gas stream can be obtained, for example, from flue gas, i.e., exhaust gas from a combustion process. Similarly, such a gas stream could be obtained from a bioethanol production plant. Since such flue gas contains no hydrogen, the hydrogen in this variant must be supplied from another source, such as electrolysis. For methanol synthesis, the gas containing the reactants is typically circulated in a closed loop, as a single pass of this gas through the reactor usually does not result in sufficiently complete conversion to methanol.

[0006] The methanol consumed is regularly removed from the circulating gas by condensation. However, inert substances also accumulate during circulation, and these cannot be sufficiently removed by condensation. To remove these substances from the cycle, it is necessary to discharge a portion of the circulating gas as purge gas, which can then be, for example, combusted.

[0007] Future-oriented processes and plants utilize an organic substance, such as biomass, which is gasified to synthesize methanol. Various approaches exist for this. Compared to plants for synthesizing methanol from fossil fuels, these plants and processes require more complex pretreatments and gas purification.

[0008] In a typical methanol plant, gasification is carried out using steam and oxygen. The reason for using steam is that the biomass undergoes thermal decomposition, and the steam reacts with the carbon from the organic matter to form hydrogen. Methanol synthesis takes place under high pressure, and if air is used for the synthesis, the nitrogen it contains increases the power required and also reduces the efficiency of the methanol synthesis. Therefore, the use of oxygen is preferred.

[0009] Conventional plants that have so far operated without biomass or comparable carbon-containing feedstocks are only conditionally competitive in terms of cost as plant systems for the synthesis of methanol specifically from biomass.

[0010] The invention is therefore based on the objective of providing a process and a plant for the production of methanol from a carbon-containing feedstock, in particular biomass or a comparable carbon-containing feedstock, in which efficiency and energy use are optimized.

[0011] This problem is initially solved in the present invention by the features of claim 1 in that the process comprises at least the following steps: processing of at least one carbon-containing feedstock; gasification in a gasifier and / or pyrolysis in a pyrolysis furnace of the processed carbon-containing feedstock to obtain a crude synthesis gas; processing of the crude synthesis gas to obtain a synthesis gas; methanol synthesis to obtain crude methanol; distillation of the crude methanol to obtain methanol and an overhead product; withdrawal of a partial stream from the methanol synthesis and feeding at least a part of the partial stream to the processing of the carbon-containing feedstock.

[0012] A carbon-containing feedstock is understood to mean, in particular, carbon-containing solids and / or carbon-containing liquids. Preferably, the carbon-containing feedstock is biomass. Particularly preferably, the carbon-containing feedstock is waste, for example, household waste, plastics, etc.

[0013] Accordingly, the processing of the carbon-containing feedstock can be designed in various ways, and it is clear to those skilled in the art that the processing can and must differ for different feedstocks. The processing can include steps such as drying and / or comminution of the carbon-containing feedstock. Torrefaction is another option for processing, for example, biomass or solids. A further possibility would be a type of carbonization.

[0014] Depending on how the gasification and / or pyrolysis of the processed carbonaceous feedstock takes place, the processing must be adapted accordingly. With a fluidized bed gasifier, it is generally necessary to break down the structure of the carbonaceous material to achieve an acceptable result. With fixed-bed or fluidized bed gasifiers, the processing is usually less complex.

[0015] Methanol synthesis takes place in a suitable reactor system. Adiabatic and quasi-isothermal reactors are the most common. In adiabatic reactors with a single catalyst bed, the reaction is quenched at multiple points by the addition of cold gas. The temperature profile along the reactor axis is therefore sawtooth-shaped. In reactors where the synthesis gas flows through several axially arranged reactor layers, the heat of reaction is removed by intercoolers. In these reactors, the synthesis gas flows axially, radially, or axially / radially through the catalyst beds.

[0016] The standard quasi-isothermal reactor consists of a tubular reactor cooled by water. The catalyst is located in tubes surrounded by water at its boiling point to dissipate the heat of reaction. The temperature of the cooling medium is controlled by a preset pressure in the steam drum. The synthesis gas flows axially through the tubes.

[0017] It is also possible to connect several reactors in series, which together form a facility for methanol synthesis.

[0018] In the first column of the distillation section of a methanol plant, primarily volatile, dissolved components such as carbon oxides, methane, and hydrogen are drawn off overhead from the crude methanol. This overhead product can then be used as fuel gas. However, it contains a large amount of CO2, which limits its calorific value, as well as many volatile components whose combustion leads to significant CO2 emissions. Furthermore, the overhead product contains a larger quantity of methanol.

[0019] The crude methanol leaving the reactor contains water and other impurities. The amount and composition of these impurities depend on the reaction conditions, the feed gas, and the type and lifetime of the catalyst. The crude methanol contains low-boiling and high-boiling components (light and heavy). The light-boiling components mainly include dissolved gases (e.g., CO₂), dimethyl ether, methyl formate, and acetone. The heavy-boiling components include higher alcohols, long-chain hydrocarbons, higher ketones, and esters of lower alcohols.

[0020] The impurities in crude methanol are generally separated in two stages. First, all components that boil at a lower temperature than methanol are removed in a low-boiling column. The pure methanol is then distilled overhead in one or more distillation columns. If the columns operate at different pressures, the heat of condensation from the vapors in the higher-pressure column can be used to heat the lower-pressure column.

[0021] Some components form azeotropic mixtures with methanol, e.g. acetone, ethyl formate, methyl acetate, ethyl acetate and methyl propionate.

[0022] According to the invention, in the proposed plant configuration, the exhaust gas stream from the methanol synthesis loop is fed directly into the processing unit as fuel gas after methanol recovery in order to utilize the energy of the electricity. This interconnection allows the residual gas streams from the methanol plant to be used effectively as fuel gas, thus reducing the need for external gas or even eliminating the need for external gas altogether.

[0023] Further preferred embodiments of the invention result from the other features mentioned in the dependent claims.

[0024] In a first embodiment of the process according to the invention, the partial stream is directed into a first methanol recovery unit before being fed into the processing of the carbon-containing feedstock, wherein a first methanol-laden stream and a first methanol-poor partial stream are generated in the first methanol recovery unit. The methanol recovery unit can, in particular, be a methanol scrubbing column.

[0025] In a further embodiment of the process according to the invention, the crude methanol is depressurized in a low-pressure separator, and the first methanol-laden stream is fed to the low-pressure separator. It is also conceivable that the first methanol-laden stream is fed directly to the distillation process.

[0026] In a further embodiment of the process according to the invention, the partial stream can be directed into a hydrogen recovery unit before being fed into the processing of the carbon-containing feedstock. This results in a hydrogen-rich stream and a hydrogen-poor partial stream, with the hydrogen-rich stream being fed into the methanol synthesis process. In this way, hydrogen losses are minimized. When the hydrogen recovery unit and the methanol recovery unit are used in combination, the hydrogen recovery unit can be located upstream or downstream of the methanol recovery unit.

[0027] In a further preferred embodiment of the process according to the invention, it is provided that at least a portion of the overhead product is recycled back into the processing of the carbon-containing feedstock. In this way, the overhead product can be used as fuel gas.

[0028] Additionally or alternatively, in a further embodiment of the process according to the invention, the overhead product is directed to a second methanol recovery unit before being recycled. In this second methanol recovery unit, a second methanol-laden stream and a second methanol-poor partial stream are generated. The second methanol-laden stream is fed to the distillation or to the crude methanol prior to distillation. The second methanol recovery unit can, in particular, be a methanol scrubbing column. The overhead product of the distillation column can also be processed in a scrubbing column after methanol recovery in order to use the gas stream as fuel gas. Thus, valuable products can be removed from the overhead product beforehand and reintroduced into the process elsewhere.

[0029] In a further embodiment of the invention, a low-pressure separator is provided for the depressurization of the crude methanol. A depressurization gas is produced in the low-pressure separator, and this gas is at least partially fed to the distillation and / or the processing of biomass or the carbon-containing feedstock. Before the crude methanol is fed into the distillation section of the plant, the pressure must be reduced to a lower value in a low-pressure separator. This process produces a depressurization gas that still contains significant amounts of methanol, carbon, and hydrogen. To recover the methanol, it can be fed into the first distillation column or into a methanol scrubbing column.

[0030] In a further advantageous embodiment of the process according to the invention, a hydrogen stream and an oxygen stream are generated by means of water electrolysis, and the hydrogen stream is introduced upstream of or into the methanol synthesis process, while the oxygen stream is introduced into the gasifier. To increase the carbon yield, it is advantageous to add external hydrogen, for example from water electrolysis. In a plant configuration with water electrolysis, the oxygen produced during water splitting can be used in the gasification process. In this case, no additional oxygen source, for example from an air separation unit (ASU), is necessary.

[0031] Furthermore, in a further embodiment of the method according to the invention, an oxygen stream is generated by means of air separation and introduced into the carburetor. Additional oxygen can be added by means of an air separation unit (ASU) without water electrolysis. This can be advantageous if no external hydrogen is required.

[0032] The aforementioned problem is also solved by a plant for the production of methanol from a carbon-containing feedstock, comprising at least the following components: a facility for the preparation of a carbon-containing feedstock; a gasifier for gasification and / or a pyrolysis furnace for the pyrolysis of the prepared carbon-containing feedstock to obtain a crude synthesis gas; a facility for the preparation of the crude synthesis gas to obtain a synthesis gas; a facility for methanol synthesis to obtain crude methanol; optionally a low-pressure separator for the expansion of the crude methanol; a distillation unit for distilling the expanded crude methanol to obtain methanol and an overhead product; a recirculation system from the facility for methanol synthesis to the facility for the preparation of the carbon-containing feedstock.The plant for the production of methanol is set up and configured to carry out a process according to the invention. The preceding descriptions concerning the process according to the invention also apply accordingly to the plant according to the invention.

[0033] In a first embodiment of the plant according to the invention, a first methanol recovery unit is provided in the return process, wherein a first methanol-loaded stream and a first methanol-poor partial stream are generated in the first methanol recovery unit.

[0034] In a further embodiment of the plant according to the invention, it is provided that a flow-technical connection is formed between the first methanol recovery unit and the low-pressure separator and / or the distillation for supplying the first methanol-loaded stream to the low-pressure separator.

[0035] In a further embodiment of the plant according to the invention, a hydrogen recovery unit is provided, wherein the hydrogen recovery unit is fluidically connected to the first methanol recovery unit and the device for processing the carbon-containing feedstock.

[0036] In a further embodiment of the plant according to the invention, a second return is provided for the return of at least a part of the head product to the device for the processing of the carbon-containing feedstock.

[0037] In a further advantageous embodiment of the plant according to the invention, a second methanol recovery unit is provided, which is arranged in the direction of flow between the head of the distillation and the device for processing the carbon-containing feedstock.

[0038] Furthermore, in a further embodiment of the plant according to the invention, a third return from the low-pressure separator to the device for processing the carbon-containing feedstock is provided for the return of a flash gas accumulating in the low-pressure separator.

[0039] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0040] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of an embodiment of a plant or process for the production of methanol from biomass, Fig. 2 a schematic representation of an exemplary embodiment of an optimized plant or process for the production of methanol from biomass and Fig. 3 a schematic representation of a further embodiment of an optimized plant or process for the production of methanol from biomass.

[0041] Fig. Figure 1 schematically shows a process or plant 1 for the production of methanol from synthesis gas obtained from a carbon-containing feedstock. First, in a processing unit for the carbon-containing feedstock 2, biological material or carbon-rich material, in this case biomass, is prepared for further processing. After processing, the biomass is gasified in a gasifier 3 and / or pyrolyzed in a pyrolysis furnace (not shown), yielding crude synthesis gas. This crude synthesis gas is treated in a processing unit 4 to obtain synthesis gas. Subsequently, the synthesis gas is converted to methanol or crude methanol in a methanol synthesis unit 5, which includes at least one reactor 6. Crude methanol leaving reactor 6 contains water and other impurities.Therefore, a low-pressure separator 7 is installed downstream of reactor 6. Before the crude methanol is fed into a distillation section of the plant, the pressure must be reduced to a lower value in the low-pressure separator 7. This process produces a flash gas containing significant amounts of methanol, carbon, and hydrogen. To recover the methanol, it is fed into distillation 8. Pure methanol is obtained in distillation 8. During distillation 8, byproducts, process water, and unreacted substances are thermally separated from the methanol.

[0042] In the present embodiment, an air separation unit (ASU) 9 is provided for the supply of oxygen, which supplies oxygen to the carburetor 3.

[0043] Fig. Figure 2 shows an optimized process or plant 1 for the production of methanol from a carbon-containing feedstock. In comparison to the previous embodiment according to Fig. 1, is in Fig. 2. Instead of the air separation plant (ASU) 9, a water electrolysis plant 10 is provided, which supplies oxygen for the gasifier and hydrogen for methanol synthesis. CO2 can be used as a carrier gas for the biomass.

[0044] Furthermore, a first recirculation 11 of at least a partial stream, for example, an exhaust gas stream, from the methanol synthesis unit 5 to the processing unit for the carbon-containing feedstock 2 is provided. In the proposed plant configuration, the exhaust gas stream from the methanol synthesis loop is fed directly to the processing unit as fuel gas after methanol recovery in order to utilize the energy of the electricity. This interconnection allows the residual gas streams from the methanol plant to be used effectively as fuel gas, thus reducing the need for external gas or even eliminating the need for external gas altogether.

[0045] In the return line 11, a first methanol recovery unit 14 can be provided, in which a first methanol-laden stream and a first methanol-poor partial stream are generated. If – as shown – a low-pressure separator 7 is provided for the pressure reduction of the crude methanol, a flow connection can be provided between the first methanol recovery unit 14 and the low-pressure separator 7 to feed the first methanol-laden stream into the low-pressure separator 7. Alternatively or additionally, the methanol-laden stream can also be fed to the distillation process.

[0046] Furthermore, a hydrogen recovery unit 15 may be provided, which is fluidically connected to the first methanol recovery unit 14 and the processing unit 2 for the carbon-containing feedstock. The hydrogen recovery unit 15 can be – as in Fig. 2 shown - upstream of the first methanol recovery unit 14, or downstream of it - according to an embodiment not shown.

[0047] It is also conceivable to have a third return 13, shown as a dashed line, which is directed from the low-pressure separator 7 into the facility for the processing of the carbon-containing input material 2.

[0048] In the Fig. In the embodiment shown in Figure 3, a second recirculation 12 is additionally provided, through which at least a portion of the overhead product is fed into the processing unit for the carbon-containing feedstock 2. In this way, the overhead product can be used as fuel gas. A second methanol recovery unit 16 can be provided in the second recirculation 13, which is arranged in the flow direction between the head of the distillation 8 and the processing unit for the carbon-containing feedstock 2.

[0049] Even in the embodiment according to Fig. 3. A third recirculation 13 can be provided, through which flash gas from the low-pressure separator 7 is directed into the facility for processing the carbon-containing feedstock 2. The recirculation 13 can be effected by directly introducing the flash gas into the facility for processing the carbon-containing feedstock 2 and / or by introducing it into the second methanol recovery unit 16.

[0050] The recirculation 13 can be carried out as an alternative or in addition to introducing part of the expansion gas into the distillation 8. Reference symbol list 1 Annex 2. Equipment for processing the carbon-containing feedstock 3 carburetors 4. Equipment for processing the raw synthesis gas 5. Methanol synthesis apparatus 6 Reactor 7 low-pressure separators 8 Distillation 9 Air separation plant (ASU) 10 Water electrolysis 11 First repatriation 12 Second repatriation 13 Third repatriation 14 first methanol recovery unit 15 hydrogen recovery units 16 second methanol recovery unit

Images