Gas scrubbing process for purifying crude synthesis gas by physical absorption in methanol

Abstract

The present invention relates to a gas scrubbing method and apparatus for purifying crude synthesis gas by physical absorption in methanol. A crude synthesis gas stream containing hydrogen and carbon monoxide as desired components and water and acid gases as undesirable components is mixed with methanol and subsequently cooled to below the freezing point of water. According to the present invention, a liquid phase containing methanol and water is separated from the cooled crude synthesis gas stream. The acid gases are removed from the remaining gas phase by physical absorption in methanol at elevated pressure. Separating water from the crude synthesis gas stream prior to acid gas absorption prevents significant amounts of water from entering the methanol circuit of the gas scrubbing method. This results in resource savings and allows certain plant components to be smaller than usual.

Description

Technical Field

[0001] The present invention relates to a method for purifying crude synthesis gas by physical absorption in methanol. The present invention further relates to a device for purifying crude synthesis gas by physical absorption in methanol and to the use of the device according to the invention in the method according to the invention. Background Art

[0002] Methods for removing undesirable byproducts from industrial crude synthesis gas by physical absorption are known from the prior art. Thus, such methods can be used to remove undesirable components of crude synthesis gas produced by gasification or reforming of carbon-containing feeds (e.g., carbon dioxide (CO), hydrogen sulfide (H2S), and carbonyl sulfide (COS)) down to trace amounts, from desirable synthesis gas components (e.g., hydrogen (H2) and carbon monoxide (CO)). These undesirable components are generally referred to collectively as "acid gases."

[0003] These methods (also known as gas scrubbing) exploit the property of liquids to absorb gaseous substances and hold them in solution in physically or chemically bound form. The efficiency with which a gas is absorbed by a liquid is expressed by the absorption coefficient. The better the gas is absorbed or dissolved in the liquid, the greater the absorption coefficient. The absorption coefficient generally increases with decreasing temperature and, according to Henry's law, with increasing pressure. The liquid used in gas scrubbing is also commonly referred to as the scrubbing medium.

[0004] After gas scrubbing, the components scrubbed from the crude synthesis gas during gas scrubbing are removed from the loaded scrubbing medium to obtain a regenerated or at least partially regenerated scrubbing medium. Known methods for regenerating the scrubbing medium are decompression (flashing), replacement of the absorbed make-up with a stripping gas (stripping), decompression with a stripping gas, and thermal regeneration, wherein the inherent vapor of the scrubbing medium serves as the stripping gas. In order to make the scrubbing medium available for reabsorption of gaseous components from the crude synthesis gas, the scrubbing medium is typically thermally regenerated in a final regeneration stage. Thermal regeneration recovers a substantially pure scrubbing medium suitable for reabsorb- ing undesirable gaseous components from the crude synthesis gas.

[0005] An important process for purifying crude synthesis gas is methanol scrubbing, also known as the Rectisol process, as described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, volume 15, pages 399 et seq. The Rectisol process utilizes, among other factors, the fact that the absorption coefficients of H2S, COS, and CO2 in liquid cryogenic methanol differ by several orders of magnitude from those of H2 and CO. After the scrubbing operation, the methanol is regenerated and recycled into the process.

[0006] In the low-temperature methanol scrubbing process known from the prior art, the crude synthesis gas is first cooled, for example, to a temperature as low as -40°C, before being supplied to the actual absorption process to avoid unnecessary heating of the low-temperature methanol used for absorption. Since the crude synthesis gas typically contains a certain proportion of water, for example from a previous water scrubbing process to remove ammonia, there is a risk of ice formation in the crude synthesis gas, which must be avoided at all costs. For this purpose, the crude synthesis gas is mixed with a sufficient amount of methanol to prevent ice formation before being supplied to the absorption column. As a result, the crude synthesis gas supplied to the absorption column already contains a certain amount of methanol, particularly water.

[0007] The presence of water in the absorption column generally leads to a higher demand for methanol in the various methanol circuits and, therefore, to a higher demand for resources. Correspondingly, higher resource consumption, in particular higher consumption of refrigerant, steam, electricity and cooling water, leads to higher operating costs (OPEX).

[0008] The higher water content in the methanol circuit further leads to a higher total flow rate in the methanol circuit and, therefore, to a higher steam flow rate in the sections for thermal regeneration and methanol-water separation (distillation) of the low-temperature methanol wash process. This requires the expansion of various equipment components in the low-temperature methanol wash process, thus leading to an increase in capital costs (CAPEX). Summary of the Invention

[0009] Therefore, improved methods are needed.

[0010] A general object of the present invention is to overcome the above-mentioned disadvantages of the prior art.

[0011] Another object of the present invention is to minimize the water concentration in the methanol loop of the low temperature methanol wash process.

[0012] The independent claims contribute to at least partially achieving at least one of the aforementioned objects. The dependent claims provide preferred embodiments that contribute to at least partially achieving at least one of the aforementioned objects. Preferred embodiments of a component according to one class of the invention are, where relevant, also preferred for the corresponding component of the same designation or corresponding class according to another class of the invention.

[0013] The terms "have", "comprise", or "include" etc. do not exclude the possible presence of additional elements, components etc. The indefinite article "a" or "an" does not exclude the possible presence of a plurality.

[0014] The object of the present invention is achieved at least in part by a method for purifying crude synthesis gas by physical absorption in methanol, wherein the method comprises the following method steps, wherein the following method steps do not necessarily have to be performed in the specified order:

[0015] (a) providing a raw synthesis gas stream, wherein the raw synthesis gas of the raw synthesis gas stream comprises hydrogen (H2) and carbon monoxide (CO) as desired components, and water (H2O) and acid gas as undesirable components;

[0016] (b) mixing the crude synthesis gas stream with methanol;

[0017] (c) cooling the crude synthesis gas stream mixed with methanol to below the freezing point of water;

[0018] (d) separating a liquid phase from the cooled raw synthesis gas stream, wherein the liquid phase comprises methanol and water and the remaining gaseous phase comprises hydrogen, carbon monoxide, and acid gases;

[0019] (e) removing the acid gases from the gaseous phase obtained according to step (d) by physical absorption in methanol at elevated pressure, so as to obtain a purified synthesis gas stream and a methanol stream laden with acid gases;

[0020] (f) regenerating the acid gas-laden methanol stream to obtain a regenerated methanol stream and an acid gas stream;

[0021] (g) reusing the regenerated methanol stream obtained according to step (f) for the removal of acid gases in methanol by physical absorption according to step (e).

[0022] Physical absorption of these acid gases is performed in cryogenic methanol at elevated pressure, wherein the methanol used for absorption is cooled to temperatures as low as -75°C as described below.

[0023] According to the present invention, the crude synthesis gas stream mixed with methanol according to step (b) is first cooled to below the freezing point of water according to step (c). Cooling can be carried out to a temperature as low as -40°C. In one example, the crude synthesis gas stream is cooled in the purified synthesis gas. After cooling the crude synthesis gas stream comprising methanol and water, the liquid phase comprising methanol and water is separated from the crude synthesis gas stream according to step (d). In one example, the separation of the liquid or condensed methanol-water phase is carried out in a separator known to those skilled in the art. This method step prevents water from the crude synthesis gas from being introduced into the actual absorption step according to (e). This greatly reduces the amount of water present in the methanol circuit.

[0024] An embodiment of the process according to the invention is characterized in that the liquid phase obtained according to step (d) is depressurized (flashed), thereby at least partially desorbing the gases dissolved in the liquid phase from the liquid phase to obtain a first desorbed gas stream.

[0025] According to step (d) of the process according to the invention, the majority of the crude synthesis gas, which essentially comprises hydrogen, carbon monoxide and acid gases, is separated from the liquid phase (methanol-water phase) by separation thereof and can be supplied to the absorption step (e). However, a non-negligible proportion of the gases remains dissolved in the methanol-water phase and can be desorbed from the methanol-water phase by decompression.

[0026] In view of this, it is preferred that the first desorption gas stream is supplied to the acid gas stream obtained according to step (f).

[0027] The acid gas obtained by regeneration according to step (f) is then no longer recycled into the methanol circuit. Therefore, it is also preferred to recycle the first desorbed gas stream, which may also contain carbon dioxide as acid gas, into the acid gas stream obtained according to step (f). This prevents components of the first desorbed gas stream from returning to one of the methanol circuits.

[0028] In view of this, it is preferred that the acid gas stream according to step (f) is at least partly obtained by thermally regenerating the acid gas-laden methanol stream, and the acid gas stream obtained by thermal regeneration contains gaseous methanol, and the gaseous methanol is separated from the acid gas stream by cooling, wherein the first desorption gas stream is supplied to the acid gas stream obtained by thermal regeneration before, during or after the methanol separation.

[0029] The last step in the cascade of methanol regeneration steps is usually a thermal regeneration, in which the inherent vapors of the absorption medium (methanol) serve as stripping gas. The methanol laden with acid gases is thus at least partially freed of acid gases by the thermal regeneration. The acid gas stream obtained in the thermal regeneration usually contains a certain proportion of methanol vapor, which is separated from the acid gases, for example, in a separator. The gas of the first desorbed gas stream can be supplied to the acid gas stream obtained according to step (f) before, during or after the methanol separation, since the desorbed gas stream obtained by the aforementioned decompression usually contains very little methanol, if any. However, it should be the case that the first desorbed gas stream is advantageously supplied to the acid gas stream obtained according to step (f) before or during the methanol separation, so that the methanol present in the first desorbed gas stream is separated together with the methanol from the acid gas stream discharged from the thermal regeneration.

[0030] An embodiment of the process according to the invention is characterized in that the first desorption gas stream is compressed to the absorption pressure and subsequently supplied to step (e) for removing acid gases from the first desorption gas stream by physical absorption in methanol.

[0031] Alternatively, it is possible that the first desorbed gas stream, rather than the acid gas stream obtained according to step (f), is first compressed to the absorption pressure (e.g., via a so-called recycle gas compressor) in order to subsequently be supplied to the absorption in the methanol according to step (e). This procedure is preferred when the proportion of valuable gases (i.e., hydrogen and carbon monoxide) in the first desorbed gas stream is relatively high. These valuable gases are thus supplied to the purified synthesis gas stream obtained according to step (e) and are not lost with the acid gas stream according to the above-described procedure.

[0032] An embodiment of the process according to the invention is characterized in that the acid gas stream according to step (f) is obtained at least partly by decompression (flashing) of the acid gas-laden methanol, and the first desorption gas stream is supplied to the acid gas stream obtained by decompression.

[0033] At least one of the steps in the cascade for regenerating the methanol is usually characterized by a decompression (also called flashing). This involves decompressing the methanol loaded with acid gases at the absorption pressure or carrying out a plurality of successive decompressions with decreasing pressure from one step to the next. This not only liberates the acid gases absorbed in the methanol, but also generally the valuable gases (hydrogen, carbon monoxide) co-absorbed in the methanol. Thus, the acid gases and valuable gases desorbed by the flash evaporation can advantageously be at least partially recompressed to the absorption pressure and supplied to the absorption according to step (e) in order to minimize the loss of valuable gases. When the first desorbed gas stream is supplied to the acid gas stream obtained by decompression, the valuable gases present in this first desorbed gas stream are also recycled accordingly and without loss.

[0034] An embodiment of the process according to the invention is characterized in that the liquid phase obtained according to step (d) is stripped, thereby at least partially desorbing from the liquid phase the gases dissolved in the liquid phase, to obtain a second desorbed gas stream.

[0035] If the "first desorption gas stream" is mentioned in the context of the present invention, it is understood to mean the desorption gas stream generated by decompression (flash) of the liquid phase. If the "second desorption gas stream" is mentioned in the context of the present invention, it is understood to mean the desorption gas stream generated by stripping the liquid phase.

[0036] Instead of simple decompression (flash evaporation), the liquid phase (methanol-water phase) obtained according to step (d) can also be stripped. Stripping involves desorption of the absorption gas via a stripping gas introduced into the liquid phase, wherein the stripping can be carried out with or without decompression. Suitable stripping gases are known to those skilled in the art.

[0037] In one embodiment of the process according to the invention, the liquid phase obtained according to step (d) is firstly depressurized as described above and subsequently stripped as also described above.

[0038] An embodiment of the process according to the invention is characterized in that methanol vapor is used as stripping medium.

[0039] When methanol vapor is used as stripping medium for stripping the liquid phase obtained according to step (d), the supply of a stripping gas specifically provided for stripping can be omitted.

[0040] In one aspect of the process according to the invention, regenerating the acid gas laden methanol stream according to step (f) is performed at least partly by removing water from the methanol via a thermal separation process, wherein methanol vapor generated in the thermal separation process is used as stripping medium.

[0041] At least one of the steps in the cascade for regenerating methanol typically features a thermal separation process (e.g., distillation) for separating methanol and water, since, even within the context of the process according to the invention, the introduction of water into the methanol absorption column cannot generally be completely avoided. The methanol vapor thus obtained at the top of the methanol-water separation column can advantageously be used as a stripping medium for the liquid phase to produce a second desorption gas stream. In this case, no additional technical complexity is required for the production of the stripping gas, since the methanol vapor is already produced during the thermal separation of methanol from water.

[0042] One aspect of the method according to the invention is characterized in that the second desorption gas stream is supplied to the acid gas stream obtained according to step (f).

[0043] As described above, the acid gas obtained by regeneration according to step (f) is then no longer recirculated into the methanol circuit. Therefore, it is also preferred to recirculate the second desorbed gas stream, which may also contain carbon dioxide as an acid gas, into the acid gas stream obtained according to step (f). This prevents components of the second desorbed gas stream from returning to one of the methanol circuits.

[0044] In view of this, it is preferred that the acid gas stream according to step (f) is at least partly obtained by thermally regenerating methanol loaded with acid gas, and the acid gas stream obtained by thermal regeneration contains gaseous methanol, and the gaseous methanol is separated from the acid gas stream by cooling, wherein the second desorption gas stream is supplied to the acid gas stream obtained by thermal regeneration before, during or after the methanol separation.

[0045] The gas of the second desorbed gas stream can be supplied to the acid gas stream obtained according to step (f) before, during or after the methanol separation (depending on whether the second desorbed gas stream obtained by the preceding stripping contains a high or low proportion of methanol). If methanol vapor is used as the stripping medium according to any of the preceding embodiments, the second desorbed gas stream is advantageously supplied to the acid gas stream obtained according to step (f) before or during the methanol separation in order to also separate the methanol entrained in the second desorbed gas stream by the stripping.

[0046] One aspect of the method according to the invention is characterized in that:

[0047] After the stripping, the liquid phase is fed to a thermal separation process for separating methanol from water. Preferably, after the stripping, the liquid phase is fed to a thermal separation process that is also used to at least partially regenerate the acid gas-laden methanol stream by removing water from the methanol according to step (f). The water from the liquid phase (i.e., the methanol-water phase) is preferably fed to the same separation column that is also used for the methanol-water separation of the main methanol stream.

[0048] One aspect of the method according to the invention is characterized in that the crude synthesis gas stream comprises ammonia (NH3) as an undesirable component and that, before step (b), the ammonia is at least partially removed from the crude synthesis gas stream by washing with water and the obtained aqueous ammonia solution is removed from the crude synthesis gas stream.

[0049] Depending on the source, the crude synthesis gas may also contain ammonia as an impurity. Ammonia is not an acid gas and, due to its essential properties, is preferably removed from the crude synthesis gas before step (b). Otherwise, ammonia may react with the acid gas in the context of methanol scrubbing to form ammonium salts, which, due to their limited solubility in methanol, especially in cold methanol, may lead to solid deposits in the methanol circuit.

[0050] In this context, one aspect of the method according to the invention is characterized in that at least part of the ammonia-free crude synthesis gas stream is cooled before step (b) to condense the aqueous ammonia solution remaining in the crude synthesis gas stream, and the aqueous ammonia solution condensed from the crude synthesis gas stream is separated from the crude synthesis gas stream before step (b).

[0051] In ammonia scrubbing, water, serving as the absorption medium, is typically run in a scrubbing column countercurrently to the crude synthesis gas stream to be purified, and the resulting aqueous ammonia solution is discharged at the bottom of the scrubbing column. The crude synthesis gas discharged at the top of the scrubbing column typically still contains residual amounts of aqueous ammonia solution. Therefore, the crude synthesis gas is preferably cooled before step (b) of the process according to the invention to allow these residual amounts to be subsequently separated from the crude synthesis gas.

[0052] The objects of the present invention are further achieved at least in part by

[0053] A device for purifying raw synthesis gas by physical absorption in methanol, in particular for carrying out the method according to the invention according to any of the above-described embodiments, is realized, wherein the device comprises the following components in fluid communication with one another:

[0054] (a) an apparatus for producing a raw synthesis gas stream, wherein the raw synthesis gas of the raw synthesis gas stream comprises hydrogen (H2) and carbon monoxide (CO) as desired components, and water (H2O) and acid gases as undesirable components;

[0055] (b) means for mixing the crude synthesis gas stream with methanol;

[0056] (c) means for cooling the crude synthesis gas stream mixed with methanol to below the freezing point of water;

[0057] (d) an apparatus for separating a liquid phase from the cooled raw synthesis gas stream, wherein the liquid phase comprises methanol and water and the remaining gaseous phase comprises hydrogen, carbon monoxide and acid gases;

[0058] (e) means for removing the acid gases from the gas phase obtainable according to (d) by physical absorption in methanol at elevated pressure, whereby a purified synthesis gas stream can be obtained and a methanol stream laden with acid gases can be obtained;

[0059] (f) means for regenerating the methanol stream laden with acid gas, thereby obtaining a regenerated methanol stream and an acid gas stream;

[0060] (g) means for reusing the regenerated methanol stream obtainable according to (f) for removing acid gases in methanol by physical absorption according to (e).

[0061] An embodiment of the device according to the invention is characterized in that:

[0062] The device according to (d) has a pressure reduction device arranged downstream thereof, wherein the gas dissolved in the liquid phase is at least partially desorbable from the liquid phase by means of the pressure reduction device, thus enabling a first desorbed gas stream to be obtained.

[0063] An embodiment of the apparatus according to the invention is characterized in that the device according to (d) has a stripping device arranged downstream thereof, wherein the gas dissolved in the liquid phase is at least partially desorbable from the liquid phase by the stripping device, thus making it possible to obtain a second desorbed gas stream.

[0064] An embodiment of the apparatus according to the invention is characterized in that the apparatus comprises means for the thermal separation of methanol from water, and that the methanol vapor obtainable in this thermal separation of methanol from water can be used as stripping medium in the stripping apparatus.

[0065] An embodiment of the plant according to the invention is characterized in that the stripping device and the device for thermal separation of methanol and water are integrated in a common column.

[0066] When using the methanol vapor obtained in the thermal separation of methanol and water in this stripping unit, this stripping unit and this device for thermal separation can advantageously be integrated in a shared tower.For example, this stripping unit can be separated from the device for thermal separation by a chimney tray or similar breathable tray, and liquid can be collected on this tray.Then the methanol vapor from the device for thermal separation passes through the chimney tray and rises upwards and enters the stripping unit, wherein liquid phase (methanol-water phase) is collected on the chimney tray and via the methanol vapor rising, the gas remaining in this liquid phase is released.Such integrated solution is more cost-effective than two separate dedicated towers.

[0067] The object of the present invention is further at least partially solved by the use of an apparatus according to the invention according to any of the preceding embodiments in a method according to the invention according to any of the preceding embodiments.

[0068] acid gas

[0069] The term "acid gas" is a general term for those undesirable gaseous components of the raw synthesis gas that are acidic in aqueous solution. These gases include, in particular, gaseous hydrogen sulfide (H2S), carbonyl sulfide (COS, which reacts in water to form carbon dioxide and hydrogen sulfide), carbon dioxide (CO2), and hydrogen cyanide (HCN).

[0070] Purified synthesis gas, purified synthesis gas stream

[0071] Purified synthesis gas is crude synthesis gas that is free of undesirable components or byproducts. Depending on the requirements, it is not always necessary to completely remove the undesirable components from the crude synthesis gas in order to obtain synthesis gas that meets the specifications. In particular, complete removal of carbon dioxide is not always desirable, since, for example, in methanol synthesis, a certain residual amount of carbon dioxide can favor the kinetics of the catalytic conversion.

[0072] Undesirable ingredients

[0073] Undesirable components or by-products in the crude synthesis gas are, for example, the aforementioned acid gases and possible catalyst poisons, such as alkyl mercaptans, in particular methyl mercaptan and carbon disulphide, as well as aromatic heterocyclic sulphur compounds, in particular thiophene. Alkyl mercaptans and aromatic heterocyclic sulphur compounds are present in particular in the crude synthesis gas from coal gasification. Other by-products that may be present in the crude synthesis gas are compounds such as ammonia and metal carbonyls, which can be formed as gaseous or volatile liquid compounds from metal ions present in coal and carbon monoxide. In metal carbonyls, carbon monoxide is coordinately bonded to the central metal atom. Metal carbonyls can cause problems, in particular due to their tendency to react with hydrogen sulphide and form insoluble metal sulphides. Metal carbonyls that occur in industrial gas scrubbing processes include, in particular, nickel carbonyls and iron carbonyls.

[0074] Other possible accompanying substances are gaseous aliphatic, cycloaliphatic and aromatic hydrocarbon compounds at standard pressure, as well as low-boiling and high-boiling representatives of these compounds. Aromatic hydrocarbon compounds include, in particular, benzene, toluene and the xylenes (o-, m- and p-xylene), as well as naphthalene. Gaseous and also low-boiling and high-boiling aliphatic and cycloaliphatic hydrocarbons include, in particular, homologues of cycloalkanes and, to a lesser extent, alkenes and alkynes, for example, having 1 to 12 carbon atoms, in particular 1 to 6 carbon atoms.

[0075] Increased pressure

[0076] The absorption of the undesirable accompanying substances in the scrubbing medium is carried out at elevated pressure, since the absorption coefficient increases with increasing pressure. Therefore, the absorption is typically carried out at a pressure between 20 bar and 100 bar.

[0077] regeneration

[0078] In order to regenerate the scrubbing medium and remove undesirable byproducts from the scrubbing medium, the pressure is generally reduced to 1.5 to 70 bar, depending on whether it is a high-pressure regeneration (20 to 70 bar), a medium-pressure regeneration (15 to 40 bar) or a low-pressure regeneration (0 to 15 bar, preferably 1.5 to 15 bar). In one embodiment, such regeneration columns are arranged in series in a cascade, with the pressure decreasing from one column to the next.

[0079] In the regeneration column, undesirable by-products can be removed by pressure reduction alone (flash evaporation), in combination with a stripping gas (stripping) with or without pressure reduction, or by thermal regeneration. An example of a suitable stripping gas is nitrogen. In thermal regeneration, the inherent vapor of the scrubbing medium (e.g. methanol) is usually used as the stripping gas.

[0080] physical absorption

[0081] Physical absorption is caused by the physical scrubbing of the medium. This means that the solubility of the gases of interest (e.g. undesirable concomitants) is caused by physical interactions.

[0082] In the case of physical scrubbing media, it is preferred to use a cold scrubbing medium cooled to below ambient temperature as the absorbent to achieve absorption of the undesirable by-products, since the absorption coefficient of the undesirable components increases with decreasing scrubbing medium temperature. Intensive mass transfer between the crude synthesis gas and the scrubbing medium takes place in an absorption tower (also known as a scrubber). Absorption towers, in which the crude synthesis gas and scrubbing medium flow in countercurrent, can be equipped with random packing or trays to improve mass transfer.

[0083] According to the invention, the absorbent is methanol, which as cold methanol is preferably cooled to -30° C., to -40° C., to -50° C., to -60° C., or even to -75° C. Methanol has the advantage that, even at very low temperatures, its viscosity is low enough to ensure that it remains easily handleable in terms of process engineering.

[0084] Working Example

[0085] The present invention is exemplified below by a working example in combination with two drawings and numerical examples, wherein the working example, the drawings and the numerical examples are not intended to limit the present invention in any way. Unless otherwise specified, the drawings are not drawn to scale.

[0086] In the attached figure:

[0087] Figure 1 a process flow diagram showing a method according to the invention or a device according to the invention, and

[0088] Figure 2 A process flow chart of a method or device according to the prior art is shown.

[0089] exist Figure 1 and Figure 2 In FIG, the gas flow is shown as a solid line, while the liquid flow is shown as a dashed line.

[0090] Figure 1 An exemplary embodiment of the method according to the invention or the device according to the invention is illustrated with the aid of a very simplified process flow diagram.

[0091] A crude synthesis gas stream containing at least hydrogen, carbon monoxide, acid gases, and ammonia is first introduced into the bottom region of an ammonia scrubber 12 via conduit 10 and passed from top to bottom using boiler feed water introduced into the top region of the ammonia scrubber 12 via conduit 11. Due to the transfer process between the crude synthesis gas and water in countercurrent to the ammonia scrubber 12, the crude synthesis gas is largely free of ammonia and is discharged from the ammonia scrubber 12 via conduit 13. The scrubbing solution (in this case, aqueous ammonia solution) produced as a bottom product in the ammonia scrubber 12 is discharged via conduit 14 and subjected to further processing outside the process (not shown). As a result of the ammonia scrubbing, the crude synthesis gas, which contains a relatively small amount of uncondensed aqueous ammonia solution, is subsequently cooled in a heat exchanger 15 against the purified synthesis gas from conduit 38. The cooled crude synthesis gas is supplied via conduit 16 to a separator 17, where, once condensed, the aqueous ammonia solution remaining in the crude synthesis gas is separated from the gaseous components of the crude synthesis gas. The aqueous ammonia solution condensed in the separator 17 is discharged from the separator 17 as bottom product via conduit 18 and is further processed outside the process (not shown).

[0092] The crude synthesis gas, which is largely free of ammonia, is discharged as a top product from the separator 17 and supplied to the heat exchanger 20 via the conduit 19. Before entering the heat exchanger 20, the crude synthesis gas, which still contains water, is mixed with methanol from the conduit 21. In the heat exchanger 20, the crude synthesis gas mixed with methanol is subsequently cooled to minus 40° C. The addition of methanol from the conduit 21 prevents the water present in the crude synthesis gas from freezing and thus prevents blockages in the conduit system of the gas scrubbing process.

[0093] The crude synthesis gas mixed with methanol, cooled to -40°C, is then supplied via conduit 22 to a separator 23, in which, once condensed, the liquid phase according to the invention (methanol-water phase) is separated from the cooled crude synthesis gas stream. The liquid phase is discharged from the separator 23 via conduit 24, while the remaining gaseous phase of the crude synthesis gas, comprising at least hydrogen, carbon monoxide and acid gases, is supplied via conduit 25 to the absorption zone of the gas scrubbing process for the removal of the acid gases at elevated pressure.

[0094] To absorb acid gases from the crude synthesis gas stream, the crude synthesis gas is first supplied via conduit 25 to a pre-scrubbing stage 26, where it is treated countercurrently with low-temperature methanol from a methanol stream 27. Methanol stream 27 is diverted from methanol stream 28 and already contains carbon dioxide absorbed from a second main scrubbing stage 29. Pre-scrubbing stage 26 releases the crude synthesis gas primarily as hydrogen cyanide (HCN), while also co-absorbing small amounts of sulfur compounds (e.g., alkyl mercaptans) and, inevitably, very small amounts of valuable gases (hydrogen, carbon monoxide). The loaded methanol obtained in the pre-scrubbing stage is supplied via conduit 30 to a regeneration system 31.

[0095] The crude synthesis gas stream, free of hydrogen cyanide and other compounds, is supplied to a first main scrubbing stage 33 via conduit 32. In the first main scrubbing stage 33, the crude synthesis gas is treated countercurrently with methanol, which is diverted from methanol stream 27 as substream 35 and already contains carbon dioxide absorbed in the second main scrubbing stage 29. In the first main scrubbing stage 33, the crude synthesis gas is essentially freed of hydrogen sulfide and carbonyl sulfide. The crude synthesis gas, which still substantially contains carbon dioxide as an undesirable component, is then discharged from the first main scrubbing stage 33 and treated in the second main scrubbing stage 29 with regenerated methanol from conduit 36 ​​to absorb carbon dioxide. The completely purified synthesis gas is then discharged from the process via conduits 37, 38, and 39, having passed through heat exchangers 15 and 20 and used to cool the crude synthesis gas stream.

[0096] The acid gas-laden methanol streams 28, 30, and 40 exiting the pre-scrub stage 26 and the two main scrub stages 29 and 33 are subsequently freed of the absorbed acid gas components in a regeneration system 31. The regeneration system 31 comprises at least a plurality of flash regeneration stages arranged in cascade, a thermal regenerator, and an optional reabsorber. The arrangement of these components, typical for a low-temperature methanol scrubbing process, is well known to those skilled in the art. For simplicity, the aforementioned components are not shown individually but rather as blocks.

[0097] The regeneration system 31 provides a carbon dioxide stream in conduit 41, two methanol streams (in each case regenerated methanol) in conduits 21 and 36, and a stream comprising primarily sulfur-containing acid gases (hydrogen sulfide, carbonyl sulfide) in conduit 42. The carbon dioxide in conduit 41 is discharged from the process and sent for further treatment (not shown). As described above, the methanol stream in conduit 21 is added to the crude synthesis gas stream from conduit 19 to prevent ice formation in the crude synthesis gas stream in conduit 19. The methanol stream in conduit 36 ​​is used to absorb carbon dioxide in the second main scrubbing stage 29.

[0098] The acid gas stream in conduit 42 originates from the thermal regeneration portion of regeneration system 31. This acid gas stream therefore contains sulfur-containing acid gases (essentially hydrogen sulfide and carbonyl sulfide) as well as methanol that did not condense during the thermal regeneration process (i.e., entrained methanol). This uncondensed (i.e., vaporous) methanol, along with the sulfur-containing acid gases, is cooled in heat exchanger 43 to such an extent that the methanol condenses in separation vessel 45 after entering separation vessel 45 via conduit 44. The resulting acid gases, i.e., the gas phase obtained in the separation vessel, consist essentially of sulfur-containing acid gases. These sulfur-containing acid gases are discharged from separation vessel 45 via conduit 46 and directed to a facility for sulfur recovery using the Claus process (not shown). The separated, condensed methanol is discharged from separation vessel 45 via conduit 47 and recycled to regeneration system 31 via conduit 49 using pump 48.

[0099] As described above, separator 23 separates the liquid phase (methanol-water phase) according to the present invention from the cooled raw synthesis gas by condensation. The liquid phase according to the present invention is discharged from separator 23 via conduit 24 and supplied to flash vessel 50. The reduced pressure in flash vessel 50 causes the gas dissolved in the liquid phase to be at least partially desorbed from the liquid phase to obtain a first desorbed gas stream according to the present invention. The first desorbed gas stream is discharged and supplied to separation vessel 45 via conduit 51. Thus, the gas desorbed by the reduced pressure in flash vessel 50 is discharged from the process together with the acid gas from separation vessel 45 via conduit 46.

[0100] The liquid phase (methanol-water phase) remaining in the flash vessel 50 and still comprising absorption gas is supplied via conduit 52 to a combined column 53 comprising a zone 54 for thermal separation of methanol by rectification and a stripping zone 55 .

[0101] A pump 58 is used to supply at least partially regenerated aqueous methanol from the regeneration system 31 to the lower region 54 of the combined tower 53 via conduits 56 and 57. The methanol-water mixture in the lower portion 54 of the combined tower 53 is heated to boiling via a boiler 59. The bottom product obtained in the lower portion 54 of the combined tower 53 is water, which is discharged via a conduit 60 and sent for further processing (not shown). After passing through the chimney tray, the methanol vapor rising in the lower portion 54 of the tower 53 enters the upper stripping region 55 of the tower 53. A water phase (methanol-water phase) is also supplied to the stripping region 55 via a conduit 52. The methanol vapor entering the stripping region 55 desorbs the other gases absorbed in the water phase, thereby providing a second desorbed gas stream according to the present invention, which is discharged from the stripping region 55 of the tower 53 via a conduit 61. Since the second desorption gas stream contains small amounts of methanol vapor from the stripping, gas from conduit 61 is supplied to the acid gas stream in conduit 42 upstream of the heat exchanger 43, so that the methanol entrained in conduit 61 can be separated as liquid by cooling in the heat exchanger 43 and subsequent condensation in the separation vessel 45 and recycled to the regeneration system 31 via pump 48. The second desorption gas stream freed from methanol can be discharged from the process together with the further acid gases via conduit 46.

[0102] The liquid phase (methanol-water phase), which is largely free of absorption gas, collects on the chimney trays of the stripping region 55 and is supplied to the lower region 54 of the column 53 via conduit 62 for methanol-water separation. The removed water leaves the column as bottom product via conduit 60, while the removed methanol leaves the lower region 54 of the column 53 as top product via conduit 63 and is supplied to the regeneration system 31. The methanol supplied to the regeneration system 31 in conduit 63 can be used directly for reabsorption, for example to absorb carbon dioxide in the second main scrubbing stage 29, or first be subjected to thermal regeneration as part of the regeneration system 31.

[0103] The process mode according to the invention ensures that, due to the removal in separator 23, water does not initially enter the absorption region of the process, which includes absorption stages 26 (prewash stage), 33, and 29 (main wash stage). Furthermore, all subsequent process steps ensure that the water removed in separator 23 cannot be returned to any methanol circuit. This is ensured by the flash vessel 50 in conjunction with the combined column 53. The process mode ensures that the water removed in separator 23, along with the methanol, is ultimately always discharged from the combined column via conduit 60 as a bottom product.

[0104] Figure 2 A method such as is known from the prior art is shown. Figure 1 The reference numerals used in the Figure 2 .

[0105] and Figure 1 In contrast to the process according to the invention, the cooled crude synthesis gas in conduit 70 is fed directly to the absorption in the scrubbing stages 26, 29 and 33, once mixed with methanol from conduit 21. This causes all the water initially present in the crude synthesis gas or entrained by the ammonia scrubber to enter the methanol circuit of the gas scrubbing process, which entails the disadvantages described above. In contrast to the process according to the invention, this process does not use the methanol according to Figure 1 Instead of using a combined tower (tower 53), a simple distillation tower 71 is used to separate methanol and water.

[0106] The following numerical examples (simulations) show the Figure 2 Compared with the non-inventive comparative example, Figure 1 Advantages of the method according to the invention of the inventive embodiment.

[0107]

[0108] Numerical examples show that the inventive process concept allows for a saving of resources (coolant, energy, cooling water and steam). The reduced water content in the methanol circuit additionally allows for smaller diameters of the thermal regenerator and the methanol-water separation column.

[0109] Embodiments of the present invention have been described with reference to different types of subject matter. Specifically, certain embodiments have been described with reference to method claims, while other embodiments have been described with reference to apparatus claims. However, from the above and below descriptions, it will be apparent to those skilled in the art that, unless otherwise stated, any combination of features relating to different types of subject matter or different types of claims is contemplated, in addition to any combination of features belonging to one type of claim. Features may be combined to achieve synergistic effects that go beyond the simple sum of the technical features.

[0110] Although the present invention has been shown and described in detail in the drawings and the foregoing description, such illustration and description should be considered illustrative or exemplary and not restrictive. The present invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments may be understood and performed by one skilled in the art of the claimed invention from a study of the drawings, the disclosure, and the appended claims.

[0111] List of Reference Numerals

[0112] 10, 13, 16, 19, 22, 25, duct (gas) 32, 34, 37, 38, 39, 41, 42, 44, 46, 51, 61, 70

[0115] 11, 14, 18, 21, 24, 27, Catheter (liquid) 28, 30, 35, 36, 40, 47, 49, 52, 56, 57, 60, 62, 63

[0119] 12 Ammonia Scrubber

[0120] 15, 20, 43, 59 heat exchangers

[0121] 17, 23 separator

[0122] 26 Pre-wash stage

[0123] 33 First main wash stage

[0124] 29 Second main wash stage

[0125] 31 Regeneration System

[0126] 35 Separation Container

[0127] 48, 58 pumps

[0128] 50 Flash Vessel

[0129] 53 Combination Tower

[0130] 54 Area for methanol-water separation

[0131] 55 Stripping Area

[0132] 71 Methanol-Water Separation Tower

Claims

1. A method for purifying crude synthesis gas by physical absorption in methanol, wherein: The method comprises the following steps: (a) providing a raw synthesis gas stream, wherein the raw synthesis gas of the raw synthesis gas stream comprises hydrogen (H2) and carbon monoxide (CO) as desired components, and water (H2O) and acid gas as undesirable components; (b) mixing the crude synthesis gas stream with methanol; (c) cooling the crude synthesis gas stream mixed with methanol to below the freezing point of water; (d) separating a liquid phase from the cooled raw synthesis gas stream, wherein the liquid phase comprises methanol and water and the remaining gaseous phase comprises hydrogen, carbon monoxide, and acid gases; (e) removing the acid gases from the gaseous phase obtained according to step (d) by physical absorption in methanol at elevated pressure, so as to obtain a purified synthesis gas stream and a methanol stream laden with acid gases; (f) regenerating the acid gas-laden methanol stream to obtain a regenerated methanol stream and an acid gas stream; (g) reusing the regenerated methanol stream obtained according to step (f) for the removal of acid gases in methanol by physical absorption according to step (e), It is characterized in that The liquid phase obtained according to step (d) is stripped, thereby at least partially desorbing the gases dissolved in the liquid phase from the liquid phase, to obtain a second desorbed gas stream, wherein Methanol vapor is used as the stripping medium, and Regenerating the acid gas laden methanol stream according to step (f) is performed at least in part by removing water from the methanol via a thermal separation process, wherein methanol vapor generated in the thermal separation process serves as stripping medium.

2. The method according to claim 1, characterized in that The liquid phase obtained according to step (d) is depressurized, thereby at least partially desorbing from the liquid phase the gases dissolved in the liquid phase, in order to obtain a first desorbed gas stream.

3. The method according to claim 2, characterized in that The first desorption gas stream is supplied to the acid gas stream obtained according to step (f).

4. The method according to claim 3, characterized in that The acid gas stream according to step (f) is obtained at least in part by thermally regenerating the acid gas-laden methanol stream, and the acid gas stream obtained by thermal regeneration contains gaseous methanol, and the gaseous methanol is separated from the acid gas stream by cooling, wherein the first desorption gas stream is supplied to the acid gas stream obtained by thermal regeneration before, during or after the methanol separation.

5. The method according to any one of claims 2 to 4, characterized in that The first desorbed gas stream is compressed to absorption pressure and then supplied to step (e) for removing acid gases from the first desorbed gas stream by physical absorption in methanol.

6. The method according to claim 2, characterized in that The acid gas stream according to step (f) is at least partly obtained by decompressing the acid gas-laden methanol, and the first desorption gas stream is supplied to the acid gas stream obtained by decompression.

7. The method according to any one of the preceding claims, characterized in that The liquid phase obtained according to step (d) is firstly depressurized according to any one of claims 2 to 6 and subsequently stripped according to claim 1 .

8. The method according to any one of claims 1 to 7, characterized in that The second desorption gas stream is supplied to the acid gas stream obtained according to step (f).

9. The method according to any one of claims 1 to 8, characterized in that After the stripping, the liquid phase is supplied to a thermal separation process for separating methanol and water.

10. The method according to any one of the preceding claims, characterized in that The raw synthesis gas stream comprises ammonia (NH 3 ) as an undesirable component and, before step (b), the ammonia is at least partially removed from the raw synthesis gas stream by washing with water and the obtained aqueous ammonia solution is removed from the raw synthesis gas stream.

11. The method according to claim 10, characterized in that At least a portion of the ammonia-free raw synthesis gas stream is cooled before step (b) to condense aqueous ammonia solution remaining in the raw synthesis gas stream, and the aqueous ammonia solution condensed from the raw synthesis gas stream is separated from the raw synthesis gas stream before step (b).

12. An apparatus for purifying crude synthesis gas by physical absorption in methanol, wherein: The apparatus comprises the following components in fluid communication with each other: (a) an apparatus for producing a raw synthesis gas stream, wherein the raw synthesis gas of the raw synthesis gas stream comprises hydrogen (H2) and carbon monoxide (CO) as desired components, and water (H2O) and acid gases as undesirable components; (b) means for mixing the crude synthesis gas stream with methanol; (c) means for cooling the crude synthesis gas stream mixed with methanol to below the freezing point of water; (d) an apparatus for separating a liquid phase from the cooled raw synthesis gas stream, wherein the liquid phase comprises methanol and water and the remaining gaseous phase comprises hydrogen, carbon monoxide and acid gases; (e) means for removing the acid gases from the gas phase obtainable according to (d) by physical absorption in methanol at elevated pressure, whereby a purified synthesis gas stream can be obtained and a methanol stream laden with acid gases can be obtained; (f) means for regenerating the methanol stream laden with acid gas, thereby obtaining a regenerated methanol stream and an acid gas stream; (g) an apparatus for reusing the regenerated methanol stream obtainable according to (f) for removing acid gases in methanol by physical absorption according to (e), It is characterized by: the device according to (d) having a stripping device arranged downstream thereof, wherein the gas dissolved in the liquid phase is at least partially desorbable from the liquid phase by means of the stripping device, thus making it possible to obtain a second desorbed gas stream, and The apparatus comprises an apparatus for the thermal separation of methanol from water, and the methanol vapor obtainable in this thermal separation of methanol from water can be used as stripping medium in the stripping apparatus.

13. The device according to claim 12, characterized in that The device according to (d) has a pressure reduction device arranged downstream thereof, wherein the gas dissolved in the liquid phase is at least partially desorbable from the liquid phase by means of the pressure reduction device, thus enabling a first desorbed gas stream to be obtained.

14. The device according to claim 12 or 13, characterized in that The stripping device and the device for thermal separation of methanol and water are integrated in a common column.

15. Use of an apparatus according to any one of claims 12 to 14 in a method according to any one of claims 1 to 11.

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