Method and apparatus for producing methanol

Abstract

The invention relates to a process and apparatus for producing methanol from an input gas comprising carbon monoxide (CO) and hydrogen (H2) using a pre-reactor stage and a main reactor stage. The input gas produced at high pressure is first introduced into the pre-reactor stage to be catalytically converted into a first methanol-containing product stream. After methanol is separated from the first methanol-containing product stream and discharged from the pre-reactor stage, the remaining gas stream is introduced into the main reactor stage after being compressed to the reaction pressure as a residual gas stream to be catalytically converted into a second methanol-containing product stream. After being separated from the second methanol-containing product stream, methanol is discharged from the main reactor stage. The use of an input gas having a carbon monoxide content of 25% to 36% by volume results in substantial savings in terms of the compressor output required during production.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for producing methanol from an input gas comprising carbon monoxide (CO) and hydrogen (H2). The present invention further relates to an apparatus for producing methanol from an input gas comprising carbon monoxide (CO) and hydrogen (H2). BACKGROUND

[0002] Today, methanol is typically produced from synthesis gas, which is an input gas comprising mainly carbon monoxide (CO) and hydrogen (H2) and usually also carbon dioxide (CO2). In modern so-called low-pressure processes, a pressure between 60 and 120 bar is used to catalytically convert the synthesis gas into raw methanol. The reaction is carried out on fixed-bed catalysts at moderate temperatures below 300°C. The catalysts employed comprise, for example, copper / zinc oxide / alumina-based materials.

[0003] The synthesis gas produced by steam reforming is usually produced at a pressure between 20 and 40 bar and has to be first compressed via a synthesis gas compressor to the higher pressure of at least 60 bar (reaction pressure) required for the methanol synthesis. The known processes operate using a large amount of recycle gas in the so-called synthesis loop, wherein the amount of recycle gas is up to five times the amount of fresh gas supplied in the synthesis gas production. Instead of a synthesis loop, the production of raw methanol can also be carried out in a multi-stage reactor system with reactors arranged in series. The number of reactors depends on the per-pass conversion rate achievable in each reactor.

[0004] The gas compressors required for compressing the synthesis gas are machines which, due to their high energy consumption, lead to high operating costs (OPEX) and, due to their size and construction, also require high capital expenditure (CAPEX). Gas compressors, including pusher technology, for compressing input gases, such as synthesis gas, can account for up to 30% of all main process equipment costs. Therefore, the output of the compressors required for compressing the gas greatly increases the total costs of the apparatus for methanol production, since not only the size of the compressors but also the output required for operating these compressors increases with the amount of gas to be compressed.

[0005] The main reactor stage of the methanol synthesis, which comprises either a synthesis loop or a multi-stage reactor system, can have a pre-reactor stage connected upstream thereof, in which a portion of the synthesis gas is converted into methanol before being introduced into the main reactor stage. The pre-reactor stage typically comprises a single pre-reactor, through which the synthesis gas is passed once, and the methanol produced is separated (condensed) at the pre-reactor outlet before the remaining synthesis gas (residual gas) is fed to the main reactor stage. The process mode comprising a pre-reactor has the advantage that the synthesis gas compressor only needs to compress the remaining synthesis gas (residual gas) and not the total amount of synthesis gas to the pressure in the main reactor stage.

[0006] As described in DE 101 26 719 A1, in the pre-reactor, the input gas supplied from the synthesis gas production can be converted into methanol without prior compression with a compressor. Thus, the energy savings achievable for the synthesis gas compressor arranged downstream of the pre-reactor are generally lower, since only a less conversion of the synthesis gas into methanol is achieved in the pre-reactor stage. The end result of this is that, despite the use of a pre-reactor, which increases the investment and operating costs of the plant, the majority of the synthesis gas will still be introduced into the main reactor stage. Thus, the use of a pre-reactor counteracts the saved costs (OPEX and CAPEX) in terms of the synthesis gas compressor arranged downstream of the pre-reactor stage in a negative sense. SUMMARY

[0007] It is therefore an object of the present application to at least partially overcome the disadvantages of the prior art.

[0008] It is a further object of the present application to provide a method which allows for a significantly greater saving of energy in terms of the gas compressor for compressing the input gas.

[0009] It is a further object of the present application to provide a method which increases the conversion of the input gas, in particular of the synthesis gas, in the pre-reactor, so that the amount of residual gas for subsequent compression is significantly reduced.

[0010] It is a further object of the present application to provide a plant which at least partially solves the above-mentioned objects.

[0011] These objects of the present application are at least partially achieved by a method for producing methanol from an input gas comprising carbon monoxide (CO) and hydrogen (H2), wherein the input gas produced at high pressure is introduced into a pre-reactor stage as an input gas stream for catalytic conversion into a first methanol-containing product stream, and

[0012] methanol is separated from the first methanol-containing product stream and discharged from the pre-reactor stage, and the residual gas in the remaining input gas stream is compressed to the reaction pressure as a residual gas stream and introduced into a main reactor stage for catalytic conversion into a second methanol-containing product stream, and methanol is separated from the second methanol-containing product stream and discharged from the main reactor stage. According to the present application, it is provided that the input gas has a carbon monoxide content of 25 to 36% by volume before being introduced into the pre-reactor stage.

[0013] The input gas preferably has a carbon monoxide content of 27 to 33% by volume, particularly preferably a carbon monoxide content of 28 to 31% by volume, more preferably a carbon monoxide content of 29 to 30% by volume, before being introduced into the pre-reactor stage.

[0014] The input gas is preferably synthesis gas from coal gasification.

[0015] It has now been found, surprisingly, that the energy savings in the gas compressor arranged downstream of the pre-reactor are significantly higher for input gases having a carbon monoxide content according to the present application, for example input gases from coal gasification, than for input gases having a relatively low carbon monoxide content. Input gases having a relatively low carbon monoxide content are, for example, input gases from steam reforming of methane (steam methane reforming - SMR) or from a combination of steam reforming and autothermal reforming (so-called combined reforming). The synthesis gas produced on the basis of these technologies usually has a CO content of significantly less than 25% by volume.

[0016] Due to the higher CO content in the input gas supplied to the pre-reactor, for example the input gas from coal gasification, the compressor output (energy consumption of the compressor) and the compressor size of the input gas compressor, in particular the synthesis gas compressor, for compressing the residual gas stream are surprisingly significantly reduced. This results in significant savings in terms of OPEX and CAPEX of the input gas compressor.

[0017] A preferred embodiment of the method according to the present application is characterized in that the input gas has a hydrogen content of 66% to 72% by volume before being introduced into the pre-reactor stage.

[0018] It is particularly preferred that the input gas has a hydrogen content of 67% to 70% by volume, more preferably 68% to 69% by volume, before being introduced into the pre-reactor stage.

[0019] It has been shown that in combination with the carbon monoxide content in the input gas of the present application, a particularly high methanol yield is achieved in the pre-reactor, thus resulting in further savings in terms of the input gas compressor.

[0020] A preferred embodiment of the method according to the present application is characterized in that the input gas has a carbon dioxide content (CO2 content) of not more than 5% by volume before being introduced into the pre-reactor stage.

[0021] The input gas has a carbon dioxide content of 2% to 4% by volume, particularly preferably 2.5% to 3.5% by volume, before being introduced into the pre-reactor stage.

[0022] Studies have shown that in combination with the carbon monoxide content and optionally the hydrogen content in the input gas of the present invention, particularly high methanol yields are achieved in the pre-reactor, thus resulting in further savings in terms of input gas compressors. In particular, it has been found that the carbon dioxide content of the present invention leads to a particularly rapid establishment of the thermodynamic equilibrium of the methanol synthesis reaction, thus being kinetically advantageous. Synthesis gas produced on the basis of SMR or a combination of autothermal reforming and SMR usually has a CO2 content significantly above 5% by volume, thus being suboptimal.

[0023] A preferred embodiment of the process according to the present invention is characterized in that the input gas has a stoichiometric number SN of 1.5 to 3.0 before being introduced into the pre-reactor stage, wherein

[0024]

[0025] The stoichiometric number indicates the stoichiometric ratio of the methanol synthesis reaction

[0026]

[0027] In the ideal stoichiometric ratio and without carbon dioxide, the stoichiometric number is 2. However, studies have shown that a smaller amount of carbon dioxide can increase the CO conversion in the pre-reactor, so that the stoichiometric number is preferably in the range of 1.8 to 3.0. Preferably, 1.8 < SN < 2.5, particularly preferably 1.9 < SN < 2.2, more preferably 1.95 < SN < 2.05.

[0028] A preferred embodiment of the process according to the present invention is characterized in that the input gas has a pressure of 20 to 100 bar, preferably a pressure of 35 to 55 bar.

[0029] Studies have shown that in combination with the carbon monoxide content and optionally the hydrogen content and optionally the carbon dioxide content in the input gas of the present invention, particularly high methanol yields are achieved in the pre-reactor in the pressure range of the present invention, thus resulting in further savings in terms of input gas compressors.

[0030] A preferred embodiment of the process according to the present invention is characterized in that the input gas produced and present at high pressure is introduced into the pre-reactor stage without further pressurization. In particular, the input gas produced and present at high pressure is introduced into the pre-reactor stage without further pressurization by a gas compressor.

[0031] The input gas comprising hydrogen and carbon monoxide is typically produced at high pressure, for example in the case of coal gasification, and can be introduced into the pre-reactor without further compression, for example by a gas compressor. This reduces the total number of required compressors, for example to one gas compressor for compressing the residual gas from the pre-reactor stage and one gas compressor for compressing the recycle gas when a synthesis loop is used.

[0032] A preferred embodiment of the process according to the application is characterized in that the residual gas in the residual gas stream is compressed to a pressure higher than the pressure of the input gas before being introduced into the main reactor stage. The residual gas stream is preferably compressed to the higher pressure by a gas compressor before being introduced into the main reactor stage.

[0033] Even in the so-called low-pressure process for the production of methanol, the main reactor stage requires a pressure of 60 bar to 120 bar, and the residual gas in the residual gas stream must be compressed to said pressure before being introduced into the main reactor stage. The pressure in the main reactor stage is typically higher than the pressure of the input gas produced at high pressure.

[0034] The residual gas stream is compressed to a pressure at least 5 bar higher than the pressure of the input gas, or to a pressure at least 10 bar higher, or to a pressure at least 25 bar higher, or to a pressure at least 40 bar higher, before being introduced into the main reactor stage.

[0035] A preferred embodiment of the process according to the application is characterized in that the main reactor stage is part of a synthesis loop, wherein a recycle gas stream remaining after separation of methanol from the second methanol-containing product stream is recycled into the main reactor stage of the synthesis loop and combined with the residual gas stream. The recycle gas in the recycle gas stream is also compressed to a pressure higher than the pressure of the input gas before or at the time of combination with the residual gas. The compression is likewise done using a gas compressor, in this case referred to as recycle gas compressor. As an alternative, it is conceivable to use a single-stage, in particular multi-stage, gas compressor which compresses the residual gas stream and the recycle gas stream to the reaction pressure required for the synthesis of methanol in the main reactor stage. After compression to the reaction pressure, the recycle gas and the residual gas are converted to the second methanol-containing product stream in the main reactor stage as a combined gas stream.

[0036] A preferred embodiment of the process according to the application comprising a synthesis loop is characterized in that, for a recycle rate R, the following applies:

[0037]

[0038] R < 2.5.

[0039] Preferably 1.5 < R < 2.5, particularly preferably 1.5 < R < 2.

[0040] A preferred embodiment of the process according to the application is characterized in that the main reactor stage comprises n partial reactor stages arranged in series, and the second methanol-containing product stream n comprises methanol-containing partial product streams, wherein methanol is separated from the n methanol-containing partial product streams and is discharged from the main reactor stage.

[0041] As an alternative to the configuration of the main reaction stage as a synthesis loop, a configuration of the main reaction stage as a system of partial reaction stages arranged in series is conceivable. The partial reactor stages preferably correspond to reactors into which the nth partial residual gas stream is introduced, wherein the partial reactor stages are passed through by the nth partial residual gas stream in a single pass, and the nth methanol-containing partial product stream is discharged from each partial reactor stage.

[0042] A preferred embodiment of the process according to the application is characterized in that the pre-reactor stage comprises a water-cooled reactor.

[0043] The cooling of the reactor of the pre-reactor stage is preferably carried out via high-pressure boiling water, wherein the steam generated thereby is fed to a steam drum for energy recovery.

[0044] A preferred embodiment of the process according to the application is characterized in that the water-cooled reactor has a cooling temperature of 180 °C to 250 °C. The water-cooled reactor preferably has a cooling temperature of less than 235 °C, particularly preferably a cooling temperature of 200 °C to 235 °C.

[0045] The cooling temperature is understood to mean the temperature of the medium used for cooling at the outlet of the cooling side of the reactor. On the process side, the temperature along the catalyst bed is adapted to the cooling temperature selected. It is important that the temperature is not below a certain temperature in order to ensure operation above the ignition temperature of the catalyst.

[0046] A preferred embodiment of the process according to the application is characterized in that the main reactor stage comprises a water-cooled reactor. The main reactor stage preferably additionally comprises a gas-cooled reactor, wherein the gas-cooled reactor is arranged in particular downstream of the water-cooled reactor.

[0047] Studies have shown that the combined use of a water-cooled reactor and a gas-cooled reactor leads to particularly great savings in terms of compressor output. Due to the use of two reactors, the expenditure on the total volume of catalyst required is slightly higher, but this can be compensated by the additional savings in compressor output.

[0048] An alternative embodiment thereof is characterized in that the main reactor stage does not comprise a gas-cooled reactor. The main reactor stage comprises in particular only a water-cooled reactor.

[0049] As the study shows, the savings in terms of compressor output when using a single water-cooled reactor are only marginally lower compared to configurations including a water-cooled reactor and a gas-cooled reactor. However, the slightly higher compressor output is compensated by the possibility to reduce the total catalyst volume.

[0050] If both the pre-reactor stage and the main reactor stage each comprise a water-cooled reactor, both water-cooled stages can be operated with the same cooling system. In other words, the pre-reactor stage and the main reactor stage are supplied by a common cooling system. This is preferred when both stages have the same target cooling temperature.

[0051] The above configuration is employed especially when the main reactor stage is configured as a synthesis loop. The synthesis loop then preferably comprises a water-cooled reactor and a downstream gas-cooled reactor, or alternatively only a water-cooled reactor

[0052] The object of the present invention is further at least partially achieved by an apparatus for producing methanol from an input gas comprising carbon monoxide (CO) and hydrogen (H2), the apparatus comprising a supply conduit for introducing the input gas at high pressure into a pre-reactor stage, wherein the pre-reactor stage is configured for catalytically converting the input gas into a first methanol-containing product stream;

[0053] a first separator arranged downstream of the pre-reactor stage and connected to the pre-reactor stage via a conduit for separating methanol from the first methanol-containing product stream and for separating a residual gas stream;

[0054] a supply conduit connected to the first separator for introducing the residual gas stream into a gas compressor;

[0055] a supply conduit for introducing the residual gas stream compressed to a reaction pressure in the gas compressor into a main reactor stage, wherein the main reactor stage is configured for catalytically converting the residual gas stream into a second methanol-containing product stream;

[0056] a second separator arranged downstream of the main reactor stage and connected to the main reactor stage via a conduit for separating methanol from the second methanol-containing product stream,

[0057] characterized in that

[0058] the pre-reactor stage is configured for converting an input gas having a carbon monoxide content of 25% to 36% by volume.

[0059] The object of the present invention is further at least partially achieved by using the above apparatus for producing methanol from an input gas comprising carbon monoxide (CO) and hydrogen (H2) to convert an input gas having a carbon monoxide content of 25% to 36% by volume.

[0060] It is preferred when the input gas has been generated by gasification of coal, by autothermal reforming or by gas POX.

[0061] Input gas

[0062] The input gas is a gas mixture comprising at least carbon monoxide (CO) and hydrogen (H2) as gas components. This makes the input gas suitable for the production of methanol. Depending on the production type, the input gas is inter alia synthesis gas, water gas or cracking gas. The input gas is preferably, but not limited to, generated by gasification of coal. Pure autothermal reformers (ATR) or plants for the partial oxidation of gaseous carbon-containing inputs (gas POX) can also produce synthesis gas with a high CO content, which are suitable for the method of the present invention.

[0063] The electrolysis of carbon dioxide is also suitable as a source of carbon monoxide, which preferably uses electricity from renewable sources to produce a CO-rich material stream.

[0064] In one embodiment of the present invention, the input gas has a carbon monoxide content of 25% to 36% by volume, the reported contents mentioned in the context of the present invention and further reported contents always relate to the dry input gas. Dry input gas is to be understood to mean that water has been completely or substantially completely removed from the input gas. In one example, the water is removed to a residual content of not more than 1% by volume, or not more than 0.5% by volume, or not more than 0.3% by volume, or not more than 0.1% by volume.

[0065] The input gas typically comprises carbon dioxide (CO2) as a further component. In certain cases, the carbon dioxide is completely removed or at least reduced to trace levels in the case of a gas wash, for example in the case of a gas wash with methanol as wash medium.

[0066] Optional components in the input gas are, for example, methane (CH4) and inert ingredients such as nitrogen (N2) or argon (Ar).

[0067] The input gas, in particular the input gas from coal gasification, is typically subjected to a gas wash before use in order to remove sulphur-containing components, such as hydrogen sulphide (H2S) and carbonyl sulphur (COS), since sulphur-containing substances are poisons for the catalysts used in methanol synthesis. In the case of a gas wash, carbon dioxide is typically also removed to some extent, but in most cases the carbon dioxide removal is incomplete. The gas wash can be a method which operates, for example, according to the principle of physical absorption or chemical absorption. One example of a gas wash method which operates according to the principle of physical absorption is the methanol wash, also known as the Rectisol method. One example of a gas wash method which operates according to the principle of chemical absorption is a gas wash using amines.

[0068] To establish a certain ratio of carbon monoxide to hydrogen in the input gas and / or to establish a certain proportion of carbon dioxide, the input gas can partly comprise synthesis gas produced by a water gas shift reaction. The water gas shift reaction serves to increase the proportion of hydrogen while reducing the proportion of carbon monoxide in the synthesis gas, water gas or cracking gas. Since the input gas preferably has a high carbon monoxide content, the proportion of gas that has been subjected to the water gas shift reaction in the input gas is preferably low.

[0069] The input gas is produced at high pressure and is at high pressure before being introduced into the pre-reactor stage. The production of the input gas is typically carried out at a pressure that is significantly higher than atmospheric pressure, usually at least at a pressure of 20 bar up to a pressure of 100 bar. The pressure at which the input gas is produced essentially corresponds to the pressure at which the input gas is before being introduced into the pre-reactor stage. Due to unavoidable pressure drops, the pressure at which the input gas is introduced into the pre-reactor is slightly lower than the pressure during production.

[0070] Pre-reactor stage, main reactor stage, residual gas stream

[0071] The input gas is first supplied to the pre-reactor stage. The stage converts the input gas partly into a first methanol-containing product stream which comprises not only methanol but also, depending on the carbon dioxide content of the input gas, water. The first methanol-containing product stream (and also the further methanol-containing product stream) further comprises by-products, such as dimethyl ether, methyl formate, acetone, ethanol and higher alcohols. The mixture of methanol-containing product streams is preferably discharged from the pre-reactor stage after condensation in a separator. The remaining input gas that is not converted in the pre-reactor stage, also referred to as residual gas, is supplied as a residual gas stream to the main reactor stage. The main reactor stage converts the residual gas substantially completely into a (second) methanol-containing product stream which in turn comprises methanol, water and by-products. The second methanol-containing product stream is preferably also discharged from the main reactor stage after condensation in a separator.

[0072] The pressure in the main reactor stage is usually higher than the pressure in the pre-reactor stage, so that a gas compressor, here also referred to as residual gas compressor, is required to compress the residual gas to the pressure required in the main reactor stage.

[0073] The methanol-containing product streams from the pre-reactor stage and the main reactor stage are typically combined and processed to produce methanol having a predetermined purity.

[0074] Reaction pressure

[0075] The reaction pressure is the prevailing pressure required for the catalytic conversion of the constituents of the residual gas and / or the recycle gas into methanol, at which the residual gas and / or the recycle gas are introduced into the main reactor stage.

[0076] In one example, the reaction pressure in the associated reactor is 60 to 120 bar, preferably 70 to 100 bar, particularly preferably 75 to 90 bar, more preferably 75 to 85 bar.

[0077] Synthesis loop and recycle gas stream

[0078] If the main reactor stage is configured as a synthesis loop, a part of the residual gas is provided as a residual gas stream from the pre-reactor stage to the reactor or reactors (arranged in series) of the main reactor stage, and a part of the recycle gas is provided which has passed through one or more reactors of the main reactor stage. In one example, both the residual gas stream and the recycle gas stream are each compressed to the pressure of the main reactor stage required for the methanol synthesis reaction by a dedicated gas compressor. In another example, a single gas compressor comprising multiple compression stages is used for compressing both gas streams. In this case, the recycle gas stream can be supplied directly to the second compression stage together with the residual gas stream, wherein both gas streams are compressed to the reaction pressure.

[0079] The ratio of the volumetric flow rate of the recycle gas stream to the volumetric flow rate of the residual gas stream is referred to as the recirculation rate R.

[0080] Partial reactor stage

[0081] If the pre-reactor stage or the main reactor stage each comprises multiple reactors, each reactor can also be referred to as a partial reactor stage (of the pre-reactor stage or the main reactor stage).

[0082] Working examples

[0083] The present application is explained more specifically below by way of examples, but without limiting the subject matter of the present application in any way. Other features, advantages and possible applications of the present application will become apparent by the following description of working examples in conjunction with the accompanying drawings and numerical examples.

[0084] In these figures:

[0085] Figure 1 is a schematic flow diagram of the inventive method 100 or the inventive apparatus 100 according to the first example of the present application, and

[0086] Figure 2 is a schematic flow diagram of the inventive method 200 or the inventive apparatus 200 according to the second example of the present application.

[0087] In accordance with Figure 1In the example of Figure 1, the process according to the application comprises a main reactor stage which is configured as a synthesis loop. The synthesis loop comprises a water-cooled reactor (WCR) and a gas-cooled reactor (GCR) as partial reactor stages. Synthesis gas from a coal gasification plant is supplied at a pressure of 50 bar via line 101 to a pre-reactor 102. According to Figure 1 The pre-reactor stage according to Figure 1 comprises only the pre-reactor 102. The synthesis gas in line 101 has a CO content of 29.3% by volume, a H2 content of 67.8% by volume, a CO2 content of 2.53% by volume, and as residual components methane (CH4), and inert components such as nitrogen (N2).

[0088] The synthesis gas from line 101 is pre-heated in heat exchanger 103 by a methanol-containing product stream from line 104 and introduced via line 105 to the pre-reactor 102. The pre-reactor 102 is configured as a water-cooled reactor and is cooled by high-pressure boiling water. Water is supplied from a drum 145 via line 106 and at least partially evaporated on the cooling side of the reactor. The drum 145 is supplied with boiler feed water 147. The steam or partially evaporated stream leaves the cooling side of the reactor via line 107 and is supplied to the drum 145. The generated steam is discharged as blowdown steam 146 from the drum 145 and can be used, for example, as heating steam at another location.

[0089] In the pre-reactor 102, CO, H2 and CO2 are partially converted to methanol on a copper-based fixed-bed catalyst at a cooling temperature of about 230°C. The resulting first methanol-containing product stream in line 104 is pre-cooled in heat exchanger 103 by the synthesis gas from line 101 and supplied via line 108 to a product cooler 109. The cooled methanol-containing product then enters a separator 111 via line 110, in which the methanol-containing product stream is separated into a liquid phase and a gas phase. The condensed raw methanol is withdrawn from the separator 111 via line 112 and combined with the raw methanol from line 131.

[0090] The unconverted synthesis gas is discharged as a residual gas stream from the separator 111 via line 113 and supplied to a compressor (residual gas compressor) 114, in which the residual gas is compressed to a pressure of 80 bar before being introduced via line 115 as a residual gas stream together with a recycling gas stream from line 143 to a main reactor stage comprising a gas-cooled reactor and a water-cooled reactor.

[0091] In the main reactor stage, the residual gas stream from conduit 115 and the recycle gas stream are first passed through a plurality of inner tubes 117 of a gas-cooled reactor 116, in which the residual gas and recycle gas from conduit 115 are preheated, while the reaction residual gas and recycle gas from conduit 118 are cooled outside the inner tubes. The preheated residual gas and recycle gas enter a water-cooled reactor 120 via conduit 119, in which they are partially converted to methanol over a copper-based fixed bed catalyst at a cooling temperature of about 230°C. The water-cooled reactor 120 is cooled by high pressure boiling water. Water is supplied from a drum 145 via conduit 121. Steam or partially evaporated stream leaves the cooling side of the reactor via conduit 122 and is supplied to the drum 145. The generated steam is discharged from the drum 145 as exhaust steam 146 and can be used, for example, as heating steam at another location.

[0092] The reaction of the residual gas and recycle gas in the water-cooled reactor 120 provides a second methanol-containing (partial) product stream, which is discharged from the water-cooled reactor 120 via conduit 123 and pre-cooled in a heat exchanger 124 by the residual gas / recycle gas from conduit 125. The pre-cooled methanol-containing product stream then enters an air cooler 127 via conduit 126 and a high-pressure separator 129 via conduit 128, in which the methanol-containing product stream is separated into a liquid phase and a gas phase. The condensed raw methanol is withdrawn from the high-pressure separator 129 via conduit 130 and further supplied to a low-pressure separator 132 via conduit 131. The gas phase separated in the high-pressure separator is withdrawn via conduit 125 as residual gas and recycle gas and heated in the heat exchanger 124 by the methanol-containing product stream from conduit 123 and introduced into the gas-cooled reactor 116 via conduit 118. In the gas-cooled reactor 116, the residual gas / recycle gas from conduit 118 is partially converted to a second methanol-containing product, which is carried out outside the inner tubes 117 over a copper-based fixed bed catalyst, and the product is withdrawn as a second methanol-containing (partial) product stream via conduit 133. The methanol-containing product is then cooled in a product cooler 134 and supplied to a high-pressure separator 136 via conduit 135. The raw methanol withdrawn from the high-pressure separator 136 via conduit 137 is combined with the raw methanol from conduit 130 and conduit 112 in conduit 131. Further gaseous components dissolved in the raw methanol are separated from the combined raw methanol in the low-pressure separator 132 and leave the low-pressure separator 132 via conduit 138. The gas withdrawn from the low-pressure separator via conduit 138 comprises about 30% by volume of hydrogen and about 25% by volume of methane and can be used, for example, for combustion in a burner for steam reforming. The condensed raw methanol is withdrawn from the low-pressure separator 132 via conduit 139 and sent for further processing to obtain pure methanol.

[0093] The gas separated in the high-pressure separator 136 is withdrawn from the high-pressure separator 136 as a recycle gas stream via a conduit 140 and is supplied via a conduit 141 to a compressor (recycle gas compressor) 142, in which the recycle gas is compressed to a pressure of 80 bar. The recycle gas stream is combined with the residual gas stream via a conduit 143 in the conduit 115 and is supplied first to the water-cooled reactor 120 and then to the gas-cooled reactor 116 as a combined stream of residual gas and recycle gas.

[0094] In the example according to Figure 1 , the ratio of the recycle gas stream to the residual gas stream, also referred to as the recirculation rate R, is 1.9. The purge gas is diverted from the recycle gas in the conduit 140 via a conduit 144 and contains not only components which are inert per se, such as nitrogen, and components which are inert with respect to the methanol synthesis, such as methane, but also, for example, unconverted hydrogen, which can subsequently be recovered, for example, using a pressure swing adsorption device (not shown).

[0095] In the example according to Figure 2 , the process according to the application likewise comprises a main reactor stage which is configured as a synthesis loop. The synthesis loop comprises only a water-cooled reactor (WCR) as reactor stage and no gas-cooled reactor (GCR). The synthesis gas from the coal gasification plant is supplied via a conduit 201 to a pre-reformer 202 at a pressure of 50 bar. The pre-reformer stage according to Figure 2 comprises only the pre-reformer 202. The synthesis gas in the conduit 201 has a CO content of 29.3% by volume, a H2 content of 67.8% by volume, a CO2 content of 2.53% by volume, and as residual components methane (CH4) and inert components such as nitrogen.

[0096] The synthesis gas from the conduit 201 is preheated in a heat exchanger 203 by a methanol-containing product stream from a conduit 204 and is introduced into the pre-reformer 202 via a conduit 205. The pre-reformer 202 is configured as a water-cooled reactor and is cooled by high-pressure boiling water. Water is supplied from a drum 230 via a conduit 206 and is at least partially evaporated on the cooling side of the reactor. The steam or partially evaporated stream leaves the cooling side of the reactor via a conduit 207 and is supplied to the drum 230. The generated steam is discharged from the drum 230 as blowdown steam 231 and can be used, for example, as heating steam at another location.

[0097] In the pre-reactor 202, CO, H2and CO2are partially converted to methanol over a copper-based fixed bed catalyst at a cooling temperature of about 230°C. The resulting first methanol-containing product stream in line 204 is pre-cooled in heat exchanger 203 from the synthesis gas in line 201 and is supplied via line 208 to product cooler 209. The cooled methanol-containing product then enters separator 211 via line 210, in which the methanol-containing product stream is separated into a liquid phase and a gas phase. The liquid crude methanol is withdrawn from the separator 211 via line 212 and combined with the crude methanol from line 229.

[0098] The unconverted synthesis gas is withdrawn from the separator 211 as a residual gas stream via line 213 and is supplied to a compressor (residual gas compressor) 214, in which the residual gas is compressed to a pressure of 80 bar before being introduced as a residual gas stream via line 215 together with a recycle gas stream from line 216 to the main reactor stage, which comprises only a water-cooled reactor.

[0099] In the main reactor stage, the residual gas stream and the recycle gas stream from line 215 are first pre-heated in heat exchanger 217 from the second methanol-containing product stream in line 218 and then introduced via line 219 to the water-cooled reactor 220. In the water-cooled reactor 220, the residual gas / recycle gas is partially converted to methanol over a copper-based fixed bed catalyst at a cooling temperature of about 230°C. The water-cooled reactor 220 is cooled by high pressure boiling water, which is supplied via line 221. Steam or partially evaporated stream leaves the cooling side of the reactor via line 222 and is supplied to the steam drum 230. The steam produced in the steam drum 230 is withdrawn from the steam drum 230 as a blowdown steam 231 and can be used, for example, as heating steam at another location. The reaction of the residual gas and the recycle gas in the water-cooled reactor 220 provides a second methanol-containing (partial) product stream, which is withdrawn from the water-cooled reactor 220 via line 218 and pre-cooled in heat exchanger 217 from the residual gas / recycle gas in line 215. The pre-cooled methanol-containing product stream then enters air cooler 224 via line 223, product cooler 226 via line 225 and finally separator 228 via line 227, in which the methanol-containing product stream is separated into a liquid phase and a gas phase. The crude methanol is withdrawn from the separator 228 via line 229 and can be further processed, for example, together with the crude methanol from line 212 to provide pure methanol.

[0100] The gas separated in the separator 228 is withdrawn from the separator 228 as a recycle gas stream via conduit 230 and is supplied via conduit 231 to a compressor (recycle gas compressor) 232 in which the recycle gas is compressed to a pressure of 80 bar. The recycle gas stream is combined with the residue gas stream in conduit 215 via conduit 216 and is supplied to the water-cooled reactor 220 as a combined stream of residue gas and recycle gas.

[0101] In the example of Figure 2 the ratio of recycle gas stream to residue gas stream, also referred to as the recycle ratio R, is 2.4. The purge gas is diverted from the recycle gas in conduit 230 via conduit 233 and contains not only components which are inert as such, such as nitrogen, but also components which are inert with respect to the methanol synthesis, such as methane, and contains, for example, unconverted hydrogen, which can subsequently be recovered, for example, using a pressure swing adsorption device (not shown).

[0102] The following numerical examples are intended to further illustrate the technical effect of the present invention.

[0103] The following table includes three comparative examples (non-inventive) examining the effect of a pre-reactor on achievable savings in total compressor output (output of residue gas compressor and recycle gas compressor) for a synthesis gas from combined reforming. The synthesis gas has a relatively low carbon monoxide content of 20.9% by volume and a relatively high carbon dioxide content of 8.46% by volume. The required compressor output of 31.5 MW according to comparative example 1 (without pre-reactor) is normalized to 100%. In the case of comparative example 2 (with pre-reactor, in the configuration illustrated according to Figure 1 , savings of 5% are achieved. In the case of comparative example 3 (with pre-reactor, in the configuration illustrated according to Figure 2 , savings of 19.5% are achieved. Savings of less than 10% of the total compressor output do not justify the use of a pre-reactor. Although the savings are higher in the comparative examples, they are still significantly lower than in similar example 2, in which the total amount of catalyst required is also significantly lower.

[0104]

[0105] The following table includes a fourth comparative example (non-inventive) and two inventive embodiments examining the effect of a pre-reactor on achievable savings in compressor output for a synthesis gas from coal gasification. In contrast to the case in the above table, the synthesis gas has a significantly higher carbon monoxide content of 29.3% by volume and a significantly lower carbon dioxide content of 2.53% by volume. The required compressor output of 17.1 MW according to comparative example 4 (without pre-reactor) is normalized to 100%. Example 1 corresponds to comparative example 4 with a pre-reactor in the configuration illustrated according to Figure 1and the configuration described in the accompanying description. Example 2 corresponds to the configuration according to Figure 2 Figure 1 and the configuration described in the accompanying description. Compared to Comparative Example 4 (without pre-reactor), Example 1 achieves a surprisingly high percentage saving of 31.7% in terms of compressor output. Compared to Comparative Example 4 (without pre-reactor), Example 2 achieves a surprisingly high percentage saving of 27.9% in terms of compressor output. Thus, when pursuing the pre-reactor concept and in combination with an input gas having a high CO content, there is a synergistic effect on the achievable savings in terms of output of the compressor. In other words, due to the significant savings in terms of total output of the compressor required, the use of a pre-reactor proves to be reasonable with input gases having a high carbon monoxide content according to the present application.

[0106] At the same time, according to Example 2, the total volume of catalyst required at unchanged production volume is reduced significantly by 17.4% and the space-time yield is increased in an advantageous manner.

[0107]

[0108] Embodiments of the application are described with reference to different types of subject matter. Specifically, some embodiments are described with reference to method claims, while other embodiments are described with reference to apparatus claims. However, as will be apparent to those skilled in the art in light of the foregoing disclosure, any combination of features from any of the different types of subject matter or claims can be contemplated, unless otherwise stated. All features can be combined in any combination to achieve a synergistic effect that is more than the simple sum of the technical features.

[0109] While the application has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The application is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in the field of the art, from a study of the drawings, the disclosure, and the appended claims.

[0110] In the claims, the word "comprising" or "including" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different claims depend on a common independent claim or claims does not indicate that the referenced dependent claims, if any, are mutually exclusive with each other in their entirety.

[0111] List of reference signs

[0112] 100 Method or apparatus

[0113] 101 Pipe

[0114] 102 Pre-reactor

[0115] 103 Heat exchanger

[0116] 104-108 pipes

[0117] 109 product cooler

[0118] 110 pipe

[0119] 111 separator

[0120] 112, 113 pipes

[0121] 114 compressor

[0122] 115 pipe

[0123] 116 gas-cooled reactor (GCR)

[0124] 117 inner tube

[0125] 118, 119 pipes

[0126] 120 water-cooled reactor (WCR)

[0127] 121-123 pipes

[0128] 124 heat exchanger

[0129] 125, 126 pipes

[0130] 127 air cooler

[0131] 128 pipe

[0132] 129 high-pressure separator

[0133] 130, 131 pipes

[0134] 132 low-pressure separator

[0135] 133 pipe

[0136] 134 product cooler

[0137] 135 pipe

[0138] 136 high-pressure separator

[0139] 137-141 pipes

[0140] 142 compressor

[0141] 143, 144 pipes

[0142] 145 drum

[0143] 146 blowdown steam

[0144] 147 boiler feed water

[0145] 200 method or apparatus

[0146] 201 conduit

[0147] 202 pre-reactor

[0148] 203 heat exchanger

[0149] 204-208 conduits

[0150] 209 product cooler

[0151] 210 conduit

[0152] 211 separator

[0153] 212, 213 conduits

[0154] 214 compressor

[0155] 215, 216 conduits

[0156] 217 heat exchanger

[0157] 218, 219 conduits

[0158] 220 water cooled reactor

[0159] 221-223 conduits

[0160] 224 air cooler

[0161] 225 conduit

[0162] 226 product cooler

[0163] 227 conduit

[0164] 228 separator

[0165] 229 conduit

[0166] 230 drum

[0167] 231 blowdown steam

[0168] 232 boiler feed water

Claims

1. A method for producing methanol from an input gas comprising carbon monoxide (CO) and hydrogen (H2), wherein, The input gas produced at high pressures of 20 to 100 bar is introduced as an input gas stream into the pre-reactor stage for catalytic conversion into a first methanol-containing product stream, and Methanol is separated from the first methanol-containing product stream and discharged from the pre-reactor stage, and The remaining residual gas in the input gas stream is compressed to the reaction pressure as a residual gas stream and introduced into the main reactor stage for catalytic conversion into a second methanol-containing product stream. Methanol is separated from the second methanol-containing product stream and discharged from the main reactor stage. Its features are, Before being introduced into this pre-reactor stage, the input gas has a carbon monoxide content of 25% to 36% by volume. The main reactor stage includes a water-cooled reactor and an air-cooled reactor, as well as The main reactor stage is part of the synthesis loop, in which the remaining recycled gas stream after separating methanol from the second methanol-containing product stream is recycled back to the main reactor stage in the synthesis loop and combined with the residual gas stream. The sum of the volume percentages of all gases contained in the input gas is 100%.

2. The method according to claim 1, characterized in that, Before being introduced into the pre-reactor stage, the input gas has a hydrogen content of 66% to 72% by volume.

3. The method according to claim 1, characterized in that, The input gas has a carbon dioxide (CO2) content of no more than 5% by volume before being introduced into the pre-reactor stage.

4. The method according to claim 2, characterized in that, The input gas has a carbon dioxide (CO2) content of no more than 5% by volume before being introduced into the pre-reactor stage.

5. The method according to claim 1, characterized in that, Before being introduced into the pre-reactor stage, the input gas has a stoichiometric number (SN) of 1.5 to 3.0, wherein, Where n is in units of [moles].

6. The method according to claim 2, characterized in that, Before being introduced into the pre-reactor stage, the input gas has a stoichiometric number (SN) of 1.5 to 3.0, wherein, Where n is in units of [moles].

7. The method according to claim 3, characterized in that, Before being introduced into the pre-reactor stage, the input gas has a stoichiometric number (SN) of 1.5 to 3.0, wherein, Where n is in units of [moles].

8. The method according to claim 4, characterized in that, Before being introduced into the pre-reactor stage, the input gas has a stoichiometric number (SN) of 1.5 to 3.0, wherein, Where n is in units of [moles].

9. The method according to claim 1, characterized in that, The input gas has a pressure of 35 to 55 bar.

10. The method according to any one of claims 1-8, characterized in that, The input gas produced and present at high pressures of 20 to 100 bar is introduced into the pre-reactor stage without further pressurization.

11. The method according to any one of claims 1-9, characterized in that, The residual gas in the residual gas stream is compressed to a pressure higher than that of the input gas before being introduced into the main reactor stage.

12. The method according to claim 10, characterized in that, The residual gas in the residual gas stream is compressed to a pressure higher than that of the input gas before being introduced into the main reactor stage.

13. The method according to any one of claims 1-9, characterized in that, The recirculation rate R is defined as follows: R≤2.5。 14. The method according to claim 12, characterized in that, The recirculation rate R is defined as follows: R≤2.5。 15. The method according to any one of claims 1-9, characterized in that, The main reactor stage comprises n partial reactor stages arranged in series, and the second methanol-containing product stream comprises n methanol-containing partial product streams, wherein methanol is separated from the n methanol-containing partial product streams and discharged from the main reactor stage.

16. The method according to claim 12, characterized in that, The main reactor stage comprises n partial reactor stages arranged in series, and the second methanol-containing product stream comprises n methanol-containing partial product streams, wherein methanol is separated from the n methanol-containing partial product streams and discharged from the main reactor stage.

17. The method according to any one of claims 1-9, characterized in that, The pre-reactor stage includes a water-cooled reactor.

18. The method according to claim 16, characterized in that, The pre-reactor stage includes a water-cooled reactor.

19. The method according to claim 17, characterized in that, The water-cooled reactor has a cooling temperature range of 180°C to 250°C.

20. The method according to claim 18, characterized in that, The water-cooled reactor has a cooling temperature range of 180°C to 250°C.

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