Process for retrofitting methanol synthesis loop

Abstract

A method for retrofitting a methanol plant, wherein: the plant comprises a synthesis loop (100) having a first converter (1); adjusting a make-up gas (19) obtained by gasification of coal or reforming of hydrocarbons, and adjusting the stoichiometric number of the gas by adding hydrogen gas (21); installing a second methanol converter (23) in the synthesis loop; feeding at least part of the fresh make-up gas added with hydrogen to the first converter (1); and a partial reactant gas (27) effluent from the first converter (1), optionally added with fresh make-up gas (29), forming a feed stream (10), which is sent to the second converter (23) via the recycle compressor (6) of the synthesis loop.

Description

Technical Field

[0001] This invention belongs to the field of methanol production and relates to a method for modifying the synthesis loop of a methanol synthesis equipment, wherein the supplementary gas for methanol synthesis is prepared by coal gasification or hydrocarbon reforming such as natural gas. Background Technology

[0002] Methanol is industrially produced by reacting supplementary syngas (MUG, or syngas) in a so-called synthesis loop. The synthesis loop essentially includes: a catalytic converter that forms methanol; one or more heat exchangers that cool the hot effluent from the converter; a condenser in which the cooled reaction effluent is condensed to produce a methanol-containing liquid product; a separator in which the product is separated from a gaseous fraction containing unreacted gases; and a pipeline arranged to return at least a portion of the gaseous fraction to the converter via a compressor. The compressor maintains the circulation in the loop and is called a recirculator. A common converter is the so-called isothermal converter, which includes a heat exchanger that contacts the catalyst to remove the heat of the reaction.

[0003] The loop receives fresh make-up gas from the main compressor (MUG compressor). This fresh gas can enter either the suction or output side of the recirculator. Therefore, the converter feed is a mixture of fresh and recirculated gas. Non-condensable gases can also be removed from the loop at appropriate locations. Heat exchangers for cooling the hot effluent may include an evaporator to generate steam, and a feed / effluent heat exchanger that preheats the converter feed using the heat removed from the reaction products.

[0004] The makeup gas is a mixture of hydrogen and carbon oxides. Key parameters for the makeup gas are the stoichiometric coefficient (SN) and the molar ratio (CO / CO2). The stoichiometric coefficient is defined as follows: SN=(H2-CO2) / (CO+CO2).

[0005] For methanol synthesis, a makeup gas with an SN of 2.0 or greater is ideal. The CO / CO2 ratio is also an important indicator, representing the reactivity of the gases in the converter and the amount of catalyst required. A high CO / CO2 ratio means less catalyst is needed to produce a given amount of methanol. Clearly, the amount of catalyst used in the converter is a major source of cost, stemming from both the cost of the catalyst itself and the size of the converter.

[0006] Make-up gas can be produced via coal gasification, an attractive method due to the large availability and relatively low cost of coal. However, coal-based methanol plants have drawbacks, namely that the gas obtained directly from gasification typically has a stoichiometric coefficient far below the ideal 2.0, making it unsuitable for methanol synthesis. The coal gasification process inherently results in an excess of carbon relative to hydrogen, thus requiring gas treatment to adjust the stoichiometric coefficient to at least 2.0 or higher.

[0007] The traditional method for adjusting the non-saturated methanol (SN) phase is CO2 removal after a water-gas shift reaction (WGS). Most existing coal-based methanol plants use this approach, producing a highly reactive gas with a CO / CO2 ratio of approximately 8. However, this method suffers from high equipment costs; furthermore, CO2 removal reduces the amount of carbon available for methanol synthesis and introduces environmental problems. Releasing CO2 into the atmosphere increases the carbon intensity of methanol, while CO2 capture increases cost and complexity. Given the growing concern about CO2 emissions, the appeal of this approach is gradually diminishing.

[0008] One possible method to increase the stoichiometric coefficient of the gas is to add hydrogen. If the hydrogen is produced without CO2 emissions (“blue hydrogen”) or from renewable energy sources (“green hydrogen”), the carbon intensity of methanol is also reduced. Therefore, conditioning the make-up gas with blue or green hydrogen is significant, potentially enabling coal-to-methanol production at low cost and with acceptable carbon intensity. However, a major drawback of this method is the low CO / CO2 ratio of the conditioned gas after H2 addition, typically around 3.0. This means the gas has relatively low reactivity and requires more catalyst at given production loads.

[0009] For example, using existing methanol catalysts, the methanol yield per cubic meter of catalyst from coal-derived syngas via conventional conditioning processes (including WGS and CO2 removal) is typically 30 to 33 MTD (metric tons per day), while the methanol yield from syngas obtained by adding hydrogen, as described above, is approximately 18 to 22 MTD / m³. Assuming the methanol synthesis loop was originally designed for coal-derived syngas with a high CO / CO2 ratio through conventional conditioning, and assuming the front end is modified to condition the syngas by adding hydrogen, the loop's converter will be unable to fully convert the new feed (due to insufficient catalyst).

[0010] Many methanol plants rely on coal gasification, creating a strong incentive to retrofit existing facilities to make them more environmentally compliant, particularly by reducing CO2 emissions. This can be considered a “green retrofit” of coal-based methanol plants. However, an attractive retrofit must be industrially acceptable without compromising methanol production efficiency. Current technologies have failed to provide a satisfactory solution in this regard.

[0011] Similar issues arise in methanol plants that produce makeup gas via steam reforming or partial oxidation of hydrocarbons, typically natural gas. In these cases, the SN of the makeup gas is usually higher than in coal-based plants, but may still be lower than 2.0, thus requiring conditioning to adjust the SN.

[0012] Another issue relates to CO2 capture. To reduce emissions into the atmosphere, a more common practice is to capture CO2, for example, from the combustion flue gas of a primary converter or open-flame furnace. CO2 capture theoretically provides additional carbon that can be used in the synthesis reaction; however, this additional carbon needs to be balanced with a suitable amount of hydrogen to maintain a proper makeup gas composition. If CO2 capture is used as an additional carbon source for methanol synthesis, the synthesis loop needs to be modified to accommodate the increased capacity and / or adjusted makeup gas composition. It has been noted that even maintaining nameplate capacity (i.e., without expansion), different compositions of the synthesis gas still require modifications to the synthesis loop, especially since the amount of catalyst in the converter is often insufficient for the reasons mentioned above.

[0013] WO 2015 / 193440 discloses a series methanol reactor; US 6608113 discloses a method and apparatus for synthesizing methanol using a methanol pre-reactor. Summary of the Invention

[0014] This invention aims to address the problem of how to retrofit existing methanol production facilities to avoid or reduce carbon emissions into the atmosphere while maintaining good energy efficiency and production capacity. Specifically, this invention addresses how to retrofit methanol production facilities when the CO2 content in the makeup gas increases, necessitating the addition of hydrogen to adjust the stoichiometry of the makeup gas. Furthermore, this invention aims to address how to utilize the additional carbon source provided by CO2 captured in the combustion flue gas.

[0015] The problem is solved by the modification method according to claim 1. The dependent claims relate to preferred technical solutions.

[0016] This invention stems from an innovative discovery: an isothermal methanol converter designed for operation under high CO / CO2 ratios, such as 8.0, is generally equally suitable for operation under low CO / CO2 ratios, such as 3.0 and below. In some embodiments of the invention, the reactor may operate as an once-through reactor or substantially as a once-through reactor, wherein the term "once-through" indicates that there is no unreacted gas stream from a once-through converter that is directly returned to the converter after effluent treatment.

[0017] Because increased CO2 content leads to a decrease in the CO / CO2 ratio, adding hydrogen to the makeup gas can adjust the stoichiometric coefficient. This invention cleverly solves this problem. Existing methanol converters, originally designed for loop processing of gases with high CO / CO2 ratios, are used to process some or all of the modified syngas with lower CO / CO2 ratios, while a new converter is installed in the synthesis loop. After the modification, methanol production is partly provided by the existing converter, now reconfigured for low CO / CO2 feed gas, and partly by the synthesis loop with the new converter. Therefore, this invention cleverly utilizes existing equipment to increase capacity or reduce coal input at a given capacity, while simultaneously reducing the overall carbon intensity of the process.

[0018] Preferably, the existing converter operates under no-loop or finite-loop conditions; in some embodiments, the existing converter operates as a single-pass reactor.

[0019] Furthermore, this invention is based on the finding that modifying existing converters to handle all of the make-up gas is impractical due to its reduced reactivity. Existing converters only handle a portion of the feed, while the new reactor installed in the synthesis loop can incorporate lower heat of reaction and is specifically designed for modified synthesis gas.

[0020] The scope of the modification may include reducing CO2 emissions at a given production capacity, or reducing CO2 emissions while increasing production. In summary, this invention enables the application of modern hydrogen production technology—which produces hydrogen in a low-carbon or zero-carbon manner—to existing coal-based methanol plants.

[0021] The method of the present invention is applicable to methanol plants, the methanol plants including a front end in which a makeup gas comprising hydrogen and carbon oxides is prepared, wherein the makeup gas is prepared by coal gasification or steam reforming or partial oxidation of another hydrocarbon such as natural gas, and the methanol plants including a synthesis loop in which the makeup gas is reacted to produce methanol, the synthesis loop including at least one methanol converter, hereinafter referred to as the "first converter".

[0022] The present invention demonstrates beneficial effects when hydrogen is added to the makeup gas to adjust the stoichiometry. The added hydrogen can be used to balance the increase in CO2 content at the front end. In several embodiments, the equipment for adding hydrogen to the makeup gas is installed as a step in the retrofit process.

[0023] The method includes the following steps: The synthesis circuit was improved by installing at least one new second methanol converter; The connections of the converters are rearranged so that the first converter operates as an upstream converter relative to the newly installed second converter, thereby processing a portion of the reactant gas effluent from the first converter, optionally supplemented with fresh make-up gas, to form a feed stream, which is delivered to the second converter via the recirculation compressor. A section of the equipment is modified to process the effluent from the first converter and obtain a first crude methanol product and a gaseous fraction; Pipelines are laid to deliver at least a portion of the fresh supplemental gas, which is infused with hydrogen, to the first converter; Piping is laid to deliver the gaseous fraction to the second reactor via the recirculation compressor; and The first crude methanol product, together with or separately from the second crude methanol product obtained from the synthesis circuit and the effluent obtained by processing the second converter, is sent to distillation.

[0024] Optionally, pipelines are arranged to feed a portion of the recycle gas from the synthesis loop to the first converter.

[0025] In one implementation, the original methanol converter (first converter) is separated from the synthesis loop and the connections are rearranged so that the converter operates as a single-pass converter. Thus, in the loop, the new methanol converter replaces the original converter.

[0026] After the modification is completed, crude methanol streams are obtained from the first converter and the second converter, respectively. The two streams are then sent to the distillation section to obtain methanol of the desired purity.

[0027] The terms "first converter" and "second converter" used in this article may refer to a single converter or a device with multiple converters, such as two converters connected in parallel.

[0028] In one embodiment, the modified equipment is configured such that all the supplemental gas, supplemented with hydrogen, passes through the first converter, and the unreacted gas separated from the first crude methanol forms the entire feed for the synthesis loop. This mode of operation can be referred to as series operation because the feed is first processed in the first converter and then in the synthesis loop.

[0029] In another embodiment, the modified equipment is configured such that the hydrogen-added makeup gas, along with a portion of the recycle gas from the synthesis loop, passes entirely through the first converter, and the unreacted gas separated from the first crude methanol forms the entire feed to the synthesis loop. In yet another embodiment, only a portion of the hydrogen-added makeup gas flows through the first converter, and the unreacted gas separated from the first crude methanol, along with the remaining makeup gas, forms the feed to the synthesis loop. This operation can be referred to as series / parallel operation because the bypass section is processed only in the synthesis loop and is connected in parallel with the first converter.

[0030] In another embodiment, a make-up gas containing only a portion of hydrogen passes through the first converter along with a portion of the recycle gas from the synthesis loop, and unreacted gas separated from the first crude methanol, together with the remaining make-up gas, forms the feed to the synthesis loop. The modified synthesis loop operates downstream of the converter relative to the portion of make-up gas fed to the first converter. This portion of make-up gas reacts in the first converter, and after separating the liquid methanol product, further reacts in the loop. A bypass portion, if present, enters directly into the loop.

[0031] In either case, the synthesis loop with the newly installed second converter provides the additional production capacity needed to process the hydrogen-conditioned syngas. However, the first converter can continue to be used, rather than being simply replaced with a larger one. This is a significant advantage of the present invention.

[0032] The feed to the synthesis loop is a stream of unreacted gas from the first converter, optionally supplemented with fresh make-up gas, which is introduced into the loop via a recirculation compressor. This stream typically flows into the suction side of the recirculation compressor. The recirculation compressor may also receive a recirculation stream containing unreacted gas separated from the effluent of the second converter.

[0033] The method may include: installing a first line arranged to deliver fresh replenishment gas to a first converter, and installing a second line arranged to deliver fresh replenishment gas bypassing the first converter to a modified circuit, and at least one valve arranged to control the amount of fresh replenishment gas in the first and second lines. The valve is preferably installed on the second line (bypass line). Therefore, the modified equipment can selectively operate in either the first operating mode (series) or the second operating mode (series / parallel). Furthermore, in the series / parallel operating mode, the amount of fresh gas bypassing the first converter can be controlled.

[0034] The bypass ratio can vary depending on the hydrogen supply, especially when the hydrogen comes from renewable energy sources and therefore the hydrogen flow rate varies over time. An adjusted CO / CO2 ratio allows equipment operators to change the amount of recirculated gas supplied to the primary pass-through converter.

[0035] Preferably, a pipeline equipped with a control valve is arranged to feed at least a portion of the recirculated gas from the synthesis loop to the first converter. A related advantage is improved operability of the modified overall process layout. In one embodiment, the pipeline is connected to the delivery pipeline of the recirculation compressor, such that a portion of the gas delivered by the recirculation compressor is sent to the first converter. This portion of gas delivered by the recirculation compressor to the first converter is preferably a small amount, for example, less than 50% by mass flow rate, such as less than 40%, or less than 30%, or less than 20%, or less than 10%.

[0036] In embodiments where no gas or only a small amount of gas is fed from the synthesis loop to the first converter, the first converter is essentially operated as a single-pass reactor separate from the synthesis loop.

[0037] In some implementations, the modified equipment may include devices for storing hydrogen and / or energy to reduce fluctuations in hydrogen feed caused by intermittent supply from renewable energy sources.

[0038] Modifications for treating the effluent from the first converter may include installing new equipment and / or modifying existing equipment. A preferred embodiment proposes modifying existing interstage coolers and interstage tanks, originally installed to handle gases delivered by the main syngas compressor, to handle the effluent from the first converter.

[0039] In one embodiment, the equipment originally included a gas line to connect the inter-stage tank to the intake side of the loop recirculator, such that gas drawn from the tank was fed into the synthesis loop; the modification included feeding the effluent of the first converter, optionally mixed with fresh make-up gas, to the inter-stage cooler and the inter-stage tank, such that liquid methanol product was collected from the inter-stage tank, while the gaseous fraction currently containing unreacted gas from the first converter was fed to the intake side of the loop recirculator.

[0040] After the addition of hydrogen, the CO / CO2 ratio of the makeup gas is relatively low, for example, not greater than 4.0 or not greater than 3.0. This invention can accommodate this low ratio determined by the hydrogen-conditioned makeup gas by sending at least a portion of the gas to the first converter and by installing a new converter in the loop.

[0041] In a preferred embodiment, the added hydrogen is at least partially and preferably entirely produced by the electrolysis of water. More preferably, the water electrolysis process is partially or entirely powered by renewable energy sources. Renewable energy sources include solar, wind, biomass, and other naturally renewable energy sources. If the hydrogen is produced entirely from renewable energy sources, the adjustment of the supplementary gas will not release CO2 into the atmosphere. Therefore, the method of the present invention may include the installation of a suitable hydrogen production unit. Hydrogen produced from renewable energy sources is commonly referred to as "green hydrogen."

[0042] The hydrogen used to regulate the makeup gas may also include hydrogen separated from the loop purge gas. This hydrogen is recovered within the process, reducing fluctuations caused by the intermittent production of green hydrogen.

[0043] In some implementations, the improved synthesis loop includes installing a waste heat collector arranged to cool the effluent from a new methanol converter. Preferably, the waste heat collector is a batch evaporator to generate steam.

[0044] The new methanol converter (second converter) is preferably an isothermal converter. This term refers to a reactor comprising a catalyst bed and a heat exchanger immersed in the catalyst and through which a cooling medium flows, such that most of the heat of reaction is transferred to the cooling medium during operation, and the temperature of the catalyst bed remains substantially constant within a target range. In a preferred embodiment, the heat exchanger may be tubular or plate-type. The cooling medium may be a gas, such as fresh make-up gas, or steam. Gas-cooled reactors have the advantage of eliminating the need for auxiliary equipment such as steam drums and recirculation pumps. In contrast, adiabatic reactors have a heat exchanger downstream of the catalyst bed so that heat is removed from the effluent gas rather than from the catalyst.

[0045] Preferably, the new methanol converter has an axial or shaft-mounted design. The gas flow passes radially through the catalyst bed. In a preferred embodiment, the novel methanol converter is a gas-cooled reactor. Preferred embodiments include any of the following forms: plate-cooled reactor, axial-radial gas-cooled reactor, and plate-cooled steam rise reactor. Axial-radial flow is preferred due to its lower pressure drop. Isothermal steam rise reactors are particularly preferred because they are suitable for regulated gas composition and have sufficient flexibility to handle variations in feed flow rate, thanks to the ability to regulate steam pressure.

[0046] If the second converter is a gas-cooled reactor, heat recovery can be advantageously achieved through a waste heat collector located downstream of the converter. The waste heat collector can be designed to generate low-pressure steam or preheat boiler feedwater or refined demineralized water.

[0047] Other equipment in the existing synthesis loop can be modified or replaced as needed. For example, the circulation machine can be modified if the improved loop has relevant requirements. As mentioned above, using an axial-radial flow converter as a second converter in the loop reduces or eliminates the need to modify the circulation machine due to the lower voltage drop.

[0048] The method may include installing a new feed-effect heat exchanger in the synthesis loop. The existing feed-effect heat exchanger is typically retained in the main loop, but for greater convenience, the feed-effect heat exchanger may be moved along with the first converter, and a new feed-effect heat exchanger may be installed in the main loop.

[0049] In a preferred embodiment, the new methanol converter integrates a new feed-effect heat exchanger housed within the pressure vessel of the converter. In a highly preferred embodiment, the feed-effect heat exchanger is fitted into the central chamber of an annular catalyst bed, such that the catalyst bed is arranged concentrically around the effect heat exchanger. This arrangement is applicable to embodiments with adiabatic or isothermal catalyst beds. The effect heat exchanger is arranged to transfer heat from the methanol-containing hot gaseous effluent from the catalyst bed to the feed stream of the converter. As an alternative or supplement to the above, the new converter may also include an internal heat exchanger arranged to transfer heat to a cooling medium such as water or steam.

[0050] The retrofitting method can include more steps depending on the specific requirements, especially when there is a significant increase in production capacity. For example, an existing hydrogen recovery unit (HRU) used to recover hydrogen from the purge gas in the loop can be retrofitted, or a new HRU can be installed. Attached Figure Description

[0051] The present invention will now be described with reference to the accompanying drawings, wherein: Figure 1 This is a simplified schematic diagram of the methanol synthesis circuit in the prior art; Figure 2 The modified version according to the embodiment of the present invention Figure 1 A schematic diagram of the circuit shown.

[0052] exist Figure 1 and Figure 2 In this context, streamline numbers represent both fluid flow and the physical connection of pipes between different devices. Detailed Implementation

[0053] Figure 1A simplified flow diagram of a methanol synthesis loop 100 is shown. The methanol synthesis loop 100 includes the following equipment: a methanol converter 1, a heat exchanger 2 arranged inside the converter 1, a feed / effluent heat exchanger 3, a loop condenser 4, a high-pressure separator 5, and a recirculating unit 6. This is well known to those skilled in the art. Figure 1 The process shown is a typical methanol synthesis loop, and will only be briefly described here.

[0054] In methanol converter 1, feed gas 16 undergoes a catalytic reaction to form methanol. The effluent (line 27) of converter 1 is cooled in feed / effluent heat exchanger 3 and then sent to loop condenser 4 and separator 5 to obtain crude methanol 7. The gaseous fraction 8 is then recycled back to converter 1 via recirculator 6. The internal heat exchanger 2 of converter 1 is connected to a steam line 9, which typically includes a steam drum (not shown).

[0055] The loop 100 receives fresh supplemental gas 10 from hydrocarbons 11 in the front end 12.

[0056] In some embodiments, hydrocarbon 11 is coal, and front-end 12 includes at least one coal gasifier. In other embodiments, front-end 12 operates via steam reforming, including pure steam reforming, pure autothermal reforming, or a combination of both. The term combined reforming refers to a process involving first-stage steam reforming followed by autothermal reforming. The term pure autothermal reforming refers to autothermal reforming without a first-stage reforming. The first-stage reforming can be carried out in an open-flame furnace or a gas-heated reactor.

[0057] Front-end 12 prepares supplementary gas 19, which is pressurized to methanol synthesis pressure by main compressor 13 (MUG compressor). The delivery line 18 of main compressor 13 is connected to interstage cooler 14 and interstage tank 15 to remove condensate. Dry gas 10 from tank 15 is sent to the suction side of recirculator 6 and forms the feed gas of synthesis loop 100.

[0058] The converter feed 16 includes fresh gas 10 and recirculated gas 8. The synthesis loop 100 discharges purge gas at line 17. In this example, the purge gas is discharged from the recirculated gas 8 at the intake side of the recirculator 6. The purge gas is typically treated to recover hydrogen (in a hydrogen recovery unit HRU), and the remaining gas can be used as fuel for an open-flame furnace, or as fuel for a first-stage converter if it is equipped with a front-end 12.

[0059] Heat exchangers, such as feed-effect heat exchangers, transfer heat from a hot medium to a cold medium without direct contact (mixing) between the materials. Therefore, the heat exchanger can be divided into a "hot side" and a "cold side," with correspondingly distinct "hot" and "cold" inlets / outlets. For example, feed / effect heat exchanger 3 has a hot side through which the converter effluent flows, and a cold side through which the feed stream 16 flows.

[0060] Figure 2 A modification scheme according to one embodiment of the present invention is shown.

[0061] A hydrogen source 20 is provided to generate a hydrogen flow 21, which is added to the syngas 19. The main compressor 13 receives the syngas 22 obtained through the above-described conditioning process. Particularly preferably, the hydrogen source 20 comprises a hydrogen generator that produces hydrogen through the electrolysis of water, and the generator is powered by renewable energy sources, such as solar or wind power.

[0062] The synthesis loop 100 is improved by adding a new catalytic methanol converter 23, a heat collector 24 arranged to remove heat from the effluent of the new converter 23, and a new feed / effluent heat exchanger 25.

[0063] The new converter 23 essentially replaces the original converter 1 as the main converter of loop 100. Hereinafter, the original converter 1 will be referred to as the "first converter," and the new converter 23 as the "second converter." A line 26 conveying the cooled effluent from the second converter 23, after passing through a heat collector 24, connects to the hot inlet of a feed-effluent heat exchanger 3, replacing the effluent from the first converter 1. The heat collector 24 is preferably a kettle-type heat exchanger to generate steam.

[0064] The effluent line 27 of the first converter 1 is disconnected from the feed-effluent heat exchanger 3 and reconnected to the hot inlet of the new feed / effluent heat exchanger 25.

[0065] The main compressor 13's delivery line 18 is divided into a first line 28 leading to the first converter 1 and a second line 29 bypassing the first converter 1 and leading to the circuit 100. The bypass flow is controlled by valve 30.

[0066] A portion of the recirculated gas in pipeline 8 can be sent to the first converter 1. Figure 2 One embodiment is shown, in which a line 41 equipped with a control valve is arranged to feed a portion of the recirculated gas from the circulator 6 to the first converter 1. In the example, the line 41 connects the feed line 16 to the line 28 leading to the first converter 1.

[0067] Pipeline 28 is connected to the cold inlet of heat exchanger 25. The effluent 27 preheats pipeline 28, and the resulting preheated gas 31 is fed into the first converter 1.

[0068] With the above modifications, the first converter 1 is effectively separated from the loop 100 and rearranged to process the feed gas in line 28, which can optionally be supplemented with a portion of the recirculated gas from the loop. On the other hand, the gas in line 29 bypasses the first converter 1 and is processed in the synthesis loop 100, which is improved by installing the second converter 23.

[0069] Clearly, the first methanol converter 1 operates as an upstream converter relative to the second converter 23, and a portion of the reactant gas effluent from the first converter 1 is sent to the second converter 23 via the recirculation compressor 6. A portion of the reactant gas from the first converter 1 reaches the second converter 23 via line 10 connected to the suction side of the recirculation compressor 6. As shown, the recirculation compressor 6 simultaneously receives recirculated gas from line 8.

[0070] The cooled effluent 32, optionally mixed with fresh gas from line 29, is sent to section 101 for crude methanol separation. In this example, the effluent is sent to inter-section cooler 14 and inter-section tank 15. A first methanol product 7.1 is obtained from inter-section tank 15, while the gaseous fraction is sent via line 10 to recirculator 6 to feed into synthesis loop 100. Recirculator 6 sends a portion of the unreacted gas from tank 15 and a portion of the recirculated gas 8 from loop 100 to section 25 and section 3. In loop 100, a second methanol product 7.2 is obtained from high-pressure separator 5.

[0071] It should be noted that the interstage cooler 14 and tank 15 receive reaction effluent via line 32, which can optionally be mixed with fresh gas from line 29, rather than as... Figure 1 The tank receives fresh gas from the main compressor. Furthermore, tank 15 now needs to separate methanol product 7.1. For this purpose, if conditions permit, cooler 14 and / or tank 15 can be modified or replaced with new units. For example, if the pressure vessel requires essentially no modification and only internal components need to be modified or replaced to meet the new application, then modification is a convenient option.

[0072] Product streams 7.1 and 7.2 are then fed to the distillation section to produce methanol of the required purity. The distillation section can be modified if necessary, especially if the modification involves a significant increase in production capacity.

[0073] Figure 2 One embodiment is shown in which the feed-effect heat exchanger 3 remains in the synthesis loop 100, and a new heat exchanger 25 is installed to preheat the feed to the first converter 1. In an alternative embodiment, the heat exchanger 3 is removed from the loop along with the converter 1 and used as a replacement. Figure 2The heat exchanger 25 in the converter preheats the feed to the converter. In this case, a new feed-effect heat exchanger can be installed in the synthesis loop 100. In a particularly preferred embodiment, the new feed-effect heat exchanger is installed inside the pressure vessel of the second converter 23. In a preferred embodiment, the heat exchanger is installed in the central chamber of the annular catalytic bed of the second converter 23.

Claims

1. A method for retrofitting methanol equipment, wherein: The methanol plant originally included a front end and a synthesis loop (100), at which a supplementary gas (19) containing hydrogen and carbon oxides was prepared by a process including coal gasification or steam reforming or partial oxidation of hydrocarbons, and the synthesis loop (100) included at least a first methanol converter (1), which was an isothermal methanol converter. The methanol plant includes a main syngas compressor (13) that feeds into the synthesis loop (100) and a recirculation compressor (6) of the synthesis loop. Hydrogen gas (21) is added to the supplementary gas, or the method includes setting up a device for adding hydrogen gas to the supplementary gas to obtain a regulated supplementary gas (22). Among them, after adding hydrogen, the CO / CO2 molar ratio of the fresh replenishment gas (22) is not greater than 4.

0. The method includes: The synthesis circuit (100) is improved by installing at least one new second methanol converter (23); The connections of the first methanol converter (1) are rearranged so that the converter operates as an upstream converter relative to the newly installed second converter (23), thereby processing a portion of the reaction gas (27) flowing out of the first converter (1) with optional addition of fresh make-up gas (29) to form a feed stream (10), which is delivered to the second converter (23) via the recirculation compressor (6). A section of the equipment (101) is modified to process the effluent (27) of the first converter (1) and obtain a first crude methanol product (7.1) and a gaseous fraction (10). A pipeline (28) is laid to deliver at least a portion of the fresh supplemental gas containing hydrogen to the first converter (1). Piping is laid to deliver the gaseous fraction (10) to the second reactor (23) via the recirculation compressor (6); and The first crude methanol product (7.1) and the second crude methanol product (7.2) are sent together or separately to distillation, the second crude methanol product (7.2) being drawn from the synthesis circuit and obtained by treating the effluent of the second converter.

2. The method according to claim 1, wherein, A pipeline (41) is arranged to feed a portion of the feed gas delivered by the circulating machine (6) to the first converter (1).

3. The method according to claim 1 or 2, wherein, The feed line for the fresh supplemental gas is modified to: The fresh supplemental gas passes entirely through the first converter, and the unreacted gas separated from the first crude methanol forms the entire feed for the synthesis loop; or Only a portion of the supplementary gas passes through the first converter, and the unreacted gas separated from the first crude methanol, together with the remainder of the supplementary gas, forms the feed for the synthesis loop.

4. The method according to claim 3, wherein, The method includes: installing a first line (28) arranged to deliver fresh supplemental gas to the first converter, and installing a second line (29) arranged to deliver fresh supplemental gas around the first converter to the synthesis loop (100), and at least one valve (30) arranged to control the amount of fresh supplemental gas in the first line (28) and the second line (29).

5. The method according to any one of the preceding claims, wherein: The equipment to be modified includes an interstage cooler (14) and an interstage tank (15), which are arranged to receive compressed make-up gas delivered by the main synthesis gas compressor (13), and a gas line (10) connects the interstage tank to the suction side of the circulator (6) of the synthesis loop (100) so that gas drawn from the tank (15) is fed into the synthesis loop; The modification process includes feeding the effluent (32) of the first converter, which can optionally be mixed with fresh make-up gas, to the inter-stage cooler and the inter-stage tank, so that the first crude methanol product is collected from the inter-stage tank. 7.1), wherein the inter-stage cooler (14) and / or the inter-stage tank (15) are modified as needed to treat the effluent and separate the crude methanol product from the unreacted gas.

6. The method according to any one of the preceding claims, wherein, After the addition of hydrogen, the molar ratio of the fresh replenishment gas (22) to CO / CO2 is not greater than 3.

0.

7. The method according to any one of the preceding claims, wherein, At least a portion of the added hydrogen (21) is prepared by the electrolysis of water.

8. The method according to claim 7, wherein, The electrolysis process of water is powered partly or entirely by renewable energy sources.

9. The method according to any one of the preceding claims, wherein, The method includes: installing a new waste heat collector (24) arranged to recover heat from the effluent of the second methanol converter (23).

10. The method according to any one of the preceding claims, wherein, The second methanol converter (23) is an isothermal converter to transfer the heat of the reaction to a cooling medium. The isothermal converter includes a catalyst bed and a heat exchanger immersed in the catalyst.

11. The method according to claim 10, wherein, The second methanol converter (23) has an axial or shaft-type design. A gas flow radially through the catalyst bed, and / or wherein the new methanol converter is a gas-cooled reactor.

12. The method according to any one of the preceding claims, wherein, The method further includes: setting a new feed-effluent heat exchanger in the synthesis loop, the new feed-effluent heat exchanger being arranged to transfer heat between the effluent stream and the feed stream of the second converter.

13. The method according to claim 12, wherein, The new feed-effect heat exchanger is installed inside the pressure vessel of the second methanol converter.

14. The method according to claim 13, wherein, The second converter includes a pressure vessel, the pressure vessel comprising at least: A catalyst bed configured to contain a catalyst and having a ring-shaped structure; the catalyst bed is configured as an adiabatic catalyst bed with cooling elements arranged downstream of the bed, or as an isothermal catalyst bed with cooling elements immersed in the catalyst bed; and An effluent heat exchanger is arranged to transfer heat from the hot methanol-containing gas flowing from the catalyst bed to a cooling medium. The effluent heat exchanger is located in the central chamber of the annular catalyst bed, such that the catalyst bed is arranged concentrically around the effluent heat exchanger.

15. The method according to any one of the preceding claims, wherein, The original feed-effect heat exchanger of the synthesis loop is disconnected from the loop and reconnected to the feed-effect heat exchanger used as the first converter.

16. The method according to any one of the preceding claims, wherein, CO2 captured from combustion flue gas provides at least a portion of the CO2 contained in the supplementary gas used for methanol synthesis.

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