Methanol synthesis plant with saturator

Abstract

An apparatus and method for synthesizing methanol from a hydrocarbon feedstock. The apparatus includes, among other things, a saturation section. The apparatus is arranged to mix at least a portion of a recycle liquid stream from the saturation section with at least a portion of an excess water stream from a methanol distillation section and to provide a mixed recycle stream. The apparatus is further arranged to heat the mixed recycle stream by heat exchange with a steam stream produced elsewhere in the apparatus.

Description

Technical Field

[0001] An apparatus and method for synthesizing methanol from a hydrocarbon feedstock. The apparatus particularly includes a saturation section. The apparatus is arranged to mix at least a portion of a recirculated liquid stream from the saturation section with at least a portion of an excess water stream from a methanol distillation section, providing a mixed recirculated stream. The apparatus is also arranged to heat the mixed recirculated stream by heat exchange with a steam stream generated elsewhere in the apparatus. Background Technology

[0002] A typical process for synthesizing methanol from hydrocarbon feedstocks involves steam reforming gaseous hydrocarbon feedstocks in a front-end stage to obtain syngas; in the methanol synthesis stage, the resulting syngas undergoes an exothermic reaction in the presence of a catalyst, and steam is generated using the heat from the synthesis stage; the steam is used as the heat input for the steam reforming process.

[0003] An important component of this type of process / unit is the saturation section (usually a saturation tower), in which the hydrocarbon feedstock is mixed with water. The saturation tower ensures a portion of the steam required for safe and efficient steam reforming.

[0004] The standard solution is to design the methanol synthesis section to provide steam at a pressure corresponding to the process steam. However, this fixes the minimum permissible boiling water pressure in the methanol synthesis reactor, which limits the flexibility of synthesis operation and design.

[0005] EP3583068A1 describes a process and related apparatus for an exothermic catalytic reaction involving syngas.

[0006] One objective of embodiments of the present invention is to provide fewer byproducts, lower emissions, and improved operational reliability in MeOH products.

[0007] Other objectives of this technology include separating the operation of the front-end saturator from the MeOH synthesis loop, retaining a portion of the steam generated in methanol synthesis as indirect process steam for the front-end reforming step, and treating excess water from the methanol distillation section. Summary of the Invention

[0008] It has now been found that these objectives can be achieved using the methanol apparatus and methods described herein.

[0009] Therefore, the present invention provides an apparatus for synthesizing methanol from hydrocarbon feedstock, the apparatus comprising: - Hydrocarbon feed, - Steam feed, - A saturation section, arranged to receive a first portion of the hydrocarbon feed, a mixed recirculation stream, and a process condensate stream, and to output a first hydrocarbon stream and a recirculation liquid stream. - The apparatus is arranged to mix the first hydrocarbon stream with a second portion of the hydrocarbon feed and the steam feed to provide a mixed hydrocarbon stream. - The reformer section is configured to convert the mixed hydrocarbon stream into the first syngas stream. - A cooling section is arranged to remove water from a first synthesis gas stream and generate a second water-lean synthesis gas stream and a process condensate stream, wherein at least a portion of the process condensate stream is arranged to feed to a saturation section.

[0010] - A methanol synthesis section is arranged such that at least a portion of the second synthesis gas stream reacts to generate a crude methanol stream. - A methanol distillation section is arranged to receive the crude methanol stream and output a purified methanol stream and an excess water stream; - The apparatus is arranged to mix at least a portion of the recirculated liquid stream from the saturation section with at least a portion of the excess water stream from the methanol distillation section, and to provide a mixed recirculated stream; - The device is also arranged to heat the mixed recirculation flow by exchanging heat with a steam flow generated at other locations in the device.

[0011] A method for synthesizing methanol from a hydrocarbon feedstock in an apparatus as defined herein is also provided. The method includes the following steps: - Provide hydrocarbon feedstock, - Provide steam feed, - The first portion of the hydrocarbon feed, the mixed recirculation stream, and the process condensate stream are fed to the saturation section, and the first hydrocarbon stream and the recirculation liquid stream are output. - The first hydrocarbon stream is mixed with a second portion of the hydrocarbon feed and the steam feed to provide a mixed hydrocarbon stream. - In the reforming section, the mixed hydrocarbon stream is converted into a syngas stream. - Water is removed from the first synthesis gas stream in the cooling section to generate a second water-lean synthesis gas stream and a process condensate stream, and at least a portion of the process condensate stream is fed into the saturation section. - In the methanol synthesis section, at least a portion of the second synthesis gas stream is reacted to generate a crude methanol stream. - The crude methanol stream is fed into the methanol distillation section, and the purified methanol stream and excess water stream are output. - At least a portion of the recirculated liquid stream from the saturation section is mixed with at least a portion of the excess water stream from the methanol distillation section to provide a mixed recirculated stream. - The mixed recirculation flow is heated by exchanging heat with the steam flow generated elsewhere in the device.

[0012] Further details are provided in the following specification text, claims and drawings.

[0013] Brief description of the attached figures

[0014] Figure 1 The overall layout of the apparatus / process according to the present invention is shown.

[0015] Figure 2 A further layout of the apparatus / process according to the present invention is shown.

[0016] Figure 3 A further layout of the apparatus / process according to the present invention is shown. Invention Details

[0018] Unless otherwise stated, any gas content percentages given are by volume. All feeds are preheated as required.

[0019] An apparatus is provided for synthesizing methanol (in the form of a purified methanol stream) from a hydrocarbon feedstock. The purified methanol stream from this apparatus / method typically has high purity (e.g., more than 98 wt%, such as more than 99 wt% or more than 99.9 wt% methanol).

[0020] In summary, the device includes: - Hydrocarbon feed, - Steam feed, - Saturation segment, - Reorganization - Cooling section - Methanol synthesis section, and - Methanol distillation section The unit contains a hydrocarbon feed. The hydrocarbon feed typically contains hydrocarbon gases, such as CH4, and optionally also higher hydrocarbons (usually in relatively small amounts), in addition to small amounts of other gases. Higher hydrocarbons are components having two or more carbon atoms, such as ethane and propane. Examples of hydrocarbon feeds can be natural gas, town gas, naphtha or a mixture of methane and higher hydrocarbons, biogas, or liquefied petroleum gas (LPG).

[0021] The hydrocarbon feed is typically a pre-reforming feed; that is, higher hydrocarbons in the feed have been reacted with steam to provide a methane-rich feed suitable for further downstream reforming. Alternatively, in this technology, the hydrocarbon feed can be a non-pre-reforming natural gas feed.

[0022] The apparatus includes a steam feed. The steam feed is a high-purity gaseous water feed, for example, with a purity higher than 95%, preferably higher than 99%.

[0023] The device includes a saturation section. This saturation section is arranged to receive a first portion of the hydrocarbon feed, a mixed recirculation stream, and a process condensate stream, and to output a first hydrocarbon stream and a recirculation liquid stream. The term "saturation" indicates that, after passing through the saturation section, the hydrocarbon feed becomes enriched with vapor (as the first hydrocarbon stream).

[0024] In one aspect, the saturation section includes a two-stage saturation tower, in which the hydrocarbon feed in the first stage is arranged to be saturated with a heated mixed recirculation stream, and in the second stage, the hydrocarbon gas from the first stage is saturated with at least a portion of the process condensate, thereby discharging the hydrocarbon gas stream from the saturation tower after the second stage.

[0025] In one aspect, a portion of the recirculated liquid stream is arranged to be discharged from the device. This reduces the accumulation of unwanted components in the stream.

[0026] The device is arranged to mix a first hydrocarbon stream with a second portion of the hydrocarbon feed and a steam feed to provide a mixed hydrocarbon stream.

[0027] The unit includes a reforming section arranged to convert a mixed hydrocarbon stream into a first synthesis gas stream. The reforming section may contain one or more reformers. The reforming section may, for example, include a pre-reformer, a main steam reformer, and a secondary reformer. The main reformer and / or the secondary reformer may, for example, be an autothermal reformer (ATR).

[0028] The term "synthesis gas stream" refers to a gas stream containing hydrogen, carbon monoxide, and carbon dioxide, along with small amounts of water and other gases (such as argon, nitrogen, methane, etc.). A suitable first synthesis gas stream has the following composition (by volume): - 0.5-5% methane (dry basis) - 40-80% H2 (dry basis) - 0-40% CO (dry basis) - 0-25% CO2 (dry basis) The apparatus includes a cooling section arranged to remove moisture from a first synthesis gas stream and produce a second lean synthesis gas stream and process condensate, wherein at least a portion of the process condensate is arranged to be fed into a saturation section. Therefore, the second synthesis gas stream has a lower moisture content than the first synthesis gas stream. For example, the second synthesis gas stream may have a moisture content of less than 5% by volume, preferably less than 2% or less than 1%. In one aspect, the cooling section includes a waste heat boiler, wherein cooling of the synthesis gas stream generates a steam stream.

[0029] Methanol synthesis section

[0030] The apparatus includes a methanol synthesis section, arranged to react at least a portion of the second synthesis gas stream to generate a crude methanol stream. The methanol synthesis reactor in the methanol synthesis section is adapted to the following two reactions:

[0031] This process can occur, for example, by feeding a synthesis gas stream into a boiling water reactor, where at least a portion of the synthesis gas stream is converted into methanol, which is then condensed and separated as a liquid phase. A tail gas stream is generated in this process. The tail gas stream from the methanol synthesis section typically contains: 85-90% H2, 5-10% CO2, and 0-3% CO.

[0032] The crude methanol stream contains a major component of methanol, such as 75-98 wt% methanol and 2-25 wt% H2O by weight. Other minor components of the stream include, but are not limited to, higher alcohols, ketones, aldehydes, dimethyl ethers (DME), organic acids, and dissolved gases.

[0033] To achieve optimized yields in methanol production, the stoichiometry of H2, CO, and CO2 needs to be considered. In a preferred embodiment, the stoichiometry of H2, CO, and CO2 in the synthesis gas stream falls within a range such that its modulus is between 1.8 and 2.3, preferably between 1.9 and 2.1, where the modulus is defined according to the molar content as:

[0034] The modulus of the syngas stream can be adjusted by adding a (further) hydrogen-rich stream, which is optionally arranged to mix with the syngas stream. The hydrogen-rich stream can be provided via an external hydrogen feed.

[0035] Methanol distillation section

[0036] The methanol distillation section is configured to receive crude methanol and output a purified methanol and excess water stream. This distillation section is configured to upgrade the crude methanol stream to a purified methanol stream of the desired grade, such as >95 wt%, >98 wt%, or >99 wt% methanol. The methanol distillation section may include one or more distillation columns, such as two or more distillation columns.

[0037] The purified methanol stream output from the distillation section is almost entirely composed of methanol, for example, more than 95 wt% methanol, more than 98 wt% methanol, or more than 99 wt% methanol.

[0038] The excess water stream exiting the distillation section originates from water formed during the production of methanol via the reaction CO2 + 3H2 = CH3OH + H2O. This water leaves the methanol synthesis section as a component of the crude methanol stream. In the distillation section, water and other byproducts are removed from the crude methanol to produce methanol of, for example, grade AA or similar quality. The separated water stream is called excess water, and the separated high-carbon components are called higher alcohols (HA). Thus, in one aspect, at least a portion of the excess water stream contains a methanol distillation impurity stream, such as a higher alcohol stream. Additionally, a stream of light components is also present, typically used as fuel.

[0039] The apparatus is arranged to mix at least a portion of the recirculated liquid stream from the saturation section with at least a portion of the excess water stream from the methanol distillation section, and to provide a mixed recirculated stream. The apparatus is also arranged to heat the mixed recirculated stream by heat exchange with a vapor stream generated elsewhere in the apparatus.

[0040] In one aspect, the apparatus includes a methanol synthesis section arranged to react at least a portion of the second synthesis gas stream to generate a crude methanol stream and output a first vapor stream. The apparatus is also arranged to heat the mixed recirculation stream by heat exchange with at least a portion of the first vapor stream from the methanol synthesis section.

[0041] In one aspect, such as Figure 2 As shown, the cooling section of the device also includes a waste heat boiler, which is arranged to output a second steam stream, wherein the device is also arranged to heat the mixed recirculation stream by exchanging heat with at least a portion of the second steam stream.

[0042] In another aspect, such as Figure 3 As shown, the device also includes an auxiliary boiler arranged to output a third steam stream, wherein the device is further arranged to heat the mixed recirculation stream by exchanging heat with at least a portion of the third steam stream.

[0043] A method for synthesizing methanol from a hydrocarbon feedstock in the apparatus described herein is provided. The method includes the following steps: - Provide hydrocarbon feedstock, - Provide steam feed, - The first portion of the hydrocarbon feed, the mixed recirculation stream, and the process condensate stream are fed to the saturation section, and the first hydrocarbon stream and the recirculation liquid stream are output. - The first hydrocarbon stream is mixed with a second portion of the hydrocarbon feed and the steam feed to provide a mixed hydrocarbon stream. - In the reforming section, the mixed hydrocarbon stream is converted into a syngas stream. - Water is removed from the first synthesis gas stream in the cooling section to generate a second water-lean synthesis gas stream and a process condensate stream, and at least a portion of the process condensate stream is fed into the saturation section. - In the methanol synthesis section, at least a portion of the second synthesis gas stream is reacted to generate a crude methanol stream. - The crude methanol stream is fed into the methanol distillation section, and the purified methanol stream and excess water stream are output. - At least a portion of the recirculated liquid stream from the saturation section is mixed with at least a portion of the excess water stream from the methanol distillation section to provide a mixed recirculated stream. - The mixed recirculation flow is heated by exchanging heat with the steam flow generated elsewhere in the device.

[0044] In one aspect of the method, the saturation section includes a two-stage saturation tower, and the method further includes saturating the hydrocarbon feed in the first stage with a heated mixed recirculation stream, and then saturating the hydrocarbon gas from the first stage with at least a portion of the process condensate in the second stage, thereby discharging the hydrocarbon gas stream from the saturation tower after the second stage.

[0045] In one aspect of the method, the caustic alkali content in the first hydrocarbon stream leaving the saturated stage is less than 0.1 ppb wt, preferably less than 0.005 ppb wt. In another aspect of the method, the amount of process condensate stream is less than 50% of the excess water stream.

[0046] In one aspect, the saturation section includes a two-stage saturation tower, where both the first saturation stage and the second saturation stage are provided with forward liquid outlets.

[0047] In one aspect, at least 40 mol% of the steam required for the reforming step is added as direct steam through the steam feed stream.

[0048] In one aspect of the method, the apparatus includes a methanol synthesis section, and the method includes the following steps: - In the methanol synthesis section, at least a portion of the second synthesis gas stream is reacted to generate a crude methanol stream, and a first vapor stream is output; and - The mixed recirculation stream is heated by heat exchange with at least a portion of the first vapor stream from the methanol synthesis section.

[0049] Key advantages of this device / method include: - Ensure that methanol in excess water is returned to the process during process fluctuations, thereby reducing downstream water treatment costs.

[0050] - Caustic alkali is added to crude methanol to release light byproduct components. The caustic alkali must then be sent to water treatment. A saturator solution concentrates the caustic alkali in a smaller discharge stream, thereby reducing the cost of the water treatment section.

[0051] - Caustic alkali is a poison in the reforming stage. A second saturator step using process condensate that does not contain caustic alkali ensures that no caustic alkali enters the reforming stage.

[0052] - Recycling the high alcohol byproduct stream HA as feed, instead of using it as fuel or waste, reduces energy consumption and eliminates potential caustic alkali contamination of the fuel system.

[0053] - Reliable steam control is particularly important for low-steam carbon reforming technology. By controlling the saturation capacity and ensuring sufficient direct steam, reliable and safe steam control is guaranteed for the reforming process.

[0054] Example

[0055] See Figure 1 A portion of the hydrocarbon feed 1 is cooled in the feed / effluent exchanger E1 and sent to the bottom gas inlet of the two-stage saturator 50. Process condensate 121 obtained by cooling the syngas 5 is sent to the top of the two-stage saturator as the liquid inlet for the second saturation stage. After an optional effluent stream 14 is separated from the recirculated liquid stream, methanol distillation excess water 142 (optionally containing methanol distillation impurities and higher alcohols) is mixed with the recirculated liquid stream 13 from the bottom of the saturator 50. The mixed stream 151 is preheated in heat exchanger 60 and then sent to the two-stage saturator 50 as the liquid inlet for the first saturation stage. The hydrocarbon-containing gas 3 exiting the top of the two-stage saturator 50 is preheated in heat exchanger 70 and mixed with the remaining hydrocarbon feed 1B, then steam stream 2 is added to obtain a mixed hydrocarbon stream 4. The mixed hydrocarbon stream 4 is fed to the reforming section 110, where the steam / carbon (mol / mol) ratio is 0.6. This ratio can vary from 0.4 to 3.0 depending on the design of the restructuring steps.

[0056] Table 1:

[0057] The present invention has been described with reference to several embodiments and accompanying drawings. However, those skilled in the art will be able to select and combine various embodiments within the scope of the invention as defined by the appended claims. All documents referenced herein are incorporated herein by reference.

Claims

1. An apparatus (100) for synthesizing methanol from hydrocarbon feedstock, the apparatus comprising: - Hydrocarbon feed (1), - Steam feed (2) - Saturation section (50), which is arranged to receive a first portion (1A) of the hydrocarbon feed (1), a mixed recirculation stream (151) and a process condensate stream (121), and output a first hydrocarbon stream (3) and a recirculation liquid stream (13). - The apparatus is arranged to mix the first hydrocarbon stream (3) with a second portion (1B) of the hydrocarbon feed (1) and the steam feed (2) to provide a mixed hydrocarbon stream (4). - The reforming section (110) is configured to convert the mixed hydrocarbon stream (4) into the first syngas stream (5). - A cooling section (120) is arranged to remove water from the first synthesis gas stream (5) and generate a second water-lean synthesis gas stream (5') and a process condensate stream (121), wherein at least a portion of the process condensate stream (121) is arranged to feed to the saturation section (50). - The methanol synthesis section (130) is arranged such that at least a portion of the second synthesis gas stream (5') reacts to generate a crude methanol stream (131). - A methanol distillation section (140) is arranged to receive the crude methanol stream (131) and output a purified methanol stream (141) and an excess water stream (142). - The device (100) is arranged to mix at least a portion of the recirculated liquid stream (13) from the saturation section (50) with at least a portion of the excess water stream (142) from the methanol distillation section (140), and to provide a mixed recirculated stream (151). - The device (100) is also arranged to heat the mixed recirculation stream (151) by exchanging heat with a steam stream generated at other locations in the device.

2. The apparatus (100) according to claim 1, comprising a methanol synthesis section (130) arranged to react at least a portion of the second synthesis gas stream (5') to generate a crude methanol stream (131) and output a first vapor stream (132). The device (100) is also arranged to heat the mixed recirculation stream (151) by exchanging heat with at least a portion of the first steam stream (132) from the methanol synthesis section (130).

3. The apparatus (100) according to any of the preceding claims, wherein the cooling section (120) further includes a waste heat boiler arranged to output a second steam stream (133), wherein the apparatus (100) is further arranged to heat the mixed recirculation stream (151) by exchanging heat with at least a portion of the second steam stream (133).

4. The apparatus (100) according to any one of the preceding claims further includes an auxiliary boiler (150), said auxiliary boiler (150) being arranged to output a third steam stream (134), wherein, The device (100) is also arranged to heat the mixed recirculation stream (151) by exchanging heat with at least a portion of the third steam stream (134).

5. The apparatus (100) according to any of the preceding claims, wherein the saturation section (50) comprises a two-stage saturation tower, in which a hydrocarbon feed (1A) is arranged to be saturated with a heated mixed recirculation stream (151), and in the second stage, a hydrocarbon gas from the first stage is saturated with at least a portion of a process condensate (121), thereby discharging the hydrocarbon gas stream (3) from the saturation tower after the second stage.

6. The apparatus (100) according to any of the preceding claims, wherein a portion of the recirculated liquid stream (13) is arranged to be discharged from the apparatus.

7. The apparatus (100) according to any of the preceding claims, wherein at least a portion of the excess water stream (142) comprises a methanol distillation impurity stream, such as a higher alcohol stream.

8. A method for synthesizing methanol from a hydrocarbon feedstock in an apparatus (100) according to any one of the preceding claims, the method comprising the steps of: - Provide hydrocarbon feedstock (1), - Provide steam feed (2), - The first portion (1A) of the hydrocarbon feed (1), the mixed recirculation stream (151), and the process condensate stream (121) are fed into the saturation section (50), and the first hydrocarbon stream (3) and the recirculation liquid stream (13) are output. - The first hydrocarbon stream (3) is mixed with the second portion (1B) of the hydrocarbon feed (1) and the steam feed (2) to provide a mixed hydrocarbon stream (4). - In the reforming section (110), the mixed hydrocarbon stream (4) is converted into a syngas stream (5). - In the cooling section (120), water is removed from the first synthesis gas stream (5) to generate a second water-lean synthesis gas stream (5') and a process condensate stream (121), and at least a portion of the process condensate stream (121) is fed into the saturation section (50). - In the methanol synthesis section (130), at least a portion of the second synthesis gas stream (5') is reacted to generate a crude methanol stream (131). - The crude methanol stream (131) is fed into the methanol distillation section (140), and the purified methanol stream (141) and excess water stream (142) are output. - At least a portion of the recirculated liquid stream (13) from the saturation section (50) is mixed with at least a portion of the excess water stream (142) from the methanol distillation section (140) to provide a mixed recirculated stream (151). - The mixed recirculation flow is heated by heat exchange with the steam flow generated at other locations in the device (151).

9. The method of claim 8, wherein the saturation section (50) comprises a two-stage saturation tower, the method further comprising saturating the hydrocarbon feed (1A) in the first stage with a heated mixed recirculation stream (151), and subsequently saturating the hydrocarbon gas from the first stage with at least a portion of the process condensate (121) in the second stage, thereby discharging the hydrocarbon gas stream (3) from the saturation tower after the second stage.

10. The method according to claim 9, wherein the caustic alkali content in the first hydrocarbon stream (3) leaving the saturation stage is less than 0.1 ppb wt, preferably less than 0.005 ppb wt.

11. The method according to any one of claims 8-10, wherein the amount of process condensate flow (121) is less than 50% of the excess water flow (142).

12. The method according to any one of claims 8-11, wherein the saturation section (50) comprises a two-stage saturation tower, and wherein both the first saturation stage and the second saturation stage are provided with forward liquid outlets.

13. The method according to any of the preceding claims, wherein at least 40 mol% of the steam required for the reforming step is added as direct steam via steam feed (2).

14. The method according to any one of claims 8-13, wherein the apparatus (100) comprises a methanol synthesis section (130), wherein the method comprises the following steps: - In the methanol synthesis section (130), at least a portion of the second synthesis gas stream (5') is reacted to generate a crude methanol stream (131), and a first vapor stream (132) is output; and - The mixed recirculation stream (151) is heated by heat exchange with at least a portion of the first steam stream (132) from the methanol synthesis section (130).

Images