High pressure methanol wash column

Abstract

The invention relates to a process for removing methanol from a methanol-containing carbon dioxide-rich stream. The process comprises the steps of: feeding the methanol-containing carbon dioxide-rich stream to a first compression section and compressing it so as to output a low-pressure carbon dioxide-rich stream, at a pressure of 10 – 100barg, preferably 15 – 45 barg; followed by feeding the low-pressure carbon dioxide-rich stream to a wash column and washing it with a demineralised water (DMW) stream in a counter-current manner, and outputting a purified carbon dioxide-rich stream and a first process condensate stream.

Description

[0001] HIGH PRESSURE METHANOL WASH COLUMN

[0002] TECHNICAL FIELD

[0003] The present invention relates to removal of methanol from a methanol-containing carbon dioxide-rich stream. The process comprises the general steps of: feeding the methanolcontaining carbon dioxide-rich stream to a first compression section and compressing it so as to output a low-pressure carbon dioxide-rich stream, at a pressure of 10 - lOObarg, preferably 15 - 45 barg; followed by feeding the low-pressure carbon dioxide-rich stream to a wash column and washing it with a demineralised water (DMW) stream in a counter-current manner, and outputting a purified carbon dioxide-rich stream and a first process condensate stream.

[0004] BACKGROUND

[0005] Carbon dioxide capture is a feature of many industrial chemical processes. Typically, such processes include a CO2removal section designed to separate a CO2-rich stream from the other product streams in the process. The CO2-rich stream from such a CO2removal section often contains small amount of impurities such as H2, H2O, CH3OH or MeOH (methanol), CH4, CO and inerts e.g. Ar. In particular, there may be limitations on the acceptable concentration of methanol in the CO2-rich stream.

[0006] WO2022058585A1 describes a process for improving the purity of a CO2-rich stream. A CO2- rich stream containing hydrocarbons, hydrogen and / or CO is combined with a stream rich in methane (CH4) and oxygen. The mixture is subjected to a catalytic oxidation step, thereby producing a purified stream having a higher CO2concentration. This process requires an oxygen stream, which can slip through into the purified CO2stream, and which requires additional costs and resources.

[0007] There is a need to provide a process that enables a new solution for increasing the purity of a CO2-rich stream, particularly in a process for producing hydrogen.

[0008] It is therefore an object of the present invention to provide an alternative and improved process for improving the purity of a CO2-rich stream, i.e. to further increase the CO2-concentration therein, thereby obtaining a high purity CO2product.

[0009] These and other objects are solved by the present invention. SUMMARY

[0010] It has been found by the present inventor(s) that the methanol content of a carbon dioxiderich stream can be reduced to an acceptable level, e.g. from 200 ppm (or higher) down to 10 ppm or even lower. The process is simple, and is a significantly cheaper solution when compared to prior art as less equipment is needed and a lower pressure drop is necessary.

[0011] So, in a first aspect the present invention relates to a process for the removal of methanol from a methanol-containing carbon dioxide-rich stream. The process comprises the general steps of: feeding the methanol-containing carbon dioxide-rich stream to a first compression section and compressing it so as to output a low-pressure carbon dioxide-rich stream, at a pressure of 10 - lOObarg, preferably 15 - 45 barg; followed by feeding the low-pressure carbon dioxiderich stream to a wash column and washing it with a demineralised water (DMW) stream in a counter-current manner, and outputting a purified carbon dioxide-rich stream and a first process condensate stream.

[0012] The operating pressure enables a more efficient methanol wash than known processes. Additional features of the technology are set out in the following description text, examples, claims and figures.

[0013] LEGENDS

[0014] Fig. 1 is a schematic layout of the process of the invention.

[0015] DETAILED DISCLOSURE

[0016] Unless otherwise specified, all pressures provided herein are determined at 40°C.

[0017] Unless otherwise specified, any given percentages for gas content are % by volume. All feeds are preheated as required. Unless specified, the concentrations will be given on dry basis, i.e. without taking any water present into account.

[0018] A process is therefore provided for removing methanol from a methanol-containing carbon dioxide-rich stream. The CO2-rich gas stream provided to the process suitably comprises at least 90 wt% CO2, such as at least 95 wt% CO2, such as at least 99.0 wt% CO2, preferably at least 99.5 wt% CO2, more preferably as at least 99.9 wt% CO2. The CO2-rich gas stream is thus already of high purity prior to the process of the present invention. The methanol- containing carbon dioxide-rich stream may e.g. originate from a hydrogen plant, an ammonia plant or a methanol plant.

[0019] The process comprises the general steps of: feeding the methanol-containing carbon dioxide-rich stream to a first compression section and compressing it so as to output a low-pressure carbon dioxide-rich stream, at a pressure of 10 - lOObarg, preferably 15 - 45 barg; followed by feeding the low-pressure carbon dioxide-rich stream to a wash column and washing it with a demineralised water (DMW) stream in a counter-current manner, and outputting a purified carbon dioxide-rich stream and a first process condensate stream.

[0020] The methanol-containing carbon dioxide-rich stream (inputted to the process) comprises at least 50ppm methanol, such as at least lOOppm or at least 200ppm methanol. In other words, the methanol-containing carbon dioxide-rich stream can comprise relatively high amounts of methanol as impurity.

[0021] In the first compression section the methanol-containing carbon dioxide-rich stream is compressed so as to output a low-pressure carbon dioxide-rich stream, at a pressure of 10 - lOObarg, preferably 15 - 45 barg.

[0022] Suitably, the first compression section comprises two or more, such as three or more, or four or more compressors, preferably arranged in series. Alternatively, or additionally, the second compression section comprises two or more, such as three or more, or four or more compressors, preferably arranged in series. The skilled person will be able to design the first compression section as required.

[0023] In one aspect, the first compression section also outputs a second process condensate stream. The first process condensate stream (from the wash column) and the second process condensate stream (from the first compression section) are combined to a third process condensate stream. It is advantageous to combine the condensate from the wash column at the discharge of the condensate pump (which takes the condensate from LP section of the CO2compressor). The alternative would be to combine the stream at the suction side of the pump, however the stream coming from the wash column would be at higher pressure, and the CO2dissolved in that condensate would flash off if mixed with process condensate at lower pressure. That is undesirable for the operation of the condensate pump.

[0024] The low-pressure carbon dioxide-rich stream is fed to a wash column where it is separated into a purified carbon dioxide-rich stream and a first process condensate stream. The wash column runs in a counter-current manner, such that the carbon dioxide-rich stream passes upwards through the column, while the DMW stream passes downwards. The CO2rich stream is thereby washed counter-currently by demineralised wash water introduced at the top of the interstage wash column. The washed CO2rich gas leaves the interstage wash column at the top as purified carbon dioxide-rich stream with the required quality.

[0025] The wash column could include a packed bed, or trays such as bubble cap trays, sieve trays or valve trays. Valve trays are preferred.

[0026] From the column bottom, the first process condensate stream containing the impurities (such as MeOH) is sent to treatment, suitably together with process condensate from the LP section of the CO2compressor.

[0027] The wash column typically comprises between 2-20 ideal stages, preferably between 5-15 ideal stages. With less than 5 stages, the washing quality is poor, and the impact of having more than 20 stages is low.

[0028] The operating pressure of the interstage wash column is expected to be the same as the discharge pressure from the 1stcompression section of the CO2compressor. That pressure can vary, depending on the compressor type, compressor suction pressure (set by process) and final discharge pressure.

[0029] In one aspect, the process further comprises a step of feeding the purified carbon dioxide-rich stream to a second compression section and compressing it so as to output a high-pressure carbon dioxide-rich stream at a pressure of between 100 - 200barg, preferably 120 - 160 barg. This provides a high-pressure carbon dioxide-rich stream at pressures sufficient for downstream use and / or storage.

[0030] The process described herein effectively removes methanol. In one aspect, the purified carbon dioxide-rich stream comprises below 50ppm methanol, such as below 30ppm methanol, such as below 20ppm methanol.

[0031] The low-pressure carbon dioxide-rich stream is suitably at a temperature of between 20 - 60°C, preferably 35-45°C at the inlet of the wash column. Specific embodiments

[0032] Figure 1 shows a simple layout of one embodiment of the process of the invention. Methanolcontaining carbon dioxide-rich stream 1 is fed to first compression section 10 and compressed it so as to output a low-pressure carbon dioxide-rich stream 11, at a pressure of 10 - lOObarg. The low-pressure carbon dioxide-rich stream 11 is subsequently fed to wash column 20 and washed with a demineralised water (DMW) stream 2 in a counter-current manner. The wash column 20 outputs purified carbon dioxide-rich stream 21 and first process condensate stream 22.

[0033] Figure 1 also shows second compression section 30 which compresses purified carbon dioxiderich stream 21. A high-pressure carbon dioxide-rich stream 31 is outputted at a pressure of between 100 - 200barg.

[0034] Figure 1 shows first process condensate stream 22 and second process condensate stream 12 being combined to a third process condensate stream 33.

[0035] EXAMPLES

[0036] Calculations are made on a system according to the invention (Example 1), without an interstage wash column (Example 2) and an alternative solution (Example 3).

[0037] The process gas from the shift section containing the methanol is purified in the CO2removal section where, CO2and methanol is removed from the process gas. The CO2rich gas containing the methanol leaves the CO2removal section at 0.9 bar g and 40°C and is sent to the 1stcompression section of the CO2compressor, where the CO2rich gas is compressed to 32.4 bar g. The process condensate in the CO2rich gas is separated from the gas phase, and contains traces of dissolved methanol.

[0038]

[0039]

[0040] In Example 1, the C02rich gas from the 1stcompression section is sent to the interstage wash column at 32.4 bar g and 40°C, where the gas is washed with 40°C demineralised water (DMW). In order to reduce methanol in the final CO2product to 25ppm, 3.6 t / h of DMW to the interstage wash column is required. Without the interstage wash column, the expected methanol in the final CO2product would be 99 ppm (Example 2).

[0041] An alternative way to reduce methanol in the CO2rich gas would be to remove the methanol from the process gas before it enters the CO2absorber. In such process scheme, 26.3 t / h of DMW to the process gas wash column is required to achieve the same methanol content in the CO2product (Example 3). The introduction of a CO2compressor interstage wash column thus gives a considerable saving of 18.7 t / h DMW .

[0042] The present invention has been described with reference to a number of aspects and figures. However, the skilled person is able to select and combine various aspects within the scope of the invention, which is defined by the appended claims. All documents referenced herein are incorporated by reference.

Claims

CLAIMS1. A process for removing methanol from a methanol-containing carbon dioxide-rich stream (1), said process comprising the steps of: feeding the methanol-containing carbon dioxide-rich stream (1) to a first compression section (10) and compressing it so as to output a low-pressure carbon dioxide-rich stream (11), at a pressure of 10 - lOObarg, preferably 15 - 45 barg; feeding the low-pressure carbon dioxide-rich stream (11) to a wash column (20) and washing it with a demineralised water (DMW) stream (2) in a counter-current manner and outputting a purified carbon dioxide-rich stream (21) and a first process condensate stream (22).

2. The process according to claim 1, further comprising a step of feeding the purified carbon dioxide-rich stream (21) to a second compression section (30), and compressing it so as to output a high-pressure carbon dioxide-rich stream (31) at a pressure of between 100 - 200barg, preferably 120 - 160 barg.

3. The process according to any one of the preceding claims, wherein the methanolcontaining carbon dioxide-rich stream (1) comprises at least 50ppm methanol, such as at least lOOppm methanol.

4. The process according to any one of the preceding claims, wherein the purified carbon dioxide-rich stream (21) comprises below 30ppm methanol, such as below 20ppm methanol.

5. The process according to any one of the preceding claims, wherein the methanolcontaining carbon dioxide-rich stream (1) originates from a hydrogen plant, an ammonia plant, a methanol plant or a combination of two or more of said plants.

6. The process according to any one of the preceding claims, wherein the first compression section (10) also outputs a second process condensate stream (12).

7. The process according to claim 6, wherein the first process condensate stream (22) and the second process condensate stream (12) are combined to a third process condensate stream (33).

8. The process according to any one of the preceding claims, wherein the low-pressure carbon dioxide-rich stream (11) is at a temperature of between 20 - 60°C, preferably 35-45°C at the inlet of the wash column.

9. System for removing methanol from a methanol-containing carbon dioxide-rich stream (1), said system comprising a first compression section (10), a wash column (20) and optionally a second compression section (30) arranged such that: a) in the first compression section (10) said methanol-containing carbon dioxide-rich stream (1) is compressed so as to output a low-pressure carbon dioxide-rich stream (11); b) stream (11) is fed to wash column (20) where it is separated into a purified carbon dioxide-rich stream (21) and a first process condensate stream (22); and c) stream (21) can be fed to an optional second compression section (30) which outputs a high-pressure carbon dioxide-rich stream (31).

10. System according to claim 9, wherein the wash column (20) comprises between 2-20 ideal stages, preferably between 5-15 ideal stages.

11. System according to any one of claims 9 or 10 wherein the wash column (20) comprises a packed bed or trays such as bubble cap trays, sieve trays or valve trays.

12. System according to any one of claims 9-11 wherein the first compression section (10) comprises two or more, such as three or more, or four or more compressors, preferably arranged in series, and / or wherein the second compression section (30) comprises two or more, such as three or more, or four or more compressors, preferably arranged in series.

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