High-pressure methanol washing column

Abstract

The present invention relates to a method for removing methanol from a methanol-containing carbon dioxide-rich flow. The method comprises the following steps: supplying a methanol-containing carbon dioxide-rich flow to a first compression section and compressing it to discharge a low-pressure carbon dioxide-rich flow at a pressure of 10 to 100 barg, preferably 15 to 45 barg; and subsequently supplying the low-pressure carbon dioxide-rich flow to a washing column and washing it in a counterflow manner with a demineralized water (DMW) flow to discharge the purified carbon dioxide-rich flow and the first process condensate flow.

Description

Technical Field

[0001] Technical Field The present invention relates to the removal of methanol from a methanol-containing carbon dioxide-rich stream. The method comprises the following general steps: feeding the methanol-containing carbon dioxide-rich stream to a first compression section, compressing the same, and discharging a low-pressure carbon dioxide-rich stream at a pressure of 10 to 100 barg, preferably 15 to 45 barg; subsequently feeding said low-pressure carbon dioxide-rich stream to a wash column, washing the same in countercurrent mode by a demineralized water (DMW) stream, and discharging a purified carbon dioxide-rich stream and a first process condensate stream.

Background Art

[0002] Background Carbon dioxide capture is a feature of many industrial chemical processes. Typically, such processes include a CO2 removal section designed to separate a carbon dioxide CO2-rich stream from other product streams within the process. The CO2-rich stream from such a CO2 removal section often contains trace amounts of impurities such as H2, H2O, CH3OH or MeOH (methanol), CH4, CO, and Ar. In particular, there may be limits on the allowable concentration of methanol in CO2-containing streams.

[0003] WO2022 / 058585A1 describes a method for improving the purity of a CO2-rich stream. A CO2-rich stream comprising hydrocarbons, hydrogen and / or CO is mixed with a methane (CH4)-rich stream and an oxygen-rich stream. Subjecting this mixture to a catalytic oxidation process produces a purified stream having a higher CO2 concentration. This process requires an oxygen stream, which may become contaminated in the purified CO2 stream, requiring additional cost and resources.

[0004] There is a need to provide a process that enables a new solution for increasing the purity of a CO2-rich stream, particularly in hydrogen production processes.

Prior Art Literature

[0005] [Patent Document 1] WO2022 / 058585A1 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Therefore, the object of the present invention is to provide an alternative and improved process for improving the purity of a CO2-rich flow, that is, for further increasing the CO2 concentration therein, thereby obtaining a high-purity CO2 product.

[0007] This invention solves these and other objectives. [Means for solving the problem]

[0008] summary The inventors have found that the methanol content in a carbon dioxide-rich flow can be reduced to an acceptable level, for example, from 200 ppm (or more) to 10 ppm or less. This method is simple, requires minimal equipment, and has low pressure loss, making it a significantly cheaper solution compared to conventional techniques.

[0009] Therefore, a first aspect of the present invention relates to a method for removing methanol from a methanol-containing carbon dioxide-rich flow. The method comprises the following general steps: supplying a methanol-containing carbon dioxide-rich flow to a first compression section and compressing it to discharge a low-pressure carbon dioxide-rich flow at a pressure of 10 to 100 barg, preferably 15 to 45 barg; subsequently, supplying the low-pressure carbon dioxide-rich flow to a washing column (washing tower) and washing it in a counterflow manner with a demineralized water (DMW) flow to discharge the purified carbon dioxide-rich flow and the first process condensate flow.

[0010] This operating pressure enables methanol washing more efficiently than known processes. Other features of this technology are described in the following description, examples, claims, and drawings.

[0011] Explanation of the diagram [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram of the method of the present invention. [Modes for carrying out the invention]

[0013] Detailed disclosure Unless otherwise specified, all pressures described herein were measured at 40°C.

[0014] Unless otherwise specified, gas content percentages are expressed as volume percentages. All supplies are preheated as needed. Unless otherwise specified, concentrations are given on a dry basis, i.e., without considering any present moisture.

[0015] Therefore, a method is provided for removing methanol from a methanol-containing carbon dioxide-rich flow. The CO2-rich gas flow supplied to this method preferably contains at least 90% by weight of CO2, for example, at least 95% by weight of CO2, at least 99.0% by weight of CO2, preferably at least 99.5% by weight of CO2, and more preferably at least 99.9% by weight of CO2. Therefore, the CO2-rich gas flow is already of high purity prior to the method of the present invention. The methanol-containing carbon dioxide-rich flow originates, for example, from a hydrogen plant, an ammonia plant, or a methanol plant.

[0016] This method includes the following general steps: - A methanol-containing carbon dioxide-rich flow is supplied to a first compression section and compressed to discharge a low-pressure carbon dioxide-rich flow at a pressure of 10 to 100 barg, preferably 15 to 45 barg; followed by - A step of supplying the low-pressure carbon dioxide-rich flow to a washing column, washing it in a countercurrent manner using demineralized water (DMW) flow, and discharging the purified carbon dioxide-rich flow and the first process condensate flow.

[0017] The methanol-containing carbon dioxide-rich stream (introduced into this method) contains at least 50 ppm of methanol, for example, at least 100 ppm of methanol or at least 200 ppm of methanol. In other words, the methanol-containing carbon dioxide-rich stream may contain a relatively large amount of methanol as an impurity.

[0018] In the first compression section, the methanol-containing carbon dioxide-rich flow is compressed to discharge a low-pressure carbon dioxide-rich flow at a pressure of 10 to 100 barg, preferably 15 to 45 barg.

[0019] Preferably, the first compression section includes three or more compressors, or four or more compressors, and these compressors are preferably arranged in series. Alternatively, or in addition to the above, the second compression section includes three or more compressors, or four or more compressors, and these compressors are preferably arranged in series. A person skilled in the art can design the first compression section as needed.

[0020] In one embodiment, the first compression section also discharges a second process condensate stream. Said first process condensate stream (from the scrubbing column) and said second process condensate stream (from the first compression section) are combined as a third process condensate stream. It is preferable to combine the condensate from the scrubbing column at the discharge outlet of a condensate pump that sucks up condensate from the low pressure (LP) section of the CO2 compressor. Alternatively, these can be combined on the suction side of the pump, but the flow from the scrubbing column is at a higher pressure, and CO2 dissolved in the condensate will flash off when mixed with the lower-pressure process condensate, which is undesirable for the operation of the condensate pump.

[0021] The low-pressure carbon dioxide-rich stream is sent to a scrubbing column, where it is separated into a purified carbon dioxide-rich stream and a first process condensate stream. The scrubbing column operates in a countercurrent mode, wherein the carbon dioxide-rich stream passes upward through the column while the DMW stream passes downward. Accordingly, the CO2-rich stream is counter-currently washed by demineralized washing water introduced from the top of the intermediate scrubbing column. The washed CO2-rich gas is withdrawn from the top of the intermediate scrubbing column as a purified carbon dioxide-rich stream having a predetermined quality.

[0022] Said scrubbing column may comprise a packed bed, or trays such as bubble-cap trays, sieve trays, valve trays, etc. Valve trays are preferred.

[0023] From the bottom of the column, the first process condensate stream containing impurities (e.g., methanol) is suitably sent to treatment together with process condensate from the LP section of the CO2 compressor.

[0024] The scrubbing column generally comprises 2 to 20 theoretical stages, preferably 5 to 15 theoretical stages. Washing quality decreases if there are less than 5 stages, and the improvement in effect is low even if the number of stages exceeds 20.

[0025] The operating pressure of the intermediate stage washing column is assumed to be the same as the discharge pressure from the first compression section of the CO2 compressor. This pressure may vary depending on the type of compressor, the compressor's suction pressure (set by the process), and the final discharge pressure.

[0026] In one embodiment, the method further includes feeding the purified carbon dioxide-rich flow to a second compression section and compressing it to discharge a high-pressure carbon dioxide-rich flow at a pressure of 100–200 barg, preferably 120–160 barg. This provides a high-pressure carbon dioxide-rich flow at a pressure sufficient for downstream use and / or storage.

[0027] The method described herein effectively removes methanol. In one embodiment, the purified carbon dioxide-rich stream contains less than 50 ppm of methanol, for example, less than 30 ppm of methanol, or less than 20 ppm of methanol.

[0028] The low-pressure, carbon dioxide-rich flow is appropriately at a temperature of 20–60°C, preferably 35–45°C, at the inlet of the washing column.

[0029] Specific Embodiments Figure 1 shows a simplified configuration of one embodiment of the method of the present invention. A methanol-containing carbon dioxide-rich flow 1 is supplied to a first compression section 10, where it is compressed and discharged as a low-pressure carbon dioxide-rich flow 11 having a pressure of 10 to 100 barg. This low-pressure carbon dioxide-rich flow 11 is then supplied to a washing column 20 and washed in a counterflow manner with demineralized water (DMW) flow 2. From the washing column 20, a purified carbon dioxide-rich flow 21 and a first process condensate flow 22 are discharged.

[0030] Furthermore, Figure 1 also shows a second compression section 30 that compresses the purified carbon dioxide-rich flow 21. The high-pressure carbon dioxide-rich flow 31 at a pressure of 100-200 barg is discharged.

[0031] Figure 1 shows that the first process condensation logistics 22 and the second process condensation logistics 12 are combined to form the third process condensation logistics 33. [Examples]

[0032] example Calculations are performed for the apparatus according to the present invention (Example 1), the apparatus without an intermediate washing column (Example 2), and an alternative (Example 3).

[0033] The methanol-containing process gas from the shift section is purified in the CO2 removal section, where CO2 and methanol are removed from the process gas. The methanol-containing CO2-rich gas exits the CO2 removal section at 0.9 barg and 40°C and is sent to the first compression section of the CO2 compressor. There, the CO2-rich gas is compressed to 32.4 barg. The process condensate in the CO2-rich gas is separated from the gas phase and contains trace amounts of dissolved methanol.

[0034] [Table 1]

[0035] In Example 1, CO2-rich gas from the first compression section is sent to an intermediate wash column at 32.4 barg and 40°C. The gas is then washed with demineralized water (DMW) at 40°C. To reduce methanol in the final CO2 product to 25 ppm, 3.6 t / h of DMW needs to be supplied to the intermediate wash column.

[0036] Without an intermediate washing column, the expected methanol concentration in the final CO2 product is 99 ppm. (Example 2).

[0037] Another method for reducing methanol in CO2-rich gas is to remove methanol from the process gas before it enters the CO2 absorption unit. In such a process scheme, 26.3 t / h of DMW is required in the process gas washing column to bring the methanol content in the CO2 product to the same level (Example 3). Therefore, by introducing an intermediate washing column in the CO2 compressor, a significant saving of 18.7 t / h of DMW can be achieved.

[0038] The present invention has been described with reference to several aspects and drawings. However, those skilled in the art can select and combine various aspects within the scope of the invention as defined by the appended claims. All documents cited herein are incorporated herein by reference.

Claims

1. A method for removing methanol from a methanol-containing carbon dioxide-rich stream (1), comprising the following steps: - A methanol-containing carbon dioxide-rich flow (1) is supplied to a first compression section (10), which is compressed to discharge a low-pressure carbon dioxide-rich flow (11) at a pressure of 10 to 100 barg, preferably 15 to 45 barg; - The low-pressure carbon dioxide-rich flow (11) is supplied to a washing column (20), which is then washed in a countercurrent manner with a demineralized water (DMW) flow (2), and the purified carbon dioxide-rich flow (21) and the first process condensate flow (22) are discharged; The method, including the method described above.

2. The method according to claim 1, further comprising the step of supplying a purified carbon dioxide-rich flow (21) to a second compression section (30), compressing it, and discharging a high-pressure carbon dioxide-rich flow (31) at a pressure of 100 to 200 barg, preferably 120 to 160 barg.

3. The method according to claim 1 or 2, wherein the methanol-containing carbon dioxide-rich stream (1) contains at least 50 ppm of methanol, for example, at least 100 ppm of methanol.

4. The method according to any one of claims 1 to 3, wherein the purified carbon dioxide-rich stream (21) contains less than 30 ppm methanol, for example, less than 20 ppm methanol.

5. The method according to any one of claims 1 to 4, wherein the methanol-containing carbon dioxide-rich flow (1) originates from a hydrogen plant, an ammonia plant, a methanol plant, or a combination of two or more of these plants.

6. The method according to any one of claims 1 to 5, wherein the first compression section (10) also discharges a second process condensate (12).

7. The method according to claim 6, wherein the first process condensation logistics (22) and the second process condensation logistics (12) are combined to form a third process condensation logistics (33).

8. The method according to any one of claims 1 to 7, wherein the low-pressure carbon dioxide-rich flow (11) has a temperature of 20 to 60°C, preferably 35 to 45°C, at the inlet of the washing column.

9. An apparatus for removing methanol from a methanol-containing carbon dioxide-rich stream (1), the system comprising a first compression section (10), a washing column (20), and an optional second compression section (30), which are as follows: a) In the first compression section (10), the methanol-containing carbon dioxide-rich flow (1) is compressed and a low-pressure carbon dioxide-rich flow (11) is discharged; b) The flow (11) is fed into a washing column (20), where it is separated into a purified carbon dioxide-rich flow (21) and a first-process condensed flow (22); and c) The flow (21) may be supplied to an optional second compression section (30) that discharges a high-pressure, carbon dioxide-rich flow (31); The apparatus is arranged in such a manner.

10. The apparatus according to claim 9, wherein the washing column (20) includes 2 to 20 ideal stages, preferably 5 to 15 ideal stages.

11. The washing column (20) comprises a packed bed or tray, for example, a bubble cap tray, a sieve tray, or a valve tray, according to claim 9 or 10.

12. The system according to any one of claims 9 to 11, wherein the first compression section (10) comprises two or more, for example, three or more, or four or more compressors, which are preferably arranged in series, and / or the second compression section (30) comprises two or more, for example, three or more, or four or more compressors, which are preferably arranged in series.

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