Low-temperature methanol washing system and process

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature methanol washing system and a low-temperature methanol washing process, the low-temperature methanol washing system comprises an ammonia washing system, a thermal regeneration system and a methanol-water separation system, and the ammonia washing system comprises a transformed gas ammonia washing tower, an untransformed gas ammonia washing tower and a first water cooler; the thermal regeneration system comprises a thermal regeneration tower, a second water cooler, a tower top separation tank, an H2S fraction cold exchanger, an H2S fraction deep freezer (13), an H2S gas separation tank, a tower top reflux pump and a first reboiler; a connecting subline is arranged between a pipeline for connecting the tower top separation tank with a tube pass inlet of the H2S fraction cold exchanger and an acid gas desulfurization recovery pipeline at a shell pass outlet of the H2S fraction cold exchanger; the methanol-water separation system comprises a methanol-water separation tower, a second reboiler, a tail gas washing tower and an alkali liquor tank, and the alkali liquor tank is connected with a pipeline at the lower part of the methanol-water separation tower. The low-temperature methanol washing system can control and reduce the ammonia content in the system, so that corrosion of equipment pipelines is inhibited, the absorption capacity of circulating methanol is improved, the circulating methanol flow of the system is reduced, and the energy consumption of the system is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of low-temperature methanol washing, and in particular to a low-temperature methanol washing system and process. Background Art

[0002] Low-temperature methanol washing uses methanol organic solvent as absorbent, and uses methanol to remove acidic gases such as CO2, H2S, COS in the raw gas under low temperature conditions. The ammonia in the conversion gas also enters the low-temperature methanol washing system. If the ammonia content in the system is too high, it will affect the normal operation of the methanol thermal regeneration tower and its related heat exchangers. If the ammonia content in the circulating methanol is too high, it will also cause the H2S content in the purified gas and CO2 product gas to exceed the standard. More seriously, it will cause the thermal regeneration system of the low-temperature methanol washing process to be blocked. However, the ammonia content in the conversion gas is not the lower the better. Ammonia has certain benefits in adjusting the pH value of the circulating methanol in the methanol washing system. By controlling the ammonia content in the circulating methanol at 30-60mmol / l, the corrosion of the system can be effectively inhibited. In a weakly alkaline environment (pH=8-9), the corrosion of metal equipment by acidic gases such as CO2 and H2S can be completely inhibited or reduced to a negligible level.

[0003] However, there is currently a lack of a low-temperature methanol washing system and process that can effectively control the ammonia content in the low-temperature methanol washing system. Summary of the invention

[0004] The purpose of the present invention is to solve the problems described in the above-mentioned background technology. A low-temperature methanol washing system and process are proposed herein. Through this system and process, the ammonia content in the low-temperature methanol washing system can be reduced and controlled, thereby effectively inhibiting the corrosion of equipment pipelines, improving the absorption capacity of circulating methanol, reducing the flow rate of circulating methanol in the system, and reducing system energy consumption.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a low-temperature methanol washing system, the low-temperature methanol washing system includes an ammonia washing system and a heat regeneration system, the ammonia washing system includes a conversion gas washing ammonia tower, an unconverted gas washing ammonia tower and a first water cooler, the water inlet of the first water cooler is provided with a boiler water inlet pipeline, the water outlet of the first water cooler is connected with the upper part of the conversion gas washing ammonia tower and the upper part of the unconverted gas washing ammonia tower through pipelines, the lower parts of the conversion gas washing ammonia tower and the unconverted gas washing ammonia tower are respectively provided with a conversion gas pipeline and an unconverted gas pipeline, and the tops of the conversion gas washing ammonia tower and the unconverted gas washing ammonia tower are respectively provided with a conversion gas to low-M pipeline and an unconverted gas to low-M pipeline;

[0006] The thermal regeneration system comprises a thermal regeneration tower, a second water cooler, a tower top separation tank, an H2S fraction cold exchanger, an H2S fraction cryogenic refrigerator, an H2S gas separation tank, a tower top reflux pump and a first reboiler, wherein the top gas outlet of the thermal regeneration tower is connected to the second water cooler through a pipeline, the second water cooler is connected to the tower top separation tank through a pipeline, the tower top separation tank is connected to the H2S fraction cold exchanger through a pipeline, the H2S fraction cold exchanger is connected to the H2S gas separation tank and the H2S fraction cryogenic refrigerator through pipelines, the H2S fraction cryogenic refrigerator is connected to the H2S gas separation tank through a pipeline, the bottom outlet of the H2S gas separation tank is provided with a methanol liquid deconcentration tower pipeline, the tower top separation tank is connected to the tower top reflux pump through a pipeline, the tower top reflux pump is connected to the upper part of the thermal regeneration tower through a pipeline, and the first reboiler is connected to the thermal regeneration tower pipeline;

[0007] A methanol-rich self-concentration tower pipeline is also provided at the top of the thermal regeneration tower, and a methanol-poor de-absorption tower pipeline is provided at the bottom of the thermal regeneration tower.

[0008] Preferably, the low-temperature methanol washing system also includes a methanol-water separation system, which includes a methanol-water separation tower, a second reboiler, a tail gas washing tower and an alkali liquid tank, wherein the second reboiler is connected to the methanol-water separation tower pipeline, the alkali liquid tank is connected to the lower part of the methanol-water separation tower through a pipeline, the top liquid outlet of the methanol-water separation tower is connected to the middle part of the thermal regeneration tower through a pipeline, the bottom of the thermal regeneration tower is connected to the methanol-water separation tower through a pipeline, and the bottom liquid outlet of the tail gas washing tower is connected to the methanol-water separation tower through a pipeline;

[0009] The alkali liquid tank is also connected to the liquid outlet pipeline at the bottom of the tail gas washing tower through a pipeline. A desalted water treatment pipeline is provided at the bottom of the methanol-water separation tower. A branch pipeline is provided on the desalted water treatment pipeline and connected to the tail gas washing tower. A desalted water pipeline is provided on the top of the tail gas washing tower, and a tail gas removal pipeline is provided on the top of the tail gas washing tower.

[0010] Preferably, the top outlet of the tower top separation tank is connected to the tube side inlet of the H2S fraction cold exchanger through a pipeline, the tube side outlet of the H2S fraction cold exchanger is connected to the H2S fraction cryogenic refrigerator through a pipeline, the shell side inlet of the H2S fraction cold exchanger is connected to the H2S gas separation tank through a pipeline, the H2S fraction cryogenic refrigerator and the H2S gas separation tank are connected through a pipeline, and the tube side outlet of the H2S fraction cold exchanger is provided with an acid gas desulfurization recovery pipeline.

[0011] Preferably, a connecting secondary line is provided between the pipeline connecting the tower top separation tank with the tube side inlet of the H2S fraction cold exchanger and the acid gas desulfurization recovery pipeline at the shell side outlet of the H2S fraction cold exchanger.

[0012] By adjusting the valve of this connecting bypass line, the NH3 accumulated in the system can be taken out with the H2S fraction, preventing the formation of crystals in the H2S fraction cold exchanger to block the acid gas channel and cause overpressure in the thermal regeneration system, thereby ensuring the safety of system equipment and pipelines.

[0013] A low-temperature methanol washing process, the low-temperature methanol washing process comprises an ammonia washing stage, a thermal regeneration stage and a methanol-water separation stage, wherein the ammonia washing stage comprises the following steps:

[0014] S1, the converted gas and the unconverted gas enter the lower part of the converted gas ammonia washing tower and the unconverted gas ammonia washing tower respectively, and the boiler water is cooled by the first water cooler and then introduced into the upper part of the converted gas ammonia washing tower and the unconverted gas ammonia washing tower respectively to spray downward, and the boiler water absorbs ammonia in the converted gas and the unconverted gas;

[0015] The thermal regeneration stage comprises the following steps:

[0016] S2, the methanol-rich liquid enters the thermal regeneration tower through the pipeline of the methanol-rich self-concentrator for thermal regeneration, the lean methanol obtained at the bottom of the thermal regeneration tower is transported to the absorption tower through the lean methanol de-absorption tower pipeline, and the acid gas rich in H2S obtained at the top of the thermal regeneration tower is cooled by the second water cooler and then transported to the top separation tank for gas-liquid separation;

[0017] The liquid phase is transported back to the thermal regeneration tower as reflux liquid through the tower top reflux pump, and the gas phase is cooled by the H2S fraction cold exchanger and the H2S fraction cryogenic cooler and then sent to the H2S gas separation tank to separate the methanol liquid and the H2S-containing acid gas;

[0018] Part of the methanol liquid is fed into the concentration tower through the methanol liquid deconcentration tower pipeline, and the H2S-containing acid gas is fed into the Claus sulfur recovery unit through the acid gas desulfurization recovery pipeline;

[0019] The methanol-water separation stage comprises the following steps:

[0020] S3. Another part of lean methanol at the bottom of the thermal regeneration tower enters the methanol-water separation tower. After heating and separation, the methanol vapor returns to the thermal regeneration tower from the top of the methanol-water separation tower, and the methanol-containing wastewater is discharged from the bottom of the methanol-water separation tower for sewage treatment.

[0021] Preferably, in step S1, the temperature of the boiler water after being cooled by the first water cooler is 35±1°C.

[0022] Preferably, in step S2, the ammonia in the low temperature methanol washing system is discharged together with the H2S-containing acid gas through a connecting secondary line and input into the Claus sulfur recovery unit.

[0023] Preferably, in step S3, alkaline solution is introduced into the bottom of the methanol-water separation tower to control the pH of the bottom liquid to be 6-7.

[0024] Preferably, the alkali solution is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 32wt%.

[0025] Preferably, the ammonia content in the lean methanol is 5-10 ppm.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention sets a first water cooler to reduce the temperature of high-pressure boiler water used for washing ammonia from the original 50°C to about 35°C, thereby significantly enhancing the washing effects of the converted gas ammonia washing tower and the unconverted gas ammonia washing tower, thereby reducing the ammonia carried in the converted gas and the unconverted gas entering the subsequent step of low-temperature methanol washing, further reducing the methanol circulation volume, and effectively reducing the methanol consumption of low-temperature methanol washing, which can control the methanol consumption to about 20kg / h.

[0028] 2. With the gradual increase of ammonia entering the low-temperature methanol washing system, ammonium bicarbonate generated by ammonia and carbon dioxide or hydrogen sulfide will cause ammonium sulfide crystals to cause blockage of the H2S fraction cold exchanger. By connecting a bypass line, the generation fluctuation problem caused by blockage can be effectively solved.

[0029] 3. By setting up an alkali liquid tank and adjusting the system pH between 6-7, the corrosion of hydrogen sulfide and carbon dioxide to the low-temperature methanol hot wash zone can be effectively controlled, and the solubility of ammonia in the wastewater can be increased to prevent ammonia from re-entering the lean methanol in the thermal regeneration tower along with the methanol vapor. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 It is a structural schematic diagram of the ammonia washing system of the present invention;

[0032] Figure 2 It is a schematic diagram of the structure of the thermal regeneration system and the methanol-water separation system of the present invention.

[0033] Illustration: 1. Conversion gas washing ammonia tower, 2. Unconversion gas washing ammonia tower, 3. First water cooler, 4. Boiler water inlet pipeline, 5. Conversion gas pipeline, 6. Unconversion gas pipeline, 7. Conversion gas to low-A pipeline, 8. Unconversion gas to low-A pipeline, 9. Hot regeneration tower, 10. Second water cooler, 11. Tower top separation tank, 12. H2S fraction cold exchanger, 13. H2S fraction deep freezer, 14. H2S gas separation tank , 15. Tower top reflux pump, 16. First reboiler, 17. Acid gas desulfurization recovery pipeline, 18. Methanol liquid to concentration tower pipeline, 19. Rich methanol self-concentration tower pipeline, 20. Lean methanol to absorption tower pipeline, 21. Methanol-water separation tower, 22. Second reboiler, 23. Tail gas washing tower, 24. Alkali liquid tank, 25. Wastewater treatment pipeline, 26. Desalted water pipeline, 27. Tail gas pipeline, 28. Connecting bypass line. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] The present invention is now further described in conjunction with specific examples. The following examples are only for explaining the present invention, but do not constitute a limitation of the present invention. The test samples and test processes used in the following examples include the following (if the specific experimental conditions are not indicated in the examples, they are usually in accordance with conventional conditions or the conditions recommended by the reagent company; the reagents, consumables, etc. used in the following examples, if not otherwise specified, can all be obtained from commercial channels).

[0037] One of the purposes of the present invention is to provide a low temperature methanol washing system, a structural schematic diagram of a specific embodiment of which is shown in Figure 1 and Figure 2 The low-temperature methanol washing system includes an ammonia washing system, a thermal regeneration system and a methanol-water separation system. It should be noted that the complete low-temperature methanol washing system also includes acid gas absorption, medium / low pressure flash evaporation, gas stripping regeneration and water washing, which are existing technologies and will not be repeated here.

[0038] The ammonia washing system consists of a conversion gas washing ammonia tower 1, an unconverted gas washing ammonia tower 2 and a first water cooler 3, wherein the water inlet of the first water cooler is provided with a boiler water inlet pipeline 4, the water outlet of the first water cooler is connected with the upper part of the conversion gas washing ammonia tower and the upper part of the unconverted gas washing ammonia tower through pipelines, respectively, the lower part of the conversion gas washing ammonia tower and the lower part of the unconverted gas washing ammonia tower are provided with a conversion gas pipeline 5 and an unconverted gas pipeline 6 respectively, and the top of the conversion gas washing ammonia tower and the unconverted gas washing ammonia tower are provided with a conversion gas to low-M pipeline 7 and an unconverted gas to low-M pipeline 8 respectively, which are used to transport the converted gas and the unconverted gas after ammonia washing to the system of the next step.

[0039] The heat regeneration system is composed of a heat regeneration tower 9, a second water cooler 10, a tower top separation tank 11, an H2S fraction cold exchanger 12, an H2S fraction cryogenic refrigerator 13, an H2S gas separation tank 14, a tower top reflux pump 15 and a first reboiler 16. The top gas outlet of the heat regeneration tower is connected to the second water cooler through a pipeline, the second water cooler is connected to the tower top separation tank through a pipeline, the top outlet of the tower top separation tank is connected to the tube side inlet of the H2S fraction cold exchanger through a pipeline, the tube side outlet of the H2S fraction cold exchanger is connected to the H2S fraction cryogenic refrigerator through a pipeline, and the H The shell side inlet of the 2S fraction cold exchanger is connected to the H2S gas separation tank through a pipeline, the H2S fraction cryogenic refrigerator and the H2S gas separation tank are connected through a pipeline, the shell side outlet of the H2S fraction cold exchanger is provided with an acid gas desulfurization recovery pipeline 17, the H2S fraction cryogenic refrigerator is connected to the H2S gas separation tank through a pipeline, the bottom outlet of the H2S gas separation tank is provided with a methanol liquid concentration tower pipeline 18, the tower top separation tank is connected to the tower top reflux pump through a pipeline, the tower top reflux pump is connected to the upper part of the thermal regeneration tower through a pipeline, and the first reboiler is connected to the thermal regeneration tower pipeline.

[0040] A methanol-rich self-concentration tower pipeline 19 is provided at the upper part of the thermal regeneration tower, and a methanol-poor de-absorption tower pipeline 20 is provided at the bottom of the thermal regeneration tower.

[0041] A connecting secondary line 28 is provided between the pipeline connecting the top separation tank with the tube side inlet of the H2S fraction cold exchanger and the acid gas desulfurization recovery pipeline at the shell side outlet of the H2S fraction cold exchanger.

[0042] The methanol-water separation system consists of a methanol-water separation tower 21, a second reboiler 22, a tail gas washing tower 23 and an alkali liquid tank 24. The second reboiler is connected to the methanol-water separation tower pipeline, the alkali liquid tank is connected to the lower part of the methanol-water separation tower through a pipeline, the top liquid outlet of the methanol-water separation tower is connected to the middle part of the thermal regeneration tower through a pipeline, the bottom of the thermal regeneration tower is connected to the methanol-water separation tower through a pipeline, and the bottom liquid outlet of the tail gas washing tower is connected to the methanol-water separation tower through a pipeline.

[0043] The alkali liquid tank is connected to the liquid outlet pipeline at the bottom of the tail gas washing tower through a pipeline. A desalted water treatment pipeline 25 is provided at the bottom of the methanol water separation tower. A branch pipeline is provided on the desalted water treatment pipeline to connect with the tail gas washing tower. A desalted water pipeline 26 is provided on the upper part of the tail gas washing tower. A tail gas removal pipeline 27 is provided on the top of the tail gas washing tower.

[0044] The second object of the present invention is to provide a low-temperature methanol washing process, which includes an ammonia washing stage, a thermal regeneration stage and a methanol-water separation stage, wherein the steps of the ammonia washing stage are as follows:

[0045] S1, the converted gas and the unconverted gas enter the lower part of the converted gas ammonia washing tower and the unconverted gas ammonia washing tower respectively, and the boiler water is cooled by the first water cooler and then introduced into the upper part of the converted gas ammonia washing tower and the unconverted gas ammonia washing tower respectively to spray downward, and the boiler water absorbs ammonia in the converted gas and the unconverted gas.

[0046] The steps of the thermal regeneration phase are as follows:

[0047] S2, the methanol-rich liquid enters the thermal regeneration tower through the pipeline of the methanol-rich self-concentrator for thermal regeneration, the lean methanol obtained at the bottom of the thermal regeneration tower is transported to the absorption tower through the lean methanol de-absorption tower pipeline, and the acid gas rich in H2S obtained at the top of the thermal regeneration tower is cooled by the second water cooler and then transported to the top separation tank for gas-liquid separation;

[0048] The liquid phase is transported back to the thermal regeneration tower as reflux liquid through the tower top reflux pump, and the gas phase is cooled by the H2S fraction cold exchanger and the H2S fraction cryogenic cooler and then sent to the H2S gas separation tank to separate the methanol liquid and the H2S-containing acid gas;

[0049] Part of the methanol liquid is input into the concentration tower through the methanol liquid deconcentration tower pipeline, and the H2S-containing acid gas is input into the Claus sulfur recovery unit through the acid gas desulfurization recovery pipeline.

[0050] The steps of the methanol-water separation stage are as follows:

[0051] S3. The alkali liquid in the alkali liquid tank is passed into the bottom of the methanol water separation tower, and another part of the lean methanol at the bottom of the thermal regeneration tower enters the methanol water separation tower. After heating and separation, the methanol vapor returns to the thermal regeneration tower from the top of the methanol water separation tower, and the methanol-containing wastewater is discharged from the bottom of the methanol water separation tower for sewage treatment.

[0052] Application Example 1

[0053] In step S1, high-pressure boiler water at a temperature of 50°C is introduced. After being cooled by the first water cooler, the temperature of the high-pressure boiler water drops to 35°C. At this time, the ammonia content in the converted gas is 0 ppm, and the ammonia content in the unconverted gas is 0 ppm; the methanol consumption in the low-temperature methanol washing system is 15 kg / h.

[0054] Comparative Example 1

[0055] In step S1, high-pressure boiler water at a temperature of 50°C is introduced, and the first water cooler is closed. At this time, the ammonia content in the converted gas is 4ppm; the ammonia content in the unconverted gas is 6ppm; and the methanol consumption in the low-temperature methanol washing system is: 20kg / h.

[0056] Application Example 2

[0057] In step S3, alkaline solution is introduced into the bottom of the methanol-water separation tower to control the pH of the bottom liquid to be 6.5. At this time, the ammonia content in the lean methanol is 7 ppm.

[0058] Comparative Example 2

[0059] In step S3, no alkali solution is introduced into the bottom of the methanol-water separation tower. At this time, the ammonia content in the lean methanol is 49 ppm.

[0060] Comparative Example 3

[0061] In step S1, high-pressure boiler water with a temperature of 50°C is introduced, the first water cooler is closed, and in step S3, no alkali solution is introduced into the bottom of the methanol-water separation tower.

[0062] Comparing the corrosion of the equipment pipelines in Comparative Example 3 and Application Example 1, take the methanol-water separation tower as an example:

[0063] Comparative Example 3: The actual wall thickness of the methanol-water separation tower was measured by online ultrasonic thickness measurement, and 8 points within one meter of the tower wall near the acidic water inlet were tested on site.

[0064] The test results are as follows: A1: 12.9, A2: 12.59, A3: 12.99, A4: 12.65, A5: 12.43, A6: 12.72, B1: 12.17, B2: 10.62, B3: 10.97, B4: 10.87, B5: 12.65, B6: 12.32, C1: 12.91, C2: 11.26, C3: 9.63, C4: 11.41, C5: 12.79, C6: 12.85, D1: 12.84, D2: 11.14, D3: 11.07, D4: 11.72, D5: 10.89, D6: 12.87, E1: 12.75, E2: 12.71, E3: 12.35, E4: 11.72, E5: 11.86, E6: 12.74. It was found that most of the tower walls tested were thinned, and some were severely thinned. For example, point B2 was thinned from 13mm to 10.62mm, a thinning of 18%, and point C3 was thinned from 13mm to 9.63mm, a thinning of 25.9%.

[0065] Application Example 1:

[0066] The test results are as follows: A1: 12.8, A2: 12.55, A3: 12.94, A4: 12.45, A5: 12.40, A6: 12.68, B1: 12.13, B2: 10.61, B3: 10.95, B4: 10.87, B5: 12.53, B6: 12.34, C1: 12.91, C2: 11.24, C3: 9. 60, C4: 11.41, C5: 12.79, C6: 12.82, D1: 12.78, D2: 11.11, D3: 11.10, D4: 11.66, D5: 10.88, D6: 12.78, E1: 12.75, E2: 12.73, E3: 12.36, E4: 11.67, E5: 11.85, E6: 12.76.

[0067] It can be seen that adjusting H2S and CO2 by pH has an inhibitory effect on the corrosion of equipment pipelines.

[0068] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0069] The above is a detailed introduction to a low-temperature methanol washing system and process provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A low temperature methanol washing system, characterized in that: The low-temperature methanol washing system comprises an ammonia washing system and a heat regeneration system. The ammonia washing system comprises a conversion gas washing ammonia tower (1), an unconverted gas washing ammonia tower (2) and a first water cooler (3). The water inlet of the first water cooler is provided with a boiler water inlet pipeline (4). The water outlet of the first water cooler is connected to the upper part of the conversion gas washing ammonia tower and the upper part of the unconverted gas washing ammonia tower through pipelines. The lower parts of the conversion gas washing ammonia tower and the unconverted gas washing ammonia tower are provided with a conversion gas pipeline (5) and an unconverted gas pipeline (6) respectively. The tops of the conversion gas washing ammonia tower and the unconverted gas washing ammonia tower are provided with a conversion gas to low-methyl-1-2 pipeline (7) and an unconverted gas to low-methyl-1-2 pipeline (8) respectively. The heat regeneration system comprises a heat regeneration tower (9), a second water cooler (10), a tower top separation tank (11), an H2S fraction cold exchanger (12), an H2S fraction cryogenic cooler (13), an H2S gas separation tank (14), a tower top reflux pump (15) and a first reboiler (16), wherein the top gas outlet of the heat regeneration tower is connected to the second water cooler via a pipeline, the second water cooler is connected to the tower top separation tank via a pipeline, and the tower top separation tank is connected to the H2S fraction cold exchanger via a pipeline. The H2S fraction cold exchanger is connected to the H2S gas separation tank and the H2S fraction cryogenic refrigerator through pipelines, the H2S fraction cryogenic refrigerator is connected to the H2S gas separation tank through pipelines, the bottom outlet of the H2S gas separation tank is provided with a methanol liquid concentration tower pipeline (18), the tower top separation tank is connected to the tower top reflux pump through pipelines, the tower top reflux pump is connected to the upper part of the hot regeneration tower through pipelines, and the first reboiler is connected to the hot regeneration tower pipeline; A methanol-rich self-concentration tower pipeline (19) is also provided at the top of the thermal regeneration tower, and a methanol-poor de-absorption tower pipeline (20) is provided at the bottom of the thermal regeneration tower.

2. The low-temperature methanol washing system according to claim 1, characterized in that: The low-temperature methanol washing system also includes a methanol-water separation system, which includes a methanol-water separation tower (21), a second reboiler (22), a tail gas washing tower (23) and an alkali liquid tank (24), wherein the second reboiler is connected to the methanol-water separation tower pipeline, the alkali liquid tank is connected to the lower part of the methanol-water separation tower through a pipeline, the top liquid outlet of the methanol-water separation tower is connected to the middle part of the thermal regeneration tower through a pipeline, the bottom of the thermal regeneration tower is connected to the methanol-water separation tower through a pipeline, and the bottom liquid outlet of the tail gas washing tower is connected to the methanol-water separation tower through a pipeline; The alkali liquid tank is also connected to the liquid outlet pipeline at the bottom of the tail gas washing tower through a pipeline. A desalted water treatment pipeline (25) is provided at the bottom of the methanol water separation tower. A branch pipeline is provided on the desalted water treatment pipeline and connected to the tail gas washing tower. A desalted water pipeline (26) is provided on the top of the tail gas washing tower. A tail gas removal pipeline (27) is provided on the top of the tail gas washing tower.

3. The low-temperature methanol washing system according to claim 1, characterized in that: The top outlet of the tower top separation tank is connected to the tube side inlet of the H2S fraction cold exchanger through a pipeline, the tube side outlet of the H2S fraction cold exchanger is connected to the H2S fraction cryogenic refrigerator through a pipeline, the shell side inlet of the H2S fraction cold exchanger is connected to the H2S gas separation tank through a pipeline, the H2S fraction cryogenic refrigerator and the H2S gas separation tank are connected through a pipeline, and the tube side outlet of the H2S fraction cold exchanger is provided with an acid gas desulfurization recovery pipeline (17).

4. The low-temperature methanol washing system according to claim 3, characterized in that: A connecting secondary line (28) is provided between the pipeline connecting the tower top separation tank with the tube side inlet of the H2S fraction cold exchanger and the acid gas desulfurization recovery pipeline at the shell side outlet of the H2S fraction cold exchanger.

5. A low-temperature methanol washing process, characterized in that: The low-temperature methanol washing process includes an ammonia washing stage, a thermal regeneration stage and a methanol-water separation stage, wherein the ammonia washing stage includes the following steps: S1, the converted gas and the unconverted gas enter the lower part of the converted gas ammonia washing tower and the unconverted gas ammonia washing tower respectively, and the boiler water is cooled by the first water cooler and then introduced into the upper part of the converted gas ammonia washing tower and the unconverted gas ammonia washing tower respectively to spray downward, and the boiler water absorbs ammonia in the converted gas and the unconverted gas; The thermal regeneration stage comprises the following steps: S2, the methanol-rich liquid enters the thermal regeneration tower through the pipeline of the methanol-rich self-concentrator for thermal regeneration, the lean methanol obtained at the bottom of the thermal regeneration tower is transported to the absorption tower through the lean methanol de-absorption tower pipeline, and the acid gas rich in H2S obtained at the top of the thermal regeneration tower is cooled by the second water cooler and then transported to the top separation tank for gas-liquid separation; The liquid phase is transported back to the thermal regeneration tower as reflux liquid through the tower top reflux pump, and the gas phase is cooled by the H2S fraction cold exchanger and the H2S fraction cryogenic cooler and then sent to the H2S gas separation tank to separate the methanol liquid and the H2S-containing acid gas; Part of the methanol liquid is fed into the concentrator through the methanol liquid concentrator pipeline, and the H2S-containing acid gas is fed into the Claus sulfur recovery unit through the acid gas desulfurization recovery pipeline; The methanol-water separation stage comprises the following steps: S3. Another part of lean methanol at the bottom of the thermal regeneration tower enters the methanol-water separation tower. After heating and separation, the methanol vapor returns to the thermal regeneration tower from the top of the methanol-water separation tower, and the methanol-containing wastewater is discharged from the bottom of the methanol-water separation tower for sewage treatment.

6. The low-temperature methanol washing process according to claim 5, characterized in that: In step S1, the temperature of the boiler water after being cooled by the first water cooler is 35±1°C.

7. The low-temperature methanol washing process according to claim 5, characterized in that: In step S2, ammonia in the low-temperature methanol wash system is discharged together with H2S-containing acid gas through a connecting bypass line and input into the Claus sulfur recovery unit.

8. The low-temperature methanol washing process according to claim 5, characterized in that: In step S3, alkaline solution is introduced into the bottom of the methanol-water separation tower to control the pH of the bottom liquid to be 6-7.

9. The low-temperature methanol washing process according to claim 8, characterized in that: The alkali solution is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 32wt%.

10. The low-temperature methanol washing process according to claim 5, characterized in that: The ammonia content in the lean methanol is 5-10 ppm.

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