System for efficiently removing organic sulfur in low-temperature methanol washing solvent through bidirectional extraction

Abstract

The utility model belongs to the technical field of chemical engineering, and particularly relates to a system for efficiently removing organic sulfur in a low-temperature methanol washing solvent through bidirectional extraction, which comprises a prewashing tower, organic sulfur in shift gas is absorbed through methanol in the prewashing tower, a shift gas inlet of the prewashing tower is connected with a shift gas outlet of a gas / gas heat exchanger of a low-temperature methanol washing device, and the shift gas inlet of the prewashing tower is connected with the shift gas outlet of the gas / gas heat exchanger. A converted gas outlet of the pre-washing tower is connected with a converted gas inlet of a desulfurizing tower of the low-temperature methanol washing device, one part of methanol flowing out of the bottom of the desulfurizing tower is fed into the pre-washing tower, the other part of methanol is fed into a medium-pressure flash tower of the low-temperature methanol washing device, and dirty methanol absorbing organic sulfur flows out of the bottom of the pre-washing tower. According to the low-temperature methanol washing device, the pre-washing tower is arranged, the shift gas enters the pre-washing tower before entering the desulfurizing tower, and organic sulfur and other organic matters in the shift gas are completely absorbed by the pre-washing tower, so that circulating methanol in the low-temperature methanol washing device does not contain the organic sulfur and other organic matters, and lean methanol subjected to thermal regeneration is very pure; the quality index is close to that of refined methanol.

Description

Technical Field

[0001] The utility model belongs to the technical field of chemical industry, and particularly relates to a system for efficiently removing organic sulfur from a low-temperature methanol washing solvent through bidirectional extraction. Background Art

[0002] After 2000, China's coal chemical industry entered a period of rapid development. A typical coal chemical plant consists of three major components: coal gasification, purification, and synthesis. While dozens of coal gasification technologies are currently in widespread use, coal gas purification options are limited, particularly for desulfurization and carbon removal, which generally utilizes low-temperature methanol scrubbing technology.

[0003] It's generally accepted in the industry that fixed-bed pressurized gasification, which contains numerous impurities such as tar, aromatics, and organic sulfur generated during the coal pyrolysis stage, makes gas purification difficult. Desulfurization and decarbonization using low-temperature methanol scrubbing is technically complex and requires a long process. However, pulverized coal pressurized gasification, which lacks macromolecular compounds, makes gas purification easier. Desulfurization and decarbonization using low-temperature methanol scrubbing is a simpler process. However, regardless of the process length, the purification effect remains stable.

[0004] However, in recent years, the newly built coal chemical plants, which are equipped with low-temperature methanol washing devices for pulverized coal pressurized gasification, have generally encountered the problem of seriously exceeding the sulfur content in the purified gas at the outlet of the low-temperature methanol washing devices.

[0005] The reasons are analyzed as follows: the higher the CO content in the raw coal gas at the converter inlet, the higher the conversion rate requirement of the downstream, and the more stages of the converter. The bed temperature of each converter gradually decreases from front to back. The temperature of the first converter is generally higher. Even if the coal gas sent from the gasification furnace contains organic sulfur, it can be hydrogenated and converted into inorganic sulfur. The bed temperature of the second and third converters is basically between 280 and 330 ° C, which is the range of organic sulfur generation. Regardless of whether the coal gas at the outlet of the first converter contains organic sulfur, the outlets of the second and third converters will contain organic sulfur. When producing pure hydrogen or synthetic ammonia, the third or fourth converter uses a low-conversion catalyst with a temperature below 280 ° C. The CO content at the end of the converter is very low, and the organic sulfur generated in the front will be reduced.

[0006] However, no matter how the conversion process is set up or which catalyst is used, organic sulfur will definitely exist in the conversion gas at the outlet of the conversion device, it is just a matter of how much it contains.

[0007] When the organic sulfur content in the shift gas is low, the negative impact on downstream processes is minimal. Conversely, it can be very significant. The performance of low-temperature methanol scrubbing units using pulverized coal gasification in China varies widely, and the main reason for this discrepancy is the organic sulfur content in the shift gas.

[0008] In the absorption tower, methanol containing dissolved organic sulfur can evaporate from the liquid phase and enter the vapor phase at the thermal regeneration column during the thermal regeneration process. However, the methanol in the vapor phase at the thermal regeneration column undergoes gradual cooling, ultimately condensing almost entirely. Because the boiling points of mercaptans / sulfides and methanol are very close, mercaptans / sulfides are also completely condensed into the methanol during methanol recovery. Therefore, once organic sulfur enters the low-temperature methanol scrubbing unit, it accumulates due to separation measures.

[0009] When the accumulated organic sulfur in the system is low—that is, when the organic sulfur content in the feed to the thermal regeneration tower is low—the organic sulfur content in the reflux liquid at the top of the tower is also low. Intermittent discharge from the reflux tank removes some of the organic sulfur in the reflux liquid. When the amount of organic sulfur entering and leaving the system reaches equilibrium, the organic sulfur content in the reflux liquid is maintained at a low level, ensuring that the refined methanol at the bottom of the thermal regeneration tower is free of organic sulfur, and the desulfurization performance of the absorption tower is largely unaffected.

[0010] However, if the shift gas carries a large amount of organic sulfur, the problem becomes serious. When the organic sulfur concentration in the overhead reflux is high, the organic sulfur content of the refined methanol at the bottom of the tower will exceed the standard, and the organic sulfur content of the purified gas exiting the absorption tower will also exceed the standard. The presence of organic sulfur also affects the regeneration and absorption of inorganic sulfur in the refined methanol, causing both organic and inorganic sulfur content in the refined methanol to exceed the standard. The result is that the organic and inorganic sulfur content in the purified gas exceeds the standard significantly.

[0011] Unable to resolve the issue of excessive sulfur content in the purified gas exiting the low-temperature methanol scrubbing unit, many companies have resorted to adding fine desulfurization units at the inlet of the synthesis system to ensure normal operation, further increasing investment and operating costs. Utility Model Content

[0012] In view of the above problems, the utility model provides a system for efficiently removing organic sulfur from a low-temperature methanol washing solvent by bidirectional extraction.

[0013] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0014] A system for efficiently removing organic sulfur from a low-temperature methanol washing solvent by bidirectional extraction comprises a pre-wash tower, wherein the organic sulfur in the conversion gas is absorbed by methanol in the pre-wash tower, the conversion gas inlet of the pre-wash tower is connected to the conversion gas outlet of the gas / gas heat exchanger of the low-temperature methanol washing device, and the conversion gas outlet of the pre-wash tower is connected to the conversion gas inlet of the desulfurization tower of the low-temperature methanol washing device, a part of the methanol flowing out from the bottom of the desulfurization tower is sent to the pre-wash tower, and the other part is sent to the medium-pressure flash tower of the low-temperature methanol washing device, and the dirty methanol that has absorbed the organic sulfur flows out from the bottom of the pre-wash tower.

[0015] Furthermore, the dirty methanol flowing out from the bottom of the pre-wash tower is sequentially subjected to reduced pressure flash evaporation in the first pre-wash flash tower and the second pre-wash flash tower to desorb most of the acid gases dissolved in the dirty methanol. The acid gases are released from the top of the first pre-wash flash tower and the second pre-wash flash tower and sent to the water washing tower for water washing; the dirty methanol discharged from the bottom of the second pre-wash flash tower is mixed with the oil phase sent by the circulating oil pump in the static mixer and then enters the lower part of the extraction tower; the upper part of the extraction tower is provided with a water inlet, and in the extraction tower, the methanol in the dirty methanol enters the water phase, and the organic sulfur in the dirty methanol enters the oil phase, and the oil phase is discharged from the top of the extraction tower and sent to the extraction tower. Oil circulation tank; After the oil phase in the oil circulation tank is pressurized by the circulating oil pump, a part of it enters the static mixer to mix with the dirty methanol, and the other part is discharged from the boundary area and sent to the crude benzene refining plant outside the boundary area; the methanol water discharged from the bottom of the extraction tower is heated by the methanol water / wastewater heat exchanger and then enters the refining tower to remove a small amount of acid gas and trace organic sulfur contained in the methanol water; the mixed gas sent out from the top of the refining tower contains methanol vapor, acid gas and organic sulfur vapor, which is cooled by the No. 1 water cooler. Most of the methanol vapor and organic sulfur vapor are condensed into liquid and enter the gas-liquid separator. The gas phase outlet of the gas-liquid separator is connected to the gas phase outlet of the water washing tower. The inlet of the gas-liquid separator is connected, the liquid phase outlet of the gas-liquid separator is connected to the reflux pump of the refining tower, part of the liquid refluxes to the upper part of the refining tower, and the other part of the liquid refluxes to the inlet of the static mixer to mix with the pre-wash methanol to prevent the accumulation of organic sulfur in the upper part of the refining tower. The relatively pure methanol water flowing out from the bottom of the refining tower enters the methanol-water distillation tower to complete the separation of methanol and water through the distillation process; the methanol vapor discharged from the top of the methanol-water distillation tower is first used as the heat source of the reboiler of the refining tower to exchange heat with the refining tower bottom liquid, and then enters the No. 2 water cooler to condense into liquid and be discharged into the reflux tank; part of the refined methanol in the reflux tank is used as the heat source of the methanol-water distillation tower Part of the reflux liquid is sent to the finished product storage tank for sale; the wastewater discharged from the bottom of the methanol-water distillation tower contains trace amounts of methanol and heavy aromatic hydrocarbons with a boiling point higher than that of water. After being cooled to room temperature through the methanol-water / wastewater heat exchanger and the No. 3 water cooler, part of it is mixed with the water sent from the water scrubber and sent to the upper part of the extraction tower, and the other part is sent to the sewage treatment plant outside the boundary area; the acid gas sent from the first pre-wash flash tower and the second pre-wash flash tower, as well as the acid gas sent from the gas-liquid separator of the refining tower contain a small amount of methanol. The three gases are mixed and sent to the bottom of the water scrubber. After the methanol in the acid gas is absorbed by water, the acid gas is sent to the sulfur recovery device of the coal chemical plant outside the boundary area.

[0016] Furthermore, a filter is provided between the pre-wash tower and the first pre-wash flash tower for filtering solid impurities in the contaminated methanol.

[0017] Furthermore, a No. 1 heat exchanger and a No. 2 heat exchanger are respectively provided at the outlets of the dirty methanol of the first pre-wash flash tower and the second pre-wash flash tower, for heat exchange and temperature increase of the dirty methanol. The heat source inlet of the No. 2 heat exchanger is connected to the bottom outlet of the heat regeneration tower, the heat source outlet of the No. 2 heat exchanger is connected to the heat source inlet of the No. 1 heat exchanger, and the heat source outlet of the No. 1 heat exchanger is connected to the heat source inlet of the lean / rich methanol heat exchanger.

[0018] Compared with the prior art, the utility model has the following advantages:

[0019] The utility model is equipped with a pre-wash tower. Before the shift gas enters the desulfurization tower, the pre-wash tower absorbs all organic sulfur and other organic matter in the shift gas. This ensures that the circulating methanol in the low-temperature methanol washing device is free of organic sulfur and other organic matter. The lean methanol after thermal regeneration is extremely pure, approaching the quality standards of refined methanol. This fundamentally ensures the long-term stability of the low-temperature methanol washing device's purification effect.

[0020] After the pre-wash tower, the utility model also regenerates the contaminated methanol produced by the pre-wash through a first pre-wash flash tower, a second pre-wash flash tower, and an extraction tower, thoroughly separating impurities such as organic sulfur, inorganic sulfur, ammonia, carbon dioxide, and water from the contaminated methanol. Finally, refined methanol is obtained and returned to the system, achieving a methanol recovery rate of nearly 100%. This significantly reduces the losses caused by the large-scale discharge of contaminated methanol.

[0021] Aiming at the characteristics of low organic sulfur content in pre-wash methanol and slight solubility of organic sulfur in water, the utility model adopts bidirectional multi-stage extraction, namely, extracting methanol with water and extracting organic sulfur with organic solvent, thereby ensuring that the organic sulfur content in the methanol-water phase is extremely low.

[0022] The utility model has low investment cost, simple process, no high-pressure equipment, no special material equipment; low energy consumption, using the top steam of the methanol-water distillation tower as the heat source of the refining tower, reducing steam consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural diagram of the utility model;

[0024] In the figure, there are pre-wash tower 1, gas / gas heat exchanger 2, desulfurization tower 3, medium-pressure flash tower 4, first pre-wash flash tower 5, second pre-wash flash tower 6, static mixer 7, circulating oil pump 8, extraction tower 9, oil circulation tank 10, methanol water / wastewater heat exchanger 11, refining tower 12, No. 1 water cooler 13, gas-liquid separator 14, reflux pump 15, methanol water distillation tower 16, refining tower reboiler 17, No. 2 water cooler 18, reflux tank 19, finished product storage tank 20, No. 3 water cooler 21, water washing tower 22, filter 23, No. 1 heat exchanger 24, No. 2 heat exchanger 25, thermal regeneration tower 26, and lean / rich methanol heat exchanger 27. DETAILED DESCRIPTION

[0025] In order to further illustrate the technical solution of the present invention, the present invention will be further described below through embodiments.

[0026] like Figure 1As shown, a system for efficiently removing organic sulfur from a low-temperature methanol washing solvent by bidirectional extraction comprises a pre-wash tower 1, wherein the organic sulfur in the conversion gas is absorbed by the methanol in the pre-wash tower 1, the conversion gas inlet of the pre-wash tower 1 is connected to the conversion gas outlet of the gas / gas heat exchanger 2 of the low-temperature methanol washing device, and the conversion gas outlet of the pre-wash tower 1 is connected to the conversion gas inlet of the desulfurization tower 3 of the low-temperature methanol washing device, a part of the methanol flowing out from the bottom of the desulfurization tower 3 is sent to the pre-wash tower 1, and the other part is sent to the medium-pressure flash tower 4 of the low-temperature methanol washing device, the dirty methanol that has absorbed the organic sulfur flows out from the bottom of the pre-wash tower 1, and the dirty methanol flowing out from the bottom of the pre-wash tower 1 is sequentially subjected to reduced-pressure flash evaporation through the first pre-wash flash tower 5 and the second pre-wash flash tower 6 to desorb the dirty methanol. Most of the dissolved acidic gases are released from the top of the first pre-wash flash tower 5 and the second pre-wash flash tower 6 and are sent to the water washing tower 22 for water washing; a filter 23 is provided between the pre-wash tower 1 and the first pre-wash flash tower 5 for filtering solid impurities in the dirty methanol, and a first heat exchanger 24 and a second heat exchanger 25 are respectively provided at the dirty methanol outlets of the first pre-wash flash tower 5 and the second pre-wash flash tower 6 for heat exchange and temperature increase of the dirty methanol, the heat source inlet of the second heat exchanger 25 is connected to the bottom outlet of the heat regeneration tower 26, the heat source outlet of the second heat exchanger 25 is connected to the heat source inlet of the first heat exchanger 24, and the heat source outlet of the first heat exchanger 24 is connected to the heat source inlet of the lean / rich methanol heat exchanger 27 The dirty methanol discharged from the bottom of the second pre-wash flash tower 6 is mixed with the oil phase sent by the circulating oil pump 8 in the static mixer 7 and then enters the lower part of the extraction tower 9; the upper part of the extraction tower 9 is provided with a water inlet, and in the extraction tower 9, the methanol in the dirty methanol enters the water phase, and the organic sulfur in the dirty methanol enters the oil phase, and the oil phase is discharged from the top of the extraction tower 9 and sent to the oil circulation tank 10; after the oil phase in the oil circulation tank 10 is pressurized by the circulating oil pump 8, a part of it enters the static mixer 7 and is mixed with the dirty methanol, and the other part is discharged from the boundary area and sent to the crude benzene refining plant outside the boundary area; the methanol water discharged from the bottom of the extraction tower 9 is heated by the methanol water / wastewater heat exchanger 11 and then enters the refining tower 12, thereby removing a small amount of acid gas and Trace organic sulfur; the mixed gas sent out from the top of the refining tower 12 contains methanol vapor, acid gas and organic sulfur vapor, which is cooled by the No. 1 water cooler 13. Most of the methanol vapor and organic sulfur vapor are condensed into liquid and enter the gas-liquid separator 14. The gas phase outlet of the gas-liquid separator 14 is connected to the gas inlet of the water washing tower 22, and the liquid phase outlet of the gas-liquid separator 14 is connected to the reflux pump 15 of the refining tower 12. Part of the liquid flows back to the upper part of the refining tower 12, and the other part of the liquid flows back to the inlet of the static mixer 7 to mix with the pre-washing methanol to prevent the organic sulfur from enriching in the upper part of the refining tower 12. The relatively pure methanol water flowing out from the bottom of the refining tower 12 enters the methanol-water distillation tower 16 to complete the separation of methanol and water through the distillation process;The methanol vapor discharged from the top of the methanol-water distillation tower 16 is first used as a heat source for the reboiler 17 of the refining tower to exchange heat with the kettle liquid of the refining tower 12, and then enters the second water cooler 18 to condense into liquid and discharge into the reflux tank 19; part of the refined methanol in the reflux tank 19 is used as the reflux liquid of the methanol-water distillation tower 16, and part is sent to the finished product storage tank 20 for sale; the wastewater discharged from the bottom of the methanol-water distillation tower 16 contains trace amounts of methanol and heavy aromatic hydrocarbons with a boiling point higher than that of water, and passes through the methanol-water / wastewater heat exchanger 1 in sequence. After cooling to room temperature in water coolers 1 and 3 (21), a portion is mixed with water from water scrubber 22 and sent to the upper portion of extraction tower 9, while the remaining portion is sent to a wastewater treatment plant outside the boundary area. The acid gas from the first and second pre-wash flash towers 5 and 6, as well as the acid gas from the gas-liquid separator 14 of refining tower 12, contains a small amount of methanol. These three streams are mixed and sent to the bottom of water scrubber 22. After the methanol in the acid gas is absorbed by water, the acid gas is sent to the sulfur recovery unit of the coal chemical plant outside the boundary area.

[0027] The above shows and describes the main features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be encompassed within the present invention.

[0028] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A system for efficiently removing organic sulfur from low-temperature methanol wash solvents by bidirectional extraction, characterized by: The invention comprises a pre-wash tower (1), wherein the organic sulfur in the conversion gas is absorbed by the methanol in the pre-wash tower (1), the conversion gas inlet of the pre-wash tower (1) is connected to the conversion gas outlet of the gas / gas heat exchanger (2) of the low-temperature methanol washing device, and the conversion gas outlet of the pre-wash tower (1) is connected to the conversion gas inlet of the desulfurization tower (3) of the low-temperature methanol washing device, a part of the methanol flowing out from the bottom of the desulfurization tower (3) is sent to the pre-wash tower (1), and the other part is sent to the medium-pressure flash tower (4) of the low-temperature methanol washing device, and the dirty methanol that has absorbed the organic sulfur flows out from the bottom of the pre-wash tower (1).

2. The system for efficiently removing organic sulfur from low-temperature methanol washing solvent by bidirectional extraction according to claim 1, characterized in that: The dirty methanol outlet at the bottom of the pre-wash tower (1) is connected to the inlets of the first pre-wash flash tower (5) and the second pre-wash flash tower (6) in sequence. The acid gas outlets at the tops of the first pre-wash flash tower (5) and the second pre-wash flash tower (6) are connected to the gas inlet of the water washing tower (22). The water outlet at the bottom of the water washing tower (22) is connected to the upper part of the extraction tower (9) and the sewage treatment plant. The bottom outlet of the second pre-wash flash tower (6) is connected to the static mixer (7), the circulating oil pump (8) and the extraction tower (9) in sequence. The upper part of the extraction tower (9) is provided with a water inlet. The oil phase outlet at the top of the extraction tower (9) is connected to the oil circulation tank (10), and the outlet of the oil circulation tank (10) is connected to the static mixer (7) and the crude benzene refining plant through a pipeline with a circulating oil pump (8). The outlet at the bottom of the extraction tower (9) is connected to the cold medium inlet of the methanol water / wastewater heat exchanger (11), and the cold medium outlet of the methanol water / wastewater heat exchanger (11) is connected to the refining tower (12). The gas outlet at the top of the refining tower (12) is connected to the No. 1 water cooler (13) and the gas-liquid separator (14) in sequence. The gas phase outlet is connected to the gas inlet of the water washing tower (22), the liquid phase outlet of the gas-liquid separator (14) is connected to the reflux pump (15) of the refining tower (12), the outlet of the reflux pump (15) is connected to the upper part of the refining tower (12) and the inlet of the static mixer (7), the methanol water outlet at the bottom of the refining tower (12) is connected to the inlet of the methanol water distillation tower (16), the steam outlet at the top of the methanol water distillation tower (16) is connected to the heat medium inlet of the refining tower reboiler (17), the heat medium outlet of the refining tower reboiler (17) is connected to the second water cooler (1 8), the outlet of the No. 2 water cooler (18) is connected to the reflux tank (19), the outlet of the reflux tank (19) is connected to the inlet of the finished product storage tank (20) and the reflux port of the methanol-water distillation tower (16) through a pipeline, the wastewater outlet at the bottom of the methanol-water distillation tower (16) is connected to the heat medium inlet of the methanol-water / wastewater heat exchanger (11), the heat medium outlet of the methanol-water / wastewater heat exchanger (11) is connected to the inlet of the No. 3 water cooler (21), and the outlet of the No. 3 water cooler (21) is connected to the upper part of the extraction tower (9) and the sewage treatment plant.

3. The system for efficiently removing organic sulfur from low-temperature methanol washing solvent by bidirectional extraction according to claim 1, characterized in that: A filter (23) is provided between the pre-wash tower (1) and the first pre-wash flash tower (5) for filtering solid impurities in the contaminated methanol.

4. The system for efficiently removing organic sulfur from low-temperature methanol washing solvent by bidirectional extraction according to claim 1, characterized in that: A first heat exchanger (24) and a second heat exchanger (25) are respectively provided at the outlets of the dirty methanol of the first pre-wash flash tower (5) and the second pre-wash flash tower (6) for exchanging heat and heating the dirty methanol. The heat source inlet of the second heat exchanger (25) is connected to the bottom outlet of the heat regeneration tower (26), the heat source outlet of the second heat exchanger (25) is connected to the heat source inlet of the first heat exchanger (24), and the heat source outlet of the first heat exchanger (24) is connected to the heat source inlet of the lean / rich methanol heat exchanger (27).

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