Systems and methods for reducing methanol regeneration steam consumption

Abstract

This invention relates to the field of methanol regeneration technology, and particularly to a system and method for reducing the amount of steam used in methanol regeneration. It includes: a secondary stripping unit for secondary stripping of CO2 from the methanol-rich solution in the original production system; a pipeline assembly connected to both the original production system and the secondary stripping unit, which introduces nitrogen and the methanol-rich solution from the original production system into the secondary stripping unit for stripping, and introduces the CO2 generated in the secondary stripping unit back into the original production system; the pipeline assembly also processes the methanol-rich solution generated in the secondary stripping unit before introducing it back into the original production system; and a valve control assembly; the valve assembly is installed on the pipeline assembly and is used to control the flow of the methanol-rich solution and gas within the pipeline assembly. This system can reduce the CO2 content in the methanol-rich solution, reduce the amount of steam used in methanol regeneration, and reduce steam consumption.

Description

Technical Field

[0001] This invention relates to the field of methanol regeneration technology, and in particular to a system and method for reducing the amount of methanol regeneration steam used. Background Technology

[0002] The original ammonia synthesis methanol washing unit only had a hydrogen sulfide concentration tower. CO2 was extracted from the methanol-rich solution using low-pressure nitrogen gas and then sent to a methanol regeneration tower for methanol regeneration. The methanol-rich solution, concentrated at the bottom of the lower section of the hydrogen sulfide concentration tower, was then heated and desorbed using 0.5 MPa steam in the methanol regeneration tower, removing the sulfides and residual CO2 contained within it. Currently, the actual steam consumption of the methanol regeneration tower in production is approximately 11 t / h.

[0003] The existing process only includes a low-temperature stripping tower, resulting in insufficient CO2 stripping from the methanol-rich methanol, leading to a large steam consumption during the heating and desorption process in the methanol regeneration tower. Therefore, this issue urgently needs to be addressed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a system and method for reducing the amount of steam used in methanol regeneration. The system can reduce the CO2 content in rich methanol, reduce the amount of steam used in methanol regeneration, and reduce steam consumption.

[0005] To achieve the aforementioned objective, the technical solution of the present invention is implemented as follows: a system for reducing the amount of methanol regeneration steam used includes: a secondary stripping unit, used to perform secondary stripping of CO2 from the methanol-rich solution in the original production system; The pipeline assembly is connected to both the original production system and the secondary gas stripping unit. Nitrogen and the methanol-rich solution from the original production system are introduced into the secondary gas stripping unit for gas stripping, and the CO2 generated in the secondary gas stripping unit is introduced into the original production system. The pipeline assembly also processes the methanol-rich solution generated in the secondary gas stripping unit before introducing it into the original production system. Valve control assembly; the valve assembly is installed on the pipeline assembly and is used to control the direction of methanol-rich solution and gas in the pipeline assembly.

[0006] Preferably, the pipeline assembly includes a new methanol delivery pipeline and a gas phase outlet pipeline of an ambient temperature stripping tower; the secondary stripping section includes an ambient temperature stripping tower; the ambient temperature stripping tower has a top feed inlet on the side of its top and a bottom air inlet on the side of its bottom, and a tower tray inside; the valve control assembly includes an ambient temperature stripping tower inlet shut-off valve. The original production system includes a methanol-rich pipeline and a second methanol heat exchanger; one end of the methanol-rich pipeline is connected to the original production system, and the other end is connected to one end of a new methanol delivery pipeline; the other end of the new methanol delivery pipeline is connected to the top inlet of the ambient temperature stripping tower; the second methanol heat exchanger is installed on the methanol-rich pipeline to heat the methanol-rich solution in the methanol-rich pipeline; the inlet shut-off valve of the ambient temperature stripping tower is installed on the new methanol delivery pipeline to control the opening and closing of the new methanol delivery pipeline.

[0007] Preferably, the pipeline assembly includes a nitrogen stripping pipeline; the valve control assembly includes a nitrogen stripping flow control valve; the nitrogen stripping pipeline is connected to the bottom inlet on the side of the bottom of the ambient temperature nitrogen stripping tower and introduces nitrogen into the ambient temperature nitrogen stripping tower; the nitrogen stripping flow control valve is installed on the nitrogen stripping pipeline and is used to control the opening and closing of the nitrogen stripping pipeline and the flow rate of nitrogen in the nitrogen stripping pipeline.

[0008] Preferably, the piping assembly includes a liquid phase outlet pipeline for the ambient temperature stripping tower, a feed pump for the methanol regeneration tower, and a new rich methanol pipeline; the valve control assembly includes a liquid level control valve for the ambient temperature stripping tower and a methanol rich outlet shut-off valve for the ambient temperature stripping tower; one end of the liquid phase outlet pipeline for the ambient temperature stripping tower is connected to the liquid phase outlet at the bottom of the ambient temperature stripping tower, and the other end is connected to the feed pump for the methanol regeneration tower; one end of the new rich methanol pipeline is connected to the feed pump for the methanol regeneration tower, and the other end is connected to the first methanol heat exchanger of the original production system; the first methanol heat exchanger is connected to the methanol regeneration tower of the original production system through a connecting pipeline; both the liquid level control valve for the ambient temperature stripping tower and the methanol rich outlet shut-off valve for the ambient temperature stripping tower are installed on the new rich methanol pipeline.

[0009] Preferably, the pipeline assembly includes a gas phase outlet pipeline of an ambient temperature stripping tower; one end of the ambient temperature stripping tower gas phase outlet pipeline is connected to the gas phase outlet at the top of the ambient temperature stripping tower, and the other end is connected to the hydrogen sulfide concentration tower of the original production system.

[0010] Preferably, the valve control assembly includes a three-way connector and a new shut-off valve for the original methanol-rich pipeline; the three-way connector is installed at the connection between the methanol pipeline and the new methanol delivery pipeline; the new shut-off valve for the original methanol-rich pipeline is installed on the original methanol delivery pipeline and is used to control the opening and closing of the original methanol delivery pipeline, with one end of the original methanol delivery pipeline connected to the three-way connector and the other end connected to the first methanol heat exchanger.

[0011] Preferably, the method of using the system for reducing methanol regeneration steam consumption includes the following steps: S1. The methanol-rich solution in the original production system is transported to the second methanol heat exchanger for heating via the methanol-rich pipeline. The original methanol-rich new shut-off valve is closed, while the inlet shut-off valve of the ambient temperature stripping tower, the outlet shut-off valve of the ambient temperature stripping tower methanol-rich solution, and the stripping nitrogen flow control valve are all open. S2. The heated methanol-rich solution is transported along the new methanol delivery pipeline to the top feed inlet of the ambient temperature stripping tower and enters the ambient temperature stripping tower; the stripping nitrogen pipeline introduces nitrogen into the ambient temperature stripping tower through the bottom air inlet on the side of the bottom of the ambient temperature stripping tower. After S3, methanol-rich solution and nitrogen react in an ambient temperature stripping tower, the CO2 released from the methanol-rich solution is transported along the vapor phase outlet pipeline of the ambient temperature stripping tower to the hydrogen sulfide concentration tower of the original production system. S4. The methanol-rich solution after CO2 desorption is discharged from the liquid phase outlet at the bottom of the ambient temperature stripping tower and transported to the methanol regeneration tower feed pump along the ambient temperature stripping tower liquid phase outlet pipeline. After being processed by the methanol regeneration tower feed pump, it is transported to the first methanol heat exchanger along the newly prepared methanol-rich pipeline. The first methanol heat exchanger heats the received methanol-rich solution and transports it to the methanol regeneration tower of the original production system. S5. When the methanol-rich solution in the original production system does not require treatment, close the inlet shut-off valve of the ambient temperature stripping tower, the nitrogen flow control valve of the stripping tower, and the methanol-rich outlet shut-off valve of the ambient temperature stripping tower, and open the newly added shut-off valve of the original methanol-rich solution. The methanol-rich solution in the original production system is transported and processed sequentially along the methanol-rich pipeline, the second methanol heat exchanger, the original methanol conveying pipeline, and the first methanol heat exchanger, and then enters the methanol regeneration tower of the original production system.

[0012] Preferably, the nitrogen gas is at room temperature, at a pressure of 0.43 MPa, and at a flow rate of 981 Nm³. 3 / h.

[0013] Preferably, the second methanol heat exchanger heats the methanol-rich solution to 31°C.

[0014] Preferably, the first methanol heat exchanger heats the methanol-rich solution after CO2 desorption to 90°C.

[0015] The beneficial effects of this invention are reflected in: (1) The technical solution provided by the present invention enables the methanol-rich solution to be stripped at low temperature in a low temperature stripping tower, then reheated to room temperature, and then subjected to secondary stripping of the methanol-rich solution by low-pressure nitrogen. The increased temperature and nitrogen reduce the solubility of CO2 in methanol, thereby achieving the purpose of CO2 removal.

[0016] (2) The technical solution provided by this invention reduces the amount of steam used for methanol regeneration of methanol-rich solutions. Before the modification, the steam usage of the methanol regeneration tower was about 11 t / h. By adding a room temperature stripping tower to perform secondary stripping of the methanol-rich solution, the steam usage can be reduced to 7.5 t / h. Based on a steam price of 120 yuan / t, the daily cost is reduced by about 10,000 yuan, which greatly reduces the production cost. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the system architecture of the present invention.

[0018] Figure labels and descriptions: 1. Methanol-rich pipeline; 2. Inlet shut-off valve of ambient temperature stripping tower; 3. New shut-off valve of the original methanol-rich tower; 4. Ambient temperature stripping tower; 5. Gas phase outlet pipeline of ambient temperature stripping tower; 6. Liquid phase outlet pipeline of ambient temperature stripping tower; 7. Feed pump of methanol regeneration tower; 8. Liquid level control valve of ambient temperature stripping tower; 9. Methanol-rich outlet shut-off valve of ambient temperature stripping tower; 10. New methanol-rich pipeline; 11. Stripping nitrogen pipeline; 12. Stripping nitrogen flow control valve; 13. Second methanol heat exchanger; 14. First methanol heat exchanger. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] like Figure 1 As shown, the present invention provides a system and method for reducing the amount of methanol regeneration steam used. The modified process flow is as follows: S1. The methanol-rich solution concentrated at the bottom of the lower section of the hydrogen sulfide concentration tower of the original production system is pressurized by the equipment and then enters the first methanol filter (20μm precision) to remove solid impurities. After that, it is transported through the methanol-rich pipeline 1 to the second methanol heat exchanger 13 for heating. The original methanol-rich new shut-off valve 3 is closed, and the ambient temperature stripping tower inlet shut-off valve 2, the ambient temperature stripping tower methanol-rich outlet shut-off valve 9, and the stripping nitrogen flow control valve 12 are all open. S2. The heated methanol-rich solution reaches a temperature of 31°C and is transported along the new methanol delivery pipeline to the top inlet of the ambient temperature stripping tower 4, where it enters the tower. To ensure sufficient CO2 removal from the methanol-rich solution entering the tower, nitrogen stripping pipeline 11 supplies nitrogen at a temperature of 40°C, a pressure of 0.43 MPa, and a flow rate of 981 Nm³. 3 Nitrogen gas at a rate of / h is used as stripping gas and introduced into the ambient temperature stripping tower 4 through the bottom air inlet on the side of the bottom to reduce the partial pressure of CO2 in the methanol-rich solution. After S3, the methanol-rich solution and nitrogen react in the ambient temperature stripping tower 4, the CO2 in the methanol-rich solution is further released. The acidic gas at the top of the ambient temperature stripping tower 4, with a temperature of 30.64℃ and a pressure of 0.11MPa, is transported to the hydrogen sulfide concentration tower of the original production system along the gas phase outlet pipeline 5 of the ambient temperature stripping tower. S4. The methanol-rich solution after CO2 removal is discharged from the liquid phase outlet at the bottom of the ambient temperature stripping tower 4 and transported to the methanol regeneration tower feed pump 7 along the ambient temperature stripping tower liquid phase outlet pipeline 6. After being processed and pressurized to 0.98 MPa by the methanol regeneration tower feed pump 7, it is transported to the first methanol heat exchanger 14 along the newly prepared methanol-rich pipeline 10. The first methanol heat exchanger 14 heats the received methanol-rich solution, and the temperature eventually rises to 90°C. It is then transported to the 26th tray of the methanol regeneration tower that originally entered the production system for heated stripping regeneration, in which the sulfides and residual CO2 contained therein are stripped and removed by methanol steam.

[0021] By installing a room temperature stripping tower level control valve 8 on the new methanol enrichment pipeline 10, the bottom liquid level of the room temperature stripping tower 4 is controlled, and a low-low interlock logic is set. When the liquid level is lower than the set value, the operation of the methanol regeneration tower feed pump 7 is automatically stopped. Therefore, the following operation situation exists in step S5: S5. Change to: When the production of the newly added secondary stripping section needs to be stopped, close the inlet shut-off valve 2 of the ambient temperature stripping tower, the stripping nitrogen flow control valve 12 and the rich methanol outlet shut-off valve 9 of the ambient temperature stripping tower, and open the original rich methanol new shut-off valve 3; the rich methanol solution of the original production system is transported and processed sequentially along the rich methanol pipeline 1, the second methanol heat exchanger 13, the original methanol conveying pipeline and the first methanol heat exchanger 14, and enters the methanol regeneration tower of the original production system.

[0022] Add a level regulating valve 8 to the normal temperature stripping tower and set a low-level interlock to stop the methanol regeneration tower feed pump.

[0023] Example This embodiment takes the low-temperature methanol washing section of a certain ammonia synthesis unit as an example to specifically illustrate the application effect of the present invention.

[0024] Before the modification, the methanol-rich solution from the bottom of the lower section of the hydrogen sulfide concentration tower in the original production system had a temperature of -48.7℃, a pressure of 0.13MPa, and a flow rate of 214m³. 3The methanol-rich methanol, with a composition (mole fraction) of approximately 78% methanol, 3.1% CO2, and 0.57% H2S, is pressurized by the methanol regeneration tower feed pump and then filtered through a first methanol filter (20μm precision) to remove solid impurities. After exchanging heat with lean methanol to 31°C in the second lean methanol cooler (i.e., the second methanol heat exchanger 13), it is directly fed into the methanol regeneration tower for thermal regeneration. At this time, the methanol regeneration tower requires approximately 11 tons / hour of 0.5MPa low-pressure steam to provide the heat needed for CO2 and H2S removal.

[0025] After modification using the device of this invention, the process flow is as described above: The composition (mole fraction) of the methanol-rich solution after heat exchange in the second methanol heat exchanger 13 is approximately: methanol 78%, CO2 3.1%, H2S 0.57%, temperature 31℃, pressure 1.13MPa. It enters the newly added ambient temperature stripping tower 4 through the liquid phase inlet. In the lower part of the newly added ambient temperature stripping tower 4, nitrogen gas at ambient temperature, pressure 0.43MPa, and flow rate 981Nm³ / h is introduced to strip the methanol-rich solution from bottom to top, releasing a large amount of CO2 and a small amount of H2S gas.

[0026] The tail gas, rising to the top of the ambient temperature stripping tower 4, has a temperature of 30.64℃, a pressure of 0.11MPa, and a flow rate of approximately 2307Nm³. 3 The gaseous composition of the gas is 78% methanol, 73.2% CO2, 1.15% H2S, 9.19% methanol, and 16.4% nitrogen. It enters the 25th tray of the hydrogen sulfide concentration tower in the original production system. This ensures that the stripped gas can be fully washed to remove H2S after entering the hydrogen sulfide concentration tower, preventing the H2S content in the tail gas from being too high. It also solves the problem of excessive stripping at the bottom of the hydrogen sulfide concentration tower, which can cause temperature runaway.

[0027] Tests showed that the CO2 content in the methanol-rich material entering the ambient temperature stripping tower 4 was 3.1% (mole fraction). After a second stripping process, the CO2 content in the methanol-rich material at the tower bottom outlet decreased to approximately 0.27% (mole fraction).

[0028] The low-CO2-content rich methanol (temperature approximately 30°C) is pressurized and heated to 90°C by exchanging heat with high-temperature lean methanol before entering the methanol regeneration tower of the original production system.

[0029] Because the CO2 content has been significantly reduced, the regeneration load of the methanol regeneration tower in the original production system has decreased markedly. The consumption of 0.5MPa low-pressure steam has steadily decreased from 11 tons / hour before the modification to 7.5 tons / hour. Based on a steam price of 120 yuan / ton, the daily cost savings are approximately (11 - 7.5) × 24 × 120 = 10,080 yuan, achieving a significant energy saving and consumption reduction target. At the same time, the methanol regeneration tower in the original production system maintains good operational stability, and the purity of the produced lean methanol meets the process requirements.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for reducing the amount of methanol regeneration steam used, characterized in that, include: The secondary gas stripping unit is used to perform secondary stripping of CO2 from the methanol-rich solution in the original production system. The pipeline assembly is connected to both the original production system and the secondary gas stripping unit. Nitrogen and the methanol-rich solution from the original production system are introduced into the secondary gas stripping unit for gas stripping, and the CO2 generated in the secondary gas stripping unit is introduced into the original production system. The pipeline assembly also processes the methanol-rich solution generated in the secondary gas stripping unit before introducing it into the original production system. Valve control assembly; the valve assembly is installed on the pipeline assembly and is used to control the direction of methanol-rich solution and gas in the pipeline assembly.

2. The system for reducing methanol regeneration steam consumption according to claim 1, characterized in that, The pipeline assembly includes a new methanol delivery pipeline and a gas phase outlet pipeline of an ambient temperature stripping tower (5); the secondary stripping section includes an ambient temperature stripping tower (4); the ambient temperature stripping tower (4) has a top feed inlet on the side of the top and a bottom air inlet on the side of the bottom, and a tower tray inside; the valve control assembly includes an ambient temperature stripping tower inlet shut-off valve (2). The original production system includes a methanol-rich pipeline (1) and a second methanol heat exchanger (13); one end of the methanol-rich pipeline (1) is connected to the original production system, and the other end is connected to one end of the new methanol delivery pipeline; the other end of the new methanol delivery pipeline is connected to the top feed inlet of the ambient temperature stripping tower (4); the second methanol heat exchanger (13) is installed on the methanol-rich pipeline (1) to heat the methanol-rich solution in the methanol-rich pipeline (1); the ambient temperature stripping tower inlet shut-off valve (2) is installed on the new methanol delivery pipeline to control the opening and closing of the new methanol delivery pipeline.

3. The system for reducing methanol regeneration steam consumption according to claim 2, characterized in that, The pipeline assembly includes a nitrogen stripping pipeline (11); the valve control assembly includes a nitrogen stripping flow control valve (12); the nitrogen stripping pipeline (11) is connected to the bottom air inlet on the bottom side of the ambient temperature nitrogen stripping tower (4) and introduces nitrogen into the ambient temperature nitrogen stripping tower (4); The nitrogen flow control valve (12) is installed on the nitrogen pipeline (11) to control the opening and closing of the nitrogen pipeline (11) and the flow rate of nitrogen in the nitrogen pipeline (11).

4. The system for reducing methanol regeneration steam consumption according to claim 3, characterized in that, The pipeline assembly includes a room temperature stripping tower liquid phase outlet pipeline (6), a methanol regeneration tower feed pump (7), and a new rich methanol pipeline (10); the valve control assembly includes a room temperature stripping tower liquid level control valve (8) and a room temperature stripping tower rich methanol outlet shut-off valve (9); one end of the room temperature stripping tower liquid phase outlet pipeline (6) is connected to the liquid phase outlet at the bottom of the room temperature stripping tower (4), and the other end is connected to the methanol regeneration tower feed pump (7); one end of the new rich methanol pipeline (10) is connected to the methanol regeneration tower feed pump (7), and the other end is connected to the first methanol heat exchanger (14) of the original production system; the first methanol heat exchanger (14) is connected to the methanol regeneration tower of the original production system through a connecting pipeline; the room temperature stripping tower liquid level control valve (8) and the room temperature stripping tower rich methanol outlet shut-off valve (9) are both installed on the new rich methanol pipeline (10).

5. The system for reducing methanol regeneration steam consumption according to claim 4, characterized in that, The pipeline assembly includes a gas phase outlet pipeline (5) of the ambient temperature stripping tower; one end of the ambient temperature stripping tower gas phase outlet pipeline (5) is connected to the gas phase outlet at the top of the ambient temperature stripping tower (4), and the other end is connected to the hydrogen sulfide concentration tower of the original production system.

6. The system for reducing methanol regeneration steam consumption according to claim 3, characterized in that, The valve control assembly includes a three-way connector and a new methanol-rich shut-off valve (3); the three-way connector is installed at the connection between the methanol pipeline (1) and the new methanol delivery pipeline; the new methanol-rich shut-off valve (3) is installed on the original methanol delivery pipeline to control the opening and closing of the original methanol delivery pipeline, and one end of the original methanol delivery pipeline is connected to the three-way connector, and the other end is connected to the first methanol heat exchanger (14).

7. The system for reducing methanol regeneration steam consumption according to claim 6, characterized in that, The nitrogen gas has a pressure of 0.43 MPa and a flow rate of 981 Nm³. 3 / h.

8. The system for reducing methanol regeneration steam consumption according to claim 6, characterized in that, The second methanol heat exchanger (13) heats the methanol-rich solution to 31°C.

9. A method of using the system for reducing methanol regeneration steam consumption according to any one of claims 1-8, characterized in that, Includes the following steps: S1. The methanol-rich solution of the original production system is transported into the second methanol heat exchanger (13) through the methanol-rich pipeline (1) for heating. The original methanol-rich new shut-off valve (3) is closed, and the ambient temperature stripping tower inlet shut-off valve (2), the ambient temperature stripping tower methanol-rich outlet shut-off valve (9) and the stripping nitrogen flow control valve (12) are all opened. S2. The heated methanol-rich solution is transported along the new methanol transport pipeline to the top feed port of the ambient temperature stripping tower (4) and enters the ambient temperature stripping tower (4); the stripping nitrogen pipeline (11) introduces nitrogen into the ambient temperature stripping tower (4) along the bottom air inlet on the side of the bottom of the ambient temperature stripping tower (4). S3, methanol-rich solution and nitrogen react in the ambient temperature stripping tower (4), and the CO2 released from the methanol-rich solution is transported to the hydrogen sulfide concentration tower of the original production system along the gas phase outlet pipeline (5) of the ambient temperature stripping tower. S4. The methanol-rich solution that has completed CO2 desorption is discharged from the liquid phase outlet at the bottom of the ambient temperature stripping tower (4) and transported to the methanol regeneration tower feed pump (7) along the ambient temperature stripping tower liquid phase outlet pipeline (6). After being processed by the methanol regeneration tower feed pump (7), it is transported to the first methanol heat exchanger (14) along the newly prepared methanol-rich pipeline (10). The first methanol heat exchanger (14) heats the received methanol-rich solution and transports it to the methanol regeneration tower of the original production system. S5. When the methanol-rich solution of the original production system does not need to be treated, close the inlet shut-off valve (2) of the ambient temperature stripping tower, the nitrogen flow control valve (12) of the stripping tower and the methanol-rich outlet shut-off valve (9) of the ambient temperature stripping tower, and open the new shut-off valve (3) of the original methanol-rich solution. The methanol-rich solution of the original production system is transported and treated along the methanol-rich pipeline (1), the second methanol heat exchanger (13), the original methanol transmission pipeline and the first methanol heat exchanger (14) in sequence, and enters the methanol regeneration tower of the original production system.

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