A deep benzene removal device for benzene distillation residue

Abstract

This application relates to the field of benzene residue resource recovery technology, and provides a device for deep benzene removal from benzene distillation residue, including a distillation column, a reboiler in the column bottom, the reboiler being connected to a steam inlet pipe and a steam outlet pipe, a column bottom remote pressure gauge being installed on the column bottom, and a nitrogen inlet pipe being connected to the column bottom, one end of the nitrogen inlet pipe being connected to a nitrogen source, and the other end extending to the bottom of the reboiler; a nitrogen remote pressure gauge and a nitrogen regulating valve are installed on the nitrogen inlet pipe between the nitrogen source and the column bottom; this device for deep benzene removal from benzene distillation residue can significantly reduce the column bottom temperature, thereby reducing steam consumption, and significantly improve the quality of gaseous benzene through nitrogen atomization, thereby improving the crude caprolactam benzene extraction efficiency, promoting the benzene residue distillation process to a more energy-efficient and greener stage, and meeting the requirements of process quality improvement and consumption reduction.

Description

Technical Field

[0001] This application belongs to the field of benzene residue resource recovery technology, and more specifically, it relates to a device for deep benzene removal from benzene distillation residue. Background Technology

[0002] In the caprolactam production industry, benzene distillation residue is mainly treated through intermittent external discharge. The residue consists of 30-40% caprolactam, 20-30% benzene, approximately 50% cyclohexanone, and small amounts of caprolactam derivatives and cyclohexanone oxime derivatives. A significant amount of benzene is lost, increasing industrial consumption. Impurity enrichment occurs in the benzene residue distillation column. As the liquid level in the storage tank rises, the steam feed flow rate must also be gradually increased. The residue column operates at temperatures exceeding 115°C for extended periods, causing a small portion of higher-boiling-point impurities to enter the refined benzene system with the benzene gas. Furthermore, the impurity content increases in the later stages of operation, significantly raising the extinction value of the gaseous benzene and ultimately affecting benzene extraction efficiency. Utility Model Content

[0003] To address the shortcomings of the prior art, the purpose of this application is to provide a deep benzene removal device for benzene distillation residues, which can significantly reduce the temperature of the reboiler, thereby reducing steam consumption. Furthermore, through nitrogen atomization, it can significantly improve the quality of gaseous benzene, thereby increasing the extraction efficiency of crude caprolactam benzene and promoting the benzene residue distillation process towards a more energy-efficient and greener stage, meeting the requirements for process quality improvement and consumption reduction.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: a benzene distillation residue deep benzene removal device is provided, comprising a distillation column, a reboiler provided in the column bottom, the reboiler being connected to a steam inlet pipe and a steam outlet pipe, a column bottom remote pressure gauge being provided on the column bottom, a nitrogen inlet pipe being connected to the column bottom, one end of the nitrogen inlet pipe being connected to a nitrogen source, and the other end extending to the bottom of the reboiler; a nitrogen remote pressure gauge and a nitrogen regulating valve are provided on the nitrogen inlet pipe between the nitrogen source and the column bottom.

[0005] In one embodiment, a nitrogen distributor is provided at one end of the nitrogen inlet pipe located inside the column, and the nitrogen distributor is located below the reboiler.

[0006] In one embodiment, the nitrogen distributor is a tubular structure with several distribution holes on its tube wall.

[0007] In one embodiment, a nitrogen flow meter front gate valve and a nitrogen flow meter rear gate valve are respectively provided on the nitrogen inlet pipe at the front and rear ends of the nitrogen regulating valve. A nitrogen flow meter bypass is connected in parallel at the front end of the nitrogen flow meter front gate valve and the rear end of the nitrogen flow meter rear gate valve. A bypass switch valve is provided on the nitrogen flow meter bypass.

[0008] In one embodiment, the nitrogen flow meter's downstream gate valve is provided with a nitrogen inlet quick-closing valve and a check valve.

[0009] In one embodiment, a cooler is connected to the top of the distillation column, the cooler is connected to a gas-liquid separator, a nitrogen reflux pipe is connected to the top of the gas-liquid separator, and the nitrogen reflux pipe is connected to the nitrogen inlet pipe at the front end of the nitrogen remote pressure gauge.

[0010] In one embodiment, both the cooler and the gas-liquid separator are connected to a condensate collection tank.

[0011] In one embodiment, a circulating fan is provided on the nitrogen reflux pipe.

[0012] In one embodiment, the gas-liquid separator is provided with a vent pipe at the top, and a vent quick-closing valve is provided on the vent pipe.

[0013] In one embodiment, the bottom of the tower is provided with a discharge pipe, and a discharge pump is provided on the discharge pipe.

[0014] The beneficial effects of the benzene distillation residue deep benzene removal device provided in this application are as follows: According to Henry's Law, the addition of nitrogen can reduce the partial pressure of benzene in the distillation column, thereby promoting the desorption of benzene in the residue. It can also reduce the temperature of the column bottom. Under nitrogen environment, benzene recovery can be achieved at a column bottom temperature of about 50°C. Therefore, the amount of steam used can be reduced, and the quality of gaseous benzene can be significantly improved through nitrogen atomization, thereby improving the extraction efficiency of crude caprolactam benzene. This promotes the benzene residue distillation process to a more energy-saving and greener stage, meeting the requirements of process quality improvement and consumption reduction. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A simplified schematic diagram of the connection relationship of the benzene distillation residue deep benzene removal device provided in the embodiments of this application.

[0017] The following are the labeling elements in the figure:

[0018] 1. Distillation column; 2. Reboiler; 3. Steam inlet pipe; 4. Steam outlet pipe; 5. Remote pressure gauge at the bottom of the column; 6. Nitrogen inlet pipe; 7. Nitrogen source; 8. Remote pressure gauge for nitrogen; 9. Nitrogen regulating valve; 10. Nitrogen distributor; 11. Gate valve before nitrogen flow meter; 12. Gate valve after nitrogen flow meter; 13. Bypass for nitrogen flow meter; 14. Bypass switch valve; 15. Quick-closing valve for nitrogen feed; 16. Check valve; 17. Cooler; 18. Gas-liquid separator; 19. Nitrogen reflux pipe; 20. Condensate collection tank; 21. Circulating fan; 22. Vent pipe; 23. Quick-closing vent valve; 24. Discharge pipe; 25. Discharge pump; 26. Main nitrogen feed valve; 27. Steam switch valve. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0020] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0021] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] like Figure 1As shown, a benzene distillation residue deep benzene removal device provided in this application embodiment will now be described. This benzene distillation residue deep benzene removal device includes: a distillation column 1, the upper part of which is the column body, and the lower part is the column kettle, which is used to hold benzene distillation residue; a reboiler 2 is provided inside the column kettle of the distillation column 1, the reboiler 2 is connected to a steam inlet pipe 3 and a steam outlet pipe 4, and a steam switch valve 27 is provided on the steam inlet pipe 3; a column kettle remote pressure gauge 5 is provided on the column kettle for monitoring the pressure inside the column kettle.

[0024] In this embodiment, the improvement lies in using a pre-installed auger at the top of the distillation column to connect to the nitrogen inlet pipe 6. One end of the nitrogen inlet pipe 6 is connected to the nitrogen source 7, and the other end extends to the bottom of the reboiler 2. The nitrogen source 7 is the existing nitrogen system in the factory. According to Henry's Law, the addition of nitrogen can reduce the partial pressure of benzene in the distillation column 1, thereby promoting the desorption of benzene in the residue and reducing the temperature of the column bottom. Under nitrogen conditions, benzene recovery can be achieved even at a column bottom temperature of around 50°C. Therefore, the amount of steam used can be reduced.

[0025] A nitrogen remote pressure gauge 8 and a nitrogen regulating valve 9 are installed on the nitrogen inlet pipe 6 between the nitrogen source 7 and the tower bottom, which are used to monitor the nitrogen inlet pressure, display the flow rate and control the flow rate.

[0026] To better remove benzene from the residual liquid with nitrogen, a nitrogen distributor 10 is installed at one end of the nitrogen inlet pipe 6 inside the column, located below the reboiler 2. The nitrogen distributor 10 generates microbubbles, which are used to strip the benzene. The nitrogen distributor 10 has a tubular structure with several distribution holes on its wall. Specifically, the nitrogen distributor 10 is 2000 mm long, 20 mm in diameter, and the pore size is 0.2 μm. The nitrogen distributor 10 is located 50 mm below the reboiler 2. The surface of the distributor is treated with a special wear-resistant, hydrophobic, and oleophobic coating, which enhances the shear force on the nitrogen-benzene residual liquid mixture and prevents benzene residue from adhering and accumulating. When the high-speed sprayed nitrogen mixes with the benzene residue, thorough micro-mixing is achieved, efficiently transferring the kinetic energy of the nitrogen to the benzene residue and improving the atomization of the benzene residue.

[0027] In this embodiment, a nitrogen flow meter front gate valve 11 and a nitrogen flow meter rear gate valve 12 are respectively installed on the nitrogen inlet pipe 6 at the front and rear ends of the nitrogen regulating valve 9. Here, the front and rear ends refer to the inflow and outflow ends of nitrogen, respectively. A nitrogen flow meter bypass 13 is connected in parallel to the front end of the nitrogen flow meter front gate valve 11 and the rear end of the nitrogen flow meter rear gate valve 12. A bypass switch valve 14 is installed on the nitrogen flow meter bypass 13. Under normal operation, the bypass switch valve 14 is closed, and the nitrogen flow meter front gate valve 11 and the nitrogen flow meter rear gate valve 12 are open. When the nitrogen regulating valve 9 malfunctions and needs maintenance, the bypass switch valve 14 is opened, and the nitrogen flow meter front gate valve 11 and the nitrogen flow meter rear gate valve 12 are closed, realizing online maintenance.

[0028] In this embodiment, a nitrogen feed quick-closing valve 15 and a check valve 16 are also provided at the rear end of the nitrogen flow meter gate valve 12. The nitrogen feed quick-closing valve 15 is used to quickly cut off the nitrogen inlet pipe 6 in case of emergency and stop the supply of nitrogen. The check valve 16 is used to prevent the gas in the tower from flowing back into the nitrogen inlet pipe 6.

[0029] In this embodiment, nitrogen is recycled to reduce nitrogen consumption. Specifically, a cooler 17 is connected to the top of the distillation column 1, and a gas-liquid separator 18 is connected to the cooler 17. A nitrogen reflux pipe 19 is connected to the top of the gas-liquid separator 18, and the nitrogen reflux pipe 19 is connected to the nitrogen inlet pipe 6 at the front end of the nitrogen remote pressure gauge 8. The mixed gas, including gaseous benzene and nitrogen, enters the cooler 17 for cooling, and then undergoes gas-liquid separation in the gas-liquid separator 18, separating out nitrogen. The separated nitrogen is then reintroduced into the nitrogen inlet pipe 6 for reuse. A nitrogen feed valve 26 is provided between the nitrogen source 7 and the nodes of the nitrogen inlet pipe 6 and the nitrogen reflux pipe 19, which can control the opening degree to adjust the amount of new nitrogen introduced. Nitrogen can be reused, reducing the amount of new nitrogen used.

[0030] In this embodiment, both the cooler 17 and the gas-liquid separator 18 are connected to a condensate collection tank 20 for collecting the cooled condensate. A circulating fan 21 is installed on the nitrogen return pipe 19 to provide power for the returning nitrogen.

[0031] To ensure the normal pressure of the gas-liquid separator 18, a vent pipe 22 is provided at the top of the gas-liquid separator 18, and a vent quick-closing valve 23 is provided on the vent pipe 22.

[0032] To ensure the normal liquid level in the tower and the discharge of materials, a discharge pipe 24 is provided at the bottom of the tower, and a discharge pump 25 is provided on the discharge pipe 24.

[0033] In this embodiment, low-pressure nitrogen at 0.6 MPa and 25°C is used as the partial pressure non-condensable vapor, and the range of nitrogen regulating valve 9 is 0-50 Nm. 3 / h, designed nitrogen consumption is 10-20 Nm 3 / h.

[0034] In actual operation, a safety interlock is also provided: to prevent material from backflowing into nitrogen in pipe 6 when the pressure inside benzene residue distillation tower 1 is high, a safety interlock protection action is set up using tower bottom remote pressure gauge 5 and nitrogen remote pressure gauge 8. When any of the following conditions are met, the interlock closes nitrogen regulating valve 9 and nitrogen feed quick-closing valve 15.

[0035] a) The remote pressure gauge 5 at the bottom of the column monitors the pressure at the bottom of the column to be higher than 0.6 MPag;

[0036] b) The pressure difference monitored by the remote pressure gauge 5 in the tower bottom and the remote pressure gauge 8 for nitrogen is less than or equal to 0 MPag;

[0037] c) When discharge pump 25 starts;

[0038] d) When the benzene distillation system shutdown sequence control is triggered;

[0039] In this embodiment, the nitrogen process commissioning steps for benzene residue distillation tower 1 are as follows: When the liquid level in benzene residue distillation tower 1 reaches 20%, the screen operator notifies the on-site operator to confirm the on-site liquid level in benzene residue distillation tower 1, check that the nitrogen remote pressure gauge and nitrogen regulating valve 9 are in normal operation, and start the on-site process; the main control releases the benzene residue shutdown interlock, the nitrogen feed quick-closing valve 15 is energized and opened, and the nitrogen regulating valve 9 is manually opened to start the nitrogen process at 10%. Observe the indication of the nitrogen regulating valve 9, and according to the display of the tower bottom remote pressure gauge 5, adjust the nitrogen regulating valve 9 feed to 10-20 Nm. 3 / h, the remote pressure gauge 5 of the control tower bottom stabilizes at around 0.05 MPag.

[0040] In this embodiment, by introducing non-condensable nitrogen gas, the partial pressure of benzene in benzene residue distillation tower 1 is reduced, thereby reducing the original temperature of the tower bottom from 115℃ to 40-60℃. This reduces the steam feed to benzene residue distillation tower 1, thereby reducing steam consumption by 1920t, lowering production costs, and improving the company's economic benefits.

[0041] In this embodiment, the temperature of the reboiler is reduced to about 55°C, thereby reducing the vaporization of high-boiling-point impurities. The extinction value of the refined benzene after nitrogen low-temperature distillation is 0.01, which is significantly lower than the extinction value of 0.127 after the existing whole benzene distillation refining process, thus effectively improving the quality of refined benzene.

[0042] In this embodiment, due to the introduction of nitrogen, low steam feeding or even no steam feeding can be achieved. The temperature and liquid level of the tower bottom can be controlled within the card range for a long time, thereby extending the loading cycle of benzene residue. As nitrogen is continuously added to reduce the partial pressure, benzene in the residue can be fully desorbed, thereby improving the benzene recovery rate and reducing losses.

[0043] In actual operation, external units handling benzene residue have long complained about issues such as low benzene content in the residue and insufficient company qualifications. This frequently leads to prolonged high liquid levels and high steam flow in the benzene residue distillation tower 1. While the system's gradual recovery temporarily solves the high liquid level problem, the return of residue to the system not only affects the unit's operating conditions but also poses a significant risk to the quality of caprolactam. After treatment by a nitrogen stripping unit, the benzene content in the residue decreases significantly, and the flash point increases from <16℃ to around 40℃, meeting incineration standards. Therefore, this residue can be sent to an incinerator, effectively solving the benzene residue treatment problem.

[0044] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A device for deep benzene removal from benzene distillation residue, comprising: a distillation column (1), wherein a reboiler (2) is provided in the reboiler of the distillation column (1), the reboiler (2) is connected to a steam inlet pipe (3) and a steam outlet pipe (4), and a reboiler remote pressure gauge (5) is provided on the reboiler, characterized in that: A nitrogen inlet pipe (6) is connected to the bottom of the column. One end of the nitrogen inlet pipe (6) is connected to a nitrogen source (7), and the other end extends to the bottom of the reboiler (2). A nitrogen remote pressure gauge (8) and a nitrogen regulating valve (9) are provided on the nitrogen inlet pipe (6) between the nitrogen source (7) and the bottom of the column.

2. The benzene distillation residue deep benzene removal device as described in claim 1, characterized in that: The nitrogen inlet pipe (6) is equipped with a nitrogen distributor (10) at one end inside the column, and the nitrogen distributor (10) is located below the reboiler (2).

3. The benzene distillation residue deep benzene removal device as described in claim 2, characterized in that: The nitrogen distributor (10) is a tubular structure with several distribution holes on its tube wall.

4. The benzene distillation residue deep benzene removal device as described in claim 3, characterized in that: The nitrogen inlet pipe (6) at the front and rear ends of the nitrogen regulating valve (9) is provided with a nitrogen flow meter front gate valve (11) and a nitrogen flow meter rear gate valve (12), respectively. A nitrogen flow meter bypass (13) is connected in parallel to the front end of the nitrogen flow meter front gate valve (11) and the rear end of the nitrogen flow meter rear gate valve (12). A bypass switch valve (14) is provided on the nitrogen flow meter bypass (13).

5. The benzene distillation residue deep benzene removal device as described in claim 4, characterized in that: The nitrogen flow meter's downstream gate valve (12) is equipped with a nitrogen inlet quick-closing valve (15) and a check valve (16).

6. The benzene distillation residue deep benzene removal apparatus according to any one of claims 1-5, characterized in that: The top of the distillation column (1) is connected to a cooler (17), the cooler (17) is connected to a gas-liquid separator (18), the top of the gas-liquid separator (18) is connected to a nitrogen reflux pipe (19), and the nitrogen reflux pipe (19) is connected to the nitrogen inlet pipe (6) at the front end of the nitrogen remote pressure gauge (8).

7. The benzene distillation residue deep benzene removal device as described in claim 6, characterized in that: Both the cooler (17) and the gas-liquid separator (18) are connected to a condensate collection tank (20).

8. The benzene distillation residue deep benzene removal device as described in claim 6, characterized in that: A circulating fan (21) is provided on the nitrogen return pipe (19).

9. The benzene distillation residue deep benzene removal device as described in claim 6, characterized in that: The gas-liquid separator (18) is provided with a vent pipe (22) at the top, and a vent quick-closing valve (23) is provided on the vent pipe (22).

10. The benzene distillation residue deep benzene removal device as described in claim 6, characterized in that: The bottom of the tower is provided with a discharge pipe (24), and a discharge pump (25) is provided on the discharge pipe (24).

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