System and method for recycling heavy oil in cyclohexanone production

Abstract

The invention provides a system and a method for recycling heavy oil in cyclohexanone production. According to the method and the system, DMAC is added into the heavy oil, so that the relative volatility of methylcyclopentane and cyclohexanol in the heavy oil can be improved, rectification separation of cyclohexanol is facilitated, cyclohexanol is convenient to recycle, the utilization rate of cyclohexanol is improved, and the enterprise cost is reduced. The pressure in the heavy oil separator can be reduced by using the two parallel vacuum pumps and the two parallel compressors, so that the boiling point of heavy oil in the heavy oil separator is reduced, and rectification separation is facilitated; and meanwhile, the use amount of 1.2 MPa live steam is also saved. The mixed steam compressed by the compressor is introduced into the second reboiler or the third reboiler according to different temperatures of the mixed steam, so that heat is provided for the heavy oil separator, meanwhile, the energy of the secondary steam is reasonably utilized, and the use amount of 1.2 MPa live steam is further saved.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy oil recovery and relates to a system and method for recovering and utilizing heavy oil in cyclohexanone production. Background Art

[0002] Cyclohexanone is a colorless transparent liquid, which is mainly used as raw material and solvent for organic synthesis in industry. It is an important organic chemical raw material.

[0003] During the production of cyclohexanone, a large amount of heavy oil will be produced in the alcohol tower and transported to the heavy oil storage tank in the tank area at a delivery rate of 30kg / h for storage. The components in the heavy oil include 35% methylcyclopentane and 64% cyclohexanol by mass, and the remaining 1% is cyclohexane and cyclohexanone. Since cyclohexanol is an important chemical product, the cyclohexanol in the heavy oil can be recycled to improve its utilization rate. However, it is difficult to completely separate cyclohexanol from heavy oil with the existing ordinary distillation method, and the separation energy consumption is relatively large. Therefore, this part of cyclohexanol will be sold as heavy oil along with methylcyclopentane, which seriously wastes the resources of the early stage and causes resource waste. Summary of the invention

[0004] The object of the present invention is to provide a system and method for recycling heavy oil in the production of cyclohexanone, so as to solve the problem that the existing distillation method is difficult to recover cyclohexanol from heavy oil.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present application provides a system for recycling heavy oil in the production of cyclohexanone, comprising a heavy oil agglomerator and a heavy oil separator which are connected to each other, the heavy oil separator being also connected to a raw steam pipeline; a second reboiler is provided at the bottom of the heavy oil separator, and a third reboiler is provided at the middle and upper part of the heavy oil separator; the top of the heavy oil separator is connected to a vacuum pump, a first buffer tank and a compressor in sequence, the compressor being connected to the second reboiler and the third reboiler respectively; the first buffer tank is also connected to the second buffer tank, and the second buffer tank is respectively connected to the second reboiler and the third reboiler; the second buffer tank is also connected to the heavy oil separator through a circulating pump.

[0006] Preferably, a first reboiler is further provided at the bottom of the heavy oil separator, and the first reboiler is connected to the raw steam pipeline.

[0007] Preferably, the vacuum pump comprises two vacuum pumps connected in parallel.

[0008] Preferably, the heavy oil separator is provided with 12 tower plates, and the third reboiler is located at the 6th tower plate.

[0009] The present application provides a method for recycling heavy oil in cyclohexanone production, the method comprising: S01: After the heavy oil and DMAC are mixed in the heavy oil coalescer, they enter the heavy oil separator with the raw steam and undergo vacuum distillation under the action of a vacuum pump. Mixed steam is obtained at the top of the tower and methylcyclopentane is obtained at the bottom of the tower.

[0010] The heavy oil in the heavy oil storage tank is mixed with DMAC in a heavy oil coalescer at a feed ratio of 1: (1.5-1.72) to increase the relative volatility of methylcyclopentane and cyclohexanol in the heavy oil. After the heavy oil is mixed with DMAC, it is passed into the heavy oil separator. When the liquid level in the heavy oil separator reaches the preset liquid level, raw steam with a pressure of 1.2MPa is slowly introduced into the heavy oil separator through the raw steam pipeline, and the vacuum pump is turned on at the same time to ensure that the pressure in the heavy oil separator is 88kPa. In the present application, the feed ratio of raw steam to heavy oil is 1: (1.3-1.5). Under the conditions of a pressure of 88kPa and a temperature of 100-130°C, the heavy oil is distilled under reduced pressure in the heavy oil separator, and a mixed steam of gaseous cyclohexanol and secondary steam is obtained at the top of the tower, and methylcyclopentane is obtained at the bottom of the tower. The mixed steam is passed into the first buffer tank, and part of the mixed steam in the first buffer tank enters the compressor for pressurization and temperature increase, and the other part of the mixed steam is passed into the second buffer tank. Methylcyclopentane is stored and then taken out.

[0011] S02: The mixed steam is compressed by the compressor and enters the second reboiler or the third reboiler, and enters the second buffer tank after heat exchange.

[0012] The compressor is turned on to pressurize and heat the mixed steam at a pressure of 0.5 MPa and a temperature of 150°C to save the heat of the gaseous cyclohexanol discharged by the vacuum pump. When the temperature of the pressurized and heated mixed steam is 115-125°C, the compressor discharges the mixed steam into the second reboiler to heat the heavy oil separator at the bottom of the heavy oil separator, reducing the amount of 1.2 MPa raw steam. When the temperature of the pressurized and heated mixed steam is 88-92°C, the compressor discharges the mixed steam into the third reboiler to heat the heavy oil separator at the middle and upper part of the heavy oil separator, reasonably saving the amount of 1.2 MPa raw steam. The mixed steam after heat exchange in the second reboiler or the third reboiler is discharged into the second buffer tank.

[0013] S03: Detect the content of cyclohexanol in the second buffer tank. If the content exceeds 75%, it is discharged; if it does not exceed 75%, it re-enters the heavy oil separator through the circulation pump.

[0014] Check the content of gaseous cyclohexanol in the second buffer tank. If the content of gaseous cyclohexanol exceeds 75%, it will be discharged and directly used in the device. If the content of gaseous cyclohexanol does not exceed 75%, it will be passed into the heavy oil separator through a circulation pump for re-separation and purification. Among them, the situation where the content of gaseous cyclohexanol does not exceed 75% is mostly unqualified waste liquid generated in the early start-up or waste liquid generated when production is unstable.

[0015] The present invention has the following beneficial effects: (1) Adding DMAC to heavy oil can increase the relative volatility of methylcyclopentane and cyclohexanol in the heavy oil, facilitate the distillation separation of cyclohexanol, facilitate the recovery of cyclohexanol, improve the utilization rate of cyclohexanol, and reduce enterprise costs.

[0016] (2) The use of two parallel vacuum pumps and compressors can reduce the pressure inside the heavy oil separator, thereby reducing the boiling point of the heavy oil in the heavy oil separator, facilitating distillation separation; at the same time, it also saves 1.2MPa of raw steam.

[0017] (3) The mixed steam compressed by the compressor is passed into the second reboiler or the third reboiler according to its temperature, providing heat for the heavy oil separator while realizing the rational utilization of secondary steam energy, further saving 1.2MPa of raw steam. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the structure of a system for recycling heavy oil in cyclohexanone production provided in an embodiment of the present application; Symbols represent: 1-heavy oil coalescer, 2-heavy oil separator, 3-raw steam pipeline, 4-second reboiler, 5-third reboiler, 6-vacuum pump, 7-first buffer tank, 8-compressor, 9-second buffer tank, 10-circulation pump, 11-first reboiler. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The present application embodiment provides a system for recycling heavy oil in cyclohexanone production, the system comprising a heavy oil coalescer 1 and a heavy oil separator 2 connected to each other, as shown in the attached Figure 1As shown. The heavy oil coalescer 1 is a component for mixing heavy oil and DMAC (English name: N,N-Dimethylacetamide; Chinese name: N,N-dimethylacetamide) produced in the production of cyclohexanone. The addition of DMAC can increase the relative volatility of methylcyclopentane and cyclohexanol in the heavy oil, which is beneficial to the distillation separation of cyclohexanol, and then facilitates the recovery of cyclohexanol. In the embodiment of the present application, the feed ratio of heavy oil to DMAC is 1: (1.5-1.72).

[0021] The heavy oil separator 2 is a component for distilling heavy oil and DMAC. The heavy oil separator 2 is also connected to a raw steam pipeline 3, into which raw steam at a pressure of 1.2 MPa is passed. The heavy oil mixed with DMAC and the raw steam at a pressure of 1.2 MPa enter the heavy oil separator 2, which is convenient for the distillation separation of cyclohexanol. In the embodiment of the present application, the feed ratio of 1.2 MPa raw steam and heavy oil is 1: (1.3-1.5). More preferably, the feed ratio of 1.2 MPa raw steam and heavy oil is 1: 1.36, so as to control the rational use of raw steam and reduce costs.

[0022] In order to heat the heavy oil separator 2, a first reboiler 11 is provided at the bottom of the heavy oil separator 2, and the first reboiler 11 is connected to the raw steam pipeline 3. Heat exchange is achieved by passing 1.2 MPa raw steam into the first reboiler 11, thereby heating the heavy oil separator 2, which is convenient for the distillation separation of the heavy oil.

[0023] The top of the heavy oil separator 2 is connected to the vacuum pump 6, the first buffer tank 7 and the compressor 8 in sequence, and the first buffer tank 7 is also connected to the second buffer tank 9. The vacuum pump 6 can reduce the pressure in the heavy oil separator 2 to 88kPa, thereby reducing the boiling point of the heavy oil in the heavy oil separator 2, which is convenient for distillation separation. In the embodiment of the present application, the temperature inside the heavy oil separator 2 is 100-130°C. At this temperature and under a relatively low vacuum pressure, gaseous cyclohexanol can be separated from the heavy oil, saving 1.2MPa of raw steam. In the embodiment of the present application, the vacuum pump 6 includes two vacuum pumps connected in parallel, and the two vacuum pumps can use smaller vacuum pumps to save operating costs and civil engineering investment costs.

[0024] Under the pressure reduction effect of the vacuum pump 6, the gaseous cyclohexanol and the generated secondary steam form mixed steam, which is then discharged from the top of the heavy oil separator 2 and temporarily stored in the first buffer tank 7. Part of the mixed steam in the first buffer tank 7 is passed into the second buffer tank 9, and the other part of the mixed steam is passed into the compressor 8 for compression treatment.

[0025] A second reboiler 4 is provided at the bottom of the heavy oil separator 2, a third reboiler 5 is provided at the middle and upper part of the heavy oil separator 2, a compressor 8 is respectively connected to the second reboiler 4 and the third reboiler 5, and a second buffer tank 9 is respectively connected to the second reboiler 4 and the third reboiler 5. The second buffer tank 9 is also connected to the heavy oil separator 2 through a circulating pump 10.

[0026] The compressor 8 pressurizes and heats the mixed steam to save the heat of the gaseous cyclohexanol discharged by the vacuum pump 6, and discharges the pressurized and heated mixed steam into the second reboiler 4 or the third reboiler 5, thereby facilitating the provision of heat for the heavy oil separator 2 and improving the utilization rate of the steam heat. In the embodiment of the present application, the pressure of the compressor 8 is 0.5 MPa, the temperature is 150°C, and the exhaust volume is 3000m 3 .

[0027] When the temperature of the pressurized and heated mixed steam is 115-125°C, the compressor 8 discharges the mixed steam into the second reboiler 4 to heat the heavy oil separator 2 at the bottom of the heavy oil separator 2, thereby reducing the amount of 1.2MPa raw steam. When the temperature of the pressurized and heated mixed steam is 88-92°C, the compressor 8 discharges the mixed steam into the third reboiler 5 to heat the heavy oil separator 2 at the middle and upper part of the heavy oil separator 2, thereby reasonably saving the amount of 1.2MPa raw steam.

[0028] The mixed steam after heat exchange in the second reboiler 4 or the third reboiler 5 is discharged into the second buffer tank 9. The content of gaseous cyclohexanol in the second buffer tank 9 is checked. If the content of gaseous cyclohexanol exceeds 75%, it is discharged and directly enters the device for use. If the content of gaseous cyclohexanol does not exceed 75%, it is passed into the heavy oil separator 2 through the circulation pump 10 for re-separation and purification. Among them, the situation where the content of gaseous cyclohexanol does not exceed 75% is mostly unqualified waste liquid generated in the early start-up or waste liquid generated when production is unstable.

[0029] In the embodiment of the present application, a packed tower is selected for the heavy oil separator 2. In order to better separate the components in the heavy oil, the packed tower is designed with a large height margin, and the height of the packed tower is set to 70m. In addition, in order to save a small amount of steel and civil engineering investment, the diameter of the packed tower is set to 500mm, and 12 stages of tower plates are arranged in the heavy oil separator 2, and the third reboiler 5 is located at the 6th stage of the tower plate.

[0030] Based on the above-mentioned system for recycling heavy oil in cyclohexanone production, the embodiment of the present application provides a method for recycling heavy oil in cyclohexanone production, the method comprising: S01: After the heavy oil and DMAC are mixed in the heavy oil coalescer, they enter the heavy oil separator with the raw steam and undergo vacuum distillation under the action of a vacuum pump. Mixed steam is obtained at the top of the tower and methylcyclopentane is obtained at the bottom of the tower.

[0031] S02: The mixed steam is compressed by the compressor and enters the second reboiler or the third reboiler, and enters the second buffer tank after heat exchange.

[0032] S03: Detect the content of cyclohexanol in the second buffer tank. If the content exceeds 75%, it is discharged; if it does not exceed 75%, it re-enters the heavy oil separator through the circulation pump.

[0033] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0034] Example 1 The present application provides a method for recycling heavy oil in cyclohexanone production, the method comprising: S101: The heavy oil in the heavy oil storage tank is mixed with DMAC in the heavy oil coalescer 1 at a feed ratio of 1:1.5 and then introduced into the heavy oil separator 2. When the liquid level in the heavy oil separator 2 reaches the preset liquid level, raw steam with a pressure of 1.2MPa is slowly introduced into the heavy oil separator 2 through the raw steam pipeline 3 at a feed ratio of raw steam to heavy oil of 1:1.36, and the vacuum pump 6 is turned on at the same time to ensure that the pressure in the heavy oil separator 2 is 88kPa. Under the conditions of a pressure of 88kPa and a temperature of 120°C, the heavy oil is decompressed and distilled in the heavy oil separator 2, and a mixed steam of gaseous cyclohexanol and secondary steam is obtained at the top of the tower, and methylcyclopentane is obtained at the bottom of the tower. The mixed steam is introduced into the first buffer tank 7, and part of the mixed steam in the first buffer tank 7 enters the compressor 8 for pressurization and temperature increase, and the other part of the mixed steam is introduced into the second buffer tank 9. Methylcyclopentane is stored and then sold.

[0035] S102: Start the compressor 8, so that the compressor 8 pressurizes and heats the mixed steam under the conditions of a pressure of 0.5 MPa and a temperature of 150°C. When the temperature of the mixed steam after pressurization and temperature increase is 120°C, the compressor 8 discharges the mixed steam into the second reboiler 4. When the temperature of the mixed steam after pressurization and temperature increase is 90°C, the compressor 8 discharges the mixed steam into the third reboiler 5. The mixed steam after heat exchange in the second reboiler 4 or the third reboiler 5 is discharged into the second buffer tank 9.

[0036] S103: Check the content of gaseous cyclohexanol in the second buffer tank 9. If the content of gaseous cyclohexanol exceeds 75%, it is discharged and directly enters the device for utilization. If the content of gaseous cyclohexanol does not exceed 75%, it is passed into the heavy oil separator 2 through the circulation pump 10 for re-separation and purification.

[0037] Example 2 The present application provides a method for recycling heavy oil in cyclohexanone production, the method comprising: S201: The heavy oil in the heavy oil storage tank is mixed with DMAC in the heavy oil coalescer 1 at a feed ratio of 1:1.72 and then introduced into the heavy oil separator 2. When the liquid level in the heavy oil separator 2 reaches the preset liquid level, raw steam with a pressure of 1.2MPa is slowly introduced into the heavy oil separator 2 through the raw steam pipeline 3 at a feed ratio of raw steam to heavy oil of 1:1.3, and the vacuum pump 6 is turned on at the same time to ensure that the pressure in the heavy oil separator 2 is 88kPa. Under the conditions of a pressure of 88kPa and a temperature of 130°C, the heavy oil is decompressed and distilled in the heavy oil separator 2, and a mixed steam of gaseous cyclohexanol and secondary steam is obtained at the top of the tower, and methylcyclopentane is obtained at the bottom of the tower. The mixed steam is introduced into the first buffer tank 7, and part of the mixed steam in the first buffer tank 7 enters the compressor 8 for pressurization and temperature increase, and the other part of the mixed steam is introduced into the second buffer tank 9. Methylcyclopentane is stored and then sold.

[0038] S202: Start the compressor 8, so that the compressor 8 pressurizes and heats the mixed steam under the conditions of a pressure of 0.5 MPa and a temperature of 150°C. When the temperature of the mixed steam after pressurization and temperature increase is 125°C, the compressor 8 discharges the mixed steam into the second reboiler 4. When the temperature of the mixed steam after pressurization and temperature increase is 88°C, the compressor 8 discharges the mixed steam into the third reboiler 5. The mixed steam after heat exchange in the second reboiler 4 or the third reboiler 5 is discharged into the second buffer tank 9.

[0039] S203: Check the content of gaseous cyclohexanol in the second buffer tank 9. If the content of gaseous cyclohexanol exceeds 75%, it is discharged and directly enters the device for utilization. If the content of gaseous cyclohexanol does not exceed 75%, it is passed into the heavy oil separator 2 through the circulation pump 10 for re-separation and purification.

[0040] Example 3 The present application provides a method for recycling heavy oil in cyclohexanone production, the method comprising: S301: The heavy oil in the heavy oil storage tank is mixed with DMAC in the heavy oil coalescer 1 at a feed ratio of 1:1.6 and then introduced into the heavy oil separator 2. When the liquid level in the heavy oil separator 2 reaches the preset liquid level, raw steam with a pressure of 1.2MPa is slowly introduced into the heavy oil separator 2 through the raw steam pipeline 3 at a feed ratio of raw steam to heavy oil of 1:1.5, and the vacuum pump 6 is turned on at the same time to ensure that the pressure in the heavy oil separator 2 is 88kPa. Under the conditions of a pressure of 88kPa and a temperature of 100°C, the heavy oil is decompressed and distilled in the heavy oil separator 2, and a mixed steam of gaseous cyclohexanol and secondary steam is obtained at the top of the tower, and methylcyclopentane is obtained at the bottom of the tower. The mixed steam is introduced into the first buffer tank 7, and part of the mixed steam in the first buffer tank 7 enters the compressor 8 for pressurization and temperature increase, and the other part of the mixed steam is introduced into the second buffer tank 9. Methylcyclopentane is stored and then sold.

[0041] S302: Start the compressor 8, so that the compressor 8 pressurizes and heats the mixed steam under the conditions of a pressure of 0.5 MPa and a temperature of 150°C. When the temperature of the mixed steam after pressurization and temperature increase is 115°C, the compressor 8 discharges the mixed steam into the second reboiler 4. When the temperature of the mixed steam after pressurization and temperature increase is 92°C, the compressor 8 discharges the mixed steam into the third reboiler 5. The mixed steam after heat exchange in the second reboiler 4 or the third reboiler 5 is discharged into the second buffer tank 9.

[0042] S303: Check the content of gaseous cyclohexanol in the second buffer tank 9. If the content of gaseous cyclohexanol exceeds 75%, it is discharged and directly enters the device for utilization. If the content of gaseous cyclohexanol does not exceed 75%, it is passed into the heavy oil separator 2 through the circulation pump 10 for re-separation and purification.

[0043] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A system for recycling heavy oil in cyclohexanone production, characterized in that: The invention comprises a heavy oil agglomerator (1) and a heavy oil separator (2) which are connected to each other, wherein the heavy oil separator (2) is also connected to a live steam pipeline (3); a second reboiler (4) is provided at the bottom of the heavy oil separator (2), and a third reboiler (5) is provided at the middle and upper part of the heavy oil separator (2); the top of the heavy oil separator (2) is connected to a vacuum pump (6), a first buffer tank (7) and a compressor (8) in sequence, and the compressor (8) is respectively connected to the second reboiler (4) and the third reboiler (5); the first buffer tank (7) is also connected to a second buffer tank (9), and the second buffer tank (9) is respectively connected to the second reboiler (4) and the third reboiler (5); the second buffer tank (9) is also connected to the heavy oil separator (2) via a circulating pump (10).

2. The system for recycling heavy oil in cyclohexanone production according to claim 1, characterized in that: A first reboiler (11) is also provided at the bottom of the heavy oil separator (2), and the first reboiler (11) is connected to the raw steam pipeline (3).

3. The system for recycling heavy oil in cyclohexanone production according to claim 1, characterized in that: The vacuum pump (6) comprises two vacuum pumps connected in parallel.

4. The system for recycling heavy oil in cyclohexanone production according to claim 1, characterized in that: The heavy oil separator (2) is provided with 12 stages of tower plates, and the third reboiler (5) is located at the sixth stage of the tower plate.

5. A method for recycling heavy oil in cyclohexanone production, characterized in that: A system for recycling heavy oil in cyclohexanone production according to any one of claims 1 to 4 is used, wherein the method comprises: After the heavy oil and DMAC are mixed in the heavy oil coalescer, they enter the heavy oil separator with the raw steam and undergo vacuum distillation under the action of a vacuum pump. Mixed steam is obtained at the top of the tower and methylcyclopentane is obtained at the bottom of the tower. The mixed steam is compressed by the compressor and enters the second reboiler or the third reboiler, and enters the second buffer tank after heat exchange; The content of cyclohexanol in the second buffer tank is detected. If the content exceeds 75%, it is discharged; if it does not exceed 75%, it re-enters the heavy oil separator through the circulation pump.

6. The method for recycling heavy oil in cyclohexanone production according to claim 5, characterized in that: The temperature in the heavy oil separator is 100-130°C and the pressure is 88 kPa.

7. The method for recycling heavy oil in cyclohexanone production according to claim 5, characterized in that: The feed ratio of the heavy oil to DMAC is 1:(1.5-1.72).

8. The method for recycling heavy oil in cyclohexanone production according to claim 5, characterized in that: The feed ratio of raw steam to heavy oil is 1:(1.3-1.5).

9. The method for recycling heavy oil in cyclohexanone production according to claim 5, characterized in that: When the temperature of the mixed steam after being compressed by the compressor is 88-92° C., the compressed mixed steam enters the third reboiler; When the temperature of the mixed steam after being compressed by the compressor is 115-125° C., the compressed mixed steam enters the second reboiler.

10. The method for recycling heavy oil in cyclohexanone production according to claim 5, characterized in that: The pressure of the compressor is 0.5 MPa and the temperature is 150°C.

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