Isomerization unit rectification system

Abstract

The utility model relates to the field of chemical industry, and discloses an isomerization unit rectification system of an aromatic hydrocarbon combination device, which comprises a heptane removal tower and an isomerization carclazyte tower which are communicated through a pipeline, a heptane removal tower bottom circulating pump and a heptane removal tower bottom delivery pump are arranged at the downstream of the heptane removal tower, and a two-way backflow channel with a first valve is arranged between the downstream of the heptane removal tower bottom circulating pump and the downstream of the heptane removal tower bottom delivery pump. Operation risks such as heat exchanger leakage, material loss, liquid impact of a rear pipeline, operation disorder of a rectifying tower, pump suffocation of a delivery pump, material mixing and overtemperature of an underground pipe network caused by difficulty in synchronous temperature rise of materials during starting and stopping of an isomerization system are solved, and time required by starting and stopping processes is saved.

Description

Technical Field

[0001] The utility model relates to the field of petrochemical industry, in particular to an isomerization unit distillation system in an aromatics combination device. Background Art

[0002] In an aromatics complex with benzene and xylene as products, the isomerization system for producing paraxylene (PX) occupies an important position. The main reactions in the isomerization unit are xylene isomerization and ethylbenzene dealkylation. The purpose of this process is to convert the p-xylene-depleted feed into a balanced mixed xylene, thereby increasing the yield of p-xylene.

[0003] The distillation system of the isomerization unit of the aromatics complex separates the light components through the deheptanizer. The bottom material of the tower needs to be processed and refined by the bleaching tower before being sent to the downstream unit. Since the operating temperature of the bleaching tower is limited, multiple heat exchangers are set up to achieve heat recovery and temperature control. Despite this, the existing technology of the isomerization unit of the aromatics complex is stable and reliable in normal operation, but it still has many shortcomings during the start-up and shutdown process.

[0004] First, during the heating process of the device, the distillation tower is started independently to establish a stable full reflux, and then connected in series with the subsequent process. However, since the heat exchanger and the kaolin tower are not heated, when the process is opened backward, the high-temperature material enters the cold heat exchanger. Due to the drastic temperature difference, the heat exchanger head usually leaks, posing a major safety hazard. Usually, a small amount of densely packed lines are used to discharge into an underground tank to preheat the entire process, resulting in a large waste of materials and delays in start-up time, and it is not easy to warm it evenly.

[0005] Secondly, the downstream distillation tower of the device is usually also independently established for single-tower full reflux operation. In the process of opening up the process backward, since the materials in the heat exchanger and the kaolin tower are not heated up, the displaced cold materials enter the subsequent process, which will cause serious impact on the system that has been heated and stabilized, causing liquid hammer in the pipeline and operational disorder of the distillation tower.

[0006] In addition, during the start-up of the device, materials need to be gradually introduced downstream. However, due to the high head of the external delivery pump and the lack of a minimum return line, there is a serious pump blocking phenomenon during the initial small flow rate delivery, which causes large vibration of the pump and poses certain safety hazards.

[0007] Finally, during the shutdown and material withdrawal process of the device, after the furnace is gradually shut down, the materials in the distillation tower and the subsequent heat exchanger bleaching tower cannot be cooled. If the high-temperature materials are directly discharged into the underground tank, it will cause damage to the underground pipeline network and over-temperature and over-pressure of the underground waste oil tank. It is necessary to establish a large-cycle cooling system in conjunction with other units. The process is complicated and easily causes material mixing. In addition, time is wasted due to the asynchronous shutdown of different units. Utility Model Content

[0008] The object of the present utility model is to overcome the problems in the prior art such as heat exchanger leakage, material loss, and external feed pump air binding during the start-up and shutdown of the rectification system in the isomerization unit, and to provide an efficient rectification system for the isomerization unit, which can save the time required for the start-up and shutdown processes and can effectively alleviate problems such as heat exchanger leakage, material loss, and external feed pump air binding.

[0009] To achieve the above object, the present utility model provides a rectification system for an isomerization unit, which includes a deheptanizer and an isomerization clay tower that are kept connected through pipelines.

[0010] A deheptanizer bottom circulation pump and a deheptanizer bottom external feed pump are arranged downstream of the deheptanizer. The deheptanizer bottom circulation pump and the deheptanizer bottom external feed pump are connected to the bottom of the deheptanizer through pipelines, so that a part of the bottom material of the deheptanizer can be circulated back into the deheptanizer through the deheptanizer bottom circulation pump, and another part of the bottom material of the deheptanizer can enter the isomerization clay tower through the deheptanizer bottom external feed pump.

[0011] Moreover, a two-way reflux channel with a first valve is arranged between the downstream of the deheptanizer bottom circulation pump and the downstream of the deheptanizer bottom external feed pump, so as to be able to adjust the flow rate of the bottom material from the deheptanizer into the deheptanizer bottom circulation pump and / or the deheptanizer bottom external feed pump.

[0012] The system further includes a separation tank arranged upstream of the deheptanizer, so that the material can be introduced into the deheptanizer from the separation tank.

[0013] In some embodiments, a circulation channel with a second valve is arranged between the downstream of the isomerization clay tower and the downstream of the separation tank, so that the bottom material of the isomerization clay tower can flow back into the deheptanizer through the circulation channel.

[0014] Preferably, the system further includes a deheptanizer inlet and outlet heat exchanger arranged between the separation tank and the deheptanizer; the number of deheptanizer inlet and outlet heat exchangers is preferably at least 2.

[0015] One end of the circulation channel is connected to the downstream of the separation tank and upstream of all the deheptanizer inlet and outlet heat exchangers.

[0016] In some embodiments, a bifurcated channel with a valve is further arranged on the circulation channel, so that the material in the bifurcated channel can be introduced into the upstream pipeline of the deheptanizer.

[0017] Preferably, one end of the bifurcated channel is connected to the upstream of the deheptanizer and downstream of all the deheptanizer inlet and outlet heat exchangers.

[0018] In some embodiments, the system further includes a feed and discharge heat exchanger of the clay tower disposed between the pump for sending out the bottom of the deheptanizer and the isomerization clay tower.

[0019] Preferably, the downstream of the pump for sending out the bottom of the deheptanizer is in communication with the activation cooler of the clay tower provided with a valve through a pipeline, so that the material can enter the activation cooler of the clay tower from the downstream of the pump for sending out the bottom of the deheptanizer.

[0020] Preferably, the downstream of the activation cooler of the clay tower is in communication with the circulation channel through a pipeline, so that the material downstream of the activation cooler of the clay tower can flow back to the deheptanizer through the circulation channel.

[0021] Through the above technical solutions, the process flow of the rectification system of the isomerization unit is optimized and transformed, and a self-circulation process for the rectification part of the isomerization unit is established, mainly including: adding a circulation channel from the end of an external delivery line to the feed line of the rain deheptanizer, and adding a two-way reflux channel between the circulation pump and the external delivery pump, which can enable the synchronous heating and cooling of equipment and materials during startup and shutdown, solve operation risks such as heat exchanger leakage, material loss, liquid hammer in the back pipeline, disordered operation of the rectification tower, external delivery pump blockage, material mixing, and overheating of the underground pipe network during the previous startup and shutdown processes, and at the same time save the time required for startup and shutdown processes. Description of the Drawings

[0022] Figure 1 is the process flow diagram of the rectification system of the isomerization unit in the specific embodiment and Embodiment 1 of the present utility model;

[0023] Figure 2 is the process flow diagram of the rectification system of the isomerization unit in Comparative Example 1.

[0024] Description of the Reference Numerals

[0025] 1. Deheptanizer; 2. Isomerization clay tower; 3. Adsorption separation unit; 4. Separation tank; 5. Feed and discharge heat exchanger of the deheptanizer; 6. Bottom circulation pump of the deheptanizer; 7. Pump for sending out the bottom of the deheptanizer; 8. First valve; 9. Two-way reflux channel; 10. Second valve; 11. Circulation channel; 12. Bifurcation channel; 13. Feed and discharge heat exchanger of the clay tower; 14. Activation cooler of the clay tower; 15. Reboiler of the deheptanizer; 16. Xylene rectification unit. Detailed Embodiments

[0026] The following details the specific embodiments of the embodiments of the present utility model with reference to the drawings. It should be understood that the specific embodiments described herein are only for explaining and illustrating the embodiments of the present utility model, and are not used to limit the embodiments of the present utility model.

[0027] In the present utility model, unless otherwise specified, directional terms such as "up and down, left and right, front and back, inside and outside" included in the terms only represent the orientation of the term in its normal use state, or the common name understood by those skilled in the art, and should not be regarded as a limitation to the term.

[0028] As shown in the Figure 1 isomerization unit rectification system shown, the system includes a deheptanizer 1 and an isomerization clay tower 2 that are kept connected through pipelines.

[0029] A deheptanizer bottom circulation pump 6 and a deheptanizer bottom external feed pump 7 are arranged downstream of the deheptanizer 1. The deheptanizer bottom circulation pump 6 and the deheptanizer bottom external feed pump 7 are connected to the bottom of the deheptanizer 1 through pipelines, so that a part of the bottom material of the deheptanizer 1 can be circulated back into the deheptanizer 1 through the deheptanizer bottom circulation pump 6, and another part of the bottom material of the deheptanizer 1 can enter the isomerization clay tower 2 through the deheptanizer bottom external feed pump 7.

[0030] Moreover, a two-way reflux channel 9 with a first valve 8 is arranged between the downstream of the deheptanizer bottom circulation pump 6 and the downstream of the deheptanizer bottom external feed pump 7, so as to be able to adjust the flow rate of the bottom material from the deheptanizer 1 into the deheptanizer bottom circulation pump 6 and / or the deheptanizer bottom external feed pump 7.

[0031] The system also includes a separation tank 4 arranged upstream of the deheptanizer 1, so that the material can be introduced from the separation tank 4 into the deheptanizer 1.

[0032] In some embodiments, a circulation channel 11 with a second valve 10 is arranged between the downstream of the isomerization clay tower 2 and the downstream of the separation tank 4, so that the bottom material of the isomerization clay tower 2 can flow back into the deheptanizer 1 through the circulation channel 11.

[0033] During the heating process of the prior art device, generally, after the deheptanizer is heated normally, the method of preheating by discharging in a dense row at the low point of the process to the underground tank is adopted. The discharge flow rate is small, the time consumption is long, the preheating effect is poor, and a large amount of materials are wasted. In addition, at the initial stage of the device operation, when the material is externally fed at a low flow rate, usually the outlet valve of the external feed pump is slightly opened to control the flow rate. It is difficult to accurately control, and the flow rate is too low, resulting in pump cavitation, and the vibration value of the pump remains relatively high.

[0034] However, during the heating-up process of the rectification system of the isomerization unit in the specific embodiment of the present utility model, it is not necessary to start the bottom external delivery pump 7 of the heptane stripper. Instead, the material of the bottom circulation pump 6 of the heptane stripper can be preheated to the back path first through the two-way reflux channel 9, and then the material is transported back to the heptane stripper 1 through the circulation channel 11, thereby establishing the circulation process of the rectification part. The synchronous heating-up and preheating of the heptane stripper 1 and the back path are completed by using the circulating material with a large flow rate, while reducing the waste oil discharge and saving the preheating and heating-up time.

[0035] Meanwhile, when the material flow rate is low at the initial stage of operation, the two-way reflux channel 9 is opened first when starting the bottom external delivery pump 7 of the heptane stripper. At this time, due to the high head of the bottom external delivery pump 7 of the heptane stripper, the two-way reflux channel 9 can return most of the material to the heptane stripper 1, and this channel can also deliver the material with a suitable flow rate to the downstream of the bottom external delivery pump 7 of the heptane stripper according to needs. That is to say, the present utility model can adjust the external delivery flow rate as needed, and the bottom external delivery pump 7 of the heptane stripper always operates under the rated working condition with a small vibration amplitude.

[0036] Preferably, the system further includes a heptane stripper inlet and outlet heat exchanger 5 provided between the separation tank 4 and the heptane stripper 1;

[0037] Preferably, the number of the heptane stripper inlet and outlet heat exchangers 5 is at least 2.

[0038] Preferably, one end of the circulation channel 11 is connected downstream of the separation tank 4 and upstream of all the heptane stripper inlet and outlet heat exchangers 5.

[0039] As described above, the rectification system of the isomerization unit in the specific embodiment of the present utility model can be heated up synchronously with the rectification column and the circulation flow rate can be adjusted. The heating of the equipment and the material is gentle and uniform, overcoming the defect in the prior art that leakage still occurs due to uneven heating of the heat exchanger when a large flow rate of material is externally delivered.

[0040] In some embodiments, a bifurcated channel 12 with a valve is further provided on the circulation channel 11, so that the material in the bifurcated channel 12 can be introduced into the upstream pipeline of the heptane stripper 1.

[0041] Preferably, one end of the bifurcated channel 12 is connected upstream of the heptane stripper 1 and downstream of all the heptane stripper inlet and outlet heat exchangers 5.

[0042] In some embodiments, the system further includes a clay tower inlet and outlet heat exchanger 13 provided between the bottom external delivery pump 7 of the heptane stripper and the isomerization clay tower 2.

[0043] In some embodiments, the downstream of the deheptanizer bottom delivery pump 7 is connected to the bleaching tower activation cooler 14 provided with a valve through a pipeline, so that the material can enter the bleaching tower activation cooler 14 from the downstream of the deheptanizer bottom delivery pump 7.

[0044] Preferably, the downstream of the bleaching tower activation cooler 14 is connected to the circulation channel 11 through a pipeline, so that the material downstream of the bleaching tower activation cooler 14 can flow back to the deheptanizer 1 through the circulation channel 11.

[0045] In some embodiments, the material downstream of the deheptanizer bottom delivery pump 7 flows through the bleaching clay tower inlet and outlet heat exchanger 13 and the deheptanizer inlet and outlet heat exchanger 5 in sequence and then enters the isomerization bleaching clay tower 2 and / or the bleaching clay tower activation cooler 14.

[0046] When the isomerization unit distillation system is shut down, the deheptanizer reboiler 15 is turned off and naturally ventilated to a low temperature, and then the material can be sent to the bleaching clay tower activation cooler 14 for cooling through the two-way reflux channel 9, and then returned to the distillation tower through the circulation channel 11, thereby establishing an internal circulation cooling process of the system and saving cooling time.

[0047] The existing technology requires linkage with other units to establish a large-circulation cooling process during shutdown. However, due to the different shutdown sequences and operating difficulties of each unit, it is difficult to match the time, which greatly prolongs the cooling time.

[0048] The isomerization unit distillation system described in this embodiment is actually a part of the xylene isomerization unit in the aromatics complex. A typical aromatics complex generally includes catalytic reforming, aromatics extraction, toluene disproportionation and transalkylation, xylene distillation, adsorption separation, and xylene isomerization. Among them, the purpose of the xylene isomerization unit is to convert other isomers into para-xylene through reaction, thereby increasing the production of para-xylene.

[0049] The material of this system comes from the adsorption separation unit 3, and the upstream of the separation tank 4 also includes a feed buffer tank, a feed pump, a heating furnace, and an isomerization reactor (not shown) which are connected in sequence through pipelines.

[0050] The main process of this system is: the p-xylene-poor raffinate separated from the adsorption separation unit is converted into a p-xylene-rich material through an isomerization reaction, and the material is separated by a xylene distillation unit and then transported to the adsorption separation unit again, so that the p-xylene product can be produced continuously.

[0051] Specifically, the raffinate side stream product from the adsorption separation unit, which is poor in p-xylene, reacts with recycle hydrogen and make-up hydrogen from the reforming unit during normal operation. After heating, this mixed material is sent to the isomerization reactor, and the reaction generates a C 8 aromatic hydrocarbon mixture and then enters the isomerization unit distillation system described in the present invention.

[0052] The material separates out the gas phase in the separation tank, is sent to the deheptanizer after heat exchange through a heat exchanger: the top gas phase is sent to fuel gas, and the liquid distillate rich in benzene is sent to the reforming unit; the bottom material rich in p-xylene is sent to the isomerization clay tower to remove olefins and diolefins, providing raw materials for the xylene unit, and heavy aromatics are separated out there. The mixed xylene is sent back to the adsorption separation unit to produce high-purity p-xylene, which is used as a raw material for petrochemical industry.

[0053] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0054] Example 1

[0055] First, the product separated by the adsorption separation unit (raffinate poor in p-xylene) is sent to the isomerization reactor for reaction, and then the product of the isomerization reactor is connected to the Figure 1 isomerization unit distillation system as described. Among them, the xylene isomerization catalyst is a deethylation type catalyst, the catalyst mass hourly space velocity is 6 - 14 hr-1, the ethylbenzene content in the feed is 2 - 5 wt%, the hydrogen-hydrocarbon ratio is 1 - 2:1, the reaction temperature is 330 - 480 °C, the reaction pressure is 1.4 - 2.0 Mpa, and the recycle hydrogen purity > 65%.

[0056] Comparative Example 1

[0057] Comparative Example 1 is carried out with reference to Example 1, the difference being that the Figure 2 isomerization unit distillation system as shown is used.

[0058] Parameters such as the preheating and temperature rising time during the startup stage, the temperature dropping time during the shutdown stage, and the heat exchanger leakage situation of the isomerization unit distillation systems described in Example 1 and Comparative Example 1 are respectively counted, as shown in Table 1 specifically.

[0059] Table 1

[0060]

[0061] It can be seen from the results in Table 1 that in Example 1 using the isomerization unit distillation system described in the present invention, the heat exchanger has no leakage and the discharge amount of preheated dirty oil is zero, which has significantly better effects compared with Comparative Example 1.

[0062] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. An isomerization unit distillation system, characterized in that: The system includes a deheptanizer (1) and an isomerization clay tower (2) which are connected via a pipeline; A deheptanizer bottom circulation pump (6) and a deheptanizer bottom delivery pump (7) are provided downstream of the deheptanizer (1). The deheptanizer bottom circulation pump (6) and the deheptanizer bottom delivery pump (7) are connected to the bottom of the deheptanizer (1) through pipelines, so that a portion of the bottom material of the deheptanizer (1) can be circulated back to the deheptanizer (1) through the deheptanizer bottom circulation pump (6), and another portion of the bottom material of the deheptanizer (1) can be passed through the deheptanizer bottom delivery pump (7) into the isomerization clay tower (2); Furthermore, a two-way reflux channel (9) with a first valve (8) is provided between the downstream of the deheptanizer bottom circulation pump (6) and the downstream of the deheptanizer bottom delivery pump (7), so as to adjust the flow rate of the bottom material from the deheptanizer (1) entering the back path of the deheptanizer bottom circulation pump (6) and / or the back path of the deheptanizer bottom delivery pump (7).

2. The isomerization unit distillation system according to claim 1, characterized in that: The system further comprises a separation tank (4) arranged upstream of the deheptanizer (1), so that materials can be introduced from the separation tank (4) into the deheptanizer (1).

3. The isomerization unit distillation system according to claim 2, characterized in that: A circulation channel (11) with a second valve (10) is provided between the downstream of the isomerization clay tower (2) and the downstream of the separation tank (4), so that the bottom material of the isomerization clay tower (2) can flow back to the deheptanizer (1) through the circulation channel (11).

4. The isomerization unit distillation system according to claim 3, characterized in that: The system also includes a deheptanizer inlet and outlet heat exchanger (5) disposed between the separation tank (4) and the deheptanizer (1).

5. The isomerization unit distillation system according to claim 4, characterized in that: The number of the deheptanizer inlet and outlet heat exchangers (5) is at least 2.

6. The isomerization unit distillation system according to claim 4, characterized in that: One end of the circulation channel (11) is connected to the downstream of the separation tank (4) and the upstream of all the deheptanizer inlet and outlet heat exchangers (5).

7. The isomerization unit distillation system according to claim 4, characterized in that: The circulation channel (11) is also provided with a branch channel (12) with a valve, so that the material in the branch channel (12) can be introduced into the upstream pipeline of the deheptanizer (1).

8. The isomerization unit distillation system according to claim 7, characterized in that: One end of the branch channel (12) is connected to the upstream of the deheptanizer (1) and downstream of all the deheptanizer inlet and outlet heat exchangers (5).

9. The isomerization unit distillation system according to claim 1, characterized in that: The system also includes a clay tower inlet and outlet heat exchanger (13) disposed between the deheptanizer bottom delivery pump (7) and the isomerization clay tower (2).

10. The isomerization unit distillation system according to claim 3, characterized in that: The downstream of the deheptanizer bottom delivery pump (7) is connected to the bleaching tower activation cooler (14) provided with a valve through a pipeline, so that the material can enter the bleaching tower activation cooler (14) from the downstream of the deheptanizer bottom delivery pump (7).

11. The isomerization unit distillation system according to claim 10, characterized in that: The downstream of the bleaching tower activation cooler (14) is connected to the circulation channel (11) through a pipeline, so that the material downstream of the bleaching tower activation cooler (14) can flow back to the deheptanizer (1) through the circulation channel (11).

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