Device for removing trace aromatics by re - contacting tail hydrogen in disproportionation and alkyl transfer and method for removing same

Abstract

A device for removing trace aromatics by re - contacting the tail hydrogen in disproportionation and alkyl transfer, characterized by comprising a thermal separation tank, a cold separation tank, a heat exchanger, an oil - gas separation tank, a chilled water pipe and a mixed oil - gas pipe. The top of the thermal separation tank has a first gas - phase transfer pipe, and the bottom has a first bottom - liquid output pipe and a second bottom - liquid output pipe; the top of the cold separation tank has a second gas - phase transfer pipe and a recycle hydrogen pipe, the middle has a first feed inlet, and the bottom has a third bottom - liquid output pipe and a fourth bottom - liquid output pipe; the present invention also discloses a method for removing trace aromatics. The present invention no longer needs to rely on a reforming unit. A part of the liquid phase and the bottom oil separated by the thermal separation tank of the disproportionation and alkyl transfer reaction products is used as absorption oil to absorb the heavy components in the disproportionation tail hydrogen, and the removal rate of aromatics can reach 80%, and the removal rate of C5+ petroleum hydrocarbons can reach 74%, and the aromatic resources therein can be effectively recovered.

Description

Technical Field

[0001] The present invention relates to a tail hydrogen treatment device, in particular to a treatment device for disproportionation and alkyl transfer tail hydrogen, and the present invention also relates to a method for removing trace aromatics from tail hydrogen. Background Art

[0002] Hydrogen is an important resource in refining enterprises. Therefore, how to efficiently recycle and utilize the by-products (hydrogen-rich tail gas) in the production process of refining units has always been a concern and emphasis for relevant professionals. Currently, methods such as pressure swing adsorption (PSA), membrane separation, and cryogenic separation are usually used for the hydrogen-rich tail gas in refining units, and the pressure swing adsorption (PSA) method is the most widely used.

[0003] The existing disproportionation and alkyl transfer tail hydrogen contains a small amount of C5+ petroleum hydrocarbons and trace aromatics (benzene, toluene, and heavier aromatics above), and if it directly enters the pressure swing adsorption (PSA) device, it is very likely to cause heavy hydrocarbon saturation poisoning of the adsorbent, and the harm of benzene, toluene, and heavier aromatics above is the greatest. Although the heavy hydrocarbon saturation poisoning of the adsorbent is reversible, the adsorption effect of the regenerated adsorbent is far from as good as that before regeneration. Therefore, before the disproportionation and alkyl transfer tail hydrogen enters the pressure swing adsorption device, pretreatment is required, and trace aromatics (benzene, toluene, and heavier aromatics above) in the tail hydrogen need to be removed as much as possible.

[0004] See the Chinese utility model patent "A Reforming and Recontacting Device for Disproportionation Tail Hydrogen" (Patent No.: ZL201521096228.1, Publication No.: CN205228000U). The tail hydrogen conveying pipeline scheme of this patent is: connected to the compressor of the disproportionation and alkyl transfer device and the PSA device at both ends respectively, and also includes a tail hydrogen reforming and recontacting bypass. This bypass is provided with an evaporator, a gas-liquid separation tank, and a first regulating valve connected in sequence by pipelines. The two ends of this bypass are respectively connected to the compressor of the disproportionation and alkyl transfer device and the PSA device. The tail hydrogen conveying pipeline includes a tail hydrogen pipeline and a second regulating valve. Its advantage is that it can effectively eliminate the influence of C5, improve the stability of the device, ensure the safe and orderly progress of production, and has the characteristics of simple structure and convenient operation.

[0005] See the Chinese invention patent application publication "A Method for Recovering Tail Hydrogen of Disproportionation and Alkylation Transfer Device" (Publication No.: CN109422243A) with the application number 201710722646.4. In this application, the tail hydrogen from the disproportionation and alkylation transfer device is led to the inlet or outlet of the last-stage air cooler or water cooler of the reforming hydrogen compressor, or to the inlet or outlet of the penultimate-stage air cooler or water cooler of the reforming hydrogen compressor, and mixed with the compressed gas passing through the reforming hydrogen compressor. Then it contacts the reformate, and then successively enters the re-contact cooler for cooling and the last-stage re-contact tank for gas-liquid separation. The separated liquid phase returns to the upper-stage re-contact tank or enters the product separation unit after recovering the cold energy, and the separated gas phase is used as the feed gas of the pressure swing adsorption device, or a part is used as supplementary hydrogen and the other part is used as the feed gas of the pressure swing adsorption device to obtain high-purity hydrogen. Its advantage is that it can effectively recover the tail hydrogen of the disproportionation and alkylation transfer device at low cost.

[0006] Both of the existing two patent technologies need to rely on the re-contact device in the reforming unit, which increases the correlation between the two units. Therefore, when the disproportionation and alkylation transfer unit or the reforming unit has production fluctuations, the two units will affect each other. In addition, the disproportionation tail hydrogen is incorporated into the reforming hydrogen and enters the re-contact tank, and the absorption oil in the reforming is used to remove the heavy components (mainly C5+ petroleum hydrocarbons and minor aromatics) in the disproportionation tail hydrogen. These heavy components are all absorbed by the reforming absorption oil and will not return to the disproportionation and alkylation transfer device. Therefore, the existing patent technologies require that the re-contact device of the reforming has sufficient load to receive the disproportionation tail hydrogen and cannot reduce the loss of aromatics in the disproportionation and alkylation transfer device. Summary of the Invention

[0007] The first technical problem to be solved by the present invention is to provide an apparatus for removing trace aromatics from the re-contact of disproportionation and alkylation transfer tail hydrogen in addition to the above technical status.

[0008] The second technical problem to be solved by the present invention is to provide an apparatus for removing trace aromatics from the re-contact of disproportionation and alkylation transfer tail hydrogen without relying on the reforming unit in view of the above technical status.

[0009] The third technical problem to be solved by the present invention is to provide a method for removing trace aromatics from the re-contact of disproportionation and alkylation transfer tail hydrogen in view of the above technical status.

[0010] The technical solutions adopted by the present invention to solve the above first and second technical problems are as follows: An apparatus for removing trace aromatics from the re-contact of disproportionation and alkylation transfer tail hydrogen, which is characterized by including

[0011] A thermal separation tank having a first gas-phase transfer pipe at the top, a first bottom liquid output pipe and a second bottom liquid output pipe at the bottom;

[0012] Cold separation tank, with a second gas-phase transfer pipe and a recycle hydrogen pipe at the top, a first feed inlet in the middle, and a third bottom liquid output pipe and a fourth bottom liquid output pipe at the bottom; the aforementioned first feed inlet is connected to the aforementioned first gas-phase transfer pipe;

[0013] Heat exchanger, having a second feed inlet, a first discharge outlet, a first heat exchange unit, a second heat exchange unit, and a third heat exchange unit

[0014] Oil-gas separation tank, with a fourth gas-phase transfer pipe at the top, a third feed inlet in the middle, and a liquid-phase condensate oil pipe at the bottom; the aforementioned fourth gas-phase transfer pipe passes through the aforementioned third heat exchange unit and can lead to the PSA unit; the aforementioned liquid-phase condensate oil pipe passes through the aforementioned first heat exchange unit;

[0015] Chilled water pipe, passing through the aforementioned second heat exchange unit; and

[0016] Mixed oil-gas pipe, with the feed end connected to the first discharge outlet of the heat exchanger and the discharge end connected to the third feed inlet of the oil-gas separation tank;

[0017] The aforementioned first bottom liquid output pipe is connected and merged with the third bottom liquid output pipe and the second gas-phase transfer pipe and then enters the second feed inlet of the aforementioned heat exchanger, and the aforementioned second bottom liquid output pipe is merged with the fourth bottom liquid output pipe and the outlet end of the liquid-phase condensate oil pipe.

[0018] Furthermore, an air cooler for cooling is provided on the aforementioned first gas-phase transfer pipe.

[0019] Furthermore, a first valve is provided on the second gas-phase transfer pipe. Second valves and third valves are respectively provided on the connecting pipelines of the first bottom liquid output pipe and the third bottom liquid output pipe.

[0020] The technical solution adopted by the present invention to solve the above-mentioned third technical problem is: a method for removing trace aromatics, using a device for removing trace aromatics, wherein the mass ratio of absorption oil to tail hydrogen in the material entering the second feed inlet is 1:1 to 4:3; the hydrogen in the second gas-phase transfer pipe is 5% to 15%, and the hydrogen in the recycle hydrogen pipe is 85% to 95%; the temperature of the mixed oil and gas in the first discharge outlet of the heat exchanger is not higher than 15°C; the temperature of the condensed oil after heat exchange in the liquid-phase condensate oil pipe is not lower than 50°C; the temperature of the tail hydrogen after heat exchange in the four-gas-phase transfer pipe is not higher than 50°C; the temperature of the chilled water in the chilled water pipe is 10 to 15°C.

[0021] Compared with the prior art, the advantages of the present invention are as follows: The present invention no longer relies on a reforming unit. A part of the liquid phase and the bottom oil separated by the thermal separation tank of the disproportionation and transalkylation reaction products is shunted as absorption oil to absorb the heavy components (trace aromatics (main) and C5+ petroleum hydrocarbons (secondary)) in the disproportionation tail hydrogen. Moreover, the removal rate (by mass) of the removed aromatics can reach 80%, and the removal rate (by mass) of C5+ petroleum hydrocarbons can reach 74%. After the absorption oil absorbs the heavy components in the tail hydrogen, it converges with the liquid phase of the two product separation tanks and continues with other processes, effectively recovering the aromatic resources therein and reducing the loss of a part of the aromatics during the disproportionation and transalkylation production process. And under the conditions given in the present invention, the consumption of chilled water can be greatly reduced, and the chilled water resources can be utilized efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The present invention will be further described in detail below in conjunction with the embodiments of the drawings.

[0024] As Figure 1 shown, the device for removing trace aromatics from the disproportionation and transalkylation tail hydrogen in this embodiment includes a thermal separation tank 1, a cold separation tank 2, a heat exchanger 3, an oil and gas separation tank 4, a chilled water pipe 36, and a mixed oil and gas pipe 35.

[0025] The top of the thermal separation tank 1 is provided with a first gas-phase conveying pipe 14, and the bottom is provided with a first bottom liquid output pipe 12 and a second bottom liquid output pipe 13; the top of the cold separation tank 2 is provided with a second gas-phase conveying pipe 22 and a recycle hydrogen pipe 23, the middle is provided with a first feed port 21, and the bottom is provided with a third bottom liquid output pipe 24 and a fourth bottom liquid output pipe 25; the first feed port 21 is connected to the first gas-phase conveying pipe 14;

[0026] The heat exchanger 3 has a second feed port 34, a first discharge port, a first heat exchange unit 31, a second heat exchange unit 32, and a third heat exchange unit 33; the top of the oil and gas separation tank 4 is provided with a fourth gas-phase conveying pipe 41, the middle is provided with a third feed port 42, and the bottom is provided with a liquid-phase condensation oil pipe 43. The fourth gas-phase conveying pipe 41 passes through the third heat exchange unit 33 and can lead to the PSA device; the liquid-phase condensation oil pipe 43 passes through the first heat exchange unit 31;

[0027] The chilled water pipe 36 passes through the second heat exchange unit 32; the feed end of the mixed oil and gas pipe 35 is connected to the first discharge port of the heat exchanger 3, and the discharge end is connected to the third feed port 42 of the oil and gas separation tank.

[0028] The first bottom liquid output pipe 12 is connected and merged with the third bottom liquid output pipe 24 and the second gas-phase transfer pipe 22, and then enters the second feed port 34 of the heat exchanger 3. The second bottom liquid output pipe 13 is merged with the fourth bottom liquid output pipe 25 and the oil outlet end of the liquid-phase condensate oil pipe 43.

[0029] An air cooler 15 for cooling is provided on the first gas-phase transfer pipe 14. A first valve 51 is provided on the second gas-phase transfer pipe 22. Second valves 52 and third valves 53 are respectively provided on the connecting pipelines of the first bottom liquid output pipe 12 and the third bottom liquid output pipe 24.

[0030] Using the above device for the method of removing trace aromatics, wherein, the mass ratio of the absorption oil to the tail hydrogen in the material entering the second feed port 34 is 1:1 to 4:3; the hydrogen in the second gas-phase transfer pipe 22 is 5% to 15%, and the hydrogen in the recycle hydrogen pipe 23 is 85% to 95%; the temperature of the mixed oil and gas in the first discharge port of the heat exchanger 3 is not higher than 15°C; the temperature of the condensed oil after heat exchange in the liquid-phase condensate oil pipe 43 is not lower than 50°C; the temperature of the tail hydrogen after heat exchange in the fourth gas-phase transfer pipe 41 is not higher than 50°C; the temperature of the chilled water in the chilled water pipe 36 is 10 to 15°C.

[0031] The mixture or single material of the bottom liquid of the hot separation tank 1 and the bottom liquid of the cold separation tank 2 is used as the absorption oil and the tail hydrogen of the disproportionation and alkyl transfer unit are merged and then enter the multi-stream heat exchanger 3. Another stream is merged with the liquid phase output from the cold separation tank 2 and the condensed oil after heat exchange and then enters the subsequent fractionation unit for treatment. The gas phase output from the top of the hot separation tank 1 enters the air cooler 15 for cooling and then is input from the middle of the cold separation tank 2 for secondary gas-liquid separation.

[0032] The liquid phase output from the bottom discharge port of the cold separation tank 2 is divided into two streams. One stream is used as the absorption oil and merged with the tail hydrogen. The other stream is merged with the liquid phase output from the bottom of the hot separation tank 2 and the condensed oil after heat exchange. The gas phase output from the top is divided into two streams. One stream is used as the recycle hydrogen, and the other stream is used as the tail hydrogen of the disproportionation and alkyl transfer unit and merged with the absorption oil and then enters the multi-stream heat exchanger 3.

[0033] The temperature of the mixed oil and gas does not exceed 15°C after being cooled three times by the multi-stream heat exchanger 3, and enters the oil and gas separation tank 4 from the middle of the oil and gas separation tank 4 for gas-liquid separation. The first time it exchanges heat with the liquid-phase condensed oil output from the bottom of the oil and gas separation tank 4, and the temperature of the condensed oil after heat exchange is not lower than 50°C; the second time it exchanges heat with the tail hydrogen after separation output from the top of the oil and gas separation tank 4, and the temperature of the tail hydrogen after heat exchange is not higher than 50°C; the third time it exchanges heat with the chilled water at 5°C, and the return water temperature of the chilled water is between 10 and 15°C.

[0034] The mixed oil and gas enters the oil and gas separation tank 4 from the middle of the oil and gas separation tank 4. After gas-liquid separation, the liquid-phase condensed oil is output from the bottom of the oil and gas separation tank 4 and then enters a multi-stream heat exchanger for heat exchange, and then converges with the bottom liquid of the thermal separation tank and the bottom liquid of the cold separation tank 2; the gas-phase hydrogen tail after separation is output from the top of the oil and gas separation tank 4 and then enters a multi-stream heat exchanger for heat exchange, and then goes to the PSA unit for purification.

Claims

1. An apparatus for removing trace aromatics by re - contacting the tail hydrogen in disproportionation and alkyl transfer, characterized in that including a thermal separation tank (1) with a first gas-phase transfer pipe (14) at the top end, a first bottom liquid output pipe (12) and a second bottom liquid output pipe (13) at the bottom end; a cold separation tank (2) with a second gas-phase transfer pipe (22) and a recycle hydrogen pipe (23) at the top, a first feed inlet (21) in the middle, a third bottom liquid output pipe (24) and a fourth bottom liquid output pipe (25) at the bottom; the aforementioned first feed inlet (21) is connected to the aforementioned first gas-phase transfer pipe (14); a heat exchanger (3) having a second feed inlet (34), a first discharge outlet, a first heat exchange unit (31), a second heat exchange unit (32) and a third heat exchange unit (33) an oil-gas separation tank (4) with a fourth gas-phase transfer pipe (41) at the top, a third feed inlet (42) in the middle, and a liquid-phase condensate oil pipe (43) at the bottom; the aforementioned fourth gas-phase transfer pipe (41) passes through the aforementioned third heat exchange unit (33) and can lead to a PSA unit; the aforementioned liquid-phase condensate oil pipe (43) passes through the aforementioned first heat exchange unit (31); a chilled water pipe (36) passing through the aforementioned second heat exchange unit (32); and a mixed oil-gas pipe (35) with the feed end connected to the first discharge outlet of the heat exchanger (3) and the discharge end connected to the third feed inlet (42) of the oil-gas separation tank; the aforementioned first bottom liquid output pipe (12) is connected and merged with the third bottom liquid output pipe (24) and the second gas-phase transfer pipe (22) and then enters the second feed inlet (34) of the aforementioned heat exchanger (3), and the aforementioned second bottom liquid output pipe (13) is merged with the fourth bottom liquid output pipe (25) and the outlet end of the liquid-phase condensate oil pipe (43).

2. The device for removing trace aromatics by disproportionation and alkyl transfer tail hydrogen recontacting according to claim 1, characterized in that An air cooler (15) for cooling is provided on the aforementioned first gas-phase transfer pipe (14).

3. The device for removing trace aromatics by disproportionation and alkyl transfer tail hydrogen recontacting according to claim 1, characterized in that A first valve (51) is provided on the aforementioned second gas-phase transfer pipe (22).

4. The device for removing trace aromatics by disproportionation and alkyl transfer tail hydrogen re-contact according to claim 1, characterized in that Second valves (52) and third valves (53) are respectively provided on the connecting pipelines of the aforementioned first bottom liquid output pipe (12) and the third bottom liquid output pipe (24).

5. A method for removing trace aromatics using any one of the devices according to claims 1 to 4, characterized in that the mass ratio of the absorption oil to the tail hydrogen in the material entering the second feed inlet (34) is 1:1 to 4:3; the hydrogen in the second gas-phase transfer pipe (22) is 5% to 15%, and the hydrogen in the recycle hydrogen pipe (23) is 85% to 95%; the temperature of the mixed oil and gas in the first discharge outlet of the heat exchanger (3) is not higher than 15°C; the temperature of the condensed oil after heat exchange in the liquid-phase condensate oil pipe (43) is not lower than 50°C; the temperature of the tail hydrogen after heat exchange in the fourth gas-phase transfer pipe (41) is not higher than 50°C; the temperature of the chilled water in the chilled water pipe (36) is 10 to 15°C.

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