Device for removing trace aromatics in disproportionation and alkyl transfer tail hydrogen by re-contact and its removal method

Abstract

An apparatus for re - contacting and removing trace aromatics from the tail hydrogen of disproportionation and alkyl transfer is characterized by comprising a thermal separation tank, a cold separation tank, a heat exchanger, a tail hydrogen cooler, an oil - gas separation tank, a chilled water pipe and a mixed oil - gas pipe. The top of the thermal separation tank is provided with a first gas - phase transfer pipe, and the bottom is provided with a first bottom - liquid output pipe and a second bottom - liquid output pipe; the top of the cold separation tank is provided with a second gas - phase transfer pipe and a recycle hydrogen pipe, the middle part is provided with a first feed inlet, and the bottom is provided with 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, uses a part of the bottom oil of the thermal separation tank or the bottom oil of the cold separation tank or a mixture of the two oils of the disproportionation and alkyl transfer unit as the 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, and in particular to a treatment device for disproportionation and alkyl transfer tail hydrogen. 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. At present, 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). 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" (Publication No.: CN205228000U) with the patent number ZL201521096228.1. 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. The 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 the 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 second-to-last-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 with the reformate, and then successively enters the re-contact refrigerator for cooling and the last-stage re-contact tank for gas-liquid separation. The separated liquid phase returns to the previous-stage re-contact tank or enters the product separation unit after recovering cold energy, and the separated gas phase is used as the feed gas of the pressure swing adsorption device, or part of it 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 rely on the re-contact device in the reforming unit, increasing 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, where 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 absorbed by the reforming absorption oil and will not return to the disproportionation and alkylation transfer device. Therefore, the existing patent technologies require the re-contact device of the reforming to have 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, in view of the above technical status, an additional device for removing trace aromatics in the tail hydrogen of disproportionation and alkylation transfer by re-contact.

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

[0009] The third technical problem to be solved by the present invention is to provide, in view of the above technical status, a method for removing trace aromatics in the tail hydrogen of disproportionation and alkylation transfer without relying on the reforming unit.

[0010] The technical solutions adopted by the present invention to solve the above first and second technical problems are as follows: The device for removing trace aromatics in the tail hydrogen of disproportionation and alkylation transfer by re-contact includes

[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] The cold separation tank has 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] The heat exchanger has a second feed inlet, a first discharge outlet, a first heat exchange unit, and a second heat exchange unit;

[0014] The tail gas cooler has a feed inlet and a discharge outlet, and the feed inlet of the tail gas cooler is connected to the first discharge outlet of the heat exchanger;

[0015] The oil-gas separation tank has 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 second 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;

[0016] The chilled water pipe passes through the aforementioned tail gas cooler; and

[0017] The mixed oil-gas pipe has its feed end connected to the discharge outlet of the tail gas cooler and its discharge end connected to the third feed inlet of the oil-gas separation tank;

[0018] After 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, it enters the second feed inlet of the aforementioned heat exchanger. 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.

[0019] Further, an air cooler for temperature reduction is provided on the aforementioned first gas-phase transfer pipe.

[0020] Further, 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.

[0021] The technical solution adopted by the present invention to solve the above-mentioned third technical problem is: a method for removing trace aromatics from tail hydrogen in disproportionation and alkyl transfer, characterized in that

[0022] In the material entering the second feed inlet, the mass ratio of the absorption oil to the tail hydrogen is 1:1 to 4:3;

[0023] The hydrogen flow rate ratio in the second gas-phase transfer pipe is 5% to 15%, and the hydrogen flow rate ratio in the recycle hydrogen pipe (23) is 85% to 95%;

[0024] The temperature of the mixed oil and gas in the discharge outlet of the tail gas cooler is not higher than 15°C;

[0025] The return water temperature in the chilled water pipe is between 10 and 15°C;

[0026] The temperature of the condensed oil after heat exchange in the liquid-phase condensation oil pipe is not lower than 50 °C;

[0027] The temperature of the tail hydrogen after heat exchange in the fourth gas-phase transfer pipe is not higher than 50 °C;

[0028] The temperature of the chilled water in the chilled water pipe is 5 - 15 °C.

[0029] Compared with the prior art, the advantages of the present invention are as follows: The present invention no longer needs to rely on a reforming unit. It uses a part of the bottom oil of the thermal separation tank or the cold separation tank or a mixture of the two bottom oils of the disproportionation and alkyl transfer unit as the absorption oil to absorb the heavy components (trace aromatics (main) and C5+ petroleum hydrocarbons (secondary)) in the disproportionation tail hydrogen. And 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 other process treatments, which can effectively recover the aromatic resources therein and reduce the loss of a part of the aromatics in the disproportionation and alkyl transfer 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

[0030] Figure 1 It is a schematic structural diagram of an embodiment. Detailed Description of the Invention

[0031] The present invention will be further described in detail below in conjunction with the embodiments with reference to the drawings.

[0032] As Figure 1 shown, the device for re-contact to remove trace aromatics in the disproportionation and alkyl transfer tail hydrogen in this embodiment includes a thermal separation tank 1, a cold separation tank 2, a heat exchanger 3, a tail gas cooler 6, an oil-gas separation tank 4, a chilled water pipe 36 and a mixed oil-gas pipe 35.

[0033] The top of the thermal separation tank 1 is provided with a first gas-phase transfer pipe 14, and the bottom is provided with a first bottom liquid output pipe 12 and a second bottom liquid output pipe 13.

[0034] The top of the cold separation tank 2 is provided with a second gas-phase transfer 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 transfer pipe 14.

[0035] The heat exchanger 3 has a second feed inlet 34, a first discharge outlet, a first heat exchange unit 31, and a second heat exchange unit 32. The tail gas cooler 6 has a feed inlet and a discharge outlet, and the feed inlet of the tail gas cooler 6 is connected to the first discharge outlet of the heat exchanger; the top of the oil-gas separation tank 4 has a fourth gas-phase transfer pipe 41, the middle has a third feed inlet 42, and the bottom has a liquid-phase condensate oil pipe 43. The fourth gas-phase transfer pipe 41 passes through the second heat exchange unit 32 and can lead to the PSA device; the liquid-phase condensate oil pipe 43 passes through the first heat exchange unit 31; the chilled water pipe 36 passes through the tail gas cooler 6.

[0036] The feed end of the mixed oil and gas pipe 35 is connected to the discharge outlet of the tail gas cooler 6, and the discharge end is connected to the third feed inlet 42 of the oil-gas separation tank 4.

[0037] 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 inlet 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 outlet end of the liquid-phase condensate oil pipe 43.

[0038] 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.

[0039] For the method of removing trace aromatics using the above device, among them, 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 flow rate ratio in the second gas-phase transfer pipe 22 is 5% to 15%, and the hydrogen flow rate ratio in the recycle hydrogen pipe 23 is 85% to 95%; the temperature of the mixed oil and gas in the discharge outlet of the tail gas cooler 6 is not higher than 15°C; the return water temperature in the chilled water pipe 36 is between 10 and 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 5 to 15°C.

[0040] The mixture or single material of the bottom liquid of the thermal separation tank 1 and the bottom liquid of the cold separation tank 2 enters the multi-stream heat exchanger 3 as the absorption oil and the tail hydrogen of the disproportionation and alkyl transfer unit after convergence. Another stream converges 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 thermal 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.

[0041] The liquid phase output from the bottom discharge port of the cold separation tank 2 is divided into two streams. One stream serves as absorption oil and converges with the tail hydrogen, and the other stream converges with the liquid phase output from the bottom of the thermal separation tank 2 and the condensed oil after heat exchange. The gas phase output from the top is divided into two streams. One stream serves as recycle hydrogen, and the other stream serves as the tail hydrogen of the disproportionation and alkyl transfer unit. After converging with the absorption oil, it enters the multi-stream heat exchanger 3.

[0042] After being cooled twice by the multi-stream heat exchanger 3, the temperature of the mixed oil and gas is not higher than 50°C, and then it is cooled to below 15°C by the tail hydrogen cooler 6 and enters the oil and gas separation tank 4 from the middle of the oil and gas separation tank 4 for gas-liquid separation. It exchanges heat with the condensed oil, the liquid phase output from the bottom of the oil and gas separation tank 4 for the first time, and the temperature of the condensed oil after heat exchange is not lower than 50°C; it exchanges heat with the tail hydrogen after separation, the gas phase output from the top of the oil and gas separation tank 4 for the second time, and the temperature of the tail hydrogen after separation after heat exchange is not higher than 50°C; the mixed oil and gas after heat exchange enters the tail hydrogen cooler 6 for further cooling and exchanges heat with the chilled water, and the return water temperature of the chilled water is between 10 and 15°C.

[0043] 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 the 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 tail hydrogen after separation, the gas phase output from the top of the oil and gas separation tank 4 enters the multi-stream heat exchanger for heat exchange and then goes to the PSA unit for purification.

Claims

1. An apparatus for removing trace aromatics in the tail hydrogen of disproportionation and alkyl transfer by re - contact, 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) with a second feed inlet (34), a first discharge port, a first heat exchange unit (31), and a second heat exchange unit (32); a tail gas cooler (6) with a feed inlet and a discharge port, and the feed inlet of the tail gas cooler (6) is connected to the first discharge port of the heat exchanger; 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 second heat exchange unit (32) and can lead to the 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 tail gas cooler (6); and a mixed oil-gas pipe (35) with the feed end connected to the discharge port of the tail gas cooler (6) and the discharge end connected to the third feed inlet (42) of the oil-gas separation tank (4); the aforementioned first bottom liquid output pipe (12) is connected to the third bottom liquid output pipe (24) and the second gas-phase transfer pipe (22), and after convergence, it enters the second feed inlet (34) of the aforementioned heat exchanger (3). The aforementioned second bottom liquid output pipe (13) converges 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 in the tail hydrogen of disproportionation and alkyl transfer by re-contact according to claim 1, characterized in that An air cooler (15) for temperature reduction is provided on the aforementioned first gas-phase transfer pipe (14).

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

4. The device for removing trace aromatics in the tail hydrogen of disproportionation and alkyl transfer by 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 in a device for removing trace aromatics in the tail hydrogen of disproportionation and alkyl transfer by recontacting using the device according to any one of claims 1 to 4, characterized in that the mass ratio of absorption oil to tail hydrogen in the material entering the second feed inlet (34) is 1:1 to 4:3; the hydrogen flow rate ratio in the second gas-phase transfer pipe (22) is 5% to 15%, and the hydrogen flow rate ratio in the recycle hydrogen pipe (23) is 85% to 95%; the temperature of the mixed oil and gas in the discharge port of the tail gas cooler (6) is not higher than 15°C; the return water temperature in the chilled water pipe (36) is between 10 and 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 5 to 15°C.

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