Fischer-Tropsch synthesis tail gas recovery system and recovery method

Abstract

The invention discloses a Fischer-Tropsch synthesis tail gas recovery system and method, and the Fischer-Tropsch synthesis tail gas recovery system comprises a gas-liquid separator, a heater, a membrane separation unit and a permeate gas collection unit which are sequentially communicated through a pipeline; the emptying unit is connected with the gas outlet end of the gas-liquid separator through a first emptying pipeline, the emptying unit is connected with the pipeline between the heater and the membrane separation unit through a second emptying pipeline, and the bottom of the gas-liquid separator is connected with a liquid level adjusting pipeline; and the compensation unit is connected with the permeated gas collection unit through a compensation pipeline so as to provide crude target gas for the permeated gas collection unit. According to the invention, the safe operation efficiency of the membrane separation group can be improved, and the membrane separation group can be timely protected from being damaged in an abnormal working condition; the service cycle of the membrane separation group is prolonged, and stable operation of a downstream device is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of Fischer-Tropsch synthesis tail gas recovery, and in particular to a Fischer-Tropsch synthesis tail gas recovery system and recovery method. Background Art

[0002] The Fischer-Tropsch synthesis tail gas separation and recovery method is a hydrogen recovery and purification method that is currently widely used. This method can provide an effective hydrogen source and improve the utilization rate of raw carbon. The Fischer-Tropsch synthesis tail gas separation and recovery method is applied to the Fischer-Tropsch synthesis tail gas recovery system. After the hydrocarbons are removed from the raw gas, it enters the membrane separation unit to separate the permeate gas with high hydrogen content and the non-permeate gas with low hydrogen content. The permeate gas is sent to the pressure swing adsorption device for further purification, and the non-permeate gas is sent to the fuel gas pipeline network, or catalytic oxidation technology is used to continue to produce hydrogen. The system runs smoothly and has strong operability, but with the expansion of scale, problems such as fluctuations in Fischer-Tropsch tail gas parameters, low tail gas separation process load, high non-permeate gas emissions and low hydrogen yields have restricted the development of the process and affected the economic benefits.

[0003] In the prior art, the membrane separation group is the core equipment of the membrane separation unit, which has strict requirements on the temperature, pressure, flow rate and other factors of the raw gas. When the membrane separation unit and the upstream unit fluctuate, the operation and life of the membrane separation group will be affected. Under abnormal conditions, the Fischer-Tropsch tail gas parameters exceed the requirements of the existing membrane separation group, resulting in the inability to achieve the separation and recovery function, and damaging the life of the membrane separation group. It is impossible to achieve dynamic adjustment of the Fischer-Tropsch tail gas separation system under different working conditions, which increases the instability of the system operation. Summary of the invention

[0004] The present invention aims to at least solve the technical problems existing in the prior art that under abnormal operating conditions, the Fischer-Tropsch tail gas parameters exceed the requirements of the existing membrane separation group, resulting in the inability to achieve the separation and recovery function, damaging the life of the membrane separation group, and failing to achieve dynamic adjustment of the Fischer-Tropsch tail gas separation system under different operating conditions.

[0005] To this end, an object of the present invention is to provide a Fischer-Tropsch synthesis tail gas recovery system, the Fischer-Tropsch synthesis tail gas recovery system comprising a gas-liquid separator, a heater, a membrane separation unit and a permeate gas collection unit which are sequentially connected through pipelines; and

[0006] A venting unit, wherein the venting unit is connected to the gas outlet end of the gas-liquid separator through a first venting pipeline, the venting unit is connected to the pipeline between the heater and the membrane separation unit through a second venting pipeline, and the bottom of the gas-liquid separator is connected to a liquid level regulating pipeline;

[0007] A compensation unit is connected to the permeate gas collection unit through a compensation pipeline to provide a crude target gas to the permeate gas collection unit.

[0008] In some embodiments, the gas-liquid separator is provided with a liquid level detector for detecting the liquid level therein, the heater is provided with a temperature detector for detecting the steam temperature, and the membrane separation unit is provided with a pressure detector for detecting its inlet and outlet pressures.

[0009] In some embodiments, a first vent valve is disposed on the first vent pipeline, a second vent valve is disposed on the second vent pipeline, and a liquid level regulating valve is disposed on the liquid level regulating pipeline.

[0010] In some embodiments, a first safety valve is provided on the first pipeline between the gas-liquid separator and the heater, and the first safety valve is provided downstream of the connection between the first vent pipeline and the first pipeline;

[0011] The inlet and outlet pipelines of the membrane separation unit are respectively provided with a second safety valve and a third safety valve, and the second safety valve is arranged downstream of the connection between the second vent pipeline and the inlet pipeline of the membrane separation unit.

[0012] In some embodiments, a temperature regulating valve and a steam quick shut-off valve are provided on the low-pressure steam inlet pipeline of the heater.

[0013] In some embodiments, the compensation pipeline is provided with a flow detector or a compensation pressure detector, and a flow regulating valve connected to the flow detector or the compensation pressure detector.

[0014] In some embodiments, the Fischer-Tropsch synthesis tail gas recovery system further comprises a compressor disposed between the membrane separation unit and the permeate gas collection unit, and a first control valve is disposed on the pipeline between the compressor and the permeate gas collection unit; and / or

[0015] The Fischer-Tropsch synthesis tail gas recovery system further includes a filter arranged between the gas-liquid separator and the heater.

[0016] In some embodiments, the permeate gas collection unit includes a PSA pressure swing adsorption hydrogen production unit.

[0017] In some embodiments, the Fischer-Tropsch synthesis tail gas recovery system further includes a non-permeate gas collection unit connected to the membrane separation unit.

[0018] Another object of the present invention is to provide a method for recovering tail gas from Fischer-Tropsch synthesis, which utilizes the above-mentioned tail gas recovery system for Fischer-Tropsch synthesis to recover permeate gas, and utilizes the permeate gas to prepare hydrogen.

[0019] A Fischer-Tropsch synthesis tail gas recovery system and recovery method provided by an embodiment of the present invention have the following beneficial effects:

[0020] By providing a venting unit connected through the first venting pipeline and the second venting pipeline, the operating conditions of the Fischer-Tropsch synthesis tail gas recovery system can be monitored in real time, and timely and effective protection measures are taken for the occurrence of various abnormal conditions to protect the membrane separation group from damage, thereby indirectly extending the service life of the membrane separation group;

[0021] The permeate gas collection unit is connected to a compensation unit. When the operating condition of the membrane separation group is abnormal, the membrane separation group stops working, and the raw gas of the downstream permeate gas collection unit is replenished by the crude target gas in time, which does not affect the normal operation of the permeate gas collection unit, and continuously provides hydrogen for the downstream process section, thereby realizing the stable operation of the Fischer-Tropsch synthesis tail gas recovery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 Schematic diagram of a Fischer-Tropsch synthesis tail gas recovery system according to an embodiment of the present invention.

[0024] Reference numerals:

[0025] 1. Gas-liquid separator; 2. Heater; 3. Membrane separation unit; 4. Permeate gas collection unit; 5. Vent unit; 6. Compensation unit; 7. Filter; 8. Liquid level detector; 9. Temperature detector; 10. Pressure detector; 11. First vent valve; 12. Second vent valve; 13. Liquid level regulating valve; 14. First safety valve; 15. Second safety valve; 16. Third safety valve; 17. Temperature regulating valve; 18. Steam quick shut-off valve; 19. Flow detector; 20. Compressor; 21. First control valve; 22. Flow regulating valve; 23. Non-permeate gas collection unit; 24. Second control valve; 25. Third control valve; 26. Pressure regulating valve; 100. First vent pipeline; 200. Second vent pipeline; 300. Liquid level regulating pipeline; 400. Compensation pipeline; 500. Low-pressure steam inlet pipeline. DETAILED DESCRIPTION

[0026] Various aspects and features of the present invention are described herein with reference to the accompanying drawings.

[0027] It should be understood that various modifications may be made to the embodiments of the present application. Therefore, the above description should not be considered as limiting, but only as an example of the embodiments. Other modifications within the scope and spirit of the present invention will occur to those skilled in the art.

[0028] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

[0029] These and other characteristics of the invention will become apparent from the following description of a preferred form of embodiment given as a non-limiting example, with reference to the accompanying drawings.

[0030] It should also be understood that, although the invention has been described with reference to some specific examples, those skilled in the art will be able to realize many other equivalent forms of the invention that have the characteristics recited in the claims and are therefore within the scope of protection defined thereby.

[0031] The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

[0032] Specific embodiments of the present invention are described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments claimed are merely examples of the present invention, which may be implemented in a variety of ways. Well-known and / or repeated functions and structures are not described in detail to avoid obscuring the present invention with unnecessary or redundant details. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as a basis and representative basis for the claims to teach those skilled in the art to use the present invention in a variety of ways with substantially any suitable detailed structure.

[0033] The first embodiment of the present invention provides a Fischer-Tropsch synthesis tail gas recovery system, such as Figure 1 As shown, the Fischer-Tropsch synthesis tail gas recovery system comprises a gas-liquid separator 1, a heater 2, a membrane separation unit 3 and a permeate gas collection unit 4 which are sequentially connected through pipelines; and,

[0034] The venting unit 5 is connected to the gas outlet end of the gas-liquid separator 1 through a first venting pipeline 100, and the venting unit 5 is connected to the pipeline between the heater 2 and the membrane separation unit 3 through a second venting pipeline 200. The bottom of the gas-liquid separator 1 is connected to a liquid level regulating pipeline 300;

[0035] The compensation unit 6 is connected to the permeate gas collection unit 4 through the compensation pipeline 400 to provide the crude target gas to the permeate gas collection unit 4. Among them, the gas-liquid separator 1 is used to remove the liquid in the liquid-containing gas, and the raw gas of the Fischer-Tropsch synthesis tail gas can be obtained after the Fischer-Tropsch synthesis tail gas is separated by gas and liquid through the gas-liquid separator 1; the heater 2 is used to heat the raw gas of the Fischer-Tropsch synthesis tail gas to obtain high-temperature raw gas; the membrane separation unit 3 is used to perform membrane separation on the high-temperature raw gas heated by the heater 2 to obtain permeate gas according to the different permeabilities and selectivities of different polymer membranes to different types of gas molecules; the permeate gas collection unit 4 is used to collect the permeate gas separated by the membrane separation unit 3, and then use the permeate gas to prepare the target gas. The target gas can be at least one of hydrogen (H2), nitrogen (N2), carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO). Since hydrogen is the gas with the smallest density and the lightest weight and has a strong permeability, the membrane separation unit 3 can separate permeate gas with high hydrogen content and non-permeate gas with low hydrogen content. The membrane separation unit 3 can also use an oxygen-rich separation membrane or a nitrogen-rich separation membrane to separate O2 or N2 from the mixed gas of O2 and N2. The oxygen-rich separation membrane has a higher permeability to O2, and can obtain O2 as a permeate gas (N2 is a non-permeate gas at this time); while the nitrogen-rich separation membrane has a higher permeability to N2, and can obtain N2 as a permeate gas (O2 is a non-permeate gas at this time). In this embodiment, the target gas is hydrogen, and the Fischer-Tropsch synthesis tail gas recovery system is specifically described.

[0036] After the Fischer-Tropsch synthesis tail gas is processed in sequence by the gas-liquid separator 1, the heater 2 and the membrane separation unit 3, the permeate gas can be separated and collected by the permeate gas collection unit 4 to realize the separation and recovery of the Fischer-Tropsch synthesis tail gas. During the separation and recovery of the Fischer-Tropsch synthesis tail gas, if an abnormal operating condition occurs, the raw gas of the Fischer-Tropsch synthesis tail gas after gas-liquid separation can be discharged to the venting unit 5 through the first venting pipeline 100, or the heated high-temperature raw gas can be discharged to the venting unit 5 through the second venting pipeline 200 before the raw gas enters the membrane separation unit 3, and the liquid level in the gas-liquid separator 1 is adjusted through the liquid level regulating pipeline 300, thereby adjusting the flow rate of the raw gas of the Fischer-Tropsch synthesis tail gas, so that the membrane group of the membrane separation unit 3 is kept under pressure, and the recovery system is driven to reduce the load or shut down; since the permeate gas flowing into the permeate gas collection unit 4 after venting is reduced (the raw gas used to prepare the target gas is reduced), the compensation unit 6 can be used to provide the crude target gas to the permeate gas collection unit 4 to maintain the normal operation of the permeate gas collection unit 4. The crude target gas comes from a coal gasification device, and its gas type is determined according to the gas type of the above-mentioned target gas. For example, in this embodiment, the main component of the crude target gas is hydrogen. Illustratively, when an abnormal condition occurs in the gas-liquid separator 1, the raw gas of the Fischer-Tropsch synthesis tail gas after gas-liquid separation is discharged to the venting unit 5 and / or the liquid level regulating pipeline 300 to adjust the liquid level in the gas-liquid separator 1, and at the same time, the compensation unit 6 provides the crude target gas to the permeate gas collection unit 4 to achieve normal operation of the permeate gas collection work until the gas-liquid separator 1 returns to normal; when an abnormal condition occurs in the heater 2, the gas treated by the gas-liquid separator 1 is discharged to the venting unit 5 through the second venting pipeline 200, and at the same time, the compensation unit 6 provides the crude target gas to the permeate gas collection unit 4 to achieve normal operation of the permeate gas collection work until the heater 2 returns to normal; when an abnormal condition occurs in the membrane separation unit 3, the gas heated by the heater 2 is discharged to the venting unit 5 through the second venting pipeline 200, and at the same time, the compensation unit 6 provides the crude target gas to the permeate gas collection unit 4 to achieve normal operation of the permeate gas collection work until the membrane separation unit 3 returns to normal.

[0037] By setting up the venting unit 5, timely and effective protection measures are taken for the occurrence of various abnormal operating conditions, thereby protecting the membrane separation unit 3 from damage and extending the service life of the membrane separation unit 3; by setting up the compensation unit 6, the synthesis gas (crude target gas) can be replenished to the permeate gas collection unit 4 in time without affecting the normal operation of the permeate gas collection unit 4, thereby achieving stable operation of the entire system.

[0038] The present invention has the advantages of clear process system control, convenient operation, high process integration, and can significantly ensure the safe and stable operation of the membrane separation unit 3, improve the economic benefits of the Fischer-Tropsch synthesis tail gas recovery system, and has a wide range of applications. It has practical value for the recovery and utilization of tail gas converted into liquid fuel from any carbon-containing resource such as coal, natural gas, and biomass.

[0039] The heater 2 is preferably a steam heater, including a low-pressure steam inlet pipeline 500, and can utilize the low-pressure steam to heat the raw gas of the Fischer-Tropsch synthesis tail gas.

[0040] In some embodiments, the Fischer-Tropsch synthesis tail gas recovery system further includes a filter 7 disposed between the gas-liquid separator 1 and the heater 2. The gas at the outlet of the gas-liquid separator 1 is filtered by the filter 7 to separate impurities in the gas entering the heater 2, thereby improving the separation effect of the Fischer-Tropsch synthesis tail gas.

[0041] In some embodiments, the gas-liquid separator 1 is provided with a liquid level detector 8 for detecting the liquid level therein, the heater 2 is provided with a temperature detector 9 for detecting the steam temperature, and the membrane separation unit 3 is provided with a pressure detector 10 for detecting its inlet and outlet pressures.

[0042] The liquid level detector 8, temperature detector 9 and pressure detector 10 respectively perform safety monitoring on the gas-liquid separator 1, heater 2 and membrane separation unit 3 in the system. When an abnormal operating condition occurs in the upstream unit of the membrane separation unit 3, the operation and life of the membrane separation group of the membrane separation unit 3 will not be affected.

[0043] Specifically, the liquid level detector 8 detects the liquid level inside the gas-liquid separator 1. If it is detected that the liquid level in the gas-liquid separator 1 reaches the first liquid level threshold, the liquid level regulating pipeline 300 regulates the liquid level in the gas-liquid separator 1 to keep the gas-liquid separator 1 in normal operation; if it is detected that the liquid level in the gas-liquid separator 1 reaches the second liquid level threshold, the first venting pipeline 100 is turned on, and the gas enters the venting unit 5 through the first venting pipeline 100, wherein the second liquid level threshold is greater than the first liquid level threshold. The temperature detector 9 detects the temperature of the air flow from the heater 2. If it is detected that the steam temperature reaches the temperature threshold, the second venting pipeline 200 is turned on, and the gas enters the venting unit 5 through the second venting pipeline 200. The pressure detector 10 is used to detect the pressure of the inlet and outlet of the membrane separation unit 3, and further obtain the pressure difference of the inlet and outlet, or the pressure detector 10 directly detects the pressure difference of the inlet and outlet of the membrane separation unit 3. If the pressure difference of the inlet and outlet reaches the pressure difference threshold, the second venting pipeline 200 is turned on, and the gas is discharged to the venting unit 5 through the second venting pipeline 200.

[0044] In some embodiments, the Fischer-Tropsch synthesis tail gas recovery system further includes a liquid level alarm electrically connected to the liquid level detector 8, a temperature alarm electrically connected to the temperature detector 9, and a pressure difference alarm electrically connected to the pressure detector 10. When the liquid level in the gas-liquid separator 1 reaches the first liquid level threshold or the second liquid level threshold, the liquid level alarm sounds an alarm; when the air flow temperature from the heater 2 reaches the temperature threshold, the temperature alarm sounds an alarm; when the inlet and outlet pressure difference of the membrane separation unit 3 reaches the pressure difference threshold, the pressure difference alarm sounds an alarm. Setting up multiple alarms allows staff to quickly obtain abnormal operating condition information.

[0045] In some embodiments, a first vent valve 11 is provided on the first vent pipeline 100, a second vent valve 12 is provided on the second vent pipeline 200, and a liquid level regulating valve 13 is provided on the liquid level regulating pipeline 300. Both the first vent valve 11 and the second vent valve 12 can be stop valves or one-way valves, and the liquid level regulating valve 13 can be a flow control valve. The first vent valve 11 is used to control the conduction and cutoff of the first vent pipeline 100, the second vent valve 12 is used to control the conduction and cutoff of the second vent pipeline 200, and the liquid level regulating valve 13 is used to adjust the flow in the liquid level regulating pipeline 300, thereby adjusting the internal liquid level of the gas-liquid separator 1.

[0046] In some embodiments, a first safety valve 14 is provided on the first pipeline between the gas-liquid separator 1 and the heater 2, and the first safety valve 14 is provided downstream of the connection between the first venting pipeline 100 and the first pipeline;

[0047] The inlet and outlet pipelines of the membrane separation unit 3 are respectively provided with a second safety valve 15 and a third safety valve 16 . The second safety valve 15 is provided downstream of the connection between the second venting pipeline 200 and the inlet pipeline of the membrane separation unit 3 .

[0048] Specifically, the first safety valve 14, the second safety valve 15 and the third safety valve 16 can all be stop valves or one-way valves. The first safety valve 14 is arranged downstream of the connection between the first venting pipeline 100 and the first pipeline, so that when the first venting pipeline 100 is turned on, the gas at the outlet of the gas-liquid separator 1 can only flow to the venting unit 5 through the first venting pipeline 100 and cannot flow into the downstream pipeline of the gas-liquid separator 1. The second safety valve 15 is arranged at the inlet of the membrane separation unit 3, and is arranged downstream of the connection between the second venting pipeline 200 and the inlet pipeline of the membrane separation unit 3, so that when the second venting pipeline 200 is turned on, the gas at the outlet of the heater 2 can only flow to the venting unit 5 through the second venting pipeline 200 and cannot flow into the downstream pipeline of the heater 2. The third safety valve 16 is arranged at the outlet of the membrane separation unit 3, and cooperates with the second safety valve 15 to realize the pressure maintenance of the membrane separation unit 3.

[0049] In some embodiments, a temperature regulating valve 17 and a steam quick shut-off valve 18 are provided on the low-pressure steam inlet pipeline 500 of the heater 2. When the temperature of the airflow from the heater 2 is low and reaches a first low-temperature threshold, the temperature regulating valve 17 is adjusted to gradually open so that the low-pressure steam is quickly replenished into the heater 2; when the temperature of the airflow from the heater 2 reaches a first high-temperature threshold, the temperature regulating valve 17 is adjusted to gradually close, wherein the first high-temperature threshold is greater than the first low-temperature threshold.

[0050] The steam quick shut-off valve 18 realizes quick shut-off of the low-pressure steam supply in the low-pressure steam inlet pipeline 500 .

[0051] In some embodiments, a flow detector 19 or a compensation pressure detector and a flow regulating valve 22 connected to the flow detector 19 or the compensation pressure detector are provided on the compensation pipeline 400. The flow detector 19 can monitor the gas flow on the compensation pipeline 400 and adjust the flow through the flow regulating valve 22 to adapt it to the needs of the permeate gas collection unit 4. The compensation pressure detector monitors the pressure on the compensation pipeline 400 to play a role in safety protection.

[0052] The compensation pipeline 400 is provided with a second control valve 24 , wherein the second control valve 24 is preferably a one-way valve, so that the crude target gas can only flow in one direction along the compensation pipeline 400 to the permeate gas collection unit 4 .

[0053] In some embodiments, the Fischer-Tropsch synthesis tail gas recovery system further includes a compressor 20 disposed between the membrane separation unit 3 and the permeate gas collection unit 4 , and a first control valve 21 is disposed on the pipeline between the compressor 20 and the permeate gas collection unit 4 .

[0054] The compressor 20 provides driving force for the permeate gas collection unit 4, and the first control valve 21 is used to control the connection or cutoff between the compressor 20 and the permeate gas collection unit 4, wherein the first control valve 21 is preferably a one-way valve.

[0055] In this embodiment, the permeate gas collection unit 4 includes a PSA pressure swing adsorption hydrogen production unit, which can use the permeate gas with a high hydrogen content after the Fischer-Tropsch synthesis tail gas is separated to produce hydrogen.

[0056] In some embodiments, the Fischer-Tropsch synthesis tail gas recovery system further includes a non-permeate gas collection unit 23 connected to the membrane separation unit 3. The gas separated by the membrane separation unit 3 includes permeate gas and non-permeate gas, and the permeate gas is collected by the permeate gas collection unit 4 to further prepare target gases such as hydrogen; the non-permeate gas is collected by the non-permeate gas collection unit 23 and connected to the fuel gas pipeline network for further use. The non-permeate gas collection unit 23 can improve the gas utilization rate and realize the full recovery and utilization of the Fischer-Tropsch synthesis tail gas.

[0057] A third control valve 25 is provided on the pipeline connecting the non-permeable gas collection unit 23 and the membrane separation unit 3 , wherein the third control valve 25 is preferably a one-way valve, so that the non-permeable gas can only flow along the membrane separation unit 3 to the non-permeable gas collection unit 23 unidirectionally.

[0058] The pipeline connecting the non-permeable gas collection unit 23 and the membrane separation unit 3 is also provided with a pressure regulating valve 26 for adjusting the pressure in the pipeline, and the pipeline is also provided with a pressure detector or a flow detector. The flow detector can monitor the flow of the non-permeable gas in the pipeline, and the pressure detector can monitor the pressure of the pipeline, thereby playing a role in safety protection.

[0059] The membrane separation unit 3 includes at least one membrane separation group. When the membrane separation group is greater than one, the multi-component membrane separation groups are arranged in parallel and / or in series.

[0060] Another object of the present invention is to provide a Fischer-Tropsch synthesis tail gas recovery method, which utilizes the above-mentioned Fischer-Tropsch synthesis tail gas recovery system to recover permeate gas and prepare hydrogen using permeate gas. After receiving any one of the detection signals of the liquid level value, temperature value and pressure difference value obtained by the liquid level detector 8, the temperature detector 9 and the pressure detector 10, the controller of the recovery system sends a control signal to connect the first venting pipeline 100 or the second venting pipeline 200 to discharge gas, and the compensation unit 6 is connected to the inlet of the permeate gas collection unit 4 to provide the crude target gas to the permeate gas collection unit 4.

[0061] In some embodiments, the recycling method specifically comprises:

[0062] S101: Acquire the liquid level detection signal of the liquid level detector 8;

[0063] S102: Determine whether the liquid level detection signal reaches a preset liquid level threshold;

[0064] S1031: If the first liquid level threshold is reached, the liquid level regulating valve 13 is opened;

[0065] S1032: If the second liquid level threshold is reached, the first vent valve 11 and the flow regulating valve 22 are opened, and the first safety valve 14 and the third safety valve 16 are closed to make the first vent pipeline 100 and the compensation pipeline 400 conductive, wherein the first liquid level threshold is less than the second liquid level threshold.

[0066] Specifically, when the liquid level in the gas-liquid separator 1 reaches a first liquid level threshold with a lower liquid level, the liquid level regulating valve 13 is opened to connect the liquid level regulating pipeline 300 to adjust the internal liquid level of the gas-liquid separator 1; when the liquid level in the gas-liquid separator 1 reaches a second liquid level threshold with a higher liquid level, the first vent pipeline 100 is connected, the pipeline from the gas-liquid separator 1 to the downstream is cut off, and the compensation pipeline 400 is connected. The Fischer-Tropsch synthesis tail gas raw gas is discharged from the system, cutting off the supply of raw gas from the gas-liquid separator 1 to the downstream pipeline. At the same time, the compensation unit 6 replenishes the crude target gas to the permeate gas collection unit 4. At this time, the compressor 20 reduces the load or stops, and the membrane separation group maintains the pressure, which does not affect the stable operation of the downstream device of the gas-liquid separator 1.

[0067] In other embodiments, the recycling method specifically includes:

[0068] S201: Acquire the temperature detection signal of the temperature detector 9;

[0069] S202: Determine whether the temperature detection signal reaches a preset temperature threshold;

[0070] S203: If the preset temperature threshold is reached, the second vent valve 12 and the flow regulating valve 22 are opened, and the second safety valve 15 and the third safety valve 16 are closed, so that the second vent pipeline 200 and the compensation pipeline 400 are connected.

[0071] When the temperature of the gas flow from the heater 2 reaches the minimum temperature threshold or the maximum temperature threshold, the second venting pipeline 200 is turned on, the pipeline from the heater 2 to the downstream is cut off, and the compensation pipeline 400 is turned on. The gas upstream of the heater 2 is discharged from the system, and the supply of raw gas from the heater 2 to the downstream pipeline is cut off. At the same time, the compensation unit 6 replenishes the crude target gas to the permeate gas collection unit 4. At this time, the compressor 20 reduces the load or stops, and the membrane separation group maintains the pressure, which does not affect the stable operation of the downstream device of the heater 2.

[0072] In some further embodiments, the recovery method specifically comprises:

[0073] S301: Acquire a pressure difference detection signal from the pressure detector 10;

[0074] S302: Determine whether the pressure difference detection signal reaches a preset pressure difference threshold;

[0075] S303: If the preset pressure difference threshold is reached, the second vent valve 12 and the flow regulating valve 22 are opened, and the second safety valve 15 and the third safety valve 16 are closed, so that the second vent pipeline 200 and the compensation pipeline 400 are connected. When the inlet and outlet pressure difference of the membrane separation unit 3 reaches the maximum pressure difference threshold, the second vent pipeline 200 is connected, the pipeline from the membrane separation unit 3 to the downstream is cut off, and the compensation pipeline 400 is connected. The gas upstream of the membrane separation unit 3 is discharged from the system, and the supply of raw gas from the membrane separation unit 3 to the downstream pipeline is cut off. At the same time, the compensation unit 6 replenishes the crude target gas to the permeate gas collection unit 4. At this time, the compressor 20 reduces the load or stops, and the membrane separation group maintains the pressure, which does not affect the stable operation of the downstream device of the heater 2.

[0076] Specifically, when the above-mentioned Fischer-Tropsch synthesis tail gas recovery system is used to recover the permeate gas and prepare hydrogen, the Fischer-Tropsch synthesis tail gas passes through the gas-liquid separator 1, the heater 2, the membrane separation unit 3 and the PSA pressure swing adsorption hydrogen production unit in sequence, and the hydrogen with a purity of more than 99.9% (V / V) is collected. Among them, the operating temperature of the membrane separation group of the membrane separation unit 3 is 50-80°C and the operating pressure is 4.0-6.0MPa. Therefore, in this embodiment, the preset liquid level threshold of the liquid level in the gas-liquid separator 1, the preset temperature threshold of the air flow temperature of the heater 2, and the preset pressure difference threshold of the inlet and outlet pressure difference of the membrane separation unit 3 are determined according to the operating temperature and pressure of the membrane separation group.

[0077] A liquid level value of 70% of the maximum liquid level of the gas-liquid separator 1 is a first liquid level threshold, a liquid level value of 80% of the maximum liquid level of the gas-liquid separator 1 is a second liquid level threshold; a liquid level value of 50% of the maximum liquid level of the gas-liquid separator 1 is a safe operation liquid level threshold.

[0078] When the liquid level of the gas-liquid separator 1 reaches the first liquid level threshold, it is determined that the liquid level is high, the liquid level alarm sounds an alarm, the liquid level regulating valve 13 on the liquid level regulating pipeline 300 is opened or the opening of the liquid level regulating valve 13 is increased, so that the liquid level of the gas-liquid separator 1 is gradually reduced until the liquid level returns to normal; when the liquid level of the gas-liquid separator 1 reaches the second liquid level threshold, it is determined that the liquid level is the highest, the liquid level alarm sounds an alarm, the first vent valve 11 is opened, the raw gas is vented, the first safety valve 14 and the third safety valve 16 are closed, and the raw gas cannot continue to enter The downstream pipeline of the gas-liquid separator 1 is inlet, the membrane separation group of the membrane separation unit 3 is maintained at pressure, the compressor 20 is operated at reduced load or shut down, the flow regulating valve 22 on the compensation pipeline 400 is opened, and the crude target gas is provided to the PSA pressure swing adsorption hydrogen production unit to maintain the normal operation of the PSA pressure swing adsorption hydrogen production unit; when the liquid level value of the gas-liquid separator 1 drops to 50% or below the maximum liquid level, the system operates normally, the system liquid level alarm is eliminated, the first safety valve 14 and the third safety valve 16 are opened, and the first vent valve 11 is closed. When the liquid level value of the gas-liquid separator 1 is between 50% of the maximum liquid level and 70% of the maximum liquid level, the system operates normally, but the liquid level may be high, and the system liquid level alarm is still prompted for timely processing.

[0079] The first high temperature threshold of heater 2 is 70°C, the second high temperature threshold is 75°C, the first low temperature threshold is 55°C, the second low temperature threshold is 50°C, and the normal airflow temperature of heater 2 is 55°C-70°C, for example, 60°C.

[0080] When the air flow temperature from heater 2 reaches 60°C, the system operates normally; when the air flow temperature from heater 2 reaches 55°C, the temperature alarm sounds, the temperature regulating valve 17 is opened or the opening of the temperature regulating valve 17 is gradually increased; when the air flow temperature from heater 2 reaches 70°C, the temperature alarm sounds, the temperature regulating valve 17 is closed or the opening of the temperature regulating valve 17 is gradually decreased; when the air flow temperature from heater 2 reaches 50°C or 75°C, it is determined that the minimum temperature or the maximum temperature has been reached, the temperature alarm sounds, the second vent valve 12 is opened, the raw gas is vented, the second safety valve 15 and the third safety valve 16 are closed, the membrane separation group is maintained, the compressor 20 is operated at reduced load or shut down, the flow regulating valve 22 on the compensation pipeline 400 is opened, and the crude target gas is provided to the PSA pressure swing adsorption hydrogen production unit to maintain the normal operation of the PSA pressure swing adsorption hydrogen production unit. When the air flow temperature from heater 2 is reduced to 60°C, the system temperature alarm is eliminated, the second safety valve 15 and the third safety valve 16 are opened, the second vent valve 12 is closed, and the flow regulating valve 22 is gradually closed.

[0081] The first pressure difference threshold of the inlet and outlet pressure difference of the membrane separation unit 3 is 4.2 MPa, the second pressure difference threshold of the inlet and outlet pressure difference of the membrane separation unit 3 is 4.5 MPa, and the normal operation pressure difference threshold of the inlet and outlet pressure difference of the membrane separation unit 3 is 3.5-4.0 MPa.

[0082] When the inlet and outlet pressure difference of the membrane separation unit 3 reaches 4.2Mpa, it is determined that a higher pressure difference has been reached, and the pressure difference alarm sounds an alarm to prompt the user to pay attention to the pressure difference, and the system can still operate normally; when the inlet and outlet pressure difference of the membrane separation unit 3 reaches 4.5Mpa, it is determined that the maximum pressure difference has been reached, and the pressure difference alarm sounds an alarm, the second vent valve 12 is opened, the second safety valve 15 and the third safety valve 16 are closed, the raw gas is vented, the compressor 20 is operated at reduced load or shut down, and the flow regulating valve 22 on the compensation pipeline 400 is opened to provide the PSA pressure swing adsorption hydrogen production unit with crude target gas to maintain its normal operation. At this time, if the membrane separation unit 3 needs to be inspected and repaired, it can be repaired.

[0083] The first safety valve 14, the second safety valve 15 and the third safety valve 16 are preferably quick shut-off valves, which can realize quick shut-off of the pipeline.

[0084] In this embodiment, two levels of temperature thresholds and two levels of pressure difference thresholds are set to improve the accuracy of safety monitoring and the accuracy of subsequent venting and other processing. The specific values ​​of the above-mentioned liquid level threshold, temperature threshold and pressure difference threshold can be determined according to actual process requirements, and more or fewer thresholds can be set (for example, only one high temperature threshold is set).

[0085] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0086] In the description of the present invention, "first feature" or "second feature" may include one or more of the features.

[0087] In the description of the present invention, "plurality" means two or more.

[0088] In the description of the present invention, a first feature being “on” or “under” a second feature may include that the first and second features are directly in contact with each other, or may include that the first and second features are not in direct contact with each other but are in contact with each other via another feature therebetween.

[0089] In the description of the present invention, "above", "over" and "on" a first feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is horizontally higher than the second feature.

[0090] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0091] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A Fischer-Tropsch synthesis tail gas recovery system, characterized in that: It includes a gas-liquid separator, a heater, a membrane separation unit and a permeate gas collection unit which are sequentially connected through pipelines; as well as, A venting unit, wherein the venting unit is connected to the gas outlet end of the gas-liquid separator through a first venting pipeline, the venting unit is connected to the pipeline between the heater and the membrane separation unit through a second venting pipeline, and the bottom of the gas-liquid separator is connected to a liquid level regulating pipeline; A compensation unit is connected to the permeate gas collection unit through a compensation pipeline to provide a crude target gas to the permeate gas collection unit.

2. A Fischer-Tropsch synthesis tail gas recovery system according to claim 1, characterized in that: The gas-liquid separator is provided with a liquid level detector for detecting the liquid level therein, the heater is provided with a temperature detector for detecting the steam temperature, and the membrane separation unit is provided with a pressure detector for detecting the inlet and outlet pressures thereof.

3. A Fischer-Tropsch synthesis tail gas recovery system according to claim 1, characterized in that: The first vent pipeline is provided with a first vent valve, the second vent pipeline is provided with a second vent valve, and the liquid level regulating pipeline is provided with a liquid level regulating valve.

4. A Fischer-Tropsch synthesis tail gas recovery system according to claim 1, characterized in that: A first safety valve is provided on the first pipeline between the gas-liquid separator and the heater, and the first safety valve is provided downstream of the connection between the first venting pipeline and the first pipeline; The inlet and outlet pipelines of the membrane separation unit are respectively provided with a second safety valve and a third safety valve, and the second safety valve is arranged downstream of the connection between the second vent pipeline and the inlet pipeline of the membrane separation unit.

5. The Fischer-Tropsch synthesis tail gas recovery system according to claim 1, characterized in that: A temperature regulating valve and a steam quick cut-off valve are arranged on the low-pressure steam inlet pipeline of the heater.

6. The Fischer-Tropsch synthesis tail gas recovery system according to claim 1, characterized in that: The compensation pipeline is provided with a flow detector or a compensation pressure detector, and a flow regulating valve connected to the flow detector or the compensation pressure detector.

7. The Fischer-Tropsch synthesis tail gas recovery system according to claim 1, characterized in that: The Fischer-Tropsch synthesis tail gas recovery system further comprises a compressor disposed between the membrane separation unit and the permeate gas collection unit, and a first control valve is disposed on the pipeline between the compressor and the permeate gas collection unit; and / or The Fischer-Tropsch synthesis tail gas recovery system further includes a filter arranged between the gas-liquid separator and the heater.

8. A Fischer-Tropsch synthesis tail gas recovery system according to any one of claims 1 to 7, characterized in that: The permeate gas collection unit includes a PSA pressure swing adsorption hydrogen production unit.

9. A Fischer-Tropsch synthesis tail gas recovery system according to any one of claims 1 to 7, characterized in that: Also included is a non-permeate gas collection unit connected to the membrane separation unit.

10. A method for recovering tail gas from Fischer-Tropsch synthesis, characterized in that: The Fischer-Tropsch synthesis tail gas recovery system according to any one of claims 1 to 9 is used to recover permeate gas, and hydrogen is prepared using the permeate gas.

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